Note: Descriptions are shown in the official language in which they were submitted.
CA 02900211 2015-08-12
LITHOGRAPHIC PRINTING PLATES PRECURSORS COMPRISING A RADIATION SENSITIVE
IMAGEABLE
LAYER WITH A CROSSLINKED SURFACE
CROSS REFERENCE TO RELATED APPLICATIONS
N/A
FIELD OF THE INVENTION
[0001] This present invention relates to a lithographic offset printing
plate. More specifically, this present
invention relates to a negative working lithographic offset printing plate
suitable for use in computer-to-plate
systems, which comprises a radiation sensitive imageable layer having a
crosslinked surface.
BACKGROUND OF THE INVENTION
[0002] In lithographic printing, a printing plate is mounted on the
cylinder of a printing press. The printing
plate bears a lithographic image of what is to be printed. A printed copy is
obtained by applying ink to the image
and then transferring the ink from the printing plate onto a receiver
material, which typically is a sheet of paper. In
fact, generally, the ink is first transferred to an intermediate blanket,
which in turn transfers the ink to the surface
of the receiver material (this is called offset printing).
[0003] In conventional, so-called "wet" lithographic printing, the
hydrophobic ink as well as an aqueous
fountain solution (also called dampening liquid) are supplied to the
lithographic image which consists of oleophilic
(or hydrophobic, i.e. ink-accepting, water-repelling) areas as well as
hydrophilic (or oleophobic, i.e. water-
accepting, ink-repelling) areas. When the surface of the printing plate is
moistened by the fountain solution and
ink, the hydrophilic regions retain water and repel ink, and the ink-receptive
regions retain ink and repel water.
During printing, the ink is transferred to the surface of the receiver
material upon which the image is to be
reproduced.
[0004] Lithographic printing plates are obtained by imaging and developing
lithographic printing plate
precursors. Such precursors typically comprise a hydrophobic imageable layer
(also called imaging layer or
coating) applied over the hydrophilic surface of a substrate, typically
aluminum.
[0005] During imaging, targeted laser radiation is used to elicit a
localized transformation of the imageable
layer. Indeed, exposure to the targeted radiation will trigger a physical
and/or chemical change in the imageable
layer so that the exposed areas become different from the unexposed areas.
This can be carried out in different
ways. In direct digital imaging (computer-to-plate), precursors are irradiated
with near infrared (NIR) or
ultraviolet-violet (UV-violet) lasers digitally controlled by computer so that
exposure of the precursor can be
performed directly from digitized information stored in a computer.
[0006] Typically, through imaging, the exposed (i.e. irradiated) areas are
made more or less susceptible to
subsequent development. Indeed, following imaging, the precursor will be
developed. During development,
CA 02900211 2015-08-12
2
either the exposed areas or the unexposed areas of the hydrophobic imageable
layer will be removed, revealing
the underlying hydrophilic surface of the substrate. If the exposed areas are
removed, the precursor is positive
working. Conversely, if the unexposed areas are removed, the precursor is
negative working. In each case, the
regions of the imageable layer that remain are hydrophobic, and the regions of
the substrate revealed by
development are hydrophilic. This produces a pattern of hydrophobic and
hydrophilic areas, i.e. the desired
lithographic image, on the printing plate.
[0007] Development can be carried out by immersing the imaged precursor in
a developer. Developers are
typically aqueous alkaline solutions, which may also contain organic solvents.
Alternatively, "on-press
developable" lithographic printing plates can be directly mounted on a press
after imaging, and are developed
through contact with the ink and/or the fountain solution during initial press
operation.
[0008] In negative-working printing plate precursors, irradiation typically
makes the exposed areas less
soluble in the developer/fountain solution and/or more adherent to the
substrate, which allows obtaining the
desired lithographic image upon development. This decrease in solubility and
increase in adhesion is generally
due to the crosslinking of the imageable layer and/or the coalescence (fusion)
of polymeric particles in the
exposed areas of the imageable layer. The crosslinking is commonly achieved
via free-radical polymerization;
the free radicals being created in the imageable layer by the laser
irradiation. The particle coalescence is due to
the heat produced in the imageable layer when some of its component absorbs
the laser irradiation. Generally,
crosslinking is the primary mechanism at work in UV-violet plates. In NIR
printing plates (which are also called
thermal plates), the coalescence of particles is more important and may
contribute as much as, or even more
than, crosslinking.
[0009] Optionally, after imaging but prior to development, the imaged
precursor may be heated, for example
at the temperature between 100 and 140 C, to complete the crosslinking
reactions and harden the formed image.
[0010] Generally speaking, the above technology is not without
shortcomings.
[0011] First, if not prevented to do so, oxygen molecules from ambient air
will penetrate into the imageable
layer of the precursor. There, they will quench the free radicals produced by
irradiation during imaging. These
radicals are however necessary for the desired photopolynnerization
(crosslinking) of the exposed areas of the
imageable layer. Therefore this will reduce the imaging speed as more energy
from the laser will be needed to
achieve a given level of crosslinking.
[0012] In addition, exposure to ambient air/humidity, especially during
longer periods (e.g. during storage) is
known to cause background staining through thermal fogging (water molecules
penetrating the imageable layer
and causing some polymerization at the imageable layer/substrate interface).
This means that areas that are
supposed to be free of ink during printing will accept some ink, which will
cause stains in the background of the
printed image.
[0013] Of course, it will be easily understood that the above sensitivity
of the negative-working precursors to
ambient air generally translates into rather short shelf-lives.
CA 02900211 2015-11-03
3
[0014] Finally, on the practical side, the imageable layers tend to be
tacky and prone to scratches. Tackiness
causes several problems during production. Among them is the problem of plate
precursors sticking together
(they are stored in piles). Scratches can reduce printing quality. They can be
reduced by using a protective
interleaving paper, which then must be removed before use.
[0015] To alleviate these problems, it has been suggested to add an
overcoat (also called top coat) over the
imaging layer. Printing plate precursors comprising a polymeric overcoat,
which are typically hydrophilic, have
several advantages. First, the overcoat act as an oxygen barrier, which
provides faster laser imaging speeds as
it prevents quenching of the initiating and propagating free radicals involved
in the photopolymerization process
by oxygen molecules from the air (especially during laser imaging and pre-
development heating when the
precursor is exposed to air). These coats also help in overcoming the surface
tackiness of the radiation sensitive
imageable layer, which is often due to the presence of viscous liquid radical
polymerizable oligomers in the
formulation. The polymeric overcoat also provides some scratching resistance
to the radiation sensitive
imageable layer during transportation, storage and pre-press operation.
[0016] Examples of negative-working precursors with or without overcoats
are provided by US patent
5,821,030 (West at al.), US patent 5,888,700 (West at al.), US patent
6,899,994 (Huang at al.), US patent
7,261,998 (Hayashi at al.), US patent 7,732,118 (Tao at al.), US patent
7,955,776 (Baumann etal.), US patent
6,830,862 (Kitson at al.). Typical overcoats are preferably transparent to the
laser radiation that will be used for
imaging and are usually coated from an aqueous solution comprising a water
soluble polymer, such as polyvinyl
alcohol, polyvinylpyrrolidone, or hydroxy alkyl cellulose.
[0017] It should be noted however that the use of such overcoats also has
some disadvantages. First,
overcoats increase production costs, since they require multiple coating
processes (steps) due to differences in
the solubility and the chemical nature of the materials used in the overcoat
compared to that used in the radiation
sensitive imageable layer. In addition, delamination of the overcoat is
commonly observed. Solving this particular
issue requires the use of adhesion promoting agents in the overcoat. However,
diffusion of such adhesion
promoting agents in the imageable layer (e.g. during storage and prepress
operation) can shorten the shelf-life of
the plate precursor and adversely modify the image forming property of the
radiation sensitive imageable layer.
Finally, when the overcoat adhere sufficiently to avoid delamination, it often
becomes difficult to remove during
development. Therefore, it may remain over to the imageable layer and
undesirably reduce its hydrophobicity. In
other words, it reduces the capacity of the imageable layer to accept as much
ink as it should. As a result, the
printing image has a lower optical density (i.e. it is paler). This phenomenon
is called "blinding".
SUMMARY OF THE INVENTION
[0018] In accordance with the present invention, there is provided:
1. A negative-working lithographic printing plate precursor comprising a
hydrophilic substrate and a NIR
and/or UV-violet photopolymerizable imageable layer coated on the hydrophilic
layer,
the imageable layer also being photopolymerizable by visible light,
CA 02900211 2015-08-12
4
the imageable layer having an outer surface and a thickness, the outer surface
of the imageable layer
being uniformly, and partially or completely crosslinked down to a depth
corresponding to at most about
70% of the thickness of the imageable layer.
2. The precursor of item 1, wherein said depth correspond to between about
5% and about 50% of the
thickness of the imageable layer.
3. The precursor of item 2, wherein said depth correspond to between about
5% and about 15% of the
thickness of the imageable layer.
4. The precursor of any one of items 1 to 3, wherein the outer surface of
the imageable layer is partially
crosslinked.
5. The precursor any one of items 1 to 4, wherein the outer surface of the
imageable layer is completely
crosslinked.
6. The precursor any one of items 1 to 5, wherein the imageable layer
comprises one or more of each of:
= a polymeric binder;
= a radical polymerizable copolymer;
= a radical polymerizable oligomer;
= a photoinitiating system sensitive to NIR and/or UV-violet radiation
comprising:
o a free radical photoinitiator sensitive to visible radiation,
o a free radical coinitiator,
o a free radical scavenger,
o a photosensitizer, and
o a photostabilizer; and
= a visible colorant.
7. The precursor of item 6, wherein said visible radiation has a wavelength
between about 400 and about
450 nm.
8. The precursor of item 6 or 7, wherein the free radical scavenger is a
free radical scavenger as defined in
any one of items 29 to 35.
9. The precursor of any one of items 6 to 8, wherein the imageable layer
further comprises a visible light
reflective pigment.
10. The precursor of item 9, wherein the visible light reflective pigment
is titanium dioxide, zinc oxide, and
aluminum oxide.
11. The precursor of any one of items 6 to 10, wherein the imageable layer
is UV-violet photopolymerizable,
the free radical photoinitiator being sensitive to visible radiation and UV-
violet radiation, and the
photosensitizer being sensitive to UV-violet radiation.
CA 02900211 2015-08-12
12. The precursor of any one of items 6 to 10, wherein the imageable layer
is NIR photopolymerizable, the
free radical photoinitiator being sensitive to visible radiation, and the
photosensitizer being sensitive to
NIR radiation.
13. The precursor of any one of items 6 to 10, wherein the imageable layer
is NIR photopolymerizable and
UV-violet photopolymerizable, the free radical photoinitiator being sensitive
to visible radiation and UV-
violet radiation, and the imageable layer comprising a photosensitizer
sensitive to NIR radiation and a
photosensitizer sensitive to UV-violet radiation.
14. The precursor of any one of items 11 to 13, wherein the photoinitiator
has one or more absorption bands
in the UV-violet range, with at least one of these bands trailing into the
visible range of the
electromagnetic spectrum or with a shoulder or one or more further minor bands
in the visible range.
15. The precursor of any one of items 11 to 14, wherein the photoinitiator
is a triazine, thioxanthone,
mercaptothioxanthone, cyanine, monomethine, coumarine, ketocoumarine,
pyrromethene, or oxime
ester photoinitiator.
16. The precursor of any one of items 11 to 15, wherein the photosensitizer
sensitive to UV-violet radiation
is a triazine, thioxanthone, mercaptothioxanthone, cyanine, monomethine,
coumarine, ketocoumarine,
pyrromethene, or oxime ester photosensitizer.
17. The precursor of any one of items 11 to 16, where the photoinitiator
and the photosensitizer sensitive to
UV-violet radiation are the same molecule.
18. The precursor of any one of items 11 to 17, wherein one or more of the
polymeric binder, the radical
polymerizable copolymer, the photoinitiator, the scavenger, and the
photosensitizer is in the form of
polymeric particles that coalesce in the presence of heat.
19. The precursor of any one of items 11 to 18, wherein the photosensitizer
sensitive to NIR radiation is a
cyanine dye or a squaraine dye.
20. A method of manufacturing a negative-working lithographic printing
plate precursor, the method
comprising the steps of:
a) providing a hydrophilic substrate coated with a NIR and/or UV-violet
photopolymerizable imageable
layer, the imageable layer comprising a free radical photoinitiator sensitive
to visible radiation, the
imageable layer having an outer surface and a thickness,
b) uniformly, and partially or completely crosslinking the outer surface of
the imageable layer down to a
depth corresponding to at most about 70% of the thickness of the imageable
layer.
21. A method of creating an oxygen barrier on an imageable layer of a
negative-working lithographic printing
plate precursor, the method comprising the steps of:
CA 02900211 2015-08-12
6
a) providing a hydrophilic substrate coated with a NIR and/or UV-violet
photopolymerizable imageable
layer, the imageable layer comprising a free radical photoinitiator sensitive
to visible radiation, the
imageable layer having an outer surface and a thickness,
b) uniformly, and partially or completely crosslinking the outer surface of
the imageable layer down to a
depth corresponding to at most about 70% of the thickness of the imageable
layer.
22. A method for protecting an imageable layer of a negative-working
lithographic printing plate precursor
from scratches, the method comprising the steps of:
a) providing a hydrophilic substrate coated with a NIR and/or UV-violet
photopolymerizable imageable
layer, the imageable layer comprising a free radical photoinitiator sensitive
to visible radiation, the
imageable layer having an outer surface and a thickness,
b) uniformly, and partially or completely crosslinking the outer surface of
the imageable layer down to a
depth corresponding to at most about 70% of the thickness of the imageable
layer.
23. A method for reducing the tackiness of an imageable layer of a negative-
working lithographic printing
plate precursor, the method comprising the steps of:
a) providing a hydrophilic substrate coated with a NIR and/or UV-violet
photopolymerizable imageable
layer, the imageable layer comprising a free radical photoinitiator sensitive
to visible radiation, the
imageable layer having an outer surface and a thickness,
b) uniformly, and partially or completely crosslinking the outer surface of
the imageable layer down to a
depth corresponding to at most about 70% of the thickness of the imageable
layer.
24. A method for reducing absorption by an imageable layer of a negative-
working lithographic printing plate
precursor of oxygen molecules from the air, the method comprising the steps
of:
a) providing a hydrophilic substrate coated with a NIR and/or UV-violet
photopolymerizable imageable
layer, the imageable layer comprising a free radical photoinitiator sensitive
to visible radiation, the
imageable layer having an outer surface and a thickness,
b) uniformly, and partially or completely crosslinking the outer surface of
the imageable layer down to a
depth corresponding to at most about 70% of the thickness of the imageable
layer.
25. A method for increasing the laser imaging speed of an imageable layer
of a negative-working
lithographic printing plate precursor, the method comprising the steps of:
a) providing a hydrophilic substrate coated with a NIR and/or UV-violet
photopolymerizable imageable
layer, the imageable layer comprising a free radical photoinitiator sensitive
to visible radiation, the
imageable layer having an outer surface and a thickness,
b) uniformly, and partially or completely crosslinking the outer surface of
the imageable layer down to a
depth corresponding to at most about 70% of the thickness of the imageable
layer.
CA 02900211 2015-08-12
7
26. A method for increasing the shelf-life of a negative-working
lithographic printing plate precursor, the
method comprising the steps of:
a) providing a hydrophilic substrate coated with a NIR and/or UV-violet
photopolymerizable imageable
layer, the imageable layer comprising a free radical photoinitiator sensitive
to visible radiation, the
imageable layer having an outer surface and a thickness,
b) uniformly, and partially or completely crosslinking the outer surface of
the imageable layer down to a
depth corresponding to at most about 70% of the thickness of the imageable
layer.
27. The method of any one of items 20 to 26, wherein step b) is carried out
by irradiating the imageable
layer with visible light.
28. A negative-working lithographic printing plate precursor produced
according to the method of any one of
items 20 to 27.
29. A free radical scavenger of formula:
(R-n-L)n-Tq,
wherein:
= P is a radical polymerizable functional group or a substituent formed by
joining two or more
radical polymerizable functional groups together;
= L is a linker having a valence equal to m+q;
= T is a thiol group, or a substituent comprising a thiol group and
optionally further comprising a
carboxylic acid group, wherein said substituent has a valence equal to n;
= m is an integer between 1 to 5;
= n is an integer between 1 to 5; and
= q is an integer between 1 to 5.
30. The free radical scavenger of item 29 being of formula:
P-L-T,
Pm-L-T,
P-L-Tq, or
(P-L)-T. .
31. The free radical scavenger of item 29 or 30, wherein P is:
= -X,
= -C-(CH2-X)3, or
O -C(CH2-X)2(CH2-0-CH2-C-(CH2-X)3),
in which X is a radical polymerizable functional group.
CA 02900211 2015-08-12
8
32. The free radical scavenger of item 31, wherein P is:
o
o,
=
0 , , or
33. The free radical scavenger of any one of items 29 to 32, wherein T is:
SH
SH
N
N-N N SH N -OH
y N S
S SH N-NH N , or 0
34. The free radical scavenger of any one of items 29 to 33, wherein L is
an alkylene or alkylyne group
comprising one or more following functional groups:
= -NH-C(=0)-S-,
= -S-C(=0)-NH-
= -NH-C(=0)-NH-,
= -NH-C(=0)-0-,
= -0-C(.0)-NH-,
= -S-,
N N'
0 N 0
=
= -NH-C(=0)-, and
= -C(=0)-NH-.
35. The free radical scavenger of any one of items 29 to 33, wherein L is a
copolymer, with P and T being
attached as pendant groups to different monomers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] In the appended drawings:
Figure 1 is a cross-sectional view of a negative working precursor according
to an embodiment of the invention;
Figure 2 is a cross-sectional view of a negative working precursor according
to another embodiment of the
invention;
CA 02900211 2015-08-12
9
Figure 3 is a cross-sectional view of a negative working precursor according
to yet another embodiment of the
invention;
Figure 4 shows the emission spectrum of the visible light source used to form
a crosslinked surface on the
radiation sensitive imageable layer in the Examples;
Figure 5 shows the absorption spectrum of the UV-violet radiation sensitive
imageable layer (solid line) of
Example 1 and the emission spectrum of the visible light source (dash line);
Figure 6 shows the dot gains at 50% dot target at different energy densities
for printing plates with a UV-violet
laser radiation sensitive imageable layer with (circles) and without (squares)
a crosslinked surface, as produced
in Example 1;
Figure 7 shows the dot gains after different aging duration for printing
plates with (circles) and without (squares) a
crosslinked surface, as produced in Example 1;
Figure 8 shows the dot gains for a printing plate with an imageable layer
without TiO2 (Example UV-7, circles) and
that for a printing plate with an imageable layer with 1% TiO2 (Example UV-8,
squares) as a function of the
duration of exposition to visible light;
Figure 9 shows the optical density of the developed printed plates (without
laser imaging) produced in Examples
7 and 8, as a function of the duration of exposition to visible light;
Figure 10 shows the absorption spectrum of the NIR radiation sensitive
imageable layer (solid line) of the
precursor of Example 9 and the emission spectrum of the visible light source
(dash line);
Figure 11 shows the dot gains at different energy densities for fresh NIR
radiation sensitive printing plates with
(circles) and without (squares) a crosslinked surface, as produced in Example
9; and
Figure 12 shows the dot gains at 120 mJ/ctri2 of the printing plates
comprising a NIR laser radiation sensitive
imageable layer with (circles) and without (squares) a crosslinked surface, as
produced in Example 9, after aging
at 40 C and 80% RH.
DETAILED DESCRIPTION OF THE INVENTION
Negative-Working Lithographic Printing Plate Precursor
[0020] Turning now to the invention in more details, there is provided a
negative-working lithographic printing
plate precursor comprising a hydrophilic substrate and a NIR and/or UV-violet
photopolymerizable imageable
layer coated on the hydrophilic layer, the imageable layer being
photopolymerizable by visible light, the
imageable layer having an outer surface and a thickness, the outer surface of
the imageable layer being
uniformly, and partially or completely, crosslinked down to a depth
corresponding to at most about 70% of the
thickness of the imageable layer.
[0021] Herein, a "lithographic printing plate precursor' refers to a
lithographic printing plate that has not yet
been imaged. A precursor bears a radiation sensitive imageable layer. However,
unlike in a printing plate, this
CA 02900211 2015-08-12
imageable layer does not (yet) bears a lithographic image. In the case of the
NIR and/or UV-violet radiation
sensitive photopolymerizable lithographic printing plate precursor above, this
means that the precursor has not
been imaged with the NIR and/or UV-violet radiation.
[0022] The precursor is suitable for use in computer-to-plate (CTP)
systems.
[0023] The precursor is suitable for development on press.
Advantages
[0024] The precursor of the present invention can, in embodiment, have the
following advantages.
[0025] In the present invention, the crosslinked outer surface of the
imageable layer acts as an overcoat.
Contrary to conventional overcoats however, the crosslinked outer surface of
the imageable layer is
advantageously an integral part of the imageable layer. This eliminates risks
of delamination.
[0026] It will be understood that since the crosslinked outer surface of
the imageable layer acts as an
overcoat, the precursor will typically be free of such overcoats. It other
words, the imageable layer will not be
covered by any coating, i.e. it will be accessible to ambient air.
[0027] For certainty, it should also be understood that, as the imageable
layer itself, the crosslinked outer
surfaced of the imageable layer is hydrophobic. In other words, the
crosslinking of the outer surface of the
imageable layer does not reduce the optical density of the printed image.
[0028] The crosslinked outer surface acts as an overcoat; as an oxygen
barrier. It thus contributes to faster
laser imaging speeds because it prevents/reduces quenching of the initiating
and propagating free radicals
involved in the photopolymerization process by oxygen molecules from the air.
In turn, this contributes to
increasing the shelf-life of the precursor, especially in non-optimal
conditions (at higher temperature and/or higher
relative humidity).
[0029] After laser imaging and development, the imageable layer with a
crosslinked surface is generally
stronger/harder than a corresponding imageable layer without a crosslinked
surface, as such the imageable layer
with a crosslinked surface provides a better print quality and longer print
length.
[0030] The crosslinked outer surface is often less tacky and/or, as stated
above, harder (i.e. more scratch-
and fingerprint-resistant) than the un-crosslinked imageable layer. Therefore,
provides some degree of physical
protection to the underlying imageable layer.
[0031] Finally, the manufacture of the precursor of the present invention
is easier and more-effective than
that of similarly precursor with overcoats. As described below, the
crosslinking of the outer surface can indeed by
carried out after coating (and drying) of the imageable layer simply by adding
a suitable visible light source in the
production line.
CA 02900211 2015-08-12
11
Imageable Layer
[0032] As stated above, the precursor comprises a hydrophilic substrate and
also comprises an imageable
layer. This imageable layer is coated on the hydrophilic substrate. Typically,
this means that it (entirely or almost
entirely) covers one side of the substrate.
[0033] The imageable layer has an outer surface and a thickness. The outer
surface is the surface of the
imageable layer that is opposite the substrate/imageable layer interface. In
other words, it is the surface
accessible to ambient air.
[0034] The thickness of the imageable layer is that commonly found in the
art. Preferably, the thickness is
between about 0.6 and about 3.0 pm, preferably from about 0.8 to about 1.0 pm.
In particular, the imageable
layer may have a coating weight between about 0.6 and about 3.0 g/m2. A
preferred coating weight is of between
about 0.8 and 1.0 g/m2.
Cross/inked Outer Surface
[0035] In the present invention, the outer surface of the imageable layer
is uniformly, and partially or
completely, crosslinked down to a depth corresponding to at most about 70% of
the thickness of the imageable
layer, preferably between about 5% and about 70%, for example between about 5%
and about 50%, between
about 5% and about 25%, between about 5% and about 15%, of the thickness of
the imageable layer, most
preferably down to about 10% of the thickness of the imageable layer.
Preferably, the imageable layer is thus
crosslinked down to a depth between about 0.06 and about 0.30 pm.
[0036] Figure 1 is a cross-sectional view of a negative working precursor
according to an embodiment of the
invention. In this figure:
= [101] is the imageable layer;
= [102] is the part of the imageable layer that is crosslinked; and
= [103] is the hydrophilic substrate.
[0037] It should be understood that the part of the imageable layer that is
crosslinked is integral to the
imageable layer. It is not a (separate) overcoat covering the imageable layer.
[0038] In the present invention, the outer surface of the imageable layer
is crosslinked "down to a depth..."
This means that the outer surface of the imageable layer is crosslinked and
that this crosslinking extends from
this outer surface down into the imageable layer towards the
substrate/imageable layer interface. For reference,
this interface is identified as [104] in Figure 1, while the outer surface is
labelled as [105]. Of note, the
crosslinking does not extend all the way down to the substrate/imageable layer
interface. Rather, as stated
above, it extends at most 70% of the way.
[0039] In that regard, the crosslinking of the outer surface of the
imageable layer is very different from the
photopolymerization that takes place when the precursor is imaged with a laser
in view of printing. The latter is
CA 02900211 2015-08-12
12
produced by a powerful and focused light source (typically a laser focused
with a condenser) in a way that
purposefully insures that the exposed areas of imageable layer are crosslinked
down to the substrate/imageable
layer interface. This indeed reduces the solubility of the exposed areas to a
minimum while adhering (almost
fusing) the exposed imageable layer on the substrate. Indeed, it is necessary
that this photopolymerization reach
down as such because, otherwise, the printing plate cannot be properly
developed (some areas that should retain
the imageable layer would be free of it for lack of adhesion) and cannot be
used for printing.
[0040] In the present invention, the outer surface the imageable layer is
"uniformly" crosslinked. This means
that this crosslinking does not form a lithographic image (which would be
characterized by a pattern of
crosslinked and un-crosslinked areas) or any other pattern on the precursor.
Rather, the crosslinking is uniform
over the whole outer surface. Perfect uniformity is not required as long as
the outer surface is crosslinked
enough to fulfill its purpose (more on that below). Rather, the "uniform"
crosslinking refers to the fact that the
precursor has not been irradiated, to imprint therein a lithographic image in
view of development and printing.
[0041] In the present invention, the outer surface of the imageable layer
is "partially or completely"
crosslinked. Complete crosslinking means that the outer surface cannot be
meaningfully crosslinked anymore.
This occurs when all the radical polymerizable functional groups that could
undergo crosslinking reactions have
done so. Partially crosslinking means that the outer surface has the potential
to be further crosslinked as there
remain therein radical polymerizable functional groups that can still undergo
crosslinking reactions.
[0042] Typically, the denser the crosslinking, the thinner the crosslinked
layer needs to be.
Photopolymerization and Light Sensitivity of the Imadeable Layer
[0043] In the present invention, the imageable layer is NIR and/or UV-
violet photopolymerizable. Further, it is
photopolymerizable by visible light.
[0044] Visible radiation is radiation at wavelengths perceived by the human
eye. It is defined as radiation
with a wavelength between about 400 (violet) to about 700 (red) nm. Near-
infrared (NIR) radiation has longer
wavelengths, while ultraviolet (UV) has shorter wavelengths. Herein, NIR is
defined as having a wavelength from
about 780 to about 1100 nm, while "UV-violet" is defined as radiation having a
wavelength between about, from
about 200 to about 420 nm.
[0045] NIR photopolymerizable and UV-violet photopolymerizable imageable
layers are well known in the art.
In fact, most negative-working printing plate precursors are either NIR-
sensitive or UV-violet-sensitive.
[0046] Typically, NIR photopolymerizable and UV-violet photopolymerizable
imageable layers comprise a
photoinitiating system sensitive of NIR and/or UV-violet radiation,
respectively. This means, in fact, that it
comprises a photoinitiator and/or a photosensitizer which, during imaging,
absorbs incoming NIR and/or UV-violet
laser radiation and produce free radicals and/or heat, respectively. These
free radicals and/or this heat will
trigger the desired crosslinking/coalescence in the imageable layer. Such
photoinitiators and photosensitizers are
well-known to the skilled person.
CA 02900211 2015-08-12
13
[0047] The UV-violet laser radiation generally has a wavelength between
about 354 and about 410 nm,
preferably 405 nm. Lasers emitting at such wavelengths are well-known in the
art and include gallium (III) nitrile,
indium gallium nitrile, and triple neodymium-doped yttrium aluminum garnet.
The NIR laser radiation generally
has a wavelength between about 780 and 1064 nm, preferably between 800 and 850
nm. Lasers emitting at
such wavelengths are well-known in the art and include aluminum and/or indium
doped gallium arsenide lasers,
gallium manganese arsenide laser, and gallium arsenide phosphide laser.
[0048] The imageable layer in the precursors of the invention is also
photopolymerizable by visible light. This
means that the imageable layer comprises a photoinitiator that is sensitive to
(i.e. absorbs) (at least slightly)
incoming visible radiation and produces at least some free radicals. These
free radicals will trigger crosslinking of
the imageable layer (photopolymerization). This allows crosslinking of the
outer surface of the imageable layer
using a visible light source emitting at such wavelengths. More specifically,
this means that the photoinitiator
already used in the precursor for imaging (if any) also absorbs visible light
or alternatively that an additional
photoinitiator is used in the precursor for the specific purpose absorbing
visible light and producing free radicals
for crosslinking the outer surface.
[0049] The visible light absorbed by the photoinitiator can be between
about 400 and about 700 nm, for
example between about 400 and about 600 nm, between about 400 and about 500
nm, between about 400 and
about 475 nm, or between about 400 and about 450 nm.
[0050] Of note, the absorption of the photoinitiator in the visible range
will typically be much lower than that of
the photoinitiator/photosensitizer in the UV-violet/NIR ranges. Indeed, as
much less crosslinking is desired (only
the outer surface should be crosslinked), a high absorption is not necessary.
The photoinitiator should simply be
sufficiently absorbent in the visible range so that crosslinking is possible
in a reasonable amount of time using a
reasonable amount of energy. However, it should not be so absorbent that the
precursor cannot be handled for a
reasonable amount of time in ambient light. Within these boundaries, the
absorption of the photoinitiator can
vary; the light source used to elicit crosslinking and the duration of
exposure will then simply be adapted to it as
described below.
[0051] It will be well-known to the skilled person that the absorption
peaks/bands in the NIR/visible/UV
regions of the electromagnetic spectrum are typically rather broad (see the
Figures herein for typical examples).
Therefore, light absorption in the various regions referred to above can be
achieved in various ways. For
example, two molecules having different absorption bands can each cover one of
the desired ranges of interest
(visible, and NIR or UV-violet). Alternatively, one molecule can have a single
broad band (perhaps with shoulders
or secondary/minor band(s)) covering at once wavelengths in more than one
desired ranges of interest. Such
variations are inconsequential as long as sufficient light is absorbed to
achieve the desired photopolymerization,
both during imaging of the precursor and when crosslinking the outer surface,
in a reasonable amount of time
using a reasonable amount of energy.
CA 02900211 2015-08-12
14
Typical Components and Their Functions
[0052] In embodiments, the imageable layer comprises one or more of each
of:
= a polymeric binder;
= a radical polymerizable copolymer;
= a radical polymerizable oligomer;
= a photoinitiating system sensitive to NIR and/or UV-violet radiation
comprising:
o a free radical photoinitiator sensitive to visible radiation,
o a free radical coinitiator,
o a free radical scavenger,
o a photosensitizer, and
o a photostabilizer; and
= a visible colorant.
[0053] As will be explained in more details in the following sections, many
of these components can be
provided in the form of polymeric particles. Such particles are advantageously
used in NIR-photopolymerizable
imageable layer as they will coalesce (fuse together) in the presence of heat.
[0054] The polymeric binders generally provide uniform film forming
properties, improves development ability,
and/or provides longer print length on press.
[0055] The radical polymerizable copolymers undergo photopolymerization in
the presence of free radicals.
Depending on the nature of their repeat units, some of these copolymers can
also improve the film forming
properties of the imageable layer, contribution to its adhesion on the
substrate, act as free radical scavengers,
etc.
[0056] The radical polymerizable oligomers, which typically comprise two or
more radical polymerizable
functional groups, also undergo photopolymerization in the presence of free
radicals.
[0057] The photoinitiators are sensitive to (i.e. absorb) incoming
radiation (typically UV and/or visible) and
generate free radicals (and some heat). The photosensitizers are sensitive to
(i.e. absorb) incoming radiation
(UV or NIR) and generate heat (and some free radicals). A molecule can act as
both a photoinitiator and a
photosensitizer when it generates both free radicals and heat in significant
amounts when absorbing incoming
radiation.
[0058] The coinitiators absorb some of the free radicals generated by the
photoinitiators and generate more
free radicals. This process may be facilitated by heat generated in the
imageable layer, more particularly in the
case of NIR-sensitive precursor.
CA 02900211 2015-08-12
[0059] The free radical scavengers prevent the free radicals from
recombining with one another and can act
as hydrogen donators. This latter function is advantageous in NIR
photopolymerizable precursors, where it is
believed to help the crosslinking and the coalescence of the particles.
[0060] The photostabilizers help to stabilize the precursor and thus
prolong its shelf-life. During storage, if
some free radicals are generated, they can react with the photostabilizer.
This molecule polymerize slowly, which
will limit the damages done to the precursor.
[0061] The purpose of the visible colorant is to color the imageable layer
and thus allow inspection of the
precursor and imaged and developed printing plate. For note, visible colorant
absorb visible light at various
wavelength (and thus appeared to be colored), but they do not produce free
radicals when they do so.
[0062] It should be noted that a single molecule can sometimes combine two
or more of the above functions.
Furthermore, two or more molecules above can be combined together. For
example, a photosensitizer,
photoinitiator, etc. can be attached as a pendant group to a polymeric binder,
a copolymer, an oligomer, etc. As
long as the functional group(s) responsible for the molecule's function are
preserved, such attachment is
expected to preserve the molecule function.
[0063] When the precursor is exposed to focused laser radiation at the
right wavelength (NIR and/or UV-
violet), the photoinitiating system will absorb this radiation and generate
free radicals and heat. The radicals will
trigger a photopolymerization via crosslinking reactions of the various
radical polymerizable functional groups
present in the imageable layer in the areas that were exposed to the laser
radiation. The heat will cause the
particles present in the areas that were exposed to the laser radiation to
coalescence. The imaged precursor may
be optionally be heated at a temperature between 100 and 140 C or radication
cured (for example UV-cured) as
known in the art to complete the crosslinking/coalescence and/or harden the
formed image. The precursor can
then be developed with an aqueous developer in a processor or on-press with
ink and a fountain solution. After
development, the resulting printing plate is ready for printing.
[0064] Radical polymerizable functional groups are well-known to the
skilled person. They typically comprise
one or more polymerizable carbon-carbon double bonds (C=C), which are also
referred to as an ethylenical
unsaturations. Preferred examples of such functional groups include acrylate,
methacrylate, acrylamide,
methacrylamide, alkylacrylate, alkylmethacrylate, alkylacrylamide,
alkylmethacrylamide, vinyl ether, allyl, and
styryl, wherein, in embodiments, the alkyl has between 1 and 10 carbon atoms,
preferably 1 or 2 carbon atoms.
Most preferred radical polymerizable functional groups are acrylate,
methacrylate, acrylannide, and
methacrylamide.
[0065] Optionally, the imageable layer may further comprise one or more of
each of:
= a visible light reflective pigment,
= a film forming surfactant; and
= an adhesion promoting agent.
CA 02900211 2015-11-03
16
Polymeric Binders
[0066] The imageable layer may comprise one or more polymeric binders.
Polymeric binders for use in
negative-working printing plate precursors are well-known to the skilled
person. Any such known binder can be
used in the present invention. Generally, polymeric binders can be used at a
concentration between about 3 and
about 50 weight percent.
[0067] The polymeric binders can be molecularly dispersed in the imageable
layer or in the form of discrete
particles, preferably having of a size ranging between about 60 and about 300
nm. Particles that can coalesce
when heated are preferred in NIR-sensitive precursors.
[0068] Preferably, the polymeric binder is a high molecular weight polymer
binder, for example having a
molecular weight of about 3,000 Dalton or more.
[0069] The polymeric binder may or may not contain radical polymerizable
functional groups.
[0070] Examples of typical polymeric binders include hydroxy-alkyl
cellulose, acetal copolymers, acrylic acid
copolymers, methacrylic acid copolymers, acrylamide copolymers, methacrylamide
copolymers, acrylonitrile
copolymers, substituted phenylimide copolymers, and alkylimide copolymers.
[0071] Examples of suitable polymeric binders can also be found in US
patent No. 8,323,867. This patent
describes solvent- and/or water-soluble cellulose ethers comprising a
functional group which can undergo radical
and/or cationic polymerization. These cellulose ethers may have the following
structure:
G5
H OH ¨ CH2
____________________ O __ /
OH H5 0 _____
/
H\ H ¨
0 0 OH I-I/
C2 H OH
I H
_a_ b
G4
wherein:
= G4 is hydroxy, hydroxyethyl and hydroxypropyl.
= G5 is the functional group that can undergo radical and/or cationic
polymerization.
[0072] More specifically, the G5 group may have the following structure:
0
0 N
0 0
_ m
0 R
wherein m is 0 or 1 and R is hydrogen or methyl.
CA 02900211 2015-11-03
17
[0073] Examples of suitable polymeric binders can also be found in US
patent no, 8,323,867 which describes
acetal copolymers having the following general structure:
0 0 OH 0
C=0
G 1 G2
CH3
wherein G1, G2, a, b, d and e are as described below in regard of an acetal
copolymeric photosensitizer of
roughly similar formula described in the "Photosensitizer" section.
[0074] Other examples of suitable polymeric binders can be found in US
patent no. 7,723,010. This patent
describes polymer binders that may be, for example, cellulose polymers having
non-ionic pendant groups, such
as hydroxy, polyethylene oxide, polypropylene oxide or polybutylene oxide. The
cellulose polymers may contain
anionic pendant groups, such as carboxylic acid, sulfonic acid, phosphoric
acid, and their corresponding lithium,
sodium and potassium alkali salts. The cellulose polymers may contain cationic
pendant groups, such as tetra-
alkyl-ammonium salts. The cellulose polymers may contain radical polymerizable
functional groups. The
cellulose polymer binder may be that commercially available from American Dye
Source, Inc. (Canada) under the
trade-name Tuxedo XCP10.
[0075] US patent no. 7,723,010, describes water soluble acetal copolymers
having 4-hydroxyphenyl, 3-
hydroxyphenyl, 2-hydroxyphenyl, alkyl, and hydroxy functional groups. In
embodiments, the alkyl may be linear or
branched alkyl having between 1 and 12 carbon atoms. The acetal copolymers may
also comprise radical
polymerizable functional groups. The water soluble acetal copolymer binder may
be that commercially available
from American Dye Source, Inc. (Canada) under the trade-name Tuxedo XAP02.
[0076] A preferred polymer binder is hydroxy propyl cellulose having a
molecular weight between 5,000 and
30,000 Dalton, which is available from American Dye Source (Quebec, Canada).
This polymeric binder can be
used at a concentration between about 3 and about 10 weight percent.
[0077] Other polymeric binders include polymeric particles having a
particle size between 60 and 300 nm,
preferably between 150-200 nm. Preferred polymeric particles include those
commercially available from MyIan
Group (Travinh, Vietnam) under tradenames PolyoNP 150, PolyoNP 180, PolyoNP
200 and PoIMP 250, which
have particle sizes of 150, 180, 200 and 250 nm respectively. Such polymeric
binders can be used at a
concentration between about 10 and about 50 weight percent. The ideal chemical
structure of the Poly NP series
of particles (wherein x and y are the number of repeating units and are 10 and
31, respectively) is:
CA 02900211 2015-11-03
18
- cH,- ci-13
0.127 _ _ 0.447 _ _01.006 _ _0.420
ON
0 0 0 0
OH3
HN 0
CH3
PolyoNP
Radical polymerizable Copolymers
[0078] The imageable layer further comprises one or more a radical
polymerizable copolymer. Those are
copolymers, i.e. polymers comprising two or more different repeat units,
wherein at least one type of repeat unit
comprises pendant groups that include one or more radical polymerizable
functional groups. Free radical
polymerizable copolymers for use in negative-working printing plate precursors
are well-known to the skilled
person. Any such known copolymer can be used in the present invention.
Generally, the radical polymerizable
copolymers can be used at a concentration between about 5 and about 50 weight
percent.
[0079] The radical polymerizable copolymers can be molecularly dispersed in
the imageable layer or in the
form of discrete particles, in particular particles having a particle size
preferably between about 60 and about 250
nm. Particles that can coalesce when heated are preferred in NIR-sensitive
precursor.
[0080] Examples of suitable known radical polymerizable copolymers include
hydroxy-alkyl cellulose, acetal
copolymers, acrylic acid copolymers, methacrylic acid copolymers, acrylamide
copolymers, methacrylamide
copolymers, acrylonitrile copolymers, substituted phenylimide copolymers, and
alkylimide copolymers, said
copolymers bearing radical polymerizable functional groups as pendant groups.
[0081] US patent no. 8,323,867, provides examples of free radical
polymerizable copolymers. More
specifically, this patent describes copolymers comprising a functional group
which can undergo radical and/or
cationic polymerization. Such copolymers can be obtained from acrylonitrile,
styrene, poly(ethylene glycol)
acrylate, poly(ethylene glycol) methacrylate and methoxymethylmethacrylamide
monomers.
[0082] Copolymers two or more of the following repeat units, at least one
unit comprising a radical
polymerizable functional group, can be used in the present invention:
CA 02900211 2015-08-12
19
0 0
CN ONH2
, R
O
0 NH
0=S=0
0 0 R 0
(:)c)P\¨OH oc)
_m OH R11 , CH
0
r%
Nr.0 HO-0
R12 OH
CA 02900211 2015-08-12
ONH
0 NH
0
,0
0
¨ rn 0
CH3
0 0 OH
¨ m
/\../
0 0
¨m H w
,and
0 0 0
P-0¨ H3N
k
\
m OH 0
wherein:
= m and w may vary between 0 and 50;
= R is hydrogen or methyl;
= R11 is H or linear and branched alkyl chain; and
= R12 is alkyl, hydroxyl, or carboxylic acid.
[0083] The chemical structures of preferred radical polymerizable
copolymers, which can be used at a
concentration between about 5 and about 50 weight percent, and which are
commercially available from Mylan
Group (Travinh, Vietnam), are shown below:
CA 02900211 2015-08-12
21
- - - - - -
0.60 _ _ 0.15 _ _ 0.20 _ _ 0.05
0 0
N 0 NH2 00H ONH
* )
0 0
PolyXP 100
- - - - -
0.60 _ -0.15 _ _0.20 _ _0.05
0 0
N ONH2 00H 00
* r
HN, 0
--,.
PolyXP 102
0.55 L _ 0.05- _ 0.15 - _, 0.20 L _0.05
0 0
N
1
0 NH2 00H 0 NH
*
r
oo
PolyXP 104
-
- -
- - - -
0.55- _ 0.05 _ _0.15 _ _0.20 _ _0.05
0 0 CN
N 0 NH2 0----OH ONH
*
0õ-,0
--v
PolyXP 106
CA 02900211 2015-08-12
22
[0084] The chemical structures of preferred radical polymerizable
copolymers in the form of nanoparticles
(preferred for NIR sensitive precursors) are shown below. These can be used at
a concentration between about 5
and about 50 weight percent. These are commercially available from MyIan Group
(Travinh, Vietnam). (x and y
are the number of repeating units and are 10 and 31, respectively.)
_
_
- cH3- CH3 -
_ 0.127 _ _ 0.847 _ _0.006_ _
0.020
CN
0 0 0 0
1
/
HN 0 HN 0
I======
H 3C 0
CH3
PolyN1)0150X
- - - - cH3- CH3 -
0.127 _ -0.847k _0.006_ _ 0.020
CN
0 0 0 0
1
)
r
..........
HN0 HN 0
, 0
H 0 .._______---- H
3C H 3C
CH3
PolyNP0150Y
- - - - - CH3 - - CH3 -
_ 0.107 - 0.020 _ _0.847 _ _0.006, _0.020
CN
i I
r) r
CD NH
S
1 HN0
HN
NS 1,r H,C
--------___ ,CH
SH - Y - .x 3
CH3
P0IyNP 1 20S
CA 02900211 2015-11-03
23
Radical polymerizable Oligomers
[0085] The imageable layer further comprises one or more radical
polymerizable oligomers. These are small
molecules comprising two or more radical polymerizable functional groups.
There are generally in liquid form and
as such can be responsible for the tackiness of the imageable layer.
[0086] Radical polymerizable oligomers for use in negative-working printing
plate precursors are well-known
to the skilled person. Any such known oligomer can be used in the present
invention. Generally, the radical
polymerizable oligomers can be used at a concentration between about 10 and
about 50 weight percent.
[0087] Examples of suitable known radical polymerizable oligomers include
those based on urethane, urea,
ether, amide, ester compounds comprising multiple free radical polymerizable
functional groups, preferably
acrylate, methacrylate, vinyl ether, allyl ether, acrylamide, and
methacrylamide.
[0088] US patent publication no. 2012/0137929 provides examples of such
radical polymerizable oligomers.
In particular, it describes gallotannic compounds comprising gallotannin
wherein at least one hydroxyl group is
replaced by a substituent. Non-limiting examples of substituents include
substituents comprising:
= crosslinkers (i.e. is a molecule, an oligomer or a polymer that comprises
a functional group capable of
undergoing a crosslinking reaction via cationic or radical polymerization),
= initiators,
= adhesion promoters,
= hydrogen bonding promoters,
= chromophores,
= binders,
= any other molecule, oligomer, or polymer used in lithographic printing
plate coatings,
= gallotannin, and
= another gallotannic compound.
[0089] Of course, several hydroxyl groups of gallotannin may be replaced to
produce the gallotannic
compound. There is no need that all the hydroxyl groups be replaced by the
same type of substituents. There is
no need that all the substituents of a particular type be the same.
[0090] The skilled person will appreciate that the substituents can be
attached directly to the gallotannin.
Alternatively, the substituent(s) is/are attached to the gallotannin through a
linking group. In embodiments, the
linking group may be alkyl optionally comprising one or more ester, ether,
amine, amido, urea, carbamate,
N 0
I I
0 0
sulfonamide, or functional group (or any combination thereof). The
alkyl may be linear,
CA 02900211 2015-11-03
24
branched and/or cyclic. In other words, the alkyl may comprise linear parts,
branched parts and cyclic parts at
the same time. The alkyl group may have 1 to 50 carbon atoms. In the above,
when it is said that the alkyl
optionally comprises the listed functional groups, it means that the
functional groups may be at end either of the
alkyl or in between any two carbon atoms of the alkyl or its substituents. For
more certainty, when more than one
functional group is comprised in an alkyl, the functional groups do not need
to be separated by carbons atoms of
the alkyl; i.e. they may be directly attached to one another. For more
certainty, herein an ether functional group is
-0-; an ester functional group (or linker) is -(C=0)-0- or -0-(C=0)-; an amine
functional group is -NR3-, an amide
(or amido) functional group (or linker) is -(C=0)-NR3- or -NR3-(C=0)-; an urea
functional group is -NR3-(C=0)-
NR3-; a sulfonamide functional group is -S02-NR3- or -NR3-S02-; and a
carbamate functional group is -NR3-
(C=0)-0- or -0-(C=0)-NR3-, R3 being hydrogen or alkyl.
[0091] A most preferred oligomer it that synthesized by reacting 1
equivalent of gallotannic acid with 10
equivalent of 2-isocyanato ethylmethacrylate using dibutyl tin dilaurate
catalyst in dioxolane solution at 50 C
according to Example 1 of the US patent publication no. 2012/0137929 (Nguyen
et al.). This oligomer can be
used at a concentration between about 5 and about 20 weight percent. The ideal
chemical structure of this
radical polymerizable gallotannic oligomer, which is commercially available
from MyIan Group (Travinh, Vietnam)
under tradename Tanmer 10X, is:
HN
0 0 0 0
JoO diali OH 0)oL ip HO 0
HN
0 0 HO 0
(D
HO 0 Ai OH
. 0
0 I 0 0
0
0 o 0
0 HO 0 0 la
0
0
HO 0 0
OH OH
HO al 0
0 40 OHO stir 0 OH
OH 0
0
0 oo
0
0N (
0 KNH
Tanmer 10X
Free Radical Photoinitiators
[0092] The photoinitiating system comprises one or more free radical
photoinitiators.
CA 02900211 2015-11-03
[0093] The photoinitiator is sensitive (i.e. absorb), at least slightly,
visible radiation. In both UV-violet and
NIR-sensitive imageable layers of the invention, the photoinitiators will
absorb visible light and produce the free
radicals that are necessary for the crosslinking of the outer surface of the
imageable layer.
[0094] When the imageable layer is UV-violet photopolymerizable, the
photoinitiator also absorbs UV-violet
(usually much more than it absorbs visible radiation during crosslinking of
the outer layer). Therefore, during
imaging with UV-violet-sensitive precursors, they will absorb UV-violet
radiation and produce the free radicals that
are necessary for imaging. Preferably, the free radical photoinitiators
exhibit at least one strong absorption band
in the UV-violet range so that they also act as photosensitizers during
imaging with UV-violet radiation.
[0095] The photoinitiators play no significant role during imaging with NIR
radiation. In NIR-sensitive
precursors, the photosensitizer will provide the heat (and the fewer free
radicals) necessary for imaging.
[0096] To produce a precursor that is both NIR and UV-violet
photopolymerizable, a photoinitiator sensitive to
both UV-violet and visible light can be used together with a photosensitizer
sensitive to NIR-radiation. In such
cases, the photoinitiator preferably also acts as a UV-violet sensitive
photosensitizer, so that a separate UV-violet
sensitive photosensitizer does not need to be added to the imageable layer. Of
course, in such precursors, it is
also possible to use a mixture of photoinitiators sensitive to various
wavelength to obtain an imageable layer with
the desired sensitivity.
[0097] Preferably, the free radical photoinitiators used in the present
invention exhibit one or more absorption
bands in the UV-violet range, with at least one of these bands trailing into
the visible range of the electromagnetic
spectrum or with a shoulder or one or more further minor bands in the visible
range.
[0098] Such photoinitiators are well-known to the skilled person.
Generally, these photoinitiators can be used
at a concentration between about 0.5 to about 10 weight percent.
[0099] Examples of suitable free radical photoinitiators include triazine,
thioxanthone, mercaptothioxanthone,
cyanine, monomethine, coumarine, ketocoumarine, pyrromethene, and oxime ester
photoinitiators, having
maximum absorption bands between 300 and 450 nm.
[00100] Examples of triazine photoinitiators include those described in US
patent no. 5,496,903, which are of
formula:
R7 N R9
R8
wherein R7, R8 and R9 each independently represent a trichloromethyl group, an
optionally-substituted alkyl group
having 1 to 10, preferably 1 to 4 carbon atoms, an aryl group having 6 to 15,
preferably 6 to 10 carbon atoms, an
aralkyi group having 7 to 25, preferably 7 to 14 carbon atoms, an alkoxy group
having 1 to 10, preferably 1 to 4
carbon atoms, an alkenyl group having 2 to 15, preferably 2 to 10 carbon
atoms, a piperidino group, a piperonyl
CA 02900211 2015-08-12
26
group, an amino group, a dialkylamino group having 2 to 20, preferably 2 to 8
carbon atoms, a thiol group or an
alkylthio group having 1 to 10, preferably 1 to 4 carbon atoms; with the
proviso that at least one of R7 to R,
represents the trichloromethyl group.
[00101] Specific examples of these S-triazine include 2,4,6-
tris(trichloromethyl)-S-triazine, 2-methy1-4,6-
bis(trichloromethyl)-S-triazine, 2-methoxy-4,6-bis(trichloromethyl)-S-
triazine, 2-pheny1-4,6-bis(trichloromethyl)-S-
triazine, 2-(p-methoxypheny1)-4,6-bis(trichloromethyl)-S-triazine, 2-(4-
methylthiopheny1)-4,6-bis(trichloromethyl)-
S-triazine, 2-(p-chloropheny1)-4,6-bis(trichloromethyl)-S-triazine, 2-(4-
methoxynaphthyl)-4,6-bis(trichloromethyl)-
S-triazine, 2-piperony1-4,6-bis(trichloromethyl)-S-triazine, 2-piperidino-4,6-
bis(trichloromethyl)-S-triazine, 2-styry1-
4,6-bis(trichloromethyl)-S-triazine, 2-(p-methoxystyry1)-4,6-
bis(trichloromethyl)-S-triazine, 2-(3,4-dimethoxystyry1)-
4,6-bis(trichloromethyl)-S-triazine, 2-(p-dimethylaminostyry1)-4,6-
bis(trichloromethyl)-S-triazine and the like.
[00102] Preferred free radical photoinitiators are triazine
photoinitiators, such as 2-(4'-methoxynaphthyl)-4,6-
bis(trichloromethyl)-1,3,5-triazine (also called Triazine B), 2-(4'-
ethoxynaphthyl)-4,6-bis(trichloromethyl)-1,3,5-
triazine, and 2-(4'-ethoxystyry1)-4,6-bis(trichloromethyl)-1,3,5-triazine.
These materials exhibit a strong absorption
bands between 305 and 420 nm with a maximum absorption peak between 370 and
390 nm, which trails into the
visible range of the electromagnetic spectrum. In fact, these compounds
strongly absorb UV-violet laser radiation
between 395 and 405 nm.
[00103] Other similar photoinitiators include those based on the polymers,
copolymers, and oligomers
described above. The photoinitiator can simply be attached to such polymers,
copolymers, and oligomers.
Alternatively, the polymers, copolymers, and oligomers can comprise
supplementary repeat units having the
photoinitiator as pendant group. Non-limiting examples polymers, copolymers,
and oligomers are provided
below. For conciseness, the whole description of these polymers, copolymers,
and oligomers, already given
above, is not repeated here.
[00104] Non-limiting examples of copolymers comprising a triazine pendant
group include:
0.55 - 0.05_ _ 0.15 _ _0.25
N 0NH, 00H
0 0
401
0
N
C130\NCCI,
=
PolyFR 100
CA 02900211 2015-08-12
27
[00105] Non-limiting examples of copolymers comprising a triazine pendant
group and a radical polymerizable
functional group include:
0.55 - _ 0.05 _ _ 0.15 _ _0.20 _0.05
0 0
0 NH2 0 OH 0 NH
0 0
=
N N
CI,C N CCI,
PolyFR 102
[00106] Non-limiting examples of polymeric nanoparticles comprising a
triazine pendant group include the
following, which is best used in NIR-sensitive precursors:
cH3
0.107 0.847 0.006 0.040
CN
0 0
1401
HNyO
0
NH
_ X _
CH-3Y
N N
CI,C N CCI,
PolyFR 104
[00107] Non-limiting examples of radical polymerizable oligomers comprising
a triazine pendant groups
include:
CA 02900211 2015-08-12
28
oyl,
o
I
HN
A
H y.L.
o o 0 0
O
.:-.,-,0..--=,....,Ny0 0 OH A
N----"`"01r., 0
0 0 HO H
0 I
0 0 HO 1411) 0 oHN
----
HO
0 0
0 0
0
0 0 0 H HO ON-'()IrL
H
0
0
0 0 0 0
111 OH
OH
HO 0 0
HO
0 0 0 HO 0 5 OH
0
H OH H
yko..--...,.õ.Ny0 0 OyNo)*
0.y,0
0 j.,
1 0
0 NH NH
o o
140 0
..-- ..-
N N N' N
..11,
CI30 N 0013 Cl3C N 0013
TANMER 2FR8X
CA 02900211 2015-11-03
. ,
29
CI,Cl'I' N CCI,
N ,N
S CI,C N Ca,
Y
N N
0
f ,
HA,0 0 0 0 lei
H
.,..11Ø---.,,N-0 OH A
ir 110 0 NI---`)y 0
J
0 HO 0 H 0
HI
0
0 0H0 0 0
HO 0 gbh OH
0 4111 0."-----'0 0 0
WI 0
H HO gai 0 0 0 0
0 H 0
OH
HO 411111-11 a 0OH
HO
0 IS OHO 0 io OH
H OH H 0
0 1 0,0 Il
1 0
0 NH f NH
? o
0
001 0
N 'N N ' N
CI,C N Ca, CI,C N CCI,
TANMER 4FR6X
Free Radical Coinitiators
[00108] The photoinitiating system comprises one or more free radical
coinitiators. Such coinitiators are well-
known to the skilled person. Any coinitiator typically used in negative
working lithographic printing plate
precursors can be used herein. Generally, the coinitiators can be used at a
concentration between about 1 to
about 30 weight percent.
[00109] Examples of typical coinitiators include aromatic ketones
coinitiators, iodonium tetraphenyl borate
salts coinitiators, and sulphonium tetraphenyl borate salts coinitiators.
[00110] US patent no. 7,910,768, taught to prepare iodonium salts
coinitiators, preferably iodonium
tetraphenyl borate salts coinitiators. In particular, this patent describes
iodonium salt comprising a positively
charged iodine atom to which two aryl rings are attached, and a negatively
charged counter ion. These iodonium
salts comprise one or more functional groups that can undergo radical and/or
cationic polymerization. More
specifically, these iodonium salts may contain radical polymerizable groups,
such
CA 02900211 2015-08-12
as acrylate, methacrylate and vinyl ether. These radical polymerizable groups
may be pendanted to the aryl rings
of the salt via urethane and/or urea bonds. These salts may have the following
general structures:
Al
I+
Y2 w Y1
w lodonium I
Al
I+
R8 $ w Y1
lodonium II
Al
R9 R9 I+
*as wY1
lodonium III
Al
R9
R9 I+
R8
0115
lodonium IV
Al
R9-
R9 +
I
Al le R8
41k
R8* lodonium V
CA 02900211 2015-08-12
31
Al
R9 R9 +
I
_
Al
110 w Y 1
if . le
Y 1
w 01
lodonium VI
wherein:
= Al represents an anionic counter ion selected from tosylate, triflate,
hexafluoroantimonate,
tetrafluoroborate, tetraphenylborate and triphenyl-n-alkylborate;
= w represents the number of repeat unit and may vary between 0 and 18;
= R8 and R9 independently represent hydrogen, linear or branched Cl ¨ C18
alkyl, alkyl oxy,
poly(ethylene oxide), poly(propylene oxide) and may comprise acrylate,
methacrylate and vinyl ether
terminated groups (In the case of lodoniums IV and V, either R8, R9 or both R8
and R9 do comprise
such acrylate, methacrylate and vinyl ether terminated groups); and
= Y1 and Y2 independently represent urethane and/or urea containing
compounds, which comprise single
or multiple polymerizable functional groups, such as acrylate, methacrylate or
vinyl ether.
[00111] Y1 and Y2 may have the following
chemical structures:
R
H --
0 N 0
R100 0
,
CA 02900211 2015-08-12
32
0 0
01 N
NN N N Q2
0 0
H N
) ____________________________________ 0
0
, or
0 0
01
N
0 0
H N
) ____________________________________ 0
0
wherein:
m varies between 1 and 18,
R is hydrogen or methyl
R10 is hydrogen or a linear or branched C1-C18 alkyl chain; and
01 and 02 independently represent an end compound comprising single or
multiple polymerizable
functional groups.
[00112] More specifically, 01 and 02 may independently have any of the
following structures:
CA 02900211 2015-08-12
33
OR
0 0
C)
0
¨ m
0 0
, or
0 0
0YR
R 0
0
0 0
0 0
wherein R is hydrogen or methyl.
[00113] Preferred free radical coinitiators, that are also radical
polymerizable oligomers, comprising iodonium
tetraphenyl borate salts include the mixture of such materials commercially
available from American Dye Source,
Inc. (Quebec, Canada) under tradename Tuxedo 06C051 D. This mixture
comprises:
0, 0 CH,
0 0 0 0 0
0 N 0
cr__(NH
H25C12 K)
0
410
OsI+ B
, and
CA 02900211 2015-08-12
34
o o
o
H H
0 0
o=0=
/
0
HõCi2
0
. 0
I+ 41 13- 11
Os .
Tuxedo 06C051D
Photosensitizers
[00114] The photoinitiating system comprises one or more photosensitizers.
[00115] As stated above, when imaging with UV-violet radiation, preferred
photoinitiators also act as
photosensitizers, so a separate photosensitizer is not required.
Nevertheless, when needed, suitable
photosensitizers for use in UV-violet-sensitive precursors are well-known to
the skilled person and include
triazine, thioxanthone, mercaptothioxanthone, cyanine, monomethine, coumarine,
ketocoumarine, pyrromethene,
and oxime ester photosensitizers, having maximum absorption bands between
about 300 and about 450 nm.
[00116] When imaging with NIR lasers (emitting at a wavelength between 780
and 880 nm), the photoinitiating
system comprises one or more photosensitizers having a strong absorption band
between 780 and 880 nm (also
called NIR dyes). Such photosensitizers are well-known to the skilled person.
Any photosensitizer typically used
in negative working lithographic printing plate precursors can be used herein.
They can be used as is (as a small
molecule) or attached for example to a radical polymerizable oligomer or
radical polymerizable copolymer.
Generally, the photosensitizers can be used at a concentration between about 1
and about 5 weight percent.
[00117] Examples of typical NIR photosensitizers include cyanine dyes,
squaraine dyes, and arylimine dyes, in
particular in the form of polymers comprising such dyes as pendant groups.
[00118] Preferred molecular NIR photosensitizers are the following, which
are commercially available from
American Dye Source, Inc. (Quebec, Canada):
CA 02900211 2015-08-12
N=N
/ \
C6HrNN
S
I I
N
I I
CH3 \/ CH3
Cl
ADS798BD
SH
N S
S
I I
N -......... -., --., -..+,......---
N
I I
CH3 \/ CH3
Cl
ADS798SH
[00119] Preferred NIR photosensitizers, that are also radical polymerizable
oligomers, include the following,
which are commercially available from MyIan Group (Travinh, Vietnam):
c o c o
o o o o
o o
o )-0
HN HN
NH NH
0 _____________ ( 0
NH NH
HN N N,,./ S
i. iN
S S
I I 1 I
I I I I
CH3 CH3 CH3 CH3
CI ,and CI .
NIROL 798H NIROL 798H
CA 02900211 2015-11-03
36
[00120] Suitable MR photosensitizers, that are also radical polymerizable
copolymers, include acetal
copolymers comprising both NIR dyes and radical polymerizable functional
groups as pendant groups; for
example that described in US patent no. 8,021,827 (Nguyen et al.). This patent
describes NIR absorbing acetal
copolymers that have a molecular weight greater than about 2,000 g/mol and are
either be soluble in organic
solvents or in aqueous solutions. Furthermore, they have the following general
structure:
c_
_
__
_d_ _e
0 0 0 0 OO 6H 0
C=0
G1 G2 G3
CH3
Formula 1
wherein:
= G1 represents an optional processing segment that provides solubility in
organic solvents such as
alcohol, ketone, and ester;
= G2 represents an optional thermal reactive segment;
= G3 represents a radiation-absorbing segment that exhibits one or more
strong absorption bands
between 700 and 1100 nm. Optionally, this segment may also exhibit strong
absorption bands between
400 and 700 nm;
= a, b, c, d and e are molar ratios that can vary from 0.01 to 0.99; and
\/
G1
= when the
optional G1 and/or G2 segments are not present, and/or
0 0
G2
, respectively are replaced by OH OH
[00121] More specifically, the G1 processing segment may be a linear or
branched alkyl or aryl compound
containing cyano, hydroxy, dialkylamino, trialkylammonium salts, ethylene
oxide, propylene oxide,
methylbenzylsufonyl-carbamate or carboxylic acid and phosphoric acid
functional groups.
CA 02900211 2015-08-12
37
[00122] The G2 thermal reactive segment may be a linear or branched alkyl or
aryl compound and may
contain a functional group capable of undergoing radical and/or cationic
polymerization, such as acrylate,
methacrylate, and vinyl ether. The G2 thermal reactive segment may have the
following structures:
R ¨
R2
0 ¨Y Formula 2
_
R R
R2 410
0¨m
0 _ y Formula 3
R
H
R2
= ON,0
¨ ¨m
0 0 _ Y Formula 4
R R ¨
H
R2
. ¨'- 0
0¨m --w
0 0 ¨Y Formula 5
R R ¨
H H
R2 0--0
,NN0
¨m --w
0 0 ¨ Y Formula 6
R
H H
= N
R2 N..,...õ/õ...---........_õ7¨ ¨
0,.......õ,....-
- ¨m
0 0 Formula 7
wherein:
= R is hydrogen or methyl;
= R2 is Cl ¨ C8 alkyl or alkoxy;
= m and w represent the number of repeat and may vary between 0 and 50;
= y is 1 or 2.
CA 02900211 2015-08-12
38
[00123] In another specific embodiment, the G2 segments may have pendant
groups to those illustrated in
formulas 2 to 7, but wherein the acrylate/methacrylate functional group is
replaced by another radical
polymerizable functional group.
[00124] The G3 segment may have the following structure:
Os
0 S
I I
NIR or NIR
wherein NIR is a near-infrared absorbing chromophore (dye) that exhibits one
or more strong absorption peaks
between 700 and 1100 nm and may optionally exhibit one or more strong
absorption peaks between 400 and 700
nm.
[00125] The acetal polymer may also comprise different G3 segments comprising
different near-infrared
absorbing chromophores.
[00126] The near-infrared absorbing chromophores (NIR dye) of these acetal
polymers --- and also of the
present invention more generally --- may be NIR absorbing organic compounds
containing cyanine and/or
arylimine functional groups. These chromophores may have the following
structures:
= =
. .
1' D2 ____ ,
, õ ___ D1 ,
Z2
4 j
1
/---õ, + 1
, = N--- ---." ---- --"" N µ. ,
......,
I I
(CH )R3 (CH 2),
I 2 h n I
SO; SO3M
NIR Chromophore I
SO I\A
/SO 3
D2 __________________________________________________ j,' ,
41 i 2
.
I N= ---- ---- -- N '
"-- '.
,
,
R4 R3 R5
n
CA 02900211 2015-08-12
39
NIR Chromophore II
02
,
______________________ D1
41 k2
N
R4 R3
R5
Al
NIR Chromophore III
Al
R6R6
**-N
R6 R6
NIR Chromophore IV
R7
_
Al
Nt,
R6 010 ,R6
`N =
R6 R6
NIR Chromophore V
wherein:
CA 02900211 2015-08-12
= D1 and D2 are identical or different and represent -0-, -S-, -Se-,
-CH = CH-, and -C(CH3)2;
= Z1 and Z2 are identical or different and represent one or more fused
substituted or unsubstituted
aromatic rings, such as phenyl and naphthyl;
= h represents integer number from 2 to 8;
= n represents 0 or 1;
= M represents hydrogen or a cationic counter ion selected from Na, K, and
tetraalkylammonium salts.
= Al represents an anionic counter ion selected from bromide, chloride,
iodide, tosylate, trif late,
trifluoromethane carbonate, dodecyl benzosylfonate and tetrafluoroborate,
tetraphenylborate and
triphenyl-n-butylborate.
= R3 and R7 represent hydrogen or alkyl; and
= R4, R5 and R6 are identical or different and represent alkyl, aryl alkyl,
hydroxy alkyl, amino alkyl,
carboxy alkyl, sulfo alkyl.
[00127] In a specific embodiment, R4, R5 and R6 may represent a
polymerizable substituents having the
following structure:
o
_ _ m
0
_ m
0 0
¨ m
0
0 0
wherein:
CA 02900211 2015-11-03
41
= m is a number of ¨CH2- on the alkyl chain and may vary between 0 and 50;
and
= R is hydrogen or methyl.
[00128] The NIR absorbing acetal copolymers may be used in the coating of the
present invention in quantities
ranging from about 5 to 50 % by solid weight.
[00129] Radical polymerizable NIR copolymers also include copolymeric
nanoparticles comprising NIR
chromophores as pendant group; in particular the particles described in US
patent 7,723,010 (Nguyen et al.). This
patent describes polymeric particles having a particle size between about 60
nm and about 1000 nm and
comprising a polymer. This polymer comprises (a) a hydrophobic backbone, (b) a
NIR absorbing segment having
attached thereto a NIR absorbing chromophore having an absorption peak between
about 700 nm and about
1100 nm; and (c) a NIR transparent segment.
[00130] In embodiments, the polymeric particle may have a particle size
between about 200 nm and 600 nm.
Also, in embodiments, the polymer may have a molecular weight of about 3000
Dalton or more. In specific
embodiments, the polymer may have the following structure:
r
G1L G2 -
_
, wherein:
= G1 represents the absorbing segment;
= G2 represents the transparent segment;
= G1 and G2 form the hydrophobic backbone;
= a and b independently represent molar ratios between 0.01 and 0.99; and
= the chromophore is covalently or electrostatically attached to the
hydrophobic backbone as a pendant
group.
[00131] In embodiments, the absorbing segment may comprise:
CA 02900211 2015-08-12
42
la
_a R1
00
110 a
I X-
X- CH,
\ -1m
R1-N-R1 0
NIR NIR NIR NIR
or
a
R1 el R1
1.1 X
Al'
R1 MR ,wherein:
= NIR represents the chromophore;
= Al represents hydrogen or C1-C18 alkyl;
= X represents a bromide, chloride, iodide, tosylate, triflate,
trifluoromethane carbonate, dodecyl
benzosulfonate, tetraphenylborate, alkyl-triphenylborate, tetrafluoroborate or
hexafluoroantimonate
anionic counter ion;
= M represents oxygen, sulfur, or dialkylamino;
= a represents a molar ratio between 0.01 and 0.99; and
= m represents a number repeating units between 1 and 5.
[00132] In other embodiments, the absorbing segment may comprise a
polyether linker covalently attaching
the chromophore to the polymer backbone. More specifically, the absorbing
segment may comprise:
CA 02900211 2015-08-12
43
L¨Q¨NIR
N 0-(-Y0 ) L¨Q¨NIR
0 0
\m
0
a
R1 40
,!\0õYO ___________________ L¨Q¨NIR
0 L¨Q¨NIR
H \ m 6 \
, or
a
R1 01 0
0 ( YO ) L Q¨NIR
, wherein:
= a represents a molar ratio between 0.01 and 0.99;
= R represents hydrogen or methyl;
= R1 represents C1¨C8 alkyl or C1¨C8 alkyloxy;
= w represents a number of repeating units between 10 and 50;
= m represents a number of repeating units between 1 and 10;
= Y represents a linear or branched C2-a4 alkyl;
= Q represents a spacer group;
= NIR represents the chromophore; and
CA 02900211 2015-08-12
44
0
NIR
(Y0) Q
= L represents , or
0 wherein the Q-NIR and the (Y0)õõ groups are indicated for
clarity
and j represents a number of repeating unit between 0 and 10.
[00133] In more specific embodiments, the spacer group may be:
_LN..,R2
R2 R2
¨L¨N ¨L¨N
R 3 401 SNN
L-11,11----R 3 A s0
NIR NIR NIR NIR
e ,
+N¨NIR N
¨L¨S
A A , or NIR
wherein the L and NIR groups are indicated for clarity, R2 represents Ci-C8
alkyl or Cl-C8 alkyloxy; R3 is the
same as 192 or a phenyl ring substituted by H or R2; and A represents an
anion. In embodiments, this anion may
be bromide, chloride, iodide, tosylate, tetraphenylborate, alkyl triphenyl
borate, tetrafluoro borate, or
hexafluoroantimonate.
[00134] In specific embodiments, two polymer backbones of the polymer
particles are cross-linked via two
absorbing segments and one chromophore.
[00135] In embodiments of these polymeric particles --- and of the present
invention generally ---, the NIR dye
may be:
CA 02900211 2015-08-12
,
1.õ D1 D2 __ (
41
Ri"
(CH2), R3 (CH2 ),
SO-3 SO3M
SO SO,M
1, D1 D2 __
41
N' N
R4 R3 R5
, or
7,
__________________ D1 02
41 k2
õ-
R4 R3 R5
Al
, wherein:
= D1 and D2 each independently represent -0-, -S-, -Se-, -CH = CH-, or -
C(CH3)2;
= Z1 and Z2 each independently represent one or more fused substituted or
unsubstituted aromatic ring;
= h represents an integer between 2 and 8;
= n represents 0 or 1;
= M represents hydrogen or a Na, K, or tetraalkylammonium salt cationic
counter ion.
= Al represents a bromide, chloride, iodide, tosylate, triflate,
trifluoromethane carbonate, dodecyl
benzosylfonate, tetrafluoroborate, tetraphenylborate or triphenyl-n-
butylborate anionic counter ion;
= R3 represents hydrogen or alkyl; and
= R4 and R5 each independently represent alkyl, aryl alkyl, hydroxy alkyl,
amino alkyl, carboxy alkyl, sulfo
alkyl, acetoxyl alkyl, polyether or a polymerizable substituent of formula:
CA 02900211 2015-08-12
46
R R
H
N
Ø.,,
00 0
, ,
R R
¨ m
0
, or
R
H
¨ 0,NO
_ _ m
0 0
wherein m represents a number of
repeating unit between 0 and 50 and R is hydrogen or methyl.
[00136] In
embodiments, the transparent segment may comprise styrene, substituted
styrene, alpha-
methylstyrene, 4-vinylphenol, 3-vinylbenzaldehyde, acrylate ester,
methacrylate ester, acrylonitrile, acrylamide,
methacrylamide, vinyl halide, vinyl ester, vinyl ether, 9-vinylcarbazole, or
vinyl phosphoric acid transparent
monomeric units, and mixtures thereof.
[00137] In
other embodiments, the transparent segment may comprise transparent monomeric
units obtained
by polymerizing polyether monomers of formula:
H2C=C(R)-000-(YO)w-Y-T
,
H2C=C(R)-000-CH2CH2-NHCO-0(CH2CH20)w-CH[CH2-(OCH2CH2)w-Y-T]2
,
or mixtures thereof, wherein:
= R represents hydrogen or methyl;
= Y represents C2-C4 alkyl;
= w represents a number repeating unit between 5 and 50; and
= T represents a hydroxy, alkoxy, aryloxy, carboxylic acid, sulfonic acid,
or phosphoric acid terminating
group and their salts.
[00138] In embodiments, the transparent segment may comprise:
= poly(ethylene glycol) (meth)acrylate,
= poly(propylene glycol) (meth)acrylate,
= poly(ethylene glycol-block-propylene glycol) (meth)acrylate,
= poly(ethylene glycol-block-caprolactone) (meth)acrylate,
= poly(ethylene glycol) alkyl ether (meth)acrylate,
= poly(propylene glycol) alkyl ether (meth)acrylate,
CA 02900211 2015-08-12
47
= poly(ethylene glycol-block-propylene glycol) alkyl ether (meth)acrylate,
= poly(ethylene glycol-block-caprolactone) alkyl ether (meth)acrylate
transparent monomeric units, or
mixtures thereof.
[00139] In embodiments, the transparent segment may comprise one or more
transparent monomeric units
obtained by polymerizing a monomer having two polymerizable functional groups,
thereby crosslinking two
polymer backbones via one transparent monomeric unit.
[00140] In more specific embodiments, the monomer having two polymerizable
functional groups may be:
= divinyl benzene,
= poly(ethylene glycol) di(meth)acrylate,
= poly(propylene glycol) di(meth)acrylate,
= poly(ethylene glycol-ran-propylene glycol) di(meth)acrylate,
= poly(propylene glycol)-block-polycaprolactone di(meth)acrylate,
= poly(ethylene glycol)-block-polytetrahydrofuran di(meth)acrylate,
= glycerol-ethoxylate-di(meth)acrylate,
= glycerol ethoxylate di(meth)acrylate, or mixtures thereof.
[00141] Preferred NIR photosensitizers in the form of particles include
those commercially available from
MyIan Group (Travinh, Vietnam) under tradename P0lyNP 795PD (180 nm in size):
cH3
0.107 0.020 0.867 0.006
CN
S. 0 0
HN 0
)N HN
N- S
\N-K
0,
CH3
CH, -Y - _x
CH, CH,
CI
[00142] Other preferred NIR photosensitizers are radical polymerizable
copolymers in the form of
nanoparticles. An example of such preferred NIR photosensitizer are the
following, which are commercially
available from Mylan Group (Travinh, Vietnam):
CA 02900211 2015-11-03
48
- - cH3- cH3 -
_ 0.107 _ 0.020 - -0.857- -g006- _0.010
ON
0 0 00
I I
/
HN 0 HN
S)
NS HN 0
\1\1--=
S ________ ,=1
1 I _
CH3 -Y - _x
CI H3 I
CH3
Cl ,and
PolyNP 797RP
- - cH3- - cH3 -
_ 0.107 _ 0.020 - -857_ -0.006 , _ 0.010
CN,
, 0 0 0 0
I I
CH3
HN 0 HN
S)
NS HN 0
\N--
-
CH3 4 y _ J X
CI H3 CI It
CI .
PolyNP0797RP
[00143] Other
photosensitizers include the cyanine dyes described in US 5,496,903, which are
of formula
R1 R3
....----.
. ,
I
I
1
: : A 1 -4- CH=CH)i, CH 1 B
i
il / `N 1=1?µ
/ I I \ \\(/i
R2 R5 R6 R4
Xe
CA 02900211 2015-08-12
49
wherein ring A and ring B each independently represent a benzene ring or a
naphthalene ring;
n is an integer of 2 to 5;
X- is CI-, Br, 1-, C104-, OH-, a carboxylate anion, a hydrogensulfate anion or
an organoboron anion;
Y1 and Y2 each independently represent a sulfur atom, an oxygen atom, an
ethylene group, a dimethylmethylene
group or a selenium atom;
R1 to R4 each independently represent a hydrogen atom, a chlorine atom, an
alkyl group having 1 to 10,
preferably 1 to 4 carbon atoms, a haloalkyl group having 1 to 10, preferably 1
to 4 carbon atoms, an ethylenyl
group, a styryl group, an alkoxy group having 1 to 10, preferably 1 to 4
carbon atoms, a phenyl group, a naphthyl
group, an alkylphenyl group having 7 to 16, preferably 7 to 10 carbon atoms, a
hydroxyphenyl group, a
halophenyl group, a nitrophenyl group, an aminophenyl group, a nitro group, an
amino group or a hydroxyl group;
and
R6 and R6 each independently represent an alkyl group having 1 to 10,
preferably 1 to 4 carbon atoms.
[00144]
Specific examples of these cyanine dye include 3,3'-diethyl-2,2'-
thiadicarbocyanine iodide, 3,3'-diethy1-
2,2'-thiatricarbocyanine iodide, 3,3'-diethyl-2,2'-thiatricarbocyanine
bromide, 3,3'-diethy1-6,6'-dimethoxy-2,2'-
thiatricarbocyanine iodide, 3,3'-diethyl-5,5',6,6'-tetramethy1-2,2'-
thiatricarbocyanine iodide, 3,3'-diethy1-2,2'-
oxatricarbocyanine iodide, 3,3'-diethyl-2,2'-thiadicarbocyanine bromide, 3,3'-
diethyl-2,2'-thiatetracarbocyanine
iodide, 3,3'-diethyl-2,2'-thiapentacarbocyanine iodide, 3,3'-dibuty1-2,2'-
thiatricarbocyanine iodide, 3,3'-diethy1-2,2'-
(4,5,4',5'-dibenzo)thiadicarbocyanine iodide, 3,3'-diethyl-2,2'-(4,5,4',5'-
dibenzo)thiatricarbocyanine iodide, 3,3'-
diethy1-2,2'-oxadicarbocyanine iodide, 3,3'-diethyl-2,2'-
oxatricarbocyanine iodide, 1,3,3,13',3'-
hexamethylindotricarbocyanine iodide, 1,3,3,1',3',3'-
hexamethylindotricarbocyanine perchlorate, 1,3,3,1',3',3'-
hexamethy1-2,2'-(4,5,4',5'-dibenzo)indotricarbocyanineindoh e xacarbocyanine
iodide and the like.
Free Radical Scavengers
[00145] The
photoinitiating system further comprises one or more free radical scavengers.
Generally, the free
radical scavengers can be used at a concentration between about 1 and about 5
weight percent.
[00146]
Commonly used free radical scavengers are organic compounds comprising thiol
functional group,
such as 1H-1,2,4-triazole-3-thiol, 3-amino-1,2,4-triazole-5-thiol, 4-methy1-4H-
1,2,4-triazole-3-thiol, 3-pheny1-1,2,4-
triazole-5-thiol, 3-(1,1-dimethylethyl)-1,2,4-triazole-5-thiol, 5-amino-1,3,4-
thiadiazole-2-thiol, 1,3,4-thiadiazole-2,5-
dithiol, and 1,3,5-triazine-2,4,6-trithiol. These and other commonly known
free radical scavengers can be used
here. However, these molecules have disadvantages: they can sublimate when the
precursor is oven dried
(during production) and can surface bloom during storage, which causes
pinholes after laser imaging and
development with aqueous developers.
[00147]
Therefore, there is provided herein free radical scavengers. These are
oligomers, polymers,
dendrimers comprising thiol groups (-SH) as well as radical polymerizable
functional groups.
CA 02900211 2015-08-12
[00148]
Further, the present inventor's made the surprising discovery that when such
free radical scavengers
additionally comprise carboxylic acid groups (-COON), they are even more
efficient scavenger. In fact, such
scavengers allow producing imageable layer exhibiting faster imaging speeds
and excellent adhesion of the
imaged area to the aluminum substrate.
[00149] These free radical scavengers can be of formula:
(13m-L)n-Tco (FORMULA 1)
wherein:
= P is a radical polymerizable functional group or a substituent formed by
joining two or more radical
polymerizable functional groups together, for example 1 to 5 such groups,
= L is a linker having a valence equal to m+q;
= T is a thiol group, or a substituent comprising a thiol group and
optionally further comprising a carboxylic
acid group, wherein said substituent has a valence equal to n;
= m is an integer between 1 to 5, preferably 1 or 2,
= n is an integer between 1 to 5, preferably 1 or 2, and
= q is an integer between 1 to 5, preferably 1 or 2.
[00150] Preferred such formulas include:
= P-L-T (the linker is bivalent and attached to one P group
and one T group),
= Pm-L-T (the linker is multivalent and attached one T group and to
m, preferably two, P groups,
which can be the same or different from one another,
= P-L-Tq (the linker is multivalent and attached to one P group and
q, preferably two, T groups,
which can be the same or different from one another, and
= (P-L),-T (the T group is multivalent and attached to n, preferably
two, P-L moieties, which can
be the same or different from one another).
[00151] In preferred embodiments, P is:
=
= -C-(CH2-X)3, or
= -C(CH2-X)2(CH2-0-CH2-C-(CH2-X)3),
cH3
in which X is a radical polymerizable functional group, preferably 0
(acrylate), methacrylate, acrylamide,
methacrylamide, alkylacrylate, alkylmethacrylate, alkylacrylamide,
alkylmethacrylannide, vinyl ether, allyl, or styryl.
[00152] In most preferred embodiment, P is:
CA 02900211 2015-08-12
51
I
,r0
(3 0
0 0 0
.ro4
CH3 0 ID 0 0 (3/(31
rO, 01
7L, 0
0 , i
, Or =
[00153] In preferred embodiments, T is:
SH
SH
N ' N
N¨N N SH N ' N ,Ii\iiLs,ri OH
,k j_i 'r y ,,,I, jj,
S SH , N¨NH , N0 .
, or
[00154] In preferred embodiments, L is a (linear, branched, or alicyclic)
alkylene (bivalent) or alkylyne
(trivalent) group comprising one or more following functional groups:
= -NH-C(=0)-S-,
= -S-C(=0)-NH-
= -NH-C(=0)-NH-,
= -NH-C(=0)-0-,
= -0-C(.0)-NH-,
= -S-,
r\i1N'
,-L
0 N 0
= I ,
= -NH-C(=0)-, and
= -C(=0)-NH-.
These functional groups being located at either or both ends of the
alkylene/alkylyne group and/or in between two
carbon atoms of the alkylene/alkylyne group.
[00155] Non-limiting examples of linkers include:
o
0 0 H
).L )1, ,Of,O,INJJ-LoS, 0
N S' '..'N N H 0,j11
0 ri 4NCY'S'
H H H H
0
0
H 0
OyN NAN
ox 0 H
H
õOyN
N- H H
H 0
, 0 , ,
CA 02900211 2015-08-12
52
0
HINI 1 0 0
.,0,1rNNAN
H H )LNN y - ,itN II, 4H H
N,,,,N,
0
0 H 0
' , 1
0
H H
OyNNANNy0s,
0 0
0 N 0
HNy0
,.0
I 5
0
H H H
,_,OyNNANNyN,
0 0
0 N 0
I\
HNy0
(0
1
0
H H H H
õNyN.,...,..--,..õ.".õ.....--.NAN..--.,......----,õõNyN,
0 0
0 N 0
L-..
HN y0
,
0 I 0 H I
H H
,,,A, .--(:),IrN-.....--"--s, ...sNy0, .,..,..01rNõ,---
-..s,
N'S S N
H H 0 0 , 0
1 1 5
0
N H
I N)-r'
H H H H
IDAN
(:).sNy0,. yNs, OyNs, HS
I.ns' 0
1 7 7
CA 02900211 2015-08-12
53
0 H
0 4H OANVNI=r '
S
(21
'LN N- .
1.1 -S H 0
li -S
H H
0 0
, and .
,
[00156] Exemplary chemical structures of preferred free radical scavengers
include:
CH3 0 Ni___;, CH3 0 N¨N
=rON).(N(S*SH
riCINAS)SSH
H H H
0 0
FRS-305 FRS-288
o
o
o, o,
o o
H H
r0,...õ air,N N).LOSY
1 SySH ,..i0,..,0,rrN
rµriLoS,-,TI-S,r(SH
HH
0 0 0 N¨N 0 0 0 N¨N
0 0
// //
1
FRS-715M
o
0
o, o,
o o
H H
.4,...õ,:,õFrOõ.õ(õ,õ0,Tr.N N-11.õ.,S,11,.S.,ir,SH
_,,,..4.---õr0,(=õ_,,01õN yS,r,SH
H H
0 0 0 N¨N 0 0 0 N¨N
0 0
// //
,
FRS-684M
o
o
(:) 0,
H 0 N_N 0 N_N
H H-kS*SH r()oyri
N N S SH
H H
0 0 0 0 0 0
0 0
// //
,
FRS-685M
CA 02900211 2015-08-12
54
o
CI
o I) 0 H H 0 0 H H
.).LOONIVNyNirNySH )t.
00).N1 N11 N)i N SH
'r
H
0 N¨NH H 0 N¨NH
C) 0
/Ln
,(:) 1 ,,
I,
FRS-637M
o
0, 0 N¨N
H H
0yNN).LN/\./\,./NI.i0
S S SH
0 0 0 /L 0
0 N 0
01
HNy0
0
(:).,00
% 0 0
0
,
FRS-1295
CA 02900211 2015-08-12
C)
0
H H
,,,ro,i,õ.0yNNANNyN,fNySH
0 0 0 0 N¨NH
0 N 0
()
HNy0
oY
0 0
FRS-1217
0
H H H H
TI IT II II II
SH
N¨N 0 0 N 0 0 N¨N
HNy0
0 0
O
0
FRS-1324
SH
0 N 0
0 N s s \ N 0 irL
0 0 ,
FRS-544
CA 02900211 2015-08-12
56
SH
0, ,0
N' N
H & H
0 0 0 0 0
0 0
i , and
FRS-910
I 0 1 0 I I
SH (31 C)
N' N 0
H
),
o o o o 0 o
o) ol o o
/ \
FRS-1360
[00157] Exemplary chemical structures of preferred free radical scavengers
comprising carboxylic acid groups
include:
r
0 N' N
H
.)LoNy-s)N)..Lsr0H
0 0
FRS-404,
0
SH
0,
NI' N
H
0 0 0 0
0
FRS-603,
CA 02900211 2015-08-12
57
1 0 I 0
SH
CD C) .L
N ' N
H I II
0 N,sN.='.sr0F1
0 0
11
FRS-829,
S
() H
0 0 N ' N
H
Nys,-1::.-Njsr OH
H
0 0
0
(LO
o= SH
0 10 0 4H N ' N
N, ,e-,- ).s= ...11,, ,OH
H
C) 0 0
IL
FRS-770M, and
o= o= SH
0 0 0 0
N " N
H
OC=00iNVNI)rS N SThr
H 0 0
0 0
A A
1 0 1 0
ID 0 rl
0 /0 0 0 H N ' N
N s N
H ,r * S"Thr OH
0 0
o__CY
Ao /L0
FRS-996M
CA 02900211 2015-08-12
58
[00158] In other embodiments, the free radical scavengers may be
incorporated into the radical polymerizable
copolymers described above. This can be done, for example, by adding a
supplementary repeat unit having as a
pending group the T group described above.
[00159] Examples of such free radical scavengers, that are also radical
polymerizable copolymers, in
dispersed form (PolyXP 120S, 130S and 132S) and in the form of discrete
particles (PolyNP 120S), which are
preferred in NIR photopolymerizable imageable layer, include:
-
- - -
0.53- _ 0.07 - _ 0.15 _ _0.20 ,_ _0.05
O 0
N ONH2 0 OH 0 NH
I
ISI
r
0 0
s
NNS
\N-K
SH
PolyXP 120S
- - - - - -
0.53 _ _ 0.07- -0.15 - _ 0.20 _ _0.05
O 0
N 0-NH 0NH2 0 OH 0 NH
I. NNH
SH X
PolyXP 130S
_
0.53- _ 0.07 _ -0.15 _ _0.20 _ _0.05
O 0
N 0 NH 0 NH2 0---0H
0NH
el N'iNS
0 0
SH
/.
PolyXP 132S
CA 02900211 2015-08-12
59
- , r - CH,- CH, '
- 0.057 - 0.070 _ - 0.847 _ _0.006. _0.020
CN
1 0 0 0 0
r0 NH rj
HN 0
-....-
S
7IN
N - S HN
-y --------_____,o0,CH3
SH - Y - _ x
CH3
PolyNP6120S
Free Radical Stabilizers
[00160] The photoinitiating system further comprises one or more free
radical stabilizer. Such free radical
stabilizers are well-known to the skilled person. Any free radical stabilizer
typically used in lithographic printing
plate precursors can be used herein. Generally, the free radical stabilizers
can be used at a concentration
between about 1 and about 5 weight percent.
[00161] A preferred free radical stabilizer is 9-vinyl carbazole. It can be
used at a concentration between 1 to
weight percent.
Visible Colorants
[00162] The imageable layer of this invention further comprises one or more
visible colorants. Visible
colorants are well-known to the skilled person. Any colorant typically used in
lithographic printing plate
precursors can be used herein. Generally, the visible colorants can be used at
a concentration between about
0.5 to about 10 weight percent.
[00163] Visible colorants may be dyes (molecules) or pigment (particles),
both being dispersed in the
imageable layer. Pigments are generally commercially available dispersed in a
liquid.
[00164] Examples of typical visible dyes include Victoria blue BO, crystal
violet, malachite green and their
derivatives. Preferred visible dyes are basic violet 3 and Victoria blue BO.
[00165] A preferred pigment dispersion is a phthalocyanine blue 15 pigment
dispersion in PolyXP 120S. This
dispersion is sold under tradename PolyBlue 15A (by Mylan Group, Travinh,
Vietnam) and can be used at a
concentration between 3 to 10 weight percent.
Visible Light Reflective Pigment
[00166] The imageable layer may optionally further comprises a visible
light reflective pigment, i.e. a pigment
that reflect visible light. Such visible light reflective pigment was found to
advantageously and surprisingly
increase the crosslinking of the outer surface of the imageable layer upon
exposure to visible light and to prevent
CA 02900211 2015-08-12
background staining. Such pigment can be used in the formulation at a
concentration between 1 and 5 weight
percent.
[00167] Non-limiting examples of visible light reflective pigment include
titanium dioxide, zinc oxide, and
aluminum oxide.
[00168] An example of visible light reflecting pigment that can be used is
titanium dioxide dispersed in
oligomers comprising radical polymerizable functional groups (see above for
examples such oligomers). A
preferred titanium dioxide dispersion is commercially available from Penn
Color (Doylestown, Pennsylvania, USA)
under tradename 9W1100. It comprises 75% titanium oxide pigment dispersed in
dipropylene glycol diacrylate.
Film Forming Surfactants
[00169] The imageable layer may optionally further comprises one or more film
forming surfactant. The
purpose of this surface is to improve the wetting of the coating composition
on the substrate and thus ease film
formation. Such surfactants are well-known to the skilled person. Any
surfactant typically used in lithographic
printing plate precursors can be used herein. Generally, the colorants can be
used at concentrations ranging
between about 0.1 and about 6.0 weight percent.
[00170] A preferred adhesion agent is BYK 307. This particular surfactant can
be used at a concentration
ranging between about 0.1 and about 1.0 weight percent.
Adhesion Promoting Agents
[00171] The imageable layer may optionally further comprises one or more
adhesion promoting agents.
[00172] Such agents are well-known to the skilled person. Any adhesion
promoting agent typically used in
lithographic printing plate precursors can be used herein. Examples of
typically agents include phosphoric acid
containing molecules, oligomers and polymers. Generally, these adhesion
promoting agents can be used at
concentrations ranging between about 0.5 and about 5.0 weight percent.
[00173] A preferred adhesion agent is a phosphate ester polypropylene glycol
methacrylate sold under
tradename Sipomero PAM-200. It can be used at a concentration ranging between
1 to 5 weight percent.
Substrate
[00174] The negative-working lithographic printing plate precursor of the
invention comprises a hydrophilic
substrate. Any substrate known by the skilled person to be useful for such
purpose can be used.
[00175] A preferred substrate is a hydrophilic grained and anodized
aluminum sheet; preferably of a thickness
between about 100 and about 400 m.
[00176] The manufacture of such substrate is carried by an electrolytic
process that is well-known to the
skilled person. This electrolytic process can be carried out on a continuous
production line with a web process or
sheet-fed process. This process typically comprises degreasing the aluminum
substrate in an alkaline solution,
electrograining in acidic solution, neutralization in an alkaline solution,
anodization in acid solution, post
anodization treatment with hydrophilic agents, drying with hot air, and ready
for coating. More specifically, the
CA 02900211 2015-08-12
61
aluminum can be first be degreased. In embodiments, this step comprises
washing the aluminum with, for
example, an aqueous alkaline solution containing sodium hydroxide (3.85 g/1)
and sodium gluconate (0.95 g/l) at
65 C to remove any organic oil and crease from its surface; neutralizing with,
for example, aqueous hydrochloric
acid (2.0 g/l); and finally washing with water to remove the excess of
hydrochloric acid solution. The clean
aluminum then undergoes electrolytic graining, for example in an aqueous
electrolyte containing an aqueous
solution of hydrochloric acid (8.0 g/l) and acetic acid (16 g/l), using carbon
electrodes at 25 C. The current and
charge density may be 38.0 A/dm, and 70.0 C/dm2, respectively. After graining,
the aluminum undergoes
desmuting, which removes unwanted impurities before anodization. This can be
accomplished, for example, with
an aqueous sodium hydroxide solution (2.5 g/1), followed by neutralizing with
an aqueous sulfuric acid solution (2
g/1); and washing with water to remove the excess acid. The aluminum then
undergoes anodizing thus producing
an aluminum oxide layer. Anodization can take place, for example, in an
aqueous electrolyte containing sulfuric
acid (140 g/l) at 25 C; the current and charge density being adjusted to
produce an aluminum oxide layer having
a thickness between about 2.5 and about 3.0 g/m2. The aluminum oxide layer is
then washed with water and
treated to enhance the hydrophilicity of its surface. This can be achieved,
for example with an aqueous solution
containing sodium dihydrophosphate (50 g/l) and sodium fluoride (0.8 g/1) at
75 C followed by washing with water
at 50 C.
[00177] At this step, the substrate can be reacted with:
an aqueous solution containing sodium dihydrogenphosphate (50 g/1) and sodium
fluoride (0.8 g/l) at
75 C, thereby producing a phosphate fluoride coating on the substrate, or
an aqueous solution containing soldium silicate (30 g/l) at 75 0C was, thereby
producing a sodium
silicate coating on the substrate.
Both coating desirably enhance the hydrophilicity of the substrate. The sodium
silicate coating is generally
preferred as it increases the adhesion of the imageable layer on the
substrate. However, when this coating is
used, it tends to become stained when a visible dye is used. So it is best
used when the imageable layer contains
a visible pigment instead. When using a visible dye, the phosphate fluoride
coating can generally be used
without staining.
[00178] Another alternative is to treat the substrate with an aqueous
solution containing polyvinyl phosphoric
acid (30 g/l) at 75 C, thereby producing polyvinyl phosphoric acid hydrophilic
coating on the substrate.
[00179] The aluminum/aluminum oxide layers are then dried, for example with
hot air at 110 C in an oven. A
specific example of such manufacture process is described in the section
entitled "Manufacturing Process" below.
[00180] This aluminum sheet can be used and coated as is. Alternatively
this aluminum sheet can be
laminated onto various other materials.
[00181] In embodiments, the aluminum sheet is laminated on a sheet of
plastic sheet or a coated paper
sheet. This reduces, or may even eliminate, the need for interleaving paper,
which is generally for packaging to
CA 02900211 2015-11-03
62
prevent the precursor from sticking to each other. This would also
significantly reduce production costs as it
allows using a thinner sheet of (expensive) aluminum.
[00182] Figure 2 is a cross-sectional view of the negative working
precursor of the invention coated on an
aluminum sheet laminated on a plastic sheet. In Figure 2,
= [201] is the imageable layer (preferably having a thickness preferably
between about 0.8 and about 3.0 pm);
= [202] is the crosslinked portion of the imageable layer (preferably
having a thickness preferably between
about 0.08 and about 0.30 pm);
= [203] is the hydrophilic grained and anodized aluminum sheet (preferably
having a thickness preferably
between about 100 and about 400 pm);
= [204] is a plastic or paper sheet (preferably having a thickness
preferably between about 30 and about 300
pm); and
= [205] is an adhesive layer (preferably having a thickness preferably
between about 1 and about 50 pm).
[00183] Figure 3 shows the cross-sectional scheme of the negative working
precursor of the invention coated
on an aluminum sheet laminated on a coated paper sheet. In Figure 3:
= [301] is the imageable layer (preferably having a thickness preferably
between about 0.8 and about 3.0 pm);
= [302] is the crosslinked portion of the imageable layer (preferably
having a thickness between about 0.08 and
about 0.30 pm); and
= [303] is the hydrophilic grained and anodized aluminum sheet (preferably
having a thickness between about
100 and about 400 pm);
= [304] is a paper sheet (preferably having a thickness preferably between
about 30 and about 300 pm);
= [305] is a polymeric protective coating; and
= [306] is an adhesive layer (preferably having a thickness between 1 and
50 pm).
[00184] US patent application publication no. 2011/0277653 and US patent
application no. 14/249, describe
laminated substrates that can be used herein.
[00185] More particularly, US patent application publication no.
2011/0277653 provides a lithographic printing
plate substrate comprising (a) a base layer, (b) a layer of a first adhesive
covering one side of the base layer
except for at least two opposite edges thereof, and (c) an aluminum layer
laminated onto the layer of first
adhesive and said opposite edges of the base layer, the aluminum layer thereby
being sealed with the base layer
at said opposite edges of the base layer.
CA 02900211 2015-08-12
63
[00186] The substrate may also comprise strips of a second adhesive covering
said opposite edges of the
base layer. Furthermore, the aluminum layer is laminated onto the layer of
first adhesive and the strips of second
adhesive. Therefore, it can be said that the aluminum layer is sealed with the
base layer through this second
adhesive. The second adhesive is typically insoluble and non-dispersible in
water and fountain solutions so as to
reduce risks of de-lamination of the substrate and therefore allow longer runs
on press. The second adhesive
may be solvent-based. In other words, it is an adhesive prepared with a
solvent that is not aqueous, for example
an organic solvent. In embodiments, the second adhesive is an urethane
adhesive.
[00187] The exact nature of the base layer material is not crucial. The
material is chosen based on cost and
handling characteristics. It is sufficient that the base layer, together with
the other layers, of the substrate, the
base layer provides the desired structural strength. In embodiments, the base
layer is between about 50 and
about 400 m thick.
[00188] The base layer may be, for example, a plastic layer, a composite
layer, a cellulose-based layer such
as cardstock or paper, or a non-woven fabric layer. When the base layer is a
plastic layer, it can be a solid plastic
layer, a multi-laminate layer, or a plastic foam layer. The base layer may
comprise a thermoplastic resin, such as
a petroleum based thermoplastic resin or a biomass based thermoplastic resin.
Example of such resins include
polystyrene (PS), polyethylene (PE), polypropylene (PP), polyester (PET),
polyamide (PA), polyvinyl chloride
(PVC), polyetheretherketone (PEEK), polyimide (PI), polyvinylacetate (PVA),
polyaklacrylate (PAAA),
polyalkylmethacrylate (PAMA), polylactide, polybutahydroburate,
polysuccinamate, cellulosic polymers,
copolymers thereof, and mixtures thereof. These thermoplastic resins, and any
plastic used as a base layer, may
comprise one or more fillers. The amount of fillers in the resins may be
between about 5 to about 85 % by
weight. The filler may be an inorganic filler, such as, for example, calcium
carbonate, silica, alumina, titanium
oxide, aluminosilicate, zeolite and fiberglass. The filler may also be an
organic carbohydrate flour, such as that
obtained from biomass and natural fibers, such as starch, sawdust, rice husks,
rice straw, wheat straw, and
sugarcane bagasse. The filler may also be carbon black or another similar
material.
[00189] The base layer may further comprise pigments or colorants. These
allow, for example, identifying a
given product or a given brand. The base layer may also comprise polymer
processing additives, such as
antioxidants and flowing agents for example.
[00190] The base layer may be produced by melt extrusion, possibly with one or
more of the other layers of
the substrate.
[00191] The layer of first adhesive provides for the adhesion of the
aluminum layer to the rest of the substrate
during processing and use. As such, the exact nature of the layer of first
adhesive is not critical. In embodiment,
the layer of first adhesive is a plastic layer. In embodiments, the layer of
first adhesive comprises a thermoplastic
resin, preferably one that is soluble or dispersible in a processing liquid.
The layer of first adhesive may be
between about 1 and about 100 urn thick.
CA 02900211 2015-11-03
64
[00192] The layer of first adhesive may be produced by melt extrusion
(possibly by co-extrusion with one or
more of the other layers of the substrate). In this case, the thermoplastic
resins may be, for example, linear
polyvinyl alcohols, branched polyvinyl alcohols (for example that described in
US2009/0286909, polyethylene
oxide (such as that available under tradenames POLYOXTm from Dow Industrial
Specialty Polymers and that
available from Sumitomo Seika, Japan), polyamides (such as that described in
US 5,324,812 and US 6,103,809),
water soluble polyesters (such as that available under tradename Zypol from
Zydex Industries, India), acrylic acid
copolymers, and methacrylic acid copolymers.
[00193] Alternatively, the layer of first adhesive may be produced by coating
(for example the aluminum layer)
with a polymeric solution following by drying (for example in an oven using
hot air or NIR heating tubes). In that
case, the polymeric solution may be an homogeneous solution or an emulsion of,
for example, a polyvinyl
alcohol, polyethylene oxide, an acrylic acid copolymer, a methacrylic acid
copolymer, an urethane polymer, an
urea polymer, an amide polymer, an ester polymer, copolymers thereof or a
mixture thereof.
[00194] In embodiments, the substrate further comprises an outer layer
covering the other side of the base
layer (i.e. the side not covered by the layer of first adhesive and mounted on
and facing the lithographic press
cylinder). This layer may be between about 1 and about 50 pm thick. This layer
may be a plastic layer. In
embodiments, the outer layer comprises a thermoplastic resin. In embodiments,
the thermoplastic resin is
polyethylene, polypropylene, polymethylmethacrylate, polyethylene phthalate,
polystyrene, polyvinyl chloride, a
copolymer thereof or a mixture thereof.
[00195] In embodiments, the outer layer is produced by melt extrusion,
possibly with one or more of the other
layers of the substrate as explained below.Like the base layer, the outer
layer may comprise, in embodiments,
pigments, colorants, fillers (such as that described above for the base
layer), and/or polymer processing additives
such as antioxidants and flowing agents.
[00196] US patent application no. 14/249,458 provides a laminated
lithographic printing plate precursor
comprising:
an aluminum layer having a first side and a second side, a first aluminum
oxide layer coating
the first side of the aluminum layer, (together the aluminum sheet discussed
above)
optionally a second aluminum oxide layer coating the second side of the
aluminum layer,
an imageable layer coating the first aluminum oxide layer,
an adhesive layer adhering to the second side of the aluminum layer or to said
second
aluminum oxide layer when the second aluminum oxide layer is present, and
a base layer coating the adhesive layer,
the adhesive layer being accessible to and insoluble in oleophilic inks and
alkaline or acidic aqueous
fountain solutions used during printing with the printing plate, and alkaline
or acidic aqueous developers
used during development of the printing plate, and
the adhesive layer being:
CA 02900211 2015-08-12
soluble in an alkaline aqueous processing liquid, when said developers and
said fountain
solutions are acidic,
soluble in an acidic aqueous processing liquid, when said developers and said
fountain
solutions are alkaline,
meltable, or
when said second aluminum oxide layer is present, a dry adhesive compliant
layer having a
hardness of 60 Shore-A or less,
thereby allowing delamination of the printing plate in view of recycling after
printing.
[00197] Generally, these printing plate precursors have a total thickness
between 100 pm and 600 p m,
preferably between 100 and 400 pm.
[00198] Together, the aluminum layer, the first aluminum oxide layer and
the imageable layer in US patent
application no. 14/249,458 embody a rather conventional lithographic printing
plate. However, the aluminum
layer can be thinner than in conventional printing plates because the base
layer provides structural support to the
printing plates of the present invention. For example, the aluminum layer may
be between about 20 and about
300 pm thick, preferably between about 20 and about 200 pm thick. However, the
aluminum may also be thicker,
such as between about 100 and about 300 pm thick. The hardness of the
aluminium layer is typical of that in
conventional plates. For example, it can be between H16 and H18.
[00199] The base layer may be between about 10 and about 350 pm thick,
preferably between about 10 to
about 300 pm, more preferably between about 50 to about 300 pm, most
preferably between 100-200 pm, such
as between 100-150 pm. The exact nature of the base layer material is not
crucial. The base layer may be a
plastic layer, a composite layer, a cellulose-based layer such as cardstock or
paper, or a non-woven fabric layer.
When the base layer is a plastic layer, it can be a solid plastic layer, a
multi-laminate layer, or a plastic foam
layer. In embodiments, the base layer comprises a thermoplastic resin, such as
a petroleum based thermoplastic
resin or a biomass based thermoplastic resin. Example of such resins include
polystyrene (PS), polyolefins such
as polyethylene (PE) and polypropylene (PP) (including oriented PP, such
biaxially oriented PP (or BOPP)),
polyesters, such as polyethylene terephthlate (PET), polyamide (PA), polyvinyl
chloride (PVC),
polyetheretherketone (PEEK), polyimide (PI), polyvinylacetate (PVA),
polyalkylacrylate (PAAA),
polyalkylmethacrylate (PAMA), polylactide, polybutahydroburate,
polysuccinamate, cellulosic polymers,
copolymers thereof, and mixtures thereof.
[00200] These thermoplastic resins, and any plastic used as a base layer,
may comprise one or more fillers.
The amount of fillers in the resins may be between about 5 to about 85 % by
weight, for example between about
10 and about 30/%, and more specifically about 20%. The filler may be an
inorganic filler, such as, for example,
calcium carbonate, silica, alumina, titanium oxide, aluminosilicate, zeolite
and fiberglass. The filler may also be
an organic carbohydrate flour, such as that obtained from biomass and natural
fibers, such as starch, sawdust,
CA 02900211 2015-11-03
66
rice husks, rice straw, wheat straw, and sugarcane bagasse. The filler may
also be carbon black or another
similar material.
[00201] In embodiments, the base layer may further comprise pigments or
colorants. The base layer may also
comprise polymer processing additives, such as antioxidants and flowing agents
for example.
[00202] In embodiments, the base layer is paper coated with a polymer layer
on at least one side (it is not
necessary to coat the paper on the side facing the adhesive layer). The
polymer layer can be a polybutyrate or
polyacetal layer.
[00203] The adhesive layer provides for the adhesion of the base layer to the
aluminum layer base layer
during use of the printing plate (including development and printing). The
adhesive layer is not soluble in the
developers, fountain solutions and developers. The adhesive layer should
indeed be insoluble or show little
solubility in these liquids otherwise the printing plate would risk
delamination during development and/or printing.
Therefore, if the printing plate is for use with alkaline developers and/or
alkaline fountain solutions, the adhesive
should be insoluble in alkaline aqueous solutions, and if the printing plate
is for use with acidic developers and/or
acidic fountain solutions, the adhesive layer should be insoluble in acidic
aqueous solutions. Also, the adhesive
should not be soluble in the inks used for printing (these inks are oleophilic
as explained above).
[00204] The adhesive layer can be of various natures. It can be a layer of
a drying adhesive, i.e. an adhesive
that hardens by drying. It can also be a layer of a hot-melt adhesive, i.e. an
adhesive that hardens by cooling.
Finally, the adhesive layer can be dry adhesive compliant layer that adhere to
the second aluminum oxide layer
as discussed below. Such dry adhesives are disclosed in International patent
publication no. WO 2012/155259
(Nguyen et al.).
[00205] The drying adhesives that can be used in the adhesive layer are
solvent based adhesives, which
typically comprise one or more ingredients (typically polymers) dissolved in a
solvent. As the solvent evaporates,
the adhesive hardens. Thus, the drying adhesives for use in the adhesive layer
should be soluble in such solvent
(water based or not) so they can be applied to the base layer. Further, once
dried, these adhesives should not be
soluble in the oleophilic inks used with the printing plate. This can be
achieve by selecting adhesives that are
soluble in aqueous solutions rather than in oleophilic solvents.
[00206] In addition, however, these adhesives should not be soluble in the
aqueous developers, and fountain
solutions that will be used with the printing plate, while being soluble in
the aqueous processing liquid to be used
for delamination (see below for more details on recycling). This is achieved
this by selecting the nature of the
processing liquid in function of the nature of the developers and/or fountain
solutions used during use of the
printing plate. If the developers and/or fountain solutions are acidic, then
the processing liquid will be alkaline. If
the developers and/or fountain solutions are alkaline, then the processing
liquid will be acidic. In other words, the
drying adhesive must be either (A) soluble in alkaline aqueous solution, but
insoluble in acidic aqueous solutions,
or (B) soluble in acidic aqueous solution, but insoluble in alkaline aqueous
solutions.
CA 02900211 2015-08-12
67
[00207] All of the above can be achieved by polymers that have a relatively
low Tg (glass transition
temperature), for example between about 10 and about 60 C, preferably between
about 15 and about 20 C, so
they are tacky. Such polymers should comprise sufficient polar functional
groups (alcohols, carboxyls, amides,
and the like) that provide solubility in aqueous solutions and limit
solubility in oleophilic media. Such polymers
include acrylate, urethane, urea, epoxy, or ester polymers. Preferred polymers
are acrylate polymers as they are
economical and are easy to modify.
[00208] Further, these polymers should comprise either sufficient acidic
functional groups (such as -COOH)
that provide solubility in alkaline aqueous solutions or sufficient basic
functional groups (such as amines) that
provide solubility in acidic aqueous solutions depending on its desired
solubility characteristics.
[00209] An example of a polymer that is soluble at an acidic pH, but
insoluble at alkaline pH, is a copolymer of
alkyl acrylate monomers with dialkylamino alkyl acrylate monomers. The
presence of dialkylamino alkyl acrylate
monomers, which contain a basic amino group, provides solubility in acidic
aqueous solutions. The solubility of
the copolymer can thus be fine-tuned by adjusting the ratio of this monomer
compared to the other monomers.
Examples of dialkylamino alkyl acrylate monomers include dimethylamino-ethyl-
acrylate, diethylamino-ethyl-
acrylate, and dibutylamino-ethyl-acrylate. Examples of alkyl acrylate monomers
include ethyl acrylate and methyl
acrylate. A specific example of such a copolymer is a copolymer of methyl
acrylate (5-15% by weight), ethyl
acrylate (50-80% by weight), and dimethylamino ethyl acrylate (5-20% by
weight). The percentages value being
based on the total weight of the copolymer. Such a polymer is, for example,
sold under the tradename ElastakTM
1020.
[00210] An example of an adhesive that is soluble at an alkaline pH, but
insoluble at acidic pH, is a copolymer
of alkyl acrylate monomers with acrylic acid monomers. The presence of acrylic
acid monomers, which contain
acidic groups, provides solubility in alkaline aqueous solutions. The
solubility of the copolymer can thus be fine-
tuned by adjusting the ratio of this monomer compared to the other monomer.
Examples of alkyl acrylate
monomers include the same as above. A specific example of such a copolymer is
a copolymer of methyl acrylate
(5-15% by weight), ethyl acrylate (50-80% by weight), and acrylic acid (5-20%
by weight). The percentages value
being based on the total weight of the copolymer. Such a polymer is, for
example, sold under the tradename
ElastakTM 1000.
[00211] In both cases above, the Tg of the copolymers is controlled by the
ratio of various monomers. For
example, pure poly(methylacrylate) has a Tg of about 10 C, pure
poly(ethylacrylate) has a Tg of about -21 C,
pure poly (dimethylamino ethyl acrylate) has a Tg of about 19 C, while pure
poly(acrylic acid) has a Tg of about
105 C.
[00212] The hot-melt adhesives that can be used in the adhesive layer are
thermoplastics applied in molten
form that solidify on cooling to form adhesive bonds between the aluminum
layer and the base layer. Again,
once cooled, these adhesives should not be soluble in the oleophilic inks used
with the printing plate. In addition,
CA 02900211 2015-08-12
68
the hot-melt adhesives should not be soluble in the developers and fountain
solutions that will be used with the
printing plate.
[00213] Examples of suitable hot-melt adhesives include ethylene-
vinylacetate polymer, polyamide, polyolefin,
reactive polyurethane, and ethylene¨acrylic ester¨maleic anhydride
terpolymers. In particular, the adhesives sold
under the tradenames:
¨ LotaderTM (including product 3210, a random terpolymer of ethylene,
acrylic ester and maleic anhydride)
from Arkema, USA,
¨ DorusTM (including product KS 351, an ethylene-vinylacetate polymer) from
Henkel, USA,
Macromelte (including product TPX 16-344 UBKTM, a polyamide) from Henkel, USA,
and
¨ AffinityTM (including product GA1875, a polyolefin elastomer) from Dow,
USA
are noted.
[00214] A sub-class of hot-melt adhesive are reactive hot-melt adhesives,
which after solidifying, undergo
further curing e.g., by moisture, by ultraviolet radiation, electron
irradiation, or by other methods.
[00215] Examples of such adhesives include the reactive urethane adhesives
sold under tradenames:
¨ Suprasec0 from Huntsman, USA,
¨ Purmelt0 (including product QR-6205) from Henkel, USA,
¨ Terorehm0 (including product MC9520 and MC9530, moisture curing
polyurethanes) from Henkel, USA,
and
¨ Mor-MeItTm (including product R5003, a moisture curing polyurethane) from
Dow, USA.
[00216] In embodiments of all of the above types of adhesives, the adhesive
layer is between about 10 and
about 300 m thick, preferably between about 10 and about 100pm, most
preferably between about 10 and 50
pm. In embodiments, the adhesive layer is about 20 pm thick.
[00217] When a dry adhesive is used, the backside of the aluminum layer
(i.e. the side opposite the image
forming layer) must be covered by a "second" aluminum oxide layer. Such
aluminum oxide layer, prepared by
graining and anodization as described below, comprises nano- and micro-pores
that are involved in the dry
adhesion. The base layer is covered by the adhesive layer, which in this case
is a dry adhesive compliant layer.
Such a dry adhesive compliant layer will reversibly adhere to the aluminum
oxide layer.
[00218] The dry adhesive compliant layer is not soluble in the oleophilic
inks, developers and fountain
solutions that will be used with the printing plate. It should be noted
however that it is not necessary that the dry
adhesive compliant layer be soluble in a processing liquid as the dry adhesion
means that the base layer bearing
the dry adhesive compliant layer can very simply be peeled off the second
alumiunum oxide layer, which allows
delaminating without using any processing liquid.
[00219] The dry adhesive compliant layer has a relatively low modulus so
that it is able to deform and conform
to the pores in the "second" aluminum oxide layer. In embodiments, the
compliant material or surface has a
hardness of 60 Shore-A or less, preferably 55, 50, 45, 40, 35, 30, or 25 Shore-
A or less. In these or other
CA 02900211 2015-08-12
69
embodiments, the compliant material or surface has a hardness of 20, 25, 30,
35, 40, 45, 50, or 55 Shore-A or
more
[00220] In embodiments, the compliant surface is made of a polymer, non-
limiting examples of which include
thermoplastic polymers, thermoplastic elastomers, and crosslinked elastomers.
[00221] Suitable polymers include, but are not limited to, natural
polyisoprene, synthethic polyisoprene,
polybutadiene, polychloroprene, butyl rubber, styrene-butadiene rubber,
nitrile rubber, ethylene propylene rubber,
epichlorohydrin rubber, polyacrylic rubber, silicone rubber, fluorosilicone
rubber, fluoroelastomers,
perfluoroelastomers, polyether block amides, chlorosulfonated polyethylene,
ethylene-butadiene copolymer
elastomers, ethylene-vinyl acetate, silicone elastomer, polyurethane
elastomer, aminopropyl terminated siloxane
dimethyl polymers, styrene-ethylene/propylene-styrene (SEPS) thermoplastic
elastomer, styrene-
ethylene/butylene-styrene (SEBS) thermoplastic elastomer, styrene-isoprene-
styrene (SIS) thermoplastic
elastomer, styrene-butadiene-styrene (SBS) thermoplastic elastomer, and/or
styrene-ethylene/butylene-styrene
grafted with maleic anhydride thermoplastic elastomer.
[00222] In embodiments, the compliant material making the thy adhesive
compliant layer is an elastomer
having a hardness between 40 and 55 Shore D.
[00223] The table below shows non-limiting examples of thermoplastic
elastomers together with some of their
physical properties. The thermoplastic elastomers are listed with their
hardness (Shore A), elongation at break
(`)/0), and/or tensile strength (psi). Kraton thermoplastic elastomers are
available through Kraton Polymers in
Houston, TX.
Elongation Tensile
Hardness
Name at break strength
(Shore A)
(%) (psi)
KRATON D SIS - Styrenic block copolymers based on styrene and isoprene
KRATONe D1114 P Polymer
(Clear, linear triblock copolymer based on styrene and 42 1300 4600
isoprene with a polystyrene content of 19%.)
KRATONO D1160 B Polymer
(Clear linear triblock copolymer based on styrene and 48 1300 4640
isoprene with bound styrene of 18.5% mass.)
KRATONO 01161 B Polymer
(Clear, linear block copolymer based on styrene and 30 1300 4060
isoprene with a polystyrene content of 15%.)
CA 02900211 2015-08-12
KRATON D1163 P Polymer
(Clear, linear triblock copolymer based on styrene and 25 1400
1500
isoprene, with a polystyrene content of 15%)
KRATON D SBS - Block copolymers composed of blocks of styrene and butadiene
KRATON D4141 K Polymer
50 1300 2750
(31% styrene)
KRATON D4150 K Polymer
(Linear triblock copolymer based on styrene and 45 1400 2800
butadiene with a polystyrene content of 31%.)
KRATON D4158 K Polymer
(Oiled, radial copolymer based on styrene and butadiene 41 1110
1330
with a polystyrene content of 31%.)
KRATON G SEBS/SEPS - Styrenic block copolymers with a hydrogenated midblock
of styrene-
ethylene/butylene-styrene (SEBS) or styrene-ethylene/propylene-styrene (SEPS)
KRATON G1645 M Polymer
(Linear triblock copolymer based on styrene and 35 600 1500
ethylene/butylene)
KRATON G1657 M Polymer
(Clear, linear triblock copolymer based on styrene and 47 750
3400
ethylene/butylene with a polystyrene content of 13%)
KRATON G1702 H Polymer
(Clear, linear diblock copolymer based on styrene and 41 <100
300
ethylene/propylene with a polystyrene content of 28%.
KRATON G4609 H Polymer
(White mineral oil extended linear triblock copolymer
based on styrene and ethylene/butylene with a 22 800
polystyrene content of 33%. Nominal oil content of the
polymer is 45.5%w (90 parts/100 parts rubber (phr)).
KRATON FG - SEBS polymers with 1.0 to 1.7 wt. % maleic anhydride (MA) grafted
onto the rubber
midblock
KRATON FG1924 G Polymer 49 750 3400
CA 02900211 2015-08-12
71
(Clear, linear triblock copolymer based on styrene and
ethylene/butylene with a polystyrene content of 13%.)
[00224] The table below shows non-limiting examples of crosslinked elastomers
together with some of their
physical properties. The crosslinked elastomers are listed with their hardness
(Shore A), elongation at break (%),
tensile strength (psi), and tear strength (kN/m). The silicone elastomers are
available through Dow Corning.
Tensile Tear
Durometer Elongation
Name Strength Strength
(Shore A) (%)
(psi) (kN/m)
Dow Corning 3631
(Two-part, solvent free, heat-cured liquid 19 800 725 16
silicone rubber.)
Dow Corning D94-20P
(Two-part, 1:1 ratio, addition cure silicone 21 900 765
N/A
elastomer)
Dow Corning D94-30P
(Two-part, 1:1 ratio, addition cure silicone 33 800 1000
16.1
elastomer)
Silastic LC-20-2004
(20 Durometer, 2 parts, 1 to 1 mix,
translucent, FDA 21 CFR 177.2600 and 20 900 940 24
BfR, XV, molding and injection molding
grade Liquid Silicone Rubber)
Silastic LC-9426
20 790 609 23
(Two-part liquid silicone rubber)
Silastic 94-595
(40 Durometer, 2-part, 1 to 1 mix, 42 610 1450 34
translucent Liquid Silicone Rubber)
Silastic 94-599
49 590 1595 32
(47 Durometer, 2-part, 1 to 1 mix,
CA 02900211 2015-08-12
72
translucent, molding grade, Liquid Silicone
Rubber)
Silastic LC-9434
33 790 797 32
(two-part liquid silicone rubber)
Silastic LC-9436
29 720 855 28
(two-part liquid silicone rubber)
Silastic LC-9451
50 540 1102 30
(two-part liquid silicone rubber)
Silastic LC-9452
50 560 1015 34
(two-part liquid silicone rubber)
Silastic LC-9454
50 530 1044 29
(two-part liquid silicone rubber)
DOW CORNING Class VI Elastomers C6-
530 30 831 1189 27.5
(heat cured elastomer raw materials)
DOW CORNING Class VI Elastomers C6-
540 40 742 1293 41.9
(heat cured elastomer raw materials)
Dow Corning S40
(Two-part platinum-catalyzed silicone 40 864 1250 31.2
elastomer)
Dow Corning S50
(Two-part platinumcatalyzed silicone 48 610 1275 42.5
elastomers)
Dow Corning D94-45M
(Two-part, 1:1 ratio, addition cure silicone 45 600 1050 45
elastomer)
[00225] Another example of compliant material is QLE1031; a heat curable
silicone elastomer available from
Quantum Silicones, Virginia, USA.
CA 02900211 2015-08-12
73
[00226] In embodiments, the dry adhesive compliant layer is between about 5
and about 80 urn thick,
preferably between about 10 and 50 pm.
Method of Manufacture and Other Methods
[00227] In a related aspect, the present invention provides methods for
manufacturing a negative-working
lithographic printing plate precursor, in particular a precursor as described
above. This method comprises the
steps of:
a) providing a hydrophilic substrate coated with a NIR photopolymerizable
or UV-violet photopolymerizable
imageable layer, the imageable layer comprising a free radical photoinitiator
sensitive to visible radiation,
the imageable layer having an outer surface and a thickness,
b) uniformly, and partially or completely crosslinking the outer surface of
the imageable layer down to a
depth corresponding to at most about 70% of the thickness of the imageable
layer.
[00228] In other related aspects, the present invention provides methods
for:
= creating an oxygen barrier on an imageable layer of a negative-working
lithographic printing plate
precursor,
= protecting an imageable layer of a negative-working lithographic printing
plate precursor from scratches,
= reducing the tackiness of an imageable layer of a negative-working
lithographic printing plate precursor,
= reducing absorption of oxygen molecules from the air by an imageable
layer of a negative-working
lithographic printing plate precursor,
= increasing the laser imaging speed of an imageable layer of a negative-
working lithographic printing
plate precursor, and
= increasing the shelf-life of a negative-working lithographic printing
plate precursor.
All these methods comprising the steps of:
a) providing a negative-working lithographic printing plate precursor
comprising a hydrophilic substrate
coated with a NIR photopolymerizable or UV-violet photopolymerizable imageable
layer, the imageable
layer comprising a free radical photoinitiator sensitive to visible radiation,
the imageable layer having an
outer surface and a thickness,
b) uniformly, and partially or completely crosslinking the outer surface of
the imageable layer down to a
depth corresponding to at most about 70% of the thickness of the imageable
layer.
[00229] All the information provided above in regard of the negative-
working lithographic printing plate
precursor (including the imaging layer and the crosslinked portion thereof,
the various components of the
imageable layer, the substrate, etc.) also applies to these methods. This
information is not repeated here.
CA 02900211 2015-08-12
74
[00230] In step a) of all the above methods, the hydrophilic substrate can
be manufactured as described
above. This can include, for example, graining and anodization of an aluminum
sheet and optionally lamination to
various substrates.
[00231] The hydrophilic substrate must be coated with a photopolymerizable
imageable layer. The
components of this layer have been described above. They can be dissolved (or
suspended in the case of
particles) in a coating solvent to produce a coating composition. Examples of
suitable solvents include C1-C8
alcohol, C4-C8 ketone, C3-05 cyclic ether, and C4-C8 ester, preferably
propylene glycol methyl ether, methyl ethyl
ketone, 1,3-dioxolane, and 1-methoxy-2-propanol.
[00232] The imageable layer is produced by coating this composition on the
substrate and drying to evaporate
the solvent. The coating can be carried using a slot-die coating head, a wire-
wound rod, a roller, or micro-gravure.
The drying can be carried out for example in an oven a temperature between 100
and 150 C.
[00233] In step b) of all the above methods, the outer surface of the
imageable layer is crosslinked down to a
certain depth. This is carried out by irradiating the imageable layer with
visible light; more specifically, by
exposing the imageable layer to a visible light source emitting between 400
and 700 nm.
[00234] The aim of the visible irradiation is to provide a rather low light
intensity (compared to that used during
imaging) to the outer surface of the imageable layer only, but across this
entire surface. As such, the visible light
source is a divergent light source, i.e. a light source that radiates light in
all directions at once. It is not a focused
intense laser beam such as that used during imaging, and which penetrates deep
into the imageable layer to
crosslink it down to the imageable layer/substrate interface. Non-limiting
examples of visible light sources include
LED visible light and fluorescent lamps. A preferred light source is the
SmartView Compact LED Light, Model
SV-CLED-8 (available from Cognex Corporation, Singapore), which has an
emission spectrum as shown in the
Examples below.
[00235] The visible light source emits light at visible wavelengths that
are partially absorbed by the imageable
layer. In other words, the absorption spectra of the photoinitiators in the
imageable layer and the emission
spectrum of the visible light source at least partially overlap (i.e. overlap
at one or more wavelengths). The extent
of this overlap will influence the level and depth of crosslinking. All other
things being equal, the greater the
overlap, the faster the crosslinking. In other words, for any given visible
wavelengths emitted by the light source,
the greater the absorbance of the photoinitiator, the faster the crosslinking.
[00236] The intensity of the light source, the distance between the light
source and the imageable layer, and
the duration of the irradiation are variable (for a given imageable layer, but
also between various imageable layer
comprising different photoinitiators), but should be controlled so as to
provide to desired level of crosslinking
down to the desired depth. All other things being equal:
= increasing the intensity of the light source,
= decreasing the distance between the light source and the imageable layer,
and/or
= increasing the duration of the irradiation
CA 02900211 2015-08-12
will increase the density of the crosslinks and/or the depth of crosslinking.
For example, a 1.5-second irradiation
with a SmartView Compact LED Light, Model SV-CLED-8 having a luminous flux of
8500 lumens and a surface
area of 0.1 m2 (in other words 85000 lumens/m2), located 15 cm away from the
imageable layer, usually
crosslinks the outer surface of the imageable layer in a suitable manner (see
the Examples).
[00237] If need, the exposure time can be increased by installing several,
for example up to 10, visible light
sources one after another on the production line.
[00238] Should an imageable layer be exposed too exposed to visible
radiation, crosslinks will reach the
imageable layer/substrate interface. This means that certain areas that should
be removed during development
will not be completely removed. This "dirty substrate" will translate into
poor printing performances. If this is
observed, the duration or intensity of the visible irradiation should simply
be shortened.
[00239] Generally speaking, the intensity of the visible light source
should usually vary between about 4,000
and about 16,000 lumen, the distance between the light source and the
imageable layer will usually vary between
about 5 and about 50 cm, and the duration of the irradiation will usually vary
between about 1 and about 60
seconds. These values however should be adjusted for imageable layer with
unusually large or small
absorbance values at the visible wavelengths emitted by the light source. The
Examples below show that when
using a set-up in which the imageable layer receives 85,000 lumen/m2,
background staining does not occur
before 50 seconds of irradiation. For reference, normal room light level is
only between about 500 and about
1,000 lumen/m2, which explains why the precursor can generally be handled
under ambient light without
background staining for at least 4 hours (depending on the intensity and type
of the room light source).
[00240] For note, because of the generally lower absorption of visible
light by the photoinitiating system
(compared to UV-violet or NIR), and because of the visible light source is of
lower intensity and is divergent
(compared to a focused laser beam), the crosslinking involved at this step
will be slower and less extensive than
that occurring during imaging (because fewer free radicals will be produced)
and located at the surface, rather
than reaching the imageable layer/substrate interface.
Definitions
[00241] The use of the terms "a" and "an" and "the" and similar referents
in the context of describing the
invention (especially in the context of the following claims) are to be
construed to cover both the singular and the
plural, unless otherwise indicated herein or clearly contradicted by context.
[00242] The terms "comprising", "having", "including", and "containing" are
to be construed as open-ended
terms (i.e., meaning "including, but not limited to") unless otherwise noted.
[00243] Recitation of ranges of values herein are merely intended to serve
as a shorthand method of referring
individually to each separate value falling within the range, unless otherwise
indicated herein, and each separate
value is incorporated into the specification as if it were individually
recited herein. All subsets of values within the
ranges are also incorporated into the specification as if they were
individually recited herein.
CA 02900211 2015-08-12 ,
76
[00244] Similarly, herein a general chemical structure with various
substituents and various radicals
enumerated for these substituents is intended to serve as a shorthand method
for referring individually to each
and every molecule obtained by the combination of any of the radicals for any
of the substituents. Each individual
molecule is incorporated into the specification as if it were individually
recited herein. Further, all subsets of
molecules within the general chemical structures are also incorporated into
the specification as if they were
individually recited herein.
[00245] All methods described herein can be performed in any suitable order
unless otherwise indicated
herein or otherwise clearly contradicted by context.
[00246] The use of any and all examples, or exemplary language (e.g., "such
as") provided herein, is intended
merely to better illuminate the invention and does not pose a limitation on
the scope of the invention unless
otherwise claimed.
[00247] No language in the specification should be construed as indicating
any non-claimed element as
essential to the practice of the invention.
[00248] Herein, the term "about" has its ordinary meaning. In embodiments,
it may mean plus or minus 10%
or plus or minus 5% of the numerical value qualified.
[00249] Unless otherwise defined, all technical and scientific terms used
herein have the same meaning as
commonly understood by one of ordinary skill in the art to which this
invention belongs.
[00250] Herein, the terms "alkyl", "alkylene", "alkylyne", and their
derivatives (such as alkoxy, alkyleneoxy,
etc.) have their ordinary meaning in the art. It is to be noted that, unless
otherwise specified, the hydrocarbon
chains of these groups can be linear or branched. Further, unless otherwise
specified, these groups can contain
between 1 and 18 carbon atoms, more specifically between 1 and 12 carbon
atoms, between 1 and 6 carbon
atoms, between 1 and 3 carbon atoms, or contain 1 or 2 carbon atoms.
[00251] Other objects, advantages and features of the present invention
will become more apparent upon
reading of the following non-restrictive description of specific embodiments
thereof, given by way of example only
with reference to the accompanying drawings.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENT
[00252] The present invention is illustrated in further details by the
following non-limiting examples.
[00253] Unless state otherwise, in the Examples below, negative-working
computer-to-plate (CTP) lithographic
printing plates precursors were produced, imaged and developed into printing
plates, and tested as follows.
[00254] The precursors presented in the Examples below could typically be
handled for at least 4 hours under
normal ambient light (depending on the intensity and type of light source)
without background staining.
Manufacturing Process
[00255] A raw aluminum alloy 1050-H18 web with a thickness of 150 1.1 m was
purchased from Sumitomo
Corporation (Tokyo, Japan).
CA 02900211 2015-08-12
77
[00256] The aluminum web was subjected to the following electrolytic process
at the speed of 12.5 meter per
minute:
1. Washing with an aqueous alkaline solution containing sodium hydroxide
(3.85 g/l) and sodium gluconate
(0.95 g/l) at 65 C;
2. Neutralizing with aqueous hydrochloric acid (2.0 g/l);
3. Washing with water;
4. Electrolytic graining in an aqueous electrolyte containing an aqueous
solution of hydrochloric acid (8.0
g/1) and acetic acid (16 g/l), using carbon electrodes at 25 C. The current
and charge density were 38.0
A/dm2 and 70.0 0/dm2, respectively;
5. Desnnuting with an aqueous sodium hydroxide solution (2.5 g/l);
6. Neutralizing with an aqueous sulfuric acid solution (2 g/l);
7. Washing with water;
8. Anodizing in an aqueous electrolyte containing sulfuric acid (140 g/1) at
25 C.; the current and charge
density were adjusted to produce an aluminum oxide layer having a thickness
between 2.5 and 3.0 g/m2;
9. Washing with water;
10. Treating with:
(a) an aqueous solution containing sodium dihydrogenphosphate (50 g/l) and
sodium fluoride (0.8
g/l) at 75 C, thereby producing a phosphate fluoride hydrophilic coating on
the substrate, or
(b) an aqueous solution containing soldium silicate (30 g/l) at 75 C was,
thereby producing a
sodium silicate (with a Si/Na ratio greater than about 2.0) hydrophilic
coating on the substrate;
11. Washing with water at a temperature between 25 and 50 C; and
12. Drying with hot air at 110 C.
[00257] Of note, the roughness of surface (Ra) of the thus treated aluminum
web was between 0.4 and 0.6
m.
[00258] The produced aluminum substrate was then subjected to the following
steps:
13. Coating the substrate with a coating solution/dispersion (of a composition
as described in the Examples
below) to produce a radiation sensitive imageable layer. The coating
solution/dispersion was filtered
through a 0.5 1.t m filter and then coated using a slot-die coating head.
14. Drying the radiation sensitive image layer at a temperature between 100
and 150 C (specified in each
Example below). The produced radiation sensitive imageable layer had a coating
weight of 1.0 g/m2.
15. Crosslinking the surface of the radiation sensitive imageable layer by
exposing it to a visible laser light
source. A SmartView Compact LED Light, Model SV-CLED-8 (available from Cognex
Corporation,
Singapore), located 15 cm above the surface of the radiation sensitive
imageable layer, was used for
CA 02900211 2015-08-12
78
this purpose. Figure 4 shows the emission spectrum of the SV-CLED-8 SmartView
Compact LED Light.
This light source has a maximum luminous flux around 8,500 lumens and a
surface of 0.1 rn2 (thus
providing 85,000 lux (i.e. lumen/m2). Considering the production line speed
(12.5 meter per minute),
each area of the precursor was exposed for about 1.5 second.
16. Optionally, laminating the coated aluminum printing plate precursor on a
plastic or paper sheet using an
adhesive; and
17. Cutting to size.
Comparative Tests
[00259] For comparison purposes, the precursors of the Examples below were
also prepared without a
crosslinked surface. These un-crosslinked precursors were produced in the
manner described above, except that
step 15 was omitted. This is shown in some figures as a crosslinking time
equal to 0 seconds.
Accelerated Aging Tests
[00260] For these tests, after production, the negative working precursors
with and without the crosslinked
surfaces were placed in an environmental control oven at 40 C and 80% relative
humidity (RH) for different
duration. Then, the precursors were removed out from this environmental
control oven and kept, under normal
room conditions, in paper boxes to avoid exposure to the ambient light for one
day.
Laser Imaging Tests
[00261] For UV-violet laser imaging evaluation, the precursors were imaged
by using a Cron Image Platesetter
(Model UVP-4648EX, Hangzhou Cron Machinery & Electronics Co. Ltd., Hangzhou,
China), equipped with forty
eight (48) 405 nm solid state lasers (at the energy density specified in each
Example below). They were then
developed with a GSP50 developer available from MyIan Group (Travinh, Vietnam)
using a Tungsung Processor
(Model 88, available from Tungsung, Malacca, Malaysia) at 25 C and 1.5
m/minute. The percent dot at different
energy density was measured with a Techkon Spectroplate.
[00262] For near infrared (NIR) laser imaging evaluation, the precursors
were imaged by using the Kodak
Trendsetter (Model III, British Columbia, Canada) equipped with 830 nm solid
state lasers at an energy density
between 100 and 300 nnJ/cm2. They were then developed with a soap water
solution (cleaning solution NP100),
available from MyIan Group (Travinh, Vietnam) using a Tungsung Processor
(Model 88, available from Tungsung,
Malacca, Malaysia) at 25 C and 1.5 m/minute.
[00263] The percent dot at different energy densities was measured with a
Techkon Spectroplate. The dot
gain depends on the imaging speed of the imageable layer. Here, dot gain is
used to evaluate imaging speed. A
higher dot gain means that photopolymerization due to laser irradiation occurs
more quickly, i.e. that the imaging
speed of the imageable layer is higher.
Printing Tests
CA 02900211 2015-08-12
79
[00264] The imaged and developed printing plates were placed on a Heidelberg
48 press, a Heidelberg Quick
Master 46-1 press, or a Heidelberg Speedmaster CD 74 UV (as noted in the
Examples below), using (unless
noted otherwise) a black ink (New Apex-G, available from DIC, Japan) and
fountain solution (UF300, available
from MyIan Group, Travinh, Vietnam).
Scratch Tests
[00265] The various precursors described below were handled similarly
during all operations, including
imaging and printing. They were then inspected for scratches and fingerprints.
The observations made are
reported below.
Example UV-1 ¨ UV-Violet Photopolvmerizable Precursor Comprising a
Conventional Free Radical
Scavenger
[00266] A negative working CTP lithographic printing plate precursor with
an imageable layer sensitive to UV-
violet laser radiation was prepared as described above. The coating
solution/dispersion had the following
composition:
Constituents Function Weight (Kg)
Hydroxy propyl cellulose Binder 3.50
PolyXP 100 Radical polymerizable copolymer 42.2
Tanmer 10X Radical polymerizable oligomer 5.00
Radical polymerizable oligomer Free
Tuxedo 06C051D 38.0
radical coinitiator
Free radical photoinitiator
Triazine B 3.00
Photosensitizer
9-Vinyl Carbazole Free radical stabilizer 2.00
1H-1,2,4-triazole-3-thiol Free radical scavenger 1.00
Basic Violet 3 Visible colorant (dye) 2.00
Sipomero PAM-200 Adhesion promoting agent 3.00
BYK 307 Surfactant 0.30
1-Methoxy-2-propanol Solvent for coating 2,000
[00267] The coating solution/dispersion was coated on an aluminum substrate
that had been treated with a
sodium dihydrogenphosphate and sodium fluoride (see step 10 a) above). The
coated web was dried at a
temperature of 1100C.
CA 02900211 2015-08-12
[00268] Figure 5 shows the absorption spectrum of the produced radiation
sensitive imageable layer (solid
line) and the emission spectrum of the visible light source (dash line). In
the absorption spectrum of the
imageable layer, the band at around 390 nm which trails in the lower end of
the visible range is due to the
photoinitiator (which produces free radicals when excited). The strong band at
about 620 nm is attributable to
visible dye (which does not produce free radicals). The visible radiation that
causes crosslinking is that at the
visible wavelengths absorbed by the photoinitiator; that is between around 400
to 450 nm. This region, where the
emission of the visible light sources and the absorption of the photoinitiator
overlap is circled in the figure.
[00269] The precursor without a crosslinked surface was soft and slightly
tacky, that is easy to scratch. In
contrast, the precursor with a crosslinked surface was harder and not tacky.
[00270] The precursor with a crosslinked surface had an excellent surface
scratching resistance for handling
in transportation, storage and pre-press operation. It had no scratches or
fingerprints. In contrast, the precursor
without a crosslinked surface showed severe scratching and fingerprints after
handling in the same manner.
[00271] The precursor was imaged at energy densities varying between 25 and 65
1.iJ/cm2. Figure 6 shows
the dot gains (measured at 50% dot from the target) measured at these energy
densities for the printing plates
with a radiation sensitive imaging layer with (circles) and without (squares)
a crosslinked surface. This figure
clearly shows that the printing plate with a crosslinked surface has
significantly higher dot gain than the printing
plate without a crosslinked surface. In other words, the crosslinked surface
is a very effective oxygen barrier that
prevents quenching of the free radicals by air oxygen molecules, and thus
provides faster laser imaging speeds.
[00272] The imaged and developed printing plates were mounted on a Heidelberg
46-1 press. The printing
plate with a crosslinked surface allowed printing over 10,000 copies with high
resolution image and no
deterioration, while the printing plate without a crosslinked surface only
allowed printing under 6,000 copies of a
lesser (but still good) quality.
[00273] Aging tests were also performed. More specifically, the precursors
were first aged at 40 C and 80%
RH for different periods of time. Figure 7 shows the dot gains (measured at
50% dot target) after imaging at 50
0/cm2 of the precursor with (circles) and without (squares) a crosslinked
surface. Both before and after aging
and storage, the printing plate with a crosslinked surface produced higher dot
gains (faster imaging speeds) than
the printing plate without a crosslinked surface. The dot gain of the plate
with a crosslinked surface decreased
steadily, but slowly, for all 8 days and that, without staining background. In
contrast, the dot gain of the plate
without a crosslinked surface decreased drastically after only 3 days.
Furthermore, the background was also
severely stained. In fact, the printing plate could not be used for printing
because of its dirty background. Again,
these results clearly confirm that the crosslinked surface is a very effective
oxygen barrier that provide fast laser
imaging speed during laser imaging. This crosslinked surface is also a very
effective barrier that reduces thermal
fogging susceptibility.
CA 02900211 2015-08-12
81
Example UV-2 ¨ Precursor Similar to Example UV-1, but Laminated on a PET Sheet
[00274] A
negative working CTP lithographic printing plate precursor with an imageable
layer sensitive to UV-
violet laser radiation was prepared as reported in Example UV-1, except that
after the radiation sensitive
imageable layer had been crosslinked using the visible laser light source, the
coated aluminum web was
laminated on a bioriented polyethylene terephthalate (PET) film having a
thickness of 130 pm using a solvent
based adhesive (JK760, available from Henkel, Vietnam). (In other words,
optional step 16 above was carried
out.) The laminated printing plate precursor was then cut to size and ready
for use.
[00275] The computer-to-plate precursor was imaged at the energy density 50
pJ/cm2. The imaged and
developed printing plate with a crosslinked surface was mounted on a
Heidelberg 46-1 press and allowed
printing over 10,000 copies with high resolution image and no deterioration.
The laminated substrate performed
well during all operations.
[00276] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. The test results were as follows:
= the precursor without a crosslinked surface was soft and slightly tacky,
while the precursor with a
crosslinked surface was not tacky;the precursor with a crosslinked surface had
an excellent surface
scratching resistance, while the precursor without a crosslinked surface did
not;
= the precursor with a crosslinked surface had faster imaging speed than
the precursor without a
crosslinked surface (for example, dot gain was around 3 to 8% (crosslinked) vs
around 1 to 7% (un-
crosslinked) for the fresh plates);
= the precursor with a crosslinked surface had longer shelf-life than the
precursor without a crosslinked
surface (for example, the substrate would get a dirty background after 9 days
(crosslinked) vs 6 days
(un-crosslinked) in the oven at 40 C and 80% humidity; and
= the printing plate with a crosslinked surface allowed printing more
copies of a higher quality than the
printing plate without a crosslinked surfaces (number of copies = 10,000
(crosslinked) vs under 6,000
(un-crosslinked)).
Example UV-3 ¨ Precursor Similar to Example UV-1, but Laminated on a Polymer
Coated Paper Sheet
[00277] A
negative working CTP precursor sensitive to UV-violet laser radiation was
prepared as reported in
Example UV-1, except that after the radiation sensitive imageable layer had
been crosslinked using the visible
laser light source, the coated aluminum web was laminated on a polymer coated
paper having a thickness of 130
pm using solvent based adhesive (JK760, available from Henkel, Vietnam). The
precursor was then cut to size
and ready for use.
[00278] The computer-to-plate precursor was imaged at an energy density 50
pJ/cm,. The imaged and
developed printing plate was mounted on a Heidelberg 48 press and allowed
printing over 10,000 copies with
high resolution image and no deterioration. The laminated substrate performed
well during all operations.
CA 02900211 2015-08-12
82
[00279] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. The test results were as follows:
= the precursor without a crosslinked surface was soft and slightly tacky,
while the precursor with a
crosslinked surface was harder and not tacky;
= the precursor with a crosslinked surface had an excellent surface
scratching resistance, while the
precursor without a crosslinked surface did not;
= the precursor with a crosslinked surface had faster imaging speed than
the precursor without a
crosslinked surface (for example, dot gain was around 3 to 8% (crosslinked) vs
around 1 to 7% (un-
crosslinked) for the fresh plates);
= the precursor with a crosslinked surface had longer shelf-life than the
precursor without a crosslinked
surface (for example, the substrate get dirty background after 9 days
(crosslinked) vs 6 days (un-
crosslinked) in the oven at 400C and 80% humidity; and
= the printing plate with a crosslinked surface allowed printing more
copies of a higher quality than the
printing plate without a crosslinked surfaces (number of copies = 10,000
(crosslinked) vs under 6,000
(un-crosslinked)).
Example UV-4 ¨ Precursor Similar to Example UV-1, but with Post-Development UV
Exposure
[00280] A negative working computer-to-plate precursor sensitive to UV-
violet laser radiation was prepared
according to Example UV-1. Then, after laser imaging and development as
reported in Example UV-1, the plate
was exposed to an array of LED light source having an emission wavelength at
395 nm and power 8W/cm2
(Model FireFlex 75X50WC, available from Phoseon Technology, USA) at the speed
of 1 meter per minute (UV
curing). Such UV-cured precursors are suitable for long run printing and use
with UV curable inks.
[00281] The UV-cured plate was mounted on a Heidelberg 46-1 press to print
over 100,000 copies with high
resolution image and no deterioration. The UV-cured plate was also mounted on
a Heidelberg Speedmaster CD
74 UV offset press to print over 20,000 copies with high resolution image
using UV curable inks (Suncure,
available from Sun Chemical).
[00282] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. The test results were as follows:
= the precursor without a crosslinked surface was soft and slightly tacky,
while the precursor with a
crosslinked surface was harder and not tacky;
= the precursor with a crosslinked surface had an excellent surface
scratching resistance, while the
precursor without a crosslinked surface did not;
= the precursor with a crosslinked surface had faster imaging speed than
the precursor without a
crosslinked surface (for example, dot gain was around 3 to 8% (crosslinked) vs
around 1 to 7% (un-
crosslinked) for the fresh plates.
CA 02900211 2015-08-12
83
= the precursor with a crosslinked surface had longer shelf-life than the
precursor without a crosslinked
surface (for example, the substrate get dirty background after 9 days
(crosslinked) vs 6 days (un-
crosslinked) in the oven at 40 C and 80% humidity; and
= the precursors with and without crosslinked surface (after post exposure
with UV light) both allowed
printing over 20,000 copies with high resolution image on papers.
Example UV-5 ¨ Precursor Comprising PolvXP 120S as Free Radical Scavenger
[00283] A negative working computer-to-plate precursor comprising a UV-
violet laser radiation sensitive
imageable layer having a crosslinked surface was produced using a coating
solution/dispersion of the following
composition:
Constituents Function Weight (Kg)
Hydroxy propyl cellulose Binder 3.50
PolyXP 100 Radical polymerizable
copolymer 32.2
Tanmer 10X Radical polymerizable
oligomer 5.00
Radical polymerizable oligomer
Tuxedo 06C051D 38.0
Free radical coinitiator
Free radical photoinitiator
Triazine B 3.00
Photosensitizer
9-Vinyl Carbazole Free radical stabilizer 2.00
PolyXP 120S Free radical scavenger 11.0
Basic Violet 3 Visible colorant (dye) 2.00
Sipomer PAM-200 Adhesion promoting agent 3.00
BYK 307 Surfactant 0.30
Dowanol PM Solvent for coating 2,000
[00284] The coating solution/dispersion was coated on a substrate that had
been treated with a sodium
dihydrogenphosphate and sodium fluoride (see step 10 a) above). The coated web
was then dried at 110 C using
hot air.
[00285] The precursor was imaged at the energy density between 20 and 80
J/cm2. The imaged and
developed printing plate was mounted on the Heidelberg 48 press and allowed
print over 10,000 copies with high
resolution image and no deterioration.
CA 02900211 2015-08-12
84
[00286] The precursor with a crosslinked surface was subjected to the
accelerated aging test at 40 C and 80%
RH. The results were similar to that obtained for the precursor of Example UV-
1 --- no background staining after 8
days in the environmental chamber.
[00287] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. The test results were as follows:
= the precursor without a crosslinked surface was soft and slightly tacky,
while the precursor with a
crosslinked surface was harder and not tacky;
= the precursor with a crosslinked surface had an excellent surface
scratching resistance, while the
precursor without a crosslinked surface did not;
= the precursor with a crosslinked surface had faster imaging speed than
the precursor without a
crosslinked surface (for example, dot gain was around 3 to 8% (crosslinked) vs
around 1 to 7% (un-
crosslinked) for the fresh plates.
= the precursor with a crosslinked surface had longer shelf-life than the
precursor without a crosslinked
surface (for example, the substrate get dirty background after 9 days
(crosslinked) vs 6 days (un-
crosslinked) in the oven at 40 C and 80% humidity; and
= the printing plate with a crosslinked surface allowed printing more
copies of a higher quality than the
printing plate without a crosslinked surfaces (number of copies = 10,000
(crosslinked) vs under 6,000
(un-crosslinked)).
Example UV-6 ¨ Precursor Comprising Poll/Blue 15A as a Visible Colorant
[00288] A negative working computer-to-plate comprising a UV-violet laser
radiation sensitive imageable layer
having a crosslinked surface was produced with a coating solution/dispersion
of the following composition:
Constituents Function Weight (Kg)
Hydroxy propyl cellulose Binder 3.50
PolyXP 100 Radical polymerizable copolymer 37.2
Tanmer 10X Radical polymerizable oligomer 5.00
Radical polymerizable oligomer
Tuxedo 06C051D 38.0
Free radical coinitiator
Free radical photoinitiator
Triazine B 3.00
Photosensitizer
9-Vinyl Carbazole Free radical stabilizer 2.00
1H-1,2,4-triazole-3-thiol Free radical scavenger 1.00
CA 02900211 2015-08-12
PolyBlue 15A Visible colorant (pigment) 7.00
Sipomero PAM-200 Adhesion promoting agent 3.00
BYK 307 Surfactant 0.30
Dowanol PM Solvent for coating 2,000
[00289] The coating solution/dispersion was coated on a substrate that had
been treated with a sodium silicate
solution (see step 10 b) above). The coated web was then dried at 110 C.
[00290] The plate was imaged at the energy density between 20 and 80 J/cm2.
The imaged and developed
plate was mounted on the Heidelberg 48 press and allowed printing over 35,000
copies (because of the substrate
treated with sodium silicate (compared to the previous examples)) with high
resolution image and no
deterioration.
[00291] The plate with a crosslinked surface was subjected to the accelerated
aging test at 40 C and 80% RH.
The results were similar to that obtained for the precursor of Example UV-1 ---
no background staining after 8
days in the environmental chamber.
[00292] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. The test results were as follows:
= the precursor without a crosslinked surface was soft and slightly tacky,
while the precursor with a
crosslinked surface was harder and not tacky;
= the precursor with a crosslinked surface had an excellent surface
scratching resistance, while the
precursor without a crosslinked surface did not;
= the precursor with a crosslinked surface had faster imaging speed than
the precursor without a
crosslinked surface (for example, dot gain was around 3 to 8% (crosslinked) vs
around 1 to 7% (un-
crosslinked) for the fresh plates.
= the precursor with a crosslinked surface had longer shelf-life than the
precursor without a crosslinked
surface (for example, the substrate get dirty background after 9 days
(crosslinked) vs 6 days (un-
crosslinked) in the oven at 40 C and 80% humidity; and
= the printing plate with a crosslinked surface allowed printing more
copies of a higher quality than the
printing plate without a crosslinked surfaces (number of copies = 35,000
(crosslinked) vs under 20,000
(un-crosslinked)).
Example UV-7 ¨ Precursor Comprising PolvXP 130S as Free Radical Scavenger
[00293] A negative working computer-to-plate precursor comprising a UV-
violet laser radiation sensitive
imageable layer having a crosslinked surface was produced using a coating
composition of following composition:
CA 02900211 2015-08-12
86
Constituents Function Weight (Kg)
Hydroxy propyl cellulose Binder 3.50
PolyXP 100 Radical polymerizable copolymer 25.2
Tanmer 10X Radical polymerizable oligomer 5.00
Radical polymerizable oligomer
Tuxedo 06C051D 38.0
Free radical coinitiator
Free radical photoinitiator
Triazine B 3.00
Photosensitizer
9-Vinyl Carbazole Free radical stabilizer 2.00
PolyXP 130S Free radical scavenger 10.0
PolyBlue 15A Visible colorant (pigment) 7.00
Sipomer PAM-200 Adhesion promoting agent 3.00
BYK 307 Surfactant 0.30
Dowanol PM Solvent for coating 2,000
[00294] The coating solution/dispersion was coated on a substrate that had
been treated with a sodium silicate
solution (see step 10 b) above). The coated web was then dried at 110 C using
hot air.
[00295] The computer-to-plate precursor was imaged at the energy density
between 20 and 80 J/cm,. The
imaged and developed printing plate was mounted on the Heidelberg 48 press to
print over 35,000 copies with
high resolution image and no deterioration.
[00296] The precursor with crosslinked surface was subjected to the
accelerated aging test at 40 C and
80 /0RH. The results were similar to that obtained for the precursor of
Example UV-1 --- no background staining
after 8 days in the environmental chamber.
[00297] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. The test results were as follows:
= the precursor without a crosslinked surface was soft and slightly tacky,
while the precursor with a
crosslinked surface was harder and not tacky;
= the precursor with a crosslinked surface had an excellent surface
scratching resistance, while the
precursor without a crosslinked surface did not;
= the precursor with a crosslinked surface had faster imaging speed than
the precursor without a
crosslinked surface (for example, dot gain was around 3 to 8% (crosslinked) vs
around 1 to 7% (un-
crosslinked) for the fresh plates.
CA 02900211 2015-08-12
87
= the precursor with a crosslinked surface had longer shelf-life than the
precursor without a crosslinked
surface (for example, the substrate get dirty background after 9 days
(crosslinked) vs 6 days (un-
crosslinked) in the oven at 40 C and 80% humidity; and
= the printing plate with a crosslinked surface allowed printing more
copies of a higher quality than the
printing plate without a crosslinked surfaces (number of copies = 35,000
(crosslinked) vs under 20,000
(un-crosslinked)).
Example UV-8 ¨ Precursor Additionally Comprising a Visible Light Reflective
Pigment
[00298] A negative working computer-to-plate precursor comprising a UV-
violet laser radiation sensitive
imageable layer having a crosslinked surface was produced using a coating
solution/dispersion of the following
composition:
Constituents Function Weight (Kg)
Hydroxy propyl cellulose Binder 3.50
PolyXP 100 Radical polymerizable copolymer 25.2
Tanmer 10 Radical polymerizable oligomer 5.00
Radical polymerizable oligomer
Tuxedo 06C051D 38.0
Free radical coinitiator
Free radical photoinitiator
Triazine B 3.00
Photosensitizer
9-Vinyl Carbazole Free radical stabilizer 2.00
_
PolyXP 130S Free radical scavenger 10.0
PolyBlue 15A Visible colorant (pigment) 6.00
9W1100 White Pigment Visible light reflecting pigment 1.00
Sipome0 PAM-200 Adhesion promoting agent 3.00
BYK 307 Surfactant 0.30
_
Dowanol PM Solvent for coating 2,000
[00299] The coating solution/dispersion was coated on a substrate that had
been treated with a sodium silicate
solution (see step 10 b) above). The coated web was then dried at 110 C.
[00300] Compared to that of Example UV-7 (crosslinked and un-crosslinked),
the crosslinked surface of the
imageable layer was found to be harder. This indicates that the titanium
dioxide pigment enhanced surface
crosslinking reactions during exposure to the LED visible light. This was
observed to further reduce tackiness
and further increase physical resistance.
CA 02900211 2015-08-12
88
[00301] The precursor was imaged at the energy density between 20 and 80
1.1J/cm2.
[00302] Figure 8 shows the dot gains measured when imaging this plate and that
of Example UV-7 at 50
J/cm2 (both crosslinked). The dot gain for the precursor comprising TiO2 light
reflective pigment was lower than
that of Example UV-7. It decreased linearly with the period of exposure of the
radiation imageable layer to the
LED visible light. These results indicate that surface crosslinks reactions
were more complete in the presence of
the TiO2 light reflective pigment. Therefore, less overall crosslink reactions
occurred in the laser imaging step.
Without Ti02, the surface crosslink reactions were less complete. More surface
crosslink reactions occurred
during laser imaging. That is why the dot gain was higher for radiation
imageable layer exposed to the LED visible
light less than 60 seconds. For exposure times longer than 60 seconds, the dot
gain of Example UV-7 is higher
than that Example UV-8, however this was found to be mainly due to background
staining as will be shown in the
next figure. It is also due to the reflection of violet laser light (405 nm)
by the titanium dioxide reflective pigment.
[00303] The precursor was developed with GSP50 developer at 25 C at 1.5 meter
per minute to produce high
resolution image. The imaged and developed plate was mounted on the Heidelberg
46-1 press and allowed
printing over 50,000 copies with high resolution image and no deterioration.
The printing quality was higher than
that of Example UV-7 (crosslinked and un-crosslinked).
[00304] Figure 9 shows the optical density of printed plates according to
Examples UV-7 and UV-8, developed
after crosslinked but without imaging, as a function of the duration of
exposition to visible light for crosslinking.
This figure shows that background staining start occurring only after about 50
second exposition in the absence
of light reflective pigments (Example UV-7) and does not occur in the measured
time period when such pigment
is present (Example UV-8).
[00305] The precursor with the crosslinked surface was subjected to the
accelerated aging test at 40 C and
80% RH. There was no background staining after 8 days in the environmental
chamber. During and after aging,
the dot gain for this precursor was almost the same as of Example UV-7
(crosslinked).
Example UV-9 ¨ Precursor Comprising an Oligomeric Photoinitiator and a Visible
Light Reflective
Pigment
[00306] A negative working computer-to-plate precursor comprising a UV-
violet laser radiation sensitive
imageable layer having a crosslinked surface was produced using a coating
solution/dispersion of the following
composition:
Constituents Function Weight (Kg)
Hydroxy propyl cellulose Binder 3.50
PolyXP 100 Radical polymerizable
copolymer 25.2
Tanmer 10X Radical polymerizable
oligomer 4.00
CA 02900211 2015-08-12
89
Radical polymerizable oligomer
Tuxedo 06C051D 38.0
Free radical coinitiator
Free radical photoinitiator (oligomer)
Tanmer 4FR6X 6.00
Photosensitizer
9-Vinyl Carbazole Free radical stabilizer 2.00
1H-1,2, 4-triazole-3-thiol Free radical scavenger 1.00
PolyBlue 15A Visible colorant (pigment) 6.00
9W1100 White Pigment Visible light reflecting pigment 1.00
Sipomer PAM-200 Adhesion promoting agent 3.00
BYK 307 Surfactant 0.30
1-Methoxy-2-propanol Solvent for coating 2,000
[00307] The coating solution/dispersion was coated on a substrate that had
been treated with a sodium silicate
solution (see step 10 b) above. The coated web was then dried at 110 C. Then,
the web was exposed to the LED
visible light at 85,000 lumen/m2 for 5 seconds.
[00308] The precursor was imaged at the energy density between 20 and 80
J/cm2, then developed with the
GSP50 developer at 25 C at 1.5 meter per minute to give high resolution image.
The developed plate was placed
on the Heidelberg 46-1 press and allowed printing over 20,000 copies with high
resolution image and no
deterioration.
[00309] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. As in Examples UV-6, the crosslinked precursor/plate
performed better than the un-
crosslinked precursor/plate in terms of tackiness, surface scratching
resistance, imaging speed, shelf-life, and
number of copies printed.
Example UV-10 ¨ Precursor Comprising a Copolymer Photoinitiator and Visible
Light Reflective Pigment
[00310] A negative working computer-to-plate precursor comprising a UV-
violet laser radiation sensitive
imageable layer having a crosslinked surface was produced using a coating
solution/dispersion of the following
composition:
Constituents Function Weight (Kg)
Hydroxy propyl cellulose Binder 3.50
PolyXP 100 Radical polymerizable copolymer 20.2
Tanmer 10X Radical polymerizable oligomer 5.00
CA 02900211 2015-08-12
Radical polymerizable oligomer
Tuxedo 06C051D 38.0
Free radical coinitiator
Copolymeric free radical photoinitiator
PolyFR 102 15.0
Photosensitizer
9-Vinyl Carbazole Free radical stabilizer 2.00
1H-1, 2,4-triazole-3-thiol Free radical scavenger 1.00
PolyBlue 15A Visible colorant (pigment) 6.00
9W1100 White Pigment Visible light reflecting pigment 1.00
Sipomero PAM-200 Adhesion promoting agent 3.00
BYK 307 Surfactant 0.30
1-Methoxy-2-propanol Solvent for coating 2,000
[00311] The coating solution/dispersion was coated on a substrate that had
been treated with a sodium silicate
solution (see step 10 b) above). The coated web was then dried at 110 C. Then,
the web was exposed to the
LED visible light at 85,000 lumen/m, for 5 seconds.
[00312] The precursor was imaged at the energy density between 20 and 80
J/cm,, then developed with the
GSP50 developer at 25 C and 1.5 meter per minute to give high resolution
image. The developed plate was
placed on the Heidelberg 46-1 press and allowed printing over 20,000 copies
with high resolution image and no
deterioration.
[00313] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. As in Examples UV-6, the crosslinked precursor/plate
performed better than the un-
crosslinked precursor/plate in terms of tackiness, surface scratching
resistance, imaging speed, shelf-life, and
number of copies printed.
Example UV-11 ¨ Precursor for On-Press Development
[00314] A negative working computer-to-plate precursor comprising a UV-
violet laser radiation sensitive
imageable layer having a crosslinked surface was produced using a coating
solution/dispersion of the following
composition:
Constituents Function Weight (Kg)
Hydroxy propyl cellulose Binder 3.50
Radical polymerizable copolymer
PolyNPo150Y 41.5
(particles)
CA 02900211 2015-08-12
91
Radical polymerizable oligomer
Tuxedo 06C051D 32.0
Free radical coinitiator
Triazine B Free radical photoinitiator 1.00
9-Vinyl Carbazole Free radical stabilizer 2.20
1H-1,2,4-triazole-3-thiol Free radical scavenger 1.00
PolyBlue 15A Visible colorant (pigment) 5.00
9W1100 White Pigment Visible light reflecting pigment 1.00
Sipomer PAM-200 Adhesion promoting agent 2.00
BYK 307 Surfactant 0.10
Dowanol PM Solvent for coating 2,000
[00315] The coating solution/dispersion was coated on a substrate that had
been treated with a sodium silicate
solution (see step 10 b) above). The coated web was then dried at 11000 using
hot air. Then, the web was
exposed to the LED visible light at 85,000 lumen/m, for 5 seconds.
[00316] The precursor was imaged at the energy density between 20 and 80
1.1,1/cm2, then preheated at 10000
and at a speed of 1.5 meter per minute. The preheated plate was placed on the
Heidelberg 46-1 press for
development using ink and fountain solution. A clean image was obtained after
20 revolutions. It alllowed printing
over 30,000 copies with high resolution image and no deterioration.
[00317] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. The crosslinked precursor/plate performed better than the
un-crosslinked precursor/plate in
terms of tackiness, surface scratching resistance, imaging speed, shelf-life,
and number of copies printed.
Example UV-12 ¨ Precursor for On-Press Development Comprising a Copolymer
Photoinitiator
[00318] A negative working computer-to-plate precursor comprising a UV-
violet laser radiation sensitive
imageable layer having a crosslinked surface was produced using a coating
solution/dispersion of the following
composition:
Constituents Function Weight (Kg)
Hydroxy propyl cellulose Binder 3.50
Radical polymerizable copolymer
P0lyNP 150Y 26.5
(particles)
Radical polymerizable oligomer
Tuxedo 06C051D 32.0
Free radical coinitiator
CA 02900211 2015-08-12
92
Copolymer free radical photoinitiator
PolyFR 104 15.0
(particles)
9-Vinyl Carbazole Free radical stabilizer 2.20
1H-1,2,4-triazole-3-thiol Free radical scavenger 1.00
PolyBlue 15A Visible colorant (pigment) 5.00
9W1100 White Pigment Visible light reflecting pigment 1.00
Sipomer PAM-200 Adhesion promoting agent 2.00
BYK 307 Surfactant 0.10
Dowanol PM Solvent for coating 2,000
[00319] The coating solution/dispersion was coated on a substrate that had
been treated with a sodium silicate
solution (see step 10 b) above). The coated web was then dried at 110 C using
hot air. Then, the web was
exposed to the LED visible light at 85,000 lumen/m2 for 5 seconds.
[00320] The precursor was imaged at the energy density between 20 and 80
J/cm2, then preheated at 100 C
and at a speed of 1.5 meter per minute. The preheated plate was placed on the
Heidelberg 46-1 press for
development using ink and fountain solution. A clean image was obtained after
20 revolutions. It allowed printing
over 30,000 copies with high resolution image and no deterioration.
[00321] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. The crosslinked precursor/plate performed better than the
un-crosslinked precursor/plate in
terms of tackiness, surface scratching resistance, imaging speed, shelf-life,
and number of copies printed.
Example NIR-1 ¨ NIR Photopolvmerizable Precursor
[00322] A negative working computer-to-plate precursor comprising a NIR
laser radiation sensitive imageable
layer having a crosslinked surface was produced using a coating
solution/dispersion of the following composition:
Constituents Function Weight (Kg)
Hydroxy propyl cellulose Binder 3.50
Radical polymerizable copolymer
PolyNP 150Y 30.0
(particles)
Radical polymerizable oligomer
Tuxedo 06C051D 34.0
Free radical coinitiator
Triazine B Free radical photoinitiator 1.00
CA 02900211 2015-08-12
93
9-Vinyl Carbazole Free radical stabilizer 2.20
Radical polymerizable copolymer
PolyN130120S (particles) 10.0
Free radical scavenger
PolyNP 795PD Photosensitizer (particles) 11.3
PolyBlue 15A Visible colorant (pigment) 5.00
Sipome0 PAM-200 Adhesion promoting agent 2.00
BYK 307 Surfactant 0.30
Dowanol PM Solvent for coating 2,000
[00323] The coating solution/dispersion was coated on a substrate that had
been treated with a sodium silicate
solution (see step 10 b) above). The coated web was then dried at 11000 using
hot air.
[00324] Figure 10 shows the absorption spectrum of the NIR radiation
sensitive imageable layer (solid line)
and the emission spectrum of the visible light source (dash line). In the
absorption spectrum of the imageable
layer, the band at around 330 nm, which trails in the lower end of the visible
range is due to the photoinitiator
(which produces free radicals when excited). The strong band at about 630 nm
is attributable to the visible
colorant (PolyBlue 15 pigment, which does not produce free radicals). The
stronger bands at 730 and 810 nm
are attributable to the near infrared dye (used as a photosensitizer). The
visible radiation that causes crosslinking
is that at the wavelengths absorbed by the photoinitiator; that is between
around 400 and 440 nm, This region
where the emission of the visible light sources and the absorption of the
triazine B photoinitiator (added to the
NIR sensitive imageable layer to allow surface crosslinking with visible
light) overlap is circled in the figure.
[00325] As with the other precursors above, the precursor with a crosslinked
surface was less tacky and more
physically resistant than that without a crosslinked surface.
[00326] The precursor was imaged at an energy density between 100 and 350
mJ/cm,. Figure 11 shows the
dot gains at different energy densities for the fresh (un-aged) NIB radiation
sensitive computer-to-plates printing
plate with (circles) and without (squares) a crosslinked surface. These
results clearly indicate that, at these
energy densities, the printing plate with a crosslinked surface has higher dot
gain than the printing plate without it.
These laser imaging results clearly confirm that the crosslinked surface is a
very effective oxygen barrier that
prevents quenching of the free radicals by the air oxygen molecules and thus
provides fast laser imaging speeds.
[00327] The imaged and developed printing plate was mounted on the Heidelberg
Quick Master 46-1 press
and allowed printing over 20,000 copies with high resolution image and no
deterioration, while the printing plate
without a crosslinked surface only allowed printing 15,000 copies of a lesser
(but still good) quality.
[00328] The precursor with the crosslinked surface was subjected to the
accelerated aging test at 40 C and
80% RH. There was no background staining after 10 days in the environmental
chamber. Figure 12 shows the
CA 02900211 2015-08-12
94
dot gains at 120 mJ/cm, for the printing plates comprising a NIR laser
radiation sensitive imageable layer with
(circles) and without (squares) a crosslinked surface after aging at 40 C and
80% RH for different duration. After
aging and storage, the printing plate with a crosslinked surface produced
higher dot gains than the printing plate
without a crosslinked surface. The dot gain of the printing plate with a
crosslinked surface decreased steadily, but
slowly, for 7 days at 40 C and 80% RH. In contrast, the printing plate without
a crosslinked surface decreased
more rapidly, especially after 3 days at 40 C and 80% RH. Furthermore, after
10 days in the environment oven,
the background of the printing plate with a crosslinked surface was clean,
while the printing plate without a
crosslinked surface was severely stained and could not be used for printing.
Again, these results clearly confirm
that the crosslinked surface is a very effective oxygen barrier, providing
fast laser imaging speed during laser
imaging. This crosslinked surface is also a very effective barrier that
reduces thermal fogging susceptibility.
[00329] As will be shown in Example NIR-5 below, this precursor can also be
imaged using UV-violet
radiation.
Example NIR-2 ¨ Precursor Similar to Example NIR-1, but Laminated on a PET
Sheet
[00330] A negative working computer-to-plate precursor sensitive to NIR
radiation was produced similarly to
Example NIR-1, except that after the radiation sensitive imaging layer was
crosslinked using the visible laser light
source, the coated aluminum web was laminated on a bioriented polyethylene
terephthalate film having a
thickness of 130 1.1rn using a solvent based adhesive (JK760, available from
Henkel, Vietnam). The laminated
precursor was then cut to size and ready for use.
[00331] The precursor was imaged at an energy density 200 mJ/cm,. Development
was carried out by
washing the imaged precursor with water containing 0.20% of sodium lauryl
sulphonate at 25 C and 1.5 meter
per minute.
[00332] The imaged and developed printing plate was mounted on a Heidelberg 46-
1 press and allowed
printing over 20,000 copies with high resolution image and no deterioration.
The laminated substrate performed
well during all operations.
[00333] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. The test results were as follows:
= the precursor without a crosslinked surface was soft and slightly tacky,
while the precursor with a
crosslinked surface was harder and not tacky;
= the precursor with a crosslinked surface had an excellent surface
scratching resistance, while the
precursor without a crosslinked surface did not;
= the precursor with a crosslinked surface had faster imaging speed than
the precursor without a
crosslinked surface (for example, dot gain was around 11 to 14% (crosslinked)
vs around 7 to 10% (un-
crosslinked) for the fresh and aged plates;
CA 02900211 2015-08-12
= the precursor with a crosslinked surface had longer shelf-life than the
precursor without a crosslinked
surface (for example, the substrate got a dirty backgound after 9 days
(crosslinked) vs 6 days (un-
crosslinked) in the oven at 4000 and 80% humidity; and
= the printing plate with a crosslinked surface allowed printing more
copies of a higher quality than the
printing plate without a crosslinked surfaces (number of copies = 20,000
(crosslinked) vs under 15,000
(un-crosslinked)).
[00334] As will be shown in Example NIR-5 below, this precursor can also be
imaged using UV-violet
radiation.
Example NIR-3 ¨ Precursor Similar to Example NIR-1, but Laminated on a Polymer
Coated Paper Sheet
[00335] A
negative working computer-to-plate precursor sensitive to NIR radiation was
produced similarly to
Example NIR-1, except that after the radiation sensitive imaging layer was
crosslinked using the visible laser light
source, the coated aluminum web was laminated on a polymer coated paper having
a thickness of 130 urn using
a solvent based adhesive (JK670, available from Henkel, Vietnam). The
laminated CTP was then cut to size and
ready for use.
[00336] The precursor was imaged at an energy density 200 mJ/cm2. Development
was carried out by
washing the imaged precursor with water containing small amount of NP100 at 25
00 and 1.5 meter per minute.
[00337] The imaged and developed printing plate was mounted on a Heidelberg 46-
1 press and allowed
printing over 10,000 copies with high resolution image and no deterioration.
The laminated substrate performed
well during all operations.
[00338] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. The test results were as follows:
= the precursor without a crosslinked surface was soft and slightly tacky,
while the precursor with a
crosslinked surface was not tacky;
= the precursor with a crosslinked surface had an excellent surface
scratching resistance, while the
precursor without a crosslinked surface did not;
= the precursor with a crosslinked surface had faster imaging speed than
the precursor without a
crosslinked surface (for example, dot gain was around 11 to 14% (crosslinked)
vs around 7 to 10% (un-
crosslinked) for the fresh and aged plates);
= the precursor with a crosslinked surface had longer shelf-life than the
precursor without a crosslinked
surface (for example, the substrate got a dirty background after 9 days
(crosslinked) vs 6 days (un-
crosslinked) in the oven at 40 C and 80% humidity; and
= the printing plate with a crosslinked surface allowed printing more
copies of a higher quality than the
printing plate without a crosslinked surfaces (number of copies = 20,000
(crosslinked) vs under 15,000
(un-crosslinked)).
CA 02900211 2015-08-12
96
[00339] As will be shown in Example NIR-5 below, this precursor can also be
imaged using UV-violet
radiation.
Example NIR-4 ¨ Precursor Additionally Comprising a Visible Light Reflective
Pigment
[00340] A negative working computer-to-plate precursor comprising a NIR
laser radiation sensitive imageable
layer having a crosslinked surface was produced using a coating composition of
the following composition:
Constituent Function Weight (Kg)
Hydroxy propyl cellulose Binder 3.50
Radical polymerizable copolymer
P0lyNP 150Y 31.0
(particles)
Radical polymerizable oligomer
Tuxedo 06C051D 32.0
Free radical coinitiator
Triazine B Free radical photoinitiator 1.00
9-Vinyl Carbazole Free radical stabilizer 2.20
Radical polymerizable copolymer
P0lyNP0120S (particles) 10.0
Free radical scavenger
PolyNP 795PD Photosensitizer (particles) 11.3
PolyBlue 15A Visible colorant (pigment) 5.00
9W1100 White Pigment Visible light reflecting pigment 1.00
Sipomer PAM-200 Adhesion promoting agent 2.00
BYK 307 Surfactant 0.30
Dowanol PM Solvent for coating 2,000
[00341] The coating solution/dispersion was coated on a substrate that had
been treated with a sodium silicate
solution (see in step 10 b) above). The coated web was then dried at 110 C.
[00342] The surface of the crosslinked imageable layer was found to be
harder (more resistant) than that
obtained in Example NIR-1 (crosslinked and un-crosslinked). This indicates
that the titanium dioxide pigment
enhanced surface crosslinking reactions during exposure to the LED visible
light. This was observed to further
increase physical resistance.
[00343] The computer-to-plate was imaged at the energy density between 100 and
350 mJ/cm, and washed
with water comprising 0.2% sodium lauryl sulphonate at 25 C at 1.5 meter per
minute to produce high resolution
image. The dot gain for this precursor was higher than that of Example NIR-1
(crosslinked and un-crosslinked).
CA 02900211 2015-08-12
97
[00344] The imaged and developed plate was mounted on a Heidelberg-46-1 press
and allowed printing over
50,000 copies with high resolution image and no deterioration. The printing
quality was higher than that of
Example NIR-1 (crosslinked and un-crosslinked).
[00345] The precursor with the crosslinked surface was subjected to the
accelerated aging test at 40 C and
80% RH. There was no background staining after 8 days in the environmental
chamber. During and after aging,
the dot gain for this precursor was higher than that of Example NIR-1
(crosslinked and un-crosslinked).
[00346] As will be shown in Example NIR-5 below, this precursor can also be
imaged using UV-violet
radiation.
Example NIR-5 ¨ Precursor for On-Press Development
[00347] A negative working computer-to-plate precursor comprising an imageable
layer having a crosslinked
surface, which is sensitive to NIR laser radiation, and as stated above is
also sensitive to UV-violet radiation, was
produced using a coating solution/dispersion of the following composition:
Constituents Function Weight (Kg)
Hydroxy propyl cellulose Binder 3.50
P0lyNP0150Y Reactive Copolymer (particles) 39.5
Radical polymerizable oligomer
Tuxedo 06C051D 32.0
Free radical coinitiator
Triazine B Free radical photoinitiator 1.00
9-Vinyl Carbazole Free radical stabilizer 2.20
1H-1,2,4-triazole-3-thiol Free radical scavenger 1.00
ADS798BD Near Infrared Sensitizer 2.00
PolyBlue 15A Visible colorant (pigment) 5.00
9W1100 White Pigment Visible light reflecting pigment 1.00
Sipomer, PAM-200 Adhesion promoting agent 2.00
BYK 307 Surfactant 0.10
Dowanol PM Solvent for coating 2,000
[00348] The coating solution/dispersion was coated on a substrate that had
been treated with a sodium silicate
solution (see step 10 b) above). The coated web was then dried at 110 C using
hot air. Then, the web was
exposed to the LED visible light at 85,000 lumen/m2 for 5 seconds.
CA 02900211 2015-08-12
98
[00349] The precursor was imaged with a UV-Violet laser (405 nm) at an energy
density between 20 and 80
1.0/cm2, then preheated at 10000 and at a speed of 1.5 meter per minute. The
preheated plate was placed on the
Heidelberg 46-1 press for development using ink and fountain solution. A clean
image was obtained after 20
revolutions. It allowed printing over 30,000 copies with high resolution image
and no deterioration.
[00350] The precursor was also imaged with a NIR laser (830 nm) at an energy
density between 80 and 300
mJ/cm,, then placed on the Heidelberg 46-1 press for development using ink and
fountain solution. A clean image
was obtained after 20 revolutions. It allowed printing over 20,000 copies with
high resolution image and no
deterioration.
[00351] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. The crosslinked precursor/plate performed better than the
un-crosslinked precursor/plate of
this Example in terms of tackiness, surface scratching resistance, imaging
speed, shelf-life, and number of copies
printed.
Example NIR-6 ¨ Precursor for On-Press Development
[00352] A negative working computer-to-plate precursor comprising an imageable
layer having a crosslinked
surface, which is sensitive to NIR laser radiation, and as stated above is
also sensitive to UV-violet radiation, was
produced using a coating solution/dispersion of the following composition:
Constituents Function Weight (Kg)
Hydroxy propyl cellulose Binder 3.50
PolyNP 150Y Reactive Copolymer (particles) 29.5
Radical polymerizable oligomer
Tuxedo 06C051D 32.0
Free radical coinitiator
PolyFR 104 Free radical photoinitiating copolymer 11.0
9-Vinyl Carbazole Free radical stabilizer 2.20
1H-1,2,4-triazole-3-thiol Free radical scavenger 1.00
ADS798BD NIR photosensitizer 2.00
PolyBlue 15A Visible colorant (pigment) 5.00
9W1100 White Pigment Visible light reflecting pigment 1.00
Sipomero PAM-200 Adhesion promoting agent 2.00
BYK 307 Surfactant 0.10
Dowanol PM Solvent for coating 2,000
CA 02900211 2015-08-12
99
[00353] The coating solution/dispersion was coated on a substrate that had
been treated with a sodium silicate
solution (see step 10 b) above). The coated web was then dried at 1100C using
hot air. Then, the web was
exposed to the LED visible light at 85,000 lumen/m, for 5 seconds.
[00354] The precursor was imaged with a UV-Violet laser (405 nm) at an energy
density between 20 and 80
J/cm,, then preheated at 1000C, and at a speed of 1.5 meter per minute. The
preheated plate was placed on the
Heidelberg 46-1 press for development using ink and fountain solution. A clean
image was obtained after 20
revolutions. It allowed printing over 30,000 copies with high resolution image
and no deterioration.
[00355] The precursor was also imaged with a NIR laser (830 nm) at an energy
density between 80 and 300
mJ/cm2, then placed on the Heidelberg 46-1 press for development using ink and
fountain solution. A clean
image was obtained after 20 revolutions. It allowed printing over 20,000
copies with high resolution image and no
deterioration.
[00356] The performances of this precursor were compared with that of an
identical precursor without a
crosslinked surface. The crosslinked precursor/plate performed better than the
un-crosslinked precursor/plate of
this Example in terms of tackiness, surface scratching resistance, imaging
speed, shelf-life, and number of copies
printed.
[00357] The scope of the claims should not be limited by the preferred
embodiments set forth in the examples,
but should be given the broadest interpretation consistent with the
description as a whole.
CA 02900211 2015-08-12
100
REFERENCES
[00358] The
present description refers to a number of documents. These include, but are
not limited to, the
following documents:
= US Patent No. 4,345,017,
= US patent no. 5,496,903,
= US patent no. 5,821,030,
= US patent no. 5,888,700,
= US patent no. 6,899,994,
= US patent no. 7,261,998,
= US patent no. 7,732,118,
= US patent no. 7,955,776,
= US patent no. 6,830,862,
= US patent no. 7,723,010,
= US patent no. 7,910,768,
= US patent no. 8,021,827,
= US patent no. 8,323,867,
= US patent no. 8,491,993 (Nguyen et al.),
= US patent publication no. 2011/0277653,
= US patent publication no. 2012/0137929,
= US patent application no. 14/249,458, and
= International patent publication no. WO 2012/155259.
