Note: Descriptions are shown in the official language in which they were submitted.
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A PLATELESS PRINTING SYSTEM
FIELD OF THE INVENTION
This present invention relates to offset printing and in particular is
directed to a method for plateless printing and to the composition of
materials
s used for this method.
BACKGROUND OF THE INVENTION
There are numerous methods known in the art for producing a master
printing plate, on which an image is written and which is then used as a
printing
plate for the reproduction of multiple copies. Examples of such methods are
~o described in "Chemistry and Technology of Printing and Imaging Systems",
edited
by P. Gregory and published by Blackie Academic & Professional in 1996.'
Typically, the plate contains one or more coating layers applied to a metal or
plastic substrate layer.
The cost of producing a plate is relatively expensive and is generally
~s only economical when utilized for printing large numbers of copies. For
short
printing runs, the cost of the printing plate adds substantially to the cost
per
printed copy. The plate cost is contributed from two sources:
a. The price of the plate itself
b. The price of preparing the plate for printing, i.e. film making,
Zo exposure, processing.
Recent developments in offset lithography have led to the use of digitally
imaged printing plates whereby information is transferred directly from a
computer
to the printing plate. Though these printing plates are relatively easily
prepared
and quickly imaged and processed, their cost is even higher than that of
Zs conventional plates, so that they still contribute a significant cost to
the printing
price.
Another significant contributing cost factor in printing is due to what is
commonly termed "make-ready". Make-ready refers to the operational stage
involved between producing the last copy of one printing job and the first
copy of
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the next job. Reducing the make-ready time improves the efficiency and allows
for better utilization of machine time and increases the capacity of the
machine.
Color printing generally involves the separating of the color information
into four or more color components each on a separate printing plate and then
s superimposing the images printed from each plate on top of one another on
each
piece of substrate. In complex color printing, there are additional problems
of
lining up images on plates and ensuring that the color balance on the printed
copies is correct, which can require more time and thus results in a further
increase in the cost per copy.
o Another time-consuming stage in conventional ("wet") offset printing is
the fine adjustment of the balance of the fountain solution with the ink. This
procedure not only is time consuming, but also requires a printer skilled in
the art.
In addition, the use of fountain solution also causes other problems, such as~
longer drying times and lower optical density. A waterless printing process
for
offset printing, which eliminates the use of fountain solution, is described
in US
Patent No: 3511178 to Curtin. A layer of silicone is used to repel the
printing ink
instead of the fountain solution.
Printing machines have been developed to minimize the make-ready by
imaging directly on press. Infra red imaging has been used for this purpose
Zo because it lends itself to digital imaging and can be done under daylight
conditions. For instance, the 74 Karat offset printer, manufactured by Karat
LP, 3,
Hamada Street, Hazily, Israel, carries such a digitally imaged infra red
system of
plate production.
Besides the plate cost issue for short runs as mentioned above, the use
25 Of a printing plate has other disadvantages. It requires mechanical
clamping
devices at each end, which produces an unusable area on the plate cylinder as
well as requiring the necessity of alignment mechanisms.
Various processes, known in the art, have been introduced for printing
which do not require the use of a printing plate. For example, as described in
30 "Chemistry and Technology of Printing and Imaging Systems", edited by P.
Gregory and published by Blackie Academic & Professional in 1996, a printing
process which may be termed "image one - print one" regenerates an image for
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each print. Ink jet printing whereby a jet of ink directly sprays the image
onto the
plate where the information is digitally applied from a computer is an example
of
an "image one - print one" process. This process is not competitive with high
quality, color process printing using a printing plate such as offset
lithography,
because it is relatively slow and has severe substrate limitations.
Xerographic copying is another example of an "image one - print one"
process. Disadvantages of this process, which may be considered as an imaging
on press process, includes its complexity and the relatively high cost per
copy that
remains almost constant, irrespective of the number of copies made.
~o Furthermore, this process has a generally inferior quality compared to
lithography.
Numerous attempts have been made to produce a re-usable imaging
surface for a printing process, examples of which are described in US Patent
Nos.
5,206,102; 5,129,321; 5,188,033; 3,741,118; 4,718,340; 5,333,548 and.
5,213,041. Generally, the above-mentioned systems generate a "master" which is
then used for conventional wet offset printing.
Reference is now made to Fig. 1, which is a cross-sectional view of a
printing member, referenced 300, used in existing conventional digital offset
lithographic printing systems. The printing member 300 is formed of at least
three
layers. A first or substrate layer 310, forms a base or substrate for the
printing
2o member 300. A second radiation absorbing layer 312, that carries the image
to
be printed (once the printing member is imaged by ablation, for example), is
over
the first layer 310. A third surface coating layer 314 is over the second
layer 312.
Generally, the imaging layer 312 comprises an infra-red radiation absorbing
material, for absorbing infra red radiation to cause ablation. The substrate
310
25 has an oleophillic surface. The surface coating layer 314 is of a material
with an
affinity for the inks) substantially different to the affinity for the inks)
of the
surface of the substrate 310. Ablation results in de-bonding between the
surface
coating layer 314 and the substrate 310. On cleaning - either dry or with a
liquid -
the materials of layers 312 and 314 are removed in the image areas, revealing
the
so surface of 310.
It would be advantageous to have an offset printing process which does
not require a printing plate. Specifically, it would be of further advantage
if such a
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process could be used in a waterless application. Imaging would be on the
printing press and preferably, any processing after imaging would be
relatively
simple. US Patents Nos: 5,440,987; 5,634,403; and 5,636,572, all to Wlliams
et.
al, describe a seamless offset lithographic printing members. The printing
s members include a hollow cylinder which is attached to the cylinder jacket
of an
offset printing press. A polymeric coating layer is coated on to the cylinder
and a
second polymeric surface layer is coated on top of the first layer. Whilst
these
patents address the problem of the void area needed for clamping plates on a
cylinder, their inventions require a cylinder or cylinders to be removed from
the
~o printing press and then to receive two or more coatings before returning to
press.
US Patents Nos: 5,713,287 to D. Gelbart, describes a plateless process
at which a solvent-based, polymeric coating layer is deposited on-press on the
cylinder. After drying, the imaging converts at least part of the coated layer
to.
have an opposite chemical property to that of the layer.
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SUMMARY OF THE INVENTION
The present invention provides a printing system which does not require
a printing plate.
It is a further object of the present invention to provide a printing system
s which uses a single layer printing member coated on to a cylinder. For
waterless
offset application, the single layer printing member consists of an oleophobic
imaging layer containing an oleophobic resin, coated on an oleophillic
cylinder.
For wet application, the single layer may either be hydrophilic, coated on a
oleophillic cylinder; or vice versa.
The single layer printing member is composed of a resin with the
required properties (i.e. oleophobic (such a silicone), hydrophilic or
oleophillic) to
which an infra red absorbing component or components may be added.
There is thus provided in accordance with an embodiment of the present
invention, a printing member including an image bearing cylinder having a
single
~s imaging layer coated thereon. On selective ablation, polymerization or
decomposition of the imaging layer, selective areas of the imaging layer are
removed thereby exposing the cylinder. The cylinder and the coated imaging
layer are configured to have opposed chemical affinities with regarding to
water
and / or ink.
2o Furthermore, in accordance with an embodiment of the invention, the
imaging layer includes a mixture including a resin and a cross-linking agent.
Furthermore, in accordance with an embodiment of the invention, the
imaging layer also includes carbon black or other infra-red absorbing
materials or
mixture thereof.
2s Additionally, in accordance with an embodiment of the invention, the
printing member can include components selected from a group consisting of:
catalysts, plastidizers, wetting agents, infra-red sensitivity enhancers,
dispersion
agents, adhesion promoters, polymers and any combinations thereof.
Furthermore, in accordance with an embodiment of the invention, the imaging
30 layer after evaporation of solvent, provides a dry layer of thickness
having a
weight within a range of 1 to 10 grams per square meter.
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Additionally, in accordance with an embodiment of the invention, the
imaging layer is deposited on the cylinder in the form of a solution.
Preferably, the
solvent is water and the polymer is either dissolved in the water or held in
as an
emulsion. Alternatively, in accordance with an embodiment of the invention,
the
imaging layer may be deposited as a solvent free layer.
Furthermore, in accordance with the invention, the imaging layer is
formulated so that it has good release properties together with high scratch
resistance, excellent substrate adhesion without the need of providing a pre-
coat
or primer or other surface treatment (e.g. corona or flame) to obtain such
~o functionality. These requirements assure that after imaging, the whole
plate
surface could be cleaned without damage (scratch resistance); the background
does not accept ink (good release) long run length could be achieved without
deterioration (good substrate adhesion) and the process could be repeated
after.
erasing, without multiple coating or surface treatments.
The inventors have found that with their claimed formulations it was
possible to achieve all these requirements in one formulation and for many
different substrates.
Furthermore, the same requirements of adhesion and scratch resistance
are applicable for infra-red digital (waterless) plates, as are used today by
direct
2o imaging (DI) offset presses. These formulations can be used for coating a
single
layer plate, which allows for low cost plates, as opposed to the multi-layer,
expensive plates which currently exist.
Furthermore, in accordance with an embodiment of the invention, the
cylinder includes material selected from a group consisting of plastics,
reinforced
2s plastics, metals, anodised aluminum, ceramics and granite.
In addition, in accordance with an alternative embodiment of the
invention, the cylinder is composed of material which is absorbent or
reflective to
imaging radiation, such as infra-red radiation. Alternatively, only the
external
surface of the cylinder is absorbent or reflective to the imaging radiation.
3o Furthermore, it is an object of this invention to provide an infra-red
ablatable
waterless printing plate with one coat only which contains a silicone resin
and an
infra-red absorbing material.
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There is further provided, in accordance with an embodiment of the
invention, a printing member including an oleophobic single coating imaging
layer
containing a silicone polymer and an infra red absorbing material, and an
oleophillic substrate underlying the imaging layer. On selective ablation the
s imaging layer, selective areas of the imaging layer are removed thereby
exposing
the substrate.
In addition, there is further provided, in accordance with an embodiment
of the invention, a printing member including a cylinder, an image bearing
substrate attached to said cylinder; and a single imaging layer coated on said
~o substrate on press. On selective ablation, polymerization or decomposition
of
said imaging layer, selective areas of the imaging layer are removed thereby
exposing the cylinder. The substrate and coated imaging layer are configured
to
have opposed chemical affinities with regarding to water and / or ink.
Furthermore, in accordance with an embodiment of the invention, the
substrate is a material selected from a group consisting of anodized aluminum,
polyimide or polyester. Further, the substrate may be inflexible and in the
form of
a machined cylinder. Alternatively, the substrate may be the surface of the
cylinder. The substrate may be a material selected from a group consisting of
metals, reinforced plastic, ceramic and granite. The cylinder may be seamless.
2o Additionally, there is provided, in accordance with an embodiment of the
invention, a printing system which includes the printing member of the
invention,
an imaging system for placing an image on the image bearing cylinder and an
inking assembly for applying ink to the imaged printing member.
The printing system may also include, for wet offset application, a
25 dampening system for applying the fountain solution to the imaged printing
member; alternatively, a single fluid of emulsified water in ink may be
applied by
the ink system alone.
Furthermore, in accordance with an embodiment of the invention, the
system further includes means for preparing the imaging layer, means for
coating
ao the imaging layer on to the cylinder and means for drying, solidifying and
cross-linking the imaging layer. The preparing means includes means for mixing
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at least two components together, one of the components being a film former
for
coating the imaging layer on to the cylinder.
The system further includes means for cooling the coated cylinder after
the drying/curing stage and/or during the printing stage and means to protect
the
s imaging system from any heat that may evolve at this stage.
The system may also include means for washing the mixing and coating
systems.
In addition, in accordance with an embodiment of the invention, the
system also includes at least one impression cylinder and a blanket cylinder
~o disposed between the print cylinder and at least one impression cylinder,
so that
the system operates as an offset system.
Furthermore, in accordance with an embodiment of the invention, the
system further includes at least one impression cylinder and a control system
for.
activating the imaging system to place an image on the image bearing cylinder
and for controlling the application of ink or an ink and water emulsion onto
the
imaged printing member, so that the system operates as a computer to press
printing system. The computer to press printing system includes a rotary
digital
offset press (DOP) printing system. Additionally, for wet offset application,
a
dampening system may be included.
2o Furthermore, in accordance with an embodiment of the invention, the
system further includes means for cleaning the imaged printing member and ,
means for removing the imaging layer.
Additionally, there is provided, in accordance with an embodiment of the
invention, a method of preparing a printing member having a single imaging
layer.
25 The method includes the steps of:
a) providing a cylinder having an affinity for ink;
b) preparing a mixture including an ink abhesive polymer, a cross
linking agent an infra-red absorbent agent and other ' appropriate
ingredients to form an imaging layer;
so c) coating the prepared mixture on to the cylinder; and
d) solidifying the prepared mixture.
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Alternatively, the cylinder may be hydrophilic, in which case the mixture
for coating the imaging layer consists of a oleophillic polymer, a cross
linking
agent and an infra-red absorbent agent; or alternatively
the cylinder may be oleophillic, in which case the mixture for coating the
imaging
s layer consists of a hydrophilic polymer, a cross linking agent and an infra-
red
absorbent agent.
Finally, there is also provided, in accordance with an embodiment of the
invention, a method of imaging the printing member of the invention. The
method
includes the steps of:
a) providing a printing member which includes a cylinder having an
affinity for ink and an oleophobic imaging layer coated on the cylinder; or
providing a printing member which includes a cylinder having an affinity
for ink and an hydrophilic imaging layer coated on the cylinder; or
providing a printing member which includes a cylinder having an affinity
for water and an oleophillic imaging layer coated on the cylinder;
and
b) placing an image on the printing member.
Furthermore, in accordance with an embodiment of the invention, the
step of providing includes the steps of:
2o preparing a mixture including the appropriate polymer and a cross
linking agent;
coating the prepared mixture on to the cylinder; and
solidifying the prepared mixture.
The prepared mixture includes solvents and the method further includes
2s the step of evaporating any solvent on the surface of the mixture.
Preferably, the
mixture is a water-based solution or an emulsion, and the method involves the
step of evaporating the water from the coated wet layer.
In a further embodiment, the mixture is solventless, in which case, an
evaporation stage is not required.
3o In addition, in accordance with an embodiment of the invention, the
method optionally includes the step of cleaning the image after the step of
placing
an image and also optionally includes the step of hardening the image areas or
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the background to the image areas. The step of printing an image includes the
steps of applying an ink to the cylinder and cooling the cylinder.
Furthermore, in accordance with an embodiment of the invention, the
method includes a step of cooling the cylinder and a step of placing an image
by
s selectively ablating the printing member with radiation that is absorbable
by the
printing member.
Alternatively, the step of placing an image includes the step of breaking
the chemical bonds of the coated imaging layer into smaller molecules or the
step
of polymerizing the imaging layer.
~o Finally, there is provided, in accordance with an embodiment of the
invention, a computer to plate system which includes means for re-constituting
a
single layer plate on an existing substrate, an imaging system for placing an
image on the image bearing substrate and means for cleaning the imaged plate.
The re-constituting means includes erasing means for removal of the
used imaged coating from a previous job, mixture means for preparing a
mixture,
coating means for coating the prepared mixture on the erased substrate, and
solidifying means for solidifying and curing the coated layer.
The coated layer is an infrared absorbing layer, having a chemical
affinity with regards to water and/ or ink opposite to that of the substrate.
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BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood and appreciated more fully
from the following detailed description taken in conjunction with the appended
drawings in which:
Fig. 1 is a cross-sectional view of a prior art printing member;
Fig. 2 is a schematic illustration of a plateless printing system,
constructed and operative in accordance with a preferred embodiment of the
present ;
Fig. 3 is a high level flow chart illustration of the operation of the
1o plateless printing system of Fig. 2;
Figs 4a - 4g illustrates the image-Ocarrying cylinder during the various
stages of plateless printing; and
Fig. 5 illustrates the web offset application of the plateless process.
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DETAILED DESCRIPTION OF THE PRESENT INVENTION
Reference is now made to Figs. 2 and 3. Fig. 2 is a schematic illustration
of a plateless printing system, constructed and operative in accordance with a
preferred embodiment of the present invention, and Fig. 3, is a high level
flow
chart illustration of the operation of the plateless printing system.
The 'plateless' printing system 10 preferably comprises an image
bearing cylinder 12, a blanket cylinder 14, a printing (or inking) system 15
and an
imaging system 16.
It is a particular feature of the present invention that, in contrast to
~o existing printing systems which carry printing plates, such as waterless IR
ablatable printing members, an image bearing cylinder 12 does not carry a
printing plate. Instead, an image bearing cylinder 12 has an imaging layer,
generally designated 100, directly coated onto the cylinder 12, thereby
creating a,
'plateless' printing member, as described in detail hereinbelow.
In an alternative version of the embodiment, the cylinder may carry a
replaceable substrate, either as a sleeve or as a sheet, that can be replaced
after
a large number of jobs. This has the advantage of protecting the cylinder from
wear.
The 'plateless' printing system 10 preferably also comprises a mixing
2o system 18 for preparing the imaging layer 100, a coating head 20 for
applying the
imaging layer 100, a plate cleaning system 25 for post-imaging cleaning, an
erasing system 22 and a drier/cross linker 24. In addition, the 'plateless'
printing
system 10 also comprises a cooling system 26 for use after the heating stage
and
during printing, an inking system 15 and imaging system 16.
2s Mixing system 18 comprises apparatus to mix at least two components,
generally referenced A and B, which are discharged via a pipe system 27, or
similar, into a mitring container 28 where components A and B are mixed
together
to form the coating mixture which is then coated onto cylinder ~-12 to form an
imaging layer 100. An automatic washing system may be added to clean the
ao mixing and coating system on press in case of a short pot-life of the
mixture.
Including the mixing (and washing if necessary) stages into the process, makes
it
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possible to use mixtures that have short-pot life or shelf-life (such as a
polymer
and its cross-linker).
The cylinder 12 is preferably an oleophillic surface and may comprise
any material which is suitable for receiving and adhesion of the oleophobic
coating layer 100. Non-limiting examples of suitable surfaces include
plastics,
reinforced plastics, metals such as aluminum (or anodised aluminum) and
copper,
ceramics and stones, such as granite. Thus, in contrast to conventional plate
processes, the surface 12 which acts as a substrate, may be of a non-pliable
material that may or may not be formable into a sheet.
~o For a wet offset application, the cylinder may be hydrophilic, where the
coating layer is oleophillic, or vice versa.
The cylinder 12 may be entirely composed of an infra-red absorbent
material or, alternatively, only the external surface of the cylinder is
composed of a
solid infra-red absorbent material. Since, in both these two alternative
embodiments, the surface of cylinder 12 (that is, the underside of the
oleophobic
layer 100) is infra-red absorbent, the coating layer 100, which is coated on
the
cylinder 12, need not itself be infra-red absorbent, but may be transparent .
Alternatively, the outer surface of the cylinder or the cylinder itself may
be composed of an IR reflecting material, to enhance the sensitivity of the
imaging
zo layer; in this case, the coated layer should be IR absorbent.
By coating an imaging layer 100 on to a base with opposite ink or water .
accepting properties (cylinder 12), a single layer printing member is created.
This
is in contrast to existing printing members, described hereinabove with
respect to
Fig. 1, which generally comprise a substrate base layer on which at least two
25 layers are coated.
Preferably, the A and B components of the coating layer 100 for
waterless offset application comprise a film former such as polysiloxane, or
other
oleophobic polymeric material (compound A) and a separated component, such
as a compound of platinum or tin, for example, as a catalyst and/or cross
linker
30 (compound B).
The coating layer 100 may be either solventless or may have been
deposited from solvents. Preferably, water is utilized as the solvent because
of
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environmental and health and safety considerations. In this case the resin may
be
held in the form of an emulsion or as a dissolved substance..
Preferably, components A and/or B should incorporate an infrared (1R)
absorbing component, such as carbon black or nigrosine. The mixture 100 may
s also contain wetting agents, adhesion promoters and polymers to enhance the
coating and bonding properties of the mixtures.
It has been found that when using water based silicone emulsions, in
order to obtain good wetting for a variety of substrates together with good
adhesion to said substrates and good release properties of the film formed and
~o good scratch resistance, the following components must be present in the
following parts by weight;
a) Polysiloxane emulsion (percentage 40% to 80%
solids
includes surfactants used during manufacture)
b) Silicone catalyst (solids content) 0.01 to 3%
c) Silicone crosslinking agent (percentage5-15%
solids)
d) Water soluble crosslinkable amine 4 % - 25
resin
e) Catalyst for amine resin 0.5% to 5%
f) Added surfactant 0.5% - 10%
g) Infrared absorber 3% - 40%
h) The remaining material is water
Examples of suitable polysiloxane water-based emulsions are as
follows, (each material is supplied with suitable catalysts and crosslinking
agent):
Polysiloxane Water-Based EmulsionsCatalysts / Crosslinking
Agents
Dehesive 410E ( 50% solids includingCrosslinker V72 (35%
a solids)
platinum catalyst)
Dehesiv~ 38197 VP ( 50% aqueousCrosslinker V72 (35%
solids)
emulsion addition cross-linkable)
Syl-off 7920 silicone emulsion Syl-off 7922 catalyst
emulsion
Silcolease E70888, 70840 Catalyst 70889S or 71823
Silcolease 71841 Catalyst 71842 or 71823
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Silcolease 71822 Catalyst 71823
Silcolease E 70840 Catalyst 70827A
Dehesive and Crosslinker products are manufactured by Wacker
Chemie GmbH, Munich, Germany). Silcolease products are manufactured by
Rhone-Poulenc Silicones UK, Surrey, England. Syl-offs products are
manufactured by Dow Corning Europe, La Hulpe, Brussels, Belgium.
Examples of suitable crosslinkable water soluble amine resins are as
follows:
a) Cymels 350, 323,327,328,373,385, 1171, 1172 (manufactured by
Dyno-Cytec);
~o b) Dynomins UM-15 (manufactured by Dyno-Cytec); and
c) BE 312 Beetle Resin (manufactured by BIP Limited,Oldbury, West
Midlands, UK.
It has been found that although catalysts for the cross-linking resins may
be sulphonic and carboxylic acids, amine blocked acids are most suitable.
An example of one preferred mixture for a waterless offset application is
a mixture based on water emulsions of silicones such as the commercially
available Syloff~ 7920 emulsion coating and Syloff~ 7922 catalyst manufactured
by Dow Corning Europe, La Halpe, Brussels, Belgium.
Sufficient material to be formed into the equivalent of a plate is mixed
2o together in the mixer 28 and coated onto the surface of the 'plateless'
cylinder 12.
Depending on the pot life of the mixture, a washing stage of the mixing and
coating system may be applied after each mixing. Even though cylinder 12 does
not carry a plate, as would be the case in conventional plate cylinder
systems, the
coating layer 100 (or "plateless" plate) carries out the functions of the
conventional
digital plate.
The imaging layer 100 is coated on to the cylinder 12 using the coating
head 20 with a dye slot, for example. After solvent evaporation or cross-
linking,
the dry coating thickness may be expressed as a weight of from 1 to 5 grams
per
square meter. Alternatively, a metered rod or any other application system
known
3o in the art may be used as the coating head 20.
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The drier/cross linking station 24 may function in varying ways. In the
embodiments where the coating 100 is polymerized or cross-linked before
imaging, it would be used to evaporate off any solvent present after initial
coating
and then possibly to cure the polymerized image areas after non-polymerized
material is removed by washing. In the embodiments where the image area is to
be destroyed during imaging, the drier/cross linker will evaporate any solvent
present after coating and would then cross-link or polymerize either before
imaging or after imaging/cleaning to harden and insolubilise the background
areas. Alternatively station 24 may comprise a heating unit such as a radiant
~o heater or an ultra-violet (U~ drier. The heating/curing stage may also be
obtained by a heated electrical blanket below the upper surface of the
cylinder, or
by hot air, by combination of means or by any other suitable heating / curing
means. With high power imaging unit, it may be used to cure the IR absorbing
coating layer as well.
Imaging system 16 comprises one or more infra red lasers which have
been modulated to radiate energy corresponding to a digital image. Such a
suitable system is described in PCT Patent Application PCT/IL97/00525
(Publication No. WO 97/27065) to the present Applicant, incorporated herein by
reference.
2o Infra-red imaging of the system may occur in various ways, as follows:
Imaging may occur due to ablation where destruction of material occurs.
In contrast to systems where the underlayer contains the infra red absorbing
material, in the present invention the infra red absorbing material is
preferably
contained in the overlayer, or alternatively in both the overlayer and the
underlying
2s cylinder. Waterless plates imaged by debonding ablative mechanisms have
been
found to be difficult to automatically clean in the post image stage. The
debonded
oleophobic rubber, such as polysiloxanes which are commonly used, maintains
its
elastomeric form and gathers into large solid deposits that clog the cleaning
system as well as the press when imaging on press. It has been found that
where
3o the infra-red material is in the oleophobic layer itself, the layer is
thermally
degraded where ablation occurs and the oleophobic resin loses its elastomeric
properties and this facilitates automatic cleaning. Where ablation occurs, the
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decomposed areas of oleophobic coating layer 100 must be removed by dry or
wet cleaning so that the exposed areas of the cylinder 12 provide the
oleophillic
areas during printing.
It is possible that layer 100, whilst free of solvent before image, may
remain in an unpolymerized state to facilitate ablation. This may be in a
liquid or a
semi-solid form in contrast to conventional plates which have to be packed and
handled before use and thus, conventional plates cannot have a wet surface.
Another possibility is that the heat generated by the thermal imaging
process will break the chemical bonds of the polymer and that the resulting
~o smaller molecules will then become less chemically or mechanically
resistant than
the original layer and then can be cleaned away as part of a post imaging
treatment.
A further possibility is that the heat generated during imaging is used to
polymerize the coating layer 100 and the unpolymerized coating is subsequently
removed by washing it away.
The cleaning system 25 comprises any suitable dry or solvent cleaning
process. The cleaning element can consist of a brush, rubber roller or other
similar element. Preferably, a vacuum suction is applied together with the
cleaning element in order to remove the debris from the press. A liquid may be
Zo used together with the rubbing action of the cleaning element to assist in
removing any loose particles (if the ablation process is involved) or pre-
polymeric
material from the background or image areas with decomposed material. If a
liquid or solvent is used, a further rotation of the cylinder 12 without
contact with
any liquid may be made so as to ensure that the surface is dry.
zs The solvent erasing system 22 is used to remove the inked up image
after the printing impressions have been made. Cleaning may be any suitable
process such as abrasion or by means of a solvent to aid loosening of the
resin
layer (layer 100) or by a combination of both methods. A suitable solvent may
be
a regular blanket wash.
so A corona treatment to decompose the layer and /or a vacuum suction to
remove the loosen material may be used as well.
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The printing (or inking) system 15 is any suitable inking system known in
the art, for applying ink to "plate" cylinders.
Cooling system 26, which is placed within the image bearing cylinder 12,
controls the temperature of the cylinder to cool it after the heating stage
and
s during printing to avoid toning that can occur with waterless inks and to
support
printing stability .
Offset printing is carried out by means of blanket cylinder 14 on to a
printing substrate conveyed by an impression cylinder (not shown). Impressions
are taken, usually onto paper, but any required substrate may be printed.
~o Reference is now made to the flow chart of Fig. 3 to illustrate the
plateless printing system.
The imaging layer mixture is prepared in mixing system 18 (step 202) by
mixing at least two components comprising a film former and a separated
component together.
15 The mixture is then coated onto the surface of the 'plateless' cylinder 12
(step 204), using a suitable coating head 20. Such a coating head should
preferably be easy to wash and not sensitive to the distance of the coating
head
to the cylinder, for instance a dye slot coater.
Depending on the pot life of the mixture, a washing stage of the mixing
2o and coating system may be applied as necessary.
After the application of the mixture 100 (step 204), the drier/cross linker
24 is used either for drying (i.e. to evaporate any solvent on the printing
drum 12,
which may be collected and condensed (step 208)), and/or for partial curing
and/or for full curing (step 206)
2s After stage 206 during which the cylinder is heated and prior to imaging,
the image bearing cylinder is cooled (step 209), in order to avoid dimensional
changes of the substrate between the imaging step and the printing step. The
imaging layer 100 is then selectively exposed by the imaging systern 16 during
multiple rotation of the cylinder (step 210).
so During further rotation of the cylinder, post-imaging cleaning system is
operated (step 212). Depending on the embodiment, cleaning either removes
ablated debris, or removes unpolymerized resin from the background or washes
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out decomposed material from the image areas. If a liquid cleaner is used,
surplus solvent is removed .
After the cleaning process (step 212) is completed, the dryer/cross linker
may be (optionally) re-operated to further harden off background or image
areas
to give optimum robustness and adhesion to the cylinder needed for the
printing
part of the cycle (Step 214). This second stage of heating is followed by a
second
cooling of the cylinder (Step 216).
The operational parameters of the dryer/cross linker could in principle be
regulated separately for each job in order to optimize the make ready time (as
~o curing time may influence sensitivity and hence imaging time, as well as
erasing
time) versus required run length (as curing will influence the coating
resistance).
The image bearing cylinder surface is now ready to print (step 218) and
the appropriate offset ink (either waterless or "wet") is applied by the
printing (or-
inking) system 15 to the cylinder. The image bearing cylinder is cooled (if
necessary) to control the temperature of the ink during printing.
The offset printing process takes place via blanket cylinder 14 by taking
a plurality of impressions, usually onto paper, but any required substrate may
be
used for printing.
The substrate to be printed can be in the form of sheets, or in the form
20 of a web. Reference is now made to Fig. 5 which illustrates a web-offset
printing
system. Fig. 5 is similar to Fig. 1 with the addition of a substrate unwind
110 and
a substrate rewind 112. The roll of substrate 115 is fed via an impression
roller
114 to receive the print from the blanket cylinder 14 and then re-wound onto
roll
112. Alternatively, sheets can be printed.
25 The application of this technology for a web offset printing has the
following advantage: as the plate cylinder can be made seamless, it can carry
a
continuous image, uninterrupted by the need for clamps which are generally
required in order to hold the plates. .
After the required number of impressions have ~ been printed, the
so remaining resin layer (mixture 100) plus the inked up image is removed
(step
220) by the solvent plate erasing system 22. Cleaning may be any suitable
process such as abrasion or by solvent aided loosening or a combination of
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both. In special conditions, a corona treatment may be used as a facilitator.
If
required, the cylinder 30 is then dried (step 222). The cylinder 30 is then
ready
for the application of the mixture, as previously described and the process
(steps 202-222) can be repeated
s It will be appreciated by persons knowledgeable in the art that the
present invention is also applicable to existing computer to press printing
machines which can be adapted to be used with a 'plateless' printing member. A
typical computer to press printing machine is described in PCT Patent
Application
PCT/US96/06207 (Publication No. WO 96/34748) to the present Applicant.
~o It will also be appreciated that such coating material as herein described
can be used in the manufacture of a one layer infra red imageable offset
printing
plate. This could be useful for existing presses which can not be modified for
the
plateless process. A single layer plate will still be cheaper than existing
plates as
coating multiple layers increase dramatically the cost of the plate.
15 Another possible application of this invention would be to make a
plate-setter which will be used for implementing the whole plateless process
for
recycling the plates. Such a plate-setter will be fed with the used plates,
erase
them, coat, dry, image and clean; the ready plates will be fed into the press.
Once
done their job, the plates will be re-fed into the platesetter and used again.
This
Zo will have advantageous of reducing plate costs as well as elimination of
used
aluminum aggregation.
Reference is now made to Fig. 4a - 4g which illustrates the image
carrying cylinder during the plateless printing sequence.
Figs. 4a - 4g are partial sectional elevations of image bearing cylinder
2s 12 (Fig. 2). Fig. 4a shows the cylinder before any coating is applied. The
cylinder
may be comprised of a single material. Alternatively it may consist of any or
all the
following components:
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1. An internal cooling system (41 )
2. A hollow cylinder (45)
3. Under-surface electrical heating elements (42)
4. A sleeve or a sheet top surface, which may be replaceable (43)
s The entire cylinder or only the top (43) may be either IR absorbing or IR
reflecting.
Fig. 4b shows the cylinder after the coating (100) is applied, dried and
(possibly) cured (101). The coating, after drying (and optionally curing) is
shown
in the right hand side (reference 101 ).
~o Fig. 4c illustrates the coating layer after imaging has taken place. In
this
case, the imaging ablates or decomposes the imaging area (102).
Fig. 4d illustrates the case where imaging cures the background area'
(reference 103).
Fig. 4-a shows the cylinder after post-imaging cleaning has taken place.
15 After cleaning (whether the imaged area or non-imaged area has been
removed),
the cured layer is left on the cylinder on the background area (103). The
cylinder
surface area functions as the ink accepting layer (43).
Fig. 4-f shows the cylinder after ink (106) is applied during the printing
cycle .
2o Fig. 4-g shows the cylinder after the erasing stage, fully cleaned, ready
for the next job (that is as Fig. 4a).
Example I- Waterless
The following formulation was prepared as a mixture (all numbers
designating parts in the formulation are in parts by weight of the entire
is formulation);
Distilled Water 10 parts
2-Butoxy Ethanol 0.86 parts
Water Soluble Nigrosine1.3 parts
Cymel 373 1.24 parts
BYK 345 0.6 parts
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Syloff 7920 10 parts
Syloff 7922 2 parts
The mixture was applied to a 175 micron polyester film to a wet
thickness of 12 grams per square meter and then dried for four minutes at
140°C.
The layer was then imaged with the infra red imaging system described in PCT
s Patent Application PCT/IL97/00525 (Publication No. WO 97/27065) to the
present
Applicant, using an imaging intensity necessary for material with a
sensitivity of
800 milli-joules per square centimeter. The image was gently cleaned with
water
and mounted on a GTO printing press running with a waterless printing ink.
After
5000 impressions, the plate surface was rubbed vigorously with a damp abrasive
~o cloth, damped with aqueous alcohol, removing both the inked image and the
silicone based background so that only the polyester surface was left. The'
polyester was removed from the printing machine and re-coated as previously
described and the entire cycle repeated.
Example II- Waterless
15 The following formulation was prepared as a mixture (all numbers
designating parts in the formulation are in parts by weight of the entire
formulation)
Dehesive 410E (Wacker Chemie GmbH, Munich,135 parts
Germany)
CAB-O-JET 200 (Cabot Corporation, Billerca,58
Massachusetts, US)
Q2-5211 Super wetting agent (Dow Corporation,6
Midland, MI, USA)
Cymel373 (Dyno-Cytec) 21
Cycat 4045 (amine blocked p-toluene sulphonic5..7
acid,
(Dyno-Cytec
Crosslinker V72 (Wacker) 25
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The complete mixture was then bar coated onto a grained anodised
aluminum plate surface and dried at 140°C for four minutes to a dry
coating
weight of 2.7 grams per square cm.
The layer was then imaged as in Example I. After imaging, the surface
was wiped with a dry cloth to remove ablated material and mounted on a GTO
printing press. 5000 impressions were made and then the plate was rubbed
vigorously with an abrasive cloth to erase all of the coating so that the
cleaned
aluminum surface could be re-coated. Imaging and printing was repeated and
again 5000 impressions were obtained.
~o It will be appreciated that this experiment signifies that the mixture can
be the coating layer 100, coated onto an anodised aluminum plateless cylinder
12
and dried, cured, imaged, printed, erased, re-coated etc., on the apparatus as
shown in Figure 2 as previously described.
It will be further appreciated that the present invention is not limited by
what has been described hereinabove and that numerous modifications, all of
which fall within the scope of the present invention, exist. Rather the scope
of the
invention is defined by the claims which follow:
23
