Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a process for recording images by means
of laser radiation, in particular for preparing printing plates.
A process for the preparation of printing plates which is able to
generate letterpress printing plates directly from computer generated "soft"
images is the kaser-Graph (trade mark) system of Laser Graphics Systems,Inc.
This type of system is described in United States Patent No. 3,832,948, and
United States Patent No. 3,461,229. The method has been used to prepare
plates from images either stored on magnetic tape or generated at another
location by means of a laser scanning reading unit and transmitted electrically
10 by wire; similar arrangements are described in United States Patent No.
3,506,77g.
The concept of using laser light to expose photosensitive coatings
also has been reported in several publications and patents. For instance,
United States Patent 3,664,737 describes the use of W emitting lasers to -:~
expose sensitized aluminum offset plates such as Litho~hemical and Supply
; D Company~s Kem-Lon Pre-cote and Minnesota Mining and Manufacturing~s IIRII plate.
Both of these plates use diazo sensitizers. Although in this case, production
of high quality printing plates is aimed at, increase in speed of exposure to
~ compete with conventional exposure coupled with chemical etching is not an
'~
20 avowed object, nor is improved photosensitivity clear rom this process~
D0~ 25 00 906 uses a YAG or Argon laser to remove the carbon parti-
cle plus nitrocellulose portion of a coating composition by infrared radiation.
The diazo part of the composition is then photohardened in a conventional
manner by overall exposure to the ultraviolet radiation of a carbon arc lamp.
This patent shows that the inventors found the radiation energy of these lasers
to be insufficient for direct imaging of a diaYo coating.
Printing plates presensitized with negative working diazos have
attained high acceptance in the lithographic printing industr~r under standard
noncoherent light sources because of their high resolution and excellence of
~ t~de n~Qrk
_l - ~ .
images obtained, easy processing, trouble~free printing, and the great length
of press runs which are obtainable.
The above-mentioned use of these materials for laser beam recording
has up to now not been possible on a commercial scale because of the mismatch
of laser light output and diazo coating spectral sensitivity. Even with the
most powerful, yet practical laser (argon ion lasers operating at between
10-20 watts), the W output (at 370 nm) is only 1.2% of its total energy when
operating in the all-line mode and with optics that do not filter out the W .
The balance of the output is above 450 nm (in the region of 457.9 to 514.5 nm)
with the buIk of power in two lines at 488.0 and 514.5 nm. In contrast, diazo
coatings are primarily sensitive below 420 nm, with negligible sensitivity
above 450 nm as described in TAGA Proceedings Preprint 'ISpectral Sensitivity
of Offset Printing Plates" by Robert E~. Gesullo and Peter G. Engeldrum. With
argon ion laser W emission so low, diazo coating exposure in a practical time
due to available W radiation was not to be expected.
It has been estimated by printing industry experts that a direct
exposure system to be economically justifiable must be at least equivalent in
cost to known methods of imaging: i.e. preparing photographic transparencies
followed by exposing sensitized plates and accomplished within a reasonable
period of time. A practical speed has been considered to be 2-3 minutes to
expose a newspaper page or 0.3 - 0.5 secs/in. when scanning techniques are
to be used.
:~ B In our copending Canadian application se -~Q / ~o ~7~ f ~6i ~
ne 3,l9~ there is disclosed that negative working diazoni~ compoun~s compris-
ing a coating on a support are sensitiveto laser light from which substantially
all W light has been removed. Mowever surprising and valuable this finding,
greater exposure speed is desirable.
It is well-known that dyes or pigments which absorb actinic light
generally decrease the sensitivity of so dyed, diazo coatings to actinic
8~;~
radiation. Nonetheless, certain thio- and selenopyronine dyes are claimed to
increase the speed of colored, polar diazonium compounds, as described in
German Patent No. 745,595 (1944) assigned to I.G. Farbenindustrie A.G. Also,
some colorless "optical brighteners" (compounds absorbing ultraviolet light
which fluoresce in the actinic region of diazonium compounds) are said to
attain a similar effect with diazonium compounds, as reported in Belgian
Patent No. 661,789 (1965) assigned to Kalle, A.G. Finally, a number of color-
less diazonium compounds are claimed to have been improved in the solid state
by means of ultraviolet light-absorbing compounds, as reported in German
Patents Nos. 906,405 (1954), 903,061 (1954) and 763,388 (1952), all assigned
to Kalle, A.G. and United States Patent No. 1,972~323 (1934) to Shiraeff ~ -~
Jacobs. However, in no instance as far as applicants are aware, has it been
possible to sensitize a diazo compound to respond rapidly to actinic light
outside of the region in which diazonium compounds are known to be sensitive; -
for instance to electro-magnetic radiation in the range of between 450 to 550
nm. It thus has come as a surprise to find that inexplicably certain coloring
matter absorbing light in the region of 450 to 550 nm can be used to render
certain diazo based coatings sensitive to exposure to radiation outside of
the known sensitivity of these diazos~ This unexpected finding makes it
practical for the first time, for instance, to use an argon ion laser scanning
device to prepare printing members at an adequate speed directly from copy
with no intervenîng photographic steps. It has been an object of the inven-
tion to provide a process for recording laser radiation, which requires only
a relatively short irradiation or a relatively low radiation intensity, resp.
The subject matter of the invention is a process for recording laser
radiation, in which a photosensitive material comprising a copying coating
and a carrier is exposed image-wise by means of visible laser light having no
W component and is then developed into an image.
The process according to the invention is characterized in that the
copying coating is composed of a negative working diazonium compound and a
colorant which absorbs light in the spectral range between 450 and 55O nm
and which sensitizes the diazonium compound for the exposure to laser light,
the diazonium compound being a diazonium salt condensation product.
The diazonium salt condensation product may be a negative working
polymeric condensation product of a substituted benzene diazonium salt with
a dialkoxyaromatic compound, and the sensitizing colorant or dye used may be
selected from the azo, triarylmethane, xanthene, or methine classes. Option-
ally, there may be added a resin such as styrene-maleic anhydride copoly-
mer or a polyvinyl acetal resin, a mineral or strong organic acid and anindicating dye such as 4-phenylazodiphenylamine.
It is surprising to find that an argon ion laser from which virtual-
ly all UV light, to which the diazos are sensitive, has been filtered out,
can be used as an exposure source. For example, a composition of this inven-
tion is exposable by a 15 watt argon ion laser in only 0.16 second per
square inch, or one minute for a 16 x 24 inch plate.
The invention makes use of printing members such as printing plates.
Such printing plate materials comprise a carrier and a homogeneous light-
sensitive coating containing a negative working diazonium compound and an --
i 20 azo, triarylmethane, xanthene, or methine dye. The coating may also contain
resins such as phenolics, polyvinylformal and vinyl copolymers containing
carboxylic acid groups or other aqueous alcohol- or base-soluble resins, a
small quantity of mineral acid such as sulfuric or phosphoric acid or an
organic acid such as alkyl or aryl sulfonic~ sulfuric, phosphoric, or phos-
phonic. An indicator dye also may be used.
The carrier may be plastic film or of metal such as magnesium or
aluminum. ~luminum, with a well developed art of preparation, is a preferred
carrier for lithographic purposes, and magnesium is a preferred carrier for
letterpress purposes. The preparation of the carriers includes the steps of
B
6~
cleaning, mechanical graining, if desired, and/or etching, if desired, which
may be performed purely chemically as by the use of aeids and bases or elect-
rochemically. If aluminum is used, further optional preparation steps include
anodizing. The last step in preparation of an aluminum carrier prior to
coating with a light-sensitive coating may include treating with alkali metal
silicate or with a phosphonic acid according to United States Patent No.
3,220,832. It is evident that dependent upon the graining, etching, anodizing,
and like procedures used, the surface area will vary. In the statements made
below regarding coating weights, the surface area referred to is merely that
of the gross dimensions of the plate.
Negative working benzenediazonium compounds must be used, such as
those described in United States Patents Nos. 3,949,392; 3,867,147; 3,679,419;
and 3,235,384. Examples of such negative working diazos are the condensation
products of 3-methoxydiphenylamine-4-diazonium salt with bis-(4-methoxymethyl-
phenyl) ether, of diphenylamine-4-diazonium salt with bis-(4-methoxymethyl-
phenyl) ether, of diphenylamine-4-diazonium salt or of 3-methoxydiphenylamine-
4-diazonium salt with formaldehyde.
These negative working diazonium compounds may be used in an amount
from about 0.01 to about 0.8 gram per square meter and preferably from about
0.1 to about 0.5 gram per square meterT ~hen the amount of the negative
working diazonium compounds in the coating is increased~ the photosensitivity
in conventional exposure decreases, as is well kno~m.
Surprisingly, under laser exposure, the photosensitivity increases.
Mineral acids or organic acids may be used in an amount of up to
about 0.005 gram per square meter~
A resin, e.g. a styrene maleic acid anhydride copolymer or a poly-
vinyl acetal, may be added to the coating to improve mechanical strength.
However, the addition thereof is not necessary to the practice of the invention,
which has as its purpose to greatly increase the speed of negative working
-- 5 --
~a~
diazo-type coatings to laser radiation. ~hen desired, a resin may be used in
an amount of up to about 3 grams per square meter.
An indicator dye may be added to the coating to show a color change
directly upon exposure. The addition of such a dye is optional and, as its
presence will not increase the speed o~ the plate, it should be selected with
care in order not to reduce it unnecessarily. Examples of suitable indicating
dyes are para-phenylazodiphenylamine, Metanil Yellow, C.I. #13065, Methyl
Orange, C.I. 13025 and 4-(p-anilino-phenylazo)benzenesulfonic acid (sodium
salt). Such a dye may be used in an amount of up to about 0.1 gr~m per square
me~er.
Not all colorants are suited for sensitizers. However, useful
colorants include the classes of Azo, Triarylmethane, Xanthene, and Methine,
as de~ined in The Colour Index, Third Edition, Volume 4. Such colorants are
generally used in an amount from about 0.01 gram per square meter to about
0.5 gram per square meter and preferably from about 0.05 to 0.1 gram per
square meter, select:ively sensitize to laser light having no W component.
XANTHE~ES such as Acridine Red 3B (Colour Index #450003, Pyronine
G ¦#45005), Rhodamine Scarlet G (#45015), C.I. Basic Red 1 (Rhodamine 6G)
(#45160), Rhodine 2G (#45165), Rhodamine 4G (#45166~, C.I. Basic Yiolet 10
(Rhodamine B) (#45170), Rhoda~ine 12 GF (#~5315), Spirit Soluble Fast Pink B,
and other xanthene type colorants or
TRIARYl~ETH~NES such as C.I. Basic Red 9 (#42500), Tryparosan
(#42505), C.I. Basic Yiolet 14 (~42510), C.I. Basic Violet 2 (Remacryl Magenta
B) (#42520) and other triarylmethane-type colorants or
METHINES such as C.I. Basic Violet 16 (Sandocryl Red B-6B) (#48013),
C.I. Basic Violet 7 (#48020), Astrazone Violet R ~#48030), and any other
methine-type colorant or
A OS such as Sudan Red BY (#11125)C.I.Solvent Red 3(#12010),C.I.
Solvent Yellow 14 (Sudan Yellow) (~12055), C.I. Solvent Orange 7 (#12140),
C.I. Solvent Red 8 (#12715), C.I. Solvent Red 100 (~eozapon Red BE) (#12716),
C.I. Acid Red 14 (#14720) and others may be used.
The laser source used in the Examples is an argon ion laser, linked
to a suitable scanning system wherein, for instance, a laser beam scanner and
modulator deliver impulses to the coating directly. This equipment is by way
of example only as it is evident that the invention resides in the interaction
of the laser beam and the photosensiti7e coating described herein. Laser beams
driven and modulated by other mechanisms are equally suitable and are within
the purview of this invention.
Examples of the inventive method will now be described after firstly
describing the scanner shown in the accompanying drawing, which scanner was
made by Laser Graphics System, Inc. and was used to make the laser exposures.
The drawing shows a laser, in this embodiment, an argon ion laser 1,
such as the Coherent Radiation model CR 8 laser or the Spectra Physics model
164 laser. A coherent, nearly parallel beam of light 2 is reflected by the
first surface mirrors 3 and 31, which in this embodiment, are strictly selec-
tive for reflection between 450 to 530 nm only so that only 5.10 5~ of light
below 450 nm is allowed to pass.
The intensity of the laser beam 2 is modulated by the modulator 4
which in this embodiment is an acousto/optical modulator such as a Spectra
Physics model I~S 100-5B. The amplitude-modulated beam 5 is then focused
into a converging beam 12 by a ~assegranian type reflective optical system 6
such as Spectra Physics model ADS 100-6. The beam 12 is scanned across the
imageable surface or plate 10 by means of the planar, first-surface mirror 13,
the frusto-pyramidal first-surface mirror 8 which is driven by a motor 7, the
planar first-surface mirror 13' and the curved, first-surface mirror 9 to
arrive at the plate 10 as indicated by the arrows, while the plate 10 is being
transported under the line of scan as indicated by the arrow. The image on
the plate results from the intensity of the laser beam being modulated in
-- 7 --
8~
accordance with an input source of information 11, which may be a computer
output, magnetic tape output, modified signal from an image reading device
with optical arrangement similar to that of Figure 1 or other suitable means.
Data in all Examples are based upon the use of a scanner equipped
with a 6 watt argon ion laser. Identical plates were exposed with another
scanner differing essentially in using a commercially available laser with an
output of 15 watts.
The results are summarized in the following Table I. From these
trials, the exposure rate appeared to be proportional to the laser output
wattage. This relationship was subsequently verified for five wattages in
the range of 3 watts to 15 watts. Laser recording speed data in the last
column of Table 1 has been normalized to the 15 watt laser.
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8~1
EXAMPLE 1
To a 2000 ml Erlenmeyer flask equipped with a mechanical stirrer
containing 990 g (13.2 moles) of 2-methoxyethanol (available from Union
~, e l/ o s ~
Carbide as ~methyl e~=ol~4L} were added sequentially over several hours
the following components : 4.9 g of a polyvinylformal resin commercially
(available from Monsanto as ''Formvar 12/85"), 4.9 g of a polymeric condensa-
tion product of 1 mol of 4-(phenylamino)-2-methoxybenzene diazonium salt and
1 mol of bis-(4-methoxymethylphenyl) ether, prepared in an 85% phosphoric acid
and isolated in the form of a mesitylenesulfonate, as described in United
States Patent No. 3,849,393 assigned to Kalle, A.G. 0.049 g (0.18 mmole)
4-phenylazodiphenylamine~ and 0.111 g (0.96 mmole) of 85% aqueous phosphoric
acid. After stirring at room temperature for one hour, the solution was
filtered through coarse filter paper. This solution will hereafter be called
Stock Solution A.
To 100 g of Stock Solution A~ 136.0/mg Remacryl Magenta B (Colour
Index #42520), (available from American Hoechst Corporation) were added. The
solution was stirred for 30 minutes and filtered through coarse filter paper.
Fifty ml of the above-dyed solution were whirler~coated at 90 rpm
on ~ydrophilic, anodized, grained aluminum treated with a 0.1% aqueous solu-
20~ tion of polyvinyl phosphonic acid in accordance with United States Patent No.3,~20,832, assigned to American Hoechst ~orporation. In the same manner7 a
control plate (contairing no dye) was prepared by whirler-coating 50 ml of
Stock Solution A on the above-described aluminum. The control plate was used
as reference for the exposure speed changes noted in columns 4 and 5 of Table
I. In both cases, the coating weight of the dried plates was 0.25 g/m .
The plates were first exposed conventionally in a Berkey/Ascor
30 x 40 inch exposure unit Model No. 1618-~0, to 20 units of light(approximate-
ly 20 seconds) as measured by means of the attached integrator. The plates
were exposed through a standard Stauffer 21 Stepwedge, developed manually for
~ frac~ ~na~ks
11
361.
45 seconds using an aqueous developer containing 20% by weight of n-propanol
about 1% of surfactant, rinsed with tap water, squeegeed, and finished with
an aqueous solution containing about lO~ of hydrolyzed starch and 0.5% of
phosphoric acid. The plates were then inked in a conventional manner using
Imperial Triple Ink available Prom Lithoplate, Inc. The solidly inked steps
on the stepwedge images were then compared, and from this the relative expos-
ure speed was calculated from the property of the Stauffer 21 Stepwedge that
each successively denser step on the wedge is 1~41 (the square root of 2)
times optically denser than the previous step. In column 4, line l, of Table
I the observation is entered that the dyed plate is 75% slower than the control.
In an analogous manner, the laser exposure speed of the plates was
measured by subjecting sections of each plate to argon laser scanning by means
of a Scan Scriber, described above, with dwell times successively decreasing
~; by a factor of 0.71 (the square root of 0.5); i.e. referring to Figure l, the
transport of the plate 10 was varied stepwise so that the first lnch to be
scanned was scanned in 50 seconds; the second, 36 seconds; the third, 25
seconds. The rotational rate of the mirror 8 was varied so as to be propor-
tional to the transporting speed. The image projected onto the plates was an
~5 line per inch screen pattern with densities in fifteen steps from solid
(100%) to zero (0~). After developing, finishing, and inking the plates as
above, the images were compared for retention of highlight dots~ shadow plug-
ging, and density of solid areas, and the rninimum adequate exposure times were
compared. The results are entered in Table I, column 5, which shows that the
control plate requires 70% more exposure ~han the dyed plate under argon laser
exposure.
E~AMPLE 2
Example 1 was repeated, except that 64.0 mg of Neozapon Red H~ (C.I.
#12716) available from BASF, was used instead of the Remacryl dye of Example 1.
The results are also recorded in Table I.
- 12 --
8~;~
P~ANPLE 3
To a 2000 ml Erlenmeyer flask, equipped ~ith a mechanical stirrer,
containing 990 g (13.0 moles) of 2~methoxyethanol, were added sequentially
the following components: 5.3 g of a styrene-maleic acid copolymer having an
acid number of about 180 and an average molecular weight of about 20.000
(available from Monsanto as "Lytron 820~), 0.50 g (2.9 mmole) of p-toluene-
sulfonic acid, and ~.2 g of the diazonium compound used in Example 1. After
stirring at room temperature for one hour, the solution was filtered through
coarse filter paper. This solution will hereafter be called Stock Solution B.
Example 1 was then repeated, except that Stock Solution B was used both for
the dyed plate and for the control plate, and 136.0 mg of Rhodamine 6GDN
Extra (C.I. #45160) available from DuPont, were used instead of the Remacryl
dye of Example 1. The results are recorded in Table I. In this case, the
laser exposure speed for the plate made from the dyed solution was 0.40 sec/in
or 2.50 min. per 16" x 2~" newspaper page when exposed with a laser with an
output of 6 watts.
~XAMPL3 4
EXample 1 was repeated7 except that 136.0 mg of Sandocryl Red B-6B
(C.I. ~48013), available from Sando~, was used instead of the Remacryl dye of
Example 1. The results are recorded in TabIe I.
EXAMPLE 5
__ .
Example 1 was repeated except that 136.0 mg of Sudan Yellow (C~I.
~12055) available from BASF, were used instead of the Remacryl dye of Example
1. The results are recorded in Table I.
~AMPLE 6
Example 1 uas repeated except that 136.0 mg of Spirit Soluble Fast
Pink B, formerly available from BASF, were used instead of the Remacryl dye of
EXample 1~ The results are recorded in Table I.
~ tr~ k
- 13 -
EXAMPIE 7
Example 1 was repeated except that 136.0 mg of Rhodamine FB (C,I.
#45170) available from BASF were used instead of the Remacryl dye of ~xample
1. The results are recorded in Table I.
EXAMPLE ~
Example 1 was repeated excep* that 136.0 mg of Oracet Red B (Colour
Index Solvent Red 16) available from CI~A-Geigy were used instead of the
Remacryl dye of Example 1. The results are recorded in Table 1.
EXAMPLE 9
Example 3 was repeated, except that 136.0 mg of A~o Eosin G (C.I.
#14710) available from DuPont were used instead of the Rhodamine dye of
~xample 3. The results are recorded in Table I.
E~AMPIE 10
Example 1 was repeated except that 136.0 mg of Rhodamine 6 GDN
(C.I. #45160) available from DuPont were used instead of the Remacryl dye of
Example 1 and Hostaphan H polyester film, available from American Hoechst
Corporation, silicated according to the published German patent applica*ion
DT-AS 1228 414 for lithographic printing plates was used instead of the
aluminum carrier of ~xample 1. The results are recorded in Table I.
EXAMPLE 11
A coating solution was prepared as in Example 1 from the diazonium
compound of ~xample 1, "Formvar 12/85", 1~22 g of Rhodamine 6 GDN, 0.045 g of
85% aqueous phosphoric acid and 0.0~ g of 4-phenylazodiphenylamine in a mix-
ture of 79.35 g of 2-methoxyethanol and 11.34 g of ethylene glycol monomethyl
ether acetate varying the ratio of the first two ingredients as shown below.
Four plates were prepared from these solutions using the method of Example 1,
and exposed and developed as in Example 1. Plate lla was the control plate.
~ 7~rRde h,;.~k
- 14 -
Plateg of Diazonium Compound g of Resin
lla 1.59 6.37
llb 2.63 5.33
llc 3.98 3.98
lld 5.33 2.63
The results are recorded in Table I.
EXAMPLE 12
Example 11 was repeated except that instead of the diazonium com-
pound of Example 11, a polymeric condensation product of 4-(phenylamino)-2-
methoxybenzene diazonium sulfate with bis-(4-methoxymethylphenyl) ether was
used, in the same four proportions to give four plates, 12a, 12b, 12c, and
12d, of which 12a was the control plate. The exposure results are recorded
in Table I.
EX~MPLE 13
Example 11 was repeated, except that, instead of the diazonium com-
pound of Example ll, a polymerio condensation product of diphenylamine 4-
diazonium chloride with formaldehyde was used. The proportions of diazonium
compound and resin were as follows:
Plate ~ g of Resin
13a 2.63 5.33
13b 3.98 3.98
13c 5.33 2.63
Plate 13a was the control; the results are recorded in Table I.
;~ EXAUPLE 14
Example 13 was repeated except that instead of the diazonium com-
pound of Example 12~ a polymeric condensation product of 3-methoxydiphenyl-4-
diazonium chloride with formaldehyde was used. Plate 14a was the control;
the results are recorded in Table I.
8fi~
EXAMPIE 15
A coating solution of 0.5 g of "Lytron 820~, 0.05 g of p-toluene-
sulfonic acid, 0.06 g of Rhodamine 6 GDN extra, 100 g of 2-methoxyethanol and
0.4 g of the diazonium compound of Example 1 was prepared and coated as in
Example 1. The plate was exposed as in Example 1, but was developed with a
dilute aqueous alkaline developer containing surfactant, rather than alcohol
containing developer used before. The exposure was satisfactory. The effec-
tive speed was 0.19 secs/in. (normalized to a 15 watt Argon Ion laser).
EXAMPLE 16
Example 1 was repeated, except that Dowetch (trade mark) Deadline
magnesium engraving plates suitable for the preparation of shallow relief
plates for letterpress printing available from Dow Chemical were used instead
of the aluminum printing plates of Example 1. The exposed and developed
plates were then etched with Dowetch (trade mark) etchant to give an image in
rellef where these raised areas corresponded to the laser hardened areas
~hich remainmd a ~r de~el~p~ent.
: ~ :
- 16 -
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