Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Hoe 79/K û2~3
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The present invention relates to a photopolymerizable copy-
ing material, the photopolymerizable layer of which contalns a
polymeric binder, a polymerizable compound and a photoinitiator.
Furthermore, the invention relates to a process for the production
of relief images, in particular printing forms and photoresists,
by using this material.
Photopolymerizable materials of the indicated type are
known. When processing these materials, it is necessary to ex-
clude, or suppress as far as possible, the influence of atmos-
pheric oxygen upon the free-radical polymerization. This is
usually achieved by coverlng the photopolymerizable layer with a
strippable cover sheet which is impermeable to oxygen (U. S.
Patent No. 3,060,026) or with a covering layer which is imper-
meable to oxygen and soluble in the developer (U. S, Patent No.
3,458,311). It is thus avoided that oxygen diffuses into the
layer during the light-induced polymerization and leads to chain-
terminatlon reactions in the layer, which result in an incomplete
polymerization and, as a consequence, a reduced sensitivity to
light .
The materials hitherto known have the dlsadvantage that
an additional working step is required for the application of the
covering film or the covering layer. In addition, the image re-
solution upon contact copying is decreased, if self-supporting
covering films are used, which have in general a thickness of
about 20~m. Covering layers which are soluble in the developer,
result in a more rapid consumption of developer and in an addi-
tional pollution of the waste water. Therefore, it has been
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attempted to produce photopolymerizable materials which, even
without the use of a covering layer, have a sufficient light-
sensitivity during the imagewise polymerization,
German Offenlegungsschrift No. 2,830,143, describes
such a material which contains specific polymerizable compounds
having an increased molecular weight and specific initiator sys-
tems and which is, therefore, less sensitive to oxygen. The
photopolymerizable layer of this material may, in the same way
as the photopolymerizable layers of other known materials of
this type, contain flllers or pigments which are transparent in the
actlnlc range, for example, silicon dioxides, bentonites, glass
powder, color pigments or colloidal carbon. These additives
cause an increase in strength and a reduction of tackiness or
they serve to dye the layer. An influence upon the surface
structure of the layer or upon its sensitivity during exposure is,
however, not mentioned.
It now has become apparent that the usual exposure of
materials of this kind, i . e . contact copying in a vacuum frame,
will, after development, give rise to patchy copies and faults in
the application, for example, as planographic printing forms.
The smoother the copying layer is, the more pronounced this
phenomenon becomes.
It is assumed that this fault is caused by the fact that
the sensitivity of the copying layer varies slightly depending
upon the presence or absence of air. When the original is
brought into close contact with the copying layer in the vacuum
frame, small air pockets may form, which may lead to areas in
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which the contact is closer, and others wherein the contact is
less close. As a result, the layer is, in places, partially over-
exposed and partially underexposed and a patchy copy is obtain-
ed .
It is an object of the present invention to provide a
photopolymerizable copying material which can be processed
without the use of an oxygen-inhibiting covering layer and which
shows no effects of an irregular exposure or polymerization upon
contact copying in the vacuum frame.
The lnvention is based upon a photopolymerizable copying
material which comprises a layer support and a photopolymeriz-
able copying layer with a bare surface, the copying layer
containing a polymeric binder, a compound having at least two
terminal, ethylenically unsaturated, free-radically polymerizable
groups, a photoinitiator for initiating the free-radical polymeri-
zation, and a finely divided pigment.
In the copying material according to the invention, the
average particle size of the pigment corresponds at least to the
thickness of the copying layer. Preferably, the thickness of the
2 0 copying layer is within the range from about 0 . S to 1 2~m .
In general, the average particle size of the pigment ls
from 2 to 3 0 ,~m .
Relative to its non-volatile components, the copying layer
has a content of finely divided pigment, which ranges generally
from 0. 05 to 5% by weight, preferably from 0.1 to 2% by weight.
Inorganic pigments are preferably used as the pigments,
especially if the material is employed for the production of
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printing forms. In addition, colorless pigments are preferred,
because they do not affect the light absorption and, as a conse-
quence, the light-sensitivity of the layer. Although it is in
prineiple possible to add color pigments to the layer in order to
obtain a visual image contrast, it is preferred to have a free
ehoiee of the quantity and the speeific absorption of the pigment
and to be able to adapt these faetors to the actual layer compo-
sition in eaeh ease. It is therefore not advisable to use the
same additive with a view to achieving the two objects.
As the particles which, according to the invention, are
embedded in the light-sensitive eopying layer, substanees may be
used which are eompatible with the copying layer, whieh do not
adversely affeet the eoating of the support and ean be removed
together with the unexposed areas of the photopolymerizable layer
by means of a developer, without reacting therewith.
Preferred examples of particles of this type are particles
of silica or of silieon dloxide which may be specially pretreat-
ed, particles of alumlnum oxide, aluminum silicate, aluminum
hydroxide, or titanium dioxide or of organic polymeric eompounds
which are insoluble in the solvents used for eoating. The par-
tieles may be eomposed of one single substanee, or partieles of
different substanees may be eombined.
For preparing the eopying layers, the particles are added
direetly to the coating solution, while stirring thoroughly. Pre-
ferahly, they are dispersed in a suitable solvent in a ball mill,
together with part of the resin or binder, whieh is used for the
copying layer. This dispersion is then added to the rest of the
coating solution while stirring thoroughly.
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The copying layer of the copying material according to the
invention is substantially composed of monomers, photoinitiators,
binders and the above-described pigments, However, it al so
may contain a number of iurther additives, for example:
- stabilizers or inhibitors to avoid a thermal
polymerization of the copying layer,
- hydrogen progenitors,
- plasticizers,
- sensitometric modifiers, and
- dyestuffs or color pigments.
A great number of substances are suitable as the photo-
initiators, for example :
Benzoin, benzoin ether, polynuclear quinones, for exam-
ple, 2-ethyl-anthraquinone; acridine derivatives, for example,
9-phenyl acridine, 9-p-methoxyphenyl acridine, 9-acetylamino
acridine, benz(a)acridine; phenazine derivatives, for example,
9,10-dimethyl-benz(a)phenazine, 9-methyl-benz(a)phenazlne, 10-
methoxy-benz(a)phenazine; quinoxaline derivatives, for example,
6,4',4"-trimethoxy-2,3-diphenylquinoxaline, 4',4"-dimethoxy-
2 ,3-diphenyl-5-aza- qulnoxaline; quinazoline derivatives; syner-
gistic mixtures of various ketones; dyestuff/oxidation-reduction
systems; thiopyrylium salts and the like,
Photopolymerizable monomers which are suitable for the
purposes of the invention are known and are, for example, de-
scribed in U. S. Patents Nos . 2, 760, 863 and 3, 060, 023 .
Preferred examples are acrylic and methacrylic acid esters,
for example, diglycerin diacrylate, polyethylene glycol dimethac-
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rylate, acrylates and methacrylates of trimethylol ethane, tri-
methylol propane and pentaerythritol and of polyvalent alicyclic
alcohols. Reaction products of diisocyanates with partial esters
of polyvalent alcohols are also advantageously used. German
Offenlegungsschriften Nos, 2,064,079 and 2,361,041 describe
monomers of this type.
Aliphatic polyethers are generally used as the hydrogen
progenitors. This function also may be assumed by the binder
or by the polymerizable monomer, lf they contain activated hy-
drogen atoms.
Many soluble organic polymers can be used as the bind-
ers. The followlng are exemplary:
Polyamides, polyvinyl esters, polyvinyl acetals, polyvinyl
,.. ~ . .
ethers, polyacrylates, polymethacrylates, polyesters, alkyd
resins, polyacrylamide, polyvinyl alcohol, polyoxyethylene,
polydimethyl acrylamide, polyvinyl pyrrolidone, polyvinyl methyl-
formamide, polyvinyl methyl acetamide, as well as copolymers of
the monomers forming the enumerated homopolymers.
Furthermore, natural substances or converted natural sub-
stances, for example gelatin, cellulose ether and the like, can
be used as the binders.
Binders which are soluble or at least swellable ln aque-
ous-alkaline solutions are particularly advantageously used, be-
cause layers which contain such binders are capable of being
developed with the preferred aqueous-alkaline developers. Bind-
ers of this type may, for example, contain the following groups:
OH ~ P3H2, -S03H, -So2NH2 ~ -SO2-NH-CO-and the like .
The following are exemplary:
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Maleic resins, polymers of N-(p-tolyl-sulfonyl)-carbamic acid-
(~-methacryloyloxy-ethyl)-ester and copolymers of these and of
similar monomers with other monomers, and styrene-maleic anhy-
dride copolymers. Preferred are methyl methacrylate-methacrylic
acid copolymers and copolymers of methacrylic acid, alkyl
methacrylates and methyl methacrylate and/or styrene, acryloni-
trile and others, as, for example, described in German Offenle-
gungsschriften Nos. 2,064,080 and 2,363,806.
Suitable supports are chosen according to the type of
printing plate to be prepared. Generally, aluminum is used which
preferably carries an anodically produced porous oxide layer.
Appropriately, the aluminum is mechanically, chemically or elec-
trolytically roughened before anodization, Anodization is carried
out in known manner, for example, in sulfuric and/or phosphoric
acid, preferably under such conditions that an oxide layer which
has a layer weight of about 0. 5 to 10 g/m2 1s obtalned,
Before applying the 11ght-sensitive layer, the oxide layer
is advantageously subjected to a pretreatment, for example, with
silicates or polyvinyl phosphonic acid, in order to improve the
2 0 printing behavior of the plate, in particular its hydrophilic prop-
erties. The support material is coated in known manner by
whirler, spray or dip-coating, by means of rolls, slot dies or
doctor blades.
It is advantageous to keep the coatlng solutlon in move-
ment by constantly stirring during the coatiny procedure. Fur-
thermore, wetting or levelling agents may be added to the coating
solution to obtain an improved wetting.
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For developing, the exposed printing plate is treated with
a suitable developing solutlon which is preferably a weakly al-
kaline aqueous solution. In this process, the unexposed layer
areas are removed and the exposed areas including the pigments
contained in the layer remain on the support.
The photopolymerizable copying material according to the
invention is exposed in the usual way, in contact with a trans-
parent original in a vacuum copying frame. During copying, a
close and simultaneously uniform contact between the original
and the photopolymerizable copying layer is produced, which re-
sults in an absolutely uniform exposure corresponding to the
image of the original over the entire image surface. It is
assumed thal: formation of local air pockets and thus a locally
varying inhibition of the polymerization are prevented by the
roughness of the layer, which is caused by the pigment particles
protruding from the layer. It is possible that a uniform repro-
duction of the original is additionally favored by the fact that
the distance between the copying layer and the original is uni-
form over the entire surface and that, consesIuently, formatlon of
local halations is avoided.-
As already mentioned, the copying material of the inven-
tion is preferably used for the production of planographic printing
forms. In principle, however, it is suitable for all applications
wherein contact copies are made in a vacuum copying frame and
wherein it is important to obtain a high degree of image resolu-
tion and an exact reproduction of the original. Further applica-
tions are, therefore, the preparation of etched printlng forms, for
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example, multimetal and intaglio printing forms, and of photore-
sists which act as etch or galvano resists, for example, ln the
production of printed circuits.
The invention will be further illustrated by reference to
the following specific examples, wherein parts by weight (p. b. w. )
and parts by volume (p.b.v.) have the same relationship as the
g to the ml, If not indicated otherwise, percentages are given
in percent by weight. The density of the dry photpolymerizable ~ -
layers has a value of about 1.1 g/ml,
Example 1
Electrochemically roughened and anodized aluminum which
has an oxide layer of 3 g/m2, is used as the layer support for
printing plates. It is coated with a solution having the follow-
ing composition:
11.7 p.b.w. of a 33.4% solution of a methyl methacrylate/
methacrylic acid copolymer having an acid
number of 110 and an average molecular weight
of 35, 000, in methylethyl ketone,
3 . 9 p . b. w . of trimethylolethane triacrylate,
0.07 p.b.w. of 9-phenyl acridine,
0.07 p.b.w. of 4-dimethylamino-4'-methyl dibenzal acetone,
0.04 p.b.w. of an azo dye of 2,4-dinitro-6-chloro-benzene
diazonium salt and 2-methoxy-5-acetylamino-
N-cyanoethyl-N-hydroxyethyl aniline,
0 . 07 p . b. w. of an amorphous highly porous silica, having
an average particle size of 8~m,
38. 0 p.b.w. of ethylene glycol monoethyl ether, and
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13 . 5 p . b . w, of butyl acetate .
The plate is coated by whirler-coating in such a manner
that a dry weight of 2 . 8 to 3 g/m2 is obtained. Then the plate
is dried for 2 minutes at a temperature of 100 C in a recirculat-
ed air drying chamber.
Samples of the printing plate obtained are exposed by
means of a 5 kW metal halide lamp for 10, 20, 40, and 80
seconds under a 13-step exposure wedge having density incre-
ments of 0.15.
Then, the plates are developed with a developer which
has the following composition:
120 p.b.w. of sodium metasilicate 9 H2O,
2.13 p.b.w. of strontium chloride,
1 . 2 p . b . w . of a non-ionogenic wetting agent (coconut
oil alcohol-polyoxyethylene ether having
approximately 8 oxyethylene units),
0 . 12 p . b . w . of a foam inhibitor, and
4000 p.b.w. of demineralized water.
The plates are acidified with 1% phosphoric acid and dyed
with a greasy printing ink. The following fully cross-linked
wedge steps are obtained:
Fully cross-linked wedge steps at
10 __ 20 40 80 _s conds
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Example 2
An electrochemically roughened and anodized aluminum
surface having an oxide layer of 3 g/m2 is whirler-coated with
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a solution of the following composition in such a way that a
layer weight of 3 . 5 g/m is obtained:
10. 0 p.b.w. of a 20% solution of a terpolymer of
styrene, n-hexyl methacrylate and metha-
crylic acid (10:60:30) having an acid num-
ber of 190, in butanone,
2 . 0 p . b . w. of the reaction product of 1 mole of 2, 2, 4-
trimethyl-hexamethylene diisocyanate, and
2 moles of 2-hydroxy-ethyl-methacrylate,
100 . 3 p . b . w. of 9-phenyl acridine,
0.15 p.b.w. of 4-chloro-benzalquinaldine,
0.03 p.b.w. of Methyl Violet (C.I. 42,535),
13.0 p.b.w. of butanone,
7 . 5 p . b . w . of butyl acetate, and
0 . 06 p . b .-w . of silicon dioxide of high purity and of an
average particle size of 3 ~m.
The coated plate is dried for 2 mlnutes at 100 C in a
recirculated air drying chamber.
The plate 1s exposed for 40 seconds under a 13-step ex-
posure wedge and then developed with a developer which has the
following composition:
5.3 p.b.w. of sodium metasilicate 9 H2O,
3.4 p.b.w. of tert. sodium phosphate . 12 H2O,
0.3 p.b.w. of sec. sodium phosphate . 12 H2O, and
91. 0 p . b . w. of deminerallzed water.
The plate is acidified with 1% phosphoric acid and dyed
with a greasy printing ink.
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ExamPle 3
An electrochemically roughened and anodized aluminum
surface which has an oxide layer of 3 g/m2 is whirler-coated
with a solution of the following composition in such a way that
a layer weight of 3 g/m2 is obtained:
11 . 4 p . b . w. of the copolymer solution indicated in
Example 1,
37.9 p.b.w. of ethylene glycol monoethyl ether,
13.45 p.b.w. of butyl acetate,
4.0 p.b.w. of trimethylolethane triacrylate,
0 . 07 p . b . w . of 4-methyl benzalquinaldine,
0.04 p.b.w. of the azo dye indicated in Example 1,
0. 07 p.b.w, of 4-dimethylamino-4'-methyl-dibenzal
acetone, and
0 . 056 p . b. w. of aluminum oxide having an average par-
ticle size of 5 ~4m.
The resultlng offset printing plate is exposed by means
of a 5 kVV metal hallde lamp for 40 seconds under a 13-step ex-
posure wedge with density increments of 0.15.
Then, the plate is developed with the developer described
in Example 1.
In a further step it is acidified with 1% phosphoric acid
and dyed with a greasy printing ink.
Exam~le 4
A solution for coating an electrochemically roughened and
anodized aluminum support which has an oxide layer of 3 g/m2
is prepared as follows:
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5.7 p.b.w. of a 35% solution of the copolymer indi-
cated in Example 1, in methylethyl ketone,
3 . 0 p . b . w . of the addition product of 2 moles of acrylic
acid and 1 mole of the bisglycide ether of
bisphenol A (Br number 66; OH number 231),
0.125 p.b.w. of 9-phenyl acridine,
0.07 p. b . w . of the azo dye indicated in Example 1,
24.0 p.b.w. of methylethyl ketone, and
12.0 p.b.w. of butyl acetate .
The solution is filtered and mixed with
0. 04 p.b.w. of an amorphous silica having an average
particle diameter of 4 ~m
and intensely stirred for half an hour.
The aluminum foil is coated in such a way that a layer
weight of about 3 g/m2 is obtained after the solution has been
applied and dried at approximately 40 C.
The coated plate is additionally dried for 2 minutes at
100 C in a recirculated air drying chamber.
By means of a 5 kW metal halide lamp, the coated plate
is exposed for 40 seconds under a negative film original and de-
veloped with a developer which has the following composition:
7.2 p. b . w . of sodium metasilicate . 9 H2O,
0.023 p . b . w . of the non -ionogenic wetting agent indi-
cated in Example 1,
0 . 01 p . b . w . of a foam inhibitor, and
92.67 p.b.w. of demineralized water.
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The plate is acidified with 1% phosphoric acid and dyed
with a greasy printing ink.
Using the plate so prepared 100, 000 prints were produced
on an offset printing machine.
Exam~le 5
A solution as described in Example 2, but containing
0. 06 p.b.w. of the silica specified in Example 1, instead of
the silica used in Example 2, is applied by whlrler-coating to
a cleaned support comprising an insulating material laminated to
a 35 ~m copper foll, in such a way that a layer thickness of
about 5 ~m is obtained. The layer is dried for 5 minutes at
100 C in the recirculated air drying chamber. The support
al so may be coated on both sides .
Samples of the material are exposed for 2, 4, 8, 16, 32
and 64 seconds under a step-wedge as described in Example 1,
using a 5 kW metal halide lamp disposed at a distance of 140
cm. The plates are developed for 30-60 seconds with an 0.8%
sodium carbonate solution in a spray apparatus.
Depending on the exposure time, the follawing completely
cross-linked wedge-steps are obtained. The numbers in brackets
added in some cases include those steps which are almost com-
pletely cross-linked: ;
ex~osure time fullY cross-linked wedqe ste~s
2 seconds 3
4 seconds 4
8 seconds 5 (6)
16 seconds 7 (8)
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exposure time fully cross-linked wedqe steps
32 seconds 9
64 seconds 10 (1~)
The cross-linked areas are resistant to the ferric chloride
etching solution which is generally employed in printed circuit
board technology. The underetching factor is below 10% of the
line width .
When the example was repeated with a photopolymerizable
layer which did not contain any silica, light-sensitivities of the
same order of magnitude were obtained. However, the results
could not be reliably reproduc`ed at identical exposure times.
The surface of the layer was tacky in exposed and unexposed
areas, so that the master could not be detached without damaging
the layer.
It will be obvious to those skilled in the art that many
modifications may be made within the scope of the present inven-
tion without departi ng from the spirit thereof, and the lnvention
includes all such modlfications.
