CA1148015A

CA1148015A - Photopolymerizable copying layer containing a pigment with size corresponding to layer thickness

Info

Publication number: CA1148015A
Application number: CA000354347A
Authority: CA
Inventors: Klaus Horn; Kurt Klupfel; Hartmut Steppan
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1979-06-29
Filing date: 1980-06-19
Publication date: 1983-06-14
Also published as: EP0021429A3; EP0021429A2; JPS569735A; BR8004033A; DE2926235A1

Abstract

Abstract of the Disclosure this invention relates to an improvement in a photopo-lymerizable copying material comprising a layer support and a photopolymerizable 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 polymerization, and a finely divided pigment, the im-provement that the average particle size of the pigment corre-sponds at least to the thickness of the copying layer.

Description

Hoe 79/K û2~3 ~8~5 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 Hoe 79/K 028 8~S
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 Hoe 79/K 028 ~8{i ~5 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 Hoe 79/K 02 ~

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.

Hoe 79/K 02 r, S

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-Hoe 79/K 02~, ~8~15 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:

Hoe 79/K 02 8 ~8~

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.

Hoe 79/K 02S

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 ~oe 79/K 02 ~

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 Hoe 79/K 02 8 ~1~8~15 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 Example 2 An electrochemically roughened and anodized aluminum surface having an oxide layer of 3 g/m2 is whirler-coated with Hoe 79/~ 02G

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.

Hoe 79/K 02~

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:

.5 Hoe 79/K 02

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.

Hoe 79/K 02'`
~8~

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) Hoe 79/K 02~3 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.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A photopolymerizable copying material comprising a layer support and a photopolymerizable copying layer with a bare surface, said copying layer containing a polymeric binder, a compound having at least two terminal ethylenically unsaturated free-radically polymerizable groups, a photoiniti-ator for initiating the free-radical polymerization, and a finely divided pigment, the average particle size of which corresponds at least to the thickness of the copying layer.

2. Copying material as claimed in claim 1 wherein the copying layer ranges in thickness from about 0.5 to 12 µm.

3. Copying material as claimed in claim 1 wherein the average particle size of the pigment ranges between about 2 and 30 µm.

4. Copying material as claimed in claim 1 wherein the copying layer contains from about 0.05 to 5% by weight of finely divided pigment, relative to those components of the photopolymerizable copying material of claim 1 which are non-volatile.

5. Copying material as claimed in claim 1 wherein the finely divided pigment comprises silica, aluminum oxide, aluminum silicate, aluminum hydro-xide or titanium dioxide.

6. Copying material as claimed in claims 4 or 5 wherein said pigment is present in an amount of from 0.1 to 2% by weight.

7. Copying material as claimed in claim 1 wherein the polymeric binder is soluble in a dilute aqueous-alkaline solution.

8. Copying material as claimed in claim l wherein the layer support is an aluminum foil with an anodically produced oxide layer.

9. A process for the production of relief images which comprises exposing a photopolymerizable copying material, comprising a layer support and a photopolymerizable copying layer with a bare surface, to light under vacuum with the bare layer surface being in direct contact with the trans-parent original, and washing away the unexposed areas of the copying layer with a developer, said copying layer containing a polymeric binder, a com-pound having at least two terminal ethylenically unsaturated free-radically polymerizable groups, a photoinitiator for initiating free-radical polymer-ization, and a finely divided pigment having an average particle size corres-ponding at least to the thickness of the copying layer.