CA1052611A - Photopolymer process - Google Patents

Abstract

Abstract of the Disclosure The invention concerns a process for making photographic images. The process involves the photooxygenation of a film of an extralinearly unsaturated polymer containing allylic hydrogens to form polymer peroxides in the exposed areas of the film, and decomposition of the peroxides to effect crosslinking of the polymer.

Description

- ~ ~o~ll Breslow & Simpson Case 2 This invention relates to photopolymer compositions and to photopolymer elements, for example, plates embodying a layer of such compositions. More particularly, the invention relates to a process for making lithographic plates.
Compositions capable of being converted under the influ-ence of actinic light to rigid, insoluble, tough structures have become increasingly important in the preparation of printing el-ements. One of the fundamental patents relating to such composi-tions is U.S. 2,760,863 to Plambeck. In the process of the Plambeck patent, printing elements are produced directly by expos-ing to actinic light, through an image bearing process transpar-ency, a layer of an essentially transparent composition containing an addition polymerizable, ethylenically unsaturated monomer and an addition polymerization initiator activatable by actinic light.
The layer of polymerizable composition is supported on a suitable support, and exposure of the composition is continued until sub-stantial polymerization of the composition has occurred in the exposed areas with substantially no polymerization occurring in the nonexposed areas. The unchanged material in the latter areas then is removed, as by treatment with a suitable solvent in which the polymerized composition in the exposed areas is insoluble.
In the case of printing plates, this results in a raised relief image which corresponds to the transparent image of the transparency and which is suitable for use in letterpress and dry off-set work.
While extremely useful in the preparation of relief printing elements, lithographic printing elements and images from dry transfer processes, certain of the photopolymer compositions of ~, the types disclosed by the Plambeck patent become less sensitive to actinic light due to the diffusion of oxygen from the air into ` 30 the photopolymer layer. The oxygen acts to inhibit the desired polymerization and cross-linking reactions. There are means of removing or preventing oxygen from saturating or desensitizing the photopolymer layer. One way is to store or treat the element ; in an essentially oxygen-free atmosphere of an inert gas such as .

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carbon dioxide. This technique gives satisfactory results but requires special equipment and is time consuming. It also is known to add certain metal compounds such as tin salts, which are soluble in the photopolymer composition but which are nonreactive with the addition polymerization ini-tia1:or. While a number of these compounds substantially reduce the influence of oxygen and improve the photographic speed of the photopolymer element, their utilization has not been entirely satisfactory.
Now, in accordance with this invention, there has been discovered a process for the preparation of printing plates, particularly lithographic plates, which process is not inhibited by oxygen. As a matter of fact, the process depends upon oxygen being present during the exposure step. The process comprises the steps of providing a polymer film with a photooxygena-tion sensitizer, said film being a film of a polymer containing extralinear olefinic unsaturation of the type in which there is no more than one hydro-; gen atom on each of the double bond carbons and in which there is at least one allylic hydrogen on at least one of the carbons adjacent to the double bond carbons, which allylic hydrogen is not on a bridgehead carbon, exposing selected areas of the sensitized film to light ha~ing a wave length of from about 3900 to about 12000 Angstroms in the presence of oxygen to form polymer peroxides in said areas, and decomposing said peroxides to form a cross-linked polymer structure in the exposed areas of the film. Preferred methods ; of decomposing the peroxides include treating the exposed film with heat, or a metal catalyst, suitably a transition metal catalyst, or a reducing agent to form a crosslinked polymer structure in the exposed areas of the film.
The process of this invention is applicable to the preparation of photoresists and relief printing plates, but is particularly useful in the ; preparation of lithographic printing plates. In the preparation of litho-graphic plates, the photopolymer compositions of the process of this inven-tion, deposited as a film on a metal backing support, are selectively exposed to light and crosslinked in the exposed areas. The unexposed areas of the film then are removed by use of a suitable solvent for the photopolymer com-position, exposing the metal substrate. Since the crosslinked ~05'~
polymer composition corresponding to the exposed areas of the film is oleophilic, it accepts greasy ink, whereas the metal surface corresponding to the unexposed areas of the film, being hydrophilic, accepts water and rejects the greasy ink.
The process is believed to involve the formation of peroxides (peroxides or hydroperoxides) and their decomposition to generate free radicals or epoxides which effect crosslinking of the photopolymer compositions. The initial reaction involves the photosensitized oxidation of a suitably substituted, unsaturated polymer, resulting in the formation of peroxide groups on and in the polymer film. The polymer peroxides formed in the light-struck areas of the film then are decomposed, either concurrently with or - subsequent to their formation, by the action of heat, or a transi-tion metal catalyst or a reducing agent to provide the free rad-icals or epoxides necessary for crosslinking.
The process of this invention is advantageous in that it is possible to utilize low light levels. Also, the process is not inhibited by oxygen during the exposure step. Furthermore, low levels of visible light are operative, thus making it possible to prepare printing plates by projection of a photographic transpar-` ency.
The process of this invention is illustrated more specifically by the following examples. In all the examples, the solution preparation, film coating and subsequent operations were carried out in the dark under safe lights.
Example 1 ; This example illustrates the crosslinking of a film of ethylene-propylene-ethyliaenenorbornene terpolymer rubber (EPsyn 40-A EPDM, Copolymer Rubber and Chemical Corp.).
A 0.750 g. portion of EPsyn 40-A EPDM (5.8xlO 4 mol unsaturation/gm.~ Mooney viscosity [ML-8' @ 250F.] 40) was dissolved in 13.0 ml. of benzene, and to the resulting solution was added 0.0038 g. of meso-tetraphenylporphin and 0.015 g. of cobalt (II) stearate (2.0% based on the rubber). This solution . ' . .

6~1 ~ s used to cast a film on a grained aluminum substrate with a 50 mil doctor blade. The film was allowed to dry at room tempera-ture in the dark~ The thickness of the dried film was about three mils. The dried film was covered with a photographic negative and then was exposed for ten minutes from a distance of 20 cm. to a 375 watt Sylvania R32 photoflood lamp. During exposure the film was cooled by an air blower. Following exposure the negative was removed, and the film was etched in benzene, resulting in removal of the photopolymer composition from the aluminum substrate in the unexposed areas of the film. A raised image remained in the exposed areas of the film.
ExamRle 2 This example illustrates the crosslinking of a film of ethylene-propylene-ethylidenenorbornene terpolymer rubber using an amine salt of rose bengal as the sensitizer.
A 0.750 g. portion of EPsyn 40-A EPDM was dissolved in 13.0 ml. of benzene, and to the resulting solution was added 0.0028 g. of acid rose bengal, 0.0004 g. of triethylenetetramine, and 0.015 g. of cobalt (II) stearate. This solution was used to cast a film on a grained aluminum substrate with a 25 mil doctor blade. The thickness of the dried film was about 1.5 mils. The dried film was exposed as described in Example 1 for 30 minutes.
Following exposure and removal of the negative, the film was heated at 110C. for one hour. Benzene etching removed the un-exposed areas of the film, leaving a sharp image with good half-tone definition.
Exam~le 3 This example illustrates the crosslinking of a film of ethylene-propylene-ethylidenenorbornene terpolymer rubber using chromium (III) acetylacetonate as a catalyst.
A 0.62 g. portion of EPsyn 40-A EPDM was dissolved in 10.7 ml. of benzene, and to the resulting solution was added 0.0031 g. of meso-tetraphenylporphin and 0.012 g. of chromium (III) acetylacetonate. This solution was used to cast a film on a - ~os~
-Jl` ained aluminum substrate with a 25 mil doctor blade. The thick-ness of t~le dried film was ahout 1 5 mils. The dried film was exposed as described in Example 1 for 15 minutes. Following ex-posure, the negative was removed and the film was etched in ben-zene, leaving an image with good half-tone definition.
A portion of the above film was exposed for five min-utes as described in Example 1 and then heated at ln5C. for 15 minutes. Benzene etching produced an image with good half-tone definition.
Example 4 This example illustrates the crosslinking of a film of ethylene-propylene-ethylidenenorbornene terpolymer rubber using cobalt naphthenate as the catalyst.
An EPsyn 40-A EPDM film was prepared as described in Example 1, replacing the cobalt (II) stearate with 0.014 g. of cobalt naphthenate (Tenneco, Nuodex, 6~ cobalt). The film was exposed and developed as described in Example 1 and resulted in the formation of a raised image.
Exa-m~l _ 5 This example illustrates the crosslinking of a film of ethylene-propylene-ethylidenenorbornene terpolymer rubber using vanadium oxyacetylacetonate as the catalyst.
An EPsyn 40-A EPDM film was prepared as described in Example 1, replacing the cobalt (II) stearate with 0.015 g. of vanadium oxyacetylacetonate. The film was exposed and developed as described in Example 1 and resulted in the formation of a raised image.
Exam~le 6 This example illustrates the crosslinking of a film of ethylene-propylene-ethylidenenorbornene terpolymer rubber using molybdenum naphthenate as the catalyst.
An EPsyn 40-A EPDM film was prepared as described in Example 1, replacing the cobalt (II) stearate with 0.015 3. of molybdenum naphthenate (Climax Molybdenum Company, 5-6% Mo). The ~r~e r~ 6 -f-` lOSZ~ll , ilm was exposed as described in Example 1 for 15 minutes. Immed-iately following exposure, the film was heated at 100C. for 15 minutes and then was etched in benzene. A relief image of the negative was formed.
Example 7 This example illustrates the crosslinking of ethylene-propylene-ethylidenenorbornene terpolymer rubber using zinc tetraphenylporphin as the sensitizer and heat as the catalyst.
A 0.375 g. portion o EPsyn 40-A EPDM was dissolved in 8.1 ml. of benzene and to the resulting solution was added 0.050 g. of zinc tetraphenylporphin.
A 12.5 x 12.5 cm. sheet of grained aluminum was pre-treated by wiping with a 0.5~ (by volume) solution of gamma-methacryloxypropyltrimethoxysilane (Union Carbide, A-174 Silane) in methanol. This pretreatment increases film adhesion.
The aluminum sheet was whirl coated with the EPsyn 40-A
EPDM solution, producing a polymer film about three microns thick.
After air drying in the dark, a section of the film was covered with a Stauffer 21 Step Sensitivity Guide (#AT 20 x 0.15) and ex-posed for 10 minutes from a distance of 60 cm. to a 375 wattSylvania R32 photoflood lamp. Immediately following exposure, the Step Guide was removed and the film was heated at 105C.
for 15 minutes under a nitrogen atmosphere. The film was then etched in benzene for about five minutes. The polymer film was removed in the unexposed areas, but a crosslinked film remained in the exposed areas that was clearly visible through step #21.
The plate was wiped with 3M Process R Gum Solution and r~ inked with Lith-Kem-Ko Rub-Up Ink~ The exposed areas of the plate accepted the ink while the unexposed areas, which had been etched to the aluminum backing, rejected the ink, resulting in the for-mation of a sharp image.
Example ~

This example illustrates the crosslinking of ethylene-propylene ethylidenenorbornene terpolymer rubber using ~` rr~d~ 7 ,, ~ .

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meso-tetraphenylporphin as the sensitizer and heat as the catalyst.
A 0.375 g. portion of EPsyn 40-A EPDM was dissolved in 8.1 ml. of benzene and 0.050 g. of meso-tetraphenylporphin was added. A film was prepared and exposed through a photographic negative as described in Example 7. Immediately following expos-ure, the film was heated and then etched as described in Example 7. A good reproduction of the negative was produced.
Example 9 This example illustrates the crosslinking of a film of a modified phenoxy resin using methylene blue as the sensitizer and cobalt naphthenate as the catalyst.
Phenoxy resin (Union Carbide, PKHC, condensation product of bisphenol-A and epichlorohydrin, viscosity of 40~ solution in methyl ethyl ketone, 3200-4500 centipoises) was modified with 5-; norbornene-2-carbonyl chloride and 1,2-dimethyl-~-chlorocarbonyl-cyclohexene in the presence of pyridine.
Union Carbide PKHC phenoxy resin, 14.2 g. (0.050 mol hydroxyl), and 4.35 g. (0.055 mol) of pyridine were dissolved in 200 ml. of dry methylene chloride under nitrogen. A solution of 1.72 g. (0.010 mol) of 1,2-dimethyl-4-chlorocarbonylcyclohexene in 5.0 ml. of dry methylene chloride was added dropwise at room temperature. The reaction mixture was stirred overnight. A solu-tion of 7.05 g. (0.045 mol) of 5-norbornene-2-carbonyl chloride in lO ml. of dry methylene chloride was then added to the reaction mixture and stirring wa~ continued for two days.
The modified polymer was precipitated by pouring the re-action mixture into one liter of rapidly stirring methanol. The polymer was isolated, redissolved in 250 ml. of methylene chloride, reprecipitated from one liter of methanol, and dried under pump i 30 vacuum at room temperature for 24 hours. NMR examination of the polymer indicated about 20~ modification with dimethylcyclohexene unsaturation and about 80~ modification with norbornene unsatura-tion.

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A 0 . 60 g. portion of the modified phenoxy resin wasdissolved in 3.0 ml. of chloroform, and to the resulting solution was added 0.020 g. of cobalt naphthenate (Tenneco, Nuodex, 6~
cobalt) and 0.55 ml. of a 3.34xlO 3 M solution of methylene blue in chloroform. This solution was used to cast a film on a grained aluminum substrate using a 10 mil doctor blade. The thickness of the dried film was about one mil. The film was covered with a photographic negative and exposed for 15 minutes from a distance of 30 cm. to a 375 watt Sylvania R32 photoflood lamp. Immediately following exposure, the film was heated at 60C. for 30 minutes under a nitrogen atmosphere. The film was then etched in methylene chloride until the unexposed areas were removed. An image was clearly visible in the exposed areas of the film.
EXample 10 This example illustrates the crosslinking of a film of a modified unsaturated polyester by addition of the catalyst sub-sequent to exposure.
' A fumarate polyester (Atlac 382E, molecular weight 3,000, Atlas Chemical Industries; based on bisphenol-A and propylene oxide) was chain extended with toluene diisocyanate and partially modified in a Diels-Alder reaction with 2,3-dimethyl-1,3-butadiene (DMB).
Atlac 382E, 25 g., was dissolved in 100 ml. of benzene and about 25 ml. of benzene was distilled off under a nitrogen atmosphere. Toluene diisocyanate, 1.16 g. (6.67x10-3 mol), and five microliters of a 10% solution of stannous octoate in hexane was added to the Atlac solution, and the reaction mixture was re-fluxed overnight. The polymer was precipitated by pouring the viscous solution into one liter of hexane. The polymer was iso-lated, redissolved in benzene, filtered through glass wool, re-precipitated from one liter of hexane, and dried at 50C. under pump vacuum overnight. A 1~ solution~of the chain extended polymer in benzene had a specific viscosity of 0.30 at 25C., compared to 0.13 for Atlac 382E.

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~)s~ ,0-The chain extended Atlac 382E was partially modified in a Diels-Alder reaction with 2,3-dimethyl-1,3-butadiene (DMB).
The chain extended Atlac, 25 g. (O.OS9 mol unsaturation), DMB, 0.9;2 g. (0.011 mol), and 0.025 g. of copper powder were added to a polymerization bottle with 90 ml. of reagent grade toluene.
The bottle was capped under air and heated at 80C. overnight.
The copper was removed and the modified polymer precipitated by filtering the solution into one liter of hexane. The polymer was isolated, redissolved in benzene, reprecipitated from one liter of hexane, and dried at ambient temperature under pump vacuum over-night. NMR examination of the polymer indicated 10-20% modifica-tion by DMB. The polymer contains units of the following struc-ture:

~C~I- CH2--O -~=~3 C~3--0-C I :2 -C H- O--C~CH-C -C- O~
~ CH3 CH2 CH2 ",' \C=C
;~ / \

A 1.00 g. portion of the chain extended, DMB modified Atlac 382E was dissolved in 10 ml. of benzene and 0.075 g. of zinc tetraphenylporphin was added. Film coating with this solution ; was carried out as described in Example 7, and the dried film was exposed as described in Example 1. Immediately following exposure, the film was lightly sprayed with a solution of 0.10 g. vanadium oxyacetylacetonate in 95 ml. of methanol and 5 ml. of chloroform ;:., .
` under a nitrogen atmosphere. After 15 minutes, the film was etched in benzene, giving a good reproduction of the negative.

Example 11 . . ' This example illustrates the crosslinking of a film of an ethylene-maleic anhydride copolymer modified with allyl alcohol and the Diels-Alder adduct of 2,3-dimethyl-1,3-butadiene and 2-nydroxyethyl methacrylate. This adduct has the formula:

CH3~,c H3 ~J--C-OCH2CH2--OH

., .... j :' :. ' . .

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n addition, molybdenum naphthenate is employed as the catalyst.
Ethylene-maleic anhydride copolymer (Monsanto, EMA-21, specific viscosity, 0.6 on a 1~ solution of the resin in dimethyl-formamide at 25C.), 25 g., and 0.050 g. of 2,6-di-t-butyl-p-cresol (Hercules, Dalpac 4C) was added to 250 g. of an equal molar mixture of allyl alcohol and the adduct of the above formula in a dry flask under nitrogen. The flask was heated at 60C. with stirring until the EMA-21 dissolved. The reaction mixture was then stirred at room temperature overnight. ~ost of the unreacted alcohols were removed by distillation under reduced pressure. The resulting viscous material was filtered through glass wool into 1.5 liters of rapidly stirring hexane. The precipitated polymer was isolated, dissolved in acetone, precipitated again from 1.5 liters of hexane, and dried at 50C. under pump vacuum for 24 hours. NMR examination of the polymer indicated the presence of both allyl and dimethylcyclohexene unsaturation.
A 0.50 g. portion of the polymer was dissolved in 10 ml.
of acetone and 0.012 g. of rose bengal was added. Film coating -with this solution was carried out as described in Example 7, and the dried film was exposed as described in Example 1 for 15 minutes.
Immediately following exposure, the film was lightly sprayed with a solution of 0.10 g. molybdenum naphthenate (Climax Molybdenum Company, 5-6% Mo) in 95 ml. of benzene and 5 ml. of acetone. The film was then heated at 100C. for 15 minutes and etched in dilute alkali solution. A good reproduction of the negative was produced.
Example 12 This example illustrates the crosslinking of a film of poly(methyl vinyl ether-maleic anhydride) modified with 2-hydroxy-ethyl methacrylate and 4,5-dimethyl-4-hexene-1-ol.
Poly(methyl vinyl ether-maleic anhydride) (GAF Corporation, Gantrez AN-139, specific viscosity 1.0-1.4, on a 1% solution of the copolymer in methyl ethyl ketone at 25C.), 25 g., and 0.250 g.
of 2,6-di-t-butyl-p-cresol (Hercules Dalpac 4C) was added to 250 g.

of a mixture containing 75 mol % 4,5-dimethyl-4-hexene-1-ol and ~ 7r~Gle /~
.

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25 mol % 2-hydro~yethyl methacrylate in a dry flask under nitrogen.
The flask was heated at ~0C. with stirring until the Gantrez AN-139 dissolved. The reaction mixture was then stirred at room temperature overnight. Polymer isolation, solution preparation, film coating, and exposure were carried out as described in Example ;
11. Immediately following exposure, the film was lightly sprayed with a solution of 0.10 g. of vanadium oxyacetylacetonate in g5 ml. of benzene and 5 ml. of acetone under a nitrogen atmosphere.
After 15 minutes, the film was etched in dilute alkali solution.
A good reproduction of the negative was produced.
Example 13 This example illustrates the crosslinking of a modified poly(methyl vinyl ether-maleic anhydride) copolymer using sulfur dioxide as a reducing agent.
The procedure outlined in Example 12 was followed ; through the exposure step. The film was then placed in a nitrogen atmosphere containing 10% by volume of sulfur dioxide. After 30 minutes the film was removed and etched, and a good reproduction of the negative was produced.
The polymers used in the process of this invention should contain at least 0.1~, and preferably at least 0.2%, by weight of extralinear olefinic unsaturation of the type in which there is no more than one hydrogen atom on each of the double bond carbons and in which there is at least one allylic hydrogen on at least one of the carbons adjacent to the double bond carbons, which allylic hydrogen is not on a bridgehead carbon. An example of this type of unsaturation is illustrated by the structural unit -C=C-CH, in R R
which R is hydrogen or Cl-C5 alkyl. In addition to the desired extralinear unsaturation, the polymers may contain certain other types of unsaturation, for example, fumarate or maleate unsatura-tion, or the type represented by the characteristic CH~=C ~ group.

Some polymers, such as certain EPDM rubbers, contain the appropri-ate type of unsaturation already built into the polymer structure.

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~ wever in other instances, the olefinic unsaturation must be introduced into a base polymer. Exemplary of such base polymers are unsaturated polyesters, into which the desired extralinear unsaturation may be introduced through utilization of the Diels-Alder reaction. Also, since esterification reactions may be used to i~ntroduce the olefinic unsaturation into polymers containing hydroxyl groups, the base polymers may include polymers such as poly(vinyl alcohol) and poly(vinyl acetate) which has been partly hydrolyzed; partly or completely hydrolyzed copolymers of vinyl acetate with other vinyl monomers such as vinyl chloride; cellu-lose and cellulose esters; starch; cellulose which has been partly or completely ~eacted with an alkylene oxide, such as ethylene oxide or propylene oxide, for example, hydroxyethyl cellulose or hydroxypropyl cellulose; phenoxy resins and other resins prepared by condensing a polyhydroxy compound with epichlorohydrin; poly-mers or copolymers of hydroxyalkyl acrylates or methacrylates;
polymers or copolymers of hydroxyalkyl vinyl sulfides; and polymers or copolymers of hydroxyalkyl acrylamides.
The reactant utilized to introduce the extralinear ole-finic unsaturation into the base polymer must provide allylic ~ hydrogen to the product polymer, that is, the latter must contain - at least one hydrogen on at least one of the carbons adjacent to the double bond carbons, which allylic hydrogen is not on a bridge-head carbon. Furthermore, it is necessary in the product polymer that there be no more than one hydrogen atom on each of the double bond carbons. The choice of reactant will depend upon the reaction involved in preparing the product polymer. Thus, 1,3-butadiene, isoprene and 2,3-dimethyl-1,3-butadiene preferably are used in a Diels-Alder reaction, as with an unsaturated polyester. However, the use of cyclopentadiene in this reaction will not provide products useful in the process of this invention, since such products have the allylic hydrogens attached to bridgehead carbons.

In an addition polymerization reaction, a reactant such as 5-ethylidene-2-norbornene is used to obtain the desired extralinear - l~)S~
~nsaturation. In an esterification reaction, the acid, acid halide, acid anhydride or ester reactant will contain the desired unsatura-tion somewhere in the molecule. Thus, depending upon the reaction invo:Lved, suitable reactants are exemplified by those which provide olef~;nic units such as those existing in butene-~, trimethyl ethy;Lene, tetramethyl ethylene, 1,2-dimethyl cyclohexene, 2-ethylidene-norbornane, 2-methyl-2-norbornene, 2,3-dimethyl-2-norbornene, cyclopentene, l-methyl cyclopentene, 1,2-dimethyl cyclopentene, a,~,~'-trimethyl styrene, indene and alkyl-substituted indenes, and alkyl-substituted furans.
More generally, suitable reactants for introducing the extralinear olefinic unsaturation into the base polymer are exem-plified by those which provide olefinic units corresponding to those of the general formula Rl c_f -R3 wherein the Rl, R2, R3 and R4 substituents may be hydrogen, an alkyl group containing one to twenty carbon atoms, an aryl group or a substituted aryl group. Furthermore, Rl and R2, R3 and R4, Rl and R3 and R2 and R4 may be combined in the form of an alicyclic or heterocyclic ring. However, one of the R's must contain the -CH
group in order that at least one allylic hydrogen atom is present, and the carbon in this group can not be a bridgehead carbon. Also, at any one time, when any of the R's is hydrogen, there can be no more than one hydrogen on each of the double bond carbons.
When the R's are alkyl, they may be straight chain alkyl, such as methyl, ethyl, n-propyl, n-butyl, n-amyl, n-hexyl, or octadecyl. Moreover one of them may be a branched chain alkyl, such as isopropyl, isobutyl, t-butyl and isoam~l, as long as none of the remaining R's is branched. Also, one of the R's may be an unsaturated alkyl group containing a carbon-carbon double bond in conjugation with the olefinic double bond. When the R's are aryl, there normally will be no more than two of them which are aryl and they ordinarily will be singly substituted on the double bond ~(~5'~

carbons. The aryl substituents, such as phenyl and naphthyl, also o may themselves be substituted with -R', -OR', -NHC-OR', -Cl, -Br and -F substituents, wherein R' is an alkyl group containing one to six carbon atoms, or is aryl, such as phenyl. Furthermore, if only one of the R's is aryl, then the aryl group may contain a -CN, O O O O
-C-R ', -~-OR ', -~-R' or -OC-NHR' substituent. These same sub-stituents, plus the -NHC-OR', -Cl, -Br and -F substituents listed earlier, also may occur elsewhere in the polymer molecule provided they are separated from the extralinear olefinic unsaturation in the polymer by at least one carbon atom, and preferably by two or more carbon atoms.
The sensitizers used in the process of this invention are generally well known and are characterized as being useful in photosensitized oxidations. Thus, they are photooxygenation sensitizers. Among the best sensitizers are those which absorb visible light, in the range of about 3900 to about 7700 Angstroms, ; namely, fluorescein derivatives, xanthene dyes, porphyrins and porphins, polycyclic aromatic hydrocarbons and phthalocyanines.

The preferred sensitizers are methylene blue and zinc tetraphenyl-porphin. Additional useful sensitizers are: erythrosin B; rose bengal; eosin Y; crystal violet; methylene green; safrin bluish;
1,1-diethyl-1,2,2'-cyanine iodide; 1-ethyl-2[3-(1-ethylnaphtho-[1,2d]-thiasolin-2-ylidene-2-methylpropenyl]-naphthol-11,2a]-thiazolium bromide; pinacyanol chloride; ethyl red; l,l'-diethyl-

2,2'-dicarbocyanine iodide; 3,3'-diethyloxycarbocyanine iodide;

3,3'-diethyl-thiazolino carbocyanine iodide; fluorescein; methylene violet; methylene blue oleate; methylene blue dodecyl benzene sulfonate; copper phthalocyanine; pentacene; naphthacene; copper tetraphenylporphin; tin tetraphenylporphin; acridine orange;
methylene violet, Bernthsen; hemin; chlorophyll; prophyrazines;
octaphenylporphins; benzoporphins; hypericin; 3,4-benzpyrene;

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acridine; rubrene; 4,4'-bis~dimethylamino) ben~ophenone; fluorenone;
anthraquinone; and phenanthrenequinone.
The amount of sensitizer is not critical, but the best re-sults are obtained when the concentration is adjusted so that more than 90~ of the incident light is absorbed at the wavelength cor-responding to the absorption maximum of the particular sensitizer employed. The sensitizer may be incorporated into the polymer when the film is being formed or diffused into the film with a suitable solvent. The oxygen required for the reaction normally is obtained from the air present. However, an atmosphere of pure oxygen may be provided, if desired.
After the polymer peroxides have been formed, they are decomposed to provide the free radicals or epoxides needed for crosslinking. The decomposition reaction is preferably carried out catalytically using, for example, a metal redox catalyst. The catalyst may be added to the photopolymer composition prior to film preparation, in which instance peroxide decomposition proceeds concurrently with peroxide formation. The catalyst also may be added subsequent to film exposure. This may be accomplished by any of several means, for example, by spraying, brush coating or contacting the film with a solution of the catalyst in a solvent which is capable of swelling the film.
The preferred catalysts are salts or complexes of metals, preferably transition metals, capable of existing in more .
than one valence state. Vanadium oxyacetylacetonate, vanadium oxy-sulfate, ferric acetylacetonate-benzoin, manganese octoate, lead ~ naphthenate, cobaltic acetylacetonate, molybdenum naphthenate, ; molybdenum oxyacetylacetonate and chromium (III) acetylacetonate are among the preferred catalysts. Other effective catalysts in-clude titanyl acetylacetonate, cobaltous naphthenate, cobaltous 2-ethylhexanoate, cobaltous stearate, cobaltic stearate, cobaltous acetylacetonate, manganous stearate, manganic stearate, manganous acetylacetonate, manganic acetylacetonate, manganese naphthenate, zirconium acetylacetonate, vanadyl naphthenate, ferrous sulfate, lOS;~
ferrous pyrophosphate, ferrous sulfide, the ferrous complex of ethylenedinitrilotetraacetic acid, ferrous o-phenanthroline, ferrous ferrocyanide, ferrous acetylacetonate, the corresponding nickel, copper, mercury and chromium compounds, molybdenum penta-chloride, molybdenum dioxide, molybdenum octoate, sodium molybdate, sodium vanadate and sodium tungstate. Reducing agents which can be used to carry out decomposition of the hydroperoxides include polyamines such as diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, monoamines, sodium hyposulfite and sulfur dioxide. The decomposition reaction can also be ini~iated thermally.
The photopolymer compositions also may contain up to about 50% by weight of an inert particulate filler which is essen-tially transparent. Representative of such fillers are the organophilic silicas, the bentonites, silica and powdered glass, all having a particle size less than 0.4 mil in their maximum dimension. Particles of 0.1 micron or less in size are preferred.
Such fillers can impart desirable properties to the photopolymer ~.
compositions. For example, use of submicron silica affords a printing plate with a harder and more durable image.
In the preparation of some of the photopolymer composi- `
tions used in the process of this invention, it may be desirable to have present a small amount of a phenolic antioxidant to act as an inhibitor for premature thermal polymerization during pro-cessing or storage of the compositions. Such antioxidants are well known in the art and they are exemplified by hydroquinone, di-t-butyl-p-cresol, hydroquinone monomethylether, pyrogallol, quinone, t-butyl-catechol, hydroquinone monobenzylether, methyl hydroquinone, amyl quinone, amyloxy hydroquinone, n-butyl phenol, phenol and hydroquinone monopropyl ether. The phenolic anti-oxidant may be used in an amount within the range of from about 0.001 to about 2~ by weight, preferably about 1% by weight, based on the polymer component of the photopolymer composition.

The photopolymer compositions of the process of this invention may be cast from solution onto a suitable support.

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~rdinarily, the support member of a lithographic plate is metal-surfaced or composed of entire sheets of metal. Metals such as aluminum, zinc, chromium, tin, magnesium and steel may be used.
Alu~linum and zinc are preferred. In the case of metallic surfaces, oxides may be present, either through exposure to air or through special treatment. For example, in the case of aluminum, the sur-face may, if desired, be chemically or electrolytically anodized.
In casting the composition onto the support, a solution of the poly-mer component in a suitable solvent may be used, and conventional coating techniques may be employed. Alternatively, those photopoly-mer compositions of the process of this invention which are thermo-plastic may be thermoformed in plastic fabrication equipment onto a metal substrate.
When the photopolymer elements prepared as described above are subjected to the process of this invention, the polymer composi-tion in the exposed areas becomes insolubilized, whereas the com-position in the unexposed areas remains soluble. Subsequent wash-ing of the plate removes the soluble material, leaving a replica in relief of the photomechanical negative or positive used in the process. The solvent used in washing the plate will vary according to the solubility of the photopolymer composition. Development may frequently be accelerated by brushing or scrubbing. In large scale ` work, application of the solvent will advantageously be carried ~ out by means of jets or sprays.
- The printing surfaces made in accordance with this inven-tion are particularly applicable in lithography. However, they also are useful in classes of printing wherein the ink is carried by the raised portion of the relief, such as in dry off-set printing and ordinary letterpress printing. Furthermore, the photopolymer com-positions of this invention may be used as photoresists over an etchable metal. In this instance, a thin layer of the composition will become insolubilized in irradiated areas and protect the metal beneath from etching, as in a photoengraving process.

Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The process of making a photographic image which comprises providing a polymer film with a photooxygenation sensi-tizer, said film being a film of a polymer containing extra-linear olefinic unsaturation of the type in which there is no more than one hydrogen atom on each of the double bond carbons and in which there is at least one allylic hydrogen on at least one of the carbons adjacent to the double bond carbons, which allylic hydrogen is not on a bridgehead carbon, exposing selected areas of the sensitized film to light having a wave length of from about 3900 to about 12000 Angstroms in the presence of oxygen to form polymer peroxides in said areas, and decomposing said peroxides to form a crosslinked polymer structure in the exposed areas of the film.

2. The process of Claim 1 wherein the light has a wave length of from about 3900 to about 7700 Angstroms.

3. The process of Claim 1 wherein the polymer peroxides are decomposed by the action of heat.

4. The process of Claim 1 wherein the polymer peroxides are decomposed by the action of a reducing agent.

5. The process of Claim 1 wherein the polymer peroxides are decomposed by the action of a metal catalyst.

6. The process of Claim 5 wherein the metal catalyst is a transition metal catalyst.

7. The process of Claim 1 wherein the photooxygenation sensitizer is methylene blue.

8. The process of Claim 1 wherein the photooxygenation sensitizer is zinc tetraphenylporphin.

9. The process of claim 1, 2 or 3 wherein the polymer contains at least 0.1% by weight of extralinear unsaturation of the type in which there is no more than one hydrogen atom on each of the double bond carbon atoms and in which there is at least one allylic hydrogen on at least one of the carbons adjacent to the double bond carbons, which allylic hydrogen is not a bridgehead carbon.

10. A photopolymer element prepared according to the process of claim 1.

11. The photopolymer element of claim 10 wherein the element is a litho-graphic plate.

12. A process of making a photographic image comprising and subsequent decomposition of hydroperoxide derivatives of polymers having C=C unsatura-tion located in pendant groups, said process comprising photooxidizing said polymers in film form by irradiating said polymers with light capable of catalyzing said reaction and of a wavelength of 3900 to 12000 Angstroms in the presence of oxygen and a photooxygenation sensitizer wherein the carbon atoms of said C=C bonds are of the type in which there is no more than one hydrogen atom on each of the double bond carbons and in which there is at least one allylic hydrogen on at least one of the carbons adjacent to the double bond carbons, which allylic hydrogen is not on a bridgehead carbon.