GB1560304A - Photopolymer process - Google Patents

Description

(54) PHOTOPOLYMER PROCESS (71) We, HERCULES INCORPORATED, a Corporation organized and existing under the laws of the State of Delaware, of 910 Market Street, City of Wilmington, State of Delaware, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method bv which it is to be performed to be particularly described in and by the following statement:- This invention relates to a process for making photographic images by exposing photo oxidizable compositions. More particularly, the invention relates to a process for making printing plates, especially lithographic plates embodying a layer of such compositions.

This invention is an improvement in, and modification of the invention claimed in our prior British Patent Application No. 38603/74 (Serial No. 1488709).

Compositions capable of being converted under the influence of radiation into rigid, insoluble, tough structures have become increasingly important in the preparation of printing elements. One of the fundamental patents relating to such compositions is U.S. Patent No. 2,760,863, according to which printing elements are produced directly by exposing to actinic light, through an image bearing process transparency, a layer of a substantially transparent composition containing an addition polymerizable, ethylenically unsaturated monomer and an addition polymerization initiator activeatable by actinic radiation. The layer of polymerizable composition is supported on a suitable support and exposure of the composition is continued until substantial polymerization of the composition has occurred in the exposed area, with substantially no polymerization occurring in the non-exposed areas. The unchanged material in the latter areas then is removed, e.g.

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 work.

While extremely useful in the preparation of relief printing elements and images from dry transfer processes, the photopolymer compositions of the types disclosed in U.S. Patent No. 2,760,863 become less sensitive to radiation due to the diffusion of oxygen from the air into the photopolymer layer. The oxygen acts to inhibit the desired polymerization and crosslinking 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 oxygen-free atmosphere of an inert gas such as 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 initiator.

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.

Our prior British Patent Application No. 38603/74 (Serial No. 1488709) claims a photo oxidizable composition which comprises: I) an ethylenically unsaturated component capable of forming a cross-linked polymer: 2) an oxidizable component containing olefinic unsaturation with no more than one hydrocarbon atom on each of the double bond carbon atoms, and having at least one allylic hydrogen atom on at least one of the carbon atoms adjacent to the double bond carbon atoms and not being a bridgehead carbon atom; and 3) a photo oxygenation sensitizer which is capable of absorbing light in the visible region of the spectrum or of photosetting oxidations initiated by light in the visible region of the spectrum.

Our prior application also claims a photosensitive element which comprises a support and coated thereon, a layer of such a photo oxidizable composition, and a process for making a photographic image which comprises imagewise exposure of such a photosensitive element to light having a wavelength of from 3900 to 12,000 A in the presence of oxygen, thereby forming peroxides at light-struck areas of said elements, and decomposing said peroxides to form a cross-linked polymer at said light-struck areas.

It has now been found that such compositions, and photosensitive elements comprising them form cross-linked polymers when irradiated by light having a shorter wavelength than that used according to our prior Application, in the presence of the appropriate sensitizers.

The present invention provides a process for making a photographic image which comprises imagewise exposure of a photosensitive composition in film form to light having a wavelength extending over the range from 2,000 to 3900 Angstroms in the presence of oxygen, thereby forming peroxides at light struck areas of said element, and decomposing said peroxides to form a cross-linked polymer at said light struck areas wherein the photo oxidizable composition comprises: 1) an ethylenically unsaturated component capable of forming a cross-linked polymer: 2) an oxidizable component containing olefinic unsaturation with no more than one hydrogen atom on each of the double bond carbon atoms, and having at least one allylic hydrogen atom bn at least one of the carbon atoms adjacent to the double bond carbon atoms and not being a bridgehead carbon atom; and 3) a photo oxygenation sensitizer which is capable of bringing about the generation of singlet oxygen when irradiated by light in the region of the spectrum extending over said range from 2000 to 3900 Angstroms.

As with our prior Application, the process in accordance with this invention is not inhibited by oxygen. As a matter of fact, the process depends upon oxygen being present during the exposure step. During exposure this ambient, triplet oxygen is converted into singlet oxygen, which is involved in the formation of hydroperoxides and peroxides. These intermediates are subsequently decomposed, preferably in the absence of oxygen, generating free radicals which effect polymerization and/or crosslinking of the photosensitive composition.

The process of this invention is applicable to the preparation of relief printing plates, but is particularly useful in the preparation of lithographic printing plates and photoresists.

The photo oxidizable compositions employed in the process of this invention deposited as a film on a support, are selectively exposed to light of the appropriate wavelength and polymerized and/or crosslinked in the exposed areas. The unexposed areas of the film then are removed by use of a suitable solvent for the photo oxidizable composition, or by other means such as use of an air knife exposing the substrate. The photo oxidizable compositions employed in the process of this invention may be used to prepare negative or positive working lithographic plates. In preparing a negative working plate, the compositions are deposited as a film on a metal backing support, are selectively exposed to light of the appropriate wavelength and crosslinked (and in some embodiments also polymerizes) in the exposed areas. The unexposed areas of the film are removed, exposing a hydrophilic metal substrate. If the high molecular weight polymer formed in 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. In preparing a positive working plate, the photo oxidizable compositions are hydrophilic and are deposited as a film on an oleophilic backing sheet. Selective exposure to light crosslinks and in some embodiments also polymerizes the exposed areas, and the unexposed areas are then removed. Since the crosslinked polymer found in the exposed areas of the film is hydrophilic, it accepts water and rejects greasy ink, whereas the oleophilic backing corresponding to the unexposed area of the film accepts the greasy ink.

The process involves the formation of peroxides (peroxides or hydroperoxides) and their decomposition to generate free radicals which effect polymerization and crosslinking, or crosslinking alone, of the photo oxidizable compositions. The initial reaction involves the photo oxidation of an allylic hydrogen-containing component of the composition, resulting in the formation of peroxide groups on and in the film of said composition. The peroxides formed in the light-struck areas of the film are then decomposed, either concurrently with or subsequently to their formation, by the action of heat, or a metal compound catalyst or a reducing agent to provide the free radicals necessary for the polymerization and/or crosslinking reactions.

The process of this invention is advantageous in that it is possible to utilize low light levels, thus making it possible to prepare printing plates by projection of a photographic transparency. Also, the process is not inhibited by oxygen during the exposure step.

The process is also applicable to the preparation of lithographic camera plates.

In this procedure, the copy is exposed to light of the appropriate wavelength, the light being absorbed in the dark areas of the copy and reflected by the light areas.

The reflected light is passed through a lens system and projected on the surface of the photosensitive composition.

The process of this invention is illustrated more specifically by the following Example. The solution preparation, film coating and subsequent operations were carried out in the dark under safe lights.

EXAMPLE This Example illustrates the insolubilization by exposure to ultraviolet light of a film of a maleated phenoxy resin as an ethylenically unsaturated polymer. It was a polymer prepared from bisphenol A and epichlorohydrin, with about 50 " of the alcohol groups esterified by treatment with maleic anhydride. Compound I was used as a photo-oxidizable component; pentaerythritol triacrylate was used as an ethylenically unsaturated monomer; benzanthrone was used as an ultraviolet photo-oxygenation sensitizer; and vanadyl acetylacetonate was used as catalyst.

Compound I was prepared as follows. Bisphenol A, 4:4 g. (0.019 mol), and triethylamine, 3.9 g (0.038 mol), were dissolved in 40 ml of anhydrous diethyl ether under a nitrogen atmosphere. A solution of 7.2 g (0.038 mol) of 1,2,4-trimethyl-4chlorocarbonylcyclohexene (prepared by the Diels-Alder reaction of 2,3-dimethyl 1,3-butadiene and methacrylyl chloride) in 10 ml of anhydrous diethyl ether was added dropwise at ambient temperature to the Bisphenol A solution, and the resulting mixture was stirred for two days under nitrogen. The reaction mixture was transferred to a separatory funnel and extracted successively with 5 ', hydrochloric acid. water and saturated aqueous sodium chloride. The ether layer was dried over anhydrous magnesium sulfate, filtered and the ether removed under vacuum to give a viscous liquid. The product was purified by column chromatography on silica gel and 7.8 g (76%) of a white solid, m.p. 54--560C was isolated. NMR, IR, and mass spectral analyses were consistent with the assigned structure.

A sheet of 14x 14 cm, grained aluminum (Lith-Kem-Ko Division of Lith-Kem Corporation, Lynbrook, N.Y. "Lith-Kem-Ko" is a Registered Trade Mark) was pretreated to improve adhesion by coating with a five percent by volume solution of 7n-methacryloxypropyltrimethoxy silane (Union Carbide, A-174 Silane) in methanol. The coating was applied with a whirl coater (Tasop Face Up Whirler, Tasop Co., Aurora, Missouri) and heated for two minutes under the whirler's infrared lamps.

A photosensitive composition containing the following components was prepared.

Grams Maleated phenoxy resin 100.0 Pentaerythritol triacrylate 40.0 Compound 1 10.5 Vanadyl acetylacetonate 0.86 Benzanthrone 2.86 Ethylene glycol ether acetate (solvent) 616.0 The solution was coated on the pretreated grained aluminum sheet using the Tasop whirler at maximum speed. The dried film thickness was about 10 microns.

This photosensitive plate was exposed through a photographic negative using a general electric RS-275 sun lamp, filtered to pass only 3650 A radiation at a distance of 4 feet for 30 seconds.

Following exposure the plate was stored in a nitrogen atmosphere for 15 minutes, then was heated at 600 for three minutes under nitrogen.

The plate was then etched by washing with agitation in a solution of 2% of sodium bicarbonate, 5% of Renex-30 (a tridecyl alcohol/ethylene oxide condensate) as wetting agent and 5% of ethylene glycol methyl ether. After 30 minutes washing and drying, an excellent reproduction of the negative resulted.

The imaged plate was run on a standard offset printing press giving 6000 copies without any signs of plate wear.

The photo oxidizable compositions used in the process of this invention must contain a photo oxidizable component which will contribute to the composition 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. Such unsaturation can be termed photo oxidizable unsaturation, and an example of this type of unsaturation is illustrated by the structural unit

in which R is hydrogen orC1-C6 alkyl. Preferably the oxidizable component will contribute at least 1.0x 10-3 moles of unsaturation per 1000 cc of the composition, and more preferably at least 1.0x10-2 moles of unsaturation per 1000 cc of the composition.

In general, suitable photo oxidizable unsaturation, whether in a polymer or a low molecular weight compound, will be that provided by a compound of the general formula

wherein the R1, 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, R1, and R2, R3 and R4, R, and R3, or R2 and R4 together with the carbon atoms to which they are attached may be combined in the form of an alicyclic or heterocyclic group. However, one of the R's must contain the

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 a 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 isoamyl, 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 carbons. The aryl substituents, such as phenyl and naphthw l, also may themselves be substituted with -R', -OR', -NH-COOR', l. -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, -CO-R', -CO-OR', -O.CO.R' or-O.CO.NHR' substituent. These same substituents, plus the -NH-CO-OR'-Cl, -Br, and -F substituents listed earlier, also may occur elsewhere in the polymer molecule provided they are separated from the olefinic unsaturation in the polymer by at least one carbon atom, and preferably by two or more carbon atoms.

The desired photo oxidizable unsaturation may be present in the composition in the form of mono-, or polyfunctional (di- or greater) unsaturated materials.

Representative examples of monounsaturated photooxidizable materials include trimethyl-ethylene, tetramethylethylene, 1,2-dimethylcyclohexane, diethyl- 1,2- dimethylcyclohexene-4,5-dicarboxylate, 2-ethylidene-norbornene, 2-methylnorbornene, 2,3-dimethyl-norbornene, cyclopentene, I-methyl-cyclopentene, 1,2dimethyl-cyclopentene, cY,P,P-trimethyl-styrene, indene, alkyl-substituted indenes, and alkyl-substituted furans.

A representative example of diunsaturated photo oxidizable materials is the reaction product of bisphenol A and 1 ,2,4-trimethyl-4-chlorocarbonylcyclohexene, I. Representative examples of polyunsaturated photo oxidizable materials include the EPDM rubbers, natural rubber, the polymers of one or more of butadiene, isoprene, 2,3-dimethyl-1,3-butadiene and 1,3-pentadiene, and the copolymers of these dienes with vinyl, vinylidene or allyl monomers, such as acrylic and methacrylic acids, their esters and amides, styrene, vinyl pyridene, vinyl ethers, sulfides, esters, ketones and halides, vinylidene halides and allyl ethers and esters.

Polyunsaturated photooxidizable materials may additionally contain certain other types of unsaturation, for example fumarate or maleate unsaturation, or the type represented by the characteristic

group.

When the photo oxidizable unsaturation is not already present in a polymer structure, it may be introduced into a base polymer. Exemplary of such base polymers are unsaturated polyesters, into which the desired unsaturation may be introduced through utilization of the Diels-Alder reaction. Also, since esterification reactions may be used to introduce 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; cellulose and cellulose esters; starch; cellulose which has been partly or completely reacted 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; polymers 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 photo oxidizable olefinic 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 bridgehead 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, 1,3butadiene, isoprene and 2,3-dimethyl-l,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 5ethylidene-2-norbornene is used to obtain the desired unsaturation. In an esterification reaction, the acid, acid halide, acid anhydride or ester reactant will contain the desired unsaturation somewhere in the molecule. Thus, depending upon the reaction involved, suitable reactants are exemplified by those which provide olefinic units such as those existing in butene-2, trimethylethylene, tetramethylethylene, 1 ,2-dimethyl cyclohexene, 2-ethylidene-norbornane, 2methyl-2-norbornene, 2,3-dimethyl-2-norbornene, cyclopentene, 1methylcyclopentene, 1,2dimethyl cyclopentene, (z, , -trimethyl styrene, indene and alkyl-substituted indenes, and alkyl-substituted furans.

Also essential to the compositions used in the process of this invention is an ethylenically unsaturated component capable of forming a high molecular weight polymer by addition polymerization or crosslinking. This component should preferably comprise at least 5% by weight of the photosensitive composition. This component may be either monomeric or polymeric, and mixtures of monomers and of polymers and of monomers with polymers may be used. The preferred monomers are those having terminal ethylenic unsaturation of the CH2=C. type.

When using a monethylenically unsaturated monomer it is desirable to have a polymeric component of a polyfunctional monomeric component also present.

Such a polymeric component is preferably an unsaturated polymer which will copolymerize with the monomer to form a crosslinked polymer. Representative of thy monoethylenically unsaturated monomers are acrylic and methyacrylic acids; their esters, for example those with C1-C20 monohydric alcohols, for example, methyl acrylate, ethylacrylate, n-butyl acrylate, methyl methacrylate and isopropyl methacrylate; their esters with other alcohols, for example, hydroxyethyl acrylate, hydroxyethyl methacrylate, dimethylaminomethyl acrylate, dimethylaminoethyl methacrylate and 2-chloroethyl acrylate; their amides, e.g., acrylamide, and methacrylamide; N-vinylpyrrolidone; acrylonitrile and methacrylonitrile; vinyl esters such as vinyl acetate, vinyl trimethylacetate, vinyl propionate and vinyl benzoate: vinyl ethers and sulfides such as methyl vinyl ether and methyl vinyl sulfide; vinyl ketones such as methyl vinyl ketone, vinyl halides and vinylidene halides such as vinyl chloride and vinylidene chloride; allyl ethers such as allyl phenyl ether and allyl iso-amyl ether; allyl esters such as allyl acetate, allyl butyrate and allyl benzoate; and vinyl aromatics such as styrene and methylstyrene.

In addition to or in place of the above monomers, which are all monoethylenically unsaturated, it is advantageous to utilize in the photosensitive composition, as all or part of the ethylenically unsaturated component, monomers which are polyethylenically unsaturated, since such monomers ordinarily provide a more tightly crosslinked system. These crosslinking monomers have their unsaturation in the form of at least two

groups, wherein R is hydrogen or a C1-C2 alkyl group. One useful monomer is l,3,5-triacryloylhexahydro-l,3,5-triazine. This compound and related compounds ssuch as the corresponding methacryloyl derivative have the structural formula

wherein R is hydrogen or a C1-C3 alkyl group.

Other suitable monomers may be defined by the structural formula

wherein R again is hydrogen or a C1-C3 alkyl group, both X's are either -NR (R is hydrogen or a C1-C3 alkyl group) or -0- and A is alkylene, substituted alkylene or alkylene oxy alkylene. Exemplary of the latter are those compounds having the formula

A preferred monomer having this formula is N,N'-oxydimethylene-bis(acrylamide).

When X in formula III above again is -NR-, but A is alkylene or substituted alkylene, this is descriptive of another preferred monomer, N,N'-methylenebis(acrylamide). This compound is one member of a group of monomers for use in the process of this invention, which monomers are represented by compounds having the formula

wherein R is hydrogen or a C1-C3 alkyl group, R' is hydrogen, a C1-C3 alkyl group or phenyl, n is 1 to 6 when R' is hydrogen and 1 when R' is a C1-C3 alkyl or phenyl group.

Representative of compounds of formula V above are N,N'-methylenebis(acrylamide), N,N'-methylene-bis(methacrylamide), N,N'-methylene bis(a-ethylacrylamide), N,N'-methylene-bis (-propyl-acrylamide), N,N'ethylene-bis(acrylamide), N,N'-ethylene-bis-(methylacrylamide), N,N'-( 1,6- hexamethylene)-bis(acrylamide), N,N'-(l 6-hexamethylene)- bis(methylacrylamide), N,N'-ethylidene-bis-(acrylamide), N,N'-ethylidenebis(methacrylamide), N,N'-methylene-bis(N-methyl acrylamide), N,N'-butylidenebis(methacrylamide) and N,N'-propylidene-bis(acrylamide). These compounds may be prepared by conventional reactions well known in the art, for example, in U.S. Patent No. 2,475,846.

Also useful monomers are those wherein X in formula III above is --OO-.

When A is alkylene or substituted alkylene, the compounds are polyacrylates of certain polyhydric alcohols. These acrylates may be illustrated by the following formulas.

When A is alkylene, this is descriptive of compounds having the formulae

wherein R is hydrogen or a C1-C3 alkyl groups, R' is hydrogen, a C1-C3 alkyl group or phenyl, m is 1 to 8 when R' is hydrogen and 1 when R' is C,--C, alkyl or phenyl, and

wherein R is hydrogen or a C1-C3 alkyl group and R" is a C1-C4 alkyl group, and n is I to 4.

Representative of compounds of formula IV are ethylene glycol diacrylate, ethylene glycol dimethacrylate, ethylene glycol di(a-ethylacrylate), ethylene glycol di(a-propylacrylate), 1,3-propylene glycol diacrylate, 1,4-butylene glycol diacrylate, 1,8-octanediol dimethacrylate, and ethylidene-bis(acrylate).

Representative of compounds of formula VII are 1,2-propylene glycol diacrylate, 1,3-butanediol dimethacrylate, and I ,2'-butanediol diacrylate.

Another group of such compounds has the formula

in which R is hydrogen or a C1C3 alkyl group, R" and R'", which may be the same or different, are each hydrogen, a C1-C3 alkyl group, or a group of the formula -CH2OH or

n is a number from 1 to 6 and the total number of carbon atoms in the group --(CR"R'")n--is no more than 11.

When X in formula Ill is 0, and A is substituted alkylene. this is descriptivc of compounds having the formulae

wherein R is hydrogen or a C1-C3 alkyl group, R"' is hydrogen or a

group and a is I to 4;

where R is hydrogen or a C1-C3 alkyl group and R"' is hydrogen or a

group, and

wherein R is hydrogen or a C1C3 alkyl group, Rte is hydrogen or a

group and R"" is a methyl or ethyl group.

Representative of compounds of formula VIII are glycerol triacrylate, 1,3glycerol dimethacrylate, erythritol diacrylate, mannitol diacrylate and mannitol trimethacrylate.

Representative of compounds of formula IX are pentaerythrilol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate and pentaerythritol tetramethacrylate.

Representative of compounds of formula X are trimethylolethane diacrylate, trimelhylolpropane triacrylate and trimethylolpropane dimethacrylate.

Closely related to the preceding acrylates are those which are derived from di-, tri-, and tetra-ethylene glycol and di-, tri-, and telra-propylene glycol. These compounds are those of formula III wherein X is -0- and A is alkylene oxyalkylene, and they may be more specifically illustrated by the formula

wherein R is hydrogen or a C1C3 alkyl group R is hydrogen or methyl and n is 2 to 4. Preferably n is 2 to 4 when R is hydrogen and 2 or 3 when R is methyl.

Representative of these compounds are diethylene glycol diacrylate. diethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, dipropylene glycol diacrylate, dipropylene glycol dimethacrylate.

tripropylene glycol diacrylate, tripropylene glycol dimethacrylate and tetrapropylene glyco Bernthsen; hemin; chlorophyll; porphyrazines; octaphenyl-porphins: benzoporphins: hypericin; 3,4-benzpyrene; acridine; rubrene; 4,4'bis(dimethylamino)benzophenone; fluorenone; anthraquinone: phenanthrenequinone; fluorene; triphenylene, phenanthrene: naphthalene: azulene; anthracene; tetracene; carbazole; benzil; benzilic acid: xanthone: anthrone; benzanthrone; coronene; di-cz-naphthyl ketone; benzylacetophenonc: chrysene: pyrene; 1 ,2-benzanthracene; acenaphthylene; a-indanone; 1,4naphthaquinone; phenyl-l-naphthyl ketone; I-acetonaphthone: 2acetonaphthone; I-naphthaldehyde; 1,2,5,6-dibenzanthracene:thioxanthone:9,10- dichloroanthracene; and benzalacetophenone.

The amount of sensitizer is not critical, but the best results are obtained when the concentration is adjusted so that 50 to 90"" or more of the incident light is absorbed at the wavelength corresponding to the absorption maximum of the particular sensitizer employed. The sensitizer may be incorporated into the photosensitive composition when the composition is being formed or it may be diffused into the film of the composition 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.

The process of the present invention makes use of light having a wavelength extending over the range from 2,000 to 3900 A, that is light in the near ultra violet region of the spectrum. It is not necessary that the light employed be exclusively within that range. All that is required is that the light have a substantial component within that range. Any lamp providing radiation in that wavelength range can be employed, for instance, a sunlamp, such as the General Electric RS-275 sunlamp used in the Example, a xenon arc or a mercury arc. A filter can if desired be employed in conjunction with the lamp to remove light having an undesired wavelength.

After the peroxides have been formed in the exposed areas of the film, they are decomposed to provide the free radicals needed for the polymerization and/or crosslinking reaction. The decomposition reaction is preferably carried out catalytically using, for example, a metal redox catalyst. The catalyst may be added to the photosensitive composition prior to film preparation. 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 oxysulfate, vanadium oxy- 1,1,1 -trifluoroacetyl acetonate, vanadium oxy-l-phenylacetylacetonate, vanadium (IV) oxide bis(2,4 pentanedionate) ferric acetylacetonate-benzoin manganese octoate, lead naphthenate and cobaltic acetylacetonate are among the preferred catalysts. Other effective catalysts include titanyl acetylacetonate, cobaltous naphthenate, cobaltous 2-ethylhexanoate, cobaltous stearate, cobaltic stearate, cobaltous acetvlacetonate, manganous stearate, manganic stearate, manganous acetylacetonate, manganic acetylacetonate, manganese naphthenate, zirconium acetylacetonate, vanadyl naphthenate, ferrous sulfate, ferrous pyrophosphate, ferrous sulfide, the ferrous complex of ethylenedinitrilotetraacetic acid, ferrous ophenanthroline, ferrous ferrocyanide, ferrous acetylacetonate and the corresponding nickel, copper, mercury and chromium compounds. Nonmetallic 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 initiated thermally.

The photooxidizable compositions may also contain up to 50% by weight of an inert particulate filler which is essentially transparent to the radiation used.

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 photosensitive 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 photooxidizable compositions 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 processing 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-butyi-catechol, hydroquinone monobenzylether. methyl hydroquinone. amyi quinone. amyloxv hqdroquinone, n-butyl phenol, phenol and hydroquinone monopropvl ether. The phenolic antioxidant may be used in an amount within the range of from 0.001 to 2'" bv weight, preferably about l"q by weight. based on the total ethvlenically unsaturated component of the photosensitive composition.

The photo oxidizable compositions of the process of this invention may be cast from solution onto a suitable support. Ordinarily, the support member of a lithographic plate is metal-surfaced or composed of entire sheets of metal. Metals such as aluminium, zinc, chromium, tin, magnesium and steel may be used.

Aluminium 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 aluminium, the surface may, if desired, be chemically or electrolytically anodized. In the case of a positive working lithographic plate it may be necessary to coat the metal support with a durable oleophilic polymer coating before applying the photo oxidizable composition. In casting the photo oxidizable composition onto the support, a solution of the components in a suitable solvent may be used, and conventional coating techniques may be employed.

Alternatively, those photo oxidizable compositions of the process of this invention which are thermoplastic may be thermoformed in plastic fabrication equipment onto a metal substrate.

When the photo oxidizable elements prepared as described above are subjected to the process of this invention, the photo sensitive composition becomes crosslinked in the exposed areas, whereas the composition in the unexposed areas remains soluble. Subsequent removal of the soluble material as by washing of the plate, leaves an image of the negative or positive used in the process. The solvent used in washing the plate will vary according to the solubility of the photo oxidizable composition. Removal of the soluble material from the unexposed areas may frequency 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 invention 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 photosensitive compositions 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.

WHAT WE CLAIM IS:- 1. A process for making a photographic image which comprises imagewise exposure of a photosensitive composition in film form to light having a wavelength extending over the range from 2,000 to 3900 Angstroms in the presence of oxygen.

thereby forming peroxides at light-struck areas of said element, and decomposing said peroxides to form a cross-linked polymer at said light struck areas wherein the photo oxidizable composition comprises: 1) an ethylenically unsaturated component capable of forming a cross-linked polymer: 2) an oxidizable component containing olefinic unsaturation with no more than one hydrogen atom on each of the double bond carbon atoms, and having at least one allylic hydrogen atom on at least one of the carbon atoms adjacent to the double bond carbon atoms and not being a bridgehead carbon atom; and 3) a photo oxygenation sensitizer which is capable of bringing about the generation of singlet oxygen when irradiated by light in the region of the spectrum extending over said range from 2000 to 3900 Angstroms.

2. A process as claimed in Claim I wherein the peroxides are decomposed in the absence of oxygen.

3. A process as claimed in Claim I or 2, wherein component (1) is an ethylenically unsaturated monomer.

4. A process as claimed in Claim I or 2 wherein component (1) is an ethylenically unsaturated polymer.

5. A process as claimed in Claim 1 or 2 wherein component (1) is a mixture of an ethylenically unsaturated monomer and an ethylenically unsaturated polymer.

6. A process as claimed in Claim 3 or 5 wherein the ethylenically unsaturated

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (36)

**WARNING** start of CLMS field may overlap end of DESC **. hydroquinone monomethylether, pyrogallol. quinone. t-butyi-catechol, hydroquinone monobenzylether. methyl hydroquinone. amyi quinone. amyloxv hqdroquinone, n-butyl phenol, phenol and hydroquinone monopropvl ether. The phenolic antioxidant may be used in an amount within the range of from 0.001 to 2'" bv weight, preferably about l"q by weight. based on the total ethvlenically unsaturated component of the photosensitive composition. The photo oxidizable compositions of the process of this invention may be cast from solution onto a suitable support. Ordinarily, the support member of a lithographic plate is metal-surfaced or composed of entire sheets of metal. Metals such as aluminium, zinc, chromium, tin, magnesium and steel may be used. Aluminium 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 aluminium, the surface may, if desired, be chemically or electrolytically anodized. In the case of a positive working lithographic plate it may be necessary to coat the metal support with a durable oleophilic polymer coating before applying the photo oxidizable composition. In casting the photo oxidizable composition onto the support, a solution of the components in a suitable solvent may be used, and conventional coating techniques may be employed. Alternatively, those photo oxidizable compositions of the process of this invention which are thermoplastic may be thermoformed in plastic fabrication equipment onto a metal substrate. When the photo oxidizable elements prepared as described above are subjected to the process of this invention, the photo sensitive composition becomes crosslinked in the exposed areas, whereas the composition in the unexposed areas remains soluble. Subsequent removal of the soluble material as by washing of the plate, leaves an image of the negative or positive used in the process. The solvent used in washing the plate will vary according to the solubility of the photo oxidizable composition. Removal of the soluble material from the unexposed areas may frequency 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 invention 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 photosensitive compositions 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. WHAT WE CLAIM IS:-

1. A process for making a photographic image which comprises imagewise exposure of a photosensitive composition in film form to light having a wavelength extending over the range from 2,000 to 3900 Angstroms in the presence of oxygen.

thereby forming peroxides at light-struck areas of said element, and decomposing said peroxides to form a cross-linked polymer at said light struck areas wherein the photo oxidizable composition comprises: 1) an ethylenically unsaturated component capable of forming a cross-linked polymer: 2) an oxidizable component containing olefinic unsaturation with no more than one hydrogen atom on each of the double bond carbon atoms, and having at least one allylic hydrogen atom on at least one of the carbon atoms adjacent to the double bond carbon atoms and not being a bridgehead carbon atom; and 3) a photo oxygenation sensitizer which is capable of bringing about the generation of singlet oxygen when irradiated by light in the region of the spectrum extending over said range from 2000 to 3900 Angstroms.

2. A process as claimed in Claim I wherein the peroxides are decomposed in the absence of oxygen.

3. A process as claimed in Claim I or 2, wherein component (1) is an ethylenically unsaturated monomer.

4. A process as claimed in Claim I or 2 wherein component (1) is an ethylenically unsaturated polymer.

5. A process as claimed in Claim 1 or 2 wherein component (1) is a mixture of an ethylenically unsaturated monomer and an ethylenically unsaturated polymer.

6. A process as claimed in Claim 3 or 5 wherein the ethylenically unsaturated

monomer is acrylic or methacrylic acid; an ester, amide or nitrile thereof; N-vinyl pyrrolidone; a vinyl ester, ether, sulfide or ketone; a vinyl or vinylidene halide; an allyl ether or ester; or a vinyl aromatic compound.

7. A process as claimed in Claim 3 or 5 wherein the ethylenically unsaturated monomer is a cross-linking monomer with at least two groups of the formula:

in which R is hydrogen or a C13 alkyl group.

8. A process as claimed in Claim 7 wherein the cross-linking monomer is a compound of the formula:

in which R is hydrogen or a C13 alkyl group.

9. A process as claimed in Claim 7 wherein the crosslinking monomer is a compound of the formula:

in which R is hydrogen or a C;~3 alkyl group, both groups X are either--NH or -0-, and A is alkylene, substituted alkylene or alkylene-oxyalkylene.

10. A process as claimed in Claim 9 wherein the crosslinking monomer is a compound of the formula:

in which R is hydrogen or a C13 alkyl group, R' is hydrogen, a C13 alkyl group, or phenyl, n is a number from 1 to 6, when R' is hydrogen, and 1 when R' is a C1-C3 alkyl or phenyl group.

11. A process as claimed in Claim 9 wherein the cross-linking monomer is a compound of the formula:

in which R is hydrogen or a C13 alkyl group, R" and R'D, which may be the same or different, are each hydrogen, a C13 alkyl group, or a group of the formula:

n is a number from I to 6 and the total number of carbon atoms in the group --CR"R'")n-- is no more than 11.

12. A process as claimed in Claim 9 wherein the cross-linking monomer is a compound of the formula:

in which R is hydrogen or a C13 alkyl group, R"" is hydrogen or methyl, and n is 2 to 4 when R"" is hydrogen and 2 or 3 when R"" is methyl.

13. A process as claimed in Claim 9 wherein the cross-linking monomer is a compound of the formula:

in which R is hydrogen or a C13 alkyl group, B is vinylene or an arylene, alkylene or substituted alkylene group, and n is 0 or 1.

14. A process as claimed in Claim 3 or 5 wherein the ethylenically unsaturated monomer is divinyl benzene, divinyl acetylene, diisopropenyl biphenyl or crotyl methacrylate.

15. A process as claimed in Claim 4 or 5 wherein the ethylenically unsaturated polymer is an unsaturated polyester of one or more diols and one or more dicarboxylic acids, at least one of the diols and dicarboxylic acids being unsaturated.

16. A process as claimed in any preceding claim wherein the oxidizable component (2) comprises a material of the formula:

in which R1, R2, R3 and R4 are each hydrogen, an alkyl group containing I to 20 carbon atoms, an aryl group or a substituted aryl group, or R1 and R2, R3 and R4, R and Rw or R2 and Ra together with the carbon atoms to which they are attached, form an alicyclic or heterocyclic group, at least one of the groups, R1, R2, R3 and R4 containing an allylic hydrogen atom not on a bridgehead carbon, and not more than one hydrogen atom being attached to each of the double bond carbon atoms.

17. A process as claimed in Claim 16 wherein the oxidizable component (2) is trimethylethylene: tetramethylethylene; I 2-dimethylcyclohexene; diethyl- 1,2- dimethyl cyclohexene-4,5-dicarboxylate; 2-ethylidene norbornene; 2-methylnorbornene; 2,3-dimethyl-norbornene; cyclopentene; I-methylcyclopentene; 1,2dimethylcyclopentene; tz,fi,-trimethylstyrene, indene, an alkyl-substituted indene; or an alkyl-substituted furan; or the reaction product of bisphenol-A and 1,2,4trimethyl-4-chlorocarbonyl-cyclohexene.

18. A process as claimed in any of Claims 1 to 15 wherein the oxidizable component (2) comprises an EPDM rubber; natural rubber; a polymer of one or more of butadiene, isoprene, 2,3-dimethyl-l,3-butadiene or 1,3-pentadiene, or a copolymer of butadiene, isoprene, 2,3-dimethyl-l,3-butadiene or 1,3-pentadiene with a vinyl, vinylidene or allyl monomer.

19. A process as claimed in any of Claims 1 to 15 wherein the oxidizable component (2) comprises a polymer modified by esterification or a Diels-Alder reaction to introduce the olefinic unsaturation with no more than one hydrogen atom on each of the double bond carbon atoms, and having at least one allylic hydrogen atom not on a bridgehead carbon.

20. A process as claimed in any preceding Claim wherein the sensitizer (3) is a fluorescein derivative, a xanthene dye, a porphyrin, a porphin, a polycyclic aromatic hydrocarbon or a phthalocyanine.

21. A process as claimed in Claim 20 wherein the sensitizer is methylene blue or zinc tetraphenylporphin.

22. A process as claimed in any of Claims I to 19 wherein the sensitizer is benzanthrone.

23. A process as claimed in any preceding Claim wherein the photosensitive composition also contains a saturated polymer.

24. A process as claimed in any preceding Claim wherein the peroxides are decomposed by the action of heat.

25. A process as claimed in any of Claims 1 to 23 wherein the peroxides are decomposed by the action of a reducing agent.

26. A process as claimed in Claim 25 wherein the reducing agent is present in the composition before exposure.

27. A process as claimed in Claim 25 wherein the reducing agent is added subsequent to exposure.

28. A process as claimed in any of Claims 25 to 27 wherein the reducing agent is a polyamine, a monoamine, sodium hyposulfite or sulphur dioxide.

29. A process as claimed in any of Claims 1 to 23 wherein the peroxides are decomposed by the action of a metal salt or compiex catalyst.

30. A process as claimed in Claim 29 wherein the metal catalyst is present in the composition before exposure.

31. A process as claimed in Claim 29 wherein the metal catalyst is added subsequent to exposure.

32. A process as claimed in Claim 29 wherein the metal catalyst is a transition metal catalyst.

33. A process as claimed in any of Claims 29 to 32 wherein the catalyst is vanadium oxyacetylacetonate, vanadium oxysulfate, vanadium (IV) oxide bis(2,4pentane-dionate), ferric acetylacetonate-benzoin, manganese octoate, lead naphthenate or cobaltic acetylacetonate.

34. A process as claimed in any preceding Claim wherein said images are developed by washing away non-crosslinked polymer.

35. A process as claimed in Claim 1 substantially as hereinbefore described with reference to the Example.

36. Photographic images when made by a process as claimed in any of the preceding claims.