PHOTOIMAGING COMPOSITIONS CONTAINING SUBSTITUTED CYCLOHEXADIENONE COMPOUNDS

Abstract: Photoimaging compositions comprising (A) a cyclohexadienone compound as defined, and (B ) addition polymerizable ethylenically unsaturated monomer, selected from the group of t-butyl-­ acrylate, N,N-diethylaminoethylacrylate, styrene and a monomeric compound having at least two terminal ethyle­ nically unsaturated groups. A polymer binder can be present in the compositions. The new imaging compositions are useful in photoimaging products such as proofing papers, printout papers, overlay films and photopolymerizable elements useful for printing and photoresist purposes. The compositions have improved thermal stability.

Description: This invention relates to new photoimaging compositions. More particularly, this invention relates to photoimaging compositions containing substituted cyclohexadienone compounds. Photoimaging compositions utilizing either a leuco dye and/or an addition polymerizable ethylenically unsaturated compound in conjunction with hexaarylbiimidazole compounds are known. Such compositions have been particularly useful in the preparation of proofing papers or in photopolymerizable elements depending on their formulation. New photopolymerizable elements are subject of a different European patent application (publication number 0 135 059). Two hexaarylbiimidazole compounds commonly used in these formulations are 2,2'-bis(o-­ chlorophenyl)-4,4',5,5'-tetrakis-(m-methoxyphenyl)­ biimidazole and 2,2'-bis(o-chlorophenyl)-4,4',5,5'-­ tetraphenylbiimidazole. These compositions, while advantageous in many respects, do not possess the degree of thermal stability that is desired to prevent color formation of films or elements during extended storage periods. D.I. Schuster et al, Mol. Photochem. (4), pages 415-432 (1969) determined the effective triplet energies of cy­ clohexadienones in solution as sensitizers for olefin isomerization and dimerization. Especially the sensiti­ zed dimerization of isoprene was described. There is, however, no indication that these cyclohexadienones might be useful for photopolymerizable compositions com­ prising an addition polymerizable ethylenically unsatu­ rated monomeric compound. It is desirable that photoimaging compositions be prepared that possess the advantages of previous photoimaging compositions and, in addition, exhibit improved thermal stability and flexibility. Disclosure of the Invention In accordance with this invention there is provided a photoimaging composition comprising (B ) an addition polymerizable ethylenically unsaturated monomeric compound selected from the group of t-butyl­ acrylate, N,N-diethylaminoethylacrylate, styrene and a monomeric compound having at least two terminal ethyleni­ cally unsaturated groups, characterized in that said composition contains (A) a cyclohexadienone compound of the formula: wherein each of A, B, D and E can be hydrogen, an alkyl group of 1 to 9 carbon atoms, bromo, chloro, an aryl group of 6 to 10 carbon atoms, an aralkyl group wherein the aryl moiety is of 6 to 10 carbon atoms and the alkyl moiety is of 1 to 5 carbon atoms, an alkaryl group wherein the aryl moiety is of 6 to 10 carbon atoms and the alkyl moiety is of 1 to 5 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, and A and B and D and E when taken together may form a benzene ring; F is CCl₃ or CHCl₂; and G can be an alkyl group of 1 to 18 carbon atoms and an aryl group of 6 to 10 carbon atoms. The photoimaging compositions of the invention comprise the specific cyclohexadienone compounds and a compound having ethylenic unsaturation. The ethylenically unsaturated compound is present in the composition as noted below. A particularly useful additive is Michler's ketone or a derivative thereof which improves printout image enhancement. It is also desirable to add to the photoimaging composition at least one film-forming polymeric binder. Suitable inert solvents are generally present in preparing the formulations. Plasticizers are commonly present in addition to the ethylenically unsaturated monomeric compounds. Additional components which can be present include: anti-blocking agents, dyes, and white and colored pigments which do not act as sensitizers, etc. In the photopolymerizable compositions, in addition to the cyclohexadienone compound, addition polymerizable ethylenically unsaturated compound and film-forming polymeric binder, there can be present inert solvents, plasticizers, inhibitors, anti-blocking agents, ultraviolet absorbers, oxygen scavengers, chain transfer agents, energy-transfer dyes, etc. It has been found useful, e.g., for purposes of image enhancement, to have optionally present in the photoimaging compositions a para-aminophenyl ketone of the formula: wherein R and R₁ can be hydrogen or an alkyl group of 1 to 4 carbon atoms, and R₂ can be an alkyl group of 1 to 4 carbon atoms, monocarbocyclic aryl, preferably phenyl; or an RR₁N phenyl group. The p-aminophenyl ketone may be present in an amount of about 10⁻³ to 10.0 and preferably 10⁻³ to 2.0 moles per mole of cyclohexadienone compound. Preferred compounds include: Michler's ketone (4,4'-bis(dimethylamino)-benzophenone) and ethyl Michler's ketone (4,4'-bis(diethylamino)-­ benzophenone). Other useful p-aminophenyl ketones are disclosed in Fishman U.S. Patent 3,552,973. The arylthioketones are disclosed in Fan U.S. Patent 3,558,322. After imagewise exposure an image pattern can be observed in the photopolymerizable composition (in layer form) by toning with a colored toner or pigment or by solvent washout. The cyclohexadienone compounds useful in the photoimaging compositions are defined above. The following list names many of these compounds. Useful -4-trichloromethyl-2,5 cyclohexadienone compounds are: 4-methyl-4-trichloromethyl-2,5-cyclohexadienone 2,6-dimethyl-4-trichloromethyl-2,5-cyclohexadienone 3,4-dimethyl-4-trichloromethyl-2,5-cyclohexadienone 4-nonyl-4-trichloromethyl-2,5-cyclohexadienone 4-trichloromethyl-3,4,5-trimethyl-2,5-cyclohexadienone 2,6-di-(t-butyl)-4-trichloromethyl-2,5-cyclohexadienone 2,6-di (t-butyl)-4-methyl-4-trichloromethyl-2,5-cyclo­ hexadienone 2,6-dichloro-4-methyl-4-trichloromethyl-2,5-cyclo­ hexadienone 2,6-dibromo-4-methyl-4-trichloromethyl-2,5-cyclo­ hexadienone 2,4-dimethyl-4-trichloromethyl-2,5-cyclohexadienone 4-trichloromethyl-2,4,5-trimethyl-2,5-cyclohexadienone 4-phenyl-4-trichloromethyl-2,5-cyclohexadienone 2-methoxy-4-methyl-4-trichloromethyl-2,5-cyclo­ hexadienone 2,6-dimethoxy-4-methyl-4-trichloromethyl-2,5-cyclo­ hexadienone 2,3-benzo-4-methyl-4-trichloromethyl-2,5-cyclo­ hexadienone 2,4,6-tri (t-butyl)-4-trichloromethyl-2,5-cyclo­ hexadienone 4-trichloromethyl-2,4,6-trimethyl-2,5-cyclohexadienone 4-t-butyl-4-trichloromethyl-2,5-cyclohexadienone 2,3,4,5,6-pentamethyl-4-trichloromethyl-2,5-cyclo­ hexadienone 2,4,6-tri (t-pentyl)-4-trichloromethyl-2,5-­ cyclohexadienone 4-benzyl-4-trichloromethyl-2,5-cyclohexadienone 2-t-butyl-4-trichloromethyl-2,5-cyclohexadienone 2-i-propyl-4-methyl-4-trichloromethyl-2,5-cyclo­ hexadienone 2-t-butyl-4-methyl-4-trichloromethyl-2,5-cyclo­ hexadienone 2-ethyl-4,5-dimethyl-4-trichloromethyl-2,5-cyclo­ hexadienone 2,3-benzo-4,5-dimethyl-4-trichloromethyl-2,5-cyclo­ hexadienone Additional useful compounds are similar -4-dichloromethyl-2,5-cyclohexadienones. Hexadienone compounds, in some cases, may be purchased commercially or, where not commercially available, may be made by procedures disclosed in the literature: M. S. Newman and L. L. Wood, Jr., J. Amer. Chem. Soc. , 81 6450 (1959); V. P. Vitullo and E. A. Logue, ibid 98 5906 (1976); M. S. Newman and A. G. Pinkus, J. Org. Chem. 19 978 (1954). Furtheron, Schuster and Lau, Mol. Photochem., 1969, 1 (4), 415-32) describe preparation and photolysis of solutions of 4-methyl-4-trichloromethyl-2,5-cyclo-hexa­ dienone (TMCH) and certain dienes or substituted olefins. The authors' objective was to detect energy transfer from TMCH to the olefins by observing isomerization or dimerization of the olefins, or in some cases observe suppression by the diene of the isomerization of TMCH itself. Optionally, other additives can be present in the photoimaging composition. Polymeric binders can be added to thicken the formulations or adhere them to substrates. The binders can also serve as a matrix for the color-forming composition. Light-transparent and film-forming polymers are preferred. Examples are ethyl cellulose, polyvinyl alcohol, polyvinyl chloride, polystyrene, polyvinyl acetate, poly-(methyl, propyl or butyl methacrylate), cellulose acetate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, chlorinated rubber, copolymers of the above vinyl monomers, etc. The binder composition can also contain inert infusible fillers such as titanium dioxide, organophilic colloidal silica, bentonite, powdered glass, micro-sized alumina and mica in minor, noninterfering amounts. Formulations containing micron-sized silicas, as, for example, the Syloid R silica gels, sold by W. R. Grace & Co., are particularly useful for providing a "tooth" for pencil or ink receptivity and eliminating blocking tendencies. With some polymers, it is desirable to add a plasticizer, e.g., solid or liquid, to give flexibility to the film or coating. Suitable plasticizers are disclosed in U.S. Patent 3,658,543, column 10, lines 20 to 73. A preferred liquid plasticizer is Nonylphenoxypoly(ethyleneoxy)-ethanol. A preferred solid plasticizer is N-ethyl-p-toluenesulfonamide. The plasticizers can be used in concentration ranging from 1:20 to 5:3, preferably 1:5 to 1:2, based on the weight of polymeric binder used. In preparing the formulation generally inert solvents are employed which are volatile at ordinary pressures. Examples include alcohols, e.g., methanol, ethanol, 1-propanol, 2-propanol, butanol, and ethylene glycol; ether alcohols, e.g., 2-ethoxy ethanol, 2-butoxy ethanol and diethylene glycol monomethyl ether; esters, e.g., methyl acetate and ethyl acetate; aromatics, e.g., benzene, o-dichlorobenzene and toluene; ketones, e.g., acetone, methyl ethyl ketone and 3-pentanone; aliphatic halocarbons, e.g., methylene chloride, chloroform, 1,1,2-trichloroethane, 1,1,2,2-tetrachloroethane and 1,1,2-trichloroethylene; miscellaneous solvents, e.g., dimethylsulfoxide, pyridine, tetrahydrofuran, dioxane, dicyanocyclobutane and 1-methyl-2-oxo-hexamethyleneimine; and mixtures of these solvents in various proportions as may be required to attain solutions. It is often beneficial to leave a small residue of solvent in the dried composition so that the desired degree of imaging can be obtained upon subsequent irradiation. Useful optional antiblocking agents present to prevent the coatings from adhering to one another include: and other known agents. In the photopolymerizable embodiment of this invention, in addition to the cyclohexadienone compounds described above, at least one addition polymerizable ethylenically unsaturated compound having at least one polymerizable ethylenic group is present. Such compounds are capable of forming a high polymer by free-radical initiated, chain-propagating, addition polymerization. Generally, polymeric components (binders) as well as inhibitors are also present in the photopolymerizable composition. Preferably, the monomeric compound has at least two terminal ethylenically unsaturated groups, e.g., 2 to 4 groups. The monomeric compounds are nongaseous, i.e., at 20°C and atmospheric pressure, have a normal boiling point about 100°C and a plasticizing action on any thermoplastic polymeric binder that may be present. Ethylenically unsaturated monomeric compounds useful in this invention include monomeric compounds or polymers wherein the ethylenic unsaturation is present as an extralinear substituent attached to the polymer backbone. Suitable monomers which can be used as the sole monomer or in combination with others include the following: t-butyl acrylate, 1,5-pentanediol diacrylate, N,N-diethylaminoethyl acrylate, ethylene glycol diacrylate, 1,4-butanediol diacrylate, diethylene glycol diacrylate, hexamethylene glycol diacrylate, 1,3-propanediol diacrylate, decamethylene glycol diacrylate, decamethylene glycol dimethacrylate, 1,4-cyclohexanediol diacrylate, 2,2-dimethylolpropane diacrylate, glycerol diacrylate, tripropylene glycol diacrylate, glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, polyoxyethylated trimethylolpropane triacrylate and trimethacrylate and similar compounds as disclosed in U.S. Patent 3,380,831 incorporated by reference, 2,2-di(p-hydroxyphenyl)-propane diacrylate, pentaerythritol tetraacrylate, 2,2-di-(p-hydroxyphenyl)-propane dimethacrylate, triethylene glycol diacrylate, polyoxyethyl-2,2-di-(p-hydroxyphenyl)-propane dimethacrylate, di-(3-methacryloxy-2-hydroxypropyl)-­ ether of bisphenol-A, di-(2-methacryloxyethyl) ether of bisphenol-A, di-(2-acryloxyethyl) ether of bisphenol-A, di-(3-methacryloxy-2-hydroxypropyl) ether of tetrachloro-bisphenol-A, di-(2-methacryloxyethyl) ether of tetrachloro-bisphenol-A, di-(3-methacryloxy-2-hydroxypropyl) ether of tetrabromo-bisphenol-A, di(2-methacryloxyethyl) ether of tetrabromo-bisphenol-A, di-(3-methacryloxy-2-hydroxypropyl) ether of 1,4-butanediol, di-(3-methacryloxy-2-hydroxypropyl) ether of diphenolic acid, triethylene glycol dimethacrylate, polyoxypropyltrimethylol propane triacrylate (462), ethylene glycol dimethacrylate, butylene glycol dimethacrylate, 1,3-propanediol dimethacrylate, 1,2,4-butanetriol trimethacrylate, 2,2,4-trimethyl-1,3-pentanediol dimethacrylate, pentaerythritol trimethacrylate, 1-phenyl ethylene-1,2-dimethacrylate, pentaerythritol tetramethacrylate, trimethylol propane trimethacrylate, 1,5-pentanediol dimethacrylate, diallyl fumarate, styrene, 1,4-benzenediol dimethacrylate, 1,4-diisopropenyl benzene, and 1,3,5-triisopropenyl benzene. In addition to the ethylenically unsaturated monomers mentioned above, the composition can also contain at least one of the following free radical-initiated, chain-propagating, addition-polymerizable, ethylenically unsaturated compounds having a molecular weight of at least 300. Preferred monomers of this type are an alkylene or a polyalkylene glycol diacrylate prepared from an alkylene glycol of 2 to 15 carbons or a polyalkylene ether glycol of 1 to 10 ether linkages, and those disclosed in U.S. Patent 2,927,022 e.g., those having a plurality of addition polymerizable ethylenic linkages, particularly when present as terminal linkages. Especially preferred are those wherein at least one and preferably most of such linkages are conjugated with a double-bonded carbon, including carbon double-bonded to carbon and to such heteroatoms as nitrogen, oxygen and sulfur. Outstanding are such materials wherein the ethylenically unsaturated groups, especially the vinylidene groups, are conjugated with ester or amide structures. Useful polymers having ethylenically unsaturated groups attached thereto are: the polymerizable, ethylenically unsaturated polymers of U.S. Patent 3,043,805 and U.S. Patent 2,929,710, e.g., polyvinyl acetate/acrylate, cellulose acetate/acrylate, cellulose acetate/methacrylate, N-acrylyloxymethyl polyamide, etc.; polyoxyethylated trimethylol propane triacrylate, polytetramethylene glycol diacrylate, etc., disclosed in U.S. Patent 3,418,295. Suitable thermal polymerization inhibitors than can be used in photopolymerizable compositions include p-methoxyphenol, hydroquinone, and alkyl- and aryl-substituted hydroquinones and quinones, tert-butyl catechol, pyrogallol, copper resinate, naphthylamines, beta-naphthol, cuprous chloride, 2,6-di-tert-butyl-p-cresol, phenothiazine, pyridine, nitrobenzene and dinitrobenzene. Other useful inhibitors, include p-toluquinone and chloranil, and thiazine dyes, e.g., Thionine Blue G (C.I. Basic Blue 25), and Toluidine Blue O (C.I. Basic Blue 17). Also useful as thermal polymerization inhibitors are the nitroso compositions disclosed in U.S. Patent 4,168,982. In certain embodiments of the invention containing certain dye photoinitiators, however, no thermal inhibitor is required since these initiators have a dual function and in the dark serve as thermal inhibitors. Suitable film-forming polymeric organic binders which can be present in the photopolymerizable photoimaging composition as the sole binder or in combination with others include: polyacrylate and alpha-alkyl polyacrylate esters, e.g., polymethyl methacrylate and polyethyl methacrylate; polyvinyl esters, e.g., polyvinyl acetate, polyvinyl acetate/acrylate, polyvinyl acetate/methacrylate and hydrolyzed polyvinyl acetate; ethylene/vinyl acetate copolymers; polystyrene polymers and copolymers, e.g., with maleic anhydride and esters; vinylidene chloride copolymers, e.g., vinylidene chloride/acrylonitrile; vinylidene chloride/methacrylate and vinylidene chloride/vinyl acetate copolymers; polyvinyl chloride and copolymers, e.g., polyvinyl chloride/acetate; saturated and unsaturated polyurethanes; synthetic rubbers, e.g., butadiene/acrylonitrile, acrylonitrile/butadiene/styrene, methacrylate/acrylonitrile/butadiene/styrene copolymers, 2-chlorobutadiene-1,3 polymers, chlorinated rubber, and styrene/butadiene/styrene, styrene/isoprene/styrene block copolymers; high molecular weight polyethylene oxides of polyglycols having number average molecular weights from about 4,000 to 1,000,000; epoxides, e.g., epoxides containing acrylate or methacrylate groups; copolyesters, e.g., those prepared from the reaction product of a polymethylene glycol of the formula HO(CH₂) n OH, where n is the whole number 2 to 10 inclusive, and (1) hexahydroterephthalic, sebacic and terephthalic acids, (2) terephthalic, isophthalic and sebacic acids, (3) terephthalic and sebacic acids, (4) terephthalic and isophthalic acids, and (5) mixtures of copolyesters prepared from said glycols and (i) terephthalic, isophthalic and sebacic acids and (ii) terephthalic, isophthalic, sebacic and adipic acids; nylons or polyamides, e.g., N-methoxymethyl polyhexamethylene adipamide; cellulose esters, e.g., cellulose acetate, cellulose acetate succinate and cellulose acetate butyrate; cellulose ethers, e.g., methyl cellulose, ethyl cellulose and benzyl cellulose; polycarbonates; polyvinyl acetal, e.g., polyvinyl butyral, polyvinyl formal; polyformaldehydes. The binder can contain sufficient acidic or other groups to render the composition processible in aqueous developer. Useful aqueous-processible binders include those disclosed in U.S. Patent 3,458,311 and in U.K. Patent 1,507,704. Useful amphoteric polymers include interpolymers derived from N-alkylacrylamides or methacrylamides, acidic film-forming comonomer and an alkyl or hydroxyalkyl acrylate such as those disclosed in U.S. Patent 3,927,199. Useful solvents, plasticizers, e.g., 10 to 50 percent by weight based on the weight of monomer, inhibitors and antiblocking agents, have been described previously above. Examples of suitable ultraviolet radiation absorbing materials are disclosed in U.S. Patent 3,854,950, columns 3 and 4, 2,2'-dihydroxy-4-­ methoxybenzophenone is a preferred material. Oxygen scavengers, e.g., 2-allyl thiourea, stannous chloride, N-phenylglycine, etc. can be present. This type compound appears to eliminate or reduce the induction period usually found in a photopolymerizable reaction, possibly by consumption of oxygen in the layer prior to exposure. In the photoimaging compositions the cyclohexadienone compound is present in an amount of about 0.01 to 90 percent by weight of solids Preferably a polymeric binder is present in the photoimaging compositions, for example, in an amount up to 99.9% by weight based on the total weight of cyclohexadienone compound and polymeric binder. Generally the cyclohexadienone compound comprises 0.01-10.0% by weight of the photoimaging composition, and binder is present in amounts of 0.5-200 parts by weight per parts of cyclohexadienone compound. In the photopolymerizable composition embodiment of this invention the cyclohexadienone compound and Michler's ketone type compounds, when used, are present in the quantity ranges set forth above. The monomeric compound and polymeric binder are present in the photoimaging composition in from 1 to 90 and 1 to 90 parts by weight, respectively. 0.001 to 2.0 parts by weight per 100 parts by weight of monomer and binder of a thermal polymerization inhibitor is preferably present. For imaging uses, the compositions of this invention may be coated upon or impregnated in substrates following known techniques. Substrates include materials commonly used in the graphic arts and in decorative applications such as paper ranging from tissue paper to heavy cardboard, films of plastics and polymeric materials such as regenerated cellulose, cellulose acetate, cellulose nitrate, polyethylene terephthalate, vinyl polymers and copolymers, polyethylene, polyvinyl-acetate, polymethyl methacrylate, polyvinylchloride; textile fabrics; glass, wood and metals. The composition, usually as a solution in a carrier solvent described above, may be sprayed, brushed, applied by a roller or an immersion coater, flowed over the surface, picked up by immersion or spread by other means, and the solvent evaporated. Any convenient source providing radiation of wavelengths in the range of 200 nm to 420 nm can be used to activate the photoimaging composition for image formation and photopolymerization initiation. The radiation may be natural or artificial, monochromatic or polychromatic, incoherent or coherent, and should be sufficiently intense to activate a substantial proportion of the photoinitiator. Conventional light sources include fluorescent lamps, mercury, metal additive and arc lamps. Coherent light sources are the pulsed nitrogen-, xenon, argon ion- and ionized neon-lasers whose emissions fall within or overlap the ultraviolet or visible absorption bands of the photoinitiator. Ultraviolet and near-visible radiation-emitting cathode ray tubes widely useful in printout systems for writing on photosensitive materials are also useful with the subject compositions. Images may be formed by writing with a beam of the activating light or by exposing to such light a selected area behind a negative, stencil, or other relatively opaque pattern. The negative may be silver on cellulose acetate or polyester film or one in which its opacity results from aggregations of areas having different refractive indices. Image formation may also be effected in conventional diazo printing apparatus, graphic arts exposure or electronic flash equipment and by projection as described in U.S. Patent 3,661,461. The light exposure time may vary from a fraction of a second to several minutes, depending upon the intensity and spectral energy distribution of the light, its distance from the composition, the nature and amount of the composition available, and the intensity of color in the image desired. The photoimaging compositions containing the cyclohexadienone compounds described herein are useful in various photoimaging formulations which are particularly advantageous in having excellent thermal stability. The formulations containing cyclohexadienone compounds as defined are used in dual response photoimaging products, where controlled sequential exposure with ultraviolet and visible light may yield negative or positive images, e.g., Dylux® proofing papers, printout papers, e.g., for the Du Pont "aca" automatic clinical analyzer, overlay films, etc.; and in photopolymerizable layers and elements useful for printing purposes as well as a variety of copying, e.g., office copying, recording, decorative, and photoresist applications. Examples The following procedures and examples illustrate the invention wherein the parts and percentages are by weight. Synthesis of Cyclohexadienone Compounds Two compounds, 4-methyl-4-trichloromethyl-­ 2,5-cyclohexadienone (TMCH), and 4-dichloro­ methyl-4-methyl-2,5-cyclohexadienone (DMCH), can be purchased from Frinton Laboratories, Vineland, New Jersey. TMCH and its various substituted derivatives are prepared by the reaction of the appropriately substituted phenol with carbon tetrachloride and aluminum chloride according to the procedures of M. S. Newman and L. L. Wood, Jr. described in J. Amer. Chem. Soc. , 81 6450 (1959). Those with ordinary skill in the art of organic synthesis may wish to make suitable modifications in the methods used to purify the products, eg., the use of crystallization or chromatographic procedures in place of the steam distillation employed in the literature cited above. The compounds 2,5-dichloro- and 2,5-dibromo-2,5-cyclohexadienone are prepared in similar fashion (M. S. Newman and A. G. Pinkus, J. Org. Chem. , 19 , 978 (1954) or, in higher yield, by addition of chlorine or bromine to the parent compound TMCH followed by dehydrohalogenation according to K. V. Auwers and W. Julicher, Ber , 55 , 2167 (1922). DMCH and its substituted derivatives are prepared by the reaction of the appropriate substituted phenol with chloroform and aqueous sodium hydroxide according to procedures described in the literature: V. P. Vitullo and E. A. Logue, J. Amer. Chem. Soc. , 98 , 5960 (1976); M. S. Newman and W. X. Bajzer, J. Org. Chem. , 35 , 270 (1970); K. V. Auwers and G. Keil, Ber ., 35 , 4207 (1902); R. C. Fuson and T. G. Miller, J. Org. Chem. , 17 , 316 (1952). Example 1 This example illustrates initiation of photopolymerization by cyclohexadienone compounds of this invention. Photopolymer compositions are prepared containing poly(methylmethacrylate) 10g of a 10 wt. % solution in acetone), triethyleneglycol diacrylate (1.3g), Michler's ketone (0.010g) and the cyclohexadienone compounds (0.59 mmole) listed in Table I. These compositions are coated with a 0.0025 inch (0.0064 cm) doctor knife on a support of 0.001 inch (0.0025 cm) poly(ethyleneterephthalate), are dried in air at ambient temperature, and are covered with film sheets the same as the support. The elements are exposed through the cover sheet and a 30-step ³√2 neutral density transmission gray scale by means of a 2kw xenon lamp in a nuArc® "Flip Top" platemaker. The cover sheets are removed from the exposed element, and the photopolymer layers are each dusted with a Cromalin® 4/C black toner. Cromalin® is a trademark of E. I. du Pont de Nemours and Company. The polymerized areas are nontacky and resist toning. In Table I photopolymerization speed is indicated by the number of steps ("clear steps") which are sufficiently polymerized to remain untoned. It can be seen that ring-substitution of the cyclohexadienone by alkyl groups is permissible while still giving good photopolymerization speed. Example 2 This example illustrates photopolymerization of a photoresist composition initiated by cyclohexadienone compounds. A coating composition stock is prepared by roll-milling the following ingredients together overnight: To 40g-aliquots of the stock are added 80 mg (0.30 mmole) Michler's ketone and the amounts of initiators, 4-methyl-4-trichloromethyl-2,5-­ cyclohexadienone (TMCH) or 4-chlorobenzophenone (CBP) indicated in Table II. The final compositions are coated on 0.001 inch (0.0025 cm) poly(ethylene­ terephthalate) support with a 0.016 inch (0.041 cm) doctor knife and air-dried at ambient temperature to a dry thickness of about 0.004 inch (0.010 cm). The element is laminated at room temperature (roller pressure) to a copper-plated phenolic circuit-board stock. The laminates are heated 2 minutes at 120°C in an oven and again passed through the roller laminator. The laminates are cooled at room temperature for one-half an hour then exposed through the polyester support and through a 20-step ³√2 neutral density transmission gray scale for 5 minutes to a 2kw xenon light source in a nuArc® "Flip Top" Platemaker. The polyester support is peeled off the exposed laminate and unpolymerized resist is washed off the copper surface for 2 minutes with 1,1,1-trichloroethane in a Riston® 1A Processor manufactured by E. I. du Pont de Nemours and Company, Wilmington, DE. The number of polymerized steps remaining on the board is recorded. Table II shows that the photopolymerization speed (the number of polymerized steps) of the resists containing TMCH is equal to or higher than the speed of the resists containing CBP. Example 3 This example illustrates the results achieved using various sensitizers in combination with cyclohexadienone compounds of the invention. Photopolymer compositions are made containing triethyleneglycol diacrylate (1.3g), a 10% by weight solution of poly(methymethacrylate) in acetone (10g), 4-methyl-4-trichloromethyl-2,5-­ cyclohexadienone (101 mg; 0.45 mmole) and the appropriate sensitizer (0.04 mmole) set forth in Table III below. The compositions are coated, covered, exposed, toned and evaluated as described in Example 4. The results in Table III show that, of the compounds tested, Michler's ketone gives the greatest number of polymerized steps for the shortest exposure time.

Claims: 1. A photoimaging composition comprising (B ) an addition polymerizable ethylenically unsaturated monomeric compound selected from the group of t-butyl-­ acrylate, N,N-diethylaminoethylacrylate, styrene and a monomeric compound having at least two terminal ethyle­ nically unsaturated groups, characterized in that said composition contains (A) a cyclohexadienone compound of the formula: wherein each of A, B, D and E can be hydrogen, an alkyl group of 1 to 9 carbon atoms, bromo, chloro, an aryl group of 6 to 10 carbon atoms, an aralkyl group wherein the aryl moiety is of 6 to 10 carbon atoms and the alkyl moiety is of 1 to 5 carbon atoms, an alkaryl group wherein the aryl moiety is of 6 to 10 carbon atoms and the alkyl moiety is of 1 to 5 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, and A and B and D and E when taken together may form a benzene ring; F is CCl₃ or CHCl₂; and G can be an alkyl group of 1 to 18 carbon atoms and an aryl group of 6 to 10 carbon atoms. 2. A photopolymerizable composition as claimed in Claim 1 characterized in that a sensitizer is present. 3. A photopolymerizable composition according to Claim 2 characterized in that in the photoimaging composi­ tions a para-aminophenyl ketone of the formula: is present wherein R and R₁ can be hydrogen or an alkyl group of 1 to 4 carbon atoms, and R₂ can be an alkyl group of 1 to 4 carbon atoms, monocarbocyclic aryl, preferably phenyl; or a RR₁N phenyl group. 4. A photopolymerizable composition according to Claim 2 characterized in that Michler's ketone or a deri­ vative thereof is present. 5. A photopolymerizable composition according to Claim 4 characterized in that 4,4'-bis(diethylamino)benzo­ phenone (ethyl Michler's ketone) is present. 6. A photopolymerizable composition according to anyone of the Claims 1 to 4 characterized in that a film-­ forming polymeric binder is present. 7. A photopolymerizable composition according to anyone of the Claims 1 to 6 characterized in that the cyclo­ hexadienone compound is 4-methyl-4-trichloromethyl-2,5-­ cyclohexadienone. 8. A photopolymerizable composition according to anyone of the Claims 1 to 7 characterized in that the cyclohexadienone compound is 4-dichloromethyl-4-methyl-­ 2,5-cyclohexadienone.

Inventors: SYSAK, PETER KEVIN
Applicants: E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1982
Main classification: G03C1
IPC codes: G03C1, G03F7