Photopolymerizable composition

Abstract: A photopolymerizable composition is described which comprises a compound polymerizable according to a free radical mechanism and a photoinitiator combination of a compound selected from acridine, quinoxaline and phena­ zine compounds and at least one organic peroxide or peroxy ester as a coinitiator. The composition has an increased photosensitivity.

Description: The present invention relates to photopolymerizable image reproduction systems. More particularly, the invention relates to a photopolymerizable composition having increased effective photosensitivity which finds use in producing photosensitive elements such as lithographic printing plates of the projection speed variety. The prior art teaches a plethora of photopolymerizable compositions. These generally comprise an ethylenically unsaturated monomer or oligomer preferably having two or more double bonds, a photoinitiator capable of causing the free radical polymerization of the unsaturated component upon exposure to actinic radiation, and usually binder resins, colorants and components to prevent premature polymerization. These compositions are widely used in photoresists and printing plates. Useful photopolymerization initiators include various substances which have been found to be practical. For example, there are benzoin compounds such as benzoin or benzoin alkyl ethers, carbonyl compounds such as benzil, benzophenone, acetophenone or Michler's ketone, as well as initiators of the acridine, quinoxaline or phenazine classes. The last mentioned types are described in DE-C 20 27 467 and 20 39 861. While such photoinitiators are certainly useful within their concepts, it is often desired to produce photographic elements which have a greater effective photospeed than these initiators can afford. EP-A 243 784 describes a photopolymerizable composition comprising an initiator combination of an acridine, quinoxaline or phenazine compound with a photosensitive organic trichloromethyl compound. The photosensitivity of this composition is increased over those comprising only one type of photoinitiator. The invention provides a photopolymerizable composition which comprises a photopolymerizable compound, preferably an acrylic or methacrylic acid ester, containing at least one and preferably two or more ethylenically unsaturated double bonds and a photopolymerization initiator composition which initiator composition comprises an acridine, quinoxaline or phenazine compound which is capable of generating a free radical upon the application of actinic radiation. The photopolymerizable composition is characterized in that it further comprises at least one organic peroxide or peroxy ester as a coinitiator. The invention also provides a photographic element which comprises a substrate and a photopolymerizable layer coated on said substrate, which photopolymerizable layer consists of the above photopolymerizable composition. The preferred photoinitiators have one of the formulae I and II wherein X, X′, Y and T are equal or different and denote N or CR'', Z and Q are different from each other and denote N or C-R′, R and R′ are equal or different aliphatic, aromatic or heterocyclic radicals, R'' is H or an organic radical, wherein two adjacent radicals R'' may form a fused benzene ring, R¹, R² and R³ are H, halogen, alkyl, alkoxy, aryl, aryloxy, amino, acylamino, and aralkenyl groups R⁴, R⁵, R⁶ and R⁷ are equal or different and denote H or fused benzene rings with not more than two fused benzene rings being present per molecule. These compounds are more fully described in DE-C 20 27 467 and 20 39 861. The organic peroxides used in the present invention include nearly all organic compounds having one or more oxygen-oxygen bonds in the molecule. Examples of them include methyl ethyl ketone peroxide, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexane peroxide, acetylacetone peroxide, 1,1-bis-(tertiary butyl peroxy)-3,3,5-trimethylcyclohexane, 1,1-bis-(tertiary butyl peroxy)cyclohexane, n-butyl-4,4-bis-(tertiary butyl peroxy)valerate, 2,2-bis-(tertiary butyl peroxy)butane, tertiary butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, di-tertiary butyl peroxide, tertiary butylcumyl peroxide, dicumyl peroxide, α,α′-bis-(tertiary butyl peroxy-isopropyl)benzene, 2,5-dimethyl-2,5-bis-(tertiary butyl peroxy)hexane, 2,5-dimethyl-2,5-bis-(tertiary butyl peroxy)hexyne-3, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, 3,5,5-trimethylhexanoyl peroxide, peroxysuccinic acid, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, m-toluyl peroxide, diisopropyl peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, dimethoxy-isopropyl peroxycarbonate, bis-(3-methyl-3-methoxybutyl)peroxydicarbonate, tertiary butyl peroxyacetate, tertiary butyl peroxyisobutyrate, tertiary butyl peroxypivalate, tertiary butyl peroxyneodecanoate, tertiary butyyl peroxyoctanoate, tertiary butyl peroxy-3,5,5-trimethylhexanoate, tertiary butyl peroxylaurate, tertiary butyl peroxybenzoate, di-tertiary butyl diperoxyisophthalate, 2,5-dimethyl-2,5-bis-(benzoylperoxy)hexane, tertiary butyl peroxymaleic acid, and tertiary butyl peroxyisopropylcarbonate. Among the above organic peroxides, benzoyl group-containing organic peroxides are preferred, for example, tertiary butyl peroxybenzoate, di-tertiary butyl diperoxyisophthalate, 2,5-dimethyl-2,5-bis-(benzoylperoxy)hexane, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide and m-toluyl peroxide. Among the benzoyl group-containing organic peroxides, peroxy ester type organic peroxides are particularly preferred, for example, tertiary butyl peroxy-benzoate, di-tertiary butyl diperoxyisophthalate and 2,5-dimethyl-2,5-bis-benzoylperoxy)hexane. Peresters non-exclusively include t-butyl perbenzoate and t-butyl-1-pernaphthoate. The ratio of acridine, quinoxaline or phenazine compound to peroxide or perester compound may range from 1:99 to 99:1 or more, preferably from about 1:25 to 65:1 and most preferably from about 2:1 to 1:2. The photopolymerizable composition of this invention generally comprises a photopolymerizable material having at least two double bonds and the foregoing photoinitiator composition. The photopolymerizable composition additionally has a binder resin in the preferred embodiment. The photopolymerizable material comprises an addition polymerizable, non-gaseous (boiling temperature above 100 °C at normal atmospheric pressure), ethylenically-unsaturated compound containing at least two terminal ethylenic groups, and being capable of forming a high molecular weight polymer by free-radical initiated, chain propagating addition polymerization. Suitable polymerizable materials non-exclusively include acrylic or methacrylic acid esters, e.g. polybutane diol diacrylate, tetraethylene glycol dimethacrylate, ethylene glycol dimethacrylate, trimethylol propane trimethacrylate, trimethylol propane triacrylate, polyethylene glycol (200) diacrylate, diethylene glycol dimethacrylate, pentaerythritoltetraacrylate, dicyclopentenyl acrylate, dicyclopentenyl methacrylate, 1,4-butane diol diacrylate, 1,6-hexane-diol dimethacrylate, dipentaerythritol monohydroxypentaacrylate, ethoxylated bisphenol-A dimethacrylate and tripropylene glycol diacrylate. Oligomers such as ®Uvithane 788 (Morton Thiokol) and ®Macromer 13KRC (Sartomer) are also suitable. Binders found suitable for this use are styrene/maleic anhydride polymers, methyl methacrylate/methacrylic acid copolymers having a ratio of monomers ranging from about 70/30 to 95/5; methyl methacrylate/ethyl acrylate/methacrylic acid copolymer having a ratio of monomers ranging from about 50/30/20 to about 90/5/5; methyl methacrylate/butyl acrylate/ methacrylic acid copolymer having a ratio of monomers ranging from about 50/30/2/ to about 90/5/5. Binders with no acid value but with the solubility characteristics to develop properly in alkaline aqueous developers are useful for the invention. Examples of this type of binders non-exclusively include polyvinyl pyrrolidone polymers K-60 and K-90 (G.A.F.), cellulosic resins such as hydroxypropyl cellulose, methyl cellulose and ethyl hydroxy ethyl cellulose polymers. Additional binders non-exclusively include polyvinyl acetals such as polyvinyl formal and polyvinyl butyral available as ®Formvar and ®Butvar from Monsanto, and polyvinyl alcohols. One preferred binding resin comprises a plurality of each of units A, B and C in ordered or random sequence, wherein A is present in said resin at about 5 % to about 20 % by weight and is a unit of the formula B is present in said resin at about 4 % to about 30 % by weight and is a unit of the formula and C is present in said resin at about 50 % to about 91 % by weight and is an acetal unit selected from the formulae where R is lower alkyl or hydrogen, and wherein said unit I is present in component C from about 75 % to about 85 %, unit II is present in component C from about 3 % to about 5 %; and unit III is present in component C from about 10 % to about 22 %; wherein said percentages are based on the number of acetal units C. This composition is more fully described in U.S. Patent 4,670,507. Pigments or dyes may typically be included in the photopolymerizable composition to provide color to the image areas. They are dispersed in a small amount of a suitable vehicle such as a solution of methyl methacrylate/methacrylic acid copolymer (85/15) in methyl ethyl ketone. Additional non-exclusive examples of colorants usable in the present invention are as follows: Benzidine Yellow G (C.I. 21090), Benzidine Yellow Gr (C.I. 21100), Permanent Yellow DHG (product of Hoechst AG), Brilliant Carmin 6B (C.I. 15850), Rhodamine 6G Lake (C.I. 45160), Rhodamine B Lake (C.I. 45170), Phthalocyanine Blue non-crystal (C.I. 74160), phthalocyanine Green (C.I. 74260), Carbon Black, Fat Yellow 5G, Fat Yellow 3G, Fat Red G, Fat Red HRR, Fat Red 58, Fat Black HB, Zapon Fast Black RE, Zapon Fast Black G, Zapon Fast Blue HFL, Zapon Fast Red BB, Zapon Fast Red GE, Zapon Fast Yellow G and quinacridone Red (C.I. 46500). In the practice of the present invention the binder is preferably present in an amount ranging from about 36 % to about 54 % based on the weight of the solids in the layer. A more preferred range is from about 38 % to about 52 % and most preferably from about 40 % to about 50 %. The photoinitiator composition is preferably present in the photopolymerizable composition in an amount ranging from about 0.2 % to about 7 % based on the weight of the solids in the layer. A more preferred range is from about 1 % to about 5.5 % and most preferably from about 1.5 % to about 4 %. The colorant component is preferably present in an amount ranging from about 0 % to about 7 % based on the weight of the solids in the layer. A more preferred range is from about 1 % to about 6 % and most preferably from about 2 % to about 5 %. The unsaturated component is preferably present in an amount ranging from about 20 % to about 60 % based on the weight of the solids in the layer. A more preferred range is from about 22 % to about 58 % and most preferably from about 25 % to about 55 %. Other components which may be included in the radiation-polymerizable composition of this invention include acid stabilizers, exposure indicators, plasticizers and photoactivators. Suitable acid stabilizers useful within the context of this invention include phosphoric, citric, benzoic, m-nitro benzoic, p-(p-anilino phenylazo)-benzene sulfonic, 4,4′-dinitro-2,2′-stilbene disulfonic, itaconic, tartaric and p-toluene sulfonic acid and mixtures thereof. Preferably, the acid stabilizer is phosphoric acid. When used, the acid stabilizer is preferably present in the radiation-polymerizable composition in the amount of from about 0.3 % to about 2.0 %, and most preferably from about 0.5 % to about 1.5 %. Exposure indicators (or photoimagers) which may be useful in conjunction with the present invention include 4-phenylazodiphenylamine, eosin, azobenzene, Calcozine Fuchsine dyes, Crystal Violet and Methylene Blue dyes. Preferably, the exposure indicator is 4-phenylazodiphenylamine. The exposure indicator, when one is used, is preferably present in the composition in an amount of from about 0.001 % to about 0.0035 % by weight. A more preferred range is from about 0.002 % to about 0.030 % and, most preferably, the exposure indicator is present in an amount of from about 0,005 % to about 0.020 %. The photoactivator should be an amino compound which combines synergistically with the free-radical photoinitiator in order to extend the effective half-life of the photoinitiator, which is normally in the approximate range of about 10⁻⁹ to 10⁻¹⁵ seconds. Suitable photoactivators include 2-(n-butoxy)-ethyl-4-dimethylamino benzoate, 2-dimethylamino-ethyl-4-amino benzoate and acrylated amines. Preferable the photoactivator is ethyl-4-dimethylamino benzoate. The photoactivator is preferably present in the composition of this invention in an amount of from about 1.0 % to about 4.0 % by weight. A plasticizer may also be included in the compositon of this invention to prevent coating brittleness and to keep the composition pliable if desired. Suitable plasticizers include dibutylphthalate, triarylphosphate and substituted analogs thereof and, preferably, dioctylphthalate. The plasticizer is preferably present in the composition of this invention in an amount of from about 0.5 % to about 1.25 % by weight. In order to form a coating composition, the composition of this invention may be dissolved in a solvent. Suitable solvents for this purpose include water, tetrahydrofuran, butyrolactone, glycol ethers such as propylene glycol monomethyl ether and 2-methoxy ethanol, alcohols such as ethanol and n-propanol, and ketones such as methyl ethyl ketone, or mixtures thereof. Preferably, the solvent comprises a mixture of tetrahydrofuran, propylene glycol monomethyl ether and butyrolactone. Substrates useful for coating with the composition of this invention to form a photographic element such as a color proofing film, silk screen stencil, photoresist or lithographic printing plate include sheets of transparent films such as polyester, aluminum and its alloys and other metals, fabrics, silicon and similar materials useful for semiconductors such as gallium arsenide which are well known in the art. Preferably, the substrate comprises aluminum. The aluminum may first be pretreated by standard graining and/or etching and/or anodizing techniques as are well known in the art, and also may be treated with a composition such as polyvinyl phosphonic acid, sodium silicate or the like suitable for use as a hydrophilizing agent. In the production of photographic elements such as lithographic printing plates, an aluminum substrate is first preferably grained by art recognized methods such as by means of a wire brush, a slurry of particulates or by chemical or electrochemical means, for example in an electrolyte solution comprising hydrochloric or nitric acid. The grained plate is preferably then anodized for example in sulfuric or phosphoric acid in a manner well known in the art. The grained and optionally anodized surface is preferably then rendered hydrophilic by treatment with polyvinyl phosphonic acid. The thusly prepared plate is then coated with the base composition of the present invention, preferably at a coating weight of from about 0.6 g/m² to about 4 g/m², more preferably from about 0.8 g/m² to about 3.0 g/m² and most preferably from about 1.0 g/m² to about 2.0 g/m², and dried. The light sensitive layer is then exposed to actinic radiation such as visible or ultraviolet or X-ray or exposed to a particle beam such as electron or ion beam. Such exposure may be conducted by exposure to a UV light source through a photomask under vacuum frame conditions. Mercury vapor discharge lamps are preferred to metal halide lamps. Filters may be used to reduce light scattering in the material. Preferably the photographic element is exposed through a negative test flat so as to yield a solid 6 on a 21 step Stouffer exposure wedge after development. The exposed plate is then developed with a suitable aqueous developer composition such as a developer which comprises an aqueous solution containing one or more of the following groups: (a) a sodium, potassium or lithium salt of monooctyl, -decyl or -dodecyl sulfate; (b) a sodium, lithium, potassium or ammonium metasilicate; and (c) a lithium, potassium, sodium or ammonium borate; and (d) an aliphatic dicarboxylic acid, or sodium, potassium or ammonium salt thereof having from 2 to 6 carbon atoms; and (e) mono-, di-, or tri-sodium or -potassium phosphate. Other suitable developers include water, aqueous solutions of benzoic acid or sodium, lithium and potassium benzoates and the hydroxy substituted analogs thereof as well as those developers described in U.S. Patent No. 4,436,807. The developer may also contain organic solvents which are well known in the art, although these are less preferred. The following examples are illustrative of the invention. Example 1 The following stock solution is prepared (amounts given in weight percent): 34.3 % methyl methacrylate/methacrylic acid copolymer solution in butanone 14.819 ethoxylated trimethylol propane triacrylate 5.365 BASF ®Basacryl blue green X5G 0.038 propylene glycol monomethyl ether 53.246 n-butyl acetate 26.532 The amounts of initiator (grams) indicated in Table I are added to 35 g of stock solution to prepare coating solutions. The solutions are spin coated on electrochemically grained, anodized aluminum. The coating is overcoated with a 3 % aqueous polyvinyl alcohol solution with a # 24 wire wound rod and dried in a 66 °C oven for 5 minutes. The coated plates are exposed in a vacuum frame through a Stouffer sensitivity guide, then developed with a solution of pH 11.4 comprising anionic surfactant (®Tergitol 04) 10 g trisodium phosphate x 12 H₂O 2.5 g monosodium dihydrogen phosphate 0.3 g deionized water 100 g The step results are given in Table I. Example 2 The following stock solution is prepared. 9-phenylacridine 0.210 ®Lupersol KDB 0.071 copolymer solution as in Example 1 8.943 propylene glycol monomethyl ether 85.529 pigment dispersion 4.907 The pigment dispersion consists of: Coating solutions are prepared by adding 0.83 g of one of the monomers in Table 2 to 30 g of stock solution. Monomer Solid Step propoxylated trimethylol propane triacrylate 7 ®Photomer 4158 (Henkel) 7 ®Photomer 5018 (Henkel) 4 pentaerythritol tetraacrylate 6 dipentaerythritol pentaacrylate 1 ®Sartomer C-9008 (ARCO)-alkoxylated trifunctional acrylate 9 ®Sartomer C-9041 (ARCO)-pentaacrylate m.w. 500 2 pentaerythritol triacrylate 7 The solutions are spin coated on electrochemically grained, anodized aluminum. The coating is overcoated with a 3 % polyvinyl alcohol solution with a 24 wire wound rod and dried in a 66 °C oven for 5 minutes. The coated plates are exposed in a vacuum frame through a Stouffer sensitivity guide for 5 seconds, then developed with the developer of Example 1. The step results are given in Table 2. Example 3 Using a # 24 wire wound rod, electrochemically grained, anodized aluminum is coated with a solution containing: copolymer solution of Example 1 23.141 trimethylol propane triacrylate 8.336 9-phenylacridine 0.141 benzoyl peroxide 0.060 pigment dispersion 2.322 n-butylacetate 22.050 propylene glycol monomethyl ether 43.950 The pigment dispersion consists of: red pigment 4.5 polymethyl methacrylate/methacrylic acid 13.5 methyl ethyl ketone 82.0 The coated plate is overcoated with 3 % polyvinyl alcohol solution with a #24 wire wound rod and dried in a 66 °C oven for 5 minutes. The plate is exposed in a vacuum frame and developed with the developer of Example 1. A two-second exposure results in a solid 9 on the Stouffer scale. A plate coated with the same solution with no benzoyl peroxide gave a solid 4 upon a two-second exposure. Example 4 Electrochemically grained, anodized aluminum is meniscus coated at a coating weight of 1.5 g/m² with the following solution: 9-phenylacridine 0.185 ®Lupersol KDB 0.065 ethoxylated trimethylolpropane triacrylate 3.570 copolymer solution of Example 1 8.620 methyl methacrylate/methacrylic acid copolymer (95:5) 0.320 propylene glycol monomethyl ether 82.500 pigment dispersion of Example 2 4.740 The coated material is overcoated with 3 % aqueous polyvinylalcohol solution to obtain a dry coating weight of 2.0 g/m². The coated plate is exposed in a vacuum frame through ®Dylux clearing film (from DuPont), which cuts off wavelengths of light less than 400 nm. The plate is developed with the developer of Example 1. An eight second exposure gives a solid 6 on the Stouffer scale. This corresponds to an energy density of about 30 mj/cm². Example 5 A stainless steel screen stencil is scoop coated with a solution prepared in the following manner: 9-phenylacridine 0.18 di-t-butyl diperoxyphthalate (40 % solution) 0.27 pentaerythritol triacrylate 7.67 polyvinyl pyrrolidone K-90 15.34 ethanol 38.27 water 38.27 The film produced from this solution is exposed for 200 units (1.2 j/cm²) and developed with water. A satisfactory image is obtained.

Claims: A photopolymerizable composition which comprises a compound polymerizable according to a free radical mechanism and a photoinitiator capable of initiating the polymerization of said polymerizable compound when exposed to actinic radiation, said photoinitiator being selected from acridine, quinoxaline and phenazine compounds, characterized in that the composition further comprises at least one organic peroxide or peroxy ester as a coinitiator. A photopolymerizable composition according to claim 1, characterized in that the weight ratio of the photoinitiator to said peroxy compound ranges from 99:1 to 1:99. A photopolymerizable composition according to claim 1, characterized in that the photoinitiator is a compound of one of the formulae I and II wherein X, X′, Y and T are equal or different and denote N or CR'', Z and Q are different from each other and denote N or C-R′, R and R′ are equal or different aliphatic, aromatic or heterocyclic radicals, R'' is H or an organic radical, wherein two adjacent radicals R'' may form a fused benzene ring, R¹, R² and R³ are H, halogen, alkyl, alkoxy, aryl, aryloxy, amino, acylamino, and aralkenyl groups R⁴, R⁵, R⁶ and R⁷ are equal or different and denote H or fused benzene rings with not more than two fused benzene rings being present per molecule. A photopolymerizable composition according to claim 1, characterized in that it further contains a polymeric binder. A photopolymerizable composition according to claim 1, characterized in that the polymerizable compound is an acrylic or methacrylic acid ester. A photopolymerizable composition according to claim 4, characterized in that the binder is water-insoluble and soluble in organic solvents and alkaline aqueous solutions. A photopolymerizable composition according to claim 4, characterized in that the binder is a polyvinylacetal.

Inventors: GEIGER MARGARET W, GEIGER, MARGARET W.
Applicants: HOECHST CELANESE CORP, HOECHST CELANESE CORPORATION
Application year: 1989
Main classification: G03F7
IPC codes: G03F7, C08F2, G03C1