FHOTOPOLYMERIZABLE COMPOSITION COMPRISING AN INITIATOR COMBINATION OF 1,4-OR 9,10-DIMETHOXYANTHRACENE AND A TRIHALOMETHYL-(3H)-QUINAZOLIN-4-ONE

Abstract: A photopolymerizable composition is disclosed which comprises a polymerizable compound and a photoinitiator combination of 1,4- or 9,10-dimethoxy-anthracene and 2-tri(chloro or bromo)-methyl-(3H)-quinazolin-4-one. The initiator is useful in preparing photopolymerizable compositions having increased effective photospeed.

Description: The present invention relates to photopolymerizable compositions which are highly sensitive to ultraviolet and visible rays and which can be used in connection with color proofing films. Useful known photopolymerizable compositions include various photoinitiators which have been found to be practical. For example, benzoin, benzoin methyl ether, or benzoin ethyl ether, etc., carbonyl compounds such as benzil, benzophenone, acetophenone, Michler's ketone, azo compounds such as azobisisobutyronitrile or azodibenzoyl, etc., sulfur compounds such as dibenzothiazolyl sulfide or tetraethylthiuram disulfide, etc., halogen compounds such as tribromomethyl-phenyl sulfone, etc., and 1,2-benzanthraquinone, etc. However, these initiators are not sufficiently satisfactory. When they are used for polymerization of various ethylenically unsaturated compounds, they do not always provide good photosensitivities. Sensitizers have been employed to broaden the spectral response of photosensitive compounds, especially in the visible portion of the light spectrum. Furthermore, it is desired to have high sensitivity photoinitiators which can be employed in compositions which can be exposed by laser light or by projection through a mask. Typical initiators have a low quantum efficiency and therefore require the use of a high powered u.v. light source while an exposure mask is held in close contact with an exposure mask in a vacuum frame. In projection exposure, light, preferably visible light, is projected through a mask and a lens onto a light sensitive target film. To allow exposure, photosensitivity must be quite high and must be of an effective wavelength. Still further, in the field of color proofing films, the color condition of the image formed is critical. Color proofing films typically comprise a transparent substrate and a colored photosensitive composition on the substrate. It is important that the non-colorant ingredients of the photosensitive composition contribute as little color modification as possible. It is desirable, therefore, to keep the amount of the initiator ingredient in the colored photosensitive composition as low as possible, for this leads to a lower amount of color contamination. The invention provides a photopolymerizable composition which comprises a polymerizable compound containing at least one, preferably at least two ethylenically unsaturated double bonds and a photopolymerization initiator combination which comprises 1,4- or 9,10-dimethoxyanthracene and 2-tri(chloro or bromo)methyl-(3H)-quinazolin-4-one, preferably in a respective weight ratio of from about 0.05:1 to about 1:1. The invention also provides a photopolymerizable recording material which comprises a substrate and a photopolymerizable layer coated thereon, wherein the photopolymerizable layer consists of a composition as defined above. 2-Trichloromethyl-(3H)-quinazolin-4-one is a free-radical photopolymerization initiator per se known in the art. It is more fully described in DE-A-3 339 228. Upon exposure to actinic radiation it releases chlorine free radicals, which are capable of initiating polymerization of suitable ethylenically unsaturated compounds. However, it only absorbs UV light of wavelengths shorter than 320 nm. It has now been found that when even catalytic amounts of 1,4- or 9,10-dimethoxyanthracene are incorporated with the quinazolinone, the thusly formed composition is capable of causing photopolymerization at 400 nm, a wavelength at which the quinazolinone alone is completely ineffective. The anthracene compounds themselves are electron donors but not polymerization initiators. The anthracene compounds act as triggers for the quinazolinone and allow photopolymerization at visible light and near UV, i.e. at 360-420 nm wavelengths. Such visible light wavelength sources are suitable for laser and projection speed imaging, and are very well suited for use in color proofing films since less initiator is necessary for exposure. This therefore translates into reduced color contamination. While the ratio of anthracene component to quinazolinone compound may normally range from 0.05:1 to 1:1 it is more preferably from about 0.1 to 1 and most preferably from about 0.5 to 1. The photopolymerizable composition of this invention generally comprises a polymerizable compound having at least one double bond and the foregoing photoinitiator composition. The photopolymerizable composition additionally has a binder resin in the preferred embodiment. The photopolymerizable compound is an addition-polymerizable, non-gaseous (boiling temperature above 100 °C at normal atmospheric pressure), ethylenically unsaturated compound, preferably 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 such acrylic or methacrylic acid esters as polybutane diol diacrylate, tetraethylene glycol dimethacrylate, ethylene glycol dimethacrylate, polyethylene glycol (200) diacrylate, diethylene glycol dimethacrylate, pentaerythritol tetraacrylate, dicyclopentenyl acrylate, dicyclopentenyl methacrylate, 1,4-butane diol diacrylate, 1,6-hexanediol dimethacrylate, dipentaerythritol pentaacrylate, ethoxylated bis-phenol A dimethacrylate and tripropylene glycol diacrylate. Binders found suitable for this use are styrene/maleic anhydride copolymers that can vary in monomer content, preferably at a ratio of from about 70/30 to about 95/5; copolymers and terpolymers of methyl methacrylate and methacylic acid, e.g. methyl methacrylate/methacrylic acid copolymers having a ratio of monomers ranging from about 70/30 to 95/5; methyl methacrylate/ethyl acrylate/methacrylic acid copolymers having a ratio of monomers ranging from about 50/30/20 to about 90/5/5; and methyl methacrylate/butyl acrylate/methacrylic acid copolymers having a ratio of monomers ranging from about 50/30/20 to about 90/5/5. Binders with no acid value should have the solubility characteristics to develop properly in the alkaline developers useful for the invention. Examples of this type of binder system include polyvinyl pyrrolidone polymers, cellulosic ethers such as hydroxypropyl cellulose, methyl cellulose and ethyl hydroxy ethyl cellulose. Additional binders include polyvinyl acetals such as polyvinyl formal and polyvinyl butyral, and polyvinyl alcohols. One preferred binding resin has the general formula -A-B-C- wherein a plurality of each of components A, B and C occur in ordered or random sequence in the resin and wherein A is present in said resin at about 5 % to about 20 % by weight and is a vinyl acetate unit, B is present in said resin at about 4 % to about 30 % by weight and is a vinyl alcohol unit, and C is present in said resin at about 50 % to about 91 % by weight and is a vinyl acetal unit consisting of units of 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 from about 3 % to about 5 %, and unit III is present from about 10 % to about 22 %; based on the total weight of acetal units C. This composition is more fully described in EP-A 216 083. Pigments or dyes may typically be included in the photopolymerizable composition to provide color to the image areas. 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), Permanet Yellow DHG (product of Hoechst AG), Brilliant Carmine 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 5B, 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, quinacridone Red (C.I. 46500). The binder component is preferably present in an amount ranging from about 18.0 % to about 40.0 % based on the weight of the solids in the layer. A more preferred range is from about 20.0 % to about 38.0 % and most prefereably from about 22.0 % to about 33.0 %. The photoinitiator combination is preferably present in an amount ranging from about 5 % to about 25 % based on the weight of the solids in the layer. A more preferred range is from about 8 % to about 22 % and most preferably from about 10 % to about 20 %. In the practice of the present invention the colorant component is preferably present in an amount ranging from about 1 % to about 20 % based on the weight of the solids in the layer. A more preferred range is from about 3 % to about 18 % and most preferably from about 5 % to about 15 %. The polymerizable compound 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 acid, 4,4'-dinitro-stilbene-2,2'-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 %, although the skilled artisan may use more or less as desired. 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 0.035 % 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 which may be included in the composition of this invention should be an amine-containing photoactivator which combines synergistically with the free-radical photoinitiator in order to extend its effective halflife, 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 and acrylated amines. Preferably 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 composition 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 in an amount of from about 0.5 % to about 1.25 % by weight. In order to form a coating composition for the production of photopolymerizable recording materials, the composition of this invention may be dissolved in a solvent or mixture of solvents to facilitate application of the composition to the substrate. 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 butanone, or mixtures thereof. Preferably, the solvent comprises a mixture of tetrahydrofuran, propylene glycol monomethyl ether and butyrolactone. In general, the solvent system is evaporated from the coating composition once it is applied to an appropriate substrate, however, some insignificant amount of solvent may remain as residue. 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 substrate may first be pretreated by standard graining and/or etching and/or anodizing techniqus as are well known in the art, and also may or may not have been 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 nitric or hydrochloric 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 by means which are also known to the skilled artisan. 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 3.0 g/m², more preferably from about 0.8 g/m² to about 2.0 g/m² and most preferably from about 1.2 g/m² to about 1.5 g/m², although these coating weights are not critical to the practice of this invention, and dried. The light-sensitive layer is then exposed to actinic radiation such as visible or ultraviolet light or x-ray or exposed to a particle beam such as an electron or ion beam. In the preferred embodiment, the photosensitive layer is imagewise exposed by means well known in the art. Such exposure may be conducted by exposure to a UV light source through a photomask under vacuum frame conditions. Exposure may be performed with actinic light through a conventional negative flat. Exposures are preferred with emulsion-to-emulsion contact. Mercury vapor discharge lamps are preferred to metal halide lamps. Filters may be used to reduce light scattering in the material. Preferably the thusly prepared photographic element is exposed to actinic radiation through a negative test flat so as to yield a solid 6 on a 21 steps 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 having from 2 to 6 carbon atoms, or a sodium, potassium or ammonium salt thereof; 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 US-A 4 436 807. The developer may also contain organic solvents which are well known in the art, although this is less preferred. The following examples are illustrative of the invention but it is understood that the invention is not limited thereto. Example 1 A photosensitive mixture is prepared, wire-rod #12 - coated on polyester film Melinex 516, air-dried, overcoated with an oxygen barrier layer of polyvinyl alcohol, air-dried, exposed for 15 units in an Ascor-Berkey device through a Schott GG - 400 nm cutoff filter and hand-developed with a solution of pH 11.4 comprising anionic surfactant (Tergitol 04) 10 g trisodium phosphate x 12H₂O 2.5 g monosodium dihydrogen phosphate 0.3 g deionized water 100 g The photosensitive coating solution was as follows: Hand development gives a good image with 4 solid steps on the Stouffer step wedge. When 9,10-dimethoxy-anthracene is not present in the formulation, no image is obtained. Example 2 Example 1 is repeated except that 1,4-dimethoxy-anthracene is substituted for 9,10-dimethoxy-anthracene. Similar results are noted.

Claims: A photopolymerizable composition comprising a polymerizable compound containing at least one terminal ethylenically unsaturated group and a photopolymerization initiator combination, characterized in that the initiator combination comprises 1,4- or 9,10-dimethoxy-anthracene and 2-tri(chloro- or bromo)methyl-(3H)-quinazolin-4-one. A photopolymerizable composition as claimed in claim 1, characterized in that the ratio of dimethoxy anthracene compound to quinazoline compound is from 0.05:1 to 1:1. A photopolymerizable composition as claimed in claim 1, characterized in that the photopolymerizable compound is an acrylic or methacrylic acid ester. A photopolymerizable composition as claimed in claim 1, characterized in that it comprises a polymeric binder. A photopolymerizable composition as claimed in claim 4, characterized in that the binder is a polyvinyl acetal, a polyvinyl pyrrolidone, a cellulosic ether, a styrene/maleic anhydride copolymer, or a copolymer or terpolymer comprising units of methyl methacrylate and methacylic acid. A photopolymerizable recording material which comprises a substrate and a photopolymerizable layer coated thereon, characterized in that the photopolymerizable layer consists of a composition according to claim 1.

Inventors: WILCZAK, WOJCIECH A.
Applicants: HOECHST CELANESE CORPORATION
Application year: 1988
Main classification: G03F7
IPC codes: C08F2, G03F7, C08L29, C08F220