Patent GB-741294-A (GB)
Title: Photosensitive element and process for preparing printing relief images
IPC: C08F2/50
Filed: 1952-08-20
Abstract: 741,294. Photo-sensitive element and process for preparing printing relief images. DU PONT DE NEMOURS & CO., E. I. Aug. 20, 1952 [Aug. 20, 1951], No. 20946/52. Class 98 (2). A layer at least 3 mils. thick of an ethylenically unsaturated photopolymerizable composition, containing a catalyst for such photopolymerization, carried on a permanent support with, normally, an intermediate polymeric anchor layer absorptive of actinic light, is exposed to actinic light through a process transparency having an image of areas, lines or dots of high and uniform opacity, to polymerize the exposed portions of the layer to the insoluble state throughout its entire thickness and the unexposed, unpolymerized portions are removed as by draining, washing or brushing or by use of a solvent to leave a relief image suitable for direct use as a printing plate. Seven specific examples describe the light-sensitive element and processing thereof always using metal plates or panels as the permanent support and provided with the intermediate light-absorptive layer, and always using solvent for processing; thus in Example I an aluminium plate is provided with the intermediate layer by coating with a composition comprising polyvinyl nbutyral, lead chromate, magnesium silicate, isopropanol, methyl isobutyl ketone, phosphoric acid and water, and drying; and then, using spacing strips at the edges of the plate, with a liquid layer comprising a mixture of methyl methacrylate monomer, polymethyl methacrylate and monomeric polyethylene glycol dimethacrylate as photopolymerizable composition together with benzoin as the catalyst. A photographic line negative on glass (protected by a transparent colourless regenerated cellulose membrane) is lowered onto the liquid to rest on the spacers and allow excess liquid to escape, exposure is effected using mercury vapour lamps, the negative is removed, unpolymerized liquid is removed by washing with an ethyl acetate ethanol mixture, and the resulting relief plate is used for printing in the same way that metal photo-engraved plates are used. Examples II to IV differ from Example I only as regards the polymeric anchor layer, these being formed from dried and baked mixtures of: II vinyl chloride/allyl glycidyl ether copolymer, xylene, methyl isobutyl ketone, citric acid, 2-methoxyethanol, stannous chloride dihydrate, 2-ethoxyethyl acetate and a red oil dye of Index No. 258 (Society of Dyers and Colourists) ; III the mixture of Example II without the dye, a dark brown colouration being provided therein by prolonged baking in an oven; IV carbon black, a maleic acid modified vinyl chloride/vinyl acetate copolymer, xylene, methyl isobutyl ketone, a monomeric polyethylene glycol dimethacrylate mixture, 1,1<SP>1</SP>- azodicyclohexanecarbonitrile and cobalt nitrate hexahydrate. In Example V a steel panel is provided with the intermediate layer by means of a composition comprising polyvinyl nbutyral, ethanol, phosphoric acid, acetone, chromium trioxide, water, butanol, magnesium silicate and carbon black, and then a photopolymerizable layer of a mixture of monomeric polyethylene glycol dimethacrylate, acrylonitrile and benzoin, for exposing and developing procedure as in Example I. Example VI describes the coating of a steel panel with the black composition of Example V, then a thin layer of the photopolymerizable composition of Example I and finally a composition comprising vinyl polysiloxane, toluene, methyl methacrylate monomer and polymer, and benzoin. Example VII is directed to a comparison of the necessary exposure times when using separately the several catalysts benzoin, alpha-methylbenzoin, benzoin methyl ether, α-allyl benzoin, diacetyl and 1,1<SP>1</SP>-azodicyclohexanecarbonitrile with the photopolymerizable composition of Example I. In addition to the substances referred to in the examples the Specification describes or suggests the use of innumerable other materials including ranges of vinyl, vinylidene, acrylic and styrene monomers, any of which may include a proportion of polymers thereof or of polymers as of glycols or glycol esters or ethers for use as the ethylenically unsaturated photopolymerizable composition; and innumerable other polymers, pigments and dyes for use in the intermediate polymeric anchor layer. An alternative method to that of Example I of preventing the negative from sticking to the polymerizable layer during or after exposure is to coat the negative with a thin layer of silicone oil or grease. Specifications 438,960, 566,795 and 618,181 are referred to.