GB922752A - Lithographic printing plate prepared by electrophotographic reproduction and a method for its production - Google Patents

Abstract

922,752. Lithographic printing plates. PLASTIC COATING CORPORATION. May 24, 1960 [June 18, 1959], No. 18200/60. Drawings to Specification. Class 98 (2). A lithographic printing plate comprises a base sheet, for attachment to the plate cylinder of a lithographic printing press, and carries on its outer surface a photoconductive, finely divided inorganic pigment in a matrix of a film-forming and insulating material which carries on predetermined image areas fuser tones for developing the image and forms a film of hydrophobic material which is wettable by a lithographic ink; the non-image areas are rendered hydrophilic by applying to them a dilute aqueous solution of a water-soluble film-forming material having free carboxyl groups. The pH of the latter solution is preferably between 3.0- 7.25. The base sheet which is electrically conducting may comprise a sheet of paper or plastic (various examples given) coated with film of casein-clay impregnated with an hydroscopic salt e.g. zinc chloride, lithium chloride, potassium acetate, calcium chloride, zinc nitrate, potassium carbonate or a film of clear lacquer containing finely divided graphite, aluminium, copper, bronze, litharge, tannic oxide, copper sulphite, silver sulphite or carbon black or a thin metal film. A thin film of a copolyester of ethylene terephthalate and ethylene sebacate may be used to promote the adhesion between a plastic base and a metal film. The film-forming insulating matrix may be styrenated alkyd copolymer resin. The material applied to the non- image area may be the complex, inorganic salt oxalate or chromic acid. Specifications 907,909 and 922,753 are referred to.