GB287460A - Method of producing printing plates - Google Patents

Abstract

287,460. Dunlop, S., (Aktiebolaget Rapido. grafi). March 19, 1928. [A Specification was laid open to inspection under Sect. 91 of the Acts, March 19, 1928]. Photo-mechanical printing-surfaces; screens; emulsions, preparing.-Printing surfaces are produced from gelatine films sensitized with a silver salt and treated with a chromium salt, the films before exposure, and preferably before incorporation of the chromium salt being hardened by a saturated alum bath, or by a preliminary bath of alum followed by a formalin bath. After exposure the hardening of the gelatin is modified by treatment with acid of suitable pH-concentration. In a detailed process, a silver chloride film is prepared in a particularly described manner with silver nitrate and sodium chloride. For making direct printing-plates the zinc or other support may be first prepared with an adhesive gelatin coating containing waterglass, and the edges of the film are coated with shellac. The hardened silver gelatin film is bathed in ammonium bichromate, and after exposure treated with dilute sulphuric acid. The exposed film may be subjected to further hardening before the acid treatment. The plates may then be moistened and inked up for direct printing. Stereotypes may be produced by a process of slow drying after inking, which results in a contraction of the unexposed gelatin. Alternatively a transfer may be made on to a zinc plate for etching. Large printing surfaces may be made by enlarging directly thereon. The Specification as open to inspection under Sect. 91 (3) (a) includes also a process for making screens according to which the sensitized films are exposed directly to evenly distributed or diffused light and treated with acid. This subject-matter does not appear in the Specification as accepted.