METHOD OF FORMING LITHOGRAPHIC PRINTING PLATE

1393785 Photo-lithography APECO CORP 17 April 1972 [15 April 1971] 17668/72 Headings G2C and G2M A lithographic printing process uses a printing plate produced by exposing a photographic silver halide emulsion layer and developing to form a hydrophilic silver image, in which either (a) the developed layer (which still contains silver halide, i.e. is unfixed) is treated with a benzotriazole, (b) the developer contains a benzotriazole, or (c) the photographic element containing the emulsion layer also contains a benzotriazole; in each case the benzotriazole is unsubstituted in the 1-position and substituted in at least one of the 4, 5, 6 and 7-positions and converts the undeveloped areas of the emulsion to an oleophilic inkreceptive state. Specified benzotriazoles are 5-Me; 5, 6-di-Me; 4, 5-di-Cl; 5-NO 2 ; 4-NH 2 ; 6-NMe 2 ; and 6-OH. In the Examples the treatment solution used in embodiment (a) is an aqueous solution of Na acetate, Cr acetate, the triazole, methanol, NaOH and colloidal gold; the solution may be mixed with a developer solution for use in embodiment (b).