GB695915A - Direct production of positive photographic images - Google Patents

Abstract

695,915. Positive photographic images. FARBENFABRIKEN BAYER. July 5, 1951 [July 6, 1950; May 7, 1951], No. 16027/51. Class 98 (ii). Photographic positive silver images are produced by developing an exposed silver halide emulsion layer in an alkaline solution in close contact with a separate receiving layer containing development nuclei and in the presence of a developing agent, a silver halide solvent, and at least one nitrogen-containing organic substance accelerating the development, said nitrogen-containing substance being different from the silver halide solvent, e.g. a thiocyanate, amine, guanidine, guanidine derivative, guanazole, guanazole derivative, hydrazine, or hydrazine derivative. The developing agent may be incorporated in the emulsion layer and the silver halide solvent, e.g. hypo, in the receiving layer. The emulsion layer may also contain a stabilizer. Stabilizers referred to are benztriazole and nitrobenztriazole, and combined stabilizers and tone-influencing compounds are organic mercapto compounds. The alkaline solution may comprise an aqueous solution of sodium sulphite, caustic soda, and potassium thiocyanate. The development accelerator may also be an alkyl-, aralkyl-, aryl-, or acyl-guanazole, or a guanazole substituted by a heterocyclic nucleus, a compound containing several guanazole nuclei, or the quanazole obtained by reacting semicarbazide with dicyandiamide. The development accelerator may be incorporated in the emulsion or receiving layer or in the developing solution, or in more than one of these. In an example, an exposed silver chlorobromide emulsion layer containing mercaptobenzthiazole and hydroquinone and a receiving layer prepared from a solution containing gelatine, colloidal silver and sodium thiosulphate are introduced separately into an aqueous solution of sodium sulphite, caustic soda, and the guanazole obtained by reacting semicarbazide and dicyandiamide, and pressed together when thoroughly wetted, and after about one minute are separated, a positive image being produced on the receiving layer. Specifications 654,630 and 695,905 are referred to.