A method for improving the hiding power and the maximum density values which can be developed photographic silver halide emulsions feinkoerniger

摘要

1,200,749. Photographic silver chloride emulsions. EASTMAN KODAK CO. Dec.21, 1967 [Dec.27, 1966], No.58066/67. Heading G2C. In the preparation of a silver halide emulsion which contains silver chloride, the physical ripening of the grains is effected in the presence of an azaindene having an acidic hydrogen atom and which forms a water-insoluble silver salt. The azaindene acts as a grain growth restrainer and increases the optical density of developed silver obtainable from the emulsion. Azaindenes specified are adenine, 4-hydroxy-6-methyl-1:2:3a: 7-tetraazaindene, 4-hydroxy-6-methyl-1:2:3:3a: 7-pentaazaindene and 4-hydroxy-6-methyl-2- methylmercapto-1:3:3a: 7-tetraazaindene. The azaindene is added to the emulsion preferably from 5 seconds to 4 minutes after the mixing of the water-soluble silver salt and the water-soluble halide in the precipitation of the silver halide. The emulsion may also contain thioured and rhodium ammonium chloride in addition to the usual chemical and optical sensitizers, hardeners, toners and surfactants. The emulsion may be coated on a support which also carries an incorporated developer layer e.g. containing hydroquinone and 1-phenyl-3-pyrazolidone.