GB659033A - Improvements in sensitive photographic emulsions - Google Patents

Abstract

659,033. Photographic emulsions. KODAK, Ltd. Aug. 30, 1949, No. 22520. Convention date, Aug. 31, 1948. Drawings to Specification. [Class 98 (ii)] A photographic developing-out silver halide emulsion is sensitized with at least one gold compound and with at least one palladium salt of either of the general formula M 2 PdX- and M 2 PdX 6 , wherein M represents an alkali metal or ammonium and X a halogen atom. The palladium salt acts as a supersensitizer. A sulphur sensitizer may also be incorporated. The gold compound may be used in a concentration not more than 0.015 mols. per cent of the silver halide, and may be auric chloride; potassium or sodium chloraurate; auric sulphate; an alkali metal aurous sulphite or thiosulphate; an auric chloride-thiourea complex; potassium chloraurite, bromaurite, iodoaurite, auricyanide or aurithiocyanate or the corresponding sodium, calcium, strontium, cadmium, or gallium salts; pyridino-trichlorogold; ethylene diamine-bis-trichlorogold; diethyl-monobromogold; diethylgold-acetone; or a gold complex with a sulphur compound such as a gold-thiosinamine complex. The gold compound may be incorporated in an aqueous or methyl or ethyl alcohol solution, and may be added at any stage in the preparation of the emulsion, i.e. before or during precipitation or the first or second digestion or just prior to coating. The palladium salt may be ammonium, potassium, or sodium chloropalladate; ammonium or sodium chloropalladite; potassium bromopalladate; or potassium iodopalladate, and may be added at any stage in the preparation of the emulsion, but preferably just prior to coating. The palladium salt may be used in a concentration of from 0.015 to 0.2 mols. per cent of the silver halide. The sulphur sensitizer may be thiourea, allyl isothiocyanate, allyl thiourea, or sodium, potassium, ammonium, calcium, or cadmium thiocyanate, and a metal or ammonium thiocyanate may be used in conjunction with another sulphur sensitizer. The sulphur sensitizer may be added at any stage in the preparation of the emulsion. The emulsion is preferably digested with the gold compound and with or without the sulphur sensitizer, and is preferably acid during such digestion and during coating. In example 1, the speed, gamma, and fog of samples of a gelatinosilver bromide emulsion containing potassium chloraurate and sodium thiocyanate with no addition, with ammonium chloropalladate, with ammonium chloropalladite, and with potassium chloropalladate are given. In example 2, potassium chloropalladate is added to a gelatino-silver bromide emulsion containing potassium chloraurate and sodium thiocyanate. The emulsion may be sensitized with erythrosin, Congo Red, or a cyanine, merocyanine, hemicyanine, or hemioxonol dye. The preparation of a gelatino silver bromide emulsion is described. Specifications 450,958, 479,970, 515,145, and 602,158 are referred to.