Patent GB-539355-A (GB)
Title: Photographic emulsions
IPC: G03C1/07
Filed: 1940-02-02
Abstract: 539,355. Photographic silver halide emulsions. KODAK, Ltd. Feb. 2, 1940, No. 2059. Convention date, Feb. 2, 1939. [Class 98 (ii)] A metal thiocyanate (containing as cation a metal which does not damage the emulsion) or ammonium thiocyanate is incorporated in a photographic gelatino silver halide developing out emulsion during its preparation, for example, during the precipitation, the first digestion, or the melting-out and second digestion into the finished emulsion. The emulsion is preferably washed. Thiocyanates specified are sodium, potassium, calcium, barium, ammonium, silver, and cadmium. The thiocyanate may be added in aqueous solution, as a colloidal dispersion in gelatin. The emulsion speed is increased over the whole range, whether or not the emulsion is optically sensitized, but when the thiocyanate is added to the finished emulsion in the proportion of not more than 3 per cent. by mols. calculated on the silver halide, the increase in violet and blue speed is small, and the speed in one spectral region is enhanced. Thiocyanates specified are sodium, potassium, calcium, barium, cadmium, silver, and ammonium thiocyanates. The emulsion binder may also be other than gelatine, and may be a resinous or cellulose derivative. The silver halide may be the bromide, bromiodide, chloride, or chlorobromide. The thiocyanate may be added to a washed or unwashed emulsion. Soluble thiocyanates may be added in aqueous solution or the solid state, and insoluble thiocyanates in the form of a colloidal dispersion in gelatine. Not more than 2 per cent. by mols. calculated on the silver halide present is preferably added. In the case of addition during preparation, the sensitizing dyes may be Eythrosin, Congo Red, and cyanine, merocyanine, hemicyanine, and hemioxonol dyes. In the other case the last four groups of dyes are preferred, and sulphonic, sulphinic, sulphuric, and carboxylic groups and their metal and ammonium salts are preferably absent. The dyes may be employed in the optimum or greater or less concentrations. Numerous particular classes of dyes are referred to. The preparation of emulsions corresponding to both cases is illustrated. Examples of the second case disclose the following supersensitizing combinations : (1) Sodium thiocyanate and 2 : 2<SP>1</SP>-diethyl-8-methylthiacarbocyanine ; (2) ammonium thiocyanate and 3- ethyl-5-[ (2-ethyl-1 (2)- benzoxazylidine-ethylene ] - rhodanine ; (3) potassium thiocyanate and 2 : 2<SP>1</SP> - diethyl - 8 - methyl - 3 : 4 : 3<SP>1</SP> : 4 - dibenzthiacarbocyanine chloride ; (4) calcium thiocyanate and 2 - [4 - (1 - piperidyl) - #<SP>1</SP>, <SP>3</SP>- butadienyl] - # - naphthathiazole ethiodide; (5) sodium thiocyanate and the dye of example (3) ; (6) silver thiocyanate and the dye of example (4) ; (7) silver thiocyanate and the dye of example (3) ; (8) sodium thiocyanate and 2 : 2<SP>1</SP>- dimethyl - 8 - ethyl - 3 : 4 : 3<SP>1</SP> : 4<SP>1</SP> - dibenzthiacarbocyanine iodide ; (9) sodium thiocyanate and the dye of example (3), and 2:21-dimethyl- 8-ethylthiocarbocyanine iodide; (10) sodium thiocyanate and the dye of example (2) ; (11) sodium thiocyanate and the dye of example (4) ; (12) silver thiocyanate and 3-ethyl-5-[-(1- piperidyl) - allylidene] - rhodanine ; (13) calcium thiocyanate and the dye of example (3), using the bromide ; and (14) cadmium thiocyanate and the dye of example (3). Mixtures of the thiocyanates may be used. The support may be of glass, paper, or cellulose derivative or resin film. Specifications 450,958, 479,970, 515,145 and 517,769 are referred to.