Patent GB-541903-A (GB)
Title: Process of colour photography
IPC: G03C7/28
Filed: 1940-04-08
Abstract: 541,903. Colour photography. KODAK, Ltd. (Eastman Kodak Co.). April 8, 1940, No. 6336. Addition to 537,256. [Class 98 (ii)] A sensitive silver salt emulsion diffusely contains a dye intermediate chemically combined with the emulsion-binder, and after exposure the dye intermediate is caused to combine with another substance to form dye diffusely. The binder may be gelatine, cellulose derivatives, synthetic resins, albumen, or degradation products of these substances having a high molecular weight, e.g. hydrolysed gelatine. The dye intermediate is preferably one containing a coupling function, e.g. a phenolic, reactive methylene, or sulphonarylamide group, and may be an acid or acid chloride such as sulphonyl chloride, which combines with basic groups in the binder. The intermediates may be converted into the dyes by treatment with a diazotized or tetrazotized amino compound. The material may comprise three silver halide emulsion layers sensitive to red, green, and blue light respectively, or to infra-red, green and blue light respectively, and containing uniformly dispersed therein dye intermediates in chemical combination with the binder of each emulsion. The dye formed may be complementary in colour to the sensitivity of the respective emulsion, e.g. blue-green, magenta, or yellow, or the sensitivity of another emulsion. The intermediates are preferably colourless and such that that they are converted to dyes of the required colours by treatment with the same reagent. After exposure silver images are produced by primary or reversal development and a coloured image is then formed by image-wise decolourization or removal of the diffuse dye or dyes. The dye may be destroyed at the silver image or at the places free from silver, and the destruction may be effected by converting the silver or unchanged silver halide to an oxidizing compound. After formation of the coloured image, any remaining silver or silver halide is removed. In an example, a film has a red-sensitive gelatino-silver halide emulsion containing 1-naphthol-5-sulphonylgelatine, a clear or a filter layer, a green-sensitive emulsion containing 2-naphthol-8-sulphonylgelatine, a clear or a filter layer, and a blue-sensitive layer containing 4-hydroxybenzenesulphonylgelatine. After exposure, developing, and fixing, the film is bathed in a solution of tetrazotized 4:4<SP>1</SP>- diaminoazobenzene which produces blue-green, magenta, and yellow dyes respectively in the three emulsion layers. After washing, a positive colour picture is produced by the dye-destruction process, using for instance sodium hydrosulphite or stannous chloride, and the silver is removed with chromic acid or Farmer's Reducer. The dye-destruction bath may comprise stannous chloride, sodium hydroxide, triethanolamine, and anthraquinone. The silver may be removed by bleaching in a 5 per cent cupric chloride bath followed by fixing in hypo or a 3 per cent potassium cyanide solution. Specifications 133,034, [Class 98 (ii)], 370,860, [Group IV], 397,159; 413,016, 437,528, [both in Group IV], 468,560, 484,698, 486,382, 488,853, 503,752 and 521,836 are referred to.