Patent GB-500720-A (GB)
Title: Improvements in processes for the production of dye images from photographic silver salt images
IPC: G03C7/26
Filed: 1937-05-10
Abstract: 500,720. Colour photography. KODAK, Ltd. May 10, 1937, No. 35100 /38. Convention date, May 9, 1936. Divided out of 500,826. [Class 98 (ii)] In the production of coloured colour component records on material comprising three differentially colour sensitized silver halide emulsions on a single support, a silver salt colour component record, which may be in the middle layer of a three-layer material, is converted into a mordant for a basic dye, dyed with a basic dye which is then rendered insoluble, and then the silver mordanting compound is removed by fixing. The material may comprise three differentially colour sensitized silver halide emulsion layers on a single support, or two layers, one containing two sets of silver halide grains respectively sensitized for red and green and the other comprising a not specially sensitized silver halide emulsion layer. The three-layer material may have a top blue-violet sensitive layer, a middle yellow, and green sensitive layer, and a bottom red- or infra-red sensitive layer, or a top blue-violet sensitive layer, a middle red and orange or infra-red sensitive layer, or a top red sensitive layer, a middle yellow-green sensitive layer, and a bottom blue sensitive layer. 4 : 4<1>- dichloro-2 : 2<1> : 8-triethylthiacarbocyanine chloride sensitizes to red and orange red but not to yellow and green. Strongly swelling gelatine is used for filter layers. The middle layer may be silver chloride, which can be converted to silver ferrocyanide, zinc ferrocyanide, copper ferrocyanide or cupric thiocyanate. Metallic silver may be removed after processing ofthe other two component images. A silver bromide middle layer may be converted to silver ferrocyanide or to a mixture of silver and lead ferrocyanides. A lead intensifier weakly acidified with acetic acid may be employed. The material may be processed by reversal or may be developed, fixed, and bleached. The metallic silver formed after general development may be converted into silver chloride or ferrocyanide. The upper layer may be similarly processed. The silver chloride may be converted to a mordant and coloured before development of the other two emulsions. In material with two silver chloride layers, one is colour developed after exposure and the other converted to a mordanting compound and coloured. The images may be colour developed by reversal or after development, fixing, and rehalogenization. The residual silver halide of the middle layer can be converted into silver iodide with 1 per cent of potassium iodide and may be dyed with 0À1 per cent solutions of basic dyes such as rhodamine 6, safranine or methylene blue. Excess of dye may be washed out with addition of acetic acid. The dye is made insoluble by treatment with a precipitating- agent such as a phosphotungstate and the silver mordanting compound is fixed out. Specifications 376,746 and 500,795 are referred to. The Specification as open to inspection under Sect. 91 comprises also the use as mordanting compounds of complexes formed by silver chloride and silver bromide with thiourea, thiosinamine, and thiosemicarbazide. This subject-matter does not appear in the Specification as accepted.