Patent GB-569495-A (GB)
Title: Improvements in photographic materials for colour photography
IPC: G03C7/30
Filed: 1942-11-24
Abstract: 569,495. Colour photography. KODAK, Ltd., and KNOTT, E. B. Nov. 24, 1942, No. 16683. Drawings to Specification. [Class 98 (ii)] Photographic multilayer sensitive material comprises a silver salt emulsion layer or layers sensitized to record red or green or both over which is coated a sensitive silver salt emulsion layer for recording blue containing silver salt particles containing silver bromide or silver chloride or both, comprising at least 10 per cent silver iodide based on the total silver salt content, the particles being dispersed in a water-permeable binder and the particle size and the quantity of silver iodide being such that the layer transmits not more than 15 per cent at the wave-length 445 and below and not less than 70 per cent at the wave-lengths 530 to 700, the measured transmitted light including scattered light. If one of the red and green sensitized emulsions has a relatively low inherent blue speed (e.g. a silver chloride emulsion), it may be mixed with the notspecially colour-sensitized emulsion of high iodide content and coated over the third emulsion. The iodide content of the bluesensitive emulsion may be about or above 35 per cent. All the sensitive layers are exposed from the same side. The iodide-containing emulsion layer may be made by precipitation from silver nitrate using a mixture of soluble iodide and bromide (or chloride), or by mixing separately precipitated silver iodide with silver bromide, iodobromide, chloride, iodochloride, or iodochlorobromide. In example 1, a support is coated with a red-sensitized gelatino-silver bromide emulsion, a green-sensitized gelatinosilver bromide emulsion, and with an emulsion prepared by pouring ammoniacal aqueous silver nitrate into an aqueous solution of active gelatine, potassium bromide, and potassium iodide, both solutions being at 50‹ C., stirring for 20 minutes, adding active gelatine, continning ripening for 30 minutes, setting, washing, adding active gelatine, and digesting at 60‹ C. to optimum speed. In example 2, a support is coated with red- and green-sensitized emulsions as in example 1, and then with an emulsion made by mixing emulsions A and B. Emulsion A is prepared by pouring aqueous silver nitrate into an aqueous solution containing gelatine, potassium iodide, and potassium bromide, both solutions being at 60‹ C., adding ammonia, ripening for 30 minutes at 60‹ C., adding gelatine and further ripening for 15 minutes, wetting, washing, adding gelatine, and digesting at 60‹ C. until optimum speed is obtained. Emulsion B is prepared by adding aqueous silver nitrate to an aqueous solution containing gelatine, much potassium iodide, and potassium bromide, both solutions being at 60‹ C., ripening for 15 minutes at 50‹ C., adding gelatine, digesting for 15 minutes at 60‹ C., setting, washing, and adding gelatine to the melted emulsion. Example 3 is similar to example 2, only emulsions A and B are coated in separate layers. In examples 2 and 3, only emulsion A developed during processing and all the silver iodide was fixed out in the hypo fixing bath. Specification 540,444 is referred to.