Patent GB-498874-A (GB)
Title: Improvements in colour photographic elements
IPC: G03C7/26
Filed: 1937-05-10
Abstract: 498,874. Colour photography. KODAK, Ltd. May 10, 1937, No. 34977/38. Convention date, May 9, 1936. Divided out of 500,826. [Class 98 (ii)] A sensitive photographic element has three silver halide emulsions respectively sensitized to three separate colours covering substantially the whole of the visible spectrum, and one of the emulsions sensitized to yellow-green or to orange-red by means of a sensitizer is also sensitized to another region, for example the infra-red, by means of another sensitizer, for example neocyanine or cryptocyanine resistant to developing or developing and oxidizing baths. The element may have blue-sensitive, yellow-green sensitive, and redsensitive emulsion layers superimposed on a support, the blue-sensitive layer being uppermost, or the middle emulsion layer may be orange-red-sensitive and the lowermost emulsion layer yellow-green sensitive. The red or the yellow green-sensitive emulsion layer may be on one side of the support and the other two layers on the other side. Alternatively, the element may have two layers on the same or different sides of the support, one containing two sets of silver halide grains respectively sensitized for red and green, while the other consists of not specially sensitized silver halide. The lowest layer in a three-layer element may contain a colour sensitizer resistant to development and the middle layer an additional infra-red sensitizer resistant to development. After exposure, the superimposed latent images are developed by an ordinary non-tanning developer such as ferrous oxalate, amidol and diamido-o-cresol. Organic developers containing sodium carbonate may be used and colour sensitivity restored by treatment with alkali sulphite or bisulphite. All three layers may first be saturated in a strong solution of the developing agent and development effected in solutions of sodium carbonate, ammonia, alkali bicarbonate, borax, trisodium phosphate, or sodium aminoacetate. Alternatively, concentrated developing solution may be allowed to diffuse into all the layers at a low temperature and development started or accelerated by warming. The residual silver halide may be used for reversal development or converted in one or more layers to silver chloride in a fine state of subdivision by treatment with potassium ferricyanide and sodium chloride or with lead chloride or with mercuric chloride. The removal of the initially reduced silver may be effected with oxidizing agents. The lower layer is exposed to red light and developed blue-green, and the middle layer is exposed through the uniformly blackened lower layer to infra-red light. The upper layer is exposed to blue or ultra-violet light or soft-X-rays and colour developed and the silver finaly removed from all the layers. If two ultra-violet filter layers are arranged on both sides of the middle layer, and the latter contains an infra-red sensitizer, the outer layers are exposed to ultra-violet light and colour developed and then the middle layer exposed to infra-red light and colour developed. The middle layer may be of silver chloride and contain an infra-red sensitizer, and is then developed black with a weak developer, exposed to infra-red light and colour developed. The latent images in the outer layers are developed and then successively exposed and colour developed, the developed silver in the middle layer acting as a screen. The upper or middle emulsion may be of silver chloride and this or the bottom emulsion may contain an infra-red sensitizer stable to the developer and to mild oxidizing agents. The residual silver halide of such an emulsion is made developable by infra-red light. Any other sensitizer for which the middle emulsion is insensitive may be added to the lower emulsion. An infra-red sensitizer stable to the developer may be added to the red-sensitized lowermost emulsion, the element developed, the residual silver bromide of the lowermost layer exposed to infra-red light and colour developed, and the other two emulsions made developable with thiourea or other fogging agent. The silver chloride and bromide emulsions are then selectively colour developed. A two layer element may comprise a blue-sensitive silver chloride emulsion layer and a mixed grain layer comprising green-sensitive grains and grains both red and infra-red sensitized, the infra-red sensitizer being stable to development. After general black development, the mixed grain layer is exposed to infra-red light and developed blue-green. The residual silver halide is made developable by thiourea or other fogging agent and the silver chloride developed yellow. The silver bromide of the other grains is developed purple and all silver removed. If the blue-sensitive emulsion is of silver bromide, the green-sensitizer is stable to development and the residual silver bromide of the green-sensitized layer developed purple after exposure to yellow-green light. The blue-sensitive emulsion is exposed to ultra-violet light and developed yellow. If the blue-sensitive emulsion is on the other side of the film, the image in the red-sensitized grains is developed to blue-green after the second exposure, and the images in the bluesensitive emulsion and the yellow-green sensitized grains rendered developable by thiourea or other fogging 'agent and selectively colour developed. Specification 427,519 is referred to.