Patent GB-500826-A (GB)
Title: Process of and materials for colour photography
IPC: G03C7/30
Filed: 1937-05-10
Abstract: 500,826. Colour photography. KODAK, Ltd. May 10, 1937, No. 13250. Convention date, May 9, 1936. [Class 98 (ii)] In material having three differentially colour sensitive silver halide emulsion layers, either all three on the same side or one on one side and two on the other side of a single support, one or two of the three emulsion layers on the side of the support or one of the two emulsion layers on one side of the support are silver chloride and the remainder on that side are silver bromide. The middle layer may be silver chloride and the others silver bromide, the layers being on the same or different sides of the support. The upper layer may be of silver chloride and the remainder silver bromide, the upper and middle layers being on the same side of the support. The upper and lower layers may be of silver chloride and the middle layer of silver bromide. Silver chloride may be developed by a weak developer such as a colour developer which is without action on the silver bromide, or; by very mild reducing agents, silver chloride but not silver bromide, is made developable. Silver chloride is more readily converted than silver bromide to coloured substances, mordantihg bodies, and silver ferrocyanide. Exposed silver bromide may be developed with a colour developer containing alkali carbonate which does not attack unexposed silver chloride. The latter is' colour developed without exposure or pretreatment with fogging agents by an ammoniacal, caustic alkaline, alcoholic, or acetonic colour developer, preferably in absence of air. Material having a silver chloride layer between two silver bromide layers is generally developed, the residual silver bromide in the outer layers is selectively exposed and colour developed with colour developers and the residual silver chloride in the middle layer colour developed by prolonged treatment with a strong colour developer. After colour processing the silver bromide, the silver chloride is, converted to silver ferrocyanide and then to nickel dimethylglyoxime or titanium ferrocyanide, the latter yielding a green-blue image with blue basic dyes. The silver ferrocyanide may be converted into other non-tanning mordanting bodies coloured purple and green-blue by basic dyes and may be removed after insolubilization of the dyes. The material may comprise three superimposed layers, the top or middle of which is silver chloride, and may be on one or both sides of the support. The red-sensitive layer may be alone on one side of the support, and the support or filter layer may contain colourless ultra-violet absorbing substances. Three-layer material containing a silver chloride layer and in which the top layer is not specially sensitized and the bottom layer is red-sensitized may be processed as follows. If the top layer is of silver chloride, after general development the bottom layer is exposed to red light from the back and developed blue-green, the top two layers are exposed to ultra-violet light, the silver chloride layer is colour developed and then the middle silver bromide layer is colour developed. Alternatively, all metallic silver is removed, the top two layers exposed from above to blue or white light, and the silver chloride and bromide layers successively developed by the successive action of weak and strong colour developers. If the middle layer is of silver chloride and there is no yellow filter, the material is similarly processed. If there is a filter in the top layer or between the top and middle layers, the lower layer is exposed to red and developed blue-green, the top layer is exposed to blue light and colour developed, and the middle layer is developed purple with a strongly alkaline colour developer. The latent image in the silver chloride layer only may be developed to silver with a weak ordinary developer followed by immediate development of the residual silver chloride with a weak colour developer not attacking the exposed silver bromide. The residual silver chloride may also be directly or indirectly converted into a coloured substance or a mordanting body. The two silver bromide layers are then simultaneously developed in an ordinary developer and the residual silver halide images successively colour developed, the rear layer being exposed to light to which it is selectively sensitive and colour developed, and the other layer being developed by a vigorous colour developer without exposure. The method may be applied if the silver chloride layer is in the middle and if the layers are on both sides of the support. If the silver chloride layer is in the middle, it is first selectively developed with a weak developer, treated with a mild reducing or sulphur-compound containing solution rendering residual silver chloride but not silver bromide developable, and the residual silver chloride colour developed, and then the two outer layers developed, and independently exposed to blue light and colour developed. The material may also be developed to silver, the residual silver chloride of the middle layer converted to silver ferrocyanide and thence to titanium ferrocyanide or nickel dimethylglyoxime or like complex compound, the two outer layers independently exposed and colour developed, the complex compound split, converted to silver bromide which is exposed to ultra-violet or X-rays and colour developed or which is developed without exposure by a vigorous colour developer, and all silver, ferrocyanides and filter dyes removed. The material may be developed, the residual silver chloride converted to silver ferrocyanide and reconverted to highly dispersed silver chloride which is colour developed without exposure, and then the other images are colour developed. The material may be developed, the residual silver halide of all layers made developable by ultra-violet or X-rays, the middle silver chloride selectively colour developed, the developing ability of the silver bromide destroyed by mild oxidizing agents, or byp-phenylenediamine and acid, light sensitivity restored by treatment with alkali sulphite or bisulphite or hydrazine or hydroxylamine or colour sensitivity created by treatment with weak ammoniacal solutions of colour sensitizers, and the outer layers independently exposed and colour developed. The middle silver chloride layer may also be developed, exposed to yellowgreen or red light, according to its sensitivity and colour developed, and the other two silver bromide layers developed and independently re-exposed and colour developed. If the yellow filter resists the first development and silver removing agents, the material is developed, silver removed, the middle and bottom layers simultaneously exposed to blue light, the residual silver chloride selectively colour developed, the bottom layer colour developed, and finally the top layer is colour developed, all silver being then removed. The top layer may be processed first. Material having a red or yellow-green sensitized silver bromide emulsion on one side of the support and a lower yellow-green or red-orange sensitized silver bromide emulsion and an upper blue-sensitive silver chloride emulsion on the other side of the support may be developed, reduced silver removed, and re-exposed. The residual silver chloride is colour developed, then the middle silver bromide, and finally the silver bromide on the other side of the support, followed by removal of silver. Treatment with thiourea or other fogging agent may replace the second exposure, or the latter may be effected with ultra-violet light. Modifications are described in which the red-sensitive emulsion is in the middle. Two-layer material may be employed, one of which is sensitized in strata with superficially-penetrating sensitizers. A yellow or red-orange filter may be placed between the coatings, which may be on the same or opposite sides of the film. A thin blue-sensitive silver chloride-gelatine or -collodion emulsion containing a decolourizable yellow dye is coated on the support, and over this a silver bromide gelatine emulsion containing erythrosin or other yellow-green sensitizer. A dilute or pure alcoholic solution of pinacyanol or other colloidal red-sensitizer is allowed to act on the latter layer. The swelled or previously hardened layer may be treated with a pure alcoholic solution applied with brushes, rollers, or sprays. Exposure is made through the support. In films coated on both sides, the support may be very thin, and development effected under conditions which prevent strong swelling of the gelatine, for example by addition of alcohol, sodium carbonate or sodium sulphate to the baths or by using developers containing a large quantity of alcohol. The lower layer of a three-layer plate or the middle layer of a film coated on both sides may be of silver halide collodion emulsion. Two layers on opposite layers of the support may consist of silver halide collodion emulsion. A layer of gelatine, dextrine, gum arabic or other - water-soluble colloid may be coated over the collodion emulsion and may serve also as the antihalation layer. The support may comprise thin films of cellulose acetate, regenerated cellulose, or synthetic colloids which may be lacquered on both sides. A thin film coated with emulsion on both sides may be temporarily mounted on permeable paper or aluminium foil. Thin regenerated cellulose or transparent paper, which may be glued on stronger paper. The residual silver halide of material having a silver bromide layer on one side of the support and silver chloride and silver bromide layers on the other side may be made developable with thiourea, the silver chloride is colour developed, and then the two silver bromide layers are processed independently. The silver chloride may first be selectively developed with a weak colour developer and the residual silver chloride converted to silver bromide, less light-sensitive than the original silver bromide layers. Tho silver bromide layers are