Patent GB-521746-A (GB)
Title: Production of coloured pictures
IPC: G03C7/28
Filed: 1938-10-22
Abstract: 521,746. Colour photography. SCHINZEL, K., and SCHINZEL, L. Oct. 22, 1938, No. 30576. Convention date, Oct. 22, 1937. [Class 98 (ii)] In the production of a three-colour photograph in material having on a single support three differentially colour - sensitized silver halide emulsions at least one of which contains initially an azo vat dye or azo vat dye derivative, after exposure to a coloured object or image, coloured images are produced in such emulsion or emulsions by a process which includes the step of treating the material to split the azo bond of the azo vat dye by reduction to yield a simple vat dye not containing an azo group. Azo triphenylmethane and azo lignone dyes may be used. Preferably the residual azo vat dye derivative is finally washed out. The azo vat dyes or their leuco esters are made from azo coupling components containing solubilizing hydroxyl or sulphonic or carboxylic acid groups. The azo vat dye may have a colour complementary to that of the parent vat dye. In an example, the bottom red-sensitive layer contains a red or yellow coloured azoindigosol, the middle green-sensitive layer a green or yellow coloured azo-indigosol and the top layer a yellow indigosol or its insoluble salt. After exposure and development the material is treated in a thiourea bath to split the azo bond of the azo indigosols, the vat dyes are formed in the areas containing silver by oxidation, and the unwanted azo vat dyes removed by treatment with sodium carbonate. The first developer may be neutral, such as ferrous oxalate, amidol, or hydroquinone-acetone bisulphite. The azo indigosols may be added to the emulsions as their insoluble salts with diphenylguanidine, cinchonine, auramine thioflavine, or trypaflavine. Other compounds which may be used are (a) the coupling products of diazotized amino- or aminohydroxy-anthraquinone with α- or #-naphthol sulphonic or 2-carboxylic acid, (b) the coupling products of diazotized meso anthramine or anthrone with a naphtholderivative, and (c) the coupling products of diazo compounds containing free hydroxyl or carboxylic or sulphonic acid groups with the stable leuco ester of vat dyes formed with sulphonic or carboxylic acid chlorides. The reduction is preferably done in the absence of atmospheric oxygen and may be effected at a raised temperature if the emulsion is tanned or the gelatine is replaced by such colloids as collodion or acetyl cellulose, In another example the material is developed and palladium is precipitated superficially on the silver image from a palladium salt or double salt solution. The reduction is effected by treatment with a 1 to 5 per cent. formic acid solution. Numerous dye derivatives suitable for the production of azo vat dyes or azo vat derivatives are referred to. In a further example of the three-layer material the top layer contains a yellow vat dye, the middle layer contains a yellow azo vat dye derived from a purple vat dye, and the bottom layer contains a yellow or red azo vat dye derived from a greenish blue vat dye. After exposure and development, the azo double bonds are split diffusely by a non-alkaline reducing bath to form simple vat dyes which are then locally reduced with a potassium cyanide bath according to Specification 521,836 or by means of a reducing compound deposited on the image areas according to Specifications 521,835 or 521,837. Derivatives of high molecular vat dyes may be used. In kinematograph films the unwanted derivatives may be left in the emulsion and actinic light filtered out in projection. Leuco azo vat dyes may be diffusely oxidized, the azo-bond split by reduction, and dye-destruction effected by alkaline potassium cyanide. The image formation may be effected catalytically using vanadium, iron, or osmium. The colour sensitizers may be rendered insoluble by precipitants and the emulsions may be saturated with excess of precipitants for colour sensitizers and filter-dyes. In reduction with acidified thiourea solution betaine hydrochloride may be used as the acid. In the use of azotriphenylmethane derivatives, precipitants such as phosphotungstates are added to the processing baths. Specifications 397,159, 416,566, 432,464, 500,826, 503,752, 512,559, 520,173, and 523,296 also are referred to. The Specification as open to inspection under Sect. 91 comprises also the subject-matter of Specifications 521,833, 521,834, 521,835, 521,836, 521,837, and 521, 888. This subject-matter does not appear in the Specification as accepted.