Patent GB-416566-A (GB)
Title: A method of producing coloured photographic images
IPC: G03C7/28
Filed: 1932-12-09
Abstract: 416,566. Colour photography. GASPAR, B., 38, Innsbruckerstrasse, Schoneberg, Berlin. Dec. 9, 1932, No. 34996. Convention date, Dec. 9, 1931. [Class 98 (ii).] Coloured photographic images are produced by incorporating in a light-sensitive silver halide layer colour formers, i.e. substances capable of forming a dyestuff or pigment and, after exposure, first converting the colour former into a colour, independently of the silver image, in such a manner as to colour the layer diffusely and subsequently selectively destroying the diffuse colour locally at the image or non-image portions. The images may be in monochrome or multicolour, a plurality of superposed layers or a mixture of different particles containing different colour formers and of differing colour-sensitivity being employed for the latter. The diffuse colour is obtained by suitable dyestuff or pigmentforming reactions and the local selective destruction is effected by oxidation or reduction, e.g., as described in Specifications 395,718, 397,159, 397,188, and 397,192. Colour formation may take place before, during or after image formation. Azo-dyes may be produced by incorporating phenols or coupling-components in the layer and subsequently developing with a diazonium salt, or diazonium salts may be incorporated in the layer and subsequently developed with phenols ; stable diazonium compounds e.g. diazo-amino compounds, triazines or nitrosamines, or hydragines or amines may be incorporated in the layer. In an example two superposed layers containing respectively the 2-phenyl-4-amino quinoline salts of S- and G-acids, after development of the silver image, are dyed respectively red and blue by treatment with 2-diazo-5-dimethylamino-4-methylphenyl sulphone, and converted into positive or negative dyestuff images by treatment in a dye-destroying bath. Leuco-bases or leuco esters, ester salts or ethers of vat dyestuffs may be incorporated in the sensitive layer and subsequently oxidized to the dyestuff which is then locally destroyed, e.g. in a thiocarbamide bath; to avoid re-formation of the dyestuff weak reducing agents, e.g. grape sugar are added to the solution or boric acid or other substance adapted to form a soluble complex. Leuco-bases may be treated with a single bath consisting of permanganate of potash and ammonium chloride which first causes diffuse dye formation and then, by continued action, results in the local destruction of the dye at the silver image points. Reference is also made to quinoneimine dyestuffs. A reversed naphthol green image may be formed by incorporating in the layer a nitroso-naphthol salt and subsequently developing with a ferrous salt, or vice versa; the naphthol green being locally destroyed at the points of the silver image by a thiocarbamide bath. The colour former itself may be a dye, e.g. an amido-azo dye. Thus a green-sensitive layer coloured yellow with amido-azo benzol is superposed on a layer coloured red-violet with Diazo Pure Blue B, the dyestuffs are diazotized with sodium nitrite and developed with #-naphthol to give an upper red, and a lower blue layer. A coloured pigment image may be obtained by incorporating an iron or lead salt in the layer converting the salt either to Prussianblue or lead chromate after fixation of the silver image and then locally destroying the colour by a thiocarbamide-citric acid bath. In a further modification, zinc ferricyamide is incorporated in the layer and the exposed material is developed with ferrous oxalate resulting in a silver image diffusely coloured with Prussian-blue which is then converted to a reversed pigment image. Multicolour images may be formed by incorporating in the emulsion a dye forming substance, e.g. a phenol which can be developed by different dye-forming reactions, e.g. with a diazo compound to form an azo dye or with a nitroso body to form an indephenal &c. ; or different layers may contain dye-forming substances of different groups, e.g. leuco ester and an amino compound which on treatment with sodium nitrite are respectively oxidized to the dye and converted into a diazo-compound, the latter being subsequently coupled with a suitable azo component. A leuco body may be simultaneously oxidized and a mineral pigment formed. The light sensitive layers containing the colour formers may be employed for ordinary or colour photography. Films may be employed for exposure or copying. The colour formers are generally such as to result in a colour similar or complementary to the colour-sensitiveness of the layer ; but the colours may be independent of the coloursensitiveness, particularly for the production of master images. Specifications 15055/12, 2562/13, 298,979, [all in Class 98 (ii)], 369,616, 376,795, 379,679, and 397,170, also are referred to. The Specification as open to inspection under Sect. 91 includes the subject-matter of Specification 416,660 and describes also a method involving development of colour simultaneously with the development of the silver image, e.g. by treating a layer containing a diazonium compound with a photographic developer containing a phenol. This subject-matter does not appear in this Specification as accepted.