Patent GB-416660-A (GB)
Title: Method of producing photographic colour images
IPC: G03C7/28
Filed: 1932-12-09
Abstract: 416,660. Colour photography. GASPAR, B., 38, Innsbruckerstrasse, Schoneberg, Berlin. Dec. 9, 1932, No. 23059/34. Convention date, Dec. 9, 1931. Divided out of 416,566. [Class 98 (ii).] Coloured photographic images are produced by incorporating in a light-sensitive silver halide emulsion layer a colour former, i.e., a substance capable of forming a dyestuff or pigment, and, after exposure and development, first destroying the colour former locally at the image or non-image places and then converting the remaining colour former into the colour independently of the silver image. The colour former may comprise a dye component, a pigment-forming salt, or a dyestuff, e.g. an amido-azo dye, which is convertible into a further dyestuff. Local selective destruction of the dye former is effected by oxidation or reduction, e.g. by the baths described in Specifications 395,718, 397,159, 397,188 and 397,192. The colour former may be applied to a single layer or to a number of superimposed part layers sensitized to different colours ; or may be in the form of different coloursensitive particles ; and may be applied to the silver halide emulsion by pressure or atomization and may be mixed with filter dyestuffs and sensitizers. Dyestuffs images may consist of nitro, nitroso, quinonimine or vat dyestuffs. Thus a naphthol green image is produced by incorporating in the emulsion a nitroso naphthol salt and subsequently treating the layer with a thiocarbamide solution which in the presence of the silver image reduces the nitroso group to an amino group ; a ferrous salt is then allowed to act on the unchanged nitroso body to form a reversed naphthol green image. Alternatively, a positive image may be obtained by incorporating a ferric salt in the layer, reducing the ferric to ferrous salt at the silver image points and then treating with a nitrosonaphthol compound. Nitrosodimethylaniline may be introduced into the layer and locally reduced at the silver image points by an acid thiocarbamide solution and the unreduced portion developed with alpha-naphthol ; alternatively, resorcin may be allowed to act on nitrosmethylaniline in the presence of tannin. For azo dyes, stable diazo compounds or stable products of conversion of diazo compounds, e.g. diazoamino compounds, triazines or nitrosamines are incorporated in the layer and are subsequently coupled, e.g. with alkaline phenols; the diazonium compounds are destroyed locally by oxidation or preferably by reduction to hydrazines. When employing dyestuffs as colour formers, e.g. amidoazo dyes, the colour is such as to transmit rays for which the layer is sensitized, e.g. a green-sensitive layer is coloured with a yellow dyestuff and a redsensitive layer with a red-violet dyestuff. Multilayer material, comprising layers situated on one or both sides of a support, may contain dyestuff forming substances which supply dyestuffs belonging to different groups. The light sensitive material may be employed for ordinary or colour photography and for exposure or copying purposes. The colour formers are generally such as result in a colour similar or complementary to the colour-sensitiveness of the layer ; but the colour may be independent of colour-sensitiveness, particularly for the production of master images. For copying, master images may comprise coloured part images or multicolour screen plates ; or copying may be effected as in Specification 397,170. Specifications 298,979, [Class 98 (ii)], 341,454, 379,679, and 416,566 also are referred to.