Patent GB-519790-A (GB)
Title: Colour photographic process
IPC: G03C7/32
Filed: 1938-10-01
Abstract: 519,790. Colour photography GASPAR, B. Oct. 1, 1938, No. 28617. [Class 98 (ii)] A filter dye present in at least one of the light-sensitive silver halide emulsion layers of a multilayer photographic material is uniformly chemically destroyed after the exposure of the material and transformed into a compound capable of coupling with the oxidation products of a colour developer to form a dye, and the developable silver salt in the layer is developed with such developer simultaneously with or subsequent to the formation of the coupler compound. The developable silver salt may be the original latent image, a developed and bleached silver image or the residual silver halide image remaining after the first development. The filter dye may be an azo dye or a dye of the kind described in Specification 506,385. In an example, a bipack comprises a front support carrying a blue-sensitive silver halide emulsion layer, and a rear support carrying an upper orthochromatic emulsion layer and a lower panchromatic emulsion layer the bipack being exposed through the front support and with the emulsion layers in contact. The orthochromatic layer is dyed yellow with the monazo dye obtained by coupling in alkaline solution 1 molecular part of diazotized sulphanilic acid with 1 molecular part of 1:1' - (4:4 - diphenylene) - bis - (3 - methyl - 5.- pyrazolone), and the panchromatic layer is dyed red violet with the monazo dye obtained by coupling in alkaline solution 1 molecular part of diazotized sulphanilic acid with 1 molecular part of 1:5 - dihydroxy - naphthalene. The two elements of the bipack are separated, developed. and fixed, and the two-layer 'film is treated to decolourize the filter dyes in a solution containing sodium hydrosulphite, anthraquinone- #-sulphonic acid, and sodium carbonate. After washing, the film is hardened with formaldehyde, washed, and the silver images bleached with cupric chloride solution. The film is colour developed with a developer comprising p-dimethylaminoaniline hydrochloride and sodium carbonate and the silver images are removed with Farmer's reducer. A magenta image is produced in the orthochromatic layer and a blue-green image is produced in the panchromatic layer. The positive material may comprise a support carrying on side a blue-sensitive emulsion layer containing a yellow coupling component and on the other side a green-sensitive layer containing a magenta coupling component and a red sensitive layer containing a bluegreen coupling component. The black-and-white blue component negative is printed on to the blue-sensitive emulsion layer, and the two colour component images on the rear support of the bipack are printed on to the emulsion layers of the opposite side of the three-layer positive material, and the latter is then colour developed. The positive material may also comprise a bluesensitive layer containing a yellow coupler such as a-chloracetoacetic ester and two other layers containing filter dyes as in the negative material. Alternatively the blue-sensitive layer may not contain a colour coupler and is then developed with a colour developer containing the colour coupler. The yellow filter dye 4:4'- methenyl - bis - (1 -p - sulphophenyl - 3 - methyl - 5-pyrazolone) is also suitable for use in the process according to the invention. The exposed film may also be treated directly with a colour developer such as alkaline p-dimethylaminoaniline. According to the Provisional Specification, the filter dyes may be diazotized after the exposure and coupled with azo-coupling components to form image - forming 'dyes either generally followed by treatment with a dyedestruction agent, or locally at the points of the silver image. Conversely the filter dyes mav be azo-coupling components and may be treated with diazo compounds. In another modification. the filter dyes may -be azo dyes containing aldehyde or ketone groups, and are transformed into image-forming dyes by treatment with hydrazines. In a further modification, the filter dyes may be coloured nitro or nitroso compounds which may be transformed into differently coloured image dyes as described in Specification 503.873. Nitroso compounds may also be treated with ferrous sulphate solution. Specification 506,385 also are referred to.