Patent GB-564446-A (GB)
Title: Improvements in the production of coloured photographic images
IPC: G03C7/28
Filed: 1943-03-25
Abstract: 564,446. Coloured photographic images. KODAK, Ltd. March 25, 1943, No. 4872. Convention date, July 10, 1942. [Class 98 (ii)] A coloured image is produced in a diffusely dyed layer containing a silver image by rehalogenizing the silver image, reconverting to a silver image, and thereafter locally destroying the dye in the region of the so-formed silver image with a reducing dye-destruction bath. In a modification, after dye-destruction, the silver is again rehalogenized and redeveloped, and any remaining dye destroyed image-wise, the process being repeatable any number of times. The material may comprise a single emulsion layer or a number of emulsion layers coated on one or both sides of a support, which may be of cellulosic material (which may be pigmented), synthetic resin, or paper. The emulsion layer or layers may contain a uniformly dispersed dye prior to exposure or a dye intermediate which may be converted to dye after exposure. Polyazo dyes as described in Specification 546,704 or vat dyes as described in Specification 477,524 may be used. Dyes specified are the azo dye formed by coupling tetrazotized 4 : 4<1>-diamino-3 : 3<1> : 6 : 6<1> - tetra - methyltriphenylmethane with N - heptoyl - H - acid, Diamine Golden Yellow, Brilliant Carmine LS, and the azo dye formed by coupling tetrazotized 4 : 4<1> - diaminotriphenylmethane with N - Lauroyl - H - acid. In three - layer material, the emulsion layers may contain dyes of colour roughly complementary to their sensitivity, or with dyes' that transmit the colours for which the layers are mainly sensitive. The material may be exposed in a camera or under a coloured positive or negative, e.g. it may be exposed to a colour transparency by a single exposure to tungsten light through suitable correcting filters or by three simultaneous or successive exposures to light transmitted by red, green and blue filters in a suitable ratio of times and intensities. The material is developed in a black-and-white developer, washed and fixed, the silver images are reconverted to silver halide (e.g. AgCl), the bleached silver images are redeveloped, and the dyes locally destroyed, e.g. in alkali stannite solution, or neutral, slightly acid, or slightly alkaline sodium hydrosulphite, with or without accelerators. In an example, the material comprises a cellulose ester or other support carrying red-, green- and blue-sensitive emulsion layers, and coloured cyan, magenta, and yellow with the dyes of Specification 546,704. A yellow filter layer, e.g. containing colloidal silver, is provided between the blue- and green-sensitive layers. Between the green- and red-sensitive layers is a colourless layer, e.g. of gelatin. After exposure to a colour transparency through suitable correcting filters, the material is developed in a metol-hydroquinone-borax developer, treated in an acetic acid stop-bath, fixed in a solution containing hypo, sodium sulphite, acetic acid, boric acid and potassium alum, treated in a cupric chloride-hydrochloric acid bleach bath, redeveloped in the initial developer, treated in a dye-destruction bath containing stannous chloride and sodium hydroxide, again treated in the bleach bath and fixed in the specified fixing bath. - Prior to removal of the silver, the steps of rehalogenizing, redeveloping and bleaching may be repeated. Alternative bleach baths comprise (a) quinone, hydrochloric acid and ethyl alcohol ; (b) ferric chloride and hydrochloric acid ; and (c) ammonium persulphate and hydrochloric acid. An organic solvent, e.g. tertiary butyl alcohol, may be added to the dye-destruction bath. Specifications 133,034, [Class 98 (ii)], 521,836, 521,837 and 553,566 also are referred to.