Patent GB-746686-A (GB)
Title: Photographic colour reproduction process
IPC: A47K10/22
Filed: 1954-01-21
Abstract: 746,686. Colour photography. KODAK, Ltd. Jan. 21, 1954 [Jan. 22, 1953], No. 1786/54. Drawings to Specification. Class 98 (2). A multicolour image is made by transfer of colour yielding substances from a single photographic representation to an absorbent receiving sheet, by exposing to a coloured subject an element containing at least two differentially colour sensitized silver halide emulsions, each having a potentially diffusible colouring material which is non-wandering during coating and negative development, but which is rendered diffusible in unexposed regions after development so that the transfer may be effected. The element may be of multilayer or mixed grain type. The potentially diffusible colouring materials may be colour couplers containing heavy metal salts of imino, mercapto or thioglycolyl groups as of Specifications 524,557, 577,804, 577,812 or 595,844, to be rendered diffusible after development by acidfixing solutions and to produce dyes in the receiving sheet by the presence of an oxidized colour developer. or of a diazonium salt, therein; or such colouring materials may be water-insoluble salts of acid dyes, to be retained in exposed emulsion areas by use of tanning developers and released from unexposed emulsion areas by the presence of alkali on the absorbent receiving surface. The particular colour produced by the colouring material at the negative silver areas, if any, is immaterial, and the invention operates equally if colour formers are rendered incapable of forming a dye, or if dyes are rendered colourless, at such areas; the requirement being the production of colours in subtractive relation at unexposed areas in conjunction with the receiving sheet. A developing agent, and if desired a different one for each of the several emulsions, may be present in the element, so that following exposure development may be initiated with an alkaline solution. Two specific examples describe, respectively, the procedure using heavy metal salts of couplers and using acid dyes; thus example 1 describes the precipitation of silver chloride into gelatin solution, addition of couplers to portions of the resulting dispersion to form silver salts of the couplers, combination of the coupler salt dispersions with light-sensitive emulsions, and coating on film base in the usual sequence to result in layers (1) red-sensitized bromo-iodide gelatin emulsion with the salt of 5-chloro-2- hydroxy-4-methylthioglycolic anilide; (2) greensensitized bromoiodide emulsion with the salt of p - acetylthioglycolyl - amino - # - cyanoacetophenone, and following the yellow filter layer (3) a blue-sensitive emulsion with the salt of #-benzoyl-4-(p-acetyl-mercaptoethanesulphonamide) acetanilide. The film is exposed, colour developed, treated in a non-hardening acid fixing bath to remove unused silver halide and also to remove silver from unused couplers in unexposed areas of the film, washed, and pressed while still moist on to a receiving sheet as of baryta coated paper containing sodium triphosphate to provide an imprint of the couplers on such sheet, which is then treated in a colour developer and in an oxidizing solution as of potassium ferricyanide to enable the oxidation products of the developing agent to couple with the couplers and provide the multicolour image. The transfer procedure may be repeated to get another copy. Variations of the process of example 1 include contacting of the exposed element after colour development but before fixing with a receiving sheet containing a silver halide solvent such as hypo together with alkali and treatment of the transferred coupler salts with a colour developing agent and an oxidizing bath to yield the dye images, and then fixing and bleaching to remove silver salts therefrom. Another variation lies in immobilization of the colour couplers in the exposed regions of the light-sensitive element by treatment with a tanning developer instead of a colour developer. Mixed grain or mixed packet assemblies as of Specifications 637,030 and 711,488 but using metal salts of couplers as described above may be treated by the process of example 1. Example 2 is directed particularly to a two-colour procedure using red and green sensitized emulsion layers containing respectively the barium salts of 4 : 8 - diamino - 1 : 5 - dihydroxy anthraquinone-2 : 6-disulphonic acid and 6-amino-1- hydroxy - 2 - p - sulphophenylazonaphthalene- 3-sulphonic acid, and such a film is treated in a pyrogallol tanning developer after exposure and subsequently squeezed against a baryta coated sheet containing an acid dye mordant such as a quaternized polyvinyl pyridine as described in Specification 654,267, [Group IV (a)], in the presence of acid to solubilize the dyes in unexposed areas of the film for transfer. Anthraquinone, azo and safranine dyes containing primary amino groups are particularly useful in this process since oxidized developing agent appears to react with such amino groups to form non-diffusible compounds in the exposed areas. Specification 536,577 also is referred to.