Patent GB-525808-A (GB)
Title: Process for making natural colour photographs
IPC: G03C7/26
Filed: 1938-12-23
Abstract: 525,808. Colour photography. SCHINZEL, K., and SCHINZEL, L. Dec. 23, 1938, No. 23023/39. Convention date, Dec. 23, 1937. Divided out of 37402/38. [Class 98 (ii)] [Also in Group IV] A process for producing three-colour photographs, wherein at least one of the dye images is produced from a dye or a leuco derivative thereof in a photographic layer, includes the step of converting dye in the image or non- image areas or both into a leuco-cyanide. Thus, unwanted dye or leuco derivative may be converted into colourless leuco-cyanide, this being left in the finished photograph ; dye may be produced image-wise either in the silver or the residual silver halide areas and converted into colourless leuco-cyanide, whereafter the residual leuco-derivative is developed into dye. When the leuco-cyanide is not completely insoluble it may be converted into a phosphotungstate or a salt with a sulphonic acid of high molecular weight or with a sulphonic or carboxylic acid of the leuco base of the dye. The dye images may be formed by the processes described in Specifications 521,746, 521,833, 521,834, 521,835, 521,836, 521,837 or 521,888. The upper layer preferably contains a yellow azo dye such as an insoluble salt of Mordant yellow G for image formation by oxidation or reduction in the silver areas, or a reducible yellow filter dye. In examples (1) each silver halide emulsion layer contains a leuco base of a suitably coloured triphenylmethane dye and, after developing the silver image, such bases are oxidized selectively in the silver areas by acidified alkali chlorate or bromate solution to produce the dyes (cf., Specification 521,833) ; these are then converted, by treatment with a dilute solution of potassium cyanide, into colourless leuco cyanides or their insoluble salts, whereupon the residual leuco bases are oxidized to the dyes, e.g., by potassium bichromate or persulphate, in presence of a phosphotungstate or other precipitant ; (2) the layers contain leuco bases and, after developing the silver image, the residual silver halide is converted, as described in Specification 521,833, into an oxidizing agent, e.g., one comprising manganese peroxide, to a catalyst, e g. one comprising vanadium, whereby the leuco bases in the residual silver halide areas are oxidized to the dyes ; alternatively the residual silver halide may be reduced to silver by a developer which deposits thereon an oxidizing agent (cf., Specification 521,834) or a catalyst (cf., Specification 521,833) serving to oxidize the leuco bases to the dyes; these are then converted into the colourless leuco cyanides, while the leuco bases in the silver areas are oxidized to the dyes, e.g. as in (1) or by acidified alkaii bromate, preferably with simultaneous removal of the silver ; (3) the layers contain leuco bases and, after developing the silver image, the bases are oxidized with simultaneous removal of the silver (cf., Specification 524,552) and residual silver bromide is reduced to silver which, on treatment with acidified thiourea solution, reduces the dyes image-wise ; alternatively, residual silver chloride may be converted into an agent which reduces the dyes (cf., Specification 521,835) ; the unreduced dyes are then converted into colourless leuco cyanides and the reduced dyes are re-oxidized ; (4) each layer contains a colourless C-derivative of a suitably coloured triphenylmethane dye and, after developing the silver image, the dyes are regenerated by treatment with dilute mineral acid and either the dyes in the silver areas are reduced by acidified thiourea solution or the silver image is replaced by one of palladium and the dyes reduced by formic acid (cf., Specification 521,746) ; the unreduced dyes are then converted into the colourless leuco-cyanides and the reduced dyes are re-oxidized ; (5) the layers contain leuco bases and, after developing and fixing the silver image, the silver is converted, e.g. by the action of cupric chloride, into silver chloride, the leuco bases are oxidized to the dyes as in (1), the silver chloride is reduced to silver, the dyes in the silver areas are reduced by thiourea, the unreduced dyes are converted into the leucocyanides and the reduced dyes are re-oxidized ; (6) a condensation product of 1:2-naphtholcarboxylic acid chloride with an aminomalachite green (e.g. obtained by condensing 3-nitrobenzaldehyde (1 mol.) with dimethylaniline.(2 mols.) and reducing the nitro group), or with a red triphenylmethane dye having a free amino or hydroxy group (e.g. fuchsine) is incorporated in the emulsion, the silver image is developed, e.g., with an aromatic amine in alkaline solution and the residual unused component and the indophenol are converted into colourless and coloured leuco-cyanides respectively ; (7) a condensation product of dibromosalicylic acid chloride with aminoleuco-malachite green (obtained as in (6)) is similarly incorporated and the image developed with a dichloro-p-aminophenol or p-aminodiethylaniline ; on treatment with acid, in presence of a'phosphotungstate, the coupled leuco compound is oxidized by the quinone, whereupon the oxidation product is converted into the colourless leuco-cyanide and the non- coupled leuco compound is then oxidized to the dye. Leuco bases used in the layers must be in an insoluble or difficulty diffusible form, e.g. as insoluble salts, e.g. with diphenylguanidine, cinchonine, polyallylamine, polyethylene diamines, quaternary quinolinium or cetylammonium salts or the product of condensation of quinine with polyallyl chloride or polyacrylic acid chloride, or as derivatives of high molecular weight (cf Specification 503,752) or alkali salts of their sulphonic or carboxylic acids, e.g. an amino-Malachite Green, obtained as in (6) above, or a hydroxy-Malachite Green, obtained by condensing salicyl aldehyde (1 mol.) with dimethylaniline (2 mols.) or pamino benzyl-fuchsine may be condensed with oc-bromostearoyl bromide,'the product treated with sodium sulphite to replace the #-bromine atoms by the sulphonic group and converted into a difficultly diffusible alkali sulphonate. Azotriarylmethane dyes or azo derivatives of leuco-auramines, of safranine or of indamine in all of which the azo linkage is split on reduction may be used ; the liberated triarylmethane dye then yields a colourless leuco-cyanide in contrast with the coloured leuco-cyanide from the unreduced dye. Leuco bases or dyes suitably coloured to function as filter dyes may be used for image formation, e.g. there may be used azotriphenylmethane dyes yielding coloured leuco-cyanides or colourless leuco-cyanides oxidizable to coloured cyanides, trypaflavine (yellow), pyronine (red), azo-pyronines, azoacridines, azo-safranines, flavindulines, or products of reaction of Michler's hydrol with azo dyes, nitroso compounds or quinones. Non- diffusing sensitizing dyes are preferably used, e.g. phthalein, pinaflavol, cyanine or isocyanine dyes carrying substituents of high molecular weight introduced, for example, by reaction of amino groups with stearyl chloride or #- bromostearic acid, by converting a hydroxy into a cetyloxy group, by treatment with cetyl iodide, cetyl p-toluenesulphonate, higher esters of bromoacetic acid or esters of oc-bromostearic or cetylsulphonic acid to produce quaternary ammonium salts. Alternatively difficultly diffusible alkali or ammonium salts of sulphonic or carboxylic acid derivatives of the sensitizing dyes may be used. Specification 477,524 also is referred to. The Specification as open to inspection under Sect. 91 comprises also the subject-matter of Specifications 524,552. 524,553, and 525,810. This subject-matter does not appear in the Specification as accepted.