Patent GB-521833-A (GB)
Title: Production of coloured pictures
IPC: G03C7/26
Filed: 1938-10-22
Abstract: 521,833. Colour photography. SCHINZEL, K., and SCHINZEL, L. Oct. 22, 1938, No. 32572/39. Convention date, Oct. 22, 1937. Divided out of 521,746. [Class 98 (ii)] In an exposed and developed three-colour photographic material having on a single support three superimposed differentially coloursensitized silver halide emulsion layers and in which at least one of two emulsions on the same side of the support contains a salt of a vat dye forming substance, which salt has attached thereto an organic radical of high molecular weight incapable of being split off by sodium carbonate, the coloured images are formed in such layer or layers by a process which includes the step of oxidising the compound to the vat dye or destroying It or the vat dye formed therefrom by oxidation and using the developed silver or a conversion product thereof to cause such oxidation or destruction by oxidation to take place image-wise. The vat dye forming substance may be a salt-forming ester of a leuco vat dye, including a leuco azo vat dye or leuco triphenylmethane dye; stable forms of leuco vat dyes having salt-forming acid radicals; saltforming esters made from thioindoxyl or indoxyl or from compounds which on oxidation give lignone dyes ; or compounds derived from the anthrone form of anthraquinone dyes and having salt-forming acid radicals. The salt may be either a salt formed with a high molecular organic base incapable of being split off with sodium carbonate or a salt formed with any base from a leuco ester of sufficiently high molecular weight to prevent diffusion of the leuco ester even if this is liberated by hydrolysis. The unwanted dye or dye derivative is preferably finally washed out. The conversion of the reduced silver or residual silver halide to a chromate, bichromate, or hypochlorite is referred to. Manganese or lead peroxide or other insoluble oxidizers may be produced from rerrocyanides. The production of the peroxides may be effected in the presence of sodium carbonate by hydrogen peroxide or ammonium persulphate. Oxidizing agents referred to are acidified bromate, or solution of chloric or bromic acid. The silver may be converted to silver chromate and treated with hydrogen peroxide. A silver image superficially converted to vanadyl or lead ferrocyanide, 'or a silver plus ferric hydroxide image produced by development with pyrocatechol ferriate may be treated with acidified bromate or a chloric acid solution. The silver images may be converted to a mixture of silver and lead ferrocyanides by means of a lead intensifier, and the images are then treated for a short time with a very dilute solution of ammonium vanadate or pyrovanadate. The silver ferrocyanide may be previously removed. Silver phosphotungstate may be similarly treated with a vanadate or pyrovanadate. Other vanadium derivatives that may be used are orthovanadic acid, higher isopolyvanadic acids, heteropolyvanadic acids, and the complex acids with oxalates or tungstic, phosphorc, silicic, or molybdic acid. The use of vanadites is referred to. Vanadyl ferrocyanide images may be produced by a potassium ferricyanide and vanadyl oxalate bath, and the tanning action minimised by the addition of complex-forming compounds such as oxalic acid, oxalates, or tartrates. After conversion to vanadyl ferrocyanide, oxalic acid solution may be allowed to diffuse into the layers which are then treated with a dilute mineral acid and chlorate solution to oxidize the leuco compounds: The silver images may be converted to the ferrocyanide of vanadic oxide or of vanadium sesquioxide or may be treated with vanadic acid or with a mixture of vanadic acid and potassium ferricyanide or bichromate. The oxidation may be assisted by heating. Watersoluble inert salts may be added to the acidified chlorate solution to prevent diffusion of vanadic or pyrovanadic acid, and oxidizable substances such as sugar, alcohol, and potassium ferrocyanide may be added. Pyrocatechin or pyrogallol complex vanadium compounds may be used for development, alkaline earth or other precipitants may be added to precipitate the vanadium liberated by the development. 4-keto or 4-acylamino or 4-substituted derivatives in which the substituent cannot be eliminated of complex compounds of oxides of iron and di-, tri-, and quadri-valent vanadium with salicylic acid or - naphthol- 2- carboxylic acid may be used as coupling components, and on development with p-aminodimethylaniline the metal hydroxide is liberated and oxidizes to the vanadate which may be precipitated with alkaline earths. Other similar coupling compounds may be used. Molybdic acid may be used instead of vanadic acid. Iron salts may be used as catalysts in the oxidising action of chlorate or bromate solutions acidified with inorganic or strong acids on the leuco derivatives. A Prussian Blue image acts as such a catalyst. Complex coupling components containing iron, vanadium, or any other catalytic metal may be employed and p-aminodimethylaniline, another p-diamine, or p-aminophenol may be used for coupling development. The leuco forms of indamines or indophenols containing the catalytic metal may be used as developers. Metallic osmium may be .superficially deposited on a silver image by bathing in a solution of an osmiate or osmium double salt. A persulphate solution containing copper salts may be used as a dye destruction agent. The dyederivatives and the material may be as described in Specification 521,888. Specifications 313.209, [Class 2 (iii)], 379,679, 487,384, [Group IV], 500,826, 503,752, 512,559; 520,173, 521,834 and 523,296 also are referred to.