Patent GB-498875-A (GB)
Title: Process of colour photography
IPC: G03C7/26
Filed: 1937-05-10
Abstract: 498,875. Colour photography. KODAK, Ltd. May 10, 1937, No. 35101/38. Convention date, May 9, 1936. Divided out of 500,826. [Class 98 (ii)] In a process of three-colour photography, in which three colour component silver salt images on a single support are processed to different colours, one image is converted into a dye image with a developer consisting of an alkaline solution or suspension of a leuco vat dye and the developed silver is subsequently removed. Two or more of the images may be developed in this manner. Leuco vat dyes referred to are indigo white ; thioindigo white ; selenoindigo white ; aminothioindigo white : highly halogenated thioindigos reduced in the presence of a small quantity of alkali; leuco derivatives of vat dyes giving difficultly soluble alkali salts such as dinaphthacridonequinone, anthraquinonethioxanthones, #- tetrahydroflavanthrene, its dimethoxy and acylamino derivatives, dihydrophenanthridine yellow, and dihydropyranthrone and its dimethyl derivatives : thionylindigo white ; 2: 2<1>-diphenylthioindigo white ; N.N<1>-diphenylindigo white ; N.N<1>-dimethylindigo white; 2: 2<1>-dibenzoylthioindigo white; leuco-#-pyrindigo; the diisobarbituric acid from 5-aminouracil ; diaminodinaphthylene oxide; completely or partially reduced dibenzothianthrene diquinone; anthranol and anthrone forms of aminoanthraquinones, including acylated, alkoxy, arylhydroxy, and acylhydroxy derivatives and also aminoanthraquinones with heterocyclic rings attached ; dianthranol ; tetrahydrohelianthrone ; and the condensation products from two molecules of indoxyl, thioindoxyl, hydroxyselenonaphthene with one molecule of a saturated or unsaturated aliphatic or aromatic-dialdehyde. Excess of potassium bromide or at least 2 per cent of potassium iodide is added to the developer. Development may be effected with complete exclusion of atmospheric oxygen, the air in the developing apparatus being replaced by nitrogen or illuminating gas. The operator may wear a gas mask. Alternatively the developing solution may be covered with a layer of benzene or petroleum, the exposed film being passed into the developing solution without contact with this layer. Excess of sodium hydrosulphite in the preparation of developing solutions may be rendered inactive by addition of formaldehyde or non-tanning aldehyde. Alkaline or ammoniacal solutions of the leuco vat dyes may be used for the formation of the last, for example of the middle, component image in a three-layer element, without reexposure. The images in a multilayer material may be successively developed with leuco vat dyes, each developer having a lower reduction potential than the one employed for a previously developed layer. The lower image may be developed to indigo and the noddle image with a leuco highly halogenated indigoid dye for example leuco 6 : 6<1>-dihalogenated indigo, containing no excess of alkali or containing sodium carbonate. The developing solutions may contain alcohol or acetone in addition to alkali. Inorganic alkali may be replaced by aliphatic amines, ethylene diamine or other inorganic base, using alcoholic or acetonic solutions. A blue-green or purple image may be produced in the uppermost red or green-sensitive emulsion of a threelayer element by an aqueous suspension of indigo white or thioindigo white containing boric acid and used after addition of potash or sodium carbonate. The magnesium salts of leuco vat dyes, and the difficultly soluble alkali salts of highly halogenated indigo! and thio indigo dyes and higher molecular vat dyes may be used for development. Aqueous suspensions or alcoholic or acetonic solutions of the leuco vat dyes containing aromatic amines reduced silver chloride either unexposed, exposed or treated with thiourea or other fogging agent. In reversal, the last developed middle layer of a three-layer element may be developed without exposure by an alkaline, alcoholic or acetonic solution of a leuco vat dye. The Specification as open to inspection under Sect. 91 comprises also the use of leuco-indophenols, leuco-indamines and leuco-azomethines and refers to the use of hydrated dinaphthacene diquinone, dihalide perylene-3: 10- hydroquinone, and dibenzoylamino-9: 10-perylene hydroquinone, and to the use of indoxyl and its derivatives and analogues. This subjectmatter does not appear in the Specification as accepted.