Patent GB-636222-A (GB)
Title: Photographic silver azo dye bleach-out process and bleaching baths for use therein
IPC: G03C7/28
Filed: 1947-06-11
Abstract: 636,222. Colour photography. GENERAL ANILINE & FILM CORPORATION. June 11, 1947, No. 15404. Convention date, Dec. 14, 1946. Drawings to Specification. [Class 98 (ii)] Image-wise destruction of an azo dye at the silver image of a photographic element is effected by an aqueous bleach-out bath containing as its essential components a silver salt former, a silver complex former incapable of reversible oxidation and reduction and consisting of quinolines of the formula or iso-quinolines of the formula in which X represents the atoms necessary to complete a benzo or naphtho ring system or the derivatives of such compounds in which a ring carbon atom is substituted by alkyl, alkoxy, hydroxy, amino or acylamino, and sufficient acid to provide a pH below 7. The silver salt formers are water soluble chlorides, bromides, iodides of which hydrogen halides and the sodium and potassium salts are specified ; of the silver complex formers which have the property of combining with silver salts to form complex salts, quinoline, iso-' quinoline, quinaldine, 6-methyl quinoline, 2,6- dimethyl quinoline, 6-methoxy quinoline, 8- hydroxyquinoline, 2,8-dimethoxyquinoline, 6- acetamidoquinoline, 2 - methyl - 6 - ethoxy quinoline, 5-aminoquinoline, 6-aminoquinoline, 8 - aminoquinoline, 6,7 - benzoquinoline, 7,8- benzoquinoline, 5,6-benzoquinoline, 1-methyl- 5,6-benzisoquinoline, and 6,7-benzisoquinoline are specified. The third essential component of the bleach-out bath may be sulphuric, hydrochloric, hydrobromic, hydriodic, phosphoric, nitric, sulphamic, formic, acetic, citric, oxalic, benzoic, p-toluene sulphonic, napthalene disulphonic, oxalic, maleic, tartaric, lactic or trichloracetic acid. Examples 1-4 specify bleach-out baths which include as ingredients the above-mentioned substances. Example - 5 describes exposure of a multilayer bleach-out material containing non-migrating yellow, magenta and cyan azo dyes in the blue, green and red-sensitive layers respectively under a colour transparency, development to a black and white image in a metol-quinol developer, fixation, hardening with aqueous sodium carbonate and formalin, dye-destruction in a bath comprising potassium iodide, quinoline, sodium hypophosphite and sulphuric acid, bleaching in an acidified solution containing copper sulphate, potassium bromide and fixing, to obtain a tricolour print. Examples 6-12 describe the bleach-out process as applied to films containing specified azo dyes. Examples 13, 14 describe the bleach-out process as applied to films containing colourless non-diffusing dyestuff components, which films are exposed and developed as in Example 5, treated in diazonium salt solutions to form azo dyes and then further processed as in Example 5, camera exposure being permissible. In example 15 an azo dye is introduced into a film after the exposure and development steps. The Specification as open to inspection under Sect. 91 comprises also the use of ferrocyanides, cyanides, thiocyanates and numerous heterocyclic compounds as silver salt formers, and of numerous additional heterocyclic compounds as silver complex formers, and has many more examples. This subject-matter does not appear in the Specification as accepted.