GB736849A - Improvements relating to dye bleach baths for color photography - Google Patents

Abstract

736,849. Photographic dye bleach baths; masking images. GENERAL ANILINE & FILM CORPORATION. Dec. 9,1953 [Dec. 10, 1952], No. 34294/53. Class 98 (2). A bath for bleaching a dye in the presence of a photographic silver image comprises an aqueous solution containing halide and hydrogen ions derived either from a water-soluble halide and a non-oxidizing mineral or water-soluble organic acid, or from a hydrogen halide, and, as an accelerator, a compound of the formula wherein A represents O or S, Z completes a carbocyclic ring of the benzene, naphthalene or phenanthene series and Z<SP>1</SP> completes a carbocyclic ring of the benzene, naphthalene or acenaphthene series. Many such compounds are specified including those wherein the carbocyclic rings contain substituents such as methyl, methoxy, ethoxy and chloro. The acid used may be hydrochloric, hydrobromic, hydriodic, sulphuric, sulphamic, phosphoric, boric, acetic, propionic, tartaric or citric acid or an aryl sulphonic acid. Where the acid does not contain halide ions these are added in the form of sodium, potassium or ammonium bromide, iodide or chloride. The pH of the solutions is preferably between 2 and 4. The formation of masking images in multilayer colour material is referred to. Thus, in Example VI a film base is coated in succession with a red sensitive silver halide emulsion containing a cyan colour former and dyed with Brilliant Purpurine 10B (reddish), a green sensitive silver halide emulsion containing a magenta colour former and dyed with Benzo Fast Yellow, a yellow filter layer and a blue sensitive silver halide emulsion containing a yellow colour former. Diphenyl biguanide hydrochloride is added to the red and green sensitive layers as a precipitant for the dyes. After exposure the film is colour developed, washed, short-stopped and bleached in an aqueous bath comprising benzofuro [2, 3-b] quinoxaline, acetic acid and potassium iodide to give positive yellow and reddish azo dye masking images in the green and red sensitive layers respectively, each layer containing also the normal negative yellow magenta or cyan image resulting from colour development. Any residual silver, including that in the blue sensitive layer is then bleached out with ferricyanide or copper chloride, followed by the usual fixer. Specifications 490,451, 514,955, 535,130, 651,124, 657,374 and 687,768 are referred to.