Patent GB-477524-A (GB)
Title: Improvements in and relating to colour photography
IPC: G03C7/28
Filed: 1936-06-29
Abstract: 477,524.. Colour photography. KODAK, Ltd. (Eastman Kodak Co.) June 29, 1936, Nos. 18020 and 28514. [Class 98 (ii)] A coloured image is produced in a gelatine layer diffusely dyed with a vat dye and containing a silver image by reducing the dye in the regions of the silver image with alkaline stannous chloride, alkaline alkali sulphide or alkaline alkali cyanide. Vat dyes referred to are (1) indigoid dyes such as Indigo, Thioindigo, Brilliant Indigo BASF /G. Brilliant Indigo BASF/4G, and 7:7<1>-dimethylindigo, (2) acylaminoanthraquinone dyes such as Indanthrene Yellow GK, and Algol Pink BBK, (3) polyanthraquinonylamine dyes such as Algol Red BTK, (4) anthraquinone hydroazine dyes such as Indanthrene Blue 5G and Caledon Blue 3G, (5) dyes such as Indanthrene Golden Yellow GK (either 3 : 4 : 8 : 9-dibenzpyrene-5 : 10-quinone or a halogen derivative of 4 : 5 : 8 : 9-dibenzpyrene-3: 10-quinone) and the dye prepared by oxidation of Algosol Golden Yellow 1GK, anthraquinone acridones such as Indanthrene Red-Violet RRK, and (6) Algol Yellow GC. A dispersion of the dye is formed in gelatine, mixed with the sensitive silver halide emulsion and coated on a support. After exposure, the photographic element is developed, washed, fixed in plain or acid hypo, washed, bleached in a solution decolourizing the dye in the region of the silver image, washed, treated with combined or separate oxidizing and fixing agents to remove silver, washed and dried. The element may have two or more such sensitive layers superimposed. The emulsion layers may be selectively colour sensitized or may be panchromatic. A modification applicable to a single emulsion layer or to the top layer of a two- or multi-layer material comprises the introduction of the dye into an initially uncoloured emulsion after exposure, development and fixing, by treatment with a solution of the leuco-dye and effecting atmospheric oxidation. The emulsions of three-layer material may be sensitized to the primary colours and dyed to the minus colours. The lowest layer only may be dyed and the upper images coloured by colour development or a vat dye introduced after development. A three-layer film may comprise a support and red-, green-, and blue-sensitized emulsions from the support outwards, the red-sensitized emulsion containing indigo, the green-sensitized emulsion Algol Pink BBK, and the blue-sensitized emulsion Algosol Golden Yellow 1GK or Indanthrene Golden Yellow GK. Clear gelatine layers may be interposed between the emulsion layers. The order of coating the layers may be reversed. Two layers may also be on one side of a support and one layer on the other. In an example a mixture of powdered Indigo, sodium hydrosulphite, and caustic potash is added to a weak solution of de-ashed gelatine, and the mixture is warmed in an air-tight container until the indigo is reduced. After filtering, the clear yellow solution is mixed with a warm solution of de-ashed gelatine, and the leucoindigo is reoxidized by potassium or ammonium persulphate or hydrogen peroxide. The gelatine solution is set, shredded, washed and remelted and the resulting colloidal dispersion of indigo is added to a red sensitive photographic emulsion and coated on a cellulose acetate support. A modified but similar procedure is described starting with Durindone Red B powder (Thioindigo). The resulting colloidal dispersion of Thioindigo is added to a green-sensitized photographic emulsion. A similar procedure is also described for the production of a colloidal dispersion of Algol Pink BBK. In another example, a solution of Algosol Golden Yellow 1GK, gelatine and sodium nitrite in water is acidified with hydrochloric acid, and to the resulting dye dispersion is added acidified gelatine solution, after which the mixture is made jointly alkaline with ammonia. After shredding and washing, the remelted dye dispersion is mixed with blue sensitive emulsion and coated on a transparent support. A colloidal dispersion of Indigo may similarly be prepared from Indigosol O. An exposed red-sensitized emulsion may be developed, washed, fixed, and washed, and the dye destroyed at the points of the silver image by a bath containing potassium sulphide and sodium hydroxide. After washing, the silver sulphide image is removed with 4 per cent potassium cyanide solution. The alkaline potassium sulphide solution may be replaced by a solution of potassium or other alkali cyanide. Pyridine is added to accelerate the action. The silver image may be removed by treatment with cupric chloride followed by hypo. The preferred dye-destruction bleaching agent comprises stannous chloride, sodium hydroxide, triethanolamine and anthraquinone. The silver image is removed by cupric chloride followed by hypo or potassium cyanide. The triethanolamine may be replaced by mono- or di-ethanolamine. The use of anthrahydroquinone is referred to. The layers may be used for printing from coloured or uncoloured component positives or negatives, using filters if necessary. Red, green and blue filters may be used in taking. The supports for the emulsion layers may be glass, cellulose ester, or paper. Specifications 446,234, 468,560, 475,784, 475,786, and 477,524 are referred to.