Patent GB-540969-A (GB)
Title: Improvements in multilayer colour photography
IPC: G03C7/28
Filed: 1940-02-16
Abstract: 540,969. Colour photography. KODAK, Ltd. (Eastman Kodak Co.). Feb. 16, 1940, No. 2965. [Class 98 (ii)] Multi-layer material has in some or all the layers dyes or dye formers suitable for the dyedestruction process, and in an intermediate layer or layers between a pair or pairs of adjacent emulsion layers (a) a filter dye not removable or not wholly removable by development and silver removal, but destructible in presence of metallic silver by a dye-destruction bath, and (b) an unfogged silver salt, for example silver chloride, of lower sensitivity than the emulsion layer and converted in reversal development step to metallic silver in an amount not substantially more than is necessary to effect destruction of the filter dye. The material is processed by reversal and the local dye-destruction then effected. The material may have a top blue-sensitive emulsion, a yellow filter layer, a middle green-sensitized emulsion, a red filter-layer, and a bottom red-sensitized emulsion. Either of the filter layers may be omitted. The material may be used in taking or printing and may be processed to false colours. The residual silver halide and the silver salt in the filter layer may be rendered developable by light exposure or chemical fogging. The filter dye should be more easily destructible than the image dyes. Suitable filter dyes are (a) the azo dye from tetrazotized benzidinesulphonic acid and 2- chloro-5-hydroxytoluene (yellow) ; (b) the azo dye from tetrazotized 3:31-dimethyl-4:41-diaminodiphenylmethane and 2-naphthol-3:6-disulphonic acid (magenta) ; and (c) Pontamine Sky Blue 6B (green). In an example, the material comprises an undyed blue-sensitive emulsion, a yellow-dyed emulsion of lower sensitivity than the colour-sensitized emulsions, a yellow dyed green-sensitized emulsion, a magenta-dyed bluesensitive emulsion, a magenta-dyed red-sensitized emulsion, and a support. The dye-destruction solution may be acid thiourea or hydrobromic acid containing 2-hydroxy-3-aminophenazine. The magenta dye may be the azo dye from tetrazotized 4 : 41-diamino-3 : 31 : 6 : 61-tetra-methyltriphenymethane and N-acetyl-H-acid. The yellow dye may be the di-n-propyl ether of the azo dye from tetrazotized 4 : 4<SP>1</SP>-diamino-stilbene-2 : 2<SP>1</SP> disulphonic acid and phenol. The second layer may be a deep-and ultra-violet sensitive silver chloride emulsion, or a very slow silver bromide emulsion. The top layer is silver bromide emulsion and may be dyed after reversal but before dye-destruction, or the image therein may be dyed after producing the other dyed images. If the material is used for the trial print, the red component negative is printed into the bluesensitive top layer by blue light, the blue component negative into the green sensitized layer by green light, and the green component negative into the red-sensitive layer by red light. The material is developed to black- and-white, washed, the negative silver images removed in a bath containing potassium dichromate, sulphuric acid and sodium sulphate, and the material washed, re-exposed to strong light, and re-developed to black-and-white. The top layer is dyed blue-green in a solution of Solophenyl Fast Blue Green BL slightly acidified with acetic acid, or with Niagara Blue G (the final fixing bath then containing a small quantity of pyridine or with Niagara Sky Blue 6B. The excess dye is squeezed off and the material treated in a dyedestruction bath containing thiourea, sulphuric acid, hydroquinone and chrome alum, or containing hydrochloric acid, sodium chloride, potassium bromide, diaminophenazine, and 2-hydroxy-3-amino-phenazine. The silver images are bleached in a cuparic chloride bath acidified with hydrochloric acid, and the material fixed, washed and dyed. Alternatively, the material is treated in a dye-destruction bath (without dyeing the top layer), the silver images bleached in a bleach-hardening bath containing potassium dichromate, acetic acid, potassium alum, potassium ferricyanide, and potassium bromide, the material fixed, and the top layer treated with a solution of a blue-green dye such as Alizarin Celesto B or Alizarin Uranol BB. Specifications 475,784 and 475,786 are referred to. The Provisional Specification refers also to dyed intermediate layers containing (a) metallic silver, such as colloidal silver, (b) silver salt reduced in the first development, (c) fogged silver helide, or (d) coloured colloidal silver. In case (d) the colloidal silver may act as the filter and the dye may have no significant filtering effect, serving only to effect removal of the colloidal silver in the dye-destruction bath. Specification 507,211 also is referred to.