Patent GB-1249040-A (GB)
Title: Photographic silver image production
Inventor: TINKER JOHN FRANK
IPC: G03C1/36
Filed: 1969-05-02
Abstract: 1,249,040. Photographic silver image production. EASTMAN KODAK CO. May 2, 1969 [May 2, 1968 (2)], No. 22546/69. Heading G2C. A method of producing two or more silver images in different portions of the area of a photographic silver halide layer comprises (a) preparing on a support a layer containing silver halide that can be made sensitive to light from part or all of the spectrum whilst in the layer, then successively, in each portion of the area of the layer where a silver image is to be formed, carrying out the following steps (b), (c) and (d), (b) making the silver halide in said portion of the area of the layer sensitive to light from said part or all of the spectrum respectively, (c) forming a latent image in said portion of the area of the layer using light from said part or all of the spectrum respectively, (d) making the silver halide in said portion insensitive to said light without affecting the latent image, except that the silver halide in the portion of the area of the layer wherein the final latent image is formed need not be rendered insensitive, and (e) simultaneously developing all the latent images formed in step (c). In each portion of the area of the layer, step (c) may be effected by passing a light image from a character along a bundle of optical fibres from the input plane of the bundle of optical fibres to the output plane thereof and thence to the layer; the latent images being formed and developed in steps (c) and (e) to produce a mask for character recognition. In step (a) a layer of vacuum deposited silver halide (e. g. silver bromide) may be formed contiguous to a vacuum deposited alkali metal halide layer (e. g. potassium bromide). A hydrophilic colloid layer which may contain a compound of the formula:- wherein Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing 5 to 6 atoms in the heterocyclic ring and SX is a mercapto function (which may be in the free -SH form or in salt form) may be formed over the vacuum deposited silver halide layer. Step (a) may be effected by coating a non-spectrally sensitized photographic silver halide emulsion on a support or forming a layer of vacuum deposited silver halide on a support, step (b) may be effected by sensitizing the silver halide in said portion of the area of the layer to a part of the spectrum using a spectral sensitizer and step (d) may be effected using a de-sensitizer such that the silver halide will not respond to light absorbed by the spectral sensitizer. Many spectral sensitizers are listed. The de-sensitizer may be a mercury salt, a rhodium salt, an anthraquinone dye containing a sulphoalkylaminosulphone radical, a non- heterocyclic aromatic compound containing at least one NO 2  group or a heterocyclic compound containing a S and/or N atom in the heterocyclic ring. Alternatively step (a) may be effected by coating a photographic silver halide emulsion on a support and incorporating a de-sensitizer in the emulsion before or after coating, or by forming a layer of vacuum-deposited silver halide on a support and applying a de-sensitizer thereto, step (b) may be effected by thermal resensitization of said portion of the layer and step (d) by using a desensitizer.