GB1373131A - Photographic silver halide products and diffusion transfer processes - Google Patents

Abstract

1373131 Photographic diffusion transfer film unit containing optical filter agent POLAROID CORP 18 Oct 1971 [23 Oct 1970(2)] 48274/71 Heading G2C A photographic film unit comprises a photosensitive silver halide layer having associated therewith dye image-forming material which is processing composition diffusible as a function of exposure, an image-receiving layer capable of receiving dye image-forming material diffusing to it, a layer between the silver halide and imagereceiving layers comprising an inorganic reflecting pigment e.g. titanium dioxide and at least one optical filter agent at a concentration effective to provide a complete barrier to incident actinic radiation when the filter agent is above its pKa, or means for forming such a layer, and means for reducing the pH from a first pH, which is above the pKa of the filter agent and at which the imageforming material is diffusible to a second pH which is below the pKa of the filter agent and at which the image-forming material is diffusible and after an interval sufficient to permit imageformation in the image-receiving layer, to a third pH at which the image-forming material is non- diffusible. The means for reducing the pH stepwise may comprise a neutralizing layer in the unit capable of reducing the pH from the first pH to the third pH and a buffering agent effective to hold the pH temporarily at the second pH. The buffering agent may be present in a layer adjacent in the image-receiving or photo-sensitive layers or in the processing composition. The buffering agent may be sodium orthosilicate, sodium metasilicate, fumed silica, a salt of salicylic acid or a salt of ethylenediamine tetraacetic acid. Alternatively, the means for reducing the pH stepwise may comprise an acidic additive in the film unit capable of reducing the pH from the first pH to the second pH and a neutralizing layer in the unit capable of reducing the pH from the second pH to the third pH. The acidic additive may be present in the photo-sensitive or image-receiving layers or a layer adjacent thereto and may be benzoic acid, salicylic acid, methyl sulphonamide or an acid salt of anti-foggant e.g. benzotriazole. The neutralizing layer may be a polymeric layer carrying acidic groups. The dye image-forming material may be a dye-developer