GB1298082A - Photographic products and diffusion transfer processes - Google Patents

Abstract

1298082 Photographic diffusion transfer process using light absorbing material POLAROID CORP 22 Dec 1969 [23 Dec 1968] 62244/69 Heading G2C A photographic film unit comprises, in order, a photo-sensitive silver halide emulsion, an image-receiving layer in which an image can be formed by diffusion transfer by development by an alkaline processing composition of the silver halide emulsion after exposure thereof, and a transparent support through which an image formed in the image-receiving layer can be viewed, and in which the film unit includes a layer, or means for forming a layer, between the emulsion layer and the image-receiving layer of a light reflecting agent effective to mask the silver halide emulsion when viewing through the transparent support, and in which the film unit includes a layer, or means for forming a layer, between the emulsion and the transparent element that contains a light-absorbing material that during at least the early stages of development will provide a light-absorbing barrier that prevents further exposure of the emulsion through the transparent support when exposed to actinic radiation and that after development will be rendered ineffective as a light-absorbing barrier and will either be colourless or will be immobilized on the silver halide side of the lightreflecting layer. An opaque support layer may be present on the side of the silver halide emulsion distant from the image-receiving layer or else an opaque sheet may be superposed after exposure. The film unit may contain an alkaline processing composition in a rupturable container. The rupturable container may be positioned to discharge its contents between the image-receiving layer and the silver halide emulsion and may contain the light-reflecting material. The light absorbing material may be present in the processing composition or in a transparent layer through which exposure is effected, the layer having an initial pH at which no visible light is absorbed. The light-absorbing material may be rendered colourless after development by change of pH in the unit due to the presence of a layer of acid reacting reagent in the film unit. Alternatively, the light-absorbing material may remain coloured after development and be mordanted to a layer in the film unit on the silver halide side of the light reflecting layer. The light-absorbing material may be an organic dye, e.g. a phthalein dye. The photo-sensitive silver halide emulsion may comprise at least two selectively sensitized silver halide emulsions each having associated therewith a dye image-forming material, e.g. a dye developer. This invention may also be used in the formation of silver transfer images.