The diffusion transfer process is well known in the art, and details thereof are hence omitted here. The transfer process is described in detail, for example, in A. Rott and E. Weyde, "Photographic Silver Halide Diffusion Processes", Focal Press (1972); J. Sturge, V. Walworth and A. Shepp, "Imaging Processes and Materials: Neblette's Eighth Edition", Van Nostrand Reinhold (1989), Chapter 6, "Instant Photography and Related Reprographic Processes"; and G. Haist, "Modern Photographic Processing Vol.2", John Wiley and Sons (1979), Chapter 8, "Diffusion Transfer". As described in detail in these references, many kinds of photographic materials can be produced by this diffusion transfer process. For example, it is known that a transferred image can be obtained by spreading a processing element comprising a highly viscous alkaline processing composition containing a developing agent and a silver halide solvent between superposed two elements, i.e., a photosensitive element comprising a support having coated thereon a silver halide emulsion and an image-receiving element comprising another support having provided thereon an image-receiving layer containing silver-precipitating nuclei.
In the above constitution, the photosensitive element is exposed to light and then superposed on the image-receiving element, with the processing element being spread therebetween. After a certain time period, the photosensitive and image-receiving elements are stripped apart to obtain a transferred image on the image-receiving element. Completing such a transferred image more rapidly is always desired.
Methods for accelerating the completion of a transferred image include a technique of using a highly reducing substance, e.g., hydroquinone or a derivative thereof, for the developing agent contained in the processing element and further using a substance which brings about a high dissolution rate, e.g., hypo, for the silver halide solvent; and a technique of changing the silver halide emulsion in the photosensitive element into an emulsion based on a silver halide having higher solubility, e.g., silver chloride or silver chlorobromide. However, the former technique is defective in that the transferred image is so instable that long-term storage thereof is impossible. This is mainly because oxidation products formed from the developing agent cause staining and the residual hypo causes sulfurization. For preventing such deterioration, it is necessary to coat the image surface with a layer of an antioxidant substance, e.g., poly(vinyl alcohol) containing an alkali neutralizer, immediately after image completion, resulting in complicated handling. The latter technique is defective in that it is unusable for photographing because of too low sensitivity, and that the transferred image has a low density since fogging tends to occur.