Patent GB-1264313-A (GB)
IPC: G03F7/008
Filed: 1968-05-15
Abstract: 1,264,313. Colour photographic processes using stripping films. AGFA GEVAERT N. V. April 29, 1969 [May 15, 1968], No.23077/68. Heading G2C. A process for producing colour images comprises (i) transferring from a temporary support to a permanent support, a layer comprising a hydrophilic colloid, a non-diffusible and a substantially water insoluble colouring substance and a photo-sensitive compound which on exposure yields a product which hardens the colloid layer directly or on subsequent treatment with an oxidizing agent, the layer being pressed into contact with the permanent support in the presence of an aqueous liquid and the temporary support is then removed, (ii) exposing the photo-sensitive layer to an original and then, if necessary, treating the layer with an oxidizing agent, (iii) developing the exposed layer with an aqueous liquid to remove the unhardened areas and to leave a coloured relief image. Multicoloured images especially for colour printing proofs are produced by using layers of different colours and preferably by using colour separation negatives for exposure by steps (i)-(iii) and then repeating the above steps (i), (ii) and (iii) wherein the layer is transferred on to the coloured relief image and thus producing a multi-coloured image on the permanent support. Specified photosensitive compounds are ferric complex salts, e.g. ammonium ferric oxalate, which are reduced to ferrous ions on exposure and then treated with an oxidizing agent such as a peroxide or dichromate to oxidize the ferrous ion and tan the hydrophilic colloid having active hydrogen atoms e. g. gelatine. The layer may also contain vinyl monomers and/or cross-linking agents, e.g. W, W<SP>1</SP> -methylese-bis acrylamide, to improve the hardening of the image. Alternatively aryl compounds containing more than one azide group which harden the colloid on exposure may be used as the photo-sensitive compound. A layer containing all the ingredients of the photosensitive layer except the dye or pigment and plus a filler such as silica may be applied over the photo-sensitive layer on the temporary support so that on transfer the permanent support is not stained by the dye or pigment. In the examples, a light-sensitive layer containing gelatine, cyan pigment, potassium or ammonium ferric oxalate and optionally acrylamide and N, N<SP>1</SP> -bismethylene acrylamide when a screening dye is present, or 4, 4<SP>1</SP>-diazido stilbene-2, 2<SP>1</SP>- disulphonic acid and glycerol and optionally a screening dye is coated on a cellulose acetate temporary support and overcoated with a photosensitive layer not containing the pigment but optionally containing silica. The material is wetted and pressed on to a permanent support which may be a polyester support coated on both sides with a hydrophilic coating as in Appn. 44114/ 67 or an an aluminium support coated on both sides with hardened gelatine and the temporary support stripped off. The material is exposed to a cyan separation half-tone negative, treated with a peroxide (if a ferric salt is used), developed by washing with water and treated with aqueous alcohol to leave a cyan relief image. A similar photosensitive material on a temporary support containing a yellow instead of a cyan pigment is pressed while wet on to the cyan relief image and the process repeated using a yellow half-tone separation negative in the exposure step. The process is repeated using a magenta pigment and carbon black in the photo-sensitive layers to obtain a 4-colour proof on the permanent support.