Patent GB-1186195-A (GB)
Title: Photomechanical Processes.
Inventor: MAURER RICHARD EDWIN
IPC: G03C1/46
Filed: 1967-09-01
Abstract: 1,186,195. Corrected photographic colour separation images. EASTMAN KODAK CO. Sept. 1, 1967 [Sept.1, 1966], No.40105/67. Heading G2C. A process for making a colour-and tonecorrected photographic colour separation image for use in preparing a colour printing plate comprises (a) exposing to a multi-colour original a black-and-white photographic material comprising a transparent support bearing a first silver halide emulsion layer sensitive to at least one colour region corresponding to the said separation, said layer having superposed thereon a removable second silver halide emulsion layer sensitive to at least one colour region different from said first layer, the exposure being made through the support, (b) developing the exposed material with aqueous alkaline solution in the presence of a developing agent, the material and/or the solution being such that the development of the image in the first layer is inhibited in proportion to the image in the second layer sufficiently to correct the first image to the desired degree and (c) removing the second emulsion layer from the material. The second emulsion layer may be strippable, a separate stripping layer being coated between the two emulsion layers, or it may be removed by washing with warm water if a low-jelly strength gelatine or polyvinyl alcohol or cellulose ether phthalate is used as the second emulsion binder. To correct for an unwanted absorption in a printing ink, the printing plate of the colour complementary to the unwanted absorption is corrected so that the coloursensitivity of the first emulsion layer is the same as that of the unwanted absorption and the removable second emulsion layer is chosen to be complementary to the colour of the printing ink in which the unwanted absorption occurs. Thus a separation image for a cyan printing plate which corrects for unwanted red absorption in the magenta ink has a first emulsion layer sensitive to red and the removable second layer sensitive to green. One or both of the emulsion layers may be sensitive to other colour regions of the spectrum but such light may be filtered off using external filters or filters integral with the material, e.g. on the back of the support or between the emulsion layers as required. The material may also include antihalation and u/vabsorbing layers. The inhibition of the development of the image in the first emulsion layer by the development of the image in the second emulsion layer may be effected by using a second emulsion layer which contains a higher mole per cent of silver iodide than the first emulsion layer, by incorporating developing agents in the layers and adjusting the kind and amount of the agents so that the degree of development in the lower layer is a function of the depletion of the developing agent in the upper layer, by using development-inhibitor-releasing couplers such as those of Specification 953, 454 or inhibitorreleasing developers such as those of 1, 066, 352 and 1, 066, 991 or by utilizing non-metallic development by-products according to U.S.A. Specification 2, 712, 995.