Patent GB-726543-A (GB)
Title: Improvements in processes of photographic reproduction
IPC: G03C5/315
Filed: 1953-01-21
Abstract: 726,543. Preparing lithographic printing plates. KODAK, Ltd. Jan. 21, 1953 [Jan. 21, 1952], No. 1827/53. Addition to 655,274. Class 98 (2). A lithographic printing plate is prepared by developing an exposed substantially unhardened light-sensitive silver salt emulsion layer in the presence of a tanning developing agent, and transferring in the presence of moisture at least a thin stratum of the unexposed and unhardened parts of the emulsion layer to a support bearing a layer having a hydrophilic surface. The tanning developing agent, which may be as described in Specification 655,273, may be incorporated in the emulsion and development effected by treatment with an alkali solution. The ink-receptivity of the transferred stratum may be increased by heating or by treatment with an alkali. The receiving support may be wood, paper, cloth, grained zinc, anodized aluminium, surfacehydrolysed cellulose ester (acetate) or synthetic resin (polyvinyl acetate), polyvinyl alcohol, gelatin, or casein, and may be pigmentcoated paper such as paper coated with a mixture of gelatin and baryta. The moisture absorption properties of the latter may be increased by moistening prior to transfer, by coating with gum arabic, or by hardening with an oxidizing solution such as acid dichromate solution containing tannic acid. Paper may be coated with a mixture of well-hardened casein and a pigment (e.g. clay or barium sulphate) and then with a layer containing gelatin and pigment. In example 1, paper sized with melamine-formaldehyde resin is coated with a mixture of gelatin and baryta containing as hardener formaldehyde or aluminium chloride and is hardened in an aqueous solution of hydrochloric acid, potassium dichromate, tannic acid, and saponin. Material as in the parent Specification is exposed, e.g. by reflex printing, developed in aqueous sodium carbonate solution containing urea, excess solution is removed by squeegeeing, and the material is pressed on to the hardened pigmented colloid surface and then removed. Ink-receptivity is improved by subjecting the printing element to dry heat, and the element may be treated, prior to inking, with a solution of zinc acetate and/or an aqueous solution of glycerin and phosphoric acid. Example 2 is similar, but the paper support is first coated with casein from a solution containing a spreading agent and formaldehyde. In example 3, sized paper is coated with a layer of a mixture of a hardened organic colloid (e.g. casein) and an inert pigment (clay or baryta) and, if desired, treated with a cuprammonium solution or a zinc acetate solution before, after, or during application to the pigmented casein coating of a sodium alginate coating. The procedure is otherwise similar to example 1. The tanning developing agent may be omitted from the emulsion and included in the alkaline developing solution, or the emulsion may contain a mixture of tanning and non-tanning developing agents as described in Specification 725,667. The emulsion may be a direct positive emulsion. The pigment of the pigmented receiving support may be also titanium oxide or carbon black, and the colloid polyvinyl alcohol, gum arabic, starch, albumin, methyl cellulose, cellulose sulphate, zein, or partially hydrolysed polyvinyl acetate. The hardened casein of example 3 may be coated on both sides of the paper, and may be replaced by a synthetic resin polymerized methyl methacrylate), cellulose ester (acetate), or rubber (natural or artificial rubber latex) applied from solution or aqueous dispersion.