GB825866A - Method of making a lithographic printing plate suitable for lithographic printing and hardening solution therefor - Google Patents

Abstract

825,866. Photolithographic printing surfaces. KODAK Ltd. Oct. 23, 1956 [Oct. 25, 1955], No. 32226/56. Class 98(2) An unhardened gelatino-silver halide layer is imagewise exposed, treated to form a hardened gelatine image therein and then to transfer in the presence of moisture at least a thin stratum of the unexposed unhardened parts of the emulsion layer to a support bearing a layer having a hydrophilic surface, and the transferred emulsion is thereafter treated with a solution containing tannic acid and thiourea. The treating solution may contain sodium bisulphate. and other ingredients such as ascorbic acid, aluminium chloride, potassium bichromate, hydrochloric acid and chromium chloride. The hydrophilic surface may be given an alkaline wash before transfer of the emulsion parts thereto to prevent frilling and subsequent unsatisfactory, offset press results. Melamine-formaldehyde sized paper stock coated with gelatine-baryta containing a hardening agent such as formaldehyde or aluminium chloride, or pigmented-casein paper which may be over-coated with sodium alginate and then located as with a cuprammonium solution or zinc acetate may be used to form such surface. Exposure, processing and transfer of the unhardened emulsion may be by the methods of Specifications 655,274 and 725,667 wherein the original unhardened gelatino-silver halide layer may be one containing a tanning developing agent or this together with a non-tanning developing agent and the exposure is effected to a line or halftone image. Three examples are provided. Specification 726,543 also is referred to.