GB916499A - Manufacture of printing plates and transparencies - Google Patents

Abstract

916,499. Electrophotographic production of printing plates. DELMONT Ltd., S. R. March 23, 1959 [March 24, 1958 ; Dec. 5, 1958], No. 9996/59. Drawings to Specification. Class 98 (2). [Also in Group XVI] A method of manufacturing printing plates comprises producing an electrostatic image on a continuous film of a photo-conductor substance substantially free of impurities and without bonding agents, which substance is applied to a base, developing the image, dissolving the photo-conductor substance, in areas not protected by the developer, in a solvent which does not attack the base or the developer, and treating the base where not protected by the photoconductor substance, the remaining photo-conductor substance acting as a resist for the subsequent treatment. A printing plate is formed by coating a zinc or magnesium block with a photo-conductive layer such as amorphous selenium, forming a developed electrostatic image thereon, dissolving out the photoconductive material where not protected by the developer with carbon disulphide, and etching the metal where now exposed with dilute nitric acid. Alternatively, the assembly with the developed image is exposed to infra-red radiation, which changes the selenium from the amorphous into hexagonal or crystalline form which does not act as an etching resist. The developer may contain radiation-absorbent particles, in which case the selenium is changed in the image areas, or may contain radiationreflective particles, so that the non-image areas are affected. Alternatively, the unchanged selenium can be dissolved away in carbon disulphide, and an etching solution used which does not attack the changed selenium. In another form, a photo-sensitive plastic plate is provided with a selenium or anthracene sulphur photo-conductive coating, on which the developed electrostatic image is formed to form a light mask. On exposure to light, the unprotected areas of the plastic plate are polymerized, and the unpolymerized parts etched away with alcohol or ethyl acetate and alcohol. The polymerizable element may comprise nylon glue. Polymerization may also be by heat. An offset printing plate is made from a steel base sheet coated with copper, then with chromium. The electrostatic image is formed and developed on a selenium coating on the copper, the unprotected selenium removed, and the chromium etched away where the selenium has been rembved. After removing the remaining selenium or developer, there is left a bimetallic plate.