GB705053A - Improvements in photomechanical printing surfaces and methods of producing the same - Google Patents

Abstract

705,053. Photomechanical printing surfaces. COATES BROS. & CO., Ltd., and BLACK, D. J. Feb. 1, 1950 [Feb. 10, 1949], No. 3647/49. Class 98(2) [Also in Group XVI] A chromium-surfaced copper, brass or zinc plate or cylinder is etched through a developed line or half-tone resist with a first etching liquid which will attack the chromium but not the underlying metal, and then the latter is etched through the resulting chromium stencil with a second etching liquid which will not attack the chromium. The result is, normally, an intaglio printing surface but if the underlying metal is only moderately deeply etched printing may be effected by lithographic means, using the ink refusing and water accepting property of chromium. A chromium plated copper sheet may be sensitized as with bichromated albumen, gum arabic, fish glue or polyvinyl alcohol, exposed under a positive, developed with water, stoved if desired, treated with hydrochloric acid, which may be modified as with glycerin, to etch the chromium, and then etching is continued with or without removal of the resist with ferric nitrate solution which acts on the exposed copper only. Dilute nitric acid or calcium or zinc nitrate may replace ferric nitrate as second etching liquid. Stagnation of the liquid during the second etch produces shallower depressions in smaller dot areas. Doctor lands for larger ink-receiving areas may result from the presence of small transparent dots in dark areas of a half-tone positive, or may be provided by exposure through a half-tone positive and a negative of the original screen in register, or by use of a cross stop in the camera when the screen image is being made. Specification 475,902, [Group XVI], is referred to.