GB512951A - Improvements in processes of producing pitted surfaces for printing plates and the products thereof - Google Patents

Abstract

512,951. Electrolytic etching. JACKSON, L. MELLERSH-.(Norris, Inc., E. O. March 22, 1938, No. 8777. [A Specification was laid open to inspection under Sect. 91 of the Acts, June 14, 1939.] [Class 41] [Also in Group XX] Pitted or perforated metal surfaces for use in photo-mechanical printing processes, or as stencils, screens or sieves or as matrices for the electrodeposition of screens are prepared . by coating a metal surface with light-sensitive material, photographically printing a series of bands thereon by means of a line screen, and printing a second series of bands crossing the first series. The material of the bands is rendered impervious to an etching agent and the surface is then etched. Suitable material for the sensitive coating is gelatin, photo-engraver's glue, albumen, or gum, sensitized with ammonium or potassium bichromate. A second coating may be applied before the second set of bands is printed. The metal plate may be of copper and the etching agent may be iron perchloride. Electrolytic etching may be used. Where the second coating is of different material from the first, etching may be effected with both sets of bands present, then one set removed and further etching effected, resulting in a sheet as in Fig. 15 in which the surface 20 has ribs 32, 33 at different levels. The intermediate pits 31 may be filled with material resistant to electrolytic deposition and the sheet used for the deposition of a screen. Suitable resistant material is asphaltum, wax, or the material known under the Registered Trade Mark "Bakelite." The line screens used for the two printings may be different or a single screen in two successive positions may be used..