GB866070A - Improvements in or relating to printing elements - Google Patents

Abstract

866,070. Printing surfaces. KEMITYPE Ltd., and GROAK, J. June 19, 1957 [March 19, 1956], No. 8548/55. Class 100(2) A printing plate, block or cylinder has a negative relief printing surface, wherein the recessed portion of the surface is divided in depth into an upper step extending continuously over the whole area of that portion to a shallow depth and a lower discontinuous step constituted by closely spaced cavities in the floor of the upper step. The plate or the like may be formed by engraving or etching the upper step and subsequently engraving or etching the lower step. The plate may be of copper, the first etch being effected through a resist covering the non-printing portions of the plate and the second etch being effected through a resist screen or pattern of slots. The resists may be produced photomechanically. A second method of producing the plate consists of engraving or etching in the printing surface of the plate the portion which is to become the recessed portion to a depth equal to the combined depth of the steps, and the applying material non-uniformly to the floor of the recessed portion e.g. by spraying or electroplating. A third method of producing the plate consists of forming the cavities of the lower step 2 (Fig. 3(a) ) in a support 1 for the printing surface, filling the cavities with a material 3 (Fig. 3(b)) to the level of the non-printing portions of the plate, coating the latter portion 4 with a resist 4, etching away the material 3 from the recessed portions of the plate and finally removing the resist (Fig. 3(c) ). In the first method the first etch may be made through a coating of a hydrophilic metal (e.g. chromium, nickel or stainless steel) and the second etch through an underlying oleophilic metal (e.g. copper or a copper alloy). In the third method the support 1 may consist of an oleophilic metal and the material 3 of a hydrophilic metal. The recessed portions of such bi-metal plates are relatively shallow, the lower step being equal to not more than three times the depth of the upper step which is preferably about 0À005 mm. thick. Such plates may be used for planographic printing. For photogravure printing the depth of the upper step may be 0À0025-0À05 mm. thick, the depth of the lower step being greater than three times that of the upper. The purpose of the cavitied lower step is to "key" the ink to the recessed portions of the plate.