GB1411423A - Process for the production of printing surfaces on printing images carriers - Google Patents

Abstract

1411423 Facsimile reproduction P ZIMMER 4 Oct 1972 [7 Oct 1971] 45645/72 Heading H4F In a process for producing a printing block or member, wherein the scanning of an original at 16 controls the flashing on and off of a light source 9 continuously scanning a photosensitive element 1, to produce a reproduction of the original with a superimposed half tone screen effect, the element 1 comprises a highly photosensitive layer, e.g. of silver halide-gelatine or chrome-gelatine, overlying a relatively insensitive photosensitive layer, e.g. of positive or negative printing lacquer, on a support matrix. Following exposure of the upper layer only, by source 9, that layer is developed and the element exposed to an intense uniform exposure to transfer the pattern to the lower layer. Such exposure may be by uniform illumination, or by scanning over the entire element with a light source. Development of the lower layer may be followed by an etching step or an electrolytic deposition step (metallic matrix) to produce the final block. As particularly described, linearly moving photodetectors 17, 17<1> alternately scan the entire original, which is mounted on a rotating cylinder 16, so that linearly moving source 9 produces a series of reproductions along the length of a rotating cylindrical element 1. A unit 22 produces an odd number of pulses for every two rotations of element 1, such pulses, being gated by a unit 21 controlled by the output of photodetector 17 or 17<1>, and used to activate the light source. A hexagonal screen effect is thereby obtained. The pulses may alternatively be obtained from the drive motor 4, if of the stepping type. Reference is also made to projecting successive recording points at random intervals, to prevent moirÚ patterns, and to the production of flat printing stencils.