GB365091A - Improvements in or relating to the formation of printing blocks - Google Patents

Abstract

365,091. Photo-mechanical printing- surfaces. LUDVIGSEN, N., 2, Rue Louvois, Paris. Oct. 15, 1930, No. 30783. Convention date, May 2. [Class 98 (ii).] To obtain a process block with an etched "make-ready," and having as many different thicknesses as there are tones to be reproduced, a normally screened image resist is produced on the printing surface of the block, and on the rear surface of the block itself (or on a separate make-ready plate for use back to back therewith), a corresponding etching resist image in which the screen is non-existent in the high lights and weakened in the half-tones. The block (or both the block and the " make-ready ") is then etched sufficiently to etch normally the printing surface having the normally screened etching resist. The image used for the " makeready " is what is obtained by over-etching a plate with normally screened image resist to the point of undercutting the small dots in the high lights. This image or an ink impression from a plate thus over-etched may be used for the etching resist of the " make-ready." Alternatively this etching resist may be made by intensifying a normally screened negative (which is used for the etching resist of the printing surface) until the light zones disappear and the opacity and volume of the screen in the half-tones is weakened. This intensified negative is used to obtain the etching resist image for the " make-ready." The Figure illustrates the normally etched printing surface ml and the " make-ready " m<2> having no etching in the dark parts g and variable depths of etching in the half-tones f and high lights e.