GB855610A - Improvements in or relating to planographic printing - Google Patents

Abstract

855,610. Photomechanical printing plates. AGFA A. G. June 23, 1959 [June 27, 1958], No. 21503/59. Class 98(2) A silver halide emulsion layer is exposed, developed, treated with a solution having a pH of 10 to 14 of an organic compound to convert the remaining silver halide into an organic silver compound which is more sparingly soluble than silver halide, and then treated with a fatty printing ink for planographic procedure. It is stated that the two treatments preferably take place in a single processing bath, but four examples use separate baths, thus in Example 1 a silver chloride emulsion of steep gradation is exposed behind a line or screen original, developed in a specified hydroquinone developer, rinsed for one hour and thereafter treated in a solution comprising water, propanol, caustic soda, potassium thiocyanate and N<1>-(N<3>-stearyl semicarbazide)-dithiocarboxylic acid methyl ester, rinsed again, clamped on a machine in which the ink is transferred directly to the paper, i.e. without interposition of a rubber blanket, inked by a few revolutions in the machine and then printed. Up to 200 copies are obtained. Examples 2 and 3 are similar but quote 1-amino-2-heptadecyl-5-mercapto-1, 3, 4 triazole and heptadecyl-7-hydroxy-2, 3, 4- triazaindolizine respectively as organic compounds. Example 4 has the organic compound of Example 1 in the developer for single bath treatment, and Example 5 this same compound in a separate bath but which also contains hypo. Numerous further organic compounds for the purpose, generally the same as those of Specification 847,436 which includes certain preparations thereof, are described. The process may be effected with negatives made by reflex exposure.