GB570035A - Improvements in or relating to planographic printing plates - Google Patents

Abstract

570,035. Printing-surfaces. ADDRESSOGRAPH - MULTIGRAPH CORPORATION. Jan. 10, 1944, Nos. 434 and 435. Convention dates, Jan. 8, 1943, and April 28, 1943. [Class 100 (ii)] A parchmentized cellulose printing-plate is formed by superposing two webs 20, 21 of cellulose as delivered from a bath 23 of sulphuric acid, and after the webs are united by rolls 25, 26 passing the united web through a washing- chamber 27 and drying-chamber 28. In the finished product the outer sections 11, 12, Fig. 2, of the united web are converted to non-fibrous amyloid cellulose, and the junction layer 13 is also of non-fibrous amyloid cellulose and, owing to the greater extent of parchmentization, the layer 13 is thicker than the combined thickness of the layers 11, 12. The printing-plate has advantages over a known plate in which a cellulose layer is attached by adhesive to a backing of Craft paper in that the plate may be thinner, being of a thickness of about 0.004 inches, a ream of plates of dimension 24" X 36" weighing 60 lbs. Also, the plate retains its shape longer and is not spoilt by contamination with the adhesive. To treat the plate so as to have a low rate of lateral water diffusion the surface is subjected to an accelerated oxidation process by exposure to light rays, to anhydrous chlorine, or non-gaseous oxidizing agents. To prevent the development of ink-retentive spots due to the presence of resinous extractives in the wood pulp a visual test is made and only pulp having an upper limit of 0.5 per cent of resinous extractives is used, and treatment by ageing may render the resinous material immobile so as to prevent it from reaching the printing-surface. Specification 430,111 is referred to.