POSITIVE TYPE PHOTOSENSITIVE LITHOGRAPHIC PRINTING PLATE

摘要

PURPOSE:To make faithful the reproducibility of a tone and to improve the reproduction of min. dots by coating the layer of a positive type photosensitive compsn. having the specified absorption intersity after exposure onto an aluminum plate which is subjected to surface roughening and anodic oxidation treatment. CONSTITUTION:Such layer of the positive type photosensitive compsn. of which the absorption intensity at 400nm after exposure is >=0.06 for each 1mum is coated on the surface of the aluminum plate subjected to the surface roughening then to the anodic oxidation treatment. The aluminum plate is cleaned and degreased by trichloroethylene and then the surface thereof is sand-grained by using a nylon brush and 400 mesh pumice-water suspension. The aluminum plate is thereafter thoroughly washed with water. Such plate is immersed for 9sec in an aq. 25% sodium hydroxide soln. kept at 45 deg.C and is thereby etched. The plate is rinsed and is further immersed in a 20% nitric acid then the plate is rinsed. A DC anodic oxide film is provided on the plate with a 7% sulfuric acid as an electrolyte and thereafter the plate is rinsed and dried. The positive type photosensitive compsn. is coated on the aluminum plate and is dried by which the positive type lithographic printing plate is obtd.