POSITIVE TYPE PHOTOSENSITIVE LITHOGRAPHIC PRINTING PLATE

摘要

PURPOSE:To obtain a printing plate having high printing resistance and satisfactory chemical resistance by forming a photosensitive layer contg. novolak resin and the o-naphthoquinonediazidosulfonic ester of a polycondensation product of polyhydric phenol. CONSTITUTION:A photosensitive layer contg. novolak resin and the o- naphthoquinonediazidosulfonic ester of resin prepd. by polycondensing polyhydric phenol with aldehyde or ketone is formed on an Al plate having an anodic oxide layer contg. 100-1,000 pores of 200-900Angstrom average diameter per 1mum<2> layer and formed by anodic oxidation in phosphoric acid or an electrolytic soln. contg. phosphoric acid as the principal component. Catechol or (methyl) resorcin is preferably used as the polyhydric phenol as one of the monomers of the stock polymer but the especially preferred phenol is pyrogallol. Acetone is preferably used as the ketone or aldehyde. Thus, a printing plate having satisfactory cleanability as well as the above-mentioned properties, causing no ground stain and also having wide development latitude can be obtd.