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 polycondensed cresol- formaldehyde resin. CONSTITUTION:A photosensitive layer contg. novolak resin and the o- naphthoquinonediazidosulfonic ester of resin prepd. by polycondensing cresol and/or phenol with aldehyde or ketone is formed on an Al platen 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. The cresol may be m-, p- or o-cresol but m-cresol is preferably used. Formaldehyde 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.