PHOTOSENSITIVE LITHOGRAPHIC PLATE

PURPOSE:To enhance image reproducibility an film strength, and to obtain high printing resistance by forming a photosensitive layer contg. a hydrophilic polymer having OH groups and a diazo compd. on an Al plate provided with a specified anodized layer. CONSTITUTION:The photosensitive layer contg. a hydrophilic polymer having OH groups, such as acrylamide having OH groups, and a diazo compd.is formed on the Al plate having the anodized layer obtained by anodizing Al in an electrolyte contg. phosphoric acid alone or as a main component and having an average bore diameter of 20-90nm and a bore density of 100-1,000/mum2. The diazo resin to be used is a condensation product of aldehyde and p-diazophenylamine represented by the formula shown on the right in which R , R , and R are each H, alkyl, or alkoxy; R is H, alkyl, or phenyl; X is PF6 or BF4; and n is an integer of 1-200. The photosensitive compsn. consisting of said polymer, said diazo resin, and necesary additives is applied to the Al plate to obtain a lithographic plate material. It is exposed to a light image of the object to be printed, and developed to obtain a printing plate, thus permitting the obtained plate to be high in film strength and printing resistance, to be erased well, and to be prevented from back ground stains, and superior in storage stability.