ORIGINAL PLATE FOR PLANOGRAPHIC PRINTING PLATE AND PROCESSING METHOD FOR THE SAME

摘要

PROBLEM TO BE SOLVED: To provide an original plate for a planographic printing plate which does not contaminate an optical system such as an exposer because ablation is prevented as a positive type original plate for an IR laser excellent in both scuffing resistance and sensitivity and capable of direct plate making particularly from digital signals of a computer or the like and to provide a processing method for the original plate. SOLUTION: In the multilayer original plate for a planographic printing plate obtained by disposing an alkali-soluble resin-containing layer and a positive type recording layer containing an IR absorbent and having solubility in an alkaline aqueous solution increased by exposure with infrared laser light in order on a support, the positive type recording layer contains an alkali-soluble novolak resin containing xylenol in a constitutional unit. The original plate is imagewise exposed and developed with an alkaline developing solution containing an organic compound having the action of a pH buffer and a base.