Patent ID: 7244546

Claim:
The planographic printing method comprising: imagewise exposing, with an infrared laser, a planographic printing plate precursor including a substrate and an image recording layer provided thereon, the image recording layer being capable of recording through exposure to an infrared ray and comprising (A) an infrared absorbing agent, (B) a polymerization initiator comprising an onium salt formed by an onium cation and a carboxylic acid anion, where the carboxylic acid anion has an acid group, a hetero atom and an aromatic group, (C) a polymerizable compound and (D) a binder polymer; and removing unexposed areas of the exposed planographic printing plate precursor, which is set in a printer without being subjected to any developing process, by feeding an oil based ink and an aqueous component onto the planographic printing plate precursor in the printer, wherein the polymerization initiator (B) is a compound represented by Formula (1) below: wherein M + represents an onium cation, X represents N, S or O, R 1 and R 2 each independently represent a hydrogen atom or a monovalent substituent formed by a non-metal atom, R 3 represents a hydrogen atom or a monovalent organic group when X is N and is not present when X is S or O, Ar represents an aromatic group, and at least one of Ar and R 1 to R 3 has an acid group.