Patent ID: 7074542

Claim:
A negative planographic printing plate precursor which is capable of directly making a printing plate using an infrared laser comprising: a substrate; a photosensitive layer disposed on the substrate, the photosensitive layer including a light-to-heat conversion agent and a compound, which is at least one of crosslinkable and polymerizable, with solubility of the photosensitive layer in an alkali developing solution being decreased by the effect of at least one of light and heat; and an overcoat layer including a polymer, which is hydrophobic and soluble in an aqueous alkali solution and which does not have sensitivity to an infrared laser, wherein the substrate, photosensitive layer and overcoat layer are provided in that order; the photosensitive layer is a photopolymerization layer comprising an infrared ray absorbing agent, a radical generating agent, and a radical polymerizable compound which polymerizes with the generated radicals and cures; and the radical generating agent is at least one onium salt.