Patent ID: 8435720

Claim:
A lithographic printing plate precursor comprising, in the following order: a support; an image-recording layer which is capable of forming an image by removing an unexposed area of the image-recording layer with at least one of printing ink and dampening water on a printing machine after exposure and contains an infrared absorbing dye, a polymerization initiator, a polymerizable compound and a binder polymer having an alkylene oxide group; and a protective layer containing a hydrophilic polymer which contains at least a repeating unit represented by the following formula (1), a repeating unit represented by the following formula (2) and a repeating unit represented by the following formula (4) and in which a content of the repeating unit represented by the formula (4) is from 0.3 to 5.0% by mole based on total repeating units of the hydrophilic polymer: wherein, in the formulae (1), (2) and (4), R 1 , R 4 and R 7 each independently represents a hydrogen atom or a methyl group, R 2 and R 3 , which may be the same or different, each represents a hydrogen atom, a methyl group or an ethyl group, and R 5 represents an alkyl group having from 2 to 10 carbon atoms; in the formula (4), X represents a single bond, a divalent connecting chain selected from structures of the following Structural Group (5) or a divalent connecting chain formed by a combination of two or more structures of the Structural Group (5), and Y represents a carboxylic acid group, a carboxylate group, a sulfonic acid group, a sulfonate group, a phosphoric acid group, a phosphate group, a phosphonic acid group, a phosphonate group, a hydroxy group, a carboxybetaine group, a sulfobetaine group, an ammonium group or a polyether group represented by the following formula (3); and in the formula (3), L represents an alkylene group having from 2 to 6 carbon atoms, R 6 represents an alkyl group having from 4 to 8 carbon atoms, and n is an average addition molar number of polyether and represents a number of from 2 to 4: