Patent ID: 6919166

Claim:
A method for preparing a lithographic printing plate comprising the steps of imagewise light-exposing to infrared radiation, a positive-working presensitized plate for use in making a lithographic printing plate, said presensitized plate having an image-forming layer which comprises an IR-absorbing agent and an alkali-soluble resin having a phenolic group, and developing the light-exposing plate with an alkaline liquid developer comprising a polyhydric alcohol-type alkylene oxide adduct in an amount of from 0.001 to 10% by weight, said polyhydnc alcohol-type alkylene oxide adduct being selected from the group consisting of the compounds represented by the following formula (I): wherein m represents an integer of from 1 to 4, R 1 , R 2 and R 3 represent each independently hydrogen atom or a group of formula (II): —(—R 4 —O) n —H (II) (wherein R 4 represents an alkylene group and n represents an integer such that the total number of moles of addition alkyleneoxides in the compound of the formula (I) is from 12 to 40), and when m is 2 or more, the 2 or more of R 3 are the same or different, provided that at least one of R 1 , R 2 and R 3 represents the group of formula (II), said image-forming layer further comprising an alkali-soluble high molecular weight compound having a carboxyl group and having as a basic skeleton, a reaction product of a diol compound having a carboxyl group represented by the following general formula (V), (VI) or (VII) and a diisocyanate compound represented by the following formula (X): wherein R 13 represents hydrogen atom, or an alkyl, alkenyl, aralkyl, aryl, alkoxy or aryloxy group which may have a substituent; R 14 , R 15 and R 16 , which may be the same or different, each represent a single bond, a bivalent aliphatic or aromatic hydrocarbon group which may have a substituent, two or three of R 13 , R 14 , R 15 and R 16 may form a ring together, and Ar represents a trivalent aromatic hydrocarbon group which may have a substituent, OCN—R 18 —NCO (X) wherein R 18 represents a bivalent aliphatic or aromatic hydrocarbon group which may have a substituent.