Patent ID: 7244543

Claim:
A positive-working lithographic printing starting plate for an infrared laser, comprising: a support having a hydrophilic surface; a heat-sensitive layer provided above the support, the heat-sensitive layer comprising a water-insoluble and alkali-soluble resin (A), an infrared-absorbing dye (B), and a sulfonium salt (C) represented by Formula (I), and the heat-sensitive layer increasing its solubility in aqueous alkaline solution upon exposure to an infrared laser wherein R 1 and R 2 independently denote an optionally substituted alkyl group having 1 to 12 carbons, an optionally substituted cycloalkyl group having 3 to 8 carbons, an optionally substituted aralkyl group having 7 to 12 carbons, or an optionally substituted aryl group having 6 to 15 carbons, and R 1 and R 2 may bond to each other to form a cyclic structure; Ar denotes an optionally substituted aromatic hydrocarbon group having 6 to 15 carbons and having at least one OH group at an ortho- and/or para-position; and X denotes an anion of an organic acid; and at least one lower layer containing as a main component a water-insoluble and alkali-soluble resin, the lower layer being provided between the heat-sensitive layer and the support having a hydrophilic surface.