Patent ID: 6846613

Claim:
A positive-working printing plate precursor for wet lithographic printing comprising a support having a hydrophilic surface and a coating comprising a first layer closest to the support, said first layer containing an oleophilic phenolic resin soluble in an aqueous alkaline developer, a second layer containing an amphyphilic polymer, and an intermediate layer between said first and second layers, wherein (a) the second layer is capable of preventing the aqueous alkaline developer from penetrating into the first layer to an extent that substantially no dissolution of unexposed coating occurs upon immersion in the aqueous alkaline developer during a time period t 2 ; (b) said capability of the second layer of preventing the aqueous alkaline developer from penetrating into the first layer is reduced upon exposure to heat or light to an extent that substantially complete dissolution of exposed coating occurs upon immersion in the aqueous alkaline developer during a time period t 1 ; t 2 >t 1 and t 2 −t 1 is at least 10 seconds; and the amphyphilic polymer is a block- or graft-polymer comprising (i) a poly(alkylene oxide) block and (ii) a block comprising siloxane and/or perfluorohydrocarbon units; and (c) said intermediate layer comprises a dye or pigment in an amount higher than the amount of dye or pigment in the first or second layer.