Patent ID: 6490975
Filing Date: 2002-12-10
Classification: B41C

Abstract:
A method of imaging a wet positive working lithographic printing member, said method comprising the steps of:(a) providing a positive-working lithographic printing member, said member comprising a hydrophilic metal substrate, a hydrophilic layer overlying said substrate, and an ink-accepting surface layer overlying said hydrophilic layer, wherein (i) said surface layer is characterized by absorption of infrared imaging radiation and by being not removable by cleaning with water or a cleaning solution prior to said absorption of infrared imaging radiation, and (ii) said hydrophilic layer is characterized by being unremovable by cleaning with said water or cleaning solution; (b) exposing, in an imagewise pattern, said member to absorbable infrared radiation to effect absorption thereof by said surface layer, thereby causing said surface layer in said laser-exposed areas to become removable by cleaning with said water or cleaning solution; and (c) removing, with said water or cleaning solution, said laser-exposed areas of said surface layer to reveal the underlying hydrophilic layer, wherein said surface layer comprises one or more polymers and an infrared-absorbing carbon black sensitizer present in said surface layer in an amount greater than 55% by weight.