Patent ID: 6186067
Filing Date: 2001-02-13
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 substrate, a hydrophilic layer overlying said substrate, an infrared-absorbing layer overlying said hydrophilic layer, and an ink-accepting surface layer overlying said infrared-absorbing layer; wherein (i) said surface layer is characterized by the absence of ablation from absorption of infrared imaging radiation; (ii) said infrared-absorbing layer is characterized by absorption of infrared imaging radiation; (iii) said surface and infrared-absorbing layers are characterized by being unremovable by cleaning with water or a cleaning solution prior to said absorption of infrared imaging radiation and by being adapted to form a wet lithographic printing surface as a result of an imagewise exposure to absorbable infrared radiation and subsequent removal of the exposed areas of said surface and infrared-absorbing layers by cleaning with water or said cleaning solution to reveal the underlying hydrophilic layer; and (iv) said hydrophilic layer is characterized by being unremovable by cleaning with water or said cleaning solution;(b) exposing, in an imagewise pattern, said member to absorbable infrared radiation to effect absorption thereof by said infrared-absorbing layer, thereby causing said surface and infrared-absorbing layers in said laser-exposed areas to become removable by cleaning with water or said cleaning solution but without significant ablation of either the surface layer or the infrared-absorbing layer; and(c) removing, with water or said cleaning solution, said laser-exposed areas of said surface and infrared-absorbing layers to reveal the underlying hydrophilic layer.