Patent ID: 6291134
Filing Date: 2001-09-18
Classification: G03F

Abstract:
A method of preparing a lithographic plate which comprises a layer of a radiation sensitive coating on a support having a hydrophilic surface, the method comprising digitally imaging the coating with a laser which emits light having a wavelength above 800 nm, then acting on the plate while the plate is on a printing press with aqueous fount solution to remove the unexposed areas of the coating to reveal the hydrophilic surface of the plate and to leave an ink receptive image, wherein the radiation sensitive coating comprises an infra-red absorbing compound and a diazo salt of the following formula: ##STR8##wherein R.sub.1 is an anion, R.sub.2 and R.sub.3 represent optional substitution, R.sub.4 is --N-- or --S-- and R.sub.5 is a group which after exposure of the plate renders the residue of the diazo salt oleophilic and fount insoluble.