Patent ID: 6346365
Filing Date: 2002-02-12
Classification: B41C

Abstract:
A method for forming a positive image comprising:exposing a photosensitive lithographic printing plate with an infrared laser in the range of 700 to 1200 nm, said photosensitive lithographic printing plate comprising a substrate and a positive photosensitive composition thereon, said positive photosensitive composition comprising: an alkali aqueous solution soluble polymer compound (A), a compound (F) which is compatible with the alkali aqueous solution soluble polymer compound, thereby lowering the solubility of the alkali aqueous solution soluble polymer compound in an alkali aqueous solution, the effect of lowering the solubility being reduced by heating, the compound (F) further having the properties of generating heat upon absorption of light, having a light absorbing band outside the range of 350 nm to 500 nm and being other than an onium salt or a quinonediazide compound wherein the thermal decomposition temperature of each of compound (A) and compound (F) is higher than 150Â° C.; and developing the photosensitive lithographic printing with an alkali aqueous solution, so that the exposed portions of the photosensitive lithographic printing plate are dissolved into the alkali aqueous solution.