Patent ID: 7270930

Claim:
Heat-sensitive element comprising (a) an optionally pretreated substrate (b) a positive working heat-sensitive coating comprising (i) at least 40 wt.-%, based on the dry weight of the coating, of at least one polymer soluble in aqueous alkaline developer selected from novolak resins, functionalized novolak resins, polyvinylphenol resins, polyvinyl cresols and poly(meth)acrylates with phenolic and/or sulfonamide side groups, (ii) 0.1-20 wt.-%, based on the dry weight of the coating, of at least one (C 4 -C 20 alkyl)phenol novolak resin insoluble in aqueous alkaline developer, and (iii) optionally at least one further component selected from polymer particles, surfactants, contrast dyes and pigments, inorganic fillers, antioxidants, print-out dyes, plasticizers and substances capable of absorbing radiation of a wavelength from the range of 650 to 1,300 nm and converting it into heat, wherein the heat-sensitive coating comprises a carboxylic acid derivative of a cellulose polymer.