Patent ID: 6235451
Filing Date: 2001-05-22
Classification: B41C,Y10S

Abstract:
A method for making lithographic printing plates comprising the following steps:a) preparing a positive-working heat mode imaging element having on a lithographic base with a hydrophilic surface a first layer including a polymer, soluble in aqueous alkaline solution, and a top layer on the same side of the lithographic base as the first layer which top layer includes an IR-dye, is sensitive to IR-radiation and is impenetrable for an alkaline developer containing SiO.sub.2 as silicate;b) exposing imagewise said heat mode imaging element to IR-radiation;c) developing said imagewise exposed heat mode imaging element with said alkaline developer so that the exposed areas of the top layer and the underlying areas of the first layer are dissolved and the unexposed areas of the first layer remain undissolved;wherein said imaging element does not contain o-quinonediazide and wherein said IR-dye is present in said top layer in an amount between 1 and 100% by weight of the total amount of said layer and is selected from the group consisting of indoaniline dyes, cyanine dyes, merocyanine dyes, oxonol dyes, porphine derivatives, anthraquinone dyes, merostyryl dyes, pyrylium compounds, diphenyl and triphenyl azo compounds and squarylium derivatives.