A method for making positive working printing plates from heat mode sensitive imaging element

摘要

According to the present invention there is provided a method for making a lithographic printing plate comprising the steps of a) exposing imagewise to IR-radiation a heat mode imaging element having on a lithographic base with a hydrophilic surface a first layer including a polymer, soluble in an aqueous alkaline solution and a top layer on the same side of the lithographic base as the first layer which top layer is unpenetrable by an alkaline developer and contains a compound capable of converting light into heat, wherein said first layer and said top layer may be one and the same layer; and b) developing said imagewise exposed heat mode imaging element with said alkaline developer whereby the exposed areas of the first and the top layer, which may be the same, are dissolved and the unexposed areas of the first layer remain undissolved characterized in that said alkaline developer has a pH of at least 12 and a surface tension of at least 30 mN/m.