US Patent 7294447 Positive-working lithographic printing plate precursor

A lithographic printing plate precursor is disclosed which comprises (i) a support having a hydrophilic surface or which is provided with a hydrophilic layer and (ii) a coating provided thereon, the coating comprising an oleophilic layer which, upon image-wise exposure to heat or infrared light and subsequent immersion in an aqueous alkaline developer, dissolves in the developer at a higher dissolution rate in exposed areas than in unexposed areas, wherein the oleophilic layer comprises a polymer that is soluble in the developer and an organic dye in a amount sufficient to provide a visible color to the coating, characterized in that said organic dye does not reduce the dissolution rate of the unexposed areas in the developer.