METHOD FOR PRODUCING NEGATIVE WORKING HEAT SENSITIVE PLANOGRAPHIC PRINTING PLATE PRECURSOR

摘要

PROBLEM TO BE SOLVED: To provide a composition capable of producing a planographic printing plate precursor which works in accordance with heat induced coalescene or fusion of hydrophobic thermoplastic polymer particles and can ensure a toning- free high run length. SOLUTION: The method for producing a negative working heat sensitive planographic printing plate precursor includes (a) a step for preparing an aqueous dispersion containing particles of a hydrophobic thermoplastic polymer A which is not soluble or swellable in an aqueous alkaline developing solution and particles of a polymer B which is soluble or swellable in the aqueous alkaline developing solution but is not soluble or swellable in water, wherein the glass transition temperature of the polymer A is higher than the softening temperature of the polymer B, (b) a step for applying the aqueous dispersion on a planographic printing substrate having a hydrophilic surface to obtain an image-recording layer and (c) a step for entirely heating the image-recording layer at a higher temperature than the softening temperature of the polymer B at which coalescene of particles of the polymer A is not caused. The resulting printing plate precursor has an enhanced mechanical resistance.