Oil-based ink for preparing printing plate by ink jet process and method for preparing printing plate by ink jet process

Abstract

An oil-based ink for a printing plate by an ink jet process comprising spraying an oil-based ink comprising at least resin particles dispersed in a nonaqueous carrier liquid having an electric resistance of 10,&OHgr;cm or more and a dielectric constant of 3.5 or less on a water-resistant support having a lithographically printable hydrophilic surface to dropwise from a nozzle form an image, wherein the resin particles dispersed are polymer particles obtained by polymerization granulation of a solution comprising (i), (ii) and (iii): (i) at least one monofunctional monomer (A) which is soluble in a nonaqueous solvent which is at least miscible with the nonaqueous carrier liquid and becomes insoluble therein by polymerization; (ii) (ii-a) at least one monomer (B) which is copolymerizable with the monomer (A), or (ii-b) at least one monofunctional macromonomer (MA) having a weight average molecular weight of 2×10,or less in which a polymerizable double bond group is combined with only one end of a main chain of a polymer comprising a repeating unit corresponding to a monomer; and (iii) at least one resin for dispersion stabilization (P) which is a polymer comprising a repeating unit and is soluble in the nonaqueous solvent, the polymer being crosslinked at a part of its main chain thereof, and a method for preparing a printing plate by an ink jet process using the ink.