Patent ID: 6174936
Filing Date: 2001-01-16
Classification: C09D

Abstract:
A method for preparing a printing plate by an ink jet process consisting essentially of discharging dropwise an oil-based ink using electrostatic attraction from a head having a discharge electrode on a lithographic printing plate precursor positioned between the discharge electrode and a counter electrode and comprising a water-resistant support having provided thereon an image receiving layer having a lithographically printable hydrophilic surface to form an image on the lithographically printable hydrophilic surface,wherein the oil-based ink comprises resin particles dispersed in a nonaqueous carrier liquid having an electric resistance of 10.sup.9 .OMEGA.cm or more and a dielectric constant of 3.5 or less, wherein the resin particles are copolymer resin 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 that is at least miscible with the nonaqueous carrier liquid and becomes insoluble in the nonaqueous solvent by polymerization;(ii) at least one monomer (C) represented by the formula (I) shown below which is copolymerizable with the monomer (A): ##STR43##wherein E.sup.1 represents an aliphatic group having 8 or more carbon atoms or a substituent having a total number of atoms of 8 or more, provided that hydrogen atoms directly attached to a carbon or nitrogen atom are excluded from the number, represented by the following formula (III): ##STR44##wherein R.sub.21 represents a hydrogen atom or an aliphatic group having from 1 to 18 carbon atoms;B.sub.1 and B.sub.2, which may be the same or different, each represents --O--, --S--, --CO--, --CO.sub.2 --, --OCO--, --SO.sub.2 --, --N(R.sub.22)--, --CON(R.sub.22)--, --N(R.sub.22)CO--, --N(R.sub.22)SO.sub.2 --, --SO.sub.2 N(R.sub.22)--, --NHCO.sub.2 -- or --NHCONH--, in which R.sub.22 has the same meaning as defined for R.sub.21 ;A.sub.1 and A.sub.2, which may be the same or different, each represents at least one group selected from the group consisting of a group represented by the following formula (IIIa) and a hydrocarbon group having from 1 to 18 carbon atoms, which each may be substituted, provided that, in the case of two or more, it represents a combination of the group represented by the formula (IIIa) and/or the hydrocarbon group: ##STR45##wherein B3 and B.sub.4, which may be the same or different, each has the same meaning as defined for B.sub.2 or B.sub.2 ;A.sub.4 represents a hydrocarbon group having from 1 to 18 carbon atoms which may be substituted;R.sub.23 has the same meaning as defined for R.sub.21 ; andm, n and p, which may be the same or different, each represents an integer of from 0 to 4, provided that m and n are not 0 at the same time;U1 represents --COO--, --CONH--, --CON(E.sub.2)--, --OCO--, --CONHCOO--, --CH.sub.2 COO--, --(CH.sub.2).sub.s OCO--, --O--, --C.sub.6 H.sub.4 -- or --C.sub.6 H.sub.4 --COO--, in which E.sub.2 represents an aliphatic group or a substituent represented by the formula (III) described above, and s represents an integer of from 1 to 4; anda.sup.1 and a.sup.2, which may be the same or different, each represents a hydrogen atom, a halogen atom, a cyano group, an alkyl group, --COO--E.sub.3 or --CH.sub.2 COO--E.sub.3, in which E.sub.3 represents an aliphatic group;(iii) at least one resin for dispersion stabilization (P) which is soluble in the nonaqueous solvent and is a copolymer represented by the formula (II) shown below: ##STR46##wherein R.sup.1 represents an alkyl group having from 10 to 32 carbon atoms or an alkenyl group having from 10 to 32 carbon atoms;b.sup.1 represents a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms;X.sup.1 and X.sup.2, which may be the same or different, each has the same meaning as defined for U.sup.1 in the formula (I);W represents a group connecting X.sup.1 and X.sup.2 and comprising a carbon atom or a hetero atom selected from an oxygen atom, a sulfur atom, a silicon atom and a nitrogen atom;d.sup.1, d.sup.2, e.sup.1 and e.sup.2, which may be the same or different, each has the same meaning as defined for a.sup.1 or a.sup.2 in the formula (I); andx and y each represents a weight ratio of each repeating unit, x represents a number of from 90 to 99, and y represents a number of from 10 to 1 to form an image;wherein the support has a specific electric resistance of 10.sup.10 .OMEGA.cm or less at least at an area directly under the image receiving layer; andwherein the resin particles dispersed in the oil-based ink are electroscopic particles positively or negatively charged.