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

A method for preparing a printing plate by an ink jet process consisting essentially of discharging an oily ink using an electrostatic field on a lithographic printing late precursor comprising a water-resistant support having provided thereon an image receiving layer having a lithographically printable hydrophilic surface dropwise from a head having a discharge electrode to form an image on the surface of the lithographically printable hydrophilic surface;

• wherein the oily ink comprises resin particles dispersed in a nonaqueous solvent having an electric resistance of 10.sup.9 .OMEGA.cm or more and a dielectric constant of 3.5 or less, and said resin particles dispersed 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 which is at least miscible with said nonaqueous carrier liquid and becomes insoluble therein by polymerization;
• (ii) (ii-a) at least one monomer (B) represented by the following formula (I-A) which is copolymerizable with said monomer (A), or
• (ii-b) at least one monofunctional macromonomer (MA) having a weight average molecular weight of 2.times.10.sup.4 or less in which a polymerizable double bond group represented by the following formula (II-B) is combined with only one end of a main chain of a polymer comprising a repeating unit corresponding to a monomer represented by the following formula (I-B);
• and
• (iii) at least one dispersion-stabilizing resin which is soluble in said nonaqueous solvent and has no graft group polymerizing with a monomer;
• ##STR34## 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-A):
• .paren open-st.A.sup.1 --B.sup.1 .paren close-st..sub.m .paren open-st.A.sup.2 --B.sup.2 .paren close-st..sub.n R.sup.21 (III-A)
• wherein R.sup.21 represents a hydrogen atom or an aliphatic group having 1 to 18 carbon atoms;
• B.sup.1 and B.sup.2 are the same or different and each represents --O--, --S--, --CO--, --CO.sub.2 --, --OCO--, --SO.sub.2 --, --N(R.sup.22)--, --CON(R.sup.22)--, --N(R.sup.22)CO--, --N(R.sup.22)SO.sub.2 --, --SO.sub.2 N(R.sup.22)--, --NHCO.sub.2 -- or --NHCONH--, in which R.sup.22 has the same meaning as R.sup.21 ;
• A.sup.1 and A.sup.2 are the same or different and each represents at least one group selected from a group represented by the following formula (III-Aa) and a hydrocarbon group having 1 to 18 carbon atoms, which each may be substituted, provided that, in the case where A.sup.1 or A.sup.2 represents two or more groups selected from a group represented by the following formula (III-Aa) and a hydrocarbon group having 1 to 18 carbon atoms, it represents (1) two or more groups represented by formula (III-Aa), (2) a combination of at least one group represented by formula (III-Aa) and at least one hydrocarbon group having 1 to 18 carbon atoms, or (3) two or more hydrocarbon groups having 1 to 18 carbon atoms:
• ##STR35## wherein B.sup.3 and B.sup.4 are the same or different and each has the same meaning as B.sup.1 and B.sup.2 ;
• A.sup.4 represents a hydrocarbon group having 1 to 18 carbon atoms which may be substituted;
• R.sup.23 has the same meaning as R.sup.21 ;
• and
• m, n and p are the same or different and each represents an integer of 0 to 4, provided that m, n and p are not 0 at the same time;
• U.sup.1 represents --COO--, --CONH--, --CON(E.sup.2)--, --OCO--, --CONHCOO--, --CH.sub.2 COO--, --(CH.sub.2).sub.k OCO--, --O--, --C.sub.6 H.sub.4 -- or --C.sub.6 H.sub.4 --COO--, in which E.sup.2 represents an aliphatic group or a substituent represented by formula (III-A) described above, and k represents an integer of 1 to 4;
• and
• a.sup.1 and a.sup.2 are the same or different and each represents a hydrogen atom, an alkyl group, a halogen atom, a cyano group, --COO--E.sup.3 or --CH.sub.2 COO--E.sup.3 in which E.sup.3 represents an aliphatic group;
• ##STR36## wherein V.sup.0 represents --COO--, --OCO--, --(CH.sub.2).sub.r COO--, --(CH.sub.2).sub.r OCO--, --O--, --SO.sub.2 --, --CONHCOO--, --CONHCONH--, --CON(D.sup.11)--, --SO.sub.2 N(D.sup.11)-- or a phenylene group, in which D.sup.11 represents a hydrogen atom or a hydrocarbon group having 1 to 22 carbon atoms, and r represents an integer of 1 to 4;
• a.sup.11 and a.sup.12 are the same or different and each represents a hydrogen atom, a halogen atom, a cyano group, a hydrocarbon group, --COO--D.sup.12 or --COO--D.sup.12 linked through a hydrocarbon group, in which D.sup.12 represents a hydrogen atom or a hydrocarbon group which may be substituted;
• D.sup.0 represents a hydrocarbon group having 8 to 22 carbon atoms or a substituent group having a total number of atoms of 8 or more, provided that hydrogen atoms attached to a carbon or nitrogen atom are excluded from the number, represented by the following formula (III-B):
• .paren open-st.A.sup.11 --B.sup.11 .paren close-st..sub.m0 .paren open-st.A.sup.12 --B.sup.12 .paren close-st..sub.n0 D.sup.21(III-B)
• wherein D.sup.21 represents a hydrogen atom or an aliphatic group having 1 to 22 carbon atoms;
• B.sup.11 and B.sup.12 are the same or different and each represents --O--, --CO--, --CO.sub.2 --, --OCO--, --SO.sub.2 --, --N(D.sup.22)--, --CON(D.sup.22)--, or --N(D.sup.22)CO--, in which D.sup.22 has the same meaning as D.sup.21 ;
• A.sup.11 and A.sup.12 are the same or different and each represents at least one group selected from a group represented by the following formula (III-Ba) and a hydrocarbon group having 1 to 18 carbon atoms, which each may be substituted, provided that, in the case where A.sup.11 or A.sup.12 represents two or more groups selected from a group represented by the following formula (III-Ba) and a hydrocarbon group having 1 to 18 carbon atoms, it represents (1) two or more groups represented by formula (III-Ba), (2) a combination of at least one group represented by formula (III-Ba) and at least one hydrocarbon group having 1 to 18 carbon atoms, or (3) two or more hydrocarbon groups having 1 to 18 carbon atoms;
• ##STR37## wherein B.sup.13 and B.sup.14 are the same or different and each has the same meaning as B.sup.11 and B.sup.12 ;
• A.sup.14 represents a hydrocarbon group having 1 to 18 carbon atoms which may be substituted;
• D.sup.23 has the same meaning as D.sup.21 ;
• and
• m.sup.0, n.sup.0 and p.sup.0 are the same or different and each represents an integer of 0 to 4, provided that m.sup.0, n.sup.0 and p.sup.0 are not 0 at the same time;
• ##STR38## wherein V.sup.1 represents --COO--, --CONHCOO--, --CONHCONH--, --CONH-- or a phenylene group;
• and
• b.sup.11 and b.sup.12 are the same or different and each has the same meaning as a.sup.11 and a.sup.12 in formula (I-B);
• wherein the support has a specific electric resistance of 10.sup.10 .OMEGA.cm or less at least an area directly under the image receiving layer;
• wherein said resin particles dispersed in the oily ink are electrically detectable particles positively or negatively charged;
• wherein the lithographically printable hydrophilic surface faces the discharge electrode, and a counter electrode is provided on the opposite side thereof.