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

An oil-based ink for the preparation of a printing plate by an ink jet process including dropwise supplying from a nozzle an oil-based ink including 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 on a lithographic printing plate precursor including a water-resistant support and a lithographically printable hydrophilic surface to form an image, wherein the resin particles dispersed are copolymer resin particles obtained by polymerization granulation of a solution including three particular components.

FIELD OF THE INVENTION
 The present invention relates to an oil-based ink for the preparation of a
 printing plate by an ink jet process, and a method for the preparation of
 a printing plate by an ink jet process using it. More particularly, the
 present invention relates to an oil-based ink excellent in dispersion
 stability, redispersibility, storage stability, image reproducibility and
 printing durability (press life), and a method for the preparation of a
 printing plate by an ink jet process using it.
 BACKGROUND OF THE INVENTION
 With recent developments in business machines and progress in office
 automation, in the field of small commercial printing, platemaking systems
 wherein an image is formed on a direct imaging type lithographic printing
 plate precursor comprising a water-resistant support having provided
 thereon an image receiving layer having a hydrophilic surface in a various
 manner to prepare an offset lithographic printing plate have been widely
 employed.
 A conventional lithographic printing plate precursor for direct imaging
 type comprises a support formed of paper subjected to water-resistant
 treatment or a plastic film having provided thereon an image accepting
 layer (or an image receiving layer) containing an inorganic pigment, a
 water-soluble resin and a water resistance imparting agent. On such a
 direct imaging type lithographic printing plate precursor, a lipophilic
 image is formed with a typewriter or by hand writing using a lipophilic
 ink, or by transferring an image from an ink ribbon by heat melting with a
 heat transfer printer, thereby preparing a printing plate.
 However, the printing plate prepared by such a method are not sufficient in
 mechanical strength of image areas, so that cutting easily takes place in
 the image areas during printing.
 On the other hand, ink jet recording is a recording method low in noise and
 printable at a high speed, and has recently been rapidly popularized.
 As such ink jet recording methods, there are proposed various systems such
 as a so-called electric field controlling system in which ink is
 discharged using electrostatic attraction, a so-called drop-on-demand
 system (pressure pulse system) in which ink is discharged using
 oscillation pressure of a piezoelectric element, and a so-called bubble
 (thermal) jet system in which ink is discharged using pressure generated
 by forming bubbles and allowing them to grow up with heating at high
 temperature. According to these systems, highly accurate images can be
 obtained.
 In these ink jet recording systems, aqueous ink using water as a main
 solvent, and oil-based ink using an organic solvent as a main solvent are
 conventionally employed.
 It is also known that plate making is performed using an ink jet printer on
 a lithographic printing plate precursor for direct imaging type described
 above. In this case, although aqueous ink in which water is used as a
 dispersion medium is employed, the aqueous ink has the problems in that
 blurs appear in images formed on the precursor and in that a picture
 drawing speed is decreased because of slow drying. In order to overcome
 such problems, a method using oil-based ink in which a nonaqueous solvent
 is used as a dispersion medium is proposed as described in JP-A-54-117203
 (the term "JP-A" as used herein means an "unexamined published Japanese
 patent application").
 However, this method is still insufficient, because blurs are observed in
 images formed by plate making and blurs are developed in prints. Further,
 the number of prints obtained is limited to several hundred at most.
 Moreover, such ink has the problem of being liable to clog a nozzle for
 discharging minute ink droplets which make it possible to obtain images
 having high resolution by the plate making.
 In the ink jet recording systems, ink is usually discharged from a nozzle
 through a filter, so that abnormal discharge of ink tends to take place by
 clogging of the nozzle or the filter, change in fluidity of the ink with
 the lapse of time, or various other factors.
 This abnormal discharge of ink occurs with respect to not only an aqueous
 ink composition, but also an oil-based ink composition. Various proposals
 for controlling the abnormal discharge of ink have been made. For example,
 in order to prevent the abnormal discharge of ink in case of using an
 oil-based ink composition, it is proposed that the viscosity and the
 specific resistance of the ink composition is controlled as described in
 JP-A-49-50935, for the ink jet recording method of the electric field
 controlling system. It is also proposed that the dielectric constant and
 the specific resistance of the solvent used in the ink composition are
 controlled as described in JP-A-53-29808.
 Furthermore, as attempts to prevent clogging of nozzles caused by ordinary
 oil-based ink for ink jet printer, there are proposed, for example,
 methods in which the dispersion stability of pigment particles is improved
 (e.g., JP-A-4-25573, JP-A-5-25413 and JP-A-5-65443) and methods in which
 specific compounds are incorporated into ink compositions (e.g.,
 JP-A-3-79677, JP-A-3-64377, JP-A-4-202386 and JP-A-7-109431).
 However, when these ink compositions are used for the image formation of
 lithographic printing plate, the images formed are poor in image strength
 during printing, and a printing plate which has a sufficient press life
 cannot been obtained.
 SUMMARY OF THE INVENTION
 An object of the present invention is to provide an oil-based ink for the
 preparation of a printing plate by an ink jet process which is excellent
 in redispersibility, storage stability, image reproducibility and press
 life.
 Another object of the present invention is to provide an oil-based ink for
 the preparation of a printing plate by an ink jet process which does not
 induce clogging in a nozzle and in the course of ink supply and which
 makes it possible to conduct stable discharge.
 A further object of the present invention is to provide a method for the
 preparation of a printing plate by an ink jet process in which ink jet
 recording is carried out stably when repeated and which provides a
 lithographic printing plate excellent in press life.
 A still further object of the present invention is to provide a method for
 the preparation of a printing plate by an ink jet process which makes it
 possible to provide many sheets of prints having clear images.
 Other objects of the present invention will become apparent from the
 following description.
 It has been found that these objects of the present invention are
 accomplished by an oil-based ink for the preparation of a printing plate
 by an ink jet process comprising dropwise supplying from a nozzle an
 oil-based ink comprising 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 on a lithographic printing plate
 precursor comprising a water-resistant support and a lithographically
 printable hydrophilic surface to form an image, wherein the 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 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):
 ##STR1##
 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):
 ##STR2##
 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:
 ##STR3##
 wherein B.sub.3 and B.sub.4, which may be the same or different, each has
 the same meaning as defined for B.sub.1 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 ; and
 m, 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;
 U.sup.1 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; and
 a.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:
 ##STR4##
 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); and
 x and y each represents a weight ratio of each repeating unit, x represents
 a number of from 90 to 99, y represents a number of from 10 to 1 and a
 method for the preparation of a printing plate by an ink jet precess
 comprising dropwise supplying from a nozzle the oil-based ink described
 above on a water-resistant support having a lithographically printable
 hydrophilic surface to form an image.
 BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
 FIG. 1 is a schematic view showing one embodiment of a device system which
 can be used in the present invention.
 FIG. 2 is a schematic view showing a main part of an ink jet recording
 device which can be used in the present invention.
 FIG. 3 is a partially sectional view showing a head of the ink jet
 recording device which can be used in the present invention.

EXPLANATION OF THE SYMBOLS

1 Ink jet recording device
 2 Master
 3 Computer
 4 Path
 5 Video camera
 6 Hard disk
 7 Floppy disk
 8 Mouse
 10 Head
 10a Discharge slit
 10b Discharge electrode
 10c Counter electrode
 11 Oil-based ink
 101 Upper unit
 102 Lower unit
 DETAILED DESCRIPTION OF THE INVENTION
 The present invention is characterized in that the above-described
 oil-based ink is discharged on a lithographic printing plate precursor by
 an ink jet process to form an image. The oil-based ink used is excellent
 in dispersion stability, redispersibility and storage stability, and the
 resulting lithographic printing plate can provide a large number of prints
 having clear images.
 The oil-based ink for use in the present invention is described in greater
 detail below.
 The nonaqueous carrier liquid having an electric resistance of 10.sup.9
 .OMEGA.cm or more and a dielectric constant of 3.5 or less used in the
 present invention preferably includes a straight chain or branched
 aliphatic hydrocarbon, an alicyclic hydrocarbon, an aromatic hydrocarbon
 and a halogen-substituted product thereof. Specific examples of the
 nonaqueous carrier liquid include octane, isooctane, decane, isodecane,
 decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane,
 cyclodecane, benzene, toluene, xylene, mesitylene Isopar E, Isopar G,
 Isopar H, Isopar L (Isopar: trade name of Exxon Co.), Shellsol 70,
 Shellsol 71 (Shellsol: trade name of Shell Oil Co.), Amsco OME and Amsco
 460 (Amsco: trade name of Spirits Co.), and mixtures thereof. The upper
 limit value of the electric resistance of the nonaqueous carrier liquid is
 about 10.sup.16 .OMEGA.cm, and the lower limit value of the dielectric
 constant thereof is about 1.80.
 The nonaqueous dispersed resin particles (hereinafter also referred to as
 "latex particles"), which are the most important constituent in the
 oil-based ink of the present invention, are those obtained by
 polymerization granulation in a nonaqueous solvent using a monofunctional
 monomer (A), a monomer (C) having the specific substituent and a resin for
 dispersion stabilization (P) which is soluble in the nonaqueous solvent
 and a random copolymer containing a polymer component having a double bond
 group copolymerizable with the monofunctional monomer (A).
 As the nonaqueous solvent, those miscible with the nonaqueous carrier
 liquid of the above-described oil-based ink are basically usable.
 Specifically, as the solvent used in the preparation of the dispersed resin
 particles, any solvent may be used as far as it is miscible with the
 above-described carrier liquid. Preferred examples thereof include a
 straight chain or branched aliphatic hydrocarbon, an alicyclic
 hydrocarbon, an aromatic hydrocarbon and a halogen-substituted product
 thereof. For example, hexane, octane, isooctane, decane, isodecane,
 decalin, nonane, dodecane, isododecane, Isopar E, Isopar G, Isopar H,
 Isopar L, Shellsol 70, Shellsol 71, Amsco OME and Amsco 460 can be used
 individually or as a mixture thereof.
 A solvent which can be used by mixing together with the nonaqueous solvent
 includes an alcohol (e.g., ethyl alcohol, propyl alcohol, butyl alcohol,
 ethylene glycol monomethyl ether, or a fluorinated alcohol), a ketone
 (e.g., methyl ethyl ketone, acetophenone, or cyclohexanone), a carboxylic
 acid ester (e.g., ethyl acetate, propyl acetate, butyl acetate, methyl
 propionate, ethyl propionate, ethyl benzoate, ethylene glycol monomethyl
 ether acetate), an ether (e.g., dipropyl ether, ethylene glycol dimethyl
 ether, propylene glycol dimethyl ether, tetrahydrofuran, or dioxane) and a
 halogenated hydrocarbon (e.g., chloroform, dichloroethane, or
 methylchloroform).
 The solvent used together with the nonaqueous solvent is desirably removed
 by distillation under heating or a reduced pressure after polymerization
 granulation. However, even if it is introduced into oil-based ink as a
 latex particle dispersion, no problem is encountered as far as the
 requirements that the electric resistance of the ink is 10.sup.9 .OMEGA.cm
 or more and that the dielectric constant thereof is 3.5 or less are
 satisfied.
 It is ordinarily preferred to employ a solvent same as the carrier liquid
 as described above in the stage of the preparation of a resin dispersion.
 Therefore, a straight chain or branched aliphatic hydrocarbon, an
 alicyclic hydrocarbon, an aromatic hydrocarbon and a halogenated
 hydrocarbon are preferably used.
 The monofunctional monomer (A) for use in the present invention may be any
 monofunctional monomer as far as it is soluble in a nonaqueous solvent,
 but insolubilized by polymerization. Specific examples thereof include a
 monomer represented by the following formula (IV):
 ##STR5##
 wherein T.sup.1 represents --COO--, --OCO--, --CH.sub.2 OCO--, --CH.sub.2
 COO--, --O--, --CONHCOO--, --CONHOCO--, --SO.sub.2 --, --CON(W.sub.1)--,
 --SO.sub.2 N(W.sub.1)-- or a phenylene group (phenylene group being
 hereinafter described as "-Ph-" sometimes, and including 1,2-, 1,3- and
 1,4-phenylene groups), in which W.sub.1 represents a hydrogen atom or an
 aliphatic group having from 1 to 8 carbon atoms which may be substituted
 (e.g., methyl, ethyl, propyl, butyl, 2-chloroethyl, 2-bromoethyl,
 2-cyanoethyl, 2-hydroxyethyl, benzyl, chlorobenzyl, methylbenzyl,
 methoxybenzyl, phenethyl, 3-phenylpropyl, dimethylbenzyl, fluorobenzyl,
 2-methoxyethyl, or 3-methoxypropyl);
 D.sup.1 represents a hydrogen atom or an aliphatic group having from 1 to 6
 carbon atoms which may be substituted (e.g., methyl, ethyl, propyl, butyl,
 2-chloroethyl, 2,2-dichloroethyl, 2,2,2-trifluoroethyl, 2-bromoethyl,
 2-hydroxyethyl, 2-hydroxypropyl, 2,3-dihydroxypropyl,
 2-hydroxy-3-chloropropyl, 2-cyanoethyl, 3-cyanopropyl, 2-nitroethyl,
 2-methoxyethyl, 2-methanesulfonylethyl, 2-ethoxyethyl,
 N,N-dimethylaminoethyl, N,N-diethylaminoethyl, trimethoxysilylpropyl,
 3-bromopropyl, 4-hydroxybutyl, 2-furfurylethyl, 2-thienylethyl,
 2-pyridylethyl, 2-morpholinoethyl, 2-carboxyethyl, 3-carboxypropyl,
 4-carboxybutyl, 2-phosphoethyl, 3-sulfopropyl, 4-sulfobutyl,
 2-carboxyamidoethyl, 3-sulfoamidopropyl, 2-N-methylcarboxyamidoethyl,
 cyclopentyl, chlorocyclohexyl, or dichlorohexyl); and
 f.sup.1 and f.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).
 Specific examples of the monofunctional monomer (A) include a vinyl ester
 or allyl ester of an aliphatic carboxylic acid having from 1 to 6 carbon
 atoms such as acetic acid, propionic acid, butyric acid, monochloroacetic
 acid, or trifluoropropionic acid; an alkyl ester or amide having from 1 to
 4 carbon atoms which may be substituted of an unsaturated carboxylic acid
 such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid or
 maleic acid (the alkyl group including, for example, methyl, ethyl,
 propyl, butyl, 2-chloroethyl, 2-bromoethyl, 2-fluoroethyl, trifluoroethyl,
 2-hydroxyethyl, 2-cyanoethyl, 2-nitroethyl, 2-methoxyethyl,
 2-methanesulfonylethyl, 2-benzenesulfonylethyl,
 2-(N,N-dimethylamino)ethyl, 2-(N,N-diethylamino)ethyl, 2-carboxyethyl,
 2-phosphoethyl, 4-carboxybutyl, 3-sulfopropyl, 4-sulfobutyl,
 3-chloropropyl, 2-hydroxy-3-chloropropyl, 2-furfurylethyl,
 2-pyridinylethyl, 2-thienylethyl, trimethoxysilylpropyl and
 2-carboxyamidoethyl); a styrene derivative (e.g., styrene, vinyltoluene,
 .alpha.-methylstyrene, vinylnaphthalene, chlorostyrene, dichlorostyrene,
 bromostyrene, vinylbenzenecarboxylic acid, vinylbenzenesulfonic acid,
 chloromethylstyrene, hydroxymethylstyrene, methoxymethylstyrene,
 N,N-dimethylaminomethylstyrene, vinylbenzenecarboxyamide, or
 vinylbenzenesulfoamide); an unsaturated carboxylic acid (e.g., acrylic
 acid, methacrylic acid, crotonic acid, maleic acid or itaconic acid); a
 cyclic acid anhydride of maleic acid or itaconic acid; an acrylonitrile; a
 methacrylonitrile; and a heterocyclic compound having a polymerizable
 double bond group (for example, compounds described in "Polymer Data
 Handbook, --Fundamental Volume--", edited by Kobunshi Gakkai, pages 175 to
 184, Baifukan (1986), specifically, N-vinylpyridine, N-vinylimidazole,
 N-vinylpyrrolidone, vinylthiophene, vinyltetrahydrofuran, vinyloxazoline,
 vinylthiazole, or N-vinylmorpholine).
 Two or more kinds of monomers (A) may be used in combination.
 The monomer (C) having the specific substituent which is employed together
 with the monomer (A) according to the present invention is a monomer
 represented by the following formula (I):
 ##STR6##
 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):
 ##STR7##
 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:
 ##STR8##
 wherein B.sub.3 and B.sub.4, which may be the same or different, each has
 the same meaning as defined for B.sub.1 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 ; and
 m, 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;
 U.sup.1 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; and
 a.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.
 First, the case where E.sup.1 represents an aliphatic group having 8 or
 more carbon atoms is described in detail below.
 E.sup.1 preferably represents an alkyl group having a total number of
 carbon atoms of 10 or more which may be substituted, or an alkenyl group
 having a total number of carbon atoms of 10 or more which may be
 substituted. Examples thereof include a decyl group, a dodecyl group, a
 tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group,
 a heptadecyl group, an octadecyl group, a docosanyl group, an eicosanyl
 group, a decenyl group, a dodecenyl group, a tridecenyl group, a
 tetradecenyl group, a hexadecenyl group, an octadecenyl group, a dococenyl
 group, a linoleyl group and an oleyl group. A substituent therefor
 includes a halogen atom (e.g., fluorine, chlorine, or bromine), a hydroxyl
 group, a cyano group, and an alkoxy group (e.g., methoxy, ethoxy, propoxy,
 or butoxy).
 U.sup.1 preferably represents --COO--, --CONH--, --CON(E.sub.2)--, (in
 which E.sub.2 preferably represents an aliphatic group having from 1 to 22
 carbon atoms (examples of the aliphatic group including an alkyl group, an
 alkenyl group and an aralkyl group)), --OCO--, --CH.sub.2 OCO-- or --O--.
 More preferably, U.sup.1 represents --COO--, --CONH-- or --CON(E.sub.2)--.
 a.sup.1 and a.sup.2, which may be the same or different, each preferably
 represents a hydrogen atom, a halogen atom (e.g., fluorine, chlorine, or
 bromine), a cyano group, an alkyl group having from 1 to 3 carbon atoms,
 --COO--E.sub.3 or --CH.sub.2 COO--E.sub.3 (in which E.sub.3 preferably
 represents an aliphatic group having from 1 to 22 carbon atoms, for
 example, methyl, ethyl, propyl, butyl, hexyl, octyl, decyl, dodecyl,
 tridecyl, tetradecyl, hexadecyl, octadecyl, docosanyl, pentenyl, hexenyl,
 heptenyl, octenyl, decenyl, dodecenyl, tetradecenyl, hexadecenyl, or
 octadecenyl). The aliphatic group may have a substituent same as set forth
 for E.sup.1 described above.
 More preferably, a.sup.1 and a.sup.2 each represents a hydrogen atom, an
 alkyl group having from 1 to 3 carbon atoms (e.g., methyl, ethyl, or
 propyl), -COO-E.sub.3 or --CH.sub.2 COO--E.sub.3 (in which E.sub.3 is more
 preferably an alkyl group having from 1 to 12 carbon atoms or an alkenyl
 group having from 2 to 12 carbon atoms, for example, methyl, ethyl,
 propyl, butyl, hexyl, octyl, decyl, dodecyl, pentenyl, hexenyl, heptenyl,
 octenyl, or decenyl), and the alkyl group or the alkenyl group may have a
 substituent same as set forth for E.sup.1 described above.
 When E.sup.1 represents an aliphatic group having 8 or more carbon atoms in
 the monomer (C) represented by the formula (I) as described above,
 specific examples thereof include an ester of an unsaturated carboxylic
 acid such as acrylic acid, .alpha.-fluoroacrylic acid,
 .alpha.-chloroacrylic acid, .alpha.-cyanoacrylic acid, methacrylic acid,
 crotonic acid, maleic acid and itaconic acid having an aliphatic group
 having a total number of carbon atoms of from 10 to 32 (the aliphatic
 group may have a substituent such as a halogen atom, a hydroxyl group, an
 amino group or an alkoxy group, or a heteroatom such as an oxygen atom, a
 sulfur atom or a nitrogen atom may intervene a carbon--carbon bond of its
 main chain) (examples of the aliphatic group including decyl, dodecyl,
 tridecyl, tetradecyl, pentadecyl, hexadecyl, octadecyl, docosanyl,
 decenyl, dodecenyl, tridecenyl, tetradecenyl, hexadecenyl, oleyl, linoleyl
 and docosenyl); an amide of the above-described unsaturated carboxylic
 acid (the aliphatic group has the same meaning as defined for the ester);
 a vinyl ester or allyl ester of a higher fatty acid (examples of the
 higher fatty acid including lauric acid, myristic acid, stearic acid,
 oleic acid, linoleic acid and behenic acid); and a vinyl ether substituted
 with an aliphatic group having a total number of carbon atoms of from 10
 to 32 (the aliphatic group has the same meaning as defined for the
 unsaturated carboxylic acid described above).
 Now, the case where E.sup.1 represents a substituent having a total number
 of atoms of 8 or more (excluding a hydrogen atom directly attached to a
 carbon or nitrogen atom) represented by the formula (III) in the monomer
 (C) represented by the formula (I) is described in detail below.
 A.sub.1 and A.sub.2 each represents at least one group selected from the
 group consisting of a group represented by the formula (III) and a
 hydrocarbon group having from 1 to 18 carbon atoms (in the case of two or
 more, each represents a combination of the group represented by the
 formula (III) and/or the hydrocarbon group). More specifically, A.sub.1
 and A.sub.2 each is composed of any appropriate combination of atomic
 groups such as --C(R.sub.24) (R.sub.25)-- (in which R.sub.24 and R.sub.25
 each represents a hydrogen atom, an alkyl group or a halogen atom),
 --(CH.dbd.CH)--, a cyclohexylene group (the cyclohexylene group is
 hereinafter often represented by "--C.sub.6 H.sub.10 --", including 1,2-,
 1,3- and 1,4-cyclohexylene groups) and the group represented by the
 formula (IIIa).
 When E.sup.1 represents the substituent having a total number of atoms of 8
 or more represented by formula (III), it is preferred that a "connecting
 main chain" composed of U.sup.1 to R.sup.21 (namely, U.sup.1, A.sub.1,
 B.sub.1, A.sub.2, B.sub.2 and R.sub.21) in a connecting group (--U.sup.1
 --(A.sub.1 --B.sub.1).sub.m --(A.sub.2 --B.sub.2).sub.n --R.sub.21) in the
 formula (I) has a total number of atoms of 8 or more.
 The number of atoms constituting the "connecting main chain" means that,
 for example, when U.sup.1 represents --COO--or --CONH--, the oxo group
 (.dbd.O) and the hydrogen atom are not contained in the number of atoms,
 and the carbon atom, the ether type oxygen atom and the nitrogen atom
 constituting the connecting main chain are contained in the number of
 atoms. Therefore, in case of --COO-- and --CONH--, the number of atoms is
 counted as 2. At the same time, when R.sub.21 represents --C.sub.9
 H.sub.19, the hydrogen atoms are not contained in the number of atoms, and
 the carbon atoms are contained therein. In this case, therefore, the
 number of atoms is counted as 9.
 When U.sup.1 represents --CON(E.sub.2)--, and E.sub.2 represents the
 substituent represented by the formula (III), namely --(A.sub.1
 --B.sub.1).sub.m --(A.sub.2 --B.sub.2).sub.n --R.sub.21, a connecting main
 chain composed of E.sub.2 is also included in the above-described
 "connecting main chain". Furthermore, when A.sub.1 and A.sub.2 each has
 the group represented by formula (IIIa), a (--B.sub.3 --(A.sub.4
 --B.sub.4).sub.p --R.sub.23) group is also included in the above-described
 "connecting main chain".
 Of the monomers (C) represented by the formula (I) as described above,
 specific examples of monomers wherein E.sup.1 represents the substituent
 shown by the formula (III) include the following compounds.
 In the following formulae (1) to (19), r.sub.1 represents --H, --CH.sub.3,
 --Cl or --CN, r.sub.2 represents --H or --CH.sub.3, l represents an
 integer of from 2 to 10, p represents an integer of from 2 to 6, q
 represents an integer of from 2 to 4, m represents an integer of from 1 to
 12, and n represents an integer of from 4 to 18.
 ##STR9##
 ##STR10##
 The resin for dispersion stabilization (P) according to the present
 invention which is employed for making a polymer insoluble in the
 nonaqueous solvent formed by polymerization of the monomers a stable resin
 dispersion in the nonaqueous solvent is a random copolymer soluble in the
 nonaqueous solvent containing a copolymer component which works for
 solubilizing the random copolymer in the nonaqueous solvent (hereinafter
 referred to component X sometimes) and a copolymer component having a
 double bond group copolymerizable with the monomer (A) at a terminal of
 the side chain thereof (hereinafter referred to component Y sometimes) and
 represented by the following formula (II):
 ##STR11##
 In the formula (II), 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, each
 of which may be a straight chain or branched. Specific examples thereof
 include a decyl group, a dodecyl group, a tridecyl group, a tetradecyl
 group, a pentadecyl group, a hexadecyl group, an octadecyl group, an
 eicosanyl group, a decenyl group, a dodecenyl group, a tridecenyl group, a
 hexadecenyl group, an octadecenyl group, an eicosenyl group, docosenyl
 group, and a linoleyl group.
 b.sup.1 represents a hydrogen atom or an alkyl group having from 1 to 4
 carbon atoms (e.g., methyl, ethyl, propyl, or butyl), and preferably a
 hydrogen atom or a methyl group.
 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.
 The connecting group includes a carbon atom-carbon atom bond (either a
 single bond or a double bond), a carbon atom-hetero atom bond (the hetero
 atom including an oxygen atom, a sulfur atom, a silicon atom and a
 nitrogen atom), a hetero atom-hetero atom bond, a heterocyclic group and
 an appropriate combination thereof. Specific examples thereof include
 ##STR12##
 wherein r.sub.1, r.sub.2, r.sub.3 and r.sub.4, which may be the same or
 different, each represents a hydrogen atom, a halogen atom (e.g.,
 fluorine, chlorine, or bromine), a cyano group, a hydroxy group or an
 alkyl group (e.g., methyl, ethyl, or propyl);
 r.sub.5, r.sub.6 and r.sub.7, which may be the same or different, each
 represents a hydrogen atom or an alkyl group (e.g., methyl, ethyl, propyl,
 or butyl); and
 r.sub.8 and r.sub.9, which may be the same or different, each represents a
 hydrogen atom, a hydrocarbon group having from 1 to 8 carbon atoms (e.g.,
 methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, phenethyl, phenyl, or
 tolyl) or --Or.sub.10 (wherein r.sub.10 represents a hydrocarbon group
 having from 1 to 8 carbon atoms (e.g., methyl, ethyl, propyl, butyl,
 pentyl, hexyl, benzyl, phenethyl, phenyl, or tolyl)).
 The heterocyclic group for the connecting group is derived from a
 heterocyclic ring containing a hetero atom, for example, an oxygen atom, a
 sulfur atom or a nitrogen atom (e.g., thiophene, pyridine, pyrane,
 imidazole, benzimidazole, furan, piperidine, pyrazine, pyrrole, or
 piperazine).
 The connecting chain group represented by --X.sup.1 --W--X.sup.2 --
 contained in the component Y of the formula (II) preferably contains a
 total number of atoms of 8 or more. The number of atoms constituting the
 connecting chain group means that, for example, when X.sup.1 represents
 --COO-- or --CONH--, the oxo group (.dbd.O) and the hydrogen atom are not
 contained in the number of atoms, and the carbon atom, the ether type
 oxygen atom and the nitrogen atom constituting the connecting chain group
 are contained in the number of atoms. Therefore, in case of --COO--
 --CONH--, the number of atoms is counted as 2.
 Specific examples of the component Y having a polymerizable double bond are
 set forth below, but the present invention should not be construed as
 being limited thereto. In the following formulae (Y-1) to (Y-12), d.sup.1
 represents --H or --CH.sub.3, d.sup.2 represents --H, --CH.sub.3, --Cl or
 --CN, k.sub.1 represents an integer of from 4 to 12, k.sub.2 represents an
 integer of from 2 to 6, L.sup.1 represents
 ##STR13##
 --CH.sub.2 CH.dbd.CH.sub.2 or
 ##STR14##
 (wherein e.sup.1 represents --H or --CH.sub.3), and L.sup.2 represents
 ##STR15##
 ##STR16##
 or --CH.sub.2 CH.dbd.CH.sub.2 (wherein e.sup.2 represents --CH.sub.3, --Cl
 or --CN).
 ##STR17##
 ##STR18##
 The resin for dispersion stabilization (P) according to the present
 invention can be easily prepared by means of conventionally known
 synthesis methods. More specifically, in order to introduce a copolymer
 component having a polymerizable double bond group (component Y), there is
 a method in which a polymerization reaction is first conducted using a
 monomer having a specific reactive group, for example, --OH, --COOH,
 --SO.sub.3 H, --NH.sub.2, --SH, --PO.sub.3 H.sub.2, --NCO, --NCS, --COCl,
 --SO.sub.2 Cl or an epoxy group and a monomer corresponding to the
 component X in the formula (II), and then a reagent having a polymerizable
 double bond group is reacted with the resulting copolymer, thereby
 introducing the polymerizable double bond group into the copolymer by a
 polymer reaction.
 Specifically, the polymerizable double bond group can be introduced
 according to methods described, for example, in P. Dreyfuss & R. P. Quirk,
 Encycl. Polym. Sci. Eng., 7, 551 (1987), Yoshiki Nakajyo & Yuya Yamashita,
 Senryo to Yakuhin, 30, 232 (1985), Akira Ueda & Susumu Nagai, Kagaku to
 Kogyo, 60, 57 (1986), P. F. Rempp & E. Franta, Advance in Polymer Science,
 58, 1 (1984), Koichi Ito, Kobunshi Kako, 35, 262 (1986), V. Percec,
 Applied Polymer Science, 285, 97 (1984), and literature references cited
 therein.
 Another method in which a bifunctional monomer having functional groups
 having different reactivity in a radical polymerization is subjected to
 copolymerization reaction with a monomer corresponding to the component X
 to prepare a copolymer represented by the formula (II) without the
 occurrence of gelation as described in JP-A-60-185962 is also utilized.
 In the resin represented by the formula (II), a weight ratio of component
 X/component Y is from 90/10 to 99/1, preferably from 92/8 to 98/2. In such
 a range of the weight ratio, the occurrence of gelation in the reaction
 mixture and the formation of coarse resin particles may be prevented, and
 the dispersion stability and redispersibility of the dispersed resin
 particles are excellent.
 The resin for dispersion stabilization (P) according to the present
 invention may contain, as a copolymer component, a repeating unit other
 than the repeating units corresponding to the components X and Y
 respectively. The copolymer component to be included may be selected from
 any monomers copolymerizable with the monomers corresponding to the
 repeating units shown in the formula (II). Such monomers, however, are
 preferably employed in a range of not more than 20 parts by weight based
 on 100 parts by weight of the total copolymer components. When the amount
 of other monomers exceeds the above-described range, the dispersion
 stability of the dispersed resin particles may tend to deteriorate.
 The resin for dispersion stabilization (P) used in the present invention is
 soluble in an organic solvent, and specifically, it is preferably
 dissolved in an amount of at least 5 parts by weight based on 100 parts by
 weight of toluene at a temperature of 25.degree. C.
 The weight average molecular weight of the resin for dispersion
 stabilization (P) according to the present invention is preferably from
 2.times.10.sup.4 to 10.times.10.sup.6, more preferably from
 3.times.10.sup.4 to 2.times.10.sup.5.
 The dispersed resin according to the present invention comprises at least
 one of the monomer (A) and at least one of the monomer (C), and it is
 important that the resin synthesized from these monomers is insoluble in a
 nonaqueous solvent, thereby being able to obtain the desired dispersed
 resin.
 The total amount of the monomer (A) and the monomer (C) is preferably from
 10 parts to 100 parts by weight, more preferably from 10 parts to 80 parts
 by weight, based on 100 parts by weight of the nonaqueous solvent. With
 respect to a ratio of each of the monomers, the monomer (C) represented by
 the formula (I) is used preferably in an amount of from 0.1% to 10% by
 weight, more preferably 0.2% to 8% by weight, based on the monomer (A)
 used.
 The resin for dispersion stabilization (P) is used preferably in an amount
 of from 1 to 25 parts by weight, more preferably 5 to 20 parts by weight,
 based on 100 parts by weight of the total amount of the monomers.
 The dispersed resin particles used in the present invention are generally
 prepared by heat polymerization of the resin for dispersion stabilization
 (P), the monomer (A) and the monomer (C) as described above in the
 nonaqueous solvent in the presence of a polymerization initiator such as
 benzoyl peroxide, azobisisobutyronitrile or butyllithium. Specifically,
 there are (1) a method of adding a polymerization initiator to a mixed
 solution of the resin for dispersion stabilization (P), the monomer (A)
 and the monomer (C), (2) a method of adding dropwise the monomer (A) and
 the monomer (C) together with a polymerization initiator to a solution in
 which the resin for dispersion stabilization (P) is dissolved, (3) a
 method of adding a polymerization initiator and the remainders of the
 monomer (A) and the monomer (C) to a mixed solution containing the total
 amount of the resin for dispersion stabilization (P) and appropriate parts
 of the monomer (A) and the monomer (C), and (4) a method of adding a mixed
 solution of the resin for dispersion stabilization (P), the monomer (A)
 and the monomer (C) to a nonaqueous solvent together with a polymerization
 initiator. The dispersed resin particles can be prepared according to any
 of these methods.
 The amount of the polymerization initiator is suitably from 0.1% to 10% by
 weight based on the total amount of monomers used. The polymerization
 temperature is preferably from about 40.degree. C. to about 180.degree.
 C., and more preferably from 50.degree. C. to 120.degree. C. The reaction
 time is preferably from 3 hours to 15 hours.
 When the polar solvent described above, such as an alcohol, a ketone, an
 ether or an ester is used in combination with the nonaqueous solvent used
 in the reaction, or when unreacted monomers of the monomer (A) and the
 monomer (C) to be subjected to polymerization granulation remain, it is
 preferred that the polar solvent or the unreacted monomers are removed by
 distillation under heating to temperature equal to or higher than a
 boiling point of the solvent or the monomers, or under a reduced pressure.
 The nonaqueous dispersed resin particles according to the present invention
 prepared as described above are present as particles which are very fine
 and uniform in particle size distribution. The average particle size
 thereof is from 0.08 .mu.m to 0.8 .mu.m, more preferably from 0.1 .mu.m to
 0.5 .mu.m. The particle size can be determined using CAPA-500 (trade name,
 manufactured by Horiba Ltd.).
 The weight average molecular weight of the dispersed resin according to the
 present invention is preferably from 5.times.10.sup.3 to 1.times.10.sup.6,
 more preferably from 8.times.10.sup.3 to 5.times.10.sup.5.
 As to thermal properties, the dispersed resin according to the present
 invention has preferably a glass transition point ranging from 15.degree.
 C. to 80.degree. C. or a softening point ranging from 35.degree. C. to
 120.degree. C., preferably a glass transition point ranging from
 20.degree. C. to 60.degree. C. or a softening point ranging from
 38.degree. C. to 90.degree. C.
 Within the range as described above, the dispersed resin particles of the
 oil-based ink of the present invention are excellent in dispersion
 stability, redispersibility and storage stability. Also, rapid fixing
 property after image formation is good, the image formed is retained in
 printing, thereby exhibiting good press life.
 More specifically, since it has very stable dispersibility, even when it is
 repeatedly used in a recording device for a long period of time, it is
 good in dispersibility and easily redispersed, so that contamination due
 to adhesion of the resin particles to each part of the device is not
 observed at all.
 Furthermore, due to its good fixing property, a strong coating is formed on
 a hydrophilic outermost surface of a lithographic printing plate precursor
 by a rapid fixing treatment with heating after ink image formation. This
 makes it possible to print a large number of sheets (good press life) in
 offset printing.
 The oil-based ink of the present invention having the effects as described
 above becomes available by a nonaqueous latex of the dispersed resin
 particles according to the present invention.
 In the dispersed resin particles of the present invention, the resin for
 dispersion stabilization (P) is chemically bonded to the insoluble resin
 particles at the time of polymerization granulation. The resin (P) which
 is bonded to the resin particle is soluble in the nonaqueous solvent, and
 thus it brings about a so-called steric repulsion effect.
 In addition, the monomer (C) having the specific substituent is
 copolymerized with the monomer (A) to be insolubilized at the time of
 polymerization granulation. The specific substituent moiety contained in
 the monomer (C) is designed so as to improve the affinity for the
 nonaqueous solvent, since particles are formed by nonaqueous dispersion
 polymerization. It is therefore orientated in the interface (surface) area
 of the particle rather than it gets into the inside of the particle,
 because of its good solvent affinity for the dispersion medium. It is
 presumed that as a result, the affinity for the dispersion medium on the
 particle surface is improved by using the monomer (C) together with the
 resin for dispersion stabilization (P) to significantly enhance the effect
 of preventing aggregation of the resin particles.
 Consequently, it is believed that aggregation and precipitation of the
 insoluble resin particles are inhibited, thereby remarkably improving the
 redispersibility.
 It is preferred that the oil-based ink used in the present invention
 contains a coloring material as a color component for visual inspection of
 a printing plate after plate making, in addition to the above-described
 dispersed resin particles.
 As the coloring material, any can be used as far as it is a pigment or a
 dye conventionally employed in an oil-based ink or a liquid developer for
 electrostatic photography.
 The pigments which can be used include those ordinarily employed in the
 technical field of printing, regardless of inorganic pigments or organic
 pigments. Specifically, known pigments, for example, carbon black, cadmium
 red, molybdenum red, chrome yellow, cadmium yellow, Titan Yellow, chromium
 oxide, pyridian, Titan Cobalt Green, ultramarine blue, Prussian blue,
 cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments,
 isoindolinone pigments, dioxazine pigments, threne pigments, perylene
 pigments, perynone pigments, thioindigo pigments, quinophthalone pigments
 and metal complex pigments can be used without particular limitation.
 Preferred examples of the dyes include oil-soluble dyes, for example, azo
 dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes,
 carbonium dyes, quinoneimine dyes, xanthene dyes, cyanine dyes, quinoline
 dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes,
 phthalocyanine dyes and metallophthalocyanine dyes.
 These pigments and dyes may be used individually or in an appropriate
 combination. They are preferably employed within the range of from 0.05%
 to 5% by weight based on the whole ink.
 The coloring material may be dispersed by itself in the nonaqueous solvent
 as dispersed particles, separately from the dispersed resin particles, or
 included in the dispersed resin particles. In order to include the
 coloring material in the dispersed resin particles, there is a method in
 which the dispersed resin is dyed with an appropriate dye as described in
 JP-A-57-48738. Alternatively, there is a method in which the dispersed
 resin is chemically bonded to a dye as described in JP-A-53-54029, or a
 method in which a monomer previously containing a dye is used at the time
 of polymerization granulation to form a dye-containing copolymer as
 described in JP-B-44-22955 (the term "JP-B" as used herein means an
 "examined Japanese patent publication").
 The dispersed resin particles and the colored particles (or coloring
 material particles) contained in the oil-based ink of the present
 invention are preferably electroscopic particles positively or negatively
 charged.
 In order to impart the electroscopicity to the particles, the technology of
 a liquid developer for electrostatic photography can be appropriately
 utilized. Specifically, it is carried out using electroscopic materials,
 for example, charge control agents and other additives as described, for
 example, in "Recent Developments and Utilization of Electrophotographic
 Development Systems and Toner Materials", pages 139 to 148, "Fundamental
 and Application of Electrophotographic Techniques", edited by Denshi
 Shashin Gakkai, pages 497 to 505 (Corona, 1988), and Yuji Harazaki,
 "Electrophotography", 16 (No. 2), page 44 (1977).
 Suitable compounds are also described, for example, in British Patents
 893,429 and 934,038, U.S. Pat. Nos. 1,122,397, 3,900,412 and 4,606,989,
 JP-B-4-51023, JP-B-6-19595, JP-B-6-19596, JP-B-6-23865, JP-A-60-185963 and
 JP-A-2-13965.
 Charge control agents are preferably added in an amount of from 0.001 part
 to 1.0 part by weight based on 1000 parts by weight of dispersing medium
 or a carrier liquid. Various additives may be further added if desired,
 and the upper limit of the total amount of these additives is restricted
 by the electric resistance of the oil-based ink. Specifically, if the
 electric resistance of the ink in a state of excluding the dispersed
 particles therefrom is lower than 10.sup.9 .OMEGA.cm, it may be difficult
 to obtain continuous gradation images of good quality. It is therefore
 desired to control the amount of each additive added within the above
 described limit.
 The oil-based ink containing the electroscopic resin particles of the
 present invention is preferably employed in the ink jet recording method
 of the electric field controlling system in which the ink is discharged
 using electrostatic attraction, since the discharge of the oil-based ink
 from a nozzle is easily performed.
 Now, the method for the preparation of a lithographic printing plate
 according to the present invention is described in detail below.
 The lithographic printing plate precursor having a lithographically
 printable hydrophilic surface used in the method of the present invention
 may be any as far as it provides a hydrophilic surface suitable for
 lithography, and printing pate precursors used for conventional offset
 printing plates can be used.
 The surface for receiving the ink image is a hydrophilic surface preferably
 having a contact angle with water of 5 degrees or less, more preferably 0
 degree, to provide prints without the generation of ink stains in the
 non-image areas.
 A lithographic printing plate precursor comprising a water-resistant
 support having provided thereon an image receiving layer having a
 lithographically printable hydrophilic surface is preferably employed in
 the present invention. Also, an aluminum plate a surface of which has been
 rendered hydrophilic, or a plate comprising a water-resistant support
 having provided thereon an aluminum layer a surface of which has been
 rendered hydrophilic is also preferably used as the printing plate
 precursor.
 Examples of the water-resistant support include a plastic sheet, paper for
 which printing durability is provided, an aluminum plate, a zinc plate, a
 bimetal plate (e.g., a copper-aluminum plate, a copper-stainless steel
 plate and a chromium-copper plate), a trimetal plate (e.g., a
 chromium-copper-aluminum plate, a chromium-lead-iron plate, and a
 chromium-copper-stainless steel plate), preferably having a thickness of
 from 0.1 to 3 mm, particularly preferably from 0.1 to 1 mm.
 Also, paper having a thickness of from 80 .mu.m to 200 .mu.m subjected to
 water-resistant treatment, paper or a plastic film laminated with a
 plastic film or a metal foil, is employed.
 It is preferred that the water-resistant support has electroconductivity,
 more specifically, a specific electric resistance of 10.sup.10 .OMEGA.cm
 or less at least at an area directly under the image receiving layer. The
 specific electric resistance is more preferably 10.sup.8 .OMEGA.cm or
 less. The smaller the specific electric resistance, the better.
 In order to provide the specific electric resistance of at least an area
 directly under the image receiving layer on a substrate such as paper and
 a film, for example, a layer comprising an electroconductive filler such
 as carbon black and a binder is applied thereto, a metal foil is stuck
 thereon, and a metal is evaporated thereon.
 On the other hand, examples of the support having an electroconductivity as
 a whole include electroconductive paper to which sodium chloride is
 impregnated, a plastic film into which an electroconductive filler is
 incorporated, and a metal plate such as aluminum.
 In the above-described range of electroconductivity, when ink droplets
 which have been charged in ink jet recording of electric field controlling
 type are adhered to the image-receiving layer, the charge of the ink
 droplets is disappeared quickly through earth, and a clear image having no
 disorder is formed.
 In the present invention, the specific electric resistance (volume specific
 electric resistance or electric resistivity) was measured by a
 three-terminal method using a guard electrode according to the method
 described in JIS K-6911.
 As to the support used in the present invention, the smoothness of a
 surface on the side adjacent to the image receiving layer is preferably
 adjusted to 300 (second/10 ml) or more by the Bekk smoothness.
 The image reproducibility and the press life can be further improved by
 restricting the smoothness of the surface on the side adjacent to the
 image receiving layer of the support to the above described value. Such an
 improving effect is obtained even if the image receiving layer having the
 same surface smoothness is used, and it is considered that an increase in
 the smoothness of the surface of the support has improved adhesion between
 the image area and the image receiving layer.
 In the present invention, the smoothness of the surface of the image
 receiving layer is preferably 50 (second/10 ml) or more, and more
 preferably 80 (second/10 ml) or more, by the Bekk smoothness.
 Defects and blurs of ink images which may be formed according to the
 unevenness of the image receiving layer are preferably inhibited at the
 Bekk smoothness of 50 or more.
 The Bekk smoothness can be measured with a Bekk smoothness tester. The Bekk
 smoothness tester is a tester for measuring a time required for a definite
 amount (10 ml) of air to pass through between a test piece and a glass
 surface under a reduced pressure, wherein the test piece is pressed to a
 highly smoothly finished circular glass plate having a hole at its center
 at a definite pressure (1 kg/cm.sup.2).
 The water-resistant support having electro-conductivity as a whole used in
 the present invention is described in more detail below.
 For instance, the support is obtained by providing both sides of an
 electroconductive paper obtained by impregnating sodium chloride into a
 substrate with a water-resistant electroconductive layer.
 In the present invention, the paper used for the substrate include wood
 pulp paper, synthetic pulp paper and mixed paper of wood pulp and
 synthetic pulp. The thickness of the paper is preferably from 80 .mu.m to
 200 .mu.m.
 The electroconductive layer is described in more detail below.
 The electroconductive layer is formed by applying a composition containing
 an electroconductive filler and a binder to both surfaces of the
 electroconductive paper. The thickness of the electroconductive layer is
 preferably from 5 .mu.m to 20 .mu.m.
 The electroconductive filler includes granulated carbon black, graphite,
 metal powder (e.g., silver powder, copper powder, a nickel powder),
 stannic oxide powder, aluminum flake, nickel flake, carbon fiber, brass,
 aluminum, copper and stainless steel.
 A resin used for the binder can be appropriately selected from various
 resins. Specifically, the resin includes a hydrophobic resin (e.g.,
 acrylic resin, vinyl chloride resin, styrene resin, styrene-butadiene
 resin, styrene-acrylic resin, urethane resin, vinylidene chloride resin,
 and vinyl acetate resin) and a hydrophilic resin (e.g., polyvinyl alcohol
 resin, cellulose derivative resin, starch and derivatives thereof,
 polyacrylamide resin, and styrene-maleic anhydride copolymer).
 The electroconductive layer can also be formed by laminating an
 electroconductive thin film. Examples of the electroconductive thin film
 include a metal foil and an electroconductive plastic film. More
 specifically, the metal foil laminating material includes an aluminum
 foil, and the electroconductive plastic film laminating material includes
 a polyethylene resin to which carbon black is incorporated. The aluminum
 foil may be any of hard type and soft type, and the thickness thereof is
 preferably from 5 .mu.m to 20 .mu.m.
 The polyethylene resin laminate film containing carbon black is preferably
 obtained using an extrusion laminating method. The method comprises
 melting polyolefin by heating, forming a film, immediately pressing the
 film on paper, and cooling it for laminating. Various apparatus are known
 for conducting the method. The thickness of the laminate layer is
 preferably from 10 .mu.m to 30 .mu.m. As the support having an
 electroconductivity as a whole, a plastic film having an
 electroconductivity and a metal sheet can be used as they are as far as
 the water-resistivity is satisfied.
 The plastic film having an electroconductivity includes a polypropylene or
 polyester film to which an electroconductive filer such as carbon fiber or
 carbon black is incorporated. The metal sheet includes aluminum. The
 thickness of the substrate is preferably from 80 .mu.m to 200 .mu.m. If it
 is less than 80 .mu.m, mechanical strength as a printing plate may be
 insufficient. On the other hand, if it exceeds 200 .mu.m, a handling
 property such as a transportability in a recording apparatus tends to
 decrease.
 The support comprising a water-resistant substrate having provided thereon
 a layer having an electroconductivity is described in more detail below.
 As the water-resistant substrate, those described above can be employed. In
 order to form an electroconductive layer on a water-resistant substrate,
 the methods as described in the formation of the support having an
 electroconductivity as a whole can be used. Specifically, one surface of
 the substrate is coated with a layer containing an electroconductive filer
 and a binder and having a thickness of from 5 .mu.m to 20 .mu.m, or
 laminated with a metal foil or a plastic film having an
 electroconductivity.
 Furthermore, in addition to the methods described above, for example, a
 vacuum evaporated film of a metal such as aluminum, tin, palladium or gold
 may be provided on a plastic film.
 According to the methods described above, the water-resistant support
 having a specific electric resistance of 10.sup.10 .OMEGA.cm or less as a
 whole of the support can be obtained.
 An under layer may be provided on a surface of the support in order to
 further improve the water resistance of the support and to enhance
 adhesion between the support and the image receiving layer provided
 thereon. In this case, the surface smoothness of the under layer should be
 controlled in the range described above.
 Also, a backcoat layer may be proved on a surface of the support opposite
 to the image receiving layer for preventing curling. When a resulting
 printing plate is mounted on an offset printing machine for printing, it
 is desired that the printing plate is accurately set on the printing
 machine without the occurrence of slide or slip. It is preferred that the
 backcoat layer has the Bekk smoothness of from 150 (second/10 ml) to 700
 (second/10 ml).
 The water-resistant support provided with the under layer and/or the
 backcoat layer is also referred to as the water-resistant support
 sometimes.
 The under layer or the backcoat layer is formed by coating and drying or
 laminating a coating composition containing a resin, a pigment and other
 additive on the support. The resin can be appropriately selected from
 various resins. Specifically, they include those described for the
 electroconductive layer above.
 Furthermore, the pigment includes clay, kaolin, talc, diatom earth, calcium
 carbonate, aluminum hydroxide, magnesium hydroxide, titanium oxide and
 mica. In order to attain the desired smoothness, the pigment is preferably
 used by appropriately selecting its grain size. For example, when a
 relatively high smoothness is required in the under layer, pigment from
 which small-sized and large-sized grains are cut off, specifically, having
 a grain size of about 0.5 .mu.m to about 10 .mu.m is preferably used. The
 pigment described above is preferably used at a ratio of 80 parts to 200
 parts by weight in the backcoat layer based on 100 parts by weight of
 resin. In order to obtain excellent water resistance, the under layer and
 the backcoat layer effectively contain a water resistance imparting agent
 such as a melamine resin and a polyamide epichlorohydrin resin. The
 above-described grain size can be measured using a scanning electron
 microscopic (SEM) photograph. When the grain is not spherical, the size is
 a diameter determined by converting a projected area to a circle.
 When the lithographic printing plate precursor is prepared according to the
 present invention, generally, a solution containing components for the
 under layer is applied onto one side of the support, followed by drying to
 form the under layer, if necessary, a solution containing components for
 the backcoat layer is further applied onto the other side of the support,
 followed by drying to form the backcoat layer, if necessary, and
 subsequently, a coating solution containing components for the image
 receiving layer is applied, followed by drying to form the image receiving
 layer. The coating amounts of the image receiving layer, the under layer
 and the backcoat layer are each suitably from 1 g/m.sup.2 to 30 g/m.sup.2,
 and preferably from 6 g/m.sup.2 to 20 g/m.sup.2.
 More preferably, the thickness of the water-resistant support provided with
 the under layer and the backcoat layer ranges from 90 .mu.m to 130 .mu.m,
 and preferably from 100 .mu.m to 120 .mu.m.
 The image receiving layer is provided on the water-resistant support, and
 the thickness thereof is preferably from 5 .mu.m to 50 .mu.m.
 The image receiving layer comprises, for example, a water-soluble binder,
 an inorganic pigment and a water-resistance imparting agent as its main
 component. The binder includes a water-soluble resin, for example, PVA,
 modified PVA (e.g., carboxy modified PVA), starch and derivatives thereof,
 CMC, hydroxyethyl cellulose, casein, gelatin, polyvinylpyrrolidone, a
 copolymer of vinyl acetate and crotonic acid, and a copolymer of styrene
 and maleic acid.
 The water resistance imparting agent includes glyoxal, a primary
 condensation product of a melamine formaldehyde resin or urea formaldehyde
 resin, a modified polyamide resin such as methylol polyamide resin, a
 polyamide-polyamine-epichlorohydrin resin, a polyamide-epichlorohydrin
 resin, and a modified polyamide-polyimide resin. Examples of the inorganic
 pigment include kaolin, clay, calcium carbonate, silica, titanium oxide,
 zinc oxide, barium sulfate, and alumina. Among these, silica is preferred.
 In addition, the image receiving layer may contain a crosslinking catalyst
 such as ammonium chloride or a silane coupling agent.
 A method for forming an image on the lithographic printing plate precursor
 as described above (hereinafter also referred to as a "master") is
 described below. One example of a device system suitable for performing
 such a method is shown in FIG. 1.
 The device system shown in FIG. 1 comprises an ink jet recording device 1
 using an oil-based ink.
 As shown in FIG. 1, pattern information of images (figures or letters) to
 be formed on a master 2 is first supplied from an information supply
 source such as a computer 3 to the ink jet recording device 1 using
 oil-based ink through a transmittal means such as a path 4. A head for ink
 jet recording 10 of the recording device 1 stores oil-based ink therein,
 and sprays fine droplets of the ink on the master 2 according to the
 above-described information, when the master 2 passes through in the
 recording device 1, whereby the ink adheres to the master 2 in accordance
 with the above-described pattern.
 Thus, the image formation on the master 2 is completed to obtain a printing
 plate.
 Components of the ink jet recording device as shown in the device system of
 FIG. 1 are shown in FIG. 2 and FIG. 3, respectively. In FIG. 2 and FIG. 3,
 members common to the members in FIG. 1 are designated using the same
 symbols. FIG. 2 is a schematic view showing a main part of such an ink jet
 recording device, and FIG. 3 is a sectional view showing a part of the
 head.
 The head 10 attached to the ink jet recording device has a slit between an
 upper unit 101 and a lower unit 102, a leading edge thereof forms a
 discharge slit 10a, a discharge electrode 10b is arranged in the slit, and
 the inside of the slit is filled with oil-based ink 11, as shown in FIG. 2
 and FIG. 3.
 In the head 10, voltage is applied to the discharge electrode 10b according
 to a digital signal of pattern information of image. As shown in FIG. 2, a
 counter electrode 10c is provided opposite to the discharge electrode 10b,
 and the master 2 is placed on the counter electrode 10c. The application
 of voltage forms a circuit between the discharge electrode 10b and the
 counter electrode 10c, and the oil-based ink 11 is discharged from the
 discharge slit 10a of the head 10, thereby forming images on the master 2
 placed on the counter electrode 10c.
 It is preferred that the width of the discharge electrode 10b is as narrow
 as possible in its leading edge, for forming images of high quality by
 printing.
 For example, the head of FIG. 3 is filled with the oil-based ink, the
 discharge electrode 10b whose leading edge has a width of 20 .mu.m is
 used, the distance between the discharge electrode 10b and the counter
 electrode 10c is adjusted to 1.5 mm, and a voltage of 3 kV is applied
 between these electrodes for 0.1 millisecond, whereby a 40 .mu.m-dot can
 be formed on the master 2.
 The present invention will be described in greater detail with reference to
 the following examples, but the present invention should not be construed
 as being limited thereto.
 SYNTHESIS EXAMPLE 1 OF RESIN FOR DISPERSION STABILIZATION (P)
 Synthesis of Resin for Dispersion Stabilization (P-1)
 A mixed solution of 96 g of octadecyl methacrylate, 4 g of
 4-(2-methacryloyloxyethyloxycarbonyl)butyric acid and 200 g of toluene was
 heated to a temperature of 75.degree. C. under nitrogen gas stream with
 stirring. To the solution was added 1.5 g of 2,2'-azobis(isobutyronitrile)
 (abbreviated as AIBN) as a polymerization initiator, followed by reacting
 for 4 hours. Then, 0.8 g of AIBN was added to the reaction mixture and the
 reaction was further continued for 4 hours.
 After cooling the reaction mixture to 25.degree. C., 6 g of allyl alcohol
 was added with stirring and then a mixed solution of 10 g of
 dicyclohexylcarbodiimide (abbreviated as DCC), 0.1 g of
 4-(N,N-diethylamino)-pyridine and 30 g of methylene chloride was dropwise
 added thereto over a period of one hour, followed by reacting for 3 hours.
 To the reaction mixture was added 10 g of a 80% aqueous solution of formic
 acid and the resulting mixture was stirred for one hour. After removing
 the insoluble substance by filtration, the filtrate was reprecipitated in
 2.5 liters of methanol. The resulting precipitate was collected by
 filtration and dissolved in 200 g of toluene. After removing the insoluble
 substance by filtration, the filtrate was reprecipitated in one liter of
 methanol. The resulting precipitate was collected by filtration and dried
 to obtain 70 g of the desired copolymer. A weight average molecular weight
 (Mw) thereof was 5.times.10.sup.4. The weight average molecular weight
 (Mw) was measured by GPC method and calculated in terms of polystyrene
 (hereinafter the same).
 Resin (P-1)
 ##STR19##
 SYNTHESIS EXAMPLE 2 OF RESIN FOR DISPERSION STABILIZATION (P)
 Synthesis of Resin for Dispersion Stabilization (P-2)
 A mixed solution of 50 g of dodecyl methacrylate, 45 g of octadecyl
 acrylate, 5 g of glycidyl methacrylate and 200 g of toluene was heated to
 a temperature of 75.degree. C. under nitrogen gas stream with stirring. To
 the solution was added 1.8 g of AIBN, followed by reacting for 4 hours.
 Then, 0.5 g of AIBN was added to the reaction mixture, followed by
 reacting for 3 hours, and further 0.3 g of AIBN was added thereto,
 followed by reacting for 3 hours.
 To the reaction mixture were added 6 g of 3-acryloyloxypropionic acid, 1.0
 g of N,N-dimethyldodecylamine and 0.5 g of tert-butylhydroquinone, and the
 mixture was stirred at a temperature of 100.degree. C. for 10 hours. After
 cooling the reaction mixture, it was reprecipitated in 2 liters of
 methanol to obtain 82 g of the desired copolymer as white powder. A weight
 average molecular weight (Mw) thereof was 4.times.10.sup.4.
 Resin (P-2)
 ##STR20##
 SYNTHESIS EXAMPLE 3 OF RESIN FOR DISPERSION STABILIZATION (P)
 Synthesis of Resin for Dispersion Stabilization (P-3)
 A mixed solution of 96 g of tridecyl methacrylate, 4 g of
 11-methacrylamidoundecanoic acid and 200 g of toluene was heated to a
 temperature of 75.degree. C. under nitrogen gas stream with stirring. To
 the solution was added 1.0 g of AIBN, followed by reacting for 4 hours.
 Then, 0.5 g of AIBN was added to the reaction mixture, followed by
 reacting for 3 hours, and further 0.3 g of AIBN was added thereto,
 followed by reacting for 3 hours.
 After cooling the reaction mixture to a temperature of 40.degree. C., 0.2 g
 of hydroquinone, 6.9 g of vinyl acetate and 0.05 g of mercury acetate were
 added thereto, followed by reacting for 2 hours. The temperature thereof
 was again raised to 70.degree. C., 7.5.times.10.sup.-3 ml of 100% of
 sulfuric acid was added thereto and the mixture was reacted for 6 hours.
 To the reaction mixture was added 0.04 g of sodium acetate trihydrate, the
 mixture was thoroughly stirred and poured into 4.5 liters of methanol for
 reprecipitation and purification to obtain 75 g of the desired copolymer
 as slightly brownish viscous solid. A weight average molecular weight (Mw)
 thereof was 5.3.times.10.sup.4.
 Resin (P-3)
 ##STR21##
 SYNTHESIS EXAMPLE 4 OF RESIN FOR DISPERSION STABILIZATION (P)
 Synthesis of Resin for Dispersion Stabilization (P-4)
 A mixed solution of 97 g of hexadecyl methacrylate, 3 g of Monomer (Y-1)
 having the structure shown below and 400 g of isodecane was heated to a
 temperature of 70.degree. C. under nitrogen gas stream with stirring. To
 the solution was added 1.5 g of 2,2'-azobis(isovaleronitrile) (abbreviated
 as AIVN) as a polymerization initiator with stirring, followed by reacting
 for 4 hours. Then, 0.8 g of AIVN was added to the reaction mixture,
 followed by reacting for 3 hours, and further 0.5 g of AIVN was added
 thereto, followed by reacting for 3 hours. The solid content of the
 resulting reaction mixture was 19.9% by weight. A weight average molecular
 weight (Mw) of the copolymer obtained was 4.times.10.sup.4.
 Monomer (Y-1)
 ##STR22##
 Resin (P-4)
 ##STR23##
 PREATION EXAMPLE 1 OF LATEX TICLE
 Preparation of Latex Particle (D-1)
 A mixed solution of 10 g of Resin for Dispersion Stabilization (P-1), 100 g
 of vinyl acetate, 3 g of octadecyl methacrylate and 392 g of Isopar H was
 heated to a temperature of 70.degree. C. under nitrogen gas stream with
 stirring. To the solution was added 1.0 g of 2,2'-azobis(isovaleronitrile)
 (abbreviated as AIVN) as a polymerization initiator with stirring,
 followed by reacting for 3 hours. Then, 0.8 g of AIBN was added as a
 polymerization initiator to the reaction mixture and the mixture was
 heated to a temperature of 80.degree. C., followed by reacting for 4
 hours. The temperature of the reaction mixture was raised to 100.degree.
 C., followed by stirring for 2 hours, thereby distilling off the unreacted
 monomers. After cooling the reaction mixture, it was passed through a
 nylon cloth of 200 mesh. The resulting white dispersion was a latex having
 a polymerization rate of 97% and an average particle diameter of 0.20
 .mu.m. The particle diameter was measured by CAPA-500 manufactured by
 Horiba Ltd. (hereinafter the same).
 A part of the above-described white dispersion was centrifuged at a
 rotation of 1.times.10.sup.4 r.p.m. for one hour and the resin particles
 precipitated were collected and dried. A weight average molecular weight
 (Mw) of the resin particles was 2.times.10.sup.5. A glass transition point
 (Tg) thereof was 36.degree. C.
 PREATION EXAMPLE 2 OF LATEX TICLE
 Preparation of Latex Particle (D-2)
 A mixed solution of 12 g of Resin for Dispersion Stabilization (P-2) and
 177 g of Isopar H was heated to a temperature of 60.degree. C. under
 nitrogen gas stream with stirring. To the solution was added dropwise a
 mixed solution of 25 g of methyl methacrylate, 75 g of ethyl acrylate, 4 g
 of octadecyl acrylate, 200 g of Isopar H and 1.5 g of AIVN over a period
 of 2 hours, followed by stirring for 2 hours. Then, 0.8 g of AIBN was
 added to the reaction mixture and the mixture was heated to a temperature
 of 80.degree. C., followed by reacting for 3 hours. After cooling the
 reaction mixture, it was passed through a nylon cloth of 200 mesh. The
 resulting white dispersion was a latex having a polymerization rate of
 100% and an average particle diameter of 0.22 .mu.m. A weight average
 molecular weight (Mw) of the resin particles was 2.times.10.sup.5. A glass
 transition point (Tg) thereof was 26.degree. C.
 PREATION EXAMPLES 3 TO 12 OF LATEX TICLE
 Preparation of Latex Particles (D-3) to (D-12)
 Each of the latex particles was prepared in the same manner as in
 Preparation Example 1 of Latex Particle expect for using a mixed solution
 of 9 g of Resin for Dispersion Stabilization (P-3), 100 g of vinyl
 acetate, Monomer (C) shown in Table 1 and 400 g of Isopar G.
 A polymerization rate of each of the resulting latex particles was in a
 range of from 96% to 98%. An Mw of each of the resin particles was in a
 range of from 1.times.10.sup.5 to 3.times.10.sup.5, and a Tg thereof was
 in a range of from 35.degree. C. to 38.degree. C.
 TABLE 1
 Latex
 Average
 Preparation Particle
 Particle
 Example (D) Monomer (C)
 Diameter
 3 D-3 Vinyl Oleate 5 g
 0.18 .mu.m
 4 D-4 Octadecyl Vinyl Ether 4.5 g
 0.19 .mu.m
 5 D-5
 ##STR24##
 2 g 0.20 .mu.m
 6 D-6
 ##STR25##
 3 g 0.22 .mu.m
 7 D-7
 ##STR26##
 3.5 g 0.21 .mu.m
 8 D-8
 ##STR27##
 5 g 0.23 .mu.m
 9 D-9
 ##STR28##
 3 g 0.22 .mu.m
 10 D-10
 ##STR29##
 2.5 g 0.20 .mu.m
 11 D-11
 ##STR30##
 3 g 0.23 .mu.m
 12 D-12
 ##STR31##
 2 g 0.21 .mu.m
 PREATION EXAMPLES 13 TO 19 OF LATEX TICLE
 Preparation of Latex Particles (D-13) to (D-19)
 Each of the latex particles was prepared in the same manner as in
 Preparation Example 2 of Latex Particle expect for using each of Resin for
 Dispersion Stabilization (P) shown in Table 2 below in place of 12 g of
 Resin for Dispersion Stabilization (P-2).
 A polymerization rate of each of the resulting latex particles was in a
 range of from 95% to 100% and an average particle diameter thereof was in
 a range of from 0.18 .mu.m to 0.25 .mu.m with good monodispercity. An Mw
 of each of the resin particles was in a range of from 1.times.10.sup.5 to
 3.times.10.sup.5, and a Tg thereof was in a range of from 24.degree. C. to
 28.degree. C.
 TABLE 2
 Latex
 Preparation Particle
 Example (D) Resin for Dispersion Stabilization (P)
 Amount
 13 D-13 P-5
 ##STR32##
 8 g
 14 D-14 P-6
 ##STR33##
 11 g
 15 D-15 P-7
 ##STR34##
 12 g
 16 D-16 P-8
 ##STR35##
 9 g
 17 D-17 P-9
 ##STR36##
 12 g
 18 D-18 P-10
 ##STR37##
 11 g
 19 D-19 P-11
 ##STR38##
 12 g
 PREATION EXAMPLES 20 TO 26 OF LATEX TICLE
 Preparation of Latex Particles (D-20) to (D-26)
 Each of the latex particles was prepared in the same manner as in
 Preparation Example 2 of Latex Particle expect for using each of the
 compounds shown in Table 3 below in place of Monomer (A) i.e., methyl
 methacrylate and ethyl acrylate, Monomer (C) i.e., octadecyl acrylate, and
 Resin for Dispersion Stabilization (P-2), respectively.
 A polymerization rate of each of the resulting latex particle was in a
 range of from 95% to 100% and an average particle diameter thereof was in
 a range of from 0.18 .mu.m to 0.25 .mu.m with good monodispercity.
 TABLE 3
 Resin for
 Pre- Latex Dispersion
 Tg of
 paration Particle Stabilization
 Resin
 Example (D) Monomer (A) (P) Monomer (C)
 Particle
 20 D-20 Methyl Methacrylate 50 g P-16 10 g CH.sub.2
 .dbd.CH--CONH(CH.sub.2).sub.3 COOC.sub.13 H.sub.27 3 g 27.degree. C.
 Ethyl Acrylate 50 g
 21 D-21 Methyl Methacrylate 25 g P-5 10 g Octadecyl
 .alpha.-Chloroacrylate 2 g 26.degree. C.
 Methyl Acrylate 75 g
 22 D-22 Methyl Methacrylate 25 g P-11 11 g Tetradecyl
 .alpha.-Cyanoacrylate 3 g 27.degree. C.
 Methyl Acrylate 75 g
 23 D-23 Ethyl Methacrylate 60 g P-6 12 g Dodecyl
 Acrylate 2 g 28.degree. C.
 Methyl Acrylate 40 g
 ##STR39##
 1 g
 24 D-24 Methyl Methacrylate 2-Cyanoethyl Acrylate Methyl Acrylate
 20 g 8 g 72 g P-13 10 g
 ##STR40##
 3 g 30.degree. C.
 25 D-25 Vinyl Acetate Styrene Vinyl Propionate 80 g 10 g 10 g P-4
 12 g
 ##STR41##
 3 g 34.degree. C.
 26 D-26 Methyl Methacrylate Acrylic Acid Methyl Acrylate 20 g 5
 g 75 g P-14 9 g Docosanyl Acrylate 4 g
 32.degree. C.
 PREATION EXAMPLE 27 OF LATEX TICLE
 Preparation of Comparative Latex Particle (D-27)
 A white dispersion of latex particles was prepared in the same manner as in
 Preparation Example 1 of Latex Particle expect for eliminating 3 g of
 octadecyl methacrylate corresponding to Monomer (C). The white dispersion
 of latex particles had a polymerization rate of 95% and an average
 particle diameter of 0.24 .mu.m. An Mw of the resin particles was
 1.times.10.sup.5 and a Tg thereof was 38.degree. C.
 EXAMPLE 1
 Preparation of Lithographic Printing Plate Precursor
 A composition having the following component was placed in a paint shaker
 (manufactured by Toyo Seiki Co., Ltd.) together with glass beads and
 dispersed for 60 minutes. Then, the glass beads were removed by filtration
 to obtain a dispersion.

10% Aqueous Solution of Gelatin 94 g
 Silica: Silysia 430 (average particle 21.9 g
 size: 2.5 .mu.m; manufactured by Fuji
 Silysia Chemical Co., Ltd.)
 20% Solution of Colloidal Silica: Snowtex 90 g
 C (average particle size: 10-20 nm;
 manufactured by Nissan Chemical
 Industries, Ltd.)
 Fluorinated Alkyl Ester: FC 430 0.24 g
 (manufactured by 3M Co.)
 Hardening Compound 1.20 g
 [CH.sub.2 .dbd.CHSO.sub.2 CH.sub.2 CONH(CH.sub.2).sub.3 NHCOCH.sub.2
 SO.sub.2 CH.dbd.CH.sub.2 ]
 Water 65 g
 On a support of Metalme 100TS (manufactured by Toyo Metalizing Co., Ltd.)
 comprising a PET film having a thickness of 100 .mu.m having provided
 thereon a vacuum evaporated aluminum layer, the above-described
 composition was coated using a wire bar and dried at 100.degree. C. for 10
 minutes to form an image receiving layer having a dry coating amount of 8
 g/m.sup.2, thereby obtaining a lithographic printing plate precursor.
 The Bekk smoothness of the surface of the printing plate precursor was 250
 (second/10 ml), and the contact angle with water thereof was 0 degree.
 The smoothness of the image receiving layer was determined by measuring the
 smoothness (second/10 ml) of the printing plate precursor using a Bekk
 smoothness tester (manufactured by Kumagaya Riko Co., Ltd.) under the
 condition of an air volume of 10 ml.
 The contact angle of the image receiving layer with water was determined by
 placing 2 .mu.l of distilled water on the surface of the printing plate
 precursor and measuring the surface contact angle (degree) after 30
 seconds using a surface contact angle meter (CA-D, manufactured by Kyowa
 Kaimen Kagaku Co., Ltd.).
 Preparation of Oil-Based Ink (IK-1)
 Ten grams of dodecyl methacrylate/acrylic acid copolymer (copolymerization
 ratio: 95/5 by weight), 10 g of Alkali Blue and 30 g of Shellsol 71 were
 placed in a paint shaker (manufactured by Toyo Seiki Co., Ltd.) together
 with glass beads and dispersed for 4 hours to obtain a fine dispersion of
 Alkali Blue.
 Fifty-five grams (as a solid basis) of Latex Particle (D-1) according to
 Preparation Example 1 of Latex Particle, 18 g of the above-described
 Alkali Blue dispersion, 20 g of tetradecyl alcohol (FDC-1400 manufactured
 by Nissan Chemical Industries, Ltd.) and 0.08 g of octadecene maleic acid
 monooctadecylamide copolymer were diluted with one liter of Isopar G,
 thereby obtaining blue oil-based ink.
 A servo plotter (DA8400, manufactured by Graphtech Co.) able to write an
 output from a personal computer was converted so that an ink discharge
 head as shown in FIG. 2 was mounted on a pen plotter section, and the
 lithographic printing plate precursor described above was placed on a
 counter electrode positioned at a distance of 1.5 mm from the ink
 discharge head. Printing was performed on the lithographic printing plate
 precursor using Oil-Based Ink (IK-1) described above to make a plate. The
 counter electrode was electrically connected with the vacuum evaporated
 aluminum layer provided directly under the image receiving layer of the
 precursor using silver paste at the plate making. Successively, heating
 was carried out for 20 seconds using a Ricoh Fuser Model 592 (manufactured
 by Ricoh Co., Ltd.) so as to adjust the surface temperature of the ink
 image formed to 70.degree. C., thereby sufficiently fixing the image area.
 The image on the resulting printing plate was visually observed under an
 optical microscope of 200 magnifications. As a result, the image had no
 problem, fine lines and fine letters were good, defect such as blur,
 disappearance or spread was not observed, and contamination was not
 observed in the non-image area.
 The printing plate was subjected to printing using, as dampening water, a
 solution prepared by diluting SLM-OD (manufactured by Mitsubishi Paper
 Mills, Ltd.) 50 times with water, Oliver 94 type (manufactured by Sakurai
 Seisakusho Co., Ltd.) as a printing machine, and a black ink for offset
 printing.
 As a result, 3000 sheets or more of prints having clear images without the
 occurrence of background stain were obtained.
 Using the above-described ink jet printer, an ink jet test was conducted.
 As a result, it was found that stable ink jet was obtained even after the
 lapse of 500 hours.
 The oil-based ink of the present invention stored at room temperature for 6
 months showed no formation of aggregates, and gave stable ink jet in the
 ink jet test same as described above.
 When a printing plate was prepared using the oil-based ink stored for 6
 months and printing was conducted in the same manner as above, 3000 sheets
 or more of prints having clear images without the occurrence of background
 stain were obtained.
 Furthermore, the redispersibility of the oil-based ink was evaluated under
 enforced conditions. Specifically, the discharge head used in the
 above-described printer was filled with the ink, taken away and allowed to
 stand at 35.degree. C. for 3 days. Then, the discharge head was immersed
 in Isopar G for 3 minutes, followed by mild stirring. Thereupon, Oil-Based
 Ink (IK-1) was all removed from the inside of the slit. This is considered
 to be caused by that Oil-Based Ink (IK-1) adhered to the leading edge of
 the slit of the discharge head in the non-fluid state during the standing
 was easily redispersed upon the solvation with the dispersing medium.
 From these results it can be seen that the oil-based ink of the present
 invention is excellent in stability of ink discharge and forms clear
 images without the occurrence of stain even when it has been continuously
 employed for a long period of time, and provides a printing plate having
 good press life.
 COMATIVE EXAMPLE A
 Comparative Example A was conducted in the same manner as in Example 1 with
 the exception that Oil-Based Ink (IKR-1) for Comparison described below
 was employed in place of Oil-Based Ink (IK-1) used in Example 1 to prepare
 a lithographic printing plate.
 Oil-Based Ink (IKR-1) for Comparison
 Oil-Based Ink (IKR-1) for Comparison was prepared in the same manner as in
 Oil-Based Ink (IK-1) with the exception that 55 g (as a solid basis) of
 Comparative Latex Particle (D-27) was employed in place of Latex Particle
 (D-1) used in Oil-Based Ink (IK-1).
 When the lithographic printing plate obtained in Comparative Example A
 described above was subjected to the printing in the same manner as in
 Example 1, 3000 sheets or more of prints having clear images without the
 occurrence of background stain were obtained.
 However, in the ink jet test, Oil-Based Ink (IKR-1) for Comparison became
 unstable in ink discharge after the lapse of 250 hours. Further, in
 Oil-Based Ink (IKR-1) for Comparison stored for 6 months, coagulated
 precipitates were deposited and were not redispersed even on shaking.
 Furthermore, with Oil-Based Ink (IKR-1) the enforced test of ink
 redispersibility was conducted under the same conditions as in Example 1.
 As a result, it was found that deposits remained in the slit of the
 discharge head.
 EXAMPLES 2 TO 6 AND COMATIVE EXAMPLES B TO C
 Using high quality paper having a basis weight of 100 g/m.sup.2 as a
 substrate, one surface of the substrate was coated with a coating for a
 backcoat layer having the composition shown below using a wire bar to form
 the backcoat layer having a dry coating amount of 12 g/m.sup.2. The Bekk
 smoothness of the surface of the backcoat layer was adjusted to 50
 (second/10 ml) by a calendar treatment.
 Coating for Backcoat Layer

Kaolin (50% aqueous dispersion) 200 parts
 Polyvinyl Alcohol (10% aqueous solution) 60 parts
 SBR Latex (solid content: 50%, Tg 0.degree. C.) 100 parts
 Melamine Resin 5 parts
 (solid content: 80%, Sumirez resin SR-613)
 The other surface of the substrate was coated with each of Coatings A to G
 for an under layer having the composition shown in Table 4 below using a
 wire bar to form the under layer having a dry coating amount of 10
 g/m.sup.2. Then, a calendar treatment was conducted so that the Bekk
 smoothness of the under layer is adjusted to about 1500 (second/10 ml).
 The resulting water-resistant supports using Coatings A to G were
 designated Support Sample Nos. 1 to 7, respectively.
 TABLE 4
 Composition
 (% by weight on solid basis) Support
 Carbon SBR Melamine Sample
 Coating Black Clay Latex Resin No.
 A 0 60 36 4 1
 B 3 57 36 4 2
 C 5.4 54.6 36 4 3
 D 7.2 52.8 36 4 4
 E 9 51 36 4 5
 F 15 45 36 4 6
 G 30 30 36 4 7
 Coating for Under Layer

Carbon Black (30% aqueous dispersion)
 Clay (50% aqueous dispersion)
 SBR Latex (solid content: 50%, Tg 25.degree. C.)
 Melamine Resin
 (solid content: 80%, Sumirez resin SR-613)
 The components were mixed according to the amounts shown in Table 4, and
 water was added thereto to adjust the total solid content to 25%, thereby
 obtaining Coatings A to G for the under layer.
 Specific Electric Resistance of Under Layer
 The specific electric resistance of the under layer was measured in the
 following manner.
 Each of Coatings A to G for the under layer was coated on a sufficiently
 degreased and washed stainless plate to prepare a layer having a dry
 coating amount of 10 g/m.sup.2. The specific electric resistance of the
 resulting 7 samples were measured by a three terminal process having a
 guard electrode according to JIS K-6911. The results are shown in Table 5
 below.
 TABLE 5
 Coating for Specific Electric
 Under Layer Resistance (.OMEGA.cm)
 A 2 .times. 10.sup.12
 B 1 .times. 10.sup.11
 C 4 .times. 10.sup.9
 D 1 .times. 10.sup.8
 E 7 .times. 10.sup.4
 F 5 .times. 10.sup.3
 G 4 .times. 10.sup.3
 On the under layer of each of Support Sample Nos. 1 to 7 was coated a
 dispersion having the composition shown below to form an image receiving
 layer having a dry coating amount of 6 g/m.sup.2, thereby preparing a
 lithographic printing plate precursor. The Bekk smoothness of the surface
 of each printing plate precursor was in a range of from 200 to 230
 (second/10 ml), and the contact angle with water thereof was 5 degrees or
 less.
 Coating for Image Receiving Layer
 A composition having the following component was placed in a paint shaker
 (manufactured by Toyo Seiki Co., Ltd.) together with glass beads and
 dispersed for 60 minutes. Then, the glass beads were removed by filtration
 to obtain a dispersion.

10% Aqueous Solution of Gelatin 100 g
 Silica: Silysia 310 (average 22 g
 particle size: 1.4 .mu.m; manufactured by
 Fuji Silysia Chemical Co., Ltd.)
 Alumina Sol 520 (average particle 90 g
 Size: 10-20 nm; manufactured by
 Nissan Chemical Industries, Ltd.)
 Fluorinated Alkyl Ester: FC 430 0.3 g
 (manufactured by 3M Co.)
 Hardening Compound 1.5 g
 [CH.sub.2 .dbd.CHSO.sub.2 (CH.sub.2).sub.2 O(CH.sub.2).sub.2
 O(CH.sub.2).sub.2 SO.sub.2 CH.dbd.CH.sub.2 ]
 Water 70 g
 Using the lithographic printing plate precursors thus prepared, plate
 making was conducted with Oil-Based Ink (IK-1) in the same manner as in
 Example 1. The counter electrode was electrically connected with the under
 layer provided directly under the image receiving layer of the precursor
 using silver paste at the plate making.
 Then, the printing plate was subjected to printing using a fully automatic
 printing machine (AM-2850 manufactured by AM Co., Ltd.) provided with
 dampening water prepared by diluting SLM-OD 50 times with distilled water
 in a dish for dampening water thereof and a black ink for offset printing.
 The properties of the printing plate and the print obtained were evaluated
 with respect to the points shown below. The results are shown in Table 6
 below.
 TABLE 6
 Support Image Quality
 Sample of Image Quality Press
 Example No. Printing Plate of Print Life
 2 3 Good Good 1500
 3 4 Very Good Very Good 3000
 4 5 Very Good Very Good 3000
 5 6 Very Good Very Good 3000
 6 7 Very Good Very Good 3000
 Comparative 1 Poor Poor 50
 Example B
 Comparative 2 Poor Poor 100
 Example C
 1) Image Quality of Printing Plate
 Images on the printing plate were visually observed under an optical
 microscope of 200 magnifications. The results are represented as follows:
 Very good: Completely no problem in images, very good fine lines and fine
 letters
 Good: No problem in images, good fine lines and fine letters
 Poor: Disappearance or blur of fine lines and fine letters
 2) Image Quality of Print
 The images of the print were evaluated in the same manner as the image
 quality of the printing plate described above. The image quality of the
 print was the same as that of the printing plate in each sample.
 3) Press Life
 The number of prints obtained was evaluated until background stain or
 disappearance of image was visually recognized on the print.
 With reference to the specific electrical resistance shown in Table 5, the
 results shown in Table 6 are investigated.
 In Examples 2 to 6 according to the present invention wherein the support
 having an under layer of a small specific electrical resistance of
 10.sup.9 to 10.sup.3 .OMEGA.cm is used, the images have no problem at all,
 reproduction of fine lines and fine letters is very good, and press life
 is also good. On the contrary, in Comparative Examples B and C wherein the
 support having an under layer of a large specific electrical resistance of
 10.sup.12 to 10.sup.11 .OMEGA.cm is used, disappearance or blur of image
 occurs on the printing plate precursor. Due to the blur, the resin layer
 of the image becomes thin and as a result, press life is poor.
 These results indicate that the higher the electroconductivity of the under
 layer provided directly under the image receiving layer, the better the
 image quality of plate making and the image quality of printing.
 EXAMPLE 7
 Preparation of Lithographic Printing Plate Precursor
 A composition having the following component was placed in a paint shaker
 (manufactured by Toyo Seiki Co., Ltd.) together with glass beads and
 dispersed for 60 minutes. Then, the glass beads were removed by filtration
 to obtain a dispersion.

10% Aqueous Solution of Gelatin 100 g
 Silica: Silysia 310 (manufactured by 25 g
 Fuji Silysia Chemical Co., Ltd.)
 Colloidal Silica: Snowtex C 100 g
 (manufactured by Nissan Chemical
 Industries, Ltd.)
 Sodium Dodecylbenzenesulfonate 2.0 g
 Hardening Compound 2.2 g
 [CH.sub.2 .dbd.CHCONH(CH.sub.2)NH(CH.sub.2).sub.2 NHCOCH.dbd.CH.sub.2
 ]
 Water 65 g
 Using the water-resistant support described in Example 6, the
 above-described composition was coated thereon using a wire bar and dried
 at 110.degree. C. for 20 minutes to form an image receiving layer having a
 coating amount of 6 g/m.sup.2, thereby obtaining a lithographic printing
 plate precursor. The Bekk smoothness of the surface of the printing plate
 precursor was 280 (second/10 ml), and the contact angle with water thereof
 was 5 degrees or less.
 Preparation of Oil-Based Ink (IK-2)
 Ten grams of poly(dodecyl methacrylate), 10 g of nigrosine and 30 g of
 Isopar H were placed in a paint shaker (manufactured by Toyo Seiki Co.,
 Ltd.) together with glass beads and dispersed for 4 hours to obtain a fine
 dispersion of nigrosine.
 Sixty grams (as a solid basis) of Latex Particle (D-2) according to
 Preparation Example 2, 35 g of the above-described nigrosine dispersion,
 20 g of isostearyl alcohol and 0.08 g of octadecyl vinyl ether maleic acid
 monododecylamide copolymer were diluted with one liter of Isopar G,
 thereby preparing black oil-based ink.
 Using the printing plate precursor and Oil-Based Ink (IK-2) described
 above, plate making was conducted to prepare a printing plate, and offset
 printing was performed in the same manner as in Example 6.
 The resulting prints had clear images without the occurrence of stain in
 the non-image area similar to the prints obtained in Example 1, and the
 press life of the printing plate was as good as 3000 sheets or more.
 Further, with Oil-Based Ink (IK-2), the ink jet test for 600 hours and the
 redispersibility under enforced conditions were carried out in the same
 manner as in Example 1. Good results similar to those in Example 1 were
 obtained.
 EXAMPLES 8 TO 30
 Plate making and printing were conducted in the same manner as in Example 1
 with the exception that each oil-based ink described in Table 7 shown
 below was used in place of Oil-Based Ink (IK-1). The oil-based inks used
 were prepared in the same manner as in Oil-Based Ink (IK-1) except for
 using 45 g (as a solid basis) of Latex Particle (D) described in Table 7
 shown below in place of Latex Particle (D-1).
 TABLE 7
 Example Oil-Based Ink Latex Particle (D)
 8 IK-3 D-8
 9 IK-4 D-3
 10 IK-5 D-4
 11 IK-6 D-5
 12 IK-7 D-6
 13 IK-8 D-7
 14 IK-9 D-9
 15 IK-10 D-10
 16 IK-11 D-11
 17 IK-12 D-12
 18 IK-13 D-13
 19 IK-14 D-14
 20 IK-15 D-15
 21 IK-16 D-16
 22 IK-17 D-18
 23 IK-18 D-19
 24 IK-19 D-21
 25 IK-20 D-23
 26 IK-21 D-24
 27 IK-22 D-20
 28 IK-23 D-17
 29 IK-24 D-22
 30 IK-25 D-25
 It has been found that the images on each printing plate had good qualities
 similar to those in Example 1, and the press life of each printing plate
 was 3000 sheets or more.
 Further, the ink jet test for 600 hours and the redispersibility under
 enforced conditions were performed in the same manner as in Example 1.
 Each oil-based ink exhibited good results similar to or more than those of
 Oil-Based Ink (IK-1) used in Example 1.
 EXAMPLE 31
 Preparation of Lithographic Printing Plate Precursor
 A composition having the following component was placed in a paint shaker
 together with glass beads and dispersed for 90 minutes. Then, the glass
 beads were removed by filtration to obtain a dispersion.

Silica: Silysia 445 (manufactured by 40 g
 Fuji Silysia Chemical Co., Ltd.)
 20% Solution of Colloidal Silica: 200 g
 Snowtex C (manufactured by Nissan
 Chemical Industries, Ltd.)
 50% Dispersion of Clay 40 g
 10% Solution of Polyvinyl Alcohol: 120 g
 PVA-117 (manufactured by Kuraray
 Co., Ltd.)
 Melamine Resin 2.0 g
 Sodium Chloride 0.2 g
 Water 50 g
 Using the support described in Example 6, the above-described dispersion
 was applied onto the support using a wire bar and dried to form an image
 receiving layer having a coating amount of 10 g/m.sup.2, thereby obtaining
 a lithographic printing plate precursor. The Bekk smoothness of the
 surface of the printing plate precursor was 230 (second/10 ml), and the
 contact angle with water thereof was 0 degree.
 The printing plate precursor was subjected to plate making and printing in
 the same manner as in Example 6 to prepare a lithographic printing plate
 except for using Oil-Based Ink (IK-26) having the composition shown below
 in place of Oil-Based Ink (IK-1).
 Preparation of Oil-Based Ink (IK-26)
 A mixture of 300 g of a white dispersion of Latex Particle (D-26) according
 to Preparation Example 26 and 5 g of Victoria Blue B was heated to a
 temperature of 100.degree. C. and stirred for 4 hours under heating. After
 cooling to room temperature, the mixture was passed through a nylon cloth
 of 200 mesh to remove the remaining dye, thereby obtaining a blue resin
 dispersion having an average particle diameter of 0.25 .mu.m.
 Then, 260 g of the above-described blue resin dispersion and 0.09 g of
 Charge Control Agent shown below were diluted with one liter of Shellsol
 71, thereby preparing blue oil-based ink. Charge Control Agent
 ##STR42##
 The prints thus-obtained had clear images without the occurrence of stain
 in the non-image area similar to the prints obtained in Example 1, and the
 press life of the printing plate was good as 3000 sheets or more.
 Further, with Oil-Based Ink (IK-26), the ink jet test for 600 hours and the
 redispersibility under enforced conditions were performed in the same
 manner as in Example 1. As a result Oil-Based Ink (IK-26) exhibited good
 results similar to those of Oil-Based Ink (IK-1).
 While the invention has been described in detail and with reference to
 specific embodiments thereof, it will be apparent to one skilled in the
 art that various changes and modifications can be made therein without
 departing from the spirit and scope thereof.