JP2011252092A - Ink composition, ink set, and image forming apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink composition that can exhibit an excellent effect in discharge stability even when the discharge of the ink composition is stopped, the ink composition is unattended for a predetermined period of time, and thereafter the discharge of the ink composition is resumed and that can prevent an image part from cracking even when a stress caused during cutting or the like is applied; and to provide an ink set and an image forming apparatus using the same.SOLUTION: The ink composition comprises: a water-soluble compound (S) and water, wherein the compound (S) contains color material particles, a predetermined water-soluble polymerizable compound, and a hydroxyl group bonded to an atom having double bond in a molecule and forming the double bond. The content of the water-soluble compound (S) is 50-10,000 ppm.

Description

  The present invention relates to an ink composition suitable for recording an image by ejecting ink by an inkjet method, an ink set, and an image forming method using the same.

  Inkjet technology has been applied as an image recording method for recording color images in the fields of office printers, home printers, and the like. As an ink used for inkjet recording, studies have been made to improve scratch resistance by adding a polymerizable monomer to an aqueous pigment ink and curing it. An ink jet recording method is disclosed in which printing is performed by attaching a reaction liquid containing a reaction agent that generates a photopolymerization initiator and an ink composition containing an acrylate monomer or a resin emulsion (for example, Patent Document 1). reference).

  Further, studies have been made to increase the degree of crosslinking of the formed image and increase the degree of adhesion to the recording medium. For example, an active energy ray-curable aqueous ink containing a polymerizable monomer having a specific structure is disclosed (for example, Patent Document 2).

  Further, as a technique for improving the storage stability of ink, it is disclosed that a polymerization inhibitor is added to a so-called solvent-based photopolymerizable ink composition that does not contain water (see, for example, Patent Document 3). .

JP-A-10-287035 JP 2007-314610 A JP 2003-127518 A

  However, in each of the above-described techniques, particularly when the ink composition is stopped from being discharged on the ink jet recording apparatus and left for a certain period of time, the discharge stability (recovery recovery performance) is extremely insufficient.

  In addition, in each of the above-described techniques, even when some stress is applied, such as when the formed image is cut into a desired size, there is no study on suppressing cracks in the image portion, and further improvements are made. It was sought after.

  The present invention has been made in view of the above, and is particularly excellent in ejection stability (restoration recovery property) even when ejection of an ink composition is stopped on an inkjet recording apparatus and left for a certain period of time, and then ejection is resumed. It is an object of the present invention to provide an ink composition, an ink set, and an image forming method using the ink composition that can obtain an effect and can suppress cracking of an image portion even when stress is applied.

Specific means for achieving the above object are as follows.
<1> Colorant particles, a water-soluble polymerizable compound represented by the following general formula (1), a water-soluble compound containing a double bond and a hydroxyl group bonded to an atom forming the double bond in the molecule An ink composition comprising (S) and water, wherein the content of the water-soluble compound (S) is from 50 ppm to 10,000 ppm on a mass basis.

[In General Formula (1), Q represents an n-valent linking group, and R ¹ represents a hydrogen atom or a methyl group. N represents an integer of 1 or more. ]

  <2> The ink composition according to <1>, wherein the content of the water-soluble compound (S) is 100 ppm or more and 5000 ppm or less on a mass basis.

  <3> The ink composition according to <1> or <2>, wherein the water-soluble compound (S) is represented by any one of the following general formulas (S1) and (S2). It is.

[In General Formula (S1), Z represents a group having a benzene ring or a condensed ring thereof, or a group having a heterocycle, and p is 1 ≦ when the number of double bonds contained in Z is q. It is an integer of p ≦ 2q. ]

[In general formula (S2), Rs represents a C1-C10 chain saturated hydrocarbon group or a C3-C10 cyclic saturated hydrocarbon group. ]

<4> The ink composition according to <3>, wherein 2 ≦ p ≦ 6 in the water-soluble compound (S1).
<5> The ink composition according to any one of <1> to <4>, further comprising an initiator that initiates polymerization of the polymerizable compound by active energy rays.
<6> An ink set comprising: the ink composition according to any one of <1> to <5>; and a treatment liquid containing a flocculant that aggregates the components in the ink composition. is there.

<7> The ink set according to <6>, wherein the flocculant is an organic acid.
<8> An ink application step for applying the ink composition according to any one of <1> to <5> onto a recording medium, and a treatment liquid containing a flocculant that aggregates the components in the ink composition. And an image forming method characterized by including a treatment liquid applying step for applying to the recording medium.

  According to the present invention, the discharge of the ink composition on the ink jet recording apparatus is stopped and allowed to stand for a certain period of time. It is possible to provide an ink composition, an ink set, and an image forming method using the same, which can suppress cracking of an image portion even when stress is applied.

It is a schematic block diagram which shows the structural example of the inkjet recording device used for implementation of the image forming method of this invention.

Hereinafter, the ink composition, ink set, and image forming method using the same according to the present invention will be described in detail.
<Ink composition>
The ink-jet ink composition of the present invention (hereinafter, also simply referred to as “ink composition”) is a so-called aqueous ink composition using water as a medium, and includes at least one kind of colorant particles and the following general formula (1). ) And at least one water-soluble compound (S) containing a double bond and a hydroxyl group bonded to an atom forming the double bond in the molecule. And the content of the water-soluble compound (S) is 50 ppm or more and 10,000 ppm or less on a mass basis. Further, the ink composition of the present invention is configured to contain other components as required.

In general formula (1), Q represents an n-valent linking group, and R ¹ represents a hydrogen atom or a methyl group. N represents an integer of 1 or more.

  The present invention uses the ink composition having such a configuration to stop the ejection of the ink composition on the ink jet recording apparatus and leave it for a certain period of time. For example, when a formed image is processed into a predetermined size, even if a stress is applied to the image portion, the crack can be suppressed.

  Although the mechanism of the present invention is not clear, the ink composition of the present invention has a structure represented by the general formula (1) in which a water-soluble polymerizable compound includes an acrylamide structure in the molecule. Since the water-soluble compound (S) containing a heavy bond and a hydroxyl group bonded to an atom forming the double bond is contained in a specific content, the polymerization of the polymerizable compound (the compound of the general formula (1)) is performed. The properties are controlled within an appropriate range, and even when the ejection of the ink composition is stopped on the ink jet recording apparatus and allowed to stand for a certain period of time, and after the ejection is resumed, an excellent effect is obtained in ejection stability (stand recovery). It is considered a thing. Furthermore, the polymerizability of the polymerizable compound (the compound of the general formula (1)) is controlled within an appropriate range, and an appropriate stretch is imparted to the formed image portion, so that stress is applied from the outside. However, it is thought that cracks can be suppressed.

(Polymerizable compound)
The ink composition in the present invention contains at least one water-soluble polymerizable compound represented by the following general formula (1) having an acrylamide structure in the molecule, and active energy rays (for example, radiation or light, or electrons). Polymerized by irradiation with a line. The image portion is reinforced by polymerization and curing of the polymerizable compound.

In general formula (1), Q represents an n-valent linking group, and R ¹ represents a hydrogen atom or a methyl group. N represents an integer of 1 or more.

  Here, the term “water-soluble” means that it can be dissolved in water at a certain concentration or higher, and any substance that can be dissolved in water-based ink (preferably uniformly) may be used. Further, the solubility may be increased by adding a water-soluble organic solvent to be described later, and it may be dissolved (desirably uniformly) in the ink. Specifically, the solubility in water at 25 ° C. is preferably 10% by mass or more, and more preferably 15% by mass or more.

In the compound of formula (1), an unsaturated monomer is bonded to the linking group Q through an amide bond. R ¹ represents a hydrogen atom or a methyl group, preferably a hydrogen atom. Although the valence n of the linking group Q is not limited, from the viewpoint of improving the polymerization efficiency and ejection stability, n = 2 or more is preferable, n = 2 or more and 6 or less is more preferable, and n = 2 or more and 4 or less is more preferable. preferable.

  The linking group Q is not particularly limited as long as it is a group that can be linked to an acrylamide structure, but it is preferable that the linking group Q is selected from linking groups that satisfy the above-mentioned water solubility. Specific examples include residues from which one or more hydrogen atoms or hydroxyl groups have been removed from the following compound group X.

-Compound group X-
Ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4 -Butanediol, 2,3-butanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4 -Pentanediol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, glycerin, 1,2,4-butanetriol, 1,2,6-hexanetriol, 1,2,5 -Pentanetriol, thioglycol, trimethylolpropane, ditrimethylolpropane Trimethylol ethane, ditrimethylol ethane, neopentyl glycol, pentaerythritol, dipentaerythritol, and their condensates, low molecular weight polyvinyl alcohol, polyols such as saccharides, ethylene diamine, diethylene triamine, triethylene tetramine, polyethylene imine, polypropylene diamine , And the like polyamines.

  Furthermore, a saturated or unsaturated group such as a methylene, ethylene, propylene, butylene group or a substituted or unsubstituted alkylene chain having 4 or less carbon atoms, and a pyridine ring, imidazole ring, pyrazine ring, piperidine ring, piperazine ring, morpholine ring, etc. The functional group etc. which have the heterocyclic ring of can be illustrated.

  Of these, the linking group Q is preferably a residue of a polyol containing an oxyalkylene group (preferably an oxyethylene group), and a polyol containing three or more oxyalkylene groups (preferably an oxyethylene group). It is particularly preferred that it is a class of residues.

  Specific examples of the water-soluble polymerizable compound having an acrylamide structure in the molecule include the following water-soluble polymerizable compounds.

A polymeric compound can be contained individually by 1 type or in combination of 2 or more types.
As content in the ink composition of a polymeric compound, 5-30 mass% is preferable, and 10-25 mass% is more preferable. When the content of the polymerizable compound is 5% by mass or more, the image strength is further improved and the image has excellent scratch resistance, and when it is 30% by mass or less, the pile height is advantageous.

(Water-soluble compound (S))
The water-soluble compound (S) includes a double bond and a hydroxyl group directly bonded to an atom forming the double bond in the molecule. Here, the water-soluble property of the water-soluble compound (S) means that it can be dissolved in water at a certain concentration or higher, and any substance that can be dissolved (desirably uniformly) in water-based ink. Further, the solubility may be increased by adding a water-soluble organic solvent to be described later, and it may be dissolved (desirably uniformly) in the ink. Specifically, the solubility in water at 25 ° C. is preferably 3% by mass or more, more preferably 10% by mass or more, and particularly preferably 20% by mass or more.

  In addition, the water-soluble compound (S) is preferably a compound represented by any one of the following general formula (S1) or (S2), and is preferably a compound represented by the general formula (S1). More preferred.

  In the general formula (S1), Z represents a group having a benzene ring or a condensed ring thereof, or a group having a heterocycle, and p is 1 ≦ when the number of double bonds contained in Z is q. It is an integer of p ≦ 2q.

  In the general formula (S1), examples of the group having a benzene ring of Z or a condensed ring thereof include a residue in which one or more hydrogen atoms have been removed from a compound such as benzene, naphthalene, anthracene, and phenanthrene. And a group having a heterocycle includes one or more hydrogen atoms from a compound such as furan, thiophene, pyrrole, oxazole, thiazole, imidazole, pyrazole, pyridine, pyrimidine, piperazine, morpholine, 2H-pyran, 4H-pyran, etc. The removed residues can be exemplified.

  The water-soluble compound (S) of the present invention contains a double bond and a hydroxyl group bonded to an atom forming the double bond in the molecule. It is preferable that the hydroxyl group is directly bonded to a benzene ring, a condensed ring of benzene ring, or a hetero ring constituting Z. That is, it is preferable that the hydroxyl group is directly bonded to an atom forming a double bond contained in a benzene ring, a condensed ring of a benzene ring, or a hetero ring.

  In addition, the group having a benzene ring or its condensed ring represented by Z, or a group having a heterocycle may have a substituent other than a hydroxyl group directly bonded on the ring. Examples of other substituents that may be included include substituted or unsubstituted alkyl groups (preferably having 1 to 4 carbon atoms, more preferably unsubstituted), substituted or unsubstituted alkyloxy groups ( Preferably, it has 1 to 4 carbon atoms and is more preferably unsubstituted.), An aldehyde group, an oxo group, a sulfo group, a carboxyl group, a carbamoyl group, a sulfamoyl group, and the like.

  The group having a benzene ring or a condensed ring thereof is preferably a residue obtained by removing one or more hydrogen atoms from benzene or naphthalene, and more preferably a residue obtained by removing one or more hydrogen atoms from naphthalene. preferable. The group having a heterocycle is preferably a heterocycle containing an oxygen atom, and more preferably a residue obtained by removing one or more hydrogen atoms from a 5-membered heterocycle containing an oxygen atom. Among these groups, most preferred are residues in which one or more hydrogen atoms have been removed from a 5-membered heterocycle containing an oxygen atom.

  Further, p in the general formula (S1) is 1 ≦ p ≦ 2q when the number of double bonds contained in Z (a group having a benzene ring or a condensed ring thereof, or a group having a heterocycle) is q. More preferably, 2 ≦ p ≦ 6, and most preferably p = 2. It is most preferable that p satisfies the above range and the hydroxyl group is directly bonded to a benzene ring, a condensed ring of benzene ring, or a heterocycle, which constitutes Z, thereby improving the effect of the present invention. .

  In General Formula (S2), Rs represents a chain saturated hydrocarbon group having 1 to 10 carbon atoms or a cyclic saturated hydrocarbon group having 3 to 10 carbon atoms.

  In the general formula (S2), the linear saturated hydrocarbon group having 1 to 10 carbon atoms of Rs may be linear or branched, and may be a methylidene group, an ethylidene group, a propylidene group, an isopropylidene group, A butylidene group, an isobutylidene group, a sec-butylidene group and the like can be exemplified, and these may further have a substituent.

  Examples of the cyclic saturated hydrocarbon group having 3 to 10 carbon atoms of Rs include cyclopropylidene group, cyclobutylidene group, cyclopentylidene group, cyclohexylidene group, cycloheptylidene group, and the like. The group may further have a substituent.

  Rs is preferably a chain saturated hydrocarbon group having 1 to 4 carbon atoms or a cyclic saturated hydrocarbon group having 5 to 6 carbon atoms. More preferably, it is a C3-C4 chain saturated hydrocarbon group, whereby the effect of the present invention can be improved.

  Examples of the water-soluble compound (S) containing a double bond and a hydroxyl group directly bonded to an atom forming the double bond in the molecule include the following water-soluble compounds.

  In the present invention, the content (mass basis) of the water-soluble compound (S) containing a double bond and a hydroxyl group bonded to an atom forming the double bond in the molecule in the ink composition is 50 ppm or more and 10,000 ppm. It is a requirement that: The content (mass basis) of the water-soluble compound (S) is preferably 100 ppm to 5000 ppm, more preferably 200 ppm to 5000 ppm, and still more preferably 500 ppm to 5000 ppm. By setting the addition amount of the water-soluble compound (S) within this range, the polymerizability of the polymerizable compound represented by the general formula (1) is controlled to an appropriate range, and the effects of the present invention can be obtained.

In the present invention, the water-soluble compound (S) can be contained singly or in combination of two or more. In the case where two or more kinds of the water-soluble compound (S) are combined, the total content thereof may be within the above range.

(Color material particles)
The ink-jet ink composition of the present invention contains at least one colorant particle. The colorant particles are not particularly limited as long as they have a function of forming an image by coloring, and any of water-insoluble dyes, colored fine particles, water-dispersible pigments and the like can be used. In the present invention, a water-dispersible pigment is preferable from the viewpoint of light resistance and the like.

Specific examples of the water-dispersible pigment include the following pigments (1) to (4).
(1) Encapsulated pigment, that is, a polymer emulsion in which a pigment is contained in polymer particles. More specifically, the pigment is coated with a water-insoluble polymer dispersant, and is made hydrophilic by a polymer layer on the pigment surface. A pigment is dispersed in water.
(2) Self-dispersed pigments, that is, pigments having at least one hydrophilic group on the surface and exhibiting water dispersibility in the absence of a dispersant, more specifically, surface oxidation treatment is mainly performed on carbon black and the like. It is made hydrophilic so that the pigment alone is dispersed in water.
(3) A resin-dispersed pigment, that is, a pigment dispersed with a water-soluble polymer compound having a weight average molecular weight of 50,000 or less.
(4) A surfactant-dispersed pigment, that is, a pigment dispersed by a surfactant.
Preferred examples in the present invention include (1) encapsulated pigment and (2) self-dispersing pigment, and particularly preferred examples include (1) encapsulated pigment. There is no restriction | limiting in the pigment itself which provides a dispersibility, According to the objective, it can select suitably, For example, any of an organic pigment and an inorganic pigment may be sufficient. The pigment is preferably a pigment that is almost insoluble or hardly soluble in water from the viewpoint of ink colorability.

  Examples of organic pigments include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Among these, azo pigments and polycyclic pigments are more preferable. Examples of the inorganic pigment include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Among these, carbon black is particularly preferable as the black pigment.

  Among the organic pigments, examples of organic pigments for orange or yellow include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 138, C.I. I. Pigment yellow 151, C.I. I. Pigment yellow 155, C.I. I. Pigment yellow 180, C.I. I. And CI Pigment Yellow 185. Examples of organic pigments for magenta or red include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. Pigment red 222, C.I. I. Pigment violet 19 and the like. Examples of organic pigments for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 15: 4, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. Pigment Green 7, and siloxane-crosslinked aluminum phthalocyanine described in U.S. Pat. No. 4,311,775. Examples of organic pigments for black include C.I. I. Pigment black 1, C.I. I. Pigment black 6, C.I. I. Pigment black 7 and the like.

(Dispersant)
The dispersant used for the colorant particles may be either a polymer dispersant or a low molecular surfactant type dispersant. The polymer dispersant may be either a water-soluble dispersant or a water-insoluble dispersant.

  The low molecular surfactant type dispersant can stably disperse the pigment in the aqueous solvent while keeping the ink at a low viscosity. The low molecular surfactant type dispersant is a low molecular dispersant having a molecular weight of 2,000 or less. The molecular weight of the low molecular surfactant type dispersant is preferably 100 to 2,000, and more preferably 200 to 2,000.

  The low molecular surfactant type dispersant has a structure including a hydrophilic group and a hydrophobic group. Moreover, the hydrophilic group and the hydrophobic group should just be independently contained 1 or more in 1 molecule, respectively, and may have multiple types of hydrophilic group and hydrophobic group. In addition, a linking group for linking a hydrophilic group and a hydrophobic group can be appropriately included.

  The hydrophilic group is anionic, cationic, nonionic, or a betaine type that combines these. The anionic group may be any one as long as it has a negative charge, and may be a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group, or a carboxylic acid group. Preferably, it is a phosphoric acid group or a carboxylic acid group, and more preferably a carboxylic acid group. The cationic group may be any one having a positive charge, but is preferably an organic cationic substituent, and more preferably a nitrogen or phosphorus cationic group. Further, it is more preferably a pyridinium cation or an ammonium cation. Examples of the nonionic group include polyethylene oxide, polyglycerin, and a part of a sugar unit.

  The hydrophilic group is preferably an anionic group. The anionic group is preferably a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group, or a carboxylic acid group, and more preferably a phosphoric acid group or a carboxylic acid group. Preferably, it is a carboxylic acid group.

  When the low molecular surfactant type dispersant has an anionic hydrophilic group, the pKa is preferably 3 or more from the viewpoint of promoting the aggregation reaction by contacting with an acidic treatment liquid. The pKa of the low molecular surfactant type dispersant is titrated with a solution of 1 mmol / L of the low molecular surfactant type dispersant in a tetrahydrofuran-water (3: 2 = V / V) solution with an acid or alkaline aqueous solution. The value obtained experimentally from the titration curve. When the pKa of the low-molecular surfactant type dispersant is 3 or more, 50% or more of the anionic groups are in a non-dissociated state when in contact with a liquid having a theoretical pH of about 3. Accordingly, the water solubility of the low-molecular surfactant type dispersant is remarkably lowered, and an agglutination reaction occurs. That is, the aggregation reactivity is improved. From this viewpoint, the low molecular surfactant type dispersant preferably has a carboxylic acid group as an anionic group.

The hydrophobic group has a hydrocarbon-based, fluorocarbon-based, silicone-based or the like structure, and is particularly preferably a hydrocarbon-based group. Further, the hydrophobic group may have a linear structure or a branched structure. Further, the hydrophobic group may have a single chain structure or a chain structure of more than this, and in the case of a structure of two or more chains, it may have a plurality of types of hydrophobic groups.
The hydrophobic group is preferably a hydrocarbon group having 2 to 24 carbon atoms, more preferably a hydrocarbon group having 4 to 24 carbon atoms, and further preferably a hydrocarbon group having 6 to 20 carbon atoms.

  Among the polymer dispersants, examples of the water-soluble dispersant include hydrophilic polymer compounds. For example, natural hydrophilic polymer compounds include plant polymers such as gum arabic, tragan gum, guar gum, karaya gum, locust bean gum, arabinogalactone, pectin, quince seed starch, seaweeds such as alginic acid, carrageenan and agar. Examples include molecules, animal polymers such as gelatin, casein, albumin and collagen, and microorganism polymers such as xanthene gum and dextran.

  In addition, in hydrophilic polymer compounds modified from natural products, fiber polymers such as methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylcellulose, starch such as sodium starch glycolate and sodium starch phosphate And seaweed polymers such as sodium alginate, propylene glycol alginate, and the like.

  Further, synthetic hydrophilic polymer compounds include vinyl polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyvinyl methyl ether, non-crosslinked polyacrylamide, polyacrylic acid or alkali metal salts thereof, water-soluble styrene acrylic resins, and the like. Acrylic resin, water-soluble styrene maleic acid resin, water-soluble vinyl naphthalene acrylic resin, water-soluble vinyl naphthalene maleic resin, polyvinyl pyrrolidone, polyvinyl alcohol, alkali metal salts of β-naphthalene sulfonic acid formalin condensate, quaternary ammonium and amino And a polymer compound having a salt of a cationic functional group such as a group in the side chain, a natural polymer compound such as shellac, and the like.

  Among these, water-soluble dispersants introduced with carboxyl groups are hydrophilic polymers such as homopolymers of acrylic acid, methacrylic acid, styrene acrylic acid, and copolymers with monomers having other hydrophilic groups. Preferred as a compound.

  Among the polymer dispersants, as the water-insoluble dispersant, a polymer having both a hydrophobic portion and a hydrophilic portion can be used. For example, styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer, (meth) acrylic acid ester- (meth) acrylic acid copolymer, polyethylene glycol ( Examples thereof include (meth) acrylate- (meth) acrylic acid copolymers, vinyl acetate-maleic acid copolymers, and styrene-maleic acid copolymers.

  The weight average molecular weight of the polymer dispersant is preferably 3,000 to 100,000, more preferably 5,000 to 100,000, still more preferably 5,000 to 70,000, particularly preferably 40,000. 000-70,000.

  The polymer dispersant preferably contains a polymer having a carboxyl group from the viewpoints of self-dispersibility and aggregation rate when the treatment liquid described below comes into contact, and has a carboxyl group and an acid value of 100 mgKOH / g or less. A polymer is preferable, and a polymer of 25 to 100 mgKOH / g is more preferable. In particular, when the ink composition of the present invention is used in combination with a treatment liquid for aggregating components in the ink composition (details will be described later), a polymer dispersion having a carboxyl group and an acid value of 25 to 100 mgKOH / g The agent is effective.

The mixing mass ratio (p: s) between the pigment (p) and the dispersant (s) is preferably in the range of 1: 0.06 to 1: 3, more preferably in the range of 1: 0.125 to 1: 2. Preferably, it is 1: 0.125 to 1: 1.5.

  In the present invention, from the viewpoint of light resistance and quality of the image, the colorant particles preferably contain a pigment and a dispersant, more preferably contain an organic pigment and a polymer dispersant, and the organic pigment and the carboxyl group. It is particularly preferable to contain a polymer dispersant containing From the viewpoint of cohesiveness, the pigment is preferably coated with a water-insoluble polymer dispersant having a carboxyl group. The water-insoluble polymer is a polymer having a dissolution amount of 10 g or less when the polymer is dried at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C., and the dissolution amount is preferably 5 g. Hereinafter, it is more preferably 1 g or less. The dissolution amount is the dissolution amount when neutralized with sodium hydroxide or acetic acid according to the kind of the salt-forming group of the water-insoluble polymer.

The average particle size of the pigment in the dispersed state is preferably 10 to 200 nm, more preferably 10 to 150 nm, and still more preferably 10 to 100 nm. When the average particle size is 200 nm or less, the color reproducibility is good, the droplet ejection characteristics when droplets are ejected by the ink jet method are good, and when it is 10 nm or more, the light resistance is good. Further, the particle size distribution of the color material is not particularly limited, and may be either a wide particle size distribution or a monodisperse particle size distribution. Two or more color materials having a monodisperse particle size distribution may be mixed and used.
Here, the average particle diameter of the pigment in the dispersed state indicates the average particle diameter in the ink state, but the same applies to the so-called concentrated ink dispersion in the previous stage before the ink is formed.

  The average particle size of the pigment in the dispersed state and the average particle size and particle size distribution of the polymer particles were measured using a dynamic light scattering method using a nanotrack particle size distribution measuring device UPA-EX150 (manufactured by Nikkiso Co., Ltd.). It is calculated | required by measuring a volume average particle diameter.

You may use a pigment individually by 1 type or in combination of 2 or more types.
The content of the pigment in the ink composition is preferably 1 to 25% by mass, more preferably 2 to 20% by mass, and more preferably 2 to 15% by mass with respect to the ink composition from the viewpoint of image density. Is more preferable, and 3 to 10% by mass is particularly preferable.

(Water-soluble organic solvent)
The ink composition in the invention may contain at least one water-soluble organic solvent. The water-soluble organic solvent can obtain an effect of preventing drying, wetting or promoting penetration. In order to prevent drying, the ink adheres to and drys at the ink discharge port of the ejection nozzle and is used as an anti-drying agent to prevent clogging. For drying prevention and wetting, the vapor pressure is lower than that of water. A water-soluble organic solvent is preferred. Further, for penetration promotion, it can be used as a penetration enhancer that enhances ink permeability to paper.

The drying inhibitor is preferably a water-soluble organic solvent having a vapor pressure lower than that of water. Specific examples of such water-soluble organic solvents include ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, thiodiglycol, dithiodiglycol, 2-methyl-1,3-propanediol, 1,2,6-hexane. Polyols represented by triols, acetylene glycol derivatives, glycerin, trimethylolpropane, etc., ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether, triethylene glycol monoethyl (or butyl) ether, etc. Lower alkyl ethers of polyhydric alcohols, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, heterocyclic rings such as N-ethylmorpholine, sulfolane, Methyl sulfoxide, sulfur-containing compounds such as 3-sulfolene, diacetone alcohol, polyfunctional compounds such as diethanolamine, and urea derivatives.
Of these, polyhydric alcohols such as glycerin and diethylene glycol are preferred as the drying inhibitor.
Anti-drying agents may be used alone or in combination of two or more. The content of the drying inhibitor is preferably in the range of 10 to 50% by mass in the ink composition.

As a penetration accelerator, it is suitable for the purpose of allowing the ink composition to penetrate better into the recording medium (printing paper or the like). Specific examples of such water-soluble organic solvents include alcohols such as ethanol, isopropanol, butanol, di (tri) ethylene glycol monobutyl ether, 1,2-hexanediol, sodium lauryl sulfate, sodium oleate, and nonionic interfaces. An activator or the like can be preferably used.
A penetration enhancer may be used individually by 1 type, or may be used together 2 or more types. The content of the penetration enhancer is preferably in the range of 5 to 30% by mass in the ink composition. Moreover, it is preferable to use the penetration enhancer within a range that does not cause image bleeding and paper loss (print-through).

  The water-soluble organic solvent is used for adjusting the viscosity in addition to the above. Specific examples of water-soluble organic solvents that can be used to adjust the viscosity include alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, t-butanol, pentanol, hexanol, cyclohexanol). Benzyl alcohol), polyhydric alcohols (eg, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodi) Glycol), glycol derivatives (eg, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether) , Ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, triethylene glycol monomethyl ether, ethylene glycol diacetate, ethylene glycol monomethyl ether acetate, tri Ethylene glycol monomethyl ether, triethylene glycol monoethyl ether, ethylene glycol monophenyl ether), amine (for example, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethyl) Diamine, diethylenetriamine, triethylenetetramine, polyethyleneimine, tetramethylpropylenediamine) and other polar solvents (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, sulfolane, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, acetonitrile, acetone). In this case, the water-soluble organic solvent may be used alone or in combination of two or more.

(Polymer particles)
The ink composition in the present invention can contain polymer particles. As the polymer particles, self-dispersing polymer particles are preferable. Hereinafter, self-dispersing polymer particles will be described in detail as an example of preferable polymer particles.

-Self-dispersing polymer particles-
The ink composition in the invention preferably contains at least one kind of self-dispersing polymer particles as polymer particles. This self-dispersing polymer has a function of fixing the ink composition by destabilizing and agglomerating and aggregating the ink to increase the viscosity of the ink when it comes into contact with a treatment liquid described later or a dried region thereof. Fixability of the composition to a recording medium and image scratch resistance can be further improved. Self-dispersing polymers are also preferred resin particles from the viewpoints of ejection stability and liquid stability (particularly dispersion stability) of the system containing the pigment.

  Self-dispersing polymer particles are water-based due to functional groups (particularly acidic groups or salts thereof) possessed by the polymer itself when dispersed (especially dispersed by phase inversion emulsification) in the absence of a surfactant. It means water-insoluble polymer particles which can be dispersed in a medium and do not contain a free emulsifier.

Here, the dispersed state refers to an emulsified state (emulsion) in which a water-insoluble polymer is dispersed in an aqueous medium and a dispersed state (suspension) in which a water-insoluble polymer is dispersed in a solid state in an aqueous medium. It includes both states.
The water-insoluble polymer in the present invention is preferably a water-insoluble polymer that can be in a dispersed state in which the water-insoluble polymer is dispersed in a solid state, from the viewpoint of aggregation rate and fixing property when a liquid composition is used.

  Examples of a method for preparing an emulsified or dispersed state of the self-dispersing polymer, that is, an aqueous dispersion of the self-dispersing polymer include a phase inversion emulsification method. As the phase inversion emulsification method, for example, a self-dispersing polymer is dissolved or dispersed in a solvent (for example, a hydrophilic organic solvent) and then poured into water as it is without adding a surfactant. Examples include a method of obtaining an aqueous dispersion in an emulsified or dispersed state after stirring and mixing in a state in which a salt-forming group (for example, an acidic group) of the polymer is neutralized and removing the solvent.

  The dispersion state of the self-dispersing polymer particles refers to a solution in which 30 g of a water-insoluble polymer is dissolved in 70 g of an organic solvent (for example, methyl ethyl ketone), a neutralizing agent (salt that can neutralize 100% of the salt-forming groups of the water-insoluble polymer). After mixing and stirring (equipment: stirring device with stirring blade, rotation speed 200 rpm, 30 minutes, 25 ° C.), sodium hydroxide if the generating group is anionic, acetic acid if cationic, and 200 g of water are mixed, It means a state in which even after removing the organic solvent from the mixed solution, it can be visually confirmed that the dispersion state exists stably at 25 ° C. for at least one week.

  In addition, water insolubility is synonymous with the definition demonstrated in the item of the above-mentioned dispersing agent.

  The aqueous medium is configured to contain water, and may contain a hydrophilic organic solvent as necessary. In the present invention, it is preferably composed of water and 0.2% by mass or less of a hydrophilic organic solvent with respect to water, and more preferably composed of water.

  The main chain skeleton of the water-insoluble polymer is not particularly limited. For example, a vinyl polymer or a condensation polymer (epoxy resin, polyester, polyurethane, polyamide, cellulose, polyether, polyurea, polyimide, polycarbonate, etc.) is used. it can. Of these, vinyl polymers are particularly preferred.

Preferable examples of the vinyl polymer and the monomer constituting the vinyl polymer include those described in JP-A Nos. 2001-181549 and 2002-88294. In addition, radical transfer of vinyl monomers using dissociable groups (or substituents that can be induced to dissociable groups), polymerization initiators, and iniferters, or dissociable groups on either initiators or terminators A vinyl polymer in which a dissociable group is introduced at the end of a polymer chain by ionic polymerization using a compound having (or a substituent that can be derived from a dissociable group) can also be used.
Moreover, as a suitable example of the monomer which comprises a condensation type polymer and a condensation type polymer, what is described in Unexamined-Japanese-Patent No. 2001-247787 can be mentioned.

  The self-dispersing polymer particles preferably contain a water-insoluble polymer containing a hydrophilic constituent unit and a constituent unit derived from an aromatic group-containing monomer from the viewpoint of self-dispersibility.

The hydrophilic structural unit is not particularly limited as long as it is derived from a hydrophilic group-containing monomer, and even if it is derived from one kind of hydrophilic group-containing monomer, it contains two or more hydrophilic groups. It may be derived from a monomer. The hydrophilic group is not particularly limited, and may be a dissociable group or a nonionic hydrophilic group.
In the present invention, the hydrophilic group is preferably a dissociable group and more preferably an anionic dissociable group from the viewpoint of promoting self-dispersion and the stability of the formed emulsified or dispersed state. Examples of the dissociable group include a carboxyl group, a phosphoric acid group, and a sulfonic acid group. Among them, a carboxyl group is preferable from the viewpoint of fixability when an ink composition is configured.

The hydrophilic group-containing monomer in the present invention is preferably a dissociable group-containing monomer from the viewpoints of self-dispersibility and aggregation, and is a dissociable group-containing monomer having a dissociable group and an ethylenically unsaturated bond. It is preferable.
Examples of the dissociable group-containing monomer include an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer.

Specific examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid.
Specific examples of the unsaturated sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, and bis- (3-sulfopropyl) -itaconate. Can be mentioned.
Specific examples of the unsaturated phosphoric acid monomer include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2 -Acryloyloxyethyl phosphate and the like.
Among the dissociable group-containing monomers, from the viewpoint of dispersion stability and ejection stability, unsaturated carboxylic acid monomers are preferable, acrylic monomers are more preferable, and acrylic acid and methacrylic acid are particularly preferable.

  When the self-dispersing polymer in the present invention has an anionic dissociable group, the acid value is preferably 200 mgKOH / g or less from the viewpoint of good cohesiveness when the treatment liquid comes into contact. Furthermore, the acid value is more preferably 25 to 120 mgKOH / g, and further preferably 30 to 80 mgKOH / g. When the acid value of the self-dispersing polymer is 25 or more, the stability of the self-dispersing property is improved.

The aromatic group-containing monomer is not particularly limited as long as it is a compound containing an aromatic group and a polymerizable group. The aromatic group may be a group derived from an aromatic hydrocarbon or a group derived from an aromatic heterocycle. In the present invention, an aromatic group derived from an aromatic hydrocarbon is preferable from the viewpoint of particle shape stability in an aqueous medium.
Further, the polymerizable group may be a condensation polymerizable polymerizable group or an addition polymerizable polymerizable group. In the present invention, from the viewpoint of particle shape stability in an aqueous medium, an addition polymerizable group is preferable, and a group containing an ethylenically unsaturated bond is more preferable.

  The aromatic group-containing monomer in the present invention is preferably a monomer having an aromatic group derived from an aromatic hydrocarbon and an ethylenically unsaturated bond. The aromatic group-containing monomer may be used alone or in combination of two or more.

Examples of the aromatic group-containing monomer include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, and a styrene monomer. Of these, aromatic group-containing (meth) acrylate monomers are preferred from the viewpoint of the balance between the hydrophilicity and hydrophobicity of the polymer chain and the ink fixability, and include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, and phenyl (meth). At least one selected from acrylates is more preferable, and phenoxyethyl (meth) acrylate and benzyl (meth) acrylate are more preferable.
“(Meth) acrylate” means acrylate or methacrylate.

The self-dispersing polymer in the present invention is preferably an acrylic resin containing a structural unit derived from a (meth) acrylate monomer, preferably an acrylic resin containing a structural unit derived from an aromatic group-containing (meth) acrylate monomer, Includes a structural unit derived from an aromatic group-containing (meth) acrylate monomer, and the content thereof is preferably 10% by mass to 95% by mass. When the content of the aromatic group-containing (meth) acrylate monomer is 10% by mass to 95% by mass, the stability of the self-emulsification or dispersion state can be improved, and further the increase in ink viscosity can be suppressed.
In the present invention, from the viewpoints of stability in a self-dispersing state, stabilization of particle shape in an aqueous medium due to hydrophobic interaction between aromatic rings, and reduction in the amount of water-soluble components due to appropriate hydrophobicization of particles. More preferably, the content is from mass% to 90 mass%, more preferably from 15 mass% to 80 mass%, and particularly preferably from 25 mass% to 70 mass%.

  The self-dispersing polymer in the present invention can be constituted using, for example, a structural unit derived from an aromatic group-containing monomer and a structural unit derived from a dissociable group-containing monomer. Furthermore, other structural units may be further included as necessary.

The monomer that forms the other structural unit is not particularly limited as long as it is a monomer copolymerizable with the aromatic group-containing monomer and the dissociable group-containing monomer. Among these, an alkyl group-containing monomer is preferable from the viewpoint of flexibility of the polymer skeleton and ease of control of the glass transition temperature (Tg).
Examples of the alkyl group-containing monomer include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, Alkyl (meth) acrylates such as t-butyl (meth) acrylate, hexyl (meth) acrylate, ethylhexyl (meth) acrylate, and hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) ) Ethylenically unsaturated monomers having hydroxyl groups such as acrylate, 4-hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, hydroxyhexyl (meth) acrylate, and dimethyl (Meth) acrylic ester monomers such as dialkylaminoalkyl (meth) acrylates such as ruaminoethyl (meth) acrylate; N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxybutyl (meth) N-hydroxyalkyl (meth) acrylamide such as acrylamide, N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N- (n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (Meth) acrylamide, such as (meth) acrylamide, N-ethoxyethyl (meth) acrylamide, N-alkoxyalkyl (meth) acrylamide such as N- (n-, iso) butoxyethyl (meth) acrylamide, etc. And (meth) acrylamide-based monomers like.

  The molecular weight of the water-insoluble polymer constituting the self-dispersing polymer particles is preferably 3000 to 200,000, more preferably 5000 to 150,000, and more preferably 10,000 to 100,000 in terms of weight average molecular weight. Further preferred. By setting the weight average molecular weight to 3000 or more, the amount of water-soluble components can be effectively suppressed. Moreover, self-dispersion stability can be improved by making a weight average molecular weight into 200,000 or less.

  The weight average molecular weight is measured by gel permeation chromatography (GPC). For GPC, HLC-8220GPC (manufactured by Tosoh Corporation) is used, and as columns, TSKgeL SuperHZM-H, TSKgeL SuperHZ4000, TSKgeL SuperHZ2000 (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) are used as eluents. Use THF (tetrahydrofuran). The conditions are as follows: the sample concentration is 0.35 / mass%, the flow rate is 0.35 ml / min, the sample injection amount is 10 μl, the measurement temperature is 40 ° C., and the RI detector is used. In addition, the calibration curve is “standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, It is prepared from 8 samples of “A-2500”, “A-1000”, “n-propylbenzene”.

The water-insoluble polymer constituting the self-dispersing polymer particles is derived from a structural unit derived from an aromatic group-containing (meth) acrylate monomer (preferably phenoxyethyl (meth) acrylate) from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. It is preferable that 15-80 mass% of the total mass of a self-dispersing polymer particle is included as a copolymerization ratio for a structural unit and / or a structural unit derived from benzyl (meth) acrylate.
In addition, the water-insoluble polymer has a constitution derived from a carboxyl group-containing monomer having a copolymerization ratio of 15 to 80% by mass of a constitutional unit derived from an aromatic group-containing (meth) acrylate monomer from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. And a structural unit derived from an alkyl group-containing monomer (preferably a structural unit derived from an alkyl ester of (meth) acrylic acid), and a structural unit derived from phenoxyethyl (meth) acrylate and / or Alternatively, a structural unit derived from benzyl (meth) acrylate as a copolymerization ratio of 15 to 80% by mass, a structural unit derived from a carboxyl group-containing monomer, and a structural unit derived from an alkyl group-containing monomer (preferably (meth) A structural unit derived from an alkyl ester having 1 to 4 carbon atoms of acrylic acid) More preferably, the acid value is 25 to 100 and the weight average molecular weight is preferably 3000 to 200,000, the acid value is 25 to 95, and the weight average molecular weight is 5000 to 150,000. It is more preferable that

  Specific examples (exemplary compounds B-01 to B-19) of water-insoluble polymers constituting the self-dispersing polymer particles are given below. However, the present invention is not limited to these. The values in parentheses represent the mass ratio of the copolymer component.

B-01: Phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (50/45/5)
B-02: Phenoxyethyl acrylate / benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (30/35/29/6)
B-03: Phenoxyethyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (50/44/6)
B-04: Phenoxyethyl acrylate / methyl methacrylate / ethyl acrylate / acrylic acid copolymer (30/55/10/5)
B-05: benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (35/59/6)
B-06: Styrene / phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (10/50/35/5)
B-07: benzyl acrylate / methyl methacrylate / acrylic acid copolymer (55/40/5)
B-08: Phenoxyethyl methacrylate / benzyl acrylate / methacrylic acid copolymer (45/47/8)
B-09: Styrene / phenoxyethyl acrylate / butyl methacrylate / acrylic acid copolymer (5/48/40/7)
B-10: benzyl methacrylate / isobutyl methacrylate / cyclohexyl methacrylate / methacrylic acid copolymer (35/30/30/5)
B-11: Phenoxyethyl acrylate / methyl methacrylate / butyl acrylate / methacrylic acid copolymer (12/50/30/8)
B-12: benzyl acrylate / isobutyl methacrylate / acrylic acid copolymer (93/2/5)
B-13: Styrene / phenoxyethyl methacrylate / butyl acrylate / acrylic acid copolymer (50/5/20/25)
B-14: Styrene / butyl acrylate / acrylic acid copolymer (62/35/3)
B-15: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/51/4)
B-16: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/49/6)
B-17: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/48/7)
B-18: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/47/8)
B-19: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/45/10)

  The production method of the water-insoluble polymer constituting the self-dispersing polymer particles in the present invention is not particularly limited. For example, emulsion polymerization is performed in the presence of a polymerizable surfactant, and the surfactant and the water-insoluble polymer are mixed. And a method of copolymerizing the monomer mixture containing the hydrophilic group-containing monomer and the aromatic group-containing monomer by a known polymerization method such as a solution polymerization method or a bulk polymerization method. Among the polymerization methods, a solution polymerization method is preferable and a solution polymerization method using an organic solvent is more preferable from the viewpoint of aggregation rate and droplet ejection stability when an ink composition is used.

  The self-dispersing polymer in the present invention includes a polymer synthesized in an organic solvent from the viewpoint of aggregation rate, and the polymer has a carboxyl group (preferably having an acid value of 25 to 50). It is preferable that some or all of the carboxyl groups are neutralized and prepared as a polymer dispersion having water as a continuous phase. That is, the production of the self-dispersing polymer particles in the present invention includes a step of synthesizing a polymer in an organic solvent and a dispersion step of making an aqueous dispersion in which at least a part of the carboxyl groups of the polymer is neutralized. It is preferable to do so.

The dispersion step preferably includes the following step (1) and step (2).
Step (1): Step of stirring a mixture containing a polymer (water-insoluble polymer), an organic solvent, a neutralizing agent, and an aqueous medium Step (2): Step of removing the organic solvent from the mixture

The step (1) is preferably a treatment in which a polymer (water-insoluble polymer) is first dissolved in an organic solvent, then a neutralizing agent and an aqueous medium are gradually added, mixed and stirred to obtain a dispersion. In this way, by adding a neutralizing agent and an aqueous medium to a water-insoluble polymer solution dissolved in an organic solvent, a self-dispersing polymer having a particle size with higher storage stability without requiring strong shearing force. Particles can be obtained.
There is no restriction | limiting in particular in the stirring method of this mixture, Dispersing machines, such as a generally used mixing stirring apparatus and an ultrasonic disperser, a high-pressure homogenizer, can be used as needed.

Preferred examples of the organic solvent include alcohol solvents, ketone solvents, and ether solvents.
Examples of the alcohol solvent include isopropyl alcohol, n-butanol, t-butanol, ethanol and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of ether solvents include dibutyl ether and dioxane. Among these solvents, ketone solvents such as methyl ethyl ketone and alcohol solvents such as isopropyl alcohol are preferable. It is also preferable to use isopropyl alcohol and methyl ethyl ketone in combination for the purpose of moderating the polarity change during the phase inversion from oil to water. By using the solvent in combination, it is possible to obtain self-dispersing polymer particles having a fine particle size with high dispersion stability without aggregation and sedimentation and fusion between particles.

  The neutralizing agent is used so that a part or all of the dissociable group is neutralized and the self-dispersing polymer forms a stable emulsified or dispersed state in water. When the self-dispersing polymer of the present invention has an anionic dissociative group (for example, a carboxyl group) as a dissociable group, the neutralizing agent used is basic such as an organic amine compound, ammonia, or an alkali metal hydroxide. Compounds. Examples of organic amine compounds include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, monoethanolamine, diethanolamine, triethanolamine, N, N-dimethyl-ethanolamine, N, N-diethyl-ethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolamine, monoisopropanolamine, diisopropanol Examples include amines and triisopropanolamine. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Among these, sodium hydroxide, potassium hydroxide, triethylamine, and triethanolamine are preferable from the viewpoint of stabilizing the dispersion of the self-dispersing polymer particles of the present invention in water.

  These basic compounds are preferably used in an amount of 5 to 120 mol%, more preferably 10 to 110 mol%, still more preferably 15 to 100 mol%, based on 100 mol% of the dissociable group. . By setting it as 15 mol% or more, the effect which stabilizes dispersion | distribution of the particle | grains in water expresses, and there exists an effect which reduces a water-soluble component by setting it as 100 mol% or less.

  In the step (2), the aqueous dispersion of the self-dispersing polymer particles is obtained by distilling off the organic solvent from the dispersion obtained in the step (1) by a conventional method such as distillation under reduced pressure and phase-inversion into an aqueous system. A dispersion can be obtained. The organic solvent in the obtained aqueous dispersion has been substantially removed, and the amount of the organic solvent is preferably 0.2% by mass or less, more preferably 0.1% by mass or less.

The average particle diameter of the polymer particles is preferably 1 nm to 70 nm in terms of volume average particle diameter, more preferably 2 to 60 nm, and still more preferably 2 to 30 nm. When the volume average particle diameter is 2 nm or more, the production suitability is improved, and when it is 70 nm or less, the local blocking resistance is improved.
The particle size distribution of the self-dispersing polymer particles is not particularly limited, and may be either a wide particle size distribution or a monodispersed particle size distribution. Further, two or more water-insoluble particles may be mixed and used.
The average particle size and particle size distribution of the self-dispersing polymer particles are measured by the dynamic light scattering method using Nanotrac particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.). Is required.

  The glass transition temperature (Tg) of the self-dispersing polymer is preferably 70 ° C. or higher, more preferably 80 ° C. or higher, and further preferably 100 ° C. or higher. When the glass transition temperature (Tg) is 70 ° C. or higher, the local blocking resistance is improved. There is no restriction | limiting in particular about the upper limit of glass transition temperature (Tg).

  The self-dispersing polymer particles can be used singly or in combination of two or more. The content of the self-dispersing polymer particles in the ink composition is preferably 1 to 10% by mass with respect to the ink composition from the viewpoint of aggregation rate and image glossiness. More preferably, it is mass%.

  As described above, self-dispersing polymer particles have been described as examples of preferred polymer particles, but the present invention is not limited to self-dispersing polymer particles, and other polymer particles can be used. For example, generally known polymer particles such as emulsion polymerization latex can be suitably used by adjusting the constituent monomers, emulsifiers, dispersion conditions, and the like.

(Initiator)
The ink composition in the invention may contain at least one initiator that initiates polymerization of the polymerizable compound by active energy rays. Further, the initiator may be contained only in the treatment liquid described later, or may be contained in both the ink composition of the present invention and the treatment liquid. An initiator can be used individually by 1 type or in mixture of 2 or more types or in combination with a sensitizer.

  The initiator can contain a compound capable of initiating a polymerization reaction by active energy rays as appropriate. For example, the initiator starts generation of active species (radicals, acids, bases, etc.) by radiation or light, or electron beams. An agent (for example, a photopolymerization initiator) can be used.

  Examples of the photopolymerization initiator include acetophenone, 2,2-diethoxyacetophenone, p-dimethylaminoacetophene, p-dimethylaminopropiophenone, benzophenone, 2-chlorobenzophenone, p, p′-dichlorobenzophene, p, p'-bisdiethylaminobenzophenone, Michler's ketone, benzyl, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-propyl ether, benzoin isobutyl ether, benzoin n-butyl ether, benzyldimethyl ketal, tetramethylthiuram mono Sulfide, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, azobisisobutyronitrile, benzoin peroxide, di tert-butyl peroxide, 1-hydroxycyclohexyl phenyl ketone, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-2- Examples include methyl-1-phenyl-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, and methylbenzoyl formate. Furthermore, for example, aromatic diazonium salts, aromatic halonium salts, aromatic sulfonium salts, metallocene compounds such as triphenylsulfonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate and the like can be mentioned.

  When the initiator is contained, the content of the initiator in the ink composition is preferably 1 to 40% by mass and more preferably 5 to 30% by mass with respect to the polymerizable compound. When the content of the initiator is 1% by mass or more, the scratch resistance of the image is further improved, which is advantageous for high-speed recording, and when it is 40% by mass or less, it is advantageous in terms of ejection stability.

Examples of the sensitizer include amines (aliphatic amines, amines containing aromatic groups, piperidine, etc.), ureas (allylic, o-tolylthiourea, etc.), sulfur compounds (sodium diethyldithiophosphate, aromatic sulfinic acid). Soluble salts, etc.), nitrile compounds (N, N, di-substituted p-aminobenzonitrile, etc.), phosphorus compounds (tri-n-butylphosphine, netium diethyldithiophos feed, etc.), nitrogen compounds (Michler ketone, N-nitriso) Hydroxylamine derivatives, oxazolidine compounds, tetrahydro 1,3-oxazine compounds, formaldehyde, acetaldehyde and diamine condensates, etc.), chlorine compounds (carbon tetrachloride, hexachloroethane, etc.), polymerized amines of reaction products of epoxy resins and amines , Triethanolamine Acrylate, and the like.
A sensitizer can be contained in the range which does not impair the effect of this invention.

(water)
The ink composition contains water, but the amount of water is not particularly limited. Especially, the preferable content of water is 10 to 99% by mass, more preferably 30 to 80% by mass, and still more preferably 50 to 70% by mass.

(Other additives)
The ink composition in the present invention can be constituted using other additives in addition to the above components. Other additives include, for example, anti-drying agents (wetting agents), anti-fading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, anti-fungal agents, pH adjusters, surface tension adjusters, Well-known additives, such as a foaming agent, a viscosity modifier, a dispersion stabilizer, a rust inhibitor, a chelating agent, are mentioned. These various additives are generally added directly to the ink in the case of an ink composition, and when an oily dye is used as a dispersion, it is generally added to the dispersion after the preparation of the dye dispersion. Sometimes it may be added to the oil or water phase.

  The ultraviolet absorber can improve image storability. Examples of the ultraviolet absorber include benzotriazoles described in JP-A Nos. 58-185677, 61-190537, JP-A-2-782, JP-A-5-97075, JP-A-9-34057, and the like. Compounds, benzophenone compounds described in JP-A No. 46-2784, JP-A No. 5-194433, US Pat. No. 3,214,463, etc., JP-B Nos. 48-30492, 56-21114, Cinnamic acid compounds described in JP-A-10-88106, etc., JP-A-4-298503, JP-A-8-53427, JP-A-8-239368, JP-A-10-182621, JP-A-8-501291 Triazine compounds described in Japanese Patent Publication No. The compounds described in No. 24239, stilbene-based compounds, and benzoxazole-based compounds, such as compounds that absorb ultraviolet rays and emit fluorescence, so-called fluorescent brighteners can also be used.

  The anti-fading agent can improve image storage stability. Examples of the anti-fading agent include various organic and metal complex anti-fading agents. Examples of the organic anti-fading agent include hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, heterocycles, and the like. Examples of the system antifading agent include nickel complexes and zinc complexes. More specifically, Research Disclosure No. No. 17643, No. VII, I to J, ibid. 15162, ibid. No. 18716, page 650, left column, ibid. No. 36544, page 527, ibid. No. 307105, page 872, ibid. The compounds described in the patent cited in Japanese Patent No. 15162, and the compounds included in the general formulas and compound examples of representative compounds described in JP-A-62-215272, pages 127 to 137 can be used.

  Examples of the antifungal agent include sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, p-hydroxybenzoic acid ethyl ester, 1,2-benzisothiazolin-3-one and salts thereof. The content of the antifungal agent is preferably in the range of 0.02 to 1.00% by mass with respect to the ink composition.

  As the pH adjuster, a neutralizer (organic base, inorganic alkali) can be used. The pH adjuster can improve the storage stability of the ink composition. The pH adjuster is preferably added so that the pH of the ink composition is 6 to 10, and more preferably added so that the pH is 7 to 10.

  Examples of the surface tension adjusting agent include nonionic surfactants, cationic surfactants, anionic surfactants, betaine surfactants, and the like. The addition amount of the surface tension adjusting agent is preferably in a range where the surface tension of the ink composition can be adjusted to 20 to 60 mN / m, more preferably in a range where the surface tension can be adjusted to 20 to 45 mN / m, and a range where the surface tension can be adjusted to 25 to 40 mN / m. Is more preferable. When the addition amount is within the above range, droplets can be ejected satisfactorily by the ink jet method.

Specific examples of the surfactant include, for hydrocarbons, fatty acid salts, alkyl sulfate esters, alkylbenzene sulfonates, alkyl naphthalene sulfonates, dialkyl sulfosuccinates, alkyl phosphate esters, naphthalene sulfonate formalin condensation. Products, anionic surfactants such as polyoxyethylene alkyl sulfates, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxy Nonionic surfactants such as ethylene alkylamine, glycerin fatty acid ester and oxyethyleneoxypropylene block copolymer are preferred. Further, SURFYNOLS (manufactured by Air Products & Chemicals), which is an acetylene-based polyoxyethylene oxide surfactant, is also preferably used. Amine oxide type amphoteric surfactants such as N, N-dimethyl-N-alkylamine oxide are also preferred.
Further, pages (37) to (38) of JP-A-59-157636, Research Disclosure No. Those listed as surfactants in 308119 (1989) can also be used.
Further, by using fluorine (fluorinated alkyl) surfactants, silicone surfactants and the like described in JP-A Nos. 2003-322926, 2004-325707, and 2004-309806. In addition, the abrasion resistance can be improved.

  These surface tension modifiers can also be used as an antifoaming agent, and fluorine compounds, silicone compounds, chelating agents represented by EDTA, and the like can also be used.

<Ink set>
(Processing liquid)
The ink composition of the present invention can be configured as an ink set together with a treatment liquid containing an aggregating agent that aggregates the components in the ink composition. The treatment liquid contains at least an aggregating agent for aggregating the components in the ink composition described above, but can be constituted using other components as necessary. By using the treatment liquid together with the ink composition, it is possible to increase the speed of ink jet recording, and an image with excellent density and resolution can be obtained even when recording at high speed (for example, reproducibility of fine lines and fine portions).

  The flocculant may be a compound capable of changing the pH of the ink composition, a polyvalent metal salt, or a polymer having a quaternary or tertiary amine such as polyallylamines. . In the present invention, from the viewpoint of cohesiveness of the ink composition, a compound capable of changing the pH of the ink composition is preferable, and a compound capable of lowering the pH of the ink composition is more preferable.

Examples of the compound that can lower the pH of the ink composition include acidic substances.
Examples of acidic substances include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, and tartaric acid. , Lactic acid, sulfonic acid, orthophosphoric acid, pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, or derivatives of these compounds, or salts thereof Etc. are preferable.
An acidic substance may be used individually by 1 type, and may use 2 or more types together.

When the treatment liquid in the present invention contains an acidic substance, the pH (25 ° C.) of the treatment liquid is preferably 6 or less, more preferably 4 or less. Especially, pH (25 degreeC) has the preferable range of 1-4, Especially preferably, pH is 1-3. At this time, the pH (25 ° C.) of the ink composition is preferably 7.5 or more (more preferably 8.0 or more).
Among them, from the viewpoint of image density, resolution, and speedup of inkjet recording, the pH (25 ° C.) of the ink composition is 8.0 or more, and the pH (25 ° C.) of the treatment liquid is 0.5 to 4. Some cases are preferred.

  Among them, as the flocculant in the present invention, an acidic substance having high water solubility is preferable, and an organic acid is preferable, and an organic acid having a valence of 2 or more is more preferable, from the viewpoint of improving the aggregation property and fixing the entire ink. Above-mentioned trivalent or less acidic substances are particularly preferred. The divalent or higher organic acid is preferably an organic acid having a first pKa of 3.5 or less, more preferably an organic acid of 3.0 or less. Specific examples include phosphoric acid, oxalic acid, malonic acid, citric acid and the like.

  Examples of the polyvalent metal salt include alkaline earth metals belonging to Group 2 of the periodic table (eg, magnesium, calcium), transition metals belonging to Group 3 of the periodic table (eg, lanthanum), and Group 13 of the periodic table. Cation (for example, aluminum) and the salt of lanthanides (for example, neodymium) can be mentioned. As these metal salts, carboxylate (formic acid, acetic acid, benzoate, etc.), nitrate, chloride, and thiocyanate are suitable. Among them, preferred are calcium salts or magnesium salts of carboxylic acids (formic acid, acetic acid, benzoates, etc.), calcium salts or magnesium salts of nitric acid, calcium chloride, magnesium chloride, and calcium salts or magnesium salts of thiocyanic acid.

A flocculant can be used individually by 1 type or in mixture of 2 or more types.
The content of the flocculant for aggregating the ink composition in the treatment liquid is preferably 1 to 50% by mass, more preferably 3 to 45% by mass, and still more preferably 5 to 40% by mass.

  The treatment liquid can further contain other additives as other components within a range not impairing the effects of the present invention. Other additives include, for example, anti-drying agents (wetting agents), anti-fading agents, emulsion stabilizers, penetration enhancers, UV absorbers, preservatives, anti-fungal agents, pH adjusters, surface tension adjusters, anti-foaming agents. Well-known additives, such as a foaming agent, a viscosity modifier, a dispersing agent, a dispersion stabilizer, a rust preventive agent, a chelating agent, are mentioned.

<Image forming method>
The image forming method of the present invention uses the ink set of the present invention described above, an ink application step of applying the ink composition to the recording medium by an ink jet method, and agglomeration of aggregating components in the ink composition And a treatment liquid application step for applying a treatment liquid containing an agent to the recording medium. The image forming method of the present invention can be configured by further providing other steps as necessary.

According to the aspect using the polymer particles of the present invention, the image is fixed by the aggregation reaction of the color material and / or polymer particles when the ink composition and the treatment liquid come into contact with each other. Since the polymer particles are present and polymerized and cured in a state in which the polymerizable compound is taken in between the particles in the fixed image, the strength of the final image can be increased. By aggregating the components in the ink composition at high speed using the treatment liquid, high-speed recording suitability for high-speed recording that prevents mixing between inks (such as bleeding and color mixing between colors), and hue and image drawing at high-speed recording are provided. State in which a polymerizable compound is moderately contained in the gap between the colorant particles and the polymer particles forming an aggregated state while improving the property (reproducibility of fine lines and fine parts in the image). In this state, the polymerizable compound entering in this state is polymerized and cured, whereby the image strength can be improved and both high-speed recording suitability and improved image scratch resistance can be achieved.
In particular, it is more effective when an image is recorded on coated paper where the color material tends to remain on the surface of the recording medium.

Hereafter, each process which comprises the image forming method of this invention is demonstrated.
-Ink application process-
In the ink application step, the ink composition of the present invention is applied to a recording medium by an ink jet method. In this step, the ink composition can be selectively applied onto the recording medium, and a desired visible image can be formed. The details and preferred aspects of the ink composition are as described above in the description of the ink composition.

  Specifically, the image recording using the ink-jet method is performed by supplying energy to obtain a desired recording medium, that is, plain paper, resin-coated paper, for example, JP-A-8-169172 and JP-A-8-27693. Publication No. 2-276670, No. 7-276789, No. 9-323475, No. JP-A-62-238783, JP-A-10-153898, No. 10-217473, No. 10- No. 235995, No. 10-337947, No. 10-217597, No. 10-337947, etc. Liquid composition for ink jet paper, film, electrophotographic co-paper, fabric, glass, metal, ceramics, etc. This can be done by discharging objects. As a preferable ink jet recording method for the present invention, the method described in paragraph Nos. 0093 to 0105 of JP-A No. 2003-306623 can be applied.

The inkjet method is not particularly limited, and is a known method, for example, a charge control method that discharges ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses vibration pressure of a piezoelectric element, an electric method An acoustic ink jet system that converts a signal into an acoustic beam, irradiates the ink with ink and ejects the ink using radiation pressure, and a thermal ink jet (bubble jet (registered trademark)) that heats the ink to form bubbles and uses the generated pressure. )) Any method may be used. As an ink jet method, in particular, the method described in Japanese Patent Application Laid-Open No. Sho 54-59936 causes an abrupt volume change of the ink subjected to the action of thermal energy, and the ink is ejected from the nozzle by the action force due to this state change. An inkjet method can also be used.
The ink jet method includes a method of ejecting many low-density inks called photo inks in a small volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent inks. The method using is included.

In addition, an ink jet head used in the ink jet method may be an on-demand method or a continuous method. In addition, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, a thermal type) Specific examples include an ink jet type, a bubble jet (registered trademark) type, an electrostatic suction type (for example, an electric field control type, a slit jet type, etc.) and a discharge type (for example, a spark jet type). However, any discharge method may be used.
There are no particular restrictions on the ink nozzles used when recording by the ink jet method, and they can be appropriately selected according to the purpose.

  In addition, a short serial head is used as an inkjet head, a shuttle system that performs recording while scanning the head in the width direction of the recording medium, and a line head in which recording elements are arranged corresponding to the entire area of one side of the recording medium There is a line system using. In the line system, an image can be recorded on the entire surface of the recording medium by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements, and a carriage system such as a carriage for scanning a short head is not necessary. Further, since complicated scanning control of the carriage movement and the recording medium is not required, and only the recording medium is moved, the recording speed can be increased as compared with the shuttle system. The image forming method of the present invention can be applied to any of these, but generally, when applied to a line system that does not use a dummy jet, the effect of improving ejection accuracy and image scratch resistance is great.

  The amount of ink droplets ejected from the inkjet head is preferably 1 to 10 pl (picoliter) and more preferably 1.5 to 6 pl from the viewpoint of obtaining a high-definition image. In addition, from the viewpoint of improving the unevenness of the image and the continuous gradation, it is also effective to discharge different amounts of liquids in combination, and even in such a case, the present invention can be suitably used.

-Treatment liquid application process-
In the treatment liquid application step, a treatment liquid containing an aggregating agent that aggregates components in the ink composition is applied to the recording medium, and the treatment liquid is brought into contact with the ink composition to form an image. In this case, the dispersed particles including the colorant and polymer particles in the ink composition are aggregated, and the image is fixed on the recording medium. The treatment liquid is configured to contain at least a flocculant, and details and preferred embodiments of each component are as described above.

  The treatment liquid can be applied by applying a known method such as a coating method, an ink jet method, or an immersion method. As a coating method, a known coating method using a bar coater, an extrusion die coater, an air doctor coater, a blade coater, a rod coater, a knife coater, a squeeze coater, a reverse roll coater or the like can be used. The details of the inkjet method are as described above.

  The treatment liquid application step may be provided either before or after the ink application step using the ink composition. In the present invention, an embodiment in which the ink application step is provided after the treatment liquid is applied in the treatment liquid application step is preferable. Specifically, before applying the ink composition on the recording medium, a treatment liquid for aggregating the coloring material and / or self-dispersing polymer particles in the ink composition is applied in advance. An embodiment in which an ink composition is applied so as to come into contact with the treatment liquid applied on the medium to form an image is preferable. Thereby, inkjet recording can be speeded up, and an image with high density and resolution can be obtained even at high speed recording.

The amount of treatment liquid applied is not particularly limited as long as the ink composition can be agglomerated, but the amount of aggregating agent applied is preferably an amount such that the amount of the aggregating agent is 0.1 g / m ² or more. Especially, the quantity from which the provision amount of a flocculant will be 0.2-0.7 g / m < ² > is preferable. When the applied amount of the flocculant is 0.1 g / m ² or more, good high-speed flocculence can be maintained according to various usage forms of the ink composition. Further, it is preferable that the amount of the flocculant applied is 0.7 g / m ² or less because the surface properties of the applied recording medium are not adversely affected (such as a change in gloss).

  In the present invention, an ink application step is provided after the treatment liquid application step, and the treatment liquid on the recording medium is heated and dried after the treatment liquid is applied on the recording medium and before the ink composition is applied. It is preferable to further provide a heat drying step. By heating and drying the treatment liquid in advance before the ink application step, ink colorability such as bleeding prevention is improved, and a visible image with good color density and hue can be recorded.

  Heating and drying can be performed by known heating means such as a heater, air blowing means using air blowing such as a dryer, or a combination of these. As the heating method, for example, a method of applying heat with a heater or the like from the side opposite to the treatment liquid application surface of the recording medium, a method of applying warm air or hot air to the treatment liquid application surface of the recording medium, or an infrared heater was used. The heating method etc. are mentioned, You may heat combining these two or more.

-Active energy ray irradiation process-
In the image forming method of the present invention, an active energy ray irradiation step is preferably provided. The active energy ray irradiating step is a step of irradiating the ink image formed by applying the ink composition with, for example, ultraviolet rays from an ultraviolet irradiation lamp. Thereby, the monomer component in the image can be surely polymerized and cured. At this time, if the ultraviolet irradiation lamp is disposed opposite the recording surface of the recording medium and the entire recording surface is irradiated, the entire image can be cured. The light source for irradiating the active energy ray is not limited to the ultraviolet irradiation lamp, and a halogen lamp, a high-pressure mercury lamp, a laser, an LED, an electron beam irradiation device, or the like can also be employed.
The active energy ray irradiation process may be installed before or after the heat drying process as long as it is after the ink ejection process and the treatment liquid application process, or may be installed both before and after the heat drying process.

As a wavelength of an active energy ray, it is preferable that it is 200-600 nm, for example, it is more preferable that it is 300-450 nm, and it is further more preferable that it is 350-420 nm.
The output of the actinic energy ray, it is preferable that the integrated irradiation dose is 5000 mJ / cm ² or less, more preferably 10~4000mJ / cm ^2, further preferably 20~3000mJ / cm ^2.

-Recording media-
The image forming method of the present invention records an image on a recording medium. The recording medium is not particularly limited, and general printing paper mainly composed of cellulose, such as so-called high-quality paper, coated paper, and art paper, used for general offset printing and the like can be used. General printing paper mainly composed of cellulose is relatively slow in absorption and drying of ink in image recording by a general ink jet method using water-based ink. However, according to the image forming method of the present invention, it is possible to record a high quality image excellent in color density and hue by suppressing the movement of the color material.

  As the recording medium, commercially available media can be used. For example, “OK Prince fine quality” manufactured by Oji Paper Co., Ltd., “Shiorai” manufactured by Nippon Paper Industries Co., Ltd., and Nippon Paper Industries ( Fine coated paper such as “New NPI fine quality” manufactured by Co., Ltd., “OK Everlight Coat” manufactured by Oji Paper Co., Ltd., and “Aurora S” manufactured by Nippon Paper Industries Co., Ltd., Oji Lightweight coated paper (A3) such as “OK Coat L” manufactured by Paper Industries Co., Ltd. and “Aurora L” manufactured by Nippon Paper Industries Co., Ltd. “OK Top Coat +” manufactured by Oji Paper Co., Ltd. and Nippon Paper Industries Co., Ltd. ) Coated paper (A2, B2) such as “Aurora Coat” manufactured by Oji Paper Co., Ltd. Art paper (A1) such as “OK Kanfuji +” manufactured by Oji Paper Co., Ltd. and “Tokuhishi Art” manufactured by Mitsubishi Paper Industries Co., Ltd. Is mentioned. It is also possible to use various photographic papers for ink jet recording.

  Among the recording media, so-called coated paper used for general offset printing is preferable. The coated paper is obtained by applying a coating material to the surface of high-quality paper, neutral paper, or the like that is mainly surface-treated with cellulose as a main component and is not surface-treated. The coated paper is liable to cause quality problems such as glossiness and scratch resistance of the image in normal aqueous inkjet image formation. However, in the image forming method of the present invention, gloss unevenness is suppressed and glossiness and resistance to abrasion are reduced. An image having good rubbing properties can be obtained. In particular, a coated paper having a base paper and a coat layer containing an inorganic pigment is preferably used, and a coated paper having a base paper and a coat layer containing kaolin and / or calcium bicarbonate is more preferably used. Specifically, art paper, coated paper, lightweight coated paper, or finely coated paper is more preferable.

―Inkjet recording device―
Next, an example of an ink jet recording apparatus suitable for carrying out the image forming method of the present invention will be specifically described with reference to FIG. FIG. 1 is a schematic configuration diagram illustrating a configuration example of the entire inkjet recording apparatus.

  As shown in FIG. 1, the ink jet recording apparatus includes a processing liquid application unit 12 including a processing liquid discharge head 12S that sequentially discharges a processing liquid in the recording medium conveyance direction (the arrow direction in the figure); A treatment liquid drying zone 13 provided with a heating means (not shown) for drying the applied treatment liquid, an ink ejection part 14 for ejecting various ink compositions, and an ink drying zone 15 for drying the ejected ink composition. Are arranged. Further, an ultraviolet irradiation unit 16 including an ultraviolet irradiation lamp 16S is disposed on the downstream side of the ink drying zone 15 in the conveyance direction of the recording medium.

  The recording medium supplied to the ink jet recording apparatus includes a processing liquid application unit 12, a processing liquid drying zone 13, and an ink discharging unit by a conveying roller from a paper feeding unit that feeds the recording medium from a case loaded with the recording medium. 14, the ink drying zone 15, and the ultraviolet irradiation unit 16 are sequentially sent and accumulated in the accumulation unit. In addition to the method using a conveyance roller, the conveyance may be performed by a drum conveyance method using a drum-shaped member, a belt conveyance method, a stage conveyance method using a stage, or the like.

  Among the plurality of transport rollers, at least one roller may be a driving roller to which the power of a motor (not shown) is transmitted. By rotating a driving roller rotated by a motor at a constant speed, the recording medium is conveyed in a predetermined direction by a predetermined conveyance amount.

  The treatment liquid application unit 12 is provided with a treatment liquid discharge head 12S connected to a storage tank that stores the treatment liquid. The treatment liquid ejection head 12S can eject the treatment liquid from ejection nozzles arranged to face the recording surface of the recording medium, and can apply the treatment liquid on the recording medium. The treatment liquid application unit 12 is not limited to a method of discharging from a nozzle-shaped head, and an application method using an application roller can also be adopted. In this coating method, the treatment liquid can be easily applied to almost the entire surface including the image area where the ink droplets land on the recording medium by the ink discharge unit 14 disposed on the downstream side. In order to make the thickness of the processing liquid on the recording medium constant, for example, an air knife or a member having a sharp corner is provided with a gap corresponding to the specified amount of the processing liquid provided between the recording medium and the recording medium. You may provide the method of doing.

  A treatment liquid drying zone 13 is disposed downstream of the treatment liquid application unit 12 in the recording medium conveyance direction. The treatment liquid drying zone 13 can be configured by using a known heating means such as a heater, an air blowing means using air blowing such as a dryer, or a combination of these. The heating means may be a method of installing a heating element such as a heater on the side opposite to the barrier layer forming surface of the recording medium (for example, below the conveyance mechanism that carries the recording medium when the recording medium is automatically conveyed) Examples include a method of applying warm air or hot air to the surface of the medium on which the barrier layer is formed, a heating method using an infrared heater, and the like.

In addition, since the surface temperature of the recording medium changes depending on the type (material, thickness, etc.) of the recording medium, the environmental temperature, etc., the measuring unit for measuring the surface temperature of the recording medium and the surface of the recording medium measured by the measuring unit It is preferable to provide a control mechanism that feeds back the temperature value to the heating control unit to form the blocking layer while controlling the temperature. As a measurement part which measures the surface temperature of a recording medium, a contact or non-contact thermometer is preferable.
Further, the solvent may be removed using a solvent removal roller or the like. As another embodiment, a method of removing excess solvent from the recording medium with an air knife is also used.

  The ink discharge unit 14 is disposed downstream of the treatment liquid drying zone 13 in the recording medium conveyance direction. The ink discharge section 14 includes a recording head (ink discharge head) 30K connected to each of the ink storage sections that store black (K), cyan (C), magenta (M), and yellow (Y) color inks. 30C, 30M, and 30Y are arranged. Each ink storage section (not shown) stores an ink composition containing a pigment corresponding to each hue, resin particles, a water-soluble organic solvent, and water, and ejects each ink as necessary when recording an image. The heads 30K, 30C, 30M, and 30Y are supplied. Further, as shown in FIG. 1, a recording head 30A for spot color ink discharge is provided on the downstream side in the transport direction of the ink discharge heads 30K, 30C, 30M, and 30Y so that spot color ink can be discharged as needed. 30B can be further provided.

  The ink ejection heads 30K, 30C, 30M, and 30Y each eject ink corresponding to an image from ejection nozzles arranged to face the recording surface of the recording medium. Thus, each color ink is applied on the recording surface of the recording medium, and a color image is recorded.

  Each of the treatment liquid ejection head 12S and the ink ejection heads 30K, 30C, 30M, 30Y, 30A, and 30B has a large number of ejection openings over the maximum recording width (maximum recording width) of an image recorded on the recording medium. It is a full line head in which (nozzles) are arranged. Compared to the serial type in which recording is performed while reciprocating a short shuttle head in the width direction of the recording medium (direction perpendicular to the conveying direction on the recording medium conveying surface), it is possible to record an image on the recording medium at a higher speed. it can. In the present invention, either a serial type recording or a method capable of relatively high-speed recording, for example, a method capable of recording by ejecting in the main scanning direction by a single pass forming one line in one scan. However, according to the image recording method of the present invention, a high-quality image with high reproducibility can be obtained even by a single-pass method.

  Here, the treatment liquid discharge head 12S and the ink discharge heads 30K, 30C, 30M, 30Y, 30A, and 30B all have the same structure.

  The application amount of the treatment liquid and the application amount of the ink composition are preferably adjusted as necessary. For example, the application amount of the treatment liquid may be changed according to the recording medium in order to adjust the physical properties such as the viscoelasticity of the aggregate formed by mixing the treatment liquid and the ink composition.

  The ink drying zone 15 is disposed downstream of the ink discharge unit 14 in the recording medium conveyance direction. The ink drying zone 15 can be configured in the same manner as the treatment liquid drying zone 13.

The ultraviolet irradiation unit 16 is arranged further downstream in the recording medium conveyance direction of the ink drying zone 15, and is irradiated with ultraviolet rays by an ultraviolet irradiation lamp 16S provided in the ultraviolet irradiation unit 16, and in the image after image drying. The monomer component is polymerized and cured. The ultraviolet irradiation lamp 16S irradiates the entire recording surface with a lamp disposed opposite to the recording surface of the recording medium, so that the entire image can be cured. The ultraviolet irradiation unit 16 is not limited to the ultraviolet irradiation lamp 16S, and a halogen lamp, a high-pressure mercury lamp, a laser, an LED, an electron beam irradiation device, or the like can also be employed.
The ultraviolet irradiation unit 16 may be installed either before or after the ink drying zone 15, or may be installed both before and after the ink drying zone 15.

  Further, in the ink jet recording apparatus, a heating unit that performs a heat treatment on the recording medium can be arranged in a conveyance path from the paper feeding unit to the stacking unit. For example, the temperature of the recording medium is raised to a desired temperature by disposing a heating unit at a desired position such as the upstream side of the treatment liquid drying zone 13 or between the ink discharge unit 14 and the ink drying zone 15. Thus, drying and fixing can be effectively performed.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. Unless otherwise specified, “part”, “%”, and “ppm” are based on mass, and the solubility is mass% with respect to water at 25 ° C.

  The weight average molecular weight was measured by gel permeation chromatography (GPC). GPC uses HLC-8220GPC (manufactured by Tosoh Corporation), and three columns are connected in series using TSKgeL SuperHZM-H, TSKgeL SuperHZ4000, and TSKgeL SuperHZ2000 (all are trade names of Tosoh Corporation). , THF (tetrahydrofuran) was used as an eluent. The conditions were as follows: the sample concentration was 0.35% by mass, the flow rate was 0.35 ml / min, the sample injection amount was 10 μl, the measurement temperature was 40 ° C., and the RI detector was used. In addition, the calibration curve is “standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, It produced from eight samples of "A-2500", "A-1000", and "n-propylbenzene".

<Preparation of ink composition>
(Synthesis of water-insoluble polymer dispersant P-1)
To a 1000 ml three-necked flask equipped with a stirrer and a condenser, 88 g of methyl ethyl ketone was added and heated to 72 ° C. under a nitrogen atmosphere. To this, 50 g of methyl ethyl ketone was added with 0.85 g of dimethyl-2,2′-azobisisobutyrate and phenoxy. A solution in which 50 g of ethyl methacrylate, 13 g of methacrylic acid, and 37 g of methyl methacrylate were dissolved was dropped over 3 hours. After completion of the dropwise addition, the reaction was further continued for 1 hour, and then a solution prepared by dissolving 0.42 g of dimethyl-2,2′-azobisisobutyrate in 2 g of methyl ethyl ketone was added, heated to 78 ° C. and heated for 4 hours. The obtained reaction solution was reprecipitated twice in an excess amount of hexane, and the precipitated resin was dried to obtain phenoxyethyl methacrylate / methyl methacrylate / methacrylic acid (copolymerization ratio [mass% ratio] = 50/37/13). 96.5 g of a copolymer (resin dispersant P-1) was obtained.
The composition of the obtained resin dispersant P-1 was confirmed by ¹ H-NMR, and the weight average molecular weight (Mw) determined by GPC was 49400. Furthermore, when the acid value of this polymer was determined by the method described in JIS standard (JIS K 0070: 1992), it was 84.8 mgKOH / g.

(Preparation of colorant particle dispersion C)
Pigment Blue 15: 3 (phthalocyanine blu-A220, manufactured by Dainichi Seika Co., Ltd .; cyan pigment), 4 parts of the polymer dispersant P-1, 42 parts of methyl ethyl ketone, and 1 mol / L NaOH aqueous solution. 4 parts and 87.2 parts of ion-exchanged water were mixed and dispersed with a bead mill using 0.1 mmφ zirconia beads for 2 to 6 hours.
After removing methyl ethyl ketone at 55 ° C. under reduced pressure and removing a part of water in the obtained dispersion, using a high-speed centrifugal cooler 7550 (manufactured by Kubota Seisakusho), using a 50 mL centrifuge, Centrifugation was performed at 8000 rpm for 30 minutes, and the supernatant liquid other than the precipitate was collected. Thereafter, the pigment concentration was determined from the absorbance spectrum, and a colorant particle dispersion C was obtained as a dispersion of resin-coated pigment particles (encapsulated pigment) having a pigment concentration of 10.2% by mass.

(Synthesis of self-dispersing polymer particles (Exemplary Compound B-01))
360.0 g of methyl ethyl ketone was charged into a 2-liter three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, and the temperature was raised to 75 ° C. Then, 180.0 g of phenoxyethyl acrylate, 162.0 g of methyl methacrylate, 18.0 g of acrylic acid, 72 g of methyl ethyl ketone, and “V-601” (manufactured by Wako Pure Chemical Industries, Ltd.) while maintaining the temperature in the flask at 75 ° C. A mixed solution consisting of 1.44 g was added dropwise at a constant speed so that the addition was completed in 2 hours. After completion of the dropwise addition, a solution composed of 0.72 g of “V-601” and 36.0 g of methyl ethyl ketone was added thereto, stirred at 75 ° C. for 2 hours, and further a solution composed of 0.72 g of “V-601” and 36.0 g of isopropanol. And stirred at 75 ° C. for 2 hours. Thereafter, the temperature was raised to 85 ° C., and stirring was further continued for 2 hours to obtain a resin solution of a phenoxyethyl acrylate / methyl methacrylate / acrylic acid (= 50/45/5 [mass ratio]) copolymer.
The weight average molecular weight (Mw) measured in the same manner as described above of the obtained copolymer was 64,000 (calculated in terms of polystyrene by gel permeation chromatography (GPC)), and the acid value was 38.9 mgKOH / g. there were.

  Next, 668.3 g of the obtained resin solution was weighed, 388.3 g of isopropanol and 145.7 ml of 1 mol / L NaOH aqueous solution were added thereto, and the temperature in the reaction vessel was raised to 80 ° C. Next, 720.1 g of distilled water was added dropwise at a rate of 20 ml / min to disperse in water, and then the reaction vessel internal temperature was 80 ° C. for 2 hours, 85 ° C. for 2 hours, and 90 ° C. for 2 hours under atmospheric pressure. After maintaining, the inside of the reaction vessel is evacuated, 913.7 g of isopropanol, methyl ethyl ketone and distilled water are distilled off in total, and water of self-dispersing polymer particles (exemplary compound B-01) having a solid content concentration of 28.0% by mass. A dispersion was obtained.

(Synthesis of polymerizable compound 1)
To a 1 L three-necked flask equipped with a stirrer was added 40.0 g (182 mmol) of 4,7,10-trioxa-1,13-tridecanediamine, 37.8 g (450 mmol) of sodium bicarbonate, 100 g of water, and 300 g of tetrahydrofuran. In an ice bath, 35.2 g (389 mmol) of acrylic acid chloride was added dropwise over 20 minutes. After dropping, the mixture was stirred at room temperature for 5 hours, and then tetrahydrofuran was distilled off from the obtained reaction mixture under reduced pressure. Next, the aqueous layer was extracted four times with 200 ml of ethyl acetate, and the obtained organic layer was dried over magnesium sulfate, filtered, and the solvent was distilled off under reduced pressure to obtain 35.0 g of the target polymerizable compound 1 solid. (107 mmol, 59% yield).

(Preparation of ink-jet ink composition)
-Ink composition C-1
Colorant particle dispersion C obtained above, self-dispersing polymer particles (Exemplary Compound B-01), polymerizable compound 1, and water-soluble compound 11 (manufactured by Wako Pure Chemical Industries, Ltd.) Each component was mixed so as to have the following ink composition. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to prepare cyan ink (ink jet ink composition) C-1.

~ Ink composition ~
-Colorant particle dispersion C 29.4%
-Self-dispersing polymer fine particle (B-01) aqueous dispersion (solid content) 1.5%
・ Polymerizable compound 1 (structure shown below) 15%
・ Diethylene glycol monoethyl ether (DEGmEE) ・ ・ ・ 1%
(Wako Pure Chemical Industries, Ltd.)
Water-soluble compound 11 (water-soluble compound (S) (compound containing a double bond and a hydroxyl group directly bonded to an atom forming the double bond in the molecule (the following structure))): 500 ppm
(Wako Pure Chemical Industries, Ltd.)
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) ・ ・ ・ 1%
・ Irgacure 2959 (Ciba Japan) ・ ・ ・ ・ 3%
・ Ion-exchanged water ・ ・ ・ Remaining amount (added to 100% by mass in total)

~ Ink composition C-2 ~ C-28 ~
In the preparation of the cyan ink C-1, the polymerizable compounds shown in Table 1 below were used in place of the polymerizable compound 1, respectively, and the water-soluble compound (S) (double bond and the double bond in the molecule). Each of the cyan inks C-2 to C-28 was prepared in the same manner as described above except that the type and amount added of the compound containing a hydroxyl group directly bonded to the atom forming A) were changed as shown in Table 1 below. Prepared.

  The structure of the polymerizable compound shown in Table 1 and the details of the water-soluble compound (S) (compound containing a double bond and a hydroxyl group directly bonded to an atom forming the double bond in the molecule) are as follows. It is as follows.

  The polymerizable compound 2 and the polymerizable compound 3 can be synthesized according to the polymerizable compound 1.

  Water-soluble compound (S) (compound containing a double bond and a hydroxyl group directly bonded to an atom forming the double bond in the molecule) The solubility described in the exemplified compound is the mass with respect to water at 25 ° C. %.

<Preparation of treatment solution>
A treatment liquid was prepared as shown below.
(Preparation of treatment liquid 1)
The component of the following composition was mixed and the processing liquid 1 was prepared. The viscosity, surface tension, and pH (25 ° C.) of the treatment liquid 1 were a viscosity of 2.5 mPa · s, a surface tension of 40 mN / m, and a pH of 1.0. The surface tension was measured using a fully automatic surface tension meter CBVP-Z manufactured by Kyowa Interface Science Co., Ltd., and the viscosity was measured using DV-III Ultra CP manufactured by Brookfield Engineering. The pH was measured using a PH meter HM-30R manufactured by Toa DKK Co., Ltd.
<Composition of treatment liquid 1>
・ Malonic acid (Wako Pure Chemical Industries, Ltd.) ... 25% by mass
・ Diethylene glycol monomethyl ether (Wako Pure Chemical Industries, Ltd.) ... 20.0% by mass
・ Emulgen P109 (manufactured by Kao Corporation, nonionic surfactant): 1.0% by mass
・ Ion exchange water: 54% by mass

<Image formation and evaluation>
Using the ink composition and the treatment liquid obtained above, image formation and evaluation (standability recovery, crack resistance) were performed as follows. The evaluation results are shown in Table 1.

First, as shown in FIG. 1, a treatment liquid application unit 12 including a treatment liquid ejection head 12S that ejects an aqueous treatment liquid sequentially in the conveyance direction of the recording medium (the arrow direction in the drawing) is applied. A treatment liquid drying zone 13 for drying the aqueous treatment liquid, an ink ejection section 14 for ejecting various aqueous inks, an ink drying zone 15 for drying the ejected aqueous ink, and UV irradiation capable of irradiating ultraviolet rays (UV). An ink jet apparatus provided with a UV irradiation unit 16 provided with a lamp 16S was prepared.
Although not shown, the processing liquid drying zone 13 is provided with a blower for drying by sending dry air to the recording surface side of the recording medium, and an infrared heater on the non-recording surface side of the recording medium. The temperature and the air volume are adjusted to evaporate (dry) 70% by mass or more of water in the aqueous treatment liquid until 900 msec after the application of the treatment liquid is started in the application unit. The ink discharge unit 14 includes a black ink discharge head 30K, a cyan ink discharge head 30C, a magenta ink discharge head 30M, and a yellow ink discharge head 30Y, which are sequentially arranged in the transport direction (arrow direction). Each head is a 1200 dpi / 10 inch wide full-line head (driving frequency: 25 kHz, recording medium conveyance speed 530 mm / sec), and can record by discharging each color in the main scanning direction by a single pass.

The storage liquid (not shown) connected to the processing liquid discharge head 12S and the cyan ink discharge head 30C of the ink jet apparatus configured as shown in FIG. A solid image and a 1200 dpi line image were recorded on the medium. The amount of the aqueous treatment liquid applied to the recording medium was 5 ml / m ² . As a recording medium, “Ulite” (basis weight 84.9 g / m ² ) manufactured by Nippon Paper Industries Co., Ltd. was used.
In recording an image, the aqueous treatment liquid and cyan ink were ejected at a resolution of 1200 dpi × 600 dpi and an ink droplet amount of 3.5 pl. At this time, the line image is recorded by ejecting a 1200-dot wide 1-dot line, a 2-dot wide line, and a 4-dot wide line in the main scanning direction in a single pass, and the solid image is printed on an A5 size recording medium. Ink was discharged onto the entire surface of the cut sample to obtain a solid image.
First, after the processing liquid is discharged from the processing liquid discharge head 12S onto the recording medium in a single pass, the processing liquid is dried in the processing liquid drying zone 13, and the processing liquid drying zone is discharged with the aqueous processing liquid. Passed by 900 msec from the start. In the treatment liquid drying zone 13, 120 ° C. is applied to the recording surface by a blower while heating the deposited aqueous treatment liquid from the back side (rear side) of the landing surface with an infrared heater so that the film surface temperature is 40 to 45 ° C. The warm air was applied to adjust the air volume to a predetermined dry amount. Subsequently, after cyan ink is ejected in a single pass by the cyan ink ejection head 30C and an image is recorded, the ink drying zone 15 is heated with an infrared heater from the back side (back surface) of the ink landing surface as described above. Then, warm air at 120 ° C. and 5 m / sec was applied to the recording surface for 15 seconds with a blower and dried. After drying the image, the UV irradiation unit 16 irradiated UV light (a metal halide lamp, maximum illumination wavelength 365 nm, manufactured by Eye Graphics Co., Ltd.) so that the integrated irradiation amount was 3000 mJ / cm ² , and the image was cured.

(Leaving recoverability (discharge stability when the ink composition is stopped on the ink jet recording apparatus and left for a certain period of time, and then restarted))
As described above, a line of 1 dot width is output every other nozzle on the A5 size Eulite, the output head is left as it is for a predetermined time, and then again on the A5 size Eulat. A line with a width of 1 dot was output every other nozzle. Image output was repeated while changing the leaving time, and the printing statuses of the output lines before and after being left were compared, and an evaluation was made by examining the leaving time at which 30% or more of the number of outputs after being left was not output.
<Evaluation criteria>
A: The leaving time in which 30% or more of the output number before leaving is not output is 60 minutes or more.
B: Leave time when 30% or more of the number of output before leaving is not output 30 minutes or more and less than 60 minutes C: Leave time when 30% or more of the number of output before leaving is not output 20 minutes or more and less than 30 minutes D: Evacuation time when 30% or more of the output number before leaving is not output 10 minutes or more and less than 20 minutes E: Leaving time when 30% or more of the output number before leaving is not output is less than 10 minutes * AC is practical There is no problem.

(Crack resistance evaluation)
The effect of the present invention capable of suppressing cracking even when stress was applied to the image area was evaluated based on crack resistance as follows.
The above-mentioned A5 size sample with a solid image formed on the entire surface was left in an environment of 25 ° C. and 50% RH for 72 hours. ) Drilling was performed using Lion Corporation))). The state of cracks in the drilled part formed in the image part was observed visually and with an optical microscope. The evaluation results are shown in Table 1.

~Evaluation criteria~
A: The periphery of the punch hole was observed at a magnification of 10 times, but no crack was observed.
B: When the periphery of the punch hole was observed at a magnification of 10 times, color unevenness was observed in the image, but the color unevenness was not visually observed.
C: When the periphery of the punch hole was observed at a magnification of 10 times, a slight crack was observed in the image, but it was a level at which no crack was visually observed.
D: Cracks occurred visually around the punch hole.
* A to C are in a range where there is no problem in practical use.

  As shown in Table 1, in the examples, even when the discharge of the ink composition is stopped and left for a certain period of time, and then the discharge is restarted, an excellent effect in discharge stability (stand recovery) is obtained, and Even if stress was applied to the image area, cracks could be suppressed. On the other hand, in the comparative example, the stand-by recovery property was particularly insufficient, and the effect was insufficient in the crack resistance.

DESCRIPTION OF SYMBOLS 12 ... Treatment liquid provision part 12S ... Treatment liquid discharge head 13 ... Treatment liquid drying zone 14 ... Ink discharge part 15 ... Ink drying zone 16 ... Ultraviolet irradiation part 16S ... Ultraviolet irradiation lamp 30K, 30C, 30M, 30Y ... ink ejection head

Claims (8)

Water-soluble compound (S) containing colorant particles, a water-soluble polymerizable compound represented by the following general formula (1), a double bond and a hydroxyl group bonded to an atom forming the double bond in the molecule And an ink composition, wherein the content of the water-soluble compound (S) is from 50 ppm to 10,000 ppm on a mass basis.

[In General Formula (1), Q represents an n-valent linking group, and R ¹ represents a hydrogen atom or a methyl group. N represents an integer of 1 or more. ]   The ink composition according to claim 1, wherein the content of the water-soluble compound (S) is 100 ppm or more and 5000 ppm or less on a mass basis. The ink composition according to claim 1, wherein the water-soluble compound (S) is represented by any one of the following general formulas (S1) and (S2).


[In General Formula (S1), Z represents a group having a benzene ring or a condensed ring thereof, or a group having a heterocycle, and p is 1 ≦ when the number of double bonds contained in Z is q. It is an integer of p ≦ 2q. ]


[In general formula (S2), Rs represents a C1-C10 chain saturated hydrocarbon group or a C3-C10 cyclic saturated hydrocarbon group. ]   The ink composition according to claim 3, wherein 2 ≦ p ≦ 6 in the water-soluble compound (S1).   The ink composition according to any one of claims 1 to 4, further comprising an initiator that initiates polymerization of the polymerizable compound by active energy rays.   An ink set comprising: the ink composition according to any one of claims 1 to 5; and a treatment liquid containing a flocculant for aggregating components in the ink composition.   The ink set according to claim 6, wherein the flocculant is an organic acid. An ink application step for applying the ink composition according to any one of claims 1 to 5 onto a recording medium, and a treatment liquid containing an aggregating agent for aggregating components in the ink composition. An image forming method comprising: a treatment liquid applying step for applying to a medium.