JP2013072044A - Ink composition, ink set and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink composition which has excellent rub-off resistance and adhesion property, and can form an image with suppressed stripe uneveness.SOLUTION: The ink composition contains at least two kinds of resin coated magenta pigments which is made by coating at least a part of the surface of each of the two kinds of magenta pigments with a resin crosslinked by a crosslinking agent, an aqueous polymerizable compound, a polymerization initiator, and water.

Description

  The present invention relates to an ink composition, an ink set, and an image forming method.

Inkjet technology is known as an image recording method for recording a color image. Ink jet technology has been applied to fields such as office printers and home printers, but in recent years, it has been applied to commercial printing fields.
A pigment is widely used as one of the components of ink (ink composition) used in the ink jet technology.
Regarding inks containing pigments (pigment inks), inks containing two or more pigments have been studied from the viewpoint of saturation and color reproducibility.
In recent years, inks have become more water-based from the viewpoints of resource protection and environmental protection.

  For example, yellow ink, magenta ink, and cyan ink are available as ink sets for inkjet recording that have excellent storage stability and ejection stability, and have both high color development on plain paper and glossy paper and high gloss on glossy paper. In each of the above inks, water and at least 50% by weight of benzyl acrylate as a polymer component and 15% by weight or less of (meth) acrylic acid are polymerized to give an acid of 50 mgKOH / g or more and 120 mgKOH / g or less. And a pigment dispersed using a polymer having a weight average molecular weight of 20000 or more and 120,000 or less, the pigment contained in the yellow ink is PY74, and the pigment contained in the magenta ink is at least selected from PV19, PR122, PR177, and PR254 One or more, including cyan ink Pigment PB15: the ink set is known is 1 (e.g., see Patent Document 1).

  In addition, as an ink set having an ink that can form an image with excellent saturation and has excellent storage stability, an ink set for ink jet recording composed of a yellow ink, a magenta ink, and a cyan ink, each ink has at least a pigment, a dispersion Containing yellowing agent and aqueous medium, yellow ink is C.I. I. Pigment Yellow 74, and magenta ink is C.I. I. Pigment red 122 and C.I. I. Pigment Violet 19, the cyan ink contains β-type phthalocyanine copper, the average particle size of the pigment of each ink is 10 to 93.6 nm, and the C.I. I. Pigment red 122 and C.I. I. An ink set for ink-jet recording having a weight ratio with Pigment Violet 19 in the range of 1/3 to 1/1 is known (for example, see Patent Document 2).

  In addition, at least two types of pigments and water are used as an aqueous ink composition that has a small hue change between a light color portion and a dark color portion, has a wide color reproduction range, and can be recorded without causing a decrease in saturation. A water-based ink composition is known (for example, see Patent Document 3).

Japanese Patent No. 4715271 Japanese Patent No. 4584552 JP 2003-313480 A

By the way, in order to improve the abrasion resistance of the image using the aqueous pigment ink and the adhesion of the image to the recording medium, the aqueous pigment ink contains a water-soluble polymerizable compound and a polymerization initiator. A curable aqueous pigment ink is also used.
However, a water-based ink containing a magenta pigment is liable to have low dispersibility. In particular, an aqueous ink containing two or more magenta pigments, particularly an aqueous curing containing two or more magenta pigments, a polymerizable compound and a polymerization initiator. It was found that in the type ink, the decrease in dispersibility was remarkable. Furthermore, it has been clarified that streaky unevenness (straight unevenness) may occur in an image due to a decrease in dispersibility.
The present invention has been made in view of the above, and an object of the present invention is to provide an ink composition, an ink set, and an image forming method that are capable of forming an image that is excellent in abrasion resistance and adhesion, and in which unevenness is suppressed.

Specific means for solving the above problems are as follows.
<1> At least two kinds of resin-coated magenta pigments, at least part of which is coated with a resin obtained by crosslinking at least two kinds of magenta pigments with a crosslinking agent, a water-soluble polymerizable compound, and a polymerization initiator And an ink composition containing water.
<2> The ink composition according to <1>, wherein an acid value of the resin crosslinked by the crosslinking agent is 50 mgKOH / g to 90 mgKOH / g.
<3> The ink composition according to <1> or <2>, wherein the at least two kinds of magenta pigments are quinacridone pigments.
<4> The at least two magenta pigments are C.I. I. Pigment red 122, C.I. I. Pigment red 202, C.I. I. Pigment red 206, C.I. I. Pigment red 207, C.I. I. Pigment red 209, and C.I. I. The ink composition according to any one of <1> to <3>, which is at least two selected from the group consisting of CI Pigment Violet 19.
<5> The ink composition according to any one of <1> to <4>, further including an acetylene glycol surfactant.
<6> The ink composition according to any one of <1> to <5>, wherein the polymerization initiator is a compound represented by the following general formula (1).

[In Formula (1), m and n represent an integer greater than or equal to 0 each independently, and m + n represents the integer of 0-3. ]

<7> The ink composition according to any one of <1> to <6>, wherein the content of the water-soluble polymerizable compound is 13 to 35% by mass with respect to the total amount of the ink composition.
<8> The ink composition according to any one of <1> to <7>, wherein the total content of the at least two kinds of magenta pigments is 4 to 7% by mass with respect to the total amount of the ink composition.
<9> The ink composition according to any one of <1> to <8>, wherein the content of the polymerization initiator is 1 to 5% by mass with respect to the total amount of the ink composition.
<10> An ink set comprising: the ink composition according to any one of <1> to <9>; and a treatment liquid containing an aggregating agent capable of forming an aggregate by contacting the ink composition. .
<11> An ink application step of applying the ink composition according to any one of <1> to <9> onto a recording medium, and an active energy ray to the ink composition applied onto the recording medium. And an active energy ray irradiating step for irradiating.
<12> Further, before the active energy ray irradiation step, a treatment liquid application step of applying a treatment liquid containing an aggregating agent capable of forming an aggregate by contacting the ink composition on the recording medium. <11> The image forming method according to <11>.

  According to the present invention, it is possible to provide an ink composition, an ink set, and an image forming method that are capable of forming an image that is excellent in abrasion resistance and adhesion and in which unevenness is suppressed.

  Hereinafter, the ink composition, the ink set, and the image forming method of the present invention will be described in detail.

≪Ink composition≫
The ink composition of the present invention (hereinafter also referred to as “ink”) includes at least two types of resin-coated magenta, in which at least part of the surface is coated with a resin in which at least two types of magenta pigments are each crosslinked by a crosslinking agent. It contains a pigment, a water-soluble polymerizable compound, a polymerization initiator, and water. The ink composition of the present invention may contain other components as necessary.

In general, in an ink containing a pigment, two or more kinds of pigments are contained in the ink from the viewpoint of saturation, color reproducibility, and the like.
However, the water-based ink containing a magenta pigment tends to lower the dispersibility of the magenta pigment, and the water-based ink containing two or more magenta pigments tends to further lower the dispersibility of the magenta pigment. Furthermore, a water-based ink containing two or more types of magenta pigments is curable by containing a water-soluble polymerizable compound and a polymerization initiator in an attempt to improve image abrasion resistance and image adhesion to a recording medium. It was found that when the ink was used, the decrease in the dispersibility of the magenta pigment was particularly remarkable. It has also been found that streaky unevenness (striking) may occur in the formed image as a result of a decrease in the dispersibility of the magenta pigment.

Therefore, the ink composition of the present invention relates to a magenta color ink composition containing at least two types of magenta pigments, a water-soluble polymerizable compound, a polymerization initiator, and water. Each of the surfaces of the resin-coated magenta pigment coated with at least a part of the resin cross-linked by a cross-linking agent can suppress the above-described decrease in dispersibility, and as a result, streak-like unevenness in the image. (Unevenness) can be suppressed.
Here, it is not clear why the resin covering at least a part of the surface of the magenta pigment is cross-linked by the cross-linking agent, thereby suppressing the decrease in dispersibility of the magenta pigment, but the resin is cross-linked. This is presumably because the resin is fixed on the surface of the magenta pigment and is not easily released from the surface.
Furthermore, the ink composition of the present invention can form an image excellent in abrasion resistance and adhesion to a recording medium by containing a water-soluble polymerizable compound and a polymerization initiator.

  Hereinafter, the components of the ink composition of the present invention will be described.

<Magenta pigment>
The ink composition of the present invention contains at least two resin-coated magenta pigments in which at least a part of the surface is coated with a resin obtained by crosslinking at least two magenta pigments with a crosslinking agent.
The at least two kinds of magenta pigments are not particularly limited. 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 202, C.I. I. Pigment red 206, C.I. I. Pigment red 207, C.I. I. Pigment red 209, C.I. I. Pigment red 222, and C.I. I. At least two selected from the group consisting of CI Pigment Violet 19 can be selected and used.
Among these, from the viewpoint of color reproducibility, C.I. I. Pigment red 122, C.I. I. Pigment red 202, C.I. I. Pigment red 206, C.I. I. Pigment red 207, C.I. I. Pigment red 209, and C.I. I. Preferably at least two selected from the group consisting of CI Pigment Violet 19; I. Pigment red 122 and C.I. I. Two types of pigment violet 19 are particularly preferable.

Of the at least two magenta pigments, at least one is preferably a quinacridone pigment, more preferably at least two are quinacridone pigments, and all the magenta pigments are quinacridone pigments. It is particularly preferred.
Since the quinacridone pigment is a pigment whose dispersibility tends to be lowered, when at least one of the magenta pigments in the present invention (more than at least two, or even all of them) is a quinacridone pigment, the present invention The effect of suppressing dispersibility deterioration and suppressing unevenness is more effectively exhibited.

Examples of the quinacridone compound constituting the quinacridone pigment include compounds represented by the following general formula (A).
_{X n -Q-Y m ··· (} A)
In the general formula (A), Q represents a quinacridone residue or a quinacridone quinone residue. X and Y each independently represent a hydrogen atom, a methyl group, a chloro group, or a methoxy group, and m and n each independently represents an integer of 1 to 4.

  Specific examples of the quinacridone compound represented by the general formula (A) include unsubstituted quinacridone, 2,9-dimethylquinacridone, 2,9-dichloroquinacridone, 2,9-dimethoxyquinacridone, 3,10- Examples thereof include dimethylquinacridone, 3,10-dichloroquinacridone, 3,10-dimethoxyquinacridone, 4,11-dimethylquinacridone, 4,11-dichloroquinacridone, 4,11-dimethoxyquinacridone, and quinacridonequinone.

  Examples of the quinacridone pigment include C.I. I. Pigment red 122, C.I. I. Pigment red 202, C.I. I. Pigment red 206, C.I. I. Pigment red 207, C.I. I. Pigment red 209, and C.I. I. Preferably at least two selected from the group consisting of CI Pigment Violet 19; I. Pigment red 122 and C.I. I. Two types of pigment violet 19 are particularly preferable.

In the present invention, preferred combinations in the case of using at least two quinacridone pigments are at least two selected from the group consisting of unsubstituted quinacridone, dimethyl-substituted quinacridone, and dichloro-substituted quinacridone from the viewpoints of hue and color gamut. The combination containing is mentioned.
More specifically, for the same reason as described above, (1) a combination containing an unsubstituted quinacridone and a dimethyl-substituted quinacridone (eg, 2,9-dimethylquinacridone), (2) an unsubstituted quinacridone and a dichloro-substituted quinacridone (Example: 2,9-dichloroquinacridone, 3,10-dichloroquinacridone, etc.), (3) Dimethyl-substituted quinacridone (eg, 2,9-dimethylquinacridone, etc.) and dichloro-substituted quinacridone (Example: 2) , 9-dichloroquinacridone, 3,10-dichloroquinacridone, etc.), and the like.

Among the above combinations, from the viewpoint of hue and color gamut, (1) a combination of unsubstituted quinacridone and dimethyl-substituted quinacridone and (2) a combination of unsubstituted quinacridone and dichloro-substituted quinacridone are preferable. More specifically, from the viewpoint of hue, a combination of unsubstituted quinacridone (CI Pigment Violet 19 etc.) and 2,9-dimethylquinacridone (CI Pigment Red 122 etc.), and nothing A combination of a substituted quinacridone (CI Pigment Violet 19 etc.) and 2,9-dichloro substituted quinacridone (CI Pigment Red 202 etc.) is preferred. Furthermore, a combination of unsubstituted quinacridone (CI Pigment Violet 19 and the like) and 2,9-dimethylquinacridone (CI Pigment Red 122 and the like) is preferable.
As the unsubstituted quinacridone, any of α-type, β-type, and γ-type can be used, but β-type or γ-type unsubstituted quinacridone is preferable from the viewpoint of storage stability.

  In the above combination, the mass ratio of unsubstituted quinacridone / dimethyl-substituted quinacridone, the mass ratio of unsubstituted quinacridone / dichloro-substituted quinacridone, and the mass ratio of dimethyl-substituted quinacridone / dichloro-substituted quinacridone are the ejection reliability of the ink composition, From the viewpoint of image density, saturation, etc., 5/95 to 95/5 is preferable, and 10/90 to 90/10 is more preferable.

The total content of the at least two kinds of magenta pigments in the ink composition of the present invention is not particularly limited, but is preferably 3 to 10% by mass and more preferably 4 to 7% by mass with respect to the total amount of the ink composition. preferable.
When the total content is 3% by mass or more, the optical density of the image can be further improved.
When the total content is 10% by mass or less, a decrease in dispersibility is further suppressed and image unevenness is further suppressed, and inhibition of polymerization by the pigment is further suppressed, so that the image has abrasion resistance and adhesion. More improved.

  In the ink composition of the present invention, each of the at least two magenta pigments is present in a form in which at least a part of the surface is coated with a resin crosslinked by a crosslinking agent (that is, in the form of a resin-coated magenta pigment). doing. Thereby, a decrease in dispersibility of the at least two kinds of magenta pigments is suppressed, and image unevenness is suppressed.

The resin-coated magenta pigment in the present invention is prepared, for example, by dispersing a magenta pigment using a resin (for example, a resin dispersant) to produce a magenta pigment having at least a part of the surface coated with the resin, and then magenta The resin covering at least a part of the surface of the pigment can be produced by crosslinking with a crosslinking agent.
The ink composition of the present invention contains at least two types of the resin-coated magenta pigment.
Hereinafter, the resin for coating the magenta pigment in the resin-coated magenta pigment will be described, and subsequently, the crosslinking agent for crosslinking the resin will be described.

<Resin>
In the resin-coated magenta pigment, the resin for covering at least a part of the surface of the magenta pigment is not particularly limited, and examples thereof include polyvinyls, polyurethanes, and polyesters, among which polyvinyls are preferable.
The resin preferably has a functional group that can be crosslinked by a crosslinking agent.
Examples of the functional group include a salt-forming group, an isocyanate group, and an epoxy group, and a salt-forming group is particularly preferable from the viewpoint of improving dispersibility.
Examples of the salt-forming group include an anionic group (hereinafter, also referred to as “acidic group”) and a cationic group, and more specifically, a carboxy group, a sulfo group, a phosphonate group, an amino group, an ammonium group, and the like. Can be mentioned.
As said salt formation group, an acidic group (for example, a carboxy group, a sulfonic acid group, a phosphoric acid group) is preferable, and especially a carboxy group is especially preferable.

The resin is preferably a water-soluble resin (hereinafter also referred to as “water-soluble resin”) from the viewpoint of dispersion stability.
Here, “water-soluble” means that the resin dissolves in 2% by mass or more in distilled water at 25 ° C., preferably 5% by mass or more, and more preferably 10% by mass or more. . In addition, when the resin has a salt-forming group (for example, an acidic group), it is preferable that the solubility is in the above range when neutralized with an equimolar amount of base or acid.

  The resin-coated magenta pigment is prepared by, for example, preparing a magenta pigment coated with a resin by dispersing the magenta pigment using a resin having a salt-forming group, and then converting the resin coated with the magenta pigment into a crosslinking agent. It can produce by bridge | crosslinking by.

As a method for coating a magenta pigment with a resin, specifically, for example,
(I) a step of mixing and dispersing a magenta pigment, a resin (resin dispersant), an aqueous solution containing a basic substance, and an organic solvent capable of dissolving or dispersing the resin (mixing / hydration step);
(Ii) a step of removing at least a part of the organic solvent (solvent removal step);
The method containing is mentioned.
The resin-coated magenta pigment in the present invention, for example, between (i) and (ii) above,
(Iii) adding a crosslinking agent to the dispersion obtained by the dispersion treatment and heating to crosslink the resin (crosslinking step);
(Iv) a step of purifying the dispersion after crosslinking to remove impurities (purification step);
It can manufacture by the method containing.
By the above (i) to (iv), a magenta pigment dispersion (dispersion of resin-coated magenta pigment) in which a magenta pigment is finely dispersed and excellent in storage stability can be produced.
A method for producing a pigment coated with a crosslinked resin is also described in, for example, Japanese Patent Application Laid-Open No. 2009-190379, and the method described in the publication can also be used in the present invention.

In addition, from the viewpoint of dispersibility of the magenta pigment, the resin preferably has an acid value before crosslinking of 50 to 250 mg KOH / g, and more preferably 50 to 150 mg KOH / g.
In addition, in this invention, the acid value of resin points out the value measured by the method as described in a JIS specification (JISK0070: 1992).

In the present invention, the acid value of the resin crosslinked by the crosslinking agent (that is, the resin after crosslinking) is preferably 40 mgKOH / g to 110 mgKOH / g, and preferably 50 mgKOH / g to 90 mgKOH / g. More preferred.
It is preferable that the acid value of the resin crosslinked by the crosslinking agent is 40 mgKOH / g or more because the ink stability is further improved.
When the acid value of the resin cross-linked by the cross-linking agent is 110 mgKOH / g or less, image unevenness is further reduced, which is preferable.

The crosslinking rate in the resin crosslinked by the crosslinking agent (that is, the resin after crosslinking) is preferably 1 to 60 mol%, more preferably 5 to 50, from the viewpoint of the dispersion stability of the pigment and the aggregation property of the ink. It is mol%, More preferably, it is 10-45 mol%. Here, the crosslinking rate (mol%) refers to a value determined by the following formula.
Crosslink rate (mol%) = [number of mole equivalents of crosslinking agent to be reacted with 1 mole of polymer × 100 / number of moles of reactive group capable of reacting with crosslinking agent of 1 mole of polymer]
Here, “the number of molar equivalents of the crosslinking agent to be reacted with 1 mol of the polymer” is a value obtained by multiplying the number of moles of the crosslinking agent to be reacted with 1 mol of the polymer by the number of reactive groups in one molecule of the crosslinking agent.

In addition, the resin preferably has a weight average molecular weight before crosslinking of 3,000 to 100,000, more preferably 5,000 to 80,000, and 10,000 to 60,000 from the viewpoint of dispersibility of the pigment. Further preferred.
The weight average molecular weight of the resin was determined by using a GPC analyzer equipped with columns of TSKgel GMHxL, TSKgel G4000HxL, and TSKgel G2000HxL (all trade names manufactured by Tosoh Corporation), using THF as a solvent, and differential refraction. The molecular weight is detected by a meter and expressed in terms of polystyrene as a standard substance.

  In the resin-coated magenta pigment, the mass ratio [resin mass / magenta pigment mass] of the resin to the magenta pigment is preferably 0.15 to 0.80 from the viewpoint of ink stability and the like. More preferably, it is 20-0.60.

(Preferred form of resin)
The resin in the present invention is preferably a resin having a salt-forming group and at least one of an aromatic ring structure and an alicyclic structure from the viewpoint of dispersion stability, and is represented by the following general formula (a). A resin containing a repeating unit and a repeating unit having a salt-forming group (hereinafter also referred to as “specific resin”) is preferable.

-Repeating unit represented by general formula (a)-

In the general formula (a), R ₁ represents a hydrogen atom, a methyl group, or a halogen atom (for example, a chlorine atom, a bromine atom, an iodine atom, etc.), and L ₁ represents ^* —COO—, ^* —OCO—, ^* —CONR ₂ —, ^* —O—, or a substituted or unsubstituted phenylene group, R ₂ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. Incidentally, symbol * in the group represented by L ₁ represents a connecting point with the main chain. L ₂ represents a single bond or a divalent linking group. A ₁ represents a monovalent group derived from an aromatic ring or an aliphatic ring.

In the general formula (a), R ₁ represents a hydrogen atom, a methyl group, or a halogen atom, preferably a methyl group.

In the general formula (a), L ₁ represents ^* —COO—, ^* —OCO—, ^* —CONR ₂ —, ^* —O—, or a substituted or unsubstituted phenylene group. When L ₁ represents a phenylene group, unsubstituted is preferred. The L ₁ is particularly preferably ^* -COO-.
In the general formula (a), R ₂ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.

L ₂ represents a single bond or a divalent linking group. The divalent linking group is preferably a linking group having 1 to 30 carbon atoms, more preferably a linking group having 1 to 25 carbon atoms, still more preferably a linking group having 1 to 20 carbon atoms, Particularly preferred is a linking group having 1 to 15 carbon atoms.
Among them, L ₂ is particularly preferably an alkyleneoxy group having 1 to 20 carbon atoms (more preferably 1 to 10), an imino group (—NH—), a sulfamoyl group, and 1 to 20 carbon atoms (more preferably 1). alkylene group or ethylene oxide group _{~15) [- (CH 2 CH} 2 O) n -, n = 1~6 of integer, such as, a divalent linking group containing an alkylene group, and two or more of them Such as a combined group.
Among them, L ₂ is most preferably a single bond, an alkylene group having 1 to 20 carbon atoms (more preferably 1 to 15, more preferably 1 to 6), an ethylene oxide group [— (CH ₂ CH ₂ O) _n — ^{*. *;} n = 1 to 6 integer, ** is] represents a bonding position to _{a 1.}

In the general formula (a), A ₁ represents a monovalent group derived from an aromatic ring or an aliphatic ring.
When A ₁ is a monovalent group derived from an aromatic ring, the aromatic ring is not particularly limited, but a benzene ring, a condensed aromatic ring having 8 or more carbon atoms, an aromatic ring condensed with a hetero ring An aromatic ring in which two or more benzene rings are condensed is mentioned.
In addition, when A ₁ is a monovalent group derived from an aliphatic ring, the aliphatic ring is not particularly limited, but an aliphatic ring having 3 to 12 carbon atoms (preferably, a cyclohexane ring or an isobornene ring). Is mentioned.

  The “condensed aromatic ring having 8 or more carbon atoms” is an aromatic ring in which at least two benzene rings are condensed, or an alicyclic hydrocarbon condensed with at least one aromatic ring and the aromatic ring. And an aromatic compound having 8 or more carbon atoms in which a ring is formed. Specific examples include naphthalene, anthracene, fluorene, phenanthrene, acenaphthene and the like.

The “aromatic ring condensed with a heterocycle” is a compound in which an aromatic compound containing no hetero atom (preferably a benzene ring) and a cyclic compound having a hetero atom are condensed. Here, the cyclic compound having a hetero atom is preferably a 5-membered ring or a 6-membered ring. As a hetero atom, a nitrogen atom, an oxygen atom, or a sulfur atom is preferable. The cyclic compound having a hetero atom may have a plurality of hetero atoms. In this case, the heteroatoms may be the same or different from each other.
Specific examples of the heterocyclic ring condensed with an aromatic ring include phthalimide, acridone, carbazole, benzoxazole, and benzothiazole.

  Specific examples of the monomer forming the repeating unit represented by the general formula (a) include vinyl monomers such as (meth) acrylates, (meth) acrylamides, styrenes, and vinyl esters. it can.

  In the specific resin, the repeating unit represented by the general formula (a) has a structure in which an aromatic ring or an aliphatic ring is bonded to an atom forming a main chain through a linking group, that is, an aromatic ring or an aliphatic ring. Has a structure that does not directly bond to the atoms forming the main chain. For this reason, since an appropriate distance is maintained between the hydrophobic aromatic ring or aliphatic ring and the repeating unit having a salt-forming group, an interaction is likely to occur between the specific resin and the pigment. Therefore, the specific resin is more strongly adsorbed to the pigment, thereby further improving the dispersibility of the pigment.

Specific examples of the monomer that forms the repeating unit represented by the general formula (a) include the following monomers as monomers having an aromatic ring.
However, the present invention is not limited to these.

  Specific examples of the monomer that forms the repeating unit represented by the general formula (a) include cyclohexyl (meth) acrylate and isobornyl (meth) acrylate as the monomer having an aliphatic ring. However, the present invention is not limited to these.

  As a monomer that forms the repeating unit represented by the general formula (a), from the viewpoint of dispersion stability of the coated pigment, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, cyclohexyl (meth) acrylate, Isobornyl (meth) acrylate is preferable, and benzyl (meth) acrylate and phenoxyethyl (meth) acrylate are particularly preferable.

The repeating unit represented by the general formula (a) can be used alone or in combination of two or more.
The content of the repeating unit represented by the general formula (a) in the polymer is preferably in the range of 20 to 90% by mass, more preferably 45 to 90% by mass with respect to the total mass of the polymer. Especially preferably, it is the range of 50-85 mass%.

-Repeating unit with salt-forming group-
In the specific resin, the repeating unit having the salt-forming group is preferably a repeating unit derived from a salt-forming group-containing monomer.
Examples of the salt-forming group-containing monomer include a cationic monomer and an anionic monomer. Examples thereof include those described in JP-A-9-286939, page 5, column 7, line 24 to column 8, line 29.

  Representative examples of the cationic monomer include unsaturated amino group-containing monomers and unsaturated ammonium salt-containing monomers. Among these, N, N-dimethylaminoethyl (meth) acrylate and N- (N ′, N′-dimethylaminopropyl) (meth) acrylamide are preferable.

Representative examples of anionic monomers include unsaturated carboxylic acid monomers, unsaturated sulfonic acid monomers, unsaturated phosphoric acid monomers, and the like.
Examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, β-carboxyethyl acrylate, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid.
Examples of unsaturated sulfonic acid monomers include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, and bis- (3-sulfopropyl) -itaconate.
Examples of unsaturated phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxy Examples thereof include ethyl phosphate.
As the salt-forming group-containing monomer, the anionic monomer is preferable. Among them, an unsaturated carboxylic acid monomer is more preferable, and acrylic acid or methacrylic acid is particularly preferable from the viewpoints of dispersion stability, dischargeability, and the like.

The specific resin may contain other repeating units.
Examples of other repeating units include repeating units derived from alkyl (meth) acrylates having 1 to 20 carbon atoms; styrene and derivatives thereof;

  The method for synthesizing the specific resin is not particularly limited, but random polymerization of vinyl monomers is preferable from the viewpoint of dispersion stability.

The resin having a salt-forming group includes at least one of an alkyl (meth) acrylate having 1 to 20 carbon atoms, a (meth) acrylate having an aromatic ring group, and a (meth) acrylate having an alicyclic group, and a carboxyl group-containing resin. And a copolymer obtained using the monomer.
Among them, as the resin having the salt-forming group, at least one of benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, cyclohexyl (meth) acrylate, and isobornyl (meth) acrylate, (meth) acrylic acid, , A repeating unit derived from at least one of benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, cyclohexyl (meth) acrylate, and isobornyl (meth) acrylate. , A copolymer containing at least a repeating unit derived from (meth) acrylic acid), and at least one of benzyl (meth) acrylate and phenoxyethyl (meth) acrylate and (meth) acrylic acid. Obtained by polymerization Copolymer (that is, at least one of a repeating unit derived from benzyl (meth) acrylate and a repeating unit derived from phenoxyethyl (meth) acrylate) and a repeating unit derived from (meth) acrylic acid A copolymer) is particularly preferred.

In the present invention, when a water-soluble resin is used as the resin, in addition to the water-soluble resin, a water-insoluble resin (for example, a water-insoluble dispersant) may be used in combination.
As the water-insoluble resin, a water-insoluble resin having a hydrophobic structural unit and a hydrophilic structural unit can be used. The hydrophilic structural unit is preferably a structural unit having a salt-forming group, more preferably a structural unit having an acidic group, and particularly preferably a structural unit having a carboxy group.
Examples of the water-insoluble resin include styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer, (meth) acrylic acid ester- (meth) acrylic acid. Examples include copolymers, polyethylene glycol (meth) acrylate- (meth) acrylic acid copolymers, vinyl acetate-maleic acid copolymers, and styrene-maleic acid copolymers.
More specifically, for example, the water-insoluble resins described in JP-A-2005-41994, JP-A-2006-238991, JP-A-2009-084494, JP-A-2009-191134, and the like are preferably used in the present invention. Can be used.

<Crosslinking agent>
In the ink composition of the present invention, the resin coating the magenta pigment is crosslinked by a crosslinking agent.
The cross-linking agent is not particularly limited as long as it is a compound having two or more sites that react with the resin, but preferably has two or more epoxies from the viewpoint of excellent reactivity with a carboxy group. It is a compound (a bifunctional or higher functional epoxy compound) having a group.
Specific examples include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, trimethylol propane tri Examples thereof include glycidyl ether, and polyethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, and trimethylolpropane triglycidyl ether are preferable.

  A commercial item can also be used as said crosslinking agent. As a commercial item, Dencol EX-321, EX-821, EX-830, EX-850, EX-851 (made by Nagase ChemteX Corporation) etc. can be used, for example.

  The molar ratio of the crosslinking site (for example, epoxy group) of the crosslinking agent to the crosslinked site (for example, carboxy group) of the resin is 1: 1 to 1:10 from the viewpoint of the crosslinking reaction rate and the dispersion stability after crosslinking. Is preferable, 1: 1 to 1: 5 is more preferable, and 1: 1 to 1: 1.5 is most preferable.

<Water-soluble polymerizable compound>
The ink composition of the present invention contains at least one water-soluble polymerizable compound.
Thereby, the ink composition of the present invention is polymerized and cured by being irradiated with an active energy ray (for example, radiation or light, or an electron beam).
Here, “water-soluble” means that it can be dissolved in water at a certain concentration or more. Specifically, the solubility in water at 25 ° C. is preferably 5% by mass or more, and more preferably 10% by mass or more. The water-soluble polymerizable compound is preferably one that can be dissolved (desirably uniformly) in the aqueous ink composition. 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 composition.

The water-soluble polymerizable compound in the present invention is not particularly limited, and may be a monofunctional polymerizable compound or a polyfunctional polymerizable compound.
The ink composition of the present invention preferably contains a polyfunctional polymerizable compound from the viewpoint of further improving image adhesion.
In addition, the ink composition of the present invention preferably contains a polyfunctional polymerizable compound and a monofunctional polymerizable compound from the viewpoint of more effectively achieving both image abrasion resistance and adhesion. It is more preferable to contain a monofunctional polymerizable compound having a polymerizable compound and a (meth) acrylamide structure.
When the ink composition of the present invention contains a polyfunctional polymerizable compound, the adhesiveness of the image is further improved, and when the ink composition of the present invention contains a monofunctional polymerizable compound, the abrasion resistance of the image is further improved. improves.

(Monofunctional polymerizable compound having (meth) acrylamide structure)
The monofunctional polymerizable compound is preferably a monofunctional polymerizable compound having a (meth) acrylamide structure from the viewpoint of curability.
The monofunctional polymerizable compound having a (meth) acrylamide structure is not limited as long as it is a polymerizable compound having a (meth) acrylamide structure in the molecule and having one polymerizable group. It is a compound represented by a formula (M-1).

In the general formula (M-1), Q ¹ represents a hydrophilic group, and R ^m represents a hydrogen atom or a methyl group.

In the general formula (M-1), examples of the hydrophilic group represented by Q ¹ include a hydroxyalkyl group (preferably having 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms), a dimethylaminoalkyl group ( C1-C10 is preferable and C1-C5 is still more preferable, and the residue from which one hydrogen atom or hydroxyl group was removed from the following compounds (1)-(4) is mentioned.
(1) Compound having saturated or unsaturated heterocyclic structure (2) Polyols (3) Condensate of polyol (4) Polyamines

  The residue from which one hydrogen atom or hydroxyl group has been removed from the compounds of (1) to (4) is not particularly limited as long as it is a group that can be linked to the nitrogen atom of (M-1). It is preferable that the compound represented by M-1) is selected from the groups satisfying the above-mentioned water solubility, specifically, a residue in which one hydrogen atom or hydroxyl group is removed from the following compound group Z: I can give you.

-Compound group Z-
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, 1,3-pentanediol, 2,4-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 2,5-hexanediol, glycerin, 1,2,4-butanetriol, 1,2,5-pentane Triol, 1,2,6-hexanetri , Trimethylolpropane, trimethylolethane, ditrimethylolpropane, ditrimethylolethane, thiodiglycol, neopentylglycol, pentaerythritol, dipentaerythritol, and their condensates, polyols such as sugars, ethylenediamine, diethylenetriamine, Polyamines such as triethylenetetramine, polyethyleneimine, and polypropylenediamine.

  Examples of the residue from which one hydrogen atom or hydroxyl group has been removed from the compounds (1) to (4) include (1) a compound having a saturated or unsaturated heterocyclic structure or (2) a hydrogen atom from a polyol or A residue from which a hydroxyl group has been removed is preferred, and specifically, a residue from which one hydrogen atom or hydroxyl group has been removed from morpholine, ethylene glycol, or propylene glycol is particularly preferred.

The hydrophilic group represented by Q ¹ in the general formula (M-1) is preferably a hydroxyalkyl group, a dimethylaminoalkyl group, or a compound having a saturated or unsaturated heterocyclic structure and a polyol. It is a residue from which one hydrogen atom or hydroxyl group has been removed from a group, and most preferably a residue from which one hydrogen atom or hydroxyl group has been removed from morpholine, ethylene glycol or propylene glycol.

  Specific examples of the compound represented by the general formula (M-1) include hydroxyethyl acrylamide, hydroxypropyl acrylamide, dimethylaminoethyl acrylamide, dimethylaminopropyl acrylamide, and the like, and particularly preferably hydroxyethyl acrylamide. .

In the ink composition of the present invention, the content of the monofunctional polymerizable compound having a (meth) acrylamide structure (for example, the compound represented by the general formula (M-1)) relative to the total content of the polymerizable compounds is as follows. 10 to 99.5% by mass, more preferably 15 to 99.5% by mass, still more preferably 25 to 95% by mass, and further preferably 30 to 70% by mass. 40 to 60% by mass is particularly preferable.
Here, the total content of the polymerizable compound refers to a monofunctional polymerizable compound having a (meth) acrylamide structure, a polyfunctional polymerizable compound described later, and other monofunctional compounds that may be used as necessary. The total content of the polymerizable compound (monofunctional polymerizable compound other than the monofunctional polymerizable compound having a (meth) acrylamide structure).

  The content of the monofunctional polymerizable compound having a (meth) acrylamide structure in the ink composition of the present invention is preferably 1 to 30% by mass and 5 to 30% by mass with respect to the total amount of the ink composition. More preferably, it is more preferably 5 to 25% by mass, and particularly preferably 5 to 15% by mass.

(Polyfunctional polymerizable compound)
The water-soluble polymerizable compound preferably contains a polyfunctional polymerizable compound from the viewpoint of further improving image adhesion.
The polyfunctional polymerizable compound is not limited as long as it is a polymerizable compound having two or more polymerizable groups in the molecule. For example, bis (4-acryloxypolyethoxyphenyl) propane, tripropylene glycol Diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, dipentaerythritol tetraacrylate, trimethylolpropane (propylene oxide modified) triacrylate, oligoester acrylate, hydroxypivalate neopentyl glycol diacrylate, tetramethylol methane triacrylate, di Methylol tricyclodecane diacrylate, modified glycerin triacrylate, bisphenol A diglycidyl ether acrylic acid adduct, modified bisphenol Diacrylate, PO (propylene oxide) adduct diacrylate of bisphenol A, EO (ethylene oxide) adduct diacrylate of bisphenol A, dipentaerythritol hexaacrylate, propylene glycol diglycidyl ether acrylic acid adduct, ditrimethylolpropane tetraacrylate, 1,9-nonanediol diacrylate, acrylate compounds such as proposyl-modified neopentyl glycol diacrylate; methacrylate compounds such as polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate 2,2-bis (4-methacryloxypolyethoxyphenyl) propane Etc. Other examples include allyl compounds such as diallyl phthalate and triallyl trimellitate.
More specifically, Shinzo Yamashita, “Crosslinker Handbook”, (1981 Taiseisha); Kato Kiyosumi, “UV / EB Curing Handbook (Materials)” (1985, Polymer Publications); Radtech Study Group, “Application and Market of UV / EB Curing Technology”, p. 79, (1989, CMC); Eiichiro Takiyama, “Polyester Resin Handbook”, (1988, Nikkan Kogyo Shimbun) Commercially available products or radically polymerizable or crosslinkable monomers known in the industry can be used.

In addition, examples of the polyfunctional polymerizable compound include polyfunctional vinyl ethers. Examples of the polyfunctional vinyl ether include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butylene glycol divinyl ether, butanediol divinyl ether, hexane. Divinyl ethers such as diol divinyl ether, cyclohexane dimethanol divinyl ether, bisphenol A alkylene oxide divinyl ether, bisphenol F alkylene oxide divinyl ether; trimethylolethane trivinyl ether, trimethylolpropane trivinyl ether, ditrimethylolpropane tetravinyl Ether, glycerin trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, dipentaerythritol hexavinyl ether, ethylene oxide-added trimethylolpropane trivinyl ether, propylene oxide-added trimethylolpropane trivinyl ether, ethylene oxide-added ditrimethylolpropane tetravinyl ether, Propylene oxide addition ditrimethylolpropane tetravinyl ether, ethylene oxide addition pentaerythritol tetravinyl ether, propylene oxide addition pentaerythritol tetravinyl ether, ethylene oxide addition dipentaerythritol hexavinyl ether, propylene oxide addition dipenta Risuri tall polyfunctional vinyl ethers such as hexa vinyl ether.
Examples of the polyfunctional polymerizable compound include polyfunctional polymerizable compounds having the following (meth) acrylamide structure.

The polyfunctional polymerizable compound is preferably a polyfunctional polymerizable compound having a (meth) acrylamide structure from the viewpoint of further improving the image adhesion.
The polyfunctional polymerizable compound having a (meth) acrylamide structure is not limited as long as it is a polymerizable compound having a (meth) acrylamide structure in the molecule and having two or more polymerizable groups. It is a compound represented by general formula (M-2).

In General Formula (M-2), Q ² represents an n-valent linking group, and R ^2m represents a hydrogen atom or a methyl group. N represents an integer of 2 or more.

The compound represented by formula (M-2) are those unsaturated monomer bonded to the linking group Q ² by an amide bond. R ^2m represents a hydrogen atom or a methyl group, preferably a hydrogen atom. Valence n of the linking group Q ² is an integer of 2 or more, more preferably 2 to 6 integer, 2 to 4 integer is more preferable.

The linking group Q ² is not particularly limited as long as it is a group that can be linked to the (meth) acrylamide structure. However, the linking group Q ² is a linking group in which the compound represented by the general formula (M-2) satisfies the aforementioned water solubility. It is preferably selected, and specifically, a residue in which two or more hydrogen atoms or hydroxyl groups are removed from the following compound group X can be exemplified.

-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, 1,3-pentanediol, 2,4-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 2,5-hexanediol, glycerin, 1,2,4-butanetriol, 1,2,5-pentane Triol, 1,2,6-hexanetri , Trimethylolpropane, trimethylolethane, ditrimethylolpropane, ditrimethylolethane, thiodiglycol, neopentylglycol, pentaerythritol, dipentaerythritol, and their condensates, polyols such as sugars, ethylenediamine, diethylenetriamine, Polyamines such as triethylenetetramine, polyethyleneimine, and polypropylenediamine.

  Furthermore, saturated or unsaturated such as methylene, ethylene, propylene, butylene group or the like substituted or unsubstituted alkylene chain having 4 or less carbon atoms, 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.

Among these, the linking group Q ² is preferably a residue of a polyol containing an oxyalkylene group (preferably an oxyethylene group), and contains 3 or more oxyalkylene groups (preferably an oxyethylene group). A residue of a polyol is particularly preferable.

  Specific examples of the polyfunctional polymerizable compound (for example, a compound represented by the general formula (M-2)) include the following water-soluble polymerizable monomers.

  The content of the polyfunctional polymerizable monomer in the ink composition of the present invention is preferably 0.1 to 30% by mass, more preferably 1 to 25% by mass, based on the total amount of the ink composition. It is more preferable that it is 20 mass%, and it is especially preferable that it is 5-15 mass%.

(Other monofunctional polymerizable compounds)
The ink composition of the present invention may contain other monofunctional polymerizable compounds other than the monofunctional polymerizable compound having a (meth) acrylamide structure.
The other monofunctional polymerizable compound is not particularly limited as long as it is a monofunctional polymerizable compound having no (meth) acrylamide structure, and examples thereof include a maleimide group, a vinylsulfonamide group, and an N-vinylamide group. And monofunctional polymerizable monomers.

  Examples of other monofunctional polymerizable compounds include 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, tridecyl acrylate, 2-phenoxyethyl acrylate, and epoxy acrylate. , Isobornyl acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, dicyclopentanyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethylphthalic acid, methoxy-polyethylene glycol acrylate, 2 -Acryloyloxyethyl-2-hydroxyethylphthalic acid, cyclic trimethylolpropane form Acrylate, 2- (2-ethoxyethoxy) ethyl acrylate, 2-methoxyethyl acrylate, 3-methoxybutyl acrylate, ethoxylated phenyl acrylate, 2-acryloyloxyethyl succinic acid, nonylphenol EO (ethylene oxide) adduct acrylate, phenoxy- Acrylate compounds such as polyethylene glycol acrylate, 2-acryloyloxyethyl hexahydrophthalic acid, stearyl acrylate, isoamyl acrylate, isomyristyl acrylate, isostearyl acrylate, lactone-modified acrylate; methyl methacrylate, n-butyl methacrylate, allyl methacrylate, glycidyl methacrylate Benzyl methacrylate, dimethylaminomethyl methacrylate, etc. Methacrylate compounds; allyl compounds such as allyl glycidyl ether.

  When the ink composition of the present invention contains other monofunctional polymerizable compound, the content of the other monofunctional polymerizable compound is preferably 0.5 to 30% by mass with respect to the total amount of the ink composition, More preferably, it is 1-30 mass%, It is still more preferable that it is 1-25 mass%, It is especially preferable that it is 1-15 mass%.

The water-soluble polymerizable compound in the present invention has been described above, but the content of the water-soluble polymerizable compound (the total content in the case of two or more types) is 5 to 5 based on the total amount of the ink composition. 40 mass% is preferable, 13-35 mass% is more preferable, and 13-30 mass% is especially preferable.
When the content of the water-soluble polymerizable compound is 5% by mass or more, the abrasion resistance and adhesion of the image can be further improved.
If the said content of a water-soluble polymeric compound is 40 mass% or less, the fall of the dispersibility of a magenta pigment can be suppressed more, and, as a result, the unevenness of an image can be suppressed more.

<Polymerization initiator>
The ink composition of the present invention contains at least one polymerization initiator.
The polymerization initiator is preferably a water-soluble polymerization initiator. Here, the water solubility in the polymerization initiator means that 0.5% by mass or more dissolves in distilled water at 25 ° C. The water-soluble polymerization initiator is preferably dissolved at 1% by mass or more in distilled water at 25 ° C., more preferably at least 3% by mass.

As a polymerization initiator in this invention, a photoinitiator is mentioned preferably. As the photopolymerization initiator, a known photopolymerization initiator can be appropriately selected and used according to the kind of the polymerizable compound and the purpose of use of the ink composition.
The photopolymerization initiator is a compound that absorbs external energy (light) to generate a radical that is a polymerization initiating species. Examples of light include active energy rays, that is, γ rays, β rays, electron rays, X rays, ultraviolet rays, visible rays, infrared rays, and the like.

  As the photopolymerization initiator, known compounds can be used, but preferred photopolymerization initiators include aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds, hexaaryls. Examples thereof include a rubiimidazole compound, a ketoxime ester compound, a borate compound, an azinium compound, a metallocene compound, an active ester compound, a compound having a carbon halogen bond, and an alkylamine compound.

Examples of the water-soluble polymerization initiator include compounds represented by the following general formula (1) and compounds described in JP-A-2005-307198.
The polymerization initiator in the present invention is preferably a water-soluble polymerization initiator represented by the following general formula (1) from the viewpoint of adhesion and abrasion resistance.

In general formula (1), m and n each independently represent an integer of 0 or more, and m + n represents an integer of 0 to 3.
In the general formula (1), m is preferably 0 to 3 and n is preferably 0 or 1, more preferably m is 0 or 1 and n is 0.
Specific examples of the compound represented by the general formula (1) are shown below, but the present invention is not limited thereto.

  The compound represented by the general formula (1) may be a compound synthesized according to the description in JP-A-2005-307198 or a commercially available compound. Examples of commercially available compounds represented by the general formula (1) include Irgacure 2959 (m = 0, n = 0).

  The content of the polymerization initiator in the ink composition of the present invention is preferably in the range of 0.1 to 30% by mass in terms of solid content, more preferably in the range of 0.5 to 20% by mass, The range is more preferably 1.0 to 15% by mass, and most preferably 1 to 5% by mass.

<Water>
The ink composition in the present invention contains water.
As water in this invention, it is preferable to use water which does not contain ionic impurities, such as ion-exchange water and distilled water. The water content in the ink composition is appropriately selected according to the purpose, but is preferably 10 to 95% by mass, and more preferably 40 to 80% by mass.

<Polymer containing repeating unit represented by general formula (i)>
The ink composition of the present invention can contain a polymer containing a repeating unit represented by the following general formula (i) (hereinafter also simply referred to as “(component a)”). When the ink composition of the invention contains the (component a), the scratch resistance and adhesion of the image are further improved.
In particular, when the ink composition of the present invention contains (Component a) and a monofunctional polymerizable compound having a (meth) acrylamide structure as a water-soluble polymerizable compound, the image is rub-resistant. And adhesion are further improved. Although this mechanism is not clear, it is guessed as follows. However, the present invention is not limited by the following inference.
Since the (component a) of the present invention has a structure represented by the general formula (i), there are many places where a monofunctional polymerizable monomer having a (meth) acrylamide structure forms a strong bond such as a hydrogen bond. It is inferred that Therefore, it is considered that the crosslinking density between the (component a) and the monofunctional polymerizable monomer having a (meth) acrylamide structure is increased. As a result, it is presumed that the abrasion resistance and adhesion of the image are remarkably improved.

  A plurality of repeating units represented by the general formula (i) present in the (component a) may be the same as or different from each other.

In general formula (i), m represents an integer of 2 to 15, and R ¹ represents a hydrogen atom or a methyl group.

In the general formula (i), R ¹ is preferably a hydrogen atom.
In the general formula (i), m is preferably an integer of 2 to 5, more preferably 3 or 5, and particularly preferably 3.
When a plurality of repeating units represented by the general formula (i) present in the (component a) are different from each other, the repeating unit in which the m in the general formula (i) is 3, and the m in the general formula (i) It is preferable that it contains the repeating unit which is 5.

  The (component a) preferably contains 50% by mass or more, more preferably 75-100% by mass of the repeating unit represented by the general formula (i) with respect to the total amount of the (component a), 80 It is particularly preferable to contain ~ 100% by mass.

  The (component a) preferably further contains a repeating unit represented by the following general formula (ii).

In the general formula (ii), R ² represents an alkyl group, and R ³ represents a hydrogen atom or a methyl group.

In the general formula (ii), the alkyl group represented by R ² is preferably an alkyl group having 1 to 5 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, and a butyl group.
In the general formula (ii), the alkyl group represented by R ² is more preferably an alkyl group having 1 to 3 carbon atoms, and particularly preferably an alkyl group having 1 carbon atom (that is, a methyl group).

In the formula (ii), R ³ is preferably a hydrogen atom.

  The (component a) preferably includes 1% by mass to 80% by mass of the repeating unit represented by the formula (ii) with respect to the total amount of the (component a), and includes 1% by mass to 50% by mass. It is more preferable to include 1% by mass to 10% by mass.

  The (component a) is preferably a molecular weight (weight average molecular weight for those having a molecular weight distribution) of 500 to 800,000, more preferably 800 to 100,000, and still more preferably 1,000 to 25,000.

  The weight average molecular weight is measured by gel permeation chromatography (GPC). GPC uses HLC-8020GPC (manufactured by Tosoh Corporation), TSKgel SuperHZM-H, TSKgel SuperHZ4000, TSKgel SuperHZ200 (4.6 mm ID × 15 cm, Tosoh Corporation) as columns and THF (tetrahydrofuran) as an eluent. Is used.

  Specific examples of the (component a) include polyvinyl pyrrolidone (PVP K12 (manufactured by Acros), PVP K15, PVP K30 (all manufactured by ASP Japan)), vinyl pyrrolidone / vinyl acetate copolymer (Luvitec). VA64W, Luviskol VA37E (all manufactured by BASF Japan), PVP / VA W635 (manufactured by ASP Japan)), vinylpyrrolidone / vinylcaprolactam copolymer (Luvitec VPC K65W (manufactured by BASF Japan)), etc. Polyvinyl pyrrolidone (PVP K15, K30 (both manufactured by ISP Japan)), vinylpyrrolidone / vinyl acetate copolymer (PVP / VA W635 (manufactured by API Japan)), L viskol VA37E (manufactured by BASF · Japan Ltd.)), vinylpyrrolidone / vinylcaprolactam copolymer (Luvitec VPC K65W (manufactured by BASF · Japan)) is preferable.

When the ink composition of the present invention contains the (component a), the (component a) may be contained singly or in combination of two or more.
When the ink composition of the present invention contains the (component a), the content of the (component a) (the total content in the case of two or more) is 0.1% relative to the total amount of the ink composition. It is preferably 10 to 10% by mass, more preferably 0.1 to 5% by mass, further preferably 0.5 to 5% by mass, and particularly preferably 0.5 to 3% by mass. preferable.

<Surfactant>
The ink composition of the present invention preferably contains at least one surfactant. The surfactant can be used as a surface tension adjusting agent.
As the surface tension modifier, a compound having a structure having both a hydrophilic part and a hydrophobic part in the molecule can be used effectively. Anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic properties Either a surfactant or a betaine surfactant can be used.
In the present invention, a nonionic surfactant is preferable from the viewpoint of suppressing droplet ejection interference of the ink composition, and among them, an acetylene glycol surfactant is more preferable.

  Examples of acetylene glycol surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl-5-decyne-4,7. -Alkylene oxide adduct of diol etc. can be mentioned, It is preferable that it is at least 1 sort (s) chosen from this. Examples of commercially available products of these compounds include E series such as Olphine E1010 manufactured by Nissin Chemical Industry Co., Ltd.

When a surfactant (surface tension adjusting agent) is contained in the ink composition, the surfactant has a surface tension of 20 to 60 mN / m from the viewpoint of satisfactorily discharging the ink composition by an ink jet method. It is preferable to contain the quantity of the range which can be adjusted, More preferably, it is 20-45 mN / m from the point of surface tension, More preferably, it is 25-40 mN / m.
The specific amount of the surfactant in the ink composition of the surfactant is not particularly limited except that the range of the surface tension is preferable, and is preferably 0.1% by mass or more, more preferably 0.8%. It is 1-10 mass%, More preferably, it is 0.2-3 mass%.

<Water-soluble organic solvent>
The ink composition of the present invention contains at least water, but may contain at least one water-soluble organic solvent in addition to water.

  Examples of water-soluble organic solvents include, for example, alkanediols (polyhydric alcohols) such as glycerin, ethylene glycol, and propylene glycol; sugar alcohols; those having 1 to 4 carbon atoms such as ethanol, methanol, butanol, propanol, and isopropanol Alkyl alcohols; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl Ether, diethylene glycol mono-iso-propyl ether, ethylene glycol -N-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, triethylene glycol monoethyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono T-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, Dipropylene glycol mono-iso-propyl ether, tripropylene glycol monomethyl ester Glycol ethers such as such as ether and the like. These can be used individually by 1 type or in combination of 2 or more types.

<Resin particles>
The ink composition in the present invention can contain resin particles as necessary.
In addition, the resin particles fix the ink composition, that is, the image by aggregating or destabilizing the ink to increase the viscosity of the ink when it comes into contact with the treatment liquid described later or a region on the recording medium on which it is dried. It is preferable to have a function of Such resin particles are preferably dispersed in at least one of water and an organic solvent.

Resin particles include acrylic resins, vinyl acetate resins, styrene-butadiene resins, vinyl chloride resins, acrylic-styrene resins, butadiene resins, styrene resins, crosslinked acrylic resins, crosslinked styrene resins, and benzoguanamine resins. A phenol resin, a silicone resin, an epoxy resin, a urethane resin, a paraffin resin, a fluorine resin, or a latex thereof can be used. Preferred examples include acrylic resins, acrylic-styrene resins, styrene resins, cross-linked acrylic resins, and cross-linked styrene resins.
The resin particles can also be used in the form of latex.

The weight average molecular weight of the resin particles is preferably 10,000 or more and 200,000 or less, more preferably 20,000 or more and 200,000 or less.
The volume average particle size of the resin particles is preferably in the range of 1 nm to 1 μm, more preferably in the range of 1 nm to 200 nm, still more preferably in the range of 1 nm to 100 nm, and particularly preferably in the range of 1 nm to 50 nm. In addition, the volume average particle diameter of the resin particles can be measured with a nanotrack particle size distribution measuring apparatus UPA-EX150 (manufactured by Nikkiso Co., Ltd.).
The glass transition temperature Tg of the resin particles is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, and further preferably 50 ° C. or higher.

It is preferable to use self-dispersing resin particles (self-dispersing resin particles) as the resin particles.
Here, the self-dispersing resin is a dispersion state in an aqueous medium due to a functional group (especially a salt-forming group) possessed by the polymer itself when it is dispersed by a phase inversion emulsification method in the absence of a surfactant. Refers to the water-insoluble polymer obtained. Specific examples of the salt-forming group that the self-dispersing resin may have are the same as the salt-forming group in the resin that coats the pigment, and the preferred range is also the same.
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 an aqueous medium. It includes both states.
As the self-dispersing resin particles, the self-dispersing resin particles described in paragraphs 0090 to 0121 of JP2010-64480A and paragraphs 0130 to 0167 of JP2011-068805A can be used. .

The addition amount of the resin particles is preferably 0.1 to 20% by mass, more preferably 0.1 to 10% by mass, and further preferably 0.1 to 5% by mass with respect to the ink composition.
Moreover, there is no restriction | limiting in particular regarding the particle size distribution of a resin microparticle, What has a wide particle size distribution or a thing with a monodispersed particle size distribution may be sufficient. Two or more kinds of resin particles having a monodispersed particle size distribution may be mixed and used.

<Other ingredients>
In addition to the above components, the ink composition of the present invention may further contain various additives as other components as necessary.
Examples of the various additives include sensitizers, co-sensitizers (strong sensitizers), conductive salts, solvents, polymer compounds, basic compounds, ultraviolet rays described in JP-A-2008-019408. Known additions such as absorbents, antifading agents, antifungal agents, pH adjusters, rust inhibitors, antioxidants, emulsion stabilizers, preservatives, antifoaming agents, viscosity modifiers, dispersion stabilizers, or chelating agents Agents.

<Physical properties of ink composition>
The surface tension (25 ° C.) of the ink composition of the present invention is preferably 20 mN / m or more and 60 mN / m or less. More preferably, it is 20 mN or more and 45 mN / m or less, More preferably, it is 25 mN / m or more and 40 mN / m or less.
The surface tension is measured using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) under the condition of 25 ° C.

The viscosity at 25 ° C. of the ink composition of the present invention is preferably 1.2 mPa · s or more and 15.0 mPa · s or less, more preferably 2 mPa · s or more and less than 13 mPa · s, and still more preferably. Is 2.5 mPa · s or more and less than 10 mPa · s.
The viscosity is measured using a VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD) under conditions of 25 ° C.

<Manufacturing method>
The ink composition of the present invention can be produced by a conventional method.
For example, for at least two types of magenta pigments, a resin-coated magenta pigment dispersion is prepared for each magenta pigment type (wherein at least two types of resin-coated magenta pigment dispersions are prepared), and the resulting resin coating is obtained. At least two dispersions of magenta pigment, at least one water-soluble polymerizable compound, at least one polymerization initiator, water, and other components (such as a surfactant) as required, It can manufacture by mixing. The mixing method is not particularly limited, and a commonly used mixing method can be appropriately selected and applied.

≪Ink set≫
The ink set of the present invention comprises at least one of the ink compositions of the present invention described above, and at least one treatment liquid containing an aggregating agent capable of forming an aggregate by contact with the ink composition. Including.
By forming an image using a treatment liquid in addition to the ink composition, unevenness is further suppressed, and an image having further excellent abrasion resistance and adhesion can be formed.
Further, by using the treatment liquid, it is possible to increase the speed of ink jet recording, and even at high speed recording, unevenness is suppressed, and an image excellent in abrasion resistance and adhesion can be obtained. Even with high-speed recording, it is possible to obtain an image with high density and resolution and excellent drawing performance (for example, reproducibility of fine lines and fine portions).

<Processing liquid>
The treatment liquid contains at least one kind of aggregating agent capable of forming an aggregate by contact with the ink composition of the present invention described above, and further contains other components as necessary.

The flocculant in the present invention is capable of aggregating (fixing) components in the ink composition by contacting the ink composition on the recording medium, and functions as, for example, a fixing agent. For example, when the treatment liquid is applied to a recording medium (preferably coated paper), the ink composition further drops and comes into contact with the aggregating agent while the aggregating agent is present on the recording medium. The components in the ink composition can be agglomerated to fix the ink composition component on the recording medium.
Examples of the flocculant include acidic compounds, polyvalent metal salts, and cationic polymers. Among these, an acidic compound is preferable from the viewpoint of cohesiveness of the ink composition component. A flocculant may be used individually by 1 type, or may use 2 or more types together.

(Acidic compounds)
Examples of the acidic compound 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, Tartaric acid, lactic acid, sulfonic acid, orthophosphoric acid, metaphosphoric acid, pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, and derivatives of these compounds Are preferable.

Among these, acidic compounds with high water solubility are preferable. Further, from the viewpoint of fixing the whole ink by reacting with the ink composition component, a trivalent or lower valent acidic compound is preferable, and a divalent or trivalent acidic compound is particularly preferable.
An acidic compound may be used individually by 1 type, and may use 2 or more types together.

  When the treatment liquid contains an acidic compound, the pH (25 ° C.) of the treatment liquid is preferably 0.1 to 6.8, more preferably 0.5 to 6.0, 0.8 More preferably, it is -5.0.

The content of the acidic compound is preferably 40% by mass or less, and more preferably 15 to 40% by mass with respect to the total mass of the treatment liquid. By setting the content of the acidic compound to 15 to 40% by mass, the components in the ink composition can be more efficiently fixed.
Furthermore, it is preferable that content of an acidic compound is 15 mass%-35 mass% with respect to the total mass of the said processing liquid, and it is more preferable that it is 20 mass%-30 mass%.

The amount of the acidic compound applied to the recording medium is not particularly limited as long as it is an amount sufficient to aggregate the ink composition, but 0.5 g / m ² to 4 from the viewpoint that the ink composition can be easily fixed. is preferably .0g / ^{m 2,} more preferably ^{0.9g / m 2 ~3.75g / m 2} .

(Polyvalent metal salt)
The polyvalent metal salt is preferably a compound containing a divalent or higher metal such as an alkaline earth metal or a zinc group metal. For example, acetate, oxide, etc. of metal ions such as Ca ²⁺ , Cu ²⁺ , and Al ³⁺ Can be mentioned.
The polyvalent metal salt preferably has a valence of 2 or more, more preferably a polyvalent metal salt composed of a trivalent or more polyvalent metal ion, from the viewpoint of agglomeration reaction.

  The polyvalent metal salt is preferably at least one of the following polyvalent metal ion and anion salts, polyaluminum hydroxide and polyaluminum chloride.

Examples of the polyvalent metal ions include Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , Sr ²⁺ , Zn ²⁺ , Ba ²⁺ , Al ³⁺ , Fe ³⁺ , Cr ³⁺ , Co ³⁺ , Fe ²⁺ , La ³⁺ , Nd ³⁺ , Y ³⁺ , Zr ^{4+ and the} like. In order to contain these polyvalent metal ions in the treatment liquid, the polyvalent metal salt may be used.
The salt is a metal salt composed of the above polyvalent metal ions and an anion that binds to these ions, but is preferably soluble in a solvent. Here, the said solvent is a medium which comprises a process liquid with a polyvalent metal salt, for example, water and the organic solvent mentioned later are mentioned.

Preferred anions for forming a salt with the polyvalent metal ion include, for example, Cl ⁻ , NO ₃ ⁻ , I ⁻ , Br ⁻ , ClO ₃ ⁻ , CH ₃ COO ⁻ , SO ₄ ^{2− and the} like. .
A polyvalent metal ion and an anion can form a salt of a polyvalent metal ion and an anion, respectively, using a single species or a plurality of species.

  Examples of other polyvalent metal salts include polyaluminum hydroxide and polyaluminum chloride.

Examples of the polyvalent metal salt, reactivity and coloring properties, more in view of ease of handling, it is preferable to use a salt of a polyvalent metal ion and an anion, the polyvalent metal ion, Ca ²⁺ , Mg ²⁺ , Sr ²⁺ , Al ³⁺ and Y ³⁺ are preferred, and Ca ²⁺ is more preferred.
Further, as the anion, NO ₃ ⁻ is particularly preferable from the viewpoint of solubility and the like.
The said polyvalent metal salt can be used individually by 1 type or in mixture of 2 or more types.

When the treatment liquid contains the polyvalent metal salt, the content of the polyvalent metal salt is preferably 15% by mass or more with respect to the total mass of the treatment liquid. When the content of the polyvalent metal salt is 15% by mass or more, the components in the ink composition can be more effectively fixed.
The content of the polyvalent metal salt is preferably 15% by mass to 35% by mass and more preferably 20% by mass to 30% by mass with respect to the total mass of the treatment liquid.

The application amount of the recording medium of the polyvalent metal salt is preferably, but not particularly limited insofar as the amount is sufficient for aggregating the ink composition is 0.5g ^/ m ² ~4.0g / m 2 , and more preferably ^{0.9g / m 2 ~3.75g / m 2} .

(Cationic polymer)
The cationic polymer includes at least one cationic polymer selected from poly (vinyl pyridine) salt, polyalkylaminoethyl acrylate, polyalkylaminoethyl methacrylate, poly (vinyl imidazole), polyethyleneimine, polybiguanide, and polyguanide. Is mentioned.
A cationic polymer may be used individually by 1 type, and may use 2 or more types together.
Among the cationic polymers, polyguanides (preferably poly (hexamethyleneguanidine) acetate, polymonoguanide, polymeric biguanide), polyethyleneimine, and poly (vinylpyridine), which are advantageous from the viewpoint of aggregation rate, are preferable.

  The weight average molecular weight of the cationic polymer is preferably smaller in terms of the viscosity of the treatment liquid. When the treatment liquid is applied to the recording medium by an inkjet method, a range of 500 to 500,000 is preferable, a range of 700 to 200,000 is more preferable, and a range of 1,000 to 100,000 is more preferable. . When the weight average molecular weight is 500 or more, it is advantageous from the viewpoint of aggregation speed, and when it is 500,000 or less, it is advantageous from the viewpoint of ejection reliability. However, this is not the case when the treatment liquid is applied to the recording medium by a method other than inkjet.

  When the treatment liquid contains a cationic polymer, the pH (25 ° C.) of the treatment liquid is preferably 1.0 to 10.0, more preferably 2.0 to 9.0, and 3. More preferably, it is 0-7.0.

When the treatment liquid contains a cationic polymer, the content of the cationic polymer is preferably 1% by mass to 35% by mass with respect to the total mass of the treatment liquid, and is 5% by mass to 25% by mass. More preferably.
The amount of the cationic polymer applied to the coated paper is not particularly limited as long as it is an amount sufficient to stabilize the ink composition, but 0.5 g / m from the viewpoint that the ink composition is easily fixed. it is preferably ^{2 ~4.0g} / ^{m 2,} more preferably ^{0.9g / m 2 ~3.75g / m 2} .

  The treatment liquid preferably contains at least one water-soluble organic solvent in addition to the flocculant. The details of the water-soluble organic solvent are the same as those in the ink composition, and the preferred embodiments are also the same.

In the ink set of the present invention, it is preferable that at least one of the ink composition and the treatment liquid contains the component a (the polymer containing the repeating unit represented by the general formula (i)). Thereby, the abrasion resistance and adhesion of the image are further improved.
When the above component a is contained in the treatment liquid, the content of the (component a) with respect to the treatment liquid is preferably 0.5 to 50% by mass, more preferably 1 to 30% by mass, It is particularly preferably 1 to 15% 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 formation method≫
The image forming method of the present invention includes an ink application step for applying the ink composition of the present invention described above onto a recording medium, and an active energy beam for irradiating the ink composition applied on the recording medium with an active energy beam. An irradiation step.
As a result, the image formed by the ink composition applied onto the recording medium can be cured more reliably, so that an image excellent in abrasion resistance and adhesion to the recording medium can be formed more effectively. it can.

<Ink application process>
In the ink application step, the ink composition of the present invention described above is applied onto the recording medium.
The ink composition application method is not particularly limited as long as the ink composition can be applied in a desired image-like manner, and a known ink application method can be used.
Examples of the method of applying the ink composition include a method of applying the ink composition onto the recording medium by means of an ink jet method, a copying method, a printing method, or the like. Among these, a method of applying the ink composition by an ink jet method is preferable from the viewpoint of compactness of the recording apparatus and high-speed recording properties.

(Inkjet method)
In image formation by an ink jet method, by supplying energy, an ink composition is discharged onto a recording medium to form a colored image. 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, Any of an acoustic ink jet method in which an electric signal is converted into an acoustic beam, irradiated onto ink, and ink is ejected using radiation pressure may be used.
The ink jet head used in the ink jet method may be an on-demand method or a continuous method. Furthermore, there are no particular limitations on the ink nozzles used when recording by the ink jet method, and they can be appropriately selected according to the purpose.
The ink jet method includes a method of ejecting a large number of 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.

  Also, as an ink jet system, a short serial head is used, 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 method, 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 moves, the recording speed can be increased as compared with the shuttle system.

<Active energy ray irradiation process>
The image forming method of the present invention includes an active energy ray irradiating step of irradiating an ink composition applied on a recording medium with an active energy ray.
In this step, the polymerizable compound contained in the ink composition is polymerized by irradiating active energy rays, and an image of the ink composition is formed as a cured film. This is because the polymerization initiator contained in the ink composition is decomposed by irradiation with active energy rays to generate radicals, acids, bases and other starting species, which initiates and accelerates the polymerization reaction of the polymerizable compound. Because.

Examples of the active energy rays include α rays, γ rays, β rays, electron rays, X rays, ultraviolet rays, visible light, and infrared rays.
The irradiation condition of the active energy ray is not particularly limited as long as the polymerizable compound can be polymerized and cured.
For example, the wavelength of the active energy ray is preferably 200 to 600 nm, more preferably 300 to 450 nm, and still more preferably 350 to 420 nm.
Further, as the output of the active energy ray, it is preferably 5000 mJ / cm ² or less, more preferably 10~4000mJ / cm ^2, further preferably 20~3000mJ / cm ^2.

As the active energy ray source, a mercury lamp, a metal halide lamp, a gas laser, a solid laser or the like can be used, and among these, a metal halide lamp is preferable.
Moreover, as an active energy ray source, a light emitting diode (LED) and a laser diode (LD) can be used from the viewpoints of small size, long life, high efficiency, and low cost. Among them, ultraviolet LED and ultraviolet LD are used. Can do. For example, Nichia Corporation has introduced a purple LED whose main emission spectrum has a wavelength between 365 nm and 420 nm. When a light emitting diode (LED) or a laser diode (LD) is used as the active energy ray, an ultraviolet LED having a peak wavelength at 350 to 420 nm is preferable.

<Processing liquid application process>
In addition to the above steps, the image forming method of the present invention includes a treatment liquid containing an aggregating agent capable of forming an aggregate by contacting with the ink composition on a recording medium (for example, the ink set of the present invention described above) It is preferable to have the process liquid provision process which provides the process liquid in.

When the image forming method of the present invention includes the treatment liquid application step, it is possible to form an image with high resolution and further excellent abrasion resistance and adhesion.
In addition, by having the treatment liquid application step, it is possible to increase the speed of ink jet recording, and an image excellent in abrasion resistance and adhesion can be obtained even at high speed recording. Even with high-speed recording, it is possible to obtain an image with high density and resolution and excellent drawing performance (for example, reproducibility of fine lines and fine portions).

It is preferable that this process liquid provision process is provided before the said active energy ray irradiation process.
Since this treatment liquid application step is a step of applying a treatment liquid containing an aggregating agent capable of forming an aggregate by contacting with the ink composition, even if the treatment liquid application step is provided before the ink application step, It may be provided after the ink application step.
However, from the viewpoint of image quality, it is preferable that the treatment liquid application step is provided before the ink application step. In other words, the ink application step is a step of providing an ink composition on the treatment liquid of the recording medium provided after the treatment liquid application step and provided with the treatment liquid by the treatment liquid application step. preferable.

  As a method for applying the treatment liquid in the treatment liquid application step, a known liquid application method can be used without any particular limitation. For example, any method such as spray application, application by an application roller, application by an inkjet method, immersion, etc. Can be selected.

  Specifically, for example, a size press method represented by a horizontal size press method, a roll coater method, a calendar size press method, etc .; a knife coater method represented by an air knife coater method; a transfer roll such as a gate roll coater method Roll coater method represented by coater method, direct roll coater method, reverse roll coater method, squeeze roll coater method, etc .; bill blade coater method, short duel coater method; blade coater method represented by two stream coater method; rod Bar coater method represented by bar coater method, etc .; Bar coater method represented by rod bar coater method, etc .; Cast coater method; Gravure coater method; Curtain coater method; Die coater method; Brush coater method; Etc., and the like.

  Moreover, the method of apply | coating by controlling a coating amount by using the coating device provided with the liquid quantity limiting member like the coating device of Unexamined-Japanese-Patent No. 10-230201 may be used.

  The area to which the treatment liquid is applied may be the entire area application to the entire recording medium or the partial application to be partially applied to the area where ink jet recording is performed in the ink application process. Above all, from the viewpoint of uniformly adjusting the application amount of the processing liquid, recording fine lines and fine image portions uniformly, and suppressing density unevenness such as image unevenness, it is applied to the entire coated paper by application using an application roller or the like. Giving the entire surface is preferable.

The amount of the treatment liquid applied to the recording medium is not particularly limited as long as it is an amount sufficient to agglomerate the ink composition, but 0.5 g / m ² to 4 from the viewpoint that the ink composition can be easily fixed. is preferably .0g / ^{m 2,} more preferably ^{0.9g / m 2 ~3.75g / m 2} .

  Examples of the method of applying the treatment liquid by controlling the application amount of the treatment liquid within the above range include a method using an anilox roller. An anilox roller is a roller with a ceramic-sprayed roller surface processed with a laser to give it a pyramid shape, a diagonal line, a turtle shell shape, or the like. The treatment liquid enters the dent portion formed on the roller surface, is transferred when it comes into contact with the paper surface, and is applied in an application amount controlled by the dent of the anilox roller.

  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 a known heating means such as a heater, an air blowing means 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.

<Ink drying process>
The image forming method of the present invention includes an ink drying step for drying and removing an ink solvent (for example, water, a water-soluble organic solvent, etc.) in the ink composition applied on the recording medium, if necessary. Also good. The ink drying step is not particularly limited as long as at least a part of the ink solvent can be removed, and a commonly used method can be applied.

  For example, the ink can be dried by a known heating means such as a heater, an 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.

Moreover, the ink drying process should just be performed after an ink provision process, and may be before or after an active energy ray irradiation process.
In this invention, it is preferable to carry out before an active energy ray irradiation process from a viewpoint of hardening sensitivity and blocking resistance.

<Recording medium>
The recording medium used in the image forming method of the present invention is not particularly limited, but general printing paper mainly composed of cellulose, such as so-called high-quality paper, coated paper, and art paper, used for general offset printing or the like is used. Can do.

  As the recording medium, commercially available media can be used. For example, “OK Prince Quality” manufactured by Oji Paper Co., Ltd., “Shiraoi” manufactured by Nippon Paper Industries Co., Ltd., and Nippon Paper Industries Co., Ltd. ) "New NPI fine quality" fine paper (A), Nippon Paper Industries' "Silver Diamond" quality coated paper, Oji Paper's "OK Everlight Coat" and Nippon Paper Industries ( Light-weight coated paper (A3) such as “Aurora S” manufactured by Co., Ltd., “OK Coat L” manufactured by Oji Paper Co., Ltd. and “Aurora L” manufactured by Nippon Paper Industries Co., Ltd., Oji Paper Co., Ltd. Coated paper (A2, B2) such as “OK Top Coat +” and “OK Top Coat N +” manufactured by Nippon Paper Industries Co., Ltd. and “OK Kinfuji” manufactured by Oji Paper Co., Ltd. "+" And "Tsubishi Art" and "Tsubishi Art" manufactured by Mitsubishi Paper Industries Co., Ltd. N "such as art paper (A1), Fuji Photo Film Co., Ltd. of inkjet paper such as" Kassai photo finishing Pro ", and the like.

Among these, preferably, the recording medium has a water absorption coefficient Ka of 0.05 to 0.5 and mL / m ² · ms ^1/2 , and more preferably 0.1 to 0.4 mL / m ² ···. ms ^1/2 recording medium, more preferably 0.2 to 0.3 mL / m ² · ms ^1/2 recording medium.

  The water absorption coefficient Ka is synonymous with that described in JAPAN TAPPI paper pulp test method No. 51: 2000 (issued by Japan Paper Pulp Technology Association). Specifically, the absorption coefficient Ka is an automatic scanning absorption meter. It is calculated from the difference in the amount of water transferred between the contact time of 100 ms and the contact time of 900 ms using KM500Win (manufactured by Kumagai Riki Co., Ltd.).

  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. In particular, it is preferable to use a coated paper having a base paper and a coat layer containing kaolin and / or calcium bicarbonate. More specifically, art paper, coated paper, lightweight coated paper, or finely coated paper is more preferable.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “part” and “%” are based on mass.

≪Synthesis of resin dispersant≫
<Synthesis of Resin Dispersant P-1>
A monomer feed composition was prepared by mixing methacrylic acid (172 parts), benzyl methacrylate (828 parts), and isopropanol (375 parts). An initiator feed composition was prepared by mixing 2,2-azobis (2-methylbutyronitrile) (22.05 parts) and isopropanol (187.5 parts).
Next, while isopropanol (187.5 parts) was heated to 80 ° C. in a nitrogen atmosphere, the mixture of the monomer supply composition and the initiator supply composition was added dropwise over 2 hours. After completion of dropping, the mixture was kept at 80 ° C. for further 4 hours, and then cooled to 25 ° C.
After cooling, the solvent was removed under reduced pressure to obtain a resin dispersant P-1 having a weight average molecular weight of about 50,000.
With respect to the obtained resin dispersant P-1, the acid value was determined by the method described in JIS standards (JIS K 0070: 1992). As a result, the acid value was 112 mgKOH / g.

<Synthesis of Resin Dispersant P-2>
Resin dispersant P- 1 except that the composition of the monomer supply composition was changed to methacrylic acid (154 parts), benzyl methacrylate (846 parts), and isopropanol (375 parts) in the synthesis of resin dispersant P-1. In the same manner as in the synthesis of 1, a resin dispersant P-2 having a weight average molecular weight of about 50,000 was obtained.
With respect to the obtained resin dispersant P-2, the acid value was determined by the method described in JIS standard (JIS K 0070: 1992). As a result, the acid value was 100 mgKOH / g.

<Synthesis of Resin Dispersant P-3>
Resin dispersant P-, except that the composition of the monomer supply composition was changed to methacrylic acid (214 parts), benzyl methacrylate (786 parts), and isopropanol (375 parts) in the synthesis of resin dispersant P-1. In the same manner as in the synthesis of 1, a resin dispersant P-3 having a weight average molecular weight of about 50,000 was obtained.
With respect to the obtained resin dispersant P-3, the acid value was determined by the method described in JIS standard (JIS K 0070: 1992). As a result, the acid value was 140 mgKOH / g.

≪Preparation of magenta ink composition≫
Inks 1 to 26, which are magenta ink compositions, were produced as follows.

<Preparation of ink 1>
(Preparation of dispersion of first resin-coated magenta pigment)
The resin dispersant P-1 (150 parts) obtained above was neutralized with 0.8 potassium equivalent of the amount of methacrylic acid in the resin dispersant using an aqueous potassium hydroxide solution, and further ion-exchanged water was added. An aqueous resin dispersant solution was prepared so that the solid concentration of the resin dispersant was 20% by mass.
This aqueous resin dispersant solution (91.9 parts) and C.I. as the first magenta pigment were used. I. Pigment Red 122 (manufactured by Dainichi Seika Kogyo Co., Ltd .; hereinafter also referred to as “PR 122”) (52.5 parts), ion-exchanged water (83.1 parts), and dipropylene glycol (122 5 parts), and a bead mill (bead diameter 0.1 mmφ, zirconia beads) until the desired volume average particle diameter is obtained, and dispersion of a resin-coated magenta pigment (uncrosslinked) having a pigment concentration of 15% by mass The product N1 was obtained.
With respect to the dispersion N1 (136 parts), ultrapure water (100 parts), Dencol EX-321 (manufactured by Nagase ChemteX Corporation) (0.5 parts) as a crosslinking agent, and an aqueous boric acid solution (boric acid) A 4 mass% aqueous solution (5.5 parts) was added, and the mixture was reacted at 70 ° C. for 5 and a half hours (crosslinking), and then cooled to 25 ° C. Furthermore, ion-exchanged water was added to the obtained crosslinked dispersion using a stirring type ultra holder (manufactured by ADVANTEC) and an ultrafiltration filter (fractional molecular weight 50,000, Q0500076E ultra filter, manufactured by ADVANTEC). Ultrafiltration is performed to refine the dipropylene glycol concentration in the dispersion to be 0.1% by mass or less, and then concentrated to a pigment concentration of 15% by mass to disperse the first resin-coated magenta pigment. I got a thing.

With respect to the obtained dispersion of the first resin-coated magenta pigment, the acid value of the resin (resin dispersant) that coats the first magenta pigment was determined by the following method.
That is, the dispersion of the first resin-coated magenta pigment is diluted with ion-exchanged water so that the concentration of the first resin-coated magenta pigment is 5% by mass, and further adjusted to pH 12 by adding a 1N KOH aqueous solution. did. Titration was performed by sequentially adding 0.2 N HCl aqueous solution to the dispersion after pH adjustment until the pH reached 3. From the titration result, the acid value (unit: mgKOH / g) of the resin (resin dispersant) covering the first magenta pigment was calculated and obtained. As shown in Table 1, the acid value of the resin (resin dispersant) covering the first magenta pigment was 84 mgKOH / g.

  Further, 0.1 part of the obtained dispersion of the first resin-coated magenta pigment and 19.9 parts of ion-exchanged water were mixed, and using this, Nanotrac particle size distribution measuring device UPA-EX150 (Nikkiso Co., Ltd.) The volume average particle diameter of the secondary particles was measured by (manufactured) to be 90 nm.

(Preparation of dispersion of second resin-coated magenta pigment)
In the preparation of the dispersion of the first resin-coated magenta pigment, C.I. I. Pigment Red 122 (manufactured by Dainichi Seika Kogyo Co., Ltd.), Pigment Violet 19 (manufactured by Dainichi Seika Kogyo Co., Ltd.) as the second magenta pigment of the same mass; hereinafter referred to as “P.V.19” A dispersion of the second resin-coated magenta pigment having a pigment concentration of 15% by mass was prepared in the same manner as the preparation of the dispersion of the first resin-coated magenta pigment, except that it was changed to (also referred to as the above).

With respect to the obtained dispersion of the second resin-coated magenta pigment, the acid value of the resin (resin dispersant) that coats the second magenta pigment is determined in the same manner as the dispersion of the first resin-coated magenta pigment. As a result, as shown in Table 1, the acid value was 84 mgKOH / g.
Further, with respect to the obtained dispersion of the second resin-coated magenta pigment, the volume average particle diameter of the secondary particles was measured by the same method as that of the dispersion of the first resin-coated magenta pigment. .

(Synthesis of polymerizable compound 2)
To a 1 L three-necked flask equipped with a stirrer was added 4,7,10-trioxa-1,13-tridecanediamine 40.0 g (182 mmol), sodium bicarbonate 37.8 g (450 mmol), water 100 g, and tetrahydrofuran 300 g. 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 2 solid. (107 mmol, 59% yield).
The structure of the polymerizable compound 2 is shown below.

(Preparation of ink 1)
The following composition was mixed, filtered through a glass filter (GS-25) manufactured by ADVANTEC, and then filtered through a filter (PVDF membrane, pore size 5 μm) manufactured by Millipore to prepare ink 1.
In Table 1, the amount of the first magenta pigment is the content (% by mass) of the first magenta pigment (PR122) with respect to the total amount of ink, and the amount of the second magenta pigment is based on the total amount of ink. The content (% by mass) of the second magenta pigment (P.V.19).

~ Ink composition ~
First resin-coated magenta pigment dispersion 20 parts Second resin-coated magenta pigment dispersion 20 parts The polymerizable compound 2 (bifunctional polymerizable compound) 10 parts Hydroxyethylacrylamide ( Monofunctional polymerizable compound) 10 parts Olfin E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant) 1 part Irgacure 2959 (manufactured by BASF Japan Ltd .; photopolymerization initiator) 3 parts Polyvinylpyrrolidone (PVP K15, manufactured by IPS Japan Co., Ltd.) ... 1 part, ion-exchanged water ... Remaining amount of 100 parts in total

<Preparation of ink 2>
Ink 2 was prepared in the same manner as ink 1 except that the ink composition was changed to the following ink composition.
~ Ink composition ~
First resin-coated magenta pigment dispersion 20 parts Second resin-coated magenta pigment dispersion 20 parts Polymeric compound 2 (bifunctional polymerizable compound) 15 parts Hydroxyethylacrylamide ( Monofunctional polymerizable compound) ··· 5 parts · Olphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant) ··· 1 part · Irgacure 2959 (manufactured by BASF Japan Ltd .; photopolymerization initiator) · · 3 parts · Ion-exchanged water: remaining amount of 100 parts in total

<Preparation of inks 3 to 6>
In the production of the ink 1, the dispersion of the first resin-coated magenta pigment and the second magenta pigment so that the contents of the first magenta pigment and the second magenta pigment in the ink are the amounts shown in Table 1 below, respectively. Inks 3 to 6 were prepared in the same manner as ink 1 except that the amount of the resin-coated magenta pigment dispersion was changed.

<Preparation of inks 7 to 11>
In preparation of the ink 3 (specifically, preparation of a dispersion of the first resin-coated magenta pigment and preparation of a dispersion of the second resin-coated magenta pigment), the first magenta pigment and the second magenta pigment are coated. Inks 7 to 11 were prepared in the same manner as in ink 3, except that the amounts of Denacol EX-321 and boric acid aqueous solution were changed so that the acid values of the resins (resin dispersants) were the values shown in Table 1, respectively. Each was produced.

<Preparation of ink 12>
In preparation of the ink 3 (specifically, preparation of the first resin-coated magenta pigment dispersion and preparation of the second resin-coated magenta pigment dispersion), the resin dispersant P-1 is changed to the resin dispersant P-2. The operation of neutralizing 0.8 equivalent of the amount of methacrylic acid in the resin dispersant using an aqueous potassium hydroxide solution was changed to 0.9 equivalent of the amount of methacrylic acid in the resin dispersant using an aqueous potassium hydroxide solution. Denol EX-321 and aqueous boric acid solution were changed so that the acid value of the resin (resin dispersant) covering the first magenta pigment and the second magenta pigment would be the values shown in Table 1, respectively. Ink 12 was produced in the same manner as ink 3 except that the amount of was changed.

<Preparation of ink 13>
In preparation of the ink 3 (specifically, preparation of the first resin-coated magenta pigment dispersion and preparation of the second resin-coated magenta pigment dispersion), the resin dispersant P-1 is changed to the resin dispersant P-3. The operation of neutralizing 0.8 equivalent of the amount of methacrylic acid in the resin dispersant using an aqueous potassium hydroxide solution was changed to 0.65 equivalent of the amount of methacrylic acid in the resin dispersant using an aqueous potassium hydroxide solution. Denol EX-321 and aqueous boric acid solution were changed so that the acid value of the resin (resin dispersant) covering the first magenta pigment and the second magenta pigment would be the values shown in Table 1, respectively. Ink 13 was prepared in the same manner as ink 3 except that the amount of the ink was changed.

<Preparation of inks 14 to 18>
In the production of the ink 3, the content of the polymerizable compound relative to the total amount of the ink (the total of the content of the polymerizable compound 2 and the content of hydroxyethyl acrylamide) was changed as shown in Table 1 below. Inks 14 to 18 were respectively prepared in the same manner as in the preparation (however, in each ink, the mass ratio [polymerizable compound 2 / hydroxyethylacrylamide] was set to 1).

<Preparation of inks 19 to 21>
In the production of ink 3, C.I. as the second magenta pigment. I. Pigment Violet 19 and C.I. I. Pigment Red 202 (manufactured by Sun Chemical Co., Ltd .; hereinafter, also referred to as “PR 202”), C.I. I. Pigment Red 207 (manufactured by Dainippon Ink & Chemicals, Inc .; hereinafter also referred to as “PR207”), or C.I. I. Inks 19 to 21 were produced in the same manner as Ink 3 except that the pigment was changed to CI Pigment Red 209 (manufactured by Dainippon Ink and Chemicals, Inc .; hereinafter also referred to as “PR209”).
With respect to the dispersion of the second resin-coated magenta pigment in the inks 19 to 21, the acid of the resin (resin dispersant) that coats the second magenta pigment in the same manner as the dispersion of the first resin-coated magenta pigment. When the value was determined, as shown in Table 1, the acid value was 84 mgKOH / g.

<Preparation of ink 22>
Denol EX-321 (0.5 parts) and an aqueous boric acid solution in preparation of ink 1 (specifically, preparation of a first resin-coated magenta pigment dispersion and preparation of a second resin-coated magenta pigment dispersion) Ink 22 was produced in the same manner as Ink 1 except that (boric acid concentration 4 mass% aqueous solution, 5.5 parts) was not added (that is, crosslinking was not performed).

<Preparation of ink 23>
In preparation of ink 3 (specifically, preparation of a dispersion of the second resin-coated magenta pigment) Denacol EX-321 (0.5 part) and boric acid aqueous solution (boric acid concentration 4 mass% aqueous solution, 5.5 parts) ) Was not added (that is, crosslinking was not performed), and ink 23 was prepared in the same manner as ink 3 was prepared.

<Preparation of Ink 24>
In preparation of ink 3 (specifically, preparation of a dispersion of the first resin-coated magenta pigment) Denacol EX-321 (0.5 part) and boric acid aqueous solution (boric acid concentration 4 mass% aqueous solution, 5.5 parts) ) Was not added (that is, crosslinking was not performed), and ink 24 was prepared in the same manner as ink 3 was prepared.

<Preparation of ink 25>
In the preparation of the ink 22, the first resin-coated magenta pigment is used so that the dispersion of the second resin-coated magenta pigment is not used and the content of the first magenta pigment in the ink is the amount shown in Table 1. Ink 6 was prepared in the same manner as ink 22 except that the amount of the dispersion was changed.

<Preparation of ink 26>
In the production of the ink 1, the first resin-coated magenta pigment is used so that the dispersion of the second resin-coated magenta pigment is not used and the content of the first magenta pigment in the ink is the amount shown in Table 1. Ink 26 was prepared in the same manner as ink 1 except that the amount of the dispersion was changed.

≪Preparation of treatment liquid≫
The processing liquid was prepared by mixing components having the following composition.
The viscosity, surface tension, and pH (25 ± 1 ° C.) of the treatment liquid were a viscosity of 2.5 mPa · s, a surface tension of 40 mN / m, and a pH of 1.0.
Here, 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 ~
・ Malonic acid (Wako Pure Chemical Industries, Ltd.) ... 11.3%
・ DL-malic acid (manufactured by Fuso Chemical Industry Co., Ltd.) 14.5%
・ Tripropylene glycol monomethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.) 4.0%
・ Diethylene glycol monobutyl ether (manufactured by Daicel Chemical Industries, Ltd.)… 4.0%
・ Ion-exchanged water ... Total remaining amount of 100%

<< Image formation and evaluation >>
<Image formation>
Prepare a printer for evaluation equipped with a GELJET GX5000 printer head (full line head manufactured by Ricoh), and store the magenta ink composition (any one of ink 1 to ink 26) obtained above in a storage tank connected to the printer. Refilled. “Special Rhibo Art Double Side N” manufactured by Mitsubishi Paper Industries Co., Ltd. was fixed as a recording medium on a stage movable in a predetermined linear direction at 500 mm / second, and the stage temperature was maintained at 30 ° C. The treatment liquid obtained above was applied to this in an amount of about 1.5 g / m ² with a wire bar coater, and dried at 50 ° C. for 2 seconds immediately after the application.
Thereafter, the inkjet head is fixedly arranged so that the direction of the line head in which the nozzles are arranged (main scanning direction) is inclined by 75.7 degrees with respect to the direction orthogonal to the moving direction (sub-scanning direction) of the stage, and recording While moving the medium at a constant speed in the sub-scanning direction, a solid image was recorded by ejecting the magenta ink composition in a line system under the ejection conditions of an ink droplet amount of 3 pL, an ejection frequency of 25.5 kHz, and a resolution of 1200 dpi × 1200 dpi. After the image was recorded, while being heated from the back side (back side) of the ink landing surface with an infrared heater, the recording surface was dried by applying warm air of 120 ° C. and 5 m / sec for 15 seconds. After the image was dried, UV light (a metal halide lamp manufactured by Eye Graphics Co., Ltd., maximum irradiation wavelength 365 nm) was irradiated so as to obtain an integrated irradiation amount of 0.8 J / cm ² to cure the image to obtain a print sample.

<Rubbing resistance evaluation>
The print sample obtained above was left in an environment of 25 ° C. and 50% RH for 15 minutes. On the surface of the solid image of the sample after being allowed to stand, the double-sided Nishi-Nishi Art N (hereinafter referred to as an unused sample in this evaluation) was superimposed and rubbed 10 times with a load of 200 kg / m ² . Thereafter, unused samples and solid images were visually observed and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1.

~ Evaluation criteria for abrasion resistance ~
A: Adherence of color to an unused sample was not recognized, and deterioration of the rubbed solid image was not observed.
B: Slight adhesion of color to the unused sample was observed, but deterioration of the rubbed solid image was not observed.
C: Adherence of color to an unused sample was recognized, and a part of the rubbed solid image (less than half of the solid image area) was deteriorated.
D: Adhesion of color to an unused sample was observed, and more than half of the rubbed solid image area was deteriorated.
* D is a level that is problematic in practice.

<Adhesion evaluation>
The print sample obtained above was left in an environment of 25 ° C. and 50% RH for 15 minutes. A 3 cm long cello tape (registered trademark) (LP-12, manufactured by Nichiban Co., Ltd.) was applied to the solid image surface of the printed sample after being left, and the cello tape (registered trademark) was peeled off after 5 seconds. Then, the cellotape (registered trademark) peeled off from the sample was visually observed and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1.

-Evaluation criteria for adhesion-
A: Adherence of color to the cello tape (registered trademark) was not recognized, and deterioration of the solid image of the print sample was not observed.
B: Slight adhesion of the color to the cello tape (registered trademark) was observed, but no deterioration of the solid image of the print sample was observed.
C: Color adhered to an area of less than half of the cello tape (registered trademark), and deterioration of the solid image of the print sample was also observed.
D: Color adhered to more than half the area of Cellotape (registered trademark), and the solid image of the print sample was dropped.
* D is a level that is problematic in practice.

<Evaluation of Sujimura>
The solid image of the print sample obtained above was observed with the naked eye, and streaks (streaky irregularities) were evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1.

~ Simula evaluation criteria ~
A: Straight stripes could not be recognized in the solid image.
B: Although slight stripe unevenness was recognized in the solid image, it was within a practically acceptable range.
C: Straight stripes were recognized in the solid image and exceeded the practical allowable range.
D: Remarkable uneven stripes were recognized in the solid image and exceeded the practically acceptable range.

<Optical density (OD)>
The optical density (OD) of the solid image of the printing sample obtained above was measured with SpectroEye manufactured by X-rite. The measurement results are shown in Table 1.

<Description of Table 1>
The “amount” of the first magenta pigment is the content (% by mass) of the first magenta pigment with respect to the total amount of the ink, and the “amount” of the second magenta pigment is the amount of the second magenta pigment with respect to the total amount of the ink. Content (mass%).
-"Acid value" shows the acid value after bridge | crosslinking, when bridge | crosslinking is performed.
“Total amount of polymerizable compound” indicates the total content (% by mass) of the polymerizable compound with respect to the total amount of the ink.

As shown in Table 1, containing two types of resin-coated magenta pigments obtained by coating two types of magenta pigments with a crosslinked resin, a water-soluble polymerizable compound, a polymerization initiator, and water. The images produced using the inks of the examples were excellent in abrasion resistance and adhesion, and streak was suppressed.
On the other hand, in the inks 22 to 25 in which the resin that coats the magenta pigment is not crosslinked, image unevenness is generated, and in particular, in the inks 22 to 24 containing two kinds of magenta pigments, the unevenness is remarkable.

Claims (12)

  At least two resin-coated magenta pigments, each of which has at least part of its surface coated with a resin obtained by crosslinking at least two types of magenta pigments with a crosslinking agent, a water-soluble polymerizable compound, a polymerization initiator, water, And an ink composition containing.   The ink composition according to claim 1, wherein the acid value of the resin crosslinked by the crosslinking agent is 50 mgKOH / g to 90 mgKOH / g.   The ink composition according to claim 1, wherein the at least two kinds of magenta pigments are quinacridone pigments.   The at least two magenta pigments are C.I. I. Pigment red 122, C.I. I. Pigment red 202, C.I. I. Pigment red 206, C.I. I. Pigment red 207, C.I. I. Pigment red 209, and C.I. I. The ink composition according to any one of claims 1 to 3, which is at least two selected from the group consisting of CI Pigment Violet 19.   The ink composition according to any one of claims 1 to 4, further comprising an acetylene glycol surfactant. The ink composition according to any one of claims 1 to 5, wherein the polymerization initiator is a compound represented by the following general formula (1).

[In Formula (1), m and n represent an integer greater than or equal to 0 each independently, and m + n represents the integer of 0-3. ]   The ink composition according to any one of claims 1 to 6, wherein a content of the water-soluble polymerizable compound is 13 to 35% by mass with respect to a total amount of the ink composition.   The ink composition according to any one of claims 1 to 7, wherein a total content of the at least two kinds of magenta pigments is 4 to 7% by mass with respect to a total amount of the ink composition.   The ink composition according to any one of claims 1 to 8, wherein a content of the polymerization initiator is 1 to 5 mass% with respect to a total amount of the ink composition. The ink composition according to any one of claims 1 to 9,
A treatment liquid containing an aggregating agent capable of forming an aggregate by contact with the ink composition;
Ink set containing. An ink application step of applying the ink composition according to any one of claims 1 to 9 onto a recording medium;
And an active energy ray irradiating step of irradiating the ink composition applied on the recording medium with an active energy ray.   Furthermore, before the said active energy ray irradiation process, it has the process liquid provision process of providing the process liquid containing the coagulant | flocculant which can form an aggregate on the said recording medium by contacting with the said ink composition. The image forming method according to 11.