JP5749119B2 - Ink composition, image forming method, and printed matter - Google Patents

Description

  The present invention relates to an ink composition that can be used for ink jet recording, an image forming method using the ink composition, and a print formed using the ink composition.

  As an image recording method for forming an image on a recording medium such as paper based on an image data signal, there is an ink jet recording method. The ink jet recording method is a recording method in which a liquid ink composition is ejected from a nozzle toward a recording medium using pressure, heat, an electric field or the like as a driving source. Such an ink jet recording system has been rapidly spread in recent years because it has a low running cost and can achieve high image quality.

  Among the ink compositions used for image recording by the ink jet recording method, the active energy ray-curable aqueous ink composition is an image printing, a pretreatment for imparting printability to a recording medium, and a printed image. It can be suitably used for the post-treatment of protection and decoration. In addition, the water-based ink composition is a technology having many excellent features and possibilities, such as being excellent in safety because it contains water as a main component, and being able to be applied to high-density inkjet recording due to low viscosity. It is.

  On the other hand, from the viewpoint of improving the bleed resistance of the ink image and improving the adhesion to the substrate, an ink-jet ink composition (for example, see Patent Documents 1 and 2) containing a water-soluble polymerizable polymer and a pigment is proposed. Has been.

JP 2007-161887 A JP 2006-249216 A

  However, conventional ink compositions as described in Patent Documents 1 and 2 have not been studied for storage stability, particularly for storage stability in a high pH region. In addition, when an image formed with an ink composition is exposed to the outdoors, for example, water resistance is required. However, there is still room for improvement with respect to the water resistance of an image formed with a conventional ink composition. There is.

The present invention has been made in light of the above circumstances, can form an image having excellent curability and high water resistance, suppresses a decrease in curability when stored for a long period of time, and is applied to an ink jet recording method. It is an object of the present invention to provide an ink composition having excellent ejection properties when an image is recorded.
Furthermore, the present invention provides an image forming method capable of forming an image excellent in curability and water resistance with high productivity, and a printed matter having an image excellent in water resistance and adhesion to a recording medium. Is an issue.

<1> An inkjet recording ink containing at least (a) a polymer compound having a repeating unit including a partial structure represented by the following general formula (1), (b) a photopolymerization initiator, and (c) water. Composition.

In the general formula (1), R ¹ represents an alkyl group having 1 to 4 carbon atoms, and n1 represents an integer of 0 to 2. * Represents a connecting position with an adjacent site.

<2> The ink composition according to <1>, wherein the polymer compound having a repeating unit including the partial structure represented by the general formula (1) further includes a hydrophilic group.
<3> The weight average molecular weight of the polymer compound having a repeating unit including the partial structure represented by the general formula (1) (a) is in a range of 3000 to 60000, according to <1> or <2>. Ink composition.
<4> The polymer compound (a) having a repeating unit including the partial structure represented by the general formula (1) is selected from alcoholic hydroxyl groups, alkyl-substituted carbamoyl groups, carboxyl groups, sulfo groups, and salts thereof. The ink composition according to any one of claims 1 to 3, further comprising a repeating unit containing at least one hydrophilic group.
<5> The ink composition according to any one of <1> to <4>, further comprising (d) a coloring material.
<6> The ink composition according to any one of <1> to <5>, wherein the content of water (c) is in the range of 10% by mass to 80% by mass with respect to the total mass of the ink composition. object.
<7> The ink composition according to <6>, wherein the content of water (c) is in the range of 40% by mass to 80% by mass with respect to the total mass of the ink composition.

< 8 > The polymer compound (a) having a repeating unit containing a partial structure represented by the general formula (1) includes a repeating unit represented by the following general formula (2): <1> to < 7 > The ink composition according to any one of the above.

In General Formula (2), R ² represents a hydrogen atom or a methyl group, and L represents a methylene group, a phenylene group, —COO—, or —CONH—. J represents a single bond or an alkylene group having 1 to 8 carbon atoms, and the alkylene group may contain an ether bond, an ester bond, a urethane bond, a ureylene bond, or a quaternary ammonium group in the alkyl chain; It may be substituted with an alkyl group having 1 to 4 carbon atoms or a hydroxyl group. R ³ represents an alkyl group having 1 to 4 carbon atoms. n2 represents an integer of 0 to 2.

<9> The ink composition according to any one of <1> to <8>, wherein the (b) photopolymerization initiator is a water-soluble photopolymerization initiator.
< 10 > The ink composition according to any one of <1> to < 9 >, further comprising (e) a polymerizable compound.
< 11 > The ink composition according to any one of <1> to < 10 >, further comprising (f) a water-soluble organic solvent.

< 12 > An ink application step of applying the ink composition according to any one of <1> to < 11 > onto a recording medium by an inkjet method , and an active energy to the ink composition applied on the recording medium And an irradiation step of irradiating a line.
< 13 > An ink application step for applying the ink composition according to any one of <1> to < 11 > onto a recording medium by an inkjet method , and an ink composition applied on the recording medium. that (c) described in water and / or (f) a heating drying step of the water-soluble organic solvent is dried and removed by heating, including an irradiation step of irradiating an active energy ray to the ink composition <12> Image forming method .
< 14> An image formed on the recording medium by the ink composition according to any one of <1> to < 11 > or the image forming method according to < 12 > or <13 >. Printed image with an image.

According to the present invention, an image having excellent curability and high water resistance can be formed, a decrease in curability when stored for a long period of time is suppressed, and an image can be recorded when applied to an ink jet recording method. An ink composition having excellent ejection properties can be provided.
Furthermore, according to the present invention, an image forming method capable of forming an image having excellent curability and water resistance with high productivity, and a printed matter having an image excellent in water resistance and adhesion to a recording medium are provided. can do.

Hereinafter, the ink composition, the image forming method, and the printed material of the present invention will be described.
In addition, in this specification, when mentioning the amount of each component in the composition, when there are a plurality of substances corresponding to each component in the composition, the present in the composition unless otherwise specified. It means the total amount of multiple substances.
Further, in the ink composition of the present invention, the solid content means the ratio of all components except the solvent to the mass of the entire ink composition among components contained in the ink composition at 25 ° C. The solid content includes liquid components.
In the present specification, a numerical range indicated using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In this specification, the term “process” is not limited to an independent process, and is included in the term if the intended action of the process is achieved even when it cannot be clearly distinguished from other processes.

[Ink composition]
The ink composition of the present invention is an ink composition containing at least a polymer compound having a repeating unit including a partial structure represented by the following general formula (1), a photopolymerization initiator, and water.

In the general formula (1), R ¹ represents an alkyl group having 1 to 4 carbon atoms, and n1 represents an integer of 0 to 2. * Represents a connecting position with an adjacent site.

  The ink composition of the present invention is preferably configured to further contain other components such as a coloring material (for example, pigment) described later. Other components such as the coloring material may be contained in the ink composition of the present invention as a solid dispersion (for example, a pigment dispersion).

  Further, the ink composition of the present invention may contain various liquid or solid compounds as additives as long as the effects of the present invention are not impaired. For example, by further containing a polymerizable compound, the curability of the image is further improved, and by further containing a polymerization inhibitor or the like, it is possible to obtain an ink composition having more excellent storage stability. Details of the compounds that the ink composition of the present invention may contain as additives will be described later.

The mechanism by which the ink composition of the present invention exerts its effect is not yet clear, but the present inventors infer as follows.
That is, since the specific polymer compound has a plurality of partial structures represented by the general formula (1) in the side chain, the mobility of the partial structure contributing to the polymerizability and crosslinkability present in the side chain is increased. It is considered that the crosslinking efficiency is improved. As a result, it is speculated that effects such as curability are improved. Furthermore, since the partial structure represented by the general formula (1) has a hydrophobic polymerizable site, it exhibits hydrolysis resistance, and the ink image obtained by the ink composition of the present invention has excellent water resistance. It is presumed that In addition, the said mechanism is inference and this invention is not limited to the said mechanism.

  Hereinafter, essential components and optional components contained in the ink composition of the present invention will be described in detail.

[(A) Polymer compound having a repeating unit including a partial structure represented by the general formula (1)]
The ink composition of the present invention contains a polymer compound having a repeating unit containing the partial structure represented by the general formula (1) (hereinafter, referred to as “specific polymer compound” as appropriate).

  The specific polymer compound only needs to have a repeating unit including a partial structure represented by the following general formula (1), and includes various vinyl polymers, polyurethanes, polyesters, polyethyleneimines, and the like. The molecular structure can be taken. From the viewpoint of ejection properties and production suitability when the ink composition of the present invention is applied to an inkjet ink composition, the specific polymer compound is preferably a vinyl polymer.

In the general formula (1), R ¹ represents an alkyl group having 1 to 4 carbon atoms, and n1 represents an integer of 0 to 2. * Represents a connecting position with an adjacent site.

In general formula (1), the alkyl group having 1 to 4 carbon atoms represented by R ¹ is preferably an alkyl group having 1 or 2 carbon atoms (that is, a methyl group or an ethyl group), and has 1 carbon atom. It is more preferable that the alkyl group is a methyl group.

  In the partial structure represented by the general formula (1), the vinyl group is preferably located at the m-position or the p-position with respect to the connecting position represented by “*-”.

  In general formula (1), n1 represents an integer of 0 to 2, preferably 0 or 1, and more preferably 0.

  Specific examples of the partial structure represented by the general formula (1) are shown below, but the present invention is not limited thereto.

  The specific polymer compound preferably has a partial structure represented by the general formula (1) in the side chain of the polymer compound.

  It is preferable from a viewpoint of an effect that a specific polymer compound is an aspect which has two or more partial structures shown by the said General formula (1). From this viewpoint, the specific polymer compound is preferably a polymer compound having a repeating unit represented by the following general formula (2).

In General Formula (2), R ² represents a hydrogen atom or a methyl group, and L represents a methylene group, a phenylene group, —COO—, or —CONH—. J represents a single bond or an alkylene group having 1 to 8 carbon atoms, and the alkylene group may contain an ether bond, an ester bond, a urethane bond, a ureylene bond, or a quaternary ammonium group in the alkyl chain; It may be substituted with an alkyl group having 1 to 4 carbon atoms or a hydroxyl group. R ³ represents an alkyl group having 1 to 4 carbon atoms. n2 represents an integer of 0 to 2.

The general formula (2) will be described in detail.
In General Formula (2), L represents a methylene group, a phenylene group, —COO—, or —CONH—, and is preferably a phenylene group or —COO—.

In General Formula (2), J represents a single bond or an alkylene group having 1 to 8 carbon atoms, and the alkylene group includes an ether bond, an ester bond, a urethane bond, a ureylene bond, or a quaternary ammonium group in the alkyl chain. And may be substituted with an alkyl group having 1 to 4 carbon atoms or a hydroxyl group.
Among these, as J, an alkylene group having 1 to 6 carbon atoms, an alkylene group having 1 to 6 carbon atoms including an ether bond, a urethane bond or a ureylene bond in the alkyl chain, and these alkylene groups are methyl groups. , An ethyl group, a butyl group or a group selected from the group consisting of a substituent substituted with a hydroxyl group is preferred, an alkylene group having 1 to 4 carbon atoms, and an alkyl chain containing an ether bond or a urethane bond having 1 to 4 carbon atoms. And a group selected from the group consisting of a substituent in which these alkylene groups are substituted with a hydroxyl group.

In General Formula (2), R ³ represents an alkyl group having 1 to 4 carbon atoms, and the alkyl group having 1 to 4 carbon atoms is preferably an alkyl group having 1 or 2 carbon atoms, More preferably, it is 1 alkyl group (methyl group).
In general formula (2), n2 represents an integer of 0 to 2, preferably 0 or 1, and more preferably 0.

  In the specific polymer compound, the content of the repeating unit including the partial structure represented by the general formula (2) is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, and 20 to 85%. Mass% is particularly preferred. By making content of the repeating unit containing the partial structure represented by General formula (2) into this range, sclerosis | hardenability and the solubility in water become especially favorable.

  Specific examples of the repeating unit represented by the general formula (2) are shown below, but the present invention is not limited thereto.

The specific polymer compound preferably further contains a hydrophilic group in the molecule.
The hydrophilic group possessed by the specific polymer compound is not particularly limited as long as it is a group having a function of enhancing the hydrophilicity of the specific polymer compound, and may be a nonionic hydrophilic group or an ionic hydrophilic group. (For example, an anionic hydrophilic group or a cationic hydrophilic group) may be used.

  The number of hydrophilic groups contained in the specific polymer compound is not limited, and the number is appropriately selected according to the type of hydrophilic group, the molecular weight of the specific polymer compound, and the like. It is preferable that the hydrophilic group is contained in such a number that the specific polymer compound is water-soluble. Here, the specific polymer compound being water-soluble means that the specific polymer compound can be dissolved by 3% by mass or more in water at 25 ° C.

(Hydrophilic group)
The hydrophilic group that can be introduced into the specific polymer compound will be described.
Preferred examples of the hydrophilic group that can be introduced into the specific polymer compound include a nonionic hydrophilic group and an ionic hydrophilic property.

  The nonionic hydrophilic group is not particularly limited. For example, a residue obtained by removing one hydrogen atom from a heterocyclic structure containing a nitrogen atom or an oxygen atom, an amide group, a carbamoyl group, an alkyl-substituted carbamoyl group, an alcoholic hydroxyl group Or a nonionic hydrophilic group such as a group having a polyalkyleneoxy structure.

  Examples of the heterocyclic structure in the residue obtained by removing one hydrogen atom from a heterocyclic structure containing a nitrogen atom or an oxygen atom include lactones such as γ-butyrolactone; cyclic ureas such as 2-pyrrolidone and ethylene urea; ethylene carbonate , Cyclic carbonates such as propylene carbonate, cyclic ethers such as tetrahydrofuran and 1,4-dioxane; and the like.

  As the amide group, an amide group having 2 to 10 carbon atoms is preferable, and a hydrogen atom is preferably bonded to a nitrogen atom in the amide group.

  The alkyl-substituted carbamoyl group is a monoalkylcarbamoyl group in which a hydrogen atom bonded to a nitrogen atom of a carbamoyl group is substituted with an alkyl group, or two hydrogen atoms bonded to a nitrogen atom of a carbamoyl group are substituted with an alkyl group And a dialkylcarbamoyl group formed. The alkyl group may further have a substituent such as a hydroxyl group. Among these alkyl-substituted carbamoyl groups, a monoalkylcarbamoyl group substituted with an alkyl group having 1 to 8 carbon atoms or an alkyl group having 1 to 4 carbon atoms substituted with a hydroxyl group is preferable.

  Although it does not specifically limit as group which has a polyalkyleneoxy structure, The polyalkyleneoxy structure which has a C1-C4 alkyleneoxy group in a repeating unit is preferable. One type of alkyleneoxy group in the polyalkyleneoxy structure may be used, or a plurality of types of alkyleneoxy groups may be combined. The terminal group of the polyalkyleneoxy structure is preferably a hydroxyl group or an alkoxy group, more preferably a hydroxyl group or a methoxy group.

  Although it does not specifically limit as an ionic hydrophilic group, For example, ionic hydrophilic groups, such as a carboxyl group, a sulfo group, a phosphoric acid group, a phosphonic acid group, a phenolic hydroxyl group, or a quaternary ammonium group, are mentioned. The ionic hydrophilic group may form a salt.

  When the ionic hydrophilic group forms a salt, examples of the counter salt include onium salts such as alkali metal salts (Li, Na, K, etc.), ammonium salts, pyridinium salts, and phosphonium salts. Among these, alkali metal salts (Li, Na, K, etc.) or ammonium salts are preferable.

  Among these hydrophilic groups, an amide group, a carbamoyl group, an alkyl-substituted carbamoyl group, an alcoholic hydroxyl group, a group having a polyalkyleneoxy structure, a carboxyl group, or a sulfo group is preferable, and an alcoholic hydroxyl group, an alkyl-substituted carbamoyl group, a carboxyl group And more preferred are sulfo groups and salts thereof.

An aspect in which the specific polymer compound has a hydrophilic group is an aspect in which a repeating unit having a hydrophilic group is included as a copolymer component together with the repeating unit having a partial structure represented by the general formula (1). preferable.
In particular, as an aspect in which the specific polymer compound has a hydrophilic group, the repeating unit having the partial structure represented by the general formula (1) is a repeating unit represented by the general formula (2). The embodiment preferably includes a repeating unit having a hydrophilic group as a copolymerization component.

  When the specific polymer compound includes a repeating unit having a hydrophilic group as a copolymerization component, the repeating unit having a hydrophilic group is preferably a repeating unit represented by the following general formula (3).

In general formula (3), R ^cy represents a hydrogen atom or a methyl group. Z ^y represents —COO— *, —CONR ^dy — *, or a single bond, and R ^dy represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. R ^y represents a single bond or a group selected from the group consisting of an alkylene group, an arylene group, and an aralkylene group. A represents a hydrophilic group. Note that * represents the position at which Z ^y is bonded to R ^y .

The general formula (3) will be described in detail.
In general formula (3), R ^cy represents a hydrogen atom or a methyl group.

In General Formula (3), Z ^y represents —COO— *, —CONR ^dy — *, or a single bond, and is preferably —COO— *. Note that * represents the position at which Z ^y is bonded to R ^y .

R ^dy represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. The alkyl group having 1 to 4 carbon atoms may have a linear structure or a branched structure. Specific examples of R ^dy include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, and a t-butyl group. R ^dy is preferably a hydrogen atom or an alkyl group having 1 or 2 carbon atoms (that is, a methyl group or an ethyl group), and particularly preferably a hydrogen atom.

R ^dy may or may not have a substituent, but preferably does not have a substituent. Examples of the substituent that R ^dy may have include an aryl group having 6 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a hydroxyl group, a carboxyl group, and a halogen atom (F, Cl, Br, I, etc.). Etc.

In the general formula (3), R ^y represents a single bond or a group selected from the group consisting of an alkylene group, an arylene group, and an aralkylene group, an alkylene group having 1 to 20 carbon atoms, and a group having 6 to 20 carbon atoms. An arylene group or an aralkylene group having 7 to 20 carbon atoms is preferable.
When ^Ry is a group selected from the group consisting of an alkylene group, an arylene group, and an aralkylene group, these groups may further have a substituent or may not have a substituent. The alkylene group, arylene group, and aralkylene group represented by R ^y may have an ether bond, an ester bond, an amide bond, or a urethane bond in the structure.
In the general formula (3), R ^y is preferably a single bond.

When ^Ry is a group selected from the group consisting of an alkylene group, an arylene group, and an aralkylene group, these groups may further have a substituent. Examples of the substituent include an aryl group having 6 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a hydroxyl group, a carboxyl group, a halogen atom (F, Cl, Br, I, etc.) and the like.

When ^Ry is an alkylene group having 1 to 20 carbon atoms, the alkylene group may have a linear structure, a branched structure, or a cyclic structure. When ^Ry is an alkylene group, the carbon number is more preferably 2 to 12, and further preferably 2 to 8.
Specific examples of the alkylene group represented by R ^y include —CH ₂ —, —C ₂ H ₄ —, —C (CH ₃ ) ₂ —CH ₂ —, —CH ₂ C (CH ₃ ) ₂ CH ₂ —. _{, -C 6 H 12 -, -} C 4 H 7 (C 4 H 9) C 4 H 8 -, C 18 H 36 -, 1,4-trans- cyclohexylene _group, -C ₂ H 4 -OCO-C _{2 H 4 -, - C 2} H 4 -OCO -, - C 2 H 4 -O-C 5 H 10 -, - CH 2 -O-C 5 H 9 (C 5 H 11) -, - C 2 H _{4 -CONH-C 2 H 4 -} , - C 4 H 8 -OCONH-C 6 H 12 -, - CH 2 -OCONHC 10 H 20 -, - CH 2 CH (OH) CH 2 -, and the like.

When ^Ry is an arylene group having 6 to 20 carbon atoms, the arylene group preferably has 6 to 18 carbon atoms, more preferably 6 to 14 carbon atoms, and particularly preferably 6 to 10 carbon atoms. . Specific examples of the arylene group represented by R ^y include a phenylene group, a biphenylene group, —C ₆ H ₄ —CO—C ₆ H ₄ —, a naphthylene group, and the like.

When ^Ry is an aralkylene group having 7 to 20 carbon atoms, the aralkylene group preferably has 7 to 18 carbon atoms, more preferably 7 to 14 carbon atoms, and particularly preferably 7 to 10 carbon atoms. . Specific examples of the aralkylene group represented by R ^y _{is, -C 3 H 6 -C 6 H} 4 -, - C 2 H 4 -C 6 H 4 -C 6 H 4 -, - CH 2 -C 6 H _{4 -C 6 H 4 -C 2 H} 4 -, - C 2 H 4 -OCO-C 6 H 4 -, can be like that mentioned.

  In the general formula (3), examples of the hydrophilic group represented by A include the hydrophilic groups described above, and preferred ranges thereof are also the same.

When the specific polymer compound has a repeating unit represented by the general formula (3), preferred contents of the repeating unit represented by the general formula (3) in the specific polymer compound are as follows.
When the hydrophilic group A in the general formula (3) is an ionic hydrophilic group, the repeating unit represented by the general formula (3) is preferably 5 to 40% by mass in the specific polymer compound, 10-35 mass% is still more preferable, and 10-30 mass% is especially preferable.
When the hydrophilic group A in the general formula (3) is a nonionic hydrophilic group, the repeating unit represented by the general formula (3) is preferably 20 to 90% by mass in the specific polymer compound. 30-80 mass% is still more preferable, and 30-70 mass% is especially preferable.

  As a monomer which forms the repeating unit represented by the general formula (3), for example, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, poly (ethylene glycol-co-propylene) Glycol) (meth) acrylate, 2-hydroxyethyl (meth) acrylate, glycerol (meth) acrylate (meth) acryloyloxyethyl ethylenurea, vinylpyrrolidone, 3- (meth) acryloyloxy-γ-butyrolactone, acrylamide, tert- Butylacrylamide, N, N-dimethyl (meth) acrylamide, diacetone acrylamide, sodium (meth) acrylate, potassium (meth) acrylate, (meth) acrylic acid Trabutylammonium, mono (meth) acryloyloxyethyl succinic acid, sodium mono (meth) acryloyloxyethyl succinate, sodium mono (meth) acryloyloxyethyl phthalate, (meth) acryloyloxyethyl acid phosphate, 2 -Sodium acrylamido-2-methylpropane sulfonate, 2-acrylamido-2-methylpropane sulfonic acid, styrene sulfonic acid, sodium styrene sulfonate, vinyl benzoic acid and the like.

  The monomer that forms the repeating unit represented by the general formula (3) can be a commercially available compound or can be produced by a generally known method.

  Further, in the present invention, in addition to the exemplified compound giving the repeating unit represented by the general formula (3), unsaturated dicarboxylic acids such as maleic acid, maleic anhydride, fumaric acid and the like, and their anhydrides, and further derived therefrom. Dicarboxylates that can be used are also preferably used.

  The content of the repeating unit having a hydrophilic group in the specific polymer compound is preferably a content at which the specific polymer compound becomes water-soluble although the preferable content varies depending on the type of the hydrophilic group.

  The specific polymer compound may be a copolymer including a repeating unit having a partial structure represented by the general formula (1) and a repeating unit other than the repeating unit having a hydrophilic group.

Other monomers that form repeating units include styrenes such as styrene and p-methoxystyrene; methyl (meth) acrylate, ethyl (meth) acrylate, allyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) Acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, bornyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) ) Acrylate, 2-ethylhexyl diglycol (meth) acrylate, butoxyethyl (meth) acrylate, butoxymethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, 2- (2- Toxiethoxy) ethyl (meth) acrylate, 2- (2-butoxyethoxy) ethyl (meth) acrylate, 2,2,2-tetrafluoroethyl (meth) acrylate, 4-butylphenyl (meth) acrylate, phenyl (meth) Acrylate, 2,4,5-tetramethylphenyl (meth) acrylate, 4-chlorophenyl (meth) acrylate, phenoxymethyl (meth) acrylate, phenoxyethyl (meth) acrylate, glycidyl (meth) acrylate, glycidyloxybutyl (meta ) Acrylate, glycidyloxyethyl (meth) acrylate, glycidyloxypropyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, butoxydiethylene glycol (meth) acrylate, trifluoroethyl (Meth) acrylates such as (meth) acrylate and perfluorooctylethyl (meth) acrylate; and methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, 2- Preferable examples include alkyl (meth) acrylates having 1 to 8 carbon atoms such as ethylhexyl (meth) acrylate.
In addition, as a monomer which forms another repeating unit, well-known monomers other than the above can also be used as needed.

  The content of other repeating units in the specific polymer compound is preferably 0 to 60% by mass, more preferably 0 to 40% by mass, and particularly preferably 0 to 30% by mass.

  The specific polymer compound preferably has a weight average molecular weight of 2000 to 100,000, more preferably a weight average molecular weight of 2000 to 80000, and particularly preferably 3000 to 60000.

  In addition, the weight average molecular weight of a specific polymer compound is measured by a gel permeation chromatograph (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.

The specific polymer compound includes, for example, a monomer for forming the repeating unit represented by the general formula (2), and a monomer for forming the repeating unit represented by the general formula (3) that is optionally used. Can be obtained by polymerizing by a known polymerization method and, if necessary, neutralizing the acidic group with an alkali metal hydroxide or the like.
Specifically, for example, a method according to the polymerization method described in JP-A-52-988, JP-A-55-154970, Langmuir Vol. 18, No. 14, pages 5414-5421 (2002), etc. A polymer compound can be produced.

  Although the exemplary compound (P-1) to the exemplary compound (P-9) are shown below as specific examples of the specific polymer compound, the present invention is not limited thereto.

  The specific polymer compound contained in the ink composition of the present invention may be only one type, or two or more types may be used in combination.

  The content of the specific polymer compound in the ink composition of the present invention is preferably 1% by mass to 25% by mass, more preferably 2% by mass to 20% by mass, with respect to the total mass of the ink composition. More preferably, it is 5 mass%-15 mass%.

[(B) Photopolymerization initiator]
The ink composition of the present invention contains a photopolymerization initiator.
The photopolymerization initiator used in the present invention is preferably water-soluble. The degree of water solubility of the photopolymerization initiator is preferably 0.5% by mass or more, preferably 1% by mass or more, and particularly preferably 3% by mass or more in distilled water at 25 ° C. . As the photopolymerization initiator, a photopolymerization initiator in which a water-insoluble photopolymerization initiator is dispersed can also be used.

In the present invention, it is preferable to use a photopolymerization initiator selected from the group consisting of α-hydroxy ketones, α-amino ketones and acylphosphine oxides.
A commercially available product may be used as the photopolymerization initiator, and a commercially available photopolymerization initiator may be 1- [4- (2-hydroxyethyl) -phenyl] -2-hydroxy-2-methyl]. Water-soluble photopolymerization initiators such as -1-propan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, and [bis (2,4 , 6-Trimethylbenzoyl) -phenylphosphine oxide] can be used as a hydrophobic photopolymerization initiator. In addition to these, water-soluble photopolymerization initiators described in paragraphs [0069] to [0075] of JP-A-2006-117795 can also be preferably used.

  The content of the photopolymerization initiator in the ink composition of the present invention is preferably 0.01% by mass to 7% by mass, more preferably 0.05% by mass to 6% by mass with respect to the total mass of the ink composition. %, More preferably 0.1% by mass to 5% by mass.

[(C) water]
The ink composition of the present invention contains water as a main solvent.
As water, it is preferable to use ion-exchanged water, distilled water or the like that does not contain impurities.

  The water content in the ink composition of the present invention is preferably 10% by mass to 80% by mass, more preferably 30% by mass to 80% by mass, and still more preferably based on the total mass of the ink composition. It is 40 mass%-80 mass%.

[(D) Color material]
The ink composition of the present invention may contain a color material. The ink composition of the present invention becomes a colored ink composition by containing a coloring material.
Known dyes and pigments can be used as the color material.
As the dye, a water-soluble dye or a disperse dye can be used.
Among the color materials, a pigment is preferably used from the viewpoint of the weather resistance of the image.
When a pigment is used as the color material, the pigment is preferably contained as a pigment dispersion in the ink composition. As the pigment dispersion, a self-dispersed pigment can be used in addition to a pigment dispersed with a pigment dispersant.

~ Pigment ~
The pigment suitably used as the color material in the ink composition of the present invention will be described in detail.
As the pigment, generally used organic pigments, inorganic pigments, and those obtained by dyeing resin particles with a dye can be used. Usually, any commercially available pigment can be used, and further, a pigment pretreated with a commercially available pigment dispersion or surface treatment agent, for example, a pigment dispersed in an insoluble resin or the like as a dispersion medium, Or what grafted resin to the pigment surface etc. can be used unless the effect of this invention is impaired.

  Examples of these pigments include, for example, “Pigment Dictionary” (2000), edited by Seijiro Ito. Herbst, K.M. Hunger “Industrial Organic Pigments”, JP 2002-12607 A, JP 2002-188025 A, JP 2003-26978 A, and JP 2003-342503 A3.

  Examples of organic pigments and inorganic pigments that can be used in the present invention are those that exhibit a yellow color, such as monoazo pigments, disazo pigments, non-benzidine azo pigments, azo lake pigments, condensed azo pigments, acidic dye lake pigments, basic pigments, and the like. Examples include dye lake pigments, anthraquinone pigments, quinophthalone pigments, pyrazolone pigments, acetolone pigments, metal complex pigments, nitroso pigments, metal complex azomethine pigments, benzimidazolone pigments, and isoindoline pigments. Of these, examples of pigments that can be preferably used in the present invention include C.I. I. Pigment Yellow (hereinafter abbreviated as PY) 1, PY3, PY12, PY13, PY14, PY16, PY17, PY18, PY24, PY60, PY74, PY83, PY93, PY94, PY95, PY97, PY100, PY109, PY110, PY115, PY117, PY120, PY128, PY138, PY139, PY150, PY151, PY153, PY154, PY155, PY166, PY167, PY173, PY175, PY180, PY181, PY185, PY194, PY213, PY213, PY213, PY214, PY213 Among them, benzimidazolone pigments such as monoazo pigments, disazo pigments, and acetolone pigments, and isoindoline are preferable, and PY74, PY120, PY151, PY155, PY180, and PY185 are preferable.

Examples of red or magenta colors include monoazo pigments, β-naphthol pigments, disazo pigments, azo lake pigments, condensed azo pigments, acidic dye lake pigments, basic dye lake pigments, anthraquinone pigments, thioindigo pigments, perinone Examples thereof include pigments, perylene pigments, quinacridone pigments, isoindolinone pigments, alizarin lake pigments, naphtholone pigments, naphthol AS-based lake pigments, naphthol AS pigments, and diketopyrrolopyrrole pigments.
Of these, examples of pigments that can be preferably used in the present invention include C.I. I. Pigment Red (hereinafter abbreviated as PR) 1, PR2, PR3, PR4, PR5, PR6, PR21, PR38, PR42, PR46, PR53: 1, PR57: 1, PR52: 1, PR46, PR48, PR81, PR83, PR88, PR144, PR149, PR166, PR179, PR178, PR190, PR224, PR123, PR224, PR19, PR122, PR202, PR207, PR209, PR180, PR83, PR170, PR171, PR172, PR174, PR175, PR176, PR177, PR179, PR185, PR194, PR208, PR214, PR220, PR221, PR242, PR247, PR254, PR255, PR256, PR262, PR268, PR264 PR269, PR272, PR282, C. I. Pigment violet 19 and the like. Of these, quinacridone pigments are preferable, and PR42, PR122, PR202, PR209, PR282, C.I. I. Pigment Violet 19 is preferable.

  Examples of pigments exhibiting blue or cyan colors include disazo pigments, phthalocyanine pigments, acidic dye lake pigments, basic dye lake pigments, anthraquinone pigments, and alkali blue pigments. Examples of the pigment that can be preferably used in the present invention include C.I. I. Pigment Blue (hereinafter abbreviated as PB) 1, PB15, PB15: 1, PB15: 2, PB15: 3, PB15: 4, PB15: 6, PB16, PB18, PB24, PB25, PB60, PB79 and the like. Among these, a copper phthalocyanine pigment is preferable, and PB15, PB15: 1, PB15: 2, PB15: 3, PB15: 4, and PB15: 6 are preferable.

Examples of the green pigment include phthalocyanine pigments and metal complex pigments. Examples of the pigment that can be preferably used in the present invention include C.I. I. Pigment green (hereinafter abbreviated as PG) 7, PG8, PG10, PG36, and the like.
Examples of the orange pigment include isoindoline pigments, anthraquinone pigments, Β-naphthol pigments, naphthol AS pigments, isoindolinone pigments, perinone pigments, disazo pigments, quinacridone pigments, acetolone pigments, pyrazolone pigments, and the like. It is done. Examples of the pigment that can be preferably used in the present invention include C.I. I. Pigment Orange (hereinafter abbreviated as PO) 2, PO3, PO4, PO5, PO13, PO15, PO16, PO22, PO24, PO34, PO36, PO38, PO43, PO48, PO49, PO51, PO55, PO60, PO61, PO62, PO64, PO66, PO72, PO74 etc. are mentioned.

Examples of the pigment exhibiting brown include naphthron pigments such as PBr25 and PBr32.
Examples of purple pigments include naphthron pigments, perylene pigments, naphthol AS pigments, dioxazine pigments, and the like. Examples of the pigment that can be preferably used in the present invention include C.I. I. Pigment violet (hereinafter abbreviated as PV) 13, PV17, PV23, PV29, PV32, PV37, PV50, and the like.

Examples of the pigment exhibiting black include, for example, carbon black, indazine pigment, perylene pigment and the like. I. Pigment black (hereinafter abbreviated as PBk) 1, PBk7, PBk31, PBk32, and the like.
Examples of white pigments include basic lead carbonate (2PbCO ₃ Pb (OH) ₂ , so-called silver white), zinc oxide (ZnO, so-called zinc white), titanium oxide (TiO ₂ , so-called titanium white). Strontium titanate (SrTiO ₃ , so-called titanium strontium white), organic hollow fine particles, white organic pigments, and the like can be used. The inorganic particles used for the white pigment may be a simple substance or, for example, oxides such as silicon, aluminum, zirconium and titanium, organometallic compounds, and composite particles with organic compounds.

  Here, titanium oxide has a smaller specific gravity than other white pigments, a large refractive index, and is chemically and physically stable, so that it has a large hiding power and coloring power as a pigment. Excellent durability against other environments. Therefore, it is preferable to use titanium oxide as the white pigment. Of course, other white pigments (may be other than the listed white pigments) may be used as necessary.

  Since pigments other than white are more excellent in color developability as the average particle size is smaller, if the pigment dispersion according to the present invention is applied to a pigment dispersion other than white, the average of the pigments contained in the pigment dispersion The particle size is preferably about 0.01 μm to 0.4 μm, more preferably 0.02 μm to 0.3 μm. The maximum particle diameter of the pigment is 3 μm or less, preferably 1 μm or less. The particle size of the pigment can be adjusted by selecting a pigment, a dispersant, a dispersion medium, setting dispersion conditions, and filtering conditions. In addition, when the pigment dispersion of the present invention is prepared as a white pigment dispersion that can be applied to a white ink composition or the like, the average particle size of the pigment contained in the pigment dispersion is sufficiently concealed. From the viewpoint of imparting properties, the thickness is preferably about 0.05 μm to 1.0 μm, more preferably about 0.1 μm to 0.4 μm. Also in the case of using a white pigment dispersion, the maximum particle size of the pigment is preferably 3 μm or less, more preferably 1 μm or less.

~ Dispersant ~
When a pigment is used as the color material, a pigment dispersant may be used as necessary when preparing the pigment particles.
Examples of the pigment dispersant that can be used in the present invention include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, alkyl phosphates, and polyoxyalkylenes. Activators such as alkyl ether phosphates, polyoxyalkylene alkyl phenyl ethers, polyoxyethylene polyoxypropylene glycols, glycerin esters, sorbitan esters, polyoxyethylene fatty acid amides, amine oxides, or styrene, styrene derivatives, vinyl naphthalene derivatives, Block copolymer consisting of two or more monomers selected from acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, random copolymers Coalescence and the like, and salts thereof.

  A self-dispersing pigment can also be used in the ink composition of the present invention. The self-dispersing pigment as used in the present invention refers to a pigment that can be dispersed without a dispersant, and particularly preferably pigment particles having a polar group on the surface.

The pigment particles having a polar group on the surface as used in the present invention are a pigment whose surface is directly modified with a polar group, or an organic substance having an organic pigment mother nucleus, which is bonded directly or via a joint. (Hereinafter referred to as pigment derivative).
Examples of the polar group include a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a boric acid group, and a hydroxyl group, preferably a sulfonic acid group and a carboxylic acid group, and more preferably a sulfonic acid group.

  Examples of a method for obtaining pigment particles having a polar group on the surface include, for example, WO 97/48769, JP-A-10-110129, JP-A-11-246807, JP-A-11-57458, 11-189739, JP-A-11-323232, JP-A-2000-265094, etc., oxidize the pigment particle surface with an appropriate oxidizing agent, so that at least a part of the pigment surface has a sulfonic acid group or The method of introduce | transducing polar groups, such as the salt, is mentioned. Specifically, it is prepared by oxidizing carbon black with concentrated nitric acid or, in the case of color pigments, by oxidizing with sulfamic acid, sulfonated pyridine salt, amidosulfuric acid, etc. in sulfolane or N-methyl-2-pyrrolidone. can do. In these reactions, the pigment dispersion can be obtained by removing and purifying the substance that has been excessively oxidized and becomes water-soluble. Moreover, when a sulfonic acid group is introduced onto the surface by oxidation, the acidic group may be neutralized with a basic compound as necessary.

  As other methods for obtaining pigment particles having polar groups on the surface, the pigment particles described in JP-A-11-49974, JP-A-2000-273383, JP-A-2000-303014, etc. are treated with a treatment such as milling. Examples include a method of adsorbing to the surface, a method described in Japanese Patent Application Nos. 2000-377068, 2001-1495, and 2001-234966, and a method of crystallizing in a poor solvent after dissolving the pigment derivative together with a solvent. In any method, pigment particles having a polar group on the surface can be easily obtained.

  The polar group on the surface of the pigment may be free or in a salt state, or may have a counter salt. Examples of the counter salt include inorganic salts (lithium, sodium, potassium, magnesium, calcium, aluminum, nickel, ammonium) and organic salts (triethylammonium, diethylammonium, pyridinium, triethanolammonium, etc.), preferably 1 A counter salt having a valence.

  Only 1 type may be used for a coloring material and it may use 2 or more types together.

  The content as a coloring material in the ink composition of the present invention is preferably 0.1% by mass to 6.0% by mass, and more preferably 0.1% by mass to 5.% by mass with respect to the total mass of the ink composition. It is 5 mass%, More preferably, it is 0.1 mass%-5.0 mass%.

[Other additives]
In addition to (a) the specific polymer compound, (b) water, (c) the photopolymerization initiator, and (d) the colorant optionally contained in the ink composition of the present invention, As long as the effects of the invention are not impaired, known additives can be used in combination. Hereinafter, additives that can be used in the ink composition will be described.

<< (e) Polymerizable compound >>
The ink composition of the present invention may contain a polymerizable compound having a structure different from that of the specific polymer compound. By containing the polymerizable compound, the curability and dischargeability of the ink composition are further improved.

  The polymerizable compound may be any water-soluble compound having at least one ethylenically unsaturated bond capable of radical polymerization in the molecule, and a polymerizable low molecular weight having a molecular weight of 100 or more and less than 1,000. Any of a compound, an oligomer having a molecular weight of 1,000 to less than 50,000, and a polymerizable polymer compound can be used.

  As the polymerizable compound, only one kind of polymerizable low molecular weight compound or polymerizable high molecular weight compound may be used, or two or more kinds may be used in combination at an arbitrary ratio in order to improve the desired properties. Both a low molecular weight compound and a polymerizable high molecular compound may be used. Two or more kinds are preferably used in combination.

  The polymerizable compound used in the present invention needs to be a water-soluble compound or water-dispersible. In the present invention, that the polymerizable compound is water-soluble or water-dispersible means that it is dissolved or dispersed in distilled water at room temperature at 2% by mass, preferably 5% by mass dissolved or dispersed. Those which are uniformly mixed with water in a proportion are particularly preferred.

  Examples of low molecular weight polymerizable compounds include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and other unsaturated carboxylic acids, unsaturated carboxylic acid esters and salts thereof; ethylenically unsaturated groups (Meth) acrylamide; styrene derivatives; vinyl ethers, N-vinyl compounds and the like.

The polymerizable compound used in the present invention is preferably a radical polymerizable compound.
Examples of the radical polymerizable compound include a radical polymerizable monofunctional monomer, a radical polymerizable polyfunctional monomer, a radical polymerizable oligomer, and a polymer polymerizable compound as shown below.

  Examples of the radical polymerizable monofunctional monomer include (meth) acrylamide, N, N-dimethyl (meth) acrylamide, methylenebis (meth) acrylamide, acryloylmorpholine, 2-hydroxyethyl (meth) acrylamide, hydroxymethyl (meth) acrylamide, t -(Meth) acrylamides such as butyl (meth) acrylamide and 3-dimethylaminopropyl (meth) acrylamide, vinyl ethers such as 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether and 2-hydroxyethoxy vinyl ether, methoxy oligoethylene glycol (Meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, tetrahydrofurfuryl acrylate Rate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, N- vinylpyrrolidone, N- vinylformamide, such as N- vinyl compounds such as N- vinyl caprolactam.

  Examples of the radical polymerizable polyfunctional monomer include oligoethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, bis [2- (methacryloyloxy) ethyl] phosphate, methylene bisacrylate, 4,7,10-trioxa Examples include -1,13-tridecanbisacrylamide, triethylene glycol divinyl ether, and acrylamides described in JP-A-2005-307198 and JP-A-2007-277380.

  In addition to the above, examples of the polymerizable compound that can be used in the present invention include polymerizable compounds described in JP-A-2005-307198 and JP-A-2007-277380. The polymerizable compound of the present invention is not limited to these.

  As the radical polymerizable oligomer, polyester oligomer, urethane oligomer, modified polyether oligomer, acrylic oligomer, epoxy oligomer, and the like can be used. Among these, from the viewpoint of hydrolysis stability, an oligomer having an acrylamide group as a polymerizable group and a water-dispersible urethane oligomer are more preferable.

  Examples of the polymer polymerizable compound include polymer compounds having a (meth) acryloyl group, a (meth) acrylamide group, a maleimidyl group, a vinyl ether group, and an allyl group.

  The content of the polymerizable compound added as an optional component in the ink composition is preferably 0 to 30% by mass, more preferably 0 to 20% by mass, and more preferably 0 to 10% by mass with respect to the total mass of the ink composition. % Is more preferable. By adjusting to this range, the fixability, the ejectability when the ink jet method is applied, and the smoothness of the ink cured film (image) tend to be good.

<< (f) Water-soluble organic solvent >>
The ink composition of the present invention contains water as a main solvent, but it is preferable to further use a water-soluble organic solvent in the solvent depending on the purpose.
Here, the water-soluble organic solvent means an organic solvent having a solubility in water at 25 ° C. of 10% by mass or more.

Examples of water-soluble organic solvents that can be used in the present invention include the following.
Alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol, etc.),
Polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, 2- Methylpropanediol, etc.)

Polyhydric alcohol ethers (for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, tripropylene Glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol Monophenyl ether, propylene glycol monophenyl ether)

-Amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentane Methyldiethylenetriamine, tetramethylpropylenediamine, etc.)
Amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.)
Heterocycles (for example, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, propylene carbonate, ethylene carbonate, ethylene urea etc)
・ Sulphoxides (eg, dimethyl sulfoxide)
・ Sulfones (for example, sulfolane)
・ Others (urea, acetonitrile, acetone, etc.)

  Preferable water-soluble organic solvents include polyhydric alcohol ethers and heterocyclic rings, and it is also preferable to use them in combination.

Among the polyhydric alcohol ethers, so-called glycol ethers are preferable, specifically, tripropylene glycol monomethyl ether, dipropylene glycol monomethyl ether, and dipropylene glycol dimethyl ether are preferable, and 2-dipropylene glycol monomethyl ether is more preferable.
As the heterocyclic ring, 2-pyrrolidone, γ-butyrolactone, propylene carbonate, ethylene urea and the like are preferable, and 2-pyrrolidone and γ-butyrolactone are particularly preferable. In particular, a solvent having a high boiling point can be preferably used, and the boiling point at normal pressure is preferably 120 ° C. or higher, more preferably 150 ° C. or higher.

  One or more water-soluble organic solvents may be used in combination. The addition amount of the water-soluble organic solvent in the ink composition is 1% by mass to 60% by mass in total, and preferably 2% by mass to 35% by mass.

<< (g) Surfactant >>
A surfactant can be added to the ink composition of the present invention.
As surfactants preferably used, anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, Nonionic surfactants such as polyoxyethylene / polyoxypropylene block copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts. In particular, an anionic surfactant and a nonionic surfactant can be preferably used.

In the present invention, a polymer surfactant can also be used, and the following water-soluble resins are mentioned as preferred polymer surfactants. As the water-soluble resin, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid copolymer, styrene-maleic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid copolymer are preferably used. Polymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-methacrylic acid copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer Etc.
In the present invention, a silicone-based surfactant having a polyalkylsiloxane and a fluorine-based surfactant having a fluorinated alkyl group can also be preferably used.

  The addition amount of the surfactant in the ink composition of the present invention is preferably 0.1% by mass or more and 2% by mass or less with respect to the mass of the ink. The content is particularly preferably 5% by mass or less.

<< (h) Aqueous polymer >>
An aqueous polymer having a structure different from that of the specific polymer compound can be added to the ink composition of the present invention.
Preferred examples of the aqueous polymer include proteins such as gelatin, casein, or albumin, natural rubbers such as gum arabic or tragacanth, glucosides such as saponin, alginic acid and propylene glycol alginate, triethanolamine alginate, or alginic acid. Alginic acid derivatives such as ammonium, cellulose derivatives such as methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, or ethylhydroxylcellulose, polyvinyl alcohols, polyvinylpyrrolidones, polyacrylic acid, acrylic acid-acrylonitrile copolymer, potassium acrylate-acrylic Nitrile copolymer, vinyl acetate-acrylic ester copolymer, or acrylic acid-acrylic Acrylic resins such as ester copolymers, styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid-acrylic acid ester copolymers, styrene-α-methylstyrene-acrylic acid copolymers Or styrene acrylic resin such as styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymer, styrene-maleic acid copolymer, styrene-maleic anhydride copolymer, vinylnaphthalene-acrylic acid copolymer , Vinyl naphthalene-maleic acid copolymer, and vinyl acetate-ethylene copolymer, vinyl acetate-fatty acid vinyl ethylene copolymer, vinyl acetate-maleic acid ester copolymer, vinyl acetate-crotonic acid copolymer, vinyl acetate -Vinyl acetate copolymers such as acrylic acid copolymers and their salts And the like.

<< (i) Sensitizing dye >>
In the present invention, a known sensitizing dye can be used in combination, and a sensitizing dye is preferably used in combination.
As the sensitizing dye to be applied to the present invention, those that dissolve 0.5% by mass or more at room temperature are preferable in distilled water, and those that dissolve 1% by mass or more are more preferable. Those that dissolve 3% by mass or more are particularly preferable.
Further, as the sensitizing dye, a photopolymerization initiator in which a water-insoluble polymerization initiator is dispersed can also be used.

  Examples of known sensitizing dyes that can be used in combination include N- [2-hydroxy-3- (3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy) propyl] -N, N, N. -Trimethylaluminum chloride, benzophenone, thioxanthone, anthraquinone derivatives and 3-acylcoumarin derivatives, terphenyl, styryl ketone and 3- (aroylmethylene) thiazoline, camphorquinone, eosin, rhodamine and erythrosine, and their modified forms And dispersions thereof. Moreover, the compound represented by the general formula (i) described in JP-A 2010-24276 and the compound represented by the general formula (I) described in JP-A-6-107718 can also be suitably used. .

  In addition to the components described above, the ink composition of the present invention has an object of improving ejection stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performances as necessary. Depending on the type, various known additives such as viscosity modifiers, surface tension modifiers, specific resistance modifiers, film forming agents, dispersants, surfactants, ultraviolet absorbers, antioxidants, anti-fading agents, A dusting agent, a rust preventive, a solid wetting agent, silica fine particles and the like can be appropriately selected and used. For example, oil droplet fine particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicon oil, and the like 74193, 57-87988 and 62-261476, JP-A-57-74192, 57-87989, 60-72785, 61 No. 146591, JP-A-1-95091 and JP-A-3-13376, etc., anti-fading agents, JP-A-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-61-228771 Examples thereof include fluorescent brighteners and pH adjusters such as sulfuric acid, phosphoric acid, citric acid, sodium hydroxide, potassium hydroxide, and potassium carbonate described in JP-A-4-219266.

<Method for Preparing Ink Composition>
The method for preparing the ink composition of the present invention is not particularly limited, and each component is mixed with a container drive medium mill such as a ball mill, a centrifugal mill or a planetary ball mill, a high-speed rotating mill such as a sand mill, or a medium agitation such as a stirring tank mill. It can be prepared by stirring, mixing and dispersing with a simple disperser such as a mill or a disper. About the addition order of each component, it is arbitrary. Preferably, the azo pigment, the polymer dispersant and the organic solvent are premixed and then subjected to a dispersion treatment, and the obtained dispersion is mixed with the resin and the organic solvent. In this case, at the time of addition or after addition, the mixture is uniformly mixed with a simple agitator such as a three-one motor, a magnetic stirrer, a disper, or a homogenizer. You may mix using mixers, such as a line mixer. Further, in order to make the dispersed particles finer, they may be mixed using a dispersing machine such as a bead mill or a high-pressure jet mill. Depending on the type of pigment or polymer dispersant, a resin may be added during premixing before pigment dispersion.

  The ink composition of the present invention preferably has a surface tension at 25 ° C. of 20 mN / m to 40 mN / m. The surface tension is measured under the condition of 25 ° C. using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

  The viscosity of the ink composition of the present invention is preferably 1 mPa · s to 40 mPa · s, and more preferably 3 mPa · s to 30 mPa · s. The viscosity of the ink composition is measured under conditions of 25 ° C. using VISCOMETER TV-22 (manufactured by TOKI SANGYOCO. LTD).

The pH of the ink composition of the present invention is preferably 5.0 to 10.0, and more preferably 7.0 to 9.5.
The ink composition of the present invention containing the specific polymer compound can exhibit excellent storage stability even when prepared at a high pH.

  The ink composition after preparation may be filtered using a filter as necessary. A filter having a pore diameter of about 1 μm to 10 μm can be used.

[Image forming method]
The image forming method of the present invention includes an ink applying step of applying the ink composition of the present invention onto a recording medium, and an irradiation step of irradiating the applied ink composition with active energy rays. By performing these steps, an image of the ink composition fixed on the recording medium is formed.

(Ink application process)
Hereinafter, the ink application process in the image forming method of the present invention will be described.
The ink application process in the present invention is not limited as long as it is a process of applying the ink composition of the present invention onto a recording medium.

  As an embodiment of applying the ink composition of the present invention on a recording medium, an embodiment of applying an ink composition by an inkjet method onto a recording medium is particularly preferable.

  In the image forming method of the present invention, the ink jet recording apparatus used when the ink applying process ink jet method is applied is not particularly limited, and a known ink jet recording apparatus capable of achieving a target resolution is arbitrarily selected. Can be used. That is, any known inkjet recording apparatus including a commercially available product can discharge the ink composition onto the recording medium in the image forming method of the present invention.

Examples of the ink jet recording apparatus that can be used in the present invention include an apparatus including an ink supply system, a temperature sensor, and a heating unit.
The ink supply system includes, for example, an original tank containing the ink composition of the present invention, a supply pipe, an ink supply tank immediately before the inkjet head, a filter, and a piezo-type inkjet head. The piezo-type inkjet head preferably has a multi-size dot of 1 to 100 pl, more preferably 8 to 30 pl, preferably 320 × 320 to 4,000 × 4,000 dpi (dot per inch), more preferably 400 × 400. ˜1,600 × 1,600 dpi, more preferably 720 × 720 dpi. The dpi referred to in the present invention represents the number of dots per 2.54 cm (1 inch).

In the ink application step, it is desirable that the discharged ink composition has a constant temperature. Therefore, the ink jet recording apparatus preferably includes a means for stabilizing the ink composition temperature. The parts to be kept at a constant temperature are all the piping systems and members from the ink tank (intermediate tank if there is an intermediate tank) to the nozzle ejection surface. That is, heat insulation and heating can be performed from the ink supply tank to the inkjet head portion.
The temperature control method is not particularly limited, but for example, it is preferable to provide a plurality of temperature sensors in each piping portion and perform heating control according to the flow rate of the ink composition and the environmental temperature. The temperature sensor can be provided near the ink supply tank and the nozzle of the inkjet head. Moreover, it is preferable that the head unit to be heated is thermally shielded or insulated so that the apparatus main body is not affected by the temperature from the outside air. In order to shorten the printer start-up time required for heating or to reduce the loss of thermal energy, it is preferable to insulate from other parts and reduce the heat capacity of the entire heating unit.

  The ink composition is discharged using the above-described ink jet recording apparatus. The ink composition is preferably heated to 25 to 80 ° C., more preferably 25 to 50 ° C., and the viscosity of the ink composition is preferably 3 to 15 mPa. It is preferable to carry out after lowering to s, more preferably 3 to 13 mPa · s. In particular, it is preferable to use an ink composition having a viscosity of 50 mPa · s or less at 25 ° C. as the ink composition of the present invention, since it can be discharged satisfactorily. By using this method, high ejection stability can be realized.

  The temperature of the ink composition during ejection is preferably constant, and the control range of the temperature of the ink composition is more preferably ± 5 ° C. of the set temperature, more preferably ± 2 ° C. of the set temperature, and most preferably set. A temperature of ± 1 ° C. is appropriate.

  In the present invention, the recording medium is not particularly limited, and a known recording medium can be used as a support or a recording material. Examples of the recording medium include paper, paper laminated with plastic (eg, polyethylene, polypropylene, polystyrene, etc.), metal plate (eg, aluminum, zinc, copper, etc.), plastic film (eg, polyvinyl chloride resin, two Cellulose acetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, polyvinyl acetal, etc.), paper or plastic laminated or vapor-deposited with the above metals A film etc. are mentioned. Among them, since the ink composition of the present invention is excellent in adhesion, it can be suitably used for a non-absorbent recording medium as a recording medium, and a plastic substrate such as polyvinyl chloride, polyethylene terephthalate, polyethylene is preferable, A polyvinyl chloride resin base material is more preferable, and a polyvinyl chloride resin sheet or film is more preferable.

(Irradiation process)
Hereinafter, the irradiation step in the image forming method of the present invention will be described.
The irradiation step in the present invention is not limited as long as it is a step of irradiating the ink composition applied on the recording medium with active energy rays.
By irradiating the ink composition of the present invention with active energy rays, radicals are generated from the photopolymerization initiator, and a vinyl group having a partial structure represented by the general formula (1) in the specific polymer compound or an arbitrary component As a result, polymerization of the ethylenically unsaturated bond site of the polymerizable compound contained in the polymer progresses, the ink is cured, and the water resistance of the printed matter can be improved.

  Examples of active energy rays that can be used in the irradiation step include ultraviolet rays (hereinafter also referred to as UV light), visible light glands, electron beams, and the like, and it is preferable to use UV light.

  Although the peak wavelength of UV light depends on the absorption characteristics of the sensitizing dye used as necessary, it is preferably, for example, 200 nm to 405 nm, more preferably 220 nm to 390 nm, and 220 nm to 350 nm. More preferably.

UV light is the illumination intensity on the exposed surface is, for example, preferably from the ^{10mW / cm 2 ~2,000mW / cm 2} , more preferably irradiated with ^{20mW / cm 2 ~1,000mW / cm 2} .

  As the UV light source, a mercury lamp, a gas / solid laser or the like is mainly used, and a mercury lamp, a metal halide lamp and a UV fluorescent lamp are widely known. In addition, replacement with GaN-based semiconductor ultraviolet light-emitting devices is very useful industrially and environmentally. LED (UV-LED) and LD (UV-LD) are small, have long life, high efficiency, and low cost. Yes, it is expected as a UV light source. In the present invention, when a sensitizing dye and a photopolymerization initiator are used in combination, a metal halide lamp, a high pressure mercury lamp, a medium pressure mercury lamp, a low pressure mercury lamp, and a UV-LED are preferable, and a sensitizing dye and a photopolymerization initiator are used in combination. If not, a metal halide lamp, medium pressure mercury lamp or low pressure mercury lamp is preferred.

In the irradiation step, the ink composition of the present invention applied on the recording medium is irradiated with such UV light, for example, for 0.01 seconds to 120 seconds, preferably 0.1 seconds to 90 seconds. It is preferable.
As the irradiation conditions and the basic irradiation method, the irradiation conditions and irradiation method disclosed in JP-A-60-132767 can be similarly applied to the present invention. Specifically, a light source is provided on both sides of the head unit including the ink ejection device, and the head unit and the light source are scanned by a so-called shuttle method, or another light source that is not driven and driven is used. Is preferred. The irradiation with the active energy ray is performed after a certain period of time (for example, 0.01 seconds to 120 seconds, preferably 0.01 seconds to 60 seconds) after ink landing and thermal fixing.

(Heat drying process)
The image forming method of the present invention preferably further includes a heat drying step after the ink application step and before the irradiation step.
In the drying step, (c) water and / or (f) water-soluble organic solvent contained in the ink composition applied onto the recording medium is removed by heating and dried.
In the drying process, the ink composition discharged onto the recording medium is removed by evaporating water and the water-soluble organic solvent used in combination as necessary, and dried by heating and fixed. Is preferred.

A process of heating and drying and fixing the discharged ink composition of the present invention (heat drying process) will be described.
The heating means is not limited as long as it can dry water and a water-soluble organic solvent used in combination as required, but a heat drum, hot air, an infrared lamp, a heat oven, a heat plate heating or the like is used. Can do.
The heating temperature is preferably 40 ° C or higher, more preferably about 40 ° C to 150 ° C, and still more preferably about 40 ° C to 80 ° C. The drying / heating time can be appropriately set in consideration of the composition and printing speed of the ink composition to be used.

  The ink composition fixed by heating is irradiated with active energy rays in the irradiation step, and is further photofixed. As described above, in the irradiation step, fixing with UV light is preferable.

[Printed matter]
The printed matter of the present invention is recorded by the image forming method of the present invention. Since the printed matter of the present invention is a printed matter recorded by the image forming method of the present invention, it becomes a printed matter excellent in water resistance of the recorded image and adhesion to the recording medium.

  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.

  First, matters relating to the preparation of the colorant (pigment) dispersion used in the examples and comparative examples and the details of each component contained in the ink composition are shown below.

[Preparation of Colorant Dispersion A]
<Synthesis of Polymer Dispersant E-1>
To a 500 ml three-necked flask equipped with a stirrer and a condenser tube, 44 g of methyl ethyl ketone was added and heated to 72 ° C. in a nitrogen atmosphere. Here, 25 g of methyl ethyl ketone was mixed with 0.43 g of dimethyl 2,2′-azobisisobutyrate and benzyl methacrylate. A solution in which 30 g, 5 g of methacrylic acid and 15 g of methyl methacrylate were dissolved was dropped over 3 hours. After completion of the dropwise addition, the mixture was further reacted for 1 hour, and then a solution of 0.21 g of dimethyl 2,2′-azobisisobutyrate dissolved in 1 g of methyl ethyl ketone was added, heated to 78 ° C. and heated for 4 hours. The obtained reaction solution was reprecipitated twice in a large excess amount of hexane, and the precipitated resin was dried to obtain 43 g of polymer dispersant E-1. In addition, the reagent made from Wako Pure Chemical Industries Ltd. was used for the reagent used in the present Example unless otherwise specified.
The composition of the obtained polymer dispersant E-1 was confirmed by ¹ H-NMR, and the weight average molecular weight (Mw) determined by GPC was 42,000. Furthermore, when the acid value was calculated | required by the method as described in JIS specification (JISK0070: 1992), it was 65.4 mgKOH / g.

<Preparation of resin-coated cyan pigment dispersion>
C. I. Pigment Blue 15: 3 (phthalocyanine blue A220, manufactured by Dainichi Seika Co., Ltd.), 5 parts of the above polymer dispersant E-1, 42 parts of methyl ethyl ketone, 5.5 parts of 1 mol / L NaOH aqueous solution, Then, 87.2 parts of ion-exchanged water was mixed and dispersed with a bead mill for 4 hours using 0.1 mmφ zirconia beads.
Methyl ethyl ketone was removed from the obtained dispersion at 55 ° C. under reduced pressure, and a part of the water was further removed to obtain a colorant dispersion A which is a dispersion of a cyan pigment coated with a resin (pigment concentration). : 10.2% by mass).

[Synthesis of specific polymer compounds]
<Synthesis of Specific Polymer Compound P-1>
After dissolving 20 g of polyacrylic acid having a weight average molecular weight of 5000 in 100 g of N-methylpyrrolidone in a 200 ml three-necked flask equipped with a stirrer and a condenser, 32.1 g of potassium carbonate was added and heated to 50 ° C. To this, 28.0 g of chloromethylstyrene (m-form, p-form mixture, trade name: CMS-P, manufactured by AGC Seimi Chemical Co., Ltd.) was added and stirred for 5 hours. The obtained polymer was reprecipitated twice in a mixed solution of 2000 g of hexane and 400 g of isopropyl alcohol, and the polymer was dried to obtain 30.2 g of the specific polymer compound P-1.
About the obtained specific polymer compound P-1, the weight average molecular weight (Mw) calculated | required by GPC was 5500, and the composition ratio calculated by 1H NMR was a / b = 75/25 mass%.

<Synthesis of Specific Polymer Compound P-2>
10 g of isopropyl alcohol was placed in a nitrogen-substituted 200 ml three-necked flask equipped with a stirrer and a condenser, and heated to 70 ° C. under a nitrogen stream. After heating for 10 minutes, 20 g of methyl methacrylate, 45.5 g of methacrylic acid, 0.81 g of 3-mercaptopropionic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.3 g of 2,2′-azobisdimethylvaleronitrile, 80 g of isopropyl alcohol Was added dropwise over 2 hours. After completion of dropping, the mixture was stirred for 1 hour, 0.2 g of 2,2′-azobisdimethylvaleronitrile was added, and after further reaction for 2 hours, 50 g of acetone was added to the polymer solution. The obtained polymer solution was reprecipitated in 5 L of hexane to obtain a methyl methacrylate / methacrylic acid copolymer. After 20 g of the obtained methyl methacrylate / methacrylic acid copolymer was dissolved in 100 g of N-methylpyrrolidone, 15.1 g of potassium carbonate was added and heated to 50 ° C. To this was added 16.6 g of chloromethylstyrene (m-form, p-form mixture, trade name CMS-P, manufactured by AGC Seimi Chemical Co., Ltd.) and stirred for 5 hours. The obtained polymer was reprecipitated twice in a mixed solution of 2000 g of hexane and 400 g of isopropyl alcohol, and the polymer was dried to obtain 30.2 g of the specific polymer compound P-2.
With respect to the obtained specific polymer compound P-2, the weight average molecular weight (Mw) determined by GPC was 24500, and the composition ratio calculated by 1H NMR was a / b / c = 21/43/46% by mass. It was.

<Synthesis of Specific Polymer Compound P-3>
To a 200 ml three-necked flask equipped with a stirrer and a condenser, 10 g of polyacrylic acid having a weight average molecular weight of 5000 and 100 g of isopropyl alcohol were added and dissolved by heating at 50 ° C. After adding 4.6 g of sodium hydroxide to this solution, 15.5 g of vinylbenzyl glycidyl ether (trade name: VBGE, manufactured by AGC Seimi Chemical Co., Ltd.) was added and stirred at 60 ° C. for 4 hours. The obtained reaction solution was reprecipitated twice in 2000 g of hexane, and the polymer was dried to obtain 23 g of the specific polymer compound P-3.
With respect to the obtained specific polymer compound P-3, the weight average molecular weight (Mw) determined by GPC was 6100, and the composition ratio calculated by 1H NMR was a / b = 68/32 mass%.

<Synthesis of Specific Polymer Compound P-4>
10 g of isopropyl alcohol was placed in a nitrogen-substituted 200 ml three-necked flask equipped with a stirrer and a condenser, and heated to 70 ° C. under a nitrogen stream. After heating for 10 minutes, 36 g of 2-hydroxyethyl methacrylate, 64 g of methacrylic acid, 1.55 g of dodecyl mercaptan (manufactured by Wako Pure Chemical Industries, Ltd.), 0.38 g of 2,2′-azobisdimethylvaleronitrile, 150 g of isopropyl alcohol The mixed solution was added dropwise over 2 hours. After completion of the dropwise addition, the mixture was stirred for 1 hour, 0.2 g of 2,2′-azobisdimethylvaleronitrile was added, and after further reaction for 2 hours, 200 g of acetone was added to the polymer solution. The obtained polymer solution was reprecipitated in 10 L of hexane to obtain a 2-hydroxyethyl methacrylate / methacrylic acid copolymer. 20 g of 2-hydroxyethyl methacrylate / methacrylic acid copolymer and 100 g of isopropyl alcohol were added to a 200 ml three-necked flask equipped with a stirrer and a condenser, and dissolved by heating at 50 ° C. After adding 5.9 g of sodium hydroxide to this solution, 12.5 g of vinylbenzyl glycidyl ether was added and stirred at 60 ° C. for 4 hours. The obtained reaction solution was reprecipitated twice in 2000 g of hexane, and the polymer was dried to obtain 22 g of the specific polymer compound P-4.
With respect to the obtained specific polymer compound P-4, the weight average molecular weight (Mw) determined by GPC was 14300, and the composition ratio calculated by 1H NMR was a / b / c = 50/20/20% by mass. It was.

<Synthesis of Comparative Polymer Compound B-1>
By applying the synthesis of the specific polymer compound P-3, the comparative polymer compound B-1 was synthesized as follows. That is, for the introduction of the acryloyl group, 4-hydroxybutyl acrylate glycidyl ether (trade name: 4HBAGE, manufactured by Nippon Kasei Co., Ltd.) is used instead of the vinyl benzyl glycidyl ether used for the synthesis of the specific polymer compound P-3. It was.
With respect to the obtained comparative polymer compound B-1, the weight average molecular weight (Mw) determined by GPC was 6300, and the composition ratio calculated by 1H NMR was a / b = 26/74% by mass.

Details of each component (component shown in Table 1 below) used in each ink composition of Examples and Comparative Examples are shown below.
(A) Specific polymer compound: Specific polymer compounds P-1, P-2, P-3, and P-4 (compounds having the structure described above)
Comparative polymer compound: Comparative polymer compound B-1 (compound having the structure described above)
(B) Photopolymerization initiator: Irgacure 2959 (trade name, manufactured by BASF Japan Ltd.), 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propane-1 -ON)
-(C) Water: Distilled water-(d) Color material: C dispersion-(e) Polymerizable compound: Methylenebisacrylamide (manufactured by Tokyo Chemical Industry Co., Ltd.)
(F) Water-soluble organic solvent: 2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.)
(G) Surfactant: ZONYL FNS (registered trademark, fluorosurfactant, manufactured by Aldrich Japan)

[Examples 1 to 7, Comparative Example 1]
<Preparation of ink composition>
Each component having the composition shown in Table 1 below was stirred at 2500 rpm using a mixer (Silverson L4R) to prepare a crude ink composition. Each obtained crude ink composition is packed into a plastic disposable syringe and filtered through a polyvinylidene fluoride (PVDF) pore size 5 μm filter (Millex-SV, Millipore, diameter 25 mm) to obtain a finished product. Ink compositions of Examples 1 to 7 and Comparative Example 1 were obtained.
In Table 1, the column for water shows the amount of water added in the preparation of the ink composition in the left column, and the total content of water contained in the prepared ink composition in the right column. It was.

The viscosity of the ink compositions obtained in Examples 1 to 7 was measured under the condition of 25 ° C. using VISCOMATE VM-10A-L (manufactured by CMC Materials Co., Ltd.). The viscosity of the ink composition was in the range of 3.0 mPa · s to 8.5 mPa · s.
The surface tensions of the ink compositions obtained in Examples 1 to 7 were measured under conditions of 25 ° C. using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.). The surface tension of each ink composition was in the range of 22.0 mN / m to 27.0 mN / m.
Further, the pH of the obtained ink composition was in the range of 7.5 to 9.1.

<Evaluation>
The obtained ink compositions of Examples and Comparative Examples were used as No. of K hand coater K hand coater manufactured by RK PRINT COAT INSTRUMENTS. Using 2 bars, an 8 cm square vinyl chloride sheet (Avery 400 GLOSS WHITE PERMANENT, manufactured by Avery Dennison Co., Ltd.) was applied to a thickness of 12 μm, and then the moisture was dried at 60 ° C. for 3 minutes to obtain a coating film.
Using the obtained coating film, the following curability and water resistance were evaluated.
Furthermore, the storage stability and ejection property shown below were evaluated using the obtained ink compositions of Examples and Comparative Examples.

(1) Curability evaluation The coating film obtained above was exposed with the low-pressure mercury lamp on the conditions which become an energy of 700 mJ / cm < ² >, and the cured film was obtained. About the cured film after exposure, the stickiness of the film surface was evaluated by palpation. When the stickiness remained, the exposure was repeated until the stickiness disappeared, and the curability was evaluated by the exposure amount until the stickiness disappeared. The evaluation results are shown in Table 1.
-Evaluation criteria-
A: No stickiness after one exposure.
B: No stickiness after 2 to 3 exposures.
C: No stickiness after 4 to 5 exposures.
D: Stickiness does not disappear even after 6 or more exposures.
Note that the evaluation ranks A and B are levels that have no practical problem.

(2) Water resistance evaluation The coating film obtained above was exposed with a low-pressure mercury lamp under the condition of an energy of 1500 mJ / cm ² to obtain a printed material having a solid image with an average film thickness of 2 µm. The surface of the obtained printed matter was rubbed with a cotton swab impregnated with water, and the density of the image was visually confirmed and evaluated according to the following criteria. The evaluation results are shown in Table 1.
-Evaluation criteria-
A: No change was observed in the image even after rubbing 20 times or more.
B: Image density decreased after 10 to 19 rubbing.
C: The image density decreased after rubbing 2 to 9 times.
D: Image density was significantly reduced by just rubbing once.
In addition, evaluation rank A-B is a level which is satisfactory practically.

(3) Storage stability Each ink composition of the obtained Examples and Comparative Examples was heated at 60 ° C. for 72 hours.
The ink storage stability was evaluated by performing curability evaluation using the same evaluation method and evaluation criteria as in the above “(1) Curability evaluation” using each heated ink composition. In addition, in a compound in which a polymerizable group is decomposed by hydrolysis or the like, curability is lowered. The evaluation results are shown in Table 1.

(4) Evaluation of ejectability A commercially available inkjet printer (SP-300V manufactured by Roland DG Inc.) was prepared as an inkjet recording apparatus. Each obtained ink composition was loaded into the inkjet printer, and ejected from a head for 30 minutes onto a vinyl chloride sheet (AVERY 400 GLOSS WHITE PERMANENT, manufactured by Avery Dennison), and a solid image and fine lines were recorded. After stopping the discharge, the obtained image was left for 5 minutes. Thereafter, the solid image and the image (5 cm × 5 cm) obtained by recording the thin line were observed again. The observed images were visually evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1.
-Evaluation criteria-
A: The occurrence of missing dots due to the occurrence of missing or the like was not recognized, and a good image was obtained.
B: Although the occurrence of missing dots due to the occurrence of omission was slightly observed, it was of a level that would not cause any practical problems.
C: The image lacked practical use due to the occurrence of missing dots due to the occurrence of omission.
Note that the evaluation ranks A and B are levels that have no practical problem.

As shown in Table 1, it can be seen that the ink compositions of the respective examples containing the specific polymer compound have excellent effects on curability and water resistance. Furthermore, the ink compositions of the respective examples maintained the same high curability as that after the ink preparation even after being stored under high temperature conditions. This is considered to be because the decomposition is suppressed by hydrolysis of the polymerizable group present in the ink composition. Moreover, it turns out that the ink composition of each Example is excellent also in the discharge property when it applies for inkjet recording.
Further, even when a polymerizable compound was used in combination as in the ink composition of Example 5, high curability was obtained.
On the other hand, the ink composition of Comparative Example 1 containing the comparative polymer compound B-1 is inferior in water resistance, has low curability after storage under high temperature conditions, and is inferior in storage stability. there were. In addition, the ink composition of Comparative Example 1 was inferior in terms of ejection properties when applied to inkjet recording.

Claims (14)

An ink composition for inkjet recording , comprising at least (a) a polymer compound having a repeating unit containing a partial structure represented by the following general formula (1), (b) a photopolymerization initiator, and (c) water.

(In general formula (1), R ¹ represents an alkyl group having 1 to 4 carbon atoms, and n1 represents an integer of 0 to 2. * represents a connecting position with an adjacent site.)   The ink composition according to claim 1, wherein the polymer compound having a repeating unit including the partial structure represented by the general formula (1) further includes a hydrophilic group.   3. The ink composition according to claim 1, wherein a weight average molecular weight of the polymer compound having a repeating unit including the partial structure represented by the general formula (1) is in the range of 3000 to 60000. 4. .   (A) The polymer compound having a repeating unit containing a partial structure represented by the general formula (1) is at least one selected from alcoholic hydroxyl groups, alkyl-substituted carbamoyl groups, carboxyl groups, sulfo groups, and salts thereof. The ink composition according to any one of claims 1 to 3, which has a repeating unit containing two hydrophilic groups.   The ink composition according to any one of claims 1 to 4, further comprising (d) a color material. 6. The ink composition according to claim 1, wherein the content of the water (c) is in the range of 10% by mass to 80% by mass with respect to the total mass of the ink composition.   The ink composition according to claim 6, wherein the content of (c) water is in the range of 40% by mass to 80% by mass with respect to the total mass of the ink composition. Wherein (a) a polymer compound having a repeating unit containing a partial structure represented by the general formula (1) is any one of claims 1 to 7 containing a repeating unit represented by the following general formula (2) 2. The ink composition according to item 1.

(In General Formula (2), R ² represents a hydrogen atom or a methyl group, L represents a methylene group, a phenylene group, —COO—, or —CONH—. J represents a single bond or a carbon number of 1; 8 represents an alkylene group, and the alkylene group may include an ether bond, an ester bond, a urethane bond, a ureylene bond, or a quaternary ammonium group in the alkyl chain, and the alkyl group or hydroxyl group having 1 to 4 carbon atoms. R ³ represents an alkyl group having 1 to 4 carbon atoms, and n2 represents an integer of 0 to 2.)   The ink composition according to any one of claims 1 to 8, wherein the (b) photopolymerization initiator is a water-soluble photopolymerization initiator. The ink composition according to any one of claims 1 to 9 , further comprising (e) a polymerizable compound. The ink composition according to any one of claims 1 to 10 , further comprising (f) a water-soluble organic solvent. An ink application step of applying the ink composition according to any one of claims 1 to 11 onto a recording medium by an inkjet method, and irradiating the ink composition applied onto the recording medium with active energy rays And an irradiating step. An ink application step of applying the ink composition according to any one of claims 1 to 11 onto a recording medium by an inkjet method , and the ink composition applied to the recording medium (c) The image formation according to claim 12 , comprising: a drying step in which water) and / or (f) a water-soluble organic solvent is removed by heating and drying; and an irradiation step in which the ink composition is irradiated with active energy rays. Method. An image formed by the ink composition according to any one of claims 1 to 11 or an image recorded by the image forming method according to claim 12 or 13 on a recording medium. Prints that have.