JP2007277354A - Water-based ink composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based ink composition excellent in color development and suppressing bronze phenomena without damaging gloss of prints. <P>SOLUTION: The water-based ink composition comprises at least a chromatic color pigment covered with a water-insoluble vinyl polymer, a titanium dioxide pigment, 2-methyl-2-propyl-1,3-propanediol and water. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

Background of the Invention

FIELD OF THE INVENTION The present invention relates to an aqueous ink composition, and more specifically, a phenomenon in which the color of a light source reflected in chromatic ink is different from the color of the light source (bronze phenomenon) without impairing the glossiness of the printed matter. ).

BACKGROUND ART Conventionally, water-based inks in which colorants composed of dyes and pigments are dispersed in water have been provided as ink compositions. In such an aqueous ink, it is generally performed to disperse a colorant in an aqueous dispersion medium using a dispersing agent such as a surfactant or a polymer dispersing agent. Proposals have been made.

  Japanese Unexamined Patent Application Publication No. 2004-75988 proposes a pigment ink capable of printing with high color development and excellent glossiness by using an aqueous dispersion of water-insoluble vinyl polymer fine particles (Patent Document 1). Japanese Patent Application Laid-Open No. 2004-124081 discloses C.I. I. By using an aqueous dispersion of water-insoluble vinyl polymer fine particles containing Pigment Blue 15: 4, a pigment ink has been proposed that enables high-print density printing and excellent color tone angle dependency (Patent Document 2). ).

  In addition, as an example in which a titanium dioxide pigment and a pigment as a colorant are used in the ink composition, JP-A-6-287492 discloses an ink containing titanium dioxide having a hydrophilic surface and carbon black. It has been disclosed that stable ejection can be performed when applied to an ink jet printer, and a good print density can be obtained even when printing on plain paper (Patent Document 3).

  Japanese Patent Application Laid-Open No. 2002-249585 discloses a still image display ink such as a whiteboard that contains a pigment of one color of yellow, magenta, cyan, or black and titanium oxide as an inorganic oxide. It is disclosed that a fine image can be formed easily and can be easily erased (Patent Document 4).

  Further, JP-A-8-319442 discloses a necessary recording in a state in which ink is applied on a recording medium, or in a state where a fixing process is performed if necessary, and in a state where a cleaning process is performed. It is disclosed that an ink-jet ink composition using fine particles (titanium oxide or the like) that does not affect color can form a clear image with little ink bleeding on a recording medium (patent) Reference 5).

  Furthermore, JP-A-2005-179482 discloses an ink composition in which titanium dioxide and a chromatic pigment are prepared so that the weight ratio thereof is 0.6 or more in order to suppress the bronze phenomenon and the flip-flop phenomenon. The thing is disclosed (patent document 6).

  On the other hand, the conventional ink composition containing a titanium dioxide pigment still has room for improvement in terms of suppressing the bronze phenomenon. This bronze phenomenon is particularly remarkable in a cyan ink composition, and an improvement thereof is desired.

However, the ink compositions using the aqueous dispersions of Patent Documents 1 and 2 are excellent in color developability, but are insufficient for suppressing the bronze phenomenon. In addition, none of the above Patent Documents 3 to 5 discloses or suggests the bronze phenomenon. Furthermore, although the ink composition disclosed in Patent Document 6 suppresses the bronze phenomenon, the glossiness of the printed matter sometimes deteriorates as the titanium dioxide concentration in the ink composition increases. That is, when the titanium dioxide concentration increases, it is necessary to increase the titanium dioxide concentration in order to suppress the bronze phenomenon. As a result, when the content of the chromatic pigment exceeds about 3% by weight, the accompanying increase in the dioxide dioxide. In some cases, the gloss of the printed material was significantly deteriorated due to the influence of titanium. In addition, with an increase in the titanium dioxide concentration, titanium dioxide may cause clogging of the nozzles of the ink jet printer, or the dispersion resin may agglomerate to significantly impair the gloss.
JP 2004-75988 A JP 2004-124081 A JP-A-6-287492 Japanese Patent Laid-Open No. 2002-249585 JP-A-8-319442 JP 2005-179482 A

Summary of the Invention

  The inventors of the present invention have recently developed a combination of a chromatic color pigment coated with a water-insoluble vinyl polymer, a titanium dioxide pigment, and a specific alcohol in an ink, thereby providing excellent color developability and a printed material. It was found that the bronzing phenomenon can be suppressed without impairing the gloss. The present invention is based on this finding.

  Accordingly, an object of the present invention is to provide an aqueous ink composition that has excellent color developability and can suppress the bronzing phenomenon without impairing the gloss of the printed matter.

  The aqueous ink composition according to the present invention contains at least a chromatic pigment coated with a water-insoluble vinyl polymer, a titanium dioxide pigment, 2-methyl-2-propyl-1,3-propanediol, and water. It is what.

  ADVANTAGE OF THE INVENTION According to this invention, the water-based ink composition which can suppress a bronze phenomenon can be implement | achieved, without impairing the gloss of printed matter.

Detailed description of the invention

  The aqueous ink composition according to the present invention comprises at least a chromatic pigment coated with a water-insoluble vinyl polymer, a titanium dioxide pigment, 2-methyl-2-propyl-1,3-propanediol, and water. Each component constituting the water-based ink composition will be described below.

<Water-insoluble vinyl polymer>
The water-insoluble vinyl polymer used in the water-based ink composition according to the present invention is used for coating chromatic pigments. By coating the chromatic pigment, the dispersibility of the pigment in the ink can be improved, and the gloss of the printed matter can be improved.

  Examples of such a water-insoluble vinyl polymer include (1) macromer, (2) polyoxyalkylene group-containing monomer, (3) salt-forming group-containing monomer, (4) macromer, polyoxyalkylene group-containing monomer, and A monomer copolymerizable with each of the salt-forming group-containing monomers (hereinafter also simply referred to as a copolymerizable monomer) is preferably copolymerized.

  More preferably, (1) macromer 0.1 to 40% by weight, (2) polyoxyalkylene group-containing monomer 5 to 50% by weight, (3) salt-forming group-containing monomer 3 to 40% by weight, (4 A polymer obtained by polymerizing a monomer containing 15 to 90% by weight of a copolymerizable monomer is preferably used.

  As a typical example of a macromer which is one of raw materials for synthesis of a water-insoluble vinyl polymer, it has a polymerizable functional group at one end (hereinafter referred to as “one end”), preferably a number average molecular weight of 500 to 500,000, More preferably, the macromer which is 1000-10000 is mentioned.

  Specific examples of the macromer include a styrene macromer having a polymerizable functional group at one end, a silicone macromer having a polymerizable functional group at one end, a methyl methacrylate macromer having a polymerizable functional group at one end, Examples thereof include a styrene / acrylonitrile macromer having a polymerizable functional group, a butyl acrylate macromer having a polymerizable functional group at one end, and an isobutyl methacrylate macromer having a polymerizable functional group at one end. Among these, a styrenic macromer having a polymerizable functional group at one end is preferable from the viewpoint of sufficiently containing a colorant in the vinyl polymer.

  Examples of the styrenic macromer having a polymerizable functional group at one end include a styrene homopolymer having a polymerizable functional group at one end and a copolymer of styrene and another monomer having a polymerizable functional group at one end. Can be mentioned.

  In the copolymer of styrene and another monomer having a polymerizable functional group at one end, examples of the other monomer include acrylonitrile. Further, the content of styrene is preferably 60% by weight or more, and more preferably 70% by weight or more from the viewpoint of sufficiently containing the pigment in the vinyl polymer.

  Among the styrenic macromers having a polymerizable functional group at one end, a styrenic macromer having an acryloyl group or a methacryloyl group as a polymerizable functional group at one end is preferable.

  Examples of commercially available styrenic macromers include AS-6, AS-6S, AN-6, AN-6S, HS-6S, and HS-6 manufactured by Toa Gosei Co., Ltd.

  The number average molecular weight of the macromer is measured using polystyrene as a standard substance by gel chromatography using 1 mmol / L dodecyldimethylamine-containing chloroform as a solvent.

  The content of the macromer in the water-insoluble vinyl polymer is preferably 0.1 to 40% by weight, more preferably 1 to 30% by weight from the viewpoint of water resistance and scratch resistance.

（式中、Ｒ¹は水素原子またはメチル基、Ｒ²は水素原子、炭素数１〜２０のアルキル基または炭素数１〜９のアルキルフェニル基、ｍは１〜３０の数を示す）
で表されるモノマー（以下、「モノマーＡ」と称する」、および
式（ＩＩＩ）：

（式中、Ｒ¹およびＲ²は前記と同じ。ｎは１〜３０の数を表す）
で表されるモノマー（以下、「モノマーＢ１」と称する）、
式（ＩＶ）：

（式中、Ｒ¹、Ｒ²、ｍおよびｎは前記と同じ。オキシエチレン基およびオキシプロピレン基は〔 〕内においてその順序は問わず、ランダムであってもブロックであってもよい）で表されるモノマー（以下、「モノマーＢ２」と称する）および
式（Ｖ）：

（式中、Ｒ¹、Ｒ²、ｍおよびｎは前記と同じ。オキシプロピレン基およびオキシテトラメチレン基は〔 〕内においてその順序は問わず、ランダムであってもブロックであってもよい）で表されるモノマー（以下、「モノマーＢ３」と称する）からなる群より選ばれた１種以上の前記モノマー（以下、「モノマーＢ」と称する）であるのが好ましい。 As a polyoxyalkylene group-containing monomer used as one of the raw materials for the synthesis of water-insoluble vinyl polymers, for example,
Formula (II):

(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms or an alkylphenyl group having 1 to 9 carbon atoms, m is a number of 1 to 30)
(Hereinafter referred to as “monomer A”) and formula (III):

(In the formula, R ¹ and R ² are the same as above. N represents a number of 1 to 30)
(Hereinafter referred to as “monomer B1”),
Formula (IV):

(Wherein R ¹ , R ² , m and n are the same as above. The oxyethylene group and oxypropylene group may be random or block in [] regardless of their order). Monomer (hereinafter referred to as “monomer B2”) and formula (V):

(Wherein R ¹ , R ² , m and n are the same as above. The oxypropylene group and the oxytetramethylene group may be random or block in [] regardless of their order). It is preferably one or more of the above-mentioned monomers (hereinafter referred to as “monomer B”) selected from the group consisting of represented monomers (hereinafter referred to as “monomer B3”).

  By using the monomer A in the water-insoluble vinyl polymer, there is an advantage that an aqueous ink composition excellent in gloss of printed images, ink storage stability and clogging recovery can be obtained. This is considered to be based on the fact that the hydrophilic hydrated layer of the highly hydrophilic oxyethylene group contained in the monomer A spreads in the ink composition.

  When the monomer B1 is used for the water-insoluble vinyl polymer, an ink composition having excellent ejection properties can be obtained. This is because the hydrophobic interaction between the highly hydrophobic oxypropylene group of the monomer B1 and the chromatic pigment becomes strong, so that the water-insoluble vinyl polymer exhibits a strong adsorptivity to the chromatic pigment. It is thought that this is based on the fact that the polymer particles containing the coloring pigment become more hydrophobic and as a result, the viscosity of the ink composition is lowered.

  Further, by using the monomer B2 or B3 in the water-insoluble vinyl polymer, excellent dispersion stability can be imparted to the chromatic pigment. This is considered to be based on the fact that a hydrophilic hydration layer having a highly hydrophilic oxyethylene group or oxytetramethylene group spreads in the ink composition.

  When the monomer A of the polyoxyalkylene group-containing monomer is used together with the macromer, the salt-forming group-containing monomer, and the copolymerizable monomer in a water-insoluble vinyl polymer, the resulting ink composition is plain paper There is a tendency to penetrate too much into (copy paper).

  Therefore, from the viewpoint of adjusting the permeability to plain paper and increasing the printing density, it is preferable to use monomer A and monomer B in combination with the water-insoluble vinyl polymer. In this case, the weight ratio of monomer A to monomer B (monomer A / monomer B) is preferably 1/5 to 5/1, more preferably 1/5 from the viewpoint of imparting excellent gloss and high printing density. It is preferably 3 to 3/1.

  In addition, it contains only a vinyl polymer obtained by copolymerizing a (meth) acrylic acid ester monomer containing only an oxypropylene group and a (meth) acrylic acid ester monomer containing only an oxyethylene group, and an oxypropylene group ( With vinyl polymers obtained by copolymerizing (meth) acrylate monomers and (meth) acrylate monomers containing only oxytetramethylene groups, the dispersion stability of water-insoluble polymers containing chromatic pigments can be improved. Can not. This is considered to be based on the fact that the hydrophilic hydration layer is not sufficiently spread in the ink composition.

As described above, in the formulas (II) to (V), R ¹ is a hydrogen atom or a methyl group. R ² is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an alkylphenyl group having 1 to 9 carbon atoms. Among these, an octyl group and a nonylphenyl group are preferable from the viewpoints of water resistance and scratch resistance.

  m is a number from 1 to 30. From the viewpoint of ejection properties and print density, m is preferably a number from 2 to 25. N is a number from 1 to 30. From the viewpoint of ejection properties and print density, n is preferably a number from 2 to 25.

  In the monomer B2, the oxyethylene group and the oxypropylene group are block-added or randomly added.

  In the monomer B3, the oxypropylene group and the oxytetramethylene group are block-added or randomly added.

  Typical examples of the monomer A include polyethylene glycol mono (meth) acrylate. Specific examples of the commercially available monomer A include NK esters M-20G, 40G, 90G, 230G manufactured by Shin-Nakamura Chemical Co., Ltd., Bremer PE series, PME-100, 200, manufactured by NOF Corporation. 400, 1000 etc. are mentioned.

  The content of monomer A in the vinyl polymer is from 2 to 45% by weight, preferably from 2 to 30% by weight, from the viewpoint of printing density and ink viscosity.

  Specific examples of the monomer B1 include polypropylene glycol mono (meth) acrylate.

  Specific examples of the monomer B2 include ethylene glycol / propylene glycol (meth) acrylate, poly (ethylene glycol / propylene glycol) mono (meth) acrylate, octoxypolyethylene glycol / polypropylene glycol mono (meth) acrylate, octoxypoly (ethylene glycol)・ Propylene glycol) mono (meth) acrylate, stearoxy polyethylene glycol ・ polypropylene glycol mono (meth) acrylate, stearoxy poly (ethylene glycol propylene glycol) mono (meth) acrylate, nonylphenoxy polyethylene glycol ・ polypropylene glycol mono (meth) Acrylate, nonylphenoxypoly (ethylene glycol / propylene glycol) (Meth) acrylate. These can be used alone or in admixture of two or more.

  Specific examples of the monomer B3 include propylene glycol / tetramethylene glycol mono (meth) acrylate, poly (propylene glycol / tetramethylene glycol) mono (meth) acrylate, propylene glycol / polybutylene glycol mono (meth) acrylate, poly ( And propylene glycol / butylene glycol) mono (meth) acrylate. These can be used alone or in admixture of two or more.

  Among the monomers B1 to B3, polypropylene glycol mono (meth) acrylate, ethylene glycol / propylene glycol (meth) acrylate and poly (ethylene glycol / propylene glycol) mono (meth) acrylate are preferable from the viewpoints of ink viscosity and dischargeability. .

  Examples of commercially available monomers B1 to B3 include Blemmer PP-1000, PP-500, PP-800, AP-150, AP-400, AP-550, AP-800 manufactured by NOF Corporation. 50PEP-300, 70PEP-350B, AEP series, 30PPT-800, 50PPT-800, 70PPT-800, APT series, 10PPB-500B, 10APB-500B, 50POEP-800B, 50AOEP-800B, ASEP series, PNEP series, PNPE Series, 43ANEP-500, 70ANEP-550 and the like.

  Further, the content of the monomer B in the water-insoluble vinyl polymer is preferably 5 to 45% by weight, more preferably 5 to 40% by weight, from the viewpoint of gloss of the printed matter and high print density.

  The content of the polyoxyalkylene group-containing monomer in the water-insoluble polymer is preferably 5 to 5 from the viewpoint of enhancing the ejection stability of the ink composition and the glossiness of the printed image, and preventing the color development from being reduced on plain paper. 50 wt%, more preferably 10 to 40 wt%.

  As the salt-forming group-containing monomer, an anionic monomer and a cationic monomer are preferable. Anionic monomers and cationic monomers can be used alone or in admixture of two or more.

  Examples of the anionic monomer include one or more selected from the group consisting of an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer.

  Examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid. These can be used alone or in admixture of two or more.

  Examples of unsaturated sulfonic acid monomers include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylic acid ester, bis- (3-sulfopropyl) -itaconic acid ester, and the like. Can be mentioned. These can be used alone or in admixture of two or more.

  Examples of unsaturated phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acrylic acid. And leuoxyethyl phosphate. These can be used alone or in admixture of two or more.

  Among the anionic monomers, unsaturated carboxylic acid monomers are preferable, and acrylic acid and methacrylic acid are more preferable from the viewpoints of ink viscosity and dischargeability.

  Examples of the cationic monomer include one or more selected from the group consisting of an unsaturated tertiary amine-containing vinyl monomer and an unsaturated ammonium salt-containing vinyl monomer.

  Examples of the unsaturated tertiary amine-containing monomer include N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, and N, N. -Dimethylaminopropyl (meth) acrylamide, N, N-dimethylarylamine, vinylpyrrolidone, 2-vinylpyridine, 4-vinylpyridine, 2-methyl-6-vinylpyridine, 5-ethyl-2-vinylpyridine, etc. It is done. These can be used alone or in admixture of two or more.

  Examples of unsaturated ammonium salt-containing monomers include N, N-dimethylaminoethyl (meth) acrylate quaternized product, N, N-diethylaminoethyl (meth) acrylate quaternized product, N, N-dimethylaminopropyl (meth). Examples include acrylate quaternized products. These can be used alone or in admixture of two or more.

  Among the cationic monomers, N, N-dimethylaminoethyl (meth) acrylate, NN-dimethylaminopropyl (meth) acrylamide and vinylpyrrolidone are preferable.

  The content of the salt-forming group-containing monomer in the water-insoluble vinyl polymer is 3 to 40% by weight, preferably 5 to 30% by weight, from the viewpoints of dispersion stability and ejection stability.

  Examples of the copolymerizable monomer (monomer copolymerizable with the macromer, the polyoxyalkylene group-containing monomer, and the salt-forming group-containing monomer) include, for example, a long-chain alkyl group-containing monomer, an aromatic ring-containing monomer, and (meth) Acrylic acid esters and the like can be mentioned, but among these, one or more of long-chain alkyl group-containing monomers and aromatic ring-containing monomers is used as an ink by a wetting agent or a dispersant added during the preparation of the ink composition. This is particularly preferable from the viewpoint of suppressing the viscosity change of the composition and improving the storage stability of the ink composition. These can be used alone or in admixture of two or more. The copolymerizable monomer preferably contains at least one selected from the group consisting of a long-chain alkyl group-containing monomer and an aromatic ring-containing monomer.

（式中、Ｒ¹ は水素原子または炭素数１〜４の低級アルキル基、Ｒ² はヘテロ原子を有していてもよい炭素数１６〜３０、好ましくは炭素数１８〜３０、より好ましくは炭素数１８〜２２の１価の炭化水素基を示す）で表されるモノマーが挙げられる。 In a long-chain alkyl group-containing monomer (hereinafter simply referred to as “long-chain alkyl group-containing monomer”), the carbon number of the long-chain alkyl group is preferably 16 to 30, more preferably 18 from the viewpoint of availability of the monomer. ~ 22. Representative examples of long-chain alkyl group-containing monomers include compounds of the formula (I):

(In the formula, R ¹ is a hydrogen atom or a lower alkyl group having 1 to 4 carbon atoms, R ² may have a hetero atom, and has 16 to 30 carbon atoms, preferably 18 to 30 carbon atoms, more preferably carbon atoms. And a monomer represented by a monovalent hydrocarbon group of formula 18-22.

  Specific examples of the long chain alkyl group-containing monomer include (meth) acrylic acid esters such as (iso) cetyl (meth) acrylate, (iso) stearyl (meth) acrylate, and (iso) behenyl (meth) acrylate. These can be used alone or in admixture of two or more. Among these, (iso) stearyl (meth) acrylate and / or (iso) behenyl (meth) acrylate are more preferable. The long-chain alkyl group-containing monomer is preferable from the viewpoint of suppressing a change in the viscosity of the ink composition due to a wetting agent or a dispersant added at the time of preparing the ink composition and sufficiently increasing storage stability. In this case, the total content of stearyl (meth) acrylate and behenyl (meth) acrylate in the monomer mixture is preferably 5 to 50% by weight from the viewpoint of suppressing the viscosity change of the ink composition and sufficiently enhancing the storage stability. More preferably, it is 10 to 30% by weight.

  From the viewpoint of water resistance, the aromatic ring-containing monomer is selected from styrene, vinyl naphthalene, α-methyl styrene, vinyl toluene, ethyl vinyl benzene, 4-vinyl biphenyl, 1,1-diphenyl ethylene, benzyl (meth) acrylate, phenoxyethyl ( Selected from the group consisting of (meth) acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-methacryloyloxyethyl-2-hydroxypropyl phthalate, 2-acryloyloxyethyl phthalate and neopentyl glycol acrylate benzoate 1 or more types are preferable. Among these, at least one selected from the group consisting of styrene, α-methylstyrene, vinyl toluene, and vinyl naphthalene is more preferable from the viewpoint of water resistance and scratch resistance.

  Examples of (meth) acrylic acid esters include methyl (meth) acrylate, ethyl (meth) acrylate, (iso) propyl (meth) acrylate, (iso or tertiary) butyl (meth) acrylate, (iso) amyl (meta) ) Acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, (iso) decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, (Meth) acrylic acid esters in which the ester moiety such as (iso) stearyl (meth) acrylate is an alkyl group having 1 to 18 carbon atoms are used, and these may be used alone or in combination of two or more. Can do.

  In addition, said (iso or tertiary) and (iso) mean both the case where these groups exist, and the case where it is not so, and when these groups do not exist, normal is shown.

  The content of the copolymerizable monomer in the water-insoluble vinyl polymer is 15 to 90% by weight, preferably 35 to 80% by weight, from the viewpoint of printing density and water resistance.

  When the water-insoluble vinyl polymer contains an aromatic ring-containing monomer, the content is preferably 0.1 to 70% by weight, more preferably from the viewpoints of water resistance, scratch resistance, ink viscosity, and ejection stability. Is 1 to 50% by weight.

  The weight average molecular weight of the water-insoluble vinyl polymer is usually preferably about 3,000 to 300,000 from the viewpoints of print density and ejection stability. The weight average molecular weight of the water-insoluble vinyl polymer can be controlled by a conventional operation of adding a chain transfer material such as mercaptan.

  The weight average molecular weight of the water-insoluble vinyl polymer was determined by drying a part of the obtained water-insoluble vinyl polymer solution at 105 ° C. under reduced pressure for 2 hours and removing the solvent. It is determined by gel permeation chromatography using 60 mmol / L phosphoric acid and 50 mmol / L lithium bromide-containing dimethylformamide.

  The water-insoluble vinyl polymer is polymerized by blending predetermined amounts of (1) macromer, (2) polyoxyalkylene group-containing monomer, (3) salt-forming group-containing monomer and (4) copolymerizable monomer. To obtain. Specifically, it is produced by polymerizing each monomer composition by a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method or an emulsion polymerization method. Among these polymerization methods, the solution polymerization method is preferable.

  The solvent used in the solution polymerization method is preferably a polar organic solvent. When the polar organic solvent is miscible with water, it can be used by mixing with water.

  Examples of the polar organic solvent include aliphatic alcohols having 1 to 3 carbon atoms such as methanol, ethanol, propanol and isopropyl alcohol; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate and the like. Among these, methanol, ethanol, isopropyl alcohol, acetone, methyl ethyl ketone, or a mixture of these with water is preferable.

  In the polymerization, a radical polymerization initiator can be used. As radical polymerization initiators, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), dimethyl-2,2′-azobisbutyrate, 2,2 An azo compound such as' -azobis (2-methylbutyronitrile) and 1,1'-azobis (1-cyclohexanecarbonitrile) is preferred. Moreover, organic peroxides, such as t-butyl peroxy octoate, di-t-butyl peroxide, dibenzoyl oxide, can also be used.

  The amount of the polymerization initiator is preferably 0.001 to 5 mol, more preferably 0.01 to 2 mol, per mol of the monomer composition.

  In the polymerization, a polymerization chain transfer agent may be further added. Specific examples of the polymerization chain transfer agent include mercaptans such as octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-tetradecyl mercaptan and 2-mercaptoethanol; xanthogen disulfides such as dimethylxanthogen disulfide and diisopropylxanthogen disulfide. ; Thiuram disulfides such as tetramethylthiuram disulfide and tetrabutylthiuram disulfide; halogenated hydrocarbons such as carbon tetrachloride and ethylene bromide; hydrocarbons such as pentaphenylethane; acrolein, methacrolein, allyl alcohol, 2- Ethylhexyl thioglycolate, terbinolene, α-terpinene, γ-terpinene, dipentene, α-methylstyrene dimer, 9,10-dihydroanthracene, , 4-dihydronaphthalene, indene, 1,4-cyclohexadiene unsaturated cyclic hydrocarbon compounds of a diene and the like; 2,5-unsaturated heterocyclic compounds dihydrofuran like, and the like. These polymerization chain transfer agents can be used alone or in admixture of two or more.

  Since the polymerization conditions of the monomer composition vary depending on the radical polymerization initiator, the monomer, the type of the solvent, and the like, it cannot be determined unconditionally. Usually, the polymerization temperature is preferably 30 to 100 ° C, more preferably 50 to 80 ° C, and the polymerization time is preferably 1 to 20 hours. The polymerization atmosphere is preferably an inert gas atmosphere such as nitrogen gas.

  After completion of the polymerization reaction, the produced water-insoluble vinyl polymer is isolated from the reaction solution by a known method such as reprecipitation or solvent distillation. The obtained water-insoluble vinyl polymer can be purified by repeating reprecipitation or removing unreacted monomers by membrane separation, chromatographic methods, extraction methods, and the like.

<Chromatic pigments>
Examples of the chromatic pigment coated with the water-insoluble vinyl polymer include a cyan pigment, a yellow pigment, and a magenta pigment. The term “chromatic color” refers to all colors other than a series of colors (achromatic colors) ranging from white to gray to black.

  Examples of cyan pigments include C.I. I. Pigment blue 1, 2, 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, and C.I. I. Bat Blue 4, 60 and the like. These cyan pigments can be used alone or in combination of two or more.

  Examples of yellow pigments include C.I. I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 35, 37, 42, 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 128, 138, 147, 150, 153, 155, 174, 180, 188, 198 and the like. These yellow pigments can be used alone or in combination.

  Examples of magenta pigments include C.I. I. Pigment Red, 1, 3, 5, 8, 9, 16, 17, 19, 22, 38, 57: 1, 90, 112, 122, 123, 127, 146, 184, 202, 207, 209, and C.I. I. Pigment violet 1, 3, 5: 1, 16, 19, 23, 38 and the like. These magenta pigments may be used alone or in combination of two or more.

  Among the chromatic pigments, a cyan pigment is more preferable because the effect of suppressing the occurrence of bronze phenomenon is greater. In particular, among cyan pigments, C.I. I. It is preferable to use one or more selected from CI Pigment Blue 15, 15: 1, 15: 2, 15: 3, 15: 4, and 16 for the same reason as described above.

  Any pigment that is not described in the color index can be used as long as it is insoluble in water.

As a method for obtaining a water-insoluble vinyl polymer containing a chromatic pigment, for example, it is produced by the following steps 1) to 4).
1) Mixing step: A raw material mixture is obtained by mixing a coloring material, an organic solvent, water, and a neutralizing agent used if necessary using a normal mixing and stirring device such as an anchor blade or a turbine blade. At that time, it is more preferable to knead the mixture using a kneader in order to sufficiently atomize the mixture. As kneaders for kneading, there are a batch type and a continuous type, and the former includes a double-arm kneader, and the latter includes a self-cleaning kneader. Among these, the former double-armed kneader is preferable from the viewpoint of product type switching, washing in the tank, and the like.
2) Dispersion step: Next, the obtained raw material mixture is diluted and subjected to a dispersion treatment to obtain a desired solid content concentration. In the dispersion treatment, a ball mill, a roll mill, a bead mill, a high-pressure homogenizer, a high-speed stirring type disperser, or the like can be used. Among these, a high-pressure homogenizer with less inorganic impurities is preferable. Examples of the high-pressure homogenizer include those having a chamber in which the flow path of the processing liquid is fixed and those having a homogeneous valve capable of adjusting the width of the flow path of the processing liquid. As a high-pressure homogenizer having a chamber in which the flow path of the processing solution is fixed, a microfluidizer (trade name, manufactured by Microfluidics), a nanomizer (trade name, manufactured by Nanomizer), an optimizer (manufactured by Sugino Machine, product) Name). Examples of high-pressure homogenizers that have a homogeneous valve include high-pressure homogenizers (trade name, manufactured by Lani), high-pressure homogenizers (trade name, manufactured by Mimaru Machinery Co., Ltd.), and high-pressure homogenizers (trade name, manufactured by Izumi Food Machinery Co., Ltd.). Can be mentioned. The pressure when dispersing with a high-pressure homogenizer is preferably 50 MPa or more, and more preferably 80 MPa or more because polymer particles having a desired particle diameter can be easily obtained in a short time.
3) Solvent removal step: Next, by removing a predetermined amount of the organic solvent and water from the raw material mixture subjected to the dispersion treatment, the aqueous ink composition according to the present invention having a desired concentration is obtained. The organic solvent removal step may be either before or after the dispersion step. The method for removing water is not particularly limited. As a method for removing the organic solvent, a vacuum distillation method, particularly a thin-film vacuum distillation method is preferable. The removal amount of the organic solvent is not particularly limited, and it is usually preferable to remove the whole amount of the organic solvent.
4) Coarse particle removal step: After removing the solvent, the coarse particles may be removed if necessary. For example, the ink obtained as described above is subjected to pressure filtration through a filter or processed by a centrifuge, and is preferably 2 μm or more, more preferably 1 μm or more, more preferably 0.5 μm or more. By removing the particles, an ink having high dispersion stability can be obtained.

  The chromatic pigment coated with the water-insoluble vinyl polymer may have a shape in which a part of the pigment is exposed without being completely covered with the water-insoluble vinyl polymer.

  Hereinafter, the mixing step 1) will be described in detail. The organic solvent used in the mixing step is preferably an alcohol solvent, a ketone solvent, an ether solvent, an aromatic hydrocarbon solvent, an aliphatic hydrocarbon solvent, or a halogenated aliphatic hydrocarbon solvent, and is hydrophilic. More preferred are organic solvents.

  Examples of the alcohol solvent include methanol, ethanol, isopropanol, n-butanol, tertiary butanol, isobutanol, diacetone alcohol and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of the ether solvent include dibutyl ether, tetrahydrofuran, dioxane and the like. Examples of the aromatic hydrocarbon solvent include benzene and toluene. Examples of the aliphatic hydrocarbon solvent include heptane, hexane, cyclohexane and the like. Examples of the halogenated aliphatic hydrocarbon solvent include methylene chloride, 1,1,1-trichloroethane, chloroform, carbon tetrachloride, 1,2-dichloroethane and the like. Of these, acetone and methyl ethyl ketone are preferred.

  If necessary, an organic solvent and a high-boiling hydrophilic organic solvent may be used in combination. Examples of the high boiling hydrophilic organic solvent include phenoxyethanol, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether and the like.

  As the neutralizing agent, an acid or a base can be used depending on the type of the salt-forming group. Examples of the acid include inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as acetic acid, propionic acid, lactic acid, succinic acid, glycolic acid, gluconic acid, and glyceric acid. Examples of the base include tertiary amines such as trimethylamine and triethylamine, ammonia, sodium hydroxide, potassium hydroxide and the like.

  There is no particular limitation on the degree of neutralization. Usually, it is preferable that the obtained aqueous dispersion has neutral liquidity, for example, pH of 4.5 to 10.

  The amount of the chromatic pigment is preferably from 100 to 700 parts by weight, more preferably from 200 to 600 parts by weight, still more preferably from 100 parts by weight of the resin solid content of the polymer, from the viewpoint of color development and clogging recovery. 300 to 500 parts by weight.

  The amount of the organic solvent is preferably 20 parts by weight or more, more preferably 30 parts by weight or more, and more preferably 50 parts by weight or more with respect to 100 parts by weight of the resin solid content of the polymer from the viewpoint of compatibility with the chromatic pigment. Further preferred. The amount of the organic solvent is preferably 500 parts by weight or less and more preferably 300 parts by weight or less with respect to 100 parts by weight of the resin solid content of the polymer from the viewpoint of obtaining an effective shearing force when the mixture is kneaded. 200 parts by weight or less is more preferable. From these viewpoints, the amount of the organic solvent is preferably 20 to 500 parts by weight, more preferably 30 to 300 parts by weight, and further preferably 50 to 200 parts by weight with respect to 100 parts by weight of the resin solid content of the polymer. .

  The amount of water is preferably 50 to 1000 parts by weight, more preferably 100 to 500 parts by weight with respect to 100 parts by weight of the organic solvent, from the viewpoint of easy compatibility with the pigment.

  The solid content concentration in the mixture is preferably 50% by weight or more, more preferably 65% by weight from the viewpoint of obtaining an effective shearing force when the mixture is kneaded, and the viscosity of the resulting kneaded product becomes too high. From the viewpoint of avoiding the inability to perform uniform kneading and avoiding the kneaded material from collapsing into particles, it is preferably 80% by weight or less, more preferably 75% by weight or less. From these viewpoints, the solid content concentration in the mixture is preferably 50% by weight or more, more preferably 50 to 80% by weight, still more preferably 65 to 80% by weight, and particularly preferably 65 to 75% by weight.

  In addition, solid content in a mixture means the total amount of solid content of a pigment, a polymer, and a neutralizing agent.

  The average particle size of the water-insoluble vinyl polymer containing a chromatic pigment is preferably 10 to 500 nm, more preferably 20 to 300 nm, and still more preferably 50, from the viewpoints of gloss of printed matter, prevention of nozzle clogging and dispersion stability. It is good to set it to -200 nm.

  The content of the chromatic pigment is not particularly limited as long as a desired printing density can be obtained. Usually, the content is from 0.1 to 15% by weight, preferably from 0.5 to 10% by weight, more preferably from 3 to 8% by weight, from the viewpoint of imparting sufficient ejection properties and printing density.

<Titanium dioxide pigment>
As the titanium dioxide pigment used in the aqueous ink composition according to the present invention, those conventionally used in paints and the like can be used, and there are no particular restrictions on the production method such as the chlorine method and the sulfuric acid method, The crystal structure may be any of rutile type, anatase type, and brookite type, but from the viewpoint of weather resistance and stability, the rutile type is preferable. Further, the titanium dioxide pigment may be surface-treated with a metal compound such as aluminum, silicon, titanium, zirconia, a phosphoric acid compound, an organic amine, or the like.

  The primary particle diameter of the titanium dioxide pigment is preferably 1 μm or less, more preferably 200 nm or less, and still more preferably 100 nm or less, from the viewpoint of the gloss of the printed matter and the effect of suppressing the bronze phenomenon.

  In the present invention, the “primary particle diameter” refers to the size of a particle formed by collecting single crystals or crystallites close thereto. The primary particle size of the pigment is measured by electron microscopy. This is to measure the size of pigment particles from an electron micrograph, and is more reliable by dispersing the pigment in an organic solvent, fixing it to a support film, and performing image processing and measurement from a transmission electron micrograph. The value can be determined. Specifically, the minor axis diameter and the major axis diameter of each primary particle diameter are measured, and the diameter of a circle equal to the area is arithmetically determined as the primary particle diameter, and 50 or more pigments from a fixed visual field. Particles are randomly selected and an average value is obtained. Other measurement methods can be used as long as the same reliability can be obtained, but when there is a substantial difference in numerical values, the value obtained by the above method is adopted.

  The content of the titanium dioxide pigment is preferably 0.01% by weight or more in terms of solid content based on the weight of the ink composition (100% by weight) from the viewpoint of the gloss of printed matter and the effect of suppressing the bronze phenomenon. More preferably, it is 0.1% by weight or more, and further preferably 0.1% by weight or more and 5% by weight or less. Furthermore, in consideration of the relationship with the amount of the chromatic pigment added, the weight ratio of the titanium dioxide pigment to the chromatic pigment is 1:20 to 5: 1 is preferable, 1: 8 to 5: 2 is more preferable, and 1: 2 to 5: 2 is further preferable.

<2-Methyl-2-propyl-1,3-propanediol>
The aqueous ink composition according to the present invention contains 2-methyl-2-propyl-1,3-propanediol as an essential component. By adding such a specific alcohol to the ink composition containing the chromatic pigment coated with the water-insoluble vinyl polymer and the titanium dioxide pigment, it is excellent in color development on plain paper and glossy paper. Excellent in glossiness. Further, by adding the above-mentioned specific alcohol, ink reliability such as ejection stability, clogging recovery property, and storage stability is improved in addition to color developability and glossiness.

<Water, other ingredients>
The aqueous ink composition according to the present invention contains water as a main solvent. As the water, it is preferable to use pure or ultrapure water such as ion exchange water, ultrafiltration water, reverse osmosis water, and distilled water. In particular, water obtained by sterilizing these waters by ultraviolet irradiation or addition of hydrogen peroxide is preferable because generation of mold and bacteria is prevented over a long period of time.

  In the aqueous ink composition according to the present invention, it is preferable to add a penetration accelerator from the viewpoint of increasing the wettability to the recording medium and increasing the permeability of the organic pigment. The penetration enhancer preferably contains a monohydric alcohol, 1,2-alkanediol and / or glycol ether.

  Specific examples of the monohydric alcohol include methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol, 2-butanol, tert-butanol, iso-butanol, n-pentanol, and 2-pentanol. 3-pentanol, 2-methyl-1-butanol, 2-ethyl-1-butanol, 3-methyl-2-butanol, tert-pentyl alcohol, neopentyl alcohol, 2,3-dimethyl-2-butanol, 3 , 3-dimethyl-2-butanol, 2,4-dimethyl-3-pentanol, 3-ethyl-3-pentanol, 2-methyl-2-pentanol, 4-methyl-2-pentanol, 2,4 , 4-Trimethyl-1-pentanol, 2,2-dimethyl-3-pentanol, 4-methyl-1- Butanol, 3-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-1-pentanol, 2-ethylhexanol, 2-methyl-2-hexanol, 2-methyl-3-hexanol, etc. Is mentioned.

  Specific examples of 2-alkanediol include 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol, 4-methyl-1,2-pentanediol and the like.

  Specific examples of the glycol ether include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether. , Ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, triethylene glycol monobutyl ether, 1-methyl -1-methoxybutanol, propylene glycol Monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, di Examples include propylene glycol mono-n-propyl ether and dipropylene glycol mono-iso-propyl ether.

  These solvents may be used alone or in combination of two or more, and are preferably contained in the ink composition in an amount of 2 to 15% by weight from the viewpoint of ensuring appropriate permeability and drying properties.

  Furthermore, other preferable examples of the penetration enhancer include a surface tension adjusting agent. As the surface tension adjusting agent, acetylene glycol surfactants and polyether-modified siloxanes are preferable. Examples of acetylene glycol surfactants include Surfynol 420, 440, 465, 485, 104, STG (product of Air Products), Olphine PD-001, SPC, E1004, E1010 (product of Nissin Chemical Industry Co., Ltd.) ), Acetylenol E00, E40, E100, LH (product of Kawaken Fine Chemical Co., Ltd.) and the like. Examples of the polyether-modified siloxanes include BYK-346, 347, 348, and UV3530 (Bic Chemie product). One or more of these can be used in the ink composition, and the surface tension is preferably adjusted to 20 to 40 mN / m, and 0.1 to 3.0% by weight in the ink composition. included.

In the present invention, it is preferable to add a wetting agent from the viewpoint of preventing the ink composition from drying and preventing clogging at the head of the ink jet printer. Examples of the wetting agent include glycerin, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol and dipropylene glycol. Polyhydric alcohols such as 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, glucose, mannose, fructose, ribose, xylose, arabinose , Sugars such as galactose, aldonic acid, glucitol (sorbitol), maltose, cellobiose, lactose, sucrose, trehalose, maltotriose, sugar alcohols, hyaluronic acids, 1,2-dimethyl C1-C4 alkyl alcohols such as ruurea, ureas, ethanol, methanol, butanol, propanol, isopropanol, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone , Formamide, acetamide, dimethyl sulfoxide, sorbit, sorbitan, acetin, diacetin, triacetin, sulfolane and the like. These can be used alone or in combination of two or more in the ink composition. From the viewpoints of ensuring proper physical properties (such as viscosity) of the ink composition, printing quality, and reliability, It is preferable that 10 to 50 weight% is contained in.

  Furthermore, a material selected from pH adjusters, preservatives, fungicides, rust inhibitors, dissolution aids, antioxidants, and the like can be added to the aqueous ink composition according to the present invention as desired. These components can be used alone or in combination of two or more. Moreover, it is not necessary to add, if it is not necessary to add. Those skilled in the art can use the preferable additive selected in a preferable amount as long as the effects of the present invention are not impaired.

  As the pH adjuster, it is possible to use alkali metal hydroxides such as lithium hydroxide, potassium hydroxide and sodium hydroxide, amines such as ammonia, triethanolamine, tripropanolamine, diethanolamine and monoethanolamine. Although it is possible, it preferably contains at least one pH adjusting agent selected from alkali metal hydroxides, ammonia, triethanolamine, and tripropanolamine, and is preferably adjusted to pH 6-10. If the pH is out of this range, the material constituting the ink jet printer will be adversely affected, and the clogging recoverability will deteriorate.

  Examples of the antiseptic or fungicide include sodium benzoate, sodium pentachlorophenol, sodium 2-pyridinethiol-1-oxide, sodium sorbate, sodium dehydroacetate, and 1,2-dibenzisothiazoline-3- ON (Proxel CRL, Proxel BDN, Proxel GXL, Proxel XL-2, Proxel TN (trade name) and the like of AVECIA can be exemplified, but not limited thereto.

  The dissolution aid is an additive for dissolving the insoluble matter and keeping the ink composition in a uniform solution when the insoluble matter is precipitated from the ink composition. Examples of solubilizers include pyrrolidones such as N-methyl-2-pyrrolidone and 2-pyrrolidone, ureas such as urea, thiourea and tetramethylurea, allophanates such as allophanate and methyl allophanate, biuret, dimethylbiuret, Biurets such as tetramethyl biuret can be exemplified, but not limited thereto.

  Examples of antioxidants include, but are not limited to, L-ascorbic acid and its salts.

<Recording method>
The recording method according to the present invention is a recording method using the above-described aqueous ink composition. Examples of the recording method using the ink composition include an inkjet recording method, a recording method using a writing instrument such as a pen, and other various printing methods. Therefore, the water-based ink composition according to the present invention can be preferably used for applications such as writing instruments such as a water-based pen, an ink jet recording method, printing, and a stamp.

  According to a preferred aspect of the recording method of the present invention, there is provided an ink jet recording method in which droplets of the above-described aqueous ink composition are ejected and adhered to a recording medium for printing. As the ink jet recording method according to the present invention, any method can be used as long as it is a method in which the water-based ink composition is ejected as droplets from a fine nozzle and the droplets adhere to a recording medium. As specific examples of such a method, methods of various modes are known.

  An example of such a method is an electrostatic suction method. In this method, a strong electric field is applied between the nozzle and the acceleration electrode placed in front of the nozzle, ink is continuously ejected in the form of droplets from the nozzle, and printing information is printed while the ink droplets fly between the deflection electrodes. A signal is applied to the deflection electrode and recorded. In this method, if necessary, ink droplets may be ejected in response to a print information signal without being deflected.

  As another aspect, there is a method of forcibly ejecting ink droplets by applying pressure to the ink liquid with a small pump and mechanically vibrating the nozzle with a crystal resonator or the like. In this method, the ejected ink droplet is charged simultaneously with the ejection, and a printing information signal is applied to the deflection electrode and recorded while the ink droplet flies between the deflection electrodes. Another embodiment includes a method using a piezoelectric element. In this method, pressure and a print information signal are simultaneously applied to ink liquid by a piezoelectric element, and ink droplets are ejected to perform recording. As yet another aspect, there is a method in which the volume of ink is rapidly expanded by the action of thermal energy. In this method, ink is heated and foamed with a microelectrode in accordance with a print information signal, ink droplets are ejected, and recording is performed.

  The recording medium is not particularly limited, and various recording media such as plain paper, ink jet exclusive paper, plastic, film, metal and the like can be used.

<Recorded material>
Furthermore, according to the present invention, a recorded matter recorded by the above recording method is also provided. This recorded matter was recorded by discharging at least the droplets of the above-described aqueous ink composition and attaching the droplets to a recording medium. Since the recorded matter according to the present invention is recorded using the above water-based ink composition, it has excellent gloss and the bronzing phenomenon is suppressed. As a specific example of the recording medium, the recording medium described above can be used.

  Hereinafter, the present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to these examples.

A. Preparation of water-insoluble vinyl polymer A reaction vessel was charged with 20% by weight of methyl ethyl ketone, 0.03% by weight of a polymerization chain transfer agent (2-mercaptan eterol), and 10% of the total amount of monomers shown in Table 1, and mixed. Thereafter, the container was replaced with nitrogen gas. Meanwhile, the dropping device was filled with the remaining 90% of the monomer composition. Polymer chain transfer agent (2-mercaptan ethanol) 0.27 wt%, methyl ethyl ketone 60 wt%, and 2,2′-azobis (2,4-dimethylvaleronitrile) were then added to the dropping apparatus and mixed. Thereafter, the dropping device was replaced with nitrogen gas. The temperature of the mixture in the reaction vessel was raised to 65 ° C. with stirring in a nitrogen atmosphere, and the mixture in the dropping apparatus was dropped into the reaction vessel over 3 hours. Two hours after the completion of dropping at 65 ° C., a solution in which 0.3% by weight of 2,2′-azobis (2,4-dimethylvaleronitrile) was dissolved in 5% by weight of methyl ethyl ketone was added. The mixture was aged at 65 ° C. for 2 hours and further at 70 ° C. for 2 hours to obtain a polymer solution.

  A part of the polymer solution obtained as described above was distilled off under reduced pressure, the solvent was removed and the product was dried and isolated to obtain desired water-insoluble vinyl polymers (water-insoluble polymers 1 to 3). Table 1 shows the monomer composition ratio (% by weight) of each water-insoluble vinyl polymer.

The weight average molecular weight of each water-insoluble vinyl polymer obtained was determined by gel permeation chromatography using polystyrene as a standard substance and phosphoric acid having a concentration of 60 mmol / L and dimethylformamide containing 50 mmol / L lithium bromide as a solvent. As a result, the weight average molecular weight was 70,000.

B. Preparation of pigment dispersion (pigment dispersion 1)
1.5% by weight of the water-insoluble vinyl polymer obtained above is dissolved in 45% by weight of methyl ethyl ketone, and a predetermined amount of neutralizing agent (20% aqueous sodium hydroxide solution) is added to completely dissolve the salt-forming groups. And chromatic pigment as C.I. I. 20% by weight of Pigment Blue 15: 4 was added and kneaded in a bead mill for 2 hours. After adding 120% by weight of ultrapure water to the kneaded product obtained above and stirring, methyl ethyl ketone was removed at 60 ° C. under reduced pressure, and a part of the water was further removed, so that the solid content concentration was 20%. A weight percent of pigment dispersion 1 was obtained.

(Pigment dispersion 2)
Similarly, pigment dispersion 2 was obtained using water-insoluble vinyl polymer 2.

(Pigment dispersion 3)
Similarly, pigment dispersion 3 was obtained using water-insoluble vinyl polymer 3.

(Titanium dioxide pigment dispersion)
Titanium dioxide pigment (Taika MT-600B, crystal form: rutile, primary particle size 50 nm) 10% by weight, styrene-acrylic resin (John Crill 61J, 30.5% aqueous solution by Johnson Polymer Co., Ltd.) 10% as a dispersant % And 70% by weight of ultrapure water were mixed and dispersed in a sand mill (manufactured by Yasukawa Seisakusho) with glass beads (1.7 mm in diameter, 1.5 times the amount of the mixture (weight)) for 2 hours. After the dispersion, the glass beads were removed to obtain a titanium dioxide pigment dispersion having a solid content concentration of 10% by weight.

C. Preparation of water-based ink composition (Reference Examples 1 to 9 and Comparative Example 1)
After mixing each component in the ratio shown in Table 2 below and stirring at room temperature for 2 hours, the mixture was filtered using a membrane filter having a pore diameter of about 8 μm (trade name, manufactured by Nihon Millipore Limited). 9 and Comparative Example 1 were prepared.

(Comparative Example 2)
C. I. Pigment Blue 15: 4, a titanium dioxide pigment (MT-600B manufactured by Teika Co., Ltd., crystal form: rutile, primary particle size: 50 nm), and a styrene-acrylic resin (John Crill 61J, 30 manufactured by Johnson Polymer Co., Ltd.) as a dispersant. 5% aqueous solution) was mixed and dispersed in a sand mill (manufactured by Yasukawa Seisakusho) with glass beads (diameter 1.7 mm, 1.5 times the amount of the mixture (weight)) for 2 hours. After dispersion, the glass beads were removed, the solvent and ultrapure water shown in Table 2 below were added, the mixture was stirred at room temperature for 30 minutes, and filtered through an 8 μm membrane filter to obtain an aqueous ink composition of Comparative Example 2.

In addition, all the addition amount shown in Table 2 is represented as weight%. The “remaining amount” of ultrapure water means adding ultrapure water so that the total amount of ink becomes 100% by weight. The weight ratio of the titanium dioxide pigment to the chromatic pigment in this aqueous ink composition (indicated as “TiO ₂ / chromatic pigment” in Table 2) was as shown in Table 2 below.

D. Evaluation Test (1) Bronze Evaluation Bronze was evaluated using the water-based ink compositions of Reference Examples 1 to 9 and Comparative Examples 1 and 2 in the following manner. Using an inkjet printer PX-A550 (trade name: manufactured by Seiko Epson Corporation), a patch pattern having a print duty of 100% and 40% on photo paper <gloss> (trade name: manufactured by Seiko Epson Corporation) is 1440 ×. Printed at a print resolution of 720 dpi, allowed to stand at 25 ° C. for 24 hours, and visually observed the color change of reflected light when the angle of the printed material was changed under a fluorescent lamp (F11 light source), and bronze based on the following criteria Evaluated.
A: In both patches of 100% duty and 40% duty, the color of reflected light is white and there is no sense of incongruity.
B: In either 100% or 40% duty patch, the color of the reflected light is white and there is no sense of incongruity.
C: In both patches of 100% duty and 40%, the color can be confirmed in the reflected light, and there is a sense of incongruity.

  The results were as shown in Table 3 below.

(2) Evaluation of glossiness The 45 degree specular glossiness of the printed material of 100% Duty used in the evaluation test (1) was measured using a goniometer (trade name: manufactured by Murakami Color Research Laboratory). The glossiness was evaluated based on this.
AA: 45 degree specular gloss is 35 or more A: 45 degree specular gloss is 30 or more and less than 35 B: 45 degree specular gloss is 25 or more and less than 30 C: 45 degree specular gloss is less than 25

  The results were as shown in Table 3 below.

(3) Evaluation of plain paper color developability Using the aqueous ink compositions of Reference Examples 1 to 9 and Comparative Examples 1 and 2, the color developability of plain paper was evaluated in the following manner. Using the inkjet printer used in the evaluation test (1), a solid pattern with a print duty of 100% was printed on Xerox-4024 at a print resolution of 720 × 720 dpi, left at 25 ° C. for 24 hours, and then the OD of the printed matter The value was measured using Spectrolino (trade name: manufactured by Gretag) and determined based on the following criteria.
A: OD value of 1.2 or more B: OD value of 1.0 to 1.2
C: OD value less than 1.0

  The results were as shown in Table 3 below.

(4) Evaluation of ejection stability Using the water-based ink compositions of Reference Examples 1 to 9 and Comparative Examples 1 and 2, ejection stability was evaluated in the following manner. Using the ink jet printer used in the evaluation test (1), each water-based ink composition was filled in an ink cartridge, mounted on the ink jet printer, and confirmed that all nozzles ejected normally. Below, patch patterns were continuously printed on photographic paper <gloss> under the same conditions as in Evaluation 1. About each water-based ink composition, the dot missing at the time of printing and the presence or absence of scattering of the water-based ink composition were observed, and the ejection stability was evaluated based on the following criteria.
A: No dot dropout or ink composition splattering occurs even after 4 hours.
B: After 3 hours, dot missing or ink composition scattering occurred.
C: After 2 hours, dot missing or ink composition scattering occurred.

  The results were as shown in Table 3 below.

(5) Evaluation of clogging recoverability Using the water-based ink compositions of Reference Examples 1 to 9 and Comparative Examples 1 and 2, the clogging recoverability was evaluated in the following manner. Using the ink jet printer used in the evaluation test (1), each water-based ink composition was filled in an ink cartridge, mounted on the ink jet printer, and confirmed that all nozzles ejected normally. The cartridge was stopped, the cartridge was removed from the ink jet printer, and the printer head was left in a 40 ° C. environment for one week without capping the printer head. After leaving, install an ink cartridge filled with the same ink composition, check the number of cleanings required until the ink composition is discharged from all nozzles again, and evaluate clogging recovery based on the following criteria. It was.
A: All nozzles were recovered by cleaning within two times.
B: All nozzles recovered after 3 to 5 cleanings.
C: All nozzles could not be recovered by cleaning 6 times.

  The results were as shown in Table 3 below.

(6) Evaluation of storage stability The storage stability was evaluated according to the following procedure using the water-based ink compositions of Reference Examples 1 to 9 and Comparative Examples 1 and 2. The ink composition was placed in an aluminum pack and left in a 60 ° C. environment for 2 weeks with 50 g of each ink composition. Visual observation of the presence or absence of foreign matter (floating matter or sediment) after standing, and for those that do not generate foreign matter, investigate further changes in physical properties (viscosity, surface tension, pH, particle size), and based on the following criteria Storage stability was evaluated.
A: No foreign matter is generated, and there is no change in physical properties.
B: No foreign matter is generated, but the physical properties slightly change.
C: Foreign matter is generated or the physical properties are remarkably changed.

The results were as shown in Table 3 below.

Claims (12)

  A water-based ink composition comprising at least a chromatic pigment coated with a water-insoluble vinyl polymer, a titanium dioxide pigment, 2-methyl-2-propyl-1,3-propanediol, and water. The water-insoluble vinyl polymer is
(1) Macromer,
(2) a polyoxyalkylene group-containing monomer,
(3) a salt-forming group-containing monomer, and
(4) a monomer copolymerizable with each of the macromer, the polyoxyalkylene group-containing monomer, and the salt-forming group-containing monomer,
The water-based ink composition according to claim 1, which is copolymerized.   The aqueous ink composition according to claim 2, wherein the copolymerizable monomer is at least one selected from the group consisting of a long-chain alkyl group-containing monomer, an aromatic ring-containing monomer, and a macromer.   The water-based ink composition according to claim 2 or 3, wherein the macromer is a styrenic macromer having a polymerizable functional group at one end. The long-chain alkyl group-containing monomer is represented by the following general formula (I):

(Wherein R ¹ represents a hydrogen atom or a lower alkyl group, and R ² represents a monovalent hydrocarbon having 16 to 30 carbon atoms which may have a hetero atom)
The water-based ink composition according to any one of claims 2 to 4, which is represented by:   The water-based ink composition according to any one of claims 1 to 5, wherein a weight ratio of the titanium dioxide pigment and the chromatic pigment is 1:20 to 5: 1.   The water-based ink composition according to any one of claims 1 to 6, wherein a primary particle diameter of the titanium dioxide pigment is 1 µm or less.   The water-based ink composition according to claim 1, wherein the chromatic pigment is a cyan pigment.   The cyan pigment is C.I. I. The aqueous ink composition according to claim 8, which is at least one selected from the group consisting of CI Pigment Blue 15, 15: 1, 15: 2, 15: 3, 15: 4, and 16.   The aqueous ink composition according to any one of claims 1 to 9, further comprising a permeable organic solvent selected from the group consisting of monohydric alcohols, glycol ethers, and 1,2-alkanediols. object.   An ink jet recording method for performing printing by discharging a droplet of an ink composition and attaching the droplet to a recording medium, wherein the aqueous ink composition according to any one of claims 1 to 10 is used. Inkjet recording method.   A recorded matter recorded by the inkjet recording method according to claim 11.