JP2005041994A - Water-based ink for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide water-based ink for inkjet recording, having excellent dispersion stability, and providing high gloss and high print density; and to provide an aqueous dispersion for the inkjet recording, usable for the ink. <P>SOLUTION: The aqueous dispersion for the inkjet recording is the aqueous dispersion of a water-insoluble vinylic polymer containing a pigment. The water-insoluble vinylic polymer is obtained by polymerizing monomer components including a nonionic (meth)acrylamide-based monomer. The water-based ink for the inkjet recording contains the aqueous dispersion. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an aqueous dispersion for inkjet recording and an aqueous ink for inkjet recording.

  The ink jet recording method is a recording method in which characters and images are obtained by ejecting ink droplets directly from a very fine nozzle onto a recording member and attaching them. According to this method, not only has the advantage that the device to be used is low noise and good operability, but also has the advantage that colorization is easy and plain paper can be used as a recording member. Widely used in recent years. In recent years, pigment-based inks have been used for inks used in inkjet printers in order to improve water resistance and light resistance. However, pigment-based inks have the disadvantages that the pigment does not remain on the surface of copy paper and the print density is low.

Therefore, a recording ink using carbon black surface-treated with an acrylamide derivative has been proposed (for example, see Patent Document 1) in order to improve printing quality. However, this method has a drawback that it is impossible to achieve both the print density of plain paper and the glossiness of special paper.
Japanese Patent Laid-Open No. 5-230410

  An object of the present invention is to provide an aqueous ink for ink jet recording which is excellent in dispersion stability, can provide high glossiness and high print density, and an aqueous dispersion for ink jet recording used therefor.

  The present invention relates to an aqueous dispersion of a water-insoluble vinyl polymer containing a pigment, wherein the water-insoluble vinyl polymer is obtained by polymerizing a monomer component containing a nonionic (meth) acrylamide monomer. Provided are an aqueous dispersion for use, and an aqueous ink for inkjet recording containing the aqueous dispersion.

  As used herein, “(meth) acryl” means “acryl” or “methacryl”.

  The water-based ink of the present invention is excellent in dispersion stability, and can impart high glossiness and high printing density, and therefore can be suitably used as a water-based ink for ink jet recording.

[Pigment]
The pigments used in the present invention are organic pigments and inorganic pigments. If necessary, extender pigments can be used in combination.

  Examples of the organic pigment include azo pigments, disazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.

  Specific examples of preferred organic pigments include CI Pigment Yellow 13, 74, 83, 109, 110, 128, 151, 155, CI Pigment Red 48, 57, 122, 177, 184, 188, 202, 254, CI Pigment Violet 19, CI Pigment Blue 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, CI Pigment Green 7, 36, and the like.

Examples of the inorganic pigment include carbon black, metal oxide, metal sulfide, and metal chloride. Of these, carbon black is preferred particularly for black aqueous inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black. Examples of extender pigments include silica, calcium carbonate, and talc.
Among these, an organic pigment having a low surface polarity is more preferable from the viewpoint of gloss.

  The content of the pigment is preferably 20 to 1200 parts by weight, more preferably 50 to 900 parts by weight with respect to 100 parts by weight of the resin solid content of the vinyl polymer, from the viewpoint of printing density and dispersion stability.

[Water-insoluble vinyl polymer]
The water-insoluble vinyl polymer used in the present invention is obtained by polymerizing a monomer component containing a nonionic (meth) acrylamide monomer (hereinafter referred to as the monomer component of the present invention).

  The nonionic (meth) acrylamide monomer is a monomer having no salt-forming group, and is preferably a monomer represented by the formula (I) (hereinafter referred to as monomer (I)).

CH ₂ = C (R ¹ ) CONR ² R ³ (I)
(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² and R ³ are the same or different and each represents a C 1-22 monovalent hydrocarbon group which may have an oxygen atom or a halogen atom. R ² and R ³ may be combined to form a ring which may have a hetero atom.)
In the formula (I), R ² and R ³ are the same or different, and may have an oxygen atom or a halogen atom, a straight or branched alkyl group or alkenyl group having 1 to 22 carbon atoms, carbon number 6-22 aryl groups are preferred. The aryl group may be an alkylaryl group, an arylalkyl group, or the like. The alkyl group is more preferably an alkyl group having 1 to 8 carbon atoms.

  As the alkyl group, methyl group, ethyl group, i-propyl group, n-propyl group, n-butyl group, t-butyl group, n-octyl group, 2-ethylhexyl group, decyl group, lauryl group, myristyl group, A cetyl group, a stearyl group, a behenyl group, etc. are mentioned. Examples of the aryl group include a phenyl group and a nonylphenyl group. Examples of the halogen atom include a chlorine atom, a fluorine atom, and a bromine atom.

  Specific examples of the monomer (I) include (meth) acrylamide, N- (1,1-dimethyl-3-oxobutyl) (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) ) Acrylamide, N, N-diisopropyl (meth) acrylamide, N, N-dibutyl (meth) acrylamide, N, N-diphenyl (meth) acrylamide, Nt-butyl (meth) acrylamide, Nt-hexyl (meta) ) Acrylamide, N-t-octyl (meth) acrylamide, N- (1-methylundecyl) (meth) acrylamide, N-isobornyl (meth) acrylamide, N-norbornyl (meth) acrylamide, N-adamantyl (meth) acrylamide N-benzyl (meth) acrylamide, N- (4-methylphenyl) methyl (meth) a Kurylamide, N-diphenyl (meth) acrylamide, phthalimidomethyl (meth) acrylamide, N- (2,2,2-trichloro-1-hydroxy) ethyl (meth) acrylamide, N- (1,1,3,5- Tetramethyl) octyl (meth) acrylamide, N- (1,5-dimethyl-1-ethyl) hexyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-methylol (meth) acrylamide, N-cyclohexyl (meth) And (meth) acrylamide monomers such as acrylamide, N- (1,1,3-trimethyl) butyl (meth) acrylamide, and N- (meth) acryloylmorpholine. The nonionic (meth) acrylamide monomer exhibits an excellent effect of enhancing glossiness when printed on the exclusive paper of the water-based ink for inkjet recording of the present invention.

  From the viewpoint of gloss, the content of the nonionic (meth) acrylamide monomer in the monomer component of the present invention is preferably 0.1 to 40% by weight, more preferably 1 to 30% by weight, and 3 to 20 Weight percent is particularly preferred.

  The monomer component of the present invention preferably further contains a salt-forming group-containing monomer and a hydrophobic monomer.

  Examples of the salt-forming group-containing monomer include an anionic monomer and a cationic monomer.

  Examples of the anionic monomer include an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer. As the unsaturated carboxylic acid monomer, (meth) acrylic acid ((meth) acrylic acid means acrylic acid, methacrylic acid or a mixture thereof), styrene carboxylic acid, maleic acid monomer (maleic anhydride, maleic acid) Maleic acid monoester, maleic acid monoamide or a mixture of two or more thereof), itaconic acid and the like. Examples of unsaturated sulfonic acid monomers include 2- (meth) acryloyloxyethanesulfonic acid, 2- (meth) acryloyloxypropanesulfonic acid, 2- (meth) acrylamido-2-alkyl (C1-4) propanesulfonic acid Vinyl sulfonic acid, styrene sulfonic acid and the like. Examples of unsaturated phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxy Examples thereof include ethyl phosphate and dibutyl-2-methacryloyloxyethyl phosphate. Among these, unsaturated carboxylic acid monomers are preferable, and acrylic acid and methacrylic acid are particularly preferable. These can be used alone or in admixture of two or more.

  Examples of the cationic monomer include unsaturated tertiary amine-containing monomers and unsaturated ammonium salt-containing monomers. Specifically, N, N-dimethylaminoethyl (meth) acrylate, N- (N ′, N ′ -Dimethylaminopropyl) (meth) acrylamide, vinylpyrrolidone, methacryloyloxyethyltrimethylammonium methyl sulfate, methacryloyloxyethyldimethylethylammonium ethyl sulfate, and the like. Of these, N, N-dimethylaminoethyl (meth) acrylate is preferred.

  The content of the salt-forming group-containing monomer in the monomer component of the present invention is preferably 1 to 50% by weight, more preferably 2 to 40% by weight, and further preferably 5 to 20% by weight from the viewpoint of dispersion stability. is there.

  Examples of the hydrophobic monomer used in the present invention include alkyl (meth) acrylates and aromatic ring-containing monomers. These can be used alone or in admixture of two or more.

  Examples of the alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, (iso) propyl (meth) acrylate, (iso or tertiary) butyl (meth) acrylate, (iso) amyl (meth) acrylate, Cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, (iso) decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, (iso) stearyl (meth) acrylate, etc. Alkyl (meth) acrylates in which the alkyl moiety is an alkyl group having 1 to 18 carbon atoms. These can be used alone or in admixture of two or more.

  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, it shows normal.

From the viewpoint of water resistance, the aromatic ring-containing monomer may be styrene, vinylnaphthalene, α-methylstyrene, vinyltoluene, ethylvinylbenzene, 4-vinylbiphenyl, 1,1-diphenylethylene, 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 One or more are preferred. Among these, at least one selected from the group consisting of styrene, α-methylstyrene, vinyl toluene, and vinyl naphthalene is more preferable from the viewpoints of water resistance and scratch resistance.
As the hydrophobic monomer, an aromatic ring-containing monomer is preferable.

  The content of the hydrophobic monomer in the monomer component of the present invention is preferably 1 to 60% by weight, more preferably 2 to 50% by weight, and further preferably 5 to 40% by weight from the viewpoint of printing density.

  The monomer component of the present invention preferably further contains a polyoxyalkylene or arylene group-containing monomer. A typical example of the polyoxyalkylene or arylene group-containing monomer used in the present invention is a monomer represented by the formula (II) (hereinafter referred to as monomer (II)).

CH ₂ = C (R ¹ ) COO (R ⁴ O) _r R ⁵ (II)
(In the formula, R ¹ represents the above meaning, R ⁴ represents a divalent hydrocarbon group having 1 to 30 carbon atoms which may have a hetero atom, and R ⁵ has a hydrogen atom or a hetero atom. And a monovalent hydrocarbon group having 1 to 30 carbon atoms, r represents a number of 1 to 60, and r R ^{4 s} may be the same or different.)
In the formula (II), examples of the hetero atom include a nitrogen atom, an oxygen atom, a halogen atom (fluorine atom, chlorine atom, bromine atom, etc.) and a sulfur atom.

Typical examples of R ⁴ include a divalent aromatic ring having 6 to 30 carbon atoms which may have a substituent, and a divalent hetero ring having 3 to 30 carbon atoms which may have a substituent. And an alkylene group having 1 to 30 carbon atoms which may have a substituent. These rings or groups may be a combination of two or more. Examples of the substituent include an aromatic ring having 6 to 29 carbon atoms, a hetero ring having 3 to 29 carbon atoms, an alkyl group having 1 to 29 carbon atoms, a halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), amino group, and the like. Is mentioned.

Preferable examples of R ⁴ include a phenylene group which may have a substituent having 1 to 24 carbon atoms, an alkylene group having 1 to 30 carbon atoms, preferably an alkylene group having 1 to 20 carbon atoms, and an aromatic ring as a substituent. And an alkylene group having 7 to 30 carbon atoms and a C 4-30 alkylene group having a heterocycle as a substituent.

In addition, preferable examples of the R ⁴ O group include ethyleneoxy group, propyleneoxy group, trimethyleneoxy group, tetramethyleneoxy group, heptamethyleneoxy group, hexamethyleneoxy group, and one or more of these alkyleneoxy groups. Examples thereof include C2-C7 alkyleneoxy groups and phenyleneoxy groups formed from combinations. Most preferred is an alkyleneoxy group having 2 or 3 carbon atoms. The r R ^{4 s} may be the same or different, and if they are different, any of block addition, random addition, alternating addition, and the like may be used.

R ⁵ is a monovalent hydrocarbon group having a hydrogen atom or 1 to 30 carbon atoms which may have a hetero atom. Examples of the hetero atom include a nitrogen atom, an oxygen atom, and a sulfur atom. Typical examples of R ⁵ include a hydrogen atom, a monovalent aromatic ring having 6 to 30 carbon atoms which may have a substituent, and a monovalent aromatic group having 3 to 30 carbon atoms which may have a substituent. Or an alkyl group having 1 to 30 carbon atoms which may have a substituent. Examples of the substituent include an aromatic ring having 6 to 29 carbon atoms, a heterocyclic ring having 4 to 29 carbon atoms, a halogen atom (fluorine atom, chlorine atom, bromine atom), an amino group, and the like.

Preferable examples of R ⁵ include a hydrogen atom, a phenyl group, an alkyl group having 1 to 30 carbon atoms, preferably 1 to 20 carbon atoms, an alkyl group having 7 to 30 carbon atoms having an aromatic ring as a substituent, and substitution. Examples of the group include an alkyl group having 4 to 30 carbon atoms having a heterocycle. More preferable examples of R ⁵ include those having 1 to 6 carbon atoms such as a hydrogen atom, a methyl group, an ethyl group, an (iso) propyl group, an (iso) butyl group, an (iso) pentyl group, and an (iso) hexyl group. An alkyl group, a phenyl group, etc. are mentioned.
Although r is a number of 1-60, Preferably it is a number of 1-30, More preferably, it is a number of 3-10.

  Specific examples of the monomer (II) include polyethylene glycol (2 to 30: the value of r in the formula (II); the same applies hereinafter) (meth) acrylate, poly (ethylene glycol (1-15) .propylene glycol ( 1-15)) (meth) acrylate, polypropylene glycol (2-30) (meth) acrylate, methoxypolyethylene glycol (1-30) (meth) acrylate, methoxypolytetramethylene glycol (1-30) (meth) acrylate, Ethoxypolyethylene glycol (1-30) (meth) acrylate, (iso) propoxypolyethylene glycol (1-30) (meth) acrylate, butoxypolyethylene glycol (1-30) (meth) acrylate, methoxypolypropylene glycol (1-30) (Meta) Acry And methoxy (ethylene glycol / propylene glycol copolymer) (1 to 30, ethylene glycol: 1 to 29 therein) (meth) acrylate, etc., and these may be used alone or in combination of two or more. Can be used.

  Among the monomers (II), polyethylene glycol (2-30) (meth) acrylate and polypropylene glycol (2-30) (meth) acrylate are preferable.

  The content of the polyoxyalkylene or arylene group-containing monomer in the monomer component of the present invention is preferably 1 to 50% by weight, more preferably 3 to 40% by weight, and still more preferably 5 to 30% by weight from the viewpoint of printing density. %.

  The monomer component of the present invention preferably further contains a macromonomer. A typical example of the macromonomer used in the present invention is a macromonomer having a polymerizable functional group at one end and preferably having a number average molecular weight of 500 to 500,000, more preferably 1,000 to 10,000.

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

  Specific examples of the macromonomer include a styrene macromonomer having a polymerizable functional group at one end, a silicone macromonomer having a polymerizable functional group at one end, and a (meth) acrylic acid having a polymerizable functional group at one end. Examples include ester-based macromonomers, such as methyl methacrylate-based macromonomers, butyl acrylate-based macromonomers, and isobutyl methacrylate-based macromonomers. Among these, a styrenic macromonomer having a polymerizable functional group at one end is preferable from the viewpoint of sufficiently containing the pigment in the vinyl polymer.

  The styrene macromonomer having a polymerizable functional group at one end includes 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. Coalescence is 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, more preferably 70% by weight or more from the viewpoint of ensuring that the pigment is sufficiently contained in the vinyl polymer.

  Among the styrenic macromonomers having a polymerizable functional group at one end, a styrenic macromonomer having an acryloyloxy group or a methacryloyloxy group as a polymerizable functional group at one end is preferable.

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

Among the silicone-based macromonomers, the formula (III):
X (Y) _p Si (R ⁶ ) _3-q (Z) _q (III)
(Wherein X is a polymerizable unsaturated group, Y is a divalent linking group, R ⁶ is independently a hydrogen atom, a lower alkyl group, an aryl group or an alkoxy group, and Z is a number average molecular weight of 500 or more. A monovalent siloxane polymer residue, p is 0 or 1, q is an integer of 1 to 3)
Is preferable from the viewpoint of preventing scorching of the head of the ink jet printer.

In the silicone-based macromonomer represented by the formula (III), representative examples of the polymerizable unsaturated group represented by X include carbon such as CH ₂ ═CH— group, CH ₂ ═C (CH ₃ ) — group, etc. The monovalent unsaturated hydrocarbon group of number 2-6 is mentioned. Representative examples of the divalent linking group represented by Y include _a divalent linking group such as a —COO— group, a —COOC _a H _2a — group (a represents an integer of 1 to 5), and a phenylene group. It is done. Of these, —COOC ₃ H ₆ — is preferable. Specific examples of R ⁶ include a hydrogen atom; a lower alkyl group having 1 to 5 carbon atoms such as a methyl group and an ethyl group; an aryl group having 6 to 20 carbon atoms such as a phenyl group; and a C 1-20 such as a methoxy group. And the like. In these, a methyl group is preferable. Z is preferably a residue of a monovalent dimethylsiloxane polymer having a number average molecular weight of 500 to 5,000. p is preferably 1. q is preferably 1.

  Examples of more suitable silicone macromonomers include macromonomers represented by the formula (IV), (V), (VI) or (VII).

CH ₂ = CR ¹ -COOC ₃ H _6- [Si (R ⁷ ) ₂ -O] _b -Si (R ⁷ ) ₃ (IV)
(In the formula, R ¹ is the same as above. R ⁷ is independently a hydrogen atom or a lower alkyl group having 1 to 5 carbon atoms, and b is a number of 5 to 60.)
CH ₂ = CR ¹ -COO- [Si (R ⁷ ) ₂ -O] _b -Si (R ⁷ ) ₃ (V)
(Wherein R ¹ , R ⁷ and b are the same as above)
CH ₂ = CR ¹ -Ph- [Si (R ⁷ ) ₂ -O] _b -Si (R ⁷ ) ₃ (VI)
(In the formula, Ph is a phenylene group, and R ¹ , R ⁷ and b are the same as above.)
CH ₂ = CR ¹ -COOC ₃ H ₆ -Si (OE) ₃ (VII)
[Wherein, R ¹ is the same as defined above. E represents a formula: — [Si (R ⁷ ) ₂ —O] _c —Si (R ⁷ ) ₃ group (R ⁷ is the same as described above, and c is a number from 5 to 65). ]
Among these silicone macromonomers, the silicone macromonomer represented by the formula (IV) is more preferable, and the formula (VIII):
CH ₂ = C (CH ₃ ) -COOC ₃ H _6- [Si (CH ₃ ) ₂ -O] _d -Si (CH ₃ ) ₃ (VIII)
(In formula, d shows the number of 8-40.)
A silicone macromonomer represented by the formula is particularly preferred. Examples of commercially available silicone macromonomers include FM-0711 [trade name, manufactured by Chisso Corporation].

  The content of the macromonomer in the monomer component of the present invention is preferably 1 to 50% by weight, more preferably 3 to 40% by weight, and further preferably 5 to 30% by weight from the viewpoint of water resistance.

  The water-insoluble vinyl polymer of the present invention can be obtained by copolymerizing monomer components 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 an organic solvent. When a water-miscible organic solvent is used as the organic solvent, a water-miscible organic solvent and water can be mixed and used. Examples of the organic solvent include aliphatic alcohols having 1 to 3 carbon atoms such as methanol, ethanol, and propanol; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; esters such as ethyl acetate. Among these, methanol, ethanol, acetone, methyl ethyl ketone, or a mixed solvent of one or more of these and water is preferable.

In the polymerization, a radical polymerization initiator can be used. Preferred radical polymerization initiators include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), dimethyl-2,2′-azobisbutyrate, 2, Examples include azo compounds such as 2′-azobis (2-methylbutyronitrile) and 1,1′-azobis (1-cyclohexanecarbonitrile). Moreover, organic peroxides, such as t-butyl peroxy octoate, di-t-butyl peroxide, dibenzoyl oxide, can also be used as a radical polymerization initiator.
The amount of the polymerization initiator with respect to the monomer component is preferably 0.001 to 5 mol%, more preferably 0.01 to 2 mol%.

  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 mercaptoethanol; xanthogen disulfides such as dimethylxanthogen disulfide and diisopropylxanthogen disulfide; Thiuram disulfides such as methylthiuram disulfide and tetrabutylthiuram disulfide; halogenated hydrocarbons such as carbon tetrachloride and ethylene bromide; hydrocarbons such as pentaphenylethane; and acrolein, methacrolein, allyl alcohol, 2-ethylhexyl Thioglycolate, terbinolene, α-terpinene, γ-terpinene, dipentene, α-methylstyrene dimer, and 9,10-dihydroanthra Unsaturated hydrocarbon compounds such as 1,4-dihydronaphthalene, indene and 1,4-cyclohexadiene; unsaturated heterocyclic compounds such as 2,5-dihydrofuran, and the like. Or 2 or more types can be mixed and used.

  The polymerization conditions of the monomer component vary depending on the radical polymerization initiator, the monomer, the type of the solvent, etc., but the polymerization temperature is usually 30 to 100 ° C., preferably 50 to 80 ° C., and the polymerization time is 1 to 20 hours. It is. The polymerization atmosphere is preferably an inert gas atmosphere such as nitrogen gas.

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

  The weight average molecular weight of the water-insoluble vinyl polymer of the present invention is preferably 10,000 to 300,000, more preferably 20,000 to 250,000, and still more preferably 30,000 to 200,000 from the viewpoints of printing density and gloss.

  The weight average molecular weight of the water-insoluble vinyl polymer is a value measured by gel permeation chromatography using polystyrene as a standard substance and dimethylformamide containing 50 mmol / L LiBr as a solvent.

[Water dispersion of water-insoluble vinyl polymer]
The water dispersion of the water-insoluble vinyl polymer of the present invention is prepared by, for example, dissolving a water-insoluble vinyl polymer in an organic solvent, adding a pigment to the resulting solution, pre-kneading, and then adding a neutralizing agent and water. It can be obtained by preparing an oil-in-water dispersion by kneading and dispersing, and removing the organic solvent from the obtained kneaded product. When performing kneading and dispersing treatment, for example, 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 is preferable from the viewpoint that the amount of inorganic impurities mixed can be reduced.

  The “organic solvent” here means an organic solvent having a boiling point of less than 130 ° C. at 101 kPa. Among organic solvents, alcohol solvents, ketone solvents and ether solvents are preferable.

  Examples of the alcohol solvent include methanol, ethanol, isopropanol, n-butanol, tertiary butanol, isobutanol, diacetone alcohol and the like. Examples of ketone solvents include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of ether solvents include dibutyl ether, tetrahydrofuran, dioxane and the like. Of these organic solvents, isopropanol, acetone and methyl ethyl ketone are preferred.

  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. The degree of neutralization is not particularly limited, but it is usually preferable that the aqueous dispersion obtained is neutral, for example, pH is 4 to 10.

  The solubility in water at 25 ° C. of the water-insoluble vinyl polymer after neutralizing the salt-forming group is preferably 15% by weight or less from the viewpoint of water resistance, and 10% by weight or less from the viewpoint of reducing the viscosity of the water-based ink. More preferred is 5% by weight or less, most preferred is 1% by weight or less.

  The particle size of the water-insoluble vinyl polymer containing the pigment in the aqueous dispersion of the present invention is preferably 0.01 to 0.50 μm, more preferably 0.00 from the viewpoint of preventing clogging of the nozzle and dispersion stability. It is 02-0.20 μm.

  The particle size of the water-insoluble vinyl polymer containing the pigment is a value measured using a laser particle analysis system [ELS-8000, manufactured by Otsuka Electronics Co., Ltd.].

  The content (solid content) of the water-insoluble vinyl polymer containing the pigment in the aqueous dispersion of the present invention is preferably 1 to 50% by weight, more preferably 5 to 30% from the viewpoint of printing density and dispersion stability. %.

In the present invention, the water-insoluble vinyl polymer containing a pigment is not particularly limited as long as the particles are formed of at least the pigment and the water-insoluble vinyl polymer. The particle form in which the pigment is encapsulated, the particle form in which the pigment is uniformly dispersed in the water-insoluble vinyl polymer, the particle form in which a part of the pigment is exposed on the particle surface, etc. included.

[Water-based ink]
The content of the aqueous dispersion in the water-based ink for ink jet recording of the present invention is preferably 1 to 30% by weight as the solid content of water-insoluble vinyl polymer particles containing a pigment, usually from the viewpoint of printing density and ejection stability. %, More preferably 2 to 15% by weight.

  If necessary, additives such as a wetting agent, a dispersant, an antifoaming agent, an antifungal agent, and a chelating agent can be added to the water-based ink of the present invention.

  Examples of the wetting agent include polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, diethylene glycol diethyl ether, diethylene glycol mono n-butyl ether, and triethylene glycol mono n-butyl ether and ethers thereof, Examples thereof include nitrogen compounds such as acetates, N-methyl-2-pyrrolidone, and 1,3-dimethylimidazolidinone. The content of the wetting agent in the water-based ink is preferably 0.1 to 50% by weight, more preferably 0.1 to 30% by weight. The water content in the water-based ink is preferably 40 to 90% by weight.

  The water-based ink of the present invention may further contain an anionic, nonionic, cationic, and amphoteric dispersant such as a surfactant. The content of the dispersant in the water-based ink is preferably 0.1 to 50% by weight, more preferably 1 to 20% by weight.

  “Parts” in the examples is “parts by weight” unless otherwise specified.

Production Examples 1-3
A monomer, an organic solvent (methyl ethyl ketone), a polymerization chain transfer agent (2-mercaptoethanol), and a polymerization initiator shown in Table 1 were used for polymerization under stirring at 75 ° C. in a reaction vessel sufficiently substituted with nitrogen gas. 2,2′-azobis (2,4-dimethylvaleronitrile) (0.9 parts) dissolved in methyl ethyl ketone (40 parts) with respect to the component (100 parts) was replaced with unreacted monomer, and then 1 at 80 ° C. The polymer solution A to C was obtained by aging for a period of time. The weight average molecular weight of the obtained polymer is shown in Table 1.

  The weight average molecular weight of the polymer was measured by gel permeation chromatography using polystyrene as a standard substance and dimethylformamide containing 50 mmol / L LiBr as a solvent.

The details of the compounds shown in Table 1 are as follows.
Acrylamide: Wako Pure Chemical Industries, Ltd. First grade reagent Polypropylene glycol monomethacrylate: Number of moles of propylene oxide added = average 9 moles, Terminal hydroxyl group Polyethylene glycol monomethacrylate: Number of moles added of ethylene oxide = average 23 moles Terminal methoxy group / styrene macromonomer: manufactured by Toagosei Co., Ltd., trade name: AS-6S, number average molecular weight: 6000, polymerizable functional group: methacryloyloxy group / V-65: manufactured by Wako Pure Chemical Industries, Ltd. Polymerization initiator, 2,2′-azobis (2,4-dimethylvaleronitrile)

Example 1
5 parts of the polymer obtained by drying under reduced pressure from the polymer solution A was dissolved in 15 parts of methyl ethyl ketone, and a predetermined amount of a neutralizing agent (5N aqueous sodium hydroxide solution) was added therein to neutralize methacrylic acid. Further, monoazo yellow pigments [C. I. Pigment Yellow 74, manufactured by Dainichi Seika Kogyo Co., Ltd.] was added, and the mixture was treated with a disperser while adding water.

  After adding 100 parts of ion-exchanged water to the obtained kneaded material and stirring, methyl ethyl ketone was removed at 60 ° C. under reduced pressure, and a part of the water was further removed, and then a 5 μm filter [acetylcellulose membrane, outer diameter : 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.] and filtered with a 25 mL needleless syringe (manufactured by Terumo Co., Ltd.) to remove coarse particles to obtain an aqueous dispersion having an average particle size of 98 nm. (25% by weight as solids).

  To the obtained aqueous dispersion, the components shown in Table 2 were added, and an aqueous ink was prepared in the same manner as in Example 1 described in JP-A No. 11-349876.

The details of the compounds shown in Table 2 are as follows.
Surfynol 465: Nonionic activator, manufactured by Air Products, Inc. Ploxel XL2 (S): Antibacterial agent, manufactured by Avicia Co., Ltd. Example 2
An aqueous dispersion having an average particle size of 107 nm was obtained in the same manner as in Example 1 except that the polymer obtained by drying under reduced pressure from the polymer solution B was used (25% by weight as a solid content). Furthermore, the components shown in Table 2 were added to the obtained aqueous dispersion, and inks were similarly prepared.

Comparative Example 1
An aqueous dispersion having an average particle size of 97 nm was obtained in the same manner as in Example 1 except that the polymer obtained by drying under reduced pressure from the polymer solution C was used (25% by weight as the solid content). Furthermore, the components shown in Table 2 were added to the obtained aqueous dispersion, and inks were similarly prepared.

  The physical properties of the water-based inks obtained in Examples 1-2 and Comparative Example 1 were evaluated based on the following methods. The results are shown in Table 2.

(1) Dispersion stability Using a laser particle analysis system [ELS-8000, manufactured by Otsuka Electronics Co., Ltd.], the average particle diameter of polymer particles containing pigments contained in the ink (hereinafter referred to as average particle before storage) Diameter)). After the polymer particles were dried for 12 hours with a vacuum dryer (manufactured by Yamato Scientific Co., Ltd., DP33) adjusted to 40 ° C., the average particle size (hereinafter referred to as the average particle size after storage) was measured by the same method. did. As an index of dispersion stability, dispersion stability was determined according to the following formula and evaluated based on the following evaluation criteria.

Dispersion stability (%) = [average particle diameter after storage / average particle diameter before storage] × 100
<Evaluation criteria>
A: Dispersion stability is 100% or more and less than 120% ○: Dispersion stability is 120% or more and less than 140% Δ: Dispersion stability is 140% or more and less than 160% X: Dispersion stability is 160% or more (2) Glossiness Using an ink jet printer (model number: EM-900C) manufactured by Seiko Epson Corporation, solid printing was performed on special paper (manufactured by Seiko Epson Corporation, PM photographic paper) and left at 25 ° C. for 1 day. It was measured by Nippon Denshoku Co., Ltd., product number: PG-1M, measurement angle 60 °, and evaluated based on the following evaluation criteria.

<Evaluation criteria>
◎: Glossiness is 100 or more ○: Glossiness is 85 or more and less than 100 △: Glossiness is 70 or more and less than 85 ×: Glossiness is less than 70 (3) Print density Using the same printer as (2), use plain paper [ A solid print was made on Xerox Co., Ltd., copy paper 4024] and left at 25 ° C. for 1 day. The print density was measured with a Macbeth densitometer (product number: RD914, manufactured by Macbeth), and evaluated based on the following evaluation criteria.

<Evaluation criteria>
◎: Print density is 1.2 or more ○: Print density is 1.1 or more and less than 1.2 △: Print density is 1.0 or more and less than 1.1 ×: Print density is less than 1.0

From the results shown in Table 2, compared to the aqueous ink of Comparative Example 1, the aqueous inks of Examples 1 and 2 both have excellent dispersion stability, high gloss on special paper, and printing on plain paper. It can be seen that a printed matter having a high density can be obtained.

Claims (7)

  An aqueous dispersion for ink jet recording, which is an aqueous dispersion of a water-insoluble vinyl polymer containing a pigment, wherein the water-insoluble vinyl polymer is obtained by polymerizing a monomer component containing a nonionic (meth) acrylamide monomer. The aqueous dispersion for inkjet recording according to claim 1, wherein the nonionic (meth) acrylamide monomer is a monomer represented by the formula (I).
CH ₂ = C (R ¹ ) CONR ² R ³ (I)
(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² and R ³ are the same or different and each represents a C 1-22 monovalent hydrocarbon group which may have an oxygen atom or a halogen atom. R ² and R ³ may be combined to form a ring which may have a hetero atom.)   The water dispersion for inkjet recording according to claim 1 or 2, wherein the water-insoluble vinyl polymer is obtained by further copolymerizing a salt-forming group-containing monomer and a hydrophobic monomer. The water dispersion for inkjet recording according to any one of claims 1 to 3, wherein the water-insoluble vinyl polymer is obtained by further copolymerizing a polyoxyalkylene or arylene group-containing monomer represented by the formula (II). .
CH ₂ = C (R ¹ ) COO (R ⁴ O) _r R ⁵ (II)
(In the formula, R ¹ represents the above meaning, R ⁴ represents a divalent hydrocarbon group having 1 to 30 carbon atoms which may have a hetero atom, and R ⁵ has a hydrogen atom or a hetero atom. And a monovalent hydrocarbon group having 1 to 30 carbon atoms, r represents a number of 1 to 60, and r R ^{4 s} may be the same or different.)   The water dispersion for inkjet recording according to any one of claims 1 to 4, wherein the water-insoluble vinyl polymer is obtained by further copolymerizing a macromonomer.   The water dispersion for inkjet recording according to any one of claims 1 to 5, wherein the water-insoluble vinyl polymer has a weight average molecular weight of 10,000 to 300,000. An aqueous ink for ink-jet recording, comprising the water dispersion according to any one of claims 1 to 6.