JP2005023284A - Water-based ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based ink for ink-jet recording which is excellent in dispersion stability and drying resistance, and also in discharge stability and is feasible to print on a plain paper in a deep color. <P>SOLUTION: The water-based ink comprises a pigment, a water dispersion of a water-insoluble vinyl polymer, which has an acid value of 30-150 KOH mg/g and a hydroxy value of 2-200 KOH mg/g and contains a carboxy group and a hydroxy group, and a 5-15C polyhydric alcohol having a hydroxy value of 200-2,000 KOH mg/g. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an aqueous ink that can be suitably used as 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, since the pigment-based ink easily penetrates on plain paper having a rough surface, the print density may not be sufficient. Further, when the content of the pigment in the ink is increased in order to improve the printing density, the ink viscosity is increased, leading to a decrease in ink ejection stability.

  As a pigment dispersant or an aqueous recording liquid, a pigment dispersant composed of a copolymer having a specific hydroxyl value or a specific acid group (see, for example, Patent Document 1), or a specific C.I. I. Aqueous recording liquid for ink jet printers comprising No. yellow pigment and colored fine particles coated with a pigment with an organic polymer compound having a carboxy group having a specific acid value and a hydroxy group having a specific hydroxyl value (for example, see Patent Document 2) Has been proposed.

However, even if only the acid value and hydroxyl value of the pigment dispersant are specified, a water-based ink excellent in dispersion stability and drying resistance cannot be obtained. Furthermore, high discharge stability for inkjet recording and high printing density on plain paper cannot be expressed.
Japanese Examined Patent Publication No. 7-103289 JP-A-11-209672

  An object of the present invention is to provide a water-based ink for ink jet recording which is excellent in dispersion stability and drying resistance, has good ejection stability, and can impart a high print density to plain paper.

  The present invention includes a water-insoluble vinyl polymer having a carboxy group and a hydroxy group (hereinafter referred to as a water-insoluble vinyl polymer) containing a colorant and having an acid value of 30 to 150 KOHmg / g and a hydroxyl value of 2 to 200 KOHmg / g. A water-based ink containing an aqueous dispersion of the above and a polyhydric alcohol having 5 to 15 carbon atoms (hereinafter referred to as polyhydric alcohol) having a hydroxyl value of 200 to 2000 KOH mg / g is provided.

  The water-based ink of the present invention is resistant to drying by increasing the affinity between the carboxy group and hydroxy group of the water-insoluble vinyl polymer having a specific range of acid value and hydroxyl value, and the hydroxy group of a specific polyhydric alcohol. It has excellent properties, ejection stability and print density. Therefore, the aqueous ink of the present invention can be suitably used as an aqueous ink for inkjet recording.

[Water-insoluble vinyl polymer]
The water-insoluble vinyl polymer having a carboxy group and a hydroxy group of the present invention is produced by copolymerizing a monomer mixture containing a polymerizable monomer having a carboxy group and a polymerizable monomer having a hydroxy group (hereinafter referred to as a monomer mixture). can do.

  The number average molecular weight of the water-insoluble vinyl polymer is preferably 8000 to 20000, more preferably 9000 to 18000, from the viewpoint of high print density and excellent ejection stability. If the number average molecular weight of the vinyl polymer is within this range, it is preferable because the discharge property is good and a high printing density is obtained. The number average molecular weight of the water-insoluble vinyl polymer can be measured by gel permeation chromatography using polystyrene as a standard substance and dimethylformamide containing 50 mmol / L LiBr as a solvent.

Preferred examples of the polymerizable monomer having a carboxy group include α, β-unsaturated carboxylic acid, and (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2- (meta ) Acrylyloxymethyl succinic acid and the like are exemplified. These can be used alone or in admixture of two or more.
As used herein, “(meth) acryl” means “acryl” or “methacryl”.

  Among the polymerizable monomers having a carboxy group, (meth) acrylic acid is more preferable from the viewpoint of good dispersion stability and high printing density. The content of the monomer having a carboxy group in the monomer mixture is preferably 5 to 30% by weight, more preferably 10 to 25% by weight from the viewpoint of achieving a high printing density.

  Examples of the neutralizing agent for the carboxy group include tertiary amines such as trimethylamine and triethylamine, and bases such as ammonia, sodium hydroxide and potassium hydroxide. From the viewpoint of dispersion stability, the amount of neutralizing agent added is preferably adjusted to a pH of 7.5 to 10.0, more preferably adjusted to pH 8.0 to 9.5.

  Depending on the degree of neutralization required for the water-based ink, the solubility of the vinyl polymer after neutralizing the carboxy group in water at 25 ° C. is preferably 15% by weight or less from the viewpoint of reducing the viscosity of the water-based ink. % By weight or less is preferable, 5% by weight or less is more preferable, and 1% by weight or less is more preferable.

  The acid value based on the carboxy group of the water-insoluble vinyl polymer is 30 to 150 KOHmg / g, preferably 40 to 140 KOHmg / g, from the viewpoint of achieving excellent dispersion stability and high printing density. When the acid value is 30 KOHmg / g or more, the dispersion stability is high, and when the acid value is 150 KOHmg / g or less, the print density is high. In addition, the acid value in this invention is represented by mg amount of potassium hydroxide required in order to neutralize 1g of polymer solids.

  The polymerizable monomer having a hydroxy group preferably has a hydroxy group such as hydroxyethyl mono (meth) acrylate, hydroxypropyl mono (meth) acrylate, hydroxybutyl mono (meth) acrylate, glycerin mono (meth) acrylate, and the like. Is an alkyl (meth) acrylate having 2 to 8 carbon atoms; hydroxypolyethylene glycol mono (meth) acrylate, hydroxypolypropylene glycol mono (meth) acrylate, hydroxypolybutylene glycol mono (meth) acrylate, hydroxypoly (ethylene glycol / propylene glycol) Poly (meth) acrylate, poly (ethylene glycol / tetramethylene glycol) mono (meth) acrylate, etc. having a hydroxyl group at the end Oxyalkylene (Polyoxyethylene, polyoxypropylene, polyoxyethylene / polyoxypropylene or polyoxyethylene / polyoxytetramethylene having preferably 1 to 30, more preferably 2 to 15 repeating units, And oxypropylene or oxytetramethylene may be block bonds or random bonds) glycol (meth) acrylate; ethylene glycol monoallyl ether, propylene glycol monoallyl ether, polyethylene glycol allyl ether, polypropylene glycol allyl ether Polyoxyalkylene having a hydroxyl group at the terminal, such as poly (ethylene glycol / propylene glycol) allyl ether (the number of repeating units is preferably 1 to 30) Preferably 2 to 15 polyoxyethylene, polyoxypropylene or polyoxyethylene-polyoxypropylene, where oxyethylene or oxypropylene may be a block bond or a random bond) glycol monoallyl ether Etc.

  Among polymerizable monomers having a hydroxy group, hydroxyethyl mono (meth) acrylate, hydroxypropyl mono (meth) acrylate, hydroxybutyl mono (meth) acrylate, hydroxypolyethylene (preferably from the viewpoint of drying resistance and printing density Glycol mono (meth) acrylate (having 2 to 30 repeating units) and hydroxypolypropylene (preferably having 2 to 30 repeating units) glycol mono (meth) acrylate are more preferred. These can be used alone or in admixture of two or more. The content of the monomer having a hydroxy group in the monomer mixture is preferably 5 to 30% by weight, more preferably 10 to 25% by weight from the viewpoint of printing density.

  The hydroxyl value of the water-insoluble vinyl polymer is 2 to 200 KOHmg / g, preferably 5 to 180 KOHmg / g, from the viewpoint of the effect of suppressing the drying property and the high printing density. When the hydroxyl value is 2 KOHmg / g or more, the drying property can be suppressed, and when the hydroxyl value is 200 KOHmg / g or less, the printing density is high. The hydroxyl value is expressed in terms of mg of potassium hydroxide necessary for neutralizing acetic acid in which 1 g of the polymer solid is bonded to the hydroxyl group.

  The monomer mixture preferably contains a macromonomer in addition to the monomer having a carboxy group and the monomer having a hydroxy group. A typical example of the macromonomer includes a macromonomer having a polymerizable functional group at one end and preferably having a number average molecular weight of 500 to 50,000, more preferably 1000 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 methyl methacrylate macromonomer having a polymerizable functional group at one end. Butyl acrylate macromonomer having a polymerizable functional group at one end, and isobutyl methacrylate macromonomer having a polymerizable functional group at one end. Among these, a styrenic macromonomer having a polymerizable functional group at one end and a silicone macromonomer having a polymerizable functional group at one end are preferred, and from the viewpoint of sufficiently containing a colorant in the vinyl polymer, one end A styrenic macromonomer having a polymerizable functional group is more preferred.

  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. 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, in the copolymer of styrene and another monomer having a polymerizable functional group at one end, the proportion of the styrene is preferably 60% by weight from the viewpoint that the pigment is sufficiently contained in the vinyl polymer. % Or more, more preferably 70% by weight or more.

  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 Toagosei Co., Ltd.

  Moreover, as a silicone type macromonomer which has a polymerizable functional group in one terminal, the silicone type macromonomer represented by Formula (I) is preferable from a viewpoint of preventing the burning of the head of an inkjet printer.

X (Y) _q Si (R ¹ ) _3-r (Z) _r (I)
(Wherein X is a polymerizable unsaturated group, Y is a divalent linking group, R ¹ 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, q is 0 or 1, and r is an integer of 1 to 3)
In the silicone macromonomer represented by the formula (I), typical examples of the polymerizable unsaturated group represented by X include carbon such as CH ₂ ═CH— group, CH ₂ ═C (CH ₃ ) — group, etc. Examples are monovalent unsaturated hydrocarbon groups of 2 to 6. 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 ¹ 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. q is preferably 1. r is preferably 1.

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

CH ₂ = CR ² -COOC ₃ H _6- [Si (R ³ ) ₂ -O] _b -Si (R ³ ) ₃ (II)
(Wherein R ² represents a hydrogen atom or a methyl group, R ³ independently represents a hydrogen atom or a lower alkyl group having 1 to 5 carbon atoms, and b represents a number of 5 to 60.)
CH ₂ = CR ² -COO- [Si (R ³ ) ₂ -O] _b -Si (R ³ ) ₃ (III)
(Wherein R ² , R ³ and b are the same as above)
CH ₂ = CR ² -Ph- [Si (R ³ ) ₂ -O] _b -Si (R ³ ) ₃ (IV)
(In the formula, Ph is a phenylene group, R ² , R ³ and b are the same as above.)
CH ₂ = CR ² -COOC ₃ H ₆ -Si (OE) ₃ (V)
[Wherein R ² is the same as defined above. E represents a formula: — [Si (R ³ ) ₂ —O] _c —Si (R ³ ) ₃ group (R ³ 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 (II) is more preferable, and the formula (VI):
CH ₂ = C (CH ₃ ) -COOC ₃ H _6- [Si (CH ₃ ) ₂ -O] _d -Si (CH ₃ ) ₃ (VI)
(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 mixture is preferably 3 to 30% by weight, and more preferably 5 to 25% by weight, from the viewpoint of adsorptivity to the pigment.

  The water-insoluble vinyl polymer used in the present invention is preferably a polymer obtained by polymerizing a monomer mixture containing (meth) acrylic acid, a polymerizable monomer having a hydroxy group, and a macromonomer.

  In particular, when a styrene-based macromonomer is used as the macromonomer, the water-based ink can obtain a particularly excellent printed matter due to drying resistance and ejection stability.

  In the monomer mixture, for example, a (meth) acrylic acid ester or an aromatic ring-containing monomer is preferably used as a copolymerizable monomer. These can be used alone or in admixture of two or more.

  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, it shows normal.

  Examples of aromatic ring-containing monomers include styrene, vinyl naphthalene, α-methyl styrene, vinyl toluene, ethyl vinyl benzene, 4-vinyl biphenyl, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, and 2-hydroxy-3-phenoxypropyl. An acrylate etc. are mentioned, These can be used individually or in mixture of 2 or more types, respectively.

  The content of the (meth) acrylic acid ester and the aromatic ring-containing monomer in the monomer mixture is preferably 10 to 87% by weight, more preferably 25 to 75% by weight, from the viewpoint of excellent dispersion stability.

  The water-insoluble vinyl polymer can be produced by polymerizing the monomer mixture 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 and propanol; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate and the like. Among these, methanol, ethanol, acetone, methyl ethyl ketone, or a mixed solution 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 mixture.

  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 mixture vary depending on the type of radical polymerization initiator, monomer, and solvent used, it cannot be determined unconditionally. Usually, polymerization temperature becomes like this. Preferably it is 30-100 degreeC, More preferably, it is 50-80 degreeC. 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 water-insoluble vinyl polymer can be isolated from the reaction solution by a known method such as reprecipitation or solvent distillation. The obtained vinyl polymer can be purified by repeating reprecipitation, removing unreacted monomers, etc. by membrane separation, chromatographic methods, extraction methods and the like.

[Colorant]
As the colorant used in the present invention, a pigment and a hydrophobic dye are preferable from the viewpoint of light resistance and water resistance. The pigment may be either an organic pigment or an inorganic pigment. If necessary, extender pigments can be used in combination.

  Examples of the organic pigment include azo pigments, diazo 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, CI Pigment Red 48, 57, 122, 184, 188, CI Pigment Violet 19, and CI Pigment Blue 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, CI Pigment Green 7, 36 etc.

  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.

  The hydrophobic dye is not particularly limited as long as it can be contained in the polymer particles. Examples of hydrophobic dyes include oily dyes and disperse dyes. The solubility of the hydrophobic dye is preferably 2 g / L or more with respect to the organic solvent used for dissolving the hydrophobic dye during the production of the aqueous dispersion, from the viewpoint of efficiently incorporating it into the polymer particles, and 20 to 500 g. / L is more preferable.

  The oil dye is not particularly limited, and examples thereof include CI solvent black 3, 7, 27, 29, 34; CI solvent yellow 14, 16, 29, 56, 82; CI solvent red 1, 3, 8, 18, 24, 27, 43, 51, 72, 73; CI Solvent Violet 3; CI Solvent Blue 2, 11, 70; CI Solvent Green 3, 7; CI Solvent Orange 2, etc. It is done.

  The disperse dye is not particularly limited, but preferred examples include CI Disperse Yellow 5, 42, 54, 64, 79, 82, 83, 93, 99, 100, 119, 122, 124, 126, 160, 184: 1, 186, 198, 199, 204, 224, 237; CI Disperse Orange 13, 29, 31: 1, 33, 49, 54, 55, 66, 73, 118, 119, 163 CI Disperse Red 54, 60, 72, 73, 86, 88, 91, 93, 111, 126, 127, 134, 135, 143, 145, 152, 153, 154, 159, 164, 167: 1, 177, 181, 204, 206, 207, 221, 239, 240, 258, 277, 278, 283, 311, 323, 343, 348, 356, 362; CI Disperse Violet 33; CI Disperse Blue 56, 60, 73, 87, 113, 128, 143, 148, 154, 158, 165, 165: 1, 165: 2, 176, 183, 185, 197, 198, 201, 214, 224, 225, 257, 266, 267, 287, 354, 358, 365, 368; CI Disperse Green 6: 1, 9 and the like. Among these, C.I. Solvent Yellow 29 and 30 as yellow, C.I. Solvent Blue 70 as cyan, C.I. Solvent Red 18 and 49 as magenta, C.I. Solvent Black 3 as black, and nigrosine black dye are preferable.

  Commercially available oil-based dyes include, for example, Nubian Black PC-0850, Oil Black HBB, Oil Black 860, Oil Yellow 129, Oil Yellow 105, Oil Pink 312, Oil Red 5B, Oil Scarlet 308, Vali Fast Blue 2606, Oil Blue BOS [above, manufactured by Orient Chemical Co., Ltd., trade name], Neopen Yellow 075, Neopen Mazenta SE1378, Neopen Blue 808, Neopen Blue FF4012, Neopen Cyan FF4238 (above, trade name, manufactured by BASF) Can be mentioned.

  The amount of the colorant is preferably 20 to 1200 parts by weight, more preferably 50 to 900 parts per 100 parts by weight of the resin solid content of the water-insoluble vinyl polymer, from the viewpoint of printing density and ease of inclusion in the polymer particles. Parts by weight.

[Aqueous dispersion of water-insoluble vinyl polymer containing colorant]
An aqueous dispersion of a water-insoluble vinyl polymer containing a hydrophobic dye as a colorant can be produced by a known emulsification method. More specifically, a water-insoluble vinyl polymer and a hydrophobic dye are dissolved in an organic solvent, and if necessary, a neutralizing agent is added to ionize a salt-forming group in the polymer. Depending on the case, dispersion is carried out using a disperser or an ultrasonic emulsifier, and the organic solvent is distilled off and the phase is changed to an aqueous system, whereby an aqueous dispersion can be obtained.

  As a method for obtaining an aqueous dispersion of a water-insoluble vinyl polymer containing a pigment as a colorant, a water-insoluble vinyl polymer is dissolved in an organic solvent, and a pigment, water, a neutralizing agent and, if necessary, a surfactant are added. In addition, after kneading, a method of diluting with water as necessary and distilling off the organic solvent to make an aqueous system is preferable.

  As the organic solvent, alcohol solvents, ketone solvents and ether solvents are preferable, and among these, hydrophilic organic solvents are more preferable. 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. Of these organic solvents, isopropanol, acetone and methyl ethyl ketone are preferred.

  Moreover, you may use together the said organic solvent and a high boiling hydrophilic organic solvent as needed. 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.

  The average particle size of the polymer particles in the aqueous dispersion of the water-insoluble vinyl polymer containing the colorant is preferably 0.01 to 0.50 μm, more preferably 0, from the viewpoint of preventing nozzle clogging and dispersion stability. 0.02 to 0.30 μm, more preferably 0.05 to 0.20 μm.

  In the aqueous dispersion of a water-insoluble vinyl polymer containing a colorant, an anionic, nonionic or amphoteric surfactant can be used as a surfactant.

[Polyhydric alcohol]
The hydroxyl value of the polyhydric alcohol used in the present invention is excellent in drying resistance and ejection stability, and is 200 to 2000 KOHmg / g, preferably 300 to 1800 KOHmg / g, more preferably from the viewpoint of high printing density. Is 500-1500 KOHmg / g. When the hydroxyl value is 200 KOHmg / g or more, the ejection properties are stable, and when the hydroxyl value is 2000 KOHmg / g or less, the printing density is high. The hydroxyl value of the polyhydric alcohol is expressed in terms of mg of potassium hydroxide necessary for neutralizing acetic acid bonded to the hydroxyl group of 1 g of the polyhydric alcohol.

  The polyhydric alcohol is a polyhydric alcohol having 5 to 15 carbon atoms from the viewpoint of excellent drying resistance and high printing density, and a diol is preferable. When the carbon number is 5 or more, the hydrophilicity is not too strong and the printing density is high, and when the carbon number is 15 or less, the hydrophobicity is not too strong and the ejection property is stable.

  Examples of the polyhydric alcohol having 5 to 15 carbon atoms include triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, 2,2-dimethyl-1,3-propanediol, 1,5-pentanediol, 2, 4-pentanediol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2,3- Dimethyl-2,3-butanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 2 -Ethyl-1,3-hexanediol, 1,8-octanediol, 2,5-dimethyl-2,5-hexanediol, 2 5-dimethyl-3-hexyne-2,5-diol, 3,6-dimethyl-4-octyne-3,6-diol, polypropylene glycol (average molecular weight 700 to 2,000, a diol type) include diols such. These may be used alone or in combination of two or more.

  The polyhydric alcohol preferably has a water / octanol distribution coefficient logarithm (logPow) of -0.5 to 3.0 from the viewpoint of ejection stability and print density, and more preferably 0.0 to 2.5. . In addition, the logarithmic value (logPow) of the water / octanol distribution coefficient can be obtained by ACD / ChemSketch software (manufactured by L Systems). When the logarithmic value (logPow) of the water / octanol partition coefficient is −0.5 or more, the hydrophilicity is not too strong and the print density becomes high, and the logarithmic value (logPow) of the water / octanol partition coefficient is 3. In the case of 0 or less, the hydrophobicity is not too strong and the ejection property is stable.

  Examples of the polyhydric alcohol having a logarithmic value (logPow) of water / octanol partition coefficient in the range of −0.5 to 3.0 include tripropylene glycol, 2,2-dimethyl-1,3-propanediol, 2, 2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2,3-dimethyl-2,3-butane Diol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 2-ethyl-1,3- Hexanediol, 1,8-octanediol, 2,5-dimethyl-2,5-hexanediol, 2,5-dimethyl-3-hexyne-2,5-diol, 3,6-dimethyl 4-octyne-3,6-diol.

  The polyhydric alcohol preferably has a solubility in water at 20 ° C. of 0.1 to 15% by weight from the viewpoint of excellent ejection stability and printing density. More preferably, the solubility is 1 to 10% by weight.

  Examples of the polyhydric alcohol having a solubility in water at 20 ° C. in the range of 0.1 to 15% by weight include 2-butyl-2-ethyl-1,3-propanediol, 2,2-dimethyl-1,3- Propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-1,3-hexanediol, 1,8-octanediol, 2,5-dimethyl-2,5-hexanediol, 2,5 -Dimethyl-3-hexyne-2,5-diol, 3,6-dimethyl-4-octyne-3,6-diol, polypropylene glycol (average molecular weight 700-1200, diol type) and the like.

[Water-based ink]
The water-based ink of the present invention has a specific hydroxyl value and a carboxy group and a hydroxy group of a water-insoluble vinyl polymer having a specific acid value and a hydroxyl value constituting an aqueous dispersion of a water-insoluble vinyl polymer containing a colorant. Due to the affinity with the hydroxy group of the polyhydric alcohol, the ink is excellent in drying resistance and ejection stability, and becomes a water-based ink for inkjet recording with a high print density. In particular, a high print density can be given to plain paper having a rough paper surface and quick ink permeability.

  The principle is not clear, but due to the interaction between the relatively hydrophobic polyhydric alcohol and the fine particles of the water-insoluble vinyl polymer containing the colorant, it tends to remain on the surface of the paper, and a high print density is expressed. It is done. A wetting agent such as glycerin is excellent in drying resistance, but if it is contained in a large amount, the viscosity increases and the dischargeability tends to be inferior.

  In the water-based ink of the present invention, the blending ratio of the water-insoluble vinyl polymer containing the colorant and the polyhydric alcohol is 100 parts by weight of the solid content of the water-insoluble vinyl polymer containing the colorant. On the other hand, the polyhydric alcohol is preferably 30 to 300 parts by weight, more preferably 40 to 200 parts by weight.

  In the water-based ink of the present invention, the content of the water dispersion of a water-insoluble vinyl polymer containing a colorant is preferably from the viewpoint of high print density and excellent ejection stability, in terms of solid content of the water dispersion. Is 1 to 20% by weight, more preferably 3 to 15% by weight. Further, the content of the polyhydric alcohol in the water-based ink of the present invention is preferably 1 to 30% by weight, more preferably 3 to 25% by weight from the viewpoint of drying resistance and printing density. The water content in the aqueous ink of the present invention is preferably 50 to 80% by weight.

  The water-based ink of the present invention may further contain additives such as a wetting agent, a dispersing agent, an antifoaming agent, an antifungal agent, and a chelating agent, if necessary.

  “Parts” and “%” in the examples are “parts by weight” and “% by weight”, respectively, unless otherwise specified.

Synthesis Example and Comparative Synthesis Example In a reaction vessel, 20 parts of methyl ethyl ketone, 0.2 part of a polymerization chain transfer agent (2-mercaptoethanol), and 10% of the number of parts of each monomer shown in Table 1 were mixed and mixed with nitrogen gas. Substitution was sufficiently performed to obtain a mixed solution.

  On the other hand, 90% of the number of parts of each monomer shown in Table 1 was charged in the dropping funnel, 0.27 part of a polymerization chain transfer agent (2-mercaptoethanol), 60 parts of methyl ethyl ketone and 2,2′-azobis (2,4- 1.2 parts of (dimethylvaleronitrile) was added and mixed, and nitrogen gas substitution was sufficiently performed to obtain a mixed solution.

  Under a nitrogen atmosphere, the mixed solution in the reaction vessel was heated to 65 ° C. while stirring, and the mixed solution in the dropping funnel was gradually added dropwise over 3 hours. After 2 hours at 65 ° C. from the end of dropping, a solution prepared by dissolving 0.3 part of 2,2′-azobis (2,4-dimethylvaleronitrile) in 5 parts of methyl ethyl ketone was added, and further at 65 ° C. for 2 hours, 70 ° C. And polymer solutions A and B were obtained.

  A portion of the resulting polymer solution was dried at 105 ° C. under reduced pressure for 2 hours and isolated by removing the solvent, and dimethylformamide containing polystyrene as a standard substance and 50 mmol / L LiBr as a solvent was used. The number average molecular weight was measured by gel permeation chromatography. Further, the acid value is measured by the amount of potassium hydroxide required to neutralize 1 g of the polymer solid, and the hydroxyl value is necessary for neutralizing acetic acid in which 1 g of the polymer solid is bonded to the hydroxyl group. It was measured by the amount of mg of potassium hydroxide. The results are shown in Table 1.

The details of the compounds shown in Table 1 are as follows.
Methoxypolyethylene glycol monomethacrylate: manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK ester M-40G
Hydroxy polypropylene glycol monomethacrylate: manufactured by Nippon Oil & Fats Co., Ltd., trade name: BLEMMER PP-500
Styrene macromonomer: manufactured by Toagosei Co., Ltd., trade name: AS-6S, number average molecular weight: 6000, polymerizable functional group: methacryloyloxy group

Examples 1-4 and Comparative Examples 1-2
5 parts of each polymer obtained by drying under reduced pressure from polymer solutions A and B was dissolved in 45 parts of methyl ethyl ketone, and a predetermined amount of neutralizing agent (16.9% aqueous sodium hydroxide) was added thereto to form a salt-forming group. After neutralization, 15 parts of dimethylquinacridone pigment [CI Pigment Red 122, manufactured by Dainichi Seika Kogyo Co., Ltd.] was added and dispersed to a predetermined particle size with a kneader to obtain a kneaded product. 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 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 (25 as solid content). %). To the obtained aqueous dispersion, the ink components shown in Table 2 were added to obtain an aqueous ink.

  The hydroxyl value of the polyhydric alcohol was measured as the amount of potassium hydroxide required to neutralize 1 g of polyhydric alcohol bound to the acetic acid.

  Next, physical properties of the obtained water-based ink were evaluated based on the following methods. The results are shown in Table 2.

(1) Drying resistance Using a laser particle analysis system (ELS-8000, manufactured by Otsuka Electronics Co., Ltd.), the average particle diameter of polymer particles containing the colorant contained in the ink (hereinafter referred to as average particle before storage) Diameter)). In a vacuum dryer adjusted to 40 ° C. (manufactured by Yamato Kagaku Co., Ltd., DP33), 3 g of water-based ink was placed in a plastic ointment container with an inner diameter of 37 mm and dried for 12 hours without a lid. The average particle diameter (hereinafter referred to as the average particle diameter after storage) was measured.

  As an index of drying resistance, the degree of drying resistance was determined according to the following formula and evaluated based on the following evaluation criteria.

Drying resistance (%) = [average particle diameter after storage / average particle diameter before storage] × 100
<Evaluation criteria>
A: Drying resistance is less than 150%. O: Drying resistance is 150% or more and less than 200%. Δ: Drying resistance is 200% or more and less than 300%. X: Drying resistance is 300% or more. That is, an ink having a dry resistance of 〜 to ◎ (dry resistance of less than 200%) indicates that the polymer particles are less likely to aggregate even if water evaporates to some extent. Accordingly, the dispersion stability is also excellent.

(2) Dischargeability The ink dischargeability was evaluated according to the following evaluation criteria using an ink jet printer (model number: EM-930C) manufactured by Seiko Epson Corporation.

<Evaluation criteria>
○: Good ejection at all nozzles △: Some nozzles have poor ejection ×: Ejection failure (3) Print density Using the printer, print solid on plain paper (Xerox Co., Ltd., copy paper 4024) at 25 ° C After leaving for 1 day, the printing density was measured with a Macbeth densitometer (manufactured by Macbeth, product number: RD914), and evaluated based on the following evaluation criteria.

<Evaluation criteria>
A: Print density is 1.2 or more. B: Print density is 1.1 or more and less than 1.2. Δ: Print density is 1.0 or more and less than 1.1. X: Print density is less than 1.0. Details of the compounds are as follows.
Tetraethylene glycol: manufactured by Wako Pure Chemical Industries, Ltd., reagent, diol having 8 carbon atoms, logarithm of water / octanol partition coefficient (logPow) = − 0.90, solubility in water at 20 ° C. = ∞
1,6-hexanediol: manufactured by Wako Pure Chemical Industries, Ltd., reagent, diol having 6 carbon atoms, logarithm of water / octanol partition coefficient (logPow) = − 0.11, solubility in water at 20 ° C. = ∞
1,8-octanediol: manufactured by Wako Pure Chemical Industries, Ltd., reagent, diol having 8 carbon atoms, logarithm of water / octanol partition coefficient (logPow) = 0.66, solubility in water at 20 ° C. = 4. 2%
3,6-dimethyl-4-octyne-3,6-diol: manufactured by Wako Pure Chemical Industries, Ltd., reagent, diol having 10 carbon atoms, logarithm of water / octanol partition coefficient (logPow) = 1.24, Solubility in water at 20 ° C. = 10.5%
-Acetylenol EH: Nonionic activator, manufactured by Kawaken Fine Chemicals Co., Ltd.

  From the results shown in Table 2, the water-based inks of the present invention obtained in Examples 1 to 4 with respect to Comparative Examples 1 and 2 are all excellent in drying resistance and discharge stability, It can be seen that printed matter with high print density can be obtained on plain paper.

Claims (5)

An aqueous dispersion of a water-insoluble vinyl polymer having a carboxy group and a hydroxy group (hereinafter referred to as a water-insoluble vinyl polymer) containing a colorant and having an acid value of 30 to 150 KOHmg / g and a hydroxyl value of 2 to 200 KOHmg / g And a water-based ink containing a polyhydric alcohol having 5 to 15 carbon atoms (hereinafter referred to as polyhydric alcohol) having a hydroxyl value of 200 to 2000 KOHmg / g. The water-based ink according to claim 1, wherein the polyhydric alcohol is a polyhydric alcohol having a logarithmic value (logPow) of a water / octanol distribution coefficient of -0.5 to 3.0. The water-based ink according to claim 1 or 2, wherein the polyhydric alcohol is a polyhydric alcohol having a solubility in water of 20 ° C of 0.1 to 15% by weight. The water-based ink according to any one of claims 1 to 3, wherein the water-insoluble vinyl polymer is a polymer obtained by polymerizing a monomer mixture containing acrylic acid or methacrylic acid, a polymerizable monomer having a hydroxy group, and a macromonomer. . The water-based ink according to any one of claims 1 to 4, wherein the colorant is a pigment or a hydrophobic dye.