JP2011157450A - Aqueous pigment dispersion liquid and recording liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pigment-dispersed recording liquid having a high print density and a high print quality with good marker resistance and low pigment sedimentation.
An aqueous pigment dispersion comprising (a) a pigment, (b) a polymer, and (c) water, wherein the aqueous pigment dispersion has a surface tension of 67 dyne / cm or more. .
[Selection figure] None

Description

The present invention relates to an aqueous pigment dispersion having a surface tension of 67 dyne / cm or more. More specifically, the present invention relates to a pigment dispersion type recording liquid suitable as a recording liquid for an ink jet printer, an ink composition containing the aqueous pigment dispersion, and an ink jet recording method using the ink composition.

  Inkjet printers can easily obtain full-color high-resolution images, have low power consumption, have low introduction costs and low running costs, and have become capable of high-speed printing equivalent to electrophotographic printing. For these reasons, the use of business youth is spreading rapidly. At present, aqueous recording liquids are mainly used as recording liquids for ink jet printers, and particularly for black inks, aqueous recording liquids using pigments as coloring materials are becoming mainstream.

In recent years, when business use is targeted, demands for high printing density comparable to electrophotographic printing and high printing durability are increasing day by day. In response to this requirement, it is desired to provide a printed matter having a low pigment sedimentation rate, a high print density, and excellent marker resistance as ink performance.
On the other hand, as a water-based pigment recording liquid targeted for business use, development is generally continued by the following two methods.

  The first method is a method using a so-called “self-dispersing” pigment recording liquid in which a hydrophilic functional group is chemically bonded to the pigment surface and dispersed in an aqueous medium by itself (for example, patent document). 1). Currently, it is used as a black ink for many printers, but the printed matter obtained with the aqueous recording liquid of this “self-dispersing carbon black” has a high printing density, but it is practically large in terms of printing quality such as marker resistance. There's a problem. In addition, there is a limit to the type and amount of functional groups that can be bonded to the pigment surface, and no further improvement in performance can be expected.

  On the other hand, a polymer-dispersed pigment dispersion in which a pigment is dispersed with a water-soluble polymer has been developed (for example, Patent Document 2). However, the printed matter obtained from the polymer-dispersed pigment dispersion generally exhibits better marker resistance than the “self-dispersing type”, but has a problem that the printing density is low, which is an obstacle to practical use. . Further, there is a demand for further improvements in pigment sedimentation.

JP 2001-55530 A Japanese Patent Laid-Open No. 10-81842

  An object of the present invention is to provide a pigment-dispersed recording liquid having a high print density, high print quality with good marker resistance, and low pigment sedimentation.

As a result of intensive studies to solve such problems, the present inventors have found that in an aqueous dispersion composed of a pigment, a polymer, and water, the surface tension of the aqueous pigment dispersion is 67 dyne / cm or more. It has been found that a printed matter having a high printing density with plain paper and a good marker resistance can be obtained. Furthermore, the inventors have found that an ink composition having a low pigment sedimentation property can be obtained by using carbon black having an average primary particle size of 20 nm or less, thereby completing the present invention.
That is, the first gist of the present invention is that, in an aqueous pigment dispersion comprising (a) a pigment, (b) a polymer, and (c) water, the surface tension of the aqueous pigment dispersion is 67 dyne / cm or more. In the aqueous pigment dispersion characterized.

The second gist of the present invention resides in an ink composition comprising the aqueous pigment dispersion.
The third gist of the present invention resides in an ink jet recording method characterized in that a droplet of the ink composition is ejected from an ink jet head and the droplet is adhered to a recording medium.

According to the aqueous pigment dispersion of the present invention, it is possible to provide a pigment-dispersed recording liquid capable of obtaining a high-print quality printed matter having a high printing density and good marker resistance.
In particular, the aqueous pigment dispersion of the present invention can be suitably used for a recording liquid such as an ink jet printer.

Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of the embodiments of the present invention, and the present invention does not exceed the gist thereof. These contents are not specified.
In the following, “(meth) acrylate” means “acrylate and / or methacrylate”, and “(meth) acryl” means “acryl and / or methacryl”.

[Aqueous pigment dispersion]
The aqueous pigment dispersion of the present invention is characterized in that in the aqueous pigment dispersion comprising (a) a pigment, (b) a polymer, and (c) water, the surface tension of the aqueous pigment dispersion is 67 dyne / cm or more. To do.
As used herein, “aqueous pigment dispersion” refers to a dispersion in which a pigment is dispersed in water with a polymer.
The surface tension is measured according to a conventional method. For example, there is a measurement by the Wilhelmy method. As the measuring device, for example, CBVP-Z manufactured by Kyowa Interface Science Co., Ltd. is used.

By setting the surface tension of the aqueous pigment dispersion to 67 dyne / cm or more, a sufficient printing density can be obtained. The reason for this is not clear, but by setting the surface tension of the aqueous pigment dispersion to 67 dyne / cm or more, in the ink composition containing the aqueous pigment dispersion of the present invention, the penetration rate of the pigment into the paper was slowed. it is conceivable that.
The surface tension of the aqueous pigment dispersion is preferably 68 dyne / cm or more, more preferably 69 dyne / cm or more, and usually 73 dyne / cm or less. The higher the surface tension, the higher the print density tends to be.
The surface tension of the aqueous pigment dispersion is affected by the type and amount of the polymer. When a polymer having a large surface activity is used, the surface tension is greatly reduced. When a polymer having a small surface activity is used, the surface tension is lowered, but the degree of the reduction is small. In order to adjust the surface tension of the aqueous pigment dispersion to a predetermined value, the type and amount of the polymer may be adjusted.

[(a) Pigment]
The pigment used in the present invention may be appropriately selected from those commonly used in each application, and is not particularly limited. Examples of typical pigments include calcium carbonate, kaolin clay, talc, bentonite, and mica. Extender pigments; metal oxide pigments such as titanium oxide, zinc oxide, goethite, magnetite, chromium oxide; titanium yellow, titanium buff, antimony yellow, vanadium tin yellow, cobalt green, cobalt chrome green, manganese green Composite oxide pigments such as cobalt blue, cerulean blue, manganese blue, tungsten blue, Egyptian blue and cobalt black; sulfide pigments such as lithobon, cadmium red yellow and cadmium red; Phosphate pigments such as violet, cobalt violet, lithium cobalt phosphate, sodium cobalt phosphate, potassium potassium phosphate, cobalt ammonium phosphate, nickel phosphate, copper phosphate; yellow lead, molybdate orange Chromate pigments; metal complex pigments such as ultramarine and Prussian blue; metal powder pigments such as aluminum paste, bronze powder, zinc powder, stainless steel flakes, nickel flakes; carbon black, bismuth oxychloride , Basic carbonate, titanium dioxide, coated mica, ITO, inorganic pigments such as pearlescent pigments and pearlescent conductive pigments such as ATO; and quinacridone pigments, quinacridone quinone pigments, dioxazine pigments, phthalocyanine pigments , Anthrapyrimidine pigment, answer Throne pigment, Indanthrone pigment, Flavanthrone pigment, Perylene pigment, Diketopyrrolopyrrole pigment, Perinone pigment, Quinophthalone pigment, Anthraquinone pigment, Thioindigo pigment, Metal complex pigment, Azomethine pigment Or organic pigments, such as an azo pigment, are mentioned.

Specific examples of the pigment include pigments having the pigment numbers shown below and known carbon blacks generally used in the color material field. Note that terms such as “CI Pigment Red 2” mentioned below mean a color index (CI).
Red colorant: C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 14, 15, 16, 17, 21, 22, 23, 31, 32, 37, 38, 41, 47, 48, 48: 1, 48: 2, 48: 3, 48: 4, 49, 49: 1, 49: 2, 50: 1, 52: 1, 52: 2, 53, 53: 1, 53: 2, 53: 3, 54, 57, 57: 1, 57: 2, 58, 58: 4, 60, 63, 63: 1, 63: 2, 64, 64: 1, 68, 69, 81, 81: 1, 81: 2, 81: 3, 81: 4, 83, 88, 90: 1, 101, 101: 1, 104, 108, 108: 1, 109, 112, 113, 114, 122, 123, 144, 146, 147, 149, 151, 166, 168, 169, 170, 172, 173, 174, 175, 176, 177, 78, 179, 181, 184, 185, 187, 188, 190, 193, 194, 200, 202, 206, 207, 208, 209, 210, 214, 216, 220, 221, 224, 230, 231, 232, 233, 235, 236, 237, 238, 239, 242, 243, 245, 247, 249, 250, 251, 253, 254, 255, 256, 257, 258, 259, 260, 262, 263, 264, 265, 266, 267, 268, 269, 270, 271, 272, 273, 274, 275, 276;
Blue colorant: C.I. I. Pigment Blue 1, 1: 2, 9, 14, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17, 19, 25, 27, 28, 29, 33, 35, 36, 56, 56: 1, 60, 61, 61: 1, 62, 63, 66, 67, 68, 71, 72, 73, 74, 75, 76, 78, 79;
Green colorant: C.I. I. Pigment Green 1, 2, 4, 7, 8, 10, 13, 14, 15, 17, 18, 19, 26, 36, 45, 48, 50, 51, 54, 55;
Yellow colorant: C.I. I. Pigment Yellow 1, 1: 1, 2, 3, 4, 5, 6, 9, 10, 12, 13, 14, 16, 17, 23, 24, 31, 32, 34, 35, 35: 1, 36, 36: 1, 37, 37: 1, 40, 41, 42, 43, 48, 53, 55, 61, 62, 62: 1, 63, 65, 73, 74, 75, 81, 83, 87, 93, 94, 95, 97, 100, 101, 104, 105, 108, 109, 110, 111, 116, 119, 120, 126, 127, 127: 1, 128, 129, 133, 134, 136, 138, 139, 142, 147, 148, 150, 151, 153, 154, 155, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166,
167,168,169,170,172,173,174,175,176,180,181,182,183,184,185,188,189,190,191,191: 1,192,193,194,195, 196, 197, 198, 199, 200, 202, 203, 204, 205, 206, 207, 208, 215;
Orange colorant: C.I. I. Pigment Orange 1, 2, 5, 13, 16, 17, 19, 20, 21, 22, 23, 24, 34, 36, 38, 39, 43, 46, 48, 49, 61, 62, 64, 65, 67, 68, 69, 70, 71, 72, 73, 74, 75, 77, 78, 79;
Violet colorant: C.I. I. Pigment Violet 1, 1: 1, 2, 2: 2, 3, 3: 1, 3: 3, 5, 5: 1, 14, 15, 16, 19, 23, 25, 27, 29, 31, 32, 37, 39, 42, 44, 47, 49, 50
Brown colorant: C.I. I. Pigment Brown 1, 6, 11, 22, 23, 24, 25, 27, 29, 30, 31, 33, 34, 35, 37, 39, 40, 41, 42, 43, 44, 45;
Black colorant: C.I. I. Pigment Black 1, 31, 32
Of the above pigments, the red pigment is preferably a quinacridone pigment, a xanthene pigment, a perylene pigment, an anthanthrone pigment, and a monoazo pigment, and specific examples thereof include CI Pigment Red-5, -7, -12, -112, -81, -122, -123, 146, -147, -168, -173, -202, -206, -207, -209, C.I. I. And CI Pigment Violet-19. Among these, the solid solution which consists of a quinacridone-type pigment and two or more types of quinacridone-type pigments is more preferable from the surface of a pigment's stability and hue.

  Of the above-mentioned pigments, monoazo pigments and disazo pigments are preferable as yellow pigments because color development as printed matter is better than other pigments. Among them, C.I. I. Pigment-1, -3, -16, -17, -74, -120, -128, -151, -175, and -215 are particularly preferable from the viewpoint of the color. I. Pigment Yellow-74 and -155 are non-halogen compounds, and are particularly preferable from the viewpoint of small influence on the environment and hue.

Of the above-described pigments, a copper phthalocyanine pigment is preferable as a blue pigment because a color as a printed matter is better than other pigments. Among them, C.I. I. Pigment Blue-15: 3 is preferable from the viewpoints of stability and hue.
Further, as the carbon black used in the present invention, various carbon blacks such as acetylene black, channel black and furnace black can be used. Among these, channel black or furnace black is preferable, and furnace black is particularly preferable.

Specific examples of the carbon black include products shown in the following (1) to (4).
(1) # 2700B, # 2650, # 2650B, # 2600, # 2600B, 2450B, 2400B, # 2350, # 2300, # 2300B, # 2200B, # 1000, # 1000B, # 995B, # 990, # 990B, # 980, # 980B, # 970
, # 960, # 960B, # 950, # 950B, # 900, # 900B, # 850, # 850B, MCF88, MCF88B, MA600, MA600B, # 750B, # 650B, # 52, # 52B, # 50, # 47 , # 47B, # 45, # 45B, # 45L, # 44, # 44B, # 40, # 40B, # 33, # 33B, # 32, # 32B, # 30, # 30B, # 25, # 25B, # 20, # 20B, # 10, # 10B, # 5, # 5B, CF9, CF9B, # 95, # 260, MA77, MA77B, MA7, MA7B, MA8, MA8B, MA11, MA11B, MA100, MA100B, MA100R, MA10
0RB, MA100S, MA230, MA220, MA200RB, MA14, # 3030B, # 3040B, # 3050B, # 3230B, # 3350B (above, manufactured by Mitsubishi Chemical Corporation).

(2) Monarch 1400, Black Pearls 1400, Monarch 1300, Black Pearls 1300, Monarch 1100, Black Pearls 1100, Monarch 1000, Black Pearls 1000, Monarch 900, Black Pearl 900 800, Monarch 700, Black Pearls 700, Black Pearls 2000, Vulcan XC72R, Vulcan
XC72, Vulcan PA90, Vulcan 9A32, Mogul L, Black Pearls L, Regal 660R, Regal 660, Black Pearls 570, Black Pearls 520, Regal 400R, Regal 400R, Regal 400R, Regal 400R, Regal 400R, Regal 400R, Regal 400R, Regal 400R 480, Black
Pearls 470, Black Pearls 460, Black Pearls 450, Black Pearls 430, Black Pearls 420, Black Pearls 410, Regal 350R, Regal 350, Regal 250R, Regal 250, Reg 99, Reg 99 Elftex 12, Monarch 280, Black Pearls 280, Black
Pearls 170, Black Pearls 160, Black Pearls 130, Monarch 120, Black Pearls 120 (above, a product of Cabot Corporation).

(3) Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Special Black 4, Special Black 4A, Special Black 4A, Special Black 4W, Color Black FW2V, Color Black FW2V, Color Black FW2 V, Printex 150T, Printex 140U, Printex 140V, Printex 95, Printex 90, Printex 85, Printex 80, Printex 75, Printex 55, Printex 45, Printex 40, Printex 40, Printex P ex XE, Printex L6, Printex L, Printex 300, Printex 30, Printex 3, Printex 35, Printex 25, Printex 200, Printex A, Printex G, Special
Black 550, Special Black 350, Special Black 250, Special Black 100 (above, Degussa product).

(4) Raven 7000, Raven 5750, Raven 5250, Raven 5000 ULTRA, Raven 3500, Raven 2000, Raven 1500, Raven 1250, Raven 1250, Raven 10170, Raven 1170, Raven 1170, Raven 1170, Raven 1170, Raven 1170, Raven 1170, Raven 1170, Raven 1170, Raven 1170, Raven 1170, Raven 1170 Raven 1000, Raven 890H, Raven 890, Raven 850, Raven 790 ULTRA, Raven 760 ULTRA, Raven 520, Raven 500, Raven 450, Raven 430, Raven 420, Raven 420, Raven 420, Raven 420, Raven 420, Raven 420, Raven 420, Raven 420 n H
2O, Raven C ULTRA (above Colombia product).

  From the viewpoint of safety, it is preferable to use carbon black in which the polycyclic aromatic component is reduced by baking at 600 to 1500 ° C. or washing with water, warm water, a solvent, or the like. In particular, baking at a high temperature is more preferable because the functional group on the surface of the carbon black is removed, whereby the dispersant is more efficiently adsorbed more firmly on the surface of the carbon black.

As the pigment according to the present invention, one of the above pigments may be used alone, or two or more of them may be used in combination. It can also be used in combination with other color materials.
The shape of the pigment may be any form such as paste, powder, solid solution and the like. The size of the primary particles of these pigments may be arbitrarily set depending on the purpose, but is usually 10 nm or more, usually 800 nm or less, preferably 500 nm or less, more preferably 300 nm or less, more preferably 200 nm or less, Especially preferably, it is 100 nm or less. Here, the primary particle diameter of the pigment is an arithmetic average diameter (number average) measured by an electron microscope.

  The pigment is not chemically modified, and a pigment that does not contain impurities other than the pigment, such as a crystallization inhibitor for promoting the reduction in the particle size of the pigment, It is preferable because it does not inhibit the adsorption. However, in order to give the pigment self-dispersibility, a pigment having self-dispersibility which has been subjected to known chemical modification in advance can also be used. That is, the pigment used in the aqueous pigment dispersion of the present invention can be any pigment, whether it is an untreated pigment or a pigment whose surface is chemically modified, as described above.

Among the pigments, carbon black is preferable, and carbon black having the following characteristics is more preferable.
That is, the average primary particle size of carbon black is preferably 20 nm or less, more preferably 18 nm or less. When the average primary particle size is too large, the storage stability is deteriorated, the particles are liable to settle, and the specific surface area is too small, so that the print density tends to be lowered. Here, the average primary particle diameter of carbon black is an arithmetic average diameter (number average) measured by an electron microscope.

Further, DBP absorption amount of carbon black, 80 cm ^3/100 g or more is preferably not more than 150 cm ^3/100 g, further 90cm ^3/100 g or more is preferably not more than 120 cm ^3/100 g. Carbon black that has too little DBP absorption tends to show through on plain paper, does not stay on the top surface of the paper, and tends to have low print density. Carbon black with too much DBP absorption is difficult to disperse and further tends to decrease storage stability and ejection stability. Here, the DBP absorption amount is the amount of dibutyl phthalate (DBP) absorbed by 100 g of carbon black defined by JISk6221.

[(B) Polymer]
As the polymer, known polymers are used, and among them, a polymer containing at least one kind of hydrophobic group and at least one kind of anionic group is preferable from the viewpoint of dispersibility of the pigment.
Examples of the hydrophobic group include aliphatic hydrophobic groups such as alkyl groups, alkenyl groups, and alkynyl groups, alicyclic hydrophobic groups such as cyclohexyl groups and isobornyl groups, and aromatic hydrophobic groups such as phenyl groups and naphthyl groups. Sex groups. These aromatic hydrophobic groups may be unsubstituted or further have a substituent. Examples of the substituent include an alkyl group which may be linear, branched or cyclic, an alkoxyl group which may be linear, branched or cyclic, a hydroxyl group, a carboxyl group, a carboxyl base, a sulfonyl group, a sulfonyl base, Examples include a phosphonyl group, a phosphonyl base, a cyano group, and a halogen group. Examples of the salt include alkali metal salts and alkaline earth metal salts.

An anionic group is a functional group that can have an anionic charge in an aqueous medium and has a pKa of 8 or less, such as an acidic group derived from an acid such as carboxylic acid, sulfonic acid, phosphoric acid, or an alkali metal salt thereof. And alkaline earth metal salt structures.
Further, as the polymer, it is more preferable that at least one or more types of hydrophobic monomers and at least one or more types of anionic monomers are used as monomer structural units.

<Definition of monomer structural unit>
In the present invention, the monomer structural unit is a structural unit of the basic structure of the polymer. The basic structure of a polymer is a structure derived from a monomer molecule used for production of the polymer by polymerization or copolymerization, or a structure modified by modification. Further, when the polymer is a natural polymer, it is a repeating structure or a structure modified by modification or the like.

The primary structure of the polymer is not limited, and specific examples include linear, star, comb, branched, and block polymers, but are not limited thereto. The polymer may be, for example, a synthetic polymer or a natural polymer, or a derivative or modified product thereof.
The polymer is preferably a water-soluble or water-dispersible polymer.
As used herein, “water-soluble” refers to a substance that dissolves in water at 25 ° C. by 2% by weight or more, more preferably a substance that dissolves in 10% by weight or more. “Water dispersibility” refers to a substance that does not cause precipitation in a 2% by weight aqueous dispersion.

<Hydrophobic monomer>
The hydrophobic monomer is not particularly limited, and a conventionally known hydrophobic monomer can be used. In particular, at least one of the hydrophobic monomers is an aromatic ring-containing monomer and / or aliphatic carbonization as described below. A monomer containing a hydrogen group is preferred.

  The aromatic ring-containing monomer is an aromatic heterocyclic ring-containing monomer or an aromatic hydrocarbon ring-containing monomer. For example, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxyethylene glycol (meth) acrylate, 2-naphthyl ( (Meth) acrylate, 9-anthracenyl (meth) acrylate, 1-pyrenylmethyl (meth) acrylate styrene, vinylnaphthalene, styrene, α-methylstyrene, t-butylstyrene, p-methylstyrene, o-methoxystyrene, m-methoxystyrene , P-methoxystyrene, ot-butoxystyrene, mt-butoxystyrene, pt-butoxystyrene, o-chloromethylstyrene, m-chloromethylstyrene, p-chloromethylstyrene, vinyltoluene, ethyl Nirubenzen, 4-vinyl biphenyl, 1,1-diphenyl ethylene, vinyl phenol, vinyl benzoate, vinyl naphthalene, benzyl vinyl ether.

The aliphatic hydrocarbon group contained in the aliphatic hydrocarbon group-containing monomer may be linear, cyclic, or branched.
Examples of the monomer having a linear or branched aliphatic hydrocarbon group include the following.
Olefins such as ethylene, propylene, 1-butene and isobutene;
Methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, i-propyl (meth) acrylate, butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, amyl ( (Meth) acrylate, i-amyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, i-octyl (meth) acrylate, decyl (meth) acrylate, i-decyl (meth) acrylate, dodecyl ( (Meth) acrylates such as (meth) acrylate, i-dodecyl (meth) acrylate, stearyl (meth) acrylate, i-stearyl (meth) acrylate, and behenyl (meth) acrylate; methyl vinyl ether, ethyl vinyl Vinyl ethers such as ether, n-propyl vinyl ether, i-propyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl chloride, vinylidene chloride, fluoride Vinyl halides such as vinyl and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; dicarboxylic acid ester derivatives such as maleic acid ester and itaconic acid ester; vinylsilyl compounds such as vinyltrimethoxysilane; vinyl acetate and isoacetic acid Vinyl esters such as propenyl:
Examples of the monomer having a cyclic aliphatic hydrocarbon group include cyclopropyl (meth) acrylate, cyclobutyl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, cyclooctyl (meth) ) Acrylate, cyclononyl (meth) acrylate, cyclodecyl (meth) acrylate, isobornyl (meth) acrylate, norbornyl (meth) acrylate, adamantyl (meth) acrylate and other (meth) acrylate esters, cyclopentene, cycloheptene, cyclooctene, cyclododecene, 1,5-cyclooctadiene, cyclopentadiene, 1,5,9-cyclododecatriene, 1-chloro-1,5-cyclooctadiene, dicyclo Examples thereof include cyclic olefins such as tantadiene, ethylidene norbornene, methyl 5-norbornene-2-carboxylate, dimethyl 5-norbornene 2,3-dicarboxylate, etc. These hydrophobic monomers may be used alone. Two or more kinds may be mixed and used.

<Anionic monomer>
As the anionic monomer, those exemplified below can be used, but the anionic monomer is not limited thereto, and conventionally known monomers can be used.
Carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, or salts thereof; vinyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, styrene sulfonic acid, 2-acrylamide ethane sulfonic acid, 2 Acrylamide-2-methylpropanesulfonic acid, 2-methacrylamideamidoethanesulfonic acid, 2-methacrylamide-2-methylpropanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 3-acryloyloxypropanesulfonic acid, 4-acryloyloxy Sulfonic acid monomers such as butanesulfonic acid, 2-methacryloyloxyethanesulfonic acid, 3-methacryloyloxypropanesulfonic acid, 4-methacryloyloxybutanesulfonic acid, or salts thereof; vinylphosphonic acid, Taacryloxyethyl phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxyethyl phosphate, dibutyl-2-methacryloyloxyethyl phosphate, dioctyl-2- Phosphoric monomers such as (meth) acryloyloxyethyl phosphate or salts thereof:
Of these, carboxylic acid groups and alkali (earth) metal salts of carboxylic acids are preferred. In this case, acrylic acid, methacrylic acid, itaconic acid, maleic acid, and fumaric acid are preferred.

The anionic monomer is preferably a salt, more preferably an alkali metal salt or an alkaline earth metal salt, and particularly preferably a sodium salt. This is because the carboxylic acid and the alkali (earth) metal salt of the carboxylic acid easily aggregate on the paper surface due to a change in pH, and thus an effect of improving the printing density can be expected.
These anionic monomers may be used individually by 1 type, and may use 2 or more types together.

<Other monomers>
In addition to the hydrophobic monomer constituent unit and the anionic monomer constituent unit, the monomer constituent unit related to the present invention may contain constituent units derived from other polymerizable monomers. Other monomers are not particularly limited and conventionally known monomers can be used.
Specifically, examples of other monomers include cationic monomers and nonionic monomers as exemplified below.

(Cationic monomer)
Although what is illustrated below can be used as a cationic monomer, It is not limited to these, A conventionally well-known thing can be used.
N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-di-t-butylaminoethyl (meth) acrylate N, N-dialkylaminoalkyl (meth) acrylates such as N, N-dimethylaminobutyl (meth) acrylate; N, N-dimethylaminoethyl (meth) acrylamide, N, N-diethylaminoethyl (meth) acrylamide, N Tertiary amino group-containing polymerizable unsaturated monomers such as N, N-dialkylaminoalkyl (meth) acrylamides such as N, dimethylaminopropyl (meth) acrylamide; (meth) acryloyloxyethyldimethyloctylammonium chloride, (meth ) Acrylloy Oxyethyldimethyloctylammonium bromide, (meth) acryloyloxyethyldimethyldodecylammonium chloride, (meth) acryloyloxyethyldimethyldodecylammonium bromide, (meth) acryloyloxyethyldimethylhexadecylammonium chloride, (meth) acryloyloxyethyldimethylhexadecyl Ammonium bromide, (meth) acryloyloxyethyl diethyl octyl ammonium chloride, (meth) acryloyloxyethyl diethyl octyl ammonium bromide, (meth) acryloyloxyethyl diethyl dodecyl ammonium chloride, (meth) acryloyloxyethyl diethyl dodecyl ammonium bromide, (meth) Acryloyloxye Rudiethylhexadecylammonium chloride, (meth) acryloyloxyethyl diethylhexadecylammonium bromide, (meth) acryloylaminopropyldimethyloctylammonium chloride, (meth) acryloylaminopropyldimethyloctylammonium bromide, (meth) acryloylaminopropyldimethyl Dodecyl ammonium chloride, (meth) acryloylaminopropyldimethyldodecyl ammonium bromide, (meth) acryloylaminopropyldimethylhexadecyl ammonium chloride, (meth) acryloylaminopropyldimethylhexadecyl ammonium bromide, (meth) acryloyloxyethyltrimethyl Ammonium chloride, (meth) acryloyloxyethyldimethyl Rubenzylammonium chloride, (meth) acryloyloxyethyltrimethylammonium methylsulfate, (meth) acryloyloxyethyldimethylethylammonium ethylsulfate, (meth) acryloyloxyethyltrimethylammonium p-toluenesulfonate, (meth) acryloylaminopropyl Trimethylammonium chloride, (meth) acryloylaminopropyldimethylbenzylammonium chloride, (meth) acryloylaminopropyltrimethylammonium methylsulfate, (meth) acryloylaminopropyldimethylethylammonium ethylsulfate, (meth) acryloylaminopropyltrimethylammonium p -Quaternary ammonia such as toluene sulfonate Base-containing polymerizable unsaturated monomers; other styrenes having a dialkylamino group such as dimethylaminostyrene and dimethylaminomethylstyrene; vinylpyridines such as 4-vinylpyridine and 2-vinylpyridine; or alkyl halides thereof; Quaternized with a known quaternizing agent such as benzyl halide, alkyl or aryl sulfonic acid or dialkyl sulfate, N-vinylformamide and N-vinylacetamide that form an amino group by hydrolysis after polymerization , Allylamine hydrochloride, etc .:

  Among them, tertiary amino group-containing polymerizable unsaturated monomers such as N, N-dimethylaminoethyl (meth) acrylate and N, N-diethylaminoethyl (meth) acrylate, (meth) acryloyloxyethyltrimethylammonium chloride, (meth) Preferred are quaternary ammonium base-containing polymerizable unsaturated monomers such as acryloyloxyethyldimethylbenzylammonium chloride, (meth) acryloyloxyethyltrimethylammonium methylsulfate, (meth) acryloyloxyethyldimethylethylammonium ethylsulfate, among which More preferred are quaternary ammonium base-containing polymerizable unsaturated monomers. Of these, (meth) acryloyloxyethyltrimethylammonium chloride is most preferred.

(Nonionic monomer)
Nonionic monomers include the following, but are not limited to the following examples, and conventionally known monomers can be used.
Monomers having primary amino groups such as aminoethyl (meth) acrylate and aminopropyl (meth) acrylate; methylaminoethyl (meth) acrylate, methylaminopropyl (meth) acrylate, ethyl (meth) acrylate Monomers having a secondary amino group such as aminoethyl, ethylaminopropyl (meth) acrylate, 2-vinylpyridine, 4-vinylpyridine; (meth) acrylamide, N-alkyl having 1 to 6 carbon atoms in the alkyl group (Meth) acrylamide, N, N-dialkyl (meth) acrylamide having 1 to 3 carbon atoms in the alkyl group, diacetone (meth) acrylamide, N-methylol (meth) acrylamide, N-2-hydroxyethyl (meth) acrylamide, N, N-diethanol (meth) acrylamide, N-vinyl Setamide, N-methyl-N-vinylacetamide, N-vinylformamide, N-methyl-N-vinylformamide, N- (2- (polyethyleneglycol) ethyl) (meth) acrylamide, N, N- (2,2 ′ Amide group-containing monomers such as-(polyethylene glycol) diethyl) (meth) acrylamide; 2-vinylpyridine, 4-vinylpyridine, 1-vinylimidazole, N-vinylpyrrolidone, 2-vinyl-2-oxazoline, 5-methyl-2 -Vinyl-2-oxazoline, N-vinyloxazolidone, 2-N-pyrrolidoneethyl (meth) acrylate, N-vinylcaprolactam, 9-vinylcarbazole, N-vinylphthalimide, glycidyl (meth) acrylate, aziridine ring-containing monomer, etc. Mo with heterocycle Monomers containing hydroxyl groups such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2,3-dihydroxypropyl (meth) acrylate, 2-hydroxyethyl vinyl ether; polyethylene glycol (Meth) acrylate, methoxy polyethylene glycol (meth) acrylate, ethoxy polyethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, lauroxy polyethylene glycol (meth) acrylate, stearoxy polyethylene glycol (meth) acrylate, nonylphenoxy polyethylene glycol (Meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, polypropylene glycol (Meth) acrylate, poly (ethylene glycol-propylene glycol) (meth) acrylate, polyethylene glycol-polypropylene glycol (meth) acrylate, poly (ethylene glycol-tetramethylene glycol) (meth) acrylate, poly (propylene glycol-tetramethylene glycol) ) (Meth) acrylate, propylene glycol polybutylene glycol (meth) acrylate, octoxy polyethylene glycol polypropylene glycol (meth) acrylate, stearoxy polyethylene glycol-polypropylene glycol (meth) acrylate, allyloxy polyethylene glycol-polypropylene glycol (meth) acrylate Nonylphenoxypoly (ethylene glycol-propylene Oxyalkylene chain monomers such as (glycol) (meth) acrylate;

Glucose, mannose, galactose, glucosamine, mannosamine, galactosamine, etc., hexoses, arabinose, xylose, ribose, etc. Disaccharides such as mannobiose and sophorose, other oligosaccharides such as maltotriose, isomaltotriose, maltotetraose, maltopentaose, mannotriose and manninotriose, polysaccharides such as cellulose and modified cellulose A monomer having a structure as derived and having a glycosyl group, such as a monomer such as glucosylethyl methacrylate;
Macromonomer having a polyvinyl alcohol structure in the side chain:
Among the nonionic monomer structural units, polyethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, and N-alkyl (meth) acrylamide having 1 to 4 carbon atoms in the N-vinylpyrrolidone alkyl group are preferable.
One kind of these nonionic monomer structural units may be contained in the polymer, or two or more kinds thereof may be contained.

<Ratio of each monomer structural unit in polymer>
The molar ratio of hydrophobic monomer structural unit / anionic monomer structural unit in the polymer according to the present invention is usually 5/95 to 95/5, preferably 20/80 to 90/10.
If the number of hydrophobic monomer structural units is less than this range and the amount of anionic monomer structural units is large, the polymer may be detached from the pigment surface, which may reduce dispersion stability or increase the viscosity. Conversely, if there are more hydrophobic monomer structural units and less anionic monomer structural units than this range, the number of dissociated anionic groups on the pigment surface will be less than the desired ratio, resulting in reduced dispersion stability and ejection properties. In addition, storage stability may be reduced.

  Moreover, when the polymer which concerns on this invention contains a nonionic monomer structural unit further, the content rate is 90 mol% or less normally, More preferably, it is 80 mol% or less. When the polymer contains a nonionic monomer structural unit, an effect of improving dispersibility and dischargeability can be obtained. However, if there are more nonionic monomer structural units than this upper limit, the content of hydrophobic monomer structural units and anionic monomer structural units in the entire polymer will decrease, and dispersion stability may decrease.

<Polymer structure>
The polymer structure may be a random copolymer, a diblock copolymer, a triblock or more multiblock copolymer, a gradient copolymer, a graft copolymer, a star copolymer, etc., among which a random copolymer or a block polymer is preferable, and a random copolymer Is most preferred.

<Polymer synthesis method>
As a method for synthesizing the polymer as described above, various known methods can be selected. For example, known polymerization methods such as radical polymerization, ionic polymerization, polyaddition, and polycondensation can be selected, and derivatives or modified products of polymers synthesized by these known polymerization methods may be used. Among these, a polymer synthesized by a radical polymerization method is more preferable because the synthesis method is simple.

(Reaction solvent for radical polymerization)
The radical polymerization reaction can be performed without solvent or in the presence of a solvent.
As a polymerization reaction solvent, ethers such as diethyl ether, tetrahydrofuran, diphenyl ether, anisole, dimethoxybenzene, N, N-dimethylformamide, N
Amides such as N, dimethylacetamide, nitriles such as acetonitrile, propionitrile, benzonitrile, carbonyl compounds such as acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, ethylene carbonate, propylene carbonate, methanol, ethanol Alcohols such as propanol, isopropanol, n-butyl alcohol, t-butyl alcohol and isoamyl alcohol, aromatic hydrocarbons such as benzene, toluene and xylene, halogens such as chlorobenzene, methylene chloride, chloroform, chlorobenzene and carbon tetrachloride Hydrocarbons.

Among these, an aqueous solvent is preferable as the polymerization reaction solvent.
The aqueous solvent refers to a solvent obtained by mixing 100% water or water and a polar organic solvent at an arbitrary ratio. The polar organic solvent is not limited as long as it can be mixed with water in an arbitrary ratio. Specifically, it is a protic solvent such as methanol, ethanol or isopropanol, or an aprotic such as acetonitrile, acetone, dimethylformamide, dityl sulfoxide or tetrahydrofuran. Illustrative solvents are exemplified. Of these, methyl alcohol, ethyl alcohol, isopropyl alcohol, tetrahydrofuran, and water are particularly preferable.
These solvents may be a single solvent composed of only one kind or a mixed solvent composed of two or more kinds.

(Radical polymerization initiator)
A known radical polymerization initiator can be used for the radical polymerization reaction in the synthesis of the polymer. As the polymerization initiator, either a water-soluble polymerization initiator or an oil-soluble polymerization initiator can be used.

<Water-soluble polymerization initiator>
Examples of the water-soluble polymerization initiator include 2,2′-azobis (2-amidinopropane) dihydrochloride, 4,4′-azobis (4-cyanovaleric acid), 2,2′-azobis [2- (2-Imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] disulfate dihydrate, 2,2′-azobis [ N- (2-carboxyethyl) -2-methylpropionamide], 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl) propane} dihydrochloride, 2, 2′-azobis (1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride, 2,2′-azobis {2-methyl-N- [2- (1-hydroxybutyl)] propionamide}, 2 , 2′-azobis [2- (5-methyl) -Imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, and other azo compound initiators , Oxidizing agents such as potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, etc., or aqueous solutions of sodium sulfite, sodium hyposulfite, ferrous sulfate, ferrous nitrate, sodium formaldehyde sulfoxylate, thiourea, etc. And redox initiators combined with an organic reducing agent.
These may be used alone or in combination of two or more.

<Oil-soluble polymerization initiator>
Examples of oil-soluble polymerization initiators include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobiscyclohexane 1-carbonitrile, , 2′-azobis-4-methoxy-2,4-dimethylvaleronitrile, 2,2′-azobis-2,4-dimethylvaleronitrile, dimethyl-2,2′-azobis (2-methylpropionate), Azo compound-based initiators such as 1,1′-azobis (1-acetoxy-1-phenylethane) and 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), acetylcyclohexylsulfonyl peroxide, Isobutyryl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, 2,4-dichloroben Ile peroxide, t-butyl peroxypivalate, 3,5,5-trimethylhexanonyl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, stearoyl peroxide, propionitrile peroxide, succinic Acid peroxide, acetyl peroxide, t-butylperoxy-2-ethylhexanoate, benzoyl peroxide, parachlorobenzoyl peroxide, t-butylperoxyisobutyrate, t-butylperoxymaleic acid, t -Butylperoxylaurate, cyclohexanone peroxide, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-dibenzoylperoxyhexane, t-butyl Peroxyacetate, t-butylperoxybenzoate, diisobutyldiperoxyphthalate, methyl ethyl ketone peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, t-butylcumyl peroxide , T-butyl hydroperoxide, di-t-butyl peroxide, diisopropylbenzene hydroperoxide, paramentane hydroperoxide, pinane hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide and cumene peroxide Peroxide polymerization initiators such as hydroperoxide (t-butylhydroxyperoxide, cumenehydroxyperoxide, etc.), dialkyl peroxides (lauroyl peroxide, etc.) and diperoxides Oil-soluble peroxides such as sil (benzoyl peroxide), tertiary amines (triethylamine, tributylamine, etc.), naphthenates, mercaptans (mercaptoethanol, lauryl mercaptan, etc.), organometallic compounds (triethylaluminum, triethylboron) And an oil-soluble redox polymerization initiator used in combination with an oil-soluble reducing agent such as diethyl zinc).
These may be used alone or in combination of two or more.

(Chain transfer agent)
The polymerization reaction may be performed in the presence of a chain transfer agent.
The chain transfer agent is not particularly limited. Examples thereof include thiol chain transfer agents such as rate, mercaptoethanol, thio-β-naphthol, and thiophenol.
These may be used alone or in combination of two or more.

(Polymerization conditions)
In carrying out the polymerization reaction, the order of addition of the radical polymerizable monomer, polymerization reaction solvent, radical initiator, chain transfer agent, etc. is arbitrary, for example, radical polymerizable monomer, chain transfer agent, polymerization reaction solvent, radical polymerization Examples thereof include a method in which the polymerization reaction is carried out by raising the temperature after charging the initiator in a batch into the reaction vessel. As another method, a radical polymerizable monomer, a chain transfer agent, and a polymerization reaction solvent are charged into a reaction vessel and the temperature is raised, and then a monomer solution, a chain transfer agent, and a polymerization reaction solvent containing a radical polymerization initiator are used. Alternatively, a method in which a polymerization reaction is performed by adding these or a mixture thereof continuously or in a divided manner can be used. Among these, from the viewpoint of simplicity of operation, a method in which the polymerization reaction is performed by raising the temperature after charging the raw materials all at once is preferable.

Although the usage-amount of a polymerization reaction solvent is not specifically limited, It is 1 weight part or more normally with respect to 100 weight part of monomers, Usually 2000 weight part or less, Preferably it is 1000 weight part or less.
The polymerization temperature is not particularly limited, but is usually 0 ° C or higher, preferably 20 ° C or higher, and the upper limit is usually 200 ° C or lower, preferably 150 ° C or lower.
The amount of the chain transfer agent used is not particularly limited, but is usually 0.01 parts by weight or more, preferably 1 part by weight or more, usually 2000 parts by weight or less, preferably 1000 parts by weight or less with respect to 100 parts by weight of the monomer.
Although the usage-amount of a radical polymerization initiator is not specifically limited, It is 0.001 to 10 weight% normally with respect to 100 weight part of monomers, Preferably it is 0.01 to 5 weight%, More preferably, it is 0.01 to 1 weight%. is there.

(Purification)
The polymer thus obtained is not particularly problematic if used as it is, but it is preferable to purify it according to a conventional method and use it for the next pigment dispersion step. As a purification method, the polymer solution is dropped into a solvent in which the polymer is insoluble and the monomer and catalyst are soluble, reprecipitation purification is repeated by repeating the precipitation and filtration of the polymer, the polymer is insoluble in the polymer solution and the monomer and the catalyst are soluble. A method of substituting the solvent with water and / or an aqueous solvent after removing the unreacted monomer and the reaction solvent by dropping the solvent, purifying the polymer by precipitation, separating the polymer by filtration, removing the unreacted monomer and the reaction solvent by distillation by heating, vacuum distillation, etc. And a method of removing low molecular impurities and low molecular weight oligomer components using an ultrafiltration membrane or a dialysis membrane.

(Molecular weight and molecular weight distribution)
The number average molecular weight of the polymer used in the present invention is preferably 2000 or more, more preferably 3000 or more, further preferably 6000 or more, and the upper limit is preferably 50000 or less, more preferably 40000 or less, and further preferably 25000 or less. If the molecular weight is larger than this range, the viscosity of the resulting aqueous pigment dispersion tends to increase. If the molecular weight is smaller, the polymer tends to peel off from the pigment surface and the dispersion may become unstable.
In addition, the value of molecular weight here is a value in terms of polystyrene measured by GPC (gel permeation chromatography).

[Properties of aqueous pigment dispersion]
The pigment concentration in the sex pigment dispersion of the present invention is usually 30% by weight or less, preferably 20% by weight or less. Here, if the pigment concentration is too high, the pigment becomes poorly dispersed, the viscosity of the dispersion increases, the dispersion becomes gelled, and the dispersion may not be used due to dispersion failure. If the pigment concentration is too low, it may take time to concentrate the ink, and it is usually 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more.

The water concentration in the aqueous pigment dispersion of the present invention is usually 70% by weight or more and 95% by weight or less. The polymer concentration in the aqueous pigment dispersion of the present invention is usually 0.1% by weight or more and 1.5% by weight, preferably 0.2% by weight or more and 1.2% by weight or less, more preferably 0.8% by weight. 3% by weight or more and 1.0% by weight or less. When the amount of the polymer is too small, the dispersion stability and the storage stability tend to decrease.
The pH of the aqueous pigment dispersion of the present invention is usually 5 or more and 12 or less, preferably 7 or more and 11 or less. If the pH is low, the degree of dissociation of the anionic group is suppressed, and the dispersibility and dispersion stability of the dispersion liquid, storage stability of the recording liquid, and ejection performance may deteriorate. Conversely, if the pH is too high, the print head may be damaged. May end up.

[Method for producing aqueous pigment dispersion]
In the method for producing the aqueous pigment dispersion of the present invention, the mixing method and the order of addition of the pigment, polymer, and water are arbitrary. For example, (a) the pigment, (b) the polymer, and (c) the water are mixed at a time. What is necessary is just to perform a dispersion | distribution process to a thing using a general disperser.

As the disperser used for the dispersion treatment, various dispersers that are generally used for pigment dispersion can be used. The disperser is not particularly limited, but a kneader, salt milling, roll mill, planetary mixer, paint shaker, ball mill, sand mill, attritor, pearl mill, coball mill, homomixer, homogenizer, wet jet mill, high pressure homogenizer. An ultrasonic homogenizer or the like can be used. Glass beads, zirconia beads, alumina beads, magnetic beads, and styrene beads can be used for those using media as a disperser. Among these, a preferable dispersion treatment method is a method of dispersing with an ultrasonic homogenizer.

The obtained dispersion is desirably subjected to pressure filtration using a filter or centrifugal separation for the purpose of removing coarse particles as necessary.
When carrying out dispersion treatment with an ultrasonic homogenizer, pigment, polymer, and water are added in advance by various methods such as kneader, salt milling, roll mill, planetary mixer, homomixer, homogenizer, wet jet mill, high-pressure homogenizer, and bead mill. This should be done after preliminary dispersion.

  The pigment concentration during the dispersion treatment with an ultrasonic homogenizer is usually 3 to 30% by weight, preferably 5 to 20% by weight, more preferably 6 to 16% by weight. When the pigment concentration is lower than this range, the dispersion efficiency is poor because the pigment particles are thin, and the pigment particle size does not tend to decrease even when the ultrasonic wave is irradiated for a long time. On the other hand, if it is higher than this range, in addition to the concentration of the pigment particles being too high, the solution viscosity becomes high and the stirring efficiency is lowered, so that the ultrasonic waves are difficult to uniformly strike the pigment particles, and the dispersion is uneven. Tend to be.

  In addition, since heat is remarkably generated by irradiation with ultrasonic waves, it is preferable to disperse while cooling with ice water or the like. In this case, it is preferable to cool the dispersion so that the temperature of the dispersion is 60 ° C. or less. If the temperature of the dispersion is too high, the aggregation of the pigments is more likely to occur than the progress of the dispersion, so the dispersion does not proceed, and the pigment aggregated on the wall surface is mixed into the dispersion, causing coarse particles to mix. , There is a tendency to lower the discharge properties.

  The output of the ultrasonic disperser is not particularly limited as long as the particle diameter of the pigment reaches a target size, but is usually 50 W or more and 1200 W or less. If the output is too small, the target particle size cannot be reduced, or it takes a long time. If the output is too large, the pigment or polymer structure is destroyed, or a large amount of minute metal pieces from the vibration element (metal tip). Care must be taken because it may be peeled off and mixed into the dispersion as an impurity, resulting in deterioration of dischargeability, storage stability, or filterability.

  The dispersion time is not particularly limited as long as the particle diameter of the pigment becomes a target size, but is usually 1 minute / dispersion 1 kg or more and 800 minutes / dispersion 1 kg or less, preferably 10 minutes / dispersion 1 kg. That's it. If the dispersion time is too short, a large amount of coarse particles remain or the adsorption of the dispersant polymer onto the pigment surface tends to be insufficient, and the dispersion stability and storage stability tend to decrease. On the other hand, if the dispersion time is too long, a large number of pigment fine particles of several nanometers to several tens of nanometers are generated, which deteriorates the dispersion stability, storage stability, and ejection stability, and further increases the print density. There is a tendency to decrease.

[Ink composition (recording liquid)]
The ink composition of the present invention containing the aqueous pigment dispersion according to the present invention exhibits excellent effects particularly as a recording liquid, particularly as an inkjet recording liquid.
The ink composition of the present invention used as a recording liquid (hereinafter referred to as “recording liquid of the present invention”) adjusts the colorant concentration of the above-described aqueous pigment dispersion of the present invention as necessary, and further uses Depending on the conditions, various additives are added. Alternatively, various additives may be added depending on the application during the production of the aqueous pigment dispersion.

As the colorant, in addition to the pigment in the aqueous pigment dispersion of the present invention described above, it is further dispersed with a self-dispersing pigment surface-treated for purposes such as toning, a dye, a surfactant, a polymer dispersant, etc. It may also contain added pigments or dyes.
The concentration of the total colorant in the recording liquid of the present invention is usually 0.1% by weight or more, preferably 0.5% by weight or more, and the upper limit is usually as the concentration of the total colorant with respect to the total amount of the recording liquid. It is 25% by weight or less, preferably 20% by weight or less, particularly preferably 15% by weight or less. If the colorant concentration is too high, the viscosity tends to increase and the discharge properties tend to decrease, and if it is too low, the print density tends to decrease. On the other hand, the amount of the colorant added to the aqueous pigment dispersion is usually 100 parts by weight or less, preferably 75 parts by weight or less, more preferably 50 parts by weight or less with respect to 100 parts by weight of the pigment in the aqueous pigment dispersion. The amount is particularly preferably 25 parts by weight or less. If the additional amount of the colorant is too large, the effect of the present invention may be reduced.

The solvent used in the recording liquid of the present invention preferably contains water and a water-soluble organic solvent, and can further contain other components as desired.
The water-soluble organic solvent is not particularly limited as long as it is generally used for this application. Specifically, the water-soluble organic solvent has a vapor pressure lower than that of water, such as ethylene glycol, diethylene glycol, triethylene glycol, Tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propylene glycol, isopropylene glycol, polypropylene glycol, pentamethylene glycol, trimethylene glycol, butylene glycol, isobutylene glycol, thiodiglycol, 1,2-hexanediol, 1,6-hexanediol, 2-ethyl-1,3-hexanediol, 1,2-pentanediol, 1,5-pentanediol, 2-methyl Multivalents such as 2,4-pentanediol, 1,3-propanediol, 1,4-butanediol, 1,7-heptanediol, 1,8-octanediol, 2-butene-1,4-diol, glycerin, etc. Alcohols;
Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol mono-t-butyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monophenyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl Ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol mono-t-butyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, Lopylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol-t-butyl ether, propylene glycol monopropyl ether, propylene glycol isopropylene ether, propylene glycol monophenyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, di Polyhydric alcohol ethers such as propylene glycol monobutyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monoisopropyl ether;

Ketones such as acetonylacetone;
Esters such as γ-butyrolactone, diacetin, triethyl phosphate;
Lower alkoxy alcohols such as 2-methoxyethanol and 2-ethoxyethanol;
Amines such as ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, triethylenetetramine, tetraethylenepentamine, pentamethyldiethylenetriamine;
Amides such as formamide, N, N-dimethylformamide, N-methylformamide, N, N-dimethylacetamide;
2-pyrrolidone, N-ethylpyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, morpholine, N-ethylmorpholine, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, imidazole, methylimidazole, hydroxyimidazole , Heterocycles such as dimethylaminopyridine, 1,3-propane sultone, hydroxyethylpiperazine, piperazine;
Sulfoxides such as dimethyl sulfoxide;
Examples include sulfones such as sulfolane.

These may be used alone or in combination of two or more.
The concentration of the water-soluble organic solvent in the recording liquid of the present invention may be appropriately selected and determined. Usually, it is preferably 1% by weight or more and 45% by weight or less, more preferably 40% by weight or less with respect to the recording liquid. Further, the water content in the recording liquid may be an amount that can appropriately set the concentration of the above-described colorant, water-soluble organic solvent, and optional additive components described below.

The content of water in the recording liquid is preferably 20 to 95% by weight, more preferably 40 to 80% by weight.
The recording liquid of the present invention may contain various additives as necessary within the range not impairing the effects of the present invention. Examples of such additives include recording liquids such as penetration enhancers, surface tension modifiers, hydrotropic agents, pH adjusters, chelating agents, preservatives, viscosity modifiers, humectants, antifungal agents, and rust inhibitors. Known additives can be used. The content of these additives in the recording liquid of the present invention is generally 30% by weight or less, particularly preferably 15% by weight or less, based on the total amount of the recording liquid.

Examples of penetration enhancers include lower alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol and pentanol, carbitols such as ethylene glycol monobutyl ether and triethylene glycol monobutyl ether glycol ether, and surfactants 1 A seed | species or 2 or more types is mentioned.
As the surfactant, any one or more of nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, polymer surfactants and the like can be used. Can be used. Of these, nonionic surfactants, anionic surfactants and polymer surfactants are preferred.

  Nonionic surfactants include, for example, polyoxyethylene alkyl ethers, polyoxyethylene alkyl aryl ethers, polyoxyethylene derivatives, oxyethylene / oxypropylene block copolymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid Examples thereof include esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, acetylene glycols, and acetylene alcohols.

  Examples of the anionic surfactant include fatty acid salts, alkyl sulfate esters, alkyl benzene sulfonates, alkyl naphthalene sulfonates, alkyl sulfosuccinates, alkyl diphenyl ether sulfonates, alkyl phosphates, polyoxyethylene alkyl sulfates. Examples include ester salts, polyoxyethylene alkylaryl sulfate esters, alkane sulfonates, naphthalene sulfonate formalin condensates, polyoxyethylene alkyl phosphates, α-olefin sulfonates, and the like.

Polymeric surfactants include polyacrylic acid, styrene / acrylic acid copolymer, styrene / acrylic acid / acrylic acid ester copolymer, styrene / maleic acid copolymer, styrene / maleic acid / acrylic acid ester copolymer, styrene / methacrylic acid. Examples thereof include acid copolymers, styrene / methacrylic acid / acrylic acid ester copolymers, styrene / maleic acid half ester copolymers, styrene / styrene sulfonic acid copolymers, vinyl naphthalene / maleic acid copolymers, vinyl naphthalene / acrylic acid copolymers, and salts thereof.

Examples of the cationic surfactant include, but are not limited to, tetraalkylammonium salts, alkylamine salts, benzalkonium salts, alkylpyridium salts, imidazolium salts, and the like.
In addition, silicone surfactants such as polysiloxane oxyethylene adducts, fluorine surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, oxyethylene perfluoroalkyl ethers, rhamnolipids, lysolecithins, etc. Surfactants such as biosurfactants can also be used.

The content of these surfactants may be selected and determined as appropriate. Usually, by adding in the range of 0.001 wt% or more and 5 wt% or less with respect to the recording liquid, the quick drying property and the print quality of the printed matter can be further improved.
Examples of the surface tension adjusting agent include alcohols such as diethanolamine, triethanolamine, glycerin, and diethylene glycol, nonions, cations, anions, and amphoteric surfactants.

As the hydrotropic agent, one or more of urea, alkylurea, ethyleneurea, propyleneurea, thiourea, guanidate, halogenated tetraalkylammonium and the like are preferable.
As a humectant, 1 type (s) or 2 or more types, such as glycerol and diethylene glycol, can also be added as what also serves as a water-soluble organic solvent.

  Furthermore, a solid moisturizing agent (a water-soluble substance having a water retaining function and solid at 25 ° C.) can also be added. Preferred solid humectants include saccharides, sugar alcohols, hyaluronate, trimethylolpropane, 1,2,6-triol and the like. Examples of the saccharide include monosaccharides, disaccharides, oligosaccharides (including trisaccharides and tetrasaccharides), and polysaccharides. Specifically, glucose, fructose, ribose, xylose, arabinose, galactose, sorbit, maltose, and lactose. , Sucrose, trehalose and the like. Examples of sugar alcohols include maltitol, sorbitol, xylitol, and the like, and one or more of these solid humectants can be added.

Although it does not specifically limit as a chelating agent, 1 type (s) or 2 or more types, such as a sodium salt of ethylenediaminetetraacetic acid, a diammonium salt of ethylenediaminetetraacetic acid, are used. These are preferably used in the range of 0.005 wt% to 0.5 wt% with respect to the recording liquid.
The antifungal agent is not particularly limited, but sodium dehydroacetate, dichlorophene, sorbic acid, sodium benzoate, p-hydroxybenzoic acid ester, 1,2-Benzisothiazole-3-one (product name: Proxel) GXL (manufactured by Arch Chemicals)) or the like is used. These are preferably contained in the range of 0.05 wt% to 1 wt% with respect to the recording liquid.

Further, in order to adjust the pH of the recording liquid and obtain the stability of the recording liquid, it is not particularly limited, but sodium hydroxide, potassium hydroxide, lithium hydroxide, nitric acid, ammonia, diethanolamine, triethanolamine, etc. PH adjusters and buffer solutions such as phosphoric acid can be used.
The pH of the recording liquid is usually in a neutral to alkaline range, and is preferably adjusted to about pH 6 to 11.

  In the recording liquid of the present invention, emulsion particles and other additives may be added as long as the effects of the present invention are not impaired. In particular, for the purpose of further improving the fixability of an image on a recording medium, it is preferable to add emulsion particles, nonionic water-soluble polymers and oligomers. Although there is no particular limitation on the method of adding such emulsion particles, for example, it may be added at the time of preparing the dispersion, or may be added at the time of preparing the recording liquid.

The obtained recording liquid is desirably subjected to pressure filtration using a filter or centrifugal separation for the purpose of removing coarse particles as necessary.
The method for producing emulsion particles is not particularly limited, and those produced by various conventionally known methods can be used. Examples include emulsion particles produced by emulsion polymerization, soap-free emulsion polymerization, and miniemulsion methods. Can do. Of these, emulsion particles produced by a soap-free emulsion polymerization method are preferred because the decrease in printing density is small.

The emulsion particles are preferably those that are stably dispersed in water and / or an aqueous medium.
The emulsion particle surfaces preferably have anionic, cationic, and specific ionic hydrophilic groups from the viewpoints of dispersion stability, storage stability, and ejection stability, but the dispersion has an anionic group. Therefore, an anionic group and a nonionic hydrophilic group are more preferable.
The particle diameter of the emulsion particles is preferably 1 nanometer or more and 1 micrometer or less from the viewpoint of ejection stability, dispersion stability, and storage stability.

The emulsion particles may or may not have a glass transition temperature, but in the case of having the emulsion particles, -20 ° C or higher and 100 ° C or lower is preferable. The minimum biofilm temperature may or may not have, but if it has, it is 80 ° C. or lower.
The molecular weight of the emulsion is not particularly limited, but usually the weight average molecular weight is 1,000 to 10,000,000.

  The shape of the emulsion particles is not particularly limited, but it is preferably a spherical shape in consideration of the influence on ejection properties. The emulsion particles may be hollow particles or core-shell type particles. The emulsion particles should have a chemical cross-linking structure inside, but they may be microgelled by a physical cross-linking structure between polymers, or when the entanglement density between polymers is high and has a pseudo cross-linking structure. In this case, it is not always necessary to have a chemical crosslinking structure.

  The type of emulsion particles is not particularly limited. For example, urethane, acrylic, polyester, silicon, vinyl acetate, styrene, vinyl chloride, vinylidene chloride, polyethylene, epoxy, petroleum resin, Examples thereof include rosin ester-based, alkyd resin-based, polybutadiene-based, polybutene-based, butyl rubber-based, polychloroprene-based, polyisoprene-based, and polysulfurized rubber-based emulsions, and composite emulsions obtained by combining two or more of these.

  Among these, a urethane emulsion, a urethane composite emulsion, a polyester emulsion, a polyester composite emulsion, a silicon emulsion, a silicon composite emulsion, an acrylic emulsion, and an ethylene / vinyl acetate composite emulsion are preferable. Preferred examples include, but are not limited to, the following.

As urethane-based emulsions and urethane-based composite emulsions, Takelac W-405, W-605, W-615, W-6010, W-6020, WS-5000, WS-5100, WS-4000 (above, Mitsui Chemical Polyurethane ( Strain)); WBR-016U, WBR-022U, WBR-601U, WBR-2018, WBR-2019, WBR-2
101, WEM-031U, WEM-202U, WEM-321U, WEM-290A, WEM-3008 (above, Taisei Fine Chemical Co., Ltd.); HUX-232, HUX-350, HUX-550, HUX-380, HUX-420A , HUX-401, HUX-522
, HUX-386 (above, ADEKA Co., Ltd.); Rezamin D-2020, Rezamin D-4080, Rezamin D-6031
, Rezamin D-6300 (above, Daiichi Seika Kogyo Co., Ltd.); UW-1100-E, UW-1200-E, UW-1300-E, UW-2200-E, UW-2050-E, UW-3100 -E, UW-3200-E, UW-3300-E, UW-4300-E, UW-5002, UW-3100, UW-3200, UW-3300 (above, Ube Industries, Ltd.); AQ AU304 (above Daicel Finechem Co., Ltd.); SU-100, SU-U0501 (Chuo Rika Kogyo Co., Ltd.), Superflex 110,
SUPERFLEX 126, SUPERFLEX 130, SUPERFLEX 150, SUPERFLEX 170, SUPERFLEX 210, SUPERFLEX 300, SUPERFLEX 420, SUPERFLEX 470, SUPERFLEX 740, SUPERFLEX 830, SUPERFLEX E-2000 Ichi Kogyo Seiyaku Co., Ltd.), HYBRIDUR 540, HYBRIDUR 570, HYBRIDUR 580, HYBRIDUR 870, HYBRIDUR 878 (above, Air Products Japan Co., Ltd.).

Examples of the polyester emulsion and the polyester composite emulsion include KT-9511, KT-8803, KT-8701, KT-9204, KT-8904, KT-0507 (above, Unitika Ltd.).
Silicon-based emulsion and silicon-based composite emulsion include KM-740T, Polon MF-14, Polon MF-14E, FZ-4658, FZ-4602, KM-9739, X-52-8164, Polon MWS, KM-9717, Polon MF-56, Polon MF-40 (above, Shin-Etsu Chemical Co., Ltd.); SM8706 EX, SM8709SR, SM87
16, SM7001EX, SZ-1642, BY 22-736 EX, BY 22-826EX, FZ-46
02, FZ4658 (above, Toray Industries, Inc.); Primal PR-29 (above, ROHM AND HAAS); AQ 914, AQ Asi-91, AQ 4790 (above, Daicel Finechem Inc.).

Acrylic emulsions include Primal SF-021, Primal AC-261P, Primal EC-1791, Primal B-15B, Primal P-376, Primal R-225, Primal JP-934HS, Primal Binder 18, 375CI, Primal 606APEF (Above, ROHM AND HASS); AQ 4635, AQ AST499, AQ 4723 (above, Daicel FineChem Corp.); FK-403, FK-462S
, FK-4300, FK-6000DH, FK-68, ES-90 (above, Chuo Rika Industry Co., Ltd.); Joncryl 450, Joncryl 74J, Joncryl 352D, Joncryl 780, Joncryl PDX-7700 (above, BASF), SE -909E, SE-1645E (above, Taisei Fine Chemical Co., Ltd.)

Examples of the ethylene / vinyl acetate composite emulsion include BE-814 (Chuo Rika Kogyo Co., Ltd.).
Polyolefin-based emulsions include Chemipearl S-100, Chemipearl S-111, Chemipearl S-120, Chemipearl S-650, Chemipearl S-75N (Mitsui Chemicals, Inc.); Seixen A, Seixen N, and Seixen L ( Above, Sumitomo Seika Co., Ltd.).

Only one type of emulsion particles may be added, or two or more types may be used in combination.
Nonionic water-soluble polymers or oligomers are preferred as other additives used for the purpose of further improving the fixability and scratch resistance of images on a recording medium. The nonionic water-soluble polymer or oligomer is a water-soluble polymer or oligomer containing the nonionic hydrophilic group.

  In the recording liquid of the present invention, the content of all polymers including emulsion particles and nonionic water-soluble polymers is usually 0.05% by weight or more, preferably 0.25% by weight or more, more preferably 0. The upper limit is preferably 20% by weight or less, more preferably 10% by weight or less.

[Method for producing ink composition]
The ink composition of the present invention is prepared by adding a colorant and various additives as necessary to the above-mentioned aqueous pigment dispersion and mixing and dispersing in the same manner. Or you may prepare by adding a coloring agent and various additives as needed at the time of manufacture of an aqueous pigment dispersion, and carrying out a dispersion process.

〔Recording method〕
A method of performing inkjet recording by ejecting droplets of the ink composition of the present invention from an inkjet head and attaching the droplets to a recording medium is preferable.

Hereinafter, the present invention will be described more specifically with reference to synthesis examples, examples, and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
In the following examples, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the polymers (b) -1 to 5 are measured under the following conditions using gel permeation chromatography (GPC). It was.

Column packing: Styrene-divinylbenzene copolymer Solvent: Tetrahydrofuran Flow rate: 0.7ml / min
Temperature: 40 ° C
Calibration was performed using polystyrene.

In addition, this time, it measured using the following apparatuses, detectors, and columns.
Apparatus: Waters 2690 manufactured by Nippon Waters Co., Ltd.
Detector: Waters 2410 manufactured by Nippon Waters
Column: Shodex KF-604 / KF-603 / KF-602.5 manufactured by Showa Denko KK
In the following notation, “co” means “co” of copolymer.
The surface tension of the aqueous pigment dispersion was measured by a conventional method using CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.

<Synthesis Example 1>
Synthesis of poly (sodium acrylate-co-styrene) (polymer (b) -1) Into a condenser with a nitrogen-substituted interior, a nitrogen introduction tube, a stirrer and a flask equipped with a thermometer, 2,2′- 3.15 g of asobis (2,4-dimethylvaleronitrile) was charged, 384 g of tetrahydrofuran as a solvent, 47.35 g of acrylic acid as a monomer, and 102.65 g of styrene. The bath temperature was raised from room temperature to 70 ° C. over 1 hour, and the polymerization reaction was carried out at 70 ° C. for 8 hours.

After completion of the reaction, the reaction solution was cooled to room temperature, and a concentrated solution obtained by distilling off part of THF as a solvent with an evaporator was reprecipitated in acetonitrile. Decant the supernatant, vacuum dry to completely remove the solvent, neutralize by adding aqueous sodium hydroxide, and purify by ultrafiltration or membrane, poly (sodium acrylate-co-styrene): polymer An aqueous solution of (b) -1 was obtained.

By drying under vacuum, a mixture of poly (sodium acrylate-co-styrene): polymer (b) -1 and sodium acrylate was obtained. The number average molecular weight (Mn) of this polymer is 12
000, the weight average molecular weight (Mw) was 20000, and the molecular weight distribution (Mw / Mn) was 1.7.
After dissolving 30.0 g of the random copolymer and sodium acrylate mixture in 970.0 g of water, sodium acrylate was removed by ultrafiltration. After removing sodium acrylate, the polymer aqueous solution was concentrated and dried to obtain the polymer (b) -1.

  When the structure of this random copolymer was confirmed by H-NMR using heavy water as a solvent, the composition ratio of acrylic acid units and styrene units in the random copolymer was 13/87 (molar ratio) = 9/91 (weight ratio). )Met.

<Synthesis Example 2>
Synthesis of poly (sodium acrylate-co-n-butyl acrylate-co-styrene) (Polymer (b) -2) Polymerization started in condenser with nitrogen purge inside, nitrogen inlet tube, stirrer and flask with thermometer 30 g of 2,2′-azobis (2,4-dimethylvaleronitrile) is charged as an agent, 3500.0 g of tetrahydrofuran as a solvent, 400.0 g of acrylic acid, 600.0 g of n-butyl acrylate, and 400.0 g of styrene as monomers. Prepared. The bath temperature was raised from room temperature to 70 ° C. over 1 hour, and the polymerization reaction was carried out at 70 ° C. for 8 hours.

  After completion of the reaction, the reaction solution was cooled to room temperature, and a concentrated solution obtained by distilling off part of THF as a solvent with an evaporator was reprecipitated in acetonitrile. The supernatant is decanted and the solvent is completely removed by vacuum drying, and then neutralized by adding an aqueous sodium hydroxide solution to poly (sodium acrylate-co-n-butyl acrylate-co-styrene): polymer ( An aqueous solution of b) -2 was obtained.

By vacuum drying, a mixture of poly (sodium acrylate-co-n-butyl acrylate-co-styrene): polymer (b) -2 and sodium acrylate was obtained. The number average molecular weight (Mn) of this polymer was 11,000, the weight average molecular weight (Mw) was 15000, and the molecular weight distribution (Mw / Mn) was 1.4.
After dissolving 30.0 g of the random copolymer and sodium acrylate mixture in 970.0 g of water, sodium acrylate was removed by ultrafiltration. After removing sodium acrylate, the polymer aqueous solution was concentrated and dried to obtain the polymer (b) -1.

  When the structure of this random copolymer was confirmed by H-NMR using heavy water as a solvent, the composition ratio of acrylic acid units, n-butyl acrylate units, and styrene units in the random copolymer was 40/21/39 (molar ratio). ) = 36/26/39 (weight ratio).

<Synthesis Example 3>
Synthesis of poly (sodium acrylate-co-n-butyl acrylate-co-styrene) (Polymer (b) -3) Polymerization started in condenser with nitrogen purge inside, nitrogen inlet tube, stirrer and flask with thermometer 30 g of 2,2′-azobis (2,4-dimethylvaleronitrile) was charged as an agent, 3500.0 g of tetrahydrofuran as a solvent, 600.0 g of acrylic acid as a monomer, 600.0 g of n-butyl acrylate, and 400.0 g of styrene. Prepared. The bath temperature was raised from room temperature to 70 ° C. over 1 hour, and the polymerization reaction was carried out at 70 ° C. for 8 hours.

After completion of the reaction, the reaction solution was cooled to room temperature, neutralized with a sodium hydroxide / methanol solution, and precipitated in isopropyl alcohol. The precipitate was filtered and dried under vacuum to obtain a mixture of poly (sodium acrylate-co-n-butyl acrylate-co-styrene): polymer (b) -3 and sodium acrylate. The number average molecular weight (Mn) of this polymer is 11
000, the weight average molecular weight (Mw) was 18000, and the molecular weight distribution (Mw / Mn) was 1.6.

After dissolving 30.0 g of the random copolymer and sodium acrylate mixture in 970.0 g of water, sodium acrylate was removed by ultrafiltration. After removing sodium acrylate, the polymer aqueous solution was concentrated and dried to obtain the polymer (b) -3.
When the structure of this random copolymer was confirmed by H-NMR using heavy water as a solvent, the composition ratio of the acrylic acid unit, n-butyl acrylate unit, and styrene unit in the random copolymer was 35/22/43 (molar ratio). ) = 38/30/32 (weight ratio).

<Synthesis Example 4>
Synthesis of poly (sodium acrylate-co-methoxypolyethyleneglycol acrylate-co-n-butyl acrylate-co-styrene) (polymer (b) -4) Capacitor, nitrogen introduction tube, stirrer and thermometer with the inside replaced with nitrogen Into a flask equipped with 3.02 g of 2,2′-azobis (2,4-dimethylvaleronitrile) as a polymerization initiator, 300 g of tetrahydrofuran as a solvent, 65.08 g of acrylic acid as a monomer, methoxypolyethylene glycol acrylate (light acrylate) 130A (Kyoeisha Chemical Co., Ltd.) 19.60 g, n-butyl acrylate 65.17 g, and styrene 50.15 g were charged. The bath temperature was raised from room temperature to 70 ° C. over 1 hour, and the polymerization reaction was carried out at 70 ° C. for 8 hours.

  After completion of the reaction, the reaction solution was cooled to room temperature, and a concentrated solution obtained by distilling off part of THF as a solvent with an evaporator was reprecipitated in acetonitrile. The supernatant was decanted and dried in a vacuum to completely remove the solvent, and then neutralized by adding an aqueous sodium hydroxide solution to poly (sodium acrylate-co-methoxypolyethylene glycol acrylate-co-n-butyl acrylate- co-styrene): An aqueous solution of polymer (b) -4 was obtained.

By drying under vacuum, a mixture of poly (sodium acrylate-co-methoxypolyethylene glycol acrylate-co-n-butyl acrylate-co-styrene): polymer (b) -4 and sodium acrylate was obtained. The number average molecular weight (Mn) of this polymer is 18
000, the weight average molecular weight (Mw) was 28000, and the molecular weight distribution (Mw / Mn) was 1.6.

After dissolving 30.0 g of the random copolymer and sodium acrylate mixture in 970.0 g of water, sodium acrylate was removed by ultrafiltration. After removing sodium acrylate, the polymer aqueous solution was concentrated and dried to obtain the polymer (b) -4.
When the structure of this random copolymer was confirmed by H-NMR using heavy water as a solvent, the composition ratio of acrylic acid units, methoxypolyethylene glycol acrylate units, n-butyl acrylate units, and styrene units in the random copolymer was 17 / 35/30/18 (molar ratio) = 33/10/32/25 (weight ratio).

Example 1 [Black pigment dispersion A]
Carbon black (a) -1 (DBP absorption 102cm ³ / 100g, an average primary particle size 16
nm), an aqueous solution of polymer (b) -1 (solid content: 9.3%) and distilled water were mixed in the following proportions and predispersed for 10 minutes with a homomixer.
Carbon black (a) -1 18.0g
13.6 g of polymer (b) -1 aqueous solution
Distilled water 118.4g
Place the above pre-dispersed liquid in a 300 ml tall beaker, immerse the beaker in ice water, and disperse for 60 minutes with an ultrasonic homogenizer (Nippon Seiki Seisakusho; US-600T; used chip 36 mmφ). Obtained.

The surface tension of the above dispersion A was measured and found to be 72 dyne / cm.
Example 2 [Black pigment dispersion B]
The polymer aqueous solution (b) -1 in Example 1 was changed to the polymer aqueous solution (b) -2 (solid content 19.7%), and the mixing ratio of each component was changed to the following, and the same as in Example 1 Dispersion treatment was performed to obtain 12% pigment dispersion B.
Carbon black (a) -1 18.0g
Polymer (b) -2 aqueous solution 6.9 g
125.1 g of distilled water
The surface tension of the dispersion B was measured and found to be 71 dyne / cm.

Example 3 [Black pigment dispersion C]
Example 1 Carbon black (a) -1 the carbon black (a) -2 (DBP absorption 105 cm ^3/100 g, average primary particle diameter 17 nm) was changed to the polymer solution (b) -1 in Example 1 The polymer aqueous solution (b) -3 was changed to a solid content (18.3%), and the dispersion treatment was performed in the same manner as in Example 1 except that the mixing ratio of each component was as follows. Obtained.
Carbon black (a) -1 18.0g
Polymer (b) -2 aqueous solution 3.0 g
129.0 g of distilled water
The surface tension of the above dispersion C was measured and found to be 70 dyne / cm.

Example 4 [Black pigment dispersion D]
The polymer aqueous solution (b) -1 in Example 1 was changed to the polymer aqueous solution (b) -3 (solid content 18.3%), and the mixing ratio of each component was changed to the following, and the same as in Example 1 Dispersion treatment was performed to obtain 12% pigment dispersion D.
Carbon black (a) -1 36.0g
Polymer (b) -3 aqueous solution 17.7g
Distilled water 246.3g
The surface tension of the dispersion D was measured and found to be 69 dyne / cm.

Comparative Example 1 [Black Pigment Dispersion E]
Example 1 Carbon black (a) -1 the carbon black (a) -3 (DBP absorption 110 cm ^3/100 g, average primary particle diameter 24 nm) was changed to the polymer solution (b) -1 in Example 1 The polymer aqueous solution (b) -4 (solid content 17.3%) was changed, and the dispersion treatment was performed in the same manner as in Example 1 except that the mixing ratio of each component was as follows. Obtained.
Carbon black (a) -3 48.0g
Polymer (b) -4 aqueous solution 13.9g
Distilled water 238.1g
The surface tension of the above dispersion E was measured and found to be 66 dyne / cm.

Comparative Example 2 [Black Pigment Dispersion Liquid F]
Example 1 Carbon black (a) -1 the carbon black (a) -4 (DBP absorption 110 cm ^3/140 g, average primary particle diameter 23 nm) was changed to the polymer solution (b) -1 in Example 1 A commercially available aqueous polymer solution (b) -5 (BASF; JONCRYL 61J (solid content: 30.5%) was changed to a dispersion ratio in the same manner as in Example 1 except that the mixing ratio of each component was as follows. An 8% pigment dispersion F was obtained.
Carbon black (a) -4 24.0g
Polymer (b) -5 aqueous solution 5.1 g
Distilled water 270.9g
The surface tension of the above dispersion E was measured and found to be 64 dyne / cm.

Comparative Example 3 [Black pigment dispersion G]
A 12% pigment dispersion G was obtained in the same manner as in Example 1 except that the same carbon black and polymer as in Example 4 were used and the mixing ratio of each component was as follows.
Carbon black (a) -1 36.0g
29.5 g of polymer (b) -3 aqueous solution
Distilled water 234.5g
The surface tension of the above dispersion E was measured and found to be 54 dyne / cm.

Comparative Example 4 [Black pigment dispersion H]
A dispersion of Cabojet 300 (manufactured by Cabot (solid content: 15.05%)) (a) -5 was used. Cabojet 300 is a self-dispersing black pigment dispersion.
<Evaluation>
An ink composition was prepared with the following ink composition and evaluated below. Here, the ink composition was obtained by mixing the following components and stirring for 15 minutes, followed by ultrasonic dispersion treatment for 30 minutes.

(Ink composition)
Dispersion (AD, G) 33.3 parts Diethylene glycol 5.0 parts Glycerin 5.0 parts Olfine E1010 (Surfactant manufactured by Air Products) 0.33 parts Trimethylolpropane 6.0 parts Distilled water 50.37 parts

Dispersion E 25.0 parts Diethylene glycol 5.0 parts Glycerin 5.0 parts Olphine E1010 (surfactant manufactured by Air Products) 0.33 parts Trimethylolpropane 6.0 parts Distilled water 58.67 parts

Dispersion F 50.0 parts Diethylene glycol 5.0 parts Glycerin 5.0 parts Olfine E1010 (surfactant manufactured by Air Products) 0.33 parts Trimethylolpropane 6.0 parts Distilled water 33.67 parts

Dispersion H 26.6 parts Diethylene glycol 5.0 parts Glycerin 5.0 parts Olfine E1010 (surfactant manufactured by Air Products) 0.33 parts Trimethylolpropane 6.0 parts Distilled water 57.07 parts

1. Printer printing evaluation of ink composition For printing evaluation of an ink composition prepared from dispersions A to G, an inkjet recording printer (Canon Co., Ltd. iP4600) was used as the printer, and commercially available plain paper (Canon ( Co., Ltd. GF-500) was used. Printing was performed in the standard mode set for plain paper.

The printed matter printed under the above conditions was dried at room temperature for 1 day, and the print density was measured. The print density measurement was performed using a spectrophotometer Spectroeye LT (manufactured by GRETAG-MACBETH AG), the solid print portion was measured 5 times, and an average value was adopted.

2. Evaluation of centrifugal sedimentation of ink composition For centrifugal sedimentation evaluation of ink compositions prepared from dispersions A to G, HIMAC manufactured by Hitachi Koki Co., Ltd. was used.
CR22G was used.

20 g of the ink composition was placed in a centrifuge tube and centrifuged at 9000 rpm for 30 minutes. 4 g of the supernatant was precisely weighed and diluted 10,000 times with water. The absorbance W1 at 800 nm of this solution was measured. Similarly, the absorbance when the ink composition before the centrifugation treatment was diluted was defined as W0, and the sedimentation degree was evaluated.
Settling degree (%) = {1- (W1 / W0)} × 100
Evaluation ○: Sedimentation degree less than 35% Evaluation x: Sedimentation degree of 35% or more

3. Marker resistance evaluation The printed matter printed under the above conditions was dried at room temperature for 1 day to evaluate the marker resistance. The solid print portion was rubbed once with a highlighter pen toward the blank paper portion, and the print density of the tailed portion on the blank paper portion was measured. The print density measurement was performed using a spectrophotometer Spectroeye LT (manufactured by Co., Ltd.), and an average value was adopted.
Evaluation ○: Print density less than 0.05 Evaluation x: Print density 0.05 or more The above evaluation results are shown in Table 1.

表１より、本発明のインク組成物では、印刷すると印字物が濃く、耐マーカー性が良好であり、さらに長期間顔料が沈降することがないことは明らかである。

From Table 1, it is clear that with the ink composition of the present invention, when printed, the printed matter is dark, the marker resistance is good, and the pigment does not settle for a long period of time.

Claims (7)

An aqueous pigment dispersion comprising: (a) a pigment, (b) a polymer, and (c) water, wherein the aqueous pigment dispersion has a surface tension of 67 dyne / cm or more. The aqueous pigment dispersion according to claim 1, wherein the pigment (a) is carbon black having an average primary particle size of 20 nm or less. ^3. The aqueous pigment dispersion according to claim 1, wherein (a) the pigment is carbon black having a DBP oil absorption of 80 cm 3/100 g or more. (b) The aqueous pigment dispersion according to any one of claims 1 to 3, wherein the polymer contains a hydrophobic group and an anionic group. The aqueous pigment dispersion according to any one of claims 1 to 4, wherein the number average molecular weight of the polymer (b) is 6000 or more and 25000 or less.   An ink composition comprising the aqueous pigment dispersion according to any one of claims 1 to 5.   An ink jet recording method comprising: ejecting droplets of the ink composition according to claim 6 from an ink jet head and attaching the droplets to a recording medium.