JP2011190400A - Water-based pigment dispersion liquid and ink composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide water-based pigment dispersion liquid excellent in dispersion stability and preservation stability; and to provide dispersion-type recording liquid which has a high printing concentration on plain paper, provides a printed matter with high quality of a printed character, and has a good discharge characteristic. <P>SOLUTION: The water-based pigment dispersion liquid comprises: (a) a pigment; (b) a hydrophobic group-containing anionic polymer; and (c) an aqueous medium, wherein the weight of (a) the pigment is 11 times or more and 99 times or less the weight of (b) the hydrophobic group-containing anionic polymer; and a molar ratio of a hydrophobic monomers structural unit/an anionic monomer structural unit in (b) the hydrophobic group-containing anionic polymer is 30/70 to 90/10. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ink composition suitable as a recording liquid for an aqueous pigment dispersion, an ink jet printer, and the like, 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. Currently, an aqueous recording liquid is mainly used as a recording liquid for an ink jet printer, and an aqueous recording liquid using a pigment as a coloring material is becoming mainstream particularly for a black ink.

  In recent years, with the improvement of the resolution of printed matter, the amount of ink discharged from the ink discharge nozzle has decreased significantly. Furthermore, when targeting business use, the demands for printing speed comparable to electrophotographic printing, high printing density, and high printing durability are increasing day by day. On the other hand, higher printing quality than before, or high pigment dispersion stability has been demanded. 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. 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 excellent water resistance, light resistance, ozone resistance, etc. There are practically significant problems with respect to printing quality such as scratch resistance and marker resistance. 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 dispersion type pigment dispersion in which a pigment is dispersed with a water-soluble polymer has been developed. However, since a free water-soluble polymer that does not contribute to the dispersion of the pigment exists in the aqueous medium, there is a problem in that the viscosity of the ink increases and the ejection stability tends to be insufficient. Or, since the charge is brought in from the water-soluble polymer more than the minimum charge necessary for dispersion stability, the aggregation of the pigment on the paper is hindered, resulting in a problem that the print density is low, and in practical terms. Has become an obstacle.

Japanese Patent Laid-Open No. 2000-239587

  For example, Patent Document 1 discloses that the printing density is improved by setting the polymer as a dispersant in the range of 5 to 15% with respect to the water-insoluble dye, but the storage stability of the ink composition is disclosed. The nature is bad. It is written that when trying to improve the storage stability, the cohesive force between the pigments becomes weak, and as a result, the print density decreases. As described above, it is difficult to improve both the print density and the storage stability.

As a result of intensive studies to solve such problems, the present inventors have determined that the weight of the pigment in the aqueous pigment dispersion containing the pigment, the hydrophobic group-containing anionic polymer, and the aqueous medium contains the hydrophobic group. By setting the molar ratio of the hydrophobic monomer structural unit / anionic monomer structural unit in the hydrophobic group-containing anionic polymer to be 30/70 to 90/10 with respect to the weight of the anionic polymer, It has been found that the aqueous pigment dispersion is excellent in dispersion stability and storage stability.

In addition, the ink composition containing this aqueous pigment dispersion has found that there is no back-through of ink on plain paper, a printed matter having a high printing density is obtained, and excellent discharge stability, and the present invention has been completed. .
That is, the first gist of the present invention is (a) a pigment, (b) a hydrophobic group-containing anionic polymer, and (c).
An aqueous pigment dispersion containing an aqueous medium, wherein the weight of (a) the pigment is 11 to 99 times the weight of (b) the hydrophobic group-containing anionic polymer, The molar ratio of hydrophobic monomer structural unit / anionic monomer structural unit is 30/70 to 90/10
An aqueous pigment dispersion characterized in that

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.

The aqueous pigment dispersion of the present invention is excellent in dispersion stability and storage stability. In addition, the ink composition of the present invention does not show through ink on plain paper, provides a printed matter with a high printing density, and has good ejection properties.
In particular, the aqueous pigment dispersion of the present invention can be suitably used for a recording liquid such as an ink jet printer, and this recording liquid is excellent in storage stability, and when an ink composition containing the aqueous pigment dispersion of the present invention is used, A high-quality and high-durability inkjet recording can be obtained.

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 an aqueous pigment dispersion comprising (a) a pigment, (b) a hydrophobic group-containing anionic polymer, and (b) an aqueous medium, wherein (a) the weight of the pigment is (b) 11 to 99 times the weight of the hydrophobic group-containing anion polymer, and the molar ratio of hydrophobic monomer structural unit / anionic monomer structural unit in the hydrophobic group-containing anionic polymer is 30/70 to 90/10. Is an aqueous pigment dispersion.

The reason why the aqueous pigment dispersion of the present invention exhibits the effects of the present invention is not clear, but is considered as follows.
That is, it is the hydrophobic group-containing anionic polymer that plays a role in stably dispersing the pigment in the aqueous pigment dispersion, but when the pigment content is too low, that is, necessary for stabilizing the pigment in dispersion. If the polymer is added in an excessive amount, free polymers that do not contribute to the dispersion stabilization of the pigment gradually aggregate to cause thickening. In addition, in order to increase the print density without causing ink back-through on plain paper, it is necessary to leave more pigment particles on the paper by agglomerating the pigments near the surface of the paper. If the added amount of the anionic polymer is too large, aggregation on the surface of the paper is unlikely to occur, and it is thought that this may be one of the causes that the printing density cannot be increased.

  In addition, regarding the monomer structural unit constituting the hydrophobic group-containing anionic polymer, if the hydrophobic monomer structural unit is small and the anionic monomer structural unit is large, the polymer is detached from the pigment surface and the dispersion stability is lowered or increased. Or stick. Conversely, if there are many hydrophobic monomer structural units and there are few anionic monomer structural units, the number of anionic groups dissociated on the pigment surface will be less than the desired ratio, and dispersion stability and ejection properties will be reduced. Storage stability also decreases.

In addition to controlling the amount of polymer required to disperse the pigment, the hydrophobic / anionic balance of the polymer is important for high print density, dispersion stability, and storage stability.
In the present invention, the weight of the pigment is 11 to 99 times the weight of the hydrophobic group-containing anionic polymer, and the molar ratio of hydrophobic monomer structural unit / anionic monomer structural unit in the hydrophobic group-containing anionic polymer is 30. By controlling to the range of / 70 to 90/10, printed matter with high print density on plain paper is achieved while ensuring dispersion stability of the dispersion, storage stability of the recording liquid, or good ejection properties. It is thought that it was made.
The weight of (a) pigment is preferably 11 times or more and 50 times or less, more preferably 11 times or more and 20 times or less with respect to the weight of (b) the hydrophobic group-containing anionic polymer. If the weight of the pigment (a) is too small relative to the weight of the (b) hydrophobic group-containing anionic polymer, the dispersion stability tends to be low and the printing density tends to be low, while if too large, the storage stability tends to be low. There is.

[(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 typified by ultramarine and Prussian blue;
Metal powder pigments such as aluminum paste, bronze powder, zinc powder, stainless steel flakes, nickel flakes; pearl luster such as carbon black, bismuth oxychloride, basic carbonate, titanium dioxide, coated mica, ITO, ATO Inorganic pigments such as pigments and nacreous conductive pigments; and quinacridone pigments, quinacridone quinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, ansanthrone pigments, indanthrone pigments, flavanthrone pigments Organic pigments such as perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, metal complex pigments, azomethine pigments or azo pigments.
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, 1
4, 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, 178, 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, 73,274,275,276

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, red pigments preferably include quinacridone pigments, xanthene pigments, perylene pigments, antanthrone pigments, and monoazo pigments, and specific examples thereof include CI Pigment Red 5 , 7, 12, 112, 81, 122, 123, 14
6, 17, 168, 173, 202, 206, 207, 209, C.I. I. And CI Pigment Biolet 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 Yellow 1, 3, 16, 17, 74, 120, 128, 151, 175, and 215 are particularly preferable from the viewpoint of the color. I. Pigment Yellows 74 and 155 are non-halogen compounds, and are particularly preferable from the viewpoint of having a small influence on the environment and color.

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, # 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, C
F9B, # 95, # 260, MA77, MA77B, MA7, MA7B, MA8, MA
8B, MA11, MA11B, MA100, MA100B, MA100R, MA100RB, MA100S, MA230, MA220, MA200RB, MA14, # 3030B, # 30430B, # 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 100
0, Monarch 900, Black Pearls 900, Monarch 880,
Black Pearls 880, Monarch 800, Black Pearls 800, Monarch 700, Black Pearls 700, Black Pearls
2000, Vulcan XC72R, Vulcan XC72, Vulcan PA90,
Vulcan 9A32, Mogul L, BlackPearls L, Regal 66
0R, Regal 660, Black Pearls 570, Black Pearls 520, Regal 400R, Regal 400, Regal 330R, Regal 330, Regal 300R, Black Pearls 490, Black Pear
ls 480, Black Pearls 470, Black Pearls 460, B
black Pearls 450, Black Pearls 430, Black Pea
rls 420, Black Pearls 410, Regal 350R, Regal 3
50, Regal 250R, Regal 250, Regal 99R, Regal 99I, Elftex Pellets 115, Elftex 8, Elftex 5, Elftex 12, Monarch 280, Black Pearls 280, Black
Pearls 170, Black Pearls 160, Black Pearls 1
30, Monarch 120, Black Pearls 120 (above, Cabot products).

(3) Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Special Black 4, Special Black 4A, Special Black 5, Beck 5, 160, Black
r Black S170, Printex U, Printex V, Printex 150T, Printex 140U, Printex 140V, Printex 95, Pr
intex 90, Printex 85, Printex 80, Printex 75, Printex 55, Printex 45, Printex 40, Printex P
, Printex 60, Printex XE, Printex L6, Printex L, Printex 300, Printex 30, Printex 3, Printe
x 35, Printex 25, Printex 200, Printex A, Pri
ntex G, Special Black 550, Special Black 350, Special Black 250, Special Black 100 (above, Degussa product).

(4) Raven 7000, Raven 5750, Raven 5250, Rave
n 5000 ULTRA, Raven 3500, Raven 2000, Raven 1500, Raven 1255, Raven 1250, Raven 1200, Raven 1170, Raven 1060 ULTRA, Raven 1040, Raven 1040, Raven 1035, Raven 1035, Raven 1035, Raven 1035 ULTRA, Raven760 ULTRA, Raven520, Raven500, Raven450, Raven430, Raven420, Raven410, CONDUCTEX975 ULTRA, CONDU
CTEX SCULTRA, RavenH2O, Raven CULTRA (product of Columbia Co., Ltd.).

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, the baking treatment at a high temperature is more preferable because the functional group on the surface of the carbon black is removed, whereby the dispersion is more efficiently adsorbed 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 according to the purpose, but is usually 10 nm or more and 800 nm or less, preferably 500 nm or less, more preferably 300 nm or less, and further preferably 200 nm. Hereinafter, it is particularly preferably 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 DBP absorption amount of carbon black is preferably 60 ml / 100 g or more and 200 ml / 100 g or less, and more preferably 100 ml / 100 g or more and 150 ml / 100 g or less. Carbon black that has too little DBP absorption tends to slip through plain paper, hardly stay on the top surface of the paper, and the print density may be low. Carbon black with too much DBP absorption is difficult to disperse, and storage stability and ejection stability may also deteriorate. Here, the DBP absorption amount is the amount of dibutyl phthalate (DBP) absorbed by 100 g of carbon black defined by JISk6221.

The average primary particle size of carbon black is preferably 10 nm or more and 50 nm or less, more preferably 15 nm or more and 40 nm or less, and further preferably 15 nm or more and 30 nm or less. If the average primary particle size is too small, the print density tends to be low, and the ejection stability and dispersibility may also deteriorate. On the other hand, if the average primary particle size is too large, the storage stability is deteriorated, and the specific surface area is too small, so that the print density may be lowered. Here, the average primary particle diameter of carbon black is an arithmetic average diameter (number average) measured by an electron microscope.

Furthermore, the pH of carbon black is more preferably 6-8. When the pH is too low, the amount of acidic groups on the surface of the carbon black is increased, so that adsorption of the dispersant polymer is inhibited, and sufficient storage stability and ejection stability may not be ensured. On the other hand, the dispersion is not too high because the dispersion of the dispersant polymer is suppressed due to the interaction between the basic functional group on the surface of the carbon black and the anionic group of the dispersant polymer. It may be insufficient. The pH of carbon black here is 100 g of distilled water added to 10 g of carbon black, boiled for 10 minutes on a hot plate, cooled to room temperature, the supernatant was separated, and the pH of the muddy material was adjusted to glass. It is the value measured using an electrode pH meter.
In addition, as said carbon black, the carbon black which has a self-dispersibility can also be used. That is, as the carbon black used in the aqueous pigment dispersion of the present invention, any of untreated carbon black and chemically modified carbon black as described above can be used.

[(B) Hydrophobic group-containing anionic polymer]
The hydrophobic group-containing anionic polymer is not limited as long as it contains an anionic monomer structural unit and a hydrophobic monomer structural unit. The hydrophobic group-containing anionic polymer includes an anionic group by including an anionic monomer structural unit, and includes a hydrophobic group by including a hydrophobic monomer structural unit. Moreover, the hydrophobic group containing anionic polymer may be contained individually by 1 type, and may contain 2 or more types.

There is no limitation on the primary structure of the hydrophobic group-containing anionic polymer, and specific examples include linear, star, comb, branched, and block polymers, but are not limited thereto. Absent. The polymer may be, for example, a synthetic polymer or a natural polymer, or a derivative or modified product thereof.
The hydrophobic group-containing anionic polymer is preferably a water-soluble or water-dispersible polymer.

<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.

<Anionic group>
The anionic group contained in the hydrophobic group-containing anionic polymer is (b) a functional group having an anionic charge in an aqueous medium and having a pKa of 8 or less. For example, carboxylic acid, sulfonic acid, phosphoric acid And acid groups derived from acids such as alkali metal salts and alkaline earth metal salt structures thereof.

Among these, carboxylic acid, alkali metal salt of carboxylic acid, and alkaline earth metal salt structure of carboxylic acid are more preferable (hereinafter referred to as “alkali metal salt and / or alkaline earth metal salt”.
Sometimes referred to as “alkaline (earth) metal salt”. ). The reason is that carboxylic acid and alkali (earth) metal salt of carboxylic acid easily aggregate on the paper surface due to pH change, so that an effect of improving printing density can be expected.

<Hydrophobic group>
Examples of the hydrophobic group contained in the hydrophobic group-containing anionic polymer include a group derived from an aliphatic hydrocarbon and a group derived from an aromatic hydrocarbon.
Here, the aliphatic hydrocarbon is saturated or unsaturated, and may be linear, branched or cyclic. In these aliphatic hydrocarbons and aromatic hydrocarbons, one or more hydrogen atoms may be substituted with halogen atoms such as fluorine, bromine, iodine and chlorine. Further, in the aromatic hydrocarbon, one or more hydrogen atoms may be substituted with an aliphatic hydrocarbon group (one or more carbon atoms).

  Examples of the aliphatic hydrocarbon-derived group include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, sec-butyl, pentyl, isopentyl, neopentyl, and t-pentyl. Group, hexyl group, heptyl group, octyl group, nonyl group, t-nonyl group, decyl group, dodecyl group, t-dodecyl group, undecyl group, lauryl group, hexadecyl group, octadecyl group, chloromethyl group, dichloromethyl group, C1-C20 alkyl groups, such as a trichloromethyl group, a trifluoromethyl group, and a cyclohexyl group, and its halogen-substituted alkyl groups; vinyl group, allyl group, isopropenyl group, 3-butenyl group, 1-methylallyl group, 1 , 1-dimethylallyl group, 2-methylallyl group, 3-methylallyl group, 2,3-dimethylallyl Group, 3,3-dimethylallyl group, cinnamyl group, etc. alkenyl group or a substituted alkenyl group having 2 to 20 carbon atoms such as 3-cyclohexyl allyl group.

Aromatic hydrocarbon-derived groups include aryl groups such as phenyl groups and naphthyl groups; 1 to 3 hydrogen atoms in aryl groups such as phenyl groups and naphthyl groups are methyl groups, ethyl groups, butyl groups, etc. Substituted aryl groups substituted with functional groups such as alkyl groups, alkoxy groups such as methoxy groups and ethoxy groups; benzyl groups, phenethyl groups, phenylbutyl groups, diphenylmethyl groups, triphenylmethyl groups, naphthylmethyl groups, naphthylethyl groups, etc. An aralkyl group, a substituted aralkyl group, and the like.
It is preferable that both an aliphatic hydrocarbon-derived group and an aromatic hydrocarbon-derived group exist in the hydrophobic group-containing anionic polymer.

<Introduction of anionic monomer structural unit and hydrophobic monomer structural unit>
In order to introduce an anionic monomer structural unit and a hydrophobic monomer structural unit into the structure of a hydrophobic group-containing anionic polymer, a method of obtaining a polymer by polymerizing at least one kind of anionic monomer and at least one kind of hydrophobic monomer Alternatively, there may be mentioned a method of polymerizing a polymerizable monomer not containing an anionic group and / or a hydrophobic group to obtain a polymer, and then introducing the anionic group and / or the hydrophobic group into the polymer by a modification or modification reaction.

(Anionic monomer structural unit)
The anionic monomer structural unit includes an anionic group in the monomer structural unit. Specific examples of the anionic monomer structural unit include, but are not limited to, the following monomer structures, and may be conventionally known anionic monomer structures.

  Anionic monomer structural units include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and other carboxylic acid monomer type structures; vinyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, styrene sulfonic acid, 2- Acrylamide ethanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamideamidoethanesulfonic acid, 2-methacrylamideamido-2-methylpropanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 3-acryloyloxypropanesulfone Structures of sulfonic acid monomers such as acid, 4-acryloyloxybutanesulfonic acid, 2-methacryloyloxyethanesulfonic acid, 3-methacryloyloxypropanesulfonic acid, 4-methacryloyloxybutanesulfonic acid; Phosphonic acid, methacryloxyethyl phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxyethyl phosphate, dibutyl-2-methacryloyloxyethyl phosphate, dioctyl -2- (meth) acryloyloxyethyl phosphate structures such as phosphoric acid monomer types; and metal salts or ammonium salts of these alkali metals and alkaline earth metals.

These anionic monomer structural units need only be contained in the hydrophobic group-containing anionic polymer, and may be contained in two or more types.
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.

(Hydrophobic monomer structural unit)
The hydrophobic monomer structural unit does not include an anionic group and a cationic group in the monomer structural unit but includes a hydrophobic group.
Specific examples of the hydrophobic monomer structural unit include, but are not limited to, the following monomer structures, and may be conventionally known hydrophobic monomer structures.

As acrylate monomer type structural units, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, dodecyl acrylate, Octadecyl acrylate, chloromethyl acrylate, dichloromethyl acrylate, trichloromethyl acrylate, trifluoromethyl acrylate, bromoethyl acrylate, vinyl acrylate, allyl acrylate, propargyl acrylate, i-propyl acrylate, i-acrylate -Butyl, sec-butyl acrylate, t-butyl acrylate, isodecyl acrylate, 2-ethylhexyl acrylate, isopentyl acrylate, isopropenyl acrylate, 3-butenyl acrylate, Cyclohexyl acrylate, cyclopentyl acrylate, isobornyl acrylate, dicyclopentenyl acrylate, phenyl acrylate, naphthyl acrylate, anthracenyl acrylate, diphenylethyl acrylate, benzyl acrylate, phenethyl acrylate, phenyl butyl acrylate, acrylic acid Examples include diphenylethyl, diphenylmethyl acrylate, triphenylmethyl acrylate, naphthylmethyl acrylate, and naphthylethyl acrylate.

The methacrylate monomer type structural units include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, dodecyl methacrylate, Octadecyl methacrylate, chloromethyl methacrylate, dichloromethyl methacrylate, trichloromethyl methacrylate, trifluoromethyl methacrylate, bromoethyl methacrylate, vinyl methacrylate, allyl methacrylate, propargyl methacrylate, i-propyl methacrylate, i-methacrylic acid i -Butyl, sec-butyl methacrylate, t-butyl methacrylate, isodecyl methacrylate, 2-ethylhexyl methacrylate, isopentyl methacrylate, Isopropenyl chlorate, 3-butenyl methacrylate, cyclohexyl methacrylate, cyclopentyl methacrylate, isobornyl methacrylate, dicyclopentenyl methacrylate, phenyl methacrylate, naphthyl methacrylate, anthracenyl methacrylate, diphenylethyl methacrylate, benzyl methacrylate, Phenethyl methacrylate, phenylbutyl methacrylate, diphenylethyl methacrylate,
Examples include diphenylmethyl methacrylate, triphenylmethyl methacrylate, naphthylmethyl methacrylate, naphthylethyl methacrylate, and the like.

  Styrene monomer type structural units include styrene, o-methoxystyrene, m-methoxystyrene, p-methoxystyrene, ot-butoxystyrene, mt-butoxystyrene, pt-butoxystyrene, o- Examples include chloromethyl styrene, m-chloromethyl styrene, p-chloromethyl styrene, p-hydroxymethyl styrene, p- (2-hydroxyethyl) styrene, p- (2-hydroxyethyloxycarbonyl) styrene.

The structural unit of the (meth) acrylamide monomer type includes N-alkyl (meth) acrylamide having 5 or more carbon atoms in the alkyl group, N, N-dialkyl (meth) acrylamide having 3 or more carbon atoms in the alkyl group, and the like. Is mentioned.
Examples of the vinyl ether monomer type structural unit include methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, benzyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether and the like.

Examples of the acrylonitrile-based monomer type structural unit include acrylonitrile and methacrylonitrile, and specific examples of the allyl ester-based monomer type structural unit include allyl acetate.
Among these, a monomer structural unit containing a group derived from an aliphatic hydrocarbon or a group derived from an aromatic compound as a hydrophobic group among styrene monomer type, acrylate monomer type, and methacrylate monomer type is more preferable. preferable.

In addition, one or more of these hydrophobic monomer structural units may be contained in the hydrophobic group-containing anion polymer, but the monomer containing an aliphatic hydrocarbon-derived group in the hydrophobic group-containing anion polymer. It is more preferable to simultaneously contain both the structural unit and the monomer structural unit containing a group derived from an aromatic compound.
(Nonionic hydrophilic monomer structural unit)
The hydrophobic group-containing anionic polymer according to the present invention includes a monomer structural unit having a nonionic hydrophilic group (nonionic hydrophilic monomer structural unit) as a monomer structural unit other than the anionic monomer structural unit and the hydrophobic monomer structural unit. ) May be contained.

The nonionic hydrophilic monomer structural unit contains a nonionic hydrophilic group without containing an anionic group and a cationic group in the monomer structural unit. In the nonionic hydrophilic monomer structural unit, the hydrophobic group may or may not be included. However, when it is included, the content of the hydrophobic group contained in the total amount of the nonionic hydrophilic monomer structural unit is The content is preferably 2.5 times or less the content of the nonionic hydrophilic group.

Here, the nonionic hydrophilic group is an amide bond, a polyalkyl ether bond having 2 to 5 carbon atoms in the alkyl group (repetition number 2 or more), a hydroxyl group, a thiol group, an amide group, a sulfonamide group, or the like. A hydrophilic chemical bond or a functional group.
Specific examples of the nonionic hydrophilic monomer structural unit include, but are not limited to, the following monomer structures, and may be conventionally known nonionic hydrophilic monomer structures.

N-vinyl-2-pyrrolidone, N-vinyl oxazolidone, N-vinyl-5-methyloxazolidone, 2-hydroxyethyl (meth) acrylate, 2,3-dihydroxypropyl (meth) acrylate, 2-N-pyrrolidone ethyl (meta ) Acrylate, N-acryloylpiperidine, N- (meth) acryloylpyrrolidine, N-vinyl lactam having 4 to 5 carbon atoms, vinyl alcohol, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, allyl alcohol, methallyl Alcohol, glycerol monoallyl ether, (meth) acrylamide, N-alkyl (meth) acrylamide having 1 to 4 carbon atoms in alkyl group, N, N-dialkyl (meth) acrylamide having 1 to 2 carbon atoms in alkyl group , Diacetone ( ) Acrylamide, N-methylol (meth) acrylamide, N-2-hydroxyethylacrylamide, N, N-diethanolacrylamide, N-vinylacetamide, N-methyl-N-vinylacetamide, N-vinylformamide, N-methyl- N-vinylformamide, N- (2- (polyethylene glycol) ethyl) (meth) acrylamide, N, N- (2,2 ′-(polyethylene glycol) diethyl), polyethylene glycol (meth) acrylate, methoxypolyethylene glycol (meta) ) Acrylate, ethoxypolyethylene glycol (meth) acrylate, lauroxy polyethylene glycol (meth) acrylate with ethylene glycol repeat number 3 or more, stearoxy with ethylene glycol repeat number 4 or more Reethylene glycol (meth) acrylate, phenoxy polyethylene 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,
Examples include (meth) acrylates having a ring-opening structure of an alkylene oxide having 2 to 5 carbon atoms, which are classified into nonionic hydrophilic groups such as allyloxy polyethylene glycol-polypropylene glycol (meth) acrylate.

Examples of the nonionic hydrophilic monomer structural unit include 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. preferable.
One kind of these nonionic hydrophilic monomer structural units may be contained in the hydrophobic group-containing anionic polymer, or two or more kinds thereof may be contained.

(Ratio of each monomer structural unit in the hydrophobic group-containing anionic polymer)
The molar ratio of the hydrophobic monomer structural unit / anionic monomer structural unit in the hydrophobic group-containing anionic polymer according to the present invention is 30/70 to 90/10, preferably 50/50 to
70/30. If there are too few or too many hydrophobic monomer structural units, the dispersion stability will be low.

Moreover, when the hydrophobic group-containing anionic polymer according to the present invention further contains a nonionic hydrophilic monomer structural unit, the content ratio is usually 90 mol% or less, more preferably 80 mol% or less. When the hydrophobic group-containing anionic polymer contains a nonionic hydrophilic monomer structural unit, an effect of improving dispersibility and dischargeability can be obtained. However, if there are more nonionic hydrophilic 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, resulting in reduced dispersion stability. There is.
The hydrophobic group-containing anionic polymer according to the present invention may contain other structural units other than the hydrophobic monomer structural unit, the anionic monomer structural unit, and the nonionic hydrophilic monomer structural unit.

<Synthesis Method of Hydrophobic Group-Containing Anionic Polymer>
As a method for synthesizing the hydrophobic group-containing anionic polymer according to the present invention, 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.

(Monomer used for radical polymerization)
When synthesizing a hydrophobic group-containing anionic polymer using a radical polymerization method, at least one radical polymerizable anionic monomer and at least one radical polymerizable hydrophobic monomer may be used. Furthermore, radically polymerizable nonionic hydrophilic monomers may be used, and other radically polymerizable monomers may be used.

As the radical polymerizable anionic monomer, the anionic monomers exemplified as the monomer structure constituting the above-mentioned hydrophobic group-containing anionic polymer can be used, but not limited to these, and conventionally known ones are used. it can.
Among the radical polymerizable anionic monomers, those having a structure of carboxylic acids are preferable, and monomers of acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and / or alkali (earth) metal salts thereof are preferable. More preferred.

As the radical polymerizable anionic monomer, at least one kind may be used as a polymerization monomer, and two or more kinds may be used.
Among these, as the radical polymerizable hydrophobic monomer, among these styrenes and (meth) acrylates, those in which the hydrophobic group is a group derived from an aliphatic hydrocarbon or an aromatic compound are preferable. More preferred are n-butyl acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, benzyl (meth) acrylate, meta or isobornyl acrylate.

(Reaction solvent for radical polymerization)
The radical polymerization reaction for synthesizing the hydrophobic group-containing anionic polymer can be carried out 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, the solvent is a protic solvent such as methanol, ethanol, or isopropanol, or a non-proton 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 hydrophobic group-containing anionic 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 water-soluble polymerization initiators 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′- Azo compound initiators such as azobis [2- (3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, oxidation of potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, etc. Redox system used alone or in combination with water-soluble reducing agents such as sodium sulfite, sodium hyposulfite, ferrous sulfate, ferrous nitrate, sodium formaldehyde sulfoxylate, thiourea, etc. Initiator, and the like.
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-carbonitol, 2,2′-azobis-4-methoxy-2,4-dimethylvaleronitrile, 2
, 2′-azobis-2,4-dimethylvaleronitrile, dimethyl-2,2′-azobis (2-methylpropionate), 1,1′-azobis (1-acetoxy-1-phenylethane) and 2, Azo compound initiators such as 2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), acetylcyclohexylsulfonyl peroxide, isobutyryl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexylperoxydi Carbonate, 2,4-dichlorobenzoyl peroxide, t-butylperoxypivalate, 3,5,5-trimethylhexanonyl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, stearoyl peroxide, pro Pionitrile -Oxide, succinic acid peroxide, acetyl peroxide, t-butylperoxy-2-ethylhexanoate, benzoyl peroxide, parachlorobenzoyl peroxide, t-butylperoxyisobutyrate, t-butylperoxymale Ic acid, t-butyl peroxylaurate, cyclohexanone peroxide, t-butyl peroxyisopropyl carbonate, 2,5-dimethyl-2,5-dibenzoyl peroxyhexane, t-butyl peroxyacetate, t-butyl peroxy Oxybenzoate, diisobutyl diperoxyphthalate, methyl ethyl ketone peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, t-butylcumyl Over oxide,
t-butyl hydroperoxide, di-t-butyl peroxide, diisopropylbenzene hydroperoxide, paramentane hydroperoxide, pinane hydroperoxide, 2,5 dimethylhexane-2,5-dihydroperoxide, cumene peroxide, etc. Peroxide polymerization initiators, oil-soluble peroxides such as hydroperoxides (t-butylhydroxyperoxide, cumenehydroxyperoxide, etc.), dialkyl peroxides (lauroyl peroxide, etc.) and diacyl peroxides (benzoyl peroxide, etc.) Products, tertiary amines (triethylamine, tributylamine, etc.), naphthenates, mercaptans (mercaptoethanol, lauryl mercaptan, etc.), organometallic compounds (triethylaluminum, triethylboron and die) Oil-soluble redox polymerization initiator used in combination with oil-soluble reducing agent Le zinc etc.) and the like.
These may be used alone or in combination of two or more.

(Chain transfer agent)
The radical 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 of adding a mixture of these continuously or dividedly and performing a polymerization reaction, etc. may be mentioned. Above all, from the simplicity of operation,
A method is preferred in which the raw material is charged all at once and then the polymerization reaction is carried out by raising the temperature.

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 hydrophobic group-containing anionic polymer thus obtained is not particularly problematic even if it is used as it is unpurified, 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 hydrophobic group-containing anionic polymer used in the present invention is preferably 2000 or more, more preferably 3000 or more, still more preferably 6000 or more, and the upper limit is preferably 50000 or less, more preferably 40000 or less, and further preferably 25000. It is as follows.
If the molecular weight is larger than this range, the viscosity of the resulting aqueous pigment dispersion may increase,
If it is small, the polymer tends to peel off from the pigment surface, and dispersion may become unstable.

Further, the content of the low molecular weight component of the hydrophobic group-containing anionic polymer used in the present invention is preferably 20% by weight or less, more preferably 10% by weight or less, for a component having a weight average molecular weight of 4000 or less. The low molecular weight component is considered to be one of the parameters that affect the dispersibility, dispersion stability, and storage stability, but when the low molecular weight component is more than the above range, it is easy to ensure dispersibility, It may be difficult to ensure dispersion stability and storage stability. Further, in a thermal type print head, long-term ejection stability tends to deteriorate.
In addition, the value of a number average molecular weight and a weight average molecular weight here is a value of polystyrene conversion measured by GPC (gel permeation chromatography).

[(C) Aqueous medium]
Examples of the aqueous medium used in the aqueous pigment dispersion of the present invention include water and / or a water-soluble organic solvent. The water-soluble organic solvent is not particularly limited as long as it is generally used in this application. Specifically, it has a vapor pressure lower than that of water, and 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, propylene 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, dipropylene glycol monobutyl ether,
Dipropylene glycol monopropyl ether, dipropylene glycol monoisopropyl
Polyhydric alcohol ethers such as pill ether; ketones such as acetonyl acetone; γ-
Esters such as butyrolactone, diacetin and triethyl phosphate; lower alkoxy alcohols such as 2-methoxyethanol and 2-ethoxyethanol; ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, triethylenetetramine Amines such as tetraethylenepentamine and pentamethyldiethylenetriamine; amides such as formamide, N, N-dimethylformamide, N-methylformamide and N, N-dimethylacetamide; 2-pyrrolidone, N-ethylpyrrolidone, N- Methyl-2-pyrrolidone, cyclohexylpyrrolidone, morpholine, N-ethylmorpholine, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, imidazole, Heterocycles such as tilimidazole, hydroxyimidazole, dimethylaminopyridine, 1,3-propane sultone, hydroxyethylpiperazine and piperazine; sulfoxides such as dimethyl sulfoxide; sulfones such as sulfolane and the like.

These may be used alone or in combination of two or more.
The aqueous medium used in the present invention is preferably water or a mixture of water and the above-mentioned water-soluble organic solvent, and more preferably water.

[Properties of aqueous pigment dispersion]
The aqueous pigment dispersion of the present invention preferably has the following properties. That is, the content (total amount) of the anionic group in (b) the hydrophobic group-containing anionic polymer in the aqueous pigment dispersion of the present invention is from 0.01 mmol / g to 1 mmol / g based on the pigment weight. Is preferred, and 0.
It is more preferably from 0.5 mmol / g to 0.8 mmol / g. When the content of the anionic group in the dispersion is too small, it becomes difficult to disperse the pigment in the aqueous medium, or the dispersion stability becomes insufficient, resulting in poor discharge stability and heat resistance. There is. On the other hand, if the amount is large, it becomes a free polymer that does not contribute to the dispersion of the pigment, which may cause deterioration in ejection stability and heat resistance, and may easily penetrate into the printed matter, which may cause back-through.

The surface tension of the aqueous pigment dispersion is (c) the upper limit of the surface tension of the aqueous medium alone is usually +1 dyne / cm, and the lower limit is usually −15 dyne / cm, preferably −7 dyne / cm. Yes, more preferably within −6 dyne / cm. When the surface tension of the aqueous pigment dispersion is out of the above range, a decrease in printing density, a deterioration in ejection stability and storage stability may be observed. Although the details of this reason have not been grasped, those in which the surface tension of the dispersion liquid is kept high compared with the surface tension of the aqueous medium does not prevent the aggregation of the pigment on the paper surface, so the print density is high, Furthermore, since the rheological properties of the recording liquid at a high shear rate are not changed, it is presumed that the ejection stability is good, that is, the dispersion maintains the adsorption equilibrium state necessary for the minimum dispersion stability. The

The viscosity of the aqueous pigment dispersion of the present invention is preferably 0.9 cp or more and 30 cp or less, more preferably 1 cp or more and 5 cp or less, and particularly preferably 3 cp or less. If the viscosity is too low, it may be difficult to control the generation / flying of inkjet droplets, and if it is too high, the inkjet drive frequency may be lowered.
The average particle diameter of the pigment in the dispersion is usually 20 nm or more, preferably 50 nm or more, more preferably 150 nm or more. The upper limit is usually 500 nm or less, preferably 300 nm or less, more preferably 250 nm or less. When the average particle diameter of the pigment is too small, it is very difficult to maintain dispersion stability, and it may be difficult to remain on the surface of plain paper, and the print density may be lowered. In addition, if it is too large, the pigment is likely to settle during storage, and the dispersion stability of the dispersion and the storage stability of the recording liquid may be lowered.

The average particle diameter can be measured using a commercially available dynamic light scattering measurement device.
The pigment concentration in the aqueous 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, and the viscosity of the dispersion increases, the dispersion may gel, or the dispersion cannot be used due to dispersion failure. If it is too low, there is a problem that it takes a lot of time to concentrate the ink, so that it is usually 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more.

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, the storage stability of the recording liquid, and the discharge performance are deteriorated. There is.
The aqueous pigment dispersion of the present invention may contain components other than the above-mentioned pigment, hydrophobic group-containing anionic polymer, and aqueous medium. In particular, the ink composition of the present invention as described below. Other additives that may be included in the emulsion may include other components such as emulsion particles, nonionic water-soluble polymers or oligomers.

[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, the hydrophobic group-containing anionic polymer, and the aqueous medium are arbitrary. For example, (a) a pigment, The anionic polymer and (c) the aqueous medium may be mixed at once, and this mixed solution may be subjected to a dispersion treatment 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.

When performing dispersion treatment with an ultrasonic homogenizer, pigments and hydrophobic group-containing anions are prepared 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. It may be performed after the polymer and the aqueous medium are predispersed.
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 low because the pigment particles are dilute, and the pigment particle size may not be reduced even when ultrasonic waves are 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. There is a case.

In addition, since the heat is remarkably generated by the irradiation of ultrasonic waves, it is preferable to disperse while cooling with ice water or the like. 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. , There is a tendency to deteriorate 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 to the pigment surface tends to be insufficient, and the dispersion stability and storage stability tend to be poor. 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. May be caused to decrease.

[Ink composition]
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 or the like is prepared by adjusting the colorant concentration of the above-described aqueous pigment dispersion of the present invention as necessary, and further adding various additives depending on the application. . 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.
In the ink composition of the present invention, the weight of the pigment is preferably 11 to 99 times the weight of the hydrophobic group-containing anionic polymer. Preferably they are 11 times or more and 50 times or less, More preferably, they are 11 times or more and 20 times or less. If the weight of the (a) pigment is too small relative to the weight of the (b) hydrophobic group-containing anionic polymer, the dispersion stability will be low, and the printing density will be low, and if it is too high, the storage stability will be low.

  The concentration of the total colorant in the ink composition of the present invention is usually 0.1% by weight or more, particularly preferably 0.5% by weight or more, and the upper limit is the total colorant concentration with respect to the total amount of the recording liquid. Usually, 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 is increased and the discharge properties are deteriorated. If the colorant concentration is too low, the print density may be too low. 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 ink composition of the present invention preferably contains water and a water-soluble organic solvent, and may further contain other components as desired.
The concentration of the water-soluble organic solvent in the ink composition 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. . In addition, the water content in the ink composition 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.

As the water-soluble organic solvent, those exemplified as the aqueous medium of the aqueous pigment dispersion of the present invention described above can be used.
The ink composition of the present invention may contain various additives as necessary within a 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 ink composition of the present invention is usually 30% by weight or less, and 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, sorbitol, 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.
Although it does not specifically limit as an antifungal agent, Sodium dehydroacetate, dichlorophen, sorbic acid, sodium benzoate, p-hydroxybenzoic acid ester, 1,2-Benzisothiazole-3-one (Product name: Proxel GXL ( Arch Chemicals)) and the like are 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 ink composition of the present invention, the content of all polymers other than the hydrophobic group-containing anionic polymer, including emulsion particles and nonionic water-soluble polymers, is usually 0.05% by weight or more, preferably 0. It is preferably 25% by weight or more, more preferably 0.5% by weight or more, and the upper limit is preferably 20% by weight or less, and more preferably 10% by weight or less. Moreover, it is preferable that it is 500 weight% or less as a usage-ratio of a hydrophobic group containing anion polymer and a polymer other than this.

[Method for producing ink composition]
The ink composition of the present invention is mixed and dispersed in the same manner by adding a colorant and various additives as necessary to the aqueous pigment dispersion produced by the method described in the method for producing an aqueous pigment dispersion. It is prepared by. 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 9 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.

<Synthesis Example 1>
Synthesis of poly (sodium acrylate-co-n-butyl acrylate-co-styrene) (Polymer (b) -1) Polymerization started in condenser with nitrogen 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) 1 and sodium acrylate. The number average molecular weight (Mn) of this polymer was 11,000, the weight average molecular weight (Mw) was 18000, and the molecular weight distribution (Mw / Mn) was 1.6. The component having a weight average molecular weight of 4000 or less was 5.6% by weight.

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 the sodium acrylate, the polymer aqueous solution is concentrated and dried to give the random copolymer (b) -1
Got.
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 43/22/35 (molar ratio). ) = 32/30/38 (weight ratio).

<Synthesis Example 2>
Synthesis of poly (styrene-co-vinylpyrrolidone-co-sodium acrylate) (
Synthesis of polymer (b) -3) 2,2′-Asobis (2,4-dimethylvaleronitrile) as a catalyst was placed in a condenser equipped with nitrogen inside, a nitrogen inlet tube, a stirrer and a flask equipped with a thermometer as a catalyst. 76 g was charged, 200 g of methanol as a solvent, 30.0 g of styrene as a monomer, 110.0 g of vinylpyrrolidone, and 10.0 g of acrylic acid were charged into the flask. The bath temperature was raised from room temperature to 70 ° C. over 30 minutes, and a polymerization reaction was carried out at 70 ° C. for 7 hours. The number average molecular weight (Mn) of this polymer was 3000, the weight average molecular weight (Mw) was 7000, and the molecular weight distribution (Mw / Mn) was 2.3. In addition, components having a weight average molecular weight of 4000 or less are 33.
It was 8% by weight.

After completion of the reaction, the reaction solution was cooled to room temperature, neutralized by adding a 5N aqueous sodium hydroxide solution while stirring, and then distilled water was added while removing methanol with an evaporator to obtain an aqueous polymer solution. After removing impurities from the aqueous polymer solution by ultrafiltration,
The aqueous polymer solution was concentrated and dried to obtain poly (styrene-co-vinylpyrrolidone-co-sodium acrylate): P (St / VP / AANa) (polymer (b) -3).
The structure of the random copolymer was confirmed by 1H-NMR using heavy water as a solvent. 13/31/57 (weight ratio)

<Synthesis Example 3>
Synthesis of poly (sodium acrylate-co-n-butyl acrylate-co-styrene) (Polymer (b) -4) 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 ( b) -4 aqueous solution was obtained.

By drying under vacuum, a mixture of poly (sodium acrylate-co-n-butyl acrylate-co-styrene): polymer (b) -4 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. The component having a weight average molecular weight of 4000 or less was 8.8% by weight.

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, n-butyl acrylate units, and styrene units in the random copolymer was 40/21/39 (molar ratio). ) = 36/26/39 (weight ratio).

<Synthesis Example 4>
Synthesis of poly (sodium acrylate-co-lauryl acrylate-co-styrene) (Polymer (b) -5) As a polymerization initiator in a condenser equipped with nitrogen, a nitrogen inlet tube, a stirrer and a thermometer flask 30 g of 2,2′-azobis (2,4-dimethylvaleronitrile) was charged, 3500.0 g of tetrahydrofuran as a solvent, 600.0 g of acrylic acid, 600.0 g of lauryl acrylate, and 400.0 g of styrene as monomers. 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 obtain polypoly (sodium acrylate-co-lauryl acrylate-co-styrene) (polymer (b) -5) was obtained.

By vacuum drying, a mixture of poly (sodium acrylate-co-lauryl acrylate-co-styrene) (polymer (b) -5) and sodium acrylate was obtained. The number average molecular weight (Mn) of this polymer was 12000, the weight average molecular weight (Mw) was 15000, and the molecular weight distribution (Mw / Mn) was 1.3. The component having a weight average molecular weight of 4000 or less was 5.8% by weight.

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) -5.
The structure of this random copolymer was confirmed by H-NMR using heavy water as a solvent. It was 52/18/30 (weight ratio).

<Synthesis Example 5>
Synthesis of poly (sodium acrylate-co-2-ethylhexyl acrylate) (Polymer (b) -6) Into a condenser equipped with nitrogen, a nitrogen introduction tube, a stirrer and a thermometer, as a polymerization initiator, 2.05 g of 2'-azobis (2,4-dimethylvaleronitrile) was charged, 205 g of tetrahydrofuran as a solvent, 55.46 g of acrylic acid as a monomer, and 94.54 g of 2-ethylhexyl acrylate. Change bath temperature from room temperature to 70
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 the solvent was completely removed by vacuum drying, and then neutralized by adding an aqueous sodium hydroxide solution to polypoly (sodium acrylate-co-2-ethylhexyl acrylate) (polymer (b) -6 ) Was obtained.

By drying under vacuum, a mixture of poly (sodium acrylate-co-2-ethylhexyl acrylate) (polymer (b) -6) and sodium acrylate was obtained. The number average molecular weight (Mn) of this polymer was 18000, the weight average molecular weight (Mw) was 22000, and the molecular weight distribution (Mw / Mn) was 1.2. The component having a weight average molecular weight of 4000 or less was 7.2% by weight.

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 the sodium acrylate, the polymer aqueous solution was concentrated and dried to obtain the polymer (b) -6.
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 2-ethylhexyl acrylate units in the random copolymer was 40/60 (molar ratio) = 21/79. (Weight ratio).

<Synthesis Example 6>
Synthesis of poly (sodium acrylate-co-styrene) (polymer (b) -7) 2,2'- as a polymerization initiator was placed in a condenser equipped with nitrogen inside, a nitrogen inlet tube, a stirrer and a flask equipped with a thermometer. 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) -7 was obtained.

By drying under vacuum, a mixture of poly (sodium acrylate-co-styrene): polymer (b) -7 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. The component having a weight average molecular weight of 4000 or less was 4.2% by weight.
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) -7.
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 7>
Synthesis of poly (isobornyl acrylate-co-sodium acrylate) (Polymer (b) -8) 405 g of tetrahydrofuran as a solvent and monomer in a condenser with a nitrogen-substituted interior, a nitrogen inlet tube, a stirrer and a thermometer As above, 75.5 g of isobornyl acrylate and 104.49 g of acrylic acid were charged into the flask. After raising the bath temperature to 60 ° C., 0.43 g of 2,2′-azobisisobutyronitrile was added as a catalyst, and a polymerization reaction was carried out for 2 hours. The bath temperature was raised to 65 ° C., and the polymerization reaction was further performed for 2 hours. The bath temperature was raised to 70 ° C., and the polymerization reaction was further performed for 4 hours.

  After completion of the reaction, the reaction solution cooled to room temperature was dropped into acetonitrile to obtain a precipitate. The precipitate was collected and vacuum dried to obtain a crude polymer. Ion exchange water was added to the crude polymer, and then neutralized with a 5N aqueous sodium hydroxide solution to form an aqueous solution. After removing impurities from the obtained aqueous polymer solution by ultrafiltration, the aqueous polymer solution was concentrated and dried to obtain poly (isobornyl acrylate-co-sodium acrylate): polymer (b) -8.

The structure of the obtained polymer was confirmed by 1H-NMR using DMSO as a solvent. The composition ratio of the isobornyl acrylate unit and the sodium acrylate unit in the polymer determined by 1H-NMR was 25/75 (molar ratio) = 49/51 (weight ratio). G
The number average molecular weight (Mn) determined from PC was 11,000, the weight average molecular weight (Mw) was 19000, and the molecular weight distribution (Mw / Mn) was 1.75. The component having a weight average molecular weight of 4000 or less was 5.8% by weight.

<Synthesis Example 8>
Synthesis of poly (sodium acrylate-co-n-butyl acrylate-co-styrene) (Polymer (b) -9) To a condenser equipped with nitrogen inside, a nitrogen inlet tube, a stirrer, and a flask equipped with a thermometer,
30 g of 2,2′-azobis (2,4-dimethylvaleronitrile) is charged as a polymerization initiator, 3500.0 g of tetrahydrofuran as a solvent, 80.0 g of acrylic acid as a monomer, 530.0 g of n-butyl acrylate, and 1000.000 of styrene. 0 g was 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, 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) -9 and sodium acrylate. The number average molecular weight (Mn) of this polymer is 11
000, the weight average molecular weight (Mw) was 20000, and the molecular weight distribution (Mw / Mn) was 1.8. The component having a weight average molecular weight of 4000 or less was 3.6% by weight.

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 aqueous polymer solution is concentrated and dried to give the random copolymer (b) -9
Got.
When the structure of the 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 8/26/66 (molar ratio). ) = 5/31/64 (weight ratio).

Example 1 [Black pigment dispersion A]
Carbon black (a) -1 (Mitsubishi Chemical Corporation: # 3230B; DBP absorption 140 ml / 100 g, primary particle size 23 nm, pH 6.4), polymer (b) -1 aqueous solution (solid content 18.3%), Distilled water was mixed in the following ratio and pre-dispersed with a homomixer for 10 minutes.
Carbon black (a) -1 24.0g
6.6 g of polymer (b) -1 aqueous solution
Distilled water 269.4g
Place the above pre-dispersion in a 500 ml tall beaker, immerse the beaker in ice water, disperse for 60 minutes with an ultrasonic homogenizer (Nippon Seiki Seisakusho; US-600T; used chip 36 mm φ), 8% pigment dispersion A Got.

When the surface tension of the above dispersion A was measured at 25 ° C. by attaching a platinum plate to a surface tension meter (CBVP-Z, Kyowa Interface Science Co., Ltd.) employing the Wilhelmy method, 72.9 dyne / cm
Met.
Moreover, when the average particle diameter of the pigment in the dispersion A and the viscosity of the dispersion A were measured by the following methods, they were 225 nm and 1.6 cp.

(Measurement of particle diameter)
The recording liquid A was diluted 10,000 times with deionized water, and measured with an Otsuka Electronics FPAR-1000 using a dilution probe. The average particle size was calculated by the Cumulant method.

(Measurement of viscosity)
Rheometer (REOLOGICA AB Instruments; VAR-100
A cone 1 ° / 55φ) was used and the value at a shear rate of 100 / sec was read.
Further, the content of the anionic group derived from the polymer (b) -1 in the dispersion A is determined from the composition ratio of acrylic acid determined by 1H-NMR, the charged weight of the polymer (b) -1, and the charged pigment weight. The calculation was 0.22 mmol / g.
In the following examples and comparative examples, the surface tension of the dispersion, the average particle diameter of the pigment in the dispersion, the viscosity of the dispersion, and the content of anionic groups derived from the polymer in the dispersion Measurement was performed in the same manner as in 1.

Example 2 [Black pigment dispersion B]
Carbon black (a) -1 of Example 1 was changed to carbon black (a) -2 (Mitsubishi Chemical Corporation: # 40; DBP absorption 110 ml / 100 g, primary particle size 24 nm, pH 7.5), and further each component The mixture ratio was changed to the following, and pre-dispersed with a homogenizer for 10 minutes in the same manner as in Example 1.
Carbon black (a) -2 10.0g
2.7 g of polymer (b) -1 aqueous solution
112.3g of distilled water
The preliminary dispersion was dispersed with an ultrasonic homogenizer for 30 minutes in the same manner as in Example 1 to obtain 8% pigment dispersion B.
Dispersion B has a surface tension of 67.0 dyne / cm, an average particle diameter of the pigment of 196 nm, and a viscosity of 1.
The content of anionic groups derived from the polymer (b) -1 in the dispersion B was 6cp, and was 0.22 mmol / g.

Example 3 [Black pigment dispersion C]
The carbon black (a) -2 of Example 2 was changed to carbon black (a) -3 (Mitsubishi Chemical Corporation: MA600B; DBP absorption 131 ml / 100 g, primary particle diameter 20 nm, pH 7), and 8% pigment dispersion Liquid C was obtained.
The surface tension of the dispersion C is 69.7 dyne / cm, the average particle diameter of the pigment is 195 nm, and the viscosity is 1.
The content of anionic group derived from polymer (b) -1 in dispersion C was 5 cp, and was 0.22 mmol / g.

Example 4 [Black Pigment Dispersion D]
Carbon black (a) -2 of Example 2 was changed to carbon black (a) -4 (Mitsubishi Chemical Corporation: # 960; DBP absorption 69 ml / 100 g, primary particle diameter 16 nm, pH 7.5). The 8% pigment dispersion D was obtained by carrying out the same dispersion treatment as in Example 2 except that the mixing ratio was changed to the following and the dispersion time with a homomixer was changed to 5 minutes.
Carbon black (a) -4 10.0g
3.3 g of aqueous solution of polymer (b) -1
Distilled water 111.7g
The surface tension of the dispersion D is 73.1 dyne / cm, the average particle diameter of the pigment is 148 nm, the viscosity is 1.4 cp, and the content of anionic groups derived from the polymer (b) -1 in the dispersion D is 0.27 mmol / g.

Example 5 [Black pigment dispersion E]
The polymer aqueous solution (b) -1 of Example 1 was changed to a commercially available hydrophobic group-containing anionic polymer (b) -2 aqueous solution (BASF; JONCRYL 501J (solid content 29.5%)), and the mixing ratio of each component was further changed. A dispersion treatment was performed in the same manner as in Example 1 except for the following, to obtain an 8% pigment dispersion E.
Carbon black (a) -1 24.0g
4.9 g of polymer (b) -2 aqueous solution
Distilled water 271.1g
Dispersion E had a surface tension of 71.9 dyne / cm, an average particle size of the pigment of 238 nm, and a viscosity of 2.0 cp. Further, the content of the anionic group derived from (b) -2 in the dispersion E was 0.22 mmol / g when calculated from the acid value (205 mg / g) of the polymer and the charged weight.

Example 6 [Black pigment dispersion F]
In addition to the components of Example 2, 2-pyrrolidone, triethylene glycol, glycerin, ethylene urea, and olefin E1010 were mixed at the following ratios, and pre-dispersion with a homomixer and ultrasonic homogenizer dispersion were performed as in Example 2. 8% pigment dispersion F was obtained.
Carbon black (a) -2 4.0g
0.44 g of polymer (b) -1 aqueous solution
34.3g of distilled water
2-pyrrolidone 1.1g
Triethylene glycol 2.4g
2.85 g of glycerin
4.4 g of ethylene urea
Olfine E1010 0.5g
The surface tension of the dispersion F is 34.9 dyne / cm, the average particle diameter of the pigment is 192 nm, and the viscosity is 2.
The content of anionic groups derived from the polymer (b) -1 in the dispersion F was 5 cp, and was 0.09 mmol / g.

Example 7 [Black pigment dispersion G]
Dispersion treatment was performed in the same manner as in Example 2 except that the aqueous polymer solution (b) -1 was changed to the aqueous polymer (b) -3 solution (solid content 10.6%) in Example 1 and the mixing ratio of each component was changed to the following. As a result, 8% pigment dispersion G was obtained.
Carbon black (a) -1 10.0g
5.7 g of polymer (b) -3 aqueous solution
109.3 g of distilled water
The surface tension of the dispersion G is 73.0 dyne / cm, the average particle diameter of the pigment is 203 nm, the viscosity is 1.5 cp, and the content of the anionic group derived from the polymer (b) -3 in the dispersion G is 0.11 mmol / g.

Example 8 [Black pigment dispersion H]
Carbon black (a) -1 of Example 2 was changed to carbon black (a) -5 (Mitsubishi Chemical Corporation prototype);
DBP absorption amount 102 ml / 100 g, primary particle diameter 16 nm, pH 7), polymer aqueous solution (b) -1 was changed to polymer (b) -4 aqueous solution (solid content 19.7%), and 8% pigment dispersion H was changed to Obtained.
Carbon black (a) -5 10.0g
4.1 g of polymer (b) -4 aqueous solution
110.9g of distilled water
The surface tension of the dispersion H is 71.1 dyne / cm, the average particle diameter of the pigment is 132 nm, the viscosity is 1.6 cp, and the content of anionic groups derived from the polymer (b) -4 in the dispersion H is 0.34 mmol / g.

Example 9 [Black Pigment Dispersion I]
The polymer aqueous solution (b) -4 of Example 8 was changed to polymer (b) -5 aqueous solution (solid content 19.8%), 8
% Pigment dispersion I was obtained.
Carbon black (a) -5 10.0g
4.4 g of polymer (b) -5 aqueous solution
Distilled water 110.6g
The surface tension of Dispersion I is 71.1 dyne / cm, the average particle diameter of the pigment is 132 nm, the viscosity is 1.6 cp, and the content of anionic groups derived from Polymer (b) -5 in Dispersion I is 0.62 mmol / g.

Example 10 [Black Pigment Dispersion Liquid J]
The aqueous polymer solution (b) -4 of Example 8 was converted into an aqueous polymer (b) -6 solution (solid content: 13.8%), and 8
% Pigment dispersion J was obtained.
Carbon black (a) -5 10.0g
6.5 g of polymer (b) -6 aqueous solution
108.5 g of distilled water
The surface tension of dispersion J is 71.0 dyne / cm, the average particle diameter of the pigment is 123 nm, the viscosity is 1.5 cp, and the content of anionic groups derived from polymer (b) -6 in dispersion J is 0.20 mmol / g.

Example 11 [Black pigment dispersion K]
The polymer aqueous solution (b) -4 of Example 8 was changed to polymer (b) -7 aqueous solution (solid content: 9.3%), and 8%
A pigment dispersion K was obtained.
Carbon black (a) -5 10.0g
9.2 g of polymer (b) -7 aqueous solution
105.8g of distilled water
The surface tension of the dispersion K is 71.8 dyne / cm, the average particle diameter of the pigment is 122 nm, the viscosity is 1.5 cp, and the content of anionic groups derived from the polymer (b) -6 in the dispersion K is 0.11 mmol / g.

Example 12 [Black pigment dispersion L]
Carbon black (a) -2 of Example 2 was mixed with carbon black (a) -6 (Mitsubishi Chemical Corporation: MA100; DBP absorption 100 ml / 100 g, primary particle size 24 nm, pH 3.5), and each component was mixed. The ratio was changed to: A dispersion treatment similar to that of Example 2 was performed except that a 10% aqueous sodium hydroxide solution was added so that the pH of the dispersion became 9 before dispersion with an ultrasonic homogenizer, thereby obtaining an 8% pigment dispersion L. .
Carbon black (a) -6 10.0g
1.6 g of polymer (b) -1 aqueous solution
113.4g of distilled water
The surface tension of the dispersion L is 72.0 dyne / cm, the average particle diameter of the pigment is 196 nm, the viscosity is 1.6 cp, and the content of the anionic group derived from the polymer (b) -1 in the dispersion L is 0.13 mmol / g.

Comparative Example 1 [Black pigment dispersion M]
A dispersion treatment was carried out in the same manner as in Example 1 except that the mixing ratio of each component in Example 1 was changed to the following, to obtain an 8% pigment dispersion M.
Carbon black (a) -1 24.0g
26.2 g of polymer (b) -1 aqueous solution
Distilled water 249.8g
The surface tension of the dispersion M is 59.1 dyne / cm, the average particle size of the pigment is 110 nm, the viscosity is 1.8 cp, and the content of anionic groups derived from the polymer (b) -1 in the dispersion M is 0.88 mmol / g.

Comparative Example 2 [Black pigment dispersion N]
A dispersion treatment was carried out in the same manner as in Example 2 except that olefin E1010 was mixed in the following ratio in addition to the components in Example 2, and 8% pigment dispersion N was obtained.
Carbon black (a) -1 10.0g
Polymer (b) -1 aqueous solution 0.55 g
113.2 g of distilled water
Olfin E1010 1.25g
The surface tension of dispersion N is 34.9 dyne / cm, the average particle size of the pigment is 184 nm, the viscosity is 1.4 cp, and the content of anionic groups derived from polymer (b) -1 in dispersion N is 0.04 mmol / g.

Comparative Example 3 [Black Pigment Dispersion O]
Dispersion treatment was performed in the same manner as in Example 2 except that the aqueous polymer solution (b) -4 was changed to the aqueous polymer (b) -8 solution (solid content: 10.8%) and the mixing ratio of each component was changed to 8% pigment dispersion O was obtained.
Carbon black (a) -5 10.0g
5.6 g of polymer (b) -8 aqueous solution
109.4 g of distilled water
The surface tension of the dispersion O is 72.6 dyne / cm, the average particle diameter of the pigment is 128 nm, the viscosity is 2.5 cp, and the content of anionic groups derived from the polymer (b) -8 in the dispersion O is 0.62 mmol / g.

Comparative Example 4 [Black pigment dispersion P]
Carbon black (a) -5, polymer aqueous solution (b) -9 (solid content 16.9%) and methyl ethyl ketone are mixed in the following proportions, using a zirconia bead of 0.3 mmΦ as a medium at 25 ° C. using a self-made bead mill. After dispersing for 3 hours and removing the beads, the dispersion was obtained by adjusting the pigment concentration to 7.7% using methyl ethyl ketone.
Carbon black (a) -5 24.0g
Polymer (b) -9 aqueous solution 1.1g
Methyl ethyl ketone 171.0g
Add 4 g of polymer aqueous solution (b) -9 (solid content 20%) to 51.8 g of the resulting dispersion, add to 40 g of water over 1 hour while applying an ultrasonic homogenizer, and remove MEK with an evaporator. 8% of pigment dispersion P was obtained.

The surface tension of the dispersion P is 65.0 dyne / cm, the average particle diameter of the pigment is 120 nm, the viscosity is 1.6 cp, and the content of the anionic group derived from the polymer (b) -9 in the dispersion P is 0.22 mmol / g.
<Evaluation>
An ink composition having the following ink composition was prepared 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. The results are shown in Table 1.

(Ink composition)
Dispersion liquid (A to P, except F) 50.0 parts Distilled water 39.5 parts
Diethylene glycol 5 parts
Glycerin 5 parts
Olfine E1010 (Surfactant manufactured by Air Products) 0.5 part

1. Evaluation of dispersion stability of dispersions
For dispersions A to P, the dispersed particle diameter and viscosity, and the dispersed particle diameter of the pigment after being held at 70 ° C. for 15 hours were measured. The smaller the increase in particle size after holding, the more stable it is.
The change in particle size with the initial physical properties was evaluated by the value of the particle size increase rate as follows.
Increase rate of particle size = (dispersed particle size after holding dispersion at 70 ° C. for 15 hours−initial particle size of dispersion) / (initial particle size of dispersion) × 100 (%)

2. Evaluation of storage stability of ink composition
For the ink composition prepared from dispersions A to P (except F), the dispersed particle diameter of the pigment immediately after preparation and the dispersed particle diameter of the pigment after being held at 70 ° C. for 15 hours were measured. The smaller the increase in particle size and viscosity after holding, the more stable it is.
The change in particle size with the initial physical properties was evaluated by the value of the particle size increase rate as follows.
Increase rate of particle size = (dispersed particle size after holding ink composition at 70 ° C. for 15 hours−initial particle size of dispersion) / (initial particle size of dispersion) × 100 (%)

3. Printer printing evaluation of ink composition
For printing evaluation of the ink composition prepared from the dispersions A to P, an inkjet recording printer (Canon BJ S700 printer) was used as the printer, and commercially available plain paper (GF manufactured by Canon Inc.) was used as the printing paper. -500) was used. Printing was performed in the clean mode with plain paper settings. Regarding the dispersion F, the dispersion was used for evaluation as it was.

(1) Print density measurement of recorded images
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) Dischargeability
The printed matter printed under the above conditions was visually observed, and the ejection stability was evaluated as follows.
Evaluation ○: There was no fading or streaking in the printed matter.
Evaluation x: Cannot be printed at all.
The evaluation results are shown in Table 1.

From Table 1, the following is clear.
In Comparative Examples 1 and 2, the weight of the pigment is 5 times and 100 times the weight of the hydrophobic group-containing anionic polymer, respectively, but Comparative Example 1 has a low print density and poor dispersion stability. Then, the storage stability of the ink is poor, and furthermore, it is not ejected by a printer.
In Comparative Example 3, the molar content of the hydrophobic monomer structural unit in the hydrophobic group-containing anionic polymer is less than the molar content of the anionic monomer structural unit, and the storage stability of the ink is poor.

Further, in Comparative Example 4, the weight of the pigment is 2.5 times the weight of the hydrophobic group-containing anionic polymer, and the molar content of the hydrophobic monomer structural unit is based on the molar content of the anionic monomer structural unit. The ink storage stability is poor and the printer does not discharge under very high conditions of 98/2.
In contrast, in Examples 1 to 12, the weight of the pigment falls within the range of 11 to 99 times the weight of the hydrophobic group-containing anionic polymer, and the hydrophobic monomer structural unit in the hydrophobic group-containing anionic polymer. / Molar ratio of anionic monomer structural units is in the range of 30/70 to 90/10, all of which have high printing density, excellent dispersion stability and storage stability, and excellent ejection properties. .

  From the above results, the aqueous pigment dispersion of the present invention not only has good dispersion stability and storage stability of the recording liquid, but also has good recording liquid ejection properties, and further, the print density of the resulting printed matter. It is clear that it is expensive.

  The ink composition using the aqueous pigment dispersion of the present invention is excellent in storage stability, dischargeability, printing density, and the like, and is industrially useful for an inkjet printer.

Claims (6)

  An aqueous pigment dispersion containing (a) a pigment, (b) a hydrophobic group-containing anionic polymer, and (c) an aqueous medium, wherein (a) the weight of the pigment is (b) the weight of the hydrophobic group-containing anionic polymer 11 to 99 times, and (b) the hydrophobic monomer structural unit / anionic monomer structural unit molar ratio in the hydrophobic group-containing anionic polymer is 30/70 to 90/10 An aqueous pigment dispersion.   (A) The pigment is carbon black, the DBP oil absorption of the carbon black is from 100 ml / 100 g to 150 ml / 100 g, and the average primary particle size of the carbon black is from 15 nm to 30 nm. Item 4. The aqueous pigment dispersion according to Item 1.   (B) The number average molecular weight of the hydrophobic group-containing anionic polymer is 6000 or more and 25,000 or less, and (b) the component having a weight average molecular weight of 4000 or less in the hydrophobic group-containing anionic polymer is 20% by weight or less. The aqueous pigment dispersion according to claim 1 or 2, characterized in that   (C) The aqueous pigment dispersion according to any one of claims 1 to 3, wherein the aqueous medium is water.   An ink composition comprising the aqueous pigment dispersion according to any one of claims 1 to 4.   6. An ink jet recording method comprising ejecting droplets of the ink composition according to claim 5 from an ink jet head and attaching the droplets to a recording medium.