JP2016069487A - Aqueous pigment dispersion and aqueous ink composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous pigment dispersion that achieves both of dispersibility and dispersion stability of a pigment at high levels and an aqueous ink composition prepared with the aqueous pigment dispersion.SOLUTION: There is provided an aqueous pigment dispersion containing an aqueous medium, a pigment and a polymer dispersion, the polymer dispersion has at least a (meth)acrylate constitutional unit having a benzene ring, a (meth)acrylate constitutional unit having an alkyl group with 12 or more carbon atoms and a constitutional unit having an ionic group, the percent content of the (meth)acrylate constitutional unit having the benzene ring is 20 to 60 mass% and the percentage content of the (meth)acrylate constitutional unit having the alkyl group with 12 or more carbon atoms is 10 to 40 mass% in the polymer dispersion. There is also provided an aqueous ink composition prepared with the same.SELECTED DRAWING: None

Description

  The present invention relates to an aqueous pigment dispersion and an aqueous ink composition using the same.

As an image recording method for forming an image on a recording medium such as paper based on an image data signal, there are recording methods such as an electrophotographic method, a sublimation type and a melt type thermal transfer method, and an ink jet method.
The ink jet recording method does not require a printing plate and ejects ink only to the image forming unit to form an image directly on the recording medium. Therefore, the ink can be used efficiently and the running cost is low. Further, the ink jet recording method has a printing apparatus with a relatively low cost compared to a conventional printing machine, can be downsized, and has less noise. Thus, the ink jet recording method has various advantages over other image recording methods.

Dye has been used as a coloring material for water-based inks of inkjet printers. However, water-based inks using dyes tend to cause image blurring, and there are restrictions on improving light resistance and water resistance. In order to overcome these drawbacks, water-based ink using a pigment as a coloring material has been used in recent years. In an aqueous ink using a pigment, it is necessary to stably disperse the pigment in an aqueous medium. For this reason, water-based inks or pigment dispersions as raw materials thereof usually use a dispersant to improve the dispersibility and dispersion stability of the pigment.
For example, Patent Document 1 describes an aqueous pigment dispersion containing a pigment and an anionic group-containing organic polymer compound having a specific structure, and a dispersion having a high color density and good dispersibility and dispersion stability. It is described that it was obtained.
Patent Document 2 describes a colored fine particle dispersion obtained by mixing a colorant and a resin having a specific structure and dispersing in water. By forming a crosslinked structure in the resin, dispersion stability and storage stability are described. It is described that a colored fine particle dispersion having good quality was obtained.
Further, Patent Document 3 describes a pigment dispersion containing a pigment whose surface is coated with a crosslinked water-soluble polymer.

JP 2001-234109 A JP 2004-182878 A JP 2013-185135 A

The pigment dispersion used as the raw material of the ink composition is required to have a higher concentration of the pigment in the dispersion so that a high image density can be printed.
However, in the aqueous pigment dispersions described in Patent Documents 1 to 3, when the pigment concentration is increased to a certain level or more, dispersibility (the pigment can be uniformly dispersed in a fine particle state in the medium without causing the pigment fine particles to aggregate Low viscosity dispersion characteristics) or dispersion stability (the above-mentioned pigment dispersion characteristics can be maintained over time or stable against external stimuli (heat, vibration, etc.)) It becomes difficult to achieve both characteristics at a high level.
It is an object of the present invention to provide an aqueous pigment dispersion in which the dispersibility and dispersion stability of the pigment are compatible at a higher level, and an aqueous ink composition using the aqueous pigment dispersion.

  As a result of intensive studies in view of the above problems, the present inventors have been able to disperse pigment fine particles having a smaller particle diameter in an aqueous medium by using a polymer dispersant having a specific structure. It has been found that a pigment dispersion having a viscosity can be obtained and that the dispersion stability of the pigment can be greatly enhanced. Furthermore, the present inventors have found that an aqueous ink composition using this pigment dispersion is also excellent in pigment dispersibility and pigment dispersion stability. The present invention has been completed based on these findings.

That is, the said subject of this invention was solved by the following means.
[1]
An aqueous pigment dispersion containing an aqueous medium, a pigment, and a polymer dispersant,
The polymer dispersant has at least a structural unit represented by the following general formula (I), a structural unit represented by the following general formula (II), and a structural unit having an ionic group,
In the polymer dispersant, the content of the structural unit represented by the following general formula (I) is 20 to 60% by mass, and the content of the structural unit represented by the following general formula (II) is 10 to 40%. An aqueous pigment dispersion which is% by weight.

In the formula, R ¹ represents a hydrogen atom or methyl.
L ¹ represents —C (═O) O—, —OC (═O) —, or —C (═O) NR ⁴ —. R ⁴ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.
L ² is a single bond or a divalent group selected from an alkylene group having 1 to 12 carbon atoms, an alkenylene group having 2 to 12 carbon atoms, —C (═O) —, —O— and —S—. Divalent formed by combining two or more groups selected from a linking group or an alkylene group having 1 to 12 carbon atoms, an alkenylene group having 2 to 12 carbon atoms, -C (= O)-, -O- and -S-. Represents a linking group.
R ² represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms.
R ³ represents an alkyl group having 12 or more carbon atoms.
[2]
The aqueous pigment dispersion according to [1], wherein the polymer dispersant has an acid value of 1.5 to 4.0 mmol / g.
[3]
The aqueous pigment dispersion according to [1] or [2], wherein the polymer dispersant has a weight average molecular weight of 5,000 to 30,000.
[4]
The aqueous pigment dispersion according to [3], wherein the polymer dispersant has a weight average molecular weight of 7000 to 15000.
[5]
In the polymer dispersant, the content of the structural unit represented by the general formula (I) is 30 to 60% by mass, and the content of the structural unit represented by the general formula (II) is 10 to 30%. The aqueous pigment dispersion according to any one of [1] to [4], which is mass%.
[6]
The aqueous pigment dispersion according to any one of [1] to [5], wherein the structural unit represented by the general formula (I) is derived from benzyl (meth) acrylate or phenoxyethyl (meth) acrylate.
[7]
The aqueous pigment dispersion according to any one of [1] to [6], wherein the polymer dispersant forms a crosslinked structure in the aqueous pigment dispersion.
[8]
The aqueous pigment dispersion according to any one of [1] to [7], wherein the pigment is carbon black.
[9]
The aqueous pigment dispersion according to any one of [1] to [8], which contains at least one water-soluble organic solvent.
[10]
A water-based ink composition using the water-based pigment dispersion according to any one of [1] to [9].
[11]
The aqueous ink composition according to [10], wherein the aqueous ink composition is for inkjet recording.

In this specification, unless otherwise specified, when there are a plurality of substituents, linking groups, ligands, repeating units, etc. (hereinafter referred to as substituents) represented by specific symbols, or a plurality of substituents, etc. Are defined simultaneously or alternatively, the respective substituents and the like may be the same as or different from each other. The same applies to the definition of the number of substituents and the like.
In the present specification, the “group” of each group described as an example of each substituent is used to include both an unsubstituted form and a form having a substituent. For example, “alkyl group” means an alkyl group which may have a substituent.
In the present specification, when the term “compound” is added at the end, or when a compound is indicated by a specific name or chemical formula, the salt, complex, or ion thereof is added to the compound itself unless otherwise specified. Used to include.
In this specification, “(meth) acrylate” is used to mean to include both acrylate and methacrylate. The same applies to “(meth) acrylic acid”.
In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

  The aqueous pigment dispersion of the present invention is excellent in both the dispersibility and dispersion stability of the pigment. The aqueous ink composition of the present invention is prepared from the aqueous pigment dispersion of the present invention and is excellent in both the dispersibility and dispersion stability of the pigment.

  Preferred embodiments of the aqueous pigment dispersion of the present invention are described below.

[Aqueous pigment dispersion]
The aqueous pigment dispersion of the present invention contains an aqueous medium, a pigment, and a polymer dispersant having a specific structure. In the aqueous pigment dispersion of the present invention, at least a part of the surface of the pigment is covered with the polymer dispersant having the specific structure and is dispersed in the aqueous medium.
The aqueous pigment dispersion of the present invention may further contain other components as necessary. Examples of other components include water-soluble resins, water-dispersible resins, surfactants, pH adjusters, inorganic salts, and organic salts.

<Aqueous medium>
The aqueous medium (hereinafter referred to as the aqueous medium (a)) used for the aqueous pigment dispersion of the present invention is water or a mixed liquid of water and a water-soluble organic solvent. In the aqueous medium contained in the aqueous pigment dispersion, the content of water is preferably 40% by mass or more, more preferably 50 to 100% by mass, further preferably 60 to 100% by mass, and more preferably 80 to 100% by mass.

  The water-soluble organic solvent that can be contained in the aqueous medium (a) preferably has a solubility in water at 20 ° C. of 5% by mass or more. Examples of the water-soluble organic solvent include alcohols, ketones, ether compounds, amide compounds, nitrile compounds, and sulfone compounds.

Among these, examples of the alcohol include ethanol, isopropanol, n-butanol, t-butanol, isobutanol, diacetone alcohol, diethylene glycol, ethylene glycol, dipropylene glycol, propylene glycol, and glycerin.
Examples of the ketone include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone.
Examples of the ether compound include dibutyl ether, tetrahydrofuran, and dioxane.
Examples of the amide compound include dimethylformamide and diethylformamide.
An example of the nitrile compound is acetonitrile.
Examples of the sulfone compound include dimethyl sulfoxide, dimethyl sulfone, and sulfolane.

  60-95 mass% is preferable, as for content of the aqueous medium (a) in the pigment dispersion of this invention, 70-90 mass% is more preferable, and 80-90 mass% is further more preferable.

<Pigment>
The aqueous pigment dispersion of the present invention is formed by dispersing one or more pigments.
There is no restriction | limiting in particular in the kind of pigment used for the aqueous pigment dispersion of this invention, A normal organic or inorganic pigment can be used.
Examples of organic pigments include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Among these, an azo pigment or a polycyclic pigment is preferable.
Examples of the azo pigment include azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments.
Examples of the polycyclic pigment include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments.
Examples of dye chelates include basic dye chelates and acid dye chelates.

  Examples of inorganic pigments include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Among these, carbon black is preferable.

  The DBP absorption amount of the carbon black pigment is not particularly limited, but is preferably 30 ml / 100 g or more and 200 ml / 100 g or less, more preferably 50 ml / 100 g or more and 150 ml / 100 g or less from the viewpoint of color tone and printing density. . The DBP absorption is measured by the JIS K6221 A method.

The BET specific surface area of the carbon black pigment is not particularly limited, but is preferably 30 m ² / g or more and 450 m ² / g or less, and 200 m ² / g or more and 400 m ² / g from the viewpoint of printing density and storage stability. The following is more preferable.

Examples of the carbon black pigment include those produced by known methods such as a contact method, a furnace method, and a thermal method.
Specific examples For example, Raven1250, Raven1200, Raven1190 ULTRA, Raven1170, Raven1255, Raven1080ULTRA, Raven1060ULTRA, Raven1040, Raven1035, Raven1020, Raven1000, Raven900, Raven890, Raven850, Raven780ULTRA, Raven860Ultra, Raven520, Raven500, Raven450, Raven460, Raven415, Raven14 , Conductex 7055 Ultra (from Colombian Carbon), Regal 400R, Regal 330R, Regal 660R, Mogu L, Black Pearls L, egal99, Regal350, MONARCH280, MONARCH120 (above, manufactured by Cabot), Color Black S160, Color Black S170, Printex35, Printex U, Printex V, Printex 140U, Printex 140V, Printex 140V, Print Black 4A, Special Black 4, Special Black 550, Special Black 350, Special Black 250, Special Black 100, NEROX 3500, NEROX 1000, NEROX 2500 (and above, Evonik) Degussa Co., Ltd.), No. 10, no. 20, no. 25, no. 33, no. 40, no. 45, no. 47, no. 52, no. 85, no. 95, no. 260, MA7, MA8, MA11, MA77, MA100, MA220, MA230, MA600 (above, manufactured by Mitsubishi Chemical Corporation). However, it is not limited to these.

  Further, specific examples of the pigment that can be used in the present invention include pigments described in paragraph numbers 0142 to 0145 of JP-A-2007-100071.

  There is no restriction | limiting in particular in the pigment density | concentration in the aqueous pigment dispersion of this invention, Usually, it is 5-25 mass%, More preferably, it is 10-20 mass%.

The particle size of the pigment dispersed in the aqueous pigment dispersion of the present invention is preferably 80 to 150 nm, and more preferably 90 to 120 nm. Here, the particle size of the pigment in the aqueous pigment dispersion means a volume average particle size. The particle size of the pigment in the aqueous pigment dispersion can be measured by the method described in Examples described later.
By setting the particle size of the pigment in the pigment dispersion to 200 nm or less, color reproducibility when used in the water-based ink composition can be improved. Moreover, the light resistance at the time of using for a water-based ink composition can be improved by making the particle size of the pigment in a pigment dispersion 10 nm or more.

<Polymer dispersant>
The polymer dispersant used for the pigment dispersion of the present invention (hereinafter also simply referred to as “dispersant”) is represented by the structural unit represented by the following general formula (I) and the following general formula (II). It has a structural unit and a structural unit having an ionic group. The polymer dispersant may be in a form having one or two or more kinds of structural units represented by the following general formula (I). Moreover, the form which has 1 type of the structural unit represented by the following general formula (II), or a form which has 2 or more types may be sufficient as the said polymer dispersing agent. In addition, the polymer dispersant may be in a form having one kind of structural unit having an ionic group or in a form having two or more kinds. Furthermore, the polymer dispersant contains other structural units other than the structural unit represented by the following general formula (I), the structural unit represented by the following general formula (II), and the structural unit having an ionic group. You may contain.
The dispersant is preferably a copolymer (preferably a random copolymer) of (meth) acrylic acid ester and (meth) acrylic acid.

In general formulas (I) and (II), R ¹ represents a hydrogen atom or methyl, and is preferably methyl.

L ¹ represents —C (═O) O—, —OC (═O) —, or —C (═O) NR ⁴ —. R ⁴ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms (a linear or branched alkyl group, preferably an alkyl group having 1 to 3 carbon atoms, more preferably methyl or ethyl). L ¹ is more preferably —C (═O) O—. R ⁴ is preferably a hydrogen atom.

L ² is a single bond, or an alkylene group having 1 to 12 carbon atoms (preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, and further preferably a straight chain or branched chain having 1 to 3 carbon atoms). An alkenylene group having 2 to 12 carbon atoms (preferably an alkenylene group having 2 to 10 carbon atoms, more preferably 2 to 6 carbon atoms, and still more preferably a straight chain or branched chain having 2 to 4 carbon atoms). , -C (= O)-, -O- and -S-, or an alkylene group having 1 to 12 carbon atoms (preferably having 1 to 10 carbon atoms, more preferably 1 to 1 carbon atoms). 5, more preferably a linear or branched alkylene group having 1 to 3 carbon atoms, an alkenylene group having 2 to 12 carbon atoms (preferably 2 to 10 carbon atoms, more preferably 2 to 6 carbon atoms, still more preferably Straight carbon number 2-4 An alkenylene group having a chain or a branch), a divalent linking group formed by combining two or more groups selected from —C (═O) —, —O— and —S—.
L ² in the general formula (I) is preferably a single bond, — (CH ₂ CH ₂ O) ₁ —, — (CH ₂ ) _m O—, or — (CH ₂ ) _n —, and — (CH _{2) m} O-or - _{(CH 2) n} - is more preferable. Note: Added PEO chain as a preferred linking chain. Here, 1 is an integer of 1 to 10, more preferably 1 to 5. m is an integer of 1-5, More preferably, it is an integer of 1-3, More preferably, it is 2. Moreover, n is an integer of 1-5, More preferably, it is an integer of 1-3, More preferably, it is 1 or 2, More preferably, it is 1.
L ² in the general formula (II) is preferably a single bond.

In general formula (I), R ² is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms (a linear alkyl group or a branched alkyl group, preferably an alkyl group having 1 to 3 carbon atoms, more preferably methyl. Or ethyl), or an alkoxy group having 1 to 6 carbon atoms (a linear alkyl group or a branched alkoxy group, preferably an alkoxy group having 1 to 3 carbon atoms, more preferably methoxy or ethoxy), and a hydrogen atom It is more preferable that
The structural unit represented by the general formula (I) is derived from benzyl (meth) acrylate or phenoxyethyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, or phenoxydiethylene glycol (meth) acrylate. Are more preferable, derived from benzyl (meth) acrylate or phenoxyethyl (meth) acrylate, and more preferably derived from phenoxyethyl (meth) acrylate. Here, the structural unit derived from a certain compound (compound X) means a structure derived from the compound X in the polymer when the compound X is polymerized as a monomer and incorporated in the polymer.

In formula (II), R ³ represents an alkyl group having 12 or more carbon atoms. R ³ may be a linear alkyl group or a branched alkyl group, and is preferably a linear alkyl group. R ³ preferably has 12 to 22 carbon atoms, more preferably 12 to 20 carbon atoms, and still more preferably 12 to 18 carbon atoms.
The structural unit represented by the general formula (II) is stearyl (meth) acrylate, lauryl (meth) acrylate, behenyl (meth) acrylate, 2-hexyldecyl (meth) acrylate, tridecyl (meth) acrylate, or isomyristyl ( It is preferably a (meth) acrylate, more preferably stearyl (meth) acrylate, lauryl (meth) acrylate, or isomyristyl (meth) acrylate.

In the structure of the dispersant, the content of the structural unit represented by the general formula (I) is 20 to 60% by mass, preferably 30 to 60% by mass, more preferably 30 to 50% by mass, More preferably, it is 35-50 mass%.
Moreover, in the structure of a dispersing agent, the content rate of the structural unit represented by the said general formula (II) is 10-40 mass%, Preferably it is 10-30 mass%, More preferably, it is 10-20 mass%. is there.

The dispersant has a structural unit having an ionic group. The “structural unit having an ionic group” means a structural unit derived from a monomer having an ionic group.
This ionic group means a group that generates ions in the presence of an acid or a base, and an acidic group is preferable. The acidic group is a substituent having a dissociative proton, and means an acidic group such as a carboxy group, a phosphonyl group, a phosphoryl group, a sulfo group, or a boric acid group. Of these, the acidic group is preferably a carboxy group, a sulfo group or a phosphonyl group, and more preferably a carboxy group. The acidic group may take a form of releasing a proton and dissociating, or may be a salt.
The structural unit having an ionic group is a structural unit derived from (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, bis (methacryloxyethyl) phosphate or 2-acrylamido-2-methylpropanesulfonic acid. It is preferable that it is a structural unit derived from methacrylic acid or acrylic acid.

  In the structure of the dispersant, the content of the structural unit having an ionic group is preferably 15 to 40% by mass, more preferably 15 to 30% by mass, and still more preferably 15 to 25% by mass.

When the dispersant has a structural unit having an ionic group (hydrophilic group), the dispersant adsorbed on the surface of the pigment becomes easily compatible with water, and the pigment can be dispersed in the aqueous medium (a).
Further, the dispersant has the structural unit represented by the general formula (I) and the structural unit represented by the general formula (II) at a specific content defined in the present invention, whereby the pigment In the aqueous medium (a), it is possible to obtain an aqueous pigment dispersion which is uniformly dispersed with a smaller particle diameter and has a lower viscosity, and further, this dispersed state can be stably maintained.

In addition to the structural unit represented by the general formula (I), the structural unit represented by the general formula (II), and the structural unit having an ionic group, the dispersant is composed of other structural units (hereinafter simply referred to as “others”). May be referred to as a “structural unit”. As the other structural unit, (meth) acrylic acid having a structure different from any of the structural unit represented by the general formula (I), the structural unit represented by the general formula (II), and the structural unit having an ionic group A structural unit derived from an ester is preferred. As specific examples, 2-ethylhexyl (meth) acrylate, hydroxyethyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) ) Alkyl (meth) acrylates such as acrylate; 2-methoxyethyl acrylate, 2- (2-methoxyethoxy) ethyl acrylate, 2- (2-methoxyethoxy) ethyl methacrylate, ethoxytriethylene glycol methacrylate, methoxypolyethylene glycol (molecular weight 200) ~ 1000) due to monomers selected from (meth) acrylates having a nonionic group such as monomethacrylate, polyethylene glycol (molecular weight 200-1000) monomethacrylate The structural units that can be mentioned.
Among them, hydroxyethyl (meth) acrylate, 2-methoxyethyl acrylate, 2- (2-methoxyethoxy) ethyl acrylate, methoxypolyethylene glycol (molecular weight 200 to 1000) monomethacrylate, polyethylene glycol (molecular weight 200 to 1000) monomethacrylate, And a structural unit derived from a monomer selected from methyl (meth) acrylate.
In the structure of the dispersant, the content of other structural units is preferably 30% by mass or less, more preferably 0 to 25% by mass, and further preferably 0 to 20% by mass.

The acid value of the dispersant is preferably 1.5 to 4.0 mmol / g, more preferably 2.0 to 3.5 mmol / g, from the viewpoint of further improving dispersibility and dispersion stability. More preferably, the acid value of the dispersant is 2.0 to 3.0 mmol / g, which can be calculated by measuring according to JIS K0070 and converting it as 1 mmol / g = 56.1 mgKOH / g.

The weight average molecular weight of the dispersant is preferably 5000 to 30000, more preferably 6000 to 20000, and even more preferably 7000 to 15000 from the viewpoint of further improving dispersibility and dispersion stability. In addition, the weight average molecular weight of a dispersing agent means the weight average molecular weight before forming a crosslinked structure, when a dispersing agent is bridge | crosslinked in an aqueous pigment dispersion so that it may mention later.
Usually, unless the molecular weight of the dispersant is large to some extent (usually about 40000 to 50000), the adsorption to the pigment surface is not stable, and sufficient dispersion stability cannot be exhibited. On the other hand, the dispersant used in the present invention has a constitutional unit represented by the above general formula (I) and a constitutional unit represented by the above general formula (II) at a specific content, thereby reducing the surface of the pigment. Both the adsorption speed and the adsorption stability are improved, and even if the weight average molecular weight is as small as about 5000 to 30000, both dispersibility and dispersion stability can be achieved at a high level. If a polymer having a small weight average molecular weight can be used as a dispersant, it is advantageous in terms of improving the dispersion speed and reducing the viscosity of the dispersion.
In this specification, the weight average molecular weight is measured by gel permeation chromatograph (GPC). GPC uses HLC-8220GPC (manufactured by Tosoh Corporation), and three columns of TSKgeL Super HZM-H, TSKgeL Super HZ4000, and TSKgeL Super HZ2000 (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) are connected in series. And NMP (N-methylpyrrolidone) is used as the eluent. As conditions, the sample concentration is 0.35% by mass, the flow rate is 0.35 ml / min, the sample injection amount is 10 μl, the measurement temperature is 40 ° C., and an IR detector is used. In addition, the calibration curve is “standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, It is prepared from 8 samples of “A-2500”, “A-1000”, “n-propylbenzene”.

  The dispersant preferably has a water solubility of 10% by mass or more at 20 ° C., more preferably 20% by mass or more.

  In the aqueous pigment dispersion of the present invention, the ratio between the pigment content and the dispersant content is not particularly limited as long as the pigment can be stably dispersed in the aqueous medium (a). Usually, pigment: dispersant = It is preferably 1: 0.1 to 1: 2 (mass ratio), and pigment: dispersant = 1: 0.2 to 1: 1 (mass ratio).

  The viscosity of the aqueous pigment dispersion of the present invention is usually 3 to 100 mPa · s, more preferably 5 to 50 mPa · s, although it depends on the pigment concentration. The viscosity of the aqueous pigment dispersion can be measured by the method described in Examples described later.

  The pH of the aqueous pigment dispersion of the present invention is preferably pH 6 to 11, more preferably pH 7 to 10, and still more preferably pH 7 to 9, from the viewpoint of dispersion stability.

<Preparation of pigment dispersion>
The method for preparing the aqueous pigment dispersion of the present invention is not particularly limited. For example, at least an aqueous medium (a), a pigment, and a dispersant are mixed, and if necessary, an aqueous solution containing a basic substance is mixed and dispersed. By doing so, the aqueous pigment dispersion of the present invention can be obtained.

  In the aqueous pigment dispersion of the present invention, a crosslinking structure may be formed in the dispersant. When the dispersing agents present on the pigment surface form a crosslinked structure, the dispersion stability of the pigment can be further improved. For the formation of the cross-linking structure of the dispersant, a cross-linking agent having two or more groups that are reactive with a specific group of the dispersant in one molecule can be used. For example, an aqueous pigment dispersion is obtained by mixing at least an aqueous medium (a), a pigment, and a dispersing agent, and if necessary, an aqueous solution containing a basic substance and dispersing the mixture to obtain an aqueous pigment dispersion. The crosslinking agent can be mixed and heated (usually heated to 40 to 70 ° C.) to form a crosslinked structure in the dispersant. For example, the method described in JP-A-2009-190379 can be used to form the crosslinked structure.

  As the cross-linking agent, two or more groups (preferably 2 to 4, more preferably 2 or 3, more preferably 2) are present in one molecule which are reactive with the ionic group of the dispersant. The compound which has can be used suitably. More preferably, the dispersant has a carboxy group as an ionic group, and the crosslinking agent has two or more epoxy groups in one molecule (preferably 2 to 4, more preferably 2 or 3, more preferably 2), and more preferably a glycidyl ether compound having 2 or more (preferably 2 to 4, more preferably 2 or 3, more preferably 2) glycidyl groups in one molecule. .

  Preferred examples of the crosslinking agent include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether. , Polypropylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, and the like, and polyethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, or trimethylolpropane triglycidyl ether are preferable.

  A commercial item can also be used as said crosslinking agent. As a commercial item, Dencol EX-321, EX-821, EX-830, EX-850, EX-851 (made by Nagase ChemteX Co., Ltd.) can be used, for example.

  The molar ratio of the crosslinking site of the crosslinking agent (for example, epoxy group) and the crosslinked site of the dispersing agent (for example, carboxy group) is determined from the viewpoint of the crosslinking reaction rate and the dispersion stability after crosslinking. Site] = 1: 1.1 to 1:10 is preferable, 1: 1.1 to 1: 5 is more preferable, and 1: 1.1 to 1: 3 is more preferable.

[Water-based ink composition]
The water-based ink composition of the present invention may be the water-based pigment dispersion of the present invention itself, but is usually prepared using the water-based pigment dispersion of the present invention as a raw material. More specifically, it is preferable to prepare the aqueous ink composition of the present invention by mixing at least the aqueous pigment dispersion of the present invention and an aqueous medium (hereinafter referred to as an aqueous medium (b)). In the water-based ink composition of the present invention, a surfactant, an anti-drying agent (swelling agent), an anti-coloring agent, a penetration accelerator, an ultraviolet absorber, an antiseptic, a rust inhibitor, an antifoaming agent, You may mix additives, such as a clay regulator, a pH adjuster, and a chelating agent. The mixing method is not particularly limited, and a water-based ink composition of the present invention can be obtained by appropriately selecting a commonly used mixing method.

  An aqueous medium (b) is synonymous with an aqueous medium (a), and its preferable range is also the same. In the aqueous ink composition of the present invention, the content of the aqueous medium (the total content of the aqueous media (a) and (b)) is preferably 10 to 99% by mass from the viewpoints of ink stability and ejection reliability. 30 to 80% by mass is more preferable, and 50 to 70% by mass is more preferable.

In the aqueous ink composition of the present invention, the pigment concentration is preferably 0.5 to 25% by mass, more preferably 1 to 15% by mass from the viewpoint of image density.
The particle size of the pigment dispersed in the aqueous ink composition of the present invention is preferably 80 to 120 nm, and more preferably 90 to 110 nm. The particle diameter of the pigment in the ink composition means a volume average particle diameter, and can be measured by the method described in Examples described later.

The surfactant that can be contained in the water-based ink composition can be used, for example, as a surface tension adjusting agent.
As the surfactant, a compound having a structure having both a hydrophilic part and a hydrophobic part in the molecule can be used effectively. Anionic surfactants, cationic surfactants, amphoteric surfactants, nonions Either a surfactant or a betaine surfactant can be used.

In the present invention, a nonionic surfactant is preferable from the viewpoint of suppressing ink droplet ejection interference, and an acetylene glycol derivative (acetylene glycol surfactant) is more preferable.
Examples of the acetylene glycol surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl-5-decyne-4, An alkylene oxide adduct of 7-diol can be used, and at least one selected from these is preferable. Examples of commercially available products of these compounds include E series such as Olphine E1010 manufactured by Nissin Chemical Industry Co., Ltd.

The surfactant is preferably contained in an amount within a range in which the surface tension of the ink composition can be adjusted to 20 to 60 mN / m, more preferably from the viewpoint of favorably discharging the ink composition by an ink jet method. The surface tension of the composition is contained in an amount that can be adjusted to 20 to 45 mN / m, more preferably 25 to 40 mN / m.
The surface tension is measured using an aqueous surface tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) and a water-based ink composition at 25 ° C.

  When the water-based ink composition of the present invention contains a surfactant, the content of the surfactant is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.1 to 10% in the water-based ink composition. It is mass%, More preferably, it is 0.2-3 mass%.

  The viscosity of the aqueous ink composition of the present invention is not particularly limited, but the viscosity at 25 ° C. is preferably 1.2 mPa · s to 15.0 mPa · s, more preferably 2 mPa · s to 13 mPa. It is less than s, more preferably 2.5 mPa · s or more and less than 10 mPa · s. The viscosity of the water-based ink composition can be measured by the method described in Examples described later.

  The pH of the aqueous ink composition of the present invention is preferably pH 6 to 11 from the viewpoint of dispersion stability. When the ink set described later is used, it is preferable that the ink composition aggregates at a high speed by contact with a treatment agent containing an acidic compound or the like, and therefore pH 7 to 10 is more preferable, and pH 7 to 9 is further preferable.

  The water-based ink composition of the present invention can be used as ink for stationery such as sign pens and markers, and as ink for various printers. Among these, because of its excellent pigment dispersibility and dispersion stability, it can be suitably used as an ink for ink jet recording.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to these Examples.

[Synthesis Example 1] Synthesis of Dispersant P-1 A dispersant composed of a polymer having the following structure was synthesized.

198 g of dipropylene glycol was added to a 2000 ml three-necked flask equipped with a stirrer and a condenser, and heated to 85 ° C. under a nitrogen atmosphere.
A solution I obtained by dissolving 135 g of benzyl methacrylate, 90 g of stearyl methacrylate, 75 g of methacrylic acid, and 5.7 g of 2-mercaptopropionic acid in 114 g of dipropylene glycol, t-butylperoxy-2-ethylhexanoate (day) Solution II obtained by dissolving 4.5 g of Yusei Chemical Perbutyl O) in 152 g of dipropylene glycol was prepared. Solution I was added dropwise to the three-necked flask over 4 hours and solution II over 5 hours.
After completion of the dropwise addition, the reaction was further continued for 2 hours, and then the temperature was raised to 95 ° C. and the mixture was heated and stirred for 3 hours to react all the unreacted monomers. The disappearance of the monomer was confirmed by ¹ H-NMR.
The obtained reaction solution was heated to 70 ° C., 82.9 g of a 50 mass% KOH aqueous solution was added, and then 833 g of pure water was added and stirred to obtain a 20 mass% solution of Dispersant P-1. The structural component of the obtained polymer was confirmed by ¹ H-NMR. Moreover, the weight average molecular weight (Mw) was calculated | required by GPC.

Example 1 Preparation of Aqueous Pigment Dispersion Using a Fricht planetary ball mill model P-7 (manufactured by Fritsch), a pigment dispersion was prepared as follows.
In a 45 ml container made of zirconia, 2.25 g of CB (carbon black) pigment powder (CB FW172 made by Orion), 5.06 g of the dispersant P-1 obtained in Synthesis Example 1, 1 N aqueous potassium hydroxide solution 2 .82 g, dipropylene glycol (DPG) 1.2 g, and ultrapure water 3.67 g were added. Furthermore, 40 g of 0.1 mmφ zirconia beads (TORERAM beads made by TORAY) were added and lightly mixed with a spatula.

  A 45 ml container made of zirconia was placed in a ball mill and dispersed at a rotation speed of 300 rpm for 5 hours. After the completion of dispersion, the beads were removed by filtration with a filter cloth to obtain an aqueous pigment dispersion having a pigment concentration of 15% by mass.

[Synthesis Example 2] Synthesis of Dispersants P-2 to P-6 and Comparative Dispersants C-1 to C-6 In Synthetic Example 1, the types and ratios of the monomers used were changed as shown in Table 1 below. Except for this, dispersants P-2 to P-6 and comparative dispersants C-1 to C-6 were obtained in the same manner as in Synthesis Example 1.

[Example 2] Preparation of aqueous pigment dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that the dispersant P-2 was used instead of the dispersant P-1. An aqueous pigment dispersion was obtained.

Example 3 Preparation of Aqueous Pigment Dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that Dispersant P-3 was used instead of Dispersant P-1. An aqueous pigment dispersion was obtained.

Example 4 Preparation of Aqueous Pigment Dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that Dispersant P-4 was used instead of Dispersant P-1. An aqueous pigment dispersion was obtained.

[Example 5] Preparation of aqueous pigment dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that the dispersant P-5 was used instead of the dispersant P-1. An aqueous pigment dispersion was obtained.

[Example 6] Preparation of aqueous pigment dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that the dispersant P-6 was used instead of the dispersant P-1. An aqueous pigment dispersion was obtained.

[Example 7] Preparation of aqueous pigment dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that the dispersant P-7 was used instead of the dispersant P-1. An aqueous pigment dispersion was obtained.

[Example 8] Preparation of aqueous pigment dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that the dispersant P-8 was used instead of the dispersant P-1. An aqueous pigment dispersion was obtained.

[Comparative Example 1] Preparation of aqueous pigment dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that Dispersant C-1 was used instead of Dispersant P-1. An aqueous pigment dispersion was obtained.

Comparative Example 2 Preparation of Aqueous Pigment Dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that Dispersant C-2 was used instead of Dispersant P-1. An aqueous pigment dispersion was obtained.

Comparative Example 3 Preparation of Aqueous Pigment Dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that Dispersant C-3 was used instead of Dispersant P-1. An aqueous pigment dispersion was obtained.

Comparative Example 4 Preparation of Aqueous Pigment Dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that Dispersant C-4 was used instead of Dispersant P-1. An aqueous pigment dispersion was obtained.

Comparative Example 5 Preparation of Aqueous Pigment Dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that Dispersant C-5 was used instead of Dispersant P-1. An aqueous pigment dispersion was obtained.

[Comparative Example 6] Preparation of aqueous pigment dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that Dispersant C-6 was used instead of Dispersant P-1. An aqueous pigment dispersion was obtained.

[Comparative Example 7] Preparation of aqueous pigment dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that Dispersant C-7 was used instead of Dispersant P-1. An aqueous pigment dispersion was obtained.

[Comparative Example 8] Preparation of aqueous pigment dispersion In Example 1, the pigment concentration was 15% by mass in the same manner as in Example 1 except that Dispersant C-8 was used instead of Dispersant P-1. An aqueous pigment dispersion was obtained.

[Test Example 1] Evaluation of dispersibility-1 (measurement of particle size)
Pigment particles in each aqueous pigment dispersion obtained in Examples 1 to 6 and Comparative Examples 1 to 6 by a dynamic light scattering method using Nanotrac particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.) The volume average particle size of was measured.
Measurement conditions: A sample diluted by adding 10 ml of water to 10 μl of an aqueous pigment dispersion was measured at 25 ° C.
The obtained results were evaluated according to the following evaluation criteria.
-Evaluation criteria-
A: Volume average particle diameter is 80 nm or more and less than 120 nm B: Volume average particle diameter is 120 nm or more and less than 140 nm C: Volume average particle diameter is 140 nm or more and less than 170 nm D: Volume average particle diameter is 170 nm or more

[Test Example 2] Evaluation of dispersibility-2 (measurement of viscosity)
The viscosity of each pigment dispersion obtained in Examples 1 to 6 and Comparative Examples 1 to 6 was measured at 25 ° C. using a TV-22 viscometer (manufactured by Toki Sangyo Co., Ltd.). The obtained results were evaluated according to the following evaluation criteria.
-Evaluation criteria-
A: The viscosity is 10 mPa · s or more and less than 30 mPa · s B: The viscosity is 30 mPa · s or more and less than 50 mPa · s C: The viscosity is 50 mPa · s or more and less than 80 mPa · s D: The viscosity is 80 mPa · s or more

[Test Example 3] Evaluation of dispersion stability (stability over time)
The obtained pigment dispersion was packed in a sample bottle, sealed, and allowed to stand at 60 ° C. for 24 hours. Then, the aggregation and thickening of the pigment dispersion were evaluated using changes in volume average particle diameter and viscosity as indexes.

(Change in volume average particle diameter) = (Average particle diameter after standing at 60 ° C. for 24 hours) − (Average particle diameter before heat treatment)
-Evaluation criteria-
A: Volume average particle size change is less than 50 nm B: Volume average particle size change is from 50 nm to less than 70 nm C: Volume average particle size change is from 70 nm to less than 100 nm D: Volume average particle size change is from 100 nm to 100 nm

(Change in viscosity) = (viscosity after standing for 24 hours at 60 ° C)-(viscosity before heat treatment)
-Evaluation criteria-
A: Viscosity change is less than 50 mPa · s B: Viscosity change is 50 mPa · s or more and less than 70 mPa · s C: Viscosity change is 70 mPa · s or more and less than 100 mPa · s D: Viscosity change is 100 mPa · s or more

  The results are shown in Table 2 below.

The aqueous pigment dispersion of Comparative Example 1 is an example in which the dispersant does not contain a structural unit having a long-chain alkyl group represented by the general formula (II). In this case, the dispersion stability was inferior.
The aqueous pigment dispersion of Comparative Example 2 is an example in which the dispersant does not include a structural unit having a benzene ring represented by the general formula (I). In this case, the dispersibility was inferior.
The aqueous pigment dispersion of Comparative Example 3 is an example in which the dispersant does not include a structural unit having a long-chain alkyl group represented by the general formula (II) but has a structural unit having a short-chain alkyl group. . Also in this case, the dispersion stability was inferior.
In the aqueous pigment dispersion of Comparative Example 4, the content of the structural unit having a benzene ring represented by the general formula (I) in the dispersant is less than that defined in the present invention, and conversely, the general formula (II) This is an example in which the content of the structural unit having a long-chain alkyl group represented by is more than that defined in the present invention. In this case, both the dispersibility and the dispersion stability were inferior.
In the aqueous pigment dispersion of Comparative Example 5, the content of the structural unit having a benzene ring represented by the general formula (I) in the dispersant is larger than that defined in the present invention, and conversely, the general formula (II) This is an example in which the content of the structural unit having a long-chain alkyl group represented by is less than that defined in the present invention. In this case as well, both the dispersibility and the dispersion stability were inferior.
The aqueous pigment dispersion of Comparative Example 6 is an example in which the dispersant contains a structural unit derived from styrene instead of the structural unit having a benzene ring represented by the general formula (I). Again, both dispersibility and dispersion stability were poor.

  On the other hand, the aqueous pigment dispersions of Examples 1 to 6 had both small pigment particle size and dispersion viscosity, excellent dispersibility, and excellent dispersion stability. From this result, it is understood that an aqueous pigment dispersion in which a high concentration of pigment is stably dispersed can be obtained by using the dispersant defined in the present invention.

[Examples 9 to 11] Preparation of aqueous pigment dispersion TRY13 (PY74), TRM11 (PR122) and TRB2 (PB15: 3) manufactured by Dainichi Seika Co., Ltd. were used as pigments, and these pigments, dispersants, DPG, 1N hydroxylation An aqueous pigment dispersion of each color of yellow (Y), magenta (M) and cyan (C) was obtained in the same manner as in Example 1 except that the potassium solution and ultrapure water were mixed in the amounts shown in Table 3 below. It was.

  For each of the aqueous pigment dispersions obtained in Examples 9 to 11, the volume average particle diameter, viscosity, change in volume average particle diameter, and change in viscosity of the pigment were evaluated in the same manner as in Test Examples 1 to 3 above. The results are shown in Table 4 below.

  As shown in Table 4, it was found that the aqueous pigment dispersion of the present invention exhibits excellent dispersibility and dispersion stability regardless of the type of pigment.

[Example 12] Preparation of water-based ink composition With respect to 136 parts by mass of the aqueous pigment dispersion obtained in Example 1, 1.4 parts by mass of Denacol EX-321 (crosslinking agent manufactured by Nagase ChemteX Corporation) And 15.4 parts by weight of an aqueous boric acid solution (4% by weight boric acid aqueous solution), reacted at 70 ° C. for 6 hours, cooled to 25 ° C., and an aqueous pigment dispersion in which the dispersant formed a crosslinked structure (Hereinafter referred to as “crosslinked dispersion”).
The obtained cross-linked dispersion was limited by adding ion-exchanged water using a stirring ultra holder (manufactured by ADVANTEC) and an ultrafiltration filter (fractionated molecular weight 50,000, Q0500076E ultra filter, manufactured by ADVANTEC). External filtration was performed to purify the dispersion so that the concentration of dipropylene glycol in the dispersion was 0.1% by mass or less. Then, it concentrated until the pigment density | concentration became 15 mass%, and obtained the aqueous black pigment dispersion K-1.

<Preparation of Black Ink KI-1>
After mixing the raw materials with the following composition, the resulting mixture was filtered through ADVANTEC glass filter (GS-25), then filtered through a Millipore filter (PVDF membrane, pore size 5 μm), and aqueous black ink KI- 1 was produced.

(Composition of black ink KI-1)
-Aqueous black pigment dispersion K-1 16.5 parts by mass-Glycerol 7 parts by mass-Diethylene glycol 9 parts by mass-Propylene glycol 9 parts by mass-Triethanolamine 1 part by mass-Olphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) , Surfactant) 1 part by mass / ion exchange water The remaining amount of 100 parts by mass as a whole

[Example 13] Preparation of aqueous ink composition In preparation of the aqueous black pigment dispersion K-1 of Example 12, the aqueous pigment dispersion obtained in Example 1 was used as the aqueous pigment dispersion obtained in Example 2. An aqueous black pigment dispersion K-2 was obtained in the same manner as in the preparation of the aqueous black pigment dispersion K-1 of Example 12, except that it was replaced with.
The aqueous black ink KI-1 of Example 12 except that the aqueous black pigment dispersion K-2 was used in place of the aqueous black pigment dispersion K-1 in the preparation of the aqueous black ink KI-1 of Example 12. A water-based black ink KI-2 was obtained in the same manner as in the preparation.

[Example 14] Preparation of aqueous ink composition In preparation of the aqueous black pigment dispersion K-1 of Example 12, the aqueous pigment dispersion obtained in Example 3 was used as the aqueous pigment dispersion obtained in Example 3. An aqueous black pigment dispersion K-3 was obtained in the same manner as in the preparation of the aqueous black pigment dispersion K-1 of Example 12, except that it was replaced with
The aqueous black ink KI-1 of Example 12 except that the aqueous black pigment dispersion K-3 was used in place of the aqueous black pigment dispersion K-1 in the preparation of the aqueous black ink KI-1 of Example 12. A water-based black ink KI-3 was obtained in the same manner as in the preparation of 1.

[Example 15] Preparation of ink composition In preparation of the aqueous black pigment dispersion K-1 of Example 12, the aqueous pigment dispersion obtained in Example 1 was changed to the aqueous pigment dispersion obtained in Example 4. Except having replaced, it carried out similarly to preparation of the aqueous black pigment dispersion K-1 of Example 12, and obtained the aqueous black pigment dispersion K-4.
The aqueous black ink KI-1 of Example 12 except that the aqueous black pigment dispersion K-4 was used in place of the aqueous black pigment dispersion K-1 in the preparation of the aqueous black ink KI-1 of Example 12. A water-based black ink KI-4 was obtained in the same manner as in the preparation of 1.

[Example 16] Preparation of ink composition In preparation of the aqueous black pigment dispersion K-1 of Example 12, the aqueous pigment dispersion obtained in Example 1 was changed to the aqueous pigment dispersion obtained in Example 5. Except having replaced, it carried out similarly to preparation of the aqueous black pigment dispersion K-1 of Example 12, and obtained the aqueous black pigment dispersion K-5.
The aqueous black ink KI-1 of Example 12 except that the aqueous black pigment dispersion K-5 was used in place of the aqueous black pigment dispersion K-1 in the preparation of the aqueous black ink KI-1 of Example 12. A water-based black ink KI-5 was obtained in the same manner as in the preparation of 1.

[Example 17] Preparation of ink composition In preparation of the aqueous black pigment dispersion K-1 of Example 12, the aqueous pigment dispersion obtained in Example 1 was changed to the aqueous pigment dispersion obtained in Example 6. Except having replaced, it carried out similarly to preparation of the black pigment dispersion K-1 of Example 12, and obtained the aqueous black pigment dispersion K-6.
The aqueous black ink KI-1 of Example 12 except that the aqueous black pigment dispersion K-6 was used in place of the aqueous black pigment dispersion K-1 in the preparation of the aqueous black ink KI-1 of Example 12. A water-based black ink KI-6 was obtained in the same manner as in the preparation of 1.

[Example 18] Preparation of ink composition In preparation of the aqueous black pigment dispersion K-1 of Example 12, the aqueous pigment dispersion obtained in Example 1 was changed to the aqueous pigment dispersion obtained in Example 7. Except having replaced, it carried out similarly to preparation of the black pigment dispersion K-1 of Example 12, and obtained the aqueous black pigment dispersion K-7.
The aqueous black ink KI-1 of Example 12 except that the aqueous black pigment dispersion K-7 was used in place of the aqueous black pigment dispersion K-1 in the preparation of the aqueous black ink KI-1 of Example 12. A water-based black ink KI-7 was obtained in the same manner as in the preparation of 1.

Example 19 Preparation of Ink Composition In the preparation of the aqueous black pigment dispersion K-1 of Example 12, the aqueous pigment dispersion obtained in Example 1 was changed to the aqueous pigment dispersion obtained in Example 8. Except having replaced, it carried out similarly to preparation of the black pigment dispersion K-1 of Example 12, and obtained the aqueous black pigment dispersion K-8.
The aqueous black ink KI-1 of Example 12 except that the aqueous black pigment dispersion K-8 was used in place of the aqueous black pigment dispersion K-1 in the preparation of the aqueous black ink KI-1 of Example 12. A water-based black ink KI-8 was obtained in the same manner as in the preparation of 1.

[Comparative Example 9] Preparation of Ink Composition In the preparation of the aqueous black pigment dispersion K-1 of Example 12, the aqueous pigment dispersion obtained in Example 1 was changed to the aqueous pigment dispersion obtained in Comparative Example 1. An aqueous black pigment dispersion KC-1 was obtained in the same manner as in the preparation of the aqueous black pigment dispersion K-1 of Example 12, except that the replacement was performed.
The aqueous black ink KI-1 of Example 12 except that the aqueous black pigment dispersion KC-1 was used in place of the aqueous black pigment dispersion K-1 in the preparation of the aqueous black ink KI-1 of Example 12. A water-based black ink KCI-1 was obtained in the same manner as in the preparation.

Comparative Example 10 Preparation of Ink Composition In the preparation of the aqueous black pigment dispersion K-1 of Example 12, the aqueous pigment dispersion obtained in Example 1 was changed to the aqueous pigment dispersion obtained in Comparative Example 2. An aqueous black pigment dispersion KC-2 was obtained in the same manner as in the preparation of the aqueous black pigment dispersion K-1 of Example 12, except that the replacement was performed.
The aqueous black ink KI-1 of Example 12 except that the aqueous black pigment dispersion KC-2 was used in place of the aqueous black pigment dispersion K-1 in the preparation of the aqueous black ink KI-1 of Example 12. A water-based black ink KCI-2 was obtained in the same manner as in the preparation of 1.

[Comparative Example 11] Preparation of Ink Composition In preparation of the aqueous black pigment dispersion K-1 of Example 12, the aqueous pigment dispersion obtained in Example 1 was changed to the aqueous pigment dispersion obtained in Comparative Example 2. Except having replaced, it carried out similarly to preparation of the aqueous black pigment dispersion K-1 of Example 12, and obtained the aqueous black pigment dispersion KC-3.
The aqueous black ink KI-1 of Example 12 except that the aqueous black pigment dispersion KC-3 was used in place of the aqueous black pigment dispersion K-1 in the preparation of the aqueous black ink KI-1 of Example 12. A water-based black ink KCI-3 was obtained in the same manner as in the preparation.

[Test Example 1] Evaluation of dispersibility-1 (measurement of particle size)
Using a nanotrack particle size distribution measuring apparatus UPA-EX150 (manufactured by Nikkiso Co., Ltd.), the pigment particles in each of the aqueous black inks obtained in Examples 12 to 19 and Comparative Examples 9 to 11 were obtained by a dynamic light scattering method. The volume average particle size was measured.

Measurement conditions: A sample diluted with 10 mL of water-based ink composition by adding 10 mL of water was measured at 25 ° C.

The obtained results were evaluated according to the following evaluation criteria.
-Evaluation criteria-
A: Volume average particle diameter is 80 nm or more and less than 110 nm B: Volume average particle diameter is 110 nm or more and less than 130 nm C: Volume average particle diameter is 130 nm or more and less than 150 nm D: Volume average particle diameter is 150 nm or more

[Test Example 2] Evaluation of dispersibility-2 (measurement of viscosity)
The viscosity of each aqueous black ink obtained in Examples 10 to 15 and Comparative Examples 7 to 9 was measured at 25 ° C. using a TV-22 viscometer (manufactured by Toki Sangyo Co., Ltd.). The obtained results were evaluated according to the following evaluation criteria.
-Evaluation criteria-
A: The viscosity is 4 mPa · s or more and less than 6 mPa · s B: The viscosity is 6 mPa · s or more and less than 8 mPa · s C: The viscosity is 8 mPa · s or more and less than 10 mPa · s D: The viscosity is 10 mPa · s or more

[Test Example 3] Evaluation of dispersion stability (stability over time)
Each aqueous black ink obtained in Examples 10 to 15 and Comparative Examples 7 to 9 was packed in a sample bottle, sealed, and allowed to stand at 60 ° C. for 24 hours, and then the volume average particle size was determined for aggregation and thickening of the pigment dispersion. Evaluation was made using changes in diameter and viscosity as indices.

(Change in volume average particle diameter) = (Average particle diameter after standing at 60 ° C. for 24 hours) − (Average particle diameter before heat treatment)
-Evaluation criteria-
A: Volume particle size change is less than 15 nm B: Volume particle size change is 15 nm or more and less than 30 nm C: Volume particle size change is 30 nm or more and less than 50 nm D: Volume particle size change is 50 nm or more

(Change in viscosity) = (viscosity after standing for 24 hours at 60 ° C)-(viscosity before heat treatment)
-Evaluation criteria-
A: Viscosity change is less than 0.3 mPa · s B: Viscosity change is 0.3 mPa · s or more and less than 1.5 mPa · s C: Viscosity change is 1.5 mPa · s or more and less than 3.0 mPa · s D: Viscosity change 3.0 mPa · s or more

  The results are shown in Table 5 below.

  From the results of Table 5, it was found that the aqueous ink prepared using the aqueous pigment dispersion of the present invention was excellent in both dispersibility and dispersion stability. That is, it was shown that the aqueous pigment dispersion of the present invention is suitable as a raw material for aqueous ink.

Claims (11)

An aqueous pigment dispersion containing an aqueous medium, a pigment, and a polymer dispersant,
The polymer dispersant has at least a structural unit represented by the following general formula (I), a structural unit represented by the following general formula (II), and a structural unit having an ionic group,
In the polymer dispersant, the content of the structural unit represented by the following general formula (I) is 20 to 60% by mass, and the content of the structural unit represented by the following general formula (II) is 10 to 40%. An aqueous pigment dispersion which is% by weight.

In the formula, R ¹ represents a hydrogen atom or methyl.
L ¹ represents —C (═O) O—, —OC (═O) —, or —C (═O) NR ⁴ —. R ⁴ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.
L ² is a single bond or a divalent group selected from an alkylene group having 1 to 12 carbon atoms, an alkenylene group having 2 to 12 carbon atoms, —C (═O) —, —O— and —S—. Divalent formed by combining two or more groups selected from a linking group or an alkylene group having 1 to 12 carbon atoms, an alkenylene group having 2 to 12 carbon atoms, -C (= O)-, -O- and -S-. Represents a linking group.
R ² represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms.
R ³ represents an alkyl group having 12 or more carbon atoms.   The aqueous pigment dispersion according to claim 1, wherein the polymer dispersant has an acid value of 1.5 to 4.0 mmol / g.   The aqueous pigment dispersion according to claim 1 or 2, wherein the polymer dispersant has a weight average molecular weight of 5,000 to 30,000.   The aqueous pigment dispersion according to claim 3, wherein the polymer dispersant has a weight average molecular weight of 7,000 to 15,000.   In the polymer dispersant, the content of the structural unit represented by the general formula (I) is 30 to 60% by mass, and the content of the structural unit represented by the general formula (II) is 10 to 30%. The aqueous pigment dispersion according to any one of claims 1 to 4, wherein the aqueous pigment dispersion is mass%.   The aqueous pigment dispersion according to any one of claims 1 to 5, wherein the structural unit represented by the general formula (I) is derived from benzyl (meth) acrylate or phenoxyethyl (meth) acrylate.   The aqueous pigment dispersion according to any one of claims 1 to 6, wherein the polymer dispersant forms a crosslinked structure in the aqueous pigment dispersion.   The aqueous pigment dispersion according to any one of claims 1 to 7, wherein the pigment is carbon black.   The aqueous pigment dispersion according to any one of claims 1 to 8, comprising at least one water-soluble organic solvent.   A water-based ink composition using the water-based pigment dispersion according to any one of claims 1 to 9.   The aqueous ink composition according to claim 10, wherein the aqueous ink composition is for inkjet recording.