JP2013124356A - Process for producing aqueous pigment dispersion for inkjet recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for efficiently producing a dispersion for inkjet recording, wherein finely grained pigment is stably dispersed.SOLUTION: [1] The process includes: a step (A) for producing an aqueous pigment dispersion containing a treated pigment by the reaction of the pigment with a treating agent that can introduce a hydrophilic group into the pigment, while a mixture that contains the pigment and an aqueous medium is ground by means of a media mill, and a step (B) for adding a polymer having an acid value of 150 to 250 mg-KOH/g to an aqueous pigment dispersion that contains the treated pigment and dispersing the resulting material by using a high pressure homogenizer. [2] An aqueous ink for inkjet recording contains the aqueous pigment dispersion produced by the process described in [1].

Description

  The present invention relates to a method for producing a water-based pigment dispersion for ink-jet recording, and a water-based ink for ink-jet recording containing a water-based pigment dispersion obtained by the method.

The ink jet recording method is easy to be full-colored and inexpensive, and has many advantages that plain paper can be used as a recording member. Among them, from the viewpoint of weather resistance and water resistance of printed materials, those using pigments as colorants are mainly used.
In addition, there is a trend toward finer pigments as the inkjet recording heads become higher in definition, and various methods are being studied to stably disperse the finer pigments.

As a method for stably dispersing the pigment, there is a method in which a functional group having a dispersing function is directly bonded to the pigment. For example, Patent Document 1 discloses an ink composition containing an organic pigment to which at least one hydrophilic organic group is bonded.
On the other hand, there is a method in which a pigment is stably dispersed by adsorbing a water-insoluble polymer to the pigment. For example, Patent Document 2 discloses an aqueous pigment dispersion for ink-jet recording having a weight molecular weight in the range of 90000-400000 and containing a water-insoluble polymer having a structural unit derived from an anionic monomer.

  Moreover, the outstanding glossiness can be expressed by atomizing a pigment more. As a means for atomizing the pigment, Patent Document 2 discloses a method including a step of further performing a dispersion treatment with a homogenizer after pulverization using a media-type disperser. Patent Document 3 discloses a method for producing a surface-modified colored pigment including a step of introducing a hydrophilic organic group into a pigment while applying high shear, and Patent Document 4 uses 0.5 mm zirconia beads. An inkjet recording ink containing a self-dispersing pigment obtained by a method of oxidizing the pigment surface with a bead mill is disclosed.

JP 2000-513396 JP 2007-092059 A JP-T-2003-513137 JP 2010-188721 A

As described above, an aqueous pigment dispersion in which a more finely divided pigment is stably dispersed is desired, but the methods of Patent Documents 1 to 4 are not satisfactory in the atomization of the pigment.
An object of the present invention is to provide a method for efficiently producing an aqueous pigment dispersion for inkjet recording in which finely divided pigments are stably dispersed.

In response to the above problems, the present inventors have focused on the fact that a pigment having a small particle diameter can be obtained by reacting a treatment agent capable of introducing a hydrophilic group with a pigment while treating the pigment with a media mill. did. This is considered to be due to the high pulverization force by the media particles and the suppression of re-aggregation of the pigment by introducing a hydrophilic group into the pigment.
However, even when the pigment is further pulverized by the media mill, the surface area and surface energy of the pigment increase with the atomization of the pigment, and the pigment starts to reaggregate in an attempt to reduce the surface energy. Therefore, it is difficult to obtain further fine pigment.

  Therefore, the inventors of the present invention, after pulverizing the pigment with a media mill, reacting the treatment agent capable of introducing a hydrophilic group with the pigment, and then dispersing it in an apparatus capable of imparting high shear using a polymer having a high acid value. By doing so, it has been found that a pigment having a finer particle diameter can be obtained and the above-mentioned problems can be solved. This is because the pigment itself has high dispersibility due to the hydrophilic group imparted, and a polymer with a relatively high acid value is used as a dispersant, making it easy to adsorb on the pigment surface and dispersibility. This is thought to be because the reaggregation of the pigment can be suppressed. Further, since the pigment is pulverized in advance by the media mill, it is considered that the pigment is easily pulverized by the shearing force of the high-pressure homogenizer.

That is, the present invention provides the following [1] to [2].
[1] A method for producing an aqueous pigment dispersion for inkjet recording, comprising the following steps (A) and (B).
Step (A): A mixture containing at least a pigment and an aqueous medium is treated with a media mill, and a treatment agent capable of introducing a hydrophilic group into the pigment is reacted with the pigment while the pigment is pulverized to contain the treated pigment. Step of obtaining an aqueous pigment dispersion Step (B): A polymer having an acid value of 150 to 250 mg-KOH / g is added to the aqueous pigment dispersion containing the treated pigment obtained in Step (A), and a high-pressure homogenizer is used. Step [2] for carrying out dispersion treatment A water-based ink for ink-jet recording containing the water-based pigment dispersion obtained by the production method of [1].

  ADVANTAGE OF THE INVENTION According to this invention, the aqueous pigment dispersion for inkjet recording in which the atomized pigment was disperse | distributed stably can be manufactured efficiently.

[Method for producing water-based pigment dispersion for inkjet recording]
The method for producing an aqueous pigment dispersion for ink-jet recording of the present invention comprises the following steps (A) to (B).
Step (A): A mixture containing at least a pigment and an aqueous medium is treated with a media mill, and a treatment agent capable of introducing a hydrophilic group into the pigment is reacted with the pigment while the pigment is pulverized to contain the treated pigment. Step of obtaining an aqueous pigment dispersion Step (B): A polymer having an acid value of 150 to 250 mg-KOH / g is added to the aqueous pigment dispersion containing the treated pigment obtained in Step (A), and a high-pressure homogenizer is used. Step of dispersing treatment In step (A), the primary surface of the pigment is pulverized by a media mill, and at the same time, the surface of the pigment is hydrophilized using a treatment agent capable of introducing a hydrophilic group into the pigment, and then in step (B) By carrying out the dispersion treatment using a polymer having a high acid value with a high-pressure homogenizer, the pigment atomized by the fine particle treatment in the step (A) can be dispersed without reaggregation.

[Process (A)]
The step (A) is a step aimed at hydrophilizing the pigment particle surface while pulverizing the pigment, and the mixture containing at least the pigment and the aqueous medium is treated with a media mill and the pigment is pulverized. In this step, a treatment agent capable of introducing a hydrophilic group into the pigment is reacted with the pigment to obtain a water-based pigment dispersion containing the treated pigment having a hydrophilic surface.
In the step (A), a pigment having a small particle diameter can be obtained by reacting a treatment agent capable of introducing a hydrophilic group into the pigment while treating the pigment with a media mill. This is considered to be due to the high pulverization force by the media particles and the suppression of re-aggregation of the pigment by introducing a hydrophilic group into the pigment.

[Pigment]
In the present invention, the primary particle diameter of the pigment is not limited, but is preferably 10 to 200 nm, more preferably 20 to 150 nm, from the viewpoint of pulverization / dispersion load accompanying the atomization of the pigment. In addition, the primary particle diameter of a pigment can be calculated | required by the method as described in an Example.
The pigment may be either an organic pigment or an inorganic pigment. If necessary, extender pigments can be used in combination.

  Examples of the organic pigment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. Specific examples of preferred organic pigments include C.I. I. Pigment yellow, C.I. I. Pigment Red, C.I. I. Pigment violet, C.I. I. Pigment blue, and C.I. I. One or more types of products selected from the group consisting of pigment green are listed. Moreover, solid solution pigments, such as a quinacridone solid solution pigment, can also be used.

Examples of the inorganic pigment include carbon black, metal oxide, metal sulfide, and metal chloride. Of these, carbon black is preferred particularly for black aqueous inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
Examples of extender pigments include silica, calcium carbonate, and talc.
The above pigments can be used alone or in admixture of two or more at any ratio.
The color of the pigment used in the present invention is not limited, but from the viewpoint of the primary particle size of the pigment, C.I. I. Pigment Red and C.I. I. It is a red pigment typified by Pigment Violet.

[Aqueous medium]
The aqueous medium contains water as an essential component, but the content of water is preferably 30 to 95% by weight, more preferably 60 to 90% by weight, from the viewpoint of pigment dispersion stability. The aqueous medium may contain an organic solvent and a neutralizing agent from the viewpoint of pigment dispersion stability.
Examples of the organic solvent include alcohol solvents, ketone solvents, ether solvents, aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, halogenated aliphatic hydrocarbon solvents, and the like. For example, ethanol etc. are mentioned as an alcohol solvent. Examples of the ketone solvent include methyl ethyl ketone. Among these organic solvents, ethanol and methyl ethyl ketone are preferable from the viewpoint of safety and operability of solvent removal in post-treatment. Moreover, it can use individually or in mixture of 2 or more types.
Examples of the neutralizing agent for neutralizing the polymer having an acid value include bases such as sodium hydroxide, potassium hydroxide and various amines. The neutralizing agent may be used alone or a plurality of neutralizing agents may be used.

[Hydrophilic group]
As for the hydrophilic group introduced into the pigment, one or more of an anionic hydrophilic group or a cationic hydrophilic group can be bonded to the surface of the pigment directly or through another atomic group.
Examples of the anionic hydrophilic group include a carboxyl group (—COOM), a sulfonic acid group (—SO ₃ M), a phosphonic acid group (—PO ₃ M ₂ ), and the like. M in the formula represents a hydrogen atom, an alkali metal, ammonium or organic ammonium. Examples of the alkali metal include lithium, sodium, potassium, rubidium and cesium. Examples of organic ammonium include methylammonium, dimethylammonium, trimethylammonium, ethylammonium, diethylammonium, triethylammonium, ethylammonium, diethylammonium, triethylammonium, monohydroxymethyl (ethyl) ammonium, dihydroxymethyl (ethyl) ammonium , Trihydroxymethyl (ethyl) ammonium, and triethanolammonium.
Examples of the cationic hydrophilic group include a quaternary ammonium group.
Examples of other intervening atomic groups include a linear or branched alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. As a substituent of a phenylene group and a naphthylene group, a C1-C6 linear or branched alkyl group is mentioned.

[Treatment agent capable of introducing hydrophilic group into pigment]
As a method for introducing a hydrophilic group onto the surface of the pigment, a treatment agent capable of introducing a hydrophilic group into the pigment is reacted with the pigment by a known method to form an anionic hydrophilic group or a cationic hydrophilic group on the pigment surface. It may be chemically bonded.
The treatment agent capable of introducing a hydrophilic group can be appropriately selected depending on the method for introducing a hydrophilic group. Specific treatment agents capable of introducing a hydrophilic group include the following (i) to (iii).
(I) In the case where an anionic hydrophilic group is introduced by oxidation treatment, an acid having an oxidizing property such as nitric acid, hypochlorous acid, or chromic acid is used.
(Ii) In the case of introducing a sulfonic acid group by thermal decomposition of a persulfate compound, examples thereof include sodium persulfate, potassium persulfate, and ammonium persulfate.
(Iii) When the anionic hydrophilic group or cationic hydrophilic group is introduced by a diazonium salt compound, the diazonium salt compound has an anionic hydrophilic group or a cationic hydrophilic group.
As the treating agent capable of introducing the hydrophilic water group to the surface of the pigment, the agent described in the above (iii) is preferable from the viewpoint of treatment efficiency, reactivity and the like.

In the above (iii), the diazonium salt compound has a diazotizable amino group (primary amino group) and an anionic group or a cationic group, and an optionally substituted aromatic group, etc. Is obtained by diazotization. The amino group can be diazotized with an acid such as sodium nitrite and hydrochloric acid.
As the anionic hydrophilic group, a carboxyl group and a sulfonic acid group are preferable.
Specifically, by using an optionally substituted aromatic group having a diazotizable amino group and an anionic hydrophilic group, -C ₆ H ₄ -COO ^- X can be used for the pigment. ^{_{+, -C 6 H 4 -SO 3}} - X +, -C 6 H 4 - (PO 3) 2- 2X +, -C 6 H 2 - (COO - X +) 3, -C 6 H 3 - ( COO ⁻ X ⁺ ) ₂ , —C ₆ H ₄ — (CH ₂ ) _z — (COO ⁻ X ⁺ ) (X ⁺ is an arbitrary cation, and z is an integer of 1 to 18). An anionic group can be introduced.
As the treatment agent capable of introducing a hydrophilic group, a diazonium salt compound obtained by diazotizing an amino group of a compound selected from the group consisting of sulfanilic acid, anthranilic acid, and p-aminobenzoic acid is preferable.

As the cationic hydrophilic group, an ammonium group, a phosphonium group, a sulfonium group, and a pyridinium group are preferable. The ammonium group also includes an amino group that can be produced by protonation.
Specifically, by using an aromatic group having a diazotizable amino group and a cationic hydrophilic group, which may have a substituent, -C ₆ H ₄ N (CH ₃ ) ₃ ⁺ Y ⁻ , —C ₆ H ₄ COCH ₂ N (CH ₃ ) ₃ ⁺ Y ⁻ , —C ₆ H ₄ (NC ₅ H ₅ ) ⁺ Y ⁻ , — (C ₅ H ₄ N) C ₂ H ₅ ⁺ Y ⁻ , —C ₆ H ₄ COCH ₂ (NC ₅ H ₅ ) ⁺ Y ⁻ , — (C ₅ H ₄ N) CH ₃ ⁺ Y ⁻ , and —C ₆ H ₄ CH ₂ N (CH ₃ ) ₃ ⁺ A cationic group such as Y ⁻ (Y ⁻ is an arbitrary halogen ion or anion) can be introduced.
As the treating agent capable of introducing a hydrophilic group, a diazonium salt compound obtained by diazotizing an amino group such as (4-aminophenyl) pyridinium chloride is preferable. For these reactions, reference can be made to Patent Document 1 and JP-T-2002-538260.

In the step (A), by adding a treatment agent capable of introducing a hydrophilic group to the media mill, the treatment agent capable of introducing a hydrophilic group is reacted with the pigment.
As a method of adding a treatment agent capable of introducing a hydrophilic group to a media mill, (I) a method of adding a mixture containing a pigment, a treatment agent capable of introducing a hydrophilic group and an aqueous medium, and (II) in the middle of pigment grinding treatment And the like. As the addition method, the method (II) is preferable from the viewpoints of processing efficiency, reactivity, dispersion stability and the like.
Moreover, in order to suppress the viscosity increase of the dispersion during the dispersion treatment, a treatment agent capable of introducing a hydrophilic group may be additionally added during the treatment.

From the viewpoint of hydrophilizing the pigment surface, the application amount of the treatment agent capable of introducing a hydrophilic group added in the step (A) is preferably 0.01 mol / kg or more, more preferably 0.05 mol / kg or more, and 1 mol / kg or more is more preferable. Further, from the viewpoint of reducing the washing load in the subsequent process, it is preferably 5 mol / kg or less, more preferably 3 mol / kg or less, and even more preferably 2 mol / kg or less. The amount to be given is defined by the following formula.
Application amount (mol / kg) = number of moles of hydrophilic group added / weight of pigment Further, the aqueous pigment dispersion obtained by the step (A) contains an organic solvent, a neutralizing agent, a surfactant and the like. Also good.

[Media mill processing]
The media mill used in the step (A) uses media particles (preferably fine beads), and can impart shearing force, collision force, and grinding force that can disperse and atomize the pigment to primary particles or less. Is preferred.
A media mill retains media particles in a dispersion chamber (mill), and disperses the pre-dispersion flowing through the media while applying dispersion energy such as grinding, shearing, and collision with the media particles. Can be separated by centrifugation or the like, and only the dispersion-treated product can flow out of the dispersion chamber.
Examples of such commercially available media mills include, for example, Star Mill (Ashizawa Finetech Co., Ltd., trade name), Ultra Apex Mill (Kotobuki Industries Co., Ltd., trade name), Pico Mill (Asada Tekko Co., Ltd., Commodity) Name), DCP Super Flow, Cosmo (Nippon Eirich Co., Ltd., trade name), MSC Mill (Nippon Coke Industrial Co., Ltd., trade name) and the like.

Examples of media particles used in the media mill include high-hardness metals such as steel and chrome alloys, high-hardness ceramics such as alumina, zirconia, zircon, and titania, and high-molecular materials such as glass, ultrahigh molecular weight polyethylene, and nylon. Is mentioned.
Since the magnitude of the shearing force, collision force, and pulverizing force for atomizing the pigment increases as the specific gravity of the media particles increases, among them, ceramic media particles having a relatively large specific gravity are preferable. From the viewpoint of wear resistance, zirconia, titania and the like are more preferable. Moreover, you may use the media particle manufactured by the high frequency induction thermal plasma method from a viewpoint of reducing the contamination generate | occur | produced from a media particle more.

As the particle size (diameter) of the media particles used in the media mill, a desired size can be used. However, the smaller the particle size of the media particles, the greater the number of contact between the media and the pigment, and the more efficient the pigment is. Since it can be atomized, the particle size of the media particles is preferably 0.5 mm or less, and more preferably 0.3 mm or less. Moreover, 0.01 mm or more is preferable from a viewpoint which isolate | separates a media particle and an aqueous pigment dispersion, and 0.03 mm or more is more preferable. From the above viewpoint, the particle size of the media particles is preferably 0.01 to 0.5 mm, more preferably 0.01 to 0.3 mm, and still more preferably 0.03 to 0.3 mm.
The peripheral speed of the tip of the agitator disk (rotor) of the media mill is not particularly limited, but is preferably 4 to 15 m / s, and more preferably 6 to 10 m / s. In the case of 4 m / s or more, the mixing and dispersing state in the dispersion chamber can be kept good, and the centrifugal force necessary to separate the media particles and the dispersion-treated product can be obtained.
The filling rate of the media particles in the dispersion chamber of the media mill is preferably in the range of 50 to 90% by volume based on the space in the dispersion chamber from the viewpoint of improving the pigment dispersion effect. The filling rate of the media particles is represented by the ratio of the apparent volume of the filled media particles to the volume of the internal space portion of the disperser vessel. The apparent volume of the media particles here is a value obtained by dividing the mass of the media particles filled in the dispersion chamber of the media mill by the bulk density. The bulk density can be obtained from a value obtained by dividing the mass of the media particles in which the media particles are closely packed in a cubic container (1L) by the volume of the cube.

In addition, it is necessary to pay attention to the manner in which the dispersion energy is applied. From the viewpoint of setting the treatment flow rate to an appropriate range and preventing changes in the particle size and viscosity of the aqueous pigment dispersion due to heat generation, the per-pass in the dispersion chamber. The average residence time is preferably in the range of 30 seconds to 10 minutes. The total average residence time obtained by multiplying the average residence time by the number of passes is preferably 3 to 100 minutes, more preferably 5 to 100 minutes, depending on the capacity and size of the disperser. The average residence time here means a value obtained by dividing the spatial volume [L] excluding the volume of media particles in the dispersion chamber by the processing flow rate [L / h].
Although the temperature at the time of a dispersion process is not specifically limited, 5-60 degreeC is preferable.

  The solid content concentration of the aqueous pigment dispersion containing the treated pigment obtained in the step (A) is preferably 3% by weight or more, more preferably 5% by weight or more, and further preferably 10% by weight or more in order to increase production efficiency. preferable. Further, from the viewpoint of facilitating uniform mixing by reducing the viscosity of the colored dispersion, it is preferably 40% by weight or less, more preferably 30% by weight or less, and even more preferably 25% by weight or less. In addition, solid content concentration can be calculated | required by the method as described in an Example.

  10-200 nm is preferable, as for the average particle diameter of the water-system pigment dispersion obtained after a process (A), 15-150 nm is more preferable, and 20-150 nm is still more preferable.

  Since the aqueous pigment dispersion containing the treated pigment obtained in the step (A) contains unreacted raw materials, by-product salts, and other reaction impurities, it is preferably purified by washing such as filtration. A well-known technique can be used for the cleaning method. For example, isolation by evaporation, dead-end filtration using a membrane or an ion exchange membrane, and a method of cross flow filtration can be mentioned. From the viewpoint of lowering productivity due to pigment clogging, membrane cleaning by crossflow filtration is preferred.

<Process (B)>
The step (B) is a step intended to further disperse and stabilize the pigment aggregate by using a polymer having a high acid value and further dispersing with a high-pressure homogenizer.
In the step (B), a pigment having a finer particle diameter can be obtained by dispersing the pigment to which a hydrophilic group has been added using a high-pressure homogenizer. This is because the hydrophilic group is imparted to the pigment and the high-pressure homogenizer is used to disperse the pigment because a polymer having a relatively high acid value (hereinafter also simply referred to as a polymer) is used as a dispersant. It is thought that it can atomize, suppressing aggregation.
Even if the pigment is further pulverized by the media mill without performing the step (B), the surface area and surface energy of the pigment increase as the pigment is atomized. However, since the pigment starts to reaggregate in order to reduce the surface energy, it is difficult to obtain a fine pigment obtained by the step (B).

The solid content concentration of the aqueous pigment dispersion obtained in the step (B) is preferably 5 to 40% by weight, more preferably 10 to 35% by weight, from the viewpoint of the dispersibility of the pigment and the stability of the dispersion. 30% by weight is more preferred. In addition, solid content concentration can be calculated | required by the method as described in an Example.
In the water-based pigment dispersion obtained in the step (B), the weight ratio of the pigment amount to the total amount of the polymer and the pigment [pigment / polymer] is 50/50 from the viewpoint of the polymer, the dispersibility of the pigment and the stability of the dispersion. 50-95 / 5 is preferable, 60 / 40-95 / 5 is more preferable, and 70 / 30-95 / 5 is still more preferable.
Moreover, the water-based pigment dispersion obtained by a process (B) may contain the organic solvent, the neutralizing agent, surfactant, etc. When an organic solvent is included, it is preferably removed from the viewpoint of pigment dispersion stability. In that case, it can be performed by a known method such as distillation under normal pressure or reduced pressure.

The high-pressure homogenizer used in the step (B) stabilizes pigment particles by pulverizing the pigment aggregate and suppressing re-aggregation by expressing a cavitation phenomenon with high impact force and instantaneous high pressure. .
Commercially available high-pressure homogenizers that can be used include high-pressure homogenizers (Izumi Food Machinery Co., Ltd., trade name), homovalve type high-pressure homogenizers represented by Minilab 8.3H (Rannie Co., trade name), and microfluidizer ( Microfluidics, trade name), Nanomizer (Yoshida Kikai Kogyo Co., Ltd., trade name), Starburst (Sugino Machine Co., trade name), Genus PY (Shiramizu Chemical Co., Ltd., trade name), DeBEE2000 (Nippon BB Corporation, Chamber type high-pressure homogenizer, etc.

The dispersion pressure during the dispersion treatment is preferably 20 MPa or more, more preferably 50 MPa or more, preferably 350 MPa or less, and more preferably 300 MPa or less, from the viewpoint of suppressing reaggregation of the pigment particles and achieving dispersion stabilization. From these viewpoints, 20 to 350 MPa is preferable, and 50 to 300 MPa is more preferable.
From the same viewpoint, the number of processing passes is at least 1 pass or more, preferably 3 passes or more, more preferably 5 passes or more, preferably 50 passes or less, more preferably 20 passes or less. From these viewpoints, 1 to 50 paths are preferable, 3 to 20 paths are more preferable, and 5 to 20 paths are still more preferable.
Although the temperature at the time of a dispersion process is not specifically limited, 5-80 degreeC is preferable.

[polymer]
The acid value of the polymer is 150 to 250 mg-KOH / g, more preferably 170 to 230 mg-KOH / g, from the viewpoint of dispersibility.
The acid value (mg-KOH / g) of the polymer is calculated by the following formula.
Acid value (mg-KOH / g) = [number of moles of salt-forming group having a polymer solid content of 1 g × number of molecules of potassium hydroxide × 1000]
In the present invention, the polymer may be a water-soluble polymer and / or a water-insoluble polymer, but a water-soluble polymer is preferred from the viewpoint of affinity with a pigment into which a hydrophilic group has been introduced.

In the present invention, the water-soluble polymer means a polymer having a dissolution amount exceeding 10 g, preferably 20 g or more, more preferably 30 g or more when dissolved in 100 g of water at 25 ° C. When the water-soluble polymer has a salt-forming group, the above-mentioned dissolution amount refers to the dissolution amount when the salt-forming group of the water-soluble polymer is neutralized with sodium hydroxide 100% according to the type.
Examples of the water-soluble polymer include a water-soluble vinyl polymer, a water-soluble ester polymer, a water-soluble urethane polymer, and the like. Among these, a vinyl polymer obtained by addition polymerization of a vinyl monomer is preferable.
In the present invention, the water-insoluble polymer means that when a neutralized product of the target polymer is dissolved in 100 g of water at a temperature of 25 ° C., the dissolution amount is 10 g or less, preferably 5 g or less, more preferably 1 g or less. Is an anionic polymer. The amount dissolved is the amount dissolved when 100% sodium hydroxide is neutralized according to the type of salt-forming group of the water-insoluble polymer.
Examples of the water-insoluble polymer include a water-insoluble vinyl polymer, a water-insoluble ester polymer, and a water-insoluble urethane polymer.
The polymer used in the present invention is more preferably a vinyl polymer obtained by copolymerizing a monomer mixture containing a salt-forming group-containing monomer (a) and a hydrophobic monomer (b).

[(A) salt-forming group-containing monomer]
(A) As a salt formation group containing monomer, a cationic monomer and an anionic monomer are mentioned, An anionic monomer is preferable.
When the hydrophilic group to be introduced in the step (A) is an anionic group, an anionic monomer is preferable, and when the hydrophilic group to be introduced in the step (A) is a cationic group, a cationic monomer is preferred.
Examples of the salt-forming group include an anionic group such as a carboxy group, a sulfonic acid group, and a phosphoric acid group, an amino group, and an ammonium group, and among them, a carboxy group is preferable.

Representative examples of the cationic monomer include amine-containing monomers and ammonium salt-containing monomers. Among these, N, N-dimethylaminoethyl (meth) acrylate, N- (N ′, N′-dimethylaminopropyl) (meth) acrylamide and vinylpyrrolidone are preferable.
Examples of the anionic monomer include a carboxylic acid monomer, a sulfonic acid monomer, and a phosphoric acid monomer.
Examples of the carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid.
Examples of the sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, and bis- (3-sulfopropyl) -itaconate.
Examples of phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxyethyl phosphate, and the like. It is done.
Among the anionic monomers, carboxylic acid monomers are preferable, acrylic acid and methacrylic acid are more preferable, and acrylic acid is still more preferable from the viewpoint of dispersibility of the pigment into which a hydrophilic group is introduced.

[(B) Hydrophobic monomer]
Examples of the (b) hydrophobic monomer include alkyl (meth) acrylates and aromatic group-containing monomers from the viewpoint of dispersibility of the pigment into which a hydrophilic group is introduced.
As the alkyl (meth) acrylate, those having an alkyl group having 1 to 22 carbon atoms, preferably 6 to 18 carbon atoms are preferable. For example, methyl (meth) acrylate, ethyl (meth) acrylate, (iso) propyl (meta) ) Acrylate, (iso or tertiary) butyl (meth) acrylate, (iso) amyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, (iso) Examples include decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, and (iso) stearyl (meth) acrylate.
In the present specification, “(iso or tertiary)” and “(iso)” mean both the case where these groups are present and the case where these groups are not present. Indicates. “(Meth) acrylate” indicates acrylate and / or methacrylate.
As the aromatic group-containing monomer, a vinyl monomer having an aromatic group having 6 to 22 carbon atoms, which may have a substituent containing a hetero atom, is preferable, and a styrene monomer or an aromatic group-containing (meth) acrylate. Are more preferable, and it is also preferable to use these in combination.
As the styrene monomer, styrene, 2-methylstyrene, vinyltoluene, and divinylbenzene are preferable, and styrene is more preferable.
Moreover, as an aromatic group containing (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, etc. are preferable, and benzyl (meth) acrylate is more preferable.
As another monomer, (c) a macromer or (d) a nonionic monomer may be contained.
As the macromer, a styrene macromer, an aromatic group-containing (meth) acrylate macromer, and a silicone macromer are preferable from the viewpoint of dispersibility.
Nonionic monomers include polyethylene glycol (n = 2 to 30, n represents the average number of moles added of oxyalkylene groups, the same applies hereinafter) (meth) acrylate, polypropylene glycol (n = 2 to 30) (meth) acrylate, Examples include poly (ethylene glycol (n = 1-15) / propylene glycol (n = 1-15)) (meth) acrylate, methoxypolyethylene glycol (1-30) (meth) acrylate, and the like.

In the polymer, the component (a) is preferably 10 to 85% by weight, more preferably 15 to 75% by weight, still more preferably 15 to 50% by weight, and the component (b) is preferably 15 to 90% by weight, more preferably. Is 25 to 85% by weight, more preferably 50 to 85% by weight.
The weight average molecular weight of the polymer is preferably 1,000 to 30,000, more preferably 1,500 to 20,000, from the viewpoint of dispersibility. In addition, the weight average molecular weight of a polymer can be measured by the method as described in an Example.
Examples of commercially available polymers include JONCRL (JONCRL, registered trademark) 57J, 60J, 61J, 63J, 70J, PD-96J, and 501J of BASF Japan Ltd., and the like. These commercially available polymers are neutralized, and a neutralizing agent may be added separately as necessary.

(Manufacture of polymers)
The polymer is produced by copolymerizing the monomer mixture by a known polymerization method. As the polymerization method, a solution polymerization method is preferable.
Although there is no restriction | limiting in the solvent used by the solution polymerization method, Polar organic solvents, such as water, a C1-C3 aliphatic alcohol, ketones, ethers, esters, are preferable, specifically, water, methanol, ethanol, Acetone, methyl ethyl ketone, and a mixed solvent thereof may be mentioned, and ethanol and a mixed solvent of ethanol and methyl ethyl ketone are preferable.
In the polymerization, a polymerization initiator or a polymerization chain transfer agent can be used. As the polymerization initiator, an azo initiator such as 2,2′-azobis (2,4-dimethylvaleronitrile) is preferable. . As the polymerization chain transfer agent, mercaptans are preferable, and 2-mercaptoethanol is preferable.
Although preferable polymerization conditions vary depending on the type of polymerization initiator and the like, the polymerization temperature is preferably 50 to 80 ° C., and the polymerization time is preferably 1 to 20 hours. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After the completion of the polymerization reaction, the solvent is preferably removed from the reaction solution and dissolved in water to prepare an aqueous dispersion as an aqueous solution.

<Process (C)>
By performing the step (A) and the step (B), a water-based pigment dispersion that has been atomized and stabilized can be obtained. From the viewpoint of further stabilization, the aqueous system obtained in the step (B). A cross-linking treatment may be performed by adding a cross-linking agent to the pigment dispersion. Hereinafter, the step of performing the crosslinking treatment after the step (B) is referred to as “step (C)”.
The solid content concentration of the aqueous pigment dispersion when the crosslinking treatment is performed in the step (C) is 5 to 50% by weight from the viewpoint of reducing the viscosity of the aqueous pigment dispersion and performing a uniform crosslinking reaction and production efficiency. It is preferably 10 to 40%, more preferably 15 to 35% by weight.
When this solid content concentration is higher than that in the step (B), an aqueous pigment dispersion having a solid content concentration in the above range can be obtained by concentration using a known method. On the other hand, when this solid content concentration is lower than the step (B), the solid content concentration can be adjusted to the above range by diluting with water.

Depending on the crosslinking agent used, the catalyst, solvent, temperature, and time can be appropriately selected and determined. The reaction time is preferably 0.5 to 10 hours, more preferably 1 to 5 hours, and the reaction temperature is preferably 40 to 95 ° C.
The molecular weight of the crosslinking agent is preferably 120 to 2000, more preferably 150 to 1500, and still more preferably 150 to 1000, from the viewpoint of the storage stability of the dispersion after being crosslinked.
The amount of the crosslinking agent used is preferably from 0.3 to 30 parts by weight, more preferably from 5 to 20 parts by weight, based on 100 parts by weight of the polymer, from the viewpoint of storage stability.
The pigment particles in the aqueous pigment dispersion obtained in this step are particles obtained by dispersing a pigment with a crosslinked polymer, particles obtained by crosslinking a plurality of polymers adsorbed on the surface of the pigment (crosslinked polymer containing a pigment). Particles).

[Crosslinking agent]
The crosslinking agent used in the present invention is a compound that reacts with a reactive functional group such as a carboxy group of the polymer used in the present invention.
The number of reactive functional groups contained in the crosslinking agent is preferably 2 to 6 from the viewpoint of controlling the molecular weight and improving storage stability. Preferred examples of the reactive functional group include one or more selected from the group consisting of an epoxy group, an oxazoline group, and an isocyanate group.
From the viewpoint of efficiently crosslinking the surface of the polymer, the crosslinking agent has a dissolution amount of preferably 50 g or less, more preferably 40 g or less, and even more preferably 30 g or less when dissolved in 100 g of water at 25 ° C.

Specific examples of the crosslinking agent include the following (i) to (iii).
(I) Compound having two or more epoxy groups in the molecule: for example, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin triglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether Polyglycidyl ethers such as trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether and hydrogenated bisphenol A type diglycidyl ether.
(Ii) Compound having two or more oxazoline groups in the molecule: for example, a compound having 2 or more, preferably 2 to 3 oxazoline groups bonded to an aliphatic group or an aromatic group, more specifically 2 , 2′-bis (2-oxazoline), 1,3-phenylenebisoxazoline, 1,3-benzobisoxazoline, and other bisoxazoline compounds.
(Iii) Compound having two or more isocyanate groups in the molecule: for example, organic polyisocyanate or isocyanate group-terminated prepolymer.
Examples of organic polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate; aromatic diisocyanates such as tolylene-2,4-diisocyanate and phenylene diisocyanate; alicyclic diisocyanates; aromatic Triisocyanate; and modified products such as urethane modified products thereof. The isocyanate group-terminated prepolymer can be obtained by reacting an organic polyisocyanate or a modified product thereof with a low molecular weight polyol or the like.
Among these, from the viewpoint of the storage stability of the dispersion, (i) a compound having two or more epoxy groups in the molecule is preferable, polyglycidyl ether is more preferable, ethylene glycol diglycidyl ether, trimethylolpropane polyglycidyl. Ether is more preferred.

[Water-based pigment dispersion for inkjet recording]
The water-based pigment dispersion for ink-jet recording of the present invention is obtained by the above production method, and can be used as a water-based ink containing water as a main medium as it is.
Examples of the aqueous pigment dispersion for inkjet recording of the present invention include those in which pigment particles are dispersed with a polymer (preferably a crosslinked polymer) in water as a main solvent.
The content of the pigment in the dispersion of the present invention is preferably 1 to 25% by weight, more preferably 2 to 20% by weight, and further preferably 4 to 15% by weight from the viewpoint of increasing the printing density. The water content is preferably 20 to 90% by weight, more preferably 30 to 80% by weight, and still more preferably 40 to 70% by weight.

From the viewpoint of printing performance such as prevention of clogging of the nozzles of the printer, dispersion stability, glossiness, and image clarity, the average particle size of the aqueous pigment dispersion of the present invention is preferably 10 to 200 nm, more preferably 30 to 150 nm. More preferably, it is 50-130 nm.
The storage stability of the aqueous pigment dispersion is preferably 70 to 150%, more preferably 80 to 130%, and still more preferably 90 to 110%. The average particle diameter of the pigment and the storage stability of the aqueous pigment dispersion can be determined by the methods described in the examples.

[Water-based ink for inkjet recording]
The aqueous ink for inkjet recording of the present invention contains the aqueous pigment dispersion of the present invention. Here, “water-based” means that water occupies the largest proportion in the medium contained in the water-based ink, and the medium may be only water, and water and one or more organic solvents. And a mixed solvent. To this water-based ink, wetting agents, penetrants, dispersants, viscosity modifiers, antifoaming agents, antifungal agents, rust preventive agents and the like that are usually used in water-based inks can be added.
The content of the pigment in the water-based ink of the present invention is preferably 1 to 25% by weight, more preferably 2 to 20% by weight, and still more preferably 4 to 15% by weight, from the viewpoint of compatibility between printing density and storage stability. %. The water content is preferably 20 to 90% by weight, more preferably 30 to 80% by weight, and still more preferably 40 to 70% by weight.

  In the following production examples, examples and comparative examples, “parts” and “%” are “parts by weight” and “% by weight” unless otherwise specified. Various physical properties of the polymer and the dispersion were measured, calculated and evaluated by the following methods.

(1) Measurement of polymer weight average molecular weight Gel chromatography method using a solution obtained by dissolving phosphoric acid and lithium bromide in N, N-dimethylformamide so as to have a concentration of 60 mmol / L and 50 mmol / L, respectively. Measurement was performed using polystyrene as a standard substance with a GPC apparatus (HLC-8120GPC) manufactured by Tosoh Corporation, a column (TSK-GEL, α-M × 2) manufactured by Tosoh Corporation, and a flow rate of 1 mL / min].
(2) Calculation of primary particle diameter of pigment Thirty primary particles are extracted from the transmission electron micrograph image of the pigment, and the number average value is obtained. The particle size is defined as the major axis (longest diameter) of the particle.
(3) Calculation of solid content concentration of dispersion About 10 g of anhydrous sodium sulfate (drying aid) sufficiently dried was put in a flat bottom dish, and the weight before drying was measured accurately together with the flat bottom dish. 1 g of the sample to be measured was precisely weighed and dried at 105 ° C. for 2 hours, and then allowed to cool to room temperature, and the weight of the dried flat bottom pan was accurately measured. The solid content concentration was determined by the following calculation formula.
Solid content concentration (%) = [[weight before drying (g) −weight after drying (g)] ÷ sample amount (g)] × 100
(4) Measurement of average particle diameter The average particle diameter of the pigment dispersion (or dispersion of polymer particles containing a pigment) was measured with a laser particle analysis system ELS-8000 (cumulant analysis) of Otsuka Electronics Co., Ltd. The measurement conditions are a temperature of 25 ° C., an angle between incident light and a detector of 90 °, and an integration count of 100. The refractive index of water (1.333) is input as the refractive index of the dispersion solvent. The measurement concentration was usually about 5 × 10 ⁻³ wt%.
(5) Viscosity measurement The viscosity was measured with an E type viscometer (model number: RE80 type) manufactured by Toki Sangyo Co., Ltd. The measurement conditions are a temperature of 20 ° C. and a rotational speed of 100 r / min.
(6) Evaluation of Storage Stability of Aqueous Pigment Dispersion The average particle diameter and viscosity of the aqueous pigment dispersion after standing for 7 days in a constant temperature bath at 70 ° C. are measured, and the storage stability is obtained by the following formula. The storage stability was evaluated according to the criteria.
[Storage stability (particle size)] (%) = [average particle size after 7 days / initial average particle size)] × 100
[Storage stability (viscosity)] (%) = [viscosity after 7 days / initial viscosity)] × 100

Production Example 1 (Production of diazonium salt aqueous solution)
Add 100 parts of ion-exchanged water to 8.8 parts of sulfanilic acid and 5.6 parts of sodium carbonate, mix well, then add 17.7 parts of 35% hydrochloric acid until the temperature is 10 ° C. or lower in an ice bath. Stir. Thereafter, an aqueous solution in which 4.5 parts of sodium nitrite was dissolved in 25 parts of ion-exchanged water was added, and the mixture was stirred in an ice bath until it became 10 ° C. or less (effective amount of diazonium salt 6.9%, obtained from sulfanilic acid). The molecular weight of the diazonium salt obtained: 220).

Production Example 2 (Production of water-insoluble polymer)
In a reaction vessel, 20 parts of methyl ethyl ketone, 0.05 part of a polymerization chain transfer agent (2-mercaptoethanol), and 10% of 200 parts of each monomer shown in Table 1 were mixed and mixed, and nitrogen gas substitution was performed sufficiently. A mixed solution was obtained.
On the other hand, the remaining 90% of the monomer shown in Table 1 was charged into a dropping funnel, and 0.45 part of the polymerization chain transfer agent, 60 parts of methyl ethyl ketone, and a radical polymerization initiator [2,2′-azobis (2,4- (Dimethylvaleronitrile)] 1.2 parts were mixed and mixed, and nitrogen gas substitution was sufficiently performed to obtain a mixed solution.
Under a nitrogen atmosphere, the mixed solution in the reaction vessel was heated to 65 ° C. while stirring, and the mixed solution in the dropping funnel was gradually dropped over 3 hours. After 2 hours at 65 ° C. from the end of dropping, a solution in which 0.3 part of the radical polymerization initiator was dissolved in 5 parts of methyl ethyl ketone was added, and further aged at 65 ° C. for 2 hours and at 70 ° C. for 2 hours, and further 115 parts of methyl ethyl ketone. The mixture was further stirred for 30 minutes to obtain a water-insoluble polymer A solution. The results are shown in Table 1.

The details of the compounds shown in Table 1 are as follows.
Styrene macromer (manufactured by Toagosei Co., Ltd., trade name: AS-6S, number average molecular weight: 6000, polymerizable functional group: methacryloyloxy group)
・ Styrene monomer (manufactured by Nippon Steel Chemical Co., Ltd., trade name: styrene monomer)
・ Methacrylic acid (Mitsubishi Gas Chemical Co., Ltd., trade name: Methacrylic acid (MAA) GE-110)
・ PP-800
Polypropylene glycol monomethacrylate (manufactured by NOF Corporation, trade name: BLEMMER PP-800, propylene oxide average added mole number = 13, terminal: hydroxyl group)
・ Acryester BzMA
Benzyl methacrylate (Mitsubishi Rayon Co., Ltd., trade name: Acryester Bz)
・ 43PAPE-600B
Phenoxypolyethylene glycol polypropylene glycol monomethacrylate (manufactured by NOF Corporation, trade name: BLEMMER 43PAPE-600B, ethylene oxide average addition mole number = 6, propylene oxide average addition mole number = 6, terminal: phenyl group)

Example 1
[Process (A)]
150 g of magenta pigment (CI Pigment Red 122, manufactured by Dainichi Seika Kogyo Co., Ltd., trade name 6111, primary particle size 44 nm) 12.5 g of 5N sodium hydroxide aqueous solution, 12.5 g of sodium carbonate, and 1163 g of ion-exchanged water Then, 162 g of the diazonium salt aqueous solution obtained in Production Example 1 was added and mixed for 1 hour to obtain a pigment dispersion (0.34 mol of diazonium salt with respect to 1 kg of pigment).
Next, the obtained pigment dispersion was subjected to media milling [ultra apex mill: model UAM-05 (trade name), manufactured by Kotobuki Kogyo Co., Ltd.], and zirconia beads having a particle diameter of 0.05 mm as media particles, Dispersion treatment was performed for 67 minutes (total average residence time in the mill: 10 minutes) under the conditions of a bead filling rate of 80% by volume, a stirring blade peripheral speed of 8 m / s, and a circulation flow rate of 200 mL / min.
In order to suppress thickening of the dispersion, 486 g of the diazonium salt aqueous solution obtained in Production Example 1, 37.5 g of 5N sodium hydroxide aqueous solution, and 37.5 g of sodium carbonate were added in three portions during the dispersion treatment. did.
The water-based pigment dispersion after the dispersion treatment is applied to a 5000D Biomax membrane (Nippon Millipore Corporation) using an ultra-membrane filter [Pericon (trade name): Model Pellicon2-mini, manufactured by Nippon Millipore Corporation]. Washing and purification were carried out to obtain an aqueous pigment dispersion (solid content concentration 21%) containing the treated pigment (average particle size 121 nm).

[Process (B)]
To 240 g of the aqueous pigment dispersion containing the treated pigment obtained in the step (A), a water-soluble polymer [acid value: 195 mg-KOH / g, trade name: Jonkrill 61J, (a) acrylic acid / (b) styrene = 25/75 (weight ratio), manufactured by BASF Japan Ltd., weight average molecular weight 1,2000 (refer to the company's HP)] 51 g, ion-exchanged water 48 g, high pressure homogenizer [manufactured by Microfluidics, microfluidizer (trade name) The aqueous pigment dispersion having a solid content concentration of 20% was obtained by carrying out a 10-pass dispersion treatment at a pressure of 150 MPa.

[Process (C)]
To 99.6 parts of the aqueous pigment dispersion obtained in the step (B), 0.9 part of a crosslinking agent (trimethylolpropane polyglycidyl ether, manufactured by Nagase ChemteX Corporation, Denacol EX-321L, epoxy equivalent 129), 9.1 parts of glycerin and 0.4 parts of ion-exchanged water were added, and the reaction was carried out at 90 ° C. for 1.5 hours while stirring. ) To obtain an aqueous pigment dispersion.

Example 2
The same as in Example 1 except that the magenta pigment used in Example 1 was changed to a magenta pigment (CI Pigment Red 122, manufactured by DIC Corporation, trade name FASTGEN SUPERMAGENTA RG, primary particle size 134 nm). Operation was performed to obtain an aqueous pigment dispersion.

Example 3
Except that the crosslinking agent was not added in the step (C) of Example 2, the same operation as in Example 2 was performed to obtain an aqueous pigment dispersion.

Comparative Example 1
To 156 g of the water-insoluble polymer solution (polymer acid value 72 mg-KOH / g) obtained in Production Example 2, 108 g of methyl ethyl ketone and 11 g of 5N aqueous sodium hydroxide solution and 686 g of ion-exchanged water were added to obtain a polymer dispersion.
150 g of the magenta pigment used in Example 2 was added to the obtained polymer dispersion, and mixed at 20 ° C. for 1 hour using a disper blade to obtain a preliminary dispersion.
Using the obtained pre-dispersion, a media mill [Ultra Apex Mill: Model UAM-05 (trade name), manufactured by Kotobuki Kogyo Co., Ltd.] was used as media particles with a zirconia bead having a particle size of 0.05 mm and a bead filling rate. Polymer particles containing pigment (average particle diameter) were dispersed for 56 minutes (total average residence time in the mill: 10 minutes) under the conditions of 80 volume%, stirring blade peripheral speed 8 m / s, and circulation flow rate 200 cc / min. 211 nm) dispersion was obtained.

Next, using a high-pressure homogenizer [Microfluidizer (trade name), manufactured by Microfluidics), dispersion treatment was performed for 10 passes at a pressure of 150 MPa to obtain an aqueous pigment dispersion having a solid content concentration of 20%.
To the obtained aqueous pigment dispersion, 371 g of ion-exchanged water was added, methyl ethyl ketone was removed using a hot water heating medium at 60 ° C. under reduced pressure, a part of water was further removed, and an aqueous system having a solid content concentration of 20%. A pigment dispersion was obtained.
To 90.8 parts of the obtained aqueous pigment dispersion, 9.1 parts of glycerin and 0.1 part of ion-exchanged water were added and reacted at 70 ° C. for 3 hours with stirring. The obtained aqueous pigment dispersion was 5 μm. An aqueous dispersion of pigment-containing polymer particles (average particle size 140 nm) was obtained by filtration using a filter (manufactured by Sartorius Stedim Japan Co., Ltd.).

Comparative Example 2
A water-based pigment dispersion was obtained in the same manner as in Example 3 except that Step (B) was not performed in Example 3.

Comparative Example 3
89 g of methyl ethyl ketone and 606 g of ion-exchanged water were added to 155 g of the water-soluble polymer (Joncrill 61J: manufactured by BASF Japan Ltd.) used in Example 1 to obtain a polymer aqueous solution.
150 g of the magenta pigment used in Example 2 was added to the obtained aqueous polymer solution and mixed at 20 ° C. for 1 hour using a disper blade to obtain a preliminary dispersion.
Next, using a high-pressure homogenizer [Microfluidizer (trade name), manufactured by Microfluidics), dispersion treatment was performed for 10 passes at a pressure of 150 MPa to obtain an aqueous pigment dispersion having a solid content concentration of 20%.
Thereafter, the same operation as in Comparative Example 1 was performed to obtain an aqueous pigment dispersion.

From Table 2, it can be seen that Examples 1 to 3 belonging to the present invention can efficiently produce a stably dispersed aqueous pigment dispersion without causing re-aggregation of the atomized pigment.
In Comparative Example 1, since the media mill treatment and the high-pressure homogenizer treatment were performed using a water-insoluble polymer having a low acid value without introducing a hydrophilic group into the pigment, the pigment could not be reduced in particle size. . In Comparative Example 2, since the high-pressure homogenizer treatment in the step (B) was not performed, the pigment could not be reduced in particle size in the step (A). This is presumably because the atomized pigment was re-agglomerated. In Comparative Example 3, since the media mill treatment in the step (A) was not performed, the pigment could not be sufficiently pulverized, and the pigment could not be reduced in particle size.

Claims (6)

The manufacturing method of the aqueous pigment dispersion for inkjet recording which has the following process (A) and process (B).
Step (A): A mixture containing at least a pigment and an aqueous medium is treated with a media mill, and a treatment agent capable of introducing a hydrophilic group into the pigment is reacted with the pigment while the pigment is pulverized to contain the treated pigment. Step of obtaining an aqueous pigment dispersion Step (B): A polymer having an acid value of 150 to 250 mg-KOH / g is added to the aqueous pigment dispersion containing the treated pigment obtained in Step (A), and a high-pressure homogenizer is used. Process for distributed processing The manufacturing method of the aqueous pigment dispersion of Claim 1 which has the following process (C) after the said process (B).
Step (C): A step of adding a crosslinking agent to the aqueous pigment dispersion obtained in the step (B) to perform a crosslinking treatment.   The method for producing an aqueous pigment dispersion according to claim 1 or 2, wherein the media particles used in the media mill have a particle size of 0.01 to 0.5 mm.   The manufacturing method of the aqueous pigment dispersion in any one of Claims 1-3 whose average particle diameter of the aqueous pigment dispersion containing the processed pigment obtained after a process (A) is 10-200 nm.   The method for producing an aqueous pigment dispersion according to claim 1, wherein the pigment is an organic pigment.   A water-based ink for ink-jet recording, comprising the water-based pigment dispersion obtained by the production method according to claim 1.