JP2007186569A - Aqueous pigment dispersion, aqueous ink, and method for producing aqueous pigment dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous ink having excellent dispersion stability and high color development on plain paper, and further providing an aqueous pigment dispersion for the ink.
SOLUTION: A polymerizable monomer composition containing 95% by mass or more of one or more polymerizable monomers having a solubility of 5% by mass or less in the presence of (meth) acrylic copolymer A particles containing a pigment. In the absence of an aqueous pigment dispersion, aqueous ink, and surfactant obtained by polymerizing (meth) acrylic copolymer B, (1) (meth) acrylic copolymer containing pigment Impregnating the coalesced A particles with a polymerizable monomer composition containing 95% by mass or more of one or more polymerizable monomers having a solubility in water at 20 ° C. of 5% by mass or less; (2) in an aqueous solvent And a step of polymerizing the polymerizable monomer composition in the particles A.
[Selection figure] None

Description

  The present invention relates to an aqueous pigment dispersion useful for an aqueous ink using a pigment as a coloring material, a method for producing the aqueous pigment dispersion, and an aqueous ink.

  Conventionally, a dye ink using a dye as a coloring material has been used as a water-based ink for inkjet recording. Dye inks have many advantages such as excellent storage stability, hardly clogging the nozzles of inkjet printers, and the printed matter obtained has excellent gloss. However, it has been pointed out that there are defects derived from dyes, such as inability to store printed matter for a long time due to poor weather resistance, and poor water resistance and light resistance. In recent years, weather resistance, water resistance and light resistance have been pointed out. Development of an aqueous ink for inkjet recording (hereinafter abbreviated as “pigment aqueous ink”) using an excellent pigment is underway.

  A pigment aqueous ink is prepared by diluting a pigment dispersion in which a pigment is dispersed in an aqueous solvent using a dispersant such as a surfactant or a polymer dispersant with water or an aqueous solvent, and if necessary, a drying inhibitor. It is prepared by adding a penetrant or other additives. However, it has been difficult to impart ink suitability for ink jet recording, particularly color developability, using various additives while ensuring the dispersion stability of the pigment in the production process. Also, the pigment particles have a drawback that they are easily influenced by the surface condition of the recording medium and the dispersant. For example, in a recording medium such as plain paper or recycled paper such as paper that is not surface-coated, pigment particles may enter between the paper fibers depending on the type of dispersant, and remain on the paper surface. In many cases, high color development cannot be obtained. In addition, bleeding and color unevenness are likely to occur due to the structure of the paper fiber and the influence of the processing agent such as a sizing agent, and the degree of bleeding and color unevenness varies, so it is difficult to provide uniform quality. In addition, in a recording medium having a surface coating such as inkjet special paper used for photographic printing, the printing density is maintained because the pigment particles do not enter between the fibers, but the gloss is not sufficient and the printing duty is different. There was a difference in glossiness.

  In contrast, several methods have been proposed in which pigments are encapsulated in polymer particles to obtain a pigment dispersion. For example, an example is known in which a coating pigment in which a particle obtained by previously kneading a pigment and a polymer is used as a core and an emulsifier or a hydrophilic monomer is used and a shell layer is provided around the core is used (see, for example, Patent Document 1). ). Further, the pigment exhibits a dispersion stability when a water-insoluble colorant is dispersed, and has a property that the stability of the resulting latex is poor when the vinyl monomer is polymerized in the presence of the dispersant alone. There is known an example in which a vinyl monomer is added and polymerized after being dispersed in an aqueous medium in the presence of a low molecular weight dispersant (specifically, a sulfonic acid group) having the above. (For example, refer patent document 2) Moreover, the example using the pigment inclusion | inner_cover polymer particle containing a hydrophilic polymer, a hydrophobic polymer, and a pigment is also known. However, in any of these methods, it is difficult to obtain an aqueous pigment ink that has good dispersion stability and excellent color developability particularly on plain paper.

JP 2003-238872 A JP 2003-34770 A JP-A-2004-277507

  The problem to be solved by the present invention is a water-based ink for ink-jet recording using a pigment as a colorant, which is excellent in dispersion stability, and provides a water-based ink for ink-jet recording having a very high color on plain paper. An object of the present invention is to provide an aqueous pigment dispersion for the ink.

The present inventors have intensively studied the cause of color development on plain paper, and that the acid value of the polymer used as the dispersant affects the color development. The lower the resin acid value of the dispersant, the higher the color development on plain paper. I found out.
However, when the acid value of the dispersant is reduced, the dispersibility of the solvent as water is lowered, and the dispersion stability of the pigment in the production process is significantly lowered.
In the dispersion process of the pigment at the time of manufacture, the present inventors have an acid value that can stably exist as dispersed particles, and when used in an inkjet ink, the acid has a high color on plain paper. The problem of the present invention has been solved by providing a pigment dispersion that has a good value.

  That is, the present invention is an aqueous pigment dispersion having water and a (meth) acrylic copolymer particle containing a pigment at 20 ° C. in the presence of the (meth) acrylic copolymer A particle containing a pigment. A polymerizable monomer composition containing 95% by mass or more of one or more polymerizable monomers having a solubility in water (hereinafter referred to as solubility at 20 ° C.) of 5% by mass or less is polymerized. An aqueous pigment dispersion containing at least one (meth) acrylic copolymer B obtained in the above manner is provided.

  The present invention also provides an aqueous ink using the above-described aqueous pigment dispersion.

The present invention is also a method for producing an aqueous pigment dispersion having water and (meth) acrylic copolymer particles containing a pigment, in the absence of a surfactant,
(1) A (meth) acrylic copolymer A particle containing a pigment is impregnated with a polymerizable monomer composition containing 95% by mass or more of one or more polymerizable monomers having a water solubility of 5% by mass or less. Process,
(2) A method for producing an aqueous pigment dispersion comprising a step of polymerizing the polymerizable monomer composition in the particles A in an aqueous solvent.

  The aqueous pigment dispersion of the present invention is excellent in dispersion stability. When the aqueous pigment dispersion of the present invention is applied to an aqueous ink, particularly an aqueous ink for inkjet recording, very high color development can be obtained on plain paper.

Details of the present invention will be described below.
(Aqueous pigment dispersion)
The aqueous pigment dispersion of the present invention has (meth) acrylic copolymer particles containing water and a pigment.

(water)
In the present invention, water serves as a dispersion medium. For example, water that has a pH of 6.5 to 7.5 and does not contain free ions, such as distilled water, ion-exchanged water, pure water, and ultrapure water, is preferable.

((Meth) acrylic copolymer particles containing pigment)
In the present invention, “a (meth) acrylic copolymer particle containing a pigment” refers to a particle having at least a pigment and a (meth) acrylic copolymer. In the present invention, “(meth) acrylic copolymer A” is a hydrophilic (meth) acrylic copolymer. Therefore, in the present invention, “(meth) acrylic copolymer A particles containing pigment” means at least resin particles of pigment and hydrophilic (meth) acrylic copolymer.

As a manufacturing method of “(meth) acrylic copolymer A particles containing pigment”, for example,
(1) A method of adding an aqueous dispersion of a pigment in the polymerization process of (meth) acrylic copolymer A,
(2) A method of performing emulsion polymerization or precipitation polymerization of (meth) acrylic copolymer A in water in which a pigment is dispersed using a surfactant,
(3) It can be obtained by a method such as a method of kneading and dispersing (meth) acrylic copolymer A and pigment in water. In the present invention, since the amount of the surfactant used can be reduced as much as possible, it is preferable to use particles obtained by the kneading and dispersing method (3). Hereinafter, a method of using the (meth) acrylic copolymer A particles containing the pigment obtained by the method (3) will be described in detail.

The shape of the (meth) acrylic copolymer A particles containing a pigment used in the present invention can be used without particular limitation as long as it is a form that can be used as a water-based ink component from a spherical shape to an amorphous shape.
The particle size is determined depending on the application. For example, when the aqueous pigment dispersion of the present invention is used as an inkjet ink, a preferable range is 200 nm or less. Moreover, when using as a gravure ink, 500 nm or less is made into a preferable range.

(Pigment)
As the pigment used in the present invention, any known and commonly used organic pigment can be used. Specifically, for example, insoluble azo pigment, soluble azo pigment, indanthrene pigment, phthalocyanine pigment, quinacridone pigment, perylene pigment, isoindolinone pigment, quinophthalone pigment, anthraquinone pigment, diketopyrrolopyrrole And pigments.

In the (meth) acrylic copolymer A used in the present invention, the hydrophilic group is preferably a carboxyl group. The number of moles per gram of the (meth) acrylic copolymer A is 1.2 mmol to 3.5 mmol (provided that the number of moles includes the number of moles of neutralized carboxyl groups, and the number of carboxyl groups below) The same holds true for the dispersion stability of the dispersion stability, and more preferably in the range of 1.2 mmol to 2.7 mmol. This is preferably in the range of 67 to 196, and more preferably in the range of 67 to 151, in terms of acid value. When the number of moles is too low, the pigment dispersibility is lowered, and particularly when an inkjet ink is prepared, the printing stability tends to deteriorate. If the number of moles is too high, the water resistance of the colored image is lowered, which is also not preferable.
When the (meth) acrylic copolymer A and the pigment are kneaded and dispersed in water, the carboxyl group is used after being neutralized with a basic substance.

  Examples of the polymerizable compound having a carboxyl group that is a raw material for the (meth) acrylic copolymer A include acrylic acid, methacrylic acid, 2- (meth) acryloyloxyethylphthalic acid, and 2- (meth) acryloyloxyethyl. Examples include succinic acid, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, ω-carboxy-polycaprolactone mono (meth) acrylate, (meth) acrylic acid dimer, and the like. The polymerizable compound may be used alone or in combination, and the blending ratio may be such that the number of carboxyl groups per 1 g of the (meth) acrylic copolymer A to be obtained falls within the above range.

  The (meth) acrylic copolymer A used in the present invention is not particularly limited except that the polymerizable compound having a carboxyl group is used, and a known polymerizable compound can be used. Specifically, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, (meth) acrylic Isobutyl acid, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate, cyclohexyl (meth) acrylate , (Meth) acrylic acid esters such as isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and styrene.

  In the present invention, the reaction rate of the polymerizable compound as a raw material is considered to be substantially the same, and the charging ratio of each monomer is regarded as the content ratio of the polymerization unit of each monomer in terms of mass. . The (meth) acrylic copolymer A can be synthesized by various conventionally known reaction methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. In this case, known and commonly used polymerization initiators, chain transfer agents, surfactants and antifoaming agents can be used in combination.

  In the (meth) acrylic copolymer A, solubility and dispersibility in water are ensured by neutralizing the carboxyl group in the copolymer with a basic substance. The amount of neutralization in the copolymer is usually in the range of 30 to 100%, particularly 70 to 100%, based on the total amount of carboxyl groups. This proportion of neutralized groups does not mean the molar ratio of anionic groups to basic substances, but takes into account dissociation equilibrium.

  As the basic substance for neutralizing the (meth) acrylic copolymer A, any known and commonly used substances can be used. For example, inorganic basic substances such as sodium hydroxide, potassium hydroxide and ammonia, and triethylamine An organic basic substance such as alkanolamine can be used.

  The molecular weight of the (meth) acrylic copolymer A is not particularly limited, but is preferably a weight average molecular weight of 5,000 to 50,000.

((Meth) acrylic copolymer A particles containing pigment)
In the (meth) acrylic copolymer A particles containing the pigment, the ratio of the pigment to the (meth) acrylic copolymer A is based on mass, [nonvolatile content of the (meth) acrylic copolymer A] / organic pigment. Is preferably 0.1 to 2.0, and most preferably 0.1 to 1.0. If the ratio is too low, the scratch resistance of the colored image and the dispersion / storage stability of the resulting aqueous ink itself may decrease, and if it is too high, the viscosity of the resulting aqueous ink may increase. In particular, in the case of inkjet ink, the ejection stability may be impaired.

  When the (meth) acrylic copolymer A particles containing the pigment are produced by the above method (3), specifically, a mixture containing a pigment, a (meth) acrylic copolymer, a basic substance and water is kneaded. Disperse. The liquid medium used for dispersion is optimally 100% water, but it may be a mixture of water and an organic solvent, and may be an aqueous medium containing at least 60% water in terms of mass. In this case, the organic solvent is preferably a water-soluble organic solvent. By using a water-soluble organic solvent in combination with water, it may be possible to reduce the liquid viscosity in the dispersion step, so if the viscosity in the dispersion step is too high, adding a water-soluble organic solvent to the solvent as appropriate It is effective.

  Examples of the water-soluble organic solvent include ketones such as acetone, methyl ethyl ketone (MEK), methyl butyl ketone, and methyl isobutyl ketone; methanol, ethanol, 2-propanol, 2-methyl-1-propanol, 1-butanol, 2 -Alcohols such as methoxyethanol; ethers such as tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane; amides such as dimethylformamide, N-methylpyrrolidone and the like. It is preferable to use a compound selected from the group consisting of -6 ketones and alcohols having 1 to 5 carbon atoms. These water-soluble organic solvents may be used as the copolymer solution or separately contained in the mixture during the dispersion step.

  In the preparation of the (meth) acrylic copolymer A particles containing the pigment, the most preferable ratio is, in terms of mass, 10 to 100 parts of (meth) acrylic copolymer A with respect to 100 parts of pigment (however, the nonvolatile content) Conversion), and the aqueous medium (which may contain a water-soluble organic solvent) is 200 to 290 parts.

  As a dispersing device that can be used when dispersing the pigment and the (meth) acrylic copolymer A, any of various well-known devices can be used. For example, a method that uses the kinetic energy of a spherical dispersion medium made of steel, stainless steel, zirconia, alumina, silicon nitride, glass, etc., with a diameter of about 0.1 to 10 mm, a method that uses shear force by mechanical stirring, and a high speed Examples of the dispersion device include a dispersion method such as a method using a pressure change of the supplied dispersed flow bundle, a flow path change, or a force generated by a collision. Specific dispersion devices include RED DEVIL paint conditioner, Toyo Seiki Co., Ltd. test disperser, Mitsui Mining Co., Ltd. SC mill SC100 / 32 type, Iwata Tekko Co., Ltd. planetary mixer PVM. -5, Dino mill manufactured by Willy et Bakkofen (WAB).

  After the dispersion step, if necessary, the water-soluble organic solvent may be distilled off by distillation or the like. The distillation contains 95% by mass or more of one or more polymerizable monomers having a solubility in water of 5% by mass or less in the presence of (meth) acrylic copolymer A particles containing a pigment, which will be described later. The polymerization may be performed during or after the polymerizable monomer composition to be polymerized.

The (meth) acrylic copolymer A particles containing the pigment preferably have no change in average particle diameter during storage. Specifically, the change rate of the average particle diameter under the condition Q is preferably 0.9 to 1.1. However, the condition Q is that an aqueous solution containing 20 parts of (meth) acrylic copolymer A particles containing the pigment and 80 parts of water is stored in a constant temperature bath at 70 ° C. for 3 days. Is a value obtained by dividing the average particle diameter after condition Q by the average particle diameter before condition Q.
In the case of having a change rate outside this range, one or more polymerizable monomers having a solubility in water of 5% by mass or less in the presence of the (meth) acrylic copolymer A particles containing a pigment described later are used. When the polymerizable monomer composition containing 95% by mass or more is polymerized, precipitation may occur.

((Meth) acrylic copolymer B)
In the present invention, in the presence of the (meth) acrylic copolymer A particles containing the pigment, polymerization containing 95% by mass or more of one or more polymerizable monomers having a water solubility of 5% by mass or less. It is characterized in that it contains one or more types of (meth) acrylic copolymer B obtained by polymerizing the polymerizable monomer composition.
The presence of the (meth) acrylic copolymer A particles containing the pigment specifically means that one or more polymerizable monomers having a solubility in water of 5% by mass or less within the particles are 95 or less. It means that a polymerizable monomer composition (hereinafter abbreviated as polymerizable monomer composition C) containing at least mass% is polymerized.

The color development of plain paper, which is the subject of the present invention, is considered to be influenced by the acid value of the polymer used as the dispersion, for example, the amount of carboxyl groups (in moles).
The acid value of the (meth) acrylic copolymer A is an amount that can maintain good dispersion stability of the pigment in the production process, but is an amount that is too much to obtain high color developability on plain paper. .
In the present invention, after the pigment is stably dispersed, the (meth) acrylic copolymer B obtained by polymerizing the polymerizable monomer composition C having a solubility in water of 5% by mass or less coexists. The absolute value of the acid value of the total amount of (meth) acrylic copolymer present in the system is lowered. This makes it possible to achieve both production stability and storage stability and color development on plain paper when converted to ink.

  Although it is difficult to quantify the reduction rate of the absolute value of the acid value of the total amount of (meth) acrylic copolymer present in the system, for example, when (meth) acrylic copolymer A has a carboxyl group, Quantification is possible by “final carboxyl group mole number (theoretical value)”. The “final carboxyl group mole number (theoretical value)” indicates the number of millimoles of carboxyl groups per 1 g of resin ((meth) acrylic copolymer A + (meth) acrylic copolymer B) contained in the aqueous pigment dispersion. It is a thing. The polymerizable monomer composition C so that the difference between the “final carboxyl group mole number (theoretical value)” and the carboxyl group amount (mmol number) of the (meth) acrylic copolymer A used is 0.3 mmol or more. By determining the addition amount of the water-based ink, it is possible to obtain a water-based ink having more excellent color development.

  Specifically, it is preferable to use the polymerizable monomer composition C in an amount of 0.5 to 10 parts with respect to 10 parts of the pigment in the (meth) acrylic copolymer A particles containing the pigment. Among these, it is preferable to use it so as to be 1 part to 5 parts.

  Examples of the polymerizable monomer that can be used as the polymerizable monomer composition C and has a solubility in water of 5% by weight or less include methyl (meth) acrylate, ethyl (meth) acrylate, and n-propyl (meth) acrylate. Isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate , Dodecyl (meth) acrylate, octadecyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) acrylate, styrene, neopentyl glycol di (meth) acrylate, ethylene glycol di (Meth) acrylate, divinylbenzene and the like can be mentioned.

  Moreover, as the polymerizable monomer that can be used as the polymerizable monomer composition C within a range of less than 5% by mass, the general-purpose polymerizable monomer described in the raw material of the (meth) acrylic copolymer A can be used.

(Production method)
Specifically, the aqueous pigment dispersion of the present invention, in the absence of a surfactant,
(1) impregnating a polymerizable monomer composition C into (meth) acrylic copolymer A particles containing a pigment;
(2) It can be manufactured through a step of polymerizing the polymerizable monomer composition C in the particles A in an aqueous solvent.

In the present invention, no surfactant is used. This is because the polymerizable monomer composition C is obtained by completely impregnating (meth) acrylic copolymer A particles containing a pigment and polymerizing the particles in the particles. The presence of the surfactant is not preferable because the polymerizable monomer composition C forms micelles outside the (meth) acrylic copolymer A particles and polymerizes.
In the present invention, the surfactant is a low molecular surfactant or reactive surfactant used in the field of emulsion polymerization or the like, specifically, EMAL 10, Emulgen 404, LATEMUL S-180 [Kao AQUALON KH-10 (Daiichi Kogyo Seiyaku Co., Ltd.), Eleminol ES-30, Eleminol RS-30 (Sanyo Kasei Co., Ltd.), Adekaria Soap SE (Asahi Denka Co., Ltd.) , Newcor 210, Antox MS-60 [manufactured by Nippon Emulsifier Co., Ltd.], etc., used in a narrow sense, the number of acid-containing (meth) acrylic copolymers, polyesters, etc. A high molecular weight surfactant having an average molecular weight of 1000 is not included.

  In the step (1), the step of impregnating the polymerizable monomer composition C into the (meth) acrylic copolymer A particles containing a pigment is specifically an aqueous solvent, preferably at room temperature for several hours. Mixing and stirring. At this time, there is no problem even if it is carried out under pressure, but it is preferably carried out under normal pressure in view of the complexity of the apparatus and operation. As a method of mixing and stirring, a known method and apparatus may be used. For example, a homodisper, an ultrasonic disperser, etc. are mentioned. This step eliminates the monomer floating on the liquid surface.

  The radical polymerization initiator may be added during the step of impregnating the polymerizable monomer composition C into the (meth) acrylic copolymer A particles containing the pigment, or may be added after mixing. However, when using an oil-soluble initiator, it is better to mix simultaneously with the pigment-encapsulated particles comprising the (meth) acrylic copolymer A and the polymerizable monomer mixture. In this case, when the added water-soluble initiator is used, it is preferably mixed and stirred at 20 to 80 ° C., and when the oil-soluble initiator is used, it is preferably mixed and stirred at 30 to 50 ° C.

Next, the aqueous dispersion in which the (meth) acrylic copolymer A particles containing the pigment are impregnated with the polymerizable monomer composition C is heated and stirred as necessary to polymerize the polymerizable monomer composition C ( Step 2).
The radical polymerization initiator used in this step includes water-soluble initiators such as ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) dihydrochloride, azobiscyanovaleric acid, etc. Agent, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2 ′ -Azobis (2,4-dimethyl-4-methoxyvaleronitrile), 2,2'-azobis (methyl 2-methylpropionate), benzoyl peroxide, lauroyl peroxide, bis (4-tert-butylcyclohexyl) per Oxydicarbonate, tert-butylperoxy-2-ethylhexanoate, ditert-butyl peroxide, tert-butylperoxy Nzoeto, 1,1-bis (tert- Buchirupaoki) -3,3,5 an oil-soluble initiator such as trimethyl cyclohexane can be used.
The amount of the radical polymerization initiator used is preferably 0.1 to 20 parts, more preferably 1 to 10 parts, with respect to 100 parts of the polymerizable monomer mixture.
The reaction conditions for radical polymerization are preferably 40 ° C to 90 ° C, and more preferably 60 ° C to 90 ° C. The reaction time is preferably 1 hour to 20 hours, and more preferably 3 hours to 15 hours.

  Further, when the (meth) acrylic copolymer B is polymerized in the aqueous pigment dispersion, after the above polymerization is completed, it is cooled to room temperature and another polymerizable monomer mixture is added. Then, what is necessary is just to repeat operation similar to said process (1) and said process (2).

  The aqueous pigment dispersion of the present invention can contain known additives and liquid media when used as a dispersion for various aqueous inks. For example, when used as an aqueous pigment ink for inkjet recording, the aqueous pigment dispersion of the present invention is diluted with water or other liquid medium so as to have a pigment solid content of 1 to 10% on a mass basis. An aqueous pigment ink for recording can be obtained. Ultracentrifugation or filtration with a microfilter may be further performed in order to remove coarse particles and undersized particles and to adjust the particle size distribution of dispersed particles.

  The aqueous pigment ink for ink-jet recording thus obtained can be recorded on a known recording medium. As the recording medium at this time, for example, plain paper such as PPC paper, exclusive paper for inkjet such as photographic paper (glossy), photographic paper (silk), synthetic resin film such as OHP film, Various films and sheets, such as metal foils, such as aluminum foil, are mentioned.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In the following examples and comparative examples, “part” and “%” are both based on mass.

(Synthesis of (meth) acrylic copolymer A)
<Synthesis Example 1> (Synthesis of Copolymer P-1)
Into a four-necked flask equipped with a thermometer, a stirrer, a nitrogen introduction tube, and a cooling tube, 550 parts of methyl ethyl ketone (hereinafter abbreviated as MEK) was charged, and the inside of the reaction vessel was purged with nitrogen while stirring. The temperature inside the reaction vessel was raised to 80 ° C. while maintaining a nitrogen atmosphere, and then 400 parts of benzyl methacrylate, 100 parts of methacrylic acid and “Perbutyl (registered trademark) O” (active ingredient peroxy 2-ethylhexanoic acid t -Butyl, manufactured by Nippon Oil & Fats Co., Ltd. (30.0 parts) was added dropwise over 2 hours and 30 minutes. After completion of dropping, the reaction was further continued for 11 hours at the same temperature. 2.5 parts of “Perbutyl (registered trademark) O” was added 3 hours and 6 hours after the completion of the dropping. After completion of the reaction, a part of MEK was distilled off under reduced pressure, and a (meth) acrylic copolymer having a carboxyl group mole number of 2.33 mmol, an acid value of 130, a weight average molecular weight of 25,500, and a glass transition temperature (calculated value) of 69 ° C. A 50% MEK solution of combined P-1 was obtained.

<Synthesis Example 2> (Synthesis of copolymer P-2)
In the same manner as in Synthesis Example 1 except that 400 parts of benzyl methacrylate and 100 parts of methacrylic acid are 439 parts of benzyl methacrylate and 61 parts of methacrylic acid, the number of moles of carboxyl groups is 1.42 mmol, the acid value is 80, A 50% MEK solution of (meth) acrylic copolymer P-2 having a weight average molecular weight of 25,500 and a glass transition temperature (calculated value) of 63 ° C. was obtained.

<Synthesis Example 3> (Synthesis of copolymer P-3)
In the same manner as in Synthesis Example 1 except that 400 parts of benzyl methacrylate in Synthesis Example 1 and 100 parts of methacrylic acid are changed to 462 parts of benzyl methacrylate and 38 parts of methacrylic acid, the number of moles of carboxyl groups is 0.88 mmol, the acid value is 50, A 50% MEK solution of (meth) acrylic copolymer P-3 having a weight average molecular weight of 23,100 and a glass transition temperature (calculated value) of 60 ° C. was obtained.

<Synthesis Example 4> (Synthesis of copolymer P-4)
In the same manner as in Synthesis Example 1 except that 400 parts of benzyl methacrylate and 100 parts of methacrylic acid were changed to 450 parts of benzyl methacrylate and 50 parts of methacrylic acid, the number of moles of carboxyl groups was 1.16 mmol, the acid value was 65, A 50% MEK solution of (meth) acrylic copolymer P-4 having a weight average molecular weight of 25,900 and a glass transition temperature (calculated value) of 61 ° C. was obtained.

(Production of dispersion liquid containing (meth) acrylic copolymer A particles containing pigment)
Dispersion C is blue, dispersion M is magenta, and dispersion Y is yellow.

<Production Example 1> (Production of Dispersion C1)
Fastgen (registered trademark) Blue TGR [Dai-Nihon Ink Chemical Co., Ltd. β-type copper phthalocyanine pigment C.I. I. Pigment Blue 15: 3], 4 parts, 1.6 parts of the copolymer P-1 solution obtained in Synthesis Example 1, 0.54 parts of 20% potassium hydroxide, 12 parts of MEK, and 12.66 parts of water were charged. The mixture was dispersed for 2 hours with a conditioner (using zirconia beads having a diameter of 0.5 mm). After the completion of dispersion, methyl ethyl ketone was distilled off from the liquid obtained by removing zirconia beads using an evaporator, and then coarse particles were removed by centrifugation. The yield at this time was 91.7% (hereinafter simply referred to as yield).
Preparation with water gave a dispersion C1 having a nonvolatile content of 22%.

<Production Example 2> (Production of Dispersion M1)
Fastgen (registered trademark) Blue TGR of Production Example 1 [beta-type copper phthalocyanine pigment manufactured by Dainippon Ink & Chemicals, Inc. C.I. I. Pigment Blue 15: 3] is a C.I. from Fastgen (registered trademark) Super Magenta RY [Dainippon Ink Chemical Co., Ltd.]. I. Pigment Red 122] was carried out in the same manner as in Production Example 1 to obtain a dispersion M1 having a nonvolatile content of 22%. The yield after centrifugation was 82.6%.

<Production Example 3> (Production of Dispersion Y1)
Fastgen (registered trademark) Blue TGR of Production Example 1 of Production Example 1 [beta] -type copper phthalocyanine pigment manufactured by Dainippon Ink & Chemicals, Inc. I. Pigment Blue 15: 3] was changed to Fast (registered trademark) Yellow 7413 (manufactured by Sanyo Dye Co., Ltd.) and dispersed and prepared in the same manner as in Production Example 1 to obtain a dispersion Y1 having a nonvolatile content of 22%. It was. The yield after centrifugation was 84.7%.

<Production Example 4> (Production of Dispersion C2)
1.6 parts of the copolymer P-1 solution of Production Example 1, 0.54 parts of 20% potassium hydroxide and 12.66 parts of water were obtained in 1.6 parts of the copolymer P-2 solution obtained in Synthesis Example 2, respectively. Parts, 20% potassium hydroxide aqueous solution 0.32 parts and water 12.88 parts were dispersed and prepared in the same manner as in Production Example 1 to obtain a dispersion C2 having a nonvolatile content of 22%. The yield after centrifugation was 86.4%.

<Production Example 5> (Production of Dispersion C3)
Fastgen (registered trademark) Blue TGR [Dai-Nihon Ink Chemical Co., Ltd. β-type copper phthalocyanine pigment C.I. I. Pigment Blue 15: 3], 4 parts, 1.6 parts of the copolymer P-1 solution obtained in Synthesis Example 1, 0.54 parts of 20% potassium hydroxide, 12 parts of MEK, and 12.66 parts of water were charged. The mixture was dispersed for 2 hours with a conditioner (using zirconia beads having a diameter of 0.5 mm). After the completion of dispersion, a liquid obtained by removing zirconia beads was prepared with water to obtain a dispersion C3 having a nonvolatile content of 18%. The yield after centrifugation was 98.0%.

<Production Example 6> (Production of Dispersion C4)
1.6 parts of copolymer P-1 solution of synthesis example 1, 0.54 part of 20% potassium hydroxide and 12.66 parts of water were each obtained in 1.6 parts of copolymer P-3 solution obtained in synthesis example 3. The dispersion and preparation were carried out in the same manner as in Production Example 1 except that the content was 0.20 part, 20% potassium hydroxide aqueous solution and 0.200 part of water, to obtain a dispersion C4 having a nonvolatile content of 12%. However, since the amount of carboxyl groups of the copolymer P-3 used was as low as 0.89, the yield after centrifugation was as low as 50%.

<Production Example 7> (Production of Dispersion C5)
1.6 parts of the copolymer P-1 solution of Production Example 1, 0.54 part of 20% potassium hydroxide, and 12.66 parts of water were obtained in 1.6 parts of the copolymer P-4 solution obtained in Synthesis Example 4, respectively. The dispersion and preparation were carried out in the same manner as in Production Example 1 except that 0.26 part of a 20% aqueous potassium hydroxide solution and 12.94 parts of water were obtained, to obtain a dispersion C5 having a nonvolatile content of 15%. However, since the amount of carboxyl groups in the copolymer P-3 used was as low as 1.16, the yield of the particles was slightly low at 70%.

<Production Example 7> (Production of Dispersion M2)
Fastgen (registered trademark) Blue TGR of Production Example 1 [beta-type copper phthalocyanine pigment manufactured by Dainippon Ink & Chemicals, Inc. C.I. I. Pigment Blue 15: 3], 1.6 parts of copolymer P-1 solution, 0.54 parts of 20% potassium hydroxide and 12.66 parts of water were added to Fastgen (registered trademark) Super Magenta RY [Dainippon Ink and Chemicals, Inc. Industrial Co., Ltd. C.I. I. Pigment Red 122], 1.6 parts of copolymer P-2 solution, 0.32 parts of 20% aqueous potassium hydroxide solution and 12.88 parts of water, and dispersion and preparation in the same manner as in Production Example 1, A dispersion M2 having a nonvolatile content of 22% was obtained.

(Method for producing aqueous pigment dispersion of the present invention)
<Example 1> (Synthesis of aqueous pigment dispersion C1-a)
167 parts of dispersion C1 obtained in Production Example 1, 23 parts of water, and 3 parts of benzyl methacrylate (water solubility 0.14% by mass) were charged into a separable flask, and a thermometer, a stirrer, a nitrogen introduction tube, The tube was set. After stirring at 40 ° C. for 2 hours, the temperature was raised to 80 ° C. When the temperature reached 80 ° C., a solution in which 0.03 part of potassium persulfate was dissolved in 2 parts of water was added. Heated at 80 ° C. for 10 hours. In addition, the solution which melt | dissolved potassium persulfate 0.03 part in 2 parts of water was added 3 hours and 5 hours after it became 80 degreeC. After completion of the reaction, the mixture was filtered through a 200 mesh nylon filter cloth to obtain an aqueous pigment dispersion C1-a having a nonvolatile content of 20%.

<Example 2> (Synthesis of aqueous pigment dispersion C1-b)
167 parts of dispersion C1 obtained in Production Example 1, 35 parts of water, and 6 parts of benzyl methacrylate were charged into a separable flask, and a thermometer, a stirrer, a nitrogen introduction tube, and a cooling tube were set. After stirring at 40 ° C. for 2 hours, the temperature was raised to 80 ° C. When the temperature reached 80 ° C., a solution in which 0.06 part of potassium persulfate was dissolved in 2 parts of water was added. Heated at 80 ° C. for 10 hours. In addition, the solution which melt | dissolved 0.06 part of potassium persulfate in 2 parts of water was added 3 hours and 5 hours after the time which became 80 degreeC. After completion of the reaction, the mixture was filtered through a 200 mesh nylon filter cloth to obtain an aqueous pigment dispersion C1-b having a nonvolatile content of 20%.

<Example 3> (Synthesis of aqueous pigment dispersion C1-c)
Aqueous pigment dispersion C1 having a nonvolatile content of 20% was prepared in the same manner as in Synthesis Example 6 except that 6 parts of benzyl methacrylate in Example 2 was changed to 6 parts of methyl methacrylate (solubility in water: 1.72% by mass). -C was obtained.

<Example 4> (Synthesis of aqueous pigment dispersion C1-d)
An aqueous pigment dispersion C1-d having a nonvolatile content of 20% was prepared in the same manner as in Synthesis Example 6 except that 6 parts of benzyl methacrylate in Example 2 was changed to 6 parts of styrene (water solubility 0.03% by mass). Got.

<Example 5> (Synthesis of aqueous pigment dispersion C1-e)
167 parts of dispersion C1 obtained in Production Example 1, 45 parts of water, and 9 parts of benzyl methacrylate were charged into a separable flask, and a thermometer, a stirrer, a nitrogen introduction tube, and a cooling tube were set. After stirring at 40 ° C. for 2 hours, the temperature was raised to 80 ° C. When the temperature reached 80 ° C., a solution in which 0.09 part of potassium persulfate was dissolved in 3 parts of water was added. Heated at 80 ° C. for 10 hours. In addition, the solution which melt | dissolved potassium persulfate 0.09 part in 3 parts of water was added 3 hours and 5 hours after it became 80 degreeC. After completion of the reaction, the mixture was filtered through a 200 mesh nylon filter cloth to obtain an aqueous pigment dispersion C1-e having a nonvolatile content of 20%.

<Example 6> (Synthesis of aqueous pigment dispersion C2-a)
166 parts of dispersion C2 obtained in Production Example 4, 26 parts of water, and 3 parts of benzyl methacrylate were charged into a separable flask, and a thermometer, a stirrer, a nitrogen introducing tube, and a cooling tube were set. After stirring at 40 ° C. for 2 hours, the temperature was raised to 80 ° C. When the temperature reached 80 ° C., a solution in which 0.03 part of potassium persulfate was dissolved in 1 part of water was added. Heated at 80 ° C. for 10 hours. In addition, the solution which melt | dissolved 0.03 part of potassium persulfate in 1 part of water was added 3 hours and 5 hours after the time which became 80 degreeC. After completion of the reaction, the mixture was filtered through a 200-mesh nylon filter cloth to obtain a synthesis of an aqueous pigment dispersion C2-a having a nonvolatile content of 20%.

<Example 7> (Synthesis of aqueous pigment dispersion C3-a)
170 parts of dispersion C3 obtained in Production Example 5, 12 parts of water, and 5 parts of benzyl methacrylate were charged into a separable flask, and a thermometer, a stirrer, a nitrogen introducing tube, and a cooling tube were set. After stirring at 40 ° C. for 2 hours, the temperature was raised to 80 ° C. When the temperature reached 80 ° C., a solution in which 0.05 part of potassium persulfate was dissolved in 1.5 parts of water was added. Heated at 80 ° C. for 10 hours. In addition, 3 hours and 5 hours after the temperature reached 80 ° C., a solution in which 0.05 part of potassium persulfate was dissolved in 1.5 parts of water was added. After completion of the reaction, the reaction mixture was filtered with a 200 mesh nylon filter cloth, and then methyl ethyl ketone was distilled off with an evaporator. The coarse particles were removed by centrifugation, and the mixture was prepared with water to obtain an aqueous pigment dispersion C3-a having a nonvolatile content of 18%.

<Example 8> (Synthesis of aqueous pigment dispersion M1-a)
An aqueous pigment dispersion M1-a having a nonvolatile content of 20% was obtained in the same manner as in Synthesis Example 3 except that the dispersion C1 of Example 2 was changed to the dispersion M1.

<Example 9> (Synthesis of aqueous pigment dispersion Y1-a)
An aqueous pigment dispersion Y1-a having a nonvolatile content of 20% was obtained in the same manner as in Synthesis Example 3 except that the dispersion C1 of Example 2 was changed to the dispersion Y1.

<Example 10> (Synthesis of aqueous pigment dispersion C1-f)
In a separable flask, 170 parts of dispersion C1 obtained in Production Example 1, 36 parts of water, 5.7 parts of benzyl methacrylate, 0.3 part of methacrylic acid (infinite solubility in water) and 1 part of 20% KOH aqueous solution were placed in a separable flask. Preparation, thermometer, stirrer, nitrogen introduction tube, and cooling tube were set. After stirring at 40 ° C. for 2 hours, the temperature was raised to 80 ° C. When the temperature reached 80 ° C., a solution in which 0.06 part of potassium persulfate was dissolved in 1.8 parts of water was added. Heated at 80 ° C. for 10 hours. In addition, 3 hours and 5 hours after the temperature reached 80 ° C., a solution in which 0.06 part of potassium persulfate was dissolved in 1.8 parts of water was added. After completion of the reaction, the reaction mixture was filtered with a 200 mesh nylon filter cloth, and then methyl ethyl ketone was distilled off with an evaporator. The coarse particles were removed by centrifugation, and the mixture was prepared with water to obtain an aqueous pigment dispersion C1-f having a nonvolatile content of 20%.

<Example 11> (Synthesis of aqueous pigment dispersion M2-a)
The same operation as in Synthesis Example 10 was performed except that the C2 dispersion liquid in Synthesis Example 10 was changed to the M2 dispersion liquid.

<Comparative Example 1> (Synthesis of aqueous pigment dispersion C1-g)
Synthetic Example 3 except that 6 parts of benzyl methacrylate in Synthesis Example 6 are changed to 4.8 parts of benzyl methacrylate and 1.2 parts of reactive surfactant Aquacron KH-10 (solubility in water of 10% by mass or more). The same operation was performed to obtain an aqueous pigment dispersion C1-g having a nonvolatile content of 20%.

<Comparative Example 2> (Synthesis of aqueous pigment dispersion C1-h)
The same operation as in Synthesis Example 3 was performed except that 6 parts of benzyl methacrylate in Synthesis Example 6 were changed to 6 parts of benzyl methacrylate and 0.3 parts of emulsifier EMAL 10 (solubility in water of 10% by mass or more). % Aqueous pigment dispersion C1-h was obtained.

<Comparative Example 3> (Synthesis of aqueous pigment dispersion C1-i)
In Synthesis Example 14, 36 parts of water, 5.7 parts of benzyl methacrylate, 0.3 part of methacrylic acid and 1 part of a 20% KOH aqueous solution were mixed with 36.3 parts of water, 4.8 parts of benzyl methacrylate, 1.2 parts of methacrylic acid. The same operation as in Synthesis Example 3 was performed except that 3.9 parts by weight and 20% KOH aqueous solution were used. Since 20% of methacrylic acid having a solubility in water of 5% or more with respect to the total amount of the monomer was contained, a large amount of blisters were generated, and the resin particles containing the pigment were precipitated. The yield after filtration was 30% or less, and a usable pigment dispersion could not be obtained.

<Comparative Example 4> (Synthesis of aqueous pigment dispersion C1-j)
334 parts of dispersion C1 obtained in Production Example 1 and 44 parts of water were charged into a separable flask, and a thermometer, a stirrer, a nitrogen introduction pipe, and a cooling pipe were set. Immediately after the preparation, the temperature was raised to 80 ° C., and a solution prepared by dissolving 12 parts of benzyl methacrylate and 0.06 part of potassium persulfate in 30 parts of water was added dropwise over 2 hours. A large amount of blisters occurred during the dropping, and the resin particles containing the pigment were precipitated. The yield after filtration was 30% or less, and a usable pigment dispersion could not be obtained.

Table 1 shows a summary of Examples 1-12 and Comparative Examples 1-2. In Table 1, (meth) acrylic copolymer A particles containing the pigments obtained in Production Examples 1 to 8 (abbreviated as “pigment / (meth) acrylic copolymer A” in the table). The average particle diameter change rate under condition Q is shown. Condition Q is shown below.
<Condition Q>
The aqueous solution containing 20 parts of the (meth) acrylic copolymer A particles containing the pigment and 80 parts of water is stored in a thermostatic bath at 70 ° C. for 3 days. It is assumed that it is a value obtained by dividing the subsequent average particle diameter by the average particle diameter before Condition Q.
After storage for 3 days in a constant temperature bath at 70 ° C. with the following ink composition, the rate of change in particle size (the value obtained by dividing the average particle size after condition Q by the average particle size before condition Q) is measured, and 0.9 to 1.1 was indicated by ○, and the others were indicated by ×.

  Table 1 also shows the amount of carboxy of (meth) acrylic copolymer A and the final number of moles of carboxyl groups (theoretical value) of the aqueous pigment dispersions obtained in Examples 1 to 11 and Comparative Examples 1 to 4. showed that. The final number of moles of carboxyl groups (theoretical value) represents the number of millimoles of carboxyl groups per gram of resin ((meth) acrylic copolymer A + (meth) acrylic copolymer B) contained in the aqueous pigment dispersion. It is.

From Examples 1 to 10, the pigment dispersions obtained by the method of the present invention all had a yield exceeding 80% and were stably obtained. In Example 11, the average particle diameter change rate under the condition Q of the (meth) acrylic copolymer A particles containing the pigment deviates from the range of 0.9 to 1.1. It was found that aggregation occurred. Therefore, the yield decreased compared to other dispersions.
On the other hand, regarding Comparative Example 1 and Comparative Example 2 using a surfactant, the yield exceeded 80%, and was obtained stably.
From Comparative Example 3, it was found that when methacrylic acid having a high solubility in water was used as one material of the polymerizable monomer composition C in excess of 5%, a large amount of aggregates were formed during the polymerization. Further, it was found from Comparative Example 4 that a large amount of agglomerates was produced even when the step of impregnating the polymerizable monomer composition C before the polymerization was not obtained.

(Creation and evaluation of water-based pigment ink for inkjet recording)
<Example 12> (Evaluation of suitability of water-based pigment ink for piezoelectric inkjet recording)
A water-based pigment ink for piezo ink jet recording was prepared with reference to Example 1 described in JP-A-7-228808. The ink composition is shown below.

Aqueous pigment dispersion C1-a 26.0 parts Triethylene glycol monobutyl ether 10.0 parts Diethylene glycol 15.0 parts Surfinol 465 (manufactured by Air Products) 0.8 parts Water 48.2 parts

(Performance evaluation of water-based pigment ink for inkjet recording)
The aqueous pigment ink for ink-jet recording prepared in Example 12 was filled in a cartridge of a commercially available piezo-type ink-jet printer (MJ-8000C type, manufactured by Seiko Epson Corporation), and printed on various recording media.

(Normal paper color evaluation)
The solid density of the printed material on recording paper Xerox 4024 (manufactured by Fuji Xerox Co., Ltd.), which is plain paper, was measured for optical density with a Macbeth reflection densitometer spectrum eye, and the color development was evaluated as the plain paper characteristics. Displayed as OD in the table.

<Example 13>
The ink composition of Example 12 was
Aqueous pigment dispersion C1-b 28.0 parts Triethylene glycol monobutyl ether 10.0 parts diethylene glycol 15.0 parts Surfinol 465 (manufactured by Air Products) 0.8 parts Water 46.2 parts In the same manner as in No. 12, an aqueous pigment ink for piezo ink jet recording was prepared and evaluated.

<Example 14>
An aqueous pigment ink for piezo ink jet recording was prepared and evaluated in the same manner as in Example 12 except that the aqueous pigment dispersion C1-b of Example 13 was changed to the aqueous pigment dispersion C1-c.

<Example 15>
An aqueous pigment ink for piezo ink jet recording was prepared and evaluated in the same manner as in Example 12 except that the aqueous pigment dispersion C1-b of Example 13 was changed to the aqueous pigment dispersion C1-d.

<Example 16>
The ink composition of Example 12 was
Aqueous pigment dispersion C1-e 30.0 parts Triethylene glycol monobutyl ether 10.0 parts diethylene glycol 15.0 parts Surfynol 465 (manufactured by Air Products) 0.8 parts Water 44.2 parts Example In the same manner as in No. 12, an aqueous pigment ink for piezo ink jet recording was prepared and evaluated.

<Example 17>
An aqueous pigment ink for piezo inkjet recording was prepared and evaluated in the same manner as in Example 12 except that the aqueous pigment dispersion C1-b of Example 13 was changed to the aqueous pigment dispersion C1-f.

<Example 18>
The ink composition of Example 12 was
Aqueous Pigment Dispersion C3-a (Synthesis Example 7) 31.1 parts triethylene glycol monobutyl ether 10.0 parts diethylene glycol 15.0 parts Surfinol 465 (manufactured by Air Products) 0.8 parts water 43.1 parts Then, a water-based pigment ink for piezo ink jet recording was prepared and evaluated in the same manner as in Example 12.

<Example 19>
The ink composition of Example 12 was
Aqueous pigment dispersion C2-a 26.0 parts Triethylene glycol monobutyl ether 10.0 parts diethylene glycol 15.0 parts Surfinol 465 (manufactured by Air Products) 0.8 parts Water 48.2 parts In the same manner as in No. 12, an aqueous pigment ink for piezo ink jet recording was prepared and evaluated.

<Example 20>
The ink composition of Example 12 was
Aqueous pigment dispersion M1-a 42.0 parts Triethylene glycol monobutyl ether 10.0 parts diethylene glycol 15.0 parts Surfinol 465 (manufactured by Air Products) 0.8 parts Water 32.2 parts In the same manner as in No. 12, an aqueous pigment ink for piezo ink jet recording was prepared and evaluated.

<Example 21>
An aqueous pigment ink for piezo ink jet recording was prepared and evaluated in the same manner as in Example 12 using the aqueous pigment dispersion Y1-a instead of the aqueous pigment dispersion M1-a of Example 13.

<Comparative Example 5>
An aqueous pigment ink for piezo ink jet recording was prepared using the dispersion C1 obtained in Production Example 1. The ink composition is shown below.
Dispersion C1 21.8 parts triethylene glycol monobutyl ether 10.0 parts diethylene glycol 15.0 parts Surfynol 465 (manufactured by Air Products) 0.8 part water 52.4 parts The evaluation method is the same as in Example 12. I did it.

<Comparative Example 6>
An aqueous pigment ink for piezo inkjet recording was prepared in the same manner as in Example 12 using the dispersion C2 obtained in Production Example 4 instead of the dispersion C1 in Comparative Example 5, and evaluated in the same manner.

<Comparative Example 7>
An aqueous pigment ink for piezo ink jet recording was prepared and evaluated in the same manner as in Example 12 except that the aqueous pigment dispersion C1-b of Example 13 was changed to the aqueous pigment dispersion C1-g.

<Comparative Example 8>
An aqueous pigment ink for piezo inkjet recording was prepared and evaluated in the same manner as in Example 12 except that the aqueous pigment dispersion C1-b of Example 13 was changed to the aqueous pigment dispersion C1-h.

<Comparative Example 9>
The ink composition of Comparative Example 6 was
Dispersion M1 32.7 parts Triethylene glycol monobutyl ether 10.0 parts diethylene glycol 15.0 parts Surfynol 465 (Air Products) 0.8 parts Water 41.5 parts A water-based pigment ink for piezo inkjet recording was prepared and evaluated.

<Comparative Example 10>
An aqueous pigment ink for piezo ink jet recording was similarly prepared using the dispersion Y1 instead of the dispersion M1 of Comparative Example 9, and evaluated in the same manner as in Example 12.

  The measurement results of each of these evaluation items are collectively shown in Tables 2 to 4.

As can be seen from Tables 2 to 4 above, all of the aqueous pigment inks for inkjet recording obtained from the aqueous pigment dispersion-containing composition of the present invention are O.D. D. The values were as high as 1.20 or more (1.20 or more for cyan, 1.25 or more for magenta, 1.27 or more for yellow), and it was found that excellent color developability was obtained.
In contrast, the water-based pigment inks for ink jet recording of Comparative Examples 7 and 8 using an emulsifier are O.D. D. The value was less than 1.20, and there were white portions where no ink was applied on the printed surface, and the color development was not excellent as compared with the Examples. Comparative Examples 5, 6, 9 and 10 are examples in which (meth) acrylic copolymer B is not included in (meth) acrylic copolymer A particles containing a pigment. D. The value was as low as 1.18 or less.

The aqueous pigment dispersion according to the present invention includes aqueous ink materials such as water-based pigment inks for inkjet recording and water-based gravure inks, water-based ink materials such as inks for writing and color filters, and water-based paints for automobiles and cans. Can also be used suitably.

Claims (7)

An aqueous pigment dispersion having water and a (meth) acrylic copolymer particle containing a pigment, the solubility in water at 20 ° C. being 5 in the presence of the (meth) acrylic copolymer A particle containing the pigment It contains at least one (meth) acrylic copolymer B obtained by polymerizing a polymerizable monomer composition containing 95% by mass or more of one or more polymerizable monomers having a mass% or less. Aqueous pigment dispersion. 2. The aqueous pigment dispersion according to claim 1, wherein the (meth) acrylic copolymer A particles containing the pigment have an average particle diameter change rate of 0.9 to 1.1 under condition Q. 3. (However, the condition Q is that an aqueous solution containing 20 parts of (meth) acrylic copolymer A particles containing the pigment and 80 parts of water is stored in a constant temperature bath at 70 ° C. for 3 days, and the average particle (The change rate of the diameter is a value obtained by dividing the average particle diameter after the condition Q by the average particle diameter before the condition Q) The aqueous pigment dispersion according to claim 1, wherein the (meth) acrylic copolymer A has a carboxyl group, and the number of moles of the carboxyl group per 1 g of the copolymer is 1.2 mmol or more. The aqueous pigment dispersion according to claim 1, wherein the (meth) acrylic copolymer B is polymerized inside the (meth) acrylic copolymer A particles containing the pigment. 2. The aqueous pigment dispersion according to claim 1, comprising 5 to 100 parts of the (meth) acrylic copolymer B with respect to 100 parts of the pigment in the (meth) acrylic copolymer A particles containing the pigment. An aqueous ink comprising the aqueous pigment dispersion according to any one of claims 1 to 5. A method for producing an aqueous pigment dispersion having water and (meth) acrylic copolymer particles containing a pigment, in the absence of a surfactant,
(1) A polymerizable monomer composition containing 95% by mass or more of one or more polymerizable monomers having a solubility in water at 20 ° C. of 5% by mass or less in (meth) acrylic copolymer A particles containing a pigment. Impregnating with C;
(2) A method for producing an aqueous pigment dispersion, comprising a step of polymerizing the polymerizable monomer composition C in the particles A in an aqueous solvent.