JP2011046800A - Method of manufacturing aqueous pigment dispersion and aqueous ink for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an aqueous pigment dispersion with high manufacturing efficiency that sharply reduces coarse particles existing in an aqueous pigment dispersion thereby to attain micronization and enhancement of dispersion stability of dispersed particles and achieves enhancement of preservation stability and good jetting stability when an aqueous ink for jet recording is prepared from the same. <P>SOLUTION: The method of manufacturing the aqueous pigment dispersion comprises a kneading step of kneading a mixture of a quinacridone pigment (a), a styrene-acrylic acid copolymer (c), a basic compound (d) and a polyoxyalkylene adduct (e) of glycerine to prepare a pigment dispersion which is solid at ordinary temperature and a mixing step of mixing an aqueous medium with the pigment dispersion thereby to lower the viscosity thereof to liquefy the pigment dispersion. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing an aqueous pigment dispersion. Furthermore, the present invention relates to a method for producing a water-based ink for inkjet recording, which is produced by using the method for producing an aqueous pigment dispersion and further subjecting it to a dilution step.

Water-based inks that use water as the main solvent have excellent characteristics that they have no or no toxicity, such as fire hazard and mutagenicity, like solvent inks. For this reason, water-based ink has become the mainstream of ink jet recording as ink for ink jet recording other than industrial use.
The characteristics required for the ink used for ink jet recording are (1) a uniform image with high color development, high resolution and high density without blurring on the recording medium, and (2) drying of the ink at the nozzle tip. (3) The ink has good drying stability on the recording medium, (4) The image has good fastness, (5) The long-term storage stability is good.
Conventionally, as a water-based ink for ink jet recording, a dye has been used as a colorant because it has high dissolution stability, has low color clogging, has good color development, and enables high-quality printing. An image using a dye has a problem that water resistance and light resistance are inferior.

  In order to solve this problem, conversion of colorants from dyes to pigments has been actively pursued. Pigment inks can be expected to have excellent water resistance and light resistance, but they are inferior in color developability compared to dyes, and nozzle clogging due to pigment aggregation and sedimentation becomes a problem. In view of this, various studies have been conducted on a method of dispersing finely divided pigments in an aqueous medium using a polymer dispersant and the dispersion method itself.

For example, an aqueous solution in which a water-soluble resin and an alkali component are dissolved in water is prepared, and a pigment is added thereto and stirred sufficiently, and then dispersed using a high-speed sand mill having a high dispersion efficiency to obtain an aqueous pigment dispersion. A method has been proposed (see, for example, Patent Document 1).
However, this method has a problem that the dispersion time is long and the production efficiency is low. Further, in the aqueous pigment dispersion obtained in this way, the dispersion stability of the pigment is still insufficient.

  In view of such a situation, a dispersion method has been proposed that passes through a pretreatment step in which a pigment and a polymer dispersant are kneaded in advance (for example, see Patent Document 2). As a result, the production efficiency was improved and the pigments could be made finer. However, even if finer particles are achieved, the dispersion stability of the pigment is insufficient, so that the storage stability of the ink remains to be improved. In particular, quinacridone pigments used in the production of magenta inks are hydrogen-bonded pigments that function as pigments through intermolecular hydrogen bonds. Pigment particles are strongly aggregated, and coarse particles that cannot be dispersed are contained in the ink. It was easy to remain. In addition, the pigment particles finely divided by dispersion are liable to re-aggregate, making it difficult to achieve dispersion stability.

  Therefore, a method for producing an aqueous pigment dispersion using a quinacridone pigment, a phthalimidomethylated quinacridone compound or further a quinacridone sulfonic acid compound, and an anionic group-containing organic polymer compound having a glass transition point of −20 to 60 ° C. is proposed. (For example, see Patent Document 3). This aqueous pigment dispersion is excellent in dispersibility and dispersion stability, has a small increase in particle diameter even when left at high temperature for a long period of time, can be maintained in a low viscosity range with little increase in viscosity, and has characteristics as an aqueous ink for inkjet recording. It is excellent.

  However, even if any of the above formulas is used for dispersing the pigment, the dispersion contains coarse particles that are not sufficiently crushed and undispersed. When used as a water-based ink for inkjet recording, it is necessary to remove coarse particles by centrifugal treatment / filtration treatment. Such residual coarse particles cause a reduction in pigment yield and greatly reduce production efficiency, which has many problems in terms of productivity, and is particularly difficult to solve when quinacridone pigments are used. there were.

JP 2001-262038 A Japanese Patent Laid-Open No. 2003-226832 JP 2004-043791 A

  The object of the present invention is to greatly reduce the poorly dispersed coarse particles, and as a result, the pigment is stably dispersed, and a good dispersion state is maintained even during long-term storage, and the aqueous pigment dispersion It is to provide a method for producing a water-based pigment dispersion capable of obtaining a water-based ink for ink jet recording having excellent ejection stability, and at the same time, the time required for production while having the above-mentioned good characteristics. It is to provide a method for producing a short aqueous pigment dispersion with high production efficiency.

As a result of intensive studies on this problem, the present inventors conducted a step of kneading a mixture containing a quinacridone pigment, a styrene-acrylic acid copolymer having a specific configuration, a basic compound, and a polyoxyalkylene adduct of glycerin. It has been found that not only can coarse particles be greatly reduced by using the aqueous pigment dispersion manufacturing method, but also the conventional dispersion device can be omitted and the above problem can be achieved. The present invention has been reached. That is, the present invention kneads a mixture containing a quinacridone pigment (a), a styrene-acrylic acid copolymer (c), a basic compound (d) and a polyoxyalkylene adduct (e) of glycerin, Provided is a method for producing an aqueous pigment dispersion having a kneading step for preparing a pigment dispersion that is solid at room temperature and a mixing step for mixing an aqueous medium with the pigment dispersion in the previous period.
In the method for producing an aqueous pigment dispersion of the present invention, it is preferable to contain a quinacridone pigment derivative in the mixture in the kneading step.

The reason why the method for producing an aqueous pigment dispersion of the present invention exerts a great effect on the reduction of coarse particles is not necessarily clear, but the following reasons are conceivable.
In the kneading, the process of dispersing the pigment in the medium is generally considered to go through the following three steps if further finely decomposed. That is, a step of wetting the pigment with respect to the dispersion medium, a step of refining the pigment using a shearing force, and a step of stabilizing the finer state of the pigment by adsorption of a resin having dispersibility. The dispersion of the pigment is basically reversible, and even if it can be dispersed, it is difficult to keep the dispersion state stable unless measures are taken to suppress reaggregation of the pigment. Therefore, it is necessary to stabilize the dispersion by forming a resin adsorption layer on the pigment particle surface. In order to stabilize the dispersion, the affinity of the dispersion medium for the pigment particle surface and the resin is important. In order for the resin to be adsorbed on the pigment particle surface, the affinity between the resin and the pigment particle surface must be higher than the affinity between the resin and the dispersion medium. However, if the affinity between the resin and the dispersion medium is too low, the resin adsorption layer is not oriented in the dispersion medium, making it difficult to achieve dispersion stability. On the other hand, when looking at the affinity between the pigment particle surface and the dispersion medium, if the affinity is too high, the adsorption of the resin is inhibited. Conversely, if the affinity is too low, the wetting process, which is one element of the dispersion mechanism, is efficient. It does not progress well and it is difficult to achieve dispersion itself. Therefore, the selection of the dispersion medium must take into account the balance of the affinity with the pigment and the resin.

  If the solvent used in the conventional dispersion medium pair is used as it is, the affinity of the dispersion medium containing the solvent to the pigment is too high to inhibit the adsorption of the resin, so that the dispersion of the pigment cannot be obtained and coarse particles cannot be obtained. It is thought that the increase of For this reason, a dispersion process using a dispersion apparatus for the purpose of reducing coarse particles is necessary. In the case of the polyoxyalkylene adduct of glycerin used in the present invention, the dispersion medium containing the adduct has an appropriate affinity for the pigment, so that swelling of the resin is considered to be partly dissolved while the wetting of the pigment proceeds. As a result, resin adsorption to the pigment also proceeds. For this reason, the refinement of the pigment and the stabilization of the dispersion proceed very efficiently, and the coarse particles in the dispersion can be greatly reduced, so that further dispersion steps using a dispersion device can be omitted. It is done.

  The method for producing an aqueous pigment dispersion of the present invention comprises a quinacridone pigment (a), a styrene-acrylic acid copolymer (c), a basic compound (d), and a polyoxyalkylene adduct (e) of glycerin. Since the kneaded product has a kneading step of kneading the kneaded material to create a solid pigment dispersion at room temperature and mixing the aqueous medium with the pigment dispersion, in the kneading step, under high shear force, The process of crushing into fine particles and coating the crushed pigment surface with resin proceeds well, and the aqueous pigment dispersion can be produced with high production efficiency by the subsequent mixing step. Further, the production method of the present invention can greatly reduce the number of coarse particles in the aqueous pigment dispersion, and can maintain the dispersion state of the pigment stably over a long period of time. Furthermore, when an aqueous ink for inkjet recording is further produced from an aqueous pigment dispersion prepared by using the method for producing an aqueous pigment dispersion of the present invention, it has good dispersibility and good dischargeability with a small number of coarse particles. An excellent ink was obtained.

Hereinafter, first, various raw materials used in the production method of the present invention will be described in detail, and then, the method for producing the aqueous pigment dispersion of the present invention using these raw materials will be described in detail.
(Quinacridone pigment)
As the pigment type of the quinacridone pigment (a) used in the present invention, any known and commonly used pigment types can be used. I. Dimethylquinacridone pigments such as CI Pigment Red 122; I. Pigment red 202, C.I. I. Dichloroquinacridone pigments such as CI Pigment Red Red 209; I. Examples thereof include unsubstituted quinacridone such as CI Pigment Violet 19 and a mixture or solid solution of at least two pigments selected from these pigments. The form of the pigment may be a dry pigment in the form of powder, granule or block, or a wet cake or slurry.

(Quinacridone pigment derivatives)
The quinacridone pigment derivative (b) preferably used in the present invention includes a dialkylaminomethyl group, an arylamidomethyl group, a sulfonic acid amide group, a sulfonic acid group and a salt thereof, and a phthalimide group on the pigment skeleton of the quinacridone pigment. And the like.
Among the quinacridone pigment derivatives (b) preferably used in the present invention, a compound represented by the following general formula (1) is more preferable.

（１）
｛式中、Ｒ１〜Ｒ１０は各々独立的に水素原子、塩素原子、炭素数１〜８個のアルキル基若しくはアルコキシ基、又は一般式（２）

(1)
{Wherein R1 to R10 are each independently a hydrogen atom, a chlorine atom, an alkyl group or an alkoxy group having 1 to 8 carbon atoms, or a general formula (2)

（２）
（式中、Ｒ_１１は炭素数１〜８個のアルキレン基若しくはアルケニレン基、Ｒ_１２〜Ｒ_１５は各々独立的に水素原子、炭素数１〜８個のアルキル基若しくはアルコキシ基、又はフェニル基を表す。）で表される基であり、Ｒ_１〜Ｒ_１０の少なくとも一つは前記式IIで表される基である。｝
一般式（１）で表される化合物の中でさらに好ましい化合物としては、下記一般式（３）で表される化合物が上げられる。

(2)
(In the formula, R ₁₁ represents an alkylene group or alkenylene group having 1 to 8 carbon atoms, R _{12 to} R ₁₅ each independently represents a hydrogen atom, an alkyl group or alkoxy group having 1 to 8 carbon atoms, or a phenyl group. And at least one of R _{1 to} R ₁₀ is a group represented by Formula II. }
Among the compounds represented by the general formula (1), more preferable compounds include compounds represented by the following general formula (3).

（３）
（式中、ＲとＲ'とは互いに独立的に水素原子、塩素原子又は炭素数１〜５個のアルキル基若しくはアルコキシ基であり、ｍは０、１または２であり、ｎは１〜４である。）
さらに下記構造式（４）で表される基を有する下記構造式（５）で表される化合物がより好ましい。

(3)
(In the formula, R and R ′ are each independently a hydrogen atom, a chlorine atom, an alkyl group or an alkoxy group having 1 to 5 carbon atoms, m is 0, 1 or 2, and n is 1 to 4) .)
Further, a compound represented by the following structural formula (5) having a group represented by the following structural formula (4) is more preferable.

（４）

(4)

（５）
（式中、ｍ及びｎはそれぞれ独立的に０、１、２又は３を表す。但し、ｍとｎが共に０となることはない。）

(5)
(In the formula, m and n each independently represent 0, 1, 2, or 3, provided that m and n are not 0.)

In addition, as the compound represented by the chemical structural formula (5) used in the present invention, among the compounds represented by the chemical structural formula (5), the group represented by the chemical structural color (4) per molecule A compound having one or a plurality of compounds is preferred, and a compound having an average of 1 to 2 compounds per molecule is preferred. Particularly preferred is a compound having an average of 1 to 1.5 molecules per molecule. When the number of groups represented by the chemical structural formula (4) is one or more on average per molecule, the effect on dispersibility tends to appear favorably. There is a high possibility that the effect will be good.
When the compound represented by the general formula (1) is, for example, a compound having a group represented by the above formula chemical structural formula (4), unsubstituted quinacridone, dimethylquinacridone, dichloroquinacridone, etc. and phthalimide and formaldehyde or It can be synthesized by reacting paraformaldehyde with concentrated sulfuric acid.

  In the aqueous pigment dispersion of the present invention, the amount of the quinacridone pigment derivative (b) used relative to 100 parts by mass of the quinacridone pigment (a) is preferably 1 part by mass or more, and preferably 2 to 15 parts by mass. More preferred. When the amount used is in the above range, the storage stability of the aqueous dispersion and the ink composition for ink jet recording produced therefrom is good. In addition, the ink discharge state is particularly good when printing is performed with a thermal jet printer.

(Styrene-acrylic acid copolymer)
The styrene-acrylic acid copolymer (c) used in the present invention contains a styrene monomer and at least one of acrylic acid and methacrylic acid as a monomer component.
A known compound can be used as the styrene monomer. For example, alkylstyrene such as styrene, α-methylstyrene, β-methylstyrene, 2,4-dimethylstyrene, α-ethylstyrene, α-butylstyrene, α-hexylstyrene, 4-chlorostyrene, 3-chlorostyrene, There are halogenated styrenes such as 3-bromostyrene, 3-nitrostyrene, 4-methoxystyrene, vinyltoluene and the like.

The use ratio of the styrene monomer that is the raw material of the styrene-acrylic acid copolymer (c) is more preferably 50 to 90% by mass, and particularly preferably 70 to 90% by mass. When the ratio of the styrene monomer used is 50% by mass or more, the affinity of the styrene-acrylic acid copolymer (c) to the quinacridone pigment (a) is improved, and the dispersion stability of the aqueous pigment dispersion is improved. Tend to. Also, the plain paper recording characteristics of the aqueous inkjet recording ink obtained from the aqueous pigment dispersion are improved, the image recording density tends to be high, and the water resistance tends to be good. When the amount of the styrenic monomer is in the above range of 90% by mass or less, the dispersibility of the quinacridone pigment coated with the styrene-acrylic acid copolymer (c) in an aqueous medium can be favorably maintained. The dispersibility and dispersion stability of the pigment in the pigment dispersion can be improved. Furthermore, the printing stability when used as an ink composition for inkjet recording is improved.
The styrene-acrylic acid copolymer (c) of the present invention is obtained by copolymerization of at least one of a styrene monomer and an acrylic acid monomer and a methacrylic acid monomer, but it is preferable to use acrylic acid and methacrylic acid in combination. The reason is that the copolymerization at the time of resin synthesis is improved, the uniformity of the resin is improved, and as a result, the storage stability is improved, and a more finely divided pigment dispersion tends to be obtained. It is.
In the styrene-acrylic acid copolymer (c) used in the present invention, the total during the copolymerization of the styrene monomer, the acrylic acid monomer, and the methacrylic acid monomer is preferably 95% by mass or more based on the total monomer components. .

  In addition to the styrene monomer, acrylic acid monomer, and methacrylic acid monomer, a known monomer that can be copolymerized with these monomers may be copolymerized with the styrene-acrylic acid copolymer (c). Examples of such monomers include methyl acrylate, methyl methacrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate, tert-butyl acrylate, 2-ethylbutyl acrylate, 1,3-dimethylbutyl Acrylic esters and methacrylic such as acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, ethyl methacrylate, n-butyl methacrylate, 2-methylbutyl methacrylate, pentyl methacrylate, heptyl methacrylate, nonyl methacrylate Acid esters; 3-ethoxypropyl acrylate, 3-ethoxybutyl acrylate, dimethylaminoethyl acrylate, 2 Acrylic acid ester derivatives and methacrylic acid ester derivatives such as hydroxyethyl acrylate, 2-hydroxybutyl acrylate, ethyl-α- (hydroxymethyl) acrylate, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate; phenyl acrylate Acrylic acid aryl esters and acrylic acid aralkyl esters such as benzyl acrylate, phenylethyl acrylate, phenylethyl methacrylate; monoacrylic acid of polyhydric alcohols such as diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, bisphenol A Esters or monomethacrylates; dimethyl maleate, malee Mention may be made of maleic acid dialkyl esters such as diethyl acid, vinyl acetate and the like. One or more of these monomers can be added as monomer components.

  As a method for producing the styrene-acrylic acid copolymer (c), a usual polymerization method can be adopted, and a method of performing a polymerization reaction in the presence of a polymerization catalyst, such as solution polymerization, suspension polymerization, bulk polymerization and the like. Can be mentioned. Examples of the polymerization catalyst include 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 1,1′-azobis (cyclohexane-1-carbonitrile), Examples thereof include benzoyl peroxide, dibutyl peroxide, butyl peroxybenzoate, and the amount used is preferably 0.1 to 10.0% by mass of the vinyl monomer component.

The weight average molecular weight of the styrene-acrylic acid copolymer (c) used in the present invention is preferably in the range of 5,000 to 20,000, and preferably in the range of 5,000 to 18,000. More preferred. Especially, it is especially preferable that it exists in the range of 5,500-15,000. When the weight average molecular weight is 5,000 or more, the ease of initial dispersion and particle size reduction of the quinacridone pigment (a) is slightly reduced, but the long-term storage stability of the aqueous pigment dispersion tends to be improved. , There is a tendency that precipitation due to aggregation of pigments is difficult to occur. When the weight average molecular weight of the styrene-acrylic acid copolymer (c) is 20,000 or less, the viscosity of the ink composition for inkjet recording prepared from the aqueous pigment dispersion using the styrene-acrylic acid copolymer (c) is very appropriate, and the ink The discharge stability tends to be improved.
Here, the weight average molecular weight is a value measured by a GPC (gel permeation chromatography) method, and is a value converted to a molecular weight of polystyrene used as a standard substance.
The styrene-acrylic acid copolymer (c) used in the present invention may be a random copolymer or a graft copolymer. As the graft copolymer, a copolymer of polystyrene or a nonionic monomer copolymerizable with styrene and styrene is used as a trunk or branch, and a copolymer of acrylic acid, methacrylic acid and other monomers including styrene is branched. Or the graft copolymer used as a trunk can be shown as the example. The styrene-acrylic acid copolymer (c) may be a mixture of this graft copolymer and random copolymer.

The styrene-acrylic acid copolymer (c) used in the present invention has a carboxyl group derived from an acrylic acid monomer and a methacrylic acid monomer, and the acid value is preferably 120 to 220 (mg KOH / g), 150 More preferably, it is -200 (mgKOH / g). If the acid value is 120 (mg KOH / g) or more, the hydrophilicity is sufficiently large and the dispersion stability of the pigment in the aqueous pigment dispersion tends to be good. On the other hand, when the acid value is 220 (mgKOH / g) or less, the aggregation of the pigment tends to be less likely to occur, and the printed matter using the ink composition for inkjet recording obtained from the aqueous pigment dispersion has sufficient water resistance. It tends to maintain sex.
The mass ratio of the styrene-acrylic acid copolymer (c) to the total mass of the quinacridone pigment (a) and the quinacridone pigment derivative (b) in the kneading step, c / (a + b) is 0.15 to 0.5. It is.
The acid value here is a value measured in accordance with Japanese Industrial Standard “K 0070: 1992. Test methods for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponified product of chemical products”. , The amount (mg) of potassium hydroxide necessary to completely neutralize 1 g of resin.

(Basic compound)
The styrene-acrylic acid copolymer (c) is used in the form of coexisting the basic compound (d) in order to neutralize the acrylic acid site and improve the dispersibility in an aqueous medium. The basic compound (d) softens the styrene-acrylic acid copolymer in the kneading step, smoothes the coating process of the pigment with the resin, and improves the dispersibility of the resin-coated pigment in the aqueous medium. . As the basic compound (d), either an inorganic basic compound or an organic basic compound can be used. Examples of the organic basic compound include amines such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and triethylamine; and alcohol amines such as triethanolamine, diethanolamine, and methyldiethanolamine. Examples of inorganic basic compounds include alkali metal hydroxides such as potassium and sodium; carbonates of alkali metals such as potassium and sodium; carbonates of alkaline earth metals such as calcium and barium; ammonium hydroxide and the like. It can be illustrated.
In particular, alkali metal hydroxides and alcohol amines are suitable from the viewpoint of dispersibility and storage stability when prepared from the pigment dispersion of the present invention to an aqueous pigment dispersion, and further to an ink composition for inkjet recording. is there. These alkali metal hydroxides and alcohol amines can also be used as a mixture. Among these basic compounds, alkali metal hydroxides typified by potassium hydroxide, sodium hydroxide, and lithium hydroxide contribute to lowering the viscosity of aqueous pigment dispersions and stabilize the ejection of ink for inkjet recording. From the viewpoint of the properties, potassium hydroxide is particularly preferable.

The basic compound is preferably used in an aqueous solution or an organic solvent solution, and more preferably in an aqueous solution. The concentration of the aqueous solution or organic solvent solution of the basic compound (d) is preferably 20% by mass to 50% by mass. Moreover, it is preferable to use alcohol solvents, such as methanol, ethanol, isopropanol, as an organic solvent which melt | dissolves a basic compound (d). Among these, in the present invention, it is preferable to use an aqueous solution of the basic compound (d), and it is particularly preferable to use an aqueous solution of an alkali metal hydroxide. The addition amount of the basic compound is preferably in the range of 80 to 120% as the neutralization rate based on the acid value of the styrene-acrylic acid copolymer (b). Setting the neutralization rate to 80% or more from the viewpoint of improving the dispersion speed in the aqueous medium when preparing an aqueous pigment dispersion from the pigment dispersion, the dispersion stability of the aqueous pigment dispersion, and the storage stability preferable. From the viewpoint of preventing gelation during long-term storage of the aqueous pigment dispersion or the ink for inkjet recording, the neutralization rate is preferably 120% or less from the viewpoint of the water resistance of the printed matter produced with the ink.
In the present invention, the neutralization rate is a numerical value indicating how much the compounding amount of the basic compound is relative to the amount necessary for neutralization of all carboxyl groups in the styrene-acrylic acid copolymer (b). And is calculated by the following equation.

(Polyoxyalkylene adduct of glycerin)
Usually, when kneading a mixture containing a resin and a pigment, an appropriate amount of a water-soluble organic solvent is added to make the mixture into one clay-like mass having a high solid content ratio, and kneading is performed by applying a high shearing force. As a water-soluble organic solvent for this purpose, it has a high boiling point and does not easily evaporate during kneading, and even if it remains in the kneaded product, it is originally added to the kneaded product as a component of an aqueous medium in the mixing step which is a post-process. A wetting agent is preferably used because it can be added and does not need to be removed.

The polyoxyalkylene adduct (e) of glycerin used in the present invention is obtained by adding a polyoxyalkylene group to at least one site of the hydroxyl group of glycerin. The chain lengths of the polyoxyalkylene groups at the respective sites are preferably equal. These may be known and conventional ones, and those having a hydroxyl value in the range of 100 (mgKOH / g) to 600 (mgKOH / g) are preferred, and 145 (mgKOH / g) to 500 ( More preferred are those in the mgKOH / g range. When the hydroxyl value is less than 100 (mgKOH / g), in a dispersion medium system containing a pigment, a styrene acrylic acid copolymer, and a polyoxyalkylene adduct of glycerin, the affinity between the pigment and the dispersion medium is Coarse particles that are too high compared to the affinity of the copolymer, tend to be less likely to swell, which appears to be a partially dissolved state of the copolymer, and the stabilization of the dispersed pigment due to resin adsorption does not proceed Will increase. In addition, when the hydroxyl value is greater than 600 (mgKOH / g), the affinity between the dispersion medium and the copolymer is improved, but the affinity with the pigment is not good. It is difficult to form a lump suitable for clay-like kneading from a mixture of coalesced and solvent, so that the kneading process itself does not proceed and the number of coarse particles in the aqueous pigment dispersion increases.
In the polyoxyalkylene adduct (e) of glycerin used in the present invention, the polyoxyalkylene skeleton is preferably composed of oxyethylene or oxypropylene, or both oxyethylene and oxypropylene, and from oxyethylene and oxypropylene. When constituted, oxyethylene and oxypropylene may be a random arrangement or a polyoxyalkylene block arrangement.
The measurement of the hydroxyl value here is in accordance with Japanese Industrial Standard “K 0070: 1992. Test method for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponified product of chemical products”.

Specific product names include EG-1 (polyethylene oxide adduct of glycerin, hydroxyl value 133 (mgKOH / g), molecular weight of about 1000, manufactured by Lipochemical), Newpol GP-400 (polypropylene oxide adduct of glycerin) , Hydroxyl value 400 (mgKOH / g), molecular weight about 400, manufactured by Sanyo Chemical Co., Ltd., New Pole GP-600 (glycerin polypropylene oxide adduct, hydroxyl value 279 (mgKOH / g), molecular weight about 600, manufactured by Sanyo Chemical Co., Ltd. ), New Pole GP-1000 (polypropylene oxide adduct of glycerin, hydroxyl value 160 (mgKOH / g), molecular weight of about 1000, manufactured by Sanyo Chemical Co., Ltd.), Sanniks GL-600 (block of polypropylene oxide and polyethylene oxide into glycerin) Sequence adduct, hydroxyl value 279 (mgKOH / g), molecular weight about 600 Sanyo Kasei Ltd.), Newpol GE-600 (glycerin ethylene oxide adduct, hydroxyl number 277 (mg KOH / g), a molecular weight of about 600, manufactured by Sanyo Chemical Industries, Ltd.) is.
In the kneading step, the mass ratio e / (a + b) of the polyoxyalkylene adduct (e) of glycerin to the total mass of the quinacridone pigment (a) and the quinacridone pigment derivative (b) is 0.3 to 0.8. It is.
In this section, the molecular weight of the polyoxyalkylene adduct of glycerin is the number average molecular weight and is calculated by the following formula.

Here, the hydroxyl value is the amount of potassium hydroxide required to neutralize the acetic acid required for acetylation by acetylating the hydroxyl group (—OH) in the sample, expressed in mg per 1 g of the sample. And is a scale showing the content of OH groups in the sample.

(Wetting agent)
In the production method of the present invention, a conventionally known wetting agent may be used in addition to the polyoxyalkylene adduct of glycerin as the water-soluble organic solvent added during the kneading. Furthermore, such a wetting agent is added to the kneaded product in the mixing step of adding and mixing the aqueous medium to the pigment dispersion after the kneading step, and is added to the kneaded material to mix and dilute it. It is also important. Examples of such a wetting agent include glycerin, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, and 1,4-butane. Diols, 1,5-pentanediol, 1,6-hexanediol, 1,2,6-hexanetriol, polyols such as trimethylolpropane, pentaerythritol, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl Polyhydric alcohol alkyl ethers such as ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether Polyhydric alcohol aryl ethers and polyhydric alcohols aralkyl ethers, 2-pyrrolidone, N- methyl-2-pyrrolidone, lactams such as ε- caprolactam, 1,3-dimethyl imidazolidinone. These wetting agents can be used alone or in combination of two or more. In particular, polyhydric alcohols having a high boiling point, low volatility and high surface tension and liquid at normal temperature are preferable, and glycols such as diethylene glycol and triethylene glycol are more preferable.

The above-mentioned wetting agents other than the polyoxyalkylene adduct (e) of glycerin that can be used for kneading do not have a strong dissolving power of the styrene-acrylic acid copolymer (c), and the wetting amount is 25% by mass. When the agent and the styrene-acrylic acid copolymer are agitated, those that do not become a homogeneous solution are preferred.
Moreover, it is preferable that the ratio of the polyoxyalkylene adduct (e) of glycerol and the polyoxyalkylene adduct (e) of glycerol in the total amount of the wetting agent is at least 75% by mass or more. When the ratio of the polyoxyalkylene adduct (e) of glycerin is 75% by mass or more, the pigment can be sufficiently crushed and dispersed, and the number of coarse particles can be easily reduced effectively.

Hereinafter, the method for producing the aqueous pigment dispersion of the present invention will be described in more detail.
(Kneading process)
In the kneading step in the production method of the present invention, the quinacridone pigment (a), the styrene-acrylic acid copolymer (c), the basic compound (d) and the polyoxyalkylene adduct (e) of glycerin, Preferably, a mixture containing the quinacridone pigment derivative (b) is kneaded to prepare a pigment dispersion that is solid at room temperature. In the production method of the present invention, a quinacridone pigment (a), a styrene-acrylic acid copolymer (c), a basic compound (d) and a polyoxyalkylene adduct (e) of glycerin, preferably a quinacridone pigment derivative ( It is preferable to knead the mixture containing b) under a high shearing force. By kneading under a high shearing force, the quinacridone pigment (a) is finely pulverized and swelled by the addition of the polyoxyalkylene adduct (e) of glycerin and the basic compound (d) to the finely divided particle surface. The styrene-acrylic acid copolymer (c) in a state is pressed, coating of the pigment surface proceeds, and a pigment composition that is solid at room temperature in which the pigment is uniformly dispersed is obtained.

In order for a high shear force to be applied to the mixture and the kneading step to proceed, the solid content concentration of the kneaded mixture is preferably 55 to 80% by mass. By kneading the solid content in such a range, a sufficient shearing force can be applied, and the quinacridone pigment (a) is not sufficiently pulverized, and the pigment is uniformly dispersed at room temperature. A solid pigment composition can be obtained.
The total amount of the polyoxyalkylene adduct of glycerin and the wetting agent added as necessary is adjusted so that the solid content concentration of the mixture kneaded in the kneading step can be kept high. The total amount of the polyoxyalkylene adduct of glycerin and the other wetting agent in the mixture kneaded in the kneading step is preferably in the range of 30 to 80% by mass with respect to the total amount of the pigment and the pigment derivative. When the total addition amount of the polyoxyalkylene adduct (e) of glycerin and the wetting agent is in the above range, the solids can be easily brought into a fused state, and sufficient shearing force can be applied during kneading. it can.

  When an alkali metal hydroxide is used as the basic compound (c), it is usually used as an aqueous solution, but the amount of water is preferably minimized, and the amount of water should be suppressed to 15% by mass or less based on the pigment. Is preferable, and it is more preferable to set it as 8 mass% or less.

  In the kneading step of the present invention, all the pigments, pigment derivatives and styrene acrylic acid copolymer (c) used in the aqueous pigment dispersion of the present invention are blended, but the quinacridone pigment (a) and the quinacridone The amount of the styrene-acrylic acid copolymer (c) used relative to 100 parts by mass in total with the pigment derivative (b) is preferably 5 to 50 parts by mass, more preferably 10 to 45 parts by mass, 15 More preferably, it is -40 mass parts. If the amount of the styrene-acrylic acid copolymer (c) used is 15 parts by mass or more, the surface of the pigment and the pigment derivative is sufficiently covered with the styrene acrylic acid copolymer. The dispersion stability of the ink jet recording ink is improved, the friction resistance of the printed matter printed with the ink jet recording ink tends to be improved, and if the amount used is 50 parts by mass or less, an aqueous pigment dispersion or When water-based ink for inkjet recording is prepared, resin that is not adsorbed to the pigment does not exist in the aqueous medium, the viscosity of the aqueous pigment dispersion or water-based ink is properly maintained, and the ink ejection property is also good. It tends to be maintained.

  The temperature at the time of kneading can be appropriately adjusted in consideration of the temperature characteristics of the styrene-acrylic acid copolymer (c) so that a sufficient shearing force is applied to the kneaded product. It is preferable that the temperature is lower than the glass transition point of the acid copolymer (c) and the temperature difference from the glass transition point is less than 50 ° C. By kneading in such a temperature range, there is no shortage of shearing force due to a decrease in the viscosity of the kneaded product accompanying the melting of the resin due to an increase in the kneading temperature.

  The kneading apparatus used in the kneading step may be any kneading apparatus that can generate a high shearing force with respect to a mixture having a high solid content ratio, and can be selected from known kneading apparatuses. It is preferable to use a kneading apparatus having a stirring tank and stirring blades and capable of sealing the stirring tank, rather than using an open kneader having no stirring tank such as a two roll. It is preferable to use a kneading apparatus having a stirring tank and stirring blades. When the kneading apparatus having such a configuration is used, the polyoxyalkylene addition / wetting agent / moisture of glycerin is not volatilized during kneading, and the kneading of the mixture having a certain solid content ratio can be continued. It is effective in reducing particles. In addition, the pigment composition that is solid at room temperature after kneading can be directly diluted with an aqueous medium to shift to a mixing step in which an aqueous pigment dispersion is prepared.

Examples of such an apparatus include a Henschel mixer, a pressure kneader, a Banbury mixer, and a planetary mixer. A planetary mixer is particularly suitable. In the present invention, since the kneading is preferably performed in a state where the pigment concentration and the solid content concentration of the pigment and the resin are high, the viscosity of the kneaded material varies in a wide range depending on the kneaded state of the kneaded material. Compared with a two-roller, etc., a mixer can be kneaded in a wide range of viscosity, and an aqueous medium can be added and distilled off under reduced pressure, making it easy to adjust the viscosity and load shear force during kneading. It is.

(Mixing process)
When an aqueous medium is mixed with a pigment dispersion that is solid at room temperature obtained by such a kneading step to produce an aqueous pigment dispersion, the solid pigment dispersion is mixed with a kneader having a stirring tank as described above. Then, an aqueous medium is added to and mixed with the stirring tank, and if necessary, the aqueous pigment dispersion can be produced by direct dilution by stirring. Further, the aqueous pigment dispersion can be prepared by mixing the solid pigment dispersion and the aqueous medium with another stirrer equipped with a stirring blade and stirring as necessary. Regarding mixing of the aqueous medium, the required amount may be mixed at once with respect to the pigment dispersion, but dilution with the aqueous medium is more efficient if the required amount is added continuously or intermittently. The aqueous pigment dispersion can be produced in a shorter time. Further, the aqueous pigment dispersion thus obtained may be further subjected to a dispersion treatment by a disperser. In the production method of the present invention, since the finer pigment and the coating with the styrene-acrylic acid copolymer are proceeding effectively, the dispersion process is performed by a disperser, and further shearing force is applied to disintegrate the pigment. Even if it does not perform, it is possible to produce an aqueous pigment dispersion having good characteristics by mixing an aqueous medium to lower the solid content ratio to liquefy it, and stirring it as necessary. However, even when coarse dispersed particles remain in the aqueous pigment dispersion due to variations in pigment properties, etc., by performing the dispersion treatment, the remaining coarse dispersed particles are further pulverized, and the particle size of the dispersed particles becomes smaller. Ink jet recording ink composition produced from an aqueous pigment dispersion improves ink jet characteristics such as ejection stability and print density.

  In addition to water, the aqueous medium used when producing an aqueous pigment dispersion from a pigment dispersion that is solid at room temperature is used to prevent drying of the aqueous pigment dispersion, and to adjust the viscosity during the dispersion treatment when using a dispersion device. Therefore, a high-boiling water-soluble organic solvent may be contained, and a conventionally known wetting agent can be used. As the water-soluble organic solvent preferably used, the polyoxyalkylene adduct of glycerin (e) used in the kneading step of the present invention and the wetness that could be added when producing a solid pigment dispersion by the kneading step Agents can be exemplified. The total amount of the water-soluble organic solvent in the aqueous pigment dispersion liquid is preferably 1 to 50% by mass, and more preferably 3 to 40% by mass. If it is less than this lower limit, the drying prevention effect tends to be insufficient, and if it exceeds the above upper limit, the dispersion stability of the dispersion tends to decrease.

As the disperser for performing the dispersion treatment, known and commonly used equipment can be used, for example, an ultrasonic homogenizer, a high-pressure homogenizer, a paint shaker, a ball mill, a roll mill, a sand mill, a sand grinder, a dyno mill, a dispar mat, a nano mill, an SC mill, Nanomizer etc. can be mentioned, One of these may be used independently and may be used in combination of 2 or more types of apparatuses. In the present invention, the disperser and the disperser are devices that are used exclusively for the dispersion process, and do not include general-purpose mixers and stirrers that are widely used for normal mixing and stirring. And
The pigment concentration of the aqueous pigment dispersion prepared after the mixing step or the dispersion treatment after the mixing step is preferably 10 to 20% by mass.

(Adjustment of water-based ink for inkjet recording)
The aqueous ink composition for inkjet recording using the aqueous pigment dispersion of the present invention can be prepared by a conventional method by diluting the aqueous pigment dispersion in an aqueous medium and adding various additives as necessary. When preparing a water-based ink composition for ink jet recording, coarse particles cause nozzle clogging and other image characteristics, and therefore, after ink preparation, coarse particles are removed by centrifugation or filtration. Also good.
When preparing an ink composition for ink jet recording using the aqueous pigment dispersion of the present invention, a polyoxyalkylene adduct of glycerin (e) or the above-described wetting agent is added for the purpose of preventing the ink from drying. be able to. The total content of the glycerin polyoxyalkylene adduct (e) and the wetting agent in the ink for the purpose of preventing drying is preferably 3 to 50% by mass.

In addition, when preparing an ink composition for ink jet recording using the aqueous pigment dispersion of the present invention, a penetrant may be added for the purpose of improving the penetrability to a recording medium and adjusting the dot diameter on the recording medium. it can.
Examples of the penetrant include lower alcohols such as ethanol and isopropyl alcohol, ethylene oxide adducts of alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether, and propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether.
The penetrant content in the ink is preferably 0.01 to 10% by mass.

  When an ink composition for ink jet recording is prepared using the pigment dispersion for ink jet ink of the present invention, a surfactant can be added in order to adjust ink characteristics such as surface tension. The surfactant that can be added for this purpose is not particularly limited, and examples include various anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Of these, anionic surfactants and nonionic surfactants are preferred.

Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, sulfate of higher fatty acid ester, sulfonate of higher fatty acid ester, higher alcohol ether. Sulfate salts and sulfonates of the above, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, etc. Specific examples include dodecylbenzene sulfonate, isopropyl naphthalene sulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenyl sulfonate, dibutylphenylphenol disulfate. , And the like salts.
Nonionic surfactants include, for example, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester , Polyoxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, fatty acid alkylolamide, alkyl alkanolamide, acetylene glycol, oxyethylene adduct of acetylene glycol, Polyethylene glycol polypropylene glycol block copolymer, etc. Among them, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, fatty acid Preference is given to alkylolamide, acetylene glycol, oxyethylene adducts of acetylene glycol and polyethylene glycol polypropylene glycol block copolymers.
Other surfactants include silicone surfactants such as polysiloxane oxyethylene adducts; fluorine surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers. Biosurfactants such as spicrispolic acid, rhamnolipid, lysolecithin and the like can also be used.

  These surfactants can be used alone or in combination of two or more. In consideration of the dissolution stability of the surfactant, the HLB is preferably in the range of 7 to 20. When a surfactant is added, the addition amount is preferably in the range of 0.001 to 1% by mass, more preferably 0.001 to 0.5% by mass, based on the total mass of the ink. More preferably, it is in the range of 01 to 0.2% by mass. When the addition amount of the surfactant is 0.001% by mass or more, the effect of addition of the surfactant tends to be obtained satisfactorily, and when it is used at 1% by mass or less, the image blurs. It tends to occur less easily.

  When preparing an ink composition for ink jet recording using the aqueous pigment dispersion of the present invention, an antiseptic, a viscosity adjuster, a pH adjuster, a chelating agent, a plasticizer, an antioxidant, and an ultraviolet absorber as necessary. An agent or the like can also be added.

The total amount of the quinacridone pigment (a) and the quinacridone pigment derivative (b) in the aqueous pigment dispersion of the present invention is preferably 5 to 25% by mass, and more preferably 5 to 20% by mass. When the total amount of the quinacridone pigment (a) and the quinacridone pigment derivative (b) is 5% by mass or more, the ink composition for ink jet recording prepared from the aqueous pigment dispersion of the present invention has good coloring performance. There is a tendency that a sufficient image density is obtained. On the other hand, when the content is 25% by mass or less, the dispersion stability of the pigment tends to hardly occur in the aqueous pigment dispersion.
The total amount of the quinacridone pigment (a) and the quinacridone pigment derivative (b) in the ink composition for ink jet recording prepared from the aqueous pigment dispersion of the present invention depends on the necessity of obtaining a sufficient image density. In order to ensure the dispersion stability of the dispersed particles, the content is preferably 1 to 10% by mass.
The ink composition for ink jet recording produced by the production method of the present invention maintains good dispersion stability even when heated, and can be suitably used as ink for ink jet recording of various systems. The inkjet method to be applied is not particularly limited, but examples of known ones such as a continuous ejection type (charge control type, spray type, etc.), an on-demand type (piezo type, thermal type, electrostatic suction type, etc.) are illustrated. can do.

Examples of the present invention will be described in detail below.
Unless otherwise specified, “part” is “part by mass” and “%” is “% by mass”.
The resins used in the examples and comparative examples are as follows.
Resin A: Styrene / acrylic acid / methacrylic acid / butyl acrylate = 74 / 11.3 / 14.6 / 0.1 (mass ratio) styrene acrylic acid copolymer in monomer composition ratio, measured acid value A resin having 172 mg KOH / g and a weight average molecular weight of 11,000.
In addition, a weight average molecular weight is a numerical value of polystyrene conversion measured using GPC (gel perchromatograph).

Example 1
Powder mixture (pigment, pigment derivative, resin) of the following composition is charged into a planetary mixer (trade name: Chemical Mixer ACM04LVTJ-B manufactured by Aikosha Mfg. Co., Ltd.), the jacket is heated, and the temperature of the contents After the temperature reached 80 ° C., kneading was carried out at a rotational speed of 80 revolutions / minute and a revolution speed of 25 revolutions / minute, and after 5 minutes, a liquid raw material of the following composition was added and further kneading was continued.
Resin A 12 parts Quinacridone pigment: Chromophthal Jet Magenta 2BC
(Manufactured by Ciba Specialty Chemicals) 38 parts phthalimidomethylated 3,10-dichloroquinacridone (average number of phthalimidomethyl groups per molecule 1.4) 2 parts glycerin polyethylene oxide adduct EG-1 (manufactured by Lipochemical) 20 parts (hydroxyl value 133 (mgKOH / g), molecular weight about 1300)
Kneading was continued until 30 minutes after the current value of the 34 mass% potassium hydroxide aqueous solution 6 parts planetary mixer showed the maximum current value, and a solid pigment dispersion was obtained at room temperature. The obtained pigment dispersion that was solid at room temperature was taken out of the jacket, cut into a 1 cm square, and placed in a commercially available juicer mixer. Thereto, 70 parts of ion exchange water was added, mixed and diluted with a mixer for 10 minutes, and ion exchange water was further added to obtain an aqueous pigment dispersion A having a quinacridone pigment concentration of 13.5% by mass.

(Examples 2 to 7)
Sanix GE-600 (hydroxyl value 277 (mgKOH / g)), Sannix GP-250 (hydroxyl value 674 (mgKOH / g)), Sanniks GP- manufactured by Sanyo Chemical Industries, Ltd. 400 (hydroxyl value 400 (mgKOH / g)), Sannix GP-600 (hydroxyl value 280 (mgKOH / g)), Sannix GP-1000 (hydroxyl value 160 (mgKOH / g)), Sannix GL-600 ( Except that the hydroxyl value was changed to 279 (mgKOH / g), Examples 2 to 6 were carried out under the same conditions as in Example 1 to obtain aqueous pigment dispersions B to G, respectively.

(Example 8)
The amount of the quinacridone pigment used in Example 1 was changed to 40 parts, the phthalimidomethylated 3,10-dichloroquinacridone was changed to 0 part, and the others were carried out under the same conditions as in Example 1 to obtain an aqueous pigment dispersion H. It was.

Example 9
EG-1 of Example 8 was changed to GL-600, and Example 9 was performed under the same conditions as in Example 8 except that, thereby obtaining an aqueous pigment dispersion I.

(Example 10)
A mixture having the following composition was charged into a planetary mixer PLM-V-50V having a capacity of 50 L (manufactured by Inoue Seisakusho Co., Ltd.), the jacket was heated, and after the jacket temperature reached 60 ° C., the speed was low (rotation speed: 21 Kneading was performed at a rotation / minute, revolution speed: 14 revolutions / minute), and after 10 minutes, the speed was changed to a high speed (automatic rotation speed: 35 revolutions / minute, revolution speed: 24 revolutions / minute), and the kneading was continued.
Resin A 150 parts Quinacridone pigment: Chromophthal Jet Magenta 2BC
(Ciba Specialty Chemicals) 475 parts phthalimidomethylated 3,10-dichloroquinacridone (average number of phthalimidomethyl groups per molecule 1.4) 25 parts Polyethylene oxide adduct of glycerin: EG-1 220 parts (lipochemical) (Made by company)

Thereafter, the kneading was continued, and the kneading was continued until the kneading was continued for 1 hour after showing the maximum current value of the planetary mixer to obtain a colored resin composition. A total amount of 1200 parts of ion exchange water was added to the obtained colored resin composition in 5 hours while continuing to stir with a planetary mixer. Further, ion-exchanged water was added little by little with stirring so that the concentration of the quinacridone pigment was 13.5% by mass to obtain an aqueous pigment dispersion J-1.
(Example 11)
18 kg of the aqueous pigment dispersion J-1 produced in Example 10 was dispersed with a bead mill (Nanomill NM-G2L manufactured by Asada Tekko) under the following conditions to obtain a pigment dispersion J-2.

・ Dispersion condition disperser Nano Mill NM-G2L (Asada Tekko)
Beads φ0.3mm zirconia beads Bead filling amount 85%
Cooling water temperature 10 ℃
Number of revolutions 2660 revolutions / minute (disk peripheral speed: 12.5 m / sec)
Liquid feed amount 200g / 10 seconds

(Comparative Example 1)
Comparative Example 1 was carried out under the same conditions as in Example 1 except that EG-1 was changed to glycerin, whereby an aqueous pigment dispersion K was obtained.

(Comparative Example 2)
Comparative Example 2 was performed under the same conditions as in Example 1 except that EG-1 was changed to DEG, and an aqueous pigment dispersion L was obtained.

(Comparative Example 3)
An aqueous pigment dispersion was prepared in the same manner as in Example 10 except that diethylene glycol was used instead of EG-1, and this was designated as aqueous pigment dispersion M-1.
(Comparative Example 4)
An aqueous pigment dispersion was prepared in the same manner as in Example 11 except that diethylene glycol was used instead of EG-1, and this was designated as aqueous pigment dispersion M-2.

(Reference Example 1)
While stirring 100 g of methyl ethyl ketone solution containing 50% of resin A as a solid content concentration, 153 ml of a commercially available 1 mol / liter KOH aqueous solution and 47 ml of ion-exchanged water are added to this solution, and styrene acrylic resin A is added. Neutralized. After distilling off methyl ethyl ketone under reduced pressure, ion-exchanged water was added to make up for water lost by azeotropy with methyl ethyl ketone to obtain a resin aqueous solution B containing resin A having a solid content concentration of 20%.
Next, after charging the following composition into a container with a capacity of 250 ml, a dispersion treatment was performed for 2 hours with the following composition using a paint shaker (manufactured by Toyo Seiki Seisakusho), and a quinacridone pigment concentration of 13.5 masses: % Aqueous pigment aqueous dispersion N was obtained.
Styrene acrylic resin aqueous solution B 10g
Quinacridone pigment 5.4g
Chromoval Jet Magenta 2BC (Ciba Specialty Chemicals)
0.6 g of phthalimidomethylated 3,10-dichloroquinacridone
(Average number of phthalimidomethyl groups per molecule 1.4)
Polyethylene oxide adduct of glycerin 4.8g
Liponic EG-1 (manufactured by Lipochemical) (hydroxyl value 133 (mgKOH / g), molecular weight about 1300)
Ion-exchanged water 19.2g
Zirconia beads (1.25mm diameter) 180g

(Reference Example 2)
Reference Example 2 was carried out under the same conditions as Reference Example 1 except that EG-1 was changed to diethylene glycol, whereby an aqueous pigment dispersion O was obtained.
The aqueous pigment dispersions prepared in the above examples and comparative examples were evaluated using the following methods.

(Evaluation of aqueous pigment dispersion)
[Volume average particle size]
With respect to the aqueous pigment dispersions of Examples and Comparative Examples obtained as described above, the particle size was measured with a Microtrac UPA150EX particle size analyzer (manufactured by Nikkiso Co., Ltd.) at a cell temperature of 25 ° C. At that time, as the particle size measurement samples, each sample was prepared by diluting the quinacridone pigment concentration to 12.5% by mass with ion-exchanged water, and further diluting 500 times with ion-exchanged water.
[Number of coarse particles]
The number of coarse particles was measured using AccuSizer 780 (Particle Sizing Systems, Inc.). At that time, as a sample for measuring the number of coarse particles, each sample was added with 200 to 10,000 times on-exchange water to lower the concentration of the quinacridone pigment, and when the sample passed 1 ml per second through the detector, the particle size was 0. The one that was diluted so that the count number of coarse particles of 5 μm or more was 1000 to 4000 was used.
The number of coarse particles was converted into the number of coarse particles present in 1 ml of an aqueous pigment dispersion having a quinacridone pigment concentration of 12.5% in consideration of the dilution ratio after measurement.

[Inkjet ejection characteristics]
In order to measure the ejection characteristics of the inkjet, first, an aqueous ink for inkjet recording was prepared from the aqueous pigment dispersions prepared in Examples 1 to 9, Comparative Examples 1 and 2, and Reference Examples 1 and 2 with the following composition.
Each aqueous pigment dispersion prepared in Examples 1 to 9, Comparative Examples 1 and 2 and Reference Examples 1 and 2 was diluted with pure water to prepare a diluted aqueous pigment dispersion having a quinacridone pigment concentration of 6% by mass. The following was added to the diluted solution.
50 parts diluted aqueous pigment dispersion
2-pyrrolidinone 8 parts Triethylene glycol mono-n-butyl ether 8 parts Purified glycerin 3 parts Surfinol 440 (manufactured by Air Products) 0.5 parts Pure water 30.5 parts

Each produced water-based ink for inkjet recording was tested using the inkjet printer (Photosmart D5360 by HP company). After filling the black cartridge with ink, a nozzle check test pattern was printed at the start of the test. Furthermore, after printing 100% of the print density setting in a range of 340 cm ^{2 on} one A4 sheet in monochrome mode, a nozzle check test pattern is printed, and the state of the nozzle before and after the test is compared.
No nozzle chip increases ...
Nozzle increase in 1-5 points or less ... △,
With nozzle missing increased by 6 or more points ×
As evaluated.

[Storage stability]
The storage stability was evaluated by storing the aqueous pigment dispersions prepared in Examples, Comparative Examples, and Reference Examples under 60 ° C. conditions. The amount of change between the initial particle size before the start of the test and the particle size after 6 weeks from the start of the test is 10% or less.
From 11 to 20% ... △,
21% or more
It was. The results are shown in Table 1.

As is clear from the comparison between Examples 1 to 9 and Comparative Examples 1 and 2, the use of a polyoxyalkylene adduct of glycerin as the water-soluble organic solvent in the kneading step allows the number of coarse particles in the aqueous pigment dispersion to be increased. is decreasing. Further, from comparison between Examples 1 to 7 and Examples 8 and 9, it is necessary to add a pigment derivative in order to reduce the number of coarse particles in the pigment dispersion and reduce the volume average particle size. I understand. Further, from the comparison between Example 10 and Example 11, even if a step of further dispersing treatment is added after the mixing step in the production method of the present invention, the volume average particle size and the number of coarse particles are further reduced greatly. In addition, it can be seen that the volume average particle size and coarse particles are sufficiently reduced only by the disruption process. On the other hand, as can be seen from Comparative Example 3 and Comparative Example 4, even if the kneading process is used, coarse particles are sufficient if the polyoxyalkylene adduct of glycerin used in the present application is not used in the kneading process. It is not reduced. In such a case, even after the kneading step, the dispersion process using a disperser using a medium is performed, but the number of coarse particles is slightly reduced, but not greatly reduced. If the polyoxyalkylene adduct is used from the beginning of the kneading step, a much better reduction in coarse particles can be achieved even if no dispersion treatment is performed.
Further, as is clear from the reference examples, when the aqueous pigment dispersion was prepared with a paint conditioner, both the number of coarse particles and the volume average particle size were much larger than when the aqueous pigment dispersion was prepared using a kneading step. It becomes. And at this time, even if it adds the polyoxyalkylene adduct of glycerol, those values are not improved. It can also be seen that the pigment dispersion having a large number of coarse particles and a large volume average particle diameter has poor storage stability and ink ejection stability. As described above, in the dispersion of quinacridone pigments, there is no conventional dispersion process using a dispersion device by using a polyoxyalkylene adduct of glycerin as a water-soluble organic solvent, adding a pigment derivative and taking a kneading prescription. However, an aqueous pigment dispersion that achieves a significant reduction in coarse particles with poor dispersion just by passing through a mixing step in which an aqueous medium is added to the pigment dispersion prepared in the kneading step, mixed, and stirred if necessary. A liquid can be produced. As a result, the pigment is stably dispersed, a good dispersion state is maintained even during long-term storage, and an excellent aqueous pigment dispersion and an aqueous ink for inkjet recording can be obtained. Provided a method for producing an aqueous pigment dispersion having a high water content.

Claims (11)

A mixture containing a quinacridone pigment (a), a styrene-acrylic acid copolymer (c), a basic compound (d) and a polyoxyalkylene adduct (e) of glycerin is kneaded, and the pigment dispersion is solid at room temperature. A method for producing an aqueous pigment dispersion, comprising a kneading step for producing a body and a mixing step for mixing an aqueous medium with the pigment dispersion. The method for producing an aqueous pigment dispersion according to claim 1, wherein the polyoxyalkylene skeleton of the polyoxyalkylene adduct (e) of glycerin is composed of oxyethylene and / or oxypropylene. The method for producing an aqueous pigment dispersion according to claim 1 or 2, wherein the polyoxyalkylene adduct (e) of glycerin has a hydroxyl value of 100 to 600 (mgKOH / g). The styrene-acrylic acid copolymer has an acid value of 120 to 220 (mgKOH / g), a weight average molecular weight of 5000 to 20000, and contains 50 to 90% by mass of styrene monomer units with respect to all monomer components. The manufacturing method of the aqueous pigment dispersion liquid of any one of 1-3. The method for producing an aqueous pigment dispersion according to any one of claims 1 to 4, further comprising a quinacridone pigment derivative (b) in the mixture. The method for producing an aqueous pigment dispersion according to claim 5, wherein the quinacridone pigment derivative (b) is a phthalimidomethylated quinacridone compound. The mass ratio of the styrene-acrylic acid copolymer (c) to the total mass of the quinacridone pigment (a) and the quinacridone pigment derivative (b) in the kneading step, c / (a + b) is 0.05 to 0.00. The mass ratio e / (a + b) of the polyoxyalkylene adduct (e) of glycerol with respect to the total mass is 0.3 to 0.8, The method for producing an aqueous pigment dispersion according to claim 5 or 6 . The method for producing an aqueous pigment dispersion according to any one of claims 1 to 7, wherein a solid content ratio of the pigment dispersion in the kneading step is 55 to 80% by mass. The manufacturing method of the aqueous ink for inkjet recording which has the process of diluting the aqueous pigment dispersion manufactured by the manufacturing method of the aqueous pigment dispersion of any one of Claims 1-8 with an aqueous medium. A pigment which is solid at room temperature and is kneaded with a mixture containing a quinacridone pigment (a), a styrene-acrylic acid copolymer (c), a basic compound (d) and a polyoxyalkylene adduct (e) of glycerin. Composition. The pigment composition according to claim 10, further comprising a quinacridone pigment derivative in the mixture.