JP2011225868A - Method for production of inkjet-recording aqueous pigment dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet-recording aqueous pigment dispersion having good dispersibility and dispersion stability important to printing for inkjet recording, and besides excellent in image density of a printed image as well as scratch resistance.SOLUTION: The aqueous pigment dispersion is produced through steps of: producing a pigment dispersion solid at room temperature by kneading a mixture of a pigment, styrene-acrylic resin, basic compound and wetting agent; and adding an aqueous medium to the solid pigment dispersion and agitating to liquefy. By adding a specific phosphoric ester-based surfactant using a specific method, a high printed image density and improved scratch resistance can be obtained while maintaining good dispersibility.

Description

  The present invention relates to a method for producing an aqueous pigment dispersion that can be used as a raw material for an aqueous ink composition for inkjet recording, an aqueous ink composition for inkjet recording using the aqueous pigment dispersion, and a method for producing the same.

Conventionally, ink for ink jet recording in which a colorant is dissolved or dispersed in a liquid medium containing water as a main component has been used. The ink jet recording method can directly form characters and images on a printed material in a non-contact manner by ejecting ink droplets from fine nozzles. .
In recent years, the use of pigment inks using pigments as colorants has been increasing in order to obtain printed matter with excellent fastness such as water resistance and light resistance. However, in an ink using a pigment as compared with an ink using a dye as a colorant, achieving a stable dispersion of the pigment has been a problem. In addition, pigment ink has problems in terms of color developability and fixability of printed images as compared with dye inks that permeate the printed material and stain, for example, fibers of printing paper. There has been a demand for improvement in scratch resistance.

With respect to stable dispersion of pigments, production methods using various dispersants have been studied. In Patent Document 1, an aqueous pigment dispersion is prepared by dispersing a pigment in an aqueous medium using a styrene acrylic acid copolymer as a dispersing agent. In Patent Document 2, before dispersing in an aqueous medium. A mixture containing a pigment, a resin, a wetting agent and a basic compound is kneaded to prepare a solid kneaded product, and then the kneaded product is dispersed in an aqueous medium.
By such a method, the dispersibility and dispersion stability of the ink for ink jet recording using the pigment have been remarkably improved, but there are still points to be improved in terms of image density and scratch resistance required for the printed coating film. It is left.
For example, in order to improve the fixability of the ink, it has been proposed to add a compound that enhances permeability such as a surfactant into the ink (see Patent Document 3) or to use a volatile ink (Patent Document). 4). However, when the penetrability is increased, the color material in the ink also penetrates deep into the recording medium, resulting in a disadvantage that the image density and saturation are lowered. Further, when ink mainly composed of a volatile solvent is used, there is a problem that clogging due to evaporation of the solvent at the nozzle portion of the recording head is likely to occur.
Originally, pigment-based inks are determined to have a low print density because pigments are unlikely to remain on the surface of the recording medium. However, if the amount of pigment in the ink is increased in order to improve the printing density, there is a drawback that the ink viscosity is increased and the ink dischargeability is lowered.

Therefore, in order to improve the printing density, in the pigment-based ink, a polymer containing a polyethylene glycol (meth) acrylate monomer and an α, β-ethylenically unsaturated carboxylic acid is added (for example, see Patent Document 5), or polyethylene. The addition of a polymer dispersant composed of a glycol (meth) acrylate monomer or a poly (trimethylene glycol) (meth) acrylate monomer has been proposed (see, for example, Patent Document 6). However, a polymer obtained by copolymerizing a (meth) acrylate monomer containing an oxyethylene group or an oxytrimethylene group has a disadvantage that the polymer itself has high hydrophilicity, easily penetrates into copy paper, and the print density decreases when printed. In addition, the ink has a high viscosity due to its hydrophilicity, and it is difficult to ensure stable ejection properties. In order to further improve the scratch resistance, it has been proposed to add a water-soluble polymer compound to the pigment ink (for example, Patent Document 7). However, even if the scratch resistance is improved, the viscosity of the pigment ink tends to increase with the addition of the polymer compound, and there is a problem that the inkjet nozzle is likely to be clogged.
Furthermore, for the purpose of improving the scratch resistance of an image obtained by the ink jet recording method, an ink in which a pigment is dispersed using a resin having a hydroxyl group has been proposed (for example, Patent Document 8). In addition, an ink using a pigment dispersant of polyglycerin polyoxyalkylene fatty acid has been proposed in order to obtain an aqueous ink having improved ejection stability and excellent printing characteristics and fixing properties (Patent Document 11). In addition, a method has been proposed in which a liquid for improving an image is previously deposited on a recording medium prior to ink ejection (Patent Document 10).
However, these conventional methods do not sufficiently improve the print density and scratch resistance, and even if they are improved, problems such as ejection failure occur, and image printing is performed with only one liquid. The advantages of the inkjet recording method that can be performed are impaired.

  On the other hand, in a thermal ink jet recording ink composition, a phosphate ester compound is used as a surfactant capable of suppressing kogation (Patent Documents 11 and 12). Further, the phosphate ester surfactant is used to form a good image on a low liquid-absorbing printing paper by using this to adjust the permeability into a printing medium (Patent Document 13). Or used in combination with a resin emulsion to obtain a good image density (Patent Document 14). However, even when these phosphoric acid ester compounds were used, the image scratch resistance was not improved.

JP 2002-256201 A JP 2004-263035 A JP 55-65269 A JP-A-55-66976 JP-A-6-306317 JP 2000-144031 A JP-A-4-59880 JP 2007-146127 A JP 2006-8881 A JP 2005-22329 A JP 2000-309735 A JP 2001-323197 A JP 2001-011348 A JP 2005-298802 A

  An object of the present invention is to provide an aqueous pigment dispersion for ink jet recording which has good dispersibility and dispersion stability, and is excellent in image density and scratch resistance of printed images.

As a method for producing an aqueous pigment dispersion for inkjet recording having excellent dispersibility and dispersion stability, the inventors kneaded a mixture containing a pigment, a styrene acrylic resin, a basic compound, and a wetting agent, A solid pigment dispersion, and a method for producing an aqueous pigment dispersion having a mixing step of adding an aqueous medium to the pigment dispersion and stirring to liquefy, each process of the production method, and By examining various materials used in the production method, it was found that the addition of a specific phosphate ester surfactant in a specific method can improve the density and scratch resistance of the printed image, The present invention has been reached.
That is, the present invention kneads a mixture containing a pigment (a), a styrene acrylic resin (b), a basic compound (c), and a wetting agent (d) to produce a solid colored kneaded material at room temperature. A method for producing an aqueous pigment dispersion for ink jet recording, comprising a mixing step of adding an aqueous medium to the colored kneaded product and stirring to liquefy, wherein the aqueous pigment dispersion for ink jet recording is in the kneading step or in the mixing step or between both steps The phosphate ester-based surfactant (e) is added to the liquid, and the addition is performed after the load current of the kneading apparatus used in the kneading step reaches the maximum value and in the colored hot kneaded liquid in the mixing step. The present invention provides a method for producing an aqueous pigment dispersion for ink-jet recording performed before the completion of the conversion.

  Phosphate-based surfactants have a very strong affinity for phosphate groups with calcium carbonate on paper. Therefore, if the phosphate ester-based surfactant can be stably adsorbed on the pigment surface in the water-based ink for inkjet recording or the pigment surface coated with the styrene acrylic acid-based copolymer, the pigment particles are firmly attached to the paper surface. It is thought that it becomes possible to fix firmly. The inventors have disclosed a method for producing an aqueous pigment dispersion having a kneading step of coating a pigment with a styrene acrylic acid copolymer in the presence of a basic compound and a wetting agent in terms of dispersibility and storage stability. Focusing on the extremely superior points, we studied the types of phosphate ester surfactants in the production method and the addition method that enables effective adsorption. Dispersibility and dispersion stability of water-based ink for inkjet recording The present inventors have found a production method capable of further improving the image density and scratch resistance while maintaining the stability and long-term storage stability.

  The aqueous pigment dispersion for inkjet recording produced by the production method of the present invention kneads a mixture containing (a) a pigment, (b) a styrene acrylic resin, (c) a basic compound, and (d) a wetting agent. And a kneading step for producing a solid colored kneaded material at room temperature, a mixing step for adding an aqueous medium to the solid colored kneaded material, stirring and liquefying, and (a) the pigment is (b) Since it is well coated with a styrene acrylic resin, it has high dispersibility and dispersion stability. Furthermore, after the start of the kneading step, after the load current of the kneading apparatus used in the kneading step shows the maximum value, and before the completion of liquefaction of the colored warm kneaded material in the mixing step, Since specific (d) phosphate ester-based surfactant is added, phosphate ester is adsorbed on the pigment surface via the resin coating the pigment, and the phosphate group is oriented outward. Therefore, the affinity for calcium carbonate in the printed material such as paper is strong, and the pigment particles are firmly held on the surface of the printed material. Therefore, it is possible to obtain a good image density and scratch resistance of the printed image.

（式中Ｘは水素原子又は一般式（２）

（２）
ここで、Rはアルキル基であって、Ｒは炭素数８〜３０のアルキル基、ｎは０〜１５の整数を表し、Ｘのうち少なくとも一つは一般式（２）で表される一価基である。）
を表すものである。すなわち一般式（１）は、Xのいずれか一つまたは二つが水素原子を表すリン酸エステルであって、リン酸モノエステルまたはリン酸ジエステルが用いられる。
とくにアルキルエーテルのリン酸エステルが一般式（１）で表されるアルキルエーテルリン酸エステル系界面活性剤の場合は、強い酸性を示すためアルカリ金属水酸化物で部分または完全中和された塩であることがさらに好ましい。
リン酸エステル系界面活性剤のＨＬＢ値は５以上１５以下であることが好ましい。とりわけＨＬＢ値が５〜７の利用が好ましい。特にＨＬＢが１５以下のものの式（１）で表されるリン酸エステル系界面活性剤の具体例としては、フォスファノール（Phosphanol）シリーズ（東邦化学工業株式会社製）が挙げられる。とりわけフォスファノールGF-185(ＨＬＢ＝５．２ アルキル基の炭素数１３、エチレンオキサイド鎖なし)、フォスファノールRS-610（ＨＬＢ＝１０．５ アルキル基の炭素数１３、エチレンオキサイドの繰り返し単位数６）、フォスファノールRD720（ＨＬＢ＝１４．４ アルキル基の炭素数１８、エチレンオキサイドの繰り返し単位数７）等があげられる。 Hereinafter, each raw material used in each step of the manufacturing method of the present invention will be described in detail, and then each process of the manufacturing method using these raw materials will be described in detail.
The phosphate ester surfactant used in the present invention is preferably an alkyl ether phosphate ester surfactant, and a phosphate ester of polyoxyalkylene alkyl ether represented by the following formula (1) and / or Or a salt thereof is more preferable.

(Wherein X is a hydrogen atom or general formula (2)

(2)
Here, R is an alkyl group, R represents an alkyl group having 8 to 30 carbon atoms, n represents an integer of 0 to 15, and at least one of X is a monovalent represented by the general formula (2). It is a group. )
Is expressed. That is, the general formula (1) is a phosphate ester in which any one or two of X represent a hydrogen atom, and a phosphate monoester or a phosphate diester is used.
In particular, when the alkyl ether phosphate ester surfactant represented by the general formula (1) is an alkyl ether phosphate ester, it is a salt partially or completely neutralized with an alkali metal hydroxide to exhibit strong acidity. More preferably it is.
The HLB value of the phosphate ester-based surfactant is preferably 5 or more and 15 or less. In particular, it is preferable to use an HLB value of 5 to 7. In particular, as a specific example of the phosphate ester surfactant represented by the formula (1) having an HLB of 15 or less, a Phosphanol series (manufactured by Toho Chemical Co., Ltd.) may be mentioned. In particular, phosphanol GF-185 (HLB = 5.2 alkyl group with 13 carbon atoms, no ethylene oxide chain), phosphanol RS-610 (HLB = 10.5 alkyl group with 13 carbon atoms, ethylene oxide repeating unit) Formula 6), Phosphanol RD720 (HLB = 14.4, carbon number of alkyl group 18, number of repeating units of ethylene oxide 7) and the like.

  As the pigment used in the present invention, known pigments can be used without particular limitation. For example, inorganic pigments such as carbon black, titanium black, bengara, zinc oxide, and titanium oxide can be used. The following organic pigments can be used. That is, C.I. I. Pigment yellow 1, C.I. I. Pigment yellow 3, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow, C.I. I. Pigment Yellow 154, monoazo pigments such as C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 81, C.I. I. Pigment yellow 83, C.I. I. Pigment red 38, C.I. I. Disazo pigments such as C.I. Pigment Orange 13; I. Pigment red 53: 1, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 48: 2, C.I. I. Azo lake pigments such as CI Pigment Red 57: 1; I. Pigment blue 16, C.I. I. Pigment blue 15: 3, C.I. I. Pigment green 7, C.I. I. Phthalocyanine pigments such as CI Pigment Green 36; I. Pigment violet 19, C.I. I. Pigment red 122, C.I. I. Pigment red 202, C.I. I. Quinacridone pigments such as CI Pigment Red 282 and solid solution pigments thereof; I. Pigment red 254, C.I. I. Pigment red 255, C.I. I. Pigment red 264, C.I. I. Pigment red 270, C.I. I. Diketopyrrolopyrrole pigments such as CI Pigment Red 272, solid solutions of quinacridone pigments and diketopyrrolopyrrole pigments, and the like can be used. In particular, C.I. I. Pigment red 122, C.I. I. Quinacridone pigments such as CI Pigment Red 282 are preferred.

  The styrene acrylic acid copolymer used in the present invention comprises a styrene monomer component and a monomer component having a carboxyl group. From the viewpoint of dispersion stability and long-term storage stability, it is preferable that the styrene monomer component is contained in an amount of 50% by mass or more. More preferably, it is 60 mass% or more, and even more preferably 70 mass% or more. Moreover, it is preferable that it is 90 mass% or less. By setting the content of the styrene monomer component in the styrene-acrylic copolymer to 50% by mass or more, the hydrophobicity of the copolymerized styrene-acrylic acid copolymer is increased, and in the aqueous system, the pigment is more strongly bonded. Styrene-acrylic acid copolymer coating is performed. As a result, when the ink composition prepared through the aqueous pigment dispersion is used for inkjet, the particle size is stable even when the styrene-acrylic acid copolymer-coated particles are heated. Improves. In addition, the ejection stability is improved and a high print density is obtained. Further, it is effective for improving the durability of the printed coating film on the recording medium. Further, when the use ratio of the styrene monomer component exceeds 90% by mass, the dispersibility in an aqueous medium tends to be insufficient, and the dispersibility and dispersion stability when producing an aqueous ink for inkjet recording tend to decrease. There is. Such characteristics are preferable when the ink composition is used particularly for thermal jet type ink jet recording. In the present invention, the term “monomer” refers to a monomer before polymerization, and the term “monomer component” refers to a structure derived from a monomer contained in a styrene-acrylic acid copolymer.

Further, the acid value of the styrene-acrylic acid copolymer used in the present invention is preferably in the range of 60 to 300 mgKOH / g, more preferably in the range of 80 to 230 mgKOH / g, and still more in the range of 120 to 220 mgKOH / g. preferable. The acid value is the number of milligrams (mg) of potassium hydroxide (KOH) necessary for neutralizing 1 g of the styrene-acrylic acid copolymer. When the acid value is less than 60 mgKOH / g, the hydrophilicity becomes small and the dispersion stability of the pigment in the aqueous medium may be lowered. On the other hand, if the acid value is greater than 300 mgKOH / g, pigment aggregation tends to occur, and the water resistance of a printed product using the ink composition may be reduced.
The weight average molecular weight of the styrene-acrylic acid copolymer used in the present invention is preferably 3000 to 20000, more preferably 5000 to 20000, still more preferably 4000 to 15000, still more preferably 6000 to 12000, and most preferably 8000 to 20000. 12000. By setting the mass average molecular weight to 3000 or more, in addition to initial dispersibility, long-term storage stability tends to be well maintained. In addition, by making the mass average molecular weight 20000 or less, it is easy to suppress the viscosity of the aqueous pigment dispersion from being increased, and the initial dispersibility and solubility of the styrene-acrylic acid copolymer are well maintained. It tends to be possible. In particular, the range of 6000 to 12000 is suitable when the ink composition is used for thermal jet type ink jet recording because the ink composition can be compatible with stability during heating and ejection properties.

When the basic compound used in the present invention is mixed with a styrene-acrylic acid copolymer having a carboxyl group, a pigment and a wetting agent are kneaded together with the styrene-acrylic acid copolymer neutralized with the carboxyl group. A pigment dispersion which is a kneaded product for an aqueous pigment dispersion is obtained. Since the carboxyl group of the styrene-acrylic acid copolymer is neutralized, the affinity between the pigment dispersion and water is improved, and the pigment that is a kneaded product for the aqueous pigment dispersion is used in the production of the aqueous pigment dispersion. The dispersion quickly disperses in water, improving the production efficiency. Further, since the pigment is coated with a styrene-acrylic acid copolymer having increased hydrophilicity, the dispersion state in the aqueous medium becomes more stable, and both the dispersion stability and the long-term storage stability are improved.
In addition, when a basic compound is blended during kneading, the styrene-acrylic acid copolymer is likely to be in a dissolved state or a swollen state due to the interaction between the basic compound and the styrene-acrylic acid copolymer having a carboxyl group, The pigment is efficiently coated on the styrene-acrylic acid copolymer with a high shearing force in the kneading step. For this reason, the fine pulverization of the pigment by the high shear force during kneading and the coating of the finely pulverized pigment surface proceed simultaneously, the coarse particles are crushed and reduced, and the crushed pigment particles are difficult to reagglomerate. The number decreases. For this reason, the process of removing coarse particles in the subsequent process can be omitted, and the effect of improving the yield can be obtained.

  As the basic compound, any of an inorganic basic compound and an organic basic compound can be used. In terms of easy adjustment of alkali strength, inorganic basic compounds are more preferable. Examples of the organic basic compound include amines. For example, common amines such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine and triethylamine can be exemplified. In the case of amine, since it is generally liquid, it can be used as it is. Examples of inorganic basic compounds include alkali metal hydroxides such as potassium and sodium, ammonium hydroxide; alkaline metal carbonates such as potassium and sodium, alkaline earth metal carbonates such as calcium and barium; It can be illustrated. Among them, a strong alkali is preferable because it is effective for enhancing the dispersibility of the styrene-acrylic acid copolymer by neutralization of the styrene-acrylic acid copolymer containing a carboxyl group. Alkali metal hydroxides such as potassium hydroxide and sodium hydroxide are preferred. The inorganic basic compound is usually used in the form of an aqueous solution having a concentration of about 20 to 50% by mass from the viewpoint of improving the mixing property.

The compounding amount of the basic compound is set to be 80% or more of the styrene-acrylic acid copolymer having a carboxyl group, which improves the dispersion speed in water-soluble solvent, dispersion stability, long-term It is preferable from the viewpoint of storage stability. Although the upper limit is not particularly limited, it is substantially 200% or less, preferably 120% or less, in order to ensure dispersion stability during long-term storage and prevent gelation. Furthermore, before kneading, the basic compound is preferably mixed together with other blending components to be blended into the mixture to prepare a mixture. The blending components are added to the kneading step by mixing a styrene-acrylic acid copolymer containing a carboxyl group, water and a basic compound in advance to prepare a styrene-acrylic acid copolymer aqueous solution. It can be mixed and manufactured in multiple stages by adding it to other compounding ingredients such as pigments, but it is better to make a mixture for kneading by mixing the basic compound and other compounding ingredients at once. The styrene-acrylic acid copolymer is preferable in that the adsorption to the surface of the pigment proceeds efficiently. Here, the neutralization rate is a value calculated by the following formula.
Neutralization rate (%) = (mass of basic compound (g) × 56 × 1000) / (styrene-acrylic acid copolymer acid value × equivalent of basic compound × styrene-acrylic acid copolymer amount ( g)) x 100

  The wetting agent used in the present invention is preferably a water-soluble organic solvent, and known ones can be used without particular limitation. For example, glycols such as ethylene glycol, diethylene glycol, triethylene glycol tetraethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol; diols such as butanediol, pentanediol, hexanediol, and diols similar to these; propylene glycol laurate Glycol esters such as diethylene glycol monoethyl, diethylene glycol monobutyl, diethylene glycol monohexyl ethers, glycol ethers such as cellosolve including propylene glycol ether, dipropylene glycol ether, and triethylene glycol ether; methanol, ethanol, isopropyl alcohol, 1-propanol, 2-pro Alcohols such as 1-butanol, 2-butanol, 2-butanol, butyl alcohol, pentyl alcohol, and homologous alcohols thereof; or sulfolanes; lactones such as γ-butyrolactone; N- (2-hydroxyethyl) pyrrolidone, etc. Other various solvents known as water-soluble organic solvents such as lactams; glycerin and derivatives thereof can be mentioned. These water-soluble organic solvents can be used alone or in combination.

The selection of the water-soluble organic solvent is determined by the styrene-acrylic acid copolymer to be used, but a solvent having a certain degree of solubility is preferable, and the addition amount is adjusted by the solubility of the styrene-acrylic acid copolymer. The
Among them, polyhydric alcohols having a high boiling point, low volatility, and high surface tension at room temperature are preferred, particularly diethylene glycol, since they also serve as wetting agents and drying inhibitors in aqueous pigment dispersions and ink compositions. And glycols such as triethylene glycol are preferred. In general, glycols are often contained in ink compositions, and there is no problem even if they remain in the final product. In particular, in the production method of the present invention, since kneading is performed in the presence of a basic compound, it is not necessary to use a water-soluble organic solvent having particularly high styrene-acrylic acid copolymer solubility.

The method for producing the aqueous pigment dispersion for inkjet recording of the present invention using the raw materials described above will be described in detail below.
The production method of the present invention comprises a kneading step of kneading a mixture containing a pigment, a styrene acrylic resin, a basic compound and a wetting agent to produce a solid colored kneaded material at room temperature, A mixing step of adding a medium and stirring to liquefy, adding a phosphate ester-based surfactant (e) during the kneading step or during the mixing step, and the addition is a kneading used in the kneading step It is carried out after the load current of the apparatus shows the maximum value and before the completion of liquefaction of the colored hot-kneaded product in the mixing step.
First, the details of the kneading step as a premise for the addition of the phosphate ester surfactant (e) will be described, and then the addition of the phosphate ester surfactant will be described.

In the kneading step in the production method of the present invention, the pigment (a), the styrene acrylic resin (b), and the wetting agent (d) are kneaded under high shear force in the presence of the basic compound (c). Thus, it is important to break up the aggregation of the pigment (a) and to coat the pigment particle surface with the styrene acrylic resin (b) swollen with the wetting agent (d).
When the kneading step is carried out in the presence of the basic compound (c) and the wetting agent (d), at least a part of the acid groups of the styrene acrylic copolymer is neutralized. It is easy to swell, and the coating of the pigment surface proceeds more effectively simultaneously with the miniaturization of the pigment. For this reason, the reduction of coarse particles and the dispersion of the refined pigment are more effectively performed, the dispersibility of the refined pigment coated with the resin is improved, and the dispersion stability is good even under high temperature storage.

  Since the material to be kneaded is a simple mixture of the raw materials at the start of kneading, it does not receive a high shearing force. However, as the mixing with the added humectant, humectant, and styrene acrylic resin swollen and softened in the presence of the basic compound proceeds and kneading proceeds, the load current of the kneading apparatus gradually increases, Gradually, a high shearing force is applied, and the entire mixture to be kneaded becomes one clay-like lump, and a peak of load current and shearing force is reached to form a solid colored kneaded product. In such a stage, it is considered that the sufficiently crushed pigment is sufficiently covered with the swollen styrene acrylic resin under a high shearing force. Note that the peak load current and shear force gradually decrease, and further crushing of the pigment and coating of the crushed pigment surface proceed more slowly, but the basic crushing and coating process is solid. It is almost completed at the peak of the first shear force when the colored kneaded product is formed, and it is considered that the solid colored kneaded product is formed as a pigment particle aggregate coated with the surface of the crushed pigment.

In order for such a kneading process to proceed, the mass ratio (b) / (a) of the pigment (a) and the styrene acrylic copolymer (b) having an anionic group is 0.1 to 0.5. preferable. When (b) / (a) is 0.05 or more, the pigment (a) tends to be sufficiently coated with the copolymer (b), and (b) / (a) is 0.5 or less. When the colored kneaded material is dispersed in an aqueous medium, there is no decrease in ejection properties when the ink composition is formed due to the presence of the copolymer (b) that is not adsorbed on the pigment in the aqueous medium. Tends to be obtained.
In the kneading step, the above mixture is kneaded with a high shearing force. Therefore, the solid content concentration in the colored kneaded product at the time of kneading is preferably 50 to 80% by mass, and more preferably 60 to 80% by mass. . When the solid content concentration is 50% by mass or less, sufficient shearing force cannot be applied, and there is a tendency that the aggregation of the pigment (a) tends to be insufficient, and at the same time a uniform colored kneaded product is obtained. It tends to be difficult to obtain. On the other hand, if the solid content ratio is 80% by mass or more, kneading tends to be difficult even if the resin is sufficiently softened by heating. In addition, if the solid content ratio is too high, it is difficult to reduce the viscosity with the aqueous medium in the step of dispersing the kneaded mixture in the aqueous medium.

  The addition amount of the wetting agent in the kneading step is preferably in the range of 10 to 80 parts by mass with respect to 100 parts by mass of the pigment (a). When the amount of the wetting agent is more than 80 parts by mass, the solid content concentration tends to decrease, so that a sufficient shear force cannot be applied. On the other hand, when the amount is less than 10 parts by mass, it becomes difficult to make the resin component into a swollen state, so that sufficient shearing force cannot be applied, the pigment (a) is sufficiently pulverized, and the styrene acrylic resin (b ) Is difficult to adsorb on the surface, and a uniform colored kneaded product tends not to be obtained.

  In the process of the method for producing an aqueous pigment dispersion for inkjet recording of the present invention, it is preferable that the temperature is kneaded at a kneading temperature lower than the glass transition point of the styrene-acrylic copolymer (b) to be used. By kneading in such a temperature range, the kneading viscosity at the time of kneading decreases as the kneading temperature rises, the shearing force applied to the kneaded product does not decrease, and the copolymer does not enter a molten state. . For this reason, in order to effectively prevent volatilization of the wetting agent, it is possible to prevent an increase in the solid content ratio in the kneaded product after completion of the kneading, and the solid kneaded product is solidified after the copolymer is melted. Since it does not become a thing, since the last kneaded material can be easily disperse | distributed in an aqueous medium, it is preferable.

  When kneading the colored kneaded product, it is preferable to use a kneader having a stirring tank and stirring blades for mixing rather than using an open kneader having no stirring tank such as a two-roller. When such a kneader is used, the pigment (a) and the fine powdery styrene acrylic copolymer (b) can be directly mixed at a high solid content ratio. Further, these solids and liquids such as wetting agents and basic compound solutions can be blended and mixed at the same time, and it is also easy to add and add appropriate wetting agents in the kneading step. By using a kneader having a stirring vessel and a stirring blade for mixing in this way, the form when the material constituting the kneaded product is put into the stirring vessel, or the form and mechanical characteristics during kneading of the kneaded product Therefore, there is a high degree of freedom in selecting the raw materials to be added to the kneading process of resin, pigment, and the like, the mixing ratio, and the timing of addition.

  Furthermore, when such a kneader is used, evaporation of a wetting agent or the like can be suppressed during kneading, and unlike an open system kneading apparatus such as a two-roller, the kneaded material during kneading with respect to the mass of the charged mixture. The mass of the aqueous pigment dispersion does not substantially change, and a kneaded product for an aqueous pigment dispersion having the same composition as the preparation can be obtained, and the production stability is improved. The final kneaded product can be taken out in the form of a lump containing a suitable solvent, and the solid content ratio does not become too high. For this reason, it is easy to produce an aqueous pigment dispersion for ink jet recording by directly diluting the colored kneaded product after kneading with an aqueous medium.

  As a kneader having a stirring tank, a kneading machine having a multi-shaft stirring blade is preferable from the viewpoint of kneading efficiency, and as a specific example, the clearance between the stirring blade and the wall surface of the kneading tank is small when the planetary mixer is stirred. This is preferable in that the dead space at the time is small. Furthermore, in the production of the aqueous pigment dispersion of the present invention, the viscosity of the kneaded product varies in a wide range in the production process of the colored kneaded product by kneading, but the planetary mixer can cope with a wide range of viscosities. Is preferred.

It is considered that the phosphate ester surfactant described in the present application is adsorbed on the styrene acrylic resin (b) that covers the pigment (a). Therefore, in order to strongly adsorb the phosphate ester-based surfactant (e), when a high shear force is applied to the surface of the styrene acrylic resin (b) covering the pigment (a), the pigment (a) The styrene acrylic resin (b), the basic compound (c), and the wetting agent (d) are preferably added to the mixture.
However, if it is added from the beginning of kneading, the adsorption on the pigment surface tends to compete with the styrene acrylic resin (b), and even if it is adsorbed, the pigment is crushed and a new pigment surface is exposed. there's a possibility that. Further, the basic compound to be used for neutralization of the anionic group of the styrene-acrylic acid resin may be consumed by the reaction with the phosphate ester surfactant, which is not preferable. Further, since the phosphate ester surfactant is usually added as an aqueous solution, the solid content ratio in the kneading step is lowered by the addition, and the shearing force applied to the pigment surface is lowered.

For this reason, it is preferable to add the phosphate ester-based surfactant (e) after the pigment (a) is almost crushed and the crushed pigment surface is coated with the styrene acrylic resin (b). It is necessary to carry out after the start of the kneading process and after the load current of the kneading apparatus being used reaches the maximum value.
By adding the phosphate ester surfactant in this way, the shearing force applied to the surface of the styrene acrylic acid copolymer that coats the pigment after the addition is such that the pigment is initially coated with the copolymer on the pigment surface. It will be lower than the shear force applied to the surface. Furthermore, by adding a phosphate ester-based surfactant as an aqueous solution, the solid content ratio of the material to be kneaded can be further reduced, and the shearing force can be adjusted in a further lower direction. In this way, while adjusting the shearing force applied by the kneading apparatus from a large shearing force when the pigment is coated with the copolymer to a smaller shearing force, the surface of the styrene acrylic acid copolymer coated on the pigment surface is coated with phosphorus. An acid ester surfactant is added.
When the phosphate ester surfactant is added in the kneading step, it may be added all at once, but the total amount added is divided into 5 or more times, and the whole mixture is stirred by the kneading apparatus after the addition. After that becomes uniform, the next stirring may be performed later. Alternatively, when the aqueous medium is added in divided portions in this way, a small amount of the aqueous medium can be added continuously over the entire time of the required mixing step. In particular, when a kneading apparatus having a large capacity is used, it takes time to homogenize the mixture. Therefore, it is preferable to take a method such as divided addition or small amount continuous addition. When a phosphate ester surfactant is added, the solid content ratio of the material to be kneaded decreases, but the kneading process is continued while confirming further decrease in load current.

The addition of the phosphate ester surfactant may be performed after the kneading step and before the mixing step. Thus, by adding the phosphate ester surfactant to the mixture after the kneading step before the mixing step, the phosphate ester surfactant is added before the aqueous medium is added in the mixing step and the solid content ratio of the mixture decreases. The phosphate ester surfactant is efficiently adsorbed under a high shear force applied to the surface of the pigment coated with the styrene acrylic acid copolymer. Furthermore, as the addition of phosphate ester surfactants progresses, the solid content ratio of the mixture after the kneading process gradually decreases and the shearing force slowly decreases, so styrene acrylic adsorbed on the pigment surface under high shearing force. The possibility that the acid copolymer is replaced with a phosphate ester surfactant is also reduced. In addition, it is preferable to add the phosphate ester-based surfactant at the time of switching between such processes from the viewpoint of improving the efficiency of the manufacturing process and stabilizing the characteristics.
The addition of phosphate ester surfactants can also be performed in a lump, but the total amount is divided into 5 or more times, stirred after the addition, and the mixture containing the added surfactant becomes uniform. Therefore, the following surfactant may be added. Alternatively, a small amount of the surfactant can be continuously added while stirring over the entire addition time required until the entire amount is added after the divided addition. In particular, when a kneading apparatus having a large capacity is used, it takes time to homogenize the mixture. Therefore, it is preferable to take a method such as divided addition or small amount continuous addition. When the phosphate ester surfactant is added immediately after the kneading step, the process proceeds to a mixing step in which an aqueous medium is subsequently added after completion of the addition.

The solid colored kneaded material produced in the kneading step of the present invention is coated with a resin while the pigment is finely divided, and an aqueous medium is added and stirred in the mixing step in the production method of the present invention. It can be quickly dispersed in an aqueous medium. Thus, in the mixing step in the production method of the present invention, an aqueous medium is added to the solid pigment dispersion, which is the colored kneaded product obtained in the kneading step, mixed, stirred, and liquefied to lower the viscosity. Add media and dilute.
It may be liquefied at a time by adding the aqueous medium all at once, but the total addition amount is divided into 5 or more times and added after stirring until the entire mixture becomes uniform. In order to realize uniform liquefaction, it is preferable to perform the following stirring. Alternatively, when the aqueous medium is added in divided portions in this way, a small amount of the aqueous medium may be added continuously over the entire time of the required mixing step. Especially when the volume of the mixture when adding, mixing and stirring the aqueous medium is large and it takes a period for the stirred aqueous medium to be mixed uniformly, the aqueous medium can be added in portions or continuously in small portions. It is preferable to add.

  In the present invention, the aqueous medium is mainly composed of water or a wetting agent that is compatible with water. Moreover, as a wetting agent used here, the thing similar to the wetting agent used in the kneading | mixing process can be used. Since it is substantially difficult to remove the wetting agent from the aqueous pigment dispersion for inkjet recording, the amount of the wetting agent is finally determined based on the aqueous ink for inkjet recording prepared from the aqueous pigment dispersion for inkjet recording. On the other hand, it is preferable to make it not more than the total amount to be finally contained. Therefore, the amount of the wetting agent in the aqueous pigment dispersion for inkjet recording is preferably 3 to 50% by mass, and more preferably 5 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.

  By the addition of such an aqueous medium, the solid content ratio of the mixture is lowered to become a highly viscous liquid. When the phosphate ester surfactant is added in the mixing step, it must be started before the mixture is liquefied. By adding before liquefaction, adsorption of the phosphate ester surfactant to the pigment surface proceeds by shearing force applied to the pigment surface during stirring of the mixture having a high solid content ratio before liquefaction. Compared with the case where it is added during the kneading step, the shearing force applied to the pigment surface is reduced when the phosphate ester is added, but the solid content ratio during kneading is reduced, so it is necessary to focus on crushing the pigment. In some cases, this method is preferred. The addition of the phosphate ester surfactant may be performed in a lump, or may be performed in small portions in the same manner as the addition of the aqueous medium. It may be added simultaneously with the addition of the aqueous medium, but the decrease in the solid content ratio due to the addition of the aqueous medium reduces the shear force generated during stirring more than when adding the iron phosphate light surfactant. In order to expedite, it is preferable to temporarily stop the addition of the aqueous medium.

In this step, it is possible to disperse the kneaded material in the aqueous medium only by mixing and stirring with a normal stirrer. However, after adding, mixing and stirring the aqueous medium, a high shear force can be obtained using a dispersing device. You may perform the distributed processing accompanied by. By carrying out such treatment, if coarse dispersed particles remain in the aqueous pigment dispersion for inkjet recording, they are further pulverized and the coarse particle components are reduced, so that the aqueous pigment dispersion is used for inkjet recording. In some cases, ink jet characteristics such as ejection stability and print density when water-based ink is produced can be further improved.
In the case of using a dispersing device to ensure the dispersion state, a known dispersing device can be used, and in the case of using a media, a paint shaker, a ball mill, an attritor, a basket mill, a sand mill, a sand grinder, a dyno mill , Disperse mat, SC mill, spike mill, agitator mill and the like. Examples of media that do not use media include juice mixers, ultrasonic homogenizers, nanomizers, resolvers, dispersers, and high-speed impeller dispersers. Among these, dispersers using media are preferable because of their high dispersibility. In addition, you may adjust a density | concentration with an aqueous medium as needed after dispersion | distribution.

The phosphoric ester surfactant is added during the kneading step or the mixing step, after the load current of the kneading apparatus used in the kneading step shows the maximum value, and at the coloring temperature in the mixing step. This is performed before the liquefaction of the paste is completed.
By adding the phosphate ester surfactant in this way, the phosphate ester surfactant can be easily added to the pigment surface coated with the styrene-acrylic acid copolymer under a high shear force. -Since the acrylic acid copolymer is sufficiently firmly fixed and coated on the pigment surface by the high shear force in the kneading step, the coating on the pigment surface is not inhibited by the phosphate ester surfactant.
Addition of the phosphate ester surfactant described in the present application, after the entire mixture becomes a clay-like lump, reaches the peak of load current and shear force, and a solid colored kneaded material is formed, Although it is before liquefaction in a mixing process, it is preferable before adding an aqueous medium in a mixing process. Preferably, the addition before adding the aqueous medium in the mixing step after the load current of the kneading apparatus becomes constant is more preferable.

  The amount of the pigment (a) in the aqueous pigment dispersion for inkjet recording of the present invention is preferably 3 to 25% by mass, and more preferably 3 to 20% by mass. When the amount of the pigment (a) is less than 3% by mass, the aqueous ink for inkjet recording prepared from the aqueous pigment dispersion for inkjet recording of the present invention is insufficiently colored, and a sufficient image density tends not to be obtained. It is in. On the other hand, when the amount is more than 25% by mass, the dispersion stability of the pigment in the aqueous pigment dispersion for ink jet recording tends to decrease with the lapse of time during long-term storage.

  An ink composition for ink-jet recording can be prepared using the aqueous pigment dispersion for ink-jet recording produced through the above steps. Basically, for example, the aqueous pigment dispersion obtained as described above can be further diluted with an aqueous medium. When preparing an aqueous ink for inkjet recording using the aqueous pigment dispersion for inkjet recording of the present invention, coarse particles generated, mixed or remaining in the process may cause nozzle clogging and other image characteristics. A process for reducing the number of coarse particles may be used by removing these by centrifugation or filtration before or after preparing the ink so as not to cause deterioration. In the present invention, since the number of coarse particles in the aqueous pigment dispersion is greatly reduced in advance by the kneading step, even if such a final step for reducing the number of coarse particles is performed, The process time is not increased and the production efficiency is not lowered, and the yield is not significantly reduced in the process. The amount of the pigment (a) in the water-based ink for ink-jet recording prepared from the water-based pigment dispersion for ink-jet recording of the present invention is determined by the necessity of obtaining a sufficient image density during ink-jet printing and the dispersion of dispersed particles in the ink. In order to ensure stability, the content is preferably 2 to 10% by mass.

In the ink composition, it is preferable to add a wetting agent to the aqueous medium for diluting the aqueous pigment dispersion because it contributes to prevention of drying, viscosity adjustment, and concentration adjustment. Examples of the wetting agent used in the aqueous medium include those used in the above-described kneading step or those similar to those used in the aqueous medium for dispersing the colored kneaded material for inkjet recording ink. Can do.
In addition, it is preferable that a water-soluble organic solvent exhibiting permeability to the recording medium is blended to impart permeability to the ink composition. In the ink composition, the permeability is a characteristic necessary for adjusting the penetrability of the ink composition into the recording medium and the dot diameter on the recording medium.
Examples of water-soluble organic solvents used for imparting permeability 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 oxides of alkyl alcohols such as propylene glycol propyl ether. Examples include adducts.

As a raw material for producing the water-based ink for ink jet recording, for example, various known additives can be blended in addition to the above.
As what can be mix | blended, an alkali agent, a pH adjuster, surfactant, antiseptic | preservative, a chelating agent, a plasticizer, antioxidant, a ultraviolet absorber, an ultraviolet curable resin etc. can be illustrated, for example.
In order to produce the water-based ink for ink-jet recording of the present invention, an aqueous pigment dispersion for ink-jet recording containing a phosphate ester-based surfactant prepared in the mixing step, and an aqueous medium for further diluting the same This can be produced by adding the above-mentioned various additives selected according to the conditions and stirring uniformly.
The water-based ink for ink-jet recording thus produced can be suitably used for various ink-jet printers as ink for ink-jet recording. Applicable ink jet methods are not particularly limited, but examples include well-known on-demand types such as a charge control type, a continuous injection type such as a spray type, a piezo type, a thermal type, and an electrostatic suction type. Can do. The water-based ink for ink jet recording of the present application enables extremely stable ink ejection when applied to these various ink jet methods, and can be suitably used particularly for thermal jet ink jet recording.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples.
(Resin synthesis)
100 parts of methyl ethyl ketone was charged into a reaction vessel having a stirring device, a dropping device, and a reflux device, and the inside of the reaction vessel was purged with nitrogen while stirring. The reaction vessel was heated to a methyl ethyl ketone reflux state while maintaining a nitrogen atmosphere, and then 83 parts of styrene, 7 parts of acrylic acid, 10 parts of methacrylic acid and a polymerization catalyst ("W- 59 ") 8 parts of the mixture was added dropwise over 2 hours. In the middle of dropping, the temperature of the reaction system was kept at 80 ° C.
After completion of the dropwise addition, the reaction was continued for another 25 hours at the same temperature. In the course of the reaction, a polymerization catalyst was added as appropriate while confirming the consumption of the raw materials. After completion of the reaction, methyl ethyl ketone was distilled off under reduced pressure, and the resulting solid was pulverized to obtain a powder of this styrene-acrylic acid copolymer (A).
Thus, styrene / acrylic acid / methacrylic acid = 83/7/10 (wt%), a styrene acrylic acid copolymer A having a weight average molecular weight of 11000 and an acid value of 116 mgKOH / g was produced.
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.
In addition, the measurement was implemented with the following apparatuses and conditions.
Liquid feed pump: LC-9A
System controller: SCL-6B
Autoinjector: SIL-6B
Detector: RID-6A
Made by Shimadzu Corporation.
Data processing software: Sic480II data station (manufactured by System Instruments).
Column: GL-R400 (guard column) + GL-R440 + GL-R450 + GL-R400M (manufactured by Hitachi Chemical Co., Ltd.)
Elution solvent: THF
Elution flow rate: 2 ml / min
Column temperature: 35 ° C

Example 1
<Kneading> A mixture having the following composition was charged into a 0.4 L planetary mixer ACM04LVJ-B (manufactured by Aikosha Seisakusho Co., Ltd.), the jacket was heated at 60 ° C., rotation speed: 80 rpm, revolution speed: Kneading was continued for 10 minutes at 25 rpm.
Styrene-acrylic acid copolymer A 10.05 parts quinacridone pigment (CI Pigment Red 282)
(Irgazin Magenta 2012 (Ciba)) 49.00 parts Dispersing aid consisting of quinacridone pigment derivatives (phthalimidomethylated 3,10-dichloroquinacridone) 1.26 parts diethylene glycol (Maruzen Petrochemical Co., Ltd.) 25.50 parts The kneaded product of 5.47 parts of 34 wt% potassium hydroxide aqueous solution was solid. Subsequently, phosphanol GF185 (phosphate surfactant HLB = 5.2 carbon number of alkyl group 13, no ethylene oxide chain, manufactured by Toho Chemical Industry Co., Ltd.) was neutralized with 1N aqueous potassium hydroxide solution. 25.00 parts of a% aqueous solution was gradually added over 30 minutes to lower the solid content ratio of the kneaded product to obtain a gum-like mixture. The gum-like mixture was taken out from the planetary mixer, 110 parts of ion-exchanged water was gradually added, and stirring with a juice mixer (manufactured by Zojirushi Co., Ltd.) was repeated to complete the addition in 15 minutes. The liquefied kneaded product (a) had a solid content concentration of 34.4% and a pigment concentration of 25.99%.

<Dilution> 90 parts of ion-exchanged water, 11 parts of diethylene glycol and 0.3 part of preservative were added to 160 parts of the liquefied kneaded product (a) to obtain a pigment dispersion (a). The solid content concentration of the pigment dispersion (a) was 20.1%, and the pigment concentration was 15.2%.
<Preparation of water-based ink composition for inkjet recording>
The following composition was mixed using the pigment dispersion (a) to prepare an ink composition for inkjet recording having a pigment concentration of 3.5% by mass.
Pigment dispersion (a) 23.03 parts Triethylene glycol monobutyl ether 8.0 parts
2-Pyrrolidinone 8.0 parts Glycerin 3.0 parts Surfynol 440 0.5 part Ion-exchanged water 57.47 parts Each component was mixed at room temperature to obtain an ink composition for ink jet recording (a).

(Example 2)
<Kneading> A mixture having the following composition was charged into a 0.4 L planetary mixer ACM04LVJ-B (manufactured by Aikosha Seisakusho Co., Ltd.), the jacket was heated at 60 ° C., rotation speed: 80 rpm, revolution speed: Kneading was continued for 10 minutes at 25 rpm.
Styrene-acrylic acid copolymer A 10.05 parts
Quinacridone pigment (PR282)
(Irgazin Magenta 2012 (Ciba)) 49.00 parts Dispersing aid consisting of quinacridone pigment derivatives (phthalimidomethylated 3,10-dichloroquinacridone) 1.26 parts diethylene glycol (Maruzen Petrochemical Co., Ltd.) 25.50 parts The kneaded product of 5.47 parts of 34 wt% potassium hydroxide aqueous solution was solid. Subsequently, phosphanol RS610 (phosphate surfactant HLB = 10.5, carbon number 13 of alkyl group, number of repeating units of ethylene oxide 6 manufactured by Toho Chemical Industry Co., Ltd.) was neutralized with 1N aqueous potassium hydroxide solution. 25.00 parts of the prepared 20% aqueous solution was gradually added over 30 minutes, and stirring of the kneaded product was continued to lower the solid content ratio of the kneaded product to obtain a gum-like mixture. The gum-like mixture was taken out from the planetary mixer, 110 parts of ion-exchanged water was gradually added, and stirring with a juice mixer (manufactured by ZOJIRUSHI) was repeated to complete the addition in 15 minutes. This liquefied kneaded product (b) had a solid content concentration of 33.8% and a pigment concentration of 25.54%.

<Dilution> 72 parts of ion-exchanged water, 9 parts of diethylene glycol and 0.2 part of preservative were added to 160 parts of the liquefied kneaded product (b) to obtain a pigment dispersion (b). The solid content concentration of the pigment dispersion (b) was 20.9%, and the pigment concentration was 15.8%.
<Preparation of water-based ink composition for inkjet recording>
The following composition was mixed using the pigment dispersion (b) to prepare an ink composition for ink jet recording having a pigment concentration of 3.5% by mass.
Pigment dispersion (b) 22.15 parts Triethylene glycol monobutyl ether 8.0 parts
2-Pyrrolidinone 8.0 parts Glycerin 3.0 parts Surfinol 440 0.5 parts Ion-exchanged water 58.8 parts Each component was mixed at room temperature to obtain an ink composition for ink jet recording (b).

(Example 3)
<Kneading> A mixture having the following composition was charged into a 0.4 L planetary mixer ACM04LVJ-B (manufactured by Aikosha Seisakusho Co., Ltd.), the jacket was heated at 60 ° C., rotation speed: 80 rpm, revolution speed: Kneading was continued for 10 minutes at 25 rpm.
Styrene-acrylic acid copolymer A 10.05 parts quinacridone pigment (PR282)
(Irgazin Magenta 2012 (Ciba)) 49.00 parts Dispersing aid consisting of quinacridone pigment derivatives (phthalimidomethylated 3,10-dichloroquinacridone) 1.26 parts diethylene glycol (Maruzen Petrochemical Co., Ltd.) 25.50 parts The kneaded product of 5.47 parts of 34 wt% potassium hydroxide aqueous solution was solid. Subsequently, phosphanol RD720 (phosphate ester surfactant HLB = 14.4 carbon number of alkyl group 18, ethylene oxide repeating unit number 7 Toho Chemical Industries Co., Ltd.) 4.9 parts gradually over 30 minutes. In addition, stirring of the kneaded material was continued to lower the solid content ratio of the kneaded material to obtain a gum-like mixture. The gum-like mixture was taken out from the planetary mixer, 110 parts of ion-exchanged water was gradually added, and stirring with a juice mixer (manufactured by ZOJIRUSHI) was repeated to finish adding the entire amount in 15 minutes. The liquefied kneaded product (c) had a solid content concentration of 30.38% and a pigment concentration of 22.94%.

<Dilution> 61 parts of ion-exchanged water, 10 parts of diethylene glycol and 0.2 part of preservative were added to 160 parts of the liquefied kneaded product (c) to obtain a pigment dispersion (c). The solid content concentration of the pigment dispersion (c) was 20.6%, and the pigment concentration was 15.57%.
<Preparation of water-based ink composition for inkjet recording>
The following composition was mixed using the pigment dispersion (c) to prepare an ink composition for ink jet recording having a pigment concentration of 3.5% by mass.
Pigment dispersion (c) 22.48 parts Triethylene glycol monobutyl ether 8.0 parts
2-Pyrrolidinone 8.0 parts Glycerin 3.0 parts Surfynol 440 0.5 parts Ion-exchanged water 58.02 parts The components were mixed at room temperature to obtain an ink composition (c) for inkjet recording.

(Comparative Example 1)
<Kneading> A mixture having the following composition was charged into a 0.4 L planetary mixer ACM04LVJ-B (manufactured by Aikosha Seisakusho Co., Ltd.), the jacket was heated at 60 ° C., rotation speed: 80 rpm, revolution speed: Kneading was continued for 10 minutes at 25 rpm.
Styrene-acrylic acid copolymer A 10.05 parts quinacridone pigment (PR282)
(Irgazin Magenta 2012 (Ciba)) 49.00 parts Dispersing aid consisting of quinacridone pigment derivatives (phthalimidomethylated 3,10-dichloroquinacridone) 1.26 parts diethylene glycol (Maruzen Petrochemical Co., Ltd.) 25.50 parts The kneaded product of 5.47 parts of 34 wt% potassium hydroxide aqueous solution was solid. The kneaded product was taken out from the planetary mixer, 110 parts of ion-exchanged water was gradually added, and stirring with a juice mixer (manufactured by Zojirushi Co., Ltd.) was repeated to finish the entire amount in 15 minutes. The liquefied kneaded product (d) had a solid content concentration of 29.3% and a pigment concentration of 23.09%.

<Dilution> To 160 parts of the liquefied kneaded product (d), 68 parts of ion-exchanged water, 10 parts of diethylene glycol, and 0.2 part of a preservative were added to obtain a pigment dispersion (d). The solid content concentration of the pigment dispersion (d) was 19.36%, and the pigment concentration was 15.26%.
<Preparation of water-based ink composition for inkjet recording>
The following composition was mixed using the pigment dispersion (d) to prepare an ink composition for inkjet recording having a pigment concentration of 3.5% by mass.
Pigment dispersion (d) 22.94 parts Triethylene glycol monobutyl ether 8.0 parts
2-Pyrrolidinone 8.0 parts Glycerin 3.0 parts Surfynol 440 0.5 parts Ion-exchanged water 57.56 parts Each component was mixed at room temperature to obtain an ink composition (d) for ink jet recording.

(Comparative Example 2)
<Kneading> A mixture having the following composition was charged into a 0.4 L planetary mixer ACM04LVJ-B (manufactured by Aikosha Seisakusho Co., Ltd.), the jacket was heated at 60 ° C., rotation speed: 80 rpm, revolution speed: Kneading was continued for 10 minutes at 25 rpm.
Styrene-acrylic acid copolymer A 10.05 parts quinacridone pigment (PR282)
(Irgazin Magenta 2012 (Ciba)) 49.00 parts Dispersing aid consisting of quinacridone pigment derivatives (phthalimidomethylated 3,10-dichloroquinacridone) 1.26 parts diethylene glycol (Maruzen Petrochemical Co., Ltd.) 25.50 parts The kneaded product of 5.47 parts of 34 wt% potassium hydroxide aqueous solution was solid. The kneaded product is taken out from the planetary mixer, and 110 parts of ion exchange water, Phosphanol GF185 (phosphate ester surfactant HLB = 5.2 carbon number of alkyl group 13, no ethylene oxide chain, manufactured by Toho Chemical Industry Co., Ltd.) By adding 25.00 parts of 20% aqueous solution prepared by neutralizing with 1N potassium hydroxide aqueous solution at a time and treating for 10 minutes with a juice mixer (manufactured by Zojirushi), liquefaction of the kneaded product and phosphate ester system The addition of surfactant hardened at the same time.
The liquefied kneaded product (e) had a solid content concentration of 30.3% and a pigment concentration of 23.19%.

<Dilution> To 160 parts of the liquefied kneaded product (e), 68 parts of ion-exchanged water, 10 parts of diethylene glycol, and 0.2 part of a preservative were added to obtain a pigment dispersion (e). The solid content concentration of the pigment dispersion (e) was 19.62%, and the pigment concentration was 14.81%.
<Preparation of water-based ink composition for inkjet recording>
The following composition was mixed using the pigment dispersion (e) to prepare an ink composition for inkjet recording having a pigment concentration of 3.5% by mass.
Pigment dispersion (e) 23.63 parts Triethylene glycol monobutyl ether 8.0 parts
2-Pyrrolidinone 8.0 parts Glycerin 3.0 parts Surfynol 440 0.5 parts Ion-exchanged water 56.87 parts The components were mixed at room temperature to obtain an ink composition for ink jet recording (a).

(Comparative Example 3)
<Kneading> A mixture having the following composition was charged into a 0.4 L planetary mixer ACM04LVJ-B (manufactured by Aikosha Seisakusho Co., Ltd.), the jacket was heated at 60 ° C., rotation speed: 80 rpm, revolution speed: Kneading was continued for 10 minutes at 25 rpm.
Styrene-acrylic acid copolymer A 10.05 parts quinacridone pigment (PR282)
(Irgazin Magenta 2012 (Ciba)) 49.00 parts Dispersing aid consisting of quinacridone pigment derivatives (phthalimidomethylated 3,10-dichloroquinacridone) 1.26 parts diethylene glycol (Maruzen Petrochemical Co., Ltd.) 25.50 parts The kneaded product of 5.47 parts of 34 wt% potassium hydroxide aqueous solution was solid. The kneaded product is taken out from the planetary mixer, 110 parts of ion exchange water, Phosphanol RS610 (phosphate surfactant HLB = 10.5, carbon number 13 of alkyl group, number of repeating units of ethylene oxide 6 Toho Chemical Co., Ltd. The product was neutralized with 1N aqueous potassium hydroxide solution and 25.00 parts of a 20% aqueous solution was added at once, and the mixture was treated with a juice mixer (manufactured by ZOJIRUSHI) for 10 minutes. The addition of the acid ester surfactant was solidified at the same time.
The liquefied kneaded product (f) had a solid content concentration of 30.87% and a pigment concentration of 23.3%.
<Dilution> To 140 parts of the liquefied kneaded product (f), 56 parts of ion-exchanged water, 9 parts of diethylene glycol, and 0.2 part of a preservative were added to obtain a pigment dispersion (f). The solid content concentration of the pigment dispersion (f) was 20.85%, and the pigment concentration was 15.73%.

(Comparative Example 4)
<Kneading> A mixture having the following composition was charged into a 0.4 L planetary mixer ACM04LVJ-B (manufactured by Aikosha Seisakusho Co., Ltd.), the jacket was heated at 60 ° C., rotation speed: 80 rpm, revolution speed: Kneading was continued for 10 minutes at 25 rpm.
Styrene-acrylic acid copolymer A 10.05 parts quinacridone pigment (PR282)
(Irgazin Magenta 2012 (Ciba)) 49.00 parts Dispersing aid consisting of quinacridone pigment derivatives (phthalimidomethylated 3,10-dichloroquinacridone) 1.26 parts diethylene glycol (Maruzen Petrochemical Co., Ltd.) 25.50 parts The kneaded product of 5.47 parts of 34 wt% potassium hydroxide aqueous solution was solid. The kneaded product was taken out from the planetary mixer, 110 parts of ion-exchanged water, Phosphanol RD720 (phosphate surfactant HLB = 14.4, carbon number 18 of alkyl group, number of repeating units of ethylene oxide 7 Toho Chemical Industry Co., Ltd. (Manufactured) 4.9 parts at a time and treated with a juice mixer (manufactured by Zojirushi) for 10 minutes solidified the liquefaction of the kneaded product and the addition of the phosphate ester surfactant at the same time. The liquefied kneaded product (g) had a solid content concentration of 30.11% and a pigment concentration of 22.7%.
<Dilution> To 160 parts of the liquefied kneaded product (g), 56 parts of ion-exchanged water, 10 parts of diethylene glycol and 0.2 part of preservative were added to obtain a pigment dispersion (g). The solid content concentration of the pigment dispersion (g) was 20.76%, and the pigment concentration was 15.67%.

(Comparative Example 5)
<Paint shaker> The following composition was charged into a 200 ml bottle and dispersed in a paint shaker for 3 hours.
Styrene-acrylic acid copolymer aqueous solution 11.62 parts quinacridone pigment (PR282)
(Irgazin Magenta 2012 (manufactured by Ciba)) 9.75 parts Dispersing aid comprising quinacridone pigment derivative (phthalimidomethylated 3,10-dichloroquinacridone) 0.25 parts diethylene glycol (manufactured by Maruzen Petrochemical Co., Ltd.) 20.00 parts Ion-exchanged water 16.66 parts Phosphanol GF185 (phosphate ester surfactant, manufactured by Toho Chemical Industry Co., Ltd.)
20% aqueous solution prepared by neutralizing with 1N aqueous potassium hydroxide solution 4.88 parts φ1.25 zirconia beads 180 parts The resulting mixture becomes mousse, and it is good even if an aqueous medium is added to lower the solid content ratio An aqueous pigment dispersion could not be formed.

<Evaluation of physical properties of pigment dispersion>
The physical properties of the ink compositions for ink jet recording obtained in Examples and Comparative Examples were measured by the following methods.
The particle size was measured at 25 ° C. by diluting about 2000 times with pure water using a Nanotrac Particle Size Analyzer Model NPA150 (Microtrac Inc.) equipped with a low-temperature thermostatic chamber LTB-125 (As One Co., Ltd.).
The coarse particle concentration was measured by accumulating with AccuSizer 780 (Particle Sizing Systems Inc.) twice with pure water at 25 ° C., and the number of coarse particles in 1 ml of the ink composition for ink jet recording was converted.
The pigment concentration was measured by holding the dispersion in a dryer at 130 ° C. for 1 hour, vacuum drying at 175 ° C. for 2 hours, evaporating to dryness, measuring the weight before and after, and adding the pigment / resin / KOH charged The ratio was calculated as retained.
Viscosity was measured at 25 ° C using VISCOMETER TV-22 (Toki Sangyo Co., Ltd.).
Absorbance was measured using a V-560 UV-VIS Spectrophotometer (JASCO Corporation).
For surface tension measurement, use Kyowa CBVP surface tension meter A3 type (Kyowa Interface Science Co., Ltd.)
Measured at 25 ° C.

<Abrasion resistance evaluation>
A water-based ink composition for inkjet recording was filled in a commercially available inkjet printer Photosmart D5360 (manufactured by Hewlett-Packard), and solid printing with 100% image density was performed on A4 size plain paper and catalog paper. After being left at room temperature for 24 hours after printing, the printed surface was rubbed with a finger, and the print density of the obtained image was measured by Spectro Scan (manufactured by Gretag Macbeth).
<Print density evaluation>
Printing was performed in the same manner as in the scratch resistance evaluation, 100% image density was recorded, and the print density of the obtained image was measured by Spectro Scan (manufactured by Gretag Macbeth).
<Comprehensive evaluation>
The above characteristics measured for each example and comparative example are shown below.

The average particle size of the pigment dispersions of Examples 1 to 3 and Comparative Examples 2 to 4 is about 120 nm, and even when a phosphate ester surfactant is added, sufficient dispersion is obtained. Similarly, the number of coarse particles is also good. It can be considered that the phosphate ester surfactant added immediately after the formation of the solid colored kneaded product does not adversely affect the dispersibility. Compared with the comparative example 1, the viscosity of the pigment dispersion liquid to which the phosphate ester surfactant is added is slightly increased. This can be considered because the phosphate ester is adsorbed on the pigment surface through the resin covering the pigment.
The pigment dispersion of Comparative Example 5 became mousse, and the physical property values could not be evaluated. When the phosphate ester surfactant is added before starting the kneading step, the adsorption on the pigment surface becomes a competition with the styrene acrylic resin, and the styrene-acrylic acid resin is adsorbed on the pigment surface. The coating tends to be inhibited, and the added basic compound is consumed, and the neutralization of the styrene-acrylic acid resin is likely to be prevented. For this reason, it is presumed that the styrene-acrylic acid resin is less likely to cover the pigment surface and a free resin is likely to be formed. Therefore, it is preferable to add the phosphate ester surfactant after the pigment is almost crushed and the crushed pigment surface is coated with a styrene acrylic resin.
Except for Comparative Example 5, the types and timing of addition of phosphate ester surfactants vary. In any of the ink compositions for ink jet recording prepared in Examples and Comparative Examples, the kneading process is not hindered by the addition of a phosphate ester surfactant. For this reason, the volume average particle size is small and shows a good value, and the number of coarse particles remains at a relatively small value. These show how the physical properties such as the volume average particle diameter and the number of coarse particles of the ink composition for ink jet recording are greatly influenced by the kneading process.

  The printed matter using the aqueous ink composed of the pigment dispersions of Examples 1 to 3 had higher print density and gloss than the printed matter based on the aqueous ink composed of the pigment dispersions of Comparative Examples 1 to 4, and had good scratch resistance. This is because the phosphate ester is adsorbed on the surface of the pigment through the resin covering the pigment, and the phosphate groups are oriented toward the outside, so it has an affinity for calcium carbonate in printed materials such as paper. It can be considered that the print density and the scratch resistance are improved as a result of the strong retention of the pigment particles on the surface of the printing material.

  The aqueous pigment dispersion for inkjet recording produced by the production method of the present invention undergoes a step of further diluting it in an aqueous medium, and in addition to good dispersibility and dispersion stability, the density of printed images and resistance It can be set as the ink composition for inkjet recording excellent in abrasion property.

Claims (13)

A kneading step of kneading a mixture containing a pigment (a), a styrene acrylic resin (b), a basic compound (c), and a wetting agent (d) to produce a solid colored kneaded material at room temperature; A method for producing an aqueous pigment dispersion for ink-jet recording, comprising a mixing step of adding an aqueous medium to a colored kneaded product and stirring to liquefy it, wherein the phosphate ester is added during the kneading step or during the mixing step or between both steps. The surfactant (e) is added, and the addition is performed after the load current of the kneading apparatus used in the kneading step reaches the maximum value and before the completion of liquefaction of the colored kneaded product in the mixing step. The manufacturing method of the aqueous | water-based pigment dispersion for inkjet recording performed before. The aqueous pigment dispersion for inkjet recording according to claim 1, wherein the addition of the phosphate ester surfactant (e) is performed after completion of the kneading step and before liquefaction in the mixing step. Liquid manufacturing method. The method for producing an aqueous pigment dispersion for inkjet recording according to claim 1, wherein the addition of the phosphate ester-based surfactant is after the end of the kneading step and before the start of the mixing step. The method for producing an aqueous pigment dispersion for inkjet recording according to any one of claims 1 to 3, wherein the phosphate ester-based surfactant chemical conversion agent is an alkyl ether phosphate ester-based surfactant. The alkyl ether phosphate surfactant is represented by the general formula (1)

(Wherein X is a hydrogen atom or general formula (2)

(2)
Wherein R represents an alkyl group having 8 to 30 carbon atoms, n represents an integer of 0 to 15, and at least one of X is represented by the general formula (2). It is a valent group. )
5. The method for producing an aqueous pigment dispersion for inkjet recording according to claim 4, wherein the phosphoric acid ester of polyoxyalkylene alkyl ether and / or a salt thereof is represented by the formula: 6. The alkyl ether phosphate ester surfactant is a salt obtained by partially or completely neutralizing an alkyl ether phosphate ester surfactant represented by the general formula (1) with an alkali metal hydroxide. A method for producing an aqueous pigment dispersion for ink-jet recording as described in 1. The method for producing an aqueous pigment dispersion for inkjet recording according to any one of claims 1 to 6, wherein the phosphate ester-based surfactant (e) has an HLB value of 15 or less. The phosphate ester-based surfactant (e) is at least partially adsorbed on the pigment surface through the styrene acrylic resin (b). A method for producing an aqueous pigment dispersion for inkjet recording. The method for producing an aqueous pigment dispersion for inkjet recording according to any one of claims 1 to 8, wherein the pigment (a) is a quinacridone pigment. The quinacridone pigment is C.I. I. The method for producing an aqueous pigment dispersion for inkjet recording according to claim 9, which is CI Pigment Red 282. The styrene acrylic resin (b) has an acid value of 60 to 300 mgKOH / g, a weight average molecular weight of 3000 to 20000, and contains 50 to 90% by mass of styrene monomer units based on all monomer components. 9. A method for producing an aqueous pigment dispersion for inkjet recording according to 8. The ink composition for inkjet recording containing the aqueous pigment dispersion for inkjet recording produced by the manufacturing method of the aqueous pigment dispersion for inkjet recording of any one of Claims 1-11. The process of further diluting the said aqueous pigment in an aqueous medium, after producing the aqueous pigment dispersion for inkjet recording by the manufacturing method of the aqueous pigment dispersion for inkjet recording of any one of Claims 1-11. A method for producing an ink composition for ink jet recording, comprising: