JP2011213792A - Method for manufacturing aqueous pigment dispersion - Google Patents

Abstract

Production of aqueous pigment dispersion for ink jet recording capable of achieving improvement in print density and scratch resistance of printed image while maintaining good dispersibility and discharge required for ink jet recording printing Providing a method.
A mixture containing a pigment (a), a styrene-acrylic acid copolymer (b), a basic compound (c) and a wetting agent (d) is kneaded to produce a solid pigment dispersion at room temperature. And a mixing step of mixing and stirring the pigment dispersion in an aqueous medium, wherein the saccharide compound is added at a specific stage of the manufacturing step of the aqueous pigment dispersion. As a result, the print density of the printed image and the scratch resistance are improved while maintaining good dispersibility and dischargeability.
[Selection figure] None

Description

The present invention relates to an aqueous pigment dispersion that can be used in a recording liquid for an ink jet printer, an ink jet ink using the same, and a method for producing the aqueous pigment dispersion.

Conventionally, an ink-jet ink in which a coloring material 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 substrate by ejecting ink droplets from fine nozzles. In recent years, ink jet recording has been studied for a wide range of applications.
Ink-jet recording methods often use water-based inks that use dyes as color materials, but recently, water-based inks that use pigment dispersions as color materials in order to obtain printed matter that is more excellent in fastness such as water resistance and light resistance. Attempts have been made to use pigment inks for on-demand ink jet recording.
Various properties are required for inks used in such ink jet recording. That is, dispersibility that can be dispersed in an aqueous medium with a fine particle size, dispersion stability so that ink physical properties do not change during long-term storage, ejection stability so as not to clog fine nozzles, and when image printing is performed Examples of the characteristics of the printed coating film include that the density of the printed matter is high and clear, and that the scratch resistance, water resistance, light resistance and the like are good.

In particular, an ink using a pigment as a coloring material is superior in water resistance and light resistance to an ink using a dye, but is difficult to stably disperse in an aqueous medium, and is manufactured using various dispersants. A method is being considered. 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.
As a result of such studies, the dispersibility and dispersion stability of inks for inkjet recording using pigments have been greatly improved. However, in terms of the high concentration and scratch resistance required for printed coatings, inks using pigments are not suitable. It is inferior to those using dyes, and there are still points to be improved.
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 have the disadvantage that the pigment is difficult to remain on the surface of the recording medium and the printing density is low. 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). In addition, in order to improve the discharge stability of pigment-based inks, it has been proposed to add polymer fine particles (for example, Patent Document 7) or to add an ethylene oxide adduct (for example, see Patent Document 8). Yes. 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, there is a drawback that 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 9). 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 10). In order to improve discharge stability and obtain a water-based ink excellent in printing characteristics and fixing properties, an ink using a pigment dispersant of polyglycerin polyoxyalkylene fatty acid has been proposed (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 12).

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, attempts have been made to add saccharides to ink jet recording ink for the purpose of improving nozzle clogging (for example, Patent Documents 13 and 14). In addition to the addition of sugars, the purpose is to suppress feathering and bleeding (Patent Document 15), the purpose is to improve the drying resistance of ink (Patent Document 16), Although it has been carried out for the purpose of controlling the bleeding of the ink used (Patent Document 17), there has been little pointed out the relationship between the addition of sugars and the improvement of printing density and scratch resistance.
Regarding the relationship between the addition of saccharides and the scratch resistance, attempts to improve the scratch resistance of aqueous pigment inks by adding cellulose derivatives and modified starches have been reported (Patent Documents 18 and 19). Simply adding these sugars as a component of the ink for ink was insufficient to improve the scratch resistance. In addition, it is necessary to add a large amount of saccharides in order to develop the effect of scratch resistance. When these saccharides are added in a large amount, they may simultaneously function as a dispersant or a wetting agent. The viscosity characteristics of the ink composition for recording may change greatly, and it may also affect ejection properties, penetrability, and the like. In addition, the addition of a large amount of sugar narrows the degree of freedom of blending of other additives, makes fine adjustment and optimization of ink physical properties difficult, and may impair the dispersibility of the original ink for ink jet recording. Therefore, there is a need for an additive that effectively improves the scratch resistance with a small amount of addition and does not hinder the dispersibility of the ink, and an ink jet of the additive that improves the scratch resistance with a small amount of addition. There has been a need for a method of blending into a recording ink composition.

JP 2002-256201 A JP 2004-263035 A JP 55-65269 A JP-A-55-66976 JP-A-6-306317 JP 2000-144031 A Japanese Patent Laid-Open No. 8-21815 JP-A-8-176481 JP-A-4-59880 JP 2007-146127 A JP 2006-8881 A JP 2005-22329 A JP-A-2-018427 Japanese Patent Laid-Open No. 9-095636 JP-A-6-228477 JP-A-2-214785 JP 7-258590 A JP-A-8-231910 JP 2000-95988 A

  An object of the present invention is an aqueous pigment dispersion for ink-jet recording that is capable of achieving improvement in print density and scratch resistance of a printed image while maintaining good dispersibility and ejection properties necessary for ink-jet recording printing. It is to provide a manufacturing method.

In order to solve the above problems, the inventors have studied the raw materials and manufacturing process of an aqueous pigment dispersion, and various additives to be added at each stage of the manufacturing process. The inventors have found that the solution to the above problems can be achieved by adding at a specific stage of the production process, and the present invention has been completed. That is, the present invention kneads a mixture containing a pigment (a), a styrene-acrylic acid copolymer (b), a basic compound (c), a wetting agent (d), and a saccharide or its derivative (e). There is provided a method for producing an aqueous pigment dispersion characterized by comprising a kneading step of producing a pigment dispersion that is solid at room temperature and a mixing step of mixing and stirring the pigment dispersion in an aqueous medium.
Furthermore, the present invention provides a method for producing an ink composition for ink jet recording, comprising a dilution step of diluting the aqueous pigment dispersion produced by the above-described method for producing an aqueous pigment dispersion with an aqueous medium.
Furthermore, the present invention is characterized by containing a pigment (a), a styrene-acrylic acid copolymer (b), a basic compound (c) a wetting agent (d), and a saccharide or a derivative thereof (e). A pigment dispersion that is solid at room temperature is provided.

The following reason can be considered that the production method of the present invention has a very remarkable effect in improving the printing density and the scratch resistance.
That is, a mixture containing a pigment (a), a styrene-acrylic acid copolymer (b), a basic compound (c), a wetting agent (d), and a saccharide or a derivative thereof (e) is kneaded at room temperature. In the kneading process for producing a solid pigment dispersion, the finer pigment is advanced by the high shearing force applied to the pigment particles, and the finer pigment surface is swollen by the wetting agent in the presence of the basic compound. It is coated with a styrene-acrylic acid copolymer. On the other hand, in kneading under a high shearing force, saccharides or derivatives thereof (e) are efficiently adsorbed on the pulverized pigment surface and / or the styrene-acrylic acid copolymer coated on the pulverized pigment surface. To do. The saccharide adsorbed on the pigment or its derivative (e) has an intermolecular hydrogen bond between the hydroxyl group possessed by it and the cellulose hydroxyl group which is the main component of the paper, and as a result, the fixing power between the pigment and the paper has been improved. It is considered that the print density is improved because it remains on the paper surface, and the scratch resistance is improved because the setting property of the pigment and paper is enhanced.

  The aqueous pigment dispersion of the present invention and the method for producing an ink composition for ink jet recording are as follows: pigment (a), styrene-acrylic acid copolymer (b), basic compound (c), wetting agent (d), And a kneading step of kneading a mixture containing saccharides or a derivative thereof (e) to produce a solid pigment dispersion at room temperature, the manufactured aqueous pigment dispersion and the ink composition for inkjet recording are good. The effect of providing a recorded image with excellent dispersibility, dischargeability, sharpness, high print density, and good scratch resistance.

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.
In the production method of the present invention, the saccharide or derivative thereof used in the kneading step may be a trisaccharide or higher polysaccharide or derivative thereof, a disaccharide or derivative thereof, or a monosaccharide or derivative thereof.
Examples of sugar derivatives include sugar fatty acid esters, sugar polyoxyalkylene fatty acid esters, sugar alcohols, sugar acids, amino sugars, and thio sugars.

  Examples of polysaccharides or derivatives thereof include starches, modified starches, polyglycerols, and celluloses. Examples of the starches include corn starch, wheat starch, rice starch, tapioca starch, potato starch, and sweet potato starch. Examples of modified starches include cationized starch, phosphate esterified starch, acetylated starch, hydroxyalkyl starch, oxidized starch, and dextrin. As polyglycerin, decaglycerin caprylic acid ester, decaglycerin lauric acid ester, decaglycerin myristic acid ester, decaglycerin palmitic acid ester, decaglycerin stearic acid ester, decaglycerin oleic acid ester, decaglycerin behenic acid ester, Examples include decaglycerin erucic acid ester. Examples of the cellulose derivative include methyl cellulose. Since these polysaccharides or their derivatives are similar to cellulose, which is the main component of sugar, it has strong hydrogen bonding force due to hydroxyl groups in cellulose molecules and hydroxyl groups in saccharides, and van der Waals force acting between saccharide and cellulose molecules. Strong binding power.

Examples of the disaccharide include maltose, isomaltose, cellobiose, lactose, sucrose, trehalose, isotrehalose, gentiobiose, melibiose, turanose, sophorose, isosaccharose and the like, and derivatives thereof include, for example, maltitol, isomaltitol, Examples include lactitol, tranitol, sucrose stearate, sucrose palmitate, sucrose myristic ester, sucrose oleate, sucrose laurate, sucrose behenate, sucrose erucate, and the like.
Examples of monosaccharides include treose, erythrulose, erythrose, arabinose, ribulose, ribose, xylose, xylulose, lyxose, glucose, fructose, mannose, idose, sorbose, gulose, talose, tagatose, galactose, allose, psicose, altrose, etc. Derivatives thereof include glycerin, threitol, erythritol, arabitol, ribitol, xylitol, lyxitol, sorbitol, mannitol, iditol, glycol, taritol, galactitol, allitol, altitol, sorbitan monolaurate, sorbitan monostearate, Sorbitan tristearate, sorbitan monooleate, sorbitan trioleate, polyoxyethylene Rubitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan tetraoleate Examples include oleate, polyoxyethylene sorbitan trioleate, glycerol monostearate, glycerol monooleate, and the like.

  Among these saccharides, monosaccharides and disaccharides and their derivatives are effective for scratch resistance of printed images because their hydroxyl groups have the same characteristics as those of polysaccharides. The change in physical properties is less than that of polysaccharides of trisaccharides or more, which is preferable. Furthermore, by forming derivatives having various functional groups, it is easy to use saccharide derivatives in which individual saccharides have been adjusted for their hydrophobicity and hydrophilicity and controlled for various properties. Particularly preferred are monosaccharides and derivatives thereof.

Monosaccharide and disaccharide derivatives are preferably alkylene oxide adducts of these sugars or sugar alcohols and / or alkyl, alkenyl and aryl ether compounds of the adducts. The number of moles of alkylene oxide added to one molecule of sugar or sugar alcohol is preferably 1 to 100, more preferably 1 to 50, and even more preferably 2 to 25. These monosaccharide and disaccharide derivatives preferably have at least one hydroxyl group per molecule, more preferably two or more.
The alkyl group, alkenyl group or aryl group for etherifying these sugar or sugar alcohol alkylene oxide adducts include C _{1 to} C ₂₀ alkyl groups, alkenyl groups and phenyl groups, substituted phenyl groups, naphthyl groups, substituted naphthyl groups. And aryl groups such as groups.
The position of etherification may be a hydroxyl group of a sugar or a sugar alcohol or a hydroxyl group at the end of an alkylene oxide chain.
The monosaccharide or disaccharide derivative used in the present invention is adsorbed on the surface of the hydrophobic pigment together with the dispersion resin in the kneading step, and after adsorbing to the pigment, the dispersion function of the dispersion resin is not hindered. It preferably has a function of enhancing the dispersibility of the resin, and preferably functions as a surfactant in an aqueous medium. In particular, the HLB is preferably 8 or more.

In the saccharides or saccharide derivatives used in the present invention, among the monosaccharides or disaccharides and derivatives thereof, monosaccharides and derivatives thereof are more preferable, and it is even more preferable that the monosaccharide is hexose. .
Specific examples of hexose include altrose, allose, idose, galactose, quinobose, gulose, diquitarose, dichitoxose, simarose, sorbose, tagaroose, talose, fucose, fructose, manose, rhamnose and the like. Examples of the hexose sugar alcohol as a derivative thereof include inositol, galactitol, mannitol, sorbitol and the like. Examples of the alkylene oxide added to hexose or its sugar alcohol include ethylene oxide, propylene oxide, butylene oxide, tetrohydrofuran, etc. The preferred number of addition moles and the form of addition are already in the form of monosaccharides and disaccharides. By the way, it is the same as the range described above, and alkyl, alkenyl, aryl ether compounds may be added to them, and preferable carbon number such as alkyl group, alkenyl group, or aryl group for etherifying the alkylene oxide adduct Is as already described.

（１）
（但し、式中、Ｘ、Ｙ、Ｚはそれぞれ独立に水素原子または−（ＣＨ_２ＣＨ_２Ｏ）ｍＲ_２または−（ＣＨ_３ＣＨＣＨ_２Ｏ）ｍＲ_２または−ＣＯＲ_３であり、Ｗは−（ＣＨ_２ＣＨ_２Ｏ）ｎ−、または−（ＣＨ_２ＣＨＣＨ_３Ｏ）ｎ−であり、Ｒ１、Ｒ２、Ｒ３はそれぞれ独立に水素原子または炭素原子数１〜３０のアルキル基であってｍは１〜１００の整数、ｎは０または１〜１００の整数であり、Ｘ，Ｙ，Ｚ中のｍはそれぞれ異なっていてもよい。）

（２）
（但し、式中、Ｘ、Ｙ、Ｚは水素原子または−（ＣＨ_２ＣＨ_２Ｏ）ｍＲ_２または
−（ＣＨ_３ＣＨＣＨ_２Ｏ）ｍＲ_２または−ＣＯＲ_３であり、Ｗは−（ＣＨ_２ＣＨ_２Ｏ）ｎ−、または−（ＣＨ_２ＣＨＣＨ_３Ｏ）ｎ−であり、Ｒ１、Ｒ２、Ｒ３は水素原子または炭素原子数１〜２０のアルキル基であってｍは１〜１００の整数、ｎは０または１〜１００の整数であり、Ｘ，Ｙ，Ｚ中のｍはそれぞれ異なっていてもよい。）
これら２つ構造のなかでは一般式（１）の構造をとるものが好ましい。
上記の式においてＸ、Ｙ、Ｚのうちの少なくとも一つは水素原子、または−（ＣＨ_２ＣＨ_２Ｏ）ｍＨであることが好ましい。
ｍは１〜５０の整数であることが好ましく、ｎは０または１〜５０の整数であることが好ましく、さらにｍは１〜２５の整数であることがさらに好ましく、ｎは０または１〜２５の整数であることがさらに好ましい。またＲ１、Ｒ２、Ｒ３は水素原子または炭素原子数５〜３０のアルキル基であることが好ましく、さらに水素原子または炭素原子５〜２０のアルキル基であることがさらに好ましい。 Among the hexose and hexose derivatives, sorbitol, which is a sugar alcohol of hexose, and derivatives thereof are preferably used. In particular, sorbitan obtained by intramolecular dehydration of sorbitol is known as a raw material for surfactants, and sorbitan and derivatives thereof are preferably used. Derivatives of sorbitan include fatty acid esters, alkylene oxide adducts, and alkyl ethers of the adducts. Compounds are preferred. Sorbitan has two different structures depending on the position of intramolecular dehydration, and as derivatives thereof, those having the structure represented by the following general formula (1) or (2) having the above functional groups are preferably used. be able to.

(1)
(Wherein, X, Y and Z are each independently a hydrogen atom, — (CH ₂ CH ₂ O) mR ₂ or — (CH ₃ CHCH ₂ O) mR ₂ or —COR ₃ , and W is — ( CH ₂ CH ₂ O) n-, or _- (CH 2 CHCH ₃ O) is n-, R1, R2, R3 is m each independently a hydrogen atom or an alkyl group having 1 to 30 carbon atoms 1 An integer of ˜100, n is 0 or an integer of 1 to 100, and m in X, Y, and Z may be different from each other.

(2)
(Wherein, X, Y and Z are a hydrogen atom or — (CH ₂ CH ₂ O) mR ₂ or — (CH ₃ CHCH ₂ O) mR ₂ or —COR ₃ , and W is — (CH ₂ CH ₂ O) n-, or _- (CH 2 CHCH ₃ O) is n-, R1, R2, R3 is a hydrogen atom or an alkyl group of carbon atoms 1 to 20 m is 1 to 100 integer, n Is 0 or an integer of 1 to 100, and m in X, Y and Z may be different from each other.)
Of these two structures, those having the structure of the general formula (1) are preferable.
In the above formula, at least one of X, Y and Z is preferably a hydrogen atom or — (CH ₂ CH ₂ O) mH.
m is preferably an integer of 1 to 50, n is preferably 0 or an integer of 1 to 50, m is more preferably an integer of 1 to 25, and n is 0 or 1 to 25. More preferably, it is an integer. R1, R2 and R3 are preferably a hydrogen atom or an alkyl group having 5 to 30 carbon atoms, more preferably a hydrogen atom or an alkyl group having 5 to 20 carbon atoms.

  Among these sorbitan derivatives, those having a function as a surfactant are basically preferable. For example, sorbitan fatty acid esters are used, and specific examples of such sorbitan derivatives already include monosaccharide derivatives. Illustrated, 1,5 sorbitan monostearate, 1,4 sorbitan tristearate, 1,5 sorbitan monolaurate, 1,4 sorbitan monopalmitate, 1,5 sorbitan trioleate, 1,4 sorbitan trimyristate Etc. Furthermore, these sorbitan fatty acid esters can also be used as a dispersant suitably used in an ink jet recording composition having a pigment as a colorant.

  The sorbitan fatty acid ester is more preferably a polyoxyethylene sorbitan fatty acid ester to which ethylene oxide is added, and the polyoxyalkylene sorbitan fatty acid ester is represented by the following general formula (3) or (4)

（３）
（但し、式中のＸ，Ｙ，Ｚはそれぞれ独立に水素原子、−（ＣＨ_２ＣＨ_２Ｏ）ｍＨ、−（ＣＨ_２ＣＨＣＨ_３）ｍＨ、または−ＣＯ−Ｒ_５であり、Ｗは−（ＣＨ_２ＣＨ_２Ｏ）ｎ−、または−（ＣＨ_２ＣＨＣＨ_３Ｏ）ｎ−であり、Ｒ４、Ｒ５はそれぞれ独立に水素原子または炭素原子数１〜３０のアルキル基であって、ｍは１〜１００の整数、ｎは０または１〜１００の整数を表し、Ｘ，Ｙ、Ｚのうちの少なくとも一つは−（ＣＨ_２ＣＨ_２Ｏ）ｍＨ、または−（ＣＨ_２ＣＨＣＨ_３）ｍＨでありＸ，Ｙ，Ｚ中のｍはそれぞれ異なっていてもよい。）

(3)
(In the formula, X, Y, and Z are each independently a hydrogen atom, — (CH ₂ CH ₂ O) mH, — (CH ₂ CHCH ₃ ) mH, or —CO—R ₅ , and W is — ( CH ₂ CH ₂ O) n-, or _- (CH 2 CHCH ₃ O) is n-, R4, R5 are each independently a hydrogen atom or an alkyl group having a carbon number of 1 to 30, m is 1 An integer of 100, n represents 0 or an integer of 1 to 100, and at least one of X, Y and Z is — (CH ₂ CH ₂ O) mH or — (CH ₂ CHCH ₃ ) mH, and X , Y and Z may be different from each other.)

（４）
（但し、式中のＸ，Ｙ，Ｚはそれぞれ独立に水素原子、−（ＣＨ_２ＣＨ_２Ｏ）ｍＨ、−（ＣＨ_２ＣＨＣＨ_３）ｍＨ、または−ＣＯ−Ｒ_５であり、Ｗは−（ＣＨ_２ＣＨ_２Ｏ）ｎ−、または−（ＣＨ_２ＣＨＣＨ_３Ｏ）ｎ−であり、Ｒ１、Ｒ２、Ｒ３はそれぞれ独立に水素原子または炭素原子数１〜３０のアルキル基であって、ｍは１〜１００の整数、ｎは０または１〜１００の整数を表し、Ｘ，Ｙ、Ｚのうちの少なくとも一つは−（ＣＨ_２ＣＨ_２Ｏ）_ｍＨ、または−（ＣＨ_２ＣＨＣＨ_３）_ｎＨでありＸ，Ｙ，Ｚ中のｍはそれぞれ異なっていてもよい。）
で表されるものが好適に使用される。
ｍは１〜５０の整数であることが好ましく、ｎは０または１〜５０の整数であることが好ましく、さらにｍは１〜２５の整数であることがさらに好ましく、ｎは０または１〜２５の整数であることがさらに好ましい。またＲ１、Ｒ２、Ｒ３は水素原子または炭素原子数５〜３０のアルキル基であることが好ましく、さらに水素原子または炭素原子５〜２０のアルキル基であることがさらに好ましい。
ポリオキシアルキレン鎖の種類と長さを調整することにより、親水性、疎水性の程度を調整しやすく、顔料への吸着性と吸着された顔料の分散性を良好にするようこれらを最適化することができる。

(4)
(In the formula, X, Y, and Z are each independently a hydrogen atom, — (CH ₂ CH ₂ O) mH, — (CH ₂ CHCH ₃ ) mH, or —CO—R ₅ , and W is — ( CH ₂ CH ₂ O) n-, or _- (CH 2 CHCH ₃ O) is n-, R1, R2, R3 are each independently a hydrogen atom or an alkyl group having a carbon number of 1 to 30, m is An integer of 1 to 100, n represents 0 or an integer of 1 to 100, and at least one of X, Y and Z is — (CH ₂ CH ₂ O) _m H or — (CH ₂ CHCH ₃ ) _n. H and m in X, Y and Z may be different from each other.)
Is preferably used.
m is preferably an integer of 1 to 50, n is preferably 0 or an integer of 1 to 50, m is more preferably an integer of 1 to 25, and n is 0 or 1 to 25. More preferably, it is an integer. R1, R2 and R3 are preferably a hydrogen atom or an alkyl group having 5 to 30 carbon atoms, more preferably a hydrogen atom or an alkyl group having 5 to 20 carbon atoms.
By adjusting the type and length of the polyoxyalkylene chain, it is easy to adjust the degree of hydrophilicity and hydrophobicity, and these are optimized to improve the adsorptivity to the pigment and the dispersibility of the adsorbed pigment. be able to.

Among these polyoxyalkylene sorbitan fatty acid esters, those having an HLB of 8 or more are preferred, and those of 13 or more are more preferred in order to adsorb to the pigment surface in the kneading step and not disturb the dispersibility of the pigment.
Specific examples of sorbitol or its derivatives are illustrated below along with product examples. That is, coconut oil fatty acid sorbitan (Ionet S-20), sorbitan monostearate (Ionet S-60V), sorbitan monooleate (Ionet S-80), sorbitan trioleate (Ionette S-85), polyoxyethylene palm Examples include oil fatty acid sorbitan (Ionette T-20C), polyoxyethylene sorbitan monostearate (Ionet T-60V), polyoxyethylene sorbitan monooleate (Ionet T-80V) (all manufactured by Sanyo Chemical Industries). .
When these saccharides and saccharide derivatives are added in the kneading step, the amount is preferably 0.2 to 50% by mass with respect to the pigment (a). If the addition amount is less than 0.2% by mass, the effect of adding saccharides and saccharide derivatives to the kneading step tends to be insufficient. On the other hand, if it exceeds 50% by mass, the optimum blending ratio of the pigment (a) and the styrene-acrylic acid resin (b) in the kneading step and the balance of the optimum solid content ratio of the kneaded product may be lost. There is a tendency that a sufficient shearing force is not applied and good coating with the resin on the pigment surface is not performed.
The addition amount of the saccharide and the saccharide derivative in the kneading step is more preferably 0.5 to 30% by mass and further preferably 1 to 15% by mass with respect to the pigment (a).

  The styrene-acrylic acid copolymer used in the kneading step in the production method of the present invention comprises, as a constituent monomer component, a monomer component having a carboxyl group with a styrene monomer component and a radical polymerizable double bond. 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 based on the total of all constituent monomers. The styrenic component is more preferably contained in an amount of 60% by mass or more, and further preferably 70% by mass or more. By setting the content of the styrene monomer component in the copolymer styrene-acrylic acid copolymer to 50% by mass or more, the hydrophobicity of the copolymer styrene-acrylic acid copolymer increases, and it is stronger in water. Further, a styrene-acrylic acid copolymer is coated on the pigment. In particular, in the present invention, saccharides or saccharide derivatives are added and kneaded in the kneading step. By containing a high amount of the styrene component in this manner, even when a saccharide or saccharide derivative is added, the adsorption of the styrene-acrylic acid-based acrylic acid copolymer onto the pigment surface is not hindered, and a good coating is achieved. Progresses. As a result, when the ink composition prepared through the aqueous pigment dispersion is used for inkjet, the dispersibility and dispersion stability are high, and even when the styrene-acrylic acid copolymer-coated particles are heated, Is stable, and the high-temperature storage stability of viscosity and particle size is improved. Since the generation of aggregates is suppressed, 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. 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.

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. 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 mass average molecular weight of the styrene-acrylic acid copolymer used in the present invention is 3000 to 20000, more preferably 4000 to 15000, still more preferably 6000 to 12000, and most preferably 8000 to 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.

  As the pigment used in the production method of the present invention, known organic pigments and inorganic pigments can be used without particular limitation. These may be used alone or in combination. Examples of the pigment include quinacridone pigments, quinacridone quinone pigments, dioxazine pigments, phthalocyanine pigments, phthalone pigments, isoindolinone pigments, methine / azomethine pigments, anthrapyrimidine pigments, ansanthrone pigments, Indanthrone pigments, flavanthrone pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimidazolone pigments, azo lake pigments, insoluble azos Pigments, organic pigments such as condensed azo pigments, titanium dioxide, zinc oxide, iron oxide, chromium oxide, iron black, cobalt blue, alumina white, iron oxide yellow, viridian, zinc sulfide, lithobon, cadmium yellow, vermilion, cadmium Red, yellow lead, molybdate me Di, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine, precipitated barium sulfate, barite powder, calcium carbonate, lead white, bitumen, manganese violet, carbon black, aluminum powder, pearl pigments and other inorganic pigments Can be mentioned. These pigments may be surface-treated and have a self-dispersing function with respect to an aqueous medium.

  More specifically, as the inorganic pigment, for example, carbon black, titanium black, bengara, zinc oxide, titanium oxide and the like can be used. Organic pigments include 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. A quinacridone pigment such as CI Pigment Red 122 can be used.

  Regarding the mass ratio of the pigment to the styrene-acrylic acid copolymer, it is sufficient that the styrene-acrylic acid copolymer is present in an amount necessary to stably coat the pigment surface. Inclusion of a styrene-acrylic acid copolymer is not preferable. When an excessive amount of styrene-acrylic acid copolymer is present, free styrene-acrylic acid copolymer that does not adsorb to the pigment increases when an aqueous pigment dispersion or ink composition is prepared. When used as an ink composition, the styrene-acrylic acid copolymer is likely to adhere to the ink nozzles and cause ink discharge failure. In particular, in a thermal jet printer, there is a risk of occurrence of this discharge failure problem. high. Therefore, in the production of the aqueous pigment dispersion of the present invention, the mass ratio of styrene-acrylic acid copolymer / pigment is preferably 0.1 to 0.6. If the blending ratio of the pigment is too large relative to the styrene-acrylic acid copolymer, the above-mentioned problems are likely to occur. If the blending ratio of the pigment is too small, the pigment is sufficiently covered with the styrene-acrylic acid copolymer. Otherwise, dispersion stability and long-term storage stability may be reduced.

  In the production method of the present invention, the pigment, basic compound, and wetting agent used in the kneading step are mixed with a styrene-acrylic acid copolymer having a carboxyl group and a basic compound to neutralize the carboxyl group. A pigment dispersion for an aqueous pigment dispersion is obtained. As a result, the affinity between the pigment dispersion for aqueous pigment dispersion and water is improved, and when the aqueous pigment dispersion is produced, the pigment dispersion for aqueous pigment dispersion is quickly dispersed in water and the production efficiency is improved. . Moreover, the dispersion state of the styrene-acrylic acid copolymer-coated pigment particles in the aqueous pigment dispersion becomes more stable, and the dispersion stability and long-term storage stability are also improved. In addition, when a basic compound is blended at the time of kneading, the styrene-acrylic acid copolymer tends to swell due to the interaction between the basic compound and the styrene-acrylic acid copolymer having a carboxyl group, and the pigment becomes styrene. -It can knead | mix in the state which is easy to fully coat | cover with an acrylic acid type copolymer. Therefore, the pigment is finely pulverized during the kneading, and the pulverization proceeds while the surface of the finely dispersed pigment is covered. After the pigment coated on the surface with styrene-acrylic acid copolymer is dispersed in the aqueous medium, reaggregation is suppressed by the steric hindrance effect between the styrene-acrylic acid copolymers adsorbed on the pigment surface, so that it is coarse. Particles tend to decrease. For this reason, it is easy to omit the step of further pulverizing the coarse particles in the subsequent step, and the effect of improving the yield is also 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 improving the dispersibility of the styrene-acrylic acid copolymer by neutralization of the styrene-acrylic acid copolymer containing a carboxyl group. For this, 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 blending amount of the basic compound is set so that the neutralization rate of the styrene-acrylic acid copolymer having a carboxyl group is 20% or more, preferably 40% or more. It is preferable from the viewpoints of improvement in dispersion speed, dispersion stability, and long-term storage stability. Although the upper limit is not particularly limited, it is substantially 200% or less, preferably 40% or more and 120% or less, more preferably 80% or more and 120%, in order to prevent dispersion during long-term storage and gelation. It is as follows. Furthermore, before kneading, the basic compound is preferably mixed together with other blending components to be blended into the mixture to prepare a mixture. For example, the mixture is prepared 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, which is then mixed with other ingredients such as pigments. It can also be mixed and manufactured in multiple stages by adding it to the components. However, it is better to prepare a mixture for kneading by mixing the basic compound and other compounding ingredients at once. This is preferable in that the adsorption of the system copolymer 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

  As the wetting agent used in the kneading step in the production method of the present invention, a known one that is usually used as a wetting agent in an aqueous pigment dispersion for inkjet recording among water-soluble organic solvents can be used without any 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 laurate Glycol esters such as glycol; glycol ethers such as diethylene glycol monoethyl, diethylene glycol monobutyl, diethylene glycol monohexyl ether, propylene glycol ether, dipropylene glycol ether, and cellosolve containing triethylene glycol ether; methanol, ethanol, isopropyl alcohol , 1-propanol, 2-p Alcohols such as panol, 1-butanol, 2-butanol, butyl alcohol, pentyl alcohol, and alcohols homologous thereto; or lactones such as sulfolane; γ-butyrolactone; N- (2-hydroxyethyl) pyrrolidone, etc. In addition to lactams; glycerin and derivatives thereof, various water-soluble organic solvents known as wetting agents can be mentioned. These water-soluble organic solvents used as the wetting agent can be used alone or in combination. The selection of the water-soluble organic solvent is preferably one having a certain degree of solubility in the styrene-acrylic acid copolymer to be used, and in the kneading step, the solubility is also determined by the solubility of the styrene-acrylic acid copolymer. The amount added is adjusted.

The water-soluble organic solvent used as these wetting agents must perform well as a wetting agent and an anti-drying agent in the aqueous pigment dispersion, and among them, it has a high boiling point, low volatility, and high surface tension. Polyhydric alcohols that are liquid at room temperature are preferred, and glycols such as diethylene glycol and triethylene glycol are particularly preferred. In general, glycols are often contained in the ink composition, and there is no problem even if they remain in the ink for inkjet recording that is the final product. From the colored kneaded material that is the material to be kneaded after the kneading step. There is no need for removal. In the production method of the present invention, since the kneading step is carried out in the presence of a basic compound, the styrene-acrylic acid copolymer is easily swollen by a water-soluble organic solvent used as a wetting agent, and is suitable for kneading. It tends to be a mixture. Therefore, it is not necessary to use a water-soluble organic solvent used in the kneading step that has a particularly high solubility for the styrene-acrylic acid copolymer.
Therefore, in the production of the aqueous pigment dispersion of the present invention, the mass ratio of the wetting agent / pigment is preferably such that the mixture at the time of hot kneading can be easily kneaded, and is preferably 0.2 to 1.4. preferable. If the amount of the wetting agent is less than 0.2 times that of the pigment, the surface of the pigment cannot be sufficiently wet at the initial stage of kneading, and the styrene-acrylic acid copolymer cannot be dissolved, partially dissolved, or swollen. There is a possibility that the effect cannot be obtained sufficiently. If the amount of the wetting agent exceeds 1.4 times that of the pigment, the viscosity of the mixture for kneading decreases and sufficient kneading cannot be performed. May be caused. In addition, as mentioned above, when what is derived from a basic compound etc. and plays the role of a solvent is mix | blended, it is preferable to determine the compounding quantity of a water-soluble organic solvent in consideration of this.

Next, the method for producing the aqueous pigment dispersion of the present invention will be described in detail.
In the method for producing an aqueous pigment dispersion of the present invention, the pigment (a), the styrene-acrylic acid copolymer (b), the basic compound (c), the wetting agent (d), and the saccharide or its derivative (e ) To prepare a pigment dispersion that is solid at room temperature, and an aqueous medium is mixed with the pigment dispersion and stirred to liquefy the pigment dispersion. A mixing step of dispersing in the medium.
In the kneading step, the styrene-acrylic acid copolymer is swollen in the presence of the basic compound and the wetting agent, and the mixture containing the pigment becomes a lump of clay-like material to be kneaded. Receives a large shear force. By the shearing force, the pigment is further crushed into fine pigment particles having a smaller particle diameter, and the pulverized fine pigment particle surface is pressed with a styrene-acrylic acid resin in a swollen state, whereby the pigment particle surface The coating with styrene-acrylic acid resin proceeds. At this time, the sugar or its derivative (e) also receives a large shearing force, and the adsorption to the surface of the fine pigment particles and the surface of the styrene-acrylic acid resin covering the surface of the fine pigment particles proceeds. Therefore, in the kneading step in the method for producing the aqueous pigment dispersion of the present application, the kneading is performed so that the solid content ratio of the pigment dispersion after kneading, which is a kneaded product for the aqueous pigment dispersion, is 50 to 80% by mass. preferable. 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.

In the kneading process, styrene acrylate resin (b) and saccharide or its derivative (e) can be adsorbed on the pigment surface, but styrene acrylate resin adsorbs the highly hydrophobic styrene part well on the pigment surface. Therefore, even if the saccharide or its derivative (e) coexists, the coating of the crushed pigment surface with the styrene acrylic acid resin is not hindered and good coating is performed. The mass ratio (b) / (a) of the styrene-acrylic acid copolymer (b) to the pigment (a) in the kneading step for this is preferably 0.1 to 0.6. When (b) / (a) is 0.1 or more, the pigment tends to be sufficiently coated with the styrene-acrylic acid resin, and there is a tendency to avoid insufficient coverage of the pigment with the resin. If (b) / (a) is 0.6 or less, the presence of excess styrene-acrylic acid resin that is not adsorbed on the pigment surface tends to avoid a decrease in ejection stability.
In the kneading step in the production method of the present invention, kneading proceeds with a high shearing force, and coarse particles are remarkably reduced. Therefore, the step of further crushing the coarse particles can be largely omitted, and the production efficiency can be improved and the yield can be improved.

  In the kneading step, it is preferable to knead so that the mass of the mixture (kneaded material) does not substantially change so that water, water-soluble organic solvent, and the like do not evaporate during kneading. Under such circumstances, there is always a certain amount of solvent in the mixture from the start to the end of kneading, and the solvent that wets the pigment surface at the beginning of kneading is preferably dissolved, swollen or It is replaced with a partially dissolved styrene-acrylic acid copolymer, and the coating of the pigment with the styrene-acrylic acid copolymer proceeds smoothly and the pigment is sufficiently coated. As a result, the dispersion stability and long-term storage stability of the aqueous pigment dispersion and the ink composition are remarkably improved. Further, even after the completion of the kneading, almost the same amount of the solvent remains as at the start of the kneading, and the dissolution and dispersion of the mixture after the kneading can proceed in a very short time. The mass ratio (d) / (a) of the wetting agent (d) to the pigment (a) in the kneading step for this is preferably 0.2 to 1.4. If this value is less than 0.2, the resin component of the pigment dispersion, which is a kneaded product for an aqueous pigment dispersion, tends not to be sufficiently swollen, and the kneaded product is not sufficiently collected in the kneading step. There is a tendency that the shear force does not work. If (d) / (a) is greater than 1.4, the solid content concentration of the kneaded product tends to decrease, so that there is a tendency that sufficient shearing force is not applied to the kneaded product.

For this purpose, a kneader for kneading in a closed system is preferred, and a kneader equipped with a stirring tank and a uniaxial or multiaxial stirring blade is preferably used. The number of stirring blades is not particularly limited, but two or more stirring blades are preferable in order to obtain a high kneading action. When a kneader having such a structure is used, after producing a pigment dispersion for an aqueous pigment dispersion, it is diluted and dispersed directly with a water-soluble solvent in the same stirring tank to produce an aqueous pigment dispersion. Can do.
Examples of such an apparatus include a Henschel mixer, a pressure kneader, a Banbury mixer, a planetary mixer, and the like, and a planetary mixer is particularly suitable. In the present invention, since the kneading is performed in a state where the solid content concentration of the pigment and the styrene-acrylic acid copolymer is high, the viscosity of the kneaded material varies in a wide range depending on the kneaded state of the kneaded material, This is because the planetary mixer can cope with a wide range from a low viscosity to a high viscosity. In particular, when preparing an aqueous pigment solution, it is necessary to disperse the kneaded product in a water-soluble solvent in a mixing step, and a mixing step is performed in which the kneaded product is reduced in viscosity as uniformly as possible and dispersed in an aqueous medium. However, if a planetary mixer is used, the transition from the kneading process with high viscosity to the mixing process with low viscosity should be carried out continuously by adding an aqueous medium in the same model after kneading. This is extremely effective in reducing coarse particles and improving production efficiency.

  A pigment dispersion which is a kneaded product for an aqueous pigment dispersion is usually a semi-solid or solid kneaded product at room temperature. Therefore, an aqueous pigment dispersion is produced by dispersing the pigment dispersion, which is a kneaded product for an aqueous pigment dispersion, in an aqueous medium by stirring and mixing. In addition, since the pigment of the pigment dispersion for the aqueous pigment dispersion is already crushed at the time of producing the pigment dispersion for the aqueous pigment dispersion, the dispersion time for obtaining the aqueous pigment dispersion is short, and the production efficiency is improved. . For this reason, it is possible to obtain an aqueous pigment dispersion with reduced coarse particles simply by adding an aqueous medium to the kneaded product, mixing and stirring, and mixing and stirring with an aqueous medium using a dispersing device. The process to be performed is reduced. For example, after completion of the kneading step, the colored kneaded product can be dispersed in the aqueous medium by stirring with a stirring blade while gradually adding the aqueous medium to the colored kneaded product in the stirring tank of the kneading apparatus. In such a case, both the kneading step and the subsequent mixing and mixing steps are performed with only one kneading apparatus. For this reason, the process for obtaining the aqueous pigment dispersion takes a short time and can be carried out very efficiently. In addition, the colored kneaded material produced in the kneading step of the present invention is coated with a resin while the pigment is finely divided, and is quickly dispersed in the aqueous medium when the aqueous medium is added. In addition, since the pigment crushed in the kneading step is better coated with the resin, excellent dispersibility is stably maintained for a long time.

In the production method of the present invention, it is possible to disperse the kneaded material in the aqueous medium only by mixing and stirring with a normal stirrer in the mixing step of mixing and stirring after adding the aqueous medium to the kneaded material. 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 those that do not use media include ultrasonic homogenizers, nanomizers, resolvers, dispersers, and high-speed impeller dispersers. Among these, dispersers that use 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.
In addition, the pigment dispersion which is the kneaded product for an aqueous pigment dispersion of the present invention is water or an aqueous medium mainly composed of water due to the interaction between a styrene-acrylic acid copolymer having a carboxyl group and a basic compound. Solubility and dispersibility with respect to water are so good that they dissolve and disperse quickly in an aqueous medium. Thus, it is one of the major features of the aqueous pigment dispersion of the present invention that it is quickly dispersed and dissolved in water or an aqueous medium mainly composed of water, and this is stably maintained.

  The ink composition for ink jet recording of the present invention can be produced by further diluting the aqueous pigment dispersion prepared as described above with an aqueous medium and adding various additives as necessary. The concentration of the pigment contained in the ink composition is preferably about 2 to 10% by mass. A water-soluble organic solvent is preferably added to the aqueous medium for diluting the aqueous pigment dispersion because it contributes to drying prevention, viscosity adjustment, and concentration adjustment in the ink composition. As the water-soluble organic solvent, those used when dispersing the above-described pigment dispersion into the aqueous pigment dispersion, or those similar to the wetting agent used when kneading the pigment dispersion for the aqueous pigment dispersion are used. It can be illustrated.

In addition to an aqueous medium containing an aqueous pigment dispersion and a water-soluble organic solvent for diluting the aqueous pigment dispersion, for example, known additives can be blended in the ink composition for ink jet recording. Examples of compounds that can be blended include penetrants, alkali agents, pH adjusters, surfactants, preservatives, chelating agents, plasticizers, antioxidants, ultraviolet absorbers, binder resins, and ultraviolet curable compounds. be able to. In order to prepare an inkjet recording ink from the components of these inkjet recording ink compositions, for example, an aqueous pigment dispersion, a solvent containing a water-soluble organic solvent, and various additives as necessary are added and stirred uniformly. As a result, an ink composition can be produced.
This ink composition can be suitably used as an ink for inkjet recording. The inkjet method to be applied is not particularly limited, and known ones such as a continuous injection type such as a charge control type and a spray type, an on-demand type such as a piezo method, a thermal method, and an electrostatic suction method can be exemplified. And when this ink composition is applied to these various inkjet systems, it becomes possible to discharge ink very stably.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by a following example, unless the summary is exceeded.
(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 resin A having a styrene / acrylic acid / methacrylic acid = 83/7/10 (wt%), a weight average molecular weight of 11,000 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

In the following, when the pigment is a phthalocyanine pigment, an example in which a saccharide derivative is used and a polyoxyethylene sorbitan fatty acid ester is added to the kneading step will be described.
Example 1
<Kneading>
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 at 60 ° C., and rotation speed was 57 rpm and revolution speed was 20 rpm for 2 hours. Kneading was continued.
Styrene-acrylic acid copolymer A 1.50 parts phthalocyanine pigment (CI Pigment Blue 15: 3)
(Fastogen Blue 5310SD (manufactured by DIC)) 5.00 parts Ionette T-20C (manufactured by Sanyo Chemical Industries) 0.26 parts diethylene glycol (manufactured by Maruzen Petrochemical Co., Ltd.) 2.90 parts 34% by weight potassium hydroxide aqueous solution The 51 parts mixture became one lump during kneading, and the state of the kneaded material after 2 hours was solid. Subsequently, 12.00 parts of ion-exchanged water was gradually added over 3 hours to liquefy the kneaded product, and the liquid was taken out from the planetary mixer. The liquefied kneaded material (a) had a solid content concentration of 30.2% and a pigment concentration of 21.8%.

<Centrifuge>
To 100 parts of the liquefied kneaded product (a), 36 parts of ion-exchanged water, 4.8 parts of diethylene glycol and 0.15 part of preservative are added, and a continuous centrifuge (H-600S, manufactured by Kokusan Centrifuge Co., Ltd., 2 L capacity) is added. The aqueous pigment dispersion (a) was obtained by continuously centrifuging at room temperature with a centrifugal force of 18900 G and a residence time of 12 minutes. The solid content concentration of the aqueous pigment liquid (a) was 20.6%, and the pigment concentration was 14.9%.

<Preparation of water-based ink composition for inkjet recording>
The following composition was mixed and stirred using the aqueous dispersion (a) to prepare an ink composition for inkjet recording having a pigment concentration of 2.7% by mass.
Aqueous pigment liquid (a) 18.1 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 62.4 parts Each component was mixed at room temperature and stirred to obtain an ink composition (a) for ink jet recording.

(Example 2)
<Kneading>
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 to 60 ° C., and the rotational speed was 57 rpm and the revolution speed was 20 rpm. The kneading was continued for a time.
Styrene-acrylic acid copolymer A 1.50 parts phthalocyanine pigment (CI Pigment Blue 15: 3)
(Fastogen Blue 5310SD (manufactured by DIC)) 5.00 parts Ionette S-20 (manufactured by Sanyo Chemical Industries) 0.25 parts diethylene glycol (manufactured by Maruzen Petrochemical Co., Ltd.) 3.20 parts 34% by weight potassium hydroxide aqueous solution The 51 parts kneaded product was a soft solid and did not reach the molten state, but was intermediate to the molten state. Subsequently, 12.00 parts of ion-exchanged water was gradually added over 3 hours to liquefy the kneaded product, and the liquid was taken out from the planetary mixer. The liquefied kneaded product (b) had a solid content concentration of 31.7% and a pigment concentration of 22.9%.

<Centrifuge>
Liquefied mixture (b) 100 parts with ion-exchanged water 44 parts, diethylene glycol 3.6 parts and preservative 0.15 parts, continuous centrifuge (H-600S, 2L capacity, manufactured by Domestic Centrifuge Co., Ltd.) Then, the mixture was continuously centrifuged at room temperature at a centrifugal force of 18900 G and a residence time of 12 minutes to obtain an aqueous pigment dispersion (b). The aqueous pigment dispersion (b) had a solid content concentration of 20.1% and a pigment concentration of 14.5%.

<Preparation of ink composition for inkjet recording>
The following composition was mixed using the aqueous pigment dispersion (b) to prepare an ink composition for inkjet recording having a pigment concentration of 2.7% by mass.
Aqueous pigment dispersion (b) 18.6 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 61.9 parts Each component was mixed at room temperature to obtain an ink composition (b) for ink jet recording.

(Comparative Example 1)
<Kneading>
A mixture containing no sugar of the following composition was charged into a 50 L capacity planetary mixer PLM-V-50V (manufactured by Inoue Seisakusho Co., Ltd.), the jacket was heated at 60 ° C., rotation speed: 57 rpm, revolution speed: Kneading was continued for 2 hours at 20 rpm.
Styrene-acrylic acid copolymer A 1.50 parts phthalocyanine pigment (CI Pigment Blue 15: 3)
(Fastogen Blue 5310SD (manufactured by DIC)) 5.00 parts diethylene glycol (manufactured by Maruzen Petrochemical Co., Ltd.) 2.70 parts 34% by weight aqueous potassium hydroxide solution 0.51 parts The kneaded material is a soft solid and does not reach a molten state Was in the middle of the molten state. Subsequently, 12.00 parts of ion-exchanged water was gradually added over 3 hours to liquefy the kneaded product, and the liquid was taken out from the planetary mixer. This extract (c) had a solid content concentration of 33.1% and a pigment concentration of 24.8%.

<Centrifuge>
Extracted water (c) 100 parts, ion-exchanged water 54 parts, diethylene glycol 6.4 parts and preservative 0.15 parts were added to the continuous centrifuge (K-600S, 2L capacity, manufactured by Kokusan Centrifuge Co., Ltd.). Centrifugation was continuously performed at room temperature with a centrifugal force of 18900 G and a residence time of 12 minutes to obtain an aqueous pigment dispersion (c). The aqueous pigment dispersion (c) had a solid content concentration of 19.5% and a pigment concentration of 14.6%.

<Preparation of ink composition for inkjet recording>
The following composition was mixed using the aqueous pigment dispersion (c) to prepare an ink composition for inkjet recording having a pigment concentration of 2.7% by mass.
Aqueous pigment dispersion (c) 18.5 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 62.0 parts Each component was mixed at room temperature to obtain an ink composition (c) for ink jet recording.

(Comparative Example 2)
<Preparation of ink composition for inkjet recording>
With respect to the aqueous pigment dispersion (c) prepared in Comparative Example 1, the following composition was mixed using Ionette T-20C used in the kneading step in Example 1 to prepare the ink composition, and the pigment concentration was 2.7 masses. % Ink composition for ink jet recording was prepared.
Aqueous pigment dispersion (b) 18.5 parts triethylene glycol monobutyl ether 8.0 parts
2-Pyrrolidinone 8.0 parts Glycerin 3.0 parts Surfinol 440 0.5 part Ionette T-20C 0.9 part Ion-exchanged water 61.1 parts Ink composition for inkjet recording (d) by mixing each component at room temperature Got.

(Comparative Example 3)
<Preparation of ink composition for inkjet recording>
With respect to the aqueous pigment dispersion (c) prepared in Comparative Example 1, Ionette S-20 used in the kneading step in Example 2 was used for adjusting the ink composition, and the following composition was mixed to obtain a pigment concentration of 2.7 mass. % Ink composition for ink jet recording was prepared.
Aqueous pigment liquid (c) 18.5 parts Triethylene glycol monobutyl ether 8.0 parts
2-Pyrrolidinone 8.0 parts Glycerin 3.0 parts Surfinol 440 0.5 part Ionette S-20 0.9 part Ion-exchanged water 61.1 parts Ink composition for ink jet recording by mixing each component at room temperature (d) Got.

The ink compositions for ink jet recording produced in Example 1, Example 2 and Comparative Examples 1 to 3 were evaluated by the following methods.
<Evaluation of initial dispersibility>
The dispersed particle diameter and the viscosity of the ink composition for ink jet recording prepared in Examples and Comparative Examples were measured. For the measurement, the ink composition for ink jet recording was diluted about 200 times, and the volume average particle diameter was measured at 25 ° C. using Microtrac UPA-150 (manufactured by Leeds & Northrop). The measurement was performed 3 times and the average value was taken. The viscosity was measured at 25 ° C. using an E-type viscose clock (VISCOMETER TV-22 manufactured by Toki Sangyo Co., Ltd.).
<Printing evaluation of ink composition for inkjet recording>
The water-based ink obtained in Examples and Comparative Examples is filled into a commercially available thermal jet type inkjet printer HP-Photomart-D5360 (manufactured by Hewlett Packard), printed on A4 size plain paper and brochure paper, and stable in ejection. Property, print density, and scratch resistance were evaluated.
<Discharge stability evaluation>
The water-based ink composition for ink jet recording obtained in Examples and Comparative Examples is filled into a commercially available thermal jet type ink jet printer HP-Photomart-D5360 (manufactured by Hewlett Packard), and is used on A4 size plain paper and pamphlet paper. A fine line pattern was printed at 100% image density, the state of the printed matter was observed, and the ejection stability was evaluated according to the following evaluation criteria.
Printing disorder does not occur (◎)
Print disorder hardly occurs (○)
Disturbance of printing is conspicuous, but almost no dot missing occurs (△)
It was performed in four stages (dots) where dot missing was conspicuous.

<Print density evaluation>
The aqueous ink composition for ink jet recording obtained in Examples and Comparative Examples was filled into a black pen of a commercially available thermal jet type ink jet printer HP-Photomart-D5360 (manufactured by Hewlett Packard), and an A4 size recording medium was used. Using plain paper and pamphlet paper, solid printing with 100% image density was performed, and the print density of the obtained image was measured by Spectro Scan (manufactured by Gretag Macbeth).

<Abrasion resistance evaluation>
Similar to the printing density evaluation, solid printing with 100% image density was performed. After printing, the printing surface was rubbed with fingers and an eraser for 12 hours after printing, and the degree of contamination was observed with the following evaluation rank.
No print stains (◎)
Dirt on printed matter is hardly noticeable (○)
Dirt on the printed material is noticeable but there is almost no fading (△)
The printing was carried out in four stages (x) where stains and faintness were noticeable.

The results of the above evaluation are summarized in Table 1.
<Comprehensive evaluation>

The ejection stability of the aqueous inks obtained from the aqueous pigment dispersions of Examples 1 and 2 and Comparative Example 1 was better than that no printing disturbance occurred. On the other hand, the ejection stability of the water-based inks obtained from the water-based pigment dispersions of Comparative Examples 2 to 3 is better than almost no printing disturbance, but the water-based pigment dispersions of Examples 1 and 2 and Comparative Example 1 The discharge stability of the water-based ink obtained from the liquid was inferior. This can be considered because free saccharides or derivatives thereof not adsorbed on the pigment affect the ejection stability.
In addition, the initial dispersibility of the ink is good in both Examples and Comparative Examples, and even if saccharides or saccharide derivatives are added in the kneading step, the dispersibility of the ink composition for ink jet recording to be produced is not adversely affected. It is clear that a good aqueous pigment dispersion is produced simply by mixing and stirring the formed pigment dispersion in an aqueous medium, and an ink composition for inkjet recording having a better dispersibility is produced.
The printed matter made of the aqueous ink composed of the aqueous pigment dispersions of Examples 1 and 2 had a higher print density and better scratch resistance than the printed matter made of the aqueous ink composed of the pigment dispersions of Comparative Examples 1 to 3. This is because the saccharide adsorbed by the pigment or its derivative is intermolecularly hydrogen bonded between the hydroxyl group of the pigment and the cellulose hydroxyl group, which is the main component of the paper, and the fixing power between the pigment and paper is improved. It can be considered that the print density is improved because it stays on the paper surface, and the scratch resistance is improved because the setting property of the pigment and paper is improved. From the point of view of print quality, it is essentially desirable that no print stains occur after printing, and it usually takes a lot of trouble to improve the print density by 0.05. deep.

Claims (12)

A mixture containing the pigment (a), the styrene-acrylic acid copolymer (b), the basic compound (c), the wetting agent (d), and the saccharide or its derivative (e) is kneaded and solid at room temperature. A method for producing an aqueous pigment dispersion, comprising: a kneading step for producing a pigment dispersion; and a mixing step for mixing and stirring the pigment dispersion in an aqueous medium. 2. The aqueous pigment dispersion according to claim 1, wherein the styrene acrylic acid copolymer has an acid value of 60 to 300, a weight average molecular weight of 3000 to 20000, and contains 50% by mass or more of styrene monomer units with respect to all monomer components. Liquid manufacturing method. The method for producing an aqueous pigment dispersion according to claim 1 or 2, wherein the saccharide or its derivative (e) is a monosaccharide, a disaccharide or a derivative thereof. The method for producing an aqueous pigment dispersion according to claim 3, wherein the saccharide or a derivative thereof is hexose or a derivative thereof. The method for producing an aqueous pigment dispersion according to claim 4, wherein the hexose or a derivative thereof is sorbitan or a derivative thereof. The method for producing an aqueous pigment dispersion according to claim 5, wherein the hexose or a derivative thereof is sorbitan fatty acid ester or a polyoxyethylene adduct of sorbitan fatty acid ester. The polyoxyethylene adduct of the sorbitan fatty acid ester has the following general formula (3) or (4)

(3)

(4)
(However, X in the formula, Y, Z are each independently a hydrogen _{atom, - (CH 2 CH 2 O} ) mH, - (CH 2 CHCH 3) mH or a _{-CO-R 5,,} W is - _{(CH 2 CH 2 O) n-} , or _- (CH 2 CHCH ₃ O) is n-, a R4, R5 are each independently a hydrogen atom or an alkyl group having a carbon number of 1 to 30, m is 1 Represents an integer of ˜100, n represents 0 or an integer of 1 to 100, and at least one of X, Y, and Z is — (CH ₂ CH ₂ O) mH, or — (CH ₂ CHCH ₃ ) mH. And m in X, Y, and Z may be different from each other.)
The method for producing an aqueous pigment dispersion according to claim 6, wherein The method for producing an aqueous pigment dispersion according to claim 7, wherein the sorbitan fatty acid ester or the polyoxyethylene adduct of sorbitan fatty acid ester has an HLB of 8 or more. Mass ratio of styrene-acrylic acid copolymer (b) to pigment (a) in the kneading step, b / a is 0.1 to 0.6, and mass of wetting agent (d) to pigment (a) Ratio d / a is 0.2-1.4, The manufacturing method of the aqueous pigment dispersion liquid of any one of Claims 1-8. The method for producing an aqueous pigment dispersion according to any one of claims 1 to 9, wherein a solid content ratio of the pigment dispersion in the kneading step is 50 to 80% by mass. The manufacturing method of the ink composition for inkjet recording which has a dilution process which dilutes the aqueous pigment dispersion manufactured by the manufacturing method of the aqueous pigment dispersion of Claim 10 with an aqueous medium. A pigment that is solid at room temperature, comprising a pigment (a), a styrene-acrylic acid copolymer (b), a basic compound (c) a wetting agent (d), and a saccharide or a derivative thereof (e) Dispersion.