JP6115054B2 - Pigment kneaded product and method for producing aqueous pigment dispersion - Google Patents

Description

  The present invention relates to a pigment kneaded material and a method for producing an aqueous pigment dispersion, and more particularly to a pigment kneaded material and a method for producing an aqueous pigment dispersion suitable for producing an ink for ink jet recording.

Conventionally, an aqueous pigment dispersion in which a pigment is dispersed in water or a liquid medium containing water as a main component has been proposed, and an ink obtained by diluting the aqueous pigment dispersion has been manufactured.
In producing an aqueous pigment dispersion, water, a liquid medium containing water as a main component (hereinafter, “water or a liquid medium containing water as a main component” is referred to as a water-soluble medium), pigment, resin, resin The neutralizing agent is mixed and the pigment is dispersed using a disperser, and an aqueous pigment dispersion in which the pigment is coated with a resin and dispersed in an aqueous medium is obtained.
Inks using pigments are used for various purposes because they have much better light resistance and water resistance than those using conventional dyes.

  Ink for ink-jet recording, which is one of the inks, is printed by ejecting ink droplets from a printer head, unlike normal printing, so that stability during ejection (ejection stability), long-term storage stability, etc. However, it is strictly required compared to other applications. That is, it is necessary that fine pigment particles having a uniform particle diameter as much as possible be stably dispersed in a water-soluble solvent for a long period of time while being coated with a resin. In order to satisfy these requirements, it is necessary to have good dispersion stability and dispersion stability that can be stored for a long time at the stage of the aqueous pigment dispersion.

  As a method for obtaining such an aqueous pigment dispersion having good dispersion stability and long-term storage stability, the present applicants first include a sealable stirring tank and a uniaxial or multiaxial stirring blade. A method of kneading in a closed system using a kneading machine, for example, a planetary mixer (see, for example, Patent Document 1), as a pigment used when kneading with a planetary mixer, spraying and drying an aqueous suspension of the pigment A method of using a pigment having an average primary particle size of 80 nm or less produced through a spraying process is developed (see, for example, Patent Document 2). By this production method, an aqueous pigment dispersion can be obtained in which the average particle diameter does not change even in a one-week heating test using a 60 ° incubator.

  However, with the recent development of inkjet recording devices, not only long-term storage stability in a high-temperature environment, but also stable ink is required even when any temperature change is applied. Has occurred. For example, in the heating and cooling test in which the storage stability test is repeated in a high temperature environment of 70 degrees and a low temperature environment of minus 40 degrees, coarse particles are expressed in the aqueous pigment dispersion obtained in Patent Documents 1 and 2. End up.

JP 2003-226831 A JP 2011153321 A

  The present invention provides a production method for obtaining an aqueous pigment dispersion that does not exhibit coarse particles even after a heating and cooling test and has particularly good long-term storage stability.

  The present inventors mixed a pigment, a resin having an anionic group, and a neutralizing agent for neutralizing an anionic group as a pigment to be used in the production method described in Patent Document 1, and water or water-soluble. The above problems were solved by using a composite pigment obtained by slurrying in a solvent and then spray drying.

  The present inventors considered that the resin must be uniformly and densely adsorbed on the pigment surface in order to maintain the stability of the obtained aqueous pigment dispersion even after the heating and cooling test. After intensive studies, the pigment is slurried together with the resin in an aqueous solution and adsorbed to the pigment in a state where the affinity between the hydrophobic surface of the pigment and the hydrophobic group of the resin is further increased, and spray-dried or frozen in that state. By drying, a resin pigment is deposited on the pigment surface to obtain a composite pigment more firmly coated with the resin, and using a pigment kneaded product obtained by kneading the composite pigment with a water-soluble organic solvent and the resin, It was found that even after the heating and cooling test, an excellent aqueous pigment dispersion was obtained in which coarse particles were not expressed, the dispersion stability was good, and the long-term storage stability was good.

  In addition, since this method can appropriately select the resin used in the slurrying step and the resin used in the kneading step, for example, a pigment kneading containing a composite pigment double-coated with resins having different physical properties and structures It is also possible to get things.

That is, in the present invention, a pigment, a resin (A) having an anionic group, and a neutralizing agent for neutralizing the anionic group are mixed and slurried in water or a liquid medium containing water as a main component. (1) obtaining a composite pigment by spray drying or freeze drying;
Provided is a method for producing a pigment kneaded product comprising the step (2) of kneading a mixture containing the composite pigment obtained in the step (1), a water-soluble organic solvent, and a resin (B) having an anionic group.

  The present invention also provides a method for producing an aqueous pigment dispersion in which water or a liquid medium containing water as a main component is added to the pigment kneaded product and stirred to liquefy.

According to the present invention, it is possible to obtain an aqueous pigment dispersion that does not exhibit coarse particles even after a heating and cooling test and has particularly good long-term storage stability.
Further, since the resin used in the slurrying process and the resin used in the kneading process can be appropriately selected, for example, the functional group contributing to dispersion on the pigment particle surface, the functional group contributing to inkjet ink characteristics, and the printing characteristics. It is also possible to produce composite particles having functional groups that contribute to the above, and to make water-based pigment dispersions having functionality.

(Process 1 Pigment)
The pigment used in the present invention is not particularly limited as long as the pigment can be dried in the spray drying process, and a known and commonly used organic pigment or inorganic pigment can be used. In addition, the present invention can be applied to either an untreated pigment or a treated pigment.

Examples of organic pigments include perylene / perinone compound pigments, quinacridone compound pigments, phthalocyanine compound pigments, anthraquinone compound pigments, phthalone compound pigments, dioxazine compound pigments, isoindolinone compound pigments, and isoindoline compounds. Examples thereof include pigments, diketopyrrolopyrrole compound pigments, insoluble azo compound pigments, soluble azo compound pigments, condensed azo compound pigments, and aniline black pigments. Specific examples of the organic pigment are as follows, for example.
Examples of perylene / perinone compound pigments include C.I. I. PigmentViolet 29, C.I. I. Pigment Red 123, 149, 178, 179, C.I. I. Pigment Black 31, 32, C.I. I. Pigment Orange 43 and the like.
Examples of quinacridone compound pigments include C.I. I. Pigment Violet 19, 42, C.I. I. Pigment Red 122, 202, 206, 207, 209, C.I. I. Pigment Orange 48, 49 and the like.
Examples of the phthalocyanine compound pigment include C.I. I. Pigment Blue 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, C.I. I. Pigment Green 7, 36 and the like.
Examples of the anthraquinone compound pigment include C.I. I. Pigment Blue 60, C.I. I. Pigment Yellow 24, 108, C.I. I. Pigment Red 168, 177, C.I. I. Pigment Orange 40 and the like.
Examples of the phthalone compound pigment include C.I. I. And pigments such as Pigment Yellow 138.
Examples of the dioxazine compound pigment include C.I. I. Pigment Violet 23, 37, and the like.
Examples of isoindolinone compound pigments include C.I. I. Pigment Yellow 109, 110, 173, C.I. I. Pigment Orange 61 and the like.
Examples of isoindoline-based compound pigments include C.I. I. Pigment Yellow 139, 185, C.I. I. Pigment Orange 66, C.I. I. Pigment Brown 38 and the like.
Examples of the diketopyrrolopyrrole compound pigment include C.I. I. Pigment Red 254, 255 and the like.
Examples of insoluble azo compound pigments include C.I. I. Pigment Yellow 1, 3, 12, 13, 14, 17, 55, 73, 74, 81, 83, 97, 130, 151, 152, 154, 156, 165, 166, 167, 170, 171, 172, 174, 175, 176, 180, 181, 188, C.I. I. Pigment Orange 16, 36, 60, C.I. I. Pigment Red5, 22, 22, 31, 112, 146, 150, 171, 175, 176, 183, 185, 208, 213, C.I. I. PigmentViolet 43, 44, C.I. I. Pigment Blue 25, 26 and the like.
Examples of the soluble azo compound pigment include C.I. I. Pigment Red 53: 1, 57: 1, 48 and the like.
Examples of the condensed azo compound pigment include C.I. I. Pigment Yellow 93, 94, 95, 128, 166, C.I. I. Pigment Orange 31C. I. Pigment Red 144, 166, 214, 220, 221, 242, 248, 262, C.I. I. Pigment Brown 41, 42 and the like.
Examples of the aniline black pigment include C.I. I. Pigment Black 1.

  Examples of inorganic pigments include titanium oxide, zinc sulfide, lead white, zinc white, lithbon, antimony white, basic lead sulfate, basic lead silicate, barium sulfate, calcium carbonate, gypsum, silica, carbon black, iron black. , Titanium black, cobalt violet, vermillion, molybdenum orange, red lead, bengara, chrome lead, cadmium yellow, zinc chromate, yellow ocher, chromium oxide, ultramarine, bitumen, cobalt blue and the like.

The average primary particle size of the pigment used in the present invention is preferably 80 nm or less, and more preferably in the range of 20 to 80 nm. More preferably, it is 30-80 nm. When the average primary particle size is less than 20 nm, dispersion tends to be difficult, and when it exceeds 80 nm, suitability for inkjet ink tends to be poor.
The average primary particle diameter of the pigment can be determined by measuring and averaging the major axis length of the pigment with n = 20 in a TEM photograph.

(Step 1 resin having an anionic group (A))
The resin (A) having an anionic group used in the present invention is not particularly limited, and various resins can be used. For example, polyvinyl resin, polyester resin, amino resin, acrylic resin, epoxy resin, polyurethane resin, polyether resin, polyamide resin, unsaturated polyester resin, phenol resin, silicone resin, fluorine Based polymer compounds and the like.
These resins preferably have a hydrophilic group and a hydrophobic group from the viewpoint of dispersion stability and long-term storage stability of the resulting dispersion. Examples of the hydrophilic group include an anionic group such as a carboxyl group, a sulfone group and a phospho group, a cationic group such as an amino group, and a nonionic group. In the present invention, a resin having an anionic group is more preferable. It is preferable because of excellent dispersion stability. The hydrophobic group preferably has an aromatic group from the viewpoint of adsorptivity to the pigment. As such a resin that can easily introduce an anionic group and an aromatic group, a copolymer of a radical polymerizable monomer having an anionic group and a radical polymerizable monomer having an aromatic group may be used. preferable. Among these, a styrene acrylic copolymer having an anionic group is preferable.

The styrene acrylic copolymer having an anionic group contains a styrene monomer having an aromatic group as a constituent monomer and a monomer having a radical polymerizable double bond and containing an anionic group. A known compound can be used as the styrene monomer. For example, alkyl styrene such as styrene, α-methyl styrene, β-methyl styrene, 2,4-dimethyl styrene, α-ethyl styrene, α-butyl styrene, α-hexyl styrene, 4-fluorostyrene, 3-chlorostyrene, There are halogenated styrenes such as 3-bromostyrene, 3-nitrostyrene, 4-methoxystyrene, vinyltoluene and the like.
The use ratio of the styrene monomer as a constituent component of the styrene acrylic copolymer is preferably 50 to 90% by mass, more preferably 60 to 90% by mass, and 70 to 90% by mass with respect to all monomer components. More preferably, it is 90 mass%. When the ratio of the styrene monomer used is less than 50% by mass, the affinity of the styrene acrylic copolymer having an anionic group to the pigment is insufficient, and the dispersion stability of the resulting aqueous pigment dispersion is lowered. Tend. When the amount of the styrene monomer is within the above range, the styrene acrylic copolymer having an anionic group is easily adsorbed on the surface of the hydrophobic pigment. In addition, since a monomer having an anionic group can be sufficiently used as a constituent component, the dispersibility of the styrene acrylic copolymer in an aqueous medium can be improved, and the dispersibility and dispersion of the pigment in the aqueous pigment dispersion for inkjet recording can be improved. The stability can be improved, and the effect on the fine particle size of the pigment is great. Furthermore, the printing stability when used as a water-based ink for inkjet recording is improved. On the other hand, when the use ratio of the styrene monomer exceeds 90% by mass, the dispersibility in an aqueous medium tends to be insufficient, and the dispersibility and dispersion stability when an aqueous ink for ink jet recording is produced decreases. Tend.

  As described above, the anionic group of the monomer having a radical polymerizable double bond and an anionic group to be copolymerized with the styrenic monomer includes a carboxyl group, a sulfone group, a phospho group, etc. In view of price, etc., an anionic group-containing monomer containing a carboxyl group or a sulfone group is preferable, and an anionic group having a carboxyl group is capable of widely controlling the coexistence range between an electrically neutral state and an anionic state. Group-containing monomers are preferred, and among them, unsaturated aliphatic carboxylic acid monomers are particularly preferred.

  Known compounds can be used as the unsaturated aliphatic carboxylic acid monomer. For example, acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, α-methylcrotonic acid, α-ethylcrotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, Etc. Among them, it is preferable to use acrylic acid and methacrylic acid, and it is particularly preferable to use both in combination. By using acrylic acid and methacrylic acid together, the copolymerizability at the time of resin synthesis is improved, the uniformity of the resin is improved, and when the pigment is dispersed with the resin, the composition of the dispersant is non-uniform. It is considered that the decrease in stability considered to be caused is suppressed.

  Thus, as a constituent monomer of the styrene acrylic copolymer having an anionic group used in the present invention, it is preferable to use three types of monomers, styrene monomer, acrylic acid, and methacrylic acid. More preferably, the sum of the monomer content ratios is 95% by mass or more based on the total monomer components.

  For the styrene acrylic copolymer having an anionic group, a known monomer other than the styrene monomer and the unsaturated aliphatic carboxylic acid having a radical polymerizable double bond can be used. Examples of such monomers include methyl acrylate, n-propyl acrylate, isopropyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-butyl acrylate, 2-ethylbutyl acrylate, 1,3-dimethylbutyl acrylate, hexyl Acrylate esters and methacrylate esters such as acrylate, 2-ethylhexyl acrylate, octyl acrylate, ethyl methacrylate, n-butyl methacrylate, 2-methylbutyl methacrylate, pentyl methacrylate, heptyl methacrylate, nonyl methacrylate; 3-ethoxypropyl acrylate, 3-ethoxybutyl acrylate, dimethylaminoethyl acrylate, hydroxyethyl acrylate, hydroxy Acrylic acid ester derivatives and methacrylic acid ester derivatives such as butyl acrylate, ethyl-α- (hydroxymethyl) acrylate, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate; phenyl acrylate, benzyl acrylate, phenylethyl acrylate, phenylethyl Acrylic acid aryl esters and acrylic acid aralkyl esters such as methacrylates; monoacrylic acid esters or monomethacrylic acid esters of polyhydric alcohols such as diethylene glycol, triethylene glycol, polyethylene glycol, glycerin and bisphenol A; Dimethyl maleate, dialkyl maleate such as diethyl maleate, acetic acid Vinyl etc. can be mentioned. One or more of these monomers can be added as monomer components.

  As a method for producing a styrene-acrylic copolymer having an anionic group, it is possible to adopt a usual polymerization method, such as solution polymerization, suspension polymerization, bulk polymerization, etc., in the presence of a polymerization catalyst. The method of performing is mentioned. Examples of the polymerization catalyst include 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 1,1′-azobis (cyclohexane-1-carbonitrile), Examples thereof include benzoyl peroxide, dibutyl peroxide, butyl peroxybenzoate, and the amount used is preferably 0.1 to 10.0% by mass of the total of the constituent monomer components.

  A resin having an anionic group such as a styrene acrylic copolymer having an anionic group obtains a stable water dispersibility by neutralizing with a neutralizing agent that neutralizes an anionic group such as a basic compound. Therefore, it is preferable to have an acid value of 50 to 300. When the acid value is less than 50, the hydrophilicity is reduced and the dispersion stability of the pigment is lowered. On the other hand, if the acid value is greater than 300, the water resistance of the printed product using the water-based ink may be lowered. The acid value is preferably from 70 to 250, and more preferably from 90 to 200.

  The weight average molecular weight of the resin having an anionic group such as a styrene acrylic copolymer having an anionic group is preferably in the range of 5,000 to 40,000, and in the range of 7,500 to 30,000. More preferably, it is within. Especially, it is especially preferable that it exists in the range of 10,000-25,000. If the weight average molecular weight is less than 5,000, the long-term storage stability tends to deteriorate when an aqueous pigment dispersion for inkjet recording of pigment is produced, and precipitation due to aggregation of the pigment may occur. When the weight average molecular weight of the styrene acrylic copolymer having an anionic group exceeds 40,000, the viscosity of the aqueous ink for inkjet recording prepared from the aqueous pigment dispersion for inkjet recording using the same increases, and the ink The discharge stability tends to become unstable. Here, the weight average molecular weight is a value in terms of polystyrene measured by a GPC (gel permeation / chromatography) method. The glass transition point of the styrene acrylic copolymer having an anionic group is preferably 90 to 150 degrees, and more preferably 100 to 150 degrees. When the glass transition point is 90 degrees or more, the thermal stability of the water-based ink is improved. For this reason, when the water-based ink for ink-jet recording produced from the water-based pigment dispersion is used for the ink jet recording of the thermal jet system, it is preferable that the characteristic change that causes the ejection failure due to repeated heating hardly occurs.

  The styrene acrylic copolymer having an anionic group used in the present invention may be a random copolymer or a block copolymer, but may also be a graft copolymer. As the graft copolymer, a copolymer of polystyrene or a nonionic monomer copolymerizable with styrene and styrene is used as a trunk or branch, and a copolymer of acrylic acid, methacrylic acid and other monomers including styrene is branched. Or the graft copolymer used as a trunk can be shown as the example. The styrene-acrylic copolymer (b) having an anionic group may be a mixture of this graft copolymer and random copolymer.

(Step 1 Neutralizing agent that neutralizes anionic groups)
In the production method of the present invention, a neutralizing agent that neutralizes the anionic group is used in step (1).
Specifically, it is preferable to use a basic compound as the neutralizing agent for neutralizing the anionic group. The basic compound neutralizes the anionic group of the resin having the anionic group and improves the dispersibility of the resin. As a result, the dispersion state of the pigment particles coated with the copolymer in the dispersion becomes more stable, and the dispersion stability and long-term storage stability are also improved.
As the basic compound to be used, either an inorganic basic compound or an organic basic compound can be used, but an inorganic basic compound is more preferable in terms of easy adjustment of alkali strength. Examples of the organic basic compound include general amines such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and triethylamine. Examples of inorganic basic compounds include hydroxides of alkali metals such as potassium and sodium; hydroxides of alkali metals such as potassium and sodium; carbonates of alkali metals such as potassium and sodium; alkaline earths such as calcium and barium Examples thereof include carbonates of similar metals; ammonium hydroxide and the like. Among these, strong alkalis are preferable because they are effective in enhancing the dispersibility of the resin by neutralizing the styrene acrylic resin. Specifically, sodium hydroxide, potassium hydroxide, lithium hydroxide, and the like can be used. However, it is particularly preferable to use potassium hydroxide.

  The addition amount of the basic compound is 0.8 to 1.2 times the addition amount necessary for neutralizing all carboxyl groups when the anionic group of the resin having an anionic group is a carboxyl group. It is preferable that the amount corresponds to. Here, the addition amount necessary for neutralization is an amount corresponding to the molar ratio of the basic compound calculated from the acid value of the resin. The basic compound is preferably used in an aqueous solution or organic solvent solution of about 20 to 50% by mass, more preferably added as an aqueous solution, from the viewpoint of improving the mixing property.

(Process 1 Water or liquid medium mainly composed of water)
In the present invention, the solvent used in Step 1 is preferably water, but may be a liquid medium containing water as a main component instead of 100% water. In the present invention, the “liquid medium containing water as a main component” refers to a liquid medium containing water that is preferably 80% by mass or more and is compatible with water. Examples of liquids that are compatible with water include methanol, ethanol, propanol, isopropyl alcohol, and acetone.

(Process 1 Slurry process)
In step 1 of the present invention, the pigment, the resin having an anionic group, and a neutralizing agent for neutralizing the anionic group are mixed and slurried in water or a liquid medium containing water as a main component. A pigment composition is obtained. There are no particular limitations on the method of slurrying, and known methods such as paint shakers using media, ball mills, attritors, basket mills, sand mills, sand grinders, dyno mills, disperse mats, SC mills, spike mills, agitator mills, And an ultrasonic homogenizer, a nanomizer, a resolver, a disper, and a high-speed impeller disperser that do not use media.

  In the slurrying, the ratio of the pigment to the resin having the anionic resin is preferably in the range of resin weight / pigment weight = 0.15 to 0.40, more preferably 0.15 to 0.00. 30. If the amount of the resin is less than the above ratio, the dispersion stability of the resulting colored liquid may be lowered. On the other hand, if the amount of the resin is more than the above ratio, the dispersion liquid may be thickened and ink jet characteristics may be deteriorated.

In the present invention, when a surfactant is used in combination with the slurry, an aqueous pigment dispersion having a smaller number of coarse particles and higher storage stability can be obtained.
As the surfactant, any of cationic, anionic, amphoteric and nonionic can be used, but anionic or nonionic surfactant is desirable from the viewpoint of dispersion stability.

  These surfactants are not particularly limited, but examples of the anionic surfactant include fatty acid soap, N-acyl-N-methylglycine salt, N-acyl-N-methyl-β-alanine salt, and N-acyl. Glutamate, acylated peptide, alkyl sulfonate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, dialkyl sulfosuccinate, alkyl sulfoacetate, α-olefin sulfonate, N-acylmethyl taurine, sulfated oil Higher alcohol sulfates, secondary higher alcohol sulfates, alkyl ether sulfates, secondary higher alcohol ethoxy sulfates, polyoxyethylene alkyl phenyl ether sulfates, monoglycolates, fatty acid alkylolamide sulfates, Alkylue -Telluric acid ester salts, alkyl phosphoric acid ester salts and the like.

  Nonionic surfactants include polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene glycerin fatty acid ester , Polyoxyethylene castor oil, hydrogenated castor oil, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid ester, fatty acid monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, sucrose fatty acid ester, fatty acid alkanolamide, poly Oxyethylene fatty acid amide, polyoxyethylene alkylamine, alkylamine oxide, Cetirizine glycol, acetylene alcohol, and the like.

Moreover, as a brand name of an anionic surfactant, sodium lauryl sulfate is mentioned, for example, Surfinol SEF is mentioned as a nonionic surfactant.
The addition amount of these surfactants is preferably 10% by mass or less, particularly preferably 5% by mass or less, based on the pigment. If it exceeds the above-mentioned mass%, the amount of resin adsorbed on the pigment decreases, and the aqueous pigment dispersion tends to thicken.

(Process 1 Spray drying or freeze drying process)
The slurry pigment composition is spray dried or freeze dried.
There is no particular limitation on the method of spray drying, that is, spray drying. For example, the slurry is made into a fine mist, sprayed into hot air, and dried instantaneously to obtain a powdered composite pigment powder. I can do it.
The method of freeze-drying is not particularly limited, and for example, the slurry can be frozen at -20 ° C. or lower and then dried in a freeze-dryer under reduced pressure to vacuum to obtain a powdered composite pigment powder.

  As described above, a pigment having a resin deposited on the pigment surface can be obtained through Step 1. This is not simply a pigment coated with resin, but by spray drying or freeze drying, the drying stress caused by normal thermal drying is reduced to the limit, and evaporation of the water and precipitation of the resin are instantaneously performed within the pores of the pigment. Alternatively, it is presumed that as a result of keeping the primary particles of the pigment kept, the composite pigment is adsorbed with the resin up to almost the entire area of the pigment particles. Therefore, in the kneading step of Step 2, it is presumed that a pigment dispersion showing good dispersibility was obtained as a result of further strengthening the resin adsorption of the composite pigment. This estimation is supported by the resin adsorption amount of the pigment dispersion, and the pigment dispersion using the composite pigment that has undergone Step 1 exhibits a resin adsorption amount that is approximately 2.5 times that of the previous method that has not undergone Step 1. It is supported from that.

(Process 2 Water-soluble organic solvent)
A pigment kneaded product is obtained through the step (2) of kneading the mixture containing the composite pigment obtained in the step 1 and the water-soluble organic solvent.
The water-soluble organic solvent used in the present invention is not particularly limited, and known ones can be used. 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. 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.

  Among them, polyhydric alcohols having a high boiling point and low volatility and high surface tension are preferable, and glycols such as diethylene glycol and triethylene glycol are particularly preferable.

The water-soluble organic solvent is preferably used in a mass ratio of 1/5 or more, and most preferably 1/3 or more of the composite pigment. By using the water-soluble organic solvent in a mass ratio of 1/3 or more of the pigment, the kneading can always proceed in the presence of a certain amount of solvent from the start to the end of the kneading step.
On the other hand, although the quantity with respect to the said resin is arbitrary, it is preferable to prepare so that it may become about 1 / 2-5 / 1 of the said resin by mass ratio, Preferably it will be 1 / 1-4 / 1.

The higher the solid content ratio in the mixture, the higher the viscosity of the kneaded product during kneading, and the greater the share (shearing force) applied to the kneaded product by the kneader during kneading, so that the pigment in the kneaded product Grinding and coating with pigment resin can proceed simultaneously. From such a viewpoint, the solid content ratio is preferably 40% by mass or more, and more preferably 50% by mass or more.
Also, from the viewpoint of keeping the viscosity high and constant, the kneading method described below uses a closed kneader, and the mass of the mixture during kneading is in the range of 90% by mass or more with respect to the charged amount before kneading. It is necessary to knead so that it may be maintained.

(Step 2 Resin (B) having an anionic group)
As the resin (B) having an anionic group used in the present invention, the same type of resin as the resin (A) having an anionic group used in Step 1 can be used. The resin (B) used here also preferably has a hydrophilic group and a hydrophobic group from the viewpoint of dispersion stability and long-term storage stability of the resulting dispersion. Examples of the hydrophilic group include an anionic group such as a carboxyl group, a sulfone group and a phospho group, a cationic group such as an amino group, and a nonionic group. In the present invention, a resin having an anionic group is more preferable. It is preferable because of excellent dispersion stability. The hydrophobic group preferably has an aromatic group from the viewpoint of adsorptivity to the pigment. As such a resin that can easily introduce an anionic group and an aromatic group, a copolymer of a radical polymerizable monomer having an anionic group and a radical polymerizable monomer having an aromatic group may be used. preferable. Among these, a styrene acrylic copolymer having an anionic group is preferable.

  The resin (B) used in step 2 may be the same type of resin as the resin (A) or a different type of resin. For example, the resin (A) may be a urethane resin having an anionic group, and the resin (B) may be an acrylic resin having an anionic group. Moreover, it is the same kind of resin, and may be a combination of resins having different glass transition temperatures and different molecular weights. For example, a styrene acrylic copolymer having an anionic group, the resin (A) having a weight average molecular weight of 5000, and the resin (B) having an average molecular weight of 20000 may be used. The resin (A) having a glass transition temperature of 100 degrees may be used, and the resin (B) may have a glass transition temperature of 150 degrees, or the resin (A) may contain a carboxylic acid. It is good also as a crosslinked structure of resin (A) and resin (B) using what has a glycidyl group as said resin (B).

  In the method for producing a pigment kneaded product of the present invention, since both step (1) and step (2) are mixed or kneaded in a state containing a resin, the top of the resin adhering so as to enclose the pigment in step (1). In addition, it is presumed that a pigment kneaded product containing a composite pigment in which the pigment used in the step (2) is also adhered, that is, the pigment is adhered in a state close to a double coat so that the resin is wrapped is obtained. Therefore, the aqueous pigment dispersion using the pigment kneaded product does not peel off the resin from the pigment even under harsh conditions such as heating and cooling tests, and does not develop coarse particles, especially for long-term storage stability. Is estimated to be good.

(Process 2 kneading method)
In the kneading method in the present invention, it is preferable to use a kneader having a stirring tank and a stirring blade for mixing, rather than using an open type kneader having no stirring tank such as a two roll. Specifically, the stirring blades may be uniaxial or multiaxial, but two or more stirring blades are preferable in order to obtain a high kneading action. When a kneader having such a configuration is used, an aqueous pigment dispersion can also be produced by producing a pigment kneaded material and then diluting and dispersing it directly with a water-soluble solvent in the same stirring tank.

Examples of such an apparatus include a Henschel mixer, a pressure kneader, a Banbury mixer, and a planetary mixer. In the present invention, the kneader is preferably a planetary mixer. The planetary mixer has a structure in which the pigment kneaded material in the stirring tank is stirred and kneaded using biaxial stirring blades that rotate and revolve with each other, and the dead where the stirring blade does not reach the stirring tank There is little space. Moreover, although the shape of a blade | wing is thick and can apply high load, on the other hand, it can also be used like the normal stirrer which rotates a stirring blade in a stirring tank. For this reason, the width | variety of the to-be-kneaded object which can be made into kneading | mixing object from a high load area | region to a low load area | region is wide. Moreover, an aqueous pigment dispersion can also be obtained continuously by adding a water-soluble medium as it is to the pigment kneaded product after completion of the kneading in step (2) and stirring to liquefy it.
The pigment kneaded product in the present invention is kneaded in a state where the solid content ratio composed of the pigment and the resin is high, so that the viscosity varies in a wide range depending on the kneaded state of the pigment kneaded product, but the planetary mixer has a low viscosity. To a wide range from high viscosity to high viscosity.

(Method for producing aqueous pigment dispersion)
The pigment kneaded product obtained by the above production method can be easily made into an aqueous pigment dispersion by adding a water-soluble medium and stirring to liquefy. In that case, when a planetary mixer is used as the kneading device, as described above, the pigment kneaded product after the kneading in the step (2) is added as it is, stirred and liquefied, An aqueous pigment dispersion can also be obtained continuously. On the other hand, it is of course possible to take out the pigment kneaded product after the kneading and liquefy it. As a dispersing device that can be used at that time, a known dispersing device can be used. 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, a disperse mat, an SC mill, a spike. A mill, an agitator mill, etc. are mentioned. 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.

The water-soluble medium used here is mainly composed of water or a water-soluble organic solvent that is compatible with water, as in step (1) described above. Moreover, as a water-soluble organic solvent used here, the thing similar to the water-soluble organic solvent used in the kneading | mixing process can be used.
The water-soluble medium may be added to the pigment kneaded material in a lump and may be liquefied all at once, but the method of gradually adding the total addition amount little by little obtains a more uniform aqueous pigment dispersion. This is preferable. Specifically, after the first water-soluble medium is added and stirred, the whole mixture becomes a smooth and uniform state, and then the next addition is gradually added repeatedly to make a uniform liquid. Alternatively, a small amount may be continuously added while stirring the pigment kneaded material, and there is no particular limitation.

  The pigment kneaded product obtained by the production method of the present invention has already been sufficiently crushed, and the pigment used is the composite pigment obtained in step (1). Coarse particles are reduced. For this reason, an aqueous pigment dispersion with reduced coarse particles can be obtained simply by adding a water-soluble medium to the kneaded product in the presence of a basic compound, mixing and stirring.

(Inkjet recording ink manufacturing method)
The aqueous pigment dispersion obtained by the production method of the present invention can be applied to various paints and printing inks. In particular, even after the heating and cooling test, coarse particles do not appear, the dispersion stability is good, and the long-term storage stability is good, so that it can be particularly preferably applied as an ink for inkjet recording.

  The ink for inkjet recording can be obtained by adding a binder resin, a wetting agent (drying inhibitor), a penetrating agent, or other additives to the pigment dispersion as necessary.

(Binder resin)
The binder resin is not particularly limited, and examples thereof include natural proteins such as glue, gelatin, casein, albumin, gum arabic, and fish mulberry, alginic acid, methylcellulose, carboxymethylcellulose, polyethylene oxide, hydroxyethylcellulose, polyvinyl alcohol, polyacrylamide, and aroma. Group amide, polyacrylic acid, polyvinyl ether, polyvinyl pyrrolidone, polyurethane, polyester, copolymers of acrylic acid-acrylic acid esters, and synthetic polymers such as styrene-maleic acid and styrene-acrylic acid resins.
When these resins are used, the content in the ink is preferably 30% by mass or less, and particularly preferably 20% by mass or less.

(Wetting agent)
The wetting agent is added for the purpose of preventing the ink from drying. The content of the wetting agent in the ink for the purpose of preventing drying is preferably 3 to 50% by mass.
The wetting agent used in the present invention is not particularly limited, but a wetting agent that is miscible with water and can prevent clogging of the head of an inkjet printer is preferable. For example, glycerin, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol having a molecular weight of 2000 or less, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propylene glycol, isopropylene glycol, isobutylene glycol, 1,4-butane Examples include diol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, mesoerythritol, pentaerythritol, and the like. Among them, the inclusion of propylene glycol and 1,3-butanediol is safe and has excellent effects in ink drying properties and ejection performance.

(Penetration agent)
The penetrant is added for the purpose of improving the permeability to a recording medium and adjusting the dot diameter on the recording medium. Examples of the penetrant include lower alcohols such as ethanol and isopropyl alcohol, ethylene oxide adducts of alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether, and propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether.
The penetrant content in the ink is preferably 0.01 to 10% by mass.

(Surfactant)
The surfactant is added to adjust ink properties such as surface tension. The surfactant that can be added for this purpose is not particularly limited, and examples include various anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Of these, anionic surfactants and nonionic surfactants are preferred.

  Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, sulfate of higher fatty acid ester, sulfonate of higher fatty acid ester, higher alcohol ether. Sulfate salts and sulfonates of the above, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, etc. Specific examples include dodecylbenzene sulfonate, isopropyl naphthalene sulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenyl sulfonate, dibutylphenylphenol disulfate. , And the like salts.

  Nonionic surfactants include, for example, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester , Polyoxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, fatty acid alkylolamide, alkyl alkanolamide, acetylene glycol, oxyethylene adduct of acetylene glycol, Polyethylene glycol polypropylene glycol block copolymer, etc. Among them, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, fatty acid Preference is given to alkylolamide, acetylene glycol, oxyethylene adducts of acetylene glycol and polyethylene glycol polypropylene glycol block copolymers.

  Other surfactants include silicone surfactants such as polysiloxane oxyethylene adducts; fluorine surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers. Biosurfactants such as spicrispolic acid, rhamnolipid, lysolecithin and the like can also be used.

  These surfactants can be used alone or in combination of two or more. In consideration of the dissolution stability of the surfactant, the HLB is preferably in the range of 7-20. When the surfactant is added, the addition amount is preferably in the range of 0.001 to 2% by mass, more preferably 0.001 to 1.5% by mass, based on the total mass of the ink. More preferably, it is in the range of 01 to 1% by mass. When the addition amount of the surfactant is less than 0.001% by mass, the effect of adding the surfactant tends to be not obtained, and when it exceeds 2% by mass, problems such as blurring of the image are likely to occur. .

  Moreover, antiseptic | preservative, a viscosity modifier, a pH adjuster, a chelating agent, a plasticizer, antioxidant, an ultraviolet absorber etc. can be added as needed.

  The amount of the pigment in the ink for ink jet recording is preferably 1 to 20% by mass in order to obtain a sufficient image density and to ensure the dispersion stability of the pigment in the ink.

  The ink jet recording ink preferably has a surface tension of 20 mN / m or more and 60 mN / m or less. More preferably, it is 20 mN / m or more and 45 mN / m or less, More preferably, it is 20 mN / m or more and 40 mN / m or less. If the surface tension is less than 20 mN / m, the liquid may overflow on the nozzle surface and printing may not be performed normally. On the other hand, when it exceeds 60 mN / m, there is a tendency that the non-absorbing base material is easily repelled.

  The viscosity of the inkjet recording ink is preferably 1.2 mPa · s or more and 20.0 mPa · s or less, more preferably 2.0 mPa · s or more and less than 15.0 mPa · s, and further preferably 3. 0 mPa · s or more and less than 12.0 mPa · s. When the viscosity is within this range, it is possible to achieve excellent dischargeability and good jetability over a long period of time. The surface tension and viscosity of the ink for ink jet recording can be maintained in the above-mentioned preferred ranges by adjusting the types and addition amounts of the surfactant and water-soluble solvent to be contained.

  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.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited to the following Example at all. In the following examples, g and% are in terms of mass.

(Reference Example 1 Production Method of Resin (A-1))
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 74 parts of styrene, 11 parts of acrylic acid, 15 parts of methacrylic acid and a polymerization catalyst (“W- 59 ") 8 parts of the mixture was added dropwise over 2 hours. Note that the temperature of the reaction system was maintained at 80 ° C. during the dropping. 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 styrene-acrylic acid copolymer (A-1) powder.
By the above, styrene acrylic resin (A-1) which is styrene / acrylic acid / methacrylic acid = 74/11/15 (mass%), has a weight average molecular weight of 9000, an acid value of 185 mgKOH / g, and Tg of 120 degrees. It was.

(Reference Example 2 Production Method of Resin (A-2))
Styrene / benzyl methacrylic acid / methacrylic as in Reference Example 1 except that the charge ratio of the radical polymerizable monomer was changed to styrene / benzyl methacrylic acid / methacrylic acid = 63/20/17 (mass%). A styrene acrylic resin (A-2) having an acid = 63/20/17 (mass%), a weight average molecular weight of 8530, an acid value of 118 mgKOH / g, and Tg of 90 degrees was obtained.

The weight average molecular weight in the present invention is a value measured by GPC (gel permeation / chromatography) method and converted to the 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

(Example 1 Production method of pigment kneaded product)
(Process (1) Slurry process)
10.5 parts of phthalocyanine pigment Fast Gen Blue (manufactured by DIC: CI Pigment Blue 15: 3), 2.1 parts of styrene acrylic copolymer (A-1), 48% aqueous potassium hydroxide solution Was added to the stirring layer, stirred and mixed with a three-one motor for 3 hours, and then dispersed with a bead mill (Nanomill NM-G2L manufactured by Asada Tekko) under the following conditions to obtain a pigment slurry.

(Bead mill dispersion conditions)
Disperser: Nanomill NM-G2L (manufactured by Asada Tekko)
Beads: φ0.3mm zirconia beads Bead filling amount: 85%
Cooling water temperature: 10 degrees Rotation speed: 2660 rpm
Liquid feed rate: 200 g / min
Dispersion time: 3 hours

(Process (1) Spray drying process)
The slurry was spray-dried with a spray dryer under the following conditions to obtain a composite pigment with a yield of 90% or more.
(Spray drying conditions)
Spray dryer: L-8i type spray dryer (Okawara Seisakusho)
Outlet temperature: 105-110 degrees

(Process (2) Kneading process)
60 parts of the composite pigment obtained in the step (1), 5 parts of styrene acrylic copolymer (A-1), 21.5 parts of diethylene glycol and 1.9 parts of 48% potassium hydroxide aqueous solution have a capacity of 0.4 L. In the planetary mixer ACM-0.4LVT (Aikosha Seisakusho Co., Ltd.), the jacket was heated to 80 degrees and kneaded for 1 hour at a rotational speed of 80 rpm. Subsequently, 150 parts of ion-exchanged water was gradually added to the kneaded product in the stirring layer, and the whole was taken out after further stirring for 1 hour to obtain a pigment kneaded product.

Example 2 Method for Producing Aqueous Pigment Dispersion
A mixed liquid consisting of 18.5 parts of diethylene glycol and 76.4 parts of ion-exchanged water was further added to the pigment kneaded product obtained in Example 1 and mixed to obtain an aqueous pigment dispersion. The obtained aqueous pigment dispersion had a solid content concentration of 19.4% and a pigment concentration of 14.3%.

(Example 3 Method for producing pigment kneaded product)
(Process (1) Slurry process)
10.5 parts of phthalocyanine-based pigment Fastgen Blue (manufactured by DIC: CI Pigment Blue 15: 3), 2.1 parts of styrene acrylic copolymer (A-1), and Surfynol SEF of 0. 5 parts, 0.8 part of 48% potassium hydroxide aqueous solution was added to the stirring layer, stirred and mixed with a three-one motor for 3 hours, dispersed in a bead mill in the same manner as in Example 1, and the pigment slurry was Obtained.

(Process (1) Spray drying process)
The slurry was spray-dried with a spray dryer in the same manner as in Example 1 to obtain a composite pigment with a yield of 90% or more.

(Process (2) Kneading process)
Example 1 60 parts of the composite pigment obtained in the step (1), 5 parts of styrene acrylic copolymer (A-1), 21.5 parts of diethylene glycol, 1.9 parts of 48% aqueous potassium hydroxide solution The pigment kneaded material was obtained by kneading in the same manner as described above.

Example 4 Method for Producing Aqueous Pigment Dispersion
A mixed liquid consisting of 18.5 parts of diethylene glycol and 76.4 parts of ion-exchanged water was further added to the pigment kneaded product obtained in Example 3 and mixed to obtain an aqueous pigment dispersion. The obtained aqueous pigment dispersion had a solid content concentration of 19.4% and a pigment concentration of 14.3%.

(Example 5 Production method of pigment kneaded product)
(Process (1) Slurry process)
10.5 parts of phthalocyanine pigment Fast Gen Blue (manufactured by DIC: CI Pigment Blue 15: 3), 1.6 parts of styrene acrylic copolymer (A-1), 48% aqueous potassium hydroxide solution 0.6 part of was added to the stirring layer, and after stirring and mixing with a three-one motor for 3 hours, dispersion was carried out with a bead mill in the same manner as in Example 1 to obtain a pigment slurry.

(Process (1) Spray drying process)
The slurry was spray-dried with a spray dryer in the same manner as in Example 1 to obtain a composite pigment with a yield of 90% or more.

(Process (2) Kneading process)
55 parts of the composite pigment obtained in the step (1), 10 parts of the styrene acrylic copolymer (A-1), 21.5 parts of diethylene glycol, and 3.8 parts of 48% aqueous potassium hydroxide solution Kneading was performed in the same manner to obtain a pigment kneaded product.

Example 6 Method for Producing Aqueous Pigment Dispersion
A mixed liquid consisting of 18.5 parts of diethylene glycol and 74.5 parts of ion-exchanged water was further added to the pigment kneaded product obtained in Example 5 and mixed to obtain an aqueous pigment dispersion. The obtained aqueous pigment dispersion had a solid content concentration of 20.0% and a pigment concentration of 14.8%.

(Example 7 Production method of pigment kneaded product)
(Process (1) Slurry process)
10.5 parts of phthalocyanine pigment Fast Gen Blue (manufactured by DIC: CI Pigment Blue 15: 3), 1.6 parts of styrene acrylic copolymer (A-1), 48% aqueous potassium hydroxide solution 0.6 part of was added to the stirring layer, and after stirring and mixing with a three-one motor for 3 hours, dispersion was carried out with a bead mill in the same manner as in Example 1 to obtain a pigment slurry.

(Process (1) Spray drying process)
The slurry was spray-dried with a spray dryer in the same manner as in Example 1 to obtain a composite pigment with a yield of 90% or more.

(Process (2) Kneading process)
Example 1 55 parts of the composite pigment obtained in the step (1), 10 parts of the styrene acrylic copolymer (A-2), 21.5 parts of diethylene glycol, 2.5 parts of 48% aqueous potassium hydroxide solution The pigment kneaded material was obtained by kneading in the same manner as described above.

Example 8 Method for Producing Aqueous Pigment Dispersion
A mixed liquid consisting of 18.5 parts of diethylene glycol and 75.8 parts of ion-exchanged water was further added to the pigment kneaded material obtained in Example 7 and mixed to obtain an aqueous pigment dispersion. The obtained aqueous pigment dispersion had a solid content concentration of 19.4% and a pigment concentration of 14.3%.

(Comparative Example 1 Production Method of Aqueous Pigment Dispersion)
In Example 1, an aqueous pigment dispersion was prepared except for the spray drying step in step (1) and the kneading step in step (2).
That is, 10.5 parts of phthalocyanine pigment Fast Gen Blue (made by DIC: CI Pigment Blue 15: 3), 3.1 parts of styrene acrylic copolymer (A-1), 48% hydroxylation 1.2 parts of an aqueous potassium solution was added to the stirring layer, and after stirring and mixing for 3 hours with a three-one motor, dispersion was carried out under the following conditions using a bead mill (Nanomill NM-G2L manufactured by Asada Tekko) to obtain an aqueous pigment dispersion. It was. The pigment concentration of this aqueous pigment dispersion was 15.0%.

Dispersion condition Disperser: Nanomill NM-G2L (manufactured by Asada Tekko)
Beads: φ0.3mm zirconia beads Bead filling amount: 85%
Cooling water temperature: 10 degrees Rotation speed: 2660 rpm
Liquid feed rate: 200 g / min
Dispersion time: 3 hours

(Comparative Example 2 Production Method of Aqueous Pigment Dispersion)
In Example 1, an aqueous pigment dispersion was prepared except for the step (1).
That is, 50 parts of phthalocyanine pigment Fast Gen Blue (manufactured by DIC: CI Pigment Blue 15: 3), 15 parts of styrene acrylic copolymer (A-1), and 5% of 48% potassium hydroxide aqueous solution. .7 parts and 21.5 parts of diethylene glycol were charged into a planetary mixer ACM-0.4LVT (Aikosha Seisakusho Co., Ltd.) with a capacity of 0.4 L. The jett was heated to 80 degrees and kneaded for 1 hour at a rotation speed of 80 rpm. To obtain a pigment kneaded product.

  Subsequently, 150 parts of ion-exchanged water was gradually added to the pigment kneaded material in the stirring layer while stirring was continued, and the whole was taken out after further stirring for 1 hour. Furthermore, the liquid mixture which consists of 18.5 parts of diethylene glycol and 72.7 parts of ion-exchange water was added and mixed with this dispersion liquid. The aqueous pigment dispersion had a solid content concentration of 19.9% and a pigment concentration of 14.7%.

The following items were measured and evaluated for the aqueous pigment dispersions produced in Examples 2, 4, 6, 8 and Comparative Examples 1-2.
<Number of coarse particles immediately after preparation (initial value)>
The aqueous pigment dispersions produced in Example 2 and Comparative Examples 1 and 2 were diluted 2000 times and measured with Accusizer 780APS (made by International Business Corporation). The number of coarse particles was converted to the number of particles per mL of the aqueous pigment dispersion before dilution.

<Number of coarse particles after storage stability test (after stability test)>
The aqueous pigment dispersions produced in the examples and comparative examples were allowed to stand in a heating and cooling thermostat for 3 days, and the number of coarse particles was measured by the same method as described above.
The above results are shown below. The notation in the table was determined according to the following criteria.

  As shown in Examples 2, 4, 6, and 8, the aqueous pigment dispersion subjected to Step 1 maintained the initial value and the number of coarse particles at an extremely low level even after the stability test. Further, as shown in Example 4, the aqueous pigment dispersion containing the surfactant was an aqueous pigment dispersion having a large number of coarse particles and high stability. As shown in Example 6, the aqueous pigment dispersion in which the resin amount in Step 1 and Step 2 was changed maintained the initial value, and the number of coarse particles was extremely low even after the stability test. As shown in Example 8, the aqueous pigment dispersion in which the resin type in Step 1 and Step 2 was changed maintained the initial value, and the number of coarse particles was extremely low even after the stability test. In contrast, the aqueous pigment dispersions of Comparative Example 1 (Step 1 only) or Comparative Example 2 (Step 2 only) both had a large number of coarse particles. From the above, through Step 1 and Step 2, even if a pigment dispersion is produced with different resin amounts and different resin types, a dispersion excellent in reduction of the number of coarse particles and long-term storage stability can be produced. I can say that.

Claims (5)

A pigment, a resin (A) having an anionic group, and a neutralizing agent that neutralizes the anionic group are mixed, and slurryed in water or a liquid medium containing water as a main component, followed by spray drying or freeze drying. Step (1) for obtaining a composite pigment, and step (2) for kneading a mixture containing the composite pigment obtained in step (1), a water-soluble organic solvent, and a resin (B) having an anionic group. A method for producing a pigment kneaded product, comprising: The pigment kneaded material according to claim 1, wherein the ratio of the pigment to the resin (A) having an anionic group in the step (1) is in the range of resin weight / pigment weight = 0.15 to 0.40. Manufacturing method. In the step (2), the mass of the mixture being kneaded using a closed kneader equipped with a sealable stirring tank and uniaxial or multiaxial agitating blades is 90 mass relative to the charged amount before kneading. The method for producing a pigment kneaded product according to claim 1 or 2, wherein the method is a step of kneading so as to be maintained within a range of at least%. The method for producing a pigment kneaded material according to any one of claims 1 to 3, which is a method for producing a pigment kneaded material used for producing an ink for inkjet recording. A method for producing an aqueous pigment dispersion, wherein water or a liquid medium containing water as a main component is added to the pigment kneaded product obtained by the production method according to any one of claims 1 to 4 and is liquefied by stirring.