JP2019206687A - Method for producing aqueous pigment dispersion - Google Patents

Abstract

To provide a method for producing an aqueous pigment dispersion which can prevent the generation of coarse particles with time, has dispersion stability capable of preventing precipitation of a pigment or the like with time and can be used for producing ink having excellent discharge stability.SOLUTION: There is provided a method for producing an aqueous pigment dispersion which comprises a step [1] of producing a kneaded product (a2) by kneading a composition (a1) having a nonvolatile content of 50 mass% or more containing at least a pigment and a resin, a step [2] of producing a composition (a3) by mixing at least the kneaded product (a2) and an aqueous medium and a step [3] of subjecting the composition (a3) to centrifugal separation treatment in a range of 30°C to 70°C.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing an aqueous pigment dispersion that can be used, for example, in the production of ink.

  The ink jet printing method is employed in various printed matter production scenes. The inkjet printing method is a method for producing a printed matter by ejecting ink from an ink ejection nozzle and landing on a surface of a recording medium such as paper or fabric. For this reason, the ink is required to have ejection stability that does not easily cause clogging of the ink ejection nozzles over time and that does not change the volume and direction of ink ejection over time.

  The ink for inkjet printing is generally produced by supplying and mixing a binder resin, a water-soluble solvent, an aqueous medium, or the like as necessary to an aqueous pigment dispersion in which a pigment is previously dispersed in an aqueous medium. Therefore, in order to impart good ejection stability to the ink, it is possible to reduce the generation of coarse particles that can cause clogging of the ink ejection nozzle, and to prevent precipitation of pigments and the like over time. It is important to use a pigment dispersion.

  As the aqueous pigment dispersion capable of reducing the generation of the coarse particles and preventing the precipitation of pigments and the like over time, for example, a mixture containing at least a resin having an anionic group, a pigment, and a basic compound is kneaded in a closed system. An aqueous pigment dispersion using a solid or semi-solid kneaded material kneaded with an apparatus is known (for example, see Patent Document 1).

  However, miniaturized and high-density ink discharge nozzles that can be used for the production of high-definition printed matter can cause clogging and abnormal ink discharge due to the influence of extremely small coarse particles and precipitates in the ink. As a result, there are cases where streaks or the like are generated in the printed matter.

  In particular, in general, the single-pass inkjet printing method using a line head causes a reduction in image quality due to clogging of the ink ejection nozzles, etc., compared to the so-called multi-pass inkjet method. Sometimes it was easy.

  As described above, it is possible to effectively suppress the generation of coarse particles and sediment in the ink that cause clogging of fine ink discharge nozzles that can be used in the production of high-definition printed matter over time. Although demanded by the industry, there are cases where the required performance has not been reached by the prior art.

Japanese Patent Laid-Open No. 2003-226832

  The problem to be solved by the present invention is that it is possible to prevent the generation of coarse particles over time, has dispersion stability capable of preventing the precipitation of pigments and the like over time, and has excellent discharge stability. It is an object of the present invention to provide a method for producing an aqueous pigment dispersion that can be used for producing an ink provided.

  The inventor has a step [1] of producing a kneaded product (a2) by kneading a composition (a1) containing at least a pigment and a resin and having a nonvolatile content of 50% by mass or more, and at least the kneaded product (a2). ) And an aqueous medium are mixed [2], and the composition (a3) is centrifuged at a temperature of 30 ° C. to 70 ° C. [3]. The above-mentioned problems have been solved by a method for producing an aqueous pigment dispersion characterized by comprising:

  The aqueous pigment dispersion obtained by the production method of the present invention has a dispersion stability capable of preventing the generation of coarse particles over time and preventing the precipitation of pigments and the like over time. The aqueous pigment dispersion can be suitably used for producing an ink for ink jet printing excellent in ejection stability.

  In the method for producing an aqueous pigment dispersion of the present invention, the kneaded product (a2) is produced by kneading a composition (a1) containing at least a pigment and a resin and having a nonvolatile content of 50% by mass or more [1]. A step [2] of producing a composition (a3) by mixing at least the kneaded product (a2) and an aqueous medium, and centrifuging the composition (a3) within a range of 30 ° C. to 70 ° C. It has the process [3] to process.

(Description of process [1])
Step [1] is a step of producing a kneaded product (a2) by kneading a composition (a1) containing at least a pigment and a resin and having a nonvolatile content of 50% by mass or more.
As the composition (a1), a composition containing a pigment, a resin, and optionally a basic compound, a solvent such as a water-soluble organic solvent or water, an optional component such as a pigment derivative or a surfactant is used. be able to.

The composition (a1) used in the step [1] preferably has a non-volatile content of 50% by mass or more, more preferably 50 to 90% by mass, and 50 to 90% by mass. It is particularly preferable to use 85% by mass.
Herein, the nonvolatile content, the composition of about 1 g (a1), under reduced pressure of 3 hPa, and the mass ¹ of the remaining ingredients after heating for 4 hours at 175 ° C., before heating the composition (a1 ) Mass ⁰ and a value calculated based on the formula [mass ¹ / mass ⁰ ] × 100.

  By using the composition (a1) having a non-volatile content of 50% by mass or more, the viscosity of the kneaded product (a2) during kneading is appropriately maintained, and the share of the kneaded product (a2) from the kneading apparatus is increased. By enlarging, the pulverization of the pigment agglomerates and the adsorption of the resin to the pigment can proceed efficiently in parallel. As a result, the generation of coarse particles over time, the pigment, etc. Thus, it is possible to obtain an aqueous pigment dispersion that can be used in the production of an ink having excellent dispersion stability and ejection stability that can simultaneously prevent the occurrence of sedimentation over time.

(Pigment)
The pigment that can be used in the composition (a1) is not particularly limited, and a known organic pigment or inorganic pigment can be used. In particular, when obtaining an aqueous pigment dispersion that can be used in the production of ink for inkjet printing, examples of the pigment include carbon black produced by a known method such as iron oxide, contact method, furnace method, thermal method, and the like. , Inorganic pigments such as titanium oxide, azo pigments (including insoluble azo pigments such as monoazo pigments, disazo pigments, pyrazolone pigments, benzimidazolone pigments, beta naphthol pigments, naphthol AS pigments, condensed azo pigments), polycyclic pigments (For example, quinacridone pigment, perylene pigment, perinone pigment, anthraquinone pigment, dioxazine pigment, thioindigo pigment, isoindolinone pigment, isoindoline pigment, quinophthalone pigment, diketopyrrolopyrrole pigment), phthalocyanine pigment, dye chelate (for example, base Sex dye type Kiret And acid dye chelates), nitro pigments, nitroso pigments, can be used organic pigments such as aniline black. As said pigment, it can use individually or in combination of 2 or more types.

  As the pigment, carbon black # 2300, # 980, # 960, # 900, # 52, # 45L, # 45, # 40, # 33, MA100, MA8, MA7, etc. manufactured by Mitsubishi Chemical Corporation, For example, Regal series and Monarch series manufactured by Cabot Corporation, Color Black series, Printex series, Special Black series, NIPEX series manufactured by Orion Engineered Carbons Co., Ltd. can be used.

  Examples of the pigment include C.I. I. Pigment Yellow 1, 2, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 138, 150, 151, Yellow pigments such as 154, 155, 174, 180, and 185 can be used.

  Examples of the pigment include C.I. I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123, 146, 149, 150, 168, 176, 184, 185, 202, 209 Magenta pigments such as 213, 269, and 282 can be used.

  Examples of the pigment include C.I. I. Cyan pigments such as CI Pigment Blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 22, 60, 63, 66 can be used.

  Examples of the pigment include C.I. I. Orange pigments such as CI Pigment Orange 5, 13, 16, 17, 34, 36, 43, 51, 64, 71 can be used.

  Examples of the pigment include C.I. I. Violet pigments such as pigment violet 1, 3, 5: 1, 16, 19, 23, 38 can be used.

  Examples of the pigment include C.I. I. Green pigments such as CI Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, 50, 58 can be used.

  As the pigment, a pigment in a dry powder state or a wet cake state can be used. As said pigment, the mixture and solid solution containing 2 or more types can be used.

  As the pigment, it is preferable to use a pigment having a primary particle size of 1.0 μm or less, and it is more preferable to use a pigment having a particle size of 0.01 μm to 0.5 μm. By using a pigment having a primary particle diameter in the above-described range, it is possible to more effectively suppress the precipitation of the pigment over time. For the measurement of the primary particle size, for example, the value of the number average particle size measured using a transmission electron microscope (TEM) can be adopted.

  The pigment is preferably used in an amount of 30 to 80% by mass based on the total amount of the composition (a1), and the use of 35 to 75% by mass keeps the viscosity of the kneaded product (a2) moderately and is kneaded. By increasing the share of the kneaded material (a2) from the apparatus, the pulverization of the pigment agglomerates and the adsorption of the resin to the pigment can proceed efficiently in parallel. An aqueous pigment dispersion that can be used in the production of ink with excellent dispersion stability and ejection stability that can both prevent generation of coarse particles over time and prevent precipitation of pigments over time Since it can obtain, it is especially preferable.

(resin)
As a resin that can be used for the composition (a1), for example, a pigment dispersion resin can be used. As the pigment dispersion resin, those conventionally known can be used. As the pigment dispersion resin, for example, a radical polymer can be used, and a radical polymer having an aromatic cyclic structure or a heterocyclic structure is preferably used, and a radical weight having an acid value of 60 to 300 mgKOH / g is used. The use of coalescence can prevent the generation of coarse particles over time, has dispersion stability that can prevent the occurrence of sedimentation of pigments and the like over time, and has excellent ejection stability It is more preferable to obtain an aqueous pigment dispersion that can be used in the production of

  When a radical polymer having an anionic group is used as the pigment-dispersed resin, it is possible to use a product obtained by neutralizing a part or all of the anionic group described later with a basic compound (neutralized product). It can be used for the production of ink that can prevent the generation of coarse particles over time, has dispersion stability that can prevent the precipitation of pigments etc. over time, and has excellent ejection stability. It is preferable when obtaining an aqueous pigment dispersion.

  Examples of the aromatic cyclic structure or the heterocyclic structure include a ring introduced into the radical polymer by using a monomer having an aromatic cyclic structure or a monomer having a heterocyclic structure, which will be described later. Structure is mentioned.

As the aromatic cyclic structure, a benzene ring structure is preferably used, and a structure derived from styrene is more preferable.
By using a pigment dispersion resin that is a radical polymer having an aromatic cyclic structure or a heterocyclic structure, it is possible to increase the adsorptivity of the pigment dispersion resin to the pigment. Aqueous pigment dispersion that can prevent the generation of coarse particles, has dispersion stability that can prevent the occurrence of sedimentation of pigments, etc. over time, and can be used for the production of ink having excellent ejection stability. Can be obtained efficiently.

  Moreover, as the pigment dispersion resin, use of an acid value of 60 to 300 mgKOH / g can improve the adsorptivity of the pigment dispersion resin to the pigment, and as a result, the generation of coarse particles over time is suppressed. And an aqueous pigment dispersion that can be used in the production of an ink having excellent dispersion stability and ejection stability capable of achieving both the prevention of sedimentation of pigments and the like over time is particularly preferable. . Specifically, the pigment dispersion resin having an acid value in the above range is easily dissolved or partially dissolved in the water-soluble organic solvent described later in the step [1], or easily swelled by the water-soluble organic solvent. It is easy to form a basic compound and a salt (neutralized product) described later. Such a pigment dispersion resin is adsorbed to the pigment, so that the hydrophilicity of the pigment is remarkably improved. As a result, the aqueous pigment dispersion that can be used for the production of ink having even better dispersion stability and ejection stability. You can get a body.

  The acid value is an acid value derived from an anionic group such as a carboxy group, a sulfo group, or a phosphoric acid group. The acid value is preferably in the range of 80 to 250 mgKOH / g, and in the range of 100 to 200 mgKOH / g can prevent the generation of coarse particles over time, and the precipitation of pigments and the like over time. It is particularly preferable for obtaining an aqueous pigment dispersion that can be used in the production of an ink that has a dispersion stability that can prevent the occurrence of the ink and that has an excellent ejection stability.

  The acid value is Japanese Industrial Standard “K0070: 1992. Acid value, saponification value, ester value, iodine value, hydroxyl value and non-saponification of chemical products, except that tetrahydrofuran is used instead of diethyl ether as a solvent. It is a numerical value measured according to “Testing method of chemical compound” and indicates the amount (mg) of potassium hydroxide necessary to completely neutralize 1 g of the resin.

  As the radical polymer that can be used for the pigment-dispersed resin, for example, a polymer obtained by radical polymerization of various monomers can be used.

  As the monomer, a monomer having an aromatic cyclic structure can be used as long as an aromatic cyclic structure is introduced into the pigment-dispersed resin, and a heterocyclic structure is introduced. If present, a monomer having a heterocyclic structure can be used.

  Examples of the monomer having an aromatic cyclic structure include styrene, p-tert-butyldimethylsiloxystyrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, p-tert-butoxystyrene, m-tert-butoxystyrene, p-tert- (1-ethoxymethyl) styrene, m-chlorostyrene, p-chlorostyrene, p-fluorostyrene, α-methylstyrene, p-methyl-α-methylstyrene, vinylnaphthalene , Vinyl anthracene and the like can be used.

  As the monomer having a heterocyclic structure, for example, a vinylpyridine monomer such as 2-vinylpyridine and 4-vinylpyridine can be used.

  When using the radical polymer having both an aromatic cyclic structure and a heterocyclic structure, as the monomer, a monomer having an aromatic cyclic structure and a monomer having a heterocyclic structure The body can be used in combination.

  In the present invention, since it is preferable to use a radical polymer having an aromatic cyclic structure as the pigment dispersion resin, it is preferable to use a monomer having an aromatic cyclic structure as the monomer. It is more preferable to use styrene, α-methylstyrene, or tert-butylstyrene.

  The monomer having an aromatic cyclic structure or a heterocyclic structure is used in an amount of 20% by mass or more based on the total amount of the monomer in order to further enhance the adsorptivity of the pigment dispersion resin to the pigment. It is preferable to use 40% by mass or more, and more preferably 95% by mass or less.

  In addition, as the pigment-dispersed resin, a monomer having an anionic group can be used as the monomer in producing the radical polymer having an acid value in the specific range described above.

  As the monomer having an anionic group, for example, a monomer having an anionic group such as a carboxy group, a sulfo group or a phosphate group can be used.

  As the monomer having an anionic group, it is easy to obtain, and the use of a monomer having a carboxy group can prevent the generation of coarse particles over time, and can prevent precipitation of pigments and the like over time. It is preferable to obtain an aqueous pigment dispersion that can be used for the production of an ink having dispersion stability capable of preventing generation and excellent discharge stability, and more preferably using acrylic acid or methacrylic acid. .

  The monomer having an anionic group is preferably used in the range of 5% by mass to 80% by mass with respect to the total amount of the monomer that can be used in the production of the pigment dispersion resin. It is more preferable to use it at 60% by mass in order to obtain a radical polymer having an acid value in the predetermined range described above.

  Moreover, as a monomer which can be used for manufacture of the said pigment dispersion resin, another monomer other than the above-mentioned thing can be used as needed.

  Examples of the other monomers include methyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl ( (Meth) acrylate, 2-ethylbutyl (meth) acrylate, 1,3-dimethylbutyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, ethyl (meth) acrylate, n -Butyl (meth) acrylate, 2-methylbutyl (meth) acrylate, pentyl (meth) acrylate, heptyl (meth) acrylate, nonyl (meth) acrylate, 3-ethoxypropyl (meth) acrylate, 3-ethoxybutyl ( ) Acrylate, dimethylaminoethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, ethyl-α- (hydroxymethyl) (meth) acrylate, dimethylaminoethyl (meth) acrylate , Hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, phenylethyl (meth) acrylate, diethylene glycol (meth) acrylate, triethylene glycol (meth) acrylate, polyethylene glycol (Meth) acrylate, glycerin (meth) acrylate, bisphenol A (meth) acrylate, dimethyl maleate, diethyl maleate, vinyl acetate, etc. Can be used alone or in combination of two or more. The “(meth) acrylate” refers to acrylate or methacrylate. As the other monomer, such acrylate or methacrylate may be used alone, or acrylate and methacrylate may be used in combination.

  The pigment-dispersed resin includes a polymer having a linear structure formed by radical polymerization of the monomer, a polymer having a branched structure, and a polymer having a crosslinked structure. Can be used. In each polymer, the monomer sequence is not particularly limited, and a random type or block type polymer can be used.

  The polymer having the crosslinked structure can be produced by using a monomer having a crosslinkable functional group as the monomer.

  Examples of the monomer having a crosslinkable functional group include ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and poly (oxyethyleneoxypropylene) glycol di (meth). ) Poly (meth) acrylates of polyhydric alcohols such as tri (meth) acrylates of acrylates and alkylene oxide adducts of glycerol; glycidyl (meth) acrylates, divinylbenzene and the like can be used.

  As the pigment dispersion resin used in the present invention, a polymer of the above-mentioned monomer can be used, but only a monomer having an anionic group and a monomer having an aromatic cyclic structure or a heterocyclic structure. It is preferable to use a polymer obtained by polymerizing.

  Among the pigment dispersion resins used in the present invention, among those described above, styrene structural units such as styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid ester- (meth) acrylic acid polymer, and the like It is preferable to use a polymer having a (meth) acrylic acid structural unit, and among them, the use of a polymer having an acid value in the above-described preferable range is more effective in generating coarse particles over time. Water-based pigments that can be used for the production of inks that have excellent dispersion stability and can be effectively prevented, and have a dispersion stability that can more effectively prevent the precipitation of pigments and the like over time It is preferable when obtaining a dispersion.

  As the styrene- (meth) acrylic acid copolymer, any of styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, and styrene-acrylic acid-methacrylic acid copolymer can be used. The use of an acid-methacrylic acid copolymer improves the copolymerizability of the monomer and, as a result, can more effectively prevent the generation of coarse particles over time, and This is preferable because an aqueous pigment dispersion that can be used in the production of an ink having dispersion stability that can more effectively prevent the occurrence of sedimentation with time and excellent discharge stability can be obtained.

  As the styrene- (meth) acrylic acid copolymer, a copolymer having a total amount of styrene, acrylic acid and methacrylic acid of 80% by mass to 100% by mass with respect to the total amount of monomers used for the production thereof is used. It is preferable to use 90% by mass to 100% by mass.

  In the present invention, the radical polymerization rate (reaction rate) of each monomer at the time of the radical polymerization is substantially the same, and the use ratio (preparation ratio) of each monomer is different for each of the radical polymers. The proportion of structural units derived from monomers was considered identical.

  The radical polymer can be produced, for example, by radical polymerization of the above-described monomer by a method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method.

  When manufacturing the said radical polymer, a well-known and usual polymerization initiator, a chain transfer agent (polymerization degree modifier), surfactant, and an antifoamer can be used as needed.

  Examples of the polymerization initiator include 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 1,1′-azobis (cyclohexane-1-carbonitrile). ), Benzoyl peroxide, dibutyl peroxide, butyl peroxybenzoate and the like. The polymerization initiator is preferably used in the range of 0.1% by mass to 10% by mass with respect to the total amount of monomers used for the production of the radical polymer.

The pigment-dispersed resin preferably has a weight average molecular weight in the range of 2000 to 40000, more preferably in the range of 5000 to 30000, and in the range of 5000 to 25000. An aqueous pigment that can prevent the generation of coarse particles over time and can be used for the production of inks with further excellent dispersion stability and ejection stability that can prevent the precipitation of pigments and the like over time. It is particularly preferable for obtaining a dispersion.
In addition, the said weight average molecular weight is a value measured by GPC (gel permeation chromatography) method, and is a value converted into the molecular weight of polystyrene used as a standard substance.

When the radical polymer obtained by the solution polymerization method is used as the pigment dispersion resin, the pigment dispersion resin is dried after removing the solvent contained in the radical polymer solution obtained by the solution polymerization method. Then, pulverized fine particles can be used.
The pigment-dispersed resin, which is the atomized radical polymer, is easily dissolved or partially dissolved in the water-soluble organic solvent described later in the step [1] or easily swelled by the water-soluble organic solvent. By being easily adsorbed, it is possible to obtain an aqueous pigment dispersion that can be used in the production of an ink having further excellent dispersion stability and ejection stability.
As the pigment-dispersed resin, it is preferable to use a resin classified by a mesh sieve having a mesh size (diameter) of 1 mm or less.

As said composition (a1), it is preferable to use what the weight ratio of the said pigment dispersion resin with respect to the said pigment is the range of 5 mass%-200 mass%, and is the range of 10 mass%-100 mass%. In the step [1], it is possible to knead the kneaded product (a2) with an appropriate viscosity, and to easily adsorb the pigment dispersion resin to the pigment. Since it is possible to obtain an aqueous pigment dispersion that can be used in the production of ink having excellent dispersion stability and ejection stability that can both prevent generation and prevent sedimentation of pigments and the like over time. preferable.
As the resin used in the present invention, in addition to the pigment-dispersed resin, a binder resin or the like can be used as necessary.

Moreover, as said composition (a1) used by the said process [1], what contains a basic compound other than the said pigment and the said pigment dispersion resin as needed can be used.
The basic compound neutralizes the anionic group when the pigment dispersion resin has an anionic group. By neutralizing the pigment dispersion resin with the basic compound, the affinity of the pigment adsorbed by the pigment dispersion resin to an aqueous medium is increased. As a result, the dispersion state of the pigment particles in the aqueous pigment dispersion becomes more stable, the generation of coarse particles over time can be more effectively prevented, and the precipitation of pigments and the like over time can be further effective. Can be prevented.

As the basic compound, for example, an inorganic basic compound or an organic basic compound can be used.
As the basic compound, known compounds can be used, such as alkali metal hydroxides such as potassium and sodium; carbonates of alkali metals such as potassium and sodium; carbonates such as alkaline earth metals such as calcium and barium. Salts: inorganic basic compounds such as ammonium hydroxide, amino alcohols such as triethanolamine, N, N-dimethanolamine, N-ethylethanolamine, dimethylethanolamine, N-butyldiethanolamine, morpholine, N- Examples include organic basic compounds such as morpholines such as methylmorpholine and N-ethylmorpholine, and piperazine such as N- (2-hydroxyethyl) piperazine and piperazine hexahydrate. Among them, as the basic compound, use of an alkali metal hydroxide represented by potassium hydroxide, sodium hydroxide, or lithium hydroxide is excellent in neutralization efficiency of the pigment dispersion resin. This is preferable because the dispersion stability of the pigment adsorbed by the dispersion resin in an aqueous medium described later is improved, and potassium hydroxide is particularly preferable.

  If the basic compound is one having an anionic group as the pigment-dispersed resin, it may be used in a range where the neutralization rate of the pigment-dispersed resin is 80% to 120%. This is preferable because the affinity of the pigment-dispersed resin for the aqueous medium is enhanced, and as a result, the dispersion stability of the pigment adsorbed by the pigment-dispersed resin in water is improved.

  Neutralization rate (%) = ((mass of basic compound (g) × 56 × 1000) / (acid value of pigment dispersion resin × equivalent of basic compound × mass of pigment dispersion resin (g))) × 100

  Moreover, as said composition (a1) used by the said process [1], what contains solvents, such as the said water-soluble organic solvent and water other than what was mentioned above as needed, can be used.

  In the step [1], the water-soluble organic solvent easily dissolves or swells part or all of the pigment dispersion resin, and as a result, the pigment dispersion resin easily adsorbs to the pigment. Thereby, the aqueous pigment dispersion which can be used for manufacture of the ink provided with much more excellent dispersion stability and discharge stability can be obtained.

  Examples of the water-soluble organic solvent include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol; diols such as butanediol, pentanediol, and hexanediol; lauric acid Glycol esters such as propylene glycol; diethylene glycol ethers such as diethylene glycol monoethyl, diethylene glycol monobutyl, diethylene glycol monohexyl, carbitol; glycol ethers such as cellosolve including propylene glycol ether, dipropylene glycol ether, and triethylene glycol ether; Methanol, ethanol, isopropyl Alcohols such as alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, butyl alcohol and pentyl alcohol; lactones such as sulfolane, ester, ketone and γ-butyrolactone, 2-pyrrolidinone, N- (2 -Other various solvents known as aqueous organic solvents such as lactams such as -hydroxyethyl) pyrrolidone, glycerin and its polyalkylene oxide adducts. These aqueous organic solvents can be used alone or in combination of two or more.

  Among them, as the water-soluble organic solvent, it is preferable to use a high boiling point, low volatility polyhydric alcohol that functions as a wetting agent, and derivatives of glycerin, particularly glycols such as diethylene glycol and triethylene glycol. It is preferable to use polyalkylene oxide adducts of glycerin such as glycerin and polyethylene oxide adducts of glycerin.

  In the step [1], the water-soluble organic solvent is preferably used in a range of 10% by mass to 200% by mass and used in a range of 15% by mass to 150% by mass with respect to the mass of the pigment. It is more preferable to obtain an aqueous pigment dispersion that can be used in the production of an ink having further excellent dispersion stability and ejection stability.

Moreover, as said composition (a1) used at the said process [1], what contains a pigment derivative as needed other than resin, such as the said pigment and the said pigment dispersion resin, can be used.
The pigment derivative imparts to the aqueous pigment dispersion of the present invention and an ink using the same a dispersion stability that makes it possible to prevent the generation of coarse particles over time and the precipitation of pigments and the like over time. be able to.

  As said pigment derivative, what introduce | transduced the specific functional group mentioned later to a pigment can be used. Examples of the pigment include phthalocyanine pigments, azo pigments, anthraquinone pigments, quinacridone pigments, diketopyrrolopyrrole pigments, and the like. Examples of the functional group include a carboxy group, a sulfo group, an amino group, a nitro group, an acid amide group, a carbonyl group, a carbamoyl group, a phthalimide group, and a sulfonyl group.

  As water used for the solvent, pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, distilled water, or ultrapure water can be used. Also, as the water, use of water sterilized by ultraviolet irradiation or addition of hydrogen peroxide prevents the generation of mold or bacteria when the aqueous pigment dispersion or ink using the same is stored for a long period of time. This is preferable.

In the step [1], examples of a kneader that can be used for kneading the composition (a1) include a Henschel mixer, a pressure kneader, a Banbury mixer, a trimix, and a planetary mixer. As the kneader, in particular, a planetary mixer can be used to give a strong shearing force to the composition (a1) having a non-volatile content of 50% by mass or more. This is preferable because the ease of adsorption of the dispersion resin to the pigment can be increased.
In addition, the planetary mixer increases the ease of pulverization of the aggregates of the pigment and the adsorption of the pigment-dispersed resin to the pigment even when the viscosity of the composition (a1) is wide. This is preferable.
The planetary mixer is preferable because the step [2] of supplying the aqueous medium into the mixer can be continued after the step [1].

  The temperature of the composition (a1) when kneading the composition (a1) in the step [1] is such that the glass transition of the pigment-dispersed resin is such that a sufficient shearing force is applied to the composition (a1). It is preferable to adjust appropriately considering temperature characteristics such as points. Specifically, the upper limit of the temperature of the composition (a1) during the kneading is preferably the glass transition temperature (Tg) of the pigment-dispersed resin. On the other hand, the lower limit of the temperature of the composition (a1) during the kneading is preferably a temperature 60 ° C. lower than the glass transition temperature of the pigment-dispersed resin. By carrying out the kneading of the composition (a1) within the temperature range, it becomes possible to give a sufficient shearing force to the composition (a1). As a result, the aggregation of the pigment and the pigment This is preferable because the ease of adsorption of the dispersion resin to the pigment can be increased.

  In the step [1], the viscosity of the composition (a1) may be significantly decreased due to a temperature increase. When the viscosity of the composition (a1) decreases, it may not be possible to apply a sufficient shearing force to the composition (a1). Therefore, in the step [1], an aqueous medium or the like to be described later is added on the way. It may be added and the composition (a1) may be intentionally cooled.

The glass transition temperature (Tg) of the pigment dispersion resin is a value calculated using the FOX equation based on the glass transition temperature of the homopolymer of each monomer used in the production of the pigment dispersion resin. Point to.
1 / Tg = W1 / Tg1 + W2 / Tg2 + W3 / Tg3... + Wn / Tgn
(Wherein, Tgn is the glass transition temperature (absolute temperature: K) of the homopolymer of each monomer used in the production of the pigment dispersion resin, and Wn is the mass fraction of the monomer)

As the kneading apparatus, it is preferable to use a closed type kneading apparatus because the content of the solvent such as the water-soluble organic solvent and water used can be prevented from changing significantly during the step [1].
The “remarkably changed” refers to a state where the ratio of the mass of the kneaded product (a2) obtained after the completion of the step [1] to the mass of the composition (a1) is less than 90% by mass.

As the closed kneading apparatus, for example, a kneading apparatus including a stirring tank and a uniaxial or multiaxial agitating blade can be used.
As the closed-type kneading apparatus, it is preferable to use an apparatus having two or more stirring blades in order to obtain a high kneading action.

  In the kneaded product (a2) obtained in the step [1], the pigment aggregate is crushed and the pigment-dispersed resin is adsorbed to the finely pulverized pigment. belongs to.

(Description of process [2])
The step [2] constituting the method for producing an aqueous pigment dispersion of the present invention comprises the kneaded product (a2) obtained in the step [1], the aqueous medium, and other components as necessary. In this step, the composition (a3) is produced by mixing.

  In the step [2], the aqueous medium or the like may be supplied to and mixed with the kneaded product (a2), or the kneaded product (a2) may be supplied and mixed with the aqueous medium or the like.

When a closed kneading apparatus such as a planetary mixer is used in the step [1], supplying the aqueous medium or the like to the kneading apparatus including the kneaded product (a2) and mixing the aqueous pigment dispersion It is preferable in improving the production efficiency of the body. In this case, supplying the aqueous medium before the temperature of the kneaded product (a2) is lowered in a state where the kneading apparatus is operated (a state in which stirring of the kneaded product (a2) is continued), It is preferable for improving the dispersion efficiency of the kneaded product (a2) in the aqueous medium and the production efficiency of the composition (a3). As the aqueous medium, it is preferable to use water at 25 ° C. to 65 ° C. in order to suppress a significant decrease in the temperature of the kneaded product (a2).
Moreover, as a method of supplying the said aqueous medium to the said kneaded material (a2), the method of supplying collectively and the method of supplying continuously or intermittently are mentioned. As a method of supplying the aqueous medium, adopting a method of supplying continuously or intermittently can efficiently disperse the kneaded product (a2) in the aqueous medium. This is preferable because the time required for production can be shortened.

  As the aqueous medium, for example, water, a water-soluble organic solvent that easily mixes with water, or a mixture of water and a water-soluble organic solvent can be used. As said water-soluble organic solvent, the thing similar to what was illustrated by the said process [1] can be used 1 type or in combination of 2 or more types.

The composition (a3) obtained through the steps [1] and [2] is a liquid in which the pigment adsorbed by the pigment dispersion resin is dispersed in an aqueous medium.
The composition (a3) preferably has a nonvolatile content of 10% by mass to 30% by mass and more preferably 12% by mass to 25% by mass with respect to the total amount of the composition (a3).

  In the present invention, the composition (a3) obtained in the step [2] may be subjected to a dispersion treatment using a dispersion device, if necessary, before the step [3]. As the dispersing device, for example, 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 mill, an agitator mill, etc. can be used as a medium. An ultrasonic homogenizer, a high-pressure homogenizer, a nanomizer, a resolver, a disper, a high-speed impeller disperser, etc. can be used without using media.

Moreover, when impurities, such as a polyvalent metal ion, are contained in the said composition (a3), in this invention, the said composition (a3) obtained at the said process [2] is made before the said process [3]. In addition, it is preferable to perform a treatment for removing impurities using a chelate resin or the like, if necessary.
As an ink jet printing method, a piezo method and a thermal method are known. In particular, in the thermal method, due to a rapid temperature rise inside the nozzle when ink is ejected, an aggregate of a resin such as a pigment-dispersed resin and a polyvalent metal ion on the surface of the heating resistor element inside the nozzle, or the polyvalent metal A phenomenon called kogation in which aggregates such as polyvalent metal salts derived from ions accumulate may occur. Since the agglomerates cause ink ejection failure, it is strongly desired to reduce polyvalent metal ions in inks for inkjet printing.

  Examples of the method of reducing the polyvalent metal ion include a method of removing polyvalent metal by bringing particles having a chelate-forming group or fibrous resin into contact with an aqueous pigment ink or an aqueous pigment dispersion.

(Description of process [3])
The step [3] constituting the method for producing an aqueous pigment dispersion of the present invention is performed at 30 ° C. to 30 ° C. from the composition (a3) obtained through at least the step [1] and the step [2]. This is a step of performing a centrifugal separation treatment within a range of 70 ° C.
The composition (a3) may cause the coarse particles of the pigment agglomerates, the pigment-dispersed resin undissolved, the pigment not sufficiently adsorbed by the pigment-dispersed resin, and the like. Ingredients may remain very slightly. Therefore, reduction of the content of the above components has been studied in the industry.

However, miniaturized and high-density ink discharge nozzles that can be used for the production of high-definition printed matter can cause clogging and ink discharge abnormalities due to the influence of very few coarse particles and precipitates in the ink. As a result, streaks or the like may occur in the printed matter. In particular, in general, the single-pass inkjet printing method using a line head causes a reduction in image quality due to clogging of the ink ejection nozzles, etc., compared to the so-called multi-pass inkjet method. Sometimes it was easy.
In the present invention, after the composition (a3) is produced, the ink discharge nozzle is applied even when applied to a fine and high density ink discharge nozzle by centrifuging under a predetermined condition. The present invention has found an aqueous pigment dispersion that can be used in the production of ink that does not cause clogging of the ink.
Here, the coarse particles referred to in the present invention are particles having a particle diameter (particle diameter) of 0.5 μm or more measured using a particle size distribution analyzer (Accumizer 780 APS) manufactured by Particle Sizing Systems. Point to.
In the step [3], it is not necessary to simply centrifuge, but centrifuge at a temperature in the range of 30 ° C to 70 ° C. When the step [3] is performed at a temperature of less than 30 ° C., the viscosity of the composition (a3) increases, and it may be difficult to remove coarse particles efficiently and practically sufficiently. is there. In addition, when the step [3] is performed at a temperature exceeding 70 ° C., water easily evaporates from the composition (a3), the viscosity tends to increase, and the coarse particles are efficiently and practically sufficient. It can be difficult to remove.
In the step [3], it is more preferable to perform a centrifugal separation treatment in the range of 40 ° C. to 65 ° C. in order to remove coarse particles efficiently and practically. The temperature refers to the temperature of the composition (a3) to be centrifuged.

The composition (a3) may be temperature-adjusted to 30 ° C. to 70 ° C. in advance using, for example, a heat exchange device or the like before being supplied to the centrifugal separator, and has a temperature setting function as the centrifugal separator. When using a thing, after supplying to a centrifuge, you may adjust to the said temperature range.
The heated composition (a3) is reduced in viscosity, whereby the centrifugal separation efficiency is improved and coarse particles can be efficiently removed. In addition, by controlling the composition (a3) in the above temperature range, it is difficult to be affected by the outside air temperature, and an aqueous pigment dispersion with few coarse particles can be stably produced.

As the composition (a3) to be centrifuged, it is more efficient to use coarse particles from the composition (a3), and those having a viscosity at 25 ° C. of 13 mPa · s or less, and This is preferable because it can be removed practically.
In particular, when a later-described cylindrical centrifuge is used as the centrifuge, the composition (a3) preferably has a viscosity at 25 ° C. of 10.5 mPa · s or less, and 2 mPa · s. It is more preferable that the viscosity is ˜10.5 mPa · s because coarse particles can be more efficiently and practically sufficiently removed from the composition (a3).

As the centrifuge, using a centrifuge with a cylindrical rotor shape effectively reduces the centrifuge efficiency caused by the accumulation of clay-like sludge containing coarse particles in the rotor. It is preferable because it can be suppressed.
The composition (a3) obtained through the step [1] and the step [2] includes various kinds such as coarse particles of the pigment, unpulverized pigment, or undissolved pigment dispersion resin. Coarse particles of a size are easily included. By performing the step [3] using the cylindrical centrifuge, the coarse particles can be efficiently and continuously removed without impairing the productivity, and as a result, the coarse particles over time. It is possible to obtain an excellent dispersion stability capable of satisfying both the generation inhibition of pigments and the prevention of sedimentation of pigments and the like over time.

  Moreover, the said process [3] supplies the said composition (a3) to the rotor with which the said cylindrical centrifuge is equipped, The state which maintained the temperature of the said composition (a3) in the range of 30 degreeC-70 degreeC It is preferable that the step is carried out in the step (2) because a suitable centrifugal efficiency can be stably maintained for a long period of time, and coarse particles can be more efficiently and sufficiently removed from the composition (a3). At that time, the ratio of the supply amount (volume) of the composition (a3) to the volume of the rotor [the supply amount (volume) of the composition (a3) / the volume of the rotor] × 100 is 1000% to 8000%. This is preferable because it is possible to suppress removal of components such as pigments that are not coarse particles, while coarse particles can be more efficiently removed from the composition (a3).

  The centrifugal acceleration of the centrifugal separator is in the range of 8000G to 20000G, so that the pigment dispersion resin can be prevented from being peeled off from the pigment, and coarse particles can be efficiently removed from the composition (a3). Is preferable.

  The centrifugal acceleration means relative centrifugal acceleration and is defined by the following equation.

Centrifugal acceleration (G) = r × (2πN / 60) ² / g
(Where N is the number of revolutions per minute (rpm), r is the radius of revolution (m), g is the acceleration of gravity (9.8 m / s ² ), and π is the circumference)

  As described above, the aqueous pigment dispersion obtained through at least the step [1], the step [2], and the step [3] can prevent the generation of coarse particles over time, and can be used for pigments and the like. It is a water-based pigment dispersion which can be used for the production of an ink having dispersion stability capable of preventing the occurrence of sedimentation over time and excellent discharge stability.

The aqueous pigment dispersion can be used as an ink by diluting to a desired concentration.
Examples of the ink include paints for automobiles and building materials, printing inks such as offset ink, gravure ink, flexo ink, silk screen ink, and ink for ink jet printing.
When the ink is used as an ink for inkjet printing, it is preferable to use an ink having a pigment concentration of 1% by mass to 10% by mass with respect to the total amount of the ink.
The ink includes an aqueous pigment dispersion of the present invention, a solvent such as a water-soluble organic solvent and water as necessary, a resin such as an acrylic resin and a polyurethane resin as a binder, a drying inhibitor, a penetrant, an interface. It can manufacture by mixing additives, such as an activator, antiseptic | preservative, a viscosity modifier, a pH adjuster, a chelating agent, a plasticizer, antioxidant, and an ultraviolet absorber. The ink may be subjected to a centrifugal separation process or a filtration process after being manufactured by the above method.
The water-soluble organic solvent can be used for preventing the ink from drying and adjusting the viscosity and concentration of the ink to a suitable range.

  As said water-soluble organic solvent, the thing similar to what was illustrated as what can be used at the said process [1] of the said aqueous pigment dispersion can be used. Among them, as the water-soluble organic solvent, for example, lower alcohol such as ethanol or isopropyl alcohol; ethylene oxide adduct of alkyl alcohol such as ethylene glycol hexyl ether or diethylene glycol butyl ether; Examples include propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether.

Examples of the anti-drying agent include glycerin, ethylene glycol, diethylene glycol, triethylene glycol, triethylene glycol mono-n-butyl ether, 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-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, mesoerythritol, pentaerythritol and the like. Among these, as the anti-drying agent, use of glycerin or triethylene glycol provides an ink that has safety, is difficult to dry, and has excellent ejection performance.
In addition, the said drying inhibitor can use the same compound as the said water-soluble organic solvent used with an aqueous pigment dispersion. Therefore, when a water-soluble organic solvent is already used in the aqueous pigment dispersion, it can also serve as a drying inhibitor.

The penetrant can be used 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; glycol monoethers of alkyl alcohols such as ethylene glycol hexyl ether, diethylene glycol butyl ether, and propylene glycol propyl ether.

  The surfactant can be used to adjust ink characteristics such as surface tension. The surfactant is not particularly limited, and examples thereof include various anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Among 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, 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 alkyl Roll amide, acetylene glycol, oxyethylene adduct of acetylene glycol, and polyethylene glycol polypropylene glycol block copolymer are preferred.

  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. Moreover, the said surfactant can be used individually or in combination of 2 or more types.

  The ink obtained by the above method can be suitably used as an ink for inkjet printing. As an inkjet printing method, in general, a single-pass inkjet printing with a line head that tends to cause a decrease in image quality due to clogging of ink discharge nozzles, etc., compared to a multi-pass (scanning) inkjet printing method. The printing method or the printed material manufacturing method used in combination with the ink of the present invention is not likely to cause a decrease in image quality due to clogging of the ink discharge nozzles, etc. It is preferable in obtaining.

  Hereinafter, the present invention will be specifically described by way of examples.

(Pigment dispersion resin)
As pigment dispersion resin A, a polymer of 72 parts by mass of styrene, 12 parts by mass of acrylic acid and 16 parts by mass of methacrylic acid (weight average molecular weight 8200, acid value 180 mgKOH / g, FOX formula based on glass transition temperature of homopolymer) (Calculated glass transition temperature 116 ° C. calculated from the above) was used.
As pigment dispersion resin B, polymer of 77 parts by mass of styrene, 10 parts by mass of acrylic acid and 13 parts by mass of methacrylic acid (weight average molecular weight 8800, acid value 154 mgKOH / g, FOX formula based on glass transition temperature of homopolymer) (Calculated glass transition temperature 113 ° C. calculated from the above).
As pigment dispersion resin C, a polymer of 72 parts by mass of styrene, 12 parts by mass of acrylic acid and 16 parts by mass of methacrylic acid (weight average molecular weight 11000, acid value 180 mgKOH / g, FOX formula based on glass transition temperature of homopolymer) (Calculated glass transition temperature 116 ° C. calculated from the above) was used.
As the glass transition temperature (Tg) of the homopolymer of each monomer used in the production of the pigment dispersion resin, the value recorded in POLYMER HANDBOOK THIRD EDITION (A WILEY-INTERSCIENCE PUBLICATION) was used. Glass transition temperature of styrene homopolymer: 100 ° C. Glass transition temperature of methacrylic acid homopolymer: 228 ° C. Glass transition temperature of acrylic acid homopolymer: 106 ° C.

The weight average molecular weights of the pigment dispersion resins A to C are values measured by a GPC (gel permeation chromatography) method, and are values converted into polystyrene molecular weights. The measurement conditions are as follows.
Liquid feed pump: LC-9A
System controller: SLC-6B
Auto injector: S1L-6B
Detector: RID-6A
Data processing software manufactured by Shimadzu Corporation: 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: tetrahydrofuran (THF)
Elution flow rate: 2 mL / min.
Column temperature: 35 ° C

  The acid value is Japanese Industrial Standard “K0070: 1992. Test method for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponified product of chemical products except that tetrahydrofuran is used instead of diethyl ether as a solvent. ”And measured.

  The viscosity of the aqueous pigment dispersion was measured using a Viscometer TVE-22L (manufactured by Toki Sangyo Co., Ltd.) using the aqueous pigment dispersion constant at 25 ° C. as a sample.

Example 1
In a tank with a 50 L jacket of a planetary mixer (PLM-50 manufactured by Inoue Seisakusho Co., Ltd.), 3.0 parts by mass of pigment dispersion resin A and 10.0 parts by mass of C.I. I. Pigment Blue 15: 3 (manufactured by DIC Corporation, Fastogen Blue TGR-SD) was added in order, and the temperature of the jacketed tank was heated to 60 ° C. After 3.80 parts by mass of triethylene glycol and 1. 59 mass parts of 34 mass% potassium hydroxide aqueous solution was supplied in order, and the composition (a1-1) was obtained.

(Process [1])
With the temperature of the jacketed tank kept at 60 ° C., the composition (a1-1) was stirred for 10 minutes at a rotation speed of 30 rpm and a revolution speed of 10 rpm, and then rotated at a rotation speed of 51 rpm and a revolution speed of 17 rpm. By kneading for 60 minutes, a solid kneaded product (a2-1) was obtained.

(Process [2])
Ion exchanged water heated to 60 ° C. was added to the kneaded product (a2-1) little by little, and the pigment concentration was adjusted to 16.3% by mass, and then the ions were further heated to 60 ° C. By supplying and mixing triethylene glycol diluted with exchange water, a composition having a pigment concentration of 14.9% by mass, a triethylene glycol concentration of 11.9% by mass and a non-volatile content of 20.2% by mass (a3 -1) was obtained. The viscosity at 25 ° C. of the composition (a3-1) was 3.5 mPa · s.

(Process [3])
The composition (a3-1) was heated to 60 ° C. with a heat exchanger (manufactured by T-L Buoy Co., Ltd., vacuum steam heating system), and then a cylindrical centrifuge (ASM260FH, rotor volume 7.7 L, Sakai Industrial Co., Ltd.) The water-based pigment dispersion (a4-1) was obtained by supplying the liquid to a company manufactured at a rate of 1.2 L / min and continuously performing centrifugal separation at a centrifugal acceleration of 20000 G. The ratio of the supply amount (volume) of the composition (a3-1) to the rotor volume [supply amount (volume) of the composition (a3-1) / rotor volume] × 100 was 3000%.

(Example 2)
The composition (a3-1) is aqueous in the same manner as in Example 1 except that the temperature at which the composition (a3-1) is heated with a heat exchanger (manufactured by T-L Buoy Co., Ltd., vacuum steam heating system) is changed from 60 ° C to 40 ° C. A pigment dispersion (a4-2) was obtained.

(Comparative Example 1)
The composition (a3-1) is aqueous in the same manner as in Example 1 except that the temperature at which the composition (a3-1) is heated with a heat exchanger (manufactured by TLV Corporation, vacuum steam heating system) is changed from 60 ° C to 25 ° C. A pigment dispersion (a4-1 ′) was obtained.

(Comparative Example 2)
The temperature at which the composition (a3-1) is heated by a heat exchange device (manufactured by TLV Corporation, vacuum steam heating system) is changed from 60 ° C. to 25 ° C., and a cylindrical centrifuge (ASM260FH, rotor volume) Using a centrifuge (H-600S, rotor volume 2.0 L, manufactured by Kokusan Co., Ltd.) having a truncated cone-shaped rotor instead of 7.7 L, manufactured by Sakai Kogyo Co., Ltd., 0.2 L / min An aqueous pigment dispersion (a4-2 ′) was obtained in the same manner as in Example 1 except that the centrifugal treatment was continuously performed at a centrifugal acceleration of 20000 G at a liquid speed.

(Example 3)
In a tank with a 50 L jacket of a planetary mixer (PLM-50 manufactured by Inoue Seisakusho Co., Ltd.), 4.0 parts by mass of pigment dispersion resin B and 10.0 parts by mass of C.I. I. Pigment Black 7 (manufactured by Mitsubishi Chemical Co., Ltd., # 960) was added in order, and the temperature of the jacketed tank was heated to 60 ° C., and then 10.9 parts by mass of triethylene glycol and 1.78 parts by mass of The composition (a1-3) was obtained by supplying 34 mass% potassium hydroxide aqueous solution in order.

(Process [1])
With the temperature of the jacketed tank kept at 60 ° C., the composition (a1-3) was stirred for 10 minutes at a rotation speed of 30 rpm and a revolution speed of 10 rpm, and then rotated at a rotation speed of 71 rpm and a revolution speed of 24 rpm. Kneading was started. 30 minutes after the start of kneading, 0.132 parts by mass of ion-exchanged water was supplied. Next, 0.132 parts by mass of ion-exchanged water was supplied 40 minutes after the start of the kneading. Next, 0.132 parts by mass of ion-exchanged water was supplied 50 minutes after the start of the kneading. Solid kneaded product (a2-3) was obtained by finishing kneading 60 minutes after the start of kneading.
(Process [2])
By adding ion-exchanged water heated to 60 ° C. and stirring to the kneaded product (a2-3), the pigment concentration is 12.9% by mass, the triethylene glycol concentration is 14.1% by mass, and the non-volatile content is 18.8 mass% composition (a3-3) was obtained. The viscosity at 25 ° C. of the composition (a3-3) was 6.5 mPa · s.
(Process [3])
A cylindrical centrifuge (ASM260FH, rotor volume 7.7 L, manufactured by Sakai Kogyo Co., Ltd.) was prepared by heating the composition (a3-3) heated to 60 ° C. with a heat exchange device (vacuum steam heating system manufactured by TLV Corporation). Was supplied at a liquid feed rate of 1.6 L / min, and was continuously centrifuged at a centrifugal acceleration of 20000 G to obtain an aqueous pigment dispersion (a4-3). The ratio of the supply amount (volume) of the composition (a3-3) to the volume of the rotor [the supply amount (volume) of the composition (a3-3) / the volume of the rotor] × 100 was 6900%.

Example 4
In a tank with a 50 L jacket of a planetary mixer (PLM-50 manufactured by Inoue Seisakusho Co., Ltd.), 4.0 parts by mass of pigment dispersion resin B and 10.0 parts by mass of C.I. I. Pigment Black 7 (manufactured by Mitsubishi Chemical Co., Ltd., # 960) was added in order, and the temperature of the jacketed tank was heated to 60 ° C., and then 10.9 parts by mass of triethylene glycol and 1.78 parts by mass of The composition (a1-3) was obtained by supplying 34 mass% potassium hydroxide aqueous solution in order.

(Process [1])
With the temperature of the jacketed tank kept at 60 ° C., the composition (a1-3) was stirred for 10 minutes at a rotation speed of 30 rpm and a revolution speed of 10 rpm, and then rotated at a rotation speed of 71 rpm and a revolution speed of 24 rpm. Kneading was started. 30 minutes after the start of kneading, 0.132 parts by mass of ion-exchanged water was supplied. Next, 0.132 parts by mass of ion-exchanged water was supplied 40 minutes after the start of the kneading. Next, 0.132 parts by mass of ion-exchanged water was supplied 50 minutes after the start of the kneading. Solid kneaded product (a2-3) was obtained by finishing kneading 60 minutes after the start of kneading.
(Process [2])
By adding and stirring ion-exchanged water heated to 60 ° C. to the kneaded product (a2-3), the pigment concentration is 15.2% by mass, the triethylene glycol concentration is 16.6% by mass, and the non-volatile content is A 22.2 mass% composition (a3-4) was obtained. The viscosity of the composition (a3-4) at 25 ° C. was 9.8 mPa · s.
(Process [3])
A cylindrical centrifuge (ASM260FH, rotor volume 7.7 L, manufactured by Sakai Kogyo Co., Ltd.) was prepared by heating the composition (a3-4) heated to 60 ° C. with a heat exchange device (vacuum steam heating system manufactured by TLV Corporation). Was supplied at a liquid feed rate of 1.6 L / min, and continuously centrifuged at a centrifugal acceleration of 20000 G to obtain an aqueous pigment dispersion (a4-4). The ratio of the supply amount (volume) of the composition (a3-4) to the rotor volume [supply amount (volume) of the composition (a3-4) / rotor volume] × 100 was 6900%.

(Example 5)
An aqueous pigment dispersion (a4-5) was obtained in the same manner as in Example 3 except that the centrifugal acceleration in the step [3] was changed from 20000 G to 9000 G.

(Example 6)
Ratio of the supply amount (volume) of the composition (a3-3) to the volume of the rotor in the step [3] [supply amount (volume) of the composition (a3-3) / rotor volume] × 100 An aqueous pigment dispersion (a4-6) was obtained in the same manner as in Example 3 except that the amount was changed from 6900% to 7900%.

(Comparative Example 3)
In a tank with a 50 L jacket of a planetary mixer (PLM-50 manufactured by Inoue Seisakusho Co., Ltd.), 4.0 parts by mass of pigment dispersion resin B and 10.0 parts by mass of C.I. I. Pigment Black 7 (manufactured by Mitsubishi Chemical Co., Ltd., # 960) was added in order, and the temperature of the jacketed tank was heated to 60 ° C., and then 13.5 parts by mass of triethylene glycol and 1.78 parts by mass of A composition (a1-3 ′) was obtained by sequentially supplying a 34 mass% potassium hydroxide aqueous solution.

(Process [1])
With the temperature of the jacketed tank kept at 60 ° C., the composition (a1-3 ′) was stirred for 10 minutes at a rotational speed of 30 rpm and a rotational speed of 10 rpm, and then rotated at a rotational speed of 71 rpm and a rotational speed of 24 rpm. The kneading was started. 30 minutes after the start of kneading, 0.132 parts by mass of ion-exchanged water was supplied. Next, 0.132 parts by mass of ion-exchanged water was supplied 40 minutes after the start of the kneading. Next, 0.132 parts by mass of ion-exchanged water was supplied 50 minutes after the start of the kneading. Solid kneaded material (a2-3 ′) was obtained by finishing kneading 60 minutes after the start of kneading.
(Process [2])
By adding and stirring ion-exchanged water heated to 60 ° C. to the kneaded product (a2-3 ′), the pigment concentration is 12.9% by mass, the triethylene glycol concentration is 17.4% by mass, the non-volatile content Obtained 18.8 mass% composition (a3-3 '). The viscosity of the composition (a3-3 ′) at 25 ° C. was 6.7 mPa · s.
(Process [3])
The composition (a3-3 ′) heated to 60 ° C. with a heat exchange device (vacuum steam heating system manufactured by T-L Buoy Co., Ltd.) was converted into a cylindrical centrifuge (ASM260FH, rotor volume 7.7 L, manufactured by Sakai Kogyo Co., Ltd.). ) At a liquid feeding speed of 1.6 L / min, and continuously subjected to centrifugal separation treatment at a centrifugal acceleration of 20000 G to obtain an aqueous pigment dispersion (a4-3 ′). The ratio of the supply amount (volume) of the composition (a3-3 ′) to the volume of the rotor [the supply amount (volume) of the composition (a3-3 ′) / the volume of the rotor] × 100 was 6900%. .

(Example 7)
In a tank with a 50 L jacket of a planetary mixer (PLM-50 manufactured by Inoue Seisakusho Co., Ltd.), 3.0 parts by mass of pigment dispersion resin C and 10.0 parts by mass of C.I. I. Pigment Yellow 74 (manufactured by Sanyo Pigment Co., Ltd., Fast Yellow 7413) was added in order, and the temperature of the jacketed tank was heated to 30 ° C. After that, 5.67 parts by mass of triethylene glycol and 1.62 parts by mass Were supplied in order to obtain a composition (a1-7).

(Process [1])
With the temperature of the jacketed tank kept at 30 ° C., the composition (a1-7) was stirred for 10 minutes at a rotation speed of 30 rpm and a revolution speed of 10 rpm, and then kneaded at a rotation speed of 36 rpm and a revolution speed of 12 rpm. Started. 30 minutes after the start of the kneading, 0.07 part by mass of triethylene glycol was supplied. Next, 0.07 parts by mass of triethylene glycol was supplied 40 minutes after the start of the kneading. Next, 0.07 parts by mass of triethylene glycol was supplied 50 minutes after the start of the kneading. Solid kneaded product (a2-7) was obtained by finishing kneading 60 minutes after the start of kneading.
(Process [2])
Ion exchanged water heated to 60 ° C. is added to the kneaded product (a2-7) and stirred to adjust the pigment concentration to 16.0% by mass, and then further heated to 60 ° C. A composition having a pigment concentration of 15.1% by mass, a triethylene glycol concentration of 11.8% by mass, and a non-volatile content of 20.4% by mass (a3-7) ) The viscosity of the composition (a3-7) at 25 ° C. was 4.5 mPa · s.
(Process [3])
A cylindrical centrifuge (ASM260FH, rotor volume 7.7 L, manufactured by Sakai Kogyo Co., Ltd.) was prepared by heating the composition (a3-7) heated to 60 ° C. with a heat exchange device (vacuum steam heating system manufactured by TLV Corporation). Was supplied at a liquid feed rate of 1.6 L / min, and continuously centrifuged at a centrifugal acceleration of 20000 G to obtain an aqueous pigment dispersion (a4-7). The ratio of the supply amount (volume) of the composition (a3-7) to the volume of the rotor [supply amount (volume) of composition (a3-7) / rotor volume] × 100 was 3000%.

(Example 8)
Ratio of the supply amount (volume) of the composition (a3-4) to the volume of the rotor in the step [3] [supply amount (volume) of the composition (a3-4) / rotor volume] × 100 An aqueous pigment dispersion (a4-8) was obtained in the same manner as in Example 7 except that the amount was changed from 3000% to 1200%.

(Method for producing water-based ink for inkjet printing)
By mixing each aqueous pigment dispersion obtained in Examples and Comparative Examples with ion-exchanged water, a diluted solution of an aqueous pigment dispersion having a pigment concentration of 6% by mass was obtained.
Next, 8.0 parts by mass of 2-pyrrolidinone, 8.0 parts by mass of triethylene glycol mono-n-butyl ether, 3.0 parts by mass of glycerin, 0.5 parts by mass of Surfynol 440 (manufactured by Air Products) ) By mixing and stirring a mixed solution containing 30.5 parts by mass of ion-exchanged water and 50 parts by mass of the diluted aqueous pigment dispersion, an aqueous ink for inkjet printing having a pigment concentration of 3% by mass is obtained. It was.

[Measurement method of volume average particle diameter]
A measurement sample was prepared by diluting the aqueous pigment dispersions obtained in Examples and Comparative Examples with ion exchange water at the following magnification. The volume average particle size of the measurement sample at 25 ° C. was measured using a particle size distribution measuring device (manufactured by Nikkiso Co., Ltd .: Microtrac model name Nanotrac-UPA150). At the time of the measurement, the setting conditions (“permeability”, “shape”, “solvent refractive index”, “density”) of the particle size distribution measuring apparatus were set as follows.

[Method for measuring the number of coarse particles]
A sample obtained by diluting the aqueous pigment dispersions obtained in Examples and Comparative Examples with ion-exchanged water was used as a measurement sample. The number of coarse particles having a diameter of 0.5 μm or more contained in the measurement sample was measured using a number counting type particle size distribution analyzer (manufactured by Particle Sizing Systems: Accusizer 780APS). The number of coarse particles contained in 1 mL of the aqueous pigment dispersions of Examples and Comparative Examples was calculated by multiplying the number of coarse particles measured by the above method by the dilution factor. The aqueous pigment dispersion was diluted so that the number of coarse particles having a particle diameter (diameter) of 0.5 μm or more passing through the detector per second was 1000 to 4000 particles / ml.

[Method for evaluating the presence or absence of coarse particles over time in an aqueous pigment dispersion (storage stability)]
The number of coarse particles contained in the aqueous pigment dispersion immediately after production was measured by the method described above.
Next, the aqueous pigment dispersion was sealed in a polypropylene container and allowed to stand at 60 ° C. for 4 weeks.
Next, the number of coarse particles contained in the aqueous pigment dispersion after standing was measured by the method described above.
Next, the change rate (%) of the number of coarse particles before and after the standing was expressed as [(number of coarse particles contained in the aqueous pigment dispersion after standing) / (coarse contained in the aqueous pigment dispersion immediately after production). Number of particles) × 100] and evaluated according to the following criteria.

○ The change rate is less than 10% Δ The change rate is 10% or more and less than 20% × The change rate is 20% or more

[Evaluation Method for Presence or Absence of Coarse Particles in Aqueous Ink for Inkjet Printing (Storage Stability)]
The number of coarse particles contained in the aqueous inkjet printing ink immediately after production was measured by the method described above.
Next, the water-based ink for inkjet printing was sealed in a polypropylene container and allowed to stand at 60 ° C. for 4 weeks.
Next, the number of coarse particles contained in the water-based ink for inkjet printing after standing was measured by the method described above.
Next, the change rate (%) of the number of coarse particles before and after the standing was expressed as [(number of coarse particles contained in the water-based inkjet printing ink after standing) / (included in the water-based ink for inkjet printing immediately after production). Number of coarse particles) × 100] and evaluated according to the following criteria.

○ The change rate is less than 10% Δ The change rate is 10% or more and less than 20% × The change rate is 20% or more

[Evaluation method for the presence or absence of sedimentation of pigments, etc. in water-based ink for inkjet printing over time (precipitation)]
The aqueous ink for inkjet printing obtained in Examples and Comparative Examples was placed in a 10 mL capacity glass vial, sealed, and allowed to stand at 25 ° C. for 2 weeks.
After the standing, when the glass vial was turned upside down, the adhesion of sediment such as the pigment to the wall surface of the glass vial was visually observed and evaluated according to the following criteria.

○ No deposits such as pigments were found on the wall of the glass vial.
Δ: A deposit such as pigment was observed on the wall of the glass vial.
X: Adherence of sediments such as pigments was remarkably observed on the wall of the glass vial.

[Initial ejection stability of water-based ink for inkjet printing]
The ejection stability of the aqueous ink for inkjet printing immediately after production was evaluated using a commercially available inkjet printer ENVY4500 (manufactured by HP). The ink-jet printing aqueous ink was filled into a black ink cartridge, and a nozzle check pattern was printed (first time). Next, in monochrome mode, solid printing was performed in a range of 340 cm ^{2 on} one A4 sheet with a print density setting of 100%. Next, the nozzle check test pattern was printed again (second time). The clogged state of the ink discharge nozzles was evaluated by comparing the first and second nozzle check test patterns.
◎ No print pattern chipping occurred in both the first and second nozzle check test patterns. ○ The number of print pattern chipping confirmed in the first nozzle check test pattern and the second one. The number of missing print patterns confirmed by the nozzle check test pattern was the same.
Δ The number of print pattern defects confirmed in the second nozzle check test pattern was 1 to 5 greater than the number of print pattern defects confirmed in the first nozzle check test pattern.
X The number of print pattern defects confirmed in the second nozzle check test pattern was 6 or more more than the number of print pattern defects confirmed in the first nozzle check test pattern.

[Aging stability of water-based ink for inkjet printing over time]
The black ink cartridge was filled with the water-based ink for ink jet printing immediately after production, and was allowed to stand at room temperature for 4 weeks.
Next, it evaluated using commercially available inkjet printer ENVY4500 (made by HP). The ink-jet printing aqueous ink was filled into a black ink cartridge, and a nozzle check pattern was printed (first time). Next, in monochrome mode, solid printing was performed in a range of 340 cm ^{2 on} one A4 sheet with a print density setting of 100%. Next, the nozzle check test pattern was printed again (second time). The clogged state of the ink discharge nozzles was evaluated by comparing the first and second nozzle check test patterns.
◎ No print pattern chipping occurred in both the first and second nozzle check test patterns. ○ The number of print pattern chipping confirmed in the first nozzle check test pattern and the second one. The number of missing print patterns confirmed by the nozzle check test pattern was the same.
Δ The number of print pattern defects confirmed in the second nozzle check test pattern was 1 to 5 greater than the number of print pattern defects confirmed in the first nozzle check test pattern.
X The number of print pattern defects confirmed in the second nozzle check test pattern was 6 or more more than the number of print pattern defects confirmed in the first nozzle check test pattern.

Claims (8)

Step [1] of producing a kneaded product (a2) by kneading a composition (a1) containing at least a pigment and a resin and having a nonvolatile content of 50% by mass or more, at least the kneaded product (a2) and an aqueous medium And a step [2] of producing a composition (a3) by mixing and a step [3] of centrifuging the composition (a3) within a range of 30 ° C to 70 ° C. A method for producing an aqueous pigment dispersion. The method for producing an aqueous pigment dispersion according to claim 1, wherein the step [3] is a step using a cylindrical centrifugal separator. The aqueous step according to claim 1, wherein the step [3] is a step of subjecting the composition (a3) having a viscosity at 25 ° C of 13 mPa · s or less to a centrifugal separation with a cylindrical centrifugal separator. A method for producing a pigment dispersion. The step [3] is performed by supplying the composition (a3) to a rotor included in the cylindrical centrifuge and maintaining the temperature of the composition (a3) within a range of 30 ° C to 70 ° C. The ratio of the supply amount (volume) of the composition (a3) to the rotor volume [the supply amount (volume) of the composition (a3) / the volume of the rotor] × 100 is 1000% to 8000%. The method for producing an aqueous pigment dispersion according to claim 2 or 3, wherein a centrifugal acceleration of the cylindrical centrifugal separator is in a range of 8000G to 20000G. The method for producing an aqueous pigment dispersion according to any one of claims 1 to 4, wherein the kneading apparatus used in the step [1] is a closed kneading apparatus. The method for producing an aqueous pigment dispersion according to claim 5, wherein the kneading apparatus is a planetary mixer. The said process [2] is a process of supplying the said aqueous medium with respect to the said kneaded material (a2), and adjusting a non volatile matter in the range of 10 mass%-30 mass%. A method for producing the aqueous pigment dispersion described in 1. The method for producing an aqueous pigment dispersion according to any one of claims 1 to 7, wherein the composition (a1) contains at least a pigment, a resin, a basic compound, and a water-soluble organic solvent.