JP2020015893A - Method for producing pigment kneaded product and aqueous pigment dispersion - Google Patents

Abstract

To provide a method for producing a pigment kneaded product which is usable in production of an aqueous pigment dispersion that has a very small volume average particle size of a dispersion and has less coarse particles, and is usable in production of ink that has such dispersion stability as to prevent occurrence of temporal coarse particles and prevent occurrence of temporal settlement of a pigment and the like and has excellent discharge stability.SOLUTION: A method for producing a pigment kneaded product includes a step [1] of supplying at least a pigment and a resin to a container provided on a kneading device, and a step [2] of kneading contents (a1) of the container until storage elastic modulus at an angular frequency of 1 rad/s determined by dynamic viscoelasticity measurement at 25°C becomes within a range of 200 kPa to 30,000 kPa.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a pigment kneaded product and an aqueous pigment dispersion that can be used, for example, for producing an ink.

  Ink jet printing is employed in various printed matter manufacturing situations. The ink jet printing method is a method of producing a printed matter by discharging ink from an ink discharge nozzle and landing on the surface of a recording medium such as paper or cloth. Therefore, the ink is required to have a discharge stability that does not easily cause clogging of the ink discharge nozzle over time and that does not change the discharge direction of the ink over time.

  The aqueous ink for inkjet printing is generally manufactured by supplying a binder resin, a water-soluble solvent, an aqueous medium, and the like, as needed, to an aqueous pigment dispersion in which a pigment is dispersed in an aqueous medium in advance. Therefore, in order to impart good ejection stability to the ink, it is possible to reduce the occurrence of coarse particles due to pigments, which can cause clogging of the ink ejection nozzles, and also to reduce the time-dependent occurrence of pigments and the like. It is important to use an aqueous pigment dispersion that can prevent settling.

  As the aqueous pigment dispersion capable of reducing the generation of the coarse particles and preventing sedimentation of the pigment or 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. BACKGROUND ART An aqueous pigment dispersion using a solid or semi-solid kneaded material kneaded by an apparatus is known (for example, see Patent Document 1).

  However, the finer and higher-density ink discharge nozzles that can be used to produce high-definition printed matter are clogged and have abnormal ink discharge directions due to the effects of extremely small coarse particles and sediment in the ink. Is likely to occur, and as a result, stripes or the like may occur on the printed matter.

  In particular, in general, a single-pass inkjet printing method using a line head causes a decrease in image quality due to clogging of ink discharge nozzles, etc., as compared with an inkjet printing method using a so-called multi-pass method (scan method). Sometimes it was easy.

  As described above, it is possible to effectively suppress the generation of coarse particles and sediment in the ink over time, which causes clogging of the finely divided ink ejection nozzles that can be used for production of high-definition printed matter, Although demanded by the industry, there are cases where the conventional technology does not reach the required performance one step further.

JP 2003-226832 A

  The problem to be solved by the present invention is that the volume average particle diameter of the dispersion is very small, and the dispersion can be used for producing an aqueous pigment dispersion having a small number of coarse particles. An object of the present invention is to provide a method for producing a pigment kneaded product which has dispersion stability capable of preventing the occurrence of sedimentation over time and which can be used for production of ink having excellent ejection stability.

  The inventor of the present invention provides a process [1] in which at least a pigment and a resin are supplied to a container provided in a kneading apparatus. The object has been solved by a method for producing a pigment kneaded product, comprising a step [2] of kneading until the storage elastic modulus at 200 g / s falls within the range of 200 kPa to 30,000 kPa.

  The aqueous pigment dispersion obtained by using the pigment kneaded product obtained by the production method of the present invention has a very small volume average particle diameter of the dispersion, few coarse particles, and prevents generation of coarse particles over time. And dispersion stability that can prevent sedimentation of pigments and the like over time. The aqueous pigment dispersion can be suitably used for producing an ink for ink jet printing having excellent ejection stability.

  In the method for producing a pigment kneaded product of the present invention, a step [1] of supplying at least a pigment and a resin to a container provided in a kneading device, and measuring the dynamic viscoelasticity at 25 ° C. Characterized in that it has a step [2] of kneading until the storage elastic modulus at an angular frequency of 1 rad / s determined by the above becomes within the range of 200 kPa to 30000 kPa.

  The step [1] is a step of supplying a pigment and a resin and, if necessary, other components to a container provided in the kneading apparatus. The contents (a1) containing at least the pigment and the resin are present in the container after the step [1].

The content (a1) preferably has a nonvolatile content of 50% by mass or more, more preferably 50% by mass to 90% by mass, and particularly preferably 50% by mass to 85% by mass.
Here, the non-volatile content refers to the mass ^{1 of} the component remaining after heating 1 g of the content (a1) at 175 ° C. for 4 hours under a reduced pressure of 3 hPa, and the content (a1) before heating. refers to the mass ^0, the value calculated on the basis of the equation [mass ¹ / mass ^0] × 100.

  By using the content (a1) having a nonvolatile content of 50% by mass or more, the viscosity of the content (a1) during kneading is maintained at a moderately high level, and the shear applied to the content (a1) from the kneading apparatus is reduced. By increasing the, the aggregation of the pigment aggregates, and the adsorption of the resin to the pigment can proceed efficiently in parallel, as a result, the volume average particle diameter of the dispersion is very small Excellent dispersion stability and discharge stability that can be used for the production of aqueous pigment dispersions with few coarse particles and can both suppress the generation of coarse particles over time and prevent sedimentation of pigments etc. over time. And a pigment kneaded product usable for the production of an ink having the following.

  The pigment contained in the content (a1) is not particularly limited, and a known organic pigment or inorganic pigment can be used. In particular, when obtaining a pigment kneaded material and an aqueous pigment dispersion that can be used in the production of an ink for inkjet printing, the pigment may be produced by a known method such as iron oxide, a contact method, a furnace method, and a thermal method. Inorganic pigments such as carbon black, titanium oxide, etc., azo pigments (including insoluble azo pigments such as monoazo pigments, disazo pigments, pyrazolone pigments and benzimidazolone pigments, beta naphthol pigments, naphthol AS pigments, condensed azo pigments, etc.), Polycyclic pigments (for example, quinacridone pigment, perylene pigment, perinone pigment, anthraquinone pigment, dioxazine pigment, thioindigo pigment, isoindolinone pigment, isoindoline pigment, quinophthalone pigment, diketopyrrolopyrrole pigment, etc.), phthalocyanine pigment, dye chelate (For example, base Dye chelates and acid dye chelates), nitro pigments, nitroso pigments, can be used organic pigments such as aniline black. The pigments can be used alone or in combination of two or more.

  As the pigment, carbon black # 2300, # 980, # 960, # 900, # 52, # 45L, # 45, # 40, # 33, MA100, MA8, MA7, etc. manufactured by Mitsubishi Chemical Corporation Color Black FW1, Color Black series, Printex series, Special Black series, NIPEX series, and the like, manufactured by Orion Engineered Carbons Co., Ltd., such as Regal series and Monarch series manufactured by Cabot Corporation 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, 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 , 213, 269, 282 and the like.

  Examples of the pigment include C.I. I. Pigment Blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 22, 60, 63, 66, and other cyan pigments 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, and 71 can be used.

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

  As the pigment, those in a dry powder state and those in a wet cake state can be used. As the pigment, a mixture or a solid solution containing two or more kinds can be used.

  As the pigment, it is preferable to use a pigment having a primary particle diameter of 1.0 μm or less, and more preferably to use a pigment having a primary particle diameter of 0.01 μm to 0.5 μm. By using a pigment having a primary particle diameter in the above range, sedimentation of the pigment over time can be more effectively suppressed. The primary particle diameter refers to a value of a number average particle diameter measured using a transmission electron microscope (TEM).

  The pigment is preferably used in a range of 30% by mass to 80% by mass, and more preferably in a range of 35% by mass to 75% by mass, based on the total amount of the content (a1). By keeping the viscosity of a1) moderately high and increasing the share of the contents (a1) from the kneading apparatus, the pulverization of the pigment aggregates and the adsorption of the resin to the pigment are efficiently performed in parallel. As a result, the volume average particle diameter of the dispersion is very small, and the dispersion can be used for producing an aqueous pigment dispersion having a small number of coarse particles. This is particularly preferable because a pigment kneaded material which can be used for producing an ink having excellent dispersion stability and ejection stability capable of simultaneously preventing the occurrence of sedimentation over time can be obtained.

  As the resin contained in the content (a1), for example, a pigment dispersion resin or a binder resin can be used. As the pigment dispersing resin, those conventionally known can be used, for example, a radical polymer can be used, and a radical polymer having an aromatic cyclic structure or a heterocyclic structure can be used. It can be used for the production of aqueous pigment dispersions with very small volume average particle diameter and few coarse particles, can prevent the generation of coarse particles over time, and prevent the sedimentation of pigments etc. over time. It is more preferable to obtain a pigment kneaded material which has a possible dispersion stability and can be used for producing an ink having excellent ejection stability.

  When a radical polymer having an anionic group is used as the resin such as the pigment dispersion resin, a resin in which a part or all of the anionic group is neutralized by a basic compound (neutralized product) is used. It can be used for the production of an aqueous pigment dispersion having a very small volume average particle diameter and a small number of coarse particles, can prevent the generation of coarse particles over time, and sedimentation of the pigment and the like over time. This is preferable for obtaining a pigment kneaded material which has dispersion stability capable of preventing the occurrence of ink and which can be used for producing an ink having excellent ejection stability.

  As the aromatic cyclic structure or heterocyclic structure, a ring introduced into the radical polymer by using a monomer having an aromatic cyclic structure or a monomer having a heterocyclic structure described below. Formula structure.

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 enhance the adsorptivity of the pigment dispersion resin to the pigment, and as a result, The volume average particle diameter is very small, and it can be used for the production of an aqueous pigment dispersion having a small number of coarse particles, the number of the coarse particles is small, the generation of the coarse particles over time can be prevented, and the sedimentation of the pigment or the like over time can be prevented. It is possible to efficiently obtain a pigment kneaded material which has dispersion stability capable of preventing generation and can be used for producing an ink having excellent ejection stability.

  As the resin such as the pigment dispersion resin, it is preferable to use a resin having an acid value of 60 to 300 mgKOH / g, more preferably 80 to 250 mgKOH / g, and more preferably 100 to 200 mgKOH / g. That is, the adsorbability of the resin such as the pigment dispersion resin to the pigment can be improved, and as a result, the volume average particle diameter of the dispersion is very small, the number of coarse particles is small, and the generation of coarse particles over time is suppressed. This is particularly preferable because a pigment kneaded product which can be used in the production of an ink having excellent dispersion stability and ejection stability capable of satisfying both the prevention of sedimentation of pigment and the like over time can be obtained. Specifically, the pigment-dispersed resin having an acid value in the above range is completely dissolved or partially dissolved in a water-soluble organic solvent when a water-soluble organic solvent and a basic compound described later are used in combination in the step [2]. It is easily dissolved or swelled by a water-soluble organic solvent, and as a result, a salt (neutralized product) with a basic compound described later is easily formed. Thereby, the hydrophilicity of the pigment to which the resin such as the pigment-dispersed resin is adsorbed is remarkably improved, and as a result, the volume average particle diameter of the dispersion is very small, and the pigment is used for producing an aqueous pigment dispersion having few coarse particles. It is possible to obtain a pigment kneaded product which can be used for producing an ink having more excellent dispersion stability and ejection stability.

  As the radical polymer that can be used as the pigment dispersion 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 dispersion resin, and when a heterocyclic structure is introduced. If so, 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, vinylpyridine monomers such as 2-vinylpyridine and 4-vinylpyridine can be used.

  When using a radical polymer having both an aromatic cyclic structure and a heterocyclic structure as the radical polymer, as the monomer, a monomer having an aromatic cyclic structure and a monomer having a heterocyclic structure The bodies 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 also as the monomer. , Styrene, α-methylstyrene, and tert-butylstyrene are more preferably used.

  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 preferably used in an amount of 40% by mass or more, more preferably 50% by mass or more and 95% by mass or less.

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

  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 anion group, it is easy to obtain, it is possible to use a monomer having a carboxy group, the volume average particle diameter of the dispersion is very small, the production of an aqueous pigment dispersion having a small number of coarse particles Production of ink with excellent dispersion stability and excellent discharge stability, capable of preventing generation of coarse particles over time, preventing precipitation of pigments and the like over time. It is preferable to obtain a pigment kneaded product that can be used for acrylic acid, and it is more preferable to use acrylic acid or methacrylic acid.

  The monomer having an anionic group is preferably used in a range of 5% by mass to 80% by mass with respect to the total amount of the monomers usable for producing the pigment dispersion resin, It is more preferably used in an amount of 60% by mass, and more preferably used in an amount of 5% by mass to 50% by mass in order to obtain a radical polymer having an acid value in the above-mentioned predetermined range.

  In addition, as the monomer that can be used in the production of the pigment-dispersed resin, other monomers can be used, if necessary, in addition to those described above.

  Examples of the other monomer include methyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, sec-butyl (meth) acrylate, and 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 ( (T) 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. May be used alone or in combination of two or more. The “(meth) acrylate” refers to acrylate or methacrylate. As the other monomer, such an acrylate or methacrylate may be used alone, or an acrylate and a methacrylate may be used in combination.

  The pigment-dispersed resin includes a polymer having a linear (linear) structure formed by radical polymerization of the monomer, a polymer having a branched (grafted) structure, and a polymer having a cross-linked 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 a 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) acrylate. ) Poly (meth) acrylates of polyhydric alcohols such as tri (meth) acrylate of alkylene oxide adduct of acrylate and glycerin; glycidyl (meth) acrylate, divinylbenzene and the like can be used.

  As the pigment dispersion resin used in the present invention, a polymer of the above-described 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 above-mentioned pigment-dispersed resins, among the above, styrene structural units such as styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid ester- (meth) acrylic acid polymer, and (meth) acrylic It is preferable to use a polymer having an acid structural unit, and among them, it is preferable to use a polymer having an acid value in the preferable range described above, since the volume average particle diameter of the dispersion is extremely small, and coarse particles are formed. It can be used for the production of a small amount of aqueous pigment dispersion, has a small number of coarse particles, can more effectively prevent the generation of coarse particles over time, and more effectively prevents the sedimentation of pigments and the like over time. It is preferable to obtain a pigment kneaded material which has preventable dispersion stability and can be used for producing an ink having excellent ejection stability.

  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, the volume average particle diameter of the dispersion is very small, and the aqueous pigment dispersion having a small number of coarse particles is used. Dispersion stability that can be used for production, has less coarse particles, can more effectively prevent the generation of coarse particles over time, and can more effectively prevent the sedimentation of pigments and the like over time. It is preferable because a pigment kneaded material which can be used for producing an ink having excellent properties and excellent ejection stability can be obtained.

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

  In the present invention, the radical polymerization rates (reaction rates) of the respective monomers during the radical polymerization are set to be substantially the same, and the usage ratio (preparation ratio) of each monomer is determined by each of the constituents of the radical polymer. It was assumed to be the same as the ratio of the structural units derived from the monomer.

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

  When producing the radical polymer, a known and commonly used polymerization initiator, chain transfer agent (polymerization degree regulator), surfactant and defoaming agent can be used as necessary.

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

When using the radical polymer obtained by the solution polymerization method as the pigment dispersion resin, the pigment dispersion resin is dried after removing a solvent contained in the radical polymer solution obtained by the solution polymerization method. And those that have been pulverized into fine particles can be used.
When the pigment-dispersed resin that is the finely divided radical polymer is used in combination with a water-soluble organic solvent and a basic compound described later in the step [2], the pigment-dispersed resin is completely or partially dissolved in the water-soluble organic solvent. Or, it is easily swelled by a water-soluble organic solvent, as a result, it is easily adsorbed on the pigment, the volume average particle diameter of the dispersion is very small, and it can be used for the production of an aqueous pigment dispersion having few coarse particles. It is possible to obtain a pigment kneaded product which has few particles and can be used for producing an ink having more excellent dispersion stability and ejection stability.
As the pigment-dispersed resin, those classified by a mesh sieve may be used, and those having a particle diameter of about 1 mm or less are preferably used.

As the resin such as the pigment dispersion resin, it is preferable to use a resin whose weight average molecular weight is in the range of 2,000 to 40,000, more preferably in the range of 5,000 to 30,000, and in the range of 5,000 to 25,000. It can be used in the production of an aqueous pigment dispersion having a very small volume average particle diameter of the dispersion and a small number of coarse particles, and has a small number of coarse particles, can prevent generation of coarse particles over time, and It is particularly preferable to obtain a pigment kneaded material which can be used for producing an ink having more excellent dispersion stability and ejection stability capable of preventing the occurrence of sedimentation over time such as the above.
The weight average molecular weight is a value measured by GPC (gel permeation chromatography), and is a value converted into the molecular weight of polystyrene used as a standard substance.

  As the content (a1), it is preferable to use one having a mass ratio of the resin such as the pigment dispersion resin to the pigment in the range of 5% by mass to 200% by mass, and preferably 10% by mass to 100% by mass. The use of a material having a range of the above allows the content (a1) to be kneaded with an appropriate viscosity in the step [2], and the resin such as the pigment dispersion resin is easily adsorbed to the pigment. By this, the volume average particle diameter of the dispersion is very small, and it can be used for the production of an aqueous pigment dispersion having a small number of coarse particles, suppressing the generation of coarse particles over time and preventing the sedimentation of pigment and the like over time. It is more preferable because a pigment kneaded material which can be used for producing an ink having excellent dispersion stability and ejection stability capable of satisfying both can be obtained.

  Further, as the content (a1), a material containing a basic compound, if necessary, in addition to the pigment and the resin such as the pigment-dispersed resin can be used.

  When the pigment dispersing resin has an anionic group, the basic compound neutralizes the anionic group. When the pigment-dispersed resin is neutralized by the basic compound, the affinity of the pigment to which the pigment-dispersed resin is adsorbed with the aqueous medium is increased in the step [3]. As a result, the volume average particle diameter of the dispersion is very small, the number of coarse particles is small, the dispersion state of the pigment particles in the aqueous pigment dispersion becomes more stable, and the generation of coarse particles over time is more effectively prevented. And the generation of sedimentation of the pigment or the like over time can be more effectively prevented.

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

  If the basic compound is a pigment-dispersed resin having an anionic group, the neutralization ratio of the pigment-dispersed resin is from 80% to 120%. In addition, the affinity of the pigment-dispersed resin for the aqueous medium is increased, and as a result, the dispersion stability of the pigment adsorbed by the dispersed resin in the aqueous medium is preferably 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

  In addition, as the content (a1), in addition to the pigment and the resin such as the pigment-dispersed resin, those containing a pigment derivative as necessary can be used.

  The pigment derivative may impart, to the aqueous pigment dispersion and the ink using the same, dispersion stability that prevents generation of coarse particles over time and prevention of sedimentation of the pigment and the like over time. it can.

  As the pigment derivative, those obtained by introducing a specific functional group described later into a pigment can be used. Examples of the pigment include phthalocyanine pigments, azo pigments, anthraquinone pigments, quinacridone pigments, and diketopyrrolopyrrole pigments. 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 the content (a1), in addition to those described above, those containing a water-soluble organic solvent, water, or the like can be used as necessary.

  In the step [2], the water-soluble organic solvent easily dissolves or swells a part or all of the resin such as the pigment-dispersed resin, and as a result, the resin such as the pigment-dispersed resin is easily adsorbed on the pigment. Thereby, the volume average particle diameter of the dispersion is very small, and it can be used for producing an aqueous pigment dispersion having a small number of coarse particles, and has a small number of coarse particles, and has more excellent dispersion stability and ejection stability. A pigment kneaded product that can be used for producing an ink can be obtained.

  Examples of the water-soluble organic solvent include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, and polypropylene glycol; butanediol, pentanediol, and hexane. Diols such as diols; glycol esters such as propylene glycol laurate; diethylene glycol ethers such as diethylene glycol monoethyl, diethylene glycol monobutyl, diethylene glycol monohexyl, and carbitol; propylene glycol ether, dipropylene glycol ether, and triethylene glycol ether. Glyco including cellosolve Ethers; alcohols such as methanol, ethanol, isopropyl alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, butyl alcohol, and pentyl alcohol; lactones such as sulfolane, ester, ketone, and γ-butyrolactone; Other various solvents known as water-soluble organic solvents, such as lactams such as N- (2-hydroxyethyl) pyrrolidone and 2-pyrrolidinone, glycerin and polyalkylene oxide adduct thereof, and the like can be mentioned. As the water-soluble organic solvent, those described above can be used alone or in combination of two or more.

  Among them, as the water-soluble organic solvent, it is preferable to use polyhydric alcohols having a high boiling point and low volatility which function as a wetting agent, and derivatives of glycerin, and particularly glycols such as diethylene glycol and triethylene glycol. And polyalkylene oxide adducts of glycerin such as 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 more preferably in a range of 15% by mass to 150% by mass based on the mass of the pigment. That is, the volume average particle diameter of the dispersion is very small, and it can be used for the production of an aqueous pigment dispersion having a small number of coarse particles, the number of coarse particles is small, the generation of coarse particles over time can be prevented, and more excellent. It is more preferable to obtain a pigment kneaded material that can be used for producing an ink having dispersion stability and ejection stability.

  As the water that can be used in the step [1], pure water such as ion-exchanged water, ultrafiltration water, reverse osmosis water, and distilled water, or ultrapure water can be used. Further, as the water, it is preferable to use water sterilized by ultraviolet irradiation or addition of hydrogen peroxide, etc., in order to prevent the generation of mold or bacteria when the aqueous pigment dispersion or the ink using the same is stored for a long time. This is preferable because it can be performed.

  In the step [1], for example, the resin, the pigment, and, if necessary, the water-soluble solvent, water, a basic compound, and the like can be supplied to a container provided in the kneading apparatus in an arbitrary order. Examples of a method of supplying the resin or the like to the container include a method of supplying the resin at once, a method of supplying the resin separately, and the like.

  Next, the step [2] constituting the present invention will be described.

  In the step [2], the content (a1) present in the container of the kneading apparatus after the step [1] is kneaded by the kneading apparatus, and the content (a1) is heated at a temperature of 25 ° C. Is a step in which kneading is continued until the storage elastic modulus at an angular frequency of 1 rad / s determined by the dynamic viscoelasticity measurement falls within the range of 200 kPa to 30,000 kPa. Thereby, the volume average particle diameter of the dispersion is very small, and it can be used for the production of an aqueous pigment dispersion having a small number of coarse particles. It is possible to obtain a pigment-kneaded product which can be used for producing an ink having excellent dispersion stability and ejection stability, which can simultaneously prevent the occurrence of sedimentation.

Here, when the kneading is finished even though the storage elastic modulus is out of the above range, a sufficient shearing force cannot be given to the content (a1), and as a result, the volume average of the dispersion It can be used for the production of aqueous pigment dispersions with very small particle size and few coarse particles.Small coarse particles are small.Suppression of generation of coarse particles over time and prevention of sedimentation of pigment etc. over time are both achieved. In some cases, it is not possible to obtain a pigment kneaded product that can be used for producing an ink having possible excellent dispersion stability and ejection stability.
The kneading may be ended immediately when the content (a1) reaches the storage elastic modulus in the above-mentioned range, or may be continued for a certain period of time while maintaining the storage elastic modulus in the above-mentioned range. . The end of the kneading can be appropriately adjusted according to the kind of the pigment to be used, and it is preferable that the kneading be ended when the storage elastic modulus is reached.
Generally, it is preferable that the kneading be completed within 5 hours after the content (a1) reaches the storage elastic modulus in the above range.
The storage elastic modulus of the content (a1) can be confirmed by collecting the content (a1) during kneading in the step [2] and measuring the storage elastic modulus by a predetermined method.

  In the kneading in the step [2], the storage elastic modulus of the content (a1) at an angular frequency of 1 rad / s determined by dynamic viscoelasticity measurement at a temperature of 25 ° C. is within a range of 200 kPa to 30000 kPa. Can be used to produce an aqueous pigment dispersion having a very small volume average particle diameter of the dispersion and a small number of coarse particles, and the generation of coarse particles with a small number of coarse particles, suppression of coarse particles over time, This is preferable for obtaining a pigment kneaded material which can be used for producing an ink having excellent dispersion stability and ejection stability capable of simultaneously preventing sedimentation from occurring over time.

  The storage elastic modulus was determined by dynamic viscoelasticity measurement at a temperature of 25 ° C. in accordance with “JIS K 7244-10: 2005 Complex shear viscosity using a parallel plate vibrating rheometer”. Indicates the storage modulus at an angular frequency of 1 rad / s in the plot of the storage modulus.

  In the step [2], as a kneading apparatus used for kneading the content (a1), for example, a Henschel mixer, a pressure kneader, a Banbury mixer, a trimix, a planetary mixer, or the like can be used.

As the kneading apparatus, for example, when a solvent such as the water-soluble organic solvent or water is used in the step [1], it is preferable to use a kneading apparatus capable of closing the inside of a container provided in the kneading apparatus. The closing means, for example, that a space formed by a container and a lid provided in the kneading device can be closed, and the use of such a closed kneading device is not limited to a solvent such as the water-soluble organic solvent or water. Is preferable in that the content of is not significantly changed in the step [2].
The “significant change” refers to a state in which the ratio of the mass of the pigment kneaded product obtained after the step [2] to the mass of the content (a1) is less than 90% by mass.

As the kneading device, for example, a kneading device having a container that is a stirring tank and a uniaxial or multiaxial stirring blade can be used, and a closed kneading device having a lid portion of the container can be used. Is preferred.
As the closed kneading apparatus, it is preferable to use an apparatus having two or more stirring blades in order to obtain a high kneading action.
As the closed-type kneading apparatus, a planetary mixer is particularly preferably used, which can give a strong shearing force when the content (a1) preferably has a nonvolatile content of 50% by mass or more. It is preferable because it is possible to increase the easiness of pulverization of the pigment aggregates and adsorption of the resin such as the pigment dispersion resin to the pigment.
Further, the planetary mixer can easily pulverize the aggregates of the pigment and adsorb the resin such as the pigment-dispersed resin to the pigment even if the content (a1) has a wide viscosity. This is preferable because the height can be increased.
When the planetary mixer is used, after the step [2] is completed, an aqueous medium described below may be continuously supplied into a container of the planetary mixer to produce an aqueous pigment dispersion. Therefore, it is preferable in improving the production efficiency of the aqueous pigment dispersion and the ink.

It is preferable that the temperature of the content (a1) at the time of kneading the content (a1) be appropriately adjusted in consideration of temperature characteristics such as a glass transition point of the pigment-dispersed resin. Specifically, the upper limit of the temperature of the content (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 content (a1) at the time of the kneading is preferably a temperature 60 ° C. lower than the glass transition temperature of the pigment-dispersed resin. By kneading the content (a1) within the above temperature range, it is possible to give a sufficient shearing force to the composition (a1), and as a result, pulverization of the aggregate of the pigment, This is preferable because the ease with which the dispersed resin is adsorbed to the pigment can be increased.
Further, the temperature of the content (a1) may have a different effect on a pigment kneaded material or the like depending on the type of the pigment. For example, C.I. I. When Pigment Yellow 74 is used, if the temperature exceeds 80 ° C., the volume average particle diameter of the dispersion immediately after the production of the obtained aqueous pigment dispersion tends to be slightly large. It is preferable to adjust the temperature by supplying a solvent such as a volatile organic solvent. On the other hand, C.I. I. When Pigment Black 7 is used, if the temperature exceeds 120 ° C., the viscosity of the content (a1) tends to decrease, and the shearing force applied to the content (a1) may decrease. The temperature is preferably adjusted by supplying water or a solvent such as the water-soluble organic solvent as described above.
Specifically, the temperature of the content (a1) at the time of kneading the content (a1) is maintained in a range of 60 ° C. to 120 ° C. It is more preferable because sufficient shearing force can be applied, and as a result, it is possible to increase the easiness of pulverization of the aggregate of the pigment and adsorption of the resin such as the pigment dispersion resin to the pigment.

  In addition, during the kneading, the viscosity of the content (a1) may significantly decrease due to a rise in temperature. If the viscosity of the content (a1) decreases, it may not be possible to apply a sufficient shearing force to the content (a1). The content (a1) may be intentionally cooled by addition.

  If necessary, a solvent such as water or a water-soluble organic solvent may be supplied to the content (a1) so that the temperature of the content (a1) does not fall outside the above range during the step [2]. The kneading apparatus and the content (a1) may be cooled using ice, liquid nitrogen, or the like.

The glass transition temperature (Tg) of the pigment-dispersed 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-dispersed resin. Point.
1 / Tg = W1 / Tg1 + W2 / Tg2 + W3 / Tg3... + Wn / Tgn
(Where Tgn is the glass transition temperature (absolute temperature: K) of the homopolymer of each monomer used in the production of the pigment-dispersed resin, and Wn is the mass fraction of the monomer)

  The pigment kneaded material obtained by the above-described production method of the present invention has a semi-solid or solid shape at room temperature, and can be easily dispersed in an aqueous medium described below.

Next, a method for producing an aqueous pigment dispersion using the pigment kneaded material obtained by the above method will be described.
The aqueous pigment dispersion can be produced, for example, by going through the step [3] of mixing the kneaded pigment obtained by the above method, the aqueous medium, and other components as necessary.

  In the step [3], the aqueous medium or the like may be supplied to and mixed with the pigment kneaded material, or the pigment kneaded material may be supplied and mixed with the aqueous medium or the like.

In the case where a closed kneading device such as a planetary mixer is used in the step [2], the aqueous medium or the like is supplied and mixed into the container of the kneading device containing the pigment kneaded product, and the aqueous pigment is mixed. It is preferable for improving the production efficiency of the dispersion. In this case, the kneading apparatus is operated (that is, the kneading in the step [2] is continued even after the storage elastic modulus of the content (a1) reaches a range of 200 kPa to 30000 kPa). It is preferable to supply the aqueous medium in the step [3] in order to improve the dispersion efficiency of the kneaded pigment in the aqueous medium and the production efficiency of the aqueous pigment dispersion. As the aqueous medium, it is preferable to use water at 25C to 65C in order to suppress a significant decrease in the temperature of the pigment kneaded material.
Examples of a method of supplying the aqueous medium to the pigment kneaded material include a method of supplying the aqueous medium collectively, a method of supplying the medium continuously or intermittently, and the like. As a method of supplying the aqueous medium, it is possible to employ a method of continuously or intermittently supplying, efficiently dispersing the pigment kneaded material in the aqueous medium, and to manufacture the aqueous pigment dispersion. This is preferable because the time required can be reduced.

  As the aqueous medium that can be used in the step [3], 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 the water-soluble organic solvent, one or a combination of two or more of the same ones exemplified as usable in the step [2] can be used.

The aqueous pigment dispersion obtained by performing the steps [1], [2] and [3] is a dispersion in which the pigment to which a resin such as the pigment dispersion resin is adsorbed is dispersed in an aqueous medium. The liquid average particle size is very small, the number of coarse particles is small, the generation of coarse particles over time can be prevented, and the dispersion of pigments and the like with the dispersion stability capable of preventing the sedimentation over time can be prevented. Things.
The aqueous pigment dispersion preferably has a nonvolatile content of 10% by mass to 30% by mass, more preferably 12% by mass to 25% by mass, based on the total amount of the aqueous pigment dispersion.

  In the present invention, for the purpose of further suppressing the generation of coarse particles over time of the aqueous pigment dispersion or the generation of sedimentation of the pigment or the like over time, before the step [4] described below, if necessary, Alternatively, the dispersion processing may be performed using a dispersion apparatus. As the dispersing device, for example, as a device using a medium, a paint shaker, a ball mill, an attritor, a basket mill, a sand mill, a sand grinder, a dyno mill, a dispermat, an SC mill, a spike mill, an agitator mill, or the like may be used. Ultrasonic homogenizers, nanomizers, dissolvers, dispersers, high-speed impeller dispersers, high-pressure homogenizers, and the like can be used without using a medium.

In addition, when the aqueous pigment dispersion contains impurities such as polyvalent metal ions, in the present invention, the aqueous pigment dispersion obtained in the step [3] is added to the aqueous pigment dispersion before a step [4] described below. It is preferable to perform a treatment for removing impurities using a chelate resin or the like as necessary.
As an inkjet printing method, a piezo method and a thermal method are known. In particular, in the thermal method, an agglutination of a resin such as a pigment-dispersed resin and a polyvalent metal ion or the polyvalent metal on the surface of the heating resistor element inside the nozzle due to a rapid temperature rise inside the nozzle when ejecting ink. A phenomenon called kogation in which aggregates such as polyvalent metal salts derived from ions are deposited may occur. Since the agglomerates cause ejection failure of the ink, it is strongly desired that the ink for inkjet recording reduce polyvalent metal ions.

  Examples of the method for reducing the polyvalent metal ion include a method in which particles or a fibrous resin having a chelating group are brought into contact with an aqueous pigment ink or an aqueous pigment dispersion to remove the polyvalent metal.

In the present invention, it is preferable that the aqueous pigment dispersion obtained through at least the steps [1], [2] and [3] is subjected to centrifugation at a temperature in the range of 30 ° C to 70 ° C. .
In the aqueous pigment dispersion, an undissolved substance of the pigment such as the unground material of the pigment or the pigment-dispersed resin, or a component that may cause the coarse particles and the like of the pigment not sufficiently adsorbed by the pigment-dispersed resin. May remain very slightly.

Micronized, high-density ink discharge nozzles that can be used to produce high-definition prints are susceptible to clogging and abnormal ink discharge due to the effects of very small coarse particles and sediment in the ink. As a result, stripes and the like are sometimes generated on printed matter. In particular, in general, a single-pass inkjet printing method using a line head causes a decrease in image quality due to clogging of ink discharge nozzles, etc., as compared with an inkjet printing method using a so-called multi-pass method (scan method). Sometimes it was easy.
In the present invention, after the aqueous pigment dispersion is manufactured, a centrifugal separation process [4] is performed under predetermined conditions to cause clogging or the like of the finely-densified and high-density ink discharge nozzles. Aqueous pigment dispersions can be made that can be used in the production of non-inks.
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 meter (Accusizer 780 APS) manufactured by Particle Sizing Systems, Inc. Point.
In the step [4], it is not always necessary to simply perform the centrifugation, but it is preferable to perform the centrifugation in the range of 30 to 70 ° C, and the centrifugation in the range of 40 to 65 ° C. It is more preferable to efficiently and practically sufficiently remove coarse particles. In addition, the said temperature points out the temperature of the said aqueous pigment dispersion centrifuged.

Before the aqueous pigment dispersion is supplied to the centrifugal separator, for example, the temperature may be adjusted to 30 ° C. to 70 ° C. using a heat exchange device or the like, and the centrifugal separator has a temperature setting function. When used, the temperature may be adjusted to the above-mentioned temperature range after being supplied to the centrifugal separator.
By lowering the viscosity of the heated aqueous pigment dispersion, centrifugal separation efficiency is improved, and coarse particles can be efficiently removed. Further, by controlling the aqueous pigment dispersion within the above-mentioned temperature range, the aqueous pigment dispersion is less susceptible to the influence of the outside air temperature, and an aqueous pigment dispersion having few coarse particles can be stably produced.

As the aqueous pigment dispersion to be subjected to the centrifugal separation, it is preferable to use a dispersion having a viscosity of 13 mPa · s or less at 25 ° C. It is preferable because it can be sufficiently removed.
In particular, when a cylindrical centrifugal separator described below is used as the centrifugal separator, the aqueous pigment dispersion preferably has a viscosity at 25 ° C. of 10.5 mPa · s or less, preferably 2 mPa · s to 2 mPa · s. A value of 10.5 mPa · s is more preferable because coarse particles can be more efficiently and practically sufficiently removed from the aqueous pigment dispersion.

As the centrifugal separator, the use of a cylindrical centrifugal separator with a rotor shape is effective in reducing the centrifugal separation efficiency caused by the clay-like sludge containing the coarse particles deposited in the rotor. It is preferable because it can be suppressed.
As described above, the aqueous pigment dispersion obtained through the step [1], the step [2], and the step [3] is, as described above, coarse particles of the pigment, an unground material of the pigment, or the pigment dispersion resin. Coarse particles of various sizes, such as undissolved resin, are likely to be included. By performing the step [4] using the cylindrical centrifugal separator, the coarse particles can be efficiently and continuously removed without impairing productivity.

  In addition, the step [4] is performed in a state where the aqueous pigment dispersion is supplied to a rotor provided in the cylindrical centrifuge and the temperature of the aqueous pigment dispersion is maintained in a range of 30 ° C to 70 ° C. The step is preferable because a suitable centrifugation efficiency can be stably maintained for a long time, and coarse particles can be more efficiently and sufficiently removed from the aqueous pigment dispersion. At this time, the ratio of the supply amount (volume) of the aqueous pigment dispersion to the rotor volume [the supply amount (volume) of the aqueous pigment dispersion / volume of the rotor] × 100 may be 1000% to 8000%. In addition, while it is possible to suppress removal of components such as pigments that are not coarse particles, it is possible to more efficiently remove coarse particles from the aqueous pigment dispersion, which is preferable.

  The centrifugal acceleration of the centrifugal separator is in the range of 8000 G to 20,000 G, which can prevent the pigment dispersion resin from being peeled off from the pigment, and efficiently remove coarse particles from the aqueous pigment dispersion. It is preferable because it is possible.

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

Relative centrifugal acceleration (G) = r × (2πN / 60) ² / g
(Where N is the number of revolutions per minute (rpm), r is the radius of rotation (m), g is the gravitational acceleration (9.8 m / s ² ), and π is the pi)

  As described above, the aqueous pigment dispersion obtained by the production method of the present invention has a very small volume average particle diameter of the dispersion, few coarse particles, can prevent the generation of coarse particles over time, and This is an aqueous pigment dispersion having dispersion stability capable of preventing the occurrence of sedimentation with the passage of time and the like, and which can be used for producing an ink having excellent ejection stability.

The aqueous pigment dispersion can be used as an ink by diluting it to a desired concentration.
Examples of the ink include paints for automobiles and building materials, printing inks such as offset inks, gravure inks, flexo inks, silk screen inks, and inks for inkjet 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 based on the total amount of the ink.
The ink is an aqueous pigment dispersion of the present invention, a solvent such as a water-soluble organic solvent or water, if necessary, a resin such as an acrylic resin or a polyurethane resin as a binder, a drying inhibitor, a penetrant, and an interface. It can be manufactured by mixing additives such as an activator, a preservative, a viscosity adjuster, a pH adjuster, a chelating agent, a plasticizer, an antioxidant, and an ultraviolet absorber. The ink may be subjected to a centrifugation treatment or a filtration treatment after being manufactured by the above method.
The water-soluble organic solvent can be used for preventing drying of the ink and adjusting the viscosity and concentration of the ink to a suitable range.

  As the water-soluble organic solvent, those similar to those exemplified as usable in the step [1] of the aqueous pigment dispersion can be used. Among them, water-soluble organic solvents include, for example, lower alcohols such as ethanol and isopropyl alcohol; and ethylene oxide adducts of alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether in order to enhance the permeability of the ink into the recording medium; Examples thereof include propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether.

Examples of the drying inhibitor 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, and 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.
The same compound as the water-soluble organic solvent used in the aqueous pigment dispersion can be used as the anti-drying agent. 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 the recording medium and adjusting the dot diameter on the recording medium.
Examples of the penetrant include lower alcohols such as ethanol and isopropyl alcohol; and 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 properties such as surface tension. The surfactant is not particularly limited, and includes various anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, and the like. Surfactants and nonionic surfactants are preferred.

  Examples of the anionic surfactant include alkyl benzene sulfonate, alkyl phenyl sulfonate, alkyl naphthalene sulfonate, higher fatty acid salt, higher fatty acid ester sulfate, higher fatty acid ester sulfonate, higher alcohol ether Sulfate and sulfonate, higher alkyl sulfosuccinate, polyoxyethylene alkyl ether carboxylate, polyoxyethylene alkyl ether sulfate, alkyl phosphate, polyoxyethylene alkyl ether phosphate, and the like, Specific examples thereof include dodecylbenzenesulfonate, isopropylnaphthalenesulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenylsulfonate, dibutylphenylphenol disulfoate. It can be mentioned acid salts.

  Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, and 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 carboxylate, perfluoroalkyl sulfonate and oxyethylene perfluoroalkyl ether Biosurfactants such as spiculisporic acid, rhamnolipid, lysolecithin and the like can also be used.
The surfactants may be used alone or in combination of two or more.

  The ink obtained by the above method can be suitably used as an ink for inkjet printing. In general, the inkjet printing method is a single-pass inkjet printing using a line head, which tends to cause a decrease in image quality due to clogging of ink discharge nozzles, as compared with a multi-pass (scanning) inkjet printing method. Select the method, the printing method and the method for manufacturing a printed material used in combination with the ink of the present invention are less likely to cause a decrease in image quality due to clogging of the ink discharge nozzles, etc. It is preferable to obtain.

  Hereinafter, the present invention will be described specifically with reference to examples.

(Pigment dispersion resin)
As the 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, calculated glass transition temperature (Tg) ) 116 ° C) was used.
As the pigment dispersing resin B, a 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, calculated glass transition temperature (Tg) calculated from the following equation) 113 ° C.).
As the pigment dispersing resin C, a polymer of 74 parts by mass of styrene, 11 parts by mass of acrylic acid, and 15 parts by mass of methacrylic acid (weight average molecular weight 11,000, acid value 173 mgKOH / g, calculated glass transition temperature (Tg) calculated from the following equation) 115 ° C.).
As the pigment dispersion resin D, a 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 11,000, acid value 154 mgKOH / g, calculated glass transition temperature (Tg) calculated from the following formula) 113 ° C.).

The glass transition temperature (Tg) of the pigment-dispersed 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-dispersed resin. Point.
1 / Tg = W1 / Tg1 + W2 / Tg2 + W3 / Tg3... + Wn / Tgn
(Where Tgn is the glass transition temperature (absolute temperature: K) of the homopolymer of each monomer used in the production of the pigment-dispersed resin, and Wn is the mass fraction of the monomer)
As the glass transition temperature (Tg) of the homopolymer of each monomer used in the production of the pigment dispersion resin, a value recorded in POLYMER HANDBOOK THIRD EDITION (A WILY-INTERSCIENCE PUBLICATION) was used. It was calculated by the equation. The values of styrene homopolymer (Tg: 100 ° C.), methacrylic acid homopolymer (Tg: 228 ° C.), and acrylic acid homopolymer (Tg: 106 ° C.) were used.

The weight average molecular weight of the pigment dispersion resins A to D is a value measured by GPC (gel permeation chromatography), and is a value converted into a polystyrene molecular weight. The measurement conditions are as follows.
Liquid 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 determined according to Japanese Industrial Standards “K0070: 1992. Test method for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponifiable substance, except that tetrahydrofuran is used instead of diethyl ether as a solvent. And the amount (mg) of potassium hydroxide required to completely neutralize 1 g of the pigment dispersion resin.

(Example 1)
(Step [1])
In a 50 L jacketed tank of a planetary mixer (PLM-50 manufactured by Inoue Seisakusho Co., Ltd.), 3.0 parts by mass of the pigment dispersion resin A and 10.0 parts by mass of C.I. I. Pigment Blue 15: 3 and FASTOGEN BLUE TGR-SD (manufactured by DIC Corporation) were sequentially charged, and the temperature of the tank with jacket was heated to 60 ° C., and then 3.80 parts by mass of triethylene glycol (Japan Co., Ltd.) (Made of catalyst) and 1.59 parts by mass of a 34% by mass aqueous solution of potassium hydroxide were sequentially supplied to obtain a content (a1-1).

(Step [2])
In a state where the temperature of the jacketed tank was kept at 60 ° C., the content (a1-1) was stirred at a rotation speed of 30 rpm and a revolution speed of 10 rpm for 10 minutes, and then at a rotation speed of 51 rpm and a revolution speed of 17 rpm. The mixture was kneaded for 60 minutes, and after confirming that the storage elastic modulus of the content reached the value (8000 kPa) shown in Table 3, the kneading was immediately terminated to thereby obtain a solid pigment kneaded product (a2-1). ) Got.

(Step [3])
To the pigment kneaded product (a2-1), ion-exchanged water heated to 60 ° C. was added little by little and stirred to adjust the pigment concentration to 16.3% by mass, and then further heated to 60 ° C. By supplying and mixing triethylene glycol diluted with ion-exchanged water, an aqueous pigment dispersion having a pigment concentration of 14.9% by mass, a triethylene glycol concentration of 11.9% by mass, and a nonvolatile content of 20.2% by mass is dispersed. A body (a3-1) was obtained.

(Step [4])
The aqueous pigment dispersion (a3-1) heated to 60 ° C. with a heat exchange device (vacuum steam heating system manufactured by TLV Co., Ltd.) was converted into a cylindrical centrifuge (ultracentrifuge ASM260FH, rotor volume 7.7 L, An aqueous pigment dispersion (a4-1) was obtained by supplying the solution at a rate of 1.2 L / min and continuously performing centrifugal separation at a centrifugal acceleration of 20,000 G.

(Comparative Example 1)
(Step [1])
In a 50 L jacketed tank of a planetary mixer (PLM-50 manufactured by Inoue Seisakusho Co., Ltd.), 3.0 parts by mass of the pigment dispersion resin A and 10.0 parts by mass of C.I. I. Pigment Blue 15: 3, FASTOGEN BLUE TGR-SD (manufactured by DIC Corporation) was sequentially charged, and the temperature of the jacketed tank was heated to 60 ° C., followed by 5.33 parts by mass of triethylene glycol (Japan Co., Ltd.). The product (a1-1 ′) was obtained by sequentially supplying 1.59 parts by mass of a 34% by mass aqueous solution of potassium hydroxide.

(Step [2])
The content (a1-1 ′) was stirred at a rotation speed of 30 rpm and a revolution speed of 10 rpm for 10 minutes while keeping the temperature of the jacketed tank at 60 ° C., and then the rotation speed was 51 rpm and the revolution speed was 17 rpm. After kneading for 60 minutes and confirming that the storage elastic modulus of the content has reached the value shown in Table 3, the kneading is immediately terminated, whereby the solid pigment kneaded product (a2-1 ′) is obtained. I got

(Step [3])
To the pigment kneaded product (a2-1 ′), ion-exchanged water heated to 60 ° C. was added little by little and stirred to adjust the pigment concentration to 15.9% by mass, and then further heated to 60 ° C. An aqueous pigment 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 is supplied by mixing and mixing triethylene glycol diluted with ion-exchanged water. A dispersion (a3-1 ′) was obtained.

(Step [4])
Aqueous pigment dispersion (a3-1 ′) cylindrical centrifuge (Ultra-centrifuge ASM260FH, rotor volume 7.7 L, volume 7.7 L) heated to 60 ° C. with a heat exchange device (vacuum steam heating system manufactured by TLB) An aqueous pigment dispersion (a4-1 ′) was obtained by supplying at a liquid feed rate of 1.2 L / min and continuously performing centrifugal separation at a centrifugal acceleration of 20,000 G.

(Example 2)
(Step [1])
In a 50 L jacketed tank of a planetary mixer (PLM-50 manufactured by Inoue Seisakusho Co., Ltd.), 4.0 parts by mass of the pigment dispersion resin B and 10.0 parts by mass of C.I. I. Pigment Black 7 was sequentially charged with # 960 (manufactured by Mitsubishi Chemical Corporation), the temperature of the jacketed tank was heated to 60 ° C., and 10.9 parts by mass of triethylene glycol (manufactured by Nippon Shokubai Co., Ltd.) was added. The contents (a1-2) were obtained by sequentially supplying 1.78 parts by mass of a 34% by mass aqueous solution of potassium hydroxide.

(Step [2])
In a state where the temperature of the jacketed tank was maintained at 60 ° C., the content (a1-2) was stirred at a rotation speed of 30 rpm and a revolution speed of 10 rpm for 10 minutes, and then stirred at a rotation speed of 71 rpm and a revolution speed of 24 rpm. Kneading was started. 30 minutes after the start of the kneading, 0.132 parts by mass of ion-exchanged water was supplied. Next, 40 minutes after the start of the kneading, 0.132 parts by mass of ion-exchanged water was supplied. Next, 50 minutes after the start of the kneading, 0.132 parts by mass of ion-exchanged water was supplied. After 60 minutes from the start of the kneading (that is, after confirming that the storage elastic modulus of the content has reached the value shown in Table 3), the kneading is immediately terminated to remove the solid kneaded material (a2-2). Obtained.
(Step [3])
To the kneaded product (a2-2), ion-exchanged water heated to 60 ° C. was added and stirred, so that the pigment concentration was 12.9% by mass, the triethylene glycol concentration was 14.1% by mass, and the nonvolatile content was An aqueous pigment dispersion (a3-2) of 18.8% by mass was obtained.
(Step [4])
The aqueous pigment dispersion (a3-2) heated to 60 ° C. with a heat exchange device (vacuum steam heating system manufactured by T-LV Co., Ltd.) was converted into a cylindrical centrifuge (ultracentrifuge ASM260FH, rotor volume 7.7 L, The solution was supplied at 1.6 L / min to the solution, and centrifuged continuously at a centrifugal acceleration of 20000 G to obtain an aqueous pigment dispersion (a4-2).

(Comparative Example 2)
(Step [1])
In a 50 L jacketed tank of a planetary mixer (PLM-50 manufactured by Inoue Seisakusho Co., Ltd.), 4.0 parts by mass of the pigment dispersion resin B and 10.0 parts by mass of C.I. I. Pigment Black 7 was sequentially charged with # 960 (manufactured by Mitsubishi Chemical Corporation), and the temperature of the jacketed tank was heated to 60 ° C., followed by 15.5 parts by mass of triethylene glycol (manufactured by Nippon Shokubai Co., Ltd.). The contents (a1-2 ′) were obtained by sequentially supplying 1.78 parts by mass of a 34% by mass aqueous solution of potassium hydroxide.

(Step [2])
In a state where the temperature of the jacketed tank is maintained at 60 ° C., the content (a1-2 ′) is stirred at a rotation speed of 30 rpm and a revolution speed of 10 rpm for 10 minutes, and thereafter, the rotation speed is 71 rpm and the revolution speed is 24 rpm. Kneading was started. 30 minutes after the start of the kneading, 0.132 parts by mass of ion-exchanged water was supplied. Next, 40 minutes after the start of the kneading, 0.132 parts by mass of ion-exchanged water was supplied. Next, 50 minutes after the start of the kneading, 0.132 parts by mass of ion-exchanged water was supplied. After 60 minutes from the start of the kneading (that is, after confirming that the storage elastic modulus of the content has reached the value shown in Table 3), the kneading is immediately terminated, whereby the solid kneaded material (a2-2 ′) is obtained. I got
(Step [3])
To the kneaded product (a2-2 ′), ion-exchanged water heated to 60 ° C. was added and stirred, so that the pigment concentration was 12.9% by mass, the triethylene glycol concentration was 19.9% by mass, To obtain an aqueous pigment dispersion (a3-2 ′) of 18.8% by mass.
(Step [4])
The aqueous pigment dispersion (a3-2 ′) heated to 60 ° C. with a heat exchange device (vacuum steam heating system manufactured by T-LV Co., Ltd.) was converted into a cylindrical centrifuge (ultracentrifuge ASM260FH, rotor volume 7.7 L). , Tomoe Kogyo Co., Ltd.) at a liquid feed rate of 1.6 L / min, and continuously centrifuged at a centrifugal acceleration of 20,000 G to obtain an aqueous pigment dispersion (a4-2 ′).

(Example 3)
(Step [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 the pigment dispersion resin C and 10.0 parts by mass of a quinacridone pigment, Cinquasia Magenta D4500J (manufactured by BASF SE) )) And 0.50 parts by mass of a pigment derivative, "phthalimidomethylated 3,10-dichloroquinacridone (average number of phthalimidomethyl groups per molecule: 1.4)" was sequentially charged, and the temperature of the jacketed tank was reduced to 60 ° C. After heating, 4.93 parts by mass of EG-1 (polyethylene oxide adduct of glycerin, manufactured by VANTAGE SPECIALTY CHEMICALS) and 1.55 parts by mass of a 34% by mass aqueous solution of potassium hydroxide were sequentially supplied. The content (a1-3) was obtained.

(Step [2])
The content (a1-3) was stirred at a rotation speed of 30 rpm and a revolution speed of 10 rpm for 10 minutes while keeping the temperature of the jacketed tank at 60 ° C., and then at a rotation speed of 36 rpm and a revolution speed of 12 rpm. Kneading was started. After 60 minutes from the start of the kneading (that is, after confirming that the storage elastic modulus of the content has reached the value shown in Table 3), the kneading is immediately terminated to remove the solid kneaded material (a2-3). Obtained.
(Step [3])
To the kneaded product (a2-3), ion-exchanged water heated to 60 ° C. was added and stirred, so that the pigment concentration was 13.4% by mass and the concentration of polyethylene oxide adduct of glycerin was 6.62% by mass. Thus, an aqueous pigment dispersion (a3-3) having a nonvolatile content of 18.2% by mass was obtained.
(Step [4])
The aqueous pigment dispersion (a3-3) heated to 60 ° C. with a heat exchange device (vacuum steam heating system manufactured by T-LV Co., Ltd.) was converted into a cylindrical centrifuge (ultracentrifuge ASM260FH, rotor volume 7.7 L, The solution was supplied at 1.6 L / min to the suspension and subjected to continuous centrifugal separation at a centrifugal acceleration of 20000 G to obtain an aqueous pigment dispersion (a4-3).

(Example 4)
(Step [1])
In a 50L jacketed tank of a planetary mixer (PLM-50 manufactured by Inoue Seisakusho Co., Ltd.), 2.05 parts by mass of pigment dispersion resin C and 10.0 parts by mass of FASTOGEN Super Magenta RY (DIC Corporation) as a quinacridone-based pigment. Phthalimidomethylated 3,10-dichloroquinacridone (average number of phthalimidomethyl groups per molecule: 1.4)] as a pigment derivative in an amount of 0.26 parts by mass, and the temperature of the jacketed tank was set to 40 ° C. After heating to 7.06 parts by mass of triethylene glycol (manufactured by Nippon Shokubai Co., Ltd.) and 1.06 parts by mass of a 34% by mass aqueous solution of potassium hydroxide, the contents (a1 -4) was obtained.

(Step [2])
The content (a1-4) was stirred at a rotation speed of 30 rpm and a revolution speed of 10 rpm for 10 minutes while keeping the temperature of the jacketed tank at 40 ° C., and then at a rotation speed of 36 rpm and a revolution speed of 12 rpm. After kneading for 60 minutes and confirming that the storage elastic modulus of the content reached the value shown in Table 3, the kneading was immediately terminated to obtain a solid kneaded product (a2-4). .
(Step [3])
To the kneaded product (a2-4), ion-exchanged water heated to 50 ° C. was added and stirred to adjust the pigment concentration to 19.0% by mass, and then ion-exchanged water further heated to 50 ° C. The aqueous pigment dispersion (a3) having a pigment concentration of 18.3% by mass, a triethylene glycol concentration of 12.9% by mass, and a non-volatile content of 22.7% by mass was supplied by mixing and mixing triethylene glycol diluted with (a3). -4) was obtained.
Subsequently, 5.65% by mass of pure water, 0.59% by mass of a crest fiber IRY-LW (manufactured by Kyrest Co., iminodiacetic acid type chelate resin), and 0.05% by mass of 48% by mass hydroxylation on a stainless steel drum. The chelate resin composition obtained by adding potassium in this order and sufficiently stirring was added to the aqueous pigment dispersion (a3-4), and stirred for 3 hours. After the completion of the stirring, the mixture of the aqueous pigment dispersion (4) and the chelate resin composition is filtered through a 270 mesh (pore size: 53 μm) sieve to remove the chelate resin, thereby removing the aqueous pigment dispersion (a3 '-4) was obtained.
(Step [4])
The aqueous pigment dispersion (a3′-4) heated to 60 ° C. by a heat exchange device (vacuum steam heating system manufactured by TLV Co., Ltd.) was converted into a cylindrical centrifuge (ultracentrifuge ASM260FH, rotor volume 7.7 L). , Manufactured by Tomoe Kogyo Co., Ltd.) at a liquid sending speed of 1.6 L / min, and continuously centrifuged at a centrifugal acceleration of 20000 G to obtain an aqueous pigment dispersion (a4-4).

(Example 5)
(Step [1])
In a 50 L jacketed tank of a planetary mixer (PLM-50 manufactured by Inoue Seisakusho Co., Ltd.), 3.0 parts by mass of the pigment dispersion resin D and 10.0 parts by mass of C.I. I. Pigment Red 149 (manufactured by BASF SE Co., Ltd.) was sequentially charged as Pigment Red 149, and the temperature of the jacketed tank was heated to 60 ° C., and then 5.58 parts by mass of triethylene glycol (manufactured by Nippon Shokubai Co., Ltd.) Then, 1.36 parts by mass of a 34% by mass aqueous solution of potassium hydroxide and 0.43% by mass of ion-exchanged water were sequentially supplied to obtain a content (a1-5).

(Step [2])
In a state where the temperature of the jacketed tank was kept at 60 ° C., the content (a1-5) was stirred at a rotation speed of 15 rpm and a revolution speed of 5 rpm for 10 minutes, and then at a rotation speed of 60 rpm and a revolution speed of 20 rpm. Kneading was started. 30 minutes after the start of the kneading, 0.10% by mass of triethylene glycol was supplied. After 60 minutes from the start of the kneading (that is, after confirming that the storage elastic modulus of the content has reached the value shown in Table 3), the kneading is immediately terminated to remove the solid kneaded material (a2-5). Obtained.
(Step [3])
To the kneaded product (a2-5), ion-exchanged water heated to 60 ° C. was added and stirred to adjust the pigment concentration to 18.9% by mass, and then ion-exchanged water further heated to 60 ° C. The aqueous pigment dispersion (a3) having a pigment concentration of 16.0% by mass, a triethylene glycol concentration of 9.1% by mass, and a nonvolatile content of 21.5% by mass was supplied and mixed by supplying triethylene glycol diluted with -5) was obtained.
The aqueous pigment dispersion (a3-5) cooled to 25 ° C. or lower was placed in a bead mill (Nanomill NM-G2L manufactured by Asada Tekko Co., Ltd.) filled with 80% of φ0.3 mm zirconia beads at a flow rate of 1.2 L / min−1. And passed through a dispersing device twice at a rotation speed of 2300 min ^-1 to obtain an aqueous pigment dispersion (a3 ″ -5).
(Step [4])
The above-mentioned aqueous pigment dispersion (a3 ″ -5) heated to 60 ° C. by a heat exchange device (vacuum steam heating system manufactured by TLB Corporation) was converted into a cylindrical centrifuge (Ultra-centrifuge ASM260FH, rotor volume 7. (L, 7 L, manufactured by Tomoe Industries Co., Ltd.) at a liquid feed rate of 0.8 L / min, and continuously centrifuged at a centrifugal acceleration of 20000 G to obtain an aqueous pigment dispersion (a4-5).

(Storage modulus in dynamic viscoelasticity measurement)
The content (a1) obtained in the example or the comparative example was placed on a sample stage of a rotary type rheometer MCR102 manufactured by Anton Paar, sandwiched between parallel plates, and according to “JIS K 7224-10: 2005”. Then, dynamic viscoelasticity was measured at 25 ° C. in the range of an angular frequency of 1 to 100 rad / s, and a storage elastic modulus at 1 rad / s was obtained.
The measurement conditions of the examples and comparative examples are as follows.

(Production method of aqueous ink for inkjet printing)
By mixing each of the aqueous pigment dispersions obtained in Examples and Comparative Examples with ion-exchanged water, a diluted solution of the 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, and 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 aqueous pigment dispersion diluent, an aqueous ink for inkjet printing having a pigment concentration of 3% by mass was obtained. Was.

(Method of measuring volume average particle size)
The aqueous pigment dispersions obtained immediately after production obtained in Examples and Comparative Examples were diluted with ion-exchanged water at the following magnifications as measurement samples, and measured under the following measurement conditions. The evaluation of the volume average particle diameter of the dispersion at 25 ° C. of the measurement sample was measured using a particle size distribution analyzer (Microtrac model name: Nanotrac-UPA150 manufactured by Nikkiso Co., Ltd.). At the time of the measurement, the setting conditions (“transmission”, “shape”, “solvent refractive index”, and “density”) of the particle size distribution measuring device were set as follows.

(Method of measuring the number of coarse particles)
The aqueous pigment dispersions obtained in Examples and Comparative Examples were diluted with ion-exchanged water to obtain 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 (Accuizer 780 APS manufactured by Particle Sizing Systems). The number of coarse particles contained in 1 mL of the aqueous pigment dispersion of each of Examples and Comparative Examples was calculated by multiplying the number of coarse particles measured by the above method by the dilution ratio. 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 / mL.

[Evaluation Method for Presence or Absence of Coarse Particles Over Time in 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 rate of change (%) in the number of coarse particles before and after the standing was determined by [(the number of coarse particles contained in the aqueous pigment dispersion after the standing) / (the number of coarse particles contained in the aqueous pigment dispersion immediately after the production). (Number of particles) × 100], and evaluated according to the following criteria.

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

[Evaluation Method for Presence or Absence of Coarse Particles Over Time in Aqueous Ink for Inkjet Printing (Storage Stability)]
The number of coarse particles contained in the aqueous ink for inkjet printing immediately after production was measured by the method described above.
Next, the aqueous ink for ink-jet 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 aqueous ink for inkjet printing after the standing was measured by the method described above.
Next, the rate of change (%) of the number of coarse particles before and after the standing is represented by [(the number of coarse particles contained in the aqueous ink for inkjet printing after the standing) / (the amount of the aqueous ink for inkjet printing immediately after production). (The number of coarse particles) × 100], and evaluated according to the following criteria.

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

[Evaluation Method for Presence or Absence of Sedimentation with Time of Pigment etc. Contained in Aqueous Ink for Ink-Jet Printing]
The aqueous inks for inkjet printing obtained in Examples and Comparative Examples were placed in glass vials having a capacity of 10 mL, sealed, and allowed to stand at 25 ° C. for 2 weeks.
After the standing, when the glass vial was inverted, the adhesion of the sediment such as the pigment on the wall surface of the glass vial was visually observed and evaluated according to the following criteria.

○ No sediment such as pigment could be found on the glass vial wall.
Δ: Precipitates such as pigments adhered to the wall surface of the glass vial.
X: Adherence of sediment such as pigment on the wall surface of the glass vial was remarkably observed.

(Initial ejection stability of aqueous 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 aqueous ink for inkjet printing was filled in a black ink cartridge, and a nozzle check pattern was printed (first time). Next, solid printing was performed in the monochrome mode in a range of 340 cm ^{2 on} one A4 sheet at a print density setting of 100%. Next, the nozzle check test pattern was printed again (second time). The clogging state of the ink discharge nozzles was evaluated by comparing the first and second nozzle check test patterns.

◎ No print pattern chipping occurred in any of the first and second nozzle check test patterns. ○ The number of print pattern chippings confirmed in the first nozzle check test pattern and the second The number of chippings in the print pattern confirmed by the nozzle check test pattern was the same.
Δ The number of missing chips in the print pattern confirmed in the second nozzle check test pattern was 1 to 5 more than the number of missing print patterns confirmed in the first nozzle check test pattern.
C: The number of chippings of the print pattern confirmed by the second nozzle check test pattern was 6 or more greater than the number of chippings of the print pattern confirmed by the first nozzle check test pattern.

(Stability over time of aqueous ink for inkjet printing)
The aqueous ink for inkjet printing immediately after the production was filled in a black ink cartridge, and allowed to stand at room temperature for 4 weeks.
Next, evaluation was performed using a commercially available ink jet printer ENVY4500 (manufactured by HP). The aqueous ink for inkjet printing was filled in a black ink cartridge, and a nozzle check pattern was printed (first time). Next, solid printing was performed in the monochrome mode in a range of 340 cm ^{2 on} one A4 sheet at a print density setting of 100%. Next, the nozzle check test pattern was printed again (second time). The clogging state of the ink discharge nozzles was evaluated by comparing the first and second nozzle check test patterns.

◎ No print pattern chipping occurred in any of the first and second nozzle check test patterns. ○ The number of print pattern chippings confirmed in the first nozzle check test pattern and the second The number of chippings in the print pattern confirmed by the nozzle check test pattern was the same.
Δ The number of missing chips in the print pattern confirmed in the second nozzle check test pattern was 1 to 5 more than the number of missing print patterns confirmed in the first nozzle check test pattern.
C: The number of chippings of the print pattern confirmed by the second nozzle check test pattern was 6 or more greater than the number of chippings of the print pattern confirmed by the first nozzle check test pattern.

Claims (8)

A step [1] of supplying at least a pigment and a resin to a container provided in a kneading apparatus, and the content (a1) of the container is subjected to storage elasticity at an angular frequency of 1 rad / s determined by dynamic viscoelasticity measurement at 25 ° C. A method for producing a kneaded pigment, comprising a step [2] of kneading until the ratio falls within a range of 200 kPa to 30000 kPa. The method for producing a pigment kneaded product according to claim 1, wherein a nonvolatile content of the content (a1) is 50% by mass or more. The method for producing a pigment kneaded product according to claim 1 or 2, wherein the step [2] is a step performed while maintaining the temperature of the content (a1) within a range of 60 ° C to 120 ° C. The method according to any one of claims 1 to 3, wherein the kneading device is a closed kneading device. 5. The method according to claim 4, wherein the kneading device is a planetary mixer. A method for producing an aqueous pigment dispersion, comprising a step [3] of mixing the kneaded pigment obtained by the production method according to any one of claims 1 to 5 with an aqueous medium. The method for producing an aqueous pigment dispersion according to claim 6, comprising a step [4] of subjecting the aqueous pigment dispersion obtained in the step [3] to a centrifugal separation treatment in a range of 30 ° C to 70 ° C. The method for producing an aqueous pigment dispersion according to claim 6 or 7, wherein the step [4] is a step using a cylindrical centrifugal separator.