JP2015196750A - Method for producing pigment dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a pigment dispersion excellent in dispersibility, storage stability after dispersion and discharging properties when used as ink.SOLUTION: There is provided a method for producing a pigment dispersion which comprises: a mixed liquid production step of producing a mixed liquid of a pigment, water, a polymer and 5 mass% to 30 mass% or less of a compound having an acetylenediol group relative to the total mass of the pigment; and a reduction step of reducing the amount of the compound having an acetylenediol group from the mixed liquid obtained in the mixed liquid production step to less than 5 mass% relative to the total mass of the pigment.

Description

  The present invention relates to a method for producing a pigment dispersion.

  In recent years, due to advances in ink jet recording technology, ink jet recording methods have come to be used for high-definition images such as photographs and offset printing, and high quality recording is required.

  In response to the above requirements, a water-based pigment dispersion having excellent temporal stability and an ink jet ink having excellent color developability, dischargeability, etc., are mixed with a pigment and a surfactant, and then a resin capable of crosslinking reaction is added. An aqueous pigment dispersion subjected to a crosslinking reaction has been proposed (see, for example, Patent Document 1).

  As a method for producing an ink having excellent dispersion stability and color development and transparency of printed matter, a step of obtaining a solution containing a water-insoluble colorant dissolved in an aprotic organic solvent in the presence of an alkali and a dispersant; Mixing the solution with water to obtain a dispersion in which particles containing a water-insoluble colorant and a dispersant are dispersed; agglomerating the dispersion by adding acid; and separating the aggregate; There has been proposed a method having a step of redispersing aggregate particles by treatment (see, for example, Patent Document 2).

JP 2002-294133 A JP 2004-43776 A

However, the inks and pigment dispersions described in Patent Document 1 and Patent Document 2 sometimes have a reduced dispersibility of the pigment due to the release of the dispersant covering the pigment. Therefore, there is room for further improving the dispersibility in the process of dispersing the pigment.
In addition, when a large amount of surfactant is present in the ink and pigment dispersion, the dispersibility is improved, but the storage stability and the discharge property tend to be lowered when used as an ink-jet ink.
For these reasons, there is a demand for inks excellent in dispersibility, storage stability, and ejection, and thus pigment dispersions.

This invention is made | formed in view of the above, and makes it a subject to achieve the following objectives.
That is, an object of the present invention is to provide a method for producing a pigment dispersion that is excellent in dispersibility, storage stability after dispersion, and ejection properties when used as an ink.

Specific means for solving the problems are as follows.
<1> A mixed liquid production process for producing a mixed liquid of a pigment, water, a polymer, and a compound having an acetylenic diol group of 5% by mass to 30% by mass with respect to the total mass of the pigment, and the mixed liquid A reduction step of reducing the compound having an acetylenic diol group from the mixed solution obtained from the production step to less than 5% by mass with respect to the total mass of the pigment, and a method for producing a pigment dispersion.

The manufacturing method of the pigment dispersion as described in <1> including the process of bridge | crosslinking a polymer after a <2> liquid mixture manufacturing process.
<3> The method for producing a pigment dispersion according to <1> or <2>, wherein the mixed liquid production step comprises mixing a pigment after mixing water, a polymer, and a compound having an acetylenic diol group.
<4> The method for producing a pigment dispersion according to any one of <1> to <3>, wherein the compound having an acetylenic diol group has an HLB value of 6 to 16.
<5> The polymer includes a hydrophilic structural unit derived from at least one of the carboxy group-containing monomers and a hydrophobic structural unit derived from at least one of (meth) acrylate having an aromatic ring group or a derivative thereof. The manufacturing method of the pigment dispersion as described in any one of <1>-<4>.
<6> The carboxy group-containing monomer is (meth) acrylic acid, and the (meth) acrylate having an aromatic ring group is an alkyl (meth) acrylate having 1 to 20 carbon atoms, benzyl (meth) acrylate, and phenoxyethyl. The method for producing a pigment dispersion according to <5>, which is at least one selected from (meth) acrylates.

<7> The method for producing a pigment dispersion according to any one of <1> to <6>, wherein the acid value of the polymer is 90 mgKOH / g to 150 mgKOH / g.
<8> The method for producing a pigment dispersion according to any one of <1> to <7>, wherein the mixed liquid further contains a crosslinking agent having a bifunctional or higher functional epoxy group.
A <9> reduction process is a manufacturing method of the pigment dispersion as described in any one of <1>-<8> which reduces the compound which has acetylene diol group by ultrafiltration.

<10> The method for producing a pigment dispersion according to <9>, wherein the size of the fine pores of the filtration membrane used for ultrafiltration is 0.2 μm or less.
<11> The method for producing a pigment dispersion according to any one of <1> to <10>, wherein the polymer has an acid value of 110 mgKOH / g to 150 mgKOH / g.
<12> The method for producing a pigment dispersion according to any one of <1> to <11>, wherein a pigment dispersion for inkjet recording is produced.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the pigment dispersion excellent in the dispersibility, the storage stability after dispersion | distribution, and the discharge property when it was set as the ink can be provided.

Hereafter, the manufacturing method of the pigment dispersion of this invention is demonstrated in detail.
In this specification, the numerical range indicated using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.

<Method for producing pigment dispersion>
The method for producing a pigment dispersion according to the present invention comprises mixing to produce a mixed solution of a pigment, water, a polymer, and a compound having an acetylenic diol group of 5% by mass to 30% by mass with respect to the total mass of the pigment. And a reduction step of reducing the compound having an acetylenic diol group from the mixture obtained from the mixture production step to less than 5% by mass with respect to the total mass of the pigment.

Although the action mechanism of the present invention is not clear, the present inventor presumes as follows.
That is, the method for producing a pigment dispersion of the present invention has an acetylenic diol group by producing a mixed liquid by mixing a pigment, a polymer, and a predetermined amount of a compound having an acetylenic diol group in the mixed liquid manufacturing step. The compound improves the wettability of the pigment surface, and the polymer is efficiently coated on the pigment surface. As a result, it is considered that the dispersibility of the pigment dispersion can be improved.
Further, when the polymer coated on the pigment surface is crosslinked, the dispersion contains a compound having an acetylenic diol group, whereby crosslinking is promoted and the dispersibility of the pigment dispersion is further improved.
In the reduction step in the method for producing a pigment dispersion of the present invention, by reducing the compound having an acetylenic diol group contained in the mixed solution to a certain amount, the influence of the compound having an acetylenic diol group is released, and the pigment dispersion It is considered that the storage stability and the ejectability when ink is used can be improved.
As described above, the method for producing a pigment dispersion according to the present invention has the above-described mixed liquid production process and reduction process, and thus maintains excellent dispersibility and is excellent in storage stability and dischargeability. It is believed that a dispersion can be obtained.
Below, each process in the manufacturing method of this invention is demonstrated.

≪Mixed liquid manufacturing process≫
The method for producing a pigment dispersion of the present invention produces a mixed liquid of at least a pigment, water, a polymer, and a compound having an acetylenic diol group of 5% by mass to 30% by mass with respect to the total mass of the pigment. A mixed liquid manufacturing process.
By mixing a predetermined amount of a compound having an acetylenic diol group, the compound having an acetylenic diol group improves the wettability of the pigment surface, so that the polymer is efficiently coated on the pigment surface and the dispersibility of the pigment dispersion is improved. Can be made.

  In the mixed liquid production process of the present invention, the order of mixing the pigment, water, polymer, and the compound having an acetylenic diol group is not particularly limited, but from the viewpoint of further improving the dispersibility of the pigment, water, polymer, and acetylenic diol. It is preferable to mix the pigment after mixing the compound having a group.

In the mixed liquid production process of the present invention, the method for mixing each component is not particularly limited. Mixing of each component in a liquid mixture manufacturing process can be performed using a ball mill, a tron mill, a disper, a kneader, a kneader, a homogenizer, or a blender.
Details of the dispersion can be referred to TC Patton's “Paint Flow and Pigment Dispersion” (published by John Wiley and Sons, 1964) and the like.

(Compound having an acetylenic diol group)
The compound having an acetylene diol group in the present invention is preferably a nonionic surfactant, and more preferably an ethylene oxide adduct of acetylene diol.

Specific examples of the compound having an acetylenic diol group include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, , 5-dimethyl-1-hexyne-3ol and the like.
Moreover, a commercial item can be used for the compound which has acetylene diol group. Specific examples include SURFYNOL82, 465, 485, DYNOL604, 607 manufactured by Air Products & Chemicals, Olfin STG, Olfin E1010 manufactured by Nissin Chemical Industry, and the like.

In the present invention, a surfactant may be further added when it is desired to further improve the wettability and dispersibility during the production of the mixed liquid.
Examples of the surfactant include nonionic surfactants, cationic surfactants, anionic surfactants, betaine surfactants and the like.

In the mixed liquid production process of the present invention, when the compounding amount of the compound having an acetylenic diol group is less than 5% by mass with respect to the total mass of the pigment, the wettability of the pigment surface is insufficient at the time of mixing, and the dispersion is obtained It is inferior to the dispersibility of the pigment. Moreover, when the compounding quantity of the compound which has acetylene diol group exceeds 30 mass% with respect to the total mass of a pigment, a liquid mixture will gelatinize and thicken and a pigment cannot be disperse | distributed.
5 mass%-25 mass% are preferable with respect to the total mass of a pigment, and, as for the compounding quantity of the compound which has an acetylene diol group in a mixture manufacturing process, 5 mass%-15 mass% are more preferable.

6-16 are preferable, as for the HLB (Hydrophile-Lipophile Balance) value of the compound which has acetylene diol group, 6-13 are more preferable, and 8-13 are more preferable.
HLB is a value calculated from the HLB value of GRIFFIN (20 Mw / M; Mw = molecular weight of hydrophilic site, M = molecular weight of nonionic surfactant).

(Pigment)
There is no restriction | limiting in particular as a pigment in this invention, According to the objective, it can select suitably, For example, any of an organic pigment and an inorganic pigment may be sufficient.

Examples of organic pigments include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Among these, azo pigments and polycyclic pigments are more preferable.
Examples of the azo pigments include azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments.
Examples of the polycyclic pigment include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments.
Examples of dye chelates include basic dye chelates and acid dye chelates.

  Examples of the inorganic pigment include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Among these, carbon black is particularly preferable. In addition, as carbon black, what was manufactured by well-known methods, such as a contact method, a furnace method, a thermal method, is mentioned, for example.

  Specific examples of carbon black include those of Raven7000, Raven5750, Raven5250, Raven5000 ULTRAII, Raven3500, Raven2000, Raven1500, Raven1250, Raven1170, Raven1170, Raven1170, Raven1170, Raven1170, Raven1170, Raven1170 (Manufactured by Carbon Co., Ltd.), Regal 400R, Regal 330R, Regal 660R, Mogu L, Black Pearls L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarc 1300, Monarch 1400 (above Cabot Corporation), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black 18, Color Black FW200, Color Black S150, Color Black S150, Color Black Sr, 160 , Printex 140U, Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (manufactured by Degussa), No. 25, no. 33, no. 40, no. 45, no. 47, no. 52, no. 900, no. 2200B, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Corporation) and the like can be mentioned, but are not limited thereto.

  Examples of the organic pigment that can be used in the present invention include C.I. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 14C, 16, 17, 24, 34, 35, 37, 42, 53, 55, 65, 73, 74, 75, 81, 83, 93, 95, 97, 98, 100, 101, 104, 108, 109, 110, 114, 117, 120, 128, 129, 138, 150, 151, 153, 154, 155, 180 etc. are mentioned.

  Examples of magenta ink pigments include C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 39, 40, 48 (Ca), 48 (Mn), 48: 2, 48: 3, 48: 4, 49, 49: 1, 50, 51, 52, 52: 2, 53: 1, 53, 55, 57 (Ca), 57: 1, 60, 60: 1, 63: 1, 63: 2, 64, 64: 1, 81, 83, 87, 88, 89, 90, 101 (Bengara) ), 104, 105, 106, 108 (cadmium red), 112, 114, 122 (quinacridone magenta), 123, 146, 149, 163, 166, 168, 170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 209, 2 9,269, and the like, and C. I. Pigment violet 19, especially C.I. I. Pigment Red 122 is preferable.

Further, as pigments for cyan ink, C.I. I. Pigment Blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15:34, 16, 17: 1, 22, 25, 56, 60, C.I. I. Bat blue 4, 60, 63 and the like. I. Pigment Blue 15: 3 is preferable.
The above pigments may be used alone or in combination of a plurality selected from the above-mentioned groups or between the groups.

As the pigment in the present invention, a pigment surface-treated with rosin acid may be used. Specific examples of the pigment surface-treated with rosin acid include FUJI FAST RED (manufactured by Fuji Dye Co., Ltd.).
In addition, rosin acid is abietic acid and its salt, neoabietic acid and its salt, dehydroabietic acid and its salt, parastrinic acid and its salt, levobimalic acid and its salt, pimaric acid and its salt, isopimaric acid and its salt And a mixture of one or more selected from citronellic acid and salts thereof.

  The content of the pigment in the present invention is 0.1% by mass or more and 20% by mass or less with respect to the total mass of the pigment dispersion from the viewpoint of color developability, granularity, storage stability, and ejection reliability. It is preferably 1% by mass or more and 18% by mass or less, more preferably 5% by mass or more and 15% by mass or less.

(polymer)
Examples of the polymer in the present invention (hereinafter appropriately referred to as a dispersant) include polymer dispersants. The polymer dispersant may be either a water-insoluble dispersion or a water-soluble dispersant.
In the present invention, “water-soluble” of a water-soluble polymer means that when the polymer is dried under reduced pressure at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C., the dissolved amount is 5.0 g or more. The dissolution amount is preferably 10.0 g or more, more preferably 15.0 g or more. The amount of dissolution is the amount of dissolution when the salt-forming group of the polymer is neutralized 100% with potassium hydroxide.

The polymer dispersant preferably has at least one hydrophilic structural unit and at least one hydrophobic structural unit.
A hydrophilic structural unit is a structural unit containing at least one hydrophilic group. Examples of hydrophilic groups include nonionic groups, carboxylic acid groups, sulfonic acid groups, and phosphoric acid groups. Examples of the nonionic group include a hydroxyl group, an amide group (nitrogen atom is unsubstituted), a group derived from an alkylene oxide polymer (for example, polyethylene oxide, polypropylene oxide, etc.), a group derived from a sugar alcohol, and the like. . The content ratio of the hydrophilic structural unit to the hydrophobic structural unit is preferably in the range of (hydrophilic part: hydrophobic part) = 15: 85 to 40:60, and (hydrophilic part: hydrophobic part) = 15: 85-30. : The range of 70 is most preferable.

The hydrophilic structural unit is preferably an acidic group, and more preferably a structural unit having a carboxy group.
Examples of the structural unit having a carboxy group include structural units derived from (meth) acrylic acid, β-carboxyethyl acrylate, fumaric acid, itaconic acid, maleic acid, crotonic acid and the like. Among these, (meth) acrylic acid And a structural unit derived from β-carboxyethyl acrylate is preferred, and a structural unit derived from (meth) acrylic acid is more preferred.

  Examples of other hydrophilic structural units include structural units derived from monomers having nonionic hydrophilic groups. For example, (meth) acrylates having hydrophilic functional groups, (meth) acrylamides, And vinyl monomers having a hydrophilic functional group, such as vinyl esters.

  Examples of the “hydrophilic functional group” include a hydroxyl group, an amino group, an amide group (unsubstituted nitrogen atom), a carboxyl group, a sulfonic acid group, a phosphoric acid group, and alkylene oxides such as polyethylene oxide and polypropylene oxide described later. It is done.

The hydrophobic structural unit is preferably at least one of (meth) acrylate having an aromatic group or a derivative thereof.
The (meth) acrylate having an aromatic group is preferably at least one selected from alkyl (meth) acrylate having 1 to 20 carbon atoms, benzyl (meth) acrylate, and phenoxyethyl (meth) acrylate.
These hydrophobic structural units may be included singly or in combination of two or more in the polymer dispersant.

  Examples of the polymer dispersant in the present invention include (meth) acrylic acid-benzyl (meth) acrylate copolymer, (meth) acrylic acid-phenoxyethyl (meth) acrylate copolymer, (meth) acrylic acid-phenoxyethyl. A (meth) acrylate-C1-C20 alkyl (meth) acrylate copolymer or the like can be suitably used.

  In the present invention, “(meth) acrylic acid” represents acrylic acid or methacrylic acid, and “(meth) acrylic ester” (“(meth) acrylate”) represents acrylic ester (acrylate) or methacrylate ester ( Methacrylate).

The polymer dispersant preferably has a hydrophilic structural unit having a carboxy group from the viewpoint of dispersibility, and the acid value is preferably 90 mgKOH / g to 150 mgKOH / g, more preferably 110 mgKOH / g to 150 mgKOH / g.
The acid value is measured by the method described in JIS standards (JISK0070, 1992).

  The weight average molecular weight of the polymer dispersant is preferably 1,000 to 100,000, more preferably 3,000 to 50,000, and still more preferably 5,000 to 40,000.

  The weight average molecular weight is measured by gel permeation chromatography (GPC). GPC uses HLC-8020GPC (manufactured by Tosoh Corporation), TSKgel, Super Multipore HZ-H (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) as columns, and THF (tetrahydrofuran) as an eluent. ) Is used. The conditions are as follows: the sample concentration is 0.45 mass%, the flow rate is 0.35 ml / min, the sample injection amount is 10 μl, the measurement temperature is 40 ° C., and the RI detector is used. In addition, the calibration curve is “standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, It is prepared from 8 samples of “A-2500”, “A-1000”, “n-propylbenzene”.

  The mixing mass ratio (p: s) of the pigment (p) and the polymer dispersant (s) is preferably in the range of 10: 1 to 10: 8, more preferably in the range of 10: 1 to 10: 7, Preferably it is 10: 1-10: 5.

  In the mixed liquid obtained in the mixed liquid production process of the present invention, the pigment is preferably coated with a polymer (polymer-coated pigment).

  The polymer can be coated on the pigment by a conventionally known method. Specifically, for example, a polymer-coated pigment in which at least a part of the pigment surface is coated with a polymer can be obtained by the method described in JP-A-2009-190379.

  The average particle size of the polymer-coated pigment in the dispersed state is preferably 10 nm to 200 nm, more preferably 50 nm to 150 nm, and still more preferably 80 nm to 130 nm. When the average particle size is 200 nm or less, the color reproducibility is good, the droplet ejection characteristics when droplets are ejected by the ink jet method are good, and when it is 10 nm or more, the light resistance is good.

  The average particle size of the polymer-coated pigment in the dispersed state is determined by measuring the volume average particle size by a dynamic light scattering method using a nanotrack particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.). Is required.

(water)
The pigment dispersion contains water, but the amount of water is not particularly limited. Especially, preferable content of water is 40 mass%-99 mass%, More preferably, it is 50 mass%-95 mass%, More preferably, it is 60 mass%-95 mass%.

≪Process to crosslink polymer≫
It is preferable that the manufacturing method of the pigment dispersion of this invention includes the process of bridge | crosslinking a polymer after a liquid mixture manufacturing process.
In the step of crosslinking the polymer, crosslinking between the polymer dispersants is performed.

  The polymer itself may be crosslinked by itself, may be crosslinked by a crosslinking agent, or may include both of them.

In the step of crosslinking the polymer, it is preferable to perform crosslinking as follows using a crosslinking agent.
As conditions for crosslinking the polymer, the mixed liquid obtained in the mixed liquid production process is heated while stirring, and the liquid temperature of the mixed liquid is set to 60 ° C to 80 ° C. Subsequently, a crosslinking agent is added, and the polymer dispersant is crosslinked by heating for 6 hours so as to maintain the liquid temperature while stirring. Thereafter, the liquid temperature is cooled to 25 ° C. to obtain a mixed liquid in which the polymer is crosslinked. The temperature of the mixed solution in the step of crosslinking the polymer is most preferably 70 ° C to 80 ° C.

When the polymer is crosslinked, the polymer (dispersant) has a functional group capable of reacting with a crosslinking agent described later to form a crosslinked structure.
Examples of the functional group capable of forming a crosslinked structure include a carboxy group or a salt thereof, an isocyanate group, and an epoxy group. Among these, it is preferable to have a carboxy group or a salt thereof from the viewpoint of improving dispersibility.

Examples of the resin having a functional group capable of forming such a crosslinked structure include an epoxy resin, a silicone resin, a hydroxyl group functional acrylic resin, a carboxy functional acrylic resin, a polyester resin, and a urethane resin.
Specifically, in the case of an epoxy resin, for example, diethylenetriamine, triethylenetetramine, m-phenylenediamine, methylenedianiline, polycarboxylic acid, dicarboxylic acid, phthalic anhydride, benzophenonetetraacid anhydride, hexahydrophthal. In the case of acid anhydride, pyromellitic dianhydride, and silicone resin, for example, in the case of polymethylsiloxane and hydroxyl functional acrylic resin, for example, amino resin and isocyanate compound may be mentioned.

The cross-linking agent is not particularly limited as long as it is a compound having two or more sites that react with the dispersant, but preferably has two or more epoxy groups from the viewpoint of excellent reactivity with a carboxyl group. It is a compound (a bifunctional or higher functional epoxy compound).
Specific examples include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, and polypropylene glycol diglycidyl. Examples include ether and trimethylolpropane triglycidyl ether, and polyethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, and trimethylolpropane triglycidyl ether are preferable.

  A commercial item can also be used as a crosslinking agent. As a commercial item, Dencol EX-321, EX-521, EX-821, EX-830, EX-850, EX-851 [above, Nagase ChemteX Co., Ltd. product] etc. can be used, for example.

  The molar ratio of the crosslinking site of the crosslinking agent to the crosslinked site of the dispersant is preferably from 1: 1.1 to 1:10 from the viewpoint of the crosslinking reaction rate and the stability of the pigment body after crosslinking, and 1: 1.1 ˜1: 5 is more preferable, and 1: 1.1 to 1: 3 is more preferable.

(water)
The pigment dispersion contains water, but the amount of water is not particularly limited. Especially, preferable content of water is 40 mass%-99 mass%, More preferably, it is 50 mass%-95 mass%, More preferably, it is 60 mass%-95 mass%.

≪Reduction process≫
The method for producing a pigment dispersion of the present invention includes at least a reduction step of reducing the compound having an acetylene diol group from the mixed solution obtained by the mixed solution manufacturing step to less than 5% by mass with respect to the total mass of the pigment. .
In the reduction process of the present invention, when the amount of the compound having an acetylenic diol group contained in the mixed solution is 5% by mass or more, the storage stability of the pigment dispersion is lowered.
That is, in the method for producing a pigment dispersion of the present invention, the compound having an acetylenic diol group added to improve the dispersibility of the pigment in the mixed liquid production step is reduced to a predetermined amount in the reduction step. Thus, it is possible to obtain a pigment dispersion that is excellent in storage stability and dischargeability when used as an inkjet ink while maintaining excellent dispersibility.

In the reduction step of the present invention, the compound having an acetylenic diol group is preferably reduced to less than 5% by mass with respect to the total mass of the pigment, and is preferably reduced to 0.25% by mass or more and less than 3.0% by mass, More preferably, the content is reduced to 0.25% by mass to 1.75% by mass.
The amount of the compound having an acetylenic diol group is preferably reduced to 50% by mass or less, and more preferably 0.83% to 35% by mass.
When the content of the compound having an acetylenic diol group is 0.25% by mass or more, the dispersibility of the pigment dispersion can be further improved.

  In the reduction step of the present invention, the method for reducing the compound having an acetylenic diol group is not particularly limited, and conventionally known concentration methods such as ultrafiltration, pressure filtration, acid precipitation, centrifugation, and vacuum distillation, desalting methods, A solvent removal method can be used. Among these, it is preferable to concentrate the mixture by ultrafiltration because a compound having an acetylenic diol group can be selectively removed to a predetermined amount.

Here, the ultrafiltration is a filtration method for submicron-sized dispersed particles in a solution, and a solution containing dispersed particles is added to a filtration membrane having fine pores with the pore size of the membrane and solute molecules. The solute is separated, fractionated, concentrated and purified by sieving at the molecular level according to the size. The ultrafiltration method includes a total amount filtration method and a crossflow method. In the present invention, it is preferable to use a crossflow method.
In general, the shape of the filtration membrane used for ultrafiltration includes a flat shape, a pipe shape, and a hollow fiber shape, and the material of the filtration membrane is a synthesis of polyethersulfone (PESU), polyacrylonitrile, etc. There are polymers and ceramics, which are selected depending on the application.

  In the reduction step of the present invention, when ultrafiltration is used, the material of the filtration membrane is preferably polyethersulfone (PESU). Moreover, 0.2 micrometer or less is preferable and the size of the micropore of a filtration membrane has more preferable 0.1 micrometer-0.2 micrometer. In ultrafiltration, a pigment dispersion is placed in a diafiltration reservoir tank, and the solution is fed using a tube pump while stirring with a magnetic stirrer. The flow rate during filtration is preferably 400 mL / min to 700 mL / min, and more preferably 600 mL / min to 700 mL / min. At this time, the liquid temperature is kept at 25 ° C., and ultrapure water is supplied in an amount that has been filtered so that the concentration is always constant. In the reduction step, filtration is performed about 10 times by volume magnification of the pigment dispersion charged with the filtrate. At this time, the number of times is counted with 1 volume ratio as 1 time, 8 to 14 times is a preferable range, and 10 to 14 times is a more preferable range of the number of times of filtration.

The average particle diameter of the polymer-coated pigment in the pigment dispersion after undergoing the mixed liquid production process and the reduction process of the present invention is preferably 10 nm to 200 nm, more preferably 50 nm to 150 nm, and still more preferably 80 nm to 130 nm.
The average particle diameter can be measured by the method described above.

As an index for evaluating the dispersibility of the polymer-coated pigment in the present invention, there is a polydispersity index (PDI).
The polydispersity index (PDI: polydispersity index) in the present invention is an index that defines the particle size distribution of dispersed particles, and is defined by the following formula (1).

    PDI = (D90−D10) / D50: Formula (1)

In Formula (1), D90, D50, and D10 are the integrals of the distribution function dG = F (D) dD, respectively, and are 0.9 (90 number%) and 0.5 (50 number%) of the total number of particles. And a particle size equal to 0.1 (10% by number). G represents the number of dispersed particles, and D represents the particle size of the dispersed particles.
D90, D50, and D10 can be estimated from an average particle size measured by a dynamic light scattering method using a nanotrack particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.). The pigment concentration at the time of measurement is adjusted to 0.75% by mass and measured at 25 ° C.

  In the above relational expression, the narrower the particle size distribution is, the closer the PDI is to 1. On the contrary, the wider the particle size distribution, that is, the greater the polydispersity, the larger the PDI.

  The polydispersity index (PDI) of the polymer-coated pigment contained in the pigment dispersion of the present invention is preferably 1.10 to 1.45, more preferably 1.15 to 1.30, and 1.15 to 1.25. Is more preferable.

  The pigment dispersion obtained by the production method of the present invention is preferably used for ink for inkjet recording.

<Ink for inkjet recording>
Ink for inkjet recording (hereinafter referred to as ink as appropriate) includes at least the pigment dispersion described above.
The ink may further contain a water-soluble solvent and other additives.
The content of the pigment in the ink is about 4% by mass to 15% by mass, preferably 4% by mass to 10% by mass, and more preferably 4% by mass to 6% by mass in terms of the total solid content of the ink.

(Water-soluble organic solvent)
The ink may contain at least one water-soluble organic solvent. The water-soluble organic solvent can obtain the effect of preventing drying, wetting or promoting penetration. In order to prevent drying, the ink adheres to and drys at the ink discharge port of the ejection nozzle and is used as an anti-drying agent to prevent clogging. For drying prevention and wetting, the vapor pressure is lower than that of water. A water-soluble organic solvent is preferred. Further, for penetration promotion, it can be used as a penetration enhancer that enhances ink permeability to paper.

The drying inhibitor is preferably a water-soluble organic solvent having a vapor pressure lower than that of water. Specific examples of such water-soluble organic solvents include ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, thiodiglycol, dithiodiglycol, 2-methyl-1,3-propanediol, 1,2,6-hexane. Polyols represented by triols, acetylene glycol derivatives, glycerin, trimethylolpropane, etc., ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether, triethylene glycol monoethyl (or butyl) ether, etc. Lower alkyl ethers of polyhydric alcohols, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, heterocyclic rings such as N-ethylmorpholine, sulfolane, Methyl sulfoxide, sulfur-containing compounds such as 3-sulfolene, diacetone alcohol, polyfunctional compounds such as diethanolamine, and urea derivatives.
Of these, polyhydric alcohols such as glycerin and diethylene glycol are preferred as the drying inhibitor.
Anti-drying agents may be used alone or in combination of two or more. The content of the drying inhibitor is preferably in the range of 10% by mass to 50% by mass in the ink.

The penetration enhancer is suitable for the purpose of better penetrating the ink into the recording medium (printing paper or the like). Specific examples of such water-soluble organic solvents include alcohols such as ethanol, isopropanol, butanol, di (tri) ethylene glycol monobutyl ether, 1,2-hexanediol, sodium lauryl sulfate, sodium oleate, and nonionic interfaces. An activator or the like can be preferably used.
A penetration enhancer may be used individually by 1 type, or may be used together 2 or more types. The content of the penetration accelerator is preferably in the range of 5% by mass to 30% by mass in the ink. Moreover, it is preferable to use the penetration enhancer within a range that does not cause image bleeding and paper loss (print-through).

  The water-soluble organic solvent is used for adjusting the viscosity in addition to the above. Specific examples of water-soluble organic solvents that can be used to adjust the viscosity include alcohols (for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, t-butanol, pentanol, hexanol, cyclohexanol). Benzyl alcohol), polyhydric alcohols (eg, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodi) Glycol), glycol derivatives (eg, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether) , Ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, triethylene glycol monomethyl ether, ethylene glycol diacetate, ethylene glycol monomethyl ether acetate, triethylene glycol Monomethyl ether, triethylene glycol monoethyl ether, ethylene glycol monophenyl ether), amine (for example, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethyl) Diamine, diethylenetriamine, triethylenetetramine, polyethyleneimine, tetramethylpropylenediamine) and other polar solvents (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, sulfolane, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, acetonitrile, acetone). Also in this case, the water-soluble organic solvent may be used alone or in combination of two or more.

(water)
The ink contains water, but the amount of water is not particularly limited. Especially, preferable content of water is 10 mass%-99 mass%, More preferably, it is 30 mass%-80 mass%, More preferably, it is 50 mass%-70 mass%.

(Other additives)
The ink can be constituted using other additives in addition to the above components. Other additives include, for example, water-soluble polymerizable compounds, polymerization initiators, resin particles, antifading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, antiseptics, antifungal agents, pH adjusters, surfaces Well-known additives, such as a tension regulator, an antifoamer, a viscosity modifier, a dispersing agent, a dispersion stabilizer, a rust preventive agent, a chelating agent, are mentioned. These various additives are added directly to the ink.

  The water-soluble polymerizable compound can improve image adhesion. Regarding the preferable form of the water-soluble polymerizable compound, the description in paragraphs 0037 to 0061 of JP2011-231315A can be appropriately referred to.

  By adding the initiator together with the water-soluble polymerizable compound, the scratch resistance of the image can be improved, and it is advantageous for high-speed recording. Regarding the preferable form of the initiator, the description in paragraphs 0062 to 0065 of JP-A-2011-231315 can be appropriately referred to.

  The ultraviolet absorber can improve the storage stability of the image. Examples of the ultraviolet absorber include benzotriazoles described in JP-A Nos. 58-185677, 61-190537, JP-A-2-782, JP-A-5-97075, JP-A-9-34057, and the like. Compounds, benzophenone compounds described in JP-A No. 46-2784, JP-A No. 5-194433, US Pat. No. 3,214,463, etc., JP-B Nos. 48-30492, 56-21114, Cinnamic acid compounds described in JP-A-10-88106, etc., JP-A-4-298503, JP-A-8-53427, JP-A-8-239368, JP-A-10-182621, JP-A-8-501291 Triazine compounds described in Japanese Patent Publication No. The compounds described in No. 24239, stilbene-based compounds, and benzoxazole-based compounds, such as compounds that absorb ultraviolet rays and emit fluorescence, so-called fluorescent brighteners can also be used.

  The anti-fading agent can improve the storage stability of the image. Examples of the anti-fading agent include various organic and metal complex anti-fading agents. Examples of the organic anti-fading agent include hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, heterocycles, and the like. Examples of the system antifading agent include nickel complexes and zinc complexes. More specifically, Research Disclosure No. No. 17643, No. VII, I to J, ibid. 15162, ibid. No. 18716, page 650, left column, ibid. No. 36544, page 527, ibid. No. 307105, page 872, ibid. The compounds described in the patent cited in Japanese Patent No. 15162, and the compounds included in the general formulas and compound examples of representative compounds described in JP-A-62-215272, pages 127 to 137 can be used.

  Examples of the antifungal agent include sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, p-hydroxybenzoic acid ethyl ester, 1,2-benzisothiazolin-3-one and salts thereof. The content of the antifungal agent is preferably in the range of 0.02% by mass to 1.00% by mass with respect to the ink.

  As the pH adjuster, a neutralizer (organic base, inorganic alkali) can be used. The pH adjuster can improve the storage stability of the ink. The pH adjusting agent is preferably added so that the ink has a pH of 6 to pH 10, and more preferably added so that the pH becomes 7 to pH 10.

Examples of the surface tension adjusting agent include nonionic surfactants, cationic surfactants, anionic surfactants, betaine surfactants, and the like.
The addition amount of the surface tension adjusting agent is preferably within a range where the surface tension of the ink can be adjusted to 20 mN / m to 60 mN / m, more preferably within a range where the ink can be adjusted to 20 mN / m to 45 mN / m, and 25 mN / m to 40 mN / m. The range which can be adjusted to is more preferable. When the addition amount is within the range, droplets can be ejected satisfactorily by the ink jet method.

As the surfactant, in the hydrocarbon type, fatty acid salt, alkyl sulfate ester salt, alkylbenzene sulfonate salt, alkyl naphthalene sulfonate salt, dialkyl sulfosuccinate salt, alkyl phosphate ester salt, naphthalene sulfonate formalin condensate, polyoxy Anionic surfactants such as ethylene alkyl sulfate ester salt, polyoxyethylene alkyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkylamine, Nonionic surfactants such as glycerin fatty acid esters and oxyethyleneoxypropylene block copolymers are preferred. Further, SURFYNOLS (manufactured by Air Products & Chemicals), which is an acetylene-based polyoxyethylene oxide surfactant, is also preferably used. Amine oxide type amphoteric surfactants such as N, N-dimethyl-N-alkylamine oxide are also preferred.
Further, pages (37) to (38) of JP-A-59-157636, Research Disclosure No. Those listed as surfactants in 308119 (1989) can also be used.
Further, by using fluorine (fluorinated alkyl) surfactants, silicone surfactants and the like described in JP-A Nos. 2003-322926, 2004-325707, and 2004-309806. In addition, the abrasion resistance can be improved.

  These surface tension modifiers can also be used as an antifoaming agent, and fluorine compounds, silicone compounds, chelating agents represented by EDTA, and the like can also be used.

The ink can be produced, for example, by the following method.
Each step in the method for producing a pigment dispersion described above, and a step of preparing an ink by mixing the pigment dispersion, a water-soluble organic solvent, and other additives, and configured as necessary. Other steps can be included.
By adopting the above-described configuration, the ink has excellent dispersibility of the pigment and excellent storage stability and dischargeability.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. Unless otherwise specified, “part” is based on mass.

[Synthesis example]
(Synthesis of polymer P-1)
Polymer P-1 was synthesized according to the following.
A monomer feed composition was prepared by mixing methacrylic acid (170 parts), benzyl methacrylate (830 parts), and isopropanol (375 parts). An initiator feed composition was prepared by mixing 2,2-azobis (2-methylbutyronitrile) (22.05 parts) and isopropanol (187.5 parts).
Next, while isopropanol (187.5 parts) was heated to 80 ° C. in a nitrogen atmosphere, a mixed solution of the monomer supply composition and the initiator supply composition was added dropwise over 2 hours. After completion of dropping, the mixture was kept at 80 ° C. for further 4 hours, and then cooled to 25 ° C. After cooling, the solvent was removed under reduced pressure to obtain polymer P-1 having a weight average molecular weight (Mw) of 29000 and an acid value of 110.8 mgKOH / g.
In addition, the weight average molecular weight and acid value of polymer P-1 were measured by the above-mentioned method.

(Synthesis of polymer P-2)
Mw was synthesized in the same manner as P-1, except that the amount of methacrylic acid in the synthesis of P-1 was changed from 170 parts to 228 parts and the amount of benzyl methacrylate was changed from 830 parts to 772 parts. Was 27000 and the acid value was 148.6 mgKOH / g.

(Synthesis of polymer P-3)
Polymer P-3 was synthesized according to the following.
To a 500 ml three-necked flask equipped with a stirrer and a condenser, 330 parts of methyl ethyl ketone was added and heated to 75 ° C. under a nitrogen atmosphere. Thereafter, 20 parts of dimethyl 2,2′-azobisisobutyrate, 500 parts of phenoxyethyl methacrylate, 150 parts of methacrylic acid, and 350 parts of methyl methacrylate were dissolved in 700 parts of methyl ethyl ketone in a three-necked flask. This solution was added dropwise over 3 hours.
After completion of the dropwise addition, the mixture was further reacted for 1 hour, and then a solution prepared by dissolving 2 parts of dimethyl 2,2′-azobisisobutyrate in 20 parts of methyl ethyl ketone was added, heated to 78 ° C. and heated for 4 hours. The obtained reaction solution was reprecipitated twice in a large excess amount of hexane, and the precipitated polymer was dried to obtain a polymer P-3 having an Mw of 30700 and an acid value of 97.8 mgKOH / g.

(Synthesis of polymer P-4)
Mw was synthesized in the same manner as P-1, except that the amount of methacrylic acid in the synthesis of P-1 was changed from 170 parts to 265 parts and the amount of benzyl methacrylate was changed from 830 parts to 735 parts. Was 31000 and the acid value was 172.8 mgKOH / g.

(Synthesis of polymer P-5)
Polymer P-5 was the same as P-1 except that the amount of methacrylic acid in the synthesis of P-1 was changed from 170 parts to 100 parts and the amount of benzyl methacrylate was changed from 830 parts to 570 parts. And polymer P-5 having an Mw of 28000 and an acid value of 65.1 mgKOH / g was obtained.

(Example 1)
[Preparation of pigment dispersion]
150 parts of the polymer P-1 obtained above is dissolved in water, and an aqueous polymer solution is prepared using a potassium hydroxide aqueous solution so that the pH after neutralization is 9 and the polymer concentration is about 25% by mass. did.
180 parts of this aqueous polymer solution, 330 parts of water, 90 parts of Pigment Red (PR) 122 (manufactured by Dainichi Seika Co., Ltd., chromofine red), 9 parts of a compound having an acetylenic diol group (Air Products & Chemicals, DYNOL607) And were subjected to a dispersion treatment for 3 hours in a bead mill (bead diameter: 0.1 mmΦ, zirconia beads). By this dispersion treatment, a dispersion (uncrosslinked dispersion) of uncrosslinked pigment-containing polymer particles having a pigment solid content concentration of 15% by mass was obtained.
To 136 parts of the resulting uncrosslinked dispersion, 0.23 parts of Denacol EX521 (manufactured by Nagase ChemteX Corp., trifunctional epoxy-based crosslinking agent) is added and reacted at 70 ° C. with stirring for 6 hours. Thereafter, by cooling to 25 ° C., a dispersion (crosslinked dispersion) of crosslinked pigment-containing polymer particles having a pigment solid content concentration of 11% by mass was obtained.
Using the cross-flow type UF (manufactured by Sartorius, ultrafiltration device), the resulting crosslinked dispersion was maintained at a liquid temperature of 25 ° C. and a flow rate of 600 g / min. The pigment dispersion 1 was obtained by performing ultrafiltration 10 times with a polyethersulfone (PESU) membrane.

(Example 2 to Example 14, Comparative Example 1 to Comparative Example 3)
Except that the polymer in pigment dispersion 1, the kind and compounding amount of the compound having an acetylenic diol group, or the kind of crosslinking agent were changed as shown in Table 1 below, Example 2 The pigment dispersion 2 to the pigment dispersion 17 in Example 14 and Comparative Examples 1 to 3 were prepared.

(Comparative Example 4)
A pigment dispersion 18 in Comparative Example 4 was produced in the same manner as in the pigment dispersion 1 except that the ultrafiltration of the crosslinked dispersion was not performed in the production of the pigment dispersion 1.

(Comparative Example 5)
In the production of pigment dispersion 1, pigment dispersion 19 in Comparative Example 5 was produced in the same manner as pigment dispersion 1, except that the number of times of ultrafiltration was changed to 5.

(Comparative Example 6)
In the preparation of Pigment Dispersion 1, Comparative Example was carried out in the same manner as Pigment Dispersion 1, except that the compound having an acetylenic diol group was changed to Emulgen 109P (manufactured by Kao Corporation, polyoxyethylene lauryl ether surfactant). The pigment dispersion 20 in No. 6 was produced.

[Preparation of ink]
Using each of Examples 1 to 14 and Comparative Examples 1 to 6 (pigment dispersions 1 to 20) obtained above, a multi-component was mixed so as to have the following composition, and a plastic disposable syringe And filtered with a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain an ink.
The obtained ink was evaluated for ejection properties. The evaluation results are shown in Table 2 below.

~ Ink composition ~
・ Pigment dispersion (pigment solid content concentration: 15% by mass): 6.5 parts ・ Tripropylene glycol monomethyl ether (TPGmME)
(Water-soluble organic solvent manufactured by Wako Pure Chemical Industries, Ltd.) 2.0 parts ・ Dipropylene glycol (DPG)
(Water-soluble organic solvent, manufactured by Wako Pure Chemical Industries, Ltd.) ... 2.0 parts ・ Sanix GP250 (Water-soluble organic solvent, manufactured by Sanyo Chemical Industries) ... 10.0 parts ・ Urea ... 5.0 parts ・ Orphine E1010 ( Nissin Chemical Industry Co., Ltd., surfactant) ... 1.5 parts ・ Ion-exchanged water ... Total remaining amount of 100 parts

[Evaluation]
(Content of compound having acetylenic diol group)
A compound having an acetylenic diol group contained in each pigment dispersion is obtained by extracting a compound having an acetylenic diol group according to the following procedure from the pigment dispersions of the above Examples and Comparative Examples, and quantifying it using gas chromatography (GC). The total amount of was determined.
In addition, about the pigment dispersion 20 of the comparative example 6, polyoxyethylene lauryl ether was extracted in the procedure similar to the extraction of the compound which has acetylene diol group, and it quantified using GC.

-Extraction procedure of compound having acetylenediol group-
1) 25 g of pigment dispersion and 25 g of chloroform were mixed, transferred to a separatory funnel and shaken well. 50 g of water was added to the separatory funnel and mixed well to reach equilibrium.
2) The lower layer (organic layer) was extracted from the cock below the separatory funnel and transferred to another container (flask, etc.). Next, the upper layer (aqueous layer) was extracted from above the separatory funnel and transferred to a container different from the container to which the organic layer was transferred.
3) The aqueous layer was returned again to the separatory funnel, 25 g of chloroform was added, and the above 2) was repeated 5 times.
4) All the organic layers were put into a separatory funnel, and 50 g of ultrapure water (water having an impurity amount of 0.01 μg / L or less) was added and mixed well so as to be in an equilibrium state.
5) The upper layer (ultra pure water layer) and the lower layer (organic layer) were separated, the organic layer was dried over sodium sulfate, and the solvent was distilled off to obtain an extract.

-Gas chromatography-
Apparatus: Gas Chromatography-14B, manufactured by Shimadzu Corporation Column used: length 2.1 m, glass column having a diameter of 5φ × 2.6φ Column filler: Silicone SE-30 Uniport B

(Polydispersity index)
For the pigment dispersions of the above Examples and Comparative Examples, the particle size distribution of the pigment coated with the polymer was measured by a dynamic light scattering method using Nanotrac particle size distribution measuring device UPA-EX150 (manufactured by Nikkiso Co., Ltd.).
From the obtained particle size distribution, the average particle diameter, D90, D50, and D10 (D90, D50, and D10 are 0.9 (90 number%), 0.5 (50 number%) and 0.5 (50 number%) of the total number of dispersed particles, respectively. 0.1 (representing a particle diameter equal to 10% by number)) was calculated, and the polydispersity index (PDI) of the following formula (1) was estimated.
PDI = (D90−D10) / D50 Formula (1)

(Storage stability)
Storage stability was determined by measuring the average particle size and viscosity of the pigments coated with the polymer after the inks prepared in the above Examples and Comparative Examples were allowed to stand at 60 ° C. for 336 hours in a sealed state. The change rate of liquid physical properties before and after aging was calculated. The rate of change can be determined by [(viscosity after aging−initial viscosity) / initial viscosity] × 100 and [(average particle diameter after aging−initial average particle diameter) / initial average particle diameter] × 100, respectively. .
The average particle size was measured by the method described above. The viscosity was measured at 30 ° C. using a B-type viscometer (manufactured by BROOK FIELD).

-Evaluation criteria-
AA: The change rate of the average particle diameter of the pigment coated with the polymer before and after the change and the change rate of the viscosity were less than 1.
A: The change rate of the average particle diameter of the pigment coated with the polymer before and after aging was 1% or more and less than 2%, and the change rate of the viscosity was 1% or more and less than 6%.
B: The change rate of the average particle diameter of the pigment coated with the polymer before and after aging was 2% or more and less than 5%, and the change rate of the viscosity was 6% or more and less than 15%.
C: The change rate of the average particle diameter of the pigment coated with the polymer before and after the aging was 5% or more and less than 10%, and the change rate of the viscosity was 15% or more and less than 25%.
D: The change rate of the average particle diameter of the pigment coated with the polymer before and after the aging was 10% or more, and the change rate of the viscosity was less than 25%.

(Dischargeability)
The direction (main scanning direction) of the line head where the nozzles are aligned in the direction perpendicular to the moving direction (sub-scanning direction) of the stage that can move the GELJET GX5000 printer head manufactured by Ricoh Co., Ltd. in a predetermined linear direction at 500 mm / sec. Fixed together.
Next, the ink 1 was refilled in a storage tank connected thereto. As a recording medium, Fuji Photo Film Co., Ltd.'s painting photographic finish Pro was pasted on the stage.
Next, the stage is moved at 248 mm / min, and 96 lines are parallel to the transport direction at an ink droplet amount of 3.4 pL, a discharge frequency of 10 kHz, a nozzle arrangement direction × transport direction of 75 dpi × 1200 dpi (dots per inch). A print sample was prepared by discharging 2000 ink droplets per nozzle (one discharge hole).
The obtained print sample was visually observed to confirm that ink was ejected from all nozzles (ejection holes).
After the ink ejection, the head was left for 3 hours in an environment of 25 ° C. and 80% RH, a new recording medium was attached, and ink was ejected again under the same conditions to produce a print sample. .
The obtained print sample was visually observed, and the number of discharge failure nozzles after 2000 discharges was evaluated.
Evaluation of AD was given according to the number of undischarge nozzles (unit: this). At this time, if the number of undischarge nozzles is 10 or less, it is within a practical allowable range.

-Evaluation criteria-
A: The number of undischarge nozzles was 0-5.
B: The number of undischarge nozzles was 6-10.
C: The number of undischarge nozzles was 11-15.
D: The number of undischarge nozzles was 16 or more.

The acetylenic diol compounds and surfactants in Table 1 will be described below.
DYNOL607: Acetylene diol surfactant, Air Products DYNOL 604: Acetylene diol surfactant, Air Products SURFYNOL 465: Acetylene diol surfactant, Air Products SURFYNOL 82: Acetylene diol product surfactant Emulgen 109P: Polyoxyethylene lauryl ether surfactant, manufactured by Kao Corporation

The crosslinking agent in Table 1 will be described below.
DENACOL EX521: Trifunctional epoxy compound, Nagase ChemteX Corp. DENACOL EX321: Trifunctional epoxy compound, Nagase ChemteX Corp. DENACOL EX111: Monofunctional epoxy compound, Nagase ChemteX Corp. Chemite PZ-33: Trifunctional aziridine compound, manufactured by Nippon Shokubai Co., Ltd.

  From Table 1 above, it can be seen that the Examples are excellent in all of the dispersibility of the pigment dispersion, the storage stability, and the ejectability when used as an ink.

Claims (12)

A mixed liquid production process for producing a mixed liquid of a pigment, water, a polymer, and a compound having an acetylenic diol group of 5% by mass to 30% by mass with respect to the total mass of the pigment;
A reduction step of reducing the compound having an acetylenic diol group from the mixture obtained from the mixture production step to less than 5% by mass with respect to the total mass of the pigment;
The manufacturing method of the pigment dispersion containing this.   The method for producing a pigment dispersion according to claim 1, further comprising a step of crosslinking the polymer after the step of producing the mixed liquid.   The method for producing a pigment dispersion according to claim 1 or 2, wherein, in the mixed liquid production step, water, a polymer, and a compound having an acetylenic diol group are mixed, and then the pigment is mixed.   The method for producing a pigment dispersion according to any one of claims 1 to 3, wherein the compound having an acetylenic diol group has an HLB value of 6 to 16.   The polymer comprises a hydrophilic structural unit derived from at least one of carboxy group-containing monomers and a hydrophobic structural unit derived from at least one of (meth) acrylate having an aromatic ring group or a derivative thereof. The manufacturing method of the pigment dispersion of any one of Claims 1-4.   The carboxy group-containing monomer is (meth) acrylic acid, and the (meth) acrylate having an aromatic ring group is an alkyl (meth) acrylate having 1 to 20 carbon atoms, benzyl (meth) acrylate and phenoxyethyl ( The method for producing a pigment dispersion according to claim 5, which is at least one selected from (meth) acrylate.   The method for producing a pigment dispersion according to any one of claims 1 to 6, wherein the acid value of the polymer is 90 mgKOH / g to 150 mgKOH / g.   The method for producing a pigment dispersion according to any one of claims 1 to 7, further comprising a crosslinking agent having a bifunctional or higher functional epoxy group in the mixed solution.   The said reduction process is a manufacturing method of the pigment dispersion of any one of Claims 1-8 which reduces the compound which has acetylene diol group by ultrafiltration.   The method for producing a pigment dispersion according to claim 9, wherein the size of the fine pores of the filtration membrane used for the ultrafiltration is 0.2 µm or less.   The method for producing a pigment dispersion according to any one of claims 1 to 10, wherein the acid value of the polymer is 110 mg KOH / g to 150 mg KOH / g.   The method for producing a pigment dispersion according to any one of claims 1 to 11, wherein a pigment dispersion for inkjet recording is produced.