JP4126036B2 - Method for producing aqueous black pigment dispersion, aqueous black pigment dispersion obtained by the method, and aqueous black pigment ink composition containing the dispersion - Google Patents

Description

  The present invention relates to a method for producing an aqueous black pigment dispersion, an aqueous black pigment dispersion obtained by the method, and an aqueous black pigment ink composition containing the dispersion.

  Aqueous pigment dispersions have long been used as a base composition for coloring materials such as aqueous printing inks, and have basic performance characteristics that they have vivid color developability and high coloring power, and have good fluidity. It has been. Such an aqueous pigment dispersion is usually mixed and stirred for adding a pigment and a resin, and if necessary, a dispersant to an aqueous medium, and moistening the pigment and the resin to some extent before the kneading process. It is manufactured through a premix process that is a treatment and a kneading process that disperses the pigment to a state where the original coloring power can be obtained.

  Usually, in the premix process, a premix mixture is obtained using a device having a stirring blade such as a propeller type, paddle type, or turbine type or a non-media type device. In the kneading process, a bead mill, a ball mill, A media-type dispersion device such as an attritor is mainly used (for example, Patent Document 1).

  Especially in black pigment dispersions using carbon black, since carbon black is inherently hydrophobic, it is good during premix mixing and in the dough process even at high concentrations and high viscosities in the presence of oil-based resins and solvents. Maintains good fluidity and can be minced and dispersed. However, in aqueous systems, it is difficult to have good flowability at high concentration and high viscosity because it is hydrophobic, ensuring fluidity in terms of formulation such as selection of resins and dispersants, and manufacturing aspects. Then, in general, after mixing and stirring with a disper, the premix mixture is forcibly sent to a bead mill using a gear pump or the like to perform meat mixing.

  However, when a bead mill is used, the particle size distribution of the pigment of the paste is a broad shape that includes overdispersed and undispersed materials, because it is kneaded by contacting and grinding the beads and the pigment. Print quality may be inferior.

  In order to solve this problem, there is an attempt to use a high pressure dispersion device or a rotor / stator type high shear mixer.

As a dispersion technique using a high-pressure dispersion apparatus, there is a technique in which a dispersion medium, a pigment, and a water-insoluble polymer are mixed and then dispersed with a shear stress of 1.0 × 10 ⁵ Pa or more (Patent Document 2). In this case as well, the composition is sent using a high-pressure pump, and it is necessary to make the composition have a low viscosity, and it cannot be sufficiently kneaded at a concentration usually used in a base composition such as aqueous printing ink.

  In addition, in the rotor / stator type high shear mixer, when the aqueous carbon black dispersion is made into a high-concentration, high-viscosity ink composition, particularly structural viscosity occurs, even if the portion where shear stress is applied flows, Due to the structure, there is a problem that the ink composition stays in a portion where a force to be drawn into the work head is not applied or a portion where no shear stress is applied, thereby causing a manufacturing defect.

Japanese Patent Laid-Open No. 11-246813 JP 2002-249690 A

  In view of the problems of the prior art, the present invention improves the productivity after improving the fluidity of the pigment-containing processed product, and further creates a more uniform dispersion state of the pigment dispersion, thereby enabling printing. An object of the present invention is to provide a method for producing an aqueous black pigment dispersion capable of improving quality and the like.

That is, the present invention provides the following method for producing an aqueous black pigment dispersion, an aqueous pigment dispersion obtained by the method, and an aqueous black pigment ink composition containing the dispersion.
(1) The average primary particle diameter is 15 to 40 nm using a disperser that can apply shear stress to the mixture by passing through at least one pair of rotor and stator, or at least one pair of rotor and rotor gaps, And an aqueous black pigment dispersion characterized in that carbon black having a bulk density of 0.3 to 0.8 g / ml is dispersed in an aqueous medium in which an alkali-soluble resin is dissolved in the presence of an alkali. Method.
(2) The aqueous black pigment according to (1), wherein the alkali-soluble resin is at least one selected from the group consisting of a styrene-acrylic resin, a styrene-maleic acid resin, and an acrylic resin. A method for producing a dispersion.
(3) The mixture containing the carbon black, the alkali-soluble resin, and the aqueous medium is dispersed by the disperser until the coloring power of the aqueous black pigment dispersion becomes 95% or more (1) or ( The method for producing an aqueous black pigment dispersion according to item 2).
(4) The disperser is a disperser composed of at least one pair of rotor and stator, the rotor peripheral speed is 15 to 25 m / sec, and the rotor outer diameter / container inner diameter ratio is 0.1 or more. The manufacturing method of the aqueous black pigment dispersion in any one of said (1)-(3) term.
(5) An aqueous black pigment dispersion obtained by the method for producing an aqueous black pigment dispersion according to any one of (1) to (4).
(6) An aqueous black pigment ink composition comprising the aqueous black pigment dispersion described in (5) above.

  Next, how the above problems are solved by the present invention will be described.

  The present invention applies shear stress to a mixture by passing a mixture containing carbon black, an alkali-soluble resin and water through at least one pair of rotors and stators or at least one pair of rotors and rotors. The carbon black is dispersed in the aqueous medium by performing a dispersion treatment using a disperser that can be used.

  In the present invention, from the viewpoint of the fluidity of the processed product containing the pigment and the mechanism of the disperser, the productivity can be improved, and further, a uniform pigment dispersion state can be created, and the printing quality can be improved.

  First, it considers from a viewpoint of the fluidity | liquidity of the processed material containing a pigment. As black pigments, various carbon blacks for printing inks are used, but carbon black is essentially a representative of hydrophobic pigments. In aqueous compositions, wetting with resins, dispersibility, etc. are used with oiliness. Compared to the case, it is greatly inferior. In particular, when finely divided carbon black is dispersed, a change in fluidity, particularly structural viscosity, may be noticeable due to a sudden increase in surface area caused by carbon black being amorphous and porous. In addition to the selection of carbon black, it is also important to select the type of resin as the polymer dispersant. In order to ensure fluidity without causing structural viscosity, it is difficult to use water-dispersible resin. It is necessary to use a soluble resin. Thus, when carbon black is dispersed in an aqueous medium, selection of the type of carbon black and the type of resin is important.

  Next, the mechanism of the disperser will be considered. When carbon black is dispersed in an aqueous medium, a kneading process that creates a wet state between the carbon black and the resin to some extent by a stirring and mixing process, which is a pre-treatment before pre-mixed meat called premix, and then finely disperses the pigment. Meat processing methods are used.

The media-type dispersion device generally used in the kneading process is characterized by being able to apply high stress to the pigment and finely dispersing in a short time, but the stress is not uniform. Therefore, the resulting pigment dispersion has a wide particle size distribution, and there are many coarse particles that have not been dispersed and particles that are excessively dispersed, leading to a decrease in performance in the final composition. .
On the other hand, as other pigment dispersing devices, a high-pressure dispersion processing device that passes through narrow orifices and nozzles at high pressure and high speed, and uses collision and shear stress, and a type in which the processed material is transferred by rotation of the rotor, the rotor and stator There is known a high-speed shearing agitation apparatus that applies a high shearing stress to a processed material by passing through a gap with the like. In these dispersing apparatuses, the stress that can be applied to the pigment is uniform as compared with the media type dispersing apparatus, but it is generally difficult to apply a high stress. In addition, a high-pressure dispersion treatment apparatus can be used only for a low-viscosity treatment, while a high-speed shearing agitation device sucks the treatment by rotation of the rotor and guides it to a narrow gap. It is necessary that the fluidity of the is better.

  Therefore, as a water-based black pigment dispersion for use in printing inks, etc., there is a demand for a production method that can ensure fluidity even at high concentrations and high viscosity, has good dispersion efficiency, and does not broaden the molecular weight distribution of the pigment after dispersion. As a disperser that satisfies these requirements, attention was paid to a rotor / stator type high-speed shear stirrer.

  As a result of intensive studies on a pigment dispersion method that meets the above-mentioned purpose, the present inventors have selected carbon black and resin, which are pigments for preparing an aqueous black pigment dispersion, from specific ones. After mixing, the place where the media-type disperser that uses the media type disperser is taken can be finished in the same time as usual using the rotor / stator type disperser that was used for the premix in the prior art. I found out that I can do it. In this way, it was possible to realize the excellent operational effects by specifying the properties of the processed material by the particle size and bulk density of the carbon black and the disperser, more preferably the peripheral speed of the disperser and the outer diameter / container of the rotor. This is due to the specification of the inner diameter ratio.

  An aqueous black pigment dispersion capable of producing a pigment dispersion in a uniform dispersion state with high productivity and improving printing quality and the like can be produced.

  The method for producing the aqueous pigment dispersion of the present invention will be described in detail.

  The carbon black used in the present invention has an average primary particle diameter of 15 to 40 nm, preferably 18 to 35 nm, more preferably 20 to 30 nm, and a bulk density of 0.3 to 0.8 g / ml, preferably 0. .3 to 0.6 g / ml. When the average primary particle size is smaller than the above range, as the dispersion proceeds, the surface area increases greatly and the dispersion tends to be difficult. When the average primary particle diameter exceeds the above range, the resulting dispersion has poor coloring power and tends to be difficult to use. Further, when the bulk density is lower than the above range, the dispersion tends to be poor because the surface area increases rapidly as the dispersion proceeds. On the other hand, when the bulk density exceeds the above range, since long structures are granulated while being entangled with each other, dispersibility tends to be inferior.

  Examples of the alkali-soluble resin used in the present invention include vinyl resins containing an anionic group such as a carboxyl group, among which styrene-acrylic resins, styrene-maleic acid resins, and acrylic resins. At least one selected from is preferred. Here, the styrene-acrylic resin is at least one styrene monomer and at least one acrylic monomer, and the styrene-maleic resin is at least one styrene monomer and at least one. One maleic monomer and acrylic resin are copolymer resins having at least two acrylic monomers as copolymerization components.

  For example, acrylic monomers that can be used in vinyl resins containing such anionic groups include acrylic acid, methacrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, and propyl (meth) acrylate. , (Meth) acrylic acid alkyl ester compounds such as butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, benzyl (meth) acrylate, naphthyl (Meth) acrylic acid ester compounds containing an aromatic ring such as (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate (meth) Hydroxyalkyl ester compounds of acrylic acid, polypropylene glycol mono (meth) acrylate compound can be utilized. As the styrene monomer, styrene, α-methylstyrene, vinyltoluene and derivatives thereof can be used. Examples of maleic monomers include (anhydrous) maleic acid, and monomethyl maleate, monoethyl maleate, monopropyl maleate, monobutyl maleate, monohexyl maleate, monooctyl maleate, mono-2-ethylhexyl maleate Further, maleic acid monoalkyl esters such as monolauryl maleate and monostearyl maleate can be used, and dialkyl maleate compounds such as dimethyl maleate, diethyl maleate and dibutyl maleate can also be used. In addition, these copolymer resins may contain other copolymers such as (meth) acrylamide, crotonic acid and its ester compound, itaconic acid and its ester compound, citraconic acid and its ester compound, acrylonitrile, and olefin compound as necessary. A polymerizable monomer may be contained as a copolymerization component.

  Examples of the alkali (basic compound) for dissolving the anionic group-containing resin in an aqueous medium include inorganic basic compounds such as sodium hydroxide and potassium hydroxide, ammonia, methylamine, ethylamine, monoethanolamine, N Organic bases such as N-dimethylethanolamine, N, N-diethylethanolamine, N, N-dibutylethanolamine, diethanolamine, N-methyldiethanolamine, triethanolamine, morpholine, N-methylmorpholine, N-ethylmorpholine Compound. These can be used alone or in admixture of two or more.

  As the aqueous medium used in the present invention, water or a mixture of water and a water-miscible organic solvent can be used.

  Examples of the water-miscible organic solvent include lower alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol and n-propyl alcohol, polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol and glycerin, ethylene glycol Alkyl ethers of (poly) alkylene glycols such as monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monoacetate, propylene glycol monoacetate (Poly) alkylene glycol mono-fatty acid such as Such as ethers, and the like. These water-miscible organic solvents can be used alone or in combination of two or more.

  The amount of each material used in a mixture obtained by mixing the above materials (referred to as a mixture subjected to dispersion treatment in the present invention) is approximately 5 to 40 parts by mass of carbon black in 100 parts by mass of the mixture. Is more preferable, and more preferably about 10 to 30 parts by mass. Moreover, it is preferable that the usage-amount of resin is about 20-120 mass parts with respect to 100 mass parts of pigments, More preferably, it is about 30-80 mass parts.

  In the present invention, it is preferable to perform a premix treatment on a mixture obtained by adding and mixing the respective materials into the aqueous medium with the above composition. The premix treatment is preferably carried out by stirring and mixing until good fluidity is obtained using an apparatus having a stirring blade such as a propeller type, paddle type, or turbine type.

  In the present invention, the mixture that has undergone the premix treatment is subjected to a dispersion treatment (kneading treatment) using a high-speed shear stirrer. Here, the high-speed shear stirrer is a system for transferring fluid by rotation of the rotor, and a narrow gap (gap, usually about 0.1 to 1 mm) between the rotor and the outer wall or the inner wall, and / or It is a device that applies high shear stress to a fluid by passing through holes provided in a mesh shape or a lattice shape at a high speed.

  The high-speed shear stirring device used in the present invention includes at least a pair of high-speed rotating rotors and a stationary stator, or at least a pair of high-speed rotating rotors and a rotor that normally rotates in the opposite direction. An apparatus that can pass through the gap and apply high shear stress to the mixture is preferred. Among them, a high-speed shearing agitation apparatus having at least one pair of rotor and stator is preferable.

  Representative examples of such devices include, for example, high shear mixers BX, CX, DX, EX, FX, GX10, GX20, 700X, HX10, HX30, JX, KX (above Silverson), High Shear Mixer IKA2000 series (manufactured by IKA), T.K. K. Homomixer (made by Special Machine Industry Co., Ltd.), ultrahomomixer (made by Mizuho Industry Co., Ltd.), Claremix (made by M Technique Co., Ltd.), Cavitron (made by Taiheiyo Kiko Co., Ltd.) and the like. Of these, a high shear mixer having a rotor and a stator and a similar structure are particularly preferred.

  A high-speed shear stirring apparatus used in the present invention will be described with reference to the drawings. FIG. 1 is a schematic explanatory view showing one embodiment of a high-speed shear stirring apparatus, and FIG. 2 is a perspective view showing the main part thereof. The high-speed shear stirrer shown in FIGS. 1 and 2 is an example of a high shear mixer having a rotor and a stator. In this high shear mixer, the dispersion part 1 composed of a rotor and a stator is configured to be immersed in a mixture 11 subjected to a dispersion process accommodated in a container 10. The rotor 2 is attached to the rotating shaft 4 of the prime mover 3 and is configured to rotate at a high speed. Reference numeral 5 denotes a fixed stator, and the stator 5 is provided with a large number of holes 6. Reference numeral 12 denotes a support for supporting the dispersion unit 1. Due to the high speed rotation of the rotor 2 in the stator 5, the mixture 11 at the bottom of the container 10 is drawn into the dispersing portion 1. The mixture 11 drawn into the dispersion portion 1 is swung out in the direction of the stator 5 by the centrifugal force generated by the rotor, and at that time, is subjected to high shear stress in the gap between the blade portion of the rotor 2 and the inner wall of the stator. The mixture subjected to high shear stress at high speed is pushed out from the hole 6 provided in the stator 5. The mixture extruded to the outside of the dispersion part 1 circulates along the inner wall of the container 10, and at the same time, new materials are continuously supplied from the lower side of the dispersion part 1 and this operation is repeated.

  The rotational speed of the rotor depends on mechanical conditions such as the gap between the power unit and the rotor and the stator and the rotor diameter, as well as the viscosity of the material to be dispersed, the amount of input electric power, etc. It is preferable to select a type capable of rotating at a peripheral speed of 15 m / sec or more, and it is advantageous in that a higher shear stress can be applied as the peripheral speed of the rotor increases. In general, from the viewpoint of the efficiency of the pigment dispersion treatment, the treatment is preferably performed at a peripheral speed of about 15 to 25 m / sec. Furthermore, in order to make the mixture in the container easy to be uniformly dispersed as a whole, the ratio of the outer diameter / inner diameter of the rotor is preferably 0.1 or more in the relationship between the rotor and the container for storing the mixture. . When the ratio of the outer diameter of the rotor / the inner diameter of the container is smaller than the above range, a place where the circulation of the mixture is deteriorated occurs, and the pigment dispersion tends to decrease. The upper limit value of the ratio of the outer diameter of the rotor / the inner diameter of the container is not particularly limited. It is.

  The dispersion treatment (kneading process) performed using the high-speed shear stirring apparatus of the present invention is preferably carried out to almost the end point (a state where the dispersion has hardly progressed even if further dispersion treatment is performed) (high-speed shearing). The time to the end point varies depending on the processing capacity of the stirrer and the amount of dispersion. Usually, it is preferable to disperse (kneaded) until the resulting aqueous black pigment dispersion is 95% or more of the original coloring power.

  The aqueous black pigment dispersion obtained by the method of the present invention may further comprise various resins, aqueous media, anti-blocking agents, wetting agents, viscosity modifiers, pH adjusters, antifoaming agents, and general surface activity, depending on applications. Various additives such as an agent can be appropriately added and used in, for example, flexographic printing inks, water-based gravure inks, water-based paints, water-based ink jet inks, and the like.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these Examples. In addition, the use ratio of each material in Table 1 represents “mass%”.

<Preparation of aqueous resin varnish>
As a dispersant, 25 parts by mass of John Crill 67 (a styrene-acrylic acid copolymer resin manufactured by Johnson Polymer Co., Ltd., acid value of 213 mg KOH / g, mass average molecular weight of 12,500) is necessary to neutralize the total amount of the copolymer. It was dissolved by heating in 75 parts by mass of water containing an appropriate amount of a basic compound (monoethanolamine) to obtain an aqueous resin varnish 1 (John Crill 67 solid content concentration: 25% by mass).

Examples 1-4 and Comparative Examples 2-4
After mixing 25 parts by mass of the aqueous resin varnish 1, 2 parts by mass of isopropyl alcohol, 15 parts by mass of water, and 15 parts by mass of carbon black described in Table 1, the mixture was stirred for 5 minutes with a disper and premixed. Using the following high-speed shear stirrer, the time dispersion treatment (grinding treatment) shown in Table 1 was performed to obtain an aqueous black pigment dispersion. Subsequently, 35 parts by mass of the aqueous resin varnish 1 and 8 parts by mass of water were added to the aqueous black pigment dispersion to obtain 100 parts by mass of an aqueous black pigment ink composition.

  The viscosity of the mixture after the premix treatment and the viscosity of the resulting aqueous black pigment dispersion were measured using a Tokimec B-type viscometer (25 ° C., 60 rpm).

  The carbon blacks used were all manufactured by Mitsubishi Chemical Corporation, and their bulk density was measured by the following method.

<High-speed shear stirrer>
Model: High Shear Mixer EX type (Silverson)
Motor capacity: 4kw
Rotation speed: 3600rpm
Rotor peripheral speed: 19.14 m / sec
Tank inner diameter: 600mm
Rotor outer diameter: 101.16mm
Evaluation scale: 200kg

<Measurement of bulk density of carbon black>
The sample previously placed in the funnel was poured from a height of 3-5 cm into a 100 ml capacity pourless cylinder with a diameter of 28 ± 2 mm and a height of 180 ± 5 mm, and the weight of the filled carbon black was weighed. g Converted to weight.

Comparative Example 1
After mixing 25 parts by mass of the aqueous resin varnish 1, 2 parts by mass of isopropyl alcohol, 15 parts by mass of water, and 15 parts by mass of carbon black described in Table 1, the mixture was stirred with a disper for 5 minutes and premixed, Using the following media-type dispersion apparatus for meat paste, time dispersion treatment (grind meat treatment) shown in Table 1 was performed to obtain an aqueous black pigment dispersion. Subsequently, 35 parts by mass of the aqueous resin varnish 1 and 8 parts by mass of water were added to the aqueous black pigment dispersion to obtain 100 parts by mass of an aqueous black pigment ink composition.

<Mixed meat distribution device>
Model: Bead mill media diameter: 1.0mm
Vessel capacity: 15 liters Discharge rate: 100 kg / hr
The following items were evaluated for the aqueous black pigment ink compositions obtained in Examples 1 to 3 and Comparative Examples 1 to 3. In Comparative Example 4, premixing was performed with a disper, but no fluidity was obtained even after 60 minutes, and therefore no subsequent dispersion treatment or ink evaluation was performed. The results are shown in Table 1.

<Particle size distribution>
About the water-based black pigment ink composition obtained in Example 1 and Comparative Example 1, the particle size distribution was measured using a particle size distribution meter (MICROTRAC UPA: MODEL 9340, manufactured by UPA Nikkiso Co., Ltd.) by light scattering. The results are shown in FIG. 3 (Example 1) and FIG. 4 (Comparative Example 1).

  As is clear from the comparison between FIG. 3 and FIG. 4, in Example 1 in which dispersion was performed using a high shear mixer which is a non-media type disperser, the particle diameters are uniform, but a bead mill which is a media type disperser. In Comparative Example 1 in which the particles were dispersed using coarse particles, coarse particles were observed, and the particle size distribution was wide.

<Coloring power>
As a white aqueous pigment ink composition for evaluating coloring power, 30 parts by mass of titanium oxide and 6 parts by mass of aqueous resin varnish 1 were stirred and mixed, and then kneaded with a bead mill dispersing device, and then further aqueous resin varnish 1 and water. The white aqueous pigment ink composition was obtained by diluting so that the viscosity of the system was 0.5 Pa · s at a total of 64 parts by mass.

  Examples 1 to 3 and Comparative Examples 2 to 4 until 10 parts by weight of the aqueous black pigment ink composition of Comparative Example 1 were diluted with 100 parts by weight of the white aqueous pigment ink composition for evaluation of coloring power. The coloring power was evaluated by the amount (part by mass) of the white aqueous pigment ink composition required to dilute 10 parts of each aqueous black pigment ink composition.

  In addition, it determines with the coloring power being high that what needs dilution with more white water-based pigment ink compositions by the time it becomes the same color density.

<Glossy>
Apply the aqueous black pigment ink compositions obtained in Examples 1 to 3 and Comparative Examples 1 to 3 to a glossy K liner, and visually evaluate them. B and those with low gloss were evaluated as C. Of the evaluations, A to B are practically acceptable.

<Abrasion resistance>
A water-based black pigment ink composition dispersion obtained in Examples 1 to 3 and Comparative Examples 1 to 3 was applied to a K liner, and a Gakushin type friction resistance tester (manufactured by Daiei Chemical Seiki Seisakusho Co., Ltd.). The friction test is performed under the conditions of 500 g load and 500 times, and the addressed paper is A with no dirt and the printed matter is not scratched. The addressed paper is dirty but the printed matter is not damaged. Those with scratches were evaluated as C. Of the evaluations, A to B are practically acceptable.

<Fluidity>
The aqueous black pigment ink compositions obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated for viscosity stability from the ratio of the initial viscosity and the viscosity after storage at 40 ° C. for 7 days.
A: Viscosity ratio is 2.0 or less B: Viscosity ratio exceeds 2.0

<Sedimentation>
About the aqueous | water-based black pigment ink composition obtained in the said Examples 1-3 and Comparative Examples 1-3, sedimentation was visually evaluated from the state change after a 7-day preservation | save at 40 degreeC. In addition, it evaluated in two steps by making a thing without sedimentation (circle) and the thing with sedimentation x.

It is a schematic explanatory drawing which shows one Example of the high-speed shear stirring apparatus used with the manufacturing method of the aqueous | water-based black pigment dispersion of this invention. It is a principal part enlarged view of the high-speed shear stirring apparatus shown in FIG. It is a graph which shows the particle size distribution of the water-based black pigment ink composition obtained in Example 1 of this specification. It is a graph which shows the particle size distribution of the water-based black pigment ink composition obtained by the comparative example 1 of this specification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dispersing part 2 Rotor 3 Motor | power_engine 4 Rotating shaft 5 Stator 6 Hole 10 Container 11 Mixture

Claims (6)

Using a disperser capable of applying shear stress to the mixture by passing through at least one pair of rotor and stator, or at least one pair of rotor and rotor, the average primary particle size is 15 to 40 nm and the bulk density A method for producing an aqueous black pigment dispersion, comprising dispersing 0.3 to 0.8 g / ml of carbon black in an aqueous medium in which an alkali-soluble resin is dissolved in the presence of an alkali. 2. The method for producing an aqueous black pigment dispersion according to claim 1, wherein the alkali-soluble resin is at least one selected from the group consisting of a styrene-acrylic resin, a styrene-maleic resin, and an acrylic resin. . The aqueous solution according to claim 1 or 2, wherein the mixture containing the carbon black, the alkali-soluble resin, and the aqueous medium is dispersed by the disperser until the coloring power of the aqueous black pigment dispersion becomes 95% or more. A method for producing a black pigment dispersion. The disperser is a disperser including at least one pair of a rotor and a stator, and the peripheral speed of the rotor is 15 to 25 m / sec, and the ratio of the outer diameter / container inner diameter of the rotor is 0.1 or more. The manufacturing method of the aqueous black pigment dispersion in any one of -3. An aqueous black pigment dispersion obtained by the method for producing an aqueous black pigment dispersion according to claim 1. An aqueous black pigment ink composition comprising the aqueous black pigment dispersion according to claim 5.

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