JP6291243B2 - Method for producing aqueous pigment dispersion - Google Patents

Description

  The present invention relates to a method for producing an aqueous pigment dispersion, and more particularly to a method for producing an aqueous pigment dispersion that can be suitably used in an aqueous ink for inkjet recording.

  The ink jet recording method is a recording method in which ink droplets are directly ejected from a very fine nozzle and adhered to a recording member to obtain characters and images, and is generally widely used.

  Patent Document 1 includes an emulsion composition and a pigment containing a water-insoluble polymer having a salt-forming group, an organic solvent having a solubility in 100 parts by weight of water of 5 to 40 parts by weight at 20 ° C., a neutralizing agent, and water. The mixture was obtained under the condition that the non-volatile component ratio was 15 to 50% by weight and the weight ratio of the organic solvent to water (the weight of the organic solvent / the weight of water) was 0.1 to 0.9. A method for producing an aqueous pigment dispersion in which the organic solvent is removed after dispersing the mixture is described.

  In Patent Document 2, as a method for producing a pigment-based ink, for example, a mixture containing a pigment, a water-insoluble polymer having a salt-forming group, an organic solvent and water is preliminarily dispersed with a stirrer and then dispersed with a high-pressure homogenizer. A method for producing a pigment dispersion for inkjet recording, which includes a step of pre-dispersing the mixture with a specific integrated power value, is described.

JP 2005-188775 A JP 2005-194322 A

The methods of Patent Documents 1 and 2 have problems that sufficient processing efficiency cannot be obtained in the preliminary dispersion, or the storage stability of the obtained dispersion is not always sufficient.
An object of the present invention is to provide a method for producing a water-based pigment dispersion, which shortens the production time by increasing the treatment efficiency of the preliminary dispersion step and is excellent in the storage stability of the obtained pigment dispersion.

That is, the present invention is a method for producing an aqueous pigment dispersion, which includes the following steps (1) and (2).
Step (1): A mixture containing a salt-forming group-containing polymer, an organic solvent having a solubility in 100 parts by mass of water of 50 parts by mass or less at 20 ° C., water and a pigment is dispersed in a phase-separated state. Step for obtaining a dispersion Step (2): Step for dispersing the dispersion obtained in step (1) in a homogeneous phase in which the organic solvent and water are not phase-separated.

  ADVANTAGE OF THE INVENTION According to this invention, while improving the process efficiency of a preliminary dispersion process, while shortening manufacturing time, the manufacturing method of the aqueous pigment dispersion excellent in the storage stability of the obtained pigment dispersion can be provided.

The method for producing an aqueous pigment dispersion of the present invention includes the following step (1) (preliminary dispersion) and step (2) (main dispersion).
Step (1): A mixture containing a salt-forming group-containing polymer, an organic solvent having a solubility in 100 parts by mass of water of 50 parts by mass or less at 20 ° C., water and a pigment is dispersed in a phase-separated state. Step for obtaining a dispersion Step (2): Step for dispersing the dispersion obtained in step (1) in a homogeneous phase in which the organic solvent and water are not phase-separated According to the method for producing an aqueous pigment dispersion of the present invention For example, the reason why it is possible to provide a method for producing a water-based pigment dispersion that improves the processing efficiency of the preliminary dispersion step of step (1) and is excellent in storage stability of the resulting pigment dispersion is not clear, but is as follows. Can be estimated as follows.

  In step (1), the organic solvent and water are dispersed in a phase-separated state, whereby the wettability of the organic solvent of the pigment can be increased, the cohesive energy can be reduced, and the coarse particles can be reduced. Therefore, since the content of coarse particles in the obtained dispersion can be reduced, the treatment time of the step (1) can be shortened, and further, the treatment by the disperser can be effectively performed during the dispersion of the step (2). it can. The amount of coarse particles contained in the dispersion can be evaluated by filterability. Furthermore, in the step (2), it is considered that the organic solvent and water are dispersed in a uniform phase that does not phase-separate, whereby the polymer having a salt-forming group is easily adsorbed to the pigment, and high storage stability is obtained. It is done.

[Step (1)]
In the step (1), a mixture containing a polymer having a salt-forming group, an organic solvent having a solubility in 100 parts by mass of water of 50 parts by mass or less at 20 ° C., water and a pigment is dispersed in a phase-separated state. To obtain a dispersion. In this step, it is preferable that a neutralizing agent is contained in the mixture from the viewpoint of dispersion stability.
Hereinafter, each component used at this process and the process conditions of the said process are demonstrated in detail.

(Polymer having salt-forming group)
A polymer having a salt-forming group (hereinafter also referred to as “polymer A”) is used because of its high adsorptivity to the pigment surface and high dispersion stability in an aqueous pigment dispersion.
The polymer A is preferably a water-insoluble polymer having a salt-forming group from the viewpoint of enhancing the dispersibility of the pigment and enhancing the particle size stability during storage.
Examples of the polymer A include vinyl polymers, polyester polymers, polyurethane polymers, and the like. Of these, vinyl polymers are preferred.

[Vinyl polymer]
As the vinyl polymer, for example, a vinyl polymer obtained by polymerizing a monomer mixture containing a salt-forming group-containing monomer, a hydrophobic monomer, a macromer, a nonionic hydrophilic monomer, and the like (hereinafter simply referred to as a monomer mixture). Polymers.

<Salt-forming monomer>
Examples of the salt-forming group-containing monomer include an anionic monomer and a cationic monomer, and an anionic monomer is preferable. Examples of anionic monomers include unsaturated carboxylic acid monomers, unsaturated sulfonic acid monomers, unsaturated phosphoric acid monomers, and the like.
Examples of the unsaturated carboxylic acid monomer include (meth) acrylic acid, styrene carboxylic acid, maleic acid monomer (one or more selected from maleic anhydride, maleic acid, maleic acid monoester and maleic acid monoamide), itacon An acid etc. are mentioned, These can be used individually or in mixture of 2 or more types, respectively.
In the present specification, “(meth) acryl” means at least one selected from “acryl” and “methacryl”.

As the unsaturated sulfonic acid monomer, for example, 2- (meth) acryloyloxyethanesulfonic acid, 2- (meth) acryloyloxypropanesulfonic acid, 2- (meth) acrylamido-2-alkyl (the carbon number of the alkyl group is preferable) 1 to 4) Propanesulfonic acid, vinylsulfonic acid, styrenesulfonic acid and the like can be mentioned, and these can be used alone or in admixture of two or more.
Examples of unsaturated phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acrylic acid. Examples include leuoxyethyl phosphate and dibutyl-2-methacryloyloxyethyl phosphate, and these can be used alone or in admixture of two or more.

  Among the anionic monomers, from the viewpoint of enhancing the dispersibility of the pigment and increasing the particle size stability during storage, the unsaturated carboxylic acid monomer is preferable, acrylic acid or methacrylic acid is more preferable, and methacrylic acid is further preferable. It is an acid.

  Examples of the cationic monomer include unsaturated tertiary amine-containing monomers such as N, N-dimethylaminoethyl (meth) acrylate and vinyl pyrrolidone, and non-standard such as N, N-dimethylaminoethyl (meth) acrylate quaternized product. And saturated ammonium salt-containing monomers. These can be used alone or in admixture of two or more.

  The content of the salt-forming group-containing monomer in the monomer mixture is preferably 1% by mass or more, more preferably 3% by mass from the viewpoint of enhancing the dispersion stability of the resulting aqueous pigment dispersion and enhancing the particle size stability during storage. % Or more, more preferably 8% by mass or more, preferably 50% by mass or less, more preferably 30% by mass or less, and still more preferably 15% by mass or less.

<Hydrophobic monomer>
Hydrophobic monomers improve water resistance, scratch resistance, printing density of the resulting aqueous pigment dispersion, dispersion stability of the resulting aqueous pigment dispersion, and improve particle size stability during storage. Used for.
Examples of the hydrophobic monomer include hydrocarbon groups having 1 to 18 carbon atoms such as octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, and benzyl (meth) acrylate. (Meth) acrylates having aromatic ring-containing monomers such as styrene, α-methylstyrene, vinyltoluene, and vinylnaphthalene. These may be used alone or in admixture of two or more.

  The content of the hydrophobic monomer in the monomer mixture is preferably 5% from the viewpoint of enhancing the water resistance, scratch resistance, printing density and dispersion stability of the resulting aqueous pigment dispersion, and improving the particle size stability during storage. % Or more, more preferably 10% by mass or more, still more preferably 30% by mass or more, and preferably 93% by mass or less, more preferably 80% by mass or less, still more preferably 60% by mass or less.

<Macromer>
As the macromer, it is used from the viewpoint of suppressing the burning of the heater surface, increasing the dispersion stability, and the particle size stability at the time of storage, for example, a styrene-based macromer, a silicone macromer, and the like. Or a mixture of two or more.
Examples of the styrenic macromer include a styrene homopolymer having a polymerizable functional group at one end or a copolymer of styrene and another monomer.
The number average molecular weight of the macromer is preferably 500 or more, more preferably 1,000 or more, and preferably 100,000 or less, more preferably 10,000 or less. The number average molecular weight of the macromer is measured using polystyrene as a standard substance by gel permeation chromatography using 1 millimol / L dodecylmethylamine-containing chloroform as a solvent.

  The content of the macromer in the monomer mixture is preferably from the viewpoint of suppressing the scorching of the heater surface and the dispersion stability in the bubble jet (registered trademark) type inkjet printer, and from the viewpoint of increasing the particle size stability during storage. 0% by mass or more, more preferably 1% by mass or more, further preferably 5% by mass or more, still more preferably 8% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass or less, Preferably it is 15 mass% or less.

<Nonionic hydrophilic monomer>
The nonionic hydrophilic monomer is used from the viewpoints of ejection stability and printing density, and examples thereof include polyoxyalkylene glycol mono (meth) acrylate having a polyoxyalkylene group as a structural unit. Among these, polyoxyalkylene glycol monomethacrylate is preferable.
The average added mole number of oxyalkylene in the polyoxyalkylene group is preferably 1 or more, more preferably 6 or more, still more preferably 10 or more, and preferably 30 or less, more preferably 25 or less, still more preferably 20 It is as follows.
The oxyalkylene group is preferably at least one selected from an oxyethylene group and an oxypropylene group.
Examples of the terminal of the polyoxyalkylene group include an aliphatic hydrocarbon group having 1 to 20 carbon atoms such as a hydrogen atom, a methyl group, a hexyl group and a lauryl group, and an aryl group having 6 to 10 carbon atoms such as a phenyl group. It is done.

  The content of the nonionic hydrophilic monomer in the monomer mixture is preferably 0% by mass or more, more preferably 5% by mass or more, and still more preferably 10% by mass or more, from the viewpoint of improving ejection stability and printing density. Preferably, it is 60 mass% or less, More preferably, it is 40 mass% or less, More preferably, it is 30 mass% or less.

(Method for producing polymer having salt-forming group)
Polymer A can be easily prepared by polymerizing a monomer mixture by a polymerization method such as a solution polymerization method using an organic solvent such as methyl ethyl ketone in the presence of a polymerization initiator such as a radical polymerization initiator. it can.

  The weight average molecular weight of the polymer A is preferably 3,000 or more from the viewpoint of improving the storage stability and ejection property of the aqueous pigment dispersion, preventing the printer head from being burnt, and durability of the printed matter after printing. Preferably it is 4,000 or more, More preferably, it is 10,000 or more, Preferably it is 300,000 or less, More preferably, it is 200,000 or less, More preferably, it is 100,000 or less.

In addition, the polymer A has a salt forming group. The salt-forming group can be introduced into the polymer A by polymerizing a monomer mixture containing a salt-forming group-containing monomer. Moreover, it is preferable that the salt formation group which the polymer A has is neutralized with the neutralizing agent.
The solubility of the water-insoluble polymer in water at 25 ° C. is preferably 10% by mass or less after neutralization with a desired degree of neutralization from the viewpoint of dissolving or uniformly dispersing the water-insoluble polymer in an organic solvent. More preferably, it is 5 mass% or less, More preferably, it is 1 mass% or less.

(Neutralizer)
As the neutralizing agent, an acid or a base can be used depending on the type of the salt-forming group. When the salt-forming group monomer is an anionic monomer, a base is preferably used. Examples of the acid include inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as acetic acid, propionic acid, lactic acid, succinic acid, glycolic acid, gluconic acid, glyceric acid, and polyethylene glycolic acid. Examples of the base include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and ammonia and tertiary amines such as trimethylamine and triethylamine. Among these, Preferably it is alkali metal hydroxide or ammonia, More preferably, it is combined use of an alkali metal hydroxide and ammonia, More preferably, it is combined use of sodium hydroxide and ammonia. The amount of alkali metal hydroxide relative to ammonia (mass of alkali metal hydroxide / mass of ammonia) is preferably 30/70 to 80/20, more preferably 40/60 to 70/30.
Although there is no particular limitation on the degree of neutralization, it is usually preferable to adjust the aqueous pigment dispersion so that the liquidity is neutral, for example, the pH is 4.5-10.

(Organic solvent)
The organic solvent used in the present invention is 100 parts by mass of water from the viewpoint of dispersion in a state of being phase-separated with water in the step (1), from the viewpoint of reducing coarse particles and increasing the filtration rate, and enhancing storage stability. Is 20 parts by mass or less at 20 ° C.
From the above viewpoint, the solubility of the organic solvent in 100 parts by mass of water is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 20 parts by mass or more, and preferably 45 at 20 ° C. It is not more than part by mass, more preferably not more than 40 parts by mass, more preferably not more than 30 parts by mass.

Examples of the organic solvent include ketone solvents, ether solvents, alcohol solvents, aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, halogenated aliphatic hydrocarbon solvents, and the like.
Examples of the ketone solvent include methyl ethyl ketone (amount dissolved in water at 20 ° C .: 29 parts by mass (100 parts by mass with respect to water)).
Examples of the alcohol solvent include 1-butanol (dissolved in water at 20 ° C .: 6.3 parts by mass (100 parts by mass of water)), 2-butanol (dissolved in water at 20 ° C .: 12. 5 parts by mass (100 parts by mass with respect to water)) and the like. These organic solvents can be used alone or in admixture of two or more.
Among these organic solvents, methyl ethyl ketone is preferred in view of safety and operability when removing the solvent in the post-treatment.

(Pigment)
As the pigment, either an organic pigment or an inorganic pigment can be used.
Examples of the organic pigment include azo pigments, disazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.

  More specific examples of the organic pigment include C.I. I. Pigment yellow 13, 74, 83, 109, 110, 128, 151, C.I. I. Pigment red 48, 57, 122, 184, 188, C.I. I. Pigment violet 19, C.I. I. Pigment Blue 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, C.I. I. Pigment green 7, 36, and the like.

Examples of inorganic pigments include carbon black, extender pigments, metal oxides, metal sulfides, and metal chlorides. Among these, when the aqueous pigment dispersion of the present invention is used for black aqueous ink, carbon black is preferable. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
Examples of extender pigments include silica, calcium carbonate, and talc.

In the step (1), a mixture containing a polymer having a salt-forming group, an organic solvent having a solubility in 100 parts by mass of water of 50 parts by mass or less at 20 ° C., water and a pigment (hereinafter also simply referred to as “mixture”) An organic solvent and water are dispersed in a phase-separated state to obtain a dispersion.
“In a phase-separated state” means that the organic solvent / water is in a phase-separated state and the organic solvent / water mixture mass ratio and temperature conditions. The method for determining whether the step (1) is in the phase separation state is based on the method described in the examples.

  In the step (1), the mass ratio of the organic solvent to water (the mass of the organic solvent / the mass of water: the value at the time of dispersion of the mixture) is in a phase separation state at the temperature of the dispersion treatment in the step (1). Although it is appropriately selected according to the type and temperature of the organic solvent, it is preferably at least 0.19, more preferably at least 0.20, even more preferably at least 0.25, even more preferably at least 0.3, , Preferably 1 or less, more preferably 0.8 or less, still more preferably 0.6 or less, even more preferably 0.5 or less, and still more preferably 0.4 or less.

In the mixture, the content of the polymer is preferably 1% by mass or more, more preferably from the viewpoint of dispersing the pigment, increasing the dispersion stability of the resulting aqueous pigment dispersion, and increasing the particle size stability during storage. 3% by mass or more, more preferably 5% by mass or more, still more preferably 7% by mass or more, and from the same viewpoint, preferably 25% by mass or less, more preferably 20% by mass or less, and further preferably 15% by mass. % Or less, still more preferably 10% by mass or less.
In the mixture, the content of the organic solvent is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 15% by mass from the viewpoint of increasing the wettability of the pigment and shortening the time of the step (1). From the viewpoint of phase separation, it is preferably 50% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, and still more preferably 25% by mass or less.
In the mixture, the content of water is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more from the viewpoint of phase separation, and from the same viewpoint, preferably 80%. It is 70 mass% or less, More preferably, it is 60 mass% or less more preferably 70 mass% or less.
In the mixture, the content of the pigment is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 7% by mass or more, and still more preferably 10% by mass or more, from the viewpoint of dispersing the pigment. Further, from the viewpoint of reducing coarse particles and shortening the time of step (1), it is preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less, and even more preferably 15% by mass. It is as follows.
The amount of the pigment relative to the polymer A (pigment / polymer) is preferably 0.5 or more, more preferably 1 or more, still more preferably 1.5 or more, from the viewpoint of increasing the dispersion efficiency of the pigment. From the viewpoint of enhancing the dispersion stability of the pigment dispersion and enhancing the particle size stability during storage, it is preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less.
The amount of the neutralizing agent is preferably 1 part by mass or more, more preferably 100 parts by mass with respect to 100 parts by mass of the polymer, from the viewpoint of increasing the dispersion stability of the resulting aqueous pigment dispersion and increasing the particle size stability during storage. Is 2 parts by mass or more, more preferably 4 parts by mass or more, and from the same viewpoint, it is preferably 30 parts by mass or less, more preferably 15 parts by mass or less, still more preferably 10 parts by mass or less.

From the viewpoint of uniformly dispersing the pigment in the emulsion composition, the mixing order of the mixture in step (1) is preferably a polymer having a salt-forming group and an organic compound having a solubility in 100 parts by mass of water of 50 parts by mass or less at 20 ° C. It is preferable to prepare an emulsified composition containing a solvent, water, and optionally a neutralizing agent, and mix the emulsified composition and the pigment to obtain a mixture.
The amount of the polymer, organic solvent, and water in the emulsified composition is adjusted so that the mixture obtained in consideration of the amount of the pigment to be mixed has the above amount.

  For dispersion in the step (1), a commonly used stirring type disperser such as an anchor blade can be used. Among the agitating type dispersers, Ultra Disper (trade name, manufactured by Asada Tekko Co., Ltd.), Ebara Milder (trade name, manufactured by Ebara Seisakusho Co., Ltd.), TK homomixer, TK pipeline mixer, TK homo jetter, TK Homomic line flow, fill mix [trade name, made by Tokushu Kika Kogyo Co., Ltd.], clear mix [made by M Technique Co., Ltd., trade name], KD mill (made by Kinetic Dispersion Co., Ltd., trade name) A high-speed stirring and mixing apparatus such as

The temperature of the dispersion treatment in the step (1) is preferably 0 ° C. or higher, more preferably 5 ° C. or higher, further preferably 10 ° C. or higher, from the viewpoint of reaching the phase separation state, reducing coarse particles, and increasing the filtration rate. From the viewpoint of achieving a phase separation state, it is preferably 80 ° C. or less, more preferably 60 ° C. or less, still more preferably 50 ° C. or less, and even more preferably 20 ° C. or more, still more preferably 25 ° C. or more. Is 40 ° C. or lower.
Among these, from the viewpoint of adjusting the phase separation in step (1) and the homogeneous phase in step (2) by temperature, the temperature in step (1) is preferably 20 ° C. or higher, more preferably 25 ° C. or higher. Moreover, it is preferably 60 ° C. or lower, more preferably 50 ° C. or lower, and further preferably 40 ° C. or lower.
The end point of the step (1) can be set when the coarse particles are reduced and the flow rate reaches 40 g in the method described in the examples. In addition, when a process (2) is performed with many coarse particles contained, it may cause clogging of the disperser used in the process (2), and therefore a great deal of time is required for the process (2).
At the end of step (1), the volume average median particle diameter (D ₅₀ ) of the pigment is preferably 200 nm or more, more preferably 220 nm or more, and preferably 400 nm or less, from the viewpoint of reducing coarse particles. More preferably, it is 300 nm or less.

[Step (2)]
In step (2), the dispersion obtained in step (1) is dispersed in a uniform phase in which the organic solvent and water are not phase-separated.
“In a homogeneous phase without phase separation” means an organic solvent / water mixture mass ratio and a temperature condition in which the organic solvent and water become a homogeneous phase. The method for determining whether the step (2) is a homogeneous phase is based on the method described in the examples.
In the step (2), in order to promote the adsorption of the polymer A to the pigment, it is dispersed in a uniform phase. This increases the particle size stability during storage.
Examples of a method for making the dispersion obtained in step (1) into a homogeneous phase include a method (2a) for adjusting the temperature, and a mass ratio of the organic solvent to water (mass of organic solvent / mass of water). The method (2b) is mentioned, and the method (2a) for adjusting the temperature is preferable from the viewpoint of productivity.
Specific examples of the method (2b) include a method of reducing the mass ratio of the organic solvent to water (the mass of the organic solvent / the mass of water) by removing the organic solvent or adding water. It is done.

The temperature of the step (2) is preferably 0 ° C. or higher, more preferably 5 ° C. or higher, still more preferably 10 ° C. or higher, and preferably 80 ° C. or lower, more preferably 60 ° C., from the viewpoint of obtaining a homogeneous phase. Hereinafter, it is more preferably 50 ° C. or less, and still more preferably 40 ° C. or less.
Among these, the temperature of the step (2) is preferably 40 ° C. or less from the viewpoint of adjusting the phase separation of the step (1) and the homogeneous phase of the step (2) by the temperature (the above method (2a)). Preferably it is 30 degrees C or less, More preferably, it is 25 degrees C or less, More preferably, it is 20 degrees C or less.
Moreover, the difference of the temperature of the process (2) with respect to the temperature of the process (1) (the temperature of the process (1) −the temperature of the process (2)) is uniform between the phase separation of the process (1) and the uniform of the process (2). From the viewpoint of adjusting the phase (the above method (2a)), it is preferably 5 ° C or higher, more preferably 7 ° C or higher, still more preferably 10 ° C or higher, and preferably 40 ° C or lower, more preferably 30 ° C. Hereinafter, it is more preferably 20 ° C. or lower.

  In step (2), in order to reduce the average particle diameter of the pigment, it is preferable to further disperse the dispersion obtained in step (1) by applying a shear stress. It is preferable that atomization is performed until the pigment has a desired particle size by the dispersion.

  Examples of the disperser used in the dispersion in the step (2) include, for example, a kneader such as a roll mill, a kneader, and an extruder, a high-pressure homogenizer [manufactured by Izumi Food Machinery Co., Ltd., trade name], Minilab 8.3H type [manufactured by Rannie, Product name] homovalve type high pressure homogenizer, microfluidizer (trade name, manufactured by Microfluidics), Nanomizer (product name, manufactured by Nanomizer Co., Ltd.), optimizer (product name, manufactured by Sugino Machine Co., Ltd.) In addition, chamber type high-pressure homogenizers such as Genus PY [product name, manufactured by Hakusui Chemical Co., Ltd.], DeBEE2000 [product name, manufactured by Nippon EE Co., Ltd.], and the like are exemplified, but the present invention is limited to such examples only. It is not something. Among these, a high-pressure homogenizer is preferable from the viewpoint of reducing the particle size of the pigment contained in the mixture.

[Water-based pigment dispersion]
In the aqueous pigment dispersion obtained by the production method of the present invention, the volume average median particle diameter (D ₅₀ ) of the pigment is preferably 10 nm or more, more preferably 30 nm or more, still more preferably 60 nm, from the viewpoint of dispersion stability. As described above, it is more preferably 80 nm or more, preferably 170 nm or less, more preferably 150 nm or less.

As described above, an aqueous pigment dispersion is obtained through the steps (1) and (2). The organic solvent contained in the aqueous pigment dispersion can be removed by a general solvent removal method such as distillation under reduced pressure.
The aqueous pigment dispersion obtained by the production method of the present invention can be suitably used for an aqueous ink for inkjet recording. The content (solid content) of the aqueous pigment dispersion in the aqueous ink for inkjet recording is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 20% by mass from the viewpoint of maintaining ink performance. Hereinafter, it is more preferably 15% by mass.
The water content in the aqueous ink for inkjet recording is preferably 40% by mass or more, more preferably 50% by mass or more, and preferably 95% by mass or less, more preferably 85% by mass, from the viewpoint of maintaining ink performance. % Or less.
The water-based ink for ink jet recording may contain additives such as a wetting agent, a dispersing agent, an antifoaming agent, a chelating agent, and an antifungal agent, if necessary.

  In this example, measurement and evaluation were performed by the following methods.

(1) Molecular weight measurement The weight average molecular weight of the polymer was measured by the following method.
Gel chromatography method Apparatus: GPC apparatus (HLC-8220GPC) manufactured by Tosoh Corporation
Eluent: N, N-dimethylformamide containing 60 mmol / L phosphoric acid and 50 mmol / L lithium bromide Column: Tosoh Corporation column (TSK-GEL, α-M × 2)
Flow rate: 1 mL / min
Column temperature: 240 ° C
Reference material: Polystyrene

(2) Measurement of liquid flow rate of pre-dispersion (dispersion of step (1)) The obtained pre-dispersion is filled with 300 g in a container attached to the bottom with a 200 mesh wire net (area 2 cm ² ) at normal pressure and room temperature. Then, the plate was left still until the wire mesh closed and no liquid passed. The liquid that passed through was collected, and the mass was measured to determine the liquid passing volume. In addition, from the viewpoint of evaluating the processing efficiency, the end point of the step (1) was when the liquid flow amount reached 40 g.

(3) Phase state Only the organic solvent and ion-exchanged water are mixed at a charging ratio in each step so that the total amount becomes 10 g. After stirring and mixing at the dispersion treatment temperature for 10 minutes, the phase state is visually observed under normal pressure. Then, it was determined whether the phases were separated or a uniform one-phase state.

(4) Method for Measuring Particle Size of Dispersion Using a laser particle analysis system ELS-8000 (20 ° C.) manufactured by Otsuka Electronics Co., Ltd., the volume average median particle size (D ₅₀ ) of the pigment dispersion after the high-pressure homogenizer treatment. ) Was measured.

(5) Particle size increase rate after 1 day storage After completion of step (2), the particle size after 1 day storage at 20 ° C. is measured by the above method, and the increase rate from the particle size immediately after dispersion is calculated. did.

Production Example 1 (Preparation of polymer A)
In a reaction vessel, 20 parts by mass of methyl ethyl ketone and 0.03 part by mass of a polymerization chain transfer agent (2-mercaptoethanol) are added. As monomers, benzyl methacrylate, methacrylic acid, styrene macromer [trade name: AS -6S, number average molecular weight: 6000, polymerizable functional group: methacryloyloxy group], polypropylene glycol monomethacrylate [addition of 12 moles of ethylene oxide, manufactured by NOF Corporation, trade name: Blenmer PP-800], phenoxy polyethylene glycol polypropylene glycol Table 1 shows monomethacrylate [6 mol addition of ethylene oxide, 6 mol addition of propylene oxide, terminal: phenyl group, manufactured by NOF Corporation, trade name: BLEMMER 43PAPE-600B], and styrene monomer. By 10% by weight of the amount indicated, mixed put total of 10 parts by weight, to obtain a mixed solution, take sufficient nitrogen gas replacement.
On the other hand, the remaining 90% by mass of each monomer (total 90 parts by mass) was charged into the dropping funnel, 0.27 parts by mass of the polymerization chain transfer agent 2-mercaptoethanol, 60 parts by mass of methyl ethyl ketone and 2,2′-. 1.2 parts by mass of azobis (2,4-dimethylvaleronitrile) was added and mixed, and sufficiently substituted with nitrogen gas to obtain a mixed solution.
Under a nitrogen atmosphere, the mixed solution in the reaction vessel was heated to 65 ° C. while stirring, and the mixed solution in the dropping funnel was gradually dropped over 3 hours. After 2 hours at 65 ° C. from the end of dropping, a solution in which 0.3 part by weight of 2,2′-azobis (2,4-dimethylvaleronitrile) was dissolved in 5 parts by weight of methyl ethyl ketone was added, and further at 65 ° C. for 2 hours. After aging at 70 ° C. for 2 hours, the solvent was removed to obtain a solid content of polymer A. The weight average molecular weight of the obtained polymer A was 55,000.

Example 1
107.7 g (7.3 mass%) of Polymer A of Production Example 1 was dissolved in 301.9 g (20.5 mass%) of methyl ethyl ketone, and 20.1 g (1.4 mass%) of 5N sodium hydroxide aqueous solution and ions The emulsion composition was obtained by adding 832.7 g (56.4% by mass) of exchange water and 13.2 g (0.8% by mass) of 25% aqueous ammonia solution.
Then, 200 g (13.6 mass%) of a yellow pigment (Fast Yellow 74, manufactured by Dainichi Seika Kogyo Co., Ltd., trade name: FY840) was added and mixed with a disper blade at 25 ° C. for 1 hour to obtain a preliminary dispersion ( Step (1)). In addition, the value of the mass% in the parenthesis is the composition ratio of the preliminary dispersion raw material.
Dispersion was terminated at the point where the liquid flow rate reached 40 g. The pre-dispersion time was 5.3 h.
Next, 1000 g of the preliminary dispersion was subjected to a dispersion process by a 10-pass continuous system at a pressure of 150 MPa using a microfluidizer (manufactured by Microfluidics, high-pressure homogenizer, trade name) (step (2)). The treatment temperature at this time was 15 ° C. It was 144 nm when the particle size was measured with a particle size measuring instrument (ELS-6100) manufactured by Otsuka Electronics Co., Ltd. Moreover, the particle size increase rate when stored for 1 day at the treatment temperature was 2%.
Furthermore, the capacity | capacitance which removed methyl ethyl ketone using the warm water heating medium under pressure reduction, removed some water, and attached the filter (acetylcellulose membrane, outer diameter: 2.5cm, Fujifilm Corporation) of 5 micrometers. By filtering with a 25 mL needleless syringe (manufactured by Terumo Corporation) and removing coarse particles, an aqueous pigment dispersion having a solid content concentration of 20% was obtained.

(Example 2)
In Example 1, a water-based pigment dispersion was obtained in the same manner as in Example 1 except that the temperature in step (1) was changed to 35 ° C.

(Comparative Example 1)
In Example 1, a water-based pigment dispersion was obtained in the same manner as in Example 1 except that the temperature in step (1) was changed to 15 ° C.

(Comparative Example 2)
In Example 2, an aqueous pigment dispersion was obtained in the same manner as in Example 2 except that the amount of methyl ethyl ketone was changed to 105.9 g and ion-exchanged water was changed to 1029 g.

(Comparative Example 3)
An aqueous pigment dispersion was obtained in the same manner as in Example 2 except that methyl ethyl ketone was changed to acetone in Example 2.

(Comparative Example 4)
In Comparative Example 3, an aqueous pigment dispersion was obtained in the same manner as in Comparative Example 2, except that the temperature in step (1) was changed to 15 ° C.

(Comparative Example 5)
An aqueous pigment dispersion was obtained in the same manner as in Example 2 except that the treatment temperature in Step 2 was changed to 35 ° C.

  In Examples 1 and 2, the time required for the step (1) is short, and the storage stability of the obtained pigment dispersion is excellent. On the other hand, in Comparative Examples 1 to 4, since the steps (1) and (2) are both in a uniform phase, the time required for the step (1) becomes long. Moreover, in Comparative Example 5, since the phase separation is performed in both step (1) and step (2), the storage stability of the dispersion obtained in step (2) is inferior.

Claims (8)

A method for producing an aqueous pigment dispersion, comprising the following steps (1) and (2).
Step (1): Step of obtaining a dispersion by dispersing a mixture containing a polymer having a salt-forming group, methyl ethyl ketone , water and a pigment in a state where the methyl ethyl ketone and water are phase-separated with a stirring type disperser Step (2): Temperature The step of dispersing the dispersion obtained in step (1) in a homogeneous phase in which the methyl ethyl ketone and water are not phase-separated by adjustment according to   The method for producing an aqueous pigment dispersion according to claim 1, wherein the polymer is a water-insoluble polymer having a structural unit derived from an anionic monomer. The method for producing an aqueous pigment dispersion according to claim 1 or 2, wherein a mass ratio of methyl ethyl ketone to water (mass of methyl ethyl ketone / mass of water ) in the step (1) is 0.19 or more and 1 or less. The difference in the temperature of the step (2) with respect to the temperature of the step (1) (the temperature of the step (1)-the temperature of the step (2)) is 5 ° C or higher and 40 ° C or lower. A method for producing the water-based pigment dispersion as described.   The method for producing an aqueous pigment dispersion according to any one of claims 1 to 4, wherein the temperature in step (1) is 20 ° C or higher and 60 ° C or lower, and the temperature in step (2) is lower than 20 ° C.   The manufacturing method of the aqueous pigment dispersion in any one of Claims 1-5 in which the mixture of a process (1) contains a neutralizing agent. In the step (1), the mass ratio of methyl ethyl ketone to water (the mass of methyl ethyl ketone / the mass of water: the value at the time of dispersion of the mixture) is 0.19 or more and 0.4 or less. A method for producing a water-based pigment dispersion.   The method for producing an aqueous pigment dispersion according to any one of claims 1 to 7, wherein the dispersion in the step (2) is performed with a high-pressure homogenizer.