JP4999540B2 - Method for producing aqueous dispersion for ink jet recording - Google Patents

Description

  The present invention relates to a method for producing an aqueous dispersion for inkjet recording, an aqueous dispersion obtained by the production method, an aqueous ink for inkjet recording containing the aqueous dispersion, and a method for reducing the electrical conductivity of the aqueous dispersion for inkjet recording.

The ink jet recording method is a recording method in which characters and images are obtained by ejecting ink droplets directly from a very fine nozzle onto a recording member and attaching them. This method is easily spread at a full color and is inexpensive, and can be used as a recording member, and can be used as a recording member. In particular, in recent years, from the viewpoint of weather resistance and water resistance of printed matter, many use pigment-based inks.
Among these, for example, when carbon black is used as the black ink pigment, there is a problem of deterioration in storage stability and dischargeability due to aggregation of the pigments. As one of the methods for solving this problem, an ink containing a so-called self-dispersing pigment in which carbon black or the like is treated with an oxidant or the like to impart a hydrophilic functional group to the surface to improve self-dispersibility. A water-based ink for recording is known (for example, see Patent Document 1). However, in particular, in oxidant treatment methods such as nitric acid and hypochlorite, by-product carboxylic acids and conductive impurities such as chlorine ions and sodium ions resulting from the oxidant remain in the liquid, and these are ink jet. There is a problem in that it becomes a solid matter at the nozzle portion and deteriorates storage stability and print quality.

As a measure for solving the above problem, Patent Document 2 discloses that the humic acid concentration in the liquid is 1 or less in terms of absorbance by removing the humic acid in the liquid from the dispersion in which the oxidized carbon black is dispersed in water. A method for producing a carbon black dispersion liquid is disclosed.
Patent Document 3 includes a step of removing particles larger than about 1 μm from a dispersion containing carbon black to which an ionic organic group is bonded and a dissolved free species, a step of removing free species, and the carbon black. A method for purifying a dispersion comprising the step of exchanging with a counter ion is disclosed.
Patent Document 4 discloses a water-based ink for inkjet recording containing water, a self-dispersing pigment having an anionic group, and a water-insoluble amine or a salt thereof.
However, the method for producing a dispersion disclosed in the above patent document is not yet satisfactory in removing the conductive substance.

Japanese Patent Laid-Open No. 10-140064 JP-A-10-212426 Japanese translation of PCT publication No. 2002-501965 JP 2006-83304 A

  INDUSTRIAL APPLICABILITY The present invention relates to a method for producing an aqueous dispersion for ink jet recording that effectively reduces electrical conductivity, an aqueous dispersion obtained by the production method, an aqueous ink for ink jet recording containing the aqueous dispersion, and an aqueous dispersion for ink jet recording. The present invention relates to a method for reducing the electrical conductivity.

The inventors of the present invention effectively reduce the conductive material derived from the production of the self-dispersing pigment that causes poor ejection properties by treating the water dispersion of the self-dispersing pigment with a poorly water-soluble amine. I found that I can do it.
That is, the present invention provides the following (1) to (4).
(1) A method for producing an aqueous dispersion for inkjet recording, comprising the following steps I and II.
Step I: Step of mixing an aqueous dispersion of a self-dispersing pigment and a poorly water-soluble amine Step II: Step of separating the aqueous dispersion of a self-dispersing pigment from the mixture obtained in Step I (2) The above (1) An aqueous dispersion for ink jet recording obtained by the method.
(3) A water-based ink for ink-jet recording containing the water dispersion of (2).
(4) A method for reducing the electrical conductivity of an aqueous dispersion for inkjet recording, comprising the following steps I and II.
Step I: Step of mixing an aqueous dispersion of a self-dispersing pigment and a poorly water-soluble amine Step II: Step of separating an aqueous dispersion of a self-dispersing pigment from the mixture obtained in Step I

  According to the present invention, an effective method for producing an aqueous dispersion for inkjet recording that effectively reduces electrical conductivity, an aqueous dispersion obtained by the production method, an aqueous ink for inkjet recording containing the aqueous dispersion, and A method for reducing the electrical conductivity of an aqueous dispersion for inkjet recording can be provided.

  The aqueous dispersion and water-based ink of the present invention can be obtained by the production method having the above steps I to II. Hereinafter, each component and process used in the present invention will be described.

(Self-dispersing pigment)
A self-dispersing pigment is an aqueous system that does not use a surfactant or a resin by bonding one or more anionic or cationic hydrophilic functional groups to the surface of the pigment directly or through other atomic groups. It means a pigment that is dispersible in a medium. Here, as the other atomic group, an alkanediyl group having 1 to 24 carbon atoms, preferably 1 to 12 carbon atoms, a phenylene group which may have a substituent, or a naphthylene which may have a substituent. Groups.
Any anionic hydrophilic functional group may be used as long as it is sufficiently hydrophilic so that the pigment particles can be stably dispersed in the aqueous medium. Specific examples thereof include a carboxy group (-COOM), a sulfonic acid group (-SO ₃ M), phosphate group _{(-PO 3 M 2), -} SO 2 NH 2, -SO 2 NHCOR 1, or dissociation thereof Acid groups such as ionic forms (—COO ⁻ , —SO ₃ ⁻ , —PO ₃ ²⁻ , —PO ₃ ⁻ M).
In the above chemical formulas, Ms may be the same or different, hydrogen atom; alkali metal such as lithium, sodium and potassium; ammonium; monomethylammonium group, dimethylammonium group, trimethylammonium group; monoethylammonium group, diethylammonium group; Triethylammonium group; organic ammonium such as monomethanolammonium group, dimethanolammonium group, and trimethanolammonium group.
R ¹ is an alkyl group which may have an optionally substituted phenyl group or a substituted naphthyl group having 1 to 12 carbon atoms.

Examples of the cationic hydrophilic functional group include an ammonium group and an amino group. Among these, a quaternary ammonium group is preferable. Among these hydrophilic functional groups, a carboxyl group (—COOM) is particularly preferable from the viewpoints of printing density and storage stability.
Among these, an anionic hydrophilic functional group is preferable from the viewpoint of miscibility with other blends in the ink.
There is no restriction | limiting in particular as a pigment used for a self-dispersion type pigment, Any of an inorganic pigment and an organic pigment may be sufficient. If necessary, they can be used in combination with extender pigments.
Examples of the inorganic pigment include carbon black, metal oxide, metal sulfide, and metal chloride. Of these, carbon black is preferred particularly for black aqueous inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
In the color water-based ink, an organic pigment is preferable. Examples of the organic pigment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthoraquinone pigments, and quinophthalone pigments.
Specific examples of preferred organic pigments include C.I. I. Pigment yellow, C.I. I. Pigment Red, C.I. I. Pigment violet, C.I. I. Pigment blue, C.I. I. One or more types of products selected from Pigment Green are listed.
Examples of extender pigments include silica, calcium carbonate, and talc.

In order to make the pigment into a self-dispersing pigment, the necessary amount of the anionic hydrophilic functional group or the cationic hydrophilic functional group may be chemically bonded to the pigment surface. Any known method can be used as such a method. For example, US Pat. Nos. 5,571,311; 5,630,868; 5,707,432; E. Filed in Johnson, Imaging Science and Technology's 50th Annual Conference (1997), Yuan Yu, Imaging Science and Technology's 53th Annual Conf.
More specifically, oxidizing acids such as nitric acid, sulfuric acid, persulfuric acid, peroxodisulfuric acid, hypochlorous acid, chromic acid and their salts, or oxidation of hydrogen peroxide, nitrogen oxide, ozone, etc. A method of introducing a carboxy group by an agent, a method of introducing a sulfone group by thermal decomposition of a persulfuric acid compound, a method of introducing the above hydrophilic functional group by a diazonium salt compound having a carboxy group, a sulfone group, an amino group, etc. However, it is not limited to these methods. Among these, the self-dispersing pigment used in the present invention is a self-dispersing pigment obtained by introducing a carboxy group by an oxidizing agent, from the viewpoint of increasing the conductivity lowering effect and from the viewpoint of storage stability and economy. Self-dispersing carbon black is particularly preferable.

The amount of the anionic hydrophilic functional group or the cationic hydrophilic functional group in the self-dispersing pigment is preferably 100 to 1000 μmol / g, and 150 to 750 μmol per gram of the self-dispersing pigment from the viewpoint of storage stability and printing density. / G is more preferable, 200 to 600 μmol / g is more preferable, and 200 to 480 μmol / g is particularly preferable.
The amount of the anionic hydrophilic functional group or the cationic hydrophilic functional group is measured by a potentiometric titration method described in Examples.
In the aqueous dispersion and in the aqueous ink, the average particle size of the self-dispersing pigment is preferably from 50 to 300 nm, more preferably from 60 to 200 nm, and more preferably from 80 to 180 nm, from the viewpoint of storage stability of the dispersion and the aqueous ink. Further preferred. In addition, the measurement of an average particle diameter is based on the method as described in an Example.
The above self-dispersing pigments can be used alone or in admixture of two or more at any ratio.

(Water-insoluble amine)
The poorly water-soluble amine used in the present invention is used to reduce the conductive material derived during the production of the self-dispersing pigment. It is considered that the poorly water-soluble amine has a high affinity with the conductive material and has a low affinity with water, so that the conductive material can be effectively reduced from the aqueous dispersion of the self-dispersing pigment.
The water-insoluble amine in the present invention is not particularly limited as long as it shows poor water solubility, and any amine can be used. More specifically, when dissolved in 100 g of water at 20 ° C., the dissolution amount is preferably 5 g or less, more preferably 1 g or less, and particularly preferably 0.1 g or less.

  As the poorly water-soluble amine of the present invention, (i) an aliphatic amine having 6 to 44 carbon atoms, (ii) an aromatic amine having 6 to 36 carbon atoms, and (iii) an amine represented by the following general formula (1) 1 or more types selected from are preferably mentioned.

(Wherein, of R ^1, R ² and R ^3, at least one is a hydrocarbon group of 6 to 22 carbon atoms having an ether bond or an amide bond, R ^1, R ² and R ³ of the residual And may be the same or different and represents a hydrocarbon group having 1 to 22 carbon atoms or a hydrogen atom.)
(I) Aliphatic amines having 6 to 44 carbon atoms, preferably 8 to 36 carbon atoms, having 1 to 3 linear or branched hydrocarbon groups, primary, secondary and tertiary Any amine may be sufficient.
Examples of the primary amine include alkylamines having 6 to 44 carbon atoms, preferably 8 to 36 carbon atoms, and more preferably 8 to 18 carbon atoms. More specifically, hexylamine (1.9 g / 100 g), n-octylamine (0.02 g / 100 g), 2-ethylhexylamine (0.25 g / 100 g), t-octylamine, decylamine, isodecyl Examples include amine, dodecylamine, stearylamine and the like. Here, the numbers in parentheses indicate the amount dissolved when dissolved in 100 g of water at 20 ° C., and the same applies to the following.

Examples of the secondary amine include dialkylamines having 6 to 44 carbon atoms, preferably 8 to 36 carbon atoms, and more preferably 8 to 24 carbon atoms. More specifically, dibutylamine (0.3 g / 100 g), diamylamine, dihexylamine, di-n-octylamine, di-2-ethylhexylamine, didecylamine and the like can be mentioned.
As the tertiary amine, a trialkylamine having a total carbon number of 6 to 44, preferably a total carbon number of 8 to 36, and more preferably a total carbon number of 8 to 24 can be mentioned. More specifically, tripropylamine (0.25 g / 100 g), tributylamine (0.0386 g / 100 g), trihexylamine, trioctylamine (0.005 mg / 100 g), tri-2-ethylhexylamine, tri Examples include dodecylamine, dimethyl-n-octylamine, dimethyl-2-ethylhexylamine, dimethyldodecylamine, and dimethylstearylamine.
The (i) aliphatic amine may be a diamine such as decane diamine or dodecane diamine or a polyvalent amine such as triamine.
Among the above (i) aliphatic amines, tertiary amines are more preferable, and trialkylamines having a total carbon number of 8 to 36, preferably 12 to 36 carbon atoms, having a linear or branched alkyl are more preferable. preferable.

(Ii) In the aromatic amine having 6 to 36 carbon atoms, the substituent bonded to the nitrogen atom is an aromatic hydrocarbon group which may have an aliphatic hydrocarbon group as a substituent, and an aromatic ring structure Also included are so-called heterocyclic compounds containing nitrogen atoms in which nitrogen atoms are incorporated. Note that the heterocyclic compound may also have an aliphatic hydrocarbon group as a substituent.
Specific examples of the aromatic amine include 2-ethylpyridine (4.5 g / 100 g), 4-ethylpyridine (4.7 g / 100 g), aniline (3.6 g / 100 g), N, N-dimethylaniline and the like. Examples thereof include amines having 6 to 22 aryl groups (including alkylaryl groups and arylalkyl groups) and phenylimidazoles.
Further, (ii) the aromatic amine may be a diamine such as N, N-diethyl-P-phenylenediamine or 1,8-diaminonaphthalene, or a polyvalent amine such as triamine.

(Iii) In the amine represented by the general formula (1), at least one of R ¹ , R ² and R ³ is a hydrocarbon group having an ether bond or an amide bond having 6 to 22 carbon atoms. A hydrocarbon group having an ether bond or an amide bond, preferably having 8 to 22 carbon atoms, more preferably 8 to 18 carbon atoms.
Examples of the hydrocarbon group having an ether bond in the present invention include a butoxypropyl group, a 2-ethylhexyloxypropyl group, and a lauryloxypropyl group. Examples of the hydrocarbon group having an amide bond include 2-acetamino-2-methyl-ethyl group.
The remaining R ¹ , R ² and R ³ may be the same or different and are a hydrocarbon group or a hydrogen atom having 1 to 22 carbon atoms, but from the viewpoint of storage stability of the ink, a methyl group, an ethyl group, C1-C3 alkyl groups, such as a propyl group and an isopropyl group, or a hydrogen atom is preferable.
Specific examples of the poorly water-soluble amine represented by the general formula (1) in the present invention include butoxypropylamine, 2-ethylhexyloxypropylamine (1.5 g / 100 g), lauroxypropylamine (0.1 g / 100 g) and the like.

(Organic solvent)
The organic solvent is used as a solvent containing the poorly water-soluble amine. Thereby, an electroconductive substance can be reduced effectively.
The organic solvent has a high affinity with a poorly water-soluble amine and preferably has a low affinity for water. When dissolved in 100 g of water at 20 ° C., the dissolved amount is preferably 5 g or less, more preferably 1 g or less. 0.5 g or less is particularly preferable.
The organic solvent is preferably 9.2 (cal / cm ³ ) ^1/2 or less when represented by the solubility parameter (δ). The solubility parameter (δ) is expressed by the parallel root ((cal / cm ³ ) ^1/2 ) of the heat of vaporization required to evaporate a 1 molar volume of liquid. (Organic Synthetic Chemistry Association, published by Ohm).
Specifically, aliphatic hydrocarbons such as hexane (solubility parameter δ = 7.42 (cal / cm ³ ) ^1/2 , unit omitted), heptane, dodecane, cyclohexane, methylcyclohexane, isooctane, hydrogenated triisobutylene, etc. Hydrocarbon solvents of aromatic hydrocarbons such as benzene (δ = 9.14), toluene (δ = 8.91), xylene and naphthalene, and cyclic hydrocarbons such as cyclohexane (7.93); methyl ethyl ketone (9 .04), ketone solvents such as diethyl ketone; ether solvents such as diethyl ether (7.74) and dibutyl ether; silicone solvents such as octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane. Among these, the solubility parameter (δ) is preferably 7.0 to 9.0 (cal / cm ³ ) ^1/2 , more preferably 7. from the viewpoint of affinity with the conductive substance and the poorly water-soluble amine. It is 4 to 9.0 (cal / cm ³ ) ^1/2 , more preferably 8.0 to 9.0 (cal / cm ³ ) ^1/2 .
These organic solvents can be used alone or in combination of two or more.

(Method for producing water dispersion for ink jet recording and method for reducing conductivity of water dispersion for ink jet recording)
The method for producing an aqueous dispersion for inkjet recording and the method for reducing the electrical conductivity of the aqueous dispersion for inkjet recording of the present invention include the following steps I and II.
Step I: Step of mixing an aqueous dispersion of a self-dispersing pigment and a poorly water-soluble amine Step II: Step of separating an aqueous dispersion of a self-dispersing pigment from the mixture obtained in Step I

(Process I)
The conductivity of the aqueous dispersion of the self-dispersing pigment used as a raw material for the production method and the method for reducing the conductivity (before the reduction of the conductivity) is preferably 1.2 to 3 mS / cm, more preferably 1. 2 to 2 mS / cm. The conductivity is measured by the method described in the examples.
The weight ratio of the self-dispersing pigment to the poorly water-soluble amine [poorly water-soluble amine / self-dispersing pigment (in terms of solid content)] is preferably [0.5 / 100] to [30/100], more preferably [0. .5 / 100] to [10/100], particularly preferably [1/100] to [5/100].
Although it is preferable that the poorly water-soluble amine is used in an organic solvent, the content of the poorly water-soluble amine is 0.01% based on the total amount of the organic solvent and the poorly water-soluble amine from the viewpoint of reducing electrical conductivity. -50% by weight is preferable, and 0.5-10% by weight is more preferable.
The solid content concentration of the aqueous dispersion of the self-dispersing pigment is preferably 1 to 50% by weight, more preferably 5 to 40% by weight, and still more preferably 10 to 30% by weight. In addition, the water dispersion should just be a solvent which has water as a main component, and the other solvent and wetting agent may exist as long as the effect of this invention is not impaired.
The mixing temperature of the self-dispersing pigment and the poorly water-soluble amine is preferably 10 to 100 ° C., more preferably 50 to 95 ° C., and can be pressurized as necessary. By treating in the above temperature range, the conductivity of the aqueous dispersion of the self-dispersing pigment can be kept low for a long period.
The mixing time is preferably from 0.1 to 24 hours, more preferably from 1 to 10 hours, from the viewpoint of production efficiency. During mixing, stirring is preferable from the viewpoint of efficiency. When stirring the mixture, a commonly used mixing and stirring device such as an anchor blade can be used.

(Process II)
In Step II, an aqueous dispersion of a self-dispersing pigment is separated from the mixture obtained in Step I.
There is no restriction | limiting in particular in a separation method, For example, the water dispersion of a lower layer self-dispersion pigment can be isolate | separated by leaving a mixture still and removing the upper layer poorly water-soluble amine. The mixture is preferably allowed to stand at about 50 to 95 ° C. for about 1 to 24 hours.
The conductivity of the aqueous dispersion of the self-dispersing pigment in the aqueous dispersion for inkjet recording obtained in Step II (measured value at a solid content of 10% by weight of the self-dispersing pigment, pH 8, temperature 25 ° C.) is storage stability. From the viewpoint of ejection properties and print density, it is preferably 1 mS / cm or less, more preferably 0.9 mS / cm or less, and even more preferably 0.5 mS / cm or less, from the viewpoint of production efficiency. Is 0.1 mS / cm or more.
The conductivity of an aqueous dispersion of a self-dispersing pigment having a small amount of hydrophilic functional group is relatively low. This is presumably because the degree of chemical treatment for generating the hydrophilic functional group is low, and the generation of substances that cause an increase in conductivity is small. However, in the present invention, it is further reduced to the above range, so that the storage stability, the discharge property, and the print density can be improved at a high level.
The conductivity of the aqueous dispersion can be adjusted by the amount of adsorbent, the processing time, and the like.

  The aqueous ink containing the aqueous dispersion obtained in the present invention preferably contains metal oxide particles and / or polymer particles from the viewpoint of further improving the printing density.

(Metal oxide particles)
The metal oxide particles used in the present invention are particles containing one or more metal oxides.
The elements constituting the metal oxide are derived from the 2A group, 2B group, 3A group, 3B group, 4A group, 4B group, 5A group, 6A group, 7A group, or 8 group of the periodic table (long period type). Is. The metal may be a semimetal. Specific examples of the metal oxide include silicon oxide (hereinafter referred to as “silica”), aluminum oxide (hereinafter referred to as “alumina”), manganese oxide, magnesium oxide, zinc oxide, titanium oxide (hereinafter referred to as “titania”), Examples thereof include cerium oxide (hereinafter referred to as “ceria”), zirconium oxide, and the like, and silica is preferable from the viewpoint of printing density and dispersibility.
The metal oxide particles are preferably metal oxide fine particles and metal oxide secondary particles from the viewpoint of improving the printing density.

The metal oxide fine particles include those obtained by modifying or surface-modifying the surface of the metal oxide fine particles with a functional group, or those obtained by forming composite particles with a surfactant.
From the viewpoint of dispersibility, the metal oxide fine particles are preferably colloidal particles, and more preferably at least one selected from colloidal silica, colloidal titania, colloidal ceria, and colloidal alumina. Of these, colloidal silica obtained by a production method produced from an aqueous silicic acid solution is particularly preferred. Furthermore, from the viewpoint of dispersibility, the dispersion medium is preferably water.
The shape of the metal oxide fine particles is not particularly limited, but from the viewpoint of printing density and storage stability, a spherical shape or a plate shape is preferable.
The average particle diameter of the metal oxide fine particles is preferably 20 to 400 nm, more preferably 30 to 350 nm, and more preferably 40 to 200 nm from the viewpoints of printing density, storage stability, dischargeability, and the like.
The average particle diameter of the metal oxide fine particles can be measured by a light scattering method similar to the average particle diameter of the self-dispersing pigment described in the examples. When the metal oxide fine particles are powder, about 0.1 parts by weight of polyacrylate (for example, “Poise 532A” manufactured by Kao Corporation) is added to water with respect to 1 part by weight of the metal oxide fine particles. It can be measured using a dispersed aqueous dispersion.

The metal oxide secondary particles are those in which a plurality of metal oxide fine particles (metal oxide primary particles) are continuously bonded by chemical bonding. The bonding site between the metal oxide primary particles may be the case where the site of the formed metal oxide secondary particle has a constriction or not, and this depends on the production method. Any form is included.
The average particle diameter of the primary particles constituting the metal oxide secondary particles is preferably 1 to 100 nm, more preferably 5 to 80 nm, from the viewpoint of improving the printing density, and 50 metals observed in an electron micrograph. It is represented by the average diameter of the oxide primary particles. Specifically, in a micrograph taken using a transmission electron microscope “JEM2100FX” manufactured by JEOL Ltd., the particle diameters of 50 primary particles were measured visually, and the average value was obtained by averaging the values. Can be measured as
The average particle diameter of the metal oxide secondary particles is preferably 40 to 300 nm, more preferably 40 to 200 nm, and still more preferably 60 to 200 nm, from the viewpoint of improving the printing density. This average particle diameter can be measured by the same light scattering method as the average particle diameter of the self-dispersing pigment described in the Examples.
In the case where the metal oxide is silica, the silica secondary particles are obtained by the method described in claim 2 of WO 00/15552 and the disclosure of the specification related thereto, Japanese Patent No. 2803134, Patent The method described in claim 2 of Japanese Patent No. 2926915 and the disclosure of the specification related thereto, or the like can be produced.

Specific examples of the silica secondary particles that can be used in the present invention include “Snowtex-OUP” (average secondary particle size: 40 to 100 nm) manufactured by Nissan Chemical Industries, Ltd., and “Snowtex-UP”. (Average secondary particle size: 40 to 100 nm), the same “Snowtex PS-M” (average secondary particle size: 80 to 150 nm), the same “Snowtex PS-MO” (average secondary particle size: 80 to 150 nm), “Snowtex PS-S” (average secondary particle size: 80-120 nm), “Snowtex PS-SO” (average secondary particle size: 80-120 nm), “IPA-ST-UP” (Average secondary particle size: 40 to 100 nm), “Quartron PL-7” (average secondary particle size: 130 nm) manufactured by Fuso Chemical Industry Co., Ltd., and the like.
Specific examples of the titanium oxide secondary particles include “PW-6030” (average secondary particle size: 93 nm) manufactured by Catalyst Kasei Kogyo Co., Ltd., and specific examples of the cerium oxide secondary particles include Taki Chemical Co., Ltd. “Nidoral P-10” (average secondary particle size: 49 nm).
These metal oxide particles can be used alone or in combination of two or more.

(Polymer particles)
The polymer particles used in the present invention are preferably polymer particles that can be dispersed as a polymer emulsion in an aqueous medium of a continuous phase in the presence or absence of a surfactant. In particular, (i) polymer particles obtained by emulsion polymerization of an ethylenically unsaturated monomer, and (ii) self-emulsifying polymer particles containing a structural unit derived from a salt-forming group-containing monomer are preferred.
Here, the polymer particle (i) is a polymer obtained by emulsion polymerization of an ethylenically unsaturated monomer using a surfactant and / or a reactive surfactant (hereinafter referred to as “emulsion polymerization polymer”). ) Fine particles. The self-emulsifying polymer particle (ii) refers to a particle of a water-insoluble polymer that is emulsified in water by a functional group (particularly a salt-forming group or a salt thereof) of the polymer itself in the absence of a surfactant.

Specific examples of the polymer constituting the polymer particles include (meth) acrylic polymers, vinyl acetate polymers, styrene-butadiene polymers, vinyl chloride polymers, styrene- (meth) acrylic polymers, butadiene polymers, styrene polymers. Examples thereof include polymers. A (meth) acrylic polymer, a (meth) acrylic-styrene polymer, and a styrene polymer are preferable, and a (meth) acrylic-styrene polymer obtained by copolymerizing a styrene monomer and a (meth) acrylic acid ester is particularly preferable.
As a monomer for synthesizing a (meth) acrylic polymer or a (meth) acrylic-styrene polymer, it is preferable to use a monomer having a (meth) acrylic group.
Among these monomers, (meth) acrylic acid esters are preferable, and alkyl (meth) acrylates and aromatic group-containing (meth) acrylates are preferable. Specific examples thereof include methyl (meth) acrylate, ethyl (meth) acrylate, (iso) propyl (meth) acrylate, (iso or tertiary) butyl (meth) acrylate, (iso) amyl (meth) acrylate, cyclohexyl (Meth) acrylate, benzyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, (iso) decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, (iso) stearyl (Meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate and the like can be mentioned.

As a styrene monomer for synthesizing a (meth) acryl-styrene polymer and a styrene polymer, styrene, vinyltoluene, 2-methylstyrene, chlorostyrene and the like are preferably exemplified.
The weight ratio (styrene monomer: (meth) acrylic acid ester) when copolymerizing the styrene monomer and (meth) acrylic acid ester is preferably 70:30 to 10:90. The solid content concentration of the obtained polymer particles is preferably 1 to 80% by weight from the viewpoints of storage stability and compoundability. In addition, (meth) acryl means acryl, methacryl, or both.

The polymer particles used in the present invention are preferably anionic polymer particles from the viewpoint of storage stability and dischargeability. The anionic polymer particles can be obtained by polymerizing one or more anionic monomers or by emulsion polymerization of a hydrophobic monomer in the presence of an anionic surfactant. Examples of the hydrophobic monomer include the (meth) acrylic acid ester and styrene monomer.
Typical examples of the anionic monomer constituting the anionic polymer particle include an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer.
Examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid.
Examples of unsaturated sulfonic acid monomers include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, and bis- (3-sulfopropyl) -itaconate.

The content of the structural unit derived from the anionic monomer in the polymer is preferably 0 to 40% by weight, more preferably 0 to 20% by weight, particularly preferably 0 to 10% by weight, from the viewpoint of storage stability of the polymer particles. It is.
When the anionic polymer contains a structural unit derived from a hydrophobic monomer, the content of the structural unit derived from the hydrophobic monomer is preferably 50 to 100 weights from the viewpoint of the storage stability of the resulting polymer particles. %, More preferably 60 to 100% by weight, particularly preferably 70 to 100% by weight.
The weight ratio of [(constituent unit derived from anionic monomer) / (constituent unit derived from hydrophobic monomer)] in the anionic polymer is preferably from 0 to 0.5, more preferably from the viewpoint of printing density and the like. 0 to 0.3, particularly preferably 0 to 0.2.

When the polymer particles are polymer particles obtained by emulsion polymerization of the (i) ethylenically unsaturated monomer, it can be produced by a known emulsion polymerization method.
As the polymerization initiator in the emulsion polymerization, known ones such as various inorganic peroxides, organic peroxides, azo initiators, redox polymerization initiators and the like can be used.
The surfactant used for emulsion polymerization is not particularly limited, but an anionic surfactant is suitable. Examples of the anionic surfactant include linear alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, fatty acid soaps such as polyoxyethylene alkyl sulfate, alkyl sulfate, sodium laurate, and alkyl phosphates. .
Examples of reactive surfactants include sulfosuccinate esters (for example, Kao Corporation, Latemul S-120P, S-180A, Sanyo Chemical Co., Ltd., Eleminol JS-2), and alkylphenol ethers ( For example, the product made from Dai-ichi Kogyo Seiyaku Co., Ltd., Aqualon HS-10, RN-20 etc.) is mentioned.

  (I) As a commercial product of polymer particles obtained by emulsion polymerization of an ethylenically unsaturated monomer, “MR172” (latex of carboxy-modified methyl methacrylate-butadiene copolymer, average particle diameter 200 nm) manufactured by Nippon A & L Co., Ltd. "MR180" (unmodified methyl methacrylate-butadiene copolymer latex, average particle size 190 nm), "SR140" (carboxy-modified styrene-methyl methacrylate-butadiene copolymer latex, average particle size 150 nm), "NA13" (Latex of modified acrylonitrile-butadiene copolymer, average particle size 130 nm), “2108” (latex of styrene-butadiene copolymer) manufactured by JSR Corporation, and the like.

When the polymer particles are the self-emulsifying polymer particles of (ii), examples of the salt-forming group-containing monomer include the anionic monomers.
The self-emulsifying polymer can be produced by copolymerizing the monomer mixture containing the salt-forming group-containing monomer by a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. .
The self-emulsifying polymer particles are dispersed in a known method by dispersing a mixture containing the self-emulsifying polymer, neutralizing agent, water and an organic solvent, and then removing the organic solvent to obtain an aqueous dispersion of the self-emulsifying polymer particles. It is preferable to obtain. Examples of the neutralizing agent include bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, triethanolamine, and tributylamine.

(Aqueous dispersion for inkjet recording, water-based ink)
The aqueous dispersion for inkjet recording obtained in the present invention is a form in which a self-dispersing pigment is dispersed in a solvent containing water as a main component. From the viewpoint of drying properties, a wetting agent is blended and stored. I often keep it. Water dispersions can be used as inks as they are, but they are dispersed in various ink vehicles according to printer specifications and applications, such as printer head and nozzle characteristics, printing performance, and stability. If necessary, an ink can be prepared by adding additives such as a solvent, a surfactant, a wetting agent, a dispersing agent, an antifoaming agent, an antifungal agent, and a chelating agent. In particular, a water-based ink having excellent performance can be obtained by dispersing in an aqueous medium to form an aqueous dispersion.

The content of the self-dispersing pigment, particularly the self-dispersing carbon black, in the aqueous dispersion and the water-based ink of the present invention is preferably 1 to 15% by weight, more preferably 2 to 2%, from the viewpoint of enhancing dischargeability and printing density. It is 10% by weight, more preferably 3 to 8% by weight.
The total and individual contents of the metal oxide particles and the polymer particles in the water-based ink for ink jet recording of the present invention are preferably 0.1 to 15% by weight, more preferably from the viewpoint of increasing the dischargeability and the print density. It is 0.5 to 5 weight%, More preferably, it is 1 to 4 weight%.
The content ratio of the total weight of the metal oxide particles and the polymer particles relative to the self-dispersion pigment [the total weight ratio of the self-dispersion pigment / metal oxide particles and the polymer particles] improves the printing density, the water dispersion, In order to obtain good storage stability in water-based ink, it is preferably 0.1 to 20, more preferably 0.5 to 10, and still more preferably 2 to 5.
The water content in the aqueous dispersion and the water-based ink of the present invention is preferably 30 to 90% by weight, more preferably 40 to 80% by weight.

The average particle diameter of the polymer particles in the aqueous dispersion and aqueous ink of the present invention is not particularly limited as long as it is stably present during storage of the ink, but is preferably 5 to 300 nm, more preferably 30 to 200 nm. is there. The average particle size of the polymer particles can be measured by the same method as the average particle size of the self-dispersing pigment.
The preferred surface tension (20 ° C.) of the aqueous dispersion and aqueous ink of the present invention is preferably 30 to 65 mN / m, more preferably 35 to 60 mN / m as the aqueous dispersion, and preferably as the aqueous ink. It is 25-50 mN / m, More preferably, it is 27-45 mN / m.
The viscosity (20 ° C.) of 20% by weight (solid content) of the aqueous dispersion of the present invention is preferably 1 to 12 mPa · s, more preferably 1 to 9 mPa · s, in order to obtain a preferable viscosity when used as an aqueous ink. s. The viscosity (20 ° C.) of the water-based ink is preferably 2 to 12 mPa · s, more preferably 2.5 to 10 mPa · s, in order to maintain good ejection properties.

In the following production examples, examples and comparative examples, “parts” and “%” are “parts by weight” and “% by weight” unless otherwise specified.
The hydrophilic functional group amount of the self-dispersing carbon black, the conductivity of the self-dispersing carbon black and the aqueous dispersion, the average particle size of the self-dispersing pigment, and the pH were measured by the following methods.
<Measurement of amount of hydrophilic functional group in self-dispersing pigment>
The amount of the anionic hydrophilic functional group (acidic group amount) can be determined by the following method as the amount reacted with a strong alkali such as NaOH or KOH.
(Measurement condition)
Apparatus: Kyoto Denshi Kogyo Co., Ltd., potentiometric automatic titrator, AT-610
Titration conditions: 0.01 N HCl, titration 0.02 ml, intermittent time 30 seconds, 25 ° C.
0.01N-NaOH used was 0.01 mol / L sodium hydroxide (for volumetric analysis) manufactured by Wako Pure Chemical Industries, and 0.01N-HCl used 0.01 mol / L hydrochloric acid (for volumetric analysis) manufactured by Wako Pure Chemical Industries.
(Measurement procedure)
By accurately weighing an aqueous dispersion of carbon black to a solid content of 0.05 g, adding ion-exchanged water to 50 ml, adding 1.5 ml (excess amount) of 0.01 N NaOH and stirring for 30 minutes. All surface acidic groups were Na salts. To this alkaline dispersion, 0.02 g of 0.01N HCl is added dropwise at 30 second intervals while stirring, and the pH is measured. Starting from the neutralization point (inflection point 1) where the excess alkali is neutralized, and the neutralization point from the most acidic (final inflection point 2) among the subsequent neutralization inflection points The amount of acidic groups on the particle surface was calculated from the amount of 0.01 N HCl used between the last inflection point 2 and the inflection point 1 and obtained as the equivalent per gram of solid content. The measurement was performed at 20 ° C.
The amount of the cationic hydrophilic functional group is obtained by adding an excess amount of 0.01N HCl and neutralizing with 0.01N NaOH in the same manner as in the case of the anionic hydrophilic functional group. Can do.

<Measurement of conductivity>
Based on JIS K0130-1995, it measured using Horiba Ltd. make, D-24 (Electroconductivity electrode 3551-10D). The measurement conditions were adjusted to pH 8 by adding a 1N sodium hydroxide aqueous solution of 25 ° C., carbon black concentration of 10%, and 1N.
In addition, since the solvent other than water, a wetting agent, etc. influence electric conductivity, it removes and measures to the measurement water dispersion. The conductivity varies depending on the pH, so when it has an anionic hydrophilic functional group, it is measured at pH 8 (20 ° C.), and when it has a cationic hydrophilic functional group, it is measured at pH 3 (20 ° C.).
<Measurement of average particle size of self-dispersing pigment>
Measurement was performed using a laser particle analysis system ELS-8000 (cumulant analysis) manufactured by Otsuka Electronics Co., Ltd. The measurement conditions were a temperature of 25 ° C., an angle between incident light and a detector of 90 °, and the number of integrations of 100. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measurement concentration was about 5 × 10 ⁻³ wt%.
<PH>
A 20% by weight aqueous suspension or mud was prepared and measured by JIS Z8802 method (20 ° C.).

Example 1
An organic solvent solution of a poorly water-soluble amine in which 0.5 g of trioctylamine is contained in 50 g of toluene [δ = 8.91 (cal / cm ³ ) ^1/2 ] is placed in a 1 L separable flask, and a self-dispersing pigment As an aqueous dispersion, an oxidation treatment was performed with peroxodisulfate having an average particle size of 130 nm, a concentration of 20%, an electric conductivity of 1.36 mS / cm, a pH of 6.0, and a total hydrophilic functional group (anionic) amount of 290 μmol / g. 100 g of a dispersion of self-dispersing carbon black (CB1) was weighed in. (Weight ratio (amine / pigment): 2.5 g / 100 g)
Next, the mixture was stirred with a Teflon (registered trademark) anchor-type stirring blade connected to a three-one motor at 100 rpm for 0.5 hours (temperature 25 ° C.), and then the separable flask was immersed in a 90 ° C. water bath for 3 hours. . Thereafter, the separable flask is slowly tilted, and only the supernatant is taken out. The taken out aqueous dispersion is filtered through a membrane filter (made by Sartorius Co., Ltd.) having a mesh size of 5 μm, and the solid content is adjusted to 15%. An aqueous dispersion of self-dispersing carbon black (CB1) with a reduced content was obtained. The conductivity was 0.43 mS / cm.

Example 2
In Example 1, self-dispersing type in which conductive material was reduced by performing the same operation as in Example 1 except that hexane [δ = 7.42 (cal / cm ³ ) ^1/2 ] was used instead of toluene. An aqueous dispersion of carbon black (CB2) was obtained. The conductivity was 0.86 mS / cm.
Comparative Example 1
In Example 1, the aqueous dispersion of the self-dispersing pigment was kept in a 90 ° C. water bath for 3 hours, then filtered through a membrane filter having an opening of 5 μm, and ion exchanged water was added to a solid content of 15%. By preparing, an aqueous dispersion of self-dispersing carbon black (CB3) that was not treated with a poorly water-soluble amine was obtained. The conductivity was 1.42 mS / cm.

(Preparation of water-based ink)
5 parts of glycerin and water (remainder) are added to 26.7 parts of the aqueous dispersion of the self-dispersing carbon black (CB1) obtained in Examples 1 and 2 and Comparative Example 1, and the total amount becomes 100 parts by weight. The resulting mixture was mixed and stirred at 25 ° C. to prepare a dispersion to obtain a water-based ink.
The water-based ink using the aqueous dispersion obtained in the present invention was excellent in dischargeability.

Claims (7)

A method for producing an aqueous dispersion for inkjet recording, comprising the following steps I and II.
Step I: Step of mixing an aqueous dispersion of a self-dispersing pigment and a poorly water-soluble amine Step II: Step of separating an aqueous dispersion of a self-dispersing pigment from the mixture obtained in Step I   The weight ratio of the self-dispersing pigment to the poorly water-soluble amine in Step I [the poorly water-soluble amine / self-dispersing pigment (in terms of solid content)] is [0.5 / 100] to [30/100]. 2. A method for producing an aqueous dispersion for inkjet recording according to 1.   The method for producing an aqueous dispersion for inkjet recording according to claim 1 or 2, wherein the poorly water-soluble amine is contained in an organic solvent. The method for producing an aqueous dispersion for inkjet recording according to claim 3, wherein the solubility parameter of the organic solvent is 9.2 (cal · cm ^-3 ) ^1/2 or less.   An aqueous dispersion for ink jet recording obtained by the production method according to claim 1.   A water-based ink for ink-jet recording, comprising the water dispersion according to claim 5. A method for reducing the electrical conductivity of an aqueous dispersion for inkjet recording, comprising the following steps I and II.
Step I: Step of mixing an aqueous dispersion of a self-dispersing pigment and a poorly water-soluble amine Step II: Step of separating an aqueous dispersion of a self-dispersing pigment from the mixture obtained in Step I