JP2002194262A - Production method for aqueous pigment dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an aqueous pigment dispersion excellent in dispersion stability and long-time storage stability, especially an aqueous pigment dispersion which, when used as a material for an ink composition for ink jet recording, enables good delivery performance and high image quality. SOLUTION: In producing an aqueous pigment dispersion comprising water, a pigment, a resin containing a non-aqueous monomer, and a water-soluble organic solvent, the pigment is dispersed in advance in a mixture of water and the water-soluble organic solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 suitable for producing an ink composition for ink jet recording.

2. Description of the Related Art An aqueous pigment dispersion obtained by dispersing a pigment in a liquid medium containing water as a main component is prepared by mixing a pigment, water, an organic solvent, a resin, and an alkaline agent, and performing a dispersion treatment using a disperser. It is common. For example, as a method of dispersing a pigment, Japanese Patent Application Laid-Open No. Hei 1-209497 is cited.
No. 69 describes an ink jet recording system using a pigment ink.

In particular, the use of a pigment as a colorant in an aqueous pigment dispersion for producing an ink for ink-jet recording is far superior to that using a conventional dye in terms of water resistance, light resistance and the like. Since a recording ink can be manufactured, various studies have begun on its composition or dispersion method. Considering its use as an ink for inkjet recording, in order to satisfy its ejection stability and long-term storage stability, it must have good dispersibility at the stage of the aqueous pigment dispersion and dispersion stability that allows long-term storage. is necessary.

[0003] However, the dispersion stability of the conventional aqueous pigment dispersion is insufficient, and when it is used as an ink for ink jet recording, the discharge characteristics, particularly in the thermal method, are not satisfactory.

That is, conventionally, in the production of an aqueous pigment dispersion, a pigment is mixed with a resin, a solvent, and the like, and the pigment is mixed with a kneader such as a two-roll, three-roll or kneader, a Henschel mixer, and the pigment is mixed with the resin. In this method, a pigment dispersion is prepared in advance by using the pigment and the pigment is used, but in the case of an ink jet recording ink prepared based on the dispersion, the ink is not necessarily discharged from a fine nozzle. Satisfactory characteristics were not obtained in characteristics and long-term dispersion stability.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and provides an aqueous pigment dispersion having excellent dispersion stability and long-term storage stability. An object of the present invention is to provide a method for producing an aqueous pigment dispersion having excellent properties, water fastness and light fastness.

[0006]

Means for Solving the Problems In order to solve the above problems, the present inventors produce an aqueous pigment dispersion comprising at least water, a pigment, a resin containing a water-insoluble monomer, and a water-soluble organic solvent. Occasionally, it has been found that an aqueous pigment dispersion having excellent dispersion stability can be obtained by using a pigment previously dispersed in a mixture of water and the water-soluble solvent as the pigment.

[0007] As in the present invention, the pigment is previously dispersed in a low-viscosity mixture containing no resin of water and a water-soluble organic solvent,
By securing the dispersion of the finely pulverized pigment in the water-soluble solvent, and then proceeding the dispersion by adding a resin etc. for the first time, it is more suitable for the production of ink for inkjet recording, which is more stable than the conventional method. Aqueous pigment dispersion can be obtained.

Further, in the method for producing an aqueous pigment dispersion described in the present invention, it is preferable to include diethylene glycol as an aqueous organic solvent since the dispersibility of the pigment can be further improved. Further, as a disperser used at the time of dispersing the pigment, it is desirable to use a disperser using a medium such as a paint shaker or a sand grinder.

The resin used in the production of the pigment dispersion of the present invention includes a water-insoluble monomer, a styrene monomer as a water-insoluble monomer,
Further, by using a copolymer resin containing a monomer component having an acid group selected from carboxylic acid, sulfonic acid and phosphoric acid, a more excellent pigment dispersion can be obtained.
The acid value of the copolymer resin is desirably from 60 to 300 mgKOH / g, and desirably from 1,000 to 30,000.

Further, the inventors have found that when the relationship between the resin used in the present invention and the water-soluble organic solvent is 25 ° C. and the resin and the water-soluble solvent are mixed at a weight ratio of 1: 4, the partially dissolved or swollen state is not obtained. As shown, it was found that an excellent pigment dispersion could be obtained by using one that did not result in a uniform resin solution.

Hereinafter, the present invention will be described in detail. The pigment that can be used in the present invention is not particularly limited, and any known and commonly used pigments can be used. For example, carbon black, titanium black, titanium white, zinc sulfide,
Inorganic pigments such as Bengala, phthalocyanine pigments, azo pigments such as monoazo and disazo pigments, phthalocyanine pigments,
Organic pigments such as quinacridone pigments are used.

In dispersing the pigment in advance in the present invention, known water-soluble organic solvents can be widely used as a mixed solution with water. For example, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, and derivatives thereof, and diols such as butanediol, pentanediol, hexanediol, and homologous diols. And glycol esters such as lau propylene glycol, ethylene glycol monobutyl ether, diethylene glycol ethers such as carbitol, diethylene glycol monoethyl, butyl, hexyl ethers, propylene glycol ether, dipropylene glycol ether, and triethylene glycol ether. Monoglycol ethers and diglycos such as cellosolve containing And long-chain alcohols such as butyl alcohol, pentyl alcohol, and homologous alcohols, and lactones such as sulfolane, esters, ketones, γ-butyrolactone, lactams such as N- (2-hydroxyethyl) pyrrolidone, and glycerin. And other solvents such as and derivatives thereof.

From the viewpoint of working efficiency and the solubility or swelling of the resin as described below, polyhydric alcohols having a high boiling point, low volatility and high surface tension are preferable, and it is particularly preferable to contain diethylene glycol. .

As described above, the water-soluble organic solvent used in the step of pre-dispersing the pigment in water and the water-soluble organic solvent (preliminary dispersion step) is obtained by adding a resin or the like to the dispersion step. However, it still functions to improve the dispersibility of the pigment, and contributes to good dispersion of the aqueous pigment dispersion.
Furthermore, when the pigment dispersion is diluted and various additives are added to form an ink for inkjet recording, it is contained in the ink as an essential component of the ink,
It contributes to its dispersibility. As in the present invention, by including the same water-soluble organic solvent as the water-soluble organic solvent used in the preliminary dispersion step in the ink composition of the ink for inkjet recording, the solvent used in the preliminary dispersion step is finalized. The ink composition does not become an impurity.

As a method for dispersing the pigment, a publicly known and used dispersing apparatus can be used. Examples thereof include an ultrasonic homogenizer, a paint shaker, a ball mill, a sand mill, a sand grinder, a dyno mill, a dispermat, an SC mill, a spike mill, a nanomizer, an agitator mill, and a planetary.

In particular, as a preferable dispersion method at a low viscosity, which is used for the preliminary dispersion of the present invention, a paint shaker, a sand grinder, a ball mill, etc., which can simultaneously carry out the pulverization and fineness of the pigment and the dispersion in a liquid, can be used. A method using a medium is preferable.

The resin used for producing the dispersion of the present invention may be a resin containing a water-insoluble monomer, such as a styrene resin, an acrylic resin, a maleic resin, a polyvinyl acetate resin, Polyvinyl sulfonic acid resin, polyester resin, polyurethane resin,
Polyamide-based resins, polyvinyl alcohol-based resins, polypyrrolidone resins, cellulose-based resins, etc., can be used various known and commonly used resins, among others, including a styrene monomer as a water-insoluble monomer, and having an acid group Copolymer resins containing monomer components are preferred.

Other water-insoluble monomer components of the resin used in the present invention include alkyl (meth) acrylates such as methyl (meth) acrylate and ethyl (meth) acrylate. Phenyl (meth) acrylate,
Allyl (meth) acrylates such as benzyl (meth) acrylate and phenylethyl (meth) acrylate. Sulfonic acid group-containing (meth) such as sulfoethyl (meth) acrylate and sulfopropyl (meth) acrylate
Acrylic esters. Hydroxy group-containing (meth) acrylates such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate. styrene,
Styrene monomers such as α-methylstyrene and vinyltoluene.

Other examples include monomers such as acrylonitonyl, acrylamide, vinyl acetate, vinyl chloride, vinyl pyrrolidone, vinyl alcohol, and ethylene. Particularly, as a water-insoluble monomer, a monomer containing at least a styrene monomer and having an acid group A copolymer resin containing the components is desirable.

As the monomer component having an acid group, those containing carboxylic acid, sulfonic acid, phosphoric acid and the like are used. In particular, a monomer component having a carboxyl group is preferable, such as (meth) acrylic acid and maleic anhydride. In the present invention, those having a structure derived from (meth) acrylic acid are particularly preferable.

Further, the resin used in the present invention is preferably a water-soluble resin obtained by neutralizing a resin having an acid group with a base.
The resin more preferably used in the present invention, styrene, substituted styrene, a monomer selected as essential styrene from the group consisting of (meth) acrylate,
It is obtained by neutralizing a radical copolymer with (meth) acrylic acid with a base.

As the base for neutralizing the monomer component having an acid group, for example, sodium hydroxide, potassium hydroxide,
In addition to alkali metal hydroxides such as lithium hydroxide, basic substances such as ammonia, triethylamine and morpholine, triethanolamine, diethanolamine, N-
A base such as an alcoholamine such as methyldiethanolamine can be used.

From the viewpoint of long-term storage stability, the acid value of the resin is preferably from 60 to 300 mgKOH / g, particularly preferably from 100 to 180 mgKOH / g. The acid value is the number of milligrams (mg) of potassium hydroxide (KOH) required to neutralize 1 g of the resin,
Expressed as H / g. If the acid value is less than 60, the dispersion effect is small and a good dispersion cannot be obtained. On the other hand, when the acid value is larger than 300, aggregation of the pigment is likely to occur.

The neutralization ratio of the resin to the acid value by an alkali agent is preferably from 30 to 200 mol%, particularly preferably from 40 to 120 mol%, in view of the pigment particle size and dispersion stability. If the neutralization ratio is less than 30 mol%, the dispersing effect is small and the pigment particle size does not become sufficiently small. On the other hand, the neutralization rate is 200
If it is more than mol%, the dispersion stability deteriorates, and it may change to a gel when left for a long time.

At this time, the neutralization ratio is a value calculated by the following equation.

(Equation 1)

In view of the adsorption power of the resin to the pigment and the dispersion stability of the pigment, the content of [(A) a styrene monomer + (B) a monomer component having an acid group] in the copolymer resin is 10 to 10. Preferably, it is 100% by mass and the mass ratio of (A) the styrene monomer to (B) the monomer component having an acid group is (A) :( B) = 9: 1 to 1: 9.

The molecular weight range of the resin is not particularly limited, but is preferably in the range of 2,000 to 100,000 in terms of weight average molecular weight. The low molecular weight resin is excellent in initial dispersibility, but is preferably 4000 or more from the viewpoint of long-term storage stability, and from the viewpoint of solubility of the resin, the molecular weight of the resin is preferably 20,000 or less.

The relationship between the resin and the water-soluble organic solvent used in the method for producing the aqueous pigment dispersion of the present invention is as follows: when the resin and the water-soluble organic solvent are mixed at a weight ratio of 1: 4 at 25 ° C. It is preferable that the resin be selected so as to show a swelling state and not form a uniform resin solution. In a system that shows such a partially dissolved or swollen state and does not become a uniform resin solution, adsorption of the resin to the pigment is likely to be effectively performed so that the resin wraps around the pigment surface and forms a stable film. . On the other hand, when the resin is completely dissolved in the water-soluble organic solvent and delocalized in the solvent, it is difficult for the effective adsorption as in the present invention to proceed. When water is added to the pigment dispersion, it becomes possible to effectively bring out the affinity between the pigment and the resin and the hydrophilicity between the resin and the water. Therefore, an aqueous pigment dispersion having excellent dispersion stability and long-term storage stability can be realized.

However, an increase in the amount of these additives causes overdissolution and overswelling of the monomer component having an acid group, and
Increase the viscosity of the aqueous pigment dispersion. Although the content of the water-soluble organic solvent varies depending on the content of the styrene monomer (A) in the copolymer resin, the ratio of the pigment (C) to the water-soluble organic solvent (D) is (C): (D) = 1: 1
１ ： 1: 10, more preferably (C) :( D) = 1: 1 to 1: 3.

The aqueous pigment dispersion of the present invention produced by selecting the above composition has excellent dispersion stability and long-term storage stability. When the aqueous pigment dispersion of the present invention is used as an ink, particularly when it is used as an ink for ink jet recording, the above-described 25
When mixed with the resin at a weight ratio of 1: 4 at ℃, the water-soluble organic solvent which shows a partially dissolved or swollen state and does not become a uniform resin solution may be used as it is if it is a high boiling water-soluble organic solvent. It also functions as a drying inhibitor in the composition.

In order to prepare an ink for ink jet recording from the aqueous pigment dispersion, an organic solvent having anti-drying properties and permeability is further added, if necessary, and then diluted with water and a water-soluble organic solvent to obtain a uniform ink. After stirring and adjusting the ink, the ink may be filtered through a filter having a desired particle size. To adjust the ink,
For example, in addition to the addition of the anti-drying agent and the organic solvent having permeability, concentration adjustment and viscosity adjustment, a pH adjusting agent, a surfactant, a preservative, a chelating agent, a plasticizer, an antioxidant, an ultraviolet absorber and the like are used. Add as needed.

The permeability of the ink is a characteristic necessary for adjusting the permeability of the ink into the recording medium and the dot diameter on the recording medium. Examples of the water-soluble organic solvent exhibiting permeability include lower alcohols such as ethanol and isopropyl alcohol, ethylene oxide adducts of alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether, and propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether. Etc.

By appropriately preparing the aqueous pigment dispersion obtained by the production method of the present invention, the aqueous pigment dispersion can be suitably used for a known and commonly used ink jet recording ink of an on-demand system, for example, a piezo system or a thermal system. In this way, extremely stable ink discharge can be performed in each type of printer.

[0034]

Next, the present invention will be described more specifically with reference to examples and comparative examples. In addition, "part" in the following examples
Represents "parts by mass".

Example 1 Styrene (72 parts), acrylic acid (10 parts), methacrylic acid (13 parts), oxidation = 15
When mixed with the resin (I) consisting of 0 mg KOH / g and a weight average molecular weight of 7200 at a weight ratio of 1: 4 at 25 ° C. (resin = 1, water-soluble organic solvent = 4), a partially dissolved or swollen state is shown. The test was performed using diethylene glycol, which does not form a uniform resin solution, as a water-soluble organic solvent.

Resin (I) 45 parts, sodium hydroxide 4.
Aqueous resin solution consisting of 8 parts and 150 parts of ion exchange water (II)
Is prepared. 10.00 parts of carbon black, 10.00 parts of diethylene glycol, 10.00 parts of ion-purified water, 400 parts of zirconium beads (1.25 mm diameter) After charging the above composition, the mixture was stirred for 2 hours using a paint shaker. Thereafter, 13.32 parts of an aqueous resin (II) solution and 10.00 parts of diethylene glycol were added, and the mixture was stirred for 3 hours using a paint shaker to obtain an aqueous pigment dispersion liquid (III).

The aqueous pigment dispersion thus obtained (II
I) 26.67 parts, 5 parts of glycerin, 5 parts of polyoxypropylene glyceryl ether, 63.3 parts of ion-exchanged water
Three parts were mixed and stirred to obtain an aqueous pigment ink for inkjet recording.

The pigment particles in the obtained aqueous pigment ink have a volume average particle size of 0.08 μm (Nikkiso Co., Ltd. laser Doppler type particle size distribution meter Microtrac U)
PA-150), no agglomerates, the same volume average particle size even after standing at 60 ° C. for 3 days in a thermostat, and stable dispersion.

Further, when this ink was filtered under pressure of 0.1 MPa with a 47 μm diameter 1 μm membrane filter, it was possible to filter 123 g before the filter could not be filtered due to clogging of the filter.

Further, using the ink left at 60 ° C. for 3 days, an ink jet printer manufactured by ENCAD, USA
When all the nozzles were simultaneously driven using NOVAJET PRO and a solid printed image of 100 cm × 50 cm was printed, a uniform image having a high image density and no printing unevenness was obtained. When the optical density of this image was measured using a reflection density diameter RD-918 manufactured by Macbeth, the image density was 1.
22.

(Comparative Example 1) Composition of carbon black 10.00 parts, resin (II) aqueous solution 13.32 parts diethylene glycol 20.00 parts, ion purified water 10.00 parts zirconium beads (1.25 mm diameter) 400 parts After the preparation, the mixture was stirred for 5 hours using a paint shaker to obtain an aqueous pigment dispersion (IV).

The aqueous pigment dispersion thus obtained (I
V) 26.67 parts, glycerin 5 parts, polyoxypropylene glyceryl ether 5 parts, ion-exchanged water 63.33
The parts were mixed and stirred to obtain an aqueous pigment ink for inkjet recording.

The volume average particle size of the carbon black in the obtained ink was 0.10 μm, which was larger than that of Example 1, and was left at 60 ° C. for 3 days in a constant temperature tester. Although slight, sedimentation of carbon black particles due to aggregation was observed.

When the ink was filtered under pressure with a 1 μ membrane filter having a diameter of 47 mm at an air pressure of 0.1 MPa, the filter was clogged at the time of filtering 12 g, and the filter could not be filtered.

Further, when the solid print image was printed in the same manner as in Example 1 using the ink left at 60 ° C. for 3 days, no clogging occurred. Occurred, and the average image density at each position of the image was as low as 1.11.

The ink of Example 1 had a fine particle diameter and was excellent in dispersion stability and filterability, and even in printing, an image having a high image density and uniform and excellent in ejection stability was obtained.

[0047]

According to the method for producing an aqueous pigment dispersion of the present invention, it is possible to provide an aqueous pigment dispersion having a fine particle diameter and excellent dispersion stability. This makes the ink excellent in water resistance, water resistance and color development.

Continued on the front page F-term (reference) 4J037 AA02 AA11 AA15 AA22 CB04 CB07 CB28 CC02 CC13 CC15 CC16 CC17 CC26 CC27 EE08 EE28 EE43 FF15 FF23 4J039 AB02 AD03 AD06 AD08 AD09 AD14 AE04 AE06 AE08 BA04 BA12 BC40 DA02 EA35 EA38 EA41 EA44 GA24

Claims (6)

[Claims] 1. A method for producing an aqueous pigment dispersion comprising at least water, a pigment, a resin containing a water-insoluble monomer, and a water-soluble organic solvent, wherein the pigment is a mixture of water and the water-soluble organic solvent in advance. A method for producing an aqueous pigment dispersion, comprising using a pigment dispersed therein. 2. The method for producing an aqueous pigment dispersion according to claim 1, wherein the water-soluble organic solvent contains diethylene glycol. 3. The resin according to claim 1, wherein the resin containing a water-insoluble monomer is a copolymer resin containing a styrene monomer as a water-insoluble monomer and a monomer component having an acid group. The method for producing an aqueous pigment dispersion according to any one of the above. , 4. An acid value of the copolymer resin is from 60 to 300 mgK.
The method for producing an aqueous pigment dispersion according to claim 3, wherein the aqueous pigment dispersion is OH / g. , 5. The relationship between the resin containing a water-insoluble monomer according to claim 1 and a water-soluble organic solvent is such that the resin and the water-soluble organic solvent are in a weight ratio at 25 ° C. A method for producing an aqueous pigment dispersion, characterized in that a mixture which shows a partially dissolved or swollen state when mixed at a ratio of 1: 4 and does not become a uniform resin solution is used. 6. The method for producing an aqueous pigment dispersion according to claim 1, wherein a dispersion method using a medium is used when dispersing the pigment.