JP2002256201A - Aqueous pigment dispersion and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an aqueous pigment dispersion having excellent dispersion stability and long-term storage stability, particularly when used as a raw material for an ink composition for ink jet recording, having good ejection performance. And an aqueous pigment dispersion which enables high image quality. An aqueous pigment dispersion comprising water, a pigment, a resin containing a non-aqueous monomer, and a water-soluble organic solvent has a temperature of 25 ° C.
In, when a resin containing a water-insoluble monomer and a water-soluble organic solvent are mixed at a weight ratio of 1: 4, the resin shows a partially dissolved state or a swollen state,
An aqueous pigment dispersion characterized by using a combination of a resin containing a water-insoluble monomer and a water-soluble organic solvent so as not to form a uniform resin solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous pigment dispersion and a method for producing the aqueous pigment dispersion, and more particularly to an aqueous pigment dispersion and an aqueous pigment dispersion suitable for producing an aqueous pigment ink composition for ink jet recording. And a method for producing the same.

[0002]

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, JP-A-1-204979 is cited as a method of dispersing a pigment, and an example of studying an ink having excellent nib drying property is disclosed in JP-A-1-24998.
No. 69 describes an ink jet recording system using a pigment ink. Further, Japanese Patent Application Laid-Open No. 5-2541
No. 3 describes an ink jet recording ink containing insoluble resin particles, and a pigment ink having improved scratch resistance and dispersion stability has been proposed.

[0003] However, the dispersion stability of the conventional aqueous pigment dispersion is insufficient, and when used as an ink for ink-jet recording, the ejection characteristics, particularly in the thermal method, are not satisfactory. Also, the scratch resistance of the ink,
Lightfastness and waterfastness also do not give satisfactory results and attempts are still being made to improve them.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an aqueous pigment dispersion having excellent dispersion stability and long-term storage stability, which solves the above-mentioned problems of the prior art. It is an object of the present invention to provide an aqueous pigment dispersion liquid which is used as a raw material of a pigment, and exhibits excellent discharge characteristics, water resistance and light resistance when applied as a thermal ink material, and a method for producing the same.

[0005]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that an aqueous pigment dispersion obtained by using a resin containing at least water, a water-insoluble monomer, a water-soluble organic solvent and a pigment. Water soluble organic solvent is 25 ° C
In the above, when mixed with the resin containing the water-insoluble monomer at a weight ratio of 4: 1 (water-soluble organic solvent: resin resin containing the water-insoluble monomer = 4: 1), the resin is partially dissolved or swelled. By using a combination of a resin containing a water-soluble organic solvent and a water-insoluble monomer, which shows a state and does not become a uniform resin solution, an aqueous face dispersion having excellent dispersion stability, light resistance and water resistance can be obtained. I found that.

When a resin having a water-insoluble monomer component, a pigment, and a resin mixed at 25 ° C. at a weight ratio of 4: 1 (resin = 1 water-soluble organic solvent = 4),
In a system containing a water-soluble organic solvent, which shows a partially dissolved or swollen state and does not become a uniform resin solution, the adsorption of the resin to the pigment causes the resin to wrap around the pigment surface and form a stable film. Easy to do effectively. 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. In such an aqueous pigment dispersion, the pigment is stably present in the aqueous medium while being encapsulated in the resin. For this reason, an aqueous pigment dispersion having excellent dispersion stability and long-term storage stability, and having extremely good water resistance and color development can be realized.

The resin containing a water-insoluble monomer in the present invention is preferably (A) a styrene monomer component and (B)
It is preferable that the copolymer resin contains a monomer component having an acid group. More preferably, the monomer having an acid group is a water-soluble monomer. Examples of the monomer component having an acid group include (meth) acrylic acid and maleic anhydride. In the present invention, a monomer having a structure derived from (meth) acrylic acid is particularly preferable.

In the present invention, as the water-insoluble monomer component, a copolymer resin containing at least a styrene monomer and a monomer component having an acid group can be more preferably used. From the viewpoint of stability, the content of [(A) a styrene monomer + (B) a monomer component having an acid group] in the copolymer resin is 50 to 50%.
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. Further, from the viewpoint of scratch resistance and water resistance, the content of [(A) styrene monomer + (B) monomer component having an acid group] in the copolymer resin is 80 to 100% by mass, and (A ) The mass ratio of the styrene monomer to the monomer component (B) having an acid group is (A) :( B) = 9: 1.
~ 6: 4.

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. If the acid value is less than 60, the dispersing effect is small, and a good dispersion cannot be obtained. On the other hand, if the acid value is larger than 300, aggregation of the pigment is likely to occur. The acid value is defined as the milligram (mOH) of potassium hydroxide (KOH) required to neutralize 1 g of the resin.
g) A number, expressed in mgKOH / g. Further, as the water-soluble organic solvent, 1,5-pentanediol or diethylene glycol is preferable. Particularly, diethylene glycol is more preferable because the volume average particle diameter of the pigment in the aqueous pigment dispersion can be reduced.

When mixed with the copolymer resin at 25.degree. C. at a weight ratio of 4: 1, it shows a partially dissolved or swollen state and does not form a uniform resin solution. It can be appropriately selected depending on the resin, for example, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, and derivatives thereof, butanediol, pentanediol, Diols such as hexanediol and homologous diols; glycol esters such as propylene glycol laurate; and diethylene glycol ethers such as ethylene glycol monobutyl ether and carbitol; Glycol mono ethyl, butyl, and mono-glycol ethers and diglycol ethers such as cellosolve, including the ether hexyl, propylene glycol ether, dipropylene glycol ether, and triethylene glycol ether,
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 other solvents such as, but not limited to, glycerin and its derivatives.

These water-soluble organic solvents are used depending on the resin.
Types or several types may be appropriately selected and used in combination.

In the method for producing an aqueous pigment dispersion of the present invention, when mixed with a resin at 25 ° C. at a weight ratio of 4: 1 (resin = 1 water-soluble organic solvent = 4),
Although a partially dissolved or swollen state is shown, and a water-soluble organic solvent characterized as not being a uniform resin solution as an essential component, a copolymer resin and a pigment are mixed, pulverized or dispersed to obtain an aqueous pigment dispersion. From the viewpoint of the working efficiency in this step and the solubility or swelling of the resin, polyhydric alcohols having a high boiling point, low volatility and high surface tension are preferred. As described above, 1,5-pentanediol or diethylene glycol is particularly preferable. Diethylene glycol is more preferred from the viewpoint of reducing the particle size of the pigment in the dispersion.

However, an increase in the amount of these additives causes excessive dissolution and excessive swelling of the monomer component having an acid group.
Since the viscosity of the aqueous pigment dispersion liquid is increased, the content of such a water-soluble organic solvent is preferably set at (A) in the copolymer resin.
Although slightly different depending on the content of styrene monomer,
The ratio of (C) pigment to (D) water-soluble organic solvent is (C):
(D) = 1: 1 to 1:10, preferably (C) :( D) = 1: 1 to 1: 3.

Since the aqueous pigment dispersion obtained as described above shows acidity, when used as an ordinary ink, a part of the resin solution or a part of the resin solution is used in order to prevent corrosion of the ink container or the member using the ink. Neutralize everything. To carry out such a neutralization operation, an alkaline agent may be used after the aqueous pigment dispersion is produced, but it is preferable to add the alkaline agent simultaneously with the aqueous dispersion in the production process of the aqueous pigment dispersion. By doing so, the copolymer resin efficiently forms micelles or polymer orientation in an aqueous solution with a pigment contained in a water-insoluble monomer component such as a styrene monomer as a nucleus.

Examples of the alkaline agent for neutralizing the monomer component having an acid group include hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide and lithium hydroxide, and basic substances such as ammonia, triethylamine and morpholine. Others, triethanolamine, diethanolamine,
A base such as an alcoholamine such as N-methyldiethanolamine can be used.

The neutralization ratio of the resin to the acid value with an alkali agent is preferably from 30 to 200 mol%, particularly preferably from 40 to 120 mol%, from the particle diameter and dispersion stability of the pigment. 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. Here, the neutralization ratio is a value calculated by the following equation.

(Equation 1)

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 resin containing a water-insoluble monomer used in the present invention is preferably a resin containing a styrene monomer as a water-insoluble monomer component and a monomer component having an acid group. Alternatively, other water-insoluble monomer components may be used, or a styrene monomer and another water-insoluble monomer may be used in combination.
Examples of such water-insoluble monomer components include alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, and hydroxybutyl (meth) acrylate and derivatives thereof; phenyl (meth) acrylate, benzyl Allyl (meth) acrylates such as (meth) acrylate and phenylethyl (meth) acrylate, and derivatives thereof, and the like.

The pigment that can be used in the present invention is not particularly limited, and any known and commonly used pigments can be used. Examples thereof include inorganic pigments such as carbon black, titanium black, titanium white, zinc sulfide, and red iron oxide, and phthalocyanine. Pigments, azo pigments such as monoazo and disazo,
Organic pigments such as phthalocyanine pigments and quinacridone pigments are used.

As a method for dispersing the pigment, a dispersing device using a medium is effective, but a known and used dispersing device can be used. For example, ultrasonic homogenizer, paint shaker, ball mill, roll mill,
Sand mill, sand grinder, dyno mill, disper mat, SC mill, spike mill, nanomizer, agitator mill, planetary and the like.

The aqueous pigment dispersion of the present invention thus produced 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 aqueous pigment dispersion is mixed with the resin at 25 ° C. so as to have a weight ratio of 4: 1. A high-boiling water-soluble organic solvent which exhibits a partially dissolved or swollen state and does not become a uniform resin solution also functions as an ink drying inhibitor. Further, if necessary, an organic solvent having anti-drying property and permeability can be added and adjusted, and the mixture can be stirred uniformly, adjusted, and then filtered through a filter having a desired particle size.

The ink may be adjusted, for example, by adding a drying inhibitor or a permeable organic solvent, adjusting the concentration and viscosity, adjusting the pH, a surfactant, a preservative, a chelating agent, and the like.
A plasticizer, an antioxidant, an ultraviolet absorber and the like are added as needed.

The permeability of the ink is a property 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 known and commonly used ink jet recording inks such as an on-demand method such as a piezo method and a thermal method. In addition, extremely stable ink discharge can be performed in each type of printer.

[0026]

The present invention will be described in more detail with reference to the following examples. The present invention is not limited to these examples. In addition,
“Parts” in the following examples represent “parts by mass”.

(Example 1) Styrene (72 parts), acrylic acid (10 parts), methacrylic acid (13 parts), oxidation = 15
When mixed with a resin (I) consisting of 0 mgKOH / g and a weight average molecular weight of 7200 so as to have a weight ratio of 4: 1 at 25 ° C., it shows a partially dissolved or swollen state,
Diethylene glycol, which does not become a uniform resin solution, was used as a water-soluble organic solvent.

Using an aqueous resin solution (II) comprising 20% by mass of resin (I), 2.14% by mass of sodium hydroxide and water.・ Resin aqueous solution (II): 20 parts ・ Carbon black # 960 (manufactured by Mitsubishi Chemical Corporation):
10 parts ・ Diethylene glycol: 10 parts ・ Purified water: 10 parts ・ Zirconia beads (1.25 mm diameter): 400 parts After charging, the mixture was stirred for 3 hours using a paint shaker to obtain an aqueous pigment dispersion (III). ) Got.
The volume average particle size of this aqueous pigment dispersion was 78 nm. The aqueous pigment dispersion (III) was heated at 60 ° C.
When a 72-hour accelerated stability test was performed, the volume average particle size was 76 nm. No coarsening of particle size change, aggregation, and sediment were observed.

Next, 5 parts of glycerin, 5 parts of polyoxypropylene glyceryl ether and 70 parts of purified water were added to 20 parts of the aqueous pigment dispersion (III) and mixed.
The solution was filtered through a membrane filter to obtain an aqueous pigment ink for inkjet recording. The obtained aqueous pigment ink showed good dispersibility without aggregation. This ink is 60 ° C, 7
After the accelerated stability test for 2 hours, no coarsening of the particle size, aggregation or sediment was observed.

A thermal ink jet printer (H
In a printing test using DesignJet 2500CP (manufactured by P Company), the ink was stable without any nozzle clogging and no unstable ejection was observed immediately after production and after the accelerated stability test. Further, even after the continuous printing test with 500 g of the ink, the nozzle was not clogged and the ejection was not unstable.

Example 2 Styrene (72 parts), acrylic acid (10 parts), methacrylic acid (13 parts), oxidation = 15
When mixed with a resin (I) consisting of 0 mgKOH / g and a weight average molecular weight of 7200 so as to have a weight ratio of 4: 1 at 25 ° C., it shows a partially dissolved or swollen state,
Diethylene glycol and 1, which do not form a uniform resin solution
Implemented using 5-pentanediol as a water-soluble organic solvent.

Using an aqueous resin solution (II) comprising 20% by mass of the resin (I), 2.14% by mass of sodium hydroxide and water.・ Resin aqueous solution (II): 20 parts ・ Carbon black # 960 (manufactured by Mitsubishi Chemical Corporation):
10 parts Diethylene glycol: 5 parts 1,5-pentanediol: 5 parts ・ Purified water: 20 parts ・ Zirconia beads (1.25 mm diameter): 400 parts After charging, the mixture was stirred for 3 hours using a paint shaker. To obtain an aqueous pigment dispersion (IV). The volume average particle size of the aqueous pigment dispersion was 84 nm.

This aqueous pigment dispersion (IV) has 60
When an accelerated stability test was performed at ゜ C for 72 hours, the volume average particle size was 83 nm. Coarsening of particle size change, aggregation,
And no sediment was observed.

Next, 5 parts of glycerin, 5 parts of polyoxypropylene glyceryl ether and 70 parts of purified water were added to 20 parts of the aqueous pigment dispersion (IV) and mixed, and the mixture was filtered through a 0.5 μm membrane filter to obtain an inkjet recording liquid. An aqueous pigment ink was used. The obtained aqueous pigment ink showed good dispersibility without aggregation. This ink is 60 ° C, 72
After the accelerated stability test with time, no coarsening of the particle size, aggregation and sediment were observed.

Thermal type ink jet printer (H
In a printing test using DesignJet 2500CP (manufactured by P Company), the ink was stable without any nozzle clogging and no unstable ejection was observed immediately after production and after the accelerated stability test. Further, even after the continuous printing test with 500 g of the ink, the nozzle was not clogged and the ejection was not unstable.

(Example 3) Styrene (72 parts), acrylic acid (10 parts), methacrylic acid (13 parts), oxidation = 15
When mixed with a resin (I) consisting of 0 mgKOH / g and a weight average molecular weight of 7200 so as to have a weight ratio of 4: 1 at 25 ° C., it shows a partially dissolved or swollen state,
Performed using 1,5-pentanediol, which does not result in a uniform resin solution, as a water-soluble organic solvent.

Using an aqueous resin solution (II) comprising 20% by mass of resin (I), 2.14% by mass of sodium hydroxide and water.・ Resin aqueous solution (II): 20 parts ・ Carbon black # 960 (manufactured by Mitsubishi Chemical Corporation):
10 parts ・ 1,5-pentanediol: 10 parts ・ Purified water: 20 parts ・ Zirconia beads (1.25 mm diameter): 400 parts After charging, the mixture was stirred for 3 hours using a paint shaker to obtain aqueous solution. A pigment dispersion (V) was obtained. The volume average particle size of this aqueous pigment dispersion was 86 nm.

This aqueous pigment dispersion (IV) has 60
When an accelerated stability test was performed at ゜ C for 72 hours, the volume average particle size was 84 nm. Coarsening of particle size change, aggregation,
And no sediment was observed.

Next, 5 parts of glycerin, 5 parts of polyoxypropylene glyceryl ether and 70 parts of purified water were added to 20 parts of the aqueous pigment dispersion (V) and mixed, and the mixture was filtered through a 0.5 μm membrane filter. An aqueous pigment ink was used. The obtained aqueous pigment ink showed good dispersibility without aggregation. This ink showed no change in particle size and no sediment even after the accelerated stability test at 60 ° C. for 72 hours.

Thermal type ink jet printer (H
In a printing test using DesignJet 2500CP (manufactured by P Company), the ink was stable without any nozzle clogging and no unstable ejection was observed immediately after production and after the accelerated stability test. Further, even after the continuous printing test with 500 g of the ink, the nozzle was not clogged and the ejection was not unstable.

(Comparative Example 1) When mixed with the resin (I) at 25 ° C. at a weight ratio of 4: 1, propylpropylene glycol which becomes a soluble and uniform resin solution was used as a water-soluble organic solvent. An aqueous pigment dispersion liquid (VI) was obtained in the same steps as in Example 1. The volume average particle size was 90 nm. The aqueous pigment dispersion (VI) showed sediment after an accelerated stability test at 60 ° C. for 72 hours. The volume average particle size was 108 nm, and a change in the particle size was observed.

Next, an aqueous pigment ink for ink-jet recording was prepared in the same formulation as in Example 1. 60 ° C for this ink,
After a 72-hour accelerated stability test, sediment was observed. The volume average particle size was 98 nm. Thermal inkjet printer (DesignJ manufactured by HP)
In a printing test using (e.g., 2500CP), the image characteristics of the ink immediately after production were good, but the ink after the accelerated stability test had unstable ejection and poor image uniformity.

(Comparative Example 2) When mixed with the water-soluble organic solvent diethylene glycol used in Example 1 at a weight ratio of 4: 1, a resin J682 (St / AA / α-methylstyrene copolymer) An aqueous pigment dispersion (V) was obtained in the same step as in Example 1 using an acid value of 235 mgKOH / g and a weight average molecular weight of 1600. The volume average particle size was 326 nm. This aqueous pigment dispersion showed aggregation and sediment after an accelerated stability test at 60 ° C. for 72 hours.

(Comparative Example 3) When mixed with the water-soluble organic solvent diethylene glycol used in Example 1 at a weight ratio of 4: 1, a resin J680 (St / AA / α-methylstyrene copolymer) An aqueous pigment dispersion (V) was obtained in the same step as in Example 1 using an acid value of 215 mgKOH / g and a weight average molecular weight of 3900. The volume average particle size was 118 nm. This aqueous pigment dispersion (VII) showed sediment after an accelerated stability test at 60 ° C. for 72 hours. The volume average particle size was 124 nm, and a change in the particle size was recognized.

Next, an aqueous pigment ink for ink jet recording was prepared according to the same formulation as in Example 1. 60 ° C for this ink,
After a 72-hour accelerated stability test, sediment was observed. The volume average particle size was 121 nm. Thermal inkjet printer (Design made by HP)
In a print test using Jet 2500CP), although the image characteristics of the ink immediately after production were good, the ink after the accelerated stability test was unstable and had poor image uniformity.

[0046]

According to the method for producing an aqueous pigment dispersion of the present invention, an ink having excellent dispersion stability and long-term storage stability can be provided, and can be suitably used for an aqueous ink, a recording liquid and the like. . When using ink for inkjet recording,
Especially when applied to the thermal method, it has excellent ejection stability,
The resulting ink has extremely good water resistance and color development. Further, the aqueous pigment dispersion obtained by the production method of the present invention can be used as a coloring material such as a writing implement, another general printing method, and an aqueous paint.

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Claims (9)

[Claims] 1. An aqueous pigment dispersion comprising at least water, a resin containing a water-insoluble monomer, a water-soluble organic solvent and a pigment, wherein at 25 ° C. the resin is mixed with the water-soluble organic solvent at a weight ratio of 1: 1: 4. An aqueous pigment dispersion, characterized by using a combination of a resin and an organic solvent that shows a partially dissolved or swollen state when mixed to give a uniform resin solution. 2. The aqueous pigment dispersion according to claim 1, wherein the resin containing the water-insoluble monomer is a copolymer resin containing (A) a styrene monomer and (B) a monomer component having an acid group. . 3. The aqueous pigment dispersion according to claim 2, wherein the monomer component having an acid group is a water-soluble monomer. 4. The content of [(A) styrene monomer + (B) monomer component having acid group] in the copolymer resin is 50%.
-100% by mass, and the mass ratio of (A) a styrene monomer to (B) a monomer component having an acid group is (A) :( B) = 9: 1 to 1: 9. The aqueous pigment dispersion according to any one of claims 2 to 3. 5. The copolymer resin having an acid value of 60 to 300 mgK.
The aqueous pigment dispersion according to any one of claims 2 to 4, wherein the aqueous pigment dispersion is OH / g. 6. The aqueous pigment dispersion according to claim 1, wherein the water-soluble organic solvent is diethylene glycol. 7. An aqueous pigment dispersion obtained by dispersing a pigment in water using a resin containing a water-insoluble monomer in the presence of a water-soluble organic solvent. When mixed at a weight ratio of 1: 4,
A method for producing an aqueous pigment dispersion, wherein the dispersion is performed using a combination of a resin and an organic solvent that exhibits a partially dissolved or swollen state and does not form a uniform resin solution. 8. The method for producing an aqueous pigment dispersion according to claim 7, wherein the aqueous pigment dispersion is dispersed by a dispersing means using a medium. 9. An aqueous pigment dispersion prepared by using the aqueous pigment dispersion according to any one of claims 1 to 6, or the aqueous pigment dispersion produced by the method according to any one of claims 7 to 8. , An aqueous pigment ink composition for inkjet recording.