JP2000345094A - Aqueous pigment dispersion and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a aqueous pigment dispersion having excellent dispersibility which excels in the initial and long-term dispersibilities of carbon black in water and difficult to cause aggregation of carbon black particles. SOLUTION: A aqueous pigment dispersion liquid comprises surface modified carbon black to be obtained by subjecting carbon black to wet oxidation with the use of a hypohalogenous acid and/or its salt with a concentration of its halide ion of not more than 1,000 ppm. The content of the surface modified carbon black is preferably 1-30 wt.% based on the total amount of the water- based pigment dispersion, and the average particle diameter of the surface modified carbon black is preferably not greater than 300 nm.

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 more particularly to an aqueous pigment dispersion containing carbon black having improved long-term water dispersibility as a colorant and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, aqueous dye inks containing a black dye have been mainly used as recording liquids for writing instruments and ink jet printers. In recent years, aqueous pigment inks using pigments such as carbon black have attracted attention in order to improve the image quality and durability of recorded matters.

For example, JP-A-64-6074 and JP-A-64-31881 disclose aqueous pigment inks in which carbon black is dispersed with a surfactant or a polymer dispersant.

However, with these inks, when the ink content of the colorant is increased in order to increase the print density of the recorded matter, there arises a problem that the viscosity of the ink sharply increases at the same time. Also, in order to stably disperse carbon black, an excess of a surfactant or a polymer dispersant is required,
These cause bubbles and decrease the defoaming property, and in particular, when used in an ink jet recording ink, there is a problem that the printing stability is deteriorated.

In order to solve these problems, Japanese Patent Laid-Open Publication No.
-3498 and JP-A-10-120958 disclose the use of carbon black with hypohalous acid and / or
Alternatively, a certain amount of surface active hydrogen or a salt thereof is introduced into carbon black by wet oxidation using a salt thereof, and the surface modified carbon black alone is spontaneously dispersed without a surfactant or a polymer dispersant. Aqueous pigment dispersions are described.

[0006]

DISCLOSURE OF THE INVENTION The present invention relates to an aqueous dispersion of the surface-modified carbon black as described above,
Further, it is an object of the present invention to provide an aqueous pigment dispersion which has further improved long-term dispersibility, hardly causes aggregation of carbon black particles, and has excellent dispersion stability.

Generally, surface-modified carbon black obtained by wet oxidation of carbon black with hypohalous acid and / or a salt thereof contains a large amount of halogen ions. This is because hypohalous acids generate halogen ions when oxidizing carbon black.

The present inventors have found that halogen ions adversely affect the dispersion stability of surface-modified carbon black in water, and remove such halogen ions from the aqueous dispersion of surface-modified carbon black to improve the surface. Specific means for significantly improving the dispersion stability of porous carbon black in water have been provided.

[0009]

The present invention comprises a surface-modified carbon black obtained by wet oxidation of carbon black with hypohalous acid and / or a salt thereof, and has a halogen ion concentration of 1000 ppm or less. It is intended to provide an aqueous pigment dispersion characterized by being
Thereby, the above object is achieved.

The aqueous pigment dispersion of the present invention is produced in a step of finely dispersing carbon black in water; a step of oxidizing the carbon black with hypohalous acid and / or a salt thereof; and a step of oxidizing the carbon black. A step of removing halogen ions to 1000 ppm or less.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The aqueous pigment dispersion of the present invention contains a surface-modified carbon black obtained by wet oxidation of carbon black with hypohalous acid and / or a salt thereof. This is an aqueous pigment dispersion in which halogen ions generated during oxidation are removed to a predetermined amount or less.

Here, the term "halogen ion" means chlorine ion, bromide ion, iodine ion and the like, and the amount of halogen ion can be measured using, for example, an ion electrode.

As the carbon black as a raw material, those generally commercially available as carbon black for color can be used. Specifically, when classified by pH, acidic carbon black, neutral carbon black, basic carbon black, and when classified by manufacturing method, furnace type carbon black, channel type carbon black,
Either acetylene type carbon black or thermal type carbon black can be used.

Specific examples of the carbon black used in the present invention include, for example, # 990, MA600, # 40 (above, manufactured by Mitsubishi Chemical Corporation) Color Black FW200,
Color Black S170, Special Black 550,
Special Black 4A, PRINTEX 30 (or more,
Degussa), Monarch 880, Regal 250R, Regal 400R, Legal 660R (all manufactured by Cabot) Raven 1040 and Raven 1255 (all manufactured by Columbian Carbon). These descriptions are examples of carbon black suitable for the present invention, and the present invention is not limited by these.

In the present invention, such a raw material carbon black is wet-oxidized in water using hypohalous acid and / or a salt thereof. Specific examples of the hypohalous acid and / or its salt include sodium hypochlorite, lithium hypochlorite, sodium hypobromite, lithium hypobromite and the like. It is particularly preferable from the viewpoint of properties and cost.

In the oxidation reaction, carbon black and a hypohalite (for example, sodium hypochlorite) having an effective halogen concentration of 5 to 15% are charged into a suitable amount of water, and the reaction is carried out for 5 hours or more, preferably about 10 to 15 hours. It is carried out by stirring at 0 ° C. or more, preferably at room temperature to 100 ° C. for a time. In this case, it is preferable that the carbon black is pulverized in advance or oxidized while pulverizing. As a grinding method, beads such as glass, zirconia, alumina, stainless steel, magnetism, etc. are crushed by a ball mill, attritor, colloid mill, sand mill, etc. And pulverize.

The amount of hypohalite used varies depending on the type and effective halogen concentration, but is generally from 0.5 to 150 in terms of 100% based on the weight of carbon black.
% By weight, preferably 1 to 75% by weight.

The surface-modified carbon black obtained is about 3
It has an oxygen content of at least about 5% by weight, preferably at least about 5% by weight. As a result of the oxidation by the method of the present invention, the oxygen content increases to several times or more the oxygen content of the carbon black before the treatment.

The oxygen content of the surface-modified carbon black is measured by an "inert gas-infrared absorption method". In this method, the surface-modified carbon black is heated in a stream of an inert gas such as helium, oxygen is extracted as carbon monoxide, and the amount is measured by an infrared absorption method. Details are described in JIS Z 2613-1976.

Generally, in the reaction between carbon black and hypohalite, oxygen functional groups such as carboxyl group, hydroxyl group and carbonyl group are formed on the surface of carbon black. The greater the oxygen content, the greater the amount of oxygen functional groups.

The surface-modified carbon black used in the aqueous pigment dispersion of the present invention preferably has a high oxygen content. This is because such surface-modified carbon black exhibits particularly good water dispersibility.

Next, the dispersion of the oxidized surface-modified carbon black is filtered (hot), and the obtained wet cake is redispersed in water. Then, beads and coarse particles are removed using a mesh wire mesh. .

Next, halogen ions generated during wet oxidation of the carbon black are removed from the surface-modified carbon black obtained by the oxidation. The removal of halogen ions is performed by washing the surface-modified carbon black with water. The water washing is preferably performed using deionized water such as ion-exchanged water.

Usually, deionized water is passed through the surface-modified carbon black through a separation membrane that does not allow the surface-modified carbon black to pass through, and the surface-modified carbon black is washed with water. As the separation membrane, a reverse osmosis membrane or an ultrafiltration membrane is used. As the reverse osmosis membrane, NTR-7250, NTR-719HF, NTR manufactured by Nitto Denko Corporation
TR-7410, NTU-2120, NTU-3150, NTU-352 manufactured by Nitto Denko Corporation as the ultrafiltration membrane
0 magnitude.

When the surface-modified carbon black is washed with water, the halogen ion concentration is 1000 ppm or less, especially 500 pp.
m or less, and more preferably 300 ppm or less. When the concentration of the halogen ion is 1000 ppm or more, aggregation of the pigment particles is likely to occur, and the initial dispersibility and long-term dispersibility of the pigment in water cannot be maintained, so that the effects of the present invention are hardly achieved.

The concentration of the halogen ions is preferably measured using an ion electrode. This is because the concentration of halogen ions can be easily measured simply by immersing in the dispersion at the time of washing or the washing water after washing. By using an ion electrode, it is possible to accurately measure the concentration of halogen ions in real time without interrupting the manufacturing process.

Preferred ion electrodes are, for example, chloride ion electrodes 8002-10C, bromide ion electrodes 8005-10C and iodide ion electrodes 80 manufactured by HORIBA, Ltd.
04-10C and the like.

Thereafter, if necessary, the pH of the dispersion of the surface-modified carbon black may be adjusted. Examples of the pH adjuster include hydroxides of alkali metals such as lithium hydroxide, sodium hydroxide, potassium hydroxide, aqueous ammonia, triethanolamine, diethanolamine, and lower alkylamines, and amines.

Further, a preservative, a fungicide and the like can be added to the aqueous pigment dispersion of the present invention.

The surface-modified carbon black according to the present invention is generally contained in an amount of 1 to 40% by weight, preferably 5 to 20% by weight, based on the total amount of the aqueous pigment dispersion. If the content of the surface-modified carbon black is less than 1% by weight, the coloring concentration becomes insufficient, and if it exceeds 30%, the surface-modified carbon black tends to agglomerate and becomes viscous or precipitate during long-term storage. Is not preferred.

The average particle diameter of the surface-modified carbon black in the aqueous pigment dispersion of the present invention is preferably 300 nm or less, more preferably 150 nm or less. If the average particle size of the surface-modified carbon black exceeds 300 nm, sedimentation of the pigment tends to occur.

The aqueous pigment dispersion of the present invention can be used as a coloring agent for various inks for ink jet recording, writing instruments, printing, stamping and the like.

[0033]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Example 1 Commercially available carbon black "Special Black 4A"
(Primary particle diameter 25nm, DBP oil absorption 90ml / 100
g, manufactured by Degussa Co., Ltd.)
It was pulverized by a ball mill using zirconia beads. Sodium hypochlorite (effective chlorine concentration = 12
%) 850 g was added dropwise, and the mixture was stirred at room temperature to 100 ° C for 10 hours. The obtained slurry was subjected to quantitative filter paper No. The mixture was filtered through 5A (manufactured by Advantech Toyo Co., Ltd.) and further washed with water. The pigment wet cake was redispersed in 5 kg of water, desalted with a reverse osmosis membrane until the chloride ion concentration reached 250 ppm, and further concentrated to a pigment concentration of 10% by weight to prepare an aqueous pigment dispersion.

The chloride ion concentration of the obtained pigment dispersion was measured using a chloride ion electrode (manufactured by HORIBA, Ltd., chloride ion electrode 80).
02-10C, ion meter F23C), it was 280 ppm.

Further, the average particle size of the surface-modified carbon black contained in the aqueous pigment dispersion was measured using a laser light diffusion type particle size distribution analyzer (LPA3000 / Otsuka Electronics Co., Ltd.).
3100) was 120 nm.

The obtained pigment dispersion was further concentrated, dried and pulverized to obtain a fine powder of oxidized carbon black. When the oxygen content of the obtained surface-modified carbon black was measured by "inert gas-infrared ray absorption method", it was 7.5% by weight. This analysis was performed under the analysis conditions shown in Table 1.

[0038]

[Table 1]

A small amount of the obtained pigment dispersion was taken and observed at 400 times magnification using an optical microscope. As a result, the whole was in a micro-Brownian motion and was in a good dispersion state.
Further, even if the observation was continued under an optical microscope, aggregation over time was not observed.

Further, the obtained pigment dispersion was placed in a sealed container and left at 50 ° C. for one month. The dispersion after standing did not cause aggregation or the like, and the viscosity and the average particle diameter were not changed from the values before standing.

Example 2 Commercially available carbon black "Color Black S170"
(Primary particle diameter 17nm, DBP oil absorption 150ml / 100
g, manufactured by Degussa Co., Ltd.) was mixed with 850 g of water and pulverized by a ball mill using zirconia beads. Sodium hypochlorite (effective chlorine concentration = 12%)
After dropping 1500 g, the mixture was reacted for 5 hours while being pulverized by a ball mill, and further stirred at room temperature to 100 ° C. for 10 hours. The obtained slurry was subjected to quantitative filter paper No. The solution was filtered through 5A (manufactured by Advantech Toyo) and washed with water. The pigment wet cake was redispersed in 5 kg of water, desalted with a reverse osmosis membrane until the chloride ion concentration reached 200 ppm, and further concentrated to a pigment concentration of 10% by weight to prepare an aqueous pigment dispersion.

The chloride ion concentration of the obtained pigment dispersion was measured by using a chloride ion electrode (manufactured by HORIBA, Ltd., chloride ion electrode 80).
02-10C, ion meter F23C), it was 220 ppm.

Further, the average particle diameter of the surface-modified carbon black contained in the aqueous pigment dispersion was measured using a laser light diffusion type particle size distribution analyzer (LPA3000 / Otsuka Electronics Co., Ltd.).
3100) was 110 nm.

The oxygen content of the surface-modified carbon black contained in the pigment dispersion was measured in the same manner as in Example 1, and it was 8.5% by weight.

A small amount of the obtained pigment dispersion was taken and observed at 400 times magnification using an optical microscope. As a result, the whole was in a micro-Brownian motion and was in a good dispersion state.
Further, even if the observation was continued under an optical microscope, aggregation over time was not observed.

Further, the obtained pigment dispersion was placed in a sealed container and left at 50 ° C. for one month. The dispersion after standing did not cause aggregation or the like, and the viscosity and the average particle diameter were not changed from the values before standing.

Example 3 100 g of commercially available carbon black "REGAL 660R" (primary particle diameter 24 nm, DBP oil absorption 60 ml / 100 g, manufactured by Degussa Co., Ltd.) was mixed with 1300 g of water and pulverized by a ball mill using zirconia beads. 500 g of sodium hypochlorite (effective chlorine concentration = 12%)
Was added dropwise, and the mixture was stirred at room temperature to 100 ° C. for 10 hours. The obtained slurry was subjected to quantitative filter paper No. The solution was filtered through 5A (manufactured by Advantech Toyo) and washed with water. The pigment wet cake was redispersed in 5 kg of water, desalted with a reverse osmosis membrane until the chloride ion concentration reached 280 ppm, and further concentrated to a pigment concentration of 10% by weight to prepare an aqueous pigment dispersion.

The chloride ion concentration of the obtained pigment dispersion was measured by using a chloride ion electrode (manufactured by HORIBA, Ltd., chloride ion electrode 80).
02-10C, ion meter F23C), it was 300 ppm.

Further, the average particle diameter of the surface-modified carbon black contained in the aqueous pigment dispersion was measured using a laser light diffusion type particle size distribution analyzer (LPA3000 / Otsuka Electronics Co., Ltd.).
3100) and found to be 70 nm.

Further, the oxygen content of the surface-modified carbon black contained in the pigment dispersion was measured in the same manner as in Example 1, and it was 6% by weight.

A small amount of the obtained pigment dispersion was taken and observed at 400 times magnification using an optical microscope. As a result, the whole was in a micro-Brownian motion and was in a good dispersion state.
Further, even if the observation was continued under an optical microscope, aggregation over time was not observed.

Further, the obtained pigment dispersion was placed in a sealed container and left at 50 ° C. for one month. The dispersion after standing did not cause aggregation or the like, and the viscosity and the average particle diameter were not changed from the values before standing.

Comparative Example 1 Commercially available carbon black "Special Black 4A"
(Primary particle diameter 25nm, DBP oil absorption 90ml / 100
g, manufactured by Degussa Co., Ltd.)
It was pulverized by a ball mill using zirconia beads. Sodium hypochlorite (effective chlorine concentration = 12
%) 850 g was added dropwise, and the mixture was stirred at room temperature to 100 ° C for 10 hours. The obtained slurry was subjected to quantitative filter paper No. It filtered with 5A (made by Advantech Toyo Co., Ltd.). The obtained wet cake was adjusted to a pigment concentration of 10% by weight to prepare an aqueous pigment dispersion.

The concentration of chloride ions in the obtained pigment dispersion was measured using a chloride ion electrode (manufactured by HORIBA, Ltd., chloride ion electrode 80).
02-10C, ion meter F23C) and found to be 9000 ppm.

Further, the average particle diameter of the surface-modified carbon black contained in the aqueous pigment dispersion was measured by a laser light diffusion type particle size distribution analyzer (LPA3000 / Otsuka Electronics Co., Ltd.).
3100) was 350 nm.

The oxygen content of the surface-modified carbon black contained in the pigment dispersion was measured in the same manner as in Example 1, and was found to be 7.5% by weight.

A small amount of the obtained pigment dispersion was taken and observed at 400 times magnification using an optical microscope.
Aggregates having a diameter of 0 nm or more were present, and if the observation was continued under an optical microscope as it was, the number of the aggregates increased over time, and the particle size also increased.

Further, the obtained pigment dispersion was placed in a sealed container and left at 50 ° C. for one month. The dispersion after standing has an increased viscosity compared to the dispersion immediately after production,
Gelation was confirmed.

Comparative Example 2 Commercially available carbon black "Color Black S170"
(Primary particle diameter 17nm, DBP oil absorption 150ml / 100
g, manufactured by Degussa Co., Ltd.) was mixed with 850 g of water and pulverized by a ball mill using zirconia beads. Sodium hypochlorite (effective chlorine concentration = 12%)
After dropping 1500 g, the mixture was reacted for 5 hours while being pulverized by a ball mill, and further stirred at room temperature to 100 ° C. for 10 hours. The obtained slurry was subjected to quantitative filter paper No. The solution was filtered through 5A (manufactured by Advantech Toyo) and washed with water. The obtained wet cake was adjusted to a pigment concentration of 10% by weight to prepare an aqueous pigment dispersion.

The chloride ion concentration of the obtained pigment dispersion was measured using a chloride ion electrode (manufactured by HORIBA, Ltd., chloride ion electrode 80).
02-10C, ion meter F23C) and found to be 3000 ppm.

Further, the average particle diameter of the surface-modified carbon black contained in the aqueous pigment dispersion was measured by using a laser light diffusion type particle size distribution analyzer (LPA3000, manufactured by Otsuka Electronics Co., Ltd.).
3100) was 180 nm.

The oxygen content of the surface-modified carbon black contained in the pigment dispersion was measured in the same manner as in Example 1, and it was 8.5% by weight.

A small amount of the obtained pigment dispersion was taken and observed at 400 times magnification using an optical microscope.
Aggregates having a diameter of 0 nm or more were present, and if the observation was continued under an optical microscope as it was, the number of the aggregates increased over time, and the particle size also increased.

Further, the obtained pigment dispersion liquid was placed in a sealed container, and this was left at 50 ° C. for one month. It was confirmed that the dispersion after standing had an increased viscosity and gelled as compared with the dispersion immediately after production.

Comparative Example 3 100 g of commercially available carbon black "REGAL 660R" (primary particle diameter 24 nm, DBP oil absorption 60 ml / 100 g, manufactured by Degussa) was mixed with 1300 g of water, and pulverized by a ball mill using zirconia beads. 500 g of sodium hypochlorite (effective chlorine concentration = 12%)
Was added dropwise, and the mixture was stirred at room temperature to 100 ° C. for 10 hours. The obtained slurry was subjected to quantitative filter paper No. The solution was filtered through 5A (manufactured by Advantech Toyo) and washed with water. This pigment wet cake was redispersed in 5 kg of water, and chlorine ions 8
Demineralized by reverse osmosis membrane to 00 ppm, and further, pigment concentration 1
The aqueous pigment dispersion was prepared by concentrating to 0% by weight.

The chloride ion concentration of the obtained pigment dispersion was measured using a chloride ion electrode (Horiba Seisakusho, chloride ion electrode 80).
02-10C, ion meter F23C), and found to be 1200 ppm.

Further, the average particle diameter of the surface-modified carbon black contained in the aqueous pigment dispersion was measured using a laser light diffusion type particle size distribution analyzer (LPA3000 / Otsuka Electronics Co., Ltd.).
3100) was 75 nm.

The oxygen content of the surface-modified carbon black contained in the pigment dispersion was measured in the same manner as in Example 1, and it was 6% by weight.

A small amount of the obtained pigment dispersion was taken and observed at 400 times magnification using an optical microscope. Immediately after the preparation of the pigment dispersion, the whole was in a good dispersion state with micro-Brownian motion. However, if the observation is continued under an optical microscope as it is, an aggregate having a particle diameter of 300 nm or more is generated,
Further, the number of aggregates increased with time, and the particle size also increased.

Further, the obtained pigment dispersion was placed in a sealed container and left at 50 ° C. for one month. It was confirmed that the dispersion after standing had an increased viscosity and gelled as compared with the dispersion immediately after production.

Table 2 shows the results of the aqueous pigment dispersions of Examples 1 to 3 and Comparative Examples 1 to 3.

[0072]

[Table 2]

[0073]

According to the aqueous pigment dispersion of the present invention, aggregation of carbon black particles hardly occurs, and initial dispersibility and long-term dispersibility are secured. Further, by the method for producing an aqueous pigment dispersion of the present invention, an aqueous pigment dispersion having such an effect can be easily produced.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Nobuyuki Murai, Inventor No. 8-1, Sanarahigashicho, Neyagawa-shi, Osaka Orient Chemical Industry Co., Ltd. (72) Makiko Matsui, No. 8-1, Sanurigashicho, Neyagawa-shi, Osaka F-term in Orient Chemical Co., Ltd. (reference) 4J037 AA02 CA14 DD05 DD20 EE02 EE19 EE28 EE33 EE43 FF05 FF15 4J039 BE01 CA06 DA02 EA19 EA44 GA07 GA24

Claims (6)

[Claims] An aqueous solution comprising a surface-modified carbon black obtained by wet-oxidizing carbon black with hypohalous acid and / or a salt thereof, and having a halogen ion concentration of 1000 ppm or less. Pigment dispersion. 2. An aqueous solution comprising a surface-modified carbon black obtained by wet-oxidizing carbon black with hypohalous acid and / or a salt thereof, and having a halogen ion concentration of 500 ppm or less. Pigment dispersion. 3. The aqueous pigment dispersion according to claim 1, wherein the content of the surface-modified carbon black is 1 to 30% by weight based on the total amount of the aqueous pigment dispersion. 4. The aqueous pigment dispersion according to claim 1, wherein the average particle diameter of the surface-modified carbon black is 300 nm or less. 5. A step of finely dispersing carbon black in water; a step of oxidizing the carbon black with hypohalous acid and / or a salt thereof; and removing halogen ions generated in the oxidizing step to 1000 ppm or less. A method for producing an aqueous pigment dispersion, comprising: 6. A step of finely dispersing carbon black in water; a step of oxidizing the carbon black with hypohalous acid and / or a salt thereof; and removing halogen ions generated in the oxidizing step to 500 ppm or less. A method for producing an aqueous pigment dispersion, comprising: