JP2000345095A - Aqueous pigment dispersion and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aqueous pigment dispersion in which carbon black contained exhibits excellent initial and long-term dispersibility and an excellent dispersion stability by using a surface-modified carbon black prepared by wet oxidation with a hypohalogenous acid and/or its salt and by specifying the concentration of a divalent metal cation in the dispersion. SOLUTION: The concentration of a divalent metal cation in the aquous pigment dispersion is adjusted to 100 ppm or lower, preferably 50 ppm or lower. Calcium, manganese, and copper ions, etc., are listed as the divalent metal cation. Preferably, the surface-modified carbon black has an average particle size of 300 nm or lower and its content in the dispersion is 1-30 wt.%. Sodium hypochlorite is preferable as the hypohalogenous acid (salt). The dispersion is prepared by finely dispersing carbon black in water, oxidizing the carbon black with a hypohalogenous acid (salt), and adjusting the concentration of a divalent metal cation in the dispersion to 100 ppm or lower.

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.
No. 3498 and JP-A-10-120958 describe that a certain amount or more of surface active hydrogen or a salt thereof is introduced into carbon black by wet oxidation of carbon black using a hypohalite, An aqueous pigment dispersion spontaneously dispersed with a surface-modified carbon black alone without a surfactant or a polymer dispersant is 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.

[0007] Generally, when surface-modified carbon black is produced by wet-oxidizing carbon black using a hypohalite, for example, a large amount of sodium chloride is generated as a by-product. A washing step is performed to remove sodium ions derived from the salt. Here, when water used for washing is ion-containing water containing divalent metal ions such as tap water, the surface-modified carbon black contains divalent metal cations, particularly calcium ions.

The present inventors have found that the presence of divalent metal cations, particularly calcium ions, adversely affects the dispersion stability of surface-modified carbon black in water,
The present invention provides a specific means for remarkably improving the dispersion stability of the surface-modified carbon black in water by removing such divalent metal cations from the aqueous dispersion of the surface-modified carbon black.

[0009]

SUMMARY OF THE INVENTION 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 a divalent metal cation concentration thereof. Is 100 ppm or less, whereby the above-mentioned object is achieved.

The aqueous pigment dispersion of the present invention comprises a step of finely dispersing carbon black in water; a step of oxidizing the carbon black with hypohalous acid and / or a salt thereof; Making the contained divalent metal cation a concentration of 100 ppm or less.

[0011]

DETAILED DESCRIPTION OF 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 divalent metal cations contained therein have been removed to a predetermined amount or less.

Here, divalent metal cations include calcium ions, manganese ions, copper ions and the like.
The amount of the valent cation can be measured using, for example, atomic absorption spectrometry.

The carbon black as a raw material is generally commercially available as a carbon black for color, and the divalent metal cation contained in the carbon black contains 200 ppm.
Below, preferably 100 ppm or less can be used. Specifically, carbon black for color is classified into acidic carbon black, neutral carbon black, and basic carbon black according to pH, and furnace carbon black, channel carbon black, acetylene carbon black, and thermal carbon black when classified according to production method. Carbon black having a divalent metal cation content of 200 ppm or less, preferably 100 ppm or less can be used.

Specific examples of the carbon black used in the present invention include, for example, # 990, MA600, MA77
(Mitsubishi Chemical Corporation) Color Black FW1
8, color black S170, special black 4
A, (above, manufactured by Degussa), Monarch 880, Regal 400R, Legal 660R (above, manufactured by Cabot)
Raven 1040, Raven 1255, Conductex SC Ultra (all manufactured by Columbian Carbon Co., Ltd.) and the like. 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 (eg, sodium hypochlorite) having an effective halogen concentration of 5 to 15% by weight are charged into a suitable amount of water, and the reaction is carried out for 5 hours or more, preferably about 10 to 10 hours. The stirring is performed for 15 hours at 0 ° C. or higher, preferably at room temperature to 100 ° C. 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-treated 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-treated carbon black is measured by an "inert gas-infrared absorption method". In this method, the surface-treated 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-treated carbon black used in the aqueous pigment dispersion of the present invention preferably has a high oxygen content. This is because such surface-treated carbon black exhibits particularly good water dispersibility.

The water used for preparing the aqueous pigment dispersion of the present invention is preferably deionized water such as ion-exchanged water. Ion-containing water such as tap water is not preferred. Ion-containing water contains divalent metal cations, for example,
If calcium ion or the like is contained and an aqueous pigment dispersion is prepared using ion-containing water, a divalent metal cation is contained in the dispersion, and the divalent metal cation is an aqueous pigment dispersion. This has an adverse effect on the performance, especially the dispersion stability.

Thereafter, the beads and coarse particles are removed using a mesh wire mesh. Alternatively, after removing the beads and coarse particles, the wet cake is washed with deionized water to remove by-product salts. As a method for removing by-product salts, washing with water and membrane purification are performed.

Since divalent metal cations cannot be removed by ordinary washing with water and membrane purification, deionized water containing no divalent metal ions is used.

As the separation membrane, a reverse osmosis membrane or an ultrafiltration membrane can be used. As the reverse osmosis membrane, NTR-7250, NTR-719HF, NTR-7 manufactured by Nitto Denko Corporation
410, as an ultrafiltration membrane, NTU- manufactured by Nitto Denko Corporation
2120, NTU-3150, NTU-3520 and the like.

Washing of the surface-modified carbon black with a divalent metal cation concentration of 100 ppm or less, especially 50 pp
m or less. When the concentration of the divalent metal cation exceeds 100 ppm, aggregation of the pigment particles is liable to occur, and the initial dispersibility and the long-term dispersibility of the pigment in water cannot be maintained.
The concentration of the divalent metal cation can be determined using, for example, atomic absorption spectrometry.

If necessary, the pH of the dispersion of the surface-treated 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 and a fungicide can be added to the dispersion of the present invention.

The surface-treated 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-treated carbon black is less than 1% by weight, the coloring concentration becomes insufficient, and if it exceeds 30% by weight, the surface-treated carbon black tends to agglomerate, and the viscosity increases during long-term storage, or precipitation occurs Is not preferred.

The average particle size of the surface-treated 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 diameter of the surface-treated 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 colorant for various inks for ink jet recording, writing instruments, printing, stamping and the like.

[0032]

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 "MA77" (primary particle size 23
nm, DBP oil absorption 68ml / 100g, manufactured by Mitsubishi Chemical Corporation)
100 g was mixed with 700 g of ion-exchanged water and pulverized by a ball mill using zirconia beads. Sodium hypochlorite (effective chlorine concentration = 12% by weight)
00 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. 5A
(Advantech Toyo Co., Ltd.), and washed with ion-exchanged water. The pigment wet cake was redispersed in 5 kg of ion-exchanged water, desalted with a reverse osmosis membrane using ion-exchanged water, and further concentrated to a pigment concentration of 10% by weight to prepare an aqueous pigment dispersion.

The calcium ion concentration of the obtained pigment dispersion was measured with an atomic absorption spectrometer (Shimadzu atomic absorption / flame spectrophotometer AA-660; manufactured by Shimadzu Corporation) and found to be 30 ppm.

Further, the average particle diameter of the surface-treated 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 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-treated carbon black was measured by "inert gas-infrared absorption method", it was 6% 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 " Conductex SC Ultra" (primary particle diameter 20 nm, DBP oil absorption 115 ml / 1
(80 g, Degussa) 80 g of ion-exchanged water
And crushed with a ball mill using zirconia beads. 1000 g of sodium hypochlorite (effective chlorine concentration = 12% by weight) was added dropwise to this dispersion, and room temperature to 100
Stirred at C for 10 hours.

The obtained slurry was subjected to quantitative filter paper No. 5A
(Advantech Toyo Co., Ltd.), and further washed with ion-exchanged water. The pigment wet cake was redispersed in 5 kg of ion-exchanged water, desalted with a reverse osmosis membrane using ion-exchanged water, and further concentrated to a pigment concentration of 10% by weight to prepare an aqueous pigment dispersion.

The calcium ion concentration of the obtained pigment dispersion was measured by an atomic absorption analyzer (Shimadzu Atomic Absorption / Frame Spectrophotometer AA-660; manufactured by Shimadzu Corporation) and found to be 25 ppm.

Further, the average particle diameter of the surface-treated 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 145 nm.

The oxygen content of the surface-treated carbon black contained in the pigment dispersion was measured in the same manner as in Example 1, and was found to be 8% 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 this was 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 Commercially available carbon black "Color Black S170"
(Primary particle diameter 17nm, DBP oil absorption 150ml / 100
g, Degussa Co., Ltd.) (200 g) was mixed with ion-exchanged water (2000 g) and pulverized by a ball mill using zirconia beads. 2500 g of sodium hypochlorite (effective chlorine concentration = 12% by weight) was added dropwise to the dispersion, and 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. 5A
(Advantech Toyo Co., Ltd.), and further washed with ion-exchanged water. This pigment wet cake was redispersed in 9 kg of ion-exchanged water, desalted with a reverse osmosis membrane using ion-exchanged water, and concentrated to a pigment concentration of 10% by weight.

The calcium ion concentration of the obtained dispersion was measured by an atomic absorption spectrometer (Shimadzu atomic absorption / flame spectrophotometer).
AA-660; manufactured by Shimadzu Corporation)
It was 40 ppm.

Further, the average particle diameter of the surface-treated 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 oxygen content of the surface-treated carbon black contained in the pigment dispersion was measured in the same manner as in Example 1, and was found to be 8.3% 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 good brown state with micro-Brownian motion.
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 “MA77” (primary particle size 23
nm, DBP oil absorption 68ml / 100g, manufactured by Mitsubishi Chemical Corporation)
100 g was mixed with 700 g of tap water and pulverized by a ball mill using zirconia beads. 500 g of sodium hypochlorite (effective chlorine concentration = 12% by weight)
Was added dropwise, followed by stirring at room temperature to 100 ° C. for 10 hours.

The obtained slurry was subjected to quantitative filter paper no. 5A
(Advantech Toyo Co., Ltd.), and washed with tap water. The pigment wet cake was redispersed in 5 kg of tap water, desalted with a reverse osmosis membrane using tap water, and further,
The aqueous pigment dispersion was prepared by concentrating to a pigment concentration of 10% by weight.

The calcium ion concentration of the obtained pigment dispersion was measured by an atomic absorption spectrometer (Shimadzu atomic absorption / flame spectrophotometer AA-660; manufactured by Shimadzu Corporation) and found to be 1.2% by weight. .

Further, the average particle diameter of the surface-treated 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 310 nm.

The oxygen content of the surface-treated carbon black contained in the pigment dispersion was measured in the same manner as in Example 1, and was found to be 6% 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 this was 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 “Conductex SC Ultra” (primary particle diameter 20 nm, DBP oil absorption 115 ml / 1
(80 g, Degussa) 80 g of ion-exchanged water
And crushed with a ball mill using zirconia beads. 1000 g of sodium hypochlorite (effective chlorine concentration = 12% by weight) was added dropwise to this dispersion, and room temperature to 100
Stirred at C for 10 hours.

The obtained slurry was subjected to quantitative filter paper No. 5A
(Advantech Toyo Co., Ltd.), and further washed with ion-exchanged water. The pigment wet cake was redispersed in 5 kg of tap water, desalted with a reverse osmosis membrane using tap water, and further concentrated to a pigment concentration of 10% by weight to prepare an aqueous pigment dispersion.

The calcium ion concentration of the obtained pigment dispersion was measured by an atomic absorption spectrometer (Shimadzu atomic absorption / flame spectrophotometer AA-660; manufactured by Shimadzu Corporation) and found to be 8000 ppm.

Further, the average particle diameter of the surface-treated carbon black contained in the aqueous pigment dispersion was measured using a laser light diffusion type particle size distribution analyzer (Otsuka Electronics Co., Ltd., LPA3000 /
3100) was 250 nm.

The oxygen content of the surface-treated carbon black contained in the pigment dispersion was measured in the same manner as in Example 1, and it was 8% 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 put in a sealed container, and this was 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 3 Commercially available carbon black "Color Black S170"
(Primary particle diameter 17nm, DBP oil absorption 150ml / 100
g, Degussa Co., Ltd.) (200 g) was mixed with tap water (2000 g) and pulverized by a ball mill using zirconia beads.
Sodium hypochlorite (effective chlorine concentration = 1)
(2% by weight) was dropped, and 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. 5A
(Advantech Toyo Co., Ltd.) and further washed with tap water. The obtained wet cake was adjusted to a pigment concentration of 10% by weight using tap water to prepare an aqueous pigment dispersion.

The calcium ion concentration of the obtained pigment dispersion was measured by an atomic absorption spectrometer (Shimadzu atomic absorption / flame spectrophotometer AA-660; manufactured by Shimadzu Corporation) and found to be 300 ppm.

Further, the average particle diameter of the surface-treated 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 120 nm.

The oxygen content of the surface-treated carbon black contained in the pigment dispersion was measured in the same manner as in Example 1, and was found to be 8.3% 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 had a micro-Brownian motion and was in a good dispersion state. 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.

The results for the aqueous pigment dispersions of Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 2.

[0077]

[Table 2]

[0078]

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.

Continued on the front page (72) Inventor Nobuyuki Murai 8-1, Sanarahigashicho, Neyagawa-shi, Osaka Orient Chemical Industry Co., Ltd. (72) Inventor Makiko Matsui 8-1, Sanurigashicho, Neyagawa-shi, Osaka Orient Chemical F term in Industrial Co., Ltd. (reference) 4J037 AA02 CA05 CA14 DD05 DD20 DD27 EE02 EE19 EE28 EE33 EE43 FF05 FF15 4J039 BA04 BE01 CA06 DA02 EA44 GA07 GA24

Claims (7)

[Claims] 1. A surface modified carbon black obtained by wet oxidation of carbon black using hypohalous acid and / or a salt thereof, wherein the divalent metal cation concentration is 100 ppm or less. Aqueous pigment dispersion. 2. A surface modified carbon black obtained by wet oxidation of carbon black using hypohalous acid and / or a salt thereof, wherein the divalent metal cation concentration is 50 ppm or less. Aqueous pigment dispersion. 3. The aqueous pigment dispersion according to claim 1, wherein the divalent metal cation is a calcium ion. 4. 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. 5. The aqueous pigment dispersion according to claim 1, wherein the average particle diameter of the surface-modified carbon black is 300 nm or less. 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 a divalent metal cation contained in the aqueous pigment dispersion. To a concentration of 100 ppm or less. 7. 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 divalent metal cation contained in the aqueous pigment dispersion. To a concentration of 50 ppm or less.