JPH11323175A - Easily water-dispersible carbon black and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an easily water-dispersible carbon black having an excellent dispersibility, i.e., easily dispersible in water and capable of stably maintaining the dispersion state for a long term. SOLUTION: This carbon black has a surface modified by oxidation and a heat of wetting with water of 0.1 J/m<2> or higher and is produced by subjecting a carbon black to wet oxidation with a peroxodisulfate, peroxodisulfate and an acid, or a halogenic acid salt and an acid followed by separation by filtration and purification, thus modifying the surface to give it a heat of wetting with water of 0.1 J/m<2> or higher. Pref., oxidation-active sites are formed on the carbon black surface by gas-phase oxidation before the wet oxidation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a water-soluble water excellent in dispersibility in water which is suitably used as a black aqueous ink pigment such as an ink pigment for an ink jet printer, a general aqueous ink pigment, a pigment for electrodeposition coating and the like. The present invention relates to a dispersible carbon black and a method for producing the same.

[0002]

2. Description of the Related Art Since carbon black is hydrophobic and has low wettability with water, it is extremely difficult to stably disperse carbon black in water at a high concentration. This is because the number of hydrophilic functional groups such as hydrogen-containing functional groups having a high affinity for water molecules existing on the carbon black surface is extremely small. Therefore, when carbon black is dispersed in water as a black pigment and used as an aqueous pigment ink,
It is necessary to improve the water dispersibility by modifying the surface properties of carbon black.

[0003] Aqueous pigment inks have attracted attention as writing materials, especially as recording liquids for ink jet printers in recent years. For example, JP-A-3-97770 discloses an aqueous medium, polyoxyethylenestyrylphenyl ether and primary particles. An ink jet recording liquid characterized by containing carbon black having a diameter of 20 to 40 nm, a DBP oil absorption of 40 to 120 ml / 100 g, and a pH of 7.0 or more has been proposed. This is to improve the storage stability of the recording liquid by using polyoxyethylene styryl phenyl ether as a dispersant. A commercially available carbon black is used as the target carbon black, and there is no Not intended.

It has long been known to improve the dispersibility of carbon black in water by oxidizing carbon black to form hydrophilic functional groups on the surface. For example, Japanese Patent Application Laid-Open No. 48-18186 discloses a method of oxidizing carbon black with an aqueous solution of hypohalite, and then washing with an organic solvent to separate and collect the oxidized carbon black from the reaction system. A method for producing carbon black is disclosed in
No. 9856 proposes a method for producing a water-dispersible modified carbon black, which comprises subjecting carbon black to low-temperature oxidation plasma treatment.

Further, JP-A-8-3498 discloses an aqueous pigment ink containing water and carbon black, wherein the carbon black has a surface active hydrogen content of 1.5 mmol / g or more, and In a method for producing an aqueous pigment ink containing water and carbon black, (a) obtaining an acidic carbon black, and (b) further oxidizing the acidic carbon black with hypohalite in water. And a method for producing an aqueous pigment ink. JP-A-8-319444 includes a step of finely dispersing carbon black having an oil absorption of 100 ml / 100 g or less in an aqueous medium; and a step of oxidizing the carbon black using a hypohalite. A method for producing an aqueous pigment ink is disclosed.

In JP-A-8-3498 and JP-A-8-319444, carbon black is oxidized to form a functional group containing a large amount of active hydrogen, which is a hydrophilic functional group, on the surface. Thus, an aqueous pigment ink having good water dispersibility and excellent long-term dispersion stability can be obtained. However, in the process of dispersing carbon black in water, the amount of hydrophilic functional groups present at the contact interface between the surface of the carbon black and water molecules plays an important function, and simply the amount of functional groups per unit weight of carbon black It is difficult to accurately judge the quality of dispersibility.

Accordingly, the present inventor has focused on the amount of hydrogen-containing functional groups present per unit surface area of carbon black as a new technique for accurately evaluating the quality of dispersibility. Development of easily water-dispersible carbon black and a method for producing the same, characterized in that the total amount of carboxyl groups and hydroxyl groups among the hydrogen-containing functional groups present on the surface is 3 μeq / m ² or more per unit surface area. Proposed (Japanese Patent Application No. 9-332405)
issue).

[0008]

As a result of further research based on the above technology, the present inventors have found that not only the amount of hydrophilic hydrogen-containing functional groups such as carboxyl groups or hydroxyl groups present on the surface of carbon black, but also It has been found that the heat of wetting carbon black into water is effective as a scale for comprehensively evaluating the function of hydrophilicity including other factors.

The present invention has been developed on the basis of this finding, and has an object of being excellent in dispersibility in water, for example, black aqueous pigments such as ink pigments for ink jet printers, general aqueous ink pigments, and pigments for electrodeposition coating. An object of the present invention is to provide a water-dispersible carbon black which can be suitably used as an ink pigment and a method for producing the same.

[0010]

The water-dispersible carbon black according to the present invention for achieving the above object is a carbon black surface-modified by an oxidation treatment and has a heat of wetting of 0.1 J / cm2. It is characterized by having a characteristic of m ² or more.

[0011] Further, the production method is such that carbon black is subjected to wet oxidation treatment using peroxodisulfate, or peroxodisulfate and an acid, or halogenate and an acid, followed by filtration and separation, followed by purification treatment. It is characterized in that the surface is modified to have a heat of water wetting of 0.1 J / m ² or more. Before the wet oxidation treatment, it is preferable to form an oxidation active site on the surface of carbon black by vapor phase oxidation in advance.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The colloidal properties of the carbon black to be used in the present invention are not particularly limited, but the carbon black surface is sufficiently wetted by water molecules in the process of dispersing the carbon black in water. In order to maintain a stable dispersion state in water, it is necessary that the area in contact with water molecules is sufficient. That is, if the specific surface area of carbon black is small, the area of the interface in contact with water molecules is also reduced, and the dispersibility is reduced. In addition, when the structure of carbon black is high, the cohesion unit in the state of being dispersed in water becomes large, so that the carbon black is liable to settle by re-aggregation during long-term dispersion.

Further, when the carbon black is used as a black pigment for water-based inks, the jet blackness of the printed image decreases as the specific surface area of the carbon black decreases. When used for ink pigments and black ink pigments for inkjet printers, the ink ejection stability and paper fixing density (paper printing density)
It is necessary to provide a good balance. From these points, it is desirable that the carbon black targeted in the present invention be set to a characteristic having a nitrogen adsorption specific surface area (N ₂ SA) value of 50 m ² / g or more and a DBP oil absorption value of 70 ml / 100 g or less. .

The dispersibility of carbon black in water is greatly affected by the wettability of the surface of the carbon black particles with water. Therefore, the heat generated when the surface of the carbon black particles comes into contact with water, that is, the magnitude of the heat of water wetting, is determined. It is possible to judge the quality of wettability comprehensively. Therefore, the easily water-dispersible carbon black of the present invention has a value of 0.1 J / m ² or more of water wetting heat obtained by converting the amount of heat generated when carbon black is put into water into the amount of heat generated per unit surface area of carbon black. Is set to the value of

The value obtained by the following measuring method is applied to the water wetting heat. Measurement method of heat of water wetting: A carbon black sample corresponding to a surface area of about 10 m ² from the value of the nitrogen adsorption specific surface area (N ₂ SA) was weighed into a glass ampoule, and the temperature was 105 ° C. and 1 × 10 ⁻⁵
After degassing under rr vacuum for 3 hours, the ampoule is opened under vacuum to prepare a measurement sample. The water temperature was measured at 30 ° C using a twin-type thermostatic wall calorimeter (TIC-2C, manufactured by Tokyo Riko Co., Ltd.).
Was performed under the following conditions.

The water-dispersible carbon black of the present invention comprises
Carbon black can be produced by subjecting carbon black to wet oxidation treatment using peroxodisulfate, or peroxodisulfate and an acid, or a halogenate and an acid, followed by filtration and separation, followed by purification treatment.

As the peroxodisulfate used as the oxidizing agent, an alkali metal salt or an ammonium salt of persulfuric acid is used, and the concentration is preferably 0.5 N or more. When a mixed solution of peroxodisulfate and an acid is used, the concentration of peroxodisulfate is 0.3 N or more and the concentration of acid is 0.1 N.
It is preferable to set it to 5N or more. In addition, hydrochloric acid or sulfuric acid is used as the acid, phosphoric acid has a low ionization degree and has a low function as an acid, and nitric acid is not preferable because nitro groups are easily formed on the carbon black surface and steric hindrance is caused to decrease dispersibility. .

The halogenate used as the oxidizing agent is
Not only halides, but also subhalites are used,
As the halogen, any of chlorine, iodine, bromine and fluorine is used, but preferably chlorine is used, and as the salt, an alkali metal salt or an ammonium salt is used. Since the oxidizing effect of a halogenate in an aqueous solution is strong in an acidic condition and extremely weak in a neutral or alkaline condition, a mixed solution of a halogenate and an acid is used as the oxidizing agent, and hydrochloric acid or sulfuric acid is preferably used as the acid. . Preferably, the concentration of the halide is 0.5 N or more, and the concentration of the acid is 0.5 N or more.

In the wet oxidation treatment, carbon black is mixed and dispersed at an appropriate ratio in a peroxodisulfate, a mixed solution of a peroxodisulfate and an acid, or a mixed solution of a halide and an acid adjusted to an appropriate concentration. The predetermined oxidation treatment is performed by appropriately controlling the treatment temperature, treatment time and the like while stirring.

If the oxidation active sites (oxidation sites) are formed on the surface of the carbon black by vapor phase oxidation with ozone or ozone-containing air in advance, the wet oxidation treatment can proceed more smoothly. Therefore, it is preferable to perform wet oxidation treatment after forming oxidation active sites by vapor phase oxidation in advance. The gas phase oxidation is performed by bringing carbon black into a dry state or a state moistened with water and contacting it with ozone or ozone-containing air for an appropriate period of time.

The wet-oxidized carbon black is filtered and separated from the oxidizing agent solution, and then sufficiently washed with pure water to remove the oxidizing agent adhering thereto with water.
In order to further purify to high purity, put carbon black in pure water, adjust the pH to 5 to 8 and disperse the carbon black, and then use electrodialysis or ultrafiltration membrane or loose filter.
Purification is performed by separating residual salts with a separation membrane such as RO. In this way, a water-dispersible carbon black having a surface modified to have a heat of water wetting of 0.1 J / m ² or more is produced.

[0022]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples.

Example 1 Nitrogen adsorption specific surface area (N ₂ SA) 135 m ² / g, DBP oil absorption 56
200 g of a 100 ml / 100 g carbon black sample was placed in an ozone treatment container, and an ozone generator [IOT-
4A6] and the ozone generation amount 18 g
The gas phase oxidation was carried out at room temperature for 1 hour under the condition of / h. 150 g of the gas-phase oxidized carbon black is placed in 3000 ml of a 1.5 N solution of ammonium peroxodisulfate and stirred (300 g).
The mixture was subjected to wet oxidation treatment at a reaction temperature of 60 ° C. for 10 hours while being subjected to filtration and separation by filtration. The obtained wet oxidized carbon black was dispersed in water, and then neutralized with an aqueous sodium hydroxide solution (concentration: 0.5N). Thus, a carbon black dispersion was obtained. Further, this carbon black dispersion was treated with an ultrafiltration membrane [APH-1010, manufactured by Asahi Kasei Kogyo Co., Ltd .;
0] to remove impurities such as residual salts, followed by drying. Thus, a surface-modified water-dispersible carbon black was produced.

EXAMPLE 2 200 g of the same carbon black sample as in Example 1 was
It was wet with 0 ml of pure water, oxidized with ozone under the same conditions as in Example 1, and then dried. Then, this carbon black 1
50 g was placed in 3000 ml of a mixed solution of 0.5N sodium chlorate and 1N sulfuric acid and subjected to wet oxidation treatment at a reaction temperature of 100 ° C. for 10 hours while stirring (300 rpm).
A water-dispersible carbon black having a modified surface was produced by filtration, separation and purification in the same manner as described above.

Example 3 Carbon black sample 1 oxidized in the gas phase in the same manner as in Example 1.
50 g was placed in 3000 ml of an aqueous solution of 1.0 N ammonium peroxodisulfate, subjected to wet oxidation treatment at a reaction temperature of 60 ° C. for 10 hours while stirring (300 rpm), and then subjected to filtration separation and purification treatment in the same manner as in Example 1 to obtain a surface. A modified water-dispersible carbon black was produced.

Comparative Example 1 Carbon black having a modified surface was produced in the same manner as in Example 2 except that a 0.5N aqueous solution of sodium chlorate was used as an oxidizing agent.

Comparative Example 2 200 g of the same carbon black sample as in Example 1 was
It was wet with 0 ml of pure water, oxidized with ozone under the same conditions as in Example 1, and then dried to produce a surface-modified carbon black.

Comparative Example 3 The same carbon black sample as in Example 1
The same amount of an olefinsulfonic acid-based dispersant [Lion Co., Ltd., LiPolan PB-800] was added, 700 g of pure water was added, and the mixture was pulverized by a ball mill for 48 hours, and then filtered, dried and carbon-modified with surface modification Was prepared.

In order to measure the heat of wetting of the carbon black thus obtained in water and to evaluate its dispersibility in water, a dispersion prepared by dispersing carbon black in water to a dispersion concentration of 20% by weight was prepared. It was prepared and tested by the following method. Table 1 shows the obtained results. Heating stability The sample is packed in a closed container, and observed for a change in viscosity from 1 week to 4 weeks in a 70 ° C incubator. Viscosity measurement was performed using a rotary vibration type viscometer [VM-100A-L, manufactured by Yamaichi Electric Co., Ltd.]
]. Freezing and thawing stability The sample was packed in a closed container, and the viscosity change when frozen and thawed at -20 ° C to 25 ° C was measured for three cycles. Particle diameter measurement The particle diameters of the sample and the sample subjected to the heating stability test were measured using a heterodyne laser Doppler type particle size distribution analyzer (UPA model 9340, manufactured by Microtrac Co., Ltd.). In this measuring device, when a laser beam is applied to particles that are performing Brownian motion in a suspension, the frequency of scattered light is modulated by the Doppler effect. The intensity of Brownian motion, that is, the particle diameter is measured from the degree of frequency modulation.

[0030]

[Table 1]

From the results shown in Table 1, it was found that carbon black whose surface was modified by oxidizing carbon black to have a heat of water wetting of 0.1 J / m ² or more was dispersed in water at a ratio of 20% by weight. Dispersions 1 to 3 tend to decrease in viscosity even after 1 to 4 weeks after being heated to 70 ° C., and the particle size of carbon black in the dispersion also tends to decrease, It can be seen that a stable dispersion state is maintained. On the other hand, the dispersions of Comparative Examples 1 and ^{2 in} which carbon black having a value of the heat of water wetting of less than 0.1 J / m ² was dispersed in water even after the oxidation treatment, were heated to 70 ° C. , The viscosity tends to increase from one week, the re-agglomeration of the carbon black remarkably progresses, and gelation occurs. Comparative Example 3 in which a surfactant was adsorbed on the carbon black surface without oxidation treatment and the value of the heat of water wetting was modified to 0.1 J / m ² or more.
Although no increase in the viscosity or increase in the average particle size or the maximum particle size was observed in the dispersion of No. 7 when heated at 70 ° C., the surfactant was desorbed and separated into carbon black and water in a freeze-thaw experiment. Also, peroxodisulfate as an oxidizing agent,
It can be seen that by performing wet oxidation treatment using peroxodisulfate and acid, the surface wettability of the water-dispersible carbon black of the present invention can be modified to a value of 0.1 J / m ² or more.

[0032]

As described above, according to the present invention, a water-dispersible carbon excellent in dispersibility, which can be easily dispersed in water and can maintain a stable dispersion state for a long period of time. A black and a method of making the same are provided. Therefore, when the water-dispersible carbon black of the present invention is used as a black aqueous ink pigment, for example, as a recording liquid for an ink jet printer, it has excellent ejection stability,
An ink having good paper fixing density, print quality, light resistance, storage stability, and the like can be obtained. Therefore, it is extremely useful as an easily water-dispersible carbon black suitably used as a black aqueous ink pigment such as an ink pigment for an ink jet printer, a general aqueous ink pigment, and a pigment for electrodeposition coating. Further, according to the production method of the present invention, it is possible to produce an easily water-dispersible carbon black having the excellent dispersion performance.

Claims (3)

[Claims] 1. A water-dispersible carbon black which is a surface-modified carbon black having an heat of wetting of 0.1 J / m ² or more. 2. The carbon black is subjected to wet oxidation treatment using peroxodisulfate, or peroxodisulfate and an acid, or a halogenate and an acid, followed by filtration and separation.
A process for producing easily water-dispersible carbon black, wherein the surface is modified to a heat of wetting of 0.1 J / m ² or more by a purification treatment. 3. The process for producing easily water-dispersible carbon black according to claim 2, wherein the carbon black is previously vapor-phase oxidized to form oxidation active sites on the surface of the carbon black, and then subjected to wet oxidation treatment.