JPH11148027A - Water-dispersible carbon black and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an easily water-dispersible carbon black which is easily dispersed in water and can stably maintain a dispersed state for a long period of time and has excellent dispersibility, and a method for producing the same. SOLUTION: The carbon black modified by oxidation treatment, wherein 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. Carbon black. The production method is to ozone oxidize carbon black to oxidize the surface functional group to 1.0 μeq / m ² or more, and then to form carboxyl groups by wet oxidation using a halogenate and an acid or a persulfate as an oxidizing agent. Oxidative modification of the total amount of hydroxyl groups to 3 μeq / m ² or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-dispersible carbon black excellent in dispersibility in water which can be suitably used, for example, as a black water-soluble ink pigment, 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 hydrogen-containing functional groups having a high affinity for water molecules existing on the carbon black surface, for example, hydrophilic functional groups such as a carboxyl group and a hydroxyl group is extremely small. Therefore, when using as a black pigment in an aqueous pigment ink in which carbon black is dispersed in water, it is necessary to improve the surface properties of the carbon black to improve the water dispersibility.

[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 intended 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 intention to modify carbon black. It has not been.

[0004] Further, improving the dispersibility of carbon black in water by oxidizing carbon black to form a hydrophilic functional group on the surface is disclosed in, for example, JP-A-48-18186. Japanese Patent Application Laid-Open No. Sho 57-157 discloses a method for producing black carbon oxide, comprising oxidizing black with an aqueous solution of hypohalite, and then washing the organic black with an organic solvent to separate and collect the carbon oxide from the reaction system. JP-A-159856 proposes a method for producing a water-dispersible modified carbon black, which comprises subjecting carbon black to low-temperature oxidation plasma treatment. 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 water and carbon black. In the method for producing an aqueous pigment ink containing carbon black, (a)
A method for producing an aqueous pigment ink has been proposed which includes a step of obtaining acidic carbon black and a step of (b) further oxidizing the acidic carbon black with hypohalite in water. JP-A-8-319444 further 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 with a hypohalite. A method for producing an aqueous pigment ink is disclosed.

In the above-mentioned JP-A-8-3498 and JP-A-8-319444, carbon black is oxidized so that the surface contains a large amount of active hydrogen which is a hydrophilic functional group, so that water dispersibility is increased. And a water-based pigment ink having excellent long-term dispersion stability.

[0006]

However, in the process of dispersing carbon black in water, the amount of hydrophilic functional groups present at the contact interface between the carbon black surface and water molecules plays an important function, Whether the dispersibility is good or not cannot be accurately determined based on the amount of the functional group per unit weight of black. Therefore, the present inventor focused on the amount of hydrogen-containing functional groups existing per unit surface area of carbon black as a new method for accurately evaluating the quality of dispersibility.

Attention has been paid to hydrophilic and stable carboxyl groups and hydroxyl groups as hydrogen-containing functional groups present on the surface of carbon black, and by controlling the total amount to a specific value or more, the dispersion performance in water is improved. It has been found that excellent carbon black can be obtained.

The present invention has been developed based on this finding, and its object is to provide, for example, a recording liquid used in an ink jet printer, which has excellent ejection stability, paper fixing density, print quality, light fastness, and storage stability. An object of the present invention is to provide an easily water-dispersible carbon black excellent in dispersibility in water, which can be suitably used as a pigment for aqueous black ink having good stability and the like, and a method for producing the same.

[0009]

The water-dispersible carbon black according to the present invention for achieving the above-mentioned object is a carbon black modified by an oxidation treatment, wherein the carbon black has a hydrogen-containing functional group present on the surface. Among them, the constitutional feature is that the total amount of the carboxyl group and the hydroxyl group is 3 μeq / m ² or more per unit surface area.

[0010] In addition, the production method is such that carbon black is subjected to ozone oxidation to oxidize the surface functional group to 1.0 μeq / m ² or more, and then a halogenate and an acid or persulfate are used as an oxidizing agent. The total amount of carboxyl groups and hydroxyl groups among the hydrogen-containing surface functional groups is 3 μeq by wet oxidation.
/ M ² or more.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS When carbon black is oxidized, for example, a carboxyl group (-
Various functional groups such as COOH), hydroxyl group (-OH), hydronium group (-H), quinone group (> C = O) are generated. Among these functional groups, the abundance of the carboxyl group (-COOH) and the hydroxyl group (-OH) containing active hydrogen is high in order to maintain high affinity with water molecules and maintain a stable dispersion state in water. Works great. That is, the hydronium group (-H) is unstable, and the quinone group (> C = O) has a low affinity for water molecules and rather inhibits dispersibility in water.

In the process of dispersing carbon black in water and in the state of dispersion in water, the amount of hydrophilic functional groups present at the contact interface between carbon black and water molecules exerts an important function. Therefore, it is not possible to accurately evaluate the quality of the dispersion performance based on the amount of the functional group per unit weight of the carbon black. That is, there are various varieties of carbon black having different specific surface areas, and even if the amount of carboxyl group or hydroxyl group-containing hydrogen-containing functional group contained in 1 g of carbon black is the same, water which greatly affects the dispersibility in water. The amount of these functional groups existing at the contact interface with the molecule differs depending on the specific surface area. Therefore, in the water-dispersible carbon black of the present invention, the amount of hydrogen-containing surface functional groups present per unit surface area of carbon black is created as a new evaluation parameter as a method for accurately evaluating the dispersing performance. The total amount of the groups is specified to be ³ μeq / m ² or more.

The values measured for these functional groups by the following method are used. Carboxyl group: O. 976N sodium bicarbonate 5
After adding 2 to 5 g of carbon black to 0 ml and shaking for 6 hours, the carbon black was separated from the reaction solution by filtration, and a 0.05N aqueous hydrochloric acid solution was added to the filtrate. Carboxyl groups are measured by performing a neutralization titration test with a 05N aqueous sodium hydroxide solution. The value obtained by dividing the measured value by the nitrogen adsorption specific surface area of carbon black (N ₂ SA; m ² / g) is defined as the amount of carboxyl groups formed per unit surface area of carbon black (μeq / m ² ).

Hydroxyl group: 2,2'-Diphenyl-1-
picrylhydrazyl (DPPH) dissolved in carbon tetrachloride to a concentration of 5
× 10 ^-4 mol / l solution was prepared, 0.1 to 0.6 g of carbon black was added to the solution, and the solution was added in a 60 ° C. constant temperature bath.
Stir for hours. Thereafter, carbon black is separated from the reaction solution by filtration, and the filtrate is measured for hydroxyl groups by an ultraviolet absorption spectrophotometer. The value obtained by dividing the value measured in this manner by the nitrogen adsorption specific surface area of carbon black (N ₂ SA; m ² / g) is the amount of hydroxyl groups formed per unit surface area of carbon black (μeq / m ² ). And

The carbon black to be oxidatively modified has a nitrogen adsorption specific surface area of 25 to 300 m ² / g, a DBP oil absorption of 50 to 160 ml / 100 g, and a primary particle diameter of 10 to 70 nm.
Those having the following characteristics are preferred. Nitrogen adsorption specific surface area is 2
Large particles having a primary particle diameter of less than 5 m ² / g and a primary particle diameter of more than 70 nm have a lower jet jetness when used as a black pigment for an aqueous ink, and conversely have a nitrogen adsorption specific surface area of more than 300 m ² / g.
Small particles having a primary particle size of less than 10 nm have poor water dispersibility and dispersion stability. DBP oil absorption is 50ml
If the amount is less than / 100 g, the jet fixing degree of the paper fixing density decreases when a black ink is used. If the amount exceeds 160 ml / 100 g, the filterability becomes poor and it becomes difficult to spray from the print head.

Such an easily water-dispersible carbon black having a total amount of carboxyl groups and hydroxyl groups as hydrogen-containing surface functional groups of 3 μeq / m ² or more on the surface of the carbon black is obtained by oxidizing the carbon black under specific conditions. Can be manufactured. That is, first, carbon black is oxidized with ozone to oxidize the surface functional group amount to 1.0 μeq / m ² or more, and then the hydrogen-containing surface is subjected to wet oxidation using a halide and an acid or persulfate as an oxidizing agent. It can be produced by oxidatively modifying the total amount of the carboxyl group and the hydroxyl group among the functional groups to 3 μeq / m ² or more.

A simple oxidation of carbon black cannot efficiently generate carboxyl groups or hydroxyl groups involved in dispersibility in water, and has a low affinity for water molecules and does not contribute to water dispersion performance. Is significantly generated. Therefore, in the present invention, carbon black is first oxidized with ozone. The oxidation treatment with ozone is performed to make the carbon black more easily compatible with water. As the oxidizing agent, not only ozone but also ozone-containing air obtained by adding ozone to air can be used.

This ozone oxidation produces functional groups such as carboxyl group, hydroxyl group and quinone group on the carbon black surface. Ozone oxidation is carried out so that the amount of these functional groups becomes 1.0 μeq / m ² or more. It is necessary to process. When the amount of the functional group is less than 1.0 μeq / m ² , the carbon black floats in water, so it is difficult to oxidize and modify the hydrophilic functional groups of the carboxyl group and the hydroxyl group to 3 μeq / m ² or more by the subsequent wet oxidation. This is because

The functional group formed on the carbon black surface by the ozone oxidation can be converted into a functional group containing active hydrogen by performing a wet oxidation treatment in water using a halogenate and an acid or a persulfate as an oxidizing agent. That is, they are converted into carboxyl groups or hydroxyl groups, and these hydrogen-containing functional groups present on the carbon black surface are oxidized and reformed to 3 μeq / m ² or more.

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 chlorine is preferably used. As the salt, an alkali metal salt or an ammonium salt is used, and preferably, a sodium salt or an ammonium salt is used. Since the oxidizing effect of the halogenate in the aqueous solution is strong under acidic conditions and extremely weak under neutral or alkaline conditions, a mixed aqueous 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. . Further, a persulfate can be used as the oxidizing agent.

In the wet oxidation treatment, the ozone-oxidized carbon black is mixed and dispersed at an appropriate ratio in a mixed aqueous solution of a halogenate and an acid or a persulfate aqueous solution adjusted to an appropriate concentration, and the treatment temperature and the treatment time are stirred. The predetermined oxidation treatment is performed by appropriately controlling the above. In this manner, the amount of the functional group formed on the surface of the carbon black, that is, the hydrogen-containing surface functional group of the carboxyl group and the hydroxyl group can be oxidatively modified to 3 μeq / m ² or more.
Furthermore, by substituting part or all of the terminal hydrogen of this functional group with an alkali metal or ammonium salt,
Dispersion performance can be further improved.

The carbon black thus oxidized and modified is separated by filtration, washed thoroughly with pure water to remove the oxidizing agent adhering thereto, and dried to obtain the easily dispersible carbon black of the present invention. Black is obtained. However, it is difficult to completely remove impurities such as an oxidizing agent only by washing with water, and when it is necessary to perform a purification treatment with high purity, carbon black is dispersed again in pure water to adjust the pH to 5 to 5.
8 and electrodialysis or ultrafiltration membrane or loose RO
High purity can be achieved by separating and purifying the residual salt using a separation membrane such as this.

[0023]

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

Examples 1-4 Nitrogen adsorption specific surface area (N ₂ SA), DBP oil absorption, primary particle diameter (D
Using carbon blacks differing in n) as a sample, 200 g of each carbon black was placed in an ozone treatment container, and oxidized at normal temperature by changing the ozone flow rate and the treatment time. Thus, carbon blacks having different functional group contents were prepared by ozone oxidation.

Next, these carbon blacks were oxidized using the following oxidizing agents. A: mixed solution of 0.5N sodium chlorate and 1N sulfuric acid B: 1.5N aqueous solution of ammonium persulfate In the oxidation treatment, 150 g of carbon black was added to 3000 ml of the above oxidizing agent solution, and the reaction temperature and reaction time Was changed by stirring and mixing. Next, an aqueous solution of sodium hydroxide was added to neutralize the mixture, followed by filtration and separation. The resulting oxidized carbon black was sufficiently washed with water to remove salts generated, and further purified by an electrodialyzer to remove impurities. Removed. Oxidation-modified in this way, the solid content of carbon black is 20% by weight, and the pH is 7 to
Carbon blacks dispersed in water having different total amounts of carboxyl groups and hydroxyl groups of 8 were produced.

Comparative Examples 1 to 4 An aqueous sodium hydroxide solution was added to carbon black oxidized and modified only by ozone treatment without performing the above-described oxidation treatment with the oxidizing agent A or B, and the solid content of the carbon black was 20% by weight. And carbon black dispersed in water having a pH of 7 to 8.

The carboxyl groups and hydroxyl groups of each of the oxidatively modified carbon blacks were measured, and
I asked for the sum. These results are shown in Table 1 in comparison with the production conditions.

[0028]

[Table 1] (Note) * 1 Total amount of carboxyl group and hydroxyl group

The dispersion water was tested by the following method to evaluate the dispersion performance, and the results are shown in Table 2.

(1) Measurement of viscosity: Dispersed water was placed in a closed container, and the viscosity was measured over time while maintaining the temperature at room temperature and 70 ° C., and the change over time in the viscosity at room temperature and heating at 70 ° C. That is, the temporal stability of the dispersed state was compared. The viscosity was measured using a rotary vibration viscometer [VM-1 manufactured by Yamaichi Electric Co., Ltd.
00A-L]. (2) Filtration test: carbon black dispersed in water was 90φ
A filtration test was performed under reduced pressure of 20 Torr using a filter paper (NO.2) and a filter having a membrane pore size of 3 μm and 0.8 μm, and the filterability was compared based on the passing ratio (% by weight).

In order to evaluate the performance as a pigment for an aqueous ink, the dispersion water was added to a carbon black concentration of 3% by weight.
Diluted into an ink jet printer (Deskjet 850c, manufactured by Hewlett-Packard), and printed on copy paper and glossy paper.
D-927), the print density was measured, and the results are also shown in Table 2.

[0032]

[Table 2]

From the results shown in Tables 1 and 2, the water-dispersible carbon of the present invention in which the total amount of carboxyl groups and hydroxyl groups present per unit surface area of the carbon black particles was modified to ³ μeq / m ² or more was obtained. It can be seen that the viscosity of the dispersion water is stable even when heated to room temperature and 70 ° C., and the change with time is small. On the other hand, in Comparative Examples in which the total amount of the carboxyl group and the hydroxyl group is less than 3 μeq / m ^{2, the} viscosity gradually increases, and it is recognized that the dispersion state deteriorates with time. This is because the dispersed carbon black reagglomerates and the dispersibility decreases, and is apparent from the results of the filtration test. Therefore, the ink using the water-dispersible carbon black of the present invention as a pigment for a black aqueous ink has a high print density and is excellent in printability. Further, according to the production method of the present invention, it is possible to easily produce the water-dispersible carbon black having the surface modified as described above.

[0034]

As described above, according to the present invention, an easily water-dispersible carbon black having excellent dispersibility, which can be easily dispersed in water and can stably maintain a dispersed state for a long period of time. And a method for manufacturing the same. Therefore, if the water-dispersible carbon black of the present invention is used as a pigment for a black aqueous ink, for example, the ejection stability is high as a recording liquid used in an ink jet printer and the like, and excellent paper fixing density, print quality, and light fastness are obtained. Inks having good properties and storage stability can be obtained. Therefore, including recording liquid for ink jet printer,
It is extremely useful as a pigment for aqueous inks used in a wide range of fields such as various writing instruments.

Claims (2)

[Claims] 1. A carbon black modified by an oxidation treatment, wherein the total amount of carboxyl groups and hydroxyl groups among the hydrogen-containing functional groups present on the surface is at least 3 μeq / m ² per unit surface area. Characteristic easy-dispersible carbon black. 2. Ozone oxidation of carbon black to oxidize the surface functional group to 1.0 μeq / m ² or more, and then contains hydrogen by wet oxidation using a halogenate and an acid or persulfate as an oxidizing agent. A method for producing easily water-dispersible carbon black, comprising oxidatively modifying the total amount of carboxyl groups and hydroxyl groups among surface functional groups to 3 μeq / m ² or more.