JPH11199810A - Aqueous pigment ink containing carbon black - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aqueous pigment ink containing carbon black, containing the carbon black excellent in dispersibility in an aqueous medium and capable of maintaining a stable dispersed state over a long period. SOLUTION: This aqueous pigment containing carbon black is obtained by adding salts of humic acid to a dispersion obtained by dispersing the carbon black modified so that the total of carboxyl groups and hydroxyl groups in hydrogen-containing functional groups present on the surface may be >=1.5 μeq/m<2> by oxidation treatment, in an aqueous medium, and mixing the dispersion with the added salts of the humic acid to regulate the pH of the dispersion so as to be 7-11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a black water-based ink using carbon black as a pigment, and more particularly to a water-based pigment ink excellent in carbon black dispersibility.

[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 it in water at a high concentration. This is because there are few functional groups having high affinity for water molecules existing on the surface of the carbon black, for example, hydrophilic hydrogen-containing functional groups such as carboxyl groups and hydroxyl groups. Therefore, when it is used as a black pigment in an aqueous pigment ink in which carbon black is dispersed in water, it is necessary to improve the water dispersibility of carbon black.

[0003] Aqueous pigment inks have been used as writing instruments and especially as recording liquids for ink jet printers in recent years. In order to stably disperse hydrophobic fine particles such as carbon black in water, an aqueous pigment ink is generally used. Activators and dispersants are used.

For example, JP-A-3-97770 discloses that an aqueous medium, polyoxyethylene styryl phenyl ether and a primary particle diameter of 20 to 40 nm, a DBP oil absorption of 40 to 120 ml / 100 g, a pH of 7.0 or more are used. An ink jet recording liquid characterized by containing a certain carbon black is disclosed. This is intended to improve the storage stability of the recording liquid by using polyoxyethylene styryl phenyl ether as a dispersant, and a commercially available carbon black is used as a target carbon black.

JP-A-59-100168 discloses a method of producing a colorant by a flushing method, wherein humic acid, a humic acid salt or a derivative of humic acid is used in an aqueous dispersion of a pigment such as carbon black. A method for producing a colorant is disclosed. According to this method, by using humic acids during the resin dispersion step, the humic acids are adsorbed on a pigment such as carbon black, so that the particles can be atomized and dispersed to near the state of primary particles.

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
JP-A-59856 proposes a method for producing a water-dispersible modified carbon black, which comprises subjecting carbon black to low-temperature oxidative 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 a method for producing an aqueous pigment ink containing carbon black,
There has been proposed a method for producing an aqueous pigment ink, comprising: (a) a step of obtaining an acidic carbon black; and (b) a step of further oxidizing the acidic carbon black with a hypohalite in water. 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 the above-mentioned JP-A-8-3498 and JP-A-8-319444, carbon black is oxidized to contain a large amount of active hydrogen, which is a hydrophilic functional group, on the surface, so that water dispersibility is improved. An object of the present invention is to obtain an aqueous pigment ink which is excellent and has excellent long-term dispersion stability.

[0009]

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 particles and water molecules plays an important role, In order to accurately evaluate the affinity with the molecule, the amount of the hydrophilic functional group existing per unit surface area of the carbon black particles is important.
Furthermore, it was confirmed that the water dispersibility was further improved when humates were adsorbed on the surface of these carbon black particles.

The present invention has been completed on the basis of the above findings, and its object is to provide, for example, a recording liquid used in an ink jet printer, a black aqueous ink or the like, which has excellent ejection stability, paper fixing density, and print quality. An object of the present invention is to provide a carbon black-containing water-based pigment ink excellent in light resistance, storage stability and the like.

[0011]

In order to achieve the above object, a carbon black-containing aqueous pigment ink according to the present invention is provided with a total amount of carboxyl groups and hydroxyl groups among the hydrogen-containing functional groups present on the surface after oxidation. 1.5 μeq
/ M ² or more, wherein the pH of the dispersion is adjusted to 7 to 11 by adding and mixing humates to a water-containing dispersion obtained by dispersing carbon black modified in an aqueous medium. And

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The carbon black applied to the present invention is not particularly limited, but in practice, furnace black produced by an oil furnace method is used. ₂ SA) is 50m ²
/ g or more, a DBP oil absorption of 80 ml / 100 g or less, and an average particle diameter of 20 to 45 nm are preferably used.

When carbon black is oxidized, a carboxyl group (--COOH) and a hydroxyl group (--O
H), hydronium group (-H), quinone group (> C = O)
And various functional groups are generated. Among these functional groups, a carboxyl group (—COOH) and a hydroxyl group containing active hydrogen having high affinity for water molecules and having excellent dispersibility in water and maintaining and maintaining a stable dispersion state in water. The amount of (-OH) functions greatly. That is, the hydronium group (-H) is unstable, and the quinone group (> C =
O) has a low affinity for water molecules, but 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 functions greatly. 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 types of carbon black having different specific surface areas.
Even if the amount of carboxyl group and hydroxyl group-containing active hydrogen-containing functional groups per g is the same, the amount of these functional groups present at the contact interface with water molecules involved in the dispersion performance in water depends on the specific surface area. Will be different. Therefore, in the present invention, the total amount of carboxyl groups and hydroxyl groups is modified to 1.5 μeq / m ² or more by oxidation treatment using the amount of hydrogen-containing functional groups present per unit surface area of carbon black as a parameter. . 1.5μeq
If it is less than / m ² , the amount of hydrophilic functional groups present at the contact interface between the surface of the carbon black particles and the water molecules is small, so that a good dispersion state in water cannot be maintained.

In the present invention, the method of oxidizing treatment is not particularly limited, and a wet method of treating with an oxidizing agent such as hydrogen peroxide, hot nitric acid or benzoyl peroxide, or a method of ozone or nitric oxide (NO _x ). Appropriate oxidizing means such as a dry method of treating with an oxidizing agent is applied.

The value of the hydrogen-containing surface functional group measured by the following method is used. Carboxyl group content: After adding 2 to 5 g of carbon black to 50 ml of 976N sodium hydrogencarbonate and shaking for 6 hours, the carbon black was separated by filtration from the reaction solution, and a 0.05N aqueous hydrochloric acid solution was added to the filtrate.
The neutralization titration test is performed with a 0.05N aqueous solution of sodium hydroxide until the carboxyl group is measured. This measured value is 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 content: 2,2'-Diphenyl-
1-picrylhydrazyl (DPPH) is dissolved in carbon tetrachloride to prepare a solution having a concentration of 5 × 10 ⁻⁴ mol / l, and 0.1 to 0.6 g of carbon black is added to the solution, and the solution is kept at a constant temperature of 60 ° C. Stir in the bath for 6 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 measured in this way was divided by the nitrogen adsorption specific surface area of carbon black (N ₂ SA; m ² / g),
The amount of hydroxyl groups formed per unit surface area of carbon black (μeq / m ² ).

The carbon black whose total amount of carboxyl groups and hydroxyl groups has been modified by oxidation treatment to 1.5 μeq / m ² or more is dispersed in an aqueous medium such as water to obtain a water-containing dispersion. The humates are adsorbed on the surface of the carbon black particles by adding and mixing with stirring. The dispersion concentration of carbon black in the aqueous dispersion is preferably adjusted in the range of 10 to 20 Wt%.

The humates to be added to the aqueous dispersion include:
Humic acid or humate or a derivative of humic acid, which is a brown-black amorphous acidic organic substance that is soluble in alkali and insoluble in acids present in soil or low-carbon coal, and is alkalized. Those that have been used are preferably used.
The humates added to and mixed with the aqueous dispersion of carbon black are preferably 5 to 15 Wt% with respect to the carbon black, and the total amount of the carbon black and the humates is preferably set to 30 Wt% or less. 30Wt
%, The fluidity is reduced and stirring and mixing becomes difficult.

The dispersion to which humates are added and mixed is pH
Is adjusted in the range of 7-11. When the pH is lower than 7 or higher than 11, the dispersibility decreases, causing an increase in viscosity and a sedimentation phenomenon, so that a stable dispersion state cannot be maintained. For pH adjustment, use ammonia, sodium hydroxide,
It can be easily adjusted by adding an alkaline aqueous solution such as sodium carbonate.

Thus, the total amount of carboxyl groups and hydroxyl groups present on the surface after the oxidation treatment is 1.5
Humic acid salts are added to a water-containing dispersion in which carbon black oxidized and modified to μeq / m ² or more is dispersed in an aqueous medium such as water, and the mixture is stirred and mixed to adjust the pH of the dispersion to 7 to 11. As a result, the humates are adsorbed on the surface of the carbon black to be modified into a surface having more hydrophilic properties. As a result, it is possible to provide a carbon black-containing aqueous pigment ink having excellent dispersibility in water.

[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
5 g of carbon black (100 ml / 100 g) was placed in 500 ml of a 35% strength aqueous nitric acid solution, and stirred at 110 ° C. for 2 hours.
Oxidized by time treatment. Then, after cooling to room temperature, an aqueous solution of sodium hydroxide was added to neutralize excess nitric acid, followed by filtration by vacuum filtration, and the filtered carbon black was sufficiently washed with distilled water until the pH of the filtrate became about 8. After drying, an oxidation-modified carbon black sample was prepared, and its carboxyl group amount and hydroxyl group amount were measured to obtain the sum.

This carbon black sample was subjected to a concentration of 15 Wt.
% Of sodium humate is added to a water-containing dispersion dispersed in water at a ratio of 5% by weight, and the mixture is sufficiently mixed by a ball mill, and then an aqueous solution of sodium hydroxide is added to adjust the pH of the dispersion to 8.5. It was adjusted. Thus, a carbon black-containing aqueous pigment ink was prepared.

The dispersion performance of the obtained carbon black-containing aqueous pigment ink was evaluated by the following method. Measurement of viscosity; measured by a B-type viscometer. Filtration test: 1 kg / cm ² using an acetylcellulose membrane filter (manufactured by Toyo Filter Paper) having a membrane pore of 1.2 μm.
The presence or absence of the residue at the time of pressure filtration at the pressure was compared. Centrifugal separation test; Centrifuge [HIMAKI Koki Co., Ltd., HIMA
(C CENTRIFUGE) and centrifuged at 12,000 rpm for 20 minutes, and the presence or absence of precipitate was compared. Settling test; 60 in a 200 ml measuring cylinder
The presence or absence of a precipitate when allowed to stand for a day was compared.

Example 2 Example 1 was repeated except that the pH of the dispersion was adjusted to 10.3.
A carbon black-containing aqueous pigment ink was prepared in the same manner and under the same conditions as described above, and its dispersing performance was evaluated.

Example 3 Oxidation treatment was carried out at 20 ° C. using a hydrogen peroxide solution having a concentration of 35%.
A carbon black-containing aqueous pigment ink was prepared in the same manner and under the same conditions as in Example 1, except that the dispersion was treated at a temperature of 48 hours and the pH of the dispersion was adjusted to 9.2, and the dispersing performance was evaluated. did.

Example 4 10 W of sodium humate was added to a water-containing dispersion in which a carbon black sample was dispersed in water at a concentration of 20 Wt%.
A carbon black-containing water-based pigment ink was prepared in the same manner and under the same conditions as in Example 1 except that it was added at a ratio of t%, and its dispersion performance was evaluated.

Comparative Example 1 The same method and conditions as in Example 1 were used, except that the same carbon black as in Example 1 was used, and the pH of the dispersion was adjusted to 8.1 using the same carbon black without oxidation treatment. Was used to prepare a carbon black-containing aqueous pigment ink, and its dispersing performance was evaluated.

Comparative Example 2 An aqueous pigment ink containing carbon black was prepared in the same manner and under the same conditions as in Example 1 except that sodium humate was not added to the aqueous dispersion prepared by the same method and under the same conditions as in Example 1. It was prepared and its dispersion performance was evaluated.

Comparative Example 3 An aqueous pigment ink containing carbon black was prepared in the same manner and under the same conditions as in Example 1 except that the pH of the dispersion was adjusted to 5.1. Was evaluated.

Comparative Example 4 A water-based pigment ink containing carbon black was prepared in the same manner and under the same conditions as in Example 1, except that the pH of the dispersion was adjusted to 12.0. Was evaluated.

The preparation conditions and dispersion performance of the carbon black-containing aqueous pigment ink thus obtained are shown in Table 1 (Example) and Table 2 (Comparative Example).

[0034]

[Table 1] (Table note) * 1 Carbon black sample * 2 C group: carboxyl group, H group: hydroxyl group

[0035]

[Table 2] (Table note) * 1 Carbon black sample * 2 C group: carboxyl group, H group: hydroxyl group

From the results shown in Tables 1 and 2, carbon black obtained by modifying carbon black to have a total amount of carboxyl groups and hydroxyl groups formed on the surface thereof of 1.5 μeq / m ² or more was dispersed in water. Sodium humate was added to and mixed with the aqueous dispersion, and the pH of the dispersion was adjusted to 7 to 11.
It can be seen that the carbon black-containing water-based pigment inks of Examples adjusted to the range described above have excellent dispersibility and can maintain a stable dispersion state for a long period of time. On the other hand, in Comparative Example 1 in which carbon black was not subjected to an oxidation treatment, or in Comparative Example 2 in which sodium humate was not added, the dispersibility was poor, a precipitate was formed by settling, and the pH of the dispersion was 7 to In Comparative Examples 3 and 4 out of the range of 11, it is recognized that the dispersibility was slightly lowered.

[0037]

As described above, according to the water-based pigment ink containing carbon black of the present invention, the carbon black as a pigment is easily dispersed in an aqueous medium and maintains a stable dispersion state for a long period of time. be able to. Therefore, for example, as a recording liquid or a black aqueous ink used for an ink jet printer, etc., it is extremely excellent as a carbon black-containing aqueous pigment ink having excellent ejection stability, good paper fixing density, print quality, light resistance, storage stability and the like. Useful.

Claims (1)

[Claims] 1. A carbon black having a total amount of carboxyl groups and hydroxyl groups of at least 1.5 μeq / m ² among the hydrogen-containing functional groups present on the surface after oxidation treatment is dispersed in an aqueous medium. A water-based pigment ink containing carbon black, wherein a humic acid salt is added to and mixed with the aqueous dispersion to adjust the pH of the dispersion to 7 to 11.