JP2002047434A - Carbon black pigment for water-base ink, and water-base ink made by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain carbon black pigment excellent in dispersibility in water and suitable for a water-base ink, and a water-base ink made by using the carbon black. SOLUTION: The carbon black pigment for a water-base ink comprises a mixture of 20-80 wt.% carbon black having an N2SA of at least 150 m2/g, a DBP of at least 100 cm3/100 g, and a Tint of at least 125 with 80-20 wt.% carbon black having an N2SA of below 150 m2/g, a DBP of below 100 cm3/100 g, and a Tint of at least 125, and is characterized in that the mixture is chemically modified by oxidation treatment to give an atomic ratio of the total carbon atoms to the total oxygen atoms determined by the X-ray photoelectron spectroscopy (the intensity of oxygen bond energy/the intensity of carbon bond energy) of at least 0.1:1 and a hydrogen-containing surface functional group content of at least 3.0 μeq/m2. The water-base ink is obtained by dispersing the carbon black mixture in water, subjecting the dispersion to oxidation treatment to chemically modify the carbon black mixture to give an atomic ratio of the total carbon atoms to the total oxygen atoms determined by the X-ray photoelectron spectroscopy (the intensity of oxygen bond energy/the intensity of carbon bond energy) of at least 0.1:1 and a hydrogen-containing surface functional group content of at least 3.0 μeq/m2, dispersing the modified carbon black mixture in an aqueous alkali after separation by filtration, and separating and purifying the salts remaining in the dispersion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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 the number of functional groups having a high affinity for water molecules existing on the carbon black surface is extremely small. Therefore, a method of forming a hydrophilic functional group on the surface by oxidatively modifying carbon black to improve water dispersibility has been known for a long time.

For example, Japanese Patent Application Laid-Open No. 48-18186 discloses that carbon black is oxidized with an aqueous solution of hypohalite and then washed with an organic solvent when separating and collecting carbon oxide from the reaction system. A method for producing oxidized carbon black is disclosed in
Japanese Unexamined Patent Publication No. 159856 discloses a method for producing a water-dispersible modified carbon black, which comprises subjecting carbon black to low-temperature oxidative plasma treatment.

[0004] Carbon black having excellent water dispersibility is useful as an aqueous pigment ink, and has attracted attention as a recording liquid for ink jet printers, especially in writing instruments in recent years. Examples of aqueous inks using water-dispersible carbon black include, for example, JP-A-8-3498.
JP-A No. 6-125087 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 an aqueous pigment ink containing water and carbon black. In the method for producing a pigment ink, (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, the method of producing an aqueous pigment ink includes Proposed. Further, Japanese Unexamined Patent Publication No.
Step to 319,444 discloses finely dispersed carbon black less absorption 100 cm ^3/100 g in an aqueous medium; manufacture encompassing aqueous pigment ink to; and step of oxidizing the carbon black using a hypohalite A method 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 good. Thus, an aqueous pigment ink having excellent long-term dispersion stability can be obtained. However, in order for carbon black to disperse in water and maintain a stable dispersion state, the amount of hydrophilic functional groups present at the contact interface between the surface of the carbon black particles and the water molecules functions greatly, and merely the carbon black unit weight It is difficult to accurately judge whether the dispersibility is good or not simply by regulating the amount of the functional group present per hit.

Accordingly, the present inventor has focused on the amount of hydrophilic hydrogen-containing functional groups present per unit surface area of carbon black as a new index for accurately judging the quality of the dispersion performance, and has conducted research to find the presence on the surface. Among the hydrogen-containing functional groups, a water-dispersible carbon black having a total amount of carboxyl groups and hydroxyl groups of 3 μeq / m ² or more per unit surface area, and a method for producing the same (JP-A-11-148027) have been developed. In addition, the nitrogen adsorption specific surface area (N ₂ SA) is 80 m ² / g or more,
A carbon black obtained by oxidizing carbon black having a DBP oil absorption of 70 ml / 100 g or less and having a ratio Dupa50% / Dst between the Stokes mode diameter Dst (nm) of the aggregate and the average particle diameter Dupa50% (nm) of the agglomerate. Value is 1.5 ~
We have proposed and developed a water-dispersible carbon black having a characteristic of 2.0 (JP-A-11-148026).

The inventor has further improved the dispersibility in water,
We are continuing research on the development of water-dispersible carbon black suitable as a black pigment for aqueous inks, and have a carbon adsorption with a nitrogen adsorption specific surface area (N ₂ SA) of 50 m ² / g or more and a DBP oil absorption of 80 ml / 100 g or less. (1) Stokes mode diameter D of carbon black aggregate
The ratio of st (nm) to the average particle size Dupa50% (nm) of agglomerate Dupa50% / Dst is 1.1 to 1.5, and (2) the value of the average particle size Dupa50% (nm) of agglomerate is 40 ~ 140 (nm),
(3) The maximum particle size of agglomerate Dupa 99% (nm) is 25
Water-dispersible carbon black having a property of not more than 0 (nm) and having a total amount of carboxyl groups and hydroxyl groups of 3 μeq / m ² or more per unit surface area among the hydrogen-containing functional groups present on the surface (Japanese Patent Laid-Open No. 11-256066).

[0008]

SUMMARY OF THE INVENTION The present invention has been completed as a result of subsequent research and development. The object of the present invention is to have excellent dispersibility in water and to be suitable as a black pigment for aqueous inks. When used as a jet ink pigment, it has excellent paper fixing density, printing density, ejection stability, light resistance, storage stability, dispersion stability, etc. when printing on plain paper, special paper, OHP sheet, art paper, etc. Another object of the present invention is to provide a carbon black pigment for water-based ink and a water-based ink using the carbon black pigment.

[0009]

In order to achieve the above object, the carbon black pigment for aqueous ink of the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of 150 m ² / g or more and a DBP absorption of 10 or more.
0-cm ³ / 100g or more, carbon black with specific coloring power (Tint) of 120% or more 20-80 wt%, nitrogen adsorption specific surface area (N ₂ SA)
150m less than ² / g, DBP absorption 100 cm ³ / below 100 g, the ratio tinting strength (Tint) 120% or more of the carbon black 80
An atomic ratio of total carbon atoms to total oxygen atoms (oxygen binding energy intensity / carbon binding energy intensity) measured by X-ray photoelectron spectroscopy after being oxidized and mixed at a ratio of 20 wt%. Is chemically modified to 0.1 or more, and the amount of hydrogen-containing surface functional groups, which is the sum of carboxyl groups and hydroxyl groups, to 3.0 μeq / m ² or more.

Further, the carbon black pigment for water-based ink of the present invention is a carbon black having the above-mentioned characteristics, wherein the carbon black agglomerate in the state of being dispersed in water has an average particle diameter Dupa50% of 50 to 110 nm.
It is characterized in that the maximum particle size Dupa 99% of the agglomerate has a particle property of 250 nm or less.

The aqueous ink of the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of 150 m ² / g or more and a DBP absorption of 100 cm ³ / g.
20 to 80% by weight of carbon black having a specific coloring power (Tint) of 120% or more and a nitrogen adsorption specific surface area (N ₂ SA) of 150 g or more.
m less than ² / g, DBP absorption 100 cm ³ / below 100 g, the ratio coloring power
(Tint) 80 ~ 20wt of carbon black of 120% or more
% Of carbon black mixed in water, oxidized and dispersed in water, and the atomic ratio of total carbon atoms to total oxygen atoms (oxygen binding energy intensity / carbon binding energy intensity) measured by X-ray photoelectron spectroscopy. ) To 0.1 or more, and the amount of hydrogen-containing surface functional groups, which is the sum of carboxyl groups and hydroxyl groups, to 3.0 μeq / m ² or more, and then chemically filtered, dispersed in an aqueous alkali solution, and then dispersed in a dispersion. Is characterized by being separated and purified from the remaining salt.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Among the characteristics of carbon black, the nitrogen adsorption specific surface area (N ₂ SA) is related to the area of the interface between the surface of carbon black particles and water molecules when carbon black is dispersed in water. This is a characteristic, and the larger this value is, the larger the area of the contact interface is, so that the water dispersion performance is improved. However, when the aqueous ink is used, the paper fixing density is low, and the print density is low. On the other hand, when the nitrogen adsorption specific surface area (N ₂ SA) is small, the contact interface with water molecules is also small, so that the water dispersibility is reduced, and the filterability and ejection stability of the aqueous ink are reduced.

The amount of DBP absorption is a characteristic related to the size of aggregates of carbon black particles in a state of being dispersed in water. As the amount of DBP absorption increases, the probability that the aggregates become entangled in an aqueous dispersion increases. Further, since carbon black is liable to settle, when a water-based ink is used, the rate of settling residue increases, and the filterability and the ejection stability decrease. However, when the DBP absorption amount is small, the paper fixing density is reduced, so that the print density is reduced.

The specific coloring power (Tint) is a characteristic related to the particle diameter (specific surface area), structure (DBP absorption amount), and aggregate diameter of carbon black. Then, since the particle size distribution is broadened, when an aqueous ink is produced, the filterability and the ejection stability are reduced, and the precipitation residue ratio is also increased.

As described above, the characteristics of carbon black greatly affect the dispersing performance in water, the paper fixing density of aqueous ink, the print density, the filterability, the discharge stability, and the like. These carbon blacks having different properties are mixed for use. That is, the nitrogen adsorption specific surface area (N ₂ SA) is 150 m ² / g or more, DBP
Absorption is 100cm ³ / 100g or more, specific coloring power (Tint) is 120
% Of carbon black of 20 to 80 wt%, nitrogen adsorption specific surface area (N ₂ SA) of less than 150 m ² / g, DBP absorption of 10
0 cm ³ / below 100 g, the ratio tinting strength (Tint) is 80～20Wt% carbon black 120% or more, the carbon black in a mixing ratio of applied.

The carbon black pigment for an aqueous ink of the present invention is obtained by mixing a carbon black having the above-mentioned characteristic range at a predetermined weight ratio with a carbon black as a functional group present on the surface of the carbon black by an oxidation treatment. Hydrogen whose atomic ratio (intensity of oxygen binding energy / intensity of carbon binding energy) of all carbon atoms to all oxygen atoms measured by photoelectron spectroscopy is 0.1 or more, and hydrogen which is the sum of a carboxyl group and a hydroxyl group 2. The surface functional group content is 3.
It is characterized by being chemically modified to 0 μeq / m ² or more.

If the atomic ratio of total carbon atoms to total oxygen atoms (oxygen binding energy intensity / carbon binding energy intensity) measured by X-ray photoelectron spectroscopy such as XPS or ESCA is less than 0.1, The self-dispersibility in a polar solvent such as water is reduced, and the storage stability is deteriorated when a water-based ink is used. The adjustment of the intensity ratio of the binding energy is performed by chemically oxidizing the surface of the carbon black particles by an oxidation treatment and forming a hydrophilic functional group by chemical modification.

It is necessary that the amount of the hydrogen-containing surface functional group which is the sum of the carboxyl group and the hydroxyl group as the hydrophilic functional group is chemically modified to be 3.0 μeq / m ² or more. Since the amount of hydrophilic functional groups present at the contact interface between carbon black and water molecules plays a major role in the performance of dispersing carbon black in water, active hydrogen is used as the amount of hydrophilic functional groups formed by chemical modification. With respect to the carboxyl group and the hydroxyl group contained, the sum of the hydrogen-containing surface functional groups is set to 3.0 μeq / m ² or more. If this value is less than 3.0 μeq / m ² , excellent dispersion performance cannot be provided because the amount of hydrophilic functional groups is small. The carboxyl group content and the hydroxyl group content are determined by the method described in Japanese Patent Application Laid-Open No. H11-148027, which has been proposed by the present inventors.

In the oxidation treatment, for example, carbon black is added to an aqueous solution of an oxidizing agent such as an alkali metal salt such as chlorite, chlorate, persulfate, perborate or percarbonate or ammonium salt to oxidize. By appropriately controlling the concentration of the oxidizing agent aqueous solution, the amount of carbon black added, the reaction temperature, the reaction time, and the like, the atomic ratio of all carbon atoms to all oxygen atoms (oxygen binding energy intensity / carbon Binding energy intensity) is 0.1 or more, and the amount of hydrogen-containing surface functional groups, which is the sum of carboxyl groups and hydroxyl groups, is 3.
The treatment is performed so as to be 0 μeq / m ² or more.

Further, the carbon black pigment for water-based ink of the present invention has, in addition to the above-mentioned characteristics, an agglomerate having an average particle diameter Dupa of 50% in a state of being dispersed in water of 5%.
It is characterized in that it has a particle property of 0 to 110 nm and a maximum agglomerate particle size Dupa of 99% is 250 nm or less.

Average particle size of agglomerate indicating the size of aggregate form of carbon black particles in water Dupa 50%
Is less than 50 nm, the frequency of carbon black passing through the gap between the paper fibers increases when the aqueous ink is used, the paper fixing density decreases, and the print density (blackness) decreases. On the other hand, the value of the average particle size Dupa50% of agglomerate is 1
If it exceeds 10 nm, the blackness is improved, but the dispersion stability of the carbon black pigment in the aqueous ink is reduced, the filterability is deteriorated, and the sedimentation is increased. On the other hand, when the value of the maximum particle diameter Dupa 99% of the agglomerate exceeds 250 nm, a large aggregate carbon black pigment is present in the aqueous ink, and the sedimentation, discharge stability and filterability are significantly reduced. is there.

The average particle size of agglomerate Dupa 50%
And the maximum particle size Dupa99% is measured by the following method. Disperse carbon black in water to 0.1-0.5
kg / m ³ dispersion was prepared and a heterodyne laser Doppler system particle size distribution analyzer (Microtrac, UPA
mode1 9340) and irradiate the dispersion with laser light.
The particle size of the agglomerate in the dispersion is measured from the degree of frequency modulation of the scattered light. The carbon black in the dispersion liquid undergoes Brownian motion, and the frequency of scattered light is modulated by the size of the dispersed carbon black aggregate due to the Doppler effect. Therefore, since the intensity of the Brownian motion varies depending on the size of the aggregate, the size of the aggregate in a state of being dispersed in water, that is, the particle size of the agglomerate can be measured. A cumulative frequency distribution curve is created from the agglomerate particle size measured in this way, and the value of 50% cumulative frequency is defined as the average particle size Dupa of agglomerate 50% (nm), and the value of 99% cumulative frequency is defined as the maximum agglomerate particle size Dupa99. % (nm).

The water-based ink of the present invention is obtained by dispersing the carbon black pigment for water-based ink of the present invention having these characteristics at a predetermined concentration in water. That is, carbon black having the above nitrogen adsorption specific surface area (N ₂ SA), DBP absorption amount, and specific coloring power (Tint) is mixed at a predetermined weight ratio, and the mixed carbon black is mixed with chlorite and chloric acid. Salt, persulfate, perborate, percarbonate and other alkali metal salts and ammonium salts are added to the oxidizing agent aqueous solution, and while stirring, the concentration of the oxidizing agent aqueous solution, the amount of carbon black added, the reaction temperature, the reaction By appropriately controlling the time and the like and performing the oxidation treatment, the atomic ratio of total carbon atoms to total oxygen atoms (oxygen bond energy intensity / carbon bond energy intensity) becomes 0.1 or more, and carboxyl group and hydroxyl group hydrogen-containing surface functional group amount is the sum of 3.0μeq / m ²
Chemical modification is performed as described above.

After the oxidation treatment, the carbon black is immediately separated by filtration to separate the carbon black, and then the separated carbon black is dispersed in an aqueous alkali solution such as sodium hydroxide, potassium hydroxide or ammonia, and the pH is adjusted to stably disperse the carbon black. That is, the carbon black particle surface is chemically modified by the oxidation treatment, and all or a part of the terminal hydrogen of the hydrophilic functional group formed on the carbon black particle surface is replaced with an alkali metal, an amino group, etc., thereby dispersing in water. The performance is improved. Next, the water-based ink of the present invention is obtained by separating and removing the residual salt generated by the oxidation reaction and purifying the same.

To remove the residual salt, the pH of the aqueous dispersion is adjusted to 6 to 11
The remaining salt is separated and purified by electrodialysis or a separation membrane (reverse osmosis membrane, ultrafiltration membrane, loose RO, etc.). In this case, it is preferable to separate and purify the residual salt concentration in the carbon black dispersion so that the conductivity is less than 5 mS / cm 2 with the carbon black content being 20 wt%, for example. In order to maintain the dispersion stability of the aqueous ink, it is desirable to adjust the dispersion concentration of the carbon black pigment to 60% by weight or less.

[0026]

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

Carbon black samples: Four types of carbon blacks A, B, C and D shown in Table 1 were used as carbon blacks having different characteristics.

[Table 1]

Example 1 Carbon blacks A and B shown in Table 1 were mixed at different ratios to prepare carbon black samples. 100 g of this carbon black sample was applied at a concentration of 0.75 mol / dm ³
To 3000 cm ³ of an aqueous sodium persulfate solution, and oxidized under the conditions of a reaction temperature of 60 ° C., a reaction time of 10 hours and a stirring speed of 5 s ⁻¹ . Next, the filtered oxidized carbon black is dispersed in pure water, neutralized with an aqueous solution of sodium hydroxide, and subjected to ultrafiltration (Asahi Kasei, AHP-1010, molecular weight cut off 500).
(00), the remaining salts were separated to prepare an aqueous dispersion of carbon black. The conductivity of the dispersion after purification was 0.6 mS / cm (carbon black content 22%).
wt%).

Example 2 A carbon black sample was prepared by mixing carbon blacks C and D shown in Table 1 at different ratios, and was the same as in Example 1 except that this carbon black sample was used. A carbon black aqueous dispersion was prepared by the method.

Comparative Examples 1 to 4 Examples 1 to 4 were used except that carbon blacks A, B, C and D shown in Table 1 were used alone as carbon black samples.
An aqueous dispersion of carbon black was prepared in the same manner as described above.

Comparative Example 5 A carbon black sample was prepared by mixing carbon blacks A and B shown in Table 1 at different ratios, and all of the same materials as in Example 1 were used except that this carbon black sample was used. A carbon black aqueous dispersion was prepared by the method.

Comparative Example 6 A carbon black sample was prepared by mixing carbon blacks C and D shown in Table 1 at different ratios, and the same procedure as in Example 1 was carried out except that this carbon black sample was used. A carbon black aqueous dispersion was prepared by the method.

These aqueous carbon black dispersions were concentrated to adjust the carbon black content to 20% by weight. The aqueous ink thus prepared was evaluated for dispersion performance, ink performance, and the like by the following methods.
Tables 2 to 5 show the obtained results.

Storage stability: The sample was packed in a closed container, and the viscosity change was measured in a 70 ° C. incubator for 1 to 4 weeks. The viscosity was measured with a rotational vibration type viscometer (VM-100A-L, manufactured by Yamaichi Electric Co., Ltd.).

Measurement of particle size: The particle size of the sample and the sample subjected to the storage stability test were measured using a heterodyne laser Doppler system particle size distribution analyzer [UPA model 9340, manufactured by Microtrac Co., Ltd.]. This measuring device is capable of tracking particles that are Brownian in suspension.
When the light is applied, the frequency of the 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.

Print density: The carbon black content of the aqueous ink was diluted to 4% by weight, and XEROX 40 was used as copy paper.
Using 24 papers, printing was performed on the paper using a # 6 bar coater, and the optical density was measured using a Macbeth densitometer (RD-927, manufactured by Colmorgen).

Filterability: 200 g of the water-based ink was applied to a 90φ NO. 2 filter paper and a membrane pore size of 3 μm, 0.8 μm, 0.65
2.66 KPa using a 0.45 μm filter.
A filtration test was performed under reduced pressure, and the weight (g) passed through the filtration was measured.

Precipitation residue rate: 20,000 G of aqueous ink
The weight ratio (M ₁ / M ₀ ) of the amount (M ₁ ) of the sediment residue after centrifugation treatment for 30 minutes at the gravitational acceleration to the weight (M ₀ ) of the carbon black before the centrifugation treatment was calculated. Rate. The lower the value, the better the dispersion stability.

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

[Table 4]

[0042]

[Table 5]

From the results of Tables 1 to 5, the specific surface area of nitrogen adsorption was
^{_{(N 2 SA) 150m 2 /}} g or more, DBP absorption amount 100 cm ^3/100 g or more, the ratio tinting strength (Tint) 20 to 80 wt% 120% or more of carbon black, the nitrogen adsorption specific surface area (N ^₂ SA) 150m ₂ / less than g, DBP absorption 100 cm ³ / below 100 g, the ratio tinting strength (Tint)
Using carbon black in which 120% or more of carbon black is mixed at a ratio of 80 to 20% by weight, a carbon black pigment chemically modified by oxidation treatment so that the atomic ratio of all carbon atoms to all oxygen atoms is 0.1 or more. Example 1 (Run No. 1 to 5) and Example 2 (Run No. 6) prepared by dispersing in water
The aqueous inks of (1) to (10) have a low initial viscosity, so that they can be easily designed into inks, have good filtration properties as a simple index of ejection stability from an orifice, and have a print density (OD value) of 1.30 or more. It is recognized that it shows sufficient blackness.

On the other hand, the aqueous inks of Comparative Examples 1 to 4 (Run Nos. 11 to 14) prepared using a single carbon black sample had high initial viscosities in Comparative Examples 1 and 3 and high filterability. Cannot pass through a filter having a membrane diameter of 0.65 μm, and the discharge stability is poor. In Comparative Examples 2 and 4, the initial viscosity, the filterability, the rate of sedimentation residue and the like are good, but the blackness (OD value) is extremely low. Comparative Example 5 (R) in which the mixing ratio of the two types of carbon blacks is out of the range of the present invention.
The aqueous inks of Examples No. 15-16 and Comparative Example 6 (Run Nos. 17-18) are greatly affected by the characteristics of carbon black, which has a high blending ratio, and thus have good initial viscosity, filterability, and precipitation residue ratio. If the blackness is low, it is recognized that the initial viscosity, the filterability, the rate of sedimentation residue and the like become poor when the blackness is high.

[0045]

As described above, according to the carbon black pigment for water-based ink of the present invention, it is possible to satisfy both the relationship between the paper fixing density and the filterability and the rate of sedimentation residue, which are contradictory as the ink properties, and the initial viscosity. Is low, and a carbon black pigment exhibiting stable water dispersion performance over a long period of time is provided. Therefore, aqueous inks prepared using this carbon black pigment for aqueous inks have high levels of paper fixing density, blackness, etc. and have excellent ejection stability, light resistance, storage stability, etc. It is extremely useful as such.

Claims (3)

[Claims] 1. A nitrogen adsorption specific surface area ^{_{(N 2 SA) 150m 2 /}} g or more, DBP absorption amount 100 cm ^3/100 g or more, the ratio tinting strength (Tint)
20 to 80 wt% of carbon black of 120% or more, nitrogen adsorption specific surface area (N ₂ SA) less than 150 m ² / g, DBP absorption 1
00cm ³ / below 100 g, the ratio tinting strength (Tint) 120% or more 80～20Wt% of carbon black, a carbon black in a mixing ratio of the total carbon atoms measured by X-ray photoelectron spectroscopy by oxidizing Ratio of oxygen to total oxygen atoms (oxygen binding energy intensity / carbon binding energy intensity)
To 0.1 or more, the amount of hydrogen-containing surface functional groups, which is the sum of carboxyl groups and hydroxyl groups, to 3.0 μeq / m ² or more,
Chemically modified carbon black pigment for water-based inks. 2. An agglomerate of carbon black having an average particle diameter Dupa50% of 50 to 1 when dispersed in water.
10nm, maximum particle size of agglomerate Dupa99% is 250nm
The carbon black pigment for aqueous inks according to claim 1, which has the following particle properties. 3. A nitrogen adsorption specific surface area ^{_{(N 2 SA) 150m 2 /}} g or more, DBP absorption amount 100 cm ^3/100 g or more, the ratio tinting strength (Tint)
20 to 80 wt% of carbon black of 120% or more, nitrogen adsorption specific surface area (N ₂ SA) less than 150 m ² / g, DBP absorption 1
00cm ³ / below 100 g, the ratio tinting strength (Tint) of 120% or more of carbon black 80～20Wt%, by oxidizing carbon black in a mixing ratio of dispersed in water, the total was measured by X-ray photoelectron spectroscopy The atomic ratio of carbon atoms to total oxygen atoms (oxygen bond energy intensity / carbon bond energy intensity) is 0.1 or more, and the amount of hydrogen-containing surface functional groups, which is the sum of carboxyl groups and hydroxyl groups, is 3.0 μeq / m ²
A water-based ink characterized by being chemically modified, separated by filtration, dispersed in an aqueous alkali solution, and then separated and purified from salts remaining in the dispersion.