JP2002241643A - Carbon black for aqueous ink and aqueous pigment ink using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon black having excellent water dispersibility and ink function, and suitable for an aqueous ink, and to provide an aqueous pigment ink using the carbon black. SOLUTION: The carbon black for an aqueous ink is obtained by subjecting a mixed carbon black obtained by blending a carbon black A having a CTAB specific area of >=140 m2/g, a tinting strength (Tint) of >=120% and a DBP absorption of >=100 cm3/100 g, and a carbon black B having a DBP absorption of <100 m3/100 g at a specific weight ratio to an oxidation treatment. The obtained chemically modified carbon black has an atomic ratio of the whole carbon atoms to the whole oxygen atoms of >=0.1 and the amount of hydrogen- containing surface functional groups of >=3.0 μeq/m2. Further, the aqueous pigment ink is obtained by dispersing the mixed carbon black in water, subjecting the dispersion to an oxidation treatment to chemically modify the carbon black, and filtering it. The material on the filter is dispersed in an alkali aqueous solution, and subsequently the dispersion is purified by removing the salt which remains in it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon black for water-based ink which is excellent in dispersibility in water and is suitable for a water-based black ink, and a water-based pigment ink using the carbon black as a 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 carbon black at a high concentration in water. 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, JP-A-48-18186 discloses a method of oxidizing carbon black with an aqueous solution of hypohalite, and JP-A-57-159856 discloses a method of oxidizing carbon black with a low-temperature oxidizing plasma. There is disclosed a method for producing a water-dispersible modified carbon black, which is characterized by treating.

[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. 2000-209, in 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.

Therefore, 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 dispersing performance, and has proceeded with research to find the presence on the surface. Water-dispersible carbon black in which the total amount of carboxyl groups and hydroxyl groups among the hydrogen-containing functional groups is 3 μeq / m ² or more per unit surface area, a method for producing the same (JP-A-11-148027), and a nitrogen adsorption ratio A carbon black obtained by oxidizing carbon black having a surface area (N ₂ SA) of 80 m ² / g or more and a DBP oil absorption of 70 ml / 100 g or less. The Stokes mode diameter Dst (nm) of the aggregate and the average particle diameter of agglomerate Dupa50% (n
m) and a water-dispersible carbon black having a characteristic having a Dupa50% / Dst value of 1.5 to 2.0 (JP-A-11-148026).
No.).

Further, the nitrogen adsorption specific surface area (N ₂ SA) is 50 m ² / g
As described above, a carbon black having a DBP oil absorption of 80 ml / 100 g or less, and (1) a ratio Dupa50% / d between the Stokes mode diameter Dst (nm) of the carbon black aggregate and the average particle diameter Dupa50% (nm) of the agglomerate. Dst value is 1.1 ~
1.5, (2) the value of the average particle size Dupa50% (nm) of agglomerate is 40 to 140 (nm), (3) the value of the maximum particle size Dupa99% (nm) of agglomerate is 250 (nm) or less, Water-dispersible carbon black having the property 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 (JP-A-11
-256066).

[0008]

However, in the course of continuing the research, aqueous pigment inks using carbon black having a low structure level generally have good ejection stability and the rate of sedimentation residue, but have low blackness. On the other hand, aqueous pigment inks prepared using carbon black with a high structure level of the regular class or higher have good blackness and the rate of sedimentation residue, but have poor filterability related to ejection stability. It turns out that there is a tendency.

The present invention has been developed on the basis of these findings, and its purpose is to provide excellent dispersibility in water and to be suitable as a black pigment for aqueous inks, for example, as an ink pigment for ink jet. For aqueous inks with excellent ink performance such as paper fixing density, printing density, ejection stability, light resistance, storage stability and dispersion stability when printing on plain paper, special paper, OHP sheet, art paper, etc. An object of the present invention is to provide carbon black and an aqueous pigment ink using the carbon black as a pigment.

[0010]

In order to achieve the above object, the carbon black for aqueous inks of the present invention is CTAB.
Specific surface area is 140m ² / g or more, specific coloring power (Tint) is 120%
Be more than, DBP absorption amount of 100 cm ^3/100 g or more of the carbon black A and the DBP absorption amount of carbon black B of less than 100 cm ^3/100 g, A: B is 70: 30 to 1
The carbon black mixed at a weight ratio of 0:90 is oxidized, 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 is calculated. It is characterized in that it is chemically modified to have a hydrogen-containing surface functional group content of not less than 0.1 and not less than 3.0 μeq / m ² .

Further, the carbon black for an aqueous ink of the present invention is a carbon black having the above-mentioned properties,
In the state of being dispersed in water, the carbon black has an agglomerate having an average particle size Dupa of 50% to 50 nm and a maximum agglomerate particle size of Dupa of 99% having a particle aggregation property of 250 nm or less.

The aqueous pigment ink of the present invention is CTAB.
Specific surface area is 140m ² / g or more, specific coloring power (Tint) is 120%
Or more, DBP absorption amount of 100 cm ^3/100 g or more of the carbon black A and the DBP absorption amount of carbon black B of less than 100 cm ^3/100 g, A: B is 70: 30-10: 90
Is oxidized in a state where carbon black mixed at a weight ratio of water is dispersed in water, and the atomic ratio of total carbon atoms to total oxygen atoms (oxygen bond energy intensity / carbon bond energy intensity) measured by X-ray photoelectron spectroscopy ) To 0.1 or more,
The structural feature is that the amount of the hydrogen-containing surface functional group is chemically modified to 3.0 μeq / m ² or more, separated by filtration, dispersed in an aqueous alkaline solution, and then the salt remaining in the dispersion is separated and purified. I do.

Furthermore, the aqueous pigment ink of the present invention has an aqueous dispersion having a carbon black dispersion concentration of less than 14 wt% at a carbon black dispersion concentration of 20 wt% and a carbon black dispersion concentration of 4 wt%. Is drawn down to plain paper (XEROX 4024) by a # 6 bar coater, and the blackness is 1.20 or more.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Among the characteristics of carbon black, C
The TAB specific surface area is a characteristic related to the area of the interface at which the surface of carbon black particles and water molecules are in contact with each other when carbon black is dispersed in water. The larger this value is, the larger the area of the contact interface is. 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, CTAB
When the specific surface area is reduced, the contact interface with water molecules is also reduced, so that the water dispersing performance is reduced, and the filterability and discharge stability of the aqueous ink are reduced, and the precipitation residue ratio is significantly increased.

The specific coloring power (Tint) is determined based on the particle size (specific surface area), structure (DBP absorption),
Furthermore, it is a characteristic related to the aggregate diameter, etc., and when this value is small, the filterability and ejection stability are reduced when the aqueous ink is produced because the particle size distribution is broadened, and the precipitation residue ratio is also increased. Becomes

The DBP absorption indicates a structure level, and is a characteristic related to the size of the aggregate of carbon black particles in a state of being dispersed in water.
When the amount of absorption increases, the print density increases and the blackness increases, but the probability of entanglement of the aggregates in the aqueous dispersion increases, and the carbon black tends to settle. Increases, and the filterability and the discharge stability decrease. On the other hand, when the DBP absorption is small, the precipitation residue ratio is small, but the paper fixing density is reduced, so that the print density, blackness and the like are reduced.

As described above, the characteristics of carbon black have a great influence on the ink performance such as the dispersing ability in water, and the paper fixing density, print density, blackness, filterability, discharge stability, and sedimentation residue rate of the aqueous ink. And give it. Therefore, the carbon black for water-based inks of the present invention is characterized in that the carbon black has a CTAB specific surface area of 140 m ² / g or more, a specific coloring power (Tint) of 120% or more, and two types of carbon black having different DBP absorption amounts. black, i.e., a DBP absorption 100 cm ^3/100 g or more of the carbon black a, D
Carbon black B with BP absorption less than 100cm ³ / 100g
Is characterized in that carbon black in which A: B is mixed in a weight ratio of 70:30 to 10:90 is used. The specific coloring power (Tint) was measured according to ASTM D3265-9.
3. Measurement of DBP absorption is performed according to ASTM D2414-93.

When the CTAB specific surface area is less than 140 m ² / g, the water dispersibility is low, the filterability and discharge stability of the aqueous ink are reduced, and the rate of the precipitation residue is significantly increased. On the other hand, when the specific coloring power (Tint) is less than 120%, the particle size distribution is broadened, so that when an aqueous ink is produced, the filterability and the ejection stability decrease, and the precipitation residue ratio increases. The CTAB specific surface area is AST
Measured according to MD3765-92a.

[0019] DBP absorption amount is 100 cm ^3/100 g or more, blackness of the aqueous ink is improved but increased precipitation residue渣率. If the DBP absorption is less than 100 cm ^3/100 g, the precipitate residue The ratio is low but the blackness is low. Therefore, in the carbon black for water-based ink of the present invention, two types of carbon blacks having different DBP absorption amounts,
That is, the DBP absorption amount is 100 cm ^3/100 g or more carbon blacks A, DBP absorption of carbon black B of less than 100 cm ^3/100 g, A: B is 70: 30-10:
A carbon black mixed at a weight ratio of 90 is applied. When the weight ratio of A exceeds 70 and the weight ratio of B is less than 30, as a mixing ratio of carbon blacks A and B, the precipitation residue ratio increases, the weight ratio of A falls below 10, and the weight ratio of B becomes 90. If it exceeds, the blackness will be significantly reduced. The difference in DBP absorption between carbon blacks A and B is 10
It is preferable that the cm ^3/100 g or more.

The carbon black for an aqueous ink of the present invention is intended for a carbon black obtained by mixing carbon blacks A and B having these properties at a predetermined weight ratio.
As a functional group present on the surface after the oxidation treatment, the value of 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 is 0. One or more is characterized in that the amount of hydrogen-containing surface functional groups is chemically modified to be 3.0 μeq / m ² or more.

When the atomic ratio of total carbon atoms to total oxygen atoms (oxygen bond energy intensity / carbon bond 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 dispersion stability is deteriorated when an aqueous ink is used. The adjustment of the strength ratio of the binding energy is performed by generating a hydrophilic functional group on the surface of the carbon black particles by an oxidation treatment.

It is necessary that the hydrophilic functional group is chemically modified to have a hydrogen-containing surface functional group such as a carboxyl group or a hydroxyl group in an amount of 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 determined as the amount of hydrophilic functional groups formed by chemical modification. The amount of hydrogen-containing surface functional groups such as carboxyl groups and hydroxyl groups containing is set to 3.0 μeq / m ² or more. This value is 3.0
For hydrophilic functional group amount is small below the μeq / m ^2,
Excellent dispersion performance cannot be imparted.

The hydrogen-containing surface functional group is measured by the following method. Carboxyl group: About 2 to 5 g of carbon black is placed in 50 ml of 0.976N aqueous sodium hydrogen carbonate solution and shaken for about 6 hours. After shaking, the carbon black and the reaction solution are separated, and the filtrate is subjected to a titration test with 0.05N sodium hydroxide to measure the amount of carboxyl groups on the surface. The value obtained by dividing this value by the nitrogen adsorption specific surface area (N ₂ SA) of the corresponding unoxidized carbon black is defined as the amount of carboxyl groups per unit surface area (μeq / m ² ). Hydroxyl group; 2,2'-Diphenyl-1-picrylhydrazyl
(DPPH) is dissolved in carbon tetrachloride to prepare a 5 × 10 ⁻⁴ mol / l solution. 0.1 to 0.6 of carbon black is added to the solution.
g and stirred in a 60 ° C. thermostat for 6 hours. Thereafter, the reaction solution and carbon black are separated, and the absorbance of the filtrate is measured at a wavelength of 520 nm with an ultraviolet absorption spectrophotometer to determine the amount of hydroxyl groups. The value obtained by dividing this value by the nitrogen adsorption specific surface area (N ₂ SA) of the corresponding unoxidized carbon black,
The amount of hydroxyl groups per unit surface area (μeq / m ² ).

The oxidation treatment may be, for example, persulfate, perborate,
This is performed by adding carbon black to an aqueous solution of an oxidizing agent such as an alkali metal salt or an ammonium salt such as percarbonate and oxidizing the solution.The concentration of the oxidizing agent aqueous solution, the amount of the carbon black added, the reaction temperature, the reaction time, etc. Appropriately controlled, a hydrogen-containing surface having an atomic ratio of total carbon atoms to total oxygen atoms (oxygen bond energy intensity / carbon bond energy intensity) of 0.1 or more, and a sum of carboxyl groups and hydroxyl groups The treatment is performed so that the amount of the functional group is 3.0 μeq / m ² or more.

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

The average particle size of the agglomerate indicating the size of the aggregated form of the carbon black particles in water Dupa 50%
Is less than 50 nm, the frequency of passage of the carbon black through the gaps between the paper fibers increases when the aqueous ink is used, so that the paper fixing density decreases and the print density decreases. On the other hand, when the value of the average particle size Dupa 50% of the agglomerate exceeds 110 nm, the print density is improved, but the dispersion stability of carbon black in the aqueous ink is reduced, the filterability is deteriorated, and the rate of sedimentation residue is increased. Will be. Further, when the value of the maximum particle diameter Dupa 99% of the agglomerate exceeds 250 nm, large aggregates of carbon black are present in the aqueous ink, the precipitation residue ratio increases, and the discharge stability and the filtration property decrease. This is because it becomes remarkable.

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 agglomerated particle size Dupa99. % (nm).

The water-based pigment ink of the present invention is obtained by dispersing the carbon black for a water-based ink of the present invention having the above characteristics at a predetermined concentration in water. That is, carbon blacks A and B having the above-mentioned CTAB specific surface area, specific coloring power (Tint) and DBP absorption amount are mixed at a predetermined weight ratio, and the mixed carbon black is mixed with persulfate, perborate, percarbonate. It is added to an aqueous solution of an oxidizing agent such as an alkali metal salt or an ammonium salt, and oxidized by appropriately controlling the concentration of the aqueous solution of the oxidizing agent, the amount of carbon black added, the reaction temperature, and the reaction time while stirring. The atomic ratio of total carbon atoms to total oxygen atoms (oxygen bond energy intensity / carbon bond energy intensity) should be 0.1 or more, and the amount of hydrogen-containing surface functional groups should be 3.0 μeq / m ² or more. Chemical modification.

After the oxidation treatment, the carbon black is immediately separated by filtration to separate carbon black, and then the separated carbon black is dispersed in an aqueous alkali solution such as sodium hydroxide, potassium hydroxide, ammonia or alkanolamine.
Adjust the pH for stable dispersion. 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 pigment ink of the present invention is obtained by separating and removing the generated residual salt for purification. For removal of residual salts, the pH of the aqueous dispersion is adjusted to 6 to 11, and electrodialysis or separation membrane (reverse osmosis membrane, ultrafiltration membrane, loose
RO, etc.) to separate and purify the remaining salts. 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 to 60% by weight or less.

The aqueous pigment ink of the present invention has a precipitation residue ratio of less than 14% by weight in an aqueous dispersion having a carbon black dispersion concentration of 20% by weight, and has excellent dispersibility of carbon black as a pigment. . The sedimentation residue ratio indicates the situation where when an external force is applied to the aqueous dispersion of carbon black, the carbon black sediments and precipitates due to the external force, and indicates the dispersion stability of the carbon black pigment in the aqueous pigment ink. It is defined as the scale shown.

That is, the precipitation residue ratio was 9.8 for an aqueous dispersion of carbon black (carbon black concentration: 20 wt%).
× a 20000 m / s ² acceleration of gravity for 30 minutes centrifugation the precipitate residual amount after performing (M1), the weight ratio of the weight of the carbon black in the aqueous dispersion before centrifugation (M0) (M1 / M0). If the precipitation residue ratio is 14% by weight or more, clogging of the ink head will occur during long-term storage.

The water-based pigment ink of the present invention is prepared by dispersing carbon black having the above characteristics as a pigment in water to obtain a black color having a high print density and a dispersion of 4 wt% carbon black. The blackness when drawn down on plain paper (XEROX 4024) by a bar coater can be 1.20 or more.

[0034]

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

Carbon black samples: Four types of carbon black samples shown in Table 1 were used as carbon blacks having different characteristics. That, CTAB specific surface area of 140 m ² / g or more, there is a specific tinting strength (Tint) of 120% or more, the sample and a DBP absorption 100 cm ^3/100 g or more carbon blacks A, DBP absorption 100 cm ³ / Samples and were used as carbon black B of less than 100 g.

[0036]

[Table 1]

Example 1, Comparative Example 5 Using carbon black samples shown in Table 1, the two were mixed at different ratios to prepare carbon black samples. 80 g of this carbon black sample was applied at a concentration of 1.17.
5 mol / dm ³ aqueous sodium persulfate solution was added to 3000 cm ³ , the reaction temperature was 60 ° C., the reaction time was 10 hours, and the stirring speed was 5
The oxidation treatment was performed under the condition of (1 / s). Next, the filtered oxidized carbon black is dispersed in pure water, neutralized with an aqueous solution of sodium hydroxide, and purified by an ultrafiltration membrane (Asahi Kasei, AHP-1010, molecular weight cut-off 50,000), and the remaining salt is removed. Was separated to produce an aqueous dispersion of carbon black. The conductivity of the purified dispersion was 0.6 mS / cm (carbon black content: 22 wt%).

Example 2 and Comparative Example 6 Carbon black samples shown in Table 1 were mixed at different ratios to prepare carbon black samples. A carbon black aqueous dispersion was prepared in the same manner as in Example 1.

Comparative Examples 1 to 4 Carbon black aqueous dispersions were prepared in the same manner as in Example 1 except that each of the carbon black samples shown in Table 1 was used alone.

These aqueous dispersions of carbon black were concentrated to prepare aqueous ink samples having a carbon black content of 20% by weight. The samples thus prepared were evaluated for water dispersion performance, ink performance, and the like by the following methods. Tables 2 to 4 show the obtained results.

Dispersion stability: The sample was packed in a closed container, and the viscosity change was measured in a 70 ° C. incubator for 3 days to 4 weeks. The viscosity was measured with a rotational vibration type viscometer (VM-100A-L, manufactured by Yamaichi Electric Co., Ltd.).

Particle size measurement: After conducting a sample and dispersion stability test, the particle size of the carbon black aggregate was measured using a heterodyne laser Doppler type particle size distribution analyzer (UPA model 9340, manufactured by Microtrac). did. In this measuring apparatus, when laser light 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.

Print density: The carbon black content of the sample was diluted to 4 wt%, printed on XEROX 4024 paper with a # 6 bar coater, and the optical density was measured using a Macbeth densitometer (RD-927, manufactured by Colmorgen). .

Filterability: 200 g of a sample was treated with 90φ N
0.2 filter paper and membrane pores 3 μm, 0.8 μm, 0.65 μm
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 (M1 / M0) of the amount (M1) of the sediment residue after centrifugation treatment for 30 minutes at the gravitational acceleration to the weight (M0) of the carbon black before the centrifugation treatment was defined as the rate of sediment residue. The lower the value, the better the dispersion stability.

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4]

From Tables 2 to 4, the CTAB specific surface area was 14%.
0 m ² / g or more, specific coloring power (Tint) is 120% or more,
DBP absorption of carbon black B of less than 100 cm ^3/100 g or more of the carbon black A and 100 cm ^3/100 g,
The carbon black mixed with A: B in a weight ratio of 70:30 to 10:90 is subjected to oxidation treatment so that the atomic ratio of all carbon atoms to all oxygen atoms is 0.1 or more, and the amount of hydrogen-containing surface functional groups is 3.
The aqueous dispersions of Examples 1 (Run Nos. 1 to 4) and 2 (Runs Nos. 7 to 10) prepared by dispersing carbon black chemically modified to 0 μeq / m ² or more in water are carbon black. Comparative Example 5 in which the mixing weight ratio of A and B is out of this range
Compared to the aqueous dispersions of Run Nos. 5 to 6 and Comparative Example 6 (Run Nos. 11 to 12), the print density (OD) was good despite the fact that the filterability was good and the precipitation residue ratio was as small as less than 14 wt%. Value) is as high as 1.20 or more, and it is recognized that both excellent dispersibility and blackness of print density are compatible. On the other hand, in the aqueous dispersions of Comparative Examples 5 and 6, the higher the print density (OD value), the higher the sedimentation residue rate, and the lower the sedimentation residue rate, the lower the print density (OD value). It can be seen that it is difficult to achieve both degrees).

The aqueous dispersions of Comparative Examples 1 to 4 (Run Nos. 13 to 16) prepared using a single carbon black sample showed that Comparative Examples 1 and 3 had a high precipitation residue ratio of 17 wt% or more. It is inferior in dispersibility, and in Comparative Examples 2 and 4, the blackness of the print density was low, and it was recognized that both the dispersibility and the blackness were not compatible.

[0051]

As described above, according to the carbon black for water-based ink of the present invention, two types of carbon blacks having a specific specific surface area and specific coloring power and having different structure levels are used in combination as a pigment. By
The water-based pigment ink produced using carbon black as a pigment has excellent water-dispersion performance, high blackness in print density, and can provide a water-based pigment ink having excellent ink performance.

Claims (5)

[Claims] 1. A CTAB specific surface area of 140 m ² / g or more, there is a specific tinting strength (Tint) of 120% or more, DBP absorption 100 cm ^3/100 g or more of the carbon black A and the DBP absorption 100 cm ³ / Less than 100 g of carbon black B,
The carbon black mixed with A: B in a weight ratio of 70:30 to 10:90 is oxidized, and the atomic ratio of total carbon atoms to total oxygen atoms (oxygen bond energy intensity) measured by X-ray photoelectron spectroscopy / Intensity of carbon bond energy) is 0.1 or more, and the amount of hydrogen-containing surface functional groups is 3.0 μeq / m ^2.
A carbon black for water-based ink, characterized by being chemically modified as described above. 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 for an aqueous ink according to claim 1, which exhibits the following particle aggregation properties. 3. A CTAB specific surface area of 140 m ² / g or more, a specific coloring power (Tint) of 120% or more, and a DBP absorption of 100%.
cm ³ / 100g or more of carbon black A and the DBP absorption amount is 1
And 00cm ³ / 100g less of the carbon black B, A: B is 70: 30-10: 90 Carbon black were mixed in a weight ratio of oxidized with dispersed state in water was measured by X-ray photoelectron spectroscopy The atomic ratio of total carbon atoms to total oxygen atoms (oxygen binding energy intensity / carbon binding energy intensity) is at least 0.1, and the amount of hydrogen-containing surface functional groups is 3.0.
An aqueous pigment ink characterized by being chemically modified to at least μeq / m ² , separated by filtration, dispersed in an aqueous alkaline solution, and then separated and purified from salts remaining in the dispersion. 4. The dispersion concentration of carbon black is 20% by weight.
Has a precipitation residue ratio of less than 14% by weight in an aqueous dispersion of
The aqueous pigment ink according to claim 3. 5. An aqueous dispersion having a carbon black dispersion concentration of 4% by weight using plain paper (XEROX 4024) with a # 6 bar coater.
The aqueous pigment ink according to claim 3 or 4, wherein the blackness when drawn down is 1.20 or more.