JP2001081355A - Carbon black pigment for aqueous ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a carbon black pigment highly dispersible in water and suitable for aqueous black inks. SOLUTION: This carbon black pigment for aqueous inks has the following characteristics: nitrogen adsorption specific surface area (N2SA) is 160-200 m2/g; iodine adsorption(IA) is 140-190 mg/g; N2SA/IA is 0.96-1.20; CTAB specific surface area is 140-170 m2/g; DBP oil absorption is 100-140 mL/100 g; 24M4DBP oil absorption is 90-110 mL/100 g; tinting strength (Tint) is >=120; the ratio of total oxygen atom to total carbon atom (oxygen bond energy intensity/carbon bond energy intensity) determined by X-ray photoelectron spectroscopy is >=0.1; the mode diameter Dst of the aggregate's Stokes-equivalent diameter distribution is 50-70 nm; half-value width ΔDst is <=60 nm; agglomerate's mean diameter Dupa50% is 60-110 nm; and agglomerate's maximum diameter Dupa99% is <=250 nm.

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 aqueous inks, which has excellent dispersibility in water and is suitable for aqueous black inks.

[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 has long been known.

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 excellent in water dispersibility has been used 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 Patent Laid-Open No. 8-
JP-A-319444 discloses a method for producing an aqueous pigment ink, comprising the steps of finely dispersing carbon black having an oil absorption of 100 ml / 100 g or less in an aqueous medium; and oxidizing the carbon black with a hypohalite. 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 inventors have 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 dispersion performance, and have proceeded with research. 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 among the hydrogen-containing functional groups to be developed, and a method for producing the same have been developed and proposed (Japanese Patent Application Laid-Open No.
No. 148027).

[0007]

SUMMARY OF THE INVENTION The present inventors have continued research on water-dispersible carbon black, and have developed a water-based ink using such water-dispersible carbon black as a black pigment, for example, a printer such as a bubble jet. Successfully developed carbon black pigments suitable as inks for printing.

[0008] That is, an object of the present invention is to provide, when printing on plain paper, special paper, OHP sheet, art paper, etc., excellent paper fixing density, print quality, ejection stability, light resistance, storage stability, and the like. An object of the present invention is to provide a carbon black pigment for an aqueous ink.

[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 160 to 200 m ² / g and an iodine adsorption amount.
(IA) is 140 to 190 mg / g, and the value of N ₂ SA / IA is 0.
96-1.20, CTAB specific surface area 140-170m ²
/ g, DBP oil absorption 100-140ml / 100g, 24M4D
BP oil absorption 90-110ml / 100g, coloring power (Tint) 1
20 or more carbon blacks, wherein 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 0.1 or more. Is a structural feature.

The carbon black pigment for water-based ink of the present invention is a carbon black having the above-mentioned properties, wherein the mode diameter Dst of the Stokes equivalent diameter distribution of the aggregate is 50 to 70 nm, and the half width ΔDst in the same distribution. Is 6
0 nm or less, the average particle size of agglomerate Dupa50% is 6
It is characterized by having a particle property of 0 to 110 nm and a value of the maximum particle size Dupa99% of agglomerate of 250 nm or less. Here, Dst is the Stokes equivalent diameter of the maximum frequency in the Stokes equivalent diameter distribution of the aggregate measured by the centrifugal sedimentation method (DCF), ΔDst is the half width of the Stokes equivalent diameter distribution, and Dupa50% is the water dispersion of carbon black. The liquid is irradiated with laser light, and the value of 50% cumulative frequency in the cumulative frequency distribution curve of the agglomerate particle size created from the frequency modulation degree of the scattered light, and Dupa 99% indicates the value of 99% cumulative frequency in the same distribution curve.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The characteristic range of carbon black is regulated as described above. When the N ₂ SA is less than 160 m ² / g, the rate of precipitation residue increases when the aqueous ink is used,
This is because the filterability and discharge stability are remarkably reduced, and if it exceeds 200 m ² / g, the paper fixing density at the time of printing becomes low. On the other hand, when the value of N ₂ SA / IA is less than 0.96, the volatile matter (surface functional group) of the carbon black is small, the wettability with the oxidizing agent aqueous solution is deteriorated, and the dispersibility is reduced. However, when the value of N ₂ SA / IA exceeds 1.20, the unburned carbon black contains a large amount of unburned matter, which hinders the wettability with the oxidizing agent aqueous solution, and the oxidation is not sufficiently performed, so that the dispersibility is reduced.

If the CTAB specific surface area is less than 140 m ² / g, the area of the liquid-solid interface becomes small, causing problems in filterability and the rate of precipitation residue, and if it exceeds 170 m ² / g, the area of the liquid-solid interface becomes large. And dispersibility becomes insufficient. If the DBP oil absorption is less than 100 ml / 100 g, the print density becomes low and the
If it exceeds 40 ml / 100 g, the precipitation residue rate will increase and the filterability will decrease. If the content of 24M4DBP is less than 90 ml / 100 g, the print density decreases, and if it exceeds 110 ml / 100 g, the rate of sedimentation residue increases, resulting in poor filterability and storage stability. Tint
Is less than 120, the particle size distribution is broad, so that the filterability and the rate of precipitation residue become poor.

The carbon black pigment of the present invention has, in addition to the above characteristic ranges, the amount of functional groups present on the surface thereof as an atomic ratio of total carbon atoms to total oxygen atoms (oxygen ratio) measured by X-ray photoelectron spectroscopy. It is characterized in that the value of (binding energy intensity / carbon binding energy intensity) is 0.1 or more. If the intensity ratio (atomic ratio) of oxygen binding energy / carbon binding energy (atomic ratio) measured by X-ray photoelectron spectroscopy such as XPS or ESCA is less than 0.1, self-dispersibility in a polar solvent such as water will be poor. The water-based ink significantly lowers the storage stability. The adjustment of the intensity ratio is performed by chemically oxidizing the surface of the carbon black particles by an oxidizing treatment and imparting a hydrophilic functional group by chemical modification.

In the oxidation treatment, for example, carbon dioxide is added to an aqueous solution of an oxidizing agent such as an alkali metal salt such as hypochlorite, chlorite, chlorate, persulfate, perborate or percarbonate or an ammonium salt. It is performed by adding and oxidizing black, the concentration of the oxidizing agent aqueous solution, the added amount of carbon black,
The reaction temperature, reaction time, etc. are appropriately controlled to determine the atomic ratio of all carbon atoms to all oxygen atoms (oxygen binding energy intensity /
(Intensity of carbon bond energy) is 0.1 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 mode diameter Dst of the Stokes equivalent diameter distribution of the aggregate is 50 to 70 nm, and the half width ΔDst in the same distribution. Is 6
0 nm or less, the average particle size of agglomerate Dupa50% is 6
More preferably, it has a particle property of 0 to 110 nm and a maximum agglomerate particle diameter Dupa of 99% is 250 nm or less.

If the mode diameter Dst of the Stokes equivalent diameter distribution of the aggregate is less than 50 nm, the agglomerate particle size in the water-dispersed state becomes small, and the blackness decreases.
If it exceeds 70 nm, the blackness is improved, but the precipitation residue ratio is increased and the filterability is reduced. The half width ΔDst is 60 nm.
Exceeding the particle size distribution broadens, the blackness and the rate of sedimentation residue increase, and the filterability deteriorates.

The average particle size of agglomerate Dupa 50%
Value of 60 to 110 nm, maximum particle size Dup of agglomerate
The value of a 99% is set to the particle property of 250 nm or less because Dupa5
If the value of 0% is less than 60 nm, the carbon black passes through the gap between the paper fibers, and the paper fixing density decreases. 110
If the thickness exceeds nm, the blackness is improved, but the filterability and the rate of the residue of precipitation are deteriorated. Also, the value of Dupa99% is 25
If it exceeds 0 nm, the precipitation residue ratio increases, and the discharge stability and the filterability decrease significantly.

The average particle size Dup of this agglomerate
The values obtained by the following measuring methods are used for a50% and the maximum particle size Dupa99%. Disperse carbon black in water to prepare a dispersion of 0.1 to 0.5 g / l, and irradiate the dispersion with laser light using a heterodyne laser Doppler system particle size distribution analyzer (Microtrac, UPAmode 19340) Then, 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, the intensity of the Brownian motion differs 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 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).

An aqueous ink can be obtained by dispersing carbon black having these properties as a black pigment at a desired concentration in an aqueous medium such as water. That is,
The pH of the aqueous dispersion in which carbon black is dispersed is 6-1.
Adjust to 1 and separate and purify the residual salts by electrodialysis or a separation membrane (reverse osmosis membrane, ultrafiltration membrane, loose RO, etc.). The residual salt concentration in the carbon black dispersion is preferably separated and purified so that the conductivity is less than 5 mS / cm 2 with the carbon black content being 20%. In order to achieve dispersion stability as an aqueous ink, it is desirable to adjust the concentration of the carbon black pigment to 60% by weight or less.

Hereinafter, examples of the present invention will be specifically described in comparison with comparative examples.

Examples 1 to 3 and Comparative Examples 1 to 4 100 g of carbon black having the characteristics shown in Table 1 was used.
The reaction mixture was added to 3000 ml of a 2N aqueous sodium persulfate solution and oxidized at a reaction temperature of 60 ° C. for a reaction time of 10 hours at a stirring speed of 300 rpm. Next, the filtered carbon black is dispersed in pure water, neutralized with an aqueous solution of sodium hydroxide, purified by an ultrafiltration membrane, and the remaining salts are separated.
The resultant was filtered to separate carbon black, washed with water and dried to prepare a carbon black pigment sample. The oxygen binding energy intensity and carbon binding energy intensity of these carbon black samples were measured by Surface Science Instruments.
Table 1 shows the atomic ratio of all carbon atoms to all oxygen atoms as measured by S-Prove ESCA 2803 type.

COMPARATIVE EXAMPLE 5 A carbon black sample was prepared in the same manner as in the example, except that it was oxidized with ozone, and its binding energy was measured. The atomic ratio of all carbon atoms to all oxygen atoms was as shown in Table 1. Also described.

[0023]

[Table 1]

Next, these carbon black samples were dispersed as pigments in pure water at a concentration of 20% by weight to prepare an aqueous ink, and the dispersing performance and the ink performance were evaluated by the following methods. Table 2 shows the obtained results.

Heating Stability: The samples were packed in a closed container, and the viscosity change was measured in a 70 ° C. incubator for 1 to 4 weeks to compare the dispersion stability at the time of heating. The viscosity was measured using a rotary viscometer [Yamaichi Denki Co., Ltd., VM-100A-L
].

Measurement of particle diameter: The particle diameter of the sample and the sample subjected to the heating stability test were measured using a heterodyne laser Doppler system particle size distribution analyzer [UPA model 9340, manufactured by Microtrac Co., Ltd.]. In this measurement device, 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 dispersion concentration of the aqueous ink was diluted to 4% by weight, and XEROX was used as copy paper.
Use 4024 paper, print on it with a # 6 bar coder,
The optical density was measured using a Macbeth densitometer (RD-927, manufactured by Colmorgen).

Filterability: 90 g of 200 g of the aqueous pigment ink
φ filter paper (NO.2) and membrane pore size 3μm, 0.8μm, 0.65μm
A filtration test was performed using a 0.45 μm filter under a reduced pressure of 20 Torr to measure the passing amount.

Precipitation residue rate: 2000% aqueous black ink
The weight ratio (M ₁ / M ₀ ) between the amount of the sediment residue (M ₁ ) after centrifugation at 0 G gravity for 30 minutes and the weight (M ₀ ) of the carbon black before centrifugation is settled. The residue rate was used. The lower this value, the better the dispersion stability.

[0030]

[Table 2]

From the results shown in Tables 1 and 2, the aqueous inks prepared by dispersing the carbon black pigments of the examples have excellent storage stability, filterability, paper fixing density, and precipitation residue ratio. Example 1 is IA, N ₂ SA, CTAB, D
Since BP, 24M4DBP, and Dst are also small, the filterability, storage stability, and precipitation residue rate are good, but the paper fixing density is extremely low. In Comparative Example 2, since IA, N ₂ SA, and CTAB were out of the range, storage stability and paper fixing density were good, but filterability and precipitation residue rate were poor. Further, Comparative Example 3 is a DB
Since P and 24M4DBP are smaller than the ranges, storage stability and filterability are good, but the paper fixing density is significantly reduced. In Comparative Example 4, since IA, N ₂ SA and CTAB were smaller than the ranges, the storage stability and the paper fixing density were good, but the filterability and the rate of precipitation residue were poor. In Comparative Example 5, although the characteristics of carbon black conformed to the range, the ratio of total carbon atoms to total oxygen atoms was small, so that the initial viscosity was high and the storage stability was extremely poor.

[0032]

As described above, according to the carbon black pigment for water-based ink of the present invention, it is possible to obtain a water-based ink which has both contradictory paper fixing density and filterability, and further exhibits stable dispersibility over a long period of time. Can be. Therefore, it is extremely useful as a black pigment for aqueous inks such as an aqueous ink for an ink jet printer.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J037 AA02 CA15 DD05 DD07 DD17 DD20 EE02 EE19 EE28 EE43 FF05 FF15 FF30 4J039 BA04 BE01 CA06 EA19 EA35 EA42 EA43 EA44 FA02 GA24

Claims (2)

[Claims] 1. A nitrogen adsorption specific surface area (N ₂ SA) of 160 to 20.
0m ² / g, iodine adsorption (IA) 140-190mg / g, N ₂ S
A / IA value: 0.96-1.20, CTAB specific surface area: 140-170 m ² / g, DBP oil absorption: 100-140
ml / 100g, 24M4DBP oil absorption 90-110ml / 100g
A carbon black having a tinting strength (Tint) of 120 or more and having an atomic ratio of total carbon atoms to total oxygen atoms (oxygen bond energy intensity / carbon bond energy intensity) measured by X-ray photoelectron spectroscopy. A carbon black pigment for water-based ink, which is 0.1 or more. 2. The mode diameter Dst of the Stokes equivalent diameter distribution of the aggregate is 50 to 70 nm, and the half width Δ in the distribution is
Dst is 60 nm or less, average particle size of agglomerate Dupa50%
Is 60 to 110 nm, the maximum particle size of agglomerate Dup
2. The composition according to claim 1, wherein a value of a99% is 250 nm or less.
The carbon black pigment for an aqueous ink according to the above. However, Dst
Is the maximum frequency Stokes equivalent diameter in the Stokes equivalent diameter distribution of the aggregate measured by centrifugal sedimentation method (DCF), ΔDst is the half width of the Stokes equivalent diameter distribution,
Dupa 50% irradiates a laser beam to an aqueous dispersion of carbon black, and the value of 50% cumulative frequency in the cumulative frequency distribution curve of agglomerate particle size created from the frequency modulation degree of scattered light, and Dupa 99% is 99% in the same distribution curve. Indicates the value of% cumulative frequency.