JP2001294776A - Carbon black pigment for water-based ink - Google Patents

Abstract

(57) [Problem] To provide a carbon black pigment excellent in dispersibility in water and suitable for use in aqueous black ink. SOLUTION: The carbon black pigment for water-based ink of the present invention comprises N ₂ SA 200 to 270 m ² / g, IA 190 to 260 mg / g, N ₂ SA /
^{IA 0.96 ~1.20, CTAB 170~240m 2 /} g, DBP 100~150cm
³ / 100g, 24M4DBP 90-120cm ³ / 100g, Tint 135 or more,
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 after chemically modifying the carbon black
0.1 or more. Furthermore, the mode diameter Dst of the Stokes equivalent diameter distribution of the aggregate is 30 to 60 nm, the half width ΔDst is 60 nm or less, and the average particle diameter of the agglomerate Dupa
50% value is 60 ~ 110nm, maximum particle size of agglomerate Dupa9
9% has a particle property of 210 nm or less.

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 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 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]

The present inventors have continued research on the dispersibility of carbon black in water, and have found that water-dispersible carbon black having excellent dispersibility in water is used as a black pigment. We have successfully developed carbon black pigments suitable as inks, for example, printer inks such as Bubble Jet (registered trademark).

[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]

The carbon black pigment for aqueous ink of the present invention for achieving the above object has a nitrogen adsorption specific surface area (N ₂ SA) of 200 to 270 m ² / g and an iodine adsorption amount.
(IA) is 190~260mg / g, the value of N ₂ SA / IA is 0.
96-1.20, CTAB specific surface area 170-240m ²
/ g, DBP absorption 100-150cm ³ / 100g, 24M4D
BP absorption 90-120cm ³ / 100g, coloring power (Tint) 1
The atomic ratio (intensity of oxygen binding energy / intensity of carbon binding energy) of all carbon atoms and all oxygen atoms measured by X-ray photoelectron spectroscopy after chemically modifying 35 or more carbon blacks is 0.1 or more. This is a structural feature.

The carbon black pigment for water-based ink of the present invention is a carbon black having the above characteristics, wherein the mode diameter Dst of the Stokes equivalent diameter distribution of the aggregate is 30 to 60 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 210 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]

BEST MODE FOR CARRYING OUT THE INVENTION The nitrogen adsorption specific surface area (N ₂ SA) is 200
When it is less than m ² / g, when the aqueous ink is used, the rate of precipitation residue increases, and the filterability and the discharge stability are remarkably reduced.
If it exceeds m ² / g, the carbon black aggregate becomes small, and the paper fixing density at the time of printing becomes low. Also, N ₂
If the value of 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. But N ₂ SA
If the value of / IA exceeds 1.20, the unburned carbon black contains a large amount of unburned matter, hinders the wettability with the oxidizing agent aqueous solution, and the oxidation is not sufficiently performed, and the dispersibility is reduced.

If the CTAB specific surface area is less than 170 m ² / g, the area of the liquid-solid interface becomes small, and surface chemical modification can be easily performed, but the particle size becomes large, causing problems in filterability and sedimentation. On the other hand, if the CTAB specific surface area exceeds 240 m ² / g, the area of the liquid-solid interface becomes large, making it difficult to carry out the chemical modification uniformly and resulting in insufficient dispersibility. Even if sufficient dispersibility is obtained, the particle size tends to be small, so that the paper fixing density decreases.

[0013] If the DBP absorption amount is printed on the paper as the carbon black dispersion is less than 100 cm ^3/100 g, for the shape of the primary aggregates are in the form close to a sphere, the print result in missing from the pores of the paper The concentration decreases. Also, 150cm ³ /
If it exceeds 100 g, on the contrary, the shape of the primary aggregates becomes complicated, the number of pores in the paper is reduced, and the blackness is improved. However, the apparent particle size is large, and the sedimentation and filtration properties are poor. 24M4D
BP absorption of 90cm ³ / is less than 100g and the DBP absorption 1
Occur 00cm ³ / 100g and less than similar phenomena, blackness decreases. A sedimentary 24M4DBP absorption exceeds 120 cm ^3/100 g, filtered, storage stability becomes poor. Tint is 1
If it is less than 35, the particle size distribution is broad, so that filterability,
Poor sedimentation.

The carbon black pigment for water-based inks of the present invention, in addition to the above characteristic ranges, includes the total number of carbon atoms and total oxygen atoms measured by X-ray photoelectron spectroscopy as the amount of functional groups present on the surface due to chemical modification. The value of the atomic ratio (strength of oxygen binding energy / strength of carbon binding energy) is 0.1 or more. XPS and ES
When the intensity ratio (atomic ratio) of oxygen binding energy / carbon binding energy (atomic ratio) measured by X-ray photoelectron spectroscopy such as CA is less than 0.1, self-dispersibility in a polar solvent such as water is significantly reduced. However, when the aqueous ink is used, the storage stability is extremely deteriorated. The adjustment of the intensity ratio 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.

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, in addition to the above-mentioned characteristics, the carbon black pigment for water-based ink of the present invention has a mode diameter Dst of a Stokes equivalent diameter distribution of carbon black aggregate of 3 or more.
0 to 60 nm, the half width ΔDst in the same distribution is 60 nm or less, and the value of the average particle diameter Dupa50% of agglomerate is 60 to 1
10 nm, the maximum particle size of agglomerate Dupa99% is 21
More preferably, it has a particle property of 0 nm or less.

If the mode diameter Dst of the Stokes equivalent diameter distribution of the aggregate is less than 30 nm, the agglomerate particle size in the water-dispersed state becomes small, and the blackness decreases.
If it exceeds 60 nm, the blackness will be improved, but the sedimentation and filtration properties will be reduced. On the other hand, when the half width ΔDst exceeds 60 nm, the particle size distribution becomes broad, and the blackness, sedimentation and filtration properties become poor.

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 210 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 sedimentation are deteriorated. Also, the value of Dupa99% is 210 nm
When the ratio exceeds the above range, the sedimentation property, the discharge stability and the filterability are significantly reduced.

The above characteristics Dst, ΔDst and Dup
For a50% and Dupa99%, values obtained by the following measurement methods are used. (1) Stokes mode diameter Dst (nm) and half width ΔDst (nm) of aggregate; JIS K6221 (1982) 5 A dry carbon black sample containing a small amount of surfactant based on “How to make dry sample” 20 A dispersion having a carbon black concentration of 0.1 kg / m ³ is prepared by mixing with a volume% aqueous solution of ethanol, and this is sufficiently dispersed with ultrasonic waves to obtain a sample. Disk Centrifuge (Joyes Lobel, UK)
Is set to 100 s ⁻¹ and 0.015 dm ^{3 of} a spin solution (2% by weight glycerin aqueous solution, 25 ° C.) is added.
Inject 0.001 dm ³ of buffer solution (20% by volume ethanol aqueous solution, 25 ° C.). Then, after adding 0.0005 dm ³ of the carbon black dispersion at a temperature of 25 ° C. with a syringe, centrifugal sedimentation was started, and at the same time, the recorder was operated to start the operation.
(Horizontal axis: elapsed time after adding the carbon black dispersion with a syringe, vertical axis: absorbance at a specific point changed with centrifugal sedimentation of carbon black). Each time T is read from this distribution curve and substituted into the following equation (Equation 1) to calculate the Stokes equivalent diameter corresponding to each time.

[0020]

(Equation 1)

In Equation 1, η is the viscosity of the spin liquid (0.935
× 10 ^-3 Pa · s), N is the disk rotation speed (100 s ^-1 ),
r ₁ is the radius of the carbon black dispersion injection point (0.0456 m)
, R ₂ is the radius to the absorbance measuring point (0.0482m), ρ _CB is the density of carbon black (kg / m ^3), the density of [rho ₁ spin liquid
(1.00178 kg / m ³ ).

The Stokes equivalent diameter having the highest frequency in the distribution curve of Stokes equivalent diameter and absorbance obtained in this manner (FIG. 2) is determined by the Stokes mode diameter Dst (n) of the aggregate.
m), and the distance between two points, large and small, corresponding to half the maximum frequency, is defined as a half width ΔDst (nm).

(2) Average particle size of agglomerate Dupa 50% (n
m), maximum particle size Dupa 99% (nm); The average particle size Dupa 50% and maximum particle size Dupa 99% of this agglomerate are values obtained by the following measurement methods. A dispersion of 0.1 to 0.5 kg / m ³ is prepared by dispersing carbon black in water, and a laser is applied to the dispersion using a heterodyne laser Doppler type particle size distribution analyzer (UPA mode1 9340, manufactured by Microtrac). The particle diameter of the agglomerate in the dispersion is measured by irradiating light and measuring 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 agglomerate can be measured. A cumulative frequency distribution curve is created from the agglomerate particle size measured in this way, and the value of the 50% cumulative frequency is calculated as the average particle size Dupa50% (nm) of the agglomerate,
The value of 99% cumulative frequency is the maximum particle size of agglomerate Dupa9
9% (nm).

The carbon black pigment for water-based ink of the present invention has a carbon black particle surface chemically modified by an oxidation treatment to form a hydrophilic functional group. -O
Displacement can be further improved by replacing all or part of the terminal hydrogen such as H group with an alkali metal, amino group or the like. The carbon black pigment for an aqueous ink of the present invention can be obtained by separating and removing the residual salt generated by the oxidation reaction and purifying it.

An aqueous ink is 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.). In this case, the residual salt concentration in the carbon black dispersion may be, for example, 5 wt.
It is preferable to separate and purify so as to be less than mS / cm 2.
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 90 g of carbon blacks having different properties shown in Table 1 were added to 3000 ml of a 2.5N aqueous sodium persulfate solution, and the reaction temperature was 60 ° C., the reaction time was 10 hours, and the mixture was stirred. Speed 30
Oxidation treatment was performed at 0 rpm. Next, the filtered carbon black was dispersed in pure water, neutralized with an aqueous sodium hydroxide solution, and then filtered with an ultrafiltration membrane (Asahi Kasei, AHP-1010, molecular weight cut off 500
(00) and the remaining salts were separated. The conductivity of the purified dispersion was 0.6 mS / cm (carbon black content: 22 wt%).

Comparative Example 5 A carbon black dispersion was prepared in the same manner as in the example, except that the ozone was oxidized. The conductivity of the dispersion was 0.5 mS / cm (carbon black content 1
2 wt%).

[0029]

[Table 1]

An aqueous ink was prepared by adjusting the carbon black content of the carbon black dispersion to 20 wt%.
Dispersion performance and ink performance were evaluated by the following methods, and the results are shown in Table 2.

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 diameter: The particle diameters 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 concentration of carbon black in 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 water-based ink (carbon black content: 20 wt%) was applied under reduced pressure of 2.7 KPa using 90φ NO.2 filter paper and filters having membrane pore sizes of 3 μm, 0.8 μm, 0.65 μm and 0.45 μm. Perform a filtration test,
The amount passed through the filter was measured.

Precipitation residue ratio: The amount of precipitation residue (M ₁ ) after centrifuging the aqueous ink (carbon black content concentration: 20 wt%) for 30 minutes at a gravitational acceleration of 20,000 G;
The weight ratio (M ₁ / M ₀ ) to the weight (M ₀ ) of the carbon black before the centrifugation treatment was defined as the precipitation residue ratio. The lower the value, the better the dispersion stability.

[0036]

[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. Examples 1 and 2 are IA, N ₂ SA, CTA
Since B, DBP and 24M4DBP are small, the filterability and storage stability are good, but the paper fixing density is extremely low and the precipitation residue ratio is high. In Comparative Example 3, since IA, N ₂ SA, and CTAB were small, storage stability, filterability, and paper fixing density were good, but the rate of sedimentation residue was high and poor. Comparative Example 4 is DBP
, The storage stability, the filterability and the rate of precipitation residue are good, but the paper fixing density is extremely low. 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.

[0038]

As described above, according to the carbon black pigment for water-based ink of the present invention, both the relation between the contradictory paper fixing density, the filterability and the rate of sedimentation residue are compatible, and the dispersibility is stable over a long period of time. The carbon black pigments shown can be provided. Therefore, it is extremely useful as a black pigment for aqueous inks such as an aqueous ink for an ink jet printer.

[Brief description of the drawings]

FIG. 1 is a distribution curve showing changes in absorbance due to centrifugal sedimentation of carbon black and elapsed time from the addition of a carbon black dispersion at the time of measurement of Dst.

FIG. 2 is a distribution curve showing the relationship between Stokes equivalent diameter and absorbance obtained at the time of measuring Dst.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J037 AA02 DD05 DD07 DD17 EE19 EE43 FF03 FF05 FF15 FF22 FF23 4J039 BA04 BE01 CA06 EA19 EA35 EA44 GA24

Claims (2)

[Claims] 1. A nitrogen adsorption specific surface area (N ₂ SA) of 200 to 27.
0 m ² / g, iodine adsorption (IA) 190-260 mg / g, N ₂ S
A / IA value: 0.96-1.20, CTAB specific surface area: 170-240 m ² / g, DBP absorption: 100-150
cm ³ / 100g, 24M4DBP absorption of 90~120cm ^3/100
g, atomic ratio of total carbon atoms to total oxygen atoms (oxygen bond energy intensity / carbon bond energy intensity) measured by X-ray photoelectron spectroscopy after chemically modifying carbon black having a tinting power (Tint) of 135 or more ) Is 0.1 or more. 2. The mode diameter Dst of the Stokes equivalent diameter distribution of the aggregate is 30 to 60 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. A particle having an a99% value of not more than 210 nm.
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.