JPH09286938A - Water-based pigment ink and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject ink, containing carbon black oxide excellent in water-dispersibility as a coloring agent, capable of printing without clotting a nozzle when used for ink jet recording and having a concentration capable of smoothly writing down even when a fine pen is used. SOLUTION: This ink contains carbon black oxide stably dispersing into water. This carbon black oxide is prepared by oxidating carbon black with a hypohalogenous acid and/or its salt and at least a part of acidic moiety existing on the surface of it is combined with an amine compound (preferably a water-soluble volatile amine) to form an ammonium salt. In order to obtain this carbon black oxide, carbon black finely dispersing into water is oxidized with the hypohalogenous acid and/or its salt and then at least a part of the acidic moiety existing on the surface of the resulting carbon black oxide is preferably neutralized with the amine compound.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an aqueous pigment ink, and more particularly to an aqueous pigment ink containing oxidized carbon black having excellent water dispersibility as a colorant and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, aqueous dye inks containing a black dye have been mainly used as recording liquids for writing instruments and ink jet printers. In recent years, water-based pigment inks using pigments such as carbon black to give light resistance and water resistance to recorded images have attracted attention.

As this type of carbon black, acidic carbon black which is commercially available as a coloring agent is often used. Acidic carbon black is a carbon black exhibiting an acidic pH, and it is considered that acidic groups such as carboxyl groups are present on the surface thereof. These are generally liquid phase or gas phase oxidation methods using conventional oxidants such as nitric acid, ozone, hydrogen peroxide and nitrogen oxides, or surface modification methods such as plasma treatment, such as furnace black or It is obtained by appropriately oxidizing carbon black for colors such as channel black.

Although such acidic carbon black exhibits a certain degree of hydrophilicity, it has insufficient affinity to an aqueous medium and dispersion stability, and is difficult to disperse in water by itself. Therefore, when these are used as a colorant of an aqueous pigment ink, they are dispersed in an aqueous medium using a disperser in the presence of a so-called pigment dispersant such as various water-soluble synthetic polymers and a surfactant, Need to stabilize.

[0005] For example, Japanese Patent Application Laid-Open Nos.
JP-A-4-31881 describes an aqueous pigment ink containing acidic carbon black having a pH of 5 or less and a pigment dispersant (an anionic surfactant or a polymer dispersant). Further, Japanese Patent Laid-Open No. 3-210373 discloses that volatile matter is 3.
Inkjet recording inks containing 5 to 8% by weight of acidic carbon black and a water-soluble resin are described.

Generally, in order to stably generate liquid droplets from the fine tip of an ink jet recording head or to write smoothly with a fine pen tip of a water-based ballpoint pen, ink is solidified at an orifice of an ink jet recording head or a ballpoint pen tip. It is necessary to prevent that.

However, conventional aqueous pigment inks include a pigment dispersant as described above. Since the resin forming the pigment dispersant is difficult to be redissolved once dried, clogging and non-ejection of liquid droplets may occur if these adhere to the orifices of the inkjet recording head. In addition, since the aqueous pigment ink containing the pigment dispersant is viscous, when performing continuous ejection or high-speed printing for a long time, resistance is generated in the path to the nozzle tip, and ejection becomes unstable and smooth recording becomes difficult. . That is, in the conventional aqueous pigment ink containing the pigment dispersant, the pigment concentration cannot be sufficiently increased in order to secure the ejection stability, and the print density becomes insufficient as compared with the aqueous dye ink (recording liquid). It has the drawback.

[0008]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned conventional problems, and an object thereof is to perform printing without causing nozzle clogging when used for ink jet recording, and An object of the present invention is to provide an aqueous pigment ink having a sufficient concentration that allows smooth writing even with a thin pen tip.

[0009]

The present invention provides an aqueous pigment ink containing water and stably dispersed oxidized carbon black, wherein the oxidized carbon black is oxidized with hypohalous acid and / or a salt thereof. And an aqueous pigment ink in which at least a part of the acidic groups present on the surface of the oxidized carbon black is combined with an amine compound to form an ammonium salt, whereby the above-mentioned The purpose is achieved.

The water-based pigment ink of the present invention containing water and stably dispersed oxidized carbon black oxidizes carbon black finely dispersed in water using hypohalous acid and / or its salt. And a step of neutralizing at least a part of the acidic groups present on the surface of the resulting oxidized carbon black with an amine compound.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Oxidized carbon black contained in the aqueous pigment ink of the present invention is obtained by oxidizing carbon black with hypohalous acid and / or its salt. Carbon black, which is a raw material of oxidized carbon black, is generally a carbon powder obtained by thermally decomposing or incompletely burning natural gas or liquid hydrocarbon (such as heavy oil or tar). These are classified into channel black, furnace black, lamp black and the like according to the manufacturing method, and are commercially available.

The type of carbon black used as a raw material is not particularly limited. Any of the above-mentioned acidic carbon black, neutral carbon black and alkaline carbon black can be used.

Specific examples of carbon black include # 10B, # 20B, # 30, # 33, # 44 manufactured by Mitsubishi Chemical Corporation.
# 45, # 50, # 55, # 95, # 260, # 90
0, # 1000, # 2200B, # 2300, # 235
0, # 2400B, # 2650, # 2700, # 400
0B, CF9, MA8, MA11, MA77, MA10
0, MA220, MA230, MA600 and MCF8
8 etc .; Monarch 120, Monarch 70 made by Cabot
0, Monarch 800, Monarch 880, Monarch 100
0, Monarch 1100, Monarch 1300, Monarch 1
400, Mogul L, Regal 99R, Regal 250
R, Regal 300R, Regal 330R, Regal 4
00R, Regal 500R, Regal 660R, etc .; Degussa's Printex A, Printex G, Printex U, Printex V, Printex 5
5, Printex 140U, Printex 140
V, Special Black 4, Special Black 4A,
Special Black 5, Special Black 6, Special Black 100, Special Black 250, Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160 and Color Black S170. To be

Acidic carbon black is preferable as a raw material because it has acidic groups such as hydroxyl groups and carboxyl groups on the surface of the particles. The acidic carbon black generally has a pH of 6 or less, preferably 4 or less.

Specific examples of the acidic carbon black include MA8, MA100, 2200B and 240 from Mitsubishi Kasei.
Color black FW2 from Tegusa under the product name 0B
00, color black FW18, color black S1
50, color black S160, color black S1
70, Printex U, Printex 1400 under the trade names of Monarch 1300, Mogul L, Regal 400R under the trade names of Cabot and Raven 1200, Raven 1220, Raven 1225 under the trade names of Colombian Carbon. There is.

Such carbon black is wet-oxidized in water using hypohalous acid and / or its salt. Examples of the hypohalous acid and / or salt thereof include sodium hypochlorite and potassium hypochlorite, and sodium hypochlorite is particularly preferable from the viewpoint of reactivity.

In the oxidation reaction, carbon black and a hypohalite (for example, sodium hypochlorite) are charged in an appropriate amount of water, for 5 hours or more, preferably for about 10 to 15 hours.
It is carried out by stirring at 50 ° C. or higher, preferably 95 to 105 ° C. At that time, the carbon black is preferably subjected to an oxidation treatment in a finely dispersed state.

In the present specification, the term "finely dispersed" means that at least secondary particles of carbon black are pulverized to be primary particles or finely divided into particles close to the primary particles. The average particle size of the finely dispersed carbon black is generally 300n.
m or less, preferably 150 nm or less, more preferably 100 nm or less.

Generally, fine dispersion is carried out by wet milling in an aqueous medium for 3 to 10 hours using a mill medium and a milling device. As the mill medium, glass beads, zirconia beads, porcelain beads, stainless beads, etc. are used. A ball mill, an attritor, a fluo jet mixer, an impeller mill, a colloidal mill, a sand mill (for example, those commercially available under the trade names of "Super mill", "Agitator mill" and "Dyno mill"), etc. are used for the crushing device.

However, depending on the type of carbon black used as a raw material, it may be finely dispersed only by stirring at high speed in a solvent (water).

The fine dispersion treatment does not necessarily have to be performed before the oxidation treatment, and the fine dispersion treatment may be performed simultaneously with the oxidation treatment by stirring or pulverizing in an aqueous solution of hypohalous acid or the like.

The amount of the hypohalous acid salt used varies depending on its type, but it is generally 1.5 to 150% by weight, preferably 4 to 75% by weight, based on 100% by weight of the carbon black. .

The resulting oxidized carbon black has an oxygen content of greater than or equal to about 3% by weight, preferably greater than or equal to about 5% by weight, and more preferably greater than or equal to 10% by weight. The oxygen content is
As a result of being oxidized by the method of the present invention, the amount of oxygen contained in the carbon black before treatment is about 1.5 to about 30.
Double, and even up to 100 times.

The oxygen content is measured by the "inert gas-infrared absorption method (JIS Z2613-1976)" described later. In this method, a sample is heated in a stream of an inert gas such as helium, oxygen is extracted as carbon monoxide, and measured by an infrared absorption method.

The characteristic feature of the water-based pigment ink of the present invention is not only the oxygen content of the oxidized carbon black contained therein. Although the reason is not clear, the oxidized carbon black of the present invention forms a stable aqueous dispersion without using a pigment dispersant even when the oxygen content is about 3 to 10% by weight.

It is generally said that in the reaction between carbon black and hypohalite, various functional groups existing on the surface of carbon black are oxidized to form a carboxyl group or a hydroxyl group. These polar groups have active hydrogen, and the amount of this active hydrogen can be measured, for example, by the Tweil method.

The oxidized carbon black of the present invention preferably has a high surface active hydrogen content (mmol / g). This is because such oxidized carbon black exhibits particularly good water dispersibility. The surface active hydrogen content of the oxidized carbon black of the present invention is not particularly limited, but is about 0.
5 mmol / g or more, preferably about 1.0 m
It is more preferably at least mol / g.

In general, carbon black having a high surface active hydrogen content has a large number of active hydrogen-containing hydroxyl groups and carboxyl groups on the surface, and therefore the hydrophilicity of the carbon black itself is improved. At the same time, the surface area is also increased, and it is thought that water dispersibility is improved by having chemical properties such as acid dyes.

The characteristics of the aqueous pigment ink of the present invention are not limited only to the surface active hydrogen content of the oxidized carbon black contained therein. That is, not all carbon blacks having an active hydrogen content of about 0.1 to about 1.0 mmol / g achieve the object of the present invention.

Next, the oxidized carbon black dispersion after the oxidation treatment is filtered (when hot) to redisperse the obtained wet cake in water, and then beads and coarse particles are removed using a mesh wire mesh. . Alternatively, after removing the beads and coarse particles, the wet cake may be washed with water to remove by-product salts. Alternatively, the slurry from which the beads and the coarse particles have been removed may be diluted with a large amount of water, and the acid treatment and the membrane purification may be performed as they are.

The oxidized carbon black wet cake is preferably dispersed again in water and acid-treated with a mineral acid (for example, hydrochloric acid or sulfuric acid). The acid treatment is generally carried out by adding hydrochloric acid to the aqueous dispersion to adjust the pH to 3 or lower, and heating and stirring at 80 ° C. or higher for 1 to 5 hours. The acid treatment is preferably performed because it is advantageous for ammonium chloride or amine chloride with aqueous ammonia or amine compound in the next step. By the acid treatment, sodium and potassium derived from the oxidizing agent can be removed in the form of salt. Then, the dispersion is filtered and washed with water, and the obtained wet cake is again dispersed in water.

The oxidized carbon black dispersion is then neutralized with a basic compound, preferably an amine compound. Since the surface of the oxidized carbon black has an acidic group, at least a part of the acidic group is bonded to the amine compound to form an ammonium salt. By amine-oxidizing the oxidized carbon black, the dispersion stability of the water-based pigment ink, the nozzle clogging prevention property, and the water resistance when recorded on paper are improved.

Preferred amine compounds include water-soluble volatile amines and alkanolamines. Specifically, ammonia, a volatile amine substituted with an alkyl group having 1 to 3 carbon atoms (for example, methylamine, trimethylamine, diethylamine, propylamine); 1 to 1 carbon atoms
Alkanolamines substituted with 3 alkanol groups (eg, ethanolamine, diethanolamine, triethanolamine); alkylalkanolamines substituted with alkyl groups having 1 to 3 carbon atoms and alkanol groups having 1 to 3 carbon atoms, and the like. . A particularly preferred amine compound is ammonia.

However, it is not necessary that all the acidic groups be amine salts. For example, amine chloride formation with an amine compound having low volatility may reduce the water resistance of the resulting aqueous pigment ink when recorded on paper.

These can be used in combination of two or more kinds. Further, the affinity and dispersion stability for an aqueous medium may be adjusted, or an acidic group on the surface of oxidized carbon black may be partly an alkali metal salt for the purpose of preventing metal corrosion, and in that case, water may be used as the basic compound. Sodium oxide, potassium hydroxide, lithium hydroxide and the like are used in combination with the amine compound.

Thereafter, the dispersion of the amine-chlorinated oxidized carbon black was added to 0.01% such as a reverse osmosis membrane or an ultrafiltration membrane.
Purify and concentrate using a separation membrane with a pore size of less than μm. Concentration is generally carried out so that the pigment dispersion has a concentrated content of oxidized carbon black of about 10 to 30% by weight with respect to water. The obtained pigment dispersion can be used as it is as an aqueous pigment ink, in which case the pigment concentration is 1
Concentration to ~ 20 wt% is preferred. The concentrated pigment dispersion may be further dried into a powdered pigment, or
It may be further concentrated to form a pigment dispersion having a pigment concentration of about 50% by weight. Thereafter, these are dispersed in an aqueous medium and adjusted to an appropriate concentration to obtain the aqueous pigment ink of the present invention.

The oxidized carbon black according to the present invention is generally contained in an amount of 0.1 to 50% by weight, preferably 1 to 20% by weight, based on the total amount of the aqueous pigment ink. Oxidized carbon black content is 1% by weight
If the amount is less than 20%, the printing or writing density becomes insufficient, and the content is 20% by weight.
If it exceeds, the carbon black is likely to coagulate and precipitates during long-term storage, or the ejection stability deteriorates.

The average particle size of the oxidized carbon black in the aqueous pigment ink of the present invention is 300 nm or less, particularly 150.
nm or less, and more preferably 100 nm or less. This is because when the average particle size of the oxidized carbon black exceeds 300 nm, the pigment tends to settle.

The water-based pigment ink of the present invention may contain a water-miscible organic solvent, if necessary. In addition, water, a water-miscible organic solvent, and a mixture thereof are referred to as an aqueous medium in the present specification.

Examples of the water-miscible organic solvent include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol,
C1-C4 alkyl alcohols such as sec-butyl alcohol and isobutyl alcohol; ketones or ketone alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran (THF) and dioxane; ethylene glycol, propylene glycol, diethylene glycol And polyalkylene glycols such as polyethylene glycol and polypropylene glycol; polyhydric alcohols such as ethylene glycol monoethyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether and triethylene glycol monoethyl ether. Lower alkyl ether; polyethylene glycol monomethyl ether Lower alkyl ether acetates such as Seteto; glycerol; and 2-pyrrolidone, 2
Pyrrolidone such as -methylpyrrolidone and N-methyl-2-pyrrolidone; The use amount of these organic solvents is not particularly limited, but is generally 3 to 50% by weight.
Range.

Since the water-based pigment ink of the present invention is sufficiently desalted and purified, it does not corrode writing instruments and ink jet printers. Furthermore, most or part of the carboxyl groups on the surface of carbon black are ammonium salts, so there is no need to adjust the pH. Further, a part of the carboxyl group may be an alkali metal salt derived from an alkali metal (Na, K) salt of hypohalous acid.

Further, the water-based pigment ink of the present invention may contain additives such as a viscosity modifier, a mildew-proofing agent and a rust-preventive agent, which are generally used in this type of ink, in an appropriate amount.

According to the present invention, there is provided an oxidized carbon black having a very high degree of oxidation and excellent water dispersibility as compared with acidic carbon black which is generally commercially available as a colorant. It is considered that in this oxidized carbon black, the amount of polar groups (eg, hydroxyl group and carboxyl group) on the surface is increased, and at the same time, the surface area is increased.

The pigment-dispersed ink of the present invention is excellent in dispersion stability for a long period of time without adding a pigment-dispersing resin, a surfactant or the like, or even without mechanical dispersion treatment. Black does not settle in the ink reservoir.

As described above, the aqueous pigment ink of the present invention contains no pigment dispersant. Therefore, the orifice of the recording head and the ball-point pen tip do not become clogged even when used as an ink for recording by an inkjet method or a writing ink such as a water-based ball-point pen. As a result, the water-based pigment ink of the present invention has excellent recording and writing characteristics and excellent high-speed printability, and letters are not faded even when written in short.

Further, the characters and figures recorded on the surface of the paper with the water-based pigment ink of the present invention are excellent in fastness (light resistance and water resistance), and the carbon black does not flow out even if it is immersed in water again, and the water resistance is high. Yes, it does not discolor even when exposed to sunlight, unlike dye ink, and has excellent light resistance.

Furthermore, since the pigment can be contained in a high concentration, the density of the printed matter is excellent, and an optical density equal to or higher than that of the water-soluble black dye is provided.

[0048]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Example 1 Commercially available acidic carbon black "MA-100" (pH 3.
5) 300 g of [Mitsubishi Chemical Co., Ltd.] was mixed well with 1000 ml of water by stirring well to finely disperse it, and then 450 g of sodium hypochlorite (effective chlorine concentration 12%) was added dropwise thereto,
The mixture was stirred at 100 to 105 ° C for 10 hours. The resulting slurry was filtered through Toyo Filter Paper No. 2 (manufactured by Advantis),
Washing was performed until the pigment particles leaked. This pigment wet cake was redispersed in 3000 ml of water, adjusted to pH 2 with hydrochloric acid, and then desalted with a reverse osmosis membrane to an electric conductivity of 5 mS.

For reference, this aqueous dispersion of oxidized carbon black before ammonium chloride was concentrated to a concentration of 10% by weight and the water dispersibility was evaluated. As a result, it was remarkably improved as compared with the commercially available acidic carbon black. It was confirmed. The results are shown in Table 2 as a reference example.

Then, the pH is adjusted with hydrochloric acid and desalted, and then ammonia water is added to the pigment dispersion to adjust the pH to 10 to 10.5.
Then, the mixture was ammonium chloride, and again desalted with a reverse osmosis membrane to an electric conductivity of 0.5 mS. Then, it was concentrated to a pigment concentration of 10% by weight.

The obtained pigment dispersion is further concentrated, dried,
And finely pulverized to obtain fine powder of oxidized carbon black. The oxygen content (% by weight) of the obtained oxidized carbon black was 8%.

The oxygen content (% by weight) of the oxidized carbon black is determined by the inert gas melting-infrared absorption method (JIS Z2613-1976).
Method) under the conditions shown in Table 1.

[0054]

[Table 1] Analytical conditions Analytical equipment HERAEUS CHN-O RAPIO Fully automatic elemental analysis equipment Sample decomposition furnace temperature 1140 ° C Fractionation tube temperature 1140 ° C Working gas N ₂ / H ₂ = 95% / 5% mixed gas Gas flow rate 70ml / min Detector Non-dispersive spectrometer (Binos)

Example 2 50 g of the pigment dispersion obtained in Example 1 was mixed with 5 parts of ethanol.
And 5 parts of 2-methylpyrrolidone were further added, and water was further added to bring the total amount to 100 g to obtain an aqueous pigment ink. The viscosity of this ink was 2 cps / 25 ° C. or less, and the average particle size of carbon black was 150 nm.

The average particle size of the oxidized carbon black is determined by measuring the aqueous dispersion of the oxidized carbon black with a dynamic light scattering method (laser Doppler scattered light analysis method, trade name:
"Microtrac UPA", manufactured by LEEDS & NORTHRUP) was used. The viscosities of the oxidized carbon black aqueous dispersion and the ink were measured using an E-type viscometer (trade name: "ELD", manufactured by Tokyo Keiki Co., Ltd.).

Next, when this pigment ink was set in an ink jet recording device [trade name HG5130 (manufactured by Epson Corporation)] and printing was performed, the printing was performed without causing nozzle clogging, and the printed matter was dipped in water after drying. Even though the pigment did not flow, the water resistance was good. The nozzle used was for a general aqueous dye ink, but the ink did not solidify, and there was no ejection failure in a printing test several hours later. Even if this ink is stored at 50 ° C. for one month, no sediment is generated, the average particle diameter and the viscosity are not changed, and the ink ejection is stable even if the printing test is performed again. Was. When the optical density of the solid print portion was measured with a Macbeth densitometer TR-927 (manufactured by Kolmogen), 1.38.
It was a value that was sufficiently satisfactory.

Example 3 300 g of commercially available carbon black "# 45" (pH 8.0) [manufactured by Mitsubishi Chemical Co., Ltd.] was thoroughly mixed with 1000 ml of water, and then,
600 g of sodium hypochlorite (effective chlorine concentration: 12%) was added dropwise, and the mixture was stirred at 100 to 105 ° C for 8 hours. Further, 150 g of sodium hypochlorite was added to this reaction liquid, and then dispersed by a bead mill for 3 hours. The resulting slurry was diluted 10 times and desalted with a reverse osmosis membrane to an electric conductivity of 5 mS. Furthermore, the pH of the pigment dispersion was adjusted to 9.5 with triethanolamine.
Adjust to 10 and heat for 1 hour under stirring (80-95
℃), and fully converted into triethanolamine salt (synonymous with triethanolammonium chloride), and the electric conductivity was reduced to 0.
It was desalted with a reverse osmosis membrane to 5 mS. After that, the pigment concentration is 20
Concentrated to wt%.

The obtained pigment dispersion was further concentrated, dried and finely pulverized to obtain fine powder of oxidized carbon black.
Oxygen content (% by weight) of the obtained oxidized carbon black
Was 10%.

Example 4 To 25 g of the pigment dispersion obtained in Example 3 was added ethanol 1
An aqueous pigment ink was obtained by adding 0 parts and further adding water to make the total amount 100 g. The viscosity of this ink was 1.8 cps / 25 ° C. or lower, and the average particle size of carbon black was 60 nm.

Next, when this ink was set in an ink jet recording apparatus and printing was performed in the same manner as in Example 2, the printing was carried out without causing nozzle clogging, and the pigment flowed even when the printed matter was dipped in water after drying. The water resistance was good. The nozzle used was for a general aqueous dye ink. However, the ink did not solidify, and there was no ejection failure in a print test several hours later. Even if this ink is stored at 50 ° C. for one month, no sediment is generated, the average particle diameter and the viscosity are not changed, and the ink ejection is stable even if the printing test is performed again. Was.

Example 5 250 g of acidic carbon black "Color Black FW200" (pH 2.5) (manufactured by Degussa) of the channel method was well mixed with 1000 ml of water, and then 450 g of sodium hypochlorite (effective chlorine concentration 12%) was added. Is added dropwise at 100-105 ° C
For 8 hours. Further, 150 g of sodium hypochlorite was added to this reaction liquid, and then dispersed by a bead mill for 3 hours.
The resulting slurry was diluted 10 times with water to obtain an electric conductivity of 5 mS.
It was desalted with a reverse osmosis membrane. Further, the pH of the pigment dispersion was adjusted to 9.5 to 10 with dimethylethanolamine, and the mixture was heated (80 to 95 ° C.) for 1 hour with stirring to sufficiently convert it into a dimethylethanolamine salt to have a conductivity of 0.5 mS again.
It was desalted with a reverse osmosis membrane. After that, the pigment concentration is 20% by weight
Concentrated.

The resulting pigment dispersion is further concentrated, dried,
And finely pulverized to obtain fine carbon black powder. The oxygen content (% by weight) of the obtained oxidized carbon black was 20%.

Example 6 To 25 g of the pigment dispersion obtained in Example 5 was added ethanol 5
g and 2-methylpyrrolidone 5 g were added, and water was further added to bring the total amount to 100 g to obtain an aqueous pigment ink. The viscosity of this ink was 1.8 cps / 25 ° C. or less, and the average particle size was 90 nm. Next, when this ink was set in an ink jet recording apparatus and printing was performed in the same manner as in Example 2, the printing was performed without causing nozzle clogging, and the printed matter did not flow with the pigment even when immersed in water after drying. And the water resistance was good. The nozzle used was for a general aqueous dye ink. However, the ink did not solidify, and there was no ejection failure in a print test several hours later. Even if this ink is stored at 50 ° C. for one month, no sediment is generated, the average particle diameter and the viscosity are not changed, and the ink ejection is stable even if the printing test is performed again. Was.

Example 7 Using a horizontal type wet disperser filled with zirconia beads having a diameter of 1 mm, carbon black "# 900" (pH 8.0) was used.
A mixture of 300 parts [manufactured by Mitsubishi Chemical Corporation] and 2700 parts of water was dispersed for 3 hours to prepare a carbon black aqueous dispersion.
3000 g of the obtained dispersion was transferred to a 4-necked flask, and sodium hypochlorite (effective chlorine concentration 12%) 150
0 g was added, and an oxidation treatment was performed at 100 to 105 ° C. for 8 hours.
Then, the treated liquid was filtered, the obtained wet cake was redispersed in 3000 ml of water, and desalted with a reverse osmosis membrane to an electric conductivity of 5 mS. Furthermore, the pH of the pigment dispersion is adjusted to 10 to 10 with aqueous ammonia.
The solution was adjusted to 10.5, ammonium chloride was added, and desalting was carried out again with a reverse osmosis membrane to an electric conductivity of 0.5 mS. Then, it was concentrated to a pigment concentration of 10% by weight to form an ink. The viscosity of this oxidized carbon black aqueous dispersion was 4 cps / 25 ° C., and the average particle size was 50 nm.

The resulting pigment dispersion is further concentrated, dried,
And finely pulverized to obtain fine carbon black powder. The oxygen content (% by weight) of the obtained oxidized carbon black was 11.5%.

Comparative Example 1 Acidic carbon black "MA-100" (pH 3.5)
[Made by Mitsubishi Kasei] 5 g of water 85 g and ethanol 5 g and 2
-Methylpyrrolidone 5 g to make the total amount 100 g,
An aqueous pigment ink was obtained by sufficiently stirring. However, this acidic carbon black was not dispersed in water at all, and after standing for a few minutes, a supernatant was formed and printing was impossible. The oxygen content of this acidic carbon black was measured and found to be 1.6%.

Comparative Example 2 Acidic carbon black "Color Black FW200"
(pH 2.5) 85 g of water, 5 g of ethanol and 5 g of 2-methylpyrrolidone were added to 5 g of [Degussa] to bring the total amount to 10
A water-based pigment ink was obtained by adjusting the amount to 0 g and thoroughly stirring. However, this acidic carbon black was not dispersed in water at all, and after standing for a few minutes, a supernatant was formed and printing was impossible. The oxygen content of this acidic carbon black was measured and found to be 15%.

Comparative Example 3 Carbon black "# 45" (p 45)
H8.0) [Made by Mitsubishi Chemical Corporation] 100g "John Cryl J
-62 "(acrylic resin aqueous solution manufactured by Johnson Polymer Co., Ltd.) and 300 g of water were added, and this was dispersed for 5 hours by a bead mill to have an average particle diameter of 120 nm.

25 g of this dispersion were mixed with 5 g of ethanol and 2-
5 g of methylpyrrolidone was added, and the total amount was 100 g with water to obtain an aqueous pigment ink. The dispersion stability was good at a viscosity of 4 cps / 25 ° C. When this ink was set in an ink jet recording apparatus and printing was performed, the ejection stability of the ink gradually deteriorated and the printing density became thin. Further, in a general nozzle for water-based dye ink, the density was further lowered in the printing test several hours after the ink was dried. And
When this was repeated, ejection failure occurred and printing could not be performed at all.

Comparative Example 4 Carbon black "# 900" (manufactured by Mitsubishi Kasei Co., pH
8.0) 10g dispersed in 30ml water, effective chlorine concentration 1
Add 5 g of 2% sodium hypochlorite, and add at room temperature (20
(~ 25 ° C) for 24 hours. Then, the supernatant was removed, and the precipitated carbon black cake was dispersed in methanol and filtered. By repeating this operation, the reaction mother liquor was replaced with methanol, the reaction solution and by-product salts were completely removed, and the powder was dried to obtain oxidized carbon black powder.

The obtained oxidized carbon black (pH 8) 5
Water (85 g), ethanol (5 g) and 2-methylpyrrolidone (5 g) were added to g to make the total amount 100 g, and the mixture was sufficiently stirred to obtain an aqueous pigment ink. When this ink was allowed to stand, a supernatant was formed and printing was impossible.

As shown separately in Table 2 below, the oxidized carbon blacks obtained in Examples 1, 3, 5 and 7 of the present invention and the commercially available carbon black "MA10".
The oxygen content and the water dispersibility of "0", "# 45", "# 900" (above, manufactured by Mitsubishi Kasei) and "Color Black FW200" (manufactured by Degussa) were compared.

Further, when water affinity and water stability as water dispersibility were compared, the carbon black obtained in the present invention was rapidly finely dispersed and was stable even after standing for 60 days. The commercially available carbon black was such that it floated on the water surface even at the initial stage of dispersion, and the dispersed state became unstable and settled over time.

Thus, it can be understood that the water dispersibility of carbon black in the recording liquid of the present invention is surprisingly excellent.

[0076]

[Table 2] Water dispersible carbon black pH acidic pH alkaline Type of oxygen content Water affinity affinity stability over time Water affinity affinity stability over time (wt%) Example 1 ◎ 40 days or more ◎ 60 days or more About 8 Example 3 ◎ 40 days or more ◎ 60 days or more about 10 Example 5 ◎ 60 days or more ◎ 90 days or more about 20 Example 7 ◎ 50 days or more ◎ 90 days or more 11 reference examples ◎ 30 days ◎ 60 days or more-MA100 × 1 minute or less x 1 minute or less About 1.5 (Comparative Example 1) FW200 △ 5 minutes or less △ 8 minutes or less About 15 (Comparative Example 2) # 45 x 1 minute or less × 1 minute or less About 0.5 (Comparative Example 3) ) # 900 x 1 minute or less x 1 minute or less About 0.5 (Comparative Example 4) [Evaluation Criteria] ⊚: Rapidly finely dispersed and excellent in water affinity Δ: Small water affinity and poor dispersion ×: No water Not dispersed in

[0077]

INDUSTRIAL APPLICABILITY The pigment-dispersed ink of the present invention can be printed without causing nozzle clogging when used for ink jet recording, and can be written smoothly even with a thin pen tip.
It has a sufficient concentration. Further, in the state where the pigment dispersant is not contained, the carbon black in the ink does not aggregate during storage, the dispersion stability is excellent, and the water resistance when recorded on paper is excellent.

Claims (9)

[Claims] 1. An aqueous pigment ink containing water and a stably dispersed oxidized carbon black, wherein the oxidized carbon black is oxidized with hypohalous acid and / or a salt thereof, and An aqueous pigment ink in which at least a part of the acidic groups present on the surface of the oxidized carbon black is combined with an amine compound to form an ammonium salt. 2. The water-based pigment ink according to claim 1, wherein the amine compound is a water-soluble volatile amine. 3. The aqueous pigment ink according to claim 1, wherein the oxidized carbon black is obtained by oxidizing carbon black finely dispersed in water. 4. The water-based pigment ink according to claim 1, wherein the oxidized carbon black has an average particle diameter of 300 nm or less. 5. The aqueous pigment ink according to claim 1, wherein the content of the oxidized carbon black is 0.1 to 50% by weight based on the total amount of the aqueous pigment ink. 6. The water-based pigment ink according to claim 1, which contains no pigment dispersant. 7. An ink composition for ink jet recording comprising the water-based pigment ink according to claim 1. 8. A method for producing an aqueous pigment ink containing water and a stable dispersed oxidized carbon black, wherein carbon black finely dispersed in water is oxidized with hypohalous acid and / or a salt thereof. And a step of neutralizing at least a part of the acidic groups existing on the surface of the resulting oxidized carbon black with an amine compound. 9. The method according to claim 8, wherein the amine compound is a water-soluble volatile amine.