JP2000017185A - Aqueous carbon black dispersion and aqueous ink using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject dispersion exhibiting excellent dispersion stability, even when left at a high temperature for a long period, capable of inhibiting the clogging of nozzles and pen tips, and useful as an aqueous ink for ink jet printers, writing tools, etc., by limiting the content of sulfate ions to a specific value or smaller. SOLUTION: This aqueous carbon black dispersion is prepared by dispersing (B) carbon black in (A) an aqueous medium. Therein, the content of sulfate ions in the dispersion is controlled to <=25 ppm, and, if necessary, the contents of halogen ions and nitrate ions are further controlled to <=20 ppm and <=30 ppm, respectively. The aqueous dispersion is preferably controlled to pH 5-10 and a component B content of 0.5-50 wt.%. The component B is preferably subjected to an ozone oxidation treatment in the presence of water, and has total acidic groups of >=3 μequ/m2, an active hydrogen content of <=2 mmol/g, a particle diameter of 10-30 nm and a DBP oil absorption volume of 50-180 cc/100 g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to carbon black, which is preferably used as a pigment for inks for ink jet and writing inks, an aqueous dispersion containing carbon black in an aqueous medium, and an aqueous ink.

[0002]

2. Description of the Related Art Ink-jet recording has characteristics such as low noise during recording, color printing, high-speed printing, printing on plain paper and high quality. It is widely used for computer printing, regardless of the type. There are various types of this ink jet printing, a method of discharging ink in thin nozzles in the print head by electrostatic energy, and a method of flowing a current to a tropical zone in the print head and generating bubbles by generating heat. A method of performing printing by ejecting ink from a nozzle.

[0003] As an ink used for such an ink jet recording, an aqueous ink in which a dye is dissolved or dispersed in water has conventionally been used. Such water-based inks are also used for writing instruments such as fountain pens and ballpoint pens. The performance required for the recording ink used in these applications includes the following items. (1) No bleeding of printed or written matter. (2) No fading of printed or written matter due to light or heat. (3) No clogging of nozzles and pens in the recording head even when left for a long time. (4) Good storage stability (5) Low viscosity of ink

[0004] As described above, conventionally, inks in which the dye is dissolved or dispersed in water have been used as a coloring agent. However, when the dye is used, bleeding tends to appear on printed or written matter. Due to the problem of fading due to light, inks using carbon black as a black pigment have recently attracted attention.

[0005]

However, when this carbon black is used as a pigment for ink, the dispersibility of the carbon black in water is poor because the surface of the carbon black is lipophilic, so that the carbon black cannot be used in a nozzle or a pen tip. The carbon black becomes clogged with eyes and aggregates during storage, making it unusable. For this reason, it is necessary to add various dispersants. Here, as the dispersant, a dispersant containing both a lipophilic group that is familiar with carbon black and a hydrophilic group that is familiar with water in the molecule, specifically, mainly a resin dispersant, It is used to improve dispersibility or dispersion stability.

However, since such a resin dispersant is expected to have its effect by binding to the surface of carbon black, the dispersing effect cannot be obtained unless it is added in an amount larger than the amount capable of binding to the surface of carbon black. For this reason, an extra dispersant remains in the liquid, and when the ink at the nozzle or the pen tip dries, it becomes a solid with poor resolubility and causes clogging. In addition, the addition of the dispersant increases the viscosity of the ink, which causes a problem that stable ink ejection properties cannot be obtained.

In order to solve such problems, the present inventors have proposed to use carbon black oxidized with ozone in a liquid (Japanese Patent Application No. 9-35891).
9). However, when such a treatment is performed, the dispersion stability is maintained when the ink is left at room temperature, but when the ink is left at 60 ° C., which is a temperature at which the ink may receive, It turned out that there was a drawback that it was agglomerated in one day. For this reason, the performance of the oxidized carbon black has not yet been sufficient particularly for use in aqueous ink jet inks in which the ink receives heat. The present invention solves the above-mentioned problems in the prior art, and provides a pigment and an ink for water-based ink having excellent dispersion stability, suppressing occurrence of clogging at a nozzle or a pen tip, and having excellent ejection stability. With the goal.

[0008]

Means for Solving the Problems After obtaining an aqueous carbon black dispersion, the present inventor added alkali to a dispersion obtained by removing sulfate ions, halogen ions and nitrate ions by treatment with an ion exchange resin. The inventors have found that an aqueous dispersion of carbon black having remarkably excellent dispersion stability can be provided by making the pH neutral, and the present invention has been achieved. It has been surprisingly found that such a simple operation makes it possible to obtain carbon black having extremely good water dispersibility.

That is, the present invention provides an aqueous carbon black dispersion having a sulfate ion content of 25 ppm or less, an aqueous carbon black dispersion having a halogen ion content of 20 ppm or less,
An aqueous carbon black dispersion having a nitrate ion content of 30 ppm or less, an aqueous carbon black dispersion having a total amount of sulfate ion, halogen ion and nitrate ion of 50 ppm or less, and the like.

[0010]

DETAILED DESCRIPTION OF THE INVENTION First, the carbon black used in the present invention is not particularly limited, and any carbon black including carbon black conventionally used as a pigment for inks can be used. The carbon black that can be used in the present invention is not particularly limited, but as a particularly preferred carbon black, various surface treatments, particularly in an aqueous medium even without the presence of a dispersant by imparting an acidic functional group to the surface by oxidation treatment. Oxidized carbon black, which can be dispersed, is preferred. This is probably because the interaction between acidic functional groups such as carboxyl groups present on the surface of these oxidized carbon blacks, and sulfate ions, halogen ions, and nitrate ions is somewhat related to the effects of the present invention. It is presumed that a very remarkable effect can be obtained when the present invention is carried out using the oxidized carbon black.

The particle size of the carbon black to be subjected to the oxidation treatment is not limited, but is not more than 100 nm, and more preferably 30 nm.
The following are optimal since the sedimentation of the particles is particularly suppressed. In addition, since sulfur and sulfur compounds in carbon black are oxidized by an oxidizing agent to form sulfate ions in a solution, as much as possible,
It is desired that the amount is small, but it is preferably 0.5% by weight, preferably 0.1% by weight or less in total sulfur analysis value. In order to reduce the sulfur content, it is possible to use an aromatic hydrocarbon used as a raw material for carbon black, a liquid hydrocarbon used as a fuel, or a low hydrocarbon content gaseous hydrocarbon as a gaseous hydrocarbon. Although halogen ions are mainly chlorine ions, they are derived from cooling water that stops the reaction during carbon black production.To reduce this, pure water is used as cooling water, and halogen ions are contained in carbon black. Halogen ions can be reduced. It is considered that nitrate ions are mainly derived from NOx generated in combustion gas used in producing carbon black. Extreme reduction of NOx in the combustion gas is difficult with current technology.

The amount of sulfur in carbon black can be determined, for example, by precisely weighing 0.1 g of carbon black and using SUSU manufactured by Vestuf.
LMHOGRAPH12A ". The amount of halogen ions in the carbon black can be measured by TOX-150 manufactured by Mitsubishi Chemical. The following is particularly preferred as a method for oxidizing carbon black. That is, after suspending carbon black in water, oxidation is performed by reacting with an oxidizing agent. The amount of water is
95: 5 to 0.5 in the ratio (weight) of carbon black and water.
5: 99.5 is suitable, more preferably 50:50.
To 2:98, more preferably 20:80 to 5:95.

The oxidizing agent is not particularly limited as long as it increases the acidic functional group in the carbon black. In general, it is preferable that the oxidizing agent does not remain in water after the oxidizing agent is oxidized. It is preferably used. Specifically, carbon black can be oxidized through ozone and / or an ozone-containing gas. Here, the oxidant, ozone, can be generated by an ozone generator. This ozone generator generally generates ozone by discharging in air or oxygen, but it can also be generated by electrolyzing water. As the generator for generating ozone used in the present invention, any generator can be used irrespective of the system. However, a higher ozone generation concentration is preferable because the reaction efficiency of oxidation of carbon black is higher. Generally, generators for generating an ozone-containing gas having an ozone concentration of 1 to 20% by weight are commercially available, and these are sufficient.

As described above, the carbon black is oxidized by ozone in the presence of water, and the total amount of acidic groups on the surface of the carbon black becomes a specific amount or the active hydrogen content becomes a specific amount as described later. By oxidizing to the extent possible, carbon black having particularly good dispersibility in an aqueous medium can be obtained. The mechanism by which such a simple operation provides oxidized carbon black with excellent properties is not clear, but if water is present on the surface of the carbon black, the ozone does not directly react with the surface of the carbon black. It is also conceivable that, by dissolving in water and reacting with water molecules, the resulting functional groups also have good compatibility with water and exhibit dispersion stability. For these reasons, compared to carbon black that has been oxidized by ozone oxidation in the gaseous phase to the extent that it has the same total acid groups, it is still an oxidized carbon black that has greatly improved dispersibility in water. It is presumed to exhibit an unexpected effect of becoming.

The carbon black to be subjected to the above-mentioned oxidation treatment with ozone in the presence of water does not need to be oxidized in advance, but prior to oxidation in the presence of water, prior to the oxidation in the presence of water, nitric acid or a gaseous phase known in the art is used. The carbon black treated with ozone may be oxidized by the above method. By the above-described oxidation treatment with ozone in the presence of water, all the acidic groups of carbon black are reduced to 3 μequ / m ^2.
It is desirable to perform the oxidation treatment until the above is reached. The amount of all acidic groups can be determined as the amount reacted with a strong alkali such as NaOH or KOH.

The method for determining all the acidic groups is as follows. The oxidized carbon black is filtered through a 0.1 micron membrane filter to separate it from water. The separated carbon black is dried all day and night with a dryer at 60 ° C., and then pulverized in an agate mortar. Take 0.2-0.5 g of this dried carbon black,
The flask is placed in an Erlenmeyer flask containing 60 cc of 0.01 N NaOH, and nitrogen is flowed into the Erlenmeyer flask. The mixture is stirred for 6 hours to react. The reaction product is filtered again using a 0.1 micron membrane filter to obtain a filtrate. Take 40 cc of this filtrate and titrate with 0.025 N hydrochloric acid using an automatic neutralization titrator to determine the NaOH concentration of the filtrate. The total acidic group of carbon black can be determined by the following calculation.

[0017]

(Equation 1) If the total acidic group is less than 3 μequ / m ² , dispersion in an aqueous medium may be difficult. More preferably, 6 μequ /
If it is at least m ² , the dispersibility in an aqueous medium will be very good.

The carbon black has an active hydrogen content of 2.0 mmol / g or less, particularly preferably 1.5 mmol / g or less.
It is preferable to use those having a concentration of mmol / g or less. Carbon black whose active hydrogen content is suppressed to a specific amount or less,
Surprisingly, it is particularly excellent in dispersibility in aqueous media,
The present inventors have found that a carbon black aqueous dispersion having good dispersion stability can be provided. Conventionally, for example, as disclosed in
As in the method described in US Pat. No. 3498, it has been thought that the oxidation treatment increases the acidic functional groups on the surface of the carbon black, which leads to hydrophilicity and simply contributes to stability in an aqueous medium. On the other hand, the present inventors surprisingly found that the functional group imparted by the oxidation treatment is detected as a total acidic group, but is not necessarily linked to an increase in the functional group detected as the active hydrogen content. Further, carbon black having a high active hydrogen content is not always said to be excellent in dispersion in an aqueous medium, and increasing the active hydrogen content does not lead to improvement in dispersibility, but rather lowers. I found it. Then, it was found that when an aqueous dispersion was prepared using carbon black having an active hydrogen content of 2.0 mmol / g or less, the dispersibility of carbon black in an aqueous medium was particularly excellent.

The active hydrogen content is determined by the following method. The active hydrogen on the carbon black is exchanged for a methyl group by dropping a diethyl ether solution of diazomethane on the carbon black. Hydrogen iodide having a specific gravity of 1 is added to the carbon black thus treated, and heated to vaporize the methyl group as methyl iodide. This gas of methyl iodide is trapped by a silver nitrate solution and precipitated as methyl silver iodide. From the weight of the silver iodide, the amount of the original methyl group, that is, the amount of active hydrogen is measured.

When the carbon black has been subjected to a treatment such as an oxidation treatment and contains a large amount of residual ions, for example, by treatment with sodium hypochlorite, desalting is performed.
An accurate active hydrogen content is obtained by performing a neutralization treatment. As a simple method of performing this desalting, a method of passing a carbon black dispersion through a column containing a cation exchange resin and an anion exchange resin can be used. By such a treatment, the cations associated with the functional groups can be removed, and the pH of the dispersion is acidic, so that the amount of active hydrogen contained in the carbon black can be accurately indicated. In such a pretreatment, the amount of cations in the carbon black is 1000 p.
pm or more. More specifically, a carbon black dispersion (if the carbon black is in a dry state, a dispersion obtained by once dispersing it in water)
After removing the cations through a column packed with a mixture of an anion exchange resin and a cation exchange resin, 0.1 g of the mixture was added.
The mixture is filtered through a 1 μm membrane filter to take out carbon black. 100 ° C
After drying all day and night in a dryer, pulverize in a mortar,
Get a sample. Take 1.0 g of this sample, place it in a flask containing an excess amount of hydrogen iodide solution, heat and boil to generate methyl iodide, transport the generated methyl iodide with nitrogen gas, and use a silver nitrate solution Collect and sediment. After the collected liquid is made acidic with nitric acid, the precipitate is collected by filtration through a membrane filter. After drying the precipitate at 50 ° C., the weight is measured to determine the amount of active hydrogen.

The carbon black is oxidized by ozone in the presence of water, and is oxidized until the active hydrogen content on the surface of the carbon black becomes a specific amount or less, as described later, thereby dispersing the carbon black in an aqueous medium. Excellent carbon black can be obtained. It has been found that when such an oxidation method is employed, the number of functional groups detected as active hydrogen content decreases and the number of acidic functional groups detected as total acidic groups increases, surprisingly. Although the mechanism by which the acidic functional groups contributing to the dispersibility in water are imparted in a well-balanced manner by such a simple oxidation treatment operation to obtain carbon black with excellent properties is not clear, it is presumed as follows.
Carbon black is composed of particles formed by carbonizing raw hydrocarbons while undergoing thermal decomposition and dehydrogenation.
Hydrogen that has not been dehydrogenated remains in the particles as active hydrogen. When this carbon black is oxidized with ozone in the presence of water, radicals are generated by the reaction of ozone and water, and a functional group that is compatible with water is generated by replacing active hydrogen, which is originally unfamiliar with water. It is considered that carbon black having good dispersibility in water can be obtained. The active hydrogen content is within the above range,
In addition, carbon black having all acidic groups within the above range is most excellent in dispersibility in water.

However, although the dispersion described above shows good dispersibility at room temperature, it has been found that carbon black agglomerates within 24 hours if left in an atmosphere at 60 ° C. In order to prevent this, it has been found that sulfate ions, halogen ions or nitrate ions may be removed by, for example, passing the aqueous dispersion through a column filled with an anion exchange resin. The content of sulfate ions is 25 ppm or less, preferably 10 ppm or less, particularly preferably 5 ppm or less. The content of halogen ions is 20 ppm or less, preferably 10 ppm or less, particularly preferably 5 ppm or less. The nitrate ion content is 30 ppm or less, preferably 10 ppm or less, particularly preferably 5 ppm or less. The total amount of sulfate ion, halogen ion and nitrate ion is 50 ppm or less, preferably 30 ppm or less, particularly preferably 10 ppm or less.

When a pigment, especially an ultrafine powder such as carbon black, is used as a coloring agent for an aqueous ink, it is necessary to solve the problem of dispersibility first, unlike the case of using a dye. Carbon black is a fine powder having a lipophilic surface, and its affinity with water is very poor. And
Rather than simply performing an oxidizing treatment, hydrophilic treatment is performed, for example, by performing an oxidizing treatment by a specific method until the number of functional groups detected by a specific method is equal to or more than a specific amount, and the dispersion to the aqueous medium is good. The present inventor has previously found that carbon black in a good state can be obtained (Japanese Patent Application No. 8-347529). However, it has been found by the present inventors that even once a good dispersion state is achieved, aggregation occurs over time. This reaggregation mechanism has not yet been elucidated.

It is known that in dye-based aqueous inks for inkjet, ions such as chlorine ions and sulfate groups cause nozzle clogging problems (Japanese Patent Publication No. Sho 60/1985).
-34993). These ions are used in the dye-based aqueous ink composition in order to satisfy various conditions such as ink ejection conditions, long-term storage stability, image clarity and density during recording, and some other additives. It is also considered to be an impurity element derived from the dye used and water. Although the mechanism by which these elements adversely affect nozzle clogging in dye-based aqueous inks has not been completely elucidated, according to the above-mentioned publication, it adversely affects the dissolution stability of the dye, and as a result, It is said that clogging occurs.

When a pigment is used as a coloring agent, there is no problem of dissolution stability like a dye. Therefore, such a problem is not expected to occur, but, on the other hand,
There was a problem of ensuring dispersion stability. According to the study of the present inventor, the dispersion stability, particularly in the mechanism of re-aggregation over time after once dispersed, because the sulfate ion, the halogen ion, and the nitrate ion affect, each with a certain upper limit or less. Thus, it was found that those having a superior re-coagulation effect were superior to those exceeding the upper limit. That is, the sulfate ion is 25p
The aqueous dispersion of carbon black at pm or less, the aqueous dispersion of carbon black at 20 ppm or less of halogen ions, and the aqueous dispersion of carbon black at 30 ppm or less of nitrate ions are each excellent in the effect of preventing re-aggregation. Furthermore, it is desirable that these anions be suppressed even in the total amount, and the aqueous carbon black dispersion in which the total amount is 50 ppm or less is particularly excellent in the effect of preventing re-aggregation.

The concentration of these ions in the liquid can be easily measured by an ion chromatogram, and the following conditions can be used. Ion chromatogram device DX-AQ column made by DIONEX AG12A, AS12A Eluent 2.7 mM Na2CO3-0.3 mM NaHCO3 Sample solution volume 200 μl When performing ion exchange, pack both cation exchange resin and anion exchange resin Thereby, even cations can be further removed, which is effective for dispersion stability. When such an ion removal treatment is performed, the pH of the dispersion becomes low, and the pH in the liquid usually becomes 1 to 3. Such an aqueous dispersion has good dispersion stability when left at room temperature, but immediately agglomerates when left at 60 ° C., so that an alkali such as NaOH or amines is added to the aqueous dispersion to adjust the pH from 5 to 5. It is desirable to adjust to 10. Even if the pH becomes 10 or more, 60 ° C
Is inferior in dispersion stability.

The inventor of the present invention has made it possible to improve the dispersibility of carbon black in an aqueous medium over a long period of time by suppressing the amount of sulfate ions, halogen ions and nitrate ions in an aqueous medium to a very low level of a specific amount or less. It has been found that it can be maintained, and such knowledge is considered to be extremely valuable in producing a high-performance inkjet ink. Although it has been known for a long time to remove ions remaining by oxidation treatment with hypochlorous acid and the like by the above-described film treatment, a low level content remaining in such a film treatment is also known. Even for sulfate ions, halogen ions, and nitrate ions, the dispersibility of carbon black in an aqueous medium, particularly carbon black imparted with a dispersibility by modifying the surface of the carbon black itself by oxidation treatment or the like, It was found by the inventor to have an effect. For this reason,
It is a simple and effective operation to perform treatment with an ion exchange resin in order to remove sulfate ions, halogen ions and nitrate ions to the level specified in the present invention.

Alternatively, it is conceivable to prepare an aqueous dispersion using carbon black having a very low sulfur content in advance, but in any case, the amount of sulfate ions in the aqueous dispersion falls within the range specified in the present invention. do it. The mechanism by which the presence of each ion affects the dispersibility of carbon black in an aqueous medium has not been elucidated yet. By mixing a polar solvent with the aqueous dispersion thus prepared, an aqueous ink having excellent performance can be obtained. Here, the aqueous carbon black dispersion refers to a dispersion of carbon black in water or a mixture of water and a water-soluble solvent. Specific examples of the polar solvent include lower alcohols such as ethanol and isopropanol, glycol solvents such as glycerin, diethylene glycol and polyethylene glycol, N-containing solvents such as N-methylpyrrolidone and 2-pyrrolidone, and urea. is there.

The concentration of the oxidized carbon black in the aqueous dispersion may be appropriately selected according to the application, but is preferably 0.5 to 50% by weight, particularly preferably 0.5 to 20% by weight. Preferably, it is a black aqueous dispersion. In this range, the printing density of the ink is good, and the viscosity of the ink is suppressed, so that an ink having excellent characteristics can be obtained. The aqueous carbon black dispersion thus obtained can be used as an aqueous ink by adding various additives such as adding a dispersant as needed when the concentration of carbon black exceeds 20 wt%, for example. If necessary, concentrate and dry,
Thereafter, it can be separately diluted and used as an ink. In this case, carbon black may be added to water, and a dispersion treatment using a bead mill, a ball mill, an impact disperser or the like may be used.

Examples of additives for forming an ink include a penetrant, a fixing agent, a fungicide and the like. Examples of the penetrant include nonionic surfactants such as polyoxyethylene alkylaryl ether, anionic surfactants such as alkylbenzene sulfonate, and fluorine surfactants.
Diethylene glycol monobutyl ether and the like can be used. As the fixing agent, in addition to water-soluble resins (nonionic water-soluble resins such as polyvinyl alcohol and polyacrylamide, anionic water-soluble resins such as polyacrylic acid and styrene / acrylic water-soluble resins), aqueous emulsions can also be used. . In general, when used as an inkjet ink, a carbon black concentration of 1 to 20% by weight, preferably 5 to 10% by weight is used. When used as an inkjet ink, it is desirable to adjust the pH to 7 to 10 before use.

The ink of the present invention obtained in this manner is required to be used as an ink for ink-jet printing, and has stability of droplet formation, ejection stability for a long time, ejection stability after a long pause, ejection stability, and storage stability. Both the fixing property to the recording material, the weather resistance of the recorded image, and the like are balanced.

[0032]

EXAMPLES The present invention will be described more specifically with reference to the following examples. In addition,% represents weight% unless otherwise specified. Example 1 Commercially available carbon black (Mitsubishi Chemical Corporation "# 47" particle size 23 nm, sulfur content 0.5%, chlorine content 220 ppm)
Was placed in 50 g of water and 500 cc of water, and dispersed with a household mixer for 5 minutes. The obtained liquid was put into a 3 liter glass container equipped with a stirrer. While stirring with an agitator, an ozone-containing gas having an ozone concentration of 10% by weight was supplied at 500 cc / min.
Time introduced.

At this time, an ozone generator of an electric discharge generating type manufactured by PCI was used as an ozone generator, and ozone was generated using oxygen as a raw material. The dispersion after the ozone treatment was taken out and the pH was measured. (The pH was measured according to JIS K 6221.) The particle size distribution in this dispersion was measured with a Nikkiso Co., Ltd. Microtrac UPA.
of this solution, and using an optical microscope,
When the magnification was doubled, it was found that the whole was in micro-Brownian motion in a good dispersion state and the dispersibility was good.

Next, this dispersion was filtered through a micropore filter having a diameter of 0.1 micron to filter the carbon black. The wet carbon black was dried at 60 ° C., and the total acid groups were measured. g. The nitrogen adsorption specific surface area was 120 m ² / g. Therefore, the total acidic groups per unit area is 4.00 μm.
equ / g. The active hydrogen content of the carbon black was measured and found to be 1.22 mmol / g. At this time, the filtrate obtained at the same time was directly subjected to ion chromatography to determine the amounts of sulfate ions, halogen ions, and nitrate ions in the solution. The sulfate ion concentration was 300 ppm, the chloride ion concentration was 30 ppm, and the nitrate ion concentration was 113 ppm. there were.

The dispersion 100c obtained by the above oxidation treatment
c into a beaker and 20 CC of an anion exchange resin (“SAN UP” manufactured by Mitsubishi Chemical Corporation) into the beaker.
After heating to 50 ° C., the mixture was stirred with a stirrer for 3 hours. Then, it was cooled to room temperature,
Centrifugation was performed for 30 minutes to remove the ion exchange resin and other foreign substances. 0.1 N NaOH was added to the supernatant.
The solution was added little by little to adjust the pH to 8. The dispersion diameter at this time was 75 nm, and the dispersion was observed with an optical microscope. As a result, it was found that the dispersibility was good. The sulfate ion concentration obtained from the liquid obtained by separating carbon black from the supernatant was 7 ppm, and the halogen ion was 3 pp.
m and nitrate ion were 10 ppm.

70 cc of the pH-adjusted dispersion was placed in a 100 cc bottle with a lid, and left in a dryer maintained at 60 ° C. Three months later, the bottle was taken out, and after cooling, the dispersion diameter was measured.
Also, good dispersion was confirmed by an optical microscope. On the other hand, this dispersion is packed into a cartridge manufactured by NEC Corporation
When printing was performed using a printer “PR101” manufactured by K.K., good printed matter without blurring or blurring was obtained.

Example 2 The same treatment was performed as in Example 1 except that the ozone reaction time was changed to 10 hours. The pH of the resulting dispersion is 2.2.
The average 50% dispersion diameter was 73 nm, and the total acidic groups per unit specific surface area was 7.5 μequ / m ² . The sulfate ion concentration in this dispersion was 430 ppm.
This dispersion was subjected to the same pretreatment as in Example 1 and left at 60 ° C. for 3 months. This dispersion liquid also had a small dispersion diameter of 78 nm similarly to Example 1, and when printing was performed by filling the ink into a cartridge manufactured by NEC Corporation, a good printed matter without bleeding or blurring was obtained. Was. The sulfate ion concentration in the dispersion after the ion exchange treatment was 7 pp.
m, halogen ion is 1 ppm, nitrate ion is 0 ppm
Met.

Example 3 The same treatment was carried out except that the carbon black in Example 2 was changed to "# 960" (manufactured by Mitsubishi Chemical Corporation, sulfur content 0.3%, particle diameter 16 nm, chloride ion content 300 ppm). Was done. The pH of the resulting dispersion was 2.2. The total acidic groups of the carbon black remaining in the filtrate are 950 μequ / g,
The specific surface area is 240 m ² / g, and the total acidic groups per unit specific surface area is 3.96 μequ / m ² . Average 50
The% dispersion diameter was 44 nm. The concentration of sulfate ions in this dispersion was 157 ppm, and the concentration of chloride ions was 50 pp.
m and nitrate ion concentration were 180 ppm.

This dispersion was subjected to the same pretreatment as in Example 1 and left at 60 ° C. for 3 months. This dispersion was also prepared in Example 1.
The dispersion diameter was as small as 47 nm as in the case of NE.
When printing was performed by filling the ink in a cartridge made of C, a good printed matter without bleeding or blurring was obtained.
Further, the concentration of sulfate ions in the dispersion after the ion exchange treatment was 1 ppm, the concentration of chloride ions was 0 ppm, and the concentration of nitrate ions was 1 ppm.

Example 4 The solution subjected to the ion exchange treatment obtained in Example 2 was treated with NaOH
After adjusting the pH to 8 with sodium acetate, 1
After adding 00 ppm, the mixture was left at 60 ° C. for 3 months. This dispersion also had a small dispersion diameter of 79 nm as in Example 1, and when printing was performed by filling the ink into a cartridge manufactured by NEC Corporation, a good printed matter without bleeding or blurring was obtained. Was.

Comparative Examples 1 to 3 Each of the dispersions obtained in Examples 1, 2 and 3 before being subjected to the ion exchange treatment was placed in a glass bottle with a lid, and left in a dryer at 60 ° C. for 24 hours. Was taken out and the state of dispersion was confirmed under a microscope. As a result, the ink was agglomerated and was useless as an aqueous ink.

Comparative Example 4 Sodium sulfate was added to the ion-exchanged dispersion obtained in Example 1 so that the concentration of sulfate ions in the solution became 40 ppm, and this dispersion was added to a glass bottle with a lid. Was placed in a dryer at 60 ° C. overnight. The dispersion was taken out, and the state of dispersion was confirmed with a microscope. As a result, the dispersion was agglomerated and was useless as an aqueous ink.

Comparative Example 5 After the sodium chloride was added to the ion-exchanged dispersion obtained in Example 1 so that the concentration of sulfate ions in the solution became 30 ppm, the dispersion was added to a glass bottle with a lid. Was placed in a dryer at 60 ° C. overnight. The dispersion was taken out, and the state of dispersion was confirmed with a microscope. As a result, the dispersion was agglomerated and was useless as an aqueous ink.

Comparative Example 6 To the ion-exchanged dispersion obtained in Example 1 was added sodium nitrate such that the concentration of sulfate ions in the solution was 50 ppm, and the dispersion was added to a glass bottle with a lid. Was placed in a dryer at 60 ° C. overnight. The dispersion was taken out, and the state of dispersion was confirmed with a microscope. As a result, the dispersion was agglomerated and was useless as an aqueous ink.

As is clear from the above Examples and Comparative Examples, the present invention is subjected to an oxidation treatment in a state where water and carbon black coexist, and the sulfate ion concentration in the solution is reduced to 20%.
By selecting and oxidizing carbon black with a low sulfur content so as to be less than ppm, it is possible to remarkably suppress the cohesiveness at high temperature due to sulfate ions, and even in a general environment for a long time. It is understood that a dispersion liquid which can be used for an aqueous ink having good printing characteristics while maintaining the dispersion state can be obtained.

[0046]

According to the present invention, there is no clogging or sediment generation in the orifice of the nozzle or at the tip thereof especially when used for ink jet or writing ink, and even after being left at a high temperature for a long time, An aqueous dispersion and an aqueous ink that provide stable ejection stability of the ink can be obtained.

Claims (14)

[Claims] 1. An aqueous carbon black dispersion having a sulfate ion content of 25 ppm or less. 2. A carbon black aqueous dispersion having a halogen ion content of 20 ppm or less. 3. An aqueous carbon black dispersion having a nitrate ion content of 30 ppm or less. 4. An aqueous carbon black dispersion having a total ion content of 50 ppm or less of a sulfate ion, a halogen ion and a nitrate ion. 5. The method according to claim 1, wherein all the acidic groups of the carbon black are 3 μequ.
/ M ² or more. 6. The carbon black having an active hydrogen content of 2.
The aqueous carbon black dispersion according to claim 1, wherein the amount is 0 mmol / g or less. 7. The aqueous carbon black dispersion according to claim 1, wherein the carbon black has been oxidized in the presence of water. 8. The aqueous carbon black dispersion according to claim 7, wherein the oxidation treatment is performed using ozone. 9. The aqueous carbon black dispersion according to claim 7, wherein the oxidation treatment is carried out using ozone in the presence of water. 10. The aqueous carbon black dispersion according to claim 1, which has a pH of 5 to 10. 11. The content of carbon black is 0.5 to 5
The aqueous carbon black dispersion according to any one of claims 1 to 10, wherein the amount is 0% by weight. 12. A carbon black having a particle size of 10 to 30.
nm and DBP oil absorption of 50-180cc / 100g
The aqueous dispersion according to any one of claims 1 to 11, wherein 13. An aqueous ink using the aqueous carbon black dispersion according to claim 1. 14. An ink jet ink according to claim 1.
14. The aqueous ink according to any one of items 13 to 13.