JP3521669B2 - Oxidized carbon black, carbon black dispersion and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxidation-treated carbon black useful as a black pigment used in ink jet inks and writing inks, a dispersion containing such oxidation-treated carbon black, and a method for producing the same.

[0002]

2. Description of the Related Art Inkjet recording is characterized by low noise during recording, color printing, high-speed printing, printing on plain paper, and high quality. Widely used for computer printing regardless. There are various methods of this ink jet printing. A method of ejecting the ink in a thin nozzle in the recording head by electrostatic energy, and an electric current flowing in the tropical zone inside the recording head, and the heat generated generate bubbles. There is a method of performing printing by discharging the ink from the nozzle. As an ink used for such ink jet recording, a water-based ink in which a dye is dissolved or dispersed in water has been conventionally used. Such water-based inks are also used in writing instruments such as fountain pens and ballpoint pens.

The properties required for recording inks used for these purposes include the following items. (1) No bleeding on the printed matter or written matter (2) The printed matter or written matter does not fade due to light or heat (3) Nozzle or pen tip inside the recording head is clogged even when left for a long time (4) Good storage stability (5) Low ink viscosity As described above, inks for these applications have conventionally used inks in which a dye is dissolved or dispersed in water as a colorant. However, when a dye is used, there is a problem that a printed matter or a written matter is easily bleeding and is discolored by light. Therefore, an ink using carbon black as a black pigment has recently been attracting attention.

[0004]

However, when this carbon black is used as an ink pigment, the dispersibility of the carbon black in water is poor because the surface of the carbon black is lipophilic, and the nozzle or pen tip As a result, carbon black becomes clogged or aggregates are formed during storage, making it unusable. For this reason, it is necessary to add various dispersants. Here, as the dispersant, a lipophilic group that is familiar with carbon black, and a dispersant containing both groups of a hydrophilic group that is familiar with water in the molecule, specifically 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 more than that which binds to the surface of carbon black. For this reason, an excessive dispersant remains in the liquid, and when the ink at the nozzle or the pen tip is dried, it becomes a solid substance having 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 a problem, Japanese Unexamined Patent Publication No. Hei 8
No. 3498 discloses an attempt to improve dispersion stability without using a dispersant by acting a sodium hypochlorite solution on carbon black to oxidize the carbon black to a level higher than that of a commercial product and hydrophilize the surface. Is listed.
However, in this method, since many chlorine ions and sodium ions used as oxidants are present in the liquid,
To use this as an ink, filter the reaction product once,
After that, it is necessary to purify by reverse osmosis membrane or ultrafiltration. Further, since the oxidation treatment is performed at a high temperature of 100 ° C. for a long time of 12 hours, humic acid soluble in water is produced.
Further, as a method for further oxidizing the commercially available carbon black, JP-A-7-258578 describes that a low concentration ozone in the gas phase is used to oxidize the commercially available carbon black for a long time or more.

However, the carbon black oxidized by such a method remarkably corrodes the surface of the carbon black probably due to the strong action of the oxidizing agent, increasing the surface area and producing humic acid soluble in water. To do. Further, although the reason for the functional group of carbon black produced by such a treatment is not clear, it was found by the study of the present inventors that the compatibility with water is insufficient and the dispersion stability is not sufficient. As described above, a large amount of humic acid and Na ions are present in the water-based ink containing the carbon black subjected to the oxidation treatment using sodium hypochlorite or ozone in the gas phase as an oxidant, which is the conventional technique described above. For example, as described in Japanese Patent Publication No. 7-51687,
These impurities become solid matter at the nozzle and the pen tip, and cause clogging.

Further, as an oxidation treatment method, JP-A-50-14 is known.
Japanese Patent No. 2626 also describes a method of aerating ozone from the lower part of a stirring tank through pores while stirring and mixing an aqueous medium and carbon black. However, here, there is described a method of dispersing in a hydrophobic vehicle such as oil by flashing (adding oil to an aqueous mixture of pigment powder with stirring to transfer the pigment powder to an oil phase), There is no description about carbon black having excellent dispersibility in an aqueous medium, which can be suitably used as a pigment for an aqueous ink, particularly an inkjet ink. It is said that it is not preferable to introduce ozone in excess of ² × 10 ⁻⁵ gr per 1 m ² of the specific surface area of furnace black, and it is intended that the carbon black obtained has a low degree of oxidation. However, no specific degree of oxidation is described. Thus, conventionally, no method has been found for obtaining carbon black having excellent dispersibility in an aqueous medium, which can be preferably used as a pigment for aqueous ink, particularly for inkjet, and carbon black is used as a pigment for aqueous ink. There was a problem to use it for.

The present invention solves the above problems in the prior art and provides a pigment for water-based ink and an ink which are excellent in dispersion stability, in which the occurrence of clogging at a nozzle or a pen tip is suppressed and in which ejection stability is excellent. The purpose is to obtain carbon black that can be provided.

[0009]

The present inventor obtains a carbon black aqueous dispersion having excellent dispersibility and further excellent ejection stability by removing humic acid from the carbon black dispersion to a specific concentration. I found that I can do it. In particular, it was also found that a dispersion having an appropriate humic acid concentration can be easily prepared by oxidizing carbon black using a specific method. That is, the present invention is an oxidation-treated carbon black obtained by oxidizing carbon black with an oxidizing agent, characterized in that all the acidic groups are 3 μequ / m ² and the concentration of humic acid extracted is 1 or less. It exists in oxidation-treated carbon black.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, carbon black is oxidized to obtain oxidized carbon black. The particle size of the carbon black to be subjected to the oxidation treatment is not limited, but particles having a particle size of 100 nm or less, further 30 nm or less are most suitable because sedimentation of the particles is particularly suppressed. Alkali metals and alkaline earth metals in carbon black dissolve in water,
Since the efficiency of ozone oxidation in a liquid is reduced, the amount is preferably as small as possible, but the total amount is preferably 1% by weight or less, more preferably 0.5% by weight or less, and further preferably 0.1% by weight or less. Further, sulfur and sulfur compounds in carbon black, or chlorine compounds are oxidized by ozone to become a strong acid in the solution, since the functional group generated on the surface of the carbon black has the effect of preventing the ions from becoming, Although it is desired to be as small as possible, the total sulfur analysis value or the total chlorine analysis value is preferably 0.5% by weight, and more preferably 0.1% by weight or less. To reduce the sulfur content, it is possible to use an aromatic hydrocarbon used as a raw material of carbon black, a liquid hydrocarbon used as a fuel, or a substance having a low sulfur content as a gaseous hydrocarbon. Further, the chlorine content can be lowered by using pure water as water used as cooling water during the production of carbon black.

The oxidation treatment of carbon black may be carried out by treatment with conventionally known nitric acid or ozone in the gas phase, but preferably the ozone treatment in the presence of water remarkably improves the dispersibility in an aqueous medium. At the same time, it was found by the present inventor that a concentration of humic acid, which will be described later, as a requirement of the present invention can be easily obtained. Here, the amount of water is preferably 95: 5 to 0.5: 99.5 in terms of the ratio (weight ratio) of carbon black and water, more preferably 50:50 to 2:98, and further preferably 20. : 80 to 5:95 is preferable. Thus, water and carbon black are mixed, and ozone is introduced into this mixture to oxidize the carbon black. Specifically, the carbon black can be oxidized through ozone and / or an ozone-containing gas.

By using ozone as the oxidant,
Oxidizing carbon black at room temperature is different from other oxidation agents that have been conventionally used for oxidizing carbon black, such as nitric acid, nitrogen oxides, sulfuric acid, and hypochlorous acid, where the oxidation reaction proceeds at high temperature. You can By generating ozone with an ozone generator and introducing it into a mixture of water and carbon black, the carbon black can be oxidized in the presence of water. It is not clear the mechanism by which oxidized carbon black with less humic acid and excellent properties can be obtained by the simple operation of oxidizing carbon black with ozone in the presence of water. Does not react directly with the carbon black surface, ozone dissolves in water
It is considered to oxidize when the oxidative power is weakened. Also, because of the presence of water, the temperature does not rise, and when it reacts with carbon black, it does not react deep inside the carbon,
It is also possible that humic acid does not occur. Further, it is considered that the functional group produced by reacting in the presence of water has a good compatibility with water and exhibits dispersion stability.

Regarding the degree of oxidation, the oxidation treatment is carried out until the total acidic groups of carbon black become ³ μequ / m ² or more. If it is more preferably 6 μequ / m ² or more, the dispersibility in an aqueous medium becomes very good. If it is less than 3 μequ / m ² , dispersibility in a dispersion medium is not sufficient, aggregation easily occurs, and it is difficult to use as an aqueous ink. 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 obtaining all the acidic groups is as follows. The oxidized carbon black is filtered using a 0.1 micron membrane filter to separate it from water. The separated carbon black is dried for one day in a dryer at 60 ° C. and then crushed in an agate mortar. 0.2 to 0.5 g of this dried carbon black is taken, placed in an Erlenmeyer flask containing 0.01 cc of NaOH in 60 cc, nitrogen is flown into the Erlenmeyer flask, and the mixture is stirred with a stirrer for 6 hours to cause reaction. The reaction product is filtered again using a 0.1 micron membrane filter to obtain a filtrate. 40 cc of this filtrate is taken and 0.0
Titrate with an automatic neutralization titrator using 25N hydrochloric acid to determine the NaOH concentration of the filtrate. The total acidic groups of carbon black can be calculated by the following calculation.

[0014]

[Formula 1] As described above, the carbon black is oxidized. It is well known that when the carbon black is oxidized, humic acid is generated on the surface thereof. On the other hand, when carbon black is oxidized, it becomes more compatible with water. Therefore, it has been attempted to use carbon black as a pigment for water-based ink alone or in combination with a dispersant. When used in this way, the surface humic acid dissolves in water. Also, the higher the pH, the greater the amount of humic acid dissolved.

Humic acid is a substance in which a functional group such as a carboxyl group or a hydroxyl group is bonded to a polycyclic aromatic condensate, which is generally produced when carbon such as coal is treated with an oxidizing agent, and is brown. Is. This substance is not a single compound but has a molecular weight distribution, but humic acid obtained by oxidizing carbon black has an absorption at a specific wavelength of ultraviolet light, and therefore it can be obtained as the absorbance at that wavelength. The concentration of humic acid contained in carbon black can be analyzed by the following method. A dispersion liquid obtained by dispersing carbon black in water is subjected to pressure filtration using a 0.1-micron membrane filter. Some carbon black leaks out at the beginning of filtration, so the initial liquid is discarded and the liquid from which carbon black has been completely removed is collected.

This solution was placed in a 10 mm square quartz absorbance measuring cell, and the absorbance at ultraviolet 255 nm was measured with a photometer.
This value is defined as the extracted humic acid concentration of carbon black.
The oxidized carbon black of the present invention has an extracted humic acid concentration of 1 or less in terms of absorbance. As described above, the oxidation-treated carbon black of the present invention having a low concentration of extracted humic acid exhibits excellent effects such as prevention of nozzle clogging even when it is made into an aqueous ink composition. When the concentration of extracted humic acid is preferably 0.5 in terms of absorbance, such an excellent effect is more remarkable.

Among the above-mentioned oxidation methods, when the oxidation treatment is carried out with ozone in the presence of water, it is surprising that even if the oxidation treatment is carried out to such an extent that the dispersion in the aqueous medium becomes good, the humic acid The acid concentration will be low. That is, it is possible to easily obtain an extracted humic acid concentration of 1 or less, more preferably 0.5 or less. Therefore, the dispersion obtained by dispersing the obtained oxidation-treated carbon black in various dispersion media can have an extremely low humic acid concentration as it is. Very suitable for preparation. On the other hand, ozone oxidation in the gas phase,
Alternatively, the generation of humic acid is not negligible in the oxidation treatment with other oxidizing agents, so various humic acid removal means are applied to the dispersion liquid in which the oxidized carbon black is dispersed to reduce the concentration of humic acid. Let Examples of means for removing humic acid include a method of treating the dispersion with activated carbon and a method of treating with an ion exchange resin.

Alternatively, the ink can be prepared by once dispersing the oxidized carbon black in an aqueous medium to dissolve the humic acid, and then taking out the carbon black and dispersing it in various vehicles for ink to prepare a dispersion liquid. . By the above method, the concentration of humic acid in the carbon black dispersion is set to 1 or less in terms of absorbance. The absorbance is particularly preferably 0.
It should be 5 or less. The humic acid concentration of the dispersion liquid can be analyzed by the following method. The dispersion is pressure filtered using a 0.1 micron membrane filter.
Some carbon black leaks out at the beginning of filtration, so the initial liquid is discarded and the liquid from which carbon black has been completely removed is collected. This solution is put into a 10 mm square quartz absorbance measuring cell, and the absorbance at UV 255 nm is measured with a photometer, and this value is taken as the humic acid concentration of the dispersion.

As described above, the oxidized carbon black of the present invention in which the concentration of the extracted humic acid is 1 or less in terms of absorbance is useful when mixed with various media, but it is particularly dispersed in an aqueous medium to form an aqueous dispersion. By using a liquid, a water-based ink having excellent performance can be obtained. The aqueous medium here refers to water or a mixture of water and a polar solvent miscible with water, and as a specific example of the polar solvent, ethanol,
Representative examples include lower alcohols such as isopropanol, glycol-based solvents such as glycerin, diethylene glycol and polyethylene glycol, N-containing solvents such as N-methylpyrrolidone and 2-pyrrolidone, and urea. 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,
A carbon black aqueous dispersion containing 0.5 to 20% by weight is particularly preferable. Within this range, the printing density when used as an ink is good, the viscosity of the ink is suppressed, and an ink having excellent characteristics can be obtained.

The carbon black aqueous dispersion thus obtained should be used as a water-based ink by adding various additives, such as adding a dispersant as needed when the concentration of carbon black exceeds 20 wt%. You can If desired, the ink may be concentrated, dried, and then diluted separately before use as an ink. In this case, it is also possible to add the oxidized carbon black to water and use dispersion treatment with a bead mill, a ball mill, an impact disperser or the like. Examples of additives for forming an ink include a penetrant, a fixing agent, and a fungicide. As the penetrant, a nonionic surfactant such as polyoxyethylene alkylaryl ether, an anionic surfactant such as alkylbenzene sulfonate, a fluorine-based surfactant, diethylene glycol monobutyl ether, or the like can be used.

Examples of the fixing agent include 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), and aqueous emulsions. Can also be used. Generally, when used as an inkjet ink, the carbon black concentration is 1
-20% by weight, particularly preferably 5-10% by weight are used. The thus-obtained ink of the present invention is stable in droplet formation, ejection stability, long-term ejection stability, ejection stability after long-term rest, storage stability, recording material, which is necessary as an inkjet ink. It has a good balance between the fixing property to the ink and the weather resistance of the recorded image. Further, it is also suitably used for water-based inks for writing instruments, various paints, color filters and the like.

[0022]

EXAMPLES The present invention will be described in more detail below with reference to examples. Example 1 Commercially available carbon black (“# 47” manufactured by Mitsubishi Chemical Corporation,
20 g of a sulfur content of 0.5% and a total content of alkali metals and alkaline earth metals of 0.1%) were placed in 500 cc of water and dispersed for 5 minutes with a household mixer. The obtained liquid was put into a 3 liter glass container equipped with a stirrer. While stirring with a stirrer, add 5% of ozone-containing gas with an ozone concentration of 8% by weight.
It was introduced at 00 cc / min for 2 hours. At this time, ozone was generated by using an electrolytic generation type ozonizer manufactured by Permelec Electrode Co. as an ozone generator.

The liquid after the ozone treatment was taken out and the pH was measured and found to be 2.5. (The pH is measured according to JIS K
According to 6221. In addition, the particle size distribution in this liquid was measured by "Microtrac UPA" manufactured by Nikkiso Co., Ltd.
nm, take this solution, and use an optical microscope to measure 400
When confirmed with a double magnification, it was found that the whole was in a good dispersion state and had a micro-Brownian motion, did not aggregate with time, and had good dispersion stability. Then
This liquid was filtered through a micropore filter having a diameter of 0.1 micron to remove carbon black and obtain a filtrate,
When the concentration of the extracted humic acid in the carbon black after the filtration was measured, it was 0.1 in terms of ultraviolet absorbance at 255 nm.

On the other hand, the carbon black remaining after filtration is heated to 60 ° C.
It was dried with and the total acidic group was measured.
/ G. The nitrogen adsorption specific surface area was 120 m ² . Therefore, the total acid group per unit area is 3.75.
It was μequ / m ² . Furthermore, 0.1% is added to this dispersion.
The pH was adjusted to 10 by adding N NaOH solution. Further, even if the pH was raised to 12, the particle size distribution did not change and was 78 microns, and the dispersed state was good even with an optical microscope. These two types of dispersion liquids were centrifuged at 5000 rpm and packed in a cartridge manufactured by NEC Corporation NEC Corporation
When printing was performed using the printer "PR101", a good printed matter without bleeding or blurring was obtained.

Example 2 20 g of carbon black "# 47" was mixed with 0.1 N of acetic acid.
It was put in 500 cc of water containing it and dispersed for 5 minutes with a household mixer. This dispersion was placed in a 3 liter glass container equipped with a stirrer. While stirring with a stirrer, ozone concentration 2
A wt% ozone-containing gas was introduced at 500 cc / min for 15 hours. At this time, the ozone generator used was a discharge type ozonizer using pure oxygen manufactured by PCI, USA. When this dispersion was taken out and the pH was measured, it was 2.0. In addition, the particle size distribution in this dispersion is "Microtrack U" manufactured by Nikkiso Co., Ltd.
When measured by "PA", the average 50% diameter was 72 nm, and when this liquid was taken and confirmed with an optical microscope at a magnification of 400 times, the whole was in a fine brown state with good dispersion and aggregated over time. It was found that the dispersion stability was good without any need.

Next, this dispersion was filtered through a micropore filter having a diameter of 0.1 micron to remove carbon black and obtain a filtrate, and the concentration of humic acid in this filtrate was measured. The concentration of this humic acid was 3.1 in terms of absorbance at UV 255 nm. 50 cc of anion exchange resin manufactured by Mitsubishi Chemical Co., Ltd. was placed in 100 cc of this dispersion liquid, and the mixture was shaken by a shaker for 1 hour for adsorption. After this, add 5000 rp of liquid.
Absorbance was determined by removing foreign matters such as ion-exchange resin with a m centrifugal separator. The absorbance was 0.8 at 255 nm UV. This dispersion was centrifuged at 5000 rpm and
When printing was performed using a printer "PR101" manufactured by NEC Co., Ltd. packed in a cartridge manufactured by NEC, the dischargeability from the nozzle was good, and a good printed matter without bleeding or blurring was obtained. On the other hand, 6 carbon black of the filtration residue
When dried at 0 ° C and measured for all acidic groups, it was 500 μe
It was qu / g. Therefore, the total acidic groups per unit area was 4.2 μequ / m ² .

[0027]

INDUSTRIAL APPLICABILITY According to the present invention, when it is used for ink for ink jet or writing in particular, there is no occurrence of clogging or sediment in the orifice of the nozzle or its tip, and stable ink ejection stability can be obtained. A carbon black suitable as a pigment is obtained.

Claims (10)

(57) [Claims] 1. An oxidation-treated carbon black obtained by oxidizing carbon black with an oxidizing agent, wherein all acidic groups are 3 or less.
An oxidation-treated carbon black characterized in that the concentration of extracted humic acid is µequ / m ² and the absorbance is 1 or less. 2. The oxidation-treated carbon black according to claim 1, wherein the oxidizing agent is ozone. 3. The oxidation-treated carbon black according to claim 1, wherein the oxidation treatment is performed in the presence of water. 4. A carbon black dispersion liquid in which the oxidation-treated carbon black according to claim 1 is dispersed in a dispersion medium. 5. The carbon black dispersion according to claim 4, wherein the dispersion medium is an aqueous medium. 6. The carbon black dispersion liquid according to claim 4, wherein the humic acid concentration in the liquid is 1 or less in terms of absorbance. 7. A carbon black characterized in that the concentration of humic acid in a liquid is reduced to 1 or less by removing humic acid in the liquid from a dispersion liquid in which oxidized carbon black is dispersed in water. A method for producing a dispersion. 8. The method for producing a carbon black dispersion according to claim 7, wherein the removal of humic acid is performed with activated carbon. 9. The method for producing a carbon black dispersion according to claim 7, wherein the humic acid is removed with an anion exchange resin. 10. The method for producing a carbon black dispersion according to claim 7, wherein the oxidation-treated carbon black is obtained by oxidizing carbon black with ozone in the presence of water.