JP2009132848A - Surface-reformed carbon black and method for producing water dispersion of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-reformed carbon black which is suitable as an aqueous black ink pigment for an inkjet printer or the like; and to provide a method for producing a water dispersion of the surface-reformed carbon black. <P>SOLUTION: In the surface-reformed carbon black, an amino group is covalently bonded to carbon black, obtained by neutralizing an acidic functional group of acidic carbon black with a basic compound. The method for producing a water dispersion of the surface-reformed carbon black includes dispersing the acidic carbon black in water, then neutralizing the acidic carbon black by adding a basic compound in the resulting dispersion, further adding an azo compound into the dispersion, and directly covalently bonding the amino group to the surface of the carbon black by heating the resulting dispersion to a temperature higher than the temperature at which the azo group is cleaved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface-modified carbon black suitable as a black pigment for an aqueous black ink including an ink for an ink jet printer, and a method for producing the surface-modified carbon black aqueous dispersion suitable for an aqueous black ink.

  Since carbon black is hydrophobic and has low wettability with water, it is extremely difficult to stably disperse it in water at a high concentration. This is due to the fact that there are very few functional groups having high affinity with water molecules present on the surface of the carbon black particles.

  Therefore, in order to improve and improve the water dispersibility of carbon black, a method has been developed in which carbon black is surface treated to give functional groups with high affinity for water molecules on the particle surface. A method of forming a hydrophilic functional group on the surface of carbon black particles has been known for a long time.

  For example, Patent Document 1 discloses a method of oxidizing carbon black with an aqueous hypohalite solution, and Patent Document 2 discloses a method of oxidizing carbon black with low-temperature oxygen plasma.

  In recent years, water-based black inks have been particularly useful as recording liquids for ink jet printers. For example, Patent Document 3 discloses an aqueous pigment ink containing water and carbon black, in which the carbon black is 1.5 mmol / An aqueous pigment ink having a surface active hydrogen content of g or more is disclosed in Patent Document 4 from a step of finely dispersing carbon black in an aqueous medium and a step of oxidizing the carbon black using hypohalite. A method for producing an aqueous pigment ink is disclosed.

Patent Document 5 discloses carbon black modified by an oxidation treatment, in which the total amount of carboxyl groups and hydroxyl groups among hydrogen-containing functional groups present on the surface is 3 μeq / m ² or more per unit surface area. Water dispersible carbon black has been proposed.

Furthermore, a method for modifying the surface of carbon black with organic radicals has been developed and proposed. For example, Patent Document 6 discloses a recording ink in which a color material composed of carbon black is dispersed in an aqueous medium. There has been proposed a recording ink using, as a coloring material, carbon black in which a functional group generated by decomposition of a radical generator composed of an azo compound represented by -N = N-A2) is chemically bonded to the surface. This is because the functional group bonded to the surface suppresses aggregation in the aqueous medium, maintains the dispersed state, and improves the storage stability of the ink.
JP-A-48-018186 JP-A-57-159856 Japanese Patent Laid-Open No. 08-003498 JP 08-319444 A Japanese Patent Laid-Open No. 11-148027 JP-A-11-323229

  Thus, in recent years, carbon black with excellent water dispersibility has been actively developed and researched mainly in applications such as ink for ink jet printers by chemically modifying the surface of carbon black with an organic substance. .

  Accordingly, the present inventor has also conducted research on a method for surface modification by bonding an organic substance to the surface of carbon black in order to improve and improve the water dispersion performance of carbon black. Then, by introducing basic functional groups such as amino groups and cyclic amines on the surface of carbon black, it is possible to improve water dispersion performance. In this case, acidic carbon black having a hydrophilic functional group is added to water. Carbon black is obtained by dispersing and neutralizing some or all of its acidic functional groups with basic compounds, then adding amines and cyclic amines and heating them to covalently bond amino groups directly to the carbon black surface. It has been found that a carbon black water dispersion having excellent dispersion performance can be obtained by suppressing particle aggregation.

  The present invention has been developed based on this finding, and an object thereof is to provide a surface-modified carbon black suitable as an aqueous black ink pigment for an ink jet printer and the like, and a method for producing an aqueous dispersion thereof.

  In order to achieve the above object, the surface modified carbon black according to the present invention is constituted by covalently bonding an amino group to carbon black obtained by neutralizing an acidic functional group of acidic carbon black with a basic compound. With the above features.

The acidic functional group of acidic carbon black is a carboxyl group and a hydroxyl group, and the functional group equivalent is preferably 0.14 μeq / m ² or more per carbon black surface area.

  In addition, the method for producing an aqueous dispersion in which the surface-modified carbon black is dispersed in water is obtained by dispersing acidic carbon black in water, adding a basic compound to neutralize, and then adding an azo compound to the dispersion. The structural feature is that the amino group is covalently bonded directly to the carbon black surface by heating to a temperature higher than the temperature at which the azo group is cleaved.

  The carbon black concentration of the surface-modified carbon black aqueous dispersion is preferably 1 to 20% by weight.

  According to the surface-modified carbon black and the water dispersion thereof of the present invention, the surface-modified carbon black that is excellent in water dispersion performance and suitable as a black pigment for black aqueous ink, and black that has good ejection properties A method for producing a surface-modified carbon black aqueous dispersion having a high concentration and suitable as a black ink for an inkjet printer or the like can be provided.

  The surface-modified carbon black of the present invention is obtained by covalently bonding an amino group to carbon black in which some or all of the acidic functional groups of the carbon black having hydrophilic acidic functional groups are neutralized with a basic compound. is there.

The carbon black applied to the surface-modified carbon black of the present invention is not particularly limited, but those having a hydrophilic acidic functional group on the surface are used, and a carboxyl group and a hydroxyl group are preferred as the acidic functional group. is there. The hydrophilic acidic functional group equivalent is preferably 0.14 μeq / m ² or more with respect to the surface area of the carbon black, and this acidic functional group is partially or entirely neutralized with a basic compound. is there. Accordingly, the acidic functional group equivalent is the sum of the carboxyl group equivalent, the hydroxyl group equivalent, and the carboxyl group equivalent and hydroxyl group equivalent neutralized and bonded with the basic compound.

  In addition, these functional group equivalents are measured by the following method.

"Carboxyl group equivalent": in 0.976mol / dm ³ of aqueous sodium bicarbonate 0.5 dm ^3, after shaking for 6 hours with the addition of carbon black 2-5 g, was filtered carbon black from the reaction solution Then, a neutralization titration test is performed with a 0.05 mol / dm ³ sodium hydroxide aqueous solution until the pH reaches 7.0, and the amount of carboxyl groups is determined.

“Hydroxyl group equivalent”: 2,2′-Diphenyl-1-picrylhydrazyl (DPPH) was dissolved in carbon tetrachloride to prepare a solution having a concentration of 50 mmol / dm ³ , and carbon black was added to the solution in an amount of 0.1 to 0. Add 6 g and stir in a constant temperature bath at 60 ° C. for 6 hours. Thereafter, carbon black is filtered off from the reaction solution, and the amount of hydroxyl groups in the filtrate is quantified using an ultraviolet absorption photometer.

"Equivalent carboxyl group neutralized with base", "Equivalent hydroxyl group neutralized with base": Treating carbon black with a strong acid such as hydrochloric acid to remove anions ion-bonded to the carboxyl group and hydroxyl group. Quantification is performed in the same manner as in the above-described method for measuring the amount of carboxyl groups and the amount of hydroxyl groups, with the end point where no anion is detected in the chromatograph.

  These acidic functional groups function to impart carbon black self-dispersibility in an aqueous medium, and some or all of the acidic functional groups are neutralized by a basic compound. Examples include metals, alkaline earth metals, ammonia, and amines.

  Carbon black in which part or all of the acidic functional group of the acidic carbon black having the acidic functional group on the surface is neutralized with a basic compound simply has a basic functional group such as an amino group or a cyclic amine. When the compound is added, the black density of the carbon black aqueous dispersion is improved, but the dispersibility is deteriorated. In order to achieve both good dispersibility and improvement in black density, it is necessary to covalently bond an amino group to the surface of carbon black.

  If only added without bonding with the carbon black surface, it is extremely difficult to improve the black density while maintaining the dispersion stability of the dispersion without suppressing the aggregation of the carbon black. . In addition, when an amino group is bonded to an acidic functional group on the surface of carbon black by ionic bond, aggregation is likely to occur due to a change in pH. However, as in the present invention, an amino group covalently bonded to the surface-modified carbon black surface. The group is less likely to aggregate the carbon black particles in water and has excellent dispersion performance in solution.

  Amino groups are, for example, primary amino groups, secondary amino groups, tertiary amino groups, cyclic amino groups, primary, secondary, tertiary amines, amines such as amidine, diamine, or pyrrolidinone, piperidine, imidazoline. Examples thereof include nitrogen-containing compounds having basic functional groups such as cyclic amines such as rings.

In these amino groups, the azo group in the same molecule is cleaved by heating, and the resulting radical is chemically bonded directly to the carbon black surface, so that the amino group exists in a stable state on the carbon black surface. In addition, it is possible to maintain a stable state against changes in external factors such as pH change, and to improve water dispersion stability. The amino group equivalent is preferably 0.14 μeq / m ² or more.

In addition, the amount of amino groups is measured by the following method.
While stirring the carbon black dispersion diluted to a predetermined concentration, titration with a 0.05 mol / l hydrochloric acid aqueous solution is performed to determine the neutralization titration from the titration amount and the inflection point of pH, and the total amount of amino groups is quantified.

Such a structure of the surface-modified carbon black of the present invention can be represented as Chemical Formula 1. In Chemical Formula 1, R ₁ represents an alkyl group, alkene group, alkane group, heteroalkyl group, heteroalkene group, or heteroalkane group, or a combination thereof, R ₂ represents H, CnH 2n + 1, and NR ₂ represents 1 It represents any one or a combination thereof having a basic functional group such as amines such as secondary, tertiary and tertiary amines, amidine and diamine, or cyclic amines such as pyrrolidinone, piperidine and imidazoline rings. M is a base and represents an alkali metal, an alkaline earth metal, ammonia, an amine, or the like.

  The surface-modified carbon black dispersed in water is dispersed in water. Acidic carbon black is dispersed in water and neutralized by adding a basic compound. Then, the azo group is cleaved by adding an azo compound to the dispersion. It is produced by heating at a temperature higher than the temperature at which the amino group is covalently bonded directly to the carbon black surface.

  Acidic carbon black is a gas phase oxidation that exposes carbon black to ozone, oxygen, NOx, SOx, etc., ozone water, hydrogen peroxide, peroxodiacid or its salts, hypohalite, dichromate It can be obtained by a liquid phase oxidation method in which it is placed in an oxidizing agent aqueous solution such as permanganate or nitric acid and mixed with stirring.

Moreover, the following carbon black etc. can be illustrated as commercially available carbon black which has a hydrophilic functional group.
Made by Mitsubishi Chemical Corporation, # 2700, # 2650, # 2400, # 2350, # 1000, MA7, MA77, MA8, MA11, MA100, MA100R, MA220, MA230, Made by Germany Degussa, Color Black FW200, FW2, FW2V, FW285, FW1, FW18, S170, S160, Special Black 6, 5, 4, 4A, Printex U, V, 140U, 140V.

  Also, carbon black processed by imparting a hydrophilic functional group to furnace black by various known methods can be used. For example, CAB-O-JET 200, 300 manufactured by Cabot, USA, Aqua-Black manufactured by Tokai Carbon Co., Ltd. Examples include 001, 162, and the like.

  Among these, Aqua-Black 162 has an appropriate amount of carboxyl groups and hydroxyl groups neutralized with sodium on its surface and is excellent in dispersibility, so that it can be preferably used. The neutralized carbon black is preferable because the electric repulsion between the carbon black particles in water is increased and good dispersibility and long-term storage stability are exhibited.

  These acidic carbon blacks can be used regardless of their physical properties, but preferably carbon black having a primary particle diameter of 0.01 to 0.3 μm measured by electron microscope observation is used. Preferably, 0.01 to 0.07 μm carbon black is used. When the primary particle size is less than 0.01 μm, the cohesive force acting between the particles is large, so that the particles are easily aggregated. However, when carbon black having a particle size exceeding 0.3 μm is used, the particle self-weight in a state where amino groups are covalently bonded Is large and tends to settle in an aqueous medium.

  A water-soluble azo compound is used to covalently bond an amino group to the surface of carbon black by a nucleophilic reaction. In the chemical formula 2, R1 and R2 represent the same or different alkyl group, alkene group, alkane group, heteroalkyl group, heteroalkene group, heteroalkane group, or a combination thereof. It may be 500 or more polymers.

  R3 and R4 are the same or different primary amino group, secondary amino group, tertiary amino group, cyclic amino group, primary amine, secondary amine, tertiary amine, amidine, diamine and other amines, pyrrolidinone, piperidine Represents a nitrogen-containing compound having a basic functional group such as cyclic amines such as imidazoline ring, and salts thereof, or a combination thereof.

  As an azo compound that can be used in the present invention, any azo compound having an azo group and containing an amino group or a cyclic amine can be used. These amino group-containing azo compounds can be mixed with acidic carbon black in water or water. And dissolved in a solvent consisting of organic solvent and heated to a temperature sufficient to cleave at the azo group part of the amino group-containing azo compound to form a radical compound, and then nucleophilically react on the carbon black surface. It becomes possible to give an amino group to the surface of the carbon black particles.

  That is, the surface-modified carbon black of the present invention is characterized in that an amino group is covalently bonded to the surface via an azo group, and is obtained by heating carbon black together with an amino group-containing azo compound.

  The reaction proceeds as long as the reaction temperature is not higher than the 10-hour half-life temperature, which is the temperature at which half is cleaved in 10 hours. However, the reaction requires a long time, and the efficiency is deteriorated. Therefore, the heating temperature may be any temperature that is not less than the 10-hour half-life temperature and does not cause thermal decomposition of the cleaved azo compound, and is set in the range of + 5 ° C. to + 50 ° C. of the 10-hour half-life temperature. More preferably, the 10-hour half-life temperature is + 10 ° C to + 40 ° C.

  If the 10-hour half-life temperature is + 50 ° C. or higher, the decomposition rate of the azo polymerization initiator becomes very fast, and radicals are generated at a stretch, making it impossible to bind effectively to the carbon black surface active hydrogen groups.

  Specific examples of the amino group-containing azo compound used in the present invention include the following chemical formulas 3 (1) to 9 (7).

  These amino group-containing azo compounds are commercially available from Wako Pure Chemical Industries, Ltd. as VA-044, VA-046B, VA-060, VA-061, VA-067, VA-50, and VA-080, respectively.

  The surface-modified carbon black aqueous dispersion of the present invention is obtained by dispersing acidic carbon black in water and adding a basic compound to neutralize it, followed by basic functional groups such as azo group, amino group, and cyclic amine in the molecule. Adding the above-mentioned amino group-containing azo compound having azo group, heating to a temperature at which the azo group is cleaved, cleaving the azo group to form a radical compound, and causing nucleophilic reaction to active hydrogen on the surface of carbon black Thus, it is manufactured by covalently bonding an amino group directly to the surface of the carbon black particles.

  In this case, if the carbon black aqueous dispersion contains coarse particles of μm units, it is not preferable because a uniform reaction field cannot be obtained when the amino group-containing azo compound is bonded. Furthermore, for example, when used for ink for an ink jet printer, it becomes a cause of clogging when ejected from a nozzle diameter of 10 μm or less due to recent development of printer head technology.

  Therefore, it is preferable to remove coarse particles by filtering, centrifugation, or a combination thereof. An appropriate amount of the carbon black aqueous dispersion from which coarse particles have been removed is transferred to a reaction vessel such as a separable flask that is highly airtight and can be sealed, and an appropriate amount of amino group-containing azo compound relative to the weight of carbon black, for example, 0.1 to 25 wt. %Added.

  Next, an inert gas such as nitrogen gas set at a predetermined flow rate is circulated while stirring. Unless an inert gas such as nitrogen gas is circulated, the azo compound is deactivated by oxygen in the solution. Therefore, it is preferable to remove dissolved oxygen as much as possible.

  Thereafter, the system is heated to a predetermined temperature and held for a predetermined time. The reaction temperature and reaction time at this time can be freely set as long as the azo compound is sufficiently decomposed. For example, conditions such as holding for 6 hours at the 10-hour half-life temperature of the azo compound to be used + 20 ° C. can be exemplified.

  Then, cool and transfer the solution to a suitable container such as a glass container. At this time, in order to prevent mixing of carbon black which is dried at the inner wall portion of the reactor, it is preferable to perform filtration with a metal mesh or filter paper having a small mesh. Furthermore, in order to remove the decomposition product of the azo compound from the solution, it is washed with an ultrafiltration membrane or a reverse osmosis membrane. These membranes are widely commercially available, and examples thereof include Microza manufactured by Asahi Kasei Co., Ltd., Vivaflow manufactured by Sartorius, Germany, and Minimate manufactured by Nihon Pall Co., Ltd. After washing, concentration and dilution are performed to adjust to a desired carbon black concentration.

  In this way, a surface-modified carbon black aqueous dispersion can be produced. In this case, the carbon black concentration is preferably adjusted to 1 to 20% by weight. When the dispersion concentration of the carbon black is less than 1% by weight, the dispersibility becomes insufficient, and the aggregation and sedimentation of the carbon black particles occurs with time. On the other hand, when the content exceeds 20% by weight, the carbon blacks are too close to each other in the aqueous dispersion and aggregate to deteriorate stability over time.

  Moreover, when preparing an inkjet ink using this aqueous dispersion, it is prepared by adding a coloring material such as resin, alkali adjuster, preservative, surfactant, other pigment or dye.

  Examples of the present invention will be specifically described below in comparison with comparative examples, but the present invention is not limited to these examples.

Example 1
200 g of carbon black water dispersion Aqua-Black 162 (carbon black concentration 20% by weight) manufactured by Tokai Carbon Co., Ltd., whose functional group equivalent of carbon black is 4.87 μeq / m ² , is placed in a 1 liter separable flask. 300 g of purified water was added thereto, and 0.8 g of an amino group-containing azo compound VA-061 (Chemical Formula 6) manufactured by Wako Pure Chemical Industries, Ltd. was further added. Further, purified water was added so that the total amount became 800 g.

  A thermocouple and a nitrogen gas introduction tube were inserted into the separable flask, and stirring of the solution was started at a speed of 200 rpm. At the same time, nitrogen was added at 150 ml / min. The oxygen in the system was sufficiently pushed out of the system. Subsequently, it heated up to 80 degreeC with the temperature increase rate of 1 degreeC / min, and hold | maintained for 3 hours.

  After a predetermined time, it was naturally cooled to room temperature. Thereafter, the entire solution was passed through a metal mesh having an opening of 25 micrometers to remove coarse particles. At this time, no aggregation or sedimentation of carbon black was observed, and it was confirmed that the carbon black was in a good dispersion state.

  Subsequently, ultrafiltration was performed with a Sartorius Vivaflow 200 until the filtrate discharge became 4 liters. Thereafter, concentration was performed until the carbon black concentration became 10% by weight, and a carbon black dispersion 1 was obtained.

Example 2
Carbon black TB # 7550F manufactured by Tokai Carbon Co., Ltd. was treated with an ozone generator CO-101 manufactured by Yamato Scientific Co., Ltd. for 7 hours to obtain an acidic carbon black having a functional group equivalent of 2.68 μeq / m ² . This acidic carbon black was dispersed in water to a concentration of 10% by weight, then sodium hydroxide was added in excess of the total amount of carboxyl groups and hydroxyl groups on the surface of the carbon black, and the temperature was raised to 95 ° C. for 6 hours. Sum processing was performed. The product was naturally cooled to room temperature and purified by ultrafiltration. After confirming that the refining treatment has been sufficiently conducted by measuring the electric conductivity, concentration is performed until the carbon black concentration becomes 10% by weight to obtain carbon black having neutralized carboxyl groups and hydroxyl groups on the particle surface. It was. A carbon black dispersion 2 was obtained in the same manner as in Example 1 except that this surface-treated carbon black was used.

Example 3
A carbon black dispersion 3 was obtained in the same manner as in Example 2, except that Gas Black Special Black 4 manufactured by EVONIK Co., Ltd., having a functional group equivalent of 3.72 μeq / m ² was used.

Example 4
A carbon black dispersion 4 was obtained in the same manner as in Example 1, except that the same amount of VA-046B (Chemical Formula 4) was used instead of VA-061.

Example 5
A carbon black dispersion 5 was obtained in the same manner as in Example 1, except that the same amount of VA-080 (Chemical 9) was used instead of VA-061 and the reaction temperature was 98 ° C.

Comparative Example 1
A carbon black dispersion 6 was obtained in the same manner as in Example 1 except that TB # 75550F in which the functional group equivalent of carbon black was 0.11 μeq / m ² was used instead of Aqua-Black 162.

Comparative Example 2
In Example 1, TB # 7550F in which the functional group equivalent of carbon black is 0.11 μeq / m ² is used instead of Aqua-Black 162, and VA-060 (Chemical Formula 5) is used instead of VA-061. Thus, a carbon black dispersion 7 was obtained.

  The amine concentrations of these carbon black dispersions 1 to 7 were measured by acid-base titration, and the measurement results are shown in Table 1.

  The dispersion performance of the dispersion was measured using a Microtrac Co. (UPA150), and the average particle size of 150 nm or less was shown as “good”, and the precipitate was confirmed as “precipitation”. It was. In addition, the results of long-term warming test are shown as “good” when the particle size measurement is performed again at 70 ° C. for 4 weeks in an incubator, and the change rate is ± 10% or less. This was shown as “precipitate”. These results are shown in Table 2.

  Table 4 shows the results obtained by observing the dischargeability and black density when the dispersions 1 to 7 were prepared with ink specifications shown in Table 3 and printed with an inkjet printer PSC 1610 manufactured by Hewlett-Packard.

  In Table 4, the discharge performance is shown as “good” when printing is repeated 100 times and no curling or lines are generated, and when the initial stage of printing or gradually curling or lines are generated, ". Also, the black density of the black solid portion of the printed matter was measured by Macbeth (TR-927), and the optical density was 1.40 or higher when the density was 1.40 or higher and 1.20 to 1.40. “B”, 1.20 or less was indicated as “C”.

  The carbon black dispersions 1 to 5 and 7 were excellent in dispersibility, but the carbon black dispersion 6 was confirmed to aggregate carbon black particles.

  In addition, when carbon black dispersions 1-7 were dried and surface functional groups were observed by FT-IR, in carbon black dispersions 1-5, an amino group-derived peak was present together with a carboxyl group-derived peak and a hydroxyl group-derived peak. was detected. On the other hand, in the carbon black dispersion 6, no amino group-derived peak was observed, and in the carbon black dispersion 7, a hydroxyl group peak was observed instead.

Claims (4)

  A surface-modified carbon black obtained by covalently bonding an amino group to carbon black obtained by neutralizing an acidic functional group of acidic carbon black with a basic compound. The surface-modified carbon black according to claim 1, wherein the acidic functional group is a carboxyl group and a hydroxyl group, and the functional group equivalent is 0.14 µeq / m ² or more per carbon black surface area.   Disperse acidic carbon black in water, add a basic compound to neutralize, add an azo compound to the dispersion, and heat it above the temperature at which the azo group is cleaved to share the amino group directly on the carbon black surface A method for producing a surface-modified carbon black aqueous dispersion, which comprises bonding.   The method for producing a surface-modified carbon black aqueous dispersion according to claim 3, wherein the concentration of the surface-modified carbon black is 1 to 20% by weight.