JP6614546B2 - Method for producing surface-treated carbon black - Google Patents

Description

  The present invention relates to a method for producing a surface-treated carbon black. More specifically, the present invention relates to a method for producing a surface-treated carbon black that has a surface modified and can be dispersed well in water by heating by microwave irradiation under pressure and in the presence of an oxidizing agent.

  Carbon black is widely used as a pigment for black printing ink. When carbon black is used as a black pigment for inkjet, in order to prevent clogging of the inkjet nozzle, it is required that the dispersed particle diameter is dispersed to 200 nm or less in a dispersion mainly containing water. However, since the surface of carbon black has very few hydrophilic groups and carbon black itself is hydrophobic, it is very difficult to disperse it well in water.

In order to improve the water dispersibility of carbon black, attempts have been made to introduce a hydrophilic group on the surface by oxidizing carbon black.
Conventionally, the introduction of a hydrophilic group has been performed by oxidizing the surface of carbon black. Oxidation treatment includes oxidation by reaction with oxidizing gas such as ozone, surface oxidation by plasma, carbon black dispersed in water, hypochlorous acid, sulfuric acid, nitric acid, hydrogen peroxide, persulfuric acid and their salts, etc. Oxidation and the like by a liquid phase reaction in which the oxidant is reacted. Among them, oxidation by liquid phase reaction that does not require special equipment is frequently used in industry.

In Patent Document 1, the acidic hydroxyl groups dibutyl phthalate (DBP) absorption was formed on the surface of carbon black particles is 120 cm ^3/100 g or more, multivalent cation having a valence of divalent or more with monovalent cations And surface-treated carbon black particles having good water dispersibility are disclosed.

  Recently, a method has been proposed in which carbons having an asymmetric molecular structure such as carbon nanotubes are irradiated with microwaves in the presence of an oxidizing agent to modify the surface of the carbons (see Patent Document 2). ).

International Publication No. 2012/121362 JP 2007-55863 A

In order to obtain carbon black that is well dispersed in water, the total amount of carboxyl groups or phenolic hydroxyl groups is preferably 400 μmol / g or more.
However, in the oxidation by the conventional liquid phase reaction, a reaction time of several hours or more is required to obtain the carbon black having the above molar amount of hydrophilic group. Also in the invention described in Patent Document 1, the liquid phase oxidation treatment in the previous stage requires 10 hours.
Also in the invention described in Patent Document 2, the reaction time is 1 to 30 minutes, and a method capable of completing the reaction in a shorter time is required from the viewpoint of improving productivity.

  This invention is made | formed in view of the said situation, Comprising: It aims at providing the manufacturing method of surface treatment carbon black which can complete a surface oxidation process in a short time.

The present inventors have intensively studied to solve the above problems, and found that the oxidation treatment of carbon black can be completed in a short time by performing the surface treatment of the carbon black by irradiating with microwaves under pressure. Was completed.
That is, this invention relates to the manufacturing method of the surface treatment carbon black which has the following characteristics.
(1) A method for producing a surface-treated carbon black, wherein a surface treatment of carbon black is performed by heating a dispersion containing carbon black, an oxidant, and water by microwave irradiation under pressure.
(2) The method for producing surface-treated carbon black according to (1), wherein the heating time is less than 60 seconds.
(3) The method for producing a surface-treated carbon black according to (1) or (2), wherein the microwave irradiation uses a single mode cavity.
(4) The method for producing a surface-treated carbon black according to any one of (1) to (3), wherein the produced surface-treated carbon black is for inkjet ink.

  The production method of the surface-treated carbon black of the present invention is excellent in productivity because the carbon black surface treatment can be completed in a short time by performing microwave irradiation under pressure. It is.

It is a schematic block diagram which shows an example of a microwave irradiation apparatus. It is a schematic block diagram which shows the other examples of a microwave irradiation apparatus.

  In the method for producing surface-treated carbon black of the present invention, the surface treatment of carbon black is performed by heating a dispersion containing carbon black, an oxidant, and water by microwave irradiation under pressure.

-Carbon black Carbon black is a fine particle of carbon produced by thermal decomposition of hydrocarbons or incomplete combustion of oil or gas.
The average particle size of carbon black used as a raw material in the present invention is preferably 1 to 200 nm, more preferably 5 to 100 nm, still more preferably 5 to 50 nm, and particularly preferably 10 to 30 nm.
The nitrogen absorption specific surface area, coloring power, DBP absorption amount and the like of carbon black used as a raw material in the present invention are not particularly limited and can be appropriately selected according to the application.

-Oxidizing agent The oxidizing agent used in the present invention is not particularly limited as long as it can oxidize carbon black satisfactorily in a liquid phase. For example, persulfates such as potassium persulfate and sodium persulfate. A known oxidant such as sodium hypochlorite or hypohalite such as potassium hypochlorite; acid such as persulfuric acid, nitric acid or hypochlorous acid can be used.

-Dispersion The dispersion of the present invention contains the carbon black, the oxidizing agent, and water. In general, a compound used as an oxidizing agent is soluble in water, so that the dispersion can contain water so that the oxidizing agent can be dissolved well in the dispersion and can function as an oxidizing agent. . In addition, in the present invention, since microwave irradiation is performed under pressurized conditions, the boiling point of water also rises. Therefore, heating by microwave irradiation can be performed exceeding the boiling point of water at 100 ° C. under normal pressure. it can.

  The content of carbon black in the dispersion is not particularly limited, but the content of carbon black with respect to the total amount of the dispersion is 0.1 to 20% by mass from the viewpoint of suitably treating in a short time. It is preferably 0.5 to 10% by mass, particularly preferably 0.8 to 5% by mass.

  Further, the content of the oxidizing agent in the dispersion is not particularly limited, but is preferably 0.5 to 60% by mass, more preferably 2 to 30% by mass, and 4 to 4%. It is particularly preferably 15% by mass.

The dispersion may contain other components other than carbon black, an oxidizing agent, and water as long as the heating and the oxidation treatment of carbon black are not hindered.
Other components include other solvents. For example, heating can be promoted by using a solvent capable of absorbing microwaves in combination with water. Further, by using a solvent having a high boiling point in combination with water, it becomes possible to heat the carbon black satisfactorily even when the pressure is weakened. Specifically, since the energy for absorbing microwaves is indicated by P in the following formula, it is preferable to use a solvent having a high conductivity and dielectric loss factor.

［式中、σは溶媒の電導率、ｆはマイクロ波の周波数、ε_０は真空の誘電率、ε_ｒ”は溶媒の誘電損率、Ｅは電界強度、μ_０は真空の透磁率、μ_ｒ”は溶媒の磁気損失、Ｈは磁場の強さを示す。］

[Where σ is the electric conductivity of the solvent, f is the frequency of the microwave, ε ₀ is the dielectric constant of the vacuum, ε _r ″ is the dielectric loss factor of the solvent, E is the electric field strength, μ ₀ is the magnetic permeability of the vacuum, μ _r ″ represents the magnetic loss of the solvent, and H represents the strength of the magnetic field. ]

Specific examples of such solvents include aqueous solutions in which electrolytes are dissolved; acids and alkalis and aqueous solutions thereof; polar organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, dimethyl sulfoxide, and sulfolane; Alcohols such as ethyl alcohol, 1-butanol, 2-butanol, 1-propanol and 2-propanol, glycols such as ethylene glycol and diethylene glycol, ketones such as acetone, glycol ethers such as propylene glycol monomethyl ether acetate The solvent which mixed these 1 or more types can also be used.
When the solvent is used in combination with water, the amount of the solvent is preferably 50 parts by mass or less, more preferably 30 parts by mass or less with respect to 100 parts by mass of water.

-Surface treatment method In this invention, the surface treatment of carbon black is performed by heating the said dispersion liquid by microwave irradiation under pressure. Since carbon black absorbs microwaves and generates heat, the surface of the carbon black becomes high temperature, and the oxidation reaction by the oxidizing agent can be promoted. On the other hand, when water is used as the solvent for the purpose of dissolving the oxidant well, the solvent (water) reaches the boiling point at 100 ° C., and it becomes difficult to irradiate microwaves any more. Therefore, in the present invention, by irradiating the microwave while applying pressure, it becomes possible to continue irradiating the microwave even when the solvent (water) becomes higher than the boiling point temperature under normal pressure. Since the temperature is high, the reaction time can be greatly shortened.
The pressure at the time of pressurization is preferably 0.5 to 10 MPa, more preferably 0.8 to 5 MPa, and particularly preferably 1 to 2 MPa.

The surface treatment method is not particularly limited as long as microwave irradiation can be performed under pressure. For example, a single mode cavity using a standing wave as disclosed in JP 2010-207735 A is used. In the microwave irradiation apparatus provided, a method of performing pressurization by further providing a back pressure valve or the like can be mentioned.
The single mode cavity has a cylindrical resonance space made of metal, and an electric field can be locally concentrated on the reaction tube by placing the reaction tube in the central portion of the cylinder. Surface treatment of carbon black (oxidation treatment) is carried out in a very short time by irradiating microwaves under pressure and in the presence of an oxidizing agent while continuously passing a dispersion liquid in which carbon black is dispersed in the reaction tube. ) Can be completed.
The temperature at which the dispersion and the carbon black in the dispersion reach by microwave irradiation is not particularly limited as long as the oxidation treatment of the carbon black can proceed satisfactorily, but is 50 to 300 ° C. Is preferred.

Hereinafter, an example of a microwave irradiation apparatus including a single mode cavity using a standing wave will be described with reference to FIG. 1 includes a microwave oscillator / controller 6, a TM010 cavity (cavity) 2, a liquid feed pump 3, and a reaction tube 7. The cavity 2 is a metal cavity resonator having a cylindrical space inside. The internal dimension of the cavity 2 can be appropriately set so that a standing wave called TM010 can be formed.
A reaction tube 7 made of a quartz glass tube, a fluororesin, or the like is arranged so as to penetrate the cavity 2 along the central axis of the cavity 2. When the microwave frequency to be irradiated is 2.4 to 2.5 GHz, the inner diameter of the reaction tube 7 is preferably 2.9 mm or less, and more preferably 0.1 to 1.5 mm. A liquid feed pump 3 is disposed on one side so that the carbon black dispersion 8 can flow through the reaction tube 7. On the opposite side of the reaction tube 7 from the direction in which the liquid feed pump 3 is disposed, a thermocouple is disposed as the thermometer 5 so that the temperature of the fluid can be measured. An electric field monitor 4 is also provided for measuring the electric field strength inside the cavity 2. Further, a back pressure valve (not shown) is disposed on the reaction tube 7 on the side opposite to the direction in which the liquid feed pump 3 is disposed, and the pressure in the reaction tube 7 is adjusted by the back pressure valve.

The microwave generated from the microwave oscillator / controller 6 is irradiated to the cylindrical cavity 2 through the microwave irradiation port 1. At this time, the microwave oscillation frequency or the inner diameter of the cylindrical cavity 2 is appropriately adjusted so that a TM010 standing wave can be formed inside the cavity 2.
The formation of the TM010 standing wave can be determined based on the signal from the electric field monitor 4. When the standing wave is not formed, the standing wave is formed by changing the microwave oscillation frequency oscillated from the microwave oscillator / controller 6 or adjusting the inner diameter of the cavity 2. Feedback control may be performed so that

In the present invention, it is preferable to use a microwave irradiation apparatus capable of uniformly and intensively irradiating the dispersion liquid with the microwave as shown in FIG.
As one of electromagnetic wave irradiation spaces with a structure that can concentrate an electric field, a method using a container that can stably form a specific standing wave using a space called a cavity resonator is known. When the electric field strength distribution of the TM010 standing wave formed in the body resonator (cavity) is examined, it can be seen that the electric field is concentrated at the center of the cylinder. Moreover, if the standing wave of TM010 is used, the electric field intensity on the center axis of the cylinder is constant regardless of the position. That is, by using a cavity resonator having a TM010 standing wave formed in a cylinder, a strong and uniform electric field is always applied to a tubular reactor disposed along the central axis of the cylinder. It becomes possible to irradiate the microwave. Although TM010 has been described above, a standing wave of TMmn0 (m is an integer of 0 or more and n is an integer of 1 or more) also has a place where the electric field concentrates in the radial direction of the cylinder, and is uniform in a portion parallel to the central axis. Since it has electric field strength, it can be used similarly. Further, although described with an electric field, since electromagnetic waves also have a heating action by a magnetic field, the same effect can be obtained even if a portion where the magnetic field is strong is used.

By using the microwave irradiation apparatus as described above, the carbon black dispersion 8 flowing in the reaction tube 7 can be heated extremely rapidly with the microwave energy irradiated intensively, and the carbon black instantaneously Can be oxidized.
The target carbon black oxidation treatment time is more than 0.005 seconds and less than about 60 seconds, and it is particularly preferable that the time is 0.01 to 10 seconds.
The temperature at which the dispersion liquid reaches by microwave irradiation is not particularly limited as long as it is equal to or higher than the temperature at which the oxidation treatment of carbon black proceeds well, but is generally 50 to 300 ° C.

The microwave irradiation apparatus used in the present invention is not limited to the apparatus shown in FIG. 1, and each configuration may be modified.
For example, as shown in FIG. 2, a plurality of (for example, 2 to 10) single mode cavities may be connected, and a hollow tube may communicate with the central axis thereof.
In the apparatus shown in FIG. 2, the microwave irradiation apparatus includes cavities 12 and 12 ′, a reaction tube 17 communicating with the cavities 12 and 12 ′, a liquid feed pump 13, a raw material liquid pool 14, a thermometer 15, a back pressure valve 18, and A liquid receiving pool 19 is provided. A microwave oscillator / controller and electric field monitor are not shown. The cavities 12 and 12 'are obtained by connecting four cavity resonators similar to the cavity 2 described above in the vertical direction. The cavity 12 is a combination of four single-mode cavities having a vertical length of 10 cm, and the cavity 12 ′ is a combination of four single-mode cavities having a vertical length of 1 cm.
With this configuration, it is possible to adjust the microwave irradiation time for the carbon black dispersion. When a plurality of single mode cavities are provided, the size of each single mode cavity may be the same or different.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited by this.

(Calculation method of the amount of carboxyl groups)
0.2 g of the surface-modified carbon black was weighed, 5 mL of 0.1 N NaHCO ₃ was added, and the reaction was allowed to stir under nitrogen for 6 hours. After the reaction, the liquid from which carbon was removed by filtration was titrated with 0.01 N HCl, and the amount of carboxyl group was calculated assuming that the amount of HCl required for titration corresponds to the amount of carboxyl group.

(Calculation method of phenolic OH group amount)
0.2 g of surface-modified carbon black was weighed, 5 mL of 0.1 N NaOH and 30 mL of distilled water were added, and the reaction was allowed to proceed with stirring under nitrogen for 6 hours. After the reaction, the solution was filtered to remove carbon and titrated with 0.01N HCl. The amount of HCl obtained by subtracting the amount required for the measurement in (1) from the amount of HCl required for titration corresponds to the phenolic OH group. As a result, the amount of phenolic OH group was calculated.

(Dispersion particle size of carbon black)
After adding 2 ml of 0.24% KOH aqueous solution to 20 mg of surface-modified carbon black and thoroughly grinding with an agate mortar, the dispersed particle size was measured using Microtrac (Nikkiso Co., Ltd.).

[Example 1]
The surface of carbon black was prepared by preparing a dispersion in which carbon black (trade name: # 960, average particle size: 16 nm, manufactured by Mitsubishi Chemical Corporation) was dispersed in an aqueous solution of 3 parts by mass of sodium persulfate and heating the dispersion. Modified.
Specifically, a microwave irradiation apparatus having a configuration as shown in FIG. 1 was used for heating. Quartz with an outer diameter of 1 mm, an outer diameter of 3 mm, and a length of 12 cm so as to penetrate the central axis of a TM010 single-mode cavity made of cylindrical aluminum having a vertical diameter of 10 cm and having an inner diameter designed based on a microwave frequency of 2.4 to 2.5 GHz. A glass tube was installed, and both ends of the quartz tube were connected to a 1/16 inch pipe made of SUS316 by a stainless steel pressure joint having a Viton O-ring seal. A 100 W microwave generator, an electric field monitor, and a radiation thermometer are connected to the cavity, and the oscillation frequency of the microwave is always applied so that the standing wave of TM010 can be formed so that the reaction solution has a predetermined temperature. Microwave power was controlled. Thermocouple thermometer installed in 1/16 inch pipe made of SUS316 connected to microwave irradiation part and back pressure valve installed at the outlet part after that (not shown), liquid temperature measurement And back pressure can be adjusted.
While adjusting the system internal pressure to 1.5 MPa with a back pressure valve, the dispersion was circulated through the glass tube at 2 mL / min with a plunger pump, irradiated with microwaves at an output of 100 W, and continuously from the outlet. The discharged liquid was received in a glass beaker while cooling with ice, and the dispersion was recovered. At this time, the temperature measured with a thermocouple was 180 ° C., and the time during which the dispersion was irradiated with microwaves was 2.3 seconds.
The resulting dispersion was washed with a dialysis membrane until the electrical conductivity was 2 mS / cm or less, and then vacuum-dried at 60 ° C. to obtain surface-modified carbon black.
The surface-modified carbon black obtained had a COOH group of 208 μmol / g and a phenolic OH group of 608 μmol / g.
The dispersed particle size was measured to be 100 nm.
From this, it was confirmed that a surface-modified carbon black easily dispersed in water was obtained in spite of a very short reaction time.

[Comparative Example 1]
A dispersion was prepared by dispersing carbon black (trade name: # 960, average particle size: 16 nm, manufactured by Mitsubishi Chemical Corporation) in an aqueous solution of 3 parts by mass of sodium persulfate.
The dispersion was passed through the microwave irradiation apparatus of Example 1 that was not pressurized at 9.2 mL / min, and was irradiated with microwaves at an output of 100 W. At this time, the temperature measured with the thermocouple was 80 degreeC. The dispersion discharged at the outlet was received in a glass beaker while cooling with ice. This dispersion was further subjected to the same microwave irradiation treatment three times. The total microwave irradiation time was 2.3 seconds.
The resulting dispersion was washed with a dialysis membrane until the electrical conductivity reached 2 mS / cm, and then vacuum-dried at 60 ° C. to obtain surface-modified carbon black.
In the obtained surface-modified carbon black, no COOH group was detected, and the phenolic OH group was 180 μmol / g.
The dispersed particle size was measured, but the particles were agglomerated and many particles of 1000 nm or more existed.
From this, it was confirmed that surface-modified carbon black easily dispersed in water was not obtained.

  The present invention can provide a method capable of producing surface-modified carbon black that is easily dispersed in water in a short time.

  DESCRIPTION OF SYMBOLS 1 ... Microwave irradiation port, 2 ... TM0101 cavity, 3, 13 ... Liquid feed pump, 4 ... Electric field monitor, 5, 15 ... Thermometer, 6 ... Microwave oscillator and controller, 7, 17 ... Reaction tube, 8 ... Carbon black dispersion, 12, 12 '... cavity, 14 ... raw material liquid pool, 18 ... back pressure valve, 19 ... liquid receiving pool

Claims (4)

A surface-treated carbon black characterized in that a carbon black, an oxidizing agent, and a water-containing dispersion are heated by microwave irradiation under a pressure of 0.5 to 10 MPa to perform a surface treatment of the carbon black. Manufacturing method.   The method for producing a surface-treated carbon black according to claim 1, wherein the heating time is less than 60 seconds.   The method for producing surface-treated carbon black according to claim 1 or 2, wherein the microwave irradiation uses a single mode cavity.   The manufacturing method of the surface treatment carbon black as described in any one of Claims 1-3 whose manufactured surface treatment carbon black is for inkjet inks.

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