Carbon black dispersion liquid and method for producing the same

Abstract

To provide a carbon black dispersion liquid that exhibits superior carbon black dispersibility without substantially using a dispersant such as a surfactant or a polymer dispersing agent.SOLUTION: A carbon black dispersion liquid contains carbon black having its average primary particle diameter of 5 to 45 nm, alkali, and a hydrophilic polar solvent, has a pH of the carbon black of 8.0 or less and a content of the alkali of 0.5 to 5 pts.mass based on 100 pts.mass of the carbon black, and does not contain a dispersion liquid for dispersing the carbon black.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a carbon black dispersion liquid and a method for producing the same.

Background Art

[0002] Carbon materials such as carbon black are materials that exhibit various properties such as electrical conductivity and heat conductivity, and methods for utilizing these properties in a wide range of fields have been studied. For example, paying attention to electrical properties, thermal properties, and properties as a filler, it has been studied to use carbon black in antistatic agents, conductive materials, plastic reinforcing materials, semiconductors, battery electrodes, and cathode rays of displays.

[0003] For these applications, a carbon black dispersion liquid is required in which the dispersibility of carbon black is good and the dispersibility is maintained over a long period of time. However, nano-sized carbon materials have a high surface energy and are prone to aggregation due to the strong van der Waals force acting. Therefore, various studies have been conducted to stably disperse carbon black in a liquid medium.

[0004] For example, a pigment dispersion liquid has been proposed in which a (meth)acrylic polymer having a carboxy group neutralized with an alkali is used as a dispersant and carbon black is dispersed in a liquid medium containing a water-soluble organic solvent (Patent Document 1). Also, a dispersion liquid for forming a conductive binder layer of an electrode, which contains carbon black, various surfactants, a polymer-based dispersant, and a dispersion medium containing water, has been proposed (Patent Document 2). Further, a dispersion liquid for forming an active material layer of an electrode, which contains carbon black, a dispersant containing two or more copolymers, and a dispersion medium such as N-methylpyrrolidone, has been proposed (Patent Document 3).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] In order to stably disperse carbon black in a liquid medium, dispersants such as various surfactants and polymer dispersants are usually used as proposed in Patent Documents 1 to 3. However, these dispersants for dispersing carbon black in a liquid medium may become impurities when manufacturing articles such as electrode layers and inks using the obtained dispersion liquid. For this reason, it has been demanded to reduce the content of these dispersants or to disperse carbon black in a liquid medium without using these dispersants. However, it has been difficult to disperse carbon black in a liquid medium without substantially using dispersants such as surfactants and polymer dispersants.

[0007] The present invention has been made in view of such problems of the prior art, and the problem to be solved is to provide a carbon black dispersion liquid having excellent dispersibility of carbon black without substantially using dispersants such as surfactants and polymer dispersants. Another problem to be solved by the present invention is to provide a method for producing a carbon black dispersion liquid that can easily obtain a carbon black dispersion liquid having excellent dispersibility of carbon black without substantially using dispersants such as surfactants and polymer dispersants.

Means for Solving the Problems

[0008] That is, according to the present invention, the following carbon black dispersion liquid is provided. [1] A carbon black dispersion liquid that contains carbon black with an average primary particle diameter of 5 to 45 nm, an alkali, and a hydrophilic polar solvent, wherein the pH of the carbon black is 8.0 or less, the content of the alkali with respect to 100 parts by mass of the carbon black is 0.5 to 5 parts by mass, and does not contain a dispersant for dispersing the carbon black. [2] The carbon black dispersion liquid according to [1] above, wherein the content of the carbon black is 5 to 15% by mass. [3] The carbon black dispersion liquid according to [1] or [2] above, wherein the alkali is at least one inorganic alkali selected from the group consisting of sodium hydroxide, lithium hydroxide, and ammonia, or at least one organic alkali selected from the group consisting of triethanolamine, diethanolamine, and 2-amino-2-methyl-1-propanol. [4] The carbon black dispersion liquid according to any one of [1] to [3] above, wherein the hydrophilic polar solvent is at least one selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, and N-methyl-2-pyrrolidone.

[0009] Further, according to the present invention, a method for producing a carbon black dispersion liquid as shown below is provided. [5] A step of subjecting a raw material mixture containing carbon black with an average primary particle diameter of 5 to 45 nm, an alkali, and a hydrophilic polar solvent to a dispersion treatment to obtain a carbon black dispersion liquid that does not contain a dispersant for dispersing the carbon black, wherein the pH of the carbon black is 8.0 or less, and in the raw material mixture, the content of the alkali with respect to 100 parts by mass of the carbon black is 0.5 to 5 parts by mass. A method for producing a carbon black dispersion liquid. [6] The method for producing a carbon black dispersion liquid according to [5] above, wherein the content of the carbon black in the raw material mixture is 5 to 15% by mass. [7] The method for producing the carbon black dispersion according to [5] or [6] above, wherein the alkali is at least one inorganic alkali selected from the group consisting of sodium hydroxide, lithium hydroxide, and ammonia, or at least one organic alkali selected from the group consisting of triethanolamine, diethanolamine, and 2-amino-2-methyl-1-propanol. [8] The method for producing the carbon black dispersion according to any one of [5] to [7] above, wherein the hydrophilic polar solvent is at least one selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, and N-methyl-2-pyrrolidone. [Advantages of the Invention]

[0010] According to the present invention, a carbon black dispersion excellent in the dispersibility of carbon black can be provided without substantially using a dispersant such as a surfactant or a polymer dispersant. Further, according to the present invention, a method for producing a carbon black dispersion capable of easily obtaining a carbon black dispersion excellent in the dispersibility of carbon black without substantially using a dispersant such as a surfactant or a polymer dispersant can be provided. [Embodiments for Carrying Out the Invention]

[0011] [Carbon Black Dispersion] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. One embodiment of the carbon black dispersion of the present invention contains carbon black having an average primary particle diameter of 5 to 50 nm, an alkali, and a hydrophilic polar solvent, and does not contain a dispersant for dispersing the carbon black. The pH of the carbon black is 8.0 or less. And in the carbon black dispersion, the content of the alkali with respect to 100 parts by mass of the carbon black is 0.5 to 5 parts by mass. Hereinafter, the details of the carbon black dispersion of this embodiment will be described.

[0012] The carbon black dispersion of this embodiment does not contain a dispersant for dispersing carbon black. "Does not contain a dispersant" means that it does not substantially contain a dispersant in an amount that contributes to the dispersion of carbon black. Examples of the dispersant include various surfactants and polymer dispersants such as polymers.

[0013] When attempting to disperse carbon black without using the above dispersant in a liquid medium (dispersion medium) mainly composed of a hydrophilic polar medium such as N-methyl-2-pyrrolidone or dimethyl sulfoxide, carbon black tends to aggregate, and it is difficult to obtain a dispersion with good dispersibility. In contrast, the present inventors have found that by containing an alkali such as sodium hydroxide in a predetermined ratio with respect to carbon black, it is possible to improve the dispersibility of carbon black without substantially using a dispersant, and thus have arrived at the present invention.

[0014] (Carbon black) Examples of carbon black include acetylene black, furnace black, thermal black, and ketjen black. Physical property values such as the structure, oil absorption amount, and specific surface area of carbon black are not particularly limited, and conventionally known carbon black can be used.

[0015] The average primary particle size of the carbon black is 5 to 45 nm, preferably 5 to 40 nm, and more preferably 5 to 20 nm. If the average primary particle size of the carbon black is outside the above range, it becomes difficult to obtain a carbon black dispersion with excellent dispersibility. The "average primary particle size" of carbon black in this specification means the cumulative 50% particle size (median diameter (D50)) in the volume-based particle size distribution.

[0016] The pH of the carbon black is 8.0 or less, preferably 7.5 or less, and more preferably 7.0 or less. If the pH of the carbon black exceeds 8.0, it becomes difficult to obtain a carbon black dispersion with excellent dispersibility even when an alkali is used.

[0017] The pH of carbon black is a physical property value measured according to the method shown below. First, 10 mg of water is added to 1 g of carbon black, and after boiling for 15 minutes and cooling to room temperature (25 °C), the supernatant is removed by the inclination method or the centrifugation method to obtain a sludge. Then, the electrode of a glass electrode pH meter is inserted into the obtained sludge, and it can be measured according to JIS 28802.

[0018] The content of carbon black in the carbon black dispersion is preferably 5 to 15% by mass, and more preferably 5 to 10% by mass. When the content of carbon black exceeds 15% by mass, the dispersibility of carbon black may slightly decrease.

[0019] (Alkali) As the alkali, inorganic alkalis or organic alkalis can be used. Examples of inorganic alkalis include lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, calcium oxide, lithium carbonate, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, magnesium carbonate, calcium carbonate, and ammonia. Examples of organic alkalis include triethanolamine, diethanolamine, 2-amino-2-methyl-1-propanol, triethylamine, and dimethylaminoethanol. These alkalis include hydrates of the alkalis. Among them, as the alkali, it is preferable to use at least one inorganic alkali selected from the group consisting of sodium hydroxide, lithium hydroxide, and ammonia, or at least one organic alkali selected from the group consisting of triethanolamine, diethanolamine, and 2-amino-2-methyl-1-propanol.

[0020] The content of the alkali with respect to 100 parts by mass of carbon black is 0.5 to 5 parts by mass, preferably 0.8 to 3.0 parts by mass, and more preferably 1.0 to 2.0 parts by mass. When the content of the alkali with respect to 100 parts by mass of carbon black is outside the above range, it becomes difficult to obtain a carbon black dispersion liquid having excellent dispersibility.

[0021] (Liquid medium (dispersion medium)) The carbon black dispersion liquid of the present embodiment contains a hydrophilic polar solvent as a liquid medium (dispersion medium) for dispersing carbon black. The liquid medium may contain a small amount of water. Examples of the hydrophilic polar solvent include alcohols such as methanol, ethanol, and isopropyl alcohol; polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin; ethers such as tetrahydrofuran; glycol ethers such as diethylene glycol, triethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether; glycol ether esters such as diethylene glycol monomethyl ether acetate; amides such as pyrrolidone, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide; urea-based solvents such as tetramethylurea and dimethyl 1,3-imidazolidinone; sulfur-containing solvents such as dimethyl sulfoxide and sulfolane; ionic liquids such as 1-ethyl-3-methylimidazolium chloride; and the like. Among them, the hydrophilic polar solvent is preferably at least one selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, and N-methyl-2-pyrrolidone.

[0022] The carbon black dispersion of this embodiment is one in which carbon black is well dispersed in the state of primary particles without substantially forming coarse aggregates. Therefore, the carbon black dispersion of this embodiment takes advantage of such characteristics and is useful as a material for manufacturing products such as paints, inks, coating agents, resin molding materials, conductive materials, heat conductive materials, and antistatic materials.

[0023] <Method for manufacturing carbon material dispersion> The carbon material dispersion of this embodiment can be manufactured, for example, according to the method shown below. That is, one embodiment of the method for manufacturing the carbon material dispersion of the present invention is to disperse a raw material mixture containing carbon black having an average primary particle diameter of 5 to 50 nm, an alkali, and a hydrophilic polar solvent to obtain a carbon black dispersion containing no dispersant for dispersing carbon black. The pH of the carbon black is 8.0 or less as described above. And in the raw material mixture, the content of the alkali with respect to 100 parts by mass of the carbon black is set to 0.5 to 5 parts by mass. Note that the alkali can be used in the state of an aqueous solution of the alkali. By such a manufacturing method, the carbon black dispersion of this embodiment excellent in the dispersibility of carbon black can be obtained.

[0024] When dispersing the raw material mixture, for example, methods using a magnetic stirrer agitation, a dissolver agitation, kneading with a three-roll mill, ultrasonic dispersion, bead mill dispersion, an emulsifying device, a homogenizer, etc. can be used. From the simplicity of the process, after stirring with a magnetic stirrer, a dissolver, a homogenizer, etc., it is preferable to disperse with a bead mill using a media disperser in which small-diameter beads coexist.

Examples

[0025] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In addition, "parts" and "%" in the examples and comparative examples are based on mass unless otherwise specified.

[0026] <Preparation of Carbon Black> Carbon blacks CB1 to 11 of the types shown in Table 1 were prepared.

[0027] TIFF2025107901000001.tif97170

[0028] <Production of Carbon Black Dispersion> (Example 1) 10 parts of CB1, 89.5 parts of N-methyl-2-pyrrolidone (NMP), and 0.5 part of a 40% aqueous sodium hydroxide (NaOH) solution were mixed and stirred using a dissolver for 30 minutes until no lumps of carbon black remained. Thereafter, using a media disperser, dispersion treatment was carried out using zirconia beads (diameter 1.0 mm) to obtain a carbon black dispersion.

[0029] (Examples 2 to 15, Comparative Examples 1 to 17) Carbon black dispersions were obtained in the same manner as in Example 1 described above, except that the formulations shown in Tables 2-1 to 2-3 were used. In Tables 2-1 to 2-3, as the "polymeric dispersant", the product name "BYK-2200" (manufactured by BYK Chemie) was used.

[0030] TIFF2025107901000002.tif153170

[0031] TIFF2025107901000003.tif172170

[0032] TIFF2025107901000004.tif172170

[0033] <Evaluation> (Measurement and Evaluation of Viscosity) The viscosity of the carbon black dispersion prepared using a B-type viscometer was measured at 25°C. For carbon black dispersions with a carbon black concentration exceeding 10%, NMP was added and diluted so that the carbon black concentration became 10%, and then the viscosity was measured. Then, the viscosity of the carbon black dispersion was evaluated according to the evaluation criteria shown below. The results are shown in Table 3. ○: The viscosity was less than 100 mPa·s. ×: The viscosity was 100 mPa·s or more.

[0034] (Measurement and Evaluation of Dispersion Particle Size) Using a particle size distribution measuring device based on the dynamic light scattering method, the dispersion particle size (median diameter; D50 (nm)) of carbon black in the prepared carbon black dispersion was measured. The results are shown in Table 3. Also, the dispersion particle size of carbon black was evaluated according to the evaluation criteria shown below. The results are shown in Table 3. ○: The dispersion particle size was less than 180 nm. △: The dispersion particle size was 180 nm or more and less than 500 nm. ×: The dispersion particle size was 500 nm or more.

[0035] (Measurement of Absorbance, Calculation and Evaluation of Absorbance Ratio) Using a spectrophotometer, the absorbance (at a wavelength of 380 nm: A380, at a wavelength of 780 nm: A780) of the carbon black dispersion prepared at 25°C was measured. For carbon black dispersions with a carbon black concentration exceeding 10%, NMP was added and diluted so that the carbon black concentration became 10%, and then the absorbance was measured. The measurement results and the absorbance ratio (A380 / A780) calculated from the measured values are shown in Table 3. Then, the absorbance ratio of the carbon black dispersion was evaluated according to the evaluation criteria shown below. The results are shown in Table 3. Note that the larger the value of the absorbance ratio, the better the dispersibility of the carbon black can be judged. ○: The absorbance ratio was 1.5 or more. ×: The absorbance ratio was less than 1.5.

[0036] TIFF2025107901000005.tif233170

Industrial Applicability

[0037] The carbon black dispersion of the present invention is useful as a material for manufacturing products such as paints, inks, coating agents, resin molding materials, conductive materials, heat conductive materials, and antistatic materials, for example.

Claims

1. A carbon black dispersion liquid containing carbon black having an average primary particle diameter of 5 to 45 nm, an alkali, and a hydrophilic polar solvent, wherein the pH of the carbon black is 8.0 or less, the content of the alkali with respect to 100 parts by mass of the carbon black is 0.5 to 5 parts by mass, and the carbon black dispersion liquid does not contain a dispersant for dispersing the carbon black.

2. The carbon black dispersion liquid according to claim 1, wherein the content of the carbon black is 5 to 15% by mass.

3. The alkali is at least one inorganic alkali selected from the group consisting of sodium hydroxide, lithium hydroxide, and ammonia, or the carbon black dispersion liquid according to claim 1, which is at least one organic alkali selected from the group consisting of triethanolamine, diethanolamine, and 2-amino-2-methyl-1-propanol.

4. The carbon black dispersion liquid according to any one of claims 1 to 3, wherein the hydrophilic polar solvent is at least one selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, and N-methyl-2-pyrrolidone.

5. A step of dispersing a raw material mixture containing carbon black having an average primary particle diameter of 5 to 45 nm, an alkali, and a hydrophilic polar solvent to obtain a carbon black dispersion liquid that does not contain a dispersant for dispersing the carbon black, wherein the pH of the carbon black is 8.0 or less, and a method for producing a carbon black dispersion liquid, wherein in the raw material mixture, the content of the alkali with respect to 100 parts by mass of the carbon black is 0.5 to 5 parts by mass.

6. The method for producing a carbon black dispersion liquid according to claim 5, wherein the content of the carbon black in the raw material mixture is 5 to 15% by mass.

7. The alkali is at least one inorganic alkali selected from the group consisting of sodium hydroxide, lithium hydroxide, and ammonia, or the method for producing a carbon black dispersion liquid according to claim 5, which is at least one organic alkali selected from the group consisting of triethanolamine, diethanolamine, and 2-amino-2-methyl-1-propanol.

8. The method for producing a carbon black dispersion according to any one of claims 5 to 7, wherein the hydrophilic polar solvent is at least one selected from the group consisting of dimethyl sulfoxide, dimethylacetamide, and N-methyl-2-pyrrolidone.

Images