Carbon nanotube dispersion liquid, use of carbon nanotube dispersion liquid, and coating film

Abstract

To provide a carbon nanotube dispersion having a high concentration of carbon nanotubes and excellent viscosity stability.SOLUTION: The carbon nanotube dispersion liquid contains multi-walled carbon nanotubes, an aqueous medium and a dispersant. The multi-walled carbon nanotubes have an average length of 2 μm or more and 40 μm or less and an average diameter of 5 nm or more and 150 nm or less, the dispersant is a polymer dispersant or the like, and the content of the dispersant is in a predetermined range, and when a dry coating film having a thickness of 1 μm is formed using a coating liquid containing the carbon nanotube dispersion and a binder resin so that the content of the multi-walled carbon nanotubes in the dry coating film is 40 mass%, the surface resistivity of the dry coating film is 1.0 * 10 3 Ω / sq or less, the dry film has a thermal diffusivity of 0. 30mm2 / s or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a carbon nanotube dispersion liquid having a high concentration of carbon nanotubes and a low viscosity. [Background technology]

[0002] Carbon materials such as carbon nanotubes, fullerenes, carbon black, and graphene have excellent properties such as electrical conductivity, thermal conductivity, and mechanical strength, and are expected to be used in a variety of applications. There is a growing demand for carbon nanotube dispersions that can easily coat these materials. However, because carbon nanotubes are nanosized, their specific surface area is very large and their cohesive force is strong, making it difficult to prepare high-concentration, low-viscosity dispersions.

[0003] Various proposals have been made to disperse carbon nanotubes in a dispersion medium at high concentrations and low viscosity. For example, the preparation of an aqueous dispersant for carbon nanotubes consisting of a polycondensation-type aromatic surfactant, a polymerization-type aromatic surfactant, an aromatic nonionic surfactant, or a combination of an aromatic nonionic surfactant and an ionic surfactant has been proposed (Patent Document 1). Furthermore, the preparation of a dispersion with high uniformity and dispersion stability by inhibiting aggregation through control of the distribution of carbon nanotube outer diameters has been proposed (Patent Document 2). The preparation of a carbon nanotube dispersion using a nonionic surfactant has also been proposed (Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-263608 [Patent Document 2] Japanese Patent Application Publication No. 2017-206412 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-50780 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the examples of both patent documents, only dispersions with a carbon nanotube concentration of 20% by mass or less in an aqueous medium are presented. In particular, for the dispersions with a carbon nanotube concentration of 15% by mass or more described in Patent Document 3, only the dispersion state, viscosity, and dispersion stability are evaluated, and no sample preparation or evaluation for specific applications is performed. The present invention has been made in view of the above-mentioned state of the art, and has an object to provide a carbon nanotube dispersion liquid having a high concentration of carbon nanotubes and excellent viscosity stability. [Means for solving the problem]

[0006] That is, according to the present invention, there are provided the following carbon nanotube dispersion, use of the carbon nanotube dispersion, and coating film. [1] A carbon nanotube dispersion containing multi-walled carbon nanotubes, an aqueous medium, and a dispersant, the content of the multi-walled carbon nanotubes is 15% by mass or more and 30% by mass or less with respect to the total amount of the carbon nanotube dispersion, The multi-walled carbon nanotubes have an average length of 2 μm or more and 40 μm or less and an average diameter of 5 nm or more and 150 nm or less, the dispersant is at least one of a surfactant, a cellulose derivative, and a polymer dispersant, The content of the dispersant is 10 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the multi-walled carbon nanotubes, When a dry film having a thickness of 1 μm is formed using a coating liquid containing the carbon nanotube dispersion and a binder resin so that the content of the multi-walled carbon nanotubes in the dry film is 40 mass %, the surface resistivity of the dry film is 1.0 × 10 3 Ω / sq or less, and the thermal diffusivity of the dry coating is 0.30 mm 2 / s or more. [2] The carbon nanotube dispersion liquid according to [1], wherein the polymer dispersant is a polymer having a structural unit (1) derived from (meth)acrylonitrile and a structural unit (2) derived from (meth)acrylic acid. [3] The carbon nanotube dispersion liquid according to [2], wherein the polymer dispersant is a polymer having 50% by mass or more and 80% by mass or less of the structural unit (1) and 20% by mass or more and 50% by mass or less of the structural unit (2), at least a portion of which has a carboxy group neutralized with an alkali (where the total of the structural unit (1) and the structural unit (2) is 100% by mass). [4] The polymer comprises a polymer block A having 60% by mass or more and 95% by mass or less of structural units (1-A) derived from acrylonitrile and 5% by mass or more and 40% by mass or less of structural units (2-A) derived from methacrylic acid (wherein the total of the structural units (1-A) and the structural units (2-A) is 100% by mass); and a polymer block B having 10% by mass or more and 70% by mass or less of structural units (1-B) derived from acrylonitrile and 30% by mass or more and 90% by mass or less of structural units (2-B) derived from methacrylic acid (wherein the total of the structural units (1-B) and the structural units (2-B) is 100% by mass), the number average molecular weight of the polymer block A is 10,000 or more and 100,000 or less, and the molecular weight distribution is 1.8 or less; The carbon nanotube dispersion liquid according to [3], wherein the number average molecular weight of the polymer block B is 3,000 or more and 200,000 or less. [5] The carbon nanotube dispersion liquid according to [1], wherein the polymer dispersant is a polymer having a number average molecular weight of 5,000 or more and 20,000 or less, comprising 5% by mass or more and 40% by mass or less of structural units (M1) derived from Monomer 1, which is at least one basic monomer selected from the group consisting of 2-vinylpyridine, 4-vinylpyridine, and 1-vinylimidazole or a quaternary ammonium salt thereof; 50% by mass or more and 80% by mass or less of structural units (M2) derived from Monomer 2 represented by the following general formula (1); and 0.5% by mass or more and 40% by mass or less of structural units (M3) derived from Monomer 3 copolymerizable with Monomer 1 and Monomer 2:

[0007] [ka]

[0008] (In the general formula (1), R1 represents a hydrogen atom or a methyl group, A represents O or NH, X represents an ethylene group or a propylene group, Y represents O, NHCOO, or NHCONH, R2 each independently represents a hydrogen atom or a methyl group, n represents the average number of repeating units of 20 to 100, and R3 represents a hydrogen atom or a methyl group. However, when R2 is a hydrogen atom, the number of repeating units, n, H is the total number of repeating units n T is more than half of the

[0009] [6] The carbon nanotube dispersion liquid according to [5], wherein the monomer 3 contains α-methylstyrene, and the content of the structural unit derived from the α-methylstyrene in the polymer is 0.5% by mass or more and 5% by mass or less. [7] The carbon nanotube dispersion liquid according to [5], wherein the monomer 3 contains (meth)acrylic acid, and the content of the structural unit derived from the (meth)acrylic acid in the polymer is 0.5% by mass or more and 30% by mass or less. [8] The carbon nanotube dispersion liquid according to any one of [5] to [7], wherein the quaternary ammonium salt of the basic monomer is a benzyl chloride salt, a naphthyl methyl chloride salt, or an anthracenyl methyl chloride salt of the basic monomer. [9] The carbon nanotube dispersion liquid according to [1], wherein the cellulose derivative is carboxymethyl cellulose or carboxymethyl cellulose sodium salt.

[10] The carbon nanotube dispersion liquid according to any one of [1] to [9], wherein the content of the multi-walled carbon nanotubes is 21% by mass or more and 30% by mass or less.

[11] The carbon nanotube dispersion liquid according to any one of [1] to

[10] , further comprising a dye derivative having an acidic functional group, the content of the dye derivative being 0.01 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the multi-walled carbon nanotubes.

[12] The carbon nanotube dispersion according to any one of [1] to

[11] , further comprising a binder resin, the content of the binder resin being 10 parts by mass or more and 300 parts by mass or less per 100 parts by mass of the multi-walled carbon nanotubes.

[13] Use of the carbon nanotube dispersion liquid according to any one of [1] to

[12] for producing any one of products including heat transfer materials, paints, inks, coating agents, resin molding materials, conductive materials, thermally conductive materials, and antistatic materials.

[14] Use of the carbon nanotube dispersion liquid according to any one of [1] to

[12] for producing a product, such as a battery material or a mechanical part, having a coating film formed from the carbon nanotube dispersion liquid.

[15] A coating film comprising the carbon nanotube dispersion liquid according to any one of [1] to

[12] , which is an antistatic coating film, a heat generating body, a heat conductor, a temperature sensitive coating film, a paint for sensors, a heat dissipating paint, an electrode material, or a paint for electromagnetic wave shielding.

[16] The coating film according to

[15] , wherein the coating film is baked at 150°C or higher and 600°C or lower. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a carbon nanotube dispersion liquid having a high carbon nanotube concentration and excellent viscosity stability. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Carbon nanotube dispersion> Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. A carbon nanotube dispersion according to this embodiment contains multi-walled carbon nanotubes, an aqueous medium, and a dispersant, and the multi-walled carbon nanotube content is 15% by mass or more and 30% by mass or less, and the dispersant is at least one of a cellulose derivative and a polymer dispersant. The multi-walled carbon nanotubes have an average length of 2 μm or more and 40 μm or less and an average diameter of 5 nm or more and 150 nm or less. Hereinafter, the carbon nanotube dispersion will also be simply referred to as a "dispersion." According to this embodiment, it is possible to easily obtain a carbon nanotube dispersion liquid that exhibits good performance when used as a heat transfer material, has low viscosity, and is excellent in stability, in which multi-walled carbon nanotubes are dispersed at a high concentration, and by achieving a high concentration, it is possible to provide a carbon nanotube dispersion liquid that has excellent transportability and whose concentration can be adjusted by dilution.

[0012] <Multi-walled carbon nanotubes> In the technical field, carbon nanotubes (hereinafter also referred to as "CNTs") refer to carbon materials in which a single graphite layer has a cylindrical structure. CNTs with a single cylindrical structure are typically classified as single-walled CNTs, CNTs with two cylindrical layers as double-walled CNTs, and CNTs with three or more cylindrical layers as multi-walled CNTs. In conductive coatings containing CNTs, increasing the number of CNT layers typically improves conductivity. In the dispersion according to this embodiment, the multi-walled CNTs preferably have 5 to 100 walls, more preferably 10 to 50 walls. If the number of walls of the multi-walled CNTs is less than the lower limit, the conductivity of the resulting coating may be reduced. Therefore, by using the dispersion according to this embodiment containing multi-walled CNTs with a number of walls within the above range, a coating with high conductivity can be formed. The carbon nanotubes may be doped with metals or metal salts such as platinum and palladium. The carbon nanotubes may be surface-modified by oxidation treatment, plasma treatment, radiation treatment, corona treatment, coupling treatment, or the like.

[0013] In the dispersion according to this embodiment, the average length of the multi-walled CNTs must be in the range of 2 μm to 40 μm, and more preferably in the range of 4 μm to 15 μm. Furthermore, the average thickness (i.e., average diameter) of the multi-walled CNTs must be in the range of 5 nm to 150 nm, and more preferably in the range of 20 nm to 60 nm. If the average length and average thickness of the multi-walled CNTs are below the lower limit, the conductivity of the resulting coating may be reduced. If the average length and average thickness of the multi-walled CNTs exceed the upper limit, intermolecular aggregation may occur, potentially creating problems with the conditions for uniform dispersion. Therefore, by using the dispersion according to this embodiment containing multi-walled CNTs having an average length and average thickness within the above range, a coating with high conductivity can be formed.

[0014] <Aqueous medium> As the aqueous medium, water or a mixed solvent of water and a water-soluble organic solvent can be used. Examples of water-soluble organic solvents 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-methylpyrrolidone, 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; and ionic liquids such as 1-ethyl-3-methylimidazolium chloride. Of these, alcohols and N-methylpyrrolidone (NMP) are preferred.

[0015] <Dispersant> The dispersant is a component for dispersing the carbon material in a liquid medium. It is necessary to use at least one of a surfactant, a cellulose derivative, and a polymer dispersant as the dispersant. Examples of dispersants that can be used include anionic, cationic, nonionic, and amphoteric surfactants, cellulose derivatives, and polymer dispersants. Among these, it is preferable to use a cellulose derivative or a graft-type or block-type polymer dispersant. The block-type polymer dispersant can be a polymer having a structural unit (1) derived from (meth)acrylonitrile and a structural unit (2) derived from (meth)acrylic acid.

[0016] When the liquid medium is water or a mixed solvent (aqueous medium) of water and a water-soluble organic solvent, examples of cellulose derivatives used as dispersants include methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, and metal salts thereof. Among these, carboxymethyl cellulose and carboxymethyl cellulose sodium salt are preferred. Furthermore, it is preferable that the cellulose derivative has a viscosity of 20 mPa·s or more and 500 mPa·s or less in a 1% by mass aqueous solution and a degree of etherification of 0.5 or more and 0.9 or less. The use of such cellulose derivatives allows for better dispersion of carbon nanotubes and improved storage stability.

[0017] When the liquid medium is water or a mixed solvent (aqueous medium) of water and a water-soluble organic solvent, the polymer dispersant used as the dispersant is preferably a polymer having a structural unit (1) derived from (meth)acrylonitrile and a structural unit (2) derived from (meth)acrylic acid, and preferably a polymer substantially composed only of the structural unit (1) derived from (meth)acrylonitrile and the structural unit (2) derived from (meth)acrylic acid. In addition, the polymer dispersant is preferably a polymer having carboxy groups at least partially neutralized with an alkali.

[0018] The structural unit (1) has a cyano group (-CN) derived from (meth)acrylonitrile. Therefore, the triple bond of the cyano group interacts with the surface of the carbon material, and the polymer dispersant is electronically adsorbed to the carbon material. Furthermore, the structural unit (2) has a carboxy group derived from (meth)acrylic acid. Therefore, by neutralizing and ionizing at least a portion of this carboxy group with an alkali, the polymer dispersant can be dissolved in an aqueous medium. By using a polymer containing these structural units (1) and (2) as a dispersant, it is possible to finely disperse carbon materials in an aqueous medium for an extended period of time.

[0019] The proportion of the (meth)acrylonitrile-derived structural unit (1) in the polymer is preferably 50% by mass or more and 80% by mass or less, more preferably 55% by mass or more and 75% by mass or less. The proportion of the (meth)acrylic acid-derived structural unit (2) in the polymer is preferably 20% by mass or more and 50% by mass or less, more preferably 25% by mass or more and 45% by mass or less. The sum of the structural units (1) and (2) is taken as 100% by mass. If the proportion of the structural unit (2) in the polymer is less than 20% by mass, the polymer tends to have insufficient water solubility. On the other hand, if the proportion of the structural unit (2) in the polymer is more than 50% by mass, the polymer tends to have excessively high water solubility. As a result, the viscosity of the carbon material dispersion becomes excessively high, and the amount of hydrophilic carboxyl groups is large, which may reduce the water resistance of the coating film formed.

[0020] The polymer dispersant (polymer) may further contain other structural units in addition to the structural units (1) and (2). Examples of monomers constituting the other structural units include conventionally known styrene-based monomers and (meth)acrylate-based monomers. Among these, it is preferable to use a monomer that does not contain a structure that is easily hydrolyzed, such as an ester bond or an amide bond. Examples of such monomers include styrene, vinyl naphthalene, vinyl toluene, vinyl biphenyl, and vinyl alcohol.

[0021] The polymer used as the polymer dispersant may be either a random copolymer or a block copolymer. However, in the case of a random copolymer, the hydrophilic and hydrophobic groups are randomly present, which may slightly reduce the effect as a dispersant. Furthermore, when a highly hydrophilic binder resin is further used, the effect of the binder resin may be more pronounced. For this reason, the polymer used as the polymer dispersant is preferably a block copolymer.

[0022] The polymer dispersant is preferably an AB block copolymer comprising a polymer block A having structural units (1-A) derived from acrylonitrile and structural units (2-A) derived from methacrylic acid, and a polymer block B having structural units (1-B) derived from acrylonitrile and structural units (2-B) derived from methacrylic acid. Polymer block A is preferably a polymer block substantially composed of structural units (1-A) derived from acrylonitrile and structural units (2-A) derived from methacrylic acid. Polymer block B is preferably a polymer block substantially composed of structural units (1-B) derived from acrylonitrile and structural units (2-B) derived from methacrylic acid.

[0023] The proportion of structural units (1-A) derived from acrylonitrile in polymer block A (hereinafter also referred to as "A chain") is preferably 60% by mass or more and 95% by mass or less, and more preferably 65% ​​by mass or more and 90% by mass or less. Furthermore, the proportion of structural units (2-A) derived from methacrylic acid in A chain is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 35% by mass or less. The total of structural units (1-A) and structural units (2-A) is taken as 100% by mass.

[0024] The A chain is a polymer block that has a lower content of carboxy groups than the polymer block B (hereinafter also referred to as the "B chain") and has relatively low water solubility. Therefore, the A chain adsorbed to the carbon material is less likely to detach than the B chain, and therefore has the function of further improving the dispersibility of the carbon material. If the proportion of the structural unit (2-A) in the A chain is less than 5% by mass, the A chain tends to have insufficient water solubility. On the other hand, if the proportion of the structural unit (2-A) in the A chain is more than 40% by mass, the A chain may have too high water solubility, and may be more likely to detach from the carbon material.

[0025] The number-average molecular weight of the polymer block A (A chain) is preferably 10,000 or more and 100,000 or less, and more preferably 20,000 or more and 90,000 or less. If the number-average molecular weight of the A chain is less than 10,000, the adsorption to the carbon material tends to be insufficient. On the other hand, if the number-average molecular weight of the A chain is more than 100,000, the water solubility may be insufficient even if the polymer contains a structural unit (2-A) having a carboxy group.

[0026] The molecular weight distribution (PDI = weight average molecular weight (Mw) / number average molecular weight (Mn)) of the polymer block A (A chain) is preferably 1.8 or less, and more preferably 1.6 or less. A relatively uniform molecular weight allows for more uniform adsorption to the carbon material and further improves dispersibility. If the molecular weight distribution (PDI value) of the A chain exceeds 1.8, many polymer blocks outside the aforementioned number average molecular weight range will be included, which tends to reduce the effect of improving dispersibility.

[0027] The proportion of the structural unit (1-B) derived from acrylonitrile in the polymer block B (B chain) is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 65% by mass or less. Furthermore, the proportion of the structural unit (2-B) derived from methacrylic acid in the B chain is preferably 30% by mass or more and 90% by mass or less, more preferably 35% by mass or more and 85% by mass or less. The total of the structural units (1-B) and (2-B) is taken as 100% by mass. The number-average molecular weight of the B chain is preferably 3,000 or more and 200,000 or less, more preferably 5,000 or more and 60,000 or less. If the number-average molecular weight of the B chain is less than 3,000, the polymer tends to be less soluble in water. On the other hand, if the number-average molecular weight of the B chain is more than 200,000, the viscosity tends to increase excessively, making dispersion difficult.

[0028] The B chain is a polymer block that contains more carboxyl groups than the A chain and has relatively high water solubility. If the proportion of the structural unit (2-B) in the B chain is less than 30% by mass, the water solubility of the entire AB block copolymer may be insufficient. On the other hand, if the proportion of the structural unit (2-B) in the B chain is more than 90% by mass, the water affinity tends to be excessively high. This may result in an excessively high viscosity of the carbon material dispersion and a reduced water resistance of the formed coating film.

[0029] The AB block copolymer can be produced by, for example, living radical polymerization. Since the AB block copolymer is composed of acrylonitrile and methacrylic acid, it is easy to control the structure and adjust the molecular weight.

[0030] The alkali that neutralizes at least a portion of the carboxy groups in the polymer dispersant (polymer) can be ammonia; organic amines such as triethylamine and dimethylaminoethanol; and alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide. Among these, from the viewpoints of improving water solubility and improving the conductivity of the coating film by ionic action, the alkali is preferably at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, and potassium hydroxide.

[0031] Although all carboxy groups in the polymer may be neutralized with alkali, it is also preferable to neutralize only some of the carboxy groups with alkali, as long as the polymer remains soluble in water. Carboxy groups (-COOH) that are not neutralized with alkali can form hydrogen bonds with the carbon material. Therefore, using a polymer in which only some of the carboxy groups have been neutralized with alkali as a dispersant can further improve the dispersion stability of the carbon material dispersion. The amount of alkali used to neutralize the carboxy groups is preferably an amount equivalent to 50 mol% to 120 mol% of the carboxy groups, and more preferably an amount equivalent to 70 mol% to 110 mol% of the carboxy groups.

[0032] The polymer used as the polymer dispersant can be produced by a conventionally known method. In particular, it can be produced by a solution polymerization method using an organic solvent; or a radical polymerization method using an azo-based radical generator or a peroxide-based radical generator. Conventionally known organic solvents can be used as the organic solvent. However, since the polymer may be poorly soluble in general-purpose organic solvents, it is preferable to use a polar organic solvent that is soluble in water. Examples of such polar organic solvents include amide-based solvents, sulfoxide-based solvents, urea-based solvents, and nitrile-based solvents. Of these, amide-based solvents, urea-based solvents, and nitrile-based solvents are preferred. After polymerization in these organic solvents, an aqueous alkali solution is added to neutralize the carboxyl groups and convert the polymer into an aqueous solution, thereby obtaining a carbon material dispersion containing the organic solvent.

[0033] Examples of amide solvents include dimethylformamide, dimethylacetamide, diethylacetamide, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide. Examples of urea solvents include tetramethylurea and 1,3-dimethylimidazolidinone. Examples of nitrile solvents include acetonitrile.

[0034] When the liquid medium is water or a mixed solvent (aqueous medium) of water and a water-soluble organic solvent, the polymer dispersant used as a dispersant is a polymer containing a structural unit (M1) derived from monomer 1, a structural unit (M2) derived from monomer 2, and a structural unit (M3) derived from monomer 3. Monomer 1 is at least one basic monomer selected from the group consisting of 2-vinylpyridine, 4-vinylpyridine, and 1-vinylimidazole, or a quaternary ammonium salt thereof. 2-vinylpyridine, 4-vinylpyridine, and 1-vinylimidazole are all basic monomers, and the structural units (M1) derived from these monomers adsorb to the carbon material and contribute to dispersibility.

[0035] Common basic monomers include dimethylaminoethyl (meth)acrylate. However, the use of at least one of 2-vinylpyridine, 4-vinylpyridine, and 1-vinylimidazole can further improve the dispersion stability of the carbon material dispersion and reduce the viscosity of the carbon material dispersion. 2-vinylpyridine, 4-vinylpyridine, and 1-vinylimidazole are all monomers with aromatic rings similar to the six-membered ring structure of carbon materials. Therefore, using structural units (M1) derived from these monomers is thought to enhance the adsorption force to the carbon material through van der Waals forces and π-π stacking. Furthermore, the surface of the carbon material may be oxidized, and carboxyl groups or phenolic hydroxyl groups may be present. Ionic bonding between the carboxyl groups or phenolic hydroxyl groups and the basic groups in the structural unit (M1) is thought to facilitate adsorption of the polymer dispersant to the carbon material, further improving dispersibility. 4-vinylpyridine is particularly preferred as the monomer 1.

[0036] The dispersibility can be further improved by using quaternary ammonium salts of 2-vinylpyridine, 4-vinylpyridine, and 1-vinylimidazole as Monomer 1. The structural units derived from 2-vinylpyridine, 4-vinylpyridine, and 1-vinylimidazole can be converted into quaternary ammonium salt-derived structural units (M1). Examples of materials for converting quaternary ammonium salts (quaternary ammonium chloride agents) include halides and sulfates. Examples of halides include methyl chloride and benzyl chloride. Examples of sulfates include dimethyl sulfate and diethyl sulfate. Preferred quaternary ammonium salts are arylmethyl halides. Examples of arylmethyl groups include benzyl, naphthylmethyl, anthracenylmethyl, and pyrenylmethyl groups. Of these, naphthylmethyl groups are preferred. The quaternary ammonium salt of a basic monomer is preferably a benzyl chloride salt, a naphthylmethyl chloride salt, or an anthracenylmethyl chloride salt of a basic monomer.

[0037] Monomer 2 is a macromonomer having a polyalkylene glycol chain, represented by the following general formula (1). By introducing a structural unit (M2) derived from monomer 2, a polymer having a structure in which a polyalkylene glycol chain is grafted can be obtained. The polyalkylene glycol chain dissolves in water, which is a liquid dispersion medium. The structural unit (M1) adsorbed to the carbon material repels the particles due to the steric hindrance caused by the dissolution of the polyalkylene glycol chain, allowing the carbon material to be stably dispersed in a good state in the liquid dispersion medium for a long period of time.

[0038] [ka]

[0039] In the general formula (1), R1 represents a hydrogen atom or a methyl group, A represents O or NH, X represents an ethylene group or a propylene group, Y represents O, NHCOO, or NHCONH, R2 each independently represents a hydrogen atom or a methyl group, n represents the average number of repeating units of 20 to 100, and R3 represents a hydrogen atom or a methyl group, provided that the number n of repeating units in which R2 is a hydrogen atom H is the total number of repeating units n T It is more than half of the

[0040] The molecular weight of the monomer 2 represented by the general formula (1) is, for example, 880 or more and 5,800 or less. H is the total number of repeating units n T In particular, when the number of repeating units n where R2 is a hydrogen atom is 1 / 2 or more, the polyalkylene glycol chain can be made water-soluble. H is the total number of repeating units n T It is preferable that the ratio is 3 / 5 or more.

[0041] Monomer 3 is a monomer copolymerizable with Monomer 1 and Monomer 2. It is preferable to use a (meth)acrylic acid-based monomer as Monomer 3. Specific examples of Monomer 3 include (meth)acrylic acid; methyl, ethyl, propyl, butyl, amyl, 2-ethylhexyl, isooctyl, nonyl, dodecyl, hexadecyl, octadecyl, isostearyl, behenyl, cyclohexyl, trimethylcyclohexyl, t-butylcyclohexyl, benzyl, methoxyethyl, butoxyethyl, phenoxyethyl, nonylphenoxyethyl, glycidyl, isobornyl, dicyclopentanyl, dicyclopentenyl, dicyclopentenyloxyethyl, isobornyl, 2-hydroxyethyl, methyl methyl ethyl propyl butyl amyl octadecyl octadecyl isostearyl behenyl cyclohexyl, methyl methyl ethyl propyl butyl am ... Monofunctional (meth)acrylates having substituents such as hydroxyethyl, 2-hydroxypropyl, and 4-hydroxybutyl; and polymeric (meth)acrylates that are macromonomers such as poly(n=2 or more) alkylene (carbon number 2 to 4) glycol mono(meth)acrylate, poly(n=2 or more) alkylene (carbon number 2 to 4) glycol monoalkyl (carbon number 1 to 22) mono(meth)acrylate, and poly(n=2 or more) hydroxyalkanoic acid (carbon number 5 to 18) mono(meth)acrylate. Vinyl monomers such as styrene, vinyl toluene, vinyl naphthalene, vinyl caprolactone, α-methyl styrene, and vinyl acetate can also be used as monomer 3.

[0042] Using α-methylstyrene as monomer 3 is preferred because it allows for easy control of the molecular weight. Specifically, monomer 3 contains α-methylstyrene, and the content of structural units derived from α-methylstyrene in the polymer is preferably 0.5% by mass or more and 5% by mass or less, and more preferably 1% by mass or more and 3% by mass or less. If the content of structural units derived from α-methylstyrene is less than 0.5% by mass, polymerization may proceed somewhat unevenly, resulting in residual monomer 2 or gelation. On the other hand, if the content of structural units derived from α-methylstyrene is more than 5% by mass, α-methylstyrene with somewhat poor polymerizability may remain, or the molecular weight may be overly controlled, resulting in a slight decrease in the polymerization rate.

[0043] It is also preferable to use (meth)acrylic acid as monomer 3. By including a structural unit derived from (meth)acrylic acid, which is an acid component, the water solubility of the polymer is improved, and when a quaternary ammonium salt group is also present in the polymer, the polymer exhibits amphoteric properties, which facilitates ionically adsorption to carbon materials and further improves dispersibility. Furthermore, by the polymer exhibiting amphoteric properties, ionic bonds are formed within or between molecules, making it easier to form crosslinked structures, which further prevents detachment from carbon materials.

[0044] The content of structural units derived from (meth)acrylic acid in the polymer is preferably 0.5% by mass or more and 30% by mass or less, and more preferably 1% by mass or more and 10% by mass or less. If the content of structural units derived from (meth)acrylic acid is less than 0.5% by mass, the effect as an acid component tends to be insufficient. On the other hand, if the content of structural units derived from (meth)acrylic acid is more than 30% by mass, the water solubility may be too high, and the water resistance of the formed coating film may be slightly reduced.

[0045] In the polymer dispersant (polymer), the content of the structural unit (M1) is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 20% by mass or less. The content of the structural unit (M2) is preferably 50% by mass or more and 80% by mass or less, more preferably 55% by mass or more and 75% by mass or less. The content of the structural unit (M3) is preferably 0.5% by mass or more and 40% by mass or less, more preferably 1% by mass or more and 31% by mass or less. The total of the structural units (M1), (M2), and (M3) is taken as 100% by mass.

[0046] If the content of the structural unit (M1) is less than 5% by mass, the structural unit (M1) cannot be sufficiently adsorbed to the carbon material. On the other hand, if the content of the structural unit (M1) is more than 40% by mass, the structural unit (M1) may become discolored or emit an odor, and may also be easily adsorbed in a lump to the carbon material, thereby functioning as a flocculant.

[0047] Of the structural units contained in the polymer, the proportion of structural unit (M2) is the largest. Therefore, the polyalkylene glycol chains present densely in the polymer act as steric hindrance, preventing the dispersed carbon materials from approaching each other and enabling stable dispersion. If the content of structural unit (M2) is less than 50% by mass, the steric hindrance will be insufficient and the material may be less soluble in water. On the other hand, if the content of structural unit (M2) is more than 80% by mass, monomer 2, which has a relatively low reactivity, will tend to remain without polymerizing. Note that if the content of structural unit (M3) is more than 40% by mass, the proportion of other structural units will be relatively reduced, and the function as a dispersant will tend to be reduced.

[0048] The number-average molecular weight of the polymer used as the polymer dispersant is, for example, 5,000 to 20,000, preferably 8,000 to 15,000. If the number-average molecular weight of the polymer is less than 5,000, the amount of structural unit (M2) derived from the macromonomer Monomer 2 introduced will be small, resulting in insufficient dispersion stability. On the other hand, if the number-average molecular weight of the polymer exceeds 20,000, the viscosity of the resulting carbon material dispersion will be excessively high, and the amount of polymer dispersant required may be too large. The number-average molecular weight in this specification is a polystyrene-equivalent value measured by gel permeation chromatography.

[0049] The polymers usable as polymer dispersants can be produced by conventionally known radical polymerization methods or living radical polymerization methods. Among these, production by living radical polymerization is preferred because it allows the molecular weight of the main chain to be uniform and, depending on the method of adding the monomers, it is possible to produce an AB block copolymer.

[0050] Living radical polymerization methods include polymerization methods that use chain transfer agents such as thiols to adjust molecular weight, atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer polymerization (RAFT), nitroxide polymerization (NMP), organotellurium polymerization (TERP), iodine transfer polymerization (ITP), reversible transfer catalyzed polymerization (RTCP), and reversible catalyst-mediated polymerization (RCMP).

[0051] The polymerization conditions are not particularly limited. An azo-based radical generator, a peroxide-based radical generator, a photosensitizer, or the like may be added to the reaction system. The polymerization method may be solventless, solution polymerization, emulsion polymerization, or the like. Among these, solution polymerization is preferred, and solution polymerization in the aforementioned water-soluble organic solvent that can be blended into the carbon material dispersion is more preferred. By performing solution polymerization in a water-soluble organic solvent, the obtained polymer solution can be blended directly into the carbon material dispersion.

[0052] The desired polymer can be obtained by polymerizing Monomer 1, Monomer 2, and Monomer 3 by solution polymerization or the like. Alternatively, after polymerizing Monomer 1, Monomer 2, and Monomer 3, an alkyl halide such as benzyl chloride, naphthylmethyl chloride, acetinylmethyl chloride, pyrenylmethyl chloride, or naphthylmethyl bromide may be added to the reaction system to convert the amino group derived from Monomer 1 into a quaternary ammonium salt. Furthermore, bis(trifluoromethylsulfone)imide lithium salt or bis(heptafluorobutylsulfone)imide lithium salt may be added to ion-exchange the quaternary ammonium salt to form a sulfonimide salt. The dispersant used in this embodiment is not particularly limited as long as it can stabilize the dispersion of carbon nanotubes. The dispersant may be a surfactant, mainly classified as anionic, cationic, nonionic, or amphoteric, or a polymeric dispersant.

[0053] The content of the dispersant in terms of solid content per 100 parts by mass of multi-walled carbon nanotubes must be 10 parts by mass or more and 150 parts by mass or less, and more preferably 20 parts by mass or more and 130 parts by mass or less. The content of the dispersant in the carbon nanotube dispersion is preferably 30% by mass or less, and more preferably 15% by mass or less. By setting the content of the dispersant relative to the carbon material within the above range, a carbon material dispersion in which the carbon material is more stably dispersed can be obtained. If the amount of dispersant is too small relative to the carbon material, the dispersant may not be able to sufficiently coat the surface of the carbon material, resulting in somewhat insufficient dispersibility. On the other hand, if the amount of dispersant is too large relative to the carbon material, the carbon material dispersion may tend to thicken and the proportion of carbon material in the solid content may become relatively low. Furthermore, when the dispersion is used as an ink or coating material, the physical properties of the formed coating, such as strength and conductivity, may be slightly reduced.

[0054] <Dye derivatives with acidic functional groups> The dye derivative having an acidic functional group is a dye in which an acidic functional group has been introduced. Examples of the dye include pigments or dyes such as phthalocyanine dyes, azo dyes, quinacridone dyes, dioxazine dyes, anthrapyrimidine dyes, anthanthrone dyes, indanthrone dyes, flavanthrone dyes, perylene dyes, perinone dyes, thioindigo dyes, isoindolinone dyes, and triphenylmethane dyes. Examples of the acidic functional group include a sulfo group, a carboxy group, and a phenol group.

[0055] The content of the dye derivative relative to 100 parts by mass of multi-walled carbon nanotubes is preferably 0.01 parts by mass or more and 50 parts by mass or less, and more preferably 0.1 parts by mass or more and 20 parts by mass or less. By setting the amount of dye derivative relative to the carbon nanotubes within the above range, a carbon nanotube dispersion in which the carbon nanotubes are more stably dispersed can be obtained. If the amount of dye derivative relative to the carbon nanotubes is too low, the dye derivative may not sufficiently coat the surface of the carbon nanotubes, resulting in somewhat insufficient dispersibility. On the other hand, if the amount of dye derivative relative to the carbon nanotubes is too high, the carbon nanotube dispersion tends to thicken, making it difficult to form a paint and reducing the proportion of carbon nanotubes in the solid content. Furthermore, the surface resistivity of the formed coating film may be somewhat high, and if an electrode is formed, the cycle performance of the electrode may be reduced. The number of acidic functional groups is determined by S analysis, and the average substitution number x is preferably 1 to 3. If the average substitution number x is less than 1, the effect on dispersibility tends to be reduced. On the other hand, if the average substitution number x exceeds 3, aggregation tends to occur more easily.

[0056] Furthermore, when the dispersant and the dye derivative are used in combination at a predetermined ratio, the carbon nanotubes can be dispersed more effectively, improving the storage stability of the carbon nanotube dispersion. Furthermore, when the carbon nanotube dispersion is mixed with a binder resin or the like, re-aggregation can be suppressed compared to when the dispersant is used alone. The content of the dye derivative relative to 100 parts by mass of the dispersant is preferably 0.05 parts by mass or more and 50 parts by mass or less, and more preferably 1 part by mass or more and 20 parts by mass or less. If the amount of dye derivative relative to the dispersant is too small, aggregation may occur when mixing the carbon nanotube dispersion with a binder resin, etc., making it difficult to form a paint. If the amount of dye derivative relative to the dispersant is too large, the carbon nanotube dispersion may easily thicken, making it difficult to form a paint, and the proportion of carbon nanotubes in the solid content may become relatively low. Furthermore, the surface resistivity of the formed coating film may become slightly high, and if an electrode is formed, the cycle characteristics of the electrode may be reduced.

[0057] <Binder resin> The carbon nanotube dispersion according to this embodiment may further contain a binder resin. By including a binder resin, it is possible to form a conductive coating film that is excellent in properties such as elongation and bending, and that has improved adhesion to a substrate or the like. As the binder resin, it is preferable to use at least one selected from the group consisting of acrylic resins, urethane resins, urea resins, epoxy resins, rubber resins, fluorine resins, polyamide resins, polyimide resins, silicone resins, and cellulose resins.

[0058] Examples of the acrylic resin include acrylic silicone resin, acrylic fluorine resin, polymethyl methacrylate (PMMA), polyethyl methacrylate, polymethyl acrylate, polyethyl acrylate, and polyhydroxy methacrylate.

[0059] Examples of urethane resins include ether-, ester-, carbonate-, acrylic-, and aliphatic-based urethane resins; and resins obtained by copolymerizing these urethane resins with silicone polyols or fluorine-based polyols. The molecular structure of the urethane resin may contain a urea bond or an imide bond.

[0060] The urea-based resin may be any resin having a urea bond in its molecular structure, and specific examples thereof include urethane urea elastomer, melamine resin, and urea formaldehyde resin.

[0061] Examples of epoxy resins include bisphenol A type epoxy resins, novolac type epoxy resins, brominated epoxy resins, polyglycol type epoxy resins, polyamide combined epoxy resins, silicone modified epoxy resins, amino resin combined epoxy resins, and alkyd resin combined epoxy resins.

[0062] Examples of rubber-based resins include natural rubber (NR), butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), hydrogenated NBR (H-NBR), styrene-butadiene rubber (SBR), isoprene rubber (IR), urethane rubber, chloroprene rubber (CR), epichlorohydrin rubber (ECO), ethylene-propylene-diene polymer (EPDM), acrylic rubber (ACM), chlorosulfonated polyethylene (CSM), polysulfide rubber, and fluororubber.

[0063] Examples of fluorine-based resins include polyvinylidene fluoride (PVDF), vinylidene fluoride-tetrafluoroethylene copolymer, and vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer.

[0064] Examples of polyamide resins include alcohol-soluble methoxymethylated nylon, etc. Examples of polyimide resins include polyamideimide (PAI), polyamic acid, and silicone imide.

[0065] Examples of cellulose-based resins include cellulose esters such as cellulose diacetate, cellulose triacetate, cellulose propionate, and cellulose acetate propionate; and cellulose ethers such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, and carboxymethyl cellulose.

[0066] The content of binder resin relative to the carbon material in the carbon nanotube dispersion is preferably 10 to 300 parts by mass, more preferably 20 to 200 parts by mass, per 100 parts by mass of multi-walled carbon nanotubes. If the amount of binder resin is too small, it may be difficult to apply it to the substrate, and a uniform coating film may not be obtained. If the amount of binder resin is too large, the proportion of carbon nanotubes decreases relatively, and the resulting coating may not have sufficient surface resistivity or thermal diffusivity.

[0067] When producing a heating element using the carbon nanotube dispersion liquid according to this embodiment, it is preferable to use, as the silica-containing epoxy resin, a silicone resin having at least one silicon-containing group and a mixture of an epoxy resin and an organometallic compound.

[0068] The silicone resin having a silicon-containing group is preferably a silicone resin having at least one silicon-containing group selected from the group consisting of an alkoxysilyl group, an alkoxysilylene group, and a siloxane bond. The silicone resin having a silicon-containing group is preferably formed by addition polymerization of a vinyl monomer having an alkoxysilyl group or an alkoxysilylene group.

[0069] Examples of epoxy resins include glycidyl ether type epoxy resins, glycidyl ester type epoxy resins, alicyclic epoxy resins, modified epoxy resins obtained by modifying these epoxy resins with at least one selected from alkylphenols and fatty acids, alkylphenyl glycidyl ethers (e.g., reaction products of alkylphenols and epichlorohydrin), and alkylphenol novolac type epoxy resins (e.g., reaction products of novolac type alkylphenol resins and epichlorohydrin).

[0070] <Additives, etc.> The carbon nanotube dispersion according to this embodiment may further contain additives, resins, etc. Examples of additives include water-soluble dyes, pigments, organometallic compounds, UV absorbers, light stabilizers, antioxidants, leveling agents, antifoaming agents, preservatives, mildew inhibitors, photopolymerization initiators, and other pigment dispersants. Examples of resins include polyolefin resins, polyhalogenated olefin resins, polyester resins, polyamide resins, polyimide resins, polyether resins, polyvinyl resins, polystyrene resins, polyvinyl alcohol resins, polymethacrylate resins, polyurethane resins, polyepoxy resins, polyphenol resins, polyurea resins, and polyethersulfone resins.

[0071] The organometallic compound is added as a crosslinking agent to improve the elasticity or strength of the coating film, etc. Examples of the organometallic compound include titanium compounds such as tetramethyl titanate, titanium acetylacetonate, tetraisopropyl titanate, and tetra-normal-butyl titanate; zirconium compounds such as zirconium monoacetylacetonate, zirconium bisacetylacetonate, and zirconium tetraacetylacetonate; aluminum compounds such as aluminum monoacetylacetonate bis(ethylacetoacetate), aluminum tris(acetylacetonate), aluminum tris(ethylacetoacetate), and ethylacetoacetate aluminum diisopropylate; and tin compounds such as dibutyltin diacetate, dioctyltin dilaurate, and dibutyltin dilaurate tin.

[0072] It is preferable that the carbon nanotube dispersion contains an antifoaming agent as an additive, depending on the apparatus used in the wetting and dispersing steps. By containing an antifoaming agent, foaming during the dispersion treatment can be suppressed, so that the shear force or collision force applied during the dispersion treatment can act effectively, resulting in a dispersion with better dispersibility.

[0073] (Carbon nanotube dispersion liquid) The carbon nanotube dispersion of this embodiment has a low viscosity even when the concentration of multi-walled carbon nanotubes is high, and the viscosity does not change easily even after a long period of time, resulting in excellent viscosity stability (storage stability). Specifically, the viscosity of the dispersion is 250 mPa·s or less when measured at 100 rpm using an E-type rotational viscometer, and the rate of change in the viscosity (mPa·s) of the binder resin-free dispersion at 25°C after 10 days at room temperature (25°C) is typically 15% or less, preferably 10% or less, and more preferably 5% or less, based on the viscosity (mPa·s) of the binder resin-free dispersion at 25°C immediately after preparation (dispersion).

[0074] If aggregates with short sides of 100 μm or more are present in a binder-resin-free dispersion, when the dispersion is used in various applications, the inherent performance of carbon nanotubes, such as electrical conductivity or thermal conductivity, is difficult to exhibit, and aggregate growth or sedimentation occurs, which tends to reduce viscosity stability and storage stability. For example, when a dispersion containing aggregates with short sides of 100 μm or more is used as a coating material, uniform coating tends to be difficult to achieve. In contrast, the dispersion according to this embodiment is substantially free of coarse aggregates formed by carbon materials, including carbon nanotubes. Specifically, even when the binder-resin-free dispersion immediately after preparation (dispersion) and the binder-resin-free dispersion after 10 days at room temperature (25°C) are observed five times at 200x magnification using an optical microscope, not even a single aggregate with short sides of 100 μm or more is typically observed. Preferably, the number (average) of aggregates with short sides of 20 μm or more is 10 or more per observation. More preferably, the number (average value) of aggregates with short sides of 20 μm or more is 1 or more and less than 10 per observation, and particularly preferably, not even one aggregate with short sides of 20 μm or more is observed even after five observations. The carbon nanotube dispersion of the present invention can be evaluated from the physical property values ​​when formed into a coating film.

[0075] The carbon nanotube dispersion according to this embodiment must have a multi-walled carbon nanotube content of 15% by mass or more and 30% by mass or less, and more preferably 21% by mass or more and 30% by mass or less. A content of less than 15% by mass requires the addition of a large amount of binder when preparing a thick coating film, but this increases the surface resistivity and decreases the thermal diffusivity, making it impossible to produce a high-performance, thick coating film, which is undesirable. A content of more than 30% by mass is undesirable because the carbon nanotube concentration is too high and they cannot be dispersed well. For example, when the content of multi-walled carbon nanotubes in the carbon nanotube dispersion is 15%, 20%, or 21% by mass or more and 30% by mass or less, there is little difference in the dispersion state and dispersion stability. However, when preparing a coating film with a multi-walled carbon nanotube content of 40% by mass, it is necessary to add a binder. If the concentration of multi-walled carbon nanotubes in the carbon nanotube dispersion becomes low, the amount of binder that can be added becomes limited, making it difficult to adjust the thickness or handling of the coating film. Therefore, a more preferable condition is that the multi-walled carbon nanotube content be 21% by mass or more and 30% by mass or less.

[0076] <Method of manufacturing carbon nanotube dispersion> A carbon nanotube dispersion can be produced by wetting a carbon material containing carbon nanotubes in a liquid medium using a dispersant and then dispersing the carbon material in accordance with a conventionally known method. For example, wetting and dispersion methods using magnetic stirrer stirring, dissolver stirring, triple-roll kneading, ultrasonic dispersion, bead mill dispersion, an emulsifier, or a homogenizer can be used. For simplicity of process, wetting by stirring with a magnetic stirrer, dissolver, or homogenizer is preferred, and dispersion in combination with a high-pressure homogenizer is preferred. For example, dispersion by a bead mill using small beads is preferred. Furthermore, considering damage to carbon materials such as carbon nanotubes, a combination of wetting and high-dispersion methods may be used.

[0077] <Coating film> A conductive coating film (film) can be formed by applying and drying the carbon nanotube dispersion liquid according to this embodiment. The concentration of the carbon material in the coating film to be formed is, for example, preferably 0.01% by mass to 50% by mass, more preferably 0.1% by mass to 30% by mass, and particularly preferably 0.5% by mass to 20% by mass. The thickness of the coating film (film thickness) can be, for example, 0.8 μm to 30 μm. The thicker the film thickness and the higher the concentration of multi-walled carbon nanotubes, the lower the surface resistivity and the higher the thermal diffusivity of the coating film. In this embodiment, it was confirmed that the surface resistivity and thermal diffusivity of the coating film hardly change when the film thickness is within the range of 1±0.2 μm and the concentration of the carbon material is within the range of 40±1% by mass.

[0078] The surface resistivity of a 1 μm-thick dried film (coating film) containing 40 mass % multi-walled carbon nanotubes, formed by applying and drying the carbon material dispersion liquid according to this embodiment, is 1.0×10 3 It must be Ω / sq or less, and preferably 9.0×10 2 The carbon content in the dried film (coating) can be calculated by heating the coating formed by applying the dispersion liquid and evaporating the liquid medium, then subtracting the mass (solid content) of the dispersant and binder resin used from the mass of the dried film. The same calculation can be performed when a baking process is performed. The surface resistivity of the dried film can be achieved by adjusting the type or amount of multi-walled carbon nanotubes or dispersant, or by adjusting the wetting method or dispersion method of the dispersion. The surface resistivity when the coating film thickness is 1 μm was calculated by preparing two or more coating films with different thicknesses and then creating a calibration curve plotting the coating film thickness and surface resistivity.

[0079] The thermal diffusivity of a dried film (coating film) having a thickness of 1 μm and containing 10 mass % multi-walled carbon nanotubes, formed by applying and drying the carbon material dispersion liquid according to this embodiment, is 0.30 mm 2 / s or more, and preferably 0.35 mm 2 / s or more. The carbon material content in the dried film (coating) can be calculated by heating the coating film formed by applying the dispersion liquid and evaporating the liquid medium, and subtracting the mass (solid content) of the dispersant and binder resin used from the mass of the dried film. The same calculation can be performed even if a baking process has been performed. The thermal diffusivity of the dried film can be achieved by adjusting the type or amount of multi-walled carbon nanotubes or dispersant, or by adjusting the wetting method or dispersion method of the dispersion.

[0080] In preparing the dried coating film, it is preferable to carry out a baking step. Baking decomposes the dispersant, increasing the concentration of multi-walled carbon nanotubes in the coating film, thereby improving the surface resistivity and thermal diffusivity. The baking temperature varies depending on the dispersant used, but it is sufficient as long as it is a temperature at which the dispersant thermally decomposes, and is preferably 150°C or higher, more preferably 200°C or higher. From the viewpoint of the heat resistance of the multi-walled carbon nanotubes, the upper limit is preferably 600°C or lower, more preferably 500°C or lower. If the temperature exceeds 600°C, there is a possibility that the carbon nanotubes will burn. Furthermore, examples of applications of the carbon material dispersion liquid according to this embodiment include antistatic coating films, heat generating bodies, heat conductors, temperature-sensitive coating films, paints for sensors, heat dissipation paints, electrode materials, and paints for electromagnetic wave shielding.

[0081] <Use of carbon material dispersion> In the carbon material dispersion according to the present embodiment, the carbon material including carbon nanotubes is well dispersed without substantially forming coarse aggregates, and the carbon material dispersion has excellent viscosity stability. Furthermore, since the carbon material dispersion according to the present embodiment is an aqueous dispersion, it is an environmentally friendly material and is useful as a material for producing heat transfer materials, paints, inks, coating agents, resin molded product materials, and the like. It is also expected to be used as an electrically conductive material or a thermally conductive material, and is also expected to be applied to antistatic materials. Furthermore, it is useful as a battery material, such as an electrode material for batteries such as lithium-ion batteries or fuel cells, or as a material for forming films for capacitor materials and films for various mechanical parts. Examples of the heating element include a fixing device used in an image forming apparatus such as an electrophotographic copier, an interior heater for an automobile used in an in-vehicle seat, steering wheel, window glass, etc., and a wearable device such as a wearable heater. A common fixing device for an image forming apparatus uses a fixing roller to heat ink or toner for fixing. However, in order to improve the image formation speed, it is important that the temperature of the fixing roller quickly reaches the target temperature. By using the carbon nanotube dispersion according to this embodiment as a heating element for the fixing roller, a fixing roller with no temperature unevenness can be manufactured, as the temperature rise rate is fast and a uniform coating film can be produced.

[0082] The aqueous paint or ink can be prepared by adding various components such as a solvent, a resin, and an additive to a carbon material dispersion. Alternatively, the carbon material dispersion may be added to a commercially available paint or ink.

[0083] A resin molded product can be produced, for example, by adding a carbon material dispersion to a molten plastic material and then removing the water. Alternatively, a resin molded product in which a carbon material is dispersed can also be produced by adding a carbon material dispersion to a finely powdered plastic material and then removing the water or precipitating the carbon material. [Example]

[0084] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are by mass unless otherwise specified.

[0085] <Preparing ingredients> The following carbon materials, dispersants, and binder resins were prepared. Note that the parts by mass of the dispersants and binder resins in the tables indicate the solid content. (multi-walled carbon nanotubes) MWCNT-1: Multi-walled carbon nanotubes (average length 8.5 μm, average diameter 40 nm), product name "ENERMAX12", manufactured by Cabot Corporation MWCNT-2: Multi-walled carbon nanotubes (average length 1.5 μm, average diameter 9.5 nm), product name "NC7000", manufactured by Nanosil Co., Ltd. MWCNT-3: Multi-walled carbon nanotubes (average length 150 μm, average diameter 7.5 nm), product name "6A", manufactured by JEIO

[0086] (dispersant) Dispersant C: Product name "Florene GW-1500", manufactured by Kyoeisha Chemical Co., Ltd. Dispersant D: Trade name "Cellogen", manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Dispersant E: Product name "Demol N", manufactured by Kao Corporation Dispersant F: Product name "Solsperse 27000", manufactured by Lubrizol Dispersant G: Product name "Disparlon AQ-380", manufactured by Kusumoto Chemicals Co., Ltd. (binder resin) Binder resin: Product name "YL-1098", styrene acrylic resin, manufactured by Seiko PMC Corporation

[0087] <Production of dispersants, etc.> (Synthesis of Dispersant A) 233.3 parts of N-methylpyrrolidone (NMP) was placed in a reaction vessel and stirred, then heated to 70°C. Additionally, 60 parts of acrylonitrile (AN), 40 parts of acrylic acid (AA), and 3.0 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (trade name "V-65", Fujifilm Wako Pure Chemical Industries, Ltd.) (V-65) were placed in a beaker, and the V-65 was completely dissolved to prepare a monomer solution. The prepared monomer solution was placed in a dropping funnel, and when the temperature in the reaction vessel reached 70°C, 1 / 3 of the total amount was added, and the remaining liquid was added dropwise over 1.5 hours. After the completion of the dropwise addition, 2.5 hours later, 1.0 part of V-65 was added. The mixture was maintained at 70°C for 1 hour, then heated to 80°C and maintained there for 2 hours to form a polymer. After cooling, the solids content was measured using a moisture meter, and it was confirmed that almost all of the monomer had been consumed. The number average molecular weight (Mn) of the polymer, calculated as polymethyl methacrylate, measured by gel permeation chromatography (GPC) using a solution of lithium bromide in N,N-dimethylformamide (lithium bromide concentration: 10 mmol / L) as the developing solvent was 25,300, and the molecular weight distribution (PDI = weight average molecular weight (Mw) / number average molecular weight (Mn)) was 2.24.

[0088] 24.4 parts of sodium hydroxide (NaOH) (110 mol% relative to AA) and 96.8 parts of ion-exchanged water were placed in a beaker, and the NaOH was completely dissolved to prepare an aqueous NaOH solution. After the temperature inside the reaction vessel reached 60°C or below, the aqueous NaOH solution was added to neutralize the carboxyl groups, yielding a solution of polymer dispersant (dispersant a). The solids content of the resulting solution of dispersant a was 22.1%. The resulting dispersant is referred to as dispersant A.

[0089] (Synthesis of Dispersant B) (a) Synthesis of macromonomer A reactor equipped with a stirrer, reflux condenser, thermometer, and dropping funnel was charged with 142.5 parts (0.067 mol) of a mono-terminated polypropylene glycol polyethylene glycol monomethyl ether copolymer (Clariant, trade name: Genamine M41 / 2000, actual amine value: 26.4 mg KOH / g, hereafter abbreviated as M41) and stirred. 10.4 parts (0.067 mol) of 2-isocyanatoethyl methacrylate (Showa Denko, trade name: Karenz MOI, hereafter abbreviated as MOI) was added dropwise to the dropping funnel over 30 minutes while cooling in a water bath. Heat generation was observed immediately after the start of the dropping. IR analysis of a sample confirmed the almost complete disappearance of the absorption of the isocyanate group derived from the raw material MOI and the formation of urea bonds. The amine value was also measured, revealing a value of 0.2 mg KOH / g, confirming that the reaction between the amino and isocyanate groups was nearly complete. Therefore, this product is a macromonomer in which a methacryloyl group is bonded to one end of a polypropylene glycol / polyethylene glycol (hereinafter abbreviated as PPG / PEG) copolymer, and corresponds to Monomer 2 represented by the general formula (1). This product is referred to as MC-1. When the molecular weight was measured by GPC measurement of the tetrahydrofuran developing solution in terms of polystyrene, the number average molecular weight (hereinafter abbreviated as Mn) was 2,800. Hereinafter, molecular weight measurements were performed under these conditions. The amine value was measured using an automatic potentiometric titrator using a 0.1 M 2-propanol hydrochloric acid solution. The amine value was measured in the same manner hereinafter.

[0090] (b) Synthesis of polymer dispersant A reactor equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube was charged with 95.0 parts of diethylene glycol monobutyl ether (hereinafter abbreviated as BDG) as a solvent, 70 parts of the MC-1 obtained above as monomer 2, 2.5 parts of α-methylstyrene (hereinafter abbreviated as αMS) as monomer 3, 10.5 parts of styrene (hereinafter abbreviated as St), and 17 parts of 4-vinylpyridine (hereinafter abbreviated as 4VP) as monomer 1, and heated to 75 ° C while bubbling nitrogen. When the temperature reached 70 ° C, 5 parts of 2,2'-azobis(isobutyrate)dimethyl (Wako Pure Chemical Industries, Ltd., V-601, hereinafter abbreviated as V-601) was added as a polymerization initiator, and the mixture was polymerized at 75 ° C for 4 hours. 2.5 parts of V-601 was then added, and the mixture was polymerized at the same temperature for another 4 hours. A sample was taken and the molecular weight was measured by GPC, revealing Mn of 9,600, polydispersity index (PDI) of 1.83, and peak top molecular weight (PT) of 22,700. There was almost no peak associated with the raw material MC-1. The amine value, calculated as the pure resin content, was 86.2 mg KOH / g, and the solid content was measured using a moisture meter, revealing a value of 50.4%. The resulting polymeric dispersant is referred to as Dispersant B.

[0091] (Synthesis of dye derivatives) 30 parts of PV23 were added to 300 parts of 95% sulfuric acid and reacted at 20 to 30°C for 3 hours. The reaction mixture was precipitated in 2700 parts of ice water, filtered, and washed with water repeatedly. After drying, 36.2 parts of a blue-purple powder (dye derivative) was obtained, which has the following structural formula and, based on elemental analysis of sulfur, contains an average of 1.1 sulfonic acid groups per molecule.

[0092] [ka]

[0093] (Method of manufacturing carbon nanotube dispersion liquid) A carbon nanotube dispersion can be produced by wetting multi-walled carbon nanotubes in a liquid medium using a dispersant and then dispersing them according to a conventionally known method. For example, wetting and dispersion methods using magnetic stirrer stirring, dissolver stirring, triple-roll kneading, ultrasonic dispersion, bead mill dispersion, emulsifiers, homogenizers, etc. can be used. From the perspective of process simplicity, wetting by stirring with a magnetic stirrer, dissolver, or homogenizer is preferred, and dispersion in combination with a high-pressure homogenizer is preferred. For example, dispersion by a bead mill using small beads is preferred. Furthermore, considering damage to the multi-walled carbon nanotubes, a combination of wetting and high-dispersion methods may be used.

[0094] <Measurement and evaluation methods> [Measurement of viscosity and evaluation of viscosity stability] Using an E-type viscometer equipped with a 1°34' x R24 rotor, the viscosity of the carbon nanotube dispersion was measured immediately after dispersion and after 10 days (after leaving it to stand at room temperature for 10 days) at a temperature of 25°C and a rotor rotation speed of 100 rpm. For carbon nanotube dispersions with a viscosity of less than 25 mPa·s, the viscosity was measured using a VISCOMETER TVE-25L (manufactured by Toki Sangyo Co., Ltd.). For carbon nanotube dispersions with a viscosity of 25 mPa·s or more, the viscosity was measured using a VISCOMETER TVE-25H (manufactured by Toki Sangyo Co., Ltd.). The viscosity stability of the carbon nanotube dispersions was then evaluated according to the following evaluation criteria. ⊚: The rate of change in viscosity after 10 days is less than 5% based on the viscosity immediately after dispersion. ◯: The rate of change in viscosity after 10 days, based on the viscosity immediately after dispersion, is 5% or more and less than 10%. △: The rate of change in viscosity after 10 days based on the viscosity immediately after dispersion is 10% or more and less than 15%. ×: The rate of change in viscosity after 10 days based on the viscosity immediately after dispersion is 15% or more.

[0095] [Aggregate observation] The carbon nanotube dispersion was collected in a polyethylene bottle and diluted with a blank solution to a multi-walled carbon nanotube concentration of 0.1% by mass. The diluted solution was obtained by stirring for 30 seconds using a vortex mixer (Scientific Industries). 30 μL of the resulting diluted solution was dropped onto a glass slide, a cover glass was placed on top, and the presence or absence of aggregates was observed using an optical microscope (200x magnification). The carbon nanotube dispersion immediately after dispersion and the carbon nanotube dispersion 10 days later (after leaving the dispersion at room temperature for 10 days) were dropped onto glass slides five times each to prepare samples, which were then observed and evaluated for the presence or absence of aggregates according to the following evaluation criteria. ⊚: Not a single aggregate with a short side of 20 μm or more was observed during five observations. ◯: The number (average value) of aggregates with short sides of 20 μm or more was 1 or more but less than 10 per observation, and no aggregates with short sides of 100 μm or more were observed in any of the five observations. △: The number (average value) of aggregates with a short side of 20 μm or more was 10 or more per observation, and not a single aggregate with a short side of 100 μm or more was observed in any of the five observations. ×: One or more aggregates with a short side of 100 μm or more were observed during five observations.

[0096] (Evaluation of coating film) [Surface resistivity measurement] Surface resistivity is 10 5 When the surface resistivity exceeded Ω / sq, a high-resistance resistivity meter (trade name "Hiresta-UP MCP-HT450", manufactured by Nitto Seiko Analytech Co., Ltd.) was used to apply 10 V and measure five points to calculate the average value of the surface resistivity of the coating film. 5 When the value was Ω / sq or less, a low-resistance resistivity meter (trade name "Loresta-GP MCP-T610", manufactured by Nitto Seiko Analytech Co., Ltd.) was used, and the average value of the surface resistivity of the coating film was calculated by measuring at five points with an applied voltage of 10 V.

[0097] [Measurement of thermal diffusivity] The thermal diffusivity was measured using a thermal diffusivity measuring device (trade name "ai-Phase Mobile M3 type1", manufactured by ai-Phase Co., Ltd.) using the cyclic heating method (temperature wave thermal analysis) in accordance with ISO 22007-3.

[0098] <Preparation and Evaluation of Dispersion Liquid (1)> (Examples 1 to 9, Comparative Examples 1 to 18) The types and amounts of each component (except CNT) shown in Table 1 were placed in a 250 mL plastic bottle (polyethylene bottle). After stirring with a magnetic stirrer until uniform, the types and amounts of CNT shown in Table 1 were added and further stirred. 200 parts of zirconia beads with an average diameter of 0.8 mm were added, and treatment was carried out for 60 minutes using a Scandex (manufactured by Scandex Corporation). The zirconia beads were then separated and removed to obtain a dispersion. The results of evaluating the viscosity stability of the obtained dispersion and the results of observing the aggregates are shown in Table 1.

[0099] <Preparation and Evaluation of Dispersion Liquid (2)> The types of dispersions and binder resins shown in Table 1 were blended in proportions such that the CNT concentration (%) in the resulting coating film (solid content) would be the value shown in Table 1, and then mixed using a magnetic stirrer to obtain carbon material dispersions. The resulting carbon material dispersions were applied to a 100-μm-thick PET film (trade name "Lumirror," manufactured by Toray Industries, Inc.) using a bar coater and then dried in an electric oven at 90°C for 30 minutes to remove volatile components, forming coating films with the thicknesses shown in Table 1. The surface resistivity and thermal diffusivity of the formed coating films are shown in Table 1. Note that in Example 9, after the coating film was formed, it was baked in an electric oven at 250°C for 30 minutes to remove volatile components and dispersant components. Of these, Comparative Examples 1 to 18 did not achieve a CNT concentration of 40% in the coating film, so Comparative Examples 1, 5, 6, 7, 12, 13, and 14, which had relatively good viscosity stability and observation of aggregates, were evaluated. In addition, Table 2 lists coatings with different thicknesses and CNT concentrations in the coatings as reference examples.

[0100] [Table 1]

[0101] [Table 2]

[0102] From Table 1, it can be seen that in Examples 1 to 9, CNT dispersions with extremely high concentrations of 22 mass % or more were obtained compared to Comparative Examples 1 to 18. Furthermore, when the CNT dispersions of Examples 1 to 9 were stored at 25°C for 30 days, no particular change in the dispersion state was observed.

[0103] (Application example (heating element)) A composition for forming a heating element was obtained by mixing 30 parts by weight of the dispersion liquid of Example 1, 6 parts by weight of a mixture of acrylic silicone resin and epoxy resin as a binder resin, and 0.6 parts by weight of an organometallic compound (aluminum monoacetylacetonate bis(ethylacetoacetate)). This composition was applied to a 60 mm x 15 mm x 1 mm glass plate using a bar coater to prepare a 60 μm thick heating layer. Next, silver paste was applied to both ends of the glass plate to prepare a heating element.

[0104] (Evaluation of heating elements) Alligator clips were attached to both ends of the heating element, which was then connected to a variable constant current power supply. A current of 250mA or 450mA was passed through the element at room temperature of 25°C. The temperature of the heating element was measured using a thermograph after 30 seconds, and was found to be 100°C at 250mA and 200°C at 450mA.

[0105] (Comparative application example (heating element)) A heating element was prepared in the same manner as in the application example, except that the dispersion liquid of Comparative Example 5 was used, and evaluation was performed. There was no temperature change under both the 250 mA and 450 mA conditions. This indicates that when the CNT concentration is low, the resistance value becomes high, and heat generation does not occur. Similarly, in the case of poor dispersion, the resistance becomes high, and heat generation does not occur. On the other hand, when the CNT concentration is high, the resistance value becomes low. In this case, heat generation occurs, but the maximum temperature is low. Therefore, it is important to set the CNT concentration and thickness to obtain an appropriate resistance value. [Industrial Applicability]

[0106] The carbon material dispersion of the present invention is useful as a constituent material for paints, inks, resin molded products, and the like that exhibit properties such as high electrical conductivity or high thermal conductivity, and is also suitable for various applications such as battery materials, electronic component trays, IC chip covers, electromagnetic wave shields, automotive components, and robot components.

Claims

1. A carbon nanotube dispersion containing multi-walled carbon nanotubes, an aqueous medium, and a dispersant, the content of the multi-walled carbon nanotubes is 15% by mass or more and 30% by mass or less with respect to the total amount of the carbon nanotube dispersion, The multi-walled carbon nanotubes have an average length of 2 μm or more and 40 μm or less and an average diameter of 5 nm or more and 150 nm or less, the dispersant is at least one of a surfactant, a cellulose derivative, and a polymer dispersant, the content of the dispersant is 10 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the multi-walled carbon nanotubes, When a dry film having a thickness of 1 μm is formed using a coating liquid containing the carbon nanotube dispersion and a binder resin so that the content of the multi-walled carbon nanotubes in the dry film is 40 mass %, the surface resistivity of the dry film is 1.0×10 ３ Ω / sq or less, and the thermal diffusivity of the dry coating is 0.30 mm ２ / s or more.

2. 2. The carbon nanotube dispersion according to claim 1, wherein the polymer dispersant is a polymer having a structural unit (1) derived from (meth)acrylonitrile and a structural unit (2) derived from (meth)acrylic acid.

3. 3. The carbon nanotube dispersion liquid according to claim 2, wherein the polymer dispersant is a polymer having 50% by mass or more and 80% by mass or less of the structural unit (1) and 20% by mass or more and 50% by mass or less of the structural unit (2), at least a portion of which has a carboxy group neutralized with an alkali (wherein the total of the structural unit (1) and the structural unit (2) is 100% by mass).

4. the polymer comprises a polymer block A having 60% by mass or more and 95% by mass or less of structural units (1-A) derived from acrylonitrile and 5% by mass or more and 40% by mass or less of structural units (2-A) derived from methacrylic acid (wherein the total of the structural units (1-A) and the structural units (2-A) is 100% by mass); and a polymer block B having 10% by mass or more and 70% by mass or less of structural units (1-B) derived from acrylonitrile and 30% by mass or more and 90% by mass or less of structural units (2-B) derived from methacrylic acid (wherein the total of the structural units (1-B) and the structural units (2-B) is 100% by mass), the number average molecular weight of the polymer block A is 10,000 or more and 100,000 or less, and the molecular weight distribution is 1.8 or less; The carbon nanotube dispersion liquid according to claim 3 , wherein the number average molecular weight of the polymer block B is 3,000 or more and 200,000 or less.

5. 2. The carbon nanotube dispersion liquid according to claim 1, wherein the polymer dispersant is a polymer having a number average molecular weight of 5,000 or more and 20,000 or less, comprising: 5% by mass or more and 40% by mass or less of structural units (M1) derived from Monomer 1, which is at least one basic monomer selected from the group consisting of 2-vinylpyridine, 4-vinylpyridine, and 1-vinylimidazole, or a quaternary ammonium salt thereof; 50% by mass or more and 80% by mass or less of structural units (M2) derived from Monomer 2 represented by the following general formula (1); and 0.5% by mass or more and 40% by mass or less of structural units (M3) derived from Monomer 3 copolymerizable with Monomer 1 and Monomer 2: 【Chemistry 1】 (In the general formula (1), R １ represents a hydrogen atom or a methyl group, A represents O or NH, X represents an ethylene group or a propylene group, Y represents O, NHCOO, or NHCONH, and R ２ are each independently a hydrogen atom or a methyl group, n is the average number of repeating units of 20 to 100, R ３ represents a hydrogen atom or a methyl group. ２ The number of repeating units n is a hydrogen atom Ｈ is the total number of repeating units n Ｔ It is more than half of the

6. 6. The carbon nanotube dispersion liquid according to claim 5, wherein the monomer 3 contains α-methylstyrene, and the content of the structural unit derived from α-methylstyrene in the polymer is 0.5% by mass or more and 5% by mass or less.

7. 6. The carbon nanotube dispersion liquid according to claim 5, wherein the monomer 3 contains (meth)acrylic acid, and the content of structural units derived from the (meth)acrylic acid in the polymer is 0.5% by mass or more and 30% by mass or less.

8. 6. The carbon nanotube dispersion liquid according to claim 5, wherein the quaternary ammonium salt of the basic monomer is a benzyl chloride salt, a naphthyl methyl chloride salt, or an anthracenyl methyl chloride salt of the basic monomer.

9. The carbon nanotube dispersion liquid according to claim 1 , wherein the cellulose derivative is carboxymethyl cellulose or carboxymethyl cellulose sodium salt.

10. The carbon nanotube dispersion according to claim 1 , wherein the content of the multi-walled carbon nanotubes is 21% by mass or more and 30% by mass or less.

11. 2. The carbon nanotube dispersion liquid according to claim 1, further comprising a dye derivative having an acidic functional group, the content of the dye derivative being 0.01 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the multi-walled carbon nanotubes.

12. 2. The carbon nanotube dispersion according to claim 1, further comprising a binder resin, the content of the binder resin being 10 parts by mass or more and 300 parts by mass or less relative to 100 parts by mass of the multi-walled carbon nanotubes.

13. Use of the carbon nanotube dispersion liquid according to claim 1 for producing any one of the following products: heat transfer materials, paints, inks, coating agents, resin molding materials, conductive materials, thermally conductive materials, and antistatic materials.

14. 10. Use of the carbon nanotube dispersion according to claim 1 for producing any one of battery materials and mechanical parts, the product having a coating film formed from the carbon nanotube dispersion.

15. A coating film comprising the carbon nanotube dispersion liquid according to claim 1, which is an antistatic coating film, a heat generating body, a heat conductor, a temperature sensitive coating film, a paint for sensors, a heat dissipating paint, an electrode material, or a paint for electromagnetic wave shielding.

16. The coating film according to claim 15, wherein the coating film is baked at 150°C or higher and 600°C or lower.

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