Carbon material dispersion and use thereof

Abstract

A carbon material dispersion according to the present invention contains: at least one type of carbon material from among single-walled carbon nanotubes and multi-walled carbon nanotubes; an aqueous medium; a dispersant; and a binder resin, and satisfies requirements (1), (2) and (3). (1) The amounts of the dispersant and the binder resin with respect to the carbon material are within respective prescribed ranges for each type of carbon material. (2) The surface resistivity of a dry film having a thickness of 1 μm and in which the content of the carbon material is 10 mass% is 1.0 × 103 Ω / sq or less. (3) A ratio (AL / AH) of an absorbance AL at a wavelength of 380 nm to an absorbance AH at a wavelength of 780 nm of a dilute dispersion obtained by diluting with a blank liquid so that the absorbance at a wavelength of 580 nm becomes 1.8 ± 0.02 is 1.45 or greater.

Description

Carbon material dispersion and its use

[0001] The present invention relates to a carbon material dispersion and its use.

[0002] Carbon materials (nanocarbon materials), such as carbon black, carbon fiber, carbon nanotubes (hereinafter also referred to as "CNT"), graphite, and graphene, have a six-membered ring graphite structure formed by covalent bonds between carbon atoms. Therefore, these materials exhibit various properties, such as electrical conductivity and thermal conductivity, and methods for utilizing these properties in a wide range of fields are being investigated. For example, focusing on the electrical properties, thermal properties, and filler properties of carbon materials, their use as antistatic agents, conductive materials, plastic reinforcing materials, semiconductors, electrodes for fuel cells or secondary batteries, and cathode rays for displays is being considered.

[0003] In recent years, these applications have required higher performance, and CNTs have been widely used as carbon materials. To improve various physical properties such as electrical conductivity, the type and amount of dispersant for dispersing CNTs in a liquid medium, as well as the selection of binder resins used to form coatings or electrodes, are also important.

[0004] As related prior art, for example, a CNT aqueous dispersion has been proposed, which is a dispersion containing CNTs with an average outer diameter of 3 nm or less and a dispersant, and is characterized in that the average particle size measured by dynamic light scattering is 200 nm or more and 1500 nm or less, and a method for evaluating the conductivity of CNTs by measuring the surface resistance of a coating film obtained by drying the dispersion (Patent Document 1).

[0005] In addition, a method has been proposed for evaluating the conductivity of CNT by measuring the surface resistance of a resin composition containing CNT and a resin synthesized using a specific catalyst, as well as a coating film containing the synthesized CNT (Patent Document 2).

[0006] Furthermore, an antistatic layer is formed from a binder resin and a single-walled carbon nanotube coating material, and the surface resistivity is 3.0×10 ５ An antistatic sheet with a resistance of Ω / sq or less has been proposed (Patent Document 3).

[0007] JP 2010-254546 A JP 2015-123410 A JP 2021-195546 A

[0008] Generally, in conductive paint coated products, the thicker the conductive paint coating layer, the higher the conductivity. For example, if the coating layer is made very thin, for example, 1 μm thick, in order to reduce the size and weight of the conductive paint coated product, the conductivity will be 1.0 × 10 ３ It has been difficult to obtain high electrical conductivity of Ω / sq or less.

[0009] Increasing the concentration of conductive material in a coating generally improves conductivity. However, the concentration of binder resin in the coating decreases relatively, making it difficult to reflect the properties of the binder resin, such as elongation or bending, and making it difficult to obtain a uniform coating. Even if a uniform coating is obtained, the durability of the coating, such as flexibility and adhesion, decreases, making it difficult to achieve both high conductivity and good coating film properties.

[0010] A carbon material dispersion containing CNTs is used, for example, as a material for improving the electrical conductivity of a target article, etc. The electrical conductivity of the carbon material dispersion can be evaluated, for example, by measuring the surface resistivity of a coating film formed by applying and drying the carbon material dispersion.

[0011] The present inventors formed coating films using the conventional CNT dispersions proposed in Patent Documents 1 and 2, and evaluated the conductivity of the formed coating films by measuring the surface resistivity of the formed coating films. As a result, it was found that none of the coating films formed using the CNT dispersions etc. exhibited the high level of conductivity required in recent years, even at a thin film and low concentration.

[0012] Furthermore, in Patent Document 3, the thickness of the antistatic layer is set to 1 μm or less and the amount of carbon nanotubes added is minimized, thereby achieving a surface resistivity of 3.0×10 ５ An antistatic sheet has been proposed that has a surface resistivity of 1.0 × 10 for a thin film of 1 μm thickness and a transmittance of 90% or more at a wavelength of 550 nm. ３ No study has been made to achieve both high conductivity of Ω / sq or less and good coating film properties.

[0013] The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a carbon material dispersion capable of forming a coating film having improved conductivity in a thin state at a low concentration of conductive material. Another object of the present invention is to provide use of the carbon material dispersion for producing various products and films that become components of various products.

[0014] That is, according to the present invention, there is provided the following carbon material dispersion: [1] A carbon material dispersion comprising at least one carbon material selected from the group consisting of single-walled carbon nanotubes and multi-walled carbon nanotubes, an aqueous medium, a dispersant, and a binder resin, wherein the dispersant is at least one selected from the group consisting of surfactants and polymer dispersants, the polymer dispersant is a styrene-maleic acid modified polymer or a polymer having a structural unit (1) derived from (meth)acrylonitrile and a structural unit (2) derived from (meth)acrylic acid, and the binder resin is at least one selected from the group consisting of cellulose derivatives, styrene-butadiene copolymers, and acrylic resins (excluding those having the structural unit (1)), and which satisfies the following requirements (1), (2), and (3): (1) When the carbon material contains the single-walled carbon nanotubes, the amount of the dispersant relative to 100 parts by mass of the single-walled carbon nanotubes is 50 parts by mass or more and 600 parts by mass or less, and the amount of the binder resin relative to 100 parts by mass of the single-walled carbon nanotubes is 300 parts by mass or more and 850 parts by mass or less; when the carbon material contains the multi-walled carbon nanotubes, the amount of the dispersant relative to 100 parts by mass of the multi-walled carbon nanotubes is 20 parts by mass or more and 200 parts by mass or less, and the amount of the binder resin relative to 100 parts by mass of the multi-walled carbon nanotubes is 700 parts by mass or more and 880 parts by mass or less. (2) When the carbon material contains the single-walled carbon nanotubes, the surface resistivity of a dry film having a thickness of 1 μm and containing 10% by mass of the carbon material is 1.0×10 ３(3) The absorbance A at a wavelength of 780 nm of a diluted dispersion obtained by diluting the dispersion with a blank solution having the same composition as the carbon material dispersion except that it does not contain the carbon material is 1.8±0.02. Ｈ Absorbance A at a wavelength of 380 nm Ｌ The ratio (A Ｌ / A Ｈ [2] A carbon material dispersion liquid comprising at least one carbon material selected from the group consisting of single-walled carbon nanotubes and multi-walled carbon nanotubes, an aqueous medium, a dispersant, and a binder resin, wherein the dispersant is a cellulose derivative, and the binder resin is at least one selected from the group consisting of styrene-butadiene copolymers and acrylic resins, and the carbon material dispersion liquid satisfies the following requirements (1), (2), and (3): (1) When the carbon material contains the single-walled carbon nanotubes, the amount of the dispersant relative to 100 parts by mass of the single-walled carbon nanotubes is 50 parts by mass or more and 600 parts by mass or less, and the amount of the binder resin relative to 100 parts by mass of the single-walled carbon nanotubes is 300 parts by mass or more and 850 parts by mass or less; when the carbon material contains the multi-walled carbon nanotubes, the amount of the dispersant relative to 100 parts by mass of the multi-walled carbon nanotubes is 20 parts by mass or more and 200 parts by mass or less, and the amount of the binder resin relative to 100 parts by mass of the multi-walled carbon nanotubes is 700 parts by mass or more and 880 parts by mass or less. (2) When the carbon material contains the single-walled carbon nanotubes, the surface resistivity of a dry film having a thickness of 1 μm and containing 10% by mass of the carbon material is 1.0×10 ３ (3) The absorbance A at a wavelength of 780 nm of a diluted dispersion obtained by diluting the dispersion with a blank solution having the same composition as the carbon material dispersion except that it does not contain the carbon material is 1.8±0.02. Ｈ Absorbance A at a wavelength of 380 nm Ｌ The ratio (A Ｌ / A Ｈ) is 1.45 or more. [3] The carbon material dispersion according to [1] or [2], wherein the single-walled carbon nanotubes have an average length of 5 μm or more and 600 μm or less, and the multi-walled carbon nanotubes have an average length of 30 μm or more and 5,000 μm or less. [4] The carbon material dispersion according to any one of [1] to [3], wherein the concentration of the carbon material in the carbon material dispersion is 20 mass% or less. [5] Use of the carbon material dispersion according to any one of [1] to [4] for producing any one of a paint, an ink, a coating agent, a resin molded product material, an electrically conductive material, a thermally conductive material, and an antistatic material. [6] Use of the carbon material dispersion according to any one of [1] to [4] for producing any one of a battery material and a machine part, comprising a film formed from the carbon material dispersion.

[0015] According to the present invention, a carbon material dispersion capable of forming a coating film having both high conductivity and good coating film properties in a thin film state at a low carbon material concentration can be provided. Furthermore, according to the present invention, it is possible to provide use of the carbon material dispersion for producing various products and films that become components of various products.

[0016] <Carbon material 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 material dispersion of the present invention contains at least one carbon material selected from single-walled carbon nanotubes and multi-walled carbon nanotubes, an aqueous medium, a dispersant, and a binder resin. The carbon material dispersion according to this embodiment satisfies the following requirements (1), (2), and (3). Hereinafter, the carbon material dispersion of the present invention (hereinafter also simply referred to as "dispersion") will be described in detail.

[0017] (1) When the carbon material contains the single-walled carbon nanotubes, the amount of the dispersant relative to 100 parts by mass of the single-walled carbon nanotubes is 50 parts by mass or more and 600 parts by mass or less, and the amount of the binder resin relative to 100 parts by mass of the single-walled carbon nanotubes is 300 parts by mass or more and 850 parts by mass or less; when the carbon material contains the multi-walled carbon nanotubes, the amount of the dispersant relative to 100 parts by mass of the multi-walled carbon nanotubes is 20 parts by mass or more and 200 parts by mass or less, and the amount of the binder resin relative to 100 parts by mass of the multi-walled carbon nanotubes is 700 parts by mass or more and 880 parts by mass or less. (2) When the carbon material contains the single-walled carbon nanotubes, the surface resistivity of a dry film having a thickness of 1 μm and containing 10% by mass of the carbon material is 1.0×10 ３ (3) The absorbance A at a wavelength of 780 nm of a diluted dispersion obtained by diluting the dispersion with a blank solution having the same composition as the carbon material dispersion except that it does not contain the carbon material is 1.8±0.02. Ｈ Absorbance A at a wavelength of 380 nm Ｌ The ratio (A Ｌ / A Ｈ ) is 1.45 or more.

[0018] (Carbon Material) The carbon material includes at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. The carbon nanotubes may be doped with a metal such as platinum or palladium or a metal salt. The carbon nanotubes may also be surface-modified by oxidation treatment, plasma treatment, radiation treatment, corona treatment, coupling treatment, or the like.

[0019] The average length of the single-walled carbon nanotubes (hereinafter also referred to as "SWCNTs") is preferably 5 μm or more and 600 μm or less, and more preferably 10 μm or more and 500 μm or less. The average length of the multi-walled carbon nanotubes (hereinafter also referred to as "MWCNTs") is preferably 30 μm or more and 5,000 μm or less. When the dispersion according to this embodiment is used as a constituent material of a battery, it is preferable that the average length of the MWCNTs is 50 μm or more and 3,000 μm or less, because this can further reduce the surface resistivity of the coating film that is formed.

[0020] The dispersion according to this embodiment may further contain other carbon materials in addition to the above-described carbon materials, such as carbon black, carbon fiber, graphite, and graphene.

[0021] Examples of carbon black (hereinafter also referred to as "CB") include acetylene black, furnace black, thermal black, and ketjen black. The average primary particle size of CB is preferably 10 nm or more and 60 nm or less. The carbon material may be doped with a metal such as platinum or palladium or a metal salt. The carbon material may also be surface-modified by oxidation treatment, plasma treatment, radiation treatment, corona treatment, coupling treatment, or the like.

[0022] Examples of carbon fibers include PAN-based carbon fibers made from polyacrylonitrile, pitch-based carbon fibers made from pitches, and recycled products thereof. Among these, carbon nanofibers with nanometer-sized fiber diameters and a cylindrical shape formed by rolling up a six-membered ring graphite structure are preferred. Graphite is a layered substance containing hexagonal plate-like crystals composed of carbon. Among these, graphene, which is a single layer of graphite exfoliated to a thickness of one atom, or graphene formed from multiple layers can be used.

[0023] The other carbon materials may be doped with a metal or a metal salt such as platinum or palladium, and may be surface-modified by oxidation treatment, plasma treatment, radiation treatment, corona treatment, coupling treatment, or the like.

[0024] The average length of CNT and the average primary particle diameter of carbon black can be measured using a disperser such as an ultrasonic homogenizer to disperse CNTs in a solvent such as water, followed by a light scattering method using a dynamic light scattering particle size distribution analyzer, or by calculation from an SEM image of the CNT powder.

[0025] The CNT content in the CNT dispersion is preferably 30% by mass or less, and more preferably 20% by mass or less.

[0026] (Aqueous Medium) The carbon material dispersion according to this embodiment contains an aqueous medium that serves as a liquid medium to disperse the carbon material in. That is, the dispersion according to this embodiment is an aqueous dispersion of a carbon material.

[0027] 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.

[0028] The content of the water-soluble organic solvent in the carbon material dispersion is preferably 70% by mass or less, and more preferably 50% by mass or less.

[0029] (Dispersant) The dispersant is a component for dispersing the carbon material in a liquid medium. Examples of dispersants that can be used include anionic, cationic, nonionic, and amphoteric surfactants; polymer dispersants; and cellulose derivatives. Among these, it is preferable to use at least one of polymer dispersants and cellulose derivatives as the dispersant.

[0030] Examples of cellulose derivatives 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 preferred 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 a cellulose derivative can improve the dispersion of the carbon material and the storage stability.

[0031] The polymer dispersant is preferably a styrene-maleic acid modified polymer or a polymer having a structural unit (1) derived from (meth)acrylonitrile and a structural unit (2) derived from (meth)acrylic acid, and is preferably a polymer substantially composed of only the structural unit (1) derived from (meth)acrylonitrile and the structural unit (2) derived from (meth)acrylic acid. The polymer dispersant is also preferably a polymer having carboxy groups at least partially neutralized with an alkali.

[0032] Examples of styrene-maleic acid modified polymers include commercially available dispersants such as "FLOWLEN GW-1500" (manufactured by Kyoeisha Chemical Co., Ltd., polyalkylene glycol-modified styrene-maleic acid copolymer, having a carboxyl group as the functional group directly bonded to the polymer chain, acid value 55 mg KOH / g, amine value 0 mg KOH / g, weight average molecular weight 5,000), "DISPERBYK-190" (manufactured by BYK-Chemie, polyalkylene glycol-modified styrene-maleic acid copolymer, acid value 10 mg KOH / g, amine value 0 mg KOH / g), and "TEGO Dispers 755W" (manufactured by Evonik, polyalkylene glycol-modified styrene-maleic acid copolymer, acid value 10 mg KOH / g, amine value 0 mg KOH / g).

[0033] 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 electronically adsorbs 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 a carbon material in an aqueous medium for an extended period of time.

[0034] The proportion of the structural unit (1) derived from (meth)acrylonitrile in the polymer is 50% by mass or more and 80% by mass or less, preferably 55% by mass or more and 75% by mass or less. The proportion of the structural unit (2) derived from (meth)acrylic acid in the polymer is 20% by mass or more and 50% by mass or less, 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 water solubility of the polymer tends to be insufficient. On the other hand, if the proportion of the structural unit (2) in the polymer is more than 50% by mass, the water solubility of the polymer tends to be excessively high. 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.

[0035] The polymer dispersant (polymer) may further contain other structural units in addition to the structural unit (1) and the structural unit (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.

[0036] 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 influence of the binder resin may be more pronounced. For this reason, the polymer used as the polymer dispersant is preferably a block copolymer.

[0037] The polymer that is the polymer dispersant is preferably an A-B block copolymer including a polymer block A having a structural unit (1-A) derived from acrylonitrile and a structural unit (2-A) derived from methacrylic acid, and a polymer block B having a structural unit (1-B) derived from acrylonitrile and a structural unit (2-B) derived from methacrylic acid. Polymer block A is preferably a polymer block substantially composed only of a structural unit (1-A) derived from acrylonitrile and a structural unit (2-A) derived from methacrylic acid. Polymer block B is preferably a polymer block substantially composed only of a structural unit (1-B) derived from acrylonitrile and a structural unit (2-B) derived from methacrylic acid.

[0038] The proportion of the structural unit (1-A) derived from acrylonitrile in the 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 the structural unit (2-A) derived from methacrylic acid in the 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 the structural unit (1-A) and the structural unit (2-A) is taken as 100% by mass.

[0039] The A chain is a polymer block that has a lower carboxyl group content than the polymer block B (hereinafter also referred to as the "B chain") and has relatively low water solubility. For this reason, 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 water solubility of the A chain may be insufficient. On the other hand, if the proportion of the structural unit (2-A) in the A chain is more than 40% by mass, the water solubility of the A chain may be too high, and the A chain may be more likely to detach from the carbon material.

[0040] 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 exceeds 100,000, the water solubility may be insufficient even if the polymer contains a structural unit (2-A) having a carboxy group.

[0041] 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 above-mentioned number average molecular weight range will be contained, which may reduce the effect of improving dispersibility.

[0042] 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, and 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, and more preferably 35% by mass or more and 85% by mass or less. The total of the structural unit (1-B) and the structural unit (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, and 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.

[0043] The B chain is a polymer block that contains more carboxy 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 A-B 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 may be excessively high. As a result, the viscosity of the carbon material dispersion may become excessively high and the water resistance of the formed coating film may decrease.

[0044] 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.

[0045] Examples of alkalis that can be used to neutralize at least a portion of the carboxy groups in the polymer dispersant (polymer) include conventionally known alkalis such as 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.

[0046] Although all carboxy groups in the polymer may be neutralized with alkali, it is also preferable to neutralize only a portion 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 a portion of the carboxy groups are 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.

[0047] The polymer used as the polymer dispersant can be produced according to 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 difficult to dissolve 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 preferable. 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.

[0048] 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.

[0049] It is difficult to produce an A-B block copolymer used as a polymer dispersant by a conventional radical polymerization method. For this reason, the A-B block copolymer is preferably produced by a polymerization method having living properties, such as a living anionic polymerization method, a living cationic polymerization method, or a living radical polymerization method. Among these, the living radical polymerization method is particularly preferred from the viewpoints of conditions, materials, equipment, and the like.

[0050] Examples of living radical polymerization methods include atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer polymerization (RAFT), nitroxide (NMP) polymerization, organotellurium (TERP) polymerization, reversible transfer catalyst polymerization (RTCP), and reversible catalyst-mediated polymerization (RCMP). Among these, the RTCP and RCMP methods, which use an organic compound as a catalyst and an organic iodide as a polymerization initiator, are preferred. These methods use relatively safe, commercially available compounds, do not use heavy metals, and do not require special compounds, and are advantageous in terms of cost and purification. Furthermore, by using tertiary iodine as the growing terminal, a highly accurate block structure can be easily formed using standard equipment.

[0051] When producing an A-B block copolymer, either polymer block A or polymer block B may be polymerized first. However, if polymer block B is polymerized first, methacrylic acid may remain in the polymerization system. In this case, an excessive amount of structural units derived from methacrylic acid may be introduced into polymer block A, which is polymerized subsequently. For this reason, it is preferable to polymerize polymer block A first, and then polymerize polymer block B.

[0052] When the carbon material contains SWCNT, the amount of dispersant per 100 parts by mass of SWCNT must be 50 parts by mass or more and 600 parts by mass or less, more preferably 70 parts by mass or more and 500 parts by mass or less, and particularly preferably 100 parts by mass or more and 300 parts by mass or less. When the carbon material contains MWCNT, the amount of dispersant per 100 parts by mass of MWCNT must be 20 parts by mass or more and 200 parts by mass or less, more preferably 25 parts by mass or more and 150 parts by mass or less, and particularly preferably 30 parts by mass or more and 100 parts by mass or less. By setting the amount of dispersant relative to the carbon material within the above ranges, a carbon material dispersion in which the carbon material is more stably dispersed can be obtained. If the amount of dispersant relative to the carbon material is too small, 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 relative to the carbon material is too large, the carbon material dispersion may be more likely to thicken and the ratio of carbon material in the solid content may be relatively low. Furthermore, the surface resistivity of the formed coating film becomes slightly high, and when an electrode is formed, the cycle characteristics of the electrode may be reduced.

[0053] (Binder Resin) The carbon material dispersion liquid according to this embodiment further contains 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, in consideration of affinity with the dispersant, it is preferable to use a cellulose derivative such as carboxymethyl cellulose (including a sodium salt); a styrene-butadiene copolymer; or an acrylic resin such as a styrene-acrylic resin.

[0054] The content of the binder resin relative to the carbon material in the carbon material dispersion, for example, in the case of single-walled carbon nanotubes, must be 300 to 850 parts by mass, preferably 350 to 800 parts by mass, per 100 parts by mass of single-walled carbon nanotubes. In the case of multi-walled carbon nanotubes, the content must be 700 to 880 parts by mass, more preferably 700 to 870 parts by mass, per 100 parts by mass of multi-walled carbon nanotubes. If the amount of binder resin is too small, coating onto the substrate may be difficult, and a homogeneous electrode may not be obtained. If the amount of binder resin is too large, the ratio of the active material (carbon material) may be relatively low, resulting in a battery that does not achieve sufficient battery capacity. Furthermore, when the carbon material dispersion is used for coating applications, the content of the binder resin relative to the carbon material in the carbon material dispersion must be 300 to 850 parts by mass, preferably 350 to 800 parts by mass, per 100 parts by mass of the carbon material. Furthermore, when the carbon material dispersion liquid is used for battery applications, the content of the binder resin relative to the carbon material in the carbon material dispersion liquid needs to be 700 parts by mass or more and 880 parts by mass or less, and more preferably 700 parts by mass or more and 870 parts by mass or less, per 100 parts by mass of the carbon material.

[0055] (Additives, etc.) The carbon material dispersion liquid according to this embodiment may further contain additives, resins, etc. Examples of additives include water-soluble dyes, pigments, 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.

[0056] It is preferable that the carbon material dispersion contains an antifoaming agent as an additive, depending on the apparatus used in the wetting and dispersing steps. The inclusion of an antifoaming agent can suppress foaming during the dispersion treatment, allowing the shear force, collision force, and the like applied during the dispersion treatment to act effectively, resulting in a dispersion with better dispersibility.

[0057] (Absorbance of Carbon Material Dispersion Liquid) The absorbance of a dispersion liquid of a carbon material containing carbon nanotubes forms a gentle curve from 300 nm to 1,000 nm in wavelength. However, this curve (absorbance curve) varies greatly depending on the dispersion state of the carbon nanotubes. For example, the absorbance on the short wavelength side shows a large value when the amount of finely dispersed carbon nanotubes is large. On the other hand, the absorbance on the long wavelength side shows a large value when the amount of carbon nanotube aggregates is large. Therefore, the absorbance on the short wavelength side (A Ｌ ) is the absorbance on the long wavelength side (A Ｈ ) and the absorbance ratio (A Ｌ / A Ｈ ) closely reflects the dispersion state of the carbon material in the liquid medium. That is, the finer and more uniformly dispersed the carbon nanotubes are, the larger the absorbance ratio is, and the smaller the absorbance ratio is when the carbon nanotubes are aggregated.

[0058] Reference wavelength W Ｍ is the wavelength W on the short wavelength side Ｌ and the wavelength on the long wavelength side W Ｈ The median of (W Ｍ = (W Ｌ +W Ｈ ) / 2) The wavelength region near the median is hardly affected by the dispersion state of the carbon material, and is therefore suitable as a criterion for evaluating the dispersibility of the carbon material.

[0059] Short wavelength W Ｌis arbitrarily selected from the range of 350 nm to 550 nm, preferably from the range of 350 nm to 450 nm, and more preferably from the range of 350 nm to 400 nm. The absorbance at wavelengths within the above range exhibits clear changes, with little noise or specific peak changes, allowing for stable measurement. If the wavelength is less than 350 nm, the absorption and scattering of light by the fine particles will have an irregular effect, causing the peak to change significantly as the dispersion progresses, making it difficult to use as an accurate indicator. On the other hand, if the wavelength is greater than 550 nm, the change in absorbance will be unclear.

[0060] Long wavelength W Ｈ is arbitrarily selected from the range of 650 nm to 850 nm, preferably the range of 700 nm to 850 nm, and more preferably the range of 700 nm to 800 nm. A wavelength within the above range allows the absorbance of particles with a low proportion of absorbing components and a high proportion of scattering components to be confirmed. Furthermore, there is little noise or specific peak change, allowing for stable measurement. If the wavelength exceeds 850 nm, noise will be mixed into the peak, making it difficult to measure an accurate value. On the other hand, a wavelength below 650 nm is not suitable as an indicator.

[0061] Wavelength W Ｌ and wavelength W Ｈ The difference between the wavelengths W is preferably 100 nm or more, and more preferably 200 nm or more. Ｌ and wavelength W Ｈ By making the difference between the wavelengths W and W equal to or greater than 100 nm, the dispersibility of the carbon material can be read more accurately. Ｌ and wavelength W Ｈ If the difference is too small, it may be difficult to accurately evaluate the dispersion state of the carbon material.

[0062] The absorbance of a dispersion varies depending on the content (concentration) of the carbon material. Therefore, the absorbance of a diluted dispersion prepared by diluting a dispersion containing no binder resin and a dispersion containing a binder resin, as necessary, is measured. It is preferable to use a blank solution with the same composition as the target dispersion except that it does not contain a carbon material as the diluting solution used to dilute the dispersion. Using such a blank solution suppresses the effects of diffusion and re-aggregation of fine particles and the environment on the absorbance, and also reduces the influence of polymer dispersants, which are sometimes used as dispersants, allowing for more accurate measurement of the absorbance.

[0063] To accurately measure absorbance, it is usually preferable that the content of the carbon material in the sample liquid (dilute dispersion) be in the range of 0.001% by mass or more and 0.01% by mass or less. If it exceeds 0.01% by mass, the amount of scattered laser light transmitted during measurement is small, making accurate measurement difficult. On the other hand, if it is less than 0.001% by mass, the absorbance value will be too small, making accurate evaluation or comparison difficult.

[0064] Wavelength W of the diluted dispersion obtained by diluting with a diluent containing a liquid medium Ｍ The absorbance of the diluted dispersion is 1.2 or more and 2.2 or less, and preferably 1.5 or more and 2.0 or less. Ｍ If the absorbance is less than 1.2, it is difficult to judge the dispersion state. On the other hand, if the absorbance is more than 2.2, it is difficult to accurately measure the absorbance.

[0065] Wavelength W of the dilute dispersion Ｈ Absorbance A Ｈ For wavelength W Ｌ Absorbance A Ｌ The ratio (A Ｌ / A Ｈ ) is the wavelength W Ｈ and W Ｌ For example, the wavelength W Ｌ = 380 nm and wavelength W Ｈ = "A" at 780 nm Ｌ / A Ｈ When the value of "1.60 → 1.45" is changed, the wavelength W Ｌ = 400 nm and wavelength WＨ = "A" at 700 nm Ｌ / A Ｈ The value of " is "1.44 → 1.29", and the wavelength W Ｌ = 350 nm and wavelength W Ｈ = "A" at 800 nm Ｌ / A Ｈ The value of " is "1.78 → 1.63". Ｌ = 380 nm and wavelength W Ｈ = "A" at 780 nm Ｌ / A Ｈ When the value of "1.65 → 1.50" is changed, the wavelength W Ｌ = 400 nm and wavelength W Ｈ = "A" at 700 nm Ｌ / A Ｈ The value of " is "1.48 → 1.33", and the wavelength W Ｌ = 350 nm and wavelength W Ｈ = "A" at 800 nm Ｌ / A Ｈ " The value is "1.85 → 1.70".

[0066] Wavelength W Ｌ The absorbance of the dilute dispersion at wavelength W is a physical property that serves as an index of the dispersion state of the carbon material. Ｈ The absorbance of the dilute dispersion at wavelength W is a physical property that serves as an index of the aggregation state of the carbon material. Ｌ and W Ｈ The wavelength W is the median value of Ｍ is used as a reference, and this wavelength W Ｍ The wavelength W of the diluted dispersion obtained by diluting with a diluent containing a liquid medium so that the absorbance of Ｈ Absorbance A Ｈ For wavelength W Ｌ Absorbance A Ｌ The ratio (A Ｌ / A Ｈ ) value, the dispersion state of the carbon material in this dispersion liquid can be accurately evaluated.

[0067] The dilute dispersion has a wavelength W Ｌ is 380 nm, wavelength W Ｈ is 780 nm, and the wavelength W Ｍ is 580 nm, and the wavelength WＭ When the absorbance at is 1.8±0.02, the absorbance A Ｈ Absorbance A Ｌ The ratio (A ３８０ / A ７８０ The absorbance ratio (A) must be 1.45 or more, and is more preferably 1.50 or more in order to make the short side of the aggregates less than 100 μm. In order to further disperse the carbon nanotubes in the liquid medium, the absorbance ratio (A) is particularly preferably 1.55 or more. ３８０ / A ７８０ By setting the absorbance ratio (A) in the above range, even if the types or amounts of the carbon material, dispersant, and binder resin are changed, it is possible to obtain a dispersion liquid that is substantially free of coarse aggregates and has better viscosity stability. ３８０ / A ７８０ The value of (a) can be achieved by adjusting the type or amount of the carbon material or dispersant, or by adjusting the wetting method or dispersion method of the dispersion.

[0068] Absorbance ratio (A ３８０ / A ７８０ If the absorbance ratio (A) is less than 1.45, the carbon nanotubes are not finely and uniformly dispersed, and the viscosity stability of the dispersion is low, and a large amount of coarse aggregates is contained. ３８０ / A ７８０ The dispersion according to the present embodiment, in which the viscosity coefficient (σ) is 1.45 or more, contains a carbon material including carbon nanotubes in a finely and uniformly dispersed state, has good viscosity stability, is substantially free of coarse aggregates, and contains only extremely small amounts of fine aggregates, even if they are present.

[0069] The absorbance ratio of the dispersion is preferably high, regardless of whether or not a binder resin is present. Adding a binder resin to a poorly dispersed dispersion that does not contain a binder resin hardly improves the absorbance ratio, and the dispersion may not exhibit sufficient performance.

[0070] (Physical Properties of Carbon Material Dispersion) The dispersion according to this embodiment is resistant to viscosity change even after a long period of time has passed, and has excellent viscosity stability (storage stability). Specifically, 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), based on the viscosity (mPa s) of the binder resin-free dispersion at 25°C immediately after preparation (dispersion), is typically 15% or less, preferably 10% or less, and more preferably 5% or less.

[0071] 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, leading to reduced 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 but less than 10 per observation, and particularly preferably, not a single aggregate with short sides of 20 μm or more is observed even after five observations.

[0072] (Method for Producing Carbon Material Dispersion) A carbon material dispersion can be produced by wetting a carbon material containing carbon nanotubes in a liquid medium using a dispersant according to a conventionally known method, and then dispersing the carbon material. For example, wetting and dispersion methods using magnetic stirrer stirring, dissolver stirring, triple-roll kneading, ultrasonic dispersion, bead mill dispersion, an emulsifier, a homogenizer, or the like 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 particle diameter beads is preferred. Furthermore, in consideration of damage to carbon materials such as carbon nanotubes, wetting methods and dispersion methods may be combined.

[0073] When mixing multiple dispersions or adding and mixing a binder resin, a disperser may be used in addition to a magnetic stirrer. Mixing using a disperser is preferred because it can prevent shock aggregation and the like, thereby allowing for a dispersion with a better dispersion state to be obtained.

[0074] When dispersing a carbon material containing carbon nanotubes, a binder resin may be added to the liquid medium, and the conductivity will not decrease if the carbon nanotubes are well dispersed in the resulting dispersion. Adding a binder resin during dispersion is preferable because it can prevent shock aggregation and the like.

[0075] (Coating Film) A conductive coating film (film) can be formed by applying and drying the carbon material 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 or more and 50% by mass or less, more preferably 0.1% by mass or more and 30% by mass or less, and particularly preferably 0.5% by mass or more and 20% by mass or less. The thickness (film thickness) of the coating film can be, for example, 0.8 μm or more and 30 μm or less. The thicker the film thickness and the higher the concentration of the carbon material, the lower the surface resistivity of the coating film. It has been confirmed that the surface resistivity of the coating film hardly changes 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 10±0.5% by mass.

[0076] The surface resistivity of a dried film (coating film) having a thickness of 1 μm and containing 10% by mass of carbon material, which is formed by applying and drying the carbon material dispersion liquid according to this embodiment, is 1.0×10 ３ It is necessary that the resistance is Ω / sq or less, and preferably 9.0×10 ２ The surface resistivity of the dried film (coating) is Ω / sq or less. The content of the carbon material in the dried film (coating) can be calculated by heating the coating film formed by applying the dispersion and evaporating the aqueous liquid medium, and subtracting the mass (solid content) of the dispersant and binder resin used from the mass of the dried film formed. The surface resistivity of the dried film can be achieved by adjusting the type or amount of the carbon material or dispersant, or by adjusting the wetting method or dispersion method of the dispersion.

[0077] <Use of Carbon Material Dispersion> In the carbon material dispersion according to this 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 this embodiment is an aqueous dispersion, it is an environmentally friendly material and is useful as a material for producing paints, inks, coating agents, resin molding materials, and the like. It is also expected to be used as an electrically conductive material or a thermally conductive material, and also as an antistatic material. Furthermore, it is useful as a material for forming films constituting battery materials such as electrode materials for batteries such as lithium-ion batteries and fuel cells, or films constituting capacitor materials, and films constituting various mechanical parts.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] <Preparation of Materials> The following carbon materials, dispersants, and binder resins were prepared.

[0082] (Carbon Materials) [Single-Walled Carbon Nanotubes (SWCNT)] SWCNT-1: Trade Name "Tuball", manufactured by OCSiAl, average length 2 to 20 μm SWCNT-2: Trade Name "SG101", manufactured by Zeon Corporation, average length 100 to 600 μm

[0083] [Multi-walled carbon nanotubes (MWCNT)] MWCNT-1: Trade name "400T", manufactured by KUMHO Corporation, average length 90 to 100 μm MWCNT-2: Trade name "s5", manufactured by SUSN Corporation, average length 40 to 80 μm MWCNT-3: Trade name "Multi-walled carbon nanotube flakes", manufactured by Hamamatsu Carbonix Co., Ltd., average length 500 to 1500 μm MWCNT-4: Trade name "s4", manufactured by SUSN Corporation, average length 5 to 20 μm

[0084] [Carbon Black (CB)] CB-1: Trade name "Li435", manufactured by Denka Company Limited

[0085] (Dispersants) Dispersant d: trade name "Floren GW-1500", styrene-maleic acid modified polymer, manufactured by Kyoeisha Chemical Co., Ltd., solid content 100%, acid value 55 mg KOH / g, amine value 0 mg KOH / g, weight average molecular weight 5,000 Dispersant e: trade name "Disparlon AQ-380", acrylic polymer, manufactured by Kusumoto Chemicals Co., Ltd., solid content 30%, acid value 15 mg KOH / g, amine value 11 mg KOH / g

[0086] (Binder resins) Binder resin A: trade name "YL-1098", styrene acrylic resin, manufactured by Seiko PMC Corporation Binder resin B: dispersant c Binder resin C: a mixture of dispersant c and styrene butadiene copolymer latex (trade name "Nalstar SR-112", manufactured by Nippon A&L Co., Ltd.) (dispersant c: styrene butadiene copolymer latex = 4:1)

[0087] <Production of Dispersant (1)> (Dispersant a) 233.3 parts of N-methylpyrrolidone (NMP) was placed in a reaction vessel and stirred, and the temperature was raised 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", manufactured by 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. After maintaining the temperature at 70°C for 1 hour, the temperature was raised to 80°C and maintained 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 an N,N-dimethylformamide solution of lithium bromide (lithium bromide concentration: 10 mmol / L) as a 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%.

[0089] (Dispersant b) 255.4 parts of 3-methoxy-N,N-dimethylpropanamide (MDMPA), 1.0 part of iodine, 3.7 parts of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (trade name "V-70", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (V-70), 0.2 parts of diphenylmethane (DPM), 106.1 parts of AN, and 26.5 parts of methacrylic acid (MAA) were placed in a reaction vessel. The mixture was stirred under a nitrogen stream, heated to 40 ° C, and polymerized for 4 hours to form an A chain. The solids content of the reaction solution was 34.8%, and the polymerization conversion calculated from the solids content was approximately 100%. The Mn of the formed A chain was 14,800, the PDI was 1.41, and the peak top molecular weight (PT) was 20,700.

[0090] After adding 3.1 parts of V-70, a monomer solution containing 30.0 parts of AN, 31.8 parts of MAA, and 216.9 parts of MDMPA was further added. Polymerization was then carried out at 40°C for 4 hours to form B chains, yielding an A-B block copolymer. The solids content of the reaction solution was 29.9%, confirming that the target product was obtained almost quantitatively. The resulting A-B block copolymer had an Mn of 21,600, a PDI of 1.52, and a PT of 32,700. The molecular weight of the B chain could be calculated by subtracting the Mn of the A chain from the Mn of the A-B block copolymer. That is, the Mn of the B chain was 6,800, and the PT was 12,000.

[0091] 29.8 parts of NaOH (110 mol % relative to MAA) and 105.1 parts of ion-exchanged water were placed in a beaker, and the NaOH was completely dissolved to prepare an aqueous NaOH solution. The aqueous NaOH solution was charged into a reaction vessel to neutralize the carboxyl groups, yielding a solution of polymer dispersant (dispersant b). The solids content of the resulting solution of dispersant b was 25.1%.

[0092] (Dispersant c) 400 g of isopropyl alcohol (IPA) and 60 g of water were placed in a 1 L stainless steel vessel equipped with a stirrer, and 10 g of sodium hydroxide (purity 98%) was added while cooling the stainless steel vessel. After the solution was cooled to below 25°C, 20 g of ground pulp was added while stirring. The mixture was then stirred and mixed (mercerized) at 15-25°C for 60 minutes to prepare alkali cellulose. Next, 30 g of a 1:2 mixed solution of monochloroacetic acid and isopropyl alcohol was added while the stainless steel vessel was cooled and maintained at 15-25°C, and the mixture was stirred and mixed for 15 minutes. The stainless steel vessel was then heated, and the temperature of the solution was raised to 70°C over approximately 30 minutes. The mixture was stirred at 65-75°C for 120 minutes to carry out an etherification reaction. After completion of the reaction, unreacted sodium hydroxide was neutralized with acetic acid, and the product was separated. The by-products were removed by washing with a 70% aqueous methanol solution. The product was dried and pulverized to obtain carboxymethyl cellulose sodium salt (dispersant c). The viscosity of a 1% aqueous solution of the obtained carboxymethyl cellulose sodium salt was 31 mPa s, and the degree of etherification (DS) was 0.84.

[0093] The degree of etherification was measured with reference to the synthetic detergent JIS-related substance test method described in Oil Chemistry 38 (11), 962-967, 1989. Specifically, approximately 1 g of carboxymethylcellulose sodium salt was precisely weighed and placed in a porcelain crucible. The mixture was then heated at a temperature not exceeding 600°C (approximately 550-590°C) for 1 hour to incinerate. After cooling to room temperature, the crucible was transferred to a 500 mL beaker and 250 mL of water was added. 50 mL of 0.05 mol / L aqueous sulfuric acid solution was added and boiled for 30 minutes. After cooling to room temperature, unreacted acid was titrated using 0.1 mol / L sodium hydroxide. Phenolphthalein was used as the indicator. The amount of 0.1 mol / L sodium hydroxide used in the titration was designated as "X" mL, and the degree of etherification (DS) was calculated using the following formula: Degree of etherification (DS) = 162X / (10,000-80X)

[0094] <Measurement and Evaluation Methods> (Calculation of CNT Average Length) The CNT powder was observed under an electron microscope, and the average length of 10 randomly selected CNTs was calculated. This operation was performed for five batches, and a numerical range was determined as the range of the average length.

[0095] (Absorbance Measurement and Absorbance Ratio Calculation) A blank solution was prepared, having the same composition as the carbon material dispersion except that it did not contain a carbon material. After measuring the baseline using the prepared blank solution, the absorbance of the sample solution was measured. The absorbance of the sample solution was measured using a spectrophotometer (trade name "Hitachi Spectrophotometer U-3310" manufactured by Hitachi High-Tech Science Corporation) equipped with a quartz cell with a 10 mm optical path length. Regarding dilution with the blank solution, a calibration curve was created by plotting the absorbance at a wavelength of 580 nm as a function of dilution ratio, and the dilution ratio was calculated to achieve an absorbance of 1.8 ± 0.02, thereby preparing a dispersion diluted to the desired concentration. It is also possible to adjust the carbon component concentration to the desired concentration before dispersion, or to adjust the carbon component concentration to satisfy the absorbance during the initial blending stage and then perform dispersion. Specifically, the sample solution was prepared by first collecting the dispersion in a polyethylene bottle and adding an appropriate amount of blank solution based on the dilution ratio determined by the calibration curve. The mixture was stirred for 30 seconds using a vortex mixer (manufactured by Scientific Industries), and the absorbance A at a wavelength of 580 nm was measured. ５８０ The absorbance A of the obtained sample solution at a wavelength of 380 nm was 1.8±0.02. ３８０ and absorbance A at a wavelength of 780 nm ７８０ The absorbance ratio (A ３８０ / A ７８０ The measurement was carried out on the dispersion immediately after dispersion and on the dispersion after the binder resin was added.

[0096] (Evaluation of Dispersion Liquid) [Viscosity Measurement and Viscosity Stability Evaluation] Using an E-type viscometer equipped with a 1°34' x R24 rotor, the viscosity of the binder resin-free dispersion liquid immediately after dispersion and after 10 days (after standing at room temperature for 10 days) was measured at a temperature of 25°C and a rotor rotation speed of 100 rpm. For dispersion liquids 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 dispersion liquids 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 dispersion liquid was then evaluated according to the following evaluation criteria. AA: The rate of change in viscosity after 10 days, based on the viscosity immediately after dispersion, is less than 5%. A: The rate of change in viscosity after 10 days, based on the viscosity immediately after dispersion, is 5% or more and less than 10%. B: The rate of change in viscosity after 10 days, based on the viscosity immediately after dispersion, is 10% or more and less than 15%. C: The rate of change in viscosity after 10 days, based on the viscosity immediately after dispersion, is 15% or more.

[0097] [Aggregate Observation] A binder-free dispersion was collected in a polyethylene bottle and diluted with a blank solution to a carbon material concentration of 0.1% by mass. The mixture was stirred for 30 seconds using a vortex mixer (manufactured by Scientific Industries, Inc.) to obtain a diluted solution. 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 binder-free dispersion immediately after dispersion and the binder-free dispersion 10 days later (after standing at room temperature for 10 days) were each dropped five times onto a glass slide to prepare samples for observation, and the presence or absence of aggregates was evaluated according to the following evaluation criteria: AA: No aggregates with a short side of 20 μm or more were observed during the five observations. A: The number (average) of aggregates with short sides of 20 μm or more was 1 or more but less than 10 per observation, and not a single aggregate with short sides of 100 μm or more was observed in any of the five observations. B: The number (average) of aggregates with short sides of 20 μm or more was 10 or more per observation, and not a single aggregate with short sides of 100 μm or more was observed in any of the five observations. C: One or more aggregates with short sides of 100 μm or more were observed in any of the five observations.

[0098] (Evaluation of coating film) [Measurement of surface resistivity] When the 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 Mitsubishi Chemical Analytech Co., Ltd.) was used to measure the surface resistivity of the coating film at five points with an applied voltage of 10 V, and the average value was calculated. ５ When the resistivity was Ω / sq or less, a low resistance resistivity meter (trade name "Loresta-GP MCP-T610", manufactured by Mitsubishi Chemical Analytech Co., Ltd.) was used to apply 10 V and measure the surface resistivity of the coating film at five points, and the average value was calculated.

[0099] [Observation of coated product] A 10 cm square dried film formed by coating a dispersion containing a binder resin on a PET film was visually observed, and the film was evaluated for cracking, peeling, and unevenness according to the following evaluation criteria. AA: No cracking, peeling, or unevenness was observed in a single location. A: Cracks, peeling, or unevenness was present in an area less than 5% of the entire area of ​​the dried film. B: Cracks, peeling, or unevenness was present in an area of ​​5% or more but less than 30% of the entire area of ​​the dried film. C: Cracks, peeling, or unevenness was present in an area of ​​30% or more of the entire area of ​​the dried film.

[0100] <Preparation and Evaluation of Dispersions (1)> (Dispersions 1 to 22) The types and amounts of dispersant and water shown in Table 1 were placed in a 200 mL plastic bottle (polyethylene bottle). After stirring with a magnetic stirrer until uniform, the types and amounts of carbon material shown in Table 1 were added and further stirred. Next, a high-pressure homogenizer (manufactured by Joko Co., Ltd.) was used to perform high-pressure treatment at a treatment pressure of approximately 10 MPa. Thereafter, a high-pressure homogenizer (manufactured by Sugino Machine Co., Ltd.) was used to perform high-pressure dispersion treatment at a treatment pressure of approximately 100 MPa to obtain a dispersion. The number of passes (number of treatments in high-pressure dispersion treatment) for the dispersion is shown in Table 1. Note that for dispersions with a pass number of 0, high-pressure dispersion treatment was not performed. Furthermore, the results of evaluating the viscosity stability of the obtained dispersions and the results of observing aggregates are shown in Table 3.

[0101] (Mixtures 1 and 2) Mixtures 1 and 2 were obtained by blending the first dispersion and the second dispersion of the types shown in Table 2 so that the carbon material 1 and the carbon material 2 were in the mass ratio shown in Table 2, and then mixing them using a magnetic stirrer. Table 3 shows the evaluation results of the viscosity stability of the obtained mixtures and the results of observing the aggregates.

[0102]

[0103]

[0104]

[0105] (Examples 1 to 5, Examples 7 to 15, Reference Examples 1 to 6, and Comparative Examples 1 to 10) The types of dispersions and binder resins shown in Table 5 were blended in proportions such that the concentration (%) of the carbon material in the resulting coating film (solid content) was the value shown in Table 5, and then mixed using a magnetic stirrer to obtain carbon material dispersions. Table 4 shows the absorbance ratios for some of the carbon material dispersions. Table 4 also shows the number of passes for each dispersion used. Each of the obtained carbon material dispersions was 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 5. Table 5 shows the surface resistivities of the formed coating films. In Comparative Example 6, extensive cracking and peeling occurred in the coating during drying, making it impossible to obtain the smooth coated surface required for surface resistivity measurement, and evaluation was therefore abandoned.

[0106]

[0107]

[0108] (Application Example 1-1: Battery Material (Anode)) The following materials were used to manufacture the anode of a lithium ion battery. [Anode activator] Graphene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Silicon monoxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) [Binder resin] 10% aqueous polyacrylic acid solution (trade name "CLPA-C07", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Carboxymethyl cellulose (trade name "CMC Daicel 2200", manufactured by Daicel Miraize Co., Ltd.) Styrene butadiene copolymer latex (trade name "Nalstar SR-112", manufactured by Nippon A&L Co., Ltd.)

[0109] 15 parts of silicon monoxide, 85 parts of graphene, 3 parts of dispersion 2, 30 parts of a 10% aqueous polyacrylic acid solution, 1.6 parts of carboxymethyl cellulose, and 0.4 parts of a styrene-butadiene copolymer latex were mixed using a planetary mixer to obtain a negative electrode material having a coating weight of 15 mg / cm after drying. ２The negative electrode material was applied to a copper foil having a thickness of 20 μm using an applicator so that the negative electrode material was applied to a copper foil having a thickness of 20 μm. The negative electrode was dried in an oven set to 120° C. for 30 minutes and then rolled with a roll press to obtain a negative electrode. The volume resistivity of the obtained negative electrode was 0.16 Ω cm, and the capacity retention rate was 95%.

[0110] (Application Example 1-2: Battery Material (Negative Electrode)) A negative electrode was produced in the same manner as in Application Example 1-1 described above, except that Dispersion 15 was used instead of Dispersion 2. The volume resistivity of the produced negative electrode was 0.31 Ω cm, and the capacity retention rate was 93%. From the above, it was found that by using a dispersion with a good dispersion evaluation, a negative electrode with a smaller volume resistivity value could be produced.

[0111] (Application Example 2-1: Antistatic Coating Agent) 100 g of dispersion 2, 100 g of polymer binder (trade name "NeoPac R-9699", manufactured by Kusumoto Chemicals Co., Ltd., acrylic urethane resin, solid content 40%), and 800 g of pure water were placed in a plastic cup and stirred with a dissolver to obtain an antistatic coating agent. The obtained antistatic coating agent was applied to the surface of a 38 μm thick polyethylene terephthalate film (manufactured by Toray Industries, Inc.) using a bar coater so that the coating film would be 0.5 μm thick after drying. The film was dried in an oven set at 80° C. for 10 minutes to obtain an antistatic coating film. The surface resistivity of the obtained film was 9.6×10 ５ Ω / cm ２ It was.

[0112] (Application Example 2-2: Antistatic Coating Agent) An antistatic coating film was produced in the same manner as in Application Example 3-1, except that Dispersion 15 was used instead of Dispersion 2. The surface resistivity of the produced film was 7.4 × 10 ７ Ω / cm ２ From the above, it was found that by using a mixed solution with a good dispersion evaluation, it is possible to produce an antistatic coating film with a lower surface resistivity value.

[0113] 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 material dispersion liquid comprising at least one carbon material selected from the group consisting of single-walled carbon nanotubes and multi-walled carbon nanotubes, an aqueous medium, a dispersant, and a binder resin, wherein the dispersant is at least one selected from the group consisting of surfactants and polymer dispersants, the polymer dispersant is a styrene-maleic acid modified polymer or a polymer having a structural unit (1) derived from (meth)acrylonitrile and a structural unit (2) derived from (meth)acrylic acid, and the binder resin is at least one selected from the group consisting of cellulose derivatives, styrene-butadiene copolymers, and acrylic resins (excluding those having the structural unit (1)), and which satisfies the following requirements (1), (2), and (3): (1) When the carbon material contains the single-walled carbon nanotubes, the amount of the dispersant relative to 100 parts by mass of the single-walled carbon nanotubes is 50 parts by mass or more and 600 parts by mass or less, and the amount of the binder resin relative to 100 parts by mass of the single-walled carbon nanotubes is 300 parts by mass or more and 850 parts by mass or less; when the carbon material contains the multi-walled carbon nanotubes, the amount of the dispersant relative to 100 parts by mass of the multi-walled carbon nanotubes is 20 parts by mass or more and 200 parts by mass or less, and the amount of the binder resin relative to 100 parts by mass of the multi-walled carbon nanotubes is 700 parts by mass or more and 880 parts by mass or less. (2) When the carbon material contains the single-walled carbon nanotubes, the surface resistivity of a dry film having a thickness of 1 μm and containing 10% by mass of the carbon material is 1.0×10 ３ (3) The absorbance A at a wavelength of 780 nm of a diluted dispersion obtained by diluting the dispersion with a blank solution having the same composition as the carbon material dispersion except that it does not contain the carbon material is 1.8±0.

02. Ｈ Absorbance A at a wavelength of 380 nm Ｌ The ratio (A Ｌ / A Ｈ ) is 1.45 or more.

2. A carbon material dispersion liquid containing at least one carbon material selected from the group consisting of single-walled carbon nanotubes and multi-walled carbon nanotubes, an aqueous medium, a dispersant, and a binder resin, wherein the dispersant is a cellulose derivative, and the binder resin is at least one selected from the group consisting of styrene-butadiene copolymers and acrylic resins, and which satisfies the following requirements (1), (2), and (3): (1) When the carbon material contains the single-walled carbon nanotubes, the amount of the dispersant relative to 100 parts by mass of the single-walled carbon nanotubes is 50 parts by mass or more and 600 parts by mass or less, and the amount of the binder resin relative to 100 parts by mass of the single-walled carbon nanotubes is 300 parts by mass or more and 850 parts by mass or less; when the carbon material contains the multi-walled carbon nanotubes, the amount of the dispersant relative to 100 parts by mass of the multi-walled carbon nanotubes is 20 parts by mass or more and 200 parts by mass or less, and the amount of the binder resin relative to 100 parts by mass of the multi-walled carbon nanotubes is 700 parts by mass or more and 880 parts by mass or less. (2) When the carbon material contains the single-walled carbon nanotubes, the surface resistivity of a dry film having a thickness of 1 μm and containing 10% by mass of the carbon material is 1.0×10 ３ (3) The absorbance A at a wavelength of 780 nm of a diluted dispersion obtained by diluting the dispersion with a blank solution having the same composition as the carbon material dispersion except that it does not contain the carbon material is 1.8±0.

02. Ｈ Absorbance A at a wavelength of 380 nm Ｌ The ratio (A Ｌ / A Ｈ ) is 1.45 or more.

3. The carbon material dispersion liquid according to claim 1 or 2, wherein the average length of the single-walled carbon nanotubes is 5 μm or more and 600 μm or less, and the average length of the multi-walled carbon nanotubes is 30 μm or more and 5,000 μm or less.

4. The carbon material dispersion liquid according to claim 1 or 2, wherein the concentration of the carbon material in the carbon material dispersion liquid is 20 mass % or less.

5. Use of the carbon material dispersion according to any one of claims 1 to 4 for producing any one of paints, inks, coating agents, resin molding materials, conductive materials, thermally conductive materials, and antistatic materials.

6. Use of the carbon material dispersion according to any one of claims 1 to 4 for producing any one of battery materials and mechanical parts, which has a coating formed from the carbon material dispersion.

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