Carbon material dispersion and use thereof

Abstract

To provide a carbon material dispersion capable of forming a coating film in a thin-film state and at a low conductive-material concentration, the coating film having improved conductivity.SOLUTION: A carbon material dispersion contains: single-walled carbon nanotubes and / or multi-walled carbon nanotubes; an aqueous medium; a dispersant; and a binder resin. The dispersion satisfies the following 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 which has 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.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Carbon materials (nanocarbon materials) such as carbon black, carbon fiber, carbon nanotube (hereinafter also referred to as "CNT"), graphite, and graphene have a six-membered ring graphite structure formed by covalent bonds of carbon atoms. Therefore, it is a material that exhibits various properties such as electrical conductivity and heat conductivity, and methods for utilizing its properties in a wide range of fields have been studied. For example, paying attention to the electrical properties, thermal properties, and properties as a filler of carbon materials, it has been studied to be used for antistatic agents, conductive materials, plastic reinforcing materials, semiconductors, electrodes for fuel cells or secondary batteries, and cathode rays of displays.

[0003] In these applications, in recent years, higher performance has been required, and CNTs have been actively used as carbon materials. In addition, in order to improve various physical properties such as electrical conductivity, in addition to the type and amount of the dispersant for dispersing CNTs in the liquid medium, the selection of the binder resin used when forming a coating film or an electrode is also important.

[0004] As related prior art, for example, a CNT aqueous dispersion liquid which is a dispersion containing CNTs with an average outer diameter of 3 nm or less and a dispersant, and having an average particle diameter measured by the dynamic light scattering method of 200 nm or more and 1,500 nm or less, and a method for evaluating the electrical conductivity of CNTs by measuring the surface resistance of a coating film obtained by drying the dispersion liquid have been proposed (Patent Document 1).

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

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

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] Generally, in a conductive paint-coated article, the higher the film thickness of the conductive paint-coated layer, the higher the conductivity. For miniaturization and weight reduction of the conductive paint-coated article, for example, if the coating layer is made very thin at 1 μm thick, it is difficult to obtain a high conductivity of 1.0×10 3 Ω / sq or less even when a conductive paint containing CNT is applied.

[0009] Generally, increasing the concentration of the conductive material in the coated article improves the conductivity. However, since the concentration of the binder resin in the coated article relatively decreases, it becomes difficult to reflect the properties of the binder resin such as elongation or bending, and it becomes difficult to obtain a uniform coated article. Alternatively, even if a uniform coated article is obtained, the durability of the coated article such as flexibility and adhesion decreases, so it has been difficult to achieve both high conductivity and good coating film physical properties.

[0010] A carbon material dispersion containing CNT is used, for example, as a material for improving the conductivity of a target article or the like. And the 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 inventors formed a coating film using a conventional CNT dispersion liquid or the like proposed in Patent Document 1 or 2, and measured the surface resistivity of the formed coating film to evaluate the conductivity. As a result, it was found that none of the coating films formed using any of the CNT dispersion liquids or the like exhibited high-level conductivity required in recent years at a thin film and low concentration.

[0012] Furthermore, in Patent Document 3, by setting the thickness of the antistatic layer to 1 μm or less and suppressing the addition amount of carbon nanotubes as much as possible, the surface resistivity is 3.0 × 10 5 Ω / sq or less and a transmittance at a wavelength of 550 nm of 90% or more, an antistatic sheet has been proposed. However, no study has been made to achieve both high conductivity with a surface resistivity of 1.0 × 10 3 Ω / sq or less and good coating film physical properties in a 1-μm-thick thin film.

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

Means for Solving the Problems

[0014] That is, according to the present invention, there is provided a carbon material dispersion liquid shown below. [1] It 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 dispersant is at least one selected from the group consisting of a surfactant and a polymer dispersant, The polymer dispersant is a polymer having a structural unit (1) derived from styrene-maleic acid-modified polymer or (meth)acrylonitrile and a structural unit (2) derived from (meth)acrylic acid. 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 constitutional unit (1)). A carbon material dispersion liquid that satisfies the following requirements (1), (2), and (3). (1) When the carbon material contains the single-walled carbon nanotube, the amount of the dispersant with respect to 100 parts by mass of the single-walled carbon nanotube is 50 parts by mass or more and 600 parts by mass or less, and the amount of the binder resin with respect to 100 parts by mass of the single-walled carbon nanotube is 300 parts by mass or more and 850 parts by mass or less. When the carbon material contains the multi-walled carbon nanotube, the amount of the dispersant with respect to 100 parts by mass of the multi-walled carbon nanotube is 20 parts by mass or more and 200 parts by mass or less, and the amount of the binder resin with respect to 100 parts by mass of the multi-walled carbon nanotube is 700 parts by mass or more and 880 parts by mass or less. (2) The surface resistivity of a dry film with a thickness of 1 μm and a carbon material content of 10% by mass is 1.0×10 3 Ω / sq or less. (3) The ratio (A H of the absorbance A at a wavelength of 380 nm to the absorbance A at a wavelength of 780 nm of a dilute dispersion liquid obtained by diluting a blank liquid having the same composition as the carbon material dispersion liquid except that it does not contain the carbon material so that the absorbance at a wavelength of 580 nm is 1.8 ± 0.02 L (A L / A H ) is 1.45 or more. [2] A carbon material dispersion liquid containing at least one carbon material of single-walled carbon nanotubes and multi-walled carbon nanotubes, an aqueous medium, a dispersant, and a binder resin. The dispersant is a cellulose derivative. The binder resin is at least one selected from the group consisting of styrene-butadiene copolymers and acrylic resins. A carbon material dispersion liquid that satisfies the following requirements (1), (2), and (3). (1) When the carbon material includes the single-walled carbon nanotube, the amount of the dispersant with respect to 100 parts by mass of the single-walled carbon nanotube is 50 parts by mass or more and 600 parts by mass or less, and the amount of the binder resin with respect to 100 parts by mass of the single-walled carbon nanotube is 300 parts by mass or more and 850 parts by mass or less. When the carbon material includes the multi-walled carbon nanotube, the amount of the dispersant with respect to 100 parts by mass of the multi-walled carbon nanotube is 20 parts by mass or more and 200 parts by mass or less, and the amount of the binder resin with respect to 100 parts by mass of the multi-walled carbon nanotube is 700 parts by mass or more and 880 parts by mass or less. (2) The surface resistivity of a 1-μm-thick dry film having a carbon material content of 10% by mass is 1.0×10 3 Ω / sq or less. (3) The ratio (A H of the absorbance A at wavelength 380 nm to the absorbance A at wavelength 780 nm of a dilute dispersion obtained by diluting with a blank solution having the same composition as the carbon material dispersion except for not containing the carbon material so that the absorbance at wavelength 580 nm is 1.8 ± 0.02 L (A L / A H ) is 1.45 or more. [3] The average length of the single-walled carbon nanotube is 5 μm or more and 600 μm or less, and the average length of the multi-walled carbon nanotube is 30 μm or more and 5,000 μm or less. The carbon material dispersion according to [1] or [2]. [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% by mass or less. [5] Use of the carbon material dispersion according to any one of [1] to [4] for manufacturing any product of paint, ink, coating agent, resin molding material, conductive material, heat conductive material, and antistatic material. [6] Use of the carbon material dispersion according to any one of [1] to [4] for manufacturing any product of battery material and mechanical parts, comprising a film formed of the carbon material dispersion.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a carbon material dispersion capable of forming a coating film that achieves both high conductivity and good coating film physical properties in a thin film state and at a low carbon material concentration. Further, according to the present invention, it is possible to provide the use of a carbon material dispersion for manufacturing various products and films that are components of various products.

Embodiments for Carrying Out the Invention

[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. And the carbon material dispersion according to this embodiment satisfies the following requirements (1), (2), and (3). Hereinafter, details of the carbon material dispersion of the present invention (hereinafter, also simply referred to as "dispersion") will be described.

[0017] (1) When the carbon material includes the single-walled carbon nanotubes, the amount of the dispersant with respect 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 with respect 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 includes the multi-walled carbon nanotubes, the amount of the dispersant with respect 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 with respect 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) The surface resistivity of a dry film with a thickness of 1 μm and a carbon material content of 10% by mass is 1.0×10 3 Ω / sq or less. (3) The absorbance A at a wavelength of 780 nm of a dilute dispersion obtained by diluting with a blank solution having the same composition as the carbon material dispersion except that it does not contain the carbon material so that the absorbance at a wavelength of 580 nm is 1.8 ± 0.02 H with respect to the absorbance A at a wavelength of 380 nm L of which 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 or metal salt such as platinum or palladium. Further, the carbon nanotubes may 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 "SWCNT") is preferably 5 μm or more and 600 μm or less, and more preferably 10 μm or more and 500 μm or less. Further, the average length of the multi-walled carbon nanotubes (hereinafter also referred to as "MWCNT") is preferably 30 μm or more and 5,000 μm or less. When the dispersion according to the present embodiment is used as a constituent material of a battery, the average length of the MWCNT is preferably 50 μm or more and 3,000 μm or less because the surface resistivity of the formed coating film can be made lower.

[0020] The dispersion according to the present embodiment may further contain other carbon materials other than the above carbon materials. As the other carbon materials, carbon black, carbon fiber, graphite, graphene, or the like can be used.

[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 diameter of CB is preferably 10 nm or more and 60 nm or less. The carbon material may be doped with a metal or metal salt such as platinum or palladium. Further, the carbon material may 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 using polyacrylonitrile as a raw material, pitch-based carbon fibers using pitches as a raw material, and recycled products thereof. Among them, carbon nanofibers having a fiber diameter in the nano size and having a shape in which a six-membered ring graphite structure is wound into a cylindrical shape are preferable. Graphite is a layered substance containing hexagonal plate-like crystals composed of carbon. Among them, graphene in which graphite is exfoliated into a single layer with a thickness of one atom or graphene formed of multiple layers can be used.

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

[0024] For the measurement of the average length of CNTs and the average primary particle diameter of carbon black, a method using a disperser such as an ultrasonic homogenizer to disperse CNTs or the like in a solvent such as water and then using the light scattering method with a dynamic light scattering type particle size distribution measuring device, or a method of calculating from the SEM image of the CNT powder can be mentioned.

[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 for dispersing the carbon material. That is, the dispersion according to this embodiment is an aqueous dispersion of the 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 the water-soluble organic solvent include alcohols such as methanol, ethanol, and isopropyl alcohol; polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin; ethers such as tetrahydrofuran; glycol ethers such as diethylene glycol, triethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether; glycol ether esters such as diethylene glycol monomethyl ether acetate; amides such as pyrrolidone, N-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. Among them, 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 carbon materials in a liquid medium. As the dispersant, anionic, cationic, nonionic, and amphoteric surfactants; polymer dispersants; and cellulose derivatives can be used. Among them, it is preferable to use at least one of a polymer dispersant and a cellulose derivative as the dispersant.

[0030] Examples of the cellulose derivative include methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, and metal salts thereof. Among them, carboxymethyl cellulose and sodium carboxymethyl cellulose are preferable. Further, the cellulose derivative preferably has a viscosity of 20 mPa·s or more and 500 mPa·s or less in a 1 mass% aqueous solution and an etherification degree of 0.5 or more and 0.9 or less. By using such a cellulose derivative, the carbon material can be dispersed better and the storage stability can be improved.

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

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

[0033] The structural unit (1) has a cyano group (-CN) derived from (meth)acrylonitrile. Therefore, the triple bond of the cyano group acts on the surface of the carbon material, and the polymer as a dispersant is electronically adsorbed to the carbon material. Further, the structural unit (2) has a carboxyl group derived from (meth)acrylic acid. Therefore, by neutralizing at least a part of this carboxyl group with an alkali and ionizing it, the polymer as a dispersant can be dissolved in an aqueous medium. By using a polymer containing these structural units (1) and structural unit (2) as a dispersant, the carbon material can be finely dispersed in the aqueous medium over a long 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. Also, 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. Note that the total of the structural unit (1) and the structural unit (2) is 100% by mass. When 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, when the proportion of the structural unit (2) in the polymer exceeds 50% by mass, the water solubility of the polymer tends to be excessively high. For this reason, the viscosity of the carbon material dispersion becomes excessively high, and since the amount of hydrophilic carboxy groups is large, the water resistance of the formed coating film may decrease.

[0035] The polymer dispersant (polymer) may further have other structural units other than the structural unit (1) and the structural unit (2). Examples of the monomers constituting the other structural units include conventionally known styrene-based monomers and (meth)acrylate-based monomers. Among them, it is preferable to use monomers that do not contain structures such as ester bonds and amide bonds that are easily hydrolyzed. Examples of such monomers include styrene, vinylnaphthalene, vinyltoluene, vinylbiphenyl, 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, since the hydrophilic groups and the hydrophobic groups are randomly present, the effect as a dispersant may be slightly reduced. Also, when a binder resin with high hydrophilicity is further used, it may be more significantly affected by the binder resin. For this reason, the polymer used as the polymer dispersant is preferably a block copolymer.

[0037] The polymer which is a polymer dispersant is preferably an A-B block copolymer containing 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. The polymer block A is preferably a polymer block substantially composed only of the structural unit (1-A) derived from acrylonitrile and the structural unit (2-A) derived from methacrylic acid. Further, the polymer block B is preferably a polymer block substantially composed only of the structural unit (1-B) derived from acrylonitrile and the 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. Further, 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. Note that the total of the structural unit (1-A) and the structural unit (2-A) is 100% by mass.

[0039] The A chain is a polymer block having a lower carboxy group content and relatively lower water solubility than the polymer block B (hereinafter also referred to as "B chain"). Therefore, the A chain adsorbed on the carbon material is more difficult to desorb than the B chain, and thus has a function of further improving the dispersibility of the carbon material. When 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, when the proportion of the structural unit (2-A) in the A chain exceeds 40% by mass, the water solubility of the A chain may become too high, and it may be easily desorbed from the carbon material.

[0040] The number average molecular weight of 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. When the number average molecular weight of the A chain is less than 10,000, the adsorptivity to the carbon material may tend to be insufficient. On the other hand, when the number average molecular weight of the A chain exceeds 100,000, even if it has a structural unit (2-A) having a carboxy group, the water solubility may become insufficient.

[0041] The molecular weight distribution of polymer block A (A chain) (PDI = weight average molecular weight (Mw) / number average molecular weight (Mn)) is preferably 1.8 or less, and more preferably 1.6 or less. Since the molecular weights are relatively uniform, it can be adsorbed more uniformly by the carbon material and the dispersibility can be further improved. When the molecular weight distribution (PDI value) of the A chain exceeds 1.8, a large amount of polymer blocks outside the above-mentioned number average molecular weight range will be contained, and the effect of improving the dispersibility may decrease.

[0042] The proportion of the structural unit (1-B) derived from acrylonitrile in 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. Also, 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. Note that the total of the structural unit (1-B) and the structural unit (2-B) is 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. When the number average molecular weight of the B chain is less than 3,000, it tends to be difficult to dissolve in water. On the other hand, when the number average molecular weight of the B chain exceeds 200,000, the viscosity tends to increase excessively and it becomes difficult to disperse.

[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 constituent 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 constituent unit (2-B) in the B chain exceeds 90% by mass, the hydrophilicity may become excessively high. For this reason, the viscosity of the carbon material dispersion may become excessively high, and the water resistance of the formed coating film may decrease.

[0044] The A-B block copolymer can be produced, for example, by a living radical polymerization method. Since the A-B block copolymer is composed of acrylonitrile and methacrylic acid, its structure control is easy and the adjustment of the molecular weight is also easy.

[0045] As the alkali that neutralizes at least a part of the carboxy groups in the polymer dispersant (polymer), for example, ammonia; organic amines such as triethylamine and dimethylaminoethanol; and conventionally known alkalis such as alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide can be used. Among them, from the viewpoints of improving water solubility and improving the conductivity of the coating film by ionic action, etc., the alkali is preferably at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, and potassium hydroxide.

[0046] All the carboxy groups in the polymer may be neutralized with an alkali, but it is also preferable to neutralize only a part of the carboxy groups with an alkali as long as the polymer is within the range of being soluble in water. The carboxy group (-COOH) that has not been neutralized with an alkali can form a hydrogen bond with the carbon material. Therefore, when using a polymer in which only a part of the carboxy groups are neutralized with an alkali as a dispersant, the dispersion stability of the carbon material dispersion can be further improved. The amount of the alkali that neutralizes the carboxy group is preferably an amount corresponding to 50 mol% or more and 120 mol% or less of the carboxy group, and more preferably an amount corresponding to 70 mol% or more and 110 mol% or less of the carboxy group.

[0047] The polymers used as the polymer dispersant can be produced according to conventionally known methods. Among them, it can be produced by a solution polymerization method using an organic solvent; and a radical polymerization method using an azo radical generator or a peroxide radical generator. As the organic solvent, conventionally known organic solvents can be used. However, since the polymer may be insoluble in general-purpose organic solvents, it is preferable to use a polar organic solvent that can be dissolved in water. Examples of such polar organic solvents include amide solvents, sulfoxide solvents, urea solvents, and nitrile solvents. Among them, it is preferable to use amide solvents, urea solvents, and nitrile solvents. After polymerization in these organic solvents, an aqueous alkali solution is added to neutralize the carboxy group to form an aqueous solution, whereby a carbon material dispersion containing an organic solvent can be obtained.

[0048] Examples of the amide solvent include dimethylformamide, dimethylacetamide, diethylacetamide, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide. Examples of the urea solvent include tetramethylurea and 1,3-dimethylimidazolidinone. Examples of the nitrile solvent include acetonitrile.

[0049] It is difficult to produce the A-B block copolymer used as the polymer dispersant by an ordinary radical polymerization method. Therefore, the A-B block copolymer is preferably produced by a living polymerization method such as a living anionic polymerization method, a living cationic polymerization method, and a living radical polymerization method. Among them, from the viewpoints of conditions, materials, and apparatuses, the living radical polymerization method is particularly preferable.

[0050] Examples of living radical polymerization methods include atom transfer radical polymerization (ATRP method), reversible addition-fragmentation chain transfer polymerization (RAFT method), nitroxide method (NMP method), organotellurium method (TERP method), reversible transfer catalysis polymerization (RTCP method), and reversible catalyst-mediated polymerization (RCMP method). Among them, the RTCP method or RCMP method that uses an organic compound as a catalyst and an organic iodide as a polymerization initiation compound is preferred. These methods use relatively safe commercially available compounds, do not use heavy metals and special compounds, and are advantageous in terms of cost and purification. Furthermore, by making the growing end a tertiary iodine, an accurate block structure can be easily formed with general 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, constitutional units derived from methacrylic acid may be excessively introduced into polymer block A to be polymerized later. 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 the dispersant with respect to 100 parts by mass of SWCNT needs to 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 the dispersant with respect to 100 parts by mass of MWCNT needs to 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 the dispersant with respect to the carbon material within the above ranges respectively, a carbon material dispersion liquid in which the carbon material is more stably dispersed can be obtained. If the amount of the dispersant with respect to the carbon material is too small, the dispersant cannot sufficiently cover the surface of the carbon material, and the dispersibility may become slightly insufficient. On the other hand, if the amount of the dispersant with respect to the carbon material is too large, the carbon material dispersion liquid tends to thicken, and the ratio of the carbon material in the solid content may relatively decrease. In addition, the surface resistivity of the formed coating film may become slightly high, and when an electrode is formed, the cycle characteristics of the electrode may deteriorate.

[0053] (Binder resin) The carbon material dispersion liquid according to the present embodiment further contains a binder resin. By containing the binder resin, a conductive coating film excellent in properties such as elongation or bending and having improved adhesion to a substrate or the like can be formed. Considering the affinity with the dispersant and the like, as the binder resin, it is preferable to use a cellulose derivative such as carboxymethyl cellulose (including the Na salt); a styrene-butadiene copolymer; and an acrylic resin such as a styrene-acrylic resin.

[0054] The content of the binder resin with respect to the carbon material in the carbon material dispersion is, for example, in the case of single-walled carbon nanotubes, it is necessary to be 300 parts by mass or more and 850 parts by mass or less, preferably 350 parts by mass or more and 800 parts by mass or less, with respect to 100 parts by mass of single-walled carbon nanotubes. In the case of multi-walled carbon nanotubes, it is necessary 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, with respect to 100 parts by mass of multi-walled carbon nanotubes. If the amount of the binder resin is too small, it may be difficult to coat the substrate and a homogeneous electrode may not be obtained. If the amount of the binder resin is too large, the ratio of the active material (carbon material) will relatively decrease, and sufficient battery capacity may not be obtained when used as a battery. Also, when the carbon material dispersion is used for coating film applications, the content of the binder resin with respect to the carbon material in the carbon material dispersion is necessary to be 300 parts by mass or more and 850 parts by mass or less, preferably 350 parts by mass or more and 800 parts by mass or less, with respect to 100 parts by mass of the carbon material. Also, when the carbon material dispersion is used for battery applications, the content of the binder resin with respect to the carbon material in the carbon material dispersion is necessary 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, with respect to 100 parts by mass of the carbon material.

[0055] (Additives, etc.) The carbon material dispersion according to this embodiment may further contain additives, resins, and the like. Examples of the additives include water-soluble dyes, pigments, ultraviolet absorbers, light stabilizers, antioxidants, leveling agents, defoaming agents, preservatives, fungicides, photoinitiators, and other pigment dispersants. Examples of the 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, epoxy resins, polyphenol resins, polyurea resins, and polyethersulfone resins.

[0056] Depending on the apparatus used in the wetting and dispersion steps, it is preferable to include an antifoaming agent as an additive in the carbon material dispersion. When an antifoaming agent is included, foaming during the dispersion treatment can be suppressed, so that the shearing force, impact force, etc. applied during the dispersion treatment act effectively, and a dispersion with more excellent dispersibility can be obtained.

[0057] (Absorbance of carbon material dispersion) The absorbance of a dispersion of a carbon material containing carbon nanotubes forms a gentle curve from a wavelength of 300 nm to 1,000 nm. 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 aggregates of carbon nanotubes is large. Therefore, the absorbance ratio (A L ) obtained by dividing the absorbance on the short wavelength side by the absorbance on the long wavelength side (A H ) (A L / A H ) well reflects the dispersion state of the carbon material in the liquid medium. That is, the finer and more uniformly the carbon nanotubes are dispersed, the larger the absorbance ratio, and the more the carbon nanotubes are aggregated, the smaller the absorbance ratio.

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

[0059] The wavelength W LIt is arbitrarily selected from within the range of 350 nm to 550 nm, preferably within the range of 350 nm to 450 nm, and more preferably within the range of 350 nm to 400 nm. At wavelengths within the above range, the change in absorbance is clear, there is little noise or specific peak change, and it can be measured stably. If it is less than 350 nm, the absorption and scattering of light by fine particles are irregularly affected, and the peak changes greatly as the dispersion progresses, making it difficult to use as an accurate indicator. On the other hand, if it exceeds 550 nm, the change in absorbance becomes unclear.

[0060] Wavelength W on the long wavelength side H It is arbitrarily selected from within the range of 650 nm to 850 nm, preferably within the range of 700 nm to 850 nm, and more preferably within the range of 700 nm to 800 nm. If the wavelength is within the above range, it is possible to confirm the absorbance of particles with a small proportion of absorption components and a large proportion of scattering components. Also, there is little noise or specific peak change, and it can be measured stably. If it exceeds 850 nm, it becomes difficult to measure an accurate value due to noise mixing into the peak. On the other hand, less than 650 nm is not an appropriate range as an indicator.

[0061] Wavelength W L and wavelength W H The difference between them is preferably 100 nm or more, and more preferably 200 nm or more. Wavelength W L and wavelength W H By setting the difference between them to 100 nm or more, the dispersibility of the carbon material can be read more accurately. Wavelength W 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 the dispersion varies depending on the content (concentration) of the carbon material. Therefore, the absorbance of the diluted dispersion prepared by diluting, as necessary, the dispersion containing no binder resin and the dispersion containing the binder resin is measured. As the diluent for diluting the dispersion, it is preferable to use a blank solution having the same composition as the target dispersion except that it does not contain the carbon material. By using such a blank solution, the diffusion and re-aggregation of the fine particles and the influence of the environment on the absorbance are suppressed, and the influence of the polymer dispersant that may be used as the dispersant is made less likely to be affected, so that the absorbance can be measured more accurately.

[0063] To accurately measure the absorbance, it is usually preferable to make the content of the carbon material in the sample solution (diluted dispersion) 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 laser scattered light transmitted during measurement is small, and it may be difficult to measure accurately. On the other hand, if it is less than 0.001% by mass, the value of the absorbance becomes too small, and accurate evaluation or comparison may be difficult.

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

[0065] The absorbance A of the diluted dispersion at wavelength W H of the ratio of the absorbance A H at wavelength W L of (A L / A [[ID=2�]] L / A H ) is the value of wavelength W H and W L varies depending on. For example, when the value of "A L = 380 nm and wavelength W H = 780 nm of "A L / A H " is "1.60 → 1.45", the wavelength WL = 400 nm and wavelength W H = 700 nm L / A H The value of " is "1.44 → 1.29", and the wavelength W L = 350 nm and wavelength W H = 800 nm L / A H The value of " is "1.78 → 1.63". Also, the wavelength W L = 380 nm and wavelength W H = 780 nm L / A H If the value of " is "1.65 → 1.50", the wavelength W L = 400 nm and wavelength W H = 700 nm L / A H The value of " is "1.48 → 1.33", and the wavelength W L = 350 nm and wavelength W H = 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 is 1.2 to 2.2 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 of W L is 380 nm, wavelength W His 780 nm, and the wavelength W M is 580 nm, and the wavelength W M When the absorbance at is 1.8 ± 0.02, the absorbance A H with respect to the absorbance A L ratio (A 380 / A 780 ) needs to be 1.45 or more. In order for the short side size of the aggregate to be less than 100 μm, it is more preferably 1.50 or more. For further dispersion treatment and for the carbon nanotubes to be more uniformly dispersed in the liquid medium, it is particularly preferably 1.55 or more. By setting the absorbance ratio (A 380 / A 780 ) within the above range, even if the types or addition amounts of the carbon material, dispersant, and binder resin vary, a dispersion liquid that does not substantially contain coarse aggregates and has excellent viscosity stability can be obtained. The value of the absorbance ratio (A 380 / A 780 ) can be achieved by adjusting the type or blending amount of the carbon material or dispersant, or by adjusting the wetting method or dispersion method of the dispersion liquid.

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

[0069] The absorbance ratio of the dispersion liquid is preferably higher regardless of the presence or absence of the binder resin. Even if a binder resin is added to a dispersion liquid with poor dispersion that does not contain a binder resin, the absorbance ratio is hardly improved and sufficient performance may not be exhibited.

[0070] (Physical properties of carbon material dispersion) The dispersion according to this embodiment has a viscosity that hardly changes even after a long period of time and is excellent in viscosity stability (storage stability). Specifically, based on the viscosity (mPa·s) at 25°C of the dispersion without the binder resin immediately after preparation (dispersion), the change rate of the viscosity (mPa·s) at 25°C of the dispersion without the binder resin after 10 days under room temperature (25°C) conditions is usually 15% or less, preferably 10% or less, and more preferably 5% or less.

[0071] When aggregates with a short side of 100 μm or more are present in the dispersion without the binder resin, when the dispersion is applied to various uses, it becomes difficult to exhibit the original performance such as the conductivity or thermal conductivity of the carbon nanotubes, and the growth or sedimentation of the aggregates occurs, making it easy for the viscosity stability and storage stability to deteriorate. For example, when a dispersion containing aggregates with a short side of 100 μm or more is used as a coating material, it tends to be difficult to obtain a uniform coating. In contrast, the dispersion according to this embodiment substantially does not contain coarse aggregates formed by the carbon material including carbon nanotubes. Specifically, even when the dispersion without the binder resin immediately after preparation (dispersion) and the dispersion without the binder resin after 10 days under room temperature (25°C) conditions are observed 5 times at a magnification of 200 times using an optical microscope, usually no aggregates with a short side of 100 μm or more are observed. Preferably, the number (average value) of aggregates with a short side of 20 μm or more is 10 or more per observation. More preferably, the number (average value) of aggregates with a short side of 20 μm or more is 1 or more and less than 10 per observation, and particularly preferably, no aggregates with a short side of 20 μm or more are observed even after 5 observations.

[0072] (Method for producing carbon material dispersion) The carbon material dispersion can be produced by using a dispersant, wetting a carbon material containing carbon nanotubes in a liquid medium in advance according to a conventionally known method, and then dispersing it. For example, wetting methods and dispersion methods using a magnetic stirrer, a dissolver, kneading with a three-roll mill, ultrasonic dispersion, bead mill dispersion, an emulsifying device, a homogenizer, etc. can be used. From the simplicity of the process, it is preferable to stir and wet with a magnetic stirrer, a dissolver, and a homogenizer, and it is preferable to disperse in combination with a high-pressure homogenizer. For example, it is preferable to disperse with a bead mill using small-sized beads. Also, in consideration of damage to carbon materials such as carbon nanotubes, a wetting method and a dispersion method may be combined.

[0073] When mixing a plurality of dispersions or adding and mixing a binder resin, in addition to a magnetic stirrer, a dispersing machine may be used. Using a dispersing machine for mixing is preferable because it can prevent shock aggregation, etc., and a dispersion with an excellent dispersion state can 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 dispersion state of the carbon nanotubes in the obtained dispersion is good. Adding the binder resin during dispersion is preferable because it can prevent shock aggregation, etc.

[0075] (Coating film) By applying and drying the carbon material dispersion according to this embodiment, a conductive coating film (film) can be formed. The concentration of the carbon material in the formed coating film is preferably, for example, 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. Further, the thickness (film thickness) of the coating film can be, for example, 0.8 μm or more and 30 μm or less. The higher the film thickness and the higher the concentration of the carbon material, the lower the surface resistivity of the coating film. It was 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 1-μm-thick dry film (coating film) containing 10% by mass of carbon material, which is formed by applying and drying the carbon material dispersion according to this embodiment, is 1.0×10 3 Ω / sq or less, preferably 9.0×10 2 Ω / sq or less. The content of the carbon material in the dry film (coating film) 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 the binder resin used from the mass of the formed dry film. The surface resistivity of the dry film can be achieved by adjusting the type or blending amount of the carbon material or the dispersant, or by adjusting the wetting method or dispersion method of the dispersion.

[0077] <Use of Carbon Material Dispersion> The carbon material dispersion according to this embodiment has the carbon material containing carbon nanotubes well dispersed without substantially forming coarse aggregates and has excellent viscosity stability. Further, 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 manufacturing paints, inks, coating agents, resin molded product materials, and the like. Further, it can be expected to be used as a conductive material or a heat conductive material, and its application to an antistatic material is also expected. Furthermore, it is useful as a material for forming a film constituting a battery material such as an electrode material of a battery such as a lithium ion battery and a fuel cell or a capacitor material, and a film constituting various mechanical parts.

[0078] An aqueous paint or ink can be prepared, for example, by adding various components such as a solvent, a resin, and an additive to the 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 manufactured, for example, by adding the carbon material dispersion to a plastic material in a molten state and then removing water. Further, a resin molded product in which the carbon material is dispersed can also be manufactured by adding the carbon material dispersion to a plastic material in a fine powder state and then removing water or depositing the carbon material.

Example

[0080] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are based on mass unless otherwise specified.

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

[0082] (Carbon Material) [Single-walled Carbon Nanotube (SWCNT)] ·SWCNT-1: Trade name "Tuball", manufactured by OCSiAl, average length 2 - 20 μm ·SWCNT-2: Trade name "SG101", manufactured by Nippon Zeon Co., Ltd., average length 100 - 600 μm

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

[0084] [Carbon black (CB)] ·CB-1: Trade name "Li435", manufactured by Denka

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

[0086] (Binder resin) · Binder resin A: Trade name "YL - 1098", styrene - acrylic resin, manufactured by Starlight PMC · Binder resin B: Dispersant c · Binder resin C: A mixture of Dispersant c and styrene - butadiene copolymer latex (trade name "Nalster SR - 112", manufactured by Nippon A&R Co., Ltd.) (Dispersant c: styrene - butadiene copolymer latex = 4:1)

[0087] <Manufacture 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. Also, 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 Fuji Film Wako Pure Chemical Corporation) (V-65) were placed in a beaker, and 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 dropping was completed, 1.0 part of V-65 was added after 2.5 hours had passed. After maintaining at 70 °C for 1 hour, the temperature was raised to 80 °C and held for 2 hours to form a polymer. After cooling, the solid content was measured using a moisture meter, and it was confirmed that almost all the monomers had been consumed. The number average molecular weight (Mn) of the polymer in terms of polymethyl methacrylate, measured by gel permeation chromatography (GPC) using a lithium bromide N,N-dimethylformamide solution (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% with respect to AA) and 96.8 parts of ion-exchanged water were placed in a beaker, and NaOH was completely dissolved to prepare an NaOH aqueous solution. After the temperature in the reaction vessel dropped below 60 °C, the NaOH aqueous solution was added to neutralize the carboxyl groups, and a solution of a polymer dispersant (dispersant a) was obtained. The solid content of the obtained dispersant a solution 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 Corporation) (V-70), 0.2 part of diphenylmethane (DPM), 106.1 parts of AN, and 26.5 parts of methacrylic acid (MAA) were placed in a reaction vessel. While stirring with nitrogen flowing, the temperature was raised to 40 °C and polymerization was carried out for 4 hours to form A chains. The solid content of the reaction solution was 34.8%, and the polymerization conversion rate calculated from the solid content was about 100%. The Mn of the formed A chains 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. Then, polymerization was carried out at 40 °C for 4 hours to form B chains, and an A-B block copolymer was obtained. The solid content of the reaction solution was 29.9%, and it was confirmed that the target product was obtained almost quantitatively. The Mn of the obtained A-B block copolymer was 21,600, the PDI was 1.52, and the PT was 32,700. The molecular weight of the B chains can be calculated by subtracting the Mn of the A chains from the Mn of the A-B block copolymer. That is, the Mn of the B chains was 6,800 and the PT was 12,000.

[0091] 29.8 parts of NaOH (110 mol% with respect to MAA) and 105.1 parts of ion-exchanged water were placed in a beaker, and NaOH was completely dissolved to prepare an aqueous NaOH solution. The aqueous NaOH solution was poured into the reaction vessel to neutralize the carboxy groups, and a solution of a polymer dispersant (dispersant b) was obtained. The solid content of the obtained dispersant b solution 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 container equipped with a stirrer. While cooling the stainless-steel container, 10 g of sodium hydroxide (purity 98%) was added. After cooling the solution to 25°C or lower, 20 g of ground pulp was added while stirring. Next, it was stirred and mixed (mercerized) at 15 - 25°C for 60 minutes to prepare alkali cellulose. Next, 30 g of a mixed solution of monochloroacetic acid / isopropyl alcohol = 1:2 was added while cooling the stainless-steel container and maintaining the temperature at 15 - 25°C, and it was stirred and mixed for 15 minutes. Then, while heating the stainless-steel container, the temperature of the solution was raised to 70°C over about 30 minutes. An etherification reaction was carried out by stirring at 65 - 75°C for 120 minutes. After the reaction was completed, unreacted sodium hydroxide was neutralized with acetic acid, and the product was separated. It was washed with a 70% aqueous methanol solution to remove by-products. The product was dried and pulverized to obtain sodium carboxymethyl cellulose salt (dispersant c). The viscosity of a 1% aqueous solution of the obtained sodium carboxymethyl cellulose 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, about 1 g of sodium carboxymethyl cellulose salt was precisely weighed and placed in a porcelain crucible, and then it was heated and ashed at a temperature not exceeding 600°C (about 550 - 590°C) for 1 hour. After cooling to room temperature, it was transferred to a 500 mL beaker together with the crucible, and 250 mL of water was added. 50 mL of 0.05 mol / L sulfuric acid aqueous solution was added and boiled for 30 minutes. After cooling to room temperature, the unreacted acid was titrated with 0.1 mol / L sodium hydroxide. Phenolphthalein was used as the indicator. Let the amount of 0.1 mol / L sodium hydroxide used for titration be "X" mL, and the degree of etherification (DS) was calculated by the following formula. Degree of etherification (DS) = 162X / (10000 - 80X)

[0094] <Measurement and evaluation method> (Calculation of average CNT length) The powder of CNTs was observed with an electron microscope, and the average length was calculated for 10 randomly selected ones. This operation was performed in 5 batches, and the numerical range of the average length was determined.

[0095] (Measurement of absorbance and calculation of absorbance ratio) A blank solution having the same composition as the carbon material dispersion except for not containing a carbon material was prepared. 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-Technologies Corporation) equipped with a quartz cell having an optical path length of 10 mm. Regarding dilution with the blank solution, a calibration curve plotting the absorbance at a wavelength of 580 nm against the change in the dilution ratio was created, and the dilution ratio at which the absorbance becomes 1.8 ± 0.02 was calculated to prepare a dispersion diluted to the target concentration. It is also possible to adjust the concentration of the target carbon component at the stage before dispersion, or to perform dispersion after adjusting the concentration of the carbon component to satisfy the absorbance at the initial blending stage. The specific method for preparing the sample solution is as follows: First, the dispersion is collected in a plastic bottle (a polyethylene bottle), and an appropriate amount of the blank solution is added based on the dilution ratio determined by the calibration curve. Stir for 30 seconds using a vortex mixer (manufactured by Scientific Industries) to obtain a sample solution with an absorbance A 580 at 1.8 ± 0.02 at a wavelength of 580 nm. The absorbance A 380 of the obtained sample solution at a wavelength of 380 nm and the absorbance A 780 at a wavelength of 780 nm were measured, and the absorbance ratio (A 380 / A 780 ) was calculated. The measurements were performed on the dispersion immediately after dispersion and the dispersion after adding the binder resin.

[0096] (Evaluation of the dispersion) [Measurement of viscosity and evaluation of viscosity stability] An E-type viscometer equipped with a rotor of 1°34’×R24 was used to measure the viscosities of the dispersion liquid without the binder resin immediately after dispersion and the dispersion liquid without the binder resin after 10 days (after standing at room temperature for 10 days) under the conditions of a temperature of 25°C and a rotor rotation speed of 100 rpm. For the dispersion liquid with a viscosity of less than 25 mPa·s, the viscosity was measured using the product named "VISCOMETER TVE-25L" (manufactured by Toki Sangyo Co., Ltd.). For the dispersion liquid with a viscosity of 25 mPa·s or more, the viscosity was measured using the product named "VISCOMETER TVE-25H" (manufactured by Toki Sangyo Co., Ltd.). Then, the viscosity stability of the dispersion liquid was evaluated according to the following evaluation criteria. ◎: The change rate of the viscosity after 10 days based on the viscosity immediately after dispersion is less than 5%. ○: The change rate of the viscosity after 10 days based on the viscosity immediately after dispersion is 5% or more and less than 10%. △: The change rate of the viscosity after 10 days based on the viscosity immediately after dispersion is 10% or more and less than 15%. ×: The change rate of the viscosity after 10 days based on the viscosity immediately after dispersion is 15% or more.

[0097] [Observation of aggregates] A dispersion liquid without the binder resin was collected in a plastic bottle (a polyethylene bottle), and a blank solution was added and diluted so that the concentration of the carbon material became 0.1% by mass. The diluted solution was obtained by stirring for 30 seconds using a vortex mixer (manufactured by Scientific Industries, Inc.). 30 μL of the obtained diluted solution was dropped onto a slide glass, and after placing a cover glass, the presence or absence of aggregates was observed (200 times magnification) using an optical microscope. For the dispersion liquid without the binder resin immediately after dispersion and the dispersion liquid without the binder resin after 10 days (after standing at room temperature for 10 days), samples dropped onto the slide glass 5 times were prepared and observed respectively, and the presence or absence of aggregates was evaluated according to the following evaluation criteria. ◎: No aggregates with a short side of 20 μm or more were observed during the 5 observations. ○: The number (average value) of aggregates with a short side of 20 μm or more was 1 or more and less than 10 per observation, and no aggregates with a short side of 100 μm or more were observed during 5 observations. △: The number (average value) of aggregates with a short side of 20 μm or more was 10 or more per observation, and no aggregates with a short side of 100 μm or more were observed during 5 observations. ×: One or more aggregates with a short side of 100 μm or more were observed during 5 observations.

[0098] (Evaluation of the coating film) [Measurement of surface resistivity] When the surface resistivity exceeded 10 5 Ω / sq, a high-resistance resistivity meter (product name "HiRester-UP MCP-HT450", manufactured by Mitsubishi Chemical Analytech Co., Ltd.) was used, and the average value of the surface resistivity of the coating film measured at 5 points with a 10 V applied voltage was calculated. Also, when the surface resistivity was 10 5 Ω / sq or less, a low-resistance resistivity meter (product name "Loresta-GP MCP-T610", manufactured by Mitsubishi Chemical Analytech Co., Ltd.) was used, and the average value of the surface resistivity of the coating film measured at 5 points with a 10 V applied voltage was calculated.

[0099] [Observation of the coated object] A 10 cm square dry film formed by coating a dispersion containing a binder resin on a PET film was visually observed, and the cracks, peeling, and unevenness of the film were evaluated according to the following evaluation criteria. ◎: None of the cracks, peeling, and unevenness were observed. 〇: Any of the cracks, peeling, and unevenness existed at a ratio of less than 5% of the total area of the dry film. △: Any of the cracks, peeling, and unevenness existed at a ratio of 5% or more and less than 30% of the total area of the dry film. ×: Any of the cracks, peeling, and unevenness existed at a ratio of 30% or more of the total area of the dry film.

[0100] (Preparation and evaluation of the dispersion (1)) (Dispersions 1 to 22) The dispersant and water of the types and amounts shown in Table 1 were placed in a 200 mL polyethylene bottle. After stirring with a magnetic stirrer until uniform, the carbon materials of the types and amounts shown in Table 1 were added and further stirred. Subsequently, high-pressure treatment was carried out using a high-pressure homogenizer (manufactured by Tokuyama Corporation) under the condition of a treatment pressure of about 10 MPa. Then, a high-pressure dispersion treatment was carried out using a high-pressure homogenizer (manufactured by Sugino Machine Limited) under the condition of a treatment pressure of about 100 MPa to obtain a dispersion liquid. The number of passes of the dispersion liquid (the number of treatment times of the high-pressure dispersion treatment) is shown in Table 1. Note that for those with 0 passes, the high-pressure dispersion treatment was not performed. Also, the evaluation results of the viscosity stability of the obtained dispersion liquid and the results of observing aggregates are shown in Table 3.

[0101] (Mixture 1 and 2) The first dispersion liquid and the second dispersion liquid of the types shown in Table 2 were blended so that Carbon Material 1 and Carbon Material 2 had the mass ratio shown in Table 2, and then mixed using a magnetic stirrer to obtain a mixed liquid. The evaluation results of the viscosity stability of the obtained mixed liquid and the results of observing aggregates are shown in Table 3.

[0102]

Table 1

[0103]

Table 2

[0104]

Table 3

[0105] (Examples 1 to 5, Examples 7 to 15, Reference Examples 1 to 6, and Comparative Examples 1 to 10) The dispersion liquid and binder resin of the type shown in Table 5 were blended at a ratio such that the concentration of the carbon material in the formed coating film (solid content) became the value (%) shown in Table 5, and then mixed using a magnetic stirrer to obtain a carbon material dispersion liquid. The absorbance ratios for some of the carbon material dispersion liquids are shown in Table 4. Also shown in Table 4 are the number of passes of the dispersion liquid used. The obtained carbon material dispersion liquid was each applied to a PET film (trade name "Lumirror", manufactured by Toray Industries, Inc.) with a thickness of 100 μm using a bar coater, and then dried in an electric oven at 90 °C for 30 minutes to remove the volatile components, thereby forming a coating film with the film thickness shown in Table 5. The surface resistivity of the formed coating film is shown in Table 5. In Comparative Example 6, cracks and peeling occurred over a wide range of the coated object during drying, and thus the evaluation was abandoned because a smooth coated surface required for measuring the surface resistivity could not be ensured.

[0106]

Table 4

[0107]

Table 5

[0108] (Application Example 1-1: Battery Material (Negative Electrode)) In manufacturing the negative electrode of a lithium-ion battery, the following materials were used. [Negative Electrode Activator] · Graphene (manufactured by Fujifilm Wako Pure Chemical Corporation) · Silicon monoxide (manufactured by Fujifilm Wako Pure Chemical Corporation) [Binder Resin] · 10% Aqueous polyacrylic acid solution (trade name "CLPA-C07", manufactured by Fujifilm Wako Pure Chemical Corporation) · Carboxymethyl cellulose (trade name "CMC Daicel 2200", manufactured by Daicel Miraiz Co., Ltd.) · Styrene-butadiene copolymer latex (trade name "Nalster SR-112", manufactured by Nippon A&R Co., Ltd.)

[0109] 15 parts of silicon monoxide, 85 parts of graphene, 23 parts of dispersion liquid, 30 parts of 10% aqueous polyacrylic acid solution, 1.6 parts of carboxymethyl cellulose, and 0.4 parts of styrene-butadiene copolymer latex were mixed using a planetary mixer to obtain a negative electrode material with a basis weight after drying of 15 mg / cm 2 The negative electrode material was applied onto a copper foil with a thickness of 20 μm using an applicator so that the basis weight would be as described above. After being placed in an oven set at 120 °C for 30 minutes for drying and then rolled using a roll press, a negative electrode was obtained. 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 manufactured in the same manner as Application Example 1-1 described above, except that dispersion liquid 15 was used instead of dispersion liquid 2. The volume resistivity of the manufactured 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 liquid with good dispersion evaluation, a negative electrode with a smaller volume resistivity value can be manufactured.

[0111] (Application Example 2-1: Antistatic Coating Agent) 100 g of dispersion liquid 2, 100 g of a polymer binder (trade name "NeoPac R-9699", manufactured by Kusumoto Chemicals, acrylic urethane resin, solid content 40%), and 800 g of pure water were placed in a polycup and stirred using a dissolver to obtain an antistatic coating agent. The obtained antistatic coating agent was applied onto the surface of a polyethylene terephthalate film (manufactured by Toray Industries, Inc.) with a thickness of 38 μm using a bar coater so that the dried coating film would be 0.5 μm. After being placed in an oven set at 80 °C for 10 minutes for drying, an antistatic coating film was obtained. 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 manufactured in the same manner as Application Example 3-1 described above, except that dispersion liquid 15 was used instead of dispersion liquid 2. The surface resistivity of the manufactured film was 7.4×107 Ω / cm 2 It was thus found that a charge prevention coating film having a smaller surface resistivity value can be produced by using a mixed solution with good dispersion evaluation.

Industrial Applicability

[0113] The carbon material dispersion of the present invention is useful as a constituent material for paints, inks, resin molded products, etc., which exhibit properties such as high conductivity or high thermal conductivity, and is suitable for various applications such as battery materials, electronic component trays, covers for IC chips, electromagnetic wave shields, automotive members, and robot parts.

Claims

1. A carbon material dispersion containing 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, wherein the dispersant is at least one selected from the group consisting of a surfactant and a polymer dispersant, the polymer dispersant is a polymer having a structural unit (1) derived from styrene-maleic acid modified polymer or (meth)acrylonitrile and a structural unit (2) derived from (meth)acrylic acid, the binder resin is at least one selected from the group consisting of a cellulose derivative, a styrene-butadiene copolymer, and an acrylic resin (excluding those having the structural unit (1)), and satisfying the following requirements (1), (2), and (3). (1) When the carbon material contains the single-walled carbon nanotubes, the amount of the dispersant with respect 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 with respect 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 with respect 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 with respect 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) The surface resistivity of a dry film with a thickness of 1 μm and a carbon material content of 10% by mass is 1.0 × 10 ３ Ω / sq or less. The absorbance A at a wavelength of 780 nm of a dilute dispersion obtained by diluting with a blank solution having the same composition as the carbon material dispersion except that it does not contain the carbon material so that the absorbance at a wavelength of 580 nm is 1.8 ± 0.02 Ｈ with respect to the absorbance A at a wavelength of 380 nm Ｌ of which ratio (A Ｌ / A Ｈ ) is 1.45 or more.

2. A carbon material dispersion containing 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, wherein the dispersant is a cellulose derivative, the binder resin is at least one selected from the group consisting of a styrene-butadiene copolymer and an acrylic resin, and satisfying the following requirements (1), (2), and (3). (1) When the carbon material contains the single-walled carbon nanotubes, the amount of the dispersant with respect 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 with respect 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 includes the multi-walled carbon nanotubes, the amount of the dispersant with respect 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 with respect 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. The surface resistivity of a dry film with a thickness of 1 μm and a carbon material content of 10% by mass is ３ 1.0 × 10 Ω / sq or less. The absorbance A at a wavelength of 780 nm of a dilute dispersion obtained by diluting with a blank solution having the same composition as the carbon material dispersion except for not containing the carbon material so that the absorbance at a wavelength of 580 nm is 1.8 ± 0.02 Ｈ with respect to the absorbance A at a wavelength of 380 nm Ｌ has a ratio (A Ｌ / A Ｈ ) of 1.45 or more.

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

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

5. Use of the carbon material dispersion liquid according to any one of claims 1 to 4 for manufacturing any product of paint, ink, coating agent, resin molding material, conductive material, heat conductive material, and antistatic material.

6. Use of the carbon material dispersion liquid according to any one of claims 1 to 4 for manufacturing any product of battery material and mechanical parts, provided with a film formed of the carbon material dispersion liquid.

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