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

Abstract

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

Description

[Technical Field]

[0001] The present invention relates to a carbon nanotube dispersion liquid that exhibits good performance when used as a heat transfer material, has a high carbon nanotube concentration, and has low viscosity. [Background technology]

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

[0003] Various proposals have been made to disperse carbon nanotubes in a dispersion medium at high concentrations and low viscosity. For example, it has been proposed to prepare a carbon nanotube dispersion using a nonionic surfactant (Patent Document 1). It has also been proposed that controlling the distribution of carbon nanotube outer diameters inhibits aggregation, thereby achieving high uniformity and dispersion stability (Patent Document 2). It has also been proposed to disperse carbon nanotubes using a polymer containing an aliphatic hydrocarbon structural unit and a nitrile group-containing structural unit (Patent Document 3).

[0004] However, in the examples of all of Patent Documents 1 to 3, only dispersions of carbon nanotubes in an organic solvent with a concentration of 10% by mass or less are presented. Furthermore, as other thermally conductive fillers, Patent Document 4 uses flaky boron nitride, and Patent Document 5 uses acicular titanium oxide, but the addition of these fillers results in insufficient coating film properties or mechanical strength. In particular, the fluidity of flaky boron nitride is reduced, making it difficult to use as a coating liquid and making spray coating impossible. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-50780 [Patent Document 2] Japanese Patent Publication No. 2023-24526 [Patent Document 3] Japanese Patent Publication No. 2022-165423 [Patent Document 4] Japanese Patent Application Publication No. 2019-159135 [Patent Document 5] International Publication No. 2016 / 013391 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above-mentioned state of the art, and has an object to provide a carbon nanotube dispersion liquid having a high concentration of carbon nanotubes and excellent viscosity stability. [Means for solving the problem]

[0007] That is, according to the present invention, there are provided the following carbon nanotube dispersion, use of the carbon nanotube dispersion, and coating film. [1] A carbon nanotube dispersion containing multi-walled carbon nanotubes, an organic solvent, and a dispersant, the content of the multi-walled carbon nanotubes is more than 10% by mass and 20% by mass or less with respect to the total amount of the carbon nanotube dispersion, The multi-walled carbon nanotubes have an average length of 2 μm or more and 40 μm or less and an average diameter of 5 nm or more and 150 nm or less, The content of the dispersant is 50 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the multi-walled carbon nanotubes, the dispersant is a polymer dispersant, When a dry film having a thickness of 1 μm is formed using a coating liquid containing the carbon nanotube dispersion and a binder resin so that the content of the multi-walled carbon nanotubes in the dry film is 40 mass %, the surface resistivity of the dry film is 1.0 × 10 3 Ω / sq or less, and the thermal diffusivity of the dry coating is 0.30 mm 2 / s or more. [2] The polymer dispersant is a polyurethane-based polymer dispersant having a polycaprolactone chain, The carbon nanotube dispersion according to [1], wherein the polyurethane-based polymer dispersant having a polycaprolactone chain has an organic isocyanate moiety, two or more polycaprolactone moieties linked to the organic isocyanate moiety via a urethane bond, a terminal moiety having a linear or branched hydrocarbon group linked to the polycaprolactone moiety via an ester bond, and a terminal moiety having a tertiary amino group linked to the organic isocyanate moiety via a urethane bond or a urea bond, and has an amine value of 10 mgKOH / g or more and 100 mgKOH / g or less. [3] The carbon nanotube dispersion liquid according to [2], wherein the solid content of the polyurethane-based polymer dispersant having a polycaprolactone chain is 40% by mass or more and 55% by mass or less. [4] The carbon nanotube dispersion liquid according to [2] or [3], wherein the number average molecular weight of the polyurethane-based polymer dispersant having a polycaprolactone chain is 4,000 or more and 8,000 or less. [5] The polymer dispersant is a polymer having 3% by mass or more and 55% by mass or less of structural units (1) represented by the following general formula (1), 45% by mass or more and 90% by mass or less of structural units (3) represented by the following general formula (3), and 0.5% by mass or more and 20% by mass or less of other structural units (4) linked to these structural units (wherein the total of all structural units is 100% by mass), the structural unit (4) includes a structural unit derived from at least one monomer selected from the group consisting of (meth)acrylic acid, a (meth)acrylic acid ester, styrene, vinyltoluene, vinylpyridine, vinylcaprolactone, vinylimidazole, α-methylstyrene, and vinyl acetate; The carbon nanotube dispersion liquid according to [1], wherein the polymer dispersant has an amine value of 100 mgKOH / g or less and a number average molecular weight of 5,000 or more and 20,000 or less.

[0008] [ka]

[0009] (In the general formula (1), R represents a hydrogen atom or a methyl group, A represents O or NH, B represents an ethylene group or a propylene group, R1 and R2 each independently represent a methyl group or an ethyl group, Ar represents a phenyl group, a naphthyl group, an anthracenyl group, or a pyrenyl group, X represents a chlorine atom, a bromine atom, bis(trifluoromethyl)sulfonimide, or bis(nonafluorobutanesulfonyl)imide, and p represents any number of repeating groups.)

[0010] [ka]

[0011] (In the general formula (3), R represents a hydrogen atom or a methyl group, A represents O or NH, Q represents an ethylene group or a methylethylene group, Y represents O, NHCOO, or NHCONH, m and n each independently represent an average number of repeating units of 0 or more, and m+n=20 to 100, R3 represents an alkyl group, aryl group, or alkylaryl group having 1 to 18 carbon atoms, and r represents an arbitrary number of repeating units.)

[0012] [6] The carbon nanotube dispersion liquid according to [5], wherein the polymer dispersant is a polymer further having a structural unit (2) represented by the following general formula (2):

[0013] [ka]

[0014] (In the general formula (2), R represents a hydrogen atom or a methyl group, A represents O or NH, B represents an ethylene group or a propylene group, R1 and R2 each independently represent a methyl group or an ethyl group, and q represents any number of repeating groups.)

[0015] [7] The structural unit (1), the structural unit (2), and the structural unit (3) are represented by the following general formula (1-1), the following general formula (2-1), and the following general formula (3-1), respectively: The carbon nanotube dispersion according to [6], wherein the structural unit (4) includes a structural unit derived from α-methylstyrene.

[0016] [ka]

[0017] (In the general formula (1-1), R1 and R2 each independently represent a methyl group or an ethyl group; Ar represents a phenyl group, a naphthyl group, an anthracenyl group, or a pyrenyl group; X represents a chlorine atom, a bromine atom, bis(trifluoromethyl)sulfonimide, or bis(nonafluorobutanesulfonyl)imide; and p represents any number of repeating groups.)

[0018] [ka]

[0019] (In the general formula (2-1), R1 and R2 each independently represent a methyl group or an ethyl group, and q represents any number of repetitions.)

[0020] [ka]

[0021] (In the general formula (3-1), Y represents NHCOO or NHCONH, m and n each independently represent an average number of repeating units of 0 or more, and m+n=20 to 100, R3 represents an alkyl group, aryl group, or alkylaryl group having 1 to 18 carbon atoms, and r represents an arbitrary number of repeating units.)

[0022] [8] The carbon nanotube dispersion liquid according to any one of [1] to [7], further comprising a dye derivative having an acidic functional group, the content of the dye derivative being 0.01 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the multi-walled carbon nanotubes. [9] The carbon nanotube dispersion according to any one of [1] to [8], further comprising a binder resin, the content of the binder resin being 10 parts by mass or more and 300 parts by mass or less per 100 parts by mass of the multi-walled carbon nanotubes.

[10] The carbon nanotube dispersion liquid according to [9], wherein the binder resin is at least one selected from the group consisting of urethane-based resins, acrylic silicone-based resins, and epoxy-based resins.

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

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

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

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

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

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

[14] The coating film according to

[13] , wherein the coating film is baked at 150°C or higher and 500°C or lower. [Effects of the Invention]

[0023] According to the present invention, it is possible to easily obtain a carbon nanotube dispersion liquid having low viscosity and excellent stability, in which multi-walled carbon nanotubes are dispersed at a high concentration, and which exhibits good performance when used as a heat transfer material. Furthermore, by achieving a high concentration, it is possible to provide a carbon nanotube dispersion liquid having excellent transportability and whose concentration can be adjusted by dilution. DETAILED DESCRIPTION OF THE INVENTION

[0024] <Carbon nanotube dispersion> Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. A carbon nanotube dispersion according to this embodiment contains multi-walled carbon nanotubes, an organic solvent, and a dispersant, and the content of the multi-walled carbon nanotubes is more than 10 mass % and not more than 20 mass %, the dispersant is a polymer dispersant, and the multi-walled carbon nanotubes have an average length of 2 μm to 40 μm and an average diameter of 5 nm to 150 nm. Hereinafter, the carbon nanotube dispersion will also be simply referred to as a "dispersion."

[0025] <Multi-walled carbon nanotubes> In the technical field, carbon nanotubes (hereinafter also referred to as "CNTs") refer to carbon materials in which a single graphite layer has a cylindrical structure. CNTs with a single cylindrical structure are typically classified as single-walled CNTs, CNTs with two cylindrical layers as double-walled CNTs, and CNTs with three or more cylindrical layers as multi-walled CNTs. In conductive coatings containing CNTs, increasing the number of CNT layers typically improves conductivity. In the dispersion according to this embodiment, the multi-walled CNTs preferably have 5 to 100 walls, more preferably 10 to 50 walls. If the number of walls of the multi-walled CNTs is less than the lower limit, the conductivity of the resulting coating may be reduced. Therefore, by using the dispersion according to this embodiment containing multi-walled CNTs with a number of walls within the above range, a coating with high conductivity can be formed. The carbon nanotubes may be doped with metals or metal salts such as platinum and palladium. The carbon nanotubes may be surface-modified by oxidation treatment, plasma treatment, radiation treatment, corona treatment, coupling treatment, or the like.

[0026] In the dispersion according to this embodiment, the average length of the multi-walled CNTs must be in the range of 2 μm to 40 μm, and more preferably in the range of 4 μm to 15 μm. Furthermore, the average thickness (i.e., average diameter) of the multi-walled CNTs must be in the range of 5 nm to 150 nm, and more preferably in the range of 20 nm to 60 nm. If the average length and average thickness of the multi-walled CNTs are below the lower limit, the conductivity of the resulting coating may be reduced. If the average length and average thickness of the multi-walled CNTs exceed the upper limit, intermolecular aggregation may occur, potentially creating problems with the conditions for uniform dispersion. Therefore, by using the dispersion according to this embodiment containing multi-walled CNTs having an average length and average thickness within the above range, a coating with high conductivity can be formed.

[0027] <Organic solvents> As the organic solvent serving as a dispersion medium for dispersing carbon nanotubes, conventionally known organic solvents can be used. As the organic solvent, non-aqueous organic solvents that are substantially free of water, as well as aqueous organic solvents that contain a small amount of water, can be used.

[0028] Examples of organic solvents include hydrocarbon solvents such as hexane, toluene, and xylene; alcohol solvents such as methanol, ethanol, isopropanol, butanol, and dodecanol; ketone solvents such as acetone, methyl ethyl ketone, diethyl ketone, and isobutyl methyl ketone; ester solvents such as ethyl acetate, butyl acetate, amyl acetate, dimethyl succinate, dimethyl adipate, methyl lactate, and dimethyl lactate; ether solvents such as dipropyl ether, tetrahydrofuran, and dioxane; carbonate solvents such as dimethyl carbonate, ethylene carbonate, and propylene carbonate; amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, pyrrolidone, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide; urea solvents such as tetramethylurea and dimethylimidazolidinone; sulfoxide solvents such as dimethyl sulfoxide; ethylene glycol, propylene Examples of the glycol monoether solvents include glycol, diethylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, diethylene glycol methyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, and dipropylene glycol monomethyl ether; glycol diether solvents such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and dipropylene glycol dimethyl ether; and glycol ether monoether ester solvents such as ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monobutyl ether acetate.

[0029] Furthermore, a reactive monomer can be used as an organic solvent. By using a reactive monomer as an organic solvent, a carbon nanotube dispersion liquid useful as an ultraviolet- or electron-beam-curable ink or coating agent can be obtained. Examples of the reactive monomer include (meth)acrylic monomers, which are vinyl-based monomers, as well as vinyl ether compounds, epoxy compounds, and oxetane compounds. These reactive monomers can be used alone or in combination of two or more. Furthermore, the reactive monomer and the aforementioned organic solvent can be used in combination.

[0030] <Dispersant> The dispersant is a component for dispersing the carbon material in the liquid medium. By preparing a dispersion in a well-dispersed state, it is possible to produce a coating film that is uniform and thick. As the dispersant, it is necessary to use a polymer dispersant. Among these, a polyurethane-based polymer dispersant having a polycaprolactone chain or a polymer dispersant having a graft structure is preferred.

[0031] (Polyurethane-based polymer dispersant with polycaprolactone chains) The polyurethane polymer dispersant having a polycaprolactone chain preferably has an organic isocyanate moiety, two or more polycaprolactone moieties linked to the organic isocyanate moiety via urethane bonds, a terminal moiety having a linear or branched hydrocarbon group linked to the polycaprolactone moiety via an ester bond, and a terminal moiety having a tertiary amino group linked to the organic isocyanate moiety via a urethane or urea bond. The amine value of this polyurethane polymer dispersant is preferably 10 mgKOH / g or more and 100 mgKOH / g or less.

[0032] In polyurethane-based polymer dispersants having polycaprolactone chains, the organic isocyanate moiety is preferably an organic moiety derived from an organic isocyanate compound having two or more isocyanate groups, such as toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, xylylene diisocyanate, diphenyl ether diisocyanate, naphthylene diisocyanate, trimethylhexane diisocyanate, lysine diisocyanate, bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane diisocyanate, norbornene diisocyanate, or a combination thereof. By deriving the organic isocyanate moiety from an organic isocyanate compound having two or more isocyanate groups, the polyurethane-based polymer dispersant can have two or more polycaprolactone moieties. The organic isocyanate moiety may be a polymer of two or more of the above-mentioned organic isocyanate compounds, for example, an organic moiety derived from an isocyanurate (trimer) of the organic isocyanate compound. By having an organic isocyanate moiety derived from a polymer of an organic isocyanate compound, the degree of polymerization of the polyurethane-based polymer dispersant can be improved. For example, when the organic isocyanate moiety is an organic moiety derived from an isocyanurate (trimer), the polyurethane-based polymer dispersant can have three polycaprolactone moieties.

[0033] In polyurethane-based polymer dispersants having polycaprolactone chains, the polycaprolactone moiety is preferably a moiety derived from a polymer of ε-caprolactone (i.e., polyε-caprolactone). In this case, the molecular weight of the polyε-caprolactone is preferably 500 or more and 10,000 or less. By having a polycaprolactone moiety with the characteristics exemplified above, affinity for multi-walled CNTs can be improved.

[0034] In the polyurethane-based polymer dispersant having a polycaprolactone chain, the terminal portion having a linear or branched hydrocarbon group is a linear or branched C6-C 20Alkyl groups, C6-C 20 Alkenyl group or C6-C 20 Alkynyl groups are preferred, and straight or branched C8 to C 18 Alkyl groups, C6-C 20 Alkenyl group or C6-C 20 An alkynyl group is more preferable, and an octyl group or a stearyl group is even more preferable. By having a terminal portion having a linear or branched hydrocarbon group having the characteristics exemplified above, the affinity for multi-walled CNTs can be improved.

[0035] In polyurethane-based polymer dispersants having polycaprolactone chains, the terminal moiety having a tertiary amino group is preferably a 5- to 6-membered heteroaryl group, a 5- to 6-membered heteroaryl-C1-C5 alkyl group, or a C1-C5 alkyl group having a tertiary amino group, and more preferably a pyridyl group, a 2-pyridylmethyl group, or a diethylaminopropyl group. By having a terminal moiety having a tertiary amino group with the characteristics exemplified above, affinity for multi-walled CNTs can be improved.

[0036] The polyurethane-based polymer dispersant having a polycaprolactone chain may have not only the terminal moieties having a linear or branched hydrocarbon group and the terminal moieties having a tertiary amino group as exemplified above, but also a terminal moiety having a polyalkylene oxide (e.g., polyethylene oxide, polypropylene oxide, or a combination thereof) linked to an organic isocyanate moiety via a urea bond. By having a terminal moiety having a polyalkylene oxide with the characteristics exemplified above, the affinity for multi-walled CNTs can be further improved.

[0037] The solid content of the polyurethane-based polymer dispersant having polycaprolactone chains is preferably 40% by mass or more and 55% by mass or less. If the solid content exceeds the upper limit, the viscosity of the polyurethane-based polymer dispersant solution having polycaprolactone chains increases, which is undesirable. On the other hand, if the solid content is less than the lower limit, the amount of solvent contained in the polyurethane-based polymer dispersant solution having polycaprolactone chains increases, which is undesirable.

[0038] The number-average molecular weight of the polyurethane-based polymer dispersant having polycaprolactone chains is preferably 4000 or more and 8000 or less. If the number-average molecular weight exceeds the upper limit, the viscosity of the solution of the polyurethane-based polymer dispersant having polycaprolactone chains increases, which is undesirable. On the other hand, if the number-average molecular weight is less than the lower limit, the polyurethane-based polymer dispersant having polycaprolactone chains does not have sufficient dispersing ability, making dispersion difficult, which is also undesirable.

[0039] (Polymer dispersant with graft structure) The polymer dispersant having a graft structure is a polymer having 3% by mass or more and 55% by mass or less of structural units (1) represented by general formula (1), 45% by mass or more and 90% by mass or less of structural units (3) represented by general formula (3), and 0.5% by mass or more and 20% by mass or less of other structural units (4) linked to these structural units (where the total of all structural units is 100% by mass).

[0040] [ka]

[0041] In the general formula (1), R represents a hydrogen atom or a methyl group, A represents O or NH, B represents an ethylene group or a propylene group, R1 and R2 each independently represent a methyl group or an ethyl group, Ar represents a phenyl group, a naphthyl group, an anthracenyl group, or a pyrenyl group, X represents a chlorine atom, a bromine atom, bis(trifluoromethyl)sulfonimide, or bis(nonafluorobutanesulfonyl)imide, and p represents any number of repeating groups.

[0042] [ka]

[0043] In the general formula (3), R represents a hydrogen atom or a methyl group, A represents O or NH, Q represents an ethylene group or a methylethylene group, Y represents O, NHCOO, or NHCONH, m and n each independently represent an average number of repeating units of 0 or more, and m+n=20 to 100, R3 represents an alkyl group, aryl group, or alkylaryl group having 1 to 18 carbon atoms, and r represents an arbitrary number of repeating units.

[0044] [Constituent unit (1)] The structural unit (1) is a structural unit having a quaternary ammonium base. Examples of monomers (monomers 1) that can constitute the structural unit (1) include monomers represented by the following general formula (1a): The quaternary ammonium base in the structural unit (1) is adsorbed onto the carbon material, which is believed to contribute to improving the dispersibility of the carbon material in a liquid medium containing an organic solvent. Furthermore, one of the substituents bonded to the nitrogen atom of the quaternary ammonium base is an arylmethyl group (—CH—Ar). The aromatic ring of this arylmethyl group is believed to have affinity for the carbon material, improving the dispersibility of the carbon material. If the carbon numbers of R1 and R2 in the general formula (1) are too large, the arylmethyl group becomes unstable due to steric hindrance, making it difficult to form a quaternary ammonium base. For this reason, it is preferable that R1 and R2 in the general formula (1) are each independently a methyl group or an ethyl group.

[0045] [ka]

[0046] In the general formula (1), R represents a hydrogen atom or a methyl group, A represents O or NH, B represents an ethylene group or a propylene group, R1 and R2 each independently represent a methyl group or an ethyl group, Ar represents a phenyl group, a naphthyl group, an anthracenyl group, or a pyrenyl group, and X represents a chlorine atom, a bromine atom, bis(trifluoromethyl)sulfonimide, or bis(nonafluorobutanesulfonyl)imide.

[0047] Because a quaternary ammonium salt group is an ionic functional group, a polymer (polymer dispersant) having a structural unit (1) with this quaternary ammonium salt group is expected to exhibit conductivity through at least one of water adsorption and ionic conduction. In other words, by using a polymer having the structural unit (1) as a polymer dispersant, it is expected that a carbon nanotube dispersion can be obtained that can form a coating film with reduced decrease in conductivity.

[0048] The structural unit (1) is preferably represented by the following general formula (1-1).

[0049] [ka]

[0050] In the general formula (1-1), R1 and R2 each independently represent a methyl group or an ethyl group; Ar represents a phenyl group, a naphthyl group, an anthracenyl group, or a pyrenyl group; X represents a chlorine atom, a bromine atom, bis(trifluoromethyl)sulfonimide, or bis(nonafluorobutanesulfonyl)imide; and p represents any number of repeating groups.

[0051] The constitutional unit represented by general formula (1-1) is composed of, for example, a monomer represented by the following general formula (1a-1).

[0052] [ka]

[0053] In the general formula (1-1), R1 and R2 each independently represent a methyl group or an ethyl group, Ar represents a phenyl group, a naphthyl group, an anthracenyl group, or a pyrenyl group, and X represents a chlorine atom, a bromine atom, bis(trifluoromethyl)sulfonimide, or bis(nonafluorobutanesulfonyl)imide.

[0054] Specific examples of monomers that can constitute the structural unit represented by general formula (1-1) include dimethylnaphthylmethylammonium ethyl methacrylate chloride, dimethylnaphthylmethylammonium ethyl methacrylate bromide, dimethylnaphthylmethylammonium ethyl methacrylate bis(trifluoromethyl)sulfonimide, dimethylnaphthylmethylammonium ethyl methacrylate bis(nonafluorobutanesulfonyl)imide, diethylnaphthylmethylammonium ethyl methacrylate chloride, diethylnaphthylmethylammonium ethyl methacrylate bromide, diethylnaphthylmethylammonium ethyl methacrylate bis(trifluoromethyl)sulfonimide, and diethylnaphthylmethylammonium ethyl methacrylate bis(nonafluorobutanesulfonyl)imide. anthracenyldimethylmethylammonium ethyl methacrylate chloride, anthracenylmethyldimethylmethylammonium ethyl methacrylate bromide, anthracenyldimethylmethylammonium ethyl methacrylate bis(trifluoromethyl)sulfonimide, anthracenyldimethylnaphthylammonium ethyl methacrylate bis(nonafluorobutanesulfonyl)imide, diethylpyrenylmethylammonium ethyl methacrylate chloride, diethylpyrenylmethylammonium ethyl methacrylate bromide, diethylpyrenylmethylammonium ethyl methacrylate bis(trifluoromethyl)sulfonimide, and diethylpyrenylmethylammonium ethyl methacrylate bis(nonafluorobutanesulfonyl)imide.

[0055] [Constituent unit (2)] The polymer dispersant is preferably a polymer further having a structural unit (2) represented by the following general formula (2). By using a polymer further having the structural unit (2) as the polymer dispersant, the dispersibility of the carbon material can be further improved. Note that, by converting the amino group in the structural unit (2) into a quaternary salt, a quaternary ammonium salt group in the structural unit (1) can be formed.

[0056] [ka]

[0057] In the general formula (2), R represents a hydrogen atom or a methyl group, A represents O or NH, B represents an ethylene group or a propylene group, R1 and R2 each independently represent a methyl group or an ethyl group, and q represents any number of repeating groups.

[0058] An example of a monomer (monomer 2) that can constitute the structural unit (2) is a monomer represented by the following general formula (2a).

[0059] [ka]

[0060] In the general formula (2), R represents a hydrogen atom or a methyl group, A represents O or NH, B represents an ethylene group or a propylene group, and R1 and R2 each independently represent a methyl group or an ethyl group.

[0061] The structural unit (2) contains an amino group, which is a basic group. Therefore, carboxyl groups or phenolic hydroxyl groups formed on the surface of the carbon material by oxidation or the like form an ionic bond with the amino group in the structural unit (2), which is thought to facilitate adsorption of the polymer dispersant to the carbon material and further improve the dispersibility of the carbon material. Furthermore, the synergistic effect of the adsorption of the quaternary ammonium base in the structural unit (1) or the polycyclic aromatic group that constitutes the quaternary ammonium base to the carbon material is thought to further improve the dispersibility of the carbon material.

[0062] The structural unit (2) is preferably represented by the following general formula (2-1).

[0063] [ka]

[0064] In the general formula (2-1), R1 and R2 each independently represent a methyl group or an ethyl group, and q represents any number of repetitions.

[0065] The constitutional unit represented by general formula (2-1) is composed of, for example, a monomer represented by the following general formula (2a-1).

[0066] [ka]

[0067] In the general formula (2-1), R1 and R2 each independently represent a methyl group or an ethyl group.

[0068] Specific examples of monomers that can form the structural unit represented by general formula (2-1) include dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate.

[0069] [Constituent unit (3)] The structural unit (3) is a structural unit having a polyalkylene glycol chain. A polymer dispersant having this structural unit (3) is a polymer having a structure in which a polyalkylene glycol chain is grafted. The polyalkylene glycol chain is a molecular chain that can be dissolved in an organic solvent, which is a dispersion medium. In general formula (3), the urethane bond (NHCOO) or urea bond (NHCONH) represented by Y forms a hydrogen bond with a hydrogen atom constituting a hydroxyl group or the like generated on the surface of the carbon material by modification. Therefore, in the polymer dispersant, the grafted polyalkylene glycol chain dissolves in the organic solvent, which is the dispersion medium, and the main chain containing the urethane bond (NHCOO) or urea bond (NHCONH) in the structural unit (3) and the structural unit (1) is adsorbed to the carbon material. The dissolved polyalkylene glycol chain acts as a steric hindrance between the particulate carbon material particles, causing repulsion, enabling the carbon material to be well and stably dispersed in the liquid medium for a long period of time.

[0070] In general formula (3), m is the average number of repeating units of propyleneoxy groups (-CH(CH3)CHO-), and n is the average number of repeating units of ethyleneoxy groups (-CH2CHO-). m and n are each independently a numerical value of 0 or greater, and m+n=20 to 100, preferably m+n=35 to 100. That is, the molecular weight of the polyalkylene glycol chain is preferably 880 to 5,800, more preferably 1,540 to 5,800. In general formula (3), the alkyl group having 1 to 18 carbon atoms represented by R3 is preferably a methyl group, ethyl group, propyl group, butyl group, dodecyl group, stearyl group, phenyl group, naphthyl group, or nonylphenyl group.

[0071] An example of a monomer (monomer 3) that can constitute the structural unit (3) is a monomer (macromonomer) represented by the following general formula (3a).

[0072] [ka]

[0073] In the general formula (3), R represents a hydrogen atom or a methyl group, A represents O or NH, Q represents an ethylene group or a methylethylene group, Y represents O, NHCOO, or NHCONH, m and n each independently represent an average number of repeating units of 0 or more, and m+n=20 to 100, and R3 represents an alkyl group, aryl group, or alkylaryl group having 1 to 18 carbon atoms.

[0074] The structural unit (3) is preferably represented by the following general formula (3-1).

[0075] [ka]

[0076] In the general formula (3-1), Y represents NHCOO or NHCONH, m and n each independently represent an average number of repeating units of 0 or more, and m+n=20 to 100, R3 represents an alkyl group, aryl group, or alkylaryl group having 1 to 18 carbon atoms, and r represents an arbitrary number of repeating units.

[0077] The constitutional unit represented by general formula (1-3) is composed of, for example, a monomer represented by the following general formula (3a-1).

[0078] [ka]

[0079] In the general formula (3-1), Y represents NHCOO or NHCONH, m and n each independently represent an average number of repeating units of 0 or more, and m+n=20 to 100, and R3 represents an alkyl group, aryl group, or alkylaryl group having 1 to 18 carbon atoms.

[0080] Examples of monomers that can constitute the structural unit represented by general formula (1-3) include macromonomers in which Y is a urethane bond (NHCOO), which are obtained by reacting methacryloyloxyethyl isocyanate with glycol ether monoalkyl ethers such as polyethylene glycol monomethyl ether, polyethylene glycol polypropylene glycol monobutyl ether, polypropylene glycol monomethyl ether, and polyethylene glycol monododecyl ether; and macromonomers in which Y is a urea bond (NHCONH), which are obtained by reacting methacryloyloxyethyl isocyanate with monoether monoamines such as polyethylene glycol polypropylene glycol monoamine.

[0081] In general formulas (3), (3a), (3-1), and (3a-1), Y is preferably a urea bond (NHCONH), which does not require a catalyst when reacting an isocyanate with an amine. Furthermore, in general formulas (3), (3a), (3-1), and (3a-1), the polyalkylene glycol chain is preferably a random copolymer of propylene oxide and ethylene oxide. Furthermore, in general formulas (3), (3a), (3-1), and (3a-1), R3 is preferably a methyl group. The molecular weight of the polyalkylene glycol chain is preferably 2,000 to 4,000, and m+n is preferably 36 to 90.

[0082] [Constituent unit (4)] Structural unit (4) is another structural unit that can be linked to the structural units described above. Examples of monomers (monomer 4) that can form structural unit (4) include (meth)acrylic acid-based monomers such as (meth)acrylic acid and (meth)acrylic acid esters; and vinyl monomers such as styrene, vinyl toluene, vinyl pyridine, vinyl caprolactone, vinyl imidazole, α-methyl styrene, and vinyl acetate. Of these, α-methyl styrene is preferred from the viewpoint of easy control of molecular weight.

[0083] (Composition and properties of polymer dispersants with graft structures) In the polymer dispersant having a graft structure (hereinafter also referred to as polymer), the proportion of the structural unit (1) relative to the total of all structural units is preferably 3% by mass or more and 55% by mass or less, more preferably 5% by mass or more and 50% by mass or less. If the proportion of the structural unit (1) is less than 3% by mass, adsorption to the carbon material tends to be insufficient. On the other hand, if the proportion of the structural unit (1) is more than 55% by mass, solubility in organic solvents tends to be insufficient.

[0084] In the polymer, the proportion of the structural unit (2) relative to the total of all structural units is preferably 30% by mass or less, more preferably 2% by mass or more and 25% by mass or less. The amine value of the polymer is preferably 100 mg KOH / g or less, more preferably 3 mg KOH / g or more and 90 mg KOH / g or less. If the proportion of the structural unit (2) exceeds 30% by mass, the polymer tends to become discolored.

[0085] The proportion of the structural unit (3) in the polymer relative to the total of all structural units is preferably 45% by mass or more and 90% by mass or less, and more preferably 50% by mass or more and 85% by mass or less. That is, the structural unit (3) is a structural unit contained in a relatively large amount in the polymer. When a large amount of the structural unit (3) is contained, the polyalkylene glycol chains are densely arranged. Therefore, when the polymer serving as a polymer dispersant is adsorbed to a carbon material, the densely arranged polyalkylene glycol chains act as steric hindrances, preventing the carbon material from approaching each other, thereby enabling the carbon material to be stably dispersed.

[0086] If the proportion of the structural unit (3) in the polymer is less than 45% by mass, sufficient steric hindrance is not formed, and it tends to be difficult to improve dispersibility. On the other hand, if the proportion of the structural unit (3) is more than 90% by mass, the reactivity of the macromonomer that constitutes the structural unit (3) is somewhat poor, and some of the macromonomer tends to remain unpolymerized.

[0087] In the polymer, the proportion of the structural unit (4) relative to the total of all structural units is preferably 0.5% by mass or more and 20% by mass or less, and more preferably 0.6% by mass or more and 16% by mass or less. If the proportion of the structural unit (4) exceeds 0.5% by mass, the content of other structural units will be relatively reduced, and the function as a dispersant will tend to be reduced.

[0088] It is preferable that the structural unit (1), the structural unit (2), and the structural unit (3) are represented by general formula (1-1), general formula (2-1), and general formula (3-1), respectively, and that the structural unit (4) contains a structural unit derived from α-methylstyrene, because this makes it possible to obtain a carbon nanotube dispersion liquid in which the carbon material is less likely to re-aggregate even at high concentrations and is more stably dispersed.

[0089] The number-average molecular weight (Mw) of the polymer used as the polymer dispersant having a graft structure, measured by gel permeation chromatography (GPC) in terms of polystyrene, is preferably 5,000 to 20,000, and more preferably 10,000 to 15,000. If the number-average molecular weight of the polymer is less than 5,000, the amount of structural unit (3) derived from the macromonomer introduced is small, and sufficient dispersion stability tends to be difficult to obtain. On the other hand, if the number-average molecular weight of the polymer is more than 20,000, the amount of polymer dispersant required to disperse the carbon material becomes too large, and the viscosity of the resulting carbon nanotube dispersion tends to be excessively high.

[0090] (Polymer dispersant content) The content of the dispersant in terms of solid content per 100 parts by mass of multi-walled carbon nanotubes must be 50 parts by mass or more and 150 parts by mass or less, and more preferably 60 parts by mass or more and 140 parts by mass or less. The content of the dispersant in the carbon nanotube dispersion is preferably 30% by mass or less, and more preferably 15% by mass or less. By setting the content of the dispersant relative to the carbon material within the above range, a carbon material dispersion in which the carbon material is more stably dispersed can be obtained. If the amount of dispersant is too small relative to the carbon material, the dispersant may not be able to sufficiently coat the surface of the carbon material, resulting in somewhat insufficient dispersibility. On the other hand, if the amount of dispersant is too large relative to the carbon material, the carbon material dispersion may tend to thicken and the proportion of carbon material in the solid content may become relatively low. Furthermore, when the dispersion is used as an ink or coating material, the physical properties of the formed coating, such as strength or conductivity, may be slightly reduced.

[0091] <Dye derivatives with acidic functional groups> The dye derivative having an acidic functional group is a dye in which an acidic functional group has been introduced. Examples of the dye include pigments or dyes such as phthalocyanine dyes, azo dyes, quinacridone dyes, dioxazine dyes, anthrapyrimidine dyes, anthanthrone dyes, indanthrone dyes, flavanthrone dyes, perylene dyes, perinone dyes, thioindigo dyes, isoindolinone dyes, and triphenylmethane dyes. Examples of the acidic functional group include a sulfo group, a carboxy group, and a phenol group.

[0092] The content of the dye derivative relative to 100 parts by mass of multi-walled carbon nanotubes is preferably 0.01 parts by mass or more and 50 parts by mass or less, and more preferably 0.1 parts by mass or more and 20 parts by mass or less. By setting the amount of dye derivative relative to the carbon nanotubes within the above range, a carbon nanotube dispersion in which the carbon nanotubes are more stably dispersed can be obtained. If the amount of dye derivative relative to the carbon nanotubes is too low, the dye derivative may not sufficiently coat the surface of the carbon nanotubes, resulting in somewhat insufficient dispersibility. On the other hand, if the amount of dye derivative relative to the carbon nanotubes is too high, the carbon nanotube dispersion tends to thicken, making it difficult to form a paint and reducing the proportion of carbon nanotubes in the solid content. Furthermore, the surface resistivity of the formed coating film may be somewhat high, and if an electrode is formed, the cycle performance of the electrode may be reduced. The number of acidic functional groups is determined by S analysis, and the average substitution number x is preferably 1 to 3. If the average substitution number x is less than 1, the effect on dispersibility tends to be reduced. On the other hand, if the average substitution number x exceeds 3, aggregation tends to occur more easily.

[0093] Furthermore, when the dispersant and the dye derivative are used in combination at a predetermined ratio, the carbon nanotubes can be dispersed more effectively, improving the storage stability of the carbon nanotube dispersion. Furthermore, when the carbon nanotube dispersion is mixed with a binder resin or the like, re-aggregation can be suppressed compared to when the dispersant is used alone. The amount of dye derivative relative to 100 parts by mass of dispersant is preferably 0.05 parts by mass or more and 20 parts by mass or less, and more preferably 1 part by mass or more and 5 parts by mass or less. If the amount of dye derivative relative to the dispersant is too small, aggregation may occur when mixing the carbon nanotube dispersion with a binder resin, etc., making it difficult to form a paint. If the amount of dye derivative relative to the dispersant is too large, the carbon nanotube dispersion may easily thicken, making it difficult to form a paint, and the proportion of carbon nanotubes in the solid content may become relatively low. Furthermore, the surface resistivity of the formed coating film may become slightly high, and if an electrode is formed, the cycle characteristics of the electrode may be reduced.

[0094] <Binder resin> The carbon nanotube dispersion according to this embodiment may further contain a binder resin. By including a binder resin, it is possible to form a conductive coating film that is excellent in properties such as elongation and bending, and that has improved adhesion to a substrate or the like. As the binder resin, it is preferable to use at least one selected from the group consisting of acrylic resins, urethane resins, urea resins, epoxy resins, rubber resins, fluorine-based resins, polyamide resins, polyimide resins, silicone resins, and cellulose resins. Among these, urethane resins, acrylic silicone resins, and epoxy resins are preferred.

[0095] Examples of the acrylic resin include acrylic silicone resin, acrylic fluorine resin, polymethyl methacrylate (PMMA), polyethyl methacrylate, polymethyl acrylate, polyethyl acrylate, and polyhydroxy methacrylate.

[0096] Examples of urethane-based resins include ether-based, ester-based, carbonate-based, acrylic-based, and aliphatic-based urethane resins; resins obtained by copolymerizing these urethane resins with silicone-based polyols or fluorine-based polyols; etc. The molecular structure of the urethane-based resin may contain a urea bond or an imide bond.

[0097] The urea-based resin may be any resin having a urea bond in its molecular structure, and specific examples thereof include urethane urea elastomer, melamine resin, and urea formaldehyde resin.

[0098] Examples of epoxy resins include bisphenol A type epoxy resins, novolac type epoxy resins, brominated epoxy resins, polyglycol type epoxy resins, polyamide combined epoxy resins, silicone modified epoxy resins, amino resin combined epoxy resins, and alkyd resin combined epoxy resins.

[0099] Examples of rubber-based resins include natural rubber (NR), butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), hydrogenated NBR (H-NBR), styrene-butadiene rubber (SBR), isoprene rubber (IR), urethane rubber, chloroprene rubber (CR), epichlorohydrin rubber (ECO), ethylene-propylene-diene polymer (EPDM), acrylic rubber (ACM), chlorosulfonated polyethylene (CSM), polysulfide rubber, fluororubber, and the like.

[0100] Examples of fluorine-based resins include polyvinylidene fluoride (PVDF), vinylidene fluoride-tetrafluoroethylene copolymer, and vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer.

[0101] Examples of polyamide resins include alcohol-soluble methoxymethylated nylon, etc. Examples of polyimide resins include polyamideimide (PAI), polyamic acid, and silicone imide.

[0102] Examples of cellulose-based resins include cellulose esters such as cellulose diacetate, cellulose triacetate, cellulose propionate, and cellulose acetate propionate; and cellulose ethers such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, and carboxymethyl cellulose.

[0103] The content of binder resin relative to the carbon material in the carbon nanotube dispersion is preferably 10 to 300 parts by mass, more preferably 20 to 200 parts by mass, per 100 parts by mass of multi-walled carbon nanotubes. If the amount of binder resin is too small, it may be difficult to apply it to the substrate, and a uniform coating film may not be obtained. If the amount of binder resin is too large, the proportion of carbon nanotubes decreases relatively, and the resulting coating may not have sufficient surface resistivity or thermal diffusivity.

[0104] When producing a heating element using the carbon nanotube dispersion liquid according to this embodiment, it is preferable to use, as the silica-containing epoxy resin, a silicone resin having at least one silicon-containing group and a mixture of an epoxy resin and an organometallic compound.

[0105] The silicone resin having a silicon-containing group is preferably a silicone resin having at least one silicon-containing group selected from the group consisting of an alkoxysilyl group, an alkoxysilylene group, and a siloxane bond.The silicone resin having a silicon-containing group is preferably formed by addition polymerization of a vinyl monomer having an alkoxysilyl group or an alkoxysilylene group.

[0106] Examples of epoxy resins include glycidyl ether type epoxy resins, glycidyl ester type epoxy resins, alicyclic epoxy resins, modified epoxy resins obtained by modifying these epoxy resins with at least one selected from alkylphenols and fatty acids, alkylphenyl glycidyl ethers (e.g., reaction products of alkylphenols and epichlorohydrin), and alkylphenol novolac type epoxy resins (e.g., reaction products of novolac type alkylphenol resins and epichlorohydrin).

[0107] <Additives, etc.> The carbon nanotube dispersion according to this embodiment may further contain additives, resins, etc. Examples of additives include water-soluble dyes, pigments, organometallic compounds, UV absorbers, light stabilizers, antioxidants, leveling agents, antifoaming agents, preservatives, mildew inhibitors, photopolymerization initiators, and other pigment dispersants. Examples of resins include polyolefin resins, polyhalogenated olefin resins, polyester resins, polyamide resins, polyimide resins, polyether resins, polyvinyl resins, polystyrene resins, polyvinyl alcohol resins, polymethacrylate resins, polyurethane resins, polyepoxy resins, polyphenol resins, polyurea resins, and polyethersulfone resins.

[0108] The organometallic compound is added as a crosslinking agent to improve the elasticity or strength of the coating film, etc. Examples of the organometallic compound include titanium compounds such as tetramethyl titanate, titanium acetylacetonate, tetraisopropyl titanate, and tetra-normal-butyl titanate; zirconium compounds such as zirconium monoacetylacetonate, zirconium bisacetylacetonate, and zirconium tetraacetylacetonate; aluminum compounds such as aluminum monoacetylacetonate bis(ethylacetoacetate), aluminum tris(acetylacetonate), aluminum tris(ethylacetoacetate), and ethylacetoacetate aluminum diisopropylate; and tin compounds such as dibutyltin diacetate, dioctyltin dilaurate, and dibutyltin dilaurate tin.

[0109] It is preferable that the carbon nanotube dispersion contains an antifoaming agent as an additive, depending on the apparatus used in the wetting and dispersing steps. By containing an antifoaming agent, foaming during the dispersion treatment can be suppressed, so that the shear force or collision force applied during the dispersion treatment can act effectively, resulting in a dispersion with better dispersibility.

[0110] (Carbon nanotube dispersion liquid) The carbon nanotube dispersion according to this embodiment has low viscosity even at high multi-walled carbon nanotube concentrations, and the viscosity does not change easily even after a long period of time, resulting in excellent viscosity stability (storage stability). Specifically, the viscosity of the dispersion is 250 mPa·s or less when measured at 100 rpm using an E-type rotational viscometer. The rate of change in the viscosity (mPa·s) of the binder-resin-free dispersion at 25°C after 10 days at room temperature (25°C) is typically 15% or less, preferably 10% or less, and more preferably 5% or less, based on the viscosity (mPa·s) of the binder-resin-free dispersion at 25°C immediately after preparation (dispersion).

[0111] 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 the growth or sedimentation of the aggregates tends to reduce viscosity stability and storage stability. For example, when a dispersion containing aggregates with short sides of 100 μm or more is used as a coating material, uniform coating tends to be difficult to achieve. In contrast, the dispersion of this embodiment is substantially free of coarse aggregates formed by carbon materials, including carbon nanotubes. Specifically, even when the binder-resin-free dispersion immediately after preparation (dispersion) and the binder-resin-free dispersion after 10 days at room temperature (25°C) are observed five times at 200x magnification using an optical microscope, not even a single aggregate with short sides of 100 μm or more is typically observed. Preferably, the number (average) of aggregates with short sides of 20 μm or more is 10 or more per observation. More preferably, the number (average value) of aggregates with short sides of 20 μm or more is 1 or more and less than 10 per observation, and particularly preferably, not even one aggregate with short sides of 20 μm or more is observed even after five observations. The carbon nanotube dispersion of the present invention can be evaluated from the physical property values ​​when formed into a coating film.

[0112] The carbon nanotube dispersion according to this embodiment must have a multi-walled carbon nanotube content of more than 10% by mass and not more than 20% by mass. If the content is 10% by mass or less, a large amount of binder resin must be added when preparing a thick coating film, but this increases the surface resistivity or decreases the thermal diffusivity, making it impossible to prepare a high-performance thick coating film, which is undesirable. On the other hand, if the content exceeds 20% by mass, the carbon nanotube concentration becomes too high and they cannot be dispersed well, which is undesirable.

[0113] <Method of manufacturing carbon nanotube dispersion> The carbon nanotube dispersion according to this embodiment can be produced by wetting a carbon material containing carbon nanotubes in a liquid medium using a dispersant and then dispersing the carbon material in accordance with a conventionally known method. For example, wetting and dispersion methods using magnetic stirrer stirring, dissolver stirring, triple-roll kneading, ultrasonic dispersion, bead mill dispersion, an emulsifier, or a homogenizer can be used. For simplicity of process, wetting by stirring with a magnetic stirrer, dissolver, or homogenizer is preferred, and dispersion in combination with a high-pressure homogenizer is preferred. For example, dispersion by a bead mill using small beads is preferred. Furthermore, considering damage to carbon materials such as carbon nanotubes, a combination of wetting and high-dispersion methods may be used.

[0114] <Coating film> A conductive coating film (film) can be formed by applying and drying the carbon nanotube dispersion liquid according to this embodiment. The concentration of the carbon material in the coating film to be formed is, for example, preferably 0.01% by mass to 50% by mass, more preferably 0.1% by mass to 30% by mass, and particularly preferably 0.5% by mass to 20% by mass. The thickness of the coating film (film thickness) can be, for example, 0.8 μm to 30 μm. The thicker the film thickness and the higher the concentration of multi-walled carbon nanotubes, the lower the surface resistivity and the higher the thermal diffusivity of the coating film. In this embodiment, it was confirmed that the surface resistivity and thermal diffusivity of the coating film hardly change when the film thickness is within the range of 1±0.2 μm and the concentration of the carbon material is within the range of 40±1% by mass.

[0115] The surface resistivity of a 1 μm-thick dried film (coating film) containing 40 mass % multi-walled carbon nanotubes, formed by applying and drying the carbon material dispersion liquid according to this embodiment, is 1.0×10 3 It must be Ω / sq or less, and preferably 9.0×10 2The carbon content in the dried film (coating) can be calculated by heating the coating formed by applying the dispersion liquid and evaporating the liquid medium, then subtracting the mass (solid content) of the dispersant and binder resin used from the mass of the dried film. The same calculation can be performed when a baking process is performed. The surface resistivity of the dried film can be achieved by adjusting the type or amount of multi-walled carbon nanotubes or dispersant, or by adjusting the wetting method or dispersion method of the dispersion. The surface resistivity when the coating thickness is 1 μm was calculated by preparing two or more coating films with different thicknesses and then creating a calibration curve plotting the coating thickness and surface resistivity.

[0116] The thermal diffusivity of a dried film (coating film) having a thickness of 1 μm and containing 10 mass % multi-walled carbon nanotubes, formed by applying and drying the carbon material dispersion liquid according to this embodiment, is 0.30 mm 2 / s or more, and preferably 0.35 mm 2 / s or more. The carbon material content in the dried film (coating) can be calculated by heating the coating film formed by applying the dispersion liquid and evaporating the liquid medium, and subtracting the mass (solid content) of the dispersant and binder resin used from the mass of the dried film. The same calculation can be performed even if a baking process has been performed. The thermal diffusivity of the dried film can be achieved by adjusting the type or amount of multi-walled carbon nanotubes or dispersant, or by adjusting the wetting method or dispersion method of the dispersion.

[0117] In preparing the dried coating film, a baking step is preferably carried out. Baking decomposes the dispersant, increasing the concentration of multi-walled carbon nanotubes in the coating film, thereby improving the surface resistivity and thermal diffusivity. The baking temperature varies depending on the dispersant used, but should be a temperature at which the dispersant thermally decomposes, and is preferably 150°C or higher, more preferably 200°C or higher. From the viewpoint of the heat resistance of the multi-walled carbon nanotubes and the binder resin, the upper limit is preferably 500°C or lower, more preferably 400°C or lower. Furthermore, examples of applications of the carbon material dispersion liquid according to this embodiment include antistatic coating films, heat generating bodies, heat conductors, temperature-sensitive coating films, paints for sensors, heat dissipation paints, electrode materials, and paints for electromagnetic wave shielding.

[0118] <Use of carbon nanotube dispersion liquid> In the carbon nanotube dispersion according to this embodiment, the multi-walled carbon nanotubes are well dispersed without substantially forming coarse aggregates, and the dispersion has excellent viscosity stability. Furthermore, the carbon nanotube dispersion according to this embodiment is useful as a material for producing heat transfer materials, paints, inks, coating agents, and materials for resin molded products. It is also expected to be used as an electrically conductive or thermally conductive material, and is also expected to be applied to antistatic materials. Furthermore, it is useful as a battery material, such as an electrode material for batteries such as lithium-ion batteries and fuel cells, or a film constituting a capacitor material, a material for forming a film constituting various mechanical parts, a heating element, and a temperature-sensitive coating film. Examples of the heating element include a fixing device used in an image forming apparatus such as an electrophotographic copier, an automobile interior heater used in an in-vehicle seat, steering wheel, or window glass, or a wearable device such as a wearable heater. A common fixing device for an image forming apparatus uses a fixing roller to heat ink or toner for fixing. However, in order to improve image formation speed, it is important that the temperature of the fixing roller quickly reaches the target temperature. By using the carbon nanotube dispersion according to this embodiment as a heating element for the fixing roller, a fixing roller with no temperature unevenness can be manufactured, as the temperature rise rate is fast and a uniform coating film can be produced.

[0119] The aqueous paint or ink can be prepared by adding various components such as a solvent, a resin, and an additive to a carbon nanotube dispersion. Alternatively, the carbon nanotube dispersion may be added to a commercially available paint or ink.

[0120] A resin molded article can be produced, for example, by adding a carbon nanotube dispersion to a molten plastic material and then removing the water. Alternatively, a resin molded article having multi-walled carbon nanotubes dispersed therein can also be produced by adding a carbon nanotube dispersion to a finely powdered plastic material and then removing the water or precipitating the multi-walled carbon nanotubes. [Example]

[0121] 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.

[0122] <Preparing ingredients> The following carbon materials, dispersants, and binder resins were prepared. Note that the parts by mass of the dispersants and binder resins in the tables indicate the solid content. (filler) MWCNT-1: Multi-walled carbon nanotubes, product name "ENERMAX12", manufactured by Cabot Corporation MWCNT-2: Multi-walled carbon nanotubes, product name "NC7000", manufactured by Nanosil Co., Ltd. MWCNT-3: Multi-walled carbon nanotubes, product name "6A", manufactured by JEIO BN: Boron nitride, product name "MBN-010T", manufactured by Mitsui Chemicals (dispersant) Dispersant 16: Product name "EFKAPX4310", manufactured by BASF, solid content 50% Dispersant 17: Product name "Homogenol L-95", manufactured by Kao Chemical Co., Ltd., 100% solids Dispersant 18: Product name "Nopcosperse 6150", manufactured by San Nopco, solid content 73% Dispersant 19: Product name "TEGODisperse 710", manufactured by Evonik, solid content 35% (binder resin) Polyurethane resin, product name "Sanprene IB-1700D", manufactured by Sanyo Chemical Industries, Ltd., solid content 30%

[0123] <Production of dispersants> (Synthesis Example 1) A 1 L separable flask equipped with a stirrer, condenser, and thermometer was charged with 174.2 parts by mass of poly-ε-caprolactone (hydroxyl value 27.3 mg KOH / g, molecular weight 2055) obtained by ring-opening polymerization using stearyl alcohol as an initiator, and 204.8 parts by mass of propylene glycol monomethyl ether acetate (PGMAc) and heated to 50 °C to dissolve and homogenize. Next, 83.3 parts by mass of isocyanate (trimer) of toluene diisocyanate and hexamethylene diisocyanate (60.0 wt% PGMAc solution, NCO content 10.7%, solids NCO content 17.8%) was charged to the flask, and 1 part of a 1% PGMAc solution of tin dilaurate was added. The mixture was allowed to react for 2 hours at 80 °C. IR confirmed that the hydroxyl groups had disappeared from the reaction product. Next, 13.8 parts by mass of 2-pyridinemethanol was added to the flask and reacted in the same manner. By IR, isocyanate (2100 to 2200 cm) was extracted from the reaction product. -1 It was confirmed that the peak (peak) disappeared. The reaction product was dried in a thermostatic chamber at 150°C until a constant weight was reached, and the solid content was calculated, which was 50.1%. The amine value of the reaction product was then measured. The amine value converted to solids, i.e., the amine value of the resulting resin, was 29.6 mg KOH / g. The amine value was calculated by diluting 0.1 parts by mass of the sample with 100 ml of toluene / isopropanol = 1 / 1 and titrating it with 0.1 N hydrogen chloride propanol solution as the titrant using bromocresol green as the indicator. The molecular weight of the reaction product was measured by GPC, and the number average molecular weight (hereinafter referred to as Mn) was 5500 and the molecular weight distribution (hereinafter referred to as PDI) was 2.67. The reaction product obtained in Synthesis Example 1 is listed as Dispersant 1 in Table 1.

[0124] (Synthesis Example 2) A flask similar to that used in Synthesis Example 1 was charged with 163.5 parts by mass of poly-ε-caprolactone prepared under the same conditions as in Synthesis Example 1, 2.80 parts by mass of diethylene glycol, and 193.3 parts by mass of PGMAc, and the mixture was heated and homogenized in the same manner as in Synthesis Example 1. Next, 83.3 parts by mass of the isocyanate used in Synthesis Example 1 was charged to the flask, and the reaction was carried out in the same manner as in Synthesis Example 1. The disappearance of hydroxyl groups from the reaction product was confirmed in the same manner as in Synthesis Example 1. The flask was then cooled to room temperature, and 10.3 parts by mass of diethylaminopropylamine was added dropwise over 1 hour, followed by stirring for 2 hours to allow the reaction to proceed. The disappearance of isocyanate from the reaction product was confirmed in the same manner as in Synthesis Example 1. The solids content was measured in the same manner as in Synthesis Example 1 to be 49.0%, and the amine value of the resin was 19.7 mgKOH / g. The Mn was 7900, and the PDI was 3.21. The reaction product obtained in Synthesis Example 2 is shown in Table 1 as Dispersant 2.

[0125] (Synthesis Example 3) A flask similar to that of Synthesis Example 1 was charged with 55.4 parts by mass of poly-ε-caprolactone (hydroxyl value 53.6 mg KOH / g, molecular weight 1047) obtained by ring-opening polymerization using octanol as an initiator, and 157.1 parts by mass of PGMAc. The mixture was heated and homogenized in the same manner as in Synthesis Example 1. Next, 83.3 parts by mass of the isocyanate used in Synthesis Example 1 was charged to the flask, and the mixture was reacted in the same manner as in Synthesis Example 1. Disappearance of the hydroxyl groups from the reaction product was confirmed in the same manner as in Synthesis Example 1. The flask was then cooled to room temperature, and a mixture of 53.0 parts by mass of methoxypolyethylene glycol polypropylene glycol monoamine (EO:PO molar ratio = 4:1, amine value 56.0 mg KOH / g, molecular weight 1001), 11.6 parts by mass of 2-pyridinemethanol, and 64.6 parts by mass of 3-methoxy-3-methyl-1-butanol was added dropwise over 2 hours, followed by stirring at room temperature. The solid content was measured in the same manner as in Synthesis Example 1 and was found to be 49.3%, and the amine value of the resin was 35.6 mg KOH / g. The Mn was 4300 and the PDI was 2.63. The reaction product obtained in Synthesis Example 3 is listed as Dispersant 3 in Table 1.

[0126] (Synthesis Example 4) A flask similar to that used in Synthesis Example 1 was charged with 163.5 parts by mass of poly-ε-caprolactone prepared under the same conditions as in Synthesis Example 1, 2.80 parts by mass of diethylene glycol, and 193.3 parts by mass of PGMAc, and the mixture was heated and homogenized in the same manner as in Synthesis Example 1. Next, 83.3 parts by mass of the isocyanate used in Synthesis Example 1 was charged to the flask and reacted in the same manner as in Synthesis Example 1. The disappearance of hydroxyl groups from the reaction product was confirmed in the same manner as in Synthesis Example 1. The flask was then cooled to room temperature, and 13.6 parts by mass of methylaminopyridine was added dropwise over 1 hour. The mixture was stirred for 2 hours to allow the reaction to proceed. The disappearance of isocyanate from the reaction product was confirmed in the same manner as in Synthesis Example 1. The solids content was measured in the same manner as in Synthesis Example 1 and found to be 49.5%, and the amine value of the resin was 19.9 mgKOH / g. The Mn was 7600, and the PDI was 3.17. The reaction product obtained in Synthesis Example 4 is listed as Dispersant 4 in Table 1.

[0127] [Table 1]

[0128] (Synthesis Example 5) A reactor equipped with a stirrer, reflux condenser, thermometer, and dropping funnel was charged with 100 parts (0.05 mol) of mono-terminated polypropylene glycol polyethylene glycol monomethyl ether (trade name "Jeffamine M2005", manufactured by Huntsman, m + n = 35 (m = 29, n = 6), measured amine value 28.05 mg KOH / g) (M2005) and 100 parts of propylene glycol monomethyl ether acetate (PGMAc), and the mixture was stirred at room temperature for 10 minutes to homogenize. In a separate container, 7.75 parts (0.05 mol) of 2-isocyanatoethyl methacrylate (trade name "Karenz MOI", manufactured by Showa Denko KK) (MOI) and 7.75 parts of PGMAc were mixed to prepare a mixed solution. The prepared mixed solution was added dropwise to the reactor over 30 minutes to allow the reaction to occur. A portion of the reaction solution was sampled and subjected to IR analysis, confirming the disappearance of isocyanate groups derived from the MOI and the formation of urea bonds. Furthermore, the amine value of the product, measured using a 0.1 mol / L 2-propanol hydrochloric acid solution, was 0.1 mg KOH / g using a potentiometric automatic titrator. This confirmed that the reaction between the amino and isocyanate groups was nearly complete. The resulting product was a macromonomer (MCR-1) in which a methacryloyl group was attached to one end of polypropylene glycol polyethylene glycol monomethyl ether (PPG / PEG). The solids content of the MCR-1 solution was measured using a moisture meter and found to be 50.0%. Furthermore, the polystyrene-equivalent number average molecular weight (Mn) of MCR-1 was determined to be 3,400 by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as the developing solution.

[0129] A reactor equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube was charged with 49.6 parts of PGMAc, 215.5 parts of MCR-1 solution, 1.8 parts of α-methylstyrene (αMS), 25.1 parts of styrene (St), and 19.2 parts (0.122 mol) of 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA). The mixture was heated with nitrogen bubbling. When the internal temperature reached 70 °C, 3.0 parts of 2,2'-azobis(isobutyrate)dimethyl (V-601, Fujifilm Wako Pure Chemical Industries, Ltd.) (V-601) were added, and the mixture was heated to 75 °C and polymerized for 4 hours. 0.5 parts of V-601 was added, and the mixture was polymerized at 75 °C for another 4 hours. A portion of the reaction solution was sampled and measured. The product had an Mn of 8,500, a polydispersity index (PDI) of 1.65, and a peak top molecular weight (PT) of 14,000, with almost no peaks attributable to MCR-1. The solids content of the reaction solution was 50.1%. The amine value of the product (based on pure resin content) was 44.6 mg KOH / g.

[0130] A solution of 7.8 parts of PGMAc and 7.8 parts (0.0616 mol) of benzyl chloride (BzCl) was added dropwise over 30 minutes at room temperature. After the dropwise addition, the mixture was heated to 80°C and maintained for 5 hours to obtain a liquid containing Dispersant 5. Dispersant 5 had an Mn of 8,700, a PDI of 1.66, and a PT of 14,400. The solids content of the liquid containing Dispersant 5 was 50.1%. The amine value of Dispersant 5 (based on pure resin content) was 21.0 mg KOH / g, confirming that the reaction had progressed almost quantitatively. The resulting Dispersant 5 is a resin in which 50% of the amino groups derived from DMAEMA have been converted into quaternary salts with BzCl.

[0131] (Synthesis Examples 6 to 9) Dispersants 6 to 9 were obtained in the same manner as in the above-mentioned Synthesis Example 5, except that the formulations shown in Table 2 were used. The meanings of the abbreviations in Table 2 are as follows. M41: one-terminally aminated polypropylene glycol polyethylene glycol methyl ether (trade name "Genamine M41 / 2000", manufactured by Clariant, m + n = 41 (m = 9, n = 32)) DMQ: Benzyl chloride salt of 2-(N,N-dimethylaminoethyl) methacrylate MMA: Methyl methacrylate

[0132] The calculation method for the DMQ composition in Table 2 will be explained using Synthesis Example 5 as an example. 19.2 parts (0.122 mol) of DMAEMA (Mw 157.1) in the polymer reacted quantitatively with 7.8 parts (0.0616 mol) of BzCl (Mw 126.6) added. Therefore, the amount of DMQ (Mw 283.6) produced was 0.0616 mol × 283.6 = 17.5 parts. The DMQ composition in the polymer was calculated in the same manner, taking into account the quaternary chloride ratio.

[0133] The method for calculating the theoretical amine value of a polymer will be explained using Synthesis Example 5 as an example. Half (0.0616 mol) of the 19.2 parts (0.122 mol) of DMAEMA in the polymer is lost upon reaction with BzCl, so the amount of DMAEMA remaining in the polymer is 0.122 × 0.5 × 157.1 = 9.6 parts. 1 g of polymer contains 9.6 / (100 + 7.75 + 17.5 + 9.6 + 1.8 + 25.1) × 100 = 0.059 g of DMAEMA. Therefore, the amine value can be calculated as 0.059 / 157.1 × 56.1 × 1000 = 21.1 mg KOH / g.

[0134] [Table 2]

[0135] (Synthesis Example 10) A reactor equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube was charged with 49.5 parts of PGMAc, 216 parts of MCR-1 solution, 1.8 parts of αMS, 12.5 parts of benzyl methacrylate (BzMA), and 31.7 parts (0.202 mol) of DMAEMA, and heated while bubbling nitrogen. When the internal temperature reached 70°C, 13.0 parts of V-60 was added, and the mixture was heated to 75°C and polymerized for 4 hours. 10.5 parts of V-60 was added, and the mixture was polymerized at 75°C for another 4 hours. A portion of the reaction solution was sampled and measured. The product had an Mn of 10,600, a PDI of 1.89, and a PT of 20,200, with almost no peaks attributed to MCR-1. The solids content of the reaction solution was 50.1%. The amine value of the product (based on pure resin content) was 113.2 mg KOH / g.

[0136] A quaternary salt reaction was carried out in the same manner as in Synthesis Example 5 above, except that 17.8 parts (0.101 mol) of 1-chloromethylnaphthalene (CMN) was used instead of BzCl, to obtain a liquid containing Dispersant 10. Dispersant 10 had an Mn of 10,900, a PDI of 1.88, and a PT of 20,300. The solids content of the liquid containing Dispersant 10 was 50.1%. The amine value of Dispersant 10 (based on the pure resin content) was 32.8 mg KOH / g. The obtained Dispersant 10 is a resin in which 50% of the amino groups derived from DMAEMA have been quaternized with CMN.

[0137] (Synthesis Examples 11 and 12) Dispersants 11 and 12 were obtained in the same manner as in the above-mentioned Synthesis Example 10, except that the formulations shown in Table 3 were used. The meanings of the abbreviations in Table 3 are as follows. CMA: 9-chloromethylanthracene ·CMP: 1-chloromethylpyrene PME-4000: Methacrylic acid-terminated methoxypolyethylene glycol (product name "Blenmer PME-4000", NOF Corporation, m=0, n=90) NQ: 1-chloromethylnaphthalene salt of 2-(N,N-dimethylaminoethyl) methacrylate AQ: 9-chloromethylanthracene salt of 2-(N,N-dimethylaminoethyl) methacrylate PQ: 1-chloromethylpyrene salt of 2-(N,N-dimethylaminoethyl) methacrylate

[0138] [Table 3]

[0139] (Synthesis Example 13) A reactor equipped with a stirrer, reflux condenser, and thermometer was charged with 100.0 parts of a solution containing dispersant 6 (50.0% solids) and 150.0 parts of PGMAc and stirred to form a homogeneous solution. 5.04 parts (0.0176 mol, 30% relative to DMQ) of bis(trifluoromethanesulfonyl)imide lithium (TFSILi) was added and dissolved. This produced a quaternary ammonium salt with bis(trifluoromethanesulfonyl)imide anion (TFSI) as the counterion, yielding a solution containing dispersant 13. The solids content of the solution containing dispersant 13 was 21.5%. The amine value (based on pure resin content) of dispersant 13 was 21.8 mg KOH / g. When attempting to measure the Mn of dispersant 13 by GPC, it was strongly adsorbed to the column, preventing accurate measurement. When TFSILi reacts with an equimolar amount of DMQ, an equimolar amount of LiCl (Mw 42.4) is produced. Therefore, the amount of quaternary salt produced by the reaction of TFSILi with DMQ can be calculated as follows: 0.0176mol×(283.7+287.1)-0.0176mol×42.4=9.30 parts

[0140] (Synthesis Examples 14 and 15) Dispersants 14 and 15 were obtained in the same manner as in the above-mentioned Synthesis Example 13, except that the formulations shown in Table 4 were used. The meanings of the abbreviations in Table 4 are as follows. DMTFSI: A quaternary salt in which the chloride ion of DMQ is exchanged with bistrifluoromethanesulfonylimide. DMNFSI: A quaternary salt in which the chloride ion of DMQ is exchanged with bisnonafluorobutanesulfonylimide. NTFSI: A quaternary salt in which the chloride ion of NQ is exchanged with bistrifluoromethanesulfonylimide

[0141] [Table 4]

[0142] (Synthesis of dye derivatives) 30 parts of PV23 were added to 300 parts of 95% sulfuric acid and reacted at 20 to 30°C for 3 hours. The reaction mixture was precipitated in 2700 parts of ice water, filtered, and washed with water repeatedly. After drying, 36.2 parts of a blue-purple powder (dye derivative) was obtained, which has the following structural formula and, based on elemental analysis of sulfur, contains an average of 1.1 sulfonic acid groups per molecule.

[0143] [ka]

[0144] (Method of manufacturing carbon nanotube dispersion liquid) A carbon nanotube dispersion can be produced by wetting multi-walled carbon nanotubes in a liquid medium using a dispersant and then dispersing them according to a conventionally known method. For example, wetting and dispersion methods using magnetic stirrer stirring, dissolver stirring, triple-roll kneading, ultrasonic dispersion, bead mill dispersion, emulsifiers, homogenizers, etc. can be used. From the perspective of process simplicity, wetting by stirring with a magnetic stirrer, dissolver, or homogenizer is preferred, and dispersion in combination with a high-pressure homogenizer is preferred. For example, dispersion by a bead mill using small beads is preferred. Furthermore, considering damage to the multi-walled carbon nanotubes, a combination of wetting and high-dispersion methods may be used.

[0145] <Measurement and evaluation methods> [Measurement of viscosity and evaluation of viscosity stability] Using an E-type viscometer equipped with a 1°34' x R24 rotor, the viscosity of the carbon nanotube dispersion was measured immediately after dispersion and after 10 days (after leaving it to stand at room temperature for 10 days) at a temperature of 25°C and a rotor rotation speed of 100 rpm. For carbon nanotube dispersions with a viscosity of less than 25 mPa·s, the viscosity was measured using a VISCOMETERTVE-25L (manufactured by Toki Sangyo Co., Ltd.). For carbon nanotube dispersions with a viscosity of 25 mPa·s or more, the viscosity was measured using a VISCOMETERTVE-25H (manufactured by Toki Sangyo Co., Ltd.). The viscosity stability of the carbon nanotube dispersions was then evaluated according to the following evaluation criteria. ⊚: The rate of change in viscosity after 10 days is less than 5% based on the viscosity immediately after dispersion. ◯: The rate of change in viscosity after 10 days, based on the viscosity immediately after dispersion, is 5% or more and less than 10%. △: The rate of change in viscosity after 10 days based on the viscosity immediately after dispersion is 10% or more and less than 15%. ×: The rate of change in viscosity after 10 days based on the viscosity immediately after dispersion is 15% or more.

[0146] [Aggregate observation] The carbon nanotube dispersion was collected in a polyethylene bottle and diluted with a blank solution to a multi-walled carbon nanotube concentration of 0.1% by mass. The diluted solution was obtained by stirring for 30 seconds using a vortex mixer (Scientific Industries). 30 μL of the resulting diluted solution was dropped onto a glass slide, a cover glass was placed on top, and the presence or absence of aggregates was observed using an optical microscope (200x magnification). The carbon nanotube dispersion immediately after dispersion and the carbon nanotube dispersion 10 days later (after leaving the dispersion at room temperature for 10 days) were dropped onto glass slides five times each to prepare samples, which were then observed and evaluated for the presence or absence of aggregates according to the following evaluation criteria. ⊚: Not a single aggregate with a short side of 20 μm or more was observed during five observations. ◯: The number (average value) of aggregates with short sides of 20 μm or more was 1 or more but less than 10 per observation, and no aggregates with short sides of 100 μm or more were observed in any of the five observations. △: The number (average value) of aggregates with a short side of 20 μm or more was 10 or more per observation, and not a single aggregate with a short side of 100 μm or more was observed in any of the five observations. ×: One or more aggregates with a short side of 100 μm or more were observed during five observations.

[0147] (Evaluation of coating film) [Surface resistivity measurement] Surface resistivity is 10 5 When the surface resistivity exceeded Ω / sq, a high-resistance resistivity meter (trade name "Hiresta-UP MCP-HT450", manufactured by Nitto Seiko Analytech Co., Ltd.) was used to apply 10 V and measure five points to calculate the average value of the surface resistivity of the coating film. 5 When the value was Ω / sq or less, a low-resistance resistivity meter (trade name "Loresta-GP MCP-T610", manufactured by Nitto Seiko Analytech Co., Ltd.) was used, and the average value of the surface resistivity of the coating film was calculated by measuring at five points with an applied voltage of 10 V.

[0148] [Measurement of thermal diffusivity] The thermal diffusivity was measured using a thermal diffusivity measuring device (trade name "ai-Phase Mobile M3 type1", manufactured by ai-Phase Co., Ltd.) using the cyclic heating method (temperature wave thermal analysis) in accordance with ISO 22007-3.

[0149] <Preparation and Evaluation of Dispersion Liquid (1)> (Examples 1 to 33, Comparative Examples 1 to 18) The types and amounts of each component (except CNT) shown in Table 5 were placed in a 250 mL plastic bottle (polyethylene bottle). After stirring with a magnetic stirrer until uniform, the types and amounts of CNT shown in Table 5 were added and further stirred. 200 parts of zirconia beads with an average diameter of 0.8 mm were added, and treatment was carried out for 60 minutes using a Scandex (manufactured by Scandex Corporation). The zirconia beads were then separated and removed to obtain a dispersion. The results of evaluating the viscosity stability of the obtained dispersion and the results of observing aggregates are shown in Table 5. The meanings of the abbreviations in Table 5 are as follows: ·BN: Boron nitride

[0150] <Preparation and Evaluation of Dispersion Liquid (2)> The types of dispersions and binder resins shown in Table 5 were blended in proportions such that the CNT concentration (%) in the resulting coating film (solid content) would be the value shown in Table 5, and then mixed using a magnetic stirrer to obtain a carbon material dispersion. The resulting carbon material dispersion 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 a coating film with the thickness shown in Table 5. The surface resistivity and thermal diffusivity of the formed coating film are shown in Table 5. In Example 33, the coating film was baked in an electric oven at 250 °C for 30 minutes after formation to remove volatile components and dispersant components. In Comparative Examples 17 and 18, extensive cracking and peeling occurred in the coating during drying, making it impossible to obtain a smooth coated surface necessary for measuring surface resistivity and thermal diffusivity, and evaluation was therefore abandoned. Of these, Comparative Examples 1 to 16 did not achieve a CNT concentration of 40% in the coating film, and therefore evaluation was performed on Comparative Examples 1, 5, 6, 11, and 12. Note that Table 6 lists, as reference examples, coating film thicknesses and CNT concentrations in the coating film that differ.

[0151] [Table 5]

[0152] Table 5 shows that in Examples 1 to 32, CNT dispersions with extremely high concentrations of 15 mass % or more were obtained compared to Comparative Examples 1 to 16. Furthermore, when the CNT dispersions of Examples 1 to 32 were stored at 25°C for 30 days, no particular change in the dispersion state was observed.

[0153] (Reference examples 1~3) Dispersions were prepared and evaluated in the same manner as in the preparation and evaluation of the dispersions described above, except for the formulation shown in Table 6. In Reference Example 1, the film thickness was 5 μm, in Reference Example 2 no binder resin was added, and in Reference Example 3, after forming the coating film, it was baked in an electric oven at 250° C. for 30 minutes to remove volatile components and dispersant components.

[0154] [Table 6]

[0155] (Application example (heating element)) A composition for forming a heating element was obtained by mixing 30 parts by weight of the dispersion liquid of Example 1, 6 parts by weight of a mixture of acrylic silicone resin and epoxy resin as a binder resin, and 0.6 parts by weight of an organometallic compound (aluminum monoacetylacetonate bis(ethylacetoacetate)). This composition was applied to a 60 mm x 15 mm x 1 mm glass plate using a bar coater to prepare a 60 μm thick heating layer. Next, silver paste was applied to both ends of the glass plate to prepare a heating element.

[0156] (Evaluation of heating elements) Alligator clips were attached to both ends of the heating element, which was then connected to a variable constant current power supply. A current of 250mA or 450mA was passed through the element at room temperature of 25°C. The temperature of the heating element was measured using a thermograph after 30 seconds, and was found to be 100°C at 250mA and 200°C at 450mA.

[0157] (Comparative application example (heating element)) A heating element was prepared and evaluated in the same manner as in the application example, except that the dispersion liquid of Comparative Example 5 was used. There was no temperature change under both 250 mA and 450 mA conditions. This indicates that when the CNT concentration is low, the resistance value becomes high, and heat generation does not occur. Similarly, in the case of poor dispersion, the resistance becomes high, and heat generation does not occur. On the other hand, when the CNT concentration is high, the resistance value becomes low. In this case, heat generation occurs, but the maximum temperature is low. Therefore, it is important to set the CNT concentration and thickness to obtain an appropriate resistance value.

Claims

1. A carbon nanotube dispersion containing multi-walled carbon nanotubes, an organic solvent, and a dispersant, the content of the multi-walled carbon nanotubes is more than 10% by mass and 20% by mass or less with respect to the total amount of the carbon nanotube dispersion, The multi-walled carbon nanotubes have an average length of 2 μm or more and 40 μm or less and an average diameter of 5 nm or more and 150 nm or less, The content of the dispersant is 50 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the multi-walled carbon nanotubes, the dispersant is a polymer dispersant, When a dry film having a thickness of 1 μm is formed using a coating liquid containing the carbon nanotube dispersion and a binder resin so that the content of the multi-walled carbon nanotubes in the dry film is 40 mass %, the surface resistivity of the dry film is 1.0×10 ３ Ω / sq or less, and the thermal diffusivity of the dry coating is 0.30 mm ２ / s or more.

2. the polymer dispersant is a polyurethane-based polymer dispersant having a polycaprolactone chain, 2. The carbon nanotube dispersion liquid according to claim 1, wherein the polyurethane-based polymer dispersant having a polycaprolactone chain has an organic isocyanate moiety, two or more polycaprolactone moieties linked to the organic isocyanate moiety via a urethane bond, a terminal moiety having a linear or branched hydrocarbon group linked to the polycaprolactone moiety via an ester bond, and a terminal moiety having a tertiary amino group linked to the organic isocyanate moiety via a urethane bond or a urea bond, and has an amine value of 10 mgKOH / g or more and 100 mgKOH / g or less.

3. 3. The carbon nanotube dispersion liquid according to claim 2, wherein the solid content of the polyurethane-based polymer dispersant having polycaprolactone chains is 40% by mass or more and 55% by mass or less.

4. 3. The carbon nanotube dispersion liquid according to claim 2, wherein the number average molecular weight of the polyurethane-based polymer dispersant having a polycaprolactone chain is 4,000 or more and 8,000 or less.

5. The polymer dispersant is a polymer having 3% by mass or more and 55% by mass or less of a structural unit (1) represented by the following general formula (1), 45% by mass or more and 90% by mass or less of a structural unit (3) represented by the following general formula (3), and 0.5% by mass or more and 20% by mass or less of another structural unit (4) linked to these structural units (provided that the total of all structural units is 100% by mass), the structural unit (4) includes a structural unit derived from at least one monomer selected from the group consisting of (meth)acrylic acid, a (meth)acrylic acid ester, styrene, vinyltoluene, vinylpyridine, vinylcaprolactone, vinylimidazole, α-methylstyrene, and vinyl acetate; 2. The carbon nanotube dispersion liquid according to claim 1, wherein the polymer dispersant has an amine value of 100 mgKOH / g or less and a number average molecular weight of 5,000 or more and 20,000 or less. 【Chemistry 1】 (In the general formula (1), R represents a hydrogen atom or a methyl group, A represents O or NH, B represents an ethylene group or a propylene group, and R １ and R ２ are each independently a methyl group or an ethyl group, Ar is a phenyl group, a naphthyl group, an anthracenyl group, or a pyrenyl group, X is a chlorine atom, a bromine atom, bis(trifluoromethyl)sulfonimide, or bis(nonafluorobutanesulfonyl)imide, and p is an arbitrary number of repetitions. 【Chemistry 2】 (In the general formula (3), R represents a hydrogen atom or a methyl group, A represents O or NH, Q represents an ethylene group or a methylethylene group, Y represents O, NHCOO, or NHCONH, m and n each independently represent an average number of repeating units of 0 or more, and m+n=20 to 100, and R ３ represents an alkyl group, an aryl group, or an alkylaryl group having 1 to 18 carbon atoms, and r represents an arbitrary number of repeating groups.

6. 6. The carbon nanotube dispersion liquid according to claim 5, wherein the polymer dispersant is a polymer further having a structural unit (2) represented by the following general formula (2): 【Transformation 3】 (In the general formula (2), R represents a hydrogen atom or a methyl group, A represents O or NH, B represents an ethylene group or a propylene group, and R １ and R ２ are each independently a methyl group or an ethyl group, and q is an arbitrary number of repetitions.

7. The structural unit (1), the structural unit (2), and the structural unit (3) are represented by the following general formulas (1-1), (2-1), and (3-1), respectively:

7. The carbon nanotube dispersion according to claim 6, wherein the structural unit (4) includes a structural unit derived from α-methylstyrene. 【Chemistry 4】 (In the general formula (1-1), R １ and R ２ are each independently a methyl group or an ethyl group, Ar is a phenyl group, a naphthyl group, an anthracenyl group, or a pyrenyl group, X is a chlorine atom, a bromine atom, bis(trifluoromethyl)sulfonimide, or bis(nonafluorobutanesulfonyl)imide, and p is an arbitrary number of repetitions. 【Transformation 5】 (In the general formula (2-1), R １ and R ２ are each independently a methyl group or an ethyl group, and q is an arbitrary number of repetitions. 【Transformation 6】 (In the general formula (3-1), Y represents NHCOO or NHCONH, m and n each independently represent the average number of repeating units of 0 or more, and m+n=20 to 100; R ３ represents an alkyl group, an aryl group, or an alkylaryl group having 1 to 18 carbon atoms, and r represents an arbitrary number of repeating groups.

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

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

10. 10. The carbon nanotube dispersion liquid according to claim 9, wherein the binder resin is at least one selected from the group consisting of urethane-based resins, acrylic silicone-based resins, and epoxy-based resins.

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

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

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

14. The coating film according to claim 13, wherein the coating film is baked at 150°C or higher and 500°C or lower.

Images