thermal conductive materials

Abstract

To provide a thermal conductive material with excellent thermal conductivity.SOLUTION: A thermal conductive material includes flaky carbon with a thickness of 1-100 nm, an organic compound with a hydrophilic group and a carbon-affinity hydrophobic group, and nanofibers that are composed of cellulose or cellulose derivatives and have a fiber diameter of 1-500 nm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermally conductive material. [Background technology]

[0002] Crystalline carbon materials such as graphite and carbon nanotubes have high thermal conductivity and are therefore sometimes used as thermal conductive materials (see, for example, Patent Document 1). However, due to the high thermal resistance between the resin and the carbon, the thermal conductivity is often not as high as expected. Furthermore, because these carbon materials have low affinity with resin, increasing the amount added to improve thermal conductivity causes problems with kneading, molding, strength, etc.

[0003] Graphene sheets are two-dimensional monolayer sheets in which carbon atoms are arranged in a honeycomb lattice pattern, and are also the building blocks of graphite, fullerenes, carbon nanotubes, etc. Flake-like carbon (in this specification, flake-like carbon includes graphene sheets) in which graphene sheets are stacked to a thickness of approximately 100 nm or less has attracted attention as a new material that can be used in a variety of applications due to its unique physical properties.

[0004] However, while nanocarbon materials such as flaky carbon have extremely high thermal conductivity, the finer their structure, the more likely they are to aggregate, making it difficult to fully utilize their potential and preventing them from fully improving thermal conductivity and heat dissipation.

[0005] Furthermore, nanocarbon materials have problems in terms of usability, such as being difficult to create into a single film or to turn into paint, and when combined with resin, there are many cases where they do not disperse due to incompatibility (they cannot be applied as paint or do not have enough strength as a sheet) and their thermal conductivity drops significantly.

[0006] Furthermore, it is more desirable for both the coating film and the sheet to be insulating. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2014 / 080743 Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above circumstances, an object of the present invention is to provide a thermally conductive material having excellent thermal conductivity. [Means for solving the problem]

[0009] As a result of intensive research into solving the above problems, the inventors have found that the above problems can be solved by using a specific organic compound, flaky carbon having a specific thickness, and specific nanofibers. Based on this finding, the inventors have conducted further research and have completed the present invention.

[0010] That is, the present invention provides the following thermally conductive material. Section 1. Thin flake carbon with a thickness of 1 to 100 nm, an organic compound having a hydrophilic group and a carbon-philic hydrophobic group; A thermally conductive material made of cellulose or a cellulose derivative and containing nanofibers with a fiber diameter of 1 to 500 nm. Section 2. Item 2. The thermally conductive material according to item 1, wherein the hydrophilic group is at least one selected from the group consisting of the following general formulae (1) to (4): [ka] [The above formula (1) represents an alcoholic hydroxyl group or a phenolic hydroxyl group. In formula (2), R represents a divalent organic group, and both oxygen atoms represent an ether bond. In formula (3), X1 represents a hydrogen atom, an alkali metal, NH4, or an organic ammonium. In formula (4), X2 represents a hydrogen atom, an alkali metal, NH4, an organic ammonium, or an alkyl group.] Section 3. Item 3. The thermally conductive material according to Item 1 or 2, wherein the hydrophilic group is a phenolic hydroxyl group or a polyoxyethylene group. Section 4. Item 4. The thermally conductive material according to any one of Items 1 to 3, wherein the carbon-affinity hydrophobic group is at least one selected from the group consisting of an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, and a polyoxyalkylene group having 3 or more carbon atoms. Section 5. Item 5. The thermally conductive material according to any one of items 1 to 4, wherein the carbon-affinity hydrophobic group is an aryl group having two or more aromatic rings. Section 6. Item 6. The thermally conductive material according to any one of items 1 to 5, wherein the nanofibers are cellulose nanofibers having a cellulose purity of 85% or more. Section 7. Item 7. The thermally conductive material according to any one of items 1 to 6, wherein the nanofibers comprise at least one type of nanofiber selected from the group consisting of methyl cellulose, carboxymethyl cellulose salts, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, and hydroxypropyl methyl cellulose. Section 8. Item 8. A paint containing the thermally conductive material according to any one of Items 1 to 7, or a coating film formed from the paint. Section 9. Item 8. A sheet comprising the thermally conductive material according to any one of Items 1 to 7. Section 10. 8. A method for producing a thermally conductive material according to any one of items 1 to 7, comprising a step of mixing a flaky carbon dispersion or a wet solid of the flaky carbon dispersion, the flaky carbon dispersion containing 1 to 100 parts by mass of an organic compound having the hydrophilic group and the carbon-affinity hydrophobic group per 100 parts by mass of the flaky carbon, with a nanofiber dispersion or a wet solid of the nanofiber dispersion. [Effects of the Invention]

[0011] The thermally conductive material of the present invention thus constructed has excellent thermal conductivity. DETAILED DESCRIPTION OF THE INVENTION

[0012] In this specification, the term "containing" is a concept that encompasses all of "comprise," "consist essentially of," and "consist only of." Furthermore, in this specification, when a numerical range is expressed as "A to B," it means A or more and B or less.

[0013] (1. Thermal Conductive Materials) The thermally conductive material of the present invention contains flaky carbon having a thickness of 1 to 100 nm, an organic compound having a hydrophilic group and a carbon-affinitive hydrophobic group, and nanofibers made of cellulose or a cellulose derivative and having a fiber diameter of 1 to 500 nm.

[0014] (1.1. Flake carbon) Thinner flaky carbon is preferable because it has better thermal conductivity and heat dissipation. Specifically, it is 1 to 100 nm, and preferably 1 to 20 nm. If the thickness of the flaky carbon exceeds 100 nm, it is not possible to obtain a thermally conductive material with sufficient thermal conductivity and heat dissipation.

[0015] Furthermore, the content of flaky carbon having a thickness of 1 to 10 nm is preferably 80% or more, and more preferably 90% or more, with the total number of flaky carbon being 100%. In other words, although flaky carbon having a thickness of more than 10 nm may be included, it is preferable that the thickness of most of the flaky carbon is 10 nm or less. The thickness of the flaky carbon is measured by observation with a transmission electron microscope (TEM).

[0016] The flaky carbon is preferably flaky carbon having a layered structure in which 300 or less layers (i.e., 1 to 300 layers) of graphene are stacked, and more preferably flaky carbon having a layered structure in which 1 to 60 layers of graphene are stacked. Similarly, the content of flaky carbon having 1 to 30 stacked layers is preferably 80% or more, and more preferably 90% or more, of the total number of flaky carbons being 100%. In other words, thick flaky carbons may be included, but the thickness of the majority of flaky carbons is preferably 30 layers or less. The stacking of flaky carbons is calculated from the thickness measured by observation with a transmission electron microscope (TEM).

[0017] Since flaky carbon usually has a planar shape with many convex and concave angles, it is difficult to define its size in general terms other than thickness. In this specification, the size of a piece of flaky carbon is defined as the distance between the furthest convex angles in that piece of flaky carbon.

[0018] The size of such flaky carbon is preferably 20 nm or more, more preferably 100 nm or more, and even more preferably 200 nm or more. By using flaky carbon of such a size, thermal conductivity and heat dissipation can be further improved. The upper limit of the size of the flaky carbon is not limited, as larger flaky carbon is known to have better thermal conductivity and heat dissipation and is therefore preferred, but is usually 100 μm. The size of the flaky carbon is measured by transmission electron microscopy (TEM).

[0019] In the thermal conductive material of the present invention, the content of flaky carbon is not particularly limited, but from the viewpoint of thermal conductivity and heat dissipation, it is preferably 50 to 99.5 mass%, and more preferably 60 to 99.2 mass%, of the total amount of the thermal conductive material of the present invention being 100 mass%.

[0020] (1.2. Organic Compounds Having Hydrophilic Groups and Carbon-Affinity Hydrophobic Groups) In the thermal conductive material of the present invention, an organic compound having a hydrophilic group and a carbon-affinitive hydrophobic group is used. If this organic compound is not used, the flaky carbon maintaining the graphene structure will aggregate and will not be able to be maintained in a uniformly dispersed state. The organic compound can also function as a dispersant to uniformly disperse the flaky carbon.

[0021] The organic compound having such a hydrophilic group and a carbon-affinitive hydrophobic group is not particularly limited, and a wide variety of organic compounds (especially water-soluble compounds) that can function as a dispersant for flaky carbon can be used.

[0022] The carbon-affinity hydrophobic group in the organic compound is not particularly limited, and examples thereof include alkyl groups, alkenyl groups, cycloalkyl groups, aryl groups, and polyoxyalkylene groups having 3 or more carbon atoms. An organic compound having a hydrophilic group and a carbon-affinity hydrophobic group can contain one or more types of such hydrophobic groups. Furthermore, when multiple hydrophobic groups are contained, the compounds may contain multiple identical hydrophobic groups or multiple different hydrophobic groups.

[0023] The alkyl group may be a chain alkyl group or a branched chain alkyl group. However, from the viewpoint of affinity with carbon, a chain alkyl group is preferable. Furthermore, in consideration of affinity with carbon, the number of carbon atoms in the alkyl group is preferably 6 or more, more preferably 8 to 28, and even more preferably 10 to 22. Examples of such alkyl groups include a hexyl group, an octyl group, a decyl group, an undecyl group, a dodecyl group (or a lauryl group), a tridecyl group, a tetradecyl group (or a myristyl group), a pentadecyl group, a hexadecyl group (or a cetyl group), an octadecyl group, and an icosyl group.

[0024] The alkyl group may or may not have a substituent. Examples of such a substituent include a cycloalkyl group, an aryl group, and an aralkyl group. Examples of the cycloalkyl group and the aryl group are described below.

[0025] The aralkyl group as a substituent of the alkyl group is preferably an aralkyl group having 7 to 14 carbon atoms and an aryl group described below and an alkyl group having 1 to 6 carbon atoms, specifically, a benzyl group, a phenethyl group, etc. are preferred.

[0026] The substituent is not limited to the above, and may have a group derived from a fluorene structure (such as a fluorenyl group). In particular, when importance is placed on water solubility, a phenyl group or the like is preferred as the substituent, and when importance is placed on compatibility with the flaky carbon, a naphthyl group, a fluorenyl group or the like is preferred as the substituent.

[0027] In consideration of the affinity with carbon and the water solubility of the compound, the alkenyl group preferably has 4 or more carbon atoms, more preferably 6 to 100, and even more preferably 8 to 30. Examples of such alkenyl groups include an oleyl group and a linoleyl group.

[0028] The alkenyl group may or may not have a substituent. Examples of such a substituent include an alkyl group, a cycloalkyl group, an aryl group, and an aralkyl group. Examples of the aralkyl group include those described above, and examples of the cycloalkyl group and the aryl group include those described below.

[0029] The alkyl group as a substituent of the alkenyl group is preferably an alkyl group having 1 to 6 carbon atoms, specifically, a methyl group, an ethyl group, a propyl group, a butyl group, a tert-butyl group, etc. are preferred.

[0030] The substituent is not limited to the above, and may have a group derived from a fluorene structure (such as a fluorenyl group). In particular, when importance is placed on water solubility, a phenyl group or the like is preferred as the substituent, and when importance is placed on compatibility with the flaky carbon, a naphthyl group, a fluorenyl group or the like is preferred as the substituent.

[0031] The cycloalkyl group is preferably a cycloalkyl group having 5 to 10 carbon atoms (preferably 5 to 8, particularly 5 to 6), and specifically, a cyclopentyl group, a cyclohexyl group, etc. are preferred.

[0032] The cycloalkyl group may or may not have a substituent, and examples of such a substituent include an alkyl group, an aryl group, and an aralkyl group.

[0033] The alkyl group as a substituent of the cycloalkyl group is preferably an alkyl group having 1 to 6 carbon atoms, specifically, a methyl group, an ethyl group, a propyl group, a butyl group, a tert-butyl group, etc. are preferred.

[0034] Examples of the aryl group and aralkyl group as the substituent of the cycloalkyl group include those exemplified above.

[0035] The substituent is not limited to the above, and may have a group derived from a fluorene structure (such as a fluorenyl group). In particular, when importance is placed on water solubility, a phenyl group or the like is preferred as the substituent, and when importance is placed on compatibility with the flaky carbon, a naphthyl group, a fluorenyl group or the like is preferred as the substituent.

[0036] The aryl group is preferably an aryl group having 6 to 18 carbon atoms (particularly 6 to 14), and any of a monocyclic aryl group, a fused ring aryl group, and a polycyclic aryl group can be used, such as a phenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a biphenyl group, a terphenyl group, a fluorenyl group, a pyrenyl group, a triphenylenyl group, etc. From the viewpoint of affinity with carbon, an aryl group having two or more aromatic rings (a fused ring aryl group and a polycyclic aryl group) is preferred.

[0037] The aryl group may or may not have a substituent, and examples of such a substituent include an alkyl group, a cycloalkyl group, and an aralkyl group.

[0038] The alkyl group as a substituent of the aryl group is preferably an alkyl group having 1 to 6 carbon atoms, specifically, a methyl group, an ethyl group, a propyl group, a butyl group, a tert-butyl group, etc. are preferred.

[0039] Examples of the cycloalkyl group and aralkyl group as the substituent of the aryl group include those exemplified above.

[0040] The substituent is not limited to the above, and may have a group derived from a fluorene structure (such as a fluorenyl group).

[0041] Polyoxyethylene groups are usually hydrophilic, but polyoxyalkylene groups having 3 or more carbon atoms, such as polyoxypropylene groups and polyoxybutylene groups, become more hydrophobic as the degree of polymerization increases, and function as hydrophobic groups. Polyoxypropylene groups with a degree of polymerization of 4 or more and polyoxybutylene groups with a degree of polymerization of 3 or more are particularly preferred. For example, when polyoxyethylene-polyoxypropylene or polyoxyethylene-polyoxybutylene is used as an organic compound having a hydrophilic group and a carbon-affinic hydrophobic group, the polyoxypropylene group and polyoxybutylene group can also function as hydrophobic groups.

[0042] This polyoxyalkylene group having 3 or more carbon atoms may or may not have a substituent, such as an alkyl group, a cycloalkyl group, an aralkyl group, or an aryl group.

[0043] The alkyl group as a substituent of the polyoxyalkylene group having 3 or more carbon atoms is preferably an alkyl group having 1 to 6 carbon atoms, specifically, a methyl group, an ethyl group, a propyl group, a butyl group, a tert-butyl group, etc. are preferred.

[0044] Examples of the cycloalkyl group, aralkyl group and aryl group as the substituent of the polyoxyalkylene group having 3 or more carbon atoms include those exemplified above.

[0045] The substituent is not limited to the above, and may have a group derived from a fluorene structure (such as a fluorenyl group). In particular, when importance is placed on water solubility, a phenyl group or the like is preferred as the substituent, and when importance is placed on compatibility with the flaky carbon, a naphthyl group, a fluorenyl group or the like is preferred as the substituent.

[0046] From the viewpoint of affinity with carbon, such hydrophobic groups are preferably aryl groups and polyoxyalkylene groups having 3 or more carbon atoms, more preferably aryl groups, and even more preferably aryl groups having two or more aromatic rings (fused aryl groups and polycyclic aryl groups).Specific examples of preferred hydrophobic groups include naphthyl groups, anthracenyl groups, phenanthrenyl groups, biphenyl groups, terphenyl groups, fluorenyl groups, pyrenyl groups, triphenylenyl groups, polyoxypropylene groups having a degree of polymerization of 4 or more, and polyoxybutylene groups having a degree of polymerization of 3 or more.

[0047] Furthermore, the hydrophilic group possessed by the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group is not particularly limited as long as it can increase the solubility in water of the organic compound having the hydrophilic group and the carbon-affinity hydrophobic group. However, taking into consideration the water solubility of the organic compound having the hydrophilic group and the carbon-affinity hydrophobic group, the dispersibility, thermal conductivity, and heat dissipation properties of the flaky carbon, it is preferable that the hydrophilic group be one of the following general formulas (1) to (4).

[0048] [ka] [The above formula (1) represents an alcoholic hydroxyl group or a phenolic hydroxyl group. In formula (2), R represents a divalent organic group, and both oxygen atoms are ether bonds. In formula (3), X1 represents a hydrogen atom, an alkali metal, NH4, or an organic ammonium. In formula (4), X2 represents a hydrogen atom, an alkali metal, NH4, an organic ammonium, or an alkyl group.]

[0049] The organic compound having a hydrophilic group and a carbon-affinity hydrophobic group may contain one or more types of such hydrophilic groups. When multiple hydrophilic groups are used, the same hydrophilic groups may be used in multiple cases, or multiple types of hydrophilic groups represented by the same general formula may be used, or multiple types of hydrophilic groups represented by different general formulas may be used.

[0050] In general formula (1), -OH may be either an alcoholic hydroxyl group or a phenolic hydroxyl group. However, from the viewpoints of the water solubility of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, the dispersibility of the flaky carbon, thermal conductivity, heat dissipation, etc., an alcoholic hydroxyl group is preferred, but when a phenolic hydroxyl group is contained (particularly when multiple phenolic hydroxyl groups are contained), a benzene ring with excellent hydrophobicity is inevitably contained, and as a whole, the water solubility of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, the dispersibility of the flaky carbon, thermal conductivity, heat dissipation, etc. are also excellent, which is preferable.

[0051] In general formula (2), the divalent organic group represented by R is not particularly limited, and is preferably a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include aliphatic hydrocarbon groups (such as alkylene groups (or alkylidene groups), cycloalkylene groups, alkylene (or alkylidene)-cycloalkylene groups, and bi- or tricycloalkylene groups), and aromatic hydrocarbon groups (such as arylene groups and alkylene (or alkylidene)-arylene groups).

[0052] In the general formula (2), the alkylene group (or alkylidene group) represented by the group R is preferably an alkylene group, and C 1-8 An alkylene group is more preferred, and C 1-4 An alkylene group is more preferred, and C 2-4 Alkylene groups are particularly preferred, and C 2-3 Alkylene groups are most preferred, and specific examples include methylene, ethylene, ethylidene, trimethylene, propylene, propylidene, tetramethylene, ethylethylene, butan-2-ylidene, 1,2-dimethylethylene, pentamethylene, and pentane-2,3-diyl groups.

[0053] In the general formula (2), the cycloalkylene group represented by the group R is C 5-10 A cycloalkylene group is preferred, and C 5-8 A cycloalkylene group is more preferred, and specific examples thereof include a cyclopentylene group, a cyclohexylene group, a methylcyclohexylene group, and a cycloheptylene group.

[0054] In the general formula (2), the alkylene (or alkylidene)-cycloalkylene group represented by the group R is preferably an alkylene-cycloalkylene group, and C 1-6 Alkylene-C 5-10 A cycloalkylene group is more preferred, and C 1-4 Alkylene-C 5-8 Cycloalkylene groups are more preferred, and specific examples include a methylene-cyclohexylene group, an ethylene-cyclohexylene group, an ethylene-methylcyclohexylene group, and an ethylidene-cyclohexylene group.

[0055] In the general formula (2), specific examples of the bi- or tricycloalkylene group represented by the group R include a norbornane-diyl group.

[0056] In the general formula (2), the arylene group represented by the group R is C 6-10 An arylene group is preferred, and specific examples thereof include a phenylene group and a naphthalenediyl group.

[0057] In the general formula (2), the alkylene (or alkylidene)-arylene group represented by the group R is preferably an alkylene-arylene group, and C 1-6 Alkylene-C 6-20 An arylene group is more preferred, and C 1-4 Alkylene-C 6-10 An arylene group is more preferred, and C 1-2 Alkylene-phenylene groups are particularly preferred, and specific examples include methylene-phenylene groups, ethylene-phenylene groups, ethylene-methylphenylene groups, and ethylidenephenylene groups.

[0058] Among these, divalent aliphatic hydrocarbon groups, particularly alkylene groups (e.g., C groups such as methylene and ethylene groups) are preferred. 1-4 alkylene groups, etc.) are preferred.

[0059] The alkylene (or alkylidene)-cycloalkylene group and the alkylene (alkylidene)-arylene group refer to a group represented by -Ra-Rb- (wherein Ra represents an alkylene group or alkylidene group bonded to different oxygen atoms in general formula (2), and Rb represents a cycloalkylene group or an arylene group).

[0060] The hydrophilic group represented by general formula (2) is not particularly limited, and examples thereof include -OC2H4O-, -OC3H6O-, and -OCHO-. A group having a plurality of these groups (preferably 3 to 100 groups) can also be preferably used, such as a polyoxymethylene group, a polyoxyethylene group, and a polyoxypropylene group. In particular, when the hydrophilic group represented by general formula (2) has a structure in which three or more hydrophilic groups are polymerized, the more carbon atoms in R (e.g., three or more carbon atoms), the lower the hydrophilicity and the higher the hydrophobicity. Therefore, -OC2H4O- and -OCHO-, which can maintain hydrophilicity even with an increased degree of polymerization, are preferred.

[0061] In the general formula (3), the alkali metal represented by X1 is not particularly limited, and examples thereof include sodium, potassium, and lithium.

[0062] In the general formula (3), the organic ammonium represented by X1 is preferably a quaternary ammonium, and tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, etc. can be suitably used.

[0063] The hydrophilic group represented by the general formula (3) is not particularly limited. For example, -SO3 - H + , -SO3 - Na + , -SO3 - K+ , -SO3 - Li + , -SO3 - NH4 + , -SO3 - N(CH3)4 + , -SO3 - N(C2H5)4 + , -SO3 - N(C3H7)4 + , -SO3 - N(C4H9)4 + etc.

[0064] In the general formula (4), examples of the alkali metal and organic ammonium represented by X2 include those exemplified above.

[0065] In general formula (4), the alkyl group represented by X2 may be a chain alkyl group or a branched chain alkyl group. However, from the viewpoint of affinity with carbon, a chain alkyl group is preferable. Furthermore, from the viewpoint of affinity with carbon, the number of carbon atoms in the alkyl group is preferably 1 to 2.

[0066] The hydrophilic group represented by the general formula (4) is not particularly limited, and examples thereof include -COOH, -COONa, -COOK, -COOLi, -COONH4, -COON(CH3)4, -COON(C2H5)4, and -COON(C3H7)4. + , -COON(C4H9)4 + etc.

[0067] Among these hydrophilic groups, the hydrophilic group represented by general formula (2) is preferred in consideration of the water solubility of organic compounds having a hydrophilic group and a carbon-affinitive hydrophobic group, stability independent of pH, dispersibility of flaky carbon, thermal conductivity, and heat dissipation properties.

[0068] However, when a compound has multiple identical hydrophilic groups represented by general formula (2), i.e., when it has a polymerized structure, the hydrophilicity of the water-soluble compound increases as the degree of polymerization increases for compounds with two or fewer carbon atoms, but the hydrophobicity of the compound may increase as the degree of polymerization increases for compounds with three or more carbon atoms.

[0069] In the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group used in the present invention, the number of carbon atoms in the constituent parts other than the hydrophilic group (such as the hydrophobic group) is preferably 6 or more, and more preferably 8 to 18, from the viewpoints of the water solubility of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, the dispersibility of the flaky carbon, thermal conductivity, heat dissipation, etc.

[0070] Furthermore, in the present invention, when a nonionic material (such as a nonionic surfactant) is used as the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, the HLB value thereof is preferably 12 or more, more preferably 13 to 19, from the viewpoints of the water solubility of the organic compound having the hydrophilic group and the carbon-affinity hydrophobic group, the dispersibility of the flaky carbon, thermal conductivity, heat dissipation, etc. When the hydrophobic group is the same (when the affinity with the flaky carbon is about the same), the higher the HLB value, the better.

[0071] The organic compound having a hydrophilic group and a carbon affinity hydrophobic group that satisfies the above-mentioned conditions is not particularly limited.For example, aromatic water-soluble compounds may be used, or non-aromatic water-soluble compounds may be used, among which aromatic water-soluble compounds are preferred.The organic compound having a hydrophilic group and a carbon affinity hydrophobic group may be, for example, polyoxyethylene lauryl ether, polyoxyethylene decyl ether, polyoxypropylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene naphthyl ether, polyoxypropylene lauryl ether, polyoxypropylene naphthyl ether, polyoxyethylene myristyl ether, polyoxypropylene myristyl ether, polyoxyethylene cetyl ether, polyoxypropylene cetyl ether, polyoxyethylene octylphenyl ether, polyoxypropylene octylphenyl ether, polyoxyethylene undecylphenyl ether. ether, polyoxypropylene undecyl phenyl ether, polyoxyethylene tridecyl phenyl ether, polyoxypropylene tridecyl phenyl ether, polyoxyethylene pentadecyl phenyl ether, polyoxypropylene pentadecyl phenyl ether, polyoxyethylene polyoxypropylene glycol, polyoxypropylene polyglyceryl ether, sodium cholate, potassium cholate, sodium dodecyl sulfonate, potassium dodecyl sulfonate, sodium dilauroyl glutamate lysine, potassium dilauroyl glutamate lysine, decaglycerin laurate, and n-decyl alcohol.

[0072] Examples of organic compounds having such hydrophilic groups and carbon-affinity hydrophobic groups include Emulgen 103, Emulgen 104P, Emulgen 105, Emulgen 106, Emulgen 108, Emulgen 109P, Emulgen 120, Emulgen 123P, Emulgen 130K, Emulgen 147, Emulgen 150, Emulgen 210P, and Emulgen 220 (all polyoxyethylene alkyl ethers manufactured by Kao Corporation), Triton X-100, Triton X-114, Triton X-305, and Triton X-405 (polyoxyethylene octylphenyl ethers manufactured by Dow Chemical Company), Noigen EN, and Noigen EN-10 (polyoxyethylene naphthyl ethers manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and the like.

[0073] The content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group in the thermally conductive material of the present invention is not particularly limited, but in order to impart sufficient thermal conductivity and heat dissipation properties to the thermally conductive material, the content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group is preferably 0.5 to 50 mass%, more preferably 0.8 to 40 mass%, of the total amount of the thermally conductive material taken as 100 mass%.

[0074] Furthermore, in order to provide the thermal conductive material with sufficient thermal conductivity and heat dissipation properties, the content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group is preferably 1 to 100 parts by mass, and more preferably 2 to 80 parts by mass, per 100 parts by mass of flaky carbon.

[0075] When the content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group is low, the thermal conductive material of the present invention has a configuration in which the surface of the flaky carbon is coated with an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group. On the other hand, when the content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group is high, the thermal conductive material of the present invention has a configuration in which the flaky carbon is dispersed in the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group. In either case, the presence of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group around the flaky carbon suppresses the aggregation of the flaky carbon, resulting in a material with excellent thermal conductivity and heat dissipation properties.

[0076] (1.3. Nanofibers) The thermally conductive material of the present invention includes nanofibers, and the nanofibers used are cellulose-based nanofibers such as cellulose or cellulose derivatives.

[0077] The use of cellulose-based nanofibers together with flaky carbon has an advantage over resin-based thermal conductive materials in that the flaky carbon is adsorbed onto the hydrophobic groups of the cellulose, allowing for easy and uniform compounding.

[0078] In other words, by using nanofibers and highly dispersible flaky carbon, the flaky carbon is adsorbed evenly over a large surface area, heat is transferred by the flaky carbon along the nanofibers, and the nanofibers themselves also assist in heat conduction.Furthermore, by creating a state in which the flaky carbon is adsorbed intermittently, it is possible to create a state in which electricity does not flow.

[0079] Conversely, if nanofibers are not used, the carbon flakes will be densely adsorbed onto a small surface area, resulting in electrical conductivity. Also, if highly dispersible carbon flakes are not used, the nanofibers and carbon cannot be uniformly combined, and the unevenly distributed carbon will be conductive.

[0080] When the strength of the thermal conductive material is important, it is preferable to use cellulose nanofibers as the cellulose-based nanofibers. When a thermal conductive material with even higher thermal conductivity and strength is required, dissolving pulp (having hemicellulose and lignin removed by purification), cotton, cotton linter pulp, and other materials with high cellulose purity can be used.

[0081] When the uniformity of the thermally conductive material is important, it is preferable to use a cellulose derivative obtained by hydrophilizing cellulose, such as methyl cellulose, carboxymethyl cellulose salt, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, and hydroxypropyl methyl cellulose.

[0082] To improve the strength of the thermal conductive material, it is preferable to use carboxymethyl cellulose salts (salts of Na, K, NH4, etc.). On the other hand, to improve affinity with flaky carbon, it is preferable to use hydroxypropyl cellulose or hydroxypropyl methyl cellulose. Furthermore, when fluidity is important, it is preferable to use the same cellulose (derivative) with a low molecular weight (degree of polymerization) of the cellulose portion, while when strength is important, it is preferable to use a high molecular weight.

[0083] (1.4. Other Ingredients) The thermally conductive material of the present invention may contain other components in addition to the flaky carbon and the organic compound having a hydrophilic group and a carbon-affinic hydrophobic group. Examples of such other components include carbon fiber (particularly carbon nanofibers with a fiber diameter of 500 nm or less), activated carbon, carbon black (acetylene black, oil furnace black, etc.; particularly, ketjen black, which has high conductivity and a large specific surface area), glassy carbon, carbon microcoils, fullerene, biomass-based carbon materials (those made from bagasse, sorghum, wood chips, sawdust, bamboo, bark, rice straw, rice husks, coffee grounds, used tea leaves, soybean pulp refuse, rice bran, pulp waste, etc.; carbon fiber produced from lignin, etc.), cellulose nanofibers, boron nitride, molybdenum compounds (molybdenum disulfide, organic molybdenum, etc.), tungsten disulfide, fluororesins (polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), etc.), melamine cyanurate, phthalocyanine, lead oxide, calcium fluoride, and layered minerals (mica, talc, etc.).

[0084] However, from the viewpoint of making it easier to disperse in the resin and further improving the uniformity and adhesion of the coating film when applied, it is preferable that the content of other components is small, and the content is preferably 0.01 to 10 mass%, and more preferably 0.02 to 5 mass%, of the total amount of the thermal conductive material of the present invention being 100 mass%.

[0085] The shape of the heat conductive material of the present invention is not particularly limited, and examples thereof include a coating film, a sheet, a mass, and a fiber.

[0086] As described above, the thermally conductive material of the present invention is a material that not only has excellent thermal conductivity but also has excellent heat dissipation properties. Therefore, the thermally conductive material of the present invention not only has excellent thermal conductivity, but also can dissipate heat more quickly after being heated, thereby cooling the temperature. Therefore, the thermally conductive material of the present invention can also function as a thermally conductive heat dissipation material.

[0087] The thermally conductive material of the present invention has excellent thermal conductivity and heat dissipation properties, and can therefore be used in applications such as thermally conductive grease for electronic materials, thermally conductive paint for electronic materials, thermally conductive rubber for electronic materials, thermally conductive paint for LEDs, paint for heat sinks, coatings for various heat exchangers, etc. Furthermore, by adding cellulose or a cellulose derivative, it is possible to prepare a self-supporting film.

[0088] (2. Manufacturing method of thermal conductive material) The present invention includes an invention relating to a method for producing a thermally conductive material, which includes a step of mixing a flaky carbon dispersion containing 1 to 100 parts by mass of an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group per 100 parts by mass of flaky carbon with a nanofiber dispersion.

[0089] (2.1. Method for producing flaky carbon dispersion) In a dispersion (flaky carbon dispersion) containing flaky carbon, an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, and a solvent, the above-mentioned explanations can be applied to the flaky carbon and the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group. In addition, the flaky carbon dispersion can contain other components as needed.

[0090] As the solvent used to prepare the flaky carbon dispersion, it is preferable to use water as the main solvent from the viewpoints of the dispersibility of the flaky carbon, the thermal conductivity and heat dissipation properties of the resulting thermal conductive material, and the like.

[0091] The water content in the solvent used is not particularly limited, but from the viewpoints of the dispersibility of the flaky carbon, the thermal conductivity and heat dissipation properties of the resulting thermal conductive material, etc., the water content is preferably 70 mass% or more (70 to 100 mass%), and more preferably 75 to 100 mass%, of the total amount of the solvent being 100 mass%.

[0092] In the present invention, only water may be used as the solvent, and an organic solvent does not necessarily have to be used. However, in order to further improve the solubility of an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group in water, organic solvents such as alcohols such as methanol, ethanol, 2-propanol, and tert-butyl alcohol; glycols such as ethylene glycol; glycerin; and 2-methoxyethanol may be used.

[0093] The content of the organic solvent in the solvent used is preferably 30% by mass or less (0 to 30% by mass), more preferably 5 to 25% by mass, based on 100% by mass of the total amount of the solvent, from the viewpoints of the solubility of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, the thermal conductivity and heat dissipation properties of the resulting thermal conductive material, etc.

[0094] In the flaky carbon dispersion, the content of flaky carbon is not particularly limited. From the viewpoint of facilitating the composition of the thermal conductive material of the present invention, the content is preferably 20% by mass or less, more preferably 0.0001 to 15% by mass, and even more preferably 0.001 to 10% by mass, based on 100% by mass of the total amount of the flaky carbon dispersion.

[0095] Furthermore, the solvent content is not particularly limited, but from the viewpoint of facilitating the composition of the thermal conductive material of the present invention, it is preferably 40 to 99.9998 mass%, more preferably 63 to 99.998 mass%, and even more preferably 85 to 99.98 mass%, of the total amount of the flaky carbon dispersion liquid being 100 mass%.

[0096] The method for producing a flaky carbon dispersion is not particularly limited, and can be obtained, for example, by adding flaky carbon and an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group to a solvent. More specifically, flaky carbon can be added to a dispersion of an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, or an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group can be added to a dispersion of flaky carbon. Furthermore, flaky carbon and an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group can be simultaneously added to a solvent.

[0097] However, in order to further improve the dispersibility of the flaky carbon and make it less likely to agglomerate, thereby further enhancing the thermal conductivity and heat dissipation properties of the resulting thermal conductive material of the present invention, it is preferable to place a composition containing a carbonaceous material having a layered structure (a material for producing flaky carbon, as described below) and an organic compound having hydrophilic groups and carbon-affinitive hydrophobic groups between a rotating turntable and a plate placed approximately parallel to the turntable, and to subject the carbonaceous material in the composition to a shearing treatment while adjusting the shortest distance between the turntable and the plate to 200 μm or less (grinding method).

[0098] The shearing treatment causes atomization of the carbonaceous material having a layered structure, and although the graphene structure may not be maintained depending on the conditions, it allows for efficient flaking of the carbonaceous material having a layered structure and reduces the treatment time. When performing this shearing treatment, the rotating disk and the disk are arranged approximately parallel to each other, but they do not need to be strictly parallel. Specifically, the angle between the axis perpendicular to the rotating disk and the axis perpendicular to the disk is preferably 10° or less, more preferably 5° or less. It is most preferable that the axis perpendicular to the rotating disk and the axis perpendicular to the disk are strictly parallel. The shortest distance between the two surfaces when performing this shearing treatment is not particularly limited as long as it can sufficiently flaked the carbonaceous material having a layered structure, but is preferably 200 μm or less, more preferably 1 to 50 μm, and even more preferably 2 to 30 μm. Although the rotating disk and the disk are arranged approximately parallel to each other, the distance between the rotating disk and the disk may vary depending on the location. In this case, the shortest distance between the turntables means the distance at the shortest point between the turntables and the disks. Furthermore, it is not necessary to space the turntables and the disks apart in advance; the material to be processed may be sandwiched between the turntables and the disks, or the turntables and the disks may be brought into contact with each other, and the gap between the turntables and the disks may be widened by sandwiching the carbonaceous material having a layered structure between them. Such shearing treatment can be performed using any device that can rotate a disk-shaped object, such as a millstone, a vibration mixer, a spin coater, or a grinder.

[0099] The size of the turntable that can be used in this case is not particularly limited, and is preferably 5 to 500 mm, more preferably 10 to 200 mm. The rotation speed of the turntable when performing the shearing treatment is not particularly limited, and is preferably within a range that allows the carbonaceous material having a layered structure to be sufficiently exfoliated, for example, preferably 1000 to 10000 ppm, more preferably 2000 to 5000 ppm.

[0100] By carrying out such a shearing treatment, the disk and the carbonaceous material having a layered structure, and the carbonaceous material having a layered structure and the carbonaceous material having a layered structure can be brought into contact with each other, and shear can be applied to the carbonaceous material having a layered structure in a direction parallel to the graphene layers of the carbonaceous material having a layered structure.

[0101] By reducing the minimum distance between the rotating disks and increasing the rotation speed of the rotating disks during the shearing treatment, it is possible to make the conditions stronger, thereby more efficiently flaking the carbonaceous material having a layered structure and further reducing the treatment time. This shearing operation can be performed one or more times, preferably three or more times.

[0102] The temperature at which the shearing treatment is carried out is not particularly limited, and may be any temperature that can sufficiently exfoliate the carbonaceous material having a layered structure, and may be 0° C. or higher, preferably 0 to 100° C., and particularly 20 to 95° C. The temperature at which the shearing treatment is carried out is preferably under conditions that result in high solubility of an organic compound having a hydrophilic group and a hydrophobic group that has high affinity for carbon, and if the higher the temperature, the higher the temperature, the greater the solubility.If a water-soluble compound having a cloud point is used, the temperature is preferably maintained at or below the cloud point.

[0103] Before carrying out the shearing treatment, in order to bring the carbonaceous material having a layered structure and the organic compound having a hydrophilic group and a hydrophobic group having a high affinity for carbon into intimate contact with each other, the materials may be stirred in advance using a stirring device, ultrasonic dispersing device, or the like before preparing the composition, thereby allowing the organic compound having a hydrophilic group and a hydrophobic group having a high affinity for carbon to blend with the surface of the carbonaceous material having a layered structure.

[0104] In the present invention, when graphite oxide is used as the carbonaceous material having a layered structure, it exists as a flaky carbon oxide in the dispersion after the shearing treatment. Therefore, when graphite oxide is used as the carbonaceous material having a layered structure, it is preferable to perform a reduction treatment as a post-treatment. Various methods, such as chemical reduction and electrochemical reduction, can be used for the reduction treatment, but chemical reduction is preferred. Among these, chemical reduction using a reducing agent such as hydrazine or sodium borohydride is preferred. The amount of the reducing agent is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass, per part by mass of the flaky carbon oxide. Furthermore, heating during reduction facilitates the reduction. The heating temperature is preferably 40 to 200°C, more preferably 50 to 150°C, and even more preferably 60 to 120°C. The reduction time is preferably 10 minutes to 64 hours, more preferably 30 minutes to 48 hours, and even more preferably 1 to 24 hours. However, it is preferable that the amount be such that the graphene structure is not excessively destroyed.

[0105] According to the above-described manufacturing method, flaky carbon can be obtained as the above-described flaky carbon dispersion. This manufacturing method contains an organic compound having a hydrophilic group and a hydrophobic group with a high affinity for carbon, and therefore the flaky carbon dispersion also contains an organic compound having a hydrophilic group and a hydrophobic group with a high affinity for carbon. This organic compound having a hydrophilic group and a hydrophobic group with a high affinity for carbon can adsorb onto the flaky carbon surface and disperse the flaky carbon in a solvent at a high concentration, thereby functioning as a dispersant in the flaky carbon dispersion. Furthermore, the organic compound having a hydrophilic group and a hydrophobic group with a high affinity for carbon can be a commercially available product, which is superior to conventional products in both cost and dispersibility. Furthermore, this organic compound having a hydrophilic group and a hydrophobic group with a high affinity for carbon remains on the flaky carbon surface, thereby exhibiting sufficient thermal conductivity and heat dissipation.

[0106] Furthermore, in conventional methods of performing oxidation and reduction treatments, it was impossible to form a flaky carbon dispersion on a plastic substrate because the plastic substrate was hydrolyzed during the reduction treatment and the flaky carbon aggregated when the reduction treatment was performed, making it impossible to exist as a dispersion.However, in the present invention, by adding an organic compound having the above-mentioned hydrophilic group and a hydrophobic group that has a high affinity for carbon and performing a specific treatment, it is also possible to form a flaky carbon dispersion on a plastic substrate such as polyethylene terephthalate (PET) without the substrate being hydrolyzed.

[0107] Alternatively, a flaky carbon dispersion can be produced by subjecting a composition containing a carbonaceous material having a layered structure and an organic compound having a hydrophilic group and a carbon-affinitive hydrophobic group to a pressure treatment of 30 MPa or more (high-pressure dispersion method).

[0108] When the high-pressure dispersion method is adopted, as described above, it is preferable to subject a composition containing a carbonaceous material having a layered structure and an organic compound having a hydrophilic group and a hydrophobic group having high affinity for carbon to a pressure treatment of 30 MPa or more.

[0109] Pressure treatment causes atomization of the carbonaceous material having a layered structure, and although it may not be possible to maintain the graphene structure depending on the conditions, it can efficiently exfoliate the carbonaceous material having a layered structure and reduce the treatment time. The pressure level when performing such pressure treatment is not particularly limited as long as it can sufficiently exfoliate the carbonaceous material having a layered structure, but is preferably 30 MPa or higher, more preferably 50 to 400 MPa, and even more preferably 100 to 300 MPa. Such pressure treatment can be performed using a high-pressure dispersion device, a supercritical water production device, or the like. A high-pressure dispersion device can disperse by applying mechanical pressure, and a supercritical water production device can increase the pressure of the system by heating the water.

[0110] Such pressure can, for example, (i) causing two or more of the carbonaceous material dispersions to collide with each other; (ii) colliding the carbonaceous material dispersion with a metal or ceramic material (a high-hardness material such as silicon carbide or alumina); (iii) The carbonaceous material dispersion is formed into a film having a cross-sectional area of ​​1 cm 2 Passing through the following spaces Processing such as the above can be performed.

[0111] According to the above (i) and (ii), it is possible to apply stronger pressure conditions, which allows the carbonaceous material having a layered structure to be exfoliated more efficiently and the processing time to be further reduced. Furthermore, according to the above (iii), the carbonaceous material having a layered structure can be more appropriately exfoliated while maintaining the graphene structure. This pressure operation can be performed one or more times, preferably ten or more times.

[0112] The pressurizing temperature is not particularly limited as long as it is a temperature at which the carbonaceous material having a layered structure can be sufficiently exfoliated, and in the cases of (i) and (ii) above, it can be 0 to 100°C, particularly 20 to 95°C. In the case of (iii) above, when pressure is applied mechanically, the temperature is preferably 0 to 100°C, and when pressure is generated by the supercritical state of water, the temperature is preferably 373 to 700°C, more preferably 380 to 450°C.

[0113] When the pressure treatment is carried out, it is preferable to carry out an ultrasonic dispersion treatment as a preliminary treatment (pretreatment) to atomize the carbonaceous material having a layered structure, which can have the effect of preventing clogging, etc.

[0114] Although there are no particular limitations on the output power when carrying out ultrasonic dispersion treatment, from the viewpoint of flaking the carbonaceous material having a layered structure, it is preferable to use an output power that is stronger than that of a commonly performed ultrasonic dispersion treatment (about 40 to 50 W). Specifically, the output power of the ultrasonic dispersion treatment is preferably 100 W or more, more preferably 300 to 20,000 W, and even more preferably 400 to 18,000 W.

[0115] The ultrasonic dispersion temperature is not particularly limited as long as it is a temperature at which the carbonaceous material having a layered structure can be sufficiently exfoliated, and may be 0 to 80° C., particularly 10 to 70° C. The ultrasonic dispersion time is not particularly limited as long as it is a time at which the carbonaceous material having a layered structure can be sufficiently exfoliated, and may be 1 to 600 minutes, particularly 3 to 120 minutes.

[0116] Furthermore, as a pre-treatment or post-treatment of these treatments, dispersion treatment using other dispersion devices such as ordinary mechanical stirring, dispersion treatment using an emulsifying device, dispersion treatment using a bead mill, etc. may be used in combination.

[0117] In the present invention, when graphite oxide is used as the carbonaceous material having a layered structure, it exists as a flaky carbon oxide in the dispersion subjected to the pressure treatment. Therefore, when graphite oxide is used as the carbonaceous material having a layered structure, it is preferable to perform a reduction treatment as a post-treatment. Various methods, such as chemical reduction and electrochemical reduction, can be used for the reduction treatment, but chemical reduction is preferred. Among these, chemical reduction using a reducing agent such as hydrazine or sodium borohydride is preferred. The amount of the reducing agent is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass, per part by mass of the flaky carbon oxide. Furthermore, heating during reduction facilitates the reduction. The heating temperature is preferably 40 to 200°C, more preferably 50 to 150°C, and even more preferably 60 to 120°C. The reduction time is preferably 10 minutes to 64 hours, more preferably 30 minutes to 48 hours, and even more preferably 1 to 24 hours. However, it is preferable that the amount be such that the graphene structure is not excessively destroyed.

[0118] From the viewpoint of the thermal conductivity and heat dissipation properties of the resulting product of the present invention, the grinding method is most preferable.

[0119] Conventionally, when producing flaky carbon by a wet method, an aqueous dispersion containing flaky carbon oxide and an aqueous solvent is subjected to a reduction treatment, but this method makes it difficult to maintain the graphene structure and results in severe aggregation of the resulting flaky carbon, making it difficult to obtain a flaky carbon aqueous dispersion. It also poses safety problems.

[0120] When high-pressure treatment is performed, it is possible to obtain an aqueous dispersion of flaky carbon, but the resulting flaky carbon is easily destroyed, the production tends to take a long time, and clumps that have not been peeled off may remain.

[0121] On the other hand, in the present invention, by using an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, flaky carbon that maintains its graphene structure can be obtained in a uniformly dispersed state (flaky carbon dispersion) without aggregation, and the obtained flaky carbon is also less likely to be destroyed, can be obtained in a short time, and unexfoliated clumps are less likely to remain. In this case, the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group can also function as a dispersant for uniformly dispersing the flaky carbon.

[0122] Similarly, the content of the organic compound having a hydrophilic group and a carbon-affinic hydrophobic group is not particularly limited, but is preferably 0.00001 to 99.9 mass%, more preferably 0.0001 to 50 mass%, and even more preferably 0.001 to 30 mass%, based on 100 mass% of the total amount of the flaky carbon dispersion, for the reason that it is easy to form the thermal conductive material of the present invention.

[0123] Similarly, the content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group in the above-mentioned flaky carbon dispersion is not particularly limited, and from the viewpoint of facilitating the composition of the thermal conductive material of the present invention, it is preferably 1 to 100 parts by mass, and more preferably 2 to 80 parts by mass, per 100 parts by mass of flaky carbon.

[0124] Furthermore, the lower the content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, the higher the content of the carbonaceous material having a layered structure, which tends to improve thermal conductivity and heat dissipation, and also makes processing easier and less expensive. On the other hand, the higher the content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, the more likely it is that exfoliation (delamination) will occur, and therefore flaky carbon tends to be obtained more efficiently, but higher viscosity may conversely reduce the exfoliation efficiency.

[0125] For this reason, it is preferable to appropriately set the content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group from the viewpoint of balancing thermal conductivity, heat dissipation, cost, exfoliation efficiency, etc. When a carbonaceous material dispersion is used in this production method, it is preferable to set the content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group in the carbonaceous material dispersion within the above range.

[0126] Furthermore, with the shearing method, the direction of force application is parallel to the surface direction of the carbonaceous material having a layered structure, and processing is carried out in a narrow space. Therefore, compared with conventional manufacturing methods using high-speed stirring, ultrasonic treatment, high-pressure treatment, etc., there is less destruction and larger-sized flaky carbon (for example, flaky carbon with a size of 1 μm or more) can be obtained. The peeling efficiency is high, processing can be carried out in a short time (few passes), and thick lumps that fail to peel are less likely to remain.

[0127] The carbonaceous material having a layered structure described above is not particularly limited, and examples thereof include natural graphite, artificial graphite, expanded graphite, amorphous graphite, and graphite oxide. Graphite oxide can be graphite oxidized with one or more oxidizing agents, such as sulfuric acid, nitric acid, potassium permanganate, and hydrogen peroxide. For example, when graphite oxide is obtained by the Hummers process, graphite is immersed in concentrated sulfuric acid, potassium permanganate is added to oxidize the graphite, and the reaction product is quenched with dilute sulfuric acid and / or hydrogen peroxide, and then washed with distilled water, whereby oxygen atoms are bonded to the carbon atoms, introducing oxygen atoms between the layers, thereby obtaining graphite oxide.

[0128] In particular, when attempting to obtain high-purity flaky carbon that does not contain heteroatoms such as oxygen, it is preferable to use graphite as a raw material, and it is more preferable to use natural graphite and expanded graphite. When using expanded graphite, it is preferable to adopt expanded graphite that has little oxidation of the graphene structure. Furthermore, when using expanded graphite, it may be used after being subjected to a heat treatment at about 300 to 1000°C for about 10 seconds to 5 hours. This makes it possible to obtain expanded graphite that has been suitably expanded.

[0129] Furthermore, when ease of production is important, graphite oxide may be used. By using graphite oxide, solvent molecules are easily inserted between the layers, making it easy to exfoliate only in the layer direction, and the exfoliation efficiency and dispersibility are improved, making it possible to further shorten the processing time. However, when graphite oxide is used, a subsequent reduction treatment is required, and from the viewpoint of better maintaining the graphene structure, conductivity, and strength, other materials (natural graphite, artificial graphite, expanded graphite, amorphous graphite) are preferred.

[0130] On the other hand, amorphous graphite can be used to further improve dispersibility, but from the viewpoints of crystallinity, purity, and structural maintenance, other materials (natural graphite, artificial graphite, expanded graphite, and graphite oxide) are preferred.

[0131] Furthermore, when emphasis is placed on the crystallinity, strength, structural integrity, etc. of the resulting flaky carbon, artificial graphite can also be used.

[0132] In the present invention, when shearing is performed between a rotating turntable and a turntable placed approximately parallel to it while maintaining the shortest distance between the two surfaces at 200 μm or less, the content of the carbonaceous material having a layered structure in the system is not particularly limited, but is preferably 20 mass% or less, more preferably 0.0001 to 15 mass%, and even more preferably 0.001 to 10 mass%, based on 100 mass% of the total amount of the composition used to produce the flaky carbon dispersion. Note that a lower content of the carbonaceous material having a layered structure is more likely to cause exfoliation (delamination), which tends to result in more efficient production of flaky carbon and fewer treatment cycles, while also facilitating shearing and other treatments while maintaining an appropriate viscosity. On the other hand, a higher content of the carbonaceous material having a layered structure results in better productivity. Therefore, it is preferable to appropriately set the content of the carbonaceous material having a layered structure from the viewpoint of balancing exfoliation efficiency, viscosity, productivity, and the like. When a carbonaceous material dispersion is used, it is preferable that the content of the carbonaceous material having a layer structure in the flaky carbon dispersion is within the above range.

[0133] When producing the above-mentioned flaky carbon dispersion, as described above, it is preferable to subject a carbonaceous material having a layered structure to a specific treatment in the coexistence of an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group. However, from the viewpoint of the efficiency of flaking the carbonaceous material having a layered structure, the thermal conductivity and heat dissipation properties of the resulting flaky carbon, etc., it is preferable to subject a carbonaceous material dispersion containing a carbonaceous material having a layered structure and an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group to a specific treatment.

[0134] As the solvent, those described above can be used. In this case, as the solvent used to prepare the carbonaceous material dispersion (carbonaceous material dispersion liquid or carbonaceous material coating film), those described above can be used.

[0135] In the present invention, when a specific treatment is performed using a carbonaceous material dispersion liquid containing a solvent, the total amount of solvent in the carbonaceous material dispersion liquid is not particularly limited, but from the viewpoints of the exfoliation efficiency of the carbonaceous material having a layered structure, the solubility of the organic compound having a hydrophilic group and a carbon-affinitive hydrophobic group, and the like, the total amount of the carbonaceous material dispersion liquid is preferably 40 to 99.9998 mass%, more preferably 63 to 99.998 mass%, and even more preferably 85 to 99.98 mass%, taking the total amount of the carbonaceous material dispersion liquid as 100 mass%.

[0136] In the present invention, when a specific treatment is performed using a carbonaceous material dispersion using a solvent, the carbonaceous material dispersion may be prepared by adding a carbonaceous material having a layered structure to a dispersion of an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, or by adding an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group to a dispersion of a carbonaceous material having a layered structure. Alternatively, the carbonaceous material having a layered structure and the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group may be simultaneously added to a solvent.

[0137] In the present invention, other components may be contained in a composition (e.g., a carbonaceous material dispersion) containing a carbonaceous material having a layered structure and an organic compound having a hydrophilic group and a hydrophobic group that has a high affinity for carbon. This allows these other components to be contained in the final flaky carbon dispersion or thermally conductive material. The above-mentioned other components can be used as such other components, and they may be used within a range that does not impair the effects of the present invention. However, from the viewpoint of easily dispersing the other components in a resin and easily obtaining a thermally conductive material that further improves the uniformity and adhesion of the coating film when applied, it is preferable that the content of the other components is small, preferably 0.00001 to 5 mass %, and more preferably 0.0001 to 2 mass %, of the total amount of the carbonaceous material dispersion as 100 mass %.

[0138] (2.2. Method for producing nanofiber dispersion) When producing the nanofiber dispersion, nanofibers made of the above-mentioned cellulose or cellulose derivative and having a fiber diameter of 1 to 500 nm are used.

[0139] The dispersion medium for the nanofiber dispersion may be water, methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, propylene glycol, glycerin, or a mixture thereof. Among these, water is preferred because it has the highest polarity and affinity with nanofibers, does not impair the dispersibility of the flaky carbon having the organic substance with hydrophilic groups adsorbed on its surface as described in 1.1, and is easily removed by heating or reducing pressure.

[0140] The content of nanofibers in the nanofiber dispersion is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1.0% by mass or more, because this reduces the amount of solvent distilled off after compounding with the flaky carbon and allows for greater freedom in blending with the flaky carbon.

[0141] On the other hand, in order to ensure the fluidity of the nanofiber dispersion and facilitate mixing with the flaky carbon dispersion, the content of nanofibers in the nanofiber dispersion is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less.

[0142] However, if the solvent ratio of the flaky carbon dispersion to be mixed is high, the fluidity of the nanofiber dispersion does not necessarily need to be high, and a wet solid may be used. In this case, the nanofiber content may be 10% by mass or more and 50% by mass or less, and preferably 10% by mass or more and 30% by mass or less.

[0143] (3.3. Step of mixing flaky carbon dispersion and nanofiber dispersion) A uniform composite can be prepared by mixing an aqueous dispersion of flaky carbon with an aqueous dispersion of nanofibers of cellulose or a cellulose derivative, but it is also possible to use a wet solid prepared by filtration or centrifugation as one of the components.

[0144] Both can also be wet solids and mixed under high shear.

[0145] A dispersion in which one or both of the solvents are replaced with an organic solvent or a wet solid thereof may be used, whereby a water-insoluble resin can be added.

[0146] Although the embodiments of the present invention have been described above, the present invention is not limited to these examples, and it goes without saying that the present invention can be embodied in various forms without departing from the spirit of the present invention. [Example]

[0147] Hereinafter, the embodiments of the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

[0148] Example 1 500 g of natural graphite (manufactured by Ito Graphite Industries Co., Ltd.), 50 g of polyoxyethylene naphthyl ether (HLB value 17), and 10,000 g of water were mixed and ground once in a ceramic grinder. The resulting dispersion had a solids content of 5.5 wt%, of which 5.0 wt% was carbon. Similarly, 300 g of cotton linter pulp and 9,700 g of water were mixed and ground five times in a grinder to produce a 3 wt% cellulose nanofiber dispersion. When 10 g of the resulting dispersion (carbon, 5 wt%) was mixed with 16.7 g of a CNF dispersion (cellulose, 3 wt%), carbon was adsorbed onto the CNF surface. The mixture was filtered and dried at 200 °C under a pressure of 20 MPa, yielding a 50 / 50 carbon / cellulose sheet. Thermal conductivity was measured and found to be high at 67 W / m·K.

[0149] Example 2 A sheet was produced in the same manner as in Example 1, except that the carbon / cellulose ratio was 5 / 95. When the thermal conductivity was measured, a high thermal conductivity of 6 W / m·K was obtained. In addition, when the surface resistance was measured, 9 It was larger than Ω / □ and was insulating.

[0150] Example 3 A sheet was produced in the same manner as in Example 1, except that the carbon / cellulose ratio was 10 / 90. When the thermal conductivity was measured, a high thermal conductivity of 10 W / m K was obtained. Furthermore, when the surface resistance was measured, it was 10 9 It was larger than Ω / □ and was insulating.

[0151] Example 4 A sheet was produced in the same manner as in Example 1, except that the carbon / cellulose ratio was 30 / 70. The thermal conductivity was measured and found to be high at 31 W / m K. The surface resistance was also measured and found to be 15 Ω / □.

[0152] (Comparative Example 1) 500 g of natural graphite (manufactured by Ito Graphite Industries Co., Ltd.), 50 g of tannic acid, and 10,000 g of water were mixed and processed once in a ceramic grinder. The resulting solution was concentrated to obtain a powder containing 90.9% by mass of flaky carbon. 0.55 g of this powder (containing 0.50 g of flaky carbon), 0.23 g of 1,6-hexanediol diglycidyl ether, and 0.22 g of the curing agent hexahydrophthalic anhydride (total: 0.45 g) were mixed in a mortar and a planetary centrifugal mill and press-molded at 150 °C to obtain a sheet containing 50% by mass of flaky carbon. The thermal conductivity was measured and found to be 19 W / m·K, lower than that of Example 1.

[0153] (Comparative Example 2) A test was conducted in the same manner as in Example 1, except that 0.23 g of 1,6-hexanediol diglycidyl ether and 0.22 g of the curing agent hexahydrophthalic anhydride (total 0.45 g) were used instead of 16.7 g of the CNF dispersion (cellulose 3% by mass), and a sheet containing 50% by mass of carbon was obtained. The thermal conductivity was measured and found to be 30 W / m K, which was lower than that of Example 1.

[0154] (Comparative Example 3) 33.3 g of the CNF dispersion (cellulose 3% by mass) was filtered, and a sheet was prepared in the same manner as in Example 1. Approximately 5% by mass of carbon was supported on the cellulose using a carbon spray. The thermal conductivity was measured and found to be 2 W / m K, which was lower than that of Example 2. The surface resistance was also measured and found to be 9 × 10 4 The conductivity was Ω / □.

[0155] Comparative Example 4 500 g of natural graphite (manufactured by Ito Graphite Industries Co., Ltd.), 50 g of tannic acid, and 10,000 g of water were mixed and processed once in a ceramic grinder. The resulting solution was concentrated to obtain a powder containing 90.9 mass% flaky carbon. 0.055 g of this powder (containing 0.050 g of flaky carbon), 0.548 g of bisphenol A diglycidyl ether, and 0.397 g of the curing agent hexahydrophthalic anhydride (total: 0.945 g) were mixed in a mortar and a planetary mill and press-molded at 150 °C to obtain a sheet containing 5 mass% flaky carbon. The thermal conductivity was measured to be 1.2 W / m·K, lower than that of Example 2. The surface resistivity was also measured to be 1.3 × 10 5 It was Ω / □ and was conductive.

[0156] (Comparative Example 5) An experiment was conducted in the same manner as in Comparative Example 4, except that 0.11 g of powder containing 90.9 mass% of flaky carbon (containing 0.10 g of flaky carbon) was mixed with 0.516 g of bisphenol A diglycidyl ether and 0.374 g of the curing agent hexahydrophthalic anhydride, to obtain a sheet containing 10 mass% of flaky carbon. The thermal conductivity was measured to be 1.3 W / m K, which was lower than that of Example 3. The surface resistance was also measured to be 1.2 × 10 3 It was Ω / □ and was conductive.

[0157] (Comparative Example 6) An experiment was conducted in the same manner as in Comparative Example 4, except that 0.33 g of powder containing 90.9 mass% flaky carbon (containing 0.30 g of flaky carbon) was mixed with 0.388 g of bisphenol A diglycidyl ether and 0.282 g of the curing agent hexahydrophthalic anhydride, to obtain a sheet containing 30 mass% flaky carbon. The thermal conductivity was measured and found to be 3.2 W / m K, which was lower than that of Example 4.

[0158] Comparisons between Example 1 and Comparative Examples 1 and 2, Example 2 and Comparative Examples 3 and 4, Example 3 and Comparative Example 5, and Example 4 and Comparative Example 6 show that by combining flaky carbon and cellulose nanofibers, a material with high thermal conductivity can be obtained even with the same carbon content. Furthermore, comparisons between Example 2 and Comparative Example 4, and Example 3 and Comparative Example 5 show that when the carbon content is low, it is easier to obtain a material with both insulation and high thermal conductivity even with the same carbon ratio.

Claims

1. flaky carbon having a thickness of 1 to 100 nm; Polyoxyethylene naphthyl ether, Nanofibers made of cellulose or a cellulose derivative and having a fiber diameter of 1 to 500 nm are contained, A thermally conductive material in which the mass ratio of the flaky carbon to the nanofibers is 5 / 95 to 50 / 50.

2. The thermally conductive material according to claim 1 , wherein the nanofibers are cellulose nanofibers having a cellulose purity of 85% or more.

3. 3. The thermally conductive material according to claim 1, wherein the nanofibers are at least one type of nanofibers selected from the group consisting of methyl cellulose, carboxymethyl cellulose salts, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, and hydroxypropyl methyl cellulose.

4. A paint containing the thermally conductive material according to any one of claims 1 to 3, or a coating film formed from the paint.

5. A sheet comprising the thermally conductive material according to any one of claims 1 to 3.

6. 4. The method for producing a thermally conductive material according to claim 1, comprising a step of mixing a flaky carbon dispersion or a wet solid of the flaky carbon dispersion, the flaky carbon dispersion containing 1 to 100 parts by mass of the polyoxyethylene naphthyl ether per 100 parts by mass of the flaky carbon, with a nanofiber dispersion or a wet solid of the nanofiber dispersion.

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