JP2023146527A - thermal conductive material - Google Patents

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

The present invention relates to thermally conductive materials.

Crystalline carbon materials such as graphite and carbon nanotubes have high thermal conductivity and are sometimes used as thermally conductive materials (see, for example, Patent Document 1); Because the thermal resistance is high, the thermal conductivity is often not as high as expected. Furthermore, since these carbon materials have low affinity with resins, increasing the amount added to improve thermal conductivity causes problems in kneading, molding, strength, etc.

A graphene sheet is a two-dimensional single-layer sheet in which carbon atoms are arranged in a honeycomb lattice, and is also a constituent unit of graphite, fullerene, carbon nanotubes, and the like. This flaky carbon in which graphene sheets are laminated to a thickness of about 100 nm or less (in this specification, flaky carbon includes graphene sheets) has unique physical properties. , is attracting attention as a new material used in various materials.

However, although nanocarbon materials such as flaky carbon have extremely high thermal conductivity, the finer the structure, the more likely they are to aggregate, making it difficult to fully utilize their potential. It cannot be improved.

In addition, nanocarbon materials have problems in terms of usability, such as difficulty in forming a single film or making them into paints, and when combined with resins, there are cases where they do not disperse due to compatibility (cannot be applied as a paint, cannot obtain strength as a sheet), and when combined with resins. There are many cases where the conductivity drops significantly.

Furthermore, insulation is more desirable for both the coating film and the sheet.

International Publication No. 2014/080743

In view of the above circumstances, an object of the present invention is to provide a thermally conductive material with excellent thermal conductivity.

As a result of intensive research to solve the above problems, the present inventors have found that the above problems can be solved by using flaky carbon having a predetermined organic compound and thickness and a predetermined nanofiber. The present inventor has conducted further research based on this knowledge and has completed the present invention.

［上記式（１）は、アルコール性水酸基又はフェノール性水酸基を示す。式（２）中、Ｒは２価の有機基を示し、両酸素原子はエーテル結合を示す。式（３）中、Ｘ_１は水素原子、アルカリ金属、ＮＨ_４又は有機アンモニウムを示す。式（４）中、Ｘ_２は水素原子、アルカリ金属、ＮＨ_４、有機アンモニウム又はアルキル基を示す。］
項３．
前記親水基がフェノール性水酸基又はポリオキシエチレン基である、項１又は２に記載の熱伝導材料。
項４．
前記炭素親和性疎水基は、アルキル基、アルケニル基、シクロアルキル基、アリール基、及び炭素数３以上のポリオキシアルキレン基からなる群より選択される少なくとも１種である、項１～３の何れかに記載の熱伝導材料。
項５．
前記炭素親和性疎水基は、２個以上の芳香環を有するアリール基である、項１～４の何れかに記載の熱伝導材料。
項６．
前記ナノファイバーは、セルロース純度８５％以上のセルロースナノファイバーである、項１～５に記載の熱伝導材料。
項７．
前記ナノファイバーは、メチルセルロース、カルボキシメチルセルロース塩、ヒドロキシエチルセルロース、ヒドロキシプロピルセルロース、ヒドロキシエチルメチルセルロース、及びヒドロキシプロピルメチルセルロースからなる群より選択される少なくとも一種のナノファイバーを含む、項１～６の何れかに記載の熱伝導材料。
項８．
項１～７の何れかに記載の熱伝導材料を含む塗料、又は該塗料により形成された塗膜。
項９．
項１～７の何れかに記載の熱伝導材料を含むシート。
項１０．
前記薄片状カーボン１００質量部に対し、前記親水基及び前記炭素親和性疎水基を有する有機化合物を１～１００質量部含有する薄片状カーボン分散液又は該薄片状カーボン分散液の湿潤固体と、ナノファイバー分散液又は該ナノファイバー分散液の湿潤固体とを混合する工程を含む、項１～７の何れかに記載の熱伝導材料の製造方法。 That is, the present invention provides the following thermally conductive material.
Item 1.
Flake-like carbon with a thickness of 1 to 100 nm,
an organic compound having a hydrophilic group and a carbon-affinity 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.
Item 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 formulas (1) to (4).

[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), X ₁ represents a hydrogen atom, an alkali metal, NH ₄ or organic ammonium. In formula (4), X ₂ represents a hydrogen atom, an alkali metal, NH ₄ , an organic ammonium, or an alkyl group. ]
Item 3.
Item 3. The heat conductive material according to Item 1 or 2, wherein the hydrophilic group is a phenolic hydroxyl group or a polyoxyethylene group.
Item 4.
Any 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. Thermal conductive material described in .
Item 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.
Item 6.
6. The thermally conductive material according to items 1 to 5, wherein the nanofibers are cellulose nanofibers with a cellulose purity of 85% or more.
Section 7.
Item 7. The nanofibers include at least one type of nanofiber selected from the group consisting of methylcellulose, carboxymethylcellulose salt, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, and hydroxypropylmethylcellulose. thermally conductive material.
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.
Item 9.
Item 8. A sheet comprising the thermally conductive material according to any one of Items 1 to 7.
Item 10.
A flaky carbon dispersion containing 1 to 100 parts by mass of an organic compound having the hydrophilic group and the carbon-affinity hydrophobic group based on 100 parts by mass of the flaky carbon, or a wet solid of the flaky carbon dispersion; Item 8. The method for producing a thermally conductive material according to any one of Items 1 to 7, comprising a step of mixing a fiber dispersion liquid or a wet solid of the nanofiber dispersion liquid.

The thermally conductive material of the present invention as described above has excellent thermal conductivity.

In this specification, "contain" is a concept that includes all of "comprise," "consist essentially of," and "consist of." Furthermore, in this specification, when a numerical range is expressed as "A to B", it means greater than or equal to A and less than or equal to B.

(1. Heat conductive material)
The thermally conductive material of the present invention is made of flaky carbon with a thickness of 1 to 100 nm, an organic compound having a hydrophilic group and a hydrophobic group with affinity for carbon, and nanofibers made of cellulose or a cellulose derivative and with a fiber diameter of 1 to 500 nm. contains.

(1.1. Flaky carbon)
The thinner the flaky carbon, the better its thermal conductivity and heat dissipation properties, so it is preferable. Specifically, the thickness is 1 to 100 nm, preferably 1 to 20 nm. If the thickness of the flaky carbon exceeds 100 nm, a thermally conductive material with sufficient thermal conductivity and heat dissipation cannot be obtained.

Further, the content ratio of flaky carbon having a thickness of 1 to 10 nm is preferably 80% or more, more preferably 90% or more, taking the total number of flaky carbon as 100%. That is, although flaky carbon having a thickness of more than 10 nm may be included, it is preferable that most of the flaky carbon has a thickness of 10 nm or less. Note that the thickness of the flaky carbon is measured by observation using a transmission electron microscope (TEM).

It is preferable that the flaky carbon has a layered structure in which 300 layers or less (that is, 1 to 300 layers) of graphene are stacked, and the flaky carbon has a layered structure in which 1 to 60 layers of graphene are stacked. It is more preferable that there be. Similarly, the content ratio of flaky carbon having a laminated number of 1 to 30 layers is preferably 80% or more, more preferably 90% or more, taking the total number of flaky carbon as 100%. . That is, although flaky carbon having a large thickness may be included, it is preferable that the thickness of the large number of flaky carbon is 30 layers or less. Note that the lamination of flaky carbon is calculated based on the thickness measured by transmission electron microscopy (TEM) observation.

Since flaky carbon usually has a planar shape with many convex and concave angles, it is difficult to define the size other than the thickness. In this specification, the distance between the most distant convex angles in a sheet of flaky carbon is defined as the size of the flaky carbon.

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 properties can be further improved. Note that the upper limit of the size of the flaky carbon is not limited, but is usually 100 μm since it is known that a larger one is better in thermal conductivity and heat dissipation. Further, the size of the flaky carbon is measured by transmission electron microscopy (TEM) observation.

In the thermally 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, the content of flaky carbon is 50 to 99.5%, assuming the total amount of the thermally conductive material of the present invention to be 100% by mass. It is preferably 60 to 99.2% by mass, more preferably 60 to 99.2% by mass.

(1.2. Organic compound having a hydrophilic group and a carbon-affinity hydrophobic group)
In the thermally conductive material of the present invention, an organic compound having a hydrophilic group and a hydrophobic group with affinity for carbon is used. If this is not used, the flaky carbon that maintains the graphene structure will aggregate and cannot be maintained in a uniformly dispersed state. Note that the organic compound can also function as a dispersant for uniformly dispersing the flaky carbon.

The organic compound having such a hydrophilic group and a carbon-affinity hydrophobic group is not particularly limited, and various organic compounds (especially water-soluble compounds) that can function as a dispersant for flaky carbon can be used. obtain.

The carbon-affinity hydrophobic group in the organic compound is not particularly limited, and examples include an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, and a polyoxyalkylene group 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 it has a plurality of hydrophobic groups, it may contain a plurality of the same hydrophobic groups or a plurality of different hydrophobic groups.

The alkyl group may be a chain alkyl group or a branched alkyl group. However, from the viewpoint of affinity with carbon, a chain alkyl group is preferable. Further, 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, in consideration of affinity with carbon. Such alkyl groups include hexyl group, octyl group, decyl group, undecyl group, dodecyl group (or lauryl group), tridecyl group, tetradecyl group (or myristyl group), pentadecyl group, hexadecyl group (or cetyl group), Examples include octadecyl group and icosyl group.

This alkyl group may or may not have a substituent. Examples of such substituents include cycloalkyl groups, aryl groups, aralkyl groups, and the like. In addition, as the cycloalkyl group and the aryl group, those mentioned below are exemplified.

The aralkyl group as a substituent for the alkyl group is preferably an aralkyl group having 7 to 14 carbon atoms and having an aryl group and an alkyl group having 1 to 6 carbon atoms, which will be described later.Specifically, benzyl group, phenethyl group, etc. preferable.

Note that the substituents are not limited to those mentioned above, and may include a group derived from a fluorene structure (such as a fluorenyl group). In particular, when emphasis is placed on water solubility, phenyl groups and the like are preferred as substituents, and when emphasis is placed on compatibility with flaky carbon, naphthyl groups, fluorenyl groups, etc. are preferred as substituents.

Considering 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 carbon atoms, and even more preferably 8 to 30 carbon atoms. Examples of such alkenyl groups include oleyl group and linoleyl group.

This alkenyl group may or may not have a substituent. Such substituents include alkyl groups, cycloalkyl groups, aryl groups, aralkyl groups, and the like. In addition, the aralkyl group is exemplified by those mentioned above, and the cycloalkyl group and aryl group are exemplified by those mentioned below.

The alkyl group as a substituent for the alkenyl group is preferably an alkyl group having 1 to 6 carbon atoms, and specifically, a methyl group, ethyl group, propyl group, butyl group, tert-butyl group, etc. are preferable.

Note that the substituents are not limited to those mentioned above, and may include a group derived from a fluorene structure (such as a fluorenyl group). In particular, when emphasis is placed on water solubility, phenyl groups and the like are preferred as substituents, and when emphasis is placed on compatibility with flaky carbon, naphthyl groups, fluorenyl groups, etc. are preferred as substituents.

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

This cycloalkyl group may or may not have a substituent. Such substituents include alkyl groups, aryl groups, aralkyl groups, and the like.

The alkyl group as a substituent for the cycloalkyl group is preferably an alkyl group having 1 to 6 carbon atoms, and specifically, a methyl group, ethyl group, propyl group, butyl group, tert-butyl group, etc. are preferable.

Examples of the aryl group and aralkyl group as a substituent for the cycloalkyl group include those exemplified above.

Note that the substituents are not limited to those mentioned above, and may include a group derived from a fluorene structure (such as a fluorenyl group). In particular, when emphasis is placed on water solubility, phenyl groups and the like are preferred as substituents, and when emphasis is placed on compatibility with flaky carbon, naphthyl groups, fluorenyl groups, etc. are preferred as substituents.

As the aryl group, an aryl group having 6 to 18 carbon atoms (especially 6 to 14 carbon atoms) is preferable, and any of a monocyclic aryl group, a condensed aryl group, and a polycyclic aryl group can be employed, such as a phenyl group, a naphthyl group, Examples include anthracenyl group, phenanthrenyl group, biphenyl group, terphenyl group, fluorenyl group, pyrenyl group, triphenylenyl group, and the like. In addition, from the viewpoint of affinity with carbon, an aryl group having two or more aromatic rings (fused ring aryl group and polycyclic aryl group) is preferable.

This aryl group may or may not have a substituent. Examples of such substituents include alkyl groups, cycloalkyl groups, aralkyl groups, and the like.

The alkyl group as a substituent for the aryl group is preferably an alkyl group having 1 to 6 carbon atoms, and specifically, a methyl group, ethyl group, propyl group, butyl group, tert-butyl group, etc. are preferable.

Examples of the cycloalkyl group and aralkyl group as a substituent for the aryl group include those exemplified above.

Note that the substituents are not limited to those mentioned above, and may include a group derived from a fluorene structure (such as a fluorenyl group).

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. In particular, a polyoxypropylene group with a polymerization degree of 4 or more and a polyoxybutylene group with a polymerization degree of 3 or more are preferred. For example, when polyoxyethylene-polyoxypropylene or polyoxyethylene-polyoxybutylene is used as an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, the polyoxypropylene group and polyoxybutylene group are also used as hydrophobic groups. It can work.

This polyoxyalkylene group having 3 or more carbon atoms may or may not have a substituent. Examples of such substituents include alkyl groups, cycloalkyl groups, aralkyl groups, and aryl groups.

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

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

Note that the substituents are not limited to those mentioned above, and may include a group derived from a fluorene structure (such as a fluorenyl group). In particular, when emphasis is placed on water solubility, phenyl groups and the like are preferred as substituents, and when emphasis is placed on compatibility with flaky carbon, naphthyl groups, fluorenyl groups, etc. are preferred as substituents.

As such a hydrophobic group, from the viewpoint of affinity with carbon, an aryl group and a polyoxyalkylene group having 3 or more carbon atoms are preferable, an aryl group is more preferable, and an aryl group having two or more aromatic rings (condensed cyclic aryl groups and polycyclic aryl groups) are more preferred. Specifically, naphthyl group, anthracenyl group, phenanthrenyl group, biphenyl group, terphenyl group, fluorenyl group, pyrenyl group, triphenylenyl group, polyoxypropylene group with polymerization degree of 4 or more, polyoxybutylene group with polymerization degree of 3 or more, etc. is preferred.

In addition, the hydrophilic group possessed by an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group is particularly limited as long as it can increase the solubility of the organic compound in water having the hydrophilic group and a carbon-affinity hydrophobic group. However, in consideration of the water solubility of the organic compound having the hydrophilic group and carbon-affinity hydrophobic group, the dispersibility of flaky carbon, thermal conductivity, heat dissipation, etc., the following general formulas (1) to (4) are used. It is preferable that there be.

［上記式（１）は、アルコール性水酸基又はフェノール性水酸基を示す。式（２）中、Ｒは２価の有機基を示し、両酸素原子はエーテル結合である。式（３）中、Ｘ_１は水素原子、アルカリ金属、ＮＨ_４又は有機アンモニウムを示す。式（４）中、Ｘ_２は水素原子、アルカリ金属、ＮＨ_４、有機アンモニウム又はアルキル基を示す。］

[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), X ₁ represents a hydrogen atom, an alkali metal, NH ₄ or organic ammonium. In formula (4), X ₂ represents a hydrogen atom, an alkali metal, NH ₄ , an organic ammonium, or an alkyl group. ]

An organic compound having a hydrophilic group and a carbon-affinity hydrophobic group can contain one or more types of such hydrophilic groups. In addition, when using multiple hydrophilic groups, the same hydrophilic group may be used multiple times, multiple types of hydrophilic groups represented by the same general formula may be used, or hydrophilic groups represented by different general formulas may be used. Multiple types of groups may be used.

In general formula (1), -OH can be either an alcoholic hydroxyl group or a phenolic hydroxyl group. However, from the viewpoints of water solubility of organic compounds having hydrophilic groups and carbon-affinity hydrophobic groups, dispersibility of flaky carbon, thermal conductivity, heat dissipation properties, etc., alcoholic hydroxyl groups are preferable; however, when containing phenolic hydroxyl groups ( In particular, when containing multiple phenolic hydroxyl groups), it inevitably also contains a benzene ring with excellent hydrophobicity. It is preferable because it has excellent dispersibility, thermal conductivity, heat dissipation, etc.

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

In general formula (2), the alkylene group (or alkylidene group) represented by the group R is preferably an alkylene group, more preferably a C _1-8 alkylene group, even more preferably a C _1-4 alkylene group, and still more preferably a C _{2- 4} alkylene groups are particularly preferred, and C _2-3 alkylene groups are most preferred. Specifically, methylene group, ethylene group, ethylidene group, trimethylene group, propylene group, propylidene group, tetramethylene group, ethylethylene group, butane-2-ylidene group, 1,2-dimethylethylene group, pentamethylene group, Examples include pentane-2,3-diyl group.

In general formula (2), the cycloalkylene group represented by the group R is preferably a C _5-10 cycloalkylene group, more preferably a C _5-8 cycloalkylene group. Specific examples include a cyclopentylene group, a cyclohexylene group, a methylcyclohexylene group, and a cycloheptylene group.

In general formula (2), the alkylene (or alkylidene)-cycloalkylene group represented by the group R is preferably an alkylene-cycloalkylene group, more preferably a C _1-6 alkylene-C _5-10 cycloalkylene group, and a C 1-6 alkylene-C 5-10 cycloalkylene group is more preferable. More preferred is a _1-4 alkylene-C _5-8 cycloalkylene group. Specific examples include methylene-cyclohexylene group, ethylene-cyclohexylene group, ethylene-methylcyclohexylene group, and ethylidene-cyclohexylene group.

In general formula (2), a specific example of the bi- or tricycloalkylene group represented by the group R is a norbornane-diyl group.

In general formula (2), the arylene group represented by the group R is preferably a C _6-10 arylene group. Specifically, phenylene group, naphthalenediyl group, etc. can be exemplified.

In general formula (2), the alkylene (or alkylidene)-arylene group represented by the group R is preferably an alkylene-arylene group, more preferably a C _1-6 alkylene-C _6-20 arylene group, and more preferably a C _1-4 alkylene-C 6-20 arylene group. An alkylene-C _6-10 arylene group is more preferred, and a C _1-2 alkylene-phenylene group is particularly preferred. Specific examples include a methylene-phenylene group, an ethylene-phenylene group, an ethylene-methylphenylene group, and an ethylidenephenylene group.

Among these, divalent aliphatic hydrocarbon groups, particularly alkylene groups (eg, C _1-4 alkylene groups such as methylene group and ethylene group) are preferred.

Note that an alkylene (or alkylidene)-cycloalkylene group and an alkylene (alkylidene)-arylene group refer to -Ra-Rb- (wherein Ra is an alkylene group bonded to a separate oxygen atom in general formula (2)). group or alkylidene group (Rb represents a cycloalkylene group or an arylene group).

The hydrophilic group represented by the general formula (2) is not particularly limited, and for example, -OC ₂ H ₄ O-, -OC ₃ H ₆ O-, -OCH ₂ O-, etc. can be used. . Those having a plurality of these (preferably 3 to 100) can also be preferably used, and for example, polyoxymethylene groups, polyoxyethylene groups, polyoxypropylene groups, etc. can be used. In particular, when the structure has a structure in which three or more hydrophilic groups represented by the general formula (2) are polymerized, the degree of polymerization decreases as the number of carbon atoms in R increases (for example, the number of carbon atoms is 3 or more), the hydrophilicity decreases and the hydrophobicity increases. Preferred are -OC ₂ H ₄ O- and -OCH ₂ O-, which can maintain hydrophilicity even when increased.

In general formula (3), the alkali metal represented by X ₁ is not particularly limited, and examples thereof include sodium, potassium, lithium, and the like.

In general formula (3), the organic ammonium represented by X ₁ is preferably quaternary ammonium, and tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, etc. can be suitably used.

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₊ , -SO ₃ ^- N(C ₂ H ₅ ) ₄ ⁺ , -SO ₃ ^- N(C ₃ H ₇ ) ₄ ⁺ , -SO ₃ ^- N(C ₄ H ₉ ) ₄ ⁺ and the like.

In general formula (4), the alkali metal and organic ammonium represented by X ₂ include those exemplified above.

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

The hydrophilic group represented by the general formula (4) is not particularly limited. For example, -COOH, -COONa, -COOK, -COOLi, -COONH4, -COON(CH ₃ ) ₄ , -COON(C ₂ H ₅ ) ₄ , -COON(C ₃ H ₇ ) ₄ ⁺ , -COON(C ₄ H ₉ ) ₄ ⁺ and the like.

Among these hydrophilic groups, the general formula is Hydrophilic groups represented by (2) are preferred.

However, if the compound has multiple identical hydrophilic groups represented by general formula (2), that is, it has a polymerized structure, the hydrophilicity of the water-soluble compound increases as the degree of polymerization increases when the number of carbon atoms is 2 or less; In the above cases, as the degree of polymerization increases, the hydrophobicity may increase.

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 (hydrophobic group, etc.) is determined by the water solubility of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group. From the viewpoint of dispersibility, thermal conductivity, heat dissipation, etc. of flaky carbon, the number is preferably 6 or more, and more preferably 8 to 18.

In addition, in the present invention, when a nonionic material (such as a nonionic surfactant) is used as an organic compound having a hydrophilic group and a hydrophobic group with carbon affinity, its HLB value is From the viewpoints of water solubility of the organic compound having a hydrophobic group, dispersibility of flaky carbon, thermal conductivity, heat dissipation, etc., the number is preferably 12 or more, and more preferably 13 to 19. Note that when the hydrophobic groups are the same (when the affinity with flaky carbon is the same), the higher the HLB value, the better.

The organic compound having a hydrophilic group and a carbon-affinity hydrophobic group that satisfies the above conditions is not particularly limited. For example, aromatic water-soluble compounds or non-aromatic water-soluble compounds may be used, with aromatic water-soluble compounds being preferred. Examples of organic compounds having a hydrophilic group and a carbon-affinity hydrophobic group include polyoxyethylene lauryl ether, polyoxyethylene decyl ether, polyoxypropylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene naphthyl ether, and 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, polyoxypropylene undecylphenyl ether, polyoxyethylene tridecylphenyl ether, polyoxypropylene tridecylphenyl ether, polyoxyethylene pentadecyl phenyl ether, polyoxypropylene pentadecyl phenyl ether, polyoxyethylene polyoxy Propylene glycol, polyoxypropylene polyglyceryl ether, sodium cholate, potassium cholate, sodium dodecylsulfonate, potassium dodecylsulfonate, sodium lysine dilauroylglutamate, potassium lysine dilauroylglutamate, decaglycerin laurate, n-decyl alcohol, etc. can be mentioned.

Examples of organic compounds having such a hydrophilic group and a carbon-affinity hydrophobic group 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, Emulgen 220 (polyoxyethylene alkyl ethers manufactured by Kao Corporation), Triton X-100, Triton X-114, Triton X-305, Triton Ethylene octylphenyl ethers), Neugen EN, Neugen EN-10 (polyoxyethylene naphthyl ether manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and the like can be used.

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. However, in order to impart sufficient thermal conductivity and heat dissipation to the thermally conductive material, the total amount of the thermally conductive material is 100% by mass, and the content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group is 0. It is preferably 5 to 50% by mass, more preferably 0.8 to 40% by mass.

In addition, in order to impart sufficient thermal conductivity and heat dissipation to the thermally conductive material, the content of organic compounds having hydrophilic groups and carbon-affinity hydrophobic groups is 1 to 100 parts by mass per 100 parts by mass of flaky carbon. The amount is preferably 2 to 80 parts by mass, and more preferably 2 to 80 parts by mass.

In addition, when the content of the organic compound having a hydrophilic group and a hydrophobic group with an affinity for carbon is small, the thermally conductive material of the present invention has an organic compound having a hydrophilic group and a hydrophobic group with a carbon affinity on the surface of the flaky carbon. It has a covered configuration. On the other hand, when the content of the organic compound having a hydrophilic group and a hydrophobic group with an affinity for carbon is large, the thermally conductive material of the present invention has flaky carbon dispersed in the organic compound having a hydrophilic group and a hydrophobic group with an affinity for carbon. It has the following configuration. In either case, an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group is present around the flaky carbon, thereby suppressing agglomeration of the flaky carbon and obtaining a material with excellent thermal conductivity and heat dissipation. be able to.

(1.3. Nanofiber)
The thermally conductive material of the present invention includes nanofibers. As the nanofibers, cellulose-based nanofibers such as cellulose or cellulose derivatives are used.

The use of cellulose nanofibers together with flaky carbon is superior to resin-based thermally conductive materials in that the flaky carbon is adsorbed to the hydrophobic groups of cellulose and can be easily and uniformly composited. It has an advantage.

In other words, by using nanofibers and highly dispersible flaky carbon, the flaky carbon is uniformly adsorbed over a vast surface area, heat is transmitted by the flaky carbon along the nanofibers, and the nanofibers themselves also conduct heat. assist. It is also possible to create a state in which electricity does not flow by creating a state in which flaky carbon is intermittently adsorbed.

Conversely, if nanofibers are not used, the carbon flakes are tightly adsorbed onto a small surface area, resulting in conductivity. Furthermore, if flaky carbon with high dispersibility is not used, nanofibers and carbon cannot be combined uniformly, and the unevenly distributed carbon becomes electrically conductive.

When the strength of the thermally conductive material is important, it is preferable to use cellulose nanofibers as the cellulose-based nanofibers. If a thermally conductive material with even higher thermal conductivity and higher strength is required, dissolving pulp (from which hemicellulose and lignin have been removed by purification), cotton, cotton linter pulp, etc., which have high cellulose purity, can be used.

If uniformity of the thermally conductive material is important, it is preferable to use a cellulose derivative obtained by making cellulose hydrophilic. Examples include methylcellulose, carboxymethylcellulose salt, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, and hydroxypropylmethylcellulose.

In order to improve the strength of the thermally conductive material, it is preferable to use carboxymethylcellulose salts (salts of Na, K, NH4, etc.). On the other hand, in order to improve the affinity with flaky carbon, it is preferable to use hydroxypropylcellulose or hydroxypropylmethylcellulose. In addition, if fluidity is important, it is preferable to use a cellulose (derivative) with a low molecular weight (degree of polymerization) in the cellulose part, and if strength is important, it is preferable to use a cellulose with a low molecular weight (degree of polymerization). preferable.

(1.4. Other ingredients)
In the thermally conductive material of the present invention, other components may be included in addition to the flaky carbon and the organic compound having a hydrophilic group and a hydrophobic group with affinity for carbon. 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.; Ketchen, which has particularly high conductivity and a large specific surface area). black), glassy carbon, carbon microcoil, fullerene, biomass-based carbon materials (bagasse, sorghum, wood chips, sawdust, bamboo, wood bark, rice straw, rice husks, coffee grounds, used tea leaves, okara kasu, rice bran, pulp scraps, etc.) Raw materials; carbon fibers manufactured from lignin, etc.), cellulose nanofibers, boron nitride, molybdenum compounds (molybdenum disulfide, organic molybdenum, etc.), tungsten disulfide, fluororesins (polytetrafluoroethylene (PTFE), tetrafluoroethylene, etc.) (ethylene/perfluoroalkyl vinyl ether copolymer (PFA), etc.), melamine cyanurate, phthalocyanine, lead oxide, calcium fluoride, layered minerals (mica, talc, etc.), etc. are used within the range that does not impair the effects of the present invention. You can also do that.

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 total amount of the thermally conductive material of the present invention It is preferably 0.01 to 10% by mass, more preferably 0.02 to 5% by mass, where 100% by mass.

The shape of the thermally conductive material of the present invention is not particularly limited, and examples thereof include a coating film, a sheet, a lump, a fiber, and the like.

As mentioned above, the thermally conductive material of the present invention is a material that not only has excellent thermal conductivity but also excellent heat dissipation. Therefore, the thermally conductive material of the present invention not only has excellent thermal conductivity, but also can quickly radiate heat and cool the temperature by radiating heat after being heated. Therefore, the thermally conductive material of the present invention can also function as a thermally conductive heat dissipating material.

Since the thermally conductive material of the present invention has excellent thermal conductivity and heat dissipation, it can be used in 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, various types of thermal conductive materials, etc. It can be used for applications such as coating for exchangers. Furthermore, by adding cellulose or a cellulose derivative, a self-supporting membrane can also be produced.

(2. Method for manufacturing thermally conductive material)
The present invention includes inventions related to methods of manufacturing thermally conductive materials. The invention relating to the method for producing a thermally conductive material of the present invention provides a flaky carbon dispersion liquid containing 1 to 100 parts by mass of an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group based on 100 parts by mass of flaky carbon; It has a step of mixing with a fiber dispersion liquid.

(2.1. Method for producing flaky carbon dispersion)
A dispersion (flake carbon dispersion) containing flaky carbon, an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, and a solvent, which has flaky carbon and a hydrophilic group and a carbon-affinity hydrophobic group. Regarding the organic compound, the above explanation can be adopted. Further, the flaky carbon dispersion can also contain the other components mentioned above, if necessary.

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

The content of water in the solvent used is not particularly limited, but from the viewpoint of dispersibility of flaky carbon, thermal conductivity and heat dissipation of the resulting thermally conductive material, etc., the content of water in the solvent used is 70% by mass, assuming the total amount of the solvent is 100% by mass. It is preferably at least 70% by mass (70 to 100% by mass), more preferably 75 to 100% by mass.

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

The content of the organic solvent in the solvent to be used is determined from the viewpoint of the solubility of the organic compound having a hydrophilic group and a hydrophobic group with carbon affinity, and the thermal conductivity and heat dissipation property of the resulting thermally conductive material, etc. % is preferably 30% by mass or less (0 to 30% by mass), more preferably 5 to 25% by mass.

In the flaky carbon dispersion, the content of flaky carbon is not particularly limited. From the viewpoint of easy composition of the thermally conductive material of the present invention, the total amount of the flaky carbon dispersion is 100% by mass, preferably 20% by mass or less, more preferably 0.0001 to 15% by mass, and 0.001 to 10% by mass. % is more preferred.

Further, the content of the solvent is not particularly limited, but from the viewpoint of easy composition of the thermally conductive material of the present invention, the content of the solvent may be 40 to 99.9998% by mass, assuming the total amount of the flaky carbon dispersion as 100% by mass. The content is preferably from 63 to 99.998% by mass, and even more preferably from 85 to 99.98% by mass.

The method for producing a flaky carbon dispersion is not particularly limited, and can be obtained by, for example, 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 flaky carbon can be added to a dispersion of flaky carbon having a hydrophilic group and a carbon-affinity hydrophobic group. Organic compounds can also be introduced. Furthermore, flaky carbon and an organic compound having a hydrophilic group and a hydrophobic group with affinity for carbon can be simultaneously introduced into the solvent.

However, in order to further improve the dispersibility of flaky carbon and make it difficult to aggregate, and to further increase the thermal conductivity and heat dissipation properties of the resulting thermally conductive material of the present invention, it is necessary to A carbonaceous material having a layered structure (as described later, this is a material for producing flaky carbon) and an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group are placed between the plates installed approximately parallel to each other. It is preferable to install a composition containing a carbonaceous material in the composition and apply shearing treatment to the carbonaceous material in the composition while adjusting the shortest distance between the rotary disk and the disk to be 200 μm or less (polishing). crushing method).

Due to the shearing process, the carbonaceous material with a layered structure becomes atomized, so depending on the conditions, it may not be possible to maintain the graphene structure, but it is possible to efficiently thin the carbonaceous material with a layered structure. processing time can be reduced. Although the rotary disk and the disk when performing such shearing treatment are installed substantially parallel to each other, they do not need to be strictly parallel to each other. Specifically, the angle between the axis perpendicular to the rotary disk and the axis perpendicular to the disk is preferably 10 degrees or less, more preferably 5 degrees or less. Note that it is most preferable that the axis perpendicular to the rotary disk and the axis perpendicular to the disk be strictly parallel. The shortest distance between two surfaces when performing such shearing treatment is not particularly limited as long as it can sufficiently thin the carbonaceous material having a layered structure, but it is preferably 200 μm or less, and 1 ~50 μm is more preferred, and 2 ~ 30 μm is even more preferred. Although the rotary disk and the disk are installed substantially parallel to each other, the distance between the rotary disk and the disk may vary depending on the location. In this case, the shortest distance between the rotary disk and the disk means the distance at the shortest point among the distances between the rotary disk and the disk. Further, it is not always necessary to vacate the rotary disk and the disk beforehand, and the material to be processed may be sandwiched between the rotary disk and the disk, or the rotary disk and the disk are brought into contact with each other, The gap between the rotary disk and the disk may be widened by sandwiching a carbonaceous material having a layered structure. Such shearing treatment may be performed using a mechanism for rotating a disc-shaped object, such as a stone mill, a vibratory mixer, a spin coater, a grinder, or the like.

The size of the rotary disk and the disk that can be used at this time is not particularly limited, and is preferably 5 to 500 mm, more preferably 10 to 200 mm. Furthermore, there is no particular restriction on the number of revolutions of the rotary disk when performing the shearing treatment, and it is preferably within a range that allows sufficient thinning of the carbonaceous material having a layered structure, for example, 1,000 to 10,000 ppm is preferable. , 2000 to 5000 ppm is more preferable.

By performing such shearing treatment, the carbonaceous material having a layered structure is brought into contact with the carbonaceous material having a layered structure, and the carbonaceous material having a layered structure is brought into contact with the carbonaceous material having a layered structure. Shearing can be applied in a direction parallel to the graphene layer of the carbonaceous material having the structure.

It is possible to make the conditions stronger by reducing the shortest distance between the rotary disks and increasing the rotation speed of the rotary disks in the shearing treatment, and it is possible to make the conditions stronger by reducing the shortest distance between the rotary disks and the disks and increasing the rotation speed of the rotary disks. processing can be performed more efficiently and processing time can be further reduced. This shearing operation may be performed one or more times, preferably three or more times.

The temperature at which the shearing treatment is performed is not particularly limited, and may be any temperature that can sufficiently thin the carbonaceous material having a layered structure, and may be 0°C or higher, further 0 to 100°C, particularly 20 to 95°C. obtain. In addition, the temperature at which the shearing treatment is performed is preferably a condition where the solubility of the organic compound having a hydrophilic group and a hydrophobic group with high affinity for carbon is high.If the solubility increases at a higher temperature, a higher temperature is preferable. When using a water-soluble compound, it is preferable to maintain the temperature below the cloud point.

Before performing the above shearing treatment, a stirring device, an ultrasonic dispersion device, etc. are used to bring the carbonaceous material having a layered structure into good contact with the organic compound having a hydrophilic group and a hydrophobic group that has a high affinity for carbon. Before preparing the composition, the organic compound having a hydrophilic group and a hydrophobic group having high affinity for carbon may be blended onto the surface of the carbonaceous material having a layered structure by stirring in advance.

In the present invention, when graphite oxide is used as the carbonaceous material having a layered structure, it is present as an oxide of flaky carbon in the sheared dispersion. 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. As the reduction treatment, various methods such as chemical reduction and electrochemical reduction can be employed, but chemical reduction is preferable. Among these, chemical reduction using a reducing agent such as hydrazine, sodium borohydride, etc. 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 1 part by mass of the flaky carbon oxide. In addition, heating during the reduction makes the reduction easier. The heating temperature is preferably 40 to 200°C, more preferably 50 to 150°C, 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 to set the amount to such an extent that the graphene structure is not excessively destroyed.

According to the above-described manufacturing method, flaky carbon can be obtained as the above-described flaky carbon dispersion. In this production method, since an organic compound having a hydrophilic group and a hydrophobic group having a high affinity for carbon is included, even in the flaky carbon dispersion, an organic compound having a hydrophilic group and a hydrophobic group having a high affinity for carbon is used. include. This organic compound having a hydrophilic group and a hydrophobic group with high affinity for carbon can be adsorbed onto the surface of flaky carbon and can isolate and disperse flaky carbon in a solvent at a high concentration. In the body, it also functions as a dispersant. Further, as the organic compound having the hydrophilic group and the hydrophobic group having high affinity for carbon, a commercially available product can be used, which is superior to conventional products in terms of both cost and dispersibility. Furthermore, this organic compound having a hydrophilic group and a hydrophobic group having high affinity for carbon can exhibit sufficient thermal conductivity and heat dissipation by remaining on the flaky carbon surface.

In addition, in the conventional method of performing oxidation treatment and reduction treatment, the plastic substrate is hydrolyzed during the reduction treatment, and when the reduction treatment is performed, the flaky carbon aggregates and cannot exist as a dispersion. Therefore, it has been impossible to form a flaky carbon dispersion on a plastic substrate. However, in the present invention, it is possible to form a flaky carbon dispersion on a plastic substrate while containing an organic compound having the above hydrophilic group and a hydrophobic group with high affinity for carbon. By performing the treatment, it is also possible to form a flaky carbon dispersion on a plastic substrate such as polyethylene terephthalate (PET) without undergoing hydrolysis.

The flaky carbon dispersion can also be obtained by subjecting a composition containing a carbonaceous material having a layered structure and an organic compound having a hydrophilic group and a hydrophobic group with carbon affinity to a pressure treatment of 30 MPa or more. can be manufactured (high pressure dispersion method).

When employing the high-pressure dispersion method, as described above, a composition containing a carbonaceous material having a layered structure and an organic compound having a hydrophilic group and a hydrophobic group with high affinity for carbon is subjected to a pressure of 30 MPa or more. Preferably, the treatment is carried out.

Pressure treatment causes the carbonaceous material with a layered structure to become atomized, so depending on the conditions, it may not be possible to maintain the graphene structure, but it is possible to efficiently thin the carbonaceous material with a layered structure. processing time can be reduced. The pressure level when performing such pressure treatment is not particularly limited as long as it can sufficiently thin the carbonaceous material having a layered structure, but it is preferably 30 MPa or more, and 50 to 400 MPa. is more preferable, 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 perform dispersion by applying mechanical pressure, and a supercritical water production device can increase the pressure of the system by heating water.

By applying such pressure, for example,
(i) Colliding two or more of the carbonaceous material dispersions with each other;
(ii) Colliding the carbonaceous material dispersion with a metal or ceramic material (high hardness material such as silicon carbide or alumina);
(iii) A process such as passing the carbonaceous material dispersion through a space having a cross-sectional area of 1 cm ² or less may be performed.

According to (i) and (ii) above, the pressurizing conditions can be made stronger, the carbonaceous material having a layered structure can be more efficiently sliced, and the processing time can be further reduced. be able to. Further, according to (iii) above, the carbonaceous material having a layered structure can be more appropriately thinned while maintaining the graphene structure. This pressurizing operation can be performed one or more times, preferably ten or more times.

The pressurizing temperature is not particularly limited and may be any temperature that can sufficiently thin the carbonaceous material having a layered structure. It can be ~95°C. In the case of (iii) above, when pressure is applied dynamically, 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, and more preferably 380 to 450°C. preferable.

Note that when performing the pressure treatment, it is preferable to perform ultrasonic dispersion treatment as a preliminary treatment (pretreatment) to atomize the carbonaceous material having a layered structure. This can have effects such as preventing clogging.

There is no particular limit to the power output when performing ultrasonic dispersion treatment, but from the perspective of thinning the carbonaceous material having a layered structure, it should be more powerful than the normally performed ultrasonic dispersion treatment (approximately 40 to 50 W). It is preferable. Specifically, the output 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.

The ultrasonic dispersion temperature is not particularly limited, and may be any temperature that can sufficiently thin the carbonaceous material having a layered structure, and may be 0 to 80°C, particularly 10 to 70°C. The ultrasonic dispersion time is not particularly limited, and may be any time that allows sufficient thinning of the carbonaceous material having a layered structure, and may be from 1 to 600 minutes, particularly from 3 to 120 minutes.

Further, as 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.

In the present invention, when graphite oxide is used as the carbonaceous material having a layered structure, it is present as an oxide of flaky carbon in the pressure-treated dispersion. 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. As the reduction treatment, various methods such as chemical reduction and electrochemical reduction can be employed, but chemical reduction is preferable. Among these, chemical reduction using a reducing agent such as hydrazine, sodium borohydride, etc. 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 1 part by mass of the flaky carbon oxide. In addition, heating during the reduction makes the reduction easier. The heating temperature is preferably 40 to 200°C, more preferably 50 to 150°C, 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 to set the amount to such an extent that the graphene structure is not excessively destroyed.

Note that the grinding method is most preferable from the viewpoint of the thermal conductivity and heat dissipation of the resulting present invention.

Conventionally, when producing flaky carbon using a wet method, an aqueous dispersion containing a flaky carbon oxide and an aqueous solvent was subjected to a reduction treatment, but with this method, it was difficult to maintain the graphene structure. At the same time, the resulting flaky carbon aggregates violently, making it difficult to obtain a flaky carbon aqueous dispersion. There are also problems from a safety perspective.

Although it is possible to obtain a flaky carbon aqueous dispersion when performing high-pressure treatment, the obtained flaky carbon tends to be easily destroyed and production tends to take time, and lumps that fail to be peeled remain. There is also.

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 the graphene structure is uniformly dispersed without agglomeration (flake carbon dispersion). The flaky carbon obtained is also difficult to break, and the flaky carbon can be obtained in a short time, and lumps that fail to be peeled off are unlikely to remain. At this time, 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.

Similarly, the content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group is not particularly limited. However, since it is easy to form the composition of the thermally conductive material of the present invention, the total amount of flaky carbon dispersion is 100% by mass, and it is preferably 0.00001 to 99.9% by mass, and 0.0001 to 50% by mass. %, and even more preferably 0.001 to 30% by mass.

Similarly, the content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group in the flaky carbon dispersion is not particularly limited, and from the viewpoint of easy composition of the thermally conductive material of the present invention, flaky carbon 100 It is preferably 1 to 100 parts by weight, more preferably 2 to 80 parts by weight.

Note that the lower the content of organic compounds having hydrophilic groups and carbon-affinity hydrophobic groups, the higher the content of carbonaceous materials with a layered structure, which tends to improve thermal conductivity and heat dissipation, and is also less expensive. Easy to process. On the other hand, when the content of an organic compound having a hydrophilic group and a hydrophobic group with carbon affinity is high, flaky carbon tends to be obtained more efficiently because flaking (delamination) occurs more easily, but the viscosity is high. If this happens, there is a possibility that the thinning efficiency will decrease.

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 the balance of thermal conductivity, heat dissipation, cost, efficiency of thinning, and the like. In addition, in this production method, when using a carbonaceous material dispersion, it is preferable that the content of the organic compound having a hydrophilic group and a carbon-affinity hydrophobic group in the carbonaceous material dispersion is within the above range. .

In addition, according to the shearing method, the direction in which the force is applied is parallel to the surface direction of the carbonaceous material having a layered structure, and since the treatment is performed in a narrow space, conventional high-speed stirring, ultrasonic treatment, high-pressure treatment, etc. Compared to the manufacturing method, this method causes less destruction, can obtain larger-sized flaky carbon (for example, flaky carbon with a size of 1 μm or more), and has good peeling efficiency in a short time (fewer passes). It is possible to perform the treatment, and it is difficult to leave thick lumps that could not be peeled off.

The carbonaceous material having the layered structure described above is not particularly limited, and examples thereof include natural graphite, artificial graphite, expanded graphite, earthy graphite, and oxidized graphite. The oxidized graphite may be, for example, graphite oxidized with one or more oxidizing agents such as sulfuric acid, nitric acid, potassium permanganate, and hydrogen peroxide. For example, when obtaining graphite oxide by the Hammers method, 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. Thereafter, by washing with distilled water or the like, oxygen atoms bond to carbon atoms, oxygen atoms are introduced between the layers, and graphite oxide can be obtained.

Among these, when trying to obtain highly pure flaky carbon that does not contain foreign atoms 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. In addition, when using expanded graphite, it is preferable to employ expanded graphite whose graphene structure is less likely to be oxidized. Furthermore, when using expanded graphite, it may be heat-treated at about 300 to 1000° C. for about 10 seconds to 5 hours before use. Thereby, it is also possible to obtain expanded graphite that has been expanded appropriately.

Furthermore, when ease of manufacture is important, graphite oxide may be used. By using graphite oxide, solvent molecules are easily inserted between the layers, making it easy to peel only in the layer direction, improving exfoliation efficiency and dispersibility, making it possible to shorten processing time. be. However, when using graphite oxide, reduction treatment is required afterwards, and from the viewpoint of maintaining the graphene structure, conductivity, and strength, other materials (natural graphite, artificial graphite, expanded graphite, earthy graphite) are recommended. is preferred.

On the other hand, in order to further improve dispersibility, it is also possible to employ earthy graphite. However, from the viewpoint of crystallinity, purity, and structure maintenance, other materials (natural graphite, artificial graphite, expanded graphite, and oxidized graphite) are preferable.

In addition, when emphasis is placed on the crystallinity, strength, structure maintenance, etc. of the obtained flaky carbon, artificial graphite can also be used.

In the present invention, the layered structure in the system is applied when shearing is performed between a rotating rotary disk and a disk installed approximately parallel to it, with the shortest distance between the two surfaces maintained at 200 μm or less. The content of the structured carbonaceous material is not particularly limited, but is preferably 20% by mass or less, and 0.0001 to 15% by mass, based on 100% by mass of the total amount of the composition used to produce the flaky carbon dispersion. It is more preferably 0.001 to 10% by mass, and even more preferably 0.001 to 10% by mass. It should be noted that the thinner the content of the carbonaceous material having a layered structure, the more likely it is that flaking (delamination) will occur, so flaky carbon can be obtained more efficiently and the number of treatments can be reduced. It tends to maintain appropriate viscosity and facilitate shearing treatment. On the other hand, the higher the content of the carbonaceous material having a layered structure, the better the productivity. For this reason, it is preferable to appropriately set the content of the carbonaceous material having a layered structure from the viewpoint of the balance of thinning efficiency, viscosity, productivity, etc. In addition, when using a carbonaceous material dispersion, it is preferable that the content of the carbonaceous material having a layered structure in the flaky carbon dispersion is within the above range.

When producing the flaky carbon dispersion described above, as described above, a carbonaceous material having a layered structure is subjected 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 exfoliation efficiency of the carbonaceous material having a layered structure, thermal conductivity and heat dissipation of the obtained flaky carbon, it is preferable to use a carbonaceous material having a layered structure, a hydrophilic group and a carbon-affinity hydrophobic group. It is preferable to perform a specific treatment on a carbonaceous material dispersion containing an organic compound having

As the solvent, those mentioned above can be employed. At this time, as the solvent used to prepare the carbonaceous material dispersion (carbonaceous material dispersion or carbonaceous material coating), the solvents described above can be employed.

In the present invention, when a specific treatment is performed using a carbonaceous material dispersion using a solvent, the total amount of the solvent in the carbonaceous material dispersion is not particularly limited; From the viewpoint of efficiency, solubility of an organic compound having a hydrophilic group and a carbon-affinity hydrophobic group, etc., the total amount of the carbonaceous material dispersion is 100% by mass, and it is preferably 40 to 99.9998% by mass, and 63 to 99% by mass. The content is more preferably .998% by mass, and even more preferably 85 to 99.98% by mass.

In the present invention, when performing a specific treatment using a carbonaceous material dispersion using a solvent, the carbonaceous material dispersion is a carbonaceous material dispersion having a layered structure in an organic compound dispersion having a hydrophilic group and a carbon-affinity hydrophobic group. Alternatively, an organic compound having a hydrophilic group and a hydrophobic group with affinity for carbon may be added to a carbonaceous material dispersion having a layered structure. Further, a carbonaceous material having a layered structure and an organic compound having a hydrophilic group and a hydrophobic group with affinity for carbon may be added into the solvent at the same time.

In the present invention, a composition (for example, a carbonaceous material dispersion) 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 contains other components. May be included. This allows these other components to be included in the flaky carbon dispersion and thermally conductive material that are finally obtained. As such other components, those mentioned above may be employed, and may be used within a range that does not impair the effects of the present invention. However, from the viewpoint of easily obtaining a heat conductive material that is easily dispersed in the resin and further improves the uniformity and adhesion of the coating film when applied, it is preferable that the content of other components is small, and carbonaceous The total amount of the material dispersion is 100% by mass, preferably 0.00001 to 5% by mass, more preferably 0.0001 to 2% by mass.

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

As the dispersion medium in the nanofiber dispersion, water, methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, propylene glycol, glycerin, and mixtures thereof can be used. Among them, it has the highest polarity and high affinity with nanofibers, does not impair the dispersibility of the flaky carbon that adsorbs organic substances having hydrophilic groups on the surface described in 1.1, and is easy to remove by heating or reduced pressure. It is preferable to use water because it satisfies the following conditions.

The content of nanofibers in the nanofiber dispersion liquid is set to 0.1 because the amount of solvent distilled off after combination with flaky carbon is small and because there is a high degree of freedom in blending with flaky carbon. It is preferably at least 0.5% by mass, more preferably at least 1.0% by mass.

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

However, when 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 that case, the nanofiber content may be 10% by mass or more and 50% by mass or less, preferably 10% by mass or more and 30% by mass or less.

(3.3. Process of mixing flaky carbon dispersion and nanofiber dispersion)
A homogeneous composite can be created by mixing an aqueous dispersion of flaky carbon and an aqueous dispersion of cellulose or cellulose derivative nanofibers, but one may also be a wet solid prepared by filtration or centrifugation. .

It is also possible to mix both as wet solids by applying strong shear.

A dispersion or a wet solid thereof in which one or both of the solvents is replaced with an organic solvent may also be used, thereby making it possible to add a water-insoluble resin.

Although the embodiments of the present invention have been described above, the present invention is not limited to these examples at all, and it goes without saying that the present invention can be implemented in various forms without departing from the gist of the present invention.

Hereinafter, embodiments of the present invention will be described in more detail based on Examples, but the present invention is not limited thereto.

(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 the mixture was treated with a ceramic grinder for one pass. The resulting dispersion had a solid content of 5.5% by weight, of which the carbon content was 5.0% by weight. Similarly, 300 g of cotton linter pulp and 9,700 g of water were mixed and treated with a grinder for 5 passes to prepare a 3 wt % cellulose nanofiber dispersion. When 10 g of the obtained dispersion (5% by mass of carbon) and 16.7g of CNF dispersion (3% by mass of cellulose) were mixed, carbon was adsorbed on the surface of the CNF. The liquid was filtered and dried at 200° C. while pressurizing at 20 MPa to obtain a sheet with a carbon/cellulose ratio of 50/50. When the thermal conductivity was measured, a high thermal conductivity of 67 W/m·K was obtained.

(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. Further, when the surface resistance was measured, it was greater than 10 ⁹ Ω/□, indicating that it was insulating.

(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. Further, when the surface resistance was measured, it was greater than 10 ⁹ Ω/□, indicating that it was insulating.

(Example 4)
A sheet was produced in the same manner as in Example 1 except that the carbon/cellulose ratio was 30/70. When the thermal conductivity was measured, a high thermal conductivity of 31 W/m·K was obtained. Moreover, when the surface resistance was measured, it was 15Ω/□.

(Comparative example 1)
500 g of natural graphite (manufactured by Ito Graphite Kogyo Co., Ltd.), 50 g of tannic acid, and 10,000 g of water were mixed and treated in one pass with a ceramic grinder. This liquid was concentrated to obtain a powder containing 90.9% by mass of flaky carbon. A mortar and A sheet containing 50% by mass of flaky carbon was obtained by mixing in a rotation-revolution mill and press-molding at 150°C. When the thermal conductivity was measured, it was 19 W/m·K, which was lower than that of Example 1.

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

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

(Comparative example 4)
500 g of natural graphite (manufactured by Ito Graphite Kogyo Co., Ltd.), 50 g of tannic acid, and 10,000 g of water were mixed and treated in one pass with a ceramic grinder. This liquid was concentrated to obtain a powder containing 90.9% by mass of flaky carbon. 0.055 g of this powder (including 0.050 g of flaky carbon), 0.548 g of bisphenol A diglycidyl ether, and 0.397 g of hardening agent hexahydrophthalic anhydride (0.945 g in total) were mixed in a mortar and a rotation-revolution mill. Then, by press-molding at 150°C, a sheet containing 5% by mass of flaky carbon was obtained. When the thermal conductivity was measured, it was 1.2 W/m·K, which was lower than that of Example 2. Further, when the surface resistance was measured, it was 1.3×10 ⁵ Ω/□, indicating that it was electrically conductive.

(Comparative example 5)
Except for mixing 0.11 g of powder containing 90.9% by mass of flaky carbon (including 0.10 g of flaky carbon), 0.516 g of bisphenol A diglycidyl ether, and 0.374 g of hardening agent hexahydrophthalic anhydride. An experiment was conducted in the same manner as in Comparative Example 4, and a sheet containing 10% by mass of flaky carbon was obtained. When the thermal conductivity was measured, it was 1.3 W/m·K, which was lower than that of Example 3. Moreover, when the surface resistance was measured, it was 1.2×10 ³ Ω/□, indicating that it was electrically conductive.

(Comparative example 6)
Except for mixing 0.33 g of powder containing 90.9% by mass of flaky carbon (including 0.30 g of flaky carbon), 0.388 g of bisphenol A diglycidyl ether, and 0.282 g of the curing agent hexahydrophthalic anhydride. An experiment was conducted in the same manner as in Comparative Example 4, and a sheet containing 30% by mass of flaky carbon was obtained. When the thermal conductivity was measured, it was 3.2 W/m·K, which was lower than that of Example 4.

Comparison of Example 1 and Comparative Examples 1 and 2, Example 2 and Comparative Example 3/4, Example 3 and Comparative Example 5, and Example 4 and Comparative Example 6 revealed that flaky carbon and cellulose nanofiber By combining these, it is possible to obtain a material with high thermal conductivity even if the carbon content is the same. Further, from Example 2 and Comparative Example 4, and Example 3 and Comparative Example 5, it was found that when the carbon content is small, it is easier to obtain an insulating and highly thermally conductive material even with the same carbon ratio.

Claims (10)

Flake-like carbon with a thickness of 1 to 100 nm,
an organic compound having a hydrophilic group and a carbon-affinity 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. The thermally conductive material according to claim 1, wherein the hydrophilic group is at least one selected from the group consisting of the following general formulas (1) to (4).

[The above formula (1) represents an alcoholic hydroxyl group or a phenolic hydroxyl group. In formula (2), R represents a divalent organic group. In formula (3), X ₁ represents a hydrogen atom, an alkali metal, NH ₄ or organic ammonium. In formula (4), X ₂ represents a hydrogen atom, an alkali metal, NH ₄ , an organic ammonium, or an alkyl group. ] The thermally conductive material according to claim 1 or 2, wherein the hydrophilic group is a phenolic hydroxyl group or a polyoxyethylene group. 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, according to claims 1 to 3. The thermally conductive material according to any one of item 1. The thermally conductive material according to any one of claims 1 to 4, wherein the carbon-affinity hydrophobic group is an aryl group having two or more aromatic rings. The thermally conductive material according to any one of claims 1 to 5, wherein the nanofibers are cellulose nanofibers with a cellulose purity of 85% or more. Any one of claims 1 to 6, wherein the nanofibers include at least one type of nanofiber selected from the group consisting of methylcellulose, carboxymethylcellulose salt, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, and hydroxypropylmethylcellulose. Thermal conductive materials described in Section. A paint comprising the thermally conductive material according to any one of claims 1 to 7, or a coating film formed from the paint. A sheet comprising the thermally conductive material according to any one of claims 1 to 7. A flaky carbon dispersion containing 1 to 100 parts by mass of an organic compound having the hydrophilic group and the carbon-affinity hydrophobic group based on 100 parts by mass of the flaky carbon, or a wet solid of the flaky carbon dispersion; A method for producing a thermally conductive material according to any one of claims 1 to 7, comprising the step of mixing a fiber dispersion or a wet solid of the nanofiber dispersion.