Thermally conductive filler, thermally conductive composite, wire harness, and method for manufacturing thermally conductive filler

Abstract

Provided are a thermally conductive filler capable of exhibiting high thermal conductivity while suppressing specific gravity to be small, a thermally conductive composite material and a wire harness each containing such a thermally conductive filler, and a method for producing a thermally conductive filler capable of producing such a thermally conductive filler. A thermally conductive filler 10 has a base material particle 11 and a coating layer 12 that coats the base material particle 11, the coating layer 12 containing: a gel-like substance 12a that is bonded to the surface of the base material particle 11 via chemical bonding and coats the surface of the base material particle 11; and a thermally conductive substance 12b that is dispersed within the layer of the gel-like substance 12a and has higher thermal conductivity and larger specific gravity than the base material particle 11 and the gel-like substance 12a. In addition, a thermally conductive composite material 1 is provided in which the thermally conductive filler 10 is dispersed in a base material 2. Further, a wire harness is provided that contains the thermally conductive composite material 1.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a thermally conductive filler, a thermally conductive composite material, a wire harness, and a method for manufacturing a thermally conductive filler. BACKGROUND

[0002] For an insulating member constituting an electrical and electronic component, a thermally conductive filler is sometimes added to an organic polymer material for the purpose of improving thermal dissipation, suppressing the influence of heat generation caused by electrification or the like. In many cases, the thermally conductive filler is constituted of an inorganic compound such as alumina, aluminum nitride, boron nitride, or the like, which has high thermal conductivity.

[0003] In recent years, in various electrical and electronic components typified by automotive electronic devices, high currentization and integration are progressing, and the amount of heat generated at the time of electrification tends to increase. As a method of suppressing the influence of this heat generation, for example, in the case of an automotive wire harness, improvement in the shape and structure of the member such as flattening of the electric wire, increase in the surface area of the electric wire, contact of the electric wire with a high-thermal-conductivity outer packaging material to make the thermal dissipation efficiency higher, and the like are promoted to improve thermal dissipation. On the other hand, improving the thermal conductivity of the material itself of the insulating member constituting the electrical and electronic component such as the electric wire covering material, the electric wire outer packaging material, and the like is also important for improving thermal dissipation.

[0004] If a large amount of filler is mixed in an organic polymer material or the like, it is possible to improve the thermal conductivity of the material, but when a large amount of filler constituted of an inorganic compound is mixed in an organic polymer material, the specific gravity of the material becomes large, and it is difficult to make the electrical and electronic component lightweight. In products such as automobiles, from the viewpoint of lightweighting of the entire product, lightweighting of the electrical and electronic component mounted in the product becomes important. Therefore, even in a material containing a thermally conductive filler, lightweighting is desired. As a method therefor, attempts have been made to suppress the amount of addition of the filler.

[0005] The shape and particle arrangement of the filler have been designed with the aim of suppressing the amount of addition of the filler while maintaining high thermal conductivity. For example, in Patent Literature 1, a filler having a void portion inside, with a void ratio set to a predetermined range, is disclosed. In Patent Literature 2, an inorganic-organic composite composition is disclosed, which is obtained by dispersing a peeling flat particle produced by a peeling process in which a primary particle layer is peeled off to form a secondary particle, in a resin as a matrix. In Patent Literature 3, a high-thermal-conductivity composite is disclosed, in which a high-thermal-conductivity filler having anisotropy in shape is in direct contact with each other, thereby forming a mesh structure in the matrix resin.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT LITERATURE

[0008] Patent Literature 1: Japanese Patent Application Laid-Open (JP A) No. 2019-1849

[0009] Patent Literature 2: Japanese Patent Application Laid-Open (JP A) No. 2012-255055

[0010] Patent Literature 3: Japanese Patent Application Laid-Open (JP A) No. 2010-13580

[0011] Patent Literature 4: Japanese Patent Application Laid-Open (JP A) No. 2012-122057

[0012] Patent Literature 5: Japanese Patent Application Laid-Open (JP A) No. 2015-178543

[0013] Patent Literature 6: Japanese Patent Application Laid-Open (JP A) No. 2015-108058

[0014] Patent Literature 7: Japanese Patent Application Laid-Open (JP A) No. 2003-221453

[0015] Patent Literature 8: Japanese Patent Application Laid-Open (JP A) No. 2014-133678

[0016] Patent Literature 9: Japanese Patent Application Laid-Open (JP A) No. 2020-29524

[0017] Patent Literature 10: Japanese Patent Application Laid-Open (JP A) No. 2019-123983

[0018] Non-Patent Literature

[0019] Non-Patent Literature 1: Shuho Watanabe et al., "Improvement of dispersibility of hollow nano-silica particles in polymers by surface modification treatment", Abstracts of the 40th Autumn Meeting of the Chemical Society of Japan, K216, September 2008 SUMMARY

[0020] PROBLEMS TO BE SOLVED BY THE INVENTION

[0021] Inorganic compounds typified by aluminum oxide, aluminum nitride, and boron nitride exhibit high thermal conductivity, and on the other hand, have a large specific gravity, and when added as a filler to an organic polymer material or the like to produce a composite material, it is difficult to achieve high thermal conductivity while keeping the specific gravity of the entire composite material small. In particular, the specific gravity of a filler composed of an oxide such as aluminum oxide tends to be large. As described in Patent Literatures 1 to 3, by designing the shape and particle arrangement of the filler, the amount of inorganic compound added can be suppressed to some extent, but there are limitations. If the specific gravity of the filler itself can be reduced by studying the constituent material of the filler, it is possible to further highly achieve the balance of light weight and high thermal conductivity in a composite material to which the filler is added.

[0022] For example, if a material having a low specific gravity and a material having a high thermal conductivity are compounded to form a filler, it is possible to achieve both lightness and high thermal conductivity as a whole of the filler. Materials formed by compounding hollow particles such as glass and other materials are disclosed in Patent Documents 8 to 10 and Non-Patent Document 1. However, it is not easy to firmly fix a layer of a substance that bears thermal conductivity and to provide the layer on the surface of a particle of an inorganic compound such as glass in a sufficient thickness to exhibit thermal conductivity. If the thermal conductive substance can be bound on the surface of a hollow particle composed of glass or the like via chemical binding, it is expected that the layer of the thermal conductive substance can be firmly fixed on the hollow particle, but the density of chemical binding that can be directly formed on the surface of a particle of an inorganic compound such as glass is limited, and in addition, the range affected by the chemical binding is limited to a very thin region of the interface between the particle and the thermal conductive substance.

[0023] Therefore, an object is to provide a thermal conductive filler that can exhibit high thermal conductivity while suppressing the specific gravity to be small, a thermal conductive composite material and a wire harness that contain such a thermal conductive filler, and a method for manufacturing a thermal conductive filler that can manufacture such a thermal conductive filler.

[0024] Means for solving the problem

[0025] The thermal conductive filler of the present disclosure has a base material particle and a coating layer that coats the base material particle, the coating layer containing: a gel-like substance that is bound to the surface of the base material particle via chemical binding and coats the surface of the base material particle; and a thermal conductive substance that is dispersed within the layer of the gel-like substance and has a higher thermal conductivity and a larger specific gravity than the base material particle and the gel-like substance.

[0026] The thermal conductive composite material of the present disclosure contains the thermal conductive filler and a matrix material, the thermal conductive filler being dispersed in the matrix material.

[0027] The wire harness of the present disclosure contains the thermal conductive composite material.

[0028] The method for manufacturing a thermal conductive filler of the present disclosure manufactures the thermal conductive filler, the manufacturing method including: a gel preparation step of preparing the gel-like substance in a state where the thermal conductive substance is dispersed inside the gel-like substance; and a coating step of causing the gel-like substance prepared in the gel preparation step, in which the thermal conductive substance is dispersed, to be bound to the surface of the base material particle via chemical binding.

[0029] Effects of the Invention

[0030] The thermally conductive filler according to the present disclosure is a thermally conductive filler capable of exerting high thermal conductivity while suppressing specific gravity to be small. In addition, the thermally conductive composite and the wire harness according to the present disclosure are a thermally conductive composite and a wire harness containing such a thermally conductive filler. According to the production method of the thermally conductive filler according to the present disclosure, such a thermally conductive filler can be produced. BRIEF DESCRIPTION OF DRAWINGS

[0031] [ Figure 1 ] Figure 1 A and 1B are schematic diagrams illustrating the constitution of the thermally conductive filler and the thermally conductive composite according to one embodiment of the present disclosure. Figure 1 A shows a thermally conductive composite containing a thermally conductive filler, Figure 1 B enlarges and illustrates a coating layer constituting the thermally conductive filler.

[0032] [ Figure 2 ] Figure 2 is a side view showing a wire harness according to one embodiment of the present disclosure.

[0033] [ Figure 3 ] Figure 3 A and 3B are optical microscope photographs obtained by observing the fillers "30-PC80" and "30-PA80" produced in Examples, respectively. The photograph on the left side focuses on the center portion of the filler particle, and the photograph on the right side focuses on the surface portion of the filler. DETAILED DESCRIPTION

[0034] [Explanation of Embodiments of the Present Disclosure]

[0035] First, an embodiment of the present disclosure is exemplified and explained.

[0036] The thermally conductive filler according to the present disclosure has a base material particle and a coating layer coating the base material particle, and the coating layer contains: a gel-like substance that is combined with the surface of the base material particle via chemical bonding and coats the surface of the base material particle; and a thermally conductive substance that is dispersed within the layer of the gel-like substance and has higher thermal conductivity and larger specific gravity than the base material particle and the gel-like substance.

[0037] The thermally conductive filler has a coating layer containing a thermally conductive substance and a gel-like substance on the surface of the base material particle. By using a substance having a smaller specific gravity than the thermally conductive substance as the base material particle, the specific gravity of the thermally conductive filler as a whole can be reduced compared to the case where the filler as a whole is composed of the thermally conductive substance. On the other hand, the thermally conductive substance contained in the coating layer, which has a higher thermal conductivity than the base material particle, contributes to the improvement of the thermal conductivity of the filler. The gel-like substance constituting the coating layer is a highly viscous substance having a crosslinked structure, and the thermally conductive substance is stably held by being dispersed in this viscous body. The thermally conductive substance held in the gel-like substance forms a thermally conductive path within the layer of the coating layer of a single filler particle, between adjacent filler particles, and between other materials surrounding the filler particles, contributing to thermal conduction. In this way, even if a base material particle having a low thermal conductivity and a gel-like substance are used, due to the effect of the thermally conductive substance held in the gel-like substance, a high thermal conductivity can be exhibited as a whole of the thermally conductive filler particle. Therefore, in the thermally conductive filler, the specific gravity can be suppressed to be small while ensuring a high thermal conductivity.

[0038] Further, the gel-like substance constituting the coating layer is bonded to the surface of the base material particle via chemical bonding, so that the coating layer is firmly fixed on the surface of the base material particle. The gel-like substance is firmly fixed on the base material particle as a whole in the thickness direction of the coating layer due to the network structure constituted by the crosslinked structure, in combination with the effect produced by the chemical bonding between the gel-like substance and the base material particle, and stably maintains this state. Therefore, a gel-like substance layer is firmly bonded to the surface of the base material particle, and a thermally conductive filler having a small specific gravity and a high thermal conductivity can be stably obtained, the gel-like substance layer having a thickness capable of holding the amount of the thermally conductive substance necessary to obtain a high thermal conductivity.

[0039] Here, the base material particle can be in a hollow shape. In this case, the specific gravity of the base material particle can be effectively reduced due to the presence of the hollow portion, and the effect of reducing the specific gravity of the thermally conductive filler as a whole is excellent. The thermal conductivity of the base material particle is reduced due to the presence of the hollow portion, but by providing the coating layer containing the thermally conductive substance on the surface, a high thermal conductivity can be ensured as a whole of the thermally conductive filler.

[0040] The base material particle is constituted in the form of a glass hollow body, and can have a functional group on the surface capable of forming chemical bonding with the functional group possessed by the gel-like substance. For the glass hollow body particle, a hollow body particle having a controlled particle diameter and shape can be relatively easily and inexpensively obtained. In addition, since a plurality of functional groups can be easily introduced into the surface of the glass particle at a high density using a silane coupling agent, it is easy to produce a base material particle capable of being stably bonded to the gel-like substance constituting the coating layer via chemical bonding.

[0041] The gel-like substance can have a carbonyl group, the base material particle can have a basic group on the surface, and the gel-like substance can be bound to the surface of the base material particle via chemical binding between the carbonyl group and the basic group. As represented by polyacrylic acid, polyvinylpyrrolidone, and their derivatives, substances known to form a gel with multiple carbonyl groups can be appropriately used as the gel-like substance that forms the coating layer. Since a carbonyl group is capable of forming chemical binding between the carbonyl group and a basic group, by providing a basic group on the surface of the base material particle, the coating layer can be bound to the base material particle via chemical binding.

[0042] In this case, the gel-like substance can include an organic polymer having a carboxyl group as the carbonyl group. As an organic polymer having a carboxyl group represented by polyacrylic acid, a variety of substances known to form a stable gel are available, and are also highly versatile, and thus can be appropriately used as the gel-like substance that forms the coating layer of the thermally conductive filler.

[0043] The base material particle can have a primary amino group as the basic group on the surface. A primary amino group can form an ionic bond with an acidic carbonyl group such as a carboxyl group, and form a salt. In addition, a primary amino group can form a covalent bond with a neutral carbonyl group such as a ketone group, and form an amide bond or an imide bond. Thus, by forming a primary amino group on the surface of the base material particle in advance, the gel-like substance having a carbonyl group can be firmly bound to the base material particle.

[0044] The thermally conductive substance can be formed in the form of a particle having anisotropy in shape. Since a thermally conductive substance has anisotropy in shape, it often exhibits high thermal conductivity, but if it is directly used as a thermally conductive filler, anisotropy occurs in thermal conduction, and it is difficult to effectively contribute to improvement in thermal conductivity in any direction. However, even if the thermally conductive substance is as anisotropic as this, by being dispersed and held in a gel-like substance, anisotropy does not easily occur in the orientation of the thermally conductive substance, and it can contribute to thermal conduction in each direction with high uniformity. As a result, an excellent thermally conductive filler that exhibits high thermal conductivity in any direction can be obtained.

[0045] In this case, the thermally conductive substance can be carbon fiber. Carbon fiber has high thermal conductivity, and on the other hand, has an elongated shape with high anisotropy, but by forming a coating layer in a state of being held in a gel-like substance, a thermally conductive filler that exhibits high thermal conductivity in any direction can be provided.

[0046] The specific gravity of the thermally conductive filler can be 1.8 or less. In this way, the low specific gravity of the thermally conductive filler can be sufficiently ensured.

[0047] The thermally conductive composite material according to the present disclosure includes the thermally conductive filler and a base material, and the thermally conductive filler is dispersed in the base material.

[0048] The thermally conductive composite material contains the thermally conductive filler described in the embodiments of this disclosure. Since the thermally conductive filler is a filler in which a coating layer containing a gel-like substance and a thermally conductive substance is formed on the surface of the substrate particles, it is possible to improve heat dissipation by utilizing the high thermal conductivity of the thermally conductive filler while keeping the overall weight of the thermally conductive composite material low.

[0049] Here, the matrix material may comprise an organic polymer. Many organic polymers have low thermal conductivity, but by mixing the thermally conductive filler having a coating layer containing a thermally conductive material, high overall heat dissipation of the thermally conductive composite material can be ensured. On the other hand, organic polymers often have relatively low specific gravity, but by using a thermally conductive filler that minimizes specific gravity, the specific gravity of the thermally conductive composite material can be kept low even when thermally conductive fillers are added.

[0050] The specific gravity of the thermally conductive composite material can be below 1.4. In this case, the overall specific gravity of the thermally conductive composite material is kept sufficiently low.

[0051] The thermal conductivity of the aforementioned thermally conductive composite material can be above 0.9 W / (m·K) at room temperature. This ensures that the overall thermal conductivity of the composite material is sufficiently high.

[0052] The wiring harnesses disclosed herein include the thermally conductive composite material.

[0053] Because the wiring harness contains the thermally conductive composite material described above, it is possible to utilize high thermal conductivity while keeping the specific gravity of the constituent components low. This allows for a low overall mass of the wiring harness while achieving high heat dissipation. Therefore, while maintaining the lightweight nature of the wiring harness, the impact of heat generation caused by energizing the wires constituting the harness can be minimized.

[0054] The present disclosure relates to a method for manufacturing a thermally conductive filler, the method comprising the following steps: a gel preparation step, wherein the gel is prepared with the thermally conductive material dispersed within the gel; and a coating step, wherein the gel containing the thermally conductive material prepared in the gel preparation step is chemically bonded to the surface of the substrate particles.

[0055] According to the above manufacturing method, a coating layer in which thermally conductive material is dispersed in a gel-like substance can be formed on the surface of the substrate particles, and thermally conductive fillers with low specific gravity and high thermal conductivity can be easily manufactured.

[0056] [Details of the implementation of this disclosure]

[0057] Hereinafter, the thermally conductive filler, thermally conductive composite material, wire harness, and manufacturing method of the thermally conductive filler according to embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The thermally conductive composite material according to embodiments of the present disclosure is constituted by including the thermally conductive filler according to embodiments of the present disclosure. Furthermore, the wire harness according to embodiments of the present disclosure is constituted by including the thermally conductive composite material according to embodiments of the present disclosure. Moreover, the thermally conductive filler according to embodiments of the present disclosure can be manufactured by the manufacturing method according to embodiments of the present disclosure.

[0058] Unless otherwise specified, all physical property values ​​in this specification are measured at room temperature and in atmospheric conditions. Furthermore, in this specification, "a component is a major component of a material" means that the component constitutes 50% or more of the total mass of the material. Additionally, in this specification, "organic polymer" also includes substances with low degrees of polymerization, such as oligomers.

[0059] Thermally conductive fillers

[0060] First, an embodiment of the present disclosure will be described, which relates to a thermally conductive filler (hereinafter, sometimes simply referred to as "filler").

[0061] (The overall composition)

[0062] like Figure 1 As shown in Figure A, one embodiment of this disclosure relates to a thermally conductive filler 10 having substrate particles 11 and a coating layer 12, which are in a particle shape. The coating layer 12 coats the surface of the substrate particles 11.

[0063] like Figure 1 As shown in Figure B, the coating layer 12 contains a gel-like substance 12a and a thermally conductive substance 12b, with the thermally conductive substance 12b dispersed within the gel-like substance 12a. The gel-like substance 12a is chemically bonded to the surface of the substrate particles 11, thereby fixing the coating layer 12 to the surface of the substrate particles 11. In the gel-like substance 12a, the constituent molecules are cross-linked through binding forces such as hydrogen bonds, forming a mesh-like network, resulting in a highly viscous state. Particles of the thermally conductive substance 12b are retained within the structure of this gel-like substance 12a.

[0064] The thermally conductive substance 12b has a higher thermal conductivity than the base material particles 11 and the gel-like substance 12a. In addition, the thermally conductive substance 12b has a larger specific gravity than the base material particles 11 and the gel-like substance 12a. As will be described later, the base material particles 11 are preferably constituted in the form of a hollow body, a porous body, but in the case where a region not occupied by a solid substance, such as a hollow portion of a hollow body, a pore portion of a porous body, etc. exists within the particle, the specific gravity and the thermal conductivity of the base material particles 11 are amounts prescribed for the entire particle including also the region not occupied by the solid substance.

[0065] By adopting the structure in which the coating layer 12 containing the thermally conductive substance 12b is formed on the surface of the base material particle 11 for the filler 10, the base material particle 11 occupies a large portion of the volume of the filler 10. By making the base material particle 11 have a smaller specific gravity than the thermally conductive substance 12b, the specific gravity of the entire filler is made smaller than in the case where the entire filler is constituted by the thermally conductive substance 12b.

[0066] On the other hand, the coating layer 12 coating the surface of the base material particle 11 is capable of improving the thermal conductivity of the entire filler 10 by containing the thermally conductive substance 12b having a high thermal conductivity. As will be described later, the thermally conductive substance 12b is dispersed in the layer of the coating layer 12, and the particles of the thermally conductive substance 12b contact each other within the layer, thereby ensuring the thermal conductivity within the interior of the coating layer 12. Figure 1 B, the particles of the thermally conductive substance 12b dispersed in the layer of the coating layer 12 contact each other within the layer, thereby ensuring the thermal conductivity within the interior of the coating layer 12. In addition, as will be described later, the coating layer 12 of the surface of the filler particle 10 contacts the coating layer 12 of the surface of another filler particle 10, thereby facilitating the thermal conduction of the thermally conductive substance 12b contained in the coating layer 12 between the filler particle 10 and the base material 2, and between the filler particles 10. Figure 1 A, the coating layer 12 of the surface of the filler particle 10 contacts the coating layer 12 of the surface of another filler particle 10, thereby facilitating the thermal conduction of the thermally conductive substance 12b contained in the coating layer 12 between the filler particle 10 and the base material 2, and between the filler particles 10. Since the coating layer 12 is provided only on the surface of the base material particle 11, the volume of the entire filler particle 10 is ensured by the base material particle 11, and the thermal conductivity is exerted by the thermally conductive substance 12b having a small volume. The adjoining filler particles 10 contact each other via the coating layer 12 of the surface layer, thereby forming a thermal conduction path.

[0067] From the viewpoint of avoiding an increase in the mass of the filler 10, the specific gravity of the entire filler 10 is 1.8 or less, further preferably 1.5 or less, and can be 1.2 or less. On the other hand, from the viewpoint of avoiding a situation in which the amount of the thermally conductive substance 12b required to ensure sufficient thermal conductivity cannot be contained in the coating layer 12 due to the specific gravity being suppressed to be too small, the specific gravity of the entire filler 10 can be 0.5 or more, further preferably 0.8 or more. The specific gravity of the filler 10 can be measured, for example, using a specific gravity meter in the form of the true density of the filler 10 in powder form.

[0068] (Base material particle)

[0069] As described above, the base material particle 11 has a smaller specific gravity than the thermally conductive substance 12b contained in the coating layer 12. As long as it has such a specific gravity, there is no particular limitation on the specific structure of the base material particle 11 or the constituent material. As the structure of the base material particle 11, a solid substance occupying the entire region, a hollow body having a hollow portion in the interior which is not occupied by a solid substance, a porous body having a plurality of fine pore portions which are not occupied by a solid substance, and the like can be exemplified. In the case of the base material particle 11 being a hollow body, the hollow portion 11a is formed by a space which is not occupied by a solid substance. In the case of the base material particle 11 being a porous body, the fine pore portions are formed by spaces which are not occupied by a solid substance. In the case of the base material particle 11 being a solid body, the solid substance itself needs to have a smaller specific gravity than the thermally conductive substance 12b. Figure 1 In the form shown in A, the case where the base material particle 11 is a hollow particle having a hollow portion 11a is shown.

[0070] In the case where the base material particle 11 is composed of a solid body, the solid substance itself constituting the base material particle 11 needs to have a smaller specific gravity than the thermally conductive substance 12b. As such a solid substance, various resins, elastomers, rubbers, and the like organic polymers can be appropriately exemplified. Since the base material particle 11 needs to bind the gel-like substance 12a to the surface via chemical bonding, in the case where the base material particle 11 is composed of an organic polymer, it is preferable that the organic polymer have a functional group capable of forming chemical bonding with the functional group possessed by the gel-like substance 12a. The organic polymer can be a polymer having such a functional group in the main chain, or a polymer having a functional group introduced in the side chain by modification or the like.

[0071] In the case where the base material particle 11 is a hollow body, a porous body, or the like having a region not occupied by a solid substance, the specific gravity of the entire base material particle 11 becomes smaller due to the presence of these regions, and thus even if the solid substance itself constituting the base material particle 11 has a high specific gravity (density), it is possible to maintain the specific gravity of the entire base material particle 11 to be smaller than the thermally conductive substance 12b, as compared with the case where it is a solid body. Therefore, as the base material particle 11, a particle composed of a plurality of constituent materials can be employed. In particular, as the base material particle 11, a particle composed of a solid body and a hollow body, a porous body, or the like is preferable. Figure 1 A, if the base material particle 11 is composed of a hollow body, the hollow portion (hollow) 11a not occupied by a solid substance is entirely surrounded by the shell 11b formed by a solid substance, and is maintained in the form of a space which is blocked from the external environment of the base material particle 11, and thus the coating layer 12 which takes a clear layered structure is formed on the surface of the base material particle 11, and it is easy to maintain the effect of reducing the specific gravity by securing a space (hollow portion 11a) not occupied by other substances. From these viewpoints, the form in which the base material particle 11 is composed of a hollow body is particularly preferable.

[0072] In the case where the base material particle 11 is configured in the form of a hollow body or a porous body, as the material of configuration, various inorganic materials can be appropriately used in addition to the organic polymers exemplified in the case of the solid body described above. As such inorganic materials, metal or inorganic compounds such as glass, ceramics can be exemplified. Various functional groups can be introduced on the surface of the inorganic material by surface treatment. The gel-like substance 12a can be bound to the surface of the base material particle 11 via chemical bonding between these functional groups and the functional groups possessed by the gel-like substance 12a.

[0073] As a preferable example of the inorganic material configuring the base material particle 11 (of the shell 11b), glass can be exemplified. Glass, as a material itself, has a relatively low specific gravity among various inorganic compounds, and has a higher thermal conductivity than organic polymers and the like, and thus by being used as the material of the base material particle 11 configuring the thermally conductive filler 10, a high effect is exhibited in terms of low specific gravity and high thermal conductivity of the thermally conductive filler 10. In addition, techniques for producing hollow particles using glass, and further controlling the particle diameter and shape, have been established, and hollow particles of glass can be obtained at a low cost compared to other kinds of hollow particles. The kind of glass configuring the base material particle 11 is not particularly limited, and various kinds of glass such as soda-lime glass, silica glass, borate glass, borosilicate glass, alkali-lime-borosilicate glass, lead glass, phosphate glass, and the like can be used. Among these kinds of glass, as described later, it is preferable to use glass containing a silicon atom capable of forming a siloxane bond with a silane coupling agent in the structure, such as soda-lime glass, silica glass, borosilicate glass, alkali-lime-borosilicate glass, and the like, so that the introduction of a functional group can be performed using a silane coupling agent. The material configuring the base material particle 11 can be only one kind, or two or more kinds can be mixed or layered and used.

[0074] The base material particle 11 has a functional group on the surface capable of forming chemical bonding with the functional group possessed by the gel-like substance 12a. The kind of the functional group possessed by the base material particle 11 is not particularly limited, and the base material particle 11 can have a functional group on the surface capable of reacting with the functional group of the gel-like substance 12a depending on the kind of the functional group possessed by the gel-like substance 12a. The chemical bonding can be electrostatic bonding (ionic bond, hydrogen bond), or can be a covalent bond. In the case of forming electrostatic bonding, a polar group having an opposite polarity to the polar group possessed by the gel-like substance 12a can exist on the surface of the base material particle 11. The polar group possessed by the base material particle 11 can be ionic or non-ionic. In most cases, since the gel-like substance 12a, the raw material substance thereof, is in a negatively charged state, a positively charged polar group can exist on the surface of the base material particle 11.

[0075] As will be described later, as the compound constituting the gel, various compounds having a carbonyl group are known, and if a functional group capable of forming a chemical bond with the carbonyl group is provided on the surface of the base material particle 11, various gel-like substances 12a can be chemically bonded to the surface of the base material particle 11. As the functional group capable of forming a chemical bond with the carbonyl group, basic groups can be cited. As the basic group, amino groups, amide groups, imide groups, and the like can be cited. Among these, the presence of an amino group, particularly a primary amino group, on the surface of the base material particle 11 is preferable. The formation of the chemical bond between these functional groups and the gel-like substance 12a will be described later together with the examples of the gel-like substance 12a.

[0076] As long as the base material particle 11 has at least a functional group capable of forming a bond with the gel-like substance 12a on the surface, the distribution and the introduction method of the functional group are not particularly limited. That is, the entire solid substance constituting the base material particle 11 can contain a compound having a polar group as a constituent material, or a functional group can be introduced only on the surface (and in the vicinity thereof) of the base material particle 11 composed of a material substantially not containing a functional group or containing only a small amount of a functional group by surface treatment or the like. From the viewpoint of the ease of introducing a functional group to the surface of the base material particle 11, in the case where the base material particle 11 is composed of an organic substance, it is preferable that the organic substance constituting the base material particle 11 itself has a functional group which is exposed on the surface of the base material particle 11. On the other hand, in the case where the base material particle 11 is composed of an inorganic substance represented by glass, it is preferable that a functional group is introduced to the surface portion by surface treatment. In the case where the base material particle 11 is composed of glass containing silicon, or in the case where the surface has a hydroxyl group, various functional groups can be easily introduced to the surface by using a silane coupling agent.

[0077] The specific shape and the particle diameter of the base material particle 11 are not particularly limited. However, from the viewpoint of easily forming the coating layer 12 on the surface, improving the affinity with the matrix material 2, and the like, a shape having a high isotropy such as a shape close to a sphere is preferable. From the viewpoint of suppressing the specific gravity of the entire filler 10 to be small, and the like, the particle diameter (median particle diameter D50; the same below) of the base material particle 11 is preferably 1 μm or more, and further preferably 5 μm or more. On the other hand, from the viewpoint of suppressing the influence on the characteristics of the matrix material 2 to which the filler 10 is added to be small, increasing the specific surface area, and the like, the particle diameter of the base material particle 11 is preferably 100 μm or less, and further preferably 60 μm or less.

[0078] From the viewpoint of suppressing the specific gravity of the entire filler 10 to be small, the specific gravity of the individual base material particles 11 is preferably also small. The specific gravity of the base material particles 11 is not particularly limited as long as the specific gravity of the entire base material particles 11 is smaller than that of the thermally conductive substance 12b, but for example, can be 1.0 or less, and preferably 0.5 or less, in terms of the specific gravity (true density) of the entire base material particles 11 including the hollow portions 11a and the like. The lower limit of the specific gravity of the base material particles 11 is not particularly set, but the specific gravity of the base material particles 11 composed of a hollow body of an inorganic material such as glass or a solid body of an organic polymer is substantially 0.1 or more.

[0079] (coating layer)

[0080] In the coating layer 12, the gel-like substance 12a is combined with the surface of the base material particle 11 in a state of coating the surface of the base material particle 11, via chemical bonding. The thermally conductive substance 12b is dispersed and held within the layer of the gel-like substance 12a.

[0081] The gel-like substance 12a forms a bond between molecules, and forms a network-like crosslinked structure. The bond that forms the crosslinked structure can be a physical bond such as a van der Waals force, but is preferably a more robust chemical bond. As the chemical bond, it can be an ionic bond, a hydrogen bond, or the like, or a covalent bond, but from the viewpoint of the ease of formation of the coating layer 12 and the like, an electrostatic bond is preferred, and if it is a hydrogen bond, it is more preferred from the viewpoint of the stability of the crosslinked structure.

[0082] The gel-like substance 12a has a functional group capable of forming a chemical bond with a functional group on the surface of the base material particle 11, and by forming a chemical bond between the functional groups of the two, the gel-like substance 12a is combined with the surface of the base material particle 11 in a state of constituting the coating layer 12. In the gel-like substance 12a, the functional group that forms a bond with the surface of the base material particle 11 can be a common functional group to the functional group that forms a crosslinked structure between molecules, or can be included in the molecule of the gel-like substance 12a as a different functional group from the functional group for crosslinking. Preferably, the common functional group can be related to both the intermolecular crosslinking and the combination with the base material particle 11, and in the gel-like substance 12a having a carbonyl group described later, the carbonyl group forms a bond in the crosslinked structure, and in the case where a basic group such as an amino group is present on the surface of the base material particle 11, the gel-like substance 12a can be combined with the surface of the base material particle 11 by bonding with these basic groups.

[0083] The gel-like substance 12a is chemically bound to the surface of the base material particle 11 to form a state in which the coating layer 12 is firmly fixed to the base material particle 11. The direct effect of this chemical binding affects only the interface between the coating layer 12 and the base material particle 11 and its immediate vicinity, but the organization within the layer of the gel-like substance 12a is continuous due to the cross-linked structure. Thus, by the chemical binding of the interface and the cross-linked structure within the layer, the state in which the layer of the gel-like substance 12a is firmly fixed to the base material particle 11 is stably maintained.

[0084] Since the gel-like substance 12a forms a network structure and has high viscosity, as Figure 1 B shows, when the particles of the thermally conductive substance 12b are dispersed in the gel-like substance 12a, the state in which the thermally conductive substance 12b is stably maintained is maintained within the layer of the gel-like substance 12a. The gel-like substance 12a is in a state of forming a gel in many cases where water, other polar solvents are contained, but even if these polar solvents are removed, the state in which the thermally conductive substance 12b is dispersed and maintained in the organization of the gel-like substance 12a is maintained. The particles of the thermally conductive substance 12b dispersed in the gel-like substance 12a are in contact with each other, and a thermally conductive path is formed between the particles, whereby the coating layer 12 as a whole exhibits thermal conductivity.

[0085] Since the retention of the thermally conductive substance 12b inside the gel-like substance 12a does not require chemical interaction, in order to disperse and maintain the thermally conductive substance 12b within the layer of the gel-like substance 12a, it is not necessary for the thermally conductive substance 12b to exhibit compatibility with the gel-like substance 12a. In addition, since the thermally conductive substance 12b is not fixed to the surface of the base material particle 11 by direct interaction with the surface of the base material particle 11, the type of the thermally conductive substance 12b is not limited by the type of the base material particle 11. That is, without being limited by the constituent material or shape of the thermally conductive substance 12b, various thermally conductive substances 12b can be disposed on the surface of the base material particle 11 in a state of being dispersed within the layer of the gel-like substance 12a, and this state can be stably maintained. In addition, from the viewpoint of improving thermal conductivity and the like, even in the case where the coating layer 12 is formed to be thick, the entire layer can be maintained in a state of being stably fixed to the surface of the base material particle 11. Similarly, from the viewpoint of improving thermal conductivity and the like, the increase in the content density of the thermally conductive substance 12b in the coating layer 12 is also not limited by the formation density of the chemical binding or the like, and can be relatively easily performed as long as the gel-like substance 12a can retain the thermally conductive substance 12b within the organization.

[0086] As the thickness of the coating layer 12, from the viewpoint of obtaining sufficiently high thermal conductivity as a whole of the filler 10, it is preferable to form the coating layer 12 at a thickness of 10:90 or more, further 20:80 or more, 30:70 or more, in terms of the ratio of [dry volume of the mixed gel including the gel-like substance 12a and the thermally conductive substance 12b]:[dry volume of the base material particle 11]. On the other hand, from the viewpoint of avoiding peeling, damage of the coating layer 12 due to the coating layer 12 being too thick, and difficulty of mixing of the filler 10 into the base material 2 along with these phenomena, the thickness of the coating layer 12 can be suppressed to 80:20 or less, further 70:30 or less, in terms of the above ratio. Here, the dry volume refers to the volume in a state where liquid components such as solvents represented by water contained in the gel-like substance 12a are removed by drying or the like. As the thickness value of the coating layer 12, it can be approximately 1 μm or more, further 5 μm or more, and also 30 μm or less.

[0087] Note that even if the gel-like substance 12a is not used, the thermally conductive substance 12b and the base material particle 11 can be added to the base material 2 in each independent state, and a certain degree of thermal conductivity improvement effect can be obtained. However, in this case, the thermally conductive substance 12b is dispersed in the base resin in a state of coating a very small area of the surface of the base material particle 11 or in a state independent of the base material particle 11. By using the gel-like substance 12a to stably hold the thermally conductive substance 12b on the surface of the base material particle 11 as in the filler 10 according to the present embodiment, the thermally conductive substance 12b can effectively contribute to the formation of the thermal conduction path.

[0088] (Gel-like substance)

[0089] The gel-like substance 12a constituting the coating layer 12 is not particularly limited as long as it can form a gel state and has a functional group capable of forming chemical bonding with the functional group on the surface of the base material particle 11. In the filler 10, the gel-like substance 12a constituting the coating layer 12 can be in a state of swelling by absorbing water, other solvents, or can be in a state where these solvents are removed by drying or extraction. From the viewpoint of stability, ease of handling, and the like of the filler 10, the gel-like substance 12a is preferably in a state where the solvents are removed.

[0090] As the gel-like substance, various gel-like substances composed of a polymer having a carbonyl group are known, and in the present embodiment, these substances can also be appropriately used as the gel-like substance 12a. Due to the high polarity and the like of the carbonyl group, molecules having a carbonyl group easily form stable gels. Here, the carbonyl group includes various functional groups having a C=0 bond, and in addition to a ketone group, can also be a carboxyl group, an amide group, an ester group, and the like. For example, a polymer having a carboxyl group such as polyacrylic acid, a polymer having an amide group such as polyvinylpyrrolidone, or a derivative of these compounds swells due to water, a highly polar solvent, and the like, and forms a stable gel state. A polymer having a ketone group also gels due to swelling caused by polyethylene glycol (PEG). As specific examples of the polymer constituting the gel-like substance 12a, polyacrylic acid, a polyacrylic acid salt, a polyethylene acrylic acid copolymer, a polyethylene acrylic acid copolymer salt, polyvinylpyrrolidone, carboxymethyl cellulose, a carboxymethyl cellulose salt, alginic acid, an alginic acid salt, and the like can be given.

[0091] In the case where the molecule constituting the gel-like substance 12a has a carbonyl group, if a basic group such as an amino group is present on the surface of the base particle 11, the gel-like substance 12a can be stably bound to the surface of the base particle 11 by forming a bond between the carbonyl group and the basic group. For example, in the case where the gel-like substance 12a has an acidic carbonyl group such as a carboxyl group, an ionic bond can be formed between the basic group of the base particle 11, and a salt can be formed. On the other hand, in the case where the gel-like substance 12a has a neutral carbonyl group such as a ketone group, a covalent bond can be formed between the basic group on the surface of the base particle 11. For example, in the case where a primary amino group is present on the surface of the base particle 11, an amide bond or an imide bond is formed by a condensation reaction.

[0092] The specific gravity and the thermal conductivity that the gel-like substance 12a should have are not particularly specified, but the gel-like substance 12a is composed of an organic substance in most cases, and has a smaller specific gravity than the thermally conductive substance 12b composed of an inorganic substance. The specific gravity of the gel-like substance 12a can be 1.5 or less, and is preferably 1.2 or less, in the state of the raw material substance (gelation polymer) before gelation. The lower limit of the specific gravity is not particularly specified, but the specific gravity of an organic polymer that can form a gel is substantially 0.5 or more. Since the gel-like substance 12a has a small specific gravity, the specific gravity of the filler 10 as a whole can be suppressed to be small, together with the effect of the small specific gravity of the base particle 11. In addition, the gel-like substance 12a is composed of an organic substance in most cases, and has a lower thermal conductivity than the thermally conductive substance 12b. However, as described above, the thermally conductive substance 12b is dispersed and held in the layer of the gel-like substance 12a, and by forming a thermally conductive path, a high thermal conductivity can be obtained as a whole of the coating layer 12.

[0093] (Thermally conductive substance)

[0094] The thermally conductive substance 12b contained in the coating layer 12 is not particularly limited in kind or shape, as long as it has a higher thermal conductivity and a larger specific gravity than the base material particles 11 and the gel-like substance 12a, and is capable of being dispersed in the gel-like substance 12a. However, from the viewpoints of high thermal conductivity and dispersibility in the gel-like substance 12a, the thermally conductive substance 12b is preferably constituted by particles of an inorganic substance such as a metal, a metal compound, or a carbon material.

[0095] As specific examples of the material constituting the thermally conductive substance 12b, as a metal, non-magnetic metals such as copper and aluminum, and alloys having these elements as the main component can be given. In addition, as a metal compound, oxides, nitrides, carbides, oxynitrides, carbonitrides, oxycarbides, hydroxides, borides, and silicates, aluminates, titanates, and the like of metal elements (including quasi-metals such as B and Si) can be given. As a metal oxide, aluminum oxide, silicon oxide, magnesium oxide, iron oxide, beryllium oxide, titanium oxide, zirconium oxide, and the like can be given as preferred examples, as a metal nitride, aluminum nitride, silicon nitride, boron nitride, and the like can be given as preferred examples, as a metal hydroxide, aluminum hydroxide, magnesium hydroxide, and the like can be given as preferred examples, and as a metal carbide, silicon carbide, and the like can be given as preferred examples. Furthermore, as a carbon material capable of constituting the thermally conductive substance 12b, graphite, carbon black, carbon fibers, carbon nanotubes, graphite, graphene, artificial diamond, and the like can be given. The thermally conductive substance 12b contained in the coating layer 12 can be one kind or a plurality of kinds. In the case where a plurality of kinds of thermally conductive substances 12b are used, these thermally conductive substances 12b can be present in a mixed state, or can form a composite. The thermally conductive substance 12b can also be subjected to surface treatment with an organic substance or the like, but since chemical interaction is not required when the thermally conductive substance 12b is held by the gel-like substance 12a, surface treatment of the thermally conductive substance 12b is not required from the viewpoint of improving the holding property by the gel-like substance 12a.

[0096] Among the above-mentioned substances, metal oxides such as alumina and magnesia, and carbon materials such as carbon black and carbon fiber are particularly preferable as the thermally conductive substance 12b from the viewpoint of thermal conductivity. In addition, the thermally conductive substance 12b is preferably in the form of particles having anisotropy in shape such as plate-like, needle-like, rod-like, and fiber-like shapes. The particles of the metal compound and the carbon material having anisotropy in shape have high thermal conductivity in a specific direction due to the anisotropy. These particles are suitable for use as a thermally conductive material because of the high thermal conductivity, but if the particles are oriented in a specific direction due to the anisotropy of the particle shape, the thermal conductivity is excellent in the specific direction, but the thermal conductivity in other directions is reduced, making it difficult to use as a thermally conductive material. However, in the filler 10 according to the present embodiment, the particles of the thermally conductive substance 12b are dispersed and held in the gel-like substance 12a, and therefore the particles of the thermally conductive substance 12b having anisotropy in shape are not oriented in a specific direction but are randomly oriented and arranged within the layer of the coating layer 12 and as a whole of the filler 10. Therefore, by utilizing the high thermal conductivity of the particles of the thermally conductive substance 12b having anisotropy in shape, a thermally conductive filler 10 having excellent thermal conductivity in any direction, not in a specific direction, can be produced. As the thermally conductive substance 12b having anisotropy in shape and high thermal conductivity, carbon fiber can be mentioned. Carbon fiber has an elongated shape with high anisotropy, and the thermal conductivity has large anisotropy, but by being dispersed in the gel-like substance 12a, the large anisotropy can be eliminated, and by forming a thermally conductive path between adjacent carbon fibers, high thermal conductivity in any direction can be exhibited.

[0097] The particle diameter of the thermally conductive substance 12b is not particularly limited, but from the viewpoint of exhibiting sufficiently high thermal conductivity, the average can be 0.1 μm or more, and further can be 0.3 μm or more. On the other hand, in the coating layer 12, from the viewpoint of being easily dispersed and held within the organization of the gel-like substance 12a, the particle diameter of the thermally conductive substance 12b can be 30 μm or less on average, and further can be 20 μm or less. In addition, the particle diameter of the thermally conductive substance 12b is preferably smaller than the particle diameter of the base material particle 11, and more preferably is half or less of the particle diameter of the base material particle 11. Here, the particle diameter of the thermally conductive substance 12b means the approximate diameter in the case where the particle can be approximated to a spherical shape, and means the length (length of the major axis) in the case of a needle-like, fiber-like, or the like, highly anisotropic shape.

[0098] The content of the thermally conductive substance 12b in the coating layer 12 is not particularly limited, but from the viewpoint of sufficiently improving the thermal conductivity within the coating layer 12 and as a result, sufficiently improving the thermal conductivity of the filler 10 as a whole, the thermally conductive substance 12b can be contained in an amount of 90: 10 or more, further 50: 50 or more, 30: 70 or more, in terms of the ratio of [dried volume of the gel-like substance 12a]: [dried volume of the thermally conductive substance 12b]. On the other hand, from the viewpoint of stably retaining the thermally conductive substance 12b inside the organization of the gel-like substance 12a, the content of the thermally conductive substance 12b can be suppressed to 1: 99 or less, further 10: 90 or less, in terms of the above ratio.

[0099] <Method for manufacturing thermally conductive filler>

[0100] Next, a method for manufacturing the thermally conductive filler according to one embodiment of the present disclosure, which enables the manufacture of the above-described thermally conductive filler 10, will be described. The thermally conductive filler 10 can be manufactured by implementing a gel preparation step and a coating step.

[0101] Prior to the manufacture of the thermally conductive filler 10, the base material particle 11 is prepared in advance. Solid particles of organic polymers, hollow particles of inorganic compounds such as glass, and porous body particles are mostly sold on the market, and these particles can be appropriately used.

[0102] In the case where the base material particle 11 does not have a functional group on the surface that can form a chemical bond with the functional group of the gel-like substance 12a, surface treatment needs to be performed on the base material particle 11 to introduce the functional group on the surface. As the surface treatment, a compound having the desired functional group can be bonded to the surface of the base material particle 11 through a chemical reaction. At this time, other compounds can be interposed between the compound having the functional group and the surface of the base material particle 11. In the case where the base material particle 11 is composed of a substance containing a silicon atom such as glass, or a substance having a hydroxyl group on the surface, it is preferable to introduce the functional group on the surface of the base material particle 11 using a silane coupling agent.

[0103] In the gel preparation step, a mixed gel that becomes the coating layer 12 is prepared. That is, a gel-like substance 12a is prepared in a state in which the thermally conductive substance 12b is dispersed in the inside. The specific method is not particularly limited, and the raw material substance that constitutes the gel, such as a gelling polymer, can be cross-linked and swelled to form the gel-like substance 12a, and at the same time as the formation of the gel-like substance 12a or after the formation of the gel-like substance 12a, the particles of the thermally conductive substance 12b can be dispersed in the gel-like substance 12a. For example, in the case in which a gelling polymer that becomes the gel-like substance 12a by being swelled with a polar solvent such as water is used as the raw material substance, the gelling polymer and the particles of the thermally conductive substance 12b can be stirred in a solvent containing the polar solvent such as water. At this time, a small amount of an aqueous metal salt solution can be added, and the gel-like substance 12a can be obtained in the form of a salt. In the gel preparation step, the amounts of the raw material substance that becomes the gel-like substance 12a and the thermally conductive substance 12b can be selected in such a manner that a desired value is obtained in terms of the ratio of [the dry volume of the gel-like substance 12a (gelling polymer)] : [the dry volume of the thermally conductive substance 12b].

[0104] In the coating step, the surface of the base material particle 11 is coated with the mixed gel prepared in the gel preparation step, and further, the gel-like substance 12a is chemically bonded to the surface of the base material particle 11. At this time, the base material particle 11 prepared in a state in which a predetermined functional group is present on the surface and the above-prepared mixed gel can be mixed and kneaded. Alternatively, a solvent that does not cause a decrease in the gel property of the gel-like substance 12a, modification of the functional group on the surface of the base material particle 11, or the like can be used, and the base material particle 11 and the mixed gel can be mixed in the solvent. Through these mixing, kneading, or mixing in the solvent operations, the mixed gel surrounds the surface of the base material particle 11, and further, chemical bonding is formed between the functional group possessed by the gel-like substance 12a that constitutes the mixed gel and the functional group present on the surface of the base material particle 11. In order to promote the formation of the chemical bonding, heating, addition of a reagent, or the like can be appropriately performed. The heating temperature is preferably set to a temperature lower than the boiling point of the solvent used.

[0105] The particle obtained through the coating step can be used as the thermally conductive filler 10 as it is, or can be used as the thermally conductive filler 10 after the liquid component is appropriately removed. The removal of the liquid component can be performed by heating, air drying, or the like under normal pressure or vacuum. In the case in which the liquid component is present in a state in which it enters the gel-like substance 12a or the like on the surface of the filler particle 10, if volatilization or flow of the liquid component occurs in the use of the filler 10, the operability of the filler 10 can be decreased, and thus it is preferable to remove the liquid component in advance.

[0106] <Thermally conductive composite material>

[0107] Next, a thermally conductive composite material (hereinafter sometimes referred to as a composite material) according to one embodiment of the present disclosure will be described. As shown in FIG. 1, the thermally conductive composite material 1 according to the present embodiment includes the thermally conductive filler 10 according to the above-described embodiment of the present disclosure and a base material 2. The filler 10 is dispersed in the base material 2. Figure 1

[0108] The composite material 1 according to the present embodiment exhibits high thermal conductivity as a whole due to the high thermal conductivity of the thermally conductive substance 12b, because the surface of the base material particle 11 contains the thermally conductive filler 10 having the coating layer 12 containing the thermally conductive substance 12b. At the same time, the composite material 1 as a whole becomes a material having a small specific gravity due to the low specific gravity effect of the thermally conductive filler 10 caused by the base material particle 11.

[0109] The kind of the base material 2 is not particularly limited, and the base material 2 preferably contains an organic polymer, and more preferably is a base material in which an organic polymer is the main component. As specific examples of the organic polymer constituting the base material 2, various resins, thermoplastic elastomers, rubbers, and the like can be given. In the case where a resin material is used as the base material 2, depending on the intended use, it can be a curable resin, a thermoplastic resin, or a plastic that is soluble in a solvent. As the kind of the resin constituting the base material 2, for example, olefin-based resins such as polyethylene and polypropylene; halogen-based resins such as polyvinyl chloride; polylactic acid, polystyrene-based resins, polyvinyl acetate, ABS resins, AS resins, acrylic resins, methacrylic resins, polyamide resins, polyurethane resins, polysiloxane resins, fluorine-containing resins, polyvinyl alcohol, polyimide, polyacetal, polycarbonate, modified polyphenylene ether (PPE), polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, and epoxy resins, or copolymers, polymer alloys of these resins can be given. The base material 2 can contain only one kind of organic polymer, or can contain a plurality of kinds of organic polymers. Note that the base material 2 is not a gel, but a material that is in a solid state at room temperature after being appropriately cured or the like. The base material 2 can appropriately contain, in addition to the organic polymer, additives such as flame retardants, fillers, colorants, and the like.

[0110] ​The specific gravity of the base material 2 itself is not particularly limited, but from the viewpoint of suppressing the specific gravity of the composite material 1 as a whole to which the filler 10 is added to be small, it is preferable to suppress the specific gravity of the base material 2 itself to be 1.5 or less. The lower limit of the specific gravity of the base material 2 is not particularly limited, but in the case where an organic polymer is used as the base material 2, the specific gravity thereof is substantially 0.8 or more. In addition, the thermal conductivity of the base material 2 itself is not particularly limited, but from the viewpoint of securing a high thermal conductivity of the composite material 1 as a whole to which the filler 10 is added, it is preferable to set the thermal conductivity of the base material 2 itself to be 0.1 W / (m·K) or more in advance. The upper limit of the thermal conductivity of the base material 2 is not particularly limited, but in the case where an organic polymer is used as the base material 2, the thermal conductivity thereof is substantially 0.6 W / (m·K) or less. Note that the specific gravity of the base material 2, the composite material 1 can be measured by a water displacement method or the like. In addition, the thermal conductivity of these materials can be measured by a laser flash method, a hot wire method, or the like.

[0111] In the composite material 1 according to the present embodiment, the content of the filler 10 can be appropriately determined as the composite material 1 as a whole in such a manner that the desired specific gravity and thermal conductivity are obtained. The more the content of the filler 10 is, the higher the thermal conductivity of the composite material 1 is, and thus the content that enables the desired thermal conductivity to be obtained can be determined as the lower limit of the content of the filler 10. For example, the content of the filler 10 can be determined in such a manner that the thermal conductivity of the composite material 1 is 5 times or more, further 7 times or more, 10 times or more, 15 times or more of the thermal conductivity of the base material 2 to which the filler 10 is not added. Alternatively, the content of the filler 10 can be determined in such a manner that the thermal conductivity of the composite material 1 is 0.9 W / (m·K) or more, further 1.5 W / (m·K) or more, 2.0 W / (m·K) or more, 3.0 W / (m·K) or more. Note that the higher the thermal conductivity of the composite material 1 is, the more preferable it is, but from the viewpoint of avoiding an increase in the specific gravity due to an excessive addition of the filler 10, the thermal conductivity of the composite material 1 can be limited to be 50 times or less, further 30 times or less of the thermal conductivity of the base material 2, and in addition, can be 8.0 W / (m·K) or less, further 5.0 W / (m·K) or less.

[0112] The upper limit of the content of the filler 10 in the composite material 1 is not particularly limited, but the content of the filler 10 can be determined in such a manner that the specific gravity of the composite material 1 is suppressed to be 1.3 times or less, further 1.2 times or less of the specific gravity of the base material 2 to which the filler 10 is not added. Further preferably, the specific gravity of the composite material 1 can be the specific gravity of the base material 2 to which the filler 10 is not added or less. Alternatively, the content of the filler 10 can be determined in such a manner that the specific gravity value of the composite material 1 is suppressed to be 1.8 or less, further 1.5 or less, 1.3 or less. Note that the smaller the specific gravity of the composite material 1 is, the more preferable it is, and the lower limit is not particularly limited.

[0113] When the content of the filler 10 is defined by the proportion of the filler 10 in the entire composite material 1, the content of the filler 10 can be set to be substantially 10% by volume or more, further 20% by volume or more, 30% by volume or more from the viewpoint of sufficiently improving the thermal conductivity of the composite material 1. Alternatively, the content of the thermally conductive substance 12b itself can be set to be 2% by volume or more, further 4% by volume or more, 6% by volume or more. On the other hand, from the viewpoint of suppressing an increase in the specific gravity of the composite material 1, the viewpoint of avoiding saturation of the effect of improving the thermal conductivity due to the addition of a large amount of the filler 10, the content can be set to be 60% by volume or less, 50% by volume or less. Alternatively, the content of the thermally conductive substance 12b itself can be set to be 15% by volume or less, further 12% by volume or less.

[0114] As described above, the composite material 1 according to the present embodiment has both high thermal conductivity and low specific gravity. Therefore, the present composite material 1 can be suitably used as a material constituting a member that requires both lightness and heat dissipation. The specific use of the composite material 1 is not particularly limited, and the use as a material constituting a wire harness is exemplified in detail below. The composite material 1 according to the present embodiment can be manufactured by mixing the powder-like filler 10 manufactured by the manufacturing method described above into the base material 2 at a predetermined mixing ratio.

[0115] Wire Harness

[0116] Finally, a wire harness according to the present embodiment is described. The wire harness 5 according to the present embodiment contains the thermally conductive composite material 1 according to the present embodiment described above. As shown in FIG. 1, the wire harness 5 has a connector 52 containing a connection terminal (not shown) provided at the end portion of an insulated wire 51 in which an insulating covering layer is provided at the outer periphery of a wire conductor. In the wire harness 5, a plurality of the insulated wires 51 can also be bundled, and in this case, a tape 53 can be used as an outer packaging material for the bundled insulated wires 51. Figure 2

[0117] In the wire harness 5 according to the present embodiment, the composite material 1 according to the present embodiment described above can constitute various members that require heat dissipation. It is preferable to use the composite material 1, which is obtained mainly by adding the filler 10 to the organic polymer as the base material 2, as an insulating member. As such an insulating member, an insulating covering layer constituting the insulated wire 51, the tape 53 arranged on the outside of the insulated wire 51, an outer packaging material such as a protection tube, an adhesive for adhesion between members or for waterproofing, a connector housing constituting the connector 52, and the like can be exemplified. In addition, the composite material 1 can be arranged between the protection tube such as a bellows and the insulated wire 51.

[0118] ​In recent years, in the field of automobiles, especially in electric cars, hybrid cars, there is a tendency that the current flowing through the electric wire becomes large, and the heat generated from the electric wire becomes large. In addition, a plurality of electric wires, electric connection members become close to be arranged. In these cases, from the viewpoint of suppressing the influence of heat generation from the electric wire, electric connection member to be small, it is important that various members constituting the wire harness 5 have high heat dissipation properties. In the wire harness 5, by using the above-mentioned composite material 1 having high thermal conductivity to constitute the members likely to be affected by heat generation, heat dissipation can be effectively performed. In addition, in the field of automobiles, lightweight of the constituent members is an important issue, by using the above-mentioned composite material 1 whose specific gravity is suppressed to be small, it is also possible to contribute to the lightweight of the wire harness 5.

[0119] Example

[0120] Hereinafter, an example will be shown. The present application is not limited to these examples. Here, a thermally conductive filler having a coating layer on the surface of a base material particle is produced, and the state of the filler particle and the specific gravity and thermal conductivity of the composite material containing the filler are evaluated. Hereinafter, unless otherwise specified, the production and evaluation of the sample are performed in the atmosphere, at room temperature.

[0121] [Experimental method]

[0122] (1) Production of filler

[0123] First, a plurality of fillers having a coating layer on the surface of a base material particle are prepared. When producing the filler, surface treatment is performed on the raw material particle, and a mixed gel is prepared in a gel preparation step, and then a coating layer is formed on the surface of the raw material particle in a coating step.

[0124] (1-1) Preparation of base material particle

[0125] Glass hollow particles to which an amino group was introduced on the surface were prepared as base particles. Specifically, alkali lime borosilicate glass-made hollow particles ("GLASS BUBBLES iM16K" manufactured by 3M Company; median particle diameter 20 μm; specific gravity 0.46) were prepared as untreated glass hollow particles (GB). Then, 5 g of GB and 100 mL of acetone were put in an eggplant-shaped flask, and stirred gently at room temperature to suspend. Further, while continuing the stirring, 0.5 g of 3-aminopropyltriethoxysilane (AP) ((C2H5O)3Si-C3H6-NH2) was added to the suspension. The stirring was continued directly at room temperature for 2 hours, and then a cooling tube was installed, 200 mL of pure water was added, and stirring was performed at 50°C for 24 hours. Then, filtration and air-drying were performed, and further heating with an oven at 140°C was performed for 24 hours. Through the above procedures, base particles on which surface treatment with aminopropyltriethoxysilane was performed (AP-GB) were obtained. The aminopropyltriethoxysilane was bonded to the surface of the glass hollow particles via a siloxane bond, and became a state in which an amino group was bonded to the surface of the particles.

[0126] (1-2) Gel preparation step

[0127] As a gelation polymer material to be a raw material of a gel-like substance, the following materials were prepared.

[0128] • PAA: polyacrylic acid (average molecular weight about 1,000,000; manufactured by FUJIFILM Wako Pure Chemical Corporation)

[0129] • EAA: (ethylene-acrylic acid copolymer; acrylic acid content 15 mass%; manufactured by Sigma-Aldrich Corporation)

[0130] In addition, as a thermally conductive substance, the following substances were prepared.

[0131] • CF: carbon fiber (length 10 μm, diameter 150 nm; vapor-phase method carbon fiber VGCF manufactured by Showa Denko K.K.)

[0132] • Al2O3: α-aluminum oxide (diameter 0.5 μm; manufactured by FUJIFILM Wako Pure Chemical Corporation)

[0133] • MgO: magnesium oxide (diameter 7 μm to 15 μm; manufactured by Ube Materials Corporation)

[0134] Each of the gelation polymer materials, tetrahydrofuran (THF) 17 mL, and pure water 33 mL, which are described in Table 1, were put in an eggplant-shaped flask, a reflux tube was installed, and stirring was performed at 60°C for 12 hours to dissolve and disperse the gelation polymer. While continuing the stirring, each of the thermally conductive substances was put in an amount described in Table 1, a reflux tube was installed again, and stirring was performed at 60°C for 2 hours to disperse the thermally conductive substance. In this way, a mixed gel was prepared.

[0135] (1-3) Coating step

[0136] While continuing to stir the mixed gel prepared in the above gel preparation step, the substrate particles (GB or AP-GB which were not subjected to surface treatment) of the input amount described in Table 1 were input into the mixed gel, a reflux tube was installed again, and stirring was performed at 60°C for 2 hours to disperse the substrate particles. Then, the dispersion liquid was cooled to room temperature. Then, while stirring 1 L of isopropyl alcohol in another beaker, the above dispersion liquid was added little by little to prepare a suspension liquid. The obtained suspension liquid was suction filtered, and the obtained filtrate was dried at 80°C for 24 hours. In this way, the thermally conductive filler was obtained.

[0137] In the following Table 1, the kinds and specific gravities of the gelation polymer material, the thermally conductive substance, and the substrate particles, and the input amounts for preparing each thermally conductive filler are summarized. In the table, as values calculated from these input amounts and specific gravities, the dry capacity ratio of [gelation polymer]:[thermally conductive substance], the dry capacity ratio of [mixed gel]:[substrate particle], and the specific gravity of the filler particle are shown together. The dry capacity ratio of [gelation polymer]:[thermally conductive substance] is calculated as the ratio after converting the input amounts of the gelation polymer material and the thermally conductive substance into volumes, and the dry capacity ratio of [mixed gel]:[substrate particle] is calculated as the ratio of the total value of the calculated volumes of the gelation polymer material and the thermally conductive substance to the volume of the substrate particle, each of which is expressed with one significant figure. The specific gravity of the filler particle is calculated from the total of the input amounts and the total of the calculated volumes of the gelation polymer, the thermally conductive substance, and the substrate particle. Note that, based on the above, the total of the input amounts of the gelation polymer material, the thermally conductive substance, and the substrate particle is 1000 g, and the total of the calculated volumes is 1000 mL. Figure 3 Microscope photographs of A, 3B, as described later, confirmed that almost the entire amounts of the gelation polymer material and the thermally conductive substance used as raw materials formed a mixed gel, becoming a state of coating the surface of the substrate particle, and as described above, the appropriateness of calculating the dry capacity ratio and the specific gravity of each component based on the input amount of each raw material was shown.

[0138]

[0139] (2) Preparation of composite material

[0140] Each of the fillers prepared above was dispersed in a base material to prepare the composite materials involved in Samples Al to Al4 and Samples Bl to B7. Here, the base material constituting the composite material was set to the cured product of the following two-component epoxy resin.

[0141] • Epoxy main agent: glycidyl ether of bisphenyl A ("jER828" manufactured by Mitsubishi Chemical Corporation; epoxy equivalent: 190 g / eq.)

[0142] • Epoxy curing agent: amine type ("ST12" manufactured by Mitsubishi Chemical Corporation; amine value: 345 to 385 KOH mg / g)

[0143] The various fillers and the epoxy base agent and the epoxy curing agent were mixed at the mass ratio shown in Table 2 below at normal temperature using an agate mortar, and were degassed under vacuum at normal temperature for 1 minute. Then, the mixture was heated at 100°C for 10 minutes using a hot press molding machine, and was cured. In the cured body, a portion in which no bubbles were visually confirmed was cut out, and a resin cured product test piece (10 mm x 10 mm x 1 mm) was produced. Note that, for Test Piece B1, no filler was added, and a resin cured product test piece was produced from only the epoxy resin.

[0144] (3) Evaluation of the state of the filler and the characteristics of the composite material

[0145] Each of the fillers prepared above was dispersed in liquid paraffin, and was observed using an optical microscope, and the state of the filler particles was evaluated.

[0146] In addition, the specific gravity and the thermal conductivity were measured for each of the resin cured product test pieces produced as a composite material above. The specific gravity was measured by a water displacement method. The thermal conductivity was measured using a thermal conductivity device ("LFA447" manufactured by NETZSCH Corporation) using a laser flash method. The direction of measurement of the thermal conductivity was set to a direction perpendicular to the face of the resin cured product test piece.

[0147] [Results of the Test]

[0148] As a representative of the fillers produced, in Figure 3 The optical microscope images of the fillers "30-PC80" and "30-PA80" are shown in A and 3B, respectively. The image on the left is an image focused on the central portion of the particle, and the image on the right is an image focused on the surface portion of the particle. In either of the two fillers, as can be seen mainly in the image focused on the central portion of the particle, the base material particle maintains a hollow state. Also, as can be seen mainly in the image focused on the surface portion of the particle, the slightly blurred layered region observed on the surface of the hollow base material particle corresponds to the coating layer formed from the mixed gel. In the image of "30-PC80", the many needle-like elongated structures observed in the coating layer correspond to the carbon fibers added as the thermally conductive substance. In addition, in the image of "30-PA80", the multiple dot-like structures like dark shadows observed in the coating layer correspond to the alumina particles added as the thermally conductive substance.

[0149] As such, it was confirmed from the microscope images that the structure in which the coating layer composed of the mixed gel in which the thermally conductive substance was dispersed was formed on the surface of the hollow particle as the base material particle was obtained in the filler produced. The mixed gel coated the surface of the hollow particle in a layer shape, forming the coating layer, and the presence of the gel-like substance was not confirmed in the portions other than the surface of the particle. That is, almost the entire amount of the mixed gel used as the raw material became the state of coating the surface of the hollow base material particle. It was thus confirmed that, as described above, the manufacturing method in which the base material particle subjected to the surface treatment was mixed with the mixed gel was able to stably form the coating layer containing the thermally conductive substance on the surface of the base material particle.

[0150] In Figure 3 In the image of "30-PC80" of A, as explained above, in the coating layer, a plurality of elongated substances protruding on the surface corresponding to the carbon fiber added as the thermally conductive substance were present. The protruding direction of the carbon fiber was random on the surface of the base material particle, and the carbon fiber became a state of not having a specific orientation by being dispersed in the gel-like substance.

[0151] The measurement results on the composition and the properties of the composite materials involved in the test samples Al to A14 and the test samples Bl to B7 are summarized in Table 2. The compounding ratio (unit: mass%) of the filler and the matrix material is shown in the upper row, and the compounding amount (unit: volume%) of the filler and the content (unit: volume%) of the thermally conductive substance are shown in the middle row. Here, the content of the thermally conductive substance is the content calculated from the volume ratio of the thermally conductive substance in the filler and the compounding amount of the filler in the composite material. The measurement results on the specific gravity and the thermal conductivity are summarized in the lower row.

[0152]

[0153] The test samples Al to A14 are the test samples in which the filler in which the coating layer in which the thermally conductive substance was dispersed in the gel-like substance was provided on the surface of the base material particle in which the amino group was introduced by the surface treatment was provided and added to the matrix material. In these test samples Al to A14, although the filler was added in a maximum of 50 volume%, the specific gravity of the composite material was suppressed to be lower than the specific gravity of the test sample Bl in which no filler was added or was increased by 10% or less with respect to the specific gravity of the test sample Bl.

[0154] Further, in the samples Al to A14, the thermal conductivities were all 1.5 W / (m-K) or more. These values correspond to 7 times or more the thermal conductivity of the sample Bl to which no filler was added. From this result, in the samples Al to A14 to which the filler obtained by disposing the coating layer obtained by dispersing the thermally conductive substance in the gel-like substance on the surface of the base material particle was added, the filler contains the low specific gravity hollow base material particle, and thus, as the entire composite material to which the filler is added, a high thermal conductivity can be obtained while the specific gravity is suppressed to be small. It can be explained that the thermally conductive substance is stably held in the organization of the gel-like substance by the coating layer, and a chemical bond is formed between the gel-like substance and the base material particle, and thus, a state in which the base material particle is stably coated with the coating layer in which the thermally conductive substance is dispersed and shows a high thermal conductivity is formed. It is considered that the particles of the thermally conductive substance held in the state of being dispersed in the gel-like substance contact each other within the layer of the coating layer, and thus, a continuous thermally conductive path is formed on the surface of each filler particle. Further, it can be explained that, due to the effect of the volume occupied by the base material particle, the coating layers of the surfaces of the adjacent fillers contact each other, and a thermally conductive path is also formed between the filler particles, and shows a high effect on the improvement of the thermal conductivity.

[0155] Here, the samples B2 to B5 were investigated. In the sample B2, the surface-treated glass hollow particle itself (AP-GB) was added to the base material, and the specific gravity was reduced compared to the sample Bl to which no filler was added. However, since the filler did not contain the thermally conductive substance, the thermal conductivity was not improved compared to the sample Bl. It can be explained that the thermal conductivity of the glass itself is about 1.0 W / (m-K), which is higher than the thermal conductivity of the base material, but becomes a hollow particle, and thus, the scattering of phonons is caused in the inside of the particle, and it is difficult to cause the thermal conduction through the particle. In this way, the glass hollow particle itself cannot be used as a thermally conductive filler.

[0156] As the thermally conductive substance, carbon fibers alone were added in sample B3, and alumina particles alone were added in sample B4, each at 7.2 vol%. The addition amount was the same as the content of the thermally conductive substance in samples Al to A5. However, in these samples B3, B4, the thermal conductivity was 0.6 W / (m-K) or less. The thermally conductive substance used in sample B3 was the same as that used in samples Al, A4, and the thermally conductive substance used in sample B4 was the same as that used in samples A2, A5, but the thermal conductivity obtained from samples B3, B4 was reduced to 1 / 4 or less as compared with these samples Al, A4 and samples A2, A5. This is considered to be because, in samples B3, B4, the volume of the filler in the composite material is small, and therefore the contact area between the filler particles is small, and the formation of the thermally conductive path between the filler particles cannot be effectively achieved. In particular, the carbon fibers used in sample B3 have a high anisotropy in shape, and in the resin cured product test piece obtained by press molding, the fiber axis is oriented in the test piece surface direction which is perpendicular to the direction of measurement of the thermal conductivity, and therefore it is considered that the thermally conductive path along the fiber axis which is effective for improving the measured thermal conductivity cannot be effectively formed in the thickness direction of the test piece.

[0157] In samples B5, B6, as the thermally conductive substance, carbon fibers alone and alumina alone were added as in samples B3, B4, but the compounding amount was increased to 30 vol%. The compounding amount was the same as the compounding amount of the filler (the volume ratio of the filler) in samples Al to A5. In these samples B5, B6, the thermal conductivity was greatly improved as compared with sample Bl in which no filler was added. This result indicates that, as compared with samples B3, B4, because the addition amount of the thermally conductive substance was increased, the contact area between the filler particles was increased, and an effective thermally conductive path was formed. However, because the volume of the thermally conductive substance itself became large, the specific gravity of the composite material approached 1.4 times or more that of sample Bl, or further increased. The thermally conductive substance used in sample B5 was the same as that used in samples Al, A4, and the thermally conductive substance used in sample B6 was the same as that used in samples A2, A5, and these groups were compared with each other. Thus, in samples B5, B6, although the content of the thermally conductive substance was 4 times or more, the thermal conductivity obtained was not improved as compared with these samples Al, A4 and samples A2, A5, and in sample B5 which used carbon fibers, the thermal conductivity was rather reduced. As such, from the results of samples B3 to B6, in the case where a filler composed of a thermally conductive substance such as carbon fibers, alumina, etc. alone is used, it can be said that it is difficult to achieve both a low specific gravity and a high thermal conductivity. In particular, it can be said that in the case where a thermally conductive substance having a high anisotropy in shape such as carbon fibers is used alone, it is difficult to control the anisotropic orientation of the thermally conductive substance, and achieve a high thermal conductivity in the desired direction.

[0158] In the sample B7, in addition to the thermally conductive substance, the base material particles and the gel-like substance were used to constitute the filler, but the base material particles used were glass hollow particles which were not subjected to surface treatment. In this sample B7, as the thermally conductive substance, the same amount of carbon fibers as in the samples Al, A4 and B3 was contained, but the thermal conductivity of the sample B7 was considerably smaller than the values of the samples Al, A4 using the gel-like substance, and was close to the value of the sample B3 in which the carbon fibers were added alone as the thermally conductive substance. It is considered that in this sample B7, since the base material particles do not have a functional group on the surface which can form a chemical bond with the gel-like substance, the coating layer is not in a state of being firmly bound to the surface of the base material particles via a chemical bond. It is considered that, in correspondence thereto, in the sample B7, the thermally conductive substance is not in a state of stably remaining to coat the surface of the base material particles, but is in a state of coating a very small area of the surface of the base material particles, or is independently dispersed in the base resin from the base material particles.

[0159] Finally, the samples Al to A14 are compared with each other. First, in the group of the samples Al to A3 and the group of the samples A4, A5, the types of the thermally conductive substance used are different from each other. When these samples are compared with each other, in the samples Al, A4 in which carbon fibers are used as the thermally conductive substance, the thermal conductivity is significantly improved compared to the other samples in which alumina particles, magnesium oxide particles are used. This corresponds to the fact that the carbon fibers have higher thermal conductivity than the alumina, the magnesium oxide. The carbon fibers have high anisotropy in shape, and as described above with respect to the sample B3, although high thermal conductivity is exhibited in the direction along the fiber axis of orientation, in directions other than this, the effect of improvement in thermal conductivity is limited. However, as shown in the microscope image of the sample A4, by dispersing the carbon fibers into the gel-like substance, the carbon fibers are randomly dispersed into the coating layer, and by being incorporated into the base resin, the influence of the anisotropy in shape is reduced, and excellent thermal conductivity can be exhibited in any direction. Figure 3 A, by dispersing the carbon fibers into the gel-like substance, the carbon fibers are randomly dispersed into the coating layer, and by being incorporated into the base resin, the influence of the anisotropy in shape is reduced, and excellent thermal conductivity can be exhibited in any direction.

[0160] In the group of the samples Al, A4 and the group of the samples A2, A5, the types of the gelated polymer material used are different. However, in these groups, when the thermal conductivities are compared with each other, the thermal conductivities do not greatly change regardless of which type of gelated polymer material is used. From this, it can be said that if the thermally conductive substance can be dispersed and maintained, the type of the gel-like substance does not greatly affect the thermal conductivity of the obtained filler.

[0161] In Samples Al, A6 to A9, the amount of the mixed gel added to the base material (dry volume ratio of [gelled polymer] : [thermally conductive substance]) was different from one another, and the content of the thermally conductive substance was different from one another. The content of the thermally conductive substance increased in the order of Samples A6, A7, Al, A8, A9, and the thermal conductivity of the composite material increased in the order. That is, the more the content of the thermally conductive substance in the filler, the higher the effect of improving the thermal conductivity. In Sample A8, the dry volume ratio of [gelled polymer] : [thermally conductive substance] was 30 : 70, and a high thermal conductivity of 2.0 W / (m-K) or more was obtained in a region where the content of the thermally conductive substance was equal to or more than this ratio.

[0162] In Samples Al, A10 to A12, the amount of the mixed gel added to the base material (dry volume ratio of [mixed gel] : [base material particle]) was different from one another, and the content of the thermally conductive substance was different from one another. The content of the thermally conductive substance increased in the order of Samples A12, Al l, Al, A10, and the specific gravity of the composite material increased and the thermal conductivity improved in the order. That is, the larger the proportion of the coating layer in the filler and the thicker the coating layer, the higher the effect of improving the thermal conductivity. In Sample Al, the dry volume ratio of [mixed gel] : [base material particle] was 30 : 70, and a high thermal conductivity of 2.0 W / (m-K) or more was obtained in a region where the proportion of the coating layer was equal to or more than this ratio.

[0163] In Samples Al, A13, A14, the amount of the filler added to the composite material was different from one another. The amount of the filler added increased in the order of Samples A14, Al, A13, and the specific gravity of the composite material increased and the thermal conductivity improved in the order. That is, the more the filler added, the higher the effect of improving the thermal conductivity. A high thermal conductivity of 2.0 W / (m-K) or more was obtained in Samples Al, A14 where the amount of the filler added was more than 20 vol%. However, even if the amount of the filler added was increased to more than 50 vol% as in Sample A14, the effect of improving the thermal conductivity was limited.

[0164] The embodiments of the present disclosure have been described in detail above, but the present application is not limited to the above-described embodiments, and various changes can be made without departing from the spirit of the present application.

[0165] Explanation of symbols

[0166] 1 (thermally conductive) composite material

[0167] 10 (thermally conductive) filler

[0168] 11 base material particle (hollow particle)

[0169] 11a hollow portion

[0170] 11b shell

[0171] 12 coating layer

[0172] 12a gel-like substance

[0173] 12b thermally conductive substance

[0174] 2 base material

[0175] 5 wire harness

[0176] 51 insulated electric wire

[0177] 52 connector

[0178] 53 tape

Claims

1. A thermally conductive filler, the thermally conductive filler having: a base particle, and a coating layer that coats the base particle, the coating layer comprising: a gel-like substance that has a network-like crosslinked structure formed by forming a bond between molecules, that is bonded to a surface of the base particle via a chemical bond, and that coats the surface of the base particle; and a thermally conductive substance that is dispersed within a layer of the gel-like substance, and that is dispersed in the network-like crosslinked structure of the gel-like substance, and that has a higher thermal conductivity and a larger specific gravity than the base particle and the gel-like substance. The base particle is hollow. The base particle is constituted in the form of a glass hollow, and has a functional group on a surface that is capable of forming a chemical bond with a functional group possessed by the gel-like substance.

4. The thermally conductive filler according to any one of claims 1 to 3, wherein: the gel-like substance has a carbonyl group, the base particle has a basic group on a surface, the gel-like substance is bonded to the surface of the base particle via a chemical bond between the carbonyl group and the basic group. The gel-like substance comprises an organic polymer that has a carboxyl group as the carbonyl group. The base particle has a primary amino group as the basic group on a surface.

2. The thermally conductive filler of claim 1, wherein, The thermally conductive substance is constituted in the form of a particle that is anisotropic in shape.

3. The thermally conductive filler of claim 2, wherein, The thermally conductive substance is a carbon fiber. The thermally conductive filler has a specific gravity of 1.8 or less. The thermally conductive composite material comprises a base material and the thermally conductive filler according to any one of claims 1 to 9, The thermally conductive filler is dispersed in the base material. The base material comprises an organic polymer.

5. The thermally conductive filler of claim 4, wherein, The thermally conductive composite material has a specific gravity of 1.4 or less.

6. The thermally conductive filler of claim 4, wherein, The thermally conductive composite material has a thermal conductivity of 0.9 W / (m-K) or more at room temperature.

7. The thermally conductive filler of any one of claims 1-3, wherein, The wire harness comprises the thermally conductive composite material according to any one of claims 10 to 13.

8. The thermally conductive filler of claim 7, wherein, The manufacturing method comprises the following steps: a gel preparation step in which the gel-like substance is prepared in a state in which the thermally conductive substance is dispersed inside the gel-like substance; and a coating step in which the gel-like substance in which the thermally conductive substance is dispersed, which is prepared in the gel preparation step, is bonded to a surface of the base particle via a chemical bond.

9. The thermally conductive filler of any one of claims 1-3, wherein, The gel-like substance is bonded to the surface of the base particle via a chemical bond between the carbonyl group and the basic group.

10. A thermally conductive composite material, wherein, ​ ​ 11. The thermally conductive composite of claim 10, wherein, ​ 12. The thermally conductive composite of claim 10 or claim 11, wherein, ​ 13. The thermally conductive composite of claim 10 or claim 11, wherein, ​ 14. A wiring harness, wherein, ​ 15. A method for producing a thermally conductive filler, the thermally conductive filler according to any one of claims 1 to 9, wherein ​ ​ ​

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