Thermally conductive material and method for manufacturing same

Abstract

According to the present invention, composite particles in which flat particles are adhered or bonded to core particles are obtained by a granulation step for applying a mechanical force including at least one among a compressive force, a shear force, an impact force, or a frictional force to a powder mixture containing substantially spherical core particles and flat particles softer than the core particles. In the composite particles, for example, shell particles obtained by subdividing the flat particles are adhered to the surfaces of the core particles. The thermally conductive material may be composite particles themselves, or may be a composite material in which the composite particles are dispersed in a matrix. The granulation step is performed, for example, by rotating a rotor in a cylindrical container containing the powder mixture. The core particles comprise, for example, at least one among aluminum nitride, aluminum oxide, or silicon oxide. The flat particles comprise, for example, hexagonal boron nitride. The core particles may be coated with resin.

Description

Thermally conductive material and its manufacturing method CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Patent Application No. 2024-110628 filed in Japan on July 10, 2024, and the contents of the original application are incorporated by reference in their entirety.

[0002] This disclosure relates to thermally conductive materials and the like.

[0003] As elements, devices, and equipment become more dense and perform better, they generate more heat, and sufficient heat dissipation is required to ensure their functionality and lifespan. For example, in the case of electronic devices (semiconductor modules, etc.), heat is dissipated through heat dissipation materials with excellent thermal conductivity (heat sinks, housings, thermally conductive sheets, etc.). In addition to metals, composite materials are often used as heat dissipation materials. Composite materials are usually obtained from molded bodies of fillers with excellent thermal conductivity and matrices that hold the fillers (e.g., resins containing elastomers, rubber, etc.).

[0004] As the filler, for example, silica (SiO ２ ), alumina (Al ２ O ３ Ceramic particles (including fibers) such as aluminum nitride (AlN) have been used. Recently, boron nitride (BN) particles, which have excellent thermal conductivity, electrical insulation, chemical stability, and the like, have also been used as fillers. Boron nitride exists in a hexagonal normal pressure phase (called "h-BN") and a cubic high pressure phase (called "c-BN"), but h-BN particles are usually used as fillers. h-BN particles are plate-shaped (flat, scale-shaped) particles composed of stacked hexagonal mesh layers similar to graphite, and have thermal conductivity anisotropy in which the thermal conductivity in the plane direction (a-axis (100) direction) is greater than the thermal conductivity in the thickness direction (c-axis (002) direction).

[0005] Furthermore, composite materials have also been proposed in which a filler in which multiple types of particles are mixed or combined is held in a matrix, and for example, there are related descriptions in the following patent documents.

[0006] JP 2008-106231 A JP 2011-184507 A JP 2019-38912 A JP 2023-70122 A

[0007] Patent Document 1 proposes an adhesive sheet (composite material) for electronic devices in which a powder (filler) made by simply mixing boron nitride powder and spherical alumina powder is mixed in an epoxy resin (matrix). See paragraph 0056, Table 1, Example 9 of Patent Document 1. The thermal conductivity of the resulting composite material is only 3.6 W / mK at most.

[0008] Patent Document 2 proposes a sheet (composite material) in which a powder (filler) made by simply mixing alumina, boron nitride, and aluminum nitride is mixed in a silicone resin (matrix). See paragraph 0027, Table 4 of Patent Document 2. The thermal conductivity of the sheet is also only 7.2 W / mK at most.

[0009] Patent Document 3 proposes a thermally conductive foam sheet that has heat dissipation properties in addition to the flexibility required for impact absorption and sealing. The sheet is made of a foamed ethylene propylene diene rubber in which plate-like fillers made of boron nitride and spherical fillers made of magnesium oxide are dispersed. It shows that when the average length (B) of the plate-like fillers is greater than the average particle size (C) of the magnesium oxide (for example, when B / C = 2), the thermal conductivity of the sheet increases both before and after foaming.

[0010] Patent Document 4 proposes composite particles (filler) in which flat h-BN particles (coated particles, bridging particles) are bonded almost directly to roughly spherical AlN particles via a resin, or a composite material in which such composite particles are dispersed in a resin. This composite material utilizes the anisotropy of thermal conductivity of the h-BN particles to increase the thermal conductivity in the parallel direction relative to the thermal conductivity in the perpendicular direction.

[0011] This disclosure has been made in view of the above circumstances, and aims to provide a new thermally conductive material and the like.

[0012] As a result of intensive research, the inventors have succeeded in obtaining composite particles with high thermal conductivity by applying a strong mechanical force between the particles. By further developing this result, the disclosure of this specification has been completed.

[0013] <Method for manufacturing thermally conductive material> One of the disclosures is a method for manufacturing a thermally conductive material, which includes a granulation step in which a mechanical force consisting of one or more of compression force, shear force, impact force, and friction force is applied to a blended powder containing approximately spherical core particles and flat particles softer than the core particles, to obtain composite particles in which the flat particles are adhered to or bonded to the core particles.

[0014] This manufacturing method can produce composite particles that exhibit high thermal conductivity, or composite materials containing such particles. Although the mechanism is unclear, it is thought that the application of a strong mechanical force between particles during the granulation process results in composite particles in which flat particles are adhered to or bonded to a core particle.

[0015] When flat particles are subdivided during the granulation process, the subdivided flat particles (shell particles) adhere to the approximately spherical surface of the core particle, resulting in composite particles with a core-shell structure that cover the core particle approximately uniformly.

[0016] Such composite particles are generally approximately spherical and can exhibit high isotropic thermal conductivity. They also have excellent fluidity (reduced friction between particles), filling properties, dispersibility, etc., and can contribute to reducing the porosity of the composite material.

[0017] <Thermal Conductive Material> One of the disclosures can also be understood as a thermal conductive material (composite particles, composite materials containing composite particles, etc.). For example, the disclosure may be a thermal conductive material containing composite particles formed by attaching shell particles that are softer and finer than the core particles to a substantially spherical core particle, or such a composite material. An example of such a thermal conductive material is a composite material in which composite particles are dispersed in a matrix.

[0018] <Thermal Conduction Member> One of the disclosed materials can also be understood as a thermal conduction member. The thermal conduction member may be, for example, a raw material (bulk material) before processing, or a product (heat dissipation member, substrate, case, sheet, film, etc.) that has been molded or processed into a desired shape. In this specification, the term "thermal conduction material" includes such thermal conduction members.

[0019] <Others> Unless otherwise specified, "x to y" in this specification includes a lower limit value x and an upper limit value y. A new range such as "a to b" may be established by setting any numerical value included in the various numerical values ​​or numerical ranges described in this specification as a new lower limit or upper limit value. Unless otherwise specified, "x to y μm" in this specification means x μm to y μm. The same applies to other unit systems (W / mK, Ωm, etc.).

[0020] 1A and 1B are SEM images (including enlarged images) of composite particles of each sample. 1C are SEM images of a composite particle of sample 3 and a cross section of a composite material containing the composite particle. 1D are images of Fig. 1 expressed by black and white halftone dots. 1E are images of Fig. 2 expressed by black and white halftone dots.

[0021] One or more components arbitrarily selected from this specification may be added to the components of this disclosure. The content described in this specification may be a "product" or a "method." A method-like component may also be a component related to a product. Which embodiment is best depends on the target, required performance, etc.

[0022] <Composite Particles> Composite particles are composed of a core particle and flat particles (further subdivided shell particles) attached to (closely attached to or bonded to) the surface of the core particle. Details of these are as follows:

[0023] (1) Core Particles The type of core particle is not important as long as it is approximately spherical. The term "approximately spherical" means, for example, that the circularity determined from an observation image of the particle (e.g., an SEM image) is 0.6 or more, and preferably 0.7 or more. The theoretical upper limit of the circularity is 1, but the practical upper limit is 0.98 or less.

[0024] The circularity is calculated from the maximum length of the particle (L / particle size) and its area (S), as follows: 4S / πL ２ Specifically, the circularity can be determined by processing the observed image using software (ImageJ, etc.). Usually, the arithmetic mean value of the circularity determined for a plurality of particles within the field of view (650 μm × 450 μm) can be used as the "circularity."

[0025] The "particle size" is indicated, for example, by the maximum length (L) of a particle. The average value of the maximum lengths (L) determined for a plurality of particles may be used as the "particle size." For example, the arithmetic mean value of the particle size of each particle within the field of view (650 μm × 450 μm) of the above-mentioned observation image may be used as the "particle size."

[0026] When the particles are in the stage of raw material powder, the 50% diameter (D50: median diameter) determined from the particle size distribution obtained by laser diffraction may be used as the "particle size" in this specification. The nominal value (catalog value) for the raw material powder may also be used as the "particle size" in this specification.

[0027] For particles contained in a composite material, the particle size may be determined for the separated or extracted particles. Note that the "particle size" referred to in this specification does not depend on the particle shape (spherical (circular) or not). The content regarding particle size (particle size) also applies to composite particles, flat particles, and shell particles.

[0028] There is no particular limitation on the particle size of the core particles, but it is, for example, 10 to 200 μm, 20 to 150 μm, 35 to 120 μm, or 40 to 95 μm.

[0029] The core particles may be of a single type or a plurality of types, and may be, for example, aluminum nitride (AlN) particles, aluminum oxide (Al ２ O ３ ) particles, silicon oxide (SiO ２ ) particles.

[0030] (2) Flat particles / shell particles The flat particles attached to the approximately spherical surface of the core particle are softer than the core particle. Furthermore, the shell particles are smaller and softer than the core particle. The shell particles are obtained, for example, by subdividing the flat particles that are the raw material particles (powder). The subdivision of the flat particles may be carried out before the granulation process, but it is more efficient to carry out the subdivision in parallel with the granulation process. Furthermore, if the flat particles or shell particles have a higher thermal conductivity than the core particle, the thermal conductivity of the composite particle can be efficiently improved.

[0031] The term "flat" refers to a particle having a large maximum length (L / diameter) relative to its minimum length (t / thickness), regardless of whether it is flat or not. Depending on the degree of subdivision of the flat particles, shell particles are also generally considered to be flat. Shell particles may be flat or may have a curved surface (e.g., foil-like) that follows the approximately spherical surface of the core particle.

[0032] The specific particle sizes of the flat particles and shell particles are not critical, but the flat particles are, for example, 1 to 100 μm or 5 to 50 μm, and the shell particles are, for example, 0.01 to 10 μm, 0.05 to 5 μm, or 0.1 to 1 μm. The ratio (ds / dc) of the particle size (ds) of the shell particles to the particle size (dc) of the core particles is, for example, 1 / 10,000 to 1 / 10, 1 / 1,000 to 1 / 50, or 1 / 500 to 1 / 100.

[0033] The term "soft" means that the flat particles or shell particles are more easily deformed in their planar direction than the core particles, i.e., have low rigidity. Specific hardness or elastic modulus is not taken into account, but if we dare to say, the Mohs hardness is an index value relating to "softness," for example, AlN: 8, h-BN: 2.

[0034] The flat particles or shell particles may be of a single type or a plurality of types. For example, boron nitride particles (e.g., hexagonal boron nitride (h-BN)) particles, which have high thermal conductivity and are soft, are used. Note that h-BN has properties similar to graphite, and can reduce friction on the surface of the composite particles and improve the sliding properties between the particles.

[0035] The flat particles or shell particles may only thinly cover the surface of the core particle. The coverage of the core particle surface with the flat particles or shell particles is, for example, 60 to 100%, 70 to 98%, or 80 to 95%. The coverage can be determined, for example, by energy dispersive X-ray spectroscopy (EDX) of an observed image of the composite particle.

[0036] Since flat particles are generally more expensive than core particles, reducing the thickness of the flat particles or shell particles reduces the cost of the composite particles. The thickness of the coating layer (shell layer) of the core particle is, for example, 0.1 to 10 μm, 0.5 to 5 μm, or 1 to 3 μm. The thickness of the shell layer can be determined, for example, by image analysis of an SEM image obtained by observing the cross section of the composite particle.

[0037] The ratio of the volume (Vs) of the flat particles (shell particles) to the total volume (Vt) of the core particles and flat particles (shell particles) (volume ratio: Vs / Vt) is, for example, 1 to 50 volume %, 5 to 40 volume %, or 10 to 35 volume %.

[0038] The volume of a particle is calculated from its mass (content) and true density. For example, if the particle is contained in a thermal conductive material, the volume is calculated from the mass and true density of the separated and extracted particles. If it is at the raw powder stage, the particle volume is calculated from the compound mass and true density.

[0039] Auxiliary particles made of flat particles (such as h-BN particles) may be further attached to the shell layer. The particle size of such auxiliary particles is, for example, 5 to 40 μm or 10 to 20 μm.

[0040] (3) Binder: The flat particles (shell particles) are physically attached to or chemically bonded to the core particles by the application of a strong mechanical force. Therefore, a binder to bind the two particles together is not necessary. Reducing the binder reduces costs and improves thermal conductivity.

[0041] If a binder is added, it may be, for example, 1 to 15 vol %, 2 to 10 vol %, or 3 to 5 vol % of the total composite particles. The binder may be, for example, the same type or the same resin as the matrix of the composite material.

[0042] The binder may be added to a blended powder consisting of core particles and flat particles, or may be attached to the core particles in advance. If the core particles are pre-coated with a binder (e.g., resin), even a small amount of binder can effectively adhere the flat particles (shell particles) to the core particles. When the core particles are resin-coated, the amount of resin may be, for example, 1 to 10% by volume, 1.5 to 8% by volume, or 2 to 3% by volume relative to the total amount of the core particles and resin.

[0043] (4) Granulation Process Composite particles are obtained, for example, by applying a strong mechanical force (one or more of compression, shear, impact, friction, etc.) to a blended powder containing core particles and flat particles. The detailed mechanism is unclear. It is thought that at least the strong force acting between the core particles and flat particles causes the soft flat particles to strongly bond to the approximately spherical surface of the core particles. At this time, the flat particles are appropriately subdivided into shell particles, which cover the core particles in an approximately spherical shape.

[0044] The granulation process is carried out, for example, using a mechanofusion device (Nobilta NOB-MINI model manufactured by Hosokawa Micron Corporation). The blended powder between the cylindrical inner wall surface and the tip end surface of the rotor rotating therein is strongly agitated, applying strong mechanical forces such as shear, compression, impact, and friction between the powder particles. The gap between the inner wall surface and the tip end surface of the rotor is, for example, 0.5 to 2 mm or 1 to 1.5 mm, depending on the particle size of the blended powder. The rotor rotation speed is, for example, 800 to 2500 rpm or 1000 to 1500 rpm. Because this granulation process is typically intense processing, the processing time may be as short as, for example, 1 to 15 minutes or 3 to 10 minutes. The load power (kW / A) is, for example, 30 / 1.3 to 350 / 3.7.

[0045] In this disclosure, the state of the grain boundary and the mechanism by which the soft flat particles (shell particles) are firmly attached to or bonded to the surfaces of the core particles are not important. Depending on the grain boundary and mechanism, the granulation process can be appropriately referred to as a mechanochemical (reaction) process, a mechanical synthesis process, a solid-state reaction process, or the like.

[0046] <Composite Material> A composite material is formed by dispersing a filler containing at least composite particles in a matrix. In a composite material (thermal conductive material) used in an electronic device, etc., the filler may also be made of a matrix non-conductive material (insulating material).

[0047] (1) Matrix The matrix is ​​made of, for example, a resin (including rubber, elastomer, etc.). The resin may be a thermosetting resin or a thermoplastic resin. The thermosetting resin is appropriately subjected to a heat curing treatment (curing treatment).

[0048] Examples of thermosetting resins include epoxy resins, phenolic resins, silicone resins, etc. Examples of thermoplastic resins include polystyrene, polymethyl methacrylate, polycarbonate, polyphenylene sulfide, etc. Examples of rubbers include ethylene-propylene-diene rubber (EPDM), butyl rubber, etc.

[0049] (2) Filler The filler may be surface-treated to enhance its affinity with the matrix. The surface treatment improves the dispersibility, packing ability, and adhesion of the filler in the matrix, thereby improving the thermal conductivity of the thermal conductive material. The surface treatment is, for example, a hydrophobic treatment or a coupling treatment. Specifically, it includes a silane coupling treatment and a fluorine plasma treatment. In addition to the surface treatment of the composite particles or raw material particles, a surface treatment agent (such as a coupling agent) may be added when mixing (kneading) the matrix and the filler.

[0050] The filler is contained in, for example, 60 to 93 volume %, 70 to 90 volume %, or 75 to 87 volume % of the entire composite. The filler filling rate (vol %) is determined from the blending amount and density of the raw materials during the production of the thermal conductive material. The filler filling rate in the composite may be determined from the amount of filler extracted and separated from the composite, or may be determined indirectly or alternatively from an observation image (SEM image, etc.) of the composite (cross section).

[0051] (3) Manufacturing Method The composite material can be obtained, for example, by pressure molding a compound (a granular mixture or kneaded product) consisting of a filler containing composite particles and a matrix (such as a resin) into a desired shape. The molding pressure is, for example, 10 to 100 MPa, or even 20 to 50 MPa. The molding process may be performed by compression molding, injection molding, transfer molding, or the like.

[0052] The molding process may be cold molding, which is performed at room temperature, or warm molding, which is performed by heating the mixture. Warm molding may be performed, for example, at a temperature at which the resin softens or melts. The molded body (thermal conductive material) may be in the shape of the final product or a shape close to that, or may be a raw material to be processed, an intermediate material, or the like.

[0053] The composite material is manufactured by appropriately referring to the contents described in JP 2023-70122 A. Therefore, part or all of the contents described in that publication are incorporated herein by reference.

[0054] <Applications> Composite particles and composite materials are used, for example, in heat-conducting materials such as heat-dissipating sheets, substrates, and cases. The thermal conductivity can be, for example, 10 to 40 W / mK, 13 to 30 W / mK, or 15 to 25 W / mK. If the thermal conductivity of the composite material is approximately isotropic, the flexibility of its manufacturing method and application can be expanded. Composite materials used in electronic devices and the like have a specific resistance of, for example, 10 ５ ~10 １５ Ωm or 10 ８ ~10 １４ It is preferable that the resistance is Ωm.

[0055] A composite material in which composite particles are dispersed in a matrix was produced and its properties were evaluated. This disclosure will be explained in more detail with reference to such specific examples.

[0056] <Preparation of Composite Particles> Composite particles for each sample shown in Table 1 were prepared as follows.

[0057] (Samples 1 to 5) (1) Raw Materials An AlN powder (FAN-f80 / D50: 80 μm, manufactured by Furukawa Electronics Co., Ltd.) serving as a core particle source and a BN powder (SGP / D50: 20 μm, manufactured by Denka Co., Ltd.) serving as a flat particle source were prepared. The AlN powder used was sieved to a particle size of -120 μm (see JIS Z 8801). The aspect ratio (AR = maximum length L / thickness t) of the BN powder was approximately 10.

[0058] (2) Granulation (Mechanofusion) 70 g of AlN powder and 1.5 g of BN powder were placed in a mechanofusion device (Nobilta NOB-MINI model manufactured by Hosokawa Micron Corporation) and processed. The processing conditions are also shown in Table 1. The rotation speeds shown in Table 1 are the set values ​​for the device, and "1" means the maximum load within the range that does not cause overload. Specifically, this corresponds to a level where the load power does not exceed 400 / 4.0. "1 / 2" means a load that is about half that of "1," and specifically corresponds to a load power of 200 / 3.7 to 100 / 2.0.

[0059] True density of AlN particles: 3.3 g / cm ３ , true density of h-BN particles: 2.27 g / cm ３ The blending ratios (volume ratios) obtained by converting the mass ratios of the above-mentioned powders into volume ratios are also shown in Table 1.

[0060] (3) Observation The powder particles (composite particles) after granulation were observed with a scanning electron microscope (SEM). The SEM images are shown in Figure 1. Figure 3 is a black and white halftone dot representation of Figure 1. In addition, the coverage of the AlN particles by the h-BN particles was calculated for each sample and is shown in Figure 1. The coverage was calculated as follows: the areas of Al (aluminum) and B (boron) were measured using EDX, and then the coverage was calculated as [(area of ​​B) / {(area of ​​Al)+(area of ​​B)}]×100(%).

[0061] (Samples 6 and 7) Resin-coated powders were also prepared by coating the above-mentioned AlN powder with epoxy resin. Specifically, a solvent (dichloromethane) was added to an epoxy resin (EP-160, one-component heat-curing epoxy adhesive, manufactured by Cemedine Co., Ltd.), and the resulting mixture was mixed with the AlN powder. Mixing was carried out at room temperature using a mixer (ARE-310 "Mixer" manufactured by Thinky Corporation) at 2000 rpm for 5 minutes. The mixture was vacuum-dried at room temperature (30 minutes) to volatilize the solvent. The resin amount (%) shown in Table 1 is the volume ratio of the resin to the total amount of AlN powder, BN powder, and epoxy resin. The volume ratio was calculated from the blended mass ratio and the true density of each.

[0062] 70 g of resin-coated powder and 1.5 g of BN powder were granulated in the same manner as in Samples 1 to 5. In this manner, composite particles containing resin were also produced.

[0063] <Production of Composite Material> 13 g of composite particle powder was mixed with 1 g of the aforementioned epoxy resin and 0.5 g of solvent. As described above, the mixture was mixed at room temperature using a mixer at 2000 rpm for 5 minutes, followed by vacuum drying (30 minutes) to volatilize the solvent. The resulting kneaded mixture (compound) was filled into the cavity of a heater-heated mold (die) and subjected to uniaxial warm compression molding. The mold temperature was 130°C and the molding pressure was 20 MPa. The pressurized state was maintained for 30 minutes to thermally cure the resin. In this way, a rectangular column-shaped composite (12 mm x 12 mm x 20 mm) was obtained in which the composite particles (filler) were held in the resin.

[0064] For comparison, a composite material (sample 8) using only the above-mentioned AlN powder instead of the composite particle powder, and a composite material (sample 9) using only the above-mentioned BN powder were also produced in the same manner.

[0065] <Observation> The cross section of the composite material was observed by SEM. As an example, an SEM image of the cross section of the composite material of Sample 3 is shown in Figure 2. Figure 2 also shows an SEM image of the composite particles used in the composite material. Figure 4 is a diagram in which Figure 2 is expressed using black and white halftone dots.

[0066] <Measurements> (1) Porosity The porosity of the composite material was determined. The porosity was calculated from the apparent density (ρ) and theoretical density (ρth) of the composite material as {(ρth - ρ) / ρth} x 100 (%). ρ was calculated from the measured mass and volume (Archimedes' method) of the composite material. ρth was calculated based on the blending ratio and density of the raw materials (particles and resin) used to produce the composite material. The results are also shown in Table 1.

[0067] (2) Thermal Conductivity The thermal conductivity of the composite was also measured. The thermal conductivity (λ) was determined by the Nanoflash method (measurement device: LFA447 manufactured by NETZSCH). Specifically, the thermal conductivity was calculated as λ = α Cp ρ from the thermal diffusivity (α) measured by the Nanoflash method, the specific heat (Cp) measured by a differential scanning calorimeter (DSC), and the density (ρ) measured by the Archimedes method.

[0068] At this time, a thin plate-shaped sample perpendicular to the axial direction (pressure direction) (referred to as a "vertical sample") and a thin plate-shaped sample parallel to the axial direction (referred to as a "parallel sample") were cut out from each composite sample, and the thermal conductivity of each sample was determined. The thermal conductivity in the vertical direction / thermal conductivity in the horizontal direction was approximately 1 to 1.3, and the difference in thermal conductivity between the two was small. In other words, the thermal conductivity characteristics of the composite were nearly isotropic. Therefore, Table 1 shows only the thermal conductivity obtained from the vertical sample.

[0069] <Evaluation> (1) Composite particles As can be seen from Figure 1, granulation (mechanofusion) caused soft h-BN particles and their fragmented particles to adhere (adhere or bond) along the surface of the spherical core particle.

[0070] As in sample 1, when the treatment time was long and the applied mechanical force (shear force, etc.) and energy became excessive, surface cracks like fissures were observed on the surface (shell) or core particle (core).

[0071] Samples 2 to 7 all had a high coverage rate, and the size (particle diameter) of the shell particles was approximately 5 to 40 μm. The thickness of the layer made of shell particles (shell layer) was approximately 0.5 to 5 μm. These were determined by measuring the cross-sectional images of the particles.

[0072] (2) Porosity As can be seen from Table 1, all composites using composite particles as fillers had low porosities. Samples 1 and 5 had relatively higher porosities than the other samples. It is believed that the high porosity of Sample 1 was due to the unevenness of the BN particles (shell particles) attached to the surface. It is believed that the high porosity of Sample 5 was due to the low coverage of the BN particles (shell particles), which increased friction between the AlN particles. Samples 1 to 7, which used composite particles as fillers, had significantly lower porosities than Sample 8, which used only AlN particles as fillers. Furthermore, Samples 2 to 4, 6, and 7 had significantly lower porosities than Sample 9, which used only BN particles as fillers.

[0073] (3) Thermal Conductivity As can be seen from Table 1, all of the composites (samples 1 to 7) that used composite particles as a filler exhibited isotropic, high thermal conductivity. This tendency was also observed in the samples with resin-coated AlN particles (samples 6 and 7). The composites of samples 1 to 7 had significantly higher thermal conductivity than not only the composite (sample 8) that used only AlN particles as a filler, but also the composite (sample 9) that used only BN particles, which have a higher thermal conductivity.

[0074] From the above, it was confirmed that the disclosed thermally conductive material has excellent thermal conductivity and the like.

[0075]

Claims

1. A method for manufacturing a thermally conductive material, comprising a granulation step in which a mechanical force consisting of one or more of compression force, shear force, impact force, or friction force is applied to a blended powder containing approximately spherical core particles and flat particles softer than the core particles, thereby obtaining composite particles in which the flat particles are adhered to or bonded to the core particles.

2. The method for producing a thermal conductive material according to claim 1, wherein the granulation step is performed by stirring the blended powder between the cylindrical inner wall surface and the rotor tip surface.

3. The method for producing a thermally conductive material according to claim 1, wherein the composite particles are formed by coating the surfaces of the core particles with shell particles formed by dividing the flat particles.

4. The method for manufacturing a thermal conductive material according to claim 1, wherein the blended powder contains a resin.

5. The method for producing a thermally conductive material according to claim 4, wherein the resin is attached to the core particles before the granulation step.

6. A method for producing a thermal conductive material according to claim 1, wherein the core particles are made of one or more of aluminum nitride, aluminum oxide, and silicon oxide, and the flat particles are made of hexagonal boron nitride.

7. A thermally conductive material comprising composite particles each consisting of a substantially spherical core particle to which shell particles that are softer and finer than the core particle are attached.

8. The thermally conductive material of claim 7, wherein said composite particles comprise a composite material dispersed in a matrix.

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