Thermally conductive material and method for producing the same

Abstract

To provide a method for producing a high thermal conductivity material.SOLUTION: Composite particles in which flat particles are adhered or bonded to core particles are obtained by a granulation step of applying a mechanical force composed of one or more of a compressive force, a shear force, an impact force, and a frictional force to a blended powder containing substantially spherical core particles and flat particles that are softer than the core particles. The composite particles are formed, for example, by adhering shell particles obtained by fragmenting flat particles to the surfaces of core particles. The thermally conductive material may be composite particles themselves or 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 blended powder. The core particles are made of, for example, one or more of aluminum nitride, aluminum oxide, and silicon oxide. The flat particles are made of, for example, hexagonal boron nitride. The core particle may be coated with a resin.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] 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 made of fillers with excellent thermal conductivity and a matrix (e.g., resins containing elastomers, rubber, etc.) that holds the fillers.

[0003] Ceramic particles (including fibers) such as silica (SiO2), alumina (Al2O3), and aluminum nitride (AlN) have been used as fillers. Recently, boron nitride (BN) particles, which have excellent thermal conductivity, electrical insulation, and chemical stability, 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 or scale-like) particles composed of stacked hexagonal mesh layers similar to graphite. They exhibit thermal conductivity anisotropy, in which the thermal conductivity in the plane direction (the a-axis (100) direction) is greater than the thermal conductivity in the thickness direction (the c-axis (002) direction).

[0004] 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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2008-106231 [Patent Document 2] Patent Publication No. 2011-184507 [Patent Document 3] Patent Publication No. 2019-38912 [Patent Document 4] Patent Publication No. 2023-70122 Summary of the Invention [Problem to be solved by the invention]

[0006] 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) (

[0056] , Example 9 in Table 1). The thermal conductivity of this material is only 3.6 W / mK at most.

[0007] 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) (

[0027] , Table 4). The thermal conductivity of this sheet is only 7.2 W / mK at most.

[0008] Patent Document 3 proposes a thermally conductive foam sheet that has heat dissipation properties in addition to the flexibility required for shock absorption and sealing properties. 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 has been shown that when the average length (B) of the plate-like filler 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.

[0009] 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 anisotropic thermal conductivity of the h-BN particles to increase the thermal conductivity in the parallel direction compared to the thermal conductivity in the perpendicular direction.

[0010] The present invention has been made in view of the above circumstances, and has an object to provide a new thermally conductive material and the like. [Means for solving the problem]

[0011] As a result of extensive research, the inventors have succeeded in obtaining composite particles with high thermal conductivity by applying a strong mechanical force between the particles. By expanding on this result, the present invention, which will be described below, has been completed.

[0012] <<Method for manufacturing thermal conductive material>> The present invention is a method for producing 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, thereby obtaining composite particles in which the flat particles are adhered to or bonded to the core particles.

[0013] According to the manufacturing method of the present invention, composite particles exhibiting high thermal conductivity, or composite materials containing the same, can be obtained. Although the mechanism is not clear, it is thought that the application of a strong mechanical force between particles in the granulation process results in composite particles in which flat particles are adhered to or bonded to a core particle.

[0014] 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.

[0015] 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.

[0016] <Thermal Conductive Material> The present invention can also be understood as a thermally conductive material (composite particles, composite materials containing composite particles, etc.). For example, the present invention may be a thermally conductive material containing composite particles formed by adhering shell particles that are softer and finer than the core particles to approximately spherical core particles, or such a composite. An example of such a thermally conductive material is a composite material in which composite particles are dispersed in a matrix.

[0017] <Heat conduction material> The present invention can also be understood as a thermally conductive member. The thermally conductive 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 formed or processed into a desired shape. In this specification, the term "thermally conductive material" includes such thermally conductive members.

[0018] "others" Unless otherwise specified, "x to y" in this specification includes a lower limit value x and an upper limit value y. Any numerical value included in the various numerical values ​​or numerical ranges described in this specification may be used as a new lower limit or upper limit value to create a new range such as "a to b." 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.). [Brief explanation of the drawings]

[0019] [Figure 1] These are SEM images (including enlarged images) of composite particles of each sample. [Figure 2] 1 shows SEM images of a composite particle according to Sample 3 and a cross section of a composite material containing the composite particle. DETAILED DESCRIPTION OF THE INVENTION

[0020] One or more components arbitrarily selected from this specification may be added to the components of the present invention. 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.

[0021] 《Composite particles》 The composite particles consist of a core particle and flat particles (furthermore, shell particles) attached to (closely attached to or bonded to) the surface of the core particle. The details of these are as follows:

[0022] (1) Core particle The core particles may be of any type as long as they are substantially spherical. "Substantially spherical" refers to, for example, a particle having a circularity of 0.6 or more, or even 0.7 or more, as determined from an observation image (e.g., an SEM image) of the particle. The theoretical upper limit of the circularity is 1, but the practical upper limit is 0.98 or less.

[0023] Circularity is calculated from the maximum length of a particle (L / particle size) and its area (S), as follows: 4S / πL 2 Specifically, it can be determined by processing the observed image using software (such as ImageJ). Usually, the arithmetic mean value of the circularity determined for multiple particles within the field of view (650 μm × 450 μm) can be used as the "circularity."

[0024] 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 multiple particles may also 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."

[0025] When the particles are in the raw material powder stage, 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.

[0026] For particles contained in composite materials, 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.

[0027] 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.

[0028] The core particles may be of a single type or of multiple types, and may be, for example, one or more of aluminum nitride (AlN) particles, aluminum oxide (Al2O3) particles, silicon oxide (SiO2) particles, and the like.

[0029] (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.

[0030] "Flat" means that the maximum length of the particle (L / diameter) is large relative to the minimum length of the particle (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.

[0031] 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 of the shell particles (ds) to the particle size of the core particles (dc) is, for example, 1 / 10,000 to 1 / 10, 1 / 1,000 to 1 / 50, or 1 / 500 to 1 / 100.

[0032] "Soft" means that the flat particles or shell particles are more easily deformed in the 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.

[0033] The flat particles or shell particles may be of a single type or a combination of multiple types. For example, boron nitride particles (e.g., hexagonal boron nitride (h-BN)) particles, which have high thermal conductivity and are soft, are used. h-BN has properties similar to graphite, and can reduce friction on the surface of composite particles and improve the sliding properties between particles.

[0034] The flat particles or shell particles may only thinly cover the surface of the core particle. The coverage of the core particle surface with them 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.

[0035] 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 of the cross section of the composite particle.

[0036] The ratio (volume ratio: Vs / Vt) of the volume (Vs) of the flat particles (shell particles) to the total volume (Vt) of the core particles and flat particles (shell particles) is, for example, 1 to 50 volume %, 5 to 40 volume %, or 10 to 35 volume %.

[0037] 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 / extracted particle. If it is at the raw powder stage, the particle volume is calculated from the compound mass and true density.

[0038] 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.

[0039] (3) Binder The flat particles (shell particles) are physically attached or chemically bonded to the core particles when a strong mechanical force is applied. Therefore, a binder to bind the two particles together is not necessary. Reducing the binder reduces costs and improves thermal conductivity.

[0040] If a binder is added, it may be, for example, 1 to 15 volume %, 2 to 10 volume %, or 3 to 5 volume % 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.

[0041] The binder may be added to a blended powder consisting of core particles and flat particles, or may be pre-attached to the core particles. 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 resin may be, for example, 1 to 10 volume %, 1.5 to 8 volume %, or 2 to 3 volume % of the total amount of the core particles and resin.

[0042] (4) Granulation process Composite particles can be 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.

[0043] 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. Since this granulation process is usually a strong process, the processing time can 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.

[0044] In the present invention, 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, etc.

[0045] 《Composite material》 The composite material is formed by dispersing a filler containing at least composite particles in a matrix. In the composite material (thermal conductive material) used in electronic devices, the filler may also be made of a matrix non-conductive material (insulating material).

[0046] (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).

[0047] 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.

[0048] (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. Examples of surface treatments include hydrophobic treatments and coupling treatments. Specific examples include silane coupling treatments and fluorine plasma treatments. In addition to surface treatments being performed on the composite particles and raw material particles, a surface treatment agent (such as a coupling agent) may be added when mixing (kneading) the matrix and filler.

[0049] 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).

[0050] (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.

[0051] 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 or an intermediate material.

[0052] 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.

[0053] 《Application》 The composite particles and composite materials are used, for example, in heat-conducting members such as heat-dissipating sheets, substrates, and cases. The thermal conductivity thereof 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. The 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. [Example]

[0054] The present invention will be described in more detail with reference to specific examples in which composite particles are dispersed in a matrix to produce a composite material and evaluate its properties.

[0055] <<Creating Composite Particles>> Composite particles for each sample shown in Table 1 were prepared as follows.

[0056] [Samples 1-5] (1) Raw materials We prepared AlN powder (FAN-f80 / D50: 80 μm, manufactured by Furukawa Electronics Co., Ltd.) as the core particle source and BN powder (SGP / D50: 20 μm, manufactured by Denka Co., Ltd.) as the flat particle source. The AlN powder used was sieved to a particle size of -120 μm (see JIS Z 8801). The aspect ratio of the BN powder (AR = maximum length L / thickness t) was approximately 10.

[0057] (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 settings for the device, with "1" representing the maximum load within the range that does not overload. Specifically, this corresponds to a load power level not exceeding 400 / 4.0. "1 / 2" means a load approximately half that of "1," and specifically corresponds to a load power of 200 / 3.7 to 100 / 2.0.

[0058] 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.

[0059] (3) Observation The powder particles (composite particles) after granulation were observed using a scanning electron microscope (SEM). The SEM images are shown in Figure 1. 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)}] x 100(%).

[0060] [Samples 6 and 7] Resin-coated powder was also prepared by coating the AlN powder with epoxy resin. Specifically, a solvent (dichloromethane) was added to epoxy resin (EP-160, one-component heat-curing epoxy adhesive, manufactured by Cemedine Co., Ltd.) and mixed with the AlN powder. Mixing was performed at room temperature using a mixer (ARE-310 "Mixer" manufactured by Thinky Corporation) at 2000 rpm for 5 min. The mixture was vacuum-dried at room temperature (30 min) to volatilize the solvent. The resin amount (%) listed 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.

[0061] 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 way, composite particles containing resin were also produced.

[0062] 《Production of composite materials》 13 g of composite particle powder was mixed with 1 g of the above-mentioned epoxy resin and 0.5 g of solvent. As described above, this 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 material (compound) was filled into the cavity of a mold (die) heated by a heater and warm compression molded in the uniaxial direction. The mold temperature was 130°C and the molding pressure was 20 MPa, and this pressurized state was maintained for 30 minutes to thermally cure the resin. In this way, a rectangular columnar composite (12 mm x 12 mm x 20 mm) was obtained in which the composite particles (filler) were held in place by the resin.

[0063] 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.

[0064] "observation" The cross section of the composite material was observed using an 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 that composite material.

[0065] "measurement" (1) Porosity The porosity of the composite material was calculated. 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.

[0066] (2) Thermal conductivity The thermal conductivity of the composite was also measured. Thermal conductivity (λ) was determined using the nanoflash method (measurement device: NETZSCH LFA447). Specifically, thermal conductivity was calculated as λ = α · Cp · ρ using the thermal diffusivity (α) measured by the nanoflash method, the specific heat (Cp) determined by differential scanning calorimetry (DSC), and the density (ρ) determined by Archimedes' method.

[0067] In this study, thin plate-shaped samples perpendicular to the axial direction (pressure direction) (referred to as "perpendicular samples") and thin plate-shaped samples parallel to the axial direction (referred to as "parallel samples") were cut from each composite, and the thermal conductivity of each sample was determined. The thermal conductivity in the perpendicular direction / the thermal conductivity in the horizontal direction was approximately 1 to 1.3, and the difference in thermal conductivity between the two directions was small. In other words, the thermal conductivity of the composite was nearly isotropic. Therefore, only the thermal conductivity obtained from the perpendicular samples is shown in Table 1.

[0068] "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.

[0069] 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).

[0070] 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 consisting of shell particles (shell layer) was approximately 0.5 to 5 μm. These were determined by measuring the cross-sectional images of the particles.

[0071] (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 filler. Furthermore, Samples 2 to 4, 6, and 7 had significantly lower porosities than Sample 9, which used only BN particles as filler.

[0072] (3) Thermal conductivity As can be seen from Table 1, all of the composites using composite particles as fillers (samples 1 to 7) exhibited isotropic, high thermal conductivity. This tendency was also observed in the samples with resin-coated AlN particles (samples 6 and 7). The thermal conductivity of the composites of samples 1 to 7 was significantly higher than not only the composite using only AlN particles as filler (sample 8), but also the composite using only BN particles, which have a higher thermal conductivity (sample 9).

[0073] From the above, it was confirmed that the thermally conductive material of the present invention has excellent thermal conductivity and the like.

[0074] [Table 1]

Claims

1. A method for manufacturing a thermally conductive material includes 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. 2. The method for producing a thermally conductive material according to claim 1, wherein the granulating step is performed by stirring the blended powder between an inner wall surface of a cylindrical rotor and a tip end surface of the rotor.

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

7. A thermally conductive material comprising composite particles each having 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 the composite particles comprise a composite material dispersed in a matrix.

Images