JP7555438B2 - Composite material, heat dissipation material, and method for manufacturing heat dissipation material - Google Patents

Description

This disclosure relates to composite materials, heat dissipation materials, and methods for manufacturing heat dissipation materials.

Boron nitride has lubricity, high thermal conductivity, and insulating properties, and is used in a variety of applications, including as a solid lubricant, release agent, cosmetic ingredient, heat dissipation material, and heat-resistant insulating sintered body.

For example, Patent Document 1 discloses a hexagonal boron nitride powder that can be filled into a resin to impart high thermal conductivity and high dielectric strength to the resulting resin composition, the hexagonal boron nitride powder being characterized by containing agglomerated particles consisting of primary particles of hexagonal boron nitride, having a BET specific surface area of 0.7 to 1.3 m ² /g, and having an oil absorption of 80 g/100 g or less as measured in accordance with JIS K 5101-13-1.

JP 2016-160134 A

The boron nitride particles described above may be used, for example, in the form of a heat dissipation material (heat dissipation sheet) that is dispersed in a resin and formed into a sheet. In this case, in order to increase the thermal conductivity of the heat dissipation material in the thickness direction, it is desirable to disperse the boron nitride particles in the heat dissipation material so that a continuous heat conduction path is formed in the thickness direction of the heat dissipation material. However, it is not necessarily easy to control the heat conduction path formed by the boron nitride particles in the heat dissipation material.

The object of the present invention is to facilitate control of the thermal conduction paths formed by boron nitride particles in heat dissipation materials.

One aspect of the present invention is a composite material comprising an inorganic substrate and a plurality of boron nitride particles disposed on one surface of the inorganic substrate, the plurality of boron nitride particles extending from the inorganic substrate.

In this composite material, multiple boron nitride particles are arranged so that they extend from the substrate. By filling the spaces between the boron nitride particles of this composite material and inside the boron nitride particles with resin, a heat dissipation material can be produced while maintaining the boron nitride particles in a state extended in the thickness direction of the heat dissipation material. This makes it easier for the boron nitride particles to form continuous heat conduction paths in the thickness direction of the resulting heat dissipation material. In other words, by using this composite material, it becomes easier to control the heat conduction paths formed by the boron nitride particles in the heat dissipation material, compared to, for example, using a powder of boron nitride particles mixed with resin.

The inorganic substrate may include one selected from the group consisting of carbon and boron nitride.

The average length of the multiple boron nitride particles in the extension direction may be 50 μm or more.

Another aspect of the present invention is a method for producing a heat dissipating material, comprising a step of filling resin between a plurality of boron nitride particles of a composite material. This method for producing a heat dissipating material may further comprise a step of removing the inorganic base material after the above step.

Another aspect of the present invention is a sheet-shaped heat dissipation material containing a plurality of boron nitride particles and a resin, in which the plurality of boron nitride particles extend from one surface of the heat dissipation material toward the other surface opposite the one surface. The average length of the plurality of boron nitride particles in the extension direction may be 50 μm or more.

The present invention makes it easy to control the thermal conduction paths formed by boron nitride particles in heat dissipation materials.

1 is a graph showing the results of X-ray diffraction measurement of boron nitride particles of Example 1. 1 is a SEM image of the composite material of Example 1. 1 is a SEM image of the composite material of Example 2. 13 is a microscope image of a cross section in the thickness direction of the heat dissipation material of Example 3.

The following describes in detail an embodiment of the present invention. The composite material according to one embodiment comprises an inorganic substrate and a plurality of boron nitride particles arranged on one surface of the inorganic substrate.

The inorganic substrate may be an inorganic substrate that can withstand heating (has heat resistance) in the production process of the composite material production method described below. The inorganic substrate may be, for example, an inorganic substrate containing an inorganic material having a melting point or sublimation point of 1500°C or higher. The content of the inorganic material having a melting point or sublimation point of 1500°C or higher may be, for example, 95% by mass or higher, 98% by mass or higher, or 99% by mass or higher based on the total amount of the inorganic substrate. The inorganic substrate may be an inorganic substrate consisting only of an inorganic material having a melting point or sublimation point of 1500°C or higher. The melting point or sublimation point of the inorganic material may be appropriately selected according to the heating temperature in the production process, and may be 1600°C or higher, 1800°C or higher, 2000°C or higher, 2200°C or higher, or 2400°C or higher. Examples of inorganic materials having a melting point or sublimation point of 1500°C or higher include carbon, boron carbide, silicon carbide, silicon nitride, alumina, boron nitride, and the like.

The inorganic substrate may be an inorganic substrate in which the weight change rate of the inorganic substrate before and after heating is 5% or less when heated at 1500°C and 0.1 MPa for 1 hour in a nitrogen atmosphere (for example, an atmosphere containing 95% or more by volume of nitrogen gas). The weight change rate of the inorganic substrate before and after heating is calculated by the following formula, where W1 is the weight of the inorganic substrate before heating and W2 is the weight of the inorganic substrate after heating. The inorganic substrate used for measuring the weight change rate is heated at 200°C for 2 hours and dried. Weight change rate = (W1 - W2) / W1 x 100

The inorganic substrate may be, for example, in the form of a sheet, a plate, a rod, etc. Examples of the inorganic substrate include a carbon sheet (graphite sheet), a carbon plate, a carbon rod, a carbon crucible, a boron nitride sheet, a boron nitride plate, a boron nitride crucible, etc. The thickness of the sheet-like inorganic substrate may be, for example, 100 μm or more and 500 μm or less.

The multiple boron nitride particles each extend from the inorganic substrate as a starting point. The inorganic substrate and the boron nitride particles may be chemically bonded to each other at the starting point. The boron nitride particles may extend linearly or curvedly. The boron nitride particles may extend by branching into two or more directions during the extension. The extension direction of the boron nitride particles may be approximately perpendicular to the surface of the inorganic substrate on which the boron nitride particles are arranged, or may be at an angle from the perpendicular direction. The extension direction of the boron nitride particles means the direction connecting the starting point of the boron nitride particles and the point at which the linear distance from the starting point is the maximum.

The average length in the extension direction of the boron nitride particles may be 50 μm or more, 80 μm or more, 100 μm or more, 125 μm or more, 150 μm or more, or 200 μm or more, and may be 500 μm or less, 400 μm or less, or 300 μm or less.

The average length in the extension direction of the boron nitride particles can be measured using a laser microscope (e.g., "Optelics HYBRID" manufactured by Lasertec Corporation). Specifically, first, the measurement range is set for the composite material so as to include the thickness of the inorganic substrate and the maximum length of the boron nitride particles, and the surface shape of the composite material is measured. Next, the length in the extension direction of the boron nitride particles is measured from the cross-sectional profile of the measured surface shape of the composite material. This measurement of the length in the extension direction is performed for 20 boron nitride particles, and the average value is taken as the average length in the extension direction of the boron nitride particles.

The boron nitride particles may have an elongated shape as described above. The average aspect ratio of the boron nitride particles may be, for example, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, 2.0 or more, 3.0 or more, 5.0 or more, or 7.0 or more, and may be 12.0 or less, 9.0 or less, or 8.0 or less.

The average aspect ratio of a boron nitride particle is defined as the average value (L1 _/ L2) of the ratio of the length of the boron nitride particle in the stretching direction ( _L1 ) to the length of the boron nitride particle in the direction perpendicular to the stretching direction for _{20 boron} nitride particles. The length of the boron nitride particle in the direction perpendicular to the stretching direction can be measured from the cross-sectional profile of the surface shape of the composite material in the same manner as for the length in the stretching direction.

Each boron nitride particle may be solid or hollow. When the boron nitride particle is hollow, the boron nitride particle may have an outer shell formed by boron nitride and a hollow portion surrounded by the outer shell. The hollow portion may be formed along the extension direction of the boron nitride particle, and may have a shape that is approximately similar to the external shape of the boron nitride particle. When the boron nitride particle is hollow, the tip of the boron nitride particle may be an open end, and the open end may be connected to the hollow portion described above.

The number of boron nitride particles arranged per unit area of the inorganic substrate may be, for example, 10 pieces/mm2 or ^more , 20 pieces/mm2 or ^more , or 30 pieces/ ^mm2 or more, and may be 300 pieces/mm2 ^{or less} , 200 pieces/mm2 or ^less , or 100 pieces/mm2 or ^less .

Next, a method for producing the above-mentioned composite material will be described below. The composite material can be produced, for example, by a production method including a step of placing a mixture containing boron carbide and boric acid and an inorganic substrate in a container formed of a carbon material (placement step), and a step of generating boron nitride particles on the inorganic substrate by heating and pressurizing the container in a nitrogen atmosphere (generation step). Another embodiment of the present invention is a method for producing such a composite material.

The container formed of a carbon material is a container capable of housing the mixture and the inorganic substrate. The container may be, for example, a carbon crucible. The container is preferably a container whose opening can be covered to increase airtightness. In the placement step, for example, the mixture may be placed at the bottom of the container, and the inorganic substrate may be placed so as to be fixed to the sidewall surface or the inside of the lid of the container. Details of the inorganic substrate are the same as those described in the above embodiment (composite material).

The boron carbide in the mixture may be, for example, in powder form (boron carbide powder). The boric acid in the mixture may be, for example, in powder form (boric acid powder). The mixture may be obtained, for example, by mixing boron carbide powder and boric acid powder by a known method.

Boron carbide powder can be produced by known production methods. For example, one method for producing boron carbide powder is to mix boric acid with acetylene black, and then heat the mixture in an inert gas (e.g., nitrogen gas) atmosphere at 1800 to 2400°C for 1 to 10 hours to obtain aggregated boron carbide particles. The aggregated boron carbide particles obtained by this method can be crushed, sieved, washed, impurities removed, dried, etc. as appropriate to obtain boron carbide powder.

The average particle size of the boron carbide powder can be adjusted by adjusting the grinding time of the aggregated carbon boron particles. The average particle size of the boron carbide powder may be 5 μm or more, 7 μm or more, or 10 μm or more, and may be 100 μm or less, 90 μm or less, 80 μm or less, or 70 μm or less. The average particle size of the boron carbide powder can be measured by a laser diffraction scattering method.

The mixing ratio of boron carbide and boric acid can be selected appropriately. From the viewpoint that boron nitride particles tend to become large, the content of boric acid in the mixture is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 8 parts by mass or more, per 100 parts by mass of boron carbide, and may be 100 parts by mass or less, 90 parts by mass or less, 80 parts by mass or less, or 70 parts by mass or less.

The mixture containing boron carbide and boric acid may further contain other components. Examples of the other components include silicon carbide, carbon, iron oxide, and the like. When the mixture containing boron carbide and boric acid further contains silicon carbide, it becomes easier to obtain boron nitride particles that do not have open ends.

The inside of the container is a nitrogen atmosphere containing, for example, 95% or more by volume of nitrogen gas. The content of nitrogen gas in the nitrogen atmosphere is preferably 95% or more by volume, more preferably 99.9% or more by volume, and may be substantially 100% by volume. In addition to nitrogen gas, the nitrogen atmosphere may also contain ammonia gas, etc.

The heating temperature is preferably 1450°C or higher, more preferably 1600°C or higher, and even more preferably 1800°C or higher, from the viewpoint that boron nitride particles tend to grow large. The heating temperature may be 2400°C or lower, 2300°C or lower, or 2200°C or lower.

The pressure applied during pressing is preferably 0.3 MPa or more, and more preferably 0.6 MPa or more, from the viewpoint that the boron nitride particles tend to become large. The pressure applied during pressing may be 1.0 MPa or less, or 0.9 MPa or less.

The time for which heating and pressurization are performed is preferably 3 hours or more, and more preferably 5 hours or more, from the viewpoint that boron nitride particles tend to become large. The time for which heating and pressurization are performed may be 40 hours or less, or 30 hours or less.

In this manner, the above-mentioned boron nitride particles are formed on the inorganic substrate, and a composite material is obtained in which multiple boron nitride particles extend from the inorganic substrate. The particles formed on the inorganic substrate are boron nitride particles, which can be confirmed by recovering a portion of the particles from the inorganic substrate, performing X-ray diffraction measurement on the recovered particles, and detecting a peak derived from boron nitride.

The composite material obtained in the above manner can be used as a heat dissipation material by filling the spaces between the boron nitride particles of the composite material with resin. That is, another embodiment of the present invention is a method for producing a heat dissipation material, which includes a step of filling the spaces between the boron nitride particles of the composite material with resin (filling step).

Examples of resins include epoxy resin, silicone resin, silicone rubber, acrylic resin, phenolic resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyimide, polyamideimide, polyetherimide, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, wholly aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide-modified resin, ABS (acrylonitrile-butadiene-styrene) resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin, etc.

The viscosity of the resin at 25°C may be 0.1 Pa·s or more, 0.3 Pa·s or more, or 0.5 Pa·s or more, and may be 200 Pa·s or less, 150 Pa·s or less, or 120 Pa·s or less. In this specification, viscosity refers to the viscosity measured using a rotational viscometer at a shear rate of 10 (1/sec).

In the filling process, the amount of resin to be filled may be adjusted as appropriate depending on the form of use of the heat dissipation material, the required characteristics, etc. The amount of resin to be filled may be, for example, 15 vol.% or more, 20 vol.% or more, 30 vol.% or more, 40 vol.% or more, 50 vol.% or more, or 60 vol.% or more based on the total volume of the heat dissipation material, and may be 70 vol.% or less, 60 vol.% or less, 50 vol.% or less, or 40 vol.% or less.

In the filling step, the spaces between the boron nitride particles of the composite material may be filled with only resin, or with a mixture containing resin and other components. Examples of other components include a curing agent. The curing agent may be any agent that can harden the resin, and is selected appropriately depending on the type of resin. Examples of curing agents used together with the epoxy resin include phenol novolac compounds, acid anhydrides, amino compounds, and imidazole compounds. The amount of curing agent added may be, for example, 0.5 parts by mass or more or 1.0 parts by mass or more, and 15 parts by mass or less or 10 parts by mass or less, relative to 100 parts by mass of the resin.

Other components may be inorganic fillers, curing accelerators (curing catalysts), coupling agents, wetting and dispersing agents, surface conditioners, etc.

The inorganic filler may be a thermally conductive filler such as aluminum oxide, magnesium oxide, silicon oxide, zinc oxide, boron nitride, silicon nitride, aluminum nitride, graphite, etc.

In the filling process, the amount of inorganic filler to be filled may be adjusted as appropriate depending on the form of use of the heat dissipation material, the required characteristics, etc. The amount of inorganic filler to be filled may be, for example, vol.% or more, 3 vol.% or more, 5 vol.% or more, 10 vol.% or more, 12 vol.% or more, or 15 vol.% or more, based on the total volume of the heat dissipation material, and may be vol.% or less, 35 vol.% or less, 30 vol.% or less, or 20 vol.% or less.

Examples of curing accelerators (curing catalysts) include phosphorus-based curing accelerators such as tetraphenylphosphonium tetraphenylborate and triphenylphosphate, imidazole-based curing accelerators such as 2-phenyl-4,5-dihydroxymethylimidazole, and amine-based curing accelerators such as boron trifluoride monoethylamine.

Coupling agents include silane-based coupling agents, titanate-based coupling agents, and aluminate-based coupling agents. Chemical bonding groups contained in these coupling agents include vinyl groups, epoxy groups, amino groups, methacryl groups, and mercapto groups.

Wetting and dispersing agents include phosphate ester salts, carboxylate esters, polyesters, acrylic copolymers, block copolymers, etc.

Examples of surface conditioners include acrylic surface conditioners, silicone surface conditioners, vinyl surface conditioners, and fluorine surface conditioners.

The viscosity of the mixture at 25°C may be 0.1 Pa·s or more, 0.3 Pa·s or more, or 0.5 Pa·s or more, and may be 200 Pa·s or less, 150 Pa·s or less, or 120 Pa·s or less. The filling amount of the mixture may be, for example, 15 vol% or more, 20 vol% or more, 30 vol% or more, 40 vol% or more, 50 vol% or more, or 60 vol% or more, and 70 vol% or less, 60 vol% or less, 50 vol% or less, or 40 vol% or less, based on the total volume of the heat dissipation material.

The method for producing a heat dissipation material may further include a step of removing the inorganic base material (removal step) after the filling step. In the removal step, the method for removing the inorganic base material may include peeling off the inorganic base material.

The method for manufacturing a heat dissipation material may further include a step of curing the resin (curing step) after the filling step. The method for curing the resin is appropriately selected depending on the type of resin (and the curing agent used if necessary). For example, when the resin is an epoxy resin and the above-mentioned curing agent is used together, the resin can be cured by heating in the curing step.

The method for producing a heat dissipating material may further include a processing step of processing the obtained heat dissipating material into a desired shape after the filling step and the curing step. For example, when the composite material is in a sheet form, the processing step may be a step of polishing the surface of the composite material opposite to the inorganic substrate to adjust the thickness of the obtained heat dissipating material. The method for producing a heat dissipating material may include a processing step before and/or after the above-mentioned removal step.

In this manner, a heat dissipating material containing a plurality of boron nitride particles and a resin can be obtained. In the heat dissipating material obtained by the above-mentioned manufacturing method, since the plurality of boron nitride particles in the composite material extend from the inorganic substrate as a starting point, the plurality of boron nitride particles in the heat dissipating material also extend in a specific direction. For example, when the heat dissipating material is in a sheet form, the plurality of boron nitride particles may extend from one surface (the surface that was in contact with the inorganic substrate) of the heat dissipating material as a starting point toward the other surface (the surface parallel to the one surface) opposite the one surface. That is, another embodiment of the present invention is a sheet-shaped heat dissipating material containing a plurality of boron nitride particles and a resin, in which the plurality of boron nitride particles extend from one surface (one main surface) of the heat dissipating material as a starting point toward the other surface (the other main surface) opposite the one surface.

In a sheet-like heat dissipation material, the fact that multiple boron nitride particles extend from one side of the heat dissipation material toward the opposite side can be confirmed by observing a cross section of the heat dissipation material in the thickness direction using a microscope.

The phrase "extending toward the other surface opposite to one surface" includes not only the case where the extension direction of the multiple boron nitride particles coincides with the direction of the perpendicular line connecting the one surface and the other surface (i.e., the thickness direction of the sheet-like heat dissipating material), but also the case where the extension direction is inclined with respect to the perpendicular line direction. The extension direction of the multiple boron nitride particles may be inclined at an angle of 45° or less, 40° or less, 30° or less, 20° or less, or 10° or less with respect to the perpendicular line direction. The extension directions of the multiple boron nitride particles may be the same or different from each other. In addition, the phrase "extending toward the other surface opposite to one surface" includes both the case where the multiple boron nitride particles reach the other surface and the case where they do not reach the other surface (i.e., it is sufficient that the multiple boron nitride particles extend in the above-mentioned extension direction).

The average length in the extension direction of the boron nitride particles may be 50 μm or more, 80 μm or more, 100 μm or more, 125 μm or more, 150 μm or more, or 200 μm or more, and may be 500 μm or less, 400 μm or less, or 300 μm or less.

The average length of the boron nitride particles in the extension direction can be measured by observing a cross section of the heat dissipation material in the thickness direction under a microscope. Specifically, first, a cross section of the heat dissipation material in the thickness direction is observed under a microscope, and the length of the boron nitride particles in the extension direction from the starting point is measured. This measurement of the extension length is performed on 20 boron nitride particles, and the average value is taken as the average length of the boron nitride particles in the extension direction.

The number of boron nitride particles arranged per unit area on one side of the heat dissipation material may be, for example, 10 particles/mm2 or ^more , 20 particles/mm2 ^or more, or 30 particles/mm2 or ^more , and may be 300 particles/mm2 ^{or less} , 200 particles/mm2 or ^less , or 100 particles/mm2 or ^less . The number of boron nitride particles arranged per unit area on one side of the heat dissipation material can be measured by observing a cross section along one side of the heat dissipation material with a SEM.

The content of boron nitride particles may be, for example, 30 volume% or more, 40 volume% or more, 50 volume% or more, or 60 volume% or more, and 85 volume% or less, 80 volume% or less, 70 volume% or less, 60 volume% or less, 50 volume% or less, or 40 volume% or less, based on the total volume of the heat dissipation material.

The resin content may be, for example, 15 volume% or more, 20 volume% or more, 30 volume% or more, 40 volume% or more, 50 volume% or more, or 60 volume% or more, and 70 volume% or less, 60 volume% or less, 50 volume% or less, or 40 volume% or less, based on the total volume of the heat dissipation material.

The thickness of the sheet-shaped heat dissipation material may be, for example, 80 μm or more, 100 μm or more, 20 μm or more, or 300 μm or more, and may be 800 μm or less, 600 μm or less, or 400 μm or less.

The heat dissipating material may further contain other components in addition to the boron nitride particles and resin described above. Details of the other components are the same as those described in the manufacturing method of the heat dissipating material above.

The heat dissipating material may be used alone or in combination with another member. For example, a sheet-shaped heat dissipating material may be used in a state where another sheet-shaped member is laminated thereon. That is, another embodiment of the present invention is a laminated sheet comprising a first sheet which is the above-mentioned sheet-shaped heat dissipating material, and a second sheet provided on at least one of the first sheet's one surface (the surface which is the origin of the extension of the above-mentioned plurality of boron nitride particles) and the other surface. In one embodiment, the laminated sheet may comprise a first sheet, a second sheet provided on one surface of the first sheet, and a third sheet provided on the other surface of the first sheet. In these embodiments, the second sheet and the third sheet may be directly laminated to the first sheet, or may be laminated via an adhesive or the like.

The second sheet and the third sheet may be formed of, for example, a resin, a metal, etc. The second sheet and the third sheet may contain a resin and an inorganic filler as described above. When the second sheet and the third sheet contain a resin, the resin may be the same resin as the resin contained in the first sheet, or may be a different resin.

The present invention will be specifically explained below using examples. However, the present invention is not limited to the following examples.

(Example 1) Lumped boron carbide particles were pulverized by a pulverizer to obtain boron carbide powder with an average particle size of 10 μm. 100 parts by mass of the obtained boron carbide powder and 9 parts by mass of boric acid were mixed and filled into a carbon crucible. The opening of the carbon crucible was covered with a carbon sheet (manufactured by NeoGraf, thickness: 130 μm, melting point: 4730°C, weight change rate: 1% or less (weight change rate before and after heating at 1500°C and 0.1 MPa for 1 hour)), and the carbon sheet was fixed by sandwiching it between the carbon crucible lid and the carbon crucible. The carbon crucible with the lid was heated in a resistance heating furnace under a nitrogen gas atmosphere at 2000°C and 0.85 MPa for 20 hours to obtain a composite material in which multiple particles extending from the carbon sheet were generated.

A portion of the particles formed on the carbon sheet was collected and subjected to X-ray diffraction measurement using an X-ray diffraction device (ULTIMA-IV, manufactured by Rigaku Corporation). The results of this X-ray diffraction measurement, and the results of an X-ray diffraction measurement of boron nitride powder (GP grade) manufactured by Denka Company Ltd. for comparison, are shown in Figure 1. As can be seen from Figure 1, only peaks derived from boron nitride were detected, confirming that boron nitride particles had been formed. Figure 2 shows an SEM image of the resulting composite material. From Figure 2, it can be confirmed that multiple boron nitride particles extend from the carbon sheet.

In addition, the length (L ₁ ) of the boron nitride particles in the extension direction and the length (L ₂ ) in the direction perpendicular to the extension direction were measured using a laser microscope ("Optelics HYBRID" manufactured by Lasertec Corporation). Specifically, first, the measurement range was set so as to include the thickness of the carbon sheet and the maximum height of the boron nitride particles for the composite material, and the surface shape of the composite material was measured. Next, the length (L ₁ ) of the boron nitride particles in the extension direction was measured from the cross-sectional profile of the measured surface shape of the composite material. In addition, the length (L ₂ ) in the direction perpendicular to the extension direction was also measured. These lengths were measured for 20 boron nitride particles. The average length of the boron nitride particles in the extension direction was 254 μm, and the average aspect ratio was 3.4.

(Example 2) In Example 1, the carbon sheet was changed to a boron nitride plate (p-BN plate, thickness: 500 μm, sublimation point: 2400°C), the boron nitride plate was placed at the opening of the carbon crucible, and the boron nitride plate was fixed by sandwiching it between the carbon crucible lid and the carbon crucible. The carbon crucible with the lid was heated in a resistance heating furnace under nitrogen gas atmosphere at 1600°C and 0.85 MPa for 5 hours, resulting in a composite material in which multiple particles were generated that extended from the boron nitride plate.

Some of the particles formed on the boron nitride plate were collected and subjected to X-ray diffraction measurement using an X-ray diffractometer (ULTIMA-IV, manufactured by Rigaku Corporation), confirming that boron nitride particles had been formed. Figure 3 shows an SEM image of the resulting composite material. Figure 3 shows that multiple boron nitride particles extend from the boron nitride plate as a starting point.

In addition, the length (L ₁ ) of the boron nitride particles in the extension direction and the length (L ₂ ) in the direction perpendicular to the extension direction were measured in the same manner as in Example 1. The average length of the boron nitride particles in the extension direction was 139 μm, and the average aspect ratio was 1.5.

(Example 3) A cylindrical jig (inner diameter 20 mm) was prepared, and the composite material obtained in Example 1 was placed inside the jig with the carbon sheet on the bottom and the boron nitride particles on the top. A mixture (viscosity at 25°C: 150 Pa·s) of 41.5 parts of epoxy resin (manufactured by DIC Corporation, product name: HP4032D), 5.1 parts of hardener (manufactured by DIC Corporation, product name: VH4150), 0.3 parts by volume of hardener (hardener catalyst) A (manufactured by Hokko Chemical Industry Co., Ltd., product name: TPP) and 0.5 parts by volume of hardener B (manufactured by Shikoku Kasei Corporation, product name: 2PHZ-PW) was poured into the inside of the jig, and the resin was filled between the multiple boron nitride particles of the composite material. The resin was hardened by heating at a temperature of 150°C for 60 minutes, and then the jig was removed. The surface of the obtained cured resin opposite the inorganic substrate was ground using a surface grinder to adjust the thickness of the cured resin to 200 μm. The cured resin was then peeled off from the carbon sheet to obtain a sheet-shaped heat dissipation material with a thickness of 200 μm and a diameter of 20 mm. The loading amount of boron nitride particles in the obtained heat dissipation material was 9 volume % based on the total volume of the heat dissipation material.

Figure 4 shows a microscope image of a cross section in the thickness direction of the obtained heat dissipation material. From Figure 4, it was confirmed that multiple boron nitride particles extend from one side of the heat dissipation material toward the opposite side. The average length of the multiple boron nitride particles in the heat dissipation material in the extension direction was 174 μm. In addition, the thermal resistance of the obtained heat dissipation material was measured using the method described below and was found to be 1.1°C/W.

(Reference Example 1) Boron nitride particles were recovered from the composite material obtained in Example 1. The recovered boron nitride particles were mixed with a mixture (viscosity at 25°C: 150 Pa·s) of 41.5 parts of epoxy resin (manufactured by DIC Corporation, product name: HP4032D), 5.1 parts of curing agent (manufactured by DIC Corporation, product name: VH4150), 0.3 parts by volume of curing accelerator (curing catalyst) A (manufactured by Hokko Chemical Industry Co., Ltd., product name: TPP) and 0.5 parts by volume of curing accelerator B (manufactured by Shikoku Chemical Industry Co., Ltd., product name: 2PHZ-PW), and then cured by heating for 60 minutes at a temperature of 150°C to obtain a sheet-shaped heat dissipation material with a thickness of 200 μm and a diameter of 20 mm. The amount of boron nitride particles filled in the obtained heat dissipation material was 10% by volume based on the total volume of the heat dissipation material. The thermal resistance of the resulting heat dissipation material was measured using the method described below and was found to be 1.82°C/W.

[Method of measuring thermal resistance] The thermal resistance of the obtained heat dissipation material was measured using a resin material thermal resistance measuring device (manufactured by Hitachi Technology and Services Co., Ltd.) in accordance with ASTM D5470. The obtained heat dissipation material was cut into 10 mm x 10 mm pieces, and the heat dissipation material with grease applied to both sides was placed between a thermocouple. It was heated and pressurized under the conditions of a sample temperature of 50°C, a heat source output of 10 W, and a load of 1 MPa. The thermal resistance value A was calculated from the temperature difference ΔT between the front and back of the test piece and the heat source output Q, using A = ΔT/Q.

(Reference Example 2)
A heat dissipating material was produced in the same manner as in Example 1, except that the boron nitride particles were changed to boron nitride ("GP" manufactured by Denka Co., Ltd.).

(Reference Example 3)
A heat dissipating material was produced in the same manner as in Example 1, except that boron nitride particles were not used.

[Method of measuring dielectric constant]
In order to evaluate the dielectric properties of the heat dissipation materials of Example 3 and Reference Examples 1 to 3, the electrostatic capacitance (C) of the heat dissipation materials was measured using an impedance analyzer (IWATSU PSM3750+IAI2) in the frequency range of 10 ^-1 to 10 ⁷ Hz. In this measurement, the applied voltage was 10V, and the evaluation temperature was room temperature of 25°C. In addition, an electrode was provided on the entire surface of one side of the heat dissipation material by gold sputtering, and a circular electrode with a diameter of 15 mm was provided on the other side by gold sputtering. The dielectric properties of the heat dissipation materials were evaluated by comparing the relative dielectric constant ε of the heat dissipation materials at a frequency of 1 kHz. The relative dielectric constant ε of the heat dissipation material was calculated from the following relational expression.
C=ε×ε ₀ ×S/d (C: capacitance of heat sink, S: area of circular electrode, d: thickness of heat sink, ε ₀ : dielectric constant of vacuum)

The relative dielectric constants of the heat dissipating materials of Example 3 and Reference Examples 1 to 3 were as follows.
Example 3: 4.58
Reference Example 1: 5.10
Reference Example 2: 4.83
Reference Example 3: 4.50
From these results, it was confirmed that the dielectric properties of the heat dissipation material of Example 3 did not decrease, and exhibited dielectric properties at or above a certain level.

Claims (6)

An inorganic substrate;
a plurality of boron nitride particles disposed on one surface of the inorganic substrate;
the plurality of boron nitride particles extend from the inorganic substrate;
The average length of the plurality of boron nitride particles in the extension direction is 50 μm or more,
The composite material, wherein the plurality of boron nitride particles have an average aspect ratio of 12.0 or less. The composite material according to claim 1, wherein the inorganic substrate comprises one selected from the group consisting of carbon and boron nitride. A method for manufacturing a heat dissipating material, comprising a step of filling the spaces between the boron nitride particles of the composite material according to claim 1 or 2 with resin. The method for producing a heat dissipation material according to claim 3 further comprises a step of removing the inorganic base material after the step. A sheet-shaped heat dissipation material containing a plurality of boron nitride particles and a resin,
A heat dissipation material, in which the plurality of boron nitride particles extend from one side of the heat dissipation material toward the other side opposite the one side (however, this does not include a laminate comprising a metal composite and an insulating material part, the metal composite having a metal body and a plurality of boron nitride nanotubes arranged on a surface of the metal body, the metal composite being arranged on the surface of the insulating material part from the boron nitride nanotube side, and the insulating material part including a cured portion of a thermosetting component containing a thermosetting compound and a thermosetting agent, and an insulating filler which is not a nanotube) . The heat dissipation material according to claim 5, wherein the average length of the plurality of boron nitride particles in the extension direction is 50 μm or more.

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