Boron nitride particles, method for producing boron nitride particles, and resin composition

Abstract

A boron nitride particle is provided, having multiple voids within the particle, wherein the area ratio of voids with an equivalent circular radius of less than 1 μm to the total area of ​​the multiple voids is 30% or more in a cross-section. A boron nitride particle is also provided, having multiple voids within the particle, wherein the area ratio of the multiple voids to the total area of ​​the region composed of boron nitride and the multiple voids is 45% or less in a cross-section.

Description

Technical Field

[0001] This invention relates to boron nitride particles, a method for manufacturing boron nitride particles, and a resin composition. Prior Technology

[0002] Boron nitride has lubricating properties, high thermal conductivity, and insulating properties, and is used in various applications such as solid lubricating materials, mold release materials, raw materials for cosmetics, heat dissipation materials, and heat-resistant insulating sintered bodies.

[0003] For example, Patent Document 1 discloses a hexagonal boron nitride powder that can impart high thermal conductivity and high dielectric strength to resin compositions obtained by filling resin. It contains aggregated particles composed of primary hexagonal boron nitride particles, has a BET specific surface area of ​​0.7~1.3 m² / g, and has an oil absorption of less than 80g / 100g as determined by JIS K 5101-13-1. [Previous Technical Documents] [Patent Documents]

[0004] Patent Document 1: Japanese Patent Application Publication No. 2016-160134 Summary of the Invention

[0005] [The problem that the invention aims to solve]

[0006] The main objective of this invention is to provide novel boron nitride particles. [Methods for solving problems]

[0007] The present invention provides the following [1] to [7] in some forms. [1] A boron nitride particle having multiple voids within the particle, and having a cross section in which the area ratio of the voids with an equivalent circular radius of less than 1 μm to the total area of ​​the aforementioned multiple voids is more than 30%. [2] A boron nitride particle having multiple voids within the particle, wherein the area ratio of the aforementioned multiple voids is less than 45% relative to the total area of ​​the region composed of the aforementioned boron nitride and the aforementioned multiple voids. [3] As described in [2], in the aforementioned cross-section, the area ratio of the voids with an equivalent circle radius of less than 1 μm to the total area of ​​the aforementioned voids is more than 30%. [4] For any of the boron nitride particles described in [1] to [3], in the aforementioned cross-section, the area ratio of the voids with an equivalent circle radius of 2 μm or more to the total area of ​​the aforementioned voids is less than 60%. [5] For boron nitride particles described in any of [1] to [4], the average equivalent circle radius of the aforementioned multiple voids in the aforementioned cross-section is less than 1.5 μm. [6] A method for manufacturing boron nitride particles includes the steps of: nitriding boron carbide particles under heat equalization pressure to obtain boron carbonitride particles, and decarburizing the aforementioned boron carbonitride particles to obtain boron nitride particles. [7] A resin composition comprising boron nitride particles as described in any one of [1] to [5], and a resin. [Effects of the Invention]

[0008] According to one embodiment of the present invention, novel boron nitride particles can be provided. Simple Explanation of the Diagram

[0009] [Figure 1] A graph showing the X-ray diffraction results of boron nitride particles in Examples 1-3. [Figure 2] SEM image of a cross-section of boron nitride particles from Example 1. [Figure 3] SEM image of the cross-section of boron nitride particles in Comparative Example 1. [Figure 4] Image obtained by binarizing the cross-section of boron nitride particles from Example 1. [Figure 5] Image obtained by binarizing the cross-section of boron nitride particles from Comparative Example 1. Implementation

[0010] The following describes in detail the embodiments of the present invention.

[0011] The boron nitride particles of this embodiment are, for example, composed of multiple boron nitride sheets. The boron nitride particles have multiple voids formed between the multiple boron nitride sheets. The boron nitride sheets, formed of boron nitride, may have, for example, a scale-like shape.

[0012] Multiple boron nitride sheets can be physically in contact with each other or chemically bonded together. Chemical bonding of multiple boron nitride sheets can be confirmed by using a scanning electron microscope (SEM) to observe the boundaries between the bonded areas.

[0013] Boron nitride particles can also have cross-sections of regions with multiple boron nitride sheet stacks. Multiple boron nitride sheet stacks can be identified by observing the cross-section of the boron nitride particles using SEM, showing that the multiple boron nitride sheets are arranged and configured in the thickness direction of the boron nitride sheets.

[0014] The average thickness of the boron nitride sheet can be 0.5 μm or more, 1 μm or more, or 1.5 μm or more, or less than 5 μm. The average length of the boron nitride sheet along its long side can be, for example, 1 μm or more, or less than 10 μm. The average thickness and average length along the long side of the boron nitride sheet are defined as the average of the thickness and length along the long side of 40 boron nitride sheets measured in the SEM image obtained by importing a cross-sectional image of boron nitride particles observed at 1000x magnification into image analysis software (e.g., "Mac-view" manufactured by Mountech Co., Ltd.).

[0015] In the cross-section of a boron nitride particle, the area ratio of voids with an equivalent circular radius of less than 1 μm to the total area of ​​multiple voids within the particle (the cumulative area of ​​multiple voids) can be 30% or more. That is, the boron nitride particle of one embodiment of the present invention (first embodiment) has multiple voids within the particle, and has a cross-section in which the area ratio of voids with an equivalent circular radius of less than 1 μm to the total area of ​​multiple voids is 30% or more.

[0016] In the cross-section of boron nitride particles, the area ratio of voids with an equivalent circular radius of less than 1 μm to the total area of ​​multiple voids can be 35% or more, or even 40% or more. The larger the area ratio of voids with an equivalent circular radius of less than 1 μm to the total area of ​​multiple voids, the smaller the total volume of voids within the boron nitride particle compared to boron nitride particles with the same total number of voids. Furthermore, the larger the area ratio of voids with an equivalent circular radius of less than 1 μm to the total area of ​​multiple voids in the cross-section of boron nitride particles, the lower the pressure during the molding of the heat dissipation material when such boron nitride particles are mixed with resin. Even with small deformation of the boron nitride particles, percolation becomes easier to occur within the boron nitride particles, making it easier to obtain a heat dissipation material with high thermal conductivity. The area ratio of the gaps with an equivalent circle radius of less than 1 μm to the total area of ​​multiple gaps can be more than 45%, more than 50%, or more than 55%, or less than 70%, less than 65%, or less than 60%.

[0017] In the cross-section of the boron nitride particle, the area ratio of the multiple voids (the proportion of the total area of ​​the multiple voids) relative to the area of ​​the region composed of boron nitride and the total area of ​​the multiple voids can be 45% or less. That is, in the boron nitride particle of another embodiment of the present invention (second embodiment), there are multiple voids within the particle, and the area ratio of the multiple voids is 45% or less relative to the total area of ​​the region composed of boron nitride and the total area of ​​the multiple voids in the cross-section.

[0018] In the cross-section of boron nitride particles, the area ratio of multiple voids relative to the area composed of boron nitride and the total area of ​​the multiple voids can be less than 40%, less than 35%, less than 30%, or less than 25%. The smaller the area ratio of multiple voids, the fewer voids are within the boron nitride particles, thus making the boron nitride particles more likely to be dense. Therefore, when such boron nitride particles are mixed with resin to make heat dissipation materials, even without pulverizing the boron nitride particles, the filling rate of the boron nitride particles will still be high, making it easier to obtain heat dissipation materials with high thermal conductivity. In the cross-section of boron nitride particles, the area ratio of multiple voids relative to the area composed of boron nitride and the total area of ​​the multiple voids can be less than 24%, less than 22%, less than 20%, or less than 18%, or more than 10%, more than 15%, or more than 20%.

[0019] In the cross-section of the boron nitride particles of the first embodiment described above, the area ratio of the plurality of voids (the ratio of the total area of ​​the plurality of voids) can also be within the aforementioned range. Furthermore, in the cross-section of the boron nitride particles of the second embodiment described above, the area ratio of voids with an equivalent circle radius of less than 1 μm to the total area of ​​the plurality of voids can also be within the aforementioned range. Unless otherwise specified, the matters described below are common to both the boron nitride particles of the first embodiment and the boron nitride particles of the second embodiment.

[0020] In the cross-section of boron nitride particles, the area ratio of voids with an equivalent circular radius of 2 μm or more to the total area of ​​multiple voids (the proportion of the total area of ​​voids with an equivalent circular radius of 2 μm or more) can be less than 80%, less than 75%, less than 70%, less than 65%, less than 60%, less than 55%, less than 50%, less than 45%, less than 40%, or less than 35%. The smaller the area ratio of voids with an equivalent circular radius of 2 μm or more to the total area of ​​multiple voids, the fewer large voids there are within the boron nitride particles, thus making such boron nitride particles more likely to become dense particles. Therefore, when such boron nitride particles are mixed with resin to make heat dissipation materials, even without pulverizing the boron nitride particles, the filling rate of the boron nitride particles will still be high, making it easier to obtain heat dissipation materials with high thermal conductivity. The area ratio of a void with an equivalent circle radius of 2μm to the total area of ​​multiple voids can be less than 30% or less than 25%, or it can be more than 5%, more than 10%, more than 15%, more than 20%, or more than 25%.

[0021] In the cross-section of boron nitride particles, the average equivalent circular radius of multiple pores can be less than 1.8 μm, less than 1.6 μm, less than 1.5 μm, less than 1.4 μm, or less than 1.3 μm. The smaller the average equivalent circular radius of multiple pores, the smaller the average size of the pores within the boron nitride particles tends to be. Therefore, when such boron nitride particles are mixed with resin to produce heat dissipation materials, the pressure during molding is low, and even with small deformation of the boron nitride particles, permeation within the particles becomes easier, making it easier to obtain heat dissipation materials with high thermal conductivity. In the cross-section of boron nitride particles, the average equivalent circular radius of multiple pores can also be greater than 0.6 μm, greater than 0.8 μm, or greater than 0.9 μm. The average equivalent circular radius of multiple pores refers to the equivalent circular radius (median particle size) of the pores whose cumulative area constitutes 50% of the pores in the distribution of equivalent circular radii.

[0022] The area of ​​the region composed of boron nitride in the cross-section of a boron nitride particle, as well as the area of ​​each of the multiple voids and the equivalent circle radius, can be determined by the following method. First, boron nitride particles are embedded in epoxy resin, which is then cured to obtain a hardened product. The hardened product is ground to expose the cross-section of the boron nitride particles, creating a test sample. The test sample is observed using SEM at 1000x magnification to obtain a BMP image that clearly shows the cross-section of a single boron nitride particle. The image is imported into the image processing software "imageJ," and focusing on a single boron nitride particle, the boundary is drawn along its outer edge. The image is then reshaped into a rectangle tangent to the drawn boundary area, and the area outside the drawn boundary area (the area where the observed boron nitride particle does not exist) is masked. A median filter (1 pixel) is used for filtering, and the area composed of boron nitride particles and the surrounding area (resin area) are binarized using the Otsu method. Finally, a maximum filter (1 pixel) is used for filtering, and hole-filling is performed to capture the outline of the boron nitride particles. For binarized images, the extracted contours are used to mask the regions outside the contours, resulting in an image for analysis. This image is then imported into the image processing software "OpenCV" (programming language Python). From this image, the areas composed of boron nitride in the cross-section of boron nitride particles, and the areas of multiple resin regions (voids) within the boron nitride particle cross-section, can be determined. Furthermore, the equivalent circle radius of each resin region (void) can be calculated from its area.

[0023] The maximum length of boron nitride particles can be, for example, greater than 20 μm, greater than 30 μm, or greater than 40 μm, or less than 120 μm, less than 100 μm, or less than 80 μm. The maximum length of a boron nitride particle refers to the longest straight-line distance between any two points on a single boron nitride particle when observed using SEM. The maximum length can also be determined by importing the SEM image into image analysis software (e.g., "Mac-view" manufactured by Mountech Inc.).

[0024] Boron nitride particles can also be composed entirely of boron nitride. This can be confirmed by detecting only peaks originating from boron nitride in X-ray diffraction measurements.

[0025] As described above, in one embodiment of the novel boron nitride particles, the proportion of small voids within the particles is greater than that of conventional boron nitride particles. Furthermore, in another embodiment of the novel boron nitride particles, the overall proportion of voids within the particles is smaller than that of conventional boron nitride particles. Therefore, when these novel boron nitride particles are mixed with resin and used as a thermally conductive material, for example, they can exhibit higher thermal conductivity compared to conventional boron nitride particles.

[0026] The aforementioned boron nitride particles can be used in various applications as boron nitride powder aggregates. That is, another embodiment of the present invention is boron nitride powder aggregates of the aforementioned boron nitride particles. The average particle size of the boron nitride powder can be, for example, 20 μm or more, 30 μm or more, or 40 μm or more, or 120 μm or less, 100 μm or less, or 80 μm or less. The average particle size of the boron nitride powder refers to the particle size at which the volumetric particle size distribution reaches 50% (D50), which can be measured by laser diffraction scattering.

[0027] The method for manufacturing the aforementioned boron nitride particles will be described below. The boron nitride particles can be manufactured, for example, by a method comprising the following steps: nitriding boron carbide particles while subjecting them to hot isostatic pressing (also known as "hot isostatic pressing") to obtain boron carbonitride particles (nitriding step), and decarburizing the boron carbonitride particles to obtain boron nitride particles (decarburizing step). That is, another embodiment of the present invention is such a method for manufacturing boron nitride particles.

[0028] Boron carbide particles can be manufactured, for example, by well-known manufacturing methods. One example is the method of mixing boric acid and acetylene black, and then heating the mixture in an inert gas environment at 1800–2400°C for 1–10 hours to obtain bulk boron carbide particles. The bulk boron carbide particles obtained by this method can also be appropriately crushed, sieved, washed, have impurities removed, and dried. The average particle size of the boron carbide particles can be, for example, 5 μm or more, 10 μm or more, or 15 μm or more, or less than 80 μm, less than 60 μm, or less than 40 μm. The average particle size of the boron carbide particles, referring to the particle size at which the volumetric particle size distribution reaches 50% (D50), can be determined by laser diffraction scattering.

[0029] In the nitriding step, boron carbide particles are nitrided to obtain boron carbonitride particles by heating while being filled with a container under thermal equalization pressure in an environment that allows the nitriding reaction to proceed. The container can be, for example, a carbon crucible. Thermal equalization pressure can be performed, for example, using a thermal equalization pressure device (e.g., manufactured by Kobe Steel).

[0030] The environment in which the nitriding reaction takes place can also be a nitriding gas environment for nitriding boron carbide particles. The nitriding gas can be nitrogen, ammonia, etc.; considering the ease of nitriding boron carbide particles and cost, nitrogen is preferred. One type of nitriding gas can be used alone or in combination of two or more types. The proportion of nitrogen in the nitriding gas can be 95% by volume or more, 99% by volume or more, or 99.9% by volume or more.

[0031] The pressure during the nitriding step can be 50 MPa or higher, 70 MPa or higher, or 100 MPa or higher. Alternatively, the pressure during the nitriding step can be 200 MPa or lower, or 150 MPa or lower.

[0032] The heating temperature in the nitriding step, considering the need for sufficient nitriding of boron carbide particles, can be above 1600°C or 1700°C. Alternatively, the heating temperature in the nitriding step can be below 2200°C or 2000°C.

[0033] The time for pressurization and heating during the nitriding step, taking into account the need for sufficient nitriding of boron carbide particles, can be 3 hours or more, 5 hours or more, or 8 hours or more. The time for pressurization and heating during the nitriding step can also be less than 30 hours, less than 20 hours, or less than 10 hours.

[0034] In the decarburization step, the boron carbonitride particles are decarburized by heating a container filled with a mixture containing boron carbonitride particles obtained in the nitriding step and a boron source. The container may be, for example, a boron nitride crucible.

[0035] Examples of boron sources include boric acid, boron oxide, or mixtures thereof. Mixtures may also contain other additives used in this field, as needed. The mixing ratio of boron carbonitride particles to the boron source is appropriately selected. When using boric acid or boron oxide as the boron source, the proportion of boric acid or boron oxide relative to 100 parts by mass of boron carbonitride may, for example, be 50 parts by mass or more, or 80 parts by mass or more, or 300 parts by mass or less, or 250 parts by mass or less.

[0036] The environment during the decarbonization step can be at atmospheric pressure or under pressure. The pressure during the decarbonization step can be, for example, below 0.5 MPa or below 0.3 MPa, or above 0.01 MPa or above 0.03 MPa.

[0037] In the decarburization step, for example, the temperature is first raised to a specified temperature (the temperature at which decarburization can begin), and then further raised to a holding temperature at the specified temperature. The specified temperature (the temperature at which decarburization can begin) can be, for example, above 1000°C, below 1500°C, or below 1200°C. The rate of heating from the specified temperature (the temperature at which decarburization can begin) to the holding temperature can be, for example, below 5°C / minute, below 4°C / minute, below 3°C / minute, or below 2°C / minute.

[0038] To ensure optimal particle growth, the temperature can be maintained above 1800℃ or 2000℃. Alternatively, the temperature can be maintained below 2200℃ or 2100℃.

[0039] The holding time at the temperature can be determined based on the viewpoint that particle growth is more likely to occur well; for example, it can be more than 0.5 hours, more than 1 hour, more than 3 hours, or more than 5 hours. The holding time at the temperature can also be less than 40 hours, less than 30 hours, or less than 20 hours.

[0040] Alternatively, the boron nitride particles obtained as described above can be classified by sieving to obtain boron nitride particles with the desired particle size (classification step).

[0041] The boron nitride particles described above are suitable for use, for example, in heat dissipation components. When used in heat dissipation components, the boron nitride particles are used, for example, as a resin composition mixed with a resin. That is, another embodiment of the present invention is a resin composition containing a resin and the aforementioned boron nitride particles.

[0042] The content of boron nitride particles, based on the total volume of the resin composition, and considering the viewpoint of improving the thermal conductivity of the resin composition and easily obtaining excellent heat dissipation performance, can be 50% by volume or more, 55% by volume or more, 60% by volume or more, 65% by volume or more, or 70% by volume or more. The content of boron nitride powder, based on the total volume of the resin composition, and considering the viewpoint of suppressing the generation of voids during molding and the reduction of insulation and mechanical strength, can also be 85% by volume or less, 80% by volume or less, or 75% by volume or less.

[0043] Examples of resins include: epoxy resins, silicone resins, silicone rubbers, acrylic resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluoropolymers, polyimides, polyamide-imides, polyether-imides, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, fully aromatic polyesters, polyurethane, liquid crystal polymers, polyether resin, polycarbonate, maleimide-modified resins, ABS (acrylonitrile-butadiene-styrene) resin, AAS (acrylonitrile-acrylic rubber / styrene) resin, and AES (acrylonitrile / ethylene / propylene / diene rubber-styrene) resin.

[0044] The resin content, based on the total volume of the resin composition, can be 15% or more, 20% or more, or 25% or more, or less than 50% or less, 45% or less, 40% or less, 35% or less, or less than 30% or less.

[0045] The resin composition may further contain a hardener to cure the resin. The hardener is selected appropriately depending on the type of resin. For example, when the resin is epoxy resin, hardeners may include: phenolic resin compounds, acid anhydrides, amine compounds, and imidazole compounds. The content of the hardener, relative to 100 parts by weight of resin, may be, for example, 0.5 parts by weight or more, or 1.0 parts by weight or more, or 15 parts by weight or less, or 10 parts by weight or less.

[0046] The resin composition may further contain other components. These other components may include curing accelerators (curing catalysts), coupling agents, wetting and dispersing agents, surface conditioners, etc.

[0047] Examples of curing accelerators (curing catalysts) include: tetraphenylphosphonium tetraphenylborate, triphenyl phosphate and other phosphorus-based curing accelerators, 2-phenyl-4,5-dihydroxymethylimidazolium and other imidazole-based curing accelerators, boron trifluoride monoethylamine and other amine-based curing accelerators.

[0048] Examples of coupling agents include silane-based coupling agents, titanate-based coupling agents, and aluminate-based coupling agents. Examples of chemical bonding groups contained in these coupling agents include vinyl, epoxy, amino, methacrylate, and mercapto groups.

[0049] Examples of wetting and dispersing agents include: phosphate salts, carboxylic acid esters, polyesters, acrylic copolymers, block copolymers, etc.

[0050] In terms of surface modifiers, examples include: acrylic surface modifiers, silicone surface modifiers, vinyl surface modifiers, and fluorine surface modifiers. [Example]

[0051] The present invention will now be specifically described through examples. However, the present invention is not limited to the following examples.

[0052] (Example 1) Boron carbide particles with an average particle size (D50) of 26 μm were filled into a carbon crucible. Using a hot homogenizing pressurization apparatus (Kobe Steel, 02-SYSTEM15× type), under nitrogen atmosphere, at 1750°C and 196 MPa for 1.5 hours, the boron carbide particles were nitrided to obtain boron carbonitride particles (B₄CN₄). 100 parts by weight of the obtained boron carbonitride particles were mixed with 150 parts by weight of boric acid using a Henschel mixer. The mixture was then filled into a boron nitride crucible and heated in a resistance furnace under normal pressure and nitrogen atmosphere at 2000°C and 0.03 MPa for 5 hours to obtain coarse particles. The coarse particles were then pulverized in a mortar for 10 minutes and classified through a 175 μm nylon sieve. This yielded particle aggregates (powder).

[0053] (Example 2) The temperature at which the boron carbide particles were nitrided was changed to 1800°C, and otherwise the process was carried out in the same manner as in Example 1 to obtain an aggregate (powder) of the particles.

[0054] (Example 3) The amount of boric acid was changed to 100 parts by mass, and otherwise the same procedure was followed as in Example 2 to obtain an aggregate (powder) of particles.

[0055] (Comparative Example 1) Boron carbide particles were nitrided to obtain boron carbonitride particles by heating and pressurizing at 2000°C and 0.85 MPa for 25 hours in a resistance heating furnace under nitrogen atmosphere. Otherwise, the process was carried out in the same manner as in Example 1 to obtain an aggregate (powder) of boron nitride particles.

[0056] [X-ray diffraction measurement] A portion of the particles obtained in each embodiment was recovered and subjected to X-ray diffraction measurements using an X-ray diffraction apparatus (manufactured by Rigaku Corporation, "ULTIMA-IV"). The X-ray diffraction measurement results of these particles and the X-ray diffraction measurement results of the boron nitride particles obtained in Comparative Example 1, which served as a comparison object, are shown in Figure 1. As can be seen from Figure 1, only peaks originating from boron nitride were detected, confirming that boron nitride particles could be obtained in each embodiment.

[0057] [Determination of the area of ​​voids and the radius of the equivalent circle in the cross-section of boron nitride particles] Boron nitride particles are embedded in epoxy resin, which is then cured to obtain a hardened product. The hardened product is ground to expose the cross-section of the boron nitride particles, creating a test sample. The test sample is observed using SEM at 1000x magnification to obtain a BMP image that clearly shows the cross-section of a single boron nitride particle. The image is imported into the image processing software "imageJ," focusing on a single boron nitride particle in the image, and its boundary is drawn along the outer edge of the particle. The image is then reshaped into a rectangle tangent to the drawn boundary area, and the area outside the drawn boundary area (the area where the observed boron nitride particle does not exist) is masked. After filtering with a median filter (1 pixel), the area composed of boron nitride particles and the surrounding area (resin area) are binarized using the Otsu method. After filtering with a maximum filter (1 pixel), hole filling is performed to capture the outline of the boron nitride particle. For the binarized image, the extracted contours are used to mask the areas outside the contours, resulting in an image for analysis. The image for analysis is imported into the image processing software "OpenCV" (programming language Python). From the image for analysis, the areas of the boron nitride-containing regions and the areas of multiple resin regions (voids) within the boron nitride particle cross-section are measured. The equivalent circle radius of each resin region (void) is calculated from its area. Furthermore, from the areas and equivalent circle radii of the multiple voids, the area ratios of voids with equivalent circle radii less than 1 μm relative to the total area of ​​the multiple voids, the area ratios of voids with equivalent circle radii greater than 2 μm relative to the total area of ​​the multiple voids, the area ratios of the multiple voids relative to the area of ​​the boron nitride-containing region and the total area of ​​the multiple voids, the average equivalent circle radius, and the maximum equivalent circle radius are calculated. The calculation results are shown in Table 1. Furthermore, SEM images of the cross-section of boron nitride particles from Example 1 are shown in Figure 2, SEM images of the cross-section of boron nitride particles from Comparative Example 1 are shown in Figure 3, binarized images of the cross-section of boron nitride particles from Example 1 are shown in Figure 4, and binarized images of the cross-section of boron nitride particles from Comparative Example 1 are shown in Figure 5.

[0058] [Determination of the maximum length of boron nitride particles] Boron nitride particles were observed using SEM, and their maximum length was determined. The results are shown in Table 1.

[0059] [Table 1]

[0060] [Determination of thermal conductivity] 100 parts by weight of naphthalene-type epoxy resin (manufactured by DIC Corporation, HP4032) and 10 parts by weight of imidazole compound (manufactured by Shikoku Chemical Co., Ltd., 2E4MZ-CN) as a curing agent were mixed. Then, boron nitride particles obtained in Examples 2 and 3 and Comparative Example 1 were mixed with boron nitride particles at a filling rate of 70% by volume to obtain a resin composition. This resin composition was degassed under reduced pressure of 500 Pa for 10 minutes and coated onto a PET sheet with a thickness of 1.0 mm. Then, it was pressed and heated at a temperature of 150°C and a pressure of 160 kg / cm² for 60 minutes to produce a 0.5 mm sheet-like heat dissipation material. A 10 mm × 10 mm test sample was cut from the produced heat dissipation material, and the thermal diffusivity A (m² / s) of the test sample was measured using the laser flash method of a xenon flash analyzer (manufactured by NETZSCH Corporation, LFA447NanoFlash). Furthermore, the specific gravity B (kg / m³) of the test sample was determined using the Archimedes method. The specific heat capacity C (J / (kg·K)) of the test sample was also determined using a differential scanning calorimeter (Rigaku Corporation, ThermoPlus EvoDSC8230). Using these property values, the thermal conductivity H (W / (mK)) was calculated using the formula H = A × B × C. The thermal conductivity of the heat dissipation material made using boron nitride particles obtained in Example 2 was 22 W / (mK), the thermal conductivity of the heat dissipation material made using boron nitride particles obtained in Example 3 was 24 W / (mK), and the thermal conductivity of the heat dissipation material made using boron nitride particles obtained in Comparative Example 1 was 17 W / (mK).

Claims

1. A boron nitride particle having multiple voids within the particle, and having a cross-section in which the area ratio of the voids with an equivalent circular radius of less than 1 μm to the total area of ​​the multiple voids is more than 30% and less than 70%.

2. A boron nitride particle having a plurality of voids within the particle, wherein the area of ​​the plurality of voids is less than 35% of the total area of ​​the region composed of the boron nitride and the plurality of voids in a cross-section.

3. For the boron nitride particles of claim 2, in the cross-section, the area ratio of voids with an equivalent circle radius of less than 1 μm to the total area of ​​the plurality of voids is more than 30%.

4. For boron nitride particles as requested in item 1 or 2, in the cross-section, the area ratio of voids with an equivalent circular radius of 2 μm or more to the total area of ​​the plurality of voids is less than 60%.

5. For boron nitride particles as claimed in claim 1 or 2, the average equivalent circle radius of the plurality of voids in the cross-section is less than 1.5 μm.

6. A method for manufacturing boron nitride particles, comprising: a step of nitriding boron carbide particles under heat and pressure to obtain boron carbonitride particles, and a step of decarburizing the boron carbonitride particles to obtain boron nitride particles.

7. A resin composition comprising boron nitride particles as claimed in any one of claims 1 to 3, and a resin.

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