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

Abstract

A boron nitride particle having a plurality of voids in the particle, and having a cross section in which the area proportion of voids having an equivalent circle diameter less than 1 μm with respect to the total area of the plurality of voids is 30% or more. A boron nitride particle having a plurality of voids in the particle, and having a cross section in which the area proportion of the plurality of voids with respect to the total area of regions formed of boron nitride and the plurality of voids is 45% or less.

Description

Technical Field

[0001] The present invention relates to boron nitride particles, a method for producing boron nitride particles, and a resin composition.

Background Art

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

[0003] For example, in Patent Document 1, as hexagonal boron nitride powder capable of imparting high thermal conductivity and high dielectric breakdown strength to a resin composition obtained by filling a resin, it contains agglomerated particles composed of primary particles of hexagonal boron nitride, and the BET specific surface area is 0.7 to 1.3 m ,

[0006] , , , , , , ,

[0005] / g, and the oil absorption measured based on JIS K 5101-13-1 is 80 g / 100 g or less. Hexagonal boron nitride powder is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The main object of the present invention is to provide novel boron nitride particles.

Means for Solving the Problems

[0006] The present invention provides the following [1] to [7] in several aspects. [1] Boron nitride particles having a plurality of voids in the particles, and having a cross-section in which the area ratio of voids having a circle-equivalent radius of less than 1 μm with respect to the total area of the plurality of voids is 30% or more. [2] A boron nitride particle having a plurality of voids within the particle, wherein the area ratio of the plurality of voids is 45% or less of the total area of ​​the region made of boron nitride and the plurality of voids. [3] The boron nitride particle according to [2], wherein in the cross-section, the area ratio of voids with an equivalent circular radius of less than 1 μm to the total area of ​​the plurality of voids is 30% or more. [4] Boron nitride particle according to any one of [1] to [3], wherein 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 60% or less. [5] Boron nitride particle according to any one of [1] to [4], wherein the average equivalent radius of the plurality of voids in the cross-section is 1.5 μm or less. [6] A method for producing boron nitride particles, comprising the steps of: nitriding boron carbide particles under hot isostatic pressure to obtain boron carbonitride particles; and decarburizing the boron carbonitride particles to obtain boron nitride particles. A resin composition comprising boron nitride particles as described in any of [1] to [5] [7] and a resin. [Effects of the Invention]

[0007] According to one aspect of the present invention, novel boron nitride particles can be provided. [Brief explanation of the drawing]

[0008] [Figure 1] This graph shows the X-ray diffraction measurement results of boron nitride particles in Examples 1-3. [Figure 2] This is an SEM image of a cross-section of boron nitride particles from Example 1. [Figure 3] This is an SEM image of a cross-section of a boron nitride particle from Comparative Example 1. [Figure 4] This is a binarized image of the cross-section of the boron nitride particles from Example 1. [Figure 5] This is a binarized image of the cross-section of the boron nitride particle in Comparative Example 1. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described in detail below.

[0010] The boron nitride particles according to this embodiment are composed of, for example, a plurality of boron nitride flakes. The boron nitride particles have a plurality of voids formed between the plurality of boron nitride flakes. The boron nitride flakes are formed of boron nitride and may have, for example, a scale-like shape.

[0011] Multiple boron nitride fragments may be in physical contact with each other, or they may be chemically bonded. Chemical bonding between multiple boron nitride fragments can be confirmed using a scanning electron microscope (SEM) by observing that no boundaries between the boron nitride fragments are visible at the bonding site.

[0012] Boron nitride particles may have a cross-section containing a region where multiple boron nitride flakes are stacked. The stacking of multiple boron nitride flakes can be confirmed by observing the cross-section of the boron nitride particle using a scanning electron microscope (SEM), where the multiple boron nitride flakes are aligned in the thickness direction of the flakes.

[0013] The average thickness of the boron nitride pieces may be 0.5 μm or more, 1 μm or more, or 1.5 μm or more, and may be 5 μm or less. The average length in the longitudinal direction of the boron nitride pieces may be, for example, 1 μm or more, and may be 10 μm or less. The average thickness and average length in the longitudinal direction of the boron nitride pieces are defined as the average values ​​of the thickness and longitudinal direction of 40 boron nitride pieces measured in an SEM image obtained by observing the cross-section of boron nitride particles at a magnification of 1000x using a SEM, and importing the SEM image into image analysis software (for example, "Mac-view" manufactured by Mountec Co., Ltd.).

[0014] In the cross-section of the boron nitride particles, the area ratio of the voids with a circle-equivalent radius of less than 1 μm to the total area of the plurality of voids (the cumulative area of the plurality of voids) may be 30% or more. That is, the boron nitride particles according to one embodiment (the first embodiment) of the present invention have a plurality of voids in the particles and have a cross-section in which the area ratio of the voids with a circle-equivalent radius of less than 1 μm to the total area of the plurality of voids is 30% or more.

[0015] In the cross-section of the boron nitride particles, the area ratio of the voids with a circle-equivalent radius of less than 1 μm to the total area of the plurality of voids may be 35% or more, or 40% or more. The larger the area ratio of the voids with a circle-equivalent radius of less than 1 μm to the total area of the plurality of voids, the smaller the total volume of the voids in the boron nitride particles compared to boron nitride particles with the same total number of voids. Also, in the cross-section of the boron nitride particles, the larger the area ratio of the voids with a circle-equivalent radius of less than 1 μm to the total area of the plurality of voids, when such boron nitride particles are mixed with a resin to produce a heat dissipation material, the pressure during molding of the heat dissipation material is small, and even if the deformation of the boron nitride particles is small, percolation is likely to occur within the boron nitride particles, and it becomes easier to obtain a heat dissipation material having high thermal conductivity. The area ratio of the voids with a circle-equivalent radius of less than 1 μm to the total area of the plurality of voids may be 45% or more, 50% or more, or 55% or more, and may also be 70% or less, 65% or less, or 60% or less.

[0016] In the cross-section of the boron nitride particles, the area ratio of the plurality of voids (the ratio of the total area of the plurality of voids) may be 45% or less with respect to the total area of the region composed of boron nitride and the plurality of voids. That is, the boron nitride particles according to another embodiment (the second embodiment) of the present invention have a plurality of voids in the particles and have a cross-section in which the area ratio of the plurality of voids is 45% or less with respect to the total area of the region composed of boron nitride and the plurality of voids.

[0017] In the cross-section of the boron nitride particles, the area ratio of the plurality of voids may be 40% or less, 35% or less, 30% or less, or 25% or less with respect to the total area of the region composed of boron nitride and the plurality of voids. The smaller the area ratio of the plurality of voids, the fewer the voids in the boron nitride particles. Therefore, such boron nitride particles tend to be dense particles. Thus, when producing a heat dissipation material by mixing such boron nitride particles with a resin, the filling rate of the boron nitride particles can be increased without crushing the boron nitride particles, and it becomes easier to obtain a heat dissipation material having a high thermal conductivity. In the cross-section of the boron nitride particles, the area ratio of the plurality of voids may be 24% or less, 22% or less, 20% or less, or 18% or less with respect to the total area of the region composed of boron nitride and the plurality of voids, and may be 10% or more, 15% or more, or 20% or more.

[0018] In the above cross-section of the boron nitride particles according to the first embodiment, the area ratio (ratio of the total area of the plurality of voids) of the plurality of voids may be within the above range. Also, in the above cross-section of the boron nitride particles according to the second embodiment, the area ratio of the voids having a circle-equivalent radius of less than 1 μm with respect to the total area of the plurality of voids may be within the above range. The matters described below are common matters for both the boron nitride particles according to the first embodiment and the boron nitride particles according to the second embodiment unless otherwise specified.

[0019] In the cross-section of boron nitride particles, the area ratio of voids with an equivalent radius of 2 μm or more to the total area of ​​multiple voids (the ratio of the total area of ​​voids with an equivalent radius of 2 μm or more) may be 80% or less, 75% or less, 70% or less, 65% or less, 60% or less, 55% or less, 50% or less, 45% or less, 40% or less, or 35% or less. The smaller the area ratio of voids with an equivalent radius of 2 μm or more to the total area of ​​multiple voids, the fewer large voids there are within the boron nitride particles, and thus such boron nitride particles tend to become dense particles. Therefore, when such boron nitride particles are mixed with resin to produce a heat dissipation material, the packing density of the boron nitride particles can be increased without crushing the boron nitride particles, making it easier to obtain a heat dissipation material with high thermal conductivity. The area ratio of voids with an equivalent circular radius of 2 μm or more to the total area of ​​multiple voids may be 30% or less, or 25% or less, and may be 5% or more, 10% or more, 15% or more, 20% or more, or 25% or more.

[0020] In the cross-section of boron nitride particles, the average equivalent radius of multiple voids may be 1.8 μm or less, 1.6 μm or less, 1.5 μm or less, 1.4 μm or less, or 1.3 μm or less. The smaller the average equivalent radius of multiple voids, the smaller the average size of the voids within the boron nitride particles tends to be. Therefore, when such boron nitride particles are mixed with a resin to produce a heat dissipation material, even if the pressure during molding of the heat dissipation material is small and the deformation of the boron nitride particles is small, percolation is more likely to occur within the boron nitride particles, making it easier to obtain a heat dissipation material with high thermal conductivity. In the cross-section of boron nitride particles, the average equivalent radius of multiple voids may be 0.6 μm or more, 0.8 μm or more, or 0.9 μm or more. The average equivalent radius of multiple voids refers to the equivalent radius (median diameter) of the void where the cumulative area of ​​the voids accounts for 50% in the distribution of the equivalent void radii of the voids.

[0021] The area of ​​the boron nitride region in the cross-section of a boron nitride particle, as well as the area and equivalent radius of each of the multiple voids, can be measured by the following method. First, boron nitride particles are embedded in epoxy resin, and the resin is cured to obtain a cured product. The cured product is polished to expose the cross-section of the boron nitride particles, which is then used as a sample for measurement. The sample for measurement is observed using a SEM at a magnification of 1000x to obtain a BMP image that shows the entire cross-section of a single boron nitride particle. The image is imported into the image processing software "imageJ," and a single boron nitride particle in the image is selected. An outline is drawn around the outer edge of the selected boron nitride particle. The image is then cropped into a rectangle circumscribing the outlined region, and the region outside the outlined region (the region where the selected boron nitride particle does not exist) is masked. A median filter (1 pixel) is applied to filter the image, and binarization is performed using the Otsu method to separate the region consisting of the boron nitride particle from the rest of the region (the resin region). A maximum filter (1 pixel) is also applied, followed by fill holes processing to extract the contour of the boron nitride particle. The extracted contours are applied to the binarized image, and the area outside the contours is masked to obtain an image for analysis. The image for analysis is imported into the image processing software "OpenCV" (language: Python), and the area of ​​the region consisting of boron nitride in the cross-section of the boron nitride particle, as well as the area of ​​each of the multiple resin regions (voids) in the cross-section of the boron nitride particle, can be measured from the image for analysis. Furthermore, the equivalent radius of each of the multiple resin regions (voids) can be calculated from the area of ​​each of the multiple resin regions (voids).

[0022] The maximum length of a boron nitride particle may be, for example, 20 μm or more, 30 μm or more, or 40 μm or more, and may be 120 μm or less, 100 μm or less, or 80 μm or less. The maximum length of a boron nitride particle refers to the maximum straight-line distance between any two points on a single boron nitride particle when the particle is observed with a SEM. The maximum length may be measured by importing SEM images into image analysis software (for example, "Mac-view" manufactured by Mountec Co., Ltd.).

[0023] Boron nitride particles may consist substantially of boron nitride. The fact that boron nitride particles consist substantially of boron nitride can be confirmed by the detection of only peaks originating from boron nitride in X-ray diffraction measurements.

[0024] In one embodiment, the novel boron nitride particles described above have a higher proportion of small voids among the multiple voids within the particle compared to conventional boron nitride particles. In another embodiment, the novel boron nitride particles have a lower overall proportion of multiple voids within the particle compared to conventional boron nitride particles. Therefore, when these novel boron nitride particles are mixed with resin and used as a thermal conductive material, for example, they can exhibit higher thermal conductivity than conventional boron nitride particles.

[0025] The boron nitride particles described above can be used in various applications as boron nitride powder, which is an aggregate of these particles. That is, another embodiment of the present invention is boron nitride powder, which is an aggregate of the boron nitride particles described above. The average particle size of the boron nitride powder may be, for example, 20 μm or more, 30 μm or more, or 40 μm or more, and may be 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 (D50) at which the volume cumulative particle size distribution is 50%, and can be measured by laser diffraction scattering.

[0026] The method for producing the boron nitride particles described above will be explained below. The boron nitride particles can be produced, for example, by a method comprising the steps of: nitriding boron carbide particles under hot isostatic pressure (also called "hot hydrostatic pressure") to obtain boron carbonitride particles (nitriding step); and decarburizing the boron carbonitride particles to obtain boron nitride particles (decarburization step). That is, another embodiment of the present invention is such a method for producing boron nitride particles.

[0027] Boron carbide particles can be produced, for example, by known manufacturing methods. For example, a method can be used to obtain lump boron carbide particles by mixing boric acid and acetylene black, and then heating the mixture in an inert gas atmosphere at 1800 to 2400°C for 1 to 10 hours. The lump boron carbide particles obtained by this method may be subjected to appropriate processes such as pulverization, sieving, washing, impurity removal, and drying. The average particle size of the boron carbide particles may be, for example, 5 μm or more, 10 μm or more, or 15 μm or more, and may be 80 μm or less, 60 μm or less, or 40 μm or less. The average particle size of the boron carbide particles refers to the particle size (D50) at which the volume cumulative particle size distribution is 50%, and can be measured by laser diffraction scattering.

[0028] In the nitriding process, boron carbide particles are heated under hot isostatic pressure while packed in a container under an atmosphere that promotes the nitriding reaction, thereby nitriding the boron carbide particles to obtain boron carbonitride particles. The container may be, for example, a carbon crucible. Hot isostatic pressure can be applied using, for example, a hot isostatic pressurizing device (e.g., manufactured by Kobe Steel, Ltd.).

[0029] The atmosphere used to carry out the nitriding reaction in the nitriding process may be a nitriding gas atmosphere that nitrides boron carbide particles. The nitriding gas may be nitrogen gas, ammonia gas, etc., and nitrogen gas may be used from the viewpoint of ease of nitriding boron carbide particles and cost. The nitriding gas may be used alone or in combination of two or more types, and the proportion of nitrogen gas in the nitriding gas may be 95% by volume or more, 99% by volume or more, or 99.9% by volume or more.

[0030] The pressure in the nitriding process may be 50 MPa or higher, 70 MPa or higher, or 100 MPa or higher. The pressure in the nitriding process may be 200 MPa or lower, or 150 MPa or lower.

[0031] The heating temperature in the nitriding process may be 1600°C or higher or 1700°C or higher, from the viewpoint of sufficiently nitriding the boron carbide particles. The heating temperature in the nitriding process may be 2200°C or lower or 2000°C or lower.

[0032] The pressurization and heating time in the nitriding process may be 3 hours or more, 5 hours or more, or 8 hours or more, from the viewpoint of sufficiently nitriding the boron carbide particles. The pressurization and heating time in the nitriding process may be 30 hours or less, 20 hours or less, or 10 hours or less.

[0033] In the decarburization process, the boron carbonitride particles obtained in the nitriding process and a mixture containing a boron source are heated in a container to remove the boron carbonitride particles. The container may be, for example, a boron nitride crucible.

[0034] Examples of boron sources include boric acid, boron oxide, or mixtures thereof. The mixture may further contain other additives used in the art as needed. The mixing ratio of boron carbonitride particles to the boron source is selected as appropriate. When boric acid or boron oxide is used as the boron source, the proportion of boric acid or boron oxide may be, for example, 50 parts by mass or more, 80 parts by mass or more, 300 parts by mass or less, or 250 parts by mass or less, per 100 parts by mass of boron carbonitride.

[0035] The atmosphere in the decarburization process may be at normal pressure (atmospheric pressure) or a pressurized atmosphere. The pressure in the decarburization process may be, for example, 0.5 MPa or less or 0.3 MPa or less, or 0.01 MPa or more or 0.03 MPa or more.

[0036] In the decarburization process, for example, the temperature is first raised to a predetermined temperature (the temperature at which decarburization can begin), and then further raised to a predetermined holding temperature. The predetermined temperature (the temperature at which decarburization can begin) may be, for example, 1000°C or higher, 1500°C or lower, or 1200°C or lower. The rate at which the temperature is raised from the predetermined temperature (the temperature at which decarburization can begin) to the holding temperature may be, for example, 5°C / min or lower, 4°C / min or lower, 3°C / min or lower, or 2°C / min or lower.

[0037] The holding temperature may be 1800°C or higher or 2000°C or higher, from the viewpoint of promoting good particle growth. The holding temperature may be 2200°C or lower or 2100°C or lower.

[0038] The holding time at the holding temperature may be, for example, 0.5 hours or more, 1 hour or more, 3 hours or more, or 5 hours or more, from the viewpoint of ensuring good particle growth. The holding time at the holding temperature may be, for example, 40 hours or less, 30 hours or less, or 20 hours or less.

[0039] The boron nitride particles obtained in the manner described above may be subjected to a classification step (sieving) to obtain boron nitride particles having a desired particle size.

[0040] The boron nitride particles described above are suitably used, for example, in heat dissipation members. When used in heat dissipation members, 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 above-mentioned boron nitride particles.

[0041] The content of the boron nitride particles described above may 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, based on the total volume of the resin composition, from the viewpoint of improving the thermal conductivity of the resin composition and easily obtaining excellent heat dissipation performance. The content of the boron nitride powder may be 85% by volume or less, 80% by volume or less, or 75% by volume or less, based on the total volume of the resin composition, from the viewpoint of suppressing the generation of voids during molding and the reduction of insulation and mechanical strength.

[0042] Examples of resins include epoxy resins, silicone resins, silicone rubbers, acrylic resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyimides, polyamideimides, polyetherimides, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ethers, polyphenylene sulfides, fully aromatic polyesters, polysulfones, liquid crystal polymers, polyethersulfones, polycarbonates, maleimide-modified resins, ABS (acrylonitrile-butadiene-styrene) resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins.

[0043] The resin content may be 15% or more by volume, 20% or more by volume, or 25% or more by volume, based on the total volume of the resin composition, and may be 50% or less by volume, 45% or less by volume, 40% or less by volume, 35% or less by volume, or 30% or less by volume.

[0044] The resin composition may further contain a curing agent for curing the resin. The curing agent is appropriately selected depending on the type of resin. For example, when the resin is an epoxy resin, examples of curing agents include phenol novolac compounds, acid anhydrides, amino compounds, and imidazole compounds. The content of the curing agent may be, for example, 0.5 parts by mass or more, or 1.0 part by mass or more, or 15 parts by mass or less, or 10 parts by mass or less, per 100 parts by mass of the resin.

[0045] The resin composition may further contain other components. These other components may include curing accelerators (curing catalysts), coupling agents, wetting and dispersing agents, surface modifiers, and the like.

[0046] Examples of curing accelerators (curing catalysts) include phosphorus-based curing accelerators such as tetraphenylphosphonium tetraphenylborate and triphenylphosphorate, imidazole-based curing accelerators such as 2-phenyl-4,5-dihydroxymethylimidazole, and amine-based curing accelerators such as boron trifluoride monoethylamine.

[0047] Examples of 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, methacrylic groups, and mercapto groups.

[0048] Examples of wetting and dispersing agents include phosphate ester salts, carboxylic acid esters, polyesters, acrylic copolymers, and block copolymers.

[0049] Examples of surface modifiers include acrylic-based surface modifiers, silicone-based surface modifiers, vinyl-based modifiers, and fluorine-based surface modifiers. [Examples]

[0050] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the following examples.

[0051] (Example 1) Boron carbide particles with an average particle size (D50) of 26 μm were packed into a carbon crucible and heated and pressurized by the HIP method for 1.5 hours at 1750°C and 196 MPa in a nitrogen gas atmosphere using a hot isostatic pressurizing device (Kobe Steel, Ltd., 02-SYSTEM15× type) to nitride the boron carbide particles and obtain boron carbonitride particles (B4CN4). 100 parts by mass of the obtained boron carbonitride particles and 150 parts by mass of boric acid were mixed using a Henschel mixer, and the mixture was packed into a boron nitride crucible and heated in a resistance heating furnace at atmospheric pressure and a nitrogen gas atmosphere at a holding temperature of 2000°C and 0.03 MPa for a holding time of 5 hours to obtain coarse particles. The coarse particles were crushed in a mortar for 10 minutes and then classified using a nylon sieve with a mesh size of 175 μm. This yielded a particle aggregate (powder).

[0052] (Example 2) A particle aggregate (powder) was obtained in the same manner as in Example 1, except that the temperature for nitriding the boron carbide particles was changed to 1800°C.

[0053] (Example 3) A particle aggregate (powder) was obtained in the same manner as in Example 2, except that the amount of boric acid was changed to 100 parts by mass.

[0054] (Comparative Example 1) An aggregate of boron nitride particles (powder) was obtained in the same manner as in Example 1, except that boron carbide particles were nitrided to boron carbonitride particles by heating and pressurizing them in a nitrogen gas atmosphere using a resistance heating furnace at 2000°C and 0.85 MPa for 25 hours.

[0055] [X-ray diffraction measurement] A portion of the particles obtained in each example were collected and subjected to X-ray diffraction measurement using an X-ray diffractometer (Rigaku Corporation, "ULTIMA-IV"). The X-ray diffraction measurement results, as well as the X-ray diffraction measurement results of boron nitride particles obtained in Comparative Example 1, 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 were obtained in each example.

[0056] [Measurement of void area and equivalent radius of circle in the cross-section of boron nitride particles] Boron nitride particles were embedded in epoxy resin, and the resin was cured to obtain a cured product. The cured product was polished to expose the cross-section of the boron nitride particles, which was then used as a sample for measurement. The sample for measurement was observed using a SEM at a magnification of 1000x, and a BMP image was obtained that allowed confirmation of the entire cross-section of a single boron nitride particle. The image was imported into the image processing software "imageJ," and a single boron nitride particle in the image was selected. An outline was drawn around the outer edge of the selected boron nitride particle. The image was cropped into a rectangle circumscribing the outlined region, and the region outside the outlined region (the region where the selected boron nitride particle does not exist) was masked. After filtering with a median filter (1 pixel), binarization was performed using the Otsu method on the region consisting of the boron nitride particle and the other region (resin region). After filtering with a maximum filter (1 pixel), fill holes processing was performed to extract the contour of the boron nitride particle. The extracted contours were applied to the binarized image, and the area outside the contours was masked to obtain an image for analysis. The image for analysis was imported into the image processing software "OpenCV" (language: Python). From the image for analysis, the area of ​​the region consisting of boron nitride in the cross-section of the boron nitride particle, and the area of ​​each of the multiple resin regions (voids) in the cross-section of the boron nitride particle were measured, and the equivalent circle radius of each of the multiple resin regions (voids) was calculated from the area of ​​each of the multiple resin regions (voids). In addition, from the area and equivalent circle radius of the multiple voids, the area ratio of voids with an equivalent circle radius of less than 1 μm to the total area of ​​the multiple voids, the area ratio of voids with an equivalent circle radius of 2 μm or more to the total area of ​​the multiple voids, the area ratio of the multiple voids to the total area of ​​the region consisting of boron nitride and the multiple voids, the average equivalent circle radius, and the maximum equivalent circle radius were calculated. The calculation results are shown in Table 1. Furthermore, Figure 2 shows an SEM image of the cross-section of the boron nitride particles of Example 1, Figure 3 shows an SEM image of the cross-section of the boron nitride particles of Comparative Example 1, Figure 4 shows a binarized image of the cross-section of the boron nitride particles of Example 1, and Figure 5 shows a binarized image of the cross-section of the boron nitride particles of Comparative Example 1.

[0057] [Measurement of the maximum length of boron nitride particles] Boron nitride particles were observed using a scanning electron microscope (SEM), and their maximum length was measured. The measurement results are shown in Table 1.

[0058] [Table 1]

[0059] [Measurement of thermal conductivity] 100 parts by mass of naphthalene-type epoxy resin (DIC Corporation, HP4032) and 10 parts by mass of imidazole compound (Shikoku Chemicals Co., Ltd., 2E4MZ-CN) as a curing agent were mixed. Then, the boron nitride particles obtained in Examples 2 and 3 and Comparative Example 1 were mixed in so that the boron nitride particle filling rate was 70% by volume to obtain a resin composition. This resin composition was subjected to degassing under reduced pressure of 500 Pa for 10 minutes and applied to a PET sheet to a thickness of 1.0 mm. After that, it was subjected to a temperature of 150°C and a pressure of 160 kg / cm². 2 A 0.5 mm thick sheet of heat dissipation material was fabricated by pressing and heating under specified conditions for 60 minutes. A 10 mm x 10 mm sample was cut from the fabricated heat dissipation material, and the thermal diffusivity A(m) of the sample was measured using the laser flash method with a xenon flash analyzer (NETZSCH, LFA447NanoFlash). 2 The specific gravity B (kg / m³) of the sample was measured. 3 The specific heat capacity (J / (kg·K)) of the sample was measured using the Archimedes method. The specific heat capacity (C) of the sample was also measured using a differential scanning calorimeter (Rigaku Corporation, ThermoPlusEvoDSC8230). Using these physical properties, the thermal conductivity (H) was calculated from the formula H = A × B × C. The thermal conductivity of the heat dissipation material made using the boron nitride particles obtained in Example 2 was 22 W / (m·K), the thermal conductivity of the heat dissipation material made using the boron nitride particles obtained in Example 3 was 24 W / (m·K), and the thermal conductivity of the heat dissipation material made using the boron nitride particles obtained in Comparative Example 1 was 17 W / (m·K).

Claims

1. A boron nitride particle having multiple voids within the particle, A boron nitride particle having 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 ​​the plurality of voids is 30% or more and 60% or less.

2. A boron nitride particle having multiple voids within the particle, A boron nitride particle having a cross-section in which the area ratio of the plurality of voids is 35% or less of the total area of ​​the region made of boron nitride and the plurality of voids.

3. The boron nitride particle according to claim 2, wherein in the cross-section, the area ratio of voids with an equivalent circular radius of less than 1 μm to the total area of ​​the plurality of voids is 30% or more.

4. The boron nitride particle according to claim 1 or 2, wherein 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 60% or less.

5. The boron nitride particle according to claim 1 or 2, wherein in the cross-section, the average equivalent radius of the plurality of voids is 1.5 μm or less.

6. A process to obtain boron carbonitride particles by nitriding boron carbide particles under hot isostatic pressure, The process involves decarburizing the boron carbonitride particles to obtain boron nitride particles, A method for producing boron nitride particles, comprising the following:

7. A resin composition comprising boron nitride particles according to any one of claims 1 to 3 and a resin.

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