Boron nitride powder and resin composition

Abstract

A boron nitride powder, which is an aggregate of boron nitride particles, wherein for 20 boron nitride particles A selected from the boron nitride powder, when each particle is crushed by gradually applying a load at a load rate of 0.7 mN / s in any direction, the average displacement Y (μm) of the boron nitride particles A in that direction until crushing is achieved is 0.20 or more relative to the average particle size X (μm) of the boron nitride powder before the load is applied.

Description

Technical Field

[0001] This invention relates to boron nitride powder and resin compositions. Background Technology

[0002] In electronic components such as power devices, transistors, thyristors, and CPUs, there is a challenge of efficiently dissipating the heat generated during operation. To address this, current methods include increasing the thermal conductivity of the insulating layer of the printed circuit board (PCB) on which the electronic components are mounted, or mounting the electronic components or PCB on heat sinks using electrically insulating thermal interface materials. Such insulating layers and thermal interface materials utilize ceramic powders with high thermal conductivity.

[0003] As a ceramic powder, boron nitride powder, with its high thermal conductivity, high insulation, and low relative permittivity, has attracted attention. For example, Patent Document 1 discloses a hexagonal boron nitride powder. In an attempt to improve filling performance by further spherizing the shape of the aggregates, while simultaneously increasing powder strength, and further improving the purity of the powder, the paper aims to enhance the insulation and stabilize the voltage resistance of heat transfer sheets and the like filled with this powder. This hexagonal boron nitride powder is characterized by an average aspect ratio of 5 to 10 for primary particles, an aggregate size of 2 μm to 200 μm with an average particle size (D50), and a bulk density of 0.5 to 1.0 g / cm³. 3 .

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2011-98882 Summary of the Invention

[0007] However, in recent years, with the increasing speed and integration of circuits within electronic components and the increasing mounting density of electronic components on printed circuit boards, the importance of heat dissipation has further increased. Therefore, heat dissipation materials with higher thermal conductivity than ever before are required.

[0008] Therefore, the main objective of this invention is to provide boron nitride powder that enables the production of heat dissipation materials with excellent thermal conductivity.

[0009] One aspect of the present invention is a boron nitride powder, which is an aggregate of boron nitride particles. For 20 boron nitride particles A selected from the boron nitride powder, when each particle is crushed by gradually applying a load at a load rate of 0.7 mN / s in any direction, the average displacement Y (μm) of the boron nitride particle A in that direction until it is crushed is relative to the average particle size X (μm) of the boron nitride powder before the load is applied, and the ratio is 0.20 or more.

[0010] The average value Y of the above displacement can be 14 μm or more.

[0011] The average crushing strength of the above boron nitride powder can be above 8 MPa.

[0012] The aforementioned boron nitride particles are composed of multiple boron nitride sheets, which are chemically bonded to each other.

[0013] Another aspect of the present invention is a resin composition comprising the aforementioned boron nitride powder and resin.

[0014] According to the present invention, a boron nitride powder can be provided, which can realize a heat dissipation material with excellent thermal conductivity. Attached Figure Description

[0015] Figure 1 This is a SEM image of a cross-section of boron nitride particles in the boron nitride powder of Example 1.

[0016] Figure 2 This is a SEM image of the surface of boron nitride particles in the boron nitride powder of Example 1.

[0017] Figure 3 SEM images of the surface of boron nitride particles in the boron nitride powder of Comparative Example 1.

[0018] Figure 4 SEM image of a cross section of a sheet made using boron nitride powder from Example 1.

[0019] Figure 5 SEM image of a cross section of a sheet made using boron nitride powder from Comparative Example 1. Detailed Implementation

[0020] The embodiments of the present invention will now be described in detail.

[0021] One aspect of the present invention is a boron nitride powder, which is an aggregate of boron nitride particles (a powder composed of multiple boron nitride particles). For 20 boron nitride particles A selected from the boron nitride powder, when each particle is crushed by gradually applying a load at a load rate of 0.7 mN / s in any direction, the average displacement Y (μm) of the boron nitride particle A in that direction until it is crushed is relative to the average particle size X (μm) of the boron nitride powder before the load is applied, and the ratio is 0.20 or more.

[0022] Boron nitride particles can be composed of multiple boron nitride flakes, which can, for example, have a scale-like shape. In this case, the length of the boron nitride flakes in the longitudinal direction can be, for example, more than 1 μm or less than 10 μm.

[0023] From the perspective of achieving a heat dissipation material with better thermal conductivity, multiple boron nitride sheets can be chemically bonded together. The chemical bonding of multiple boron nitride sheets can be confirmed using scanning electron microscopy (SEM) by not observing the boundaries between the boron nitride sheets at the bonded portions.

[0024] The average thickness of the boron nitride sheet can be less than 0.30 μm, less than 0.25 μm, less than 0.25 μm, less than 0.20 μm, or less than 0.15 μm, or greater than 0.05 μm or greater than 0.10 μm. The average thickness of the boron nitride sheet is defined as the average thickness of 40 boron nitride sheets measured in a scanning electron microscope (SEM) at 10,000x magnification, after the SEM image of the surface of the boron nitride particles is imported into image analysis software (e.g., "Mac-view" manufactured by MOUNTECH Co., Ltd).

[0025] From the perspective of achieving heat dissipation materials with superior thermal conductivity, the average major diameter of boron nitride sheets can be greater than 0.5 μm, greater than 1.0 μm, or greater than 1.5 μm, or less than 4.0 μm, less than 3.5 μm, or less than 3.0 μm. The major diameter refers to the maximum length perpendicular to the thickness direction. The average major diameter of boron nitride sheets is defined as follows: the average major diameter of 40 boron nitride sheets measured in a scanning electron microscope (SEM) image obtained by observing the surface of boron nitride particles at 10,000x magnification and importing it into image analysis software (e.g., "Mac-view" manufactured by MOUNTECH Co., Ltd).

[0026] Considering the possibility of achieving heat dissipation materials with superior thermal conductivity, the average aspect ratio of boron nitride sheets can be 7.0 or higher, 8.0 or higher, 9.0 or higher, 9.5 or higher, 10.0 or higher, or 10.5 or higher. The average aspect ratio of boron nitride sheets can be 20.0 or lower, 17.0 or lower, or 15.0 or lower. The average aspect ratio of boron nitride sheets is defined as the average of the aspect ratio (length / thickness) calculated from the length and thickness of 40 boron nitride sheets.

[0027] Boron nitride particles can also consist essentially of only boron nitride. This can be confirmed in X-ray diffraction measurements by detecting only the state of the peaks originating from boron nitride.

[0028] The average particle size X of the boron nitride powder can be, for example, 20 μm or more, 40 μm or more, 50 μm or more, 60 μm or more, 70 μm or more, or 80 μm or more, and can be less than 150 μm, 120 μm or less, 110 μm or less, or 100 μm or less. The average particle size X of the boron nitride powder can be determined by laser diffraction scattering. The average particle size X of the boron nitride powder can be considered as the average particle size of 20 selected boron nitride particles A from the boron nitride powder.

[0029] The crushing of boron nitride particles was performed on 20 boron nitride particles A selected from boron nitride powder, according to JIS R 1639-5:2007, using a micro compression tester (e.g., the "MCT-211" manufactured by Shimadzu Corporation). Specifically, boron nitride particles A were placed on a test stage, and the indenter (e.g., 200 μm in diameter) of the micro compression tester (e.g., the MCT-211 manufactured by Shimadzu Corporation) was lowered toward each boron nitride particle A on the test stage, gradually applying a load to crush the boron nitride particles A at a load rate of 0.7 mN / s. At this time, the displacement in the load direction of boron nitride particles A until crushing was measured (unit: μm; the absolute value of the difference between the particle size in the load direction and the particle size in the load direction before crushing).

[0030] The displacement of boron nitride particle A can be observed, for example, using a microscope attached to a micro compression testing machine (e.g., Shimadzu Corporation, MCT-211), and the observed image can be imported into image analysis software (e.g., software attached to the micro compression testing machine) for measurement.

[0031] From the perspective of achieving a heat dissipation material with superior thermal conductivity, the average displacement Y of boron nitride particles A can be 14 μm or more, 17 μm or more, 20 μm or more, or 23 μm or more. From the perspective of achieving a heat dissipation material with superior thermal conductivity, the average displacement Y of boron nitride particles A can be 40 μm or less, 30 μm or less, or 27 μm or less.

[0032] Y / X is calculated from the average particle size X of the boron nitride powder and the average displacement Y of boron nitride particles A. The Y / X of 20 boron nitride particles A is then calculated. Considering the possibility of achieving a heat dissipation material with superior thermal conductivity, the Y / X of boron nitride particles A can be 0.20 or higher, 0.22 or higher, 0.24 or higher, 0.25 or higher, 0.26 or higher, 0.28 or higher, or 0.29 or higher. Considering the possibility of achieving a heat dissipation material with superior thermal conductivity, the Y / X of boron nitride particles A can be 0.50 or lower, 0.40 or lower, or 0.30 or lower.

[0033] Considering that boron nitride powder (boron nitride particles) is less prone to breakage when mixed with resin, thus enabling the development of a heat dissipation material with superior thermal conductivity, the average crushing strength of the boron nitride powder can be 8 MPa or higher, 9 MPa or higher, 10 MPa or higher, or 12 MPa or higher. Considering the possibility of achieving a heat dissipation material with even better thermal conductivity, the average crushing strength of the boron nitride powder can be 17 MPa or lower, 15 MPa or lower, or 13 MPa or lower. The average crushing strength of the boron nitride powder is the average value measured for 20 boron nitride particles in the boron nitride powder, according to JIS R1639-5:2007, using a micro-compression testing machine (e.g., the "MCT-211" manufactured by Shimadzu Corporation).

[0034] From the perspective of achieving heat dissipation materials with better thermal conductivity, the nitrogen defect amount of boron nitride powder can be 1.0 × 10⁻⁶. 14 1.0 × 10⁻⁶ or higher, or 1.0 × 10⁻⁶. 18 The nitrogen defect count is below 1 / g. The thermal conductivity of boron nitride decreases due to defects; therefore, it can be considered that a heat dissipation material with better thermal conductivity can be achieved by reducing the nitrogen defect count. The nitrogen defect count of boron nitride powder was determined by electron spin resonance (ESR) measurement using a JEMFA-200 electron spin resonance apparatus manufactured by Nippon Electron Ltd., with 60 mg of boron nitride powder filled into a quartz glass sample tube. More specifically, in the ESR measurement performed under the following conditions, the integral intensity of the ESR signal that can be confirmed at g = 2.00 ± 0.04 after calculating the g value is defined as the nitrogen defect count.

[0035] [Measurement Conditions]

[0036] Magnetic field scanning range: 0~3290gauss (0~329mT)

[0037] Magnetic field modulation: 5 gauss (0.5 mT)

[0038] Time constant: 0.3s

[0039] Electromagnetic waves irradiated: 0.5mW, approximately 9.16GHz (the frequency of the irradiated electromagnetic waves was slightly adjusted in each measurement to make it the resonant frequency).

[0040] Scan time: 15 min

[0041] Amplifier gain: 200

[0042] Mn marking: 750

[0043] Measurement environment: room temperature (25℃)

[0044] Standard specimen: Coal standard specimen manufactured by Nippon Electron Ltd. (spin: 3.56 × 10⁻⁶) 13 (per g)

[0045] By using the boron nitride powder described above, a heat dissipation material with excellent thermal conductivity can be achieved. The inventors speculate the following reasons for this: By maximizing the Y / X ratio of boron nitride particles A in the boron nitride powder, it can be said that when a load is applied to boron nitride particles A, they easily deform in the load direction until they are crushed. Therefore, it can be considered that even when an external force is applied to boron nitride particles A, they become less prone to crushing due to deformation. By mixing boron nitride powder (boron nitride particles) containing such boron nitride particles A with resin and molding it into a heat dissipation material, it can be considered that because the boron nitride particles in the boron nitride powder are less prone to breakage and appropriately deform to form inter-particle flow on the surface, an efficient heat transfer path provided by the boron nitride particles is easily formed and maintained in the heat dissipation material. Therefore, the heat dissipation material has excellent thermal conductivity. However, the reasons for achieving a heat dissipation material with excellent thermal conductivity are not limited to the above reasons.

[0046] The aforementioned boron nitride powder can be manufactured, for example, by a manufacturing method comprising the following steps: a nitriding step, wherein boron carbide-containing particles (hereinafter sometimes referred to as "boron carbide particles") are nitrided to obtain boron carbonitride-containing particles (hereinafter sometimes referred to as "boron carbonitride particles"); a filling step, wherein a mixture comprising the boron carbonitride-containing particles and a boron source containing at least one selected from boric acid and boron oxide is filled into a container; a decarburization step, wherein the boron carbonitride-containing particles are decarburized by pressurizing and heating the mixture while improving the airtightness of the container; in the filling step, the amount of boron atoms in the boron source is 1.0 to 2.2 mol relative to 1 mol of boron carbonitride in the mixture. That is, another embodiment of the present invention is the above-described method for manufacturing boron nitride powder.

[0047] In the above manufacturing method, the boron carbide particles in the nitriding process can be, for example, in powder form (boron carbide powder). Boron carbide powder can be manufactured by known manufacturing methods. One method for manufacturing boron carbide particles (boron carbide powder) is to mix boric acid with acetylene black and then heat the mixture in an inert gas environment (e.g., nitrogen or argon) at 1800–2400°C for 1–10 hours to obtain blocky boron carbide particles. The blocky boron carbide particles obtained by this method are then appropriately pulverized, sieved, washed, impurities removed, and dried to obtain boron carbide powder.

[0048] The average particle size of boron carbide powder can be adjusted by changing the pulverization time of the blocky boron carbide particles. The average particle size of boron carbide powder can be greater than 5 μm, greater than 7 μm, or greater than 10 μm, or less than 100 μm, less than 90 μm, less than 80 μm, or less than 70 μm. The average particle size of boron carbide powder can be determined by laser diffraction scattering.

[0049] The nitriding process involves filling boron carbide particles into a container (such as a graphite crucible), pressurizing and heating them in an environment that allows the nitriding reaction to occur, thereby nitriding the boron carbide particles to obtain boron carbonitride particles.

[0050] The environment in which the nitriding reaction takes place during the nitriding process can 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, and the proportion of nitrogen in the nitriding gas can be 95.0% by volume or more, 99.0% by volume or more, or 99.9% by volume or more.

[0051] From the perspective of ensuring sufficient nitriding of boron carbide particles, the pressure during the nitriding process can be 0.6 MPa or higher, or 0.7 MPa or higher. Alternatively, the pressure during the nitriding process can be 1.0 MPa or lower, or 0.9 MPa or lower.

[0052] From the perspective of ensuring sufficient nitriding of boron carbide particles, the heating temperature in the nitriding process can be above 1800℃ or above 1900℃. Alternatively, the heating temperature in the nitriding process can be below 2400℃ or below 2200℃.

[0053] From the perspective of ensuring sufficient nitriding of boron carbide particles, the time for pressurization and heating in the nitriding process can be more than 3 hours, more than 5 hours, or more than 8 hours. The time for pressurization and heating in the nitriding process can be less than 30 hours, less than 20 hours, or less than 10 hours.

[0054] In the filling process, a mixture is filled into a container, the mixture comprising boron carbonitride particles obtained in the nitriding process and a boron source containing at least one selected from boric acid and boron oxide.

[0055] The container used in the filling process can be, for example, a boron nitride crucible. During the filling process, the mixture can be filled to the bottom of the container, for example. To improve the airtightness of the container, the opening can be capped, or part or all of the gap between the container and the cap can be filled with resin. The filling resin can be, for example, epoxy resin, and may also contain a curing agent. To inhibit resin flow, the filling resin can be a high-viscosity resin.

[0056] The amount of boron atoms in the boron source in the mixture during the filling process can be 1.0 to 2.2 mol relative to 1 mol of boron carbonitride in the mixture. Considering the viewpoint that the obtained boron nitride powder can achieve a heat dissipation material with better thermal conductivity, the amount of boron atoms relative to 1 mol of boron carbonitride in the mixture can be 2.0 mol or less, 1.9 mol or less, 1.8 mol or less, 1.7 mol or less, 1.6 mol or less, 1.5 mol or less, 1.4 mol or less, or 1.3 mol or less. Considering the viewpoint of increasing the average thickness of the boron nitride sheet, the amount of boron atoms relative to 1 mol of boron carbonitride in the mixture can be 1.1 mol or more, or 1.2 mol or more.

[0057] The decarburization process involves heating a mixture containing boron carbonitride particles and a boron source at an environment above atmospheric pressure to decarburize the boron carbonitride particles, thereby obtaining boron nitride particles (boron nitride powder).

[0058] The environment in the decarburization process can be a nitrogen environment, or a normal pressure (atmospheric pressure) or a pressurized nitrogen environment. Considering the need for sufficient decarburization of boron carbonitride particles, the pressure in the decarburization process can be below 0.5 MPa or below 0.3 MPa.

[0059] Heating in the decarburization process can be performed, for example, by raising the temperature to a specified temperature (decarburization start temperature) and then further raising the temperature to a specified temperature (holding temperature) at a specified heating rate. The heating rate from the decarburization start temperature to the holding temperature can be, for example, less than 5°C / min, less than 3°C / min, or less than 2°C / min.

[0060] From the perspective of ensuring sufficient decarburization of boron carbonitride particles, the decarburization initiation temperature can be above 1000℃ or above 1100℃. Alternatively, the decarburization initiation temperature can be below 1500℃ or below 1400℃.

[0061] Considering the need for sufficient decarburization of boron carbonitride particles, the holding temperature can be above 1800℃ or 2000℃. Alternatively, the holding temperature can be below 2200℃ or 2100℃.

[0062] From the perspective of ensuring sufficient decarburization of boron carbonitride particles, the heating time at the holding temperature can be 0.5 hours or more, 1 hour or more, 3 hours or more, 5 hours or more, or 10 hours or more. The heating time at the holding temperature can be less than 40 hours, less than 30 hours, or less than 20 hours.

[0063] For the boron nitride powder obtained as described above, a process of classifying the boron nitride powder with the desired particle size by sieving (classification process) can also be implemented.

[0064] The boron nitride powder obtained as described above can be mixed with resin for example and used as a resin composition. That is, another embodiment of the present invention is a resin composition containing the above-described boron nitride powder and resin.

[0065] As resins, for example, 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, 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 can be used.

[0066] From the perspective of achieving a heat dissipation material with superior thermal conductivity, the content of boron nitride powder can be 30% or more, 40% or more, 50% or more, or 60% or more, based on the total volume of the resin composition. From the perspective of suppressing the formation of voids during the molding of the heat dissipation material and suppressing the reduction of the insulation and mechanical strength of the heat dissipation material, the content of boron nitride powder can be 85% or less or 80% or less, based on the total volume of the resin composition.

[0067] The resin content can be appropriately adjusted according to the intended use and required properties of the resin composition. Based on the total volume of the resin composition, the resin content can be 15% or more, 20% or more, 30% or more, or 40% or more, or it can be less than 70% or less, 60% or less, or 50% or less, for example.

[0068] The resin composition may further contain a curing agent for curing the resin. The curing agent may be appropriately selected depending on the type of resin. Examples of curing agents that can be used with epoxy resins include phenolic varnish compounds, acid anhydrides, amino compounds, imidazole compounds, etc. The content of the curing agent may be 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, relative to 100 parts by weight of the resin.

[0069] The resin composition may further contain other components. These other components may include, for example, curing accelerators (curing catalysts), coupling agents, wetting and dispersing agents, and surface conditioners.

[0070] Examples of curing accelerators (curing catalysts) include phosphorus-based curing accelerators such as tetraphenylphosphonium tetraphenylborate and triphenyl phosphate, imidazole-based curing accelerators such as 2-phenyl-4,5-dihydroxymethylimidazolium, and amine-based curing accelerators such as boron trifluoride monoethylamine.

[0071] 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.

[0072] Examples of wetting and dispersing agents include phosphate salts, carboxylic acid esters, polyesters, acrylic copolymers, and block copolymers.

[0073] Examples of surface modifiers include acrylic surface modifiers, silicone surface modifiers, ethylene surface modifiers, and fluorine surface modifiers.

[0074] The resin composition can be manufactured, for example, by a method comprising the steps of preparing boron nitride powder according to one embodiment (preparation step) and mixing the boron nitride powder with resin (mixing step). That is, another embodiment of the present invention is the method for manufacturing the above-described resin composition. In the mixing step, in addition to the boron nitride powder and resin, the above-described curing agent or other components may also be further mixed.

[0075] One embodiment of the method for manufacturing the resin composition may further include a step of pulverizing boron nitride powder (pulverization step). The pulverization step may be performed between the preparation step and the mixing step, or it may be performed simultaneously with the mixing step (the boron nitride powder may be pulverized while the boron nitride powder is being mixed with the resin).

[0076] The above-described resin composition can be used, for example, as a heat dissipation material. The heat dissipation material can be manufactured, for example, by curing the resin composition. The method for curing the resin composition can be appropriately selected depending on the type of resin contained in the resin composition (and the curing agent used as needed). For example, when the resin is an epoxy resin and the above-described curing agent is used, the resin can be cured by heating.

[0077] Example

[0078] The present invention will now be described in detail with reference to embodiments. However, the present invention is not limited to the embodiments described below.

[0079] (Example 1)

[0080] Boron carbide particles with an average particle size of 55 μm were filled into a graphite crucible, which was then heated at 2000 °C and 0.8 MPa for 20 hours under nitrogen atmosphere to obtain boron carbonitride particles. 100 parts by mass of the obtained boron carbonitride particles and 66.7 parts by mass of boric acid were mixed using a Henschel mixer to obtain a mixture in which the amount of boron atoms from the boron source was 1.2 mol per mol of boron carbonitride. This mixture was then filled into a boron nitride crucible, which was covered, and the entire gap between the crucible and the cover was filled with epoxy resin. The boron nitride crucible containing the mixture was heated in a carbon box within a resistance heating furnace at atmospheric pressure and nitrogen atmosphere for 10 hours to obtain coarse boron nitride particles. The coarse boron nitride particles were crushed in a mortar for 10 minutes and then classified using a nylon sieve with a mesh size of 109 μm to obtain boron nitride particles (boron nitride powder).

[0081] The SEM image of the cross-section of the obtained boron nitride particles is shown in Figure 1 .from Figure 1 It can be seen that multiple boron nitride sheets are chemically bonded to each other within the boron nitride particles.

[0082] (Example 2)

[0083] The amount of boric acid was varied such that the amount of boron atoms from the boron source was 1.4 mol relative to 1 mol of boron carbonitride in the mixture. Otherwise, boron nitride particles (boron nitride powder) were obtained under the same conditions as in Example 1. When the cross-section of the obtained boron nitride particles was confirmed by SEM, it was confirmed that multiple boron nitride sheets were chemically bonded to each other.

[0084] (Example 3)

[0085] The amount of boric acid was varied such that the amount of boron atoms from the boron source was 1.6 mol relative to 1 mol of boron carbonitride in the mixture. Otherwise, boron nitride particles (boron nitride powder) were obtained under the same conditions as in Example 1. When the cross-section of the obtained boron nitride particles was confirmed by SEM, it was confirmed that multiple boron nitride sheets were chemically bonded to each other.

[0086] (Example 4)

[0087] The amount of boric acid was varied such that the amount of boron atoms from the boron source was 1.8 mol relative to 1 mol of boron carbonitride in the mixture. Otherwise, boron nitride particles (boron nitride powder) were obtained under the same conditions as in Example 1. When the cross-section of the obtained boron nitride particles was confirmed by SEM, it was found that multiple boron nitride sheets were chemically bonded to each other.

[0088] (Example 5)

[0089] The amount of boric acid was varied such that the amount of boron atoms from the boron source was 1.1 mol relative to 1 mol of boron carbonitride in the mixture. Otherwise, boron nitride particles (boron nitride powder) were obtained under the same conditions as in Example 1.

[0090] (Comparative Example 1)

[0091] The amount of boric acid was varied such that the amount of boron atoms from the boron source was 2.7 mol relative to 1 mol of boron carbonitride in the mixture. Otherwise, boron nitride particles (boron nitride powder) were obtained under the same conditions as in Example 1.

[0092] [Determination of average particle size X]

[0093] The average particle size X of boron nitride powder was determined using a laser diffraction scattering particle size distribution measuring apparatus (LS-13 320) manufactured by Beckman Coulter Inc. The results of the average particle size X determination are shown in Table 1.

[0094] [Determination of the average displacement Y and Y / X]

[0095] For each boron nitride powder, 20 boron nitride particles were crushed using a micro-compression testing machine (Shimadzu Corporation, MCT-211) according to JIS R1639-5:2007, with each particle gradually subjected to a load at a rate of 0.7 mN / s. For each of the 20 boron nitride particles, the displacement in the load direction from before the application of the load to the point of crushing was measured using a microscope and image analysis software attached to the micro-compression testing machine. The average displacement value Y was calculated, and Y / X was calculated from the average particle size X and the average displacement value Y. The average displacement value Y and Y / X are shown in Table 1.

[0096] [Determination of crushing strength]

[0097] For each boron nitride powder obtained, 20 boron nitride particles were subjected to crushing strength testing according to JIS R1639-5:2007. A micro-compression testing machine (Shimadzu Corporation, “MCT-211”) was used as the testing apparatus. The crushing strength σ (unit: MPa) of each boron nitride particle was calculated using the following formula: σ = α × P / (π × d) where α is the dimensionless number α (=2.48) varying according to the particle's position, the crushing test force P (unit: N), and the average particle size d (unit: μm). 2 The crushing strength was calculated using the formula. The average value of the crushing strength of 20 boron nitride particles is shown in Table 1.

[0098] [Determination of the thickness, major diameter, and aspect ratio of boron nitride sheets]

[0099] The surface of boron nitride particles in boron nitride powder observed at 10,000x magnification was examined using a scanning electron microscope (JSM-7001F, manufactured by Nippon Electron Ltd.). SEM images of the boron nitride particle surface were imported into image analysis software (Mac-view, manufactured by MOUNTECH Co., Ltd.) to measure the thickness and major diameter (maximum length perpendicular to the thickness direction) of the boron nitride sheets disposed on the surface of the boron nitride particles. The thickness and major diameter of 40 boron nitride sheets were measured, and the average thickness and average major diameter of the boron nitride sheets constituting the boron nitride particles were calculated from the measured thickness and major diameter. Furthermore, the aspect ratio (length / thickness) of each boron nitride sheet was calculated from the measured thickness and major diameter, and the average aspect ratio was calculated from the aspect ratios of the 40 boron nitride sheets. The calculated average thickness, average major diameter, and average aspect ratio are shown in Table 1. SEM images of the surface of the boron nitride particles of Example 1 and Comparative Example 1 are shown in Table 1. Figure 2 and 3 .

[0100] [Determination of thermal conductivity]

[0101] A resin composition was obtained by mixing 100 parts by weight of a naphthalene-type epoxy resin (manufactured by DIC Corporation, HP4032) and 10 parts by weight of an imidazole compound (manufactured by Shikoku Kasei Corporation, 2E4MZ-CN) as a curing agent, and then further mixing 81 parts by weight of boron nitride powder obtained in the examples and comparative examples. The resin composition was subjected to degassing under reduced pressure of 500 Pa for 10 minutes and coated onto a PET sheet with a thickness of 1.0 mm. Subsequently, it was subjected to a temperature of 150°C and a pressure of 160 kg / cm². 2 The material was pressed and heated under pressure for 60 minutes to produce a 0.5 mm sheet of heat-dissipating material. A 10 mm × 10 mm sample was cut from the material for testing. The thermal diffusivity A(m) of the sample was determined using a xenon flash analyzer (NETZSCH LFA447NanoFlash) via laser flash method. 2 / second). Furthermore, the specific gravity B (kg / m³) of the test sample was determined using the Archimedes method. 3 Furthermore, the specific heat capacity C (J / (kg·K)) of the test sample was determined using a differential scanning calorimeter (Rigaku Corporation, ThermoPlus EvoDSC8230). Using these property values, the thermal conductivity H (W / (m·K)) was calculated from the formula H = A × B × C. The results of the thermal conductivity measurements are shown in Table 1. SEM images of the cross-sections of the heat dissipation materials prepared using boron nitride powders from Example 1 and Comparative Example 1 are shown in Table 1. Figure 4 and 5 .

[0102] Table 1

[0103]

Claims

1. A boron nitride powder, which is an aggregate of boron nitride particles. The boron nitride particles are composed of multiple boron nitride sheets, which are chemically bonded to each other; For 20 boron nitride particles A selected from the boron nitride powder, when crushing them by gradually applying a load at a load rate of 0.7 mN / s in any direction, the ratio of the average displacement Y of the boron nitride particle A in that direction until crushing to the average particle size X of the boron nitride powder before the load is applied is 0.20 to 0.29, where the units of the average value Y and the average particle size X are μm.

2. The boron nitride powder according to claim 1, wherein, The average displacement Y is greater than 14 μm.

3. The boron nitride powder according to claim 1 or 2, wherein, The average crushing strength is above 8 MPa.

4. A resin composition comprising boron nitride powder and resin as described in any one of claims 1 to 3.

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