Hexagonal boron nitride powder and resin composition

Abstract

One aspect of the present disclosure provides a hexagonal boron nitride powder including primary particles of hexagonal boron nitride, the hexagonal boron nitride powder having a specific surface area of 2.5 m 2 / g or less, a graphitization index of 2.0 or less, and a purity of 99 mass% or more.

Description

Technical Field

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

[0002] In electronic components such as transistors, thyristors, and CPUs, efficiently dissipating the heat generated during operation is a crucial issue. Therefore, heat dissipation components with high thermal conductivity are used alongside these components. On the other hand, boron nitride particles, due to their high thermal conductivity and high insulation properties, are widely used as filler materials in heat dissipation components.

[0003] For example, Patent Document 1 discloses a hexagonal boron nitride powder and its manufacturing method that can improve the thermal conductivity and withstand voltage (insulation breakdown voltage) of the aforementioned resins when used as a filler material for insulating and heat-dissipating materials such as resins.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-116401 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] In recent years, devices equipped with electronic components have seen continuous development towards high-speed and high-capacity signal transmission. Therefore, heat dissipation components are required to meet these demands. Specifically, heat dissipation components with small dielectric loss tangents are desirable.

[0009] As a method to reduce the dielectric loss tangent of heat dissipation components, for example, using a resin with a low dielectric loss tangent has been considered. However, while liquid crystal polymers and fluoropolymers, known as resins with low dielectric loss tangents, possess low dielectric loss tangents, their processability, thermal properties, and mechanical properties are insufficient for this application. Therefore, from the viewpoint of improving thermal properties, filler materials are typically used. However, due to the composition of the filler material, situations may arise where the low dielectric loss tangent characteristic of the resin cannot be fully utilized.

[0010] The purpose of this disclosure is to provide hexagonal boron nitride powder and resin compositions capable of manufacturing heat dissipation components with low dielectric loss tangent.

[0011] Methods for solving problems

[0012] One aspect of this disclosure provides a hexagonal boron nitride powder comprising primary particles of hexagonal boron nitride, said hexagonal boron nitride powder having a specific surface area of ​​2.5 m². 2The content is below / g, the graphitization index is below 2.0, and the purity is above 99% by mass.

[0013] The hexagonal boron nitride powder described above has a small specific surface area, which can suppress the adsorption of water and impurities that cause an increase in the dielectric loss tangent. Furthermore, by keeping the graphitization index and purity within a specified range, the generation of components from the hexagonal boron nitride itself that cause an increase in the dielectric loss tangent can be suppressed. Therefore, it is suitable as a filler material for manufacturing heat dissipation components with a low dielectric loss tangent.

[0014] The circularity of the aforementioned primary particles can be 0.8 or higher.

[0015] The water content per unit mass of the above-mentioned hexagonal boron nitride powder when heated to 500°C can be less than 300 ppm.

[0016] The water content per unit mass of the above-mentioned hexagonal boron nitride powder when heated to 200°C can be less than 250 ppm.

[0017] The water content per unit mass of the above-mentioned hexagonal boron nitride powder when heated from 201°C to 500°C can be less than 100 ppm.

[0018] In the above-mentioned hexagonal boron nitride powder, the average particle size of the primary particles is above 7.0 μm.

[0019] One aspect of this disclosure provides a resin composition comprising a resin and the aforementioned hexagonal boron nitride powder.

[0020] Because the above-mentioned resin composition contains the aforementioned hexagonal boron nitride powder, it can achieve a low dielectric loss tangent.

[0021] Invention Effects

[0022] According to this disclosure, hexagonal boron nitride powder and resin composition are available for manufacturing heat dissipation components with low dielectric loss tangent. Detailed Implementation

[0023] The following describes embodiments of this disclosure. However, these embodiments are merely examples for illustrating this disclosure and are not intended to limit this disclosure to its contents.

[0024] Unless otherwise specified, the materials exemplified in this specification may be used alone or in combination of two or more. Regarding the content of each component in the composition, where multiple substances belonging to the composition exist, unless otherwise specified, the total amount of such substances present in the composition is referred to.

[0025] One embodiment of the hexagonal boron nitride powder comprises primary particles of hexagonal boron nitride with a specific surface area of ​​2.5 m². 2 Hexagonal boron nitride powder has a particle size of less than 1 g, a graphitization index of less than 2.0, and a purity of more than 99% by mass. It can be an aggregate of primary particles of hexagonal boron nitride.

[0026] The upper limit of the specific surface area of ​​hexagonal boron nitride powder is 2.5 m². 2 Below / g, for example, it can be 2.2m 2 / g or less, 2.0m 2 / g or less, 1.8m 2 / g or less, or 1.6m 2 Below / g. When the upper limit of the specific surface area is within the above range, the adsorption of moisture, etc., can be suppressed, and the dielectric loss tangent can be further reduced. The lower limit of the specific surface area of ​​hexagonal boron nitride powder can be, for example, 0.5m². 2 / g or more, 0.8m 2 / g or more, 1.0m 2 / g or more, 1.2m 2 / g or more, or 1.4m 2 / g or higher. When the lower limit of the specific surface area is within the above range, the dielectric loss tangent of the hexagonal boron nitride powder can be further reduced. The specific surface area of ​​the hexagonal boron nitride powder can be adjusted within the above range, for example, it can be 0.5 to 2.5m². 2 / g, or 1.0~2.2m 2 / g.

[0027] The specific surface area referred to in this specification is the value measured using a specific surface area measuring device according to JIS Z 8830:2013 "Method for determination of specific surface area of ​​powders (solids) based on gas adsorption", and is calculated using the BET single-point method with nitrogen. More specifically, it is measured using the method described in the examples of this specification.

[0028] High crystallinity is preferred for hexagonal boron nitride. In the boron nitride powder of this embodiment, the graphitization index (sometimes also called the graphitization index (GI)) is used as an indicator of the crystallinity mentioned above. That is, for boron nitride powder containing hexagonal boron nitride with a low graphitization index, impurities are further reduced, and the increase of dielectric loss tangent can be suppressed. The upper limit of the graphitization index of hexagonal boron nitride powder is 2.0 or less, for example, it can be 1.9 or less, 1.5 or less, or 1.3 or less. By keeping the upper limit of the graphitization index of hexagonal boron nitride powder within the above range, the dielectric loss tangent can be further reduced. The lower limit of the graphitization index of hexagonal boron nitride powder is not particularly limited, for example, it can be 0.8 or more, or 1.0 or more. By keeping the lower limit of the graphitization index of hexagonal boron nitride powder within the above range, low dielectric loss tangent and high heat dissipation can be achieved at a higher level. The graphitization index of hexagonal boron nitride powder can be adjusted within the above range, for example, it can be 1.0 to 2.0.

[0029] The graphitization index in this specification is also a known indicator of the degree of crystallinity of graphite (e.g., J. Thomas et al., J. Am. Chem. Soc. 84, 4619 (1962)). The graphitization index is calculated based on the spectrum obtained by measuring the primary particles of hexagonal boron nitride using powder X-ray diffraction. First, in the X-ray diffraction spectrum, the area values ​​(in arbitrary units) enclosed by the integrated intensity (i.e., each diffraction peak) of each diffraction peak corresponding to the (100), (101), and (102) planes of the primary particles of hexagonal boron nitride are calculated from the baselines of the diffraction peaks, and are denoted as S100, S101, and S102, respectively. Using the calculated area values, the value of [(S100+S101) / S102] is calculated to determine the graphitization index. More specifically, it is determined using the method described in the embodiments of this specification.

[0030] The purity of hexagonal boron nitride powder can be high, for example, 99.5% by mass or higher, or 99.8% by mass or higher. The purity of the boron nitride powder in this specification refers to a value calculated by titration. More specifically, it is determined by titration using the methods described in the examples of this specification.

[0031] From the viewpoint of improving the filling properties of resins and the like in the fabrication of heat dissipation components, and making the thermal conductivity and dielectric constant of the heat dissipation components isotropic, the primary particles of hexagonal boron nitride are preferably spherical or nearly spherical in shape. The sphericity of the primary particles can be, for example, 0.80 or more, 0.85 or more, 0.88 or more, or 0.90 or more.

[0032] The roundness of primary particles in this specification refers to the average roundness measured using the following method. Specifically, for images of boron nitride particles taken using a scanning electron microscope (SEM) (magnification: 10,000x, image resolution: 1280 × 1024 pixels), the projected area (S) and perimeter (L) of the boron nitride particles are calculated using image analysis software. Then, using the obtained projected area (S) and perimeter (L), the roundness is calculated according to the following formula: Roundness = 4πS / L 2 The roundness is then calculated. The average roundness is defined as the mean roundness calculated for any 100 selected boron nitride particles. Image analysis software, such as "MacView" (trade name) manufactured by Mountech, can be used.

[0033] In the above-mentioned hexagonal boron nitride powder, the lower limit of the average particle size of the primary particles can be, for example, 7.0 μm or more, 7.5 μm or more, 8.0 μm or more, 8.5 μm or more, or 9.0 μm or more. When the lower limit of the average particle size is within the above range, it is suitable for use from the viewpoint of filling and heat dissipation. The upper limit of the average particle size of the primary particles can be, for example, 40 μm or less, 30 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less. When the upper limit of the average particle size is within the above range, the resin composition can have good formability. The average particle size of the primary particles in the hexagonal boron nitride powder can be adjusted within the above range, for example, it can be 7.0 to 40 μm, or 7.5 to 15 μm. For example, when the hexagonal boron nitride powder is dispersed in a resin and molded into a sheet, the average particle size of the primary particles can be selected according to the thickness of the sheet.

[0034] The average particle size in this specification is the value obtained by measuring a sample obtained by homogenizing hexagonal boron nitride powder, and is the average particle size excluding aggregated particles. The average particle size in this specification is also the particle size at which the cumulative value of the cumulative particle size distribution reaches 50% (median particle size, d50). The average particle size in this specification is measured using a laser diffraction scattering particle size distribution measuring apparatus as described in ISO 13320:2009. Specifically, it is measured using the method described in the examples of this specification. For example, a "LS-13 320" (apparatus name) manufactured by BECKMAN COULTER can be used as a laser diffraction scattering particle size distribution measuring apparatus.

[0035] Hexagonal boron nitride powder can adsorb moisture on its surface. When a periodic electric field is applied to hexagonal boron nitride powder that has adsorbed moisture, a portion of the electrical energy is consumed as heat, thus tending to increase the dielectric loss tangent. From the viewpoint of further reducing the dielectric loss tangent, hexagonal boron nitride powder with low moisture content is preferred. The moisture content per unit mass of hexagonal boron nitride powder when heated to 500°C can be, for example, below 300 ppm, 280 ppm, 260 ppm, 240 ppm, or 220 ppm.

[0036] By heating to 200°C, moisture on the surface of hexagonal boron nitride powder can be removed. The water content per unit mass of hexagonal boron nitride powder when heated to 200°C can be, for example, less than 250 ppm, less than 200 ppm, less than 180 ppm, less than 160 ppm, or less than 150 ppm.

[0037] When hydroxyl groups (OH groups) are present on the surface of hexagonal boron nitride powder, for example, at temperatures exceeding 200°C, some of it can detach as moisture. That is, moisture may be generated after use at high temperatures. Therefore, it is preferable that moisture generation at high temperatures is also suppressed in hexagonal boron nitride powder. The water content per unit mass of hexagonal boron nitride powder when heated from 201°C to 500°C can be, for example, below 100 ppm, 90 ppm or less, 80 ppm or less, or 70 ppm or less. When the water content per unit mass when heated from 201°C to 500°C is within the above range, the moisture adsorption performance of hexagonal boron nitride powder is suppressed to a lower level, further suppressing moisture adsorption during storage.

[0038] The moisture content in this instruction manual refers to the value measured based on the Karl Fischer method according to JIS K 0068:2001 "Method for Determination of Moisture in Chemical Products". Specifically, firstly, a specified amount of the above-mentioned sample is collected in an alumina boat that has been refluxed and then placed in a furnace preheated to 25°C. Using nitrogen as the carrier gas, the moisture content generated when heated to the test temperature (200°C or 500°C) is measured using potentiometric titration. The result is converted to a unit mass (1g), thereby determining the moisture content. For example, the "Trace Moisture Analyzer CA-06" (product name) manufactured by Mitsubishi Chemical can be used. For example, the titration solution can be "Aquamicron AX" (trade name) manufactured by Mitsubishi Chemical as the catholyte, and "Aquamicron CXU" (trade name) manufactured by Mitsubishi Chemical as the anolyte.

[0039] The dielectric loss tangent of such hexagonal boron nitride powder is suppressed to a low level. For example, the dielectric loss tangent of hexagonal boron nitride powder can be lower than 0.0020, 0.0015, 0.0012, or 0.0010.

[0040] The dielectric loss tangent mentioned in this specification refers to the value measured at 1 GHz according to the method described in JIS C 2138:2007 "Electrically insulating materials—Method for determination of relative permittivity and dielectric loss tangent". Specifically, hexagonal boron nitride powder is prepared on a holder and used as the measurement unit. For example, the "Vector Network Analyzer E5063A" (product name) manufactured by Keysight Corporation can be used as the measurement device for the cavity resonator perturbation method.

[0041] The aforementioned hexagonal boron nitride powder can be manufactured, for example, by the following method. One embodiment of the manufacturing method for hexagonal boron nitride powder is a manufacturing method employing the so-called carbon reduction method, comprising: a step of calcining a mixed powder containing a boron-containing compound including boric acid and a carbon-containing compound under a nitrogen pressurized atmosphere to obtain a calcined product containing boron nitride (hereinafter also referred to as a low-temperature calcination step); and a step of heat-treating the calcined product at a temperature higher than that of the above step but lower than 2050°C to generate primary particles of hexagonal boron nitride (hBN) to obtain powder containing aggregated particles composed of a portion of the primary particles (hereinafter also referred to as a calcination step).

[0042] Boron-containing compounds are compounds that have boron as a constituent element. High-purity and relatively inexpensive raw materials can be used as boron-containing compounds. Examples of such boron-containing compounds, besides boric acid, include boron oxide. Boron-containing compounds contain boric acid, which dehydrates upon heating to become boron oxide, forming a liquid phase during the heat treatment of the raw material powder. This boron oxide also functions as an aid in promoting particle growth.

[0043] Carbon-containing compounds are compounds that have carbon atoms as their constituent elements. High-purity and relatively inexpensive raw materials can be used to produce carbon-containing compounds. Examples of such carbon-containing compounds include carbon black and acetylene black.

[0044] In the mixed powder, a boron-containing compound can be incorporated in excess relative to the carbon-containing compound. Besides the carbon-containing and boron-containing compounds, the mixed powder may also contain other compounds. Examples of other compounds include boron nitride as a nucleating agent. By containing boron nitride as a nucleating agent, the average particle size of the synthesized hexagonal boron nitride powder can be more easily controlled. The mixed powder preferably contains a nucleating agent. When the mixed powder contains a nucleating agent, hexagonal boron nitride powder with a small specific surface area (e.g., a specific surface area of ​​2.5 μm) is produced. 2 The preparation of hexagonal boron nitride powder (with a density of less than 1 g) has become easier.

[0045] The low-temperature calcination process is carried out under pressure. The pressure in the low-temperature calcination process can be, for example, 0.25 MPa or more but less than 5.0 MPa, 0.25–3.0 MPa, 0.25–2.0 MPa, 0.25–1.0 MPa, 0.25 MPa or more but less than 1.0 MPa, 0.30–2.0 MPa, or 0.50–2.0 MPa. By increasing the pressure in the low-temperature calcination process, the volatilization of raw materials such as boron compounds can be further suppressed, and the formation of boron carbide as a byproduct can be suppressed. Furthermore, by increasing the pressure in the low-temperature calcination process, the increase in the specific surface area of ​​the boron nitride powder can be suppressed. By keeping the upper limit of the pressure in the low-temperature calcination process within the above-mentioned range, the growth of primary boron nitride particles can be further promoted.

[0046] The heating temperature in the low-temperature calcination process can be, for example, above 1650°C but below 1800°C, 1650–1750°C, or 1650–1700°C. By keeping the lower limit of the heating temperature in the low-temperature calcination process within the above range, the reaction can be promoted and the yield of boron nitride can be increased. By keeping the upper limit of the heating temperature in the low-temperature calcination process within the above range, the formation of by-products can be sufficiently suppressed.

[0047] The heating time in the low-temperature calcination process can be, for example, 1–10 hours, 1–5 hours, or 2–4 hours. By maintaining a lower temperature for a specified time in the initial stage of the reaction to synthesize boron nitride, the reaction system can be further homogenized, thereby further homogenizing the formed boron nitride. It should be noted that, in this specification, the heating time refers to the time (holding time) from when the ambient temperature of the object being heated reaches the specified temperature until that temperature is maintained.

[0048] The firing process involves heating the material obtained in the low-temperature firing process at a higher temperature than that of the low-temperature firing process to generate primary particles of hexagonal boron nitride (hBN), thereby obtaining powder containing aggregated particles composed of the aforementioned primary particles.

[0049] The heating temperature in the firing process is higher than that in the low-temperature firing process but lower than 2050°C. By keeping the heating temperature in the firing process within the vapor range, the graphitization index can be further improved, resulting in hexagonal boron nitride with excellent crystallinity. The heating temperature in the firing process can be below 2000°C. The heating time in the firing process can be, for example, 3–15 hours, 5–10 hours, or 6–9 hours.

[0050] The pressure during the firing process can be, for example, 0.25 MPa or higher but lower than 5.0 MPa, 0.25–3.0 MPa, 0.25–2.0 MPa, 0.25–1.0 MPa, 0.25 MPa or higher but lower than 1.0 MPa, 0.30–2.0 MPa, or 0.50–2.0 MPa. Increasing the pressure during the firing process can further improve the purity of the obtained raw material powder. By keeping the upper limit of the pressure during the firing process within the above ranges, the preparation cost of the raw material powder can be further reduced, which is industrially advantageous.

[0051] Through the above processes, hexagonal boron nitride powder can be obtained. A pulverizing process can be performed after the low-temperature sintering process or the sintering process. In the pulverizing process, a conventional pulverizer or crusher can be used.

[0052] The hexagonal boron nitride powder disclosed herein, due to its low dielectric loss tangent, can also be used in applications where high-frequency voltages are applied. The hexagonal boron nitride powder disclosed herein is suitable as a filler material, for example, for use in resin compositions constituting electronic components of high-frequency circuits. One embodiment of the resin composition comprises a resin and the aforementioned hexagonal boron nitride powder.

[0053] Based on the total volume of the resin composition, the lower limit of the content of hexagonal boron nitride powder can be, for example, 30% by volume or more, 40% by volume or more, or 50% by volume or more. By keeping the lower limit of the content of hexagonal boron nitride powder within the above range, the thermal conductivity of the resin composition can be improved, resulting in excellent heat dissipation performance. Based on the total volume of the resin composition, the upper limit of the content of hexagonal boron nitride powder can be, for example, 85% by volume or less, 80% by volume or less, or 70% by volume or less. By keeping the upper limit of the content of hexagonal boron nitride powder within the above range, the generation of voids inside the resin composition during molding can be further suppressed, and the reduction in insulation and mechanical strength can also be suppressed.

[0054] Examples of resins include liquid crystal polymers, fluoropolymers, silicone resins, silicone rubber, acrylic resins, polyolefins (polyethylene, etc.), epoxy resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, polyimides, polyamide-imides, polyether-imides, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, fully aromatic polyesters, polysulfones, 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.

[0055] Based on the total volume of the resin composition, the resin content may be, for example, 15% by volume or more, 20% by volume or more, or 30% by volume or more. Based on the total volume of the resin composition, the resin content may be, for example, 70% by volume or less, 60% by volume or less, or 50% by volume or less.

[0056] The resin composition may also contain a curing agent for curing the resin. The curing agent may be appropriately selected depending on the type of resin. For example, when the resin is an epoxy resin, examples of curing agents include phenol (Novolac), acid anhydrides, amino compounds, and imidazole compounds. The content of the curing agent relative to 100 parts by weight of the 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.

[0057] Several embodiments have been described above, but this disclosure is not limited to any of the above embodiments. Furthermore, the descriptions of the above embodiments are applicable to each other.

[0058] Example

[0059] The present disclosure will now be described in more detail using embodiments and comparative examples. It should be noted that the present disclosure is not limited to the embodiments described below.

[0060] (Example 1)

[0061] [Preparation of hexagonal boron nitride powder]

[0062] 100 parts by mass of boric acid (manufactured by High Purity Chemical Research Institute, Co., Ltd.) and 22 parts by mass of acetylene black (manufactured by Denka Co., Ltd., grade: Li400) were mixed using a Henschel mixer to obtain a mixed powder (raw material powder). The obtained mixed powder was placed in a dryer at 250°C and kept for 3 hours to dehydrate the boric acid. The dehydrated mixed powder was placed into a 100Φ diameter mold of a compression molding machine and shaped under heating temperature of 200°C and pressing pressure of 30MPa. The raw material powder granules obtained in this way were then used for subsequent heat treatment.

[0063] First, the above-mentioned granules were placed in a carbon atmosphere furnace and heated to 1750°C at a rate of 5°C / min in a nitrogen atmosphere pressurized to 0.85 MPa. The temperature was maintained at 1750°C for 3 hours to obtain the first heat-treated product (first step). Next, the temperature in the carbon atmosphere furnace was further increased to 1800°C at a rate of 2°C / min and maintained at 1800°C for 3 hours to obtain the second heat-treated product (second step). Then, the temperature in the carbon atmosphere furnace was further increased to 2050°C at a rate of 2°C / min and maintained at 2050°C for 7 hours to calcine the second heat-treated product at a high temperature (third step). The loosely aggregated boron nitride after calcination was crushed using a Henschel mixer. The crushed powder was dried at 250°C for 5 hours using a vacuum dryer and then passed through a sieve with a mesh size of 63 μm to obtain the powder that passed through the sieve. Hexagonal boron nitride powder was prepared in this way.

[0064] <Determination of physical properties of hexagonal boron nitride powder>

[0065] The specific surface area, graphitization index, purity, sphericity and average particle size of the primary particles, as well as the moisture content when heated from 25°C to 200°C and from 201°C to 500°C were determined using the method described below. The results are shown in Table 1.

[0066] [Specific surface area]

[0067] The specific surface area of ​​the hexagonal boron nitride powder was calculated using the BET single-point method with nitrogen, in accordance with JIS Z 8830:2013 "Method for determination of specific surface area of ​​powders (solids) based on gas adsorption". A specific surface area measuring apparatus (device name: Quantasorb) manufactured by Yuasa Ionics Co., Ltd. was used as the measuring device. It should be noted that the measurement was performed after the boron nitride powder was dried and degassed at 300°C for 15 minutes.

[0068] [Graphitization Index]

[0069] The graphitization index of boron nitride powder was calculated based on the results of powder X-ray diffraction. In the obtained X-ray diffraction pattern, the area values ​​(in arbitrary units) enclosed by the integrated intensity (i.e., each diffraction peak) and its baseline corresponding to the (100), (101), and (102) planes of the primary particles of hexagonal boron nitride were calculated and denoted as S100, S101, and S102, respectively. Using the area values ​​thus calculated, the graphitization index was determined based on the following equation (1).

[0070] GI=(S100+S101) / S102···(1)

[0071] [purity]

[0072] Hexagonal boron nitride powder was decomposed using sodium hydroxide, and ammonia was distilled from the decomposition solution using steam distillation and collected in a boric acid aqueous solution. This collected solution was then titrated using a standard sulfuric acid solution. Based on the titration results, the nitrogen (N) content in the boron nitride powder was calculated. Based on the obtained nitrogen content, the hexagonal boron nitride (hBN) content in the boron nitride powder was determined using equation (2), and the purity of the hexagonal boron nitride powder was calculated. It should be noted that the formula weight of hexagonal boron nitride is 24.818 g / mol, and the atomic weight of nitrogen is 14.006 g / mol.

[0073] The content of hexagonal boron nitride (hBN) in the sample [mass%] = the content of nitrogen atoms (N) [mass%] × 1.772···(2)

[0074] [Sphericity of primary particles]

[0075] For hexagonal boron nitride powder, images of the particles were captured using a scanning electron microscope (SEM) (magnification: 10,000x, image resolution: 1280 × 1024 pixels). Then, using image analysis software (Mountech, trade name "MacView"), the projected area (S) and perimeter (L) of the boron nitride particles were calculated based on the obtained images. Finally, using the obtained projected area (S) and perimeter (L), the circularity was calculated according to the following formula: Circularity = 4πS / L 2 The roundness is determined by randomly selecting 100 boron nitride particles from those whose overall particle structure and plate-like plane (ab-axis crystal plane) can be identified. The average roundness is calculated and used as the mean roundness.

[0076] [Average particle size of primary particles]

[0077] The average particle size of the primary particles in the hexagonal boron nitride powder was measured according to ISO 13320:2009 using a laser diffraction scattering particle size distribution measuring apparatus (BECKMAN COULTER, trade name "LS-13 320"). It should be noted that, for the hexagonal boron nitride powder, an ultrasonic homogenizer (Nippon Seiki Co., Ltd., trade name "US-300E") was used to prepare a dispersion of the hexagonal boron nitride powder by ultrasonic dispersion once every 1 minute and 30 seconds at 80% amplitude. For the particle size distribution measurement, water was used as the solvent for dispersing the hexagonal boron nitride powder, and hexametaphosphate was used as the dispersant. The refractive index of water was 1.33, and the refractive index of the boron nitride powder was 1.80.

[0078] [Moisture content]

[0079] Based on the Karl Fischer method, the moisture content of hexagonal boron nitride powder when heated from 25°C to 200°C and from 201°C to 500°C was determined. First, a specified amount of the sample was collected in an alumina boat that had been refluxed and then placed in a furnace preheated to 25°C. Potentiometric titration was used to determine the moisture content generated when heated from 25°C to the test temperature (200°C or 500°C). The result was converted to a unit mass (1g) to determine the moisture content (unit: ppm).

[0080] <Evaluation of Hexagonal Boron Nitride Powder as a Filler Material>

[0081] The dielectric loss tangent of the obtained hexagonal boron nitride powder was measured when used as a filler material. Specifically, the measurement was performed using a cavity resonator method apparatus (Keycom DPS18 perturbation method cavity resonator) at a temperature of 25°C to determine the dielectric loss tangent of the hexagonal boron nitride powder at 1 GHz. The results are shown in Table 1.

[0082] (Example 2)

[0083] Except for changing the acetylene black used as a raw material to acetylene black (manufactured by Denka Corporation, grade: FX35), hexagonal boron nitride powder was prepared by operating in the same manner as in Example 1.

[0084] (Example 3)

[0085] Hexagonal boron nitride powder was prepared in the same manner as in Example 1, except that 2% by mass of boron nitride powder (manufactured by Denka Corporation, grade: SGP) was added to the raw material.

[0086] (Example 4)

[0087] Except for changing the firing temperature of the third step to 2070°C, the same procedure as in Example 1 was followed to prepare hexagonal boron nitride powder.

[0088] (Example 5)

[0089] Except for changing the firing temperature of the third step to 1970°C, the same procedure as in Example 1 was followed to prepare hexagonal boron nitride powder.

[0090] (Example 6)

[0091] The amount of acetylene black (manufactured by Denka Corporation, grade name: Li400) was changed to 20 parts by mass, and the vacuum drying temperature was changed to 300°C. Otherwise, the same procedure as in Example 1 was followed to prepare hexagonal boron nitride powder.

[0092] (Example 7)

[0093] Except for changing the amount of acetylene black (manufactured by Denka Corporation, grade name: Li400) to 27 parts by mass, hexagonal boron nitride powder was prepared in the same manner as in Example 1.

[0094] (Example 8)

[0095] Hexagonal boron nitride powder was prepared in the same manner as in Example 1, except that 1% by mass of boron nitride powder (manufactured by Denka Corporation, Denka BoronNitride, grade: MGP) was added to the raw material.

[0096] For the hexagonal boron nitride powders obtained in Examples 1-8, the specific surface area, graphitization index, purity, sphericity and average particle size of the primary particles, and the moisture content when heated from 25°C to 200°C and from 201°C to 500°C were measured in the same manner as in Example 1. The hexagonal boron nitride powders obtained in Examples 1-8 were evaluated as filler materials in the same manner as in Example 1. The results are shown in Table 1.

[0097] [Table 1]

[0098]

[0099] (Comparative Example 1)

[0100] 100 parts by weight of boric acid powder (purity ≥ 99.8% by mass, manufactured by Kanto Chemical Co., Ltd.), 9 parts by weight of melamine powder (purity ≥ 99.0% by mass, manufactured by Fujifilm and Koko Pure Chemical Co., Ltd.), and 13 parts by weight of sodium carbonate (purity ≥ 99.5% by mass) as an adjuvant were added and mixed for 10 minutes using an alumina mortar to obtain a mixed powder. The dried mixed powder was placed in a container made of hexagonal boron nitride and placed in an electric furnace. While circulating nitrogen gas in the furnace, the temperature was increased from room temperature to 1000°C at a rate of 10°C / min. After holding at 1000°C for 2 hours, heating was stopped, and the mixture was allowed to cool naturally. The furnace was then opened when the temperature dropped below 100°C. In this way, a pre-calcined product containing low-crystallinity hexagonal boron nitride was obtained.

[0101] 100g of the pre-calcined material was placed in the electric furnace described above. While circulating nitrogen gas within the furnace, the temperature was increased from room temperature to 1800°C at a rate of 10°C / min. After maintaining the calcination temperature at 1800°C for 4 hours, heating was stopped, and the material was allowed to cool naturally. The furnace was then opened when the temperature dropped below 100°C. The resulting calcined material was recovered and pulverized for 10 minutes using an alumina mortar to obtain a coarse powder containing hexagonal boron nitride.

[0102] Next, to remove impurities from the coarse powder, 30g of the coarse powder was added to 500g of dilute nitric acid (nitric acid concentration: 5% by mass), and stirred at room temperature for 60 minutes. After stirring, solid-liquid separation was performed by vacuum filtration, with water replaced until the filtrate became neutral. The filtrate was then washed until the conductivity of the washing solution finally became below 1 mS / m. After washing, the powder was dried at 120°C for 3 hours using a dryer to obtain a dried powder. This dried powder was used as the hexagonal boron nitride powder of Comparative Example 1.

[0103] (Comparative Example 2)

[0104] The acetylene black used as a raw material was changed to acetylene black (manufactured by Denka Corporation, grade name: FX35), the amount was changed to 24 parts by mass, the molding pressure of the compression molding machine was set to 5 MPa, and vacuum drying was not performed. Otherwise, the same procedure as in Example 1 was followed to prepare hexagonal boron nitride powder.

[0105] (Comparative Example 3)

[0106] The amount of boric acid was changed to 150 parts by mass, 5 parts by mass of calcium carbonate (purity ≥99.5% by mass) were added to the raw materials, and the firing temperature was changed to 1900°C. Otherwise, the same procedure as in Comparative Example 1 was followed to prepare hexagonal boron nitride powder.

[0107] (Comparative Example 4)

[0108] The firing conditions of step 3 were changed to 1750°C for 20 hours, and vacuum drying was not performed. Otherwise, the same procedure as in Comparative Example 1 was followed to prepare hexagonal boron nitride powder.

[0109] For the hexagonal boron nitride powders obtained in Comparative Examples 1-4, the specific surface area, graphitization index, purity, sphericity and average particle size of the primary particles, and the moisture content when heated from 25°C to 200°C and from 201°C to 500°C were measured in the same manner as in Example 1. The hexagonal boron nitride powders obtained in Comparative Examples 1-4 were evaluated as filler materials in the same manner as in Example 1. The results are shown in Table 2.

[0110] [Table 2]

[0111]

[0112] Industrial availability

[0113] According to this disclosure, hexagonal boron nitride powder can be provided that is useful for manufacturing heat dissipation components with low dielectric loss tangent.

Claims

1. Hexagonal boron nitride powder, comprising primary particles of hexagonal boron nitride. The specific surface area of ​​the hexagonal boron nitride powder is 2.5 m². 2 The material has a density of less than 1 g, a graphitization index of less than 2.0, a purity of more than 99% by mass, and a water content of less than 300 ppm per unit mass when heated to 500℃.

2. The hexagonal boron nitride powder as described in claim 1, wherein, The sphericity of the primary particles is 0.8 or higher.

3. The hexagonal boron nitride powder as described in claim 1 or 2, wherein the water content per unit mass when heated to 200°C is less than 250 ppm.

4. The hexagonal boron nitride powder as described in claim 1 or 2, wherein the water content per unit mass is less than 100 ppm when heated from 201°C to 500°C.

5. The hexagonal boron nitride powder as described in claim 1 or 2, wherein, The average particle size of the primary particles is greater than 7.0 μm.

6. A resin composition comprising a resin and hexagonal boron nitride powder according to any one of claims 1 to 5.

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