Hexagonal boron nitride particle powder, method for producing same, resin composition, and heat dissipation material

Abstract

In order to provide a technology that makes it possible to suppress generation of voids while maintaining the structure of an agglomerate of plate-shaped hexagonal boron nitride particles when the agglomerate is shaped into a thermally conductive insulating sheet, a hexagonal boron nitride particle powder according to on aspect of the present disclosure contains an agglomerate of plate-shaped hexagonal boron nitride particles, the agglomerate in the powder has a compression fracture strength of 0.5-3.0 MPa, the powder has an average particle diameter of 25-60 μm, and when the power has been subjected to ultrasonic treatment under prescribed conditions, the ratio of the cumulative volume 90% particle diameter of the powder after the treatment to the cumulative volume 90% particle diameter of the powder before the treatment is 50-90%.

Description

Hexagonal boron nitride particle powder, its manufacturing method, resin composition, and heat dissipation material

[0001] The present invention relates to hexagonal boron nitride particles, a method for producing the same, a resin composition, and a heat dissipating material.

[0002] Hexagonal boron nitride is a white powder that generally has a hexagonal layered structure similar to that of graphite, and is a material that has many properties such as high thermal conductivity, high heat resistance, high electrical insulation, high lubricity, corrosion resistance, high mold release properties, and high chemical stability. Therefore, resin compositions filled with hexagonal boron nitride powder can be suitably used as thermally conductive and insulating sheets by molding.

[0003] In recent years, along with the trend toward miniaturization and increased power of electronic components, there has been an increasing demand for thermally conductive insulating sheets with low dielectric constants and low dielectric loss tangents. In particular, thermally conductive insulating sheets for in-vehicle electronic components are required to have a low specific gravity, and hexagonal boron nitride powder, which has a lower specific gravity than other highly thermally conductive fillers such as aluminum nitride and aluminum oxide, has been attracting attention (see Patent Documents 1 and 2).

[0004] Japanese Patent Publication No. 2022-178471 Japanese Patent Publication No. 2017-222522

[0005] Hexagonal boron nitride particles have anisotropy, i.e., they have high thermal conductivity only in the long axis direction. Therefore, a sheet filled with hexagonal boron nitride particles with their short axes aligned in the thickness direction of the sheet cannot exhibit sufficient thermal conductivity in the thickness direction. Therefore, in order for a resin composition filled with hexagonal boron nitride particle powder to have high thermal conductivity, it is necessary to contain agglomerates of hexagonal boron nitride particles in the resin composition. Furthermore, when molding the resin composition for various applications, it is considered important to increase the cohesive strength so that the agglomerates can be maintained even under a certain molding pressure. However, hexagonal boron nitride particle agglomerates with high cohesive strength tend to contain voids within them, and the presence of voids is thought to cause deterioration of insulation properties.

[0006] In Patent Document 1, the generation of voids can be suppressed by partially collapsing the aggregates due to the force applied during molding into a sheet, etc. However, if the aggregates have a cohesive strength that causes them to collapse when kneaded with a resin, the hexagonal boron nitride particle aggregates are lost during the kneading process, and the long axis direction of the particles becomes oriented in the plane direction of the sheet when the sheet is formed, which can result in a decrease in the thermal conductivity of the sheet in the thickness direction.

[0007] In addition, in Patent Document 2, when a powder containing aggregates is filled into a resin, the aggregates can have a compressive fracture strength such that some of the aggregates collapse while maintaining an aggregated state overall. However, there is still room for improvement in that the hexagonal boron nitride particle aggregates further collapse and are lost during the kneading process after filling, and when a sheet is formed, the long axis direction of the particles becomes oriented in the plane direction of the sheet, which can result in a decrease in the thermal conductivity of the sheet in the thickness direction.

[0008] Therefore, one aspect of the present invention aims to provide a hexagonal boron nitride particle agglomerate that, when molded into a thermally conductive insulating sheet, can maintain the structure of the agglomerate while suppressing the generation of voids that lead to a decrease in insulating properties, and a hexagonal boron nitride particle powder containing the hexagonal boron nitride particle agglomerate.

[0009] In order to solve the above-mentioned problems, a hexagonal boron nitride particle powder according to one embodiment of the present invention is a hexagonal boron nitride particle powder comprising agglomerates of plate-like hexagonal boron nitride particles, wherein the agglomerates in the powder have a compressive fracture strength of 0.5 to 3.0 MPa, the powder has an average particle size of 25 to 60 μm, and when 0.5 g of the powder is subjected to ultrasonic treatment in 20 g of an ethanol dispersion medium using a homogenizer for 20 minutes at an amplitude of 35%, the ratio of the particle size at 90% cumulative volume of the powder after the treatment to the particle size at 90% cumulative volume of the powder before the treatment is 50 to 90%.

[0010] According to one aspect of the present invention, there are provided hexagonal boron nitride particle agglomerates that, when molded into a thermally conductive insulating sheet, can maintain the structure of the agglomerates while suppressing the generation of voids that lead to a decrease in insulating properties, and a hexagonal boron nitride particle powder containing the hexagonal boron nitride particle agglomerates.

[0011] The present inventors conducted extensive research to solve the above-mentioned problems. The production of thermally conductive insulating sheets involves a process of mixing hexagonal boron nitride particle powder with a resin, followed by a resin molding process to mold the mixture. Therefore, the inventors investigated hexagonal boron nitride particle aggregates with various compressive fracture strengths. As a result, they discovered hexagonal boron nitride particle aggregates that can maintain their structure when mixed with a resin using a general-purpose mixer, but that have a compressive fracture strength sufficient to cause partial collapse of the aggregate during resin molding using a general-purpose molding machine. Furthermore, they discovered that when these aggregates are molded, they can maintain their structure while suppressing the generation of voids that would otherwise lead to a decrease in insulating properties.

[0012] The present inventors also discovered that by employing a specific manufacturing method in which hexagonal boron nitride particles are calcined in the presence of an oxygen-containing calcium compound and, optionally, an oxygen-containing boron compound, it is possible to efficiently obtain hexagonal boron nitride particle agglomerates having the above-mentioned compressive fracture strength, and have completed the present invention.

[0013] That is, the first invention is a hexagonal boron nitride particle powder containing agglomerates of plate-like hexagonal boron nitride particles, wherein the agglomerates in the powder have a compressive fracture strength of 0.5 to 3.0 MPa, the powder has an average particle size of 25 to 60 μm, and when 0.5 g of the powder is subjected to ultrasonic treatment in 20 g of an ethanol dispersion medium using a homogenizer for 20 minutes at an amplitude of 35%, the ratio of the particle size at 90% cumulative volume of the powder after the treatment to the particle size at 90% cumulative volume of the powder before the treatment is 50 to 90%.

[0014] The first aspect of the present invention preferably has the following features: (1-1) The content of the aggregates is in the range of 10 to 90% by volume; (1-2) The particle diameter of the hexagonal boron nitride particle powder at 90% of its cumulative volume before ultrasonic treatment is 90 to 160 μm; (1-3) The BET specific surface area of ​​the hexagonal boron nitride particle powder is 1.5 to 3.0 m; ２ (1-4) The Ca concentration in the aggregate is 100 ppm by mass or less. (1-5) The oil absorption per 100 g of the powder is 70 to 85 mL.

[0015] The hexagonal boron nitride particles are preferably used for a resin composition containing the powder, and further for a heat dissipation material for electronic parts made of the resin composition.

[0016] Furthermore, the second invention of the present invention is a method for producing hexagonal boron nitride particles according to the first invention, which comprises firing plate-like hexagonal boron nitride particles in the presence of an oxygen-containing calcium compound.

[0017] In the second aspect of the present invention, the following embodiments can be preferably adopted: (2-1) 10 to 5,000 ppm by mass of an oxygen-containing calcium compound is present in terms of Ca relative to 100 parts by mass of the hexagonal boron nitride powder containing the plate-like hexagonal boron nitride particles; (2-2) Firing is carried out at 1,700 to 2,200°C in a nitrogen atmosphere.

[0018] The hexagonal boron nitride particle powder according to one embodiment of the present invention has a compressive fracture strength sufficient to maintain the aggregate structure of the hexagonal boron nitride particle aggregates contained in the powder when kneaded with a resin using a general-purpose mixer, thereby reducing the anisotropy of the thermal conductivity of the hexagonal boron nitride particles and imparting high thermal conductivity to the resulting resin composition.

[0019] On the other hand, in the sheet formation process, the aggregates disintegrate as they are molded, which makes it possible to reduce the voids contained within the aggregates, thereby imparting high insulating properties to the resulting sheet-shaped resin composition.

[0020] In this way, a resin composition filled with the hexagonal boron nitride particle powder according to one aspect of the present invention can be a material that combines high thermal conductivity and insulating properties.

[0021] The hexagonal boron nitride particle powder according to one aspect of the present invention can be produced by calcining hexagonal boron nitride particle powder in the presence of an oxygen-containing calcium compound. The reason why the hexagonal boron nitride particle powder according to one aspect of the present invention can be obtained by the above-described production method is unclear. The inventors speculate that the reason is that, during the calcination process of the hexagonal boron nitride particle powder, the oxygen-containing calcium compound promotes particle growth and particle bonding driven by a reduction in the energy on the surface of the hexagonal boron nitride particles.

[0022] The hexagonal boron nitride particle powder according to one embodiment of the present invention is characterized by having both a specific compression fracture strength and a specific disintegrability. This hexagonal boron nitride particle powder maintains the aggregate structure of the aggregates contained in the powder during kneading with a resin using a general-purpose mixer, and can reduce voids contained within the aggregates after sheet formation.

[0023] Hereinafter, hexagonal boron nitride particles according to one embodiment of the present invention will be described in detail. In this specification, unless otherwise specified, the notation "A to B" for numerical values ​​A and B means "A or more and B or less." In such notation, when a unit is assigned only to numerical value B, the unit also applies to numerical value A.

[0024] (Hexagonal Boron Nitride Particle Powder) The hexagonal boron nitride particle powder of the present invention is characterized by having a compressive fracture strength of 0.5 to 3.0 MPa. When the lower limit of the compressive fracture strength is within the above range, agglomerates contained in the powder collapse during kneading with a resin using a general-purpose mixer, generating plate-like hexagonal boron nitride particles. This prevents the particles from orienting their major axis direction in the sheet plane during sheet formation, resulting in a decrease in thermal conductivity. Furthermore, when the upper limit of the compressive fracture strength is within the above range, a portion of the agglomerates collapses in response to the pressure applied during sheet formation, reducing voids within the agglomerates and preventing a decrease in insulating properties. The compressive fracture strength is preferably 0.9 to 2.7 MPa, and particularly preferably 1.2 to 2.5 MPa. The compressive fracture strength of the hexagonal boron nitride particle powder can be measured by separating the agglomerates from the powder and measuring the agglomerates using a microcompression tester.

[0025] As described above, the hexagonal boron nitride particle powder of the present invention contains agglomerates of plate-like hexagonal boron nitride particles. The proportion of the agglomerates in the powder may be appropriately set depending on the desired purpose. The content of the plate-like hexagonal boron nitride particle agglomerates in the hexagonal boron nitride particle powder is preferably in the range of 10 to 90 volume %, more preferably 20 to 80 volume %, and particularly preferably 30 to 70 volume %, relative to 100 volume % of the powder. By having the content of the agglomerates within this range, when the powder is added to a resin, the phenomenon of the plate-like hexagonal boron nitride particles becoming oriented can be suppressed, and a decrease in thermal conductivity can be suppressed. The content of the agglomerates can be measured using the method described in the Examples.

[0026] The average particle size of the hexagonal boron nitride particle powder of the present invention is the 50% cumulative volume particle size measured by dispersing the powder in ethanol as a dispersion medium and measuring the particle size distribution using a laser diffraction / scattering particle size distribution analyzer. The hexagonal boron nitride particle powder of the present invention is characterized by having an average particle size in the range of 25 to 60 μm. By setting the lower limit of the average particle size of the powder within the above range, the plate-like hexagonal boron nitride particles can be randomly oriented during sheet formation, thereby suppressing the phenomenon of reduced thermal conductivity. By setting the upper limit of the average particle size within the above range, the amount of resin absorbed by the aggregates can be reduced, thereby suppressing the increase in viscosity when the powder is filled into the resin. The average particle size is preferably in the range of 30 to 55 μm, and particularly preferably in the range of 35 to 50 μm.

[0027] Furthermore, the hexagonal boron nitride particle powder of the present invention is characterized by its moderate disintegrability upon ultrasonic treatment. Specifically, when 0.5 g of the powder is subjected to ultrasonic treatment in 20 g of an ethanol dispersion medium at an amplitude of 35% for 20 minutes using a homogenizer, the ratio of the cumulative 90% volume particle diameter of the powder after the ultrasonic treatment to the cumulative 90% volume particle diameter of the powder before the treatment is 50 to 90%. By setting the lower limit of the ratio of the cumulative 90% volume particle diameter after the treatment to the cumulative 90% volume particle diameter before the treatment within the above range, the proportion of aggregates that disintegrate when using a general-purpose mixer can be reduced, thereby suppressing a decrease in thermal conductivity. Furthermore, by setting the upper limit of this ratio within the above range, the voids present between the aggregates and plate-like particles can be reduced, thereby suppressing an increase in viscosity of the resin composition. The ratio of the cumulative 90% volume particle diameter after the treatment to the cumulative 90% volume particle diameter before the treatment is preferably 55 to 85%, and particularly preferably 60 to 80%. The particle size distribution of the powder can be measured using a laser diffraction / scattering particle size distribution measuring device.

[0028] The hexagonal boron nitride particle powder of the present invention preferably has a 90% cumulative volume particle size in the range of 90 to 160 μm, more preferably 95 to 150 μm, and particularly preferably 100 to 140 μm, before the ultrasonic treatment. By having the lower limit of the 90% cumulative volume particle size within the above range, the plate-like hexagonal boron nitride particles can be present as aggregates, and high thermal conductivity can be achieved when a resin composition containing the powder is formed into a sheet. Furthermore, by having the upper limit of the 90% cumulative volume particle size within the above range, the generation of voids within the aggregates can be suppressed, and a decrease in insulating properties can be suppressed when a resin composition containing the powder is formed into a sheet.

[0029] Furthermore, in the hexagonal boron nitride particle powder of the present invention, the BET specific surface area is 1.5 to 3.0 m ２ / g, and 1.7 to 2.9 m ２ / g, and more preferably in the range of 2.0 to 2.7 m ２ / g. By setting the lower limit of the specific surface area within the above range, it is possible to suppress a decrease in the compressive fracture strength of the aggregate, which may occur when the particle size of the plate-like hexagonal boron nitride particles becomes coarse. Furthermore, by setting the upper limit of the specific surface area within the above range, it is possible to suppress a decrease in thermal conductivity, which may occur when the plate-like hexagonal boron nitride particles become fine. The BET specific surface area of ​​the aggregate can be confirmed by measurement using the BET single-point method with nitrogen gas as the adsorption gas.

[0030] The hexagonal boron nitride particle powder of the present invention can be produced, for example, by calcining plate-like hexagonal boron nitride particles in the presence of an oxygen-containing calcium compound, as described below. During production, Ca derived from the oxygen-containing calcium compound may remain in the powder. Therefore, the Ca concentration in the hexagonal boron nitride particle powder of the present invention is preferably 100 ppm by mass or less, more preferably 80 ppm by mass or less, and particularly preferably 50 ppm by mass or less. By having the Ca concentration within the above range, for example, in the hexagonal boron nitride particle powder obtained by the production method described below, the amount of Ca that inhibits interparticle bonding can be reduced, and the collapse of aggregates during kneading with a resin can be suppressed. Furthermore, the lower the Ca content in the hexagonal boron nitride particle powder of the present invention, the better; for example, it may be 0.1 ppm by mass or more, or even 0.0 ppm by mass. The Ca concentration in the hexagonal boron nitride particle powder can be confirmed by immersing the powder in a sulfuric acid aqueous solution having a concentration of 2 mol / L at a liquid temperature of 25°C for 120 minutes, and quantifying the Ca dissolved into the aqueous solution using ICP-OES.

[0031] The hexagonal boron nitride particle powder of the present invention preferably has an oil absorption of 70 to 85 mL per 100 g of the powder, which is preferable for industrial use because the oil absorption of the powder within this range can suppress an increase in viscosity when kneaded with a resin.

[0032] (Uses of Hexagonal Boron Nitride Particle Powder) The hexagonal boron nitride particle powder of the present invention is a material that combines high thermal conductivity and electrical insulation. Therefore, when used as a filler in resins for the purposes of improving electrical insulation and imparting thermal conductivity, the resulting resin composition has high electrical insulation and thermal conductivity.

[0033] The hexagonal boron nitride particle powder of the present invention can also be used as a raw material for boron nitride processed products such as cubic boron nitride and boron nitride molded products, a nucleating agent for engineering plastics, a phase change material, a solid or liquid thermal interface material, a release agent for molten metal or molten glass molds, cosmetics, a composite ceramic raw material, and the like.

[0034] Examples of resins used to obtain the resin composition include thermoplastic resins such as polyolefins, vinyl chloride resins, methyl methacrylate resins, nylons, and fluororesins; thermosetting resins such as epoxy resins, phenolic resins, urea resins, melamine resins, unsaturated polyester resins, and silicone resins; and synthetic rubbers. Furthermore, if necessary, the resin composition may contain known additives as compounding agents, such as known polymerization initiators, curing agents, polymerization inhibitors, polymerization retarders, coupling agents, plasticizers, UV absorbers, pigments, dyes, antibacterial agents, organic fillers, and organic-inorganic composite fillers. Furthermore, the resin composition may contain other inorganic fillers as long as the effects of the present invention are not impaired.

[0035] Furthermore, when the hexagonal boron nitride particle powder of the present invention is mixed with a thermally conductive filler such as aluminum nitride or aluminum oxide, which is a common highly thermally conductive insulating filler, during the preparation of a resin composition, the thermal conductivity of the resulting resin composition can be improved. In this case, the amount of the thermally conductive filler used is preferably 60% by volume or less relative to 100% by volume of the hexagonal boron nitride particle powder, so as not to significantly reduce the water resistance, insulation resistance, and other properties of boron nitride.

[0036] The thermally conductive resin composition thus obtained, or a thermally conductive molded article molded from the composition, can be preferably used for applications such as: thermal interface materials such as polymer-based heat dissipation sheets and phase change sheets; heat dissipation tapes; heat dissipation greases; heat dissipation adhesives; organic heat dissipation sheets such as gap fillers; heat dissipation paints such as heat dissipation paints and heat dissipation coats; heat dissipation resin substrates such as PWB (Printed Wiring Board)-based resin substrates and CCL (Copper Clad Layer)-based resin substrates, insulating layers for metal-based substrates such as aluminum-based substrates and copper-based substrates; and sealing materials for power devices.

[0037] (Method for producing hexagonal boron nitride particle powder) The method for producing hexagonal boron nitride particle powder of the present invention will be described in detail below. The hexagonal boron nitride particle powder of the present invention can be produced by firing plate-like hexagonal boron nitride particles in the presence of an oxygen-containing calcium compound. In the production method of the present invention, the oxygen-containing calcium compound has the effect of promoting the growth of the plate-like hexagonal boron nitride particles and the bonding between the plate-like hexagonal boron nitride particles, making it possible to efficiently produce the plate-like hexagonal boron nitride particle agglomerate according to the first invention.

[0038] The plate-like hexagonal boron nitride particles used in the manufacturing method of the present invention can be those contained in hexagonal boron nitride powder obtained by known manufacturing methods. Known manufacturing methods include the following: (I) a method of directly nitriding boron using nitrogen, ammonia, or the like; (II) a method of reacting a boron halide with ammonia or an ammonium salt; (III) a melamine method in which a boron compound such as boric acid or boron oxide is reacted with a nitrogen-containing compound such as melamine at a temperature of about 800°C; (IV) a reduction-nitridation method in which an oxygen-containing boron compound and a carbon source are heated to a high temperature of 1600°C or higher in a nitrogen atmosphere to reduce and nitride the oxygen-containing boron compound; and (V) a method in which boron carbide is calcined in a nitrogen atmosphere, and then mixed with boron oxide and re-calcined. Among these manufacturing methods, the reduction-nitridation method (IV) is particularly preferred because high crystallization due to high temperature calcination allows for high thermal conductivity and makes it easy to adjust the compressive fracture strength to a lower level. In the production method of the present invention, hexagonal boron nitride powder produced by a known production method may be directly subjected to firing in the presence of an oxygen-containing calcium compound. Alternatively, plate-like hexagonal boron nitride particles may be recovered from hexagonal boron nitride powder produced by a known production method, and the resulting aggregate of particles may be subjected to firing. Here, the recovered aggregate of particles is also one embodiment of a powder containing plate-like hexagonal boron nitride particles.

[0039] Known compounds can be used as the oxygen-containing calcium compound in the production method of the present invention. Among these, calcium oxide and calcium carbonate are preferred. The amount of oxygen-containing calcium compound used can be appropriately determined depending on the desired physical properties of the hexagonal boron nitride particle aggregates. If the amount is too small, the formation of aggregates tends to be insufficient, while if the amount is too large, Ca tends to remain in the aggregates. Therefore, the amount of oxygen-containing calcium compound used is preferably 10 to 5,000 ppm by mass, more preferably 50 to 4,000 ppm by mass, and particularly preferably 100 to 3,000 ppm by mass, calculated as Ca, per 100 parts by mass of hexagonal boron nitride powder containing plate-like hexagonal boron nitride particles. The amount of oxygen-containing calcium compound used can be adjusted to the above range by simply mixing the oxygen-containing calcium compound with the hexagonal boron nitride powder to a predetermined content.

[0040] The content of the oxygen-containing calcium compound in the hexagonal boron nitride powder can be calculated by the following formula.

[0041]

[0033] (Calcium equivalent value) = ((Ca content (g) in hexagonal boron nitride powder) + (amount of Ca component (g) contained in added oxygen-containing calcium) / (total amount (g) of hexagonal boron nitride powder and oxygen-containing calcium compound) In the production method of the present invention, the hexagonal boron nitride powder having the oxygen-containing calcium compound present therein is fired. The firing temperature may be appropriately determined within a range that results in hexagonal boron nitride particle aggregates with sufficient compressive fracture strength. Specifically, the firing temperature is preferably in the range of 1700 to 2200°C, more preferably 1750 to 2150°C, and particularly preferably 1800 to 2100°C. When the temperature is within the above range, growth of crystals present in the plate-like hexagonal boron nitride particles and bonding between the plate-like hexagonal boron nitride particles can be promoted, making it possible to exhibit high thermal conductivity.

[0042] In the production method of the present invention, the calcination is preferably carried out in a nitrogen atmosphere to prevent unexpected side reactions. The nitrogen atmosphere contains nitrogen gas as a main component, for example, 90% by volume or more of nitrogen gas, and preferably 100% by volume of nitrogen gas. The nitrogen atmosphere may contain a non-oxidizing gas such as argon gas or helium gas as the balance.

[0043] The above-mentioned calcination can produce the hexagonal boron nitride particle powder of the present invention. The obtained hexagonal boron nitride particle powder can be separated into hexagonal boron nitride particle agglomerates using a known classifier such as a sieve or an air classifier. Furthermore, the hexagonal boron nitride particle powder produced by the production method of the present invention may be subjected to removal of coarse particles and fine particles using a known classifier such as a sieve or an air classifier, as necessary. Furthermore, the content of hexagonal boron nitride particle agglomerates can be appropriately adjusted by mixing hexagonal boron nitride particle agglomerates into the hexagonal boron nitride particles, or by mixing hexagonal boron nitride particles into the hexagonal boron nitride particle powder.

[0044] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, the values ​​measured were determined by the following methods.

[0045] [Compression fracture strength of hexagonal boron nitride particle aggregates] 0.5 g of hexagonal boron nitride particle powder was subjected to ultrasonic treatment at an amplitude of 35% for 20 minutes in 20 g of an ethanol dispersion medium using a homogenizer (SONIFER SFX250) manufactured by BRANSON. The dispersion was then suction filtered through a 20 μm mesh and dried at 40°C for 12 hours to separate hexagonal boron nitride particle aggregates. A compression test was conducted using a micro-compression tester (MCT-510) manufactured by Shimadzu Corporation to measure the compression fracture strength of the aggregates. The compression test was performed by applying a load to a sample with an indenter, and a graph of test force (mN) vs. displacement (μm) at which the sample fractured was shown. The test force (mN) at which the displacement became constant was designated as the fracture point P, and the fracture strength (MPa) was calculated using the following formula:

[0046] Breaking strength (MPa) = (2.48P) / (3.14d ２ ) d: average particle diameter The measurement was performed under the following conditions: indenter = FLAT200 (200 μm flat indenter), test force = 50 (mN), loading rate = 4.8420 (mN / sec), load holding time = 5 (sec).

[0047] [Average particle size of hexagonal boron nitride particle powder] 0.5 g of hexagonal boron nitride particle powder was dispersed in 20 g of an ethanol dispersion medium, and then the particle size at 50% cumulative volume of the powder was measured using a particle size distribution measuring device (MT-3000) manufactured by Microtrac-Bell Corporation, and this was taken as the average particle size of the powder.

[0048] [Disintegrability of hexagonal boron nitride particle powder by ultrasonic treatment] 0.5 g of hexagonal boron nitride particle powder was subjected to ultrasonic treatment at an amplitude of 35% for 20 minutes in 20 g of an ethanol dispersion medium using a homogenizer (SONIFER SFX250) manufactured by BRANSON, and the cumulative 90% volume particle size of the powder after the treatment was measured using a particle size distribution measuring device (MT-3000) manufactured by Microtrac-Bell Co., Ltd. Furthermore, the cumulative 90% volume particle size of the powder before the ultrasonic treatment was measured, and the ratio of the cumulative 90% volume particle size after the treatment to the cumulative 90% volume particle size of the powder before the treatment was determined, and this was used as a disintegrability index.

[0049] [BET Specific Surface Area of ​​Hexagonal Boron Nitride Particle Powder] 0.5 g of hexagonal boron nitride particle powder was weighed out and degassed at 200°C for 10 minutes, and then the BET specific surface area of ​​the powder was measured by the BET single-point method using nitrogen gas as the adsorption gas. The measurement was performed using a BET specific surface area analyzer (Flowsorb III) manufactured by Shimadzu Corporation.

[0050] [Ca Concentration in Hexagonal Boron Nitride Particle Powder] 2.0 g of hexagonal boron nitride particle powder was weighed out, diluted to 50 mL with 0.4% by mass sulfuric acid, and immersed for 2 hours. The filtrate was then collected using a filter with an opening diameter of 0.25 μm, and 2.5 mL of the resulting filtrate was diluted to 50 mL with pure water to prepare an aqueous solution in which Ca had been eluted from the powder. The aqueous solution after this treatment was analyzed using an ICP-OES apparatus (iCAP 6500 DUO) manufactured by Thermo Fisher Scientific Co., Ltd. to quantify Ca. The Ca concentration of the powder was calculated by multiplying the quantitative Ca value by 500.

[0051] [Content of the Aggregates in the Hexagonal Boron Nitride Particle Powder] 0.5 g of the hexagonal boron nitride particle powder was subjected to ultrasonic treatment at an amplitude of 35% for 20 minutes in 20 g of an ethanol dispersion medium using a homogenizer (SONIFER SFX250) manufactured by BRANSON, and the dispersion was then suction filtered through a mesh with 20 μm openings and dried for 12 hours at 40° C. to separate hexagonal boron nitride particle aggregates. The yield was measured by weighing the aggregates using an electronic balance, and the proportion of hexagonal boron nitride particle aggregates relative to 0.5 g of the hexagonal boron nitride particle powder was calculated.

[0052] [Oil absorption of hexagonal boron nitride particle powder] 25 g of hexagonal boron nitride particle powder was kneaded by rotating a blade at a speed of 1240 rpm, while dibutyl phthalate (DBP) at 23°C was added dropwise at a rate of 4 mL per minute, and the maximum torque was measured. Next, the amount of dibutyl phthalate added when 70% of the maximum torque was reached was calculated to determine the oil absorption per 100 g of the powder. The above measurement was performed using an oil absorption measuring device manufactured by Asahi Research Institute Co., Ltd.

[0053] [Method for measuring thermal conductivity and dielectric strength of hexagonal boron nitride particle powder] Hexagonal boron nitride particle powder was filled into an epoxy resin to prepare a resin composition, and the thermal conductivity and dielectric breakdown voltage were measured. A mixture of 100 parts by mass of epoxy resin (JER806 manufactured by Mitsubishi Chemical Corporation) and 28 parts by mass of a curing agent (alicyclic polyamine curing agent, JER Cure 113 manufactured by Mitsubishi Chemical Corporation) was prepared. Next, 40% by volume of the mixture and 60% by volume of hexagonal boron nitride particle powder were mixed in a rotation / revolution mixer (MAZERUSTAR manufactured by Kurabo Industries, Ltd.) to obtain a resin composition.

[0054] This was poured into a mold and cured using a heat press under conditions of a temperature of 200°C, a pressure of 5 MPa, and a holding time of 30 minutes to produce sheets with a diameter of 40 mm and a thickness of 0.22 mm. Five of the sheets were divided into four, and 20 sheets were analyzed using a temperature wave thermal analyzer (ai-Phase Mobile 1u) manufactured by Ai-Phase Corporation. The average value of the calculated thermal conductivity was used as an index of the thermal conductivity of the hexagonal boron nitride particle powder. Furthermore, the dielectric strength of the 20 sheets was measured using a voltage resistance tester (YPAD-0225) manufactured by Kyonan Electric Co., Ltd., and the average value of the dielectric strength was used as an index of the insulating properties of the hexagonal boron nitride particle powder.

[0055] Example 1 0.24 g of calcium oxide was added to 100 g of a powder of plate-like hexagonal boron nitride particles synthesized by a reduction-nitridation method to adjust the Ca equivalent value to 1000 ppm by mass, and the mixture was mixed using a V-type mixer. Next, 100 g of the mixture was calcined in a graphite Tammann furnace at 1900°C for 6 hours under a nitrogen gas atmosphere to produce a hexagonal boron nitride particle powder.

[0056] Example 2 Hexagonal boron nitride particle powder obtained in the same manner as in Example 1 was passed through a sieve with 120 μm openings to separate out coarse particles, thereby producing hexagonal boron nitride particle powder.

[0057] Examples 3 to 5 Hexagonal boron nitride particle powders were produced in the same manner as in Example 1, except that the Ca-equivalent values ​​described in the above embodiment were changed to those shown in Table 1.

[0058] Example 6 Hexagonal boron nitride particle powder obtained in the same manner as in Example 1 was passed through a sieve with 90 μm openings to separate out coarse particles, thereby producing hexagonal boron nitride particle powder.

[0059] Examples 7 to 10 Hexagonal boron nitride particle powder was produced and coarse particles were classified in the same manner as in Example 2, except that the Ca equivalent values ​​described in the above embodiment were changed to those shown in Table 1.

[0060] Comparative Example 1 The powder of plate-like hexagonal boron nitride particles synthesized by the reduction-nitridation method used in Examples 1 to 10 was used as Comparative Example 1 without modification.

[0061] Comparative Examples 2 to 5 Hexagonal boron nitride particle powders were produced in the same manner as in Example 1, except that the Ca-equivalent values ​​described in the above embodiment were changed to those shown in Table 1.

[0062] For Examples 1 to 10 and Comparative Examples 1 to 5, evaluations were carried out for compressive fracture strength, average particle size, disintegrability index by ultrasonic treatment, diameter at 90% of cumulative volume before ultrasonic treatment, BET specific surface area, Ca concentration, aggregate content, oil absorption, thermal conductivity, and electrical insulation, and the results are shown in Tables 1, 2, and 3.

[0063]

[0064]

[0065]

[0066] (Summary) As can be understood from the above description, the present invention includes the following aspects.

[0067] [1] A hexagonal boron nitride particle powder comprising agglomerates of plate-like hexagonal boron nitride particles, wherein the agglomerates in the powder have a compressive fracture strength of 0.5 to 3.0 MPa, and the powder has an average particle size of 25 to 60 μm. When 0.5 g of the powder is subjected to ultrasonic treatment in 20 g of an ethanol dispersion medium using a homogenizer for 20 minutes at an amplitude of 35%, the ratio of the particle size at 90% cumulative volume of the powder after the treatment to the particle size at 90% cumulative volume of the powder before the treatment is 50 to 90%.

[0068] [2] The hexagonal boron nitride particle powder according to [1], characterized in that the content of the agglomerates is in the range of 10 to 90% by volume.

[0069] [3] The hexagonal boron nitride particle powder according to [1] or [2], wherein the particle size at 90% cumulative volume of the hexagonal boron nitride particle powder before ultrasonic treatment is 90 to 160 μm.

[0070] [4] The BET specific surface area of ​​the hexagonal boron nitride particles is 1.5 to 3.0 m ２

[0023] The hexagonal boron nitride particle powder according to any one of [1] to [3], wherein the hexagonal boron nitride particle powder has a porosity of 0.15 to 0.25g / g.

[0071] [5] The hexagonal boron nitride particle powder according to any one of [1] to [4], wherein the Ca concentration in the agglomerates is 100 ppm by mass or less.

[0072] [6] The hexagonal boron nitride particle powder according to any one of [1] to [5], wherein the oil absorption per 100 g of the powder is 70 to 85 mL.

[0073] [7] A resin composition filled with any one of the hexagonal boron nitride particle powders [1] to [6].

[0074] [8] A heat dissipation material for electronic components comprising the resin composition of [7].

[0075] [9] A method for producing a powder of hexagonal boron nitride particles according to any one of [1] to [7], characterized in that plate-like hexagonal boron nitride particles are fired in the presence of an oxygen-containing calcium compound.

[0076]

[10] The method for producing a hexagonal boron nitride particle powder according to [9], characterized in that an oxygen-containing calcium compound is present in an amount of 10 to 5,000 ppm by mass, calculated as Ca, relative to 100 parts by mass of the hexagonal boron nitride powder containing the plate-like hexagonal boron nitride particles.

[0077]

[11] The method for producing hexagonal boron nitride particles according to [9] or

[10] , wherein the firing is carried out at 1700 to 2200°C in a nitrogen atmosphere.

[0078] The hexagonal boron nitride particle powder of the present invention can impart high thermal conductivity and high insulating properties to a target when used as a filler, and therefore can be used as a raw material for materials used in electronic components.

Claims

1. A hexagonal boron nitride particle powder comprising agglomerates of plate-like hexagonal boron nitride particles, wherein the agglomerates in the powder have a compressive fracture strength of 0.5 to 3.0 MPa, the powder has an average particle size of 25 to 60 μm, and when 0.5 g of the powder is subjected to ultrasonic treatment in 20 g of an ethanol dispersion medium using a homogenizer for 20 minutes at an amplitude of 35%, the ratio of the cumulative 90% volume particle size of the powder after the treatment to the cumulative 90% volume particle size of the powder before the treatment is 50 to 90%.

2. The hexagonal boron nitride particle powder according to claim 1, wherein the content of said agglomerates is in the range of 10 to 90% by volume.

3. The hexagonal boron nitride particle powder according to claim 1 or 2, wherein the particle size at 90% of the cumulative volume of the hexagonal boron nitride particle powder before ultrasonic treatment is 90 to 160 μm.

4. The BET specific surface area of ​​the hexagonal boron nitride particle powder is 1.5 to 3.0 m ２ 3. The hexagonal boron nitride particles according to claim 1, wherein the hexagonal boron nitride particle powder has a molecular weight of 1 / g.

5. The hexagonal boron nitride particle powder according to claim 1 or 2, wherein the Ca concentration in the agglomerates is 100 ppm by mass or less.

6. The hexagonal boron nitride particles according to claim 1 or 2, having an oil absorption of 70 to 85 mL per 100 g of the powder.

7. A resin composition filled with the hexagonal boron nitride particles according to claim 1 or 2.

8. A heat dissipating material for electronic parts made from the resin composition according to claim 7.

9. A method for producing a powder of hexagonal boron nitride particles according to claim 1 or 2, characterized in that the plate-like hexagonal boron nitride particles are fired in the presence of an oxygen-containing calcium compound.

10. A method for producing a hexagonal boron nitride particle powder according to claim 9, characterized in that an oxygen-containing calcium compound is present in an amount of 10 to 5,000 ppm by mass, calculated as Ca, per 100 parts by mass of the hexagonal boron nitride powder containing the plate-like hexagonal boron nitride particles.

11. The method for producing hexagonal boron nitride particles according to claim 9, wherein the firing is carried out at 1700 to 2200°C in a nitrogen atmosphere.

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