Boron nitride powder and inorganic filler

Abstract

To provide a boron nitride powder capable of providing a resin molded product having excellent thermal conductivity and insulating properties. [Solution] The present disclosure provides a boron nitride powder. The boron nitride powder comprises agglomerated particles formed by agglomeration of primary particles of hexagonal boron nitride, and has an orientation index of 10 or less. The boron nitride powder is compression-molded at a pressure of 10 MPa to prepare a molded body made of the boron nitride powder. In a pore distribution curve of the molded body obtained by measuring the molded body using mercury intrusion porosimetry, when the cumulative pore volume in the pore diameter range of 0.001 to 300 μm is defined as cumulative pore volume X and the cumulative pore volume in the pore diameter range of 1 to 300 μm is defined as cumulative pore volume Y, the ratio of cumulative pore volume Y to cumulative pore volume X is 30% or less, and the highest pore volume peak exists in the pore diameter range of 2 μm or less.

Description

[Technical Field]

[0001] The present disclosure relates to boron nitride powder, an inorganic filler, and a method for evaluating the boron nitride powder. [Background technology]

[0002] Boron nitride powder has high thermal conductivity and insulating properties, and is widely used as a thermally conductive filler, an insulating filler, etc. Boron nitride powder is used as a filler in heat dissipation components, which require particularly high thermal conductivity.

[0003] Hexagonal boron nitride primary particles have a relatively thin, scale-like shape. When filled into a resin or other material and molded, the primary particles tend to orient in a certain direction due to factors such as molding pressure. For example, in resin sheets formed by filling hexagonal boron nitride powder and molding it into a sheet using extrusion molding, the major surfaces of the resin sheet generally tend to be oriented parallel to the long axes of the boron nitride primary particles. Furthermore, due to the anisotropy of their shape, the primary particles of hexagonal boron nitride can also exhibit anisotropy in various physical properties. While the thermal conductivity of hexagonal boron nitride primary particles in the in-plane direction (a-axis direction) is high at approximately 400 W / (m·K), the thermal conductivity in the thickness direction (c-axis direction) is only approximately 2 W / (m·K), demonstrating significant anisotropy of physical properties depending on the direction.

[0004] For the reasons mentioned above, methods have been investigated in which hexagonal boron nitride powder is used as a filler for resin, and when preparing a heat-dissipating sheet, the a-axis direction of the primary particles is adjusted to be parallel to the thickness direction of the heat-dissipating sheet, thereby making the most of the high thermal conductivity in the a-axis direction of the primary particles. For example, a technique is known in which the a-axis direction of the primary particles of hexagonal boron nitride is oriented so that it is parallel to the thickness direction of the heat-dissipating sheet (for example, Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-154265 Summary of the Invention [Problem to be solved by the invention]

[0006] Resin molded articles containing boron nitride powder (for example, heat dissipation sheets) are used in heat-generating components such as electronic devices, and therefore are required to have excellent insulating properties in addition to excellent thermal conductivity.

[0007] An object of the present disclosure is to provide a boron nitride powder capable of providing a resin molded product having excellent thermal conductivity and insulating properties. Another object of the present disclosure is to provide a method for evaluating the insulating properties of a resin molded product obtained by compression molding the boron nitride powder. [Means for solving the problem]

[0008] To improve the insulating properties of resin molded bodies, it is desirable to reduce the microvoids that occur during the manufacturing process. While methods such as adjusting the specific surface area of ​​boron nitride particles to be filled into resin or surface modification have been proposed to reduce voids, it is difficult to estimate the void ratio, etc., of a resin molded body prepared before filling into resin, and no appropriate evaluation index has been provided. Through research, the inventors prepared a molded body from boron nitride powder by compression molding at a predetermined pressure, and performed mercury porosimetry on the compression molded body. They found that the ratio of pores in the compression molded body having a predetermined cumulative pore volume in the pore distribution curve is useful as an index for estimating the void ratio of a resin molded body. Information obtained by mercury porosimetry on the above-described compression molded body differs from information obtained by mercury porosimetry on boron nitride powder without compression molding. The present disclosure is based on the above-mentioned findings.

[0009] The difference between the pore size distribution curve obtained by mercury intrusion porosimetry for boron nitride powder and the pore size distribution curve obtained by mercury intrusion porosimetry for a compression-molded body of boron nitride powder will be explained in more detail. When a resin molded body is obtained by molding a mixture of boron nitride powder and resin, some of the agglomerated particles constituting the boron nitride powder may collapse and deform due to the molding pressure. Therefore, unlike the pore size distribution curve for the powder, the pore size distribution curve for the compression-molded body can reflect the collapse and deformation of some of the agglomerated particles, allowing for more precise evaluation of the porosity of the resin molded body. Furthermore, since the particle size and particle strength of powders are not uniform, for example, if particles with large pore sizes have high particle strength, even if there are few voids in the powder state, large voids may remain when the powder is compressed into a compact. Therefore, the amount of voids in the powder does not necessarily correspond to the amount of voids in the compression-molded body. From the above, by using the pore size distribution curve obtained by mercury intrusion porosimetry for a compression molded body, the proportion of voids in a resin molded body containing boron nitride powder can be evaluated more precisely.

[0010] The present disclosure provides the following [1] to [9].

[0011] [1] A boron nitride powder comprising: the boron nitride powder contains agglomerated particles formed by agglomeration of primary particles of hexagonal boron nitride, The orientation index is 10 or less, The boron nitride powder is compression-molded at a pressure of 10 MPa to prepare a molded body made of the boron nitride powder, and the molded body is measured by mercury intrusion porosimetry to obtain a pore distribution curve of the molded body, When the integral pore volume in the pore diameter range of 0.001 to 300 μm is defined as the integral pore volume X and the integral pore volume in the pore diameter range of 1 to 300 μm is defined as the integral pore volume Y, the ratio of the integral pore volume Y to the integral pore volume X is 30% or less, Boron nitride powder with the highest peak in pore volume in the pore diameter range of 2 μm or less. [2] The boron nitride powder according to [1], wherein the cumulative pore volume X is 0.5 mL / g or less. [3] The boron nitride powder according to [1] or [2], which has an average particle size of 5 to 60 μm. [4] Bulk density is 0.7g / cm 3 The boron nitride powder according to any one of [1] to [3] above. [5] [1] to [4], and the boron nitride powder according to any one of [1] to [4]. and at least one aluminum compound selected from the group consisting of aluminum oxide and aluminum nitride. [6] a measuring step of preparing a molded body made of the boron nitride powder by compression molding the boron nitride powder, and measuring the molded body by mercury intrusion porosimetry to obtain a pore distribution curve of the molded body; and evaluating the pore distribution of the molded body from the pore distribution curve. [7] The evaluation method according to [6], wherein the orientation index of the boron nitride powder is 10 or less. [8] The evaluation method according to [6] or [7], wherein the boron nitride powder has an average particle size of 5 to 60 μm. [9] The bulk density of the boron nitride powder is 0.7 g / cm 3 The evaluation method according to any one of [6] to [8] above. [Effects of the Invention]

[0012] According to the present disclosure, there is provided a boron nitride powder capable of providing a resin molded body having excellent thermal conductivity and insulating properties. The present disclosure also provides a method for evaluating the insulating properties of a resin molded body obtained by compression-molding the boron nitride powder. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. In this specification, a numerical range indicated by the symbol "to" includes a lower limit and an upper limit. In other words, a numerical range indicated by "x to y" means not less than x and not more than y. In addition, in this specification, "pore diameter" means the diameter of a pore.

[0014] Unless otherwise specified, the materials exemplified in this specification can be used singly or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified.

[0015] One embodiment of the present disclosure is a boron nitride powder comprising agglomerated particles formed by agglomeration of primary particles of hexagonal boron nitride, and having an orientation index of 10 or less. The boron nitride powder is obtained by compression-molding the boron nitride powder at a pressure of 10 MPa to prepare a molded body made of the boron nitride powder, and measuring the molded body by mercury intrusion porosimetry. In a pore distribution curve of the molded body obtained, when the integral pore volume in the pore diameter range of 0.001 to 300 μm is defined as integral pore volume X and the integral pore volume in the pore diameter range of 1 to 300 μm is defined as integral pore volume Y, the ratio of the integral pore volume Y to the integral pore volume X (hereinafter simply referred to as the "ratio of the integral pore volume Y") is 30% or less, and the highest pore volume peak exists in the pore diameter range of 2 μm or less in the pore distribution curve.

[0016] The boron nitride powder has excellent thermal conductivity and insulating properties. The reasons for this are presumed to be the following factors, although the factors are not limited to these. The boron nitride powder contains agglomerated particles formed by agglomeration of primary particles of hexagonal boron nitride, has an orientation index of 10 or less, and the proportion of agglomerated particles in which the primary particles (single particles) of hexagonal boron nitride in the powder are not substantially oriented is relatively high. As a result, the boron nitride powder easily conducts heat isotropically, and when a resin molded product is produced, the resin molded product has excellent thermal conductivity. Furthermore, a molded body made of the boron nitride powder according to this embodiment is prepared by compression molding the boron nitride powder at a predetermined pressure. The pore distribution curve of the molded body obtained by measuring the molded body using mercury intrusion porosimetry shows that the cumulative pore volume Y is 30% or less and the highest pore volume peak is in the pore diameter range of 2 μm or less. This indicates that the boron nitride powder has the property of reducing the pore volume of the molded body even when molded at a relatively low press pressure (e.g., 10 MPa). Therefore, when such boron nitride powder is used in a resin molded body, voids can be reduced even in the resin molded body. As a result, dielectric breakdown of the resin molded body due to voids can be suppressed, and the insulating properties of the resin molded body can be improved. Furthermore, the lack of coarse voids suggests that primary particles within the agglomerated particles or the agglomerated particles themselves are in close contact, which also contributes to the excellent thermal conductivity of the boron nitride powder.

[0017] In this specification, the term "aggregated particles" refers to secondary particles in which five or more primary particles (single particles) are aggregated together, and the c-axis directions of the primary particles are random. The aggregated state of the primary particles can be confirmed, for example, by using a scanning electron microscope (SEM).

[0018] The boron nitride powder may include primary particles of hexagonal boron nitride and aggregated particles formed by aggregation of a plurality of primary particles of hexagonal boron nitride.

[0019] The orientation index of the boron nitride powder according to this embodiment may be 2 or more, 4 or more, 6 or more, or 6.6 or more. From the viewpoint of further improving the thermal conductivity of a resin molded body, the orientation index of the boron nitride powder may be 9 or less, 8.5 or less, 8 or less, or 7.6 or less. The orientation index of the boron nitride powder may be adjusted within the above-mentioned range, and may be, for example, 2 to 10 or 4 to 9.

[0020] The orientation index in this specification refers to a value measured according to the following method. An X-ray diffraction spectrum of boron nitride powder is obtained by performing X-ray diffraction measurement on the boron nitride powder, and the peak intensities I(002) and I(100) corresponding to the (002) and (100) planes are obtained from the X-ray diffraction spectrum. The obtained peak intensities are used to calculate the orientation index [I(002) / I(100)] of the boron nitride powder. An X-ray diffraction device that can be used is, for example, an "ULTIMA-IV" (product name) manufactured by Rigaku Corporation.

[0021] Since the orientation index is measured on boron nitride powder, when agglomerated particles are present in the powder and the proportion of these particles is high, the orientation index value tends to decrease and approach a value of about 6 to 7. On the other hand, when the powder is composed only of primary particles without agglomerated particles, or when the proportion of the primary particles is high, the orientation index value tends to increase.

[0022] The average particle size (D50) of the boron nitride powder may be 5 μm or more, 10 μm or more, or 15 μm or more, from the viewpoint of easily ensuring the thermal conductivity of the resin molded body. The boron nitride powder according to the present disclosure is a powder containing a large number of agglomerated particles, but has a relatively small average particle size. The average particle size of the boron nitride may be 60 μm or less, 50 μm or less, or 47 μm or less. Adjusting the average particle size of the boron nitride to be within the above range also reduces the particle size of the agglomerated particles contained in the boron nitride powder. Reducing the particle size of the agglomerated particles reduces the voids between the agglomerated particles in the compression-molded body, making it easier to reduce the pore size of the pores in the compression-molded body. When a resin molded body is prepared using such a boron nitride powder, the generation of voids in the resin molded body is suppressed, and even if voids do occur, they are more easily suppressed to small sizes. This further improves the insulating properties and thermal conductivity of the resin molded body. The average particle size of the boron nitride powder may be adjusted within the above range, and may be, for example, 5 to 60 μm.

[0023] The average particle size (D50) in this specification refers to a value measured in accordance with the method described in JIS Z 8825:2013, "Particle size analysis - laser diffraction and scattering method." A laser diffraction and scattering particle size distribution analyzer is used for the measurement. Examples of laser diffraction and scattering particle size distribution analyzers that can be used include the "LS-13 320" (trade name) manufactured by Beckman Coulter and the Microtrac "MT-3300EXII" (trade name) manufactured by Microtrac-Bell. Note that when measuring the average particle size of boron nitride powder, the powder to be measured is not treated with a homogenizer or the like.

[0024] The agglomerated particles of boron nitride contained in the boron nitride powder according to the present disclosure have a higher density than the agglomerated particles contained in conventional boron nitride powders. From the viewpoint of further improving the insulating properties of resin molded articles, the bulk density of the boron nitride powder is set to 0.7 g / cm. 3 More than 0.75g / cm 3or more than 0.8g / cm 3 The bulk density of the boron nitride powder may be 2 g / cm or more. 3 Below 1.5g / cm 3 Less than or equal to 1g / cm 3 The bulk density of the boron nitride powder may be adjusted within the above range, for example, 0.7 to 2 g / cm 3 or 0.75 to 1.5 g / cm 3 It may be.

[0025] The bulk density in this specification refers to a value determined in accordance with the method described in JIS R 1628:1997 "Method for measuring bulk density of fine ceramic powders." Measurement can be performed using a commercially available device.

[0026] The crushing strength of the agglomerated particles in the boron nitride powder may be 5 MPa or more, 7 MPa or more, or 9 MPa or more, from the viewpoint of preventing excessive collapse of the agglomerated particles during the production process of a resin molded body. The crushing strength of the agglomerated particles in the boron nitride powder may be 14 MPa or less, 13 MPa or less, 12 MPa or less, or 11 MPa or less, from the viewpoint of reducing voids in the resin molded body and further improving the insulating properties of the resin molded body. The crushing strength of the agglomerated particles may be adjusted within the above-mentioned range, and may be, for example, 5 to 14 MPa.

[0027] The crushing strength in this specification refers to a value measured in accordance with JIS R 1639-5:2007 "Fine Ceramics - Measurement Methods for Granule Properties - Part 5: Single Granule Crushing Strength." The crushing strength σ (unit: MPa) of a single granule is calculated using the equation σ = α × P / (π × d²) from the dimensionless number α (α = 2.48), which varies depending on the position within the granule, the crushing test force P (unit: N), and the particle diameter d (unit: μm). Measurements are performed on 20 or more granules, and the value at a cumulative fracture rate of 63.2% is calculated. A microcompression tester can be used for the measurement. Examples of the microcompression tester include the "MCT-210" (trade name) manufactured by Shimadzu Corporation.

[0028] The boron nitride powder according to this embodiment is compression-molded at a pressure of 10 MPa to prepare a molded body. A pore distribution curve obtained by measuring the molded body using mercury intrusion porosimetry shows a predetermined ratio of cumulative pore volume Y to cumulative pore volume X, and the maximum peak position on the pore distribution curve corresponds to the region of small pores. The pore distribution in this specification is measured in accordance with JIS R 1655:2003, "Method for testing pore size distribution in molded fine ceramics by mercury intrusion porosimetry." The pore size range on the pore distribution curve may be 0.001 to 300 μm. The measurement using mercury intrusion porosimetry may be performed using a mercury porosimeter. The pore distribution curve of the molded body exhibits behavior different from that of powdered boron nitride powder.

[0029] In the boron nitride powder according to this embodiment, the ratio of the cumulative pore volume Y to the cumulative pore volume X in the pore distribution curve of the molded body is 30% or less. A ratio of the cumulative pore volume Y in the pore distribution curve of the molded body of 30% or less indicates that the proportion of pores with relatively large pore diameters is small. In other words, this indicates that the molded body is denser. Boron nitride powder capable of preparing such a molded body can be filled into a resin and, through processes such as kneading and molding, achieve a denser arrangement within the resin. As a result, the voids in the resin molded body are reduced, and dielectric breakdown caused by the voids is suppressed, thereby improving the insulating properties of the resin molded body. Furthermore, close contact between primary particles within the agglomerated particles or between agglomerated particles also improves the thermal conductivity of the resin molded body. The proportion of the cumulative pore volume Y can be adjusted, for example, by the content of acetylene black and the content of boron source in the decarburization step relative to the total mass of the boron carbonitride powder that has been subjected to the firing step, the boron source, and the acetylene black, or by the content of boron source in the particle growth step described below relative to the total mass of the boron nitride powder obtained in the decarburization step and the boron source.

[0030] In the pore distribution curve of the molded body, the proportion of the cumulative pore volume Y may be 1% or more, 3% or more, or 5% or more. In the pore distribution curve of the molded body, the proportion of the cumulative pore volume Y may be 25% or less, 22% or less, 20% or less, 13% or less, or 10% or less, from the viewpoint of further improving the insulating properties of the resin molded body. In the pore distribution curve of the molded body, the proportion of the cumulative pore volume Y may be adjusted within the above-mentioned range, and may be, for example, 1 to 30% or 3 to 25%.

[0031] In the pore distribution curve of the molded body, the highest pore volume peak exists in the pore diameter range of 2 μm or less. "Existence of a peak in the range of 2 μm or less" means that the pore volume is maximized (the pore diameter at which the slope of the pore distribution curve changes from positive to negative) in the range of 2 μm or less. The presence of the highest peak in the pore distribution curve of the molded body in the pore diameter range of 2 μm or less means that the molded body of boron nitride powder is densely packed, meaning that even if pores exist in the molded body, the pore diameter is small. Furthermore, the boron nitride powder also densely packs the resin molded body, reducing voids in the resin molded body and suppressing dielectric breakdown due to voids, thereby improving the insulating properties of the resin molded body. Furthermore, close contact between primary particles within the agglomerated particles or between agglomerated particles also improves the thermal conductivity of the resin molded body. The position at which the highest peak of the pore volume exists can be adjusted, for example, in the decarburization step by adjusting the contents of acetylene black and boron source relative to the total mass of the boron carbonitride powder that has been subjected to the firing step, the boron source, and acetylene black; or in the particle growth step described below, by adjusting the content of boron source relative to the total mass of the boron nitride powder and boron source obtained in the decarburization step or by controlling the particle size of the aggregated particles.

[0032] In the pore distribution curve of the molded body, the range in which the highest pore volume peak exists may be 0.1 μm or more, 0.2 μm or more, or 0.3 μm or more. From the viewpoint of further improving the insulating properties of the resin molded body, the range in which the highest pore volume peak exists in the pore distribution curve of the molded body may be 1.8 μm or less, 1.5 μm or less, 1 μm or less, 0.6 μm or less, or 0.4 μm or less. In the pore distribution curve of the molded body, the range in which the highest pore volume peak exists may be adjusted within the above-mentioned range, and may be, for example, 0.1 to 2 μm or 0.2 to 1.8 μm.

[0033] In the pore distribution curve of the molded body, the number of pore volume peaks may be one or more, and may be five or less.

[0034] In the pore distribution curve of the molded body, the cumulative pore volume X may be 0.1 mL / g or more, 0.15 mL / g or more, or 0.2 mL / g or more. In the pore distribution curve of the molded body, the cumulative pore volume X may be 0.9 mL / g or less, 0.7 mL / g or less, 0.5 mL / g or less, 0.3 mL / g or less, or 0.25 mL / g or less, from the viewpoint of further improving the insulating properties of the resin molded body. In the pore distribution curve of the molded body, the cumulative pore volume X may be adjusted within the above-mentioned range, and may be, for example, 0.1 to 0.9 mL / g, 0.15 to 0.7 mL / g, or 0.2 to 0.5 mL / g. The cumulative pore volume X can be adjusted, for example, by the contents of acetylene black and boron source in the decarburization step relative to the total mass of the boron carbonitride powder that has been subjected to the firing step, the boron source, and acetylene black, or by the content of boron source in the particle growth step described below relative to the total mass of the boron nitride powder obtained in the decarburization step and the boron source.

[0035] One embodiment of the present disclosure is a method for evaluating boron nitride powder, comprising: a measurement step of preparing a molded body made of boron nitride powder by compression molding the boron nitride powder, and measuring the molded body by mercury intrusion porosimetry to obtain a pore distribution curve of the molded body, and an evaluation step of evaluating the pore distribution of the molded body from the pore distribution curve. The inventors have found that by evaluating the pore distribution of a molded body obtained by compression molding of boron nitride powder from the pore distribution curve of the molded body, it is possible to predict the insulating properties of a resin molded body without producing the resin molded body.

[0036] In the pore distribution measurement step, the molding pressure of the molded body may be 6 MPa or more, 8 MPa or more, or 9 MPa or more, and may be 30 MPa or less, 25 MPa or less, 20 MPa or less, 15 MPa or less, 12 MPa or less, or 11 MPa or less, or may be 10 MPa.

[0037] In the evaluation step, the pore distribution may be evaluated based on the ratio of the cumulative pore volume Y, the highest peak position of the pore volume, the cumulative pore volume X, and the like.

[0038] The orientation index of the boron nitride powder to be evaluated in the above evaluation method may be the same as the orientation index of the boron nitride powder described above.

[0039] The average particle size of the boron nitride powder to be evaluated in the above evaluation method may be the same as the average particle size of the boron nitride powder described above.

[0040] The bulk density of the boron nitride powder to be evaluated in the above evaluation method may be the same as the bulk density of the boron nitride powder described above.

[0041] The crushing strength of the boron nitride agglomerated particles to be evaluated in the above evaluation method may be the same as the crushing strength of the agglomerated particles described above.

[0042] One embodiment of the present disclosure is a method for selecting boron nitride powder suitable for use as an inorganic filler, comprising the steps of: measuring the orientation index of boron nitride powder containing agglomerated particles formed by agglomeration of primary particles of hexagonal boron nitride; compressing the boron nitride powder at a pressure of 10 MPa to prepare a molded body made of the boron nitride powder and measuring the molded body using mercury intrusion porosimetry to obtain a pore distribution curve of the molded body; and selecting boron nitride powder having an orientation index of 10 or less, and in which, in the pore distribution curve of the molded body, the proportion of cumulative pore volume Y is 30% or less and the highest pore volume peak exists in the pore diameter range of 2 μm or less. The order in which the selection conditions are applied in the selection step is not particularly limited. The boron nitride powder selected as described above is suitable as a thermally conductive filler for preparing resin molded bodies having excellent thermal conductivity and insulating properties.

[0043] As a selection condition, the orientation index may be 2 or more, 4 or more, 6 or more, or 6.6 or more. As a selection condition, the orientation index may be 9 or less, 8.5 or less, 8 or less, or 7.6 or less, from the viewpoint of further improving the thermal conductivity of the resin molded body. As a selection condition, the orientation index may be adjusted within the above-mentioned range, and may be, for example, 2 to 10 or 4 to 9.

[0044] The above-mentioned selection method may further comprise a step of measuring the average particle size of the boron nitride powder. As a selection condition, the average particle size may be 5 μm or more, 10 μm or more, or 15 μm or more, from the viewpoint of easily ensuring the thermal conductivity of the resin molded body. As a selection condition, the average particle size may be 60 μm or less, 50 μm or less, or 47 μm or less, from the viewpoint of further improving the insulating properties of the resin molded body. As a selection condition, the average particle size may be adjusted within the above-mentioned range, for example, 5 to 60 μm.

[0045] The above screening method may further include a step of measuring the bulk density of the boron nitride powder. As a screening condition, the bulk density is set to 0.7 g / cm from the viewpoint of further improving the insulating properties of the resin molded body. 3 More than 0.75g / cm 3or more than 0.8g / cm 3 As a selection condition, the bulk density is 2 g / cm 3 Below 1.5g / cm 3 Less than or equal to 1g / cm 3 As a screening condition, the bulk density may be adjusted within the above range, for example, 0.7 to 2 g / cm 3 or 0.75 to 1.5 g / cm 3 It may be.

[0046] The above-mentioned sorting method may further include a step of measuring the crushing strength of the agglomerated particles. As a sorting condition, the crushing strength of the agglomerated particles may be 5 MPa or more, 7 MPa or more, or 9 MPa or more, or 14 MPa or less, 13 MPa or less, 12 MPa or less, or 11 MPa or less, or may be 5 to 14 MPa.

[0047] As a selection condition, the proportion of the cumulative pore volume Y may be 1% or more, 3% or more, or 5% or more. As a selection condition, from the viewpoint of further improving the insulating properties of the resin molded article, the proportion of the cumulative pore volume Y may be 25% or less, 22% or less, 20% or less, 13% or less, or 10% or less. As a selection condition, the proportion of the cumulative pore volume Y may be adjusted within the above-mentioned range, and may be, for example, 1 to 30% or 3 to 25%.

[0048] As a selection condition, the range in which the highest pore volume peak exists may be 0.1 μm or more, 0.2 μm or more, or 0.3 μm or more. As a selection condition, the range in which the highest pore volume peak exists may be 1.8 μm or less, 1.5 μm or less, 1 μm or less, 0.6 μm or less, or 0.4 μm or less, from the viewpoint of further improving the insulating properties of the resin molded article. As a selection condition, the range in which the highest pore volume peak exists may be adjusted within the above-mentioned range, and may be, for example, 0.1 to 2 μm or 0.2 to 1.8 μm.

[0049] In the above screening method, the boron nitride powder may be further screened based on the cumulative pore volume X in the pore distribution curve of the molded body. As a screening condition, the cumulative pore volume X may be 0.1 mL / g or more, 0.15 mL / g or more, or 0.2 mL / g or more. As a screening condition, from the viewpoint of further improving the insulating properties of the resin molded body, the cumulative pore volume X may be 0.9 mL / g or less, 0.7 mL / g or less, 0.5 mL / g or less, 0.3 mL / g or less, or 0.25 mL / g or less. As a screening condition, the cumulative pore volume X may be adjusted within the above-mentioned range, for example, 0.1 to 0.9 mL / g, 0.15 to 0.7 mL / g, or 0.2 to 0.5 mL / g.

[0050] One embodiment of a method for producing boron nitride powder includes a nitriding step of calcining boron carbide powder in a pressurized nitrogen atmosphere to obtain boron carbonitride powder; a calcining step of calcining the boron carbonitride powder in air; a decarburizing step of mixing the boron carbonitride powder that has undergone the calcining step with a boron source and acetylene black, and calcining the mixture in a nitrogen-containing atmosphere to obtain boron nitride powder; and a particle growth step of mixing the boron nitride obtained in the decarburizing step with the boron source, and calcining the mixture in a nitrogen atmosphere.

[0051] The boron carbide powder may be obtained by calcining a mixture of a boron source and carbon black under an argon atmosphere. The boron source may include at least one selected from the group consisting of boric acid and boron oxide.

[0052] The content of the boron source may be 60% by mass or more, 85% by mass or less, or 60 to 85% by mass based on the total mass of the boron source and carbon black. The content of boric acid based on the total mass of boric acid and carbon black may also be within the above-mentioned ranges.

[0053] The firing temperature when obtaining the boron carbide powder may be 1800° C. or higher, or 2500° C. or lower, or may be in the range of 1800 to 2500° C. The firing time when obtaining the boron carbide powder may be 2 hours or longer, or 8 hours or shorter, or may be 2 to 8 hours.

[0054] The average particle size of the boron carbide powder may be 5 μm or more, 25 μm or less, or may be 5 to 25 μm. The average particle size of the boron carbide powder is measured in accordance with the method described in JIS Z 8825:2013 "Particle size analysis - Laser diffraction and scattering method."

[0055] The pressure in the nitriding step may be 0.4 MPa or more or 0.6 MPa or more, from the viewpoint of allowing the nitriding of boron carbide to proceed more sufficiently. The pressure in the nitriding step may be 1.2 MPa or less or 1 MPa or less, from the viewpoint of preventing an increase in the production cost of the boron nitride powder. The pressure in the nitriding step may be adjusted within the above-mentioned range, and may be, for example, 0.4 to 1.2 MPa or 0.6 to 1 MPa.

[0056] The firing temperature in the nitriding step may be 1500°C or higher or 1800°C or higher, from the viewpoint of allowing the nitriding of boron carbide to proceed more sufficiently. The firing temperature in the nitriding step may be 2500°C or lower or 2200°C or lower, from the viewpoint of preventing an increase in the production cost of the boron nitride powder. The firing temperature in the nitriding step may be adjusted within the above-mentioned range, and may be, for example, 1500 to 2500°C or 1800 to 2200°C.

[0057] The firing time in the nitriding step may be 20 hours or more or 30 hours or more, from the viewpoint of allowing the nitriding of boron carbide to proceed more sufficiently. The firing time in the nitriding step may be 50 hours or less or 40 hours or less, from the viewpoint of preventing an increase in the production cost of the boron nitride powder. The firing time in the nitriding step may be adjusted within the above-mentioned range, and may be, for example, 20 to 50 hours or 30 to 40 hours.

[0058] In the firing step, the boron carbonitride powder is fired in the atmosphere, thereby reducing the carbon content in the boron carbonitride powder.

[0059] The firing temperature in the firing step may be 400°C or higher or 600°C or higher from the viewpoint of further reducing the carbon content in the boron carbonitride powder. The firing temperature in the firing step may be 1500°C or lower or 1000°C or lower from the viewpoint of suppressing oxidation of boron carbonitride after firing. The firing temperature in the firing step may be adjusted within the above-mentioned range, and may be, for example, 400 to 1500°C or 600 to 1000°C.

[0060] The firing time in the firing step may be 4 hours or more or 6 hours or more from the viewpoint of further reducing the carbon content in the boron carbonitride powder. The firing time in the firing step may be 15 hours or less or 10 hours or less from the viewpoint of more sufficiently suppressing a decrease in the processing efficiency of the firing step. The firing time in the firing step may be adjusted within the above-mentioned range, and may be, for example, 4 to 15 hours or 6 to 10 hours.

[0061] In the decarburization step, boron carbonitride powder, a boron source, and acetylene black are coexistent and heat-treated. In the particle growth step described below, boron nitride crystals are dissolved and reprecipitated to grow boron nitride particles (Ostwald ripening). Therefore, the low-crystalline boron nitride produced by the reaction between the boron source and acetylene black is more soluble than primary particle boron nitride crystals and is advantageous for dissolution and reprecipitation. As described above, this step reduces carbon from boron carbonitride and reacts the boron source with acetylene black to produce low-crystalline boron nitride, thereby further improving the density of the resulting boron nitride powder.

[0062] The boron nitride powder obtained in the decarburization step may contain primary particles of hexagonal boron nitride, may contain agglomerated particles formed by agglomeration of multiple primary particles, or may contain primary particles and agglomerated particles.

[0063] The boron source in the decarburization step may include at least one selected from the group consisting of boric acid and boron oxide.

[0064] The content of the boron source in the decarburization step may be 20% by mass or more, 40% by mass or more, or 48% by mass or more based on the total mass of the boron carbonitride powder, acetylene black, and boron source, from the viewpoint of further improving the crystallinity of boron nitride. The content of the boron source in the decarburization step may be 80% by mass or less or 65% by mass or less based on the total mass of the boron carbonitride powder, acetylene black, and boron source, from the viewpoint of suppressing excessive growth of primary particles and producing boron nitride containing agglomerated particles superior in crushing strength. The content of the boron source in the decarburization step may be adjusted within the above-mentioned range, and may be, for example, 20 to 80% by mass or 40 to 65% by mass based on the total mass of the boron carbonitride powder, acetylene black, and boron source.

[0065] The content of acetylene black in the decarburization step may be 3% by mass or more or 5% by mass or more based on the total mass of the boron carbonitride powder, acetylene black, and boron source, from the viewpoint of further improving the density of boron nitride. The content of acetylene black in the decarburization step may be 15% by mass or less or 10% by mass or less based on the total mass of the boron carbonitride powder, acetylene black, and boron source, from the viewpoint of suppressing excessive growth of primary particles and suppressing the generation of a large amount of boron nitride primary particles not incorporated into agglomerated particles, which would increase orientation. The content of acetylene black in the decarburization step may be adjusted within the above-mentioned range, and may be, for example, 3 to 15% by mass or 5 to 10% by mass based on the total mass of the boron carbonitride powder, acetylene black, and boron source.

[0066] The pressure in the decarburization step may be 10 kPa or more, 20 kPa or less, or may be in the range of 10 to 20 kPa.

[0067] The firing temperature in the decarburization step may be 1500°C or higher or 1800°C or higher from the viewpoint of further reducing the carbon content in the boron carbonitride powder. The firing temperature in the decarburization step may be 2500°C or lower or 2200°C or lower from the viewpoint of suppressing yellowing of the boron nitride powder. The firing temperature in the decarburization step may be adjusted within the above-mentioned range, and may be, for example, 1500 to 2500°C or 1800 to 2200°C.

[0068] The firing time in the decarburization step may be 1 hour or more or 2 hours or more from the viewpoint of further reducing the carbon content in the boron carbonitride powder. The firing time in the decarburization step may be 10 hours or less or 5 hours or less from the viewpoint of more sufficiently suppressing a decrease in the processing efficiency of the decarburization step. The firing time in the decarburization step may be adjusted within the above-mentioned range, and may be, for example, 1 to 10 hours or 2 to 5 hours.

[0069] The method for producing boron nitride powder may further include a crushing step after the decarburization step, in which the boron nitride powder obtained by crushing may be classified.

[0070] The crushing time in the crushing step may be 5 minutes or more, or 8 minutes or more, and may be 15 minutes or less, or 12 minutes or less, for example, 5 to 15 minutes, or 8 to 12 minutes.

[0071] In the method for producing boron nitride powder according to this embodiment, low-crystalline boron nitride is produced by adding acetylene black in the decarburization step. Then, in the particle growth step, small-sized low-crystalline boron nitride particles present inside and outside the agglomerated particles are absorbed into larger-sized hexagonal boron nitride particles and disappear. This increases the size of the primary particles within the agglomerated particles, reduces the orientation index of the resulting boron nitride powder, and reduces the voids inside and between the agglomerated particles, thereby improving the density of the boron nitride powder. As a result, this production method can produce boron nitride powder with an orientation index of 10 or less, a pore distribution curve with a cumulative pore volume Y of 30% or less, and a pore size distribution curve with the highest pore volume peak in the pore diameter range of 2 μm or less.

[0072] The boron source in the particle growth step may include at least one selected from the group consisting of boric acid and boron oxide. The method for supplying the boron source in the particle growth step may be, for example, a method in which the boron source is directly mixed with the boron nitride powder and then heated.

[0073] The content of the boron source in the particle growth step may be 3% by mass or more, 5% by mass or more, 8% by mass or more, or 15% by mass or more, based on the total mass of the boron nitride powder and the boron source obtained in the decarburization step, from the viewpoint of further improving the insulating properties of the resin molded body. The content of the boron source in the particle growth step may be 50% by mass or less, 40% by mass or less, or 35% by mass or less, based on the total mass of the boron nitride powder and the boron source obtained in the decarburization step, from the viewpoint of preventing excessive growth of primary particles from increasing their orientation and decreasing the thermal conductivity of the resin molded body. The content of the boron source in the particle growth step may be adjusted within the above-mentioned range, and may be, for example, 3 to 50% by mass or 5 to 40% by mass, based on the total mass of the boron nitride powder and the boron source obtained in the decarburization step. The content of boric acid, based on the total mass of the boron nitride powder and the boron source obtained in the decarburization step, may also be within the above-mentioned ranges.

[0074] The pressure in the particle growth step may be 10 kPa or more, or 20 kPa or less, for example, 10 to 20 kPa.

[0075] The firing temperature in the particle growth step may be 1500°C or higher or 1800°C or higher from the viewpoint of further improving the insulating properties of the resin molded body and suppressing residual boron oxide. The firing temperature in the particle growth step may be 2500°C or lower or 2200°C or lower from the viewpoint of suppressing yellowing of the boron nitride powder. The firing temperature in the particle growth step may be adjusted within the above-mentioned range, and may be, for example, 1500 to 2500°C or 1800 to 2200°C.

[0076] The firing time in the particle growth step may be 1 hour or more or 2 hours or more from the viewpoint of further improving the insulating properties of the resin molded body. The firing time in the particle growth step may be 10 hours or less, 7 hours or less, or 4 hours or less from the viewpoint of suppressing a decrease in the thermal conductivity of the resin molded body due to an increase in orientation caused by excessive growth of primary particles. The firing time in the particle growth step may be adjusted within the above-mentioned range, and may be, for example, 1 to 10 hours or 2 to 7 hours.

[0077] The method for producing a boron nitride powder may further include a crushing step after the particle growing step. Details of the crushing step may be the same as those described above.

[0078] One embodiment of the present disclosure is an inorganic filler comprising the above-described boron nitride powder and at least one aluminum compound selected from the group consisting of aluminum oxide and aluminum nitride.

[0079] The content of boron nitride powder in the inorganic filler may be 20% by mass or more, or 40% by mass or more, or 100% by mass, or 90% by mass or less, or 80% by mass or less, or may be 20 to 100% by mass, 20 to 90% by mass, or 40 to 80% by mass, based on the total mass of the inorganic filler.

[0080] The content of the aluminum compound in the inorganic filler may be 0 mass%, 10 mass% or more, or 20 mass% or more, 80 mass% or less, or 60 mass% or less, or may be 0 to 80 mass%, 10 to 80 mass%, or 20 to 60 mass%, based on the total mass of the inorganic filler.

[0081] The inorganic filler may contain other compounds in addition to the boron nitride powder and the aluminum compound. Examples of other compounds include silicon oxide, silicon nitride, zinc oxide, magnesium oxide, etc. The content of the other compounds may be 0.1% by mass or more, 1% by mass or less, 0.1 to 1% by mass, or even 0% by mass, based on the total mass of the inorganic filler.

[0082] One embodiment of the present disclosure is a resin molded product comprising the above-described boron nitride powder and a resin. The resin molded product may further comprise at least one aluminum compound selected from the group consisting of aluminum oxide and aluminum nitride. That is, the resin molded product may comprise the above-described inorganic filler and a resin. The resin molded product may be formed from a resin composition comprising the above-described boron nitride powder and a resin, or may be a cured product of the resin composition. The resin composition may be cured by, for example, heat-pressure molding using a hot press or the like. The resin molded product may be in the form of a sheet, and may be a heat-dissipating sheet.

[0083] The content of boron nitride powder in the resin molded body may be 20% by volume or more, 30% by volume or more, or 40% by volume or more, based on the total volume of the resin molded body, from the viewpoint of further improving the heat dissipation properties of the resin molded body. The content of boron nitride powder in the resin molded body may be 85% by volume or less, 80% by volume or less, or 70% by volume or less, based on the total volume of the resin molded body, from the viewpoint of suppressing deterioration in insulation properties and mechanical strength. The content of boron nitride powder in the resin molded body may be adjusted within the above-mentioned range, and may be, for example, 20 to 85% by volume, based on the total volume of the resin molded body.

[0084] The resin may contain or consist of a cured resin, such as epoxy resin, silicone resin, phenol resin, melamine resin, urea resin, polyimide, polyamideimide, polyetherimide, and maleimide-modified resin.

[0085] The resin composition may contain other components in addition to the boron nitride powder and resin. Examples of other components include a curing agent. The curing agent may be selected appropriately depending on the type of thermosetting resin. For example, when the resin is an epoxy resin, examples of the curing agent include phenol novolac compounds, acid anhydrides, amino compounds, and imidazole compounds. The content of the curing agent may be 0.5 parts by mass or more or 1 part by mass or more, and 20 parts by mass or less or 15 parts by mass or less, per 100 parts by mass of the resin.

[0086] When the resin molded body is in the form of a sheet, the thickness of the resin molded body may be 0.1 mm or more, 1 mm or less, or may be 0.1 to 1 mm.

[0087] A method for producing a heat dissipation sheet may include the steps of: molding a mixture containing the above-mentioned boron nitride powder, a cured resin, and a curing agent to obtain a sheet-like molded product; and curing the cured resin by heating the molded product while applying pressure in the thickness direction, thereby obtaining a heat dissipation sheet. The details of the boron nitride powder, cured resin, and curing agent may be the same as those for the resin composition described above. The method for producing a heat dissipation sheet according to the present disclosure uses the above-mentioned boron nitride powder, so that a heat dissipation sheet with excellent thermal conductivity and insulation can be provided even if the pressure used in kneading with the resin or molding the resin composition is low. The molding pressure is 50 kgf / cm. 2 It may be more than 110 kgf / cm 2 or less, 50 to 110 kgf / cm 2 It may be.

[0088] Although several embodiments have been described above, the present disclosure is not limited to the above embodiments. Furthermore, the descriptions of the above embodiments can be applied to each other. [Example]

[0089] The present disclosure will be described in more detail below using examples and comparative examples, but the present disclosure is not limited to the following examples.

[0090] Example 1 [Preparation of boron carbide powder] 100 parts by mass of orthoboric acid (manufactured by Nippon Denko Corporation, hereinafter simply referred to as "boric acid") and 35 parts by mass of acetylene black (product name: HS100, manufactured by Denka Company Limited) were mixed using a Henschel mixer and then loaded into a graphite crucible. This graphite crucible was placed in an arc furnace and heated at 2200°C for 5 hours in an argon atmosphere to synthesize a boron carbide (BC) powder. The synthesized boron carbide powder was pulverized in a ball mill for 1 hour and sieved through a sieve to remove coarse particles, producing a boron carbide powder (BC powder) with an average particle size of 17 μm.

[0091] [Preparation of boron carbonitride powder] The prepared boron carbide powder was loaded into a boron nitride crucible. The crucible was placed in a resistance heating furnace and heated at 2050°C for 35 hours under a nitrogen gas atmosphere of 0.80 MPa to obtain a fired product containing boron carbonitride (B4CN4) powder (nitriding step). The fired product obtained as described above was heated at 800°C for 7 hours under an air atmosphere to obtain a heat-treated product containing boron carbonitride powder (firing step).

[0092] [Preparation of boron nitride powder] Boric acid was added so that the acetylene black content was 5% by mass and the boron source content was 51% by mass, based on the total mass of the heat-treated product, acetylene black, and boric acid (boron source), and mixed using a Henschel mixer to obtain a mixture. Next, 1.55 kg of the mixture was filled into a boron nitride container while being appropriately compression-molded. The container was then placed in a resistance heating furnace, and the temperature was increased from room temperature to 2000°C in a nitrogen gas atmosphere at a pressure of 13 kPa, and the heat treatment was carried out by holding the temperature at 2000°C for 5 hours (decarburization step). This decarburization and crystallization of the individual boron carbonitride particles in the aggregated boron carbonitride particles into hexagonal boron nitride primary particles resulted in the synthesis of a boron nitride powder containing agglomerated particles of a plurality of the primary particles. The synthesized boron nitride powder was crushed in a mortar for 10 minutes, and then classified using a nylon sieve with 75 μm mesh.

[0093] [Particle growth treatment] Boric acid was added so that the boric acid content was 20% by mass, based on the total mass of the boron nitride powder and boric acid, and the mixture was mixed using a Henschel mixer to obtain a mixture. Next, 1.55 kg of the mixture was filled into a boron nitride container while being moderately compressed. The container was then placed in a resistance heating furnace, heated from room temperature to 2000°C in a nitrogen gas atmosphere at a pressure of 13 kPa, and held at 2000°C for 3 hours for heat treatment (particle growth process). This allowed the hexagonal boron nitride primary particles in the aggregated boron nitride particles to undergo Ostwald ripening in the boron oxide phase, synthesizing a boron nitride powder containing aggregated particles formed by the growth of the primary particles. The synthesized boron nitride powder was crushed in a mortar for 10 minutes and then classified using a nylon sieve with a mesh size of 75 μm.

[0094] Example 2 Boron nitride powder was produced in the same manner as in Example 1, except that the content of boric acid in the particle growth step was set to 8 mass %.

[0095] Example 3 Boron nitride powder was produced in the same manner as in Example 1, except that the content of boric acid in the particle growth step was set to 25 mass %.

[0096] Example 4 Boron nitride powder was produced in the same manner as in Example 1, except that the raw material boron carbide powder had an average particle size of 12 μm.

[0097] Example 5 Boron nitride powder was produced in the same manner as in Example 1, except that the content of boric acid in the particle growth step was set to 30 mass % and the particle growth step was held for 5 hours.

[0098] (Comparative Example 1) Boron nitride powder was produced in the same manner as in Example 1, except that the particle growth treatment was not carried out.

[0099] (Comparative Example 2) Boron nitride powder was produced in the same manner as in Example 1, except that in the decarburization step, the content of acetylene black was 0 mass% and the content of boric acid as the boron source was 43 mass% based on the total mass of the heat-treated product, acetylene black, and boric acid (boron source).

[0100] (Comparative Example 3) Boron nitride powder was produced in the same manner as in Example 1, except that the average particle size of the boron carbide was set to 62 μm.

[0101] <Evaluation of boron nitride powder properties> [Orientation index] First, an X-ray diffraction spectrum of the boron nitride powder was obtained by performing X-ray diffraction measurements on the boron nitride powder. From the X-ray diffraction spectrum, the peak intensities I(002) and I(100) corresponding to the (002) and (100) planes were obtained, and the orientation index [I(002) / I(100)] of the boron nitride powder was calculated. The results are shown in Table 1. The X-ray diffractometer used was an "ULTIMA-IV" (product name) manufactured by Rigaku Corporation.

[0102] [Pore distribution measurement] 4 g of the boron nitride powder obtained above was compression-molded under conditions of a diameter of 30 mm and a pressure of 10 MPa to produce a compression-molded body. The pore distribution of the compression-molded body was then measured, and a pore distribution curve was obtained. From the obtained pore distribution curve, the ratio of the cumulative pore volume Y to the cumulative pore volume X, the position of the highest pore volume peak, and the value of the cumulative pore volume X were calculated. The results are shown in Table 1.

[0103] [Average particle size] The particle size distribution of the boron nitride powder was measured in accordance with the method described in JIS Z 8825:2013, "Particle size analysis - laser diffraction and scattering method." A laser diffraction and scattering particle size distribution analyzer (Microtrac "MT-3300EXII" (product name) manufactured by Microtrac-Bell) was used for the measurement. The D50 value in the obtained particle size distribution was taken as the average particle size of the boron nitride powder. The results are shown in Table 1.

[0104] [Bulk density] The bulk density was determined in accordance with the method described in JIS R 1628:1997 "Method for measuring bulk density of fine ceramic powders." The results are shown in Table 1.

[0105] [Preparation of evaluation sheet] A resin composition was obtained by mixing 100 parts by mass of naphthalene-type epoxy resin (product name: HP4032, manufactured by DIC Corporation) with 10 parts by mass of an imidazole compound (product name: 2E4MZ-CN, manufactured by Shikoku Kasei Holdings Co., Ltd.) as a curing agent, with boron nitride powder at 50% by volume. A Thinky Mixer manufactured by Thinky Corporation was used to knead the resin. The kneading conditions were 1600 rpm for 3 minutes. The obtained resin composition was applied to a PET film to a thickness of 0.3 mm. Thereafter, the mixture was kneaded at a temperature of 150°C and 100 kgf / cm. 2 Heating and pressure were applied under the conditions above to prepare a 0.3 mm resin sheet (evaluation sheet).

[0106] [Measurement of thermal conductivity] The thermal conductivity of the above evaluation sheet was measured. The thermal conductivity H (unit: W / (m K)) is calculated by multiplying the thermal diffusivity A (unit: m 2 / sec), density B (unit: kg / m 3 The thermal diffusivity A was calculated from the values ​​of the specific heat capacity C (unit: J / (kg K)) using the formula H = A × B × C. The evaluation sheet was cut into a length of 10 mm, a width of 10 mm, and a thickness of 0.3 mm, and the thermal diffusivity A was measured by the laser flash method. The measurement device used was a xenon flash analyzer (product name: LFA447 NanoFlash, manufactured by NETZSCH). The density B was measured using the Archimedes method. The specific heat capacity C was measured using a DSC (product name: ThermoPlusEvoDSC8230, manufactured by Rigaku Corporation). The results are shown in Table 1.

[0107] [Measurement of breakdown voltage] The dielectric breakdown voltage of the evaluation sheet was measured. The dielectric breakdown voltage of the obtained evaluation sheet was measured using a voltage tester (device name: TOS-8650, manufactured by Kikusui Electronics Co., Ltd.) in accordance with the description of JIS C 6481-1996 "Test method for copper-clad laminates for printed wiring boards." The results are shown in Table 1.

[0108] [Table 1]

Claims

1. A boron nitride powder comprising: the boron nitride powder contains agglomerated particles formed by agglomeration of primary particles of hexagonal boron nitride, The orientation index is 10 or less, The boron nitride powder is compression-molded at a pressure of 10 MPa to prepare a molded body made of the boron nitride powder, and the molded body is measured by mercury intrusion porosimetry to obtain a pore distribution curve of the molded body, When the integral pore volume in the pore diameter range of 0.001 to 300 μm is defined as the integral pore volume X and the integral pore volume in the pore diameter range of 1 to 300 μm is defined as the integral pore volume Y, the ratio of the integral pore volume Y to the integral pore volume X is 30% or less, A boron nitride powder in which the highest peak of pore volume exists in the range of pore diameters of 2 μm or less.

2. 2. The boron nitride powder according to claim 1, wherein the cumulative pore volume X is 0.5 mL / g or less.

3. 2. The boron nitride powder according to claim 1, having an average particle size of 5 to 60 μm.

4. Bulk density is 0.7 g / cm ３ The boron nitride powder according to claim 1 .

5. The boron nitride powder according to any one of claims 1 to 4, and at least one aluminum compound selected from the group consisting of aluminum oxide and aluminum nitride.

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