Boron nitride powder, inorganic filler, resin composition, and resin molded article

Abstract

To provide boron nitride powder that is useful for forming resin molded articles with excellent heat dissipation properties and whose heat dissipation properties do not deteriorate even at high temperatures. [Solution] A boron nitride powder containing aggregated particles composed of aggregated primary particles of hexagonal boron nitride, wherein the orientation index is 15 or less, and in the Raman spectrum obtained by irradiating the aggregated particles with a laser of wavelength 532 nm, the peak showing the maximum intensity is a Raman shift of 1360 cm⁻¹. -1 ~1370cm -1 It exists in this region, and the Raman shift is 1280 cm when the peak maximum intensity is set to 100. -1 The intensity at this point is 1.0 or less, and the Raman shift is 920 cm when the peak maximum intensity is set to 100. -1 The present invention provides boron nitride powder having an intensity of 0.5 or less.

Description

[Technical Field]

[0001] This disclosure relates to boron nitride powder, inorganic fillers, resin compositions, resin molded articles, etc. [Background technology]

[0002] Boron nitride powder possesses high thermal conductivity and insulating properties, and is widely used in applications such as thermal conductive fillers and insulating fillers. In particular, boron nitride powder is used as a filler in heat dissipation components where thermal conductivity is required (for example, Patent Document 1, etc.). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2000-154265 [Overview of the project] [Problems that the invention aims to solve]

[0004] Resin molded articles containing boron nitride powder (e.g., heat dissipation sheets) are used as heat-generating components in electronic devices and the like. In recent years, the amount of heat generated has increased with the performance improvement of electronic devices, but conventional resin molded articles tended to have decreased thermal conductivity in the high-temperature range (120-150°C). Therefore, it is preferable that the resin molded article not only has excellent heat dissipation properties but also maintains its heat dissipation performance even at high temperatures of 120-150°C.

[0005] One aspect of this disclosure aims to provide boron nitride powder, inorganic fillers, and resin compositions useful for forming resin molded articles that have excellent heat dissipation properties and whose heat dissipation properties do not deteriorate even at high temperatures. Another aspect of this disclosure aims to provide resin molded articles that have excellent heat dissipation properties and whose heat dissipation properties do not deteriorate even at high temperatures. [Means for solving the problem]

[0006] Factors that reduce the thermal conductivity include scattering due to grain boundaries, lattice defects, etc. (extrinsic scattering) and scattering due to collisions between phonons (intrinsic scattering, phonon-phonon scattering). As the temperature of hexagonal boron nitride increases (for example, in a region exceeding about 120 °C near the Debye temperature of hexagonal boron nitride), phonon-phonon scattering, especially Umklapp scattering, becomes the dominant factor in thermal resistance. This phonon-phonon scattering is a factor different from defects and grain boundaries, and it has been difficult to infer from conventional crystallinity evaluations (analysis using XRD, etc.). The inventors of the present invention have found that the ratio of the intensity at a specific Raman shift with respect to the peak showing the maximum intensity in the Raman spectrum is closely related to the phonon density of states, particularly the ease of occurrence of phonon-phonon scattering.

[0007] One aspect of the present disclosure includes the following [1] to [9]. [1] Boron nitride powder containing agglomerated particles composed of agglomeration of primary particles of hexagonal boron nitride, having an orientation index of 15 or less, in the Raman spectrum obtained by irradiating the agglomerated particles with a laser having a wavelength of 532 nm, the peak showing the maximum intensity is at a Raman shift of 1360 cm -1 ~1370 cm -1 in the region, when the maximum intensity of the peak is set to 100, the intensity at a Raman shift of 1280 cm -1 is 1.0 or less, when the maximum intensity of the peak is set to 100, the intensity at a Raman shift of 920 cm -1 is 0.5 or less, boron nitride powder. [2] The boron nitride powder according to [1], wherein the 50% passing particle diameter (D50) in the particle size distribution measured by the laser diffraction scattering method is 5 to 150 μm. [3] The boron nitride powder according to [1] or [2], wherein the crushing strength of the agglomerated particles is 5 MPa or more. [4] The boron nitride powder according to any one of [1] to [3], having a graphitization index of 2.3 or less. [5] The boron nitride powder according to any one of [1] to [4] above, and an aluminum compound powder containing at least one selected from the group consisting of aluminum oxide and aluminum nitride, an inorganic filler. [6] The boron nitride powder according to any one of [1] to [4] above, and a resin, a resin composition. [7] The inorganic filler according to [5] above, and a resin, a resin composition. [8] The boron nitride powder according to any one of [1] to [4] above, and a resin, a resin molded body. [9] The inorganic filler according to [5] above, and a resin, a resin molded body.

[0008] Raman shift 1280 cm -1 The intensity at and Raman shift 920 cm -1 The intensity at are considered to be indicators of the second-order scattering of phonons in boron nitride. When these intensities are relatively small, it suggests that the phonon state density in the crystal is low and the probability of phonon-phonon collisions (scattering) is low. The boron nitride powders of [1] to [4] above, in the Raman spectrum obtained by irradiating the agglomerated particles with a laser having a wavelength of 532 nm, the peak showing the maximum intensity is in the region of Raman shift 1360 cm -1 ~ 1370 cm -1 When the maximum intensity of the above peak is set to 100, the intensity at Raman shift 1280 cm -1 is 1.0 or less, and when the maximum intensity of the above peak is set to 100, the intensity at Raman shift 920 cm -1 is 0.5 or less. The boron nitride powder satisfying the above range can be said to have a sufficiently low phonon state density and be less likely to cause phonon-phonon scattering (Umklapp scattering). Therefore, it is推测 that the above boron nitride powder is useful for forming a resin molded body having excellent heat dissipation properties and being less likely to reduce heat dissipation properties even at high temperatures.

[0009] The inorganic filler described in [5] above contains the boron nitride powder mentioned above, and is therefore useful for forming resin molded articles that have excellent heat dissipation properties and whose heat dissipation properties do not deteriorate even at high temperatures.

[0010] The resin compositions described in [6] or [7] above contain the boron nitride powder or the inorganic filler described above, and are therefore useful for forming resin molded articles that have excellent heat dissipation properties and whose heat dissipation properties do not deteriorate even at high temperatures.

[0011] The resin molded articles described in [8] or [9] above contain the boron nitride powder or the inorganic filler described above, and therefore have excellent heat dissipation properties, and their heat dissipation properties do not deteriorate easily even at high temperatures. [Effects of the Invention]

[0012] According to this disclosure, boron nitride powder, inorganic fillers, and resin compositions useful for forming resin molded articles that have excellent heat dissipation properties and whose heat dissipation properties do not deteriorate even at high temperatures can be provided. Furthermore, according to this disclosure, resin molded articles that have excellent heat dissipation properties and whose heat dissipation properties do not deteriorate even at high temperatures can be provided. [Modes for carrying out the invention]

[0013] Embodiments of the present disclosure are described below. However, the following embodiments are illustrative for the purpose of illustrating the present disclosure and are not intended to limit the present disclosure to the following. In this specification, numerical ranges indicated by the symbol "~" include lower and upper limits. That is, a numerical range indicated by "x~y" means x or greater and y or less.

[0014] Unless otherwise specified, the materials exemplified herein may be used individually or in combination of two or more. The content of each component in a composition means the total amount of any multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition.

[0015] A boron nitride powder according to one embodiment of the present disclosure includes aggregated particles composed of aggregated primary particles of hexagonal boron nitride. In the Raman spectrum obtained by irradiating these aggregated particles with a laser of wavelength 532 nm, the peak showing the maximum intensity (hereinafter also referred to as "peak A") corresponds to a Raman shift of 1360 cm⁻¹. -1 ~1370cm -1 It exists in the region, and the Raman shift is 1280 cm when the maximum intensity of Peak A is set to 100. -1 The intensity at this point is 1.0 or less, and the Raman shift is 920 cm when the maximum intensity of Peak A is set to 100. -1 The intensity at this point is 0.5 or less. In this specification, the range of the Raman shift (horizontal axis) in the Raman spectrum is 900 to 3000 cm. -1 Furthermore, the peak intensity of the Raman spectrum is assumed to represent the height of the peak from the baseline.

[0016] In this specification, "Raman shift 1280 cm" -1 The intensity at is the Raman spectrum of boron nitride obtained by the method described later, at a Raman shift of 1280 cm⁻¹. -1 This is obtained by reading the corresponding intensity. Similarly, "Raman shift 920cm -1 The intensity at [location] is the Raman spectrum of boron nitride obtained by the method described later, at a Raman shift of 920 cm⁻¹. -1 This is obtained by reading the corresponding intensity.

[0017] If multiple peaks exhibiting maximum intensity exist in the Raman spectrum, the "peak exhibiting maximum intensity (Peak A)" in this specification refers to the peak with a Raman shift of 1366 cm⁻¹ among those peaks. -1 It refers to the peak that is closest to [the specified value].

[0018] Raman spectroscopy measurements of boron nitride powder shall be performed by the following method. Specifically, first, a cross-sectional sample of aggregated particles in the powder is prepared using a cross-sectional sample preparation device. Next, the obtained cross-sectional sample is used as the measurement target, and the Raman spectrum is obtained by measuring it using a Raman spectrometer under the measurement conditions described in the examples (horizontal axis: Raman shift (unit is cm)). -1 The vertical axis (intensity) is obtained. For cross-sectional sample preparation equipment, for example, the "CP-9010" (product name) manufactured by JEOL Ltd. can be used. For Raman spectrometers, for example, the "Raman Microscope XploRA" (product name) manufactured by Horiba, Ltd. can be used.

[0019] Raman shift of 1280 cm when the maximum intensity of Peak A is set to 100. -1 The intensity at (hereinafter also referred to as "relative intensity 1") is 1.0 or less. Boron nitride powder with relative intensity 1 of 1.0 or less has a low density of states of phonons and suppresses phonon-phonon scattering. Therefore, resin molded articles containing the boron nitride powder have excellent heat dissipation and their heat dissipation does not easily decrease even at high temperatures. Relative intensity 1 may be greater than 0, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.6 or more, 0.65 or more, or 0.8 or more. From the viewpoint of further improving the heat dissipation of the resin molded article and from the viewpoint of not easily decreasing the heat dissipation of the resin molded article even at high temperatures, relative intensity 1 may be 0.95 or less, 0.92 or less, 0.9 or less, 0.88 or less, 0.8 or less, 0.75 or less, 0.7 or less, 0.64 or less, or 0.5 or less. The relative intensity 1 may be adjusted within the above range, for example, 0.1 to 0.95, 0.2 to 0.92, or 0.3 to 0.9. The relative intensity 1 can be adjusted by the pressure in the nitriding process described later, the supply of diboron trioxide gas in the crystallization process, etc.

[0020] Raman shift of 920 cm when the maximum intensity of Peak A is set to 100. -1The intensity at (hereinafter also referred to as "relative intensity 2") is 0.5 or less. Boron nitride powder with relative intensity 2 of 0.5 or less has a low density of states of phonons and suppresses phonon-phonon scattering. Therefore, resin molded articles containing the boron nitride powder have excellent heat dissipation and their heat dissipation does not easily decrease even at high temperatures. Relative intensity 2 may be greater than 0, 0.02 or more, 0.05 or more, 0.08 or more, 0.2 or more, or 0.3 or more. From the viewpoint of further improving the heat dissipation of the resin molded article and from the viewpoint of not easily decreasing the heat dissipation of the resin molded article even at high temperatures, relative intensity 2 may be 0.48 or less, 0.45 or less, 0.42 or less, 0.4 or less, 0.35 or less, 0.3 or less, 0.25 or less, 0.2 or less, or 0.13 or less. The relative intensity 2 may be adjusted within the above range, for example, 0.02 to 0.48, 0.05 to 0.45, or 0.08 to 0.42. The relative intensity 2 can be adjusted by the pressure in the nitriding process described later, the supply of diboron trioxide gas in the crystallization process, etc.

[0021] The boron nitride powder described above may include primary particles of hexagonal boron nitride and aggregated particles composed of multiple aggregated primary particles of hexagonal boron nitride. In this specification, aggregated particles refer to secondary particles that exist in an aggregated state of multiple primary particles (single particles), where the c-axis direction of each primary particle is random. The aggregated state of primary particles can be confirmed, for example, by SEM (scanning electron microscope). Aggregated particles may be approximately spherical. In aggregated particles, primary particles may be strongly bound to each other.

[0022] The particle size of boron nitride powder that passes through 50% of the particle size distribution measured by laser diffraction scattering (D50) may be 1 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, 18 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, 40 μm or more, or 45 μm or more, from the viewpoint of ensuring the heat dissipation of the resin molded article. The particle size of boron nitride powder that passes through 50% of the particle size (D50) may be 150 μm or less, 130 μm or less, 120 μm or less, 100 μm or less, 80 μm or less, 60 μm or less, 55 μm or less, 50 μm or less, 43 μm or less, 40 μm or less, or 30 μm or less, from the viewpoint of further improving the insulation properties of the resin molded article and reducing the viscosity of the resin composition. The 50% passable particle size (D50) of the boron nitride powder can be adjusted within the above range, for example, 1-150 μm, 5-150 μm, 10-120 μm, or 15-100 μm.

[0023] In this specification, the 50% passable particle size (D50) of boron nitride powder refers to the 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" (product name) from Beckman Coulter and the Microtrac "MT-3300EXII" (product name) from Microtrac-Bell. When measuring the 50% passable particle size (D50, volume basis) of boron nitride powder, the measurement should be performed without any homogenization or other treatment of the powder to be measured.

[0024] The orientation index of the boron nitride powder is 15 or less. By having an orientation index of 15 or less, the thermal anisotropy of boron nitride can be further reduced, and the heat dissipation of the resin molded article can be improved. The orientation index of the boron nitride powder may be 2 or more, 4 or more, 5 or more, 6 or more, 7.5 or more, or 8.5 or more. From the viewpoint of further improving the heat dissipation of the resin molded article, the orientation index of the boron nitride powder may be 14 or less, 13 or less, 12 or less, 11 or less, 10 or less, 9.8 or less, 9.5 or less, 9.2 or less, 8.5 or less, or 7.5 or less. The orientation index of the boron nitride powder may be adjusted within the above range, for example, 2 to 15 or 4 to 14.

[0025] In this specification, the orientation index refers to a value measured according to the following method: An X-ray diffraction spectrum of boron nitride powder is obtained by performing an X-ray diffraction measurement on the boron nitride powder, and peak intensities I(002) and I(100) corresponding to the (002) plane and (100) plane are obtained from the said X-ray diffraction spectrum. The orientation index [I(002) / I(100)] of the boron nitride powder is calculated using the obtained peak intensities. As an X-ray diffractometer, for example, "ULTIMA-IV" (product name) manufactured by Rigaku Corporation can be used.

[0026] Since the orientation index is measured on boron nitride powder, if aggregated particles are present in the powder and their proportion is large, the orientation index value tends to decrease and approach a value of around 6 to 7. On the other hand, if the powder consists only of primary particles without aggregated particles, or if the proportion of the above primary particles is large, the orientation index value tends to increase.

[0027] The crushing strength of aggregated particles in boron nitride powder may be 1 MPa or higher, 3 MPa or higher, 4 MPa or higher, 5 MPa or higher, 5.5 MPa or higher, 6.5 MPa or higher, 7.5 MPa or higher, or 10 MPa or higher, from the viewpoint of suppressing the collapse of aggregated particles and further improving the heat dissipation of the resin molded article. The crushing strength of aggregated particles in boron nitride powder may be 30 MPa or lower, 25 MPa or lower, 20 MPa or lower, 18 MPa or lower, 15 MPa or lower, 13 MPa or lower, 10 MPa or lower, 7.5 MPa or lower, or 6.5 MPa or lower, from the viewpoint of reducing voids in the resin molded article and further improving the insulation properties of the resin molded article. The crushing strength of aggregated particles may be adjusted within the above range, for example, 1 to 30 MPa, 3 to 25 MPa, or 4 to 20 MPa.

[0028] In this specification, crushing strength refers to the value measured in accordance with JIS R 1639-5:2007 "Fine ceramics - Method for measuring grain properties - Part 5: Single grain crushing strength". The crushing strength σ (unit: MPa) of a single granule is given by σ = α × P / (π × d), where α (α = 2.48), a dimensionless number that changes depending on the position within the granule, P (unit: N), and d (unit: μm). 2 The value is calculated using the following formula: ( ). The measurement shall be performed on 20 or more granules (aggregated particles), and the value at the point of cumulative destruction rate of 63.2% shall be calculated. A microcompression tester can be used for the measurement. For example, the "MCT-W500" (product name) manufactured by Shimadzu Corporation can be used as a microcompression tester.

[0029] The graphitization index of the boron nitride powder may be 1.0 or higher, 1.2 or higher, 1.3 or higher, 1.4 or higher, 1.5 or higher, 1.6 or higher, or 1.7 or higher. When the graphitization index of the boron nitride powder is above the lower limit, the collapse of aggregated particles due to excessive growth of primary particles is sufficiently suppressed, and the increase in the orientation index of the boron nitride powder is easily suppressed. The graphitization index of the boron nitride powder may be 4.0 or lower, 3.0 or lower, 2.5 or lower, 2.3 or lower, 2.0 or lower, 1.8 or lower, or 1.7 or lower. When the graphitization index of the boron nitride powder is below the upper limit, the crystallinity of the boron nitride primary particles is high, and a resin molded article with excellent heat dissipation is easily obtained. The graphitization index of the boron nitride powder may be adjusted within the above range, for example, 1.0 to 4.0, 1.2 to 3.0, or 1.3 to 2.5. The graphitization index (sometimes called GI) is an indicator of the crystallinity of boron nitride powder.

[0030] The graphitization index used herein is also known as an index value indicating the degree of crystallinity of graphite (e.g., J. Thomas, et al., J. Am. Chem. Soc. 84, 4619 (1962), etc.). The graphitization index is calculated based on the spectrum measured by powder X-ray diffraction of boron nitride powder. First, in the X-ray diffraction spectrum, the area value (in arbitrary units) enclosed by the integrated intensity (i.e., each diffraction peak) of each diffraction peak corresponding to the (100), (101), and (102) planes of the primary particles of hexagonal boron nitride and its baseline is calculated and designated as S100, S101, and S102, respectively. Using the calculated area value, the value of [(S100 + S101) / S102] is calculated to determine the graphitization index. More specifically, it is determined by the method described in the examples herein.

[0031] One embodiment of a method for producing boron nitride powder comprises a nitriding step of obtaining boron carbonitride powder by calcining boron carbide powder under a nitrogen-pressurized atmosphere; a calcination step of calcining the boron carbonitride powder under an atmosphere; and a crystallization step of obtaining boron nitride powder by calcining the boron carbonitride powder obtained through the calcination step under a nitrogen-containing atmosphere. In the crystallization step, diboron trioxide gas is supplied to the boron carbonitride powder.

[0032] Boron carbide powder may be obtained by calcining a mixture of a boron source and carbon black (e.g., acetylene black) under an argon atmosphere. The boron source may include at least one selected from the group consisting of boric acid and boron oxide.

[0033] The boron source content may be 60% by mass or more, 85% by mass or less, or 60-85% by mass, based on the total mass of the boron source and carbon black. The boric acid content, based on the total mass of boric acid and carbon black, may also be within the above ranges. The carbon black content may be 15% by mass or more, 40% by mass or less, or 15-40% by mass, based on the total mass of the boron source and carbon black.

[0034] The calcination temperature when obtaining boron carbide powder may be 1800°C or higher, 2500°C or lower, or 1800 to 2500°C. The calcination time when obtaining boron carbide powder may be 2 hours or more, 8 hours or less, or 2 to 8 hours.

[0035] The average particle size of the boron carbide powder may be 5 μm or more, 10 μm or more, or 15 μm or more. From the viewpoint of further improving the insulating properties of the resin molded article, the average particle size of the boron carbide powder may be 40 μm or less or 30 μm or less. The average particle size of the boron carbide powder may be adjusted within the above range, for example, 5 to 40 μm. The average particle size of the boron carbide powder is the 50% passing particle size (D50) in the volume-based particle size distribution measured in accordance with the method described in JIS Z 8825:2013 "Particle size analysis - Laser diffraction and scattering method".

[0036] The pressure in the nitriding process may be 5 MPa or higher or 9 MPa or higher. When the pressure in the nitriding process is above the lower limit, the phase separation of C and BN progresses in the boron carbonitride powder, which is a multiphase of tC (randomly layered carbon) and t-BN (randomly layered boron nitride), and the crystallinity of t-BN improves, resulting in a crystal structure closer to h-BN. As a result, it is possible to lower the relative strength 1 and relative strength 2 of the boron nitride powder, making it easier to obtain boron nitride powder that is useful for forming resin molded articles with excellent heat dissipation and less reduction in heat dissipation even at high temperatures. From the viewpoint of suppressing an increase in the manufacturing cost of boron nitride powder, the pressure in the nitriding process may be 40 MPa or lower or 30 MPa or lower. The pressure in the nitriding process may be adjusted within the above range, for example, 5 to 40 MPa or 9 to 30 MPa.

[0037] The firing temperature in the nitriding process 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 process may be 2500°C or lower or 2300°C or lower, from the viewpoint of suppressing an increase in the manufacturing cost of boron nitride powder. The firing temperature in the nitriding process may be adjusted within the above range, for example, 1500 to 2500°C or 1800 to 2300°C.

[0038] The firing time in the nitriding process may be 30 hours or more, from the viewpoint of allowing the nitriding of boron carbide to proceed more sufficiently and from the viewpoint of allowing the phase separation between C and BN to proceed sufficiently and improving the crystallinity of t-BN. The firing time in the nitriding process may be 70 hours or less, from the viewpoint of suppressing an increase in the manufacturing cost of boron nitride powder. The firing time in the nitriding process may be adjusted within the above range, for example, 30 to 70 hours.

[0039] In the firing process, the carbon content in the boron carbonitride powder can be reduced by firing the boron carbonitride powder under atmospheric pressure.

[0040] The firing temperature in the firing process may be 650°C or higher, 700°C or higher, or 750°C or higher. The firing temperature in the firing process may be 1050°C or lower. By setting the firing temperature in the firing process within the above range, excessive crystal growth of primary boron nitride particles can be suppressed. As a result, the orientation index of the boron nitride powder can be reduced, and boron nitride powder can be obtained that further improves the heat dissipation performance in the resin molded article. The firing temperature in the firing process may be adjusted within the above range, for example, 650 to 1050°C.

[0041] The firing time in the firing process may be 4 hours or more, from the viewpoint of further reducing the carbon content in the boron carbonitride powder. The firing time in the firing process may be 10 hours or less, from the viewpoint of more sufficiently suppressing a decrease in the processing efficiency of the firing process. The firing time in the firing process may be adjusted within the above range, for example, 4 to 10 hours.

[0042] After the firing process and before the crystallization process, the boron carbonitride powder and the boron source may be mixed. The boron source may contain at least one selected from the group consisting of boric acid and boron oxide. From the viewpoint of further improving the crystallinity of boron nitride, the content of the boron source may be 30% by mass or more, based on the total mass of the boron carbonitride powder and the boron source. From the viewpoint of suppressing the excessive growth of primary boron nitride particles and producing boron nitride powder containing aggregated particles with superior crushing strength, the content of the boron source may be 45% by mass or less, based on the total mass of the boron carbonitride powder and the boron source. The content of the boron source may be adjusted within the above range, for example, 30 to 45% by mass, based on the total mass of the boron carbonitride powder and the boron source.

[0043] In the crystallization process, diboron trioxide gas is supplied to the boron carbonitride powder. The diboron trioxide gas may be supplied directly, or a solid or liquid boron source may be prepared and the boron source may be volatilized during the crystallization process. The boron source used to supply the diboron trioxide gas may include at least one selected from the group consisting of boric acid and boron oxide.

[0044] In the crystallization process, supplying diboron trioxide gas to the boron carbonitride powder allows for efficient decarburization through a gas-solid reaction between diboron trioxide gas, nitrogen gas, and boron carbonitride, while suppressing excessive growth of primary particles. As a result, it is possible to reduce relative strength 1 and relative strength 2, making it easier to obtain boron nitride powder useful for forming resin molded articles with excellent heat dissipation properties and less reduction in heat dissipation even at high temperatures.

[0045] When preparing a solid or liquid boron source, a raw material 1 containing boron carbonitride powder and a raw material 2 containing the boron source may be prepared, and a crystallization process may be carried out. Specifically, raw material 1 containing boron carbonitride powder is placed in a first container, raw material 2 containing a solid or liquid boron source is placed in a second container, and the first and second containers are placed in the same furnace to supply diboron trioxide gas to the boron carbonitride powder. Raw material 1 may further contain a boron source.

[0046] The amount of raw material 2 may be 70 parts by mass or more, 200 parts by mass or less, or 70 to 200 parts by mass, relative to 100 parts by mass of raw material 1.

[0047] The pressure during the crystallization process may be 5 kPa or more, and 20 kPa or less, for example, 5 to 20 kPa.

[0048] The firing temperature in the crystallization process may be 1800°C or higher, from the viewpoint of further reducing the carbon content in the boron carbonitride powder. The firing temperature in the crystallization process may be 2200°C or lower, from the viewpoint of suppressing the yellowing of the boron nitride powder. The firing temperature in the crystallization process may be adjusted within the above range, for example, 1800 to 2200°C.

[0049] The firing time in the crystallization process may be 3 hours or more, or 6 hours or more, from the viewpoint of preventing further deterioration of heat dissipation even at high temperatures in the resin molded body. The firing time in the crystallization process may be 10 hours or less, from the viewpoint of more sufficiently suppressing a decrease in the processing efficiency of the crystallization process. The firing time in the crystallization process may be adjusted within the above range, for example, 3 to 10 hours.

[0050] The boron nitride powder obtained in the crystallization process may contain primary particles of hexagonal boron nitride, may contain aggregated particles composed of multiple aggregated primary particles, or may contain both primary particles and aggregated particles.

[0051] The method for producing boron nitride powder may further include a crushing step after the crystallization step. In the crushing step, the boron nitride powder obtained by crushing may be classified.

[0052] The crushing time in the crushing process may be 8 minutes or more and 15 minutes or less, for example, 8 to 15 minutes.

[0053] An inorganic filler according to one embodiment of the present disclosure is an inorganic filler comprising the boron nitride powder described above and an aluminum compound powder containing at least one selected from the group consisting of aluminum oxide and aluminum nitride.

[0054] The content of boron nitride powder in the inorganic filler may be 20% by mass or more, or 40% by mass or more, based on the total mass of the inorganic filler. The content of boron nitride powder in the inorganic filler may be 90% by mass or less, or 80% by mass or less, based on the total mass of the inorganic filler. The content of boron nitride powder in the inorganic filler may be 20-90% by mass or 40-80% by mass, based on the total mass of the inorganic filler.

[0055] The content of aluminum compound powder in the inorganic filler may be greater than 0% by mass, and may be 10% or more by mass, or 20% or more by mass, based on the total mass of the inorganic filler. The content of aluminum compound powder in the inorganic filler may be 80% or less by mass, or 60% or less by mass. The content of aluminum compound powder in the inorganic filler may be 10 to 80% by mass, or 20 to 60% by mass.

[0056] The inorganic filler may contain other compound powders besides boron nitride powder and the aluminum compound powder mentioned above. Examples of other compound powders include silicon oxide powder, silicon nitride powder, zinc oxide powder, and magnesium oxide powder. The content of other compound powders may be 0.1% by mass or more, 1% by mass or less, 0.1 to 1% by mass, or 0% by mass, based on the total mass of the inorganic filler.

[0057] Since the inorganic filler according to this embodiment contains the boron nitride powder described above, it is useful for forming resin molded articles that have excellent heat dissipation properties and whose heat dissipation properties do not deteriorate even at high temperatures.

[0058] A resin composition according to one embodiment of the present disclosure comprises the boron nitride powder described above and a resin. The resin composition may further comprise an aluminum compound powder comprising at least one selected from the group consisting of aluminum oxide and aluminum nitride. That is, the resin composition may comprise the inorganic filler described above and a resin.

[0059] The content of boron nitride powder in the resin composition 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 composition, from the viewpoint of further improving the heat dissipation of the resin molded article and from the viewpoint of not reducing the heat dissipation of the resin molded article even at high temperatures. The content of boron nitride powder in the resin composition 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 composition, from the viewpoint of suppressing a decrease in mechanical strength. The content of boron nitride powder in the resin composition may be adjusted within the above range, for example, 20 to 85% by volume, based on the total volume of the resin composition.

[0060] The resin may contain a curable resin (e.g., a thermosetting resin) or consist solely of a curable resin. Examples of curable resins include epoxy resins, silicone resins, phenolic resins, melamine resins, urea resins, polyimides, polyamideimides, polyetherimides, maleimide-modified resins, and the like.

[0061] The resin composition may contain other components in addition to the boron nitride powder and resin described above. Other components may include, for example, a curing agent. The curing agent may be appropriately selected depending on the type of curable resin. For example, if the resin is an epoxy resin, examples of curing agents include phenol novolac compounds, acid anhydrides, amino compounds, imidazole compounds, etc. The content of the curing agent may be 0.5 parts by mass or more, 1 part by mass or more, or 5 parts by mass or more, or 20 parts by mass or less, or 15 parts by mass or less, per 100 parts by mass of resin.

[0062] The resin composition according to this embodiment contains the above-mentioned boron nitride powder or inorganic filler, and is therefore useful for forming resin molded articles that have excellent heat dissipation properties and whose heat dissipation properties do not deteriorate even at high temperatures.

[0063] One embodiment of the present disclosure is a resin molded article comprising the boron nitride powder described above and a resin. The resin molded article may further contain an aluminum compound powder comprising at least one selected from the group consisting of aluminum oxide and aluminum nitride. That is, the resin molded article may contain the inorganic filler described above and a resin. The resin molded article may be formed from the resin composition described above, or it may be a cured product of the resin composition described above. That is, the resin molded article may contain the inorganic filler described above and a cured product of the resin composition. The curing of the resin composition may be, for example, by heat press molding. The resin molded article may be in the form of a sheet, or it may be a heat dissipation sheet.

[0064] The content of boron nitride powder in the resin molded article may be 20% or more by volume, 30% or more by volume, or 40% or more by volume, based on the total volume of the resin molded article, from the viewpoint of further improving the heat dissipation of the resin molded article and from the viewpoint of not reducing the heat dissipation of the resin molded article even at high temperatures. The content of boron nitride powder in the resin molded article may be 85% or less by volume, 80% or less by volume, or 70% or less by volume, based on the total volume of the resin molded article, from the viewpoint of suppressing a decrease in mechanical strength. The content of boron nitride powder in the resin molded article may be adjusted within the above range, for example, 20 to 85% by volume, based on the total volume of the resin molded article.

[0065] When the resin molded product is in the form of a sheet, the thickness of the resin molded product may be 0.1 mm or more, 1 mm or less, or between 0.1 and 1 mm.

[0066] The resin molded article according to this embodiment contains the above-mentioned boron nitride powder or inorganic filler, and therefore has excellent heat dissipation properties, and its heat dissipation properties do not deteriorate easily even at high temperatures.

[0067] A method for manufacturing a resin molded article (heat dissipation sheet) may include the steps of: molding a mixture containing the above-mentioned boron nitride powder, a curable resin, and a curing agent to obtain a sheet-like molded article; and curing the curable resin by heating while applying pressure in the thickness direction of the molded article to obtain a resin molded article. The details of the boron nitride powder, curable resin, and curing agent may be the same as those in the above-mentioned resin composition. The molding pressure is 100 kgf / cm². 2 The above is sufficient, and 300 kgf / cm² 2 The following may apply: 100-300 kgf / cm² 2 That's fine.

[0068] Although several embodiments have been described above, this disclosure is not limited in any way to the embodiments described above. Furthermore, the descriptions of the embodiments described above are applicable to each other. [Examples]

[0069] The present disclosure will be described in more detail below with reference to examples and comparative examples. However, the present disclosure is not limited to the following examples.

[0070] (Example 1) [Preparation of boron carbide powder] 100 parts by mass of orthoboric acid (manufactured by Nippon Denko Co., Ltd., hereinafter simply referred to as "boric acid") and 35 parts by mass of acetylene black (product name: "HS100", manufactured by Denka Co., Ltd.) were mixed using a Henschel mixer and then packed 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 lump of boron carbide (B4C) powder. The synthesized lump of boron carbide powder was pulverized in a ball mill for 1 hour, and then sieved using a sieve to remove coarse particles, thereby producing boron carbide powder (B4C powder) with an average particle size of 25 μm.

[0071] [Preparation of boron carbonitride powder] The prepared boron carbide powder was packed into a boron nitride crucible. The crucible was placed in a resistance heating furnace and heated under nitrogen gas atmosphere, pressure of 12.0 MPa, firing temperature of 2070°C, and firing time of 50 hours to obtain a calcined product containing boron carbonitride (B4CN4) powder (nitriding process). The calcined product obtained as described above was heated under air atmosphere at a firing temperature of 950°C for 8 hours to obtain a heat-treated product (calcination process).

[0072] [Preparation of boron nitride powder] Based on the total mass of the above heat-treated material and boric acid (boron source), boric acid was added so that the boron source content reached 40% by mass, and the mixture was mixed using a Henschel mixer to obtain a mixture. Next, 1.80 kg of the above mixture was filled into a boron nitride container while appropriately compressing it. Then, the above container and a container filled with 4.00 kg of boric acid (boron source) in a boron nitride container were placed in a resistance heating furnace and heated in a nitrogen gas atmosphere at a pressure of 15 kPa, from room temperature to 2030°C, and held at 2030°C for 8 hours (crystallization process). This decarburized the above heat-treated material and crystallized the individual boron carbonitride particles in the lump boron carbonitride particles into hexagonal boron nitride primary particles, thereby synthesizing boron nitride powder containing aggregated particles formed by the aggregation of multiple primary particles. The synthesized boron nitride powder was crushed in a mortar for 10 minutes, and then further classified using a nylon sieve with a mesh size of 75 μm. The residue below the sieve was the boron nitride powder of Example 1.

[0073] (Example 2) Boron nitride powder was prepared in the same manner as in Example 1, except that the boric acid content was set to 35% by mass and the holding time at 2030°C was set to 4 hours when obtaining the mixture of the heat-treated product and boric acid in the crystallization process.

[0074] (Example 3) Boron nitride powder was prepared in the same manner as in Example 1, except that the average particle size of the boron carbide powder was set to 16 μm by changing the sieving conditions when preparing the boron carbide powder, and the sieve size during classification when preparing the boron nitride powder was set to 63 μm.

[0075] (Example 4) Boron nitride powder was prepared in the same manner as in Example 1, except that the firing temperature was set to 1000°C during the firing process.

[0076] (Comparative Example 1) Boron nitride powder was prepared in the same manner as in Example 1, except that the pressure in the nitriding process was set to 0.80 MPa.

[0077] (Comparative Example 2) Boron nitride powder was prepared in the same manner as in Example 1, except that a separate container filled with boric acid was not placed inside the furnace during the crystallization process.

[0078] (Comparative Example 3) Boron nitride powder was prepared in the same manner as in Example 1, except that the firing temperature was set to 1100°C during the firing process.

[0079] <Evaluation of the properties of boron nitride powder> [Raman spectroscopy measurement] For Examples 1-4 and Comparative Examples 1-3, cross-sectional samples of aggregated particles in boron nitride powder were prepared using a cross-sectional sample preparation device (product name "CP-9010", manufactured by JEOL Ltd.). The obtained cross-sectional samples were measured by Raman spectroscopy using a Raman microscope "XploRA" (product name) manufactured by Horiba, Ltd., under the following measurement conditions, and Raman spectra were obtained. The measurement involved mapping measurements at approximately 10 μm squares in the center of the aggregated particles observed in the cross-sectional samples, in 1 μm steps (10 points × 10 points), and the spectra from 100 points were integrated. Subsequently, a process was performed to correct for the fluorescence-derived baseline using a polynomial model, and the Raman spectrum was obtained. From each obtained Raman spectrum, the peak showing the maximum intensity (maximum height) (peak A), the maximum intensity of peak A, and the Raman shift of 1280 cm⁻¹ were identified. -1 Strength in and Raman shift 920cm -1 The intensity at this point was identified. In each Raman spectrum, the peak showing the maximum intensity was at a Raman shift of 1360 cm. -1 ~1370cm -1 It was present in the region. The Raman shift of 1280 cm was set to 100 when the maximum intensity of peak A in each Raman spectrum was set to 100. -1 The intensity at that point ("Relative Intensity 1" in Table 1), and the Raman shift of 920 cm when the maximum intensity of Peak A is set to 100. -1 The intensity ("Relative Intensity 2" in Table 1) was calculated. The results are shown in Table 1.

[0080] <Raman spectroscopy measurement conditions> Laser: 532nm (light-reducing filter: 10%) Range: 900~3000cm -1 Objective lens: 100x Grating: 1200g Slit: 100 μm Confocal hole: 100 μm Laser polarization: Circular Exposure time: 1 second Number of exposures: 3

[0081] [Particle size distribution measurement] The particle size distribution of boron nitride powder in each example and comparative example was measured in accordance with the method described in JIS Z 8825:2013 "Particle size analysis - Laser diffraction and scattering method". A laser diffraction 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 volume-based particle size distribution was defined as the 50% passing particle size (D50) of the boron nitride powder. The results are shown in Table 1.

[0082] [Orientation Index] X-ray diffraction spectra were obtained by performing X-ray diffraction measurements on boron nitride powder for each example and comparative example. From these X-ray diffraction spectra, 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. Note that "peak intensity" refers to the peak height. The results are shown in Table 1. The X-ray diffractometer used was "ULTIMA-IV" (product name) manufactured by Rigaku Corporation.

[0083] [Crushing strength] The crushing strength of the aggregated particles contained in the boron nitride powder of each example and comparative example was measured in accordance with JIS R 1639-5:2007 "Fine ceramics - Method for measuring particle properties - Part 5: Single particle crushing strength". A microcompression tester (manufactured by Shimadzu Corporation, product name "MCT-W500") was used for the measurement. The measurement was performed on 20 or more aggregated particles, and the value was calculated at a cumulative fracture rate of 63.2%. The results are shown in Table 1.

[0084] [Graphitization Index] The graphitization index of the boron nitride powder in each example and comparative example was calculated from the results of powder X-ray diffraction measurements. In the obtained X-ray diffraction spectra, the area value (in arbitrary units) enclosed by the integrated intensity of each diffraction peak (i.e., each diffraction peak) corresponding to the (100), (101), and (102) planes of the hexagonal boron nitride primary particles and their baseline was calculated and designated as S100, S101, and S102, respectively. Using the area values ​​thus calculated, the graphitization index was determined based on the following equation (1). The results are shown in Table 1. Graphitization index = (S100 + S101) / S102 ... (1)

[0085] [Preparation of evaluation sheet] A mixture of 100 parts by mass of naphthalene-type epoxy resin (product name: HP4032, manufactured by DIC Corporation) and 10 parts by mass of an imidazole compound (product name: 2E4MZ-CN, manufactured by Shikoku Chemicals Holdings Co., Ltd.) as a curing agent was prepared. The mixture was then mixed so that the boron nitride powder of each example and comparative example reached 65% by volume. A solvent (toluene) was added to achieve a coating viscosity to obtain a resin composition. A rotary-orbital stirring and defoaming machine (manufactured by Thinky Co., Ltd., product name: Awatori Rentaro (registered trademark)) was used for mixing with the resin. The mixing conditions were 2000 rpm for 3 minutes. The obtained resin composition was coated onto a PET film using a coater to a thickness of 0.2 mm. Afterwards, a temperature of 150°C and a load of 150 kgf / cm² were applied. 2 A 0.2 mm thick resin sheet (evaluation sheet) was prepared by heating and pressurizing under the specified conditions.

[0086] [Measurement of thermal conductivity, evaluation of heat dissipation, and evaluation of the rate of decrease in heat dissipation] The thermal conductivity of the evaluation sheet described above was measured. Thermal conductivity H (unit: W / (m·K)) is equal to the thermal diffusivity α H (Unit: m) 2 / sec), density ρ (unit: kg / m 3 ) and specific heat capacity C p From the value (unit: J / (kg·K)), H=α H ×ρ×C p The thermal diffusivity α was calculated based on the following formula. HThe specific heat capacity C was determined by processing an evaluation sheet to 10mm (length) x 10mm (width) x 0.2mm (thickness) and using the laser flash method. The measurement device used was a xenon flash analyzer (product name: LFA774NanoFlash, manufactured by NETZSCH). The density ρ was determined using the Archimedes method. p The thermal conductivity was determined using a DSC (product name: ThermoPlusEvoDSC8230, manufactured by Rigaku Corporation). Thermal conductivity measurements were performed at room temperature (25°C) and high temperature (150°C, which is above the Debye temperature of boron nitride). From the results of each thermal conductivity measurement, the thermal conductivity at 25°C (H 25℃ Thermal conductivity (H) at 150°C for ) 150℃ The rate of decrease of ) was determined according to the following equation (2). The obtained thermal conductivity and rate of decrease of thermal conductivity were evaluated for heat dissipation and the rate of decrease of heat dissipation according to the following criteria. The results are shown in Table 1. The smaller the rate of decrease of thermal conductivity, the less the heat dissipation of the resin molded product deteriorates even at high temperatures. The rate of decrease in thermal conductivity (%) = (1 - (H 150℃ / H 25℃ )) × 100···(2)

[0087] [Evaluation of heat dissipation (25℃)] A: Thermal conductivity at 25℃ (H 25℃ The pressure is 14.0 W / (m·K) or higher. B: Thermal conductivity at 25℃ (H 25℃ The value is between 12.0 W / (m·K) and less than 14.0 W / (m·K). C: Thermal conductivity at 25℃ (H 25℃ The pressure is between 10.0 W / (m·K) and less than 12.0 W / (m·K). D: Thermal conductivity at 25℃ (H 25℃ The value is between 8.0 W / (m·K) and less than 10.0 W / (m·K). E: Thermal conductivity at 25℃ (H 25℃ ) is less than 8.0 W / (m·K).

[0088] [Evaluation of the rate of decrease in heat dissipation] A: The decrease in thermal conductivity is less than 30.0%. B: The decrease in thermal conductivity is between 30.0% and 40.0%. C: The decrease in thermal conductivity is between 40.0% and 50.0%. D: The rate of decrease in thermal conductivity is 50.0% or more but less than 60.0%. E: The decrease in thermal conductivity is 60.0% or more.

[0089] [Measurement of dielectric breakdown voltage and evaluation of insulation properties] The dielectric breakdown voltage was measured for the evaluation sheets described above. The dielectric breakdown voltage of the obtained evaluation sheets was measured using a withstand voltage tester (device name: TOS-8650, manufactured by Kikusui Electronics Co., Ltd.) in accordance with the description in JIS C 6481-1996 "Test Method for Copper-Clad Laminates for Printed Wiring Boards". Twenty dielectric breakdown voltages were measured for each of Examples 1-4 and Comparative Examples 1-3, and the arithmetic mean was calculated. The insulation properties were evaluated based on the arithmetic mean of the obtained dielectric breakdown voltages according to the following criteria. The results are shown in Table 1.

[0090] A: The average dielectric breakdown voltage is 70kV / mm or higher. B: The average dielectric breakdown voltage is between 60kV / mm and 70kV / mm. C: The average dielectric breakdown voltage is between 50kV / mm and 60kV / mm. D: The average dielectric breakdown voltage is between 40kV / mm and 50kV / mm. E: The average dielectric breakdown voltage is less than 40kV / mm.

[0091] [Table 1]

Claims

1. A boron nitride powder containing aggregated particles composed of aggregated primary particles of hexagonal boron nitride, The orientation index is 15 or less. In the Raman spectrum obtained by irradiating the aggregated particles with a laser of wavelength 532 nm, the peak showing the maximum intensity corresponds to a Raman shift of 1360 cm⁻¹. －１ ~1370cm －１ It exists in the realm of, The Raman shift of 1280 cm is set to 100 when the maximum intensity of the aforementioned peak is 100. －１ The intensity in is 1.0 or less. The Raman shift of 920 cm is set to 100 when the maximum intensity of the aforementioned peak is 100. －１ Boron nitride powder having an intensity of 0.5 or less.

2. The boron nitride powder according to claim 1, wherein the 50% passing particle size (D50) in the particle size distribution measured by laser diffraction scattering is 5 to 150 μm.

3. The boron nitride powder according to claim 1, wherein the crushing strength of the aggregated particles is 5 MPa or more.

4. The boron nitride powder according to claim 1, wherein the graphitization index is 2.3 or less.

5. Boron nitride powder according to any one of claims 1 to 4, An inorganic filler comprising an aluminum compound powder containing at least one selected from the group consisting of aluminum oxide and aluminum nitride.

6. A resin composition comprising boron nitride powder according to any one of claims 1 to 4 and a resin.

7. A resin composition comprising the inorganic filler described in claim 5 and a resin.

8. A resin molded article comprising boron nitride powder according to any one of claims 1 to 4 and a resin.

9. A resin molded article comprising the inorganic filler described in claim 5 and a resin.

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