Boron nitride powder and resin molded article

Abstract

To provide a boron nitride powder capable of yielding a resin molded article excellent in thermal conductivity.SOLUTION: One aspect of the present disclosure provides a boron nitride powder comprising agglomerated particles formed by aggregation of a plurality of primary particles of hexagonal boron nitride, and primary particles of hexagonal boron nitride. In one example, in the boron nitride powder, the agglomerated particles contain calcium borate, and, if the average particle diameter in a volume-based particle size distribution A measured by a laser diffraction / scattering method after dispersion treatment is defined as D50(A), and the average particle diameter in a volume-based particle size distribution B measured by the laser diffraction / scattering method without dispersion treatment is defined as D50(B), then D50(A) is greater than 15 μm, and the ratio of D50(B) to D50(A) is 1.5 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a boron nitride powder and a resin molded body. [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.).

[0005] Furthermore, from the viewpoint of reducing the anisotropy due to the shape as described above, a method of forming an aggregate composed of a plurality of primary particles, which are aggregated and fused together so that the orientation of the a-axis direction of adjacent primary particles differs, has been investigated. Patent Document 2 discloses boron nitride aggregate particles formed by agglomerating primary particles of boron nitride, and describes that by increasing the strength of the aggregate particles to a degree that the collapse of the aggregate particles can be suppressed even when a predetermined molding pressure is applied, the alignment of the boron nitride primary particles to the same direction can be suppressed. Patent Document 3 discloses a powder containing primary particles of hexagonal boron nitride having a scale shape, an average particle size of 4.0 to 15.0 μm, an orientation index of 25.0 or less, and a tap density of 0.70 g / cm. 3 Thus, a boron nitride powder is disclosed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-154265 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-135731 [Patent Document 3] International Publication No. 2023 / 204139 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present disclosure is to provide a boron nitride powder capable of providing a resin molded article having excellent thermal conductivity. Another object of the present disclosure is to provide a resin molded article having excellent thermal conductivity. [Means for solving the problem]

[0008] The present disclosure provides the following [1] to [8].

[0009] [1] A boron nitride powder comprising agglomerated particles formed by agglomerating a plurality of primary particles of hexagonal boron nitride, and primary particles of hexagonal boron nitride, the agglomerated particles comprise calcium borate; A boron nitride powder that satisfies at least one of the following (1) or (2): (1) When the average particle diameter in volume-based particle size distribution A measured by a laser diffraction / scattering method after dispersion treatment is defined as D50(A) and the average particle diameter in volume-based particle size distribution B measured by the laser diffraction / scattering method without dispersion treatment is defined as D50(B), the D50(A) is greater than 15 μm, and the ratio of the D50(B) to the D50(A) is 1.5 or more. (2) When the average particle diameter in the volume-based particle size distribution A measured by a laser diffraction / scattering method after the dispersion treatment is defined as D50(A), D50(A) is more than 15 μm, When the maximum volume frequency in a volume-based particle size distribution B measured by the laser diffraction / scattering method without dispersion treatment is defined as H, the particle size showing the largest particle size among particle sizes showing a volume frequency of H / 2 is defined as L, and the particle size showing the smallest particle size is defined as S, the ratio of L to S is 5 or more. [2] A boron nitride powder comprising agglomerated particles formed by agglomerating a plurality of primary particles of hexagonal boron nitride, and primary particles of hexagonal boron nitride, the agglomerated particles comprise calcium borate; A boron nitride powder in which, when D50(A) is the average particle diameter in volume-based particle size distribution A measured by laser diffraction / scattering after dispersion treatment and D50(B) is the average particle diameter in volume-based particle size distribution B measured by laser diffraction / scattering without dispersion treatment, D50(A) is greater than 15 μm and the ratio of D50(B) to D50(A) is 1.5 or more. [3] A boron nitride powder comprising agglomerated particles formed by agglomerating a plurality of primary particles of hexagonal boron nitride, and primary particles of hexagonal boron nitride, the agglomerated particles comprise calcium borate; When the average particle diameter in volume-based particle size distribution A measured by a laser diffraction / scattering method after dispersion treatment is defined as D50(A), D50(A) is more than 15 μm, A boron nitride powder in which, when the maximum volume frequency in a volume-based particle size distribution B measured by the laser diffraction / scattering method without dispersion treatment is defined as H, the particle size showing the largest particle size among particle sizes showing a volume frequency of H / 2 is defined as L, and the particle size showing the smallest particle size is defined as S, the ratio of L to S is 5 or more. [4] The boron nitride powder according to any one of [1] to [3], which has an orientation index of 30 or more. [5] BET specific surface area is 1.30m 2 The boron nitride powder according to any one of [1] to [4], wherein the boron nitride powder has a molecular weight of 1000 or less. [6] Tap density is 0.80g / cm 3 The boron nitride powder according to any one of [1] to [5] above. [7] The boron nitride powder according to any one of [1] to [6], wherein the total oxygen content is 2.0 mass % or more. [8] A resin molded product comprising the boron nitride powder according to any one of [1] to [7] and a resin. [Effects of the Invention]

[0010] According to the present disclosure, a boron nitride powder capable of providing a resin molded article having excellent thermal conductivity can be provided. According to the present disclosure, a resin molded article having excellent thermal conductivity can also be provided. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a graph showing the particle size distribution of the boron nitride powder of Example 1. [Figure 2] FIG. 2 is a graph showing the particle size distribution of the boron nitride powder of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are merely 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 equal to or greater than x and equal to or less than y.

[0013] 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.

[0014] One embodiment of the boron nitride powder is a boron nitride powder including agglomerated particles formed by agglomerating a plurality of primary particles of hexagonal boron nitride, and primary particles of hexagonal boron nitride.

[0015] The agglomerated particles include calcium borate.

[0016] The boron nitride powder satisfies at least one of the following conditions (1) and (2). Condition (1): When the average particle diameter in volume-based particle size distribution A measured by laser diffraction / scattering after dispersion treatment is defined as D50(A), and the average particle diameter in volume-based particle size distribution B measured by laser diffraction / scattering without dispersion treatment is defined as D50(B), the D50(A) is greater than 15 μm, and the ratio of the D50(B) to the D50(A) is 1.5 or greater. Condition (2): When the average particle diameter in the volume-based particle size distribution A measured by a laser diffraction / scattering method after dispersion treatment is defined as D50(A), D50(A) is greater than 15 μm, When the maximum volume frequency in a volume-based particle size distribution B measured by the laser diffraction / scattering method without dispersion treatment is defined as H, the particle size showing the largest particle size among particle sizes showing a volume frequency of H / 2 is defined as L, and the particle size showing the smallest particle size is defined as S, the ratio of S to L is 5 or more.

[0017] When the boron nitride powder satisfies condition (1), the average particle size (D50(A)) of the primary particles of hexagonal boron nitride is relatively large, and the particle size distribution has a ratio (D50(B) / D50(A)) of D50(B) to D50(A) equal to or greater than the predetermined value. A D50(B) / D50(A) ratio equal to or greater than the predetermined value indicates that the particle size distribution is broad and contains a certain number of agglomerated particles that are strong enough to be broken down by homogenization. Because the boron nitride powder has the above-described structure, a certain number of agglomerated particles remain even when blended as a filler in a resin, thereby reducing thermal anisotropy overall and improving the thermal conductivity of the resin molded product.

[0018] The boron nitride powder may have an upper limit of the D50(B) / D50(A) ratio of, for example, 1.8 or less, 1.7 or less, or 1.6 or less. The fact that the upper limit of the D50(B) / D50(A) ratio falls within the above ranges means that the strength of the agglomerated particles is not excessively high, further reducing the amount of voids formed between the agglomerated particles and further preventing a decrease in insulating properties. The D50(B) / D50(A) ratio of the boron nitride powder may be adjusted within the above range, and may be, for example, 1.5 to 1.8.

[0019] When the above boron nitride powder satisfies condition (2), the average particle size (D50(A)) of the primary particles of hexagonal boron nitride is relatively large, and furthermore, the particle size distribution has a particle size distribution in which the ratio (L / S) of the particle size L on the larger particle size side to the particle size S on the smaller particle size side showing a predetermined volume frequency in the particle size distribution B is equal to or greater than the predetermined value. A relatively large D50(A) and an L / S equal to or less than the predetermined value correspond to a particle size distribution that is broadened toward the larger particle size side. Because the above boron nitride powder has the above-mentioned configuration, a certain amount of agglomerated particles remain even when blended as a filler in resin, thereby reducing thermal anisotropy overall and improving the thermal conductivity of the resin molded body.

[0020] The lower limit of the L / S ratio in the boron nitride powder may be, for example, 5.2 or more, 5.4 or more, 5.5 or more, or 5.6 or more. The lower limit of the L / S ratio within the above range means that the boron nitride powder contains agglomerated particles with a more appropriate variation in particle size, and when blended as a filler in a resin, a resin molded product with superior thermal conductivity can be provided. The upper limit of the L / S ratio in the boron nitride powder may be, for example, 7.4 or less, 7.2 or less, 7.0 or less, or 6.8 or less. The upper limit of the L / S ratio within the above range means that the particle size distribution contains an appropriate amount of coarse particles and fine particles, and when a resin molded product containing the boron nitride powder is prepared, the resin molded product can achieve both high levels of thermal conductivity and insulating properties. The L / S ratio in the boron nitride powder may be adjusted within the above range, for example, 5.2 to 7.2, or 5.4 to 7.0.

[0021] The lower limit of D50(A) in particle size distribution A may be, for example, 15.5 μm or more, 16.0 μm or more, or 16.2 μm or more. D50(A) reflects the average particle size of boron nitride primary particles. Having the lower limit of D50(A) within the above range contributes to improving thermal conductivity even when boron nitride exists as primary particles without agglomeration. The upper limit of D50(A) in particle size distribution A may be, for example, 18.0 μm or less, 17.5 μm or less, or 17.0 μm or less. When D50(A) is large and the boron nitride primary particles are too large, it tends to be difficult to form agglomerated particles. Therefore, having the lower limit of D50(A) within the above range facilitates the formation of agglomerated particles, which in turn facilitates the improvement of the thermal conductivity of a resin molded product containing the boron nitride powder. D50(A) in particle size distribution A may be adjusted within the above range and may be 15.5 to 18.0 μm.

[0022] D50(B) in particle size distribution B refers to the average particle size of the boron nitride powder, including agglomerated particles. The lower limit of D50(B) in particle size distribution B may be, for example, 22.0 μm or more, 23.0 μm or more, 24.0 μm or more, or 25.0 μm or more. The fact that the lower limit of D50(B) is within the above range means that the agglomerated particles and primary particle sizes are large, and when a resin molded product containing the boron nitride powder is prepared, the thermal conductivity of the resin molded product can be further improved. The upper limit of D50(B) in particle size distribution B may be, for example, 30.0 μm or less, 28.0 μm or less, 27.0 μm or less, or 26.0 μm or less. When the upper limit of D50(B) is within the above range, the proportion of coarse agglomerated particles is kept appropriate, and when a resin molded product containing the boron nitride powder is prepared, a decrease in the insulating properties of the resin molded product can be suppressed. D50(B) in particle size distribution B may be adjusted within the above range, and may be, for example, 22.0 to 30.0 μm.

[0023] The lower limit of D90(B) in particle size distribution B may be, for example, 70.0 μm or more, 75.0 μm or more, or 80.0 μm or more. By ensuring that the lower limit of D90(B) is within the above range, a moderate proportion of coarse agglomerates can be present, which can significantly contribute to improving the thermal conductivity of a resin molded product containing the boron nitride powder when prepared. The upper limit of D90(B) in particle size distribution B may be, for example, 100.0 μm or less, 95.0 μm or less, or 90.0 μm or less. By ensuring that the upper limit of D90(B) is within the above range, the proportion of coarse agglomerates can be kept moderate, which can suppress a decrease in the insulating properties of a resin molded product containing the boron nitride powder when prepared. D90(B) in particle size distribution B may be adjusted within the above range, for example, 70.0 to 100.0 μm.

[0024] In this specification, D50(A), D50(B), and D90(B) for boron nitride powder refer to values ​​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 measurements. 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.

[0025] In the boron nitride powder, the primary particles of hexagonal boron nitride may not be aggregated but may be contained as single particles. In other words, the boron nitride powder can be said to contain primary particles of hexagonal boron nitride and aggregated particles formed by aggregation of a plurality of primary particles of hexagonal boron nitride.

[0026] The orientation index of the boron nitride powder may be a relatively large value. The lower limit of the orientation index of the boron nitride powder may be, for example, 30 or more, 35 or more, 38 or more, 40 or more, or 42 or more. The upper limit of the orientation index of the boron nitride powder may be, for example, 60 or less, 55 or less, 52 or less, or 50 or less. The orientation index of the boron nitride powder may be adjusted within the above-mentioned range, and may be, for example, 30 to 60.

[0027] Since the orientation index is measured on boron nitride powder, when the powder contains agglomerated particles in which the primary particles are not substantially oriented and the proportion of these particles is high, the orientation index tends to approach a value of about 6 to 7. On the other hand, when the powder is composed of primary particles that do not contain agglomerated particles, or when the proportion of these primary particles is high, the orientation index tends to be high. Furthermore, when the average particle diameter of the primary particles is large or the average thickness of the primary particles is small, the orientation between particles is easier, and the orientation index tends to be high.

[0028] 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.

[0029] The boron nitride powder according to this embodiment contains a certain amount of primary particles of hexagonal boron nitride as single particles, and the influence of the primary particles is also seen in the BET specific surface area. The small BET specific surface area of ​​the boron nitride powder according to this embodiment is an indicator that the primary particles constituting the powder contain particles with a small aspect ratio. The upper limit of the BET specific surface area of ​​the boron nitride powder is, for example, 1.30 m 2 / g or less, 1.20m 2 / g or less, 1.10m 2 / g or less, 1.00m 2 / g or less, or 0.95m 2 / g or less. When the upper limit of the BET specific surface area is within the above range, the aspect ratio of the primary particles constituting the boron nitride powder is small, and the proportion of thick particles is large, which corresponds to a decrease in the anisotropy of the primary particles. This makes it possible to further reduce the anisotropy of the heat dissipation properties of a resin molded product using the boron nitride powder as a filler. The lower limit of the BET specific surface area of ​​the boron nitride powder is not particularly limited, but may be, for example, 0.60 m 2 / g or more, 0.70m 2 / g or more, 0.80m 2 / g or more, or 0.85m 2 The BET specific surface area of ​​the boron nitride powder may be adjusted within the above range, for example, 0.60 to 1.30 m 2 / g.

[0030] The BET specific surface area in this specification refers to a value measured using a specific surface area analyzer in accordance with JIS Z 8830:2013 "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption," and is a value calculated by applying the BET single-point method using nitrogen gas. Examples of specific surface area analyzers that can be used include the "MONOSORBMS-22" (product name) manufactured by QUANTACHROME.

[0031] The lower limit of the tap density of the boron nitride powder is, for example, 0.80 g / cm 3 More than 0.82g / cm 3 More than 0.84g / cm 3 More than 0.86g / cm 3 or more, or 0.88 g / cm 3 When the lower limit of the tap density is within the above range, the boron nitride powder can be packed into the resin at a higher density, and the heat dissipation properties of a resin molded article using the boron nitride powder as a filler can be further improved. There is no particular restriction on the upper limit of the tap density of the boron nitride powder, but it may be, for example, 1.00 g / cm. 3 Below, 0.98g / cm 3Below, 0.96g / cm 3 or less than 0.94 g / cm 3 The tap density of the boron nitride powder may be adjusted within the above range, for example, 0.80 to 1.00 g / cm 3 , or 0.84 to 1.00 g / cm 3 It may be.

[0032] The tap density in this specification means a value determined in accordance with the method described in JIS R 1628:1997 "Method for measuring bulk density of fine ceramic powders." 3 The bulk density is measured after tapping under the conditions of a tapping time of 180 seconds, tapping count of 180 times, and tap lift of 18 mm, and the obtained value is taken as the tap density. For the measurement, a commercially available device, such as "Powder Tester" (trade name) manufactured by Hosokawa Micron, can be used.

[0033] In the boron nitride powder, the agglomerated particles contain calcium borate. The agglomerated particles may be formed by agglomerating primary particles of hexagonal boron nitride with calcium borate interposed between them. When the amount of calcium borate interposed is large, the shape of the agglomerated particles is more likely to be maintained than when the amount of calcium borate interposed is small, even when external force is applied during blending with a resin, etc. The calcium borate may be at least one selected from the group consisting of calcium metaborate (CaB2O4), calcium pyroborate (Ca2B2O5), and calcium borate (Ca3B2O6).

[0034] The presence of calcium borate in boron nitride powder can be determined by X-ray diffraction measurement of the boron nitride powder and Rietveld analysis of the obtained X-ray diffraction spectrum. An X-ray diffraction device such as "ULTIMA-IV" (product name) manufactured by Rigaku Corporation can be used. For Rietveld analysis, software such as "TOPAS" manufactured by BRUKER can be used, allowing for qualitative and quantitative analysis.

[0035] The lower limit of the total oxygen content of the boron nitride powder may be, for example, 2.0% by mass or more, 2.5% by mass or more, 3.0% by mass or more, or 3.5% by mass or more. When the lower limit of the total oxygen content is within the above range, the amount of calcium borate in the boron nitride powder stream tends to be high, thereby further improving the performance of the boron nitride powder containing aggregates as a filler. The upper limit of the total oxygen content of the boron nitride powder, which can further reduce the anisotropy of the heat dissipation of resin molded articles using such boron nitride powder as a filler, may be, for example, 7.0% by mass or less, 6.5% by mass or less, 6.0% by mass or less, or 5.5% by mass or less. The total oxygen content of the boron nitride powder may be adjusted within the above range, and may be, for example, 2.0 to 7.0% by mass.

[0036] The total oxygen content in this specification refers to the value measured for 0.02 g of boron nitride granules using an oxygen / nitrogen simultaneous analyzer, such as the oxygen / nitrogen analyzer "EMGA-920" (product name) manufactured by Horiba, Ltd.

[0037] The crushing strength of the agglomerated particles in the boron nitride powder may be relatively low. The upper limit of the crushing strength of the agglomerated particles may be, for example, 5.0 MPa or less, 4.6 MPa or less, 4.5 MPa or less, 4.0 MPa or less, 3.5 MPa or less, or 3.0 MPa or less. When the upper limit of the crushing strength is within the above range, the agglomerated particles can be appropriately deformed during the production process of a resin molded body obtained by filling the boron nitride powder, thereby further reducing the amount of voids formed between the agglomerated particles and further preventing a decrease in insulating properties. The lower limit of the crushing strength of the agglomerated particles may be, for example, 1.0 MPa or more, 1.5 MPa or more, or 2.0 MPa or more. When the upper limit of the crushing strength is within the above range, excessive collapse of the agglomerated particles can be suppressed during the production process of a resin molded body obtained by filling the boron nitride powder. The crushing strength of the agglomerated particles may be adjusted within the above range, for example, 1.0 to 3.5 MPa.

[0038] 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.

[0039] The boron nitride powder has a relatively large average particle size of primary particles, a broad particle size distribution, and contains a certain number of agglomerated particles strong enough to be broken down by homogenizer treatment. The boron nitride powder is suitable as a filler for resin molded products. The resin molded products are suitable as heat dissipation components. The resin molded products may be in the form of a plate or a sheet. The sheet-like resin molded product may be a heat dissipation sheet.

[0040] One embodiment of the resin molded body includes the boron nitride powder described above and a resin. The resin molded body may be formed from a resin composition containing the 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.

[0041] The lower limit of the content of boron nitride powder in the resin molded body may be, for example, 30% by volume or more, 40% by volume or more, or 50% by volume or more, based on the total volume of the resin molded body. When the lower limit of the content of boron nitride powder is within the above range, the heat dissipation properties of the resin molded body can be further improved. The upper limit of the content of boron nitride powder in the resin molded body may be, for example, 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. When the upper limit of the content of boron nitride powder is within the above range, the generation of voids inside the resin molded body during molding can be further suppressed, and a decrease in insulation properties and mechanical strength can be suppressed. The content of boron nitride powder in the resin molded body may be adjusted within the above range, and may be, for example, 30 to 80% by volume, based on the total volume of the resin molded body.

[0042] The resin may contain or consist of a cured resin, such as epoxy resin, phenol resin, melamine resin, urea resin, polyimide, polyamideimide, polyetherimide, and maleimide-modified resin.

[0043] 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 a phenol novolac compound, an acid anhydride, an amino compound, and an imidazole compound. The lower limit of the curing agent content may be, for example, 0.5 parts by mass or more, or 1.0 parts by mass or more, per 100 parts by mass of the resin. The upper limit of the curing agent content may be, for example, 15 parts by mass or less, or 10 parts by mass or less, per 100 parts by mass of the resin.

[0044] One example of a method for producing boron nitride powder includes a step of forming a raw material powder containing a carbon material, at least one of boric acid and boron oxide, and calcium carbonate into a compact, and then firing the compact in a pressurized nitrogen atmosphere to obtain a fired product containing aggregated particles formed by aggregating a plurality of primary particles of hexagonal boron nitride. The calcium carbonate has an average particle size of 25 μm or more and a bulk density of 0.80 g / cm. 3 That's all.

[0045] The method for producing the boron nitride powder is a production method that applies the so-called carbon reduction method, and is different from boron nitride synthesis methods such as the melamine borate method, etc. That is, by reacting carbon with a boron source such as boric acid in a nitrogen-containing atmosphere, oxygen is extracted from the boron source and nitrogen is reacted to synthesize boron nitride.

[0046] In the above-mentioned production method, the calcium carbonate has an average particle size of 25 μm or more and a bulk density of 0.80 g / cm 3 That is all. By using such calcium carbonate, the density of the molded body can be increased, firing can be performed at high density, and by providing a calcium carbonate concentration in a portion, the proportion of agglomerated particles can be increased and the particle size distribution of the boron nitride powder can be broadened. The average particle size of the calcium carbonate may be, for example, 30.0 μm or less, or 10.0 μm or less. The bulk density of the calcium carbonate may be, for example, 1.0 g / cm 3 or less than 0.6g / cm 3 It may be the following:

[0047] The carbon material is a carbon source for removing oxygen from a boron source such as boric acid. Any compound capable of supplying carbon can be used as the carbon material, but it is preferable to use a highly pure and relatively inexpensive raw material. Examples of such carbon materials include carbon black and acetylene black.

[0048] The boron source can be a compound containing boron and oxygen. Examples of such a boron source include boric acid and boron oxide. It is preferable to use at least one of boric acid and boron oxide, and it is more preferable to use boric acid. When boric acid is used, it is dehydrated by heating to form boron oxide, which forms a liquid phase during the heat treatment of the raw material powder and also functions as an auxiliary agent for promoting grain growth.

[0049] Calcium carbonate reacts with a boron source, etc., to form a liquid phase, which promotes the growth of primary particles of boron nitride. Calcium oxide, which is produced when calcium carbonate is decarbonized, reacts with boron oxide contained in the boron source to produce calcium borate, and the calcium borate becomes liquid and remains without volatilizing even after firing, causing it to intervene between primary particles of hexagonal boron nitride, causing them to aggregate and form aggregated particles.

[0050] The calcium carbonate may have a large average particle size and a relatively small specific surface area. The upper limit of the BET specific surface area of ​​calcium carbonate is, for example, 4.0 m 2 / g or less, 3.0m 2 / g or less, or 2.0m 2 / g or less. By using calcium carbonate having an upper limit of the BET specific surface area within the above range, moldability is good and a molded product (e.g., a pellet-shaped molded product) with higher density can be obtained. The lower limit of the BET specific surface area of ​​calcium carbonate is not particularly limited, but may be, for example, 0.2 m 2 / g or more, 0.5m 2 / g or more, or 0.8m 2 The BET specific surface area of ​​calcium carbonate may be adjusted within the above range, for example, 0.2 to 4.0 m 2 / g.

[0051] The upper limit of the calcium carbonate content may be, for example, 8.0 mass% or less, 7.0 mass% or less, or 6.0 mass% or less, based on the total amount of raw material powder. By setting the upper limit of the content within the above range, it is possible to further suppress a decrease in density of the compact and improve the purity of the obtained boron nitride, thereby achieving a higher level of both heat dissipation and insulation properties of the boron nitride powder. The lower limit of the calcium carbonate content may be, for example, 1.0 mass% or more, 2.0 mass% or more, or 3.0 mass% or more, based on the total amount of raw material powder. Setting the lower limit of the content within the above range further promotes the growth of primary particles of hexagonal boron nitride and the formation of aggregated particles, thereby further improving the yield of the boron nitride powder. The content of calcium carbonate may be adjusted within the above range and may be, for example, 1.0 to 8.0 mass% based on the total amount of raw material powder.

[0052] The lower limit of the density of the molded body is, for example, 0.90 g / cm 3 More than 1.00g / cm 3 More than 1.10g / cm 3 More than 1.20g / cm 3 or more, or 1.30 g / cm 3 The upper limit of the density of the molded body is not particularly limited, but may be, for example, 1.70 g / cm 3 Below 1.60g / cm 3 Below 1.50g / cm 3 or less, or 1.40 g / cm 3 The density of the molded body can be adjusted within the above range, for example, 0.90 to 1.70 g / cm 3 It can be said that:

[0053] The density of a molded body in this specification refers to a value measured by the method described below. More specifically, the volume is calculated from the external shape (length, thickness, etc.) of the molded body, and the density is determined by taking the ratio to the mass of the molded body. When the molded body is in the form of a pellet, the volume is calculated according to the shape of the tablet. For example, when a pellet has a circular horizontal surface (land portion) on the outer periphery of the central portion in a plan view, the density is determined by taking the value of the molded body as the volume of the molded body using the diameter, thickness, width of the land portion, and radius of curvature of the pellet, and taking the ratio to the mass of the molded body.

[0054] The lower limit of the breaking strength of the compact may be, for example, 20N or more, 22N or more, 24N or more, or 26N or more. When the lower limit of the breaking strength is within the above range, the compact has good shape retention and is less likely to break, making it possible to produce a compact that is easy to handle in the production of boron nitride powder. The upper limit of the breaking strength of the compact may be, for example, 46N or less, 44N or less, 42N or less, or 40N or less. When the upper limit of the breaking strength is within the above range, the compact can be stably released in the compacting step, further improving the productivity of the compact. The breaking strength of the compact can be adjusted within the above range, and can be, for example, 20 to 46N.

[0055] The term "breaking strength" as used herein refers to a value measured using a digital hardness tester. Measurements are performed using pellets with a pressure surface diameter of 5 mm at a pressure speed of 1 mm / sec. Examples of digital hardness testers that can be used include the "KHT-20N" digital hardness tester manufactured by Fujiwara Seisakusho Co., Ltd.

[0056] The above compact has a density of 1.30 g / cm 3 or more, and the breaking strength may be 20N or more.

[0057] The firing process is carried out under a pressurized nitrogen atmosphere. By performing firing under such conditions, it is possible to provide a sufficient supply of nitrogen as a raw material for boron nitride. In this process, a fired product containing agglomerated particles formed by agglomeration of multiple primary particles of hexagonal boron nitride can be obtained.

[0058] The lower limit of the atmospheric pressure in the firing step may be, for example, 0.5 MPaG or more, 0.6 MPaG or more, 0.7 MPaG or more, or 0.8 MPaG or more. By setting the lower limit of the atmospheric pressure within the above range, volatilization of the boron source is suppressed and the liquid phase of the boron source is maintained, thereby further promoting the growth of primary particles of hexagonal boron nitride and further suppressing the generation of boron carbide as a by-product. The upper limit of the atmospheric pressure in the firing step is not particularly limited, but may be 0.9 MPaG or less in industrial applications. The atmospheric pressure in the firing step may be adjusted within the above range, and may be, for example, 0.5 to 0.9 MPaG. In this specification, pressure refers to gauge pressure.

[0059] The firing temperature in the firing step is, for example, 1800 to 2200°C. The upper limit of the firing temperature may be, for example, 2150°C or lower, or 2100°C or lower. By setting the upper limit of the firing temperature within the above range, it is possible to more sufficiently suppress the generation of by-products. The lower limit of the firing temperature may be, for example, 1850°C or higher, 1900°C or higher, 1950°C or higher, 2000°C or higher, or 2050°C or higher. By setting the lower limit of the firing temperature within the above range, it is possible to further promote the reaction on the carbon material and further improve the yield of boron nitride obtained.

[0060] In the calcination step, it is desirable to set a relatively long time (retention time) for maintaining the temperature after reaching the calcination temperature under the pressure environment. The lower limit of the retention time in the calcination step may be, for example, 7 hours or more, or 8 hours or more. By setting the lower limit of the retention time within the above range, unreacted carbon source in the raw materials can be more thoroughly removed, and boron nitride powder with fewer impurities can be obtained. The upper limit of the retention time in the calcination step is not particularly limited, but from the viewpoint of reducing the production cost of boron nitride powder, it may be, for example, 20 hours or less, 18 hours or less, 16 hours or less, 14 hours or less, or 12 hours or less. The retention time in the calcination step may be adjusted within the above range, and may be, for example, 7 to 20 hours, or 7 to 12 hours.

[0061] The above-described manufacturing method may include other steps in addition to the firing step, such as a crushing step.

[0062] In the crushing step, for example, a crusher such as a Henschel mixer or a grinder mill can be used.

[0063] When a Henschel mixer is used, the rotation speed of the crusher may be as follows: The upper limit of the rotation speed of the crusher may be, for example, 950 rpm or less, 900 rpm or less, or 850 rpm or less. When the upper limit of the rotation speed of the crusher is within the above range, over-crushing of the particles can be prevented. The lower limit of the rotation speed of the crusher may be, for example, 500 rpm or more, or 550 rpm or more. When the lower limit of the rotation speed of the crusher is within the above range, the fired product can be sufficiently crushed, and loose agglomerations of the boron nitride primary particles can be released.

[0064] The lower limit of the disintegration time in the disintegration step may be, for example, 5 minutes or more, 6 minutes or more, 7 minutes or more, or 8 minutes or more. By setting the lower limit of the disintegration time within the above range, the fired product can be sufficiently disintegrated, loose agglomerations of boron nitride primary particles can be broken down, and the sieving yield can be further improved. The upper limit of the disintegration time in the disintegration step may be, for example, 15 minutes or less, 14 minutes or less, 13 minutes or less, or 12 minutes or less. By setting the upper limit of the disintegration time within the above range, excessive crushing of agglomerated particles of hexagonal boron nitride can be more sufficiently suppressed. The disintegration time may be adjusted within the above range, and may be, for example, 5 to 15 minutes, or 8 to 12 minutes.

[0065] 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]

[0066] 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.

[0067] Example 1 A mixture of 100 parts by mass of boric acid (manufactured by Kojundo Chemical Laboratory Co., Ltd.), 26 parts by mass of acetylene black (manufactured by Denka Co., Ltd., grade name: Li-400), and calcium carbonate (manufactured by Calfine Co., Ltd., average particle size: 27 μm, bulk density: 0.870 g / cm 3 , BET specific surface area: 1.0m 2 The raw material powder was obtained by mixing using a Henschel mixer. The amount of calcium carbonate in the raw material powder was 5.5% by mass.

[0068] The obtained mixed powder was placed in a dryer at 250°C and held for 3 hours to dehydrate the boric acid. The dehydrated mixed powder was placed in a 9 mm diameter mold of a rotary press molding machine and molded under pressure to obtain pellets. The maximum pressure required for continuous operation during pellet molding was 33 kN. The density of the pellets was 1.32 g / cm. 3 The breaking strength measured by a digital hardness tester (manufactured by Fujiwara Seisakusho, product name: KHT-20N type) was 28N.

[0069] Next, the pellets were placed in a carbon container (capacity: 3000 cm 3 The pellets were packed into a container, heated to 1900°C at a heating rate of 5°C / min in a nitrogen atmosphere pressurized to 0.5 MPaG, and held at 1900°C for 8 hours to heat-treat the pellets, thereby obtaining a fired product (firing step). At this time, the pellet packing density in the container was 0.831 g / cm. 3 It was.

[0070] The resulting fired product was crushed in a Henschel mixer at a rotation speed of 900 rpm for a crushing time of 10 minutes (crushing step), to prepare a powder containing boron nitride particles.

[0071] Example 2 The raw material powder of calcium carbonate (Takehara Chemical Industry Co., Ltd., average particle size: 6 μm, bulk density: 0.540 g / cm 3 , BET specific surface area: 3.2m 2 Except for changing the mass fraction of the boron nitride powder to 1 / g, the boron nitride powder was produced in the same manner as in Example 1. The maximum pressure at which continuous operation was possible during pellet molding was 33 kN.

[0072] (Comparative Example 1) As calcium carbonate, calcium carbonate (manufactured by New Lime Co., Ltd., average particle size: 4 μm, bulk density: 0.378 g / cm 3 , BET specific surface area: 5.5m 2 Except for using 100% ammonium nitrate powder (0.05 wt. / g), boron nitride powder was produced in the same manner as in Example 1. The maximum pressure at which continuous operation was possible during pellet molding was 20 kN.

[0073] <Evaluation of boron nitride powder properties> The boron nitride powders prepared in the Examples and Comparative Examples were evaluated for the presence or absence of calcium borate, particle size distribution, orientation index, BET specific surface area, tap density, total oxygen content, and agglomerated particle crushing strength according to the methods described below. The results are shown in Table 1. For reference, the particle size distributions of the boron nitride powders prepared in Example 1 and Comparative Example 1 are shown in Figures 1 and 2, respectively.

[0074] [With or without calcium borate] The presence or absence of calcium borate was confirmed by X-ray diffraction measurements of boron nitride powder and Rietveld analysis of the obtained X-ray diffraction spectrum. The X-ray diffractometer used was the "ULTIMA-IV" (product name) manufactured by Rigaku Corporation. The Rietveld analysis was performed using the "TOPAS" software manufactured by BRUKER.

[0075] [Particle size distribution] The particle size distribution of boron nitride powder was measured according to the method described in JIS Z 8825:2013, "Particle Size Analysis - Laser Diffraction and Scattering Method." To measure particle size distribution A, 2 mL of a 20% aqueous solution of sodium hexametaphosphate and 0.06 g of boron nitride powder were first weighed into a container and dispersed in an ultrasonic disperser for 2 minutes with the probe tip positioned 10 mm from the bottom. This sample was then used to measure the particle size distribution. The ultrasonic processor used had a cylindrical probe with a diameter of 13 mm, model VC-505 manufactured by Sonics & Materials. A laser diffraction and scattering particle size distribution analyzer (Microtrac MT-3300EXII, manufactured by Microtrac-Bell) was used for the measurement. To measure particle size distribution B, 2 mL of a 20% aqueous solution of sodium hexametaphosphate was used without the ultrasonic disperser.

[0076] [Orientation index] First, an X-ray diffraction spectrum of the boron nitride powder was obtained by X-ray diffraction measurement of 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 X-ray diffractometer used was an "ULTIMA-IV" (product name) manufactured by Rigaku Corporation.

[0077] [BET specific surface area] The BET specific surface area was calculated using a specific surface area measuring device, the "MONOSORBMS-22" (product name) manufactured by QUANTACHROME, in accordance with the description in JIS Z 8830:2013 "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption."

[0078] [Tap Density] The tap density was determined in accordance with the method described in JIS R 1628:1997 "Method for measuring bulk density of fine ceramic powders." Specifically, the boron nitride powder was3 The bulk density was measured after tapping under the conditions of a tapping time of 180 seconds, tapping count of 180 times, and tap lift of 18 mm. The measured value was taken as the tap density. For the measurement, a "Powder Tester" (trade name) manufactured by Hosokawa Micron was used.

[0079] [Total oxygen] The total oxygen content was measured for 0.02 g of boron nitride granules using an oxygen / nitrogen simultaneous analyzer, model EMGA-920 (product name) manufactured by Horiba, Ltd.

[0080] [Agglomerate crushing strength] The crushing strength was measured in accordance with JIS R 1639-5:2007 "Fine ceramics - Measurement methods for granule characteristics - Part 5: Single granule crushing strength." Measurements were performed on 20 or more granules, and the value at a cumulative fracture rate of 63.2% was calculated. A microcompression tester (Shimadzu Corporation's "MCT-210" (trade name)) was used for the measurements.

[0081] <Boron nitride powder evaluation: sheet thermal conductivity> The boron nitride powders prepared in the examples and comparative examples were used to evaluate the sheet thermal conductivity. The results are shown in Table 1.

[0082] First, the boron nitride powder was mixed with a two-component heat-curing liquid silicone resin (manufactured by Momentive, product name: TSE3033 A / B) so that the boron nitride powder was 50% by volume, to obtain a resin composition. A Thinky Mixer (Awatori Rentaro) 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 1 mm. Then, a uniaxial press was used to apply a surface pressure of 150 kgf / cm. 2 While applying a pressure of 1000 kJ / cm 2 , the mixture was heated and pressed under relatively mild conditions at a temperature of 150° C. for 45 minutes to prepare a 1 mm resin sheet (evaluation sheet).

[0083] The thermal conductivity H (unit: W / (m K)) of the above laminated sheet for evaluation in the uniaxial press direction was calculated using the thermal resistance R (unit: K / W), sheet thickness t (unit: m), and sheet heat transfer area A (unit: m 2 ) was used to calculate the thermal diffusivity using the formula H = (1 / R) × t × (1 / A). The thermal diffusivity was determined by measuring the thermal resistance of a sample prepared by processing the evaluation lamination sheet into a size of length × width × thickness = 10 mm × 10 mm × 1 mm. The measurement device used was a thermal resistance measurement device (manufactured by Hitachi Technology and Services Co., Ltd., product name: Resin Material Thermal Resistance Measurement Device).

[0084] [Table 1] [Industrial Applicability]

[0085] According to the present disclosure, a boron nitride powder capable of providing a resin molded article having excellent thermal conductivity can be provided. According to the present disclosure, a resin molded article having excellent thermal conductivity can also be provided.

Claims

1. A boron nitride powder comprising agglomerated particles formed by agglomerating a plurality of primary particles of hexagonal boron nitride, and primary particles of hexagonal boron nitride, the agglomerated particles comprise calcium borate; A boron nitride powder that satisfies at least one of the following (1) or (2): (1) When the average particle diameter in volume-based particle size distribution A measured by a laser diffraction / scattering method after dispersion treatment is defined as D50(A) and the average particle diameter in volume-based particle size distribution B measured by the laser diffraction / scattering method without dispersion treatment is defined as D50(B), the D50(A) is more than 15 μm, and the ratio of the D50(B) to the D50(A) is 1.5 or more. (2) When the average particle diameter in a volume-based particle size distribution A measured by a laser diffraction / scattering method after dispersion treatment is defined as D50(A), D50(A) is more than 15 μm, When the maximum volume frequency in a volume-based particle size distribution B measured by the laser diffraction / scattering method without dispersion treatment is defined as H, the particle size showing the largest particle size among particle sizes showing a volume frequency of H / 2 is defined as L, and the particle size showing the smallest particle size is defined as S, the ratio of L to S is 5 or more.

2. 2. The boron nitride powder according to claim 1, having an orientation index of 30 or more.

3. BET specific surface area is 1.30 m ２ 3. The boron nitride powder according to claim 1, wherein the boron nitride powder has a SiO2 content of 0.1g or less.

4. Tap density is 0.80 g / cm ３ The boron nitride powder according to claim 1 or 2.

5. 3. The boron nitride powder according to claim 1, wherein the total oxygen content is 2.0 mass% or more.

6. A resin molded product comprising the boron nitride powder according to claim 1 or 2 and a resin.

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