Boron nitride powder and method for producing the same

Abstract

To provide boron nitride powder which improves flowability of a resin composition obtained by mixed with a resin, and can enhance thermal conductivity of a composite body of boron nitride powder obtained by molding the resin composition, and a resin, and a method for producing the boron nitride powder.SOLUTION: Boron nitride powder has a particle diameter (D90) at the cumulative frequency of 90 vol.% of the particle size distribution measured by a laser diffraction scattering method of 10 μm or more, and an aspect ratio (F / t) of a maximum length (length of major axis) (F) in a surface direction to a length (T) in a thickness direction of 5.0 or less. A method for producing boron nitride powder includes a step (A) of melting a mixture containing an amorphous boron nitride obtained by baking a boric acid and melamine, and lithium borate, and preparing a melt, a step (B) of cooling the melt, and a step (C) of dissolving the lithium borate by an acid, and taking out the boron nitride particles from the lithium borate.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to boron nitride powder and a method for producing the boron nitride powder.

[0002] In heat-generating electronic components such as power devices, transistors, thyristors, and CPUs, how to efficiently dissipate the heat generated during use is an important issue. Conventionally, as such heat dissipation measures, (1) making the insulating layer of the printed wiring board on which the heat-generating electronic component is mounted have high thermal conductivity, or (2) attaching the heat-generating electronic component or the printed wiring board on which the heat-generating electronic component is mounted to a heat sink via an electrically insulating thermal interface material (Thermal Interface Materials) has been generally performed. As the insulating layer of the printed wiring board and the thermal interface material, a resin composition in which ceramic powder is filled in silicone resin or epoxy resin has been used.

[0003] In recent years, with the increase in the speed and integration of circuits in heat-generating electronic components and the increase in the mounting density of heat-generating electronic components on printed wiring boards, the heat generation density inside electronic devices has been increasing year by year. Therefore, there has been a demand for ceramic powder having a higher thermal conductivity than before.

[0004] Under the above background, hexagonal boron nitride powder, which has excellent properties as an electrical insulating material such as high thermal conductivity, high insulation, and low relative permittivity, has attracted attention.

[0005] However, the hexagonal boron nitride particles have a thermal conductivity of 400 W / (m·K) in the in-plane direction (a-axis direction), while the thermal conductivity in the thickness direction (c-axis direction) is 2 W / (m·K), and the anisotropy of the thermal conductivity due to the crystal structure and flaky shape is large. Furthermore, when the hexagonal boron nitride powder is filled in a resin, the particles are aligned in the same direction.

[0006] Therefore, attempts have been made to increase the thickness of hexagonal boron nitride particles and reduce their aspect ratio. As an example of such hexagonal boron nitride particles, the hexagonal boron nitride single crystal described in Patent Document 1 is known as prior art. The hexagonal boron nitride single crystal described in Patent Document 1 is manufactured by the flux method and has an aspect ratio of 0.3 or more, defined as the maximum thickness in the crystal c-axis direction / the maximum width of the crystal ab-plane. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2016-141600 [Overview of the project] [Problems that the invention aims to solve]

[0008] Paragraph 0015 of Patent Document 1 states that the maximum width of the crystal ab plane of the hexagonal boron nitride single crystal described in Patent Document 1 is usually 200 μm or less, preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 10 μm or less. However, Patent Document 1 has not actually been able to produce a large hexagonal boron nitride single crystal with a maximum crystal ab plane width of about 10 μm, and the maximum width of the crystal ab plane of the hexagonal boron nitride single crystal was 100 to 500 nm (0.1 to 0.5 μm). When such fine hexagonal boron nitride single crystals are mixed with a resin to produce a resin composition, the fluidity of the resin composition deteriorates, resulting in poor moldability of the resin composition. Therefore, the present invention aims to provide boron nitride powder and a method for producing the boron nitride powder, which, when mixed with a resin to produce a resin composition, can improve the fluidity of the resulting resin composition and increase the thermal conductivity of the composite of boron nitride powder and resin obtained by molding the resin composition. [Means for solving the problem]

[0009] Through diligent research, the inventors have discovered that when producing boron nitride particles using the flux method, by using amorphous boron nitride obtained by calcining boric acid and melamine as the raw material for the boron nitride particles and lithium borate as the flux, it is possible to obtain boron nitride powder that can solve the above problems. This invention is based on the above findings and its gist is as follows. [1] Boron nitride powder having a particle size (D90) of 90% volume cumulative frequency of the particle size distribution measured by laser diffraction scattering method of 10 μm or more, and an aspect ratio (F / T) of the maximum length in the plane direction (length of the major axis) (F) to the length in the thickness direction (T) of 5.0 or less. [2] The boron nitride powder described in [1] above, wherein the particle size (D10) at the cumulative frequency of 10% by volume of the particle size distribution measured by laser diffraction scattering is 1.5 μm or larger. [3] The boron nitride powder according to [1] or [2] above, wherein the length of the long axis is 1.0 μm or more. [4] Boron nitride powder according to any one of [1] to [3] above, wherein the cumulative frequency up to 1.0 μm of the particle size distribution measured by laser diffraction scattering is 3 volume% or less. [5] Boron nitride powder according to any one of the above [1] to [4], wherein the difference (D90-D10) between the particle size at the cumulative frequency of 90% by volume (D90) and the particle size at the cumulative frequency of 10% by volume (D10) of the particle size distribution measured by laser diffraction scattering is 7.0 μm or more. [6] A method for producing boron nitride powder according to any one of [1] to [5] above, comprising the steps of: (A) melting a mixture containing amorphous boron nitride obtained by calcining boric acid and melamine and lithium borate to produce a melt; (B) cooling the melt; and (C) dissolving the lithium borate with an acid to extract the boron nitride particles from the lithium borate. [Effects of the Invention]

[0010] According to the present invention, when mixed with a resin to produce a resin composition, the resulting resin composition can be made to have good fluidity, and the thermal conductivity of the composite of boron nitride powder and resin obtained by molding the resin composition can be increased. The present invention provides boron nitride powder and a method for producing the boron nitride powder. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows the X-ray diffraction pattern of amorphous boron nitride. [Figure 2] Figure 2 is a scanning electron microscope image of the boron nitride powder from Example 1. [Figure 3] Figure 3 is a scanning electron microscope image of the boron nitride powder of Comparative Example 1. [Modes for carrying out the invention]

[0012] [Boron Nitride Powder] The boron nitride powder of the present invention has a particle size (D90) of 10 μm or more at the cumulative frequency of 90% by volume of the particle size distribution measured by laser diffraction scattering, and an aspect ratio (F / T) of the maximum length in the plane direction (length of the major axis) (F) to the length in the thickness direction (T) of 5.0 or less.

[0013] The particle size (D90) at the cumulative frequency of 90% by volume of the particle size distribution measured by laser diffraction scattering in the boron nitride powder of the present invention is 10 μm or larger. If the D90 of the boron nitride powder is less than 10 μm, when it is mixed with a resin to prepare a resin composition, the fluidity of the resulting resin composition may be poor. Furthermore, the packing of the boron nitride powder in the composite of boron nitride powder and resin obtained by molding the resin composition may be poor, and the thermal conductivity of the composite may be low. From this viewpoint, the D90 of the boron nitride powder of the present invention is preferably 13 μm or larger, and more preferably 15 μm or larger. The upper limit of the range of the D90 of the boron nitride powder of the present invention is not particularly limited, but is usually 40 μm, and preferably 30 μm. The D90 of the boron nitride powder can be measured by the method described in the examples below.

[0014] The aspect ratio (F / T) of the boron nitride powder of the present invention, which is the ratio of the maximum length in the planar direction (length of the major axis) (F) to the length in the thickness direction (T), is 5.0 or less. If the aspect ratio (F / T) of the boron nitride powder is greater than 5.0, the boron nitride powder is more likely to be oriented. As a result, when a resin composition is made by mixing boron nitride powder with a resin, the boron nitride powder in the composite of boron nitride powder and resin obtained by molding the resin composition may become oriented, and the thermal conductivity of the composite may be reduced. From this viewpoint, the aspect ratio (F / T) of the boron nitride powder of the present invention is preferably 4.5 or less, and more preferably 4.0 or less. Furthermore, the lower limit of the range of the aspect ratio (F / T) of the boron nitride powder of the present invention is not particularly limited, but is usually 0.5, and preferably 1.0. The length in the thickness direction (T) and the maximum length in the planar direction (length of the major axis) of the boron nitride powder can be measured by the method described in the examples below.

[0015] The particle size (D10) at the cumulative frequency of 10% by volume of the particle size distribution measured by laser diffraction scattering in the boron nitride powder of the present invention is preferably 1.5 μm or more. When the D10 of the boron nitride powder is 1.5 μm or more, the number of interparticle interfaces decreases, thereby increasing the thermal conductivity of the composite. Furthermore, when mixed with a resin to prepare a resin composition, the fluidity of the resulting resin composition can be further improved. In addition, the packing of the boron nitride powder in the composite of boron nitride powder and resin obtained by molding the resin composition is improved, and the thermal conductivity of the composite can be further improved. From this viewpoint, the D10 of the boron nitride powder of the present invention is more preferably 2.0 μm or more, and even more preferably 2.5 μm or more. The upper limit of the range of D10 of the boron nitride powder of the present invention is not particularly limited, but is usually 5.0 μm, and preferably 4.0 μm. The D10 of the boron nitride powder can be measured by the method described in the examples below.

[0016] The length of the long axis (F) of the boron nitride powder of the present invention is preferably 1.0 μm or more. When the length of the long axis (F) of the boron nitride powder is 1.0 μm or more, the number of interparticle interfaces decreases, thereby increasing the thermal conductivity of the composite. Furthermore, when mixed with a resin to prepare a resin composition, the fluidity of the resulting resin composition can be further improved. In addition, the packing of the boron nitride powder in the composite of boron nitride powder and resin obtained by molding the resin composition is improved, and the thermal conductivity of the composite can be further improved. From this viewpoint, the length of the long axis (F) of the boron nitride powder of the present invention is more preferably 1.2 μm or more, and even more preferably 1.5 μm or more. The upper limit of the range of the length of the long axis (F) of the boron nitride powder of the present invention is not particularly limited, but is usually 10 μm, and preferably 5 μm. The length of the long axis (F) of the boron nitride powder can be measured by the method described in the examples below.

[0017] The cumulative frequency up to 1.0 μm of the particle size distribution measured by the laser diffraction scattering method in the boron nitride powder of the present invention is preferably 3% by volume or less. When the cumulative frequency up to 1.0 μm of the particle size distribution measured by the laser diffraction scattering method in the boron nitride powder is 3% by volume or less, the number of interfaces between particles decreases, and the thermal conductivity of the composite can be increased. Further, when a resin composition is prepared by mixing with a resin, the fluidity of the obtained resin composition can be further improved. And, in the composite of boron nitride powder and resin obtained by molding the resin composition, the filling property of the boron nitride powder is improved, and the thermal conductivity of the composite may be improved. From such a viewpoint, the cumulative frequency up to 1.0 μm of the particle size distribution measured by the laser diffraction scattering method of the boron nitride powder of the present invention is more preferably 2.5% by volume or less, and even more preferably 2.0% by volume or less. The lower limit value of the range of the cumulative frequency up to 1.0 μm of the particle size distribution measured by the laser diffraction scattering method of the boron nitride powder of the present invention is not particularly limited, but is usually 0.1% by volume, and preferably 0% by volume. The cumulative frequency up to 1.0 μm of the particle size distribution measured by the laser diffraction scattering method in the boron nitride powder can be measured by the method described in the examples below.

[0018] The difference (D90 - D10) between the particle diameter (D90) of the cumulative frequency of 90% by volume and the particle diameter (D10) of the cumulative frequency of 10% by volume of the particle size distribution measured by the laser diffraction scattering method in the boron nitride powder of the present invention is preferably 7.0 μm or more. When the difference (D90 - D10) of the particle diameter of the boron nitride powder is 7.0 μm or more, the filling property of the boron nitride powder in the composite of boron nitride powder and resin obtained by molding the resin composition prepared by mixing with the resin is further improved, and the thermal conductivity of the composite can be further improved. From such a viewpoint, the difference (D90 - D10) of the particle diameter of the boron nitride powder is more preferably 10 μm or more, and even more preferably 15 μm or more. The upper limit value of the range of the difference (D90 - D10) of the particle diameter of the boron nitride powder is not particularly limited, but is usually 40 μm, and preferably 35 μm.

[0019] The average particle diameter (D50) of the boron nitride powder of the present invention measured by the laser diffraction scattering method is preferably 5.0 μm or more. When the D50 of the boron nitride powder is 5.0 μm or more, the number of interfaces between particles decreases, so that the thermal conductivity of the composite can be increased. Further, when a resin composition is prepared by mixing with a resin, the fluidity of the obtained resin composition can be further improved. And the filling property of the boron nitride powder in the composite of the boron nitride powder and the resin obtained by molding the resin composition is improved, and the thermal conductivity of the composite can be further improved. From such a viewpoint, the D50 of the boron nitride powder of the present invention is more preferably 5.3 μm or more, and still more preferably 5.5 μm or more. The upper limit value of the range of D50 of the boron nitride powder of the present invention is not particularly limited, but is usually 20 μm, preferably 10 μm. The D50 of the boron nitride powder can be measured by the same method as the method described in the examples below.

[0020] [Method for producing boron nitride powder] The method for producing the boron nitride powder of the present invention includes a step (A) of melting a mixture containing amorphous boron nitride obtained by firing boric acid and melamine and lithium borate to prepare a melt, a step (B) of cooling the melt, and a step (C) of dissolving lithium borate with an acid to extract boron nitride particles from lithium borate. Hereinafter, each step of the method for producing the boron nitride powder of the present invention will be described in detail.

[0021] (1) Step (A) In step (A), a mixture containing amorphous boron nitride obtained by firing boric acid and melamine and lithium borate is melted to prepare a melt. [Amorphous boron nitride] As described above, the amorphous boron nitride used in step (A) is obtained by firing boric acid and melamine. The molar ratio of boron atoms to nitrogen atoms in the whole of boric acid and melamine does not necessarily have to be fixed at 5:5, and the molar ratio of boron atoms to nitrogen atoms can be appropriately changed in the range of 2:8 to 8:2, preferably in the range of 3:7 to 7:3, according to the reactivity and yield.

[0022] The firing is preferably carried out in a non-oxidizing atmosphere, with a firing temperature of 400 to 1200°C and a firing time of 1 to 5 hours. By setting the firing temperature to 400°C or higher, the residual oxygen and carbon in amorphous boron nitride can be suppressed. Furthermore, by setting the firing temperature to 1200°C or lower, the crystallization of boron nitride can be suppressed. The firing temperature may be kept constant, or it may be changed continuously or discontinuously, and there are no particular restrictions on the firing time or the rate of heating and cooling. Furthermore, there are no particular restrictions on the firing apparatus, but for example, a container made of hexagonal boron nitride can be used to store the raw material, and for example, a firing furnace using an electric heater can be used as the heating device.

[0023] Amorphous boron nitride does not need to be completely amorphous; it may be partially crystalline as long as it does not hinder the effects of the present invention. Furthermore, to improve reaction efficiency by increasing the adhesion between boric acid particles and melamine particles, briquetting or tableting may be performed on the mixed powder of boric acid and melamine.

[0024] By using amorphous boron nitride as a raw material for boron nitride powder, the boron nitride can be dissolved more completely in lithium borate, resulting in a more uniform dissolution of boron nitride in lithium borate. This promotes crystal growth in the thickness direction (c-axis direction) of the boron nitride particles, and reduces the aspect ratio (F / T) of the maximum length in the plane direction (length of the major axis) (F) to the thickness direction length (T) of the boron nitride particles. On the other hand, if crystalline boron nitride is used as a raw material for boron nitride powder, it is thought that the crystalline boron nitride does not dissolve easily in lithium borate, and the formation of low aspect ratio boron nitride particles does not progress. Furthermore, it is thought that undissolved boron nitride exists in lithium borate, and this acts as a nucleus to promote crystal growth in the plane direction (a-axis direction or b-axis direction) of the boron nitride particles, so the aspect ratio (F / T) of the maximum length in the plane direction (length of the major axis) (F) to the thickness direction length (T) of the boron nitride particles is thought to be large.

[0025] <Lithium borate> By using lithium borate as a flux in step (A), crystal growth in the thickness direction (c-axis direction) of boron nitride particles is promoted, and the aspect ratio (F / T) of the maximum length in the plane direction (length of the major axis) (F) to the length in the thickness direction (T) of boron nitride particles can be reduced. Examples of lithium borate used in step (A) include lithium tetraborate (Li2B4O7), trilithium borate (Li3BO3), and lithium metaborate (LiBO2). These lithium borates can be used individually or in combination of two or more. Among these lithium borates, trilithium borate (Li3BO3) is preferred.

[0026] <Mixture containing amorphous boron nitride and lithium borate> In a mixture containing amorphous boron nitride and lithium borate, the number of moles of amorphous boron nitride is preferably 10 to 0.5 moles per mole of lithium borate. When the number of moles of amorphous boron nitride is 8 to 0.7 moles, the boron nitride powder of the present invention can be easily prepared. From this viewpoint, the number of moles of amorphous boron nitride is more preferably 8 to 0.7 moles, and even more preferably 5 to 1 mole, per mole of lithium borate.

[0027] <Preparation of the melt> In step (A), the mixture is melted to produce a molten material. A carbon crucible or a boron nitride crucible is preferred for melting the mixture. The melting temperature is not particularly limited as long as it is a temperature at which the mixture is completely dissolved and the volatilization of lithium borate is suppressed. For example, the melting temperature is 1000 to 1700°C, preferably 1100 to 1500°C. The melting time is not particularly limited as long as it is the time required for the mixture to be completely dissolved. For example, the melting time is 1 to 30 hours, preferably 5 to 20 hours. A nitrogen atmosphere is preferred when melting the mixture.

[0028] (2) Process (B) In step (B), the melt is cooled. The cooling of the melt is not particularly limited; it may be cooled slowly or allowed to cool naturally. When cooling the melt slowly, the slow cooling rate is, for example, 0.5 to 10°C / min.

[0029] (3) Process (C) In step (C), lithium borate is dissolved with an acid to extract boron nitride particles from the lithium borate. The crucible containing the lithium borate and boron nitride particles may be placed in the acid, or the contents removed from the crucible may be placed in the acid. From the viewpoint of dissolving the lithium borate without dissolving the boron nitride particles too much, dilute nitric acid is preferred as the acid used to dissolve the lithium borate.

[0030] [Composite of boron nitride powder and resin] A composite of boron nitride powder and resin can be produced by curing a resin composition containing the boron nitride powder and resin of the present invention. Examples of the composite of boron nitride powder and resin include heat dissipation sheets and substrates.

[0031] (resin) Examples of resins used in resin compositions include epoxy resins, silicone resins (including silicone rubber), acrylic resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyamides (e.g., polyimide, polyamideimide, polyetherimide, etc.), polyesters (e.g., polybutylene terephthalate, polyethylene terephthalate, etc.), polyphenylene ethers, polyphenylene sulfides, fully aromatic polyesters, polysulfones, liquid crystal polymers, polyethersulfones, polycarbonates, maleimide-modified resins, ABS resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins. When the composite is a heat dissipation sheet, silicone resins are preferred among these. When the composite is a substrate, epoxy resins are preferred among these.

[0032] The content of boron nitride powder in the resin composition relative to 100 volume% of the total of boron nitride powder and resin is preferably 30 to 85 volume%, and more preferably 40 to 80 volume%. When the boron nitride powder content is 30 volume% or more, the thermal conductivity is improved, and sufficient heat dissipation performance is easily obtained. When the boron nitride powder content is 85 volume% or less, the likelihood of voids being generated during molding can be reduced, and the decrease in insulation and mechanical strength can be reduced. Furthermore, the content of resin relative to 100 volume% of the total of boron nitride powder and resin is preferably 15 to 70 volume%, and more preferably 20 to 60 volume%.

[0033] (solvent) To adjust the viscosity of the resin composition, the resin composition may further contain a solvent. The solvent is not particularly limited as long as it can dissolve the resin and can be easily removed from the applied resin composition after application. Examples of solvents include toluene, xylene, and chlorinated hydrocarbons. These solvents can be used individually or in combination of two or more. From the viewpoint of ease of removal, toluene is preferred among these solvents. The solvent content can be appropriately selected depending on the desired viscosity of the resin composition. For example, the solvent content is 40 to 200 parts by mass per 100 parts by mass of the components other than the solvent in the resin composition.

[0034] The resin composition may also contain components other than boron nitride powder, resin components, and solvents. These other components include inorganic fillers other than boron nitride powder, additives, impurities, etc. The content of these other components is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 1 part by mass or less, based on 100 parts by mass of the total of boron nitride powder and resin.

[0035] [Method for producing the composite] A composite containing the boron nitride powder of the present invention can be manufactured, for example, by a manufacturing method comprising the steps of (X) of blending the boron nitride powder of the present invention with a resin to produce a resin composition, (Y) molding the resin composition to produce a molded article, and (Z) heating and pressurizing the molded article.

[0036] (Process (X)) In step (X), a resin composition is prepared by blending the boron nitride powder of the present invention with a resin. The boron nitride powder and resin used in step (X) have already been described, so their description will be omitted.

[0037] (Process (Y)) In step (Y), a molded body is produced by molding the resin composition. For example, the resin composition can be molded by the doctor blade method. By using the boron nitride powder of the present invention, the fluidity of the resin composition is improved, making it easier to mold the resin composition. Furthermore, by using the boron nitride powder of the present invention, the packing density of the boron nitride powder in the molded body is increased, thereby increasing the thermal conductivity of the molded body.

[0038] (Process (Z)) In step (Z), the molded body is heated and pressurized. This further improves the packing density of the boron nitride powder in the composite and further improves the thermal conductivity of the composite. From the viewpoint of improving the packing density of the boron nitride powder, the heating temperature of the molded body is preferably 100 to 200°C, and more preferably 120 to 180°C. Furthermore, the pressure applied when pressurizing the molded body is preferably 5 to 30 MPa, and more preferably 10 to 20 MPa. [Examples]

[0039] The present invention will be described in detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

[0040] (particle size distribution) The particle size distribution of boron nitride powder was measured using a laser diffraction scattering particle size distribution analyzer (LS-13 320) manufactured by Beckman Coulter, Inc. From the obtained particle size distribution, the particle size at the cumulative frequency of 90% by volume (D90), the particle size at the cumulative frequency of 50% by volume (D50), the particle size at the cumulative frequency of 10% by volume (D10), and the cumulative frequency up to 1.0 μm were determined.

[0041] (Length of the major axis and aspect ratio) Using a scanning electron microscope (JEOL Ltd., product name "JSM-7001F"), the thickness direction length and the maximum length (length of the major axis) in the plane direction were measured for 100 boron nitride particles. The average values ​​of these measurements were then defined as the thickness direction length (T) and the maximum length (length of the major axis) in the plane direction (F). The aspect ratio (F / T) was calculated from these results.

[0042] (Liquidity) Boron nitride powder and epoxy resin (DIC Corporation, product name "EPICLON830-S") were weighed so that the amount of boron nitride powder was 20% by volume relative to the total volume of boron nitride powder and epoxy resin (100% by volume). The weighed boron nitride powder and epoxy resin were then placed in a stirrer (Thinky Co., Ltd., product name "Awatori Rentaro ARE-310") and mixed twice for 1.5 minutes at a rotation speed of 1500 rpm to prepare a resin composition. The viscosity of the obtained resin composition was measured using a rheometer (Anton Paar, product name "MCR92"), and the fluidity of the resin composition was evaluated based on the viscosity at a shear rate of 1 (1 / s).

[0043] (Thermal conductivity) A 10mm x 10mm x 1mm sample was cut from the resin composite obtained by curing the resin composition. Then, the thermal diffusivity A(m) of the sample was measured using the laser flash method with a xenon flash analyzer (NETZSCH, product name "LFA467HyperFlash"). 2 The specific gravity B (kg / m³) of the sample was measured. 3The specific heat capacity (C) of the sample was measured using the Archimedes method. Furthermore, the specific heat capacity C (J / (kg·K)) of the sample was measured using a differential scanning calorimeter (DSC; manufactured by Rigaku Corporation, product name "ThermoPlusEvo DSC8230"). Using these measured values, the thermal conductivity H (W / (m·K)) of the resin composite was calculated from the following formula. Thermal conductivity H(W / (m·K)) = A × B × C

[0044] (Example 1) <Preparation of amorphous boron nitride> A mixed powder was prepared by mixing 100g of boric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 100g of melamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The prepared mixed powder was placed in a constant temperature and humidity chamber, humidified at 80°C and 95% relative humidity for 1 hour, and then dried for 1 hour to obtain melamine borate salt. The melamine borate salt was calcined in a nitrogen atmosphere at a calcination temperature of 1000°C for 2 hours to prepare amorphous boron nitride. The X-ray diffraction pattern of the prepared amorphous boron nitride is shown in Figure 1. For comparison, the X-ray diffraction pattern of hexagonal boron nitride powder (manufactured by Denka Co., Ltd., product name "SP-3") is also shown in Figure 1. From the X-ray diffraction pattern, it was confirmed that the obtained amorphous boron nitride was amorphous.

[0045] <Preparation of boron nitride powder> A mixture was prepared by mixing amorphous boron nitride (BN) and trilithium borate (Li3BO3), with a molar ratio of 2:1 between the amorphous boron nitride and trilithium borate (Li3BO3), using Toyoshima Seisakusho Co., Ltd. as an equivalent. The mixture was then placed in a low-frequency resonant acoustic mixer (Resodyn Acoustic Mixers, Inc., product name "LabRAM II") and mixed. The resulting mixture was filled into a boron nitride container, which was then placed in a tubular furnace. The mixture was then melted at a melting temperature of 1300°C for 20 hours in a nitrogen atmosphere (nitrogen gas flow rate of 1 L / min) to produce a molten mixture. Subsequently, the molten mixture was cooled to a temperature of 650°C at a cooling rate of 5°C / min, and at temperatures above 650°C, natural cooling was allowed to precipitate and grow boron nitride particles. After the boron nitride container cooled to room temperature, its contents were removed. After adding the contents of a 5g boron nitride container, 22mL of distilled water, and 10mL of 60% nitric acid to a beaker, the contents of the beaker were stirred for 1 hour using a stirrer to dissolve the trilithium borate in the contents of the boron nitride container with dilute nitric acid. Then, boron nitride particles were extracted from the contents of the beaker by suction filtration. The extracted boron nitride particles were dried at a drying temperature of 100°C for 2 hours to obtain boron nitride powder. A scanning electron microscope image of the boron nitride powder from Example 1 is shown in Figure 2.

[0046] <Preparation of resin composition> 1 g of the obtained boron nitride powder, and for a total of 100 parts by volume of the obtained boron nitride powder and epoxy resin, 30.8 parts by volume of epoxy resin (manufactured by DIC Corporation, product name: HP4032), 4.2 parts by volume of curing agent (manufactured by DIC Corporation, product name: VH4150), 0.2 parts by volume of two curing accelerators (curing catalysts) (manufactured by Hokko Chemical Industry Co., Ltd., product name: TPP) and 0.3 parts by volume of (manufactured by Shikoku Chemicals Co., Ltd., product name: 2PHZ-PW), and a cup A resin composition was prepared by adding 1.1 parts by volume of a ringing agent (manufactured by Toray Dow Corning Co., Ltd., product name: Z6040), 0.2 parts by volume of a wetting and dispersing agent (manufactured by BIC Chemie Japan Co., Ltd., product name: DIS-111), and 0.3 parts by volume of a surface modifier (manufactured by BIC Chemie Japan Co., Ltd., product name: BYK-300) to a stirrer (manufactured by Thinky Co., Ltd., product name: "Awatori Rentaro ARE-310") and mixing for 1.5 minutes at a rotation speed of 1500 rpm.

[0047] <Molding of resin compositions> A molded body was obtained by pouring a resin composition into a mold measuring 1 cm in length, 1 cm in width, and 1 cm in depth to shape the resin composition.

[0048] <Pressing Process> Using a flat plate press (manufactured by Yanase Seisakusho Co., Ltd.), the molded body was subjected to a heating press at 120°C and a pressure of 10 MPa for 30 minutes, and then to a heating press at 180°C and a pressure of 10 MPa for 60 minutes to produce a composite material with a thickness of 1.0 mm.

[0049] (Example 2) Boron nitride powder, resin compositions, and composites were prepared in the same manner as in Example 1, except that the molar ratio of amorphous boron nitride and trilithium borate (Li3BO3), calculated as boron nitride (BN) and trilithium borate (Li3BO3), was changed from 2:1 to 4:1.

[0050] (Example 3) In the preparation of boron nitride powder, boron nitride powder, resin composition, and composite were prepared in the same manner as in Example 1, except that the molar ratio of amorphous boron nitride and trilithium borate (Li3BO3) was changed from 2:1 to 1:1, and the melting time of the mixture was changed from 20 hours to 5 hours.

[0051] (Example 4) Boron nitride powder, resin compositions, and composites were prepared in the same manner as in Example 1, except that the molar ratio of amorphous boron nitride and trilithium borate (Li3BO3), calculated as boron nitride (BN) and trilithium borate (Li3BO3), was changed from 2:1 to 1:1.

[0052] (Example 5) Boron nitride powder, resin composition, and composite were prepared in the same manner as in Example 1, except that the melting temperature of the mixture was changed from 1300°C to 1500°C and the melting time of the mixture was changed from 20 hours to 1 hour.

[0053] (Example 6) Boron nitride powder, resin composition, and composite were prepared in the same manner as in Example 1, except that the molar ratio of amorphous boron nitride and trilithium borate (Li3BO3) was changed from 2:1 to 1:1, and the melting time of the mixture was changed from 20 hours to 1 hour.

[0054] (Example 7) Boron nitride powder, a resin composition, and a composite were prepared in the same manner as in Example 1, except that the melting time of the mixture was changed from 20 hours to 1 hour.

[0055] (Comparative Example 1) <Preparation of boron nitride powder> A mixture was prepared by adding boron nitride powder (manufactured by Denka Co., Ltd., trade name "SP-3", hexagonal boron nitride), lithium carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and boric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to a low-frequency resonant acoustic mixer (manufactured by Resodyn Acoustic Mixers, Inc., trade name "LabRAM II") and mixing them so that the molar ratio of lithium carbonate to boric acid was 3:1, and the molar ratio of boron nitride powder (calculated as boron nitride (BN) and trilithium borate (Li3BO3)) to the total of lithium carbonate and boric acid was 2:1. The obtained mixture was filled into a boron nitride container and placed in a tubular furnace. The mixture was then melted at a melting temperature of 1300°C for 1 hour in a nitrogen atmosphere (nitrogen gas flow rate of 1 L / min) to prepare a molten mixture. Thereafter, boron nitride powder was obtained in the same manner as in Example 1. Figure 2 shows a scanning electron microscope image of the boron nitride powder of Comparative Example 1.

[0056] <Preparation of resin composition> A resin composition was prepared in the same manner as in Example 1.

[0057] <Molding of resin compositions> A molded article was obtained in the same manner as in Example 1.

[0058] <Pressing Process> A composite material with a thickness of 1.0 mm was fabricated in the same manner as in Example 1.

[0059] (Comparative Example 2) <Preparation of boron nitride powder> In Example 1, amorphous boron nitride (BN) and trilithium borate (Li3BO3) were added to a low-frequency resonant acoustic mixer (Resodyn Acoustic Mixers, Inc., product name "LabRAM II") and mixed so that the molar ratio of lithium carbonate to boric acid was 3:1, and the molar ratio of amorphous boron nitride to the total of lithium carbonate and boric acid was 2:1. The mixture was then prepared by filling a boron nitride container with the mixture and placing the container in a tubular furnace. The mixture was then melted at a melting temperature of 1300°C for 1 hour in a nitrogen atmosphere (nitrogen gas flow rate of 1 L / min) to produce a molten mixture. Thereafter, boron nitride powder was obtained in the same manner as in Example 1.

[0060] <Preparation of resin composition> A resin composition was prepared in the same manner as in Example 1.

[0061] <Molding of resin compositions> A molded article was obtained in the same manner as in Example 1.

[0062] <Pressing Process> A composite material with a thickness of 1.0 mm was fabricated in the same manner as in Example 1.

[0063] (Comparative Example 3) <Preparation of boron nitride powder> Boron nitride (BN) powder and trilithium borate (Li3BO3) were mixed in a low-frequency resonant acoustic mixer (Resodyn Acoustic Mixers, Inc., product name "LabRAM II") so that the molar ratio of boron nitride powder to trilithium borate was 2:1. The mixture was then placed in a tubular furnace. The resulting mixture was filled into a boron nitride container, and the container was melted at a melting temperature of 1300°C for 1 hour in a nitrogen atmosphere (nitrogen gas flow rate of 1 L / min) to produce a molten mixture. Thereafter, boron nitride powder was obtained in the same manner as in Example 1.

[0064] <Preparation of resin composition> A resin composition was prepared in the same manner as in Example 1.

[0065] <Molding of resin compositions> A molded article was obtained in the same manner as in Example 1.

[0066] <Pressing Process> A composite material with a thickness of 1.0 mm was fabricated in the same manner as in Example 1.

[0067] Table 1 shows the evaluation results of the boron nitride powder, resin composition, and composite of Examples 1-7 and Comparative Examples 1-3.

[0068] [Table 1]

[0069] In Examples 1-7, the boron nitride powder had a D90 of 10 μm or more and an aspect ratio of 5.0 or less. As a result, the resin compositions of Examples 1-7 had good fluidity and the thermal conductivity of the composites was high. On the other hand, although the boron nitride powder of Comparative Example 1 had a D90 of 10 μm or more, its aspect ratio was greater than 5.0. As a result, the resin composition of Comparative Example 1 had poor fluidity and the thermal conductivity of the composite was low. Furthermore, the boron nitride powder of Comparative Example 2 had a D90 of less than 10 μm and an aspect ratio greater than 5.0. As a result, the resin composition of Comparative Example 2 had poor fluidity and the thermal conductivity of the composite was low. In addition, although the boron nitride powder of Comparative Example 3 had a D90 of 10 μm or more, its aspect ratio was greater than 5.0. As a result, the composite of Comparative Example 3 had low thermal conductivity.

Claims

1. The particle size (D90) at which the cumulative frequency of 90% by volume of the particle size distribution measured by laser diffraction scattering is 15 μm or larger. Boron nitride powder having an aspect ratio (F / T) of 5.0 or less between the length in the thickness direction (T) and the maximum length in the plane direction (length of the major axis) (F).

2. The boron nitride powder according to claim 1, wherein the particle size (D10) at the cumulative frequency of 10% by volume of the particle size distribution measured by laser diffraction scattering is 1.5 μm or larger.

3. The boron nitride powder according to claim 1 or 2, wherein the length of the long axis is 1.0 μm or more.

4. Boron nitride powder according to any one of claims 1 to 3, wherein the cumulative frequency of particles up to 1.0 μm in the particle size distribution measured by laser diffraction scattering is 3 volume% or less.

5. Boron nitride powder according to any one of claims 1 to 4, wherein the difference (D90-D10) between the particle size at the cumulative frequency of 90% by volume (D90) and the particle size at the cumulative frequency of 10% by volume (D10) of the particle size distribution measured by laser diffraction scattering is 7.0 μm or more.

6. A step (A) involves melting a mixture containing amorphous boron nitride obtained by calcining boric acid and melamine, and lithium borate to produce a melt. The step of cooling the melt (B), and A method for producing boron nitride powder according to any one of claims 1 to 5, comprising the step (C) of dissolving the lithium borate with an acid to extract the boron nitride powder from the lithium borate.

Images