Boron nitride powder, resin composition, and cured product of the resin composition

Abstract

To provide a boron nitride powder capable of preparing a resin composition capable of producing a heat transfer sheet with excellent fillability in resin and excellent heat dissipation, a resin composition containing such a boron nitride powder and a cured product of the resin composition, and a method for producing a boron nitride powder.SOLUTION: One aspect of the present disclosure provides a boron nitride powder containing aggregated particles composed of aggregated primary particles of boron nitride, having a tap density greater than 0.9 g / cm3, an average particle size of 20 μm or less, and a crushing strength of the aggregated particles of 10 MPa or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a boron nitride powder, a resin composition, a cured product of the resin composition, and a method for producing the boron nitride powder. [Background technology]

[0002] Boron nitride powder has lubricity, high thermal conductivity, insulating properties, etc., and is widely used in applications such as solid lubricants, thermally conductive fillers, insulating fillers, etc. In recent years, due to the increasing performance of electronic devices, there is a demand for boron nitride such as the above to have excellent thermal conductivity.

[0003] For example, Patent Document 1 proposes a hexagonal boron nitride powder and a method for producing the same, which, when used as a filler for insulating heat dissipation materials such as resins, can increase the thermal conductivity and withstand voltage (dielectric breakdown voltage) of the resins.

[0004] Hexagonal boron nitride powder is produced, for example, by a production method including a pressure nitriding step in which boron carbide is nitrided in a pressurized nitrogen-containing atmosphere to obtain a nitride, and a decarburization and crystallization step in which the nitride is mixed with a boron source and heat-treated to decarburize and promote crystallization, thereby obtaining hexagonal boron nitride (see, for example, Patent Document 2). The above-mentioned production method aims to improve the decarburization performance in the subsequent step by nitriding boron carbide once. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-116401 [Patent Document 2] International Publication No. 2019 / 073690 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present disclosure is to provide a boron nitride powder that can be used to prepare a resin composition that has excellent fillability in resin and can be used to prepare a heat transfer sheet that has excellent heat dissipation properties; a resin composition containing such boron nitride powder; a cured product of the resin composition; and a method for producing the boron nitride powder. [Means for solving the problem]

[0007] One aspect of the present disclosure is a method for producing a boron nitride composite material comprising agglomerated particles formed by agglomerating primary particles of boron nitride, the agglomerated particles having a tap density of 0.9 g / cm 3 The boron nitride powder has an average particle size of 20 μm or less, and the crushing strength of the agglomerated particles is 10 MPa or more.

[0008] The boron nitride powder has a relatively small average particle size and a high tap density. This means that there are fewer voids in the aggregated particles, allowing for a larger loading when filling the same volume of resin than conventional boron nitride powders. The boron nitride powder also contains agglomerated particles with excellent crushing strength. This prevents the agglomerated particles from breaking down during kneading with resin, preventing the generation of primary particles or their pulverized products. As a result, the increase in viscosity associated with kneading with resin can be suppressed. In other words, the amount of boron nitride powder blended into the resin composition until the viscosity of the resulting resin composition becomes excessive can be increased compared to conventional boron nitride powders. These effects enable the boron nitride powder to have excellent resin filling properties, and the increased loading rate of the boron nitride powder can improve the heat dissipation performance of heat transfer sheets produced.

[0009] The boron nitride powder may have an average particle size of 2 μm or more. When the lower limit of the average particle size is within the above range, an increase in viscosity when kneaded with a resin can be further reduced.

[0010] The boron nitride powder may have an orientation index of 10 or less. An orientation index within this range means that there is a large proportion of agglomerated particles that can suppress the thermal conductivity anisotropy associated with the shape of the primary particles of boron nitride. This prevents the primary particles from orienting in the in-plane direction within the sheet in a heat transfer sheet or the like made using the boron nitride powder, making it possible to take advantage of the high thermal conductivity of the boron nitride powder and exhibiting higher heat dissipation properties.

[0011] One aspect of the present disclosure provides a resin composition containing a resin and the above-described boron nitride powder.

[0012] Since the resin composition contains the boron nitride powder described above, the content of the boron nitride powder can be easily adjusted, and the resin composition is useful for producing a heat transfer sheet with excellent heat dissipation properties.

[0013] One aspect of the present disclosure provides a cured product of a resin composition containing a resin and the above-described boron nitride powder.

[0014] Since the cured product is a cured product of a resin composition containing the above-mentioned boron nitride powder, the content of the boron nitride powder can be easily adjusted, and the cured product can be suitably used as a heat transfer sheet with excellent heat dissipation properties.

[0015] One aspect of the present disclosure provides a method for producing boron nitride powder, comprising: a pressure nitriding step of calcining boron carbide powder having an average particle size of 15 μm or less in a pressurized nitrogen atmosphere to obtain a calcined product; an oxidation step of heating the calcined product in an atmosphere having an oxygen partial pressure of 20% or more to obtain a heat-treated product; and a crystallization step of heating a mixture containing the heat-treated product and a boron source to generate primary particles of boron nitride and obtain aggregated particles constituted by agglomeration of the primary particles, wherein the content of the boron source is less than 50 parts by mass per 100 parts by mass of the heat-treated product.

[0016] The method for producing the boron nitride powder described above includes an oxidation step in which the material is heated in an atmosphere (e.g., air) with an oxygen partial pressure of 20% or higher after the pressure nitriding step, thereby reducing the carbon content in the sintered product after nitriding. This allows for a reduction in the amount of boron source used in the subsequent crystallization step. In the crystallization step, the boron source melts and forms a liquid phase, promoting the dissolution and recrystallization of boron nitride in the sintered product. However, this liquid phase can become trapped within agglomerated particles formed by the aggregation of boron nitride primary particles. Removal of the liquid phase trapped within the agglomerated particles results in voids within the agglomerated particles. Therefore, an increase in the liquid phase can result in the formation of agglomerated particles with a high void ratio, resulting in a powder with a low tap density. In this case, when kneaded with a resin, resin impregnation into the agglomerated particles can occur, raising concerns about the associated increase in viscosity and reduced handleability, making it difficult to increase the packing density to an expected level. In contrast, the manufacturing method according to the present disclosure makes it possible to reduce the amount of boron source blended, and to produce boron nitride powder that has excellent tap density and excellent crushing strength of agglomerated particles.

[0017] Furthermore, in the above manufacturing method, by using a boron carbide powder with a relatively small average particle size, the particle size of the fired product obtained in the pressure nitriding step can be kept small and the particle surface area can be maintained large. This increases the surface area that comes into contact with oxygen in the oxidation step, improves decarburization efficiency, and makes it possible to use a relatively small amount of boron source in the subsequent crystallization step. As a result, agglomerated particles with an appropriate average particle size can be obtained, and boron nitride powder can be prepared that suppresses viscosity increases when kneaded with resin.

[0018] The oxygen content of the heat-treated product may be 4 mass % or less based on the total amount of the heat-treated product. By setting the oxygen content of the heat-treated product within this range, the fillability of the resulting boron nitride powder into resin can be further improved. [Effects of the Invention]

[0019] The present disclosure provides a boron nitride powder that can be used to prepare a resin composition that can be used to fabricate a heat transfer sheet that has excellent fillability in resin and excellent heat dissipation properties, a resin composition containing such boron nitride powder, a cured product of the resin composition, and a method for producing the boron nitride powder. DETAILED DESCRIPTION OF THE INVENTION

[0020] 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 contents.

[0021] 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.

[0022] One embodiment of the boron nitride powder according to the present disclosure includes agglomerated particles formed by agglomeration of primary particles of boron nitride. The boron nitride powder has a tap density of 0.9 g / cm. 3 and an average particle size of 20 μm or less. In the boron nitride powder, the agglomerated particles have a crushing strength of 10 MPa or more. The primary particles of the boron nitride may be primary particles of hexagonal boron nitride. The hexagonal boron nitride may have a small variation in particle shape. The shape of the primary particles of hexagonal boron nitride may be, for example, scale-like or disk-like.

[0023] The boron nitride powder has a high tap density because the voids in the aggregated particles are sufficiently suppressed. However, the porosity of the aggregated particles varies depending on the measurement, and the correlation with the tap density of the phosphor powder is not necessarily good.

[0024] The lower limit of the tap density of the above boron nitride powder is 0.9 g / cm 3 For example, 0.91 g / cm 3 More than 0.92g / cm 3More than 0.93g / cm 3 More than 0.94g / cm 3 or more, or 0.95 g / cm 3 The tap density may be equal to or greater than the theoretical density of boron nitride (2.26 g / cm). When the lower limit of the tap density is within the above range, the fillability of the boron nitride powder in resin can be further improved. The upper limit of the tap density of the boron nitride powder is not particularly limited, but it is preferable that the tap density is within the theoretical density of boron nitride (2.26 g / cm). 3 ) for example, 1.5g / cm 3 It may be a value of about 1.3 g / cm 3 or less than 1g / cm 3 The tap density of the boron nitride powder may be adjusted within the above range, for example, 0.9 g / cm or less. 3 Super 1.5g / cm 3 or less, or 0.91 to 1 g / cm 3 It may be.

[0025] The term "tap density" as used herein refers to a value determined in accordance with the method described in JIS R 1628:1997 "Method for measuring bulk density of fine ceramic powders." Specifically, when boron nitride powder is tapped at 100 cm 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 the tap density. A commercially available device can be used for the measurement, such as "Powder Tester" (product name) manufactured by Hosokawa Micron.

[0026] The upper limit of the average particle size of the boron nitride powder is 20 μm or less, but may be, for example, 19 μm or less or 18 μm or less. When the upper limit of the average particle size is within the above range, for example, when the boron nitride powder is filled into a resin and molded into a sheet-like molded body having a thickness of several tens of μm, the difference between the thickness of the molded body and the particle size of the boron nitride particles can be sufficiently large, and the molded body can be produced without defects. The lower limit of the average particle size of the boron nitride powder may be, for example, 2 μm or more, 3 μm or more, 5 μm or more, 7 μm or more, or 10 μm or more. When the lower limit of the average particle size is within the above range, the boron nitride powder can have excellent packing properties. This can further suppress an increase in viscosity when the boron nitride powder is mixed with a resin. The average particle size of the boron nitride powder may be adjusted within the above range, for example, 2 to 20 μm, 5 to 19 μm, or 7 to 18 μm.

[0027] The average particle size of aggregated particles in this specification refers to the 50% cumulative diameter (median diameter) in the volume-based cumulative particle size distribution. More specifically, it refers to the particle size (D50) at which the cumulative value reaches 50% in the volume-based cumulative particle size distribution obtained by laser diffraction scattering for boron nitride powder. Laser diffraction scattering is measured in accordance with the method described in JIS Z 8825:2013, "Particle size analysis - Laser diffraction and scattering method." A laser diffraction scattering particle size distribution analyzer, such as the "LS-13 320" (product name) manufactured by Beckman Coulter, Inc., can be used for the measurement. Note that the measurement is performed without homogenization, in the presence of aggregated particles.

[0028] The lower limit of the crushing strength of the agglomerated particles is 10 MPa or more, but may be, for example, 11 MPa or more, 12 MPa or more, or 13 MPa or more. When the lower limit of the crushing strength is within the above range, the heat dissipation properties of the resin composition and molded article obtained by kneading with the resin can be further improved. The upper limit of the crushing strength of the agglomerated particles may be, for example, 30 MPa or less, 28 MPa or less, 25 MPa or less, or 20 MPa or less. When the upper limit of the crushing strength is within the above range, at least a portion of the agglomerated particles disintegrates appropriately during kneading with the resin, suppressing the generation of voids and thereby further improving the insulating properties of the resin composition and molded article obtained. The crushing strength of the agglomerated particles may be adjusted within the above range, for example, 10 to 30 MPa, 11 to 25 MPa, or 13 to 20 MPa.

[0029] The crushing strength in this specification refers to a value measured in accordance with the description in JIS R 1639-5:2007 "Fine ceramics - Measurement methods for granule characteristics - Part 5: Single granule crushing strength." The crushing strength σ (unit: MPa) of a single agglomerate particle is calculated from the dimensionless number α (α=2.48), which varies depending on the position within the agglomerate particle, the crushing test force P (unit: N), and the particle diameter d (unit: μm), as follows: σ=α×P / (π×d 2 ) is calculated using the formula. Measurements were performed on 20 or more agglomerated particles, and the value at the cumulative destruction rate of 63.2% was calculated. A micro-compression tester can be used for the measurement. For example, the "MCT-W500" (product name) manufactured by Shimadzu Corporation can be used as a micro-compression tester.

[0030] The orientation of the primary particles of the boron nitride powder is sufficiently suppressed. The upper limit of the orientation index of the boron nitride powder may be, for example, 10 or less, 9.8 or less, 9.6 or less, 9.5 or less, or 9 or less. When the upper limit of the orientation index is within the above range, the resin composition and molded article can exhibit practically sufficient heat dissipation properties. The lower limit of the orientation index of the boron nitride powder is not limited, but it is not easy to produce a boron nitride powder with an index of less than 6, and may be, for example, 6 or more, 6.2 or more, 6.5 or more, or 6.7 or more. The orientation index of the boron nitride powder may be adjusted within the above range, and may be, for example, 6.0 to 10, 6.2 to 9.5, or 6.5 to 9.

[0031] 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.

[0032] The upper limit of the specific surface area of ​​boron nitride powder is, for example, 7 m 2 / g or less, 6.5m 2 / g or less, 6m 2 / g or less, or 5.5m 2 When the upper limit of the specific surface area is within the above range, the primary particle diameter of the boron nitride powder is sufficiently large, and when the boron nitride powder is made into a resin composition or a molded article, it can exhibit better heat dissipation properties. The lower limit of the specific surface area of ​​the boron nitride powder is, for example, 1.5 m 2 / g or more, 2m 2 / g or more, 2.5m 2 / g or more, or 3m 2 / g or more. When the lower limit of the specific surface area is within the above range, the agglomeration of the primary particles of boron nitride is dense, and the crushing strength of the agglomerated particles tends to be sufficiently high, which makes it possible to further suppress the collapse of the agglomerated particles when the boron nitride powder is kneaded with a resin or molded. The specific surface area of ​​the boron nitride powder may be adjusted within the above range, for example, 1.5 to 7 m 2 / g, 2-6.5m 2 / g, or 2.5 to 6 m 2 / g.

[0033] The 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 "MONOSORB MS-22" (product name) manufactured by QUANTACHROME.

[0034] The boron nitride powder can be produced, for example, by the following method. One embodiment of the method for producing boron nitride powder comprises a pressure nitriding step of calcining boron carbide powder having an average particle size of 15 μm or less in a pressurized nitrogen atmosphere to obtain a calcined product, an oxidation step of heating the calcined product in an atmosphere having an oxygen partial pressure of 20% or more to obtain a heat-treated product, and a crystallization step of heating a mixture containing the heat-treated product and a boron source to generate primary particles of boron nitride and obtain aggregated particles composed of the primary particles agglomerated. The content of the boron source in the mixture is less than 50 parts by mass per 100 parts by mass of the heat-treated product.

[0035] The boron carbide powder (BC powder) used in the pressure nitriding step has an average particle size of 15 μm or less. The upper limit of the average particle size of the boron carbide powder may be, for example, 14 μm or less, 13 μm or less, 12 μm or less, or 11 μm or less. When the upper limit of the average particle size of the boron carbide powder is within the above range, the particle size of the fired product obtained in the pressure nitriding step can be kept small. This allows the particle surface area to be maintained large, increasing the surface area in contact with oxygen in the oxidation step, and thereby improving decarburization efficiency. The lower limit of the average particle size of the boron carbide powder may be, for example, 1 μm or more, 2 μm or more, 4 μm or more, or 5 μm or more. When the lower limit of the average particle size of the boron carbide powder is within the above range, the particle size of the resulting agglomerated particles can be appropriately increased, thereby further suppressing an increase in viscosity when the boron nitride powder is kneaded into a resin to form a resin composition. The average particle size of the boron carbide powder means a value measured by the same method as the method for measuring the average particle size of the agglomerated particles in the boron nitride powder described above.

[0036] In the pressure nitriding step, boron carbide powder is sintered in a pressurized nitrogen atmosphere to obtain a sintered product containing boron carbonitride powder (B4CN4 powder). The lower limit of the sintering temperature in the pressure nitriding step may be 2000°C or higher, or 2100°C or higher. By setting the lower limit of the sintering temperature within the above range, the crystallinity of the obtained boron carbonitride can be improved, and the proportion of hexagonal boron carbonitride can be increased. Increasing the proportion of hexagonal boron carbonitride in the pressure nitriding step can further improve the thermal conductivity of the boron nitride powder obtained later. The upper limit of the sintering temperature in the pressure nitriding step may be 2300°C or lower, or 2250°C or lower. The sintering temperature may be adjusted within the above range, for example, 2000 to 2300°C.

[0037] The lower limit of the pressure (atmospheric pressure) in the pressure nitriding step may be, for example, 0.6 MPa or more, 0.7 MPa or more, or 0.8 MPa or more. By setting the lower limit of the pressure in the pressure nitriding step within the above range, the nitriding of boron carbide can be sufficiently promoted. The upper limit of the pressure (atmospheric pressure) in the pressure nitriding step may be, for example, 1 MPa or less, or 0.9 MPa or less. By setting the upper limit of the pressure in the pressure nitriding step within the above range, an increase in the production cost of the boron nitride powder can be suppressed. The pressure may be adjusted within the above range, and may be, for example, 0.6 to 1 MPa, or 0.8 to 0.9 MPa.

[0038] The nitrogen gas concentration in the pressurized nitrogen atmosphere in the pressure nitriding step may be, for example, 95% by volume or more, 98% by volume or more, or 99.9% by volume or more. The firing time in the pressure nitriding step is not particularly limited as long as nitriding proceeds sufficiently, and may be, for example, 6 to 30 hours, 8 to 25 hours, or 10 to 20 hours.

[0039] In the oxidation step, a calcined product containing boron carbonitride powder is calcined in an oxygen-containing atmosphere to decarburize some of the carbon contained in the calcined product. This decarburization allows for a reduction in the amount of boron source used in the subsequent crystallization step. As a result, the proportion of liquid phase in the crystallization step can be reduced, resulting in a boron nitride powder with a high tap density and excellent agglomerate particle crushing strength.

[0040] The oxygen-containing atmosphere in the oxidation step may be an atmosphere with an oxygen partial pressure of 20% or more, for example, air, etc. The pressure in the oxidation step (atmospheric pressure) may be, for example, 0.1 to 0.5 MPa, 0.1 to 0.3 MPa, or 0.1 to 0.2 MPa, or may be atmospheric pressure (0.1 MPa).

[0041] The lower limit of the firing temperature in the oxidation step may be, for example, 600°C or higher, 650°C or higher, or 700°C or higher. When the lower limit of the firing temperature is within the above range, the carbon content in the boron carbonitride can be further reduced. The upper limit of the firing temperature in the oxidation step may be, for example, 1000°C or lower, or 950°C or lower. When the upper limit of the firing temperature is within the above range, oxidation of the boron carbonitride after firing can be suppressed.

[0042] The lower limit of the calcination time in the oxidation step may be, for example, 6 hours or more, or 7 hours or more. When the lower limit of the calcination time is within the above range, the carbon content in the boron carbonitride can be sufficiently reduced. The upper limit of the calcination time in the oxidation step is not particularly limited, but may be, for example, 20 hours or less, or 15 hours or less. When the upper limit of the calcination time is within the above range, a decrease in the processing efficiency of the step can be more sufficiently suppressed. If the calcination time is too short, the carbon content will not be sufficiently reduced. By setting the upper limit of the calcination time within the above range, it is possible to more sufficiently suppress the oxidation of some of the boron atoms in the heat-treated product to produce boric acid, thereby more effectively suppressing a decrease in the tap density of the boron nitride powder that occurs with an increase in the amount of boric acid.

[0043] The heat-treated product obtained in the oxidation step has a reduced oxygen content compared to the oxygen content of the fired product before the heat treatment. The upper limit of the oxygen content of the heat-treated product may be, for example, 4% by mass or less, 3% by mass or less, 2% by mass or less, or 1.5% by mass or less, based on the total amount of the heat-treated product. By keeping the oxygen content of the heat-treated product within this range, it is possible to suppress an increase in the amount of liquid phase during firing in the subsequent crystallization step, and to further increase the tap density of the obtained boron nitride powder. The lower limit of the oxygen content of the heat-treated product is not particularly limited, but may be, for example, 0.1% by mass or more, or 0.5% by mass or more, based on the total amount of the heat-treated product.

[0044] The oxygen amount in this specification refers to a value measured by an oxygen / nitrogen simultaneous analyzer. As the oxygen / nitrogen simultaneous analyzer, for example, the "EMGA-910" (product name) manufactured by Horiba Ltd. can be used.

[0045] In the crystallization step, primary particles of boron nitride are generated by heating a mixture containing the heat-treated product obtained in the oxidation step and a boron source, and the primary particles are aggregated to obtain agglomerated particles. That is, in the crystallization step, boron carbonitride is decarbonized and the crystallinity of the boron nitride is increased, thereby obtaining a boron nitride powder containing agglomerated particles in which predetermined boron nitride primary particles are aggregated.

[0046] The boron source may include, for example, at least one selected from the group consisting of boric acid and boron oxide. More specifically, the boron source may be boric acid, boron oxide, or a mixture thereof. The mixture heated in the crystallization step may contain, in addition to boron carbonitride and a boron source, known additives used in the B4C method.

[0047] The upper limit of the amount of boron source in the mixture is less than 50 parts by mass, per 100 parts by mass of the heat-treated product, and may be, for example, 45 parts by mass or less, 43 parts by mass or less, or 40 parts by mass or less. By setting the upper limit of the amount of boron source within the above range, the tap density of the resulting boron nitride powder can be further increased, and the crushing strength of the agglomerated particles can be further improved. The amount of boron source in the mixture may be 30 parts by mass or more, 32 parts by mass or more, 34 parts by mass or more, or 36 parts by mass or more, per 100 parts by mass of the heat-treated product. Setting the lower limit of the amount of boron source in the above range can promote particle growth of boron nitride primary particles. The amount of boron source in the mixture may be adjusted within the above range, and may be, for example, 30 parts by mass or more but less than 50 parts by mass, 34 to 45 parts by mass, or 36 to 40 parts by mass, per 100 parts by mass of the heat-treated product.

[0048] The lower limit of the firing temperature to which the mixture is heated in the crystallization step may be, for example, 1900°C or higher, or 2000°C or higher. By setting the lower limit of the firing temperature within the above range, particle growth can be sufficiently promoted. The upper limit of the firing temperature to which the mixture is heated in the crystallization step may be, for example, 2200°C or lower, or 2150°C or lower. By setting the upper limit of the firing temperature within the above range, yellowing of the boron nitride powder can be suppressed. The firing temperature in the crystallization step may be adjusted within the above range, and may be, for example, 1900 to 2200°C, or 2000 to 2150°C. The firing temperature to which the mixture is heated in the crystallization step is preferably lower than the firing temperature of the boron carbide powder in the pressure nitriding step.

[0049] The crystallization step may be carried out under normal pressure or under a pressure equal to or higher than atmospheric pressure. Note that all atmospheric pressures in this specification refer to gauge pressure. The lower limit of the pressure (atmospheric pressure) in the crystallization step may be, for example, 10 kPa or more, 15 kPa or more, or 20 kPa or more. By setting the lower limit of the pressure within the above range, it is possible to prevent auxiliary agents such as boric acid from being removed from the system and to make the reaction field of the boron nitride particles more uniform. The upper limit of the pressure (atmospheric pressure) in the crystallization step may be, for example, 80 kPa or less, 60 kPa or less, or 40 kPa or less. By setting the upper limit of the pressure within the above range, it is possible to more sufficiently prevent the aggregated particles from collapsing during the crystallization step. The pressure (atmospheric pressure) in the crystallization step may be adjusted within the above range, for example, 10 to 80 kPa, 10 to 60 kPa, or 20 to 40 kPa.

[0050] The lower limit of the calcination time in the crystallization step may be, for example, 0.5 hours or more, 1 hour or more, or 3 hours or more. By setting the lower limit of the calcination time within the above range, particle growth can be sufficiently promoted. The upper limit of the calcination time in the crystallization step may be, for example, 40 hours or less, 30 hours or less, 20 hours or less, or 10 hours or less. By setting the upper limit of the calcination time within the above range, an increase in production costs can be suppressed. The calcination time may be adjusted within the above range, and may be, for example, 0.5 to 40 hours, or 1.0 to 30 hours.

[0051] The method for producing boron nitride powder may include other steps. Examples of such other steps include a pulverization step and a classification step. In the method for producing boron nitride powder, for example, a pulverization step may be carried out after the crystallization step. In the pulverization step, a general pulverizer or crusher can be used. For example, a ball mill, a vibration mill, a jet mill, or the like can be used. In this specification, "pulverization" also includes "crushing."

[0052] The boron nitride powder according to the present disclosure has a small average particle size, a relatively large tap density, and high crushing strength of the agglomerated particles contained therein, making it suitable for use as a filler to be mixed with resins and the like. Furthermore, since the boron nitride powder can suppress an increase in viscosity when mixed with resin, the amount of boron nitride powder filled can be increased compared to conventional methods, and molded articles (e.g., heat transfer sheets) formed using the resin composition can be expected to have excellent heat dissipation properties. One embodiment of a resin composition contains a resin and the boron nitride powder described above.

[0053] The resin composition can be used after molding, curing, etc. One embodiment of the cured product is a cured product of a resin composition containing a resin and the above-mentioned boron nitride powder. The shape of the cured product is not particularly limited and may be a block, sheet, or film. In the case of a sheet-shaped cured product (sheet), the thickness of the sheet may be, for example, 0.5 mm or less, 0.2 mm or less, or 0.1 mm or less. Since the sheet contains the above-mentioned boron nitride, which has a relatively small particle size, a relatively thin sheet can be produced. Since the above-mentioned cured product contains the above-mentioned boron nitride, it is useful, for example, for heat dissipation components, etc.

[0054] Examples of resins include liquid crystal polymers, fluororesins, silicone resins, silicone rubber, acrylic resins, polyolefins (such as polyethylene), epoxy resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, polyimides, polyamideimides, polyetherimides, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, wholly aromatic polyesters, polysulfones, polyethersulfones, polycarbonates, maleimide-modified resins, ABS (acrylonitrile-butadiene-styrene) resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins.

[0055] The lower limit of the resin content may be, for example, 15% by volume or more, 20% by volume or more, or 30% by volume or more, based on the total volume of the resin composition. When the lower limit of the resin content is within the above range, deterioration of the moldability of the resin composition can be more sufficiently suppressed. The upper limit of the resin content may be, for example, 60% by volume or less, 50% by volume or less, or 40% by volume or less, based on the total volume of the resin composition. When the lower limit of the resin content is within the above range, the thermal conductivity of the resin composition can be further improved.

[0056] The resin composition of the present disclosure uses the above-described boron nitride powder, allowing a relatively large amount of boron nitride powder to be contained. The lower limit of the boron nitride powder content may be, for example, 40% by volume or more, 50% by volume or more, 60% by volume or more, or 65% by volume or more, based on the total volume of the resin composition. When the lower limit of the boron nitride powder content is within the above range, the thermal conductivity of the resin composition is improved, and a molded product with excellent heat dissipation properties can be obtained. The upper limit of the boron nitride powder content 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 composition. When the upper limit of the boron nitride powder content is within the above range, deterioration in the moldability of the resin composition can be suppressed.

[0057] In addition to the resin and boron nitride powder, the resin composition may further contain a curing agent that cures the resin. The curing agent can be appropriately selected depending on the type of resin. When the resin is an epoxy resin, examples of the curing agent include phenol novolac compounds, acid anhydrides, amino compounds, and imidazole compounds. The lower limit of the curing agent content may be, for example, 0.5 parts by mass or more, or 1 part 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.

[0058] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. Furthermore, the descriptions of the above-described embodiments can be mutually applied. [Example]

[0059] 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.

[0060] Example 1 [Preparation of boron carbide powder] 100 parts by mass of orthoboric acid (manufactured by Nippon Denko Corporation, hereinafter simply referred to as "boric acid") and 35 parts by mass of acetylene black (HS100, manufactured by Denka Co., Ltd.) were mixed using a Henschel mixer and then loaded into a graphite crucible. This graphite crucible was placed in an arc furnace and heated at 2200°C for 5 hours in an argon atmosphere to synthesize a lump of boron carbide (BC) powder. The synthesized lump of boron carbide powder was pulverized in a ball mill for 1 hour and classified using a sieve with 63 μm mesh. The boron carbide powder remaining under the sieve was further washed with an aqueous nitric acid solution to remove impurities such as iron, filtered, and dried to produce a boron carbide powder (BC powder) with an average particle size of 15 μm.

[0061] [Preparation of boron carbonitride powder] The boron carbide powder was placed in a boron nitride crucible and heated in a resistance heating furnace at 2100°C for 25 hours under a nitrogen gas atmosphere of 0.85 MPa to obtain boron carbonitride (BCN) powder (pressure nitriding process).

[0062] The obtained boron carbonitride powder was placed in a muffle furnace and heated at 700°C for 5 hours in an air atmosphere (oxidation step), to obtain a heat-treated product. The oxygen content of the heat-treated product was 1.8% by mass. The oxygen content was measured using an oxygen / nitrogen simultaneous analyzer (EMGA-910, manufactured by Horiba, Ltd.).

[0063] [Preparation of boron nitride powder] Boric acid, the boron source, was added to 100 parts by mass of the heat-treated product so that the content of boric acid was 40 parts by mass, and the mixture was mixed using a Henschel mixer to obtain a mixture. The mixture was filled into a boron nitride crucible and decarbonized by heating using a resistance heating furnace to synthesize boron nitride powder containing aggregated particles formed by aggregation of primary particles (crystallization step). The conditions for the crystallization step were as follows: in a nitrogen gas atmosphere at a pressure of 13 kPa, the temperature was raised from room temperature to 2000°C, and the mixture was held at 2000°C for 5 hours. The synthesized boron nitride powder was crushed in a mortar for 10 minutes and then classified using a nylon sieve with 75 μm mesh.

[0064] Example 2 Boron nitride powder was prepared in the same manner as in Example 1, except that the boron carbide powder used was changed to one with an average particle size of 10 μm, and the oxygen content of the heat-treated product was 2.3.

[0065] Example 3 Boron nitride powder was prepared in the same manner as in Example 1, except that the boron carbide powder used was changed to one with an average particle size of 3 μm, and the oxygen content of the heat-treated material was 2.5%.

[0066] (Comparative Example 1) A boron nitride powder was prepared in the same manner as in Example 1, except that a powder with an average particle size of 16 μm was used as the boron carbide powder, the oxygen content of the heat-treated product was 2.2, and the content of boric acid was changed to 55 parts by mass per 100 parts by mass of the heat-treated product.

[0067] (Comparative Example 2) A boron nitride powder was prepared in the same manner as in Example 1, except that a powder with an average particle size of 10 μm was used as the boron carbide powder, the oxygen content of the heat-treated product was 1.9, and the content of boric acid was changed to 55 parts by mass per 100 parts by mass of the heat-treated product.

[0068] (Comparative Example 3) A boron nitride powder was prepared in the same manner as in Example 1, except that a powder with an average particle size of 26 μm was used as the boron carbide powder, the oxygen content of the heat-treated product was 2.2, and the content of boric acid was changed to 40 parts by mass per 100 parts by mass of the heat-treated product.

[0069] Comparative Example 4 A boron nitride powder was prepared in the same manner as in Example 1, except that a powder with an average particle size of 16 μm was used as the boron carbide powder, the oxygen content of the heat-treated product was 2.0, and the content of boric acid was changed to 75 parts by mass per 100 parts by mass of the heat-treated product.

[0070] (Comparative Example 5) Boron nitride powder was prepared in the same manner as in Example 1, except that a powder with an average particle size of 16 μm was used as the boron carbide powder and the content of boric acid was changed to 55 parts by mass per 100 parts by mass of the heat-treated product.

[0071] (Comparative Example 5) For comparison, boron nitride powder containing aggregated particles was prepared by the so-called melamine borate method, in which boron nitride was prepared and granulated. Specifically, 100 parts by mass of boric acid powder (purity 99.8% by mass or higher, manufactured by Kanto Chemical Co., Inc.) and 90 parts by mass of melamine powder (purity 99.0% by mass or higher, manufactured by Wako Pure Chemical Industries, Ltd.) were mixed in an alumina mortar for 10 minutes to obtain a mixed raw material. After drying, the mixed raw material was placed in a hexagonal boron nitride container and placed in an electric furnace. While flowing nitrogen gas through the electric furnace, the temperature was increased from room temperature to 1000°C at a rate of 10°C / min. After holding at 1000°C for 4 hours, heating was stopped and the material was allowed to cool naturally. When the temperature reached 100°C or below, the electric furnace was opened. In this manner, a calcined product containing low-crystalline boron nitride was obtained.

[0072] Next, 20 parts by mass of boric acid and 3 parts by mass of sodium carbonate (purity 99.5% by mass or higher) as an auxiliary agent were added to 100 parts by mass of the above-mentioned calcined product, and mixed for 10 minutes using an alumina mortar. The mixture was placed in the above-mentioned electric furnace. While circulating nitrogen gas through the electric furnace, the temperature was increased from room temperature to 2000°C at a rate of 10°C / min. After maintaining the firing temperature of 2000°C for 4 hours, heating was stopped and the mixture was allowed to cool naturally. When the temperature reached 100°C or below, the electric furnace was opened. The resulting fired product was collected and pulverized in an alumina mortar for 3 minutes to obtain coarse powder of boron nitride.

[0073] To 100 parts by mass of the boron nitride coarse powder obtained as described above, 3 parts by mass of calcium carbonate as an auxiliary agent and 140 parts by mass of water were added, mixed using a Henschel mixer, and then pulverized in a ball mill for 5 hours to obtain a slurry. To 100 parts by mass of the obtained slurry, 0.5 parts by mass of polyvinyl alcohol resin and 0.5 parts by mass of anionic surfactant were added, and the mixture was stirred at 50°C until dissolved to obtain a solution. The resulting solution was sprayed using a rotary atomizer into a spray dryer adjusted to a rotation speed of 17,000 rpm and a temperature of 230°C, yielding a powder of loosely agglomerated boron nitride primary particles. The resulting powder was further heat-treated in a batch-type high-frequency furnace under a nitrogen atmosphere at 1,850°C for 4 hours to produce boron nitride powder.

[0074] <Evaluation of boron nitride powder properties> The tap density, average particle size, crushing strength, and orientation index were evaluated for each of the boron nitride powders obtained in Examples 1 and 2 and Comparative Examples 1 to 5. The results are shown in Table 1.

[0075] <Evaluation of boron nitride powder as a filler> Resin compositions were prepared using the boron nitride powders obtained in Examples 1 and 2 and Comparative Examples 1 to 5, and the boron nitride powders were evaluated as fillers for resins by the methods described below. In Table 1, the viscosity and thermal conductivity are shown as relative values ​​based on the measured values ​​for the boron nitride powder of Comparative Example 1.

[0076] [Film forming property] A resin composition was obtained by mixing boron nitride powder with a mixture of 100 parts by mass of naphthalene-type epoxy resin (HP4032, manufactured by DIC Corporation) and 10 parts by mass of an imidazole compound (2E4MZ-CN, manufactured by Shikoku Chemicals Corporation) as a curing agent, so that the boron nitride powder was 60% by volume. A Thinky Mixer (product name) 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 500 μm. Then, the mixture was kneaded at a temperature of 150°C and 50 kgf / cm. 2The resin was cured by heating and pressing under relatively mild conditions for 60 minutes under the conditions of 1.0 to 1.5 mm to prepare a 50 μm resin sheet (evaluation sheet). The film obtained as described above was visually observed and evaluated according to the following criteria. A: No defects were observed in the film. B: Defects were observed in the film.

[0077] [Viscosity of resin composition] A composition was obtained by mixing boron nitride powder with silicone oil (product name: KF-96L, manufactured by Shin-Etsu Chemical Co., Ltd.). The amount of boron nitride powder was adjusted to 25% by volume in the resin composition. A Thinky Mixer (product name) was used to knead the resin. The kneading conditions were 1600 rpm for 3 minutes. The viscosity of the obtained composition was measured using a rotational viscometer (product name: MCR302, manufactured by Anton Paar Japan) to confirm the shear rate dependency of the viscosity. Measurements were taken at 25°C and shear rates of 0.01 to 100 sec. -1 The results are shown in Table 1. In Table 1, the resin composition using the boron nitride powder prepared in Comparative Example 1 was subjected to shear rate of 1 sec -1 The viscosity at this point is set to 1, and the relative values ​​are shown.

[0078] [Thermal conductivity of resin sheet] The thermal conductivity of a resin sheet (evaluation sheet) manufactured in the same manner as the resin sheet used to evaluate the film formability was evaluated. The thermal conductivity H (unit: W / (m K)) was calculated by multiplying the thermal diffusivity A (unit: m 2 / sec), density B (unit: kg / m 3The thermal diffusivity A was calculated from the values ​​of the specific heat capacity C (unit: J / (kg·K)) using the formula H = A × B × C. The evaluation sheet was cut into a length of 10 mm, a width of 10 mm, and a thickness of 0.3 mm, and the thermal diffusivity A was measured using the laser flash method. The measurement device used was a xenon flash analyzer (NETZSCH, product name: LFA447 NanoFlash). The density B was measured using the Archimedes method. The specific heat capacity C was measured using a DSC (Rigaku, product name: ThermoPlusEvoDSC8230).

[0079] [Table 1] [Industrial Applicability]

[0080] The present disclosure provides a boron nitride powder that can be used to prepare a resin composition that can be used to fabricate a heat transfer sheet that has excellent fillability in resin and excellent heat dissipation properties, a resin composition containing such boron nitride powder, a cured product of the resin composition, and a method for producing the boron nitride powder.

Claims

1. The boron nitride powder contains agglomerated particles formed by agglomerating primary particles of boron nitride, Tap density is 0.9 g / cm ３ and the average particle size is 20 μm or less, The boron nitride powder has a crushing strength of 10 MPa or more.

2. 2. The boron nitride powder according to claim 1, having an average particle size of 2 μm or more.

3. 3. The boron nitride powder according to claim 1, having an orientation index of 10 or less.

4. A resin composition comprising a resin and the boron nitride powder according to any one of claims 1 to 3.

5. A cured product of a resin composition comprising a resin and the boron nitride powder according to any one of claims 1 to 3.

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