Method for adjusting particle crushing strength of boron nitride powder, boron nitride powder, and method for producing the same

Abstract

An aspect of the present invention has a decarbonizing step for obtaining boron nitride powder by heating boron carbonitride powder in the presence of calcium carbonate, and provides a method for adjusting the particle crush strength of the boron nitride powder by adjusting the amount of calcium carbonate to be added in the decarbonizing step.

Description

Technical Field

[0001] The present invention relates to a method for adjusting the particle crushing strength of boron nitride powder, boron nitride powder, and a method for producing the same.

Background Art

[0002] In electronic components such as power devices, transistors, thyristors, and CPUs, it is an issue to efficiently dissipate the heat generated during use. Conventionally, to address this issue, the insulation layer of a printed wiring board on which electronic components are mounted has been made to have high thermal conductivity, or the electronic components or the printed wiring board have been attached to a heat sink via an electrically insulating thermal interface material. For such insulation layers and thermal interface materials, ceramic powders with high thermal conductivity are used.

[0003] As the ceramic powder, boron nitride powder having characteristics such as high thermal conductivity, high insulation, and low relative permittivity has been attracting attention. For example, in Patent Document 1, the shape of the aggregates is further spheroidized to improve the fillability, the powder strength is improved, and further, by increasing the purity, the insulation improvement and the breakdown voltage stabilization of a heat transfer sheet filled with the powder are achieved. As the hexagonal boron nitride powder, the ratio of the major axis to the thickness of the primary particles is on average 5 to 10, the size of the aggregates of the primary particles is 2 μm or more and 200 μm or less in average particle diameter (D50), and the bulk density is 0.5 to 1.0 g / cm 3 There is disclosed a hexagonal boron nitride powder characterized by being as follows.

[0004] 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 hexagonal boron nitride powder is filled into a resin, the particles align in the same direction. Therefore, for example, when manufacturing a thermal interface material, the in-plane direction (a-axis direction) of the hexagonal boron nitride particles is perpendicular to the thickness direction of the thermal interface material, and the high thermal conductivity in the in-plane direction (a-axis direction) of the hexagonal boron nitride particles cannot be fully utilized.

[0005] On the other hand, Patent Document 2 describes that in boron nitride aggregated particles formed by aggregation of boron nitride primary particles, by increasing the strength to such an extent that the collapse of the aggregated particles can be suppressed even at a predetermined molding pressure, the alignment of the boron nitride primary particles in the same direction is suppressed.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In boron nitride aggregated particles in which primary particles are aggregated as disclosed in Patent Document 2, it is considered important to increase the strength of the aggregated particles in order to suppress the reduction in thermal conductivity due to the alignment of the primary particles in the same direction. On the other hand, according to the studies of the present inventors, in order to obtain boron nitride aggregated particles having desired characteristics, it has been found that it is effective to use a combination of aggregated particles not only with a large strength (crushing strength) but also with an appropriate strength.

[0008] That is, conventionally, the focus has been on increasing the strength of boron nitride agglomerated particles, but it has been found that a technique for obtaining agglomerated particles with an appropriate strength for combination with high-strength agglomerated particles is necessary. However, since the degree of appropriate strength for combination varies depending on the strength of the high-strength agglomerated particles, a technique for accurately adjusting the strength of the agglomerated particles is required.

[0009] Therefore, one aspect of the present invention aims to provide a novel method for adjusting the particle crushing strength of boron nitride powder.

Means for Solving the Problems

[0010] The inventors of the present invention examined many factors affecting the crushing strength of agglomerated particles. As a result, when obtaining boron nitride powder by heating boron carbonitride powder in the presence of calcium carbonate, it was found that the particle crushing strength of the produced boron nitride powder can be easily adjusted by adjusting the addition amount of calcium carbonate, and the present invention was completed.

[0011] One aspect of the present invention provides a method for adjusting the particle crushing strength of boron nitride powder, comprising a decarbonization step of heating boron carbonitride powder in the presence of calcium carbonate to obtain boron nitride powder, and adjusting the addition amount of calcium carbonate in the decarbonization step.

[0012] Another aspect of the present invention provides a method for producing boron nitride powder, comprising a step of adding calcium carbonate to boron carbonitride powder to adjust the particle crushing strength, and a step of heating and decarbonizing the boron carbonitride powder in the presence of calcium carbonate.

[0013] In this production method, in the step of adding calcium carbonate, calcium carbonate may be added in an amount of 0.125 to 1 part by mass with respect to 100 parts by mass of the boron carbonitride powder.

[0014] Another aspect of the present invention provides boron nitride powder having a standard deviation of the particle crushing strength of 3 MPa or less.

[0015] Another aspect of the present invention is a set composed of a plurality of aggregates, wherein the plurality of aggregates each have boron nitride powder of different production lots, and the standard deviation of the particle crushing strength of the boron nitride powder in the set is 3 MPa or less. A set is provided.

Advantages of the Invention

[0016] According to one aspect of the present invention, a novel method for adjusting the particle crushing strength of boron nitride powder can be provided.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments.

[0018] The boron nitride powder in this specification is an aggregate (also referred to as massive particles) formed by aggregation of primary particles of boron nitride, and is obtained in the same production lot (details will be described later). The primary particles of boron nitride may be, for example, flaky hexagonal boron nitride particles.

[0019] In this specification, the particle crushing strength refers to the crushing strength of the aggregated particles. The particle crushing strength (σ: unit MPa) can be measured according to JIS R1639-5, and from the dimensionless number (α = 2.48) that changes depending on the position within the aggregated particles, the crushing test force (P: unit N), and the particle diameter (d: unit μm), it can be calculated using the formula σ = α × P / (π × d 2 ). The crushing strength of the boron nitride powder (the crushing strength of the entire powder) can be obtained as the strength at which the cumulative failure rate becomes 63.2% by measuring the particle crushing strength of 20 aggregated particles. In the above formula for obtaining the particle crushing strength, the crushing test force can be measured using a micro compression tester (for example, MCT-W500 manufactured by Shimadzu Corporation).

[0020] The boron nitride powder according to one embodiment is boron carbonitride (B 4 CN 4) It is obtained by a manufacturing method including a step of adding calcium carbonate to adjust the particle crushing strength (addition step) and a step of heating boron carbonitride powder in the presence of calcium carbonate to decarburize it (decarburization step).

[0021] In one embodiment, the addition step includes a step of firing boron carbide (B 4 C) powder to obtain boron carbonitride powder (nitridation step).

[0022] In the nitridation step, the average particle size of the boron carbide powder may be 3 μm or more, 5 μm or more, or 10 μm or more, and may be 100 μm or less, 60 μm or less, or 40 μm or less. The average particle size of the boron carbide powder is measured using a laser diffraction scattering method particle size distribution measuring device (LS-13 320) manufactured by Beckman Coulter without applying a homogenizer to the sample before the measurement process, and is the particle size (median diameter, D50) at a cumulative value of 50% of the cumulative particle size distribution.

[0023] The carbon content of the boron carbide powder is desirably less than B 4 C (21.7 mass%). The carbon content is preferably 18 mass% or more, more preferably 19 mass% or more, and may be 20.5 mass% or less. When the carbon content is 18 mass% or more, the deviation from the theoretical composition is small, so it becomes stable. By the carbon content being 20.5 mass% or less, the amount of carbon volatilized during the decarburization step described later can be reduced, and dense aggregated particles can be obtained. The carbon content of the boron carbide powder can be measured with a carbon analyzer (for example, IR-412 type manufactured by LECO).

[0024] The boron carbide powder can be obtained by a known manufacturing method. For example, after mixing boric acid and acetylene black, it can be heated at 1800 to 2400 °C for 1 to 10 hours in an inert gas atmosphere to obtain a boron carbide mass. By appropriately performing pulverization, sieving, washing, impurity removal, drying, etc. on this boron carbide mass, boron carbide powder can be obtained. Commercially available products may be used as the boron carbide powder.

[0025] In the nitriding process, boron carbide powder is heated under a nitrogen atmosphere and under pressure conditions. Thereby, the boron carbide powder is fired to obtain boron carbonitride powder.

[0026] The atmosphere in the nitriding process is an atmosphere that allows the nitriding reaction to proceed. For example, it may be nitrogen gas, ammonia gas, etc., and these may be used alone or in combination of two or more. From the viewpoints of ease of nitriding and cost, the atmosphere is preferably nitrogen gas. The content of nitrogen gas in the atmosphere is preferably 95% by volume or more, more preferably 99.9% by volume or more.

[0027] The pressure (atmospheric pressure) in the nitriding process is preferably 0.6 MPa or more, more preferably 0.7 MPa or more, preferably 1.0 MPa or less, more preferably 0.9 MPa or less. The pressure is more preferably 0.7 to 1.0 MPa. The firing temperature in the nitriding process is preferably 1800 °C or more, more preferably 1900 °C or more, preferably 2400 °C or less, more preferably 2200 °C or less. The firing temperature is more preferably 1800 to 2200 °C. Since the pressure conditions and the firing temperature allow the nitriding of boron carbide to proceed more suitably and are also industrially appropriate conditions, preferably, it is 1800 °C or more and 0.7 to 1.0 MPa.

[0028] The firing time (heating time) in the nitriding process is appropriately selected within the range where nitriding proceeds sufficiently, and is preferably 6 hours or more, more preferably 8 hours or more, and may be preferably 40 hours or less, more preferably 30 hours or less.

[0029] Commercially available products may be used for the boron carbonitride powder. That is, the addition process may not include the above-described nitriding process.

[0030] In the addition process, calcium carbonate is added to the boron carbonitride powder to adjust the particle crushing strength.

[0031] In the addition step, calcium carbonate is added to adjust the particle crushing strength of the finally produced boron nitride powder. That is, calcium carbonate is added for a purpose different from the conventionally used purposes, such as as a sintering aid. When using calcium carbonate as a sintering aid, since the boron carbonitride powder only needs to be sufficiently sintered, it is different from the case of using calcium carbonate for the purpose of adjusting the particle crushing strength, and it is not necessary to accurately adjust the addition amount on the order of 1% or less. That is, in the addition step of this manufacturing method, the addition amount of calcium carbonate is adjusted on the order of 1% or less. As the calcium carbonate, commercially available products can be appropriately used.

[0032] In the addition step, in order to make calcium carbonate act uniformly on the boron carbonitride powder, calcium carbonate and boron carbonitride powder may be mixed using a ball mill, a low-frequency resonance acoustic mixer, etc. Thereby, the particle crushing strength can be adjusted more accurately.

[0033] The addition amount of calcium carbonate is adjusted to obtain a desired particle crushing strength. The addition amount of calcium carbonate is not particularly limited, but may be set in the range of 0.125 to 1 part by mass with respect to 100 parts by mass of boron carbonitride. When setting in this range, an appropriate addition amount is set from the range of 0.125 to 1 part by mass according to the desired particle crushing strength. Here, it is important to adjust so that the set addition amount does not vary for adjusting the particle crushing strength. That the set addition amount does not vary means that it is added in the range of the set addition amount ±0.05 part by mass with respect to 100 parts by mass of boron carbonitride. In addition, the appropriate addition amount may be determined in advance by obtaining the relationship between the addition amount of calcium carbonate and the particle crushing strength, or may be determined based on past measurement results. Also, as described below, it may be predicted and determined from the tendency that the smaller the addition amount of calcium carbonate, the greater the particle crushing strength, and the larger the addition amount of calcium carbonate, the smaller the particle crushing strength.

[0034] The addition amount of calcium carbonate may be 0.025 parts by mass or more, 0.075 parts by mass or more, or 0.125 parts by mass or more, and may be 0.45 parts by mass or less, 0.375 parts by mass or less, or 0.325 parts by mass or less with respect to 100 parts by mass of boron carbonitride powder in order to make the particle crushing strength of the boron nitride powder 6 MPa or more, 6.5 MPa or more, or 7 MPa or more.

[0035] The addition amount of calcium carbonate may be 0.375 parts by mass or more, 0.45 parts by mass or more, or 0.5 parts by mass or more, and may be 1 part by mass or less, 0.95 parts by mass or less, or 0.875 parts by mass or less with respect to 100 parts by mass of boron carbonitride powder in order to make the particle crushing strength of the boron nitride powder less than 6 MPa, 5.5 MPa or less, or 5 MPa or less.

[0036] From the viewpoints of facilitating the obtaining of boron nitride powder with a larger particle crushing strength and facilitating the obtaining of boron nitride powder with a smaller variation in particle crushing strength, the addition amount of calcium carbonate is preferably 0.125 parts by mass or more, more preferably 0.15 parts by mass or more, and still more preferably 0.2 parts by mass or more with respect to 100 parts by mass of boron carbonitride powder. From the viewpoints of facilitating the obtaining of boron nitride powder with a smaller particle crushing strength and facilitating the obtaining of boron nitride powder with a smaller variation in crushing strength, the addition amount of calcium carbonate is preferably 1 part by mass or less, more preferably 0.9 parts by mass or less, and still more preferably 0.88 parts by mass or less with respect to 100 parts by mass of boron carbonitride powder. There is a tendency that when the addition amount of calcium carbonate is decreased, the particle crushing strength can be adjusted in a larger range, and when the addition amount is increased, the particle crushing strength can be adjusted in a smaller range.

[0037] In the addition step, a boron source may be further added in addition to the boron carbonitride powder. Examples of the boron source include boric acid, boron oxide, or a mixture thereof.

[0038] The addition ratio of the boron source to the amount of boron carbonitride powder may be appropriately selected. The ratio of the boron source may be, for example, 100 parts by mass or more, preferably 150 parts by mass or more, based on 100 parts by mass of the boron carbonitride powder, and may be, for example, 300 parts by mass or less, preferably 250 parts by mass or less.

[0039] In the addition step, other additives used in the art may be further added to the boron carbonitride powder as necessary.

[0040] Next, the above-described boron carbonitride powder (including the boron carbonitride powder to which a boron source or the like is added) is decarburized by heating in the presence of calcium carbonate to obtain a boron nitride powder (decarburization step). In the decarburization step, aggregated particles of boron nitride can be obtained in which primary particles of decarburized and further crystallized boron nitride (the primary particles are flaky hexagonal boron nitride) are aggregated.

[0041] The atmosphere in the decarburization step may be, for example, nitrogen gas, ammonia gas, or the like, and may be a single one of these or a combination of two or more thereof. From the viewpoints of ease of decarburization and cost, the atmosphere is preferably nitrogen gas. The content of nitrogen gas in the atmosphere is preferably 95% by volume or more, more preferably 99.9% by volume or more.

[0042] The pressure (atmospheric pressure) in the decarburization step may be normal pressure (atmospheric pressure) or a pressure higher than normal pressure. When it is a pressurized pressure, the pressure may be, for example, 0.5 MPa or less, or 0.3 MPa or less.

[0043] In the decarburization process, for example, first, the boron carbonitride powder is heated to a predetermined temperature (a temperature at which decarburization can start), and then further heated to the holding temperature at the predetermined temperature. The predetermined temperature (a temperature at which decarburization can start) can be set according to the system, and for example, it may be 1000 °C or higher, may be 1500 °C or lower, and preferably is 1200 °C or lower. The rate of temperature increase from the predetermined temperature (a temperature at which decarburization can start) to the holding temperature may be, for example, 5 °C / min or lower, and preferably may be 4 °C / min or lower, 3 °C / min or lower, or 2 °C / min or lower.

[0044] From the viewpoint that particle growth easily occurs favorably and the thermal conductivity of the obtained boron nitride powder can be improved, the holding temperature is preferably 1600 °C or higher, more preferably 1800 °C or higher. The holding temperature is preferably 2200 °C or lower, more preferably 2100 °C or lower.

[0045] The holding time at the holding temperature is appropriately selected within the range where crystallization sufficiently proceeds. For example, it may be more than 0.5 hours. From the viewpoint that particle growth easily occurs favorably, it is preferably 1 hour or longer, more preferably 3 hours or longer, and still more preferably 5 hours or longer. The holding time at the holding temperature may be, for example, less than 40 hours. From the viewpoint that it is possible to reduce the excessive progress of particle growth and the decrease in crushing strength, and also reduce industrial inconveniences, it is preferably 30 hours or shorter, more preferably 20 hours or shorter.

[0046] In the decarburization process, it is preferable to set the rate of temperature increase to the holding temperature within the range of 5 °C / min or lower so that the heat applied to the boron carbonitride particles is uniform, and to set the holding time within the range of 1 hour or longer and 30 hours or shorter. If the rate of temperature increase is slow and the holding time is long, heat is applied more uniformly, and the variation in the particle crushing strength of the aggregated particles can be suppressed.

[0047] The boron nitride powder obtained in this way is a powder having aggregated particles in which primary particles are aggregated. A classification step (classification step) may be performed on the boron nitride powder so that a boron nitride powder having a desired particle size distribution can be obtained by sieving as necessary.

[0048] In the boron nitride powder obtained by the manufacturing method described above, the particle crushing strength of the agglomerated particles is adjusted by adjusting the addition amount of calcium carbonate. Therefore, according to the manufacturing method described above, agglomerated particles having a desired particle crushing strength can be obtained, and further, boron nitride powder having a desired crushing strength can be obtained. Conventionally, as a factor affecting the particle crushing strength, the addition amount of the boron source is known. However, by adjusting the addition amount of calcium carbonate, carbon is less likely to remain in the boron nitride powder than by adjusting the addition amount of the boron source, and the yield of the boron nitride powder can be increased.

[0049] The average particle size of the boron nitride powder is not particularly limited, but may be 2 μm or more, 4 μm or more, 6 μm or more, or 8 μm or more, and may be 40 μm or less, 30 μm or less, 20 μm or less, or 15 μm or less. The average particle size may be larger than 40 μm, 45 μm or more, 50 μm or more, or 55 μm or more, and may be 100 μm or less, 80 μm or less, or 75 μm or less. The average particle size of the boron nitride powder is measured using a laser diffraction scattering particle size distribution measuring device (LS-13 320) manufactured by Beckman Coulter without applying a homogenizer to the sample before the measurement process, and is the particle size (median diameter, D50) at a cumulative value of 50% of the cumulative particle size distribution.

[0050] The particle crushing strength in the boron nitride powder may be 1 MPa or more, 1.5 MPa or more, or 2 MPa or more, and may be 20 MPa or less, 15 MPa or less, or 10 MPa or less. When the average particle size of the boron nitride powder is 40 μm or less, the particle crushing strength may be 1 MPa or more, 1.5 MPa or more, or 2 MPa or more, and may be 10 MPa or less, 7 MPa or less, or 5 MPa or less. When the average particle size of the boron nitride powder exceeds 40 μm, the particle crushing strength may be 1 MPa or more, 3 MPa or more, 5 MPa or more, or 7 MPa or more, and may be 20 MPa or less, 15 MPa or less, or 10 MPa or less.

[0051] The crushing strength of the boron nitride powder (the strength at which the cumulative fracture rate is 63.2%) may be 1 MPa or more, 1.5 MPa or more, or 2 MPa or more, and may be 20 MPa or less, 15 MPa or less, or 10 MPa or less.

[0052] Another embodiment of the present invention includes a decarbonization step of heating boron carbonitride powder in the presence of calcium carbonate to obtain boron nitride powder. In the decarbonization step, by adjusting the addition amount of calcium carbonate, it can be said that a method for adjusting the particle crushing strength of boron nitride powder (a method for adjusting the particle crushing strength) is provided. The detailed aspects of the decarbonization step are as described above. By this method, it becomes easy to adjust the particle crushing strength of boron nitride powder within a desired range.

[0053] Further, according to the above-described production method, by adjusting the addition amount of calcium carbonate in the decarbonization step, boron nitride powder with reduced variation in particle crushing strength can be obtained. The variation in particle crushing strength in boron nitride powder means that the standard deviation of the particle crushing strength between agglomerated particles contained in the boron nitride powder is small.

[0054] Since the boron nitride powder in this specification refers to that obtained from the same production lot, the fact that the variation in particle crushing strength in this boron nitride powder is small means that the variation in agglomerated particles within the same production lot of boron nitride powder is small. Note that the production lot in this specification refers to boron nitride powder produced at once by a series of processes using the same equipment according to the above-described production method.

[0055] Another embodiment of the present invention can be a boron nitride powder having a standard deviation of particle crushing strength of 3 MPa or less. That is, this boron nitride powder is boron nitride powder from the same production lot, and the standard deviation of the particle crushing strength between agglomerated particles is 3 MPa or less. The standard deviation of the particle crushing strength between agglomerated particles is obtained by taking out 20 agglomerated particles from the boron nitride powder obtained by the above-described production method, measuring the particle crushing strength of each particle, and then calculating the standard deviation.

[0056] In this boron nitride powder, the standard deviation of the particle crushing strength is 3 MPa or less, and may also be 2.9 MPa or less, 2.5 MPa or less, 2.3 MPa or less, or 2 MPa or less. When the average particle size of the boron nitride powder is 40 μm or less, the standard deviation of the particle crushing strength of the boron nitride powder may be 3 MPa or less, 2.5 MPa or less, 2 MPa or less, or 1.7 MPa or less. When the average particle size of the boron nitride powder exceeds 40 μm, the standard deviation of the particle crushing strength of the boron nitride powder may be 3 MPa or less, 2.9 MPa or less, or 2.5 MPa or less. Increasing the addition amount of calcium carbonate tends to reduce the above standard deviation.

[0057] Furthermore, according to the above-described production method, by adjusting the addition amount of calcium carbonate in the decarbonization step, it is possible to suppress the variation in the particle crushing strength even between boron nitride powders of different production lots.

[0058] Another embodiment of the present invention is a set composed of a plurality of aggregates, wherein the plurality of aggregates each have boron nitride powder of different production lots, and the standard deviation of the particle crushing strength of the boron nitride powder in the set is 3 MPa or less, which can be referred to as a set.

[0059] The set according to one embodiment is composed of a plurality of aggregates. The plurality of aggregates each have boron nitride powder obtained by the above-described production method, and the plurality of aggregates each have boron nitride powder of different production lots.

[0060] In this set, the first aggregate among the plurality of aggregates constituting the set has boron nitride powder of one production lot obtained by the above-described production method.

[0061] In one embodiment, the first aggregate may be composed of only boron nitride powder of one production lot (referred to as lot A). In this case, the first aggregate may be composed of the boron nitride powder of lot A contained in one packaging bag or the like, or may be composed of a group of the boron nitride powder of lot A separately contained in a plurality of packaging bags or the like.

[0062] In another embodiment, the first aggregate may be a mixture (referred to as mixture A) of the boron nitride powder of lot A and the boron nitride powder of one or more production lots different from lot A. In this case, the first aggregate may be composed of the boron nitride powder of mixture A contained in one packaging bag or the like, or may be composed of a group of the boron nitride powder of mixture A separately contained in a plurality of packaging bags or the like.

[0063] In each embodiment, the second aggregate among the plurality of aggregates has boron nitride powder of at least a lot (lot B) different from lot A. The "production lot different from lot A" means a lot that is manufactured at a different time from lot A although the production conditions are set the same as those of lot A and are manufactured with the same equipment or the like. The same meaning applies to expressions such as "production lot different from lot B".

[0064] The second aggregate may be composed of only the boron nitride powder of lot B. In this case, the second aggregate may be composed of the boron nitride powder of lot B contained in one packaging bag or the like, or may be composed of a group of the boron nitride powder of lot B separately contained in a plurality of packaging bags or the like.

[0065] Alternatively, the second aggregate may be a mixture (mixture B) of the boron nitride powder of lot B and the boron nitride powder of one or more production lots different from lot B. In this case, the second aggregate may be composed of mixture B contained in one packaging bag or the like, or may be composed of a group of mixture B contained in a plurality of packaging bags or the like. As long as the first aggregate and the second aggregate are not exactly the same, mixture B may contain the boron nitride powder of lot A.

[0066] In this embodiment, the set may further include other aggregates (a third aggregate, a fourth aggregate, etc.). At this time, the relationship between each aggregate is the same as the relationship between the first aggregate and the second aggregate described above.

[0067] In the set described above, since it has boron nitride powder manufactured by the manufacturing method described above, it is possible to reduce the variation in the particle crushing strength of the boron nitride powder among a plurality of aggregates. That is, in this set, the standard deviation of the particle crushing strength between each aggregate can be made 3 MPa or less.

[0068] The particle crushing strength in the set is obtained by taking out 20 aggregated particles of boron nitride powder from each of the aggregates constituting the set, measuring the particle crushing strength of all the particles, and then calculating the standard deviation.

[0069] The standard deviation of the particle crushing strength in the set is 3 MPa or less, and may be 2.9 MPa or less, 2.5 MPa or less, 2.3 MPa or less, or 2 MPa or less.

[0070] The standard deviation of the particle crushing strength in the set may be 3 MPa or less, 2.5 MPa or less, 2 MPa or less, or 1.7 MPa or less when the average particle diameter of the boron nitride powder is 40 μm or less. The standard deviation of the particle crushing strength in the set may be 3 MPa or less, 2.9 MPa or less, or 2.5 MPa or less when the average particle diameter of the boron nitride powder exceeds 40 μm.

[0071] Note that the set exists in the form of a plurality of packages for, for example, boron nitride powder of the same product, and a state where a plurality of packages are stored in a spatially proximate manner in a warehouse or the like corresponds to a set. Also, even if there is no situation where a plurality of aggregates exist simultaneously in terms of time, if the same manufacturing entity manufactures a plurality of aggregates and immediately transports each aggregate after manufacturing, it also corresponds to the manufacture of a set. Further, even if the packages transported from a warehouse, a manufacturing factory, or the like are subsequently stored as raw materials for the same product, for example, it corresponds to a set. Also, even if not simultaneously in terms of time, if a plurality of packages are purchased or the like for the manufacture of the same product, it corresponds to the purchase or the like of a set.

[0072] Using the boron nitride powder described above and a set composed of a plurality of aggregates having the boron nitride powder, a resin composition filled with the boron nitride powder can be manufactured. When boron nitride powder having an adjusted particle crushing strength and having a predetermined particle crushing strength is combined with boron nitride powder having a stronger particle crushing strength and filled into a resin for use as a resin composition, a resin composition having desired properties can be stably manufactured.

Example

[0073] Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to the following examples.

[0074] <Example 1> [Production of boron carbonitride 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 filled 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 massive boron carbide (B 4 C) powder. The synthesized massive boron carbide powder was pulverized with a ball mill for 1 hour and sieved to a particle size of 75 μm or less using a sieve. The sieved boron carbide powder was further washed with an aqueous nitric acid solution to remove impurities such as iron content, and filtered and dried to obtain boron carbide powder having an average particle size of 39.9 μm (B4 C powder) was prepared.

[0075] The prepared boron carbide powder was filled into a boron nitride crucible. Using a resistance heating furnace, the boron carbide powder was heated for 20 hours under the conditions of 2000 °C and 0.85 MPa in an atmosphere of nitrogen gas, whereby boron carbonitride (B 4 CN 4 ) powder was obtained.

[0076] [Preparation of Boron Nitride Powder] To 40 parts by mass of boron carbonitride powder and 60 parts by mass of boric acid, calcium carbonate in an amount of 0.125% by mass based on 100 parts by mass of the boron carbonitride powder was added, and these were mixed by a Henschel mixer. This mixture was filled into a boron nitride crucible and decarburized by heating using a resistance heating furnace to synthesize boron nitride powder having agglomerated particles in which primary particles were agglomerated. As the heating conditions, in an atmosphere of nitrogen gas at normal pressure, the temperature was raised from room temperature to 1000 °C at a rate of 10 °C / min and from 1000 °C at a rate of 0.5 °C / min, and the holding temperature was 2000 °C and the holding time was 5 hours. The synthesized boron nitride powder was pulverized 10 times with a mortar and then classified using a nylon sieve with a mesh size of 75 μm. Thereby, boron nitride powder having an average particle size of 55.8 μm (also referred to as "BN powder") was obtained.

[0077] [Preparation of Another Lot] Another lot of boron nitride powder was prepared by the method of Example 1. A total of 3 lots of boron nitride powder were obtained.

[0078] [Examples 2 to 7] Boron carbide powder (B as a raw material 4 C powder) and / or the amount of calcium carbonate added were changed as shown in Table 1, and boron nitride powder was prepared by the same method as in Example 1. In any of Examples 2 to 7, 3 lots of boron nitride powder were prepared each.

[0079] [Measurement of Particle Crushing Strength] Regarding the boron nitride powder according to the examples, the particle crushing strength was measured in accordance with JIS R1639-5:2007. As the measuring device, a micro compression tester (MCT-W500, manufactured by Shimadzu Corporation) was used. The particle crushing strength (σ: unit MPa) was measured using the formula σ = α × P / (π × d2), where α is a dimensionless number (α = 2.48) that varies depending on the position within the particle, P is the crushing test force (unit N), and d is the particle diameter (unit μm). For each lot of each example, the particle crushing strength was measured for 20 aggregated particles each. Also, from the measured particle crushing strengths of the 20 particles, the value at the point of 63.2% cumulative fracture rate was calculated as the crushing strength of the boron nitride powder.

[0080] Table 1 shows the values of the crushing strength of the boron nitride powder at the point of 63.2% cumulative fracture rate. As shown in Table 1, it was found that in the production of boron nitride powder, by adjusting the addition amount of calcium carbonate, the particle crushing strength can be adjusted, and thus the crushing strength of the boron nitride powder can be adjusted.

[0081] Next, in each example, the standard deviation of the particle crushing strengths of 20 aggregated particles of the same lot was calculated. The results are shown in Table 1. In each example, since the standard deviations within each of the three lots were values that could be considered equivalent (±0.2), one representative value was shown. As shown in Table 1, for the boron nitride powder according to the examples, the variation in the particle crushing strength of the boron nitride powder within the same production lot was small. It was found that in Examples 1 and 2, the crushing strengths of the boron nitride powder were equivalent, but in Example 2 where the addition amount of calcium carbonate was increased, the standard deviation was smaller than that in Example 1, and the variation in the particle crushing strength became even smaller.

[0082] Also, in each example, the boron nitride powder of the first lot was used as the first aggregate, the boron nitride powder of the second lot was used as the second aggregate, and the boron nitride powder of the third lot was used as the third aggregate to form a set of boron nitride powders composed of three aggregates. Twenty agglomerated particles were taken out from each of the aggregates, and the standard deviation of the particle crushing strength (the standard deviation of a total of 60 particles) was calculated as the standard deviation within the set (the standard deviation between the aggregates). As a result, the standard deviation between the aggregates in each example was a value equivalent (±0.2) to the standard deviation within the lot described above.

[0083] On the other hand, one lot of boron nitride powder produced by the method of Example 2 was used as the first aggregate, one lot of boron nitride powder produced by the method of Example 3 was used as the second aggregate, and one lot of boron nitride powder produced by the method of Example 4 was used as the third aggregate to form a set of boron nitride powders composed of three aggregates. Twenty agglomerated particles were taken out from each of the aggregates, and the standard deviation of the particle crushing strength (the standard deviation of a total of 60 particles) was calculated as the standard deviation within the set (the standard deviation between the aggregates). As a result, it was 3.3. That is, in the production of boron nitride powder, it was found that by finely adjusting the addition amount of calcium carbonate, the variation in the particle crushing strength can be reduced in a set composed of a plurality of aggregates having boron nitride powders of different production lots.

[0084] Regarding Example 1, when a resin composition was produced using the boron nitride powders of the above three production lots separately, a resin composition having desired properties was obtained under the same production conditions. On the other hand, in Example 5, a resin composition could be obtained in the same manner using the boron nitride powders of three production lots. However, since the particle crushing strength was different from that of Example 1, the production conditions were different. Considering that it is substantially very difficult to produce a resin composition while finely changing the production conditions, it can be said that a resin composition having desired properties can be stably produced by adjusting the particle crushing strength by the addition amount of calcium carbonate.

[0085]

Table 1

Claims

1. A decarbonization step of heating boron carbonitride powder in the presence of calcium carbonate to obtain boron nitride powder, A method of adjusting the particle crushing strength of the boron nitride powder by adjusting the addition amount of the calcium carbonate in the decarbonization step.

2. A step of adding calcium carbonate to the boron carbonitride powder to adjust the particle crushing strength, and A step of heating and decarbonizing the boron carbonitride powder in the presence of the calcium carbonate, a method for producing boron nitride powder.

3. The production method according to claim 2, wherein in the step of adding the calcium carbonate, the calcium carbonate is added so as to be 0.125 to 1 part by mass with respect to 100 parts by mass of the boron carbonitride powder.

4. Boron nitride powder having a particle crushing strength of 2 MPa or more and a standard deviation of the particle crushing strength of 3 MPa or less.

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