TW202124261A - Method for adjusting particle crushing strength of boron nitride powder, boron nitride powder and method for producing same - Google Patents

Abstract

One aspect of the invention provides a method for adjusting the particle crushing strength of a boron nitride powder, the method including a decarbonization step of obtaining a boron nitride powder by heating a boron carbonitride powder in the presence of calcium carbonate, wherein in the decarbonization step, the amount of calcium carbonate added is adjusted.

Description

Method for adjusting particle compressive strength of boron nitride powder, boron nitride powder and manufacturing method thereof

The invention relates to a method for adjusting the compressive strength of particles of boron nitride powder, boron nitride powder and a manufacturing method thereof.

In electronic components such as power components, transistors, thyristors, and CPUs, it is a problem to effectively dissipate heat generated during use. To solve this problem, in the past, "high thermal conductivity of the insulating layer of the printed circuit board on which electronic components are mounted", or electronic components or printed circuit boards are mounted on the thermal interface material (Thermal Interface Materials) with electrical insulation heat sink. In such insulating layer and thermal interface materials, ceramic powder with high thermal conductivity is used.

The boron nitride powder, which has the characteristics of high thermal conductivity, high insulation, and low relative permittivity, is attracting attention as a ceramic powder. For example, Patent Document 1 discloses a kind of Hexagonal Boron Nitride powder, as "the shape of the agglomerate is further spheroidized to increase the filling property, and the strength of the powder is improved, and further by Hexagonal boron nitride powder with high purity and improved insulation and stabilized withstand voltage for heat transfer sheets filled with the powder has an average primary particle length-to-thickness ratio of 5-10. The size of the aggregates of the particles is 2 μm or more and 200 μm or less in the average particle diameter (D50), and the bulk density is 0.5 to 1.0 g/cm ³ .

In the hexagonal boron nitride particles, the thermal conductivity in the in-plane direction (a-axis direction) is 400W/(m·K), and the thermal conductivity in the thickness direction (c-axis direction) is 2W/(m·K). The thermal conductivity of the crystalline structure and the scaly shape has a large anisotropy. Furthermore, if the hexagonal boron nitride powder is filled in the resin, the particles will be oriented in the same direction. Therefore, for example, when manufacturing thermal interface materials, the in-plane direction (a-axis direction) of the hexagonal boron nitride particles becomes perpendicular to the thickness direction of the thermal interface material, and the in-plane direction (a-axis direction) of the hexagonal boron nitride particles cannot be fully utilized. (Axial direction) high thermal conductivity.

On the other hand, Patent Document 2 describes the following: In the boron nitride aggregated particles formed by the aggregation of boron nitride primary particles, the strength is increased to suppress the collapse of the aggregated particles even at a predetermined molding pressure. To the extent that it is bad, the primary particles of boron nitride are prevented from oriented in the same direction. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] JP 2011-98882 A [Patent Document 2] JP 2016-135731 A

[The problem to be solved by the invention]

In the boron nitride agglomerated particles formed by agglomerating primary particles as disclosed in Patent Document 2, in order to prevent the primary particles from being oriented in the same direction and reducing the thermal conductivity, we believe that it is important to increase the strength of the agglomerated particles. On the other hand, according to the investigation conducted by the present inventors, in order to obtain boron nitride aggregated particles with desired characteristics, not only agglomerated particles with greater strength (compressive strength), but also agglomerated particles with appropriate strength can be combined and added. Use also has its effect.

That is, in the past, the study focused on improving the strength of the boron nitride aggregated particles, but we have found that a technique for obtaining the appropriate strength of aggregated particles for combination with high-strength aggregated particles is also needed. However, since the degree of the appropriate strength combined with the strength of the high-strength agglomerated particles changes according to the strength of the high-strength agglomerated particles, a technique capable of adjusting the strength of the agglomerated particles with high precision is required.

In addition, an object of one aspect of the present invention is to provide a new method for adjusting the compressive strength of particles of boron nitride powder. [Technical means to solve the problem]

The inventors of this case have investigated many factors that affect the compressive strength of the agglomerated particles and found that when the carbon boron nitride powder is heated in the presence of calcium carbonate to obtain boron nitride powder, the addition amount of calcium carbonate can be adjusted. It is easier to adjust the particle compressive strength of the boron nitride powder produced, thus completing the present invention.

One aspect of the present invention provides a method for adjusting the compressive strength of particles of boron nitride powder, which comprises the following steps: a decarburization step, heating the carbon boron nitride powder in the presence of calcium carbonate to obtain boron nitride powder ; In the decarburization step, the particle compressive strength of the boron nitride powder is adjusted by adjusting the amount of calcium carbonate added.

Another aspect of the present invention provides a method for manufacturing boron nitride powder, which includes the steps of: adding calcium carbonate to the boron carbonitride powder in order to adjust the compressive strength of particles; and adding calcium carbonate to the boron nitride powder in the presence of calcium carbonate The step of decarburizing the boron carbonitride powder by heating.

In this manufacturing method, in the step of adding calcium carbonate, calcium carbonate may be added so as to be 0.125 to 1 part by mass with respect to 100 parts by mass of the boron carbonitride powder.

Another aspect of the present invention provides a boron nitride powder, the standard deviation of the compressive strength of the particles is below 3 MPa.

Another aspect of the present invention is to provide a set, which is composed of a plurality of aggregates, and the plurality of sets respectively have boron nitride powders of different manufacturing batches, and the particles of the boron nitride powder in the set are The standard deviation of compressive strength is below 3MPa. [Effects of the invention]

According to one aspect of the present invention, a new method for adjusting the compressive strength of particles of boron nitride powder can be provided.

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

The boron nitride powder in this specification refers to a collection of aggregated particles (also called block particles) formed by the agglomeration of primary particles of boron nitride (bulk boron nitride powder), and refers to the same manufacturing batch (The details will be described later). The primary particles of boron nitride are preferably scaly hexagonal boron nitride particles, for example.

In this specification, particle compressive strength refers to the compressive strength of aggregated particles. The compressive strength of particles (σ: unit MPa) can be measured in accordance with JIS R1639-5, and the formula ^{σ=α×P/(π×d 2) can be used.} It is calculated by the number of times (α=2.48), the compressive test force (P: unit N), and the particle diameter (d: unit μm). The compressive strength (compressive strength of the powder as a whole) of the boron nitride powder can be obtained by the following method: measure the particle compressive strength of agglomerated particles of 20 particles, and use the strength when the cumulative damage rate becomes 63.2% as the nitrogen Compressive strength of boron powder. In the above formula for obtaining the compressive strength of particles, the compressive test force can be measured using a micro-compression tester (for example, MCT-W500 manufactured by Shimadzu Corporation).

The boron nitride powder according to one embodiment of the present invention is obtained by a manufacturing method having the following steps: a step of adding calcium carbonate to boron carbonitride (B ₄ CN ₄ ) in order to adjust the compressive strength of particles (Addition step); and a step of decarburizing by heating the carbon boron nitride powder in the presence of calcium carbonate (decarburization step).

In one embodiment of the present invention, the adding step includes _{the step of calcining boron carbide (B 4} C) powder to obtain boron carbonitride powder (nitriding step).

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

The carbon element content of the boron carbide powder is desirably smaller than the compositional B ₄ C (21.7 mass %). The amount of carbon element is preferably 18% by mass or more, more preferably 19% by mass or more, and preferably 20.5% by mass or less. If the amount of carbon element is 18% by mass or more, the deviation from the theoretical composition is small, so it is relatively stable. By making the amount of carbon element 20.5% by mass or less, the amount of carbon element volatilized during the decarburization step described later can be reduced, and dense agglomerated particles can be obtained. The carbon element content of the boron carbide powder can be measured with a carbon element analyzer (for example, Model IR-412 manufactured by LECO).

The boron carbide powder can be obtained by a conventional manufacturing method. For example, after mixing boric acid and acetylene black, it is heated at 1800-2400°C for 1-10 hours in a passive gas environment to obtain boron carbide blocks. After crushing the boron carbide block, properly sieving, washing, removing impurities, drying, etc., boron carbide powder can be obtained. Commercial products can also be used as boron carbide powder.

In the nitriding step, the boron carbide powder is heated under a nitrogen atmosphere and under pressure. In this way, the boron carbide powder is calcined to obtain boron carbide nitride powder.

In the nitriding step, the ambient gas system that advances the nitridation reaction is preferably, for example, nitrogen gas, ammonia gas, etc., and these gases are preferably used singly or in combination of two or more. From the viewpoint of easier nitriding and cost, the ambient gas is preferably nitrogen. The content of nitrogen in the ambient gas is preferably 95% by volume or more, more preferably 99.9% by volume or more.

The pressure (ambient pressure) in the nitriding step is preferably 0.6 MPa or more, more preferably 0.7 MPa or more, preferably 1.0 MPa or less, and more preferably 0.9 MPa or less. The pressure is still more preferably 0.7 to 1.0 MPa. The calcining temperature in the nitriding step is preferably 1800°C or higher, more preferably 1900°C or higher, preferably 2400°C or lower, and more preferably 2200°C or lower. The calcining temperature is still more preferably 1800-2200°C. The pressure conditions and the calcination temperature are such that the nitridation of boron carbide can progress more appropriately, and from the viewpoint of industrially appropriate conditions, it is preferably 1800° C. or higher and 0.7 to 1.0 MPa.

The calcining time (heating time) in the nitriding step is suitably selected within the range where the nitriding can fully progress, preferably 6 hours or more, more preferably 8 hours or more, preferably 40 hours or less, more preferably 30 Less than hours.

Commercially available products can also be used as the boron carbonitride powder. That is, the adding step may not include the above-mentioned nitriding step.

In the adding step, calcium carbonate is added to the boron carbonitride powder in order to adjust the compressive strength of the particles.

In the adding step, calcium carbonate is added in order to adjust the particle compressive strength of the boron nitride powder finally manufactured. That is, calcium carbonate is added for a purpose different from "the purpose of conventional use, such as the purpose of a sintering aid". In the case of using calcium carbonate as a sintering aid, it is only necessary to fully sinter the boron carbonitride powder. Therefore, unlike the case of using calcium carbonate for the purpose of adjusting the compressive strength of the particles, it is not necessary to precisely adjust the addition amount. Adjust to the order of less than 1%. That is, in the adding step in this manufacturing method, the addition amount of calcium carbonate is adjusted to the order of 1% or less. Regarding calcium carbonate, commercially available products can be suitably used.

In the adding step, in order to make calcium carbonate uniformly act on the boron carbonitride powder, a ball mill, a low-frequency resonance acoustic wave mixer, etc. may be used to mix the calcium carbonate and the boron carbonitride powder. In this way, the compressive strength of the particles can be adjusted more accurately.

The amount of calcium carbonate added is adjusted in order to obtain the desired compressive strength of the particles. The addition amount of calcium carbonate is not particularly limited, but it is preferably set in the range of 0.125 to 1 part by mass relative to 100 parts by mass of boron carbonitride. In the case of setting in this range, an appropriate addition amount is set from the range of 0.125 to 1 part by mass in accordance with the desired compressive strength of the particles. In order to adjust the compressive strength of the particles here, the key point is to make adjustments in such a way that the set addition amount does not change. So that the set addition amount does not change means that the addition is performed within the range of ±0.05 parts by mass relative to 100 parts by mass of carbon boron nitride. In addition, the relationship between the addition amount of calcium carbonate and the compressive strength of the particles may be determined in advance to determine the appropriate addition amount, or it may be determined based on past measurement results. In addition, as described below, it is also possible to predict and decide from the tendency that the smaller the addition amount of calcium carbonate, the greater the particle compressive strength, and the larger the addition amount of calcium carbonate, the lower the particle compression strength.

In order to make the particle compressive strength of the boron nitride powder 6MPa or more, 6.5MPa or more, or 7MPa or more, the amount of calcium carbonate added relative to 100 parts by mass of the carbon boron nitride powder is preferably 0.025 parts by mass or more and 0.075 parts by mass Or more, or 0.125 parts by mass or more, preferably 0.45 parts by mass or less, 0.375 parts by mass or less, or 0.325 parts by mass or less.

In order to make the particle compressive strength of boron nitride powder less than 6MPa, 5.5MPa or less, or 5MPa or less, the amount of calcium carbonate added to 100 parts by mass of carbon boron nitride powder is preferably 0.375 parts by mass or more and 0.45 parts by mass Part or more, or 0.5 part by mass or more, preferably 1 part by mass or less, 0.95 parts by mass or less, or 0.875 parts by mass or less.

From the point of view that it is easier to obtain boron nitride powder with higher particle compressive strength, and from the point of view that it is easier to obtain boron nitride powder with less variation in particle compressive strength, the amount of calcium carbonate added is relative to that of carbonitride 100 parts by mass of the boron powder 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. From the point of view that it is easier to obtain boron nitride powder with smaller particle compressive strength, and from the point of view that it is easier to obtain boron nitride powder with less variation in compressive strength, the amount of calcium carbonate added is relative to that of carbon boron nitride. 100 parts by mass of the powder 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. If the amount of calcium carbonate added is small, it will tend to be adjusted in the range where the compressive strength of the particles is larger. If the amount added is larger, it may be adjusted in the range where the compressive strength of the particles is small. Propensity.

In the adding step, in addition to the carbon boron nitride powder, a boron source can also be added. Examples of the boron source include boric acid, boron oxide, or a mixture of these.

The addition ratio of the boron source relative to the amount of carbon boron nitride powder should be appropriately selected. The ratio of the boron source relative to 100 parts by mass of the carbon boron nitride powder is, for example, preferably 100 parts by mass or more, preferably 150 parts by mass or more, and for example, 300 parts by mass or less, and preferably 250 parts by mass or less.

In the adding step, other additives used in the technical field may be further added to the carbon boron nitride powder as needed.

Next, the above-mentioned carbon boron nitride powder (including the carbon boron nitride powder to which a boron source or the like has been added) is heated in the presence of calcium carbonate to perform decarburization to obtain boron nitride powder (decarburization step). In the decarburization step, agglomerated particles of boron nitride formed by agglomeration of decarburized and further crystallized primary particles of boron nitride (primary particles are scaly hexagonal boron nitride) can be obtained.

The ambient gas in the decarburization step is preferably, for example, nitrogen gas, ammonia gas, etc., preferably one of these alone or a combination of two or more of them. From the viewpoint of ease of decarburization and cost, the ambient gas is preferably nitrogen. The nitrogen content in the ambient gas is preferably 95% by volume or more, more preferably 99.9% by volume or more.

The pressure (ambient pressure) in the decarburization step is preferably normal pressure (atmospheric pressure), and may also be a pressure after being pressurized from normal pressure. In the case of the pressurized pressure, the pressure is preferably 0.5 MPa or less or 0.3 MPa or less, for example.

In the decarburization step, for example, first, the carbon boron nitride powder is raised to a predetermined temperature (a temperature at which decarburization can be started), and then the predetermined temperature is further raised to the holding temperature. The predetermined temperature (the temperature at which decarburization can be started) can be set according to the system, for example, preferably 1000°C or higher, preferably 1500°C or lower, and preferably 1200°C or lower. The rate of temperature rise from the predetermined temperature (the temperature at which decarburization can start) to the holding temperature is, for example, preferably 5°C/min or less, preferably 4°C/min or less, or 3°C/min or less, or 2°C/min. The following points.

From the viewpoint of easier and good particle growth and improvement of the thermal conductivity of the obtained boron nitride powder, 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.

The holding time in the holding temperature is appropriately selected within the range where the crystallization can fully progress. For example, it is preferably more than 0.5 hours. From the viewpoint of easier and good particle growth, it is preferably 1 time or more, more preferably 3 More than time, more preferably more than 5 hours. The holding time in the holding temperature is preferably less than 40 hours, for example, since the particle growth can progress and the decrease in compressive strength can be reduced, and from the viewpoint of reducing industrial inconvenience, it is preferably 30 hours. Hereinafter, it is more preferably 20 hours or less.

In the decarburization step, in order to make the heat applied to the carbon boron nitride particles uniform, the heating rate up to the holding temperature is preferably set in the range of 5°C/min or less, and the holding time is preferably set at Within the range of 1 hour to 30 hours. If the heating rate is slower and the holding time is longer, the heat can be applied more uniformly, and the fluctuation of the particle compressive strength of the aggregated particles can be suppressed.

The boron nitride powder obtained in this way is a powder having aggregated particles formed by agglomeration of primary particles. A step of classifying the boron nitride powder (classification step) may also be performed as needed to obtain boron nitride powder having a desired particle size distribution by sieving.

In the boron nitride powder obtained by the manufacturing method described above, the particle compressive strength of the agglomerated particles is adjusted by adjusting the addition amount of calcium carbonate. Therefore, according to the above-mentioned manufacturing method, agglomerated particles having a desired particle compressive strength can be obtained, and furthermore, boron nitride powder having a desired compressive strength can be obtained. In the past, as a factor that affects the compressive strength of particles, we are aware of the amount of boron source added. However, compared with adjusting the amount of boron source added, if the amount of calcium carbonate added is adjusted, it will make it difficult for carbon to remain in the boron nitride. In the powder, and improve the yield of boron nitride powder.

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

The compressive strength of the particles in the boron nitride powder is preferably 1 MPa or more, 1.5 MPa or more, or 2 MPa or more, preferably 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 compressive strength may be 1 MPa or more, 1.5 MPa or more, or 2 MPa or more, or 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 compressive strength may be 1 MPa or more, 3 MPa or more, 5 MPa or more, or 7 MPa or more, or 20 MPa or less, 15 MPa or less, or 10 MPa or less.

The compressive strength of the boron nitride powder (the strength at which the cumulative failure rate is 63.2%) is preferably 1 MPa or more, 1.5 MPa or more, or 2 MPa or more, preferably 20 MPa or less, 15 MPa or less, or 10 MPa or less.

Another embodiment of the present invention is a method (a method for adjusting the compressive strength of particles), which may include a decarburization step, in which carbon boron nitride powder is heated in the presence of calcium carbonate to obtain boron nitride powder; In the step, the particle compressive strength of the boron nitride powder is adjusted by adjusting the amount of calcium carbonate added. The detailed aspect of the decarburization step is as described above. With this method, it is easier to adjust the compressive strength of the particles in the boron nitride powder to a desired range.

Furthermore, according to the above-mentioned manufacturing method, by adjusting the addition amount of calcium carbonate in the decarburization step, it is possible to obtain boron nitride powder with suppressed variation in particle compressive strength. The variation of the particle compressive strength of the boron nitride powder means that the standard deviation of the particle compressive strength between the agglomerated particles contained in the boron nitride powder is small.

Since the boron nitride powder in this specification refers to those obtained in the same manufacturing batch, the so-called change in the compressive strength of the particles in the boron nitride powder is small, which means that the boron nitride powder is in the same manufacturing batch. The changes in the condensed particles inside are small. In addition, the manufacturing batch referred to in this specification refers to the boron nitride powder manufactured by the above-mentioned manufacturing method in a series of steps in the same equipment at a time.

Another embodiment of the present invention can be described as boron nitride powder with a standard deviation of particle compressive strength below 3 MPa. That is, the boron nitride powder is boron nitride powder of the same manufacturing batch, and the standard deviation of the particle compressive strength between the agglomerated particles is 3 MPa or less. The standard deviation of the particle compressive strength between the agglomerated particles is obtained by taking 20 particles of agglomerated particles from the boron nitride powder obtained by the above-mentioned manufacturing method, and calculating the standard deviation by measuring the particle compressive strength of each particle And get.

In this boron nitride powder, the standard deviation of the particle compressive strength is 3 MPa or less, and it may be 2.9 MPa or less, 2.5 MPa or less, 2.3 MPa or less, or 2 MPa or less. The standard deviation of the particle compressive 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 is 40 μm or less. The standard deviation of the particle compressive strength of the boron nitride powder may be 3 MPa or less, 2.9 MPa or less, or 2.5 MPa or less when the average particle size of the boron nitride powder exceeds 40 μm. When the amount of calcium carbonate added is increased, there is a tendency to make the above standard deviation smaller.

Furthermore, according to the above-mentioned manufacturing method, by adjusting the addition amount of calcium carbonate in the decarburization step, even in the boron nitride powders of different manufacturing batches, it is possible to suppress variation in particle compressive strength.

Another embodiment of the present invention can be described as a kit, which is composed of a plurality of aggregates, each of the plurality of aggregates has boron nitride powder manufactured in different batches from each other, and the particles of the boron nitride powder in the set are resistant to particles. The standard deviation of compressive strength is below 3MPa.

The set according to one embodiment of the present invention is composed of a plurality of aggregates. Each of the plurality of aggregates has boron nitride powder obtained by the above-mentioned manufacturing method, and each of the plurality of aggregates has boron nitride powders of different manufacturing batches.

In this set, the first aggregate among the plurality of aggregates constituting the set has one manufacturing lot of boron nitride powder obtained by the above-mentioned manufacturing method.

In an embodiment of the present invention, the first assembly is preferably composed of only one manufacturing batch (referred to as batch A) of boron nitride powder. In this case, the first assembly should preferably be composed of the boron nitride powder of batch A placed in a packaging bag, etc., or it can be composed of a group of boron nitride powders of batch A placed in a plurality of packaging bags, etc. Constituted.

In another embodiment of the present invention, the first aggregate may also be the "batch A of boron nitride powder", and the "batch of more than one manufacturing batch of boron nitride powder different from the batch A". Mixture (referred to as Mixture A). In this case, the first assembly is preferably composed of boron nitride powder of mixture A placed in a packaging bag, etc., or it may be composed of a group of boron nitride powders of mixture A placed in a plurality of packaging bags, etc. .

In each embodiment, the second aggregate of the plurality of aggregates has at least a batch of boron nitride powder (batch B) different from that of batch A. The so-called "manufacturing batch different from batch A" means that the manufacturing conditions are set to be the same as batch A and manufactured in the same equipment, but it is a batch manufactured at a different time from batch A. It also means the same meaning in expressions such as "manufacturing batch different from batch B".

The second aggregate is preferably composed only of batch B boron nitride powder. In this case, the second assembly should preferably be composed of the boron nitride powder of batch B placed in one packaging bag, etc., or it may be composed of the group of boron nitride powders of batch B placed in a plurality of packaging bags, etc. Constituted.

Alternatively, the second aggregate may be a mixture of "boron nitride powder of batch B" and "boron nitride powder of one or more manufacturing batches different from batch B" (mixture B). In this case, the second aggregate is preferably composed of the mixture B placed in one packaging bag or the like, and may also be composed of a group of the mixture B placed in a plurality of packaging bags, etc. As long as the first assembly and the second assembly are not completely the same, the batch A boron nitride powder may also be included in the mixture B.

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

Since the set described above has the boron nitride powder produced by the above-mentioned production method, the variation in the particle compressive strength of the boron nitride powder between the plural aggregates can be reduced. That is, in this set, the standard deviation of the compressive strength of the particles between the aggregates can be 3 MPa or less.

The compressive strength of the particles in the set is obtained by taking out 20 agglomerated particles of boron nitride powder from the aggregates constituting the set, measuring the compressive strength of all particles and calculating the standard deviation.

The standard deviation of the compressive strength of the particles in the set is below 3MPa, and can also be below 2.9MPa, 2.5MPa or less, 2.3MPa or less, or 2MPa or less.

The standard deviation of the compressive strength of the particles 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 size of the boron nitride powder is 40 μm or less. The standard deviation of the compressive strength of the particles in the set may be 3 MPa or less, 2.9 MPa or less, or 2.5 MPa or less when the average particle size of the boron nitride powder exceeds 40 μm.

In addition, a set is, for example, a set of boron nitride powders of the same product in the state of a plurality of packages, and a state in which the plurality of packages are placed close to each other and stored in a warehouse or the like is also equivalent to a set. In addition, even if there are no multiple aggregates at the same time in time, the case where the multiple aggregates are manufactured by the same manufacturing body and each aggregate is immediately transported out after manufacturing is equivalent to a manufacturing set. In addition, a package that is moved out from a warehouse, a manufacturing plant, etc., is later stored as a raw material of the same product, which is also equivalent to a set. In addition, even if they are not at the same time in time, purchasing a plurality of packages and the like for manufacturing the same product is equivalent to purchasing a set and the like.

The above-mentioned boron nitride powder and a set composed of a plurality of aggregates having boron nitride powder can be used to produce a resin composition filled with boron nitride powder. If you combine "Boron Nitride powder with particle compressive strength adjusted to have a predetermined particle compressive strength" and "Boron Nitride powder with stronger particle compressive strength" and fill it with resin to use as a resin composition , The resin composition with the desired characteristics can be manufactured stably. [Example]

Hereinafter, the present invention will be explained more specifically based on examples, but the present invention is not limited to the following examples.

<Example 1> [Production of Boron Carbonitride Powder] Using a Hanser mixer, 100 parts by mass of orthoboric acid (manufactured by Nippon Electric Co., Ltd., hereinafter referred to as "boric acid"), and acetylene black (HS100, Denki Kogyo Co., Ltd.) (Manufactured by Denka) 35 parts by mass were mixed and filled in a graphite crucible. The graphite crucible was placed in an electric arc furnace and heated at 2200°C for 5 hours in an argon atmosphere to synthesize bulk boron carbide (B ₄ C) powder. The synthesized bulk boron carbide powder is pulverized by 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, and filtered and dried to produce boron carbide powder (B ₄ C powder) with an average particle diameter of 39.9 μm.

The prepared boron carbide powder is filled into a boron nitride crucible. By using a resistance heating furnace, the boron carbide powder was heated under the conditions of 2000° C. and 0.85 MPa for 20 hours in a nitrogen atmosphere to obtain boron carbonitride (B ₄ CN ₄ ) powder.

[Production of Boron Nitride Powder] To 40 parts by mass of boron carbonitride powder and 60 parts by mass of boric acid, calcium carbonate was added in an amount of 0.125 mass% with respect to 100 parts by mass of boron carbonitride powder, and these were mixed by a Hanse mixer. The mixture is filled into a boron nitride crucible and heated in a resistance heating furnace to decarburize, thereby synthesizing boron nitride powder having aggregated particles formed by agglomeration of primary particles. Regarding the heating conditions, in a nitrogen atmosphere at normal pressure, the temperature rise rate from room temperature to 1000°C is set to 10°C/min, and the temperature rise rate from 1000°C is increased at 0.5°C/min, and the holding temperature is set. It is 2000°C and the holding time is set to 5 hours. The synthesized boron nitride powder was crushed in a mortar for ten minutes, and then classified with a nylon sieve with a mesh size of 75 μm. In this way, boron nitride powder (also referred to as "BN powder") with an average particle diameter of 55.8 μm can be obtained.

＜The production of another batch＞ Another batch of boron nitride powder was produced by the method of Example 1. A total of three batches of boron nitride powder were obtained.

<Examples 2-7> As described in Table 1, in addition to changing _{the average particle size of the raw material, namely the boron carbide powder (B 4} C powder), and/or the addition amount of calcium carbonate, it was implemented by and In the same manner as in Example 1, boron nitride powder was produced. In any of Examples 2-7, three batches of boron nitride powder were produced respectively.

[Measurement of particle compressive strength] For the boron nitride powder according to the examples, the particle compressive strength was measured in accordance with JIS R1639-5:2007. As for the measuring device, a micro compression tester (MCT-W500, manufactured by Shimadzu Corporation) was used. Particle compressive strength (σ: unit MPa), using the formula of σ=α×P/(π×d2), and from the non-factor number (α=2.48) and compressive test that varies according to the position within the particle Force (P: unit N) and particle diameter (d: unit μm) are measured. For one batch of each example, the particle compressive strength was measured for 20 agglomerated particles. Furthermore, from the measured particle compressive strength of 20 particles, the value at the point when the cumulative failure rate was 63.2% was calculated as the compressive strength of the boron nitride powder.

Table 1 shows the value of the compressive strength of the boron nitride powder at the point where the cumulative failure rate is 63.2%. As shown in Table 1, we know that in the manufacture of boron nitride powder, by adjusting the addition amount of calcium carbonate, the particle compressive strength can be adjusted, thereby adjusting the compressive strength of the boron nitride powder.

Next, in each embodiment, the standard deviation of the particle compressive strength of 20 particles of the same batch of agglomerated particles was calculated. The results are shown in Table 1. In each embodiment, since the standard deviation within each of the three batches can be said to be the same (±0.2) value, a representative value is displayed. As shown in Table 1, among the boron nitride powders according to the examples, the particle compressive strength of the boron nitride powders in the same manufacturing batch varies little. We know that in Example 1 and Example 2, the compressive strength of the boron nitride powder is the same, but in Example 2 where the addition amount of calcium carbonate is increased, the standard deviation is smaller than that in Example 1, and the particles The change in compressive strength is smaller.

In addition, in each embodiment, the first batch of boron nitride powder is used as the first aggregate, the second batch of boron nitride powder is used as the second aggregate, and the third batch of boron nitride powder is used as the second aggregate. As the third aggregate, a set of boron nitride powder composed of three aggregates is constituted. Agglomerated particles of 20 particles were taken out from each aggregate, and the standard deviation of particle compressive strength (standard deviation of 60 particles in total) was calculated as the standard deviation in the set (standard deviation between aggregates). As a result, the standard deviation between the aggregates in each example can be said to be the same (±0.2) value as the standard deviation within the batch described above.

On the other hand, the batch of boron nitride powder manufactured by the method of Example 2 is used as the first assembly, and the batch of boron nitride powder manufactured by the method of Example 3 is used as the second assembly. As the third assembly, the boron nitride powder in one batch manufactured by the method of Example 4 was used as the third assembly to form a set of boron nitride powder composed of three assemblies. Take out the aggregated particles of 20 particles from each aggregate, and calculate the standard deviation of the particle compressive strength (standard deviation of 60 particles in total) as the standard deviation (standard deviation between aggregates) in the set, the standard The deviation is 3.3. That is, we know that in the manufacture of boron nitride powder, by finely adjusting the amount of calcium carbonate added, it can be in a set consisting of a plurality of aggregates of boron nitride powders with different manufacturing batches. Reduce the variation of particle compressive strength.

For Example 1, when the above three production batches of boron nitride powder were used to produce the resin composition, the resin composition having the desired characteristics was obtained under the same production conditions. On the other hand, in Example 5, although three manufacturing batches of boron nitride powder can be used in the same manner to obtain a resin composition, since the particle compressive strength is different from that in Example 1, the manufacturing conditions are different. From the point of view of "it is very difficult to make resin composition while changing the manufacturing conditions finely", by adjusting the particle compressive strength through the addition of calcium carbonate, it can be said that it is possible to stably manufacture a resin composition with desired characteristics. Things.

[Table 1] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Average particle size of B ₄ C powder [μm] 39.9 39.9 39.9 39.9 39.9 11.2 11.2 The _{amount of CaCO 3} added [relative to the mass of _{B 4 C100]} 0.125 0.250 0.313 0.500 0.625 0.750 0.875 Average particle size of BN powder [μm] 55.8 60.1 56.4 69.2 65.6 26.7 26.5 Compressive strength of BN powder [MPa] (Weiptu cumulative failure rate 63.2%) 8.9 8.6 7.6 3.6 4.9 2.8 4.1 Standard deviation within the same batch [MPa] 3.0 2.4 2.9 1.4 2.1 1.6 1.6

Claims (5)

A method for adjusting the compressive strength of particles of boron nitride powder, which comprises the following steps: In the decarburization step, the carbon boron nitride powder is heated in the presence of calcium carbonate to obtain boron nitride powder; In the decarburization step, the particle compressive strength of the boron nitride powder is adjusted by adjusting the addition amount of the calcium carbonate. A manufacturing method of boron nitride powder, which comprises the following steps: The step of adding calcium carbonate to the boron carbonitride powder in order to adjust the compressive strength of the particles; and In the presence of the calcium carbonate, the carbon boron nitride powder is heated to perform a decarburization step. The manufacturing 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 relative to 100 parts by mass of the boron carbonitride powder. A boron nitride powder, the standard deviation of the compressive strength of its particles is below 3MPa. A set consisting of a collection of plural numbers; The plurality of aggregates respectively have boron nitride powders with different manufacturing batches; The standard deviation of the particle compressive strength of the boron nitride powder in this set is below 3MPa.