Boron nitride powder and resin composition

Abstract

This boron nitride powder is an aggregate of a plurality of boron nitride particles and has a displacement ratio, as calculated by steps (1) to (4), with a standard deviation of less than 7%. (1) With regard to an n-th boron nitride particle An selected from the boron nitride powder, a step for measuring the particle diameter of the boron nitride particle An. (2) With regard to the boron nitride particle An, a step for applying a load to the boron nitride particle An at a load speed of 0.27 mN / sec and measuring the amount of compressive displacement by which the boron nitride particle An was displaced in the direction in which the load was applied before being crushed. (3) A step for calculating the displacement ratio of the boron nitride particle An by dividing the amount of compressive displacement by the particle diameter. (4) Where n = 1 to 10, a step for performing steps (1) to (3) and calculating the standard deviation of the displacement ratios of ten boron nitride particles A1 to A10.

Description

Boron nitride powder and resin composition

[0001] The present invention relates to a boron nitride powder and a resin composition.

[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. Boron nitride powder is used as a filler in heat dissipation components, which require particularly high thermal conductivity.

[0003] Hexagonal boron nitride primary particles have a relatively thin, scale-like shape. When filled into a resin or the like and molded, the primary particles tend to be oriented in a certain direction due to factors such as molding pressure. For example, in a heat dissipation material filled with hexagonal boron nitride powder and molded into a sheet by extrusion molding or the like, the major surface of the resin sheet and the long axes of the boron nitride primary particles generally tend to be oriented parallel to each other. Furthermore, the anisotropy of the shape of the primary particles of hexagonal boron nitride can also lead to anisotropy in various physical properties. While the thermal conductivity of the primary particles of hexagonal boron nitride in the in-plane direction (a-axis direction) is high at approximately 400 W / (m·K), the thermal conductivity in the thickness direction (c-axis direction) is only approximately 2 W / (m·K), demonstrating significant anisotropy of the physical properties depending on the direction.

[0004] From the viewpoint of reducing the anisotropy due to the shape as described above, a method of forming an aggregate composed of a plurality of primary particles by aggregating and fusing adjacent primary particles so that the orientation of the a-axis direction of each primary particle is different has been studied. For example, Patent Document 1 discloses boron nitride aggregate particles formed by aggregating primary particles of boron nitride having a specific average particle size.

[0005] JP 2013-241321 A

[0006] When a resin composition is prepared by mixing boron nitride powder, which is an aggregate of boron nitride particles, with a resin and a molded body is produced from the resin composition, the boron nitride particles may be crushed by the pressure applied during molding. At this time, the primary particles of boron nitride tend to be oriented in the same direction. However, for example, when the molded body is a heat dissipation material, if the primary particles of boron nitride are oriented in a direction different from the heat dissipation direction of the heat dissipation material, the thermal conductivity of the heat dissipation material will be insufficient. Therefore, it is necessary to prevent the primary particles of boron nitride from being oriented in the same direction.

[0007] Therefore, a main object of the present invention is to provide a boron nitride powder that can prevent primary particles of boron nitride from being oriented in the same direction when a molded body is produced from the boron nitride powder. Another object of the present invention is to provide a resin composition using the boron nitride powder.

[0008] In some aspects, the present invention provides, for example, the following [1] to [6]. [1] A boron nitride powder which is an aggregate of a plurality of boron nitride particles, wherein the standard deviation of the displacement ratio calculated from the following steps (1) to (4) is less than 7%. (1) An nth boron nitride particle A selected from the boron nitride powder. ｎ Regarding the boron nitride particles A ｎ (2) A step of measuring the particle diameter of the boron nitride particles A. ｎ Regarding the boron nitride particles A ｎ (3) A step of applying a load at a loading rate of 0.27 mN / sec to the boron nitride particles A and measuring the amount of compressive displacement in the direction of the load application until the particles are crushed. ｎ (4) The steps (1) to (3) are carried out for n=1 to 10 to obtain 10 boron nitride particles A. １～１０ [2] A step of calculating the standard deviation of the displacement ratio of the 10 boron nitride particles A. １～１０ [3] The boron nitride powder according to [1], wherein the average value of the displacement ratio is 25% or less. ｎand measuring the magnitude of the load when the ten boron nitride particles A are crushed as a load force. １～１０ [4] The boron nitride powder according to [1] or [2], wherein the average value of the ratio of the load force to the compressive displacement (the load force / the compressive displacement) of each of the ten boron nitride particles A is 3 mN / μm or more. １～１０ [5] The boron nitride powder according to any one of [1] to [3], wherein the average value of the crushing strength of the ten boron nitride particles A is 8.5 MPa or more. １～１０ [6] A resin composition comprising the boron nitride powder according to any one of [1] to [5] and a resin.

[0009] According to one aspect of the present invention, there is provided a boron nitride powder that can prevent primary particles of boron nitride from being oriented in the same direction when a molded body is produced from the boron nitride powder. According to another aspect of the present invention, there is provided a resin composition using the boron nitride powder.

[0010] Fig. 1 is an SEM image of a cross section of a boron nitride particle of Example 1. Fig. 2 is an SEM image of a cross section of a boron nitride particle of Comparative Example 1.

[0011] Hereinafter, embodiments of the present invention will be described in detail.

[0012] The boron nitride powder according to this embodiment is an aggregate of a plurality of boron nitride particles. The boron nitride particles have, for example, a cross section consisting of boron nitride and voids. The boron nitride particles are, for example, composed of a plurality of boron nitride primary particles. The boron nitride primary particles are formed of boron nitride and may be, for example, boron nitride flakes having a scale-like shape.

[0013] The plurality of boron nitride primary particles may be in physical contact with each other or may be chemically bonded to each other. Chemical bonding of the plurality of boron nitride primary particles can be confirmed by observing, using a scanning electron microscope (SEM), that no boundaries between the boron nitride primary particles are observed at the bonded portions between the boron nitride primary particles.

[0014] The average thickness of the boron nitride primary particles may be 0.5 μm or more, 1 μm or more, or 1.5 μm or more, and may be 5 μm or less. The average longitudinal length of the boron nitride primary particles may be, for example, 1 μm or more and 10 μm or less. The average thickness and average longitudinal length of the boron nitride primary particles are defined as the average values ​​of the thickness and longitudinal length of 40 boron nitride primary particles measured in an SEM image obtained by observing the cross section of a boron nitride particle at a magnification of 1000 times using an SEM, which is imported into image analysis software (for example, "Mac-view" manufactured by Mountec Co., Ltd.).

[0015] The boron nitride powder according to this embodiment has a standard deviation of less than 7% in the displacement ratio calculated from the following steps (1) to (4): (1) n-th boron nitride particle A selected from boron nitride powder; ｎ Regarding boron nitride particles A ｎ (2) A step of measuring the particle size of boron nitride particles A. ｎ Regarding boron nitride particles A ｎ (3) A step of applying a load at a loading rate of 0.27 mN / sec to the boron nitride particles A and measuring the amount of compressive displacement in the direction of the load until the particles are crushed. ｎ (4) Steps (1) to (3) are performed for n=1 to 10 to obtain 10 boron nitride particles A. １～１０ Calculating the standard deviation of the deviation percentage.

[0016] First, in step (1), 10 or more boron nitride particles selected from boron nitride powder are placed on a sample stage, and one boron nitride particle is selected from the 10 or more placed boron nitride particles, and the particle diameter (unit: μm) of the selected boron nitride particle is measured.

[0017] The particle diameter of boron nitride particles refers to the average diameter measured in any two directions on a single boron nitride particle when the boron nitride particle is observed under a microscope. The microscope may be, for example, a microscope attached to a microcompression tester (e.g., MCT series manufactured by Shimadzu Corporation). The particle diameter may be measured by importing the observed image into image analysis software (e.g., software attached to the microcompression tester).

[0018] One boron nitride particle (n-th boron nitride particle A ｎ The particle size of 10 boron nitride particles A may be 30 μm or more, 35 μm or more, 40 μm or more, 45 μm or more, 50 μm or more, or 55 μm or more, and may be 100 μm or less, 90 μm or less, 80 μm or less, 70 μm or less, or 60 μm or less, or may be 30 to 100 μm. １～１０ The average particle size of the boron nitride particles may be within the above range. The particle size can be adjusted by changing the production conditions of the boron nitride particles (conditions for the nitriding step, decarburization step, classification step, etc.).

[0019] Next, in step (2), an indenter (for example, an indenter diameter of 200 μm) of a micro-compression testing machine (for example, MCT series manufactured by Shimadzu Corporation) is placed on one boron nitride particle (n-th boron nitride particle A) on the sample stage. ｎ ) and apply a load at a loading rate of 0.27 mN / sec. The amount of displacement in the direction of the load application until the amount of displacement of the boron nitride particles A in the direction of the load application suddenly increases is measured as the amount of compressive displacement (unit: μm). In step (2), the magnitude of the load when the amount of displacement of the boron nitride particles A in the direction of the load application suddenly increases may also be measured as the load force (unit: N) at which the boron nitride particles are crushed.

[0020] One boron nitride particle (n-th boron nitride particle A ｎ The compressive displacement of 10 boron nitride particles A may be 5 μm or more, 7 μm or more, or 9 μm or more, and may be 20 μm or less, 15 μm or less, 13 μm or less, or 11 μm or less, or may be 5 to 20 μm. １～１０The average value of the compressive displacement may be within the above range. The smaller the compressive displacement, the less likely the boron nitride particles are to deform even when a load is applied. When a molded body is produced by mixing boron nitride powder with a resin, the boron nitride particles are more likely to maintain their shape even when a load is applied, and the primary particles of boron nitride are more likely to be prevented from aligning in the same direction. The larger the compressive displacement, the more likely the boron nitride particles are to deform under a load when a molded body is produced by mixing boron nitride powder with a resin, and the less likely voids are to be generated in the molded body. The compressive displacement can be adjusted, for example, by changing the conditions of the nitriding step when obtaining the boron nitride powder (heating temperature, atmosphere, pressure, pressurization and heating time, etc.), and the higher the heating temperature, the smaller the compressive displacement tends to be.

[0021] 10 boron nitride particles A １～１０ The standard deviation of the compressive displacement may be 3 μm or less, 2.5 μm or less, or 2.2 μm or less. It can be said that the smaller the standard deviation of the compressive displacement, the smaller the variation in the compressive displacement of the boron nitride particles in the boron nitride powder tends to be, and when the boron nitride powder is mixed with a resin to produce a compact, it is easier to prevent the primary particles of boron nitride from being locally oriented in the same direction in the compact. The standard deviation of the compressive displacement can be adjusted, for example, by changing the conditions of the nitriding step when obtaining the boron nitride powder (heating temperature, atmosphere, pressure, pressurization and heating time, etc.), and the higher the heating temperature, the smaller the standard deviation of the compressive displacement tends to be.

[0022] One boron nitride particle (n-th boron nitride particle A ｎ The load force of 10 boron nitride particles A may be 20 mN or more, 25 mN or more, 30 mN or more, or 35 mN or more, and may be 60 mN or less, 55 mN or less, 50 mN or less, 45 mN or less, or 40 mN or less, or may be 20 to 60 mN. １～１０The average value of the load force may be within the above range. The larger the load force, the more resistant the boron nitride particles tend to be to crushing. When a molded body is produced by mixing boron nitride powder with a resin, the boron nitride particles are more likely to maintain their shape even when a load is applied, and the primary particles of boron nitride are more likely to be prevented from aligning in the same direction. The smaller the load force, the more resistant the boron nitride particles are to deformation under load when a molded body is produced by mixing boron nitride powder with a resin, and the less likely voids are to occur in the molded body. The load force can be adjusted, for example, by changing the conditions of the nitriding step in obtaining the boron nitride powder (heating temperature, atmosphere, pressure, pressurization and heating time, etc.), and the load force tends to increase as the heating temperature increases.

[0023] 10 boron nitride particles A １～１０ The standard deviation of the loading force may be 15 mN or less, 14 mN or less, or 13 mN or less. It can be said that the smaller the standard deviation of the loading force, the smaller the variation in the loading force of the boron nitride particles in the boron nitride powder tends to be, and when the boron nitride powder is mixed with a resin to produce a compact, it is easier to prevent the primary particles of boron nitride from being locally oriented in the same direction in the compact. The standard deviation of the loading force can be adjusted, for example, by changing the conditions of the nitriding step when obtaining the boron nitride powder (heating temperature, atmosphere, pressure, pressurization and heating time, etc.), and the higher the heating temperature, the smaller the standard deviation of the loading force tends to be.

[0024] One boron nitride particle (n-th boron nitride particle A ｎ The ratio of the load force to the compressive displacement (=load force / compressive displacement) of 10 boron nitride particles A may be 1.5 mN / μm or more, 2 mN / μm or more, 2.5 mN / μm or more, 3 mN / μm or more, 3.5 mN / μm or more, or 4 mN / μm or more, and may be 8 mN / μm or less, 7.5 mN / μm or less, 7 mN / μm or less, 6.5 mN / μm or less, 6 mN / μm or less, 5.5 mN / μm or less, 5 mN / μm or less, or 4.5 mN / μm or less, or may be 1.5 to 8 mN / μm. １～１０The average ratio of the load force to the compressive displacement may be within the above range. The larger the ratio of the load force to the compressive displacement, the more resistant the boron nitride particles to deformation under load. When a molded body is produced by mixing boron nitride powder with a resin, the boron nitride particles are more likely to maintain their shape under load, and the primary particles of boron nitride are more likely to be prevented from aligning in the same direction. The smaller the ratio of the load force to the compressive displacement, the more resistant the boron nitride particles are to deformation under load when a molded body is produced by mixing boron nitride powder with a resin, and the less likely voids are to be generated in the molded body. The ratio of the load force to the compressive displacement can be adjusted, for example, by changing the conditions of the nitriding step (heating temperature, atmosphere, pressure, pressurization and heating time, etc.) used to obtain the boron nitride powder. The higher the heating temperature, the greater the ratio of the load force to the compressive displacement.

[0025] 10 boron nitride particles A １～１０ The standard deviation of the ratio of the load force to the compressive displacement may be 3 N / μm or less, 2.5 N / μm or less, or 2 N / μm or less. The smaller the standard deviation of the ratio of the load force to the compressive displacement, the smaller the variation in the load force of the boron nitride particles in the boron nitride powder. This makes it easier to prevent the primary particles of boron nitride from being locally oriented in the same direction in a compact when the boron nitride powder is mixed with a resin to produce a compact. The standard deviation of the ratio of the load force to the compressive displacement can be adjusted, for example, by changing the conditions of the nitriding step when obtaining the boron nitride powder (heating temperature, atmosphere, pressure, pressurization and heating time, etc.). The higher the heating temperature, the smaller the standard deviation of the ratio of the load force to the compressive displacement.

[0026] One boron nitride particle (n-th boron nitride particle A ｎ The crushing strength of boron nitride particles A can be calculated from the load force and particle diameter of the boron nitride particles A. Specifically, the crushing strength σ (unit: MPa) of a boron nitride particle is calculated as follows: σ = α × P / (π × d) where α (= 2.48), a dimensionless similarity ratio that varies depending on the position within the particle, P (unit: N), and d (unit: μm). ２ ) is calculated by the formula:ｎ The crushing strength of 10 boron nitride particles A may be 8.5 MPa or more, 9 MPa or more, 10 MPa or more, 11 MPa or more, or 12 MPa or more, or may be 20 MPa or less, 19 MPa or less, 18 MPa or less, 17 MPa or less, 16 MPa or less, 15 MPa or less, 14 MPa or less, or 13 MPa or less. １～１０ The average value of the crushing strength of 10 boron nitride particles A may be within the above range, １～１０ This crushing strength may be treated as the crushing strength of the boron nitride powder. The higher the crushing strength, the more resistant the boron nitride particles are to deformation even when a load is applied, and when a molded body is produced by mixing the boron nitride powder with a resin, the boron nitride particles are more likely to maintain their shape even when a load is applied, and the primary particles of boron nitride are more likely to be prevented from orienting in the same direction. The lower the crushing strength, the more resistant the boron nitride particles are to deformation when a load is applied, and the less likely voids are to occur in the molded body when a molded body is produced by mixing the boron nitride powder with a resin.

[0027] 10 boron nitride particles A １～１０ The standard deviation of the crushing strength may be 6 MPa or less, 5.5 MPa or less, or 5 MPa or less. The smaller the standard deviation of the crushing strength, the smaller the variation in the load force of the boron nitride particles in the boron nitride powder tends to be, and when the boron nitride powder is mixed with a resin to produce a molded body, it is easier to prevent the primary particles of boron nitride from being locally oriented in the same direction in the molded body.

[0028] Subsequently, in step (3), one boron nitride particle (n-th boron nitride particle A) measured in step (2) is ｎ The compressive displacement of one boron nitride particle (n-th boron nitride particle A) measured in step (1) was ｎ ) by the particle diameter of one boron nitride particle (n-th boron nitride particle A ｎ ) and calculate the displacement ratio (= compression displacement amount / particle diameter).

[0029] One boron nitride particle (n-th boron nitride particle A ｎThe displacement ratio of 10 boron nitride particles A may be 9% or more, 10% or more, 12% or more, 14% or more, 16% or more, or 18% or more, and may be 40% or less, 38% or less, 36% or less, 34% or less, 32% or less, 30% or less, 28% or less, 26% or less, or 25% or less. １～１０ The average value of the displacement ratio may be within the above range. The smaller the displacement ratio, the more resistant the boron nitride particles to deformation even when a load is applied. When a molded body is produced by mixing boron nitride powder with a resin, the boron nitride particles are more likely to maintain their shape even when a load is applied, and the primary particles of boron nitride are more likely to be prevented from aligning in the same direction. The larger the displacement ratio, the more resistant the boron nitride particles are to deformation under the load of molding pressure when a molded body is produced by mixing boron nitride powder with a resin, and the less likely voids are to occur in the molded body. The displacement ratio can be adjusted, for example, by changing the conditions of the nitriding step when obtaining the boron nitride powder (heating temperature, atmosphere, pressure, pressurization and heating time, etc.), and the higher the heating temperature, the smaller the displacement ratio tends to be.

[0030] Then, in the step (4), the steps (1) to (3) are carried out for n=1 to 10, that is, for the first boron nitride particle to the tenth boron nitride particle, to obtain 10 boron nitride particles A １～１０ The standard deviation of the displacement ratio is calculated from the displacement ratio measured from each of the above.

[0031] 10 boron nitride particles A １～１０ The standard deviation of the displacement ratio is less than 7%. １～１０ Since the standard deviation of the displacement rate is less than 7%, the variation in the standard deviation of the displacement rate of the boron nitride particles in the boron nitride powder is relatively small, and when a compact is produced by mixing the boron nitride powder with a resin, the mixture of particles that are too large in deformation and particles that are too small in deformation under the molding pressure is suppressed, and it is possible to suppress the orientation of the entire compact from becoming too large. Furthermore, by producing a compact by mixing a boron nitride powder containing such boron nitride particles with a resin, it is possible to suppress the primary particles of boron nitride from being oriented in the same direction in the compact.

[0032] 10 boron nitride particles A １～１０ The standard deviation of the displacement ratio may be 6.5% or less, or 6% or less. The smaller the standard deviation of the displacement ratio, the smaller the variation in the displacement ratio of boron nitride particles in the boron nitride powder tends to be, and when the boron nitride powder is mixed with a resin to produce a molded body, it is easier to prevent the primary particles of boron nitride from being locally oriented in the same direction in the molded body. The standard deviation of the displacement ratio can be adjusted, for example, by changing the conditions of the nitriding step when obtaining the boron nitride powder (heating temperature, atmosphere, pressure, pressurization and heating time, etc.), and the higher the heating temperature, the smaller the standard deviation of the displacement ratio tends to be.

[0033] The average particle size of the boron nitride powder may be, for example, 20 μm or more, 25 μm or more, 30 μm or more, or 35 μm or more, or 120 μm or less, 100 μm or less, 80 μm or less, 60 μm or less, 50 μm or less, or 40 μm or less, or may be 20 to 120 μm. The average particle size of the boron nitride powder means the particle size (D50) at which the volume cumulative particle size distribution is 50%, and can be measured by a laser diffraction scattering method.

[0034] The average value of the orientation degree of the boron nitride powder may be, for example, 9 or less, 8 or less, 7.5 or less, 7.3 or less, 7.2 or less, or 7.1 or less, or may be 5 or more, 6 or more, or 7 or more. The maximum value of the orientation degree of the boron nitride powder may be, for example, 9 or less, 8.5 or less, 8 or less, 7.8 or less, or 7.6 or less, or may be 5 or more, 6 or more, or 7 or more. The minimum value of the orientation degree of the boron nitride powder may be, for example, 9 or less, 8 or less, 7 or less, 6.8 or less, or 6.6 or less, or may be 5 or more, 6 or more, or 6.5 or more. The standard deviation of the orientation degree of the boron nitride powder may be, for example, 5 or less, 4.5 or less, 4 or less, 3.5 or less, 3.3 or less, or 3.1 or less, or may be 2 or more, 2.5 or more, or 3 or more. The orientation degree of the boron nitride powder can be measured by the method described in the examples below.

[0035] The boron nitride particles may consist essentially of boron nitride. Whether the boron nitride particles consist essentially of boron nitride can be confirmed by detecting only peaks attributable to boron nitride in X-ray diffraction measurement.

[0036] By mixing the boron nitride powder described above with a resin to produce a molded body, it is possible to prevent the primary particles of boron nitride from aligning in the same direction. Furthermore, a heat dissipation material using such a boron nitride powder can exhibit higher thermal conductivity than heat dissipation materials using conventional boron nitride powders.

[0037] A method for producing the above-mentioned boron nitride powder will be described below. The above-mentioned boron nitride powder can be produced, for example, by a method comprising a step of nitriding boron carbide powder while heating it at 2200°C or higher to obtain boron carbonitride powder (nitriding step), and a step of decarburizing the boron carbonitride powder to obtain boron nitride powder (decarburizing step). That is, another embodiment of the present invention is a method for producing such a boron nitride powder.

[0038] Boron carbide powder can be produced by, for example, a known production method. One example is a method in which boric acid and acetylene black are mixed together and then heated in an inert gas atmosphere at 1800 to 2400°C for 1 to 10 hours to obtain agglomerated boron carbide powder. The agglomerated boron carbide powder obtained by this method may be appropriately subjected to pulverization, sieving, washing, impurity removal, drying, and the like. The average particle size of the boron carbide powder may be, for example, 5 μm or more, 10 μm or more, or 15 μm or more, and may be 80 μm or less, 60 μm or less, or 40 μm or less. The average particle size of the boron carbide powder refers to the particle size (D50) at which the volume cumulative particle size distribution becomes 50%, and can be measured by a laser diffraction scattering method.

[0039] In the nitriding step, the boron carbide powder is nitrided to obtain boron carbonitride powder by heating the boron carbide powder at 2200°C or higher in an atmosphere that promotes the nitriding reaction. The boron carbide powder may be heated in a container, which may be, for example, a carbon crucible, from the viewpoint of facilitating the production of the boron nitride powder.

[0040] The heating temperature in the nitriding step is 2200° C. or higher. When the heating temperature in the nitriding step is relatively high, the standard deviation of the displacement ratio tends to be relatively small. The heating temperature in the nitriding step may be 2400° C. or lower or 2300° C. or lower.

[0041] The atmosphere in which the nitriding reaction proceeds in the nitriding step may be a nitriding gas atmosphere that nitrides the boron carbide powder. The nitriding gas may be nitrogen gas, ammonia gas, etc., and nitrogen gas is preferred from the viewpoints of ease of nitriding the boron carbide powder and cost. The nitriding gas may be used alone or in combination of two or more types, and the proportion of nitrogen gas in the nitriding gas may be 95 vol% or more, 99 vol% or more, or 99.9 vol% or more, from the viewpoint of ease of obtaining the boron nitride powder.

[0042] The pressure in the nitriding step may be 0.6 MPa or more, 0.7 MPa or more, or 0.8 MPa or more from the viewpoint of facilitating the production of the boron nitride powder, and may be 1.0 MPa or less, or 0.9 MPa or less from the viewpoint of facilitating the production of the boron nitride powder.

[0043] The time for which pressure and heating are applied in the nitriding step may be 3 hours or more, 5 hours or more, 10 hours or more, 15 hours or more, or 20 hours or more, from the viewpoint of sufficiently nitriding the boron carbide powder. The time for which pressure and heating are applied in the nitriding step may be 30 hours or less, 25 hours or less, or 20 hours or less, from the viewpoint of facilitating the production of the boron nitride powder.

[0044] The boron carbonitride powder obtained in the nitriding step does not need to be sintered in the atmosphere, from the viewpoint of densifying the obtained boron nitride particles and easily reducing the standard deviation of the displacement ratio of the boron nitride powder. In other words, the method for producing boron nitride powder does not need to include the step of sintering the boron carbonitride powder in the atmosphere.

[0045] In the decarburization step, a mixture containing the boron carbonitride powder obtained in the nitriding step and a boron source is filled in a container and heated to decarburize the boron carbonitride powder. The container may be, for example, a boron nitride crucible.

[0046] Examples of the boron source include boric acid, boron oxide, or a mixture thereof. The mixture may further contain other additives used in the art, as necessary. The mixing ratio of the boron carbonitride powder and the boron source is appropriately selected. When boric acid or boron oxide is used as the boron source, the ratio of boric acid or boron oxide may be, for example, 40 parts by mass or more or 60 parts by mass or more, and 300 parts by mass or less, 200 parts by mass or less, 150 parts by mass or less, or 100 parts by mass or less, per 100 parts by mass of boron carbonitride.

[0047] The boron carbonitride powder and the boron source may be mixed by a known method, for example, using a Henschel mixer. The rotation speed when mixing the boron carbonitride powder and the boron source may be 500 to 1500 rpm, from the viewpoints of densifying the resulting boron nitride particles and easily reducing the standard deviation of the displacement ratio of the boron nitride powder. The time for mixing the boron carbonitride powder and the boron source may be adjusted depending on the rotation speed, and may be 5 to 60 minutes.

[0048] The atmosphere in the decarburization step may be an atmosphere of normal pressure (atmospheric pressure) or a pressurized atmosphere. The pressure in the decarburization step may be, for example, 0.5 MPa or less or 0.3 MPa or less, or 0.01 MPa or more or 0.03 MPa or more.

[0049] In the decarburization step, for example, the temperature is first raised to a predetermined temperature (a temperature at which decarburization can start), and then further raised to a holding temperature at the predetermined temperature. The predetermined temperature (a temperature at which decarburization can start) may be, for example, 1000° C. or higher, and may be 1500° C. or lower, or 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, 4° C. / min. or lower, 3° C. / min. or lower, or 2° C. / min. or lower.

[0050] From the viewpoint of favorable particle growth, the holding temperature may be 1800° C. or higher or 2000° C. or higher. The holding temperature may be 2200° C. or lower or 2100° C. or lower.

[0051] The holding time at the holding temperature may be, for example, 0.5 hours or more, 1 hour or more, 3 hours or more, or 5 hours or more, from the viewpoint of favorable particle growth, and may be, for example, 40 hours or less, 30 hours or less, 20 hours or less, or 10 hours or less.

[0052] The boron nitride powder obtained as described above may be subjected to a step of classifying the powder using a sieve so as to obtain boron nitride powder having a desired average particle size (classifying step).

[0053] The boron nitride powder described above is suitable for use in, for example, heat dissipation materials. When used in heat dissipation materials, the boron nitride powder is used as a resin composition mixed with, for example, a resin. That is, another embodiment of the present invention is a resin composition containing the above-mentioned boron nitride powder and a resin.

[0054] The content of the boron nitride powder may be 50% by volume or more, 55% by volume or more, 60% by volume or more, 65% by volume or more, or 70% by volume or more, based on the total volume of the resin composition, from the viewpoint of improving the thermal conductivity of the resin composition and making it easier to obtain excellent heat dissipation performance. The content of the boron nitride powder may be 85% by volume or less, 80% by volume or less, or 75% by volume or less, based on the total volume of the resin composition, from the viewpoint of being able to suppress the generation of voids during molding and the deterioration of insulation and mechanical strength.

[0055] Examples of the resin include epoxy resin, silicone resin, silicone rubber, acrylic resin, phenolic resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyimide, polyamideimide, polyetherimide, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, wholly aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide-modified resin, ABS (acrylonitrile-butadiene-styrene) resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin.

[0056] The resin content may be 15% by volume or more, 20% by volume or more, or 25% by volume or more, based on the total volume of the resin composition, and may be 50% by volume or less, 45% by volume or less, 40% by volume or less, 35% by volume or less, or 30% by volume or less.

[0057] The resin composition may further contain a curing agent for curing the resin. The curing agent is appropriately selected depending on the type of resin. For example, when the resin is an epoxy resin, examples of the curing agent include a phenol novolac compound, an acid anhydride, an amino compound, and an imidazole compound. The content of the curing agent may be, for example, 0.5 parts by mass or more or 1.0 parts by mass or more, and 15 parts by mass or less or 10 parts by mass or less, relative to 100 parts by mass of the resin.

[0058] The resin composition may further contain other components, such as a curing accelerator (curing catalyst), a coupling agent, a wetting / dispersing agent, and a surface conditioner.

[0059] Examples of the curing accelerator (curing catalyst) include phosphorus-based curing accelerators such as tetraphenylphosphonium tetraphenylborate and triphenylphosphate, imidazole-based curing accelerators such as 2-phenyl-4,5-dihydroxymethylimidazole, and amine-based curing accelerators such as boron trifluoride monoethylamine.

[0060] Examples of the coupling agent include a silane-based coupling agent, a titanate-based coupling agent, an aluminate-based coupling agent, etc. Examples of the chemical bonding group contained in these coupling agents include a vinyl group, an epoxy group, an amino group, a methacryl group, a mercapto group, etc.

[0061] Examples of wetting and dispersing agents include phosphate ester salts, carboxylic acid esters, polyesters, acrylic copolymers, and block copolymers.

[0062] Examples of the surface conditioner include acrylic surface conditioners, silicone surface conditioners, vinyl surface conditioners, and fluorine surface conditioners.

[0063] A heat dissipating material can be obtained using the resin composition (i.e., the boron nitride powder). The average orientation degree of a molded body produced using the resin composition may be 19 or less, 17 or less, 15 or less, 13 or less, or 11 or less, or 5 or more, or 10 or more. The maximum orientation degree of a molded body produced using the resin composition may be 22 or less, 20 or less, 18 or less, 16 or less, 14 or less, or 12 or less, or 5 or more, or 10 or more. The minimum orientation degree of a molded body produced using the resin composition may be 18 or less, 16 or less, 14 or less, 12 or less, or 10 or more, or 5 or more, or 9 or more. The standard deviation of the orientation degree of a molded body produced using the resin composition may be 1.2 or less, 1 or less, 0.8 or less, or 0.6 or less, or 0.3 or more, or 0.5 or more. The orientation degree of a molded body produced using the resin composition can be measured by the method described in the Examples below.

[0064] The thermal conductivity of a molded article produced using the resin composition tends to be higher than that of conventional heat dissipation materials. The thermal conductivity of a molded article produced using the resin composition may be, for example, 17 W / (m K) or more, 18 W / (m K) or more, or 18.5 W / (m K) or more. The thermal conductivity can be measured by the method described in the Examples below.

[0065] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the following examples.

[0066] Example 1 Preparation of Hexagonal Boron Carbonitride Boron carbide powder with an average particle size (D50) of 26 μm was heated in a resistance heating furnace under a nitrogen gas atmosphere at a firing temperature of 2200° C. and a pressure of 0.85 MPa for 20 hours. During firing, nitrogen gas was supplied in an amount exceeding the stoichiometric amount, i.e., 20 equivalents more than the required amount. In this manner, boron carbonitride (B ４ CN ４ ) was obtained.

[0067] The calcined product and boric acid were blended in a ratio of 40 parts by mass of boron carbonitride to 60 parts by mass of boric acid, and mixed for 10 minutes at 1000 rpm using a Henschel mixer to obtain a uniform mixture. The resulting mixture was loaded into a boron nitride crucible, evacuated using a resistance heating furnace, and then heated from room temperature to 1000°C at a heating rate of 10°C / min under atmospheric pressure in a nitrogen gas atmosphere. The temperature was then increased from 1000°C to 2000°C at a heating rate of 2°C / min. The mixture was heated at a calcination temperature of 2000°C and a pressure of 0.03 MPa for 5 hours to obtain boron nitride containing agglomerated particles composed of aggregated primary particles. The resulting boron nitride was crushed to 2000°C using a Henschel mixer and then sieved through a vibrating sieve with 75 μm openings to obtain boron nitride powder. An SEM image of the resulting boron nitride powder is shown in FIG. 1.

[0068] Comparative Example 1 A boron nitride powder was obtained in the same manner as in Example 1, except that the temperature for firing the boron carbide powder was changed to 2000°C, and the fired material containing boron carbonitride was filled into an alumina crucible and then heated in a muffle furnace in an air atmosphere at a firing temperature of 700°C for 5 hours, and then mixed with boric acid. An SEM image of the obtained boron nitride powder is shown in Figure 2.

[0069] [Measurement of Compression Displacement, etc.] The n-th boron nitride particle A in the boron nitride powder obtained in the Examples and Comparative Examples was ｎ The particle diameter of each of the n-th boron nitride particles A was measured by observing the particle diameter with a microscope attached to a micro-compression tester (MCT series, manufactured by Shimadzu Corporation). ｎ Regarding boron nitride particles A ｎ A load was gradually applied to the boron nitride particles A at a loading rate of 0.27 mN / sec. ｎ At this time, the boron nitride particles A ｎ Boron nitride particles A ｎ The amount of compression displacement in the direction of the load and the amount of boron nitride particle A ｎ The magnitude of the load (load force) when the boron nitride particles A were crushed was measured. ｎThe compressive displacement measured in the above step is divided by the particle diameter to obtain the boron nitride particle A. ｎ The displacement ratio of 10 boron nitride particles A was calculated by performing the above operation for n=1 to 10. １～１０ The standard deviation of the displacement ratio was calculated from the respective displacement ratios of 10 boron nitride particles A. １～１０ The ratio of the load force to the compressive displacement (load force / compressive displacement) and the crushing strength were calculated. The crushing strength σ (unit: MPa) was calculated from the dimensionless similarity ratio α (=2.48) which changes depending on the position within the particle, the load force P (unit: N), and the particle diameter d (unit: μm) of the boron nitride particles, as follows: σ = α × P / (π × d ２ The measured and calculated parameters are shown in Tables 1 and 2.

[0070] [Measurement of Average Particle Size] The average particle size of the boron nitride powder obtained in the Examples and Comparative Examples was measured in accordance with ISO 13320:2009 using a laser diffraction / scattering particle size distribution analyzer (product name "SYNC" manufactured by Microtrac-Bell). However, the measurement was performed without subjecting the sample to a homogenizer before the measurement process. When measuring the particle size distribution, water was used as the solvent to disperse the boron nitride powder, and hexametaphosphoric acid was used as the dispersant. The refractive index of water was 1.33, and the refractive index of the boron nitride powder was 1.7. The results of the average particle size measurements are shown in Table 3.

[0071] [Measurement of Orientation Degree] The boron nitride powder obtained in the Examples and Comparative Examples was packed into a 15 mmφ mold using a Riken Seiki manual pump P-16B and a mold, and 0.2 g of BN powder was pressed at 15 MPa for 1 minute to produce a pellet. The produced pellet was placed in the sample holder of an X-ray diffractometer (Rigaku Corporation, Ultima IV-N) and irradiated with X-rays. The orientation degree of the produced pellet was measured using the peak intensity of the (002) plane / peak intensity of the (100) plane calculated from the measured X-ray diffraction peak. Ten pellets were produced using the same procedure, and the orientation degree was measured. The average, maximum, and minimum orientation degrees of the 10 pellets, as well as the standard deviation of the orientation degree, are shown in Table 3. Furthermore, the boron nitride powder obtained in the Examples and Comparative Examples was placed on a glass plate, and the orientation degree was measured at 10 points. Table 3 shows the measurement results of the average, maximum, and minimum degrees of orientation of the boron nitride powder, as well as the standard deviation of the degrees of orientation.

[0072] [Measurement of Thermal Conductivity] 100 parts by mass of a 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 were mixed, and then the boron nitride powder obtained in the Examples and Comparative Examples was mixed so that the filling rate of the boron nitride powder was 70% by volume, to obtain a resin composition. This resin composition was degassed under reduced pressure of 500 Pa for 10 minutes and applied to a PET sheet to a thickness of 1.0 mm. Thereafter, the mixture was heated at a temperature of 150°C and a pressure of 160 kg / cm. ２ A 0.5 mm sheet-shaped heat dissipation material was prepared by pressing under the conditions of heating and pressing for 60 minutes. A measurement sample of 10 mm x 10 mm was cut out from the prepared heat dissipation material, and the thermal diffusivity A (m ２ The specific gravity B (kg / m ３) was measured by Archimedes' method. The specific heat capacity C (J / (kg K)) of the measurement sample was also measured using a differential scanning calorimeter (Rigaku Corporation, Thermo Plus Evo DSC8230). Using these physical property values, the thermal conductivity H (W / (m K)) was calculated from the formula H = A x B x C. The thermal conductivity measurement results are shown in Table 3.

[0073]

[0074]

[0075]

[0076] It can be seen from Table 3 that the average degrees of orientation of the boron nitride powders obtained in the Examples and Comparative Examples are approximately the same. On the other hand, since the pellets produced using the boron nitride powder obtained in the Examples have a smaller average degree of orientation than the pellets produced using the boron nitride powder obtained in the Comparative Examples, it can be said that the boron nitride powder obtained in the Examples (i.e., boron nitride powder with a standard deviation of the displacement rate of less than 7%) can prevent the primary particles of boron nitride from being oriented in the same direction when a compact is produced from the boron nitride powder.

Claims

1. A boron nitride powder that is an aggregate of a plurality of boron nitride particles, wherein the standard deviation of the displacement ratio calculated by the following steps (1) to (4) is less than 7%. (1) An nth boron nitride particle A selected from the boron nitride powder ｎ Regarding the boron nitride particles A ｎ (2) A step of measuring the particle diameter of the boron nitride particles A. ｎ Regarding the boron nitride particles A ｎ (3) A step of applying a load at a loading rate of 0.27 mN / sec to the boron nitride particles A and measuring the amount of compressive displacement in the direction of the load application until the particles are crushed. ｎ (4) The steps (1) to (3) are carried out for n=1 to 10 to obtain 10 boron nitride particles A. １～１０ Calculating the standard deviation of the displacement ratio.

2. The 10 boron nitride particles A １～１０ 2. The boron nitride powder according to claim 1, wherein the average value of the displacement ratio is 25% or less.

3. The step (2) is carried out by using the boron nitride particles A. ｎ and measuring the magnitude of the load when the ten boron nitride particles A are crushed as a load force. １～１０ 2. The boron nitride powder according to claim 1, wherein an average value of the ratio of the load force to the compressive displacement (load force / compressive displacement) of each of the above is 3 mN / μm or more.

4. The 10 boron nitride particles A １～１０ 2. The boron nitride powder according to claim 1, wherein the average value of the crushing strength is 8.5 MPa or more.

5. The 10 boron nitride particles A １～１０ 2. The boron nitride powder according to claim 1, wherein the average particle size is 30 to 100 μm.

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

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