Boron nitride powder and resin composition

Abstract

Provided is a boron nitride powder that is an aggregation of a plurality of boron nitride particles, wherein the cross section of each of the plurality of boron nitride particles comprises boron nitride and voids, and when, in the cross section, region A is the region surrounded by the periphery of the cross section, region B is a region obtained by reducing region A using a similarity ratio α with the center of gravity of region A serving as the center of similarity, and region C is the region of region A other than region B, the average of the ratio RB / RC of the areal proportion RB of boron nitride in region B to the areal proportion RC of boron nitride in region C when using a similarity ratio α of 0.6 is 1.3 or greater.

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, due to the anisotropy of their shape, the primary particles of hexagonal boron nitride can also exhibit anisotropy in various physical properties. While the thermal conductivity of hexagonal boron nitride primary particles 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 physical properties depending on the direction.

[0004] For the reasons mentioned above, methods have been investigated in which hexagonal boron nitride powder is used as a filler for resin, and when preparing a heat-dissipating sheet, the a-axis direction of the primary particles is adjusted to be parallel to the thickness direction of the heat-dissipating sheet, thereby making use of the high thermal conductivity in the a-axis direction of the primary particles. For example, a technique is known in which the a-axis direction of the primary particles of hexagonal boron nitride is aligned parallel to the thickness direction of the heat-dissipating sheet (see, for example, Patent Document 1).

[0005] Furthermore, 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, which are aggregated and fused together so that the orientation of the a-axis direction of adjacent primary particles differs, has been studied. Patent Document 2 discloses boron nitride aggregate particles formed by aggregating primary particles of boron nitride, and describes that by increasing the strength of the aggregate particles to a degree that prevents the agglomerated particles from collapsing even when a predetermined molding pressure is applied, the primary particles of boron nitride are prevented from being oriented uniformly in the same direction.

[0006] JP 2000-154265 A JP 2016-135731 A

[0007] When producing a heat dissipation material, when mixing boron nitride powder with a resin to obtain a resin composition, it is necessary to further increase the crushing strength of the boron nitride particles in the boron nitride powder so that the boron nitride particles in the boron nitride powder are less likely to disintegrate, in order to prevent the primary particles of boron nitride from orienting in the same direction.

[0008] Therefore, a primary object of the present invention is to provide a boron nitride powder containing boron nitride particles having excellent crushing strength. Another object of the present invention is to provide a resin composition using the boron nitride powder.

[0009] In some aspects, the present invention provides the following [1] to [8]: [1] A boron nitride powder which is an aggregate of a plurality of boron nitride particles, each of the plurality of boron nitride particles having a cross section consisting of boron nitride and voids, wherein, in the cross section, when a region surrounded by the periphery of the cross section is defined as region A, a region obtained by reducing region A with the center of gravity of region A as the center of similarity at a similarity ratio α is defined as region B, and a region of region A other than region B is defined as region C, when the similarity ratio α is 0.6, the area ratio R of the boron nitride in region C is Ｃ The area ratio R of the boron nitride in the region B to Ｂ Ratio R Ｂ / R Ｃ [2] The average value of the ratio R is 1.3 or more when the similarity ratio α is 0.4, 0.5, or 0.7.Ｂ / R Ｃ [3] The boron nitride powder according to [1], wherein the average value of the area ratio R of the boron nitride in the region A is 1.3 or more. Ａ [4] The boron nitride powder according to [1] or [2], wherein the average value of the area ratio R of the boron nitride in the region A when the similarity ratio α is 0.6 is 55 to 75%. Ａ The area ratio R of the boron nitride in the region B to Ｂ Ratio R Ｂ / R Ａ [5] The boron nitride powder according to any one of [1] to [3], wherein the average value of the area ratio R of the boron nitride in the region A when the similarity ratio α is 0.6 is 1.1 or more. Ａ The area ratio R of the boron nitride in the region C to Ｃ Ratio R Ｃ / R Ａ [6] The boron nitride powder according to any one of [1] to [5], having an average particle size of 20 to 120 μm. [7] The boron nitride powder according to any one of [1] to [6], having a crushing strength of 12 MPa or more. [8] A resin composition comprising the boron nitride powder according to any one of [1] to [7], and a resin.

[0010] According to one aspect of the present invention, there is provided a boron nitride powder containing boron nitride particles having excellent crushing strength. According to another aspect of the present invention, there is provided a resin composition using the boron nitride powder.

[0011] 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. FIG. 3 is a binarized image of a cross section of a boron nitride particle a of Example 1. FIG. 4(a) is a binarized image of region B of the cross section of a boron nitride particle a of Example 1, and FIG. 4(b) is a binarized image of region C of the cross section of a boron nitride particle a of Example 1. FIG. 5 is a binarized image of a cross section of a boron nitride particle b of Example 1. FIG. 6(a) is a binarized image of region B of the cross section of a boron nitride particle b of Example 1, and FIG. 6(b) is a binarized image of region C of the cross section of a boron nitride particle b of Example 1.

[0012] Hereinafter, embodiments of the present invention will be described in detail.

[0013] The boron nitride powder according to this embodiment is an aggregate of a plurality of boron nitride particles, each of which has a cross section consisting of boron nitride and voids. The boron nitride particles are, for example, composed of a plurality of boron nitride flakes. The boron nitride flakes are formed from boron nitride and may have, for example, a scale-like shape.

[0014] The boron nitride pieces may be in physical contact with each other or may be chemically bonded to each other, which can be confirmed by observing, using a scanning electron microscope (SEM), that no boundaries between the boron nitride pieces are observed at the bonded portions of the boron nitride pieces.

[0015] The average thickness of the boron nitride pieces 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 pieces may be, for example, 1 μm or more and 10 μm or less. The average thickness and average longitudinal length of the boron nitride pieces are defined as the average values ​​of the thickness and longitudinal length of 40 boron nitride pieces 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.).

[0016] In the cross section of a boron nitride particle, the area surrounded by the periphery of the cross section is called region A, the area obtained by shrinking region A with the center of gravity of region A as the center of similarity at a similarity ratio α is called region B, and the area of ​​region A other than region B is called region C. When the similarity ratio α is 0.6, the area ratio R of boron nitride in region C is Ｃ The area ratio R of boron nitride in region B Ｂ Ratio R Ｂ / R Ｃ The average value of the ratio R is 1.3 or more. Ｂ / R Ｃ The average value of R is the ratio of 10 boron nitride particles in the boron nitride powder. Ｂ / R Ｃ means the average value of

[0017] The ratio R when the similarity ratio α is 0.6 Ｂ / R Ｃ Since the average value of is 1.3 or more, the boron nitride particles contained in the boron nitride powder have a somewhat higher boron nitride density near the center of gravity of the boron nitride particles than near the surface of the boron nitride particles. Therefore, when an external force is applied to such boron nitride particles, the shape near the surface of the boron nitride particles tends to collapse, but the shape near the center of gravity of the boron nitride particles tends to be maintained. The crushing strength of such boron nitride particles tends to be higher than that of conventional boron nitride particles, and by mixing boron nitride powder containing such boron nitride particles with a resin to produce a heat dissipating material, it is possible to prevent the boron nitride flakes in the heat dissipating material from being oriented in the same direction.

[0018] Area fraction R of boron nitride in regions A, B, and C Ａ , R Ｂ , and R ｃcan be measured by the following procedure. First, boron nitride particles are embedded in epoxy resin, and the epoxy resin is cured to obtain a cured product. The cured product is polished to expose the cross-section of the boron nitride particle, which serves as a measurement sample. The measurement sample is observed using an SEM at 500x magnification, and a bmp-format image is obtained that allows the entire cross-section of a single boron nitride particle to be confirmed. The image is imported into the image processing software "ImageJ," and a single boron nitride particle in the image is focused on, with a border being drawn along the outer edge (the periphery of the cross-section) of the focused boron nitride particle. The image is then trimmed to a rectangle circumscribing the bordered area, and the area outside the bordered area (the area where the focused boron nitride particle does not exist) is masked. The image for analysis is imported into the image processing software "OpenCV" (Python language), where filtering is performed using a Median filter (kernel size 5), and binarization is performed using Otsu's method to separate the area consisting of boron nitride particles from the other area (resin area). Dilation processing (kernel size 5) and hole filling processing are performed to extract the perimeter of the cross section of the boron nitride particle with the largest area in the image. The perimeter of the extracted cross section is applied to the binarized image, and the region inside the perimeter of the cross section (the region where the boron nitride particle of interest is present, including the perimeter of region A) is designated as region A, and the centroid coordinates are calculated from the perimeter coordinates. Furthermore, a region obtained by reducing region A at a similarity ratio of 0.6, with the center of gravity of region A as the center of similarity, is designated as region B, and the perimeter of region B (the perimeter obtained by reducing the perimeter of region A at a similarity ratio of 0.6) is applied to the binarized image so that the centers of gravity of region A and B overlap. In the binarized image, the region of region A other than region B (the region inside the perimeter of region A and outside the perimeter of region B, including the perimeter of region A but not the perimeter of region B) is designated as region C. From the analysis image, the areas of the regions consisting of boron nitride in regions A, B, and C, and the areas of each of the multiple resin regions (voids) in the cross section of the boron nitride particle are measured, and the area proportion of the regions consisting of boron nitride (boron nitride regions) can be calculated.

[0019] Area ratio R of boron nitride in region A ＡFrom the viewpoint of achieving a better crushing strength, the average value of the area ratio R of boron nitride in region A may be 50% or more, 55% or more, or 60% or more. Ａ The average value of the area ratio R of boron nitride in region A may be 80% or less, 75% or less, 70% or less, or 65% or less. Ａ The average value of the area ratio R may be 50 to 80% or 55 to 75%. Ａ The average value of the area ratio R of 10 boron nitride particles in the boron nitride powder Ａ The area ratio R of boron nitride in region A is the average value of Ａ The average value of can be adjusted, for example, by changing the conditions of the nitriding step when obtaining boron nitride powder (heating temperature, atmosphere, pressure, time for applying pressure and heating, etc.).

[0020] The area ratio R of boron nitride in region B when the similarity ratio α is 0.6 Ｂ From the viewpoint of achieving a better crushing strength, the average value of the area ratio R of boron nitride in region B may be 60% or more, 65% or more, or 70% or more. Ｂ The average value of the area ratio R of boron nitride in region B may be 90% or less, 85% or less, or 80% or less. Ｂ The average value of the area ratio R may be within the above range. Ｂ The average value of the area ratio R of 10 boron nitride particles in the boron nitride powder Ｂ The area ratio R of boron nitride in region B is the average value of Ｂ The average value of can be adjusted, for example, by changing the conditions of the nitriding step when obtaining boron nitride powder (heating temperature, atmosphere, pressure, time for applying pressure and heating, etc.).

[0021] The area ratio R of boron nitride in region C when the similarity ratio α is 0.6 Ｃ From the viewpoint of achieving a better crushing strength, the average value of the area ratio R of boron nitride in region C may be 65% or less, 60% or more, or 55% or more. ＣThe average value of the area ratio R of boron nitride in the region C may be 40% or more, 45% or more, or 50% or more. Ｃ The average value of the area ratio R may be within the above range. Ｃ The average value of the area ratio R of 10 boron nitride particles in the boron nitride powder Ｃ The area ratio R of boron nitride in region C is the average value of Ｃ The average value of can be adjusted, for example, by changing the conditions of the nitriding step when obtaining boron nitride powder (heating temperature, atmosphere, pressure, time for applying pressure and heating, etc.).

[0022] The ratio R when the similarity ratio α is 0.6 Ｂ / R Ｃ From the viewpoint of achieving a better crushing strength, the average value of the ratio R when the similarity ratio α is 0.6 may be 1.32 or more, 1.34 or more, or 1.35 or more. Ｂ / R Ｃ The average value of may be 1.5 or less, 1.45 or less, 1.4 or less, 1.38 or less, or 1.36 or less.

[0023] The ratio R when the similarity ratio α is 0.4 Ｂ / R Ｃ The average value of the ratio R may be 1.3 or more, 1.32 or more, or 1.34 or more. Ｂ / R Ｃ When the average value of the ratio R when the similarity ratio α is 0.4 is 1.3 or more, the boron nitride particles have a relatively high and uniform boron nitride density near the center of gravity, and therefore tend to have better crushing strength. Ｂ / R Ｃ The average value of may be 1.5 or less, 1.45 or less, 1.4 or less, or 1.35 or less.

[0024] The ratio R when the similarity ratio α is 0.5 Ｂ / R Ｃ The average value of the ratio R may be 1.3 or more, 1.32 or more, or 1.34 or more. Ｂ / R ＣWhen the average value of the ratio R when the similarity ratio α is 0.5 is 1.3 or more, the boron nitride particles have a relatively high and uniform boron nitride density near the center of gravity, and therefore tend to have better crushing strength. Ｂ / R Ｃ The average value of may be 1.5 or less, 1.45 or less, 1.4 or less, or 1.35 or less.

[0025] The ratio R when the similarity ratio α is 0.7 Ｂ / R Ｃ The average value of the ratio R may be 1.3 or more. Ｂ / R Ｃ When the average value of the ratio R when the similarity ratio α is 0.7 is 1.3 or more, the boron nitride particles can be said to have more regions where the boron nitride density is relatively high, and therefore tend to have better crushing strength. Ｂ / R Ｃ The average value of may be 1.4 or less, or 1.35 or less.

[0026] The area ratio R of boron nitride in region B when the similarity ratio α is 0.6 Ｂ is the area ratio R of boron nitride in region A when the similarity ratio α is 0.6. Ａ The area ratio R of boron nitride in the region A when the homothetic ratio α is 0.6 may be larger than Ａ The area ratio R of boron nitride in region B Ｂ Ratio R Ｂ / R Ａ From the viewpoint of achieving a better crushing strength, the average value of the ratio R may be 1.1 or more, 1.13 or more, or 1.15 or more. Ｂ / R Ａ The average value of the area ratio R of boron nitride in the region B when the similarity ratio α is 0.4 or more may be 1.3 or less or 1.2 or less. Ｂ is the area ratio R of boron nitride in region A Ａ Even when the similarity ratio α is 0.4, 0.5, or 0.7, the ratio R Ｂ / R Ａ may be within the above range, and the ratio RＢ / R Ａ The average value of the ratio R may be within the above range. Ｂ / R Ａ The average value of R is the ratio of 10 boron nitride particles in the boron nitride powder. Ｂ / R Ａ means the average value of

[0027] The area ratio R of boron nitride in region C when the similarity ratio α is 0.6 Ｃ is the area ratio R of boron nitride in region A when the similarity ratio α is 0.6. Ａ The area ratio R of boron nitride in the region A when the homothetic ratio α is 0.6 may be smaller than Ａ The area ratio R of boron nitride in region C to Ｃ Ratio R Ｃ / R Ａ From the viewpoint of achieving a better crushing strength, the average value of the ratio R may be 0.92 or less, 0.9 or less, or 0.89 or less. Ｃ / R Ａ The average value of the area ratio R of boron nitride in the region C when the similarity ratio α is 0.4 or more may be 0.8 or more, or 0.85 or more. Ｃ is the area ratio R of boron nitride in region A Ａ Even when the similarity ratio α is 0.4, 0.5, or 0.7, the ratio R Ｃ / R Ａ may be within the above range, and the ratio R Ｃ / R Ａ The average value of the ratio R may be within the above range. Ｃ / R Ａ The average value of R is the ratio of 10 boron nitride particles in the boron nitride powder. Ｃ / R Ａ means the average value of

[0028] 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.

[0029] The crushing strength of the boron nitride powder may be 12 MPa or more, 13 MPa or more, or 14 MPa or more. The crushing strength can be measured by the method described in the examples below.

[0030] 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.

[0031] The boron nitride powder described above has a higher crushing strength because the density of boron nitride is somewhat higher near the center of gravity of the boron nitride particles contained in the boron nitride powder than near the surface. When a heat dissipating material is made by mixing boron nitride powder containing such boron nitride particles with a resin, the shape of the boron nitride particles near the surface tends to collapse, but the shape of the particles near the center of gravity tends to be maintained. This prevents the boron nitride flakes from aligning in the same direction in the heat dissipating material. Furthermore, heat dissipating materials using such boron nitride powder can exhibit higher thermal conductivity than heat dissipating materials using conventional boron nitride powder.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The heating temperature in the nitriding step is 2200°C or higher. When the heating temperature in the nitriding step is relatively high, the density of the obtained boron nitride particles tends to be somewhat higher near the center of gravity than near the surface. The heating temperature in the nitriding step may be 2400°C or lower, or 2300°C or lower.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] The boron carbonitride powder obtained in the nitriding step does not need to be fired in air, since the resulting boron nitride particles can be easily densified. In other words, the method for producing boron nitride powder does not need to include a step of firing the boron carbonitride powder in air.

[0040] 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.

[0041] 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.

[0042] 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 viewpoint of facilitating densification of the resulting boron nitride particles. 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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).

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] Examples of wetting and dispersing agents include phosphate ester salts, carboxylic acid esters, polyesters, acrylic copolymers, and block copolymers.

[0057] Examples of the surface conditioner include acrylic surface conditioners, silicone surface conditioners, vinyl surface conditioners, and fluorine surface conditioners.

[0058] A heat dissipation material can be obtained using the resin composition (i.e., the boron nitride powder). The thermal conductivity of the heat dissipation material produced using the resin composition tends to be higher than that of conventional heat dissipation materials. The thermal conductivity of the heat dissipation material 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.

[0059] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the following examples.

[0060] 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.

[0061] 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 filled 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.

[0062] 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.

[0063] (Comparative Example 2) Boron carbide powder having an average particle size (D50) of 26 μm was filled into a carbon crucible, and heated and pressurized by a HIP method in a nitrogen gas atmosphere under conditions of 1800° C. and 196 MPa for 1.5 hours using a hot isostatic pressing device (manufactured by Kobe Steel, Ltd., 02-SYSTEM15x type). The boron carbide powder was nitrided to obtain boron carbonitride powder (B ４ CN ４ ) was obtained. 100 parts by mass of the obtained boron carbonitride powder and 150 parts by mass of boric acid were mixed using a Henschel mixer, and the mixture was then filled into a boron nitride crucible and heated using a resistance heating furnace under atmospheric pressure in a nitrogen gas atmosphere at a holding temperature of 2000°C and 0.03 MPa for a holding time of 5 hours to obtain coarse particles. The coarse particles were crushed in a mortar for 10 minutes and then classified using a nylon sieve with 75 μm mesh. This yielded boron nitride powder.

[0064] [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 (manufactured by Microtrac-Bell, product name "SYNC"). 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 1.

[0065] [Measurement of Area Percentage and Area Percentage Ratio of Boron Nitride] First, the boron nitride powder obtained in the examples and comparative examples was embedded in epoxy resin, and the resin was cured to obtain a cured product. The measurement sample was observed using an SEM at 500x magnification to obtain a bmp-format image that allowed the entire cross section of a single boron nitride particle to be confirmed. The image was imported into the image processing software "ImageJ," and a single boron nitride particle in the image was focused on, with a border being drawn along the outer edge (periphery of the cross section) of the focused boron nitride particle. The image was then trimmed to a rectangle circumscribing the bordered area, and the area outside the bordered area (area where the focused boron nitride particle was not present) was masked. The image for analysis was imported into the image processing software "OpenCV" (Python language), filtered using a Median filter (kernel size 5), and the area consisting of boron nitride particles and the other area (resin area) were binarized using Otsu's method. Dilation processing (kernel size 5) and hole filling processing were performed to extract the perimeter of the cross section of the boron nitride particle with the largest area in the image. The perimeter of the extracted cross section was applied to the binarized image, and the region inside the perimeter of the cross section (the region where the boron nitride particle of interest exists, including the perimeter of region A) was designated as region A, and the center of gravity coordinates were calculated from the perimeter coordinates. Furthermore, a region obtained by reducing region A at a similarity ratio of 0.6, with the center of gravity of region A as the center of similarity, was designated as region B, and the perimeter of region B (the perimeter obtained by reducing the perimeter of region A at a similarity ratio of 0.6) was applied to the binarized image so that the centers of gravity of region A and region B overlap. In the binarized image, the region of region A other than region B (the region inside the perimeter of region A and outside the perimeter of region B, including the perimeter of region A but not the perimeter of region B) was designated as region C. The areas of the regions made of boron nitride in regions A, B, and C from the analysis image, and the areas of the multiple resin regions (voids) in the cross section of the boron nitride particle were measured, and the area ratio of the boron nitride region was calculated. The area ratios of regions A, B, and C were measured for 10 boron nitride particles, and the average value was calculated. In addition, the area ratio R of boron nitride in region C for 10 boron nitride particles was calculated. Ｃ The area ratio R of boron nitride in region B Ｂ Ratio RＢ / R Ｃ Average value of the area ratio R of boron nitride in region A Ａ The area ratio R of boron nitride in region B Ｂ Ratio R Ｂ / R Ａ Average value of the area ratio R of boron nitride in region A Ａ The area ratio R of boron nitride in region C to Ｃ Ratio R Ｃ / R Ａ The average value of the area ratio R of boron nitride in each of the regions A, B, and C was calculated. Ａ , R Ｂ , and R Ｃ The average value and ratio R Ｂ / R Ｃ , R Ｂ / R Ａ , and R Ｃ / R Ａ The results of measuring the average values ​​of the above are shown in Table 1. In Example 1, the similarity ratio between region A and region B was changed from 0.6 to 0.7, 0.5, or 0.4, and the area ratio R of boron nitride in each of regions A, B, and C was Ａ , R Ｂ , and R Ｃ The average value of and the ratio R Ｂ / R Ｃ , R Ｂ / R Ａ , and R Ｃ / R Ａ The average values ​​of the respective values ​​were calculated. The measurement results are shown in Table 2. Furthermore, SEM images of the cross sections of boron nitride particles a and b of Example 1 are shown in FIG. 1 , an SEM image of the cross section of boron nitride particles of Comparative Example 1 is shown in FIG. 2 , an analytical image of boron nitride particles a of Example 1 is shown in FIG. 3 , an analytical image of region B of boron nitride particles a of Example 1 is shown in FIG. 4( a ), an analytical image of region C of boron nitride particles a of Example 1 is shown in FIG. 4( b ), an analytical image of boron nitride particles b of Example 1 is shown in FIG. 5 , an analytical image of region B of boron nitride particles b of Example 1 is shown in FIG. 6( a ), and an analytical image of region C of boron nitride particles b of Example 1 is shown in FIG. 6( b ). In FIGS. 3 and 5 , the center G of the dotted line is the center of gravity, and the dashed-dotted line L is the periphery of region B.

[0066] [Measurement of Crushing Strength] The crushing strength of 20 boron nitride particles in the boron nitride powder obtained in the Examples and Comparative Examples was measured in accordance with JIS R 1639-5:2007. A microcompression tester (MCT-211, manufactured by Shimadzu Corporation) was used as the measuring device. The crushing strength σ (unit: MPa) of each boron nitride particle was calculated using the following equation: σ = similarity ratio α × P / (π × d ２ The crushing strength was measured for 20 boron nitride particles, and the average value was taken as the crushing strength of the boron nitride powder. The crushing strength measurement results are shown in Table 1.

[0067] [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 measured using a differential scanning calorimeter (Rigaku Corporation, ThermoPlusEvoDSC8230). 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 1. In Table 1, "-" means that the value was not measured.

[0068]

[0069]

Claims

1. A boron nitride powder that is an aggregate of a plurality of boron nitride particles, each of the plurality of boron nitride particles having a cross section consisting of boron nitride and voids, wherein, in the cross section, when a region surrounded by the periphery of the cross section is defined as region A, a region obtained by reducing region A with the center of gravity of region A as the center of similarity at a similarity ratio α is defined as region B, and the region of region A other than region B is defined as region C, when the similarity ratio α is 0.6, the area ratio R of the boron nitride in region C is Ｃ The area ratio R of the boron nitride in the region B to Ｂ Ratio R Ｂ / R Ｃ The boron nitride powder has an average value of 1.3 or more.

2. When the similarity ratio α is 0.4, 0.5, or 0.7, the ratio R Ｂ / R Ｃ 2. The boron nitride powder according to claim 1, wherein the average value of is 1.3 or more.

3. Area ratio R of the boron nitride in the region A Ａ 2. The boron nitride powder according to claim 1, wherein the average value of is 55 to 75%.

4. The area ratio R of the boron nitride in the region A when the similarity ratio α is 0.6 Ａ The area ratio R of the boron nitride in the region B to Ｂ Ratio R Ｂ / R Ａ 2. The boron nitride powder according to claim 1, wherein the average value of is 1.1 or more.

5. The area ratio R of the boron nitride in the region A when the similarity ratio α is 0.6 Ａ The area ratio R of the boron nitride in the region C to Ｃ Ratio R Ｃ / R Ａ 2. The boron nitride powder according to claim 1, wherein the average value of is 0.9 or less.

6. The boron nitride powder according to claim 1, having an average particle size of 20 to 120 μm.

7. The boron nitride powder according to claim 1, having a crushing strength of 12 MPa or more.

8. A resin composition comprising the boron nitride powder according to any one of claims 1 to 7 and a resin.

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