Boron nitride powder and method for producing boron nitride powder

Abstract

To provide a boron nitride powder suitable for a heat dissipation filler capable of preparing a resin molded article having excellent insulating properties.SOLUTION: One aspect of the present disclosure provides a boron nitride powder comprising primary particles of hexagonal boron nitride having a scaly shape, wherein the BET specific surface area is 0.5 to 4.0 cm2 / g, and the total amount of Na+, Ca2+, Mg2+, NH4+, F-, NO3-, and Cl- measured by ion chromatography is 1500.0 mass ppm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to boron nitride powder and methods for making the boron nitride powder. [Background technology]

[0002] In electronic components such as transistors, thyristors, and CPUs, efficient heat dissipation is an important issue. Therefore, heat dissipation materials with high thermal conductivity are used together with these electronic components. Meanwhile, boron nitride particles, with their high thermal conductivity and high insulating properties, are widely used as a filler in heat dissipation materials.

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

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-116401 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to improve the purity and crystallinity of boron nitride powder, auxiliary agents are used in the production process to promote grain growth of primary particles of hexagonal boron nitride. When compounds containing alkali metals or alkaline earth metals as constituent elements are used as auxiliary agents, ionic impurities derived from the auxiliary agents remain in the resulting boron nitride powder. In addition to the auxiliary agents, ionic impurities derived from raw materials or processes, or ionic impurities generated by hydrolysis of boron nitride itself, may also be present. Such ionic impurities can cause poor curing when resin compositions containing boron nitride powder as a filler are cured, and the incorporation of ionic impurities can cause increased conductivity and reduced insulation in cured resin molded products due to water absorption.

[0006] An object of the present disclosure is to provide a boron nitride powder suitable for use as a thermally conductive filler that can be used to prepare resin molded articles with excellent electrical insulation. Another object of the present disclosure is to provide a method for producing such a boron nitride powder. [Means for solving the problem]

[0007] The present disclosure provides the following [1] to [8].

[0008] [1] A boron nitride powder containing primary particles of hexagonal boron nitride having a scale shape, BET specific surface area is 0.5 to 4.0 cm 2 / g, Na measured by ion chromatography + , Ca 2+ , Mg 2+ , N.H. 4+ , F - , NO 3- , and Cl - The total amount of 1500.0 ppm by mass or less of the powder. [2] Na measured by ion chromatography + , Ca 2+ , and NO 3-The powder according to [1], wherein the total amount of is 3.0 mass ppm or more. [3] The powder according to [1] or [2], having a graphitization index of 1.5 or less. [4] The powder according to any one of [1] to [3], wherein the total oxygen content is 1.0 mass % or less. [5] The powder according to any one of [1] to [4], which has an average particle size of 7.5 to 20.0 μm. [6] A method for producing a dispersion by mixing a boron nitride raw material powder containing scaly hexagonal boron nitride primary particles with a solution containing hydrofluoric acid; reducing the content of said solution from said dispersion to obtain an acid-treated boron nitride powder. [7] The manufacturing method according to [6], wherein the content of hydrofluoric acid in the solution is 20 to 80 mass % with the total amount of the solution being 100 mass %. [8] The manufacturing method according to [6] or [7], wherein the content of the solution in the dispersion is 10 times or more the total volume of the boron nitride raw material powder. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a boron nitride powder suitable for a thermally conductive filler that can be used to prepare a resin molded product having excellent insulating properties. According to the present disclosure, it is also possible to provide a method for producing the above-mentioned boron nitride powder. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. In this specification, a numerical range indicated by the symbol "to" includes a lower limit and an upper limit. In other words, a numerical range indicated by "x to y" means equal to or greater than x and equal to or less than y.

[0011] Unless otherwise specified, the materials exemplified in this specification can be used singly or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified.

[0012] One embodiment of the boron nitride powder is a powder containing primary particles of hexagonal boron nitride having a scale shape. Here, the primary particles refer to single particles of hexagonal boron nitride. The boron nitride powder may consist of primary particles of hexagonal boron nitride.

[0013] The BET specific surface area of ​​the above boron nitride powder is 0.5 to 4.0 cm 2 The upper limit of the BET specific surface area is, for example, 3.0 cm 2 / g or less, 2.5cm 2 / g or less, 2.0cm 2 / g or less, 1.5cm 2 / g or less, or 1.3cm 2 The lower limit of the BET specific surface area may be, for example, 0.7 cm 2 / g or more, 0.9cm 2 / g or more, or 1.1cm 2 / g or more.

[0014] The specific surface area in this specification refers to a value measured using a specific surface area analyzer in accordance with JIS Z 8830:2013 "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption," and is a value calculated by applying the BET single-point method using nitrogen gas. Examples of specific surface area analyzers that can be used include the "MONOSORB MS-22" (product name) manufactured by QUANTACHROME.

[0015] The boron nitride powder contains Na, which is derived from the raw materials used, the treatment for promoting the grain growth of the primary particles of hexagonal boron nitride, and the degree of progress of crystallization. + , Ca 2+ , Mg 2+ , N.H. 4+ , NO3- , F - , and Cl - The boron nitride powder has a reduced proportion of Na (also referred to as specific ions in the present disclosure) as measured by ion chromatography. + , Ca 2+ , Mg 2+ , N.H. 4+ , F - , NO 3- , and Cl - The total amount of the specific ions is 1500.0 ppm by mass or less, but may be, for example, 1400.0 ppm by mass or less, 1300.0 ppm by mass or less, 1100.0 ppm by mass or less, 900.0 ppm by mass or less, 700.0 ppm by mass or less, or 750.0 ppm by mass or less. When a resin molded body is prepared by blending a boron nitride powder in which the upper limit of the total amount of the specific ions falls within the above range, the resin molded body can exhibit better insulating properties. In the boron nitride powder, the lower limit of the total amount of the specific ions is not particularly limited, but may be, for example, 100.0 ppm by mass or more, 150.0 ppm by mass or more, 300.0 ppm by mass or more, 500.0 ppm by mass or more, or 600.0 ppm by mass or more. NH 4+ , NO 3- Nitrogen-containing components such as NH are easily observed when the crystallinity of boron nitride is insufficient. 4+ , NO 3- While it can reduce + , Ca 2+ , Mg 2+ There is a tendency for the amount of ingredients derived from auxiliary agents such as these to increase.

[0016] Among the specific ions mentioned above, Na + , Ca 2+ , and NO 3- is a component that can reduce insulation properties, and it is desirable to reduce its content as much as possible, but it contributes to improving the flame retardancy of resin moldings obtained by filling boron nitride powder as a heat dissipating filler. Therefore, if flame retardancy is required depending on the application of the resin molding, it is recommended to use Na. + , Ca 2+ , and NO3- The boron nitride powder may be adjusted to contain a trace amount of Na as measured by ion chromatography. + , Ca 2+ , and NO 3- The total amount of may be, for example, 3.0 mass ppm or more, 4.0 mass ppm or more, 5.0 mass ppm or more, 7.0 mass ppm or more, 9.0 mass ppm or more, 10.0 mass ppm or more, 11.0 mass ppm or more, or 12.0 mass ppm or more. The boron nitride powder has a Na content measured by ion chromatography. + , Ca 2+ , and NO 3- The upper limit of the total amount may be, for example, 50.0 ppm by mass or less, 40.0 ppm by mass or less, 30.0 ppm by mass or less, or 20.0 ppm by mass or less.

[0017] The content of the specific ions in this specification refers to a value measured by ion chromatography, specifically, by the method described in the examples.

[0018] The boron nitride powder may contain primary particles of hexagonal boron nitride with excellent crystallinity. The upper limit of the graphitization index of the boron nitride powder may be, for example, 1.5 or less, 1.4 or less, 1.3 or less, or 1.2 or less. The fact that the upper limit of the graphitization index is within the above range is considered to correspond to the primary particles of hexagonal boron nitride contained in the boron nitride powder having excellent crystallinity, and may result in fewer impurities (components that can produce the above-mentioned specific ions). The lower limit of the graphitization index of the boron nitride powder may be, for example, 0.7 or more, 0.8 or more, 0.9 or more, or 1.0 or more. When the upper limit of the graphitization index is within the above range, defects in the primary particles of hexagonal boron nitride are further reduced, and the insulating properties of a resin molded body obtained by filling such a boron nitride powder can be further improved.

[0019] The graphitization index in this specification is also known as an index value indicating the degree of crystallinity of graphite (for example, J. Thomas, et. al., J. Am. Chem. Soc. 84, 4619 (1962)). The graphitization index is calculated based on a spectrum measured by powder X-ray diffraction for the above powder containing primary particles of hexagonal boron nitride. First, in the X-ray diffraction spectrum, the integrated intensities of each diffraction peak corresponding to the (100), (101), and (102) planes of the primary particles of hexagonal boron nitride (i.e., each diffraction peak) and its baseline are calculated, and these are designated as S100, S101, and S102, respectively. The graphitization index is determined using the calculated area values ​​based on the following formula (1): GI=(S100+S101) / S102...Equation (1)

[0020] The purity of the boron nitride powder may be, for example, 98% by mass or more, or 99% by mass or more. When the purity of boron nitride is within the above range, the insulating properties of the resin molded article obtained by filling the boron nitride powder can be further improved.

[0021] The purity of boron nitride powder in this specification refers to a value calculated from the following formula (2) based on the measured value obtained by titration. Specifically, the powder to be measured is first alkaline decomposed with sodium hydroxide, and ammonia is distilled from the decomposition liquid by steam distillation and collected in an aqueous boric acid solution. This collected liquid is then titrated with a normal sulfuric acid solution. The content of nitrogen atoms (N) in the powder is calculated from the titration results. The content of hexagonal boron nitride (hBN) in the powder is determined from the obtained nitrogen atom content using the following formula (2), and the purity of the powder is calculated. The formula weight of hexagonal boron nitride is 24.818 g / mol, and the atomic weight of nitrogen atoms is 14.006 g / mol. Hexagonal boron nitride (hBN) content in sample [mass%] = nitrogen atom (N) content [mass%] × 1.772 (2)

[0022] The total oxygen content of the boron nitride powder tends to increase with an increase in the number of hydrophilic functional groups (e.g., hydroxyl groups) that the primary particles of hexagonal boron nitride may have on their side surfaces. Because these functional groups can adsorb moisture, a low proportion of these groups is desirable. The upper limit of the total oxygen content of the boron nitride powder may be, for example, 1.0% by mass or less, 0.8% by mass or less, 0.6% by mass or less, 0.4% by mass or less, or 0.3% by mass or less. By ensuring that the upper limit of the total oxygen content is within the above range, the hygroscopicity of the entire boron nitride powder can be more sufficiently reduced, thereby more sufficiently suppressing the deterioration of the insulating properties of a resin molded article obtained by filling the boron nitride powder with the boron nitride powder. The lower limit of the total oxygen content of the boron nitride powder may be, for example, 0.02% by mass or more, 0.05% by mass or more, 0.1% by mass or more, or 0.15% by mass or more.

[0023] In this specification, the total oxygen content refers to the total oxygen content of the boron nitride powder. The total oxygen content can be determined using the following procedure. The oxygen and nitrogen content of the boron nitride powder is analyzed using an oxygen / nitrogen analyzer. The measurement sample is heated in a helium gas atmosphere from 20°C to approximately 2500°C, i.e., above the reactive decomposition temperature of boron nitride. The oxygen released as the temperature increases is detected. At the beginning of the temperature increase, oxygen bound to the surface of the boron nitride powder is released. The surface oxygen content is determined by quantifying the released oxygen. After that, when the temperature reaches approximately 1400°C, boron nitride begins to decompose. The start of boron nitride decomposition can be determined by detecting nitrogen. As boron nitride begins to decompose, oxygen inside the boron nitride particles is released. The internal oxygen content is determined by quantifying the released oxygen at this stage. The sum of the surface oxygen content and the internal oxygen content obtained in this manner is the total oxygen content. As the oxygen / nitrogen simultaneous analyzer, for example, an oxygen / nitrogen analyzer "EMGA-920" (trade name) manufactured by Horiba Ltd. can be used.

[0024] The upper limit of the average particle size of the boron nitride powder may be, for example, 20.0 μm or less, 18.0 μm or less, 17.0 μm or less, or 16 μm or less. The upper limit of the average particle size within the above range corresponds to a reduction in coarse particles, thereby further improving the surface smoothness of a resin molded body obtained by filling the boron nitride powder. The lower limit of the average particle size of the boron nitride powder may be, for example, 7.5 μm or more, 9.0 μm or more, 10.5 μm or more, 12.0 μm or more, 14.0 μm or more, or 15.0 μm or more. The lower limit of the average particle size within the above range corresponds to a reduction in fine particles, thereby suppressing moisture absorption, thereby further improving the insulating properties of a resin molded body obtained by filling the boron nitride powder. The average particle size of the boron nitride powder may be adjusted within the above range, for example, 7.5 to 20.0 μm.

[0025] In this specification, the average particle size refers to the 50% cumulative diameter (median diameter) in the volume-based cumulative particle size distribution. More specifically, it refers to the particle size (D50) at which the cumulative value reaches 50% in the volume-based cumulative particle size distribution obtained by laser diffraction scattering for a powder. Laser diffraction scattering is measured in accordance with the method described in JIS Z 8825:2013, "Particle Size Analysis - Laser Diffraction and Scattering Method." Measurements can be performed using a laser diffraction scattering particle size distribution analyzer. Examples of laser diffraction scattering particle size distribution analyzers that can be used include the "LS-13 320" (product name) manufactured by Beckman Coulter and the Microtrac "MT-3300EXII" (product name) manufactured by Microtrac-Bell. Note that the powder to be measured may contain aggregates in which primary particles are loosely associated with each other. Therefore, measurements should be performed after processing the powder using a homogenizer or the like.

[0026] The boron nitride powder is mainly composed of hexagonal boron nitride primary particles, but the content of agglomerates formed by the aggregation of multiple hexagonal boron nitride primary particles may be kept low. The agglomerates are formed by agglomerating the primary particles in multiple directions rather than being oriented in one direction in the in-plane direction (a-axis direction), and can be called secondary particles. The boron nitride powder may be mainly composed of the primary particles and may not contain aggregated particles.

[0027] One embodiment of a method for producing boron nitride powder includes the steps of: mixing a boron nitride raw material powder containing scaly hexagonal boron nitride primary particles with a solution containing hydrofluoric acid to obtain a dispersion (hereinafter, sometimes referred to as an acid treatment step); and reducing the content of the solution in the dispersion to obtain acid-treated boron nitride powder. Specifically, the raw material powder is introduced into the aqueous solution containing hydrofluoric acid to prepare a dispersion, and the dispersion is treated with stirring for a predetermined period of time.

[0028] In the above-mentioned production method, by bringing the boron nitride raw material powder into contact with the solution in the dispersion, the above-mentioned specific ions are eluted from the raw material powder, and the content of these ions can be reduced.

[0029] The boron nitride raw material powder containing scaly hexagonal boron nitride primary particles may be commercially available or may be separately prepared and used. The boron nitride raw material powder can be prepared, for example, by a method of firing a mixture of a boron compound such as boric acid and a nitrogen-containing compound such as melamine (particularly when boric acid and melamine are used, this method is also called the borate-melamine method).

[0030] The solution contains hydrofluoric acid, which may be hydrofluoric acid alone or may be a mixed acid with, for example, nitric acid. From the viewpoint of excellent oxidizing power and dissolving power, the solution may be a mixed acid of hydrofluoric acid and nitric acid (hydrofluoric nitric acid).

[0031] The content of hydrofluoric acid in the solution may be, for example, 20 to 80% by mass, where the total amount of the solution is 100% by mass. The lower limit of the content of hydrofluoric acid may be, for example, 22% by mass or more, 24% by mass or more, or 25% by mass or more, where the total amount of the solution is 100% by mass. By setting the lower limit of the content of hydrofluoric acid within the above range, the content of specific ions in the obtained boron nitride powder can be further reduced. The upper limit of the content of hydrofluoric acid may be, for example, 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, or 28% by mass or less, where the total amount of the solution is 100% by mass. By setting the upper limit of the content of hydrofluoric acid within the above range, oxidation of hexagonal boron nitride during treatment with the solution can be more sufficiently prevented.

[0032] The lower limit of the content of the solution in the dispersion may be, for example, 10 times or more, 12 times or more, 14 times or more, 16 times or more, 18 times or more, or 20 times or more, based on the total volume of the boron nitride raw material powder. By setting the lower limit of the content of the solution within the above range, the efficiency of the treatment with the solution is improved, and the content of specific ions in the obtained boron nitride powder can be further reduced. The upper limit of the content of the solution in the dispersion is not particularly limited, but may be, for example, 50 times or less, 40 times or less, or 30 times or less, based on the total volume of the boron nitride raw material powder.

[0033] In the acid treatment step, in order to more effectively bring the raw material powder into contact with the solution, the acid treatment step may be carried out while stirring the dispersion liquid.

[0034] In the acid treatment step, it is desirable to maintain contact between the raw material powder and the solution for a predetermined time. The time (acid treatment time) may be, for example, 5 to 180 minutes, 10 to 120 minutes, or 20 to 60 minutes. The stirring speed may be 50 to 1000 rpm, 100 to 700 rpm, or 200 to 400 rpm. The shape of the stirrer or stirring blade is not particularly limited.

[0035] In the acid treatment step, the acid treatment may be carried out while the dispersion is cooled, heated, or boiled. From the viewpoint of promoting the elution of the specific ions from the raw material powder into the solution, the temperature of the dispersion may be, for example, 25 to 90°C, 28 to 80°C, or 30 to 75°C. After the acid treatment, the treated powder may be washed with water to remove the acid, and then dried. The drying temperature may be, for example, 100 to 120°C. The drying time may be, for example, about 2 to 12 hours.

[0036] One embodiment of the resin composition includes a resin and a filler. The filler includes the boron nitride powder described above, and may also include other heat-dissipating fillers in addition to the boron nitride powder. Examples of other heat-dissipating fillers include alumina powder. In this embodiment, the filler is the boron nitride powder described above.

[0037] Examples of the resin include liquid crystal polymers, fluororesins, silicone resins, silicone rubber, acrylic resins, polyolefins (such as polyethylene), epoxy resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, polyimides, polyamideimides, polyetherimides, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, wholly aromatic polyesters, polysulfones, polyethersulfones, polycarbonates, maleimide-modified resins, ABS (acrylonitrile-butadiene-styrene) resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins.

[0038] The upper limit of the filler content may be, for example, 70% by mass or less, 60% by mass or less, or 55% by mass or less, based on the total volume of the resin composition. By setting the upper limit of the filler content within the above range, the insulating properties of a resin molded product can be further improved. The lower limit of the filler content may be, for example, 30% by mass or more, 40% by mass or more, or 50% by mass or more, based on the total volume of the resin composition. By setting the lower limit of the filler content within the above range, the heat dissipation properties of a resin molded product can be further improved. Note that, since the hygroscopicity of the boron nitride powder described above is suppressed by reducing specific ions, a decrease in insulating properties can be suppressed even when the filling amount in the resin composition is increased.

[0039] In addition to the resin and filler, the resin composition may further contain a curing agent that cures the resin. The curing agent can be appropriately selected depending on the type of resin. When the resin is an epoxy resin, examples of the curing agent include phenol novolac compounds, acid anhydrides, amino compounds, and imidazole compounds. The lower limit of the content of the curing agent may be, for example, 0.5 parts by mass or more, or 1 part by mass or more, per 100 parts by mass of the resin. The upper limit of the content of the curing agent may be, for example, 15 parts by mass or less, or 10 parts by mass or less, per 100 parts by mass of the resin.

[0040] The resin composition can be used after molding, curing, etc. One embodiment of the cured product is a cured product of a resin composition containing a cured resin and the above-mentioned boron nitride powder. The shape of the cured product is not particularly limited and may be a block, sheet, or film. In the case of a sheet-shaped cured product (sheet), the thickness of the sheet may be, for example, 0.5 mm or less, 0.2 mm or less, or 0.1 mm or less. Since the above-mentioned sheet contains the above-mentioned boron nitride, which has a relatively small particle size, a relatively thin sheet can be produced. Since the above-mentioned cured product contains the above-mentioned boron nitride powder, it is useful, for example, for heat dissipation components (e.g., heat dissipation sheets, etc.).

[0041] Although several embodiments have been described above, the present disclosure is not limited to the above embodiments. Furthermore, the descriptions of the above embodiments can be applied to each other. [Example]

[0042] The present disclosure will be described in more detail below using examples and comparative examples, but the present disclosure is not limited to the following examples.

[0043] Example 1 65 parts by mass of boric acid and 35 parts by mass of melamine were mixed and fired in a nitrogen atmosphere at 1000°C to obtain a calcined product containing low-crystalline boron nitride. Next, 5 parts by mass of sodium carbonate and 5 parts by mass of calcium carbonate were mixed with 100 parts by mass of the calcined product and fired in a nitrogen atmosphere at 1900°C to grow primary particles of hexagonal boron nitride and aggregate a plurality of the primary particles, thereby obtaining a raw material powder containing aggregated particles.

[0044] Hydrofluoric acid (50% by mass, aqueous solution) and nitric acid (density: 1.38 g / cm 3 ) was used to prepare a solution containing hydrofluoric acid in the blending ratio shown in Table 1. The above solution was mixed in an amount 22 times the volume of the raw material powder obtained as described above to prepare a dispersion. A stirrer was placed in the dispersion and stirred at 300 rpm for 2 hours. Thereafter, the solid matter was separated from the dispersion, washed with water, dehydrated, and dried to obtain boron nitride powder. A sufficient amount of pure water was used for washing, and dehydration was performed by centrifugation (300 rpm, 5 minutes). Thereafter, the solid matter was dried at 120°C for 10 hours.

[0045] (Examples 2 and 3) Boron nitride powder was prepared in the same manner as in Example 1, except that the compounding ratio of hydrofluoric acid and nitric acid in the solution for preparing the dispersion was changed as shown in Table 1.

[0046] (Comparative Example 1) Boron nitride powder was prepared in the same manner as in Example 1, except that nitric acid was used as the solution for preparing the dispersion.

[0047] (Comparative Example 2) Boron nitride powder was prepared in the same manner as in Example 1, except that pure water was used instead of the solution for preparing the dispersion.

[0048] (Comparative Example 3) 65 parts by mass of boric acid and 35 parts by mass of melamine were fired under a nitrogen atmosphere at 1900 °C to aggregate a plurality of boron nitride primary particles, and a powder containing agglomerated particles was obtained. At this time, no auxiliary agent was used.

[0049] Pure water amounting to 22 times the volume of the powder obtained as described above was mixed to prepare a dispersion. A stirrer was placed in the dispersion and stirred at 300 rpm for two hours. Thereafter, the solid matter was separated from the dispersion, washed with water, dehydrated, and dried to obtain boron nitride powder. A sufficient amount of pure water was used for washing with water, and dehydration was performed by centrifugation (300 rpm, 5 minutes). Thereafter, it was dried at 120 °C for 10 hours.

[0050] [Evaluation of Properties of Boron Nitride Powder] For the boron nitride powders prepared in the examples and comparative examples, the BET specific surface area, the content of various ions, the graphitization index, the total oxygen amount, and the average particle diameter were measured. The results are shown in Table 1.

[0051] <BET Specific Surface Area> The BET specific surface area of the boron nitride powder was measured by the BET single-point method using nitrogen gas in accordance with the description in JIS Z 8803:2013 "Method for Measuring Specific Surface Area of Powder (Solid) by Gas Adsorption".

[0052] <Content of Various Ions> The content of various ions in the boron nitride powder was measured by ion chromatography. First, 1 g of boron nitride powder was immersed in 20 mL of pure water and eluted in a water bath (80°C) for 1 hour, and the solution was then subjected to ion chromatography measurement. The measurement conditions for the ion chromatography method were as follows: Equipment: Ion chromatograph (Thermo Fisher Scientific, product name: ICS-2100) Column: AS17-C (product name, manufactured by Thermo Fisher Scientific) Introduced amount: 25μL Eluent: Potassium hydroxide (KOH) solution Flow rate: 1.00 mL / min Measurement temperature: 35℃

[0053] <Graphitization index> The graphitization index of boron nitride powder was calculated from the results of measurement by powder X-ray diffraction. First, an X-ray diffractometer (manufactured by Rigaku Corporation, product name: "ULTIMA-IV") was used to prepare a measurement sample by filling and solidifying boron nitride powder into the recess of a glass cell with a 0.2 mm depth attached to the device. The measurement sample was irradiated with X-rays and baseline correction was performed.

[0054] In the obtained X-ray diffraction spectrum, the integrated intensity of each diffraction peak corresponding to the (100), (101), and (102) planes of the primary particles of hexagonal boron nitride (i.e., the area surrounded by each diffraction peak and its baseline) (in arbitrary units) was calculated and designated as S100, S101, and S102, respectively. Using the area values ​​calculated in this way, the graphitization index was determined based on the following formula (1). GI=(S100+S101) / S102...Equation (1)

[0055] <Total oxygen amount> The total oxygen content of the boron nitride powder was measured using an oxygen / nitrogen analyzer (manufactured by Horiba Ltd., trade name: EMGA-920).

[0056] <Average particle size> The average particle size of boron nitride powder was measured in accordance with the method described in JIS Z 8825:2013, "Particle size analysis - laser diffraction and scattering method." Measurements were performed using a laser diffraction and scattering particle size distribution analyzer (Microtrac "MT-3300EXII" (product name) manufactured by Microtrac-Bell). Note that, because the powder to be measured may contain aggregates in which primary particles are loosely associated with each other, the powder to be measured was processed using a homogenizer.

[0057] [Evaluation of boron nitride powder as a filler] Resin sheets were prepared using the boron nitride powders prepared in the examples and comparative examples, and the insulating properties, moisture absorption, and flame retardancy were evaluated according to the methods described below. The results are shown in Table 1.

[0058] <Preparation of Resin Sheet> A mixture was obtained by mixing 22.5 parts by mass of silicone resin (Dow-Toray Industries, Inc., product name: CF3110) and 0.225 parts by mass of organic peroxide (Mitsui Fine Chemicals, Inc., product name: Trigonox 101) as a curing agent. 100 parts by mass of toluene was added to the mixture. Next, 77.5 parts by mass of the boron nitride powder synthesized separately as described above and 0.00775 parts by mass of a silane coupling agent (Dow-Toray Industries, Inc., product name: Z6329) were mixed, and then further mixed with the mixture to which the toluene had been added. The mixture containing the curing agent was stirred for 1 hour using a planetary mixer to prepare a mixed solution.

[0059] The resulting mixture was applied to a PET sheet to a thickness of 250 μm, and then left to stand at room temperature for 4 hours to volatilize the toluene. Thereafter, the PET sheet was cut into 100 mm × 100 mm pieces and heated at 150 °C and 160 kgf / cm 2 The silicone resin was heat-cured by hot pressing under the conditions of 100° C., ...

[0060] <Insulation evaluation> A 50 mm x 50 mm test piece was cut out from the resin sheet and left in an environment of 85°C x 85% humidity for 24 hours. After that, both sides of the test piece were sandwiched between electrodes and the insulation resistance value (GΩ) was measured in accordance with JIS K 6911. Evaluation was made according to the following criteria. A: The insulation resistance is 5GΩ or more. B: The insulation resistance value is 1 GΩ or more and less than 5 GΩ. C: The insulation resistance value is less than 1 GΩ.

[0061] <Evaluation of moisture absorption> A 50mm x 50mm test piece was cut from the resin sheet and immersed in ion-exchanged water at 25°C for 1 hour. The entire surface was then clamped between JK wipers at 0.5 MPa for 5 seconds. The mass was then measured, and the mass increase rate (mass%) before and after immersion was measured. Based on the measurement results, moisture absorption was evaluated according to the following criteria. A: The mass increase rate is less than 0.01% by mass. B: The mass increase rate is 0.01% by mass or more and less than 0.05% by mass. C: The mass increase rate is 0.05% by mass or more.

[0062] <Flame retardancy evaluation> The resin sheet was cut into approximately 5 mg pieces, which were then measured in a differential thermal-thermogravimetric simultaneous analyzer (TG-DTA) in a nitrogen atmosphere from room temperature (25°C) to 800°C at a heating rate of 10°C / min, and the mass loss rate during this period was measured. The results were evaluated according to the following criteria. A: The mass loss rate is less than 10% by mass. B: The mass loss rate is 10% by mass or more and less than 20% by mass. C: The mass loss rate is 20% by mass or more.

[0063] [Table 1] [Industrial Applicability]

[0064] According to the present disclosure, it is possible to provide a boron nitride powder suitable for a thermally conductive filler that can be used to prepare a resin molded product having excellent insulating properties. According to the present disclosure, it is also possible to provide a method for producing the above-mentioned boron nitride powder.

Claims

1. A boron nitride powder containing primary particles of hexagonal boron nitride having a scale shape, BET specific surface area is 0.5 to 4.0 cm ２ / g, Na measured by ion chromatography ＋ , Ca ２＋ , Mg ２＋ , N.H. ４＋ , F － , NO ３－ , and Cl － The powder, wherein the total amount of

2. Na measured by ion chromatography ＋ , Ca ２＋ , and NO ３－ The powder according to claim 1, wherein the total amount of is 3.0 mass ppm or more.

3. 3. The powder according to claim 1, having a graphitization index of 1.5 or less.

4. The powder according to claim 1 or 2, wherein the total oxygen content is 1.0 mass % or less.

5. The powder according to claim 1 or 2, having an average particle size of 7.5 to 20.0 μm.

6. A method for producing a dispersion by mixing a boron nitride raw material powder containing scaly hexagonal boron nitride primary particles with a solution containing hydrofluoric acid; reducing the content of said solution from said dispersion to obtain an acid-treated boron nitride powder.

7. 7. The method according to claim 6, wherein the content of hydrofluoric acid in the solution is 20 to 80 mass % with the total amount of the solution being 100 mass %.

8. 8. The method according to claim 6, wherein the content of the solution in the dispersion is 10 times or more the total volume of the boron nitride raw material powder.

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