Hexagonal boron nitride powder

Abstract

To provide hexagonal boron nitride powder which, when used as a filler to be filled into a resin to form a resin composition, has low frequency dependence of dielectric dissipation factor in a high frequency band of the resin composition.SOLUTION: A hexagonal boron nitride powder has a median diameter (D50) as measured by a laser diffraction method of 1 to 10 μm and a specific surface area as measured by a nitrogen adsorption method of 1 to 10 m2 / g. The hexagonal boron nitride powder is kneaded at a ratio of 30 vol.% into a polypropylene resin to obtain a resin composition which is then formed into a shape of a sheet having a thickness of 0.35 mm to 0.45 mm, and then the sheet, when measured for dielectric dissipation factor by a resonator method, has the ratio tanδ91 / tanδ10 between the dielectric dissipation factor tanδ10 measured at a frequency of 10 GHz and the dielectric dissipation factor tanδ91 measured at a frequency of 91 GHz of 1.4 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to hexagonal boron nitride powder. [Background technology]

[0002] Resin compositions containing resins such as epoxy resins and silicone resins filled with hexagonal boron nitride powder are widely used for semiconductor encapsulation, insulating layer applications for printed wiring boards, etc. In particular, with the increasing performance and high-speed communication of electronic devices and information terminals, it is necessary to control the dielectric loss tangent of resin compositions in order to control the dielectric properties of semiconductor encapsulation materials and insulating layer materials.

[0003] One method for reducing the dielectric loss tangent of a resin composition is to control the dielectric loss tangent of the hexagonal boron nitride powder to be filled, and various studies have been conducted on this. For example, Patent Document 1 discloses that in hexagonal boron nitride powder, the proportion of side surfaces of primary particles is reduced in order to suppress an increase in the proportion of functional groups that cause an increase in the dielectric loss tangent, and in the examples, specifically discloses a hexagonal boron nitride powder having a dielectric loss tangent of 0.0007 or less at 1 GHz. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO2023 / 204140 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, with the development of communication technologies such as beyond 5G and 6G, importance has begun to be placed on dielectric properties in high frequency bands of several tens of GHz or more for resin compositions used for semiconductor encapsulation, insulating layers for printed wiring boards, etc. In addition, when the frequency bands used are so diverse, if the dielectric properties change with frequency, the design of the equipment becomes complicated, so it is preferable that the behavior of the dielectric properties does not change significantly over a wide frequency range.

[0006] However, as mentioned above, while hexagonal boron nitride powders with low dielectric loss tangents in the 1 GHz band are known, the behavior of their dielectric properties in high-frequency bands of several tens of GHz or higher has not been fully investigated. In particular, the dielectric loss tangent of hexagonal boron nitride powders generally exhibits frequency dependence, increasing with increasing frequency. However, no studies have focused on the frequency dependence in high-frequency bands of several tens of GHz or higher. In fact, when the dielectric properties of S02 (manufactured by Tokuyama Corporation), an example of an existing hexagonal boron nitride powder, were evaluated in the high-frequency band, as shown in the Reference Example below, although the relative permittivity was low, the dielectric loss tangent at 91 GHz was approximately 1.5 times that at 10 GHz, indicating a relatively high frequency dependence of the dielectric loss tangent. When such conventional hexagonal boron nitride powders were used as fillers in resins to prepare resin compositions, the resulting resin compositions exhibited a high frequency dependence of the dielectric loss tangent in the high-frequency band.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hexagonal boron nitride powder which, when used as a filler in a resin to form a resin composition, exhibits little frequency dependence of the dielectric loss tangent in the high frequency band of the resin composition. [Means for solving the problem]

[0008] As a result of extensive research, the inventors have succeeded in obtaining a hexagonal boron nitride powder that has a smaller difference in dielectric loss tangent measured at a frequency of 10 GHz and that measured at a frequency of 91 GHz, compared to existing hexagonal boron nitride powders.

[0009] That is, the present invention provides a method for producing a cellulose ester having a median diameter D50 of 1 to 10 μm measured by a laser diffraction method and a specific surface area of ​​1 to 10 m measured by a nitrogen adsorption method. 2 / g, and when a resin composition obtained by kneading the hexagonal boron nitride powder into a polypropylene resin at a ratio of 30 volume % is formed into a sheet having a thickness of 0.35 mm to 0.45 mm and the dielectric loss tangent of the sheet is measured by a resonator method, the dielectric loss tangent tanδ measured at a frequency of 10 GHz is 10 and the dielectric loss tangent tanδ measured at a frequency of 91 GHz 91 The ratio tanδ 91 / tanδ 10 The hexagonal boron nitride powder is characterized by having a relative dielectric constant of 1.4 or less. The hexagonal boron nitride powder is preferably kneaded into a polypropylene resin at a ratio of 30 volume % to obtain a resin composition, which is formed into a sheet having a thickness of 0.35 mm to 0.45 mm and measured at a frequency of 10 GHz by a resonator method, and the relative dielectric constant is preferably 3.3 or less. Furthermore, the hexagonal boron nitride powder preferably has an average aspect ratio of 10 or less. Another aspect of the present invention is a resin composition comprising the hexagonal boron nitride powder and a resin. [Effects of the Invention]

[0010] The hexagonal boron nitride powder of the present invention makes it possible to provide a resin composition whose dielectric loss tangent has little frequency dependence in the 10 to 91 GHz band. By using such a resin composition for semiconductor encapsulation or insulating layer applications, the behavior of the dielectric properties becomes stable over a wide frequency range, making the design of communication devices and the like easier than ever before. DETAILED DESCRIPTION OF THE INVENTION

[0011] The hexagonal boron nitride powder of the present invention is prepared by kneading 30% by volume of hexagonal boron nitride powder into polypropylene resin to obtain a test composition, which is then molded into a sheet having a thickness of 0.35 mm to 0.45 mm. When the dielectric loss tangent of the sheet is measured by the resonator method, the dielectric loss tangent tanδ measured at a frequency of 10 GHz is 10 and the dielectric loss tangent tanδ measured at a frequency of 91 GHz 91The ratio tanδ 91 / tanδ 10 is 1.4 or less.

[0012] The dielectric loss tangent is a value that indicates the degree of electrical energy loss, and the larger this value, the greater the energy loss and transmission loss. In hexagonal boron nitride powder, the dielectric loss tangent is generally frequency-dependent, being affected by the frequency of the applied current, and the higher the frequency, the greater the dielectric loss tangent.

[0013] On the other hand, the hexagonal boron nitride powder of the present invention has a dielectric loss tangent tanδ measured at a frequency of 10 GHz. 10 and the dielectric loss tangent tanδ measured at a frequency of 91 GHz 91 The ratio tanδ 91 / tanδ 10 The tan δ is 1.4 or less, and has small frequency dependency. Due to this characteristic, the resin composition using hexagonal boron nitride of the present invention can exhibit stable behavior over a wide frequency range from several GHz to several tens of GHz. 91 / tanδ 10 is preferably 1.3 or less, and more preferably 1.2 or less. 91 / tanδ 10 Although there are no particular restrictions on the lower limit of the dielectric loss tangent, as mentioned above, the higher the frequency, the larger the dielectric loss tangent, and the lower limit is usually 1.0 or more.

[0014] The hexagonal boron nitride powder has a dielectric loss tangent tanδ measured at a frequency of 28 GHz. 28 , dielectric tangent tanδ measured at a frequency of 35 GHz 35 , dielectric loss tangent tanδ measured at a frequency of 56 GHz 56 , dielectric loss tangent tanδ measured at a frequency of 74 GHz 74 Regarding the dielectric loss tangent, the difference between the dielectric loss tangent and tanδ is small. 10 and tanδ 91 It is preferable that the difference between tanδ and 74 / tanδ 10 , tanδ 56 / tanδ 10, tanδ 35 / tanδ 10 , tanδ 28 / tanδ 10 , tanδ 91 / tanδ 28 , tanδ 56 / tanδ 28 , tanδ 35 / tanδ 28 , tanδ 91 / tanδ 35 , tanδ 74 / tanδ 35 , tanδ 56 / tanδ 35 , tanδ 91 / tanδ 56 and tanδ 74 / tanδ 56 are each preferably 1.4 or less, more preferably 1.3 or less, even more preferably 1.2 or less, and generally 1.0 or more. These properties make it easy for resin compositions using the hexagonal boron nitride powder of the present invention to exhibit stable behavior over a wide range of frequencies.

[0015] Also, tanδ 10 , tanδ 28 , tanδ 35 , tanδ 56 , tanδ 74 , tanδ 91 are preferably 0.00050 or less, more preferably 0.00040 or less, and even more preferably 0.00035 or less. By being in the above ranges, the transmission loss at each frequency can be reduced. 10 , tanδ 28 , tanδ 35 , tanδ 56 , tanδ 74 , tanδ 91 The lower limit of is not particularly limited, but is generally 0.00010 or more.

[0016] The hexagonal boron nitride powder was prepared by kneading the hexagonal boron nitride powder into a polypropylene resin at a ratio of 30% by volume, forming the obtained test composition into a sheet having a thickness of 0.35 mm to 0.45 mm, and measuring the relative dielectric constant εr at a frequency of 10 GHz using a resonator method. 10 is preferably 3.3 or less, and more preferably 3.1 or less. Similarly, the relative dielectric constant εr measured at a frequency of 28 GHz is 28 , relative permittivity εr measured at a frequency of 35 GHz 35 , relative permittivity εr measured at a frequency of 56 GHz 56 , relative permittivity εr measured at a frequency of 74 GHz 74 , relative permittivity εr measured at a frequency of 91 GHz 91 is also preferably 3.3 or less, more preferably 3.1 or less. By keeping the relative permittivity at each frequency within the above range, it becomes easy to reduce the transmission loss at each frequency. 10 , εr 28 , εr 35 , εr 56 , εr 74 , εr 91 The lower limit of is not particularly limited, but is generally 2.0 or more.

[0017] The relative permittivity and dielectric loss tangent in the present invention are measured using an evaluation sample obtained by kneading hexagonal boron nitride powder into polypropylene resin at a ratio of 30% by volume, and molding the obtained test composition into a sheet having a thickness of 0.35 to 0.45 mm. As the polypropylene resin, for example, Novatec PP MA3 manufactured by Japan Polypropylene Corporation can be used. The hexagonal boron nitride powder can be kneaded into the polypropylene resin using a kneading device. The hexagonal boron nitride powder and polypropylene resin can be measured out so that the hexagonal boron nitride powder accounts for 30% by volume of the total, and then charged into a heated mixing section of the kneading device and kneaded to obtain the test composition. Specifically, a Labo Plastomill 3S150 kneading machine manufactured by Toyo Seiki Seisakusho, Ltd. was used, and the mixing section was heated to 200°C. A predetermined amount of polypropylene was then added to the mixing section and dissolved. A predetermined amount of hexagonal boron nitride powder was then added to the mixing section, and the mixture was kneaded at 200°C for 10 minutes at a rotation speed of 30 rpm to obtain a test composition. The test composition was then pressed using a 0.4 mm thick SUS mold at 2 tons and 180°C for 2 minutes, and then at 2 tons and 40°C for 2 minutes to form a sheet with a thickness of 0.35 mm to 0.45 mm, thereby obtaining an evaluation sample.

[0018] In the present invention, the dielectric constant and dielectric loss tangent are measured using a resonance method. Specifically, a resonator tuned to a predetermined frequency is connected to a network analyzer, and an evaluation sample is placed on the resonator for measurement. The dielectric constant and dielectric loss tangent can be calculated by this method. The measurement is performed in a constant temperature and humidity chamber at a temperature of 25°C and a humidity of 50% RH. Note that, although the frequency of the resonator may change slightly due to the influence of the evaluation sample when the evaluation sample is placed on the resonator during measurement, the measurement frequency in this application refers to the frequency of the resonator before the evaluation sample is placed on the resonator. For example, "measured at a frequency of 10 GHz" means that the frequency of the resonator was 10 GHz before the evaluation sample was placed on the resonator, and "measured at a frequency of 91 GHz" means that the frequency of the resonator was 91 GHz before the evaluation sample was placed on the resonator. The resonator frequency is strongly affected by the thickness of the evaluation sample, but this effect can be minimized by adjusting the thickness of the evaluation sample to a specific range of 0.35 mm to 0.45 mm.

[0019] The hexagonal boron nitride powder of the present invention has a median diameter D50 measured by a laser diffraction method of 1 to 10 μm, preferably 2.0 to 8.0 μm, and a specific surface area measured by a nitrogen adsorption method of 1 to 10 m 2 / g, 1.5 to 9.5 m 2 / g, and 3.5 to 9.0m 2 / g is more preferable. By making the median diameter D50 1 μm or more, it becomes easy to improve the flow characteristics and processability of the resin composition. By making the median diameter D50 10 μm or less, it becomes easy to improve the permeability into gaps when used as a material for semiconductor packaging, which is becoming increasingly miniaturized. Similarly, when the specific surface area is 10 m 2 / g or less, the flow characteristics and processability of the resin composition can be easily improved, and the specific surface area can be reduced to 1 m 2 By making the molecular weight ρ / g or more, it is easy to ensure good permeability into gaps when used as a material for semiconductor packages, which are becoming increasingly miniaturized.

[0020] The hexagonal boron nitride powder of the present invention preferably has an average aspect ratio of 10 or less, more preferably 8 or less. There is no particular lower limit to the average aspect ratio, but it is generally 1 or more. In this specification, primary particles of hexagonal boron nitride are usually plate-like particles, and the longest diameter on the plate surface of a plate-like particle is defined as the longest diameter, and the length perpendicular to this plate surface is defined as the thickness. The value obtained by dividing the longest diameter by the thickness is referred to as the aspect ratio. The hexagonal boron nitride powder is observed with a scanning electron microscope (SEM) to obtain SEM images, and at least 100 hexagonal boron nitride primary particles are randomly selected to calculate the aspect ratio of each particle. The arithmetic average is then used to determine the average aspect ratio of the hexagonal boron nitride powder.

[0021] Hexagonal boron nitride particles generally have anisotropic thermal conductivity, with high thermal conductivity in the plate surface direction and low thermal conductivity in the plate thickness direction. Because they are plate-shaped particles, they tend to orient when filled with resin, which can easily cause thermal conductivity anisotropy in the resin composition. However, because they have a small average aspect ratio, they are less likely to orient when filled with resin compositions, making it easier to suppress the anisotropy of thermal conductivity.

[0022] Furthermore, hexagonal boron nitride primary particles usually have few surface functional groups on the particle plate surfaces and many surface functional groups on the particle side surfaces. As will be described later, control of surface functional groups is considered necessary to control the dielectric loss tangent. When the aspect ratio is small, the area of ​​the particle side surfaces increases and the number of surface functional groups increases, making it difficult to control the dielectric loss tangent. However, with the hexagonal boron nitride powder of the present invention, the frequency dependence of the dielectric loss tangent can be controlled to be small despite the small average aspect ratio.

[0023] The hexagonal boron nitride powder of the present invention can be obtained, for example, by synthesizing hexagonal boron nitride, pickling it, and then subjecting it to a surface stabilization treatment in an inert gas atmosphere. The reason for this is unclear, but it is presumed that the behavior of the surface state of the hexagonal boron nitride powder, which affects its dielectric properties, can be controlled by the surface stabilization treatment.

[0024] Hexagonal boron nitride powder before surface stabilization treatment (hereinafter, sometimes referred to as "crude boron nitride powder") can be produced using known methods, such as a reduction nitridation method or a melamine method.

[0025] The reduction-nitridation method is a method for obtaining highly crystalline boron nitride (nitride powder) by heating an oxygen-containing boron compound, a carbon source, and an oxygen-containing alkaline earth metal compound in a nitrogen atmosphere to a temperature of about 1700 to 2200°C to carry out a nitriding reaction. The types and amounts of the oxygen-containing boron compound, the carbon source, and the oxygen-containing alkaline earth metal compound, as well as the heating conditions and washing conditions, may be appropriately adjusted under known conditions depending on the desired physical properties such as the median diameter D50, specific surface area, and average aspect ratio.

[0026] The melamine method involves reacting boric acid and melamine at a temperature of about 1000°C to obtain low-crystalline boron nitride powder, and then heating the resulting mixture to a temperature of about 1700 to 2200°C to carry out a nitriding reaction, thereby obtaining highly crystalline boron nitride (nitride powder).The types and amounts of the oxygen-containing boron compound, carbon source, and oxygen-containing alkaline earth metal compound, as well as heating conditions, may be appropriately adjusted under known conditions depending on the desired physical properties, such as the median diameter D50, specific surface area, and average aspect ratio.

[0027] In the production of the hexagonal boron nitride powder of the present invention, it is important to subject the crude boron nitride powder, which has been subjected to acid washing to remove impurities, to a surface stabilization treatment in an inert gas atmosphere.

[0028] The acid washing conditions are not particularly limited, and examples include a method in which 50 to 200 parts by mass of concentrated hydrochloric acid (37% by mass HCl) and 200 to 500 parts by mass of pure water are added to 100 parts by mass of nitride powder and allowed to contact for at least 4 hours. In addition to hydrochloric acid, acids such as nitric acid, sulfuric acid, and acetic acid can also be used for the acid washing. After the acid washing, water washing may be performed to remove any remaining acid. Water washing may be performed by a known method, such as washing with pure water. For example, after filtering the acid used in the acid washing, the acid-washed boron nitride is dispersed in pure water in an amount equal to the amount of acid used, filtered again, and then repeatedly washed with pure water and filtered until the filtrate becomes neutral. After the acid washing and water washing, a drying treatment may be performed. The drying treatment may be performed, for example, by air drying at 50 to 250°C, or by drying under reduced pressure. The drying time may be appropriately determined so that the moisture content approaches 0% (for example, the moisture content is 0.50% or less), and may be, for example, 1 to 48 hours at the above temperature.

[0029] The surface passivation treatment can be carried out by leaving the crude boron nitride powder in an inert gas atmosphere at 10 to 50°C for 12 hours or more. Examples of the inert gas include rare gases such as helium and argon, and nitrogen, but from an economical standpoint, argon or nitrogen is preferred. The inert gas preferably has a dew point of -76°C or lower. Having a dew point within this range allows for effective control of functional groups and moisture removal, as described below.

[0030] The boron nitride powder that has undergone surface passivation treatment may be further calcined in a nitrogen atmosphere at a temperature of 1200°C or higher for at least one hour. This can further reduce the frequency dependence of the dielectric loss tangent in the high-frequency band. This is presumably because prior acid washing and surface passivation treatment significantly reduce impurities on the boron nitride powder surface, and then calcination treatment can further reduce surface functional groups. Simply performing calcination is insufficient; it is important to perform acid washing and surface passivation treatment in advance to significantly reduce impurities. If a large amount of impurities (especially boron oxide) are present during calcination, these can become the starting point for functional group generation. Therefore, calcination treatment cannot significantly reduce the surface functional groups, resulting in increased dielectric loss tangent and its frequency dependence. Furthermore, by performing a surface stabilization treatment before the calcination treatment, moisture is removed from the boron nitride particles while reducing the surface reactivity, making it difficult for boron oxide to be generated during the calcination treatment. This is thought to enable the calcination treatment to thoroughly remove surface functional groups and further reduce the dielectric loss tangent and its frequency dependence.

[0031] The crude boron nitride powder preferably has an eluted boron content of 100 ppm or less, more preferably 60 ppm or less, which makes it easier to reduce the dielectric loss tangent and its frequency dependence.

[0032] The use of the hexagonal boron nitride powder of the present invention is not particularly limited, but it is preferably used as a filler to be filled into resins. When the hexagonal boron nitride powder of the present invention is used as a filler, a resin composition containing the hexagonal boron nitride powder of the present invention and a resin can be obtained. Furthermore, compared to when other hexagonal boron nitride powders are used, the resin composition has smaller frequency dependence in the high-frequency range, and therefore can be suitably used for substrate applications, semiconductor encapsulation applications, and insulating layer applications for printed wiring boards and package substrates, where dielectric properties are important. Among these applications, its use as a material for substrates such as printed wiring boards and package substrates is particularly preferred, and substrates containing the resin composition or a cured product thereof are suitable examples.

[0033] The resin of the resin composition may be a thermoplastic resin or a thermosetting resin, such as an epoxy resin, a phenolic resin, a melamine resin, a urea resin, an unsaturated polyester resin, an acrylic resin, a methacrylic resin, a silicone resin, a fluororesin, a polyphenylene ether, or an LCP. The resin may have a polymerizable functional group, and may be a cured product obtained by polymerizing and curing a resin composition containing the hexagonal boron nitride powder of the present invention and a resin having a polymerizable functional group. The amount of the hexagonal boron nitride powder of the present invention in the resin composition is not particularly limited and can be adjusted appropriately depending on the application. For example, the amount of the hexagonal boron nitride powder may be 1 to 900 parts by mass, preferably 30 to 800 parts by mass, per 100 parts by mass of the resin. When the resin composition is used as a substrate material, the resin is preferably an epoxy resin, a polyphenylene ether, or an LCP. The amount of the hexagonal boron nitride powder is preferably 10 to 400 parts by mass, more preferably 30 to 250 parts by mass, per 100 parts by mass of the resin.

[0034] The resin composition may contain other components such as fillers other than the hexagonal boron nitride powder, flame retardants, rubber particles, thickeners, antifoaming agents, leveling agents, adhesion promoters, antioxidants, ultraviolet degradation inhibitors, and colorants.

[0035] Examples of substrate materials made of the resin composition include build-up films and prepregs, and examples of substrate materials containing the resin composition include copper-clad laminates in which the resin composition and copper are laminated together. [Example]

[0036] Examples will be described below to specifically explain the present invention, but the present invention is not limited to these examples. The measurements of the various items in the examples and comparative examples were performed by the following methods.

[0037] <Measurement of median diameter D50> 0.3 g of hexagonal boron nitride powder was put together with 50 cc of ethanol into a screw tube bottle with a volume of 100 cc and a diameter of 4 cm. With a probe having a diameter of 0.2 cm inserted 1 cm into water, ultrasonic waves were applied at an output of 100 W from the above probe for 20 minutes at room temperature, and the suspension after that was used. The volume-based particle size distribution was measured using a laser diffraction / scattering particle size distribution measuring device (LA-950V2 manufactured by HORIBA), and the median diameter D50 was determined.

[0038] <Measurement of BET specific surface area> It was determined by the BET method (nitrogen adsorption one-point method) using a rapid surface area measuring device (SA-1000 manufactured by Shibata Scientific Co., Ltd.). For the measurement, 2 g of a powder sample was used, which had been previously dried at 100 °C for 1 hour in a nitrogen gas flow. ​​​​​​​​​​​​​​​​Polypropylene resin (Novatec PP MA3, manufactured by Japan Polypropylene Corporation) and hexagonal boron nitride powder were weighed out so that the hexagonal boron nitride powder accounted for 30% by volume of the total, and then placed in a mixing section of a kneading machine (Labo Plastomill 3S150, manufactured by Toyo Seiki Seisakusho Co., Ltd.) heated to 200°C. The kneading was then carried out at 200°C for 10 minutes at a rotation speed of 30 rpm to obtain a test composition. The test composition was then pressed using a 0.4 mm thick SUS mold at 2 tons and 180°C for 2 minutes, followed by another press at 2 tons and 40°C for 2 minutes to obtain a sheet-like molded product with a thickness of 0.35 mm to 0.45 mm. The molded product was then cut into the size of the resonator to be used depending on the frequency, and evaluation samples were obtained. The dielectric properties were measured by connecting a split cylinder resonator of a predetermined frequency to a network analyzer (N5290A for measurements at 10 GHz and 28 GHz, HP8510 for measurements at 35 GHz, and HP8757 for measurements at 56 GHz, 74 GHz, and 91 GHz), setting the evaluation sample in the resonator, and performing measurements in TE011 mode to determine the relative permittivity and dielectric loss tangent from the obtained results. The measurements were performed in a constant temperature and humidity environment room at a temperature of 25°C and a humidity of 50% RH.

[0042] [Example 1] 700g of boron oxide, 300g of carbon black, and 200g of calcium carbonate were mixed in a mixer. This mixture was heated to 1500°C in a graphite Tammann furnace under a nitrogen gas atmosphere and held at 1500°C for 6 hours. After holding at 1500°C, the mixture was heated to 1840°C and subjected to reduction-nitriding treatment at 1840°C for 2 hours to obtain nitrided powder. Next, the obtained nitride powder was crushed in a stone mill and then placed in a polyethylene container, and 500 g of the nitride powder was mixed with 500 g of hydrochloric acid (37% by mass HCl) and 1500 g of pure water to prepare an acid slurry, which was then stirred for 8 hours for acid washing. After acid washing, the acid slurry was filtered using a Buchner funnel, and then pure water in an amount 10 times (by mass) or more of the nitride powder was added to prepare a water slurry for washing, and the mixture was then dehydrated by suction filtration until the moisture content of the nitride powder reached 40% by mass or less. The nitride powder was then dried under reduced pressure of 30 kPa at 200°C for 15 hours to reduce the moisture content to 0.50% or less, and then classified using a 90 μm sieve, and the undersieve was collected to obtain crude boron nitride powder. The amount of eluted boron in the resulting crude boron nitride powder was 18 ppm.

[0043] The obtained crude boron nitride powder was subjected to a surface stabilization treatment by standing at 25°C for 8 hours in a nitrogen atmosphere (dew point -85°C). It was then subjected to a sintering treatment at 1650°C or higher for 4 hours in a nitrogen atmosphere. It was then classified using a sieve with 90µm openings, and the undersieve was collected to obtain hexagonal boron nitride powder. The obtained hexagonal boron nitride powder was evaluated, and the evaluation results are shown in Tables 1 to 3.

[0044] [Example 2] 700g of boron oxide, 300g of carbon black, and 200g of calcium carbonate were mixed in a mixer. This mixture was heated to 1600°C in a graphite Tammann furnace under a nitrogen gas atmosphere and held at 1600°C for 6 hours. After holding at 1600°C, the mixture was heated to 1840°C and subjected to reduction-nitriding treatment at 1840°C for 2 hours to obtain nitrided powder. Next, the obtained nitride powder was crushed in a stone mill and then placed in a polyethylene container, and 500 g of the nitride powder was mixed with 500 g of hydrochloric acid (37% by mass HCl) and 1500 g of pure water to prepare an acid slurry, which was then stirred for 8 hours for acid washing. After acid washing, the acid slurry was filtered using a Buchner funnel, and then pure water in an amount 10 times (by mass) or more of the nitride powder was added to prepare a water slurry for washing, and the mixture was then dehydrated by suction filtration until the moisture content of the nitride powder reached 40% by mass or less. The nitride powder was then dried under reduced pressure of 30 kPa at 200°C for 15 hours to reduce the moisture content to 0.50% or less, and then classified using a 90 μm sieve, and the undersieve was collected to obtain crude boron nitride powder. The amount of eluted boron in the resulting crude boron nitride powder was 18 ppm.

[0045] The obtained crude boron nitride powder was subjected to a surface stabilization treatment by standing at 25°C for 8 hours in a nitrogen atmosphere (dew point -80°C). It was then subjected to a sintering treatment at 1650°C or higher for 4 hours in a nitrogen atmosphere. It was then classified using a sieve with 90µm openings, and the undersieve was collected to obtain hexagonal boron nitride powder. The obtained hexagonal boron nitride powder was evaluated, and the evaluation results are shown in Tables 1 to 3.

[0046] [Example 3] A mixed powder was prepared by mixing 80 g of anhydrous borax, 50 g of boron oxide, and 45 g of melamine. This mixture was heated to 1250°C in a graphite Tammann furnace under a nitrogen gas atmosphere, and then heated at 1250°C for 2 hours to obtain nitrided powder by the melamine method. Next, the obtained nitride powder was crushed in a stone mill and then placed in a polyethylene container, and 100 g of the nitride powder was mixed with 100 g of hydrochloric acid (37% by mass HCl) and 300 g of pure water to prepare an acid slurry, which was then stirred for 8 hours for acid washing. After acid washing, the acid slurry was filtered using a Buchner funnel, and then pure water in an amount 10 times (by mass) or more of the nitride powder was added to prepare a water slurry for washing, and the mixture was then dehydrated by suction filtration until the moisture content of the nitride powder reached 40% by mass or less. The nitride powder was then dried under reduced pressure of 30 kPa at 150°C for 15 hours to reduce the moisture content to 0.50% or less, and then classified using a 90 μm mesh sieve, and the undersieve was collected to obtain crude boron nitride powder. The amount of eluted boron in the resulting crude boron nitride powder was 57 ppm.

[0047] The obtained crude boron nitride powder was allowed to stand in a nitrogen atmosphere (dew point -85°C) at 25°C for 8 hours to perform a surface stabilization treatment, thereby obtaining hexagonal boron nitride powder. The obtained hexagonal boron nitride powder was evaluated, and the evaluation results are shown in Tables 1 to 3.

[0048] [Example 4] A mixed powder was prepared by mixing 80 g of anhydrous borax, 50 g of boron oxide, and 45 g of melamine. This mixture was heated to 1250°C in a graphite Tammann furnace under a nitrogen gas atmosphere, and then heated at 1250°C for 2 hours to obtain nitrided powder by the melamine method. Next, the obtained nitride powder was crushed in a stone mill and then placed in a polyethylene container, and 100 g of the nitride powder was mixed with 100 g of hydrochloric acid (37% by mass HCl) and 300 g of pure water to prepare an acid slurry, which was then stirred for 8 hours for acid washing. After acid washing, the acid slurry was filtered using a Buchner funnel, and then pure water in an amount 10 times (by mass) or more of the nitride powder was added to prepare a water slurry for washing, and the mixture was then dehydrated by suction filtration until the moisture content of the nitride powder reached 40% by mass or less. The nitride powder was then dried under reduced pressure at 150°C for 15 hours at a reduced pressure of 30 kPa to reduce the moisture content to 0.50% or less. The resulting powder was then sieved through a 90 μm sieve, and the undersieve fraction was collected to obtain crude boron nitride powder. The amount of eluted boron in the resulting crude boron nitride powder was 57 ppm. The resulting crude boron nitride powder was subjected to a surface stabilization treatment by standing at 25°C for 8 hours in a nitrogen atmosphere (dew point -85°C). It was then fired for 4 hours at 1250°C in a nitrogen atmosphere. The powder was then sieved through a 90 μm sieve, and the undersieve fraction was collected to obtain hexagonal boron nitride powder. The resulting hexagonal boron nitride powder was evaluated, and the evaluation results are shown in Tables 1 to 3.

[0049] [Comparative Example 1] In Example 1 of the present application, evaluation was carried out on the hexagonal boron nitride powder (crude boron nitride powder) immediately before the surface stabilization treatment. The evaluation results are shown in Tables 1 to 3.

[0050] Comparative Example 2 In Example 2 of the present application, hexagonal boron nitride powder was obtained by performing the firing treatment without performing the surface stabilization treatment. The obtained hexagonal boron nitride powder was evaluated, and the evaluation results are shown in Tables 1 to 3.

[0051] Comparative Example 3 In Example 1 of the present application, crude boron nitride powder was obtained without acid washing, and then surface stabilization treatment and firing treatment were performed to obtain hexagonal boron nitride powder. The obtained hexagonal boron nitride powder was evaluated, and the evaluation results are shown in Tables 1 to 3.

[0052] [Reference example 1] As a commercially available hexagonal boron nitride powder, S02 (manufactured by Tokuyama Corporation) was evaluated. The evaluation results are shown in Tables 1 to 3.

[0053] [Table 1]

[0054] [Table 2]

[0055] [Table 3]

Claims

1. The median diameter D50 measured by the laser diffraction method is 1 to 10 μm, and the specific surface area measured by the nitrogen adsorption method is 1 to 10 m ２ / g hexagonal boron nitride powder, The resin composition obtained by kneading the hexagonal boron nitride powder into a polypropylene resin at a ratio of 30% by volume was formed into a sheet having a thickness of 0.35 mm to 0.45 mm, and when the dielectric loss tangent of the sheet was measured by a resonator method, the dielectric loss tangent tanδ measured at a frequency of 10 GHz was １０ and the dielectric loss tangent tanδ measured at a frequency of 91 GHz ９１ The ratio tan δ ９１ / tanδ １０ is 1.4 or less, Hexagonal boron nitride powder.

2. The hexagonal boron nitride powder according to claim 1, wherein a resin composition obtained by kneading the hexagonal boron nitride powder into a polypropylene resin at a ratio of 30 volume % is formed into a sheet having a thickness of 0.35 mm to 0.45 mm, and the relative dielectric constant measured at a frequency of 10 GHz by a resonator method is 3.3 or less.

3. 2. The hexagonal boron nitride powder according to claim 1, having an average aspect ratio of 10 or less.

4. A resin composition comprising the hexagonal boron nitride powder according to any one of claims 1 to 3 and a resin.

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