JP7302115B2 - Hexagonal boron nitride powder and resin composition - Google Patents

Description

The present disclosure relates to hexagonal boron nitride powders and resin compositions.

Efficiently dissipating heat generated during use of electronic components such as transistors, thyristors, and CPUs is an important issue. Therefore, heat dissipation members having high thermal conductivity are used together with such electronic components. On the other hand, boron nitride particles are widely used as fillers in heat dissipating members because of their high thermal conductivity and high insulating properties.

For example, in Patent Document 1, when used as a filler for an insulating heat dissipating material such as resin, hexagonal boron nitride powder and its A manufacturing method has been proposed.

Japanese Patent Application Laid-Open No. 2019-116401

2. Description of the Related Art In recent years, high-speed signal transmission and large-capacity transmission have been progressing in devices equipped with electronic components. For this reason, the heat dissipating member is also required to have characteristics capable of coping with the above-described tendency. Specifically, a heat radiating member having a small dielectric loss tangent is desirable.

As a method for reducing the dielectric loss tangent of the heat radiating member, for example, it is conceivable to use a resin having a small dielectric loss tangent as the resin to be used. However, although liquid crystalline polymers and fluororesins known as low dielectric loss tangent resins have low dielectric loss tangents, they lack workability, thermal properties, mechanical properties, and the like for the intended use. Therefore, fillers are generally used from the viewpoint of improving thermal characteristics. However, depending on the blending of the filler, the low dielectric loss tangent characteristic of the resin may not be sufficiently exhibited.

An object of the present disclosure is to provide a hexagonal boron nitride powder and a resin composition capable of producing a heat dissipation member with a low dielectric loss tangent.

One aspect of the present disclosure includes primary particles of hexagonal boron nitride, having a specific surface area of 2.5 m ² /g or less, a graphitization index of 2.0 or less, and a purity of 99% by mass or more. A hexagonal boron nitride powder is provided.

The hexagonal boron nitride powder has a small specific surface area, suppresses adsorption of water and impurities that cause an increase in dielectric loss tangent, and further has a graphitization index and purity within a predetermined range. Generation of a component that increases the dielectric loss tangent from boron itself is suppressed. As a result, it is suitable as a filling material for producing a heat radiating member with a low dielectric loss tangent.

The circularity of the primary particles may be 0.8 or more.

The hexagonal boron nitride powder may have a water content per unit mass of less than 300 ppm when heated to 500°C.

The hexagonal boron nitride powder may have a water content per unit mass of less than 250 ppm when heated to 200°C.

The hexagonal boron nitride powder may have a water content per unit mass of less than 100 ppm when heated to 201 to 500°C.

In the hexagonal boron nitride powder, the average particle size of the primary particles may be 7.0 μm or more.

One aspect of the present disclosure provides a resin composition containing a resin and the hexagonal boron nitride powder described above.

Since the resin composition contains the hexagonal boron nitride powder described above, it can have a low dielectric loss tangent.

According to the present disclosure, it is possible to provide a hexagonal boron nitride powder and a resin composition capable of producing a heat dissipation member with a low dielectric loss tangent.

Embodiments of the present disclosure will be described below. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following contents.

The materials exemplified in this specification can be used singly or in combination of two or more unless otherwise specified. The content of each component in the composition means the total amount of the multiple substances present in the composition unless otherwise specified when there are multiple substances corresponding to each component in the composition. .

One embodiment of the hexagonal boron nitride powder comprises primary particles of hexagonal boron nitride, has a specific surface area of 2.5 m ² /g or less, a graphitization index of 2.0 or less, and a purity of 99% by mass. That's it. The hexagonal boron nitride powder may be an aggregate of primary particles of hexagonal boron nitride.

The upper limit of the specific surface area of the hexagonal boron nitride powder is 2.5 m ² /g or less, for example, 2.2 m ² /g or less, 2.0 m ² /g or less, 1.8 m ² /g or less, or It may be 1.6 m ² /g or less. When the upper limit of the specific surface area is within the above range, the adsorption of moisture and the like can be suppressed, and the dielectric loss tangent can be further reduced. The lower limit of the specific surface area of the hexagonal boron nitride powder is, for example, 0.5 m ² /g or more, 0.8 m ² /g or more, 1.0 m ² /g or more, 1.2 m ² /g or more, or 1. It may be 4 m ² /g or more. When the lower limit of the specific surface area is within the above range, the hexagonal boron nitride powder can have a lower dielectric loss tangent. The specific surface area of the hexagonal boron nitride powder can be adjusted within the above range, and can be, for example, 0.5-2.5 m ² /g, or 1.0-2.2 m ² /g.

The specific surface area in this specification means a value measured using a specific surface area measuring device in accordance with the description of JIS Z 8830:2013 "Method for measuring specific surface area of powder (solid) by gas adsorption", nitrogen It is a value calculated by applying the BET one-point method using gas. More specifically, it is measured by the method described in the Examples of this specification.

The hexagonal boron nitride is preferably highly crystalline. In the boron nitride powder of the present embodiment, a graphitization index (G.I.) is used as an index of crystallinity. That is, the boron nitride powder containing hexagonal boron nitride with a low graphitization index has fewer impurities and can suppress an increase in dielectric loss tangent. The upper limit of the graphitization index of the hexagonal boron nitride powder is 2.0 or less, and may be, for example, 1.9 or less, 1.5 or less, or 1.3 or less. When the upper limit of the graphitization index of the hexagonal boron nitride powder is within the above range, the dielectric loss tangent can be further reduced. The lower limit of the graphitization index of the hexagonal boron nitride powder is not particularly limited, but may be, for example, 0.8 or more, or 1.0 or more. When the lower limit of the graphitization index of the hexagonal boron nitride powder is within the above range, both low dielectric loss tangent and high heat dissipation can be achieved at a higher level. The graphitization index of the hexagonal boron nitride powder can be adjusted within the range described above, and can be, for example, 1.0 to 2.0.

The graphitization index herein is an index 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) etc.). The graphitization index is calculated based on the spectrum of primary particles of hexagonal boron nitride measured by powder X-ray diffraction. First, in the X-ray diffraction spectrum, the integrated intensity of each diffraction peak corresponding to the (100) plane, (101) plane and (102) plane of the hexagonal boron nitride primary particles (that is, each diffraction peak) and its baseline and S100, S101, and S102, respectively. Using the calculated area value, the value of [(S100+S101)/S102] is calculated to determine the graphitization index. More specifically, it is determined by the method described in the Examples of this specification.

The purity of the hexagonal boron nitride powder may be higher, for example, 99.5 wt% or higher, or 99.8 wt% or higher. The purity of boron nitride powder herein means a value calculated by titration. More specifically, titration is performed and determined by the method described in the Examples of the present specification.

The primary particles of hexagonal boron nitride improve the fillability in a resin or the like when preparing a heat dissipating member or the like, and from the viewpoint of isotropic properties such as thermal conductivity and dielectric constant of the heat dissipating member, preferably: It may be spherical or nearly spherical. The circularity of the primary particles may be, for example, 0.80 or greater, 0.85 or greater, 0.88 or greater, or 0.90 or greater.

The circularity of primary particles as used herein means the average circularity measured by the following method. Specifically, an image of boron nitride particles taken using a scanning electron microscope (SEM) (magnification: 10,000 times, image resolution: 1280 × 1024 pixels) was analyzed using image analysis software. Calculate the projected area (S) and perimeter (L) of the boron nitride particles. Then, using the obtained projected area (S) and perimeter (L), the circularity is obtained according to the following formula: circularity=4πS/ ^L2 . The average circularity obtained for 100 arbitrarily selected boron nitride particles is defined as the average circularity. As the image analysis software, for example, "MacView" (trade name) manufactured by Mountec Co., etc. can be used.

In the hexagonal boron nitride powder, the lower limit of the average particle size of the primary particles may be, for example, 7.0 μm or more, 7.5 μm or more, 8.0 μm or more, 8.5 μm or more, or 9.0 μm or more. . When the lower limit of the average particle size is within the above range, it can be suitably used from the viewpoint of filling properties and heat dissipation. The upper limit of the average particle size of the primary particles may be, for example, 40 μm or less, 30 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less. When the upper limit of the average particle size is within the above range, the moldability of the resin composition can be improved. The average particle size of primary particles in the hexagonal boron nitride powder may be adjusted within the range described above, and may be, for example, 7.0 to 40 μm, or 7.5 to 15 μm. For example, when hexagonal boron nitride powder is dispersed in a resin and molded into a sheet for use, the average particle size of the primary particles may be selected according to the thickness of the sheet.

The average particle size in the present specification is a value obtained by measuring a sample of hexagonal boron nitride powder subjected to homogenizer treatment, and is an average particle size that does not contain agglomerated particles. The average particle size in this specification is also the particle size at which the cumulative value of the cumulative particle size distribution is 50% (median size, d50). The average particle size in this specification is measured using a laser diffraction scattering particle size distribution analyzer in accordance with ISO 13320:2009. Specifically, it is measured by the method described in the Examples of this specification. As a laser diffraction scattering particle size distribution analyzer, for example, "LS-13 320" (apparatus name) manufactured by Beckman Coulter can be used.

Hexagonal boron nitride powder can adsorb moisture on its surface. When a periodic electric field is applied to the hexagonal boron nitride powder that adsorbs moisture, a part of the electrical energy can be promoted to be consumed as thermal energy, so the dielectric loss tangent tends to increase. . The hexagonal boron nitride powder may preferably have a low water content from the viewpoint of further reducing the dielectric loss tangent. The hexagonal boron nitride powder may have a water content per unit mass when heated to 500° C., for example, less than 300 ppm, 280 ppm or less, 260 ppm or less, 240 ppm or less, or 220 ppm or less.

Moisture on the surface of hexagonal boron nitride powder can be desorbed by heating up to 200°C. The hexagonal boron nitride powder may have a water content per unit mass of less than 250 ppm, less than 200 ppm, 180 ppm or less, 160 ppm or less, or 150 ppm or less when heated to 200°C.

When hydroxyl groups (OH groups) are present on the surface of the hexagonal boron nitride powder, they can partially desorb as moisture at high temperatures exceeding 200° C., for example. In other words, moisture may be generated afterward during use at high temperatures. Therefore, it is preferable that the hexagonal boron nitride powder also suppresses moisture generation at high temperatures. The hexagonal boron nitride powder may have a water content per unit mass of less than 100 ppm, less than 90 ppm, less than 80 ppm, or less than 70 ppm when heated to 201 to 500° C., for example. When the water content per unit mass when heated to 201 to 500° C. is within the above range, the hexagonal boron nitride powder has a relatively low water adsorption performance, and water adsorption during storage is further suppressed. can be done.

The water content as used herein means a value measured based on the Karl Fischer method in accordance with the description of JIS K 0068:2001 "Method for measuring water content of chemical products". Specifically, first, a predetermined amount of the measurement sample is taken on a pre-fired alumina board, which is placed in a furnace whose temperature is adjusted to 25 ° C., and nitrogen gas is used as a carrier gas to measure the temperature ( The moisture content can be determined by measuring the moisture generated when heated to 200° C. or 500° C. by coulometric titration and converting the obtained results into per unit mass (1 g). As the measuring device, for example, "trace moisture measuring device CA-06" (product name) manufactured by Mitsubishi Chemical can be used. As the titrant solution, for example, "Aquamicron AX" (trade name) manufactured by Mitsubishi Chemical can be used as the catholyte, and "Aquamicron CXU" (trade name) manufactured by Mitsubishi Chemical can be used as the anolyte.

The dielectric loss tangent of the hexagonal boron nitride powder as described above is kept low. The dielectric loss tangent of the hexagonal boron nitride powder can be, for example, less than 0.0020, 0.0015 or less, 0.0012 or less, or 0.0010 or less.

The dielectric loss tangent in this specification means a value at 1 GHz measured according to the method described in JIS C 2138:2007 "Electrical insulating materials--Methods for measuring relative permittivity and dielectric loss tangent." Specifically, hexagonal boron nitride powder is prepared in a holder to form a measurement cell. As a measurement device for the cavity resonator perturbation method, for example, Keysight's "Vector Network Analyzer E5063A" (product name) can be used.

The hexagonal boron nitride powder described above can be produced, for example, by the following method. One embodiment of the method for producing hexagonal boron nitride powder is a production method applying a so-called carbon reduction method, in which a mixed powder containing a boron-containing compound containing boric acid and a carbon-containing compound is subjected to a pressurized nitrogen atmosphere. to obtain a fired product containing boron nitride (hereinafter also referred to as a low-temperature firing step); hBN), and obtaining a powder containing agglomerated particles formed by agglomeration of some of the primary particles (hereinafter also referred to as a sintering step).

A boron-containing compound is a compound having boron as a constituent element. As the boron-containing compound, a raw material with high purity and relatively low cost can be used. Examples of such boron-containing compounds include boric acid as well as boron oxide. The boron-containing compound includes boric acid, which is dehydrated by heating to form boron oxide, which forms a liquid phase during the heat treatment of the raw material powder and can also serve as an aid for promoting grain growth.

A carbon-containing compound is a compound having a carbon atom as a constituent element. As the carbon-containing compound, a raw material with high purity and relatively low cost can be used. Examples of such carbon-containing compounds include carbon black and acetylene black.

In the mixed powder, the boron-containing compound may be blended in an excess amount relative to the carbon-containing compound. The mixed powder may contain other compounds in addition to the carbon-containing compound and the boron-containing compound. Other compounds include, for example, boron nitride as a nucleating agent. By containing boron nitride as a nucleating agent in the mixed powder, the average particle size of the synthesized hexagonal boron nitride powder can be more easily controlled. The mixed powder preferably contains a nucleating agent. When the mixed powder contains a nucleating agent, it becomes easier to prepare a hexagonal boron nitride powder with a small specific surface area (for example, a hexagonal boron nitride powder with a specific surface area of 2.5 m ² /g or less).

The low temperature firing process is performed under pressure. The pressure in the low-temperature firing step is, for example, 0.25 MPa or more and less than 5.0 MPa, 0.25 to 3.0 MPa, 0.25 to 2.0 MPa, 0.25 to 1.0 MPa, 0.25 MPa or more and less than 1.0 MPa. , 0.30-2.0 MPa, or 0.50-2.0 MPa. By increasing the pressure in the low-temperature firing step, volatilization of raw materials such as boron-containing compounds can be further suppressed, and the formation of boron carbide, which is a by-product, can be suppressed. Also, by increasing the pressure in the low-temperature firing step, it is possible to suppress an increase in the specific surface area of the boron nitride powder. By setting the upper limit of the pressure in the low-temperature firing step within the above range, the growth of the primary particles of boron nitride can be further promoted.

The heating temperature in the low-temperature firing step may be, for example, 1650°C or higher and lower than 1800°C, 1650 to 1750°C, or 1650 to 1700°C. By setting the lower limit of the heating temperature in the low-temperature firing step within the above range, the reaction can be promoted and the yield of boron nitride obtained can be improved. By setting the upper limit of the heating temperature in the low-temperature firing step within the above range, it is possible to sufficiently suppress the generation of by-products.

The heating time in the low temperature firing step may be, for example, 1 to 10 hours, 1 to 5 hours, or 2 to 4 hours. By maintaining a relatively low temperature for a predetermined time in the initial stage of the reaction for synthesizing boron nitride, the reaction system can be made more homogeneous, and thus the boron nitride to be formed can be made more homogeneous. In this specification, the term "heating time" refers to the time (holding time) during which the ambient temperature of the object to be heated reaches a predetermined temperature and is maintained at that temperature.

In the firing step, the fired product obtained in the low-temperature firing step is heat-treated at a temperature higher than the low-temperature firing step to generate primary particles of hexagonal boron nitride (hBN), and the primary particles are aggregated. It is a step of obtaining a powder containing agglomerated particles.

The heating temperature in the firing step is higher than that in the low-temperature firing step and is less than 2050°C. By setting the heating temperature in the firing step within the steam range, the graphitization index can be further increased, and hexagonal boron nitride having excellent crystallinity can be obtained. The heating temperature in the firing step may be 2000° C. or lower. The heating time in the firing step may be, for example, 3-15 hours, 5-10 hours, or 6-9 hours.

The pressure of the firing step is, for example, 0.25 MPa or more and less than 5.0 MPa, 0.25 to 3.0 MPa, 0.25 to 2.0 MPa, 0.25 to 1.0 MPa, 0.25 MPa or more to less than 1.0 MPa, It may be 0.30-2.0 MPa, or 0.50-2.0 MPa. By increasing the pressure in the firing process, the purity of the obtained raw material powder can be further improved. By setting the upper limit of the pressure in the firing process within the above range, the preparation cost of the raw material powder can be further reduced, which is industrially advantageous.

A hexagonal boron nitride powder can be obtained by the above steps. A pulverization step may be performed after the low-temperature firing step or the firing step. In the pulverization step, a general pulverizer or pulverizer can be used.

Since the hexagonal boron nitride powder according to the present disclosure has a low dielectric loss tangent, it can be used in applications where high frequency voltage is applied. The hexagonal boron nitride powder according to the present disclosure is suitable, for example, as a filler for resin compositions used in electronic components that constitute high-frequency circuits. One embodiment of the resin composition contains a resin and the hexagonal boron nitride powder described above.

The lower limit of the content of the hexagonal boron nitride powder may be, for example, 30% by volume or more, 40% by volume or more, or 50% by volume or more based on the total volume of the resin composition. When the lower limit of the content of the hexagonal boron nitride powder is within the above range, the thermal conductivity of the resin composition can be improved, and excellent heat dissipation performance can be obtained. The upper limit of the content of the hexagonal boron nitride powder may be, for example, 85% by volume or less, 80% by volume or less, or 70% by volume or less based on the total volume of the resin composition. When the upper limit of the content of the hexagonal boron nitride powder is within the above range, it is possible to further suppress the generation of voids inside during molding of the resin composition, and to prevent deterioration of insulation and mechanical strength. can be suppressed.

Resins include, for example, liquid crystal polymers, fluororesins, silicone resins, silicone rubbers, acrylic resins, polyolefins (polyethylene, etc.), epoxy resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, polyimides, polyamideimides, and polyetherimides. , polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, wholly aromatic polyester, polysulfone, polyethersulfone, polycarbonate, maleimide modified resin, ABS (acrylonitrile-butadiene-styrene) resin, AAS (acrylonitrile-acrylic rubber/styrene) resins, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins.

The resin content may be, for example, 15% by volume or more, 20% by volume or more, or 30% by volume or more based on the total volume of the resin composition. The resin content may be, for example, 70% by volume or less, 60% by volume or less, or 50% by volume or less based on the total volume of the resin composition.

The resin composition may further contain a curing agent that cures the resin. The curing agent may be appropriately selected according to the type of resin. For example, when the resin is an epoxy resin, curing agents include, for example, phenol novolak compounds, acid anhydrides, amino compounds, imidazole compounds, and the like. 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 may be 15 parts by mass or less or 10 parts by mass or less with respect to 100 parts by mass of the resin.

Although several embodiments have been described above, the present disclosure is not limited to the above embodiments. Also, the descriptions of the above-described embodiments can be applied to each other.

Hereinafter, the present disclosure will be described in more detail using examples and comparative examples. It should be noted that the present disclosure is not limited to the following examples.

(Example 1)
[Preparation of hexagonal boron nitride powder]
100 parts by mass of boric acid (manufactured by Kojundo Chemical Laboratory Co., Ltd.) and 22 parts by mass of acetylene black (manufactured by Denka Co., Ltd., grade name: Li400) are mixed using a Henschel mixer to obtain a mixed powder (raw material powder). Obtained. The obtained mixed powder was placed in a drier at 250° C. and held for 3 hours to dehydrate boric acid. The mixed powder after dehydration was placed in a mold with a diameter of 100Φ of a press molding machine, and molded under the conditions of heating temperature: 200°C and press pressure: 30 MPa. The raw material powder pellets thus obtained were subjected to subsequent heat treatment.

First, the pellets were placed in a carbon atmosphere furnace, heated to 1750° C. at a rate of 5° C./min in a nitrogen atmosphere pressurized to 0.85 MPa, and held at 1750° C. for 3 hours. The pellets were heat-treated to obtain a first heat-treated product (first step). Next, the temperature in the carbon atmosphere furnace is further increased to 1800°C at a temperature increase rate of 2°C/min, and the first heat-treated product is heat-treated by holding at 1800°C for 3 hours, followed by the second heat-treatment. obtained (second step). Thereafter, the temperature in the carbon atmosphere furnace was further increased to 2050° C. at a rate of temperature increase of 2° C./min, and held at 2050° C. for 7 hours to sinter the second heat-treated product at a high temperature (third step). Loosely agglomerated boron nitride after firing was pulverized with a Henschel mixer, and the pulverized powder was dried at 250 ° C. for 5 hours using a vacuum dryer, and then passed through a sieve with an opening of 63 μm. A powder was obtained. Thus, a hexagonal boron nitride powder was prepared.

<Measurement of physical properties of hexagonal boron nitride powder>
For the obtained hexagonal boron nitride powder, the specific surface area, graphitization index, purity, circularity and average particle size of primary particles, and moisture content when heated to 25 to 200 ° C. The amount of water and the moisture content when heated from 201 to 500° C. were measured. Table 1 shows the results.

[Specific surface area]
The specific surface area of the hexagonal boron nitride powder is based on the description of JIS Z 8830:2013 "Method for measuring the specific surface area of powder (solid) by gas adsorption", and was calculated by applying the BET one-point method using nitrogen gas. . As a specific surface area measuring device, a specific surface area measuring device manufactured by Yuasa Ionics Co., Ltd. (device name: Kantersorb) was used. The measurement was performed after the boron nitride powder was dried and degassed at 300° C. for 15 minutes.

[Graphitization index]
The graphitization index of the boron nitride powder was calculated from the measurement results by the powder X-ray diffraction method. In the obtained X-ray diffraction spectrum, the integrated intensity of each diffraction peak corresponding to the (100) plane, (101) plane and (102) plane of the hexagonal boron nitride primary particles (that is, each diffraction peak) and its base The area values (in arbitrary units) surrounded by the lines were calculated and designated as S100, S101, and S102, respectively. Using the area value thus calculated, the graphitization index was determined based on the following formula (1).
GI=(S100+S101)/S102 (1)

[purity]
Hexagonal boron nitride powder was alkali-decomposed with sodium hydroxide, ammonia was distilled from the decomposed solution by steam distillation, and collected in an aqueous boric acid solution. This collected liquid was subjected to titration with a normal sulfuric acid solution. The content of nitrogen atoms (N) in the boron nitride powder was calculated from the titration results. Based on the obtained nitrogen atom content, the content of hexagonal boron nitride (hBN) in the boron nitride powder was determined based on the formula (2), and the purity of the hexagonal boron nitride powder was calculated. The formula weight of hexagonal boron nitride was 24.818 g/mol, and the atomic weight of nitrogen atoms was 14.006 g/mol.
Hexagonal boron nitride (hBN) content [mass%] in the sample = nitrogen atom (N) content [mass%] x 1.772 (2)

[Circularity of primary particles]
For the hexagonal boron nitride powder, images of primary particles (magnification: 10,000 times, image resolution: 1280×1024 pixels) were taken using a scanning electron microscope (SEM). Next, the projected area (S) and perimeter (L) of the boron nitride particles were calculated from the obtained image by image analysis using image analysis software (manufactured by Mountech, trade name "MacView"). Then, using the obtained projected area (S) and peripheral length (L), the circularity was obtained according to the following formula: circularity = 4πS/ ^L2 . Obtained for 100 boron nitride particles arbitrarily selected from particles in which the entire primary particles can be confirmed and plate-like planes (ab-axis crystal planes) can be confirmed, and the average circularity is calculated. adopted as a measure.

[Average particle size of primary particles]
The average particle size of the primary particles in the hexagonal boron nitride powder is measured using a laser diffraction scattering method particle size distribution analyzer (Beckman Coulter, trade name "LS-13 320") in accordance with ISO 13320:2009. It was measured. In addition, when measuring the hexagonal boron nitride powder, an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho, trade name "US-300E") is used, and AMPLITUDE (amplitude) is 80%. Ultrasonic dispersion is performed once for 1 minute and 30 seconds. By doing so, a dispersion liquid of hexagonal boron nitride powder was prepared, and this was used as a measurement target. In measuring the particle size distribution, water was used as a solvent for dispersing the hexagonal boron nitride powder, and hexametaphosphoric acid was used as a dispersant. At this time, a numerical value of 1.33 was used as the refractive index of water, and a numerical value of 1.80 was used as the refractive index of the boron nitride powder.

[amount of water]
The water content when the hexagonal boron nitride powder was heated to 25 to 200° C. and the water content when heated to 201 to 500° C. were measured based on the Karl Fischer method. First, a predetermined amount of the measurement sample was taken on a pre-baked alumina board, placed in a furnace whose temperature was adjusted to 25 ° C., and heated from 25 ° C. to the measurement temperature (200 ° C. or 500 ° C.). The water content (unit: ppm) was determined by measuring the water content generated at the time by a coulometric titration method and converting the obtained result per unit mass (1 g).

<Evaluation of hexagonal boron nitride powder as filler>
The dielectric loss tangent was measured when the obtained hexagonal boron nitride powder was used as a filler. Specifically, using a cavity resonator method measurement device (measurement system perturbation method cavity resonator type DPS18 manufactured by Keycom), the dielectric of hexagonal boron nitride powder at 1 GHz was measured at a temperature of 25 ° C. Asked for tangent. Table 1 shows the results.

(Example 2)
A hexagonal boron nitride powder was prepared in the same manner as in Example 1, except that the raw material acetylene black was changed to acetylene black (manufactured by Denka Co., Ltd., grade name: FX35).

(Example 3)
Hexagonal boron nitride powder was prepared in the same manner as in Example 1, except that 2% by mass of boron nitride powder (Denka boron nitride powder, grade name: SGP) was added to the raw material. bottom.

(Example 4)
A hexagonal boron nitride powder was prepared in the same manner as in Example 1, except that the firing temperature in the third step was changed to 2070°C.

(Example 5)
A hexagonal boron nitride powder was prepared in the same manner as in Example 1, except that the firing temperature in the third step was changed to 1970°C.

(Example 6)
Hexagonal boron nitride in the same manner as in Example 1, except that the amount of acetylene black (manufactured by Denka Co., Ltd., grade name: Li400) was changed to 20 parts by mass, and the vacuum drying temperature was changed to 300 ° C. A powder was prepared.

(Example 7)
A hexagonal boron nitride powder was prepared in the same manner as in Example 1, except that the amount of acetylene black (manufactured by Denka Co., Ltd., grade name: Li400) was changed to 27 parts by mass.

( Reference example )
Hexagonal boron nitride powder was prepared in the same manner as in Example 1, except that 1% by mass of boron nitride powder (Denka boron nitride powder, grade name: MGP) was added to the raw material. prepared.

For the hexagonal boron nitride powders obtained in Examples 1 to 7 and Reference Example , specific surface area, graphitization index, purity, circularity and average particle size of primary particles, and moisture content when heated to 25 to 200 ° C. The amount and moisture content when heated to 201 to 500° C. were measured in the same manner as in Example 1. The hexagonal boron nitride powders obtained in Examples 1 to 7 and Reference Example were evaluated as fillers in the same manner as in Example 1. Table 1 shows the results.

(Comparative example 1)
100 parts by mass of boric acid powder (purity of 99.8% by mass or more, manufactured by Kanto Chemical Co., Ltd.), 9 parts by mass of melamine powder (purity of 99.0% by mass or more, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), sodium carbonate as an auxiliary agent 13 parts by mass (purity of 99.5% by mass or more) was added and mixed for 10 minutes using an alumina mortar to obtain a mixed powder. The mixed powder after drying was placed in a container made of hexagonal boron nitride and placed in an electric furnace. The temperature was raised from room temperature to 1000° C. at a rate of 10° C./min while nitrogen gas was circulated in the electric furnace. After holding at 1000° C. for 2 hours, the heating was stopped and the mixture was allowed to cool naturally. The electric furnace was opened when the temperature became 100° C. or lower. Thus, a calcined product containing low-crystalline hexagonal boron nitride was obtained.

100 g of the calcined product was placed in the above electric furnace. The temperature was raised from room temperature to 1800° C. at a rate of 10° C./min while nitrogen gas was circulated in the electric furnace. After holding the sintering temperature of 1800° C. for 4 hours, the heating was stopped and the product was allowed to cool naturally. The electric furnace was opened when the temperature became 100° C. or lower. The obtained fired product was recovered and ground in an alumina mortar for 10 minutes to obtain coarse powder containing hexagonal boron nitride.

Next, in order to remove impurities contained in the coarse powder, 30 g of the coarse powder was added to 500 g of dilute nitric acid (nitric acid concentration: 5% by mass) and stirred at room temperature for 60 minutes. After stirring, solid-liquid separation was carried out by suction filtration, water was replaced until the filtrate became neutral, and washing was carried out until the electric conductivity of the washing liquid finally became 1 mS/m or less. After washing, dry powder was obtained by drying at 120° C. for 3 hours using a dryer. The dry powder was used as the hexagonal boron nitride powder of Comparative Example 1.

(Comparative example 2)
The raw material acetylene black was changed to acetylene black (manufactured by Denka Co., Ltd., grade name: FX35), the blending amount was changed to 24 parts by mass, the molding pressure of the press molding machine was set to 5 MPa, and vacuum drying processing A hexagonal boron nitride powder was prepared in the same manner as in Example 1, except that the

(Comparative Example 3)
Comparative Example 1 except that the amount of boric acid was changed to 150 parts by mass, 5 parts by mass of calcium carbonate (purity of 99.5% by mass or more) was added to the raw material, and the firing temperature was changed to 1900 ° C. A hexagonal boron nitride powder was prepared in the same manner.

(Comparative Example 4)
A hexagonal boron nitride powder was prepared in the same manner as in Comparative Example 1, except that the firing conditions in the third step were changed to 1750° C. for 20 hours and the vacuum drying treatment was not performed.

Regarding the hexagonal boron nitride powders obtained in Comparative Examples 1 to 4, the specific surface area, graphitization index, purity, circularity and average particle size of primary particles, and water content and 201 when heated to 25 to 200 ° C. The water content when heated up to 500° C. was measured in the same manner as in Example 1. The hexagonal boron nitride powders obtained in Comparative Examples 1 to 4 were evaluated as fillers in the same manner as in Example 1. Table 2 shows the results.

According to the present disclosure, it is possible to provide a hexagonal boron nitride powder that is useful for producing a heat dissipation member with a low dielectric loss tangent.

Claims (6)

comprising primary particles of hexagonal boron nitride,
a specific surface area of 2.5 m ² /g or less, a graphitization index of 2.0 or less, and a purity of 99% by mass or more ;
A hexagonal boron nitride powder having a water content per unit mass of less than 300 ppm when heated to 500°C . The hexagonal boron nitride powder according to claim 1, wherein the primary particles have a circularity of 0.8 or more. 3. The hexagonal boron nitride powder according to claim 1 , wherein the water content per unit mass when heated to 200° C. is less than 250 ppm. The hexagonal boron nitride powder according to any one of claims 1 to 3 , wherein the water content per unit mass when heated to 201 to 500°C is less than 100 ppm. The hexagonal boron nitride powder according to any one of claims 1 to 4 , wherein the average particle size of primary particles is 7.0 µm or more. A resin composition containing a resin and the hexagonal boron nitride powder according to any one of claims 1 to 5 .