TWI598291B - Hexagonal boron nitride powder, a method for producing the same, a resin composition and a resin sheet - Google Patents

Description

Hexagonal boron nitride powder, a method for producing the same, a resin composition, and a resin sheet

The present invention relates to a hexagonal crystal boron nitride (hereinafter also referred to as "hBN") powder and a resin sheet using the same, particularly an aggregate composed of primary particles of hBN, and high purity. The hBN powder, the method for producing the hBN powder, the resin composition using the hBN powder, and the resin sheet.

hBN particles have a layered structure similar to graphite, and since hBN powder is excellent in thermal conductivity, electrical insulation, chemical stability, solid lubricity, thermal shock resistance, etc., it has been used as insulation using these characteristics. Heat-dissipating material, solid lubricating/release agent, material for manufacturing hBN sintered body, etc.

Previously, the hBN powder was generally mixed with a boron compound such as boric acid and borax, and a nitrogen compound such as melamine or urea, and then calcined at a lower temperature under ammonia gas or a non-oxidizing gas to produce a crude hBN powder having low crystallinity. Then, the obtained crude hBN is obtained by firing at a high temperature under a non-oxidizing gas to grow crystals (Patent Documents 1 to 3).

A sheet, a tape, a grease, or the like which is contained in a resin material such as an epoxy resin or a ruthenium rubber as a filler, and is used as an electrical insulation for efficiently removing heat generated by an electronic component. Thermal conductive sheet materials such as heat conductive sheets and heat conductive greases. In order to further improve the thermal conductivity of a thermally conductive component material such as such a thermally conductive sheet, a test for increasing the filling rate of the hBN powder is performed. However, since hBN is generally a scaly particle shape, the ratio of the length of the primary particles to the thickness is high, and when the filling rate is increased, the particles are easily aligned in a certain direction. Therefore, the properties of the obtained resin and the rubber molded article are likely to be anisotropic. When such anisotropy occurs, characteristics such as thermal conductivity, electrical insulating properties, and thermal shock resistance of a thermally conductive component material such as a thermally conductive sheet are deteriorated.

Therefore, in recent years, in order to suppress the anisotropy in the thermally conductive sheet and to improve the filling property of the hBN powder, hBN powder containing secondary particles (aggregates) of primary particles containing aggregated hBN is used, and mixed in the resin. Method (Patent Documents 4 and 5).

However, if the strength of the aggregate is insufficient, the aggregate tends to disintegrate during the process of compounding with the resin, so that the anisotropy is generated in the heat conductive sheet, and the filling rate of the hBN powder is lowered in the heat conductive sheet. There is a problem of reduced thermal conductivity and electrical insulation.

At the same time, in order to increase the filling and electrical insulating properties of the hBN powder, it is also tested to use boron carbide in nitrogen under nitriding conditions of 1800 ° C or higher, followed by mixing of boron trioxide and/or its precursor. The carbon component is removed by firing to obtain hBN powder (Patent Documents 6 and 7).

However, since the boron nitride reaction rate of boron carbide is very slow, in the method of reacting boron carbide with nitrogen alone, there is a problem that it takes a long time to increase the manufacturing cost. Moreover, in such a manufacturing method, it is very difficult to remove the remaining carbon component, so that there is a problem of remaining black foreign matter. At the same time, there is a problem in that the dielectric breakdown voltage due to the remaining black foreign matter is lowered and the appearance of the thermally conductive sheet is deteriorated. Therefore, it is expected that a thermally conductive sheet capable of reducing the number of black foreign matter can be obtained.

[Previous Technical Literature] Patent literature

Patent Document 1: Japanese Laid-Open Patent Publication No. 61-286207

Patent Document 2: Japanese Patent No. 3461651

Patent Document 3: Japanese Patent Publication No. 5-85482

Patent Document 4: JP-A-2011-098882

Patent Document 5: Japanese Laid-Open Patent Publication No. 2005-343728

Patent Document 6: Japanese Patent No. 4750220

Patent Document 7: Japanese Patent No. 5081488

An object of the present invention is to provide a high-purity hBN powder containing an aggregate composed of primary particles of hBN (hereinafter, simply referred to as "aggregate"), which is a resin composition produced from the hBN powder. And resin sheets, which can exhibit higher thermal conductivity and higher power than before. The hBN powder of the edge, the method for producing the hBN powder, and the resin composition and the resin sheet containing the hBN powder.

The inventors of the present invention have found that the hBN powder containing aggregates composed of primary particles of hBN has a specific crystallite diameter and particle diameter, and the strength of the aggregate is within a specific range. In the particle size distribution curve of the hBN powder, one maximum (maximum) peak is contained in a specific range, and the maximum (maximum) peak when the dispersion obtained by dispersing the hBN powder in water is subjected to ultrasonic treatment for 1 minute is focused. Reduce the rate and adjust the strength of the aggregate.

The present invention has been completed in light of the above teachings.

That is, the present invention provides the following items [1] to [9].

[1] A hexagonal boron nitride powder comprising an aggregate of hexagonal boron nitride primary particles and a powder having a pore diameter of 106 μm and having a powder content of 80% by mass or more of hexagonal boron nitride powder, of which 50% by volume The cumulative particle diameter D ₅₀ is 10-20 μm, the crystallite diameter is 260-1000 Å, and the particle size distribution curve of the hexagonal boron nitride powder having a particle size of 45-106 μm is in the range of 45-150 μm. There is one maximum peak in the inside, and the dispersion obtained by dispersing the above-mentioned hexagonal boron nitride powder having a particle size of 45 to 106 μm in water for 1 minute is subjected to ultrasonic treatment for 1 minute, and the maximum is calculated by the following formula (1). The peak reduction rate of the peak is 40 to 90%.

Peak reduction rate = [(maximum peak height before treatment (a)) - (maximum peak height after treatment (b))] / (maximum peak height before treatment (a)) (1)

[2] The hexagonal boron nitride powder according to the above [1], wherein the powder content in the sieve having a pore size of 45 μm is 45% by mass or less.

[3] The hexagonal boron nitride powder according to the above [1] or [2], wherein the BET specific surface area is 1.5 to 10 m ² /g.

[4] The hexagonal boron nitride powder according to any one of [1] to [3] above, wherein the bulk density is 0.3 g/cm ³ or more.

[5] A resin composition containing 10 to 90% by volume of the hexagonal boron nitride powder according to any one of [1] to [4] above.

[6] A resin sheet comprising the resin composition of the above item [5] or a cured product thereof.

[7] The method for producing a hexagonal boron nitride powder according to any one of the above [1] to [4], which comprises 20 to 90% by mass of boron nitride and 10 to 80% by mass of boron oxide. 100 parts by mass of the crude hexagonal boron nitride powder, a carbon source of 3 to 15 parts by mass in terms of carbon, and 0.01 to 1 part by mass of a calcium compound are mixed, and after firing, firing is performed in an atmosphere containing nitrogen. step.

[8] The method for producing a hexagonal boron nitride powder according to the above [7], wherein the carbon source is one or two selected from the group consisting of graphite and boron carbide.

[9] The method for producing a hexagonal boron nitride powder according to the above [7] or [8], further comprising: after the baking step, using a sieve having a pore size of 106 μm and a sieve having a pore diameter of 45 μm, and classifying the particles to 45 to 106 μm. After the hexagonal boron nitride powder [hBN powder (A)] and the hexagonal boron nitride powder [hBN powder (B)] under a 45 μm sieve, the hBN powder (A) and the hBN powder (B) are mixed to become a relative The ratio of the hBN powder (A) to the total amount of the hBN powders (A) and (B) is 40. ~90% by mass of the mixing step.

In the present invention, a high-purity hBN powder containing an aggregate composed of primary particles of hBN can be provided, which can exhibit higher thermal conductivity and higher than the previous one when the resin composition and the resin sheet are produced from the hBN powder. An electrically insulating hBN powder, a method for producing the hBN powder, and a resin composition containing the hBN powder and a resin sheet.

[Fig. 1] is a schematic view showing an aggregate of primary particles of hBN in the present invention.

[Fig. 2] SEM photographing of aggregates of primary particles of hBN obtained in Example 1.

[Fig. 3] SEM photographing of aggregates of primary particles of hBN obtained in Example 1.

[Fig. 4] SEM photographing of aggregates of primary particles of hBN obtained in Comparative Example 1.

[Fig. 5] SEM photographing of aggregates of primary particles of hBN obtained in Comparative Example 1.

[Fig. 6] A schematic view of a resin sheet containing the hexagonal boron nitride powder of the present invention.

[Fig. 7] The particle size distribution of Examples 1 and 3 before and after ultrasonic treatment Cloth graph.

[Embodiment of the Invention] [hexagonal boron nitride powder]

The hexagonal boron nitride powder of the present invention is a hexagonal boron nitride powder containing an aggregate of hexagonal boron nitride primary particles and having a powder content of 80 μm or more in a pore size of 106 μm, wherein 50% by volume of the cumulative particles The diameter D ₅₀ is 10-20 μm, the crystallite diameter is 260-1000 Å, and the particle size distribution curve of the hexagonal boron nitride powder having a particle size of 45-106 μm is in the range of 45-150 μm. One of the largest peaks, and the maximum peak is calculated by the above formula (1) when the dispersion obtained by dispersing the above-mentioned hexagonal boron nitride powder having a particle size of 45 to 106 μm in water for 1 minute is subjected to ultrasonic treatment for 1 minute. The peak reduction rate is 40 to 90%.

In the present invention, a high-purity hBN powder containing an aggregate composed of primary particles of hBN can be obtained, which can exhibit higher thermal conductivity and higher electric power than when the resin composition and the resin sheet are produced from the hBN powder. Insulating hBN powder. The reason for obtaining this effect is not clear, but it should be the following.

Since the hBN powder of the present invention contains an aggregate of hBN powder composed of primary particles of hBN, and has a specific crystallite diameter and particle diameter, and the strength of the aggregate measured by the hBN powder under specific conditions is Within the specific range, it is speculated that the resin is produced from the hBN powder. In the composition and the resin sheet, the aggregate can be maintained in a particle shape without excessive disintegration, and since the strength of the aggregate is in an appropriate range and is similar to the resin component, high thermal conductivity and high performance can be exhibited. Electrical insulation. However, the present invention is not limited to such a mechanism as the case is presumed.

<primary particle>

The primary particle diameter of the hBN powder of the present invention is preferably from 20 μm or less, more preferably from 1 to 15 μm, more preferably from 5 to 13 μm, more preferably from 8 to 12 μm, and from 8.5 to 10.5, from the viewpoint of improving thermal conductivity. Μm is even better. The hBN powder containing an aggregate composed of primary particles having a primary particle diameter of 5 μm or more, when the resin composition is produced from the hBN powder, has a property similar to that of the resin component, and can obtain good thermal conductivity and high electrical insulation. Sex.

Further, the primary particle diameter is a numerical average value of the major diameter of the primary particles, which can be measured by the method described in the examples.

The primary particles contained in the hBN powder of the present invention may be in the form of scales. Here, the "scaly shape" means a shape in which the ratio of the major axis (long diameter/thickness) of the primary particles to the thickness of the primary particles is 5 to 20. In the case where the primary particles are in the form of scales, since the aggregates can be aggregated, even if the filling ratio of the hBN powder in the resin composition and the resin sheet is increased, it is possible to prevent or suppress the primary particles from being aligned in a certain direction.

The ratio of the major axis to the thickness (long diameter/thickness) of the primary particles of the hBN powder of the present invention is from the viewpoint of improving thermal conductivity, and is 5 to 20 Good, 10~20 is better, 13~20 is better, 15~18 is better, and 15.5~16 is better.

In the present specification, the "longitudinal diameter of primary particles" means the numerical average of the major diameters of primary particles; "the thickness of primary particles" means the numerical average of the thickness of primary particles. Meanwhile, when the primary particles of hBN are scaly particles, "long diameter" means the largest diameter in the plane direction of the scaly particles. The ratio of the major diameter to the thickness of the primary particles (long diameter/thickness) can be determined by the method contained in the examples.

The hBN powder of the present invention has a maximum peak in a particle size distribution range of 45 to 150 μm in a particle size distribution curve of the hBN powder having a particle size of 45 to 106 μm, and is classified as a particle size of 45 to 106 μm. When the dispersion obtained by dispersing the hBN powder in water for 1 minute of ultrasonic treatment, the peak reduction rate of the maximum peak calculated by the following formula (1) (hereinafter, also referred to as "peak reduction rate") is 40~. 90%.

Peak reduction rate = [(maximum peak height before treatment (a)) - (maximum peak height after treatment (b))] / (maximum peak height before treatment (a)) (1)

The particle size distribution curve is determined by a particle size distribution analyzer of a laser light diffraction scattering method, and the lower the reduction rate, that is, the higher the disintegration strength of the hBN powder. When the hBN powder is filled in the organic matrix to adjust the disintegration strength to produce the resin composition and the resin sheet, or when the resin sheet is used, the disintegration of the aggregate can be prevented or suppressed, and at the same time, the resin composition is similar in nature. It can exhibit high thermal conductivity and high electrical insulation. From this point of view, the peak reduction rate of hBN powder is preferably 42-85%, 45~70% is better, 50~60% is better, and 50~55% is better.

Further, the peak reduction ratio of the hBN powder can be measured by the method described in the examples.

<hBN powder>

The hBN powder of the present invention has a powder content of 80% by mass or more in a pore size of 106 μm obtained by using a vacuum evacuation type sieving machine (jet screen) from the viewpoint of thermal conductivity and electrical insulation. More than or equal to the mass%, more preferably 87% by mass or more, more preferably 88% by mass or more, and even more preferably 90% by mass or more.

Further, the hBN powder of the present invention has a powder content of 15% by mass on a sieve having a pore size of 106 μm obtained by using a vacuum suction type sifter (jet screen) from the viewpoint of improving thermal conductivity and electrical insulation. The following is preferable, preferably 13% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less.

In the meantime, the hBN powder of the present invention has a powder content of 45 μm or less in a pore size of 45 μm obtained by a vacuum evacuation type sieving machine (jet screen) from the viewpoint of improving heat conductivity. 40% by mass or less is more preferable, 30% by mass or less is more preferable, and 25% by mass or less is more preferable. Further, from the viewpoint of improving electrical insulation, the powder content of the sieve having a pore size of 45 μm is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and more preferably 20% by mass or more. good. Further, from the viewpoint of improving thermal conductivity and electrical insulation, the powder content in a sieve having a pore diameter of 45 μm is preferably 5 to 45% by mass, more preferably 10 to 45% by mass, and even more preferably 15 to 45% by mass. 20~45% by mass, even better, 30~40 The quality % is even better.

Further, the powder content of the sieve having a pore size of 106 μm and the sieve, and the powder content of the sieve having a pore size of 45 μm were measured by the method described in the examples.

The BET specific surface area of the hBN powder of the present invention is preferably from 1.5 to 10 m ² /g, more preferably from 2 to 10 m ² /g, from the viewpoint of improving the disintegration strength of the aggregate and improving electrical insulation. ~8m ² /g is even better, 3~7m ² /g is better, 3~6m ² /g is better, and 3~5m ² /g is better. When the BET specific surface area is 10 m ² /g or less, the specific surface area of the aggregate contained in the hBN powder can be made small, and the amount of the resin component mixed into the aggregate when the resin composition and the resin sheet are produced can be reduced. Therefore, the amount of the resin component existing between the aggregates can be relatively increased, and the dispersibility of the resin component with respect to the aggregate can be increased, and the hBN powder can be made close to the resin component.

Further, the BET specific surface area is measured by the method described in the examples.

The 50% volume cumulative particle diameter (D ₅₀ ) of the hBN powder of the present invention can be 10 to 20 μm from the viewpoint of improving the disintegration strength of the aggregate and improving the filling property in the resin composition and the resin sheet. It is preferably 10.5~18μm, 11~15μm is better, 11.5~14μm is better, 12~13.5μm is better, and 12.2~13μm is better.

Further, the 50% volume cumulative particle diameter (D ₅₀ ) of the hBN powder was measured by the method described in the examples.

The bulk density of the hBN powder of the present invention is preferably 0.3 g/cm ³ or more, more preferably 0.35 g/cm ³ or more, and even more preferably 0.4 g/cm ³ or more, from the viewpoint of improving the disintegration strength of the aggregate. More preferably, it is 0.5 g/cm ³ or more, and more preferably 0.6 g/cm ³ or more.

Further, the bulk density of the hBN powder is determined by the method described in the examples.

The crystallite diameter of the hBN powder of the present invention is 260 to 1000 Å, preferably 280 to 750 Å, more preferably 300 to 500 Å, and more preferably 320 to 400 Å, from the viewpoint of improving thermal conductivity and electrical insulation. ~380Å is even better, and 340~360A is even better.

Further, the crystallite diameter can be measured by the method described in the examples.

Since the hBN powder of the present invention contains the aggregate, the aggregate can be maintained in a particle shape. Therefore, even if the filling ratio of the hBN powder in the resin composition and the resin sheet is increased, the primary particles can be prevented or inhibited from being aligned in a certain direction. The resin composition and the resin sheet obtained from the hBN powder are excellent in thermal conductivity and electrical insulation.

The purity of the hBN powder of the present invention, that is, the purity of hBN in the hBN powder of the present invention is preferably 96% by mass or more, and more preferably 98% by mass or more, from the viewpoint of improving thermal conductivity and electrical insulating properties. More preferably, 99% by mass or more, more preferably 99.5% by mass or more, and even more preferably 99.8% by mass or more. Further, the purity of the hBN powder can be measured by the method described in the examples.

The amount of boron oxide (hereinafter also referred to as "B ₂ O ₃ amount") in the hBN powder of the present invention is preferably from 0.001 to 0.12% by mass from the viewpoint of improving thermal conductivity, electrical insulation, and production advantage. , 0.005 to 0.11% by mass is more preferable, 0.0075 to 0.10% by mass is more preferably, 0.01 to 0.05% by mass is more preferably, and 0.015 to 0.03% by mass is more preferable.

Further, the amount of B ₂ O ₃ can be measured by the method described in the examples.

The content of calcium oxide (CaO) in the hBN powder of the present invention is preferably 0.5% by mass or less, more preferably 0.2% by mass or less, even more preferably 0.1% by mass or less, from the viewpoint of improving thermal conductivity and electrical insulating properties. It is more preferably 0.05% by mass or less, more preferably 0.03% by mass or less, and still more preferably 0.02% by mass or less. Further, the content of CaO in the hBN powder can be measured by the method described in the examples.

The content of carbon in the hBN powder of the present invention is preferably 0.5% by mass or less, more preferably 0.2% by mass or less, even more preferably 0.1% by mass or less, and 0.05% by mass, from the viewpoint of improving thermal conductivity and electrical insulating properties. Further preferably, it is more preferably 0.04% by mass or less, more preferably 0.03% by mass or less, and even more preferably 0.02% by mass or less. Further, the content of carbon in the hBN powder can be measured by the method described in the examples.

<surface treatment>

When the resin composition and the resin sheet are produced by dispersing in the resin component, the hBN powder of the present invention may be used in various dispersing agents, for the purpose of increasing the dispersibility with respect to the resin component and improving the workability. Surface treatment.

(coupling agent)

Examples of the coupling agent include a decane system, a titanate system, and an aluminum system. Among them, a decane coupling agent is preferred from the viewpoint of the effect. In the case of decane coupling agents, in particular: γ-aminopropyltrimethoxydecane, γ-aminopropyltriethoxydecane, γ-(2-aminoethyl)aminopropyltrimethoxy Decane, γ-(2-aminoethyl)aminopropyltriethoxydecane, γ-anilinopropyltrimethoxydecane, γ-anilinopropyltriethoxydecane, N-β-( N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxydecane and N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltriethyl An aminodecane compound such as oxydecane is preferred.

[Manufacturing method of hexagonal crystal boron nitride powder]

The hexagonal boron nitride powder (hBN powder) of the present invention has 100 parts by mass of a crude hexagonal boron nitride powder containing 20 to 90% by mass of boron nitride and 10 to 80% by mass of boron oxide in terms of carbon. A method of producing a hexagonal boron nitride powder by mixing a carbon source of 15 parts by mass with 0.01 to 1 part by mass of a calcium compound and forming it in a firing step in a nitrogen-containing atmosphere is preferably carried out.

Further, in the hBN powder of the present invention, it is preferable to further prepare the hBN powder by performing at least one of pulverization and classification after the calcination step, and it is more preferable to obtain both of the pulverization and the classification to obtain the hBN powder.

Next, the raw materials used in the production method, that is, the raw hexagonal boron nitride powder and the carbon source will be described, and then, the steps of mixing, forming, baking, pulverizing, and classifying will be described.

(crude hexagonal boron nitride powder)

The crude hexagonal boron nitride powder (crude hBN powder) used in the above production method contains 20 to 90% by mass of boron nitride and 10 to 80% by mass of boron oxide. The crude hBN powder containing a large amount of boron oxide can be easily produced as described later. Further, in the above-described production method, since the crude hBN powder is not directly subjected to high-purification treatment such as baking and is directly used as a raw material, the production efficiency is high.

Further, the content of boron oxide in the crude hBN powder can be measured by the method described in the examples. Meanwhile, the determination of the content of boron nitride in the crude hBN powder can be carried out by subtracting the content of boron oxide from the total mass. The calculation method of the content of boron oxide has been described in the examples.

When the content of boron nitride is 20% by mass or more, the hBN powder can be efficiently produced using the crude hBN powder as a raw material. When the content of boron nitride is 90% by mass or less, the crude hBN powder of the raw material can be efficiently produced. Therefore, from this viewpoint, the content of boron nitride in the crude hBN powder is preferably 45 mass% or more, more preferably 50 mass% or more, more preferably 55 mass% or more, and still more preferably 60 mass% or more; It is preferably 85 mass% or less, more preferably 80 mass% or less, more preferably 75 mass% or less, and more preferably 70 mass% or less; and 45 to 85 mass%, preferably 50 to 80 mass%. 55~75% by mass is better, and 60~70% by mass is better.

Moreover, when the content of boron oxide is 10% by mass or more, high efficiency is achieved. The crude hBN powder of the raw material was produced. When the content of boron oxide is 80% by mass or less, the hBN powder can be efficiently produced using the crude hBN powder as a raw material. Therefore, from the viewpoint of the above, the content of boron oxide in the crude hBN powder is preferably 15% by mass or more, more preferably 20% by mass or more, more preferably 25% by mass or more, and still more preferably 30% by mass or more; moreover, It is preferably 55 mass% or less, more preferably 50 mass% or less, more preferably 45 mass% or less, more preferably 40 mass% or less, and preferably 15 to 55 mass%, more preferably 20 to 50 mass%. 25~45% by mass is better, and 30~40% by mass is better.

Further, in the crude hBN powder, the total content of boron nitride and boron oxide is preferably 90% by mass or more, more preferably 95% by mass or more, more preferably 99% by mass or more, and still more preferably 100% by mass or more. .

The crude hBN powder may further contain other components within the range of not inhibiting the effects of the present invention. In the crude hBN powder, the content of the other components is preferably 10% by mass or less, more preferably 5% by mass or less. 1% by mass or less is more preferable, and other ingredients are not preferred.

<Method for Producing Crude Hexagonal Boron Nitride Powder>

The crude hBN powder may be suitably mixed with a compound containing oxygen and boron and an amine group-containing compound, and after heating, pulverized, it can be obtained.

Therefore, first, the raw materials used in the production method, that is, the compound containing oxygen and boron, and the compound containing an amine group will be described. Next, each step of mixing, molding, heating, and pulverization will be described.

(compounds containing oxygen and boron)

Examples of the compound containing oxygen and boron include orthoboric acid (H ₃ BO ₃ ), metaboric acid (HBO ₂ ), tetraboric acid (H ₂ B ₄ O ₇ ), and dehydroboric acid (B ₂ O ₃ ). One or two or more compounds of the formula (B ₂ O ₃ )‧(H ₂ O) _X [wherein, X = 0 to 3]. Among them, orthoboric acid is easily obtained and is excellent in miscibility with an amine group-containing compound such as melamine.

The purity of the compound containing oxygen and boron is preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 99% by mass or more, and still more preferably 100% by mass or more.

(amine-containing compound)

Examples of the amine group-containing compound include an aminotriazine compound, an anthraquinone compound, and urea. Examples of the aminotriazine compound include melamine, melamine, benzocyanamide, and melamines, melem, and melamine of these condensates. Wait.

Among such compounds, a compound containing a nitrogen atom at a site other than the amine group and the amine group, such as melamine, hydrazine or the like, is preferred.

The purity of the amine group-containing compound is preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 99% by mass or more, and still more preferably 100% by mass or more.

(mixing)

First, the above oxygen-containing and boron-containing compounds and amine-containing compounds are mixing.

The mixing method is not particularly limited, and any of wet mixing and dry mixing may be employed, but wet mixing is preferred. In the wet mixing, the precursor can be formed first. For example, when water is further added with boric acid or dehydrated boric acid mixed with melamine, a precursor such as a molecular formula of C ₃ N ₃ (NH ₂ ‧H ₃ BO ₃ ) ₃ can be obtained. Wet mixing can be carried out using a Henschel mixer, a ball mill, a general mixer with a mixer, and the like.

The ratio of the compound containing oxygen and boron to the compound containing an amine group is the atomic ratio of the boron atom (B) in the compound containing oxygen and boron to the nitrogen atom (N) in the compound containing an amine group (B/N) ), preferably in a ratio of 1/3 to 2/1. When the atomic ratio of B/N is 1/3 or more, since the amine group-containing compound which cannot form a precursor in the presence of water can be prevented or suppressed, it is possible to prevent or suppress the carbonization of boron nitride in the firing to become black. Or brown. Meanwhile, the atomic ratio to B/N is 2/1 or less, and the more boron atoms, the higher the crystallinity of hBN.

When melamine is used as the amine group-containing compound, the amount of melamine is preferably 100 to 65 parts by mass, and more preferably 35 to 60 parts by mass, based on 100 parts by mass of the compound containing oxygen and boron. 40 to 55 parts by mass is better, and 45 to 50 parts by mass is better.

(forming)

Secondly, it is preferred to form the precursor-containing mixture obtained by the above mixing.

Forming the mixture containing the precursor into a shaped body increases the bulk density of the mixture, and a large amount of the mixture can be charged in a heating device of a certain capacity, thereby improving productivity. Moreover, the thermal conductivity can be improved by increasing the bulk density by molding, so that the temperature can be rapidly increased while uniformly heating the mixture. Further, the gas generated by the decomposition and decomposition of the mixture can be easily released from the gap between the molded bodies, so that the mixture can be prevented from being sprayed and scattered. At the same time, the forming can also increase the bulk density, and the dehydrated boric acid remains at a high temperature for a long time, thereby promoting the crystal growth of hBN. This molding is preferably carried out so that the obtained molded body density is preferably about 0.6 to 0.8 g/cm ³ .

(heating)

Next, the formed body obtained by the above molding can be heated. By this heating, a compound containing oxygen and boron in the molded body can be reacted with an amine compound-containing nitrogen compound to form hBN.

The gas when heated is ammonia or a non-oxidizing gas. As the non-oxidizing gas, an inert gas such as nitrogen gas or argon gas is preferred. Among them, ammonia gas is better.

The heating temperature is preferably from 800 to 1400 ° C, more preferably from 900 to 1,350 ° C, more preferably from 1,000 to 1,300 ° C, and more preferably from 1,050 to 1,200 ° C, from the viewpoint of improving reactivity and ease of pulverization.

(crush)

Next, the obtained product obtained by heating is pulverized to obtain a crude hBN powder.

The method of pulverization is not particularly limited, and smashing, coarse pulverization, or the like can be employed.

<Method for Producing Hexagonal Boron Nitride Powder>

The method for producing the hexagonal boron nitride powder (hBN powder) of the present invention is a carbon source and a 0.01 to 1 part by mass of 3 to 15 parts by mass in terms of carbon, based on 100 parts by mass of the above-mentioned crude hBN powder. The calcium (Ca) compound is mixed.

When the carbon source is 3 parts by mass or more in terms of carbon, the growth of the particles of the primary particles can be promoted, and the nitridation of the boron oxide can be promoted to improve the crystallinity of the aggregate, so that the disintegration strength of the aggregate can be improved. When the carbon source is 15 parts by mass or less in terms of carbon, it is possible to prevent the unreacted carbon component from remaining as a foreign matter, that is, a black foreign matter, thereby improving whiteness and electrical insulation.

From this point of view, the amount of the carbon source can be 3 to 15 parts by mass, more preferably 4 to 14 parts by mass, and more preferably 5 to 13 parts by mass, based on 100 parts by mass of the crude hBN powder. 6~12 parts by mass is better, and 8~10 parts by mass is better.

In addition, when the amount of the Ca compound is 1 part by mass or less, the growth of the particles of the primary particles can be promoted while maintaining high purity, so that the crystallinity can be improved.

From this point of view, the compounding amount of the Ca compound may be 0.01 to 1 part by mass, more preferably 0.05 to 0.8 part by mass, more preferably 0.1 to 0.6 part by mass, and more preferably 0.2 to 0.5 mass, based on 100 parts by mass of the crude hBN powder. The portion is even better, and the 0.3 to 0.45 parts by mass is even better.

(carbon source)

The carbon source used in the method for producing a hexagonal boron nitride powder (hBN powder) of the present invention is carbon or a carbon-containing compound. The carbon source used in the present invention may be, in addition to graphite, carbon black, boron carbide, saccharide, melamine, phenol resin or the like, and one or two selected from the group consisting of graphite and boron carbide. Further, the carbon source is preferably a combination of graphite and boron carbide from the viewpoint of thermal conductivity, and graphite is preferred from the viewpoint of electrical insulation.

The content of carbon in the carbon source is preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 99% by mass or more, and still more preferably 100% by mass or more.

(boron carbide)

In the method for producing the hBN powder of the present invention, the carbon source is preferably made of boron carbide (hereinafter also referred to as "B ₄ C") from the viewpoint of thermal conductivity. With respect to 100 parts by mass of the crude hBN powder, the amount of boron carbide of the carbon source is preferably 0.01 to 14.8 parts by mass, more preferably 0.01 to 12 parts by mass, more preferably 0.01 to 10 parts by mass, and 0.05 to 8 parts by mass. The portion is even better, 0.1 to 6 parts by mass is better, 0.5 to 5 parts by mass is better, and 1 to 3 parts by mass is better.

In this way, the growth of the particles of the hBN primary particles in the thickness direction can be promoted, and the crystallization can be promoted. Therefore, the alignment of the hBN particles can be controlled, which contributes to high thermal conductivity. Further, since boron is generated by using carbon in the boron carbide crystal as a starting point, it is considered that the boron carbide can be produced and maintained. The hBN powder in the form of particles, and the hBN powder grown by dissolution precipitation from the crystal nucleus formed on the graphite surface when graphite is used alone, can make the thickness of the hBN primary particles thicker. Therefore, when the organic matrix is filled with the hBN powder to produce the resin composition and the resin sheet or when the resin sheet is used, it can be maintained in a particle shape to prevent or suppress disintegration.

Further, when graphite and boron carbide are used in combination with the carbon source, when the boron carbide is used alone, the firing time can be shortened, and the number of black foreign matter caused by the boron carbide can be reduced.

The content of boron carbide in the boron carbide is preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 99% by mass or more, and still more preferably 100% by mass or more.

At the same time, when the graphite and boron carbide are used together (boron carbide/carbon source), the mass ratio is preferably 0.003 to 0.99 in terms of carbon, preferably 0.015 to 0.8, more preferably 0.02 to 0.6, and even more preferably 0.085 to 0.4. 0.15~0.3 is even better.

(Ca compound)

In the calcium compound (hereinafter also referred to as "Ca compound") used in the method for producing the hBN powder of the present invention, in addition to calcium carbonate, calcium oxide, calcium fluoride, and calcium chloride may be mentioned. Calcium carbonate is preferred.

The content of the calcium carbonate in the Ca compound is preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 99% by mass or more, and still more preferably 100% by mass or more.

(mixing)

The method of mixing is not particularly limited, and any of wet mixing and dry mixing may be used, and wet mixing is preferred. Wet mixing can be carried out using a Henschel mixer, a ball mill, a general mixer with a mixer, and the like.

Moreover, when mixing, a binder may be added and then mixed. The binder is not particularly limited, and examples thereof include resins such as polyvinyl alcohol (PVA), cellulose, and polyvinylidene fluoride (PVDF), and polyvinyl alcohol is preferably used.

The binder is preferably an aqueous solution of a binder in which such a resin is dissolved in water. The content of the resin in the aqueous solution of the binder is preferably from 1 to 10% by mass, more preferably from 1 to 5% by mass, even more preferably from 1 to 4% by mass. The mixed aqueous solution of the binder is preferably 1 to 20 parts by mass, more preferably 5 to 15 parts by mass, even more preferably 8 to 12 parts by mass, based on 100 parts by mass of the crude hBN powder.

Further, when the binder is added in this manner, the binder is also converted into the above carbon source.

(forming)

Next, the mixture obtained by the above mixing is further shaped into an appropriate shape.

In the molding, the strength of the aggregate formed by the aggregation of the primary particles of hBN, the productivity, the easiness of handling, and the reactivity are considered to be 0.5 g/cm ³ or more. It is more preferably 0.8 g/cm ³ or more, more preferably 1 g/cm ³ or more, more preferably 2 g/cm ³ or less, still more preferably 1.8 g/cm ³ or less, and still more preferably 1.5 g/cm ³ or less.

(burning)

The method for producing the hBN powder of the present invention also includes a baking step of firing the formed body obtained by the above molding. The crude hBN powder is press-formed into a molded body and then fired, whereby the boron oxide contained in the crude hBN powder in the molded body is reacted with carbon contained in the carbon source to form a hexagonal compound having high compressive and disintegrating strength. A boron nitride (hBN) aggregate is obtained to obtain the hBN powder of the present invention. Further, when firing is performed without being formed, it is difficult to sufficiently produce a hBN aggregate having high disintegration strength.

The gas at the time of firing is a gas containing nitrogen. In the nitrogen-containing gas, the concentration of nitrogen gas is preferably 60% by volume or more, more preferably 80% by volume or more, more preferably 90% by volume or more, and still more preferably 99% by volume or more. It is better to use less oxygen.

The firing temperature is preferably from 1000 to 2200 °C. When the firing temperature is 1000 ° C or higher, the reduction nitridation reaction can be sufficiently performed. Moreover, below 2200 ° C, the decomposition of hBN can be prevented. Therefore, from this point of view, the firing temperature is preferably 1500 to 2200 ° C, more preferably 1600 to 2200 ° C, more preferably 1700 to 2200 ° C, and more preferably 1730 to 2190 ° C.

The firing time is preferably 1 to 20 hours. When the firing time is 1 hour or longer, a sufficient reduction nitridation reaction can be performed, and the unreacted carbon component can be prevented from remaining as a black substance. When it is less than 20 hours, the cost of firing can be reduced. From this point of view, it is better to use 1 to 15 hours, 5 to 10 hours is better, 6 to 9 hours is better, and 6 to 7 hours is better.

Moreover, it can also be dried before baking. The drying temperature is preferably 150 to 400 ° C, more preferably 200 to 400 ° C; and the drying time is preferably 6 to 8 hours.

(crush)

Next, it is preferred that the product obtained by firing is further pulverized.

The method of pulverization is not particularly limited, and smashing, coarse pulverization, or the like can be employed.

(grading)

Next, after the above-described baking step, it is preferred to further classify the pulverized material obtained by the pulverization.

The method of classification is not particularly limited, and it can be classified by a vibrating sieve device, a gas flow classification, a water sieve, a centrifugal separation, or the like. Among them, it is preferred to classify via a vibrating screen device. When the vibrating screen device is used, a dry vibrating screen device [manufactured by Akira Sangyo Co., Ltd., trade name "Sato Vibrating Screening Machine") can be used, and it is preferably classified by using a sieve having a pore size of 106 μm in a classification time of 60 minutes.

(mixing of hBN powder)

Further, the method for producing the hBN powder of the present invention has a viewpoint of improving thermal conductivity and electrical insulating properties, and further comprises using a sieve having a pore size of 106 μm and a sieve having a pore diameter of 45 μm as the hexagonal boron nitride powder obtained in the above. And a vibrating screen device, hBN powder of 45 to 106 μm (hereinafter also referred to as "hBN powder (A)") and hBN powder under 45 μm sieve (hereinafter also referred to as "hBN powder (B)"). Thereafter, the hBN powder (A) and the hBN powder (B) are mixed as a ratio of the hBN powder (A) to the total amount of the hBN powders (A) and (B) (hereinafter, also referred to as the particle ratio (% by mass) ) = [(A) / [(A) + (B)]].) A mixing step of 40 to 90% by mass is preferred.

The method of mixing is not particularly limited, and any of wet mixing and dry mixing may be used, and dry mixing is preferred. The dry mixing can be carried out using a general mixer such as a Henschel mixer, a ball mill, a mixer, and a V-type mixer, and a V-type mixer is preferable from the viewpoint of uniformly mixing the hBN powder. The mixing time is preferably 20 to 90 minutes, and 50 to 70 minutes is better.

hBN powder (A) powder with a pore size of 106 μm obtained by a vacuum suction type sieving machine (jet screen), the content of which is preferably 5 to 20% by mass, more preferably 10 to 18% by mass, and 14 to 17 mass. % is even better. At the same time, the hBN powder (B) is a powder having a pore size of 45 μm obtained by a vacuum suction type sieving machine (jet screen), and the content is preferably 1 to 20% by mass, more preferably 1 to 10% by mass, 4~ Further, 8 mass% is more preferable, and 5 to 7 mass% is more preferable. Further, the content of the powder on the sieve having a pore size of 106 μm and the content of the powder on the sieve having a pore diameter of 45 μm can be measured by the method described in the examples.

The particle ratio is preferably from 40 to 90% by mass, more preferably from 50 to 85% by mass, more preferably from 55 to 80% by mass, more preferably from 60 to 70% by mass, from the viewpoint of improving thermal conductivity and electrical insulation. .

[Resin composition]

The resin composition of the present invention contains 1 to 90% by volume of the above-mentioned hexagonal boron nitride powder (hBN powder). The content of the hBN powder in the resin composition of the present invention is preferably from 10 to 90% by volume from the viewpoint of the thermal conductivity of the resin composition and the resin sheet formed by molding the resin composition, and the formability of the resin sheet. 20 to 80% by volume is more preferable, 30 to 70% by volume is more preferable, 35 to 65% by volume is more preferable, and 40 to 60% by volume is more preferable.

When the above-mentioned hBN powder is used to produce a resin composition, it is similar in properties to the resin component, so that the resin composition can be made low in viscosity and excellent in electrical insulation properties.

In the present invention, the volume-based content (% by volume) of the hBN powder can be determined from the specific gravity of the hBN powder and the specific gravity of various resins of the organic matrix to be used.

(organic matrix)

The resin composition of the present invention contains a resin of an organic matrix.

The resin used in the present invention is preferably one or more resins selected from the group consisting of thermosetting resins, thermoplastic resins, various rubbers, thermoplastic elastomers, and fats and oils.

Examples of the thermosetting resin include an epoxy resin, a decyl alkane resin, a phenol resin, a urea resin, an unsaturated polyester resin, a melamine resin, a polyimide resin, a polybenzoxazole resin, and a urea. Alkane resin and the like.

Examples of the thermoplastic resin include polyolefin resins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer; and polyethylene terephthalic acid; Polyester resin such as ester, polybutylene terephthalate, liquid crystal polyester; polyvinyl chloride resin, acrylic resin, polysulfurized benzene resin, polyphenylene ether resin, polyamide resin, polyamidimide Resin, polycarbonate resin, etc.

Examples of various rubbers include natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, polybutadiene rubber, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, Butadiene-acrylonitrile copolymer, isobutylene-isoprene copolymer, chloroprene rubber, decane rubber, fluorine rubber, chlorine-deuterated polyethylene, polyurethane rubber, and the like. Such rubbers are preferably used after cross-linking.

Examples of the thermoplastic elastomer include an olefin-based thermoplastic elastomer, a styrene-based thermoplastic elastomer, a vinyl chloride-based thermoplastic elastomer, an amine-ester thermoplastic elastomer, and an ester-based thermoplastic elastomer.

Examples of the oil and fat component include greases such as polyoxyalkylene oil.

These organic substrates may be used alone or in combination of two or more.

The resin composition of the present invention has mechanical strength, heat resistance, and durability of a heat conductive material such as a heat conductive material obtained by using the resin composition and a resin sheet formed by molding the resin composition. The properties required for properties such as properties, flexibility, flexibility, and the like include one or more selected from the group consisting of organic resins conventionally used as resin sheets, thermosetting resins, thermoplastic resins, various rubbers, and thermoplastic elastomers. Resin is preferred. Such organic substrates may be used alone or in combination of two or more. In the present invention, It is preferred to use a curable epoxy resin or a curable siloxane resin.

The content of the organic matrix in the resin composition is preferably from 10 to 90% by volume, more preferably from 20 to 80% by volume, from the viewpoint of moldability of the resin sheet formed by molding the resin composition, 30~ 70% by volume is even better, 35 to 65 vol% is better, and 40 to 60 vol% is even better.

In the present invention, the volume-based content (% by volume) of the organic matrix can be determined from the specific gravity of the hBN powder and the specific gravity of various resins using the organic matrix.

(curable epoxy resin)

The resin composition of the present invention is based on the viewpoint of dispersibility of the organic matrix by the hBN powder mixture in terms of the use of the curable epoxy resin which is an organic matrix, and is an epoxy resin which is liquid at normal temperature and at room temperature. An epoxy resin having a low softening point in a solid state is preferred.

The epoxy resin is not particularly limited as long as it is a compound containing two or more epoxy groups in one molecule, and any one of conventionally known compounds which are conventionally used as an epoxy resin can be appropriately selected and used. . Examples of such epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, polycarboxylate epoxidized propyl ether, and epoxidation of a cyclohexane derivative. Epoxy resin, etc. These items may be used alone or in combination of two or more. In the epoxy resin, an epoxy resin obtained by epoxidizing a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, or a cyclohexane derivative is used from the viewpoints of heat resistance and workability. Preferably.

(hardener for epoxy resin)

In curing the curable epoxy resin, a curing agent for an epoxy resin is usually used. The epoxy resin hardener is not particularly limited, and may be any one selected from the group consisting of hardeners for epoxy resins, and examples thereof include an amine system, a phenol system, and an acid anhydride system. Wait. Examples of the amine-based hardener are, for example, dicyandiamide, and m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylanthracene, An aromatic diamine such as m-xylylenediamine or the like is preferred; examples of the phenolic hardener are, for example, a phenol novolak resin, a cresol novolak resin, a bisphenol A novolak resin, a triazine modified phenol novolac A varnish resin or the like is preferred. Further, examples of the acid anhydride-based curing agent include an alicyclic acid anhydride such as methyl hexahydrophthalic anhydride, an aromatic acid anhydride such as phthalic anhydride, an aliphatic acid anhydride such as an aliphatic dibasic acid anhydride, and a chlorine bridge. A halogen acid anhydride such as an acid anhydride.

These hardeners may be used alone or in combination of two or more. The amount of the curing agent for the epoxy resin is determined by the balance between the curability and the properties of the cured resin, and the equivalent ratio of the curable epoxy resin is usually about 0.5 to 1.5 equivalents. It is preferred to select a range of 0.7 to 1.3 equivalent ratio.

(hardening accelerator for epoxy resin)

In the resin composition of the present invention, a curing accelerator for an epoxy resin may be used in combination with a curing agent for an epoxy resin, if necessary.

The hardening accelerator for the epoxy resin is not particularly limited, and Among the hardening accelerators which have been conventionally used as epoxy resins, any one of them is appropriately selected, and examples thereof include 2-ethyl-4-methylimidazole and 1-benzyl-2-methyl group. Imidazole compounds such as imidazole, 2-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2,4,6-tri (two Methylaminomethyl)phenol, boron trifluoride amine complex, triphenylphosphine, and the like. These hardening accelerators may be used alone or in combination of two or more. The amount of use of the curing accelerator for the epoxy resin is preferably from 0.1 to 10 parts by mass based on 100 parts by mass of the curable epoxy resin, in terms of the balance between the curing accelerator property and the cured resin property. It is preferred to select in the range of 0.4 to 5 parts by mass.

(curable rhodium oxide resin)

As the curable oxime resin, a mixture of an addition reaction type decane resin and a decane-based crosslinking agent can be used. Examples of the addition reaction type siloxane oxide include at least one selected from the group consisting of polyorganosiloxanes having an alkenyl group as a functional group in the molecule. The polyorganosiloxane having an alkenyl group as a functional group in the above molecule, such as a polydimethylsiloxane having a functional group of a vinyl group, a polydimethylsiloxane having a functional group of a hexenyl group, and the like Mixtures and the like are preferred.

The oxoxane-based crosslinking agent may be a polyorganooxy oxane having at least two hydrogen atoms bonded to a ruthenium atom in a molecule, and specifically, a dimethylhydroquinone-terminated terminal is exemplified. a methyl methoxy alkane-methylhydroquinoxane copolymer, a trimethyl decyloxy terminated dimethyl methoxy oxane-methylhydroquinoxane copolymer, a trimethyl decyloxyalkyl end-blocked Poly Alkyl hydroquinone), poly(hydroperoxypropane), and the like.

Further, in terms of curing the catalyst, a platinum-based compound can be usually used. Examples of the platinum compound include, for example, particulate platinum, particulate platinum adsorbed on a carbon powder carrier, chloroplatinic acid, alcohol-modified platinum chloride acid, and chloroplatinic acid olefins. Materials, palladium, rhodium catalysts, and the like.

The resin composition of the present invention may further contain other components within the range in which the effects of the present invention can be obtained. Examples of such a component include nitride particles such as aluminum nitride, tantalum nitride, and fibrous boron nitride, and electrical insulation such as alumina, fibrous alumina, zinc oxide, magnesium oxide, cerium oxide, and titanium oxide. Electrically insulating carbon components such as metal oxides, diamonds, and fullerenes, plasticizers, adhesives, reinforcing agents, colorants, heat resistance improvers, viscosity modifiers, dispersion stabilizers, and solvents.

Meanwhile, in the resin composition containing the hexagonal boron nitride powder of the present invention, in addition to the effects of the nitride particles and the electrically insulating metal oxide, it may be added: An inorganic filler such as aluminum or magnesium hydroxide, a surface treatment agent such as a decane coupling agent which improves the interface strength between the inorganic filler and the matrix resin, a reducing agent, and the like.

The resin composition of the present invention can be used for a thermally conductive material such as a thermally conductive sheet, a thermally conductive colloid, a thermally conductive grease, a thermally conductive adhesive, or a phase change sheet. As a result, heat from heat-generating electronic components such as MPUs, power transistors, and transformers can be efficiently conducted to heat-dissipating components such as heat sinks and cooling fans.

Among the above thermally conductive part materials, used as a thin thermal conductivity It is preferred that the sheet is in a resin sheet. The resin composition described above is particularly effective in improving the thermal conductivity and electrical insulating properties of the resin sheet.

[resin sheet]

The resin sheet of the present invention is formed of the above-described resin composition or a cured product thereof, that is, formed by forming the resin composition into a sheet. On the other hand, when the resin composition is curable, it can be cured after being formed into a sheet.

The resin sheet of the present invention can be produced by the following resin composition.

First, the hBN powder of the present invention is dispersed in a suitable solvent to prepare a hBN powder suspension having a concentration of about 50 to 80% by mass.

Next, in the suspension, the organic substrate is added in such a ratio that the hBN powder and the organic substrate contain 10 to 90% by volume of the hBN powder. Then, the weight of the hBN powder and the resin are set so as to have a specific gravity of the hBN powder and the specific gravity of the resin used as the organic matrix, and the weights of the hBN powder and the resin are separately weighed and mixed to prepare a resin composition.

Further, the method of preparing the resin composition can be prepared as follows.

First, the resin is further mixed with a curing agent and a solvent to prepare an organic substrate.

Next, the hBN powder is contained in the organic matrix to contain the hBN powder 10 to 90 in the total amount of the hBN powder and the organic matrix. The percentage of the product is added in a way. Then, the weight of the hBN powder and the resin are set so as to be a desired volume by the specific gravity of the hBN powder and the specific gravity of the resin used as the organic matrix, and the respective components are weighed and mixed to prepare a resin composition.

In the case of using a curable epoxy resin as a main component of the organic substrate, a mixture of the curable epoxy resin, the epoxy resin hardener, and the epoxy resin hardening accelerator to be used as needed.

Further, in the case of using a curable siloxane oxide resin as a main component of the organic substrate, a mixture of a reaction-type siloxane oxide, a siloxane-based crosslinking agent, and a curing catalyst is added to the organic system.

The resin composition can be applied to a substrate such as a release film such as a resin film containing a release layer by a general coating machine or the like, and a solvent such as a far-infrared radiation oven or a hot air supply can be used when the resin composition contains a solvent. Dry and exfoliate.

As the release layer, a melamine resin or the like can be used. Meanwhile, as the resin film, a polyester resin such as polyethylene terephthalate or the like can be used.

When the organic substrate in the resin composition is not a curable organic substrate such as a curable epoxy resin or a curable siloxane oxide resin, the resin sheet which is directly flaky may be the resin sheet of the present invention.

Further, in the case of the organic-based system curable organic substrate, the resin sheet formed on the substrate obtained as described above may be pressurized by the substrate from the uncoated resin composition side as needed. Thereafter, the resin sheet of the present invention can be obtained by heat treatment and hardening. The pressurization condition is preferably 15 to 20 MPa, and more preferably 17 to 19 MPa. Heating conditions, It is also preferably 80~200°C, and 100~150°C is better. Further, the substrate such as the release film is usually finally peeled off or removed.

The film thickness of the resin sheet of the present invention obtained in this manner is preferably 50 to 150 μm in the range of 50 to 150 μm from the viewpoint of moldability and the thickness of the electronic component using the resin sheet. The range of 140 μm is better, and the range of 100 to 130 μm is even better.

Further, the resin sheet of the present invention preferably has a thermal conductivity in the thickness direction of 3 W/m‧K or more, more preferably 7 W/m ‧ or more, more preferably 9 W/m ‧ K or more, and more preferably 10 W/m ‧ K or more Good, 14W/m‧K and above is even better, and 18W/m‧K is even better.

The resin sheet of the present invention preferably has a specific gravity of 90 to 100%, more preferably 95 to 100%, more preferably 98 to 100%, and more preferably 100%, from the viewpoint of electrical insulation.

The resin sheet of the present invention is preferably used in a sheet-like, fibrous or mesh-like component material on one side or both sides and in a sheet for further improvement in workability and reinforcement.

The resin sheet obtained in this manner can be peeled off from the release film or the release film can be used as a protective film to provide a product which is used as a resin sheet.

Further, the resin sheet of the present invention may have a structure in which the adhesive layer is further provided on the upper side or the lower side of the resin sheet, so that the convenience in use of the product can be further increased.

The resin sheet of the present invention can be used to conduct heat to heat sinks of heat generating electronic parts such as MPUs and power transistors, transformers, and the like. A heat dissipating component such as a cooling fan can be used between a heat-generating electronic component and a heat-dissipating component. In this way, heat transfer between the heat-generating electronic component and the heat-dissipating component is improved, so that the non-action of the heat-generating electronic component is remarkably reduced.

[Examples]

Hereinafter, the present invention will be specifically described by way of Examples and Comparative Examples, but the present invention is not limited to these examples.

[Example 1] (1) Production of crude hBN powder

First, 4 g of boric acid, 2 g of melamine, and 1 g of water were added, stirred and mixed, and then pressurized in a mold to obtain a molded body having a density of 0.7 g/cm ³ . The formed body was then dried in a dryer at 300 ° C for 100 minutes and then preheated at 1100 ° C for 120 minutes under NH ₃ gas. The obtained preheated material (crude hBN) was further pulverized to obtain a crude hBN powder (boron oxide content of 35 mass%).

(2) Production of hBN powder

Then, 10 parts by mass of the artificial graphite fine powder "UF-G30" manufactured by Showa Denko Co., Ltd. is used as a carbon source, 0.4 parts by mass of Ca compound calcium carbonate, and a PVA aqueous solution (concentration: 2.5% by mass) 10 based on 100 parts by mass of the above crude hBN powder. A mixture of 10 parts by mass of carbon in terms of carbon source of 100 parts by mass of the carbon source of the crude hBN powder and 0.4 parts by mass of the content of the Ca compound can be obtained. Then, the mixture was stirred and mixed by a mixer, and then introduced into a mold and pressurized to obtain a molded body having a density of 1.2 g/cm ³ . The formed body was further dried in a dryer at 300 ° C for 6 hours to obtain a dried product. Thereafter, the dried product was fired in a high-frequency electric furnace under nitrogen at 1750 ° C to 2200 ° C for 6 hours to obtain a hBN fired product.

Then, the obtained hBN fired product is pulverized by a jaw mill and a column pulverizer, and then a dry vibrating screen apparatus [manufactured by Akira Sangyo Co., Ltd., trade name "Sato-type vibrating sieving machine"] is used, and the sifting time is 60. Under a minute condition, a sieve having a pore size of 106 μm and a sieve having a pore size of 45 μm were classified into hBN powder (A) of 45 to 106 μm and hBN powder (B) of 45 μm sieve. Then, the hBN powder (A) of 45 to 106 μm and the hBN powder (B) of 45 μm sieve prepared as described above, and a vacuum evacuation type sieving machine (air-jet sieve [manufactured by Alpine, model name "A200LS"] to be described later] The powder content is determined, the powder content of the hBN powder of 45 to 106 μm (A) and the powder content of the sieve of 106 μm of the sieve are 15% by mass, and the powder content of the hBN powder (B) of 45 μm sieve is 45 μm. %. The hBN powder (A) of 45 to 106 μm and the hBN powder (B) of 45 μm sieve were mixed at a particle ratio shown in Table 1, and the hBN powder of Example 1 was obtained.

Further, the particle ratio is a ratio of the total amount of the hBN powder (A) to the hBN powder (A) of 45 to 106 μm and the hBN powder (B) of the 45 μm sieve by the following formula.

Particle ratio (% by mass) = [(A) / [(A) + (B)]]

The hBN powder of Example 1 obtained as described above, and the vacuum evacuation type sieving machine (jet screen [Alpine Company, machine" described later) The name "A200LS"]), after the sieve was divided into a sieve having a pore size of 106 μm, the powder content of the hBN powder having a pore size of 106 μm was 6% by mass, and the powder content of the sieve having a pore size of 106 μm was 94% by mass. At the same time, the powder content of the sieve having a pore diameter of 45 μm was 39% by mass in the above-mentioned vacuum evacuation type sieving sieve when sieved into a sieve having a pore size of 45 μm.

Thereafter, the hBN powder was observed by SEM, and as shown in Fig. 2, it was confirmed that the primary particles contained hBN aggregates in a random direction. Further, Fig. 1 is a schematic view showing the aggregate of hBNs present in Fig. 2.

(3) Modification of resin composition

For the organic substrate, a liquid curable epoxy resin (manufactured by Nippon Epoxy Resin Co., Ltd., trade name "jER828", bisphenol A type, epoxy equivalent 184 to 194 g/eq], 100 parts by mass of an imidazole with a hardener [ 5 parts by mass of the product manufactured by Shikoku Chemicals Co., Ltd., trade name "2E4MZ-CN".

First, the hBN powder was added to the total amount of the hBN powder and the organic matrix in an amount of 60% by volume based on 100 parts by mass of the organic substrate, and then stirred and mixed with MAZERUSTAR manufactured by Kurabo Industries. A resin composition.

Further, the volume-based content (% by volume) of the hBN powder can be determined from the specific gravity of the hBN powder (2.27) and the specific gravity (1.17) of the liquid curable epoxy resin used as the organic matrix.

(4) Production of resin sheets

After being cut into a release film having a width of 10.5 cm and a length of 13 cm, and using a mold to form a cured film having a thickness of 500 μm or less, the mold is sandwiched between the release films, and the release film is separated at 120 ° C and 18 MPa. The resin composition was cured by pressing for 10 minutes under conditions, and a resin sheet was produced.

[Embodiment 2]

In (2) of the first embodiment, the hBN powder, the resin composition, and the resin sheet were produced in the same manner as in Example 1 except that the artificial graphite fine powder having a blending amount of 5 parts by mass was added to 100 parts by mass of the above-mentioned crude hBN powder.

[Example 3]

In (2) of Example 1, the same procedure as in Example 1 was carried out except that the above-mentioned particle ratio was 80% by mass, and the hBN powder (A) of 45 to 106 μm and the hBN powder (B) of 45 μm sieve were mixed. hBN powder, resin composition and resin sheet.

[Example 4]

In (2) of the first embodiment, the artificial graphite fine powder having a blending amount of 5 parts by mass is added to 100 parts by mass of the above-mentioned crude hBN powder, and the hBN powder of 45 to 106 μm is mixed at a particle ratio of 80% by mass ( A) The hBN powder, the resin composition, and the resin sheet were produced in the same manner as in Example 1 except that the hBN powder (B) under a 45 μm sieve was used.

[Example 5]

In the (2) of the first embodiment, the artificial graphite fine powder having a blending amount of 8 parts by mass (8 parts by mass in terms of carbon) was added to 100 parts by mass of the above-mentioned crude hBN powder, and boron carbide (manufactured by Riken Emery Co., Ltd.) was added. In a mass fraction (2.2 parts by mass in terms of carbon), a mixed carbon source is contained in an amount of 10.2 parts by mass based on 100 parts by mass of the crude hBN powder, and then mixed with 45 to 106 μm of hBN powder at a particle ratio of 80% by mass (A) In the same manner as in Example 1 except that the hBN powder (B) under a 45 μm sieve was used, a hBN powder, a resin composition, and a resin sheet were produced.

[Comparative Example 1]

In the (2) of the first embodiment, the Ca compound (calcium carbonate) is added in an amount of 100 parts by mass based on the above-mentioned crude hBN powder, and the bBN powder of 45 to 106 μm is mixed in such a manner that the particle ratio is 60% by mass (A) In the same manner as in Example 1, except that the hBN powder (B) under a 45 μm sieve was used, a hBN powder, a resin composition, and a resin sheet were produced.

[Comparative Example 2]

Using the above-mentioned dry vibrating screen apparatus and the hBN powder (A) of 45-106 μm and the hBN powder of 45 μm sieve by using a sieve having a pore size of 106 μm and a sieve having a pore size of 45 μm for 60 minutes. B). Thereafter, the 45-106 μm hBN powder (A) was mixed in such a manner that the particle ratio was 60% by mass (the powder content on the sieve having a pore size of 106 μm was 2 The hBN powder, the resin composition, and the resin sheet were produced in the same manner as in Example 1 except that the hBN powder (B) in a 45 μm sieve (the powder content on the sieve having a pore size of 45 μm was 4% by mass).

[Comparative Example 3]

In (2) of Example 1, except that 100 parts by mass of the Ca compound (calcium carbonate) with respect to the above-mentioned crude hBN powder was not added, and 45 to 106 μm of hBN powder was mixed at a particle ratio of 80% by mass (A) In the same manner as in Example 1, except that the hBN powder (B) under a 45 μm sieve was used, a hBN powder, a resin composition, and a resin sheet were produced.

[Comparative Example 4]

In addition to the commercial product A used in Comparative Example 2, the 45-106 μm hBN powder (A) (the powder content on the 106 μm sieve is 2% by mass) and the 45 μm sieve hBN powder (B) (pore size 45 μm on the sieve) The powder content was 4% by mass. The mixture was mixed in the same manner as in Example 1 except that the pellet ratio was 80% by mass. The hBN powder, the resin composition and the resin sheet were produced.

[Comparative Example 5]

In (2) of the first embodiment, in addition to 100 parts by mass of the graphite fine powder and the Ca compound (calcium carbonate) with respect to the crude hBN powder, 30 parts by mass of boron carbide (manufactured by Riken Emery Co., Ltd.) was changed (6.6 parts by mass in terms of carbon). And mixing 45-106 μm of hBN powder in a manner of a particle ratio of 80% by mass The hBN powder, the resin composition, and the resin sheet were produced in the same manner as in Example 1 except that the (H) and the hBN powder (B) under a 45 μm sieve were used.

[rating]

Thereafter, the obtained crude hBN powder, hBN powder, resin composition, and resin sheet were subjected to the following evaluation.

(content of boron oxide in crude hBN powder)

In terms of the crude hBN powder, the powder is considered to be composed of boron oxide (hereinafter also referred to as "B ₂ O ₃ ") on the surface and an internal BON bond structure. Further, the BON bond structure constituting the crude hBN is used to form the internal oxygen, and in the firing step in the case of producing the hBN powder from the crude hBN powder, the reaction can be carried out by high-temperature heat treatment to gradually exude B ₂ O _{3 from the} surface. Accordingly, the content of B and C when the reaction of the carbon source to the crude powder of hBN powder production hBN ₂ O ₃ in the crude powder of hBN, the surface may be B ₂ O ₃ and the amount of oxygen inside the B ₂ O ₃ in terms of the amount of The total amount is obtained.

₂ O ₃ amount B surface may be acid treatment B crude hBN powder surface ₂ O ₃ eluted, and then determining the amount of the acid treatment dissolved B ₂ O _3, oxygen inside the B ₂ O ₃ in terms of quantity, can be processed The remaining residue is subjected to oxygen analysis, and the amount of oxygen in the residual slag is measured to obtain a B ₂ O ₃ equivalent amount.

Specifically, the following is the case. The crude hBN powder was first acid treated with a 0.1 N dilute sulfuric acid solution.

The amount of ammonia produced by hydrolysis of BN in the crude hBN powder treated with the acid was measured by a spectrophotometer [manufactured by Hitachi, Ltd., model name "U-1100"), and the amount of ammonia was used to calculate the hydrolysis by BN. The amount of B element. Further, the total amount of the B element present in the acid solution after the acid treatment (the total amount of the B element derived from the BN hydrolysis and the amount of the B element derived from the B ₂ O ₃ dissolution) is determined by an ICP analyzer [SII]. Manufactured by Nano Technology Inc., model name "SPS3500"]. Then, the amount of B ₂ O ₃ dissolved by the acid treatment can be calculated from the total amount of the B element present in the acid solution after the acid treatment and the amount of the B element derived from the BN hydrolysis in terms of the amount of the ammonia.

In addition, the amount of oxygen in the residual slag is measured by an oxygen measuring device "LECO Japan Contract Company, model name "TC-600", and the amount of B ₂ O _{3 is} calculated from the measured value.

Obtained in such operation, in terms of the total amount of the dissolved by the acid treatment and the amount of B ₂ O ₃ B ₂ O _3, the total amount of the crude powder of hBN supply acid treatment, can be calculated in the crude oxidation hBN powder Boron content (B ₂ O ₃ content).

(primary particle size of hBN powder)

Then, the SEM photographs were taken with the hBN powders obtained in the examples and the comparative examples, and then the length of the long diameter was measured for any 100 hBN primary particles selected from the SEM photographs, and the numerical average of the long diameters was hBN. Primary particle size of the powder.

(The ratio of primary particles of hBN powder (long diameter / thickness))

Filming SEM with hBN powder obtained in the examples and comparative examples Photographing, measuring the long diameter and thickness of any 100 hBN primary particles selected from the SEM image, and calculating the long diameter and thickness of the primary particle by the numerical average of the long diameter and the numerical average of the thickness. Ratio (long diameter / thickness).

(BET specific surface area)

The hBN powder obtained in the examples and the comparative examples was measured for a specific surface area by a fully automatic BET specific surface area measuring device [manufactured by YUASA Ionics Co., Ltd., model name "MULTISORB 16").

(50% volume cumulative particle size (D ₅₀ ) of hBN powder)

The 50% volume cumulative particle diameter (D ₅₀ ) of the hBN powder volume basis was measured by a particle size distribution analyzer [manufactured by Nikkiso Co., Ltd., model name "Microtrac MT3300EXII").

The particle size distribution measurement was carried out by using 0.06 g of hBN powder obtained in Examples and Comparative Examples, and a dispersion prepared by ultrasonic treatment for 3 minutes in 50 g of pure water. The ultrasonic processing was performed using an ultrasonic processing device [manufactured by Nippon Seiki Co., Ltd., model name "Ultrasonic homogenizer US-150V") under the conditions of a power of 150 W and an oscillation frequency of 19.5 kHz.

(HBN powder content on a sieve having a pore size of 106 μm and a sieve having a pore size of 106 μm)

First, a sieve having a diameter of 20 cm and a diameter of 4.5 cm and a diameter of 106 μm was prepared, and 10 g of the hBN powder obtained in the examples and the comparative examples was placed, and placed in a vacuum-extracting type sieving machine [manufactured by Alpine Co., Ltd., model name "jet screen" A200LS"]. Thereafter, the powder was taken up by a pressure difference of 1 kPa from the lower portion of the screen, and sieved for 360 seconds for screening. Then, the weight of the hBN powder remaining under the screen and on the screen was measured, and the hBN powder content (the pore diameter of the pore size of 106 μm) and the hBN powder content of the sieve having a pore size of 106 μm were calculated. The pore diameter of the sieve was 106 μm.

Further, after the hBN fired product obtained in the examples and the comparative examples was pulverized, the dry vibrating screen apparatus having a pore size of 106 μm was used, and after classification by a sieving time of 60 minutes, the hBN powder was all passed through a sieve having a pore size of 106 μm. network.

(hBN powder content under a 45 μm pore size sieve)

First, a sieve having a diameter of 20 cm and a diameter of 4.5 cm and a diameter of 45 μm was prepared, and 10 g of the hBN powder obtained in the examples and the comparative examples was placed, and placed in a vacuum-extracting type sieving machine [manufactured by Alpine Co., Ltd., the model name "jet screen" A200LS"]. Thereafter, the powder was taken up by a pressure difference of 1 kPa from the lower portion of the screen, and sieved for 180 seconds to carry out sieving. Then, the weight of the hBN powder remaining under the sieve and on the sieve was measured, and the hBN powder content (the pore diameter of 45 μm under the sieve) of the sieve having a pore size of 45 μm was calculated.

(volume density of hBN powder)

100 g of the hBN powder obtained in the examples and the comparative examples was placed in a 300 mL quantitative cylinder, and the bulk density was measured by the oscillation bulk density of the hBN powder after shaking for 3 minutes with a shaker.

(The density of the formed body of the hBN powder and the formed body of the crude hBN powder)

The mass and volume of the molded body were measured, and the density of the molded body was calculated at these values.

(peak reduction rate)

In the present invention, the measurement of the peak reduction rate is performed by a particle size distribution analyzer manufactured by a laser diffraction scattering method [manufactured by Nikkiso Co., Ltd., model name "Microtrac MT3300EXII"].

After the hBN fired products of the examples and the comparative examples were pulverized, a sieve having a pore diameter of 106 μm and a pore diameter of 45 μm was superposed and used in two stages, and the dry vibrating screen apparatus (screening time of 60 minutes) was classified and contained 45 to 106 μm. 0.06 g of the particle size hBN powder was dispersed in 50 g of water to prepare a dispersion. Then, the maximum peak between 45 and 150 μm after ultrasonic treatment for 1 minute at the power of 150 W and the oscillation frequency of 19.5 kHz is compared with the maximum peak between 45 and 150 μm before the ultrasonic treatment. . Fig. 7 is a graph showing the particle size distribution of Examples 1 and 3. In the figure, the peak reduction rate calculated is [=[(maximum peak height (a) before processing) - (maximum peak height after processing (b))] / (maximum peak height before processing (a) )]. The lower the peak reduction rate, that is, the higher the disintegration strength. Further, in the present invention, the ultrasonic processing is performed using an ultrasonic processing device [manufactured by Nippon Seiki Co., Ltd., model name "ultrasonic homogenizer US-150V").

Further, in Comparative Examples 2 and 4, the product A was used instead of the hBN fired product.

(crystallite diameter of hBN powder)

The crystallite diameter of the hBN powder obtained in the examples and the comparative examples was calculated by X-ray diffraction measurement. For the X-ray diffraction measuring apparatus, a model name "X'Pert PRO" manufactured by PANalytical Co., Ltd. was used, and a copper target was used and Cu-Kα1 ray was used.

(Boron oxide (B ₂ O ₃ ) content, CaO content of hBN powder)

The hBN powder obtained in the examples and the comparative examples was first acid-treated with a 0.1 N diluted sulfuric acid solution. After the acid treatment, at least part of the BN in the hBN powder can be hydrolyzed to produce ammonia while the B element of the BN is dissolved in the acid solution, and at least the boron oxide (B ₂ O ₃ ) in the hBN powder can be partially dissolved. In an acid solution.

The total amount of B element present in the acid solution after acid treatment (the amount of B element derived from BN hydrolysis and the total amount of B element dissolved from B ₂ O ₃ ) is then used as an ICP analyzer [SII Nano Technology Inc. The company manufactures the model name "SPS3500"]. Then, the amount of B ₂ O ₃ dissolved in the acid treatment was calculated from the total amount of the B element present in the acid solution after the acid treatment.

The Ca element present in the acid solution after the above acid treatment can be measured by the above-described ICP analyzer, and the CaO content can be calculated from the amount of Ca element.

(content of carbon in hBN powder)

The hBN powder obtained in the examples and the comparative examples was measured by a carbon analyzer (manufactured by LECO Japan Contract Co., Ltd., model name "CS230"). The content of carbon (carbon content).

(purity of hBN powder)

The total amount of B ₂ O ₃ , CaO content, and carbon content in the hBN powder measured as described above was the amount of impurities, and the purity of the hBN powder was determined.

(black foreign object number)

1 g of the hBN powder obtained in the examples and the comparative examples was weighed in a 50 cc screw cap tube, and after adding about 40 cc of methanol to the mixture, the mixture was stirred for 3 hours or more, and the bottom of the spiral cap tube was photographed and then measured. The number of black objects in the image (the number of black foreign objects). Further, the black matter is considered to be an unreacted carbon component.

(thermal conductivity of resin sheet)

The resin sheets obtained in the examples and the comparative examples were measured by the NETZSCH company, and the model name "LFA447 NanoFlash" was used to measure the thermal diffusivity, and then multiplied by the theoretical value of the specific heat and density of each resin sheet. As the thermal conductivity of the thickness direction of the resin sheet.

Further, the theoretical values of the densities of the resin sheets of the respective examples or comparative examples were calculated by the theoretical density of boron nitride being 2.27 g/cm ³ and the theoretical density of the resin component being 1.17 g/cm ³ .

(specific gravity ratio of resin sheet)

The specific gravity ratio of the resin sheet obtained in the examples and the comparative examples was measured using an electronic scale (model name "CP224S") manufactured by Sartorius Mechanitronics Japan Co., Ltd. and a specific gravity/density measuring kit (model name "YDK01/YDK01-OD/ YDK01LP") and the specific gravity of the resin sheet of each of the examples or the comparative examples measured by the Archimedes method is divided by the theoretical specific gravity of the resin sheets of the respective examples or comparative examples by 100 times [(Examples or comparisons) The specific gravity measured by the resin sheet of the example/the theoretical specific gravity of the resin sheet of each of the examples or the comparative examples) × 100] was calculated.

Further, in the calculation of the theoretical specific gravity of the resin sheet of each of the examples or the comparative examples, the theoretical density of boron nitride was 2.27 g/cm ³ and the theoretical density of the resin component was 1.17 g/cm ³ .

(insulation breakdown voltage)

For the resin sheets obtained in the examples and the comparative examples, the withstand voltage/insulation resistance measuring device (model name "TOS9201") manufactured by Kikusui Electronics Co., Ltd. was used, and the dielectric breakdown voltage was measured at a voltage increase rate of 1 kV/sec.

The production conditions of the hBN powders of the above examples and comparative examples are shown in Table 1, and the evaluation results are shown in Table 2.

In addition, the carbon source and the Ca compound in Table 1 represent the content of 100 parts by mass of the crude hBN powder in the mixture obtained by mixing the crude hBN powder, the carbon source and the Ca compound in the preparation of the hBN powder. Meanwhile, the hBN powders (A) and (B) in Table 1 each represent a hBN powder (A) of 45 to 106 μm and a hBN powder (B) of a sieve of 45 μm.

[Table 2]

As shown in Table 2, the resin sheets of Examples 1 to 5 were found to have high thermal conductivity and excellent withstand voltage characteristics as compared with the resin sheets of Comparative Examples 1 to 5, and were able to satisfy both high thermal conductivity and high electrical insulating properties. In this case, it is considered that the aggregate of primary particles of the hBN powder is not excessively broken due to the hBN powder of the present invention, and the particle shape as shown in the schematic diagram of Fig. 6 can be maintained, thereby making the aggregate have Appropriate strength, similar to the nature of the resin composition. Further, the hBN powder of the present invention is considered to have a low carbon content and a high purity, and is considered to contribute to the discovery of excellent electrical insulation properties. Further, it is also known that the hBN powders of Examples 1 and 2 suitably contain a small particle diameter because the content of the powder under the 45 μm sieve is in a specific range. hBN powder, therefore, electrical insulation is also good under the maintenance of good thermal conductivity.

Claims (9)

A hexagonal boron nitride powder comprising an aggregate of hexagonal boron nitride primary particles and a hexagonal crystal boron nitride powder having a powder content of 80% by mass or more in a pore size of 106 μm, wherein 50% by volume cumulative particle diameter The D ₅₀ is 10-20 μm, the crystallite diameter is 260-1000 Å, and the particle size distribution curve of the hexagonal boron nitride powder having a particle size of 45-106 μm is 1 in the range of 45-150 μm. The maximum peak, the peak obtained by dispersing the above-mentioned hexagonal boron nitride powder having a particle size of 45 to 106 μm in water and dispersing it in water for 1 minute, and calculating the peak of the largest peak by the following formula (1) The reduction rate is 40 to 90%, and the peak reduction rate = [(maximum peak height before treatment (a)) - (maximum peak height after treatment (b))] / (maximum peak height before treatment (a)) ( 1). The hexagonal boron nitride powder of claim 1, wherein the powder content under a sieve having a pore size of 45 μm is 45% by mass or less. The hexagonal boron nitride powder according to claim 1 or 2, wherein the BET specific surface area is from 1.5 to 10 m ² /g. The hexagonal boron nitride powder according to claim 1 or 2, wherein the bulk density is 0.3 g/cm ³ or more. A resin composition containing 10 to 90% by volume of the hexagonal boron nitride powder according to any one of claims 1 to 4. A resin sheet comprising the resin composition of claim 5 or a cured product thereof. A method for producing a hexagonal boron nitride powder according to any one of claims 1 to 4, which comprises containing 20 to 90% by mass of boron nitride and oxygen 100 parts by mass of a crude hexagonal boron nitride powder having a boron content of 10 to 80% by mass, a carbon source of 3 to 15 parts by mass in terms of carbon, and a calcium compound of 0.01 to 1 part by mass are mixed and formed in an atmosphere containing nitrogen. The firing step of firing is performed. The method for producing a hexagonal boron nitride powder according to claim 7, wherein the carbon source is one or two selected from the group consisting of graphite and boron carbide. The method for producing a hexagonal boron nitride powder according to claim 7 or 8, further comprising a sieve having a pore size of 106 μm and a sieve having a pore size of 45 μm after the calcination step, and a hexagonal boron nitride powder having a classification of 45 to 106 μm [ After the hBN powder (A)] and the hexagonal boron nitride powder [hBN powder (B)] under a 45 μm sieve, the hBN powder (A) and the hBN powder (B) are mixed to form the hBN powder (A) and (B). The mixing ratio of the total amount of the hBN powder (A) is 40 to 90% by mass.