JP6483508B2 - Hexagonal boron nitride powder and method for producing the same - Google Patents

Description

  The present invention relates to a novel hexagonal boron nitride powder and a method for producing the same, which are suitable for applications requiring thermal conductivity such as an insulating heat dissipation material.

  Boron nitride is a white powder that generally has a hexagonal layered structure similar to graphite, and has many features such as thermal conductivity, electrical insulation, lubricity, corrosion resistance, mold release, high temperature stability, and chemical stability. Because of its excellent characteristics, it can be used as a filler for heat conductive insulating sheets, highly flexible heat conductive rubber, heat dissipating grease, heat dissipating sealant, semiconductor sealing resin, molten metal and molten glass molds. It is used in many applications such as molds, solid lubricants and cosmetic raw materials.

  As a method for producing boron nitride, (i) a method of directly nitriding boron using nitrogen, ammonia or the like, (ii) a method of reacting boron halide with ammonia or an ammonium salt, (iii) boric acid, boron oxide or the like (Iv) A method in which a boron compound is reacted with a nitrogen-containing compound such as melamine at a temperature of about 800 ° C. to reduce and nitride the boron compound, and (iv) the boron compound and the carbon source are heated to a high temperature of 1600 ° C. or higher in a nitrogen atmosphere. Thus, there is a method of reducing and nitriding a boron compound. Among them, the method (iv) can use a low-cost raw material and is the most suitable method for producing boron nitride.

  In the method (iv), in order to improve the crystallinity of the obtained boron nitride and obtain hexagonal boron nitride, a technique of adding a crystallization catalyst to the raw material is usually employed and used at that time. As the crystallization catalyst, an oxygen-containing calcium compound is often used.

  For example, a method is proposed in which a mixture of boric acid, acetylene black, and calcium oxide is heated in the atmosphere at 330 ° C. for 20 hours to form a bulk body and then reacted in a nitrogen stream at 1900 ° C. for 6 hours (Patent Document). 1).

  Further, a method is proposed in which hexagonal boron nitride powder is mixed as a seed crystal with a mixture of boric acid, carbon, and calcium carbonate, the temperature is raised at 15 ° C./min in a nitrogen gas atmosphere, and the reaction is performed at 1980 ° C. (See Patent Document 2).

According to the confirmation of the present inventors, a mixture of boric acid, carbon, and oxygen-containing calcium compound is used as a raw material, and the conventional heat treatment conditions reported so far, for example, under a nitrogen atmosphere, a temperature rising rate of 15 When the temperature was raised to 1900 ° C. at a temperature of 1 ° C./minute and heat treatment was performed at that temperature for 6 hours to produce hexagonal boron nitride powder, a large amount of calcium hexaboride (CaB ₆ ) was found in the obtained hexagonal boron nitride powder. It became clear that it was a by-product. Such CaB ₆ is black, and is difficult to remove by an operation such as acid cleaning which is a subsequent process, and the appearance of hexagonal boron nitride powder which is a white powder is impaired. Therefore, a hexagonal boron nitride powder that suppresses the CaB ₆ content is required.

  On the other hand, the primary particles of the hexagonal boron nitride powder are in the form of scales derived from the crystalline form, and the particles have thermal anisotropy, and the thermal conductivity in the thickness direction is greater than the planar direction. It has the characteristic that it is remarkably superior. Therefore, in the case of a thermally conductive insulating sheet using the hexagonal boron nitride powder containing the above flaky particles as a filler, the flaky particles are oriented in the surface direction of the thermally conductive insulating sheet. There are few opportunities for contact, and there is a problem that the thermal conductivity in the thickness direction of the thermal conductivity insulating sheet is low.

  In order to improve such thermal anisotropy, hexagonal boron nitride aggregated particles in which the scaly particles are aggregated in multiple directions have been proposed (see Patent Document 3).

  However, the molded body of the resin composition filled with the hexagonal boron nitride aggregated particles is likely to contain air bubbles because of the irregularities on the surface of the filled hexagonal boron nitride aggregated particles. A decline is inevitable. In recent years, there has been an increasing demand for insulation for thermally conductive insulating sheets, and there has been a demand for hexagonal boron nitride powder that stably suppresses the amount of entrained bubbles when filled with the above resin and stably expresses a high level of dielectric strength. It has been.

JP-A-10-203806 JP 2012-111657 A JP-A-11-26661

Therefore, the object of the present invention is that the crystallinity is high, coloring by CaB ₆ is suppressed, and high thermal conductivity is exhibited when filled in a resin, and the amount of entrainment of bubbles is small, and a high level of insulation resistance is achieved. An object of the present invention is to provide a hexagonal boron nitride powder that can be exerted.

The present inventors first studied a method for producing hexagonal boron nitride powder in which the CaB ₆ content was suppressed. As a result, in a relatively low temperature region of 1400 ° C. or lower, boron oxide production reaction (1) by thermal decomposition of the boron compound, and formation reaction of calcium borate which is a low melting point compound by reaction of boron oxide with the oxygen-containing calcium compound When (2) occurs and the temperature exceeds 1400 ° C., it is estimated that the reductive nitridation reaction (3) occurs due to calcium borate, carbon and nitrogen. It was found that the reaction (4) for producing boron carbide from the carbon, and further the reaction (5) for producing black CaB ₆ by the reaction between boron carbide and calcium borate are likely to occur.

2H ₃ BO ₃ → B ₂ O ₃ + 3H ₂ O (1)
CaO + B ₂ O ₃ → CaB ₂ O ₄ (2)
CaB ₂ O ₄ + 3C + N ₂ → 2BN + 3CO + CaO (3)
2B ₂ O ₃ + 7C → B ₄ C + 6CO (4)
B ₄ C + CaB ₂ O ₄ + 3C → CaB ₆ + 4CO (5)
Conventionally, a method of producing hexagonal boron nitride by a reduction nitridation method using an oxygen-containing calcium compound as a crystallization catalyst is a reduction nitridation by setting the reaction temperature to a high temperature of 1900 ° C. at which hexagonal boron nitride is generated. Since the reaction (3) was performed, the carbon and calcium borate were spent in the above (4) and (5) without being sufficiently used in the reductive nitridation reaction, and promoted the formation of CaB _6. Presumed.

Based on the above findings, the present inventors have optimized the use ratio of the carbon source and sufficiently advanced the reductive nitriding reaction to reach a specific temperature range, thereby reducing the carbon charged as a raw material by the reaction. allowed by the carbon concentration in the reactants and the following specific concentration, then be heated in order to obtain the hexagonal boron nitride, the formation of boron carbide is suppressed, and by extension, the CaB ₆ It has been found that the production can be suppressed very effectively.

Further, the hexagonal boron nitride powder produced under the above conditions not only suppresses the formation of CaB ₆ but also special production conditions in which the reduction nitridation reaction conditions are performed in at least two different temperature regions as described above. Is obtained as a mixed powder of agglomerated particles in which primary particles are densely aggregated and single particles having a small aspect ratio and a thick aspect, and further, such a hexagonal boron nitride powder is novel as a powder, and The combination of particle structures is one of the above-mentioned problems. It has been found that the amount of entrained bubbles is small, can exhibit a high level of insulation resistance, and exhibits high thermal conductivity, and the present invention is completed. It came to do.

That is, according to the present invention, hexagonal boron nitride aggregated particles and hexagonal boron nitride single particles having an average aspect ratio of 3 to 25, particularly 3 to 5, and an average particle size of 4 to 30 μm, The abundance of the crystalline boron nitride single particles is 10 to 50% by mass, the BET specific surface area is 0.5 to 6.0 m ² / g, and the oil absorption measured based on JIS K 5101-13-1 is 100 g / 100 g or less. And a hexagonal boron nitride powder characterized by having a CaB ₆ content of 500 ppm or less.

  The hexagonal boron nitride powder is preferably obtained by a reduction nitriding method using a boron compound, a carbon source and an oxygen-containing calcium compound as raw materials in order to exhibit high crystallinity.

  In addition, according to the present invention, there are provided a resin composition excellent in thermal conductivity and insulation resistance, which is filled with the hexagonal boron nitride powder, and further a heat dissipating material for an electronic component comprising the resin composition. The

The hexagonal boron nitride powder of the present invention comprises a boron compound, a carbon source and an oxygen-containing calcium compound, wherein the ratio of the boron compound to the carbon source is 0.5 to 1.0 in terms of B / C (element ratio), boron. In a nitrogen atmosphere, a mixture containing the oxygen-containing calcium compound in a proportion of 3 to 30 parts by mass in terms of CaO with respect to 100 parts by mass of the total amount of the compound and the carbon source (H ₃ BO ₃ , C equivalent) By heating and reaching a temperature of 1550 ° C., the reaction product is reacted so that the carbon concentration is 5% by mass or less, and then heated to a temperature of 1700 ° C. or higher to complete the reductive nitriding reaction. I can do it.

Since the hexagonal boron nitride powder of the present invention is obtained by the above-described special manufacturing method, the production of CaB _{6 that} causes coloring is extremely effectively suppressed, and the hexagonal boron nitride aggregated particles and the average aspect ratio are reduced. A novel powder having a high ratio of 3 to 25 and a thick hexagonal boron nitride single particle mixed in a specific ratio is provided. The hexagonal boron nitride powder of the present invention has a low specific surface area and a low oil absorption due to the presence of the thick hexagonal boron nitride single particles while improving the thermal conductivity anisotropy by the aggregated particles. When the resin is filled, it is difficult for air bubbles to be involved, and when a thermally conductive insulating sheet is used, a high dielectric strength is exhibited.

  Further, in the production method of the present invention, the thick hexagonal boron nitride particles are retained in a temperature range of 1200 to 1550 ° C. so that the carbon concentration in the reaction product is 5% by mass or less. And calcium oxide form a liquid phase, and are produced by grain growth by a reaction involving the liquid phase. After that, in a temperature range of 1700 ° C. or higher after the temperature rises, By nitriding, primary particles having a relatively small diameter are generated, and the primary particles are estimated to form aggregated particles.

(Hexagonal boron nitride powder)
The hexagonal boron nitride powder of the present invention is hexagonal boron nitride having an average aspect ratio (A1) of 3 to 25, an average particle diameter (d) of 4 to 30 μm, and a single particle ratio of 10 to 50%. It is a mixed powder of boron single particles, has a BET specific surface area of 1 to 6 m ² / g, an oil absorption of 100 g / 100 g or less, and a CaB ₆ content of 500 ppm or less.

That is, the boron nitride powder of the present invention controls the carbon concentration in the reactant in a controlled temperature range in a production method by a reduction nitriding method using an oxygen-containing calcium compound as a crystallization catalyst, which will be described in detail later. This is a hexagonal boron nitride powder containing a specific ratio of hexagonal boron nitride single particles having a large aspect ratio. Due to the presence of such single particles, the BET specific surface area is small while containing aggregated hexagonal boron nitride particles. And, it has a novel characteristic that the oil absorption is small. In addition, the CaB ₆ content, which is usually generated by using an oxygen-containing calcium compound, is also suppressed to an extremely low level, and coloring due to the black CaB ₆ can be effectively prevented.

  The average aspect ratio (A1) of the hexagonal boron nitride single particles in the hexagonal boron nitride powder of the present invention is 3 to 25, and the smaller the value, the closer to the spherical shape, so that the filling property to the resin is improved. 3-20 are preferable, 3-10 are especially preferable, Most preferably, it is 3-5. Such hexagonal boron nitride single particles having an average aspect ratio of less than 3 are difficult to produce, and when it exceeds 25, the composition with the hexagonal boron nitride aggregated particles increases the viscosity at the time of resin filling, which is not preferable.

  The average particle diameter (d) of the hexagonal boron nitride single particles in the hexagonal boron nitride powder is 4 to 30 μm, preferably 6 to 25 μm, more preferably 8 to 20 μm, and still more preferably 10 to 15 μm. When the average particle size is less than 4 μm, the BET specific surface area of the hexagonal boron nitride powder increases, which is not preferable, and in order to produce single particles exceeding 30 μm, it is necessary to calcinate for a long time, which is industrially disadvantageous. Become.

  Moreover, the mass part of the boron nitride single particle with respect to 100 mass parts of boron nitride aggregated particles in the hexagonal boron nitride powder is 10 to 50 parts by mass, preferably 10 to 40 parts, and more preferably 10 to 30 parts. When the ratio of the hexagonal boron nitride single particles is less than 10 parts, the aggregated particles almost occupy, and the BET specific surface area and the oil absorption amount tend to increase beyond the above ranges. Entrainment is likely to occur and the dielectric strength of the resin composition may be reduced. On the other hand, when it exceeds 50 parts by mass, the thermal conductivity of the resin composition may be reduced, which is not preferable.

The hexagonal boron nitride powder of the present invention contains hexagonal boron nitride single particles having the above-mentioned characteristics in a specific ratio, so that the BET specific surface area is 0.5 even though it contains hexagonal boron nitride aggregate particles. ˜6.0 m ² / g, and the oil absorption is 100 g / 100 g or less, each showing a small value.

The BET specific surface area is preferably 0.7~5.0m ² / g, more preferably 1.0~3.0m ² / g. When the BET specific surface area exceeds 6.0 m ² / g, the filling property into the resin is deteriorated for the above reasons, which is not preferable.

  The hexagonal boron nitride powder in the hexagonal boron nitride powder has an oil absorption of 100 g / 100 g or less. The oil absorption is preferably 90 g / g, more preferably 80 g / g.

  The hexagonal boron nitride powder of the present invention is not particularly limited as long as it has the above-mentioned characteristics, but in order to realize more preferable characteristics such as BET specific surface area and oil absorption, hexagonal nitriding The average particle diameter (D1) of the hexagonal boron nitride aggregated particles contained in the boron powder is 5 to 150 μm, preferably 10 to 100 μm, more preferably 20 to 60 μm, and constitutes the primary hexagonal boron nitride aggregated particles. It is particularly preferable that the aspect ratio (A2) of the particles is 3 to 20, preferably 10 to 15, and the primary particle diameter (D2) is 3 to 40, preferably 5 to 30 μm.

  Further, the hexagonal boron nitride powder of the present invention is obtained with high crystallinity by using an oxygen-containing calcium compound, and has a good graphitization index (GI value) indicating a crystallinity of 1.7 or less. The GI value is an index of crystallinity of hexagonal boron nitride powder, and this value decreases as the crystallinity increases. The fully crystallized (graphitized) hexagonal boron nitride powder has a GI value of 1.6. However, in the case of hexagonal boron nitride powder with high crystallinity and sufficient grain growth, the GI value depends on the orientation of the powder. Becomes even smaller.

  The application of the hexagonal boron nitride powder of the present invention is not particularly limited, and can be used for various applications known as applications of the hexagonal boron nitride powder. Among these, a particularly preferable application is exemplified by a use as a filler for a resin that is filled in a resin to improve electrical insulation or impart thermal conductivity. Such resins include thermoplastic resins (polyolefin, vinyl chloride resin, methyl methacrylate resin, nylon, fluororesin), thermosetting resins (epoxy resin, phenol resin, urea resin, melamine resin, unsaturated polyester resin, silicon resin). Synthetic rubber, liquid gel, etc. can be used.

  According to the characteristics of the hexagonal boron nitride powder, the resin composition obtained by filling the hexagonal boron nitride powder of the present invention has low thermal anisotropy, high thermal conductivity, and air bubbles. Involves less and shows high insulation resistance. Furthermore, even if the resin is highly filled, an increase in viscosity at the time of kneading is suppressed, and excellent moldability is exhibited.

  Other applications include raw materials for processed hexagonal boron nitride products such as cubic hexagonal boron nitride and hexagonal boron nitride molded products, nucleating agents for engineering plastics, phase change materials, solid or liquid thermal products. Examples include interface materials, mold release agents for molten metals and molten glass molds, cosmetics, and composite ceramic materials.

(Method for producing hexagonal boron nitride powder)
The hexagonal boron nitride powder of the present invention comprises a boron compound, a carbon source and an oxygen-containing calcium compound, wherein the ratio of the boron compound to the carbon source is 0.5 to 1.0 in terms of B / C (element ratio). A mixture containing an oxygen-containing calcium compound at a ratio of 3 to 30 parts by mass in terms of CaO with respect to 100 parts by mass of the total amount of carbon and a carbon source (H ₃ BO ₃ , C equivalent) However, the reaction can be carried out so that the carbon concentration in the reaction product becomes 5% by mass or less before reaching a temperature of 1550 ° C., and then heated to a temperature of 1700 ° C. or higher.

(Preparation of raw materials)
In the production method of the present invention, as the boron compound, any compound containing a boron atom can be used without limitation. For example, boric acid, anhydrous boric acid, metaboric acid, perboric acid, hypoboric acid, sodium tetraborate, sodium perborate and the like can be used, but generally boric acid which is easily available is preferably used. . Although the average particle diameter of the boron compound to be used is not particularly limited, it is preferably 1 to 1000 μm, more preferably 10 to 900 μm, and still more preferably 20 to 800 μm from the viewpoints of operability and reduction reaction control. That is, when the average particle diameter of the boron compound is larger than 1 μm, handling becomes easy, and when the average particle diameter is smaller than 1000 μm, the reduction reaction of the boron compound becomes easy to control.

  In the production method of the present invention, a known carbon material is used as the carbon source without any particular limitation. For example, in addition to amorphous carbon such as carbon black, activated carbon, and carbon fiber, crystalline carbon such as diamond, graphite, and nanocarbon, pyrolytic carbon obtained by pyrolyzing a monomer or polymer, etc. are used without particular limitation. The Of these, highly reactive amorphous carbon is preferable, and carbon black is particularly preferably used in terms of industrial quality control. Moreover, as said carbon black, acetylene black, furnace black, thermal black, etc. can be used. Moreover, 0.01-5 micrometers is preferable, as for the average particle diameter of the said carbon source, 0.02-4 micrometers is more preferable, and 0.05-3 micrometers is especially preferable. That is, when the average particle diameter of the carbon source is 5 μm or less, the reactivity of the carbon source is increased, and when it is 0.01 μm or more, handling is facilitated.

In the production method of the present invention, the ratio between the boron compound and the carbon source needs to be 0.5 to 1.0 in terms of B / C (element ratio). That is, when the molar ratio exceeds 1.0, the ratio of the boron compound that volatilizes without being reduced increases and the yield decreases, and the above-mentioned volatilizing component adversely affects the production line. When the molar ratio is less than 0.5, the proportion of the unreacted carbon source increases, and it is difficult to implement the present invention in which the carbon concentration in the reactant is 5% or less by 1550 ° C. during nitriding. As a result, the boron nitride seed crystal is generated at an accelerated rate because many boron nitride formation temperatures are 1550 ° C. or more, and not only causes the generation of black foreign substances, but boron nitride particles with a small particle diameter are generated. In addition, the BET specific surface area is 6.0 m ² / g or more, and the oil absorption measured based on JIS K 5101-13-1 is 100 g / 100 g or more, which is not preferable.

In the production method of the present invention, as the oxygen-containing calcium compound used as a crystallization catalyst, a compound containing oxygen and calcium can be used without particular limitation. For example, calcium carbonate, calcium hydrogen carbonate, calcium hydroxide, calcium oxide, calcium nitrate, calcium sulfate, calcium phosphate, calcium oxalate and the like can be used, or a mixture of two or more of these can be used. . Among them, in order to form a porous bulk body to be described later, it is preferable to use calcium oxide or calcium carbonate, and calcium carbonate is particularly preferable because it has foamability. The average particle size of the calcium carbonate is preferably 0.01 to 500 μm, more preferably 0.05 to 400 μm, and particularly preferably 0.1 to 300 μm, from the viewpoint of easy control of the carbon dioxide production reaction. The addition amount of the oxygen-containing calcium compound is preferably 3 to 30 parts by mass in terms of CaO with respect to 100 parts by mass of the total amount of boron compound and carbon source (H ₃ BO ₃ , C equivalent). 5 to 25 parts by mass, more preferably 10 to 20 parts by mass. If the amount of the oxygen-containing calcium compound used is less than 3 parts by mass, highly hexagonal boron nitride powder cannot be obtained. Further, the amount of liquid phase for growing boron nitride particles is small, and the obtained hexagonal boron nitride powder has a deposition ratio of more than 50% of the flocculent aggregated particles in which flakes are aggregated, and the BET specific surface area is 6.0 m ² / g. As mentioned above, since the oil absorption measured based on JISK5101-13-1 becomes 100g / 100g or more, the filling rate to resin falls and it is not preferable. When it exceeds 30 parts by mass, the impurity concentration of the obtained hexagonal boron nitride powder becomes high, which is not preferable, and the ratio of calcium oxide in the composite oxide formed from boron oxide and calcium oxide is large, and the liquid phase The formation temperature becomes 2000 ° C. or more, and the obtained hexagonal boron nitride single particles cannot be sufficiently grown, and the boron nitride single particles having an average aspect ratio of 3 to 25 and an average particle size of 4 to 30 μm cannot be obtained. It is not preferable.

  In the production method of the present invention, the form of the mixture containing the respective raw materials is not particularly limited, and may remain in a powder form, but a porous bulk body may be formed. The porous bulk body is formed by, for example, heating the mixed powder containing the boron compound, the carbon source, and calcium carbonate to form a bulk body by generating metaboric acid from boric acid and melting the metaboric acid. In the melted state, carbon dioxide gas is generated by decomposition of calcium carbonate and foamed.

  In addition, the shape of the porous bulk body may be appropriately determined according to the shape of the container or the like used for heating the mixed powder, and is not particularly limited, but for example, a quadrangular prism shape, a cylindrical shape, a spherical shape, Examples of the shape include a polygonal shape, an indefinite shape, a needle shape, and a plate shape. From the viewpoint of handling properties, a shape such as a quadrangular prism shape, a cylindrical shape, or a spherical shape is preferable. Further, the size is generally about 5 to 300 mm in diameter (equivalent diameter other than spherical).

  In the production method of the present invention, the mixing method of the boron compound, the carbon source, and the oxygen-containing calcium compound is not particularly limited. A typical blender can be used.

(Production conditions)
In the present invention, reductive nitriding can be performed by heating a mixture containing the boron compound, carbon source and oxygen-containing calcium compound (hereinafter also referred to as a raw material mixture) in an atmosphere containing nitrogen gas. It is important to control the temperature and the amount of carbon in the reaction product. That is, the raw material mixture is reacted in a nitrogen atmosphere so that the carbon concentration in the reactant is 5 mass% or less before reaching a temperature of 1550 ° C., and then hexagonal boron nitride at a temperature of 1700 ° C. or higher. Must be generated.

When the carbon concentration in the reaction product exceeds 5 mass% by the time the temperature reaches 1550 ° C., boron carbide is easily generated by the subsequent temperature increase, and as a result, the amount of CaB ₆ generated increases, and the present invention. Cannot achieve the goal. The carbon concentration in the reactant is preferably maintained at the above temperature until it becomes 3% by mass or less. Moreover, although the carbon concentration in the said reaction material is so preferable that it is small, industrially a minimum is 1 mass%.

  In the production method of the present invention, the carbon concentration in the reaction product described above is a value measured using the fluorescent X-ray analyzer shown in the examples.

  In the production method of the present invention, the reaction temperature for proceeding the reductive nitridation reaction up to 1550 ° C. is not particularly limited, but in general, the boron compound reduction reaction with a carbon source starts at 1200 ° C. or higher, Since crystalline hexagonal boron nitride begins to form, it is preferable to adjust the temperature to 1200 ° C. or higher, preferably 1300 ° C. or higher. Further, the temperature profile up to 1550 ° C. may include a pattern in which the temperature is kept constant at a specific temperature, or may include a pattern in which the temperature is increased with a specific gradient.

  In the production method of the present invention, the method for confirming whether or not the carbon concentration in the reaction product satisfies the above range before reaching the temperature of 1550 ° C. is not particularly limited. For example, it is straightforward to measure the carbon concentration in the reaction product at a temperature of 1550 ° C., but it is confirmed that the carbon concentration in the reaction product satisfies the above range at any temperature below 1550 ° C. May be. In addition, although the present invention may be carried out by measuring the carbon concentration every time of production, the carbon concentration in the reaction product becomes 5% by mass or less under the operating conditions including the temperature profile by conducting experiments in advance. It is industrially preferable that the time is specified and managed by the processing time under the above operating conditions. The treatment time varies depending on the operating requirements and cannot be determined unconditionally. In general, the treatment time is generally in the range of 2 to 10 hours, particularly 3 to 8 hours at a temperature of 1200 ° C. or higher.

  In the present invention, after the above step, in order to obtain highly crystalline hexagonal boron nitride powder, heat treatment is usually performed at 1700 ° C. or higher, preferably 1700-2200 ° C., more preferably 1800-2000 ° C. Get. That is, when the heat treatment temperature is less than 1700 ° C., not only high crystallinity hexagonal boron nitride can be obtained but also grain growth hardly occurs, and it is difficult to obtain single particles having a low aspect ratio in the present invention. At 2200 ° C. or higher, the effect reaches its peak and is economically disadvantageous.

  In the production method of the present invention, the nitrogen atmosphere can be formed by known means. The gas to be used is not particularly limited as long as it is a gas that can give nitrogen to boron under the above nitriding conditions, and nitrogen gas and ammonia gas can also be used. A gas in which a non-oxidizing gas such as hydrogen, argon, or helium is mixed can also be used.

  The production method of the present invention can be carried out using a known apparatus capable of controlling the reaction atmosphere. For example, an atmosphere-controlled high-temperature furnace that performs heat treatment by high-frequency induction heating or heater heating can be used. In addition to a batch furnace, a continuous furnace such as a pusher-type tunnel furnace or a vertical reaction furnace can also be used.

  In the present invention, immediately after performing the above nitriding treatment, hexagonal boron nitride is the main component, but since compounds such as calcium borate are also included, washing with an acid if necessary, It is possible to obtain hexagonal boron nitride having high purity and high crystallinity.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.

  Various physical properties in Examples and Comparative Examples were measured by the following methods.

1) GI value X-ray diffraction measurement was performed using a fully automatic horizontal multi-purpose X-ray diffractometer SmartLab manufactured by Rigaku. The measurement conditions were a scan speed of 20 degrees / minute, a step width of 0.02 degrees, and a scan range of 10 to 90 degrees. The GI value is calculated from the integral intensity ratio (area ratio) of (100), (101) and (102) diffraction lines of the X-ray diffraction spectrum of the hexagonal boron nitride powder: GI = [{(100) + (101 )} / [(102)].

2) Carbon concentration of the reactant The carbon concentration of the reactant was measured using a fluorescent X-ray analyzer. The reaction product taken out was cooled to room temperature, and then ground in an alumina mortar to a particle size of about 1 to 1000 μm to obtain a measurement sample. As a fluorescent X-ray analyzer, ZSX Primus 2 manufactured by Rigaku was used.

3) CaB ₆ concentration in boron nitride powder From the X-ray diffraction spectrum of the obtained boron nitride powder, the presence or absence of a CaB ₆ -derived peak was confirmed. Also from the fluorescent X-ray analysis measurements Ca concentration of hexagonal boron nitride powder obtained was measured for the content of CaB _6.

4) Average particle diameter (d) and aspect ratio (A1) of boron nitride single particles
Boron nitride powder was observed at a magnification of 2000 times, and a plurality of 60 μm × 40 μm square SEM observation images were analyzed with an image analyzer (A image-kun: manufactured by Asahi Kasei Engineering Co., Ltd.), and different single particles were randomly selected and long The length of the shaft was measured, and the average value of the above measured values was calculated for a total of 1000 primary particles to obtain the average particle diameter (d). At the same time, the length in the thickness direction was measured, and the length of the major axis / the length in the thickness direction was defined as the aspect ratio (A1).

5) Average particle size (D1) of boron nitride aggregated particles, average particle size (D2) of primary particles constituting the aggregated particles, aspect ratio (A2)
A plurality of 60 μm × 40 μm square SEM observation images of boron nitride powder observed at a magnification of 2000 times are analyzed by an image analyzer (A image-kun: manufactured by Asahi Kasei Engineering Co., Ltd.), and 100 different aggregated particles are randomly selected. The length of the major axis of each aggregated particle was measured and used as the average particle diameter (D1) of the aggregated particles. Ten primary particles are randomly selected from each aggregated particle, the length of the major axis is measured for each primary particle, and the average value of the above measured values is calculated for a total of 1000 primary particles to obtain the average primary particle. The diameter (D2) was used. At the same time, the length in the thickness direction was measured, and the length of the long axis / the length in the thickness direction was defined as the aspect ratio (A2).

6) Mass parts of boron nitride single particles with respect to 100 parts by mass of boron nitride aggregated particles Boron nitride powder was observed at an image magnification of 500 × 250 μm × 170 μm square SEM observation image (A Image-kun: manufactured by Asahi Kasei Engineering Co., Ltd.) ) And randomly selected until 5000 different particles were obtained, and then sorted into aggregated particles and single particles. A particle containing two or more single particles was defined as an agglomerated particle. The mass part of the boron nitride single particle with respect to 100 parts by mass of the boron nitride aggregated particles was calculated by image analysis on the selected particles.

7) BET specific surface area and oil absorption of hexagonal boron nitride powder The BET specific surface area of the obtained hexagonal boron nitride powder was measured by a nitrogen gas adsorption BET one-point method, and the oil absorption was based on JIS K 5101-13-1. It was measured.

Example 1
100 g boric acid, 24 g acetylene black, and 12 g calcium oxide as a crystallization catalyst were mixed in a ball mill. The mixture was heated to 1300 ° C. at 15 ° C./min in a nitrogen gas atmosphere using a graphite Tamman furnace, and held at 1300 ° C. for 4 hours. After maintaining at 1300 ° C., the temperature was raised to 1800 ° C. at 15 ° C./min, and nitriding was performed at 1800 ° C. for 2 hours. Next, acid cleaning was performed to obtain white hexagonal boron nitride powder. No black foreign matter was visually confirmed in the obtained hexagonal boron nitride powder.

  Table 1 shows the results of measuring the carbon concentration in the reaction product when the temperature reached 1550 ° C. under the same conditions as those described above.

The GI value of the obtained hexagonal boron nitride powder was measured. Further, the content of CaB ₆ was measured from the Ca concentration of the obtained hexagonal boron nitride powder, and the results are shown in Table 1. The obtained hexagonal boron nitride powder had a low CaB ₆ content of 260 ppm. Further, X-ray diffraction spectrum of CaB ₆ was not confirmed. Further, when the particle shape of the hexagonal boron nitride powder was confirmed by SEM observation, the presence of hexagonal boron nitride particles having a primary particle major axis / thickness ratio of 3 to 10 was confirmed. The average particle diameter (d), aspect ratio (A1), average particle diameter (D1) of boron nitride aggregated particles, and boron nitride single particles with respect to 100 parts by mass of boron nitride aggregated particles of the hexagonal boron nitride powder. The average particle diameter (D2), aspect ratio (A2), BET specific surface area, and oil absorption of primary particles constituting the mass part and aggregated particles were measured and shown in Table 2.

Example 2
100 g of boric acid, 24 g of carbon black, and 44 g of calcium carbonate as a crystallization catalyst were mixed in a ball mill. The mixture was heated to 1200 ° C. at 15 ° C./min in a nitrogen gas atmosphere using a graphite Tamman furnace, and held at 1200 ° C. for 6 hours. After maintaining at 1200 ° C., the temperature was raised to 2000 ° C. at 15 ° C./min, and nitriding was performed at 2000 ° C. for 3 hours. Next, crushing and acid cleaning were performed to obtain white hexagonal boron nitride powder. No black foreign matter was visually confirmed in the obtained hexagonal boron nitride powder.

  The results of measuring the carbon concentration in the reaction product when the temperature reaches 1550 ° C. under the same conditions as in the above method are shown in Table 1.

The GI value of the obtained hexagonal boron nitride powder was measured. Further, the content of CaB ₆ was measured from the Ca concentration of the obtained hexagonal boron nitride powder, and the results are shown in Table 1. Further, when the particle shape of the hexagonal boron nitride powder was confirmed by SEM observation, the presence of hexagonal boron nitride particles having a primary particle major axis / thickness ratio of 3 to 10 was confirmed. The average particle diameter (d), aspect ratio (A1), average particle diameter (D1) of boron nitride aggregated particles, and boron nitride single particles with respect to 100 parts by mass of boron nitride aggregated particles of the hexagonal boron nitride powder. The average particle diameter (D2), aspect ratio (A2), BET specific surface area, and oil absorption of primary particles constituting the mass part and aggregated particles were measured and shown in Table 2.

Example 3
100 g boric acid, 22 g acetylene black, and 11 g calcium carbonate as a crystallization catalyst were mixed in a ball mill. The mixture was heated to 1500 ° C. at 15 ° C./min in a nitrogen gas atmosphere using a graphite Tamman furnace, and held at 1500 ° C. for 3 hours. After maintaining at 1500 ° C., the temperature was raised to 1750 ° C. at 15 ° C./min, and nitriding was performed at 1750 ° C. for 3 hours. Next, crushing and acid cleaning were performed to obtain white hexagonal boron nitride powder. No black foreign matter was visually confirmed in the obtained hexagonal boron nitride powder.

  The results of measuring the carbon concentration in the reaction product when the temperature reaches 1550 ° C. under the same conditions as in the above method are shown in Table 1.

The GI value of the obtained hexagonal boron nitride powder was measured. Further, the content of CaB ₆ was measured from the Ca concentration of the obtained hexagonal boron nitride powder, and the results are shown in Table 1. Further, when the particle shape of the hexagonal boron nitride powder was confirmed by SEM observation, the presence of hexagonal boron nitride particles having a primary particle major axis / thickness ratio of 3 to 10 was confirmed. The average particle diameter (d), aspect ratio (A1), average particle diameter (D1) of boron nitride aggregated particles, and boron nitride single particles with respect to 100 parts by mass of boron nitride aggregated particles of the hexagonal boron nitride powder. The average particle diameter (D2), aspect ratio (A2), BET specific surface area, and oil absorption of primary particles constituting the mass part and aggregated particles were measured and shown in Table 2.

Example 4
100 g of boric acid, 32 g of carbon black, and 59 g of calcium carbonate as a crystallization catalyst were mixed in a ball mill. The mixture was heated to 1350 ° C. at 15 ° C./min in a nitrogen gas atmosphere using a graphite Tamman furnace, and held at 1350 ° C. for 5 hours. After holding at 1500 ° C., the temperature was raised to 1800 ° C. at 15 ° C./min, and nitriding was performed at 1800 ° C. for 4 hours. Next, crushing and acid cleaning were performed to obtain white hexagonal boron nitride powder. No black foreign matter was visually confirmed in the obtained hexagonal boron nitride powder.

  The results of measuring the carbon concentration in the reaction product when the temperature reaches 1550 ° C. under the same conditions as in the above method are shown in Table 1.

The GI value of the obtained hexagonal boron nitride powder was measured. Further, the content of CaB ₆ was measured from the Ca concentration of the obtained hexagonal boron nitride powder, and the results are shown in Table 1. Further, when the particle shape of the hexagonal boron nitride powder was confirmed by SEM observation, the presence of hexagonal boron nitride particles having a primary particle major axis / thickness ratio of 3 to 10 was confirmed. The average particle diameter (d), aspect ratio (A1), average particle diameter (D1) of boron nitride aggregated particles, and boron nitride single particles with respect to 100 parts by mass of boron nitride aggregated particles of the hexagonal boron nitride powder. The average particle diameter (D2), aspect ratio (A2), BET specific surface area, and oil absorption of primary particles constituting the mass part and aggregated particles were measured and shown in Table 2.

Example 5
100 g boric acid, 28 g carbon black, and 38 g calcium oxide as a crystallization catalyst were mixed in a ball mill. The mixture was heated to 1400 ° C. at 15 ° C./min in a nitrogen gas atmosphere using a graphite Tamman furnace, and held at 1400 ° C. for 4 hours. After maintaining at 1400 ° C., the temperature was raised to 1750 ° C. at 15 ° C./min, and nitriding was performed at 1750 ° C. for 3 hours. Next, crushing and acid cleaning were performed to obtain white hexagonal boron nitride powder. No black foreign matter was visually confirmed in the obtained hexagonal boron nitride powder.

  The results of measuring the carbon concentration in the reaction product when the temperature reaches 1550 ° C. under the same conditions as in the above method are shown in Table 1.

The GI value of the obtained hexagonal boron nitride powder was measured. Further, the content of CaB ₆ was measured from the Ca concentration of the obtained hexagonal boron nitride powder, and the results are shown in Table 1. Further, when the particle shape of the hexagonal boron nitride powder was confirmed by SEM observation, the presence of hexagonal boron nitride particles having a primary particle major axis / thickness ratio of 3 to 10 was confirmed. The average particle diameter (d), aspect ratio (A1), average particle diameter (D1) of boron nitride aggregated particles, and boron nitride single particles with respect to 100 parts by mass of boron nitride aggregated particles of the hexagonal boron nitride powder. The average particle diameter (D2), aspect ratio (A2), BET specific surface area, and oil absorption of primary particles constituting the mass part and aggregated particles were measured and shown in Table 2.

Comparative Example 1
100 g boric acid, 24 g carbon black, and 12 g calcium oxide as a crystallization catalyst were mixed in a ball mill. The mixture was heated to 1800 ° C. at 15 ° C./min in a nitrogen gas atmosphere using a graphite Tamman furnace, and held at 1800 ° C. for 4 hours. At this time, the holding time in the temperature region at 1200 to 1550 ° C. is 23 minutes. Next, crushing and acid cleaning were performed to obtain hexagonal boron nitride powder. In the obtained hexagonal boron nitride powder, black foreign matter was visually confirmed. The results of measuring the carbon concentration in the reaction product when the temperature reaches 1550 ° C. under the same conditions as in the above method are shown in Table 1.

The GI value of the obtained hexagonal boron nitride powder was measured. Further, the content of CaB ₆ was measured from the Ca concentration of the obtained hexagonal boron nitride powder, and the results are shown in Table 1. The carbon concentration of the intermediate product at 1550 ° C. was as high as 7.5% by mass. Hexagonal boron nitride powder obtained also CaB ₆ content as high as 26000Ppm, from X-ray diffraction measurement results contained CaB _6. The average particle diameter (d), aspect ratio (A1), average particle diameter (D1) of boron nitride aggregated particles, and boron nitride single particles with respect to 100 parts by mass of boron nitride aggregated particles of the hexagonal boron nitride powder. The average particle diameter (D2), aspect ratio (A2), BET specific surface area, and oil absorption of primary particles constituting the mass part and aggregated particles were measured and shown in Table 2.

Comparative Example 2
100 g boric acid, 28 g acetylene black, and 38 g calcium oxide as a crystallization catalyst were mixed in a ball mill. The mixture was heated to 1250 ° C. at 15 ° C./min in a nitrogen gas atmosphere using a graphite Tamman furnace, and held at 1250 ° C. for 5 hours. After maintaining at 1250 ° C., the temperature was raised to 1650 ° C. at 15 ° C./min, and nitriding was performed at 1650 ° C. for 4 hours. Next, crushing and acid cleaning were performed to obtain white hexagonal boron nitride powder. No black foreign matter was visually confirmed in the obtained hexagonal boron nitride powder. The results of measuring the carbon concentration in the reaction product when the temperature reaches 1550 ° C. under the same conditions as in the above method are shown in Table 1.

The GI value of the obtained hexagonal boron nitride powder was measured. Further, the content of CaB ₆ was measured from the Ca concentration of the obtained hexagonal boron nitride powder, and the results are shown in Table 1. The obtained hexagonal boron nitride powder has a low crystallinity of 2.5 because the maximum firing temperature is as low as 1650 ° C. Further, when the particle shape was confirmed by SEM observation, hexagonal boron nitride particles having a major axis / thickness ratio of primary particles of 3 to 10 were not confirmed, and only scaly particles and aggregated particles were confirmed. The average particle diameter (d), aspect ratio (A1), average particle diameter (D1) of boron nitride aggregated particles, and boron nitride single particles with respect to 100 parts by mass of boron nitride aggregated particles of the hexagonal boron nitride powder. The average particle diameter (D2), aspect ratio (A2), BET specific surface area, and oil absorption of primary particles constituting the mass part and aggregated particles were measured and shown in Table 2.

Comparative Example 3
100 g boric acid, 48 g carbon black, and 30 g calcium oxide as a crystallization catalyst were mixed in a ball mill. The mixture was heated to 1500 ° C. at 15 ° C./min in a nitrogen gas atmosphere using a graphite Tamman furnace, and held at 1500 ° C. for 4 hours. After holding at 1500 ° C., the temperature was raised to 1800 ° C. at 15 ° C./min, and nitriding was performed at 1800 ° C. for 3 hours. Next, crushing and acid cleaning were performed to obtain hexagonal boron nitride powder. In the obtained hexagonal boron nitride powder, black foreign matter was visually confirmed. The results of measuring the carbon concentration in the reaction product when the temperature reaches 1550 ° C. under the same conditions as in the above method are shown in Table 1.

The GI value of the obtained hexagonal boron nitride powder was measured. Further, the content of CaB ₆ was measured from the Ca concentration of the obtained hexagonal boron nitride powder, and the results are shown in Table 1. The carbon concentration of the intermediate product at 1550 ° C. was as high as 9.5% by mass. Hexagonal boron nitride powder obtained also CaB ₆ content as high as 55000Ppm, from X-ray diffraction measurement results contained CaB _6. The average particle diameter (d), aspect ratio (A1), average particle diameter (D1) of boron nitride aggregated particles, and boron nitride single particles with respect to 100 parts by mass of boron nitride aggregated particles of the hexagonal boron nitride powder. The average particle diameter (D2), aspect ratio (A2), BET specific surface area, and oil absorption of primary particles constituting the mass part and aggregated particles were measured and shown in Table 2.

Comparative Example 4
100 g boric acid, 28 g carbon black, and 92 g calcium carbonate as a crystallization catalyst were mixed in a ball mill. The mixture was heated to 1500 ° C. at 15 ° C./min in a nitrogen gas atmosphere using a graphite Tamman furnace, and held at 1500 ° C. for 4 hours. After holding at 1500 ° C., the temperature was raised to 1800 ° C. at 15 ° C./min, and nitriding was performed at 1800 ° C. for 2 hours. Next, crushing and acid cleaning were performed to obtain hexagonal boron nitride powder. In the obtained hexagonal boron nitride powder, black foreign matter was visually confirmed. The results of measuring the carbon concentration in the reaction product when the temperature reaches 1550 ° C. under the same conditions as in the above method are shown in Table 1.

The GI value of the obtained hexagonal boron nitride powder was measured. Further, the content of CaB ₆ was measured from the Ca concentration of the obtained hexagonal boron nitride powder, and the results are shown in Table 1. Hexagonal boron nitride powder obtained also CaB ₆ content as high as 2100 ppm, from X-ray diffraction measurement results contained CaB _6. The average particle diameter (d), aspect ratio (A1), average particle diameter (D1) of boron nitride aggregated particles, and boron nitride single particles with respect to 100 parts by mass of boron nitride aggregated particles of the hexagonal boron nitride powder. The average particle diameter (D2), aspect ratio (A2), BET specific surface area, and oil absorption of primary particles constituting the mass part and aggregated particles were measured and shown in Table 2.

  Tables 1 and 2 summarize the results of Examples 1 to 5 and Comparative Examples 1 to 4.

Examples 6-10
In this example, a performance comparison test as an additive to a resin molded product of hexagonal boron nitride powder was performed. That is, after mixing a hexagonal boron nitride powder and a silicone resin (KE106: manufactured by Shin-Etsu Chemical Co., Ltd.) at a volume ratio of 40:60, a B-type viscometer TBA-10 (Toki Industries Co., Ltd.) at a measurement temperature of 25 ° C. The viscosity was measured. The results are shown in Table 3. The viscosity of the resin composition containing the hexagonal boron nitride powder produced in Examples 1 to 5 was 150 Pa · s or less, and further high filling was possible.

Comparative Examples 5-8
The hexagonal boron nitride powder produced in Comparative Examples 1 to 4 was also subjected to a performance comparison test as an additive to the same resin molded product. The results are shown in Table 3. The viscosity of the resin composition including the hexagonal boron nitride powder manufactured in Comparative Example 2 is 200 Pa · s or higher, which is higher than the viscosity of the resin composition including the hexagonal boron nitride powder manufactured in Example 1. There was no further high filling.

Examples 6-10
Comparative Examples 5-8
Evaluation of thermal conductivity and dielectric strength with boron nitride powder filled in resin Evaluation of thermal conductivity and dielectric strength when the obtained boron nitride powder was filled into resin was performed as follows.

  As a base resin, a mixture of 100 parts by weight of an epoxy resin (JER806 manufactured by Mitsubishi Chemical Corporation) and 28 parts by weight of a curing agent (alicyclic polyamine-based curing agent, JER Cure 113 manufactured by Mitsubishi Chemical Corporation) (in Table 3, “ And a mixture of 100 parts by weight of a silicone resin (KE-106 manufactured by Shin-Etsu Chemical Co., Ltd.) and 10 parts by weight of a curing agent (CAT-RG manufactured by Shin-Etsu Chemical Co., Ltd.). ”) Was prepared.

  Next, 35% by volume of each base resin and 65% by volume of the specific boron nitride powder were mixed using methyl ethyl ketone as a solvent, and then the solvent was dried to obtain a resin composition.

  This is cast into a mold body, using a hot press, cured at a temperature of 150 ° C., a pressure of 5 MPa, and a holding time of 1 hour to produce a sheet having a diameter of 10 mm and a thickness of 0.2 mm. The thermal conductivity was measured by temperature wave thermal analysis. In addition, the dielectric strength was measured with a withstand voltage tester (manufactured by Tama Denso Co., Ltd.) The measurement results are shown in Table 3. The resin composition using the hexagonal boron nitride powder obtained in Examples 1 to 5 had 10 W / m · K and 25 kV / mm, and had high thermal conductivity and high dielectric strength.

Claims (5)

Containing hexagonal boron nitride aggregated particles and hexagonal boron nitride single particles having an average aspect ratio of 3 to 25 and an average particle size of 4 to 30 μm, and the mass parts of the boron nitride single particles with respect to 100 parts by mass of the boron nitride aggregated particles Is 10 to 50 parts by mass, the BET specific surface area is 0.5 to 6.0 m ² / g, the oil absorption measured based on JIS K 5101-13-1 is 100 g / 100 g or less, and CaB ₆ A hexagonal boron nitride powder having a content of 500 ppm or less.   The hexagonal boron nitride powder according to claim 1, wherein the hexagonal boron nitride single particles according to claim 1 have an average aspect ratio of 3 to 5. Resin composition obtained by filling the hexagonal boron nitride powder according to claim 1 or 2. A heat dissipating material for an electronic component comprising the resin composition according to claim 3 . The boron compound, the carbon source, and the oxygen-containing calcium compound are such that the ratio of the boron compound to the carbon source is 0.5 to 1.0 in terms of B / C (element ratio), and the total amount of the boron compound and the carbon source (H ₃ BO ₃ , C conversion value) A mixture containing an oxygen-containing calcium compound in a proportion of 3 to 30 parts by mass in terms of CaO with respect to 100 parts by mass is heated in a nitrogen atmosphere and reaches a temperature of 1550 ° C. The method for producing a hexagonal boron nitride powder, wherein the reaction is performed so that the carbon concentration in the reaction product is 5% by mass or less, and then heated to a temperature of 1700 ° C. or higher.