JP6441027B2 - Method for producing boron nitride powder - Google Patents

Description

  The present invention relates to a novel method for producing boron nitride powder. Specifically, the present invention provides a method for producing a boron nitride powder that suppresses an increase in viscosity when highly filled into a resin and can impart high thermal conductivity and dielectric strength to the resulting resin composition. is there.

  Boron nitride is a white powder that generally has a hexagonal layered structure similar to graphite, and has high thermal conductivity, high electrical insulation, high lubricity, corrosion resistance, mold release, high temperature stability, and chemical stability. It has many characteristics such as sex. Therefore, the resin composition filled with boron nitride powder is suitably used as a heat conductive insulating sheet by molding.

  The method for producing boron nitride includes (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. A melamine 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; There is a reduction nitriding method for reducing and nitriding a boron compound. The reduction nitriding method (iv) can use a low-cost raw material, and is the most suitable method for producing boron nitride.

  In the reduction nitriding method, 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. As the crystallization catalyst used at that time, a metal oxide is often used. Of these, oxygen-containing calcium compounds are often used.

  The boron nitride powder thus obtained contains primary particles composed of scaly particles derived from a crystalline form, and the scaly particles have thermal anisotropy. That is, the scale-like particles have a much better thermal conductivity in the thickness direction than in the plane direction. Usually, in the case of a thermally conductive insulating sheet using boron nitride powder containing the above flaky particles as a filler, since the flaky particles are oriented in the surface direction of the thermally conductive insulating sheet, the contact between the flaky particles There are few opportunities, and the thermal conductivity in the thickness direction of the thermal conductivity insulating sheet is low. In order to improve such thermal anisotropy, boron nitride aggregated particles in which the scaly particles are aggregated in multiple directions have been proposed (see Patent Document 1).

  However, the boron nitride agglomerated particles have poor filling properties in the resin, and there is a problem that, when highly filled, bubbles are present in the resin composition, causing a decrease in thermal conductivity and dielectric strength.

  As an improvement measure for increasing the filling properties of the boron nitride aggregated particles into the resin, a method of suppressing an increase in viscosity by mixing particles having different particle diameters and specific surface areas has been proposed. However, the boron nitride powder obtained by such a technique can prevent an increase in viscosity, but cannot avoid a decrease in thermal conductivity.

JP-A-11-26661 Japanese Patent No. 5,607,928

  Accordingly, an object of the present invention is to provide a method for producing boron nitride powder that can be highly filled into a resin and can impart high thermal conductivity and high dielectric strength to the resulting resin composition.

  The present inventors have intensively studied to solve the above problems. As a result, the boron nitride powder containing a thick, low aspect ratio boron nitride single particle and the boron nitride aggregated particle has a thermal anisotropy inherent to the boron nitride aggregated particle when filled with resin. While maintaining the improvement effect of the above, it is possible to improve the dielectric strength, further suppress the increase in viscosity, and can be highly filled into the resin, and the resin composition obtained by filling this with high thermal conductivity and The knowledge that high dielectric strength can be provided was obtained. Then, in the reduction nitriding method using the crystallization catalyst, by using a specific amount of a polyol compound having a specific particle size as a part of the carbon source, the low aspect ratio boron nitride single particles and the boron nitride aggregated particles are used. As a result, it was found that boron nitride powder uniformly containing the above can be obtained, and the present invention has been completed.

That is, according to the present invention, a mixture containing a boron compound, carbon black, a polyol compound having an average particle size of 100 to 2000 μm, and an oxygen-containing calcium compound is mixed with a ratio of the boron compound and the polyol compound in an element ratio (B / C) 5.1 to 40 in terms of boron , the ratio of boron compound to carbon black is 0.5 to 1.0 in terms of element ratio (B / C), and the ratio of oxygen-containing calcium compound is boron compound and carbon black , And a total amount of polyol compound (H ₃ BO ₃ , C converted value) of 100 parts by mass , the mixture is 3-30 parts by mass in terms of CaO, and heated to a temperature of 1700 ° C. or higher in a nitrogen atmosphere. A method for producing boron nitride powder is provided.

  The present invention also provides a resin composition formed by filling the boron nitride powder obtained by the above production method, and further a heat radiating material for electronic parts comprising the resin composition.

  The method for producing boron nitride powder of the present invention can produce boron nitride powder containing uniformly boron nitride agglomerated particles and single particles, and the obtained boron nitride powder is formed by the presence of the boron nitride agglomerated particles. The effect of improving the thermal anisotropy inherent in the aggregated particles is brought about, and the presence of the boron nitride single particles suppresses an increase in viscosity when filled in the resin, thereby enabling high filling. In addition, since the boron nitride single particles are interposed between the boron nitride aggregated particles and perform thermal conduction between the particles, it is possible to impart excellent thermal conductivity to the obtained resin composition. Moreover, due to the presence of the boron nitride single particles, when the resin is filled, it is possible to reduce the entrainment of bubbles and to suppress the decrease in the dielectric strength.

  In addition, a mixture of boron nitride agglomerated particles and single particles can be produced by a one-step process, which can be said to be an industrially extremely advantageous method.

2 is a SEM (Scanning Electron Microscope) photograph showing a typical particle structure of boron nitride powder obtained by the production method of the present invention specifically shown in Example 1.

(Method for producing boron nitride powder)
The method for producing boron nitride powder according to the present invention is based on a method of reducing and nitriding a boron compound by heating a mixture of a boron compound, a carbon source and a crystallization catalyst in a nitrogen atmosphere, and is specific to the above raw material composition. A specific amount of the polyol compound is used in combination.

(material)
In the production method of the present invention, as a raw material boron compound, a compound containing a boron atom is used without limitation. For example, boric acid, boric anhydride, metaboric acid, perboric acid, hypoboric acid, sodium tetraborate, sodium perborate and the like can be used. In general, boric acid, which is easily available, is preferably used. Moreover, 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 viewpoint of operability and reduction reaction control. That is, use of a boron compound having an average particle size larger than 1 μm facilitates handling. However, if it exceeds 1000 μm, the reduction reaction of the boron compound may not easily proceed.

  In the production method of the present invention, acetylene black, furnace black, thermal black or the like can be used as carbon black used as a carbon source. The average particle size of the carbon black is preferably 0.01 to 5 μm, more preferably 0.02 to 4 μm, and particularly preferably 0.05 to 3 μm. That is, when the average particle size of the carbon black is 5 μm or less, the reactivity 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 carbon black is generally 0.5 to 1.0 in terms of element ratio (B / C). When the ratio exceeds 1.0, the ratio of the boron compound that volatilizes without being reduced increases and the yield decreases, and the volatilization component may adversely affect the production line. Moreover, if the said ratio is less than 0.5, the presence rate of an unreacted carbon source will increase and will cause coloring.

The greatest feature of the present invention is that a polyol compound having an average particle diameter of 100 to 2000 μm is mixed with a raw material containing the boron compound, carbon black and oxygen-containing calcium compound, and the ratio of the boron compound to the polyol compound is an element ratio (B / C) It is blended so as to be 5.1 to 40 in terms of conversion.

  The polyol compound has a function as the carbon source, but has an important function of generating particles having different aspect ratios. Regarding the above function, the present inventors act as a reducing agent by specifically acting on the oxygen-containing calcium compound of the crystallization catalyst in which the OH group of the polyol compound becomes a liquid phase component in which crystals grow, It is presumed that the region where the compound is reduced is locally generated, and the generation of low aspect ratio boron nitride particles is promoted with respect to the region where the other crystallizing agent sufficiently acts.

  As the polyol compound, an organic compound containing a plurality of hydroxyl groups is used without particular limitation. For example, saccharides, mannitol, citric acid, polyvinyl alcohol (PVA) and the like can be mentioned, and PVA is particularly preferable.

  In the production method of the present invention, it is preferable to use a granular powder having an average particle size of the polyol compound of 100 to 2000 μm, preferably 200 to 1800 μm, more preferably 300 to 1500 μm. That is, when the thickness is less than 100 μm, it is difficult to stably generate a region where the oxygen-containing calcium compound is insufficient, and it becomes difficult to provide a sufficient difference in aspect ratio between the generated boron nitride particles. Moreover, when it exceeds 2000 micrometers, there exists a tendency for unreacted carbon to remain easily, and there exists a possibility of causing coloring.

  The ratio of the boron compound to the polyol is required to be 5.1 to 40, preferably 5.5 to 30 in terms of element ratio (B / C). When the ratio is less than 5.1, the ratio of aggregated particles is increased, and the viscosity when filling the generated boron nitride powder into the resin tends to increase. On the other hand, if it exceeds 40, the proportion of boron nitride single particles produced increases, and the thermal conductivity of the resin composition obtained by filling the produced boron nitride powder with resin tends to decrease.

  Note that pyrolytic carbon obtained by pyrolyzing the polymer also acts as a carbon source, and the polyol compound also acts as a carbon source.

  In the production method of the present invention, known oxygen-containing calcium compounds used as crystallization catalysts are not particularly limited. Examples of the oxygen-containing calcium compound include calcium carbonate, calcium hydrogen carbonate, calcium hydroxide, calcium oxide, calcium nitrate, calcium sulfate, calcium phosphate, and calcium oxalate. Among these, oxygen-containing calcium compounds can be preferably used. As the oxygen-containing calcium compound, 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, and these two or more kinds can be mixed. It is also possible to use it. Among these, it is preferable to use calcium oxide or calcium carbonate.

  Two or more kinds of the oxygen-containing calcium compounds can be mixed and used. The average particle size of the oxygen-containing calcium compound is preferably 0.01 to 600 μm, more preferably 0.05 to 500 μm, and particularly preferably 0.1 to 400 μm.

The proportion of the oxygen-containing calcium compound is 3 to 30 masses in terms of CaO with respect to 100 parts by mass of the total amount (H ₃ BO ₃ , C equivalent value) of the boron compound, carbon black, and polyol compound. Part, preferably 5 to 25 parts by weight, more preferably 5 to 15 parts by weight.

  When the amount of the oxygen-containing calcium compound used is less than 3 parts by mass, it becomes difficult to obtain boron nitride powder having a high aspect ratio and high crystallinity in a region where the polyol compound is not present. Further, when the amount of the oxygen-containing metal compound used exceeds 30 parts by mass, sufficient removal from the product boron nitride powder becomes difficult, and the impurity concentration of the resulting boron nitride powder tends to increase.

  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 and a granulated body may be formed. The porous bulk body is formed by heating a mixed powder containing, for example, boric acid, a carbon source, calcium carbonate, and a polyol to form a bulk body by generating metaboric acid from boric acid and melting the metaboric acid. In a molten 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 metal compound is not particularly limited. A typical blender can be used.
(Reduction nitriding)
In the production method of the present invention, in order to obtain hexagonal boron nitride powder having high crystallinity, heat treatment is usually performed at 1700 ° C. or higher, preferably 1700-2200 ° C., more preferably 1800-2000 ° C. That is, if the heat treatment temperature is less than 1700 ° C., highly crystalline hexagonal boron nitride tends to be difficult to obtain, and if it exceeds 2200 ° C., the effect reaches its peak and is economically disadvantageous.

  In the boron nitride manufacturing method of the present invention, the nitrogen atmosphere can be formed by a 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 boron nitride production method of the present invention can be performed 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.
(Acid cleaning)
In the production method of the present invention, boron nitride is the main component immediately after the above-described reduction nitriding treatment, but it contains a by-product such as calcium borate. Become. The method of acid cleaning is not particularly limited, and a known method is adopted without limitation. For example, by-product-containing boron nitride obtained after nitriding is crushed and put into a container, and the by-product containing A method of adding 5 to 10 times the amount of dilute hydrochloric acid (10 to 20% by weight HCl) of boron nitride and allowing to contact for 4 to 8 hours can be mentioned.

  In addition to hydrochloric acid, nitric acid, sulfuric acid, acetic acid and the like can be used as the acid used for the acid cleaning.

  After the acid cleaning, cleaning is performed using pure water for the purpose of cleaning the remaining acid. As the washing method, after filtering the acid at the time of the acid washing, boron nitride washed with acid is dispersed in the same amount of pure water as the acid used, and filtered again. By performing this operation several times, the purity of the boron nitride powder of the present invention can be achieved.

(Boron nitride powder)
According to the method for producing boron nitride powder of the present invention, it is possible to obtain a boron nitride powder having a large thickness and a low aspect ratio boron nitride single particle and the boron nitride agglomerated particles uniformly. Specifically, boron nitride aggregated particles having an average particle diameter of 1 to 15 μm, an aspect ratio of more than 10 and boron nitride primary particles of 30 or less aggregated, an average particle diameter of 20 to 150 μm, and an average particle diameter of A boron nitride powder containing 10 to 75 μm of boron nitride single particles having an aspect ratio of 3 to 10 in a proportion of 10 to 60% by mass of the boron nitride single particles with respect to 100 parts by mass of the boron nitride aggregated particles is produced. be able to.

  The average particle diameter (D1) of the boron nitride aggregated particles in the boron nitride powder, the average particle diameter (D2) of the primary particles constituting the aggregated particles, the aspect ratio (A1), the average particle diameter of the boron nitride single particles ( The values of d) and aspect ratio (A2) were obtained by obtaining an observation image of 500 and 2000 times by SEM with respect to boron nitride powder using an image analysis apparatus, and details will be described in Examples.

  The average particle diameter (D1) of the boron nitride agglomerated particles constituting the boron nitride powder is 20 to 150 μm, preferably 20 to 100 μm, and more preferably 30 to 60 μm. That is, the boron nitride agglomerated particles act as a main circuit for heat conduction when filled with resin. For this reason, when the average particle diameter (D1) is less than 20 μm, there are too many contacts that become thermal resistance, and the thermal conductivity tends to decrease. On the other hand, when the average particle diameter of the boron nitride aggregated particles exceeds 150 μm, the aggregated particles may float on the surface of the resin molded body and cause an appearance defect.

  The primary particles constituting the boron nitride aggregated particles have an aspect ratio (A1) of more than 10 and 30 or less, preferably 11 to 25, and an average particle diameter (D2) of 1 to 15 μm, preferably It is preferable that it is 5-10 micrometers. Agglomerated particles having an aspect ratio (A1) of the primary particles of 10 or less are difficult to produce. When the primary particles exceed 30, the primary particles are easily oriented in the resin composition thickness direction when released from the aggregated particles. The thermal conductivity of the resulting resin composition tends to be reduced. On the other hand, when the average particle diameter (D2) of the primary particles constituting the boron nitride aggregated particles is less than 1 μm, not only the production is difficult, but also the factor of increasing the thermal resistance when the primary particles are released from the aggregated particles There is a risk of becoming. Further, when the average particle diameter (D2) of the primary particles exceeds 15 μm, the cohesive force of the particles tends to decrease, and the strength of the aggregated particles tends to decrease, and the aspect ratio that exists without forming the aggregated particles is large. Many primary particles are present. As a result, when the resin is filled, there is a tendency for the viscosity to increase during kneading or the thermal anisotropy becomes strong, resulting in a decrease in the thermal conductivity of the resulting resin composition. Become.

  In the particle size distribution of the boron nitride powder of the present invention, the boron nitride single particle is present as a region having a small particle diameter, which suppresses an increase in viscosity when filled in the resin, and entraps bubbles in the resin. In addition, it is preferable to effectively conduct heat conduction between the boron nitride aggregated particles by suppressing the anisotropy of heat conduction.

  Therefore, the average particle diameter (d) of the boron nitride single particles is 10 to 60%, preferably 20 to 50% of the average particle diameter of the boron nitride aggregate. It is preferable in order to fully exhibit.

  The aspect ratio of the boron nitride single particles is preferably 3 to 10, preferably 3.5 to 8, and more preferably 4 to 7 in terms of high filling into the resin and suppression of lowering of thermal conductivity. By including such a low aspect ratio boron nitride single particle, not only the filling property to the resin is improved, but also the orientation in the resin composition thickness direction is eliminated, and the thermal conductivity is reduced by including the boron nitride single particle. Can be relaxed. Therefore, when the aspect ratio of the boron nitride single particles exceeds 10, the effect of suppressing the increase in the viscosity of the resin composition and the decrease in the thermal conductivity tends to decrease. On the other hand, boron nitride single particles having an aspect ratio of less than 3 are difficult to produce.

  In the boron nitride powder of the present invention, the boron nitride aggregated particles and the boron nitride single particles are present in an amount of 10 to 60% by mass, preferably 15%, based on 100 parts by mass of the boron nitride aggregated particles. It is preferable to contain in the ratio of -50 mass%, More preferably, 20-45 mass%. That is, when the boron nitride single particle is less than 10% by mass with respect to 100 parts by mass of the boron nitride aggregated particles, the effect of suppressing the increase in viscosity is reduced, and the resulting resin composition bubbles are likely to enter, leading to a decrease in dielectric strength. There is. On the other hand, when it exceeds 60 mass%, the thermal conductivity anisotropy may become strong, and the thermal conductivity of the resulting resin composition tends to decrease.

  In the production method of the present invention, it is possible to obtain boron nitride powder having the above composition. If necessary, boron nitride agglomerated particles and / or boron nitride single particles may be obtained separately from the obtained boron nitride powder. It is also possible to mix the particles. The mixing method is not particularly limited, and general mixers such as a vibration mill, a bead mill, a ball mill, a Henschel mixer, a drum mixer, a vibration stirrer, and a V-shaped mixer can be used.

(Use of boron nitride powder)
The use of the boron nitride powder of the present invention is not particularly limited, and can be applied to known uses without particular limitation. If the use used suitably is illustrated, the use used as a filler for resin for the purpose of electrical insulation improvement, thermal conductivity provision, etc. is mentioned. In the use of the boron nitride powder, the obtained resin composition has high electrical insulation and thermal conductivity.

  Therefore, the boron nitride powder of the present invention can be suitably used as a filler for a solid or liquid thermal interface material typified by a heat dissipation sheet or a heat dissipation gel of an electronic component.

  Examples of the resin include thermoplastic resins such as polyolefin, vinyl chloride resin, methyl methacrylate resin, nylon, and fluorine resin, and thermosetting resins such as epoxy resin, phenol resin, urea resin, melamine resin, unsaturated polyester resin, and silicon resin. Examples thereof include resins and synthetic rubbers.

  Further, the boron nitride powder of the present invention is a raw material for processed boron nitride products such as cubic boron nitride and boron nitride molded products, nucleating agents for engineering plastics, phase change materials, solid or liquid thermal interface materials, It can also be used for applications such as mold release agents for molten metal and molten glass molds, cosmetics, and composite ceramic raw materials.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples at all.

  In the examples, each measured value is a value measured by the following method.

(1) Average particle diameter (D1) of boron nitride aggregated particles, average particle diameter (D2) of primary particles constituting the aggregated particles, aspect ratio (A1)
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 major axis / the length in the thickness direction was defined as the aspect ratio (A1).

(2) Average particle diameter (d) and aspect ratio (A2) of boron nitride single particles
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 different single particles are 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 long axis / the length in the thickness direction was defined as the aspect ratio (A2).

(3) Mass ratio of boron nitride single particles with respect to 100 parts by mass of boron nitride aggregated particles An image analysis apparatus (A image-kun: Asahi Kasei Engineering Co., Ltd.) observed SEM observation image of 250 μm × 170 μm square of boron nitride powder observed at a magnification of 500 times. The product was randomly selected until it became 5000 different particles, and was classified into aggregated particles and single particles. A particle containing two or more single particles was defined as an aggregated particle. The mass ratio of the selected particles was calculated by image analysis.

(4) Evaluation of viscosity, thermal conductivity and dielectric strength when filling resin with boron nitride powder Evaluation of viscosity, thermal conductivity and dielectric strength when filling the obtained boron nitride powder with resin is as follows. It was done like that.

  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-109 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, 80% by volume of each base resin and 20% by volume of the specific boron nitride powder were mixed in a mortar under the same conditions for each test, and then at a measurement temperature of 25 ° C., a B-type viscometer TBA-10 (Toki The viscosity was measured by Kogyo Co., Ltd. Further, 40% by volume of each base resin and 60% 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. Similarly, a resin composition comprising 30% by volume of the base resin and 70% by volume of the specific boron nitride powder was obtained.

  This is cast into a mold body, using a hot press, cured under conditions of temperature: 150 ° C., pressure: 5 MPa, holding time: 1 hour, producing a sheet having a diameter of 10 mm and a thickness of 1.2 mm, The thermal conductivity was measured by a laser flash method. In addition, the dielectric strength was measured with a withstand voltage tester (manufactured by Tama Denso Co., Ltd.)

Example 1
100 g of a mixture containing boric acid (average particle size 75 μm), furnace black (average particle size 0.08 μm), calcium oxide (average particle size: 100 μm), and PVA having an average particle size of 500 μm in the ratio (element ratio) shown in Table 1 Were mixed in a ball mill. 50 g of the mixture was subjected to nitriding treatment using a graphite tamman furnace by raising the temperature to 1900 ° C. at 15 ° C./min and holding at 1900 ° C. for 6 hours in a nitrogen gas atmosphere.

  Next, the by-product-containing boron nitride was crushed and charged into a container, 5 times the amount of hydrochloric acid (10 wt% HCl) of the by-product-containing boron nitride was added, and the mixture was stirred at a rotation speed of 800 rpm for 24 hours. After the acid washing, the acid was filtered, and boron nitride obtained by filtration was dispersed in pure water in the same amount as the acid used, and filtered again. This operation was repeated 5 times and then dried at 150 ° C. for 8 hours.

  The powder obtained after drying was passed through a sieve having an opening of 90 μm to remove coarse particles, and white hexagonal boron nitride powder was obtained. About the obtained hexagonal boron nitride powder, the average particle diameter (D1) of the aggregated particles, the average particle diameter (D2) of the primary particles constituting the aggregated particles, the aspect ratio (A1), the average particle diameter of the boron nitride single particles ( d) The aspect ratio (A2) was calculated and shown in Table 2.

  Table 3 shows the results of evaluation of the viscosity, the thermal conductivity of the resin composition, and the dielectric strength when the obtained boron nitride powder is filled in a silicone resin and an epoxy resin.

Example 2
A white hexagonal boron nitride powder was obtained in the same manner as in Example 1 except that the average particle diameter of PVA was changed to 1500 μm. The measured values are shown in Table 2.

  Table 3 shows the results of evaluation of the viscosity, the thermal conductivity of the resin composition, and the dielectric strength when the obtained boron nitride powder is filled in a silicone resin and an epoxy resin.

Example 3
A white hexagonal boron nitride powder was obtained in the same manner as in Example 1 except that the ratio of boric acid to PVA (element ratio (B / C conversion)) was 15.0. The measured values are shown in Table 2.

  Table 3 shows the results of evaluation of the viscosity, the thermal conductivity of the resin composition, and the dielectric strength when the obtained boron nitride powder is filled in a silicone resin and an epoxy resin.

Example 4
A white hexagonal boron nitride powder was obtained in the same manner as in Example 1 except that the ratio of boric acid to PVA (element ratio (B / C conversion)) was 15.0 and the average particle diameter of PVA was 1500 μm. The measured values are shown in Table 2.

  Table 3 shows the results of evaluation of the viscosity, the thermal conductivity of the resin composition, and the dielectric strength when the obtained boron nitride powder is filled in a silicone resin and an epoxy resin.

Example 5
A white hexagonal boron nitride powder was obtained in the same manner as in Example 1 except that the ratio of boric acid to PVA (element ratio (B / C conversion)) was 18.0. The measured values are shown in Table 2.

  Table 3 shows the results of evaluation of the viscosity, the thermal conductivity of the resin composition, and the dielectric strength when the obtained boron nitride powder is filled in a silicone resin and an epoxy resin.

Example 6
A white hexagonal boron nitride powder was obtained in the same manner as in Example 1 except that the ratio of boric acid to PVA (element ratio (B / C) conversion) was 18.0 and the average particle diameter of PVA was 1500 μm. The measured values are shown in Table 2.

  Table 3 shows the results of evaluation of the viscosity, the thermal conductivity of the resin composition, and the dielectric strength when the obtained boron nitride powder is filled in a silicone resin and an epoxy resin.

Comparative Example 1
A hexagonal boron nitride powder was obtained in the same manner as in Example 1 except that no polyol was added. The measured values are shown in Table 2. Since no polyol was added, the primary particle size was as large as 15.0 μm, and the ratio of boron nitride single particles to 100 parts by mass of boron nitride aggregated particles was as high as 72% by mass.

  Table 3 shows the results of evaluation of the viscosity, the thermal conductivity of the resin composition, and the dielectric strength when the obtained boron nitride powder is filled in a silicone resin and an epoxy resin.

Comparative Example 2
A hexagonal boron nitride powder was obtained in the same manner as in Example 2 except that the ratio of boric acid to PVA (element ratio (B / C) conversion) was 3.0. The measured values are shown in Table 2. Since the added PVA increased, the aspect ratio of boron nitride single particles was as high as 24, and the ratio of boron nitride single particles to 100 parts by mass of boron nitride aggregated particles was as low as 8% by mass.

  Table 3 shows the results of evaluation of the viscosity, the thermal conductivity of the resin composition, and the dielectric strength when the obtained boron nitride powder is filled in a silicone resin and an epoxy resin.

Comparative Example 3
The same procedure as in Example 3 was performed except that the average particle diameter of PVA was 1 μm. The measured values are shown in Table 2 to obtain hexagonal boron nitride powder. Since the particle size of the added PVA was reduced, the average particle diameter of primary particles constituting the boron nitride aggregated particles was as large as 12.0 μm, and the ratio of boron nitride single particles to 100 parts by mass of boron nitride aggregated particles was 65 masses. % Was high.

  Table 3 shows the results of evaluation of the viscosity, the thermal conductivity of the resin composition, and the dielectric strength when the obtained boron nitride powder is filled in a silicone resin and an epoxy resin.

Comparative Example 4
Boron nitride aggregated particles and high aspect ratio single particles were mixed in a V-shaped mixer for 10 minutes to prepare boron nitride powder shown in Table 2 Comparative Example 4. The obtained boron nitride powder is characterized in that the aspect ratio of boron nitride single particles is as high as 13.1.

  Table 3 shows the results of evaluation of the viscosity, the thermal conductivity of the resin composition, and the dielectric strength when the obtained boron nitride powder is filled in a silicone resin and an epoxy resin.

Claims (1)

A mixture containing a boron compound, carbon black, a polyol compound having an average particle size of 100 to 2000 μm, and an oxygen-containing calcium compound ,
The ratio of boron compound and polyol compound is 5.1 to 40 in terms of element ratio (B / C) ,
The ratio of boron compound to carbon black is 0.5 to 1.0 in terms of element ratio (B / C),
The proportion of the oxygen-containing calcium compound is 3 to 30 parts by mass in terms of CaO with respect to 100 parts by mass of the total amount of boron compound, carbon black, and polyol compound (H ₃ BO ₃ , C equivalent). ,
A method for producing boron nitride powder, comprising heating to a temperature of 1700 ° C. or higher in a nitrogen atmosphere.

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