JP2019182737A - Hexagonal boron nitride powder and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hexagonal boron nitride powder having a low aspect ratio, which is difficult to be highly purified due to a production method, in which metal elements such as calcium, impurities such as chlorine, and soluble boron present on the particle surface are significantly reduced. Further, the present invention provides a hexagonal boron nitride powder containing very little water. SOLUTION: The average aspect ratio of single particles is in the range of 1.5 to 10, and the amount of eluted boron after being immersed in a 0.5 mol / L sulfuric acid aqueous solution at 25 ° C for 120 minutes is converted to B2O3. 100 ppm or less, the amount of eluted calcium is 50 ppm or less, the amount of eluted sodium and the amount of eluted copper are each 5 ppm or less, the amount of eluted chlorine after immersion in water at 160 ° C. for 30 hours is 10 ppm or less, and the water content is 0.1 mass or less. % Or less, and in particular, a powder in which the rate of increase in the amount of the eluted boron after standing for 10 days in an atmosphere at a humidity of 90% and a temperature of 50 ° C. is 10% or less. [Selection diagram] None

Description

  The present invention relates to a novel hexagonal boron nitride powder and a method for producing the same.

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

As a method for producing the hexagonal 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 ammonium salt,
(Iii) a melamine method in which a boron compound such as boric acid and boron oxide is reacted with a nitrogen-containing compound such as melamine at a temperature of about 800 ° C.
(Iv) a reduction nitriding method in which the oxygen-containing boron compound and the carbon source are heated to a high temperature of 1600 ° C. or higher in a nitrogen atmosphere to reduce and nitride the oxygen-containing boron compound;
(V) A method in which boron carbide is fired in a nitrogen atmosphere and then mixed with boron trioxide and refired.
Etc.

  The hexagonal boron nitride powder obtained by the above method includes primary particles composed of scaly particles derived from a crystal structure, and the scaly particles have thermal anisotropy. 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 thermal conductivity of the flaky particles Heat is transmitted in the low c-axis direction, and the thermal conductivity in the thickness direction of the thermally conductive insulating sheet is low. In addition, the scale-like hexagonal boron nitride particles are easy to aggregate, and when filled in the resin, there is a problem that bubbles are contained in the aggregate and the insulation resistance of the resulting resin molded product is lowered.

  In order to improve the thermal anisotropy of hexagonal boron nitride particles having such a scale-like structure, an attempt to obtain hexagonal boron nitride powder containing so-called “thick particles” with a low aspect ratio of the particles (See Patent Document 1). That is, the hexagonal boron nitride powder having a low aspect ratio is difficult to be oriented in the resin, and even if an aggregate is formed, the aggregation is weak. Therefore, when used as a filler, the powder should be highly dispersed in the resin. In addition, since the orientation is small, the thermal conductivity of the resin molded body is not significantly reduced, and a decrease in insulation resistance due to bubbles can be suppressed.

  However, the thick particles of hexagonal boron nitride require a calcium-containing compound as a raw material, and a large amount of calcium components such as unreacted calcium-containing compounds remain in the product. In order to remove the calcium component, washing with an aqueous hydrochloric acid solution is performed. By this operation, chlorine also adheres to the hexagonal boron nitride powder and remains as an impurity.

  Conventionally, after the pickling, a water washing step is provided to remove these impurities. In such a step, the obtained hexagonal boron nitride powder is washed at a level that is conscious of the high insulation resistance. Is not made.

  On the other hand, in the hexagonal boron nitride powder, soluble boron also poses a problem because it reduces the insulation resistance when the resin is filled. It has been reported that such soluble boron is produced by hydrolysis of boron nitride when the hexagonal boron nitride powder is dried (Patent Document 2). The above-mentioned Patent Document 2 mainly provides hexagonal boron nitride powder as a raw material for cubic boron nitride, but in order to prevent the formation of soluble boron, the temperature is 100 ° C. or lower. And drying at 80 ° C. for a long time.

  However, the above-mentioned drying does not sufficiently remove moisture, and even if soluble boron can be reduced, generation of bubbles due to moisture when the resin is filled in use as a filler targeted by the present invention. This may cause a decrease in insulation resistance.

  Moreover, in order to remove the water, a method of heat-treating the obtained hexagonal boron nitride powder again can be considered, but not only the manufacturing process becomes complicated, but also the manufacturing cost may increase. Is done. Moreover, excessive heating generates an oxide film on the particle surface of the hexagonal boron nitride powder, and further heating at higher temperatures causes sintering of the particles and generation of sintered particles containing bubbles. There is also a risk of inviting.

JP2015-212217A Japanese Patent Laid-Open No. 1-160811

  Accordingly, an object of the present invention is to reduce impurities in impurities such as metal elements such as calcium and chlorine present on the particle surface in the hexagonal boron nitride powder having a low aspect ratio, which is difficult to achieve high purity due to the manufacturing method. It is an object of the present invention to provide a hexagonal boron nitride powder in which soluble boron is remarkably reduced and the water content is extremely small.

  The present inventors have intensively studied to solve the above problems. As a result, after obtaining a rough hexagonal boron nitride powder having a specific low aspect ratio by a reductive nitriding reaction using an oxygen-containing boron compound, a carbon source and an oxygen-containing calcium compound, Thus, it has been found that by applying a specific cleaning method and a specific drying method, a novel hexagonal boron nitride powder capable of achieving all of the above objects can be obtained, and the present invention has been completed.

  That is, according to the present invention, the average aspect ratio of single particles is in the range of 1.5 to 10, and the amount of dissolved boron after immersion in a sulfuric acid aqueous solution having a concentration of 0.5 mol / L at 25 ° C. for 120 minutes. In terms of B2O3, 100 ppm or less, eluted calcium amount is 50 ppm or less, eluted sodium amount and eluted copper amount are each 5 ppm or less, eluted chlorine amount after immersion in water at 160 ° C. for 30 hours is 10 ppm or less, and the moisture content is A hexagonal boron nitride powder characterized by being 0.1% by mass or less is provided.

  The amount of each impurity eluted is a value based on the mass of the hexagonal boron nitride powder.

  The hexagonal boron nitride powder preferably has an average particle size in the range of 5 to 20 μm.

  Further, the hexagonal boron nitride powder has a characteristic that the increase rate of the eluted boron amount after standing for 10 days in an atmosphere of 90% humidity and 50 ° C. is 10% or less.

  The above hexagonal boron nitride powder of the present invention is obtained by subjecting a raw material mixture containing an oxygen-containing boron compound, a carbon source and an oxygen-containing calcium compound to a temperature of 1700 to 2200 ° C. in a nitrogen atmosphere and reducing and nitriding the average. After producing a crude hexagonal boron nitride powder having an aspect ratio of 10 or less, the crude hexagonal boron nitride powder is washed with an aqueous hydrochloric acid solution, and then purified into pure water having a specific resistance at 25 ° C. of 0.2 MΩ · cm or more. Further, the washed hexagonal boron nitride powder can be obtained by heat treatment at a temperature of 140 ° C. to 500 ° C. under a pressure of 20 kPaA or less, particularly 10 kPaA or less, for 8 hours or more, particularly for 10 hours or more. Is possible.

In the manufacturing method, the raw material mixture has an element ratio (B / C) of boron to a carbon source contained in the oxygen-containing boron compound of 0.60 to 0.85, and the oxygen-containing boron compound and oxygen-containing material. In order to reliably produce a hexagonal boron nitride powder having a low aspect ratio, it is preferable that the molar ratio (B ₂ O ₃ / CaO) in terms of oxide to the calcium compound is 4 to 6.

  Furthermore, in the heat treatment, heating is performed such that the time from when the heating temperature reaches 100 ° C. until the water content of the hexagonal boron nitride powder is 5% by mass or less is within 2 hours, The soluble boron in the obtained hexagonal boron nitride powder can be further reduced, which is preferable.

  According to the present invention, there is provided a novel hexagonal boron nitride powder having a low aspect ratio and a very low amount of the eluted impurities and water.

  Therefore, when the hexagonal boron nitride powder of the present invention is filled with a resin to form a resin molded body, the orientation of the particles is low due to the low aspect ratio, and the thermal conductivity of the resin molded body is low. In addition, since it does not have strong cohesiveness, bubbles are not caught by the aggregate, and the insulation resistance of the resin molded body is also prevented from being lowered.

Moreover, despite the fact that the hexagonal boron nitride powder of the present invention has the above low aspect ratio, the amount of impurities such as metal elements such as calcium and chlorine, and the cause of generating bubbles is further reduced. Therefore, it is possible to further effectively suppress a decrease in the insulation resistance of the resin molded body.
In addition, according to the production method of the present invention, the crude hexagonal boron nitride powder having a specific aspect ratio obtained by the reaction is subjected to a specific cleaning method and a specific heat treatment drying method, thereby enabling The hexagonal boron nitride powder having the above characteristics can be advantageously produced industrially without going through a complicated process such as reheating.

(Hexagonal boron nitride powder)
The hexagonal boron nitride powder of the present invention is
(1) The average aspect ratio of single particles is in the range of 1.5 to 10,
(2) The amount of eluted boron after being immersed in a sulfuric acid aqueous solution having a concentration of 0.5 mol / L at 25 ° C. for 120 minutes is 100 ppm or less in terms of B2O3,
(3) The amount of calcium eluted is 50 ppm or less,
(4) The amount of eluted sodium and the amount of eluted copper are each 5 ppm or less,
(5) The amount of eluted chlorine is 10 ppm or less after being immersed in water at 160 ° C. for 30 hours.
(6) The water content is 0.1% by mass or less,
It is characterized by satisfying all the characteristics of Hereinafter, each characteristic will be described.

  In the hexagonal boron nitride powder of the present invention, as shown in (1) above, the average aspect ratio of single particles needs to be in the range of 1.5 to 10, preferably 2 to 5. That is, when the average aspect ratio exceeds 10, when the resin is filled, the orientation becomes high and the cohesion between particles becomes high, so the object of the present invention cannot be achieved. In addition, it is difficult to manufacture a product having an average aspect ratio of less than 1.5.

  Further, by using the hexagonal boron nitride powder having the above low aspect ratio, in a specific cleaning method described later, a cleaning effect is remarkably exhibited, a high impurity removal effect is exhibited, and a specific heat treatment is performed. Also in the drying method according to, production of soluble boron can be effectively suppressed.

  The average aspect ratio was calculated by arbitrarily taking 100 samples from hexagonal boron nitride powder and dividing the length of the major axis of the primary particles by the length in the thickness direction.

The hexagonal boron nitride powder of the present invention is a cause of soluble boron at the time of drying by applying a drying method by specific heat treatment to the hexagonal boron nitride powder obtained after washing in the manufacturing method described later. The amount of B ₂ O ₃ produced can be suppressed very low, and the amount of dissolved boron after immersion in a sulfuric acid aqueous solution having a concentration of 0.5 mol / L at 25 ° C. for 120 minutes is 100 ppm or less in terms of B ₂ O ₃ , In particular, an extremely low value of 50 ppm or less can be achieved. By satisfying such a value, it is possible to extremely effectively suppress a decrease in insulation resistance of a resin molded body obtained by filling a resin with hexagonal boron nitride powder.

  In addition, since the hexagonal boron nitride powder of the present invention has the low aspect ratio, the specific surface area with respect to the particle size of the powder is small, and it is difficult to absorb moisture. In addition, the rate of increase in the amount of eluted boron after standing for 10 days is 10% or less, particularly 5% or less.

  By the way, although the hexagonal boron nitride powder having the low aspect ratio has been proposed in the past, the production method includes an oxygen-containing calcium compound as shown in the production method described later, and the obtained hexagonal Crystalline boron nitride powder contains a uniformly large amount of calcium component and associated impurities. Such a calcium component can be removed by an acid. Examples of such an acid include sulfuric acid, nitric acid, hydrochloric acid, and weak acid. Insoluble salts are generated in sulfuric acid and weak acid, and nitric acid has strong oxidizing power. It is difficult to use because it is prone to occur and can cause eluting boron after drying. For these reasons, hydrochloric acid is used.

  Therefore, in the hexagonal boron nitride powder having the low aspect ratio, many impurities are likely to remain due to such a manufacturing method, and the purity thereof is limited to 98% at most.

  In the present invention, in the hexagonal boron nitride powder, the characteristics (3) to (5) can be realized by selecting the low aspect ratio and adopting a specific cleaning method described later.

  That is, the impurities shown in the above (3) to (5) exist between and between the surfaces of the particles constituting the hexagonal boron nitride powder, but the hexagonal boron nitride powder having the low aspect ratio depends on its shape. The cleaning solution is sufficiently contacted with an aqueous hydrochloric acid solution or water, and further, by using high-purity water as cleaning water, its cleaning action is enhanced and the impurities are removed extremely effectively. To be sedated.

  In the present invention, by satisfying the impurity concentrations described in the above (3) to (5), a decrease in insulation resistance of a resin molded product obtained by filling a resin with hexagonal boron nitride powder is extremely effectively suppressed. However, the eluted calcium amount is preferably 40 ppm or less, and the eluted sodium amount and the eluted copper amount are each preferably 3 ppm or less. Moreover, it is preferable that the said elution chlorine amount is 5 ppm or less.

  In the hexagonal boron nitride powder of the present invention, the water content of the above (6) is such that the washed hexagonal boron nitride powder has a pressure of 20 kPaA or less, particularly 10 kPaA or less, at a temperature of 140 ° C. to 500 ° C. for 8 hours. As described above, the heat treatment is achieved particularly by heating for 10 hours or more.

  The water content of the hexagonal boron nitride powder of the present invention affects the insulation resistance of the resin molded body when the resin is filled. That is, by lowering the water content, generation of water vapor due to moisture when the resin is filled is suppressed, and a decrease in insulation resistance of the resin molded body can be suppressed. The water content is acceptable up to 0.1% by mass, but is preferably 0.02% by mass or less, and particularly preferably 0.01% by mass or less.

  Although the average particle diameter of the hexagonal boron nitride powder of the present invention is not particularly limited, it is preferably about 5 to 20 μm, particularly about 7 to 15 μm, for use as a filler for filling a resin.

  In addition, in the use as the filler, as the resin to be filled, energy (heat, light, etc.) such as thermoplastic resin such as vinyl chloride resin, fluorine resin, nylon, epoxy resin, melamine resin, unsaturated polyester resin, silicone resin, etc. ) Curable resin. Moreover, the filling amount with respect to resin is 50-1000 mass parts with respect to 100 mass parts of resin, Preferably, 200-700 mass parts is suitable.

  Of course, the hexagonal boron nitride powder of the present invention can be used in combination with other powders when filling the resin.

(Method for producing hexagonal boron nitride powder)
The hexagonal boron nitride powder of the present invention has an average aspect ratio obtained by reducing and nitriding a raw material mixture containing an oxygen-containing boron compound, a carbon source and an oxygen-containing calcium compound at a temperature of 1700 to 2200 ° C. in a nitrogen atmosphere. After producing a crude hexagonal boron nitride powder having a ratio of 10 or less, the crude hexagonal boron nitride powder is washed with an aqueous hydrochloric acid solution, and then washed with pure water having a specific resistance at 25 ° C. of 1 MΩ · cm or more. Furthermore, the hexagonal boron nitride powder after washing can be obtained by heat treatment at a temperature of 140 ° C. to 500 ° C. for 8 hours or more, particularly 10 hours or more under a pressure of 20 kPaA or less, particularly 10 kPaA or less.

In the production method of the present invention, boron oxide (B ₂ O ₃ ) is used as the oxygen-containing boron compound, carbon black (C) is used as the carbon source, and calcium carbonate is used as the oxygen-containing calcium compound. The

  In the above production method, the amount ratio of the raw material mixture is such that the elemental ratio (B / C) between boron and the carbon source contained in the oxygen-containing boron compound is 0.60 to 0.85, preferably 0.65. ~ 0.80. When the B / C is less than 0.60, the proportion of the unreacted carbon source is increased, and the desired hexagonal boron nitride particles cannot be obtained. Not only does the proportion of the volatilized boron compound increase and the yield decreases, but the exhaust line is blocked by the volatile components, which adversely affects the production line.

The molar ratio (B ₂ O ₃ / CaO) in terms of oxide between the oxygen-containing boron compound and the oxygen-containing calcium compound is 4 to 6, preferably 4.5 to 5.5.

When the B ₂ O ₃ / CaO is less than 4, not only calcium-derived impurities may remain, but plate-like hexagonal boron nitride is difficult to grow, which is not preferable. On the other hand, when the ratio is larger than 6, the ratio of the boron compound volatilized without being reduced is increased, the yield is lowered, and the exhaust line is blocked by the volatile components, which adversely affects the production line. .

  As a method for mixing the raw materials, a method in which the respective raw materials are uniformly mixed is suitably employed. Specifically, a mixing method using a mixing device such as a vibration mill, a ball mill, or a drum mixer vibration stirrer is preferable.

  The raw material mixture is reduced and nitrided by heating to a temperature of 1700 to 2200 ° C., preferably 1800 to 2100 ° C., under a nitrogen atmosphere. When the temperature is lower than 1700 ° C., it is difficult to perform sufficient reductive nitriding, and when it is higher than 2200 ° C., the generated boron nitride may be volatilized.

  For such reduction nitriding, a method using a known apparatus is employed without any particular limitation. 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 reactor can be used.

  When the hexagonal boron nitride obtained by the above method is obtained in bulk, it is crushed into powder. For the pulverization, a pulverizing apparatus such as a ball mill is used, and it is preferable to pulverize to a primary particle size.

  By the above method, a crude hexagonal boron nitride powder having an average aspect ratio of 5 or less, preferably 2 to 4 is produced.

(Acid cleaning)
In the method for producing hexagonal boron nitride powder of the present invention, the crude hexagonal boron nitride powder obtained by reductive nitridation is washed with an aqueous hydrochloric acid solution, and then purified at 25 ° C. with a specific resistance of 0.2 MΩ · cm or more. It is cleaned by washing with water.

  In the washing with the hydrochloric acid aqueous solution, the hydrochloric acid concentration in the aqueous solution to be used is preferably 10 to 15% by mass, and contact with 10 cc of the hydrochloric acid aqueous solution per 1 g of the crude hexagonal boron nitride powder results in the crude hexagonal boron nitride powder. This is preferable for sufficiently removing calcium components such as unreacted boron-containing compounds and unreacted calcium-containing compounds, and other metal components. The washing temperature is suitably 20 to 60 ° C., and the washing time is suitably 12 to 15 hours. As a preferred embodiment, an embodiment in which washing is performed with stirring using a stirring blade or the like can be mentioned.

  After washing with an aqueous hydrochloric acid solution, the hexagonal boron nitride powder is preferably subjected to washing with pure water by removing the aqueous hydrochloric acid solution as much as possible, specifically, until the chlorine concentration is 10 ppm or less. As the method for removing the hydrochloric acid aqueous solution, a removal method by removing liquid by centrifugation or the like, a removal method by preliminary washing with water, and the like are appropriately performed.

  In the cleaning with pure water, the water to be used needs to be pure water having a specific resistance at 25 ° C. of 0.2 MΩ · cm or more, preferably 1 MΩ · cm or more. That is, when the specific resistance of water is smaller than the above range, the impurity component adhering to the hexagonal boron nitride powder cannot be sufficiently removed. The washing is preferably performed with 300 cc of pure water per 1 g of hexagonal boron nitride powder, and the washing temperature is appropriately 20 to 60 ° C. As water used for cleaning, for example, when water with a specific resistance of less than 0.1 MΩ · cm, such as tap water, is used, chlorine, sodium, copper, etc. contained in tap water may remain in the hexagonal boron nitride powder. Because it is, it is not appropriate.

  After washing with pure water, the hexagonal boron nitride powder is preferably dehydrated as much as possible by filtration. Specifically, it is preferable to dehydrate until the water content after filtration becomes 40 wt% or less. As the filtration method, vacuum filtration by suction, filtration by centrifugation, and the like are appropriately performed.

  In the reduction nitriding reaction, since the average aspect ratio of the hexagonal boron nitride powder is adjusted to 5 or less, the cleaning action by the above cleaning works extremely effectively, which cannot be achieved with the conventional hexagonal boron nitride powder. A pure hexagonal boron nitride powder can be obtained.

(Dry)
In the present invention, the washed hexagonal boron nitride powder has a pressure of 20 kPaA or less, particularly 10 kPaA or less, preferably 5 kPaA or less, a temperature of 140 ° C. to 500 ° C., preferably 150 to 250 ° C., and more than 8 hours. In particular, it is necessary to obtain heat-treated hexagonal boron nitride powder that is suppressed in the amount of dissolved boron and rich in water resistance by drying for 10 hours or more, preferably 10 to 20 hours.

  In addition, it is effective in order to reduce the water vapor partial pressure at the time of drying, and to suppress the production | generation of soluble boron by making a moisture content into 40 wt% or less by the said filtration process.

  Furthermore, in the heat treatment, heating is performed such that the time from when the heating temperature reaches 100 ° C. until the water content of the hexagonal boron nitride powder is 5% by mass or less is within 2 hours, The soluble boron in the obtained hexagonal boron nitride powder can be further reduced, which is preferable.

  EXAMPLES Hereinafter, examples will be shown to describe the present invention more specifically, but the present invention is not limited to these examples.

  In the examples, the measurement is performed by the following method.

(1) Average aspect ratio About the obtained hexagonal boron nitride powder, 100 arbitrary plate-shaped hexagonal boron nitride particles were selected from an SEM observation image at a magnification of 200 times, and the long axis of the plate-shaped hexagonal boron nitride single particle The length (l: average particle diameter) and thickness were measured, and the average value of the long diameter / thickness (A) was calculated.

(2) Average particle size 1.0 g of the obtained hexagonal powder was introduced into a 50 cc screw tube together with 20 g of ethanol, and the hexagonal boron nitride suspension dispersed by shaking and stirring was subjected to laser diffraction / scattering particle size distribution. The particle size distribution was measured by using a measuring device (LA-950V2 manufactured by HORIBA), and D50 was obtained to obtain the average particle size of the hexagonal boron nitride powder.

(3) Amount of dissolved boron 50 g of sulfuric acid aqueous solution having a concentration of 0.5 mol / L and 2 g of hexagonal boron nitride powder are put into a 50 cc beaker, and the mixture is shaken and stirred while adjusting the temperature of the solution to 25 ° C. After standing for 120 minutes, boron in the obtained liquid was analyzed with an ICP emission spectroscopic analyzer (iCAP6500 manufactured by THERMO FISHER) to convert the eluted boron amount to B ₂ O ₃ , which was converted into the hexagonal boron nitride. The amount of dissolved boron (ppm) was determined by dividing by the mass of the powder.

(4) The amount of eluted calcium, the amount of eluted sodium and the amount of eluted copper were analyzed in the same manner as described above, and the amount of eluted calcium (ppm), the amount of eluted sodium (ppm) and the amount of eluted copper (ppm) were determined.

(5) Amount of eluted chlorine 0.5 g of the obtained hexagonal boron nitride powder and 10 mL of ultrapure water were placed in a pressure-resistant PTFE pressure vessel for pressure decomposition, heated at 160 ° C. for 30 hours, and then filtered. The separated filtrate was subjected to ion chromatograph (ICS-2100, manufactured by Nippon Dionest Co., Ltd.) to determine the amount of eluted chlorine (ppm).

(7) Moisture content The moisture content of 10 g of hexagonal boron nitride powder after drying was determined using a moisture meter (MX-50 manufactured by A & D).

Example 1
1950 g of boron oxide, 830 g of carbon black, and 600 g of calcium carbonate were mixed in a ball mill. Using a graphitic Tamman furnace, the mixture was heated to 1400 ° C. at 15 ° C./min in a nitrogen gas atmosphere and held at 1400 ° C. for 8 hours. After holding at 1400 ° C., the temperature was raised to 1800 ° C. at 15 ° C./min, held at 1800 ° C. for 2 hours, and subjected to reduction nitriding treatment.

  Next, the obtained crude hexagonal boron nitride powder was put into a polyethylene container, 10 times the amount of hydrochloric acid aqueous solution (10 wt% HCl) of the crude hexagonal boron nitride was added, and the mixture was stirred at a rotation speed of 300 rpm for 15 hours. After the acid cleaning, the acid was filtered, and after washing again with pure water having a specific resistance of 1 MΩ · cm at 25 ° C. of 300 times the amount of the added crude hexagonal boron nitride, filtration by suction was performed. Dehydration was performed until the moisture content in the powder was 40 wt% or less.

  After washing with pure water, the obtained powder was dried under reduced pressure at 200 ° C. for 15 hours under a pressure of 1 kPaA to obtain white hexagonal boron nitride.

  During drying, the moisture content of the hexagonal boron nitride powder during drying when the drying temperature exceeded 100 ° C. for 2 hours was 3.3 wt%.

  The dried powder was passed through a sieve having an opening of 90 μm to remove coarse particles, and the obtained boron nitride powder was measured for each of the above (1) to (7) in Table 1.

The obtained hexagonal boron nitride powder was placed in a thermostat with a humidity of 90% and a temperature of 50 ° C., and after 10 days, the amount of dissolved boron was measured in the same manner as in (3) above, and the value converted to B ₂ O ₃ was It was 24 ppm.

Example 2
White hexagonal boron nitride was obtained in the same manner as in Example 1 except that the specific resistance of pure water used for washing was 0.5 MΩ · cm and the drying time was 12 hours.

  During drying, the moisture content of the hexagonal boron nitride powder during drying when the drying temperature exceeded 100 ° C. for 2 hours was 3.8 wt%.

  The dried powder was passed through a sieve having an opening of 90 μm to remove coarse particles, and the obtained boron nitride powder was measured for each of the above (1) to (7) in Table 1.

The obtained hexagonal boron nitride powder was placed in a thermostat with a humidity of 90% and a temperature of 50 ° C., and after 10 days, the amount of dissolved boron was measured in the same manner as in (3) above, and the value converted to B ₂ O ₃ was It was 19 ppm.

Example 3
White hexagonal boron nitride was obtained in the same manner as in Example 1 except that the pressure during drying was 5 kPaA and the drying temperature was 180 ° C.

  During drying, the moisture content of the hexagonal boron nitride powder during drying when the drying temperature exceeded 100 ° C. for 2 hours was 4.4 wt%.

  The dried powder was passed through a sieve having an opening of 90 μm to remove coarse particles, and the obtained boron nitride powder was measured for each of the above (1) to (7) in Table 1.

The obtained hexagonal boron nitride powder was placed in a thermostat with a humidity of 90% and a temperature of 50 ° C., and after 10 days, the amount of dissolved boron was measured in the same manner as in (3) above, and the value converted to B ₂ O ₃ was It was 35 ppm.

Example 4
2100 g of boron oxide, 800 g of carbon black, and 700 g of calcium carbonate were mixed in a ball mill. The mixture was heated to 1400 ° C. at 15 ° C./min in a nitrogen gas atmosphere using a graphitic Tamman furnace, and held at 1400 ° C. for 8 hours. After holding at 1400 ° C., the temperature was raised to 1850 ° C. at 15 ° C./min, held at 1850 ° C. for 2 hours, and subjected to reduction nitriding treatment.

  Next, the obtained crude hexagonal boron nitride powder was put into a polyethylene container, 10 times the amount of hydrochloric acid aqueous solution (10 wt% HCl) of the crude hexagonal boron nitride was added, and the mixture was stirred at a rotation speed of 300 rpm for 15 hours. After the acid cleaning, the acid was filtered, and after washing again with pure water having a specific resistance of 1 MΩ · cm at 25 ° C. of 300 times the amount of the added crude hexagonal boron nitride, filtration by suction was performed. Dehydration was performed until the moisture content in the powder was 40 wt% or less.

  After washing with pure water, the obtained powder was dried under reduced pressure at 150 ° C. for 15 hours under a pressure of 1 kPaA to obtain white hexagonal boron nitride.

  During drying, the moisture content of the hexagonal boron nitride powder during drying when the drying temperature exceeded 100 ° C. for 2 hours was 4.8 wt%.

  The dried powder was passed through a sieve having an opening of 90 μm to remove coarse particles, and the obtained boron nitride powder was measured for each of the above (1) to (7) in Table 1.

The obtained hexagonal boron nitride powder was placed in a thermostat with a humidity of 90% and a temperature of 50 ° C., and after 10 days, the amount of dissolved boron was measured in the same manner as in (3) above, and the value converted to B ₂ O ₃ was It was 75 ppm.

Example 5
1800 g of boron oxide, 900 g of carbon black, and 700 g of calcium carbonate were mixed in a ball mill. The mixture was heated to 1400 ° C. at 15 ° C./min in a nitrogen gas atmosphere using a graphitic Tamman furnace, and held at 1400 ° C. for 8 hours. After holding at 1400 ° C., the temperature was raised to 1900 ° C. at 15 ° C./min, held at 1900 ° C. for 2 hours, and subjected to reduction nitriding treatment.

  Next, the obtained crude hexagonal boron nitride powder was put into a polyethylene container, 10 times the amount of hydrochloric acid aqueous solution (10 wt% HCl) of the crude hexagonal boron nitride was added, and the mixture was stirred at a rotation speed of 300 rpm for 15 hours. After the acid cleaning, the acid was filtered, and after washing again with pure water having a specific resistance of 1 MΩ · cm at 25 ° C. of 300 times the amount of the added crude hexagonal boron nitride, filtration by suction was performed. Dehydration was performed until the moisture content in the powder was 40 wt% or less.

  After washing with pure water, the obtained powder was dried under reduced pressure at 200 ° C. for 15 hours under a pressure of 1 kPaA to obtain white hexagonal boron nitride.

  During drying, the moisture content of the hexagonal boron nitride powder during drying when the drying temperature exceeded 100 ° C. for 2 hours was 3.0 wt%.

  The dried powder was passed through a sieve having an opening of 90 μm to remove coarse particles, and the obtained boron nitride powder was measured for each of the above (1) to (7) in Table 1.

The obtained hexagonal boron nitride powder was placed in a thermostat with a humidity of 90% and a temperature of 50 ° C., and after 10 days, the amount of dissolved boron was measured in the same manner as in (3) above, and the value converted to B ₂ O ₃ was It was 29 ppm.

Example 6
White hexagonal boron nitride was obtained in the same manner as in Example 5 except that the specific resistance of pure water used for washing was 10 MΩ · cm, the drying temperature was 200 ° C., and the drying time was 12 hours.

  During drying, the moisture content of the hexagonal boron nitride powder during drying when the drying temperature exceeded 100 ° C. for 2 hours was 3.7 wt%.

  The dried powder was passed through a sieve having an opening of 90 μm to remove coarse particles, and the obtained boron nitride powder was measured for each of the above (1) to (7) in Table 1.

The obtained hexagonal boron nitride powder was placed in a thermostat with a humidity of 90% and a temperature of 50 ° C., and after 10 days, the amount of dissolved boron was measured in the same manner as in (3) above, and the value converted to B ₂ O ₃ was It was 43 ppm.

Example 7
The boron nitride powder before washing and after drying obtained in Example 1 was dried under reduced pressure at 140 ° C. for 9 hours under a pressure of 1 kPaA to obtain white hexagonal boron nitride. The dried powder was passed through a sieve having an opening of 90 μm to remove coarse particles, and the obtained boron nitride powder was measured for each of the above (1) to (7) in Table 1. During drying, the moisture content of the hexagonal boron nitride powder during drying when the drying temperature exceeded 100 ° C. for 2 hours was 4.9 wt%. The obtained hexagonal boron nitride powder was placed in a thermostat with a humidity of 90% and a temperature of 50 ° C., and after 10 days, the amount of dissolved boron was measured in the same manner as in (3) above, and the value converted to B ₂ O ₃ was It was 89 ppm.

Example 8
The boron nitride powder after washing and before drying obtained in Example 3 was dried under reduced pressure at 180 ° C. for 15 hours under a pressure of 15 kPaA to obtain white hexagonal boron nitride. The dried powder was passed through a sieve having an opening of 90 μm to remove coarse particles, and the obtained boron nitride powder was measured for each of the above (1) to (7) in Table 1. During drying, the moisture content of the hexagonal boron nitride powder during drying when the drying temperature exceeded 100 ° C. for 2 hours was 4.7 wt%. The obtained hexagonal boron nitride powder was placed in a thermostat with a humidity of 90% and a temperature of 50 ° C., and after 10 days, the amount of dissolved boron was measured in the same manner as in (3) above, and the value converted to B ₂ O ₃ was It was 99 ppm.

Example 9
The boron nitride powder before washing and after drying obtained in Example 4 was dried under reduced pressure at 150 ° C. for 12 hours under a pressure of 1 kPaA to obtain white hexagonal boron nitride. The dried powder was passed through a sieve having an opening of 90 μm to remove coarse particles, and the obtained boron nitride powder was measured for each of the above (1) to (7) in Table 1. During drying, the moisture content of the hexagonal boron nitride powder during drying when the drying temperature exceeded 100 ° C. for 2 hours was 4.8 wt%. The obtained hexagonal boron nitride powder was placed in a thermostat with a humidity of 90% and a temperature of 50 ° C., and after 10 days, the amount of dissolved boron was measured in the same manner as in (3) above, and the value converted to B ₂ O ₃ was It was 78 ppm.

Comparative Example 1
1600 g of boron oxide, 960 g of carbon black, and 600 g of calcium carbonate were mixed in a ball mill. The mixture was heated to 1400 ° C. at 15 ° C./min in a nitrogen gas atmosphere using a graphitic Tamman furnace, and held at 1400 ° C. for 8 hours. After holding at 1400 ° C., the temperature was raised to 1800 ° C. at 15 ° C./min, held at 1800 ° C. for 2 hours, and nitrided.

  Next, the obtained crude hexagonal boron nitride powder was put into a polyethylene container, 10 times the amount of hydrochloric acid aqueous solution (10 wt% HCl) of the crude hexagonal boron nitride was added, and the mixture was stirred at a rotation speed of 300 rpm for 15 hours. After the acid cleaning, the acid is filtered, and the purified hexagonal boron nitride is washed 300 times more with pure water having a specific resistance of 1 MΩ · cm at 25 ° C. In the powder after filtration by suction filtration Dehydration was performed until the water content was 40 wt% or less.

  After washing with pure water, the obtained powder was dried under reduced pressure at 200 ° C. for 15 hours under a pressure of 1 kPaA to obtain white hexagonal boron nitride.

  During drying, the moisture content of the hexagonal boron nitride powder during drying when the drying temperature exceeded 100 ° C. for 2 hours was 3.0 wt%.

  The dried powder was passed through a sieve having an opening of 90 μm to remove coarse particles, and the obtained boron nitride powder was measured for each of the above (1) to (7) in Table 1.

Comparative Example 2
1950 g of boron oxide, 830 g of carbon black, and 600 g of calcium carbonate were mixed in a ball mill. The mixture was heated to 1400 ° C. at 15 ° C./min in a nitrogen gas atmosphere using a graphitic Tamman furnace, and held at 1400 ° C. for 8 hours. After holding at 1400 ° C., the temperature was raised to 1800 ° C. at 15 ° C./min, held at 1800 ° C. for 2 hours, and nitrided.

  Next, the obtained crude hexagonal boron nitride powder was put into a polyethylene container, 10 times the amount of hydrochloric acid aqueous solution (10 wt% HCl) of the crude hexagonal boron nitride was added, and the mixture was stirred at a rotation speed of 300 rpm for 15 hours. After the acid cleaning, the acid is filtered, and after washing again with water having a specific resistance at 25 ° C. of 0.01 MΩ · cm, which is 300 times the amount of the added crude hexagonal boron nitride, filtration is performed by suction filtration. Dehydration was performed until the water content in the powder afterwards became 40 wt% or less.

  After washing with pure water, the obtained powder was dried under reduced pressure at 120 ° C. for 15 hours under a pressure of 1 kPaA to obtain white hexagonal boron nitride.

  During drying, the moisture content of the hexagonal boron nitride powder during drying when the drying temperature exceeded 100 ° C. for 2 hours was 12.0 wt%.

  The dried powder was passed through a sieve having an opening of 90 μm to remove coarse particles, and the obtained boron nitride powder was measured for each of the above (1) to (7) in Table 1.

Claims (7)

The average aspect ratio of single particles is in the range of 1.5 to 10, and the amount of dissolved boron after being immersed in a 0.5 mol / L sulfuric acid aqueous solution at 25 ° C. for 120 minutes is converted to B ₂ O _3. 100 ppm or less, eluted calcium amount is 50 ppm or less, eluted sodium amount and eluted copper amount are each 5 ppm or less, eluted chlorine amount after immersion in water at 160 ° C. for 30 hours is 10 ppm or less, and water content is 0.1% by mass A hexagonal boron nitride powder characterized by:   The hexagonal boron nitride powder according to claim 1, wherein the hexagonal boron nitride powder has an average particle size in the range of 5 to 20 µm.   The hexagonal boron nitride powder according to claim 1 or 2, wherein an increase rate of the eluted boron amount after being left for 10 days in an atmosphere of 90% humidity and 50 ° C is 10% or less.   A raw hexagonal boron nitride having an average aspect ratio of 10 or less is obtained by heating a raw material mixture containing an oxygen-containing boron compound, a carbon source and an oxygen-containing calcium compound to a temperature of 1700 to 2200 ° C. in a nitrogen atmosphere and reducing and nitriding. After producing the powder, the crude hexagonal boron nitride powder is washed with an aqueous hydrochloric acid solution, then washed with pure water having a specific resistance at 25 ° C. of 0.2 MΩ · cm or more, and the hexagonal crystal after washing is further washed. A method for producing a hexagonal boron nitride powder, wherein the boron nitride powder is heat-treated at a temperature of 140 ° C. to 500 ° C. for 8 hours or more under a pressure of 20 kPaA or less. The raw material mixture has an element ratio (B / C) between boron and a carbon source contained in the oxygen-containing boron compound of 0.60 to 0.85, and oxide conversion of the oxygen-containing boron compound and oxygen-containing calcium compound the molar ratio _{(B 2} O 3 / CaO) is the rate at which a 4-6, claim 4 manufacturing method of hexagonal boron nitride powder as claimed in.   The method for producing a hexagonal boron nitride powder according to claim 4 or 5, wherein the heat treatment is performed after dehydrating the washed hexagonal boron nitride powder to reduce the amount of adhering moisture to 40% by mass or less.   In the heat treatment, heating is performed such that the time from when the heating temperature reaches 100 ° C until the water content of the hexagonal boron nitride powder becomes 5 mass% or less is within 2 hours. The manufacturing method of the hexagonal boron nitride as described in any one of these.