JPH0551525B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to hexagonal boron nitride, and particularly to a method for producing hexagonal boron nitride containing less water-soluble boron compounds. [Conventional technology] Hexagonal boron nitride (hereinafter boron nitride is referred to as BN)
The powder is white, has a layered structure similar to graphite, and has various properties. Especially thermal conductivity, electrical insulation,
It has excellent chemical stability, lubricity, heat resistance, etc.
Taking advantage of these properties, it is used for a wide variety of purposes. For powder applications, plastic additives,
It is often used as a lubricant. Recently, with advances in electronic technology, there has been an increasing demand for high-purity BN in applications such as fillers and additives that take advantage of BN's heat resistance and electrical insulation properties. In addition, cubic boron nitride (c-BN) can be obtained by subjecting BN to high-temperature and high-pressure treatment, and therefore it is also used as a raw material for this. BN as a c-BN raw material includes:
High purity is required. Furthermore, when producing c-BN, BN is molded in advance, but if the density of this molded product is low, there are disadvantages such as a decrease in the yield of c-BN. Conventional methods for producing high-purity BN suitable for such uses can be broadly classified into the following two methods. (1) A method of evaporating or decomposing impurities by heating to a high temperature (invention described in JP-A-58-60603 and invention described in JP-A-58-181708). (2) A method to obtain high purity BN from boron trichloride and ammonia using the following formula. BCl ₃ +NH ₃ →BN+3HCl …(1) [Problems to be solved by the invention] According to the method (1), impurity oxygen components are decomposed and volatilized and removed by heating BN at high temperature. I can do it. However, when processing a small amount of sample with a thin packed bed, the oxygen component can be easily removed by thermal convection and diffusion outside the sample packed bed, but when processing a large amount, it remains in the packed bed in a gaseous state and solidifies during the cooling process. BN
It precipitates as an impurity on the surface or between particles. For this reason, method (1) is difficult to process in large quantities, and energy costs are also high due to high temperature processing. Furthermore, high purity BN is obtained from BCl ₃ and NH ₃ in (2) above.
Although it is possible to obtain highly pure BN, it is difficult to obtain highly crystalline BN, which has the disadvantage of inferior insulation and thermal conductivity, and the hydrolyzability is lower than that of crystalline BN.
larger than. In addition, when mass-producing it industrially, there is a drawback that the manufacturing cost increases. In order to solve the above problems, the inventors
62-176904 discloses a BN powder containing less water-soluble boron compounds and a method for producing the same.
However, as a result of subsequent research by the inventors, it was found that a small particle size is effective in increasing the bulk density of a BN molded product. That is, in the drying step, which is the final step in the production of boron nitride that contains few water-soluble boron compounds, the BN purified by washing is slightly hydrolyzed;
The degree of this hydrolysis increases as the particle size of the BN powder becomes finer, in other words, as the specific surface area increases.
Therefore, there were many difficulties in making fine BN powder highly pure. The formula for the hydrolysis of BN is as follows. 2BN+ _3H2O → _{B2O3 + 2NH3 ...} (2) BN+ _3H2O → _H3BO3 + _NH3 ...(3) The present invention has been improved by focusing on such conventional problems. [Means for Solving the Problems] Therefore, in order to obtain BN with a small particle size and a small amount of water-soluble boron compounds, the present invention aims to sufficiently remove the water-soluble boron compounds on the surface using an appropriate dispersant and water. It is necessary to wash and remove the powder, and to dry it at a low temperature for a short time to keep hydrolysis to a minimum. Focusing on the fact that drying is more effective, we developed a microorganism with a specific surface area of 5 m ² /g or more, and an amount of boron in the extracted water of 100μ when boiled with pure water.
The composition is hexagonal boron nitride with a high purity of g/g-BN or less, and after dispersing the hexagonal boron nitride powder in water or hot water, washing and removing water-soluble boron compounds, and drying, The solution is to add alcohol or immerse it in alcohol and then dry it again. [Effect] The amount of water-soluble boron is determined by boiling and leaching BN with pure water and quantifying the amount of boron in the extract, but it is desirable that the amount of water-soluble boron is 100 μg/g-BN. . If the amount exceeds 100 μg/g-BN, not only the yield of c-BN will be poor, but also the strength of the obtained product will be poor. Preferably, the water-soluble boron content is 50 μg/g-BN or less. The particle size is indicated using the specific surface area as an index.
It is desirable that the specific surface area of the high purity BN powder is 5 m ² /g or more. When it is smaller than 5 m ² /g, the molded bulk density becomes small and the yield of c-BN decreases. Preferably it is 7 m ² /g or more. [Example] The manufacturing method of the present invention will be described in detail. Normally, BN powder contains 1 to 20% oxygen as an impurity. This oxygen combines with boron and exists as boron oxide, and sometimes boron oxide is hydrated and exists as boric acid. These boron oxides or boric acids are highly soluble in water. Therefore, when attempting to obtain hexagonal BN containing less water-soluble boron compounds, it is effective to wash and remove these easily soluble substances with water. In order to effectively wash and remove water-soluble boron compounds, the crystalline BN powder needs to be well dispersed in water or hot water. BN powder is difficult to wet with water and will not be dispersed in water as it is, so cleaning operations will not proceed easily. When dispersing in water, it is effective to use a dispersant. As a dispersant, (1) HLB (Hydrophile-Lipophile Balance), which indicates the balance between hydrophilic groups and lipophilic groups in the molecule;
Anionic, nonionic, or cationic surfactants with values ranging from 10 to 16. (2) Alternatively, an aqueous solution of a water-soluble organic solvent can be used. As surfactants, those with an HLB value in the range of 10 to 16 have a high cleaning effect, such as polyoxyethylene (5) sorbitan monostearate, polyoxyethylene (4) sorbitan trioleate, and polyoxyethylene glycol. 400 monooleate,
Triethanolamine oleate, polyoxyethylene (9) nonylphenol, polyethylene glycol 400 monooleate, triethanolamine oleate, polyoxyethylene (9) nonylphenol, polyethylene glycol 400 monolaurate,
Polyoxyethylene (4) sorbitan molaurate and the like can be used. The concentration of the surfactant is preferably in the range of 0.001 to 5% by weight. The reason for this is that if the amount exceeds 5% by weight, there is no difference in the dispersion effect even if more than 5% by weight is added, and it is economically undesirable to add too much. Also 0.001
This is because if the amount is less than % by weight, the effect will not be sufficiently expressed. As the water-soluble organic solvent, alcohols such as metal alcohol, ethyl alcohol, glycol, and glycerin, and acetone, acetylacetone, ethylamine, acetaldehyde, and phenol can be used. Among water-soluble organic solvents, methyl alcohol and ethyl alcohol are the most suitable in terms of price and availability. First, the method for dispersing BN powder into the cleaning solution is as follows.
If BN powder is dispersed in a water-soluble organic solvent such as methyl alcohol or ethyl alcohol to form a highly concentrated slurry and then washing water is added, the amount of alcohol used can be reduced and the dispersibility is very good. Ta. Moreover, the combination of a water-soluble organic solvent and a surfactant is even more effective. Although the temperature of the cleaning solution is not specified, the higher the temperature, the more effectively the soluble boron compound can be dissolved. Also, BN
By sufficiently stirring the slurry in which the powder is dispersed, dissolution can be carried out quickly and effectively.
It is desirable to stir thoroughly. The thinner the slurry concentration during cleaning, the greater the cleaning effect, but there is an optimal range from an economic standpoint. The upper limit is a slurry containing 50% by weight of BN. If it becomes thicker than this, stirring will not be done uniformly and sufficiently, and friction with the stirring impeller and container wall will increase, causing impurities to be mixed in. Although there is no positive reason to specify the lower limit, it is preferably up to 2.5% by weight from the point of view of economy and dewatering efficiency. For stirring the slurry, the most effective method can be adopted depending on the shape of the cleaning device, such as normal stirring, high-speed stirring, or dispersion based on shear force. The operation at this time may be either a continuous method or a batch method. It is effective to dehydrate the slurry after washing. Dehydration may be performed by centrifugal dehydration, vacuum dehydration, pressure dehydration, dehydration by natural sedimentation, filtration, suction filtration, or pressure filtration. Moreover, it is more effective to repeatedly wash the BN powder after dehydration. In order to obtain BN powder with a low content of water-soluble boron compounds, the final drying process must be carefully performed. That is, although most of the soluble boron compounds from the BN powder are removed by thorough washing, the BN is hydrolyzed during drying and the soluble boron compounds increase. In particular, the specific surface area is 5 m ² /g
This tendency is greater for larger fine particles. In the drying process, hydrolysis of BN must be suppressed as much as possible. In order to suppress the hydrolysis of BN, the drying time should be set to a [hour] and the drying temperature to be set to b.
When it is [°C], it is desirable that a/2+≦100. When (a/2+b) becomes larger than 100, that is, when the drying temperature becomes higher or the drying time becomes longer, the amount of water-soluble boron compounds increases. Preferably, a/2+≦80. If the above conditions are satisfied, the drying method is not specified. Hot air drying, hot air drying, normal drying, vacuum drying,
Various drying methods such as cold drying can be used. By adding alcohol to the dry BN powder obtained in this way, or by immersing the powder in alcohol and then drying it again, it becomes possible to reduce water-soluble boron compounds more effectively. As the alcohol, one type or a mixture of two or more types of alcohols such as ethanol, methanol, propanol, butanol, and pentanol can be used, and alcohols with lower boiling points are preferable because drying operations are easier. Further, organic solvents other than alcohol may be added. Removal of water-soluble boron compounds by alcohol is thought to occur as follows. That is, taking methanol as an example of alcohol, B ₂ O ₃ +6CH ₃ OH→2B(OCH ₃ ) ₃ +3H ₂ O…(4) H ₃ BO ₃ +3CH ₃ OH→B(OCH ₃ ) ₃ +3H ₂ O… (5) Boric acid esters (such as B(OCH ₃ ) ₃ ) have a low boiling point, so the boron component evaporates as boric ester when drying. Alcohol may be added to the powder, or
The powder may also be soaked in alcohol. It is effective to stir at this time. Upon addition of alcohol or immersion in alcohol, the ratio of alcohol to powder ranges from 0.05 to 100 alcohol/powder. If the amount of alcohol is small, the surface of the powder cannot be sufficiently wetted with alcohol, and unreacted portions remain. Too much alcohol is not economical. Preferably alcohol/powder is 0.5-20
is within the range of It is desirable that BN be sufficiently dry when adding alcohol or immersing it in alcohol. If drying is insufficient and a lot of moisture remains,
Reduction of water-soluble boron compounds is not performed effectively. In the presence of large amounts of water, hydrolysis of boric acid esters [B(OCH ₃ ) _3, etc.] (i.e., (4),
It is presumed that the boron compound does not volatilize because the reverse reaction of equation (5) occurs. Furthermore, even if alcohol is added to BN powder that contains a large amount of water-soluble impurities, water-soluble boron compounds are not effectively reduced. In other words, by treating BN powder with a reduced amount of water-soluble boron compounds to a certain extent with alcohol, it is possible to effectively obtain BN powder with a reduced amount of water-soluble boron compounds. This is because when a large amount of water-soluble impurities are contained, a large amount of H ₂ O is produced by the reaction (4) or (5), and the reaction stops after it has progressed to a certain extent, making it less efficient. It is assumed that water-soluble boron compounds are not reduced. Alcohol treatment is sufficiently effective as long as water-soluble boron compounds are reduced to a certain extent, so the conditions for water washing and subsequent drying are not limited to the above-mentioned ranges. The amount of water-soluble boron before alcohol treatment is preferably 500 ppm or less. Preferably it is 200 ppm or less. Even during drying after addition of alcohol or immersion in alcohol, water generated by the reactions (2) and (3) or water in the drying atmosphere may
Since hydration of BN occurs, it is desirable to take the same precautions and operations as drying after water washing. In this case as well, the drying method is not specified. The BN purified in this way has extremely low water-soluble boron compounds of less than 100 μg/g-BN, has a high purity that cannot be obtained with conventional methods, and has a small particle size with a specific surface area of 5 m ² /g. Because, c-
Suitable as BN raw material. In addition, the present invention uses a wet method instead of a dry method to achieve high purity.
Being able to produce BN is an industrially extremely advantageous method. High purity obtained with less water-soluble boron
BN can be fully applied to new fields that will be developed in the future. [Example] (Example 1) Purification was carried out by washing using BN powder having a specific surface area of 7.2 m ² /g and an impurity oxygen content of 4.3%. A 0.5% aqueous solution 5 of an ethylene alcohol-based anionic surfactant having an HLB value of 14 was heated to 90°C, 250 g of BN powder was dispersed therein, and the mixture was maintained for 1 hour while stirring. Vacuum filter the slurry to obtain a cake. Thereafter, the cake was redispersed in water, stirred and washed, and vacuum filtered to obtain a cake. This procedure was repeated twice. The cake was dried with hot air at 100°C for 24 hours to obtain BN powder. When the amount of boron in the extraction water of the BN powder obtained in this way was determined at 100℃, it was found to be 185μg/g-
It was BN. After washing, add 1.5 times the amount of ethanol to the powder,
After stirring, it was dried in a hot air dryer at 80°C for 15 hours. When the amount of boron in the extraction water of the obtained BN powder at 100°C was determined, it was 75 μg/g-BN. (Comparative Example 1) On the other hand, as Comparative Example 1, the above-mentioned cake after being washed with water twice was used, and the cake was washed with water again and filtered under vacuum to obtain a cake. This cake was dried at 100°C for 24 hours, and the amount of boron in the extraction water of the obtained BN powder at 100°C was determined to be 141 ppm. (Example 2) BN powder having a specific surface area of 9.6 m ² /g was washed in the same manner as in Example 1, and a cake was obtained after washing three times with water. This cake was vacuum dried at 95°C, 10 torr, and 12 hours. The amount of boron in the extraction water of the obtained BN powder at 100°C was 126 μg/g-BN. Two times the amount of methanol was added to this dry powder, stirred, and then dried at 75°C for 12 hours. obtained
When the amount of boron in the water extracted from the BN powder at 100°C was determined, it was 73 μg/g-BN. (Comparative Example 2) On the other hand, as a comparative example, the cake after washing with water four times was
After vacuum drying at 95℃, 100torr for 12 hours,
The amount of boron in the extraction water at 100℃ is 121μg/g-BN
It was hot. (Example 3) BN with impurity oxygen content of 6.3% and specific surface area of 8.3 m ² /g
The amount of boron in the extracted water after washing the powder with water at 100℃
A dried BN powder having a concentration of 210 μg/g-BN was obtained. this
After adding the same amount of methanol to the BN powder and stirring it, we dried it in a hot air dryer at 80℃ for 15 hours.
The amount of boron in the extraction water at 100℃ is 72μg/g-BN.
BN powder was obtained. (Comparative example 3) On the other hand, impurity oxygen content 6.3%, specific surface area 8.3m ² /g
After adding the same amount of methanol to the BN powder and stirring,
I dried it in a hot air dryer at 80℃ for 15 hours, but this
The amount of boron in the extraction water of BN powder at 100℃ is 2350μg/
It was g-BN. (Example 4), (Comparative Example 4) High purity BN with different specific surface areas according to Example 1
A powder was produced, and the powder was compacted under a surface pressure of 1 ton/cm ² . Table 1 shows the molding bulk density and molding workability.

[Table] As is clear from the table, the molded bulk density of the BN powder according to the present invention is increased, and molding is easy. (Example 5) BN with specific surface area 6.0m ² /g and impurity oxygen content 5.2%
The powder was used for purification by washing. Washing was carried out according to Example 1, and a cake was obtained after washing with water four times. This cake was dried at 60° C. for 10 hours using a vacuum dryer. obtained in this way
The amount of boron in the extraction water of BN powder at 100℃ is 23μg/g
-It was BN. 3 parts by weight of ethanol was added to 1 part by weight of BN powder with an extracted boron content of 23 μg/g, and after stirring, it was dried using a hot air dryer at 50°C for 6 hours to purify it.
Obtained BN powder. The amount of boron in the extraction water of this purified BN powder at 100°C was 7 μg/g-BN. [Effects of the Invention] As is clear from the above explanation, in the present invention, by lowering the content of water-soluble boron compounds, the yield of c-BN can be improved, and the resulting product can be improved. It also has the effect of improving strength. In addition, according to the present invention, the particle size of hexagonal boron nitride can be reduced and the specific surface area can be increased.
It is possible to increase the density of the BN molded body, which has the effect of lowering manufacturing costs compared to conventional products.

Claims (1)

[Claims] 1 Disperse hexagonal boron nitride with a specific surface area of 5 m ² /g or more in water or hot water, wash and remove water-soluble boron compounds, dry it, then add alcohol or immerse it in alcohol, and The boron nitride obtained by drying again after boiling with pure water has a boron content of 100μg/g-BN in the extracted water.
A method for producing hexagonal boron nitride, characterized by the following: