JPH01157409A - Hexagonal system boron nitride and its production - Google Patents

Abstract

PURPOSE:To obtain hexagonal system BN giving molded article having high density and strength, and having small particle size and the low content of water-soluble B compd. at a low cost, by dispersing the hexagonal system BN powder in (hot)water to wash out water-soluble B compd., thereafter by drying, by adding to alcohol or immersing in alcohol, and by drying again. CONSTITUTION:The hexagonal system BN powder is dispersed in water or hot water dissolving to 0.001-5wt.% concn. of anionic, nonionic or cationic surface active agent having 10-16HLB [e.g., polyoxyethylene(5)solbitan monostearate] to dissolve out the water-soluble B compd. preferably with well stirring, thereafter dehydrated by centrifuging, filtering, etc., and, as occasion demands, repeatedly washed. Then, the washed BN powder is added with the alcohol (e.g., methanol) or immersed in the alcohol (where, alcohol/powder ratio=0.05-100) after drying, and then, dried again to obtain the hexagonal system BN having >=5m<2>/g specific surface area and giving <=100mug/g-BN the amt. of B in the percolate when percolated with boiling pure water.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to hexagonal boron nitride, and particularly to hexagonal boron nitride containing less water-soluble boron compounds and a method for producing the same.

[Prior Art] Hexagonal boron nitride (hereinafter referred to as BN) powder is white, has a layered structure similar to graphite, and has various properties. Especially thermal conductivity and electrical insulation.

It is known for its chemical stability, lubricity, and heat resistance, and it is used in a wide variety of applications by taking advantage of these properties. Plastic additive for powder applications.

It is often used as a lubricant.

Recently, with the progress of electronic technology, there has been an increasing demand for high-purity BH in applications such as fillers and additives that utilize f3N's heat resistance and electrical insulation properties.

In addition, cubic boron nitride (
c-BN), it is also used as this raw material. BH as a c-BN raw material is required to have high purity. Also, when making c-BN, BN is molded in advance,
If the density of this compact 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 No. 58-60603 and invention described in JP-A-58-181708).

(2) A method of obtaining highly pure N from boron trichloride and ammonia using the following formula.

BC(!, +NH3→BN+3HCρ...(1
) [Problems to be Solved by the Invention] According to the method (1), impurity oxygen components can be decomposed and volatilized and removed by heating BN at a high temperature. 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. It precipitates as an impurity on the BN surface or between particles.

For this reason, method (1) is difficult to process in large quantities, and is expensive in terms of energy costs due to high temperature processing.

Furthermore, in the method (2) for producing high-purity BN from BCl23 and N I (3), although high-purity BN can be obtained, it is difficult to obtain highly crystalline BN, and the disadvantage is that it is inferior in insulation properties and thermal conductivity. It has a higher hydrolyzability than crystalline BH.Furthermore, it has the disadvantage that the manufacturing cost increases when it is industrially mass-produced.

In order to solve the above problems, the inventors
No. 76904 discloses a BH 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 article.

In other words, in the drying step, which is the final step in the production of boron nitride that contains few water-soluble boron compounds, BN purified by washing is slightly hydrolyzed, but the degree of hydrolysis becomes smaller as the particle size of the BH powder becomes smaller. The larger the specific surface area, the more difficult it is to make fine N powder highly pure. The formula for the hydrolysis of BH is as follows.

28N+3H, O→B, o3+2NHa...(2)
BN+3H,O→H3B Os+N H3...(
3) The present invention has been improved by paying attention to 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 provides the following methods: (1) It is necessary to dry the powder at a low temperature for a short time in order to suppress the hydrolysis to a small amount. (2) After the operation of (1), alcohol is added to the powder or the powder is Focusing on the fact that drying it after immersing it in the liquid is very effective,
The amount of boron in the extracted water when boiled with pure water is 100μ9/g
- Its composition is hexagonal boron nitride with a high purity of BN or less, and the hexagonal boron nitride powder is dispersed in water or hot water, washed to remove water-soluble boron compounds, dried, and then mixed with alcohol. The solution is to add alcohol or immerse it in alcohol and then dry it again.

[Function] 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, and it is desirable that the amount of water-soluble boron is 100μ9/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 is 50μ? /g-B
N 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 BH powder is 5R2/g or more. When it is smaller than 5II+2/g, the molded bulk density becomes small and the yield of c-BH decreases. Preferably 7m
2/g or more.

[Example] The manufacturing method of the present invention will be explained in detail.

BH powder usually contains 1 to 20% oxygen as an impurity. This oxygen combines with boron and exists as boron oxide,
Also, sometimes boron oxide is hydrated and exists as boric acid. These boron oxides or boric acids are very easily soluble in water.

Therefore, hexagonal r3N with less water-soluble boron compounds
When attempting to obtain these substances, 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. BH powder is difficult to wet with water and will not be dispersed in water as it is, and therefore cleaning operations will not proceed easily. When dispersing in water, it is effective to use a dispersant. As a dispersant, (1) HL I3 (1lydrophile-
1,1pophile Ba1ance) value is lO~1
Anionic, mono-nonionic or cationic surfactants within the range of 6.

(2) Alternatively, an aqueous solution of a water-soluble organic solvent can be used.

As surfactants, those having an I-IL B value in the range of 10 to 16 have a high cleaning effect, such as polyol, oxyethylene (5) sorbitan monostearate, and polyoxyethylene (4) sorbitan trioleate. Polyoxyethylene glycol 400 monooleate, triethanolamine oleate, polyoxyethylene (9)
Nonylphenol.

Polyethylene glycol 400 monooleate.

Triethanolamine oleate, polyoxyethylene (9) nonylphenol, polyethylene glycol 40
0 monolaurate, polyoxyethylene (4) sorbitan molaurate, etc. 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. Moreover, if it is less than 0,001% by weight, the effect will not be sufficiently expressed.

Water-soluble organic solvents include alcohols such as methyl alcohol, ethyl alcohol, glycol, and glycerin, and acetone, acetylacetone, ethylamine,
Acetaldehyde, phenol, etc. can be used.

Among water-soluble organic solvents, methyl alcohol and ethyl alcohol are the most suitable in terms of price and availability. B N
The method for dispersing the powder into a cleaning solution is to first disperse the BN powder in a water-soluble organic solvent such as methyl alcohol or ethyl alcohol to form a highly concentrated slurry, and then add cleaning water. The dispersibility was also very good. 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, soluble boron compounds are effectively dissolved at high temperatures. Further, by sufficiently stirring the slurry in which the INN powder is dispersed, dissolution can be effected in a short time and effectively, so it is desirable to sufficiently stir the slurry.

The thinner the slurry concentration during cleaning, the greater the cleaning effect, but there is an optimum range from an economic standpoint. The upper limit is BN 50
% slurry by weight. If it becomes thicker than this, the stirring will not be uniform and sufficient, and the friction with the stirring impeller and the container wall will increase, causing the contamination of impurities.

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. At this time, the operation can be done either by continuous method or badge method.

It is effective to dehydrate the slurry after washing. Dehydration includes centrifugal dehydration, vacuum dehydration, pressure dehydration, natural sedimentation dehydration,
Alternatively, any method such as filtration, suction filtration, or pressure filtration may be used.

Moreover, it is more effective to repeatedly wash the BH powder after dehydration.

In order to obtain BH powder with a low content of water-soluble boron compounds, the final drying step must be carried out carefully.

That is, although most of the soluble boron compounds from the BH powder are removed by thorough washing, the BN is hydrolyzed during drying and the soluble boron compounds increase. This tendency is particularly strong for fine powders with a specific surface area larger than 5z''/g.

In the drying process, hydrolysis of BH must be suppressed as much as possible. In order to suppress the hydrolysis of I3N, it is desirable that 10b≦100, where drying time is a [hour] and drying temperature is b [°C].

When ('-+ b ) becomes larger than 100, that is, when the drying temperature becomes high or the drying time becomes long, the amount of water-soluble boron compounds increases.

If the above conditions are satisfied, the drying method is not specified. Hot air drying, hot air drying 1 normal drying, vacuum drying.

Various drying methods such as cold drying can be used.

By adding alcohol to the dried 3N powder obtained in this way, or by immersing the powder in alcohol and then drying it again, it becomes possible to effectively reduce the amount of water-soluble boron compounds.

Alcohols include ethanol and methanol.

Although IFIj or a mixture of two or more alcohols such as propatool, butanol, and pentanol can be used, alcohols with lower boiling points are preferred because drying operations are easier. Further, other organic solvents may be added to the alcohol.

It is thought that the removal of water-soluble boron compounds by alcohol occurs as follows. In other words, if we take methanol as an example, B! Oi+ 6 CH30H→
2B (OCI-13) 3+31120...(
4) H3BO3+3CIl*0r-I→B (OCII
, )ff+3H20・ (5) Boric acid ester (B (O
CII3) s, etc.) has a low boiling point, so the boron component volatilizes as boric acid ester during drying.

Alcohol can be added to the powder, or it can be soaked in the 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 +00 alcohol/powder. If the amount of alcohol is small, the surface of the powder will not be sufficiently wetted with alcohol, and some unreacted portion will remain. Too much alcohol q is not economical. Preferably alcohol/powder is 05-2
It is in the range of 0.

It is desirable that the BN be sufficiently dry when adding alcohol or immersing it in alcohol.

If drying is insufficient and a large amount of moisture remains, water-soluble boron compounds will not be effectively reduced.

When a large amount of moisture is present, boric acid ester [B (OCI
-r, )3, etc.] (i.e., (4).

It is presumed that the 61111 elementary compound does not volatilize because the reverse reaction of formula (5) occurs.

Further, even if alcohol is added to BN material containing a large amount of water-soluble impurities, the amount of water-soluble boron compounds cannot be effectively reduced. In other words, it is possible to effectively obtain BN powder with a reduced amount of water-soluble boron compounds by treating the 3N powder with a reduced amount of water-soluble boron compounds to a certain extent with alcohol. This is because if water-soluble impurities are included in polyr11, a large amount of H and O will be produced by the reaction (4) or (5), and the reaction will stop after it has progressed to a certain extent, so that water cannot be efficiently It is assumed that soluble boron compounds are not reduced.

Since alcohol treatment is sufficiently effective as long as water-soluble boron compounds are reduced to a certain extent, the conditions for water washing and subsequent drying are not limited to the above-mentioned ranges. The amount of water-soluble boron on the alcohol-treated surface is 500p.
It is desirable that it is below pm. Preferably 200pp
m or less.

As with alcohol addition, even during drying after immersion in alcohol, hydration of BN occurs due to moisture generated by the reactions (2) and (3) or moisture in the drying atmosphere, so drying after washing with water Similar considerations and operations are desirable. In this case as well, the drying method is not specified.

BN purified in this way has a particularly low water-soluble boron compound of less than 100μ9/g-BN, has a high purity that cannot be obtained by conventional methods, and has a specific surface area of 5jI
``Due to its small particle size of 7g, it is suitable as a C-13N raw material.

Furthermore, the present invention is an industrially extremely useful method in that it is possible to produce high-purity RN by a wet method instead of a dry method.

The obtained high-purity BN containing less water-soluble boron can be fully applied to new fields that will be developed in the future.

[Example] (Example 1) Specific surface vt7, 2 m2/'i impurity oxygen F114.
Purification was performed by washing using 3% BN.

5 g of a 0.5% aqueous solution of an ethylene alcohol-based anionic surfactant having a HLBIa of 14 was heated to 90° C., and after dispersing 250 g of BN, the mixture was held for 1 hour while stirring. Vacuum filter the slurry to obtain a cake. Thereafter, the operation of dispersing M in water, stirring and washing the cake, and filtering it under vacuum to obtain a cake 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 thus obtained at 100°C was determined, it was 185μ9/g-BN.

After washing, add 1.5 times more ethanol to the powder! After stirring, drying was performed at 80°C for 15 hours using a hot air dryer. The amount of boron in the extraction water of the obtained BN powder at 100° C. was determined to be 75 μ9/g-I3N.

(Comparative Example 1) On the other hand, as Comparative Example 1, the cake described above was used after being washed twice with water, and the cake was washed with water again and filtered under vacuum to obtain a cake. This cake was dried at +00° C. for 124 hours, and the amount of boron in the water extracted from the obtained BN layer at 100° C. was determined to be 141 ppm.

(Example 2) BN powder having a specific surface area of 9.6 and 7 g was washed in the same manner as in Example 1, and a cake was obtained after washing three times with water. This cake 9
5°C, I 0torr, ! Vacuum drying was performed for 2 hours. The amount of boron in the extraction water of the obtained BN powder at 100° C. was 126 μg/g13N.

After adding twice the amount of methanol to this dry powder and stirring,
Drying was performed at 75°C for 12 hours. 1 of the obtained BN powder
When the amount of boron in the extracted water was quantified at 00℃, it was found to be 73
It was ug/g-BN.

(Comparative Example 2) On the other hand, as a comparative example, the cake after being washed four times with water was heated to 95°C.
When dried under vacuum for 12 hours at 100 torr, the amount of boron in the extracted water at 100°C was 121μ9.
/g-BN.

(Example 3) Impurity oxygen! i16, 3%, specific surface area 8.3/g
The r3N powder was washed with water to obtain dried I3N powder with a boron content of 210 μg798N in the loo'c extraction water.

After adding the same amount of methanol to this 13N powder and stirring, it was dried in a hot air dryer at 80°C for 15 hours.
I3N powder with a boron content of 72 μg/@-I3N in the extraction water at 00°C was obtained.

(Comparative Example 3) On the other hand, the same amount of methanol was added to BN powder with impurity oxygen content of 163% and specific surface area of 8.31/g, stirred 1'1, and then dried at 80°C for 15 hours in a hot air dryer. -] But this B
Boron+i in the extraction water of N powder at 100℃ is 2350μ9
/g-BN.

(Example 4), (Comparative Example 4) High purity BN powders having different specific surface areas were produced according to Example 1, and the powders were molded using a force having a surface pressure of I Lon/cz2. Table 1 shows the molding bulk density and molding workability.

Table 1 Amount of boron in extraction water at 1100°C As is clear from the table, the molded bulk density of the BN dressing of the present invention has increased, and the molded bulk density is 5.

(Example 5) Specific surface area6. Purification by washing was performed using BN filter containing 7 g of Om' and 15.2% of impurity oxygen Fi. Washing was carried out in accordance with Example I, and a cake was obtained after washing with water four times. This cake was dried at (')0°C for 10 hours using a vacuum dryer. 100 of the I3N powder thus obtained
The boron rh in the extraction water at °C was 23 μ9/g r3N.

For 1 part by weight of extracted boron powder 23 μ9/g-BN,
After adding 3 parts by weight of ethanol and stirring, the mixture was dried using a hot air dryer at 50°C for 6 hours to obtain purified BN powder. The amount of boron in the extraction water of this purified I3N powder at 100°C is 7 μy.
/g-BN.

[Effects of the Invention] As is clear from the above explanation, in the present invention, by lowering the content of the water-soluble boron compound, c-
It has the effect of improving the yield of r3N and also improving the strength of the resulting product.

Furthermore, according to the present invention, the particle size of hexagonal boron nitride can be reduced and the specific surface area can be increased, making it possible to increase the density of the BN molded body and lower manufacturing costs compared to conventional ones. effective.

Claims (2)

[Claims] (1) Hexagonal nitride characterized in that when boron nitride is boiled and leached with pure water, the amount of boron in the extracted water is 100μg/g-BN or less, and the specific surface area is 5m^2/g or more boron. (2) Dispersing hexagonal boron nitride powder in water or hot water to wash and remove water-soluble boron compounds, drying, then adding alcohol or immersing in alcohol, and then drying again. A method for producing hexagonal boron nitride, characterized by: