JPS6065767A - Manufacture of boron nitride sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing a highly pure and dense boron nitride (BN) sintered body. BN sintered compact A juice 1/■-#- produced by a cold press sintering method (hereinafter referred to as cold press method) to produce a BN sintered compact having a density of 1.82 g/α2 or more (80% or more of the theoretical density) SBN has electrical insulation, lubricity, thermal conductivity, chemical resistance,
Because it has excellent properties such as heat resistance, it is used in various fields that utilize this property.

However, since the BN obtained by the currently used Yuzu BNM production method is all in powder form, it is necessary to sinter and shape these BN powders in order to use them.

There are two methods for forming a BN sintered body: a hot press method and a cold press method.

The former method involves heating and sintering at the same time as press forming, and although it has the advantage of being able to obtain a high-density sintered body relatively easily, it requires an extremely large amount of equipment costs, and it also reduces work efficiency. This is disadvantageous due to high production costs.

In addition, the latter method is a method in which BN powder is press-formed in advance at a temperature of 200°C or less using a method such as a mold press or a rubber press, and then sintered, so although it has high work efficiency and is advantageous in terms of cost, Since it is a substance that is extremely difficult to sinter, it has the disadvantage that a high-density sintered body cannot be easily obtained.

Furthermore, a known method for producing a BN sintered body by a cold press method will be explained by giving a specific example. (A method for obtaining high-purity BN* solids by press-molding in the presence of 1 to 5% boric anhydride and then heating in a nitrogen stream to convert the boric anhydride to BN. 12547),
(2) A method of forming a topographical body by rubber pressing and then heating it under conditions that restrict the free expansion of the formed body (% Kosho 46
-17676). However, the density of the BN sintered body obtained by these methods is about 1.5 g/crn'' (66% of the theoretical density), and the sintered body density of the BN sintered body obtained by the hot pressing method is 1.8. ~2.1 Compared to C1r〆1 (79% to 98% of theoretical density), it is significantly lower in terms of chemical resistance, thermal conductivity, electrical insulation, etc., so B'N by cold pressing method The method for producing the sintered body was not practical.

The present invention provides a method for producing a BN sintered body having a sintered body density equal to or higher than that of a high-purity BN sintered body obtained by a hot pressing method, using a cold pressing method with extremely high work efficiency. That is, the purity of the present invention is 999 parts by weight or more.
For 1 part of 100ml of BN powder with a particle size of 44 to 710μ, 0% monovalent saturated fatty acid, which is solid at current temperature, is added as a lubricant.
．． 6 to 5.0 parts by weight) was added to the mixture at a temperature of 2.
It is characterized in that it is press-molded under conditions of 00°C or less and a pressure of 'I 000 Ky/cm' or more, and then heated in an oxidizing atmosphere at a temperature of 200 to 850°C.

The present invention will be explained in more detail below.

The raw material BN powder used in the present invention preferably has a BNN purity of 99 parts by weight or more.
The use of powder is not preferable because it tends to cause wear and tear on the mold during cold pressing. This phenomenon is particularly noticeable when a component such as Cal/Rum borate, which is harder than BN and has poor lubricity, is used.

In the cold press method, for example, when chamotte particles are used in the production of refractory bricks, it is necessary to increase the density of the raw material particles, or to obtain a molded product with a high density, but it is necessary to obtain a molded product with high purity. Since the BN powder particles themselves are loosely intertwined and bonded with BN crystals, these bonds are not broken during cold pressing and the BN crystals are rearranged, so there is no need to increase the particle density.

According to the knowledge of the present inventor, the particle size of the BN powder is determined from the viewpoint of the target size of the sintered body and the uniformity of the sintered body structure. Large particle size is preferable in terms of workability, etc.
It has been found that if the particle size is larger than necessary, defects such as cavities are likely to occur in the resulting sintered body, significantly reducing the product value.

In the present invention, the particle size of the raw material BN powder is limited to 44 to 710 μm. When producing a sintered body with a diameter of 6 to 40+n+++ and a height of 5 to 50 μm, the particle size of the BN powder is limited to 71 μm.
If it exceeds 0 μ, cavities may occur in the sintered body, and
If the powder contains BN powder with a small particle size of less than 4μ, the fluidity of the raw material powder will be extremely poor, and the work efficiency of the cold press process will be significantly reduced.
Problems such as the BN powder entering the gap between the die and the bar/steel constituting the IψΔka 11 cause damage to the mold, making it impossible to achieve the purpose of the invention.

In the present invention, a lubricant is used to reduce the frictional force between the BN powders and between the powder and the mold.

For the purpose of the invention, organic substances that are removed by oxidation and do not leave any ash can be used as lubricants, and specific examples thereof include aliphatic compounds, alicyclic compounds, and aromatic compounds. Typical examples include wax, wax, and naphthalene.

However, many alicyclic compounds and aromatic compounds are carcinogenic, which is undesirable in terms of the working environment.Furthermore, they cannot be easily removed during the heat removal process, leaving behind carbon. . In addition, the use of aliphatic compounds
Using an aliphatic carboxylic acid that does not have the above problems can prevent carbon from remaining in the heat removal process, but using a strong carboxylic acid can shorten the life of the metal mold. Press-fitting cost is 1/1, melon catfish 1 hη
-L1←, r

The blending amount is 100 parts by weight of Bn and 0.6 to 5 parts by weight of the lubricant. Methods for adding it include mixing with a general-purpose mixer such as a beam-pump blender and methods of unevenly distributing it on the grain surface, but the latter method is preferred.

A specific example of the latter method is a method in which stearic acid is dissolved in ethyl alcohol and then dried while being mixed with BN powder to evaporate the ethyl alcohol. The above fatty acids may be used alone or in combination as a lubricant, but if the amount added is less than 0.3 parts by weight, it will be difficult to perform cold pressing continuously, and the work efficiency will be extremely low. 5. to decrease; If the amount exceeds the OM amount, the density of the obtained sintered body will decrease, which is undesirable.

Regarding the molding pressure, if the molding pressure is 1000~/cm2, the density of the sintered body is low and it is impossible to obtain a BN sintered body having a density of 1.82'9/(:m3 or more (80% or more of the theoretical density)).

Regarding the molding temperature, room temperature is sufficient, and there is no case where the hot press method requires a high temperature of 1000°C or more. This is heated under an oxidizing atmosphere at a temperature of 200 to 85
[Heat to 1'O and remove. If the temperature exceeds 8500C, BN itself will be oxidized, and if the temperature is less than 20°C, the lubricant cannot be oxidized and removed, making it impossible to achieve the object of the present invention.

Next, a detailed explanation will be given with reference to examples.

Example BN powder (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name [Denka Boron Nitride] purity 999-41 IC, %) 1, 2 and 6009 of water were added, and then water was removed at 80°C to form a cake-like product. And so. Next, this was crushed with a porcelain roll mill and sieved to obtain a 44-710μ BN powder. For 1001 parts of this powder, add 1.5 m of the lubricant shown in the coating.
After adding and mixing an ethyl alcohol solution containing 20% of the lubricant at the ratio shown in the table in terms of lubricant, the ethyl alcohol was removed by drying at 60° C. to obtain a mixed powder. Next, this mixed powder was cold pressed using a mold at a molding pressure below room temperature to obtain a cylindrical molded body with an outer diameter of 1 (ll+i and a height of 15 mm).The physical properties and molding of this BN molded body The results of the observation at the time are shown in the table.Next, the BN molded body obtained by the above operation was heated in a Matsufuru furnace at the temperature shown in the table in an atmospheric atmosphere to obtain a BN sintered body. The physical properties of the BN sintered body are shown in the table.

Comparative Example 1 The same procedure as in Example 1 was conducted except that BN powder manufactured by Denki Kagaku Kogyo Co., Ltd. under the trade name "Denka Boron Nitride JBN" with a purity of 98.4% was used and the conditions shown in the table were used.

A molded product could not be obtained due to galling of the mold.

Comparative Examples 2 to 6 Comparative Examples 2 to 6 were carried out in the same manner as in Example 1, except that the amount of lubricant added, molding pressure, and firing temperature were changed as shown in the table.

Show the results on the cloth.

Claims (1)

[Claims] To 100 parts by weight of boron nitride powder with a purity of 99% by weight or more and a grain size of 44 to 710μ, add 0.6 to 5 parts of a temperature-sensitive solid monovalent saturated fatty acid as a lubricant, FIB
The mixture was heated at a temperature of 200°C or less and a pressure of 1000 Kt.
/cm2 or more, and the molded product is heated to [
A method for producing a boron nitride sintered body, which comprises heating in an oxidizing atmosphere at 200 to 850°C.