JP2000128647A - Production of hexagonal boron nitride sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a hexagonal boron nitride sintered body suitable for making a setter for firing large ceramics by forming a raw material mixture comprising a specific amount of highly fillable hexagonal boron nitride powder having a specific (surface-average diameter)/(50% volume cumulative particle size Dp50) ratio and a specified Dp50 and a specific amount of hexagonal boron nitride powder having a specific Dp50 value or less, and subsequently sintering the formed body. SOLUTION: Mixed powder comprising <=80 wt.% of highly fillable hexagonal boron nitride powder having a (surface-average diameter)/(Dp50) ratio of >=0.6 and a Dp50 of >=15 μm and >=20 wt.% of hexagonal boron nitride powder having a Dp50 of <=1.5 μm is used as raw material powder. The mixed powder is, if necessary, mixed with a sintering auxiliary and an organic binder, shaped, if necessary, defatted, and subsequently sintered in a non-oxidizing atmosphere. Since the raw material powder has excellent fillability, shape retainability and formability, a large molded product can be molded, and a sintered body having a largest length of >=450 mm can easily be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a hexagonal boron nitride sintered body. For details, hexagonal boron nitride sintering that can easily manufacture large-sized products with a maximum length of 450 mm or more, suitable for manufacturing large ceramics setters without joining structures such as fitting and screwing It relates to a method for producing a body.

[0002]

2. Description of the Related Art Hexagonal boron nitride has a layered structure similar to graphite, and is excellent in properties such as thermal conductivity, electrical insulation, chemical stability, solid lubricity, and thermal shock resistance. Further, since the sintered body is excellent in corrosion resistance, machinability, heat resistance, low dielectric property, low dielectric loss property and the like, it is widely used in various fields. In particular, recently, there has been an increasing demand as a ceramic firing setter for producing large-sized ceramic products. For example, a setter having a maximum length of more than 400 mm and up to about 1000 mm has been used. The maximum length here refers to, for example, a diagonal line for a square shape, a diameter for a circular shape, and a length of a major axis for an elliptical shape.

Conventionally, such a large-sized setter is manufactured by assembling a small-sized hexagonal boron nitride sintered body manufactured by a hot press method, a normal pressure sintering method or the like by physical means such as fitting and screwing. In practice, the following problems have been encountered.

[0004] When a material to be fired is placed on a setter and debinding is performed, the way of removing the binder is different between an assembled part and a non-assembled part of the setter. Was needed. If sintering is not performed enough for binder removal,
The binder easily remained in the portion of the object to be fired that had been in contact with the setter assembly portion, and warping and cracks were generated from that portion by repeated use, resulting in a shorter life. Such a short life is also caused by the fact that stress is concentrated on the assembled portion due to the load applied from the object to be fired. Also, due to the ventilation from the setter assembling part, the part of the object to be fired that was in contact with that part may be discolored, or the dimensions of the object to be fired may be out of order due to slight steps or the like generated in the setter assembling part Therefore, it was necessary to carefully select and use the same components for the setters, so that sufficient consideration was required for assembling the setters.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and has as its object to provide a large-sized hexagonal boron nitride sintered body having a maximum length of 450 mm or more suitable as a setter material for firing large-sized ceramics. Is to be easily manufactured.

[0006]

That is, the present invention provides:
(Area average diameter D _a ) / (50% volume cumulative particle size D _p50 ) ratio (hereinafter referred to as “B value”) is 0.6 or more and D _p50 is 1
Features and 80 wt% or less high packing property hexagonal boron nitride powder is not less than 5 [mu] m, that D _p50 is molding and firing the raw material powder containing the following hexagonal boron nitride powder 20 wt% or more 1.5μm Is a method for producing a hexagonal boron nitride sintered body.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

According to the present invention, a hexagonal boron nitride raw material powder is
Mold using sintering aids such as calcium borate and calcium oxide and organic binders such as acryl, paraffin, wax, and methylcellulose as required. If an organic binder is used, degrease it and use a non-oxidizing atmosphere. In the method of firing under the following conditions, the hexagonal boron nitride raw material powder is a highly-fillable hexagonal boron nitride powder having a B value of 0.6 or more and a D _p50 of 15 μm or more;
Hexagonal boron nitride powder 20 having a _p50 of 1.5 μm or less
In this case, a powder mixture of at least 1% by weight is used.

The raw material powder used in the present invention is excellent in fillability, shape retention, and moldability, so that a large-sized molded body can be formed, and a large hexagonal nitride having a maximum length of 450 mm or more can be formed. The manufacture of the sintered element becomes easy.

[0010] That is, if B values of the high filling properties hexagonal boron nitride powder is less than 0.6, or when D _p50 high filling ability hexagonal boron nitride powder is smaller than 15 [mu] m, the molding of the raw material powder The fluidity at the time is impaired, which causes cracks and lamination during molding. On the other hand, if D _p50 of hexagonal boron nitride powder to be blended therewith exceeds 1.5 [mu] m, the filling property of deteriorated during molding, causing cracking and lamination during molding as well. Furthermore, even if the particle size characteristics of the two powders are appropriate, if the mixing ratio of the two powders is inappropriate, the filling property is also deteriorated. That is, if the proportion of the highly-fillable boron nitride powder exceeds 80% by weight, it causes cracks and lamination.

The oxygen content of the hexagonal boron nitride raw material powder is
It is desirable that the content be 0.4 to 1.7% by weight, whereby a high-strength hexagonal boron nitride sintered body having less dimensional change during use of the setter can be manufactured.

As a method for molding the raw material powder, a general method such as a mold pressing method, an isostatic pressing method, a slurry casting method, an extrusion molding method, and an injection molding method can be employed. These can also be combined. However, when an organic binder is used, it is necessary to degrease it before firing. In particular, in order to obtain a hexagonal boron nitride sintered body having a high strength and a small dimensional change during use of the setter, it is desirable to apply an isostatic press of 0.5 ton / cm ² or more before firing.

The calcination is performed at a temperature of 1700 ° C. or more in a non-oxidizing atmosphere such as nitrogen, ammonia, hydrogen, carbon dioxide, carbon monoxide, argon, and helium.

In order to manufacture a setter from the hexagonal boron nitride sintered body manufactured according to the present invention, machining such as cutting, cutting, and polishing is performed. According to such a setter, the above-mentioned problems of the conventional assembly structure can be solved, and a long life can be achieved.

[0015]

The present invention will be described more specifically with reference to examples and comparative examples.

In order to evaluate the formability and shape retention of the hexagonal boron nitride raw material powder, first, the B value was 0.83,
Hexagonal and 50 wt% boron nitride powder is D _p50 is 16μm in 0.72,0.55, D _p50 mixed material (each of the 50 wt% hexagonal boron nitride powder 0.9 .mu.m,
Mixed raw material a, mixed raw material b, and mixed raw material c), a hexagonal boron nitride powder having a B value of 0.72 and a D _p50 of 13 μm, and a hexagonal boron nitride powder having a D _p50 of 0.9 μm. A raw material mixed with 50% by weight of elemental powder (this is referred to as a mixed raw material d); 50% by weight of hexagonal boron nitride powder having a B value of 0.72 and D _p50 of 16 μm; and D _p50 of 1.8 μm.
And a CIP pressure of 1000 kg using a mixed raw material (hereinafter referred to as mixed raw material e) with 50% by weight of hexagonal boron nitride powder of
Molded at f / cm ² .

As a result, when the mixed raw material a and the mixed raw material b were used, both the moldability and the shape retention were good, but when the mixed raw material c, the mixed raw material d, and the mixed raw material e were cracked, I couldn't be with my body.

Therefore, next, a high-filling hexagonal boron nitride powder having a B value of 0.83 and a D _p50 of 16 μm is used.
Moldability and shape retention were evaluated in the same manner using a mixed powder in which 0 wt% and a hexagonal boron nitride powder having a _Dp50 of 0.9 _μm were variously changed from 0 to 100 wt%. Table 1 shows the conditions and results.

[0019]

[Table 1]

Example 1 70% by weight of highly-filled hexagonal boron nitride having a B value of 0.83 and D _p50 of 16 μm, and 30% by weight of hexagonal boron nitride powder having a D _p50 of 0.9 μm Raw material powder (oxygen content 2.
After 0 wt%) was molded by CIP pressure 1000 kgf / cm ^2, under an argon atmosphere at 1800 ° C. under atmospheric pressure of 10
By firing for a time, a boron nitride sintered body was manufactured. Using the obtained boron nitride sintered body, an integrated setter having a shape of 500 × 125 × 8 mm was manufactured.

Next, ten extruded silicon nitride green sheets are stacked and placed on the setter, degreased at 500 ° C. in the air, and then dried in a nitrogen atmosphere.
Sintering was performed at 750 ° C. This operation was repeated on the same setter, and the state of the setter after sintering and the state of the lowermost silicon nitride sheet were sequentially observed.

Comparative Examples 1 and 2 From the boron nitride sintered body produced in Example 1, 125 ×
A 125 × 8 mm sintered body was cut out. These were combined by fitting (Comparative Example 1) or screwing (Comparative Example 2) to produce a setter of the same size as in Example 1, and the same sintering test as in Example 1 was performed. At this time, the silicon nitride green sheet was placed so as to cover the bonding portion of the setter.

The above results are shown in Tables 2 and 3.

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

According to the present invention, even a large hexagonal boron nitride sintered body having a maximum length of 450 mm or more can be easily manufactured. The hexagonal boron nitride sintered body manufactured by the present invention is suitable for manufacturing a large-sized ceramic firing setter having no joining structure such as fitting and screwing.

Claims (1)

[Claims] 1. A highly-fillable hexagonal boron nitride powder having a ratio of (area average diameter D _a ) / (50% volume cumulative particle diameter D _p50 ) of 0.6 or more and D _p50 of 15 μm or more is 80% by weight or less. , D
_A method for producing a hexagonal boron nitride sintered body, comprising molding and firing a raw material powder containing 20% by weight or more of hexagonal boron nitride powder having a _p50 of 1.5 μm or less.