JPS6131343A - Manufacture of ceramic product - 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] [Industrial Application Field] The present invention relates to a method for manufacturing a ceramic product, which comprises a mixing step, a molding step, a degreasing step, and a sintering step. The present invention relates to a manufacturing method that prevents defects from occurring during degreasing.

[Prior Art] A method for manufacturing ceramic products includes, for example, blending ceramic raw material powder with a thermoplastic resin as a binder, molding this mixture by injection molding, etc., degreasing the obtained molded body, and then sintering it. There is a way to do it. This method has been adopted as a method for efficiently manufacturing products with complex shapes with good rust resistance. However, this method requires a degreasing step to remove the binder after molding. In order to prevent defects during degreasing, degreasing is carried out in a non-oxidizing atmosphere such as nitrogen gas or vacuum, and the heating rate is extremely slow, e.g. 2°C/hour, or at a relatively low concentration for 5 to 5 days. It was degreased by keeping it for several weeks.

[Problems to be solved by the invention] Conventionally, in injection molding methods for ceramic products, especially when manufacturing thick materials, the amount of gas generated during the degreasing process increases, internal stress is large, and cracks and blisters occur. In some cases, such defects may occur. In order to prevent this problem, it has been necessary to extremely slow down the temperature rise rate during degreasing, to keep the temperature at a constant temperature for a long time, or to degrease in an inert atmosphere such as nitrogen gas. Therefore, the degreasing process is expensive, and the yield and quality are unstable, and this problem has been a major obstacle to the practical application of injection molding methods for ceramics.

In view of the above-mentioned problems, the inventors of the present invention have discovered a method of reducing the occurrence of defects during degreasing as a result of intensive research, and have completed the present invention. That is, an object of the present invention is to provide a method for manufacturing a ceramic product that prevents defects from occurring during the degreasing process of a ceramic molded body.

Means for Solving Problem L] The present invention provides a method for manufacturing a ceramic product, in which a ceramic product is produced by mixing a lamic powder and an organic material, molding the mixture, degreasing the mixture, and then sintering the organic material. , a thermoplastic resin of which at least 10 vol % decomposes due to a depolymerization reaction when thermally decomposed in the atmosphere is present in 10 to 9 of 11 parts of 100 ffif of the organic material.
It is characterized by containing 0 parts by weight.

Here, as the ceramic powder, silicon nitride (Si3N
+), silicon carbide (s+c>), and in some cases aluminum nitride <AIN>, boron nitride (B
Nitride such as N), carbide such as titanium carbide (TiC), titanium boride (TiB2), zirconium boride (ZrB2)
borides such as, oxynitrides such as sialon, zirconia (Z
r02>, alumina (Al2O2), cordierite, barium titanate (BaT i○3), titanium oxide (1'
i 02 ) and the like can be used.

This ceramic powder may be used alone or as a mixture of two or more types of ceramic powder.

The above-mentioned ceramic powder is mixed with an organic material, and it is desirable that the mixture composition contains 70 to 90% by weight, particularly 76 to 85% by weight of ceramic powder. When the ceramic powder is less than 70% by weight, it is difficult to obtain a ceramic product with a desired density, and when it exceeds 90% by weight, injection molding becomes difficult. Further, the particle size of the ceramic powder is preferably within a range of 5μ at the most,
A range of 0°1 to 2.0μ is particularly desirable. At the same time, the surface area of the ceramic powder is preferably in the range of 1 to 100 m2/Q, particularly preferably in the range of 5 to 20 m'/Q.

The organic material mixed with the ceramic powder has the role of imparting fluidity to the mixture during molding, covering the ceramic powder to protect the molding equipment, and sufficiently bonding the molded product to maintain its shape. ing.

Therefore, it is desirable that the organic material is a thermoplastic material. However, the organic material is almost unnecessary for the final product, and it is preferable that it be easily decomposed and vaporized in the degreasing process, and preferably have a decomposition temperature of 150 to 500°C.

The feature of the present invention lies in the composition of the above organic material. In other words, the main feature of the organic material is that it contains a thermoplastic resin (hereinafter referred to as depolymerizable resin), at least 10vol% of which decomposes through a depolymerization reaction when thermally decomposed in the atmosphere. A typical example of this depolymerizable resin is polyisobutylene.For example, polyisobutylene is popular, and even if it is thermally decomposed, there is little oxidative decomposition; The amount of gas generated during decomposition is extremely small compared to other thermoplastic resins.The present invention was made in view of this point.In other words, depolymerizable resins such as polyisobutylene are incorporated into the above organic materials. It is characterized by containing 10 to 901% by weight.If the depolymerizable resin is less than 10% by weight, the effect cannot be achieved and defects such as blistering and cracking may occur during degreasing. If the amount exceeds 90% by weight, the strength of the molded product during injection molding will be low, and cracks may occur in the molded product when taken out from the mold.

Therefore, the proportion of depolymerizable resin in the organic material is 10~
It is desirable that it be 90%.

One of the most important features of the present invention is that the organic material contains 20 to 80 parts by weight of paraffin or wax. The volatilization temperature of this paraffin or wax needs to be lower than the decomposition temperature of the thermoplastic resin contained in the organic material, and is preferably in the range of about 50°C to about 190°C. Paraffin or wax is a thermoplastic substance that functions as a binder and evaporates at a lower temperature than the decomposition temperature of thermoplastic resin, so it uniformizes the decomposition and vaporization of organic materials during degreasing, prevents sudden changes, and improves degreasing. It has the effect of relieving stress that is sometimes applied to ceramic products. If the paraffin or wax content is less than 20% by weight, the effect may not be achieved and defects such as blistering and cracking may occur during degreasing, and if it exceeds 80% by weight, molding during injection molding may occur. The body strength is low, and cracks may occur when removed from the mold, and problems may arise in the dimensional stability of the molded product.

Organic materials include depolymerizable resins and conventionally used thermoplastic resins in addition to paraffin and wax.

A mold release agent, a plasticizer, etc. can be used. Examples of this thermoplastic resin include polyethylene, atactic polypropylene, polypropylene, ethylene-vinyl acetate copolymer,
Examples include polybutadiene, styrene-7tadiene copolymer, polystyrene, α-methylstyrene, acrylic resin, methacrylic resin, and one type or a mixture of two or more of these can be used. Mold release agents include stearic acid, etc.
Examples of plasticizers include diethyl phthalate and dibutyl phthalate. Further, oil such as vegetable oil or mineral oil may be added if necessary. These organic materials are not particularly limited, and conventionally used organic materials can be used in the same amount as conventionally.

The characteristic step in the manufacturing method of the present invention is the degreasing step, and the other steps can be performed in the same manner as conventional methods. That is, the ceramic powder and the organic material, which is a feature of the present invention, are hot mixed and pelletized in the same manner as in the prior art. This pellet is fed to an injection molding machine or the like and molded in the same manner as before. Degreasing of the molded body may be carried out in an air atmosphere or in a non-oxidizing atmosphere such as nitrogen gas, but in view of workability, cost, etc., it is desirable to carry out the degreasing in an air atmosphere as it has many advantages. In addition, 4 of the degreasing process
There is no need to extremely slow down the heating rate or keep it warm for a long time at a relatively low temperature, as in the past, and it is degreased by heating to 5-450°C. The degreased molded body is sintered at a predetermined temperature r in the same manner as in the past to produce a ceramic product.

The manufacturing method of the present invention is mainly applied to injection molding, but any manufacturing method that includes a degreasing step can be applied not only to injection molding.

[Effect]

When the degreasing step of the @I manufacturing method of the present invention is carried out in a popular atmosphere, paraffin or wax begins to volatilize and separate from the molded product from about 150° C. when the temperature starts to rise. The temperature further rises to about 00℃~250℃
At this point, other organic materials begin to decompose and the temperature reaches approximately 400°C to 5°C.
Degreasing is completed at 00°C. During this time, the depolymerizable resin is mainly decomposed and vaporized by depolymerization reaction, and oxidative decomposition reaction is small. Therefore, the amount of gas generated is extremely small compared to conventional manufacturing methods, and therefore the risk of defects such as bulges and cracks in the ceramic molded body due to volume expansion is extremely reduced. Further, during the degreasing process at about 50°C to about 500°C, the organic material decomposes and evaporates on average, and the weight gradually decreases. Therefore, the internal stress of the Hiramic product is reduced, and the risk of defects is further reduced.

[Example〕 The manufacturing method of the present invention will be explained below with reference to Examples.

80% by weight of silicon nitride (3i3N4) powder with an average particle size of 0.7μ, 10% by weight of wax with a melting point of 60°C (manufactured by Nippon Oil), and 6% by weight of polyiso-1-tyrene (manufactured by Shiraishi Chemical) with a weight average molecular weight of 80,000. Add 4 parts by weight of high-density polyethylene (manufactured by Mitsui Polychemicals) with a softening point of 120°C or higher and knead in a high-temperature kneader at 170°C for 2 hours, then remix and pelletize using a twin-screw high-temperature extruder. .

Next, using an injection molding machine at 170℃, 500kg/cmt
Injected into a mold under the following conditions, width i 5mm, height 15mm
A rectangular parallelepiped molded body having a length of 7 Qmm was manufactured. This molded body was heated from 20°C to 4°C at a heating rate of 8°C/hour in the air.
It was degreased for 50 hours up to 00℃. The average weight loss during degreasing was 17.5% by weight, that is, degreasing was almost completed under the above conditions. When the surfaces of the obtained degreased bodies were observed with the naked eye, no cracks or blisters were observed on the surfaces of all 30 pieces, indicating that the degreased bodies were in good condition. Furthermore, X-ray inspection was conducted to investigate the internal condition, but no internal defects were found in all 30 pieces.

When this degreased body was sintered by keeping it at 1750° C. for 4 hours in a nitrogen gas atmosphere, a good sintered body with a specific gravity of 3.21 was obtained.

Next, as a comparative example, degreasing was performed using a conventional manufacturing method. That is, instead of polyisobutylene, the softening temperature is 120°C.
The same materials as in the example were used, except that the same weight percent of ethylene-α olefin copolymer (Chiba Fine Chemicals) was used, and cross-wire, pelletization, and injection molding were carried out in the same manner as in the example to produce a product with the same shape as in the example. A total of 30 molded bodies were produced. This molded body was degreased under the same conditions as in the example, and the weight loss during degreasing was 17.5% by weight on average, that is, the degreasing was almost completed under these conditions. The obtained degreased body was 30
In all of the degreased products, R bubbles were generated from the center of the degreased body, and blisters and cracks were generated on the surface, resulting in defective degreased products.

The figure shows the thermal decomposition curve of polyisobutylene used in the examples. The conditions are 10℃ in the air atmosphere.
The heating was carried out by heating from room temperature to 450° C. at a heating rate of /min. In the figure, from TG curve 1, polyisobutylene is 2
Thermal decomposition occurs approximately in proportion to temperature in the range of 60°C to 390°C. Since almost no exothermic reaction peak was observed on the DSC80 curve, it can be seen that most of this decomposition is due to depolymerization decomposition rather than oxidative decomposition. Furthermore, when the gas produced during thermal decomposition was analyzed by gas chromatography, it was found that the products from depolymerization and decomposition accounted for about 9Qvo 1% of the produced gas. That is, it is clear that most of polyisobutylene is decomposed by depolymerization and decomposition during thermal decomposition.

It is clear that the results of the above examples are due to the effect of polyisobutylene, and the reason for this can be explained by the depolymerization and decomposition of polyisobutylene from the thermal decomposition results shown in the figure. That is, the method of manufacturing a ceramic product of the present invention can prevent defects from occurring during the degreasing process.

[Effects of the Invention] By applying the method for manufacturing ceramic products of the present invention, products that were conventionally degreased in a non-oxidizing atmosphere such as nitrogen gas or vacuum can now be degreased in the air. Furthermore, there is no need to make the temperature increase rate extremely slow, and there is no need to maintain the temperature at a relatively low temperature for a long time, making it possible to degrease in a shorter time than in the past. Therefore, in the method for manufacturing a ceramic product of the present invention, it is possible to supply a product with stable yield and quality for these reasons, and it is possible to reduce the cost of the degreasing process.

[Brief explanation of the drawing]

The figure shows the thermal decomposition of polyisobutylene used in the example.
It is a diagram showing a TG convex curve and a DSC curve. 1...TG convex curve...DSC curve Patent applicant Nippondenso Co., Ltd. Agent Patent attorney Hirodo Okawa Patent attorney Shudo Fujitani Patent attorney Akio Maruyama

Claims (5)

[Claims] (1) In a method of manufacturing a ceramic product in which a ceramic powder and an organic material are mixed, the mixture is molded, degreased, and then sintered to produce a product, the organic material has at least 1. A method for producing a ceramic product, characterized in that 10 to 90 parts by weight of a thermoplastic resin, of which 10 vol % decomposes through a depolymerization reaction, is contained in 100 parts by weight of the organic material. (2) The method for manufacturing a ceramic product according to claim 1, wherein the thermoplastic resin is polyisobutylene. (3) The organic material contains paraffin or wax from 20 to
A method for producing a ceramic product according to claim 1, wherein the content is 80% by weight. (4) The method for manufacturing a ceramic product according to claim 3, wherein the volatilization temperature of the paraffin or wax is lower than the decomposition temperature of the thermoplastic resin. (5) The method for manufacturing a ceramic product according to claim 1, wherein the degreasing step is performed in an atmospheric atmosphere.