JPS62191474A - Method of dewaxing ceramic green formed 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 Field of Industrial Application The present invention relates to a method of degreasing performed as a pre-sintering step when producing a ceramic sintered body by sintering a ceramic green molded body.

Conventional Technology When manufacturing ceramic sintered bodies, the removal of organic forming aids (i.e., degreasing) from the ceramic green molded body before sintering is an extremely important process, and it is difficult to ensure that the degreasing is uniform. This is a very important factor in determining the quality of the product after sintering. Therefore, how to perform degreasing and how to operate to achieve uniform degreasing are extremely important issues, and many proposals have been made regarding degreasing methods.

For example, in Published Patent Publication No. 11271/1980,
A method is described in which a ceramic green molded body is placed in an activated carbon incubator J-, and an adsorbent (e.g., activated carbon) wrapped in a mesh belt is placed on top of it at a certain distance and heated, and is disclosed in Japanese Patent Publication No. IV. (60-46972
The issue describes a method in which natural graphite particles are placed between a ceramic green molded body and a graphite table on which it is placed and then heated. Also, published patent publication No. 60-118664
No. 1, No. 2003-11-113 describes a method of degreasing a ceramic green molded body by embedding it in a degreasing agent having an aggregate structure made of a ceramic material and heating it. According to this method, the organic molding aid released from the ceramic green molded body does not accumulate at a particularly high concentration even in the portion of the degreasing material (or adsorbent) surrounding the ceramic green molded body that is close to the molded body. It is stated that a degreased ceramic body with fewer defects such as cracks and blisters can be obtained.

Problems to be Solved by the Invention However, even with these methods, it is necessary to delicately control the temperature increase rate in the degreasing process, the type of gas around the atmosphere, the pressure, the flow rate, etc.
Degreasing is extremely difficult, and it is extremely difficult to produce a perfect ceramic fired product obtained by firing after degreasing.

Many conventional degreasing methods rely exclusively on the evaporation of organic forming aids in ceramic greens at high temperatures, resulting in low humidity in the temperature range where the vapor partial pressure of these materials is high. Alternatively, while the inventors had paid attention to the control of the carrier gas, the inventors discovered that the adsorbent material surrounding the ceramic green compact, in particular the adsorption force of fine graphite powder at low temperatures, and at temperatures above approximately 250°C. However, even if degreasing progresses, the degree of deformation of the ceramic green molded body is extremely small, and furthermore, at temperatures above 300°C, the molded body shrinks again due to thermal decomposition of the non-volatile organic pinter and ceramic organic precursor. The present invention was developed based on the discovery that in this case, the shrinkage occurs evenly, and almost no distortion or damage occurs due to the shrinkage.

That is, the present invention provides a method for heating and degreasing a ceramic green molded body obtained by molding a mixture containing a ceramic powder, an organic lubricant, and a ceramic organic precursor or/and an organic binder. The ceramic green molded body is embedded in fine powder of a substance having a one-year-old strength (hereinafter referred to as "adsorbent fine powder"), and the organic lubricant and ceramic organic precursor formed in the ceramic green molded body. or/and 'fE 'j(
This is a method for degreasing a ceramic green molded body, which is characterized by heating until the temperature becomes almost constant, and then increasing the temperature further to complete the degreasing. The constituent elements of the present invention will be explained in detail below.

(Ceramics Powder) Examples of the ceramics powder in the present invention include silicon carbide, titanium carbide, boron carbide, boron nitride, silicon nitride, titanium oxide, zirconium oxide, aluminum oxide, zirconium oxide, Titanium oxide, barium titanate, aluminum silicate, sialon, nisilite,
Examples include powders such as mullite, but are not limited to these, and two or more of these can also be used in combination.

(Organic Lubricant) Examples of the organic lubricant in the present invention include low molecular weight polyolefins, paraffin wax, metal soaps, saturated or unsaturated higher fatty acids, their esters or amides, and higher alcohols.

(Organic binder) Organic binders include substances added to maintain shape or impart viscosity, such as polyethylene, polypropylene, polybutadiene, polystyrene,
polyacrylic ester, polymethacrylic ester,
Phenolic resin, polyvinyl alcohol, low molecular weight polyolefin.

Examples include paraffin wax and higher fatty acids, but are not limited to these.

(Organic Precursor for Ceramics) Examples of organic precursors for ceramics include borazine polymers having organic groups, carbosilazane resins, polysilastyrene described in Published Patent Publication No. 58-500717, and Polycarbosilane used in the invention No. 59-174575 or JP-A-59
Examples include, but are not limited to, olefin-containing polysilastyrene described in Japanese Patent No. 210940.

When the ceramic powder used is silicon carbide powder, the combination of using the above-mentioned organosilicon compound as an organic precursor and using a higher fatty acid as a lubricant gives very good results. However, the combination of ceramic powder and ceramic organic precursor is not necessarily limited to those of the same type.

(Mixture that is the source of ceramic green) The mixture that is the source of the ceramic green molded body in the present invention is a mixture that is a mixture of ceramic powder, an organic lubricant, a ceramic organic precursor, or/and an organic binder, and an organic lubricant such as toluene. By mixing well in a volatile inert solvent that dissolves the agent and the ceramic organic precursor, and volatilizing the solvent while kneading, or by uniformly kneading the above various components while heating. In addition to the above-mentioned components, this mixture may optionally contain, for example, an inorganic or organic sintering aid, or the above-mentioned polymeric plasticizer.

(Adsorptive fine powder) As the adsorbent fine powder in the present invention, for example, activated carbon,
graphite, silicon carbide, silicon nitride, boron nitride,
Examples include fine powders such as calcined vermiculite.

(Usage ratio) The usage ratio of organic lubricant, organic binder, and ceramic organic precursor to ceramic powder depends on the type of ceramic powder, average particle size, particle size distribution, or organic lubricant,
It cannot be determined uniquely by the type of ceramic organic precursor, organic binder, etc. Generally, when the average particle size of ceramic powder is small, that is, when the specific surface area is large, it is necessary to use a large proportion of ceramic powder, and as the average particle size increases, the optimum proportion of its use decreases. When the ceramic powder is silicon carbide powder, the organic lubricant is a higher fatty acid, and the ceramic organic precursor is polycarbosilane, the silicon carbide powder has an average particle size of 6 JLm and a specific surface area of 21T+'7g. In this case, the total amount of higher fatty acids and polycarbosilane used per long silicon carbide powder is suitable to be 5 to 20 g, and the average particle size of the silicon carbide powder is 0.27 uLm and the specific surface area is 17.7 m'. /g, silicon carbide powder 1
A suitable total usage ratio of higher fatty acids and polycarbosilane to 00g is 10 to 30g. And in this case,
The ratio of higher fatty acids and polycarbosilane is 1:2 to 2:l
is appropriate.

(Operation method) In the present invention, first, a ceramic green molded body is embedded in an adsorbent fine powder stored in a container, and then the organic lubricant in the ceramic green molded body and the ceramic organic precursor or/and and above the melting point of the phase mixture with the organic binder and below 150°C, preferably 80°C
Heating is carried out at a temperature of ~100°C, and at this time, a part of the mixture of the organic lubricant and the ceramic organic precursor or/and the organic binder flows out of the molded body and is adsorbed by the adsorbent fine powder. At the same time, a part of the evaporable components in the organic lubricant and organic binder are volatilized by the adsorption power of the adsorbent fine powder and are adsorbed by the adsorbent fine powder. Therefore, the organic lubricant and the binder are uniformly degreased in all directions without boiling in the molded body. In this way, as the degreasing progresses, a layer of adsorbed organic lubricant, organic ceramic precursor, or organic binder is formed surrounding the compact in the part of the adsorbent fine powder close to the compact. A large number of continuous micropores are formed inside. Eventually, even if you continue heating at that temperature,
No decrease in the weight of the molded body is observed. This is approximately 30 to 50 hours after the start of heating. The amount of degreasing at this stage can be adjusted depending on the type and amount of components constituting the ceramic green molded body, the type of adsorbent material, etc., and in many cases it is 2 to 5 times the weight of the molded body. % or more, and a considerable amount of the organic lubricant, ceramic organic precursor, or organic binder remains in the molded article.

At this stage, the weight of the molded body has decreased by about 2 to 10% from that before heating.

If heating is continued while increasing the concentration, the adsorption ability of the adsorbent substance decreases, and the organic lubricant or organic binder is transferred to the outside of the adsorbent fine powder from the adsorption layer that had formed near the compact. and the concentration of organic substances in that layer decreases.

Organic substances also begin to be degreased from the molded body. However, at temperatures above about 200°C, ceramic green loses its internal lubricity, and therefore, even if degreasing occurs above this temperature, shrinkage and deformation of the molded body are extremely difficult to occur, and the inside of the molded body has many continuous pores, so even if the temperature is raised rapidly, the molded product will not be distorted, damaged, or destroyed due to rapid volatilization or boiling of the organic lubricant or organic binder.
Degreasing is almost completed when the temperature reaches 450°C.

After degreasing, the compact is further heated to a high temperature for sintering. The organic lubricant, organic binder, or ceramic organic precursor remaining in ceramic green is
In many cases, decomposition begins to occur at temperatures above 350°C, and the molded product shrinks in shape as ff1ffi decreases.
At this time, the shrinkage progresses evenly, so distortion, damage, or destruction of the molded product hardly occurs.

The progress of degreasing has been explained in each stage above, but in industrial production, sintering is completed by continuously heating and increasing the temperature without removing the adsorbent material from the compact midway through production. let Alternatively, the degreasing step, which requires a long time, and the sintering step, which requires high temperature, may be performed using separate heating devices.In the sintering step, the adsorbent fine powder surrounding the compact is not necessarily required.

When a ceramic organic precursor is used in the ceramic green molded body in the above-mentioned process, 15
Preferably, the heating at a temperature of 0° C. or higher is carried out in an inert gas atmosphere.

Further, it is preferable to cover the container in which the adsorbent fine powder is stored in order to keep the adsorption layer stable.

Examples Example 1 A borophenylsiloxane compound was added to polydimethylsilane prepared by dechlorinating and condensing dimethyldichlorosilane with metallic sodium in xylene to give about 40%
10 parts by weight of polycarbosilane (melting point is 70 to 80°C), which is an organosilicon compound synthesized at 0°C, and 10 parts by weight of stearic acid (grade 1 reagent) are dissolved in 100 parts by weight of toluene, and silicon carbide is dissolved in 100 parts by weight of toluene. Base powder (manufactured by IBIDEN Co., Ltd., "Beta Random Ultra Fine" average particle size 0.27 pm)
, specific surface area 17.7 d/g, cumulative weight% on 7 At.
is 68%. ) was added at 80°C, and the toluene was volatilized while kneading in a mortar to obtain a granular mixture. This granular mixture was applied to an injection molding machine to form a 35mm x 35mm
A ceramic green molded body in the shape of a rectangular plate with a diameter of 5 mm was manufactured. The melting point of the mixture of polycarbosilane and stearic acid used in this case was approximately 55°C. 200mm x 200mm x 100maz7) A tin can was filled with graphite powder with a particle size of 100 to 200 mesh, and the above green molded body was placed in it. 48 sheets were buried, placed in a dry base with a lid, and heated from 55°C to 100°C at a rate of 10°C/h, and kept at a temperature of approximately 100°C for 50 hours. When the molded product was taken out at this stage (first stage), there were no cracks or bends in the molded product, and the weight was 5.5%.
The weight has been reduced by 0% ± 0.1%, and the length of the − side is 3.0 ± 0.
．． It was down 1%.

The same ceramic green molded body as above was heated to the first stage in the same manner as above, then heated to 600°C at a rate of 5°C/h in nitrogen gas, and further heated to 50°C.
The mixture was heated to 1250°C at a rate of /h. At this stage, the weight loss of the molded body was 12±1.5% (relative to the ceramic green molded body).

The same applies hereafter), and the change in dimensions was 5.0±0.2%. These molded bodies were further heated to 160°C in an argon stream.
Firing was completed by heating to 0°C.

As a result, the dimensions of the molded body did not change, but the weight increased by 1.
There was a decrease of 6.5±0.2%. Note that among the 48 molded products, there were 2 defective products.

Example 2 Silica nitride powder (average particle size is 0.6 gm) 77
Parts by weight, 3 parts of magnesia powder, 1 part of polyethylene resin
04IQ part and stearic acid! Off! A ceramic green molded body was prepared in the same manner as in Example 1 using a mixture obtained by heating and kneading 1 part of , 'j.

This ceramic green molded body was embedded in graphite powder and heated in the same manner as in Example 1. Heating was maintained at a temperature of 100°C for 25 hours, then raised to 600°C over 25 hours, further raised to 1600°C over 10 hours, and taken out after cooling. 1 defective product out of 48 molded products
It was.

Example 3 CHS from methyltrichlorosilane and methylamine
i(N HCH3) 3 was synthesized and heat treated at 520°C to produce a carbosilazane resin. 70 parts by weight of this carbosilazane resin, 10 parts by weight of stearic acid, 4OffiM parts of silica nitride powder (same as above) and 40 parts by weight of silica carbide powder (same as above) were kneaded in toluene. was evaporated to create a mixture that would become the basis for a ceramic green molded body.

Using this mixture, molding, degreasing, and sintering were performed in the same manner as in Example 1 to produce a silicon carbide-silicon nitride composite sintered body. All 48 molded bodies were good products.

Effects of the Invention According to the method of the present invention, distortion and damage in the degreasing process of ceramic green molded bodies can be easily avoided,
As a result, a ceramic sintered body can be produced with good yield.

Claims (3)

[Claims] (1) Adsorption capacity stored in a container when heating and degreasing a ceramic green molded body obtained by molding a mixture containing a ceramic powder, an organic lubricant, and a ceramic organic precursor or/and an organic binder. embedding the ceramic green molded body in fine powder of a substance having And 1
A method for degreasing a ceramic green molded body, which comprises heating the ceramic molded body at a temperature of 50° C. or lower until the weight of the ceramic molded body becomes almost constant, and then further raising the temperature to complete the degreasing. (2) Claim 1 consisting of the ceramic powder being a silicon carbide powder, the organic lubricant being a higher fatty acid, and the ceramic organic precursor being an organosilicon compound.
A method for degreasing a ceramic green molded body as described in . (3) Claim 1 or 2 in which the fine powder of the substance having adsorption ability is fine graphite powder.
A method for degreasing a ceramic green molded body as described in .