JPH0438708B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a new method for producing ceramics, and is considered to be applicable to the production of all ceramics at a stage prior to sintering the ceramics.

(Conventional technology) Conventionally, the method for molding ceramic powder is as follows:
There are various methods such as press molding, injection molding, and rubber press molding, but press molding cannot produce large or complex shapes. Furthermore, in the injection molding method, it is difficult to remove the binder that is mixed together with the ceramic powder. Furthermore, in the rubber press method, the apparatus itself is large-scale, and it is impossible to mold products with complex shapes.

Methods proposed to solve these problems include JP-A-61-101447 ``Method for manufacturing ceramic molded bodies'' and JP-A 62-30654 ``Method for manufacturing ceramics''.

Among these two inventions, the use of methylcellulose, which is a type of gelling component, in a molding material having ceramic powder and a plasticizing component containing water and a gelling component that gels when heated, ester of _a polyhydric alcohol ether compound; a plasticizer or mold release agent of one or a mixture of propylene glycol and polyethylene oxide;
This invention uses a molding material made of a composition containing a specific amount of a solvent such as water, and thermally gels a gelling component in a molded article.

(Problems to be Solved by the Invention) However, these conventional techniques have the following problems.

Even if low molecular weight methylcellulose is used, it is difficult to increase the concentration of methylcellulose and also the concentration of ceramics. Furthermore, unless the concentration of methylcellulose is increased, the molded article will not solidify even when heated. Furthermore, if the concentration of ceramics is low, even if a green molded body is produced, it is difficult to make a sintered body with high density.

The property of a liquid in which methylcellulose is dissolved is that the viscosity increases at a temperature slightly lower than the gelling concentration, but the viscosity decreases again at temperatures above the gelling temperature. For this reason, strict temperature control of the mold is required.

In both inventions, the strength of the green molded product obtained is low, and when creating a product with a complicated shape, it is extremely difficult to remove it from the mold.

Both inventions use dissolved methylcellulose, which increases the viscosity at room temperature.
It was necessary to apply pressure to inject into the mold.

(Means for Solving the Problems) The present invention has been made by focusing on the above-mentioned problems. As a method for this purpose, a composition of 100% ceramic powder containing cellulose ether is used.
The slurry is made into a low-viscosity slurry by heating to a little less than 0.9°C, then poured into a mold, and solidified by cooling within the mold.

In this method, since the amount of organic binder contained in the ceramic is extremely small, the degreasing step for removing the binder can be almost omitted. Furthermore,
Injection into the mold can also be carried out by gravity, without the need for an injection machine or pressure device. Furthermore, the strength of the gelled product when cooled is extremely high, and products with complex shapes can be easily demolded.

Therefore, in this invention, in order to produce ceramics, ceramic powder, water, and cellulose ether powder are mixed and dispersed while being heated to a temperature higher than the gelation temperature of the cellulose ether, and the resulting ceramic slurry is used to produce the cellulose ether. This is achieved by injecting it into a mold cooled to below the gelling temperature of ether, solidifying it, taking it out as a molded body, and then sintering it in a furnace.

The cellulose ether used in this invention is
OH in glucose residues contained in cellulose
A group in which a portion of the group is substituted with one or more of methoxy, ethoxy, hydroxyethoxy, and hydroxypropoxy groups, and is soluble in cold water, but gels and precipitates in hot water. Say something that has properties. The degree of polymerization of cellulose ether and the degree of substitution of hydroxyethoxy groups and hydroxypropoxy groups, which govern the thermal gelation temperature, may have any value.

Examples of cellulose ethers include alkylcelluloses including methylcellulose, hydroxyalkylcelluloses including hydroxypropylcellulose, hydroxyalkylalkylcelluloses such as hydroxyethylmethylcellulose and hydroxypropylmethylcellulose, and hydroxylcelluloses including hydroxyethylhydroxypropylcellulose. Examples include alkylhydroxyalkylcellulose.

However, the smaller the particle size of the methylcellulose powder, the fewer the structural defects in the sintered body.

The type of ceramic powder used in this invention is, for example, in the case of silicon nitride, it may react with water and generate NH ₃ gas, but as long as it does not interact with water, it may be oxide-based or carbide-based. Not only can ceramic powders such as nitride-based ceramic powders alone, mixtures of two or more of these ceramic powders, and solid solutions thereof, but also metal-based powders be widely applicable.

Moreover, it is also possible to use surfactants, antifoaming agents, solvents, water-soluble polymers, etc. in combination without impairing the spirit of the invention.

As a manufacturing method for obtaining a ceramic slurry, water, ceramic powder, and, if necessary, a surfactant are mixed into a heated container, and the mixture is thoroughly dispersed and kneaded using a Henschel mixer, high-speed impeller mill, or the like. At this time, the temperature of the mixed liquid must be maintained at a temperature higher than the gelling temperature of the cellulose ether to be mixed subsequently. If the temperature is below the gelation temperature, the cellulose ether will dissolve and thicken, making it impossible to knead it with the above-mentioned apparatus. The amount of cellulose ether added is about several percent based on water, and needs to be slightly modified depending on the degree of polymerization of cellulose ether. That is, if the degree of polymerization is low, the amount added may be increased, and if the degree of polymerization is high, the amount added may be reduced.

The thoroughly kneaded slurry is then moved into a storage bottle while maintaining the heating temperature, where it is cooled and solidified. During molding, the slurry is heated to become flowable again, and a molded article can be obtained by injecting it into a cooled mold. At this time, the temperature of the mold must be kept below the gelation temperature of cellulose ether. If the temperature is too close to the gelling temperature, it will take a long time to solidify, but if it is cooled to room temperature or below, molding can be done in a short time. Regarding the injection method, equipment such as an injection machine, pressure casting, or compression molding can be used. However, the greatest feature of this invention is that if a suitable sprue is provided in the mold, molding can be performed simply by pouring heated ceramic slurry.

By the above method, the ceramic slurry of the present invention is solidified by being cooled in the mold,
It can be taken out as a molded body. Although this molded body contains water, it is strong and does not cause blisters or cracks even after drying the water and performing post-furnace sintering. During furnace sintering, the temperature increase rate is 600℃
There is no abnormality even if the temperature is increased up to 200℃/hour and the temperature exceeded 600℃ at 500℃/hour, and it is possible to further increase the heating rate depending on the shape, size, thickness, type of ceramic powder, etc. of the molded product. be.

The sintered body thus obtained has excellent dimensional accuracy and theoretical density ratio.

(Function) In this invention, when preparing a ceramic slurry, cellulose ether is used as a binder.
Methyl cellulose is typically used. Although the reaction mechanism of gelation is unclear, this cellulose ether behaves as a kind of powder in hot water, but when cooled, it solvates with the water in the ceramic slurry. At that time, it is thought that the dispersion water of the ceramics is rapidly taken away, resulting in an agglomerated state and solidification. Moreover, the ceramic slurry that has been cooled and solidified can be turned into a slurry again by heating, as long as water and evaporation are not present.

(Example) Hereinafter, it will be explained in detail using examples.

Example 1 100 parts by weight of aluminum oxide (purity 99.9%, average particle size 0.4μ) as ceramic powder, 2 ammonium salts of polymeric carboxylic acids as surfactants
Parts by weight, methylcellulose [Metrose 6OSH
4000, manufactured by Shin-Etsu Chemical Co., Ltd.] and 40 parts by weight of water were dispersed and mixed using a high-speed impeller mill in a container heated and maintained at 80°C to obtain a ceramic slurry. Next, the ceramic slurry kept at 80°C was manually poured into a mold that was kept or cooled at room temperature of 20°C and held for 1 minute.
Thereafter, it was taken out as a molded body, dried in a drying oven to remove moisture, and then subjected to oven sintering. The temperature schedule at this time is 200℃/hour up to 600℃, 600℃~
After heating at 1600°C at 500°C/hour and maintaining the temperature at 1600°C for 2 hours, it was cooled in a furnace and taken out as a sintered body. The density ratio of the sintered body is 99.6%, and the bending strength is 45Kg/mm ²
The dimensional accuracy was 0.5%. Of course, there was nothing abnormal about the exterior.

Example 2 Hydroxyethyl methylcellulose [Metrose] was used instead of methylcellulose used in Example 1.
SEB 04T, manufactured by Shin-Etsu Chemical Co., Ltd.] was used to create a ceramic slurry, and molding was performed using an injection machine in an injection mold with the same shape as in Example 1.
Injected at a pressure of 300Kg/ ^cm2 , other conditions were as in Example 1.
A molded body and a sintered body were obtained in the same manner as in the case of .
The sintered body obtained in this case had good performance values and good appearance.

Comparative Example 1 Using the same formulation as in Example 1, an attempt was made to knead this time using a high-speed impeller mill at a room temperature of 20°C, but the viscosity was too high and kneading was impossible. For this purpose, a kneader was used to perform dispersion kneading. The ceramic solid obtained by kneading had no fluidity at all, and it was impossible to pour it into a mold manually. Therefore, an attempt was made to use a plunger type injection molding machine to inject into a mold at 60°C, which is the gelling temperature of methylcellulose, hold it for 3 minutes, open the mold, and try to take out the molded product using the ejector mechanism, but the molding failed. Due to lack of physical strength, I lost my shape.
Sintering was not performed due to poor molding.

(Effects of the Invention) According to the method of the present invention, a ceramic slurry can be created with extremely low viscosity, so even if the shape of the ceramic sintered body to be manufactured is complex, molding is very easy. Since the molded body solidified by cooling has sufficient strength, it will not be damaged during demolding or during the drying process before sintering.

Additionally, the equipment required to create ceramic slurry can be small-scale, and impurities from entering the container wall, stirring blades, etc. during dispersion and mixing are extremely reduced, and high-quality ceramic sintered bodies can be produced. can get.

Furthermore, since the ceramic slurry of the present invention can be reversibly turned into liquid or solid, it is very easy to manage the slurry or change its molding application.

As described above, the present invention has many effects.

Claims (1)

[Claims] 1. Mix and disperse ceramic powder, water, and cellulose ether powder while heating above the gelling temperature of the cellulose ether to form a ceramic slurry, which is then heated to below the gelling temperature of the cellulose ether. A method for manufacturing ceramics, which comprises injecting the ceramic into a cooled mold, solidifying it, taking it out as a molded body, and then sintering it in a furnace. 2. The cellulose ether according to claim 1 is a cellulose in which some of the OH groups in the glucose residues contained in the cellulose are formed by one or more of methoxy groups, ethoxy groups, hydroxyethoxy groups, and hydroxypropoxy groups. A method for producing ceramics, characterized in that the composition is a substituted composition.