JPS61101447A - Manufacture of ceramic 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 [Industrial Field] The present invention relates to a method for manufacturing a ceramic molded body.

The present invention can be used particularly in the automobile industry, ceramics industry, etc., which have relatively complex shapes and require large quantities of ceramic sintered bodies.

[Prior Art] Injection molding and slip casting are known as methods for manufacturing ceramic molded bodies with relatively complex shapes.

In the injection molding method, ceramic powder is mixed and kneaded with a binder consisting of resin such as polyethylene or polystyrene and wax, and this mixed raw material is molded by injection molding, which is commonly known as a molding method for plastics. This method involves degreasing the molded body and producing a pudding-compact ceramic molded body. The slurry is poured into a mold, and the plaster mold absorbs water, forming a ceramic molded body on the surface of the mold. After being removed from the plaster mold, it dries to obtain a pudding compact ceramic molded body. .

[Problems to be Solved by the Invention] The conventional injection molding method described above requires a long degreasing time under strict temperatures of 100 to 400 hours in the degreasing step of the injection molded article obtained by injection molding. In other words, injection molding requires a long time to produce ceramic molded bodies;
There are many problems in terms of quality control.

On the other hand, in the slip casting method, it is easy to make a stable slurry when the particle size of the ceramic powder is relatively large, but it uses extremely fine ceramic powder such as the recent submicron particles, and It is difficult to make a stable slurry of ceramic powder containing .

In addition, the molding speed is slow, and in order to obtain a large quantity of ceramic molded bodies, a large number of plaster molds are required, resulting in productivity problems.

The object of the present invention is to provide a new method for manufacturing and processing ceramic molded bodies that does not have the drawbacks of these conventional manufacturing methods.

[Means for Solving the Problems] The method for producing a ceramic molded body of the present invention includes a first step of obtaining a molding raw material containing ceramic powder and a plasticizer containing water and a gelling component that gels when heated. , a second step of bringing the molding raw material into contact with a mold surface before gelation of the gelling component to obtain a first molded body; holding the first molded body at a high temperature to remove the gel in the first molded body; a third step of gelling the chemical component to obtain a hardened second molded body; and a fourth step of heating the second molded body to remove the plasticizer and obtaining a third molded body made of ceramic powder. It is characterized by being carried out sequentially.

In the manufacturing method of the present invention, water is used as the main substance that imparts plasticity to the molding raw material. While this water is functioning sufficiently as a plasticizer, the molding raw material is brought into contact with the mold surface and molded into a predetermined shape. Thereafter, when heated, the gelling component contained in the plasticizer, which gels when heated, gels, thereby reducing the plasticity of the molded article and hardening it, thereby improving handleability. After this, water, gelling components, and plasticizers other than gelling components are removed by drying, heating, etc.
A molded body made of ceramic powder is obtained.

Since the present invention uses a plasticizer mainly composed of water in place of the binder used in conventional injection molding methods, the plasticizer can be easily removed during conventional degreasing. Therefore, in the method of the present invention, vM3! Time is shortened and manufacturing management becomes easier.

[Detailed Description of the Structure of the Invention] The method for producing a ceramic molded body of the present invention includes a first step of obtaining a molding raw material, a second step of molding the molding raw material with a mold to obtain a first molded body, and a first molded body. Achieved by sequentially carrying out the third step of gelling the gelled component inside to obtain a hardened second compact, and the fourth step of removing water and plasticizer to obtain a third compact made of ceramic powder. be done.

The first step, the step of obtaining a molding raw material, is a step of obtaining a molding raw material containing ceramic powder, water, and a plasticizer containing a gelling component that gels when heated.

As the ceramic powder, in addition to conventional oxide-based ceramic powders, powders of nitrides such as silicon nitride and aluminum nitride, carbides such as silicon carbide, and other borides, which are known as new ceramics, can be used. Ceramic powders having particle sizes in a wide range from microns to nabumicrons in diameter can be used.

The main parts of the plasticizing component are water and a gelling component that gels when heated. Water exists between particles of ceramic powder and facilitates movement between particles.

The gelling component takes the form of a solution or a fluid paste at low temperatures, and when heated, it gels and has the effect of solidifying and hardening the ceramic powder. As the gelling component, methylcellulose or the like can be used. In addition to the gelling component, water-soluble polymers such as organic substances such as polyvinyl alcohol, polyethylene glycol, and polyacrylic acid amide, and gelling components that have already been gelled can be used.

These impart appropriate viscosity to the molding raw material, and impart fluidity, shape retention, etc. to the first molded body.

The blending ratio of the molding raw materials varies depending on the particle size of the ceramic powder, etc., but when the entire molding raw material is 100% by volume, the ceramic powder is 40-60% by volume, and the water is 20-60% by volume.
40% by volume, and the gelling component is about 5-20% by volume.

When the blending ratio of ceramic powder decreases, the shrinkage of the obtained ceramic molded body increases, making it difficult to obtain a ceramic molded body with high dimensional accuracy. On the other hand, if the blending ratio is too high, the viscosity of the molding raw material becomes too high, which impairs moldability. Regarding the mixing ratio of the gelling component, if it is too large, the crosstalk with the ceramic powder tends to be poor and it is difficult to obtain a homogeneous molding raw material.On the other hand, if it is too small, such as 5% by volume or less, it tends to be difficult to obtain a homogeneous molding material. Also, the hardness of the molded product is low, making it inconvenient to handle.If the proportion of water is too high, cracks tend to appear during drying, while if it is too low, the viscosity of the molding raw material becomes high, resulting in poor moldability. .

Points A and B in FIG. 1 show suitable blending ratios of ceramic powder, water, and a plasticizer containing a gelling component.

The trapezoidal range surrounded by C and D is a preferable range.

The molding raw material is obtained by mixing the above-mentioned ceramic powder and a plasticizer and kneading the mixture. This molding raw material is usually in a state called clay.

The second step is a step of bringing the molding raw material into contact with the mold surface to obtain a first molded body.

Molding molds include injection molds used for ceramic injection molding, extrusion molds used for ceramic extrusion molding, press molding for press molding, which is one of the traditional molding methods for tableware, etc. can be used. As for the molding method, the same methods as conventional ceramic molding methods such as injection molding, extrusion molding, and press pressing can be used.

In the second step, the molding raw material must be in a state before the gelling component gels. However, it may be the case that gelation has partially started. In this case, the plasticity of the molding raw material must not be impaired due to gelation.

The third step is to gel the gelling component contained in the first molded body.

The gelation of the gelling component in this gelling step is mainly caused by heat. That is, gelling components are gelled by maintaining the temperature at or above the gelling temperature. For example, by gelatinizing starch, water adsorption increases and a large amount of water can be retained.

Heating can be employed as a method of maintaining the temperature at a high temperature.

The heating may be performed by heating the mold itself used when molding the first molded body, and heating the first molded body through the mold. However, in the case of heat transfer, the heat is transmitted from the surface of the first molded body, and it takes a relatively long time for the heat to be transmitted to the inside of the molded body. For this reason, a heating method such as high-frequency heating in which both the surface and the inside of the molded body are heated at the same time is preferable. If the first molded body has extremely high plasticity and is difficult to take out from the mold, it is preferable to heat the first molded body within the mold to gel it. In addition, by making the molding mold from a material with a low dielectric loss coefficient, such as ceramics, resin, fluorocarbon resin, etc., and heating the first molded body together with the molding mold by high frequency,
It may be gelled. Even when obtaining the first molded body by extrusion molding, the extrusion mold is heated to promote partial gelation during extrusion molding, and the molded body released from the mold is continuously heated using high-frequency heating, etc. It is also preferable to do so. Due to gelation, the first molded body loses its plasticity, and becomes a second molded body that is relatively hard and easy to handle.

In the fourth step, the plasticizing component is removed from the second molded body by heating or the like. This fourth step is mainly accomplished by heating. Due to the heating, water is vaporized and evaporated from the second molded body. Furthermore, plasticizers, water-soluble binders such as polyvinyl alcohol, etc. are removed by thermal decomposition or thermal decomposition and oxidative decomposition. The removal of plasticizers, binders, etc. is similar to the degreasing of conventional ceramic injection molded bodies. However, in the case of the present invention, since water is used as the main component of the plasticizer, after the water evaporates, low molecular weight components of decomposed organic substances come out of the molded article. Also, the amount of organic matter blended is relatively small. For this reason, the fourth step of the present invention takes an extremely short time compared to the conventional degreasing step.

[Effects of the Invention] In the method for manufacturing a ceramic molded body of the present invention, water is mainly used as a plasticizer for ceramic powder. Therefore, the removal of the plasticizer is relatively easy, compared to the degreasing process of conventional ceramic injection molding.
The plasticizer can be removed in an extremely short time. Further, in order to eliminate the plasticity of the first molded body formed by the mold, a gelling component is included in the plasticizer to gel the gelling component. For this reason, the ceramic molded body (second molded body) after gelation has relatively high hardness and is easy to handle.

[Example 1] A composition of 47% by volume of silicon nitride powder with a particle size of 0.75μ containing a sintering aid, 36% by volume of water, 12% by volume of methyl cellulose, and 5% by volume of starch was mixed, and thoroughly mixed in a kneader. The mixture was kneaded to prepare a molding raw material.

Next, FIG. 2 shows a perspective view of the central axis with a diameter of about 15 mm and a thickness of about 1 mm that protrudes from the central axis on both sides.
A rotating test specimen with 5 mm thin blades was molded using a plunger injection molding machine.

Here, a phenol resin mold was used as the mold. A metal frame was incorporated into a phenolic resin mold to withstand the pressure during injection molding. After molding, the molded body obtained together with the phenolic resin mold was heated for 20 seconds using a conventional microwave oven, and the molded body was heated to about 75°C. As a result, a relatively hard second molded body was obtained. This second molded product had sufficient hardness even when removed from the phenol resin mold and was easy to handle. Next, this second molded body was heated at 110°C for 15 hours, and then heated to 45°C for 2 hours.
The temperature was raised to 0° C. to remove the plasticizer, and a ceramic molded body made of ceramic was obtained.

In addition, the obtained ceramic molded body was heated in a nitrogen gas atmosphere for 1
Sintering was performed at 750° C. for 4 hours to obtain a ceramic sintered body. The obtained ceramic sintered body showed no defects such as cracks.

[Example 2] Zirconia powder partially stabilized with ittria (specific surface area: 15 m''/a), methyl cellulose, polyvinyl alcohol, starch and water were blended in the proportions shown in Table 1, and kneaded in a kneader to form a forming raw material. Using this molding raw material,
A combustion chamber of a direct injection diesel engine having an outer diameter of 60 mm, a depth of 25 mm, and a wall thickness of approximately 10 mm, whose cross-sectional view is shown in FIG. 3, was molded to obtain a first molded body. This molding uses an outer mold made of polycarbonate and an inner mold made of metal, and is press-molded using a press machine in which the inner mold rotates. After press molding, the outer polycarbonate mold and the obtained mold were removed from the press molding machine, and placed in a microwave oven to heat the first molded body by applying electromagnetic waves for about 20 seconds.

The second molded body thus obtained was removed from the polycarbonate mold and transferred to an air circulation dryer kept at 65°C for about 10 minutes.
Dry for an hour. After that, it was placed on a stainless steel wire mesh with a surfaceless surface, and the organic matter, which is another plasticizer, was decomposed and removed in the air at a heating rate of 3-b. In this molding step and dry decomposition step, the normality of the molding raw material and the minimum time required to obtain a ceramic molded body are shown in Table 1. As is clear from Table 1, sufficient plasticization was not obtained when the water content was 30%. Furthermore, when the amount of ceramic powder blended was as low as 35%, cracks occurred in the molded product during drying.

[Brief explanation of drawings]

Figure 1 is a diagram showing the volume ratio of the three components of ceramic powder, plasticizer, and water, Figure 2 is a perspective view of the ceramic molded body molded in Example 1, and Figure 3 is a diagram showing the volume ratio of the three components of ceramic powder, plasticizer, and water. FIG. 2 is a central sectional view of a ceramic molded body.

Claims (7)

[Claims] (1) The first step of obtaining a molding raw material containing ceramic powder and a plasticizer containing a gelling component that gels with water and heating, in which the molding raw material is applied to the mold surface before the gelling component gels. a second step of contacting to obtain a first molded body; a third step of holding the first molded body at a high temperature and gelling the gelling component in the first molded body to obtain a hardened second molded body; A method for manufacturing a ceramic molded body, comprising sequentially performing a fourth step of heating the second molded body to remove the plasticizer and obtaining a third molded body made of ceramic powder. (2) The manufacturing method according to claim 1, wherein the third step is carried out by heating to a temperature higher than the gelling temperature of the gelling component. (3) The manufacturing method according to claim 2, wherein the third step is performed in a mold. (4) The mold is made of a material with a low dielectric loss coefficient, and the first
4. The manufacturing method according to claim 3, wherein the first molded body in the mold is heated by dielectric heating to maintain the molded body at a high temperature. (5) The manufacturing method according to claim 3, wherein the mold is heated to a gelling temperature, and the first molded body is heated by the mold. (6) The manufacturing method according to claim 1, wherein the third step is performed by heating the first molded body after taking it out of the mold. (7) The manufacturing method according to claim 6, wherein the heating is performed by dielectric heating.