JPS6364977A - Manufacture of ceramic dewaxed body - Google Patents

Abstract

(57) [Abstract] 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 degreased body.

[Prior Art] When manufacturing ceramic products, for example, about 5 to 30 wt% of a binder is added in order to improve molding performance.

This binder is removed by volatilization by thermal decomposition before the main sintering of the ceramic molded body, but rapid thermal decomposition causes defects such as swelling and scraping in the ceramic molded body, so this degreasing process by heating is necessary. It takes a long time, for example, several days. This tendency is particularly remarkable when the binder content is large or when the ceramic molded body is thick. Therefore, a degreasing method has recently been developed in which the pressure atmosphere in the degreasing furnace is controlled, but this method cannot be expected to significantly shorten the degreasing time.

Therefore, in recent years, a method for producing ceramic degreased bodies using supercritical fluid as a solvent has been proposed (Chemical Engineering, May 1986 issue, P46-P49).
. Here, supercritical fluid refers to the critical point of gas-liquid of a substance (ILL
It means a fluid that exceeds the critical temperature and critical pressure, and is a high-density fluid that cannot be called a gas or a liquid. Supercritical fluids have excellent dissolution ability.

If such a supercritical fluid is used as a solvent and a low molecular weight organic binder is used, a ceramic molded body can be degreased in an extremely short time.

By the way, when an organic binder is degreased using a supercritical fluid, the degreasing rate is adjusted to tJJ @ to ensure shape retention.
There is a need to. Therefore, the pressure and temperature of supercritical fluid,
Conditions such as degreasing time must be carefully controlled.

In addition, if all the low-molecular-weight organic binder is degreased using supercritical fluid, it is likely to be difficult to retain the shape of the degreased body.
There is a fear that handling of the degreased body will not be easy. The first reason for this is that when degreasing by heating, the ceramic powder aggregates and the strength of the degreased body can be ensured, but in the case of degreasing using supercritical fluid, the ceramic powder does not aggregate, so The second reason is that it is difficult to ensure the strength of the body.When degreasing by heating, the degreasing temperature is as high as about 440 degrees, which causes the degreased body to burn, but the degreasing temperature with supercritical fluid is 30 to 200 degrees. It is assumed that this is because the temperature is as low as ℃, making it difficult for the degreased body to harden. Therefore, recently, we have developed ceramic molded bodies using supercritical fluid as a solvent and blending low-molecular-weight organic binders.
A first step of extracting the low-molecular-weight organic binder into the solvent, interrupting the extraction midway through, and obtaining a semi-defatted body in which a predetermined amount of the low-molecular-weight organic binder remains; and heating the semi-defatted body. A method for manufacturing a ceramic degreased body has been developed, which includes a second step of volatilizing and removing the remaining low-molecular-weight organic binder in the semi-12WI body to obtain a degreased body.

In this method, since the second culm is degreased by heating in the same way as normal heating degreasing, the shape retention of the degreased body can be improved, but on the other hand,
In order to form a semi-defatted body in which a predetermined amount of low-molecular organic binder remains in the first step by extraction with a supercritical fluid, the first step
Pressure, supercritical conditions, and degreasing time in the process must be precisely controlled. The reason for this is that supercritical fluid has an extremely fast degreasing speed, so if the control is slightly erroneous, all of the low-molecular organic binder will be degreased, making it impossible to obtain a semi-degreased body.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned circumstances, and its purpose is to suppress variations in degreasing rate as much as possible without requiring detailed control of supercritical conditions. The object of the present invention is to provide a method for producing a ceramic degreased body in which the shape retention of the degreased body is improved.

[Means for Solving the Problems] The present inventor found that low molecular weight binders can be easily extracted into supercritical fluids such as carbon dioxide, fluoromethane, and chloroform, while high molecular weight organic binders can be easily extracted into supercritical fluids such as carbon dioxide, fluoromethane, and chloroform. The present invention was developed based on the fact that it is difficult to extract with supercritical fluids such as fluoromethane, chloroform, etc.

That is, the method for producing a ceramic degreased body according to the present invention uses, as main ingredients, a low-molecular organic binder that is easily extracted with a supercritical fluid, a clear polymeric binder that is difficult to extract with the supercritical fluid, and a ceramic powder. The first step is to obtain a ceramic molded body, and the solvent is used as a solvent! 1. A second step of extracting mainly the low-molecular-weight organic binder in the ceramic molded body into the supercritical fluid using a critical fluid to obtain a semi-defatted body in which the high-molecular-weight organic binder remains; A third step of heating the body to 200 to 500°C to remove mainly the polymeric organic binder remaining in the semi-defatted body to obtain a defatted body. It is.

The ceramic molded body formed in the first step of the method according to the present invention includes a ceramic powder containing a polymeric organic binder,
and a low-molecular-weight organic binder.

The first step usually includes a mixing step in which ceramic powder, a low-molecular organic binder, and a polymeric organic binder are blended and kneaded, and an injection molding step in which the kneaded product is molded into a predetermined shape by injection molding. As the ceramic powder, silicon nitride, silicon carbide, alumina, zirconia, aluminum nitride, boron nitride, etc. can be used. in this case,
A sintering aid may be added. As a sintering aid, magnesia, alumina, itria oxide, beryllium oxide, selenium oxide, etc. can be used.

The low molecular weight organic binder needs to have the property of being extracted by a supercritical fluid and the property of being able to bind ceramic powder to some extent. When supercritical carbon dioxide, fluoromethane, chloroform, etc. are used as the supercritical fluid, the low molecular weight organic binder is paraffin,
It can be formed from at least one of stearic acid, stearyl alcohol, paraffin, phthalate, and the like.

The polymeric organic binder can be formed of at least iw such as atactic polypropylene, ethylene vinyl acetate, polyethylene, and polyethylene.

The total binder contained in the ceramic molded body is 1
00% by volume, the amount of the low molecular weight organic binder contained in the ceramic molded body is usually 20 to 95% by volume.

In the second step, using the supercritical fluid as a solvent, all or most of the mainly low-molecular organic binder in the ceramic molded body is extracted into the supercritical fluid, and this leaves a semi-degreased state in which the high-molecular organic binder remains. Get a body. The second step is
The ceramic molded body is housed in a degreasing furnace, and the temperature and pressure in the degreasing furnace are adjusted to bring the fluid in the degreasing furnace into a supercritical state.

In the third step, the semi-defatted body is heated to remove mainly the polymeric organic binder remaining in the semi-IIQ fat body, thereby obtaining a defatted body. In this case, as in the case of a normal thermal degreasing method, the inside of the degreasing furnace containing the ceramic molded body is set to an inert gas atmosphere, and the inside of the degreasing furnace is heated to a temperature higher than the volatilization temperature of the binder.

In the degreasing method according to the present invention, the second step usually has a
The third step takes about 1 to 8 hours.

[Effects of the Invention] According to the degreasing method according to the present invention, in the second step, degreasing is performed using supercritical fluid, and in the third step, normal heating degreasing is performed, so that the entire degreasing step is performed using supercritical fluid. Compared to the case of degreasing, variations in the degreasing rate are less likely to occur in the parts of the ceramic molded body without finely controlling conditions such as the pressure, temperature, and degreasing time of the supercritical i-body.

In addition, in the present invention, the polymeric organic binder is heated and removed in the third step in the same way as in the normal thermal degreasing method, so the shape retention of the degreased body is improved compared to the case where the entire degreasing step is performed using a supercritical fluid. can also be improved.

Further, the degreasing rate of the semi-defatted body, that is, the amount of binder contained in the semi-defatted body, is determined by the amount of the polymeric organic binder that is difficult to extract with a supercritical fluid.

Therefore, if the ratio of the polymer organic binder and the low molecular organic binder is set constant, if all or most of the low molecular organic binder is extracted into the supercritical fluid in the second step, Even without strictly controlling supercritical conditions such as pressure and temperature in the second step, it is possible to always maintain a constant degreasing rate of the semi-debonded body formed in the second step.

[Example] (Example 1) In the first step, silicon nitride powder was mixed with wt% as a sintering aid and 18% of an organic binder, and then injected into the cavity of a mold by injection molding. Then, a ceramic molded body having a predetermined shape was formed. Here, the organic binder is composed of ethylene vinyl acetate copolymer (EVA) as a high molecular organic binder and stearic acid as a low molecular organic binder. And 100% by volume of organic binder
When, ethylene vinyl acetate copolymer is 10% by volume
and stearic acid was 90% by volume.

Next, as a second step, with the ceramic molded body inserted into the degreasing furnace, carbon dioxide, which functions as a solvent, was introduced from a cylinder into the degreasing furnace. Then, the temperature and pressure of carbon dioxide in the l112 oil furnace were controlled to bring the carbon dioxide into an electric field, making it a supercritical fluid. The critical temperature of carbon dioxide is 31°3℃, and the critical pressure is 72.9℃.
Since it is an ATM, carbon dioxide can be brought into a supercritical state at around room temperature. As a result, almost all of the stearic acid as a low-molecular-weight organic binder contained in the ceramic molded body was degreased, and a semi-degreased body (ethylene-vinyl acetate copolymer remained) was formed.

Next, as a third step, nitrogen gas was sent from the cylinder into the degreasing furnace using a pump, and the inside of the degreasing furnace was replaced with nitrogen gas. With these substitutions, the heating rate was 50°C per hour.
The mixture was heated to 50° C. and maintained, whereby the ethylene-vinyl acetate copolymer as a polymeric organic binder remaining in the semi-defatted body was heated and volatilized, thereby forming a degreased body.

The degreased body thus formed was placed in a nitrogen pressurized atmosphere for 1
Heating up to 750°C at a heating rate of 1 to 5°C per minute,
It was held and fired at 1800°C for 4 hours. As a result of inspecting this fired body, no defects were found inside or on the surface of the fired body. The reason for this is thought to be that no cracks or defects occurred in the degreased body.

Claims (4)

[Claims] (1) A low-molecular organic binder that can be easily extracted with supercritical fluid;
A first step of obtaining a ceramic molded body containing a polymeric organic binder that is difficult to extract in the supercritical fluid and ceramic powder as the main ingredients; a second step of extracting the low-molecular organic binder into the supercritical fluid to obtain a semi-defatted body in which the high-molecular organic binder remains; heating the semi-defatted body to 200 to 500°C to obtain the semi-defatted body; A method for manufacturing a ceramic degreased body, characterized in that a third step of removing mainly the polymeric organic binder remaining therein to obtain a degreased body is carried out in order. (2) The method for producing a ceramic degreased body according to claim 1, wherein the supercritical fluid is formed of carbon dioxide, chloroform, and fluoromethane in a supercritical state. (3) The low-molecular organic binder is made of at least one of stearic acid, stearyl alcohol, paraffin, and phthalate, and the high-molecular organic binder is made of atactic polypropylene, ethylene vinyl acetate,
The method for manufacturing a ceramic degreased body according to claim 1, wherein the ceramic degreased body is made of at least one of polyethylene and polyethylene. (4) When the total binder contained in the ceramic molded body is 100 volume %, the low molecular weight organic binder contained in the ceramic molded body is 20 to 95 volume %.Claim 1 A method for producing a ceramic degreased body as described in .