JPH0415191B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method for removing additives from a powder compact, and more specifically, in order to obtain a ceramic sintered body, the present invention relates to a method for removing additives from a powder compact formed by injection molding or slurry casting. This invention relates to a method of heating and scattering an additive used as an auxiliary agent, a so-called method of degreasing a powder compact. [Background technology] Ceramic sintered bodies, which have complex shapes and are mass-produced, are produced by molding raw material powders of alumina, zirconia, silicon carbide, silicon nitride, etc. into the desired shape by injection molding or slurry casting. It is produced industrially by compacting, degreasing, and then igniting the powder compact to a temperature necessary for sintering. The injection molding method here refers to polystyrene, which exhibits plasticity as a whole and becomes easy to mold when mixed with the above-mentioned powder such as alumina.
20 to 35 parts by weight of additives such as polyethylene, diethylene phthalate, paraffin, fatty acid ester, polyvinyl alcohol, etc. are added to 100 parts by weight of powder and kneaded, and the kneaded product is press-fitted into a mold of the desired shape and molded. This is the way to do it. The obtained powder compact is taken out from the mold, the additives are scattered and removed by heating, and then ignited to form a ceramic sintered body in a desired shape. In addition, the slurry casting method involves adding 20 to 40 parts by weight of an additive made of water or a mixture of water and alcohol to 100 parts by weight of powder such as alumina.
A small amount of deflocculant such as HCl, AlCl ₃ , NaOH, or water glass is added and mixed well to form a stable slurry that is fluid and does not easily allow powder to settle.This slurry is made of a porous material similar to gypsum. This is a method in which the slurry is poured into a mold, at least the additives contained in the slurry are absorbed into the mold until the slurry loses its fluidity, and then taken out from the mold as a powder compact. The powder compact obtained by this method usually contains 10 to 15% by weight of additives such as water, so the remaining additives are dispersed by heating, as in the injection molding method, and then For example, a ceramic sintered body can be obtained by igniting at about 1300 to 2300°C. Hereinafter, in the present invention, thermoplasticizers, plasticizers, dispersants, solvents, etc. added to powder in injection molding and slurry casting will be collectively referred to as additives. The operation of scattering the additives remaining in the molded body obtained by the above injection molding method and slurry casting method by heating is hereinafter referred to as "degreasing" using the common terminology of those skilled in the art. do. However, ceramic sintered bodies obtained by the method described above, that is, by degreasing and igniting a powder compact obtained by injection molding or slurry casting, do not exhibit cracks or surface peeling. There is a problem in that a considerable number of defective products (that cannot be considered as products) occur. Furthermore, if these defects occur inside the sintered body, it is difficult to detect the defects at the stage of product production, so some of the products end up being produced as is, causing damage during use and causing accidents. There is also a big problem. However, what I would particularly like to point out here is that most of the defects such as the above-mentioned cracks and surface peeling occur during the degreasing process. In other words, if any additives remain in the powder compact, when the powder compact is ignited to form a ceramic sintered body, the residual additive will rapidly vaporize, and this expansion force will cause the ceramic sintering to fail. Cracks and fissures appear in the structure. In order to prevent this, the powder compact is subjected to a degreasing step prior to ignition to remove additives. Therefore, although it is self-evident,
In the degreasing process, it is desirable to remove additives as completely as possible. However, as mentioned above, powder compacts
Even in the case of slurry casting, the amount of additives is 10% by weight or more, and in the case of injection molded products, it is even higher, ie, 20% by weight or more. In this way, it is possible to remove the additives by scattering them from a powder compact containing a large amount of additives by heating without causing cracks or cracks. This is essentially an extremely difficult problem because it acts strongly on powder compacts with extremely low viscosity. Therefore, conventionally, this process involves forming powder compacts under atmospheric pressure or a pressure of about 5 kg/cm ² or less.
This is done by heating the powder to around 600°C and scattering and removing the additive through vaporization, decomposition, combustion, etc. However, due to the need to keep the expansion force of the additive low, the rise of the powder compact is difficult. The heating rate is extremely slow, such as 1 to 3°C/h. Since the degreasing process has no choice but to adopt such a slow temperature increase rate, it usually takes a long time of 5 to 7 days, which poses a problem that productivity is significantly inhibited. In addition, in the injection molding method, when the amount of additives is increased, the voids formed when the additives are removed in the degreasing process increase, so it is necessary to use as few additives as possible and to improve moldability. At the same time, properties that make it easy to heat and scatter are also required. However, it is difficult to satisfy all of these properties by using the polystyrene mentioned above,
Even if expensive materials such as polyethylene were used, the problem was that it was inherently extremely difficult. Furthermore, since the mechanical strength of a degreased powder compact is almost zero, it can easily crack or crack due to slight vibrations or shakes during the process of transferring or transporting the compact to the next sintering process. This is likely to occur, and in order to prevent this, it was necessary to prevent vibrations, shaking, etc. at this time as much as possible. In this way, despite being produced with extremely low productivity and with extremely careful operations,
The resulting ceramic sintered bodies had quite a few defective products, and the actual situation was that these were mainly caused by defects in the powder compacts that occurred during this degreasing process. [Summary of the Invention] The purpose of the present invention is to solve the drawbacks of the conventional techniques using a completely new method. According to the method of the present invention, the degreasing process can be carried out in an extremely short time. In addition, a novel degreasing method is provided which can significantly suppress the occurrence of defects in powder compacts as described above. [Disclosure of the Invention] The present inventors have conducted intensive studies with the aim of fundamentally eliminating the drawbacks of the conventional technology, and have found that even if additives are removed at extremely low temperatures and in a short period of time, cracks in powder compacts do not occur. We have discovered a method that can significantly suppress the occurrence of defects such as cracks and cracks compared to conventional methods.
This has led to the completion of the present invention. That is, the above-mentioned object of the present invention is to provide a method for removing additives from a powder compact formed by adding additives to powder by heating and scattering the additives, and in which at least a portion of the surface of the powder compact is removed in advance. Except for leaving the exposed surface, the remaining surface is covered with an airtight resin thin film, and the powder compact is heated while the coated surface is subjected to hydrostatic pressure to scatter the additive through the exposed surface. It is achieved by doing so. [Specific Requirements for Carrying Out the Invention] The present invention will be described in detail below. In the present invention, when degreasing a powder compact that still contains additives, for example, a powder compact that still contains additives obtained by injection molding, slurry molding, etc., Except for a portion of the body surface left exposed, the rest is covered with an airtight resin thin film. For coating with such a thin resin film, for example, a liquid resin that solidifies by volatilization of a solvent or a chemical reaction is applied directly to the surface of the molded object, by spraying, or by dipping and pulling up, and if necessary, it is dried or heated. This can be carried out by forming a resin coating on the surface by applying treatments such as the following. Examples of liquid resins that can be used in this method include industrially produced resins such as vinyl acetate emulsion, styrene-butadiene latex, acrylic emulsion, and natural rubber latex.
Further, polyurethane resins, silicone resins, epoxy resins, acrylic resins, polyester resins, chlorprene resins, phenolic resins, etc. can also be used. Furthermore, acrylic resin, epoxy resin,
Among polyester resins, there are resins that are processed so that when applied in the form of powder and heated, the powder fuses to form a coating film, and such resins can also be used. The thickness of the thin film to be coated may be selected appropriately depending on the shape of the powder compact, the particle size of the powder, the pressure of hydrostatic pressing, the type of thin film, etc., and should be at least the minimum thickness necessary to maintain airtightness. That's fine. According to the experimental findings of the present inventors, the thickness of the thin film is usually preferably 10 μm or more. In addition, although the upper limit of the thickness of the thin film is not particularly defined,
For convenience of handling, it is preferably up to about 5 mm. Of course, depending on the type of thin film, the thickness may be less than or greater than this. Further, it is more preferable that the resin thin film has some degree of elasticity. By coating the surface of the molded body with such a resin thin film and heating and degreasing the coating thin film under hydrostatic pressure as described later, the resin thin film always adheres to the surface of the molded body due to the hydrostatic pressure, In addition, the hydrostatic pressure is effectively transmitted to the molded body through the thin film, and the air in the molded body created by the scattering of additives is removed by isotropic contraction of the molded body due to hydrostatic pressure.
It can be erased very effectively. Note that for this purpose, it is preferable that the resin forming the thin film has some degree of elasticity. This can be based on the fact that the glass transition point of the resin is below the operating temperature at the temperature during the degreasing operation. In the present invention, it is necessary that at least a part of the surface of the powder compact be left uncovered and exposed. During degreasing, additives are scattered from the exposed surface. The position of the exposed surface should be selected in consideration of the shape of the powder compact and the local mechanical load when it is made into a ceramic sintered body. For example, if the shape of the powder compact is axially symmetrical, it is preferable to use the ends in the axial direction because the pressing operation is easy. Further, the exposed surface is preferably a cross section of one end if the powder compact has a cylindrical shape as shown in FIG. 1, or a cross section of one end of the rotating shaft if the shape is a propeller as shown in FIG. The reason is that it is difficult for the powder to be evenly compressed near the exposed surface.
This is because this portion does not receive a large mechanical load when it is made into a ceramic sintered body. The exposed surface 1 as shown in FIGS. 1 and 2 above meets the above conditions. The area of the exposed surface is required to prevent additives from scattering from this surface, so if the area is too small, the time required for degreasing will be longer; on the other hand, if the exposed area is too large, it will not be possible to compress the powder evenly into a compact. There are more and more difficult parts. An appropriate exposed area is selected by considering these trends together with the size and shape of the powder compact. According to the experimental findings of the present inventors, the exposed area is approximately 0.5 to 0.5 of the total surface area.
It is carried out in a range of about 20%, preferably about 1 to 10%. The powder compact whose remaining portion is coated with a resin thin film in this manner is then heated while the coated surface is subjected to hydrostatic pressure. Hydrostatic pressurization can be done by immersing the coated surface in liquid and pressurizing the liquid with a pump, etc. The pressurizing liquid may be boric acid water with a concentration of about 30% by weight, hydraulic oil, etc. is suitable. The pressure applied to the liquid here should be such that the expansion force generated when the additive is heated will not cause defects such as cracks in the powder compact, and the pressure must be such that the type of additive, heating temperature, powder compaction, etc. The pressure is selected appropriately depending on the shape of the body, etc., but in order to achieve this purpose, the pressure should be 5.
It is preferable that it is Kg/cm ² or more. Furthermore, it is desirable that the pressure of the hydrostatic pressurization is such that the air space created by the scattering of the additive can be eliminated by the isotropic contraction of the powder compact due to the hydrostatic pressurization. For this purpose, 500Kg/cm2 ^or more
The pressure is preferably 10T/cm ² or less. As a method of applying pressure only to the coated surface, for example,
There is a method as shown in FIG. That is, the powder compact 3 shown in FIG. 3 and the hollow pressure tube 5 are connected, and the surface of the powder compact and the outer surface of the pressure tube are coated with an integral thin film. In this way, the surface of the powder compact that is in contact with the inside of the hollow pressure tube becomes an exposed surface that is not covered with a thin film, and the coated surface can be pressurized in this state. In the present invention, in order to avoid distortion in the vicinity of the exposed surface, it is preferable to press the exposed surface by some method. For example, as shown in FIG. An effective method is to place it in a hollow pressure tube in contact with a surface.
The pore diameter of the porous body is preferably at least 5 mm or less, preferably 1 mm or less, and more preferably 0.1 mm or less and 0.01 μm or more. In this way, while the coated surface of the formed body is subjected to hydrostatic pressure, the formed body is heated from the outside to vaporize the additive by evaporation, decomposition, sublimation, etc.
The thus vaporized additive is scattered out of the molded body through the exposed surface of the molded body that is not covered with the thin film, and is removed. Heating the powder compact to disperse the additives can be done by heating a liquid such as pressurized boric acid water or hydraulic oil, and the heating rate, temperature reached, and holding time depend on the type of additive. Therefore, it is selected appropriately. In addition, in the present invention, the following industrial advantages can be realized by selecting the type of additive. That is, since the present invention is a method of scattering additives while applying hydrostatic pressure to a powder compact, even if this scattering causes voids inside the compact,
The voids can be easily eliminated by isotropic shrinkage of the molded product by isostatic pressure. Therefore, when an injection molded article is used in the present invention, it is not necessarily necessary to use expensive additives such as conventionally used polystyrene and polyethylene; for example, it is not necessary to use expensive additives such as polystyrene, polyethylene, etc. A viscous liquid containing 0.1 to 5% of water-soluble polymer dissolved in alcohol, or 1 to 20% of oils and fats such as lauric acid, palmitic acid, stearic acid, and glycerin in alcohol.
Inexpensive liquids such as liquids that have been dissolved to some extent can also be used satisfactorily. In addition, in the present invention, when adopting the slurry casting method, the additives are water or a mixture of water and alcohol with a small amount of HCl, AlCl ₃ ,
A deflocculant such as NaOH or water glass is added. In the present invention, since it is possible to use as an additive a substance having a boiling point lower than that of the conventional polystyrene or polyethylene as described above, it is also possible to carry out the heating temperature during degreasing at a much lower temperature. In the present invention, the method of heating the powder compact during degreasing is of course arbitrary, but the following method is listed as one of the preferable methods based on the experimental findings of the present inventors. In other words, the temperature may be raised at any rate from room temperature to a temperature approximately 15°C lower than the boiling point of the volatile components in the additive, but once this temperature is reached, the temperature must be increased from this temperature to a temperature approximately 2°C lower than the boiling point of the volatile components. Hold in range for 3-10 hours, during which time 40% of the volatile components
~60% will be scattered and removed. Next, the remaining volatile components are scattered and removed by heating above the boiling point of the volatile components to complete degreasing. In addition, when heating as described above, it is also a preferred embodiment to suction through the exposed surface with an exhaust device such as a fan or blower in order to quickly scatter volatile components out of the molded article. Since the present invention is such a degreasing method, for example, if the volume of the powder compact is about 1, the total heating time is less than 24 hours, which is much shorter than the conventional method. . [Effects of the Invention] The present invention exposes a part of the surface of a powder compact and covers the rest with an airtight resin thin film, and then adds additives while applying hydrostatic pressure at a pressure of, for example, 500 kg/cm ² or more. Since this is a method of scattering through the exposed surface, according to the present invention, the expansion force generated when the additive is heated and vaporized can be effectively suppressed by the hydrostatic pressure. For this reason, degreasing can be carried out in an extremely short period of time, and at the same time, the occurrence of defects such as cracks and cracks due to degreasing can be significantly suppressed compared to conventional methods. In addition, the voids inside the powder compact that occur in the area where the additive has been removed can be easily eliminated by isotropic compression of the compact, so even if the amount added is small, the plasticity will be reduced when kneaded with the powder. Easy to display and heating/
Another advantage is that there is no need to use expensive polystyrene, which has been developed as an additive that easily scatters. Furthermore, since the resin thin film coated on the powder compact also has the role of reinforcing the powder compact, it is also effective in preventing cracks and cracks that occur during the process of transferring the powder compact after degreasing to the sintering process. be. In addition, in the present invention, since it is possible to use a substance with a lower boiling point than polystyrene or polyethylene as an additive, it is not necessarily necessary to degrease at a high temperature of about 600°C as in the case of using polystyrene or polyethylene. In some cases it is much lower than this, for example 250 as shown in the example below.
It can even be carried out at temperatures below ℃,
It is also extremely advantageous in terms of heat energy consumption. In addition, the implementation temperature is preferably in the range of about 300 to 50°C. Since the present invention has such advantageous effects,
It is particularly effective when manufacturing ceramic sintered bodies with relatively complex shapes that require methods such as injection molding or slurry casting, and also require reliability in mechanical strength. It can be applied to [Examples and Comparative Examples] The present invention will be specifically described below with reference to Examples and Comparative Examples. Example 1 As raw material powders, 100 parts by weight of silicon nitride powder with a specific surface area of 15 m ² /g and an average particle diameter as determined by an electron microscope image of 0.3 μm and a specific surface area of 12 m ² /g and an average particle diameter determined as an electron microscope image were used. Using 5 parts by weight of 0.35 μm magnesium oxide, 25 parts by weight of ethanol and 5 parts by weight of lauric acid were added as additives, and the resulting mixture was then injection molded at an injection pressure of 500 Kg/cm ² to form a mold with a diameter of 15 mm. A cylindrical silicon nitride powder compact with a length of 50 mm was obtained. The volume occupied by the raw material powder with respect to the apparent volume of the obtained powder compact (hereinafter referred to as "powder filling ratio") was 57%. As shown in Fig. 4, an alumina porous body 8 (diameter 15 mm, length 10 mm, average pore diameter 10 μm) is superimposed on one end of this powder compact 3, and a hollow pressure-resistant tube is fixed to a pressure-resistant container. When connected to 5,
These surfaces were coated with a resin thin film 2 having a thickness of 120 μm. The exposed area was 6% of the total surface area. The coating method is to apply liquid styrene-butadiene latex (a copolymer of 60% styrene and 40% butadiene) to the powder compact by dipping and pulling up, and then drying the water in the latex to form a thin resin film on the surface. This was done by forming a Next, the pressure container is filled with boric acid water with a concentration of 30% by weight, and this boric acid water is compressed with a pump to 1500%
The powder compact was degreased by heating it with a heater under pressure of Kg/cm ² to raise the temperature. The heating method for the boric acid water was as follows. That is, increase the temperature from room temperature to 75℃ at a rate of 30℃/h, hold at 75℃ for 3 hours, and increase the temperature from 75℃ to 174℃ at a rate of 30℃/h.
Increase temperature at a rate of ℃/h, hold at 174℃ for 2 hours, 174℃
Temperature rises at a rate of 30°C/h from to 210°C, 1 at 210°C
Hold for a while and then cool to room temperature by natural cooling. The total time from the start of temperature rise until cooling to room temperature was 19 hours. During this time, the boric acid solution was maintained at a pressure of 1500 kg/cm ² . Note that the ethanol and lauric acid contained in the powder compact were scattered to the outside of the pressure container through the alumina porous body 8 and the hollow pressure tube 5 from the exposed surface not covered with the resin thin film. , this external pressure was atmospheric pressure. The powder compact 3 taken out from the pressure container showed no changes in appearance such as cracks or damage to the resin thin film, and ethanol and lauric acid were not present.
More than 99% of the particles were scattered. Also, the powder filling rate is 62%
and increased compared to before degreasing. Next, this powder compact was heated at 1800°C for 2 hours in a nitrogen gas atmosphere at a pressure of 5 kg/cm ² G to obtain a ceramic sintered body. The density of the obtained sintered body is 3.14
g/cm ³ , which corresponds to 99% of the theoretical density of silicon nitride. Cut out 20 test pieces from this sintered body,
As a result of measuring the bending strength according to the regulations of JISR-1601, the average strength was 82Kg/mm ² and the standard deviation was 3.1Kg/mm2.
It was warm in ^mm2 . Comparative Example 1 A cylindrical silicon nitride powder molded body obtained by injection molding in exactly the same manner as in Example 1 was heated in the same manner as in Example 1 in air at normal pressure without being coated with a resin thin film. It was then heated and degreased. After degreasing, the powder compact had many cracks in the range of 2 to 4 mm, and peeling with a thickness of 1 to 2 mm had occurred on about 40% of the surface. Comparative Example 2 Raw material powder consisting of 100 parts by weight of the same silicon nitride powder and 5 parts by weight of magnesium oxide used in Example 1 was added with 19 parts by weight of polypropylene and 10 parts by weight of polyethylene.
parts by weight, and 1 part by weight of stearic acid were added, and the mixture obtained by kneading these was injection molded in exactly the same manner as in Example 1 to obtain a powder compact with a powder filling rate of 59%. Next, this powder compact was degreased by the following conventional heating method at high temperature and for a long time.
In other words, the temperature is raised from room temperature to 100℃ at a rate of 30℃/h, 100℃
The temperature was raised from ℃ to 600℃ at a rate of 2℃/h, held at 600℃ for 2 hours, and then cooled to room temperature by natural cooling. At the stage where the temperature was maintained at 600°C for 2 hours, the atmosphere was set to air in order to oxidize and decompose the additives, and at other stages, the atmosphere was set to nitrogen gas and the pressure was set to atmospheric pressure. The total time from the start of temperature rise until cooling to room temperature is 260 minutes.
It took a long time. No changes in appearance such as cracking or surface peeling were observed in the powder compact taken out from the container, more than 99.5% of additives such as polypropylene were scattered, and the powder filling rate was the same as before degreasing. It was the same 59%. Next, this powder compact was heated and sintered at 1800° C. for 2 hours in exactly the same manner as in Example 1. The density of the sintered body was 3.10 g/cm ³ . A test piece was cut out from the obtained sintered body in exactly the same manner as in Example 1, and the bending strength was measured. As a result, the average strength was 68 Kg/mm ² and the standard deviation was 6.6 Kg/mm ² . A comparison between Example 1 and Comparative Example 1 shows that coating a powder compact with a thin film and degreasing the coated surface while applying hydrostatic pressure has a remarkable effect on preventing cracks and surface peeling. I understand. Furthermore, a comparison between Example 1 and Comparative Example 2, which is a conventional degreasing method, shows that although the powder compacts degreased by the present invention were degreased at a much lower temperature and in a shorter time, this powder filling rate was lower than that of the conventional technique. It can be seen that the bending strength of the sintered body of the present invention is higher than that of , and that the bending strength of the sintered body is increased and the variation thereof is also much smaller. Examples 2 to 4 The same silicon nitride powder and magnesium oxide powder as in Example 1 were used as raw material powders, and the additives shown in Table 1 were added to 100 parts by weight and 5 parts by weight of these powders. The resulting mixture was injection molded in exactly the same manner as in Example 1 to obtain silicon nitride powder compacts having the powder filling percentages shown in Table 1. Next, in the same manner as in Example 1, these powder compacts were joined to a hollow pressure tube via an alumina porous body as shown in Fig. 4, and their surfaces were coated with a resin thin film. did. As for the coating method, in Example 2, acrylic emulsion was applied in the same manner and the water was dried, and in Examples 3 and 4, chlorprene resin using ethyl acetate as a solvent was applied and the solvent was dried. I went there. The thickness of the resin thin film was 120 μm in Example 2, and 230 μm in Examples 3 and 4. Next, the coated surface of these powder compacts was hydrostatically pressurized to a pressure of 1500 kg/cm ² with boric acid water with a concentration of 30% by weight in the same manner as in Example 1, and the boric acid water was applied with a heater. Degreasing was performed by heating and raising the temperature. Here, the heating mode in Example 2 was exactly the same as in Example 1, and in Examples 3 and 4, it was as follows.
In other words, the temperature is raised from room temperature to 98°C at a rate of 30°C/h, 98
Hold at ℃ for 5 hours, raise temperature from 98℃ to 110℃ at 10℃/h, hold at 110℃ for 2 hours, then cool to room temperature by natural cooling. The total time from the start of temperature rise until cooling to room temperature was 15 hours. There were no visible changes in the powder compacts taken out from the pressure container, such as cracks or thin film damage, and more than 99% of the additives had been scattered. In addition, as shown in Table 1, the powder filling rate increased in all cases compared to before degreasing. Next, these powder compacts were heated in exactly the same manner as in Example 1 at 1800°C for 2 hours to obtain sintered bodies having the densities shown in Table 1.

[Table] ** Carboxymethyl cellulose A test piece was cut out from the obtained sintered body in exactly the same manner as in Example 1, and the bending strength was measured. As a result, the average value and standard deviation were the values shown in Table 1. . Examples 5 to 7 The following experiments were conducted for the purpose of examining the effect of hydrostatic pressurization. As a raw material powder, the specific surface area is 17m ² /
A silicon carbide powder with an average particle size of 0.25 μm as determined by an electron microscope image in g, a single boron powder with a specific surface area of 10 m ² /g and an average particle size of 0.4 μm, and a specific surface area of 90 μm.
m ² /g and carbon black with an average particle size of 0.03 μm, 100 parts by weight of each of these,
A mixture obtained by adding 1 part by weight, 2 parts by weight, 30 parts by weight of isopropanol and 3 parts by weight of myristic acid as additives and kneading was injection molded in exactly the same manner as in Example 1, and the powder filling rate was 57%. Three powder compacts were obtained. Each of these silicon carbide powder compacts was bonded to a hollow pressure tube 5 via an alumina porous body 8 in exactly the same manner as in Example 1, and styrene-butadiene latex was applied to their surfaces. Then, the water was dried and a resin thin film with a thickness of 120 μm was coated. Next, these were heated in the same heating manner as in Example 1 to degrease them while maintaining the state of hydrostatic pressurization at the pressures shown in Table 2. The powder filling rates after degreasing were the values shown in Table 2. Next, these powder compacts were placed in a vacuum (1 mmHg
(below) for 1 hour at 2050°C to obtain a silicon carbide sintered body. The densities of the obtained sintered bodies were as shown in Table 2.

[Table] Using this sintered body, test pieces were cut out in the same manner as in Example 1, and the bending strength was measured. As a result, the average value and standard deviation were the values shown in Table-2.

[Brief explanation of drawings]

FIGS. 1 and 2 are perspective views showing examples of shapes of powder compacts used in the present invention. Third
4 and 4 are cross-sectional views showing a state in which the powder compact used in the present invention is placed in a pressurized container. In the drawings, 1...exposed surface, 2...resin thin film, 3...powder compact, 4...pressure container wall, 5...
...Hollow pressure tube, 6 ... Pressurized liquid, 7 ... Atmosphere, 8
...Indicates a porous body made of alumina.

Claims (1)

[Scope of Claims] 1. A method for removing additives from a powder compact formed by adding additives to powder by heating and scattering the additives, the method comprising: removing at least a part of the surface of the powder compact from an exposed surface in advance; In addition to leaving it as a powder, the remaining part is covered with an airtight resin thin film, and the powder compact is heated while the coated surface is subjected to hydrostatic pressure, and the additive is dispersed through the exposed surface. A method for removing additives from a powder compact. 2. The method according to claim 1, wherein the powder is a ceramic powder. 3. The method according to claim 1, wherein the powder compact is molded by an injection molding method. 4. The method according to claim 1, wherein the powder compact is formed by a slurry casting method. 5. The method according to any one of claims 1 to 4, wherein the powder compact from which additives have been removed is subsequently ignited to produce a shaped ceramic sintered body.