JPS6131340A - Manufacture of ceramic sintered 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 Application of the Invention] The present invention relates to a method for manufacturing a ceramic sintered body, and includes
The present invention relates to a method for manufacturing a ceramic sintered body that allows an organic fluidizing agent in an injection molded body to be absorbed and removed during injection molding.

[Background of the invention]

In general, ceramic sintered bodies produced by injection molding and pressureless sintering are produced by injection molding a mixture whose main components are ceramic powder and thermoplastic resin into the cavity of a mold. The thermoplastic resin component is removed by thermal decomposition, and the molded body is then sintered.

In this conventional method for manufacturing ceramics using injection molding, the degreasing process, which involves thermal decomposition and removal of thermoplastic resin components from the molded body, takes a long time, so other molding methods are not recommended. This method has the disadvantage that the process time is considerably longer than the ceramic sintered body manufacturing method employed. Further, the rate of temperature increase when heating the molded body in the degreasing process varies depending on the shape, size, wall thickness, etc. of the molded body, but is currently approximately 1.0-10 C/h. The maximum heating temperature during degreasing is 400~
700C, and degreasing takes a long time, 55 to 550 hours. Therefore, in the conventional degreasing process, it is necessary to shorten the degreasing time by increasing the temperature as quickly as possible. Sometimes, in molded bodies with a wall thickness of 2511III+ or more, it is not possible to remove the organic fluidizing agent by pyrolysis.

In the conventional method, the proportion of specific plasticizer in the mixture of organic plasticizer on ceramic powder is 30 to 70 Vo.
L% te;h le.

Therefore, a molded article obtained by injection molding contains a large amount of organic fluidizing agent. When this molded body is heated, the organic fluidizing agent in the molded body undergoes a thermal decomposition reaction, the decomposed gas is released from the surface of the molded body, and the organic fluidizing agent gradually disappears.

However, the thermal decomposition reaction of organic fluidizing agents is intense, and the reaction rate progresses exponentially with respect to the heating temperature.

On the other hand, the density of the molded body is close to the theoretical density, and there are no ventilation holes inside the molded body. For this reason, the thermally decomposed gas is difficult to be released from the surface of the compact, and the thermal decomposition reaction rate is often higher than the rate of release of the thermally decomposed gas.

When this phenomenon occurs, gas stays in the molded body, and the gas pressure in the molded body gradually increases over time.When the gas pressure in the molded body exceeds the material strength of the molded body, the molded body may develop cracks or cracks. occurs. Furthermore, when a crack occurs, gas is released from that part all at once, and deformation occurs due to the pressure of the released gas.

Therefore, in order to prevent breakage and deformation during degreasing, degreasing is performed under conditions such that the rate of thermal decomposition is less than the rate of gas release. The essential condition to satisfy this requirement is to reduce the amount of pyrolysis gas generated per unit time. Conventionally, as a means for this purpose, a method has been adopted in which the thermal decomposition temperature of the organic fluidizing agent is widened. Specifically, an organic fluidizing agent that is a blend of several types of organic fluidizing agents having different thermal decomposition temperatures is used. In this way, when the compact is heated and the temperature rises, thermal decomposition proceeds in order from the organic fluidizing agent with a lower thermal decomposition temperature to the organic fluidizing agent with a higher thermal decomposition temperature, so that the thermal decomposition gas is released. It does not occur instantly and in large quantities.

Hitherto, various methods have been proposed for shortening the entire degreasing process, including a method of adding 5 to 6 types of organic fluidizing agents having different thermal decomposition temperatures, and a method of heating a molded article with four non-oxidizing atmospheres. For example, there is a method using an organic fluidizing agent in which silicon carbide powder is mixed with polystyrene, stearic acid wax, and oil-containing 40 (% patent publication No. 55-23097), and a method in which silicon carbide powder is mixed with polystyrene, vegetable oil, and mineral oil. Method using an organic fluidizing agent (% 1976-9561)
7), and a method using an organic fluidizing agent in which polystyrene, polypropylene, a silane compound, diethyl phthalate, and stearic acid are mixed into silicon nitride powder (
JP-A-55-113510) and the like are disclosed.

However, in the conventional method, the organic fluidizing agent starts a thermal decomposition reaction and the rate of temperature rise above the temperature at which the decomposition rate increases is slow at 1 to 4 C/h or less, which significantly increases the time required for the degreasing process. It has the disadvantage that it cannot be shortened. Furthermore, in the conventional method, the time required for degreasing is 100 to 750 hours, including the time required for cooling the compact in the furnace after heating it.

[Purpose of the invention]

An object of the present invention is to provide a method for producing a ceramic sintered body that can shorten the time required for a degreasing process for thermally decomposing and removing an organic fluidizing agent in a molded body.

[Summary of the invention]

The present invention investigated the main reason why the degreasing process for removing the organic fluidizing agent in the ceramic molded body takes a long time, and found that the liquid fluidizing agent in the molded body is vaporized and converted into a gas with a high coefficient of volumetric expansion. It was created in the process of researching a method to remove the liquid while it is still in liquid form.

That is, the present invention injects a mixed material of ceramic raw material powder and an organic fluidizing agent into a mold to form a molded body, and heats the molded body to thermally decompose the fluidizing agent and remove it. In a method for manufacturing a ceramic sintered body, the method includes a step of
The mold is porous and the organic fluidizing agent is absorbed and removed by the porous mold during injection molding. By reducing the content of fluidizing agent, the time required for the next degreasing step can be significantly shortened.

FIG. 1 is a cross section showing an example of a porous mold used in the present invention.
A mold space is formed from the mold 1, and an injection inlet 9 is opened in the upper part of the mold l for press-fitting the mixed molding material 8 from the injection molding machine nozzle 6 into the mold space 7.

Further, the mold 1 has a mold space communicated with the outside through a plurality of through holes 10 in each porous plate. Note that this is a stopper for stopping the upper and lower molds 4 and 5 of the 11°12ti type.

Next, a method for manufacturing a ceramic sintered body using the porous mold described above will be explained.

First, the pressurizing force of the first stage in which the mixed molding material 8 is filled from the injection molding machine nozzle 6 into the space 7 of the porous mold 1 is 30 to 10
Must be below 0Kg/cIA.

If the pressing force is less than 30 kg/ci, the mixed molding material cannot be filled into the porous mold. Moreover, if it is 100 Ap/c+d or more, the ceramic raw material powder and the organic fluidizing agent will separate, making it impossible to fill the mold space with the mixed molding material.

Further, the molecular weight of the organic fluidizing agent added to fluidize the ceramic raw material powder must be 300 to 5,000. If it is 300 or less, the viscosity when fluid is low;
The ceramic powder and the organic fluidizing agent will separate at a pressure below t O0Ktz/ad during the first stage pressurization, impairing their function.

Moreover, if it is 5,000 or more, the viscosity in the fluid state is large, and even if the pressure during the second stage pressurization is 1 OIK/cfA or more, the organic fluidizing agent cannot be separated from the molded body, and it is absorbed into the porous mold. I can't.

The porous body that forms the mold is made of sintered metal powder.
Must be m. If the pore diameter is 5 μm or less, the organic fluidizing agent cannot be absorbed, and if the pore diameter is 100 μm or more, the ceramic powder will also be absorbed, making it impossible to separate the ceramic powder and the organic fluidizing agent.

As described above, according to one aspect of the present invention, the proportion of the organic fluidizing agent in the molded body can be 5Qwt% or less of the amount added to fluidize the ceramic powder. moreover,
After molding, the molded body is heated to reduce the temperature increase rate when the organic fluidizing agent in the molded body is thermally decomposed and removed. Therefore, the degreasing process can be significantly shortened compared to conventional methods. Furthermore, the greatest feature of the method of the present invention is that it is possible to produce a ceramic sintered body with a wall thickness of 30 m or more. This is because the proportion of the organic resin binder in the molded body obtained by the method of the present invention is slightly lower than the proportion of the organic resin binder in the molded body obtained by the conventional method, which is less than 50%.

[Embodiments of the invention]

Next, the present invention will be explained in detail.

As a mixed molding material, SiC with an average particle size of 0.7 μm is used.
After dry premixing of 72 wt% powder, 8 wt% SIC sintering aid, and 20 wt% paraffin wax with an average molecular weight of 500, this mixture was heated to 150 CK for 5 minutes in a sigma mixer. Knead. After cooling this mixed wire material in liquid nitrogen, it was crushed into pieces of 3 to 6 m square on average using a crusher. This was injection molded into a porous mold shown in FIG.

The injection molding conditions are 1st stage pressure crab 50Ky/cd,
In the second stage pressurized crab 20OK, injection temperature: 150C1
Injection time: 100 seconds.

Next, the molded body was placed in a degreasing furnace with an argon atmosphere, and then heated to 4,500 ℃ at various heating rates to thermally decompose and remove the paraffin wax in the molded body.

Thereafter, the surface of the molded body after degreasing was visually inspected for the presence or absence of cracks and blisters. The time required to obtain a good degreased product without cranks or blisters was calculated from the rising rate.

FIG. 2 is a diagram showing the degreasing time versus the thickness of the formed cell in the method of the present invention and the comparative method. The comparative method has an average particle diameter of 0.7 μms + c 2%, AtN: 8, polyethylene resin (average molecular weight: 20.000): 8
．． 5, polyethylene wax (average molecular weight: 2,0
00): A molded article was molded from a mixed molding material consisting of 8.5 h and stearic acid: 3 h in the same manner as in the examples of the present invention, and degreased. The weight loss of the molded article after molding in the comparative method was only 1%.

In FIG. 2, curve a is a comparative example, and the song IVj! b is the present invention. As is clear from the figure, the degreasing time of the method of the present invention is considerably shorter than that of the comparative method. For example, when the thickness of the molded body is 20 m, the comparative method requires 450 hours, whereas
It can be seen that the method of the present invention was 175 times the comparative example after 90 hours.

〔Effect of the invention〕

1. Degreasing time can be significantly shortened.

For example, if the thickness of the molded body is 20 mm, it can be reduced to 115 mm or less using the conventional method. Furthermore, if the thickness of the molded body is lO+m, the thickness can be reduced to 2/9 or less of the conventional method.

2. Ceramic sintered bodies with a wall thickness of 30 m or more can be manufactured.

As described above, according to the present invention, the mixed molding material 1
It has the remarkable effect that the degreasing step when producing a ceramic sintered body through molding and sintering can be significantly shortened, and the manufacturing cost can be significantly reduced.

Further, the present invention has the advantage that a ceramic sintered body having a wall thickness of 30 m or more can be manufactured without causing defects such as cracks and blisters.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of a porous mold used in the method of the present invention, and FIG. 2 is a diagram showing the relationship between the thickness of the molded body and the degreasing time in the method of the present invention and the comparative method. ■... Porous type, 2, 3, 4.5... Porous plate, 6
... r extrusion molding machine nozzle, 7 ... mold space, 8 ...
Mixed molding material 10 Foil 27

Claims (1)

[Claims] 1. A mixed material of ceramic raw material powder and an organic fluidizing agent is injected into a mold to form a molded body, and the molded body is heated to thermally decompose and remove the fluidizing agent. 1. A method for producing a ceramic sintered body comprising the steps of: making the mold a porous body; and making the porous mold absorb an organic fluidizing agent during injection molding. 2. In claim 1, the injection molding method employs two-stage pressurization, and the pressure at the first stage pressurization is 30 to 100 kg.
/cm^2, pressure during second stage pressurization is 101kg/cm^
A method for producing a ceramic sintered body, characterized in that the number of ceramics is 2 or more. 3. Claim 1 or 2, wherein the organic fluidizing agent has a molecular weight of 300 to 5,000 and is fluidized at room temperature or fluidized when heated. Method for producing solids. 4. A method for manufacturing a ceramic sintered body according to any one of claims 1 to 3, wherein the porous mold has a through hole having an outer diameter in the range of 5 to 100 μm. .