JPH01219070A - Production of sintered body - Google Patents

Abstract

PURPOSE:To shorten a degreasing time in a stage of producing a sintered body with an org. binder by causing a chemical reaction by allowing a molded body to contact with fluid in a stage of degreasing, and removing the binder in the molded body by the effect of gene rated gas. CONSTITUTION:A powdery material (e.g., aluminum nitride powder, powdery metallic Si) for a sintered body is mixed with a sintering additive and an org. binder (e.g., liquid paraffin, polyethylene wax). After prepg. a molded body by compressing the powder mixture, the molded body is allowed to contact with fluid (e.g., water, aq. HCl), and a chemical reaction is caused between the fluid and the powdery raw material, and a gas is generated. The org. binder is separated from the powdery raw material by the pressure of the generated gas and moved toward a surface side of the molded body, from where it is discharged to the outside of the system. A sintered body is obtd. by sintering then the molded body freed of the org. binder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a sintered body by removing an organic binder from a molded body.

[Conventional technology]

In general, ceramic sintered products are produced by pressure-forming a mixture mainly composed of ceramic powder raw materials, sintering aids, and organic binders into the cavity of a mold, and then evaporating or removing the organic binder remaining in the molded body. It is removed by thermal decomposition to produce a ceramic degreased body, and this degreased molded body is sintered.

The purpose of adding an organic binder to the mixture before forming a molded body is to impart fluidity to the non-flowable ceramic powder and improve the fluidity of the mixture.

Therefore, a mixture with a high proportion of organic binder has excellent fluidity.

The amount of organic binder in the mixture varies depending on the shape, size, wall thickness, etc. of the product to be molded. in general.

If the product shape is complex and thin, the flow resistance of the mixture will increase when it is filled into the cavity of the mold, so when making a product with such a shape, a mixture with a large amount of binder should be used. There is a need to. On the other hand, if the amount of organic binder contained in the molded article is large, the degreasing treatment time will be longer when the organic binder is removed by evaporation or thermal decomposition by heating.

Next, an example of a degreasing process for an injection molded body produced using a mixture containing a large amount of organic binder will be described below. Of course, it varies depending on the shape, size, and thickness of the molded object, but
In general, the heating rate of the molded body is usually about 1 to 1.degree. C., and the maximum heating temperature during degreasing is 400 to 700.degree. C., so the degreasing treatment requires 55 to 550 hours. On the other hand, in the case of a molded article having a wall thickness of 25W11 or more, the removal method by heating requires a degreasing treatment time of 550 hours or more. For this reason, various methods have been proposed to shorten the degreasing process. It can be broadly divided into the following three categories.

(1) A method of removing the organic binder from the molded body while controlling the heating atmosphere.

(2) A method of removing the organic binder in the molded body using an organic solvent.

(3) A method of removing the organic binder in the molded body using a supercritical fluid.

These methods will be explained by citing representative examples for each item. First, as an example of (1) heating, there is
There is a publication No. 7-17468. This is a method in which the organic binder is removed by performing a degreasing step by heating the molded body under high pressure gas higher than at least 1 atmosphere using a non-oxidizing gas. Specifically, alumina powder with a particle size of 44 μm or less is used as a ceramic powder, and 20 parts by weight of a mixture of polystyrene, diethyl phthalate, and stearic acid are mixed as an organic binder, with the alumina powder being 100%, and this is mixed in a kneader at the softening temperature of the resin at 160°C. Knead. After cooling it and making it into pellets, it was injected under the following conditions: injection pressure: 800 kgf/a#, injection temperature: 180°C, mold temperature: 35°C, width: 10++m, thickness: 5f
A plate-shaped test piece with an fI of 11 and a length of 50 mm was molded. This was heated from room temperature to 50℃ for 1 hour under a N2 atmosphere of 10 atm.
It is heated slowly over a period of time, and then heated from 50° C. to 450° C. at a temperature increase rate of 6° C./h, and the resin is decomposed and removed in 50 hours, producing a defect-free degreased body. Also, if you try to shorten the degreasing time by increasing the temperature increase rate.

If the molded object cracks, swells, or deforms,
It is stated that a quality product cannot be produced.

An example of (2) in which the organic binder in the molded body is removed using an organic solvent is disclosed in JP-A-59-27743. This is silicon nitride powder 76.4% as a ceramic powder.
wt%, as organic binder.

Polystyrene 15.3wt%, polyethylene 3.8wt%
%, stearic acid 2.8wt%, diethyl phthalate 1
．． 7 wt% using a kneader at 180°C.

The mixture was sufficiently kneaded at 2.5 atm and then made into pellets of 3 to 5 ffI. This was heated at a heating cylinder temperature of 250℃, an injection pressure of 1000kg/a#, a mold temperature of 50℃, a width of 60m,
A plate-shaped test piece with a length of iooms and a thickness of 8 m was injection molded. In the degreasing step, the binder was removed by immersing the test piece in methylene chloride at a temperature of 15° C., which was filled in a two-volume container with a lid, for 40 hours. Of the organic binders, 93% of polystyrene, stearic acid, and diethyl phthalate excluding polyethylene were eluted and removed. Since polyethylene remains among the organic binders, the elution removal rate of the organic binders as a whole is 35%. No cracks or deformation were observed in this molded product.However, since polyethylene remains in the molded product in this method, the temperature was raised from room temperature to 1750°C at a rate of 200"C/h in a nitrogen atmosphere. It is removed by heating at high speed.

Therefore, the degreasing time by this method is 4
It takes a long time, which is the total time including 0 hour and removal time by heating.

An example of (3) in which the organic binder in a molded body is removed using a supercritical fluid is disclosed in JP-A-61-155265. This is alumina powder 10 as a ceramic powder.
0 parts by weight, 15 parts by weight of octadecanol as an organic binder was added and mixed, this was put into a hydraulic press and pressure-molded at 700 kgf/al, and this was brought into contact with a supercritical fluid of carbon dioxide gas. Degreased. The conditions for the supercritical state of carbon dioxide during degreasing are a temperature of 45°C and a pressure of 200 kgf/a.
&, the fluid amount is 200Q. Binder removal rate is 70%
The degreasing time is 2.2 hours.

The above are conventional examples of removing an organic binder from a molded body. Among the three methods mentioned above, the most common method is (1) removal method by heating.

[Problem to be solved by the invention]

The problems of the three conventional techniques mentioned above will be described in turn.

In the method of prior art (1), which removes the organic binder from the molded body while controlling the heating atmosphere, increasing the temperature increase rate during heating in order to shorten the degreasing time causes expansion of the organic binder and vaporization. Due to pressure, pyrolysis gas, etc., cracks, blisters, deformations, etc. occur in the molded product, making it impossible to produce a good degreased product.

Therefore, in this method, the degreasing process must be carried out gradually over a long period of time. For example, the thickness of the molded body is 5 m.
Even in the case of M, the degreasing treatment requires 50 hours or more.

If the wall thickness is 5+m or more, a longer degreasing process is required. Furthermore, if the degreasing process takes a long time, the power consumption will be large and the cost of the ceramic product will be high.

In the case of the conventional technique (2), in which the organic binder in the molded body is removed using an organic solvent, an organic binder that does not dissolve in the organic solvent may be used, so the molded body is immersed in the solvent to dissolve and remove the binder. After that, the remaining binder is removed by heating. In this way, since the one-method method combines two methods for removal, the degreasing process requires a long time. In the cited example, the dissolution and removal treatment by immersion takes 40 hours,
Since the heating treatment time is 25 hours, the total degreasing time is 65 hours or more. When the wall thickness is 511ffi+, the degreasing process takes a long time, so when the wall thickness is 51 m or more, the degreasing process requires 65 hours or more. Furthermore, since the two degreasing treatment methods are combined, the number of man-hours in the manufacturing process increases, and this expense is added, resulting in a disadvantage that the product cost increases.

In conventional technology (3), a method of removing an organic binder from a molded body using a supercritical fluid, carbon dioxide gas,
It states that the removal process takes 2.2 hours when octadecanol is used as the organic binder and the binder removal rate is 70%. However, the degreasing process of this method includes a pre-process from normal temperature and pressure to a supercritical state, and a post-process from the supercritical state to return to normal temperature and pressure. It is considered that this time should also be added to the degreasing treatment time. However, since the cited example does not specify the time required for the preceding and following steps, it is unclear how much time is required. According to other documents, for example, in the post-process 2
If the rate of pressure reduction from the high pressure of 000 atm to the normal pressure of 1 atm is increased, the molded article will swell or deform, so this is done gradually. After all, since it is thought that more than one day and night is required for the pre- and post-processing, a long time is required for the degreasing process. Further, although the thickness of the molded body is not described in the cited example, it is thought that the wall thickness is about 5IIfl, and a molded body with a wall thickness of 51 or more requires 24 hours or more for degreasing.

Furthermore, since the method of creating a supercritical state of carbon dioxide gas in the cited example requires an ultra-high pressure vessel, the degreasing equipment is quite expensive. For this reason, there is a drawback that the cost of ceramic products increases.

As described above, the conventional technology has a problem in that the degreasing process for removing the organic binder from the molded body requires a long time. Furthermore, since an expensive degreasing device is used, there is also the problem that the cost of the ceramic product increases.

An object of the present invention is to provide a method for manufacturing a sintered body that can shorten the so-called degreasing time for removing an organic binder from a molded body. Another objective is to reduce the cost of ceramic products.

[Means to solve the problem]

The above purpose is to bring the molded body into contact with a fluid during the degreasing process, to cause a chemical reaction between the powder raw material in the molded body and the fluid, to generate gas, and to use the gas pressure and the buoyancy of the fluid to move the molded body into contact with the fluid. This is achieved by removing the organic binder.

That is, the present invention includes a step of mixing a powder raw material for a sintered body, a sintering aid, and an organic binder to form a mixture, a step of pressurizing the mixture to form a molded body, and a step of removing the organic binder from the molded body. In the method for producing a sintered body, which includes a degreasing step and a sintering step, during the degreasing step, the compact is brought into contact with a fluid, and at least one powder raw material component in the compact is brought into contact with the fluid. The organic binder inside the molded body is removed by causing a chemical reaction and using the gas pressure and fluid buoyancy generated at that time.

The powder raw material for the sintered body used in the present invention consists of at least one of metal powder and ceramic powder. Metal powders include various metal powders such as metallic silicon powder, iron or iron alloy powder such as high-speed steel, superalloy powder such as titanium, tungsten, and boron powder, and magnetic material powder. There are various powders such as silicon nitride powder, silicon carbide powder, alumina powder, zirconia powder, sialon powder, etc. Further, it can be used as a cermet powder that is a mixture of metal powder and ceramic powder, and if necessary, one or more of these various metal powders and ceramic powders can be mixed and used as appropriate. Further, in addition to the raw material powder, sintering aids, forming aids, other aids for improving physical properties, etc. can be added to these powders in advance as appropriate.

The powder raw material for the sintered body can be made from a mixture of a plurality of components, and the fluid can react with one of the components, thereby efficiently removing the organic binder.

The organic binder used in the present invention is liquid at room temperature or liquefied by heating, and has a viscosity of 10 to 200 cP.

For example, liquid paraffin, which is liquid at room temperature, has a melting point of 60-70.
Paraffin wax (solid wax) at ℃ 64-6
Examples include stearic acid at 8°C, polyethylene wax (synthetic wax) at 118 to 128°C, and the like. By being liquid, high fluidity can be imparted to the ceramic powder. Further, if the viscosity of the liquid is 10 cP or less, the force for binding the ceramic particles is small, and the molded body cannot be kept in shape. In addition, if the viscosity of the liquid is 200 cP or more, the adhesive force between the ceramic particles and the organic binder is large, and it is difficult to remove the organic binder from the molded body due to the gas pressure and buoyancy of the fluid generated by the chemical reaction between the ceramic particles and the fluid. .

The fluid used in the present invention includes gases such as water and steam, aqueous solutions of inorganic acids such as hydrochloric acid and sulfuric acid, and aqueous solutions of caustic soda and caustic potash. The combination of these fluids and the powder raw material for the sintered body causes a chemical reaction when the two come into contact, generates gas, and can remove the organic binder in the molded body.

For example, when the fluid is water, the powder raw material is Si3N<+
Examples include AflN and the like. When the fluid is a caustic soda aqueous solution, the powder raw material is S L Ot #Si, N,,Si
C* Affi20. , AfiN, etc. When the fluid is an inorganic acid, powder raw materials include SL, N4°AQN, etc.

[Effect]

When the compact is brought into contact with a fluid, a chemical reaction occurs between the raw material powder such as ceramic powder in the compact and the fluid, generating gas. As the chemical reaction progresses, the amount of gas generated increases, and the gas pressure increases accordingly. When this gas pressure exceeds the adhesive force of the organic binder that binds and binds the ceramic particles in the molded body, the organic binder separates from the particles. Further, the generated gas moves to the side where the gas pressure is lower, that is, to the surface side of the molded body, and is released to the outside of the system at the surface of the molded body. At this time, the separated organic binder is extruded out of the system through the gap between the molded bodies together with the gas, and is removed. In addition, if the wettability of the ceramic particles and the fluid is higher than the wettability of the organic binder, the organic binder attached to the ceramic particles will be gradually replaced by the fluid, and the adhesive force of the fluid will push the organic binder out of the system. The organic binder is removed.

The chemical reaction between the ceramic particles and the fluid proceeds sequentially from the surface of the molded body toward the center. Therefore, the organic binder is removed from the surface of the molded body toward the center. In this degreasing step, the liquid organic binder is discharged with a slight gas pressure, and high stress is not generated in the molded body. Therefore, when degreasing, the molded product is less likely to crack or deform, and the organic binder can be easily removed in a short time even in thick molded products without causing stress. In the method of removing the organic binder in the molded body by heating according to technique (1).

The organic binder is thermally decomposed and gasified, and the gap between the molded bodies is moved and removed. This is the method.

When the temperature of the uniformly heated molded body reaches the thermal decomposition temperature of the organic binder, thermal decomposition occurs simultaneously on the surface and inside of the molded body, and pyrolysis gas is generated almost at the same time, so gas movement is prevented. is not going smoothly. As a result, the gas pressure increases, and this force causes the molded body to crack, swell, or deform.

If the wall thickness of the molded body is large, it becomes increasingly difficult for gas to move, and therefore, in the case of a thick molded body, it is particularly difficult to remove the organic binder by heating.

〔Example〕

Example 1 Aluminum nitride powder (average particle size 0.6 μm) 82w
t% and liquid paraffin 18wt% are mixed in a sieve machine, the mixture is filled into the cavity of the mold, and then pressurized at 100 kgf/cd with a mechanical press to form a mold with a width of 70 mm.
A plate-shaped test piece having a length of LooIIIm and a thickness of 15 ng++ was prepared. In the degreasing process, lacquer is sprayed onto the surface of the test piece and the solvent in the lacquer is evaporated. This was immersed in distilled water 1 at <20° C. as shown in FIG. Aluminum nitride reacted with water to generate ammonia gas 2, and this generated gas was used for degreasing. In the figure, 3 indicates the molded body and 4 indicates the removed organic binder. The results are shown in FIG.

In the figure, 5 shows the case of the present invention, and 6 shows the case of a comparative example described later.

The degreased body obtained by removing liquid paraffin from the molded body had no cracks in appearance. Furthermore, when the degreased body was divided into several parts and the inside was examined, no internal cracks were found. Here, examples of the lacquer include clear lacquer (finishing clear lacquer, etc.), colored lacquer (transparent colored lacquer, etc.), high solid lacquer, and the like.

Comparative Example 1 The test piece prepared in Example 1 was degreased by heating according to Prior Art 1. In the degreasing process, heating was performed in a degreasing furnace with an argon gas atmosphere. The heating conditions were from room temperature to 120°C at a heating rate of 50°C/h, and held at 120°C for 10 hours. Next, the temperature was raised from 120°C to 500°C at a rate of 5°C/h, and held at 500°C for 10 hours. Thereafter, it was cooled in a furnace and degreased. The degreased body had no cracks in appearance, and when the body was divided into several parts and examined internally, no internal cracks were found. However, the temperature increase rate from 120℃ to 500℃ is 1
When the degreasing was carried out at 0°C/h, cracks appeared in the appearance of the degreased body.

As can be seen from FIG. 2, when looking at the degreasing rate of 90% or more, the degreasing time of Example 5 of the present invention was 1/2 of the degreasing time of Comparative Example 6, and according to this example, the molded product It has the effect of significantly shortening the degreasing time by removing liquid paraffin from the machine.

Example 2 A mixture of 62 wt% metal silicon powder (average particle size 2 μm), 23 wt% nitrogen silicon powder (average particle size 1 μm), and 15 wt% liquid paraffin was pressurized in the same manner as in Example 1 to form a mixture with a width of 70 mm and a thickness of 70 mm. 15I and a length of 100+ am was prepared. In the degreasing process, lacquer was sprayed on the surface of the test piece in the same manner as in Example 1 to volatilize the solvent, and then the test piece was heated at 50°C.
It was immersed in distilled water warmed to 50 hours. Nitrogen silicon reacted with water to generate ammonia gas, and this generated gas was used for degreasing. The degreasing rate is 90% or more, and the degreased body has no cracks on the outside. Also, when we divided the car into several parts and inspected the inside, we found many internal cracks.

Next, the degreased body was heated at 1100'C in a nitrogen atmosphere for 10 hours.
When nitrided at 200° C. for 10 hours and at 1350° C. for 10 hours, a good nitrogen silicon sintered body was obtained.

〔Effect of the invention〕

According to the present invention, the removal rate of the organic binder in the molded body can be increased, so that the degreasing time can be shortened. For example, when liquid paraffin is used as the organic binder and the thickness of the compact is 15 mm, the conventional heat removal method requires 100 hours for degreasing;
According to the instructions, it can be removed in 50 hours.

[Brief explanation of the drawing]

FIG. 1 is a side view showing the degreasing process according to the present invention, and FIG. 2 is a diagram showing the relationship between the degreasing time and the degreasing rate. 1... Water (fluid), 2... Gas, 3... Molded object. 4...Organic binder (removed).

Claims (4)

[Claims] 1. A process of mixing the powder raw material for the sintered body, a sintering aid, and an organic binder to form a mixture, a process of pressurizing this mixture to form a molded body, a degreasing process of removing the organic binder from this molded body, and a sintering process. A method for manufacturing a sintered body including a binding step, characterized in that during the degreasing step, the molded body is brought into contact with a fluid to cause a chemical reaction, and the binder in the molded body is removed by the gas generated at that time. A method for producing a sintered body. 2. 2. The method for producing a sintered body according to claim 1, wherein the powder raw material for the sintered body comprises at least one of metal powder and ceramic powder. 3. 2. The method for manufacturing a sintered body according to claim 1, wherein the powder raw material for the sintered body is made of a mixture of a plurality of types of components, and the fluid reacts with one component in the mixture. 4. A method for producing a sintered body in which the organic binder is liquid at room temperature or liquefied by heating, and has a viscosity of 10 to 200 cP in the liquid state.