JPS6335459A - Method of dewaxing formed body of sinterable substance-containing mixture - 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] The present invention relates to a method for degreasing a molded body of a mixture containing a sinterable substance formed by a molding method such as an injection molding method, an extrusion molding method, or a press molding method. The purpose is to provide a degreased product of a molded body of a mixture containing a sinterable substance that not only significantly shortens the degreasing time but also does not cause blisters, cracks, or harmful deformation that occur during degreasing. It is.

Currently, we are mixing powders of ceramic materials such as alumina, silicon carbide, ferrite, barium titanate, and silicon nitride, and metals such as nickel, titanium, and iron with a few percent of water-soluble substances such as polyvinyl alcohol. The granulated powder is shaped using a press method and then sintered, or an organic substance such as polyvinyl butyral is mixed with an organic solvent such as toluene and a sheet is formed using a doctor blade method. After the sheet is manufactured and dried, it is generally punched out using a punching die, degreased and dried to obtain a molded product. However, in such a method,
It was not possible to obtain a molded product that was three-dimensional and had a complicated shape. Recently, a method for obtaining green bodies by injection molding has been developed in order to obtain molded articles having complex three-dimensional shapes. In order to obtain a green body with a complicated shape by this injection molding method, 10 to 30% by weight of a low polymer of various polymers such as wax, styrene polymer, acrylic polymer, etc. is added to the ceramic material or metal. It is carried out by filling the mixed mixture into a mold using an injection molding machine. In order to sinter the green body thus obtained, a degreasing step is required to remove the polymeric substances and organic substances used in shaping the green body. After removing polymeric substances and organic substances,
A sintered body can be obtained through a sintering process, but conventional methods such as the press method and doctor blade method do not cause blisters, cracks, or harmful deformation in the compact during the degreasing process, and The time required for degreasing is also short.

However, due to molding methods such as injection molding and extrusion molding, the molded product contains a large amount of polymeric substances and organic substances, so the degreasing process takes significantly longer than conventional methods. There are problems such as blisters and cracks on the surface of the green body and deformation of the molded body.

From the above, the present invention does not have these problems (defects), and is more efficient than green bodies produced by injection molding, extrusion, etc., and requires a degreasing process to produce a sintered body. The objective is to obtain a product by a method that shortens the process and does not cause harmful deformations such as blisters and cracks during degreasing.

According to the present invention, the problem is that the molded body of the sinterable substance-containing mixture is heated to a pressure of 10 Pa to 8×10'.
Pa (0,1 to 80 mbar) and temperature 20 to
The binder in the molded product is 5.0 to 5 at 300°C.
After processing until the reduction is 0% by weight, further 2.0X1
0 Pa to 1. OX 10” Pa (2~10K
g/cm”) (7) Maximum temperature under conditions of 300~
Temperature increase rate is 0.5 to 100℃ per hour up to 600℃
The problem can be solved by a method for degreasing a molded body of a sinterable substance-containing mixture, which is characterized by degreasing a molded body of a sinterable substance-containing mixture. The present invention will be explained in detail below.

The sinterable substance-containing mixture in the present invention essentially consists of the following sinterable substance and a binder.

(A) Sinterable substance The melting point, decomposition temperature or sublimation point of the sinterable substance of the present invention is usually 600°C or higher, preferably t,ooo°C or higher, and particularly preferably l,400°C or higher. The use of metals or inorganic compounds with melting points, decomposition temperatures or sublimation points below 600° C. as sinterable substances results in harmful deformation and blistering during degreasing (calcination).

Moreover, the average particle size is 0.1 to 500 microns.

This average particle size varies depending on the type of sinterable substance, but in the case of metal it is usually 1 to 500 microns, and 1 to 500 microns.
300 microns is preferred, and 1-200 microns is most suitable. When a metal with an average particle size of less than 1 micron is used, crosstalk is difficult.

On the other hand, if a metal with a diameter exceeding 500 microns is used, the mechanical properties of the molded product obtained by sintering will deteriorate. In the case of inorganic compounds, the thickness is generally 0.1 to 200 microns, preferably 0.1 to 150 microns, and particularly preferably 0.1 to 100 microns. Average particle size is 0.
If an inorganic compound with a diameter of less than 1 micron is used, it is difficult to uniformly disperse the inorganic compound during kneading during production of the composition.

On the other hand, if an inorganic compound with a diameter exceeding 200 microns is used, shape retention will be poor when sintering a molded product of the composition, the density after sintering will be reduced, and the mechanical strength of the sintered body will be reduced. do.

Typical examples of metals used as sinterable materials in the present invention include metals such as aluminum, iron, copper, titanium, molybdenum, zirconium, cobalt, nickel, and chromium, and metals based on these metals (at least 50% by weight). Examples include alloys that Powders of these metals and alloys are widely used as bearing base metals, free-cutting steel, heat-resistant materials, wear-resistant materials, etc., and are generally referred to as powder metallurgy materials. Furthermore, typical examples of inorganic compounds include ceramic materials such as alumina, silicon carbide, silicon nitride, zirconia, cordierite, tungsten carbide, and aluminum nitride. Furthermore, as a sintering aid, boron, beryllium, carbon, yttrilam oxide, cerium oxide, magnesium oxide, lithium oxide, etc. are added in an appropriate small amount (generally at most 20 parts by weight per 100 parts by weight of the inorganic compound). It's okay.

(B) Binder Resins that can be used as binders include ethylene polymers, styrene polymers, propylene polymers, ethylene-vinyl acetate copolymers, alkyl (carbon number
6 or less) methacrylate as the main component (50% by weight or more) (e.g., polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate) and alkyl (6 or less carbon atoms) acrylate as the main component (50% by weight) % or more) (for example,
0 or more including polymethyl acrylate, polyethyl acrylate, polybutyl 7 acrylate),
The term "based polymer" means a homopolymer of the heptamer and a copolymer containing the monomer as a main component (at least 50% by weight) and other monomers. The number average molecular weight of these binders [vapor osmotic pressure method (vapor pres,
[measured by the sureosmo ■6ter) method] is usually 2,000 to 10,000, preferably 4,000 or more. These binders are widely used in the field of manufacturing sintered materials by mixing with ceramic materials. .

(C) Production of mixture In producing the mixture of the present invention, the sinterable material 1
The mixing ratio of binder to 00 parts by weight is generally 5
~40 parts by weight, preferably 10 to 40 parts by weight, particularly preferably 10 to 30 parts by weight.

If the mixing ratio of the binder to 100 parts by weight of the sinterable material is less than 5 parts by weight, not only will the kneadability, moldability and dispersibility of the mixture be poor, but it will also be difficult to produce a homogeneous mixture. Even if a mixture is obtained, good green bodies cannot be obtained, while 40
If it exceeds the weight part, the physical properties of the green body (strength, shape retention) are good, but the density after removing the binder is low, and furthermore, it is difficult to sinter.

Furthermore, if necessary, halogen-free processing aids such as fatty acid amides, fatty acids or their esters, fatty alcohols, phthalates, aliphatic ethers, paraffin waxes, silane-based or titanate-based coupling agents are added. be able to. At this time, the amount of processing aid added is at most 2 parts by weight per 100 parts by weight of the sinterable material.
0 parts by weight, particularly preferably 10 parts by weight or less.

The sinterable substance-containing mixture of the present invention can be produced by uniformly mixing the above sinterable substance and the binder or these and the processing aid. As a mixing method, it can be produced by tri-blending using a mixer such as a Henschel mixer, which is commonly used in the field of thermoplastic resins, or by using a Banbury mixer,
It can also be obtained by melt-kneading using a mixer such as a kneader, roll mill, or screw extruder. At this time, a homogeneous mixture can be obtained by triblending in advance and melt-kneading the resulting mixture. In this case, the mixture is generally melt-kneaded and then molded into pellets, which are then subjected to the molding described later.

(D) Molding method The molded body of the sinterable substance-containing mixture used in the degreasing method of the present invention is molded using an injection molding machine, extrusion molding machine, press molding machine, etc. at a temperature where the binder in the mixture melts. It is obtained by molding at a temperature that does not decompose. The molding temperature cannot be limited by the type of binder in the sinterable substance-containing mixture, but is generally 70°C.
~300°C. The obtained molded bodies of the sinterable substance-containing mixture in various shapes are subjected to degreasing described later.

The degreasing method, which is an important element of the present invention, can be divided into two steps. It is characterized in that it is first heat-treated under reduced pressure (hereinafter referred to as the "second degreasing step") and then further heated under pressure (hereinafter referred to as the "second degreasing step").

(E) First degreasing step When carrying out the first degreasing step of the present invention, the pressure is 10
Pa to 8X104Pa, preferably 100Pa to 7X10Pa, particularly preferably 1X103Pa to 5X10'Pa. This process is 10Pa
No matter how low the processing temperature is,
Blisters occur on the surface of the molded product. On the other hand, 8X 10'
If the temperature exceeds Pa, blisters or cracks will occur on the surface of the molded product unless the treatment temperature is lowered and the treatment time is significantly extended.

In addition, the treatment temperature is 20 to 300°C, and 40 to 250°C.
℃ is desirable, and 50 to 230℃ is suitable. If this treatment is performed at a temperature lower than 20° C., blisters will occur on the surface of the molded product even if various conditions are changed in the second degreasing step described later. On the other hand, if the degreasing is carried out at a temperature higher than 300° C., the molded body will be deformed in this first degreasing step. The rate of heating up to the highest treatment temperature in this first degreasing step is not particularly limited, but is generally 10 to 100°C per hour. Furthermore, even under reduced pressure by the time of temperature rise,
Further, pressure reduction may be started after reaching a predetermined temperature.

When carrying out this first degreasing step, the relationship between pressure and temperature is not particularly limited, but if the temperature is low, it is necessary to lower the pressure. On the other hand, when the pressure is high, it is desirable to carry out the process at a relatively high temperature.

In this first degreasing step, the binder in the molded body is
It is important to process at the pressures and temperatures mentioned until a reduction of ~50% by weight (preferably 5-45% by weight) is achieved. If the treatment is carried out for a short period of time, the molded product may blister, crack or deform, which is undesirable.However, if the treatment is carried out for a long time, it is not desirable from an industrial perspective.Therefore, the treatment time is generally 0. The time is 1 to 10 hours, preferably 0.2 to 5 hours.

In the first degreasing step of the present invention, 2.5X 10'P
a to 4. At a pressure of OX 10' Pa, 120~1
It is preferred to treat at a temperature of 80°C for 0.5 to 2 hours.

(F) Second degreasing step By subjecting the molded body thus obtained in the first degreasing step to pressure treatment (second degreasing step), the degreasing time can be significantly shortened.

The pressure in this second degreasing step is 2.5X 105Pa
Or 1. OX 10”pa (2~10Kg
/ cm') and 3, OX 10 Pa to 9. OX 105Pa is preferred, especially 4.0X10
Pa to 8.5×105 Pa is preferred.

In this step, 2. If carried out at a pressure lower than OX 10” Pa, even if the heating rate is slowed down,
Blisters occur on the molded product. On the other hand, 1. OX 108P
If this step is carried out beyond step a, there will be problems in manufacturing.

The temperature increase rate in this process is 0.5 to 10 per hour.
0°C, preferably 1.0 to 100°C, particularly preferably 20 to 70°C. The heating rate is 0.0 per hour.
If this step is carried out below 5°C, the degreasing time will not be shortened. On the other hand, if the temperature exceeds 100°C per hour, blisters will occur in the molded product. Also, the maximum temperature is 300
-800°C, preferably 350-600°C, particularly preferably 400-580°C. If the maximum temperature is less than 300°C, cracks will occur during sintering due to the large amount of residual carbon etc. in the resulting molded body. On the other hand, the maximum temperature is 60
If the temperature exceeds 0°C, handling becomes a problem when sintering the compact.

Both of the above first treatment step and second treatment step may be performed in an inert gas (for example, nitrogen gas),
It may be carried out in oxygen or air.

According to the present invention, when degreasing a molded body of a sinterable substance-containing mixture, the surface of the mold is No harmful deformations such as blisters, cracks, or deformations occur.
In addition, the degreasing time can be significantly shortened compared to degreasing under atmospheric pressure when conventional degreasing is carried out only by pressurization or by vacuum only. The degreased body thus obtained can be finished into a final product by sintering.

- Hereinafter, the present invention will be explained in more detail with reference to Examples.

Examples 1 to 10, Comparative Examples 1 to 3 Average particle size is 1. Op, vs alumina (manufactured by Showa Light Metal Co., Ltd., trade name AL-45-A), average particle size is 0
．． 6gm of silicon carbide (manufactured by Showa Denko, trade name DU)
A-2S) and pure iron (manufactured by Showa Denko K.K., trade name: 7 Tomilon) having an average particle size of 40IL were used as the sinterable material.

9 of each of these sinterable substances shown in Table 1.
0 parts by weight, 10 parts by weight of polymethyl acrylate having a number average molecular weight of about 300,000, 2.0 parts by weight of dibutyl phthalate, and 1.0 parts by weight of stearic acid were pre-triblended for 5 minutes using a Henschel mixer. I did it. The composition (
pellets) were produced. Each of the obtained pellets was molded using an injection molding machine at 160°C, with a wall thickness of 5 m,
A cylindrical molded body with a height of 130 mm and an outer diameter of 25 mm was manufactured.

Each of the obtained molded bodies was placed in a vacuum furnace and subjected to a vacuum treatment (first degreasing step) under the pressure and temperature conditions shown in Table 1 for the time shown in Table 1. The amount of decrease (
Degreased amount) was determined. The results are shown in Table 1.

Each molded body degreased in this way is placed in a pressure furnace, heated to the maximum temperature under the conditions of pressure and temperature rise rate shown in Table 1 in a nitrogen atmosphere, and then subjected to pressure treatment (second Degreasing step) was performed. With the exception of Comparative Example 1, no abnormalities were observed in the external appearance of the molded articles degreased in this manner, but in Comparative Example 1, blistering had occurred in the external appearance.

Each molded body thus degreased was placed in a sintering furnace and heated to 1600°C under a nitrogen atmosphere (however, in Example 9,
In Example 10, up to 2200°C under an argon atmosphere.
Sintering was carried out by raising the temperature at a rate of 100°C/hour (up to 1100°C under vacuum). No abnormality was observed in any of the sintered bodies obtained in all Examples. However, in Comparative Examples 2 and 3, blistering occurred on the surface of the sintered body.

Moreover, in Comparative Example 1, cracks were generated in the sintered body.

(Hereinafter in the margin) ``LL''L button According to the method of the present invention, the following effects (characteristics) are exhibited.

(1) Degreasing time is significantly shortened.

(2) There is no occurrence of blistering, cracking, deformation, etc. in the degreased molded product.

(3) Even if the molded article has a complicated shape, it can be degreased without the above abnormalities.

Claims (1)

[Claims] After treating the molded body of the sinterable substance-containing mixture at a pressure of 10 Pa to 8×10^4 Pa and a temperature of 20 to 300°C until the binder in the molded body is reduced by 5 to 50% by weight, further Maximum temperature is 300℃ under pressure of 2.0×10^5Pa to 1.0×10^6Pa
Temperature increase rate is 0.5-100℃ per hour up to ~600℃
A method for degreasing a molded body of a mixture containing a sinterable substance, the method comprising degreasing a molded body of a mixture containing a sinterable substance.