JPH06263548A - Production of powder injection molding - Google Patents

Abstract

PURPOSE:To obtain a compact without causing cracking or blistering at a low temperature in a short time by subjecting the compact to the treatment for oxidizing decomposition in an ozone atmosphere in a powder injection molding method for a metal and a ceramic product. CONSTITUTION:This method for producing a part as a particle constituent unit is to form a mixture of powder for sintering with an organic binder and sinter the resultant formed compact. The compact is treated in an ozone atmosphere to subject the organic binder to the oxidizing decomposition in removing the organic binder of the compact. The organic binder can be removed from the compact at a low temperature in a short time without using a toxic organic solvent, etc. The productivity can be improved without causing the cracking or blistering in the resultant compact.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a powder injection molded part, and more specifically, it mixes a metal powder and / or a ceramic powder with an organic binder and injection-molds the mixture into a desired shape. After that, the present invention relates to a method for producing a powder injection-molded article, which comprises oxidatively decomposing and removing the organic binder from the molded article and firing.

[0002]

2. Description of the Related Art As a method for producing a component having a complicated shape using metal and / or ceramic powder, a thermoplastic resin serving as a binder is dispersed and mixed in these powders, and this is molded by an injection molding method, Then, after removing the resin contained in the molded body, that is, degreasing, the molded body is fired to obtain a desired metal or ceramic part. This powder injection molding method has an advantage over a compression molding method called powder metallurgy in that a product having a three-dimensionally complicated shape can be mass-produced with high dimensional accuracy.

The organic binder used in this powder injection molding is a mixture of several kinds of resins such as a binder, a lubricant and a plasticizer. Conventionally, some thermoplastic resins have been investigated as these organic binder components. In order to obtain a defect-free product in the powder injection molding process, the organic binder must be removed from the molded body without causing cracks, swelling or deformation.

As one method for removing the organic binder, a thermal decomposition method (for example, Japanese Patent Laid-Open No. 55-11351).
No. 1) has been proposed and implemented. However, in the degreasing method only by the above-mentioned thermal decomposition, not only is it difficult to select the resin that serves as the organic binder, but in order to prevent cracks and swelling that occur on the product surface, the heating rate per unit time is made small Must be
It has a drawback that the degreasing process requires a long time of tens to hundreds. In order to improve these problems, a method of removing a part of the organic binder from the molded body by solvent extraction and thermally decomposing and removing the remaining organic binder has been proposed and implemented. (Japanese Patent Publication No. 59-27743) However, in this degreasing method by solvent extraction,
However, there are problems such as working environment problems due to the toxicity of the solvent and costs for recovering and recycling the solvent.

[0005]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to solve the above-mentioned problems, and in the powder injection molding method of metal and / or ceramic products, without causing cracks, swelling or deformation of the obtained molded body. An object of the present invention is to provide a method for efficiently removing an organic binder in a short time and without causing a toxicity problem such as a solvent.

[0006]

In order to achieve the above object, the present invention is directed to a powder injection molding method for a metal and / or ceramic product, in which ozone is allowed to act on the molded body when the organic binder is removed, and the organic binder It is characterized by comprising a step of oxidizing and reforming a part of the above.

Generally, polymer compounds undergo oxidative deterioration due to radical chain reaction in an oxidizing atmosphere. Ozone oxidation introduces carbonyl, hydroperoxide, and the like into the main chain and terminal of the polymer, and photopolymerization, thermal decomposition, and the like facilitate the reduction of molecular weight. That is, in an oxidizing atmosphere, the deterioration can be started at a lower temperature. Here, in the powder injection molding method, it is necessary to remove the organic binder at a temperature lower than the temperature at which the sintering of the raw material powder starts. This is because the residual binder hinders the sintering of the raw material powder and reduces the density of the fired body. Therefore, in the present invention, since the organic binder can be decomposed and removed at a lower temperature by the action of ozone, it is possible to obtain a high-density fired product even in the case of a powder having a relatively low temperature at which sintering is started.

Further, in the present invention, the surface of the molded product is modified by oxidative decomposition, and micropaths can be formed. Therefore, when the residual organic binder is removed by thermal decomposition, the decomposition gas of the organic binder that is generated passes through the micropaths previously formed by ozone decomposition to the outside of the molded body, so that cracks and swelling should occur in the molded body. Can improve quality rather than.

The method of manufacturing the powder injection molded article according to the present invention will be described below. The metal powder used in the present invention includes iron or iron alloy powder, titanium-based powder, tungsten-based powder, or magnetic material powder, and the ceramic powder includes silicon nitride powder, silicon carbide powder, alumina powder, and zirconia powder. There is. It can also be used as cermet powder in which metal powder and ceramic powder are mixed.

First, a sinterable powder and an organic binder are melted and mixed to prepare a powder injection molding composition. Next, this powder injection molding composition is molded by a known method using an injection molding machine to obtain a molded product having a desired shape. Here, polyethylene, polystyrene, polyacetal or the like is used as the organic binder. It is also possible to use a photodegradable resin having a tertiary carbon atom in the main chain, such as polymethacrylic acid ester and poly α-methylstyrene.

In order to remove the organic binder added here, the organic binder is oxidized and decomposed in an ozone atmosphere. As a method for generating ozone, it is possible to use silent discharge in clean dry air or oxygen, or to use a light source such as an ultra-low pressure mercury lamp in an atmosphere with oxygen. It is possible.

The removal of the organic binder in the present invention can be carried out by using, for example, an ozone decomposing device as shown in FIG. In FIG. 1, a molded body produced from the powder injection molding composition is placed on a sample table 3. In order to perform degreasing uniformly, the sample stage 3 preferably has a mesh shape. Ozone in the furnace is generated by a method such as silent discharge in clean dry air or oxygen in the ozone generator 6 and introduced through the ozone introduction port 5, or oxygen gas or through the replacement gas introduction port 7. It is also possible to use ozone obtained by introducing a gas containing oxygen and irradiating ultraviolet rays from the ultraviolet light source 10. As the introduction gas, oxygen gas, dry air, a mixed gas of oxygen and argon, a mixed gas of oxygen and nitrogen, or the like is used. As the ultraviolet light source 10, a mercury lamp, a mercury-xenon lamp, a microwave discharge lamp, an excimer laser or the like is used. When using a mercury lamp, a low pressure mercury lamp is preferable in order to make ozone generation more efficient.
The atmosphere in the furnace is agitated by the fan 2 to maintain a uniform atmosphere. Ozone concentration is a parameter that affects the degreasing rate, and the optimum concentration of ozone is selected according to the shape of the target product to oxidize and remove the organic binder. The ozone decomposition in the present invention is preferably carried out by using the heater 1 while maintaining the furnace atmosphere at a temperature at which the organic binder is decomposed and removed by heating. By simultaneously performing thermal decomposition and removal of the low-melting point component in the organic binder, surface modification of the molded body is promoted, and degreasing defects can be reduced in a short time. Further, the present ozone decomposing apparatus can reduce the pressure by using the vacuum pump 9 and introduce a desired gas such as an inert gas or a reducing gas through the substitution paths 7 and 8. Further, when a photo-disintegrating resin is used as the organic binder, it is possible to irradiate ultraviolet rays from the ultraviolet light source 10 for photodecomposition together. By freely setting the height of the sample support base 4, the amount of light applied to the surface of the molded body can be controlled. Further, the shutter 12 can control the irradiation of ultraviolet rays. The shutter part has excellent heat resistance and blocks the heat of the furnace body part. In addition, this apparatus can also perform baking continuously after completing the degreasing step.

Conventionally, degreasing in an oxidizing atmosphere has not been carried out so much because it has a problem that it also oxidizes the metal powder as a material. However, in the present invention, for materials such as metal powders that are easily oxidized by ozone treatment, desired components can be obtained without problems by performing reduction treatment with hydrogen gas or the like in the initial stage of firing and then firing by a conventional method. It has been found. On the other hand, the ceramic powder can be fired in the same atmosphere and firing temperature as the conventional one.

[0014]

In the present invention, by treating a molded product obtained by the powder injection molding method in an ozone atmosphere, the organic binder is reduced in molecular weight by oxidative decomposition and removed from the molded product. By decomposing the organic binder in an oxidizing atmosphere, degreasing can be performed at a lower temperature in a shorter time, and productivity can be improved without causing cracks or swelling in the obtained molded body.

[0015]

EXAMPLES The present invention will be further described below with reference to examples.

Example 1 Stainless steel powder (SUS
316) After using 93.5% by weight of polyethylene, 2.5% by weight of polyethylene, 2.5% by weight of polystyrene and 1.5% by weight of paraffin wax as an organic binder were sufficiently melt-mixed at 150 ° C. using a pressure kneader. , Pelletized. Using an injection molding machine using these pellets, molding temperature 130 ° C, injection pressure 1t / cm 2, mold temperature 20 ° C.
Thus, a plate-shaped molded body having a size of 3 mm × 12 mm × 60 mm was obtained. Next, the organic binder was removed using an ozone decomposing device configured as shown in FIG. Ozone was generated in an oxygen atmosphere using a low-pressure mercury lamp as a UV light source. In the binder removal, the atmosphere in the furnace was heated to 100 ° C. in 0.5 hours in the presence of ozone, further heated to 300 ° C. in 2.5 hours, and held at 300 ° C. for 1 hour. Here, the removal rate of the organic binder, that is, the degreasing rate was 95%. Next, this molded body was heated in a hydrogen stream atmosphere from room temperature to 1000 ° C. for 4 hours, kept at that temperature for 1 hour, and reduced. Then 1000 ℃ to 1330 ℃ in a vacuum atmosphere
The temperature was raised in 1 hour, and the temperature was maintained for 3 hours to obtain a fired body. No crack, swelling, or deformation was observed in the obtained organic binder-removed body and fired body.

Example 2 Stainless steel powder (SUS
316) To 93.5% by weight, 2.0% by weight of paraffin wax and 4.5% by weight of polybutylmethacrylate, which is a photodegradable resin, were used as organic binders sufficiently at 150 ° C using a pressure kneader. After melt mixing, pelletized. Using the pellets, an injection molding machine was used to obtain a plate-shaped molded body of 3 mm × 12 mm × 60 mm at a molding temperature of 130 ° C., an injection pressure of 1 t / cm 2, and a mold temperature of 20 ° C. Next, the organic binder was removed using an ozone decomposing device configured as shown in FIG. Ozone was generated in the same manner as in Example 1. To remove the binder, in the presence of ozone, irradiate with ultraviolet rays 1
After raising the temperature to 00 ° C over 0.5 hours, the temperature is further increased to 300
The temperature was raised to ° C over 2.5 hours. Here, the removal rate of the organic binder, that is, the degreasing rate was 98%. Thereafter, firing was performed in the same manner as in Example 1. The obtained organic binder removed body and fired body, cracks and swelling,
No deformation was observed. The ozonolysis according to the present invention was able to further improve the degreasing rate by using the conventional thermal decomposition and photolysis by ultraviolet irradiation in combination.

Comparative Example 1 In Example 1, the organic binder was not deoxidized by ozone, and degreasing was performed only by a conventional thermal decomposition method. Except for the degreasing step, the same procedure as in Example 1 was performed. The binder should be heated from room temperature to 200 ° C for 3 hours in a nitrogen atmosphere, heated from 200 ° C to 350 ° C for 3 hours, and further heated from 350 ° C to 550 ° C for 1.5 hours. It was done by. The degreasing rate was 90%, and swelling was observed in a part of the removed body of the organic binder. In this method, not only the time required for degreasing is long, but also uniform degreasing is not performed, so that improvement in productivity cannot be expected.

The results of Examples and Comparative Examples are shown in Table 1.

[0020]

[Table 1]

[0021]

According to the present invention, metal powder and / or ceramic powder and an organic binder are uniformly mixed,
After injection molding this into a desired shape, by treating the organic binder in an oxidizing atmosphere in the presence of ozone,
It is possible to remove the organic binder from the molded body at low temperature and in a short time without using a harmful organic solvent or the like. Further, by using it together with the conventional thermal decomposition method and photodecomposition method, degreasing can be performed more efficiently and the quality can be further improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an ozone decomposing apparatus that can be used to carry out the present invention.

[Explanation of symbols]

 1 Heater 2 Fan 3 Sample Table 4 Sample Support Table 5 Ozone Inlet 6 Ozone Generator 7 Replacement Gas Inlet 8 Replacement Gas Outlet 9 Vacuum Pump 10 Ultraviolet Light Source 11 Quartz Glass 12 Shutter 13 Reflector 14 Heat Insulation 15 Control Plate

Claims (3)

[Claims] 1. A method for producing a component as a particle constituent by sintering a compact formed by using a mixture of sintering powder and an organic binder, in the step of removing the organic binder of the compact, A method for producing a powder injection-molded article, comprising a process of oxidizing and decomposing the organic binder by causing ozone to act on the compact. 2. A method for producing a component as a particle constituent by sintering a compact formed by using a mixture of sintering powder and an organic binder, wherein at least one kind of photodegradable resin is used as the organic binder. Using an organic binder mixture containing, a process of oxidizing and decomposing the organic binder by causing ozone to act on the molded body, and ultraviolet light as light having a predetermined energy or more in the molded body,
A method for producing a powder injection-molded article, comprising a step of subjecting the organic binder to photolysis by irradiating it with an electron beam or an X-ray. 3. The method according to claim 1, wherein the action of ozone in the step of removing the organic binder is performed while the molded body is heated.