JPH10317005A - Manufacture of powder injection molded sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a powder injection molded sintered body in which the flow stability of the composition for injection molding is improved, the ratio of generation of defects in an injection molded body obtained through the injection molding is reduced, the injection molded body obtained in the injection molding process can be cyclically used as the composition for injection molding, the water extraction and degreasing process is achieved after the injection process, and the powder injection molded sintered body excellent in dimensional stability can be obtained in a short time. SOLUTION: When the composition for injection molding is prepared, the composition is injection-molded to form an injection molded body, the injection molded body is degreased and then sintered to manufacture the powder injection molded sintered body, the mixture of the powder for injection molding, the thermoplastic organic binder and the antioxidant is used for the composition for injection molding, segmentation of the polymer chain in the thermoplastic organic binder under the fast shearing stress is suppressed preferably, in addition to the powder for injection molding, the thermoplastic organic binder and the antioxidant, the injection molded body obtained in the injection molding process is used as the composition for injection molding. In addition, the injection molded body obtained in the injection process after the injection molding process is brought into contact with water, and heated, and then, sintered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a powder injection sintered body, and more particularly to a method for manufacturing a powder injection sintered body including an injection molding step performed under high-speed shear stress.

[0002]

2. Description of the Related Art Conventionally, as a method of producing a sintered body from a metal powder or a ceramic powder, a method of mixing and kneading a metal powder or a ceramic powder and an organic binder, and plastically molding this to obtain a molded body. In general, a method for obtaining a sintered body by degreasing the molded body and then performing a sintering process is used. As a plastic molding method, a product having a three-dimensional complicated shape is relatively accurately formed. An injection molding method that can be mass-produced is suitably used.

[0003] The injection molding method is disclosed in Japanese Patent Application Laid-Open No. Hei 3-1350.
No. 5 discloses a method of performing injection molding by adding an antioxidant to a powder containing a metal or ceramic powder and a binder.

[0004] As a method for degreasing an injection molded article obtained by injection molding, a method of decomposing and evaporating an organic binder by heating the injection molded article (hereinafter referred to as "heat degreasing method"), There is a method in which an organic binder is eluted from an injection-molded article using an organic solvent (hereinafter referred to as "extraction degreasing method"). It is difficult to degrease in time, and in the extraction degreasing method, the organic solvent is expensive, and may be dangerous depending on handling, and there is also a problem in environmental measures.

[0005] To improve this point, Japanese Patent Publication No. 6-53
No. 884 discloses a method for producing a sintered body by mixing a powder and an organic binder, subjecting the mixture to injection molding to obtain an injection molded body, and performing each of degreasing and sintering processes. As the binder, an organic binder containing at least one water-soluble thermoplastic organic polymer and at least one water-insoluble thermoplastic organic polymer is used. As the degreasing treatment, the injection molded body is brought into contact with water. Eluting the water-soluble thermoplastic organic polymer by heating the remaining organic binder in a heating furnace to remove the binder from the powder injection-molded article (hereinafter referred to as "water extraction degreasing method"). ) Are disclosed. Such a water extraction degreasing method can perform degreasing without causing defects in an injection molded article in a shorter time as compared with a heat degreasing method, and does not require the use of an organic solvent as compared with the extraction degreasing method. It has the advantage that there is no danger and no environmental problems arise.

However, when an injection molding composition containing a water-soluble thermoplastic polymer at a high content (for example, the proportion of the water-soluble thermoplastic polymer in an organic binder is 60 to 90% by weight) is injection-molded, The problem arises that the fluidity of the composition for application becomes unstable. Specifically, in injection molding, things other than the original injection molded articles such as "sprue" and "runner" occur, and these are generally recycled as an injection molding composition. When the water-soluble thermoplastic polymer is contained in the binder at a high content of 60% by weight or more, the flowability of the composition for injection plastic molding fluctuates every time recycling is performed. When the fluidity of the composition for injection molding fluctuates, the injection molding conditions become unstable, resulting in a defective injection molded article, reduced dimensional accuracy, and deformation. In such a case, a method of stabilizing the fluidity by mixing a certain amount of virgin material with the recycled material is adopted, but it is not enough to stabilize the fluidity, and the recycled material and the virgin material are also used. It is difficult to control the mixing ratio with the material.

[0007] As a result, there is a problem in producing an injection sintered body by combining the injection molding step and the water extraction degreasing step, and the use range of the water extraction degreasing method is narrowed. I have.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to include an injection molding step in which the flow stability of an injection molding composition is improved and the incidence of defects in an injection molded article obtained by injection molding is small. An object of the present invention is to provide a method for manufacturing a powder injection sintered body.

Still another object of the present invention is to provide a powder injection sintering method including an injection molding step in which an injection molded article obtained in the injection molding step can be cycle-used as an injection molding composition. An object of the present invention is to provide a method for producing a body.

Another object of the present invention, in addition to the above object, is to carry out a water extraction degreasing step after the injection step, thereby obtaining a powder injection sintered body having excellent dimensional stability in a short time. An object of the present invention is to provide a method for manufacturing a powder injection sintered body.

[0011]

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a method for preparing an injection molding composition, injection molding the injection molding composition into an injection molded article, degreasing, and then sintering. In producing a powder injection sintered body, a mixture of an injection molding powder, a thermoplastic organic binder, and an antioxidant is used as the injection molding composition to suppress the fragmentation of polymer chains in the thermoplastic organic binder. It is characterized by including an injection molding step.

[0012] The invention according to claim 2 is characterized in that the thermoplastic organic binder contains at least one water-soluble thermoplastic polymer and at least one water-insoluble thermoplastic polymer.

[0013] The invention according to claim 3 is characterized in that the antioxidant is one selected from the group consisting of phenol-based, phosphorus-based and sulfate-based antioxidants.

According to a fourth aspect of the present invention, the antioxidant is 0.1 to 10% by weight based on the total amount of the thermoplastic organic binder.
It is characterized by being.

According to a fifth aspect of the present invention, in addition to the injection molding powder, the thermoplastic organic binder and the antioxidant, an injection molded product obtained in the injection molding step is used as the injection molding composition. Features.

[0016] The invention according to claim 6 is characterized in that, after the injection molding step, a step of bringing the injection molded body obtained in the injection step into contact with water, heating, and then sintering is provided. .

In the present invention, the injection molded body includes not only an original injection molded body for obtaining a final injection sintered body but also a spur and a runner. It shall include all resulting products.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The composition for injection molding used in the present invention contains a powder, an organic binder, and an antioxidant for preventing oxidation of the organic binder. As the powder, all sinterable powders such as metal powder and ceramic powder can be used.

As the organic binder, any of the conventional ones can be used. In particular, a mixture of a water-soluble thermoplastic polymer and a water-insoluble thermoplastic polymer is preferable. This is because the water-soluble thermoplastic polymer is eluted and removed by the water extraction degreasing method, whereby the organic binder contained in the injection molded body is sufficiently reduced, and the softening and deformation of the formed body when the remaining organic binder is removed by heating is reduced. This is because blistering and cracking caused by the effect of the eluted organic polymer are prevented.

The water-soluble thermoplastic organic polymers include polyethylene oxide, polyethylene glycol, methylcellulose, carboxymethylcellulose,
Polyacrylamide, polyzonyl ether, polyacrylic acid, polymethacrylic acid, and the like are used, and among them, polyethylene oxide is preferably used. That is, polyethylene oxide has excellent injection moldability and good compatibility with other water-soluble polymers, as well as water-insoluble thermoplastic polymers such as polystyrene, polyethylene, polymethacrylate, and ethylene vinyl acetate. This is because it has good compatibility with polymers and the like, and further has good thermal decomposability. As the water-insoluble thermoplastic organic polymer, the above-mentioned thermoplastic polymers used for injection molding of ordinary metal powders and ceramic powders such as polystyrene, polyethylene, polymethacrylate, and ethylene-vinyl acetate copolymer are used. Can be The amount of these organic binders varies depending on the characteristics of the powder to be blended, but is usually about 5 to 25% by weight. This range is preferable from the viewpoint of injection moldability.
The mixing ratio (weight ratio) of the water-soluble thermoplastic polymer to the water-insoluble thermoplastic polymer is usually 60:40 to
The ratio is about 90:10, and this range is preferable from the viewpoint of shortening the degreasing time.

The antioxidant used in the present invention prevents oxidation of the organic binder, prevents deterioration of the polymer chain of the organic binder polymer due to shear stress and heat in the injection molding step, This has the effect of suppressing the separation of Suppressing the fragmentation of the polymer chains in the organic binder is to stabilize the fluidity of the composition for injection molding, and is specifically shown in Examples described later.

As the organic binder, in particular, the antioxidant for preventing the oxidation of the water-soluble thermoplastic polymer, those which do not remain in the powder injection sintered body as impurities after sintering the injection molded body are preferable. For example, BHT (2,6-di-tert-butyl-4-methylphenol) is used as a phenol-based additive, thiodipropionate is used as a sulfur-based additive, and trisnonylphenyl is used as a phosphorus-based additive. Phosphate and the like are suitably used, and these are easily decomposed and removed by the subsequent heat degreasing and sintering processes.

The addition amount of the antioxidant is preferably 0.1 to 10% by weight based on the total amount of the organic binder.
If the added amount is less than 0.1% by weight, the above effect is not exhibited, and
If it exceeds 0% by weight, it has an adverse effect on injection moldability and sinterability. It is particularly preferably 0.1 to 1% by weight.

The composition for injection molding of the present invention comprises the above powder, an organic binder, preferably an organic binder containing at least one water-soluble thermoplastic polymer and at least one water-insoluble thermoplastic polymer, An additive for preventing the oxidation of the organic binder and, if necessary, an additive such as a lubricant such as stearic acid which is usually added to the injection molding composition by those skilled in the art, using a processing kneader, a means such as a plastomill. And obtained by kneading.

By using the above-mentioned composition for injection molding, the fragmentation of the polymer chain of the organic binder can be suppressed even in injection molding, and the dimensional accuracy of the obtained injection molded article can be improved.

Preferably, the injection molded article obtained in the injection step can be used as an injection molding composition in the injection molding step. This is because the use of the above antioxidant can prevent the polymer chains in the organic binder in the injection molding composition, particularly the polymer chains of the water-soluble thermoplastic polymer, from being cut off in the injection step. This is because, even when used as a composition for use, the fluidity does not fluctuate so much and the fluidity stability is improved. The injection molded article used as the injection molding composition is preferably contained at 60 to 100% by weight based on the total amount of the injection molding composition.

Further, in the degreasing step following the injection step, it is preferable to use a water extraction degreasing method since degreasing can be performed in a short time without causing deformation, blistering and cracking. Because of its excellent fluid stability, the range of application of the water extraction degreasing method can be greatly improved. Specifically, as the degreasing treatment, first, the injection molded body is brought into contact with water (including room temperature water and heated water), whereby the water-soluble thermoplastic organic polymer is eluted. Here, as a method for contacting the injection molded body with water, it is preferable to perform the treatment by immersing the injection molded body in water, from the viewpoint of workability and the like and also from the viewpoint of shortening the elution time.

Next, heat degreasing is performed in a heating furnace,
The remaining organic binder such as a water-insoluble thermoplastic organic polymer is removed. Here, in performing the heat degreasing, heat degreasing may be performed at normal pressure, but performed under reduced pressure is preferable because the time for removing the organic binder can be further reduced, and particularly vacuum degreasing is performed. It is desirable.

Next, the degreased body is subjected to a heat sintering treatment to obtain a sintered body made of metal, ceramics, or the like.

[0030]

The present invention will be described with reference to the following examples and comparative examples. Example 1 7.5 parts by weight of polyethylene oxide as a water-soluble polymer, 3 parts by weight of polyethylene as a water-insoluble polymer, and 0.5 part by weight of stearic acid as a lubricant were added to 100 parts by weight of iron (Fe) powder having an average particle diameter of 5 μm. And 0.5 part by weight of phenolic BHT as an antioxidant were mixed and kneaded with a kneader at 150 ° C. for 60 minutes to obtain a composition for injection molding. The fluidity of the kneaded product of the obtained composition for injection molding was measured with a Koka type flow tester.

Next, the above-mentioned composition for injection molding was injected at an injection molding temperature of 170 ° C. and an injection molding pressure of 1000 using an injection molding machine.
Injection molding was performed at Kg / cm ² to obtain a 7 mm × 7 mm × 70 mm rectangular molded article. This injection molded article was used as an injection molding composition, but the virgin material was not mixed at all and the injection step was performed 10 times. The flowability of the composition for injection molding was measured by a Koka type flow tester at each regeneration. The result is shown in FIG. On the other hand, there was no surface defect of the injection-molded article at any number of times of reproduction.

Thereafter, the obtained injection-molded article was placed in water for 8 hours.
Immersed for a time, degreased about 60% of the polymer in the injection molded body, put the obtained degreased body in a degreasing furnace, and heated in a hydrogen atmosphere at 400 ° C. for 2 hours to degrease the remaining polymer;
Further, a sintering treatment was performed at 1300 ° C. to obtain a powder injection sintered body. No surface defect was observed in any of the obtained powder injection sintered bodies at any number of regenerations.

Example 2 The addition amount of phenolic BHT, which is an antioxidant, was set to 0.
Except for using 1 part by weight, the same procedure was performed as in Example 1 to measure the fluidity of the injection-forming composition at each regeneration. The result is shown in FIG. In addition, no surface defect was observed in the shape of the injection molded article at any number of times of reproduction. Further, when the obtained injection molded body was degreased and sintered in the same manner as in Example 1, no surface defect was observed at any number of times of regeneration.

Example 3 The addition amount of phenolic BHT, which is an antioxidant, was set at 0.
Except for using 7 parts by weight, the same procedure was performed as in Example 1 to measure the fluidity of the injection molding composition for each regeneration. The result is shown in FIG. In addition, no surface defect was observed in the shape of the injection molded article at any number of times of reproduction. Further, when the obtained injection molded body was degreased and sintered in the same manner as in Example 1, no surface defect was observed at any number of times of regeneration.

Example 4 Example 1 was repeated except that 0.5 parts by weight of phosphorus-based trisnonylphenyl phosphate was used as an antioxidant.
The flowability of the injection molding composition was measured every regeneration. The result is shown in FIG. Regarding the shape of the injection molded body, no surface defect was observed in the molded body at any number of reproductions. Further, when the obtained injection molded body was degreased and sintered in the same manner as in Example 1, no surface defect was observed at any number of times of regeneration.

Example 5 The procedure of Example 1 was repeated, except that 0.5 parts by weight of ionic thiodipropionate was used as an antioxidant. The properties were measured. The result is shown in FIG. In addition, no surface defect was observed in the shape of the injection molded article at any number of times of reproduction. Further, when the obtained injection molded body was degreased and sintered in the same manner as in Example 1, no surface defect was observed at any number of times of regeneration.

Example 6 Except that 0.25 parts by weight of each of phenol-based BHT and phosphorus-based trisnonylphenyl phosphate were used as the antioxidant, the same procedure as in Example 1 was carried out. The flowability of the molding composition was measured. The result is shown in FIG. In addition, no surface defect was observed in the shape of the injection molded article at any number of times of reproduction. Further, when the obtained injection molded body was degreased and sintered in the same manner as in Example 1, no surface defect was observed at any number of times of regeneration.

COMPARATIVE EXAMPLE 1 The procedure of Example 1 was repeated, except that no antioxidant was used, and the flowability of the composition for injection molding was measured every regeneration.
The result is shown in FIG. 1, and the fluidity of the injection molding material greatly decreases with respect to the number of times of regeneration. On the other hand, regarding the appearance of the injection molded article, surface defects occurred at any number of times of reproduction. Next, a sintered body was obtained from the obtained injection molded body in the same manner as in Example 1. In each of the obtained sintered bodies, a depression was formed around the φ3 hole.

[0039]

The method for producing a powder injection molded article of the present invention comprises:
In the injection molding process, it is possible to prevent degradation of the polymer in the organic binder due to shear stress and heat,
The injection molded article has excellent dimensional stability and can reduce the incidence of defects.

Furthermore, in addition to the above effects, the method for producing a powder injection sintered body of the present invention has a stable injection molding condition because the change in fluidity is reduced even if the injection molding composition is recycled. Thus, a sintered body having high dimensional accuracy can be obtained.

In addition to the above-mentioned effects, the method for producing a powder injection sintered body of the present invention can further effectively utilize the water extraction degreasing method, so that it is safe, simple and economical.
A powder injection sintered body can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the number of regenerations and the fluidity of the composition for injection molding according to the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08K 5/36 C08K 5/49 5/49 C08L 101/12 C08L 101/12 101/14 101/14 C09K 15/04 // C09K 15/04 C04B 35/00 108

Claims (6)

[Claims] An injection molding composition is prepared, and the injection molding composition is injection molded into an injection molded body, degreased, and then sintered to produce a powder injection sintered body. A powder injection sintering method comprising: using a mixture of an injection molding powder, a thermoplastic organic binder, and an antioxidant as a molding composition, and including an injection molding step of suppressing fragmentation of polymer chains in the thermoplastic organic binder. The method of manufacturing the aggregate. 2. The method according to claim 1, wherein the thermoplastic organic binder comprises at least one powder.
A method for producing a powder injection sintered body, comprising: a kind of water-soluble thermoplastic polymer and at least one kind of a water-insoluble thermoplastic polymer. 3. An antioxidant for producing the powder injection sintered body according to claim 1, wherein the antioxidant is one selected from the group consisting of phenol-based, phosphorus-based, and sulfate-based antioxidants. A method for producing a powder injection sintered body, characterized by comprising: 4. The method according to claim 1, wherein the amount of the antioxidant is 0.1 to 10% by weight based on the total amount of the thermoplastic organic binder. A method for producing a powder injection sintered body characterized by the following. 5. In producing the powder injection sintered body according to any one of claims 1 to 4, the composition for injection molding further comprises, in addition to the powder for injection molding, a thermoplastic organic binder, and an antioxidant, A method for producing a powder injection sintered body, characterized by using an injection molded body obtained in an injection molding step. 6. In producing the powder injection sintered body according to claim 1, after the injection molding step, after contacting the injection molded body obtained in the injection step with water. A method for producing a powder injection sintered body, comprising a step of heating and then sintering.