JPH0533006A - Production of injected and sintered body of powder - Google Patents

Abstract

PURPOSE:To rapidly remove a binder from a compact while ensuring strength without causing defects and to produce an injection-compacted and sintered body. CONSTITUTION:A binder used in an injection compacting process is composed of 1st and 2nd binder components. Both the 1st and 2nd binder components have powder bonding functions but do not dissolve in the same solvent. In a binder removing process, the 1st binder component is first extracted with a solvent and then the 2nd binder component is thermally decomposed and vaporized. Since strength is imparted to the resulting compact by the bonding functions of the binder components, the compact is made easy to handle and breakage is prevented. Since the binder is removed in two stages, deformation and defects are not caused and the binder can rapidly be removed.

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 sintered body, and more particularly to a method for producing a powder injection sintered body which smoothly performs a binder removal step.

[0002]

2. Description of the Related Art In recent years, with advances in powder technology, metal and ceramics as processing materials have become available in high purity as ultrafine powders, and the demand for sintered products of metal powders or ceramic powders has increased. It is rising. The injection molding method has excellent dimensional accuracy, and compared to the conventional powder press molding method or casting method or forging method, the sharpness of corners and edges,
Suitable for expressing fine shapes such as small diameter holes. Also,
In many cases, a material that cannot be handled by a molding method at a high temperature such as a casting method or a forging method, such as an alloy having a fine structure or a composite material thereof, can be molded by an injection molding method. The injection molding method using these powder materials has been attracting attention as a diversified molding method for sintered members.

The molding of a sintered body by the powder injection molding method is carried out by adding a binder to the powder material in an amount of 33 to 55 vol% in order to impart fluidity and bondability to the powder material. It is carried out by injecting into a mold cavity to form a compact, removing the binder in a binder removal step, and finally sintering the pressure compact of the powder material.

As a binder removal method for injection-molded articles, many proposals have been made in Japan, including Japanese Patent Publication No. 61-48563 and Japanese Patent Publication No. 62-33282, most of which involve heating the molded article. Therefore, it takes the position of a thermal decomposition method in which a binder is vaporized through a molten state.

However, in the thermal decomposition method, the molded body is heated to a temperature higher than the melting point of the binder to promote the debindering, so that the molded body tends to be deformed or collapsed by its own weight during the debindering. . Therefore, it is inevitable to prevent the deformation by a method such as making the temperature rising rate of the compact extremely slow, or immersing the compact in a powder material such as ceramic powder to remove the binder depending on the shape of the compact. ing.

Also, since the binder is basically decomposed and vaporized by heating, swelling and cracks are likely to occur near the surface of the molded body, and in order to prevent such swelling and cracks, it is possible to prevent deformation due to its own weight. Similarly, it is necessary to slow the temperature rising rate. Although it depends on the wall thickness of the molded body, it is not rare that it takes 2-3 days to complete the predetermined binder removal.

On the other hand, as a method different from the binder removal method by thermal decomposition, USP 2,939,199, USP 4,1
The extraction method with an organic solvent as proposed in 97,118 specification or USP 4,765,950 specification is known. In the solvent extraction method, since the binder removal proceeds without applying a temperature such that the molded body is deformed, there is an advantage that it is easy to avoid the problem of deformation during binder removal as seen in the case of the thermal decomposition vaporization method. Is recognized.

[0008]

However, the conventional binder removal method by solvent extraction has the following problems. First, in the method proposed in USP 2,939,199, the molded body is directly immersed in the organic solvent.
A swelling phenomenon occurs in which the binder component takes in solvent molecules before the binder component is extracted into the solvent. At this time, since the molded body expands and its strength decreases, defects such as cracks are likely to occur.

In the method of USP 4,197,118, a method of advancing the binder removal by immersing the molded body in an organic solvent and placing the molded body in solvent vapor to extract the binder is adopted. ing. in this way,
Since extraction is performed more gently than the method of USP 2,939,199, it is effective in preventing defects such as cracks. However, it takes a long time to complete the removal of the binder, and in this respect, the thermal decomposition method has not been improved.

In the method proposed in USP 4,197,118, some of the binder components are USP 2,939,199.
As in the method of the specification, the molded body is extracted by directly immersing it in an organic solvent, and the remaining binder component is decomposed and vaporized by heating, that is, the binder is removed by both the solvent extraction method and the thermal decomposition vaporization method. To do. As the extraction component of the binder, 50 to 99% of the binder, usually 2/3 of an oil such as vegetable oil or a mixture of oil and wax, and a polymer such as polypropylene is used as a component to be thermally decomposed without extraction. ing.

The oil used as the binder extraction component in the method of USP 4,197,118 is liquid at room temperature and can be extracted very easily by an organic solvent, so that the binder removal surely proceeds rapidly. . For example, most of the extracted components are extracted from a molded product having a thickness of 6 mm in about 4 hours. Then, the polymer component remaining without being extracted is decomposed and vaporized by heating for about 3 hours, whereby the binder removal is completed.

However, the oil or the mixture of oil and wax which is the extraction component of the binder has a small binding function of the powder material in maintaining the shape of the molded body. Therefore, most of the function of binding the powder material to give the strength of the shaped body will be devoted to the polymer of the non-extracting component, which accounts for only about one third of the total binder.

As a result, the molded product using such a binder is inferior in strength to the molded product produced by the conventional powder injection molding method, which hinders the handling of the molded product, or This causes problems such as easy breakage of small or thin parts of the body. From these points, the industrially applicable range of the method of USP 4,197,118 is extremely limited.

The first object of the present invention is to remove the binder from the molded product in a short time, and the second object is to prevent the molded product from being deformed, cracked, swollen or the like during binder removal. A third object of the present invention is to provide a method for producing a powder injection-molded product, which can easily handle the molded product and maintain sufficient strength without causing damage to the molded product.

[0015]

The fastest method for removing the binder from the molded body is a solvent extraction method in which the molded body is directly immersed in a solvent. In order to advance the binder removal of the molded body by solvent extraction, it is necessary that the binder contains a component that is easily extracted by the solvent.

However, if the binder is composed of only this extracted component, the binder swells and the shape of the molded body cannot be kept sound. Therefore, it is effective to maintain the shape of the molded body by including a non-extracting component that does not swell or be extracted by the same solvent as the extracting component in the binder together with the extracting component.

However, in the method of USP 2,939,199, the binder is composed of the extraction component and the non-extraction component in this way, but the oil or the mixture of the oil and the wax as the extraction component has a binding function as a binder. As described above, since the strength of the molded body is insufficient at the time of forming the molded body, the disadvantage is caused because it has almost no.

Therefore, in the present invention, in order to secure the strength of the molded product, not only the non-extracting component of the binder but also the polymer serving as the extracting component having the binding function of the powder material is used.

That is, according to the present invention, in the method for producing a powder injection sintered body, which is performed through an injection molding step, a binder removal step, and a sintering step of a powder material mixed with a binder, the binder binds the powder material. A binder composed of at least two or more thermoplastic resins having a function and composed of a first binder component and a second binder component which are insoluble in a common organic solvent is used. In the first step, the first binder component is extracted using an organic solvent, and in the second step, the second binder component is pyrolyzed and removed to remove the powder injection-sintered body. It is a manufacturing method.

A first binder component used in the present invention,
That is, as the binder extraction component, one kind or two or more kinds of thermoplastic resins having a solubility parameter in the range of 8 to 10 can be used. Specifically, polystyrene, acrylic resin, and the like are preferable because they are easily soluble in an organic solvent and many types of organic solvents are soluble.

The second binder component, ie, the non-extractor component of the binder, has a solubility parameter of less than 8 1
It is possible to use one kind or two or more kinds of thermoplastic resins, or one kind or two or more kinds of thermoplastic resins having a solubility parameter exceeding 10. Specific examples of the former include polyethylene and polypropylene, and specific examples of the latter include polyamide and the like.

The mixing ratio of the first binder component and the second binder component is such that the first binder component is contained in the entire binder.
It is preferable that the content is 25 to 95 wt% and the rest is the second binder component. If the proportion of the first binder component is less than 25 wt%, the extraction will be difficult to proceed.

Because the extraction progresses from the surface of the molded body toward the inside, the portion occupied by the extracted binder becomes voids after the extraction, and the binder inside is further extracted. It becomes a passage for the organic solvent.
Also, the dissolved binder is also eluted through the pores. Therefore, when the ratio of the extracted binder is small, the formation of the portion serving as the passage of the organic solvent and the dissolved substance is limited, so that the speed at which the extraction proceeds inside the molded body becomes slow.

If the proportion of the first binder component exceeds 95 wt /%, the molded body after the completion of extraction will retain its shape with less than 5 wt /% of non-extracted component, resulting in weak strength. It is not suitable for practical use.

In addition to the first binder component and the second binder component, additives for improving fluidity, such as plasticizers and lubricants generally added to resins, are appropriately added to the binder. Is possible.

As the organic solvent used in the present invention, those which are soluble in the first binder component are selected according to the kind of the first binder component. As a measure of the solubility, it is desirable to select and use a solvent having a solubility parameter close to the value of the solubility parameter of the first binder.

Organic solvents having a solubility parameter in the range of 8 to 10 include turpentine oil, aliphatic hydrocarbons such as cyclohexane; aromatic hydrocarbons such as xylene and toluene; halogenated tetrachloroethylene, methylene chloride and the like. Hydrocarbons; ethers such as dichloroethyl ether;
Mention may be made of esters such as methyl acetate and ethyl acetate; ketones such as acetone, methyl ethyl ketone and methyl propyl ketone. It is also possible to use a mixture of these solvents to adjust the value of the solubility parameter.

The solvent extraction, which is the first step of the binder removal step of the present invention, is carried out by immersing the molded body in the above-mentioned organic solvent. The temperature at this time may be room temperature, but at a temperature below the boiling point of the solvent. If heated, the progress of solvent extraction can be further promoted.

After the first binder component is extracted, the molded body is heated to decompose and vaporize the second binder component to complete the binder removal.

Following this step, the molded body is sintered to obtain a sintered body.

The molded body is formed by injecting into the mold cavity a mixture of a powder material and a binder composed of the first binder component and the second binder component,
As the powder material, one kind or a mixture of two or more kinds of various metals, ceramics and cermets is used.

[0032]

The powder material is first mixed with a binder and injection-molded. Both the first binder component and the second binder component forming the binder have a function of binding the powder material, so that the injection molded body is firmly bound. As a result, the molded body to which strength has been imparted is not easily damaged at a thin-walled portion, a small-diameter portion, or the like, and is easy to handle.

Next, the molded body is sent to the binder removal step,
In the first step, only the first binder component is selectively solvent-extracted. When the first binder component is extracted into the solvent, the second binder component does not swell because it is not soluble in the solvent that dissolves the first binder component,
The binding of the powder with the second binder component remains functional in the shaped body. Therefore, cracks and the like do not occur, and the shape of the molded body is kept sound.

As the first binder is extracted, the regions occupied by the first binder component in the molded body become voids in sequence. These holes serve as a solvent extraction passage for extracting the first binder component existing inside the molded body when the solvent extraction is in progress, and when the first binder component is dissolved, It serves as a passage for the melt.

After completion of solvent extraction of the first binder component,
Even in the thermal decomposition of the second binder component, which is the second step of the binder removal process, many holes remain after the first binder component has escaped, and these holes are thermally decomposed and vaporized. It serves as a passage for the second binder component to flow out of the molded body. Due to the existence of the pores, the thermal decomposition vaporization of the second binder component proceeds remarkably rapidly from the beginning.

The compact after the first binder component is removed has a relatively small amount of binder relative to the powder, and therefore does not fluidize even when heated, so that the compact is prevented from being deformed by its own weight. To be done. Further, the thermally decomposed second binder smoothly flows out from the first vaporized portion to the outside of the molded body through the passage formed by the holes. Since the passage for the vaporized second binder to exit is secured from the beginning in this way, the pressure of the vaporized second binder is applied and cracks and swelling occur on the surface of the molded body. Nor.

[0037]

【Example】

Example 1 As the powder material, spherical iron powder having an average particle size of 4.5 μm, carbon content of 0.01% and oxygen content of 0.2% was used. The binder has a molecular weight of 30,000 to 40,000 and a glass transition temperature of 100 to 105 ° C.
6 parts by weight per 100 parts by weight of the powder material, and 3 parts by weight of low density polyethylene having a density of 0.92 g / cm ³ or less were used. Add 1 part by weight of these binders and dibutyl phthalate as a plasticizer to the powder material,
The mixture was kneaded in a pressure kneader at 200 ° C. for 1 hour.

After cooling, the kneaded product was pulverized and supplied to an injection molding machine, and injection-molded under the conditions of an injection temperature of 200 ° C. and an injection pressure of 1.5 ton / cm ² to form a molded body of φ10 × 30 Lmm.

The obtained molded body was immersed in toluene which was 5 times the weight of the molded body, and solvent extraction was carried out. The components of the molded body extracted are polystyrene and dibutyl phthalate. The temperature during extraction was kept constant at 30 ° C., and the container containing the toluene and the molded body was sealed with a lid to prevent the evaporation of toluene.

15 minutes after immersing the molded body in toluene, 40
After 1 minute, 2 hours, 4 hours, and 9 hours, the molded body was taken out from toluene, sufficiently dried, and weighed. The weight of the molded body decreases at each measurement time. This amount of reduction corresponds to the weight of polystyrene and dibutyl phthalate extracted in toluene.

From the measurement results, the relationship between the extraction time and the extraction rate of the extracted components shown in FIG. 1 was obtained. From FIG. 1, it can be seen that 90% or more of the components extracted in 4 hours were extracted.

Next, the molded body which had been extracted for 4 hours was placed in a furnace, and 100 ° C./hour from room temperature to 150 ° C. and 40 ° C./hour from 150 ° C. to 350 ° C. in a vacuum atmosphere.
The temperature was raised from 350 ° C. to 1200 ° C. at a heating rate of 600 ° C./hour, and further held at 1200 ° C. for 1 hour.

In this step, the temperature rising rate was reduced to 150 ° C.
During the temperature rise from 1 to 350 ° C., polyethylene which is a non-extracting component and the remaining extracted polystyrene and dibutylene phthalate are thermally decomposed and vaporized to remove the binder.

Then, following the binder removal, the powder material is sintered at a high temperature of 1200 ° C. After cooling, the sintered body taken out of the furnace had a relative density of 95 ± 0.5%, and no defects such as cracks and pores (cavities) were found by visual inspection, permeation inspection and internal inspection by X-ray. A healthy sintered body was obtained.

In the case of a binder removal method using only the conventional thermal decomposition method, it took about 3 days to remove the binder of a molded body of φ10 × 30 Lmm, which is the same as in this embodiment. In this example, extraction takes 4 hours, drying takes 30 minutes, and pyrolysis vaporization takes 6.5 hours (from room temperature to 3 hours).
Since it is the total of the heating time up to 50 ° C and the time of holding at 350 ° C), the binder removal is completed in 11 hours in total, which means that the binder removal time can be shortened to less than one-fifth of the conventional time. .

(Example 2) As a powder material, an average particle size of 0.
Alumina powder having a particle size of 5 μm, a purity of 99.5% and a specific gravity of 3.94 was used. The binder has a molecular weight of 100,000 or less and a glass transition temperature of 80.
Acrylic resin below ℃ for 100 parts by weight of powder material
11.9 parts by weight and 5.1 parts by weight of polypropylene having a melt index value of 50 or more specified by JIS-K7210 were used.

These binders and 0.85 parts by weight of stearic acid as a lubricant were added to the powder material, and the mixture was kneaded in a pressure kneader at 180 ° C. for 1 hour. After cooling, the kneaded product was pulverized and supplied to an injection molding machine. , Injection temperature 180 ℃, injection pressure 1.5 ton / c
Injection molding was performed under the condition of m ² to form a molded body of φ10 × 30 Lmm.

The obtained molded body was immersed in acetone which was 8 times the weight of the molded body, the container was covered and the temperature was kept at 30 ° C. for extraction. Although the extraction time was slightly longer than that of Example 1 because the particle size of the powder material was small, 90% or more of the acrylic resin as the extraction component was extracted in 6 hours.

Next, the molded body after the above-mentioned extraction for 6 hours is charged into a furnace, and at room temperature to 150 ° C., 100 ° C./hour, and from 150 ° C. to 300 ° C., 20 ° C. Per hour, the temperature was raised from 300 ° C. to 1640 ° C. at a heating rate of 100 ° C./hour, and the temperature was maintained at 1640 ° C. for 1 hour.

In this step, polypropylene and stearic acid which are non-extracting components and the remaining acrylic resin extracted are pyrolyzed and vaporized during the temperature rise from 150 ° C. to 300 ° C., and the binder removal proceeds.

Then, following the binder removal, the powder material is sintered at a high temperature of 1640 ° C. After cooling, the sintered body taken out of the furnace was subjected to the same external and internal inspections as in Example 1, but no defect was observed and a sound sintered body was obtained.

[0052]

As described above, according to the method of the present invention in which the solvent extraction method and the thermal decomposition method are used together as the binder removal method, the binder removal method which cannot be performed by the conventional binder removal method only by the solvent extraction or the thermal decomposition is not possible. It has become possible to achieve both shortening of time and prevention of defects in the molded body.

The greatest bottleneck in the powder injection sintered body manufacturing process, that is, the time required for the binder removal, which was the rate-determining step in all steps, can be shortened, which leads to the improvement of the efficiency of the whole powder injection sintered body manufacturing process. In addition, it will lead to more efficient utilization of equipment, reduction of equipment running cost, and shortening of lead time for commercialization.

Further, since it is possible to prevent the occurrence of defects in the molded body during binder removal and handling of the molded body, the product yield is improved and the manufacturing cost is reduced.

When the binder is used in a large amount of oil or a mixture of oil and wax, the solvent is extracted, and the remaining binder is pyrolyzed and vaporized, the resulting binder is compared with the binder removal method. It is excellent in strength and solves the problems in work such as the breakage of the molded body during molding and handling of the molded body.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between extraction time and extraction rate of extracted components.

Claims (10)

[Claims] 1. In a method for producing a powder injection sintered body, which is performed through an injection molding step, a binder removal step, and a sintering step of a powder material mixed with a binder, the binder has a function of binding the powder material. A binder composed of at least two kinds of thermoplastic resins and composed of a first binder component and a second binder component which are insoluble in common organic solvents is used, and the first step of the binder removal step is performed. 2. The method for producing a powder injection-sintered body according to claim 1, wherein the first binder component is extracted with an organic solvent, and the second binder component is thermally decomposed and removed in the second step. 2. The method for producing a powder injection sintered body according to claim 1, wherein the first binder component is a thermoplastic resin having a solubility parameter in the range of 8 to 10. 3. The first binder component is polystyrene or acrylic resin.
The method for producing a powder injection sintered body according to. 4. The method for producing a powder injection sintered body according to claim 1, wherein the second binder component is a thermoplastic resin having a solubility parameter of less than 8. 5. The fourth binder component is polyethylene or polypropylene.
The method for producing a powder injection sintered body according to. 6. The method for producing a powder injection-sintered body according to claim 1, wherein the second binder component is a thermoplastic resin having a solubility parameter of more than 10. 7. The method for producing a powder injection sintered body according to claim 6, wherein the second binder component is polyamide. 8. The method for producing a powder injection-sintered body according to claim 1, wherein the proportion of the first binder component is in the range of 25 to 95 wt% of the total binder. 9. The first step of the binder removal step is performed by immersing the molded body in an organic solvent and at room temperature or at a temperature heated below the boiling point of the solvent. Of the powder injection-sintered body of. 10. The method for producing a powder injection-sintered body according to claim 1, wherein a solvent having a solubility parameter in the range of 8 to 10 is used as the organic solvent.