JPH0711010B2 - COMPOSITION FOR METAL POWDER INJECTION MOLDING, SINTERED METAL MEMBER AND PROCESS FOR PRODUCING SAID MEMBER - Google Patents

Description

TECHNICAL FIELD The present invention relates to a composition for metal injection molding comprising metal powder and a specific organic binder, a metal sintered member made from the same, and a method for producing the sintered member. More specifically, it has excellent injection moldability, exhibits extremely high shape retention without deformation during debinding, and then provides high-density sintered members with high yield without defects such as warpage and cracks by sintering. And a metal sintered member thereof, and a method for producing the sintered member.

[Problems to be solved by conventional techniques and inventions]

In recent years, in the field of ceramics, a green product is obtained by mixing a raw material powder with an organic binder, imparting plasticity, and injection-molding to obtain a green molded body, followed by debinding and firing to produce a ceramic product. ing. The feature is that a member having a complicated shape that cannot be molded by press molding or the like can be industrially mass-produced and manufactured.

On the other hand, in the field of metal sintered members, metal oxide members have been manufactured for a long time by mixing a small amount of an organic material with a raw material powder, molding by a press molding method, and then sintering, that is, by a so-called powder metallurgy method. However, in recent years, in order to manufacture a high-density complex-shaped member with mass productivity, an attempt has been made to apply the injection molding method used in the manufacture of the ceramic product to the manufacture of a sintered metal member. .

However, in the production of a sintered metal member by the injection molding method, (1) the average particle size of the ceramic raw material powder is as fine as 3 μm or less, whereas that of the metal powder has a relatively coarse particle size. 2) The raw material powder used for the metal sintered member is often higher in specific gravity than general ceramic powder, such as alumina powder, (3) General ceramic powder, for example, oxide-based ceramic powder such as alumina. Compared to, due to the poor wettability with binders, it is more likely to be deformed than the ceramic when debinding, and even if it is attempted to manufacture under the same conditions as when manufacturing ceramic products Producing a good sintered member such as in the case of manufacturing ceramic products, such as poor moldability, insufficient strength of green compact, deformation at debinding Or it is just that it is difficult to, in some cases that can not be before even the satisfaction produced a green molded body of the process.

In order to solve such a problem, there is an attempt to solve the problem by a special debinding process or a specific debinding condition, but the satisfactory result is not always obtained.

On the other hand, normally, when a molded product from the composition for metal injection molding is subjected to a binder removal treatment by thermal decomposition, it is usually carried out by embedding it in a powder of alumina, zirconia or the like which does not react with the molded product. As a result, the oozing effect of the binder due to the capillary phenomenon is promoted, the debinding time is shortened, and the shape retention of the molded product is also increased. However, such a method requires more space than the case where only the molded product that is a product is used, and often the surface of the molded product is damaged when the molded product is taken in and out of the filling powder. (The surface roughness of the sintered body is reduced), and it is often difficult to completely remove the powder adhering to the surroundings of the brittle molded body after debinding. This is often the case.

In terms of the organic binder, examples of the organic binder used for molding the ceramic powder include ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), polystyrene, polyethylene, and acrylic. Although methods using resin, wax, etc. have been proposed, moldability (flow characteristics, molding stability, releasability, etc.), green compact strength, debinding property, residual carbon amount after sintering, etc. Each binder has advantages and disadvantages in terms of various properties.

For example, EVA used in the present invention, when mixed with a metal powder, can impart strength and elasticity to the molded body without impairing the fluidity of the mixture, but if the amount used is too large, it will be decomposed by heat. When the binder is removed, blisters, cracks and the like are generated on the molded product, and it is difficult to perform the binder removal treatment without damaging the molded product.

Polystyrene and methacrylic resin (for example, polyisobutylmethacrylate) have an excellent binder effect on metal powders, impart high strength to green compacts, and are particularly effective in preventing damage to thin parts. In addition to providing excellent shape retention to the molded product, it is also excellent in heat decomposability and can be easily debindered, but if the amount used is too large, the fluidity of the mixture with the metal powder will be insufficient. , Injection failure such as insufficient filling and weld line is likely to occur.

Therefore, it is desirable to use resins with different performances in a well-balanced combination, but each resin is formed,
In addition to having different softening points, it is very difficult to mix uniformly because the compatibility is not sufficient, and it is usual that the blending occurs even if mixing for a long time. Generally, unless sufficient mixing is possible, the fluidity is not stable, it takes a lot of time to determine the molding conditions, the homogeneity of the molded product is impaired, and the dimensional stability of the molded product In addition to affecting the above, it causes the occurrence of cracks in the sintered body.

[Means for Solving the Problems]

The present invention has been made in view of the above circumstances, and a metal powder having a complicated shape by an injection molding method and capable of industrially mass-producing a high-density metal sintered member with high mass productivity. An injection molding composition, a metal sintered member made from the same, and a method for producing the sintered member, which is an injection molding composition comprising a metal powder and an organic binder. The binder is (a) an ethylene-vinyl acetate copolymer or an ethylene-ethyl acrylate copolymer, (b) a (meth) acrylic acid ester monomer alone or a (meth) acrylic acid ester monomer and a styrene-based monomer A solution of the mixture of (1) and (c) a polymerization initiator in a water-based medium containing a dispersant and suspension polymerized, and Also comprises a binder containing two components, a metal powder injection molding composition, a metal sintered member obtained by sintering a molded product of the metal powder injection molding composition, and the metal powder injection A molded body obtained by injection molding the molding composition is heated in a gas atmosphere at a temperature rising rate of 3 to 300 ° C./hr at a maximum temperature of 45
The present invention relates to a method for producing a metal sintered member, which comprises heating to 0 to 600 ° C., debinding treatment, and then sintering.

〔Example〕

The metal powder injection molding composition of the present invention is prepared from a metal powder and an organic binder.

The metal powder is not particularly limited as long as it is a metal powder that has been conventionally used for forming a molded body with an organic binder and is used as a sintered member, but the powder particle shape is close to a spherical shape, and the average particle size is The diameter is preferably about 1 to 50 μm, more preferably about 1 to 12 μm. When the average particle size is smaller than 1 μm, the specific surface area of the powder is relatively increased, and even if the amount of the binder used is reduced, it is often difficult to obtain a mixture having flow characteristics suitable for injection molding. Even if injection molding is possible, it is difficult to smoothly carry out the subsequent debinding process, and the molded product after debinding tends to be brittle and difficult to handle. On the other hand, in the case of a powder having a coarse particle size of more than 50 μm, the strength of the green molded body and the molded body after debinding will tend to be remarkably reduced.

Examples of the metal powder include, but are not limited to, pure iron, iron-nickel, iron, cobalt, iron-based alloys such as stainless steel, metal powders such as tungsten, aluminum alloys, copper, and copper alloys. Not something.

The organic binder used in the present invention is a component (a) ethylene-vinyl acetate copolymer (EVA) or ethylene-ethyl acrylate copolymer (EEA), (b) component (meth) acrylic acid ester monomer Quantifier alone or (meta)
A mixture of an acrylic acid ester monomer and a styrenic monomer and a solution comprising a polymerization initiator which is the component (c),
Includes a composite acrylic resin dispersed in an aqueous medium containing a dispersant and suspension-polymerized, and atactic polypropylene, and if necessary, imparts plasticity to the organic binder and improves the fluidity of wax and phthalic acid. In addition to plasticizers such as esters, lubricants and release agents such as higher fatty acids,
It contains a surfactant, a surface treatment agent (coupling agent) and the like in order to improve the wettability of the surface of the metal powder.

The composite acrylic resin, when mixed with a metal powder, imparts sufficient fluidity to the mixture, exhibits an excellent binder effect on the metal powder, strongly binds particles to each other, and is sufficient for a green molded body. It is a component for imparting strength and elasticity, and also has excellent debindering properties.

Composite acrylic resin dissolves EVA or EEA in advance in (meth) acrylic acid ester monomer alone or in (meth) acrylic acid ester monomer and styrene type monomer, and disperse this in aqueous medium for suspension polymerization Because of this, the composite acrylic resin looks like a kind of polymer alloy that is very homogeneously mixed microscopically (see FIGS. 1 and 3), and is simply a blend of polymers ( As compared with FIG. 2 and FIG. 4), the molding conditions of the mixture with the metal powder can be more easily determined, the fluidity is stable, and a good sintered member with little variation and high yield can be obtained.

The ethylene-vinyl acetate copolymer (EVA) is not particularly limited and may be any one generally called an ethylene-vinyl acetate copolymer, but ethylene / vinyl acetate is 85 / by weight. It is preferably a copolymer of 15 to 50/50, more preferably 80/20 to 60/40. When the ratio exceeds 85/15, it is difficult to dissolve the ethylene-vinyl acetate copolymer in the (meth) acrylic acid ester monomer or the mixture of the (meth) acrylic acid ester monomer and the styrene monomer. When it is less than 50/50, it is difficult to obtain the ethylene-vinyl acetate copolymer, and the green molded body strength tends to be lowered.

Further, the melt index (MI value) of the ethylene-vinyl acetate copolymer is preferably about 10 to 500, particularly from the viewpoint of the viscosity when dissolved and used, and the fluidity during molding and green. From the viewpoint of the strength of the molded product, those having a hardness of about 20 to 400 are more preferred.

The ethylene-ethyl acrylate copolymer (EEA) is not particularly limited, and any one generally called an ethylene-ethyl acrylate copolymer may be used, but ethylene / ethyl acrylate is 85 / by weight. 15 ~ 5
It is preferably 0/50 copolymer, more preferably 80 / 20-60 / 40 copolymer. When the ratio exceeds 85/15, it is difficult to dissolve the ethylene-ethyl acrylate copolymer in the (meth) acrylic acid ester monomer or the mixture of the (meth) acrylic acid ester monomer and the styrene monomer. When it becomes less than 50/50, it is difficult to obtain an ethylene-ethyl acrylate copolymer,
In addition, the strength of the green molded body tends to decrease.

Further, the melt index (MI value) of the ethylene-ethyl acrylate copolymer is preferably about 10/2000, particularly from the viewpoint of viscosity when used in a dissolved state, and also in fluidity during molding, green. From the standpoint of the strength of the molded product, those of about 100 to 1500 are more preferred.

The (meth) acrylic acid ester monomer is also not particularly limited, but in view of fluidity at the time of molding, strength of the green molded product, debinding property, etc., alcohol having 1 to 8 carbon atoms and (meth) acrylic It is preferably an ester with an acid. Specific examples of such a (meth) acrylic acid ester monomer include, for example, an alkyl group having 1 to 8 carbon atoms.
N-alkyl (meth) acrylate, isopropyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl Examples include (meth) acrylate. Of these, especially n-
Preferred are n-alkyl (meth) acrylates having an alkyl group having 1 to 4 carbon atoms such as butyl (meth) acrylate, isopropyl (meth) acrylate, isobutyl (meth) acrylate, and t-butyl (meth) acrylate. These may be used alone or in combination of two or more.

Specific examples of the styrene-based monomer include styrene, α-methylstyrene, p-methylstyrene, vinylstyrene and the like.

When the (meth) acrylic acid ester monomer and the styrene-based monomer are mixed and used, the ratio of the styrene-based monomer contained in the mixture is 80% (% by weight or less). Is preferred. As the proportion of the styrenic monomer contained in the mixture increases, the fluidity of the obtained organic binder becomes poor, and molding tends to be difficult.

In addition, other monomers, for example, (meth) acrylic acid, maleic acid, itaconic acid, vinyl acetate, vinyl chloride, etc. may be used in a small amount in combination as long as the essence of the composite acrylic resin used in the present invention is not damaged. Good.

The ratio of the components (a) and (b) used is (a) component / (b)
The weight ratio of the components is preferably about 5/95 to 80/20, more preferably about 20/80 to 70/30. When the ratio is less than 5/95, the fluidity of the mixture with the metal powder prepared by using the obtained organic binder tends to be insufficient, and molding defects are likely to occur. Again 80
If it exceeds / 20, the blistering phenomenon of the molded body that occurs when debinding by heat decomposition tends to be remarkable,
The strength of the molded body is liable to decrease, and the binder removal and handling become difficult.

Specific preferred examples of the polymerization initiator include benzoyl peroxide, lauroyl peroxide,
Examples thereof include organic peroxides such as t-butylperoxy-2-ethylhexanate and oil-soluble polymerization initiators such as azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These may be used alone or in combination of two or more.

The amount of the polymerization initiator used is 100 parts by weight of component (b) (parts by weight,
The same applies hereinafter), from the viewpoint of controlling the reaction rate and the molecular weight, etc., it is preferably 0.05 to 1.5 parts, and more preferably 0.1 to 0.6 parts.

During the polymerization, a chain transfer agent may be used for controlling the molecular weight, if desired. Specific preferred examples of such a chain transfer agent include n-dodecyl mercaptan and t-octyl mercaptan. Examples thereof include mercapto compounds and α-methylstyrene double bodies.
These may be used alone or in combination of two or more.

When a chain transfer agent is used, the amount used is preferably 0.01 to 1.0 part, and more preferably 0.03 to 0.5 part, relative to 100 parts of component (b) from the viewpoint of adjusting the molecular weight.

There is no particular limitation on the method for preparing a solution from the component (a), the component (b), the component (c) and the chain transfer agent used if necessary, and the temperature at which the component (c) does not decompose is not particularly limited. It may be prepared by any method as long as it is available.

The prepared solution is dispersed in an aqueous medium containing a dispersant and suspension-polymerized.

Specific examples of the dispersant include, for example, water-soluble organic polymer compounds such as polyvinyl alcohol, hydroxyethyl cellulose and polyvinylpyrrolidone, and poorly water-soluble fine particles such as hydroxyapatite and magnesium pyrophosphate in combination with an anionic surfactant. And so on. The amount of these dispersants used is preferably 0.1 to 1 part, and more preferably 0.2 to 0.5 part, relative to 100 parts of water used.

The ratio of the solution consisting of the components (a) to (c) and optionally the chain transfer agent to the aqueous medium containing the dispersant is 30 to 120 with respect to 100 parts of the aqueous medium.
Is preferable from the viewpoint of stability and productivity of the dispersion suspension, and more preferably 50 to 100 parts.

There are no particular restrictions on the conditions for carrying out suspension polymerization,
The method usually used may be used. For example, the polymerization reaction temperature is usually in the range of 50 to 130 ° C, although an appropriate temperature is determined depending on the decomposition temperature of the polymerization initiator used.

Thus, for example, as shown in FIG. 1, a composite acrylic resin used as an organic binder in which the component (a) is uniformly and microscopically dispersed in the component (a) is obtained. This composite acrylic resin can be suitably used for molding a metal powder to obtain a fired member.

In addition, FIG. 1 shows the internal structure of the particles of the composite acrylic resin by observing the state after etching the composite acrylic resin used in the composition of the present invention with a solvent with a scanning electron microscope (5000 times). It is the electron micrograph which it did.

The ratio of the composite acrylic resin in the organic binder is usually 20 to 80%, preferably 35 to 65%. If the ratio of the composite acrylic resin is less than 20%, the strength of the molded body is insufficient and it becomes difficult to take it out of the mold during molding.
Handling also tends to become extremely difficult, and if it exceeds 80%, when kneading with metal powder, due to lack of wettability, etc.,
It takes a long time for kneading, and the fluidity of the kneaded product tends to be insufficient.

Further, the atactic polypropylene is a component for improving the shape retention property when the molded product from the composition for metal powder injection molding is heated to remove the binder, and when used in combination with the composite acrylic resin. It is possible to significantly reduce the deformation of the molded body when debinding by thermal decomposition.

The atactic polypropylene can be used without particular limitation as long as it is called atactic polypropylene, but the softening point is 110 ° C. or lower from the viewpoint of fluidity of the mixture of the metal powder and the organic binder. preferable.

The ratio of the atactic polypropylene in the organic binder is usually 8 to 50%, preferably 12 to 35%. If the ratio of the atactic polypropylene is less than 8%, the above effect is not sufficient, and if it exceeds 50%, the mold release property is a major drawback of the atactic polypropylene. Remarkably appears, it becomes difficult to remove the molded product from the mold, the molding efficiency is lowered, and the strength of the molded product tends to be insufficient.

The wax to be contained in the organic binder used in the present invention may be either synthetic wax or natural wax, and specific examples thereof include paraffin wax, microcrystalline wax, carnauba wax and montan wax. And so on.
Further, as the plasticizer, for example, dibutyl phthalate,
Examples of lubricants such as dioctyl phthalate, phosphoric acid ester, and fatty acid ester include higher fatty acids, higher fatty acid amides, higher fatty acid esters, and higher fatty acid salts, which are additives usually used for injection molding of ceramics. As long as it can be used without particular limitation.

If necessary, the ratio of the components used in the organic binder is preferably 50% or less from the viewpoint of the strength of the molded product, the shape retention property at the time of debinding, and the like.

The ratio of the metal powder in the composition for injection molding of the present invention and the organic binder containing a composite acrylic resin and atactic polypropylene as essential components is adjusted to be 100/4 to 100/15 by weight ratio. Preferably.
When the ratio is more than 100/4, the fluidity of the injection molding composition tends to be insufficient, and it tends to be difficult to mold it into a desired shape, while when it is less than 100/15. The density of molded products does not increase, shrinkage during firing becomes large, and not only dimensional accuracy is reduced, but when debinding by thermal decomposition, a large amount of gas is generated, so cracks, blisters, etc. in the molded body Defects tend to occur remarkably.

The production of a metal sintered member using the injection molding composition of the present invention as described above is carried out, for example, as follows, but is not limited to such a method.

First, the metal powder and the organic binder are sufficiently kneaded by a kneader such as a pressure kneader, and the metal powder is uniformly dispersed in the organic binder, and then formed into an appropriate shape, for example, a coarsely pulverized product or pellets, An injection molding composition is prepared.

Next, the obtained composition is injection-molded by a known apparatus and method used in ordinary plastic molding to obtain a molded product having a desired shape.

After that, the molded body is heated in a gas atmosphere at a temperature rising rate of 3 to 300.
A sintered metal member having a desired shape can be obtained by heating at a maximum temperature of 450 to 600 ° C. at a temperature of ° C./hr, debinding treatment, and then firing.

The temperature rising rate varies depending on the shape, wall thickness, etc. of the molded body and is appropriately selected. It is normal to perform the debinding process under the condition that the debinding process can be performed at the highest speed possible. However, if the heating rate is increased above 300 ° C / hr, defects such as blisters and cracks will occur, and the debinding process will be performed satisfactorily. On the other hand, if it is less than 3 ° C./hr, it takes too long time for debinding, which is not practical. Further, if the maximum heating temperature is lower than 450 ° C., it may not be possible to sufficiently remove the binder depending on the molded product having a large wall thickness, and if the heating temperature exceeds 600 ° C., deformation may occur, which is not preferable.

When the composite acrylic resin used in the present invention and the organic binder containing atactic polypropylene as an essential component are used, the binder is removed by immersing the molded body in a filler such as alumina which is a general debinding method. Even if debinding is not performed by the method or other special debinding method, the binder is left standing directly on the alumina plate, etc., and the heat treatment is performed by a simple heating and heating pattern to remove the binder, followed by firing. However, a good sintered body with no defects can be obtained. The high shape-retaining force of the organic binder used in the present invention is particularly effective for a molded product having an extremely high shape-retaining force having an elongated protruding portion such as a pin.

In addition, it goes without saying that the binder may be removed by a method of removing the binder by burying the molded body in the filling powder according to the conventional method and then firing.

Next, the present invention will be described based on examples.

Production Example 15 n-butyl methacrylate (BMA) 700 was added to the reactor of Example 5.
g, styrene 500g and n-dodecyl mercaptan 0.35g
After adding and dissolving, 300 g of EVA (Ultrasen 722, manufactured by Tosoh Corp.) was added with stirring and the temperature was raised to 75 ° C. to dissolve, and further benzoyl peroxide 4.8 g, t
-0.25 g of butyl peroxybenzoate was added and dissolved. Ion-exchanged water 1840 prepared separately in advance
ml and 160 ml of 3% aqueous solution of PVA were added at 80 ° C., and the mixture was stirred and suspended. Then, the space was replaced with nitrogen, and the reaction was carried out at 80 ° C. for 5 hours and 110 ° C. for 2 hours to complete the polymerization. After that, it was cooled, washed with water, and dried to obtain white spherical particles having a particle size of 0.3 to 1.0 mm. The intrinsic viscosity [η] of the polymer particles at 30 ° C in a toluene solution was 0.70. The obtained polymer is called a composite acrylic resin (A).

Preparation Example 25 600 g of BMA and 0.3 g of n-dodecyl mercaptan were added to the reactor of Example 5, and the temperature was raised to 75 ° C. with stirring.
900 g (Ultrasen 722, manufactured by Tosoh Corp.) and 2.4 g of benzoyl peroxide as a polymerization initiator were added and dissolved. Ion-exchanged water 18
40 ml and 160 ml of 3% aqueous solution of polyvinyl alcohol (PVA)
An aqueous dispersant solution consisting of and was added and stirred to suspend the EVA-BMA solution. Then, after substituting with nitrogen, reaction was carried out at 80 ° C. for 3 hours and at 100 ° C. for 2 hours to polymerize, followed by cooling, taking out, washing, and drying.

The obtained polymer was spherical particles having a particle size in the range of 0.3 to 1 mm, and the intrinsic viscosity [η] at 30 ° C in a toluene solution was 0.85. The obtained polymer is called a composite acrylic resin (B).

Comparative Production Example 1 EVA used in Production Example 1 (Ultrasen 722, Tosoh Corporation)
, Polybutyl methacrylate (molecular weight 300,000) and polystyrene are kneaded well at 150 ° C for 30 minutes using a roll so that they have almost the same composition and intrinsic viscosity [η], and the mixture (mixed acrylic resin (A)) I got it.

Comparative Production Example 2 EVA (Ultrasen 722, Tosoh Corporation) used in Production Example 2
Produced) and polybutylmethacrylate (molecular weight 300,000) were kneaded well at 140 ° C. for 30 minutes using a roll so as to have almost the same composition and intrinsic viscosity [η] to obtain a mixture (mixed acrylic resin (B)). .

Reference Example 1 Suspension polymers obtained in Production Examples 1 and 2 and Comparative Production Example 1
By observing with a scanning electron microscope (5000 times) what was treated by the solvent etching method (immersing in hexane for 2 minutes) and the simple mixture obtained in 2 and 2, the internal structure was observed. Was observed. The results are shown in FIGS. 1 and 3 and FIGS. 2 and 4 which are respective observation photographs.

As you can see from the comparison between Fig. 1 and Fig. 2, EVA-BMA-
In the styrene suspension polymer (Production Example 1), fine particles are uniformly dispersed, and a remarkable difference from the dispersed state in the simple mixture (Comparative Production Example 1) is recognized.

Further, from the comparison between FIG. 3 and FIG. 4, it can be seen that the same difference is observed between the EVA-BMA suspension polymer (Production Example 2) and the simple mixture (Comparative Production Example 2).

Examples 1 to 6 and Comparative Examples 1 to 4 As raw material powder, JIS SUS 304 having an average particle size of 8.9 μm
JIS S with L stainless steel powder, average particle size 10.5μm
Prepare stainless steel powder of US 316L, carbonyl iron powder having an average particle size of 12.0 μm, and mix 100 parts of metal powder with the organic binder having the composition shown in Table 1 in the amount shown in Table 1 to prepare Laboplast. Using a mill (Toyo Seiki Co., Ltd.)
The mixture was thoroughly kneaded at 140 ± 10 ° C for 30 minutes. Then, the kneaded material is crushed into a lump of 3 to 5 mmφ, and the injection temperature is 120 to 170 ° C and the injection pressure is 500 to 700 kg by an injection molding machine (manufactured by Yamashiro Seiki Co., Ltd., vertical plunger injection molding machine). / cm ² in the frame-shaped product shown in FIG. 5 (1) was molded. This coma-shaped molded product was directly placed on an alumina plate without being buried in a filling powder such as alumina powder and heated in a nitrogen atmosphere from room temperature to 500 ° C at a heating rate of 10 ° C / hr to remove the binder. After that, the first
Sintering was performed under the sintering conditions shown in the table to obtain a metal sintered member.

Table 1 shows the theoretical density ratio and appearance of the obtained metal sintered member. In addition, four patterns shown in FIGS. 6A to 6D show the state after debinding ((1a): non-defective non-defective product, (1b):
Slightly tilted, (1c): 90 ° tilted, (1
d): Crushed).

From the results shown in Table 1, it can be seen that when the organic binder used in the present invention is used, a good metal sintered body having a high theoretical density ratio without any defects can be obtained.

〔The invention's effect〕

According to the present invention, it is possible to produce a metal injection-molded article having extremely high shape retention properties without cracks and deformation during debinding, and then debinding and sintering under appropriate sintering conditions, A metal sintered member having a complicated shape can be manufactured with high productivity. Further, the binder removal can be performed without using the filling powder.

[Brief description of drawings]

1 to 4 show the states after the acrylic resins obtained in Production Example 1, Comparative Production Example 1, Production Example 2 and Comparative Production Example 2 were etched with a solvent, respectively, by a scanning electron microscope (5000).
2), and an electron micrograph showing the internal structure of the particles of the acrylic resin, and FIG. 5 is an explanatory view of the shape of the coma-shaped molded product produced in Examples and Comparative Examples.
FIGS. 6A to 6D are 4 for showing the state after the binder removal of the top-shaped molded bodies manufactured in the examples and comparative examples.
It is explanatory drawing about one pattern. (Main symbols in the drawing) (1): Top-shaped molded product

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Claims (3)

[Claims] 1. An injection molding composition comprising a metal powder and an organic binder, wherein the organic binder is (a) an ethylene-vinyl acetate copolymer or an ethylene-ethyl acrylate copolymer, and (b) (meth). Acrylic ester monomer alone or a solution consisting of a mixture of (meth) acrylic acid ester monomer and styrenic monomer and (c) polymerization initiator is dispersed and suspended in an aqueous medium containing a dispersant. A composition for metal powder injection molding, comprising a binder containing at least two components of a polymerized composite acrylic resin and atactic polypropylene. 2. A sintered metal member obtained by sintering a molded product of the composition for metal powder injection molding according to claim 1. 3. A molded body obtained by injection molding the composition for metal powder injection molding according to claim 1, in a gas atmosphere, at a heating rate of 3 to 3.
A method for producing a metal sintered member, which comprises heating at a maximum temperature of 450 to 600 ° C. at 300 ° C./hr to perform binder removal treatment, and then sintering.