JPH0641601B2 - Molding composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a molding composition comprising metal powder or a mixed powder of metal powder and ceramic powder and an organic binder.

[Prior Art] As a conventional molding composition comprising a metal powder or ceramic powder and an organic binder, heat-generating materials such as polypropylene, methacrylic acid ester, polystyrene, ethylene-vinyl acetate copolymer and low density polyethylene can be used as the organic binder. Known are plastic resins, or those in which a plasticizer such as paraffin wax, diethyl phthalate, stearic acid or a lubricant is used in combination.

[Problems to be Solved by the Invention] However, in the conventional composition, when degreasing, the molded body is easily deformed by its own weight, or cracked or swelled due to decomposed gas, so that the molded body may be a ceramic powder or a metal powder. It was necessary to degrease by embedding it in the inside to prevent deformation, or to suppress the amount of decomposed gas generated at a slow temperature rising rate of usually 1 to 10 ° C./hr. Therefore, industrial production has been difficult because a step of removing powder adhering to the surface of the molded body is required before proceeding to sintering, and it takes a long time for degreasing.

The present invention was devised to solve the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a composition that can be degreased in a short time without thermal deformation during degreasing.

[Means for Solving the Problems] The molding composition of the present invention comprises a metal powder or a mixed powder of a metal powder and a ceramic powder, a polyacetal (A component) having a heat distortion temperature of 130 ° C. or higher, and a melting point of 30 to 100 ° C. A molding composition obtained by mixing an organic binder composed of polyalkylene glycols (component B). Here, the heat distortion temperature is a load of 4.6 kg / cm ² according to ASTM D648.
Shall be indicated by the value measured in.

The heat distortion temperature of the component A in the composition of the present invention is 130 ° C.
Examples of the polyacetal include homopolymers consisting only of trioxane, and copolymers of trioxane and ethylene oxide, dioxolane, substituted dioxolane, 1,4-dioxane, and the like, and one or more of these are appropriately mixed. Can be used. Of these, the heat distortion temperature is preferably 150.
℃ or above. Polyacetal has a low melt viscosity, is easy to mold, and has good thermal decomposition.

In the composition of the present invention, the melting point which is the component B is 30 to 100.
Examples of the polyalkylene glycols at 0 ° C include polyethylene glycol, polytetramethylene glycol, ethylene oxide-propylene oxide copolymers and the like having a normal molecular weight of 1,000 to 20,000, and one or more of these may be used. They can be appropriately mixed and used.

The polyalkylene glycols as the B component have excellent compatibility with the polyacetal as the A component. Of the polyalkylene glycols, polyethylene glycol is preferred. The molecular weight of polyethylene glycol is usually 100
The molecular weight of 1,000 to 10,000 is more preferable since it is excellent in moldability and the effect of preventing deformation during degreasing.

By using the A component and the B component together, a good degreasing rate is exhibited as described in Examples.

In addition to the components A and B, a third component (component C) may be added to the organic binder in order to improve moldability. Examples of the C component include polycarbonate, polyphenylene oxide, polyphenylene sulfide, polyvinylidene fluoride, polyamide (for example, nylon 6, 11, 1
2,66 or their copolymers) polyester (eg polyethylene terephthalate, polybutylene terephthalate) polyaryl sulfone, polyaryl ether, polyether sulfone, polyether ether ketone, waxes (petroleum wax, natural wax, synthetic ax) Etc.), various low molecular weight compounds that are solid at room temperature (metal soaps such as stearic acid, aliphatic amines such as distearylamine, various surfactants), polyethylene,
Examples thereof include polypropylene, poly-4-methylpentene-1, polystyrene, poly-α-methylstyrene, ethylene-vinyl acetate copolymer, polymethacrylic acid ester, polyethylene oxide and the like. Polyethylene oxide is preferable from the viewpoint of compatibility.

The organic binder further contains a plasticizer (diethyl phthalate, dibutyl phthalate, etc.) which is liquid at room temperature, a surfactant for improving the wettability of the binder with respect to the metal powder, various coupling agents, etc. within the range which is usually used. May be.

The polyacetal (A component) having a heat distortion temperature of 130 ° C. or higher in the organic binder serves to impart fluidity to the composition and to prevent deformation during degreasing. Heat distortion temperature is 13
If it is less than 0 ° C, the deformation preventing effect becomes insufficient.

The amount of the component A in the binder is usually 20 to 60% by weight, preferably 30 to 60% by weight. When the amount of the component A is less than 20% by weight, the strength of the molded product is insufficient and handling becomes difficult.

Polyalkylene glycols (B having a melting point of 30 to 100 ° C.)
The component) serves to increase the fluidity of the composition, facilitate injection molding, further enhance the deformation preventing effect during degreasing, and accelerate the degreasing speed. When the melting point is 30 ° C. or lower, the strength of the molded article becomes weak, and when it exceeds 100 ° C., the deformation preventing effect becomes insufficient.

The amount of component B in the binder is usually 40 to 80% by weight,
It is preferably 40 to 70% by weight. The amount of B component is 80
If the content is more than wt%, the strength of the molded product will be insufficient.

The amount of C component in the binder is usually 0 to 60% by weight, preferably 0 to 30% by weight. The amount of C component is 6
If it exceeds 0%, the molded body tends to be deformed during degreasing.

In the present invention, as the metal powder, iron, aluminum,
Metal powders such as copper, titanium, molybdenum, zirconium, cobalt, nickel and chromium, and alloy powders containing these metals as main components (for example, stainless powder, high speed steel powder,
Cemented carbide powder, magnetic material powder, etc.)
One kind or two or more kinds can be appropriately mixed and used as necessary.

Ceramic powder may be added to these metal powders in the range of 0 to 95% by weight. Such ceramic powders include oxides (aluminum oxide, silicon oxide, zirconia oxide, titanium oxide, mullite, cordierite, etc.), carbides (silicon carbide, boron carbide, zirconia carbide, etc.), nitrides (silicon nitride, aluminum nitride, boron nitride). , Titanium nitride, etc.) and other powders.

These powders include powders, sintering aids, molding aids,
Other powders or the like for improving the physical properties may be appropriately added in advance. The addition method may be simple mixing or coating on the surface of the powder.

The average particle size of metal powder and ceramic powder is usually 0.0
It is 1 μm to 50 μm, preferably 0.1 μm to 20 μm. When the particle size is smaller than 0.01 μm, the sinterability is improved, but the bulkiness is high and the handleability is poor, and the moldability is poor. If the particle size exceeds 50 μm, the sinterability deteriorates.

In the composition of the present invention, the amount of the powder in the whole composition is usually 40 to 70% by volume, preferably 50 to 60% by volume. If the powder amount exceeds 70% by volume, it becomes difficult to uniformly knead the powder and the binder, and it becomes difficult to perform injection molding. Further, if it is less than 40% by volume, the deformation of the molded body during degreasing becomes large.

The method for molding the composition of the present invention and the composition to obtain a sintered body will be described below.

The composition of the present invention can be produced by melt-kneading the respective components, cooling and then crushing (roughly crushing) or pelletizing. In the above, kneading is a Banbury mixer, plastomill,
It can be carried out using an ordinary kneader such as a kneader, a pressure kneader, a roll mill, a screw type extruder. The kneading temperature is usually 150 to 350 ° C, preferably 150 to 2
At 50 ° C., the kneading time is usually 20 minutes to 2 hours, preferably 30 minutes to 1 hour.

If necessary, each component or mixture may be dried before kneading. As the kneading method, there are a method in which all components are charged at once and kneaded, a binder component alone is first added and kneaded, and then ceramic powder or metal powder is added and kneaded, and a binder component is added later.

When injection molding is performed using the composition of the present invention, an ordinary plunger type, screw type or other injection molding machine can be used. Molding conditions vary depending on the shape of the mold and the composition for injection molding, but the molding pressure is usually 100 to 3000 Kg / c.
m ² , preferably 200 to 2000 kg / cm ² , and the molding temperature is usually 150 to 350 ° C, preferably 150 to 250 ° C. In addition, extrusion molding, press molding and the like can be performed using the composition of the present invention. For a composition which is easily thermally decomposed by heating, a method of kneading and molding under reduced pressure or in an inert atmosphere may be adopted.

Degreasing is performed in an oxidizing, reducing or inert gas atmosphere under reduced pressure, normal pressure or increased pressure, usually at 1 to 60 ° C./hr, preferably at 10 to 40 ° C./hr at a heating rate of 250 to 500.
Up to about ℃, preferably 250 ~ 350 ℃,
It is carried out by holding at that temperature for usually 0 to 10 hours, preferably 1 to 5 hours.

The molded product made of the composition of the present invention does not need to be embedded in the powder or supported by a jig in order to maintain the shape, and can be directly degreased by arranging it on the shelf plate in the degreasing furnace.
Here, it is possible to shorten the degreasing time by using a shelf plate on which the molded body is placed and having a structure that allows ventilation, and by applying a flow of atmospheric gas to the lower surface of the molded body. As such a shelf plate, a wire mesh made of stainless steel or the like, a ceramic formed in a lattice shape, or the like is used.

Sintering is usually carried out in an oxidizing, reducing or inert gas atmosphere under vacuum, atmospheric pressure or pressure, with the temperature raised to about 600 to 2000 ° C. The rate of temperature rise is usually 50 to 1000 ° C
/ Hr, and hold at maximum temperature for 10 minutes to 10 hours.
When performing sintering in a vacuum, the degree of vacuum is usually 10 ^-2 torr.
Or more, preferably 10 ⁻³ torr or more.

In the conventional method of embedding degreasing in powder, it is necessary to remove the powder adhering to the surface of the degreasing body before proceeding to sintering, and it is difficult to continuously perform from degreasing to sintering. However, by using the composition of the present invention, such a step is unnecessary, and it is possible to continuously perform sintering in the same heating furnace.

[Examples] Hereinafter, the present invention will be further described with reference to Examples, but the present invention is not limited thereto.

Examples 1 to 3 Metal powders and organic binders having the composition ratios shown in Table 1 were kneaded with a pressure kneader at 150 to 180 ° C. for 45 minutes and crushed while cooling to obtain an injection molding composition.

Comparative Examples 1 and 2 Metal powders having the composition ratios shown in Table 1 and an organic binder were kneaded with a pressure kneader at 150 ° C. for 45 minutes and crushed while cooling to obtain an injection molding composition.

Evaluation The compositions of Examples 1 to 3 were heated using an injection molding machine at a heating cylinder temperature of 150 to 170 ° C., a mold temperature of 50 ° C., and an injection pressure of:
Under the condition of 1500 Kg / cm ^2, the test piece (1
It was molded into a size of 00 mm × 10 mm × 4 mm). Observation of the obtained moldings revealed that they all had a good appearance.

Next, the above-mentioned molded body was placed on a support rod installed at a constant distance L (1, 2, and 3 cm) as shown in FIG. 2, and the temperature was raised in a circulating air oven at a rate of 20 ° C./hr. 350 ° C
Degreasing was performed by raising the temperature to and holding at that temperature for 2 hours. After degreasing, the deformation amount (h) was evaluated as shown in FIG. The degreasing rate and the amount of deformation are shown in Table 2.

The compositions of Comparative Examples 1 and 2 were prepared except that the heating cylinder temperature of the injection molding machine was 150 ° C. and the injection pressure was 1000 kg / cm ² .
Molding and degreasing were performed in the same manner as in Example 1. The degreasing rate and the amount of deformation are shown in Table 2.

The degreased bodies of the compositions of Examples 1 to 3 of the present invention were not deformed at all as shown in Table 2, the degreasing rate was about 98% by weight, and the appearances of the molded articles were all good.

On the other hand, the degreased bodies of the compositions of Comparative Examples 1 and 2 had a degreasing rate of about 85% by weight as shown in Table 2, and the amount of deformation was slightly deformed even when the distance between the supporting rods was as narrow as 1 cm. It was greatly deformed at 2 cm or more.

That is, as can be seen from the examples and comparative examples, when the organic binder is polypropylene and wax, deformation due to its own weight tends to occur during degreasing.

On the other hand, according to the composition of the present invention, by using as a binder component a polyacetal having a heat distortion temperature of 130 ° C. or more and being easily thermally decomposed and a polyalkylene glycol having a melting point of 30 to 100 ° C. and being easily thermally decomposed, It is possible to obtain a good degreased body that does not deform even if the distance between the support rods is wide (that is, the molded product is large), and degreasing can be performed at a relatively low temperature in a short time. did it.

In addition, in the above-mentioned Examples, only the results obtained by carrying out the metal powder are shown, but the results of the deformation of the degreased body being smaller than those of the conventional composition are obtained also for the mixture of the metal powder and the ceramic powder.

[Effects of the Invention] The composition of the present invention has the following effects.

Since deformation due to its own weight at the time of degreasing is prevented, embedding in the powder and jigs for shape retention, which were conventionally required at the time of degreasing, are unnecessary, and productivity and product accuracy are improved.

Degreasing that does not deform even if it is difficult to embed in powder or retain shape by a jig, such as complicated shaped products or large molded products, and if it is easily deformed during degreasing, such as molded products using stainless steel powder You can get the body.

Since the step of removing the degreased body from the powder is unnecessary,
It is possible to continuously produce from degreasing to sintering, and productivity can be improved.

The temperature rising rate can be increased as compared with the conventional composition, and the degreasing time can be shortened.

[Brief description of drawings]

FIG. 1 is a perspective view of a test piece, FIG. 2 is a view showing a method for measuring the deformation of the test piece, and FIG. 3 is an explanatory view of the amount of deformation.

Claims (2)

[Claims] 1. An organic binder comprising a metal powder or a mixed powder of a metal powder and a ceramic powder, a polyacetal (component A) having a heat distortion temperature of 130 ° C. or higher, and a polyalkylene glycol (component B) having a melting point of 30 to 100 ° C. A molding composition obtained by mixing. 2. The composition according to claim 1, wherein the component B comprises 40 to 70% by weight of the organic binder.