JP2677675B2 - Method for producing sintered product consisting of powder molding binder and metal powder or ceramic powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention mass-produces a sintered product through a degreasing and sintering process after mixing and molding a metal powder or a ceramic powder and a thermoplastic binder. The present invention relates to a powder molding binder suitable for use in this case and a method for producing the sintered product.

[Prior Art] Generally, in a method of producing a sintered product of metal or ceramic through a degreasing and sintering process after mixing and molding a raw material powder and a thermoplastic binder, a three-dimensionally complicated shape is formed. If high dimensional accuracy is required, the molded body should be degreased by embedding it in an inert powder such as ceramics (eg alumina) to prevent deformation and cracking during degreasing when degreasing the molded body. Was.

[Problems to be Solved by the Invention] However, when degreasing is performed using the method as described above, it takes a long time to remove the inert powder such as ceramics adhered to the surface of the degreased body after degreasing, which is an industrial problem. It wasn't the way.

Therefore, an object of the present invention is to provide a binder that can be degreased without causing deformation or cracking without burying the molded body composed of raw material powder and binder in an inert powder, and a method for producing a sintered product using the binder. To provide.

[Means for Solving the Problem] The present inventors have completed the present invention as a result of solving the problems described above and conducting research to mass-produce a sintered product on an industrial scale by powder molding. Came to do.

That is, the present invention is an ethylene vinyl acetate copolymer or ethylene-ethyl acrylate copolymer or both 10 to 40 wt%, polypropylene or atactic polypropylene or both 10 to 40 wt%, polystyrene or polyethylene or both Of 10 to 40% by weight and paraffin wax or carnauba wax or both of them in an amount of 20 to 50% by weight.

The powder molding binder according to the present invention may contain a plasticizer, a lubricant, or both in an amount of less than 15% by weight.

Furthermore, the present invention is a method for producing a sintered product from a metal powder or a ceramic powder, which comprises a mixing step of mixing a metal powder or a ceramic powder with a thermoplastic binder, a molding step, a degreasing step and a sintering step. The present invention relates to a method for producing a sintered product from metal powder or ceramic powder, which comprises using a molding binder.

[Function] In the powder molding binder of the present invention, an ethylene vinyl acetate copolymer (EVA) or an ethylene-ethyl acrylate copolymer (EEA) or both of them are contained in an amount of 10 to 40% by weight.
Add and blend. EVA or EEA is a thermoplastic resin and has good heat fluidity, so that good moldability can be imparted when molding a mixture of raw material powder and binder. Further, since the strength of the obtained molded body is increased and the thermal stability is high, it has an action of maintaining the shape of the molded body during decomposition and removal of other components at low temperature.

If the added amount of EVA and / or EEA is less than 10% by weight, the addition effect does not appear, which is not preferable, and if the added amount of those exceeds 40% by weight, a large amount is caused by excuse during degreasing. It is not preferable because gas may be generated and large voids and cracks may be generated in the molded body, and they may remain in the sintered body to deteriorate the characteristics of the sintered body.

For the powder molding binder of the present invention, polypropylene (PP) or atactic polypropylene (APP) is used.
Add ~ 40% by weight. PP and APP are also EVA and EE mentioned above
It is a thermoplastic resin similar to A, and has the same effect, but it has higher adhesiveness than EVA and EEA, and it enhances the strength of the molded body, and since it has a high softening point, it retains the shape of the molded body during degreasing. It is especially effective to do. If the amount of PP and / or APP added is less than 10% by weight, the effect of addition is not obtained, which is not preferable. If the amount of addition of PP and / or APP exceeds 40% by weight, fluidity at the time of molding is deteriorated and fluidity is deteriorated. Molding at a high temperature to improve the quality is not preferable because it causes evaporation of other components having a low thermal decomposition temperature.

Next, 10 to 40% by weight of polystyrene (PS) or polyethylene (PE) or both of them are added to the powder molding binder of the present invention. PS and PE are also thermoplastic resins, but the softening point is the temperature between EVA and EEA and PP and APP, and in the coexistence with these, the thermal decomposition of the binder during degreasing gradually progresses, so the binder It prevents deformation and cracking of the molded body due to the rapid thermal decomposition of. In addition, PS has particularly good degreasing property among resins, and has an effect of degreasing without damaging the molded body during degreasing. PS and /
If the amount of PE added is less than 10% by weight, it is not preferable because the effect of addition is not obtained.
When it exceeds, it is not preferable because the same result as EVA and EEA is produced. In addition, since PS has poor tackiness, excessive addition may reduce the strength of the molded product.

Further, the powder molding binder of the present invention contains paraffin wax, carnauba wax or both of them.
Add 20-50% by weight. Paraffin wax and carnauba wax have the effects of increasing the fluidity of the compound during molding, improving the wettability between the raw material powder and the binder, and uniformly dispersing the raw material powder in the compact. Further, these components have a degreasing mechanism different from the resin component, in which the components exude to the surface of the molded product and evaporate during degreasing, and are degreased without damaging the molded product. Carnauba wax has a higher strength at a lower temperature than a paraffin wax and a high melting point, and therefore is effective in maintaining the shape of a molded body at a low temperature. If the amount of paraffin wax and / or carnauba wax added is less than 20% by weight, the above-mentioned effects cannot be obtained, which is not preferable.
If the content is more than 10% by weight, the moldability is deteriorated due to low tackiness, and the shape retention during degreasing may be deteriorated to cause deformation of the molded body, which is not preferable.

The powder molding binder of the present invention may further contain up to 15% by weight of a plasticizer, a lubricant, or both.

Examples of plasticizers include diethyl phthalate (DEP),
Dibutyl phthalate (DBP) or dioctyl phthalate (DOP) can be used. The plasticizer has the effect of improving the compatibility of the above-mentioned components and homogenizing the binder, and has the effect of improving the fluidity of the compound during molding. The above plasticizers may be used alone or in combination of two or more.

As the lubricant, for example, stearic acid, oleic acid or the like can be used. The lubricant is also effective as a release agent when the mold release during molding is poor. The above lubricants can be used alone or in combination of two or more.

When the amount of the plasticizer and / or the lubricant added is 15% by weight or more, the strength of the molded product is lowered and deformation may occur during degreasing, which is not preferable.

The powder molding binder of the present invention can be prepared by simply mixing the above components.

The powder molding binder of the present invention is suitable as a powder molding binder when a sintered product is made from raw material powder such as metal powder such as stainless steel powder, WC-Co powder and the like and ceramic powder such as alumina powder and zirconia powder. It is a thing.

When mixing the raw material powder and the thermoplastic binder in the mixing step of the conventional operation consisting of the mixing step for producing a sintered product from the raw material powder as described above, the molding step, the degreasing step and the sintering step, The powder molding binders of the invention can be used. By this, after molding a mixture consisting of the raw material powder and the binder, when degreasing the obtained molded body, it is molded into an inert powder that has been performed so far to prevent cracking and deformation of the molded body. It is not necessary to embed the body and perform a degreasing operation, thereby eliminating the need to remove the inert powder adhering to the surface of the molded body after degreasing, which can greatly simplify the sintered product manufacturing process.

In addition, in the method for producing a sintered product using the powder molding binder of the present invention, the mixing step, the molding step and the sintering step can be performed by conventional operations without any particular limitation.

[Examples] Next, the present invention will be further described by describing examples of the present invention.

Examples Powder-forming binders of the present invention and comparative products were obtained by mixing the components shown in Table 1 below.

Next, in order to investigate the performance of the product of the present invention and the comparative product, a sintered product was manufactured by using injection molding as described below.

Particle size as raw material powder is 10μm or less (average particle size 8.5μ
m) SUS304L water atomized powder, 9.0% by weight of the product of the present invention (the products of the present invention 1 to 7 in Table 1) was added, and the mixture was kneaded for 1 hour at a temperature of 170 ° C. using a pressure kneader. After homogenizing, a sheet was formed using a roll mill, and then pulverized to prepare an injection molding material having an average particle size of about 5 mm.

The obtained injection-molding material was injection-molded using an injection molding machine into a shape in which a thin plate and a cylinder are combined, the front view of which is shown in FIG. 1 and the sectional view of which is shown in FIG. The dimensions in the figure are d ₁ = d ₂ = 15m
m, d ₃ = 8 mm, d ₄ = 1 mm, h ₁ = 7.5 mm, h ₂ = 2 mm.

Each of the obtained molded bodies was placed on an alumina plate and heated to 350 ° C in a N ₂ atmosphere at a temperature rising rate of 5 ° C / hour to degrease 70 to 80% of the binder component, and then 1350 ° C in vacuum. Sintered for 1 hour to obtain a sintered product.

This sintered product was not cracked or deformed during the degreasing and sintering steps, and was a sintered product having a density of 95% of the theoretical density contracted by about 20% from the compact.

Further, in order to demonstrate the effect of the binder for powder molding of the present invention, a molded article was prepared by degreasing using the same raw material and conditions as described above with the comparative binder composition and addition amount in Table 1. The deformation rate of the obtained degreased body is shown by h _{1 in} Fig. 2.
Is calculated based on the following formula and is also shown in Table 1.
For the degreased body using the product of the present invention, the deformation rate is similarly obtained and is also shown in Table 1.

h ₁ : dimension of molded body h ₁ ′: dimension of degreased body As shown in Table 1, in the binder for powder molding of the present invention, the deformation rate of the degreased body is less than 1%, which depends on the weight of the molded body. It can be seen that the deformation is very small.

Further, using the powder molding binder of the present invention to create a molded body similar to the above for WC-Co powder, TiC-Ni powder, Al alloy powder, alumina powder, etc. as described above, degreasing, and sintering. As a result, all the sintered products were sound without cracking or deformation.

[Advantages of the Invention] As described above, the molded body has an effect that it can be degreased without being deformed or cracked without being embedded in an inert powder, and has a three-dimensionally complicated shape and high dimensional accuracy. The required sintered product can be mass-produced.

[Brief description of the drawings]

FIG. 1 is a front view of the molded body obtained in the example, and FIG.
The figure is a cross-sectional view of the molded body shown in FIG.

Claims (3)

(57) [Claims] 1. An ethylene vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, or both of them are used.
-40% by weight, polypropylene or atactic polypropylene or both 10-40% by weight, polystyrene or polyethylene or both 10-40% by weight, and paraffin wax or carnauba wax or both 20-50% by weight. Binder for powder molding. 2. The binder for powder molding according to claim 1, which comprises a plasticizer, a lubricant, or both in an amount of less than 15% by weight. 3. A method for producing a sintered product from metal powder or ceramic powder, which comprises a mixing step of mixing metal powder or ceramic powder and a thermoplastic binder, a molding step, a degreasing step, and a sintering step. 1. A method for producing a sintered product from a metal powder or a ceramic powder, which comprises using the powder molding binder according to 1 or 2.