KR970010296B1 - Polyethylene glycol binders and production thereof - Google Patents

Abstract

The polyethylene glycol series binding material for powder injection molding of inorganic powder consists of the following material: (a) 1-15 weight% polyethylene glycol, (b) 2-10 weight% wax like paraffin wax with low molecular mass, (c) 2-10 weight% polymer binding material and (d) 0.5-5 weight% plasticizer like dimethyphthlate. The binding materials effectively eliminates the mixed solvent.

Description

Polyethyleneglycol-based binder for powder injection molding and manufacturing method of parts using the same

1 is a comparison of the solvent extraction process of the binder used in the known WITEC process and AMAX process and the binder according to the present invention.

The present invention relates to a polyethylene glycol-based binder for powder injection molding and a method for producing a precision component using the same.

In general, the powder injection molding process of the inorganic powder is injection molded by uniformly mixing the inorganic powder and the organic binder, as shown in FIG. 1, and then removing the binder present in the molded body, and finally, the molded body from which the binder is removed. Sintering is a process for manufacturing precision parts that do not require post-processing.

On the other hand, compared with powder injection molding, there was a powder metallurgy method which was previously formed by sintering by known press molding and CIP molding. However, in the case of press molding, it is impossible to manufacture a part having a shape other than uniaxial molding. In addition, CIP molding has a disadvantage in that precision is low because molding is possible in a three-dimensional shape while molding in a rubber mold.

Therefore, powder injection molding has been recently used. Such powder injection molding technology is classified into WITEC process, AMAX process, and Reverse process according to a binder and a binder removal method.

First, the WITEC process (US Pat. Nos. 4,197,118, 4,305,756, Japanese Patent Publication Nos. 86-33,282, 89-51,521) is injection molded by mixing inorganic powders with waxes and thermoplastic resins, and then the molded body is prepared in one step. Low molecular weight waxes are solvent-extracted using a solvent such as heptane and hexane, and the residual binder is removed by pyrolysis using wicking using capillary action in two steps.

In addition, the AMAX process (US Pat. No. 4,765,950), which is a known manufacturing method, is composed of vegetable oil having a low melting point binder, high molecular weight polyethylene, polypropylene, and the like. After injection molding, the molded product is solvent-extracted from the oil component using a solvent such as methylene chloride, trichloroethane, trichloroethylene, and the like, and the remaining polymer is removed by thermal decomposition upon sintering.

WITEC process and AMAX process have the advantage of fast binder removal and thick product manufacturing, while heptane, hexane, methylene chloride, trichloroethane and trichloroethylene used as solvents cause pollution and environmental problems. Therefore, its use is strictly regulated in other countries, and the price is high, which is a factor in limiting usage and raising prices.

The reverse process (US Pat. Nos. 4,113,4870, 4,721,599) is performed by injection molding at low temperature using water, methylcellulose, glycerin, boric acid, etc. as a binder, and gelation of methylcellulose in a mold at 80-100 ° C. It is a method of solidifying using a phenomenon. This process has the advantage that the binder can be removed only by pyrolysis without solvent extraction, while the regeneration of the gelled compound is difficult.

As described above, the conventional powder injection molding technique has various problems as previously described depending on the binder and the binder removal method.

In the present invention, the study was carried out to solve the problems caused during the powder injection molding, the polyethylene glycol-based binder is a low cost such as ethanol or water when solvent extraction in the binder removal process and does not cause pollution and environmental problems The present invention has been accomplished by focusing on the use of a solvent.

Accordingly, an object of the present invention is to provide a polyethylene glycol-based binder for powder injection molding of an inorganic powder composed of polyethylene glycol, low molecular weight waxes, a polymer binder, and a plasticizer.

Another object of the present invention is to provide a method for producing a precision part, which is characterized by using the binder in the powder injection molding method of the inorganic powder. That is, in the method for manufacturing a precision part according to the present invention, the inorganic powder and the binder are mixed to obtain a pelletized sample, which is injection molded, and then the polyethylene glycol in the binder is extracted and removed from the molded body by a solvent, and the residual binder is removed. The components are pyrolyzed and removed and then subjected to a sintering process.

Next, a polyethylene glycol-based binder for powder injection molding according to the present invention and a manufacturing method of a precision component using the same will be described in more detail.

The binder according to the present invention consists of ethanol, water, polyethylene glycol and waxes, polymers such as polyethylene, and a plasticizer which can be solvent-extracted from a solvent in a mixture of ethanol and water.

In one embodiment of the present invention, the inorganic powder consisting of 1-15% by weight polyethylene glycol, 2-10% by weight low molecular weight wax, 2-10% by weight polymer binder and 0.5-5% by weight plasticizer based on the total amount of inorganic powder A polyethylene glycol-based binder for powder injection molding is provided.

In this case, 8-30% by weight of the multicomponent binder may be used based on the total amount of the inorganic powder, and polyethylene glycol, which is an important component of the binder, is 1-based on the total amount of the inorganic powder. It is used in the range of 15% by weight. Since the molecular weight of polyethylene glycol increases as the molecular weight of solvent extraction decreases, 62-10000 is preferable in order to maintain an appropriate solvent extraction rate.

In the conventional WITEC process and AMAX process, low molecular weight waxes or low melting point solvents are removed by solvent extraction using a solvent causing pollution and environmental problems such as heptane, hexane, methylene chloride, trichloroethane, trichloroethylene, etc. The polyethylene glycol used in the above can be removed from the molded body using one of ethanol, water and a mixture of ethanol and water at a temperature of 50-90 ° C. as a solvent.

Waxes are used in an amount of 2 to 10% by weight based on the total amount of the inorganic powder in order to improve fluidity and formability and to increase the blendability of the polyethylene glycol and the polymer binder. The waxes used are not extracted in a solvent such as ethanol, but are removed by pyrolysis, and one of paraffin wax, canuba wax, polyethylene wax and bis wax is used.

The polymeric binder is used in an amount of 2 to 10% by weight based on the total amount of the inorganic powder for morphological stability of the molded body during the injection process and the binder removal process. The polymer binder used may be variously used, such as high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), ethylene vinyl acetate (EVA).

One of the plasticizers added to increase the moldability is dimethyl phthalate, diethyl phthalate, dibutyl phthalate. The plasticizer is preferably in the range of 0.5-5% by weight based on the total amount of the inorganic powder. If the amount of plasticizer added is 0.5% by weight or less, the fluidity required for molding cannot be obtained, while in 5% by weight or more, the fluidity increases, but it is uneconomical because sufficient strength of the molded product cannot be obtained.

The inorganic powders which can use the binder of the present invention are selected from metal powders, ceramic powders, or alloy powders having an average particle size of 0.1-100 μm.

On the other hand, the powder injection molding process of the inorganic powder using the binder according to the present invention comprises the following steps.

First, the inorganic powder and the binder component according to the present invention are mixed in a mixer at a temperature of 130-180 ° C. for 1-2 hours at an inorganic powder filling rate of 70-92 wt%. If the filling rate of the inorganic powder is less than 70% by weight, it is difficult to maintain the strength of the molded body after removal and to obtain sufficient sintered density during sintering, since the amount of the binder to be removed is large. One mixing process and injection molding is difficult. As the inorganic powder, metal powder, alloy powder, ceramic powder and the like can be used. In this case, the average particle size of the inorganic powder is preferably 0.1-100 μm in consideration of the molding state.

The pelletized sample obtained by mixing the inorganic powder and the binder is injection molded in the injection molding machine at a temperature of 160-200 ° C, wherein the molding conditions are determined by controlling the molding temperature, the molding pressure, the mold temperature, and the holding time in the mold. do.

Polyethylene glycol of the binder is removed from the molded body using a mixture of ethanol, water and a mixture of ethanol and water at a temperature of 50-90 ° C. as a solvent. The time taken for solvent extraction of all polyethylene glycol components from the molded body is about 5-15 hours depending on the solvent temperature and the thickness of the molded body. The residual binder of the polyethylene glycol-free molded body is removed by pyrolysis. When the inorganic powder used is a metal powder or an alloy powder, since the oxidation of the powder may worsen the sintering ability, it is preferable to remove the binder in a non-oxidizing or reducing atmosphere such as hydrogen, argon, vacuum or nitrogen. The temperature rise rate during pyrolysis is 50-200 ° C./hour, controlled by the thickness of the shaped body and the residual binder component is removed at a temperature of 200-700 ° C.

The binder removed is sintered in a non-oxidizing or reducing atmosphere such as hydrogen, argon, vacuum, and nitrogen, and this sintering process densifies the molded body by controlling the sintering time, the sintering temperature, and the atmosphere. It depends on the type of.

The present invention is more clearly illustrated by the following examples, but the present invention is not intended to be limited to these examples.

Example 1

The inorganic powder is an anisotropic SrO-6Fe ₂ O ₃ (Sr-ferrite) powder, which is a kind of ceramic powder, has an average particle size of 0.7-1.2 µm and a filling rate of 85 wt%. The composition of the binder is based on inorganic powder: (a) 6% by weight polyethylene glycol (molecular weight 1500), (b) 4% by weight canoe wax, (c) 4% by weight high density polyethylene, and (d) dibutyl as a plasticizer. Phthalate 1% by weight. The powder and binder were mixed at 150 ° C. for 2 hours in a mixer. Samples made of pellets were injected in the form of a cylinder in an injection molding machine under magnetic field, and the mold temperature was 60 ° C. The solvent-extracted polyethylene glycol in the binder component of the injection molded product was removed from the molded product for 10 hours using a mixture of ethanol and water at a temperature of 70 ° C. as a solvent. Residual binder was pyrolyzed under N ₂ atmosphere and removed at a temperature of 200-500 ° C. At a heating rate of 60 ° C./hour, the 10 mm thick molded body was free of binder without defects. The binder removed the molded body was sintered in air for 1 hour at a temperature of 1235 ℃. The magnetic properties of the manufactured anisotropic cylindrical Sr-ferrite permanent magnet were 3.8 kG residual magnetic flux density and 3.7 kOe coercive force.

Example 2

The inorganic powder was a rare earth Nd-Fe-B magnetic powder having an average particle size of 3-10 µm and a filling rate of 90% by weight. The composition of the binder is based on the inorganic powder: (a) 4% by weight polyethylene glycol (molecular weight 600), (b) 2% by weight paraffin wax, (c) 3% by weight polypropylene, (d) diethyl phthalate 1 as a plasticizer. % By weight. The inorganic powder and the binder were mixed at 170 ° C. for 2 hours in a mixer. Samples made of pellets were injected in the form of a cylinder in an injection molding machine under magnetic field, and the mold temperature was 60 ° C. The solvent-extracted polyethylene glycol in the binder component of the injection molded product was removed from the molded product for 5 hours using ethanol as a solvent at a temperature of 70 ° C. The residual binder component of the injection molded body was pyrolyzed in a vacuum or argon atmosphere. The molded article from which the binder was removed was sintered under H ₂ atmosphere at a temperature of 110 ° C. for 1 hour. Thereafter, heat treatment was performed at a temperature of 600-800 ° C for 1 hour. The magnetic properties of the manufactured rare earth Nd-Fe-B permanent magnet were 12 kG of residual magnetic flux density and 10 kOe of coercive force.

Example 3

The inorganic powder was a stainless steel powder which is a kind of metal powder, and the average particle size was 6-8 mu m. The powder prepared by the water-atomizing method was composed of 13% by weight of Ni, 17% by weight of Cr, 2% by weight of Mo, 1% by weight of Si, and the rest of the Fe component, and the density was 7.8 g / cm 3. . The composition of the binder was the same as in Example 1 except that 8 wt% of polyethylene glycol (molecular weight 200) and polyethylene glycol (molecular weight 6000) were used in the same weight ratio based on the inorganic powder. A sample made of pellets was mixed in a mixer at 180 ° C. for 2 hours, and was injected in an injection molding machine, and the mold temperature was 50 ° C. The solvent-extracted polyethylene glycol in the binder component of the injection molded product was removed from the molded product for 7 hours using ethanol having a temperature of 70 ° C. as a solvent. When only a low molecular weight polyethylene glycol (molecular weight 200 or less) is used, the solvent extraction rate is increased, but the viscosity is too low to separate from the inorganic powder when mixing, effective mixing was difficult. When only polyethylene glycol (molecular weight 6000 or more) is used, solvent extraction rate decreases, but mixing with inorganic powder is easy, so it is advantageous for powder injection molding to mix polyethylene glycol having different molecular weights in an appropriate ratio. After solvent extraction, the residual binder component of the injection molded product was pyrolyzed under H ₂ atmosphere. The molded article from which the binder was removed was sintered in a hydrogen atmosphere at a temperature of 1250-1350 ° C. for 1 hour.

Example 4

The inorganic powder was tungsten carbide powder which is a kind of alloy powder, and the average particle size was 0.8-4 탆. The density of the prepared powder was very high as 17 g / cm ³ , so the volume fraction of the powder was small. Therefore, the content ratio of the powder and the binder was 90: 100% by weight. The composition of the binder is based on the inorganic powder (a) 4% by weight polyethylene glycol (molecular weight 400), (b) 2% by weight paraffin wax, (c) 3% by weight ethylene vinyl acetate, (d) diethyl phthalate as a plasticizer. 1 weight%. Samples made of pellets were mixed at 150-180 ° C. for 2 hours in a mixer and injected into an injection molding machine, and the mold temperature was 50 ° C. The solvent-extracted polyethylene glycol in the binder component of the injection molded body was removed from the molded body using ethanol and water having a temperature of 70 ° C. as a solvent, respectively. It was easier to remove polyethylene glycol from the molded body when ethanol was a solvent than when water was a solvent. After solvent extraction, the residual binder component of the injection molded product was pyrolyzed under H ₂ atmosphere. The molded article from which the binder was removed was sintered under a hydrogen atmosphere at a temperature of 1500 ° C. for 1 hour.

Claims (9)

Polyethylene glycol-based binder for powder injection molding of an inorganic powder consisting of polyethylene glycol, low molecular weight waxes, a polymer binder, and a plasticizer. According to claim 1, containing 1-15% by weight polyethylene glycol, 2-10% by weight low molecular weight wax, 2-10% by weight polymer binder, 0.5-5% by weight plasticizer based on the total amount of inorganic powder Characteristic binder. The binder according to claim 1, wherein the polyethylene glycol has a molecular weight of 62-10000. The binder according to claim 1, wherein the low molecular weight waxes are selected from paraffin wax, canuba wax, polyethylene wax, and bis wax. The binder of claim 1 wherein the plasticizer is selected from dimethyl phthalate, diethyl phthalate, dibutyl phthalate. The binder of claim 1 wherein the inorganic powder is selected from metal powders, ceramic powders, or alloy powders with an average particle size of 0.1-100 μm. The inorganic powder and the binder of claim 1 are mixed, and the obtained pellet is injection molded to obtain a molded product, and solvent extraction is carried out from the molded product to remove polyethylene glycol, and then the residual binder component is removed by thermal decomposition, and the molded product from which the binder is removed is sintered. Method for producing a precision component consisting of processing. 8. A process according to claim 7, wherein the solvent is selected from ethanol, water or a mixture of ethanol and water. The process according to claim 7 or 8, wherein the temperature of the solvent is 50-90 ° C.