KR20010055794A - High strength binder composition for powder injection molding - Google Patents

Abstract

PURPOSE: Provided is a high strong binding agent used in a powder injection-molding or extruding, which can be mixed with fine metal, fine particles, and ceramic powder, therefore can produce excellent mixed bodies. CONSTITUTION: The high strong binding agent comprises 20 to 80wt% of polyethylene acrylic acid having an average molecular weight of 3,000 to 30,000 and 80 to 20wt% of polyethylene glycol having an average molecular weight of 1,000 to 30,000, wherein the content of the acrylic acid in the polyethylene acrylic acid is 3 to 20% based on the weight ratio.

Description

High strength binder composition for powder injection molding

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder used in powder injection molding technology or an extrusion process. Particularly, the present invention relates to a binder used in a powder injection molding technique or an extrusion process. It relates to a high-strength binder for powder injection molding that can prevent the separation phenomenon to produce a good mixture used to produce a high-quality molded article.

Powder injection molding technology is a technology to economically mass-produce precision parts of three-dimensional complex shape, and extrusion process is a technology to economically mass-produce two-dimensional shapes. As described above, a fine metal, a cemented carbide, a ceramic, or the like is mixed with a thermoplastic polymer material (binder) to prepare a moldable mixture. The molded article of a specific shape manufactured by powder injection molding technology or extrusion process is removed by a thermal decomposition method or a solvent extraction method to produce a porous degreasing body and finally hot sintered to produce a product of precise dimensions.

Since the mixture used in the powder injection molding process or the extrusion process has a very high powder filling rate, the binder should provide excellent fluidity to the mixture to facilitate molding, and should have high strength. The phenomenon which breaks in can be prevented. In addition, the binder should be removed before the final sintering process, so it should be easy to remove and free of residual material after degreasing.

The most commonly used material for such a binder is a thermoplastic polymer, which is easy to reuse. The typical composition of the binder is a main binder which maintains its shape until the final point of binder removal and is the main agent of the flow, a sub binder which promotes viscosity reduction and lubrication of the mold, a plasticizer which improves the flexibility of the polymer, powder and polymer It is composed of a surfactant for improving the wetting (wetting) or adhesion (adhesion). The main binders are polypropylene, polystyrene, polyethylene, etc., and the secondary binders include waxes such as carnauba wax, paraffin wax, charcoal wax, beeswax, oils such as edible oil and peanut oil. As a plasticizer, solutions, such as DBP and DOP, are mainly used, and stearic acid, oleic acid, etc. are used as surfactant.

Conventional powder injection molding binders are those disclosed in US Patent No. 4,404,166, the composition of which is as follows. Mainly used for 5-50% polypropylene at a melting point of 170 ° C. as a material of high melting point for maintaining shape, 10% of carnauba wax is added as a low melting point material, and the remainder is composed of paraffin wax. Polypropylene maintains the shape of the injection molded body while the low melting point material is removed. However, the binder in the patent is a metal powder mixture composed of 20% by weight of polypropylene, 10% by weight of carnauba wax, 69% by weight of paraffin wax and 1% by weight of stearic acid. Therefore, even though high melting point polypropylene is added, a softening point appears at the melting point of paraffin. Therefore, when the binder is to be removed by pyrolysis, it is difficult to maintain the shape and also has a low strength of the molded body.

The binder disclosed in U.S. Patent No. 4,765,950 uses non-polar polypropylene, polyethylene, and paraffin wax as its constituents to separate the binder and powder during injection molding, resulting in density variation of the injection molded parts. There was a problem of using the methylene chloride (methylene chloride) as a solvent to remove the environmental pollution.

The present invention was invented to solve the problems of the conventional powder injection molding binder in view of the above situation, and is mixed with a fine metal, cemented carbide, ceramic powder, which is difficult to mix, and a mixing process or injection molding in which high shear stress is applied. It is an object of the present invention to provide a binder for producing a good mixture which is used to prepare a high-quality molded article by preventing separation of the powder and the binder.

1 is a graph showing the melting behavior by differential scanning calorimetry showing compatibility of heating polyethylene acrylic acid and polyethylene glycol.

In order to achieve the above object, the binder for powder injection molding of the present invention is a binder used in a powder injection molding method or an extrusion process using metal, cemented carbide and ceramic powder, and has an average molecular weight of 3,000 to 30,000 polyethylene acrylic acid. acid) 20 to 80% by weight, the average molecular weight of 1,000 to 30,000 polyethylene glycol (polyethylene glycol) is characterized in that composed of 80 to 20% by weight.

In addition, the content of the acrylic acid in the polyethylene acrylic acid is characterized in that 3 to 20% by weight,

Polyethylene glycol is characterized by selectively mixing one or more types of polyethylene glycols having an average molecular weight of 1,000 to 30,000.

Hereinafter, the high strength binder for powder injection molding of the present invention will be described in detail.

Polyethylene acrylic acid in the binder component of the present invention has a polar group in the structure of the carboxyl group has excellent adhesion properties with the powder, so that the separation of the powder and the binder when injection molding than non-polar polypropylene or polyethylene can be minimized In addition, the compatibility between the polyethylene glycol and the melt heating is also excellent to prevent separation between the binder during injection molding. The content of the acrylic acid in the polyethylene acrylic acid can be selected by using 3 to 20% by weight. The lower the content of the acrylic acid can not only ensure high strength of the molded body but also increase the melting point, thereby maintaining the shape in the pyrolysis process. It is advantageous.

Polyethylene glycol is used as a lubricant and dispersant as well as a plasticizer to reduce viscosity when mixed with polyethylene acrylic acid. The molecular weight is suitably 1000 or more, but the molecular weight of less than 1000 is mainly present as a liquid, resulting in a decrease in strength of the molded body. When the molecular weight is 30000 or more, the molded article has a high strength, but since the viscosity is high, molding becomes difficult. In the case of removing the binder by pure heat, there is no residual material such as carbon after pyrolysis, thereby minimizing contamination of the sintered body. In addition, a solvent extraction process may also be used as another binder removal method, in which case water, alcohol, and the like may be used as the solvent, which is also environmentally friendly.

The composition of polyethylene acrylic acid and polyethylene glycol can be variously configured according to the strength of the molded body or the binder removal process required by variously selecting the content of the acrylic acid in the polyethylene acrylic acid and the molecular weight of polyethylene glycol.

Figure 1 shows the melting behavior with differential scanning calorimetry (DSC) when the binder component is composed of 35% polyethylene acrylic acid by weight and polyethylene glycol by 65% by weight. The melt peak temperature of the polyethylene acrylic acid single phase was 76 ° C, and the melt peak temperature of the polyethylene glycol single phase was 67 ° C, but after mixing, it was 61.65 ° C, indicating compatibility between the two binders.

The present invention will be described in detail through the following examples.

Example

1. Bending strength indicating the strength of the binder was measured. As shown in Table 1, Comparative Example 1 blended conventionally used low-density polyethylene and paraffin wax at 150 ° C. at a weight ratio of 30% and 70%, respectively. The bending strength was measured by extrusion molding with a specimen of 27.2 × 6.8 × 1.7mm according to ASTM D790, and the value was 85Mpa.

Binder weight ratio (%) Bending strength (Mpa) LDPE PW Comparative Example 1 30 70 85

* LDPE: Low density polyethylene, PW: Paraffin wax

Inventive Examples 1, 2, 3 and Inventive Example 6 of Table 2 were prepared in the same manner as Comparative Example 1 in the composition of polyethylene acrylic acid and polyethylene glycol. The bending strengths of Inventive Examples 1, 2, 3 and Inventive Example 6 were superior to Comparative Example 1, and Inventive Examples 4, 5, 7 and 8 were also superior to Comparative Examples.

division Polyethylene acrylic acid Polyethylene glycol Bending strength (Mpa) PEAA Weight Ratio (%) AA content (%) PEG weight (%) Average molecular weight Inventive Example 1 30 3 70 6000 324 Inventive Example 2 30 9 70 6000 305 Inventive Example 3 30 20 70 6000 282 Inventive Example 4 35 20 65 6000 395 Inventive Example 5 40 20 60 6000 135 Inventive Example 6 30 20 70 20000 317 Inventive Example 7 35 20 65 20000 309 Inventive Example 8 40 20 60 20000 217

2. The binder powder of the invention example 1 and the average particle diameter prepared by the spray method was mixed with dry powder in a volume ratio of 30:70 in a volume ratio of 30:70 and extruded at 150 ℃ to prepare a mixture and then crushed. The crushed mixture was injection molded at 150 ° C. to prepare a molded body. The binder was removed by pyrolysis and nitrogen atmosphere was used. Heating conditions were gradually elevated to 180 ℃ to maintain for 2 hours, and again to increase the temperature was maintained for 1 hour at 320 ℃ and finally heated to 550 ℃ to maintain for 2 hours to completely remove the binder. When the degreasing body is sintered at 1250 ~ 1350 ° C. in a hydrogen atmosphere, a sintered body having a relative density of 95% or more can be obtained. The heating rate during pyrolysis or sintering should be adjusted according to the thickness or size of the molded body.

3. The binder composition of the invention example 4 and the powder for injection molding used were zirconia powder with an average particle diameter of 0.3 mu m. In the preparation of the mixture, the volume ratio of the binder and the powder was 57:43, prepared at a temperature of 150 ° C. in a horizontal sigma mixer, and then cooled and crushed. Injection molded bodies were prepared in the same manner as in Example 1, and the thermal decomposition conditions were the same, but the atmosphere was used. Sintering was carried out at 1400 ~ 1500 ℃ in the atmosphere and the holding time was within 4 hours. The relative density of the sintered compact was 98% or more.

4. The binder composition of Example 8 and the cemented carbide powder (WC-7% Co) having an average particle diameter of 0.5 µm were used, and the injection molding mixture had a powder and a binder of 46:54 by volume ratio. The mixture was crushed by cooling after mixing for 1 hour at 150 ° C. in a sigma mixer. The molded body was prepared and pyrolyzed in the same manner as in Example 2. The degreasing body was vacuum sintered between 1350 and 1450 ° C. and the relative density after sintering was 99% or more.

In the case of using the binder of the present invention, the separation of the powder and the binder during the injection molding and the separation between the binder do not easily occur, which is advantageous for maintaining the shape, and there is no residual material such as carbon after thermal decomposition of the binder, thereby minimizing contamination of the sintered body. Even when the solvent extraction process is used to remove the environmental pollution there is no advantage.

Claims (3)

Binder used for powder injection molding or extrusion process using metal, cemented carbide, ceramic powder, polyethylene acrylic acid having an average molecular weight of 3,000 to 30,000 is 20 to 80% by weight, and the average molecular weight is 1000 to 30000 Phosphorus polyethylene glycol (Polyethylene glycol) is a high strength binder for injection molding, characterized in that consisting of 80 to 20% by weight. The high strength binder for powder injection molding according to claim 1, wherein the content of the acrylic acid in the polyethylene acrylic acid is 3 to 20% by weight. The high strength binder for powder injection molding according to claim 1, wherein the polyethylene glycol is a mixture of one or more kinds of polyethylene glycols having an average molecular weight of 1,000 to 30,000.