JP2006257485A - Composition to be injection-molded - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composition to be injection-molded which does not cause flaw or deformation in a sintered compact even when obtained in a short degreasing time, and has more excellent injection moldability and dimensional stability than a conventionally well-known composition to be injection-molded. <P>SOLUTION: The composition to be injection-molded includes a binder and a sintering powder consisting of a metallic powder or a ceramic powder, wherein the binder comprises, by vol.%, a paraffin wax of 45 to 65%, a polyacetal resin of 0.5 to 4.5%, a modified polyolefin resin of 0.5 to 4.5%, polypropylene of 30.5 to 50% and a phthalate of 0.5 to 10%, and the binder occupies 35 to 50% of the whole composition. The phthalate is dibutyl phthalate or dioctyl phthalate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an injection molding composition for use in the production of an injection molded sintered product, and more particularly to a binder for an injection molding composition.

  In the injection molding powder metallurgy method, an injection molding composition obtained by kneading a sintering powder such as metal powder and a binder is injection molded with a mold having a predetermined shape, and the resulting molded body is heated. This is a method of manufacturing a sintered product by performing degreasing (debinding) and then sintering, and is particularly suitable for manufacturing a product having a three-dimensionally complicated shape.

  In order to improve the fluidity at the time of injection molding and the sinterability, a spherical powder of about 10 μm is used for the powder for sintering, and it can be used by mixing two or more kinds of powders as well as using metal or alloy powder alone A sintered alloy can also be used.

  The binder is used for imparting fluidity at the time of injection molding to the powder for sintering, and the injection molding is performed at a temperature at which only the binder is plasticized. Therefore, in the composition for injection molding, the higher the binder content, and the lower the molecular weight of the binder, the lower the viscosity and the better the fluidity, but when the content is increased, the shrinkage rate when the binder is cured Therefore, defects such as surface sinks and cracks are likely to occur in the molded body. Even if the binder has a high molecular weight, the fluidity is improved by increasing the molding temperature. However, it is necessary to take a long cooling time, and the molded body tends to have sink marks and warpage.

  As components of the binder, a lubricant such as wax that contributes to fluidity during injection molding, a binder resin that affects the shape retention of the molded body, and a dispersion that contributes to the affinity between the sintering powder and the binder. The materials are roughly classified into three types, and generally those selected so that the melting point and boiling point thereof become higher in the order of the dispersing agent, the lubricant, and the binder resin are used. By using a binder composed of a plurality of components having different boiling points, stepwise vaporization in the temperature rising process is performed at the time of degreasing, so that deformation due to rapid vaporization of the binder at a specific temperature can be prevented. .

  In addition, since fine and spherical powder is used as the sintering powder as described above, the binder serves to maintain the shape of the molded body as a binder between the sintering powders in the molded body. Accordingly, the shape retention is reduced with vaporization of the binder at the time of degreasing, and thus degreasing requires a long time to prevent deformation of the molded product due to rapid vaporization of the binder.

  In general, the shape retention of the binder increases as the molecular weight increases, but at the same time, the viscosity also increases, and the injection moldability tends to decrease.

  Japanese Patent Application Laid-Open No. 11-140503 discloses an injection molding composition using a polyacetal resin, a modified polyolefin resin, polypropylene, or the like as a binder as proposed to enable degreasing in a short time. The composition for injection molding is composed of a polyacetal resin having a high boiling point and a high heat deformation temperature and another binder component having a boiling point lower than that of the polyacetal resin. Further, it is characterized in that high shape retention is obtained.

However, the conventionally known composition for injection molding has a problem that the viscosity of the binder is so high that importance is placed on the shape retention during degreasing, and the injection moldability is poor. As a result, when applying to thin-walled products and thick-walled products with high molding difficulty, cracks in the weld due to insufficient fluidity, sink marks and warpage due to an increase in molding temperature to improve this, and further However, there has been a problem in that the size of the sintered body is likely to vary due to the variation in the weight of the compact.
JP-A-11-140503

  The present invention has been made in view of the above problems, and provides an injection molding composition that is superior in injection moldability to a conventionally known injection molding composition and can reduce variation in the size of a sintered body. The purpose is to do.

  The injection molding composition of the present invention is an injection molding composition containing a sintering powder comprising a metal powder or a ceramic powder and a binder, wherein the binder is 45 to 65 vol% paraffin wax, 0.5 -4.5% by volume polyacetal resin, 0.5-4.5% by volume modified polyolefin resin, 30.5-50% by volume polypropylene, 0.5-10% by volume phthalate, and The binder is contained in an amount of 35 to 50% by volume based on the whole.

  Furthermore, the phthalic acid ester is preferably dibutyl phthalate or dioctyl phthalate.

  By using the injection molding composition of the present invention, it becomes possible to injection-mold a product having a thin part or a thick part with a high degree of molding difficulty. From a sintered body obtained by a conventionally known injection molding composition A sintered body with high dimensional accuracy can be obtained.

As a result of intensive studies to solve the above problems, the inventors of the present invention are required to maintain the shape of the polyacetal resin, which is excellent in shape retainability but significantly reduces moldability, while other low-boiling components are vaporized. By using polypropylene as the main component of the binder resin, which has a low viscosity and excellent moldability, among the crystallized resins that have a minimum amount and excellent shape retainability, the shape retainability and injection moldability of the binder resin component are improved. The present inventors have found that it is possible to draw out to the maximum, and have completed the present invention.

  Regarding the constituent components of the binder in the present invention, the reasons for limitation relating to each component will be described below.

  The binder in the composition for injection molding is necessary as a lubricant for enabling injection molding of the powder for sintering and as a binder for maintaining the shape of the molded body, but its content is 35. If it is less than volume%, the amount added to the sintering powder is small, and sufficient fluidity cannot be obtained. On the other hand, if it exceeds 50% by volume, defects such as surface sink marks and cracks are likely to occur during injection molding, and the time required for degreasing increases. Accordingly, the content of the binder is preferably 35 to 50% by volume per whole.

  Paraffin wax is a component excellent in fluidity and degreasing properties during injection molding, and generally has a melting point of 35 to 80 ° C. When the content of paraffin wax is less than 45% by volume, the injection moldability and degreasing properties are lowered. On the other hand, if it exceeds 65% by volume, the mold release property of the molded product is lowered and the molded product becomes brittle. Accordingly, the content of paraffin wax is preferably 45 to 65% by volume.

  The polyacetal resin is excellent in shape retention due to its high strength and high heat deformation temperature, and can be degreased in a short time because it is a depolymerized resin that is sequentially cut from the end of the molecule. In addition, since the boiling point is the highest among the binder components in the present invention, it is a component that is finally vaporized in the stepwise vaporization at the time of degreasing, and the presence of a polyacetal resin having high shape retention is degreasing It is possible to shorten the time. When the content of the polyacetal resin is less than 0.5% by volume, it is insufficient as an amount for playing the role of a binder from the volume ratio with the sintering powder. On the other hand, if it exceeds 4.5% by volume, the plasticization temperature of the entire binder rises, and it becomes necessary to increase the molding temperature, so that surface sinks and warpage are likely to occur, and cracks in the weld part due to increased viscosity Variations in the weight of the compact are also likely to occur. Accordingly, the content of the polyacetal resin is preferably 0.5 to 4.5% by volume.

  The modified polyolefin resin has a role as a compatibilizer of the polyacetal resin and other binder components. Examples of the modified polyolefin resin include polyethylene, polypropylene, ethylene-glycidyl methacrylate copolymer, acrylonitrile-styrene copolymer, poly A resin copolymerized with methyl methacrylate or polystyrene is preferred. When the content of the modified polyolefin resin is less than 0.5% by volume, the compatibility is insufficient, and when it exceeds 4.5% by volume, the moldability is lowered. Accordingly, the content of the modified polyolefin resin is preferably 0.5 to 4.5% by volume.

  Polypropylene is excellent in shape retention because it has a heat deformation temperature close to that of polyacetal resin, and also belongs to a class having low viscosity among crystalline resins, and also has high toughness, and therefore has excellent moldability. Moreover, since the compatibility with many organic components is good, the obtained composition for injection molding has a uniform composition, and variations in the size of the sintered body due to variations in the weight of the molded body hardly occur. When the content of polypropylene is less than 30.5% by volume, the molded body becomes brittle and cracks tend to occur, and the shape retainability decreases and deformation tends to occur. On the other hand, if it exceeds 50% by volume, the blending ratio of other binder components is relatively reduced, and the degreasing time cannot be shortened by stepwise vaporization. Therefore, the content of polypropylene is desirably 30.5 to 50% by volume.

  The phthalate ester has an effect of improving dispersibility because it is compatible with other binder components and has excellent affinity with the sintered powder. Moreover, since it contributes also to the fall of the viscosity of the whole composition for injection molding, and the improvement of mold release property, a moldability improves. As phthalic acid esters, dibutyl phthalate and dioctyl phthalate are preferably used because they are relatively inexpensive and stable. If the content of phthalate is less than 0.5% by volume, sufficient dispersibility cannot be obtained from the volume ratio with the metal powder. On the other hand, if the content exceeds 10% by volume, the molded product becomes brittle and cracks are likely to occur. Become. Therefore, the content of phthalic acid ester is preferably 0.5 to 10% by volume.

  As the powder for sintering, metal powder such as iron, stainless steel, copper-nickel alloy, or ceramic powder such as alumina or zirconia is selected and used depending on the use of the sinterable product.

  The composition for injection molding according to the present invention is easily adjusted by uniformly kneading the sintering powder and binder at the above ratios, and then the final product by going through the steps of injection molding, degreasing and sintering. It becomes the sintered compact which is. Injection molding can be performed using a normal injection molding machine used for plastic injection molding. Degreasing is performed by heat-treating the compact, but when a metal that is easily oxidized is used as the sintering powder, the heat-treatment is preferably performed in an inert gas atmosphere. Sintering is generally performed in a vacuum, an inert gas atmosphere, or a reducing atmosphere, although it varies depending on the type of sintering powder used.

[Example 1]
Polyacetal resin: 1 volume%, modified polyolefin resin using polyethylene: 1 volume%, paraffin wax having a melting point of 65 ° C .: 50 volume%, dibutyl phthalate: 4 volume%, polypropylene: 44 volume% The composition for injection molding of Example 1 was prepared by mixing and kneading the carbonyl iron powder having a diameter of 5 μm at a ratio of 40% by volume. The melt flow rate (MFR) measurement results of the obtained injection molding composition using a flow tester are shown in Table 1. MFR was measured under the conditions of a die hole: φ1 mm × 1 mm, a heating temperature: 150 ° C., and a load: 20 kgf / cm ² .

  Using the box-shaped product shown in FIG. 1 and the die of the die-shaped product shown in FIG. 2, 50 injection moldings of the composition for injection molding were continuously produced. Table 2 shows the evaluation results of the moldability at this time. The dimensions of the mold are A = B = 30 mm, C = 25 mm, D = E = F = G = 2 mm, H = 3 mm, and I = J = K = 30 mm. The body was visually confirmed and evaluated for the presence of surface sink marks, cracks, poorly filled portions, and the like.

  The obtained molded body was heated in a nitrogen stream at a rate of 50 ° C./hour and degreased for 10 hours. Table 2 shows the evaluation results of degreasing properties at this time. In addition, about the degreasing property, the molded object after degreasing was confirmed visually, and the presence or absence of a crack, a deformation | transformation, etc. was evaluated.

Next, the compact after degreasing was subjected to a sintering treatment at 1200 ° C. for 2 hours in a vacuum atmosphere to obtain a sintered body. Table 2 shows the presence or absence of defects in the sintered body and the standard deviation of the dimensions of the I, J, and K portions of the die-shaped shaped product sintered body. K is the height direction during degreasing and sintering. The presence or absence of defects in the sintered body was evaluated by visual observation and soft X-ray photography, and the dimensions of the die-shaped shaped product sintered body were measured with a digital caliper having a minimum scale of 0.01 mm.
[Examples 2 to 5, Comparative Examples 1 to 5]
As shown in Table 1, compositions for injection molding of Examples 2 to 5 were prepared in the same manner as in Example 1 except that the blending ratio of the binder component was changed. Subsequently, the properties of the injection molding composition were evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

以上の結果によれば、本発明による射出成形用組成物は、従来公知の射出成形用組成物と同等以上の脱脂性を有し、且つ、射出成形性および得られる焼結体の寸法安定性については従来公知の射出成形用組成物によりも優れていることが明らかである。

According to the above results, the composition for injection molding according to the present invention has a degreasing property equal to or higher than that of a conventionally known composition for injection molding, and also has injection moldability and dimensional stability of the obtained sintered body. Is clearly superior to the conventionally known composition for injection molding.

It is a three-plane figure of the metal mold | die for box-shaped goods used for the injection molding test. It is a three-plane figure of the die for dice type shape goods used for the injection molding test.

Claims (2)

  An injection molding composition comprising a sintering powder comprising a metal powder or a ceramic powder and a binder, wherein the binder is 45 to 65 vol% paraffin wax, 0.5 to 4.5 vol% polyacetal resin, 0.5 to 4.5% by volume modified polyolefin resin, 30.5 to 50% by volume polypropylene, 0.5 to 10% by volume phthalate ester, and the binder is 35 to 50% by volume per total An injection molding composition characterized by being contained in an amount. The composition for injection molding according to claim 1, wherein the phthalic acid ester is dibutyl phthalate or dioctyl phthalate.

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