JP5163596B2 - Composition for injection molding - Google Patents

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, a composition for injection molding 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 debindered (degreasing). ) And then sintering to produce a sintered product, which is particularly suitable for the production of a product having a three-dimensionally complicated shape.

 As a degreasing method, heating degreasing is most commonly used in which a compact is heated in a vacuum or an inert atmosphere to evaporate or thermally decompose the binder. The binder is reduced as a binder between the sintering powders until the start of metallurgical bonding between the sintering powders due to the decrease in the binder and the resulting shrinkage of the compacts during the temperature rise. Has the role of holding the shape (hereinafter referred to as shape retention).

In general, the shape retention of the molded body improves with an increase in the molecular weight of the binder, but at the same time the viscosity increases and the fluidity during injection molding (hereinafter referred to as moldability) decreases.
As proposed in order to improve the moldability and degreasing property, Japanese Patent No. 2751966 discloses a low density polyethylene, paraffin wax, boric acid ester, polyoxyethylene alkyl ester or polyoxyethylene alkyl ether. An injection molding composition is described using as a binder.

 However, conventionally known injection molding compositions are excellent in degreasing properties, but are not sufficiently moldable for products with a high degree of molding difficulty such as thin-walled products and thick-walled products, and cracks in the welds There is a problem in the generation of molding defects such as sinks, warpage, and the like, as well as the dimensional variation of the sintered body due to the mass variation generated during molding, and improvement of moldability has been an issue.

Japanese Patent No. 2751966

 The present invention has been made in view of the above problems, and provides an injection molding composition having a degreasing property equal to or higher than that of conventionally known injection molding compositions and excellent in moldability. Objective.

 The composition for injection molding of the present invention is a composition for injection molding containing a sintering powder comprising a metal powder or a ceramic powder and a binder, wherein the binder is 30 to 70% by mass of paraffin wax, 10 to 50 % By weight low density polyethylene, 0.1-10% by weight polycarboxylic acid, 0.1-10% by weight alkylamine, 0.1-10% by weight polysiloxane, 1-20% by weight phthalate ester And the binder is contained in an amount of 30 to 60% by volume based on the whole.

 Or it is the composition for injection molding containing the powder for sintering which consists of metal powder or ceramics powder, and a binder, The said binder is 30-70 mass% paraffin wax, 10-50 mass% low density polyethylene, 0 .1-10% by weight polycarboxylic acid, 0.1-10% by weight alkylamine, 0.1-10% by weight polysiloxane, 1-20% by weight phthalic acid ester, 5-30% by weight polypropylene It is desirable that the binder is contained in an amount of 30 to 60% by volume based on the whole.

 Or it is the composition for injection molding containing the powder for sintering which consists of metal powder or ceramics powder, and a binder, The said binder is 30-70 mass% paraffin wax, 10-50 mass% low density polyethylene, 0 .1-10% by weight polycarboxylic acid, 0.1-10% by weight alkylamine, 0.1-10% by weight polysiloxane, 1-20% by weight phthalic acid ester, 5-30% by weight polypropylene The binder is preferably contained in an amount of 30 to 60% by volume based on the total amount of the ethylene vinyl acetate copolymer.

  By using the injection molding composition of the present invention, a degreasing property equal to or higher than that of a conventionally known injection molding composition is obtained, and the moldability is improved.

It is a three-plane figure of the metal mold | die for box-shaped products 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.

  The inventors have completed the present invention as a result of intensive studies on the influence of the binder component, the mixing ratio of the sintering powder and the binder (volume ratio), and the mass ratio of each binder composition in order to solve the above problems. It came to do.

 The reason for limitation concerning the binder component and the blending ratio of the binder in the composition for injection molding of the present invention will be described below.

 Paraffin wax is a component that is excellent in fluidity and degreasing properties during injection molding, and those having a melting point of 35 to 80 ° C. are particularly suitable. When the content of the paraffin wax is less than 30% by mass, the moldability and degreasing properties are lowered. On the other hand, if it exceeds 70% by mass, the mold release property of the molded product is lowered and the molded product becomes brittle.

 Low density polyethylene is a component excellent in shape retention, and has good compatibility with many organic components, so that the resulting injection molding composition has a uniform composition. When the content of the low density polyethylene is less than 10% by mass, the shape retention is insufficient and deformation occurs during degreasing. On the other hand, if it exceeds 50% by mass, the moldability is lowered, and defects such as sink marks and cracks occur in the molded product.

 Polycarboxylic acid, alkylamine, and polysiloxane are components having excellent moldability. When dissolved in a solvent such as glycol ether or alcohol and blended as a solution of about 40 to 80% by mass, sintering powder and organic The mixing property of the binder is further improved. Therefore, in this case, the binder composition also contains a certain amount of solvent as a component. When the content of polycarboxylic acid, alkylamine, and polysiloxane is less than 0.1% by mass, sufficient moldability cannot be obtained. On the other hand, when the content exceeds 10% by mass, the shape retention is reduced and deformation occurs during degreasing. Occurs.

As the polycarboxylic acid, a saturated cyclic polycarboxylic acid, an unsaturated polycarboxylic acid, an aromatic polycarboxylic acid, an oil-modified polycarboxylic acid, and the like are preferable.
As the glycol ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate and the like are suitable.

 As the alcohol, propyl alcohol, butyl alcohol, butanediol and the like are preferable.

 Phthalate esters have an effect of improving dispersibility because they are compatible with other binder components and have excellent affinity with 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. If the content of phthalic acid ester is less than 1% by mass, sufficient dispersibility and moldability cannot be obtained. On the other hand, if the content exceeds 20% by mass, the molded product becomes brittle and cracks tend to occur.

 As the phthalic acid ester, dibutyl phthalate, dioctyl phthalate and the like are preferable.

Polypropylene is a component excellent in shape retention, and polypropylene can be added for the purpose of further improving the strength of the molded body. When the content of polypropylene is less than 5% by mass, shape retention is insufficient and deformation occurs during degreasing. On the other hand, if it exceeds 30% by mass, the moldability is lowered, and defects such as sink marks and cracks occur in the molded product.
The ethylene vinyl acetate copolymer is a component having excellent shape retention, and an ethylene vinyl acetate copolymer can be added for the purpose of further improving the strength of the molded body. When the content of the ethylene vinyl acetate copolymer is less than 5% by mass, shape retention is insufficient and deformation occurs during degreasing. On the other hand, if it exceeds 30% by mass, the moldability is lowered, and defects such as sink marks and cracks occur in the molded product.

 When the content of the binder in the composition for injection molding is less than 30% by volume, the amount added to the sintering powder is small, and sufficient moldability cannot be obtained. On the other hand, if it exceeds 60% by volume, defects such as surface sink marks and cracks are likely to occur in the molded product, and the time required for degreasing increases.

  As the powder for sintering, metal powder such as iron, stainless steel and copper-nickel alloy, and ceramic powder such as alumina and zirconia are selected and used depending on the use of the sintered product. In order to improve the formability and sinterability, a spherical powder of around 10 μm is suitable, and it is possible to use a sintered alloy by mixing two or more kinds of powders as well as using each alone or alloy powder alone. Is possible.

 The composition for injection molding of 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 a certain sintered body. Injection molding can be performed using a normal injection molding machine used for plastic injection molding. Degreasing is performed by heat-treating the molded body, but when a metal that easily oxidizes is used as the sintering powder, it is preferable to perform the heat-treatment 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]
An average particle size of a binder composed of paraffin wax: 30% by mass, low density polyethylene: 45% by mass, polycarboxylic acid: 5% by mass, alkylamine: 5% by mass, polysiloxane: 5% by mass, dibutyl phthalate: 10% by mass The composition for injection molding of Example 1 was obtained by mixing and kneading the carbonyl iron powder having a diameter of 5 μm at a ratio of 42% by volume. The melt flow rate (MFR) of the obtained injection molding composition was measured and used as an index of moldability. The MFR was measured using a flow tester under the conditions of a die hole: φ1 mm × 1 mm, a heating temperature: 90 ° C., and a load: 10 kgf / cm ² . The MFR measurement results are shown in Table 2.

  Using the box-shaped product shown in FIG. 1 and the die of the dice-shaped product shown in FIG. 2, 50 injection moldings of the composition for injection molding were continuously obtained. Table 2 shows the evaluation results for the presence or absence of defects in the obtained molded product. The dimensions of the mold are A = B = 30 mm, C = 25 mm, D = E = F = G = 2 mm, H = 3 mm, I = J = K = 30 mm. The presence or absence of sink marks, cracks, poorly filled portions, etc. was confirmed visually.

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 on the presence or absence of defects in the molded body obtained after degreasing. In addition, about the presence or absence of the defect of the molded object after degreasing, the presence or absence of a crack, a deformation | transformation, etc. was confirmed visually.
Next, the compact after degreasing was subjected to a sintering treatment at 1250 ° C. for 2 hours in a vacuum atmosphere to obtain a sintered body. Table 2 shows the presence or absence of defects in the obtained sintered body and the standard deviations of the dimensions of the I, J, and K portions of the die-shaped shaped product sintered body (K: height direction during degreasing and sintering). As for the presence or absence of defects in the sintered body, the presence or absence of cracks and deformations is confirmed by visual observation and X-ray photography. did.
[Examples 2 to 12, Comparative Examples 1 to 12]
As shown in Table 1, compositions for injection molding of Examples 2 to 12 and Comparative Examples 1 to 12 were prepared in the same manner as in Example 1 except that the blending ratio of the binder component was changed. Next, in the same manner as in Example 1, various properties of the injection molding composition were evaluated. The evaluation results are shown in Table 2.

  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.

 The present invention relates to an injection molding composition used for the production of an injection molded sintered product, and more particularly to a binder for an injection molding composition, which has a difficulty in molding a thin-walled product or a thick-walled product. Excellent moldability and degreasing properties even for high-quality products, generation of cracks, sink marks, warpage, and other molding defects in the weld, as well as dimensional variations of the sintered body due to mass variations during molding It can be used for improvement.

Claims (3)

An injection molding composition comprising a sintering powder comprising a metal powder or a ceramic powder and a binder, wherein the binder is 30 to 70 mass% paraffin wax, 10 to 50 mass% low density polyethylene, 0.1 10 mass% polycarboxylic acid, 0.1-10 mass% alkylamine, 0.1-10 mass% polysiloxane, 1-20 mass% phthalate ester, and the binder is 30 A composition for injection molding, which is contained in an amount of ˜60% by volume. An injection molding composition comprising a sintering powder comprising a metal powder or a ceramic powder and a binder, wherein the binder is 30 to 70 mass% paraffin wax, 10 to 50 mass% low density polyethylene, 0.1 10 to 10% by weight polycarboxylic acid, 0.1 to 10% by weight alkylamine, 0.1 to 10% by weight polysiloxane, 1 to 20% by weight phthalic acid ester, 5 to 30% by weight polypropylene The composition for injection molding is characterized in that the binder is contained in an amount of 30 to 60% by volume based on the whole. An injection molding composition comprising a sintering powder comprising a metal powder or a ceramic powder and a binder, wherein the binder is 30 to 70 mass% paraffin wax, 10 to 50 mass% low density polyethylene, 0.1 10 mass% polycarboxylic acid, 0.1-10 mass% alkylamine, 0.1-10 mass% polysiloxane, 1-20 mass% phthalic acid ester, 5-30 mass% polypropylene, 5 An injection molding composition comprising -30 mass% ethylene vinyl acetate copolymer, and the binder is contained in an amount of 30-60 volume% per whole.