JPH0673404A - Composition for injection molding - Google Patents

Abstract

PURPOSE:To produce the compsn. for infection molding in which powder for sintering is uniformly dispersed by compounding metallic powder for sintering, wax, a binder consisting of a thermoplastic resin and a dispersant under specific conditions. CONSTITUTION:The compsn. for injection molding which contains the powder for sintering consisting of metals (iron, copper, Ni, etc.) or their alloys, the wax (paraffin wax, etc.) having 50 to 90 deg.C softening point, the binder consisting of the thermoplastic resin (polyethylene, etc.) having 100 to 300g/10 minutes melt flow (ASTM D 1236, 230 deg.C) and the dispersant (polyisoprene, etc.) consisting of a polymer having iminium ion as a functional group, contains the binder at 30 to 70vol.% of the entire part and contains the dispersant at 0.1 to 15vol.% of the total volume of the dispersant and the binder is prepd. As a result, the powder for sintering is uniformly dispersed. As a result, the compsn. which effectively averts the generation of defects at the time of removing the binder and the generation of deformation at the time of sintering is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding composition used for producing an injection molded sintered product.

[0002]

2. Description of the Related Art The injection molding powder metallurgy method is an injection molding composition obtained by kneading a sintering powder such as a metal powder and a binder, into a mold having a predetermined shape, and molding the obtained molded product. It is a method of producing a sintered product by heating and debinding to perform sintering, and in particular, it produces a product having a three-dimensional complex shape or a product having a thin portion such as a knife edge. Is an effective method (Japanese Patent Laid-Open No. 57-16
103, JP-A-57-26105, etc.).

[0003]

However, conventionally known compositions for injection molding have insufficient dispersibility of the sintering powder, and for this reason, they are deformed, swollen, or depressed during debinding or sintering. , Various defects such as cracks,
The sintered product obtained from the injection-molded product has a large variation in shape and has a problem that the dimensional accuracy becomes extremely unsatisfactory. Therefore, an object of the present invention is to provide an injection molding composition in which the sintering powder is uniformly dispersed, and the generation of defects during debinding and the generation of deformation during sintering can be effectively avoided. is there.

[0004]

According to the present invention, a sintering powder made of a metal or an alloy, waxes having a softening point of 50 to 90 ° C. and a melt flow rate (ASTM D 1236, 230 ° C.)
Containing 100 to 300 g / 10 min of a thermoplastic resin and a dispersant consisting of a polymer having iminium ions as functional groups, said binder being in an amount of 30 to 70% by volume based on the whole. The dispersant is contained in an amount of 0.1 to 15% by volume based on the total amount of the dispersant and the binder.
An injection molding composition is provided which is characterized by being contained in an amount of

[0005]

An important feature of the present invention is that waxes and a thermoplastic resin are used together as a binder and a polymer having an iminium ion as a functional group is used as a dispersant. That is, such a dispersant has excellent compatibility with the thermoplastic resin in the binder and also has excellent affinity with the sintering powder due to the presence of iminium ions. Therefore, in the composition of the present invention, this dispersant acts as a bridge between the sintering powder and the thermoplastic resin, and as a result, separation of the sintering powder from the binder due to sedimentation is effectively avoided. It is believed that uniform dispersibility is ensured.

Powder for Sintering In the present invention, as the powder for sintering, a metal powder of iron, copper, nickel or the like, or a powder of an alloy of these metals may be used depending on the intended use of the sintered product to be finally manufactured. Used.

Binder In the composition for injection molding of the present invention, in order to enable the injection molding of the sintering powder and to secure a certain strength in the obtained injection molded product, the amount of 30 to 70% by volume is used as a whole. The binder is included. The content of this binder is 30% by volume
If it is less than the above range, the fluidity of the composition is lowered and injection molding becomes difficult. On the other hand, if it exceeds 70% by volume, a defect called chamfering will occur on the surface of the molded body during molding, and the packing density of the sintering powder in the obtained injection molded body will be low, resulting in a sintered product finally obtained. It becomes difficult to improve the density.

In the present invention, as the binder, a wax, a thermoplastic resin and a dispersant are used in combination as described above. Waxes contribute to improving the fluidity of the composition during injection molding,
A softening point of 50 to 90 ° C is used. If the softening point is less than 50 ° C, the cycle time of the injection molding work becomes long, and the workability during molding remarkably deteriorates because it is easily softened.
Further, when a softening point of more than 90 ° C. is used, the fluidity of the composition is lowered and the thermal decomposition point is increased, so that the debinding property is lowered. In the present invention, as such waxes, for example, paraffin wax, microcrystalline wax, low molecular weight polyethylene wax, modified wax and the like are suitable.

The thermoplastic resin contributes to maintaining the shape of the molded body after injection molding, and has a melt flow rate (M
FR) of 100 to 300 g / 10 minutes is used. MF
If R is less than 100 g / 10 min, the injection moldability becomes unsatisfactory, and if R exceeds 300 g / 10 min, the strength and shape retention of the injection molded product deteriorate. In the present invention, suitable examples of such thermoplastic resin include polyethylene, polypropylene, ethylene / vinyl acetate copolymer, ethylene / acrylate copolymer, polystyrene and the like.

In the present invention, the above waxes and the thermoplastic resin are generally used in a ratio of 4: 1 to 1: 4 on a volume basis, but when polyisoprene or EPDM is used as a dispersant described later. It is particularly preferable to use a ratio of 4: 1 to 1: 1 and, when using polyolefin, it is particularly preferable to use a ratio of 3: 1 to 1: 3. If the amount of waxes used is greater than this range, the strength of the injection-molded product may be unsatisfactory, and it may be difficult to maintain the shape of the molded product. If it is less than the above range, the composition There is a possibility that the viscosity of the product becomes high and the injection molding becomes difficult, and the debinding process becomes difficult.

Dispersant In the present invention, a polymer having an iminium ion introduced into the polymer chain is used as the dispersant. Introduction of an iminium ion into the polymer chain is performed, for example, by the following formula (1):

[Chemical 1] [Wherein R ¹ , R ² and R ³ are each a hydrogen atom, an alkyl group such as a methyl group, and X is an aryl group such as an O ⁻ , S ⁻ or a phenyl group]. It can be carried out by reacting the imino compound with the molecular chain end of the polymer using, for example, the Grignard reaction or the like.

Examples of the polymer into which the iminium ion should be introduced include polyisoprene, ethylene-propylene-diene terpolymer (EPDM), poly α-olefin and the like. Examples of the diene component in EPDM include conjugated dienes such as 1,4-butadiene, dicyclopentadiene, ethylidene norbornene and 1,4-hexadiene. Furthermore, examples of the poly α-olefin include polyethylene, polypropylene, polybutene-1, poly-4-methylpentene-1 and the like. In this polymer used as a dispersant, the iminium ion content (that is, the content of the constitutional unit derived from the compound of the formula (1)) and the molecular weight of the polymer are determined depending on the binder component used. It may be appropriately selected so as to have good dispersibility.
Generally, in the case of polyisoprene and EPDM-based iminium ion-containing polymers, the molecular weight is preferably 200,000 or less, and in the case of polyolefin-based iminium ion-containing polymers, the molecular weight is preferably 10,000 or less.

Such a dispersant is used in an amount of 0.1 to 15% by volume based on the total amount of the dispersant and the binder. 0.1
When the content is less than the volume%, the effect of improving the dispersibility, which is the object of the present invention, is not sufficient, and defects are likely to occur during debinding and sintering. On the other hand, if it exceeds 15% by volume, the strength of the obtained injection-molded product is lowered, and when the molded product is taken out of the mold at the end of injection molding, it is likely to be damaged, which makes the injection molding work difficult.

Injection Molding Composition The injection molding composition of the present invention is easily prepared by uniformly kneading the sintering powder, the binder and the dispersant in the proportions described above. This composition is made into a final product through the steps of injection molding, debinding and sintering.

The injection molding can be carried out by using an ordinary injection molding machine used for injection molding of plastics, for example, a heating temperature of 80 to 200 ° C. and an injection pressure of 500 to 20.
Injection molding is performed under the condition of 00 kg / cm ² . The product rate of injection molded products in injection molding work is usually 25-85% by volume.
The remaining 75 to 15% (mainly the sprue part and the runner part) is again subjected to injection molding to be a product in the same ratio, and the rest is recycled again. Such recycling is usually repeated several times. The binder removal treatment is performed by heating the injection-molded body, but when a metal that is easily oxidized is used as the sintering powder, the heating treatment is performed under an inert gas atmosphere or a reducing atmosphere. It is preferable to carry out. The heating temperature is generally set to about 250 to 300 ° C at a heating rate of about 12 to 30 ° C / h. The sintering is generally carried out at a temperature of 1000 to 1500 ° C. for about 1 to 4 hours, although it varies depending on the kind of the sintering powder used.

[0016]

Examples 1 to 6 Paraffin wax, microcrystalline wax, low molecular weight polyethylene wax or modified wax is used as the wax for the binder, and polypropylene (P) is used as the thermoplastic resin for the binder.
P), polyethylene (PE), ethylene-vinyl acetate copolymer (EVA), polystyrene (PS) or ethylene-acrylate copolymer (EAC) is used. As the dispersant, polyisoprene having an iminium ion as a functional group (molecular weight: 7 × 10 ⁴ , Zeophine AX-01 manufactured by Zeon Corporation) is used.

A carbonyl iron powder having an average particle size of about 5 μm was mixed with a binder of the type and amount shown in Table 1 and a dispersant in the amount shown in the same table and kneaded to prepare an injection molding composition. Next, using a pinpoint gate type mold,
Injection molding was performed on each of the above compositions under the conditions of an injection speed of 100 mm / sec, and the pitch circle diameter was 20 mm, the thickness was 5 mm, and the number of teeth was 18
A gear-shaped molded body was manufactured. The injection moldability of each composition at this time was evaluated by the presence or absence of defective filling in the injection mold, the presence or absence of cracks in the molded product, and the presence or absence of damage to the molded product that occurs when the molded product is taken out of the injection mold. . The results are shown in Table 2.

Further, the molded body obtained above was heated in a nitrogen stream to be subjected to a binder removal treatment until the residual amount of the binder was 1% by weight or less of the molded body. The molded body after the treatment was observed, and the debinding property was evaluated by the presence or absence of defects such as deformation. The results are shown in Table 2.

The debindered compact was sintered in vacuum at 1350 ° C. for 2 hours to obtain a sintered product. The sinterability was evaluated by measuring the presence or absence of defects such as cracks and deformation of the obtained sintered product, the diameter dimension (maximum and minimum values) of the sintered product, and the variation width thereof. The results are shown in Table 2.

Comparative Example 1 An injection molding composition was prepared in the same manner as in the above Example except that the dispersant was not used, and injection molding, binder removal treatment and sintering were performed using the composition, and Similar evaluation was performed. The evaluation results are shown in Table 2.

Comparative Example 2 An injection molding composition was prepared in the same manner as in the above Example except that the dispersant was used in a larger amount than the range specified in the present invention, and injection molding was performed using the composition. The binder removal treatment and the sintering were performed, and the same evaluation was performed. The evaluation results are shown in Table 2.

Comparative Examples 3 and 4 Injection molding compositions were prepared in the same manner as in the above Examples except that carnauba wax was used as the dispersant, and the compositions were used for injection molding, debinding treatment and baking. Finally, the same evaluation was performed. The evaluation results are shown in Table 2.

[0023]

[Table 1]

[0024]

[Table 2]

Examples 7 to 12 and Comparative Example 5 The above-mentioned examples except that EPDM having an iminium ion as a functional group (molecular weight: 1 × 10 ⁵ , Zeophine AY-03 manufactured by Nippon Zeon) was used as the dispersant. An injection-molding composition was prepared in the same manner as above, injection-molding, debinding and sintering were performed using the composition, and the same evaluation was performed. The evaluation results were the same as in Table 2. However, Examples 7 to 12 correspond to Examples 1 to 6 in order, and Comparative Example 5 was performed corresponding to Comparative Example 2.

Examples 13 to 18 and Comparative Example 6 As the dispersant, a polyolefin having an iminium ion as a functional group (molecular weight: 450, Zeophine AW-06 manufactured by Nippon Zeon Co., Ltd.) was used. An injection molding composition was prepared in the same manner as in the above example except that the binder and the dispersant in the amounts shown in the same table were mixed and kneaded, and injection molding, debinding treatment and sintering were performed using the composition. The same evaluation was performed. Table 3 shows the evaluation results.
Shown in.

As is clear from the above evaluation results, the injection molding composition of the present invention has good injection moldability, no defects are generated during the binder removal treatment and during sintering, and the obtained sintered product is obtained. It is understood that the dimensional variation of the body is significantly reduced in the range of 1/3 to 1/10 as compared with the sintered body obtained from the composition of the comparative example.

[0028]

According to the present invention, it becomes possible to disperse the sintering powder in the composition for injection molding sufficiently uniformly.
The final sintered product without defects such as cracks can be manufactured with high dimensional accuracy. The composition for injection molding of the present invention,
It is extremely useful for producing sintered products having complicated three-dimensional shapes.

[Table 3]

Claims (5)

[Claims] 1. A powder for sintering comprising a metal or an alloy,
A polymer comprising a wax having a softening point of 50 to 90 ° C. and a thermoplastic resin having a melt flow rate (ASTM D 1236, 230 ° C.) of 100 to 300 g / 10 min, and a polymer having an iminium ion as a functional group. The binder is contained in an amount of 30 to 70% by volume based on the total amount, and the dispersant is 0.1 to 0.1% based on the total amount of the dispersant and the binder.
The composition for injection molding is characterized in that it is contained in an amount of ˜15% by volume. 2. The composition for injection molding according to claim 1, wherein the dispersant is polyisoprene into which iminium ions are introduced. 3. The dispersant is ethylene-propylene-
The composition for injection molding according to claim 1, which is obtained by introducing an iminium ion into a diene terpolymer (EPDM). 4. The composition for injection molding according to claim 1, wherein the dispersant is a polyolefin in which iminium ions are introduced. 5. The composition for injection molding according to claim 1, wherein the waxes and the thermoplastic resin are used in a ratio of 4: 1 to 1: 4 on a volume basis.