JPH0559402A - Composition for injection molding - Google Patents

Abstract

PURPOSE:To enhance the recyclability of the composition and to improve the strength and debindering property of the formed body by specifying the mixing ratio of the powder to be sintered to a binder and the composition of the binder. CONSTITUTION:The volume ratio of the powder to be sintered consisting of at least one kind among metals and alloys to the binder is controlled to 70/30 to 30/70. The binder contains 10-80wt.% low-density PE, 10-80% of an ethylene- vinyl acetate copolymer and 5-35% of the paraffins contg. boron. This composition for injection molding is high in strength of the formed body and excellent in debindering property. The binder is stable to the heating when the binder is mixed with the power to be sintered and to the heating in injection molding, and the recyclability of the composition is improved.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an injection molding composition used in injection molding powder metallurgy.

[0002]

2. Description of the Related Art Injection molding powder metallurgy is a method for producing a sintered product by injection-molding a kneaded product of a metal or alloy powder and a binder, subjecting the resulting molded product to binder removal processing, and then sintering. And is an effective method for producing a product having a three-dimensionally complicated shape. Conventionally, various binders for use in such injection molding compositions have been proposed, and various binders are used in consideration of kneading properties, moldability, strength, binder removal property, recyclability and the like. For example, Japanese Patent Application Laid-Open No. 2-107703 proposes a binder excellent in binder removal property.

[0003]

However, in the conventional composition for injection molding, the paraffin wax mainly in the binder is partially decomposed by heating at the time of kneading with metal powder or the like or heating at the time of injection molding. , Difficult to recycle. In the present specification, recycling means that the defective portion or unnecessary portion of the injection-molded article before the binder removal processing is reused in the kneading processing. For example, excellent recyclability means that a part such as a burr that is removed as a defective part or an unnecessary part from the injection-molded product before the binder removal processing (for example, a runner or sprue part).
Can be used again as a component in the composition for injection molding, and is industrially extremely important from the viewpoint of resource saving.

Therefore, the present invention has excellent recyclability, and even when an injection-molded article is manufactured by reuse, the injection-molded article can be obtained without impairing the properties such as strength and binder removal property. The object is to provide a molding composition.

[0005]

According to the present invention, there is provided an injection molding composition comprising a sintering powder composed of at least one of a metal and an alloy, and a binder, wherein the mixing ratio of the sintering powder and the binder is: , 70/30 to 30/70 based on capacity,
The binder is 10 to 80% by weight of low density polyethylene, 10
~ 80 wt% ethylene-vinyl acetate copolymer and 5 ~ 35
An injection molding composition, characterized in that it is composed of paraffins containing boron by weight. Less than,
The present invention will be described in detail.

Powder for Sintering As the powder for sintering used in the present invention, powders of various metals and alloys such as pure iron, stainless steel, carbonyl iron, and pure cobalt are used. Depending on the product, they may be used alone or in combination of two or more.

Binder The binder contained in the injection molding composition of the present invention comprises low density polyethylene, ethylene vinyl acetate copolymer and boron-containing paraffins. The low-density polyethylene, which is one component of the binder, is a component that contributes to the shape retention of the injection-molded article, and the compounding amount thereof is 10 to 80% by weight, preferably 40 to 60% by weight of the binder. If the low-density polyethylene is less than 10% by weight, the strength and shape retention of the injection-molded product will be reduced, cracks will easily occur on the surface of the molded product, and recyclability will also be reduced. On the other hand, when the low density polyethylene exceeds 80% by weight, the binder removal treatment time becomes long. Such low-density polyethylene has, for example, an average molecular weight of
Those of 20,000 to 40,000 are preferable, and commercially available products can be used.

The ethylene-vinyl acetate copolymer, which is one component of the binder, is a component that contributes to the injection moldability of the composition, and its content is 10 to 80% by weight, preferably 10 to 40% by weight of the binder. Is. When the ethylene-vinyl acetate copolymer is less than 10% by weight, the composition has insufficient injection moldability, the binder removal treatment time becomes long, and the binder removal treatment temperature becomes high. On the other hand, if the ethylene-vinyl acetate copolymer exceeds 80% by weight, the strength and shape retention of the injection molded product will be insufficient, and the molded product will be difficult to handle. As the ethylene-vinyl acetate copolymer, for example, one having a vinyl acetate content of 10 to 30% by weight is used, and a commercially available product can be used.

The boron-containing paraffins, which are one component of the binder, have the function of improving the miscibility between the sintering powder and the binder, and thus the sintering powder is uniformly dispersed. Further, in the binder removal treatment, for example, it has a function of suppressing the generation of defects such as cracking or swelling and stabilizing the treatment, so that the density and dimensional accuracy of the finally obtained sintered product are improved. Furthermore, the strength and shape retention of the injection-molded product can be improved and the action of the ethylene-vinyl acetate copolymer lost by heating can be supplemented. Most importantly, since boron-containing paraffins are stable even when heated up to 200 ° C, the use of these boron-containing paraffins improves the recyclability of the obtained injection molding composition. That's what it means.

The boron-containing paraffins are, for example,
Boric acid ester at 100 to 200 ° C, preferably 120 to 160
Obtained by heating at ℃ for 1 to 24 hours, preferably 5 to 18 hours. When the heating temperature is less than 100 ° C and / or the heating time is less than 1 hour, it becomes difficult to form the boron-containing paraffins, while the heating temperature exceeds 200 ° C and / or
Alternatively, if the heating time exceeds 24 hours, the once-formed boron-containing paraffins may deteriorate.

Examples of the above boric acid ester include:
Mention may be made of triglycol diborates, trialkyl borates, glycerol borates and alkyne diborates. More specifically, examples of triglycol diborates include 1,6-bis (5-ethyl-4-
Propyl-1,3,2-dioxabora-2-cyclohexyloxy) hexane and 1,4-bis (5-ethyl-4-propyl-1,3,2-dioxabora-2-cyclohexyloxy) butane, trialkylborate Examples thereof include trimethyl borate, triethyl borate, tributyl borate and triamyl borate and the like, glycerol borates such as glycerol borate stearate and polyoxyethylene glycerol borate palmitate and the like, and alkyne diborates such as , Methyl diborate, ethyl diborate and the like.

These borate esters may be used alone or in combination.
It can also be used as a combination of two or more species. When mixed with other components, for example, it is preferable to use it by dissolving it in a solvent such as benzene, toluene and xylene so that the concentration becomes about 60 to 80% by weight, whereby the metal powder and the organic binder are dissolved. Mixability is further improved. Therefore, in this case, the binder also contains a certain amount of solvent as a component.

In the present invention, the content of the above-mentioned boron-containing paraffins is 5 to 35% by weight of the binder, preferably 15 to 30% by weight. If the blending amount is less than 5% by weight, the recyclability is not improved, and the miscibility between the sintering powder and the binder is reduced, so that the sintering powder is not uniformly dispersed in the composition and the binder removal treatment is performed. Porous defects are likely to occur in the subsequent injection molded body. If the blending amount exceeds 35% by weight, the strength of the injection molded article becomes insufficient.

Injection-Molding Composition The injection-molding composition of the present invention comprises the above-mentioned sintering powder and binder on a volume basis of 70/30 to 30/70, preferably 60.
It is obtained by uniformly kneading at a ratio of / 40 to 40/60. If the amount of sintering powder used is less than the above range,
The fluidity of the composition decreases, making injection molding work difficult,
In addition, the packing density of the sintering powder in injection molding is reduced, making it difficult to improve the density of the final sintered part.
On the other hand, when the amount of the sintering powder used is more than the above range, the strength of the injection-molded product is lowered, or the surface of the injection-molded product is apt to have a defect referred to as chamfering, which significantly increases the injection moldability of the composition. Lower to.

The composition for injection molding obtained as described above is
After each process such as injection molding, binder removal processing and sintering,
It will be the final product. The injection molding can be carried out, for example, by using the equipment and device used for ordinary plastic injection molding, and for example, molding is performed under the conditions of a heating temperature of 80 to 200 ° C. and an injection pressure of 50 to 200 MPa. The binder removal is performed by heating the injection-molded body at a temperature of 200 to 600 ° C. Further, the sintering is generally performed at a temperature of 1200 to 1700 ° C. for about 1 to 4 hours, though it varies depending on the kind of the sintering powder to be used.

Utility The composition for injection molding of the present invention has the following properties :
In addition to being excellent in binder removal property and the like, it is excellent in recyclability because the binder is stable against heating during kneading with sintering powder and the like and heating during injection molding. That is, a portion such as a burr that is removed as a defective portion or an unnecessary portion from the injection molded body before the binder removal treatment (for example, a runner or sprue portion) can be used again as a component in the composition for injection molding. It is possible and extremely industrially useful from the viewpoint of resource saving.

[0017]

Examples 1 to 8 Trimethyl borate was used as boric acid ester, and heat treatment was carried out at various heating temperatures and heating times shown in Examples 1 to 8 in Table 1. In addition, when a change due to heating of trimethylborate in each example was examined using a hydrogen flame ionization detector of gas chromatography, the heat-treated products of Examples 1 to 8 all had 18 to 40 carbon atoms. A paraffin peak was confirmed.

The trimethylborate heat-treated product thus obtained was mixed with a low-density polyethylene (average molecular weight: 25,000) and an ethylene-vinyl acetate copolymer (vinyl acetate content: 10% by weight) in a ratio shown in Table 1 with a binder. Average particle size 5
10 kg of carbonyl iron powder of μm was blended in the blending amount (volume%) shown in Table 1, kneaded at 150 ° C., and then granulated into pellets.

Using this pellet, a cylinder temperature of 100
℃, nozzle temperature 120 ℃, injection pressure 180MPa, outer diameter 5m
It was injection molded into a mold of a test piece of m and 25 mm in length. Next, the operation of crushing the obtained injection-molded article, granulating it, and performing injection molding again under the above conditions was repeated. The number of repetitions is shown in the number of recycles in Table 1.

In addition, after recycling the examples 1 to 4 five times, the obtained injection-molded bodies were pulverized again, and the heat-treated trimethylborate products shown in Table 1 were added.
After kneading and granulating at 150 ° C, injection molding was performed. The injection moldability at that time is shown in Table 1. For Examples 5-8,
After recycling 5 times, after crushing the obtained injection-molded body, 100 g of the trimethylborate heat-treated product in the amount shown in Table 1 was added and kneaded and granulated at 150 ° C. The obtained injection-molded body was crushed, and the remaining heat-treated product was added, kneaded and granulated, and injection-molded. The injection moldability at that time is shown in Table 1.

[0021]

[Table 1]

A change in the binder after the recycling was completed in each example was examined by gas chromatography. The above-mentioned paraffin peak did not change, and the binder was stable. In addition, the generation of substances that inhibit recycling was not observed.

Comparative Examples 1 to 8 For injection molding in the same manner as in Examples, using the heat-treated trimethylborate heat-treated under the conditions shown in Table 2 and using the binder prepared in the proportions shown in Table 2. Compositions were prepared and injection molded recycling tests were performed and Examples 1-4 are performed.
An injection moldability test was conducted in the same manner as in. The results are shown in Table 2.

[0024]

[Table 2]

As in the examples, changes in trimethylborate in each comparative example due to heating were investigated by gas chromatography. As a result, no paraffin peak was observed in Comparative Example 1. In addition, Comparative Examples 2, 3, 4
It was confirmed from the change in the paraffin peak before and after heating that lower hydrocarbons were produced, and recycling and injection molding were impossible. In Comparative Examples 5, 6, 7 and 8, the paraffin peak was observed as in the case of the Examples. However, in Comparative Examples 5 to 8, although stable paraffin was obtained, the injection moldability was deteriorated because the compounding amount was small or large.

[0026]

INDUSTRIAL APPLICABILITY The composition for injection molding of the present invention is excellent in strength and binder removal property of the obtained molded product, and is not affected by heat such as heating during kneading or heating during injection molding. Excellent recyclability.

Claims (3)

[Claims] 1. An injection molding composition comprising a sintering powder composed of at least one of a metal and an alloy and a binder, wherein the mixing ratio of the sintering powder and the binder is 70 / volume basis.
30 to 30/70, and the binder is 10 to 80% by weight of low density polyethylene, 10
~ 80 wt% ethylene-vinyl acetate copolymer and 5 ~ 35
An injection molding composition, characterized in that it comprises paraffins containing boron by weight. 2. The composition for injection molding according to claim 1, wherein the boron-containing paraffins are 100 to 200 boric acid esters.
An injection molding composition, which is obtained by heating at 1 ° C. for 1 to 24 hours. 3. The composition for injection molding according to claim 2, wherein the boric acid ester is at least one selected from triglycol diborates, trialkyl borates, glycerol borates and alkyne diborates. An injection molding composition comprising: