JPH0517803A - Composition for injection molding - Google Patents

Abstract

PURPOSE:To produce the compsn. for injection molding which is extremely improved in a recycling property and is extremely industrially useful since the unnecessary parts, such as burrs, of, for example, resulted injection moldings, can be reutilized by recycling. CONSTITUTION:This compsn. for injection molding contains powder for sintering consisting of at least one kind of metals and alloys and a binder at 70/30 to 30/70 ratio by volume. This binder consists of 10 to 80wt.% atactic polypropylene, 10 to 80wt.% dioctyl phthalate and 5 to 35wt.% boron-contg. paraffin. This boron-contg. paraffin is obtd. by subjecting borate to a heating treatment for 1 to 24 hours at 100 to 200 deg.C temp.

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 The injection molding powder metallurgy method produces a sintered product by injection-molding a kneaded product of a metal or alloy powder and a binder, subjecting the obtained molded product to debinding processing, and then sintering. In particular, it is an effective method for producing a product having a three-dimensionally complicated shape. The binder used in such an injection molding composition is
It is used in consideration of kneading property, moldability, debinding property, recyclability, strength of the obtained molded product, and the like, for example, in JP-A-2-107703, 10-80% by weight of low density polyethylene, 10- 80% by weight of paraffin wax and 5-35
An injection molding composition using a binder consisting of borate ester by weight% is disclosed.

[0003]

However, the above-mentioned prior art injection molding compositions and the like still have a drawback in that the recyclability is still unsatisfactory. That is, it is considered that mainly the paraffin wax in the binder is partially decomposed by heating during kneading with the metal powder or the like and heating during injection molding, which makes recycling difficult. In the present specification, recycling means reuse of the injection-molded product before the binder removal process during the kneading process. For example, excellent recyclability means that parts such as burrs (such as runners and sprues) that are removed as defective parts or unnecessary parts from the injection-molded product before the debinding process are again subjected to the injection molding composition. It is meant to be used as a component in a product, and is extremely important industrially from the viewpoint of resource saving. Therefore, the object of the present invention is excellent in recyclability, and even when an injection-molded article is manufactured by reuse, the injection-molded article does not lose its properties such as strength and debinding property of the obtained molded article. The present invention provides a composition for use.

[0004]

The present invention is characterized in that it is important to use a boron-containing paraffin obtained by subjecting a boric acid ester to a certain heat treatment in combination with a certain binder component. By using paraffin, the above-mentioned object was successfully achieved.

According to the present invention, there is provided an injection molding composition containing a sintering powder composed of at least one of metals and alloys and a binder in a ratio of 70/30 to 30/70 on a volume basis. An injection molding composition is provided, wherein the binder comprises 10 to 80% by weight of atactic polypropylene, 10 to 80% by weight of dioctyl phthalate and 5 to 35% by weight of boron-containing paraffin. .

[0006]

[Function] Sintering powder In the present invention, as the sintering powder, for example, pure iron,
Powders of various metals or alloys such as stainless steel, carbonyl iron, pure cobalt and the like are used, and these are used alone or in combination of two or more depending on the intended sintered product.

Binder The binder used in the injection molding composition of the present invention comprises atactic polypropylene, dioctyl phthalate and boron-containing paraffin.

Atactic polypropylene is a component that contributes to maintaining the shape of an injection-molded article, and
It is compounded in a proportion of 10 to 80% by weight, particularly 40 to 60% by weight.
If the blending amount is less than 10% by weight, the shape retention and strength of the injection-molded product may be deteriorated, and cracks may occur on the surface of the injection-molded product. Further, the recyclability which is the object of the present invention is also unsatisfactory. On the other hand, if it is blended in excess of 80% by weight, the time required for the debinding process performed on the injection-molded product before sintering becomes unnecessarily long, resulting in extremely low productivity. As such atactic polypropylene, for example, one having an average molecular weight of about 15,000 to 40,000 is preferably used, and such an atactic polypropylene is generally commercially available.

Dioctyl phthalate is a component added to improve the injection moldability, and is contained in the binder.
It is mixed in a proportion of 10 to 80% by weight, particularly 10 to 40% by weight.
If the blending amount is less than 10% by weight, it becomes difficult to effectively perform the injection molding of the composition, and the debinding process time becomes long and the processing temperature becomes high. Further, if it is blended in excess of 80% by weight, the shape retention and strength of the obtained injection molded product will be deteriorated, making it difficult to handle the molded product thereafter, for example, debinding or sintering cannot be performed. Becomes

The boron-containing paraffin has the function of improving the miscibility of the sintering powder and the binder, whereby the sintering powder is uniformly dispersed in the composition. In addition, it is possible to prevent the occurrence of defects such as blisters and cracks in the binder removal treatment, and to stabilize the treatment. Therefore, the use of boron-containing paraffins improves the density and dimensional accuracy of the final sintered product.

And, most importantly, as already mentioned,
By using the boron-containing paraffin, the recyclability of the obtained injection molding composition is remarkably improved. The boron-containing paraffin may be, for example, boric acid ester at a temperature of 100 to 200 ° C, particularly 120 to 160 ° C, in an amount of 1-2
It can be obtained by heat treatment for 4 hours, especially 5 to 18 hours. For example, if the heat treatment temperature of the borate ester is less than 100 ° C. or the heat treatment time is less than 1 hour, the boron-containing paraffin is not effectively produced, and it becomes difficult to improve the recyclability. Further, if the heat treatment temperature of the borate ester exceeds 200 ° C. or the heat treatment time exceeds 24 hours, the once-formed boron-containing paraffin is altered or decomposed, which makes it difficult to improve the recyclability.

The boric acid ester to be heat-treated is, for example, 1,6-bis (5-ethyl-4-propyl-1,
3,2-Dioxabora-2-cyclohexyloxy) hexane, 1,4-bis (5-ethyl-4-propyl-1, 3,2-
Triglycol diborate such as dioxabora-2-cyclohexyloxy) butane; Trialkyl borate such as trimethyl borate, triethyl borate, tributyl borate, triamyl borate; glycerol borate stearate, glycerol borate such as polyoxyethylene glycerol borate palmitate Examples thereof include alkyne diborate such as methyl diborate and ethyl diborate, and these borate esters can be used alone or in combination of two or more in the heat treatment. The boron-containing paraffin most preferably used in the present invention is a heat-treated product of triglycol diborates.

In the present invention, the above-mentioned boron-containing paraffin is compounded in the binder in an amount of 5 to 35% by weight, particularly 10 to 30% by weight. If the blending amount is less than 5% by weight, not only the recyclability which is the object of the present invention is not improved, but also the sintering powder is not uniformly dispersed in the composition,
Porous defects are likely to occur in the injection-molded article after debinding. If the amount is more than 35% by weight, the strength of the obtained injection-molded article becomes unsatisfactory. The boron-containing paraffin obtained by heat-treating these boric acid esters can be used alone or in combination of two or more, and when mixed with other components, for example, benzene, toluene, xylene, etc. Dissolve in 60 to 80
It is desirable to mix them as a solution of about wt%, which further improves the mixing properties of the metal powder and binder. Therefore, in this case, the binder composition also contains a certain amount of solvent as a component.

As long as the binder used in the present invention does not impair the object of the present invention to improve recyclability, in addition to the above-mentioned components, low density polyethylene, polyolefin wax, paraffin wax. It is possible to use binder components known per se, such as

Injection Molding Composition The injection molding composition of the present invention comprises the above-mentioned sintering powder and binder in a volumetric standard of 70/30 to 30/70, preferably
It is prepared by uniformly kneading in a ratio of 60/40 to 40/60. When the amount of the sintering powder used is less than the above range, the fluidity of the composition increases and injection molding becomes difficult,
Further, the packing density of the sintering powder in the obtained molded body becomes low, and it becomes difficult to improve the density of the final sintered product. Further, if it is used in a larger amount than the above range, the strength of the injection-molded product is lowered, or a defect called "chamfering" tends to occur on the surface of the molded product. The thus obtained composition for injection molding of the present invention is made into a final product through the steps of injection molding, binder removal and sintering. The injection molding can be performed using, for example, an injection molding machine used for injection molding of ordinary plastics, for example, a heating temperature of 80 to 20.
It is carried out under the conditions of 0 ° C. and 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. In addition, the sintering varies depending on the type of the sintering powder to be used, but generally 1000 ~
It is carried out at a temperature of 1400 ° C for about 1 to 10 hours.

[0016]

Examples 1 to 8 Trimethyl borate was used as the borate ester, and the boron-containing paraffin obtained by variously changing the heat treatment conditions as shown in Table 1 was used as the binder component. still,
Using a flame ion detector of gas chromatography, the heating change of trimethylborate was examined. For all heat-treated trimethylborate heat-treated products used in Examples 1 to 8, paraffins having 18 to 40 carbon atoms were detected. A peak was confirmed. A binder in which the above various boron-containing paraffins are used in combination with other binder components in the proportions shown in Table 1,
It was sufficiently kneaded with carbonyl iron powder having an average particle size of 5 μm at 150 ° C., and then granulated into pellets. The pellets were injection-molded into a test piece mold having an outer diameter of 5 mm and a length of 25 mm under the conditions of a cylinder temperature of 100 ° C., a nozzle temperature of 120 ° C., and an injection pressure of 180 MPa. The obtained injection-molded body was crushed, then granulated, injection-molded again under the above conditions, and this operation was repeated. Table 1 shows the number of recycles and the injection moldability at that time.

[0017]

[Table 1]

The composition of each Example was examined for the change of the binder component by gas chromatography after the recycling shown in Table 1, and the above-mentioned paraffin peak did not change and the binder was stable. Was there. In addition, the generation of substances that inhibit recycling was not observed.

Comparative Examples 1 to 8 Injection molding compositions were prepared in the same manner as in Examples except that the heat-treated trimethylborate heat-treated under the conditions shown in Table 2 was used, and a recycling test was conducted. . The results are shown in Table 2.

[0020]

[Table 2]

As for the heat-treated trimethylborate used in each comparative example, its heating change was examined by gas chromatography as in the examples. As a result, no paraffin peak was observed in Comparative Example 1. Further, in Comparative Examples 2, 3, and 4, the paraffin peak was changed before and after injection molding, and generation of lower hydrocarbons was observed, and it was impossible to recycle as well as the first injection molding. . In the heat-treated trimethylborate products used in Comparative Examples 5, 6, 7 and 8, stable paraffin was found even in injection molding, but the injection amount was difficult because the blending amount was too large or too small. Molded bodies with certain or sufficient strength were not obtained.

[0022]

INDUSTRIAL APPLICABILITY The composition for injection molding of the present invention has remarkably improved recyclability. For example, defective parts of the obtained injection-molded product and unnecessary parts such as burrs can be reused by recycling. Extremely useful.

Claims (2)

[Claims] 1. A powder for sintering comprising at least one of metals and alloys and a binder are contained in a volume ratio of 70/30 to 30 /.
In a composition for injection molding containing 70 parts by weight, the binder consists of 10-80% by weight atactic polypropylene, 10-80% by weight dioctyl phthalate and 5-35% by weight boron-containing paraffin. An injection molding composition comprising: 2. The boron-containing paraffin is at least one boric acid ester selected from triglycol diborate, trialkyl borate, glycerol borate and alkyne diborate at a temperature of 100 to 200 ° C.
The composition for injection molding according to claim 1, which is obtained by heating for 24 hours.