JP2001138366A - Gate structure of mold for injection molding of thermoplastic elastomer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the gate structure improved in gate cutting and shortening the cooling time of a sprue runner part to enhance productivity. SOLUTION: A taper 5 is formed at the gate land 4 connected to a gate 3 and an undercut 6 is formed at the terminal part 8 of the taper or formed so as to provide a predetermined interval from the terminal 8. The cross-sectional area of the sprue runner 7 connected to the undercut 6 is formed so as to be made small in diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gate structure of a mold for injection molding of a thermoplastic elastomer (elastic body) capable of automatic gate cutting, and particularly to a molded product having a good gate cut and cooling a sprue runner portion. The present invention relates to a gate structure in a mold for injection molding of a thermoplastic elastomer in which time can be reduced to improve productivity.

[0002]

2. Description of the Related Art Pinpoint gates and submarine gates are generally known as gate structures in which a gate is automatically cut in a mold. Of these, the pinpoint gate is designed so that the gate is automatically cut when the mold is opened by making the cross-sectional area of the gate extremely small.The submarine gate has a cross-sectional area that is inconspicuous on the molded product. The gate is made smaller.

FIGS. 4 and 5 show an example of a conventional mold structure capable of automatically cutting a gate. FIG.
In the conventional example shown in FIG. 1, a mold element 21 is provided with a gate 22 having a reduced cross-sectional area. A large taper is not formed in a gate land 23, and no undercut is provided.

In the conventional example shown in FIG. 5, a mold element 21 is provided with a gate 22 having a reduced cross-sectional area and a gate land 23 is formed with a large taper. Nothing is provided.

[0005]

When a thermoplastic elastomer is injection-molded with the above-mentioned conventional gate structure, FIG.
In the case of the conventional example shown in (1), since the gate land 23 is not provided with a large taper and the undercut portion is not formed, the gate portion of the molded product which has been automatically gate-cut has poor gate breakage. There is a problem that finishing is indispensable. Further, the molded product may be depressed as if the periphery of the gate is peeled off, or may be deformed such that the periphery of the gate is swollen. In such a case, the molded product is discarded.

In the case of the conventional example shown in FIG. 5, although a relatively large taper is formed in the gate land 23, no undercut portion is provided, so that the cross-sectional area of the gate land 23 is large. As a result, the sprue runner is connected to the sprue runner, and the time required for cooling for each shot must be long, resulting in a problem that productivity is extremely poor.

Accordingly, the present invention solves the above-mentioned problems associated with the conventional thermoplastic elastomer injection mold,
An object of the present invention is to provide a gate structure in a thermoplastic elastomer injection molding die that has a good gate cut, does not require post-treatment, and can shorten the cooling time and improve productivity. It is.

[0008]

The structure of the present invention for achieving the above object will be described in detail. In the structure around the gate portion of the mold when the molten thermoplastic elastomer molding material is injected into the cavity, A taper is formed in a gate land portion connected to the gate portion so that the gate portion side has a small diameter and the gate land portion side has a large diameter, and an end of the large diameter taper or a predetermined distance from the end. An undercut portion is formed, and a sprue runner connected to the undercut portion is formed to have a small cross-sectional area. This is a gate structure in a thermoplastic elastomer injection mold.

According to the present invention, as described above, a relatively large taper is formed in the gate land portion and an undercut portion is formed in the back of the gate land portion. No force is directly applied to the part,
Since the power is transmitted to the gate portion via the resistance of the undercut portion, the breakage of the gate becomes extremely good, and a molded product that does not require post-processing can be obtained. In addition, since the sprue runner connected to the gate land can be made thinner than before, the time required for cooling can be reduced by that amount, and the productivity is improved.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a specific structure of a gate structure in a mold for injection molding of a thermoplastic elastomer according to the present invention will be described in detail based on the illustrated embodiment. FIG. 1 is a sectional view showing an embodiment of a gate structure according to the present invention, and FIG.
FIG. 3 is a sectional view showing another embodiment of the gate structure according to the present invention, and FIGS. 3A, 3B and 3C are explanatory views showing details of the gate structure according to the present invention. The molding material targeted by the present invention is not only a styrene-based elastomer but also a polymer material having remarkable elasticity such as an olefin-based elastomer, a polyester-based elastomer, a urethane-based elastomer, and a polyamide-based elastomer.

FIG. 1 shows an example of a mold for injection molding of a thermoplastic elastomer having a submarine gate. In the figure, reference numerals 1a, 1b, and 1c denote mold elements. By assembling the three divided mold elements 1a, 1b, 1c, a cavity 2 is formed inside. Reference numeral 3 denotes a gate portion formed on the mold element 1b, and reference numeral 4 denotes a gate land portion connected to the gate portion 3.

In this embodiment, as shown in FIG. 3A, the gate land portion 4 connected to the gate portion 3 has a small diameter on the side of the gate portion 3 and a large diameter on the side of the gate land portion 4 on the rear side of the gate portion 3. A relatively large taper 5 is formed to have a large diameter, and the large diameter taper 5 is formed.
The undercut portion 6 is formed at the terminal end portion 8 of the first embodiment, and the cross-sectional area of the sprue runner 7 connected to the undercut portion 6 is formed to have a small diameter. In this case, the relationship between the cross-sectional area of the sprue runner 7 and the cross-sectional area of the gate 3 is as follows: sprue runner ≧ gate.

FIG. 2 shows an example of a thermoplastic elastomer injection mold having a pinpoint gate. In the figure, reference numerals 1a and 1b denote mold elements. Reference numeral 2 denotes a cavity formed by assembling the two mold elements 1a and 1b. A gate portion 3 for injecting the molten thermoplastic elastomer into the cavity 2 is formed in the mold element 1a. ing. Reference numeral 4 denotes a gate land portion connected to the gate portion 3 as described above.

In this embodiment, similarly to the above, as shown in FIG. 3A, the gate land portion 4 connected to the gate portion 3 has a small diameter on the gate portion 3 side and a gate land portion 4 on the rear side of the gate portion 3. A relatively large taper 5 is formed so that the side has a large diameter, an undercut portion 6 is formed at a terminal end 8 of the large diameter taper 5, and a sprue runner 7 connected to the undercut portion 6 is formed. Is formed to have a small cross-sectional area. In this case, it goes without saying that the relationship between the cross-sectional area of the sprue runner 7 and the cross-sectional area of the gate portion 3 satisfies sprue runner ≧ gate portion as described above.

Each of the undercut portions 6 shown in FIGS. 1 to 3A is formed so as to be continuous with the large-diameter end portion 8 of the taper 5 formed in the gate land portion 4. However, in addition to the embodiment, as shown in FIG. 3B, a second gate land portion having a common cross-sectional area with the large-diameter portion is provided at the terminal portion 8 on the large-diameter side of the taper 5. 9
May be formed, and the undercut portion 6 may be formed at the rear end of the second gate land portion 9.

Further, the shape of the undercut portion 6 is not limited to the embodiment shown in FIGS. 3 (A) and 3 (B).
As shown in FIG. 3 (C), a slope portion is formed so that the taper 10 opposite to the taper 5 described above, that is, the cross-sectional area on the sprue runner 7 side has a small diameter, and the undercut portion 6 is formed. You may make it.

In any of the above embodiments, when the thermoplastic elastomer is injection-molded, the load is not directly applied to the gate portion 3 when the mold is opened, and the resistance of the undercut portion 6 of the gate lands 4 and 9 is reduced. Since it is transmitted to the gate portion through the gate, the cut of the gate becomes extremely good, and the phenomenon of the gate portion remaining in a conical shape and the sinking of the periphery of the gate portion as in the prior art was not observed at all. In addition, post-processing of the molded article is completely unnecessary.

In addition, since the undercut portion 6 is formed, the cross-sectional area of the sprue runner 7 connected to the undercut portion 6 can be reduced, whereby the cooling time for each shot can be reduced and the productivity can be reduced. Improved.

On the other hand, when the thermoplastic elastomer is injection-molded in the mold having the conventional structure shown in FIG. 4, since the undercut portion is not provided, a load is directly applied to the gate portion 22 when the mold is opened. As a result, a defective gate was found in the molded product that had been subjected to automatic gate cutting.

Further, the thermoplastic elastomer was injection-molded by using a mold having a conventional structure shown in FIG. 5, but in this case, although the gate land portion is provided with a taper, the undercut portion is not provided. As a result, a remarkable gate residue occurred in the molded product, and post-treatment was required. Further, in the case of this conventional example, since the cross-sectional area of the sprue runner remains large, the time required for cooling becomes longer, the molding cycle becomes longer, and the productivity decreases.

[0021]

As described above, according to the present invention, a taper is formed in a gate land portion, and an undercut portion is formed at an end portion of the taper or at a predetermined distance from the end portion. Since the cross-sectional area of the sprue runner connected to the part was formed to have a small diameter, when the thermoplastic elastomer molding material was injection-molded, the gate breakage became extremely good, and a molded product that did not require finish processing could be obtained. . Further, since the cooling time for each shot can be shortened, the productivity has been remarkably improved as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a gate structure in a mold for injection molding of a thermoplastic elastomer according to the present invention.

FIG. 2 is a sectional view showing another embodiment of the gate structure according to the present invention.

FIG. 3 is an explanatory diagram showing details of a gate structure according to the present invention.

FIG. 4 is a cross-sectional view showing an example of a conventional mold for injection molding of a thermoplastic elastomer which can be automatically gate-cut.

FIG. 5 is a cross-sectional view showing another example of a conventional thermoplastic elastomer injection mold that can be automatically gate-cut.

[Explanation of symbols]

 1a: mold element 1b: mold element 1c: mold element 2: cavity 3: gate section 4: gate land section 5: taper 6: undercut section 7: sprue runner 8: terminal section 9: second gate land Part 10: Taper

Claims (1)

[Claims] In a structure around a gate portion of a mold when a molten thermoplastic elastomer molding material is injected into a cavity, a gate land portion connected to the gate portion has a small diameter on the gate portion side and a large diameter on the gate land portion side. While forming a taper so that it becomes a shape, an end portion of the large diameter taper or an undercut portion is formed at a predetermined interval from the end portion, and a cross-sectional area of a sprue runner connected to the undercut portion is formed. A gate structure in a mold for injection molding of a thermoplastic elastomer, which is formed in a small diameter.