JPH10217272A - Gas injection pin for gas injection molding and mold using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a smooth gas injection into a molten resin and reduce the depressurizing operation time of the gas by having a construction comprising an inner pin and an outer tube, and disposing the tip end of the inner pin inwardly of the tip end of the outer tube. SOLUTION: A gas injection pin is constructed in such a manner that the tip end of an inner pin 1 is disposed inwardly of the tip end of an outer tube 2. In addition, the tip end of the outer tube of the gas injection pin installed in a cavity mold is caused to project from an inner wall surface 5 of the cavity mold into a molten resin 4. First, a molten resin is filled in a space (tip end space) formed of the outer tube 2 and the inner pin 1, and in that state, when gas is injected from a gap between the outer tube 2 and the inner pin 1, the whole of molten resin inside the tip end space is pushed outwardly. This makes an injection hole 3 substantially as large as the external configuration of the inner pin. Thus, a larger hole is formed so as not only to enable a smooth injection of gas but also to remarkably reduce the depressurizing operation time of gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding method for injecting a molten resin into a mold and injecting a high-pressure gas before the molten resin solidifies to obtain a hollow molded article, that is, a gas used in a gas injection molding method. The present invention relates to an injection pin and a molding die using the same.

[0002]

2. Description of the Related Art Conventionally, in gas injection molding, a method is known in which a gas injection needle is incorporated into a mold and a gas is injected into a molten resin from a cavity or a runner to obtain a hollow molded product. . As shown in FIG. 2, the gas injection needle includes an inner pin 1 and an outer cylinder 2, and has a structure in which the tip of the inner pin projects outward from the tip of the outer cylinder. General. Using such a gas injection pin,
When gas is injected into the molten resin, the gas injection hole 3 formed in the resin has various shapes and is not stable. A long time. For this reason, development of a technique capable of further reducing the molding cycle time has been desired.

[0003]

SUMMARY OF THE INVENTION According to the present invention, in a gas injection molding method, a gas injection hole in a cavity or a runner formed by a gas injection pin is formed larger and more stably so that gas injection can be performed smoothly. It is another object of the present invention to provide a gas injection pin which shortens the depressurizing operation time and a molding die using the same.

[0004]

Means for Solving the Problems The present inventors have a conventional gas injection pin, that is, a structure in which the tip of the inner pin projects outside the tip of the outer cylinder, and the gap between the inner pin and the tip of the outer cylinder. The phenomenon in the case of injecting a gas using a gas (gas inlet) formed in an annular shape was examined in detail. As a result, in this case, as shown in FIG.
There is a tendency for injection to penetrate the weakest point (one place) near the injection port, so that the injection hole formed in the resin becomes smaller than the annular gap of the gas injection port, and the pressure of the gas is reduced. It has been found that the operation time is lengthened.

As a result of intensive studies based on this finding, the present inventors have completed the present invention having the following contents. (1) A gas injection molding gas injection pin comprising an inner pin and an outer cylinder, wherein the tip of the inner pin is inside the tip of the outer cylinder. (2) The gas injection pin for gas injection molding according to (1), wherein the tip of the inner pin is a flat surface or a curved surface. (3) The above (1), wherein the tip of the inner pin is a cone or a pyramid.
4. The gas injection pin for gas injection molding according to 1. (4) A gas injection molding die incorporating the gas injection molding gas injection pin according to any one of the above (1) to (3) such that its tip protrudes from the inner wall surface of the die.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. FIG. 1 showing an embodiment of the present invention is a gas pin comprising an inner pin 1 and an outer cylinder 2, wherein the tip of the inner pin 1 is
5 shows a gas injection pin located inside the tip of the outer cylinder 2. or,
FIG. 1 shows a usage mode of the gas injection pin in which the tip of the outer cylinder of the gas injection pin incorporated in the cavity mold projects from the inner wall surface 5 of the cavity mold (projects into the molten resin 4). It is also a thing.

The conventional gas injection pin is shown in FIG.
As shown in the figure, the tip of the inner pin 1 was outside the tip of the outer cylinder 2, whereas the gas injection pin of the present invention was inside. Since the tip of the inner pin 1 is located inside the outer cylinder 2, a space formed by the outer cylinder 2 and the tip of the inner pin 1 (hereinafter referred to as “tip space”) is first filled with a molten resin. In this state, when gas is injected from the gap (gas injection port) between the distal end of the outer cylinder 2 and the inner pin 1, the entire molten resin in the distal end space is pushed outward by the gas.
Therefore, the tendency for gas to break through and be injected from one location is extremely reduced, and the injection hole 3 formed in the resin has a size substantially equal to the outer diameter of the inner pin 1 as shown in FIG.

[0008] The gas injection pin of the present invention thus forms a larger hole than the hole formed by the conventional type of gas injection pin, not only making the gas injection smoother but also the gas injection. This has the effect of significantly reducing the depressurizing operation time. Further, an embodiment example of the gas injection pin of the present invention is shown in the drawings. FIG. 3 is a perspective view of the inner pin, and FIG. 4 is a cross-sectional view of the gas injection pin in which the inner pin 1 and the outer cylinder 2 are assembled (the inner pin corresponds to a section taken along line XX in FIG. 3). This figure shows a structure in which a gap corresponding to a gas flow path is constituted by two grooves 6 cut in parallel to the axis, and the depth of the groove 7 is reduced near the gas flow path outlet. In this example, the gap corresponding to the gas flow path is cut parallel to the axis,
Although the two grooves are formed, the groove may be formed of two or more grooves. Also, a thread groove along the circumference of the axis may be used.
From the balance of cutting workability, securing a large capacity flow path, and maintaining the small diameter of the gas injection pin, an inner pin having two grooves cut parallel to the axis as shown in FIGS. Can be particularly preferably used.

The depth of the groove is made shallower near the outlet than at the upstream thereof, and the depth of the groove 7 near the outlet is set to 0.00.
5 to 0.15 mm, more preferably 0.01 to 0.1 m
The gas injection pin of m is effective for smoothly injecting the gas and preventing the backflow of the molten resin.
The shape of the tip of the inner pin may be a flat or curved surface as shown in FIGS. 3 and 4, or a pointed tip as shown in FIG. 5, that is, a cone or pyramid. Can be.

When gas injection molding is performed using the gas injection pin of the present invention, as shown in FIG.
The hollow structure formed in the molten resin is such that the injection hole 3 has a size substantially equal to the outer diameter of the inner pin 1, so that the gas can be smoothly injected and the depressurization operation time of the gas is extremely long. Can be done in a short time.

[0011]

EXAMPLES Further, the function and operation of the gas injection pin of the present invention will be described in more detail with reference to examples. Example Gas injection molding of polypropylene was performed using the gas injection pin of the present invention and the test die for gas injection molding shown in FIG. 6 under the molding conditions shown below.

Molding conditions: (1) Injection molding machine: manufactured by Toshiba Machine Co., Ltd. (clamping force: 200 tons) (2) Molding material: IDEMITSU PP (polypropylene) J-700G (MI = 8) (3) Molding temperature : 240 ° C (4) Mold temperature: 50 ° C (5) Injection time: 2.6 seconds (6) Gas delay time (time from injection filling of resin to start of gas injection): 2.0 seconds (7 ) Gas injection time: 2.0 seconds (8) Gas pressure holding time: 15 seconds (9) Gas depressurization time: 5 seconds (10) Gas set pressure: 10 MPa (11) Die plate (420 mm × 100 mm × 3 mm) ) Side gate / cold runner with gas channel (Fig. 6) (12) Gas injection pin As shown in Fig. 4, total length 20mm, pin protrusion length (outside die) 5mm, outer cylinder diameter 5mm, inner pin tip 3m diameter
m, the tip of the inner pin is 5 mm inside the tip of the outer cylinder, the depth of the groove 6 is 0.5 mm, and the depth of the groove 7 is 0.1 mm.

Molding result: The gas injection hole is 5 mm in diameter.
The blister seen when the depressurization is not completed (the external pressure of the molded product becomes the atmospheric pressure when the mold is opened, and when the depressurization of the hollow part of the molded product is not completed, the molded product expands due to the residual gas pressure. ) Was not observed.

Comparative Example Instead of the gas injection pin used in the embodiment, a gas injection pin (conventional pin) in which the tip of the inner pin 1 projects outside the tip of the outer cylinder 2 as shown in FIG. Except for using, gas injection molding was performed under the same conditions. The gas injection pin used was
Total length 20 mm, pin protrusion length (outside the mold) 5 mm, outer cylinder diameter 5 mm, inner pin tip diameter 3 mm, inner pin tip 5 mm outside tip of outer cylinder, groove 6 depth: 0.5 mm, groove 7
Depth: 0.1 mm.

Molding result: Gas injection hole was 2 mm in diameter,
Swelling, which was seen when the decompression was not completed, was observed.

[0016]

By using the gas injection pin of the present invention and the mold incorporating the same, gas injection into the molten resin is performed smoothly in gas injection molding, and the gas depressurization operation time is shortened. Can be

[0017]

[Brief description of the drawings]

FIG. 1 is a schematic functional diagram of a gas injection pin used for carrying out the present invention.

FIG. 2 is a schematic functional diagram of a conventionally used gas injection pin.

FIG. 3 is a perspective view of an inner pin of a gas injection pin used for carrying out the present invention.

FIG. 4 is a cross-sectional view of a gas injection pin used in the embodiment of the present invention (the inner pin corresponds to a section taken along line XX in FIG. 3).

FIG. 5 is a cross-sectional view of a gas injection pin used to implement another aspect of the present invention.

FIG. 6 is a schematic view of a test evaluation mold for gas injection molding.

[Explanation of symbols]

 1: Inner pin 2: Outer cylinder 3: Gas injection hole 4: Melt resin 5: Mold inner wall surface 6: Groove (gas flow path / upstream) 7: Groove (gas flow path / outlet) 8: Sprue 9: Runner 10: Gate 11: Gas injection pin installation position 12: Gas channel 13: Plate length = 420 mm 14: Plate width = 100 mm 15: Plate thickness = 3 mm 16: Gas channel height = 10 mm

Claims (4)

[Claims] 1. An inner pin and an outer cylinder, wherein the tip of the inner pin is
Gas injection pin for gas injection molding inside the tip of the outer cylinder. 2. The gas injection molding gas injection pin according to claim 1, wherein the tip of the inner pin has a flat surface or a curved surface. 3. The gas injection molding gas injection pin according to claim 1, wherein the tip of the inner pin is a cone or a pyramid. 4. A gas injection molding die incorporating the gas injection molding gas injection pin according to any one of claims 1 to 3 so that its tip projects from an inner wall surface of the die.