JP2874835B2 - Gas injection molding die and gas injection molding method using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas injection molding die for producing a hollow resin molded product and a gas injection molding method using the same.

[0002]

2. Description of the Related Art Gas injection molding is already widely used as a method for producing a hollow molded article having a lightweight and excellent surface appearance which does not show sink marks even in a thick portion. In this method, after injecting a resin into the cavity and before the resin is cured, a gas is injected to form a hollow portion. In the case of this molding method, if the gas injected into the hollow portion of the molded product remains, the product may be deformed or damaged immediately after the mold is opened. After the molding, the gas injected into the hollow portion is discharged. Devices for injecting and discharging gas into such cavities have also been proposed. For example, JP-A-5-4
No. 252 discloses that a drilling member slides in and out of a nozzle hole to make a hole in a part of a surface layer of a molten resin in a cavity, a gas is injected into the resin, and a gas pressure is maintained to cure the resin. After that, an improvement relating to an apparatus for recovering gas is disclosed.

[0003] However, in the gas injection and recovery device as described above, a device such as a piston is indispensable for a drilling member (pin) that slides in the nozzle hole and moves forward and backward. The mold with the device is also complicated. In addition, the gas injection hole in the surface layer may be crushed while maintaining the gas pressure in the above-mentioned improved technology. In such a case, the hole-forming member (pin) in the nozzle hole is protruded into the cavity again, and the hole is surely formed. The pin is later retracted to discharge the high-pressure gas in the hollow interior.At this time, the resin is also drawn into the nozzle hole together with the gas drawing force due to the retracting of the pin, and the inside of the nozzle hole is closed. Gas may not be able to be discharged.

[0004]

There is also a structure in which the inner pin is fixed inside the outer pin without moving the inner pin forward / backward (FIG. 5). In this case, the mold does not need a driving unit such as a piston and can have a simple structure. However, as shown in FIG. 5C, when the injection gas is discharged from the center, the uncured resin 1a is drawn to the gas injection port. The lever resin 1a may prevent the gas from being discharged, and the pressurized gas may remain in the hollow portion. According to the present invention, the gas in the hollow portion can be reliably discharged after forming the hollow portion in the molded product with a simple structure without requiring a special driving device such as a piston under such circumstances. It is an object of the present invention to provide a gas injection molding die having a gas injection / discharge device and a molding method using the same.

[0005]

Means for Solving the Problems To solve the above-mentioned problems, the present inventors have made intensive studies on the structure of a gas injection and discharge pin which is fixed to a mold without using a piston or the like. Reached. That is, the present invention provides: (1) an inner pin having a minute gap between an outer pin held in a state in which a tip portion protrudes into a mold cavity and the outer pin;
In a gas injection molding die having at least a fixed inner pin and a gas passage communicating and injecting gas into and out of the minute gap, the mold is surrounded by the inner pin distal end surface and the outer pin distal end inner peripheral surface. (2) After injecting a resin into the cavity of the mold described in 1 above, injecting a gas into the cavity from the minute gap through the gas passage; Then, in a gas injection injection molding method of discharging an injection gas, at the time of gas recovery, the uncured resin near the tip of the outer pin is drawn into the cavity to form a plug-like resin body. The present invention relates to a gas injection molding method for recovering a gas through a break formed from an inner edge of a pin tip. The mold for gas injection molding of the present invention is characterized by a structure for injecting and discharging a gas into a mold cavity, and there is no particular limitation on other matters.

[0006]

The gas injection / discharge mechanism of the present invention will be described below. In the present invention, the structure of the pin for gas injection and discharge is composed of the outer pin and the inner pin having a minute gap communicating with the gas passage between the outer pin as described above, and projecting this into the mold cavity. A cavity is provided which is fixed and surrounded by the inner peripheral surface of the tip of the outer pin and the tip of the inner pin. According to the present invention, after the resin is injected by such a structure, a gas is injected into the cavity through the gas passage and the minute gap while the resin is in an uncured state, and a predetermined hollow portion is formed in the molded product while maintaining the gas pressure. Then, the gas in the hollow portion is discharged by a pressure difference through a gas passage opened to the atmosphere. During this gas discharge, the uncured resin protruding into the cavity near the tip of the outer pin is also drawn into the cavity by the pressure difference. However, the resin that has flowed into the hollow portion breaks at the inner edge of the outer pin and communicates with the gas passage opened to the atmosphere, so that the gas in the molded product hollow portion can be reliably discharged.

Thus, in the present invention, gas injection,
It is important to provide a cavity between the tip of the outer pin and the inner pin in the discharge pin structure, so that the injected gas can be reliably discharged from the hollow part of the molded product without moving the inner pin back and forth. Can be. The cavity,
Preferably, the capacity of the uncured resin drawn in is set larger than the volume of the resin drawn therein so that the uncured resin does not enter the micro-cavities 7a and block them. Although the reason why the resin drawn into the cavity breaks from the inner edge of the outer pin has not been elucidated in detail, it is considered that shrinkage during curing of the resin is also involved.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view of a main part of a mold for gas injection injection molding of the present invention. For example, a mold for molding a hollow molded article having an assist grip as shown in FIG. In FIG. 1, 1 is a product (resin), 2 is a mold cavity, and 3 is 3 to 5 in the cavity.
mm, outer pins, 4 are inner pins,
5a and 5b are molds, 6 is a pin holder such as a blind cover, 12 is a hollow part of a molded product, and 13 is an introduction path of a gas supplied from a gas supply unit (not shown). FIG. 2 is a partially enlarged explanatory view of the gas injection / discharge structure of FIG.
b is a cross-sectional explanatory view showing a state in which the inner pin is inserted into the outer pin, 7 is a gas passage, and 7a is a 0.05 to 0.0 formed between the outer pin and the inner pin.
Micro gap of about 7mm, 8 is 2-3mmφ × 5-10m
m indicates a cavity. Next, a gas injection injection molding method using the mold shown in FIGS.

A resin is injected into a mold cavity shown in FIG. 1 from a resin injection port (not shown). Next, while the resin in the cavity is still molten, the gas passage 7 and the minute gap 7a are formed.
40 to 120 k from a gas supply unit (not shown)
A gas is injected at about g / cm ² . The injected gas is 7
The flow rate is increased by a, and the resin 1a covering the pin is broken and pressed into the resin, whereby a hollow portion 12 is formed in the resin molded product 1 (FIG. 4a). Prior to opening the mold, the end of the gas supply unit is released to the atmosphere in order to discharge the pressurized gas in the hollow portion. Then, as shown in FIG. 4b, the uncured resin 1a near the tip of the outer pin protruding into the mold cavity.
Is drawn into the cavity 8 by the pressure difference generated at this time. However, the plug-shaped resin body 1b drawn into the hollow portion receives the internal pressure in the hollow portion at the inner edge portion 11 of the outer pin and naturally breaks, and communicates with the open end of the gas supply portion via 7, 7a. (FIG. 4c). Therefore, it is possible to reliably prevent the pressurized gas from remaining in the hollow portion, so that the molded product does not expand and deform or burst when the mold is opened. In addition, 9 and 10 show the flow direction of gas.

[0010]

As described above, the gas injection / injection mold according to the present invention does not require a mechanism for moving the gas injection / discharge pins forward and backward, has a simple structure, and has a structure in the hollow portion of the molded product. The pressurized gas can be reliably discharged to prevent the molded product from expanding and bursting when the mold is opened.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a main part of a mold for gas injection injection molding of the present invention,

FIG. 2 is a partially enlarged explanatory view of the gas injection / discharge structure of FIG.

FIG. 3 is a perspective view a of an example (assist grip) of a product manufactured by the molding method of the present invention, and a sectional view b thereof;

FIG. 4 shows the gas injection of the gas injection mold of the present invention;
Explanatory diagram of the operation of the discharge structure, a is a state in which a gas is injected into the cavity after resin injection, b is a state in which a gas passage is communicated with the atmosphere to discharge a pressurized gas in the hollow part after forming the hollow part, c is an explanatory view showing a state in which the resin drawn into the hollow portion of the outer pin is broken at the inner edge of the outer pin, and the pressurized gas in the hollow portion is discharged through the gas passage;

5A and 5B are explanatory views showing a conventional pin structure, wherein a is a structural explanatory view of a pin tip, b is a circumferential sectional explanatory view thereof, and c is a state in which a gas injection port is closed by an uncured resin at the time of gas discharge. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Resin 2 Mold cavity 3 Outer pin 4 Inner pin 5a, b Die 6 Pin holder 7 Gas passage 7a Micro gap 8 Cavity part 11 Break part 12 Molded part hollow part

Claims (2)

(57) [Claims] 1. An outer pin held in a state in which a tip portion protrudes into a mold cavity, an inner pin inserted and fixed with a minute gap between the outer pin,
In a gas injection injection mold having at least a gas passage communicating and injecting gas into and out of the minute gap, a cavity surrounded by the inner pin tip surface and the outer pin tip inner peripheral surface is provided. A mold for gas injection injection molding, characterized in that: 2. A gas injection injection molding method according to claim 1, wherein after injecting the resin into the cavity of the mold, a gas is injected into the cavity from the minute gap through the gas passage, and then the injected gas is discharged. At the time of gas recovery, the uncured resin near the tip of the outer pin is drawn into the cavity to form a plug-shaped resin body, and the plug-shaped resin body has a broken portion formed from the inner edge of the outer pin tip. A gas injection injection molding method, wherein the gas is recovered through a gas injection injection molding method.