JPH0732402A - Hollow injection mold - Google Patents

Abstract

(57) [Summary] [Objective] To provide an injection molding technique for efficiently manufacturing a hollow molded article having an excellent appearance. In a hollow injection molding die equipped with a hole (4) for injecting a pressurized gas provided in a template and a gas injecting means, a gas injection needle (13) is installed adjacent to the outside of the hole (4). Accessible through the shut-off valve mechanism provided;
The shut-off valve mechanism is composed of a valve body (8), a valve holder (5) and a valve body driving means, and a valve hole (10) and a gas having a size capable of advancing and retracting a gas injection needle are provided in the valve body and the valve holder. Injecting needle insertion holes (6) are provided respectively; and these holes are arranged at positions where they can be communicated with each other only by the valve body driving means when the gas injecting needle approaches the hole (4). It

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding die, and more particularly to injection molding for injecting a pressurized gas into a molten resin in a mold cavity and expanding the cavity to obtain a molded product having a large hollow portion. Regarding suitable molds.

[0002]

2. Description of the Related Art When a molded product having a hollow structure is manufactured from a thermoplastic resin as a raw material by an injection molding method, conventionally, (1) a hollow molding method using an extruded parison, and (2) two molded products are manufactured. Then, a method of adhering these to form a molded product having a desired hollow structure has been carried out. These methods have the drawback that the shape, size, etc. of the molded product are limited, and that the cost of manufacturing the molded product is high. Therefore, a more excellent injection molding technique for manufacturing a molded product having a hollow structure is required. Development was sought after.

In order to respond to this, Japanese Patent Publication No. 57-1496
The technique described in Japanese Patent No. 8 has been proposed. This technique employs a method of injecting an amount of molten resin which is insufficient to fill the cavity into the cavity of the injection molding die, and subsequently pressurizing a pressurized gas from the same port to fill the cavity. The molten resin is inflated by the action of pressurized gas that is pressed into the molten resin, pressed against the surface of the cavity, and the pattern, characters, etc. imprinted on the surface of the cavity are accurately transferred to the surface of the molded product, and the hollow resin A molded product is obtained. In addition, this publication describes that it is preferable to increase the cavity capacity at the time of pressurizing gas under pressure when the molded product to be manufactured is thick or when the surface resin layer is too thick. In this case, before taking out the molded product, the gas in the hollow portion is released to the atmosphere by retracting the resin inlet, that is, the nozzle of the injection molding machine. The gas has a drawback that it cools the nozzle of the molding machine and the originally required temperature control becomes unstable and stable production cannot be performed.

Separately, a technique described in Japanese Patent Laid-Open No. 64-14012 has been proposed. In this technique, the pressurized gas in the hollow part of the molded article is released to the atmosphere by opening the valve arrangement. To open the valve arrangement, from the closed position with the conical valve seat attached, it is pulled down by the piston and the piston of the cylinder to the open position, and the pressurized gas is released around the valve arrangement to the atmosphere. A check valve is provided at the outlet end of the central bore of the valve arrangement to prevent backflow of plastic material and gas. In this case, there is a drawback that the check valve does not operate normally, and in order to meet this technical problem, JP-A-4-31015 proposes to heat the nozzle tip including the check valve by a heating device. ing. However, in this case as well, since the exhaust gas passes around the heating device and is released to the atmosphere, there is a drawback that the heating device is cooled and the temperature control becomes unstable.

[0005]

In the case of hollow molding in which the cavity is expanded, the volume of the hollow portion is large and the amount of gas to be exhausted is large. Therefore, the temperature drop of the molding machine nozzle and the gas injection nozzle also becomes large, and the temperature control becomes more unstable.
Under such circumstances, as a result of intensive studies for the purpose of providing an injection molding technique for efficiently manufacturing a hollow molded article having an excellent appearance, as a result, a cavity is cut off from the gas injection needle during resin injection, and a gas injection needle is used. Found that the object was achieved by incorporating a separate valve mechanism into the mold, and completed the present invention.

[0006]

SUMMARY OF THE INVENTION The gist of the present invention, however, is to provide a hollow injection molding die having a hole (4) for injecting a pressurized gas provided in a mold plate and a gas injecting means. The gas injection needle (13) is accessible to the hole through a shut-off valve mechanism provided adjacent to the outside of the hole (4); the shut-off valve mechanism includes a valve body (8) and a valve. A valve hole (10) comprising a holder (5) and a valve body driving means, the valve body and the valve holder having a size capable of advancing and retracting a gas injection needle.
And a gas injecting needle insertion hole (6) are provided respectively; and these holes are provided at positions that can be communicated with each other only when the gas injecting needle approaches the hole (4) by the valve body driving means. It is in a hollow injection mold characterized by being arranged.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The drawings are conceptual views showing an embodiment of the present invention. FIG. 1 shows a state where a molten resin is filled in a mold cavity by injection molding, and FIG. 2 shows a state where gas injection into the molten resin is started. Show. In the drawings, (1) is a fixed mold plate, (2) is a movable mold plate, (3) is a mold cavity, (4) is a hole, (5) is a valve holder, and (6) is a gas injection needle insertion Hole, (7) gas injection needle side cam, (8) valve body, (9) valve body side cam, (10) valve hole, (11) spring, (12) spring retainer, (13) Is a gas injection needle, (14) is a gas injection hole, (15) is a gas pipe joint attachment port, (16) is a cylinder, (17) is a gas conduit, (18) is a cylinder working fluid conduit, and (19).
Is a gas introduction valve, (20) is a gas exhaust valve, (21) is a gas exhaust conduit, (22) is a column, and (23) is a cylinder pressing plate. In addition, the gas injection needle insertion hole (6) is distinguished by attaching a symbol (6a) to a portion located far from the template when it is necessary for convenience of description.

The hollow injection molding die of the present invention has a sprue, a runner and a gate for guiding the molten resin to the cavity, like the ordinary injection molding die, and the molding cavity is melted by resin injection during molding. Almost filled with resin. At this time, that is, when the molten resin is injected, the mold is
Is in the state of. Further, the mold of the present invention is a pressurized gas, for example, nitrogen gas, air, helium gas, carbon dioxide gas, etc., preferably air, nitrogen gas, etc. into the injected molten resin for molding a hollow product. In order to enable the injection of the gas, a hole for injection provided in the mold plate of the mold and a gas injection means are provided. Further, the mold of the present invention is provided with a shut-off valve mechanism so as to enable injection only when the gas injection means approaches the hole provided in the mold plate. The mold is in the state shown in FIG. 2 when the pressurized gas is injected.

In the mold of the present invention, the number of holes (4) provided in the stationary mold plate (1) for injecting pressurized gas is as follows.
Although only one piece is shown in the drawings, a plurality of pieces may be provided depending on the size and shape of the molded product. Further, it is convenient to provide this hole (4) in the fixed-side template because it can be controlled separately from the operation of various mechanisms provided in the movable-side template for expanding the cavity, but in some cases, it may be in the movable side. It can also be provided on the template. The shape and size of the hole (4) are not particularly limited, but a cylindrical shape is usually used for the convenience of cutting, and there is no passage of pressurized gas in the molten resin filled in this hole at the time of injection. The diameter that can be formed is necessary. Of course, it is not preferable that the diameter is larger than necessary from the viewpoint of molding operation and cutting, and a diameter of 5 to 10 mm is usually selected. Also, because of the ease of mold release, the depth is not too deep, usually 10 to 30 mm.
It is preferable to use a so-called taper, which has a diameter that increases toward the surface of the mold at a certain depth, if possible.

In the mold of the present invention, the gas injection means is
Specifically, as shown in the drawing, a gas injection needle (13), means for bringing this needle close to a hole (4) provided in the template,
It includes a gas injection hole (14) provided inside the needle, a gas conduit (17) connected to the injection hole and guiding a pressurized gas, and the like. Gas injection hole (1) provided inside the gas injection needle (13)
4) is connected via a gas conduit (17) to a source of pressurized gas not shown. A gas introduction valve (19) may be provided in the gas conduit (17) to control the introduction of the pressurized gas. On the other hand, the gas conduit (17) is connected to the gas exhaust valve (2
It is convenient to connect with 0), by opening this valve at the end of molding, the injected pressurized gas can be released outside the molded article using the same conduit and injection needle. Further, in the present invention, it is not necessary to provide a valve for preventing backflow at the tip of the gas injection needle. It is considered that this is because when the injection needle is inserted into the semi-molten resin, a pressing force acts between the resin and the needle to ensure the sealing property with the outer peripheral surface of the needle.

The gas injection needle shown in the drawings comprises at least two parts, a tip part having a small outer diameter and a base part having a large outer diameter connected to the tip part, and the outer diameter of the tip part is equal to that of the valve body (8 ) Is sufficiently smaller than both the inner diameter of the valve hole (10) bored in (1) and the inner diameter of the gas injection needle insertion hole (6) bored at least on the template side of the valve holder, and outside the base. The diameter is almost the same as the inner diameter of the gas injection needle insertion hole (6a) formed at least on the side of the valve holder far from the template. If the outer diameter of the tip is close to the inner diameter of the gas injection needle insertion hole (6) on the template side, when the needle is inserted, the solidified resin layer formed on the inner wall of the polygonal hole (6) is peeled off. It is not preferable because it will happen. The outer diameter of the tip is usually a hole (6)
It is selected from the range of 50 to 80% of the inner diameter of. The same applies to the inner diameter of the valve hole (10) as the hole (6). Further, as long as the insertion of the tip into the resin is secured, the outer diameter of the base does not necessarily need to be air-tightly fitted with at least the gas injection needle insertion hole (6a) on the side far from the template of the valve holder. If the inner diameter of the insertion hole (6a) is substantially the same, it is convenient for the gas injection needle to be stably moved forward and backward.

The means for approaching the gas injection needle (13) to the hole (4) provided in the template is not particularly limited, but a cylinder (16) having a piston for advancing and retracting the needle is shown in the drawing. )showed that. Typically, the cylinder is hydraulically actuated and is connected to two cylinder working fluid conduits (18) to alternately transfer the fluid pressure to the cylinder chambers on either side of the piston. By arranging the gas injection needle (13), the piston and the cylinder (16) in the pocket provided in the stationary mold plate (1) including the shutoff valve mechanism described later, the injection molding mold is compact. Becomes The drawing shows a cylinder retainer plate (23) for fixing the cylinder in place.

In the mold of the present invention, the shut-off valve mechanism comprises a valve body (8), a valve holder (5) and valve body driving means as shown in the drawing, and the operation of the valve body driving means is pressurization. The opening formed when the shut-off valve is opened is selected so that it can be synchronized with the operation of the gas injection needle and can be large enough to receive the gas injection needle. That is, the valve body and the valve holder have a valve hole (10) and a gas injection needle insertion hole (6) that are large enough for the gas injection needle to move forward and backward.
Are drilled respectively. Moreover, these holes are arranged at positions where they can communicate with each other only when the gas injection needle approaches the hole (4) by the valve body driving means. In the shut-off valve mechanism shown in the drawings, the valve holder (5) has a relatively simple shape in which two orthogonal holes are formed in a cylindrical block with a part cut away. One hole is a gas injection needle insertion hole (6) usually located at the center of the cylinder, and the other is a hole for accommodating the valve body (8) and mounting it on the valve holder. The valve body (8) is usually cylindrical, and a valve hole (10) orthogonal to the central axis penetrates at a predetermined position. The diameter of the gas injection needle insertion hole (6) is 0.5 to 1 from the hole (4) of the template.
The diameter of the valve hole (10) is preferably smaller than that of the hole (6). Also, if necessary, the diameter of the holes (6) can be increased toward the template. A pocket is formed at a position communicating with the hole (4) provided in the fixed-side template (1), a shutoff valve mechanism is incorporated in the pocket, and this is fixed by using a column (22). A cartridge heater may be provided at an appropriate portion of the valve body (8) and other shutoff valve mechanisms, but it is not essential.

The valve element driving means shown in the drawings comprises a spring (11), a spring retainer (12), a gas injection needle side cam (7) and a valve element side cam (9). A groove is provided at the right end of the valve body (8) so that the spring (11) can be held, and is pulled to the right by the force of the spring. A valve body side cam (9) is attached to the left end of the valve body, and the position of the valve body (8) is regulated by the gas injection side cam (7). In the case shown, the tension coil spring is used, so the cam is tilted downward to the left.
If a compression coil spring is used, the cam tilts in the opposite direction to the right. The valve body driving means or the shutoff valve mechanism is not limited to the one shown in the figure, and can be replaced with any one having a function of shutting off the pressure in the cavity. Although an example using a spring mechanism is shown in the drawings, it may be a type that opens and closes by rotation. Also, an example has been shown in which the opening and closing of the valve body (8) and the advance and retreat of the gas injection needle (13) are interlocked with each other by a cam mechanism. May be. The point is that there is no limitation as long as it can be synchronized so as to be arranged in a position where it can communicate only when the gas injection needle approaches the gas injection hole (4) provided in the template.

The gas injection process will be described with reference to FIG.
By flowing oil or air or the like through the cylinder working fluid conduit (18), the piston of the cylinder and the gas injection needle (13) connected thereto are moved upward and the tip thereof is brought close to the hole (4). A cam (7) is attached to the gas injection nozzle (13) and moves the cam (9) and the valve body (8) to the left against the force of the spring (11). At this time, the shapes and mounting positions of the cams (7) and (9) are adjusted in advance so that the position of the valve hole (10) matches the position of the gas injection needle insertion hole (6). The tip of the gas injection needle (13) is moved further into the molten resin. The approach limit position is determined by selecting the stroke of the cylinder (16) and the mounting position. Normally, it is not necessary for the tip of the injection needle to enter the hole (4) of the template during gas injection, and as shown in the figure, it only reaches the gas injection needle insertion hole (6) provided in the valve holder. , Can achieve the purpose enough. The timing of the movement is synchronized with the molding operation by receiving a signal from the molding machine. After that, the gas injection valve (19) is opened, and pressurized gas is introduced into the gas injection hole (14) through the gas conduit (17) and injected into the molten resin.

In hollow injection molding using this mold, the gas injection step is combined with the expansion step of the mold cavity, but the expansion of the cavity is usually performed after or in parallel with the gas injection. When the molded product is solidified, the gas introduction valve (19) is closed and the gas exhaust valve (20) is opened to release the gas in the molded product. Furthermore, the cylinder (16)
The piston of (3) is operated to withdraw the gas injection needle (13) and move it downward to return to the state of FIG. The valve body (8) returns to its original position by the force of the spring, and when the valve (20) is closed, it returns to its original state. When the molded product is released from the mold, the resin filling the holes (4) is taken out while adhering to the molded product, which does not hinder the next molding.
Further, since the adhered portion is easily separated, it does not adversely affect the appearance of the molded product.

[0017]

EFFECTS OF THE INVENTION When a thermoplastic resin is molded using the mold of the present invention, the following remarkable effects are exhibited and its industrial utility value is extremely large. 1. An extremely stable pressurized gas injection can be performed at room temperature without providing a heating device for the gas injection needle. 2. The molded product can be stably molded with the same wall thickness.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing one embodiment of the present invention, showing a state where molten resin is injected into a cavity.

FIG. 2 is a conceptual diagram showing an embodiment of the present invention, showing a state in which pressurized gas has begun to be injected into a cavity.

[Explanation of symbols]

 1: Fixed-side mold plate 2: Movable-side mold plate 3: Mold cavity 4: Hole 5: Valve holder 6, 6a: Gas injection needle insertion hole 7: Gas injection needle side cam 8: Valve body 9: Valve body side cam 10 : Valve hole 11: Spring 12: Spring retainer 13: Gas injection needle 14: Gas injection hole 15: Gas pipe joint mounting port 16: Cylinder 17: Gas conduit 18: Cylinder working fluid conduit 19: Gas introduction valve 20: Gas exhaust valve 21: Gas exhaust conduit 22: Strut 23: Cylinder pressing plate

Claims (7)

[Claims] 1. A hole (4) for injecting a pressurized gas provided in a template.
In the hollow injection molding die including the gas injection means, the gas injection needle (13) is accessible to the hole through the shutoff valve mechanism provided adjacent to the outside of the hole (4). The shutoff valve mechanism includes a valve body (8) and a valve holder (5)
And a valve body driving means, and the valve body and the valve holder are provided with a valve hole (10) and a gas injection needle insertion hole (6) each having a size capable of advancing and retracting the gas injection needle;
The hollow injection molding die characterized in that these holes are arranged at positions that can communicate with each other only when the gas injection needle approaches the hole (4) by the valve body driving means. 2. A gas injecting needle is composed of at least two parts, a tip part having a small outer diameter and a base part having a large outer diameter connected to the tip part, and the outer diameter of the tip part is perforated in the valve body (8). It is sufficiently smaller than the inner diameters of the valve hole (10) provided and the gas injection needle insertion hole (6) formed at least on the mold plate side of the valve holder, and the outer diameter of the base is at least the mold of the valve holder. The hollow injection molding die according to claim 1, wherein the inner diameter of the gas injection needle insertion hole formed on the side far from the plate is substantially the same. 3. The hollow injection mold according to claim 1, wherein the gas injection means comprises a piston (16) for advancing and retracting the gas injection needle (13). 4. The hollow injection mold according to claim 3, wherein the shut-off valve mechanism, the gas injection needle (13) and the piston (16) are arranged in a pocket provided in the stationary mold plate (1). 5. A gas injection needle (13) is provided with a gas conduit (1).
7) via the gas introduction valve (19) and the gas exhaust valve (2)
0) is connected to the hollow injection molding die according to any one of claims 1 to 4. 6. The valve body driving means comprises a spring (11),
The hollow injection mold according to claim 1, comprising a spring retainer (12), a gas injection needle side cam (7) and a valve body side cam (9). 7. The hollow injection molding die according to claim 1, wherein the valve body driving means comprises a rotating mechanism.