JP3213137B2 - Gas injection molding method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for gas injection molding, and more particularly, to a large sheet-like product such as an interior / exterior product such as a bumper or a dashboard of an automobile or a casing of a home electric appliance, or a resin which rapidly solidifies by cooling. It can be used for molding products.

[0002]

2. Description of the Related Art Conventionally, a mold having a cavity provided with a thick-walled portion is filled with a molten resin, and an inert gas such as nitrogen gas is injected into the filled molten resin to perform molding. Molding methods are known. According to this method, the molten resin is guided to the thick portion of the cavity,
Even a large mold can easily fill the molten resin up to the end.
Further, since the inside of the molten resin filled in the thick-walled portion has a thickness, the passage of gas becomes easy. For this reason, the gas injected into the molten resin reaches the end of the mold along the thick-walled portion and presses the entire surface of the molten resin against the inner surface of the cavity. However, there is no defective portion such as "sink", and a good molded product following the mold can be obtained.

In such a gas injection injection molding method, the larger the size of the molded product, the longer the path through which the gas must pass and the higher the flow resistance. However, there is a disadvantage that a large gas supply source is required. In order to remedy this drawback, there has been proposed a multi-point gas injection injection molding method in which a plurality of gas injection holes are provided in a mold and gas is simultaneously injected from these gas injection holes. According to this method, the path through which the gas passes through the plurality of gas injection holes is shortened, the gas pressure required for injection is relatively low, and injection molding can be performed even with a small gas supply source.

[0004]

In such a multi-point gas injection injection molding method, if there is at least one gas injection hole to which the molten resin has not reached, the gas flows between the surface of the molten resin and the inner surface of the cavity. Injected during the molding, it cannot be molded according to the mold. Therefore, gas injection is started after the molten resin reaches all the gas injection holes. However, after the molten resin reaches all the gas injection holes, there is no room for moving the molten resin displaced by the gas from inside the cavity, and the volume of the hollow portion formed by the gas injection is reduced, so that the volume is large. When molding a molded article, there is still a problem that a high-pressure gas is required. In particular, when the molten resin reaches all of the gas injection holes, almost the entire cavity is occupied by the molten resin. There is a problem that deformation occurs or deformation and warping occur after molding.

SUMMARY OF THE INVENTION An object of the present invention is to provide a gas injection molding method and a gas injection molding method capable of molding a large thin and long molded product at a low gas pressure.

[0006]

According to a first aspect of the present invention, a plurality of gas injection holes are provided in a mold, and a gas is injected from the gas injection holes into a molten resin filled in a cavity of the mold. a gas injection injection molding method of performing molding with, dissolved
After the start of filling of the molten resin and at the time of completion of filling
The method is characterized in that gas injection is performed before, and gas injection is sequentially started from a gas injection hole on an upstream side of a flow of the molten resin generated when the cavity is filled with the molten resin.

A second invention of the present invention is a gas injection molding apparatus for performing molding by injecting a gas into a molten resin filled in a cavity of a mold, wherein the cavity is filled with the molten resin. a said fused and the mold having a plurality of gas injection holes for injecting the gas in the flow direction of the resin, since the time of starting the filling of the molten resin occurs, filling Kan
Control means for performing gas injection before the end of the injection and sequentially starting gas injection from a gas injection hole on the upstream side of the flow when filling the molten resin.

[0008]

In the present invention as described above, each gas injection hole is focused on that gas injection can be started at any time after the molten resin filled in the cavity arrives at that position. Immediately after the gas arrives, if the gas is sequentially injected from the gas injection hole, the gas can form a hollow portion in the molten resin while the space for the gas to displace the molten resin is sufficient. , Molten resin
Is in a fluid state, its internal pressure is low,
Even a low-pressure gas can be injected, and the movement of the molten resin filled in the cavity is promoted by the newly injected gas each time it reaches each gas injection hole. Therefore, by starting the gas injection along the flow direction of the molten resin, even if the gas pressure injected from the injection hole is low,
In addition to being able to mold a large or long molded article, a sufficiently large hollow portion can be formed inside the molded article, thereby achieving the above object.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a gas injection molding apparatus 1 according to a first embodiment of the present invention. This molding apparatus 1 is a hot runner type, and a molten resin is placed inside a two-part mold 10. 2 is injected, and gas is injected into the filled molten resin 2 to perform injection molding. When a cold runner type is used, a three-piece mold can be used. The molding apparatus 1 includes an extruder (not shown) that pushes the molten resin 2 by bringing the nozzle 3 into contact with the bush 11 of the mold 10, and a gas supply source 4 that supplies gas injected into the molten resin 2. And a control device 5 which is a control means for controlling a timing of injecting a gas into the molten resin 2 and the like.

The mold 10 is divided into a core portion 10A having a bush 11 on the surface and a cavity portion 10B having a cavity 12 serving as a mold. The core portion 10A includes a sprue 13, a runner 14, and a passage for introducing the molten resin 2 pushed from the extruder into the cavity 12.
And a gate section 15 provided therein. The gate portion 15 communicates with the upper end of the cavity 12 in the figure, and the molten resin 2 flows through the cavity 12 from the upper side to the lower side in the figure. Cavity part 10B
In the figure, a cavity 12 is formed by recessing the upper surface in the figure. The cavity portion 10B is provided with gas injection holes 16, 17 for injecting gas into the cavity 12. The gas injection holes 16 and 17 are arranged along the flow direction of the molten resin 2.

The cavity 12 is, as shown in FIG.
In the figure, a length L1 in the left-right direction has a rectangular planar shape larger than a width W1 in the up-down direction. cavity
In the central part of 12, a groove-shaped thick portion 18 having a depth dimension D and a width dimension W2 is provided along the longitudinal direction. A thin-walled portion 19 for molding a portion is provided. The thick part 18 is
This is a portion where the thickness of the molten resin 2 filled in the cavity 12 is increased to reduce the passage resistance of the gas injected therein. As a result, the gas injected into the cavity 12 travels inside the molten resin 2 along the thick molded portion 18. A gas injection hole 16 is formed in the thick-walled portion 18 at a position of a dimension P1 from the end face on the upstream side (left side in FIG. 2) of the cavity 12.
The outlet of the gas injection hole 17 is arranged at a position of the dimension P2 on the downstream side of the outlet. The thin-wall forming section 19
It has two levels of depth, with the downstream being deeper than the upstream. Upstream thin section 19A
Has a depth dimension t1, and the downstream thin-walled portion 19B has a dimension t1.
It has a greater depth dimension t2.

Returning to FIG. 1, the gas supply source 4 is for taking out an inert gas such as high-pressure nitrogen gas from a cylinder and compressing the same.
It is connected to 6, 17 by piping. By operating the control valves 6 and 7 to open and close the control valves 5, when performing gas injection injection molding, the gas flows from the gas injection holes 16 and 17 of the gas injection holes 16 on the upstream side of the flow of the molten resin 2. Is started. The control device 5 includes a timer in which the time from when the extruder starts filling the molten resin 2 to when the extruder reaches the outlets of the gas injection holes 16 and 17 is set in advance. This timer allows the gas injection holes 16 and 17 to start gas injection after the molten resin 2 arrives.

In this embodiment, the timer of the control device 5 is started simultaneously with the start of the filling of the extruder, and the molten resin 2
Arrives at the gas injection hole 16, the control valve 6 of the upstream gas injection hole 16 is opened, and when the molten resin 2 arrives at the gas injection hole 17, the control valve 7 of the downstream gas injection hole 17 is opened. You. As a result, the molten resin 2 filled in the cavity 12
Will receive a new gas every time it arrives at each of the gas injection holes 16 and 17, so even if the cavity 12 is large and long, Can be easily moved, and a large hollow portion is formed inside.

According to this embodiment as described above, the following effects can be obtained. That is, a plurality of gas injection holes 16 and 17 are provided in the mold 10 along the flow direction of the molten resin 2, and the gas injection is started sequentially from the gas injection holes 16 and 17 from the one where the molten resin 2 arrives. Therefore, gas can be injected before the molten resin 2 is filled and there is no room to form a hollow portion in the cavity 12, and each gas injection hole 1
Since a new gas is sequentially injected from steps 6 and 17, the movement of the molten resin 2 is promoted, and good molding can be performed even with a large and long molded article.

Further, since the gas pressure of the gas supply source 4 can be directly applied to the intermediate portion of the molten resin 2 filled in the cavity 12 by the gas injection hole 17, the gas flow resistance can be reduced, and the gas supply resistance can be reduced. The gas pressure of the source 4 can be set lower than before.

Further, by setting the gas pressure to a low pressure, the gas consumption can be reduced, and the injected gas does not leak to the outside of the molten resin 2, so that the cavity can be prevented.
Problems such as gas entering the surface of the thin-walled portion 19 can be prevented.

FIG. 3 shows a second embodiment of the present invention. In this embodiment, the gas injection holes 16 in the first embodiment are used.
The mold 10 in which the gate portion 15 and the gate portion 15 are separately provided is the mold 20 in which the gate portion 25 also serving as the gas injection hole is provided. That is, the nozzle 3A of the extruder is also connected to the gas supply source 4 via the control valve 6A. The control valve 6A is opened at an appropriate timing after the filling of the molten resin 2 is started. Thus, gas is injected from the nozzle 3A into the mold 20 through the gate portion 25. The mold 20 has a core 20A and a cavity 20B.
And is divided into As shown in FIG. 4, the core portion 20A includes an elongated flat pentagonal cavity 22 having one end tapered, and a gas injection hole 17A provided at a substantially central portion of the cavity 22. It has become. The gas injection hole 17A is connected to the gas supply source 4 via the control valve 7A. The control valve 7A is opened after the molten resin 2 filled in the cavity 22 arrives. In this embodiment, the same operation and effect as those of the first embodiment can be obtained. In addition, since one gas injection hole is omitted, the structure of the mold 20 can be simplified. Can be added.

Next, the specific effects of the present invention will be described based on the following comparative experiments 1 and 2. [Comparative Experiment 1] This Comparative Experiment 1 clarifies the specific effects of the present invention based on the experimental results of Experimental Example 1 based on the first embodiment of the present invention and Comparative Example 1 corresponding to the prior art. is there. In Experimental Example 1, gas injection molding is performed based on the first embodiment described above. On the other hand, in Comparative Example 1, gas injection molding is performed using the same mold, apparatus, and conditions as in Experimental Example 1. However, the comparative example differs from the experimental example in that molding is performed with the gas injection hole 17 closed until the end. [Dimensions of Cavity] Each dimension of the cavity 12 shown in FIG. 2 is L1 = 420 mm, W1 = 100 mm, W2 = 10 mm, t1 = 3.0 m
m, t2 = 5.0 mm, P1 = 20 mm, P2 = 220 mm, and D = 12 mm. [Molding conditions] In this comparative experiment 1, the following molding conditions are employed. Resin Idemitsu Polypro (J-3054H) Resin temperature 220 ° C Mold temperature 30 ° C Resin injection time 2.0 seconds Injection gas pressure 4.0 MPa Gas injection timing Gas injection hole 16: 1.5 seconds after the start of resin charging Gas injection Hole 17: 2.0 seconds after the start of resin filling (Experimental Example 1)
Only) Molding machine IS-200CN manufactured by Toshiba Machine Co., Ltd.

[Experimental Results] In Experimental Example 1, a good molded product could be obtained. The average weight of the molded product obtained by performing the experiment several times was as light as 113 g, which indicates that a sufficiently large hollow portion was formed inside. On the other hand, in Comparative Example 1, the gas did not reach the end of the thick portion 18 of the cavity 12, and an unfilled portion where the molten resin 2 did not reach the corners of the cavity 12 was formed. Became defective. In Comparative Example 1, the injection gas pressure was increased from 4 MPa to 6 MPa to perform injection molding.
The molten resin 2 was able to reach the entirety of the molten resin 2. However, near the upstream end of the cavity 12, as shown in FIG. A defective portion 8 extending to the portion 19A was formed, and a defect occurred in the molded product obtained even when the pressure was increased.

[Comparative Experiment 2] This Comparative Experiment 2 clearly shows the specific effects of the present invention from the experimental results of Experimental Example 2 based on the second embodiment of the present invention and Comparative Example 2 corresponding to the prior art. Is what you do. In Experimental Example 2, gas injection molding is performed based on the second embodiment described above. In contrast, in Comparative Example 2,
Gas injection molding is performed using the same mold, apparatus, and conditions as in Experimental Example 2. However, in the comparative example, the gas
The difference from the experimental example is that molding is performed with 17A closed. [Dimensions of Cavity] Each dimension of the cavity 22 shown in FIG. 4 is L1 = 700 mm, L2 = 100 mm, D = 25 mm, W1 = 100
mm, P2 = 350 mm. [Molding conditions] In this comparative experiment 2, the following molding conditions are employed. Resin Idemitsu Polypro (J-3054H) Resin temperature 220 ° C Mold temperature 30 ° C Injection gas pressure 12.0MPa Gas injection timing Gate 25: 2.8 seconds after the start of resin filling Gas injection hole 17A: 5. After 8 seconds (Experimental example 2 only) Molding machine MG-850W manufactured by Mitsubishi Heavy Industries, Ltd.

[Experimental Results] In Experimental Example 2, a good molded product could be obtained. On the other hand, in Comparative Example 2, the cavity
The flow of the molten resin 2 was stopped at a position of 600 mm from the uppermost stream portion of No. 22 and the molten resin 2 could not be completely filled, and the resulting molded product was defective.

Although the present invention has been described with reference to preferred embodiments, the present invention is not limited to these embodiments, and various modifications and changes in design may be made without departing from the spirit of the present invention. It is possible. For example, the molten resin used for injection molding is not limited to polypropylene, but may be another synthetic resin such as polycarbonate. In addition, the shape of the molded product is not limited to a rectangular plate-like or prismatic shape, and at least a part is a thick part, such as a disk-like or dice-like one, a thin part having a thick part in a part, and the like. If it does, another shape may be used.

Further, the number of gas injection holes is not limited to two, but may be three or more. The arrangement is not limited to a straight line, and may be arranged radially around a gate filled with molten resin. Can be arranged according to the shape of the molded article. In addition, the control device is not limited to one that operates the control valve according to the arrival time of the molten resin by the timer, and one that operates the control valve by detecting the arrival of the molten resin by a sensor attached to the surface of the mold. May be. In this case, as a sensor for detecting the arrival of the molten resin, an ultrasonic sensor, a strain sensor, or the like can be employed.

[0024]

As described above, according to the present invention, it is possible to form a large thin-walled or long-sized molded product at a low gas pressure.

[Brief description of the drawings]

FIG. 1 is a schematic view of a gas injection molding apparatus according to a first embodiment of the present invention.

FIG. 2 is a three side view showing a cavity of the mold according to the embodiment.

FIG. 3 is a schematic view of a gas injection molding apparatus according to a second embodiment of the present invention.

FIG. 4 is a three-view drawing showing a cavity of the mold according to the embodiment.

FIG. 5 is a plan view showing a defective portion of a molded product of a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas injection injection molding apparatus 2 Molten resin 5 Control device as control means 10, 20 Die 12, 22 Cavity 16,17,17A Gas injection hole 25 Gate part which also serves as gas injection hole

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-6-23781 (JP, A) JP-A-5-261748 (JP, A) JP-A-6-238698 (JP, A) JP-A-4- 62122 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 45/00-45/84

Claims (2)

(57) [Claims] 1. A gas injection / injection molding method in which a plurality of gas injection holes are provided in a mold, and gas is injected from the gas injection holes into a molten resin filled in a cavity of the mold to perform molding. Therefore, after the start of the filling of the molten resin,
Injecting gas before the completion of filling, and sequentially starting gas injection from a gas injection hole on the upstream side of the flow of the molten resin generated when the cavity is filled with the molten resin. Injection injection molding method. 2. A gas injection injection molding apparatus for performing molding by injecting a gas into a molten resin filled in a cavity of a mold, wherein the flow of the molten resin is generated when the cavity is filled with the molten resin. A mold having a plurality of gas injection holes for injecting the gas along a direction, and filling with a molten resin
Gas injection after the start and before the completion of filling
And a control means for sequentially starting gas injection from a gas injection hole on the upstream side of the flow when filling the molten resin.