JPH0985772A - Manufacture of injection molded article with hollow shape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To close off a gas inflow port without increasing cost by injecting resin again after gas injection molding and closing off the gas inflow port. SOLUTION: Gas is injected from a gas gate 9 so as to make resin within the cavity 3 into a hollow shape. Molten resin is injected from the injection molding machine 1 and comes into the cold runner 5 from the second gate 6 to be filled in the hollow part. At this time, since the check valve within the gas nozzle 8a comes to be in a closed condition, molten resin does not comes into the gas nozzle 8a. In addition, molten resin comes into the hollow part of the cavity 3 via the first gate 4. In this instance, resin coming into the cavity 3 does not need to fill the hollow part, thus it is sufficient to be a quantity capable of closing off the first gate 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an injection molded product having a hollow shape.

[0002]

2. Description of the Related Art In recent years, in the production of resin molded products by injection molding, a so-called gas injection method has been attracting attention, in which a pressurized fluid such as gas is injected during injection molding to manufacture hollow injection molded products. This gas injection method saves resin material, reduces the weight of molded products, prevents sinking of molded products, etc.
It has various advantages. A conventional gas injection method will be described with reference to FIGS. 6 and 7.

In FIG. 6, the mold 20 comprises a fixed mold 21 and a movable mold 22. A cavity 23 is formed in the mold 20. A gas gate 24 is provided in the cavity 23, and a gas nozzle 25 of a gas injector (not shown) is connected to the gas gate 24.

In the above structure, when the molten resin heated by the injection molding machine 26 is injected, the molten resin is injected into the mold 20.
Which is introduced into the cavity 23 through the sprue 27
To be filled. At this time, the gas gate 24 is provided in the gas nozzle 25, and is opened in the direction from the gas nozzle 25 side toward the cavity 23 side.
In the direction from the 3rd side to the gas nozzle 25 side, a backflow prevention valve (not shown) that is closed closes the gas nozzle 25.

After the filling of the molten resin is completed, a high-pressure gas is injected from a gas injection machine as shown in FIG. Then, the check valve in the gas nozzle 25 is opened and gas is injected from the gas gate 24 into the cavity 23. Therefore, the gas is the molded product portion 23a of the cavity 23.
And the molded product has a hollow shape. After that, the mold is opened through the processes of cooling, holding pressure, and residual pressure release, and the molded product is taken out.

Since the product molded in this way is hollow, it is possible to reduce the weight and save the resin material, and by applying pressure from inside the molded product during gas injection, it is also useful for preventing sink marks.

[0007]

In the product molded by the above-mentioned conventional gas injection method, a gas injection hole (gas inflow hole) is formed in the molded product. Therefore, when the molded product is subjected to a plating treatment or the like, the plating liquid will enter the hollow portion of the product unless the gas inflow hole is completely sealed. Therefore, conventionally, the portion of the gas gate hole of the molded product after injection molding has been sealed by heat caulking or the like. However, such a hole sealing step increases the number of manufacturing steps after injection molding, which leads to an increase in cost. Therefore, it is a technical object of the present invention to provide a method for producing an injection-molded article having a hollow shape capable of sealing a gas inflow hole without adding an extra production step.

[0008]

In order to solve the above technical problems, the technical measures taken in claim 1 of the present invention are as follows: a cavity formed in a mold; A first resin retention part connected by a gate and the first resin retention part
The molten resin is injected from the second resin retaining portion side into a second resin retaining portion connected to the resin retaining portion by a second gate, and the second resin retaining portion is injected into the second resin retaining portion.
The first resin injection step of filling the resin retention portion, the first resin retention portion and the cavity with molten resin, and the first gate by sealing the second gate by a valve opening / closing mechanism provided in a mold. A second gate blocking step of blocking the resin retention part and the second resin retention part, and injecting gas from a gas gate provided in the first resin retention part to the first resin retention part and the molded product part. A gas injection step of forming a hollow portion by filling a gas, and the second gate portion is unsealed by the valve opening / closing mechanism provided in the mold to release the first resin retaining portion and the first resin retaining portion. The second gate communicating step of communicating the two resin retaining portions with each other, and the molten resin is injected again from the second resin retaining portion, and the first of the hollow portions formed in the gas injection step in the cavity All of the resin retention part and the molded product part A second resin injection step of filling the molten resin in part, is that a method for manufacturing an injection-molded article having a hollow shape made of.

In order to solve the above technical problems, the technical means taken in claim 2 of the present invention is characterized in that the first resin retaining portion is a cold runner. That is, the method is for producing an injection-molded product having a hollow shape.

In order to solve the above technical problems, the technical means taken in claim 3 of the present invention is characterized in that the second resin retaining portion is a hot runner. That is, the method for producing an injection-molded product having the hollow shape described above is employed.

After the molten resin is filled in the cavities and the first and second resin retaining portions in the first resin injecting step, the second gate is closed in the second gate blocking step to seal the first resin retaining section and the second resin. Cut off the retention area. Then, in the gas injection step, gas is injected from the gas gate to make the resin in the first resin retaining portion and the cavity hollow. Further, the first resin retaining portion and the second resin retaining portion are communicated with each other in the second gate communicating step, and the resin is filled again in the second resin injecting step. The filling amount of the resin at this time is such that the entire hollow part of the first resin retention part and a part of the hollow part of the cavity are filled. Therefore, the gas inflow hole generated in the first gate is
It is sealed by the resin filled in the resin injection process.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1 to 4 are partial cross-sectional views of an injection molding machine and a mold according to an embodiment of the present invention. FIG. 1 is a first resin injection step, FIG. 2 is a shutoff step, and FIG. FIG. 4 shows the gas injection step, and FIG. 4 shows the second resin injection step.

In FIG. 1, the mold 2 is composed of a fixed mold 2a and a movable mold 2b, and a cavity 3 in the mold 2 communicates with a cold runner 5 through a first gate 4. The cold runner 5 communicates with the hot runner 7 at the second gate 6. The other end of the hot runner 7 has an opening on the surface of the fixed mold 2a, and the injection nozzle of the injection molding machine 1 communicates with this opening. A gas nozzle 8a, which is in communication with the gas injection machine 8, is embedded in the movable mold 2b, and is in communication with the cold runner 5 through a gas gate 9. Inside the gas nozzle 8a, there is provided a check valve that opens in the direction from the gas nozzle 8a side to the cold runner 5 side and closes in the direction from the cold runner 5 side to the gas nozzle 8a side. . A second gate opening / closing mechanism 10 is embedded in the fixed mold 2a. The second gate opening / closing mechanism 10 has a valve pin 10a penetrating the hot runner 7, and the valve pin 8a is actuated leftward in the drawing by a driving means such as hydraulic pressure to shut off the second gate 6 (closed state).
Further, it operates to the right in the figure to open the second gate 6 (open state).

The operation of the injection molding apparatus having the above structure will be described below for each step.

First Resin Injection Step FIG. 1 shows the first resin injection step. In FIG. 1, the second
The gate opening / closing mechanism 10 operates the valve pin 8a to the right in the drawing, and the hot runner 7 and the cold runner portion 5 communicate with each other (open state). In this state, when the molten resin is injected from the injection molding machine 1, the molten resin first fills the hot runner 7 and then enters the cold runner 5 through the second gate 6. When the cold runner 5 is filled with the molten resin, the molten resin passes through the first gate 4 and the cavity 3
And the inside of the cavity 3 is filled with the molten resin.
At this time, the gas nozzle 8a and the cold runner 5 are operated by the action of the check valve provided inside.
Since the communication with is cut off, the molten resin does not enter the gas nozzle 8a.

Second Gate Blocking Step FIG. 2 shows the second gate blocking step. In FIG. 2, the injection of the molten resin from the injection molding machine 1 is stopped. At the same time, the second gate opening / closing mechanism 10 is operated by a driving means such as hydraulic pressure to move the valve pin 10a to the left in the drawing. Then, the tip of the valve pin 10a contacts the second gate 6 to seal the second gate 6 and cut off the communication between the hot runner 7 and the cold runner 5 (closed state).

Gas Injection Process FIG. 3 shows the gas injection process. In FIG. 3, with the second gate opening / closing mechanism kept closed, the gas injector 6 is operated to inject gas. Then, the check valve in the gas nozzle 8a is opened, and the gas enters the cold runner 5 from the gas gate 9 through the gas nozzle 8a, and the first
It penetrates into the cavity 3 through the gate 4. At this time, the hot runner 7 is blocked from the cold runner 5 by the second gate opening / closing mechanism 10, so that gas does not enter. Further, the gas that has entered the hot runner 7 and the cavity 3 preferentially flows in a region where the temperature is high, that is, a portion where the viscosity of the resin is low. Therefore, the resin does not flow to the mold surface having a relatively low temperature, and the hot runner 7 and the cavity 3
The resin in the hot runner 7 and the cavity 3 has a hollow shape because it flows in the vicinity of the central portion of the. After injecting a predetermined amount of gas, the pressure of the gas injection machine is controlled so that the hollow portion has a constant pressure, and the molten resin is held and cooled in that state.

Second Gate Communication Process FIG. 4 shows the communication process. In FIG. 4, the second gate opening / closing mechanism 10 is operated by a driving means such as hydraulic pressure to move the valve pin 10a to the right in the drawing. Then, valve pin 1
The sealing state of the second gate 6 by 0a is released (open state), and the hot runner 7 and the cold runner 5 are communicated with each other.

Second Resin Injection Step FIG. 5 shows the second resin injection step. In FIG. 5, a molten resin is injected from the injection molding machine 1. Since the second gate 6 has been opened by the second gate communication step, the molten resin enters the cold runner 5 through the second gate portion 6 and fills the hollow portion. At this time, the check valve in the gas nozzle 8a is closed, so that the molten resin does not enter the gas nozzle 8a. When the hollow portion of the cold runner 5 is filled with the resin, the molten resin further enters the hollow portion of the cavity 3 through the first gate 4. At this time, the resin that enters the cavity 3 does not need to fill the hollow portion, and may be a resin that closes the first gate 4.

Then, the mold is opened and the molded product is taken out.

The molded product molded through the above steps is the first part which is the connecting portion between the cavity 3 and the cold runner 5.
The gate 4 serves as a gas inflow hole in the molded product, and this gas inflow hole is sealed with resin. Therefore, the process can be directly transferred to the subsequent process such as the plating process, and there is no need to provide the gas inflow hole sealing process such as the heat caulking process in the middle of the process.

[0023]

The invention of claim 1 has the following effects.

In the injection molding method, since the resin is injected again after the gas injection molding to seal the gas inflow hole, there is no need to provide a gas inflow hole sealing step after the resin molding, and the cost is not increased. It is possible to seal the gas inflow hole.

The invention of claim 2 has the following effects.

In the injection molding method, since the resin is injected again after gas injection molding to seal the gas inflow hole, there is no need to provide a gas inflow hole sealing step after resin molding, and the cost is not increased. It is possible to seal the gas inflow hole. Further, by using the cold runner as the first resin retaining portion communicating with the molded product portion, the resin material can be saved.

The invention of claim 3 has the following effects.

In the injection molding method, since the resin is injected again after the gas injection molding to seal the gas inflow hole, there is no need to provide a gas inflow hole sealing step after the resin molding, and the cost is not increased. It is possible to seal the gas inflow hole. Further, by using the hot runner as the second resin retaining portion that communicates with the first resin retaining portion, the resin in the hot runner used at the time of previous molding can be utilized at the time of molding this time, and further saving of resin material can be achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing a first resin injection step in the present invention.

FIG. 2 is a diagram showing a second gate blocking step in the present invention.

FIG. 3 is a diagram showing a gas injection step in the present invention.

FIG. 4 is a diagram showing a second gate communication step in the present invention.

FIG. 5 is a diagram showing a second resin injection step in the present invention.

FIG. 6 is a diagram showing a resin injection process in a conventional technique.

FIG. 7 is a diagram showing a gas injecting step in the prior art.

[Explanation of symbols]

 1 Injection Molding Machine 2 Mold 2a Fixed Mold 2b Movable Mold 3 Cavity 4 First Gate 5 Cold Runner (First Resin Retaining Part) 6 Second Gate 7 Hot Runner (Second Resin Retaining Part) 8 Gas Injection Machine 8a Gas Nozzle 9 gas gate 10 second gate opening / closing mechanism (valve opening / closing mechanism) 10a valve pin

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shogo Izawa 2-1, Asahi-cho, Kariya city, Aichi Prefecture Aisin Seiki Co., Ltd. (72) Inventor Mitsuru Gotanda 2-1-1, Asahi-cho, Kariya city, Aichi prefecture Aisin Seiki Co., Ltd. (72) Inventor Toshihiko Saito 2-1, Asahi-cho, Kariya City, Aichi Aisin Seiki Co., Ltd.

Claims (3)

[Claims] 1. A cavity formed in a mold, a first resin retaining portion connected to the cavity by a first gate, and a second resin retaining portion connected to the first resin by a second gate. A first resin injection step of injecting a molten resin into the resin retention part from the second resin retention part side to fill the second resin retention part, the first resin retention part and the cavity with the molten resin; A second gate shut-off step of sealing the second gate by a valve opening / closing mechanism provided inside to shut off the first resin retention part and the second resin retention part; A gas injection step of forming a hollow portion by injecting gas from the gas gate provided to fill the first resin retention portion and the molded product portion with gas; and the valve opening / closing mechanism provided in the mold. The second
A second gate communication step of releasing the sealing of the gate part to communicate the first resin retention part and the second resin retention part, and injecting molten resin again from the second resin retention part to generate the gas. A second resin injection step of filling the entire first resin retention portion and a part of the molded product portion with molten resin in the hollow portion formed in the injection step, Method of manufacturing injection molded products. 2. The method for manufacturing an injection-molded article having a hollow shape according to claim 1, wherein the first resin retention portion is a cold runner. 3. The method for producing an injection-molded article having a hollow shape according to claim 1, wherein the second resin retaining section is a hot runner.