JPH04284213A - Gas injection molding method - Google Patents

Abstract

PURPOSE:To bond securely with the wall face of a cavity by filling the resin in the cavity in the state of opening the mold to a certain extent that the resin is not leaked. CONSTITUTION:First, a mold 11b on the movable side is moved forward to the side of a mold 11a on the fixed side, and the mold is closed. At that time, a small space X is formed between the molds 11a and 11b. In said state, molten resin is injected into a mold 11, and the molten resin is filled in a resin filling section 12 through a sprue 13. After that, the mold 11b is further moved forward to the side of mold 11a, and the state of closing the mold 11 completely is formed. Then, a gas injection needle 15 is moved forward in the arrow A direction, and gas is injected into the mold 11. After that, the gas is exhausted and then the gas injection needle 15 is moved back in the arrow B direction and a molded product is released.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention involves filling a cavity of an injection mold with resin and then injecting gas into the cavity to form a void in a desired area of the filled resin in the cavity. This invention relates to a gas injection molding method.

0002

2. Description of the Related Art Sinks and the like occur in parts of molded products where the wall thickness is thicker than other parts, such as rib parts. For this reason,
Conventionally, by injecting gas into this rib part,
A gas injection molding method has been proposed in which the wall thickness is reduced to prevent the occurrence of sink marks and the like.

[0003] This gas injection molding method is carried out by filling the cavity with resin while the mold is completely closed, and then injecting gas into the desired area while leaving the mold in that state. .

0004

[Problems to be Solved by the Invention] However, in the conventional gas injection method described above, there are problems with the filling state of the resin in the mold (that is, how well the resin fits), the timing of gas injection into the mold, and the gas injection method. In some cases, gas could not be successfully injected into a desired area due to pressure or the like. Furthermore, gas may sometimes flow into areas where it is desired to avoid gas flow, resulting in a situation where the desired molded product cannot be successfully obtained.

For example, when gas is injected, the amount of resin filled into the mold is set to be slightly smaller than in the case of normal molding without gas injection, and the gas is injected in this state. At this time, if the resin is not in close contact with the cavity wall surface within the mold, the injected gas may break through the resin surface.

FIG. 6 shows a state in which a defect has occurred in a molded product 32 on which a reinforcing rib 31 is formed, and FIG. 7 shows a cross-sectional view of the portion of the reinforcing rib 31 where the defect has occurred.

In a good molded product, a void 33 (the part surrounded by the solid line and the dashed-dotted line) is formed by injecting gas into the thick part that is the connection part between the main body part 33 and the reinforcing rib 31. However, due to the occurrence of the above-mentioned defect, the injection gas breaks through the surface 33a of the main body portion 33, and the hollow portion 33 becomes V-shaped.

[0008] Such a situation may be improved by adjusting the gas pressure or the timing of gas injection, but these adjustments are troublesome, and even if they can be adjusted, the molding conditions will change. As a result, there was a possibility that defective products would be produced again.

[0009] Incidentally, the occurrence of such defective products occurs because the resin filled in the mold is not in close contact with the cavity wall surface, as described above. That is, if the resin filled in the mold is in close contact with the cavity wall surface, the above problem will not occur.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a gas injection molding method which ensures that the resin filled in the mold is in close contact with the wall surface of the cavity.

[0011]

[Means for Solving the Problems] In order to solve the above problems, the gas injection molding method of the present invention involves filling the cavity of an injection mold with resin, and then injecting gas into the cavity. In the case where a cavity is formed in the desired area of filling resin in the cavity, the resin is filled into the cavity with the mold slightly open to the extent that the resin does not leak, and then the mold is completely closed before filling the cavity. Gas is injected into the cavity.

0012

[Operation] Fill the cavity with resin while keeping the mold slightly open to prevent resin from leaking, and then close the mold completely. As a result, the resin filled in the mold comes into close contact with the wall surface of the cavity in the mold by closing the mold, and conditions for gas injection are established. Thereafter, by injecting gas into the cavity, it is possible to accurately inject gas into a desired region.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 4 and 5 show an example of a molded article 1 molded by the gas injection molding method of the present invention.

This molded product 1 includes a main body portion 2 formed in a downward U-shape, and a plurality of reinforcements (in this embodiment, two reinforcements are formed) formed on the back surface of the main body portion 2. A hollow portion 4 is formed along the reinforcing ribs 3 in a thick wall portion that is a connecting portion between the main body portion 2 and each reinforcing rib 3.

FIGS. 1 to 3 show the structure of an injection mold for molding the molded article 1 having the above structure and the molding procedure thereof.

The mold 11 of this embodiment is the mold 11 on the fixed side.
A resin-filled part (cavity part) 12 whose inner surface has the outer shape of the molded product 1 described above is formed at the joint surface between the mold 11b on the moving side and the mold 11b, and corresponds to the center part of the front side of the molded product 1. A sprue 13 for filling resin is molded into the portion 12a. In this embodiment, this sprue 13 is provided on the stationary mold 11a.

Further, a gas injection path 14 for injecting gas is formed so that the tip 14b reaches a portion 12b of the resin filled portion 12 corresponding to the reinforcing rib 3 of the molded product 1. In this embodiment, this gas injection path 14 is provided in the mold 11b on the moving side.

That is, in this embodiment, gas is injected from the back side of the reinforcing rib 3.

Further, the gas injection passages 14 may be provided at a plurality of locations for one reinforcing rib 3 depending on the size of the molded product 1 and the length and thickness of the reinforcing rib 3.

A gas injection needle 15 is disposed at the injection port 14a of the gas injection path 14 formed in this manner.

Although not shown, the gas injection needle 15 is provided so as to be able to reciprocate in the direction of arrow A and the direction of arrow B in the drawing by hydraulic pressure, gas pressure, or the like.

However, the gas injection needle 15 is connected to the mold 1.
It is also possible to provide it by directly embedding it in 1b.

Next, a method of molding the molded product 1 shown in FIG. 4 using the mold 11 having the above structure will be explained.

First, the movable mold 11b is advanced toward the stationary mold 11a, and the mold 11 is closed. At this time, the mold 11 is left slightly open to the extent that the filled resin does not leak to the outside. That is, a slight gap x is maintained between the stationary mold 11a and the movable mold 11b (see FIG. 1).

In this state, an injection molding machine (not shown) is driven to inject the molten resin into the mold 11, and the sprue 1 is injected into the mold 11.
3, the resin filling part 12 is filled with molten resin.

Thereafter, the movable mold 11b is further advanced toward the stationary mold 11a to reduce the gap x to zero. That is, the mold 11 is completely closed (see FIG. 2).
.

[0028] As a result, the resin filling portion 12 in the mold 11
The resin filled in (hereinafter referred to as filled resin) will surely come into close contact with the wall surface of the resin filling part 12.

Thereafter, the gas injection needle 15 is moved forward in the direction of arrow A and brought into pressure contact with the gas injection port 14a of the mold 11. That is, the connection is made such that the gas injected from the gas injection needle 15 is injected into the gas injection path 14 without leaking to the outside of the mold from the injection port 14a.

Subsequently, gas is injected into the mold 11 (specifically, the portion 12b of the resin filling portion 12 corresponding to the reinforcing rib 3) through the gas injection needle 15.

The injected gas flows inside the thick part of the filled resin (the thick part that is the connection part between the main body part 2 and the reinforcing rib 3 of the molded product 1) and along the reinforcing rib 13, as shown in FIG. 3 and 5 are formed. The injection gas does not reach the resin surface because the filled resin is in close contact with the wall surface of the resin filled portion 12.

Thereafter, after degassing, the gas injection needle 15 is moved back in the direction of arrow B, and the molded product 1 is taken out through a cooling process and a mold opening process.

In the above embodiment, the gas injection needle 15 is described as a movable type, but in the case of an embedded type as described above, the step of moving in the direction of arrow A or B becomes unnecessary.

Furthermore, the material of the resin is not particularly limited and may be any material as long as it can be injection molded. For example, it is also possible to use thermosetting resin.

Furthermore, the gas used is preferably an inert gas, such as nitrogen.

[0036]

[Effects of the Invention] In the gas injection molding method of the present invention, resin is filled into the cavity with the mold slightly opened to the extent that the resin does not leak, and then the mold is completely closed before being filled into the cavity. Since the gas is injected, the filling resin is in close contact with the wall surface of the cavity when the gas is injected, so that the gas can be reliably injected into the target area.

[0037] Since the gas injection timing can be advanced, the molding cycle time can be shortened.

[0038] Since the time for filling the resin into the mold can be shortened and the temperature of the resin inside the mold can be uniformly lowered, it is easy to set the gas injection pressure and injection timing.

[0039] Since the molding cycle time can be shortened, various effects such as improved productivity can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of an injection mold to which the gas injection molding method of the present invention is applied.

FIG. 2 is a sectional view showing the structure of an injection mold to which the gas injection molding method of the present invention is applied.

FIG. 3 is a sectional view showing the structure of an injection mold to which the gas injection molding method of the present invention is applied.

FIG. 4 is an overall perspective view showing an example of a molded article molded by the gas injection molding method of the present invention.

FIG. 5 is a partial cross-sectional view showing an example of a molded article molded by the gas injection molding method of the present invention.

FIG. 6 is a perspective view showing an example of a molded article molded by a conventional gas injection molding method.

FIG. 7 is a partial cross-sectional view showing an example of a molded article molded by a conventional gas injection molding method.

[Explanation of symbols]

1 Molded product 3 Reinforcement rib 4. Vacant space 11 Mold 12 Resin filling part (cavity part) 14 Gas injection path

Claims (1)

[Claims] 1. A gas injection molding method in which a cavity of an injection mold is filled with resin, and then gas is injected into the cavity to form a void in a desired region of the filled resin in the cavity. A gas injection molding method characterized in that a cavity is filled with resin while the mold is slightly opened to prevent the resin from leaking, and then gas is injected into the cavity after the mold is completely closed.