JPH0635138B2 - Injection compression molding method and apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to an injection compression molding method and apparatus.

(B) Conventional Technology As a conventional injection compression molding device, for example, Japanese Patent Laid-Open No. 61-
There is one disclosed in Japanese Patent No. 283520. In the injection compression molding apparatus shown in the figure, a fixed mold and a movable mold are attached to a fixed plate and a movable plate of a mold clamping device, and when the mold is closed, the convex and concave portions of the fixed mold and the movable mold fit together. However, when the molds are not completely in close contact with each other, that is, when there is a gap between the parting surfaces of the two dies, the molds are temporarily closed, injection is performed in this stopped state, and then The movable platen is moved forward and the mold is clamped to compress the molded product. This makes it possible to obtain a molded product with less distortion and high shape accuracy.

(C) Problems to be Solved by the Invention However, in the conventional injection compression molding apparatus as described above, a normal resin is used to mold a solid molded product in which the resin is clogged, or foamability is increased. Although it is possible to mold a porous molded product having a large amount of foamy air inside by using a resin, there is a problem that a hollow molded product cannot be manufactured.

The present invention aims to solve such problems.

(D) Means for Solving the Problems The present invention is to provide a cavity C of the molds 14 and 16 before completion of mold closing.
By injecting the molten resin 30 into a solid state, injecting a gas into the molten resin 30 to form a balloon-shaped parison 30a, and performing mold clamping during or after injecting the gas. In the injection compression molding method in which the parison 30a is compressed to mold the molded product 30b, the gas introduction pipe 20 is projected near the central portion of the molten resin 30 in the cavity C at the time of gas injection, and retracts after the gas injection. By doing so, the above problem is solved.

Further, it has a male mold 14 and a female mold 16, and the male mold 1
4 or the female mold 16 is formed with a resin passage 18 passing through the female mold 16 and opening to a wall surface forming a part of the wall of the cavity C. The resin passage 18 is formed in the male mold 14 or the female mold 16 through the resin passage 18. In an injection compression molding apparatus in which a gas introduction pipe 20 having a gas ejection port 20a extending through the wall surface forming a part of the wall of C and extending into the cavity C is formed, the gas introduction pipe 20 is provided with the gas injection pipe 20. By having the gas introduction pipe drive devices 21 and 22 which are formed by the outlet 20a and the gas passage 20b and move the gas introduction pipe 20 forward and backward, the gas introduction pipe 20 is further retracted after the gas is injected. The above problem can also be solved by making the tip surface and the cavity C surface flush with each other and closing the gas ejection port 20a.

(E) Action Molten resin is injected into the cavity before the mold is closed so as to form a solid mass. A gas introduction pipe is projected near the central portion of this mass, and a predetermined amount of gas such as air is injected. This causes the molten resin to become a balloon-shaped parison. After injecting the gas, the gas introducing pipe is retracted, and the parison is pressure-molded by performing mold clamping with the tip surface of the gas introducing pipe and the cavity surface flush with each other. After cooling the mold, open it. By doing so, a hollow molded article can be manufactured.

(F) Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

1 to 4 show an embodiment of the present invention. The fixed platen 10 and the movable platen 12 of the mold clamping device are provided so as to face each other. The movable platen 12 can be moved by a mold clamping cylinder (not shown) in a direction toward and away from the fixed platen 10. A male die 14 is attached to the fixed platen 10, and a female die 16 is attached to the movable platen 12. The male mold 14 is formed in a columnar shape having two stepped protrusions. The female die 16 is formed to have a "concave" cross section. The middle outer diameter portion of the male mold 14 can be fitted into the cylindrical hole of the female mold 16. Female type 16 and male type 1
In the state in which the molds 4 and 4 are fitted to each other, a cavity C having a "U" -shaped cross section is formed by the space between the molds 14 and 16. The dimensions of the fitting portions of the male mold 14 and the female mold 16 are selected in the clearance that allows the air in the cavity C to be discharged when the female mold 16 further moves in the mold closing direction from the position shown in FIG. Has been done.

A resin passage 18 that opens into the cavity C is formed in the male mold 14. That is, the resin passage 18 is provided from the wall surface on the left side of the male mold 14 toward the center of the mold, bends upward in the middle, and opens at the center of the upper surface of the mold. Molten resin can be injected into the cavity C through a resin passage 18 from an injection device (not shown).

Further, the female mold 16 is formed with a gas introduction pipe 20 which can be moved forward and backward to the center of the molten resin 30 in the cavity C by a pneumatic cylinder 21 piston 22.

That is, the gas introduction pipe 20 can extend to the center of the cavity C by penetrating the upper surface and the lower surface of the female die 16 in the figure. The tip surface of the gas introduction pipe 20 is
It is arranged at a position facing the opening of the resin passage 18. As shown in FIG. 4, the gas introduction pipe 20 is formed of the gas ejection port 20a and the gas passage 20b, and the tip end surface of the gas introduction pipe 20 and the cavity C surface are flush with each other when retreating after the gas injection. The gas ejection port 20a is closed. As will be described later, after the molten resin 30 is supplied into the cavity C in a solid state, the gas introduction pipe 20 is projected near the central portion of the molten resin 30 by the operation of the piston 22 of the pneumatic cylinder 21, which is not shown. It is possible to supply air from the air source into the molten resin 30 through the gas introduction pipe 20.

Next, the operation of this embodiment will be described. The movable platen 12 is the first
It is stopped once it has moved to the middle position of the mold closing shown in the figure. Next, the molten resin 30 is injected from the injection device (not shown) into the cavity C through the resin passage 18 in a highly viscous state. Since the molten resin 30 is injected before the molds 14 and 16 are closed, the injection pressure can be low. After that, the gas introduction pipe 20 is caused to project near the center of the molten resin 30 by the operation of the piston 22 of the pneumatic cylinder 21. As a result, the molten resin 30 is in the form of a solid that encloses the gas ejection port 20a of the gas introduction pipe 20. Next, a predetermined amount of air is blown into the molten resin 30 from an air source (not shown) through the gas introduction pipe 20 and the gas ejection port 20a. This allows molten resin 3
As shown in FIG. 2, 0 is a balloon-shaped parison 30a having air therein. After the injection of air is completed, the gas introducing pipe 20 is retracted, and when the tip surface of the gas introducing pipe 20 and the cavity C surface are flush with each other, the movable platen 12 is driven again to perform mold clamping as shown in FIG. . This makes the parison 30
A is a hollow molded product 30b having a "U" -shaped cross section. Both molds 14 and 16 are cooled, the movable platen 12 is moved in the mold opening direction to open the movable mold 16, and the molded product 30b is taken out.

By the method as described above, the balloon-shaped parison 30a is compression-molded according to the cavity C, so that a hollow molded product having a uniform wall thickness can be manufactured.

In the above description, the resin passage 18 is provided in the male mold 14,
Although the gas introduction pipe 20 is provided in the female die 16, they may be arranged in reverse. In addition, the resin passage 18
And the gas introduction pipe 20 to one mold, for example, the fixed mold 1.
No. 4 may be provided on the mating female mold 16, for example.

Further, in the above description, the movable platen 12 is stopped at an intermediate position of mold closing to inject the molten resin 30, but the movable platen 12 is not stopped, and the molten resin 30 is moving at a slight speed in the mold closing direction. It is also possible to perform 30 injections.

Further, although the injection of air is performed after the injection of the molten resin 30 is finished, the injection of the air can be started during the injection of the molten resin 30.

Although the injection of air was supposed to be completed before the mold clamping,
It is also possible to continue the injection of air during compression molding or cooling.

Further, in the above description, air is used as the gas injected into the molten resin 30, but a gas other than air, for example, nitrogen may be used.

(G) Effects of the Invention As described above, according to the present invention, 1. It is possible to manufacture a hollow molded product having a uniform wall thickness.

2. Even if the molded product has a thin portion or a rib portion, these portions can be surely made hollow.

3. Since the molten resin is injected into the cavity before the mold is closed, the injection pressure may be low and the apparatus can be inexpensive.

4. Since the gas pressure acts on the inside of the molded product until it is cooled and solidified, a molded product having a good surface without sink marks can be obtained.

5. No trace of gas introduction pipe.

[Brief description of drawings]

FIG. 1 is a sectional view of an injection compression apparatus according to an embodiment of the present invention, FIG. 2 is a view showing a state in which gas injection is completed, and FIG. 3 is a view showing a state in which compression molding is completed. FIG. 4 is an enlarged view of the gas introduction pipe. 10: Fixed plate, 12: Movable plate, 14: Male type, 16
...... Female type, 18 …… Resin passage, 20 …… Gas inlet tube, 2
0a ... gas outlet, 20b ... gas passage, 21 ... pneumatic cylinder, 22 ... piston, 30 ... molten resin, 3
0a ... Parison, 30b ... Molded product, C ... Capity.

Claims (3)

[Claims] 1. A molten resin (30) is injected into a cavity (C) of a mold (14, 16) before completion of mold closing so as to form a mass, and a gas is injected into the molten resin (30). An injection compression molding method of injecting to form a balloon-shaped parison (30a) and compressing the parison (30a) to mold a molded article (30b) by performing mold clamping during or after injecting the gas. In the press molding method, the gas introduction pipe (20) is projected near the center of the molten resin (30) in the cavity (C) at the time of gas injection, and is retracted after the gas injection. 2. A male mold (14) and a female mold (16) which pass through the male mold (14) or the female mold (16) and a part of the wall of the cavity (C). A resin passageway (18) opening to the wall surface of the male mold (1
4) Or gas introduction into the female mold (16) having a gas ejection port (20a) extending through the wall surface forming a part of the wall of the cavity (C) and extending into the cavity (C). In an injection compression molding apparatus in which a pipe (20) is formed, the gas introduction pipe (20) is formed by the gas ejection port (20a) and a gas passage (20b), and the gas introduction pipe (20) is Gas introduction tube drive device (21,
22). 3. When retreating after injecting gas, the tip surface of the gas introduction pipe (20) and the surface of the cavity (C) are flush with each other, and the gas ejection port (20a) is closed. The injection compression molding apparatus according to claim 2.