JPH0259048B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an injection compression molding method in which a molten molding material is injected into a mold cavity and compression molded before solidifying.

Conventionally, molding material was injected into the cavity and filled.
After the gate part has solidified, the movable mold is moved before the molding material has solidified, and the molding material in the cavity is compressed. A method of applying pressure only locally is disclosed in, for example, Japanese Patent Laid-Open No. 55-97941, and is well known, but these methods fill the cavity with resin to every corner and then apply pressure, so high injection pressure cannot be applied. Either it is not possible to selectively apply pressure only to the required area, or even if it is possible, it is not possible to form a complex product shape on the front of the pressure plunger, or it is not possible to form a complex product shape on the front of the pressure plunger, When molding, the shrinkage rate during the shrinkage process after molding differs depending on the part of the product, so even if you design a mold that takes into account the temporary shrinkage, the product molded with the mold will always have dimensional defects. The problem was that the molds had to be modified repeatedly through trial and error.

In the present invention, a molding material with a volume smaller than the cavity volume is injected into the cavity from the injection mold gate, and after the gate part solidifies, the compression mold is protruded into the cavity, and the compression mold tip molding surface and the injection mold inner surface are molded. The object of this invention is to eliminate the drawbacks of the conventional method by compression molding between the molding surface and the molding surface and simultaneously forming an annular bottleneck around the outer periphery of the molding surface to suppress the flow of the molding material within the region.

Next, an embodiment of the apparatus used in the method of the present invention will be described. A is an injection mold with the first plate 1,
It has a three-plate structure of a second plate 2 and a third plate 3, and a cavity 4 is formed on the opposing surface of the second plate 2 and third plate 3, and a compression mold B is installed in the third plate 3. 4. It is attached so that it can appear and disappear freely. A pinpoint gate 7 opens into the cavity 4 from the gate 5 through the runner 6 in the first plate 1. As shown in FIG. 2, a textured surface 8 and a recess 9 for forming a fitting convex part with other parts are formed on the inner surface of the cavity of the second plate 2 facing the compression mold B. A molding surface 10, a convex portion 11 for forming a fitting recess with other parts are formed, and an annular protrusion 12 is further formed on the outer periphery of the convex portion 11.
is formed. 13 is a nozzle of a molding machine that can move toward and away from the gate 5.

Next, the method of the present invention will be explained. With the compression molding mold B retracted as shown in Fig. 1, the nozzle 13
is brought into contact with the gate 5 and a molding material 14 such as a crystalline polymer material is injected into the cavity 4 via the runner 6 and the pinpoint gate 7. At this time, the injection volume is smaller than the cavity volume and is the amount necessary to form the final molded product. After the gate 5 has solidified, the compression mold B is projected into the cavity 4 as shown in FIG. A bottleneck 16 is formed, and the molding material 14 is flowed and compressed to every corner of the cavity 4 to form a molded product 17. After cooling and solidifying, the third plate 3 is moved back to release the molded product 15 from the second plate 2, and at the same time the pinpoint gate 7 is cut, and then the compression mold B is moved back to release the molded product 17. Then, an ejector pin (not shown) is ejected to release the molded product 17 from the third plate 3.

According to the present invention, a volume of molding material smaller than the cavity volume is injected into the cavity from the injection mold gate, and after the gate part solidifies, the compression mold is protruded into the cavity, and the molding surface formed on the inner surface of the compression mold and the compression mold are Since compression molding is performed with the molding surface at the tip of the mold, the unhardened molding material can effectively flow to every corner of the cavity, and the molding material in the area surrounded by the bottleneck can flow out of the bottleneck. The flow is suppressed and the molding material pressure in the region is kept relatively high,
During the cooling and hardening process, it is possible to block out harmful influences from outside the area, allowing selective precision molding of only the necessary areas of the product, and improving the shape, dimensions, and appearance of the product parts within the area. The requirements can be met, and the need for mold modification can be greatly reduced. In particular, the effects of the present invention are remarkable when molding crystalline polymer materials such as polyolefins and polyamides whose molecular orientation differs depending on the part of the product and therefore the molding shrinkage rate varies depending on the part of the product.

[Brief explanation of drawings]

FIG. 1 is a front cross-sectional view during injection according to the method of the present invention;
Figure 2 shows the inner molding surface of the second plate in Figure 1, Figure 3 shows the molding surface at the tip of the compression mold in Figure 1, and Figure 4 shows the compression mold in Figure 1 inside the cavity. FIG. 3 is a front cross-sectional view when compression molding is performed to protrude. A...Injection mold, B...Compression mold, 4...Cavity, 5...Gate, 6...Runner, 7...
Pinpoint gate, 8... Grained surface, 10... Molding surface, 12... Ring projection, 16... Bottle, 14...
Molding material injected into the cavity, 17...molded product.

Claims (1)

[Claims] 1. A compression mold is installed in the cavity of the injection mold so that it can freely protrude and retract, and the molding surface on the inner surface of the injection mold and the molding surface on the front surface of the compression mold are arranged to face each other, and a ring protrusion is formed on the outer periphery of the molding surface of the compression mold. forming a strip, injecting a volume of synthetic resin molding material smaller than the cavity volume into the cavity from the gate of the injection mold while holding the compression mold in the retracted position, and then ejecting the compression mold into the cavity; A bottleneck is formed between the ring protrusion on the outer periphery of the molding surface at the tip of the compression mold and the inner molding surface of the injection mold, suppressing the flow of the molding material outside the bottleneck, and relatively controlling the pressure of the molding material inside the bottleneck. An injection compression molding method in which compression molding is cooled and solidified while being held at a high temperature.