JPS6021225A - Injection compression molding method - Google Patents

Abstract

PURPOSE:To shorten a closing cycle by simplifying structure of a mold, by a method wherein after the majority of molten resin has been injected and filled, reclosing is done while injection and filling of the remaining molten resin is being kept on, in an injection compression molding method. CONSTITUTION:When a closing cylinder 11 is made to advance and operate by a controller 13, a moving mold 5 is moved toward a stationary mold 6 and suspended at a position P2 decided in consideration of compressing stock of molten resin 9 in relation to thickness of a molded article. Then the molten resin 9 in an injection cylinder 8 is injected and filled within a cavity 10. When about an extent of 80-90% of the cavity is filled with the molten resin 9 reclosing instructions RPC is applied to a hydraulic pressure control circuit 13 from a timer circuit 14, through which reclosing is done, the moving mold 5 is moved up to a position P3 of the thickness of the molded article and amount corresponding to the compressing stock is compressed. After the molten resin 9 has been cooled and cured, the closing cylinder 11 is retreated and returned to a mold opening position P1.

Description

[Detailed description of the invention] The present invention relates to an injection compression molding method.

In general, articles molded by injection molding methods, particularly relatively large and flat articles, suffer from major drawbacks such as warpage and racking.

As a method to solve this problem, after the mold is clamped to a position that takes into account the compression allowance, molten resin is injected and filled into the mold, and after the injection filling is completed, the mold is clamped again to compress the compression allowance. An injection compression molding method is known.

However, in this injection compression molding method, when the mold is re-clamped after injection filling is completed, if the filled resin has not solidified, the resin in the mold will flow back through the gate, launch, and stool. Although a backflow prevention mechanism such as a cutting mechanism is provided, it is also necessary to re-clamp the mold after waiting for the resin at the gate to cool and solidify.

However, providing a backflow prevention mechanism has the disadvantage of complicating the mold. On the other hand, if the mold is re-clamped after waiting for the resin at the gate to cool and solidify, the cooled and solidified resin will move and the compressive force between the gate and the end will become uneven, etc. However, it has the disadvantage of being prone to poor dimensional accuracy and poor appearance (flow marks).

Another drawback is that the mold clamping cycle time becomes longer due to the start-up delay of the hydraulic system from the completion of injection to the re-clamping of the mold. In particular, the conventional mold clamping cycle is low pressure high speed → (injection filling) → low pressure low speed → high pressure low speed, so the mold clamping cycle is long and cannot be said to be highly efficient.

Here, the object of the present invention is to be able to simplify the structure of the mold and at the same time obtain a molded product with good quality.
Another object of the present invention is to provide an injection compression molding method that can also shorten the mold clamping cycle time.

Therefore, in the present invention, in the injection compression molding method, the mold is clamped to a position that takes into account the compression allowance, then the molten resin is injected and filled into the mold, and then the mold is re-clamped to compress the compression allowance. The above object was achieved by injecting most of the resin and then re-clamping the mold while continuing to inject and fill the remaining molten resin.

In short, if most of the molten resin is injected and filled, and the mold is re-clamped while continuing to inject and fill the remaining molten resin, the mold can be re-clamped without a backflow prevention mechanism, or even if the resin at the gate is not cooled and solidified. Since the resin filled in the mold does not flow back when the mold is re-clamped, the structure of the mold can be simplified. Furthermore, since the molten resin is compressed without being cooled and solidified, a uniform compressive force is applied to the gate and end portions of the molded product, resulting in a molded product with good dimensional accuracy and appearance. Furthermore, since re-clamping is started at the time when most of the molten resin has been injected and before the injection and filling of the mold is completed, it is possible to shorten the mold-clamping cycle time.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows an injection compression molding apparatus implementing the method of the invention. In the figure, a fixed die plate 1 and a fixed plate 2 are connected to each other via a plurality of tie bars 3. The tie bar 3 has the fixed die plate 1
A movable die plate 4 that moves toward and away from the die is slidably provided.

A movable die 5 is attached to the movable die plate 4, and a fixed die 6 is attached to the fixed die plate 1. An injection lower is formed in the fixed mold 6, and a molten resin 9, for example, polycarbonate having a molecular weight of about 20,000 to 30,000, is injected by an injection cylinder 8 through the injection lower into both pot molds 5.
, 6 is injected into a cavity 10 formed therein.

On the other hand, a mold clamping cylinder 11 is attached to the fixed plate 2, and the tip of a mold clamping ram 12 of the mold clamping cylinder 11 is connected to the movable die plate 4. The operation of the mold clamping cylinder 11 is controlled by a hydraulic control circuit 13. The hydraulic control circuit 13 operates at low pressure (approximately 50 to 80 to 9/crIL・G) and at high speed (approximately 30 m/g) from the open state of the movable mold 5 to a position that takes into account the compression allowance for the molten resin 9 in the thickness of the molded product. (seconds or more), then the injection cylinder 8
When the re-clamping command RPC is given from the timer circuit 14 after the operation of , the movable mold 5 is further operated at high pressure (xooxy7'α・0 or higher in 80% or more of the mold clamping capacity of the molding machine) and at high speed by the compression allowance. The operation of the mold clamping cylinder 11 is controlled so that the mold clamping cylinder 11 moves forward at a speed of about 30 m/sec or more.

The timer circuit 14 issues a re-clamping command R when the operating time of the injection cylinder 8 reaches a preset time T.
The PC is output to the hydraulic control circuit 13.

In this embodiment, the molten resin 9 enters the cavity 10 by approximately 8
Set time T is the time it takes for injection filling to be approximately 0 to 90%
It is preset as .

Next, an injection compression molding method using the above apparatus will be explained with reference to FIG. Now, the movable mold 5 is at the opening limit rijtP1
In this state, when the mold clamping cylinder/11 is advanced by the control device 13, the movable mold 5 is moved to the fixed mold 6.
The molded article is moved forward at low pressure and high speed, and is stopped at a position P2, which takes into account the compression allowance for the molten resin 9 in the thickness of the molded product. Thereafter, the injection cylinder 8 is operated while the hydraulic pressure of the mold clamping cylinder 11 is maintained at a low pressure. When the injection cylinder 8 is actuated, the molten resin 9 in the injection cylinder 8 is injected and filled into the cavity 10 through the injection lower. At this time, due to the injection pressure of the molten resin 9, the movable mold 5 is slightly moved in the direction of retreating from the fixed mold 6 and in the direction of opening the tab BFM.

Eventually, the operating time of the injection cylinder 8 is determined by the timer circuit 14.
When the set time T has elapsed and about 80 to 90% of the molten resin 9 is injected and filled into the shim cavity 10, the timer circuit 14 issues a re-clamping command 1 (, PC
is output to the hydraulic control circuit 13. Then, the mold clamping cylinder 11 is advanced by the hydraulic control circuit 13 at high pressure and high speed, and the mold is clamped again. During this re-clamping, the movable mold 5 is moved to the molded product thickness position P3, and the mold is compressed by the compression amount. During this time, the injection cylinder 8 continues to inject and fill the remaining 9 pieces of molten resin.

After that, the molten resin 9 injected and filled into the cavity 10 is in a state where the compression allowance is compressed by re-clamping.
After the clamping cylinder 11 is cooled and solidified, the mold clamping cylinder 11 is moved backward to return to the initial position and the pawl opening limit fitP1. By repeating this cycle, the product is formed.

Therefore, according to this embodiment, the molds are clamped to a position taking into account the compression allowance, and then the molten resin 9 is injected and filled into the cavities 10 of the molds 5 and 6, and the molten resin 9 is about 80 to 90% At the time of injection filling, the mold is re-clamped while continuing the injection filling of the remaining molten resin 9, so that the injection filling of the remaining molten resin 9 and the re-clamping are performed at the same time. For example, even if a backflow prevention mechanism such as a gate cut mechanism is not provided, or even if the molten resin 9 at the gate part is not cooled and solidified, the molten resin 9 in the cavity 10 will flow back when the mold is re-clamped. Never.

This eliminates the need to provide a backflow prevention mechanism, so the structure of the molds 5 and 6 can be simplified. Also, cavity 1
Since the molten resin 9 in the molded product can be compressed to the thickness of the molded product without cooling and solidifying, uniform compressive force is applied to the gate and end portions of the molded product, resulting in good dimensional accuracy and appearance, and no internal distortion. It is possible to obtain molded products without

In particular, since the re-clamping process is started before the completion of injection filling and is performed at high pressure and high speed, the mold-clamping cycle time can be shortened compared to the conventional mold-clamping cycle shown by the broken line in Figure 2. In addition, since the surface of the molten resin 90 in the cavity 10 can be compressed without giving time for cooling and solidifying, even thin-walled large molded products can be manufactured with good quality. By the way, according to the method of this embodiment, the thickness is 1,
Even products with a projection area of about 0 to 6.6 cm, a projected area of 800 c+n'' or more, especially 1000 crn2 or more, and a relatively large curvature without undercuts can be manufactured with good quality and easily.

In addition, in the above embodiment, the molten resin 9 is placed in the cavity 10.
The re-clamping was started when the inside of the mold was injected to about 80-90%, but if the starting point of re-clamping is around 9 above, it is not necessarily within the 80-90% range. There is no need to be limited.

In the above embodiment, the start time of re-clamping is set from the operation time of the injection cylinder f8, but for example, the injection filling amount of the molten resin 9 may be estimated from the stroke of the injection plunger of the injection cylinder f8, or the injection filling amount of the molten resin 9 may be estimated from the stroke of the injection plunger of the injection cylinder f8, or It is also possible to directly measure the amount of filling within 10, and start re-clamping when the amount of filling reaches the above percentage.

As described above, according to the present invention, it is possible to provide an injection compression molding method in which the structure of the mold is simple, a molded product of good quality can be obtained, and the mold clamping cycle time can be shortened.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an injection compression molding apparatus for carrying out the method of the present invention, and the second diagram is a diagram showing a mold clamping cycle. 5... Moving mold, 6... Fixed mold, 9... Molten resin. Agent: Patent attorney Sanzo Kinoshita (and 1 other person) a:'d:'
o knee 41-1, C maker, etc.-

Claims (1)

[Scope of Claims] (11) In an injection compression molding method in which the mold is clamped to a position that allows for a compression allowance, the mold is injected and filled with molten resin, and the mold is re-clamped to compress the compression allowance. An injection compression molding method characterized in that after most of the resin is injected and filled, the mold is re-clamped while continuing injection and filling of the remaining molten resin. 80
An injection compression molding method characterized in that re-clamping is started when ~90% of the injection filling is completed. (3) The injection compression molding method according to claim 1 or 2, characterized in that the re-clamping is performed at high pressure and high speed.