JPS59185636A - Injection compression molding method - Google Patents

Abstract

PURPOSE:To prevent contraction producing and improve the dimension accuracy, by a method wherein a moving die is moved thereby pressure within a mold decreasing according to shrink of resin is increased to high pressure state once and then decreased gradually and made low pressure state at finishing the molding. CONSTITUTION:Both molds 1, 2 are tightened and a moving die is moved rearwards to the utmost, and then resin A heated and melted in fluid state is injected from a spool 4 into a mold cavity 3. As time elapses after finishing the injection, the resin A is cured and contracted thereby pressure within the mold decreases. After elapse of a prescribed time, the moving die 5 is driven by hydraulic means thereby pressure within the mold is rapidly increased to the high pressure state once. And then the pressure within the mold is gradually decreased, and when the resin A is wholly cured and the molding is finished the pressure is made low pressure state and the mold is opened and the finished molding product is taken out. In this constitution, a molding product of good transferring property and high dimensional accuracy is obtained without producing contraction.

Description

[Detailed description of the invention] This invention relates to an injection compression molding method in which resin filled in a mold cavity is compressed and cured by a moving piece. This relates to the injection compression molding method that made molding possible.

One method for molding resin is to heat and melt the resin, inject it into a mold cavity under high pressure, and then harden it by cooling or heating to form a molded product. obtain,
The so-called injection molding method has been used for a long time, but in this injection molding method, the volume of the mold cavity is remained constant, and as the molding pressure was not controlled, the pressure inside the mold at the end of molding could be lower than the atmospheric pressure overall or locally, and the resulting molded product would have whiskers. There were problems such as the occurrence of

Therefore, in order to prevent the occurrence of sink marks, it is necessary to control the molding pressure even during the curing process of the resin, and the injection compression molding method shown in FIGS. 1 to 3 improves this point.

In the figure, 1 and 2 are molds, 3 is a mold cavity, and 4 is a sprue. Reference numeral 5 denotes a movable piece that is assembled to the mold 1 so as to be able to move forward and backward, and is designed to protrude toward the mold cavity 3 at a position that does not impair the function of the molded product. 6 is an oil inlet/outlet, and the oil pressure of the movable piece 5 is transmitted through this oil inlet/outlet 6.

First, as shown in Fig. 1, both molds 1 and 2 are clamped, and the movable piece 5 is moved back as much as possible, and then the resin A, which has been heated and melted into a fluid state, is poured into the metal from the sprue 4. Inject into the mold cavity 3. As the resin A is injected, the pressure P inside the mold increases rapidly by atmospheric pressure 1].

When the time 'r1 has elapsed, the injection of the resin A is finished and the molding machine is maintained as it is, but the pressure inside the mold continues to rise, reaches the maximum pressure P1, and then begins to fall.

After time T2 has elapsed, the resin A near the gate hardens and the gate 1- is closed, so cooling or heating is started from this point on to accelerate the curing of the resin A as a whole.

Furthermore, when the pressure P in the mold decreases and reaches the pressure Pc,
That is, after the time T3 has elapsed, the moving piece 5 is hydraulically driven as shown in FIG. 2, and the subsequent pressure inside the mold is set to a constant value Pc.
Make sure to keep it in place. Note that the pressure Pc is generally 20
It is set in the range of 0 to 300 meters.

When the time To from when the resin is completely cured to the end of molding has elapsed, the mold is opened and the completed molded product is taken out.

In this injection compression molding method, the mold cavity 3
Even if the resin A filled inside the mold shrinks as it hardens, the pressure inside the mold is maintained at a constant value P by hydraulically driving the movable piece 5.
Since the pressure inside the mold is maintained at C, the pressure P in the mold is generally or locally atmospheric pressure P. As the temperature becomes lower, defects such as hairs on the resulting molded product will no longer occur.

In addition, in the injection molding method described earlier, it was necessary to increase the injection pressure to a considerably high pressure in anticipation of the shrinkage of resin A after injection, or in the case of this injection compression molding method, the in-mold pressure P was
The injection pressure does not need to be so high because the injection pressure is controlled sequentially even after injection, so the capacity of the injection device can be small.

However, in such conventional injection compression molding methods, the mold internal pressure 1] at the end of molding is 200 to 30
The pressure Pc is about 0 atm, which is considerably higher than atmospheric pressure, so when the finished molded product is opened and taken out of the mold, internal stress is released and it expands. ``There was a problem that one could not obtain something with high Dharma spirit.

This invention was made in view of these problems,
The eleventh objective is to provide an injection compression molding method that improves dimensional accuracy while preventing the occurrence of whiskers.

■Structure The present invention will be explained below based on the drawings.

FIG. 3 is a diagram showing an embodiment of the present invention, and shows the relationship between elapsed time T and mold pressure P.

In addition, the molding machine used here is the same as the molding machine shown in the conventional example of the injection compression molding method mentioned earlier, and the operation of the molding machine will be explained using Figs. 1 and 2. I decided to. It is assumed that the hydraulic pressure for driving the movable piece 5 is program-controlled so that the pressure P in the mold changes sequentially according to a preset profile.

First, as shown in Fig. 1, after both molds 1 and 2 are clamped and the movable piece 5 is moved back as much as possible, resin A, which has been heated and melted into a fluid state, is poured from the sprue 4 into the mold cavity. 3
Eject inside. In-mold pressure P rises rapidly from atmospheric pressure PO as resin A is injected.

When time T1' has elapsed, the injection of resin A is finished,
Either the molding machine is held as it is, or the mold pressure P continues to rise until it reaches pressure P1' and then begins to fall.

After a period of time T2' has elapsed, the resin A near the gate solidifies and the gate is closed, and from this point cooling or heating is started to promote hardening of the resin as a whole. As the resin A contracts as it hardens, the pressure P inside the mold further decreases.

Next, when the time T4 has elapsed, the moving piece 5 moves as shown in FIG.
is hydraulically driven to rapidly raise the pressure P inside the mold to a high pressure state P2. This hole allows the resin A to completely spread inside the mold cavity 3, thereby improving the transferability of the molded product. Note that the pressure P2 is generally 400 to 60
It is set in the range of 0 a L m.

Thereafter, the pressure P in the mold is gradually lowered so that the low pressure state P:I is reached when the time To' from when the entire resin is cured to the end of molding has elapsed. Once molding is complete, open the mold and remove the finished molded product. At this time, in order to prevent the molded product from expanding and causing dimensional deviations, it is theoretically desirable to set the pressure P to be equal to the atmospheric pressure P0. Considering the characteristics of the pressure P:], it is realistic to set it to about 10% of the high pressure state P2, that is, about 40 to 60 atm, and this level of residual pressure depends on the dimensional accuracy of the molded product. It is effective because it has almost no effect on hair growth, and it completely prevents the formation of whiskers.

Note that when the mold pressure P is gradually lowered from the high pressure state P2 to the low pressure state P:I, the pressure change does not necessarily have to be linear with respect to time as shown in FIG.

(Effects) As explained above, the present invention has the advantage that it is possible to obtain a molded product with no sink marks, good transferability, and high dimensional accuracy.

[Brief explanation of the drawing]

Figures 1 to 3 are diagrams showing the conventional injection compression molding method, and Figure 1 is a longitudinal sectional view of the mold part of the molding machine, showing the state immediately after the resin is injected into the mold cavity. , Fig. 2 is a vertical cross-sectional view of the mold part of the molding machine, showing the state in which the transfer mtl+ piece is driven to sequentially control the pressure inside the mold after passing through the state shown in Fig. 1, and Fig. 3 shows the elapsed time. A diagram showing the relationship between and mold pressure,
FIG. 4 is a diagram similar to FIG. 33 showing the injection compression molding method according to the present invention. 1.2...Mold, 3...Mold cavity, 5 Moving piece, A...Resin, P2...High pressure state, Pi...Low pressure state, To'...The entire resin hardens and molding is completed. Time to finish.

Claims (1)

[Scope of Claims] In an injection compression molding method in which resin filled in a mold cavity is cured while being compressed by a movable piece, by moving the movable piece, the inside of the mold is lowered as the resin contracts. An injection compression molding method that is characterized by increasing the pressure to a high pressure state and then gradually lowering it to a low pressure state at the end of molding.