JPH08323813A - Mold for injection compression molding of thermoplastic resin, and injection compression molding method using the mold - Google Patents

Abstract

(57) [Summary] [Purpose] In injection molding accompanied by compression, to prevent the compression effect from decreasing. A structure in which a pin gate 10 is provided in the center of the upper mold 7 and a protruding pin 14 is provided in the center position of a cavity forming recess 5 formed in the lower mold 3 so as to be retractable, and the mold is slightly opened. Then, after the molten resin is injected and filled into the cavity 13 from the pin gate 10, the ejection pin 14
Is projected to close the injection port 10 at its tip, and the lower mold 3 is further raised to compress the molten resin in the cavity 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for injection compression molding of thermoplastic resin, and an injection compression molding method using the mold.

[0002]

2. Description of the Related Art As a thermoplastic resin injection molding technique,
Injection molding of thermoplastic resin (molten resin) into the cavity corresponding to the shape of the molded product, waiting for solidification as it is, the normal injection molding method, and making the movable mold stand by just before the cavity matches the shape of the molded product An injection compression molding method is known in which, after injection filling of a molten resin, the movable mold is moved until the cavity matches the shape of the molded product, and compression is applied. The latter injection compression molding method in which pressure is applied during molding is a means effective in preventing warpage, sink marks, deformation, etc. that occur with the orientation and molding shrinkage of the resin, and is a technology that has been drawing attention in recent years. If only compression is applied, the molten resin filled in the cavity will flow back from the gate at the time of compression, the compression effect will be impaired, and the effect of preventing warpage, sink marks, deformation, etc. will be insufficient, and in the plate part The effect is noticeable, and the resin in the runner and sprue is pressed, and the mold separation becomes worse. The backflow can be prevented by performing compression after the gate portion is solidified, but at this point, the skin layer in contact with the inner surface of the cavity begins to solidify, and the compression effect becomes insufficient. Therefore, in the prior art, for example, as disclosed in Japanese Patent Laid-Open No. 57-95429, a fixed side mold is provided with a gate cutoff pin, and the gate cutoff pin closes the gate at its inner portion to thereby reverse flow of the molten resin. Means to prevent this have been proposed.

[0003]

If the gate blocking pin is provided on the fixed side mold, the fixed side mold becomes large and the injection flow path becomes long, so that the temperature in the flow path is lowered and the resin is removed. And the tip of the gate part adheres to the molded product taken out.

[0004]

DISCLOSURE OF THE INVENTION The present invention is directed to a thermoplastic resin molded article having a pinhole or having no problem even if it has a pinhole, and an object thereof is to enhance the compression effect at the time of molding. The structure is such that a cavity corresponding to the outer shape of the thermoplastic resin molded product can be formed by the movable side mold and the fixed side mold, and in the molding operation, the movable side mold is Injection compression molding in which the mold can be positioned at a first position where the mold is completely closed and the cavity matches the shape of the molded product, and at a second position where the mold is opened slightly before reaching a predetermined dimension. A fixed mold is provided with a pin gate as a gate for injecting and introducing a molten resin, while a movable mold is pierced through the cavity from a position facing the pin gate and a tip is picked up. A mold for injection compression molding of a thermoplastic resin, characterized in that a protruding pin for closing the injection port of the gate is provided so that it can be retracted and retracted, and the movable mold is set to the second position by using the mold. After positioning and injecting the molten resin into the cavity, the ejection pin is projected to close the injection port of the pin gate, and the movable side mold is compressed to the first position. Injection molding of thermoplastic resin. On the way. The injection compression molding mold and the injection compression molding method are suitable for a thermoplastic resin molded product having a plate-shaped portion and having a pinhole in the plate-shaped portion. In this case, a vibration function can be added to the ejecting pin in the ejecting direction. Therefore, in the injection compression molding method, the ejecting pin can be ejected while vibrating. The second position of the movable mold is
The cavity volume formed by this is 1.005 to 1 ... of the cavity volume formed by the first position.
It is desirable to set the position to be 100 times, and as a runner system for supplying the molten resin, either a cold runner or a hot runner can be used.

[0005]

[Function] The flow path to the nozzle is blocked at the boundary between the pin gate and the cavity, the molded product taken out has no accessories, and the compressive force is confined in the cavity, and the injected resin is injected. It works 100%. Since the compressive force does not act on the inside of the flow path, the compressive force does not affect the runner and the sprue portion.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A mold for injection compression molding of molten resin according to the present invention and an injection compression molding method using the mold will be described with reference to the drawings. FIG. 1 shows a mold for injection compression molding, in which side plates 1b, 1b of low height are formed to hang down on opposite side edges of a back surface of a square substrate 1a.
A mold for molding a lid-shaped molded product 1 having a pinhole 2 in the center is illustrated, and 3 is a lower mold as a movable side mold, which is molded by a movable side mounting plate 4. It is fixed to a movable plate (not shown) of the machine, and a recess 5 is formed in the center of the upper surface of the lower mold 3. The recess 5 corresponds to the side plates 1b and 1b of the molded product on both sides of the bottom surface. Step 5
It has a and 5a and is formed deeper than the thickness of the molded product. Ejector pins 6, 6 ... Are arranged at the bottoms of the steps 5a, 5a.

Reference numeral 7 denotes an upper die as a fixed-side die, which is fixed to a fixed plate (not shown) of a molding machine by a fixed-side mounting plate 8. The upper die 7 has a recess 5 at the center of its lower surface. When fitted and completely pushed in, it has a raised portion 9 that forms a cavity faithful to the shape of the molded product, and further, the injection opening of the pin gate 10 opened at the central lower surface of the raised portion 9 and its injection opening. An injection flow path including a runner 11 and a sprue 12 that communicate with each other is formed. Then, by pushing up the movable plate of the molding machine, the lower mold 3 fixed to this is raised, and the raised portion 9 is fitted into the concave portion 5. As shown in FIG. The cavity 13 is formed by 7 and. Further, the lower mold 3 is operated by an injection molding machine,
The mold is closed, and the cavity 13 can be accurately positioned at the first position P _{1 where} the shape of the mold matches the shape of the molded product and the second position P ₂ where the mold is slightly opened. The tip of the pin 6 can project into the recess 5 (cavity 13) from the same height as the bottom surface of the step 5a in the recess 5 of the lower mold 3. Further, a protrusion pin 14 is inserted through the center of the lower mold 3, and the protrusion pin 14
Is moved up and down integrally with the lower mold 3 while the tip is immersed in the lower mold 3, penetrates through the cavity 13, and is press-fitted into the injection port of the pin gate 10 that is opened in the upper mold 7 facing the cavity 13. It is designed to be protruded to the position (Fig. 4). The protruding pin 14 is provided with a vibration mechanism (not shown).

In the injection compression molding die thus formed, the lower die 3 is positioned at the second position P ₂ and the die is slightly opened, and the lower die 3 is placed at the first position P 2. The volume of the cavity 13 can be changed to a state in which the mold is completely closed by raising it to _1, and the ejection port of the pin gate 10 can be closed by protruding the ejection pin 14. An injection cylinder (not shown) is connected to the injection passage formed by the sprue 11 and the runner 12.

Next, a molding method using the injection compression molding die thus formed will be described. First, the movable plate of the molding machine to which the lower mold 3 is fixed is lifted up, the lower mold 3 having the protruding pin 14 in the retracted state is made to stand by at the second position P ₂ , and the molten resin is injected into the cavity 13 via the pin gate 10. Is ejected (a in FIG. 5). Then, the ejection pin 14 is projected to close the injection port of the pin gate 10 (b in FIG. 5), and then the lower mold 3 is raised to the first position P ₁ to apply a compressive force to the molten resin in the cavity 13. (C in FIG. 5).
Since the injection flow path is blocked by the injection port which is the boundary with the cavity, there is no escape route for the molten resin in the cavity, and the compression force acts 100%. When the ejection pin is projected, a vibrating mechanism is activated to give vibration to the ejection pin, thereby controlling the amount of projection when the sprue portion is beginning to solidify, thereby preventing damage to the ejection pin. When the resin is solidified, the movable platen of the lower mold 3 is lowered to open the mold, and the ejector pin 6 is projected to form the molded product 15
The upper mold 7 is divided at the same time, and the sprue and runner portion 16 separated from the molded product 15 are removed (FIG. 6). According to this method, no weld line is generated around the pinhole portion, and when the protruding pin closes the gate, the molded product is separated from the sprue and runner portion at the same time when the pinhole is formed. It is possible to omit the step of drilling and cutting the gate portion.

Comparative data of the molded product molded by the method of the above-mentioned embodiment by the conventional method will be illustrated. A liquid crystal polymer containing 30% by weight of glass fiber was used as the thermoplastic resin.

[Table 1]

From this table, the injection molding method with compression (injection compression molding method) has a smaller molding shrinkage ratio than the injection molding method without compression, so that both the warp deformation amount and the sink amount are good. The results are confirmed, and among the injection compression molding methods accompanied by the compression, the molded article formed by the method of the present invention for closing the gate is more effective in improving the accuracy since warpage and sink marks are further reduced. I understand. When the method of the present invention is used, a compression action works before the resin in the cavity begins to harden, so that the volume reduction caused by cooling and crystallization is minimized, and it can be said that it is suitable for a crystalline resin having a large molding shrinkage ratio. In the above embodiment, the lower mold is the movable side mold and the upper mold is the fixed side mold, but the arrangement of the fixed side mold and the movable side mold is not limited to the example, and the mold structure is also According to the shape of the molded product, etc., it can be appropriately changed within the range where the above-mentioned object of the present invention is achieved.

In the present invention, the position of the injection port is determined by the position of the pinhole formed in the molded product or the position of the pinhole which does not hinder the formation, and the moldable product has a pinhole. However, if a process for filling the pinhole is added, it can be applied to a molded product having no pinhole. Further, it can be applied not only to a plate-shaped portion having a pinhole but also to a cylindrical body having a through hole. Further, the diameter of the pinhole is not limited, and the pin gate of the present invention includes anything in the shape of a hole, and the ejector pin causes the movable side mold to start the compression action and then to start the protrusion. It is also possible to intentionally adjust the compression force low by shifting the closing timing.

[0013]

According to the injection compression molding die of the present invention,
Since the gate is closed by the protruding pin that penetrates the cavity, the formation of the pinhole and the gate cut are completed at the same time when the gate is closed, and it is possible to prevent the molten resin in the cavity from flowing back to the sprue side during compression. According to the method of the present invention, it is possible to maximize the compression effect without letting out the pressure in the cavity, and it is possible to provide a highly accurate molded product with less warpage, sinking, and deformation.

[Brief description of drawings]

FIG. 1 is an explanatory view of a molding die according to the present invention.

FIG. 2 is an explanatory view showing the shape of a molded product to be molded.

FIG. 3 is an operation explanatory view of a molding die.

FIG. 4 is an operation explanatory view of a molding die.

5A, 5B, and 5C are explanatory views showing steps of a molding method.

FIG. 6 is an explanatory view showing an operation of taking out a molded product.

[Explanation of symbols]

1 ... Molded product, 1a ... Substrate, 1b ... Side plate, 2 ... Pinhole, 3 ... Lower mold, 4 ... Movable side mounting plate, 5 ... Recess, 5a ... Step, 6 ... Ejector pin, 7 ・ ・ Upper mold, 8 ・ ・ Fixed side mounting plate, 9 ・ ・ Raised part, 10 ・ ・ Pin gate, 11 ・ ・ Runner, 12 ・ ・ Sprue, 13 ・ ・
Cavity, 14 ... Ejection pin, 15 ... Molded product,
16 ... Sprue and runner section

Claims (5)

[Claims] 1. A cavity corresponding to the outer shape of a thermoplastic resin molded article can be formed by a movable side mold and a fixed side mold, and in the molding operation, the movable side mold is
The first position where the mold is completely closed and the cavity matches the shape of the molded product, and a predetermined size before that,
An injection compression molding die which can be respectively positioned at a second position where the die is slightly opened, and a pin gate is provided in the fixed die as a gate for injecting resin, A mold for injection compression molding of a thermoplastic resin, characterized in that a movable side mold is provided with a protruding pin that penetrates through a cavity from a position facing the pin gate and closes an injection port of the pin gate at a tip end so as to be retractable. . 2. The mold for injection compression molding of a thermoplastic resin according to claim 1, wherein the thermoplastic resin molded product has a plate-shaped portion, and the plate-shaped portion has a pinhole. 3. The mold according to claim 1, wherein the movable mold is positioned at the second position, the thermoplastic resin is injected into the cavity, and then the ejection pin is projected to eject the pin gate. An injection compression molding method for a thermoplastic resin, in which an outlet is closed and a movable side mold is compressed to a first position. 4. The injection compression molding method for a thermoplastic resin according to claim 3, wherein the protrusion of the protrusion pin is performed while applying vibration. 5. The second volume so that the cavity volume formed by the second position is 1.005 to 1.100 times the cavity volume formed by the first position.
The injection compression molding method for a thermoplastic resin according to claim 3, wherein the positioning is performed.