JPH0957794A - Injection compression molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection compression molding method for obtaining a molding in which appearance is excellent without a weld and both deformation in the weld part and deterioration of physical properties are not caused. SOLUTION: In a slightly opening state of a mold, a resin is injected by simultaneously opening valve gates 1, 2 and the inside of a mold cavity is filled with the resin by a press. Successively, the valve gate 2 is closed and furthermore the resin is compressed and excess resin is allowed to flow back from the valve gate 1 to a screw side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection compression molding method capable of providing a molded product having no weld and having an excellent appearance and having no deformation in the weld portion.

[0002]

2. Description of the Related Art In general, injection compression molding is performed by starting resin filling in a mold open state and then closing and compressing the resin while filling the resin or after the completion of the filling, thereby making it thinner and lower in thickness than ordinary injection molding. There is a great merit in obtaining a molded product without warping and sink marks.

Conventionally, in an injection compression molding method, a mold cavity is filled with a resin having an excess amount, and the excess amount is once discharged to the outside of the cavity to equalize the resin pressure distribution in the mold cavity. At the same time, there is known a technique for obtaining an injection compression-molded article free from sink marks and warpage by changing the flow direction of the resin.

For example, Japanese Laid-Open Patent Publication No. 6-134810,
In Japanese Patent Laid-Open No. 6-246791, an injection molding die apparatus having two types of gates, large and small, is used to operate a compression device at least once after injecting a resin so that a part of the resin in the cavity is removed. This method describes a method of obtaining a highly accurate molded article of a fiber-reinforced grade resin or an anisotropic resin without the influence of fiber orientation or anisotropy.

[0005]

However, in the above-mentioned conventional technique, the reverse flow of the resin is carried out by utilizing only the difference in the heat transmittance of the gate, that is, the difference in the solidification time of the resin in the gate. Specifically, it is a method in which the resin in the small gate is solidified and the resin is discharged from the large gate before the resin in the large gate is solidified. Therefore, the change of the resin flow direction due to the backflow is limited to one direction and the timing thereof is also limited, so that there is a problem that the weld cannot be completely erased. Further, when a filler such as glass fiber is included, the warp is emphasized due to the influence of the filler, and the physical properties of the welded portion are unavoidably deteriorated.

The present invention has been made in view of the above conventional problems. In injection compression molding, even when a filler such as glass fiber is included, it has no weld and has an excellent appearance, and at the weld portion. It is an object of the present invention to provide a molded product that is free from deformation and deterioration of physical properties.

[0007]

According to the present invention, in a hot runner die having a plurality of gates that can be forcibly opened and closed, resin is filled into a die cavity from an arbitrary gate in a mold open state, and then the die cavity is opened. While compressing to the set position,
Disclosed is an injection compression molding method, characterized in that a part of resin in a mold cavity is discharged from an arbitrary gate to the outside of the cavity.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a view showing a mold used in the injection compression molding method according to the present invention. In FIG. 1, 1 and 2
Is a valve gate that can be forcibly opened and closed by air, 3 is an injection nozzle, 4 is a hot runner, 5 is a fixed mold, and 6 is a movable mold.

In the present invention, a hot runner die having a plurality of gates that can be forcibly opened and closed is used. By opening and closing the gate, the resin can be taken in and out and the cavity internal pressure can be adjusted. The gate 4 may be any mechanism as long as it can be forcibly opened and closed, but, for example, a gate driven by hydraulic pressure or air pressure can be applied.

First, in a mold open state, the valve gates 1 and 2 are opened, and the injection nozzle 3 fills the mold cavity with resin of 100 to 300% of the volume of the mold cavity after the mold is closed and compressed.

Next, while the resin injection is being continued, the movable mold 6 is
Is advanced, the mold is clamped to a predetermined position, and the injection is completed almost at the same time. By this mold clamping, the resin in the mold cavity is stretched, spreads to every corner of the mold cavity, and is brought into close contact with the entire inner surface of the mold.

Clamping the resin while injecting the resin prevents the appearance defects such as so-called hesitation marks from occurring by injecting the resin without stopping the flow of the resin in the mold. This is because. On the other hand, if the mold is clamped after the completion of the injection of the resin, the flow of the resin in the mold stops once between the completion of the injection and the start of the mold clamping, and at this time, the resin contacting the inner surface of the mold A poor appearance such as a so-called hesitation mark occurs near the boundary of the resin that is not in contact with the resin.

As the resin used in the present invention, thermoplastic resins generally used in injection molding and extrusion molding can be widely used. Further, a thermosetting resin can be used if necessary. Furthermore, fillers such as feelers and various additives can be added to these resins as needed.

In the first aspect of the present invention, subsequently, the valve gate 2 is closed and the screw is momentarily retracted while applying a pressing pressure, so that the resin in the mold cavity is caused to flow backward toward the valve gate 1. While pushing back to the screw side, compress to the mold open position when final compression is completed. Due to this resin backflow, the flow direction of the resin changes, and the weld formed in the middle part of the molded product disappears. The excess resin may be discharged into a cavity set outside the product of the mold. Further, the timing of closing the valve gate 2 may be determined according to the thickness of the molded product to be molded and the like.

In the second aspect of the present invention, after the injection is completed, the valve gate 2 is closed and the screw is momentarily retracted while applying the pressing pressure, so that the resin in the mold cavity flows back toward the valve gate 1. While pushing back to the screw side, it is compressed to a predetermined position. Next, the valve gate 1 is closed, the valve gate 2 is opened and further compressed, and excess resin is back-flowed in the direction of the valve gate 2 and pushed back to the screw side, and compressed to the mold open position at the time of final compression completion. By thus changing the flow direction of the resin twice, the weld formed in the middle part of the molded product can be more completely eliminated. The excess resin may be discharged into a cavity set outside the product of the mold. Further, the timing of closing the valve gate 2 and the timing of opening the valve gate 2 and closing the valve gate 1 may be determined according to the thickness of the molded product to be molded and the like.

Although the case where two gates that can be forcibly opened and closed are provided above, it goes without saying that more gates may be provided depending on the shape of the molded product. Similarly, the case where the resin is discharged once or twice is described, but the resin may be discharged three times or more.

[0018]

【Example】

(Example 1) The plate-shaped molded product shown in FIG. 2 was molded using an ABS resin (Styrac ABS 191F: manufactured by Asahi Kasei Kogyo Co., Ltd.) with the mold shown in FIG. 1 (completely closed, 1.5 mm). This mold is a hot runner 4 and has two air-driven forced opening / closing gates 1 and 2 (gate diameter φ3 mm), which can be opened and closed at any injection position and mold opening position. The injection molding machine can press at any screw position and mold opening position,
Komatsu IP1050, whose press pressure can be freely set, was used.

At a mold opening position of 4 mm, a shut-off valve (not shown) is opened, and the resin for 1.5 times the product weight is simultaneously opened in the bubble gate 1 and the bubble gate 2 for 250.
injected at a pressure of kg / cm ^2, followed by 280 kg / cm ²
The press was started with the pressure of, and the mold cavity was filled with the press.

Subsequently, the valve gate 2 was closed and further compressed, and excess resin was made to flow backward from the valve gate 1 to the screw side.

The obtained molded product showed almost no weld in the middle part.

(Example 2) Injection compression molding was carried out using the same molded product, mold and molding machine as in Example 1.

At a mold opening position of 4 mm, a shut-off valve (not shown) is opened, and the resin for 1.5 times the product weight is simultaneously opened in the bubble gate 1 and the bubble gate 2 for 250 times.
injected at a pressure of kg / cm ^2, followed by 280 kg / cm ²
The press was started with the pressure of, and the mold cavity was filled with the press.

Subsequently, the valve gate 2 was closed and further compressed, and excess resin was made to flow backward from the valve gate 1 to the screw side.

Subsequently, the valve gate 1 was closed, the valve gate 2 was opened and further compressed, and excess resin was made to flow backward from the valve gate 2 to the screw side.

The obtained molded product had a completely disappeared weld in the middle portion and was excellent in appearance.

Example 3 A molded product was obtained in the same manner as in Example 1 except that a nylon resin containing 33% GF (Leona 1402G: manufactured by Asahi Kasei Corporation) was used.

In the obtained molded product, almost no weld was seen in the middle part, and almost all the glass fibers were oriented in the longitudinal direction, so that no deformation was observed.

(Example 4) A molded article was obtained in the same manner as in Example 2 except that AS resin (Styrac AS: manufactured by Asahi Kasei Co., Ltd.) containing 33% GF was used.

The obtained molded product was excellent in that the weld in the middle part disappeared completely and there was no deformation.

(Comparative Example 1) Injection compression molding was carried out using the same molded product, mold and molding machine as in Example 1.

When the mold opening position is 4 mm, the shut-off valve is opened, the product weight + 5% of the resin is injected at a pressure of 250 kg / cm ² , then the press is started at a pressure of 280 kg / cm ² , and the resin in the mold cavity is pressed by the press. Filled with

The obtained molded product had a weld 13 clearly appearing in the middle portion as shown in FIG. 3 and had a problem in appearance.

Comparative Example 2 A molded article was obtained in the same manner as in Comparative Example 1 except that a nylon resin containing 33% GF (Leona 1402G: manufactured by Asahi Kasei Corporation) was used.

The obtained molded product had a weld 13 clearly appearing in the middle portion as shown in FIGS. 4 and 5, and the glass fiber 14 was oriented perpendicular to the flow direction of the resin.
Both deformations were problematic.

[0036]

EFFECTS OF THE INVENTION According to the molding method of the present invention, in the injection compression molding method, even when a filler such as glass fiber is included, the molded article has no weld and has an excellent appearance, and there is no deformation in the weld portion and no deterioration in physical properties. Can be obtained.

[Brief description of drawings]

FIG. 1 is a view showing a mold used in an injection compression molding method according to the present invention.

FIG. 2 is a plan view of a molded product molded in the example.

3 is a plan view of a molded product molded in Comparative Example 1. FIG.

4 is a plan view of a molded product molded in Comparative Example 2. FIG.

FIG. 5 is a side view of FIG. 4;

[Explanation of symbols]

 1 Valve Gate 2 Valve Gate 3 Injection Nozzle 4 Hot Runner 5 Fixed Mold 6 Movable Mold 11 Gate 12 Gate 13 Weld 14 Glass Fiber

Claims (3)

[Claims] 1. In a hot runner die having a plurality of gates that can be forcibly opened and closed, a die cavity is filled with resin from an arbitrary gate, and then the die cavity is compressed to a set position while the die cavity is compressed. An injection compression molding method characterized in that a part of the resin in the mold cavity is discharged from the arbitrary gate to the outside of the cavity. 2. The injection compression molding method according to claim 1, wherein a part of the resin in the mold cavity is returned into the injection cylinder. 3. The injection compression molding method according to claim 1, wherein the gate for discharging the resin is switched to discharge a part of the resin outside the cavity in a plurality of times.