JPH0679747A - Injection nozzle for gas-assisted injection molding - Google Patents

Abstract

PURPOSE:To simplify a nozzle operating mechanism by providing a resin passage in the center of a core which slides along the inner wall of a nozzle jacket, then forming a gas incoming/outgoing passage by the front boundary parts of the core and the jacket, and allowing the core to advance by high pressure during the injection to realize a tight contact between the core tip and the inner wall and the subsequent blocking of the incoming/outgoing passage. CONSTITUTION:A core rear 2-1 is installed in a freely slidable manner to the inner wall rear 1-1 of a jacket 1 for an injection nozzle, and a gas outgoing/incoming passage 3 is formed between an inner wall front 1-2 and a core 2. Both outgoing/incoming passage 3 and a core rear resin chamber 4 are shielded off to the other between slide parts 1-1, 1-2. If the resin 7 is pushed to move forward by a screw during the injection, resin 7 in the resin chamber 4 generates pressure to the rear end of the core 2, and the core, in turns, moves forward. The core tip 2-4 becomes engaged with the inner wall tip 1-3 resulting in the shut-off of a contact between the outgoing/incoming passage 3 and a resin passage 2-3. Consequently, the resin 7, passing through the resin passage 2-3, is injected from a nozzle 1-4. After the injection, a gas send-in valve 10 is opened to move the core 2 backward. Thus the operating mechanism is simplified.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel injection nozzle for gas-assisted injection molding.

[0002]

2. Description of the Related Art In recent years, gas-assisted injection molding technology has been expanding as a technology for producing a synthetic resin molded product used in a device requiring precision and strength such as an electronic application device. The reason why the technique is used for such purpose is that, as an essential property of a synthetic resin, there is a molding shrinkage due to a linear expansion coefficient of 10 times that of a general metal. This is because a molded product of On the other hand, the gas-assisted injection molding method is
Immediately after injection, 200 kg /
By applying high-pressure gas inside and outside of cm ^2, the volume of cooling and shrinking of the thermal resin can be supplemented by the expansion of this internal high-pressure gas, and the external shape is exactly the mold cavity shape up to the curing temperature of the resin. Can be kept at.

Conventionally, as a gas blowing method for this purpose,
The method of blowing from a resin injection port is often used. However, as the gas used there, nitrogen is generally used to avoid the risk of combustion due to high temperature and high pressure, so abandonment for each step is economically expensive and recovery is repeatedly used for each step. ing. However, the injection resin may infiltrate into the recovery passage for closing the gas supply / recovery passage. Therefore, many studies have been conducted to prevent this. Most of the methods obtained as a result have been the method of providing the injection nozzle with a valve capable of opening and closing the gas inlet / outlet passage by an external force operation.

[0004]

However, it is easily conceivable that it is difficult to provide an externally operated valve for gas injection and recovery at the narrow tip of the nozzle.
Therefore, it is unavoidable that the mechanism becomes complicated and large, and that the mechanism becomes complicated and causes a failure, and in addition, the overlap between the resin flow path and the gas flow path often causes a defect such as a so-called silver streak. There was a problem that it became a problem. The present invention solves the above-mentioned problems, and provides an injection nozzle for gas-assisted injection molding, which has a simple mechanism and thus has a low probability of failure and eliminates the cause of the above-mentioned defects.

[0005]

That is, according to the present invention which has succeeded in solving the above-mentioned problems, in an injection nozzle for gas-assisted injection molding, a resin passage is provided at the center which can slide along the inner wall of the outer jacket. A core provided, and the front boundary portion between the core and the outer shell constitutes a gas inlet / outlet path, and by the advance of the core due to the high pressure behind the core during resin injection,
An injection knot for gas assist injection molding capable of closing the gas inlet / outlet path by closely engaging the tip of the core with the inner wall or sprue bush of the outer jacket in front of the core.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to FIGS. 1 and 2 which are the embodiments thereof. FIG. 1 is a cross-sectional view of the main part of a nozzle according to an embodiment of the present invention. Figure 1
The nozzle of the present invention shown in FIG. 1 has a mantle 1 and a movable core 2 inside of which. The inner core rear part 1-1 of the mantle 1 has a core rear part 2-
1 is slidably mounted, and the gas inlet / outlet path 3 and the core rear resin chamber 4 which are formed between the inner wall front part 1-2 of the outer jacket 1 and the front part outer periphery 2-2 of the core are mutually described above. Sliding part 1-1, 1-2
It is shut off airtightly.

Next, the process of gas-assisted injection molding using the injection nozzle of the present invention will be described. An injection unit composed of the injection cylinder 5 and the plasticizing / injecting screw 6 shown in FIG. 1 is given a forward force by a forward device (not shown), and the tip opening 1- of the nozzle mantle 1 is provided.
4 closely engages with the sprue 8-1 of the front sprue bush 8. The gate 8-1 communicates with the mold cavity 9 that has been clamped. During this time, the resin 7 plasticized by the rotation of the screw 6 is accumulated in the resin chamber 4 in a predetermined amount,
After that, the screw 6 stops rotating.

Next, when the screw 6 is moved forward to inject the resin, the resin 7 in the resin chamber 4 gives a strong pressure to the rear end of the core 1, so that the core 2 advances and its The tip 2-4 engages with the tip 1-3 of the inner wall of the mantle, and blocks the communication between the resin chamber 3 and the resin passage 2-3 of the core. So resin 7
Passes through the resin passage 2-3, and further passes through the nodule opening 1-4 at the tip of the mantle that engages with the resin passage 2-3. After that, a predetermined amount of resin 7 is injected into the mold cavity 9 through the sprue 8-1 engaged as described above and then the runner 8-2. Here, the advancing force of the screw 6 is released, and the process proceeds to the next plasticizing step.

During or immediately after the injection of the resin, the injection pressure drops due to the opening operation of the gas inlet valve 10 communicating with the pressure gas source (not shown), and at the same time, the pressure gas retreats the core 2 by its force. The gas inlet / outlet path is communicated with the nozzle port 1-4, the injection resin in the sprue 8-1 and the sprue 8-2 is eliminated, and a path to the resin 7 in the mold cavity 9 is created. enter in. After supplying a predetermined amount of pressure gas, the pressure gas inlet valve 10 is closed. During this time, the resin 7 in the mold cavity is cooled and shrunk, but as long as it is in the softened state, the external resin is expanded by the expansion of the internal pressure gas, and its size is maintained faithfully to the shape of the mold cavity. After the required time, by opening the gas release valve 11, the pressure gas in the molded product expands to a low pressure, and after that, the gas recovery device (not shown) collects the gas, and then the release valve 11 is closed. Thus, one process is completed.

In the above example, the gas inlet / outlet passage is closed by the injection of the resin by the engagement between the tip of the core and the inner wall of the mantle, but in another example shown in FIG. As described above, a direct close engagement between the tip of the core and the sprue bush can be performed.
In addition, the above example is useful for an injection molding method called open knots used when the viscosity of the resin is relatively high and the plasticized resin does not flow out from the resin flow path 2-3 even during injection. However, when the plasticized resin has a low viscosity, it is difficult to use. In addition, when the pressure gas is fed, the pressure gas may flow back to the rear resin chamber, which may cause a decrease in defects such as the above-mentioned silver strip marks and, in some cases, defective foaming.

Next, FIG. 2 shows a principal cross-sectional view of a knotzle which has improved the above-mentioned two problems and provided a preventive means. Note that FIG. 2 shows a state during injection of resin in the injection molding process. In FIG. 2, the core 2 is moved forward by the injection pressure as in the case of the injection of the above-mentioned example of FIG. 1, but in FIG. 2, a portion 1-4 ′ corresponding to the nodule port 1-4 at the tip of the outer cover is shown.
Since the core tip 2-4 'is provided concentrically in the inside of the core, the core tip 2-4' projects through the nozzle port 1-4 'and directly engages with the fixed immovable sprue bush 8. To meet. Since the advancing force of the core 2 due to this injection pressure is strong, it overwhelms the advancing force of the injection unit and relatively retracts the injection unit. Therefore, the directly connected nodule mantle tip 1-4 'is disengaged from the sprue bush 8, only the tip 2-4' of the core is engaged with the sprue bush 8, and the resin 7 is completely in any part of the mantle 1. There is no contact with
It is injected into the mold cavity 9. Therefore, the resin is free from the gas inlet / outlet port formed by the jacket 1 and the core 2.

When the injection pressure disappears after the completion of the injection of the above-mentioned resin, the forward opening force of the injection unit causes the tip opening 1-4 'of the mantle and the sprue bush 8 to engage again.
At this time, in the example of FIG.
Since the spring 12 is interposed between and, a retreating force is always generated by the force, and the retreating in response to the force automatically connects the gas inlet / outlet 3 and the sprue bush 8 to the spout 8-1. At this point, the pressure gas inlet valve is opened, and the supplied pressure gas enters the injection resin 7 in the mold cavity 9. The subsequent steps are performed in the same manner as the embodiment shown in FIG.

In the example of FIG. 2, the injected gas does not flow back to the resin chamber 4 at the rear by the normal in-line check valve 13. Further, after the injection is completed, when the resin is plasticized, the rear end 2-5 of the core closes the resin passage 4-1 communicating with the resin chamber 4 by the force of the spring 12, so that the above-mentioned resin outflow problem occurs. Is resolved.

It is also possible to adopt a method in which the above-mentioned spring force is substituted by the advancing force of the injection device by setting the tip 2-4 'of the core to a size that allows it to be constantly projected.
In any case, the resin 7 and the gas inlet / outlet passage 3 are blocked by the further relative advance of the core 2 during the injection. Therefore, the protrusion limit of this core tip 2-4 'is
-4 ', the size for engaging the tapered portion 2-6 immediately before -4' and the mating outer jacket inner wall 1-5 can be arbitrarily determined. And
This engagement is also effective in preventing the leakage of resin during injection.

Further, when the above-mentioned spring 12 is used, it is not necessary to constantly apply forward force to the injection unit,
Only at the time of injection is sufficient. In this method, the gas flow path and the resin flow path are completely blocked up to the sprue bush 8, so that when residual resin is injected in the next step, so-called silver streak defects due to the influence of gas in the previous step The cause of can be reduced.

[0016]

According to the conventional gas-assisted injection molding method,
In order to collect and reuse the used gas and prevent the injection resin from entering the gas inlet / outlet path to realize it, a complicated and large valve and a mechanism for opening / closing the valve were required. As a result, there is a problem that the valve is not only expensive but also prone to failure and the defective rate of the molded product is high. However, the present invention does not require actuation by an external force at all, and the gas inlet / outlet path is not required. The present invention has made it possible to completely open and close the door using a specific core and a mechanism using the core, and to solve all the problems of the conventional method at once.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a knotzle according to an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of a knotz according to another embodiment of the present invention.

[Explanation of symbols]

 1 Injection Nozzle Outer 2 Core that can slide in Outer 1 3 Gas inlet / outlet path 4 Resin chamber 5 Cylinder of injection molding machine 6 Plasticizing and injection screw 7 Plasticized synthetic resin 8 Sprue bush 9 Mold cavity 10 Pressure Gas supply valve 11 Gas release valve 12 Spring 13 In-line check valve

Claims (5)

[Claims] 1. An injection nozzle for gas-assisted injection molding, comprising a core provided with a resin passage at a center thereof that can slide along an inner wall of the outer jacket, and the front of the inner shell and the outer jacket. The boundary portion constitutes a gas inlet / outlet path, and when the core is advanced due to the high pressure behind the core during resin injection, the tip of the core and the inner wall or sprue bush of the outer jacket in front of the core are separated. An injection knot for gas-assisted injection molding capable of closing the gas inlet / outlet path by closely engaging with each other. 2. The tip of the core is located in a concentric cylindrical shape along the inner wall of the tip opening of the mantle, and is projected from the outer tip opening of the mantle by the advance of the core during injection of resin. , A structure which closely engages with the front sprue bush.
The injection nozzle for gas-assisted injection molding described. 3. The core has a force capable of always retracting,
The injection nozzle for gas-assisted injection molding according to claim 1 or 2, which has a structure in which the rear resin flow path can be always blocked at the rear portion of the core except during injection. 4. The injection nozzle for gas-assisted injection molding according to claim 3, wherein the retracting force of the core is caused by a spring. 5. The injection nozzle for gas-assisted injection molding according to claim 3, wherein the retracting force of the core is due to the advancing force of the injection unit.