JPH06328527A - Method for injection molding and injection molding machine - Google Patents

Abstract

PURPOSE:To prevent simultaneously air from being sucked and a resin from leaking by performing to suck back by a more delayed timing than to start retreating of a plasticizing apparatus. CONSTITUTION:A screw (not illustrated) is rotated and a resin is plasticized and metered by starting a plasticization metering motor 4 under a condition where a mold 14 is closed and a plasticization metering apparatus contg. a plasticization cylinder is advanced. After metering is completed, the plasticization metering apparatus is retreated and it is made to watch and wait for the next injection. In this instance, the resin at the apex of an injection nozzle 1 leaks bit by bit caused by a back pressure but when the timing for starting of suck back is delayed by about 0-1.0sec than retreating of the plasticization apparatus (that is a time when the injection nozzle 1 is separated from a sprue bush 2), leakage of the resin from the apex of the injection nozzle 1 is made min.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an injection molding method,
Especially in the open nozzle type injection molding machine,
The present invention relates to an injection molding method and an injection molding apparatus capable of preventing resin from leaking from the tip of an injection nozzle when the plasticizing and weighing device is retracted to separate the injection nozzle from the sprue bush.

[0002]

2. Description of the Related Art There are needle valve type and open nozzle type plasticizing cylinders for injection molding machines.
In the former case, a needle pin driven by hydraulic pressure is provided in the plasticizing cylinder, and the tip of the nozzle is closed by this needle pin during plasticizing and metering to prevent the resin from leaking from the nozzle tip. This type does not leak resin from the tip of the nozzle at all, but since parts with extremely complicated shapes such as needle pins and torpedo are inserted in the resin passage, the resin is easily carbonized in the plasticizing cylinder It is easy to get black spots. Optical parts such as lenses and prisms and C
In optical disks such as D and VD, black spots due to this carbide cause fatal damage. Therefore, an open nozzle type plasticizing cylinder is usually used in these moldings.

The open nozzle type has no means for preventing the resin from leaking from the tip of the nozzle, and frequently causes molding defects such as stringing, cold, and silver. In order to prevent this resin leakage, the temperature at the nozzle tip is lowered, or the nozzle is molded while it is in close contact with the sprue bush, but in any case, injection will not be possible if the nozzle tip temperature is lowered to the extent that resin does not leak. However, even if it could be injected, there was a problem that the semi-solidified resin would flow into the molded product and damage the mirror surface of the mold and the stamper.

When an open nozzle type plasticizing cylinder is used, as a method for preventing the resin from leaking from the tip of the nozzle, a method of sucking back after the completion of plasticizing and weighing is adopted. This is a method in which the screw is forcibly retracted without rotating and the resin that is about to leak from the tip of the nozzle is sucked into the nozzle. Most disk molding machines have this function, and usually, the amount of stroke of this suck back is optimized to prevent resin leakage from the nozzle tip.

[0005]

However, in the above-mentioned prior art, since the screw is forcibly retracted immediately after the completion of the plasticizing measurement, the suck back is performed while the nozzle is in close contact with the sprue bush. In order to suck the resin of No. 2 into the nozzle, it was necessary to take a large suck back stroke amount. Therefore, air is easily sucked together, and the sucked air is caught in the resin at the time of the next injection and flows into the molded product, causing silver, cold, and other appearance defects. To prevent inhalation of air,
It was necessary to reduce the suck back stroke amount as much as possible, which would lead to resin leakage, which is a contradictory relationship, and it was very difficult to find the optimum condition.

Further, regardless of the temperature and back pressure of the resin being measured and the sliding resistance of the screw, the screw was always forced to retreat at high speed and high pressure, so that the measurement itself became very unstable, This caused variations in the quality of molded products.

The present invention has been made in view of the above problems of the prior art. By sucking back at a timing later than the start of retreating the plasticizing device, air suction and resin leakage are prevented at the same time. It is an object of the present invention to provide an injection molding method and an injection molding device that can be manufactured without causing defective products.

Another object of the present invention is to provide an injection molding method and an injection molding apparatus in which the speed and pressure of forced screw retraction are arbitrarily changed and suck back is performed in multiple stages.

Further, by providing a device capable of directly monitoring the resin leakage state at the tip of the injection nozzle, there is provided an injection molding method and an injection molding apparatus for sucking back with a suck back slack amount according to the resin leakage state at the tip of the injection nozzle. The purpose is to do.

[0010]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides an injection molding method in which an injection nozzle is retracted from a sprue bush after completion of plasticization and measurement, and is kept waiting until the next injection. It is characterized in that the screw is forcibly retracted after the completion of the pressure and after the plasticizer is started to retract.

Further, it is characterized in that at least one of a speed and a pressure for forcibly retracting the screw without rotation is changed.

Further, it is characterized in that the screw is forcibly retracted non-rotatingly in a plurality of times.

After completion of the plasticization measurement, the resin leaking from the tip of the injection nozzle is detected, and the screw is forcibly retracted by a necessary amount in accordance with the amount of the resin leaking.

The injection molding apparatus of the present invention is equipped with an injection nozzle and a plasticizing and metering device, and after the plasticizing and metering is completed, the injection nozzle is retracted from the sprue bush and stands by until the next injection. In the vicinity of the tip of the nozzle, a device that detects resin leaking from the tip of the injection nozzle after completion of plasticization measurement, and a control unit that forcibly retracts the screw by the required amount according to the amount of resin that leaks,
It is characterized by having.

Further, the apparatus for detecting the resin leaking from the tip of the injection nozzle inputs the video sent from the television camera and the television camera for monitoring the tip of the injection nozzle, captures it as a binary signal, and sets it. It consists of a monitor that outputs an output signal when the resin leaks out more than the specified value.

[0016]

In the present invention for achieving the above object, suck back is performed with the injection nozzle separated from the sprue bush by forcibly retracting the screw after the plasticizer is retracted. Since the resin at the tip of the injection nozzle is sucked into the nozzle, the suck back stroke amount can be small and air is not sucked.

[0017]

An embodiment of the present invention will be described with reference to the drawings.

First, the injection molding apparatus will be described. FIG. 1 is a configuration diagram of essential parts of an embodiment of an injection molding apparatus of the present invention.

As shown in FIG. 1, a mold 14 is provided with a sprue bush 2, and a molten resin is injected into the mold 14 from an injection nozzle 1 of a well-known open nozzle type plasticizing cylinder. The screw (not shown) is moved forward and backward by the injection cylinder 3, and the screw (not shown) is rotated by the plasticizing metering motor 4. Further, the plurality of suck back hydraulic cylinders 5a and 5b are for forcibly retracting a screw (not shown) in a non-rotating state during suck back. Suck back hydraulic cylinder 5
A and 5b are driven by speed or pressure control. This injection molding machine uses optical components such as lenses and prisms and C
It is for molding optical discs such as D and VD.

Further, a TV camera 7 is provided in the mold 14 in the vicinity of the injection nozzle 1, and the TV camera 7 can directly monitor the amount (thickness) of the resin 11 leaking from the tip of the injection nozzle 1. It is like this. At this time, the image of the television camera 7 may be difficult to see, and in that case, a clear image can be obtained by providing the illumination 10 in a direction opposite to the television camera 7 or in a direction of 90 degrees. The image of the tip of the injection nozzle 1 sent from the television camera 7 is captured as a binarized signal on the monitor 8. When the monitor 8 determines that the resin has leaked out beyond the set value, the output signal is passed through the cable 9 and the control circuit 6 as the control unit of the suck back hydraulic cylinders 5a and 5b.
Send to. As a result, suck back is performed by the required suck back stroke amount.

Next, the injection molding method of this embodiment will be described in detail. FIG. 2 is a diagram showing the timing of each step in injection molding.

As shown in FIGS. 1 and 2, with the mold 14 closed and the plasticizing and weighing device including the plasticizing cylinder 15 moved forward (moved to the left in FIG. 1),
By activating the plasticizing and metering motor 4, a screw (not shown) is rotated to plasticize and measure the resin. After the measurement is completed, the plasticizing and measuring device is retracted (moved to the right in FIG. 1) and waits until the next injection. At this time, the resin 11 at the tip of the injection nozzle 1 leaks little by little due to the back pressure. The leakage of the resin 11 occurs from the moment when the injection nozzle 1 separates from the sprue bush 2. As in the conventional suckback method, as described above, when suckback is performed immediately after the completion of plasticizing and weighing, since the screw is forcedly retracted while the injection nozzle is in close contact with the sprue bush, the resin at the tip of the injection nozzle is Could not be sucked into the injection nozzle well. Even if it sucked in, it required a considerable amount of suck back stroke and sucked in air at the same time as the resin. In the present embodiment, as shown in the timing chart of FIG. ₂ , suck back can be performed at an arbitrary timing T ₂ after the completion of the injection holding pressure.

FIG. 3 shows the result of the experiment. As can be seen from this, when the suck back timing is delayed from the plasticizer retreat (when the nozzle separates from the sprue bush) by T ₃ seconds, and in this embodiment by about 0 to 1.0 second, the resin leaks from the tip of the injection nozzle 1. Is the least. This is a result when the screw diameter is φ28 mm, the type of resin is polycarbonate resin, and the resin temperature is 320 to 340 ° C. The optimum timing is different under other conditions.

In the conventional suckback method, the screen is
The speed of retreat is only one fixed value (typically 50-
It was one value in the range of 200 mm / sec.)
In the embodiment, this is set in the range of 0 to 200 mm / sec.
Enabled to set the value. As a result of the experiment, screw retreat
When the speed is 3 to 100 mm / sec, the screw retraction amount (
Back stroke amount) in the range of 0.5 to 5.0 mm
Suck back allows continuous molding without resin leakage
I was sure that. Among them, the speed is 3 to 30 mm /
In seconds, suck back stroke of 0.7 ~ 1.5 mm
The case was most stable. However, screw diameter and resin
If so, the optimum suckback condition naturally differs. Also,
The speed and pressure required to retract the screw without rotation are small.
At least one may be changed arbitrarily, and
As force, 5-15kg / cm ²(Hydraulic value) is preferred
Yes.

Furthermore, by performing suck back in multiple stages, the range of optimum suck back conditions can be expanded. For example, as shown in FIG. 4, the screw retreat speed is 100 m from the screw position at the time of completion of measurement to 0.5 mm.
m / sec, 50 when the screw position is 0.5 to 1.0 mm
mm / sec, 5 when the screw position is 1.0 to 1.5 mm
mm / sec, 3m when the screw position is 1.5-2.0m
By performing the suck back by setting the screw retreat speed to m / sec, continuous molding can be performed without resin leakage. It was confirmed that the allowable condition range for continuous molding without resin leakage is wider in the case of multi-stage setting than in the case of being fixed to the conventional one setting.

Then, as described above, the television camera 7
The image of the tip of the injection nozzle sent from the device is captured as a binarized signal on the monitor 8, and when the resin leaks above the set value, the output signal is passed through the cable 9 to the control circuit for the suck back hydraulic cylinders 5a, 5b. Send to No. 6 and perform suck back by the required amount. When the resin leaks again after a lapse of time, the suck back signal is sent to the suck back hydraulic cylinders 5a and 5b again to suck back the required amount. While repeating this, when the next cycle starts, the entire plasticizing apparatus is moved forward again (to the left in FIG. 1) to perform injection after the nozzle touch. By performing suck back while directly monitoring the resin leak state at the tip of the injection nozzle in this way, the maximum resin leak prevention effect can be obtained with the minimum necessary suck back.

In the above embodiment, it is assumed that there is a relatively large space at the tip of the nozzle, but there is often no space. In this case, the following embodiment can be considered.

FIG. 5 shows another embodiment. When the television camera cannot be mounted in the vicinity of the injection nozzle as in the above embodiment, the first mirror 12 is provided at or near the sprue bush 2. In addition, the second mirror is used to insert the image near the nozzle into the TV camera 7 located away from the nozzle, and the image is displayed as a binarized signal on the monitor 8. The resin leaks above the set value. When it comes, the output signal is sent to the control circuit 6 of the suck back hydraulic cylinders 5a and 5b through the cable 9 to perform suck back by a required amount.

In addition to the above embodiments, an optical sensor or a proximity switch may be used as a method for directly monitoring the resin leaking from the tip of the nozzle.

[0030]

Since the present invention is configured as described above, by forcibly retracting the screw after the start of retreating the plasticizer, the injection nozzle is sucked back from the sprue bush. Since the resin at the tip of the injection nozzle is sucked into the injection nozzle, the suck back stroke amount can be small, and the suction of air does not occur, so that only a good product can be molded.

Further, the suck back speed and pressure can be set arbitrarily, and the setting can be performed in multiple steps, whereby continuous molding can be performed in a wide condition range without resin leakage from the nozzle tip.

Further, since the suck back stroke amount can be set while directly monitoring the resin leaking from the tip of the injection nozzle, the optimum condition can be set very easily.

From the above, it is possible to obtain the maximum resin leakage prevention effect with the minimum required suck back, and continuous molding without silver, cold or other appearance defects regardless of the molding cycle or nozzle tip temperature. I can do it now.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of an embodiment of an injection molding apparatus of the present invention.

FIG. 2 is a diagram showing the timing of each step in injection molding.

FIG. 3 is a graph showing the relationship between suck back delay time and the amount of resin leakage.

FIG. 4 is a graph showing multi-stage control of suck back.

FIG. 5 is a main part configuration diagram of another example of the injection molding apparatus of the present invention.

[Explanation of symbols]

 1 injection nozzle 2 sprue bush 3 injection cylinder 4 plasticizing metering motor 5a, 5b suck back hydraulic cylinder 6 control circuit 7 TV camera 8 monitor 9 cable 10 lighting 11 resin 12 first mirror 13 second mirror 14 mold 15 plastic Chemical cylinder

Claims (6)

[Claims] 1. In an injection molding method in which an injection nozzle is retracted from a sprue bush after completion of plasticization measurement and stands by until the next injection, a screw is forced after the start of retraction of the plasticization device after completion of injection holding pressure. An injection molding method characterized by reversing without rotation. 2. The injection molding method according to claim 1, wherein at least one of a speed and a pressure at which the screw is forcibly retracted without rotation is changed. 3. The injection molding method according to claim 1, wherein the screw is forcibly retracted non-rotatingly in a plurality of times. 4. The resin leaking from the tip of the injection nozzle is detected after the completion of the plasticizing measurement, and the screw is forcibly retracted by a necessary amount in accordance with the leaking resin amount. The injection molding method described. 5. An injection molding apparatus comprising an injection nozzle and a plasticizing and measuring device, wherein the injection nozzle is retracted from the sprue bush after the completion of the plasticizing and measuring and stands by until the next injection, in the vicinity of the tip of the injection nozzle. Injection molding characterized by having a device that detects resin leaking from the tip of the injection nozzle after completion of plasticization measurement, and a control unit that forcibly retracts the screw by the required amount according to the amount of resin that leaks apparatus. 6. A device for detecting resin leaking from the tip of an injection nozzle receives a television camera for monitoring the tip of the injection nozzle, and an image sent from the television camera as input.
6. A monitor which is regarded as a digitized signal and which outputs an output signal when the resin leaks out more than a set value.
The injection molding apparatus according to.