JP2640715B2 - Injection molding method for undried polyethylene terephthalate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method for molding undried polyethylene terephthalate into a required molded product.

[0002]

2. Description of the Related Art Polyethylene terephthalate (hereinafter referred to as PE) generally used as a material resin for packaging containers and the like.
(Abbreviated as T) has a hygroscopic property, so if it is supplied as it is as a molding material to an injection device, it will not penetrate the screw well, and will vary in measurement and will cause hydrolysis due to vaporization of the contained water. Pre-drying is required for use.

[0003] Particularly, in a molding material produced by pulverizing a used PET product into flakes for reuse, the size of the flakes varies and the moisture content due to moisture absorption varies from flake to flake. Preliminary drying needs to be performed more thoroughly than the used unused molding material.

[0004]

In the case of PET used as a crystalline resin, the preheating is performed at 150 ° C. for about 4 hours.
Takes time. For this reason, preliminary drying must be started in the early morning, and when performing automatic molding continuously day and night, it is necessary to strictly set the supply amount so that drying and molding are compatible. Further, even if the injection molding is performed smoothly, there is also a disadvantage that the molding must be stopped if a trouble occurs in the dryer.

The present invention has been conceived in order to solve the problem of injection molding of PET by predrying. The object of the present invention is to eliminate the need for predrying by using an injection device having a vent function. It is an object of the present invention to provide an injection molding method which enables molding of a resin.

[0006] PE using an injection device having a vent function
Although injection molding of T is a known technique,
They close the vent opening in conjunction with the screw stop to prevent vent up during holding pressure.To continue molding without venting up when the screw stops, a specific molding It is said that a good molded product cannot be obtained unless conditions are found.

The molding conditions include a heating temperature, a compression ratio, a vent position, a vent means, and the like. The present inventors have conducted studies on them, and as a result, it is preferable to forcibly perform venting under specific conditions by suction under reduced pressure, and also to perform the depressurization in a range of vacuum degree which is not known so far. We have found the most favorable.

[0008]

SUMMARY OF THE INVENTION Accordingly, a feature of the present invention is that when a molding material made of undried polyethylene terephthalate is fed to an injection device having a vent function and is subjected to injection molding, the molding material is connected to a vent port of a heating cylinder wall. In the decompression circuit, the inside of the casing composed of the jacket is formed alternately by partition walls, and the partition walls form passages for the volatile components sucked into the inside of the casing, thereby removing volatile components from the molding material. That is, a recovery tank for cooling and removing is provided, and the pressure reducing circuit is depressurized to a degree of vacuum of 50 to 150 torr and vented.

[0009]

[Operation] In the above configuration, even when the screw is stopped, volatile components such as water in the molten material are removed without venting up, no hydrolysis occurs, and the molded product has excellent transparency and strength. In addition, the volatile components are cooled and removed by the recovery tank to prevent the working environment from deteriorating.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawing, reference numeral 1 denotes a heating cylinder having a nozzle 2 at the tip, and a feeder 5 of a molding material containing a feed screw 4 is attached to a supply port 3 at the rear. A band heater 6 is attached to the outer periphery of the heating cylinder 1, and an injection screw 7 is provided inside the heating cylinder 1 so as to rotate and move forward and backward.

The injection screw 7 is constituted by a front screw 7a and a rear screw 7b, each of which has a shaft diameter at a front end portion larger than the shaft diameter of the other portion and serves as a compression portion, and the front screw 7a A vent port 8 is provided on the wall of the heating cylinder on the rear part of the heater.

As shown in FIG. 2, the vent port 8
A decompression circuit 10 by a vacuum pump 9 is connected via a member 11, and the inside of the vent port is
The plasticization and kneading of the molding material can be performed while reducing the pressure to 150 torr.

In the pressure reducing circuit 10, a recovery tank 12 for cooling and removing volatile components from the molding material and a filter 13 are provided. The recovery tank 12 is formed by alternately partitioning a casing whose peripheral side wall is constituted by a jacket 14 by partition walls 15 and forming a passage 16 for volatile components sucked inside by the partition walls 15. The volatile components guided into the box from the port 8 are collected by cooling with the cooling water flowing through the jacket 14.

In the molding using the injection device having the vent function, the temperature of the heating cylinder 1 is set to 260 to 280 ° C. by the band heater 6. In the conventional injection molding of PET, it is necessary to dry the molding material in advance. In this embodiment, the molding material is directly supplied from the feeder 5 into the heating cylinder without drying. The undried molding material is fed into the supply port by rotation of the feed screw 4 irrespective of the granular or flake shape, thereby improving poor penetration and preventing the weighing variation of the molding material.

The molding material is measured and melted and kneaded while transferring the molding material supplied into the heating cylinder to the front by the injection screw 7, as in the case of ordinary injection molding. The screw 7b is not completely melted up to the compression portion, but is sent to the compression portion in a softened state where the surface is molten and is compressed.

The compressed molding material is extruded to the rear of the front screw 7a, and the diameter of the front screw 7a is smaller than that of the compression part of the rear screw 7b, and the space around the shaft is large. At the same time, volatile components such as water in the molding material expand and escape at the rear of the front screw 7a, and at the same time, the volatile components are continuously sucked by the vacuum pump 9 so that the volatile components are discharged from the vent port 8 to the recovery tank of the pressure reducing circuit 10. 12
Spill out to

As a result, the moisture in the molding material is completely removed, and the molding material is heated and compressed by the compression section of the front screw 7a, further melt-kneaded, and weighed in the cylinder tip in front of the screw. The molding material is injected and filled into a mold by the forward movement of the injection screw 7, and is formed into a desired molded product.

[0018]

As described above, according to the present invention, a molding material made of undried polyethylene terephthalate (PET) is vented to a degree of vacuum of 50 by an injection device having a vent function.
The pressure is reduced to 150 torr, whereby water and the like in the molding material are forcibly removed during plasticization and kneading, so that the molding material is not only unused granules, but also varies in water content. Even a large number of flakes that can be reused can be directly supplied to an injection device and molded without performing preliminary drying.

If the pressure reduction range is other than the vacuum degree of 50 to 150 torr, the molding becomes difficult due to the occurrence of hydrolysis due to the residual water and the occurrence of vent-up, but in the range of the vacuum degree specified by the present invention. The above-mentioned molding obstacle does not occur by continuous suction of PET, and undried granular or flake-shaped PET
Despite using as a molding material, a high-quality molded article having a transparent and improved strength is obtained, and volatile components generated from the molding material are cooled and removed to a recovery tank.

As a result, the time, labor and equipment required for predrying become unnecessary, and automatic molding using undried PET as a molding material becomes possible, so that productivity is improved and molding cost is reduced. It also has the advantage that the working environment is prevented from deteriorating due to volatile components.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of an injection apparatus that can carry out an injection molding method for undried polyethylene terephthalate according to the present invention.

FIG. 2 is a schematic sectional view of a decompression device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating cylinder 2 Nozzle 3 Supply port 5 Feeder 7 Screw 7a Front screw 7b Rear screw 8 Vent port 9 Vacuum pump 10 Pressure reducing circuit 12 Recovery tank

Claims (1)

(57) [Claims] When a molding material made of undried polyethylene terephthalate is fed to an injection device having a venting function to perform injection molding, a peripheral wall is provided with a jacket in a pressure reducing circuit connected to a vent port of a heating cylinder wall. The constructed casing is alternately partitioned by partition walls, and the partition walls form passages for the volatile components sucked into the interior, and a recovery tank is provided for cooling and removing volatile components from the molding material. An injection molding method for undried polyethylene terephthalate, wherein the circuit is vented under reduced pressure to a degree of vacuum of 50 to 150 torr.