JPH06315959A - Injection molding method of polyethylene terephthalate - Google Patents

Abstract

PURPOSE:To eliminate the need for crystallized molding material and contrive to reduce material cost by a method wherein uncrystallized polyethylene terephthalate is employed as molding material, which is fed to an injection device so as to be turned into semi-molten state and, after being deaerated, thermally melted and injected. CONSTITUTION:At molding operation, uncrystallized polyethylene terephthalate as molding material without being dried is fed directly from a hopper 3 into a heating cylinder 1 by properly utilizing a feeding device. Next, the molding material in the heating cylinder 1 is melted under the condition being transferred ahead and metered. At this time, the molding material in semi-molten state is fed under compression to a compression zone 8. The compressed molding material in semi-molten state is extruded to the rear part of a forward screw 6a so as to be expanded at its rear part, resulting in separating water content and volatiles content from the molding material. The deaeration molding material is heated up to the temperature higher than its melting temperature and, at the same time, compressed so as to be injected in a mold under fully kneaded condition in order to obtain the desired molded article.

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 capable of molding undried polyethylene terephthalate into various molded articles by using an injection device.

[0002]

2. Description of the Related Art Most of conventional polyethylene terephthalate moldings using an injection device use a crystalline resin as a molding material. In addition, in injection molding, it requires drying for about 4 hours at a temperature of 150 ° C before being supplied to the injection device, and the molding material is heated to 280 ° C to 300 ° C and melted in the heating cylinder inside the injection screw. After kneading, it is injected into the mold.

[0003]

In such a conventional injection molding method, since it is necessary to dry the molding material before injection molding, it takes time to prepare before molding, and a dryer is indispensable as an apparatus. Therefore, there is a problem that material cost and molding cost are required.

The present invention has been conceived in order to solve this conventional problem, and its purpose is to change the melting process of the molding material in the heating cylinder from the conventional one and dry it before injection molding. It is to provide a new method that enables injection molding of a molding material using polyethylene terephthalate without performing the above.

[0005]

The features of the present invention according to the above-mentioned object are that after using amorphous polyethylene terephthalate as a molding material and supplying the molding material directly to an injection device without drying it, it becomes a semi-molten state. Degassing is performed below the melting temperature, the molding material after degassing is heated to above the melting temperature to perform compression and melt-kneading of the molding material, and then to inject the molding material.

Another feature of the present invention is that a molded product to be injection-molded is a preform, and the preform is blow-molded into a hollow molded product.

Furthermore, the present invention is also characterized in that flaky polyethylene terephthalate crushed for reuse and undried crystalline polyethylene terephthalate are used as a molding material.

[0008]

1 is a heating cylinder having a nozzle 2 at the front end and a supply port 4 having a hopper 3 at the rear end. A band heater 5 is attached to the outer periphery of the heating cylinder 1 including the nozzle 2, and the ratio of the screw length to the diameter (L / L) is provided inside.
D) is an injection screen 6 of 26, which is rotatable and movable back and forth.

The injection screw 6 is composed of a front screw 6a and a rear screw 6b which are formed as compression parts 7 and 8 by forming the shaft diameter of the tip end portion larger than the shaft diameters of the other parts. A deaeration hole 9 is provided in the heating cylinder wall on the rear portion of the partial screw 6a.

A band heater 10 for preheating is attached around the rear end of the heating cylinder in which the supply port 3 is located, so that the screw of the molding material flowing into the supply port from the hopper 3 can be smoothly absorbed.

Further, between the heating cylinder 1 and the nozzle 2, temperature detectors 11, 12, 13, 14, by thermocouples,
Nos. 15 and 16 are provided at predetermined intervals, and the temperature of the internal molding material can be controlled within a predetermined temperature range by ordinary means from the measurement of the heating cylinder temperature and the nozzle temperature by these detectors.

In the molding using the above injection device, first, the temperature of the heating cylinder 1 is set for each detector as follows. The detector numbers are indicated by the reference numerals in the figure. Detector 11 12 13 14 15 16 Temperature 275 270 260 260 275 280

Whether the molding material of polyethylene terephthalate is in an uncrystallized state, a crystalline state, or a flaked state by reuse, it is heated and melted, degassed and melt-kneaded under the same means in the heating cylinder. Since it is injected into a mold (not shown) through the above process to be molded into a desired molded product, it will be collectively referred to as a molding material hereinafter.

In the conventional injection molding of polyethylene terephthalate, it is necessary to dry the molding material in advance, but in the present invention, the material is directly supplied from the hopper 3 into the heating without drying. In this case, since the molding material in an uncrystallized state or in a flake state has some difficulty in falling into the supply port 4, it is preferable to use a material having a feeding device in the hopper.

The molding material supplied into the heating cylinder is melted and measured while being transferred forward by the injection screw 5, but the molding material is not completely melted to the compression portion 8 of the rear screw 5b and is semi-melted. In this state, it is sent to the compression unit 8 to be compressed.

The compressed molding material in a semi-molten state is extruded to the rear portion of the front screw 6a, and also the front screw 6a.
Since the shaft diameter is smaller than that of the compression portion 8 and the space around the shaft portion is large, it expands at the rear portion of the front screw 6a.
This facilitates the separation of water and volatiles in the molding material.

Further, since the heating cylinder temperature before and after the deaeration hole 9 is set to 260 ° C. which is lower than the melting temperature (270 ° C.), the molding material is sent forward in a semi-molten state. Therefore, the separated water or the like is discharged from the deaeration hole 9 to the outside of the heating cylinder until the molding material reaches the front compression section 7. Depending on the case, deaeration may be forcedly performed by using a vacuum pump together with decompression.

The degassed molding material is heated and compressed by the compression section 7 of the front screw 6a whose heating cylinder temperature is higher than the melting temperature (275 ° C.), whereby it is completely melted and kneaded to form a cylinder in front of the screw. Weighed into the tip.

By the forward movement of the injection screw 6, the molding material is injection-filled in the mold and molded into a desired molded product.

When the molded product is a preform, the preform can be further molded into a hollow molded product such as a bottle. As a molding means for this hollow molded article,
Immediately transfer the injection-molded preform to the blow mold in the heated state to form a hollow molded product by blowing air, or heat it later and transfer it to the blow mold, and blow the air to blow it It can be applied to any case of molding into a product.

[0021]

As described above, the present invention uses amorphous polyethylene terephthalate as a molding material, and directly supplies the molding material to the injection apparatus without drying it to bring it into a semi-molten state. Degassing is performed, and the molding material after degassing is heated to a temperature above the melting temperature to compress and knead and melt the molding material, and then the molding material is injected, so polyethylene terephthalate is used as before. There is no need to crystallize and use as a molding material. Therefore, the material cost in injection molding is reduced.

Further, even in the case of a crystallized molding material or a flake-shaped molding material, drying is not required, so that a drying time for injection molding is not required and a device such as a dryer is not required, which results in a molding cost. Significantly reduced.

Furthermore, since the molding material can be primarily molded into a preform and the preform can be blow-molded into a hollow molded product, various molded products can be molded with polyethylene terephthalate, and polyethylene terephthalate can be reused. Also has very effective advantages.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional side view of an injection device used for injection molding of polyethylene terephthalate according to the present invention.

[Explanation of symbols]

 1 Heating Cylinder 2 Nozzle 3 Hopper 4 Supply Port 5 Band Heater 6 Injection Screw 6a Front Screw 6b Rear Screw 7 Front Compression Portion 8 Rear Compression Portion 9 Degassing Hole

Claims (4)

[Claims] 1. A non-crystalline polyethylene terephthalate is used as a molding material, and the molding material is directly supplied to an injection device without being dried to be in a semi-molten state, and then degassing is performed at a temperature equal to or lower than a melting temperature. An injection molding method of polyethylene terephthalate, characterized in that the molding material after the above is heated to a melting temperature or higher to compress and melt-knead the molding material, and then the molding material is injected. 2. Uncrystallized polyethylene terephthalate is used as a molding material, the molding material is directly supplied to an injection device without being dried to be in a semi-molten state, and then degassing is performed at a temperature not higher than the melting temperature. The subsequent molding material is heated above the melting temperature to perform compression and melt-kneading of the molding material, after which the molding material is injected to form a preform, and the preform is blow molded into a hollow molding product. A characteristic method of injection molding polyethylene terephthalate. 3. The method of injection molding polyethylene terephthalate according to claim 1, wherein the molding material is flaky polyethylene terephthalate crushed for reuse. 4. The method of injection molding polyethylene terephthalate according to claim 1, wherein the molding material is undried crystalline polyethylene terephthalate.