What Should Be Paid Attention to in the Injection Molding of PET Plastic Bottles?

Ⅰ. Production background of PET plastic bottles

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Ⅱ. Matters needing attention during injection molding of PET plastic bottles

1. Plastic processing

Since the macromolecules of PET plastic bottles contain fat bases and have certain hydrophilicity, the pellets are more sensitive to water at high temperatures. When the moisture content exceeds the limit, the molecular weight of PET plastic bottles will decrease during processing, and the products will become colored and  brittle. Because of this, the materials must be dried before processing. The drying temperature is 150°C for 4 hours or more, generally 170°C for 3-4 hours. The air shot method can be used to check whether the material is completely dry. The proportion of recycled materials should generally not exceed 25%, and the recycled materials must be thoroughly dried.

2. Selection of injection molding machine

Since PET plastic bottles have a short stabilization time after melting point and high melting point, it is necessary to choose an injection system with more temperature control sections and less self-friction heat generation during plasticization, and the actual weight of the product (water-containing material) cannot be less than 2/3 of the injection volume of the machine. 

3. Mould and gate design

PET plastic preforms are generally formed by hot runner molds. It is better to have a heat shield between the mold and the injection molding machine template, the thickness of which is about 12mm, and the heat shield must be able to withstand high pressure. Exhaust must be sufficient to avoid local overheating or chipping, but the depth of the exhaust port should generally not exceed 0.03mm, otherwise it is easy to produce flash.

4. Melting temperature can be measured by air shot method

The temperature ranges from 270-295℃, and the reinforced GF-PET plastic bottle can be set at 290-315℃.

5. Injection speed

Generally, the injection speed should be fast to prevent premature solidification during injection. But too fast and high shear rate make the material fragile. Injection is usually completed within 4 seconds.

6. Back pressure

The lower the back pressure, the better to avoid wear. Generally not more than 100bar. Usually not needed.

7. Detention time

Do not use too long a residence time to prevent molecular weight drop. Try to avoid temperatures above 300°C. If the shutdown is less than 15 minutes. Only need to do air injection treatment; if it exceeds 15 minutes, clean with viscosity PE, and reduce the barrel temperature to PE temperature until it is turned on again.

Zhejiang B.I. Industrial Co., Ltd. has many PET plastic bottles for sale, welcome to contact us to buy!