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

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

Ⅰ. Production background of PET plastic bottles


Since ancient times, pursuiting beauty has been the nature of women. With the development of the economy and the improvement of people's living standards, more and more women have begun to pay attention to skin management, and makeup has become a daily necessity for many women. How is the cosmetic bottle with good looks produced, and what special crafts does it have?


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!

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