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1. Plastic material
Because PET plastic material has strong hygroscopicity, the material must be dried before processing. The drying temperature is 150°C for more than 4 hours; generally 170°C for 3-4 hours. The air jet method can be used to check whether the material is completely dry. The proportion of recycled PET bottle blanks generally does not exceed 25%, and the recycled material should be thoroughly dried.
2. Selection of injection molding machine
Since PET preform molds are generally multi-cavity and heavy, pay attention to the injection weight when selecting an injection molding machine.
The total weight of the product should be 2/3 of the injection weight.
3. Mold and gate design
PET preforms are generally molded with hot runner molds. It is best to have a heat shield between the preform mold and the injection molding machine template, and the heat shield must be able to withstand high pressure. The exhaust must be sufficient to avoid local overheating or fragmentation, but the depth of the exhaust port should generally not exceed 0.03mm, otherwise it is easy to produce flash.
4. Melting temperature
It can be measured by air jet method, the range is 270-295℃, and enhanced GF-PET can be set to 290-315℃
5. Injection speed
The injection speed should be fast to prevent premature solidification during injection. But if it is too fast, the shear rate will be high, making the material brittle. Injection is usually completed within 4 seconds.
6. Back pressure
The lower the better to avoid wear. Generally not exceeding 100bar, usually not needed.
7. Detention time
Do not use too long a retention time to prevent molecular weight from decreasing, and try to avoid temperatures above 300°C. If the machine downtime is less than 15 minutes, only air injection is required; if it exceeds 15 minutes, viscosity PE should be used for cleaning, and the barrel temperature should be reduced to PE temperature until it is started again.