PET chemical name polyterephthalate ethanol ester, also known as polyester. At present, GF-PET is used more in customers, mainly for bottling embryos. The rheology of PET in the molten state is better, and the influence of pressure on viscosity is greater than that of temperature, so the flow of melt is mainly changed from pressure.
1, plastic treatment
Since PET macromolecules contain lipid groups and have a certain hydrophilicity, the particles are more sensitive to water at high temperatures, and when the moisture content exceeds the limit, the molecular weight of PET decreases during processing, and the products are colored and brittle. Therefore, the material must be dried before processing, and the drying temperature is 150 ° C for more than 4 hours, generally 170 ° C for 3-4 hours. The material can be tested completely dry by air shooting. Generally, the proportion of recycled materials should not exceed 25%, and the recycled materials should be thoroughly dried.
2, injection molding machine selection
Because PET has a short time to stabilize after the melting point and a 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 mouth material) can not be less than 2/3 of the machine injection amount. Based on these requirements, Ramada has developed a small and medium series of PET plasticizing systems in recent years. The clamping force should be greater than 6300t/m2.
3. Mold and gate design
PET bottle embryo is generally formed by hot runner mold, and there should be a heat insulation plate between the mold and the injection molding machine template, whose thickness is about 12mm, and the heat insulation plate 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 is generally not more than 0.03mm, otherwise it is easy to produce flash.
4, melting temperature
It can be measured by air emission. 270-295℃ range, enhanced grade GF-PET can be set to 290-315℃.
5. Injection speed
Generally, the injection speed should be fast, which can prevent premature solidification during injection. But too fast, high shear rate makes the material fragile. The shot is usually completed within 4 seconds.
6. Back pressure
The lower the better to avoid wear and tear. Generally not more than 100bar. Usually not needed.
7. Retention time
Do not use too long retention time to prevent molecular weight drop. Try to avoid temperatures above 300 ° C. If the shutdown is less than 15 minutes. Only air fire processing is required; If it is more than 15 minutes, it is necessary to clean with viscosity PE, and reduce the barrel temperature to PE temperature until it is turned on again.
8. Precautions
(1) The recovered material should not be too large, otherwise it is easy to produce "bridge" at the bottom of the material and affect plasticization.
(2) If the mold temperature control is not good or the material temperature control is improper, it is easy to produce "white fog" and not transparent. The mold temperature is low and uniform, the cooling speed is fast, and the product is transparent with less crystallization.
anti-uv pet bottle packaging https://www.plasticsproduct.com/Unveiling-the-Benefits-of-Anti-UV-Pet-Bottles.html
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