PET chemical name is polyethylene terephthalate, also known as polyester. Currently the most used among customers is GF-PET, which is mainly used to make Pet Preform.
The rheology of PET in molten state is better, and the effect of pressure on viscosity is greater than temperature. Therefore, the fluidity of the melt is mainly changed from pressure.
1, plastic processing
Since the PET macromolecule contains a lipid group and has a certain hydrophilicity, the pellet is sensitive to water at a high temperature. When the moisture content exceeds the limit, the molecular weight of the PET decreases during processing, and the product is colored and brittle. Therefore, the material must be dried before processing, and its drying temperature is 150 ° C, 4 hours or more, generally 170 ° C, 3-4 hours. Airborne methods can be used to verify that the material is completely dry.
The proportion of recycled materials should not exceed 25%, and the recycled materials should be thoroughly dried.
2, injection molding machine selection
Since PET has a stable time after melting point and a high melting point, it is necessary to use an injection system with more temperature control sections and less self-friction heat during plasticization, and the actual weight of the product (aqueous mouth material) cannot be less than the machine injection. 2/3 of the amount.
3, mold and gate design
Pet preforms are generally formed by hot runner molds. There is preferably a heat shield between the mold and the injection molding machine. The thickness of the preform is about 12 mm, and the insulation board must withstand high pressure. Exhaust gas must be sufficient to avoid local overheating or chipping, but the depth of the exhaust port should not exceed 0.03mm, otherwise it will easily produce flash.
4, the melting temperature
It can be measured by air-to-air method. Between 270 and 295 ° C, the enhanced grade GF-PET can be set to 290-315 ° C and the like.
5, injection speed
Generally, the injection speed is fast, which prevents premature coagulation during injection. But too fast, the high shear rate makes the material brittle. The shot is usually completed in 4 seconds.
6, back pressure
The lower the better, so as not to wear. Generally no more than 100bar. Usually no need to use.
7, staying time
Do not use excessive residence times to prevent molecular weight degradation. Try to avoid temperatures above 300 °C. If the shutdown is less than 15 minutes. Only need to be air-blasted; if it is more than 15 minutes, clean it with viscosity PE and reduce the temperature of the barrel to PE temperature until it is turned on again.
8, matters needing attention
(1) The recycled material should not be too large, otherwise it will easily cause “bridge” at the blanking and affect plasticization.
(2) If the mold temperature is not well controlled or the material temperature is not properly controlled, it is easy to produce “white fog” and is opaque. The mold temperature is low and uniform, the cooling rate is fast, and the crystallization is less, the product is transparent.
Jilian Plastic Mould is an experienced China Pet Bottle design and manufacturer. We are experts in this field. We can provide you with product solutions in the shortest time and can deliver in the shortest time, so Feel free to choose us.