What should I pay attention to when molding PET bottles?
1, plastic processing
Because PET macromolecules contain lipid groups and have certain hydrophilicity, the pellets are sensitive to water at high temperature. When the moisture content exceeds the limit, the molecular weight of PET decreases during processing, and the products become brittle and brittle. In this case, the material must be dried before being processed. The drying temperature is 150 degrees centigrade and more than 4 hours. The temperature is usually 170 DEG C and 3-4 hours. The air can be used to check whether the material is completely dry.
The ratio of recycled materials should not exceed 25%, and the recycled materials should be thoroughly dried.
2 、 selection of injection molding machine
PET due to stability in the melting point after a short time, while the melting point is higher, so the selection of temperature control, more self plasticizing injection system less friction heat, and products (water outlet) the actual weight of not less than the amount of 2/3 injection machine. Based on these requirements, the Ramada has developed a small and medium series of PET special plasticizing system in recent years. Clamping force is greater than 6300t/m2.
3 、 die and gate design
PET bottle embryo is usually molded with hot runner mold. It is better to have a heat shield between the mold and the injection moulding board, the thickness is about 12mm, and the insulation board can withstand the high pressure. Exhaust must be sufficient, so as to avoid local overheating or fragmentation, but the exhaust depth is generally not more than 0.03mm, otherwise it is easy to generate flying edge.
4, melt temperature
Measured by an empty shot. 270-295 degrees of difference, the enhanced grade GF-PET can be set to 290-315 degrees, etc..
5, injection speed
Generally, the injection speed is fast, can prevent premature solidification when injection. But too fast, high shear rate, brittle material. The shot is usually finished within 4 seconds.
6, back pressure
The lower the better, so as not to wear. Generally not more than 100bar. It is usually not necessary to use.
7. Retention time
Do not use excessive dwell time to prevent molecular weight loss. Try to avoid temperatures above 300 degrees celsius. If the stop is less than 15 minutes. Only for empty handling; if more than 15 minutes, then use viscosity PE cleaning, and the cylinder temperature to PE temperature, until the boot.
8, matters needing attention
The recycled material can not be too large, otherwise easy to produce in the material at the "bridge" and the effect of plasticization.
If the mold temperature control is not good or the material temperature control is undeserved, easy to produce "white and opaque". Mould temperature is low and uniform, cooling speed is fast, crystallization is little, then the product is transparent.