What should I look for when injection moulding PET bottle blanks?

1. Treatment of plastic

As PET macromolecules contain lipid groups, with a certain hydrophilic, granules at high temperatures are more sensitive to water, when the water content exceeds the limit, in the processing of PET molecular weight decline, the product with colour, brittle. Therefore, the material must be dried before processing at a drying temperature of 150°C for more than 4 hours, generally 170°C for 3-4 hours. The material can be tested for complete drying by the air injection method. The proportion of recycled material should not exceed 25% in general, and the recycled material should be dried thoroughly.
 

2. Injection moulding machine selection

PET due to the melting point after the stabilization time is short, and the melting point is high, so need to choose more temperature control section, plasticization since the friction of heat generation less injection system, and the actual weight of the product (including water mouth material) can not be less than 2/3 of the injection volume of the machine. based on these requirements, huamida in recent years developed a small and medium series of PET special plasticization system. The clamping force is greater than 6300t/m2.
 

3. Mould and gate design

PET bottle blanks are generally moulded in hot runner moulds. It is best to have a heat insulation plate between the mould and the injection moulding machine template, the thickness of which is about 12mm, while the heat insulation plate must be able to withstand high pressure. Exhaust gas must be sufficient to avoid local overheating or shattering, but the depth of its exhaust port generally should not exceed 0.03mm, otherwise it is easy to produce flying edges.
 

4. Melting temperature

It can be measured by the air injection method. 270-295℃, and the reinforced GF-PET can be set to 290-315℃.
 

5. Injection speed

The general injection speed should be fast to prevent premature solidification during injection. However, too fast, the high shear rate makes the material fragile. The injection is usually completed within 4 seconds.
 

6. Backpressure

The lower the better to avoid wear and tear. Usually not more than 100 bar, usually no need to use.
 

7. Dwell time

Do not use too long a retention time to prevent a drop in molecular weight. Try to avoid temperatures above 300°C. If stopping for less than 15 minutes. Only empty shot treatment is required; if more than 15 minutes, clean with viscosity PE and lower the barrel temperature to PE temperature until the machine is switched on again.
 

8. Cautions

1). The recycled material should not be too large, otherwise, it will easily produce "bridging" at the lower material and affect the plasticization.
2). If the mould temperature is not well controlled or the material temperature is not properly controlled, it is easy to produce "white mist" and opaque. Low and uniform mould temperature, fast cooling speed, less crystallization, then the product is transparent.