In our daily life, we have been exposed to a variety of plastic products , some are colorful, some are colorless and transparent. Let's take a look at the magical magic that makes plastic products transparent. Process characteristics of transparent plastics: In addition to the common problems in the injection molding process of plastic products, transparent plastics also have some process characteristics, which are described as follows:
1. Process characteristics of PMMA
PMMA has high viscosity and poor fluidity. Therefore, it must be filled with high material temperature and high injection pressure. The injection temperature is greater than the injection pressure, but the injection pressure is increased, which is beneficial to improve the shrinkage rate of the product. The injection temperature range is wide, the melting temperature is 160 ° C, and the decomposition temperature is 270 ° C, so the material temperature adjustment range is wide and the processability is good. Therefore, improving fluidity can be started from the injection temperature. Poor impact, poor wear resistance, easy to scratch, easy to brittle, it should improve the mold temperature, improve the condensation process, to overcome these defects.
2, PC process characteristics
PC has high viscosity, high melt temperature and poor fluidity. Therefore, it must be injection molded at a higher temperature (between 270 and 320 °C). Relatively speaking, the temperature adjustment range is narrower and the processability is not as good as PMMA. The injection pressure has little effect on the fluidity, but due to the large viscosity, the injection pressure is still large, and the pressure holding time should be as short as possible in order to prevent the internal stress. The shrinkage rate is large and the size is stable, but the internal stress of the product is large and easy to crack. Therefore, it is better to increase the temperature instead of the pressure to improve the fluidity, and to improve the mold temperature and improve the mold structure and post-treatment to reduce the possibility of cracking. When the injection speed is low, the gate is prone to ripples and other defects, the temperature of the nozzle is controlled separately, the mold temperature is high, and the runner and gate resistance are small.
3, PET process characteristics
PET molding temperature is high, and the material temperature adjustment range is narrow (260-300 ° C), but after melting, the fluidity is good, so the processability is poor, and the anti-ducting device is often added in the nozzle. Mechanical strength and performance are not high after injection, and performance must be improved by stretching and modification. The mold temperature is accurately controlled to prevent warpage. An important factor in deformation is therefore recommended for hot runner molds. The mold temperature should be high, otherwise it will cause poor surface gloss and difficulty in demolding.
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