Generally, there are 3 plastic materials to be selected to make a high transparent profile or channels or plastic edge trims. What material characteristics are needed to make transparent plastic profiles?
- First, high transparency
- Secondly, strength. It means high impact resistance, abrasion resistance, heat resistance, chemical resistance with a low rate of water absorption. Plastic resin with these necessary proprieties can be used for transparent profiles extrusion.
Polycarbonate -PC- is an ideal choice, but the price is high and the injection molding process is difficult, so most manufacturers choose PMMA as a second substitute, and also some PET can also be extruded for transparent plastic profiles. It has to be stretched to obtain good mechanical properties, so it is mostly used in the packaging and containers industries.
PMMA: High viscosity, poor fluidity, high material temperature, and high injection pressure. The influence of injection temperature is greater than the injection pressure. The increase in injection pressure helps to improve the shrinkage of the extruded 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 manufacturability is better. Therefore, to improve fluidity, start from the injection temperature. The impact resistance is poor, the wear resistance is not good, it is easy to scratch, and it is easy to be brittle. Therefore, it is necessary to increase the mold temperature and improve the condensation process to overcome these defects.
PC: High viscosity, high melting temperature, poor fluidity, it must be injection molded at a higher temperature (between 270~320℃). Relatively speaking, the temperature adjustment range of the material is narrow, and the manufacturability is not as good as PMMA.
The injection pressure has little effect on the fluidity, but due to the high viscosity, the injection pressure is still higher. In order to prevent internal stress, the pressure holding time should be as short as possible.
The shrinkage rate is large and the size is stable, but the product has high internal stress and is easy to crack. Therefore, it is better to increase the temperature instead of pressure to improve the fluidity, and the possibility of cracking can be reduced by increasing the mold temperature, improving the mold structure, and post-processing.
When the injection speed is low, defects such as ripples are likely to occur at the gate, the temperature of the radiating nozzle must be controlled separately, the mold temperature must be high, and the runner and gate resistance should be small.
Transparent PET profile extrusion parts
The PET molding temperature is high, and the material temperature adjustment range is narrow (260-300℃), but after melting, it has good fluidity, so the manufacturability is poor, and it is often necessary to add anti-spreading devices in the nozzle.
The mechanical strength and performance are not high after injection, and the performance must be improved through the stretching process and modification.
Accurate control of mold temperature is an important factor in preventing warpage and deformation. Hot runner molds are recommended.
The above is the analysis of Plastic Extrusion processing characteristics of three commonly used transparent plastic