Due to the high light transmittance of transparent plastics, the surface quality of plastic products must be strictly required, and there should be no markings, pores, and whitening. Haze, black spots, discoloration, poor gloss and other defects, so in the entire injection molding process, raw materials, equipment.
Secondly, because most of the transparent plastics have high melting point and poor fluidity, in order to ensure the surface quality of the product, it is often necessary to make fine adjustments to the process parameters such as high machine temperature, injection pressure, injection speed, etc., so that the plastic injection can not only fill the mold, but also not. Internal stress will cause product deformation and cracking.
1、Preparation and drying of materials Because any impurities in the plastic may affect the transparency of the product, and therefore storage and transportation.
During the feeding process, attention must be paid to sealing to ensure that the raw materials are clean. In particular, the raw material contains moisture, which will cause the raw material to deteriorate after heating, so it must be dried, and a drying hopper must be used for feeding during injection molding.
It should also be noted that in the drying process, the input air should preferably be filtered and dehumidified to ensure that the raw materials will not be polluted.
Its drying process, such as the drying process of transparent plastic: material process drying temperature (℃) drying time (h) material layer thickness (mm) remarks pmma70～802～430～40pc120～130>6<30, use hot air circulation to dry pet140～1803 ~4 It is better to use continuous drying and feeding device
2、Cleaning of barrel, screw and accessories In order to prevent the contamination of raw materials and the existence of old materials or impurities in the depression of screw and accessories, especially the resin with poor thermal stability, screw cleaning agent should be used before use and after shutdown. Clean all parts so that there are no impurities. When there is no screw cleaning agent, you can use pe, ps and other resins to clean the screw.
When temporarily shutting down, in order to prevent the raw materials from staying at high temperature for a long time and causing degradation, the temperature of the dryer and the barrel should be lowered, such as the barrel temperature of pc, pmma, etc. should be lowered to below 160 °C. (Hopper temperature should drop below 100°C for pc)
Problems that should be paid attention to in mold design (including product design) In order to prevent poor backflow or uneven cooling, resulting in poor plastic molding, surface defects and deterioration, generally in mold design, the following points should be paid attention to .
a = The wall thickness should be as uniform as possible, and the demolding slope should be large enough;
b = The transition part should be gradual. Smooth transitions to prevent sharp corners. Sharp edges are generated, especially PC products must not have gaps;
c = gate. The runner should be as wide and stubby as possible, and the gate position should be set according to the shrinkage and condensation process, and a cold well should be added if necessary;
d=The surface of the mold should be smooth and low in roughness (preferably lower than 0.8);
e = vent hole. The tank must be sufficient to discharge air and gas in the melt in time;
f = Except for pet, the wall thickness should not be too thin, generally not less than 1mm.