The injection molding process of transparent plastic products is strict
Due to the high light transmittance of transparent plastics, plastic product processing manufacturers must require strict surface quality requirements for plastic products, and there can be no markings, pores, and whitening. Fog halo, black spots, discoloration, poor gloss and other defects, so in the whole injection molding process on raw materials, equipment. The design of molds and even products must pay great attention to and put forward strict and even special requirements. Secondly, because transparent plastics mostly 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 temperature, injection pressure, injection speed, etc., so that the plastic injection can not only fill the mold, but also will not produce internal stress and cause product deformation and cracking. Therefore, strict operations must be carried out from the preparation of raw materials, equipment and mold requirements, injection molding processes and raw material handling of products.
First, the preparation and drying of the material may affect the transparency of the product because it contains any impurities in the plastic, so it is stored and transported. During the feeding process, attention must be paid to sealing to ensure that the raw materials are clean. In particular, the raw materials contain moisture, which will cause the raw materials to deteriorate after heating, so be sure to dry, and when injection molding, the drying hopper must be used for feeding. It should also be noted that during the drying process, the input air should be filtered and dehumidified to ensure that the raw materials will not be contaminated. Its drying process, such as, the drying process of transparent plastics: material process, drying temperature (°C), drying time (h), material layer thickness (mm), remarks: pmma70~802~430~40pc120~130>6<30 hot air circulation drying PET140~1803~4, continuous drying feeding device is preferred.
Second, the cleaning of the barrel, screw and its accessories to prevent raw material pollution and in the screw and accessories depression stored old materials or impurities, especially poor thermal stability of the resin exists, so before use, after shutdown are used screw cleaning agent to clean each piece, so that it must not stick to impurities, when there is no screw cleaning agent, can be used PE, PS and other resins to clean the screw. When temporarily stopped, in order to prevent the raw materials from staying at high temperature for a long time and causing dissolution, the dryer and barrel temperature should be reduced, such as PC, PMMA and other barrel temperatures should be reduced to below 160 °C. (Hopper temperature for PC should be reduced below 100°C)
Third, in the mold design should pay attention to the problem (including product design) in order to prevent poor backflow, or uneven cooling caused by poor plastic molding, surface defects and deterioration, generally in the mold design, should pay attention to the following points. 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. Sleek transitions to prevent sharp corners. Sharp edge generation, especially PC products must not have notches; c = gate. The runner should be as wide and short as possible, and the gate position should be set according to the shrinkage condensation process, and a cold material well should be added if necessary; d = mold surface should be smooth, roughness low (less than 0.8); e = exhaust hole. The tank must be sufficient to discharge the air and the gas from the melt in time; f = except for PET, the wall thickness should not be too thin, generally not less than lmm.
