Due to the high light transmittance of transparent plas […]
Due to the high light transmittance of transparent plastics, the surface quality of plastic products must be strict, and there must be no markings, pores or whitening. Fog, black spots, discoloration, poor gloss and other defects, so the raw materials, equipment throughout the injection process. Molds and even product designs must pay great attention to and impose strict or even special requirements.
Secondly, because transparent plastics have high melting point and poor fluidity, in order to ensure the surface quality of the products, the process parameters such as machine temperature, injection pressure and injection speed are often finely adjusted so that the plastic can be filled with mold without Internal stress is generated to cause deformation and cracking of the product. Therefore, strict preparation is required from the preparation of raw materials, equipment and mold requirements, injection molding processes and raw material handling of products.
The preparation and drying of the material may affect the transparency of the product due to the inclusion of any impurities in the plastic, and therefore storage and transportation. During the feeding process, attention must be paid to the sealing to ensure that the raw materials are clean. In particular, the raw material contains moisture, which causes deterioration of the raw material after heating, so it must be dried, and when it is injected, the drying hopper must be used for the feeding.
It should also be noted that during the drying process, the input air should preferably be filtered and dehumidified to ensure that the raw materials are not contaminated. Drying process, such as drying process of transparent plastic: material process drying temperature (°C) drying time (h) material layer thickness (mm) Remarks pmma70~802~430~40pc120~130>6<30 using hot air circulation drying pet140~1803 ~4 The continuous drying feeding device is better, the barrel, the screw and its accessories are cleaned to prevent contamination of raw materials and old materials or impurities in the recesses of the screw and accessories.
Specially, the resin with poor thermal stability exists. Therefore, the screw cleaning agent should be used to clean the parts before use and after shutdown, so that they do not stick to impurities. When there is no screw cleaning agent, the screw can be cleaned with pe, ps and other resins. When temporarily stopping, in order to prevent the raw material from staying at high temperature for a long time, causing the solution to fall, the temperature of the dryer and the barrel should be lowered. For example, the temperature of the barrel such as pc and pmma should be reduced to below 160 °C.
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