Brief introduction of transparent plastic injection molding

Due to the high light transmittance of transparent plastics, the surface quality of plastic products is strictly controlled, and there should be no streaks, pores, or whitening. Defects such as halo, black spots, discoloration, and poor gloss exist, so raw materials and equipment are affected during the entire injection molding process. The design of molds and even products must be very careful and even harsh. 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 in process parameters such as high temperature, injection pressure, and injection speed, so that the injection molded parts can be filled with the mold without Will produce internal stress and cause product deformation and cracking. Therefore, strict operations must be carried out in terms of raw material preparation, equipment and mold requirements, injection molding process and raw material handling of products. The operation of these points is beyond doubt.


In the process of injection molding, the preparation and drying of raw materials should not contain any impurities in the plastic, any impurities may affect the transparency of the product, so it is related to storage and transportation. During the feeding process, attention must be paid to sealing to ensure that the raw materials are clean. Especially the raw material contains moisture, which will cause the raw material to deteriorate after heating, so it must be dried, and when injecting parts, a drying hopper must be used for 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 will not be polluted. Drying process of transparent plastic: material process drying temperature (°C) drying time (h) material layer thickness (mm) remarks pmma70～802～430～40 pc120～130>6<30 Drying with hot air circulation
Pet140～1803～4 is better to adopt continuous drying feeding device.


There are many areas that require special attention. Cleaning of barrel, screw and its accessories. In order to prevent contamination of raw materials and the presence of old materials or impurities in the recesses of the screw and accessories, especially resins with poor thermal stability, the screw cleaning agent should be used to clean all parts before use and after shutdown to prevent impurities from sticking. When there is no screw cleaning agent, resins such as PE and PS can be used 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 temperature of the pc, pmma and other barrels should be lowered below 160 °C.


Attention should be paid to the problems that should be paid attention to in the mold design. In order to prevent poor back flow or uneven cooling, resulting in poor plastic molding, surface defects and deterioration, the following points should be paid attention to in mold design. a) The wall thickness should be as uniform as possible, and the demoulding slope should be large enough; b) The transition part should be gradual. Smooth transitions to avoid sharp corners. Sharp edges are produced, especially pc products must not have gaps; c) Gate. The runner should be as wide and short 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; e) Vent holes. The groove must be sufficient to discharge the air and the gas in the melt in time.


Schematic of clear plastic injection molding. Here, the surface quality of plastic products is required to be strict without any defects. The injection molding process and the raw material handling of the product must be strictly operated. Injection molding requires good technology to support. The preparation and drying of raw materials must not contain any impurities in the plastic. The raw material must not contain any moisture. Clean all parts with screw cleaning agent before use and after shutdown. Problems that should be paid attention to in mold design In order to prevent poor back flow, or uneven cooling, resulting in poor plastic molding, surface defects and deterioration. Many issues require attention. Such as thickness, draft angle, gate, etc.