Transparent plastics are widely used in life and have become one of the necessities. Transparent plastic products should be strictly operated in terms of raw material preparation, equipment and mold requirements, injection molding process and raw material handling of products.
1、 The preparation and drying of materials may affect the transparency of products due to any impurities contained in the plastic, so it is necessary to store and transport the materials. During the feeding process, attention must be paid to sealing to ensure that the raw materials are clean. In particular, the raw materials contain water, which will deteriorate after heating, so they must be dried. During injection molding, the 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 it will not pollute the raw materials.
Its drying process, such as the drying process of transparent plastics: material process drying temperature (℃) drying time (h) material layer thickness (mm) Remarks: pmma70 ～ 802 ～ 430 ～ 40pc120 ～ 130>6<30 Use hot air circulation drying pet140 ～ 1803 ～ 4 Use continuous drying feeding device is preferred
2、 Cleaning of barrel, screw and its accessories In order to prevent raw material pollution and the existence of old materials or impurities in the concave of screw and its accessories, especially the existence of resins with poor thermal stability, screw cleaning agents should be used to clean all parts before use and after shutdown to make them free from impurities. When there is no screw cleaning agent, the screw can be cleaned with PE, PS and other resins. In case of temporary shutdown, in order to prevent the raw materials from staying at high temperature for a long time, which may cause desorbing, the temperature of the dryer and the barrel should be reduced, such as the temperature of the PC, pmma and other barrel should be reduced to below 160 ℃. (The hopper temperature should drop below 100 ℃ for pc)
3、 Problems needing attention in mold design (including product design) In order to prevent poor plastic molding due to poor reflow or uneven cooling, surface defects and deterioration, the following points should be paid attention to in mold design. A=The wall thickness shall be uniform as far as possible, and the demoulding slope shall be large enough; B=The transition shall be gradual. Smooth transition to prevent sharp corners. Sharp edges, especially PC products must not have gaps; C=gate. The runner shall be as wide and short as possible and shall be
The gate position shall be set during the contraction and condensation process, and the cold charging well shall be added if necessary; D=The mold surface shall be smooth and clean with low roughness (preferably less than 0.8); E=vent. The tank must be sufficient to discharge air and gas in the melt in time; F=Except for PET, the wall thickness shall not be too thin, generally not less than 1mm.
Under such strict operation, the transparent plastic products we usually see will appear.