Characteristics and injection molding process of commonly used transparent raw materials in plastics

（1） The preparation and dryness of materials may affect the transparency of the product due to the presence of any impurities in the plastic. Therefore, it is necessary to pay attention to sealing during storage, transportation, and feeding processes to ensure the cleanliness of the materials. Especially when the material contains moisture, heating can cause the material to transform, so it must be dry. During injection molding, it is necessary to use a dry hopper for feeding. It should also be noted that during the drying process, the input air should be filtered and dehumidified to ensure that it does not contaminate the material. The dry process is shown in Table 2,
Drying process of transparent plastics
（2） Cleaning of the barrel, screw and its accessories
To avoid material contamination and the presence of old materials or impurities in the depressions of the screw and accessories, especially in the presence of resin with poor thermal stability, screw cleaning agents should be used to clean all parts before use and after shutdown to prevent impurities from sticking to them. When there is no screw cleaning agent, PE, PS and other resins can be used to clean the screw.
（3） Issues to pay attention to in mold planning (including product planning)
In order to avoid poor plastic molding, appearance defects, and deformation caused by poor activity or uneven cooling, the following points should be taken into account when planning the mold.
a) The wall thickness should be as uniform as possible, and the demolding angle should be satisfactory;
b) The transition should be gradual. Smooth transition to avoid sharp corners. Sharp edges, especially PC products, must not have gaps;
c) Gate. The flow channel should be as wide and short as possible, and the gate orientation should be set according to the shortened condensation process. If necessary, a cold material well should be added;
d) The surface of the mold should be bright and have a low roughness (less than 0.8);
e) Exhaust hole. It is necessary to be satisfied with the groove to timely discharge air and gas from the melt;
f) Except for PET, the wall thickness should not be too thin, generally not less than 1mm.
（4） Issues to pay attention to in terms of injection molding process (including requirements for injection molding machines)
In order to reduce internal stress and external quality defects, attention should be paid to the following issues in the injection molding process.
a) Injection molding machines with dedicated screws and separate temperature controlled nozzles should be selected;
b) The injection temperature should be higher than the injection humidity, provided that the plastic resin does not decompose;
c) Injection pressure: generally high to overcome the disadvantage of high melt viscosity, but too high a pressure can cause internal stress, causing difficulty in demolding and deformation;
d) Injection speed: In the case of satisfactory mold filling, it should generally be low, and slow fast slow multi-stage injection can be selected;
e) Pressure holding time and forming cycle: under the condition of satisfactory product filling without any depression or bubbles; It is advisable to keep it as short as possible to minimize the dwell time of the molten material in the machine barrel;
f) Screw speed and back pressure: On the premise of satisfying the plasticizing quality, it should be as low as possible to avoid the possibility of detachment;
g) Mold temperature: The cooling quality of the product has a significant impact on the quality, so the mold temperature must be able to accurately control its progress. If possible, the mold temperature should be higher.