PC GF20 method of reducing internal stress, in addition to avoiding notch, sharp angle, thickness and disparity in design of product, and adopting correct molding process parameters, etc., it is preferable to heat-treat product, and heat treatment is controlled at 125 to 135 ° C (resin Tg or less) 10~20°C), treatment time is about 2h, and thicker product, longer treatment time. Generally, product has a wall thickness of less than 5 mm, and time is 8 hours; product is larger than 20 mm, and time is 24 hours. internal stress of article can be determined by a polarization test and a solvent dipping method. polarized light test method is applicable to various transparent products. It uses transparency of PC GF20 to place product between polarized lenses, observes colored light strip area on surface of product from mirror, and determines inside of product by size of colored strip area. magnitude of stress, if observed area of ribbon is large, indicating that internal stress of product is large; solvent impregnation method is a commonly used detection method in factory, which is to immerse PC GF20 product in certain solvents (such as benzene and tetrachloride). Among carbonized carbon, cyclohexane, ethanol, methanol, etc., stress is determined by time required for product to be cracked, and longer time, smaller stress. If it is immersed for 5 to 15 s, it will crack, indicating that internal stress is very large. If immersion does not occur for 1 to 2 minutes, internal stress is small, and product generally does not crack during use. Injection molding process Drying treatment: PC GF20 materials are hygroscopic, and drying before processing is important. Dry conditions are recommended from 100C to 200C for 3 to 4 hours.