Most PPA resins are processed by conventional injection molding methods. The PPA materials are pre-dried to a moisture level of less than 0.1% and then placed in a heat-sealed metal bag or box. These containers ensure that the PPA material is not used before processing. Dry again. The acceptable humidity level for the process is 0.15% or less. The processing of wet resins results in a reduction in molecular weight, resulting in a corresponding loss of mechanical properties. Using a desiccant bucket dryer, it is easy to dry the resin to a dew point humidity of -25 °F or even lower at 175 °F. The drying time depends on the amount of water absorbed, generally in the range of 4-16 hours. The melting temperature during injection molding is in the range of 615-650 °F, and the material stays in the barrel for no more than 10 minutes, so that the molded product has excellent performance. The mold temperature is required to be at least 275 °F in order to obtain a product with excellent crystallization and excellent dimensional stability. Partially thick-walled parts can be injection molded at lower mold temperatures due to slower cooling rates. The mold temperature is critical to the superior surface feel of the finished part. The mineral filler grade PPA resin used for vacuum metallization into electroplated metal has a mold surface temperature of 350 °F.
