High creep resistance and low-moisture absorption give the polyesters excellent dimensional stability. Black-pigmented grades are recommended for maximum strength retention in outdoor uses. Although impact strength, is exceptional, special care must be observed in designing parts beca polyesters are notch sensitive. Stiffness and creep resistance can be increased by the addition of high glass loadings to thermoplastic polymers. Warpage, which is caused by anisotropic shrinkage, has long been a problem with glass-reinforced thermoplastic polyester.
Several options are available, however, to reduce warpage.
For applications requiring maximum toughness, an amorphous resin, such as polycarbonate, can be blended with the polyester. Warpage is also reduced considerably with the addition of glass and mica reinforcement. Glass-reinforced polyesters have outstanding electrical properties, which are retained after prolonged exposure to a wide range of temperature and humidity conditions. Polyester film is tough, durable, and dimensionally stable. It can be metallized, embossed, slit, die cut, and laminated.