Tracking Resistance of Flame Retardant Glass Reinforced PBT

While polybutylene terephthalate (PBT) resins have excellent electrical properties, addition of standard brominated flame retardants (FR) is known to diminish electrical performance. However many electrical devices, such as switches and especially circuit breakers, require ignition resistance imparted by the bromine additives. A new mineral glass filled FR-PBT technology has been developed that retains the mechanical properties and easy flow of the existing FR-PBT thermoplastics while improving electrical properties to the level of performance seen in thermoset resins. Products using the new additive technology have been developed that give UL-94 FR ratings of V-0 at 0.75 mm, 5VA at 2 mm and CTI values of over 600 volts. Devices made from this resin also show arc resistance of > 180 sec (class 4) High amp arc ignition is >120 arcs. Thermal index with electrical proper- ties is 130°C.