Tracking Properties

Tracking breakdown refers to the formation of tracking (a conducting carbonized path) on either or both of the surface and the inside of a molded product due to the combined action of the electrical field and electrolyte contamination, resulting in dielectric breakdown. To determine the tracking resistance, electrodes (an electrical field) are brought into contact with a flat plate shaped test piece and drops of electrolyte are put between those electrodes, such that the voltage that results in dielectric breakdown can be determined, as shown in the schematic diagram (Fig. 7.14). For the tracking properties, the comparative tracking index (CTI) is often used. In the UL standards, the breakdown voltage is classified into six classes (PLCs).

It is known that, in general, PPS is more likely to form a conducting carbonized path than nylon or polyester, and has a low tracking resistance. TORELINA™ A660MB is a grade that has a drastically improved tracking resistance, as it suppresses the formation of a conducting carbonized path. It has been assigned the highest rank (rank 0) of the UL standards. TORELINA™ A660EXB is a grade for which the mechanical strength has been enhanced to a level comparable to a general high-filler PPS, while maintaining its tracking resistance. (Table. 7.4)