Resistors having different degrees of crosslinking were made by curing carbon black-graft polymers (grafted with n-butyl acrylate and acrylic acid) with an epoxy resin on porcelain plates, in order to obtain some information concerned with the effect of crosslinking on the large positive temperature coefficient of. electrical resistivity.

For the resistors prepared with the ratio 1/1 of carboxyl group/epoxy group, the gel fraction increased with increasing curing temperature or curing time, and therefore, the crosslinks increased. The volume resistivity decreased with increasing crosslinking and was in the range of 1-8Ωcm. The resistance temperature curves showed a distinct positive anomaly at about 80-100℃ attributable to volume expansion of polymer. The variation of resistance at 140℃ decreased with increasing crosslinking except for the samples which showed bad thermal stability against heating cycle between 40-140℃.

On the other hand, all the resistors made of polymer compositions having different ratios of carboxyl group/epoxy group and cured at 160℃ for 2 hr exhibited good thermal stability against heating cycle between 40-140℃, though their degrees of crosslinking were different. The least crosslinked resistor showed no anomaly of resistivity. It is considered that rearrangement of the carbon black network may occur toward lowering the resistance by static electric force in less crosslinked resistors.