Effect of gradient distribution of fillers on polymeric PTC thermistors prepared by solution mixing and subsiding method

Abstract

The PTC materials are widely utilized in regulating components of heat and electricity by virtue of the special resistivity-temperature characteristics. The high room temperature resistivity and low PTC intensity restrict the application of polymeric PTC thermistors. A solution mixing and subsiding method was developed to fabricate the thermistors with different gradient distributions of TiC and CB fillers in PVDF matrix, owing to the low viscosity of dispersion and the difference in density of fillers and solution. The easily settleable TiC assembled at the interface of copper foil and PTC material could provide abundant conductive sites to significantly reduce the interface resistances. The difficultly settleable CB uniformly distributed over the matrix could effectively decrease the bulk resistance. Through adjusting the subsidence time and filler compositions, the optimal conductivity (ρ = 0.58 Ω cm) and PTC intensity (7.0) of polymeric PTC thermistor were obtained. Moreover, the switch temperature was markedly improved and the NTC effect was weakened.