Dielectric studies of epoxy/polyester powder coatings containing titanium dioxide, silica, and zinc oxide pigments

Abstract

Dielectric measurements are reported covering a frequency range from 10−3 to 105 Hz and a temperature range from ~355 to 410 K for a pigmented epoxy/polyester resin powder coating system. A large low frequency ohmic conduction was observed in all these systems and the electrical modulus representation was used to aid analysis. A space charge relaxation indicative of heterogeneity in the matrix was observed in the pure resin and the pigmented coatings. In the pure resin, the heterogeneity is associated with nanoscale phase separation. A study with the resin modified with Modaflow, an ester copolymer dispersion agent, shows that the dipole relaxation is more ideal and the activation energy for dipole relaxation is reduced compared with that observed in the pure resin. The introduction of titanium dioxide pigment reduces the activation energy but also increases the magnitude of the ohmic conductivity and space charge contributions to the dielectric permittivity. All the systems exhibit heterogeneity and in the case of a pigmented system charge carriers can be introduced into the system by the pigment. Clear differences are observed between TiO2 produced via the chloride and sulfate routes, reflecting different levels of charge carriers and ion mobile in the resin system. High levels of mobile ions were also observed when zinc oxide and silica were used as pigments.