Effects of ionic component on the dielectric and thermal properties of epoxy resins

Epoxy casting resin is used for important insulating parts in the high-voltage engineering industry. Such insulators are required to be highly reliable, and their reliability depends greatly on the curing process for epoxy resins in molds. In particular, the long-term reliability of insulation parts depends largely on residual stress and initial defects such as voids, cracks and shrinkage. For this reason we have carried out an advanced investigation of the dielectric analysis (DEA) for the process control. Upon studying the DEA of the curing process of epoxy resins, it was found that the equivalent resistivity derived from the dielectric loss factor was closely related to the glass transition temperature, the mechanical viscosity, and the volume shrinkage factor of the cured epoxy resins. For this paper, we measured the equivalent resistivity of the epoxy/filler mixtures with DEA and investigated the relation between mixing time of epoxy/filler and equivalent resistivity. The results showed that variations in the equivalent resistivity were due to the dissolution of ionic components from the surface of the filler particles into the matrix resins. We further examined the effects of the ionic concentration in epoxy/filler mixture on mechanical strength, dielectric properties, and thermal aging properties of the cured epoxy resins