Charge trapping in interfaces of laminated PE/EVA dielectrics

Voltage-induced charge in dielectric interfaces was measured for laminated sheets of polyethylene (PE) in contact with ethylene vinyl acetate (EVA) with thickness 250 μm each by the laser induced pressure pulse (LIPP) method. A sheet of the laminate with 500 μm was stressed by voltage up to 15 kV. Charge is accumulated in the interface by the application of voltage, and remains trapped, even when voltage is turned off. Remaining trapped charge has at least two kinds of decay time constants, about one hour as short time term, and about 5 hours as long time term. The short time constant decreases as the content of vinyl acetate (VA) content. It is elucidated that the electrical conductivity of EVA increases with the increase in VA content. The short decay time constant was found to be proportional to about 0.4 th power of the dielectric relaxation time of EVA. Mechanism of charge decay was, to some extent, understood by the classical CR circuit model, but not quantitatively. A trapping modified relaxation model is temporarily proposed in the paper