Polarization behaviour of paper during corona charging

Abstract

The polarization phenomenon of papers containing different amounts and different types of inorganic fillers during corona charging was studied using a dose-charging method. This method enables to investigate the phenomena in the conditions close to the real ones. It revealed that the paper composition affects the polarization tendency during the corona charging of paper. The filler influences the paper’s dielectric constant and hence its electrical capacitance, charging potential and polarizing electric field. It was shown that paper polarization depends mainly on the electric field and this is caused by the orientation polarization and the role of the filler origin and its concentration in the polarization was surprisingly low. Polarization temperature dependences enable to propose the paper polarization mechanism. Paper polarizability is dominated by cellulose and the moisture content in it, and the liability of cellulose and hydrogen bonds hydroxyl groups. During transfer of charge carriers from the needle onto the surface of the insulating layer, the largest potential is obtained at the point corresponding to radial coordinate r = 0, but this potential is still smaller than the electromotive force that causes electric current in the circuit (i.e., the difference between the power supply voltage and the voltage on the capacitor formed by the needle and the substrate, when no charge has been deposited yet). The time dependence of charging current and of the potential difference between the needle and the substrate is not monotonic: at first the current increases, then it begins to decrease, and the potential difference at first decreases, then it begins to increase. The initial parts of those dependences can be explained by the "breakdown" of the capacitor formed by the needle and the substrate, and the subsequent time dependence is determined by the increase of the insulating layer potential due to accumulation of charge on it.