Polymer electrets corona charged at high temperature

Abstract Polymer films of Teflon (PTFE) and polypropylene (PP) are negatively corona charged above room temperature (R.T.), and the charge stability of these films for different charging temperatures is studied using thermally stimulated charge decay (TSCD) and short-circuit thermally stimulated current (TSC). Charging PTFE samples at and above 250° C and PP at 120° C dramatically increases their charge stability. As the charging temperature is increased, one tends to fill deeper traps because of changes in relative capture and escape probabilities. A distinction is made between near-surface “free” charge which is neutralized on metallization and grounding, and trapped charge which gives rise to the TSC. Both charges contribute to the surface potential in TSCD. In the production of long-lived electrets for practical use, corona charging should be carried out at high temperatures.