Charge storage in a corona-charged polypropylene film analyzed by LIPP and TSC method

The charge storage in a corona-charged polypropylene (PP) film is studied. After a 50 /spl mu/m thick PP film is negatively charged, the spatial and energy distribution of charge in the PP is measured by laser induced pressure pulse (LIPP) and thermally stimulated current (TSC). The LIPP experiments show that a large negative homocharge forms on the charged surface of the PP. Almost all the homocharge is removed when the PP is dipped into ethanol because it is located on the surface. Some amount of the homocharge penetrates from the surface to 5-8 /spl mu/m depth which cannot be eliminated by the ethanol treatment. The ratio of the deep located homocharge increases with charging temperature. As charging temperature increases, homocharges on both surfaces penetrate into the middle of the PP. At charging temperature higher than 80/spl deg/C, a bulk charge forms inside the PP. It is shown that some charges observed by TSC are invisible by LIPP. The invisible charge Q/sub i/ is formed on the charged surface when charged at room temperature. At charging temperature higher than 80/spl deg/C, the Q/sub i/ is formed also inside the sample.