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Negatively corona-charged 50-[micro]m-thick polypropylene (PP) film is measured using laser-induced pressure pulse (LIPP) and thermally stimulated current (TSC) in order to study the charge storage mechanism in the PP film. The LIPP can reveal the space-charge distribution in the depth direction of the PP films and the TSC can be used to measure the energetic depth of the charge trap. The LIPP shows that negative charge is deposited on the charged surface of the sample. Almost all surface charges are removed by soaking the sample in ethanol. However, about 5% of the surface charge is injected into the sample up to a depth of about 7 [micro]m from the surface. The injected charge is not removed by the dip-in-ethanol method because the ethanol does not penetrate into the sample. The injection of the surface charge increases with corona-charging temperature. Besides the negative charge injection, the injection of positive charge from the opposite surface is also observed when the sample is charged at higher than 60 [degrees]C. In addition, negative bulk charge is formed when the sample is charged at higher than 80 [degrees]C. The LIPP profile is compared with the TSC spectrum. It is shown that the space charge observed using LIPP disappears when the temperature of the sample exceeds 80 [degrees]C. However, TSC is observed at even higher than 80 [degrees]C. This indicates that the TSC is observed even after the disappearance of the space charge measured using LIPP. Index Terms--Corona charging, laser-induced pressure pulse (LIPP), polypropylene (PP) film, thermally stimulated current (TSC).

The dielectric breakdown behavior of thin metalized PP films for use in HV capacitors was studied as function of temperature with and without rape-seed oil as impregnation medium. The impregnating oil penetrates into the amorphous regions of the dielectric. With oil impregnation, the dielectric breakdown strength of the PP film is increased by > 25%. A correlation between the breakdown strength and the degree of impregnation was found. With increasing temperature the breakdown strength of PP films decreases. Moreover, the measurements showed abrupt changes of slope in the breakdown strength at defined temperatures. From these results a correlation was established between the dielectric breakdown strength of PP films and temperature induced structure changes. It was shown that the abrupt changes of slope in the breakdown strength occurring at defined temperatures are due to the additives contained in the Pp capacitor films used. Finally, guidelines for further development of impregnated PP films as dielectrics for high power capacitor applications are presented.

The surface charge decay of corona-charged polyether ether ketone (PEEK) and polypropylene (PP) for different charging potentials in humid environment is studied. The PEEK charge decay consists of a fast decay followed by a slow decay. The fast decay process may have originated from a field-induced dielectric polarization and the slow process from a thermal hopping process. The PP charge decay is insignificant over an extended period of time. The adsorption of water in humid environment is more for PEEK with gamma irradiation and less for PP.

A novel plasma chemical process PPCP (Pulse Corona Induced Plasma Chemical Process) can produce copious active radicals in air under NTP (Normal Temperature and Pressure) by using an extremely fast rising narrow high voltage pulse between corona electrodes and grounded counter electrodes so that intense streamer coronas are generated. This provides an effective means of surface treatment to a plastic material placed between the two electrodes through generation of free bonds on the surface directed to the corona electrodes. Special features of this method are that it can cope with a complex shape of the material to be treated, and that it does not spark even at the periphery near the grounded counter electrode. This method is suitable for the surface treatment of polypropylene bumpers so as to provide a strong adhesion of color paint to it. The adhesion strength of a paint film is raised from zero to ca. 1000 g/cm squared by PPCP treatment for 60 seconds.

The radiation-induced conductivity (RIC) in polypropylene, polyethylene terephthalate, and polyimide due to electron-beam irradiation is measured with an external bias method and, in the case of polypropylene, also with a short-circuit method, as function of dose rate and time of irradiation or total dose. The results substantiate the power-law dependence of the RIC on dose rate in all cases, but indicate that the dependence on time is different for the materials under investigation. In addition, the delayed radiation-induced conductivity (DRIC) is determined. The DRIC shows a hyperbolic time dependence with different exponents for the different materials.

The aging of impregnated PP film has been carried out on capacitor models at 80 [degrees] C under 50 Hz ac electrical stress (137 [V.sub.rms]/[mu]m). The damage was estimated from the local measurement of the breakdown voltage of the PP film. The effects of impurities (electrolyte, water, oxygen) added to the impregnating liquid were observed. The relatively low breakdown voltages of the aged film measured in the electrically stressed region were no longer found when the liquid contained epoxides. A chemical degradation analyzed by FT-IR microspectroscopy and gel permeation chromatography was observed and found only in the region of lower dielectric strength.