On the effect of corona treatment on polypropylene for capacitors

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Abstract
In order to improve the adhesion of the electrodes which are most often vacuum-evaporated, the surface of the polypropylene film has been subjected to a high-pressure corona discharge at a frequency of the order of 10 kHz or higher. This type of surface treatment is very easily used and does not produce any transformation of the material for short expositions. In certain atmospheres and for longer exposition times, appreciable, and sometimes important, transformations of the dielectric characteristics appear. The evolution of these properties has been studied as a function of various corona discharge parameters, at a frequency of 50 Hz. This frequency, which is low compared with frequencies usually chosen, causes a slowing down of transformations which remains qualitatively identical. In order to establish a correlation between the species created by the discharge, the superficial and volume chemical transformations, and the dielectric properties of the material, several types of measurement were made: multi-internal reflectance (MIR) IR spectroscopy, the tan delta variations as a function of frequency and measurement of dielectric strength.

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