Investigation into Layer Number Effect on Breakdown Strength of Multi-Layer Polymer Films.

The layer number effect on electric breakdown strength () of multi-layer polymer films is investigated using 10-μm polypropylene (PP) films under a dc condition. The layer number, , of the films during the test is as large as 120. It is observed that the relation between and conforms to a minus power law, i.e., () = , where the power exponent, , is 0.27, is a constant. By reviewing the experimental data in references, it is found that the power law holds true for different types of polymers in different test conditions, but the value of varies from 0.072 to 0.5. The variation of is explained in perspective of the discontinuous structures within films and those between films. A small value of means a good purity level of the film, which is due to the decrease of the size of the inter-layer defects. A large value of means a poor purity level of the films, which is due to the increase of the amount of intra-layer defects. Both factors influence the value of , leading to the variation of .