In order to meet the stringent requirements for advanced electrical and power applications, polymer capacitor films need to exhibit high energy density, high operation temperature, and low loss simultaneously. However, the current state-of-the-art biaxially oriented polypropylene (BOPP) film has low energy density (4.88 J/cm3 at breakdown strength of 700 MV/m) due to its low dielectric constant of 2.25, and low temperature rating (only up to 85 °C). In response to these issues, a unique coextrusion technique was utilized to produce multilayer polymer films for capacitor applications. In this study, a high dielectric constant poly(vinylidene fluoride) (PVDF) and high glass transition temperature polycarbonate (HTPC) were extruded into multilayer films with different layer thicknesses. When cooling naturally from the melt after coextrusion, PVDF always forms edge-on α-form crystals. This edge-on crystal structure of PVDF layers could be changed into flat-on crystal structure via reducing the layer thicknesses and subsequent melt-recrystallization, as a result of the confined crystallization of PVDF by the HTPC layers. The flat-on crystal structure is able to block the conduction of impurity ions and thus reduce the ionic conduction loss for multilayer films.<br/>

Achieving flat-on crystals and blocking ionic conduction in polycarbonate/poly(vinylidene fluoride) multilayer films

2019 Fall National Meeting

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