Effect of Cyclic Olefin Copolymer on Dielectric Performance of Polypropylene Films for Capacitors

In this article, aiming at the high conductance loss and low breakdown strength of the polypropylene (PP) film under a high-temperature environment, we attempt to improve the dielectric properties of PP films by blending cyclic olefin copolymer (COC). It is shown that these two materials have good interfacial compatibility. COC has little effect on the crystal form and dielectric loss of the PP/COC film because it is an amorphous polymer without the polar group. At 105 °C, a low proportion of the COC is beneficial to the decrease of dc conductivity and the increase of the breakdown strength. Since the glass transition temperature of COC is much higher than PP, the dimensional stability of the PP/COC film is improved at high temperatures. The cyclic structure of COC restricts the movement of PP molecular chains in the free volume, which plays an important role in inhibiting the migration of carriers and improving the breakdown properties. This method provides a feasible idea to improve the high-temperature resistance of metalized film capacitors (MFCs).