Surface morphology and raman analysis of the polyimide film aged under bipolar pulse voltage

Polyimide film has the weakness of high processing temperature and low corona resistance, which restrain its further development. Kapton 100 HN polyimide films with a thickness of 50 μm were aged by needle-plane electrode under 4 kV bipolar pulse voltages for 4 h at different frequencies (300 - 900 Hz). The surface morphologies of the pristine and aged polyimide films were analyzed using an atomic force microscope, and the changes in chemical bonds during corona aging were analyzed by Raman spectra. Different surface morphologies are observed using AFM, and the parameters all have sharp increases, which reveal that the surface morphology is obviously influenced by the corona aging under the bipolar pulse voltage. Raman results show that there are peak shifts and changes of the relative band intensities, which demonstrate that the chemical bonds in the polymer chains are reoriented by the electric field. Moreover, the corona aging of the polyimide film became severe at high frequency.