Research On The Structure,Electrical And Thermal Properties Of PI/SiO₂ Composite Films With Three Layers

Polyimide?PI?is a kind of polymer insulation material containing imide ring,which has excellent heat resistance,wear resistance,chemical resistance,high gas permeability,electrical insulation and so on.With the development of society and the progress of science and technology,polyimide materials are widely used in electric power transportation,energy storage,motor insulation,aerospace and other fields.Inorganic nanoparticles have good physical and chemical properties,and the incorporation of inorganic particles into the polyimide film will improve the properties of the films,such as electrical properties,mechanical properties,thermal properties and optical properties.In addition,due to the three layer structure,polyimide composite films can reduce the longitudinal conduction of electrons and heat,and the integrity of the molecular structure of intermediate pure PI layer is protected and improve the electrical and thermal properties of polyimide films.The modified nano-SiO₂ particles were incorporated into the polyimide composite film by in-situ polymerization.The doped components of the nano-SiO₂ particles were5 wt.%,10 wt.%,15 wt.%,20 wt.%,And the traditional thin film preparation process is improved,the three-layer composite film with thickness?30?m?.The structure of the composite film was SiO₂-PI/PI/SiO₂-PI,and the upper and lower layers were composed of nano-silica particles doped with the same composition and the middle layer is pure PI,and each layer has thickness of 10?m.The dispersion state of the nanoparticles and the surface and cross-sectional structure of the three layer films were characterized by means of transmission electron microscopy?TEM?,scanning electron microscopy?SEM?,X-ray diffraction?XRD?and infrared spectroscopy?FTIR?.The effects of the three-layer structure on the electrical and thermal properties of the polyimide composite film were studied by means of an electric strength tester,dielectric spectrometer,corona-resistant apparatus and differential thermal gravimetric analyzer.The results of TEM of nano-SiO₂ particles show that the dispersion of nano-SiO₂ particles is better and the particle size is between 10-20 nm.The FTIR and XRD tests of pure PI films and PI/SiO₂ nano-composite films show that the PI films and PI/SiO₂nano-composite films imidization is complete by in situ polymerization.The surface of the composite film and the surface morphology of the composite film can be seen by SEM.The nano-SiO₂ particles are uniformly dispersed in the PI matrix,and the three layer composite The film has a clear interface and no interpenetration and the each layer with a thickness of about 10?m.The dielectric properties of single layer and three layer composite films were improved by the nano-SiO₂ particles,the dielectric properties of single layer films were higher than those of three layer films,and the three layer polyimide films had excellent corona-resistance time and electrical strength than the single layer.When the doping content is 20 wt.%,The corona aging time of the single layer composite film reaches 74 hours,and the corona aging time of the three layer composite film reaches 157 hours;when the doped is 15 wt.%,the electric strength reached the maximum?280.6k V/mm?.The thermal stability of the three-layer composite film was higher than that of the single layer composite film.Because of the barrier effect of the intervening pure PI layer and the conduction of electrons and heat in the two doped layers,which reduces the longitudinal conduction of electrons and heat in the composite film,Thereby improving the electrical and thermal properties of the polyimide composite film.