Dynamic behavior of surface charge on direct- fluorinated polyimide films

Abstract

Polyimide film, as a special type of engineering plastic film, is a kind of basic insulating material and is widely applied in the aerial, nuclear, microelectronic industry, turn to turn insulation and turn to ground insulation of inverter-fed motors. However, premature insulation failures occur frequently in motors with the disadvantage of pure PI inherent in all organic materials. The existence of surface charge has a great effect on breakdown characteristic and is the main reason leading to dielectric breakdown. Fluorination as change the chemical component in surface layer of polymers should give rise to the corresponding change in electrical properties of the surface layer thus influence the charge injection from electrodes when they are used as an insulator. This paper presents a study aimed at clarifying the effect of fluorination time on surface charge accumulation and decay behaviors of fluorinated polyimide film. Samples were surface fluorinated in a laboratory vessel at about 328 K (55 ℃) using a F 2 /N 2 mixture with 20% F 2 by volume and 0.05 MPa (500 mbar) for respectively 15, 30, 45 and 60 minutes. Corona charging tests were performed at room temperature with a relative humidity of ~ 40%. The charge distribution was measured by means of an electrostatic voltmeter. Obtained results show the dependence of the charge density as well as the charge decay rate upon the fluorination time of samples, varying as a function of the charge polarity and charging time. It is suggested that the fluorination can significantly improve the decay rate of the surface charge in polyimide films.

Fluorine gas treatment improves surface degradation inhibiting property of alumina-filled epoxy composite

“…19 Du has investigated the electrical properties of various polymers under different fluorinating conditions. 20,21 He finds that by fluorination, the corona resistant time is significantly improved and the partial discharge intensity is reduced. 22,23 However, most of the previous researches aim at the investigation on the direct fluorination using the unfilled pure epoxy resin samples, and fewer focused on Al 2 O 3 -filled epoxy resin which is wildly used as insulator materials in GIS or GIL.…”

Effects of ZnO magnetron sputtering on surface charge and flashover voltage of oil‐impregnated paper

“…The possible routes for the surface charge dissipation can be divided into the following three main patterns: lateral diffusion, recombination with the ions in the air and transfer through the bulk. Charge passing through the bulk of sample in a way of trapping and de-trapping is regarded as the dominant path of charge dissipation considering that the vertical electrical field built by the surface charges is much larger than the horizontal electrical field because of the thin thickness of the sample [20]. According to the decay curves of the surface potential, the decay process of the surface potential could be roughly divided into two stages.…”

Enduring and Stable Surface Dielectric Barrier Discharge (SDBD) Plasma Using Fluorinated Multi-Layered Polyimide

“…The total thickness of the barrier dielectric was 0.37 mm. Surface fluorination of the dielectrics was carried out in a stainless reactor kettle with polytetrafluoroethylene lining at about 328 K (55 • C) using a F 2 /N 2 mixture with 20% F 2 by volume [22]. After evacuation and purification with nitrogen gas more than three times, the reactive gas mixture was introduced slowly into the vessel until the mixture pressure in the vessel had reached 0.05 MPa (500 mbar).…”

“…For example, An et al [20,21] indicated that surface fluorination of PE has a significant influence on the charge injection and accumulation. Du et al [22,23] found that surface fluorination is an effective method for modulating the electrical properties and restraining the surface charge and space charge accumulation of the PI film.…”