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, with the disadvantage of organic polymer, its corona-resistance property is not good enough, which makes insulation early failures occur frequently. 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 328K (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.

Effect of surface fluorination on space charge behavior in multilayered polyimide films

“…Our previous research has shown that the fluorination can not only decrease surface energy for polyimide film but also change the electrical properties, such as dielectric property, work function and the trap depth [18]. As shown in Figure 6, the conductivity of fluorinated film is higher than the untreated film.…”

“…The results show that the property of the interfacial charge changed a lot after the LDPE layer is surface fluorinated [17]. Our recent research has indicated that direct fluorination is also effective in modulating the electrical properties of the surface layers of polyimide film [18].…”

Surface flashover characteristics of fluorinated polyimide films in liquid nitrogen

“…After fluorination, the fluorinated layer will be occurred on the surface of PI film [8]. The fluorination can restrain the charge accumulation in the surface layer of the specimen and accelerate the decay of surface charge, which reduces the amount of charge accumulated on the surface of the fluorinated specimen and improves the surface flashover strength of the fluorinated specimen.…”

“…PI films used in the experiment were prepared by a twostep method using 4, 4' -oxy dianiline (ODA) and pyromellitic dianhydride (PMDA) commercially available, according to the procedure described in our paper [8]. Surface fluorination of PI film was completed in a stainless reaction kettle at 55 °C using the mixture of F 2 and N 2 with 20% F 2 by volume and 0.05 MPa.…”

“…Surface fluorination is widely employed in research and development of material modification. Our previous research has found that fluorination is an effective method for modulating the electrical properties and can accelerate the surface charge decay of the PI film surface at room temperature [8]. For extending the insulation life of the HTS power cable system, the study on surface flashover characteristics of fluorinated PI film in LN2 is essential.…”