Preparation And Properties Of Low-viscosity Polyimide Enameled Varnish And Its Coatings

With the rapid development of China's high-speed rail technology and electrical apparatus,higher and various requirements were put forward for the enameled insulated wire.Currently,polyimide enameled insulated wire(PI)is one of the best heat resistant enameled insulated wire.And the performance of the polyimide enameled insulated wire is closely related to polyimide enameled varnish.At present,the main problem of PI enameled varnish is that the apparent viscosity of enameled varnish is high,which leads to a poor property of coating enameled insulated wire.At the same time,the storage stability of polyimide enameled varnish is poor,and it is difficult to guarantee the performance of the enameled insulated wire in the end.Therefore,the academic and industry pay close attention to the development of polyimide enameled varnish,which its performance is low apparent viscosity,good storage stability and high heat resistance.In this dissertation,1,2,4,5-Benzenetetracarboxylic anhydride(PMDA),Bis-(3-phthalyl anhydride)ether(ODPA),3,3',4,4'-Biphenyltetracarboxylic dianhydride(BPDA),3,3',4,4'-Benzophenonetetracarboxylic dianhydride(BTDA),4,4'-(4,4'-Isopropylidenediphenyl-1,1-diyldioxy)dianiline(BAPP)and 4,4'-Oxydianiline(ODA)were used as reactive monomers to prepare the polyamic acid solution with different formulations by decreasing the molar ratio of dianhydride to diamine(PI enameled varnish).The mechanical properties,thermal properties,surface properties,dielectric properties,insulation resistance and water absorption of polyimide film were investigated by means of rotational viscometer,including infrared spectrometer,thermogravimetric analyzer,universal electronic tension machine,contact angle meter,insulation resistance meter and impedance analyzer.With the decreasing molar ratio of dianhydride to diamine,the apparent viscosity of PI enameled varnish and the tensile strength of PI film decreased and the storage stability of PI terminated enameled varnish was inferior.The mechanical properties of PI that its formula was PMDA-ODA,ODPA-ODA,BTDA-ODA or BPDA-ODA films were still in good condition,and polyimide enameled varnish had lower apparent viscosity.Secondly,when polyamic acid solution was synthesized,the blocking agent of phthalic anhydride(PA)was introduced to investigate the influence of PA on the properties of PI enameled wire and PI film.It was found that PA could effectively decrease the apparent viscosity of PI enameled varnish,and the storage stability of PI enameled varnish was good.When the molar ratio of PA to ODA was more than 0.1,the polyimide film that its formulation was PMDA-ODA-PA appeared bits.When the molar ratio of PA to ODA was more than 0.08,the polyimide film that its formulation was BPDA-ODA-PA or BTDA-BPDA-DA-PA appeared bits.When the molar ratio of PA to ODA was more than 0.06,the polyimide film that formulation was ODPA-ODA-PA or BTDA-ODA-PA appeared bits.The apparent viscosity of BTDA-BPDA-ODA-PA type and BPDA-ODA-PA type PI enameled varnish was moderate,and the mechanical properties of PI film were excellent.The better mechanical properties of PI films were prepared based on the appropriate apparent viscosity of polyamic acid solution.Through the introduction of norbornene imide groups,we prepared norbornene(NA)anhydride terminated PI enameled wire and discussed the effect of NA on the mechanical property and thermal stability of PI film deeply.Compared with PA-terminated polyimide,it was found that the tensile strength of PI films was improved and the thermal stability of the PI films was decreased with the addition of NA.Meanwhile,NA could effectively reduce the dielectric constant of the films.In addition,the PA and NA-terminated PI enameled varnish was prepared to improve the thermal stability of PI films on the basis of PA and NA.Through the comparative analysis of the thermal stability of PMDA-ODA-NA-PA and PMDA-ODA-NA,it was found that the introduction of PA improved the thermal stability of polyimide films at the same molar ratio of anhydride and amine.At last,the 3-Aminophenylacetylene(APA)terminated PI enameled varnish was prepared by crosslinking of acetylene at high temperature and the aromatic characteristics.It was found that the apparent viscosity of APA-terminated PI enamel varnish was lower in the case of ensuring mechanical and other properties.When the molar ratio of ODA to APA was 9:1,the apparent viscosity of APA-terminated PI enameled varnish was 143.6cp.Importantly,the tensile strength of PI film was 115.55MPa,and the elongation was 11.36%.