Preparation And Properties Of Transparent Polyimide Films

With the development of material science and technology,electronic optical devices show the trend of lightweight,flexible and integrated,ordinary transparent materials have been unable to adapt to the standard of flexible display technology.Colorless transparent polyimide film(CPI)has been widely studied for its excellent properties such as high and low-temperature resistance,corrosion resistance,high strength,high modulus,lightweight,and colorless transparency,and it is expected to be applied to flexible displays and solar panels and other optical materials.Common polyimide films show characteristic yellow color due to charge transfer complex(CTC).Therefore,how eliminating the effect of charge transfer complex is an important research field to design and prepare colorless and transparent polyimide films.This thesis study found that in addition to the cause of polyimide yellowing CTC effect,there exist polyamide amino acid side will happen in the process of imine into membrane oxidation reaction generated nitro anhydride of chromophores and end electrophilic substitution reaction by-products generated anthraquinone structure color problem,so this paper adopts two-step method of End-sealing side to remove end amino and end anhydride base,To further reduce the formation of charge transfer complex,the specific results are as follows:(1)Polyimide precursors are prepared by using 4,4’-Oxydianiline(ODA),3,3’,4,4’-Biphenyl tetracarboxylic diandhydride(BPDA),and Ethylene glycol(EG)as monomers.Polyamide acid(PAA)is synthesized by using ODA and BPDA as monomers,then an appropriate amount of BPDA and EG are added.Preparation of two-step sealed polyamide acid precursor,in the mechanical rotating coating and thermal amination method to remove the solvent,complete the thermal amination,preparation of high transparency,low yellow polyimide film,the resulting amino PIOBt-B/E film compared with the unsealed PIOB_R,PIOBt-B/E UV cutoff wave-length shifted from 417 nm to 410nm.The results show that the formation of colored nitro compounds or anthraquinone structures is effectively reduced after the amino group is capped,and the transmittance of the visible light region is also increased,the maximum transmittance is increased from 94.5%to 99.5%.The transmittance increased from 17%to 39.0%at 450 nm,mainly because the flexible ethylene glycol end sealer destroyed the nanoscale ordered structure of the rigid aromatic ring of polyimide,avoided Rayleigh scattering,and improved the transparency of polyimide film in UV/VIS region.(2)Polyimide precursors are prepared by using 4,4’-(4,4’-Isopropylidenediphenyl-1,1’-diyldioxy)dianiline(BAPP),3,3’,4,4’-Biphenyl tetracarboxylic diandhydride(BPDA),4,4’-(Hexafluoroisopropylidene)diphthalic anhydride(6FDA)and Ethylene glycol(EG)as monomers.Firstly,polyamide acid(PAA)is synthesized with BAPP and BPDA as monomers,and then an appropriate amount of BPDA and EG or 6FDA and EG is added to prepare a two-step sealed polyamide acid precursor.After removing the solvent by mechanical spin coating and thermal amination,thermal amination is completed to prepare polyimide film with high transparency and low yellowing.Compared with the unsealed PIBB_Rfilm,the UV cutoff wavelength of PIBBt-F/E film with capped amino group moved from 425 nm to 375 nm,indicating that the formation of colored nitro compounds or anthraquinone structures is effectively reduced after the capped amino group,and the transmittance of the visible light region is also increased accordingly.The maximum transmittance is 96%and increased from 20%to 77%at 450 nm.(3)Polyimide precursors are prepared by using 3,3’-Sulfonyldianiline(APS),4,4’-(Hexafluoroisopropylidene)diphthalic anhydride(6FDA),and Ethylene glycol(EG)as monomers.First,polyamide acid(PAA)is synthesized by using APS and6FDA as monomers,and then an appropriate amount of 6FDA and EG is added to prepare two-step sealed polyamide acid precursors.In the mechanical rotary coating and thermal amination method to remove the solvent,complete thermal amination,preparation of high transparency,low yellowing polyimide film,where the PISFt-F/E film with the capped amino group is compared with the uncapped PISF_R,PISFt-F/E UV cutoff wavelength moves from 340 nm to 333 nm,indicating that after the amino group is capped,It can effectively reduce the formation of colored nitro compounds or anthraquinone structures,meanwhile,the transmittance of the visible light region is correspondingly increased,the maximum transmittance is increased from 82%to 92%.The transmittance at 400 nm increases from 70%to 84%.