Preparation And Properties Of Colorless Transparent Polyimide Materials With High Tgs

In recent years,flexible display technology is active in various fields of electronic information.The rapid development of flexible display drives the prosperity of flexible substrate market.Flexible substrate is an important part of flexible display device,which also requires high performance of substrate material.Rigid imide ring endows polyimide(PI)with excellent comprehensive properties,which makes it the first choice of flexible display substrate materials.The manufacturing process of large-scale flexible display screen is mainly based on the oxide(IGZO)-TFT bottom light-emitting process.The process requires that the light transmittance of colorless PI substrate at 500 nm is greater than 87%;secondly,the process temperature of IGZO-TFT is above 300°C.Therefore,it is of great significance to prepare colorless transparent polyimide materials with high glass transition temperatures(Tgs)and excellent comprehensive properties.In this thesis,the colorless transparent polyimide thin films with high Tgs were prepared by means of homopolymerization,copolymerization,biaxial stretching and high temperature heat treatment.Firstly,a variety of fluorine-containing monomers and non-fluorine-containing monomers were used as raw materials to produce colorless transparent PI films by pairwise polymerization,and the influence of fluorine-containing monomers and flexible structure on the comprehensive properties of PI films was discussed.Then,on the basis of the homopolymer formula 6FDA-TFMB with the best comprehensive performance,a certain amount of homopolymer monomers(PMDA,p-PDA)and biphenyl monomers(s-BPDA,HMB,m-TOL)were introduced to study the influence of the types of copolymer monomers on the properties of PI films.Then,the trimerization of biphenyl monomers s-BPDA and o-TOL with different contents was introduced to prepare 6FDA-s-BPDA-TFMB and 6FDA-TFMB-o-TOL copolymerization PI films to study the effects of different copolymerization ratios on PI performance.The best copolymerization formula 6FDA-s-BPDA(5:5)-TFMB was used as the research object,and the films were subjected to biaxial stretching and high temperature heat treatment respectively,hoping to obtain colorless transparent polyimide(CPI)films with better comprehensive performance through post-processing.Finally,heterocyclic monomers DAPBI and i-DAPBI were introduced into 6FDA-TFMB matrix to investigate the effect of benzimidazole group and isomerism on the properties of PI thin films,and further improve the glass transition temperature and comprehensive properties of CPI.The chemical structure,mechanical properties,optical properties,thermal properties,hydrophobic properties and other aspects of PI thin films were studied by using infrared spectrometer,universal tensile testing machine,ultraviolet spectrophotometer,differential scanning calorimeter,thermogravimetric analyzer,static thermal mechanical analyzer,contact Angle tester and other instruments.The results show that the introduction of fluorine-containing monomers and flexible structures can improve the optical properties of PI films,and the effect of the former is more obvious.Among the homopolymer series,the 6FDA-TFMB PI has the best comprehensive performance,with fluorine content of 29.78%,T_?=500nm up to 90.17%,and Tg of 305.96°C.The addition of rigid diphenyl monomer and biphenyl monomer into 6FDA-TFMB can improve the mechanical properties and Tg of the film,but the optical properties and hydrophobic properties of the film decrease.In the 6FDA-s-BPDA-TFMB system,with the increase of s-BPDA content,the mechanical properties and thermal stability of PI films become better,while Tg increases,but the optical properties become worse.In the 6FDA-TFMB-o-TOL system,with the increase of o-TOL content,Tg increased,and mechanical properties,optical properties and thermal stability deteriorated.Of the two series,the best comprehensive performance is 6FDA-s-BPDA(5:5)-TFMB PI film:Tg is 320.61°C,T_?=500nm over 88%,good mechanical properties,hydrophobic performance.The bidirectional stretching of PI films can be carried out without adding defiler,which can improve the Tg by about 5°C while maintaining the excellent optical properties of PI.High temperature heat treatment can effectively improve Tg,but will reduce the optical properties.The 6FDA-TFMB-DAPBI and 6FDA-TFMB-i-DAPBI copolymer PI films have good mechanical properties,optical properties,thermal properties and hydrophobic properties.With the increase of DAPBI and i-DAPBI contents,Tg increased and optical properties decreased.The Tg of DAPBI series PI films is higher,and the optical performance of i-DAPBI series PI films is better.When n(TFMB):n(DAPBI)=6:4,the tensile strength of the 6FDA-TFMB-DAPBI PI thin film is 86.02 MPa,the contact Angle is 103.37°,the water absorption is 0.46%,T_?=500nm is 88.04%,and the Tg is up to 340.54°C.