Preparation Of Colorless And Highly Transparent Thermal Resistant Polyimide Films And Research On Their Flame Retardancy

Colorless and transparent polyimide(CPI)films have seen wide applications in advanced optoelectronic fields such as flexible electronics due to the high flexibility,high transparency,and high thermal stability.However,the efforts of improving the optical transparency of traditional polyimide(PI)films via introducing alicyclic structure often sacrify the inherent flame retardancy of the PI films,making it have a great potential safety concerns in practical applications.Therefore,from the viewpoint of structure design,a series of new CPI/flame retardant composite films were developed by combining the optimizing flame retardant with the CPI matrix films.The developed CPI composite films showed good comprehensive properties,including good optical transparency,high thermal stabiity,and excellent flame retardancy.First,three flame retardants(FRs)which might be potentially used for the flame retardant modification of the alicyclic CPI films,including phenyloxyphosphazene oligomer(PPZ),trisilanolphenyl polyhedral oligomeric silsesquioxane(TSP-POSS),and brominated styrene-butadiene copolymers(PolyFR)were evaluated.Then,the PPZ with the best comprehensive properties was chosen as the FR additives for the alicyclic CPI films.Secondly,the flame retardant behaviors of the PPZ FRs for two alicyclic CPI matrixes,including poly(hydrogenated biphenylene tetracarboxylic dianhydride-co-4,4’-oxydianline)(PI-1,HBPDA-ODA)and poly(hydrogenated pyromellitic tetracarboxylic dianhydride-co-4,4’-oxydianline)(CPI-1,HPMDA-ODA)were investigated.The experimental results indicated that the PPZ FRs showed good miscibility with the CPI matrixes and could maintain the intrinsic optical transparency and thermal properties of the prinstine films when the loading amount was lower than 10 wt%.Comparatively,the CPI-1/PPZ composite films exhibited the best cmprehensive properties.For example,CPI-2 film with the PPZ content of 5 wt%showed good thermal stability with the glass transition temperature(T_g)of 325.6 ~oC,good optical transparency with the transmittiance of 86.4%at the wavelength of 450 nm,low yellow index of 3.28,and low haze of2.14%.Most importantly,the CPI-2 film exhibited good flame retardancy with the class of UL94 VTM-0 and limited oxygen index(LOI)as high as 41.2%.At last,on the basis of the above work,the continuous production of the CPI-2 films with the best comprehensive propeties was studied.The flame retardant CPI-2 film with a width of 1000 mm was successfully prepared in the industrial production line.The measurement results indicated that the film possesses excellent flame retardancy and good optical and thermal properties.