Synthesis And Characterization Of Polyimide Used As Optical Compensation Film

As the viewing angle of the liquid crystal display changes,the contrast of the image will change,and the color deviation will eventually appear.These limitations of the LCD monitor must be considered in aviation and other fields.For example,the flight driver has high requirements for the visibility of the display instrument within a certain viewing angle.Therefore,it is extremely important to improve the liquid crystal display so that it can have a large contrast and a high quality image over a wide viewing angle range.The phase difference compensation on the liquid crystal display can improve the contrast of the display and maintain a high quality image over a wide angle range.The phase difference compensation film used for liquid crystal displays shall have the following necessary conditions:?1?It should have high transmittance within the visible wavelength range of 400-700nm.In this way,the light loss caused by the film can be reduced.?2?Films having a sufficient phase retardation value?nd?where:?n is the birefringence index of the film and d is the thickness of the film?,which varies according to different applications.Normally,this value should be between 1/8?-???is the wavelength of the light wave?;?3?The film should have a certain mechanical strength,and the optical uniformity of the entire display should be maintained.The negative birefringence properties of polyimide films can compensate for the phase difference between ordinary and extraordinary light,thereby improving it's contrast.It has been found that the introduction of the structure of 1,3,4-oxadiazole into the polymer chain will lead to better thermal stability and higher birefringence.Due to the conjugate structure of the molecule,the polyimide can absorbs light and becomes yellow or reddish-brown in the visible light range.However,it is difficult for general polyimide to meet the applications requiring colorless and transparent such as optical compensation films.Therefore it is necessary to improve the transparency of polyimide.It has been found that luorinated polyamides are introduced into trifluoromethyl?-CF₃?groups with large free volume products from the splitonic junctions,which can effectively block the tight stacking of molecular chains.Thus,the formation of charge transfer complexes between molecular chains is inhibited,and the optical properties of the films can be improved significantl.In this paper,a diamine monomer containing a 1,3,4-oxadiazole structure is prepared and a polyimide film is obtained through a two-step process with a fluorine-containing dianhydride and polycondensed at high temperature.Finally,the resulting film is subjected to the structure,optical properties,thermalproperties,mechanicalpropertiesandaseriesoftestsand characterizations,which provide some reference data for the subsequent study of optical compensation films.