OPTICAL PHASE DIFFERENCE PLATE

PURPOSE:To obtain the phase difference plate for which a high-polymer stretched film having small phase difference unevenness, high double refractive index and wavelength dispersibility to some extent and small coefft. of light elasticity by using a film formed by uniaxially orienting a crystalline copolymer of trifluoroethylene monochloride and vinylidene fluoride. CONSTITUTION:The substantially uniaxially oriented film consisting of the crystalline copolymer composed of 80 to 98wt.% trifluoroethylene monochloride and 2 to 20wt.% vinylidene fluoride is used. The phase difference unevenness is large and the phase difference plate which is practicably usable is not obtainable if the content of the trifluoroethylene monochloride exceeds 98wt.% or the content of the vinylidene fluoride is below 2wt.%. On the other hand, the crystallization degree is low and the rubberlike film is resulted if the content of the trifluoroethylene monochloride is below 80wt.%. A large change in the phase difference and dimensional change at a high temp. are resulted and such plate is not practicably usable when the film is made into the phase difference plate. More preferably, the film consists of 90 to 97wt.% trifluoroethylene monochloride and 3 to 10wt.% vinylidene fluoride.