| 摘要 |
PURPOSE:To prevent the ply separation of a composite film from occurring by a method wherein an inner layer consisting of a film, the areal degree of orientation (DELTAP) and man refractive index (n<->) of which satisfy a specified formula, and surface layers, each consisting of a film, DELTAP and N<-> of which satisfy specified formulae, which are different from that hust mentioned above, are laminated to one another by coextrusion in such a manner the thickness of each of the respective surface layers is 5 mum or more. CONSTITUTION:An inner layer consisting of an oriented film, which is made of copolymerized polyethylene 2,6-naphtalate and the areal degree of orientation ((DELTAP) represented by the formula (5) and mean refractive index (n<->) represented by the formula (4) of which satisfy the formula (1) and surface layers consisting respectively of an oriented film, which is substantially made of polyethylene 2,6-naphtalate and the areal degree of orientation (DELTAP) and mean refractive index (n<->) of which satisfy the formulae (3) and (3) are coextruded in such a manner that surface layers are laminated to both surfaces of the inner layer. At the same time, the thickness of each of the surface layers is made to be 5 mum or more. (In the formulae, nalpha and ngamma represent the refractive index in the direction of th4 thickness of the film after being biaxially oriented and heat-set, that within its film plane and that within its film plane and normal to the direction of gamma. |
