US Patent 7851068 Optical compensation film and display element using the same

In an optical compensation film, when a direction that gives the maximum in-plane refractive index is X axis, an in-plane direction perpendicular to X axis is Y axis, a film thickness direction is Z axis, refractive indexes at the wavelength of 590 nm in each axis direction are nX, nY, and nZ respectively, and the film thickness is d, an in-plane retardation value defined as R=(nX−nY)·d and a thickness direction retardation value defined as Rth=|(nX+nY)/2−nZ|·d, both of which are measured under conditions at 23 degrees centigrade and a relative humidity of 50%, satisfy the inequalities of Rth/R≧5 and R≦9.5 (nm).