Patent ID: 7867414

Claim:
A method of manufacturing a birefringent film comprising stretching a polymer film in a widthwise direction while at the same time shrinking the same polymer film in a lengthwise direction, wherein the widthwise direction is a direction perpendicular to the lengthwise direction, so as to satisfy the relational expression: (1/STD) 1/2 ≦SMD<1, in which the length in the widthwise direction and the length in the lengthwise direction, of said polymer film before being stretched are respectively designated as 1, and STD represents a change ratio of the length in the widthwise direction of said polymer film due to stretching and SMD represents a change ratio of the length in the lengthwise direction of said polymer film due to shrinking, and make the stretched polymer film have an Nz coefficient of 0.9-1.1, where Nz=(nx−nz)/(nx−ny), in which nx=maximum in-plane refractive index of the polymer film, ny=in-plane refractive index in a direction crossing at right angles to an in-plane nx direction that gives the maximum in-plane refractive index of the polymer film, and nz=thickness-wise refractive index in a direction crossing at right angles to a refractive index angle of nx and a refractive index angle of ny of the polymer film, and the stretching treatment and the shrinking treatment which are to be made simultaneously are indirectly applied to the polymer film, by laminating the polymer film on a substrate and simultaneously applying the stretching and shrinking treatments to the substrate, where the stretching ratio of the polymer film in the widthwise direction is controlled while simultaneously controlling the shrinking length of the polymer film in the lengthwise direction by changing the distance between the opposite ends of the substrate.