US Patent 7479312 Retardation film, polarizing plate, and liquid crystal display device

A retardation film which contains a cellulose derivative and a plasticizer wherein the thickness of the film is 10 to 50 μm, Ro in Equation (i) is in the range of 30 to 100 nm, Rt in Equation (ii) is in the range of 100 to 300 nm, and S in Equation (iii) is 0.0002 or more but not exceeding 0.030.Ro=(nx−ny)×d  Equation (i)Rt=S×d  Equation (ii)S=((nx+ny)/2−nz)  Equation (iii)(where “nx” is a maximum refraction index of the film surface, “ny” is a refraction index in the direction perpendicular to “nx,” “nz” is a refraction index along the thickness of the film, and “d” is the thickness of the film.)