| abstract |
To provide a retardation film that, while maintaining a high retardation value, has increased durability such as moist heat resistance and can prevent the occurrence of color unevenness even if made in a size having a large area. The retardation film contains a cellulose ester as the primary component, has a film thickness of 15 μm or more and less than 40 μm, has a film thickness variation both in the widthwise direction and lengthwise direction of 0 to 4 μm, and satisfies an Rt humidity fluctuation represented by the formula (1) described below of 1% to 12%. n Formula (1): Rt humidity fluctuation=(ΔRt value, a difference of retardation Rt(590) values in the thickness direction represented by the following formula (ii) measured at a wavelength of 590 nm after the film has been left to stand for 5 hours in each of a 23° C., 20% relative humidity environment and a 23° C., 80% relative humidity environment)/(Rt(590) value measured after the film has been left to stand for 5 hours in a 23° C., 55% relative humidity environment)×100. n Formula (ii): Rt(590)={(n x +n y )/ 2 −n z }×d n (wherein n x represents a refractive index in the slow axis direction in the film plane, n y represents a refractive index in the direction perpendicular to the slow axis in the film plane, n z represents a refractive index in the thickness direction of the film, and d represents a film thickness (nm), respectively). |