Patent ID: 8120849

Claim:
A retardation film manufactured by the manufacturing method comprising feeding a thermoplastic resin film; and stretching the thermoplastic resin film while adjusting stretching ratio α [%], temperature β [° C.], and stretching speed γ [%/min] so that the following formulas (1) and (2) are satisfied when the thermoplastic resin film is stretched at the stretching ratio α[%], the temperature β [° C.], and the stretching speed γ [%/min]: Z>X (1) ( X× 100/ k)× 0.2<( Y−X )×100/ k (2) wherein X represents yield stress [MPa] in a stress-strain curve, Y represents stress [MPa] in the stress-strain curve when the film is further stretched from the yield stress by k [%] which is an amount of strain until the yield stress, and Z represents stress [MPa] in the stress-strain curve when the film is stretched to α [%]; wherein the retardation film has in-plane retardation Re whose unevenness in a transverse direction is 10 nm or less, and thickness direction retardation Rth whose unevenness in the transverse direction is 20 nm or less.