Patent ID: 8270076

Claim:
A retardation film composed of a laminated film which comprises a layer A composed of a material having a positive intrinsic birefringence and a deflection temperature under load of Ts(A) and a layer B composed of a material having a negative intrinsic birefringence and a deflection temperature under load of Ts(B),in which a difference between Ts(A) and Ts(B) is 5° C. or more; and the retardation film has a property that a stretching temperature T α applied to said retardation film causes a delay of a first phase with respect to a second phase after the stretching, as compared to a phase difference between said first and second phases before the stretching, when uniaxially stretching said retardation film in a direction of an X axis by a draw ratio of 1.25 at said temperature T α , said X axis being the uniaxially stretching direction, and a stretching temperature T β applied to said retardation film causes a hastening of the first phase with respect to the second phase after the stretching, as compared to a phase difference between said first and second phases before the stretching, when uniaxially stretching said retardation film in a direction of the X axis by the draw ratio of 1.25 at said temperature T β , said X axis being the uniaxially stretching direction, and wherein a Y axis is a direction perpendicular to a direction of said X axis in the film plane, and a Z axis is a direction of a thickness of the film, and an X-Z plane is defined by said X axis and said Z axis, and an Y-Z plane is defined by said Y axis and said Z axis, and wherein said first phase is a phase of linearly polarized light ΨX having an oscillating surface of an electric vector in said X-Z plane and entering at an incident angle of 0 degree, and said second phase is a phase of linearly polarized light ΨY having an oscillating surface of an electric vector in said Y-Z plane and entering at an incident angle of 0 degree, the retardation film meets a relation of 0.92≦R 40 /Re ≦1.08, wherein Re (nm) is a retardation value of light having a wavelength of 550 nm at an incident angle of 0 degree, and R 40 (r =n) is a retardation value of light having a wavelength of 550 mm at an incident angle of 40 degrees.