Method for producing retardation film

A method for producing a retardation film,

• in which the method comprising steps of:
• co-extruding or simultaneously casting a thermoplastic resin A and a thermoplastic resin B to obtain a laminated film for production of the retardation film, wherein the laminated film comprises a layer A0 composed of the thermoplastic resin A and a layer B0 composed of the thermoplastic resin B, the thermoplastic resin A has a positive intrinsic birefringence and a deflection temperature under load (TsA), the thermoplastic resin B has a negative intrinsic birefringence and a deflection temperature under load (TsB), the deflection temperature under load (TsA) is higher than the deflection temperature under load (TsB), the ratio of the sum total thickness of the layer A to the sum total thickness of the layer B is from 1:5 to 1:15, and
• if and when the laminated film is uniaxially stretched at a temperature of T1 which is not less than TsB+5° C. and not more than TsA+3° C., a uniaxially stretched film t1 is obtained, the uniaxially stretched film t1 has an oriented layer AT1 derived from the layer A0 and an oriented layer BT1 derived from the layer B0, the absolute value of a phase difference in the oriented layer AT1 is larger than that in the oriented layer BT1, and
• if and when the laminated film is uniaxially stretched at a temperature of T2 which is not more than TsB+3° C., a uniaxially stretched film t2 is obtained, the uniaxially stretched film t2 has an oriented layer AT2 derived from the layer A0 and an oriented layer BT2 derived from the layer B0, the absolute value of a phase difference in the oriented layer AT2 is smaller than that in the oriented layer BT2,
• uniaxially stretching the laminated film at the temperature of T1 to obtain the uniaxially stretched film t1, and then
• uniaxially stretching the uniaxially stretched film t1 at the temperature of T2 at an angle of 70 degrees to 110 degrees with respect to the stretching direction of the previous stretching step to obtain the retardation film comprising an oriented layer A2 derived from the layer AT1 and an oriented layer B2 derived from the layer BT1, and a molecular orientation axis in the oriented layer A2 and a molecular orientation axis in the oriented layer B2 are crossed at an angle of 70 degrees to 110 degrees.