Method for producing retardation film

A method for producing a retardation film, comprising steps of:

• co-extruding or simultaneously casting a thermoplastic resin A and a thermoplastic resin B to obtain a laminated film comprising a layer of the thermoplastic resin A and a layer of the thermoplastic resin B,
• wherein the thermoplastic resin A has a positive or negative intrinsic birefringence, the thermoplastic resin B has an intrinsic birefringence of the same sign as a sign of the thermoplastic resin A,
• optimizing the thickness of the thermoplastic resin layer A and the thermoplastic resin layer B, wherein the optimizing includes determining if a first condition and a second condition are true or false, and adjusting the thickness of at least one of the thermoplastic layer A and the thermoplastic layer B if either of the first and second conditions are false,
• wherein the first condition is that an absolute value of a phase difference which appears in the layer of the thermoplastic resin A is smaller than an absolute value of a phase difference which appears in the layer of the thermoplastic resin B when the laminated film is stretched at a temperature of TL, and the second condition is that an absolute value of a phase difference which appears in the layer of the thermoplastic resin B is smaller than an absolute value of a phase difference which appears in the layer of the thermoplastic resin A when the laminated film is stretched at a temperature of TH, wherein TsA is a deflection temperature under load of the thermoplastic resin A, TsB is a deflection temperature under load of the thermoplastic resin B and TsA is higher than TsB;
• first uniaxially stretching the laminated film at a temperature of T1 to obtain an uniaxially stretched film having an absolute value of a phase difference in the layer of the thermoplastic resin A smaller than an absolute value of a phase difference in the layer of the thermoplastic resin B, wherein T1 is TL;
• then
• second uniaxially stretching the uniaxially stretched film at a temperature of T2 to obtain a biaxially stretched film having an angle between a molecular orientation axis in the layer of the thermoplastic resin A and a molecular orientation axis in the layer of the thermoplastic resin B of 70 degrees to 110 degrees, wherein T2 is TH and TH is higher than TL.

A method for producing a retardation film, comprising steps of:

• co-extruding or simultaneously casting a thermoplastic resin A and a thermoplastic resin B to obtain a laminated film comprising a layer of the thermoplastic resin A and a layer of the thermoplastic resin B,
• wherein the thermoplastic resin A has a positive or negative intrinsic birefringence, the thermoplastic resin B has an intrinsic birefringence of the same sign as a sign of the thermoplastic resin A,
• optimizing the thickness of the thermoplastic resin layer A and the thermoplastic resin layer B, wherein the optimizing includes determining if a first condition and a second condition are true or false, and adjusting the thickness of at least one of the thermoplastic layer A and the thermoplastic layer B if either of the first and second conditions are false,
• wherein the first condition is that an absolute value of a phase difference which appears in the layer of the thermoplastic resin B is smaller than an absolute value of a phase difference which appears in the layer of the thermoplastic resin A when the laminated film is stretched at a temperature of TL, and the second condition is that an absolute value of a phase difference which appears in the layer of the thermoplastic resin A is smaller than an absolute value of a phase difference which appears in the layer of the thermoplastic resin B when the laminated film is stretched at a temperature of TH, wherein TsA is a deflection temperature under load of the thermoplastic resin A, TsB is a deflection temperature under load of the thermoplastic resin B and TsB is higher than TsA;
• first uniaxially stretching the laminated film at a temperature of T1 to obtain an uniaxially stretched film having an absolute value of a phase difference in the layer of the thermoplastic resin B smaller than an absolute value of a phase difference in the layer of the thermoplastic resin A, wherein T1 is TL;
• then
• second uniaxially stretching the uniaxially stretched film at a temperature of T2 to obtain a biaxially stretched film having an angle between a molecular orientation axis in the layer of the thermoplastic resin A and a molecular orientation axis in the layer of the thermoplastic resin B of 70 degrees to 110 degrees, wherein T2 is TH and TH is higher than TL.

A method for producing a retardation film, comprising steps of:

• co-extruding or simultaneously casting a thermoplastic resin A and a thermoplastic resin B to obtain a laminated film comprising a layer of the thermoplastic resin A and a layer of the thermoplastic resin B,
• wherein the thermoplastic resin A has a positive or negative intrinsic birefringence, the thermoplastic resin B has an intrinsic birefringence of the same sign as a sign of the thermoplastic resin A,
• optimizing the thickness of the thermoplastic resin layer A and the thermoplastic resin layer B, wherein the optimizing includes determining if a first condition and a second condition are true or false, and adjusting the thickness of at least one of the thermoplastic layer A and the thermoplastic layer B if either of the first and second conditions are false,
• wherein the first condition is that an absolute value of a phase difference which appears in the layer of the thermoplastic resin B is smaller than an absolute value of a phase difference which appears in the layer of the thermoplastic resin A when the laminated film is stretched at a temperature of TL, and the second condition is that an absolute value of a phase difference which appears in the layer of the thermoplastic resin A is smaller than an absolute value of a phase difference which appears in the layer of the thermoplastic resin B when the laminated film is stretched at a temperature of TH, wherein TsA is a deflection temperature under load of the thermoplastic resin A, TsB is a deflection temperature under load of the thermoplastic resin B and TsB is higher than TsA;
• first uniaxially stretching the laminated film at a temperature of T1 to obtain an uniaxially stretched film having an absolute value of a phase difference in the layer of the thermoplastic resin A smaller than an absolute value of a phase difference in the layer of the thermoplastic resin B, wherein T1 is TH;
• then
• second uniaxially stretching the uniaxially stretched film at a temperature of T2 to obtain a biaxially stretched film having an angle between a molecular orientation axis in the layer of the thermoplastic resin A and a molecular orientation axis in the layer of the thermoplastic resin B of 70 degrees to 110 degrees, wherein T2 is TL and TH is higher than TL.