Method for producing retardation film

Abstract

A method for producing a retardation film comprising the steps of: (a) uniaxially stretching an original film for producing retardation film in one direction at either a temperature T 1 or T 2 ; and then (b) uniaxially stretching the film stretched in the step (a) in a direction perpendicular to the above-mentioned direction of stretching at a temperature T 2 or T 1 different from the above-mentioned temperature, in which the original film for producing retardation film has a characteristic that a phase of linearly polarized light entering vertically into the film plane and having an oscillating surface of an electric vector in an X-Z plane against linearly polarized light entering vertically into the film plane and having an oscillating surface of an electric vector in a Y-Z plane lags by uniaxially stretching in the direction of the X axis at a temperature T 1 , and leads by uniaxially stretching in the direction of the X axis at a temperature T 2 different from the above-mentioned temperature T 1 , in which the X axis is an uniaxially stretching direction, the Y axis is a direction perpendicular to the uniaxially stretching direction in the film plane, and the z axis is a direction of a thickness of the film.

1 . A method for producing a retardation film which satisfies a relation of n x >n z >n y , in which n x  is a refractive index in a direction of a slow axis in a plane of the film, n y  is a refractive index in a direction perpendicular to the direction of the slow axis in the planer and n z  is a refractive index in a thickness direction, Comprising the steps of:
 (a) uniaxially stretching an original film for producing retardation film in one direction at either a temperature T 1  or T 2 ; and then   (b) uniaxially stretching the film stretched in the step (a) in a direction perpendicular to the direction of stretching in the step (a) at a temperature T 2  or T 1  different from the above-mentioned temperature in the step (a),   in which the original film for producing retardation film has a characteristic that a phase of linearly polarized light entering vertically into the film plane and having an oscillating surface of an electric, vector in an x-Z plane against a phase of linearly polarized light entering vertically into the film plane and having an oscillating surface of an electric vector in a Y-Z plane lags by uniaxially stretching in a direction of the X axis at a temperature T 1 , and leads by uniaxially stretching in a direction of the X axis at a temperature T 2  different from the above-mentioned temperature T 1 , in which the X axis is an uniaxially stretching direction, the Y axis is a direction perpendicular to the uniaxially stretching direction in the film plane, and the Z axis is a direction of a thickness of the film.   
   
   
       2 . A method for producing a retardation film which satisfies a relation of 0.92≦R 40 /Re≦1.08, in which Re is a retardation value at an incident angle of 0 degrees, and R 40  is a retardation value at an incident angle of 40 degrees, comprising the steps of:
 (a) uniaxially stretching an original film for producing retardation film in one direction at either a temperature T 1  or T 2 ; and then   (b) uniaxially stretching the film stretched in the step (a) in a direction perpendicular to the above-mentioned direction of stretching in the step (a) at a temperature T 2  or T 1  different from the above-mentioned temperature in the step (a),   in which the original film for producing retardation film has a characteristic that a phase of linearly polarized light entering vertically into the film plane and having an oscillating surface of an electric vector in an X-Z plane against a phase of linearly polarized light entering vertically into the film plane and having an oscillating surface of an electric vector in a Y-Z plane lags by uniaxially stretching in the direction of the X axis at a temperature T 1 , and leads by uniaxially stretching in the direction of the X axis as a different temperature T 2  from the above-mentioned temperature T 1 , in which the X axis is an uniaxially stretching direction, the Y axis is a direction perpendicular to the uniaxially stretching direction in the film plane, and the Z axis is a direction of a thickness of the film.   
   
   
       3 . An original film for producing retardation film having a characteristic that a phase of linearly polarized light entering vertically into the film plane and having an oscillating surface of an electric vector in an X-Z plane against a phase of linearly polarized light entering vertically into the film plane and having an oscillating surface of an electric vector in a Y-Z plane lags by uniaxially stretching in the direction of the X axis at a temperature T 1 , and leads by uniaxially stretching in the direction of the X axis at a temperature T 2  different from the above-mentioned temperature T 1 , in which the X axis is an uniaxially stretching direction, the Y axis is a direction perpendicular to the uniaxially stretching direction in the film plane, and the Z axis is a direction of a thickness of the film. 
   
   
       4 . The original film for producing retardation film according to the  claim 3 , in which the original film is a laminate of a layer composed of a thermoplastic resin A having a positive intrinsic birefringence and a layer composed of a thermoplastic resin B having a negative intrinsic birefringence. 
   
   
       5 . The original film for producing retardation film according to the  claim 3 , in which an absolute value of difference between a deflection temperature under load Ts A  of the thermoplastic Resin A and a deflection temperature under load Ts B  of the thermoplastic resin B is 5° C. or more. 
   
   
       6 . The original film for producing retardation film according to the  claim 3 , in which a rupture elongation of the thermoplastic resin A at the temperature Ts B  and a rupture elongation of the thermoplastic resin B at the temperature Ts A  are both 50% or more. 
   
   
       7 . The original film for producing retardation film according to the  claim 3 , in which the thermoplastic resin A is a polycarbonate resins and the thermoplastic resin B is a polystyrene resins. 
   
   
       8 . The original film for producing retardation film according to the  claim 3 , in which a ratio of sum total thickness of layers composed of the thermoplastic resin A and sum total thickness of layers composed of the thermoplastic resin B is 1:5 to 1:10.