Laminated quarter-wave plate or circularly polarizing plate, liquid-crystal display device using the same and method for producing the same
A laminated quarter-wave plate having: a laminate of a quarter-wave plate and a half-wave plate, wherein: the quarter-wave plate and the half-wave plate are laminated on each other so that directions of in-plane slow axes intersect each other; and each of the quarter-wave plate and the half-wave plate satisfies a relation Nz=(nx−nz)/(nx−ny)>1.05 in which nx and ny are in-plane main refractive indices, and nz is a thicknesswise refractive index; and a circularly polarizing plate having: a laminate of a laminated quarter-wave plate defined above and a polarizer.
1. A method of producing a phase retarder, said method comprising:
preparing a quarter-wave plate and a half-wave plate each by stretching a transparent polymer film with a thickness of 5 to 500 μm by one of tenter lateral stretching and biaxial stretching as part of producing said plates; and
laminating said quarter-wave plate and said half-wave plate so that directions of in-plane slow axes of said plates intersect each other,
wherein said quarter-wave plate and said half-wave plate each satisfy a relation Nz=(nx−nz)/(nx−ny)>1.05 in which nx and ny are in-plane main refractive indices, and nz is a thicknesswise refractive index.
2. The method of claim 1 , wherein said biaxial stretching comprises one of simultaneous biaxial stretching using a full tentering method and successive biaxial stretching using a roll tentering method.
3. The method of claim 1 , wherein a temperature at which said stretching is performed is at or above the glass transition point of the transparent polymer film.
4. The method of claim 1 , wherein said polymer film is stretched laterally by a stretching magnification of 50 to 200% or biaxially stretched by a stretching magnification of 50 to 200% in a main stretching direction.