POLARIZING PLATE AND OPTICAL DISPLAY DEVICE
A polarizing plate and an optical display device are disclosed. A polarizing plate includes a polarizer, and a retardation layer laminated on a surface of the polarizer, the retardation layer includes a retardation film that satisfies a relationship of nx>nz>ny, where nx, ny, and nz are indexes of refraction of the retardation film in a slow axis direction, a fast axis direction, and a thickness direction of the retardation film, respectively, at a wavelength of 550 nm, an alignment direction of a main chain of a resin contained in the retardation film with respect to a light transmission axis of the polarizer is in a range from −5° to +5°, and the retardation film has a degree of biaxiality of 0.2 to 0.6 at the wavelength of 550 nm.
1 . A polarizing plate comprising:
a polarizer; and
a retardation layer laminated on a surface of the polarizer,
wherein the retardation layer comprises a retardation film that satisfies a relationship of nx>nz>ny, where nx, ny, and nz are indexes of refraction of the retardation film in a slow axis direction, a fast axis direction, and a thickness direction of the retardation film, respectively, at a wavelength of 550 nm,
an alignment direction of a main chain of a resin contained in the retardation film with respect to a light transmission axis of the polarizer is in a range from −5° to +5°, and
the retardation film has a degree of biaxiality of 0.2 to 0.6 at the wavelength of 550 nm.
2 . The polarizing plate as claimed in claim 1 , wherein the retardation film is a retardation film of a single layer.
3 . The polarizing plate as claimed in claim 1 , wherein the retardation film has an in-plane retardation of 220 to 300 nm at the wavelength of 550 nm.
4 . The polarizing plate as claimed in claim 1 , wherein, in the retardation film, a value of the following Equation 1 is in a range from 0.8 to 1.2, and a value of the following Equation 2 is in a range from 0.9 to 1.1:
Re
(
450
nm
)
/
Re
(
550
nm
)
;
Equation
1
Re
(
650
nm
)
/
Re
(
550
nm
)
,
Equation
2
where in Equations 1 and 2, Re(450 nm), Re(550 nm), and Re(650 nm) are in-plane retardations of the retardation film at wavelengths of 450 nm, 550 nm, and 650 nm, respectively (unit: nm).
5 . The polarizing plate as claimed in claim 1 , wherein a slow axis of the retardation film with respect to a light absorption axis of the polarizer is in a range from −50 to +5°.
6 . The polarizing plate as claimed in claim 1 , wherein a slow axis of the retardation film is parallel to a mechanical direction of the retardation film.
7 . The polarizing plate as claimed in claim 1 , wherein the retardation film is a transverse direction (TD)-stretched retardation film.
8 . The polarizing plate as claimed in claim 1 , wherein
(nx−ny) is in a range from 0.0022 to 0.0075, and
(nx−nz) is in a range from 0.00044 to 0.0045.
9 . The polarizing plate as claimed in claim 1 , wherein
nx is in a range from 1.500 to 1.710,
ny is in a range from 1.480 to 1.700, and
nz is in a range from 1.500 to 1.705.
10 . The polarizing plate as claimed in claim 1 , wherein the resin is a main component of the retardation film.
11 . The polarizing plate as claimed in claim 1 , wherein the resin is a cellulose ester resin.
12 . The polarizing plate as claimed in claim 1 , wherein the cellulose ester resin comprises a cellulose ester resin regioselectively substituted with a plurality of aromatic-CO-groups, a plurality of first unsaturated or saturated (C 1-6 )alkyl-CO-groups, and a plurality of hydroxy groups, as substituents.
13 . The polarizing plate as claimed in claim 12 , wherein, in the cellulose ester resin,
a hydroxyl degree of substitution is in a range from 0.2 to 2.0,
a C2 degree of substitution is in a range from 0.15 to 0.8,
a C3 degree of substitution is in a range from 0.05 to 0.6,
a C6 degree of substitution is in a range from 0.05 to 0.6, and
a total degree of substitution is in a range from 0.25 to 2.5.
14 . The polarizing plate as claimed in claim 1 , wherein the retardation layer is formed of only the retardation film.
15 . The polarizing plate as claimed in claim 1 , wherein the retardation film has a thickness of 40 μm to 100 μm.
16 . The polarizing plate as claimed in claim 1 , further comprising a protective layer laminated on another surface of the polarizer.
17 . An optical display device comprising the polarizing plate as claimed in claim 1 .