Polarizing plate and optical display including the same

1. A polarizing plate comprising:

a polarizer;

a first retardation film on a lower surface of the polarizer and having an in-plane retardation (Ro) at a wavelength of about 550 nm of about 180 nm to about 220 nm; and

a second retardation film on a lower surface of the first retardation film and having an in-plane retardation (Ro) at a wavelength of about 550 nm of about 50 nm to about 80 nm,

wherein the first retardation film has a thickness direction retardation (Rth) at a wavelength of about 550 nm having a positive (+) value, and the second retardation film has a thickness direction retardation (Rth) at a wavelength of about 550 nm having a negative (−) value.

2. The polarizing plate according to claim 1 , wherein the first retardation film has a thickness direction retardation (Rth) at a wavelength of about 550 nm of about 100 nm to about 120 nm, as calculated by Equation 1:

Rth =(( nx+ny )/2− nz )× d   (1)

wherein nx, ny and nz are indices of refraction at a wavelength of about 550 nm in x-, y- and z-axis directions of the first retardation film, respectively, and d is a thickness of the first retardation film in nm.

3. The polarizing plate according to claim 1 , wherein the first retardation film has a degree of bi-axiality (NZ) at a wavelength of about 550 nm of about 1.05 to about 1.07, as calculated by Equation 2:

NZ =( nx−nz )/( nx−ny )  (2)

wherein nx, ny and nz are indices of refraction at a wavelength of about 550 nm in x-, y- and z-axis directions of the first retardation film, respectively.

4. The polarizing plate according to claim 1 , wherein the second retardation film has a thickness direction retardation (Rth) at a wavelength of about 550 nm of about −50 nm to about −20 nm, as calculated by Equation 1:

Rth =(( nx+ny )/2− nz )× d   (1)

wherein nx, ny and nz are indices of refraction at a wavelength of about 550 nm in x-, y- and z-axis directions of the second retardation film, respectively, and d is a thickness of the second retardation film in nm.

5. The polarizing plate according to claim 1 , wherein the second retardation film has a degree of bi-axiality (NZ) at a wavelength of about 550 nm of about −0.1 to about 0, as calculated by Equation 2:

NZ =( nx−nz )/( nx−ny )  (2)

wherein nx, ny and nz are indices of refraction at a wavelength of about 550 nm in x-, y- and z-axis directions of the second retardation film, respectively.

6. The polarizing plate according to claim 1 , wherein a stack body of the first and second retardation films has a degree of bi-axiality (NZ) at a wavelength of about 550 nm of about 0.4 to about 0.5, as calculated by Equation 4:

NZ =( nx−nz )/( nx−ny )  (4)

where nx, ny and nz are indices of refraction at a wavelength of about 550 nm in x-, y- and z-axis directions of the stack body of the retardation films, respectively.

7. The polarizing plate according to claim 1 , wherein a stack body of the first and second retardation films has a thickness direction retardation (Rth) at a wavelength of about 550 nm of about −5 nm to about 5 nm, as calculated by Equation 3:

Rth =(( nx+ny )/2− nz )× d   (3)

wherein nx, ny and nz are indices of refraction at a wavelength of about 550 nm in x-, y- and z-axis directions, respectively, of the stack body of the retardation films, and d is a thickness of the stack body of the retardation films in nm.

8. The polarizing plate according to claim 1 , wherein at least one of the first and second retardation films is a multilayer film having two or more layers.

9. The polarizing plate according to claim 1 , further comprising:

a protective film on an upper surface of the polarizer.

10. An optical display comprising the polarizing plate according to claim 1 .