Polarizing plate and optical display comprising the same

1. A polarizing plate comprising:

a polarizer; and a first protective layer and a second protective layer sequentially stacked on a surface of the polarizer,

wherein the second protective layer comprises a positive C retardation layer,

the positive C retardation layer having a thickness of about 10 μm or less, an index of refraction of about 1.50 to about 1.55, and a glass transition temperature (Tg) of about 150° C. to about 250° C., and

wherein a difference in index of refraction between the positive C retardation layer and the polarizer is about 0.05 or less, and

an index of refraction of the first protective layer is the same or less than that of the positive C retardation layer.

2. The polarizing plate according to claim 1 , wherein a difference in index of refraction between the positive C retardation layer and the first protective layer is about 0.1 or less.

3. The polarizing plate according to claim 1 , wherein the positive C retardation layer is a non-liquid crystal layer.

4. The polarizing plate according to claim 1 , wherein the positive C retardation layer comprises at least one compound selected from among a cellulose ester compound or a polymer thereof and an aromatic compound or a polymer thereof.

5. The polarizing plate according to claim 4 , wherein the aromatic compound comprises a polystyrene compound.

6. The polarizing plate according to claim 5 , wherein the polystyrene compound comprises a halogen.

7. The polarizing plate according to claim 1 , wherein the positive C retardation layer has an out-of-plane retardation of about −180 nm to about 0 nm and an in-plane retardation of about 0 nm to about 10 nm at a wavelength of about 550 nm.

8. The polarizing plate according to claim 1 , wherein a laminate of the first protective layer and the second protective layer satisfies at least one of the following Relations 5 and 6:

Re(450)/Re(550)>Re(650)/Re(550),  Relation 5

where Re(450), Re(550), and Re(650) denote in-plane retardations (unit: nm) of the laminate of the first protective layer and the second protective layer at wavelengths of about 450 nm, 550 nm, and 650 nm, respectively; and

| R th(450)|/| R th(550)|>| R th(650)|/| R th(550)|,  Relation 6

where Re(450), Re(550), and Re(650) denote out-of-plane retardations (unit: nm) of the laminate of the first protective layer and the second protective layer at wavelengths of about 450 nm, 550 nm, and 650 nm, respectively.

9. The polarizing plate according to claim 8 , wherein the laminate of the first protective layer and the second protective layer has Re(450)/Re(550) of about 0.1 to about 10 and Re(650)/Re(550) of about 0.1 to about 5.

10. The polarizing plate according to claim 8 , wherein the laminate of the first protective layer and the second protective layer has |Rth(450)|/|Rth(550)| of about 0.1 to about 10 and |Rth(650)|/|Rth(550)| of about 0.1 to about 5.

11. The polarizing plate according to claim 1 , wherein a laminate of the first protective layer and the second protective layer satisfies the following Relation 7:

R th(550)/Re(550)≤−50,

where Rth(550) denotes an out-of-plane retardation (unit: nm) of the laminate of the first protective layer and the second protective layer at a wavelength of about 550 nm, and

Re(550) denotes an in-plane retardation (unit: nm) of the laminate of the first protective layer and the second protective layer at a wavelength of about 550 nm.

12. The polarizing plate according to claim 1 , wherein the first protective layer has an in-plane retardation of about 10 nm or less and an out-of-plane retardation of about −10 nm to about 10 nm at a wavelength of about 550 nm.

13. The polarizing plate according to claim 1 , wherein the first protective layer comprises a cellulose ester resin film.

14. The polarizing plate according to claim 1 , wherein the first protective layer and the second protective layer are sequentially stacked on the surface of the polarizer in the stated order or an order opposite to the stated order.

15. The polarizing plate according to claim 1 , further comprising: a third protective layer on another surface of the polarizer.

16. The polarizing plate according to claim 15 , wherein the third protective layer has an in-plane retardation of about 5,000 nm or more at a wavelength of about 550 nm.

17. The polarizing plate according to claim 1 , wherein a laminate of the first protective layer and the second protective layer has an out-of-plane retardation variation rate of about −15% to 0%, as calculated by the following Equation 1:

Out-of-plane retardation variation rate=[( A−B )/ B ]×100,

where B denotes an initial out-of-plane retardation (unit: nm) of the laminate of the first protective layer and the second protective layer at a wavelength of about 550 nm, and

A denotes an out-of-plane retardation (unit: nm) of the laminate of the first protective layer and the second protective layer at a wavelength of about 550 nm after the laminate is left at about 60° C. and about 95% relative humidity (RH) for about 250 hours.

18. The polarizing plate according to claim 1 , wherein the polarizing plate has an MD shrinkage rate of about −0.48% to 0%, as calculated by the following Equation 2:

MD shrinkage rate=[( C−D )/ D ]×100,

where D denotes an initial MD length (unit: mm) of the polarizing plate, and

C denotes an MD length (unit: mm) of the polarizing plate after the polarizing plate is left at about 85° C. for about 24 hours.

19. The polarizing plate according to claim 1 , further comprising a fourth protective layer, the fourth protective layer comprising a positive A retardation layer.

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

21. The polarizing plate according to claim 1 , wherein the index of refraction of the first protective layer is about 1.45 to about 1.50.