Oval polarizing plate and organic light emitting device

1. An elliptically polarizing plate comprising, sequentially, a linear polarizer, a first retardation film, a second retardation film, a third retardation film and a fourth retardation film,

wherein the first retardation film is a −B plate having an Nz value of more than 1 in Equation 1 and having in-plane retardation value of 0.1 nm to 35 nm for light having a wavelength of 550 nm, or a −C plate satisfying Expression 1:

Nz= ( nx−nz )/( nx−ny ),   [Equation 1]

nx=ny>nz;   [Expression 1]

wherein the second retardation film is a +B plate or a −A plate having an Nz value of less than 1 in Equation 1;

wherein the third retardation film has an Nz value of 0.8 to 1.2 in Equation 1, and an in-plane slow axis of the third retardation film forms and angle of 43 degrees to 47 degrees with an absorption axis of the linear polarizer; and

wherein the fourth retardation film is a +B plate having a Nz value of −4.0 or less in Equation 1, or a +C plate satisfying Expression 2:

nx=ny<nz; and   [Expression 2]

wherein a sum of a thickness direction retardation value of the first retardation film and a thickness direction retardation value of the second retardation film is in a range of 0 nm to 180 nm and wherein the thickness direction retardation (Rth) is defined by Equation 2:

Rth= ( nz−ny )× d   [Equation 2]

wherein, nx, ny and nz are refractive indexes of the first to fourth retardation films in x-axis, y-axis and z-axis directions, respectively, and

wherein the x-axis is a direction parallel to an in-plane slow axis of the first to fourth retardation films, the y-axis is a direction parallel to an in-plane fast axis of the first to fourth retardation films, the z-axis is a thickness direction of the first to fourth retardation films, and d is a thickness of the first to fourth retardation films.

2. The elliptically polarizing plate according to claim 1 , wherein the first retardation film is a −B plate having an Nz value of 3.1 or more.

3. The elliptically polarizing plate according to claim 1 , wherein the first retardation film is a −B plate, and wherein the thickness direction retardation value of the first retardation film is from −120 nm to −1 nm.

4. The elliptically polarizing plate according to claim 1 , wherein the first retardation film is a −B plate, and wherein the in-plane slow axis of the first retardation film is perpendicular or parallel to the absorption axis of the linear polarizer.

5. The elliptically polarizing plate according to claim 1 , wherein the first retardation film has an R(450)/R(550) value of 0.6 to 1.3 or an Rth(450)/Rth(550) value of 0.6 to 1.3, wherein R(λ) is an in-plane retardation value of the first retardation film for light having a wavelength of 2 nm, and Rth(λ) is the thickness direction retardation value of the first retardation film for light having a wavelength of λ nm.

6. The elliptically polarizing plate according to claim 1 , wherein the second retardation film has an Nz value of −6 to 0.

7. The elliptically polarizing plate according to claim 1 , wherein the second retardation film has an in-plane retardation value of 0 nm to 200 nm for light having a wavelength of 550 nm.

8. The elliptically polarizing plate according to claim 1 , wherein the thickness direction retardation value of the second retardation film is from 0 nm to 200 nm.

9. The elliptically polarizing plate according to claim 1 , wherein the in-plane slow axis of the second retardation film is perpendicular to the absorption axis of the linear polarizer.

10. The elliptically polarizing plate according to claim 1 , wherein the second retardation film has an R(450)/R(550) value of 0.6 to 1.3, where R(2) is an in-plane retardation value of the second retardation film for light having a wavelength of λ nm.

11. The elliptically polarizing plate according to claim 1 , wherein the third retardation film has an in-plane retardation value of 130 nm to 150 nm for light having a wavelength of 550 nm.

12. The elliptically polarizing plate according to claim 1 , wherein the third retardation film has an R(450)/R(550) value of 0.6 to 1.0, where R(2) is an in-plane retardation value of the third retardation film for light having a wavelength of λ nm.

13. The elliptically polarizing plate according to claim 1 , wherein a thickness direction retardation value of the fourth retardation film is from 0 nm to 300 nm.

14. The elliptically polarizing plate according to claim 1 , wherein the fourth retardation film has an Rth(450)/Rth(550) value of 0.6 to 1.3, where Rth(2) is a thickness direction retardation value of the fourth retardation film for light having a wavelength of λ nm.

15. An organic light-emitting device comprising the elliptically polarizing plate of claim 1 and an organic light-emitting display panel.

16. The organic light-emitting device according to claim 15 , wherein the fourth retardation film of the elliptically polarizing plate is disposed adjacent to the organic light-emitting display panel.