Patent ID: 11937487
Assignee: LG CHEM, LTD.
Field: Optics (Instruments)
Classification: CPC G  H | IPC G  H

Claim 0:
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 or a −A plate having an Nz value of less than 1 in Equation 1:

Nz=(nx−nz)/(nx−ny).  [Equation 1]

wherein the second retardation film is a −B plate having an Nz value of more than 1 in Equation 1, or a −C plate satisfying Expression 1:

nx=ny>nz  [Expression 1]

wherein the third retardation film has an Nz value of 0.8 to 1.2 in Equation 1, and wherein an in-plane slow axis of the third retardation film forms an 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 an Nz value of −4.0 or less in Equation 1, or a +C plate satisfying Expression 2:

nx=ny<nz  [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 −40 nm to 70 nm and 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.