Polarizer protective film, polarization plate comprising same, and optical display apparatus comprising same
A protective film for polarizers, a polarizing plate including the same, and an optical display apparatus including the same. The polyester-based film is a polyester protective film, has a thickness of about 10 μm to about 50 μm and a refractive index difference (nx−ny) of about 0.01 or more (nx and ny being indexes of refraction of the protective film at a wavelength of about 550 nm in the slow axis direction and the fast axis direction of the protective film, respectively), and is a biaxially stretched film. The slow axis direction of the protective film is coincident with a transverse direction (TD) thereof and an angle of about 70° to about 90° is defined between an external optical axis of the protective film and a normal direction with respect to an in-plane direction of the protective film.
1. A protective film for polarizers,
wherein the protective film is a polyester protective film, has a thickness of about 10 μm to about 50 μm and a refractive index difference (nx−ny) of about 0.01 or more, nx and ny being indexes of refraction of the protective film at a wavelength of about 550 nm in a slow axis direction and a fast axis direction of the protective film, respectively, and is a biaxially stretched film, an internal optical axis of the protective film being an axis thereof which provides no phase retardation, and an external optical axis of the protective film being an axis thereof along which light having traveled along the internal optical axis and emitted from the protective film travels,
the slow axis direction of the protective film being coincident with a transverse direction (TD) thereof,
an angle of about 70° to about 90° being defined between the external optical axis of the protective film and a normal direction with respect to an in-plane direction of the protective film.
2. The protective film for polarizers according to claim 1 , wherein the protective film has a fast axis tilted at an angle of about 60° to about 120° with respect to the TD of the protective film.
3. The protective film for polarizers according to claim 1 , wherein the protective film has an in-plane retardation of about 2,000 nm to about 7,000 nm at a wavelength of about 550 nm.
4. The protective film for polarizers according to claim 1 , wherein the polyester protective film comprises a film formed of at least one resin selected from among polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, and polybutylene naphthalate.
5. A polarizing plate comprising: a polarizer; and a protective film for polarizers stacked on a light exit surface of the polarizer, the protective film for polarizers being the protective film for polarizers according to claim 1 .
6. The polarizing plate according to claim 5 , wherein the polarizing plate has a major length direction and a minor length direction, and an absorption axis of the polarizer is coincident with the major length direction of the polarizing plate.
7. The polarizing plate according to claim 5 , wherein, assuming that the absorption axis of the polarizer is placed at an angle of 0°, the protective film for polarizers has a slow axis tilted at an angle of about 60° to about 120° or at an angle of about −120° to about −60° thereto.
8. The polarizing plate according to claim 5 , further comprising: an optical film formed on a light incidence surface of the polarizer.
9. An optical display apparatus comprising the polarizing plate according to claim 5 .