Polarizing plate, method of preparing the same, and liquid crystal display apparatus including the same
A polarizing plate, a method of preparing the same and a liquid crystal display apparatus including the same are disclosed. The polarizing plate includes a polarizer and a polyester film formed on a surface of the polarizer, wherein the polyester film has a ratio of an elongation ratio in a machine direction to an elongation ratio in a transverse direction of about 1:0.8 to about 1:1.2, an in-plane retardation (Re) of about 500 nm or less at a wavelength of 550 nm, and an out-of-plane retardation (Rth) of about 10,000 nm or less at a wavelength of 550 nm.
1. A polarizing plate comprising:
a polarizer; and
a polyester film on a surface of the polarizer, and
an optical film on an other surface of the polarizer, the optical film having an angle of axis distortion of a fast axis of the optical film with respect to an absorption axis of the polarizer of about +0.03° or greater and less than about +0.2°;
the polyester film having a ratio of an elongation ratio in a machine direction to an elongation ratio in a transverse direction of about 1:0.8 to about 1:1.2, an in-plane retardation (Re) of about 500 nm or less at a wavelength of 550 nm as calculated by Equation 1, and an out-of-plane retardation (Rth) of about 1,000 nm to about 10,000 nm at a wavelength of 550 nm as calculated by Equation 2:
Re =( nx−ny )× d Equation 1
Rth =(( nx+ny )/2 −nz )× d Equation 2
wherein mc is a refractive index at a wavelength of 550 nm in an x-axis direction of the polyester film, ny is a refractive index of the polyester film at a wavelength of 550 nm in a y-axis direction of the polyester film, nz is a refractive index at a wavelength of 550 nm in a z-axis direction of the polyester film, and d is a thickness of the polyester film in nm.
2. The polarizing plate according to claim 1 , wherein the ratio of the elongation ratio in the machine direction to the elongation ratio in the transverse direction of the polyester film is about 1:1.
3. The polarizing plate according to claim 1 , wherein the polyester film has a degree of biaxiality (NZ) of about 1 or greater as represented by Equation 3:
NZ =( nx−nz )/( nx−ny ) Equation 3
wherein nx is the refractive index at a wavelength of 550 nm in the x-axis direction of the polyester film, ny is the refractive index of the polyester film at a wavelength of 550 nm in the y-axis direction of the polyester film, and nz is the refractive index at a wavelength of 550 nm in the z-axis direction of the polyester film.
4. The polarizing plate according to claim 1 , wherein the polyester film has a difference of nx−ny of about 0 to about 0.1, and the polyester film has a degree of biaxiality (NZ) of about 15 or greater as represented by Equation 3:
NZ =( n−nz )/( nx−ny ) Equation 3
wherein nx is the refractive index at a wavelength of 550 nm in the x-axis direction of the polyester film, ny is the refractive index of the polyester film at a wavelength of 550 nm in the y-axis direction of the polyester film, and nz is the refractive index at a wavelength of 550 nm in the z-axis direction of the polyester film.
5. The polarizing plate according to claim 1 , wherein the polyester film is non-birefringent.
6. The polarizing plate according to claim 1 , wherein the polyester film comprises polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and/or polybutylene naphthalate resins.
7. The polarizing plate according to claim 1 , wherein the optical film is a retardation film.
8. The polarizing plate according to claim 1 , wherein the optical film comprises cellulose, polyester, cyclic polyolefin, polycarbonate, polyether sulfone, polysulfone, polyamide, polyimide, polyolefin, polyacrylate, polyvinyl alcohol, polyvinyl chloride, and/or polyvinylidene chloride resins.
9. A liquid crystal display apparatus comprising the polarizing plate according to claim 1 .
10. A method of preparing a polarizing plate, comprising:
preparing a polyester film by concurrent elongation of a melt-extruded polyester resin in machine and transverse directions in a ratio of an elongation ratio in a machine direction to an elongation ratio in a transverse direction of about 1:0.8 to about 1:1.2;
bonding the polyester film to a surface of a polarizer; and
bonding an optical film to an other surface of the polarizer, the optical film being bonded to the polarizer such that an angle of axis distortion of a fast axis of the optical film with respect to an absorption axis of the polarizer is about +0.03° or greater and less than about +0.2°.
11. The method according to claim 10 , wherein the polyester film has an in-plane retardation (Re) of about 500 nm or less at a wavelength of 550 nm as represented by Equation 1, and an out-of-plane retardation (Rth) of about 10,000 nm or less at a wavelength of 550 nm as represented by Equation 2:
Re =( nx−ny )× d Equation 1
Rth =(( nx +ny )/2 −nz )× d Equation 2
wherein nx is a refractive index at a wavelength of 550 nm in an x-axis direction of the polyester film, ny is a refractive index of the polyester film at a wavelength of 550 nm in a y-axis direction of the polyester film, nz is a refractive index at a wavelength of 550 nm in a z-axis direction of the polyester film, and d is a thickness of the film in nanometers.
12. The method according to claim 10 , wherein the polyester film has a degree of biaxiality (NZ) of 15 or greater as represented by Equation 3:
NZ =( nx−nz )/( nx−ny ) Equation 3
wherein nx is a refractive index at a wavelength of 550 nm in an x-axis direction of the polyester film, ny is a refractive index of the polyester film at a wavelength of 550 nm in a y-axis direction of the polyester film, and nz is a refractive index at a wavelength of 550 nm in a z-axis direction of the polyester film.
13. The method according to claim 10 , wherein the polyester resin comprises polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and/or polybutylene naphthalate.
14. The method according to claim 10 , wherein the ratio of the elongation ratio in the machine direction to the elongation ratio in the transverse direction of the polyester film is about 1:1.