Protective film for polarizing plate, polarizing plate including the same, and liquid crystal display including the same
A protective film for a polarizing plate includes a base film and a primer layer on one or both sides of the base film. The protective film has a transmittance of about 90% or greater at a wavelength of 550 nm, and a ratio of the refractive index (B) of the primer layer to the refractive index (A) of the base film of about 0.6 to about 1.0. The protective film exhibits good adhesiveness to the polarizer and improves the transmittance of the polarizing plate. A polarizing plate including the same, and a liquid crystal display including the same are also disclosed.
1. A protective film for a polarizing plate, the protective film comprising:
a base film having an out-of-plane retardation (Rth) at a wavelength of 550 nm of about 4,000 nm to about 15,000 nm as calculated using Equation 2:
Rth =(( nx+ny )/2− nz )× d Equation 2
wherein Rth is the out-of-plane retardation, nx, ny and nz are refractive indices in x-, y- and z-axis directions, respectively, at a wavelength of 550 nm, and d is a thickness of the base film in nm; and
a primer layer on one or both sides of the base film,
wherein the base film has a refractive index of about 1.3 to about 1.7, and the primer layer has a refractive index of about 1.0 to about 1.6, and
wherein the protective film has a transmittance of about 90% or greater at a wavelength of 550 nm, and a ratio of a refractive index of the primer layer to a refractive index of the base film of about 0.6 to about 1.0,
wherein the base film has a degree of biaxiality (NZ) at a wavelength of 550 nm of about 1.5 to about 1.7, as calculated using Equation 3:
NZ =( nx−nz )/( nx−ny ) Equation 3
wherein NZ is the degree of biaxiality, nx, ny and nz are refractive indices in x-, y- and z-axis directions, respectively, at a wavelength of 550 nm.
2. The protective film according to claim 1 , wherein the primer layer has a thickness of about 1 nm to about 200 nm.
3. The protective film according to claim 1 , wherein the primer layer comprises a polyester, an acrylic resin, or a combination thereof.
4. The protective film according to claim 1 , wherein the base film has an in-plane retardation (Re) at a wavelength of 550 nm of about 10,000 nm or more, as calculated using Equation 1:
Re =( nx−ny )× d Equation 1
wherein Re is an in-plane retardation, nx and ny are refractive indices in x- and y-axis directions, respectively, at a wavelength of 550 nm, and d is a thickness of the base film in nm.
5. The protective film according to claim 1 , wherein the base film has an in-plane retardation (Re) at a wavelength of 550 nm as calculated using Equation 1,
and wherein a ratio of the out-of-plane retardation to the in-plane retardation is about 1.3 or less:
Re =( nx−ny )× d Equation 1
wherein Re is an in-plane retardation, nx, ny and nz are refractive indices in x-, y- and z-axis directions, respectively, at a wavelength of 550 nm, and d is a thickness of the base film in nm.
6. The protective film according to claim 1 , wherein the base film comprises a polyethylene terephthalate (PET) film.
7. A polarizing plate comprising:
a polarizer; and
the protective film according to claim 1 on a first side of the polarizer.
8. The polarizing plate according to claim 7 , further comprising: an optical compensation film on a second side of the polarizer.
9. A liquid crystal display comprising the polarizing plate according to claim 8 .