Optical compensation film and liquid crystal display device using the same
An optical compensation film comprising a light absorbing layer capable of absorbing at least light of wavelength λ nm in the visible light region is disclosed. The light absorbing layer has absorption anisotropy, light absorption coefficient kz(λ) in the direction normal to the surface of layer (in the direction of z-axis), with respect to light of wavelength λ nm in the visible light region, being larger than in-plane (x-y plane) light absorption coefficients kx(λ) and ky(λ); and the light absorbing layer has the larger degree of absorption anisotropy at the light of longer wavelength. A liquid crystal display device employing the film is also disclosed.
1. An optical compensation film comprising a light absorbing layer capable of absorbing at least light of wavelength λ nm in the visible light region,
Wherein
the light absorbing layer has absorption anisotropy, light absorption coefficient kz(λ) in the direction normal to the surface of layer (in the direction of z-axis), with respect to light of wavelength λ nm in the visible light region, being larger than in-plane (x-y plane) light absorption coefficients kx(λ) and ky(λ), and
the light absorbing layer has the larger degree of absorption anisotropy at the light of longer wavelength.
2. The optical compensation film of claim 1 , wherein the light absorbing layer has a parameter A(λ) with respect to light of wavelength λ nm in the visible light region, which satisfies A(450)<A(550)<A(630):
A(λ) being defined as
A (λ)={ kz (λ)−( kx (λ)+ ky (λ))/2 }×d/λ,
where d represents the thickness of the light absorbing layer, kx(λ) and ky(λ) represent absorption coefficients with respect to light of wavelength λ respectively in the directions of x-axis and y-axis which are orthogonal to each other in the plane of the light absorbing layer, and kz(λ) represents a light absorption coefficient with respect to light of wavelength λ in the direction of z-axis which is normal to the plane (x-y plane) of the layer.
3. The optical compensation film of claim 2 , wherein the light absorbing layer has A(450) of from 0 to 0.01, A(550) of from 0.02 to 0.03, and A(630) of from 0.03 to 0.05.
4. The optical compensation film of claim 1 , wherein the light absorbing layer comprises at least a rod-like liquid crystal fixed in a vertical alignment, and a dye.
5. The optical compensation film of claim 1 , further comprising a transparent film.
6. The optical compensation film of claim 1 , further comprising a biaxial transparent film.
7. The optical compensation film of claim 1 , further comprising an optically anisotropic layer comprising a discotic liquid crystal fixed in a hybrid alignment, or the light absorbing layer comprising a discotic liquid crystal fixed in a hybrid alignment.
8. A liquid crystal display device comprising the optical compensation film of claim 1 .
9. A VA-mode liquid crystal display device comprising:
a pair of polarizers,
a VA-mode liquid crystal cell disposed therebetween, and
the optical compensation film of claim 6 disposed between each of the pair of polarizers and the liquid crystal cell.
10. A TN-mode liquid crystal display device comprising:
a pair of polarizers,
a TN-mode liquid crystal cell disposed therebetween, and
the optical compensation film of claim 7 disposed between each of the pair of polarizers and the liquid crystal cell.