Vertically aligned liquid crystal display having negative compensation film
The present invention relates to a vertically aligned LCD (VA-LCD) comprising a negative compensation film including one or more of a first retardation film (+A-plate) satisfying the condition of n x >n y =n z and a first retardation film (−A-plate) satisfying the condition of n x <n y =n z , and one or more of a second retardation film (−C-plate) satisfying the condition of n x =n y >n z , wherein the first retardation film is arranged such that its optical axis is perpendicular to an optical absorption axis of a neighboring polarizing plate, and a total thickness retardation (R −C +R VA ) including the thickness retardation of the second retardation film and the thickness retardation of a VA-panel has a negative value. The VA-LCD in accordance with the present invention improves contrast characteristics on a front surface and at a tilt angle and minimizes coloring in a black state according to the tilt angle.
1. A vertically aligned LCD (VA-LCD) in a multi-domain mode or using a chiral additive, provided with a negative compensation film, in which a vertically aligned panel (VA-panel) is obtained by injecting liquid crystal having a negative dielectric anisotropy (Δε<0) or a positive dielectric anisotropy (Δε>0) into a gap between upper and lower glass substrates, upper and lower polarizing plates are arranged above the upper and lower surfaces of the VA-panel so that optical absorption axes of the polarizing plates are perpendicular to each other, and a cell gap in the range of 3 μm to 8 μm is maintained, comprising:
the negative compensation film including one or more of a first retardation film (+A-plate) satisfying the condition of n x >n y =n z , and a first retardation film (−A-plate) satisfying the condition of n x <n y =n z , and one or more of a second retardation film (−C-plate) satisfying the condition of n x =n y >n z , for forming a liquid crystal cell, wherein said n x and n y represent in-plane refractive indexes between the VA-panel and the upper and lower polarizing plates, and said n z represents a thickness refractive index,
wherein said first retardation film is arranged such that an optical axis of said first retardation film is perpendicular to an optical absorption axis of the neighboring polarizing plate, and a total thickness retardation (R −C +R VA ) including the thickness retardation of said second retardation film and the thickness retardation of the VA-panel has a negative value.
2. The VA-LCD according to claim 1 , wherein
said negative compensation film includes one of said first retardation film (+A-plate and −A-plate) and one of said second retardation film (−C-plate) in which
one of said first retardation film and said second retardation film is selectively arranged between the VA-panel and the upper polarizing plate, and the other one of said second retardation film is arranged between the VA-panel and the lower polarizing plate, or
said first retardation film and said second retardation film are arranged at one area between the VA-panel and the upper polarizing plate, or between the VA-panel and the lower polarizing plate.
3. The VA-LCD according to claim 1 , wherein
said negative compensation film includes two of said first retardation film (+A-plates or −A-plates) and one of said second retardation film (−C-plate) in which
one of said first retardation film, and one of said second retardation film are arranged at one area between the VA-panel and the upper polarizing plate, or between the VA-panel and the lower polarizing plate, and the other one of said first retardation films is arranged at the other area between the VA-panel and the upper polarizing plate, or between the VA-panel and the lower polarizing plate.
4. The VA-LCD according to claim 1 , wherein
said negative compensation film includes two of said first retardation film (+A-plates or −A-plates) and two of said second retardation film (−C-plate) in which
one of said first retardation film and one of said second retardation film are arranged between the VA-panel and the upper polarizing plate, and the other one of said first retardation film and the other one of said second retardation film are arranged between the VA-panel and the lower polarizing plate.
5. The VA-LCD according to claim 1 , wherein
said first retardation film (+A-plate and −A-plate) has a reversed wavelength dispersion in which retardation is increased in proportion to the increase of a wavelength in the range of visible rays; and
the total thickness retardation (R −C +R VA ) including the thickness retardation of said second retardation film and the thickness retardation of the VA-panel is in the range of −10 nm to −180 nm, being proportional to a wavelength in the range of visible rays.
6. The VA-LCD according to 5 , wherein
said first retardation film (+A-plate) has an in-plane retardation (R A (550)) at a wavelength of 550 nm, which is in the range of 250 nm to 500 nm, and said first retardation film (−A-plate) has an in-plane retardation (R A (550)) at a wavelength of 550 nm, which is more than −250 nm; and
said second retardation film (−C-plate) has a thickness retardation (R −C (550)) at a wavelength of 550 nm, which is in the range of −500 nm to −180 nm, and the absolute value (|R −C (550)|) thereof, which is larger than the absolute value (|R VA (550)|) of the thickness retardation of the VA-panel.
7. The VA-LCD according to 5 , wherein
the ratio (R 450 /R 550 ) of the thickness retardations of said second retardation film (−C-plate) is smaller than that of the VA-panel; and
the ratio (R 550 /R 550 ) of the thickness retardations of said second retardation film (−C-plate) is larger than that of the VA-panel, wherein said R 450 , R 550 and R 650 represent thickness retardations of said second retardation film (−C-plate) at wavelengths of 450 nm, 550 nm and 650 nm, respectively.
8. The VA-LCD according to 5 , wherein directors of liquid crystalline polymers of the VA-panel, under the condition that no voltage is applied to the VA-panel, have a pretilt angle in the range of 75° to 90° between the upper and lower glass substrates.
9. The VA-LCD according to claim 8 , wherein said pretilt angle is in the range of 87° to 90°.
10. The VA-LCD according to claim 8 , wherein said pretilt angle is in the range of 89° to 90°.
11. The VA-LCD according to claim 5 , wherein a liquid crystalline layer formed on said VA-panel has a retardation in the range of 80 nm to 400 nm at a wavelength of 550 nm.
12. The VA-LCD according to claim 11 , wherein a liquid crystalline layer formed on said VA-panel has a retardation in the range of 80 nm to 300 nm at a wavelength of 550 nm.
13. The VA-LCD according to claim 5 , wherein a rubbed direction of the liquid crystals injected into said VA-panel has an angle of 45° with the optical absorption axes of said polarizing plates.
14. The VA-LCD as set forth in claim 5 , wherein
the ratio (R A,450 /R A,550 ) of the in-plane retardations of said first retardation film (A-plate) is in the range of 0.6 to 0.9; and
the ratio (R A,550 /R A,650 ) of the in-plane retardations of said first retardation film (A-plate) is in the range of 1.1 to 1.5, wherein said R A,450 , R A,550 and R A,650 represent in-plane retardations at wavelengths of 450 nm, 550 nm and 650 nm, respectively.
15. The VA-LCD as set forth in claim 5 , wherein:
the ratio (R −C,450 /R −C,550 ) of the thickness retardations of said second retardation film (−C-plate) is in the range of 0.9 to 1.2; and
the ratio (R −C,550 /R −C,650 ) of the thickness retardations of said second retardation film (−C-plate) is in the range of 0.9 to 1.2, wherein said R −C,450 , R −C,550 and R −C,650 represent thickness retardations at wavelengths of 450 nm, 550 nm and 650 nm, respectively.