Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1997-04-30
2001-02-27
Kim, Robert (Department: 2877)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S129000
Reexamination Certificate
active
06195144
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a liquid crystal display, and more particularly to, a twisted nematic(TN) type liquid crystal display with normally black(NB) mode.
BACKGROUND OF THE INVENTION
In a twisted nematic(TN) type liquid crystal display with normally white mode(rW mode), which is generally used, the polarization axes of upper and lower polarization films are disposed to be orthogonal to each other, where a white tone is displayed when a voltage is not applied. The NW mode liquid crystal display has a problem that the viewing angle is narrow due to a proper behavior of liquid crystal molecule when applying the voltage, in particular, the transmittance in the oblique direction while displaying a black tone is increased to reduce the contrast. On the other hand, there is a normally black(NB) mode liquid crystal display in which the polarization axes of upper and lower polarization films are disposed to be nearly parallel to each other, where a black tone is displayed when a voltage is not applied. Though the NB mode liquid crystal display also has a tendency that the transmittance an the oblique direction is increased, the transmittance-increasing tendency is lower than the NW mode.
For the purpose of enlarging the viewing angle, for example, Japanese patent application laid-open No.7-104284(1995), which is filed by this commonly assigned applicant, discloses a liquid crystal display which comprises a liquid crystal display panel with a twisted liquid crystal orientation, and an optical compensation plate which is composed of molecules with a refractive index anisotropy opposite to that of the liquid crystal molecules, and has a twisted orientation structure reverse to that of the liquid crystal molecules Also, T.Kamada et al., “Wide Viewing Angle Full Color TFT LCDs”, Technical Report of IEICE, EID92-82(1992-12) suggests a NB mode liquid crystal display which comprises transparent electrodes and alignment films formed on a pair of substrates and; a liquid crystal layer which is sandwiched between the alignment films, where each pixel is divided into two domains with different rising directions of liquid crystal molecules by a domain-dividing technique and an enlarged viewing angle is obtained by using a uniaxial compensation film.
Furthermore, another technique called ‘multi-gap manner’ has been suggested. This technique is based on the optical transmittance of a NB mode liquid crystal display which is determined by optical wavelength &lgr;, birefringence &Dgr;n of liquid crystal layer and thickness d of cell, regardless of the existence of the divided pixel or uniaxial compensation film as shown in FIG.
2
. In this case, since &Dgr;n can be approximated at a constant, a NB mode full color liquid crystal display utilizing three primary colors of RGB is provided with different cell thicknesses d to the respective wavelengths &lgr; in order to display a black tone, i.e., uneven areas are formed corresponding to pixels of RGB on the substrate.
However, the viewing angle in conventional liquid crystal displays is actually limited within a low range. In particular, the requirement for a larger viewing angle in a large-screen liquid crystal display or an onboard liquid crystal display is not satisfied. Though the ‘multi-gap manner’ described above is effective to some extent, forming the uneven areas corresponding to the pixels of RGB and controlling gaps to the respective pixels are very difficult. Also, there occurs a problem that the rubbing operation for alignment of liquid crystal molecules is obstructed by the uneven ares.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a liquid crystal display in which the viewing angle can be substantially enlarged.
It is a further object of the invention to provide a liquid crystal display which can be easily produced and controlled in its operation.
According to the invention, a liquid crystal display, which includes at least a polarization film and a liquid crystal layer and displays a black tone when a voltage is not applied, comprising:
a compensation film which is disposed between the liquid crystal layer and the polarization film and has an optical structure having a twist direction reverse to the twist direction of liquid crystal in the liquid crystal layer;
wherein a pixel in the liquid crystal layer is divided into a plurality of domains.
REFERENCES:
patent: 5473455 (1995-12-01), Koike et al.
patent: 2-256021 (1990-10-01), None
patent: 3-73920 (1991-03-01), None
patent: 3-103823 (1991-04-01), None
patent: 4-55830 (1992-02-01), None
patent: 4-55827 (1992-02-01), None
patent: 7-104284 (1995-04-01), None
patent: 7-175037 (1995-07-01), None
patent: 7-253578 (1995-10-01), None
patent: 9-203894 (1997-08-01), None
T. Kamada et al., “Wide Viewing Angle Full Color TFT LCSs”, Technical Report of IEICE, EID92-98 (1992-12), pp. 35-40.
B. Bahadur, Liquid Crystals Application and Uses, vol. 1, 1990, pp. 263-265.
Murai Hideya
Suzuki Masayoshi
Suzuki Teruaki
Kim Robert
Lee Andrew H.
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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