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Semi-transmissive LCD device including an optical film having negative uniaxial double refractive index ellipsoids
| Details |
Inventors: Fukuda, Koichi; Nakamura, Yoshiaki;
Assignee: Hitachi Displays, Ltd. (Chiba-ken, JP)
Primary Examiner: Kim; Robert H.
Assistant Examiner: Chien; Lucy
Attorney, Agent or Firm: Reed Smith LLP, Fisher, Esq.; Stanley P., Marquez, Esq.; Juan Carlos A.
The present invention provides a liquid crystal display device. An optical film having negative uniaxial double refractive index ellipsoids is arranged below a semi-transmitting liquid crystal display cell and, thereafter, a λ/4 phase difference plate, a λ/2 phase difference plate and a polarizer are arranged. The orientation axis direction of the optical film having negative uniaxial double refractive index ellipsoids is substantially equal to the direction which is rotated by 90° in the clockwise direction from a resultant vector of the orientation axis direction of the upper orientation film and the orientation axis direction of the lower orientation film of the liquid crystal display cell. Further, phase lagging axis of the upper and lower λ/4 phase difference plate is set substantially equal to the orientation axis direction of the optical film having negative uniaxial double refractive index ellipsoids. |
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DETAILED DESCRIPTION With respect to angles of respective optical axes in the above-mentioned conventional semi-transmissive type liquid crystal display device, viewing angles are narrow and the intensities of the transmitting light are asymmetrical with respect to left and right viewing angles and hence, there arises a color tone shift in the left and right viewing-angle directions in a color display.
This has been one of the tasks to be solved by the present invention.
It is an advantage of the present invention to provide a semi-transmissive type liquid crystal display device which realizes image display of high quality with no color tone shift in left and right viewing-angle directions by enhancing contrast and by having high-luminance and wide viewing angles by enlarging viewing angles.
According to the present invention, an optical film having negative uniaxial double refractive index ellipsoids is provided to a lower side (a surface opposite to an observation side) of a semi-transmissive type liquid crystal display cell and, thereafter, a phase difference plate corresponding to λ/4 (a λ/4 phase difference plate), a phase difference plate corresponding to λ/2 (a λ/2 phase difference plate) and a polarizer are arranged in a stacked manner in this order.
Here, the orientation axis direction of the optical film having negative uniaxial double refractive index ellipsoids is substantially equal to the direction which is rotated in the clockwise direction by 90° from a resultant vector of the orientation axis direction of an upper orientation film and the orientation axis direction of a lower orientation film of the liquid crystal display cell, and phase lagging axes of the upper and lower phase difference plates corresponding to λ/4 are set substantially equal to the orientation axis direction of the optical film having negative uniaxial double refractive index ellipsoids.
Here, in a case of a twist angle 0° at which the resultant vector of the orientation axes of the upper and lower orientation films disappears, the orientation axis direction of the optical film having negative uniaxial double refractive index ellipsoids is set substantially equal to the orientation axis direction of the lower orientation film of the liquid crystal display cell
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