Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-05-24
2003-07-29
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S094000, C349S119000
Reexamination Certificate
active
06600538
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display utilized as a wide-viewing-angle liquid crystal television or a wide-viewing-angle liquid crystal monitor for CAD or office automation devices. The invention specifically relates to a wide-viewing-angle liquid crystal panel including a lens sheet applied to a vertical-oriented or parallel-oriented liquid crystal panel with high response speed that develops good front contrast characteristics without sacrificing brightness or response speed.
DESCRIPTION OF THE RELATED ART
Along with the development of the information infrastructure, television devices and PC monitors used as terminals for image and voice information are continuously developing. Especially, since there is a strong requirement to save space and minimize power consumption, applying liquid crystal display to the middle and small sized television and PC monitor for office appliances has now become a trend. Active-type twisted-nematic-mode and passive-type super-twisted-nematic-mode for liquid crystals are discovered and utilized widely for television and PC monitors.
However, the liquid crystal panel used for small-sized liquid crystal television or personal monitor mainly utilizes a twist nematic (TN) arrangement or a super twist nematic (STN) arrangement. The TN or STN liquid crystal has the following problems when utilized as television: the viewing angle is narrow, the colors on both ends of the screen are different, the image that each viewer sees differ when plural viewers watch the same display, and the image that the viewer sees when he or she is sitting upright differs from the image that he or she sees when lying down. Further, the TN or STN liquid crystal applied to a large PC monitor had problems such as the tone of color being changed according to the display area. These problems prevented the liquid crystal from being widely applied to televisions and monitors.
Methods aimed at solving the above-mentioned problems include a multi-domain TN (orientation division method) (Japanese Patent Application Laid-Open No. 5-107544), an ASM display method (Japanese Patent Application Laid-Open No. 6-301015), an MVA display method (Japanese Patent Application Laid-Open No. 8-43825), and an IPS display method (Japanese Patent Application Laid-Open No. 7-36058). These methods lack to provide displays with sufficient performances, and the displays were expensive to manufacture.
Moreover, along with the increase of display information density mainly caused by digital broadcasting and DVD, a liquid crystal display having high-speed response which not only characterizes in wide viewing angle but also in advanced motion image display performance is required. However, displays such as MVA and ASM have increased viewing angle, but poor response speed.
As for liquid crystal displays, various methods are being studied, including a horizontal arrangement method where a nematic liquid crystal material having positive anisotropy of dielectric constant is horizontally arranged, and a vertical arrangement method where a nematic liquid crystal material having negative anisotropy of dielectric constant is vertically arranged. The horizontal arrangement method has higher response speed and reliability compared to the twist nematic mode and the IPS mode, but these advantages were lost according to the conventional method for improving the viewing angle.
For example, in order to reduce the residual retardation directly, there is a need to provide very high voltage. This improves the viewing angle characteristic remarkably related to contrast, but it does not solve the problem of tone reversal.
A method is proposed where the pre-tilt angle is increased to reduce the tone reversal angle. However, the method utilizes an orientation film material having very weak anchoring power, which may deteriorate the orientation reliability. Even further, since the retardation of the whole display reduces according to the method, the brightness of the display is reduced. Therefore, it is effective to apply a twist arrangement or a large panel gap in order to improve the brightness of the display, but both methods reduce the response speed greatly. Therefore, the original performance of the display is lost.
Therefore, the best method to improve the viewing angle is to divide the orientation region into four parts. However, this deteriorates the viewing angle performance from all angles compared to the vertical arrangement. Further, a simple and highly reliable control method of the four-divided regions is not yet known.
There are many reports on how to improve the viewing angle using a lens film. However, most of the methods relate to the twisted nematic mode, which is inferior to MVA and IPS in the viewing angle performance, and has no improvement in its motion picture display performance.
SUMMARY OF THE INVENTION
The present invention aims at solving the problems related to the viewing angle that are generated when utilizing the conventional TN panel. Further, the present invention aims at providing a liquid crystal display having a liquid crystal panel capable of high-speed response and with a wide viewing angle performance, which, unlike the ASM or the four-division MVA, will not have any trade-off for manufacturing cost.
In order to solve the above problems, the present invention provides a liquid crystal display with a display portion formed of a transmission-type liquid crystal panel comprising a nematic liquid crystal layer having a horizontal arrangement and positive anisotropy of dielectric constant, a pair of transparent substrates having the liquid crystal layer sandwiched therebetween and equipped with transparent electrodes, and a pair of polarizing plates arranged in cross-Nicol and having absorption axes each oriented differently from the direction of liquid crystal orientation; wherein the liquid crystal layer includes two kinds of orientation regions, each region having a direction of liquid crystal orientation at an angle of approximately 180 degrees to the direction of liquid crystal orientation of the other region, and the display is further equipped with a lens sheet mounted to the viewing surface side of the liquid crystal panel for either scattering or refracting wider than its incident angle a light ray being stretched in the direction substantially parallel to the direction of liquid crystal orientation.
Further, the present invention provides a liquid crystal display further comprising a first retardation plate for compensating the birefringence of a liquid crystal layer that is parallel to the substrate surface, the birefringence generated when a specific voltage has been impressed, the first retardation plate being positioned so that its slow-phase axis direction is substantially orthogonal to the direction of liquid crystal orientation.
The present invention provides a liquid crystal display further comprising a second retardation plate having a negative retardation in the direction perpendicular to the substrate surface.
The present invention provides a liquid crystal display further comprising a third retardation plate having a slow-phase axis in the direction corresponding to the absorption axis direction of the polarizing plate.
The present invention provides a liquid crystal display wherein each retardation plate comprises two or more plates that are mounted on both outer sides of the substrates of the liquid crystal panel, and which are mounted in the following order: polarizing plate, third retardation plate, second retardation plate, first retardation plate, substrate, liquid crystal layer, substrate, first retardation plate, second retardation plate, third retardation plate, and polarizing plate.
Moreover, the present invention provides a liquid crystal display, wherein each retardation plate is formed so that the retardation plate mounted on one outer side of the substrate shows substantially the same birefringence as that of the retardation plate mounted on the other outer side of the substrate.
Further, the present invention provi
Mizushima Shigeaki
Shiomi Makoto
Dudek James
Mizushima Shigeaki
Rude Timothy
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