Liquid crystal cells – elements and systems – Cell containing liquid crystal of specific composition – Polymer liquid crystal
Reexamination Certificate
2003-01-30
2004-08-24
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Cell containing liquid crystal of specific composition
Polymer liquid crystal
Reexamination Certificate
active
06781665
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a liquid crystal display (LCD) in which a liquid crystal material including a polymeric component (a monomer or oligomer) that is optically or thermally polymerized is sealed between substrates and in which the polymeric component is polymerized to form a polymer while adjusting a voltage applied to the liquid crystal layer (the applied voltage may be zero, and this operating may be hereinafter simply stated as “while applying a voltage” as occasions demand), the direction of alignment of liquid crystal molecules being regulated during driving by the alignment regulating capability of the polymer, the invention also relating to a method of manufacturing the same.
Referring to liquid crystal displays utilizing an active matrix according to the related art, TN (twisted nematic) mode liquid crystal displays are widely used in which a liquid crystal material having positive dielectric constant anisotropy is aligned horizontally on a substrate surface such that it is twisted at 90 degrees between substrates that are opposite to each other in a dark state. Such TN mode liquid crystal displays have a problem in that they have poor viewing angle characteristics, and various studies have been made to improve the viewing angle characteristics.
IPS mode (in-plane-switching mode) liquid crystal displays (hereinafter briefly referred to as IPS-LCDs) in which a liquid crystal having positive dielectric constant anisotropy is horizontally aligned and applied with a transverse electric field are known as liquid crystal displays that are better than TN mode liquid crystal display according to the related art in viewing angle characteristics. However, liquid crystal molecules are switched in a horizontal plane with a comb-shaped electrode in an IPS-LCD, and there is a need for a backlight unit having high optical intensity because the comb-shaped electrode reduces the aperture ratio of pixels significantly.
On the contrary, multi-domain vertical alignment mode liquid crystal displays (hereinafter briefly referred to as MVA-LCDs) are known in which a liquid crystal having negative dielectric constant anisotropy is vertically aligned and in which banks (linear protrusions) are provided on a substrate or blanks (slits) are provide in an electrode as an alignment regulating structure. An MVA-LCD exhibits excellent viewing angle characteristics because it is provided with an alignment regulating structure which makes it possible to control the alignment of the liquid crystal such that it is oriented in a plurality of orientations when a voltage is applied without performing any rubbing process on alignment film.
However, the optical transmittance of the panel of an MVA-LCD is lower than that of a TN mode LCD although the reduction in the substantial aperture ratio of the pixels attributable to the protrusions or slits is not as significant as that caused by the comb-shaped electrode of an IPS-LCD. For this reason, MVA-LCDs and IPS-LCDs are presently considered unsuitable for notebook type PCs for which low power consumption is a must.
MVA-LCDs according to the related art have a problem in that it appears dark when displaying white because of low luminance. This is principally attributable to the fact that dark lines appear above protrusions or slits that are boundaries between separate alignments to reduce transmittance during white display and to consequently present dark appearance. Although this problem can be mitigated by maintaining sufficient intervals between the protrusions or slits, since this results in a decrease in the number of the protrusions or slits that are alignment regulating structures, another problem arises in that response time is increased because it takes a long time to stabilize the alignment of the liquid crystal when a predetermined voltage is applied.
In order to solve this problem and to provide an MVA-LCD having high luminance capable of high speed response, a method has been proposed in which the direction of alignment of liquid crystal molecules during driving is regulated using a polymer. According to the method of regulating the direction of alignment of liquid crystal molecules during driving using a polymer, a liquid crystal material that is a liquid crystal mixed with a polymeric component such as a monomer or oligomer (hereinafter briefly referred to as a monomer) is sealed between substrates. The monomer is polymerized into a polymer with the liquid crystal molecules tilted by applying a voltage between the substrates. This provides a liquid crystal layer that is tilted at a predetermined pretilt angle even when voltage application is stopped. A material that is polymerized by heat or light (ultraviolet rays) is chosen as the monomer.
However, in the case of an MVA-LCD manufactured according to the method of regulating the alignment direction of liquid crystal molecules during driving using a polymer, when an image is displayed for a long time, the image can remain visible (image sticking) even when the display is switched. This problematically reduces display quality.
SUMMARY OF THE INVENTION
The invention provides a liquid crystal display whose display characteristics are easily and reliably improved to achieve highly reliable display by mitigating image-sticking that is caused by the method of regulating the alignment direction of liquid crystal molecules during driving using a polymer and provides a method of manufacturing the same.
The above-described problem is solved by a liquid crystal display in which a liquid crystal material is sealed between two substrates provided opposite to each other, characterized in that the liquid crystal material includes a polymeric component that is optically or thermally polymerized, a polymerization initiator, and a liquid crystal composition and in that the polymerization initiator in the liquid crystal material has a concentration x that satisfies 0≦x≦0.002 (% by weight).
REFERENCES:
patent: 5698134 (1997-12-01), Jubb et al.
patent: 2003/0090617 (2003-05-01), Kawamoto et al.
patent: 11-142831 (1999-05-01), None
patent: 11-183881 (1999-07-01), None
patent: 2001-100212 (2001-04-01), None
Hanaoka Kazutaka
Inoue Hiroyasu
Inoue Yuichi
Kanii Kengo
Nakahata Yuji
Fujitsu Display Technologies Corporation
Greer Burns & Crain Ltd.
Ton Toan
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