Liquid crystal cells – elements and systems – Cell containing liquid crystal of specific composition
Patent
1998-11-20
2000-11-21
Kelly, C. H.
Liquid crystal cells, elements and systems
Cell containing liquid crystal of specific composition
349174, 25229966, 25229967, C09K 1912, C09K 1920, C09K 1902
Patent
active
061510955
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an antiferroelectric liquid crystal cell or, in particular, to a liquid crystal cell having a satisfactory display quality using an antiferroelectric liquid crystal for a liquid crystal display device, etc.
BACKGROUND ART
The antiferroelectric liquid crystal (AFLC) is known to have a large spontaneous polarization. Spontaneous polarization is one of the features of liquid crystal materials. Also, an antiferroelectric liquid crystal cell holding an antiferroelectric liquid crystal between a pair of substrates is known to have such a structure that the antiferroelectric liquid crystal molecules assume a spatial arrangement, i.e. form layers and cancel the spontaneous polarization Ps between the layers when no voltage is applied thereto. The antiferroelectric liquid crystal material was discovered in 1988 and was initially introduced as a material capable preventing an image sticking phenomenon, i.e. a phenomenon in which information written previously remains on the liquid crystal panel, as compared with the conventional nematic liquid crystal.
Since then, the antiferroelectric liquid crystal material has been developed to produce a liquid crystal panel taking advantage of this feature. In order to secure a fast response characteristic, a great effort has so far been concentrated on developing an antiferroelectric liquid crystal material having a large spontaneous polarization Ps and a blending technique, with the result that the display characteristic or, mainly the response characteristic, of the liquid crystal display panel using the antiferroelectric liquid crystal was greatly improved.
With the advance of the development of a liquid crystal display panel using an antiferroelectric liquid crystal panel having a satisfactory display characteristic, however, an image sticking phenomenon, which is considered to be due to the layer switching which is one of the features of the antiferroelectric liquid crystal material, appeared. Since then, obviating this phenomenon has become important for the liquid crystal display panel using the antiferroelectric liquid crystal.
In the case where the device using the antiferroelectric liquid crystal cell is driven for display, a method is available in which the antiferroelectric liquid crystal cell is held by a pair of polarizing plates with the polarizing axes set as cross nicols and the polarizing plate is set in such a manner that the polarization axis of one polarizing plate substantially coincides with the direction of the average antiferroelectric liquid crystal molecules in the absence of electric field. Once this polarizing plate is set, an antiferroelectric liquid crystal panel is obtained which is capable of producing a black display in the absence of electric field and producing a white display when a voltage is applied.
On the other hand, as a result of vigorous analysis of the above-mentioned image sticking phenomenon specific to the antiferroelectric liquid crystal, the present inventors have found that there are two types of such a phenomenon, i.e. an image sticking phenomenon caused when black display is newly written in the area where a white display was previously written, and an image sticking phenomenon caused when a white display is newly written in the area where a black display was written. In other words, they are the image sticking phenomenon generated after the antiferroelectric liquid crystal system is held in ferroelectric state, and the image sticking phenomenon generated after the antiferroelectric liquid crystal system is held in antiferroelectric state. The present inventors have discovered that the liquid crystal material property substantially in control of the image sticking phenomena is a dielectric constant characteristic, i.e. the frequency dispersion characteristic.
There is, however, another important problem to be solved while obviating the image sticking phenomenon. It is to provide a superior antiferroelectric liquid crystal display device, i.e. to secure a high-speed response
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Johno Masahiro
Matsumoto Takahiro
Suguro Akira
Suzuki Yasushi
Yui Tomoyuki
Citizen Watch Co. Ltd.
Kelly C. H.
Mitsubishi Gas Chemical Company Inc.
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