Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Patent
1997-09-12
2000-02-22
Wu, Shean C.
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
25229901, 25229963, 25229966, 25229967, 349132, C09K 1952, C09K 1934, G02F 11333
Patent
active
060276657
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an electro-optical liquid-crystal display having a realignment layer for realigning the liquid crystals, where the field thereof has a significant component parallel to the liquid-crystal layer, comprising a liquid-crystalline medium having negative dielectric anisotropy, where the medium comprises at least one mesogenic compound which contains a group of the formula A ##STR3## and at least one compound which contains a group of the formula B ##STR4##
In conventional liquid-crystal displays (TN, STN, OMI and AMD-TN), the electric fields for realignment are produced essentially perpendicular to the liquid-crystal layer.
International Patent Application WO 91/10936 discloses a liquid-crystal display in which the electric signals are produced in such a way that the electric fields have a significant component parallel to the liquid-crystal layer (IPS, in-plane switching). The principles of operating such a display are described, for example, by R. A. Soref in Journal of Applied Physics, Vol. 45, No. 12, pp. 5466-5468 (1974).
EP 0 588 568 discloses various ways of addressing such a display.
These IPS displays can be operated with liquid-crystalline materials either having a positive dielectric anisotropy or having a negative dielectric anisotropy (.DELTA..epsilon..noteq.0). The specification describes, inter alia, an IPS display containing the mixture ZLI-2806 (E. Merck, Darmstadt) having negative dielectric anisotropy.
This mixture is based on compounds which contain a structural unit of the formula A. However, IPS displays containing this material have relatively high threshold voltages and long response times. The object was therefore to indicate liquid-crystalline materials which are suitable for achieving relatively low threshold voltages and short response times in IPS displays.
Surprisingly, this object has been achieved by using liquid-crystalline materials which comprise at least one compound which contains a group of the formula A ##STR5## and at least one compound which contains a group of the formula B ##STR6##
Such compounds are disclosed, for example, in EP 0 107 759 (formula A) and EP 0 332 007 (formula B).
However, these specifications give no indication that these substances can be used to improve the threshold voltages and the response times of IPS displays.
The invention thus relates to an electro-optical liquid-crystal display having a realignment layer for realigning the liquid crystals, where the field thereof has a significant component parallel to the liquid-crystal layer, comprising a liquid-crystalline medium having negative dielectric anisotropy, where the medium comprises at least one mesogenic compound which contains a group of the formula A ##STR7## and at least one compound which contains a group of the formula B ##STR8## a) Preferred embodiments are IPS displays in which the medium comprises at least one compound of the formula I ##STR9## and at least one compound of the formula II ##STR10## in each of which R.sup.1 and R.sup.2 are each an alkyl or alkenyl radical having 1 to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF.sub.3 or at least monosubstituted by halogen, where, in addition, one or more CH.sub.2 groups in these radicals may each, independently of one another, be replaced by --O--, --S--, ##STR11## --CO--, --CO--O--, --O--CO-- or --O--CO--O-- in such a way that O atoms are not linked directly to one another, non-adjacent CH.sub.2 groups may be replaced by --O-- and/or --S--, be replaced by N, 1,4-bi-cyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6,diyl, atoms, --O--CO--, --CH.sub.2 O--, --OCH.sub.2 --, --CH.sub.2 CH.sub.2 --, --CH.dbd.CH--, --C.tbd.C.phi.-- or a single bond, or one of the radicals Z.sup.1 and Z.sup.2 is alternatively --(CH.sub.2 ).sub.4 -- or --CH.dbd.CH--CH.sub.2 CH.sub.2 --, preferably between -4.7 and -8; R.sup.1, A.sup.1 and A.sup.2, Z.sup.1 and Z.sup.2 and,
Preference is even more given to an IPS display in which the p
REFERENCES:
patent: 5279764 (1994-01-01), Reiffenrath et al.
Pausch Axel
Reiffenrath Volker
Tarumi Kazuaki
Merck Patent Gesellschaft mit beschrankter Haftung
Wu Shean C.
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