Compositions – Liquid crystal compositions
Patent
1989-05-15
1993-01-12
Stoll, Robert L.
Compositions
Liquid crystal compositions
25229963, 25229967, C09K 1952, C09K 1930, C09K 1920
Patent
active
051787903
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a supertwist liquid crystal display with dielectric anisotropy and at least one chiral doping material, carrier plates, of the molecules at the surface of the carrier plates and the carrier plates, and layer to orientation layer of an amount between 160.degree. and 450.degree., following conditions: dielectric anisotropy and .epsilon..perp. is the dielectric constant in the direction of the short axis of the liquid crystal molecule.
Supertwist liquid crystal displays (SLC displays) according to the preamble are known, for example from EP 0,131,216 B1; DE 3,423,993 A1; EP 0,098,070 A2; M. Schadt and F. Leenhouts, 17th Freiburger Arbeitstagung Flussigkristalle [Freiburg Working Meeting on Liquid Crystals] (8.-10.04.87); K. Kawasaki et al., SID 87 Digest 391 (20.6); M. Schadt and F. Leenhouts, SID 87 Digest 372 (20.1); K. Katoh et al., Japanese Journal of Applied Physics, volume 26, No. 11, L 1784-L-1786 (1987); F. Leenhouts et al., Appl. Phys. Lett. 50 (21), 1468 (1987); H. A. van Sprang and H. G. Koopman, J. Appl. Phys. 62 (5), 1734 (1987); T. J. Scheffer and J. Nehring, Appl. Phys. Lett. 45 (10), 1021 (1984), M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (5), 236 (1987) and E. P. Raynes, Mol. Cryst. Liq. Cryst. Letters volume 4 (1), pages 1-8 (1986). The term SLC display here comprises any more highly twisted display with an amount of twist angle between 160.degree. and 360.degree., such as, for example, the displays according to Waters et al. (C. M. Waters et al., Proc. Soc. Inf. Disp. (New York) (1985) (3rd Intern. Display Conference, Kobe, Japan), the STN-LCD's (German Offenlegungsschrift 3,503,259), SBE-LCD's (T. J. Scheffer and J. Nehring, Appl. Phys. Lett. 45 (1984) 1021), OMI-LCD's (M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (1987), 236, DST-LCD's (European Published Application 0,246,842) or BW-STN-LCD's (K. Kawasaki et al., SID 87 Digest 391 (20.6)).
Compared with standard twisted nematic displays, displays of this type are distinguished by substantially better steepness of the electro-optical characteristic and thus associated better contrast values and by a substantially smaller angle dependence of the contrast. Supertwist displays with a very high steepness of the characteristic are here of particular interest. The measure taken for the steepness of the characteristic is in general the ratio V.sub.50 /V.sub.10 (V.sub.50 =voltage at 50% contrast/V.sub.10 =voltage at 10% contrast). To achieve high steepnesses of the characteristics, especially the elastic properties of the liquid crystal mixture have hitherto been optimized. However, the steepnesses achieved were not adequate for some applications.
SUMMARY OF THE INVENTION
There is thus still a great demand for SLC displays with very high steepnesses of the characteristics coupled with, at the same time, a wide range of working temperature, short switching times and low threshold voltage.
The invention is based on the object of providing SLC displays which show the above-indicated disadvantages only to a smaller extent or not at all and, at the same time, have very high steepnesses of the characteristics.
It has now been found that this object can be achieved if, in these displays, nematic liquid crystal mixtures are used which satisfy the following conditions: dielectric anisotropy and .epsilon..perp. is the dielectric constant in the direction of the short axis of the liquid crystal molecules.
The subject of the invention is thus a supertwist liquid crystal display with dielectric anisotropy and at least one chiral doping material, carrier plates, of the molecules at the surface of the carrier plates and the carrier plates, and layer to orientation layer of an amount between 160.degree. and 450.degree., following conditions: dielectric anisotropy and .epsilon..perp. is the dielectric constant in the direction of the short axis of the liquid crystal molecules.
Further subjects of the invention are corresponding preferred displays, which satisfy the following conditions: liquid cry
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Hittich Reinhard
Plach Herbert
Reiffenrath Volker
Weber Georg
Merck Patent Gesellschaft mit beschraenkter Haftung
Stoll Robert L.
Wu Shean C.
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