This invention relates to nematic liquid crystal phases containing at least one liquid-crystalline compound which exhibits at least one discotic phase, suitable for use in liquid crystal display elements.
Liquid crystal phases are of great importance for liquid crystal display elements, in particular in dielectrics for electro-optical display elements which are based, for example, on the principle of the twisted cell (TN cell), the guest-host effect, the effect of the deformation of aligned phases or the effect of dynamic scattering. Liquid crystal display elements for a large flow of information, such as occurs, for example, in the office section, in data processing (inter alia, graphical representations on computer terminals) and in televisions, are gaining increasing importance. The information density is limited in these applications by the multiplexing capability of the liquid crystal displays. Electro-optic effects with a pronounced non-linearity of the electrooptic characteristic are therefore required. At present, the principle of the twisted cell is most widely used. The technology for the TN cell has undergone the most extensive development. Theoretical calculations and experimental investigations have now shown that the steepness of the transmission characteristic of a TN cell depends very substantially on the elastic constants of the liquid crystal phase used.
To obtain a very steep transmission characteristic for a TN cell, it is necessary in particular that the ratio K.sub.3 /K.sub.1 of the elastic constants for bending and spreading is as small as possible (see, for example, D. W. Berreman, Nonemissive Electrooptic Displays, Plenum, New York, 1976, pages 9 et seq., in particular page 23; G. Baur, The Physics and Chemistry of Liquid Crystal Devices, Plenum, New York, 1980, page 61; B. S. Scheuble and G. Baur, 11. Freiburger Arbeitstagung Flussigkristalle (11th Freiburg Liquid Crystal Symposium), Freiburg, 1981, 8).
The way in which a small ratio K.sub.3 /K.sub.1 in nematic liquid crystal phases can be obtained is discussed, for example, in "B. S. Scheuble and G. Baur, Proceedings of Japan Display '83, Kobe, Japan, 1983, page 224". Herein, "small" relates in general to ratios of about 1.6 or lower.