Compositions – Liquid crystal compositions
Patent
1997-01-30
1999-01-12
Wu, Shean C.
Compositions
Liquid crystal compositions
25229961, 25229963, 25229966, 570127, 570128, 570129, 570130, 570131, C09K 1952, C09K 1934, C09K 1930, C07C 1908
Patent
active
058582703
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a difluoromethane derivative as a liquid crystalline compound suitable as a liquid crystal material in several liquid crystal displays and a liquid crystal composition containing the derivative.
BACKGROUND ART
Liquid crystal display devices employ optical anisotropy and dielectric anisotropy of liquid crystal materials. As display mode, twisted nematic (TN) mode, super twisted nematic (STN) rode, dynamic scattering (DS) mode, guest-host (G-H) mode, and DAP mode are known. Further, as driving mode of the devices, static driving mode, time division driving mode, active matrix driving mode, and dual frequency driving mode are know,. While the properties of liquid crystal materials used for such liquid crystal display devices are different depending on their applications, it is required to any liquid crystal material that the material is stable against external environmental factors such as moisture, air, heat, and light, that the material exhibits a liquid crystal phase at a range of temperatures as wide as possible with room temperature being at its center, that the material has a low viscosity, and that the material is low in its driving voltage. Besides, liquid crystal materials used for liquid crystal display devices are usually composed of several kinds or 10-odd kinds of liquid crystalline compounds in order to obtain optimum dielectric anisotropy (.DELTA..epsilon.) or optical anisotropy (.DELTA.n) required to each display device. Accordingly, the miscibility with other liquid crystal compounds, miscibility at low temperatures is desired for liquid crystal materials from the recent needs of being used under several environments in particular.
On the other hand, active matrix mode, particularly TFT (thin film transistor) mode is popularly adopted recent years as a display mode for television or viewfinder from the aspect of display performances such as contrast, display capacity, and response time. Also, STN mode which is simple in manufacturing process and less expensive in production cost while having a large display capacity is largely adopted as display for personal computers and others.
As the trend in recent years, development in this field is being advanced with miniaturization of liquid crystal display devices or their downsizing to portable dimensions being centered, as typified by televisions which are characterized in that they are small-sized, light weight, and portable, and by notebook type personal computers. From the aspect of materials, development is being carried out with liquid crystalline compounds and liquid crystal composition having a low driving voltage, that is, a low threshold voltage as its center from the aspect of withstand voltage of IC.
It is known that threshold voltage can be expressed by the following equation (H. J. Deuling et al., Mol. Cryst. Liq. Cryst., 27 (1975) 81): vacuum. From the equation mentioned above, it is a common way to use a material having a large dielectric anisotropy (.DELTA..epsilon.) in order to reduce the threshold voltage, and thus, development of compounds having a large value of dielectric anisotropy is being actively carried out.
On the other hand, in liquid crystalline compounds having fluorine atom as substituent, it is known to be effective to increase the number of substitution on the molecule with fluorine atom for increasing dielectric anisotropy. However, the number of substitution on the molecule of compounds with fluorine atom has a proportional relationship with viscosity, and it is also empirically known among the person skilled in the art that when the number of substitution with fluorine atom is increased, mesomorphic range will be narrowed. Accordingly, it is considered to be difficult to increase only dielectric anisotropy while suppressing the raising of viscosity and narrowing of mesomorphic range.
As examples of conventional liquid crystalline compounds substituted with multiple number of fluorine atoms, the followings are disclosed: ##STR2##
Any of compounds (a) and (b-1) t
REFERENCES:
patent: 5045229 (1991-09-01), Bartmann et al.
patent: 5589102 (1996-12-01), Bartmann et al.
Goto Yasuyuki
Haseba Yasuhiro
Matsui Shuichi
Miyazawa Kazutoshi
Nakagawa Etsuo
Chisso Corporation
Wu Shean C.
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