Compositions – Liquid crystal compositions
Patent
1997-04-29
1998-08-11
Wu, Shean C.
Compositions
Liquid crystal compositions
25229963, 25229966, 25229967, C09K 1952, C09K 1930
Patent
active
057923868
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/JP 95/0401, filed Oct. 13, 1995, published as WO96/11995 Apr. 25, 1996.
TECHNICAL FIELD
The present invention relates to a nematic liquid crystal composition and a liquid crystal display device using the liquid crystal composition. More specifically, the present invention relates to a liquid crystal composition for active matrix liquid crystal display device and a liquid crystal display device using the composition.
BACKGROUND ART
Since liquid crystal display device (LCD) can reduce its electric power consumption and can downsize its shape compared with CRT (cathode ray tube display), several types of LCDs such as twist nematic (TN) mode, super twist nematic (STN) mode, and thin-film transistor (TFT) mode LCDs have practically been used. Among them, active matrix LCD (AM-LCD) such as thin-film transistor (TFT) has been progressed in actualization of colored display and of fine picture image, and thus the AM-LCD has attracted public attention.
As the characteristics required of liquid crystal composition for AM-LCD, the following can be mentioned: LCD. environment. cell thickness.
As driving mode of AM-LCD, the TN display mode is adopted in which the alignment of liquid crystal molecules placed between an upper and lower substrates are twisted by 90.degree.. In this TN display mode, the product (.DELTA.n.multidot.d) of optical anisotropy (.DELTA.n) and cell thickness (d) .mu.m must be established to a certain value (for example, .DELTA.n.multidot.d.about.0.5 .mu.m) to prevent the coloring of the background of the liquid crystal cell due to the interference of liquid crystal cells when voltage is not applied and to obtain a best contrast.
Under these restrictions, the value of about 0.07 to about 0.11, particularly about 0.08 to about 0.10 has become a main .DELTA.n of the liquid crystal composition currently in practical use for TFT for the device which employs a light transmittance of about first minimum value.
Also, the development of LCD with a purpose of coping with dynamic picture came to be strongly sought in recent years. Since the response speed (.tau.) is proportional to the viscosity (.eta.) of liquid crystal material, the development of liquid crystal composition having a low viscosity has come to be sought.
Further, with the development of portable LCD, the development on the assumption of using it outdoors has come to be studied. In order to withstand outdoor use, it is required to exhibit nematic phase over a range beyond the temperature range of application environment. From these viewpoints, liquid crystal compositions having a nematic-isotropic phase transition temperature (clearing point: TNI) of higher than 60.degree. C. and smectic-nematic phase transition temperature (TSN) of lower than -20.degree. C. have become main liquid crystal compositions currently in practical use for TFT.
With such background, trifluoro compounds having a comparatively large dielectric anisotropy (.DELTA..epsilon.) are disclosed in Japanese Patent Application Laid-open No. Hei 2-233626. Whereas a composition comprising 15% by weight of a trifluoro compound and 85% by weight of a difluoro compound is disclosed as an example in its Application Example 2, the composition has the defect of being short of practicability since its threshold voltage is high, miscibility is poor at low temperatures in particular, and nematic phase range is narrow. Besides, the composition has a defect of having a high viscosity.
In WO 94/03558 publication, examples of compositions comprising a trifluoro compound and a difluoro compound are disclosed. However, the compositions disclosed in its Examples 1 and 2 are as low as 50.degree. C. or lower in clearing point, and less than 0.06 in .DELTA.n; and thus they are short of utility. Besides, the compositions disclosed in and after Example 4 have a defect of having a high threshold voltage.
Whereas liquid crystal compositions are diligently being studied depending on several purposes as mentioned above, it is a present situation that new improvements
REFERENCES:
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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