Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
2000-10-25
2002-12-24
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299630, C252S299660
Reexamination Certificate
active
06497929
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a nematic liquid crystal composition and, more specifically, relates to a liquid crystal composition for active matrix (AM) mode and to a liquid crystal display device (LCD) using the liquid crystal composition.
BACKGROUND ART
An active matrix mode-liquid crystal display devices (AM-LCD) is attracting a great deal of attention as the likely winner among LCD's as it enable to display with extreme precision, and is applied for displays such as monitors, note-type personal computers, digital still cameras and digital video cameras. Characteristics required for the liquid crystal composition of AM-LCD are shown in the items (1) to (5) below.
(1) A liquid crystal composition should show a nematic phase in the range of temperature as wide as possible in order to widen the usable temperature range of the liquid crystal display devices (elevating the upper temperature limit of a nematic phase as high as possible, and lowering the lower temperature limit of a nematic phase as low as possible).
(2) Viscosity of the liquid crystal composition should be as low as possible in order to accelerate the response speed of the liquid crystal display device.
(3) Optical anisotropy (&Dgr;n) of the liquid crystal composition should be able to have a proper value depending on the cell thickness (d) in order to enhance the contrast of the liquid crystal display device.
(4) Values of specific resistivity (specific resistance) on the liquid crystal composition should be increased and the voltage holding ratio of the cell containing the liquid crystal composition should be large, in order to enhance the contrast of the liquid crystal display device. The voltage holding ratio should be large especially at a high temperature region.
(5) Threshold voltage of the liquid crystal composition should be lowered in order to downsize the battery which is the power source to drive liquid crystal display device.
Recently it has been requested keenly to apply for an animation in the LCD and various LCD display modes have been studied. The addressing mode of the AM-LCD employs TN display mode in which the orientation of liquid crystal molecules between the upper and lower substrates is twisted by 900°. In the TN display mode, it is necessary to keep the product, &Dgr;n·d, of optical anisotropy (&Dgr;n) of a liquid crystal material to be filled in a cell and cell thickness (d &mgr;m) at a certain value (for example &Dgr;n·d=0.5 etc.) in order to obtain an optimum contrast and to avoid coloration by the interference of the liquid crystal cell when no voltage is applied, as reported by G.Bauer (Cryst. Liq., 63, 45 (1981)). Therefore, if the liquid crystal material having large &Dgr;n is used, the value of d can be decreased. Response speed (&tgr;) is proportional to viscosity (&eegr;) of the liquid crystal material and to d squared, as proposed by E. Jakeman et al. (Phys. Lett. , A, 39 (1972) 69). When the liquid crystal material having large &Dgr;n is used, the thickness of cell constituting liquid crystal display device can be decreased, and thus &tgr; can be increased. As such, the liquid crystal composition having large &Dgr;n and low viscosity is very useful for the liquid crystal display devices.
Also the development of the display intended for outdoor use has been requested with the increase of a portable type display. For being bearable in the outdoor use, materials are requested to have a nematic phase over the wide range of temperature exceeding the temperature range-of environment in use. To widen a nematic phase range of the liquid crystal composition, it is necessary to use liquid crystal compounds having a high clearing point and good miscibility with other liquid crystal compounds. Generally, a compound having a high clearing point, namely having many six member-rings in the chemical structure may be used for elevating the clearing point. However, miscibility at a low temperature region may tend to be a problem in such case.
It is also requested the liquid crystal composition with high reliability such as a high voltage holding ratio (V.H.R.) or large specific resistivity in order to keep a high contrast especially in the AM-LCD.
Based on the background described above, the specification of WO 96/11897 discloses a novel liquid crystal compound having large dielectric anisotropy (&Dgr;n) together with extremely low viscosity and disclosed a liquid crystal composition comprising the compound for low voltage driving in various modes such as a AM mode or a super twisted nematic mode (STN mode). JP 10-251186 A describes a compound similar to the compound of formula (1-3) in the present invention as the compound having large &Dgr;&egr; and small temperature dependence.
The liquid crystal composition for the AM-LCD disclosed in WO 96/11897 described above (the composition does not contain compounds having cyano in the terminal, and compounds having cyano can not be used for the liquid crystal composition of the AM-LCD because of its low voltage holding ratio) has drawbacks that the V.H.R. is low and optical anisotropy is low as is shown in the Comparative Example of the present invention.
JP 10-251186 A discloses a composition using the compound similar to that of formulae (1-1) to (1-3) of the present invention, however, the similar compound has large and positive &Dgr;&egr;. When such compound is used, viscosity of the composition is increased. Then, the compound has a drawback of low response speed in the LCD. The similar compound has a drawback that &Dgr;n is small and that a high voltage holding ratio required for the composition of TFT can not be attained by the combination of a cyano compound.
Although liquid crystal compositions were studied, the liquid crystal composition for AM-LCD has been required especially to keep a high voltage holding ratio at a high temperature region in order to enhance the contrast of the liquid crystal display device, to have a wide range of a liquid crystal phase in order to have a wide addressing temperature range, and to have low viscosity in order to accelerate response speed, while maintaining the characteristics (1) to (5) described above. Enlarging &Dgr;n has also been requested by the requirement being smaller cell gap.
The liquid crystal composition has been always required to be improved though enthusiastic efforts are made for various purposes.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide a liquid crystal composition especially having a high voltage holding ratio at a high temperature region in order to enhance the contrast of a liquid crystal display device, having a wide range of a liquid crystal phase which means a high clearing point and good miscibility at low temperature, having low viscosity in order to accelerate response speed of the liquid crystal display device, and having properly large &Dgr;n in order to enhance the contrast in the liquid crystal display device, while satisfying general characteristics required for the liquid crystal composition of the AM-LCD.
The present inventors have made enthusiastic efforts to achieve the above object, have found the liquid crystal composition described below can achieve the purpose of the present invention, and have completed the present invention.
The liquid crystal composition of the present invention is described in the items 1 to 4 below.
1. A liquid crystal composition characterized by comprising at least one compound selected from the group of compounds expressed by formulae (1-1), (1-2) and (1-3) as a first component and comprising at least one compound selected from the group of compounds expressed by formulae (2-1), (2-2), (2-3), (2-4), (2-5), and (2-6) as a second component.
wherein R
1
to R
9
each independently represents alkyl or alkoxy having 1 to 10 carbon, alkenyl or alkoxymethyl having 2 to 10 carbon; R
10
to R
12
each independently represents alkyl or alkoxy having 1 to 10 carbon, alkenyl or alkoxymethyl having 2 to 10 carbon, F, Cl, CF
3
, OCF
3
, or OCF
2
H; X
1
to X
6
each independently
Kubo Yasuhiro
Miyairi Takahiro
Nakagawa Etsuo
Chisso Corporation
Wenderoth , Lind & Ponack, L.L.P.
Wu Shean C.
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