Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
2001-04-26
2002-12-31
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299610, C252S299630, C252S299660, C252S299100, C570S127000, C570S129000, C549S369000
Reexamination Certificate
active
06500503
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to cyclohexane derivatives which are liquid crystalline compounds suitable as a component in a liquid crystal composition, liquid crystal compositions comprising the same and liquid crystal display devices composed of these liquid crystal compositions.
2. Description of Related Art
A liquid crystal display device utilizing an optical anisotoropy and a dielectric anisotropy of a liquid crystal substance is classified into a twisted nematic type (TN type), a super twisted nematic type (STN type), a dynamic scattering type (DS type), a guest-host type (G-H type) and DAP type, in view of a display system. It is also classified into a static drive system, a time rate drive system, an active matrix drive system and 2 cycle drive system, in view of a drive system. Various liquid crystal substances having different properties depending on their application are used for these liquid crystal display devices. As a common property, any liquid crystal substance needs to have a stability to external environmental factors such as moisture, air, heat and light, to exhibit liquid crystal phase within as broad the temperature range as possible focusing on room temperature, to have low viscosity and to make the driving voltage low when the display device is driven. Further, it needs to have the characteristics desired according to each display device, for example, the optimum dielectric anisotropy (&Dgr;&egr;) and the optimum optical anisotropy (&Dgr;n).
However, there is no substance which meets such all requirements with a single compound now. The present condition is mixing several to about twenty sorts of liquid crystalline compounds to prepare a liquid crystal composition and using the composition as liquid crystal material. The term “liquid crystalline compound” as used herein refers generically to a compound having a liquid crystal phase and a compound not impairing a liquid crystal phase when mixed with other liquid crystal compounds.
Therefore, it is desirable that liquid crystalline compounds used as a component in the composition have good compatibility each other and also they have good compatibility even at a cryostatic temperature, since the demand to the use under various environment is increasing recently.
In recent years, liquid crystal display device is required with higher quality, especially in a display performance, for example, contrast, display capacity, response time, etc. To meet the requirement, the demand for the display device of an active matrix system represented by a TFT (thin film transistor) system is increasing in display mode fields, mainly television and a view finder.
The display device of STN system has been often used in the display fields such as a pocket phone and a personal computer, because of its low cost, easy manufacturing process while having large display capacity.
The development tendency in recent years in these fields is advanced focusing on a downsizing and portability of a liquid crystal display device as observed in the television and note type personal computer which are portable by downsizing and light saving. The liquid crystal material used in connection with this requires a liquid crystalline compound of low driving voltage, i.e., those capable of providing reduced threshold voltage, and a liquid crystal composition of low driving voltage comprising the same.
The threshold voltage (V
th
) is shown by the following formula as known well (H. J. Deuling, et al., Mol. Cryst. Liq. Cryst., 27 (1975) 81).
V
th
=&eegr;(K/&egr;
0
&Dgr;&egr;)
½
in which K is an elastic constant of liquid crystal material and &egr;
0
is a dielectric constant in a vacuum. As seen from the above formula, two ways can be considered whether &Dgr;&egr; is increased or K is decreased, in order to reduce V
th
. However, with the present technology, it is still difficult to control the elastic constant K of liquid crystal material actually. Under the present circumstances, one complies with a demand by using a liquid crystal material of large &Dgr;&egr;. For such circumstances, liquid crystalline compounds of large &Dgr;&egr; have been developed actively.
At present, most liquid crystal compositions used for the display device of TFT system are composed of fluorine-containing liquid crystal materials. The reason is that the display device of TFT system requires the liquid crystal composition capable of providing high voltage holding rate (V.H.R) under low temperature dependence, but there is no other liquid crystalline compound except for fluorine-containing compounds to meet such requirements.
To increase &Dgr;&egr; in the liquid crystalline compound, it is effective to maintain a substituent having large dipole moment such as cyano and trifluoromethyl in the terminal group as well known, or to replace 1,4-phenylene in the compound by halogen such as fluorine, so that the direction of a dipole moment may become identical with that of the terminal substituent. However, it has been considered to be difficult to increase only &Dgr;&egr;, while controlling both an increase in viscosity and a reduction in the temperature range of a liquid crystal phase, since the number of replaced fluorine atom is proportional to the viscosity and the number of replaced fluorine atom is increased with reducing the temperature range of a liquid crystal phase.
In recent years, development of the liquid crystal display, especially using a reflected type TFT system is also active. For this reflected type liquid crystal display, a compound of low &Dgr;n is required.
As compounds already reported, U.S. Pat. No. 4,797,228 discloses the compound of the following formula (A) and Japanese Patent Kokai 2-233626 discloses the compound of the following formula (B).
in which R represents a straight-chain alkyl.
Among these, the compound of formula (A) is reported to be comparatively stable and highly reliable. However, &Dgr;&egr; of the compound (A) is comparatively as small as about 3-5 and also &Dgr;&egr; of the liquid crystal composition consisting of only the same is small, which cannot reduce the driving voltage. To make up for this defect, the compound of formula (B) was developed. This compound had large &Dgr;&egr; and low viscosity, and could reduce the driving voltage without increasing the viscosity of the liquid crystal composition.
Accordingly, it has been desired to develop a liquid crystal material of large &Dgr;&egr; without reducing the liquid crystal phase temperature range, and further of small &Dgr;n and high stability.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a new liquid crystalline compound having large &Dgr;&egr; and relatively low viscosity which can overcome the defects of the prior art as mentioned above, a liquid crystal composition comprising said liquid crystalline compound and a liquid crystal display device composed of said liquid crystal composition.
We have investigated various compounds in an effort to solve the aforesaid problems and found new liquid crystalline compounds having more improved characteristics than known liquid crystalline compounds, thus leading to the completion of the present invention.
In the first aspect, the present invention relates to a liquid crystalline compound represented by formula (1)
wherein R
1
represents hydrogen or C
1
-C
15
alkyl in which one or more non-adjacent methylene may be replaced by oxygen, sulfur or —CH═CH— and one or more hydrogen may be replaced by halogen; R
2
represents hydrogen, cyano, halogen or C
1
-C
15
alkyl in which one or more non-adjacent methylene may be replaced by oxygen, sulfur or —CH═CH— and one or more hydrogen may be replaced by halogen; L represents halogen or hydrogen; A
1
, A
2
, A
4
and A
5
each independently represent trans-1,4-cyclohexylene or 1,4-phenylene, one or more —CH
2
— in the trans-1,4-cyclohexylene may be replaced by oxygen or sulfur, one or more ═CH— in the 1,4-phenylene may be replaced by nitrogen, and one or more hydrogen in the 1,4-phenylene r
Kawano Katsuyuki
Kubo Yasuhiro
Matsui Shuichi
Nakagawa Etsuo
Shibata Koichi
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