Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
2000-04-24
2002-02-19
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299610, C252S299630, C252S299660, C549S356000, C549S369000, C570S127000, C570S129000, C570S131000
Reexamination Certificate
active
06348244
ABSTRACT:
This application is a 371 application of PCT/JP98/04834 filed Oct. 26, 1998.
TECHNICAL FIELD
The present invention relates to novel liquid crystalline compounds and liquid crystal compositions. More specifically, the invention relates to liquid crystalline compounds having 2,3-difluorophenyl moiety, liquid crystal compositions comprising the compound, and liquid crystal display devices fabricated by using the liquid crystal composition.
BACKGROUND ART
Liquid crystal display devices fabricated by using liquid crystalline compounds (the term “liquid crystalline compounds” is used in this specification as a generic name for the compounds which exhibit a liquid crystal phase and the compounds which do not exhibit a liquid crystal phase but are useful as a component of liquid crystal compositions) are widely being used for the display of computers, television sets, and the likes.
For the purpose of reducing the power consumption and decreasing the leakage of electromagnetic wave, liquid crystal compositions are required to lower their driving voltage. Driving voltage (threshold voltage) is known to be a function of dielectric anisotropy value and elastic constant according to the following equation (M. F. Leslie, Mol. Cryst. Liq. Cryst., 12, 57 (1970)):
Vth=&pgr;(K/&egr;
0
&Dgr;&egr;)½
wherein Vth represents a threshold voltage, &egr;
0
: a dielectric constant in vacuum, K: an elastic constant, and &Dgr;&egr;: a dielectric anisotropy, respectively.
That is, it can be understood that in order to lower driving voltage, it is necessary 1) to increase dielectric anisotropy value or 2) to decrease elastic constant.
It is generally considered to be difficult to adjust the value of the elastic constant of liquid crystalline compounds, and thus a means in which the dielectric anisotropy value is increased is principally adopted to lower the driving voltage. Accordingly, novel liquid crystalline compounds having a large dielectric anisotropy value are long-expected.
From some time ago, a characteristic of narrow visual angle is considered to be a most serious problem to liquid crystal display devices, and various display modes have been proposed in recent years for the purpose of improving the narrow visual angle. In-plane switching (IPS) display devices proposed in 1995 greatly widened the visual angle compared with conventional display devices (Liquid Crystal Conference in Japan 2A07 (1995), ASIA DISPLAY '95, 557 (1995) and ASIA DISPLAY '95, 707 (1995)).
Also, in 1997, an attempt was reported in which a vertical alignment (VA) cell was used (SID 97 DIGEST, 845 (1997)), and the display devices of this mode are considerably wide in visual angle compared with conventional display devices.
In either mode of IPS and VA, characteristics required of liquid crystal compositions are
1) a negative and large dielectric anisotropy value (&Dgr;&egr;) for lowering driving voltage, and
2) a small optical anisotropy value (&Dgr;n) for keeping &Dgr;n·d (product of optical anisotropy value multiplied by cell thickness) at an optimum value.
However, compounds having simultaneously a negative and large dielectric anisotropy value and a small optical anisotropy value are heretofere unknown, and thus novel liquid crystalline compounds having such characteristics have been long-expected.
As compounds having a negative and large dielectric anisotropy value and a comparatively small optical anisotropy value, the compound of the following formula (13) is known (V. Reifffenrath et al., Liq. Cryst., 5 (1), 159 (1989)). It is reported that the dielectric anisotropy value of this compound is (&Dgr;&egr;=−4.1) and optical anisotropy value is (&Dgr;n=0.18).
However, the dielectric anisotropy value of the compound can not be said to be sufficiently large, and a satisfactory lowering of driving voltage was unable to actualize.
As compounds having a negative dielectric anisotropy value, the terphenyl compound of the formula (14) is known (J. Chem. Soc. Perkin Trans. II 2, 2041 (1989)). This compound is narrow (10.5° C.) in the temperature range showing nematic phase and exhibits smectic phase in a wide temperature range (50.5° C.). Further, terphenyl compounds were extremely large in optical anisotropy value in general and were unsuitable as component of liquid crystal compositions for IPS mode or VA mode.
The phenomenon that dielectric anisotropy value is increased in negative when fluorine atom is introduced at a lateral position of a phenylene group which constitutes the skeleton of liquid crystalline compounds is well known to a person skilled in the art. On the other hand, the order parameters of liquid crystalline compounds are decreased by the introduction of fluorine atom to the lateral position. Dielectric anisotropy value and optical anisotropy value are regarded as functions of the order parameters (W. Maier and G. Meier, Z. Naturf. (a), 16 262 (1961)), and the decrease of the order parameters caused by the introduction of fluorine atom will bring about the decrease in dielectric anisotropy value. Accordingly, the introduction of fluorine atom to the lateral position does not necessarily produce a large increase in negative dielectric anisotropy value (Theory of Maier and Meier).
DISCLOSURE OF THE INVENTION
In view of the several characteristics described above and required of liquid crystal compositions, an object of the present invention is to provide liquid crystalline compounds having a negative and extremely large dielectric anisotropy value and a small optical anisotropy value at the same time, to provide liquid crystal compositions comprising the compound, and to provide liquid crystal display devices fabricated by using the liquid crystal composition.
As a result of diligent research and development conducted by the present inventors to solve the problems described above, it has been found that the liquid crystalline compounds expressed by the general formula (1) have desired characteristics, leading to the accomplishment of the present invention.
wherein Ra and Rb each independently represent a straight chain or branched alkyl group or alkoxy group having 1 to 10 carbon atoms, or a straight chain or branched alkenyl group or alkynyl group having 2 to 10 carbon atoms; ring A
1
represents cyclohexane-1,4-diyl in which ring not-adjacent any methylene group may be replaced by —O—; ring A
2
represents 2,3-difluoro-1,4-phenylene in which phenylene hydrogen atoms at 5-position and 6-position may each independently be replaced by fluorine atoms, but there is not a case wherein both of the hydrogen atoms are simultaneously replaced; Z
1
and Z
2
each independently represent single bond or —CH
2
CH
2
—; Xa, Xb, Xc, and Xd each independently represent hydrogen atom, fluorine atom, or chlorine atom, but at least one of Xa, Xb, Xc, and Xd is fluorine atom or chlorine atom; and any atom which constitutes the compound may be replaced by its isotope.
Among the liquid crystalline compounds expressed by the general formula (1), the compounds which exhibit particularly preferable characteristics are those expressed by one of the following general formulas (1-1) to (1-18)
In the general formula (1), Ra and Rb are alkyl groups, alkoxy groups, alkoxyalkyl groups, alkoxyalkoxy groups, alkenyl groups, or alkynyl groups. Compounds in which Ra and Rb are alkyl groups, alkoxy groups, alkoxyalkyl groups, or alkoxyalkoxy groups are chemically stable, and the compounds in which Ra and Rb are alkenyl groups or alkynyl groups exhibit a slightly large optical anisotropy.
Also, the compounds in which Ra and Rb are alkyl groups, alkoxy groups, or alkenyl groups are preferable since they have a low viscosity. Further, when used for display devices of IPS mode or VA mode, the compounds in which Ra and Rb are alkyl groups or alkoxy groups are optimum since a high chemical stability and a small optical anisotropy value are required in such case.
While Z
1
and Z
2
are each independently single bond or —CH
2
CH
2
—, the compounds in which one of Z
1
and Z
2
is single bond have a low
Kubo Yasuhiro
Miyazawa Kazutoshi
Nakagawa Etsuo
Takeshita Fusayuki
Takeuchi Hiroyuki
Chisso Corporation
Wenderoth , Lind & Ponack, L.L.P.
Wu Shean C.
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