Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
1999-03-16
2001-01-23
Wu, Shean C. (Department: 1721)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299610, C252S299630, C252S299640, C252S299650, C252S299660, C544S298000, C544S335000, C549S374000, C560S061000, C560S062000, C568S631000, C568S634000
Reexamination Certificate
active
06177154
ABSTRACT:
TECHNICAL FIELD
The present invention relates to novel liquid crystalline compounds which can develop intended physical properties by mixing them with a liquid crystal composition used for liquid crystal display devices and relates to the liquid crystal compositions thus produced. Further, the present invention relates to liquid crystal display devices fabricated by using the liquid crystal composition.
BACKGROUND ART
Liquid crystal display devices have widely been utilized for tabletop calculators, word processors, television sets, and the likes, including watches. As their applications became upscale, however, liquid crystal compositions having more appropriate physical property values became necessary. As the result, liquid crystal compositions having such a low threshold voltage that devices were capable of being driven at a low voltage, and liquid crystal compositions having such a high voltage holding ratio that the reliability of devices was increased were developed.
Threshold voltage (Vth) is expressed by the following equation (H. J. Deuling et al., Mol. Cryst. Liq. Cryst., 27 (1975) 81):
Vth=&pgr;
(
K/
∈0&Dgr;∈)
½
wherein K denotes an elastic constant, ∈0: a dielectric constant in vacuum, and &Dgr;∈: a dielectric anisotropy value. From this equation, it can be understood that in order to lower threshold voltage, it is sufficient to increase the dielectric anisotropy or decrease the elastic constant. Generally, dielectric anisotropy is more often controlled than elastic constant, since many liquid crystal compounds having a high dielectric anisotropy are known.
Besides, threshold voltage depends also on the pretilt angle of liquid crystal compositions induced in a device. When both dielectric anisotropy and elastic constant are constant, the larger the pretilt angle is, the lower the threshold voltage tends to be. Compounds of the formula (10) described in Laid-open Japanese Patent Publication No. Hei 2-501311 induce a comparatively large pretilt angle.
in the structural formula described above, R represents an alkyl group.
Liquid crystal compositions comprising a compound of the formula (10) are promising since they are low in dependency of voltage holding ratio on temperature, induce a comparatively large pretilt angle, and have a high reliability. However, they are not suitable for the applications wherein devices are driven at such a low voltage of 2.5 V, because their dielectric anisotropy values are such a medium extent as about 7 since contribution of trifluoromethoxy group to dielectric anisotropy is small.
On the other hand, it is known that liquid crystal compositions comprising a fluorine type liquid crystalline compound are high in voltage holding ratio and low in their dependency on temperature.
in the structural formulas described above, R represents an alkyl group.
Compounds having a plural number of fluorine atom at a terminal of the molecule of the formula (11) (DE-4027840A1), and formulas (12-1) and (12-2) (Laid-open Japanese Patent Publication No. Hei 2-233626) have a comparatively high dielectric anisotropy. However, when compounds of the formula (11) are used as component of liquid crystal compositions, the extent to which threshold voltage of the compositions is lowered is small since the compounds have a large elastic constant whereas trifluoromethyl group in the compounds contributes to a high dielectric anisotropy. Also, they induce a low pretilt angle. Accordingly, the compounds can not be said to be suitable for the applications at a low voltage. When compounds of the formulas (12-1) are used, the compositions exhibit a comparatively high voltage holding ratio and are small in dependency of voltage holding ratio on temperature. However, their dielectric anisotropy is lower than the case where a compound of the formula (11) is used. Whereas compounds of the formula (12-2) have a high dielectric anisotropy due to the contribution by 3,4,5-trifulorophenyl group and ester bonding group, and are larger in contribution to the pretilt angle in liquid crystal compositions than compounds of the formula (11), the compounds are large in dependency of voltage holding ratio on temperature. Thus, applications of compounds of the formula (12-2) are limited. Accordingly, liquid crystalline compounds from which liquid crystal compositions having a low threshold voltage, exhibiting a high voltage holding ratio, and being small in dependency of voltage holding ratio on temperature can be produced have been desired.
DISCLOSURE OF THE INVENTION
A subject of the present invention is to provide liquid crystal compositions which
1) are low in threshold voltage,
2) induce a large pretilt angle, and
3) are high in voltage holding ratio and are low in its dependency on temperature,
to make the driving of liquid crystal display devices at a low voltage possible and to impart a high reliability to the devices at the same time. Further subject of the present invention is to find novel liquid crystalline compounds which are essential as component of the liquid crystal compositions and are excellent in miscibility with other liquid crystal compositions, particularly in the miscibility at low temperatures.
It was predicted by the present inventors that in the compounds of the formula (10) disclosed in the Laid-open Japanese Patent Publication No. Hei 2-501311 mentioned above, the oxygen atom in trifluoromethoxy group contributes in increasing pretilt angle. Based on this forecast, the following model compounds (13) (Compound No. 195) and (14) (Compound No. 199) in which one or two alkoxy groups are introduced at position 3 and position 5 in 4-fluorophenyl group were synthesized and then their physical property values were compared to study.
As the result, it has been found out that these compounds have a remarkably higher dielectric anisotropy than the compounds in which a halogen atom is introduced at the same position as those in the compounds (13) and (14), and are excellent in miscibility with liquid crystal compositions, particularly in the miscibility at low temperatures. When liquid crystal compositions were prepared by using the compounds in which one or more alkoxy groups were introduced, it was found out that pretilt angle of the compositions became larger than expected, their voltage holding ratio was high, and dependency of voltage holding ratio on temperature was small. As the result of further investigation to generalize the forecast described above, the present invention has now been accomplished.
The present invention to achieve the purposes described above is summarized in the following aspects [1] to [23]:
[1] A liquid crystalline compound expressed by the general formula (1)
wherein R
0
and R
1
independently represent an alkyl group having 1 to 10 carbon atoms in which alkyl group one or more not-adjacent methylene groups may be replaced by oxygen atom, sulfur atom, —SiH
2
—, —CH═CH—, or —C≡C—, and any hydrogen atom in the alkyl group may be replaced by a halogen atom;
ring A
0
, ring A
1
, ring A
2
, and ring A
3
independently represent 1,4-cyclohexylene group, 1,3-dioxane-2,5-diyl group, 1,4-phenylene group in which one or more hydrogen atoms on the ring may be replaced by a halogen atom or R
2
O group, pyridine-2,5-diyl group, or pyrimidine-2,5-diyl group;
Z
0
, Z
1
, Z
2
, and Z
3
independently represent —CH
2
CH
2
—, —CH═CH—, —C≡C—, —CH
2
O—, —OCH
2
—, —CF
2
O—, —OCF
2
—, —COO—, —OCO—, —(CH
2
)
4
—, or single bond;
Q
1
and Q
2
independently represent hydrogen atom or a halogen atom;
Q
3
represents hydrogen atom, a halogen atom, or R
2
O group;
R
2
represents an alkyl group having 1 to 10 carbon atoms in which alkyl group one or more not-adjacent methylene groups may be replaced by —SiH
2
—, —CH═CH—, or —C≡C—, and any hydrogen atom in the alkyl group may be replaced by a halogen atom;
Y represents a halogen atom, cyano group, or an alkyl group having 1 to 10 carbon atoms in which alkyl group one or more not-adjacent methylene groups may be rep
Andou Tugumiti
Hisatsune Yasusuke
Matsui Shuichi
Miyazawa Kazutoshi
Nakagawa Etsuo
Chisso Corporation
Wenderoth , Lind & Ponack, L.L.P.
Wu Shean C.
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