Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
2000-09-28
2002-12-17
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299630, C252S299660, C252S299670
Reexamination Certificate
active
06495219
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a nematic liquid crystal composition. More specifically it relates to a liquid crystal composition preferably used for liquid crystal display devices using STN (super twisted nematic) mode; and to a liquid crystal display device using the liquid crystal composition.
BACKGROUND ART
As for the liquid crystal display mode, display modes such as TN (twisted nematic) mode, STN (super twisted nematic) mode, and active matrix mode have been proposed and utilized one after another. Among these, STN mode proposed by T. J. Scheffer et al. (Appl. Phys. Lett., 45 (10), 1021 (1984)), in which orientation of liquid crystal molecules among upper and lower plates is twisted by 180 to 270°, has been adopted as a liquid crystal display device for personal computers and others.
Recently STN mode has been used as liquid crystal display devices for mobile information terminals used frequently in the outdoors such as electronic notes or small size note-type personal computers.
General characteristics required for STN mode was items (1) to (4) below, and items (5), (6) and (7) below are additionally required for liquid crystal materials for STN mode used in the outdoors.
(1) Steepness (&ggr;) of voltage versus transmittance curve (V-T curve) of the liquid crystal composition should be as close to 1 as possible in order to enhance the contrast of the liquid crystal display device.
(2) Viscosity (&eegr;) of the liquid crystal composition should be as low as possible in order to accelerate the speed for display (response speed) of the liquid crystal display device.
(3) Optical anisotropy of the liquid crystal composition (&Dgr;n) should be able to have a proper value depending on the cell thickness of the liquid crystal display device in order to optimize the contrast of the liquid crystal display device.
(4) A liquid crystal composition should have a nematic phase over the wide range of temperature in order to widen temperature range of environment wherein the liquid crystal display device is used.
(5) Threshold voltage (V
th
) of the liquid crystal composition should be low and the temperature dependence (&dgr;) of the threshold voltage of the liquid crystal composition should be small in order to downsize the battery which is the power source to drive the liquid crystal display device.
(6) The liquid crystal composition should be highly stable against heat and ultraviolet rays in order to prevent deterioration of the liquid crystal composition and to keep displaying quality of the liquid crystal display device semi-permanently.
(7) Frequency dependence of dielectric anisotropy (&Dgr;∈) at low temperature region (below −10° C.) should be improved in order to enable display at such low temperature. Namely, &Dgr;∈ value should be constant toward higher frequency area (F
10
value described later should be large).
As for the liquid crystal composition for STN mode which has relatively low threshold voltage and relatively good temperature characteristics of the threshold voltage (namely, small temperature dependence) , compositions described in JP 7-300582 A, JP 7-300585 A and JP 7-300584 A can be illustrated.
However, the liquid crystal compositions disclosed therein have a drawback of poor stability against heat and ultraviolet rays as shown in Comparative Examples of the present application. WO 96/11897 proposed to provide a novel liquid crystal compound having large dielectric anisotropy together with extremely low viscosity as liquid crystal compounds used for low voltage in various modes such as active matrix mode or STN mode, and to provide a liquid crystal composition comprising the compound. It discloses the composition comprising the compound having —CF
2
O— as a bonding group and 3,5-difluoro-4-cyanophenyl as a terminal group (Composition Examples 19 to 22). Furthermore, among these, the Composition Example 19 is similar to the composition of the present invention. However, the composition of Example 19 has drawbacks such as poor steepness, high threshold voltage, large temperature dependence of the threshold voltage, and large frequency dependence of dielectric anisotropy (&Dgr;∈) at low temperature as shown in the Comparative Examples of the present invention.
Although many liquid crystal compositions have been studied, the liquid crystal composition for STN display mode used in the outdoors is currently required to fulfill further characteristics (5) and (6) described above in addition to characteristics (1) to (4) described above.
Further, for the use in a portable telephone, higher duty is intended in order to enlarge display capacity. Accordingly actual driving frequency goes higher and higher. As driving frequency goes higher, movement of liquid crystal molecules at low temperature can hardly follow frequency change of voltage resulting in severe problems such as tailing phenomena or poor displaying caused by lowering contrast. To avoid such poor displaying, the liquid crystal material is requested more and more to have excellent frequency dependence (small dependence of frequency) of &Dgr;∈ at low temperature region in item (7): described above, namely, to have a constant value of &Dgr;∈ up to the higher frequency region.
Examples 46, 47 and 49 of JP 10-251186 A disclose liquid crystal compositions which are similar to that of the present invention, however, these compositions did not solve the problem of the present invention which requires the improvement of frequency dependence of &Dgr;∈ at low temperature region in item (7) described above, as Comparative Example of the present invention shows later.
DISCLOSURE OF THE INVENTION
The subject of the present invention is to provide a liquid crystal composition having low threshold voltage, small temperature dependence of the threshold voltage, high stability against heat and ultraviolet rays and, furthermore small frequency dependence of &Dgr;∈ at low temperature.
The present inventors enthusiastically studied to evaluate compositions using various liquid crystal compounds for solving the problem. As a result, they found that the composition comprising specific two components of a first component and a second component, and furthermore excluding specific components from other components can solve the problem described above, and completed the present invention.
The liquid crystal composition of the present invention is indicated in items 1 to 4, and the liquid crystal display device of the present invention is shown in item 5 in the following.
The item 1 of the present invention is a liquid crystal composition characterized by comprising a first component consisting of the compound(s) expressed by formula (1) and a second component consisting of least one compound selected from the group of the compounds expressed by formulae (2-1) to (2-4).
wherein R
1
represents alkyl having 1 to 10 carbon in, which one methylene may be replaced by —O— or —CH═CH—; R
2
, R
3
and R
4
each independently represents alkyl having 1 to 10 carbon in which one methylene may be replaced by —O— or —CH═CH—, and one or more hydrogen may be replaced by fluorine; R
5
represents alkyl having 1 to 10 carbon in which one methylene may be replaced by —O—; R
6
, R
7
and R
9
each independently represents alkyl having 1 to 10 carbon; R
8
represents alkyl having 1 to 10 carbon in which one methylene may be replaced by —O—; A
1
, A
2
, A
3
and A
5
each independently represents trans-1,4-cyclohexylene or 1,4-phenylene; A
4
represents 1,4-phenylene in which H at the lateral position may be replaced by F; Z
1
represents —C≡C— or a single bond; m and n each independently is an integer of 0 or 1; X
1
, X
2
and X
3
each independently represents H or F.
The item 2 is a liquid crystal composition according to the item 1 which comprises 5 to 40% of the first component and 10 to 90% of the second component each based on the total weight of the liquid crystal composition.
The item 3 is a liquid crystal composition according to the item 1 or 2 wherein the liquid crys
Fujita Hiroaki
Murashiro Katsuyuki
Nakagawa Etsuo
Chisso Corporation
Wenderoth , Lind & Ponack, L.L.P.
Wu Shean C.
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