Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
2001-11-06
2003-11-04
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299610, C252S299630
Reexamination Certificate
active
06641872
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a nematic liquid crystal composition. More specifically, it relates to a liquid crystal composition for an active matrix liquid crystal display element and the liquid crystal display element comprising the liquid crystal composition.
BACKGROUND ART
Transmission type active matrix liquid crystal display elements (AM-LCD) using a back-light as a light source have been practically utilized as elements being possible to display in full color. The back-light has the disadvantage that the consumption of electric power is large. Digital still cameras and digital video cameras having such AM-LCD are disadvantaged by the fact that they can not be used for extended periods.
Reflection type AM-LCD has been developed to solve the problem associated with the consumption of electric power. As light passes through liquid crystal layers two times, the reflection type AM-LCD requires a small value product of (&Dgr;n×d), where (d) is the thickness of the liquid crystal layers and (&Dgr;n) is the optical anisotropy in the liquid crystals. This fact was reported in the SID '97, Digest/643 by S. T. Wu, C. S. Wu and C. L. Kuo et al. The liquid crystals in a conventional transmission-TN type AM-LCD required &Dgr;n of about 0.075 to 0.120. However, the liquid crystals in a reflection-TN type AM-LCD requires &Dgr;n of 0.75 and less.
The physical properties required the reflection type AM-LCD except &Dgr;n are similar to those required for the transmission type AM-LCD, and are the following.
(a) a high specific resistance value and a high voltage holding ratio in order to increase the contrast of the LCD.
(b) a wide temperature range of a nematic phase in order to enable the LCD to be used in an outdoor environment. Namely, the upper temperature limit of the nematic phase is high and the lower temperature limit of the nematic phase is low.
(c) low threshold voltage in order to reduce the electric power consumption.
(d) low viscosity in order to increase response speed of the LCD.
The Japanese Patent Applications of JP 11-29771 A, JP 10-245559 A, JP 9-255956 A, and JP 9-249881 A can be cited as examples of literature that discloses liquid crystal compounds or liquid crystal compositions usable in AM-LCD's. However, the liquid crystal compositions disclosed in these documents have disadvantages such that &Dgr;n is large, the lower temperature limit of a nematic phase is high although &Dgr;n is relatively small, or the voltage holding ratio is low, as is made clear in the Comparative Examples of the present application. Consequently, the compositions were not suitable for the reflection-TN type AM-LCD use.
An object of the present invention is to provide a liquid crystal composition that satisfies the general physical properties required for an AM-LCD, and especially that the upper temperature limit of the nematic phase is high, the lower temperature limit of the nematic phase is low, and the &Dgr;n value is small.
DETAILED DESCRIPTION
Having carefully studied compositions comprising a variety of liquid crystal compounds in order to solve the problems referred to above, the applicants discovered that the problems could be overcome by developing a composition comprising the following components.
(1) A liquid crystal composition comprising component I that consists of at least one compound represented by formula (I), and component II that consists of at least one compound selected from a group of compounds represented by formulas (II-1) to (II-7).
wherein R
1
, R
2
, R
3
, and R
4
each independently represent alkyl, alkoxy or alkoxymethyl having 1 to 10 carbon, or alkenyl having 2 to 10 carbon; Z
1
and Z
2
each independently represent a single bond or —C
2
H
4
—; Z
3
represents a single bond, —C
2
H
4
— or —COO—; Z
4
represents a single bond, —C
2
H
4
— or —CH═CH—; Z
5
represents a single bond or —C
2
H
4
—; X
1
represents fluorine, chlorine, CF
3
, OCF
2
H, or OCF
3
; and Y
1
and Y
2
each independently represent hydrogen or fluorine.
(2) The liquid crystal composition according to (1), wherein it comprises from 5% to 30% by weight of component I, based on the total weight of the composition, and from 35% to 95% by weight of component II, based on the total weight of the composition.
(3) The liquid crystal composition according to (1) or (2), wherein it comprises component I, component II and component III, and component III consists of at least one compound selected from a group of compounds represented by formulas (III-1) to (III-5).
wherein R
5
and R
8
each independently represent alkyl, alkoxy or alkoxymethyl having 1 to 10 carbon, or alkenyl having 2 to 10 carbon; R
6
represents alkyl, alkoxy or alkoxymethyl having 1 to 10 carbon, alkenyl having 2 to 10 carbon, or —COO—R
9
, R
9
represents alkyl having 1 to 10 carbon; R
7
represents alkyl or alkoxy having 1 to 10 carbon, alkenyl having 2 to 10 carbon, or fluorine; ring A represents 1,4-phenylene or 1,4-cyclohexylene; Z
6
and Z
8
each independently represent a single bond, —C
2
H
4
—, —COO—, or —CH═CH—; Z
7
represents a single bond, —C
2
H
4
— or —COO—; and Q represents hydrogen or fluorine.
(4) The liquid crystal composition according to (3), wherein it comprises from 5% to 30% by weight of component I, based on the total weight of the composition, from 35% to 90% by weight of component II, based on the total weight of the composition, and from 5% to 60% by weight of component III, based on the total weight of the composition.
(5) The liquid crystal display element comprising the liquid crystal composition according to (1), (2), (3), or (4).
Component I in the liquid crystal composition of the present invention consists of at least one compound selected from the group represented by formula (I) described above. Component I has an optical anisotropy (&Dgr;n) value in the range from 0.06 to 0.09, a clearing point (Tc) in the range from about 170 to 200° C., and a dielectric anisotropy (&Dgr;∈) value of about zero, and is excellent in thermal stability, chemical stability and miscibility. Thus, component I is used mainly for maintaining a high Tc and reducing the &Dgr;n in liquid crystal compositions for a thin film transistors (TFT) mode which require high reliability. However, the composition prepared using only these compounds may have an overly narrow temperature range of a nematic phase and too high threshold voltage.
The preferred compounds for component I are the following:
wherein R and R′ each independently represent alkyl, alkoxy and alkoxymethyl having 1 to 10 carbon.
Component II consists of at least one compound selected from a group of compounds represented by formulas (II-1) to (II-7) described above. Component II has a Tc in the range of about −50 to 160° C., &Dgr;∈ in the range of about 5 to 12, and &Dgr;n in the range of about 0.03 to 0.12, and is excellent in thermal stability, chemical stability, and miscibility. Thus, component II plays a role especially in lowering threshold voltage in the liquid crystal composition for thin film transistors (TFT) mode which requires high reliability. However, the composition prepared by using only these compounds may have a tendency towards lowering the miscibility of the composition and may increase both the &Dgr;n and the viscosity.
The preferred compounds for component II are the following:
wherein R represents alkyl, alkoxy or alkoxymethyl having 1 to 10 carbon, or alkenyl having 2 to 10 carbon.
Especially preferred compounds in formula (II-1) are formulas (II-1-3) to (II-1-7). Especially preferred compounds in formula (II-2) are formulas (II-2-2) and (II-2-3). Especially preferred compounds in formula (II-3) are formula (II-3-1), (II-3-4), (II-3-6) to (II-3-9), and (II-3-11). Especially preferred compounds in formula (II-4) are formulas (II-4-1) to (II-4-3). Especially preferred compounds in formula (II-5) are formulas (II-5-5) and (II-5-6). Especially preferred compounds in formula (II-6) are formulas (II-6-2), (II-6-4) to (II-6-6), (II-6-8), and (II-6-9). Especially preferred
Kubo Yasuhiro
Terashima Kanetsugu
LandOfFree
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