Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
2002-03-20
2004-01-27
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299630, C252S299660, C252S299670
Reexamination Certificate
active
06682784
ABSTRACT:
TECHNICAL FIELD
This invention relates to nematic liquid crystal compositions comprising a liquid crystalline compound as a main component. More particularly, the invention relates to liquid crystal compositions for an active-matrix liquid crystal display device and liquid crystal display devices using these liquid crystal compositions. For convenience, a liquid crystalline compound may be abbreviated hereafter to a compound, and a liquid crystal composition to a composition.
BACKGROUND ART
Liquid crystal display devices (LCD) easily permit low power consumption and a lightweight, planar, flat surface, as compared with CRT (cathode-ray tube mode display). Therefore, a variety of LCD have been put to practical use, including a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a thin-film transistor (TFT) mode and the like. Among them, active-matrix LCD (AM-LCD) such as TFT or the like has been advanced in the high definition and high view angle, attracting the attention as the favorite of flat display panels.
The following general properties (1) to (4) are required for the liquid crystal compositions for AM-LCD.
(1) The specific resistance and voltage holding ratio are high for achieving a better contrast of LCD.
(2) The temperature range of nematic phase is broad for enabling the outdoor use of LCD. That is, the upper limit of the temperature exhibiting nematic phase is high, while the lower limit is low.
(3) The threshold voltage is low for reducing a consumption power of LCD.
(4) The viscosity is low for increasing the response rate of LCD.
Japanese Patent No. 3,086,228, WO91/13947 (Japanese Patent Hyo Hei 4-505477 (JP-A-4-505477)), Japanese Patent Kokai Hei 5-105876 (JP-A-5-105876), etc. disclose the compositions usable in AM-LCD. These compositions, however, show the tendency that the nematic phase range is narrow, the viscosity is high and the threshold voltage is high, and therefore they are not suitable for use in AM-LCD. The components for the composition have been investigated in accordance with the intended use, but more improvement is always required.
DISCLOSURE OF THE INVENTION
An object of the invention is to provide a liquid crystal composition, especially having broad nematic phase range, low viscosity, low threshold voltage and large pre-tilt angle, while meeting the general properties required for AM-LCD.
Another object of the invention is to provide a liquid crystal display device composed of the liquid crystal composition.
We have studied various liquid crystal compositions comprising liquid crystalline compounds in an effort to solve the above-mentioned problems, and as a result the above objects could be accomplished by the present invention as mentioned below.
In a first aspect, the present invention relates to a liquid crystal composition which comprises Component I comprising at least one compound selected from the compounds of the formulas (I-1) to (I-3), Component II comprising at least one compound selected from the compounds of the formulas (II-1) to (II-4), Component III comprising at least one compound selected from the compounds of the formulas (III-1) and (III-2), and Component IV comprising at least one compound selected from the compounds of the formulas (IV-1) to (IV-3).
wherein R and R′ each independently represent an alkyl group of 2 to 7 carbon atoms, Y independently represents H or F, and n represents an integer of 0 to 4.
0.1 to 3% by weight of an optically active material may be added to the composition, based on the total weight thereof.
In an embodiment of the first aspect, Component I comprises the compound of the formula (I-1), the compound of the formula (I-2), or the compound of the formula (I-3).
In another embodiment of the first aspect, the content of Component I is 5 to 30% by weight, the content of Component II is 30 to 70% by weight, the content of Component III is 5 to 45% by weight, and the content of Component IV is 5 to 30% by weight, based on the total weight of the composition.
In a second aspect, the present invention relates to a liquid crystal composition which consists essentially of four components of Component I comprising at least one compound selected from the compounds of the formulas (I-1) to (I-3), Component II comprising at least one compound selected from the compounds of the formulas (II-1) to (II-4), Component III comprising at least one compound selected from the compounds of the formulas (III-1) and (III-2), and Component IV comprising at least one compound selected from the compounds of the formulas (IV-1) to (IV-3),
in which R and R′ each independently represent an alkyl group of 2 to 7 carbon atoms, Y independently represents H or F, and n represents an integer of 0 to 4.
This composition may contain impurities such as by-products produced during the synthesis of each compound. So far as the objects of the present invention are achieved, several percent of liquid crystalline compounds may be added to the composition. In addition to the liquid crystalline compounds, small amounts of additives may be added to the composition, if necessary.
0.1 to 3% by weight of an optically active material may be added to the composition, based on the total weight thereof.
In an embodiment of the third aspect, the content of Component I is 5 to 30% by weight, the content of Component II is 30 to 70% by weight, the content of Component III is 5 to 45% by weight, and the content of Component IV is 5 to 30% by weight, based on the total weight of the composition.
In a third aspect, the present invention relates to a liquid crystal composition of the first aspect, which further contains Component V comprising at least one compound selected from the compounds of the formulas (V-1) and (V-2),
wherein R independently represents an alkyl group of 2 to 7 carbon atoms.
0.1 to 3% by weight of an optically active material may be added to the composition, based on the total weight thereof.
In an embodiment of the second aspect, the content of Component I is 5 to 30% by weight, the content of Component II is 30 to 70% by weight, the content of Component III is 5 to 45% by weight, the content of Component IV is 5 to 30% by weight, and the content of Component V is 5 to 25% by weight, based on the total weight of the composition.
In a fourth aspect, the present invention relates to a liquid crystal display device in which each of the liquid crystal compositions of the above-mentioned aspects is used.
In an embodiment of the fourth aspect, the liquid crystal composition used is that of the first aspect.
In another embodiment, the liquid crystal composition used is that of the second aspect.
In a further embodiment, the liquid crystal composition used is that of the third aspect.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
Component I in the composition of the invention is the compounds of the formulas (I-1) to (I-3). The formula (I-2) is specified as follows:
Component I has an optical anisotropy (&Dgr;n) of about 0.02 to 0.07, a clearing point (Tc) of about −30 to 20° C. and a dielectric anisotropy (&Dgr; &egr;) of 3 to 8, and shows excellent thermal and chemical stabilities and excellent solubility. Component I reduces the lower limit of nematic phase range of the composition, while lowering the viscosity. However, the composition comprising Component I only tends to have a reduced pre-tilt angle, in addition to an exceedingly lowered upper limit of nematic phase range.
Component II is the compounds of the formulas (II-1) to (II-4). The formula (II-1) is specified as follows:
Component II has Tc of about 50 to 120° C., &Dgr; &egr; of about 5 to 10 and &Dgr;n of about 0.07 to 0.14, and shows excellent thermal and chemical stabilities and excellent solubility. Component II increases the upper limit of nematic phase range of the composition, while reducing the threshold voltage. However, the composition comprising Component II only tends to have an increased lower limit of nematic phase range.
Component III is the compounds of the formulas (III-1) and (III-2). The formulas (III-1) and (III-2) are sp
Kubo Yasuhiro
Terashima Kanetsugu
Chisso Corporation
Wu Shean C.
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