| CORP. SALE | Benzene-1-F-2-CF3-5-(CH2CH2-C6H10-CH2CH2-C6H10-Me) |
| PATENT ASSIGNEE'S COUNTRY | Japan |
| UPDATE | 01.00 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 11.01.00 |
| PATENT TITLE |
Liquid crystalline compound replaced by fluorine containing group, liquid crystal composition, and liquid crystal display device |
| PATENT ABSTRACT |
Liquid crystalline compounds are disclosed which compounds are expressed by general formula (1) ##STR1## wherein R.sub.1 represents an alkyl group having 1 to 10 carbon atoms, ring A represents 1,4-phenylene or 1,4-cyclohexylene, each of X.sub.1, X.sub.2, X.sub.3, and X.sub.4 independently represents hydrogen atom or fluorine atom, Y.sub.1 represents CF.sub.3 or OCF.sub.3, and each of m, n, and p is independently an integer of 1 or 0. The liquid crystalline compounds have a wide temperature. The liquid crystalline compounds have a wide temperature range of nematic phase, low viscosity, large positive .DELTA..epsilon., high chemical stability, high miscibility with other liquid crystalline compounds at low temperatures, small temperature dependency of viscosity and .DELTA..epsilon., extremely high specific resistance (high voltage holding ratio), and good UV stability, and are preferably used for TFT. Also, disclosed are liquid crystal compositions containing the liquid crystalline compounds mentioned above, and liquid crystal display devices using the liquid crystal composition. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 02.09.97 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT REFERENCES CITED | This data is not available for free |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
We claim: 1. A liquid crystalline compound expressed by general formula (1) ##STR32## wherein R.sub.1 represents an alkyl group having 1 to 10 carbon atoms, ring A represents 1,4- cyclohexylene, X.sub.1 and X.sub.2 both represent hydrogen atom, X.sub.3 represents fluorine atom, X.sub.4 represents hydrogen atom or fluorine atom, Y.sub.1 represents CF.sub.3 or OCF.sub.3, and m, n and p are all 1. 2. A liquid crystal compositions containing at least one liquid crystalline compound defined in claim 1. 3. A liquid crystal composition containing, as a first compound, at least one liquid crystalline compound defined in claim 1, and containing, as a second component, at least one compound selected from the group of the compounds expressed by any one of general formulas (2), (3), and (4) ##STR33## wherein R.sub.2 represents an alkyl group having 1 to 10 carbon atoms, Y.sub.2 represents fluorine atom, chlorine atom, OCF.sub.3, OCF.sub.2 H, CF.sub.3, CF.sub.2 H, or CFH.sub.2, L.sub.1, L.sub.2, L.sub.3, and L.sub.4 represent, independently with one another, hydrogen atom or fluorine atom, Z.sub.1 and Z.sub.2 represent, independently with each other, --(CH.sub.2).sub.2 --, --CH.dbd.CH--, or a covalent bond, and a is 1 or 2. 4. A liquid crystal composition containing, as a first compound at least one liquid crystalline compound defined in claim 1, and containing, as a second component, at least one compound selected from the group of the compounds expressed by any one of general formulas (5), (6), (7), (8), and (9) ##STR34## wherein R.sub.3 represents fluorine atom, an alkyl group having 1 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms, any methylene group in the alkyl group or alkenyl group may be replaced by oxygen atom provided that in no case two or more methylene groups are continually replaced by oxygen atom; ring B represents 1,4-cyclohexylene, 1,4-phenylene, or 1,3-dioxane-2,5-diyl, ring C represents 1,4-cyclohexylene, 1,4-phenylene, or pyrimidine-2,5-diyl, ring D represents 1,4-cyclohexylene or 1,4-phenylene, Z.sub.3 represents --(CH.sub.2).sub.2 --, --COO--, or a covalent bond, L.sub.5 and L.sub.6 represent, independently with each other, hydrogen atom or fluorine atom, and b and c are, independently with each other, 0 or 1, ##STR35## wherein R.sub.4 represents an alkyl group having 1 to 10 carbon atoms, L.sub.7 represents hydrogen atom or fluorine atom, and d is 0 or 1, ##STR36## wherein R.sub.5 represents an alkyl group having 1 to 10 carbon atoms, ring E and ring F represent, independently with each other, 1,4-cyclohexylene or 1,4-phenylene, Z.sub.4 and Z.sub.5 represent, independently with each other, --COO-- or a covalent bond, Z.sub.6 represents --COO-- or --C.tbd.C--, L.sub.8 and L.sub.9 represent, independently with each other, hydrogen atom or fluorine atom, Y.sub.3 represents fluorine atom, OCF.sub.3, OCF.sub.2 H, CF.sub.3, CF.sub.2 H, or CFH.sub.2 provided that when Y.sub.3 represents OCF.sub.3, OCF.sub.2 H, CF.sub.3, CF.sub.2 H, or CFH.sub.2, both L.sub.8 and L.sub.9 represent hydrogen atom; and all of e, f, and g are, independently with one another, 0 or 1, ##STR37## wherein R.sub.6 and R.sub.7 represent, independently with each other, an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, any methylene group in either the alkyl group and alkylene group may be replaced by oxygen atom provided that in no case two or more methylene groups are continually replaced by oxygen atom; ring H represents 1,4-cyclohexylene, 1,4-phenylene, or pyrimidine-2,5-diyl, ring I represents 1,4-cyclohexylene or 1,4-phenylene, Z.sub.6 represents --C.tbd.C--, --COO--, --(CH.sub.2).sub.2 --, --CH.dbd.CH--C.tbd.C--, or a covalent bond, and Z.sub.7 represents --COO-- or a covalent bond, ##STR38## wherein R.sub.8 and R.sub.9 represent, independently with each other, an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, any methylene group in either the alkyl group and alkylene group may be replaced by oxygen atom provided that in no case two or more methylene groups are continually replaced by oxygen atom; ring J represents 1,4-cyclohexylene, 1,4-phenylene, or pyrimidine-2,5-diyl, ring K represents 1,4-cyclohexylene, 1,4-phenylene one or more hydrogen atoms on the ring of which may be replaced by fluorine atom, or pyrimidine-2,5-diyl, ring L represents 1,4-cyclohexylene or 1,4-phenylene, Z.sub.8 and Z.sub.10 represent, independently with each other, --COO--, --(CH.sub.2).sub.2 --, or a covalent bond, Z.sub.9 represents --CH.dbd.CH--, --C.tbd.C--, --COO--, or a covalent bond, and h is 0 or 1. 5. A liquid crystal composition containing, as a first component, at least one liquid crystalline compound defined in claim 1, containing, as a part of a second component, at least one compound selected from the group of the compounds expressed by any one of general formulas (2), (3), and (4) defined in claim 3, and containing, as other part of the second component, at least one compound selected from the group of the compounds expressed by any one of general formulas (5), (6), (7), (8), and (9) defined in claim 4. 6. A liquid crystal display device composed by using a liquid crystal composition defined in claim 2. 7. A liquid crystal display device composed by using a liquid crystal composition defined in claim 3. 8. A liquid crystal display device composed by using a liquid crystal composition defined in claim 4. 9. A liquid crystal display device composed by using a liquid crystal composition defined in claim 5. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
TECHNICAL FIELD The present invention relates to a liquid crystalline compound and a liquid crystal composition. More specifically, the present invention relates to a novel liquid crystalline compound replaced by a fluorine containing group, a liquid crystal composition containing the liquid crystalline compound, and a liquid crystal display device composed by using the liquid crystal composition. BACKGROUND ART Liquid crystal display devices are widely used for watches, desktop calculators, several kinds of measuring apparatus, panels for automobiles, word processors, electronic note-books, printers, computers, and televisions. These liquid crystal display devices employ optical anisotropy (.DELTA.n) and dielectric anisotropy (.DELTA..epsilon.) of liquid crystal compounds. As display mode, dynamic scattering (DS) mode, guest-host (GH) mode, twisted nematic (TN) mode, super twisted nematic (STN) mode, thin-film transistor (TFT) mode, and ferroelectric liquid crystal (FLC) mode are known. As their driving mode, static driving mode, time sharing addressing mode, active matrix driving mode, and dual frequency driving mode are known. Among them, TFT mode is being paid public attention in particular. While several characteristics are required of liquid crystal materials for TFT mode, the following three are considered to be necessary as common characteristics: 1) Temperature range of nematic phase of the liquid crystal materials is wide to such an extent that the materials do not cause the reduction in the temperature range of the nematic phase of a liquid crystal composition when the materials were added to a liquid crystal composition. 2) Viscosity of the liquid crystal materials is low including at a low temperature region. 3) Liquid crystal materials have a large .DELTA..epsilon.. Among the characteristics mentioned above, 1) includes the requirements that the upper limit of the temperature of nematic phase is high and that the melting point of the liquid crystal materials is low so that the phase separation of the materials due to the precipitation of crystals hardly occurs even at a low temperature region. Characteristic 2) is an extremely important factor to increase the response speed of oriented liquid crystal molecules to the electric field in a liquid crystal panel (Phys. Lett., 39A, 69 (1972)), and the increase in the response speed is most eagerly demanded at present to improve the quality of the display of liquid crystal compositions. At that time, small dependence on temperature of the response speed mentioned above, that is, small temperature dependence of the viscosity of materials and maintenance of a low viscosity of the materials even at low temperatures are considered to be important from the viewpoint that the deterioration in the quality of the display is not caused even at low temperatures. Reasons why characteristic 3) is desired are as follows: In order to actualize the reduction of power consumption and the production of a large image screen, the reduction of driving voltage is necessary. Driving voltage, particularly, threshold voltage (V.sub.th) is a function of .DELTA..epsilon. as expressed by the following equation ##EQU1## wherein k is a proportional constant and K is an elastic constant. As will be seen from the equation shown above, compounds having a large positive .DELTA..epsilon. is necessary for reducing power consumption. In addition, a small temperature dependence of V.sub.th is desired even at low temperatures in particular in order to raise the quality of the display of liquid crystal compositions and keep it in a wide temperature range. In order to respond to such requirements, the exploration for compounds having a large positive .DELTA..epsilon. is being conducted. Among the compounds already discovered, trifluoromethylphenyl derivatives expressed by formula (a) proposed in Laid-open Japanese Patent Publication No. Sho 59-78129 and trifluoromethoxyphenyl derivatives expressed by formula (b) proposed in Laid-open WO Japanese Patent Publication No. Hei 2-501311 are known as examples of the compounds having particularly a large .DELTA..epsilon.. ##STR2## While these compounds have a three rings structure having CF.sub.3 or OCF.sub.3 at a terminal of the molecule, all of the bonding groups which link the three rings in a straight line are limited to a covalent bond. Based on this fact, in part, those compounds can not completely be said to fully satisfy required characteristics other than .DELTA..epsilon.. Some of the compounds having CF.sub.3 or OCF.sub.3 at a terminal of the molecule are described in Liq. Cryst., 18 (4), 665 (1995), Laid-open WO Japanese Publication Nos. Sho 63-503226, Hei 3-503771, Hei 4-500214, Hei 4-500217, Hei 4-500682, Hei 4-501575, Hei 4-501576, Hei 4-507104, Hei 5-502676, and Hei 6-504032, DE Nos. 4004650 A1, 4013083, 4106345, 4108705 A1, and 4113053 A1, and EP Nos. 0439089 A1 and 0449288, in addition to the publications mentioned above. However, physical parameters of the compounds are not sufficiently described in those publications. Further, the liquid crystalline compounds used in the liquid crystal compositions for TFT must be stable against external environmental factors such as moisture, air, heat, and light. In order to develop characteristics required for particular display devices, liquid crystalline compounds are used in the form of a mixture of several or twenty-odd compounds. Accordingly, it is demanded that liquid crystalline compounds have a good miscibility with other liquid crystalline compounds, and a good miscibility even at low temperatures since the use environment of the compounds is expanded recently, in particular. That is, liquid crystal compositions having a nematic phase particularly at low temperatures, precipitating no crystals, and developing no smectic phase are desired for the liquid crystal compositions for TFT in order to make it possible to use the compositions at a wide range of temperatures. Accordingly, liquid crystalline compounds having an excellent miscibility with other liquid crystalline compounds at low temperatures are particularly desired for the liquid crystalline compounds to be used in TFT. TFT contains integrated nonlinear devices for switching particular image segments and is one type of active matrix mode liquid crystal displays which are considered to be suitable for high grade information displays such as for televisions, computers, automobiles, and airplanes. Liquid crystal compositions designed for such uses must have an extremely high specific resistance (high voltage holding ratio) and a good UV stability in addition to the large positive .DELTA..epsilon. mentioned above. When liquid crystal compositions having no such characteristics were used, image contrast is decreased with the reduction of electric resistance in liquid crystal panels to raise a problem of "image sticking". Besides, there is a strong tendency of the liquid crystal compositions to shorten their utilization life particularly at the time of driving at a low voltage. Liquid crystalline compounds similar to those of the present invention are disclosed in U.S. Pat. Nos. 4,871,469 and 5,292,454. However, the compounds disclosed in these patents are distinguished from the compounds of the present invention in their structure. Also, U.S. Pat. Nos. 5,286,411 and 5,516,454 described general formulas of liquid crystalline compounds which encompass some compounds of the present invention. However, the compounds of the present invention are not substantially disclosed in these patents. Besides, the compounds disclosed in these patents have, for example, a low clearing point or a poor capability of exhibiting nematic property compared with those of the present invention. DISCLOSURE OF THE INVENTION An object of the present invention is to dissolve the problems in the prior art mentioned above and to provide a liquid crystalline compound for TFT which satisfy required characteristics such as a wide temperature range of nematic phase, lower viscosity, larger positive .DELTA..epsilon., high chemical stability, high miscibility with other liquid crystalline compounds at low temperatures, small temperature dependency of viscosity and .DELTA..epsilon., extremely high specific resistance (high voltage holding ratio), and good UV stability at the same time, and to provide a liquid crystal composition containing the liquid crystalline compound. As a result of the investigation by the present inventors, it has been found that a liquid crystalline compound provided with the characteristics mentioned above can be obtained by modifying liquid crystalline compounds so that the compounds have a trifluoromethylphenyl group or trifluoromethoxyphenyl group as example of known terminal substituent and, characteristically have a specific main skeleton at the same time, leading to the achievement of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION In order to achieve the objects mentioned above, the present invention has the following aspects: 1. A liquid crystalline compound expressed by general formula (1) ##STR3## wherein R.sub.1 represents an alkyl group having 1 to 10 carbon atoms, ring A represents 1,4-phenylene or 1,4-cyclohexylene, each of X.sub.1, X.sub.2, X.sub.3, and X.sub.4 independently represents hydrogen atom or fluorine atom provided that at least one of X.sub.1 to X.sub.4 is fluorine atom, Y.sub.1 represents CF.sub.3 or OCF.sub.3, and each of m, n, and p is independently an integer of 1 or 0 provided that at least one of m and p is 1. 2. The liquid crystalline compound recited in the aspect 1 mentioned above wherein n is 0, m is 1, X.sub.3 is fluorine atom, and X.sub.4 is hydrogen atom. 3. The liquid crystalline compound recited in the aspect 1 mentioned above wherein n is 1, ring A is 1,4-cyclohexylene, both m and p are 1, and X.sub.3 is fluorine atom. 4. The liquid crystal compound recited in the aspect 1 mentioned above wherein n is 1, ring A is 1,4-phenylene, m is 1, p is 0, all of X.sub.1, X.sub.2 and X.sub.4 are hydrogen atom, and X.sub.3 is fluorine atom. 5. The liquid crystalline compound recited in the aspect 1 mentioned above wherein n is 1, ring A is 1,4-phenylene, m is 0, p is 1, X.sub.1 is fluorine atom, and X.sub.2 is hydrogen atom. 6. The liquid crystal compound recited in the aspect 1 mentioned above wherein n is 1, ring A is 1,4-phenylene, m is 1, p is 0, each of X.sub.1 and X.sub.3 is fluorine atom, and X.sub.2 and X.sub.4 are independently hydrogen atom or fluorine atom. 7. A liquid crystal composition containing at least one liquid crystalline compound defined in any one of the aspects 1 to 6 mentioned above. 8. A liquid crystal composition containing, as a first compound, at least one liquid crystalline compound defined in any one of the aspects 1 to 6 mentioned above, and containing, as a second component, at least one compound selected from the group of the compounds expressed by any one of general formulas (2), (3), and (4) ##STR4## wherein R.sub.2 represents an alkyl group having 1 to 10 carbon atoms, Y.sub.2 represents fluorine atom, chlorine atom, OCF.sub.3, OCF.sub.2 H, CF.sub.3, CF.sub.2 H, or CFH.sub.2, L.sub.1, L.sub.2, L.sub.3, and L.sub.4 represent, independently with one another, hydrogen atom or fluorine atom, Z.sub.1 and Z.sub.2 represent, independently with each other, --(CH.sub.2).sub.2 --, --CH.dbd.CH--, or a covalent bond, and a is 1 or 2. 9. A liquid crystal composition containing, as a first compound, at least one liquid crystalline compound defined in any one of the aspects 1 to 6 mentioned above, and containing, as a second component, at least one compound selected from the group of the compounds expressed by any one of general formulas (5), (6), (7), (8), and (9) ##STR5## wherein R.sub.3 represents fluorine atom, an alkyl group having 1 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms, any methylene group in the alkyl group or alkenyl group may be replaced by oxygen atom provided that in no case two or more methylene groups are continually replaced by oxygen atom; ring B represents 1,4-cyclohexylene, 1,4-phenylene, or 1,3-dioxane-2,5-diyl, ring C represents 1,4-cyclohexylene, 1,4-phenylene, or pyrimidine-2,5-diyl, ring D represents 1,4-cyclohexylene or 1,4-phenylene, Z.sub.3 represents --(CH.sub.2).sub.2 --, --COO--, or a covalent bond, L.sub.5 and L.sub.6 represent, independently with each other, hydrogen atom or fluorine atom, and b and c are, independently with each other, 0 or 1, ##STR6## wherein R.sub.4 represents an alkyl group having 1 to 10 carbon atoms, L.sub.7 represents hydrogen atom or fluorine atom, and d is 0 or 1, ##STR7## wherein R.sub.5 represents an alkyl group having 1 to 10 carbon atoms, ring E and ring F represent, independently with each other, 1,4-cyclohexylene or 1,4-phenylene, Z.sub.4 and Z.sub.5 represent, independently with each other, --COO-- or a covalent bond, Z.sub.6 represents --COO-- or --C.tbd.C--, L.sub.8 and L.sub.9 represent, independently with each other, hydrogen atom or fluorine atom, Y.sub.3 represents fluorine atom, OCF.sub.3, OCF.sub.2 H, CF.sub.3, CF.sub.2 H, or CFH.sub.2 provided that when Y.sub.3 represents OCF.sub.3, OCF.sub.2 H, CF.sub.3, CF.sub.2 H, or CFH.sub.2, both L.sub.8 and L.sub.9 represent hydrogen atom; and all of e, f, and g are, independently with one another, 0 or 1, ##STR8## wherein R.sub.6 and R.sub.7 represent, independently with each other, an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, any methylene group in either the alkyl group and alkylene group may be replaced by oxygen atom provided that in no case two or more methylene groups are continually replaced by oxygen atom; ring H represents 1,4-cyclohexylene, 1,4-phenylene, or pyrimidine-2,5-diyl, ring I represents 1,4-cyclohexylene or 1,4-phenylene, Z.sub.6 represents --C.tbd.C--, --COO--, --(CH.sub.2).sub.2 --, --CH.dbd.CH--C.tbd.C--, or a covalent bond, Z.sub.7 represents --COO-- or a covalent bond, ##STR9## wherein R.sub.8 and R represent, independently with each other, an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, any methylene group in either the alkyl group and alkylene group may be replaced by oxygen atom provided that in no case two or more methylene groups are continually replaced by oxygen atom; ring J represents 1,4-cyclohexylene, 1,4-phenylene, or pyrimidine-2,5-diyl, ring K represents 1,4-cyclohexylene, 1,4-phenylene one or more hydrogen atoms on the ring of which may be replaced by fluorine atom, or pyrimidine-2,5-diyl, ring L represents 1,4-cyclohexylene or 1,4-phenylene, Z.sub.8 and Z.sub.10 represent, independently with each other, --COO--, --(CH.sub.2).sub.2 --, or a covalent bond, Z.sub.9 represents --CH.dbd.CH--, --C.tbd.C--, --COO--, or a covalent bond, and h is 0 or 1. 10. A liquid crystal composition containing, as a first component, at least one liquid crystalline compound defined in any one of the aspects 1 to 6 mentioned above, containing, as a part of a second component, at least one compound selected from the group of the compounds expressed by any one of general formulas (2), (3), and (4) defined in the aspect 8 mentioned above, and containing, as other part of the second component, at least one compound selected from the group of the compounds expressed by any one of general formulas (5), (6), (7), (8), and (9) defined in the aspect 9 mentioned above. 11. A liquid crystal display device composed by using a liquid crystal composition defined in any one of the aspects 7 to 10 mentioned above. Compounds of the present invention expressed by general formula (1) is characterized by having a specific skeleton comprising two or three rings including 1,2-ethylene group or 1,4-butylene group as central bonding group, and at the same time having known trifluoromethyl group or trifluoromethoxy group on the terminal phenylene group. These compounds can roughly be classified into two rings compounds expressed by any one of formulas (1-1) to (1-3) (first group); three rings compounds expressed by any one of formulas (1-4) to (1-7) central ring in which compounds is 1,4-cyclohexylene (second group); three rings compounds expressed by formula (1-8) or (1-9) in which compounds central ring is 1,4-phenylene group, and the bonding group linking the 1,4-phenylene group with terminal phenyl group is a covalent bond (third group); and three rings compounds expressed by any one of formulas (1-10) to (1-15) in which compounds central ring is 1,4-phenylene group, and the bonding group linking the 1,4-phenylene group with terminal phenylene group is 1,2-ethylene group (fourth group). ##STR10## in each of the formulas, R.sub.1 has the same meaning as mentioned above. Any of these compounds of the present invention exhibit a wide temperature range of nematic phase, low viscosity, large positive .DELTA..epsilon., high chemical stability, high miscibility with other liquid crystalline compounds at low temperatures, extremely high specific resistance (high voltage holding ratio), and high stability against UV and heat .and the dependency of .DELTA..epsilon. and viscosity of the compounds on temperature is extremely low. Thus, the compounds are useful as the component for liquid crystal compositions for TFT. Optical anisotropy (.DELTA.n) can optionally be controlled by suitably selecting R.sub.1, ring A, X.sub.1, X.sub.2, X.sub.3, X.sub.4, m, n, and p in general formula (1) by which the compounds of the present invention are exhibited. For instance, it is sufficient to select compounds containing more 1,4-phenylene groups as ring A when a large .DELTA.n is desired containing more 1,4-cyclohexylene groups as ring A conversely when a small .DELTA.n is desired. Among the compounds of the present invention, the ones included in the first group, mentioned above particularly exhibit a large positive .DELTA..epsilon., low viscosity, and high clearing point, and thus the compounds are excellent as component of liquid crystal compositions. Compounds of the second group particularly exhibit an extremely excellent nematic characteristics, and thus the liquid crystal compositions using the compounds as one of components exhibit such a preferable characteristic that the development of a smectic phase is not observed in the liquid crystal composition at low temperatures. Compounds of the third group particularly exhibit a high clearing point and low viscosity, have a large positive .DELTA..epsilon., are small in the viscosity increase at low temperatures in particular since the dependency of the viscosity of the compounds on temperature is small, and are excellent even in the miscibility with other liquid crystalline compounds, and thus the compounds are excellent as component of liquid crystal compositions. Further, the compounds of the fourth group particularly exhibit a high clearing point and low viscosity, have a large .DELTA..epsilon. and .DELTA.n, are small in the viscosity increase at low temperatures in particular since the dependency of the viscosity of the compounds on temperature is small, and beside, have a good miscibility with other liquid crystalline compounds, and thus the compounds are also preferable as component of liquid crystal compositions. Compounds of the present invention are most preferably used as component for the liquid crystal compositions for TFT. However, since the compounds have such excellent characteristics as mentioned above, the compounds can preferably be used not only in such use but also in other uses, for example, for TN mode, STN mode, Guest-Host mode, and polymer dispersion type liquid crystal display deice, and as the liquid crystalline compound for dynamic scattering mode. While the liquid crystal compositions provided by the present invention may be comprised only of the first component containing at least one liquid crystalline compound expressed by general formula (1), the liquid crystal compositions preferably contain, as a second component, at least one compound selected from the group of the compounds expressed by any one of general formulas (2), (3), and (4) mentioned above (hereinafter the compounds are referred to as second A component) and/or at least one compound selected from the group of the compounds expressed by any one of general formulas (5), (6), (7), (8), and (9) mentioned above (hereinafter the compounds are referred to as second B component), in addition to the compounds of general formula (1). Further, a known compound may be blended to the liquid crystal compositions as a third component for the purpose of adjusting threshold voltage, the temperature range of liquid crystal phase, .DELTA.n, .DELTA..epsilon., and viscosity. Among the second A component, the compounds expressed by any one of formulas (2-1) to (2-15), (3-1) to (3-48), and (4-1) to (4-53) can be mentioned as examples of preferable compounds included in the compounds expressed by general formula (2), (3), or (4). ##STR11## in each of the formulas, R.sub.2 has the same meaning as mentioned above. Compounds expressed by any one of general formulas (2) to (4) have a positive .DELTA..epsilon. and are remarkably excellent in heat resistance and chemical resistance. Thus, while the compounds are indispensable when the liquid crystal compositions for TFT to which a high reliability particularly such as a high voltage holding ratio (VHR) or a large specific resistance is required are produced, the compounds can be used even when liquid crystal compositions for STN display mode or ordinary TN display mode are produced. Amount of the compounds to be used is suitably in the range of 1 to 99% by weight, preferably 10 to 97% by weight, and more desirably 40 to 95% by weight based on the total weight of liquid crystal composition when the liquid crystal compositions for TFT are produced. Among the second B component mentioned above, compounds expressed by any one of formulas (5-1) to (5-24), (6-1) to (6-3), and (7-1) to (7-17) can be mentioned as examples of preferable compounds included in the compounds expressed by general formula (5), (6) or (7). ##STR12## in each of the formulas, R.sub.3, R.sub.4, and R.sub.5 have the same meaning as mentioned above. Compounds expressed by any one of general formulas (5) to (7) have a large positive .DELTA..epsilon. and thus are used as component of liquid crystal compositions for the purpose of reducing V.sub.th. The compounds are also used for adjusting viscosity and .DELTA.n, raising clearing point, widening nematic range, and improving the steepness of V.sub.th. Among the second B component, compounds expressed by any one of formulas (8-1) to (8-8) and (9-1) to (9-12) can be mentioned as examples of preferable compounds included in the compounds expressed by general formulas (8) or (9). ##STR13## wherein R.sub.6, R.sub.7, R.sub.8, and R.sub.9 have the same meaning as mentioned above. Compounds expressed by general formula (8) or (9) exhibit a negative or small positive .DELTA..epsilon.. Among them, the compounds expressed by general formula (8) are used mainly for the purpose of reducing viscosity and adjusting .DELTA.n, and the compounds expressed by general formula (9) are used mainly for the purpose of raising clearing point, and the purpose of widening nematic range and/or adjusting .DELTA.n. While the compounds expressed by any one of general formulas (5) to (9) are indispensable particularly when the liquid crystal compositions for STN display mode or ordinary TN display mode are produced, the compounds can be used even when the liquid crystal compositions for TFT are produced. Amount of the compounds to be used is suitably in the range of 1 to 99% by weight, preferably 10 to 97% by weight, and more desirably in the range of 40 to 95% by weight based on the total weight of liquid crystal composition when the liquid crystal compositions for ordinary TN display mode or STN display mode are produced. The steepness of V.sub.th and viewing angle can be improved by using the liquid crystal compositions of the present invention produced by such methods mentioned above for TFT liquid crystal composition display devices. Also, the response speed of liquid crystal display device can be improved by using the compounds of the present invention expressed by general formula (1) since the compounds have a low viscosity. Liquid crystal compositions of the present invention preferably contain at least one liquid crystalline compounds expressed by general formula (1) in an amount of 0.1 to 99% by weight to develop excellent characteristics. Liquid crystal compositions of the present invention are generally produced by conventional methods, for instance, by a method in which each component is mixed to dissolve each other at a high temperature, or each component is dissolved in an organic solvent to mix and then the solvent is distilled off under a reduced pressure. Also, the liquid crystal compositions of the present invention are improved and optimized in accordance with intended use by adding a suitable additive. Such additives are well known in the art and described in literatures in detail. Usually, a chiral dopant or likes which have an effect of causing a helical structure of liquid crystal to adjust a required twisting angle, and avoiding reverse twist are added. Further, the liquid crystal compositions of the present invention can be used as ones for guest-host (GH) mode when a dichroic dye such as merocyanine type, styryl type, azo type, azomethine type, azoxy type, quinophthalone type, anthraquinone type, and tetrazine type was added. Liquid crystal compositions of the present invention can be used even as ones for polymer dispersion type liquid crystal display devices (PDLCD) typified by NCAP which is prepared by forming a nematic liquid crystal into a microcapsule or typified by a polymer network liquid crystal display device (PNLCD) which is prepared by forming a polymer of three-dimensional network structure in a liquid crystal; for electrically controlled birefringence (ECB) mode; and for dynamic scattering (DS) mode. While the liquid crystal compositions of the present invention are produced by the methods mentioned above, the following compositions 1 to 21 can be mentioned as examples of the compositions: In the following composition examples, compounds are designated according to the understanding shown in Table 1. That is, left side terminal group is expressed by r-, rO-, rOs-, Vr-, rvs-, or rVsVk- (in which r, s, and k are an integer of 1 or more); bonding group is expressed by 2, E, T, V, or CF20; ring structure is expressed by B, B(F), B(F,F), H, Py, D, or Ch; and right side terminal group is expressed by --F, --CL, --C, --CF3, --OCF3, OCF2H, --w, --Ow, or --EMe (in which w is an integer of 1 or more). The number attached to the compounds of the present invention is the same as that shown in the Examples below. |
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