Liquid crystal composition and liquid crystal display device using the same

Abstract: A liquid crystal composition having a positive dielectric anisotropy contains 20 wt% to 70 wt% of a first liquid crystal material consisting of at least one liquid crystal compound represented by a formula (wherein R₁ represents a linear alkyl group having 2 to 9 carbon atoms and R₂ represents a linear alkyl group or alkoxy group having 2 to 9 carbon atoms), and 30 wt% to 80 wt% of a third liquid crystal material consisting of at least one liquid crystal compound in which a value of a dielectric anisotropy Δε is negative or substantially "0". The liquid crystal composition optionally contains 10 wt% or less of a second liquid crystal material con­ sisting of at least one liquid crystal compound having a positive dielectric anisotropy Δε. A liquid crystal display device is arranged such that the liquid crystal composition is interposed between a pair of substrates on which electrodes are formed.

Description: The present invention relates to a liquid crystal composition suitable for multiplex drive and a liquid crystal display device using the same. A liquid crystal display apparatus having a plurality of pixels arranged in a matrix manner is applied to a display unit of a computer terminal, an image display unit of a television receiver, and the like. Recently, a demand has arisen for a large size and high image quality of the image display unit. Therefore, an increase in number of pixels and an improvement in contrast are desired. A liquid crystal display apparatus applied to the image display unit has a simple matrix type twisted nematic liquid crystal display device (to be referred to as a matrix TN. LC. device) arranged such that a plurality of electrodes are aligned on inner surfaces of a pair of opposing substrates and opposing portions of the electrodes form a plurality of pixels aligned in a matrix manner. The matrix TN. LC. device is driven in a multiplexed manner. In the matrix TN. LC. device, if the number of pixels is increased in order to improve the resolution and increase a display area, the number of scanning lines is naturally increased. Therefore, high multiplex drive must be performed. However, if a multiplexing degree is increased, a difference in effective voltages between an on electric field to be applied to a liquid crystal to turn on pixels and an off electric field to be applied to the liquid crystal to turn off the pixels is reduced. As a result, an operating margin of a drive voltage is reduced, the contrast is lowered, and a viewing angle characteristic is degraded. The operating margin and the contrast of a liquid crystal display device depend on a voltage-luminance characteristic. That is, when a change in transmittivity with respect to a change in intensity of the electric field to be applied to the liquid crystal is steep, the operating margin can be increased, and the contrast can be increased. As shown in Fig. 1, the steepness of the voltage-luminance characteristic is represented by a ratio (to be referred to as γ value hereinafter) between voltage V 50 at which the transmittivity is 50% and threshold voltage V C . When the γ value becomes closer to 1, the change in transmittivity becomes steeper. Therefore, the operating margin can be increased, and the contrast can be increased. In addition, in the matrix TN. LC. device which is of high multiplex drive type, a multiplexing degree is increased, and one selection period is shortened. Therefore, the matrix TN. LC. device must respond at high speed. As described above, the matrix TN. LC. device of high multiplex drive must have: (1) a γ characteristic close to 1; (2) a wide viewing angle; and (3) a high response speed. The γ characteristic is studied by M. Schadt et al. According to their studies, the γ value representing the steepness of the voltage-luminance characteristic is given by the following equation (I) and coincides well with the characteristic of an actual device: γ = V 50 /V C = [2.044 - 1.044/(1 + K 33 /K 11 )]· {(1 + 0.123[(Δε/ε⊥) 0.6 - 1]}· [1 + 0.132ℓn(Δn·d/2λ)] where V 50 : the applied voltage when a transmittivity of 50% is obtained V C : the threshold voltage K 11 : the splay elastic constant of the liquid crystal K 33 : the bending elastic constant of the liquid crystal Δε : the dielectric anisotropy of the liquid crystal ε⊥ : the dielectric constant in a direction perpendicular to a liquid crystal molecular axis Δn : the optical anisotropy of the liquid crystal d : the liquid crystal layer thickness λ : the wavelength of light According to equation (I), it is apparent that when the first, second, and third terms of equation (I) are close to 1, the γ value is close to 1. Therefore, in order to improve the γ value characteristic, the following conditions must be simultaneously satisfied: (a) a ratio (to be referred to as elastic constant ratio K 33 /K 11 hereinafter) of bending elastic constant K 33 to splay elastic constant K 11 is small; (b) a ratio (to be referred to as dielectric ratio Δε/ε⊥ hereinafter) of dielectric anisotropy Δε to the dielectric constant in a direction perpendicular to the liquid crystal molecular axis; and (c) a value of product Δn·d of liquid crystal optical anisotropy Δn and liquid crystal layer thickness d is 1.1 (µm) when a wavelength of incident light is 550 nm. Dependency (to be referred to as a viewing angle characteristic hereinafter) of the contrast to an observing direction is studied by Mr. G. BAUR and reported in "The Influence of Material and Device Parameters on the Optical Characteristics of Liquid Crystal Displays", Molecula Crystals and Liquid Crystals, Volume 63, Nos. 1 to 4, 1981. According to this report, the viewing angle characteristic depends on liquid crystal layer thickness d and liquid crystal optical anisotropy Δn of a liquid crystal. That is, in a liquid crystal display device having large product Δn·d (to be referred to as Δn·d hereinafter) of layer thickness d and optical anisotropy Δn, an apparent change rate of Δn·d obtained when the liquid crystal display device is viewed from its front and in an oblique direction is large, resulting in a poor viewing angle characteristic. To the contrary, a liquid crystal display device having small Δn·d has a good viewing angle characteristic. In addition, when liquid crystal display devices having equal Δn·d are compared, a better viewing angle characteristic is obtained with smaller optical anisotropy Δn of the liquid crystal. That is, a better viewing angle characteristic is obtained when a change in contrast with respect to a change in observing direction is small. Therefore, in order to improve the viewing angle characteristic: (d) Δn·d must be reduced; and (e) Δn must be reduced. As for the response characteristic, response time t ON required for turning on the liquid crystal display device and response time t OFF required for turning off the liquid crystal display device are represented by the following logic equations (II) and (III), respectively, and coincide well with measurement values: t ON = η/(ε 0 ΔεE 2 - Kq 2 ) tOFF = η/Kq 2 where q = π/d, K = K 11 + [(K 33 - 2K 22 )/4] η : viscosity ε 0 : dielectric constant in vacuum E : electric field intensity K 22 : torsional (twist) elastic constant According to equations (II) and (III), the response speed depends on viscosity η and electric field intensity E. That is, in order to increase the response speed: (f) viscosity η must be reduced; and (g) the electric field intensity must be increased. Therefore, in order to obtain a steep γ characteristic, the conventional liquid crystal display device has been designed to satisfy condition (c) concerning Δn·d of conditions (a) to (c). That is, a value of Δn·d is set to be 1.1 (µm) because the center of a wavelength range of a visual light beam is about 550 nm. However, conditions (a) and (b) are not sufficiently taken into consideration. The reasons for this are as follows. That is, in order to reduce Δε/ε⊥ of condition (b), a value of Δε may be reduced. In this case, however, a response speed is reduced. In addition, since a liquid crystal composition in which K 33 /K 11 of condition (a) is reduced has high viscosity, a smectic phase is easily generated. As a result, the response speed is reduced, and an operation temperature range is narrowed. Optical anisotropy Δn of the conventional liquid crystal composition generally falls within the range of 0.13 to 0.16. Therefore, if the Δn·d value is set to be 1.1 (µm), liquid crystal layer thickness (interelectrode gap) d falls within the range of 7.0 to 8.8 (µm). In this case, since layer thickness d is large, the intensity of an electric field is reduced to reduce the response speed. In addition, a viewing angle characteristic is poor because Δn·d is large. In order to increase the response speed, a liquid crystal composition used in the above conventional liquid crystal display device has a cyano group at its terminal end. In this liquid crystal composition, a large amount of a liquid crystal compound in which a value of dielectric anisotropy Δε is largely positive is mixed to increase the dielectric anisotropy Δε value of the liquid crystal composition. In addition, a large amount of a liquid crystal compound having a large optical anisotropy Δn value is mixed to increase an optical anisotropy Δn value of the liquid crystal composition. Furthermore, a value of liquid crystal layer thickness d of the liquid crystal display device is reduced to increase the electric field intensity, and the value of Δn·d is set to be 1.1 (µm) (λ = 550 nm) to obtain a good γ characteristic, i.e., high contrast and a large operating margin. In conventional liquid crystal compositions an alkyl-alkoxy-pyrimidin compound having a high molecular weight and a high clearing point (c.p.) is used as one component of the composition (EP-A-0 151 446; EP-A-0 137 210; EP-A-0174 541). However, in the above conventional liquid crystal composition, the Δε/ε⊥ value is, e.g., 1.1 or more because the value of ε⊥ is small. In addition, in order to prevent low viscosity and a smectic phase, a mixing ratio of a liquid crystal compound with which a low-viscosity liquid crystal and a stable smectic phase can be obtained is increased. Therefore, the value of elastic constant ratio K 33 /K 13 is, e.g., 1.2 to 1.3 or more. As described above, since the conventional liquid crystal composition has large Δε/ε⊥ and K 33 /K 11 values, it is difficult to improve the γ characteristic of the liquid crystal display device using this liquid crystal composition. In addition, since the Δn·d value is large, it is difficult to improve the viewing angle characteristic. The present invention has been made in consideration of the above situation and has as its object to provide a liquid crystal composition having small elastic constant ratio K 33 /K 11 and dielectric ratio Δε/ε⊥ in order to improve a γ characteristic, a viewing angle characteristic, and/or a response speed of a liquid crystal display device which is driven in a multiplex manner and to provide a liquid crystal display device using the above liquid crystal composition. In order to achieve the above object of the present invention, a liquid crystal composition according to the present invention comprises: 20 wt% to 70 wt% of a first liquid crystal material consisting of at least one liquid crystal compound represented by formula (wherein R 1 represents a linear alkyl group having 2 to 9 carbon atoms and R 2 represents a linear alkyl group or alkoxy group having 2 to 9 carbon atoms); 30 wt% to 80 wt% of a third liquid crystal material consisting of at least one liquid crystal compound in which a value of a dielectric anisotropy Δε is negative or substantially "0"; and optionally, not more than 7% wt% of a second liquid crystal material consisting of at least one liquid crystal compound having a positive dielectric anisotropy Δε, wherein the first liquid crystal material contains at least one liquid crystal compound of formula (I) in which R 1 and R 2 represent the linear alkyl group, respectively, with R 1 and R 2 having a total of 10 or less carbon atoms, and at least one liquid crystal compound of formula (I) in which R 1 represents the linear alkyl group and R 2 represents the linear alkoxy group, and the entire liquid crystal composition has a dielectric ratio Δε/ε⊥ smaller than 0.5, and an elastic constant ratio K 33 /K 11 smaller than 0.8. and a liquid crystal display device according to the present invention comprises: a pair of substrates having electrodes, inner surfaces of which oppose each other; and the liquid crystal composition of the present invention interposed between the pair of substrates. A mixing ratio of a pyrimidine liquid crystal compound having large splay elastic constant K 11 and small elastic constant ratio K 33 /K 11 is large in the liquid crystal composition of the present invention. Therefore, the value of elastic constant ratio K 33 /K 11 of the entire liquid crystal composition is small. In addition, in the liquid crystal composition of the present invention, a pyrimidine liquid crystal compound in which the value of dielectric anisotropy Δε is slightly positive and a low-viscosity liquid crystal compound and a high-temperature liquid crystal compound in which the value of dielectric constant ε⊥ in a direction perpendicular to a liquid crystal molecular axis is large and the value of dielectric anisotropy Δε is negative or substantially 0 are mixed. A liquid crystal compound in which the value of dielectric anisotropy Δε is largely positive is not mixed at all or mixed in a very small amount if necessary. Therefore, the liquid crystal composition of the present invention has small dielectric ratio Δε/ε⊥ and low viscosity. In the liquid crystal display device using the liquid crystal composition of the present invention, since elastic constant ratio K 33 /K 11 and dielectric ratio Δε/ε⊥ are small, the best γ characteristic can be obtained when the value of Δn·d is smaller than 1.1. As a result, high contrast, a large operating margin, and a high response speed can be obtained. In addition, since the value of Δn·d is small, the viewing angle characteristic can be improved. Furthermore, the response speed can be improved because liquid crystal layer thickness d can be reduced. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a graph showing a luminance-voltage characteristic for defining a γ characteristic of a liquid crystal display device; Fig. 2 is a sectional view showing a liquid crystal display device using a liquid crystal composition of the present invention; Fig. 3 is a schematic exploded perspective view showing a structure of the liquid crystal display device shown in Fig. 2; Figs. 4A and 4B are views for explaining a relationship between orienting directions of oriented films and directions of polarizing axes of polarizing plates of the liquid crystal display device shown in Fig. 2; and Fig. 5 is a perspective view for defining a viewing angle characteristic. A preferred embodiment of a liquid crystal composition according to the present invention will be described in detail below. A liquid crystal composition of the present invention mainly consists of a pyrimidine liquid crystal compound in which the value of elastic constant ratio K 33 /K 11 is small and the value of dielectric anisotropy Δε is 0 or slightly positive. In addition, at least one of a high-temperature liquid crystal for widening a temperature range showing a nematic phase, a low-viscosity liquid crystal for reducing a viscosity, and the like as an N n liquid crystal compound in which the value of dielectric anisotropy Δε is substantially 0 or negative is mixed in the liquid crystal composition such that dielectric anisotropy Δε of the entire composition becomes a positive value smaller than 3. Alternatively, the liquid crystal composition of the present invention can be achieved by mixing, in addition to the above composition, a small amount of an N p liquid crystal in which the value of dielectric anisotropy Δε is largely positive such that dielectric anisotropy Δε of the entire composition becomes positive. The values of elastic constant ratio K 33 /K 11 and dielectric ratio Δε/ε⊥ of the liquid crystal composition mixed as described above can be reduced by using a large amount of a liquid crystal compound having very large splay elastic constant K 11 and mixing a large amount of a liquid crystal compound having very large dielectric constant ε⊥ in a direction perpendicular to a liquid crystal molecular axis. In addition, according to a liquid crystal display device using a liquid crystal composition having small elastic constant ratio K 33 /K 11 and dielectric ratio Δε/ε⊥ such as the liquid crystal composition of the present invention, the best γ characteristic can be obtained by a range of Δn·d not satisfying equation (I). As a result, excellent characteristics such as high contrast, a large operating margin, a wide viewing angle characteristic, and a high response speed can be obtained. The liquid crystal composition of the present invention will be described in more detail below. The pyrimidine liquid crystal compound has an alkyl or alkoxy group at its terminal end. The value of elastic constant ratio K 33 /K 11 of the compound is as small as about 0.55, and the value of K 11 is as large as 18 × 10 -12 . An example of such a liquid crystal compound is a compound represented by formula (I), and its physical characteristics are summarized in Table 1 below: (wherein R 1 represents a linear alkyl group having 2 to 9 carbon atoms and R 2 represents a linear alkyl group or alkoxy group having 2 to 9 carbon atoms.) In a liquid crystal compound represented by formula (I), dielectric anisotropy Δε is slightly positive. At least one of such compounds is mixed to prepare a first liquid crystal. The N p liquid crystal compound has a cyano group at its terminal end and large positive dielectric anisotropy Δε. Examples of the N p liquid crystal compound are pyrimidine, phenylcyclohexane, dioxane, and biphenyl liquid crystal compounds. In these liquid crystal compounds, since the value of Δε is as very large as 10 to 30, the value of dielectric anisotropy Δε of the liquid crystal composition becomes positive. Physical characteristics of these compounds are summarized in Table 2 below. Liquid crystal compounds as listed in Table 2 can be used as the N p liquid crystal compound. (wherein R 3 represents a linear alkyl group having 4 to 7 carbon atoms, R 4 represents a propyl group, R 5 represents a linear alkyl group having 3 to 5 carbon atoms. Of the liquid crystal compounds listed in Table 2, a pyrimidine liquid crystal compound represented by formula (II) has small elastic constant ratio K 33 /K 11 and therefore is effective to reduce the value of elastic constant ratio K 33 /K 11 of the entire liquid crystal composition. At least one of the liquid crystal compounds listed in Table 2 is used to prepare a second liquid crystal material. Examples of the N n liquid crystal compound are estercyclohexane, phenylcyclohexane, and biphenylcyclohexane liquid crystal compounds. These compounds consist of a low-viscosity liquid crystal compound for adjusting viscosity, a high-temperature liquid crystal compound for widening a temperature range showing a nematic phase, and the like. Examples of the low-viscosity liquid crystal compound are those having a viscosity of 20 to 10 or less as listed in Table 3 together with their physical characteristics. (wherein R 7 represents a linear alkyl group having 2 to 5 carbon atoms, R 8 represents a linear alkyl group or alkoxy group having 1 to 5 carbon atoms, R 9 represents an alkyl group having 3 to 5 carbon atoms, R 10 represents a linear alkyl group or alkoxy group having 1 to 4 carbon atoms, R 25 represents a propyl group, and R 26 represents an ethoxy group.) Of the above liquid crystal compounds listed in Table 3, a liquid crystal compound represented by formula (VI) has a very large ⊥ε value and therefore is effective to reduce the value of Δε/ε⊥. Since any of the above liquid crystal compounds has a small Δn value, the Δn value of the liquid crystal composition is not increased. Examples of the high-temperature liquid crystal compound are liquid crystal compounds in which a dislocation temperature between a nematic phase and an isotropic liquid and a C.P. temperature (clearing point temperature) are about 60°C to 190°C as listed in Table 4 together with their physical characteristics. (wherein R 11 represents a propyl group, each of R 12 and R 13 independently represents a linear alkyl group having 4 or 5 carbon atoms, R 14 represents a linear alkyl group having 5 to 7 carbon atoms, R 15 represents a propyl group, R 16 represents a linear alkyl group having 1 to 3 carbon atoms, R 17 represents a linear alkyl group having 3 to 5 carbon atoms, R 18 represents an alkoxy group having 1 or 2 carbon atoms, R 19 represents a pentyl group, R 20 represents an ethyl group, R 21 represents a linear alkyl group having 3 or 4 carbon atoms, R 22 represents a linear alkyl group having 3 to 5 carbon atoms, R 23 represents a linear alkyl group having 3 or 4 carbon atoms, and R 24 represents a linear alkyl group having 2 to 4 carbon atoms.) At least one of the liquid crystal compounds listed in Tables 3 and 4 is used to prepare-a third liquid crystal material. The liquid crystal composition of the present invention is achieved by mixing at least the first and third liquid crystal materials of the first, second, and third liquid crystal materials. In order to effectively reduce elastic constant ratio K 33 /K 11 , 20 wt% or more of the first liquid crystal material is mixed. However, if only the first liquid crystal material is used, the viscosity is increased too high, and an operation temperature range is narrowed. Therefore, 30 wt% or more of the third liquid crystal material is mixed. That is, 20 to 70 wt% of the first liquid crystal material is mixed. The compound of formula (I) in which R 1 and R 2 represent the alkyl groups is mixed in an amount of 4 wt% to 30 wt%. Preferably, mixing ratios of the first and third liquid crystal materials are 24 to 54 wt% and 46 to 76 wt%, respectively. In this case, the third liquid crystal material essentially consists of at least one liquid crystal compound represented by formula (VI) and at least one liquid crystal compound represented by at least one of formulas (VIII), (IX), (X), and (XI) and optionally consists of a liquid crystal compound represented by formula (VII). Preferable mixing ratios of the liquid crystal compounds represented by formulas (VI), (VII), (VIII), (IX), (X), and (XI) are 8 to 60 wt%, 15 to 22 wt%, 12 to 18 wt%, 4 to 8 wt%, 7 to 25 wt%, and 2 to 4 wt%, respectively. More preferably, the third liquid crystal material is prepared by mixing at least one liquid crystal compound represented by formula (VI) and at least one liquid crystal compound represented by formula (VIII), and if necessary, a liquid crystal compound represented by formula (IX) having a large negative Δε value. In this case, mixing ratios of the liquid crystal compounds represented by formulas (I), (VI), (VIII), and (IX) are 26 to 30 wt%, 50 to 60 wt%, 12 to 18 wt%, and 8 wt% or less, respectively. In the third liquid crystal material, in addition to the liquid crystal compound represented by formula (VI), a liquid crystal compound represented by formula (X), and if necessary, a liquid crystal compound represented by formula (VII) having low viscosity and a liquid crystal compound represented by formula (XI) having a large Δn value are mixed. In this case, mixing ratios of the liquid crystal compounds represented by formulas (I), (VI), (X), (VII), and (XI) are preferably 42 to 54 wt%, 12 to 35 wt%, 7 to 25 wt%, 22 wt% or less, and 4 wt% or less, respectively. The liquid crystal composition of the present invention is achieved by mixing the first liquid crystal material for reducing elastic constant ratio K 33 /K 11 , the second liquid crystal material for obtaining a positive dielectric anisotropy Δε of the entire liquid crystal composition, and the third liquid crystal material for reducing the viscosity and widening an operation temperature range. In this case, a mixing ratio of the first liquid crystal material is set to be 20 to 65 wt% in order to obtain a sufficient effect for reducing elastic constant ratio K 33 /K 11 , that of the second liquid crystal material is set to be 7 wt% or less so that the value of dielectric anisotropy Δε is not unnecessarily increased to reduce the Δε/ε⊥ value, and that of the third liquid crystal material is set to be 30 to 75 wt%. As the second liquid crystal material, it is preferable to use a liquid crystal compound represented by formula (II) having a cyano group at its terminal end because a pyrimidine liquid crystal compound has small elastic constant ratio K 33 /K 11 . In this case, a mixing ratio of the liquid crystal compound represented by formula (II) is preferably 5 wt% or less. The third liquid crystal material is prepared by mixing at least one of the liquid crystal compounds represented by formulas (VI), (VII), and (XV) and at least one of the liquid crystal compounds represented by formulas (VIII), (IX), (X), (XI), and (XIV). Mixing ratios of the liquid crystal compounds represented by formulas (VI), (VII), (VIII), (IX), (X), (XI), (XIV), and (XV) are 6 to 62 wt%, 8 to 27 wt%, 10 to 20 wt%, 3 to 22 wt%, 2 to 25 wt%, 1 to 22 wt%, 5 to 12 wt%, and 15 to 20 wt%, respectively. That is, in the third liquid crystal material, a liquid crystal compound represented by formula (VI) and/or a liquid crystal compound represented by formula (VII), and a liquid crystal compound represented by formula (X) and/or a liquid crystal compound represented by formula (XI) are preferably mixed. Of the liquid crystal compounds represented by formulas (VI) and (VII), when only a liquid crystal compound represented by formula (VI) is used, liquid crystal compounds represented by formulas (VIII) and (IX) or those represented by formulas (X) and (XI) are selectively mixed. When both of the liquid crystal compounds represented by formulas (VI) and (VII) are used, liquid crystal compounds represented by formulas (VIII) and (IX), that represented by formula (X), or those represented by formulas (X) and (XI) are mixed. In addition, liquid crystal compounds represented by formulas (IX), (X), and (XI), and if necessary, that represented by formula (XIV) are selectively mixed. Mixing ratios of the liquid crystal compounds represented by formulas (VI), (VII), (VIII), (IX), (X), (XI), and (XlV) are preferably 6 to 60 wt%, 8 to 27 wt%, 10 to 20 wt%, 3 to 22 wt%, 2.5 to 22 wt%, 1 to 13 wt%, and 5 to 11 wt%, respectively. More preferably, the mixing ratios of the liquid crystal compounds represented by formulas (X), (XI), and (XIV) are 2.5 to 22 wt%, 1 to 13 wt%, and 5 to 11 wt%, respectively. When the mixing ratio of the second liquid crystal material represented by formula (II) is 5 to 7 wt%, those of the liquid crystal material represented by formula (I) and the liquid crystal compounds represented by formulas (VI) and (VII) are preferably 20 to 30 wt%, 30 to 45 wt%, and 14 to 20 wt%, respectively. In addition, it is preferable to selectively mix 10 to 21 wt% and 5 to 11 wt% of the liquid crystal compounds represented by formulas (IX) and (XIV), respectively. When a liquid crystal compound represented by formula (III) is used in the second liquid crystal material, the third liquid crystal material is prepared by mixing liquid crystal compounds represented by formulas (VI), (VII), and (VIII). Mixing ratios of the first and second liquid crystal materials represented by formulas (I) and (III) are preferably 20 to 32 wt% and 3 to 7 wt%, respectively, and those of the liquid crystal compounds represented by formulas (VI), (VII), and (VIII) of the third liquid crystal material are preferably 42 to 52 wt%, 8 wt% or less, and 18 to 25 wt%, respectively. When a liquid crystal compound represented by formula (IV) is used as the second liquid crystal material, the third liquid crystal material is prepared by selectively mixing liquid crystal compounds represented by formulas (VI), (VIII), (X), (XII), and (XIV) in the liquid crystal compound represented by formula (VII). Mixing ratios of the first and second liquid crystal materials are preferably 40 to 45 wt% and 2 to 7 wt%, respectively, and that of the liquid crystal compound represented by formula (VII) of the third liquid crystal material is preferably 20 to 22 wt%. In addition, it is preferable to mix 10 to 12 wt%, substantially 19 wt%, 18 to 22 wt%, substantially 2 wt%, and substantially 10 wt% of the liquid crystal compounds represented by formulas (VI), (VIII), (X), (XII), and (XIV), respectively. [Examples] The liquid crystal composition of the present invention will be described in detail below by way of its examples. 6 Examples 1 to 6 prepared by mixing only the first and third liquid crystal materials are listed in Table 5. In Table 5, MIX-11 and MIX-12 are mixtures of a plurality of liquid crystal compounds represented by formula (I) in Table 6. In compositions of Examples 1 to 4, low-viscosity liquid crystal compounds represented by formulas (VI) and (VII) and a high-temperature liquid crystal compound represented by formula (X) are mixed as the third liquid crystal material, and a liquid crystal compound represented by formula (XI) having a large optical anisotropy Δn value is selectively mixed in order to adjust Δn of the composition. Since the liquid crystal compound represented by formula (VII) has very low viscosity, the viscosity of the composition can be significantly reduced. In a composition of Example 5, a large amount of a liquid crystal compound represented by formula (VI) having a large ε⊥ value is mixed as the third liquid crystal material, and a liquid crystal compound represented by formula (XI) having large Δn is mixed as the high-temperature liquid crystal compound. Therefore, the liquid crystal composition of Example 5 has a large Δn value and a small Δε/ε⊥ value. The liquid crystal compositions of Examples 1 to 5 have positive dielectric anisotropy Δε values because the liquid crystal compounds represented by formula (I) used in the first liquid crystal material have positive dielectric anisotropy Δε values. Examples 6 to 29 exemplify compositions of the present invention prepared by mixing the first, second, and third liquid crystal materials. In Examples 6 to 29, MIX-21 is a mixture of three pyrimidine liquid crystal compounds as shown in Table 7, MIX-22 is a mixture of three dioxane liquid crystal compounds as shown in Table 8, and MIX-31 is a mixture of seven ester-cyclohexane liquid crystal compounds as shown in Table 9. Examples 6 to 24 in which a pyrimidine liquid crystal compound having a cyano group at its terminal end is used as the second liquid crystal material are listed in Tables 10 to 13. In Examples 6 and 7, liquid crystal compounds represented by formulas (VI), (VII), (VIII), (IX), and (XIV) are selectively mixed as the third liquid crystal compound. In Example 6, a mixing ratio of the liquid crystal material represented by formula (XIV) in which dielectric anisotropy Δε is negatively large is increased, and that of the second liquid crystal material is relatively increased accordingly. In Example 7 to 17, a mixing ratio of the liquid crystal compound represented by formula (VI) used as the third liquid crystal material and having a large ε⊥ value is increased to reduce the Δε/ε⊥ value. In Examples 8 to 13 listed in Table 11, liquid crystal compounds represented by formulas (VI), (VII), and (X) are mixed as the third liquid crystal material. Since the liquid crystal compound represented by formula (VII) has very low viscosity, a low-viscosity liquid crystal composition can be prepared. In Examples 14 to 19 listed in Table 12, liquid crystal compounds represented by formulas (VI), (VII), (X), and (XI) are mixed as the third liquid crystal material at different mixing ratios. In these examples, optical anisotropy Δn of the resultant a composition is relatively large because the liquid crystal compound represented by formula (XI) having large optical anisotropy Δn is mixed. In Examples 20 to 24 listed in Table, the liquid crystal compounds represented by formulas (VI), (VII), (VIII), (IX), (X), (XI), and (XV) are selectively mixed as the third liquid crystal material. In these liquid crystal compositions, optical anisotropy Δn, the viscosity, and dielectric anisotropy Δε are adjusted. Examples in which a phenylcyclohexane liquid crystal compound having a cyano group at its terminal end is used as the second liquid crystal material are listed in Table 14. In Examples 25 to 27, a liquid crystal compound represented by formula (III) is used as the second liquid crystal material, and liquid crystal compounds represented by formulas (VI), (VII), and (VIII) are mixed as the third liquid crystal material at different mixing ratios. Since the liquid crystal compound represented by formula (III) used as the second liquid crystal material has lower viscosity than those of the liquid crystal compounds represented by formulas (II) and (IV), the viscosities of the liquid crystal compositions can be reduced. Examples using a dioxane liquid crystal compound having a cyano group at its terminal end as the second liquid crystal material are listed in Table 15. In Examples 28 and 29, a liquid crystal compound represented by formula (IV) is used as the second liquid crystal material, and liquid crystal compounds represented by formulas (VI), (VII), (VIII), (X), (XII), and (XIV) are selectively mixed as the third liquid crystal material. The liquid crystal compound represented by formula (IV) used as the second liquid crystal material has a larger Δε value than those of the other liquid crystal compounds used as the second liquid crystal material. As the second liquid crystal material, a plurality of liquid crystal compounds having different chemical structures may be used. In Examples 1 to 29 described above, a relatively large amount of a pyrimidine liquid crystal compound represented by formula (I) having a small elastic constant ratio K 33 /K 11 value is mixed. Therefore, elastic constant ratios of the liquid crystal compositions of these examples are less than 1.0. In addition, in these examples, a relatively large amount of a liquid crystal compound represented by formula (I) in which the dielectric anisotropy Δε is positively small is mixed or a mixing ratio of the second liquid crystal material. in which the dielectric anisotropy is positively large is very small, and the liquid crystal compounds in which dielectric anisotropy Δε is negative or almost 0 are mixed in the third liquid crystal material. Therefore, Δε/ε⊥ values of the liquid crystal compositions of the above examples are 0.5 or less. Of the above examples, physical characteristics of the main compositions are summarized in Table 16 below. The liquid crystal composition of the present invention is used in a multiplex drive twisted nematic liquid crystal display device as shown in Figs. 2 and 3. This liquid crystal display device is arranged as follows. In Figs. 2 and 3, a plurality of first electrodes 2 which vertically extend in Fig. 3 are arranged on lower substrate 1 consisting of a transparent glass plate or an optically isotropic plastic plate. Aligning film 3 which is subjected to an aligning treatment is formed to cover the substrate surface on which electrodes 2 are arranged. A plurality of second electrodes 5 which extend in a transverse direction in Fig. 3 are arranged on upper substrate 4 consisting of a material similar to that of lower substrate 1. Aligning film 6 which is subjected to an aligning treatment is formed to cover the substrate surface on which second electrodes 5 are arranged. Lower and upper substrates 1 and 4 oppose each other with a predetermined interval therebetween such that the surfaces on which first and second electrodes 2. and 5 are formed face inward, and are adhered by sealing member 7. Nematic liquid crystal 8 to be described below is sealed between substrates 1 and 4. Nematic liquid crystal 8 forms a liquid crystal layer having thickness d between first and second electrodes 2 and 5. A pair of polarizing plates 9 and 10 are arranged on the outer surfaces of substrates 1 and 4, respectively. Figs. 4A and 4B show an orienting direction of aligning films 3 and 6 and a direction of polarizing axes of polarizing plates 9 and 10. Films 3 and 6 formed on the electrode-formed surfaces of lower and upper substrates 1 and 4 are rubbed as shown in Fig. 4A. That is, film 3 on substrate 1 is rubbed in orienting direction 11 indicated by a broken arrow, and film 6 on substrate 4 is rubbed in orienting direction 12 indicated by a solid arrow which crosses direction 11 at substantially 90°. In this manner, nematic liquid crystal 8 sealed between substrates 1 and 4 rubbed in directions separated by substantially 90° is subjected to twisted alignment in which liquid crystal molecules are twisted through substantially 90°. As shown in Fig. 4A, polarizing axis 13 (indicated by the broken arrow) of lower polarizing plate 9 and polarizing zxis 14 (indicated by the solid arrow) of upper polarizing plate 10 are substantially parallel to each other and to direction 12 of film 6 formed on substrate 4. Note that as shown in Fig. 4B, polarizing axes 13 and 14 of plates 9 and 10 may be substantially parallel to each other and to direction 11 of film 3 formed on substrate 1. As shown in Fig. 3, in the above liquid crystal display device, terminals 2a of first electrodes 2 extending from an end portion of lower substrate 1 are connected to driver 16 through lead lines 15, and terminals 5a of second electrodes 5 extending from an end portion of upper substrate 4 are connected to driver 16 through lead lines 17. In the liquid crystal display device having the above arrangement, electrodes 2 formed on substrate 1 constitute column electrode 18, and electrodes 5 formed on substrate 4 constitute row electrode 19. Each portion at which column electrode 18 crosses row electrode 19 through the nematic liquid crystal forms a pixel. A scanning signal for applying a voltage sequentially to electrodes 5 is supplied from driver 16 to row electrode 19, and a data signal corresponding to image data is supplied to electrodes 2 of column electrode 18 in synchronism with the scanning signal. In this manner, an electric field is applied to the nematic liquid crystal at a portion at which row electrode 19 crosses column electrode 18 to activate liquid crystal molecules, thereby controlling an on/off state of each pixel. That is, this liquid crystal display device is driven in a multiplex manner. The liquid crystal compositions of the present invention were used in the above liquid crystal display device, and electrooptical characteristics of the liquid crystal display device were measured. Tables 22 and 23 show the electrooptical characteristics of the liquid crystal display device using the main liquid crystal compositions of the examples of the present invention. In Table 22, optical anisotropy Δn is a measured value obtained when λ = 589 nm, and the contrast is a maximum value of a value (Y ON /Y OFF ) obtained by dividing value Y ON of transmittivity in an ON state when the device was driven by a drive signal of 1/64 duty by value Y OFF of transmittivity in an OFF state in each viewinq anqle direction. Threshold voltage V th is an applied voltage when a maximum contrast is obtained. The response speed is defined as (T r + T D )/2 assuming that a rise time required for the luminance to reach from 10% to 90% is T r and a decay time required for the luminance to reach from 90% to 10% is T D . The viewing angle characteristic is defined as V th ( = 30°)/V th ( = 10°) or V th ( = -10°)/V th ( = 10°) at a temperature of 25°C assuming that a threshold voltage observed from direction P inclined through 10° from the Z axis perpendicular to the substrate surface of liquid crystal display device A toward a viewing angle direction is V th ( = 10°) and a threshold voltage observed from direction Q inclined from the Z axis toward a direction opposite to the viewing angle direction is V th ( = -10°). Note that the viewing angle characteristic is better when its value is closer to 1, i.e., the viewing angle is wider. As is apparent from Tables 17 and 18, the contrast values obtained when the viewing angle is 10° are 11 to 26, and the response speeds are 63 msec or less. The viewing angle characteristics obtained when the viewing angle is in a -10° direction are 1.15 or less, and those obtained when the viewing angle is in a 30° direction are 0.921 or more. In each of the above liquid crystal display devices, a product value Δn·d of liquid crystal layer thickness d and the optical anisotropy of the liquid crystal composition is set to be a value smaller than 1.1. That is, the Δn·d values of the liquid crystal display devices are 0.51 to 0.76. In this manner, the liquid crystal display devices having good contrast can be obtained with the Δn·d values different from 1.1. As in the present invention, a liquid crystal display device using a liquid crystal composition having small elastic constant ratio K 33 /K 11 and Δε/ε⊥ values provides better electrooptical characteristics when the elastic constant ratio K 33 /K 11 value is smaller than 0.8 and the dielectric ratio Δε/ε⊥ value is smaller than 0.5 as much as possible. More specifically, in a liquid crystal composition in which ratio Δε/ε⊥ of dielectric anisotropy Δε to dielectric constant ε⊥ in a direction perpendicular to a liquid crystal molecular axis is small, a change in dielectric constant corresponding to a change in alignment of liquid crystal molecules is small, and a change in equivalent impedance of the liquid crystal is small. Therefore, since the linearity of the electric field to be applied to the liquid crystal with respect to the voltage to be applied between the electrodes is improved, the contrast is improved. The response speed of the liquid crystal display device is represented by equations (2) and (3) described above. In this case, assuming that: V C = K/ε 0 Δε the following equation (5) is obtained: t ON = η 1 d 2 /π 2 k(V 2 /V C 2 - 1) As is apparent from equations (5) and (3), in the liquid crystal display device of the present invention using a liquid crystal composition in which splay elastic constant K 11 of the nematic liquid crystal is increased to reduce elastic constant ratio K 33 /K 11 , both of rise time t ON and decay time t OFF are reduced to provide a high response speed. The liquid crystal display device having a small Δn·d value provides a better viewing angle characteristic, and its liquid crystal layer thickness d can be reduced. Therefore, the intensity of the electric field to be applied to the liquid crystal composition can be increased to achieve high-speed response. Especially when the above liquid crystal display device is used for displaying a motion picture such an a television image, the response speed must be 30 msec or less. In this case, if the Δn·d values are 0.73, 0.76, and 0.71 as in Examples 8, 13, and 21, respectively, the response speed is reduced. If the Δn·d values are 0.52, and 0.51, respectively, as in Examples 26, and 25 and 27, the contrast is lowered. Therefore, the Δn·d value is set within the range of 0.54 to 0.70. If liquid crystal layer thickness d is large, the response speed is lowered, and the viewing angle characteristic is degraded. Therefore, layer thickness d is set to be 7 (µm) or less. If the optical anisotropy Δn value is large, the viewing angle characteristic is degraded. Therefore, the optical anisotropy Δn value of the liquid crystal composition is set to be 0.14 or less. The liquid crystal display devices using the liquid crystal compositions of the above examples provide high contrast values, better viewing angle characteristics, and high response speeds but have relatively high threshold voltages. This is because in order to reduce dielectric ratio Δε/ε⊥ to be 0.5 or less, the value of Δε of the composition can be increased to at most 3 because the value of ε⊥ of a liquid crystal compound which is normally used is 3 to 5. Therefore, as represented by equation (4), threshold voltage V C is increased when Δε is reduced. High threshold voltage V C increases a voltage of a drive signal for driving the liquid crystal display device. However, the drive signal can be arbitrarily set by a driver. As has been described above, the elastic constant ratio K 33 /K 11 values of the liquid crystal compositions of the present invention are smaller than those of the conventional liquid crystal composition, and their Δε/ε⊥ values are 0.5 or less. Therefore, the multiplex drive liquid crystal display device having better characteristics such as contrast can be obtained with a Δn·d value of less than 1.1. The liquid crystal display device using the liquid crystal composition of the present invention is suitable for use in a matrix display apparatus for displaying characters, figures, and the like using a number of dots. Especially for use in a liquid crystal display device which must respond at high speed in order to display a television image or the like, the liquid crystal composition having low-viscosity and an optical anisotropy Δn value of 0.14 or less is suitable.

Claims: A liquid crystal composition having a positive dielectric anisotropy comprising: 20 wt% to 70 wt% of a first liquid crystal material consisting of at least one liquid crystal compound represented by a formula: (wherein R 1 represents a linear alkyl group having 2 to 9 carbon atoms and R 2 represents a linear alkyl group or alkoxy group having 2 to 9 carbon atoms); 30 wt% to 80 wt% of a third liquid crystal material consisting of at least one liquid crystal compound in which a value of a dielectric anisotropy Δε is negative or substantially "0"; and optionally not more than 7 wt% of a second liquid crystal material consisting of at least one liquid crystal compound having a positive dielectric anisotropy Δε; wherein said first liquid crystal material contains at least one liquid crystal compound of formula (I) in which said R 1 and R 2 represent the linear alkyl group, respectively, with R 1 and R 2 having a total of 10 or less carbon atoms, and at least one liquid crystal compound of formula (I) in which said R 1 represents the linear alkyl group and said R 2 represents the linear alkoxy group, and said entire liquid crystal composition has a dielectric ratio Δε/ε⊥ smaller than 0.5, and an eleastic constant ratio K 33 /K 11 smaller than 0.8. A composition according to claim 1, characterized in that a total of mixing ratios of said first and third liquid crystal materials is 100 wt%, and the dielectric anisotropy Δε value of the entire composition is not more than 3. A composition according to claim 2, characterized in that said third liquid crystal material consists of: 8 wt% to 60 wt% of at least one liquid crystal compound represented by a formula (wherein R 7 represents a linear alkyl group having 3 to 5 carbon atoms and R 8 represents a linear alkyl group or alkoxy group having 1 to 5 carbon atoms); and optionally, at least one liquid crystal compound represented by formulas (wherein R 9 represents a linear alkyl group having 3 to 5 carbon atoms, R 10 represents a linear alkyl group or alkoxy group having 1 to 4 carbon atoms, R 11 represents a propyl group, each of R 12 and R 13 independently represents a linear alkyl group having 4 or 5 carbon atoms, R 14 represents a linear alkyl group having 5 to 7 carbon atoms, R 15 represents a propyl group, R 16 represents a linear alkyl group having 1 to 3 carbon atoms, R 17 represents a linear alkyl group having 3 to 5 carbon atoms, and R 18 represents an alkoxy group having 1 or 2 carbon atoms) and mixed such that mixing ratios of said liquid crystal compounds represented by the formulas (VII), (VIII), (IX), (X), and (XI) are 15 wt% to 22 wt%, 12 wt% to 18 wt%, 4 wt% to 8 wt%, 7 wt% to 25 wt%, and 2 wt% to 4 wt%, respectively. A composition according to Claim 1, characterized in that at least one liquid crystal compound represented by the formula (I) is mixed at a mixing ratio of 20 to 65 wt% as said first liquid crystal material, said second liquid crystal material consisting of at least one liquid crystal compound represented by the formula (wherein R 3 represents a linear alkyl group having 4 to 7 carbon atoms, and said third liquid crystal material is mixed at a mixing ratio of 30 to 75 wt%. A composition according to Claim 1, characterized in that said first liquid crystal material is mixed at a mixing ratio of 20 wt% to 65 wt%; at least one liquid crystal compound represented by formulas (wherein R 3 represents a linear alkyl group having 4 to 7 carbon atoms, R 4 represents a propyl group and R 5 represents a linear alkyl group having 3 to 5 carbon atoms) is mixed at a mixing ratio of not more than 7 wt% as said second liquid crystal material; and said third liquid crystal material consists of at least one liquid crystal compound represented by formulas (wherein R 11 represents a propyl group, each of R 12 and R 13 independently represents a linear alkyl group having 4 or 5 carbon atoms, R 14 represents a linear alkyl group having 5 to 7 carbon atoms, R 15 represents a propyl group, R 16 represents a linear alkyl group having 1 to 3 carbon atoms, R 17 represents a linear alkyl group having 3 to 5 carbon atoms, R 18 represents a linear alkoxy group having 1 or 2 carbon atoms, R 23 represents a linear alkyl group having 3 or 4 carbon atoms, and R 24 represents a linear alkyl group having 2 to 4 carbon atoms), and optionally, at least one liquid crystal compound represented by formulas (wherein R 7 represents a linear alkyl group having 3 to 5 carbon atoms, R 8 represents a linear alkyl group or alkoxy group having 1 to 5 carbon atoms, R 9 represents a linear alkyl group having 3 to 5 carbon atoms, R 10 represents a linear alkyl group or alkoxy group having 1 to 4 carbon atoms, R 25 represents a propyl group, and R 26 represents an ethoxy group), said third liquid crystal material being mixed at a mixing ratio of 30 wt% to 75 wt%. A composition according to claim 5, characterized in that mixing ratios of said liquid crystal compounds represented by the formulas (VIII), (IX), (X), (XI), and (XIV) are 10 wt% to 20 wt%, 3 wt% to 22 wt%, 2 wt% to 25 wt%, 1 wt% to 22 wt%, and 5 wt% to 12 wt%, respectively, and mixing ratios of said liquid crystal compounds represented by the formulas (VI), (VII), and (XV) are 6 wt% to 62 wt%, 8 wt% to 27 wt%, and 15 wt% to 20 wt%, respectively. A composition according to claim 5, characterized in that at least one liquid crystal compound represented by the formula (II) is mixed at a mixing ratio of 0.5 wt% to 5 wt% as said second liquid crystal material. A composition according to Claim 5, characterized in that at least one liquid crystal compound represented by the formula (I) is mixed at a mixing ratio of 20 wt% to 30 wt% as said first liquid crystal material; at least one liquid crystal compound represented by the formula (II) is mixed at a mixing ratio of more than 5 wt% to not more than 7 wt% as said second liquid crystal material; and said liquid crystal compounds represented by the formulas (VI), (VII), (IX), and (XIV) are mixed at mixing ratios of 30 wt% to 45 wt%, 14 wt% to 20 wt%, 10 wt% to 21 wt%, and 5 wt% to 11 wt%, respectively, as said third liquid crystal material. A composition according to claim 5, characterized in that said third liquid crystal material consists of said liquid crystal compounds represented by the formulas (VI), (VIII), and (IX). A composition according to claim 5, characterized in that said third liquid crystal material consists of said liquid crystal compounds represented by the formulas (VI), (X), and (XI). A composition according to claim 5, characterized in that at least one liquid crystal compound selected from the group consisting of said liquid crystal compounds represented by the formulas (VIII), (IX), (X), (XI), and (XIV) are mixed at mixing ratios of 10 wt% to 20 wt%, 3 wt% to 20 wt%, 2.5 wt% to 22 wt%, 1 wt% to 13 wt%, and 5 wt% to 11 wt%, respectively, and said liquid crystal compounds represented by the formulas (VI) and (VII) are mixed at mixing ratios of 6 wt% to 50 wt% and 8 wt% to 27 wt%, respectively, as said third liquid crystal material. A composition according to claim 11, characterized in that said third liquid crystal material contains said liquid crystal compounds represented by the formulas (VIII) and (IX). A composition according to claim 11, characterized in that said third liquid crystal material contains said liquid crystal compound represented by the formula (X). A composition according to claim 11, characterized in that said third liquid crystal material contains said liquid crystal compounds represented by the formulas (X) and (XI). A composition according to claim 11, characterized in that said third liquid crystal material contains said liquid crystal compounds represented by the formulas (IX), (X), and (XI). A composition according to claim 11, characterized in that said third liquid crystal material contains said liquid crystal compound represented by the formula (VIII). A composition accordin9 to claim 11, characterized in that said third liquid crystal material contains said liquid crystal compound represented by the formula (XIV). A liquid crystal display device comprising: a pair of substrates having electrodes formed such that inner surfaces of said electrodes oppose each other; and a liquid crystal composition interposed between said pair of substrates, said liquid crystal composition comprising: 20 wt% to 70 wt% of a first liquid crystal material consisting of at least one liquid crystal compound represented by a formula: (wherein R 1 represents a linear alkyl group having 2 to 9 carbon atoms and R 2 represents a linear alkyl group or alkoxy group having 2 to 9 carbon atoms); 30 wt% to 80 wt% of a third liquid crystal material consisting of at least one liquid crystal compound in which a dielectric anisotropy Δε value is negative or substantially "0"; and optionally not more than 7 wt% of a second liquid crystal material consisting of at least one liquid crystal compound having a positive dielectric anisotropy Δε; wherein said first liquid crystal material contains at least one liquid crystal compound of formula (I) in which said R 1 and R 2 represent the linear alkyl group, respectively, with R 1 and R 2 having a total of 10 or less carbon atoms, and at least one liquid crystal compound of formula (I) in which said R 1 represents the linear alkyl group and said R 2 represents the linear alkoxy group, and said entire liquid crystal composition has a dielectric ratio Δε/ε⊥ smaller than 0.5, and an elastic constant ratio K 33 /K 11 smaller than 0.8. A device according to Claim 18, characterized in that said liquid crystal composition comprises only said first and third liquid crystal materials and has the dielectric anisotropy Δε value of less than 3. A device according to claim 18, characterized in that said liquid crystal composition comprises: 20 to 65 wt% of said first liquid crystal material; not more than 7 wt% of a second liquid crystal material, said second liquid crystal material consisting of at least one liquid crystal compound represented by the formulas (wherein R 3 represents a linear alkyl group having 4 to 7 carbon atoms, R 4 represents a propyl group and R 5 represents a linear alkyl group having 3 to 5 carbon atoms); and 30 to 75 wt% of a third liquid crystal material, said third liquid crystal material consisting of at least one liquid crystal compound represented by the formulas (wherein R 11 represents a propyl group, each of R 12 and R 13 independently represents a linear alkyl group having 4 or 5 carbon atoms, R 14 represents a linear alkyl group having 5 to 7 carbon atoms, R 15 represents a propyl group, R 16 represents a linear alkyl group having 1 to 3 carbon atoms, R 17 represents a linear alkyl group having 3 to 5 carbon atoms, R 18 represents an alkoxy group having 1 or 2 carbon atoms, R 23 represents a linear alkyl group having 3 or 4 carbon atoms, and R 24 represents a linear alkyl group having 2 to 4 carbon atoms), and optionally, at least one liquid crystal compound represented by formulas (wherein R 7 represents a linear alkyl group having 3 to 5 carbon atoms, R 8 represents a linear alkyl group or alkoxy group having 1 to 5 carbon atoms, R 9 represents a linear alkyl group having 3 to 5 carbon atoms, R 10 represents a linear alkyl group or alkoxy group having 1 to 4 carbon atoms, R 25 represents a propyl group, and R 26 represents an ethoxy group). A composition according to claim 5, characterized in that said liquid crystal composition has a clearing point temperature of 56° C or more. A composition according to claim 1, characterized in that said liquid crystal compound of formula (I) in which said R 1 and R 2 represent the linear alkyl groups, respectively, is contained in a total amount of 4 wt% to 30 wt%.

Inventors: KOZIMA KEN, YOSHIDA TETSUSHI, KOZIMA, KEN, YOSHIDA, TETSUSHI, Kozima, Ken Patent Dep. Dev. Div. Hamura R &amp; D, Yoshida, Tetsushi Pat. Dep. Dev. Div. Hamura R &amp; D
Applicants: CASIO COMPUTER CO LTD, CASIO COMPUTER COMPANY LIMITED
Application year: 1988
Main classification: C09K19
IPC codes: C09K19