Liquid crystal composition and liquid crystal display element

A liquid crystal composition which comprises 1 to 15% of a first component (a compound selected from compounds of the formulae I-a and I-b), 8 to 40% of a second component (a compound of the formula II), 10 to 30% of a third component (a compound of the formula III), and 10 to 45% of a fourth component (a compound selected from compounds of the formulae IV-a, IV-b, IV-c and IV-d) ##STR1## wherein each of R.sup.1, R.sup.2, R.sup.8 and R.sup.12 is a C.sub.1 -C.sub.10 alkyl group, R.sup.3 is a C.sub.1 -C.sub.10 alkyl group or a C.sub.2 -C.sub.10 alkenyl group, each of R.sup.4, R.sup.7 and R.sup.11 is a C.sub.1 -C.sub.10 alkyl group or alkoxy group, each of R.sup.5 and R.sup.9 is a C.sub.2 -C.sub.10 alkenyl group or alkenyloxy group, each of R.sup.6 and R.sup.10 is a C.sub.2 -C.sub.10 alkenyl group, and R.sup.13 is a C.sub.2 -C.sub.10 alkoxyalkyl group.

TECHNICAL FIELD 
The present invention relates to a liquid crystal composition for liquid 
crystal display and a liquid crystal display element using this 
composition. More specifically, it relates to a nematic liquid crystal 
composition for liquid crystal display of a super twisted nematic (STN) 
system and a liquid crystal display element using this composition. 
BACKGROUND ART 
With the development of information equipment, particularly portable 
terminal equipment in recent years, the demand for a small, thin and low 
electric power consumption type display element which can maintain such 
display capacity and display quality as in a conventional CRT has 
increased more and more. Accordingly, liquid crystal display using a super 
twisted nematic (STN) system as a display system has mainly been employed. 
This system has been suggested by T. J. Scheffer et al. in 1984, and it is 
an epoch-making system beyond the limit of a twisted nematic (TN) system 
having a twist angle of 90.degree. which has heretofore widely been used 
as the liquid crystal display system. That is to say, it has been reported 
that, in the STN system, the twist angle is set between 180.degree. and 
270.degree. and the birefringence effect of a liquid crystal cell is 
utilized, whereby a better contrast and a wider view angle than the TN 
system having a twist angle of 90.degree. can be obtained and even if a 
duty number is increased (to 1/480 duty), the deterioration of display 
quality does not occur e.g., refer to T. J. Scheffer et al., Appln. Phys. 
Lett., Vol. 45, p. 1021 (1984)!. 
The characteristics currently required for a liquid crystal material which 
can be used in this STN system are that electro-optic properties are steep 
to obtain a high contrast, that viscosity is low to obtain a high-speed 
response, that the dependence of threshold voltage on temperature is low 
to obtain a uniform display screen without display unevenness due to the 
nonuniform heat distribution of a back light (for the achievement of this 
purpose, an NI transition temperature is required to be high), that 
voltage holding ratio is low to eliminate the display unevenness on the 
display screen due to contaminants taken in during a step such as the 
assembly of a panel and to remove display failure such as a baking (after 
image) phenomenon caused by long-time lighting, and that a d/p margin is 
broad to heighten the yield of panel manufacture (for the achievement of 
this purpose, a pretilt is required to be high). 
DISCLOSURE OF THE INVENTION 
Heretofore, in order to develop a liquid crystal composition having a high 
contrast and a low viscosity, various investigations have been conducted 
(refer to Japanese Patent Application Laid-open No. Hei 5-125363 and the 
like), but it has been difficult to obtain the satisfactory liquid crystal 
composition. Under such circumstances, the present invention has been 
intended, and an object of the present invention is to provide a liquid 
crystal display element which is equipped with a uniform display screen 
having a high contrast and a high-speed response and not having any 
display unevenness and which enables a high manufacture yield. Another 
object of the present invention is to provide a liquid crystal composition 
which can realize the above-mentioned characteristics. 
The present inventors have intensively investigated to solve the 
above-mentioned problems, and as a result, it has been found that a 
specific liquid crystal composition suitable for an STN system can achieve 
these objects. 
A liquid crystal composition of the present invention comprises each of the 
following constitutions. 
(1) A liquid crystal composition which comprises 1 to 15% by weight of at 
least one compound as a first component selected from the group consisting 
of compounds represented by the formulae (I-a) and (I-b), 8 to 40% by 
weight of at least one compound as a second component selected from the 
group consisting of compounds represented by the formula (II), 10 to 30% 
by weight of at least one compound as a third component selected from the 
group consisting of compounds represented by the formula (III), and 10 to 
45% by weight of at least one compound as a fourth component selected from 
the group consisting of compounds represented by the formulae (IV-a), 
(IV-b), (IV-c) and (IV-d), 
said first component being a compound represented by the formula (I-a) 
##STR2## 
wherein R.sup.1 is an alkyl group having 1 to 10 carbon atoms, or a 
compound represented by the formula (I-b) 
##STR3## 
wherein R.sup.2 is an alkyl group having 1 to 10 carbon atoms, said second 
component being a compound represented by the formula (II) 
##STR4## 
wherein R.sup.3 is an alkyl group having 1 to 10 carbon atoms or an 
alkenyl group having 2 to 10 carbon atoms, 
said third component being a compound represented by the formula (III) 
##STR5## 
wherein R.sup.4 is an alkyl group or an alkoxy group having 1 to 10 carbon 
atoms, and R.sup.5 is an alkenyl group or an alkenyloxy group having 2 to 
10 carbon atoms, 
said fourth component being a compound represented by the formula (IV-a) 
##STR6## 
wherein R.sup.6 is an alkenyl group having 2 to 10 carbon atoms, and 
R.sup.7 is an alkyl group or an alkoxy group having 1 to 10 carbon atoms, 
a compound represented by the formula (IV-b) 
##STR7## 
wherein R.sup.8 is an alkyl group having 1 to 10 carbon atoms, and R.sup.9 
is an alkenyl group or an alkenyloxy group having 2 to 10 carbon atoms, 
a compound represented by the formula (IV-c) 
##STR8## 
wherein R.sup.10 is an alkenyl group having 2 to 10 carbon atoms, and 
R.sup.11 is an alkyl group or an alkoxy group having 1 to 10 carbon atoms, 
or a compound represented by the formula (IV-d) 
##STR9## 
wherein R.sup.12 is an alkyl group having 1 to 10 carbon atoms, and 
R.sup.13 is an alkoxyalkyl group having 2 to 10 carbon atoms. 
(2) The liquid crystal composition according to the above-mentioned 
paragraph (1) which further contains 5 to 25% by weight of at least one 
compound as a fifth component selected from the group consisting of 
compounds represented by the formula (V), 
said fifth component being a compound represented by the formula (V) 
##STR10## 
wherein R is an alkyl group having 1 to 10 carbon atoms or an alkenyl 
group having 2 to 10 carbon atoms, and X is a single bond or --COO--. 
(3) The liquid crystal composition according to the above-mentioned 
paragraph (1) or (2) which further contains 1 to 10% by weight of at least 
one compound as a sixth component selected from the group consisting of 
compounds represented by the formula (VI), 
said sixth component being a compound represented by the formula (VI) 
##STR11## 
wherein R.sup.15 is an alkoxyalkyl group having 2 to 10 carbon atoms. 
(4) The liquid crystal composition according to any one of the 
above-mentioned paragraphs (1) to (3) which further contains 1 to 15% by 
weight of at least one compound as a seventh component selected from the 
group consisting of compounds represented by the formula (VII), 
said seventh component being a compound represented by the formula (VII) 
##STR12## 
wherein each of R.sup.16 and R.sup.17 is independently an alkyl group or 
an alkoxy group having 1 to 10 carbon atoms or an alkenyl group having 2 
to 10 carbon atoms. 
(5) The liquid crystal composition according to any one of the 
above-mentioned paragraphs (1) to (4) which further contains 1 to 10% by 
weight of at least one compound as a eighth component selected from the 
group consisting of compounds represented by the formula (VIII), 
said eighth component being a compound represented by the formula (VIII) 
##STR13## 
wherein R.sup.18 is an alkyl group having 1 to 10 carbon atoms or an 
alkenyl group having 2 to 10 carbon atoms, and R.sup.19 is an alkyl group 
having 1 to 10 carbon atoms. 
(6) The liquid crystal composition according to any one of the 
above-mentioned paragraphs (1) to (5) which comprises a compound 
represented by the formula (I-a) wherein R.sup.1 is an alkyl group having 
1 to 7 carbon atoms, 
a compound represented by the formula (I-b) wherein R.sup.2 is an alkyl 
group having 1 to 7 carbon atoms, 
a compound represented by the formula (II) wherein R.sup.3 is an alkyl 
group having 1 to 7 carbon atoms, CH.sub.2 .dbd.CH--, CH.sub.3 
--CH.dbd.CH--, CH.sub.2 .dbd.CH--CH.sub.2 --CH.sub.2 --, CH.sub.3 
--CH.sub.2 --CH.sub.2 --CH.dbd.CH-- or CH.sub.3 --CH.dbd.CH--CH.sub.2 
--CH.sub.2 --, 
a compound represented by the formula (III) wherein R.sup.4 is an alkyl 
group or an alkoxy group having 1 to 7 carbon atoms, and R.sup.5 is 
--CH.dbd.CH.sub.2, --CH.dbd.CH--CH.sub.3, --CH.sub.2 --CH.sub.2 
--CH.dbd.CH.sub.2, --CH.sub.2 --CH.sub.2 --CH.dbd.CH--CH.sub.3, 
--CH.dbd.CH--CH.sub.2 --CH.sub.3, --CH.dbd.CH--CH.sub.2 --CH.sub.2 
--CH.sub.3, --O--CH.sub.2 --CH.dbd.CH.sub.2 or --O--CH.sub.2 
--CH.dbd.CH--CH.sub.3, 
a compound represented by the formula (IV-a) wherein R.sup.6 is CH.sub.2 
.dbd.CH--, CH.sub.3 --CH.dbd.CH-- or CH.sub.2 .dbd.CH--CH.sub.2 --CH.sub.2 
--, and R.sup.7 is an alkyl group having 1 to 7 carbon atoms, 
a compound represented by the formula (IV-b) wherein R.sup.8 is an alkyl 
group having 1 to 7 carbon atoms, and R.sup.9 is --O--CH.sub.2 
--CH.dbd.CH.sub.2 or --O--CH.sub.2 --CH.dbd.CH--CH.sub.3, 
a compound represented by the formula (IV-c) wherein R.sup.10 is CH.sub.2 
.dbd.CH--, CH.sub.3 --CH.dbd.CH--, CH.sub.2 .dbd.CH--CH.sub.2 --CH.sub.2 
-- or CH.sub.3 --CH.dbd.CH--CH.sub.2 --CH.sub.2 --, and R.sup.11 is an 
alkyl group having 1 to 7 carbon atoms, 
a compound represented by the formula (IV-d) wherein R.sup.12 is an alkyl 
group having 1 to 7 carbon atoms, and R.sup.13 is an alkoxyalkyl group 
having 2 to 7 carbon atoms, 
a compound represented by the formula (V) wherein R.sup.14 is an alkyl 
group having 1 to 7 carbon atoms, CH.sub.2 .dbd.CH--, CH.sub.3 
--CH.dbd.CH--, CH.sub.2 .dbd.CH--CH.sub.2 --CH.sub.2 -- or CH.sub.3 
--CH.dbd.CH--CH.sub.2 --CH.sub.2 --, and X is 
a single bond or --COO--, 
a compound represented by the formula (VI) wherein R.sup.15 is an 
alkoxyalkyl group having 2 to 7 carbon atoms, 
a compound represented by the formula (VII) wherein each of R.sup.16 and 
R.sup.17 is independently an alkyl group having 1 to 7 carbon atoms, and 
a compound represented by the formula (VIII) wherein R.sup.18 is an alkyl 
group having 1 to 7 carbon atoms, CH.sub.2 .dbd.CH--, CH.sub.3 
--CH.dbd.CH--, CH.sub.2 .dbd.CH--CH.sub.2 --CH.sub.2 -- or CH.sub.3 
--CH.dbd.CH--CH.sub.2 --CH.sub.2 --, and R.sup.19 is an alkyl group having 
1 to 7 carbon atoms. 
A liquid crystal display element of the present invention comprises the 
following constitution. 
(7) A liquid crystal display element using a liquid crystal composition 
described in any one of the above-mentioned paragraphs (1) to (6). 
BEST MODE FOR CARRYING OUT THE INVENTION 
Next, compounds of the respective components constituting a liquid crystal 
composition of the present invention will be described. 
A compound represented by the formula (I-a) or (I-b) constituting a first 
component of the liquid crystal composition according to the present 
invention has a very large positive dielectric anisotropy and a low 
voltage holding ratio. When this first component is added to another 
liquid crystal compound or liquid crystal composition, the threshold 
voltage and the voltage holding ratio of the liquid crystal composition 
can be lowered, and the dependence of the threshold voltage on temperature 
can also be reduced. These compounds represented by the formulae (I-a) and 
(I-b) can play an important role in providing the liquid crystal 
composition for realizing a uniform display screen without display 
unevenness in the present invention. The preferable compound represented 
by the formula (I-a) or (I-b) in the present invention is a compound 
represented by the formula (I-a) in which R.sup.1 is an alkyl group having 
1 to 7 carbon atoms, or a compound represented by the formula (I-b) in 
which R.sup.2 is an alkyl group having 1 to 7 carbon atoms. 
A compound represented by the formula (II) constituting a second component 
of the liquid crystal composition has a positive dielectric anisotropy and 
a very large elastic constant ratio (K.sub.33 /K.sub.11). When this second 
component is added to another liquid crystal compound or liquid crystal 
composition, the elastic constant ratio (K.sub.33 /K.sub.11) of the liquid 
crystal composition can be increased. This compound can play an important 
role in providing the liquid crystal composition having steep 
electro-optic properties in the present invention. The preferable compound 
represented by the formula (II) in the present invention is a compound 
represented by the formula (I-a) in which R.sup.3 is an alkyl group having 
1 to 7 carbon atoms, CH.sub.2 .dbd.CH--, CH.sub.3 --CH.dbd.CH--, CH.sub.2 
.dbd.CH--CH.sub.2 --CH.sub.2 --, CH.sub.3 --CH.sub.2 --CH.sub.2 
--CH.dbd.CH-- or CH.sub.3 --CH.dbd.CH--CH.sub.2 --CH.sub.2 --. 
A compound represented by the formula (III) constituting a third component 
of the liquid crystal composition has a very low viscosity and a 
relatively large elastic constant ratio (K.sub.33 /K.sub.11). When this 
third component is added to another liquid crystal compound or liquid 
crystal composition, the viscosity of the liquid crystal composition can 
be lowered and the elastic constant ratio (K.sub.33 /K.sub.11) can be 
increased. This compound can play an important role in providing the 
liquid crystal composition for particularly realizing a high-speed 
response in the present invention. The preferable compound represented by 
the formula (III) in the present invention is a compound represented by 
the formula (III) wherein R is an alkyl group or an alkoxy group having 1 
to 7 carbon atoms, and R is --CH.dbd.CH.sub.2, --CH.dbd.CH--CH.sub.3, 
--CH.sub.2 --CH.sub.2 --CH.dbd.CH.sub.2, --CH.sub.2 --CH.sub.2 
--CH.dbd.CH--CH.sub.3, --CH.dbd.CH--CH.sub.2 --CH.sub.3, 
--CH.dbd.CH--CH.sub.2 --CH.sub.2 --CH.sub.3, --O--CH.sub.2 
--CH.dbd.CH.sub.2 or --O--CH.sub.2 --CH.dbd.CH--CH.sub.3, and a 
particularly preferable compound represented by the formula (III) is a 
compound represented by the formula (III) wherein R.sup.4 is an alkyl 
group having 1 to 7 carbon atoms, and R.sup.5 is --CH.dbd.CH.sub.2, 
--CH.dbd.CH--CH.sub.3, --CH.sub.2 --CH.sub.2 --CH.dbd.CH.sub.2, --CH.sub.2 
--CH.sub.2 --CH.dbd.CH--CH.sub.3, --CH.dbd.CH--CH.sub.2 --CH.sub.3 or 
--CH.dbd.CH--CH.sub.2 --CH.sub.2 --CH.sub.3. 
A compound represented by the formula (IV-a), (IV-b), (IV-c) or (IV-d) 
constituting a fourth component of the liquid crystal composition has a 
high NI transition temperature, a low viscosity, a relatively large 
elastic constant ratio (K.sub.33 /K.sub.11) and a broad d/p margin. When 
this fourth component is added to another liquid crystal compound or 
liquid crystal composition, the NI transition temperature of the liquid 
crystal composition can be raised, the dependence of a threshold voltage 
on temperature can be reduced, the elastic constant ratio (K.sub.33 
/K.sub.11) of the liquid crystal composition can be increased, and the d/p 
margin can also be broadened. These compounds represented by the formulae 
(IV-a), (IV-b), (IV-c) or (IV-d) can play an important role in providing 
the liquid crystal composition having the particularly high NI transition 
temperature in the present invention. The preferable compound represented 
by the formula (IV-a), (IV-b), (IV-c) or (IV-d) in the present invention 
is a compound represented by the formula (IV-a) wherein R.sup.6 is 
CH.sub.2 .dbd.CH--, CH.sub.3 --CH.dbd.CH-- or CH.sub.2 .dbd.CH--CH.sub.2 
--CH.sub.2 -- and R is an alkyl group having 1 to 7 carbon atoms, a 
compound represented by the formula (IV-b) wherein R.sup.8 is an alkyl 
group having 1 to 7 carbon atoms and R.sup.9 is --O--CH.sub.2 
--CH.dbd.CH.sub.2 or ---O--CH.sub.2 --CH.dbd.CH--CH.sub.3, a compound 
represented by the formula (IV-c) wherein R.sup.10 is CH.sub.2 .dbd.CH--, 
CH.sub.3 --CH.dbd.CH--, CH.sub.2 .dbd.CH--CH.sub.2 --CH.sub.2 -- or 
CH.sub.3 --CH.dbd.CH--CH.sub.2 --CH.sub.2 -- and R.sup.11 is an alkyl 
group having 1 to 7 carbon atoms, or a compound represented by the formula 
(IV-d) wherein R.sup.12 is an alkyl group having 1 to 7 carbon atoms and 
R.sup.13 is an alkoxyalkyl group having 2 to 7 carbon atoms. 
A compound represented by the formula (V) constituting a fifth component of 
the liquid crystal composition has a high NI transition temperature and 
the low dependence of a threshold voltage on temperature. When this fifth 
component is added to another liquid crystal compound or liquid crystal 
composition, the NI transition temperature of the liquid crystal 
composition can be raised, and the dependence of the threshold voltage on 
temperature can be reduced. This compound can play an important role in 
providing the liquid crystal composition for realizing a uniform display 
screen without display unevenness in the present invention. The preferable 
compound represented by the formula (V) in the present invention is a 
compound represented by the formula (V) wherein R.sup.14 is an alkyl group 
having 1 to 7 carbon atoms, CH.sub.2 .dbd.CH--, CH.sub.3 --CH.dbd.CH--, 
CH.sub.2 .dbd.CH--CH.sub.2 --CH.sub.2 -- or CH.sub.3 --CH.dbd.CH--CH.sub.2 
--CH.sub.2 --, and X is a single bond or --COO--. 
A compound represented by the formula (VI) constituting a sixth component 
of the liquid crystal composition has a relatively large positive 
dielectric anisotropy and a broad d/p margin. When this sixth component is 
added to another liquid crystal compound or liquid crystal composition, 
the d/p margin of the liquid crystal composition can be broadened. This 
compound can play an important role to improve the yield of panel 
manufacture. The preferable compound represented by the formula (VI) in 
the present invention is a compound represented by the formula (VI) 
wherein R.sup.15 is an alkoxyalkyl group having 2 to 7 carbon atoms, and 
the particularly preferable compound is a compound represented by the 
formula (VI) wherein R.sup.15 is CH.sub.3 OCH.sub.2 --, CH.sub.3 OC.sub.2 
H.sub.4 --, CH.sub.3 OC.sub.3 H.sub.6 --, CH.sub.3 OC.sub.4 H.sub.8 --or 
CH.sub.3 OC.sub.5 H.sub.10 --. 
A compound represented by the formula (VII) constituting a seventh 
component of the liquid crystal composition has a relatively low viscosity 
and a large .DELTA.n. When this seventh component is added to another 
liquid crystal compound or liquid crystal composition, the .DELTA.n of the 
liquid crystal composition can be optionally adjusted, and the viscosity 
can be lowered. The preferable compound represented by the formula (VII) 
in the present invention is a compound represented by the formula (VII) 
wherein each of R.sup.16 and R.sup.17 is independently an alkyl group 
having 1 to 7 carbon atoms. 
A compound represented by the formula (VIII) constituting an eighth 
component of the liquid crystal composition has a high NI transition 
temperature and a relatively large elastic constant ratio (K.sub.33 
/K.sub.11). When this eighth component is added to another liquid crystal 
compound or liquid crystal composition, the NI transition temperature of 
the liquid crystal composition can be raised, and the elastic constant 
ratio (K.sub.33 /K.sub.11) can also be increased. The preferable compound 
represented by the formula (VIII) in the present invention is a compound 
represented by the formula (VIII) wherein R.sup.18 is an alkyl group 
having 1 to 7 carbon atoms, CH.sub.2 .dbd.CH--, CH.sub.3 --CH.dbd.CH--, 
CH.sub.2 .dbd.CH--CH.sub.2 --CH.sub.2 -- or CH.sub.3 --CH.dbd.CH--CH.sub.2 
--CH.sub.2 -- and R.sup.19 is an alkyl group having 1 to 7 carbon atoms. 
A mixing ratio of the compound represented by the formula (I-a) or (I-b) 
which is the first component in the liquid crystal composition of the 
present invention is preferably in the range of 1 to 15% with respect to 
the total weight of the liquid crystal composition. If the mixing ratio of 
the compound is less than 1% by weight, the reduction of the dependence of 
the threshold voltage on temperature which is a characteristic of the 
present invention cannot be achieved and the voltage holding ratio cannot 
be lowered, either. On the other hand, if it is more than 15% by weight, 
the viscosity of the obtained liquid crystal composition inconveniently 
increases. 
A mixing ratio of the compound represented by the formula (II) which is the 
second component is preferably in the range of 8 to 40% with respect to 
the total weight of the liquid crystal composition. If the mixing ratio of 
the compound is less than 8% by weight, the increase in the value of the 
elastic constant ratio (K.sub.33 /K.sub.11) which is a characteristic of 
the present invention cannot be achieved. On the other hand, if it is more 
than 40% by weight, the viscosity of the obtained liquid crystal 
composition inconveniently increases. 
A mixing ratio of the compound represented by the formula (III) which is 
the third component is preferably in the range of 10 to 30% with respect 
to the total weight of the liquid crystal composition. If the mixing ratio 
of the compound is less than 10% by weight, the decrease in the viscosity 
which is a characteristic of the present invention cannot be achieved, and 
the value of the elastic constant ratio (K.sub.33 /K.sub.11) cannot be 
increased, either. On the other hand, if it is more than 30% by weight, 
the threshold voltage of the obtained liquid crystal composition 
inconveniently increases. 
A mixing ratio of the compound represented by the formula (IV-a), (IV-b), 
(IV-c) or (IV-d) which is the fourth component is preferably in the range 
of 10 to 45% with respect to the total weight of the liquid crystal 
composition. If the mixing ratio of the compound is less than 10% by 
weight, the rise of the NI transition temperature which is a 
characteristic of the present invention cannot be achieved, and the value 
of the elastic constant ratio (K.sub.33 /K.sub.11) cannot be increased, 
either. On the other hand, if it is more than 45% by weight, the threshold 
voltage of the obtained liquid crystal composition inconveniently 
increases. 
A mixing ratio of the compound represented by the formula (V) which is the 
fifth component is preferably in the range of 5 to 25% with respect to the 
total weight of the liquid crystal composition. If the mixing ratio of the 
compound is less than 5% by weight, the reduction of the dependence of the 
threshold voltage on temperature which is a characteristic of the present 
invention cannot be achieved. On the other hand, if it is more than 25% by 
weight, the viscosity of the obtained liquid crystal composition 
inconveniently increases. 
A mixing ratio of the compound represented by the formula (VI) which is the 
sixth component is preferably in the range of 1 to 10% with respect to the 
total weight of the liquid crystal composition. If the mixing ratio of the 
compound is less than 1% by weight, the expansion of the d/p margin which 
is a characteristic of the present invention cannot be achieved. On the 
other hand, if it is more than 10% by weight, the viscosity of the 
obtained liquid crystal composition inconveniently increases. 
A mixing ratio of the compound represented by the formula (VII) which is 
the seventh component is preferably in the range of 1 to 15% with respect 
to the total weight of the liquid crystal composition. If the mixing ratio 
of the compound is less than 1% by weight, the decrease in the viscosity 
which is a characteristic of the present invention cannot be achieved. On 
the other hand, if it is more than 15% by weight, the threshold voltage of 
the obtained liquid crystal composition inconveniently increases. 
A mixing ratio of the compound represented by the formula (VIII) which is 
the eighth component is preferably in the range of 1 to 10% with respect 
to the total weight of the liquid crystal composition. If the mixing ratio 
of the compound is less than 1% by weight, the rise of the NI transition 
temperature which is a characteristic of the present invention cannot be 
achieved. On the other hand, if it is more than 10% by weight, the 
threshold voltage of the obtained liquid crystal composition 
inconveniently increases. 
For the purpose of regulating the threshold voltage, the nematic phase 
temperature range, the .DELTA.n, the viscosity and the like of the 
obtained liquid crystal composition in compliance with the use purpose of 
the liquid crystal display element, compounds other than the compounds 
represented by the above-mentioned formulae (I-a) to (VIII) can be added 
to the liquid crystal composition of the present invention, so far as the 
objects of the present invention are not impaired. Examples of such other 
compounds include the following compounds: 
##STR14## 
wherein R.sup.20 is an alkyl group having 1 to 10 carbon atoms, each of 
R.sup.21 and R.sup.22 is independently an alkyl group or an alkoxy group 
having 1 to 10 carbon atoms, R.sup.23 is an alkyl group having 1 to 10 
carbon atoms, R.sup.24 is an alkyl group or an alkoxy group having 1 to 10 
carbon atoms, and each of R.sup.25 and R.sup.26 is independently an alkyl 
group having 1 to 10 carbon atoms.

EXAMPLES 
Next, the present invention will be described in more detail with reference 
to examples, but the scope of the present invention should not be limited 
to these examples. It is to be noted that the amount of each component in 
these example means "% by weight". The abbreviations in the examples have 
the following meanings. 
NI: Nematic-isotropic phase transition temperature (.degree.C.) 
.eta.: Viscosity at 20.degree. C. (mPa.s) 
Vth: Threshold voltage (V) at 25.degree. C. 
.DELTA.n: Optical anisotropy at 25 C. 
.gamma.: Steepness V.sub.90 /V.sub.10 at 25.degree. C. 
(V.sub.90 : voltage at which transmittance is 90%, 
V.sub.10 : voltage at which transmittance is 10%) 
.tau.: Response speed (msec) at 1/240 duty drive at 25.degree. C. 
Example 1 
A liquid crystal composition comprising 
##STR15## 
as first components formula (I-a)! 
##STR16## 
as second components formula (II)! 
##STR17## 
as a third component formula (III)! 
##STR18## 
as fourth components formula (IV-a)! 
##STR19## 
as a fourth component formula (IV-c)! 
##STR20## 
as a fifth component formula (V)! 
##STR21## 
as other compounds 
##STR22## 
as other compounds 
##STR23## 
as another compound had the following parameters: 
NI: 82.3.degree. C. 
.eta.: 23.6 mPa.s 
Vth: 2.00 V 
.DELTA.n: 0.140 
.gamma.: 1.033 
An STN display element having the following parameters: 
twist angle: 240.degree. 
tilt angle: 40.degree. 
d/p (cell thickness/pitch): 0.5 
d.times..DELTA.n: 0.84 
exerted a response time of 385 msec. Furthermore, the voltage holding ratio 
of the display element was 75%, and neither a display failure nor an after 
image phenomenon was observed. 
Example 2 
A liquid crystal composition comprising 
##STR24## 
as first components formula (I-a)! 
##STR25## 
as a second component formula (II)! 
##STR26## 
as a third component formula (III)! 
##STR27## 
as fourth components formula (IV-a)! 
##STR28## 
as a fourth component formula (IV-d)! 
##STR29## 
as fifth components formula (V)! 
##STR30## 
as fifth components formula (V)! 
##STR31## 
as another compound had the following parameters: 
NI: 84.9.degree. C. 
.eta.: 18.3 mPa.s 
Vth: 2.00 V 
.DELTA.n: 0.139 
.beta.: 1.042 
An STN display element having the following parameters: 
twist angle: 240.degree. 
tilt angle: 4.degree. 
d/p (cell thickness/pitch): 0.5 
d.times..DELTA.n: 0.83 
exerted a response time of 290 msec. Furthermore, the voltage holding ratio 
of the display element was 65%, and neither a display failure nor an after 
image phenomenon was observed. 
Example 3 
A liquid crystal composition comprising 
##STR32## 
as first components formula (I-b)! 
##STR33## 
as second components formula (II)! 
##STR34## 
as a third component formula (III)! 
##STR35## 
as fourth components formula (IV-a)! 
##STR36## 
as a fourth component formula (IV-c)! 
##STR37## 
as a fourth component formula (IV-d)! 
##STR38## 
as a sixth component formula (VI)! 
##STR39## 
as other compounds had the following parameters: 
NI: 75.2.degree. C. 
.eta.: 19.3 mPa.s 
Vth: 2.02 V 
.DELTA.n: 0.136 
.gamma.: 1.043 
An STN display element having the following parameters: 
twist angle: 240.degree. 
tilt angle: 4.degree. 
d/p (cell thickness/pitch): 0.5 
d.times..DELTA.n: 0.82 
exerted a response time of 247 msec. Furthermore, the voltage holding ratio 
of the display element was 70%, and neither a display failure nor an after 
image phenomenon was observed. 
Example 4 
A liquid crystal composition comprising 
##STR40## 
as a first component formula (I-a)! 
##STR41## 
as second components formula (II)! 
##STR42## 
as third components formula (III)! 
##STR43## 
as a fourth component formula (IV-c)! 
##STR44## 
as fourth components formula (IV-d)! 
##STR45## 
as eighth components formula (VIII)! 
##STR46## 
as other compounds had the following parameters: 
NI: 85.2.degree. C. 
.eta.: 18.7 mPa.s 
Vth: 2.09 V 
.DELTA.n: 0.137 
.gamma.: 1.045 
An STN display element having the following parameters: 
twist angle: 240.degree. 
tilt angle: 4.degree. 
d/p (cell thickness/pitch): 0.5 
d.times..DELTA.n: 0.82 
exerted a response time of 320 msec. Furthermore, the voltage holding ratio 
of the display element was 75%, and neither a display failure nor an after 
image phenomenon was observed. 
Example 5 
A liquid crystal composition comprising 
##STR47## 
as a first component formula (I-a)! 
##STR48## 
as a first component formula (I-b)! 
##STR49## 
as second components formula (II)! 
##STR50## 
as third components formula (III)! 
##STR51## 
as fourth components formula (IV-a)! 
##STR52## 
as a fourth component formula (IV-d)! 
##STR53## 
as fifth components formula (V)! 
##STR54## 
as a fifth component formula (V)! 
##STR55## 
as a sixth component formula (VI)! 
##STR56## 
as a seventh component formula (VII)! 
##STR57## 
as an eighth component formula (VIII)! 
##STR58## 
as another compound had the following parameters: 
NI: 100.5.degree. C. 
.eta.: 18.7 mPa.s 
Vth: 2.22 V 
.DELTA.n: 0.133 
.gamma.: 1.045 
An STN display element having the following parameters: 
twist angle: 260.degree. 
tilt angle: 6.degree. 
d/p (cell thickness/pitch): 0.55 
d.times..DELTA.n: 0.8 
exerted a response time of 295 msec. Furthermore, the voltage holding ratio 
of the display element was 68%, and neither a display failure nor an after 
image phenomenon was observed. 
Example 6 
A liquid crystal composition comprising 
##STR59## 
as a first component formula (I-a)! 
##STR60## 
as a first component formula (I-b)! 
##STR61## 
as second components formula (II)! 
##STR62## 
as third components formula (III)! 
##STR63## 
as fourth components formula (IV-a)! 
##STR64## 
as a fourth component formula (IV-c)! 
##STR65## 
as a fourth component formula (IV-d)! 
##STR66## 
as other compounds had the following parameters: 
NI: 85.4.degree. C. 
.eta.: 18.5 mPa.s 
Vth: 1.99 V 
.DELTA.n: 0.136 
.gamma.: 1.047 
An STN display element having the following parameters: 
twist angle: 240.degree. 
tilt angle: 4.degree. 
d/p (cell thickness/pitch): 0.5 
d.times..DELTA.n: 0.82 
exerted a response time of 258 msec. Furthermore, the voltage holding ratio 
of the display element was 65%, and neither a display failure nor an after 
image phenomenon was observed. 
Example 7 
A liquid crystal composition comprising 
##STR67## 
as first components formula (I-a)! 
##STR68## 
as first components formula (I-b)! 
##STR69## 
as a second component formula (II)! 
##STR70## 
as a third component formula (III)! 
##STR71## 
as fourth components formula (IV-a)! 
##STR72## 
as a fourth component formula (IV-b)! 
##STR73## 
as a fourth component formula (IV-c)! 
##STR74## 
as a seventh component formula (VII)! 
##STR75## 
as other compounds had the following parameters: 
NI: 100.3.degree. C. 
.eta.: 17.1 mPa.s 
Vth: 2.30 V 
.DELTA.n: 0.134 
.gamma.: 1.047 
An STN display element having the following parameters: 
twist angle: 240.degree. 
tilt angle: 4.degree. 
d/p (cell thickness/pitch): 0.5 
d.times..DELTA.n: 0.82 
exerted a response time of 288 msec. Furthermore, the voltage holding ratio 
of the display element was 65%, and neither a display failure nor an after 
image phenomenon was observed. 
Example 8 
A liquid crystal composition comprising 
##STR76## 
as first components formula (I-a)! 
##STR77## 
as first components formula (I-b)! 
##STR78## 
as a second component formula (II)! 
##STR79## 
as a third component formula (III)! 
##STR80## 
as fourth components formula (IV-a)! 
##STR81## 
as a fourth component formula (IV-b)! 
##STR82## 
as a fourth component formula (IV-c)! 
##STR83## 
as a fourth component formula (IV-d)! 
##STR84## 
as a seventh component formula (VII)! 
##STR85## 
as other compounds had the following parameters: 
NI: 103.8.degree. C. 
.eta.: 18.2 mPa.s 
Vth: 2.35 V 
.DELTA.n: 0.136 
.beta..gamma.: 1.042 
An STN display element having the following parameters: 
twist angle: 260.degree. 
tilt angle: 6.degree. 
d/p (cell thickness/pitch): 0.55 
d.times..DELTA.n: 0.82 
exerted a response time of 277 msec. Furthermore, the voltage holding ratio 
of the display element was 63%, and neither a display failure nor an after 
image phenomenon was observed. 
Possibility of Industrial Utilization 
According to the present invention, a liquid crystal composition having 
steep electro-optic properties and a low viscosity can be obtained, and 
thus, there can be provided an STN system liquid crystal display element 
which is equipped with a uniform display screen having a high contrast and 
a high-speed response and not having any display unevenness and which 
enables a high manufacture yield.