Liquid crystal display element

The invention relates to a new liquid crystal display element with static or multiplex control with a low multiplex ratio and an operating voltage below 3.3 volts, containing a liquid crystal dielectric, wherein the operating temperature range extends from -30.degree. C. to +80.degree. C. and the viscosity of the dielectric at 20.degree. C. is less than 40 mPa.s.

The invention relates to a liquid crystal display element (LC display 
element) with a low multiplex ratio and low operating voltage. 
For LC display elements, the properties of nematic or nematic-cholesteric 
liquid crystal materials are utilized to modify their optical properties, 
such as absorption of light, light scattering, birefringence, reflectance 
or color, under the influence of electrical fields. Functioning of such 
display elements is based here, for example, on the phenomenon of dynamic 
scattering, the deformation of aligned phases, the guest-host effect, the 
Schadt-Helfrich effect in the twisted cell or the cholesteric-nematic 
phase transfer. 
LC phases which must meet a number of requirements are required for 
technical use of these effects in electronic components. mechanical 
stability towards moisture, air and physical influences, such as heat, 
radiation in the infrared, visible and ultraviolet range and constant and 
alternating electrical fields, are particularly important here. 
Technically usable LC phases are also required to have a liquid crystal 
mesophase in a suitable temperature range, a low viscosity, a low optical 
anisotropy, a high gradient of the electrooptical characteristic line and 
an adequate dissolving power for pleochroic dyestuffs. 
In none of the series of compounds so far known with a liquid crystal 
mesophase is there a single compound which meets all these requirements. 
Mixtures of two to 25, preferably three to 18, compounds are therefore 
prepared in order to obtain substances which can be used as LC phases. 
However, optimum phases cannot easily be prepared in this manner, since 
components with high melting and clear points frequently also impart to 
the mixtures a high viscosity. The switching times of the electrooptical 
display elements produced with these components are thereby modified in an 
undesirable manner. 
There is therefore still a great need for LC phases with a wider operating 
temperature range, a low viscosity (and therefore short switching times) 
and a low threshold voltage. 
Most LC display elements produced today are controlled in multiplex 
operation with multiplex ratios of about 1:2 to 1:4 and with operating 
voltages of about 3 volts. The operating temperature range of such display 
elements is in general between about -10.degree.and +50.degree.. 
However, a wider operating temperature range is desirable for applications 
in the open air, for example also in cars. 
The invention is based on the object of providing LC display elements which 
have a wide operating temperature range and display the abovementioned 
disadvantages to only a small extent, if at all. 
It has been found that this object can be achieved if liquid crystal 
dielectrics which have operating temperature ranges of between -30.degree. 
and +80.degree. C. and viscosities of less than 40 mPa.s at 20.degree. are 
used in these display elements. 
The invention thus relates to an LC display element with static or 
multiplex control with a low multiplex ratio and an operating voltage 
below 3.3 volts, containing a liquid crystal dielectric, wherein the 
operating temperature range extends from -30.degree. C. to +80.degree. C. 
and the viscosity of the dielectric at 20.degree. C. is less than 40 
mPa.s. 
The invention particularly relates to LC display elements of the type 
mentioned, in which the threshold voltage of the dielectric is not more 
than 1.7, preferably not more than 1.5 volts. 
The invention furthermore relates to LC display elements, wherein the 
dielectric contains at least one component of one of the formulae I to 
VII: 
##STR1## 
wherein 
R.sup.1 is alkyl with 1 to 12 C atoms, wherein one or two non-adjacent 
CH.sub.2 groups can also be replaced by O atoms, --CO--, --O--CO--, 
--CO--O-- and/or --CH.dbd.CH-- groups, 
A.sup.o and A.sup.1 each independently of one another are Cy, Dio or Phe, Z 
is --CO--O--, --O--CO--, --CH.sub.2 --O--, --O--CH.sub.2 -- or a single 
bond, 
X.sub.1 is F, Cl, --CN or --NCS, 
X.sup.2 is F, Cl or, in the case where X.sup.1 =NCS, also H, 
m is 0 or 1, 
Cy is trans-1,4-cyclohexylene, 
Dio is trans-1,3-dioxane-2,5-diyl and 
Phe is 1,4-phenylene which is unsubstituted or substituted by fluorine; 
##STR2## 
wherein R.sup.1, have the meanings given in the case of X.sup.1 and 
X.sup.2 formula I, 
Q.sup.1 is trans-1,4-cyclohexylene, wherein one or two non-adjacent 
CH.sub.2 groups can also be replaced by O and/or S, 
Q.sup.2 is trans-1,4-cyclohexylene, wherein one or two non-adjacent 
CH.sub.2 groups can also be replaced by O and/or S, or 1,4-phenylene which 
is unsubstituted or substituted by fluorine and wherein one or more CH 
groups can be replaced by N, and 
Z.sup.o is --CO--O--, --CH.sub.2 O-- or --CH.sub.2 CH.sub.2 --; 
EQU R.sup.1 --Q.sup.1 --(Q.sup.2).sub.n --X.sup.3 III 
wherein 
R.sup.1 has the meanings given in the case of formula I, 
Q.sup.1 and Q.sup.2 have the meanings given in the case of formula II, 
n is 1 or 2 and 
X.sup.3 is --CN or --NCS; 
EQU R.sup.1 --(Q.sup.1 --Z.sup.1).sub.m --Q.sup.2 --Q.sup.2 --(Z.sup.1 
--Q.sup.1).sub.P --R.sup.2 IV 
wherein 
Q.sup.1 and Q.sup.2 (each independently of one another) have the meanings 
given in the case of formula II, 
R.sup.1 and R.sup.2 each independently of one another are alkyl with 1 to 
12 C atoms, wherein one or two non-adjacent CH.sub.2 groups can also be 
replaced by --O--, --CO--, --O--CO--, --CO--O-- and/or --CH.dbd.CH--, 
the symbols Z.sup.1 each independently of one another are --CO--O--, 
--O--CO--, --CH.sub.2 O--, --OCH.sub.2 -- --CH.sub.2 CH.sub.2 -- or a 
single bond, and 
m and P are each 0 or 1; 
EQU R.sup.1 --Cy--Q.sup.o --R.sup.2 V 
wherein Q.sup.o is Cy or Phe and 
Phe and Cy have the meanings given in the case of formula I, and 
R.sup.1 and R.sup.2 have the meanings given in the case of formula IV; 
EQU R.sup.1 --Phe--Phe--CN VI 
wherein 
R.sup.1 and Phe have the meanings given in the case of formula I; 
EQU R.sup.1 --(Q).sub.n --COO--Phe--R.sup.2 VII 
wherein Phe has the meanings given in the case of formula I, 
R.sup.1 and R.sup.2 have the meanings given in the case of formula IV, 
R.sup.2 is also CN, 
Q is trans-1,4-cyclohexylene, wherein one or two non-adjacent CH.sub.2 
groups can also be replaced by O and/or S, or Phe and 
n is 1 or 2, and if n=2, the two groups Q can be identical or different 
from one another. 
Finally, the invention relates to a liquid crystal dielectric with an 
operating temperature range of -30.degree. to +80.degree. C., a viscosity 
of less than 40, preferably less than 30 mPa.s at 20.degree. C. and a 
threshold voltage of not more than 1.7, preferably not more than 1.5 
volts. 
Preferred compounds of the formulae I to VII correspond to the following 
part formulae (wherein FCP is the 3-fluoro-4-cyanophenyl radical): 
##STR3## 
Other preferred compounds correspond to the following part formulae: 
##STR4## 
The radicals R.sup.1 and R.sup.2 are preferably in each case straight-chain 
alkyl with 1-9 C atoms, such as methyl, ethyl, propyl, butyl, pentyl, 
hexyl, heptyl, octyl or nonyl, or furthermore straight-chain alkoxy with 
1-9 C atoms, such as methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy, 
heptoxy, octoxy or nonoxy, or furthermore alkoxyalkyl with 2-9 C atoms 
such methoxymethyl or ethoxymethyl. 
Phe is preferably an unsubstituted 1,4-phenylene group, or furthermore 
preferably a 2-fluoro-1,4-phenylene group. 
The individual compounds of the formulae I to VII which can be used in the 
LC display elements according to the invention are known or can be 
prepared analogously to known compounds. 
Preferred dielectrics which can be used according to the invention contain, 
for example, over 7-20% of I, 10-45% of III, 20-40% of IV, 8-50% of V, 
0-5% of VI and 0-10% of VII. They contain in total preferably 10-20, in 
particular 12-18 components. 
The operating temperature range of these dielectrics is between -30.degree. 
and +80.degree., preferably between -40.degree. and +85.degree.. Their 
viscosity at 20.degree. is less than 40, preferably less than 30 mPa.s and 
their threshold voltage is preferably not more than 1.7, in particular not 
more than 1.5 volts. 
The dielectrics which can be used according to the invention are prepared 
in a manner which is customary per se. As a rule, the desired amount of 
the components used in the smaller amount is dissolved in the component 
which makes up the main constituent, advantageously at elevated 
temperature. It is also possible for solutions of the components in an 
organic solvent, for example in acetone, chloroform or methanol, to be 
mixed and for the solvent to be removed again, for example by 
distillation, after thorough mixing. 
The dielectrics can also contain other additives which are known to the 
expert and are described in the literature. For example, 0-15% of 
pleochroic dyestuffs can be added, as well as conductive salts, preferably 
ethyldimethyldodecylammonium 4-hexoxybenzoate, tetrabutylammonium 
tetraphenylboranate or complex salts of crown ethers (compare, for 
example, Haller et al., Mol. Cryst. Liq. Cryst. Volume 24, pages 249-258 
(1973)) for improving the conductivity or substances for modifying the 
dielectric anisotrophy, the viscosity and/or the orientation of the 
nematic phases. Such substances are described, for example, in German 
Offenlegungsschriften 2,209,127, 2,240,864, 2,321,632, 2,338,281, 
2,450,088, 2,637,430 and 2,853,728. 
The following examples are intended to illustrate the invention without 
limiting it. 
The symbols have the following meanings: 
S-N: Smectic-nemetic phase transition temperature, 
c.p.: Clear point, 
visc.: Viscosity at 20.degree. (mPa.s), 
t.v.: Threshold voltage of a TN cell at 20.degree., observation angle 
0.degree. (perpendicular) and 10% contrast. 
All the temperatures above and below are given in .degree.C. The percentage 
figures are percentages by weight.