The invention concerns a matrix liquid crystal display con¬ taining

two plane parallel support plates which together with a frame form a cell.

integrated non-linear elements for switching individual picture elements on the support plates and

nematic liquid crystal mixture which is present in the cell, has a positive dielectric anisotropy, a high specific resistivity, a nematic phase range of at least 60 °C, a maximum viscosity at 20 °C of 30 mPa.s and a mean dielectricity constant ε < 8,

cheuracterized in that the liquid crystal mixture comprises one or more compounds selected from the group consisting of la to lg:

l-<H>-<^- CF, la

L.

R-{H -CH ₂ CH ₂ -(H -(O - CF, Id

/

R-<H CH ₂ CH ₂ -<όXθ)-CF ₃ If

L

R-(H)b-(θ)-CH ₂ CH ₂ -(θ)-ιCF ₃ lg

wherein R denotes n-alkγl, n-oxaalkyl or n-alkenγl with up to 9 carbon atoms, and L is H or F, preferably H.

Matrix liquid crystal displays (MLC displays) according to the preamble are known. For example, active elements (diodes or transistors) can be used as non-linear elements for the individual switching of the individual picture elements. This is referred to as an "active maxtrix" , in which two types can be distinguished:

1. MOS (metal oxide semiconductor) transistors on a silicon wafer as the substrate.

2. Thin film transistors (TFT) on a glass plate as the substrate.

In the case of type 1, dynamic scattering or the guest/ hos effect is usually used as the electrooptical effect. The use of single-crystal silicon as the substrate material limits the size of the display, since, even if different partial displays are put together in the form of modules, difficul¬ ties arise at the joints.

In the case of the more promising type 2. which is preferred, the TN effect is usually used as the electrooptical effect. Two technologies are distinguished: TFTs consisting of com¬ pound semiconductors, such as, for example, CdSe, or TFTs based on polycrystalline or amorphous silicon. The latter technology is the subject of intense development work world ^¬ wide.

The TFT matrix is disposed on the inside surface of one of the glass plates of the display, while the other glass plate carries the transparent counter electrode on its inside surface. Compared with the size of the picture element elec ^¬ trode, the TFT is very small and essentially does not inter¬ fere with the picture. This technology can also be extended to picture displays in fully satisfactory colours by arrang ^¬ ing a mosaic of red, green and blue filters in such a manner that each filter element is opposite to a switchable picture element.

The TFT displays usually operate as TN cells which contain crossed polarizers in transmission and are illuminated from behind.

The term MLC displays in this context comprises each matrix display which has integrated non-linear elements, i.e. apart from the active axtrix also displays which contain passive elements such as varistors or diodes (MIM = metal/insula¬ tor/metal) .

MLC displays of this type are in particular suitable for TV applications (e.g. portable TVs) or for highly informative displays in automobile and aircraft construction. In addition to problems regarding the angle dependency of the contrast and the switching times, difficulties in MLC displays arise from the insufficient resistivity of the liquid crystal mixtures (Togashi, S. , Sekiguchi, K. , Tanabe, H. , Yamamoto, E. , Sorimachi, . , Tajima, E. , Watanabe, H. , Shimizu, H. , Proc. Eurodisplay 84, Sept. 1984: A 210-288 Matrix LCD Con¬ trolled by Double Stage Diode Rings, p. 141 ff., Paris; Stromer, M. , Proc. Eurodisplay 84, Sept. 1984: Design of Thin Film Transistors for Matrix Addressing of Television Liquid Crystal Displays, p. 145 ff., Paris) . With decreasing resis¬ tivity, the contrast of an MLC display deteriorates. Since the resistivity of the liquid crystal mixture usually decreases by interaction with the inside surfaces of the displays over the lifetime of an MLC display, a high (ini¬ tial) resistance is very important for achieving acceptable service lives.

Therefore, there is still a high demand for MLC displays which have very high resistivity in combination with a large range of operating temperature, short switching times and low threshold voltage.

To provide a good contrast over a wide viewing angle, opera¬ tion of the MLC displays in the first minimum of transmission is preferred. These MLC are very well suited for TV applica¬ tions and consequently are of high commercial interest. For these applications some physical properties of the liquid crystals become more important than for passive TN displays. Some of the decisive properties for the performance of an MLC are the resistivity and the storability of the liquid crys¬ tal.

In a MLC display the non-linear switching elements are addressed in a multiplex scheme. So they charge the elec¬ trodes of a pixel in the limited time they are active. Then- they become inactive until they are addressed again in the next cycle. Consequently the change of the voltage of an activated (charged) pixel is determined by two factors. They are the capacity of the electrodes of the pixel and the resitivity of the dielectric material between the electrodes, namely the liquid crystal. The characteristic time constant of the decay of the voltage at a pixel, the RC time, has to be significantly bigger than the time between two addressing cycles (t _βdr ) . A parameter frequently used to describe the performance of an MLC is the voltage holding ratio HR of a picture element. As the voltage at a pixel decays exponen¬ tially an increase of the holding ratio necessitates liquid crystal materials with exceptionally high resistivities.

There are several points of importance for the resistivity of the liquid crystal inside a display, e.g. the orientation layers used and the curing conditions of the orientation material. But by no means less important are the electrical properties of the liquid crystal used. Especially the resis ^¬ tivity of the liquid crystal in the display determines the

magnituted of the voltage drop at the pixel. This resistiv- itiy usually can not be higher than the bulk resistivity of the liquid crystal material.

In an actual MLC display the driving voltage at a pixel is not applied as single pulses, changing the electrodes only once, but as a continuous waveform with a frequency of 60 Hz. So the free decay of the voltage at a pixel characterized by the RC time is not necessarily determining the performance of the display. Especially the occurrence of a multiexponential decay of the voltage may lead to deviations. The property directly correlated to the performance of MLC displays is the ratio ot the actual voltages at the individual pixel directly after one addressing pulse and directly before the next addressing pulse. The holding ratio can be determined by simultaneous monitoring of the RMS values of the driving voltage applied to the TFT and the acutal voltage at the electrodes of the picture element.

The object of the invention is to provide MLC displays which do not or only to a small extent have the above disadvantages and, at the same time, have very high resistivities.

It has now been found that this object can be achieved by using nematic liquid crystal mixtures in these display ele¬ ments, which contain one or more compounds selected from the above mentioned group consisting of la to lg.

It has been found that already a relatively low percentage of compounds selected from the group consisting of la to lg (e.g. 5 % (preferably 10 %) or more) allows to realize

improved MLC displays. In addition, the corresponding mix ^¬ tures show an improved low temperature behaviour, e.g. very low viscosity at -30° and low temperature for the transition smectic-ne atic.

Accordingly, the invention relates to an MLC display contain¬ ing

two plane parallel support plates which together with a frame form a cell,

integrated non-linear elements for switching individual picture elements on the support plates and

nematic liquid crystal mixture which is present in the cell, has a positive dielectric anisotropy, a high specific resistivity, a nematic phase range of at least 60 ^β C, a maximum viscosity at 20 ^β C of 30 mPa.s and a mean dielectricity constant ^~ ε ≤ 8 ,

cheuracterized in that the liquid crystal mixture comprises one or more compounds selected from the group consisting of la to lg:

I-(H>-<O> CF, la

L

R-{H -CH ₂ CH ₂ -{O - CF, lb

JL

R I-(HH-{HH <OO>λC(F, lc

_ L_

R-(H)-(O)-CH ₂ CH ₂ -(O)-CF ₃ lg

wherein R denotes n-alkyl, n-oxaalkyl or n-alkenγl with up to 9 carbon atoms, and L is H or F, preferably H.

The invention also relates to the corresponding liquid crys¬ tal mixtures, in particular for use in MLC displays. However, the mixtures are also suitable for many other applications, such as, for example, TN, STN or OMI .

Nematic liquid crystal mixtures which instead of the com¬ pounds of the formulae la to lg contain analogous cyano compounds are known and commercially utilized in various designs. However, these liquide crystal mixtures are ditin- guished by values for the resistivity which are too low and

are often between 5xl0 ⁹ and l.lxlO ¹¹ Ωcm or less at 20°. The corresponding MLC displays have values for the resistivity which are too low for some commercial applications.

The resistivity of liquid crystal mixtures is in general high, if the dielectric anisotropy is small, since the polar components which are present in mixtures which have a high Δε have a stabilizing effect on ions and thus lead to high conductivity or low resistance. Surprisingly, it has now been found that the resistivity is particularly high, if the mean dielectricity constant F [= 1/3 (2 εl + ε _u ) ] is small and, at the same time, the dielectrically positive (Δε 1.5) compo¬ nent B contains in addition to compounds which have a termi¬ nal cyano or even instead of those cyano compounds one or more compounds selected from the group consisting of la to lg. Component B may also contain compounds which have a terminal -NCS, F, Cl, -CHF ₂ , -0CF ₃ , -0CHF ₂ , -0CF ₂ CF ₂ H or

-OCA.

Preferably the liquid crystal mixture comprises

a) at least 10 % by weight of a liquid-crystalline compo¬ nent B comprising one or more compounds having a dielec¬ tric anisotropy of more than +1.5,

b) up to 90 % by weight of a liquid-crystalline component A comprising one or more compounds having a dielectric anisotropy of -1.5 to +1.5 of the general formula I

R--<A-y-z--ι- -)-z--ι -(A-)-B.-

10 -

in which

R ¹ and R ² are each, independently of one another, n-alkyl, -fluoroalkyl or n-alkenγl having up to 9 carbon atoms,

the rings

A ⁱ , A ² and A ³ are each, independently of one another, 1,4- phenylene, 2- or 3-fluoro-l,4-phenylene, trans-1,4-cγclohexγlene or 1,4-cγclohexe- nylene,

Z ^l and Z ² are each, independently of one another, -CH ₂ CH ₂ or a single bond, and

m is 0, 1 or 2, and A ² and Z ² are each identical or different if m = 2, and

c) 0 to 20 % by weight of a liquid-crystalline component C comprising one or more compounds having a dielectric anisotropy of less than -1.5.

The following preferred embodiments are of particular impor¬ tance:

Component B essentially consists of one or more com¬ pounds selected from the group consisting of la to lg and nitrile-containing compounds.

Component B contains one or more compounds selected from the group consisting of la to lg, nitrile-containing and nitrile-free, halogenated compounds other than those of the formulae la to lg.

Component B essentially consists of one or more com¬ pounds selected from the group consisting of la to lg and nitrile-free, halogenated compounds other than those of the formulae la to lg.

Component B contains one or more compounds selected from the group consisting of compounds of the formula Ila to Ilf:

R-®-(A^-X Ila

R-<Ai>-CH ₇ CH _? -U ² /-X lib

R- AV -<A ² > -(A ³ / -X He

R- AV-<A ² >-CH,CH ₂ - <A ³ >-X lid

R~®-CH ₂ CH ₂ -<® -®-X Ilf

in which

R is n-alkyl or n-alkenyl of up to 9 carbon atoms,

X is cyano, -NCS, F, Cl, -CHF ₂ , -0CF ₃ , -0CHF ₂ , -0CF ₂ CF ₂ H or -OC^Fg, and

the rings

A ⁱ , A ² and A ³ are each, independently of one another, 1,4- phenylene, 2- or 3-fluoro-l,4-phenγlene, 2,3-di- fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenγlene, trans-l,4-cγclohexγlene or 1,4-cγclohexenγlene.

Component B contains compounds of the formulae Ila to Ilf in which X is -NCS, F, Cl, -CHF ₂ , -0CF ₃ , -0CHF ₂ ,

-0CF ₂ CF^1 or -OC^Fg and the amount of cyano compounds in. component B is 0 to 50 % by weight.

Component B does not contain any compounds of the formu¬ lae Ila to Ilf in which X is cyano.

X is F, Cl, -OCF3, -OCHF2 or -CHF2.

Component A contains one or more compounds selected from the group consisting of III to 117:

R ^I -(H)-(H)-R ² 116

R -(H -CH ₂ CH ₂ -(H -R ² 117

in which R ¹ and R ² have the meaning given in Claim 2.

Component A additionally contains one or more compounds selected from the group consisting of 118 to I120:

R--^^(O -H^-R- 118

R- H -CH ₂ CH ₂ -(θ)-<HyR ² 119

R ^! -{o)-(o)*-(g)-R ² nil

R ⁱ - H -CH ₂ CH ₂ - θ)-( )-R ² 1112

^RI °) ^{~R2 II14}

R-(H)rCH ₂ CH ₂ - H)-(θ)-R ² 1115

R-(H -(H -CH ₂ CH ₂ -(θ)-R ² 1116

R-®-CH ₂ CH ₂ - H)^CH ₂ CH ₂ -(θ)-R ² 1117

^RI -( ^R X®- - ^{2 πi9}

in which Ri and R ² have the meaning given in Claim 2 and the 1,4-phenylene groups in 118 to 1117 can each, inde¬ pendently of one another, also be mono- or polysubsti- tuted by fluorine.

Component A additionally contains of one or more com ^¬ pounds selected from the group consisting of 1121 to 1125:

R1-®*-(0 -(0)-(H -R 1121

RI-{H -<H O>-(H)»-R ² 1123

R-S H}-CH ₂ CH ₂ -(0)-(H R ² 1124

in which R ¹ and R ² have the meaning given in Claim 2 and the 1,4-phenylene groups in I121 to II25 can each, independently of one another, also be mono- or polysub- stituted by fluorine.

Component A contains one or more compounds selected from the group consisting of I126 to I127:

C _r H _2r+1 -<H <H CH ₂ -F 1126

C _r H _2r -( HyCH ₂ CH ₂ -F 1127

in which C^ _r+ i is a straight-chain alkyl group of up to 7 carbon atoms .

The liquid crystal mixture additionally contains , in addition to components A, B and C, one or more compounds selected from the group consisting of III , IV and IVa :

in which R ¹ and R ^z have the meaning given in Claim 2.

The liquid crystal mixture additionally contains, in addition to components A, B and C, one or more compounds of the formula

in which

R ⁱ and R ² have the meaning given in Claim 2, and

Z° is a single bond, -CH ₂ CH ₂ -, -{H)T or

-(H -CH ₂ CH ₂ -.

The liquid crystal mixture additionally contains, in addition to components A, B and C, one or more compounds selected from the group consisting of V and VI:

in which R ¹ and R ² have the meaning given in Claim 2.

The liquid crystal mixture additionally contains, in addition to components A, B and C, one or more compounds selected from the group consisting of VII to XIII :

R-(-<S-),-CH ₂ CH ₂ -5>-: R ² VII

F F R ⁱ - ⁽ -<H ^H >--) ⁾ .--(®OV-R ^I2 VIII

F F

F F

R--(H -CH ₂ CH ₂ -(H)-(CH ₂ CH ₂ ) _B -\O - -IR ² X

F F

R ⁱ -^-CH ₂ CH ₂ -5)-(CH ₂ CH ₂ ) ₈ -{H)-R ² XI

SUBSTITUTESHξET

F r F Γ

R ^{i L} -- ((-- HH)>--)) ₈ --<<HH>>--CCHH ₂₇ 00O---<<(00O/)---IRI ² XII

Ri -{H -CH ₂ O-^O}- (CH ₂ CH ₂ ) .- i n- XIII

in which

R ⁱ and R ² have the meaning given in Claim 2, and

s is 0 or 1.

Particular preference is given to liquid crystal mixtures which contain nitrile-containing and nitrile-free, haloge¬ nated compounds, the latter preferably conforming to the formulae Ila to Ilf in which X is F, Cl, -CHF ₂ , -0CF ₃ , -0CHF ₂ ,

-0CF ₂ CF ₂ H or -OC^Fg.

The ratio of nitrile-free to nitrile-containing compounds in component B is preferably > 1:1, in particular > 2:1. Partic¬ ularly preferred ranges are 2.5:1 to 6:1. The nitrile-free compounds are preferably those of the formulae la to lg and Ha to Ilf in which X is different from CN.

However, very particular preference is given to liquid crys¬ tal mixtures whose component B essentially consists of nitrile-free, halogenated compounds. Preferably, the above mentioned preferred compounds of the formulae la to lg are used alone or together with those of the formulae Ila to Ilf.

The mixtures according to the invention may also contain one or more compound with high optical anisotropy, for example compounds selected from the following group:

R ⁱ -(θ)-C-C-(θ)-R ²

R-{^C ₂ H ₄ -( )-C-C-(θ)-R ²

wherein R ⁱ and R ² have the meaning given above and one of the the 1,4-phenylene rings in each molecule may also be later ^¬ ally substituted by fluorine.

The residues R, R ¹ and R ² have the following preferred mean ^¬ ings.

If R ⁱ , R ² and/or R are an alkyl or oxaalkyl radical these radicals are straight-chained. Preferably, it has 2, 3, 4, 5, 6 or 7 C atoms and is accordingly perferably ethyl, propyl, butyl, pentyl, hexyl or heptyl.

Oxaalkyl is preferably straight chain 2-oxapropyl (= meth- oxymethyl) , 2- (= ethoxymethyl) or 3-oxabutyl (= 2 methoxy- ethyl) , 2-, 3- oder 4-oxapentγl, 2-, 3-, 4- or 5-oxahexγl, 2-, 3-, 4-, 5- or 6-oxaheptγl, 1,3-dioxabutγl (= meth- oxymethoxy) , 1,3-, 1,4-, 2,4-dioxapentyl, 1,3-, 1,4-, 1,5-, 2,4-, 2,5- or 3,5-dioxahexyl, 1,3-, 1,4-, 1,5-, 1,6-, 2,4-, 2,5-, 2,6-, 3,5-, 3,6- or 4,6-dioxaheptyl.

If R ¹ , R ² and/or R are an alkenyl radical, it is straight- chained and has preferably 2 to 7 C atoms. Accordingly, it is vinyl, prop-1-, or prop-2-enyl, but-1-, 2- or but-3-enyl, pent-1-, 2-, 3- or pent-4-enγl, hex-1-, 2-, 3-, 4- or hex-5- enyl, hept-1-, 2-, 3-, 4-, 5- or hept-6-enyl.

If R ¹ and/or R ² are a -fluoralkyl radical, it is straight- chained and has preferably 1 to 7 C atoms. Accordingly, it is fluoromethyl, 2-fluoroethγl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentγl, 6-fluorohexγl or 7-fluoroheptyl.

"Essentially" is understood to mean that the amount of fur¬ ther compounds in the corresponding component is 20 %, in particular < 10 %.

Preference is also given to liquid crystal mixtures whose component B contains compounds whose end groups are chlori¬ nated. Compounds of this type are known to one skilled in the art and preferably conform to the formulae Ila to Ilf where X

is Cl. In a particularly preferred embodiment, the mixtures contain one or more compounds of the formula Ila to Ilf in

F which A ² -X or A ³ -X is -(θ)-X where X is CF ₃ , -0CF ₃ -, 0CHF ₂ or

Cl or wherein A ² -X or A ³ -X is "(0)-F.

Furthermore, component B can also contain tetranuclear com¬ pounds, for example in accordance with formulae He to Ilf in which one of the rings A ¹ to A ³ is present twice.

In a particularly preferred embodiment, the mixtures contain compounds which have a terminal nitrile and are present in component B in an amount from 0 to 50 % by weight. Particular preference is given to mixtures which do not contain any compounds which have a terminal nitrile. Suprisingly, it has been found that groups such as -0CF ₃ , -0CHF ₂ , -0CF ₂ CF ₂ H or -OCA have a considerably less stabilizing effect on ions in the displays than -0CH ₃ or -0C ₂ H ₅ . The same is true for ali- phatically bound alkoxy (compounds of the formulae HI and IV).

The mixtures according to the invention preferably have a resistivity of > 10 ^x2 Ω x cm, particularly preferably > 10 ¹³ Ω x cm, at 20°. The mean £ is preferably < 7, in particular < 5.

The values of dielectric anisotropy of the individual com¬ pounds of components A to C are determined at 20° by extrapo¬ lation from a polar mixture (containing 24 % of p-trans-4- propylcyclohexylbenzonitrile, 36 % of p-trans-4-pentγlcyclo-

hexylbenzonitrile, 25 % of p-trans-4-heptylcyclohexylbenzo- nitrile and 15 % of 4-cyano-4'-(trans-4-pentylcyclohexyl)bi- phenyl) , if the compound to be determined contains a dipole along the longitudinal axis of the molecule, or from a neu¬ tral mixture (containing 22 % of trans-l-p-ethylphenγl-4-pro- pylcyclohexane, 20 % of trans-1-p-methoxyphenγl-l-propylcγ- clohexane, 15 % of trans-l-p-ethoxγphenγl-4-propylcyclohex- ane, 19 % of 4-ethyl-4-(trans-4-propylcyclohexyl)biphenγl, 14 % of 4-ethyl-4'-(trans-4-pentγlcyclohexγl)biphenyl, 5 % of 4,4'-bis(trans-4-propylcyclohexyl)biphenγl and 5 % of 4-(trans-4-pentylcγclohexyl)-4'-(trans-4-propylcyclohexγl) bi- phenyl) in the case of neutral compounds.

The liquid crystal mixtures according to the invention make it possible to achieve a high value for the resistivitiy in combination with low viscosities, which allows to produce excellent MLC displays. The MLC displays according to the invention preferably operate in the first transmission mini¬ mum according to Gooch and Tarry [C.H. Gooch and H.A. Tarry, Electron. Lett. 10, 2-4, 1974; C.H. Gooch and H.A. Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975], in which case in addition to particularly favourable elctrooptical properties such as, for example, high steepness of the characteristic curve and low angle dependence of the contrast (German Patent Specification 3,022,818) in combination with the same thresh¬ old voltage as in analogous display, a smaller dielectric anisotropy is sufficient in the second minimum. This makes it possible to achieve significantly higher resistivities in the first minimum, when the mixtures according to the invention are used.

The viscositiy at 20 °C is peferably 25 mPa.s. The nematic phase range is preferably at least 70°, in particular at least 80°. Preferably, this range extends at least from -20° to +70°.

The individual compounds of the formulae la to lg and I to IV and their subformulae which can be used in the MLC displays according to the invention are either known or can be pre¬ pared analogously to known compounds.

If component B is not composed predominantly of strongly dielectrically positive nitrile components but predominantly only of weakly dielectrically positive compounds such as, for example, the halogenated compounds mentioned below, component A can be omitted entirely, and the mixtures according to the invention can in this special embodiment be solely based on component B and, if desired, component C.

The rings A ¹ , A ² and A ³ are each preferably, independently of one another, trans-1,4-cyclohexylene or 1,4-phenylene. In a preferred embodiment, one of the rings A ¹ , A ² and A ³ is 2- or 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene or 2,6-di- fluoro-1,4-phenγlene. The ring bound to X (i.e. A ² in Ha and Hb and A ³ in He to Ilf) is preferably 1,4-phenylene which is unsubstituted or even mono- or disubstituted by fluorine. A ² -X and A ³ ~X are preferably a group selected from the formu¬ lae (a) to (i) :

F -(0 F(C1) -(θ)-F(Cl) -<OVF(CI) (a) (b) (c)

/

-(θ)-F(Cl) -(θ)-OCF ₃ -@>-OCF ₃

(d) (e) (f)

-(θ)-OCHF ₂ -(θ)-OCHF ₂ - θ - ^■ F(C1)

\ F

(g) (h) (i)

of which (a) , (b) , (d) , (e) , (g) , (h) and (i) are particularly preferred.

Particularly preferred smaller groups of compounds are listed below:

Y

R-(H)-CH ₂ CH ₂ - O)-X Hbl

Z Y z

R-<H>-<H>-®-X IIc3

Z Y Z Y

R-®-®- - CCHHo,CCHH,—- tt 'θ>-X Idl

Z Y Z Y

/

RHHH>-\OO >CH ₂ CH ₂ -<£)-X Id2

Z

- 25

Z Y Z Y Z Y

R-(θ) @-CΗ ₂ CΗ ₂ -(θ)-X Id3

Z

Z

In the partial formulae Hal to If3, R is in each case n-alkyl or n-alkenyl of up to 9 carbon atoms. Y and Z are each, independently of one another, H or F although one or two of the radicals Y and Z is preferably fluorine. However, X is preferably F, Cl, -CF ₃ , -0CF ₃ or -0CHF ₂ .

Component B preferably represents 10 % to 100 %. in paticular 20 % to 80 %, of the mixture according to the invention.

The amounts of the compounds of the formulae HI to XI in the mixtures according to the invention (preferred ranges) can be seen from the table below:

Sum of compounds HI and IV: 0 % to 40 %, preferably 10 % to 30 %

Sum of compounds V and VI: 0 % to 40 %, preferably 5 % to 20 %

Sum of compounds VII to XI: 0 % to 20 %. preferably 5 % to 15 %

It goes without saying that the mixtures according to the invention, which preferably consist essentially of the com¬ pounds mentioned as preferred for components A to C, may additionally also contain further compounds not mentioned here explicitly. However, this leads in many cases to more unfavourable properties. One skilled in the art can easily determine whether and in which amounts further compounds can be used.

The design of the MLC display according to the invention which consists of polarizers, electrode base plates and electrodes which have been subjected to surface treatment is that which is customary for this type of display. The defini¬ tion of customary design is in this case very broad and also comprises all modifications and alterations of the MLC dis¬ play, in particular also matrix display elements based on poly-Si TFT or MIM.

However, a significant difference between the displays according to the invention and those which have been custom¬ ary so far and are based on the twisted nematic cell is the selection of the liquid crystal parameters of the liquid crystal layer.

The preparation of the liquid crystal mixtures to be used according to the invention is carried out in the usual man¬ ner. As a rule, the desired amount of the components used in a minor amout is dissolved in the components which constitute the major component, advantageously at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or metha- nol, and remove the solvent again after the mixing, for example by destination.

The dielectrics can also contain further additives known to one skilled in the art and described in the literature. For example, 0-15 % pleochroic colorants or chiral doping sub¬ stances can be added.

The examples which follow are intended to illustrate the invention without limiting it. Hereinbefore and hereinafter all temperatures are given in °C. The percentages are by weight.

We have filled the new mixtures into test cells and measured the RC times, characterizing the exponential decay of the voltage at the electrodes of the pixel. The voltage was applied in form of 60 μs pulses of variable amplitude between 1 V and 4 V. The subsequent evolution of the actual voltage at the pixel was detected via a fast, high impedance opera¬ tional amplifier and recorded with a storage oscilloscope. This method has already been reported (RIEGER, B. , BOHM, E. and WEBER, G. , 1989, Presentation at Freiburger Arbeitstagung Flύssige ristalle, Conference Proceedings, Freiburg) .

Example 1

A matrix liquid crystal display of the TFT type containing a nematic liquid crystal mixture consisting of

12 % of trans-l-p-trifluoromethγl-4-propγlcγclohexane, 12 % of trans-l-p-trifluoromethγl-4-pentγlcγclohexane, 8 % of trans-l-p-methoxyphenγl-4-propylcγclohexane, 14 % of l-[trans-4-(trans-4-propγlyclohexyl)-cγclohexyl]- 2-(p-fluorophenyl)-ethane,

14 % of l-[trans-4-(trans-4-pentylyclohexγl)-cγclohexyl]-

2-(p-fluorophenyl)-ethane, 10 % of l-[trans-4-(trans-4-propγlyclohexγl)-cγclohexγl]- 2-(3,4~difluorophenyl)-ethane,

15 % of l-[trans-4-(trans-4-propγlγclohexγl)-cγclohexyl]-

4-trifluoro ethoxybenzene and 15 % of l-[trans-4-(trans-4-butγlγclohexγl)-cyclohexγl]- 4-trifluoromethoxybenzene

shows a RC time of more than 200 msec at 80 °C and a thresh¬ old voltage V ₁₀ of 2.22 V (1 min) . The nematic mixture has a clearpoint C. of 102 °C, a viscosity η of 17 mPa.s at 20° and an optical anisotropy Δn of 0.080.

The composition of the mixtures of Examples 2 to 14 is given below, the individual compounds being coded as follows:

PCH-301: trans-l-p-methoxyphenγl-4-propγlcyclohexane CCH-301: trans,trans-4-methoxy-4'-propylcyclohexyl- cyclohexane CBC-33F: 4,4'-bis-(trans-4-propγlcγclohexγl)-2-fluoro- biphenyl

CBC-55F : 4,4'-bis-(trans-4-pentγlcyclohexyl) -2- fluoro- biphenyl

CBC-53F : 4-(trans-4-pentγlcyclohexyl)-4'-(trans-4-pro- pylcyclohexyl)-2-fluorobiphenyl

CBC-33 4,4'-bis-(trans-4-propγlcγclohexyl)- biphenyl CBC-55 4,4'-bis-(trans-4-pentylcyclohexyl)-biphenyl CBC-53 4-(trans-4-pentylcγclohexγl)-4'-(trans-4-pro- pylcyclohexyl)-biphenyl

ECCP-33: 1-[trans-4-(trans-4-propγlcγclohexyl)-cyclo- hexyl] -__-(p-propylphenyl)-ethane

CCH-51F: trans,trans-4-fluoromethyl-4'-pentylcyclo- hexylcyclohexane

CCH-31F: trans,trans-4-fluoromethyl-4'-propylcyclo- hexy1eye1ohexane

PTP-102: 4-methγl-4'-ethoxy-tolan

PTP-201: 4-methoxγ-4'-ethyl-tolan

CPTP-301 4-(trans-4-propy1eyelohexy1)-4'-methoxyto1an

CPTP-302 4-(trans-4-propγlcγclohexγl)-4'-ethoxytolan

CPTP-303 4-(trans-4-propylcyclohexγl)-4'-propoxytolan

PCH-5F trans-1-p-fluorophenγl-4-pentγlcyclohexane

PCH-6F trans-1-p-fluorophenyl-4-hexγleye1ohexane

PCH-7F trans-l-p-fluorophenγl-4-heptylcγclohexane

EPCH-20CF 1-(trans-4-ethγlcγclohexγl)-2-(p-trifluoro- methoxyphenyl)-ethane

EPCH-30CF, 1-(trans-4-propylcγclohexyl)-2-(p-trifluoro- ethoxyphenyl)-ethane

EPCH-50CF, 1-(trans-4-pentγlcγclohexγl)-2-(p-trifluoro- ethoxyphenyl)-ethane

EPCH-70CF, 1-(trans-4-heptγlcyclohexγl)-2-(p-trifluoro- methoxyphenyl)-ethane

PCH-30CF, trans-l-p-trifluoromethoxyphenγl-4-propyl- cyclohexane

PCH-50CF, trans-l-p-trifluoromethoxγphenγl-4-pentγl- cyclohexane

ECCP-30CF, 1-[trans-4-(trans-4-propγlcyclohexyl)- cyclohexyl] -2-(p-trifluoromethoxyphenyl)- ethane

ECCP-50CF ₃ l-[trans-4-(trans-4-pentylcγclohexγl)-cyclo¬ hexyl]-2-(p-trifluoromethoxyphenyl)-ethane

CCP-20CF, p-[trans-4-(trans-4-ethγlcyclohexγl)-cyclo¬ hexyl]-trifluoromethoxybenzene

CCP-30CF, p-[trans-4-(trans-4-propγlcγclohexγl)-cyclo¬ hexyl]-trifluoromethoxybenzene

CCP-40CF ₃ : p-[trans-4-(trans-4-butylcyclohexyl)-cyclo¬ hexyl]-trifluoromethoxybenzene

CCP-50CF ₃ : p-[trans-4-(trans-4-pentylcyclohexyl)-cyclo¬ hexyl]-trifluoromethoxybenzene BCH-30CF ₃ : 4-trifluoromethoxγ-4'-(trans-4-propγlcγclo- hexyl)-biphenyl

ECCP-3F.F: 1-[trans-4-(trans-4-propγlcyclohexγl)-cyclo¬ hexyl]-2-(3,4-difluorophenyl)-ethane

ECCP-5F.F: 1-[trans-4-(trans-4-pentγlcγclohexγl)-cyclo¬ hexyl]-2-(3,4-difluorophenyl)-ethane

CCP-3F.F: 4-[trans-4-(trans-4-propylcγclohexyl)-cyclo¬ hexyl]-1,2-difluorobenzene

CCP-5F.F: 4-[trans-4-(trans-4-pentylcγclohexγl)-cyclo¬ hexyl]-1,2-difluorobenzene

CCP-3F: 4-[trans-4-(trans-4-propγlcγclohexγl) -cyclo¬ hexyl]-fluorobenzene

ECCP-3F: 1-[trans-4-(trans-4-propylcyclohexγl)-cyclo¬ hexyl]-2-(p-fluorophenyl)-ethane

ECCP-5F: 1-[trans-4-(trans-4-pentylcyclohexγl)-cyclo¬ hexyl]-2-(p-fluorophenyl)-ethane

CP-3F: p-fluorophenyl trans-4-(trans-4-propylcγclo- hexyl)-cyclohexanecarboxylate

CP-5F: p-fluorophenyl trans-4-(trans-4-propylcyclo- hexyl)-cyclohexanecarboxylate

PYP-5F: 2-p-fluorophenyl-5-pentγlpγrimidine

PYP-6F: 2-p-fluorophenyl-5-hexγlpγrimidine

PYP-7F: 2-p-fluorophenγl-5-heptγlpγrimidine

PYP-30CF ₃ 2-p-trifluoromethoxγphenyl-5-propylpγrimidine

PYP-50CF ₃ 2-p-trifluoromethoxγphenγl-5-peήtγlpγrimidine

PYP-70CF ₃ 2-p-trifluoromethoxyphenyl-5-heptγlpγrimidine

PCH-3: p-trans-4-propylcyclohexγl-benzonitrile

PCH-4: p-trans-4-butγlcγclohexγl-benzonitrile

PCH-5: p-trans-4-pentylcγclohexγl-benzonitrile

ECCP-3: 1-[trans-4-(trans-4-propγlcyclohexγl)-cyclo¬ hexyl]-2-(p-cyanophenγl)-ethane

ECCP-3CF ₃ : 1-[trans-4-(trans-4-propylcyclohexγl)-cyclo¬ hexyl]-2-(p-trifluoromethylphenyl)-ethane

ECCP-5CF ₃ : 1-[trans-4-(trans-4-pentγlcyclohexyl)-cyclo¬ hexyl]-2-(p-trifluoromethylphenyl)-ethane

PYP-5N.F: 2-(3-fluoro-4-cyanophenγl)-5-pentγlpγrmidine PYP-7N.F: 2-(3-fluoro-4-cγanophenγl)-5-heptγlpγrimidine PCH-30CF ₂ : trans-1-p-difluoromethoxyphenyl-4-propγl- cyclohexane

PCH-50CF, trans-1-p-difluoromethoxγphenyl-4-pentγl- cyclohexane

PCH-30CF ₂ : trans-1-p-difluoromethoxyphenyl-4-propyl- cyclohexane

PCH-3CF ₃ : trans-1-p-trifluoromethyl-4-propγlcγclohexane

PCH-5CF ₃ : trans-1-p-trifluoromethyl-4-pentγlcyclohexane

EPCH-5CF ₃ : 1-(trans-4-pentγlcyclohexγl)-2-(p-trifluoro ^¬ methylphenyl)-ethane

CCP-2CF ₃ : 4-[trans-4-(trans-4-ethγlcyclohexyl)-cyclo¬ hexyl]-1-trifluoromethylbenzene

CCP-3CF ₃ : 4-[trans-4-(trans-4-propylcyclohexγl)-cyclo¬ hexyl]-1-trifluoromethylbenzene

CCP-5CF ₃ : 4-[trans-4-(trans-4-pentylcyclohexyl)-cyclo¬ hexyl]-1-trifluoromethylbenzene

CECP-3CF ₃ : 4-[trans-4-(trans-4-propγlcγclohexyl)-cyclo¬ hexyl]-1-trifluoromethylbenzene

BCH-3CF ₃ : 4-trifluoromethγl-4'-(trans-4-propγlcyclo- hexyl)-biphenyl BECH-3CF ₃ : 4-trifluoromethγl-4'-(trans-4-propγlcγclo- hexylethyl)-biphenyl EBCH-3CF ₃ : 4-[p-(trans-4-propγlcγclohexγl)-phenyl- ethyl]-1-trifluoromethylbenzene

CCP-3CF ₃ .F: 4-[trans-4-(trans-propylcyclohexyl)-cyclo¬ hexyl]-2-fluoro-l-trifluoromethylbenzene

BCH-3F.F: 3,4-difluoro-4'-(trans-4-propγlcyclohexγl)- biphenyl

BCH-5F.F: 3,4-difluoro-4'-(trans-4-pentylcγclohexγl)- biphenyl

CCP-5F.F.F: 4-[trans-4-(trans-pentylcyclohexyl)- cyclohexyl]-1,2,6-trifluorobenzene

C. 91 ^β C, Δn = 0,09 η = 19 mPa.s, V ₁₀ = 1,8 V

V ₁₀ = 2,1 V, η = 16 mPa.s

C. 102°, Δn = 0,14 η = 19 mPa.s, V ₁₀ = 2,0 V

Example 14

PCH-3 10.00

PCH-5CF ₃ 18.00

PCH-6F 14.00

PCH-7F 10.00

CCP-3F.F 9.00

CCP-5F.F 7.00

CBC-33 5.00

CBC-53 6.00

CBC-55 5.00

CBC-33F 5.00

CBC-53F 6.00 C. 65 ^β C, Δn = 0,0892

CBC-55F 5.00 V ₁₀ = 1 ,59 V,

C. 100 ^β C, Δn = 0, 10

V ₁₀ = 2,3 V, η = 16 mPa. s

C. 63 °C, Δn = 0,0873 C. 65 °C, Δn = 0,0827

V ₁₀ = 1,59 V,

C. 91 °C, Δn = 0,0945

V ₁₀ = 1,71 V,