DE10235340B4 - Liquid crystalline mixtures and their use - Google Patents

Abstract

eine oder mehrere Verbindungen der Formel II,

eine oder mehrere Verbindungen der Formel III*j,

und eine oder mehrere Verbindungen der Formel I**C1

enthält,
worin die einzelnen Reste folgende Bedeutungen besitzen:
R¹¹, R²¹, R²² einen unsubstituierten, einen einfach durch CN oder CF₃ oder mindestens einfach durch Halogen substituierten Alkyl- oder Alkenylrest mit bis zu 15 C-Atomen, woebei in diesen Resten auch eine oder mehere CH2-Gruppen durch -O-, -S-, -C≡C-, -OC-O-, oder -O-CO- so ersetzt sein können, dass O-Atome nicht direkt miteinander verknüpft sind,
alkyl einen Alkylrest mit 1 bis 7...Nematic liquid-crystal mixture, characterized in that it contains 15-75% by weight of a liquid-crystalline component A consisting of several compounds having a dielectric anisotropy of more than +1.5 and 25-85% by weight of a liquid-crystalline component B consisting of a or more compounds having a dielectric anisotropy between -1.5 and +1.5, wherein component A is each
one or more compounds of the formula Ii,

one or more compounds of the formula II,

one or more compounds of the formula III * j,

and one or more compounds of the formula I ** C1

contains
in which the individual radicals have the following meanings:
R ¹¹ , R ²¹ , R ^{22 is} an unsubstituted, a simply by CN or CF ₃ or at least simply substituted by halogen alkyl or alkenyl radical having up to 15 carbon atoms, where in these radicals also one or more CH 2 groups by -O -, -S-, -C≡C-, -OC-O-, or -O-CO- can be replaced so that O atoms are not directly linked,
alkyl is an alkyl radical with 1 to 7 ...

Description

The invention relates to liquid-crystalline mixtures and their use in twisted and highly twisted nematic liquid crystal displays (English: Twisted Nematic, short: TN or Supertwisted Nematic, short: STN) with very short switching times and good slopes and angle dependencies.

TN displays are known, e.g. From M. Schadt and W. Helfrich, Appl. Phys. Lett., 18, 127 (1971). STN ads are known, for. B. off EP 0 131 216 B1 ; DE 34 23 993 A1 ; EP 0 098 070 A2 ; M. Schadt and F. Leenhouts, 17th Freiburger Workshop on Liquid Crystals (8.-10.04.87); K. Kawasaki et al., SID 87 Digest 391 (20.6); M. Schadt and F. Leenhouts, SID 87 Digest 372 (20.1); K. Katoh et al., Japanese Journal of Applied Physics, Vol. 11, L 1784-L 1786 (1987); F. Leenhouts et al., Appl. Phys. Lett. 50 (21), 1468 (1987); HA van Sprang and HG Koopman, J. Appl. Phys. 62 (5), 1734 (1987); TJ Scheffer and J. Nehring, Appl. Phys. Lett. 45 (10), 1021 (1984), M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (5), 236 (1987) and EP Raynes, Mol. Cryst. Liq. Cryst. Letters Vol. 4 (1), pp. 1-8 (1986). The term STN here includes any higher-twist display element with a twist angle in the amount of between 160 ° and 360 °, such as the display elements according to Waters et al. (CM Waters et al., Proc. Soc. Inf. Disp. (New York) (1985) (3rd International Display Conference, Kobe, Japan), the STN-LCD's ( DE OS 35 03 259 SBE-LCD's (TJ Scheffer and J. Nehring, Appl. Phys. Lett., 45: 1021 (1984)), OMI-LCD's (M. Schadt and F. Leenhouts, Appl. Phys. Lett., 50, 236 (1987)) , DST-LCD's ( EP OS 0 246 842 ) or BW-STN-LCD's (K.Kawasaki et al., SID 87 Digest 391 (20.6)).

In particular STN displays are characterized by significantly better slopes of the electro-optical characteristic and associated better contrast values and by a much lower angle dependence of the contrast in comparison to standard TN displays.

Of particular interest are TN and STN displays with very short switching times, especially at lower temperatures. To achieve short switching times, the rotational viscosities ν _{20 of} the liquid-crystal mixtures have hitherto been optimized by using most monotropic additives with a relatively high vapor pressure. However, the achieved switching times were not sufficient for every application.

To achieve a steep electro-optical characteristic curve in the displays according to the invention, the liquid-crystal mixtures should have relatively large values for the ratio of the elastic constants K ₃₃ / K ₁₁ and relatively small values for Δε / ε _⊥ . where Δε is the dielectric anisotropy and ε _{⊥ is} the dielectric constant perpendicular to the molecular _longitudinal axis.

• 1. Breites d/p-Fenster
• 2. Hohe chemische Dauerstabilität
• 3. Hoher elektrischer Widerstand
• 4. Geringe Frequenz- und Temperaturabhängigkeit der Schwellenspannung.

In addition to optimizing the contrast and the switching times, further important requirements are placed on such mixtures:

• 1. Wide d / p window
• 2. High chemical stability
• 3. High electrical resistance
• 4. Low frequency and temperature dependence of the threshold voltage.

The obtained parameter combinations are far from sufficient, especially for high-multiplex STN displays (with a multiplex rate in the range of about 1/400), but also for medium and low-multiplex STN (with multiplex rates in the range of about 1 / 64 or 1/16), and TN displays. This is partly due to the fact that the different requirements are counteracted by material parameters.

In the EP 0 837 045 A1 are liquid crystalline compounds having the end group - (CH ₂ ) _u -C≡CR ₂ , wherein u is 1 to 5 and R _{2 is} H or alkyl, and such compounds containing liquid-crystalline media described. The advantages of these compounds and mixtures are high Δn values, a nematic phase even at low temperatures, low viscosity and high stability.

Other liquid-crystalline media for TN or STN displays are off EP 1 142 977 A1 . EP 1 261 679 A1 and WO 01/64814 A1 known.

There is thus still a great need for liquid-crystalline mixtures, in particular for TN and STN displays with very short switching times with simultaneously large operating temperature range, high slope, good angle dependence of the contrast and low threshold voltage, which meet the above requirements.

The invention has for its object to provide TN and STN displays that have the disadvantages mentioned above not or only to a lesser extent and at the same time short switching times, especially at low temperatures, and very good slopes.

It has now been found that this object can be achieved by using nematic liquid-crystal mixtures.

eine oder mehrere Verbindungen der Formel II,

eine oder mehrere Verbindungen der Formel III*j,

und eine oder mehrere Verbindungen der Formel I**C1

enthält,
worin die einzelnen Reste folgende Bedeutungen besitzen:
R¹¹, R²¹, R²² einen unsubstituierten, einen einfach durch CN oder CF₃ oder mindestens einfach durch Halogen substituierten Alkyl- oder Alkenylrest mit bis zu 15 C-Atomen, woebei in diesen Resten auch eine oder mehere CH2-Gruppen durch -O-, -S-, -C≡C-, -OC-O-, oder -O-CO- so ersetzt sein können, dass O-Atome nicht direkt miteinander verknüpft sind,
alkyl einen Alkylrest mit 1 bis 7 C-Atomen,
Alkenyl ein Alkenylrest mit 2 bis 7 C-Atomen.Nematic liquid-crystal mixture, characterized in that it contains 15-75% by weight of a liquid-crystalline component A consisting of several compounds having a dielectric anisotropy of more than +1.5 and 25-85% by weight of a liquid-crystalline component B consisting of a or more compounds having a dielectric anisotropy between -1.5 and +1.5, wherein component A is each
one or more compounds of the formula Ii

one or more compounds of the formula II,

one or more compounds of the formula III * j,

and one or more compounds of the formula I ** C1

contains
in which the individual radicals have the following meanings:
R ¹¹ , R ²¹ , R ^{22 is} an unsubstituted, a simply by CN or CF ₃ or at least simply substituted by halogen alkyl or alkenyl radical having up to 15 carbon atoms, where in these radicals also one or more CH 2 groups by -O -, -S-, -C≡C-, -OC-O-, or -O-CO- can be replaced so that O atoms are not directly linked,
alkyl is an alkyl radical having 1 to 7 C atoms,
Alkenyl is an alkenyl radical having 2 to 7 C atoms.

• • sehr schnelle Schaltzeiten, insbesondere bei tiefen Temperaturen,
• • hoher Klärpunkt,
• • niedrige Schwellenspannung und Operationsspannung und/oder
• • geringe Temperaturabhängigkeit der Schwellenspannung und Operationsspannung, insbesondere im Bereich von 20°C und bei tiefen Temperaturen.

The use of the compounds of the formulas Ii and II in the mixtures for TN and STN displays causes

• • very fast switching times, especially at low temperatures,
• • high clearing point,
• Low threshold voltage and operating voltage and / or
• • low temperature dependence of the threshold voltage and operating voltage, especially in the range of 20 ° C and at low temperatures.

In particular, the compounds of the formulas Ii and II markedly shorten the switching times of TN and STN mixtures while at the same time having a low temperature dependence of the threshold voltage.

• – hohe Steilheit der elektrooptischen Kennlinie,
• – niedrige Viskosität,
• – lange Lagerzeiten im Display bei tiefen Temperaturen.

Furthermore, the mixtures according to the invention are characterized by the following properties:

• High steepness of the electro-optical characteristic,
• Low viscosity,
• - Long storage times in the display at low temperatures.

• – zwei Trägerplatten, die mit einer Umrandung eine Zelle bilden,
• – einer in einer Zelle befindlichen nematischen Flüssigkristallmischung mit positiver dielektrischer Anisotropie,
• – Elektrodenschichten mit Orientierungsschichten auf den Innenseiten der Trägerplatten,
• – einem Anstellwinkel zwischen der Längsachse der Moleküle an der Oberfläche der Trägerplatten und den Trägerplatten von 0 Grad bis 30 Grad, und
• – einem Verdrillungswinkel der Flüssigkristallmischung in der Zelle von Orientierungsschicht zu Orientierungsschicht dem Betrag nach zwischen 22,5° und 600°.

The invention further relates to the use of FK media according to the invention in a liquid crystal display

• Two support plates, which form a cell with a border,
• A nematic liquid-crystal mixture having a positive dielectric anisotropy in a cell,
• Electrode layers with orientation layers on the insides of the carrier plates,
• An angle of attack between the longitudinal axis of the molecules on the surface of the carrier plates and the carrier plates of 0 degrees to 30 degrees, and
• A twist angle of the liquid crystal mixture in the cell from orientation layer to orientation layer in the amount between 22.5 ° and 600 °.

• – einer nematischen Flüssigkristallmischung bestehend aus
• a) 15–75 Gew.-% einer flüssigkristallinen Komponente A, bestehend aus einer oder mehreren Verbindungen mit einer dielektrischen Anisotropie von über +1,5;
• b) 25–85 Gew.-% einer flüssigkristallinen Komponente B, bestehend aus einer oder mehreren Verbindungen mit einer dielektrischen Anisotropie zwischen –1,5 und +1,5;
• c) 0–20 Gew.-% einer flüssigkristallinen Komponente D, bestehend aus einer oder mehreren Verbindungen mit einer dielektrischen Anisotropie von unter –1,5 und
• d) gegebenenfalls einer optisch aktiven Komponente C in einer Menge, dass das Verhältnis zwischen Schichtdicke Abstand der Trägerplatten) und natürlicher Ganghöhe der chiralen nematischen Flüssigkristallmischung etwa 0,2 bis 1,3 beträgt,

wobei die Komponente A mindestens eine Verbindung der Formel Ii, mindestens eine Verbindung der Formel II, mindestens eine Verbindung der Formel III*j und mindestens eine Verbindung der Formel I**C1 enthält.In a particularly preferred embodiment, the mixture according to the invention consists of

• - A nematic liquid crystal mixture consisting of
• a) 15-75 wt .-% of a liquid-crystalline component A, consisting of one or more compounds having a dielectric anisotropy of over +1.5;
• b) 25-85 wt .-% of a liquid-crystalline component B, consisting of one or more compounds having a dielectric anisotropy between -1.5 and +1.5;
• c) 0-20 wt .-% of a liquid-crystalline component D, consisting of one or more compounds having a dielectric anisotropy of less than -1.5 and
• d) optionally an optically active component C in an amount such that the ratio between the layer thickness of the carrier plates) and the natural pitch of the chiral nematic liquid-crystal mixture is about 0.2 to 1.3,

wherein component A contains at least one compound of the formula Ii, at least one compound of the formula II, at least one compound of the formula III * j and at least one compound of the formula I ** C1.

The invention also relates to corresponding liquid-crystal mixtures for use in TN and STN displays, in particular in medium and low-multiplex STN displays.

worin alkyl einen Alkylrest mit 1 bis 7 C-Atomen und alkenyl einen Alkenylrest mit 2 bis 7 C-Atomen bedeutet.Very particular preference is therefore given to mixtures according to the invention which contain at least one compound of the formulas Iia and / or Iib,

wherein alkyl is an alkyl radical having 1 to 7 carbon atoms and alkenyl an alkenyl radical having 2 to 7 carbon atoms.

The proportion of the compounds of the formula Ii in the mixtures is 3.0 to 50% by weight, preferably 5.0 to 30% by weight, in particular 5.0 to 25% by weight.

The preferred compounds of the formula II include in particular the compounds in which R ²¹ and R ²² independently of one another are an alkyl, alkoxy or oxaalkyl radical having 1 to 7 C atoms or an alkenyl, alkenyloxy or oxaalkenyl radical having 2 to 7 C atoms. Mean atoms. Preferably, R ²¹ and R ²² independently of one another are methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl or n-heptyl.

worin x und y jeweils 1 bis 10 bedeuten, wobei x + y ≤ 10 und z 1 bis 5 bedeutet.Particular preference is given to mixtures according to the invention which comprise one or more, more preferably one, two or three, compounds of the formulas IIa to IId,

wherein x and y are each 1 to 10, wherein x + y ≤ 10 and z is 1 to 5.

The proportion of the compounds of formula II in the mixtures is 3.0 to 50 wt .-%, preferably 5.0 to 30 wt .-%, in particular 5.0 to 25 wt .-%.

The compounds of the formula Ii and the compounds of the formulas II having a dielectric ansiotropy of> 1.5 can be assigned to the component A defined above.

• • sehr kurzen Schaltzeiten, insbesondere bei tiefen Temperaturen,
• • niedriger Schwellenspannung und Operationsspannung und/oder
• • geringer Temperaturabhängigkeit der Schwellenspannung und Operationsspannung, insbesondere im Bereich von 20°C und bei tiefen Temperaturen.

The use of compounds of the formulas Ii and II leads in liquid-crystal mixtures to high clearing points and to TN and STN displays

• • very short switching times, especially at low temperatures,
• Low threshold voltage and operating voltage and / or
• • Low temperature dependence of the threshold voltage and operating voltage, especially in the range of 20 ° C and at low temperatures.

worin R³ eine der in Formel Ii für R¹¹ angegebenen Bedeutungen besitzt und L¹ bis L⁴ jeweils unabhängig voneinander H oder F bedeuten. R³ bedeutet in diesen Verbindungen besonders bevorzugt Alkyl, Alkenyl oder Alkoxy mit bis zu 8 C-Atomen. R^3' bedeutet einen Alkyl-, Alkoxy- oder Oxaalkylrest mit 1 bis 7 C-Atomen.Component A preferably contains one or more cyano compounds of the formulas IIIa to IIIj in addition to one or more compounds of the formulas Ii, II, III * and I ** C1,

wherein R ^{3 has} one of the meanings given in formula II for R ¹¹ and L ¹ to L ^{4 are} each independently H or F. R ³ in these compounds particularly preferably denotes alkyl, alkenyl or alkoxy having up to 8 C atoms. R ^{3 '} is an alkyl, alkoxy or oxaalkyl radical having 1 to 7 carbon atoms.

Particular preference is given to mixtures which contain one or more compounds of the formulas IIIb and IIIc, in particular those in which L ¹ and / or L ² denote F. Especially preferred are compounds of the formulas

wobei Alkenyl vorzugsweise 1E- oder 3E-Alkenyl mit bis zu 6 C-Atomen bedeutet.Further preferred are compounds of the formula

where alkenyl is preferably 1E or 3E alkenyl having up to 6 carbon atoms.

Particularly preferred here are the compounds of the formulas

sowie gegebenenfalls ein oder mehrere Verbindungen mit polarer Endgruppe der Formeln I**A bis I**R,

worin R* und R** eine der für R¹¹ in Formel 1 angegebenen Bedeutungen besitzen und L³ und L⁴ jeweils unabhängig voneinander H oder F bedeuten. R* und R** bedeuten in diesen Verbindungen besonders bevorzugt Alkyl, Alkenyl oder Alkoxy mit bis zu 8 C-Atomen.In addition to one or more compounds of the formula I, component A preferably contains one or more 3,4,5-trifluorophenyl compounds of the formulas I * A to I * J

and optionally one or more compounds having a polar end group of the formulas I ** A to I ** R,

wherein R * and R ** have one of the meanings given for R ¹¹ in formula 1 and L ³ and L ^{4 are} each independently H or F. R * and R ** in these compounds particularly preferably alkyl, alkenyl or alkoxy having up to 8 carbon atoms.

The individual compounds of the formulas Ii, I * A to I * J, I ** A to I ** R, II, IIIa to IIIj, III * a to III * i, III * k to III * n and III * j or their sub-formulas or other compounds which can be used in the mixtures according to the invention are either known or they can be prepared analogously to the known compounds.

Preferred liquid-crystal mixtures contain a plurality of compounds of component A in a proportion of 15% to 75%, particularly preferably from 20% to 65%. These compounds have a dielectric anisotropy Δε ≥ +3, in particular Δε ≥ +8, particularly preferably Δε ≥ +12.

• • eine oder zwei Verbindungen der Formeln Ii, insbesondere der Formeln Iia und/oder Iib,
• • eine oder mehrere, insbesondere ein oder zwei, Verbindungen der Formel II,
• • eine, zwei oder mehrere der Formel IIIc, insbesondere der Formel III*e, besonders bevorzugt der Formel III*j,
• • keine Verbindung der Formel IIIb, worin L¹ und L² H bedeuten.

Other preferred mixtures

• One or two compounds of the formulas Ii, in particular of the formulas Iia and / or Iib,
• One or more, in particular one or two, compounds of the formula II,
• One, two or more of the formula IIIc, in particular of the formula III * e, particularly preferably of the formula III * j,
• No compound of the formula IIIb in which L ¹ and L ^{2 are} H.

Liquid crystal mixtures according to the invention contain one or more compounds of component B in a proportion of 25 to 85%. The compounds of group B are distinguished in particular by their low values for the rotational viscosity γ ₁ .

und/oder eine oder mehrere Verbindungen ausgewählt aus der Gruppe bestehend aus den Dreiringverbindungen den Formeln IV10 bis IV29,

und/oder ein oder mehrere Verbindungen ausgewählt aus der Gruppe bestehend aus den Vierringverbindungen den Formeln IV30 bis IV36

worin R⁴ und R^4' die für R¹¹ in Formel I angegebenen Bedeutungen haben, L H oder F bedeutet, und die 1,4-Phenylenringe jeweils unabhängig voneinander auch ein- oder mehrfach durch Fluor substituiert sein können.Component B preferably contains one or more compounds selected from the group consisting of the two-ring compounds of the following formulas IV1 to IV9

and / or one or more compounds selected from the group consisting of the three-membered compounds of the formulas IV10 to IV29,

and / or one or more compounds selected from the group consisting of the four-ring compounds of the formulas IV30 to IV36

wherein R ⁴ and R ^{4 'have} the meanings given for R ¹¹ in formula I, L is H or F, and the 1,4-phenylene rings may each independently be mono- or polysubstituted by fluorine.

Particular preference is given to compounds of the formulas IV29 to IV36 in which R ^{4 is} alkyl and R ^{4 * is} alkyl or alkoxy, in particular alkoxy, in each case having 1 to 7 C atoms. Preference is furthermore given to compounds of the formulas IV28 and IV34 in which LF is

R ⁴ and R ^{4 *} in the compounds of the formulas IV1 to IV36 are particularly preferably straight-chain alkyl or alkoxy having 1 to 12 C atoms.

Preferred liquid-crystal mixtures contain one, two, three or four compounds of the formulas IV27 and / or IV28.

Preferred compounds of the formula IV27 are

Particular preference is given to mixtures according to the invention which contain at least one compound of the formula IV 35, preferably the proportion of the quadrupters in the mixture is at least 8% by weight. Particularly preferred are mixtures containing two, three or more homologues of formula IV 35. In the formula IV 35, R ⁴ and R ^{4 * are} preferably straight-chain alkyl.

Preferably, mixtures according to the invention comprise at least one compound of the formulas IV27a, IV27b and / or IV27c. In particular, the mixtures contain at least two compounds of the formulas IV27a to IV27c.

The liquid-crystalline mixtures optionally contain an optically active component C in an amount such that the ratio between the layer thickness (distance between the carrier plates) and the natural pitch of the chiral nematic liquid-crystal mixture is greater than 0.2. For the component, the person skilled in a variety, sometimes commercially available chiral dopants are available for. Such as cholesteryl nonanoate (CN), S-811 S-1011, S-2011 from Merck KGaA, Darmstadt and CB15 (BDH, Poole, UK). The choice of dopants is not critical per se.

The proportion of the compounds of component C is preferably 0 to 10%, in particular 0 to 5%, particularly preferably 0 to 3%.

The mixtures according to the invention may also optionally contain up to 20% of one or more compounds having a dielectric anisotropy of less than -2 (component D).

If the mixtures contain compounds of component D, these are preferably one or more compounds having the structural element 2,3-difluoro-1,4-phenylene, eg. B. compounds according to DE-OS 38 07 801 . 38 07 861 . 38 07 863 . 38 07 864 or 38 07 908 , Particularly preferred are tolans with this structural element according to the International Patent Application PCT / DE 88/00133 ,

gemäß DE-OS 32 31 707 bzw. DE-OS 34 07 013 .Other known compounds of component D are, for. B. derivatives of 2,3-Dicyanhydrochinone or cyclohexane derivatives with the structural element

according to DE-OS 32 31 707 respectively. DE-OS 34 07 013 ,

The liquid-crystal displays according to the invention preferably contain no compounds of component D.

• – zusätzlich eine oder mehrere, besonders bevorzugt eine, zwei oder drei, heterocyclische Verbindungen der Formel Va und/oder Vb enthalten

worin
R⁵ und R⁶ unabhängig voneinander Alkyl mit 1 bis 7 C-Atomen, und
Y⁶ F oder Cl
bedeuten,Further preferred embodiments relate to liquid-crystal mixtures according to the invention which

• - In addition, one or more, more preferably one, two or three, heterocyclic compounds of the formula Va and / or Vb included

wherein
R ⁵ and R ^{6 are} independently alkyl having 1 to 7 carbon atoms, and
Y ⁶ F or Cl
mean,

• – zusätzlich eine oder mehrere, besonders bevorzugt eine, zwei oder drei, Tolan-Verbindungen der Formeln T2a bis T2c enthalten,

worin R⁷ und R⁸ unabhängig voneinander die für R²¹ und R²² angegebenen Bedeutungen besitzen. The proportion of the compounds from the group containing Va and / or Vb is preferably 2 to 35%, in particular 5 to 20%.

• Additionally contain one or more, more preferably one, two or three, tolan compounds of the formulas T2a to T2c,

wherein R ⁷ and R ⁸ independently of one another have the meanings given for R ²¹ and R ²² .

The proportion of the compounds from the group comprising T2a and T2b is preferably 0 to 30%, in particular 0 to 20%.

The term "alkenyl", in particular in the meaning of R ¹¹ , R ²¹ , R ²² , R ⁴ , R ^{4 *} , R ⁵ , R ⁶ , R ⁷ and R ⁸ , includes straight-chain and branched alkenyl groups, in particular the straight-chain groups. Particularly preferred alkenyl groups are C ₂ -C ₇ -1E-alkenyl, C ₄ -C ₇ 3E-alkenyl, C ₅ -C ₇ -alkenyl, C ₆ -C ₇ -5-alkenyl, and C ₇ -6- Alkenyl, in particular C ₂ -C ₇ -1E-alkenyl, C ₄ -C ₇ 3E-alkenyl and C ₅ -C ₇ -4-alkenyl.

Examples of preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups of up to 5 carbon atoms are generally preferred.

• – eine oder mehrere Verbindungen der folgenden Formeln
  
  worin R⁴, R^4* und L die oben angegebenen Bedeutungen und L in Formel IV25 besonders bevorzugt F bedeutet. Der Anteil dieser Verbindungen in den Flüssigkristallmischungen liegt vorzugsweise bei 5 bis 45%, insbesondere bei 10 bis 40%,
• – wenigstens zwei Verbindungen der Formel IIIc, und gegebenenfalls zusätzlich wenigstens eine Verbindung der Formel IIIb, worin L¹ und L² F bedeuten. Der Anteil dieser Verbindungen in den Flüssigkristallmischungen liegt vorzugsweise bei 5 bis 50%, insbesondere bei 7 bis 40%;
• – wenigstens eine Verbindung der Formeln VIa bis VIe,
  
  worin R⁶ und R^6* jeweils unabhängig voneinander H, CH₃, C₂H₅ oder n-C₃H₇ und Alkyl eine geradkettige Alkylgruppe mit 1 bis 7 C-Atomen bedeuten, vorzugsweise n-Propyl und n-Pentyl.

In particularly preferred embodiments, the mixtures contain

• - One or more compounds of the following formulas
  
  wherein R ⁴ , R ^{4 *} and L are as defined above and L in formula IV25 particularly preferably F. The proportion of these compounds in the liquid-crystal mixtures is preferably from 5 to 45%, in particular from 10 to 40%,
• At least two compounds of formula IIIc, and optionally additionally at least one compound of formula IIIb, wherein L ¹ and L ^{2 are} F. The proportion of these compounds in the liquid-crystal mixtures is preferably from 5 to 50%, in particular from 7 to 40%;
• At least one compound of the formulas VIa to VIe,
  
  wherein R ⁶ and R ^{6 * are} each independently H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ and alkyl is a straight-chain alkyl group having 1 to 7 carbon atoms, preferably n-propyl and n-pentyl.

The mixtures according to the invention are distinguished, in particular when used in TN and STN displays with high layer thicknesses, by very low sum switching times (t _ges = t _on + t _off ).

The liquid-crystal mixtures used in the TN and STN cells are dielectrically positive with Δ∈ ≥ 1. Particular preference is given to liquid-crystal mixtures with Δ∈ ≥ 3, in particular with Δ∈ ≥ 5.

The liquid-crystal _{mixtures according} to the invention have favorable values for the threshold voltage V _10/0/20 and for the rotational _viscosity γ ₁ . If the value for the optical path difference d · Δn is predetermined, the value for the layer thickness d is determined by the optical anisotropy Δn. In particular, at relatively high values for Δn, the use of liquid-crystal mixtures according to the invention having a relatively high optical anisotropy value is generally preferred, since then the value for d can be chosen to be relatively small, which leads to more favorable values for the switching times. However, even liquid crystal displays containing liquid crystal mixtures according to the invention with smaller values for Δn are characterized by advantageous values for the switching times.

The liquid-crystal mixtures according to the invention are further characterized by advantageous values for the steepness of the electro-optical characteristic, and can be operated in particular at temperatures above 20 ° C. with high multiplex rates. In addition, the liquid-crystal mixtures according to the invention have a high stability and favorable values for the electrical resistance and the frequency dependence of the threshold voltage. The liquid crystal displays have a wide working temperature range and good angular dependence of the contrast.

The structure of the liquid crystal display elements made of polarizers, electrode base plates and electrodes having such a surface treatment that the preferred orientation (director) of each adjacent liquid crystal molecules from one to the other electrode is usually rotated by 160 ° to 720 ° relative to each other corresponds to for such display elements usual construction. Here the term of the usual construction is here broadly and covers also all modifications and Modifications of TN and STN cell, in particular matrix display elements and the additional magnets containing display elements.

The surface angle of the two support plates may be the same or different. Same tilt angles are preferred. Preferred TN displays have angles of attack between the longitudinal axis of the molecules on the surface of the carrier plates and the carrier plates of 0 ° to 7 °, preferably 0.01 ° to 5 °, in particular 0.1 to 2 °. In the STN displays, the angle of attack is 1 ° to 30 °, preferably 1 ° to 12 ° and especially 3 ° to 10 °.

The twist angle of the TN mixture in the cell is in the amount between 22.5 ° and 170 °, preferably between 45 ° and 130 ° and in particular between 80 ° and 115 °. The twist angle of the STN mixture in the cell from orientation layer to orientation layer is in the range between 100 ° and 600 °, preferably between 170 ° and 300 ° and in particular between 180 ° and 270 °.

The preparation of the liquid crystal mixtures which can be used according to the invention is carried out in a conventional manner. In general, the desired amount of the components used in lesser amount is dissolved in the constituent of the main component, expediently at elevated temperature. It is also possible to use solutions of the components in an organic solvent, e.g. B. in acetone, chloroform or methanol, to mix and remove the solvent after mixing again, for example by distillation.

The dielectrics may also contain further additives known to the person skilled in the art and described in the literature. For example, 0-15% pleochroic dyes may be added.

In the present application and in the following examples, the structures of the liquid crystal compounds are indicated by acronyms, wherein the transformation into chemical formulas according to following Tables A and B takes place. All radicals C _n H _{2n + 1} and C _m H _{2m + 1} are straight-chain alkyl radicals with n or m C atoms. The alkenyl radicals have the trans configuration. The coding according to Table B is self-evident. In Table A, only the acronym for the main body is given. In individual cases, the code for the substituents R ¹ , R ² , L ¹ , L ² and L ³ given below in the table below is separated from the acronym for the main body.

The TN and STN displays preferably contain liquid crystalline mixtures which are composed of one or more compounds from Tables A and B. Code for R ¹ , R ² , L ¹ , L ² , L ³ R ¹ R ² L ¹ L ² L ³ nm C _n H _{2n + 1} C _m H _{2m + 1} H H H n Om OC _n H _{2n + 1} C _m H _{2m + 1} H H H nO.m C _n H _{2n + 1} OC _m H _{2m + 1} H H H n C _n H _{2n + 1} CN H H H nN.F C _n H _{2n + 1} CN H H F nN.FF C _n H _{2n + 1} CN H F F nF C _n H _{2n + 1} F H H H nOF OC _n H _{2n + 1} F H H H nF.F C _n H _{2n + 1} F H H F NMF C _n H _{2n + 1} C _m H _{2m + 1} F H H nOCF ₃ C _n H _{2n + 1} OCF ₃ H H H n-Vm C _n H _{2n + 1} -CH = CH-C _m H _{2m + 1} H H H nV-Vm C _n H _{2n + 1} -CH = CH- -CH = CH-C _m H _{2m + 1} H H H

Table A: (L ¹ , L ² , L ³ = H or F)

Table B:

Table C:

In Table C possible dopants are given, which are usually added to the mixtures of the invention.

Klp.

Klärpunkt (Phasenübergangstemperatur nematisch-isotrop),

S-N

Phasenübergangs-Temperatur smektisch-nematisch,

Visk.

Fließviskosität (mm²/s, soweit nicht anders angegeben, bei 20°C),

n_o

ordentlicher Brechungsindex (589 nm, 20°C)

Δn

optische Anisotropie (589 nm, 20°C),

Δε

dielektrische Anisotropie (1 kHz, 20°C),

S

Kennliniensteilheit = V₉₀/V₁₀

V₁₀

Schwellenspannung = charakteristische Spannung bei einem relativen Kontrast von 10%,

V₉₀

charakteristische Spannung bei einem relativen Kontrast von 90%,

t_on

Zeit vom Einschalten bis zur Erreichung von 90% des maximalen Kontrastes,

t_off

Zeit vom Ausschalten bis zur Erreichung von 10% des maximalen Kontrastes,

Mux

Multiplexrate,

t_store

Tieftemperatur-Lagerstabilität in Stunden (–20°C, –30°C, –40°C)

The following examples are intended to illustrate the invention without limiting it. It means

Klp.

Clearing point (phase transition temperature nematic-isotropic),

SN

Phase transition temperature smectic-nematic,

Visc.

Flow viscosity (mm ² / s, unless otherwise stated, at 20 ° C),

n _o

ordinary refractive index (589 nm, 20 ° C)

.DELTA.n

optical anisotropy (589 nm, 20 ° C.),

Δε

dielectric anisotropy (1 kHz, 20 ° C),

S

Slope slope = V ₉₀ / V ₁₀

V ₁₀

Threshold voltage = characteristic voltage at a relative contrast of 10%,

V ₉₀

characteristic stress at a relative contrast of 90%,

t _on

Time from power up to 90% of maximum contrast,

t _off

Time from switching off to reaching 10% of the maximum contrast,

Mux

Multiplexing rate,

t _store

Low-temperature storage stability in hours (-20 ° C, -30 ° C, -40 ° C)

Above and below, all temperatures are given in ° C. The percentages are weight protests. All values are based on 20 ° C, unless stated otherwise. The values for V ₁₀ and the slope S are determined using square wave control (80 Hz). The values for the switching times are determined when controlled with a multiplex ratio of 1/64 and a bias ratio of 1/9. The twist is 240 °, unless stated otherwise.

Examples

Comparative Example 1

A TN and STN mixture consisting of PCH 3N.FF 10.00% klp .: 95.0 ° C ME2N.F 3:00% .DELTA.n: .1385 ME3N.F 3:00% n _o : 1.4960 ME4N.F 4:00% V ₁₀ : 1.24 V ME5N.F 5.00% S: 1,076 UZU-3A-N 10.00% t _ave (-20 ° C): 3260 ms CCG-VF 13.00% t _ave (+ 20 ° C): 210 ms CC-5-V 12:00% CCP-V-1 13.00% CCP-V2-1 6:00 am% PPTUI-3-2 10.00% CCPC-33 3:00% CCPC-34 4:00% CCPC-35 4:00%

example 1

A TN and STN mixture consisting of PCH 3N.FF 10.00% klp .: 98.0 ° C ME2N.F 2:00% .DELTA.n: .1398 UZU-3A-N 10.00% no: 1.4950 CCG-VF 11.00% V10: 1.24 V CC-5-V 15.00% S: 1,093 CCP-V-1 10.00% t _ave (-20 ° C): 2800 ms CCP-V2-1 8.00% t _ave (+ 20 ° C): 185 ms PPTUI-3-2 12:00% CCPC-33 4:00% CCPC-34 4:00% CCPC-35 4:00% PZU-V2-N 10.00%

Comparative Example 2

A TN and STN mixture consisting of PCH 3N.FF 8.00% klp .: 86.5 ° C ME2N.F 2:00% .DELTA.n: .1604 ME3N.F 2:00% no: 1.5030 UZU-3A-N 10.00% V10: 1.57 V CC-5-V 12:00% S: 1,070 CCG-VF 14.00% t _ave (+ 20 ° C): 118 ms CCP-V-1 8.00% CCP-V2-1 6:00 am% CVCP-V-1 4:00% CVCP V O1 5.00% CVCP-1V-O1 4:00% PTP 102 4:00% PTP 201 5.00% PTP 301 5.00% PPTUI-3-2 11.00%

Comparative Example 3

A TN and STN mixture consisting of PCH 3N.FF 8.00% klp .: 89.0 ° C ME2N.F 2:00% .DELTA.n: .1616 ME3N.F 2:00% no: 1.5027 UZU-3A-N 10.00% V10: 1.65 V CC-5-V 13.00% S: 1.067 CCG-VF 8.00% t _ave (-20 ° C): 1460 ms CCP-V-1 9.00% t _ave (+ 20 ° C): 110 ms CCP-V2-1 8.00% CVCP-V-1 5.00% CVCP V O1 5.00% CVCP-1V-O1 5.00% PTP 102 5.00% PTP 201 5.00% PTP 301 5.00% PPTUI-3-2 10.00%

Example 2

A TN and STN mixture consisting of PCH 3N.FF 4:00% klp .: 89.5 ° C UZU-3A-N 8.00% .DELTA.n: 0.1590 CC-5-V 16:00% no: 1.5025 CCG-VF 6:00 am% V10: 1.68 V CCP-V-1 11.00% S: 1,076 CCP-V2-1 11.00% t _ave (-20 ° C): 1120 ms CVCP-V-1 4:00% t _ave (+ 20 ° C): 95 ms CVCP V O1 4:00% CVCP-1V-O1 3:00% PTP 102 5.00% PTP 201 5.00% PTP 301 5.00% PPTUI-3-2 10.00% PZU-V2-N 8.00%

Claims (8)

Nematic liquid-crystal mixture, characterized in that it contains 15-75% by weight of a liquid-crystalline component A consisting of a plurality of compounds having a dielectric anisotropy of over +1.5 and 25-85 wt .-% of a liquid-crystalline component B, consisting of one or more compounds having a dielectric anisotropy between -1.5 and +1.5, wherein the component A is in each case one or more compounds of the formula ii,

one or more compounds of the formula II,

one or more compounds of the formula III * j,

and one or more compounds of the formula I ** C1

in which the individual radicals have the following meanings: R ¹¹ , R ²¹ , R ^{22 is} an unsubstituted, an alkyl or alkenyl radical having up to 15 carbon atoms which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen, where in these radicals also one or more CH 2 groups can be replaced by -O-, -S-, -C≡C-, -OC-O-, or -O-CO- such that O atoms are not directly linked to one another, alkyl an alkyl radical having 1 to 7 carbon atoms, alkenyl an alkenyl radical having 2 to 7 carbon atoms. Nematic liquid-crystal mixture according to Claim 1, characterized in that R ¹¹ , R ²¹ and / or R ²² independently of one another are an alkyl, alkoxy or oxaalkyl radical having 1 to 7 C atoms or an alkenyl, alkenyloxy or oxaalkenyl radical having 2 to 7 C atoms means. Nematic liquid-crystal mixture according to Claim 1 or 2, characterized in that the compounds of the formula Ii are selected from one or more compounds of the formulas Iia and / or Iib,

wherein alkyl is an alkyl radical having 1 to 7 carbon atoms and alkenyl an alkenyl radical having 2 to 7 carbon atoms. Nematic liquid-crystal mixture according to one or more of claims 1 to 3, characterized in that it contains one or more compounds of the formulas IIa to IId,

wherein z is 1 to 5 and x and y are independently of one another 1 to 10, where x + y ≤ 10. Nematic liquid-crystal mixture according to one or more of claims 1 to 4, characterized in that it additionally contains one or more compounds of formula IIIc,

wherein R ^{3 is} an alkyl, alkoxy or oxaalkyl radical having 1 to 7 carbon atoms and L ¹ , L ^{2 are} each independently H or F. Nematic liquid-crystal mixture according to one or more of claims 1 to 5, characterized in that it optionally contains 0-20 wt .-% of a liquid-crystalline component D, consisting of one or more compounds having a dielectric anisotropy of less than -1.5. Nematic liquid-crystal mixture according to one or more of Claims 1 to 6, characterized in that it optionally contains an optically active component C in an amount such that the ratio between layer thickness (spacing of the carrier plates) and natural pitch of the chiral nematic liquid-crystal mixture is about 0.2 to 1 , 3, contains. Use of a liquid-crystal mixture according to one or more of claims 1 to 7 in a TN or STN liquid-crystal display with Two support plates, which form a cell with a border, An in-cell nematic liquid-crystal mixture having positive dielectric anisotropy, Electrode layers with orientation layers on the insides of the carrier plates, An angle of attack between the longitudinal axis of the molecules at the surface of the carrier plates and the carrier plates from 0 degrees to 30 degrees, and A twist angle of the liquid crystal mixture in the cell from orientation layer to orientation layer in the amount between 22.5 ° and 600 °.