DE10058474B4 - Liquid crystal mixture and their use in TN and STN liquid crystal displays - Google Patents

Abstract

sowie eine oder mehrere Verbindungen der Formel II

enthält,
worin
R¹ und R⁴ jeweils unabhängig voneinander eine Alkyl-, Alkoxy- oder Alkenylgruppe mit 1 bis 12 C-Atomen, wobei auch ein oder zwei nicht benachbarte CH2-Gruppen durch -O-, -CH=CH-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind,
R³ eine Alkenylgruppe mit 2 bis 7 C-Atomen,
L F, und
a 0 oder 1
bedeuten.Nematic liquid-crystal mixture containing
a) 15-80 wt.% Of a liquid-crystalline component A, consisting of one or more compounds having a dielectric anisotropy of more than +1.5;
b) 20-85% by weight of a liquid-crystalline component B consisting of one or more compounds having a dielectric anisotropy between -1.5 and +1.5;
characterized in that the liquid-crystal mixture comprises at least one compound of the formula I

and one or more compounds of the formula II

contains
wherein
R ¹ and R ^{4 are} each independently an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, wherein also one or two non-adjacent CH 2 groups by -O-, -CH = CH-, -CO-, - OCO- or -COO- can be replaced so that O atoms are not directly linked to each other,
R ^{3 is} an alkenyl group having 2 to 7 C atoms,
LF, and
a 0 or 1
mean.

Description

The invention relates to nematic liquid-crystal 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 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)).

STN displays are characterized by significantly better electro-optic characteristics and, at medium and higher multiplex rates, such as 32 to 64 and higher, better contrast levels compared to standard TN displays. In contrast, in TN displays, the contrast is higher due to the better dark value and the angle dependence of the contrast is lower than in STN displays with low multiplexing rates of, for example, less than 32.

DE 199 14 373 A1 and JP 10-008065 (A) mention liquid crystal mixtures for use in liquid crystal 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 of the liquid-crystal mixtures have hitherto been optimized by using mostly 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, 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 the dielectric constant is perpendicular to the molecular longitudinal axis is.

• 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, in particular 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. In part, this is due to the fact that the different requirements are counteracted by material parameters.

Thus, there is still a great need for TN and STN displays, especially for medium and low-multiplex STN displays, with very short switching times with a large operating temperature range, high slope, good angle dependence of contrast, and low threshold voltage, the above meet specified 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.

sowie eine oder mehrere Alkenyl-Verbindungen der Formel II

enthalten,
worin
R¹ und R⁴ jeweils unabhängig voneinander eine Alkyl-, Alkoxy- oder Alkenylgruppe mit 1 bis 12 C-Atomen, wobei auch ein oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind,
R³ eine Alkenylgruppe mit 2 bis 7 C-Atomen,
L F, und
a 0 oder 1
bedeuten.It has now been found that this object can be achieved by using nematic liquid-crystal mixtures which contain one or more compounds of the formula I.

and one or more alkenyl compounds of the formula II

contain,
wherein
R ¹ and R ⁴ each independently represent an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, whereby also one or two non-adjacent CH ₂ groups are represented by -O-, -CH = CH-, -CO-, -OCO- or -COO- can be replaced so that O atoms are not directly linked to one another,
R ^{3 is} an alkenyl group having 2 to 7 C atoms,
LF, and
a 0 or 1
mean.

• • hohe Steilheit der elektrooptischen Kennlinie
• • geringe Temperaturabhängigkeit der Schwellenspannung und
• • sehr schnelle Schaltzeiten, insbesondere bei tiefen Temperaturen.

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

• • high slope of the electro-optical characteristic
• • low temperature dependence of the threshold voltage and
• • very fast switching times, especially at low temperatures.

The compounds of the formula I and II in particular significantly shorten the switching times of TN and STN mixtures while increasing the steepness and low temperature dependence of the threshold voltage.

• – sie besitzen eine niedrige Viskosität,
• – sie besitzen eine niedrige Schwellenspannung und Operationsspannung,
• – sie bewirken lange Lagerzeiten in der FK-Anzeige bei tiefen Temperaturen.

Furthermore, the mixtures according to the invention are distinguished by the following advantages

• They have a low viscosity,
• They have a low threshold voltage and operating voltage,
• - They cause long storage times in the FK display at low temperatures.

• – zwei Trägerplatten, die mit einer Umrandung eine Zelle bilden,
• – einer in der 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°,
• – einer nematischen Flüssigkristallmischung bestehend aus a) 15–80 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,

dadurch gekennzeichnet, daß Komponente A mindestens eine Verbindung der Formel I enthält

und Komponente B mindestens eine Verbindung der Formel II enthält

worin
R¹ und R⁴ jeweils unabhängig voneinander eine Alkyl-, Alkoxy- oder Alkenylgruppe mit 1 bis 12 C-Atomen, wobei auch ein oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind,
R³ eine Alkenylgruppe mit 2 bis 7 C-Atomen,
L F, und
a 0 oder 1
bedeuten.The invention also relates to the use of the liquid-crystal mixtures in a liquid-crystal display

• 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 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 °,
• A nematic liquid-crystal mixture consisting of a) 15-80% by weight of a liquid-crystalline component A consisting of one or more compounds having a dielectric anisotropy of more than +1.5; b) 25-85% by weight 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 layer thickness (distance of Support plates) and natural pitch of the chiral nematic liquid-crystal mixture is about 0.2 to 1.3,

characterized in that component A contains at least one compound of formula I.

and component B contains at least one compound of formula II

wherein
R ¹ and R ⁴ each independently represent an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, whereby also one or two non-adjacent CH ₂ groups are represented by -O-, -CH = CH-, -CO-, -OCO- or -COO- can be replaced so that O atoms are not directly linked to one another,
R ^{3 is} an alkenyl group having 2 to 7 C atoms,
LF, and
a 0 or 1
mean.

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

Particular preference is given to liquid-crystal mixtures which comprise one or more compounds of the formula I in which R ¹ denotes a straight-chain alkyl group having 1 to 8 C atoms.

Preference is furthermore given to liquid-crystal mixtures which contain one or more compounds of the formula I in which R ¹ denotes a straight-chain alkenyl group having 2 to 7 C atoms.

worin R¹ die oben angegebene Bedeutung besitzt.Formula I includes the following compounds

wherein R ^{1 has} the meaning given above.

worin R^1a H, CH₃, C₂H₅ oder n-C₃H₇ und alkyl eine Alkylgruppe mit 1 bis 8 C-Atomen bedeuten.Particularly preferred compounds of the formula I-2 are those selected from the following group

wherein R ^{1a is} H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ and alkyl is an alkyl group having 1 to 8 carbon atoms.

Particular preference is given to compounds of the formula I-2a.

Further preferred compounds are those of the formulas I-2b and I-2c, wherein R ^{1a is} H.

The media according to the invention contain one or more compounds of the formula I-2, in particular those of the abovementioned preferred sub-formulas.

worin R³ und R⁴ die oben angegebene Bedeutung besitzen.Formula II includes the following compounds

wherein R ³ and R ^{4 have} the meaning given above.

Particular preference is given to TN and STN displays which contain at least one compound of the formula II-1.

Also preferred are TN and STN displays which contain at least one compound of the formulas II-1 and II-2.

In the formulas II-1 and II-2, R ³ particularly preferably 1E-alkenyl or 3E-alkenyl having 2 to 7 carbon atoms.

worin R^3a und R^4a jeweils unabhängig voneinander H, CH₃, C₂H₅ oder n-C₃H₇ und alkyl eine Alkylgruppe mit 1 bis 8 C-Atomen bedeuten.Particularly preferred compounds of the formula II-1 are those in which R ^{4 is} alkenyl having 2 to 7 carbon atoms, and compounds selected from the formulas II-1a to II-1e

wherein R ^3a and R ^{4a are} each independently H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ and alkyl is an alkyl group having 1 to 8 carbon atoms.

Particular preference is given to compounds of the formula II-1a, in particular those in which R ^3a and R ^{4a are} CH ₃ , and also compounds of the formula II-1e in which R ^{3a is} H.

Particular preference is given to liquid-crystal mixtures according to the invention comprising at least one compound of the formula II-1a and / or II-1c in which R ^3a and R ^4a each have the same meaning, and liquid-crystal ^mixtures comprising at least one compound of the formula II-1e.

In a further preferred embodiment, the liquid-crystal mixtures according to the invention contain one or more compounds of the formula II-2.

worin R^3a voneinander H, CH₃, C₂H₅ oder n-C₃H₇, insbesondere H, und alkyl eine Alkylgruppe mit 1 bis 8, insbesondere 1, 2 oder 3 C-Atomen bedeuten.Particular preference is given to compounds of the formula II-2 in which R ^{4 is} alkyl having 1 to 8, in particular 1, 2 or 3 C atoms, and R ^{3 is} 1E-alkenyl or 3E-alkenyl having 2 to 7, in particular 2, 3 or 4 C atoms, as well as compounds selected from the formulas II-2a and II-2b

wherein R ^3a each other is H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ , in particular H, and alkyl is an alkyl group having 1 to 8, in particular 1, 2 or 3 C-atoms.

The use of compounds of the formula II leads in the liquid-crystal mixtures according to the invention to particularly low values of the rotational viscosity and to TN and STN displays with a high steepness and fast switching times, in particular at low temperatures.

worin
R³ die in Formel II angegebenen Bedeutungen besitzt,
Q CF₂, OCF₂, CFH, OCFH oder eine Einfachbindung,
Y F oder Cl, und
L¹ und L² jeweils unabhängig voneinander H oder F bedeuten.The mixtures according to the invention preferably contain, in addition to the dielectrically neutral alkenyl compounds of the formula II, one or more dielectrically positive alkenyl compounds of the formula II *

wherein
R ^{3 has} the meanings given in formula II,
Q CF ₂ , OCF ₂ , CFH, OCFH or a single bond,
YF or Cl, and
L ¹ and L ^{2 are} each independently H or F.

Particularly preferred compounds of the formula II * are those in which L ¹ and / or L ^{2 are} F and QY is F or OCF ₃ . Preference is furthermore given to compounds of the formula II * in which R ^{3 is} 1E-alkenyl or 3E-alkenyl having 2 to 7, in particular 2, 3 or 4, C atoms.

The polar compounds of the formula II * having a dielectric anisotropy of more than +1.5 are assigned to the component A defined above.

worin

d 0 oder 1,
L¹ bis L⁷ jeweils unabhängig voneinander H oder F,
Q -CF₂-, -CHF-, -OCF₂-, -OCHF- oder eine Einfachbindung,
Y F oder Cl,
Z⁴ -CO-O-, -CH₂CH₂- oder eine Einfachbindung bedeuten,
R¹ die oben angegebene Bedeutung besitzt und
R² eine der für R¹ angegebenen Bedeutungen besitzt.In addition to the compounds of the formulas I and II, the mixtures according to the invention preferably contain one or more liquid-crystalline tolane compounds. Due to the high birefringence Δn of the tolan compounds, it is possible to work with lower layer thicknesses, as a result of which the switching times become significantly shorter. The tolan compounds are preferably selected from the group T consisting of the compounds of the formulas T1 and T2:

wherein

d 0 or 1,
L ¹ to L ^{7 are} each independently H or F,
Q is -CF ₂ -, -CHF-, -OCF ₂ -, -OCHF- or a single bond,
YF or Cl,
Z ^{4 is} -CO-O-, -CH ₂ CH ₂ - or a single bond,
R ^{1 has} the meaning given above and
R ^{2 has} one of the meanings given for R ¹ .

worin L¹ bis L⁴ H oder F und Q-Y F, Cl oder OCF₃, insbesondere F oder OCF₃ bedeuten. Preferred compounds of the formula T1 correspond to the sub-formulas T1a and T1b

wherein L ¹ to L ^{4 is} H or F and QY is F, Cl or OCF ₃ , in particular F or OCF ₃ .

worin R¹ die oben angegebene Bedeutung besitzt.Particular preference is given to compounds of the formula T1b-1

wherein R ^{1 has} the meaning given above.

worin R¹, R² und Z⁴ die oben angegebene Bedeutung besitzen, und L¹ bis L⁶ H oder F bedeuten.Preferred compounds of the formula T2 correspond to the sub-formulas T2a to T2h

wherein R ¹ , R ² and Z ^{4 have} the abovementioned meaning, and L ¹ to L ^{6 is} H or F.

Particular preference is given to compounds of the formulas T2a and T2b.

In a further preferred embodiment, the mixtures contain one or more compounds of the formula T2h.

Particularly preferred compounds of formula T2e are those in which one, two or three of the radicals L ¹ to L ⁶ F and the other H, wherein L ¹ and L ² or L ³ and L ⁴ or L ⁵ and L ⁶ not both mean F at the same time.

The proportion of the compounds from the group containing T2a and T2b is preferably 5 to 50%, in particular 10 to 40%.

The proportion of the compounds of the formula T2h is preferably 2 to 35%, in particular 4 to 25%.

The proportion of the compounds of the formula T1b-1 is preferably 2 to 25%, in particular 4 to 15%.

The proportion of the compounds from the group T is preferably 2 to 55%, in particular 5 to 35%.

worin R eine der für R¹ in Formel I angegebenen Bedeutungen besitzt und L¹ und L² jeweils unabhängig voneinander H oder F bedeuten. R bedeutet in diesen Verbindungen besonders bevorzugt Alkyl oder Alkoxy mit 1 bis 8 C-Atomen.Component A preferably contains one or more cyano compounds of the following formulas

wherein R has one of the meanings given for R ¹ in formula I and L ¹ and L ^{2 are} each independently H or F. R in these compounds particularly preferably denotes alkyl or alkoxy having 1 to 8 C atoms.

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

Preference is furthermore given to mixtures which comprise one or more compounds of the formula IIIh in which L ^{2 is} H and L ^{1 is} H or F, in particular F.

sowie gegebenenfalls eine oder mehrere Verbindungen mit polarer Endgruppe der folgenden Formeln

worin R eine der für R¹ in Formel I angegebenen Bedeutungen besitzt und L³ und L⁴ jeweils unabhängig voneinander H oder F bedeuten. R bedeutet in diesen Verbindungen besonders bevorzugt Alkyl oder Alkoxy mit 1 bis 8 C-Atomen. In a specific embodiment, component A preferably contains one or more 3,4,5-trifluorophenyl compounds of the following formulas

and optionally one or more compounds having a polar end group of the following formulas

wherein R has one of the meanings given for R ¹ in formula I and L ³ and L ^{4 are} each independently H or F. R in these compounds particularly preferably denotes alkyl or alkoxy having 1 to 8 C atoms.

Particular preference is given to compounds of the formulas IVa, IVb, IVc, IVd, IVh and VI, in particular compounds of the formulas IVa, IVh and Vi.

The individual compounds of the formulas I, II, III, IV and V or their sub-formulas or other compounds which can be used in the TN and STN displays are either known or they can be prepared analogously to the known compounds ,

The compounds of the formula II have low viscosities, in particular low rotational viscosities, and low values for the ratio of the elastic constant K ₃₃ / K ₁₁ , and therefore lead to short switching times in the displays, while the presence of compounds of the formula I with high dielectric Anisotropy, especially in elevated concentrations, causes a reduction of the threshold voltage.

Preferred liquid-crystal mixtures preferably comprise one or more compounds of component A in an amount of from 15% to 80%, particularly preferably from 20% to 70%. These compounds have a dielectric anisotropy Δε ≥ +3, in particular Δε ≥ +8, particularly preferably Δε ≥ +12.

Preferred liquid-crystal mixtures comprise one or more compounds of component B, preferably in a proportion of 20 to 85%, particularly preferably in a proportion of 30 to 75%. The compounds of group B, in particular those having alkenyl groups, 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 der folgenden Formeln

und/oder eine oder mehrere Verbindungen ausgewählt aus der Gruppe bestehend aus den Vierringverbindungen der folgenden Formeln

worin R¹ und R² die oben angegebene Bedeutung haben, L H oder F bedeutet, und die 1,4-Phenylengruppen in IV10 bis IV19 und IV23 bis IV32 jeweils unabhängig voneinander auch durch Fluor ein- oder mehrfach substituiert sein können.In addition to one or more compounds of the formula II, component B preferably contains one or more compounds selected from the group consisting of the two-ring compounds of the following formulas

and / or one or more compounds selected from the group consisting of the three-membered compounds of the following formulas

and / or one or more compounds selected from the group consisting of the four-membered compounds of the following formulas

wherein R ¹ and R ^{2 have} the abovementioned meaning, LH or F, and the 1,4-phenylene groups in IV10 to IV19 and IV23 to IV32 each independently of one another by fluorine may be mono- or polysubstituted.

Particular preference is given to compounds of the formulas IV25 to IV31 in which R ^{1 is} alkyl and R ^{2 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 IV25 and IV31 in which L is F.

R ¹ and R ² in the compounds of the formulas IV1 to IV30 particularly preferably denote straight-chain alkyl or alkoxy having 1 to 12 C atoms.

The liquid-crystalline mixtures optionally contain an optically active component C in an amount such that the ratio between layer thickness (distance of the carrier plates) and 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, S-811 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 ,

Preferably, the liquid crystal displays do not contain compounds of component D.

The term "alkenyl" in the meaning of R, R ¹ , R ² , R ³ and R ⁴ includes straight-chain and branched alkenyl groups, in the case of R, R ¹ and R ² with 2-12, in the case of R ³ and R ⁴ with 2-7 carbon atoms, 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, insbesondere eine, zwei oder drei Verbindungen der Formel I,
• – eine, zwei oder drei Verbindungen der Formel I-1, worin R¹ alkyl mit 1 bis 8 C-Atomen bedeutet, und/oder eine, zwei oder drei Verbindungen der Formel I-1, worin R¹ alkenyl mit 2 bis 7 C-Atomen bedeutet,
• – 5 bis 40%, insbesondere 8 bis 25% einer oder mehrerer Verbindungen der Formel I,
• – 5 bis 60%, insbesondere 15 bis 50% einer oder mehrerer Alkenylverbindungen der Formel II,
• – eine oder mehrere, besonders bevorzugt eine, zwei oder drei Tolan-Verbindungen der Formel T2h
  
  worin R¹ und R² die oben angegebene Bedeutung besitzen,
• – eine oder mehrere, besonders bevorzugt jeweils zwei bis vier, Tolan-Verbindungen der folgenden Formeln
  
  worin R¹ und R² die oben angegebene Bedeutung besitzen.
• – eine oder mehrere Verbindungen der folgenden Formeln
  
  worin R¹, R² und L die bevorzugten Bedeutungen, die unter Verbindungen der Komponente B genannt sind, besitzen, und L in Formel IV25 H oder F, besonders bevorzugt F bedeutet. Der Anteil dieser Verbindungen in den Flüssigkristallmischungen liegt vorzugsweise bei 10 bis 45%, insbesondere bei 15 bis 40%,
• – eine oder mehrere, insbesondere zwei bis fünf Verbindungen der Formel IIIb, IIIc und/oder IIIh.
• – wenigstens zwei Verbindungen der Formel IIIc, und gegebenenfalls zusätzlich wenigstens eine Verbindung der Formel IIIb, worin L¹ und/oder L² F bedeuten. Der Anteil dieser Verbindungen in den Flüssigkristallmischungen liegt vorzugsweise bei 7 bis 50%, insbesondere bei 10 bis 40%;
• – wenigstens eine Verbindung der Formel II-1a und/oder II-3e,
• – wenigstens eine Verbindung ausgewählt aus der folgenden Gruppe
  
  worin alkyl eine Alkylgruppe mit 1 bis 8 C-Atomen und R^3a H oder CH₃ bedeutet,
• – mehr als 20% an Verbindungen mit positiver dielektrischer Anisotropie, insbesondere mit Δε ≥ +12,

In particularly preferred embodiments, the mixtures contain

• One or more, in particular one, two or three compounds of the formula I,
• - One, two or three compounds of formula I-1, wherein R ^{1 is} alkyl having 1 to 8 carbon atoms, and / or one, two or three compounds of formula I-1, wherein R ¹ alkenyl with 2 to 7 C Atoms means
• From 5 to 40%, in particular from 8 to 25%, of one or more compounds of the formula I,
• From 5 to 60%, in particular from 15 to 50%, of one or more alkenyl compounds of the formula II,
• One or more, more preferably one, two or three tolan compounds of the formula T2h
  
  in which R ¹ and R ^{2 have} the abovementioned meaning,
• - One or more, more preferably in each case two to four, tolan compounds of the following formulas
  
  wherein R ¹ and R ^{2 have} the meaning given above.
• - One or more compounds of the following formulas
  
  wherein R ¹ , R ² and L have the preferred meanings mentioned under compounds of component B, and L in formula IV25 is H or F, particularly preferably F. The proportion of these compounds in the liquid-crystal mixtures is preferably from 10 to 45%, in particular from 15 to 40%,
• - One or more, especially two to five compounds of formula IIIb, IIIc and / or IIIh.
• At least two compounds of the formula IIIc, and if appropriate additionally at least one compound of the formula IIIb, in which L ¹ and / or L ^{2 are} F. The proportion of these compounds in the liquid-crystal mixtures is preferably from 7 to 50%, in particular from 10 to 40%;
• At least one compound of the formula II-1a and / or II-3e,
• At least one compound selected from the following group
  
  wherein alkyl is an alkyl group having 1 to 8 C atoms and R ^{3a is} H or CH ₃ ,
• More than 20% of compounds with positive dielectric anisotropy, in particular Δε ≥ +12,

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 value for the optical anisotropy 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 in which the liquid crystal mixtures of the present invention are preferably used consists of polarizers, electrode base plates, and electrodes having such a surface treatment that the preferential orientation (director) of the respective adjacent liquid crystal molecules from one to the other electrode is usually 160 times ° to 720 ° is rotated against each other, corresponds to the usual for such display elements construction. The term of the usual construction is here broadly and includes all modifications and modifications of the 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 the 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. 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

Tabelle B:

The TN and STN displays preferably contain liquid crystalline mixtures which are composed of one or more compounds from Tables A and B. Table A: (L ¹ , L ² , L ³ = H or F)

Table B:

Klp.

Klärpunkt (Phasenübergangs-Temperatur nematisch-isotrop),

S-N

Phasenübergangs-Temperatur smektisch-nematisch,

Visk.

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

Δn

optische Anisotropie (589 nm, 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),

.DELTA.n

optical anisotropy (589 nm, 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 by weight. All values are based on 20 ° C, unless stated otherwise. Unless otherwise stated, the displays are controlled at a multiplex rate of 1/240 and a bias of 1/16. The twist is 240 °, unless stated otherwise.

example 1

A TN and STN mixture consisting of CG-3-AN 18.00% klp .: 97.5 ° C PCH-301 17.00% .DELTA.n: .1850 CC-5-V 19.00% V ₁₀ : 2.32 V PTP 102 5.00% S: 1,037 PTP 201 5.00% t _ave (-20 ° C): 225 ms PTP 301 5.00% Mux: 1.4 PTP 302 4:00% bias: 3.1 CPTP-301 4:00% twist: 90 ° CPTP-302 4:00% CPTP-303 4:00% CPTP-30CF3 4:00% CPTP-50CF3 4:00% CBC-33F 4:00% CBC-53F 3:00%

Claims (13)

A nematic liquid-crystal mixture comprising a) 15-80% by weight of a liquid-crystalline component A consisting of one or more compounds having a dielectric anisotropy of more than +1.5; b) 20-85% by weight of a liquid-crystalline component B consisting of one or more compounds having a dielectric anisotropy between -1.5 and +1.5; characterized in that the liquid-crystal mixture comprises at least one compound of the formula I

and one or more compounds of the formula II

wherein R ¹ and R ^{4 are} each independently an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, wherein also one or two non-adjacent CH 2 groups by -O-, -CH = CH-, -CO -, -OCO- or -COO- can be replaced so that O atoms are not directly linked to each other, R ^{3 is} an alkenyl group having 2 to 7 carbon atoms, LF, and a is 0 or 1. A liquid-crystal mixture according to claim 1, characterized in that it comprises at least one compound selected from the formulas II-1a to II-1e

and / or at least one compound selected from the formulas II-2a and II-2b

wherein R ^3a and R ^{4a are} each independently H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ and alkyl is an alkyl group having 1 to 7 carbon atoms. Liquid-crystal mixture according to Claim 1 or 2, characterized in that it contains at least one compound of the formula II *

wherein R ^{3 has} the meaning given in formula II, Q is CF ₂ , OCF ₂ , CFH, OCFH or a single bond, YF or Cl, and L ¹ and L ^{2 are} each independently H or F. A liquid-crystal mixture according to claim 1, 2 or 3, characterized in that it contains at least one compound selected from the following formulas

wherein

d 0 or 1, L ¹ to L ^{7 are} each independently H or F, Q -CF ₂ -, -CHF-, -OCF ₂ -, -OCHF- or a single bond, YF or Cl, Z ⁴ -CO-O- , -CH ₂ CH ₂ - or a single bond, R ^{1 has} the meaning given in claim 1 and R ^{2 has} one of the meanings given for R ¹ . Liquid-crystal mixture according to one or more of claims 1 to 4, characterized in that component A contains one or more compounds of the following formulas

wherein R has one of the meanings given for R ¹ in claim 1 and L ¹ and L ^{2 are} each independently H or F. Liquid-crystal mixture according to one or more of claims 1 to 5, characterized in that it contains one or more compounds of the following formula

wherein R ¹ and R ^{2 have} the meanings given in claim 4, and L is H or F. Liquid-crystal mixture according to one or more of claims 1 to 6, characterized in that it contains one or more tolan compounds selected from the following formulas.

wherein R ¹ and R ^{2 have} the meaning given in claim 4. Liquid-crystal mixture according to one or more of Claims 1 to 7, characterized in that it contains up to 20% by weight of a liquid-crystalline component D consisting of one or more compounds having a dielectric anisotropy of less than -1.5. Liquid-crystal mixture according to one or more of Claims 1 to 8, characterized in that it contains an optically active component C in an amount such that the layer thickness (spacing of the carrier plates) and natural pitch of the chiral nematic liquid-crystal mixture is approximately 0.2 to 1.3 , contains. Liquid-crystal mixture according to one or more of claims 1 to 9, characterized in that it contains 5 to 40% of one or more compounds of the formula I. Liquid-crystal mixture according to one or more of claims 1 to 10, characterized in that it contains 5 to 60% of one or more compounds of the formula II. Use of a liquid-crystal mixture according to one or more of Claims 1 to 11 in a TN or STN liquid-crystal display. Use of a liquid-crystal mixture according to one or more of claims 1 to 11 in a TN or STN liquid-crystal display with Two support plates, which form a cell with a border, A cell-sensitive 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 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 °.