DE60101239T2 - Supertwist nematic liquid crystal displays - Google Patents

Description

The invention relates to highly twisted nematic liquid crystal displays (English: Supertwisted Nematic Liquid-Crystal Displays, short: STN-LCDs) with short switching times and good slopes and angle dependencies as well as the new nematic liquid crystal mixtures used therein.

STN LCDs as in the heading are known, e.g. B. from EP 0 131 216 B1 ; DE 3 423 993 A1 ; EP 0 098 070 A2 ; M. Schadt and F. Leenhouts, 17th Freiburg Working Conference on Liquid Crystals (April 8-10, 1987); 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. 26, No. 11, L1784-L1786 (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-LCD here includes any higher twisted display element with a twist angle between 160 ° and 720 °, such as the display elements of Waters et al. (CM Waters et al., Proc. Soc. Inf. Disp. (New York) (1985) (3rd International Display Conference, Kobe, Japan), the STN-LCDs (DE OS 3 503 259), SBE-LCDs ( TJ Scheffer and J. Nehring, Appl. Phys. Lett. 45 (1984) 1021), OMI-LCDs (M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (1987), 236, DST-LCDs (EP OS 0 246 842) or BW-STN-LCDs (K. Kawasaki et al., SID 87 Digest 391 (20.6)).

Compared to standard TN displays STN-LCDs of this type are characterized by significantly better slopes the electro-optical characteristic curve (hereinafter simply referred to as “slope”) and associated with this in the case of medium and high multiplex ratios from Z. B. 32 to 64 and higher, better contrast values. On the other hand, TN displays usually point due to better dark values and less angle dependency a higher contrast Contrast as STN displays with low multiplex ratios from Z. B. less than 32.

STN LCDs are of particular interest with very short switching times, especially at lower temperatures. In order to achieve short shaft times, the rotational viscosities have so far been particularly important of liquid crystal mixtures optimized, mostly using optimized combinations of liquid crystal components and optionally also monotropic additives with a relatively high vapor pressure. The switching times achieved were not sufficient for all applications.

shorter Switching times can also be achieved by changing the thickness of the liquid crystal layer the STN-LCD decreased and liquid crystal mixtures with a higher one Birefringence Δn used. All of these approaches for shorter switching times however, still result in blends that are not for every use were sufficient.

Further requirements for STN-LCD are higher Multiplexability (resulting in fewer driver circuits leads), lower threshold voltages and a high slope.

To achieve a high slope in the STN-LCDs, 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 / e _⊥ , with Δε the dielectric anisotropy and ε _⊥ the dielectric constant perpendicular to the molecular axis.

• 1. Ein breites d/p-Fenster von Schichtdicke d und Ganghöhe p, das als der Bereich zwischen der unteren und der oberen Grenze der d/p-Werte definiert ist.
• 2. Hohe chemische Stabilität.
• 3. Hoher elektrischer Widerstand.
• 4. Geringe Temperatur- und Frequenzabhängigkeit der Schwellenspannung.

In addition to the optimization of the contrast and the switching times, other important requirements are placed on such liquid crystal mixtures, such as:

• 1. A wide d / p window of layer thickness d and pitch p, which is defined as the range between the lower and the upper limit of the d / p values.
• 2. High chemical stability.
• 3. High electrical resistance.
• 4. Low temperature and frequency dependence of the threshold voltage.

Due to the opposing influences of different Material parameters such as dielectric and elastic properties However, optimal parameters cannot be set simultaneously for all of the above achieve mentioned properties. The parameter combinations achieved so far are therefore not yet sufficient, especially for high-multiplex STN LCDs (with a multiplex rate in the range of 1/400), but also for medium and low-multiplex STN-LCD (multiplex rate in the range of 1/64 or 1/16).

So there is still a great need for improved STN LCDs with short switching times and a wide working temperature range, high slope (i.e. low slope values), good angle dependence of contrast and low threshold voltage that are given above To fit in requirements.

The invention is based on the object To provide STN LCDs that do not have the disadvantages noted above or only to a lesser extent and very useful at the same time Overall properties, especially short switching times at low Temperatures, high slope and improved temperature dependence the operating voltage due to an improved frequency dependence of the dielectric constant.

und eine oder mehrere Alkenylverbindungen der Formel II

enthalten, worin
R¹ und R² unabhängig voneinander eine gegebenenfalls fluorierte Alkyl-, Alkoxy-, Alkenyl- oder Alkenyloxygruppe mit 1 bis 12 C-Atomen bedeuten, worin eine oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -CO-, -OCO- oder -COO- so ersetzt sein können, dass O-Atome einander nicht direkt benachbart sind,
R³ eine Alkenylgruppe mit 2 bis 7 C-Atomen bedeutet, und
L¹ und L² jeweils unabhängig H oder F bedeuten.It has now been found that this object can be achieved by using nematic liquid-crystal mixtures which comprise one or more compounds of the formula I.

and one or more alkenyl compounds of the formula II

included in what
R ¹ and R ² independently of one another represent an optionally fluorinated alkyl, alkoxy, alkenyl or alkenyloxy group having 1 to 12 carbon atoms, in which 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 adjacent to each other,
R ^{3 represents} an alkenyl group with 2 to 7 carbon atoms, and
L ¹ and L ² each independently represent H or F.

• – hoher Steilheit
• – niedriger Schwellenspannung mit geringer Temperaturabhängigkeit und
• – kurzen Schaltzeiten, insbesondere bei tiefen Temperaturen.

The use of the compounds of the formulas I and II in the liquid-crystal mixtures according to the invention for STN-LCDs leads in particular to

• - high slope
• - low threshold voltage with low temperature dependence and
• - short switching times, especially at low temperatures.

• – niedrige Viskosität,
• – geringe Temperaturabhängigkeit der Schwellenspannung und der Betriebsspannung,
• – verbesserte Stabilität der Mischung in der Anzeige bei tiefen Temperaturen.

Furthermore, the liquid crystal mixtures according to the invention have the following advantageous properties

• - low viscosity,
• - low temperature dependence of the threshold voltage and the operating voltage,
• - Improved stability of the mixture in the display at low temperatures.

• – zwei planparallelen Trägerplatten, die zusammen mit einer Umrandung eine Zelle bilden,
• – einer in der Zelle befindlichen nematischen Flüssigkristallmischung mit positiver dielektrischer Anisotropie,
• – Elektrodenschichten mit darüberliegenden Orientierungsschichten auf den Innenseiten der Trägerplatten,
• – einem Anstellwinkel zwischen der Längsachse der Moleküle an der Oberfläche der Trägerplatten und den Trägerplatten von 1 Grad bis 30 Grad, und
• – einem Verdrillungswinkel der Flüssigkristallmischung in der Zelle von Orientierungsschicht zu Orientierungsschicht dem Betrag nach zwischen 22,5 und 600°,

wobei die nematische Flüssigkristallmischung im wesentlichen besteht aus

• a) 15–80 Gew.-% einer flüssigkristallinen Komponente A, bestehend aus einer oder mehreren Verbindungen mit einer dielektrischen Anisotropie von über +1,5;
• b) 20–85 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 planparallelen Trägerplatten) und natürlicher Ganghöhe der chiralen nematischen Flüssigkristallmischung 0,2 bis 1,3 beträgt,

dadurch gekennzeichnet, dass die Flüssigkristallmischung mindestens eine Verbindung der Formel I

und mindestens eine Alkenylverbindung der Formel II

enthält, worin
R¹ und R² unabhängig voneinander eine gegebenenfalls fluorierte Alkyl-, Alkoxy-, Alkenyl- oder Alkenyloxygruppe mit 1 bis 12 C-Atomen bedeuten, worin eine oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -CO-, -OCO- oder -COO- so ersetzt sein können, dass O-Atome einander nicht direkt benachbart sind,
R³ eine Alkenylgruppe mit 2 bis 7 C-Atomen bedeutet, und
L¹ und L² jeweils unabhängig H oder F bedeuten.The invention therefore relates to an STN-LCD

• - two plane-parallel carrier plates, which together with a border form a cell,
• A nematic liquid crystal mixture in the cell with positive dielectric anisotropy,
• Electrode layers with overlying orientation layers on the inside 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 1 degree to 30 degrees, and
• An angle of twist of the liquid crystal mixture in the cell from orientation layer to orientation layer between 22.5 and 600 °,

the nematic liquid crystal mixture consists essentially of

• a) 15-80% by weight of a liquid-crystalline component A, consisting of one or more compounds with 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 with a dielectric anisotropy between -1.5 and +1.5;
• c) 0-20% by weight of a liquid-crystalline component D, consisting of one or more compounds with 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 (distance of the plane-parallel carrier plates) and the natural pitch of the chiral nematic liquid crystal mixture is 0.2 to 1.3,

characterized in that the liquid crystal mixture at least one compound of formula I

and at least one alkenyl compound of the formula II

contains what
R ¹ and R ² independently of one another represent an optionally fluorinated alkyl, alkoxy, alkenyl or alkenyloxy group having 1 to 12 carbon atoms, in which 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 adjacent to each other,
R ^{3 represents} an alkenyl group with 2 to 7 carbon atoms, and
L ¹ and L ² each independently represent H or F.

Another object of the invention are liquid crystal mixtures according to the invention as described above and below for use in STN LCDs.

Compounds of the formula I in which L ¹ and L ^{2 are} F are particularly preferred.

Also preferred are compounds of the formula I in which R ^{1 is} straight-chain alkyl having 1 to 8, in particular 1 to 5, carbon atoms.

Compounds of the formula II in which R ^{3 is} 1E-alkenyl or 3E-alkenyl having 2 to 7 C atoms are particularly preferred.

Also preferred are compounds of the formula II in which R ^{2 is} alkyl or alkoxy, in particular alkoxy, having 1 to 8 carbon atoms.

worin
k 1, 2, 3, 4 oder 5 bedeutet,
m und n unabhängig voneinander 0, 1, 2 oder 3 bedeuten, wobei m + n ≤ 5 ist, und
o 0 oder 1 bedeutet.Particularly preferred compounds of formula II are those of sub-formula IIa

wherein
k means 1, 2, 3, 4 or 5,
m and n independently of one another represent 0, 1, 2 or 3, where m + n ≤ 5, and
o means 0 or 1.

worin R eine der für R¹ in Formel I angegebenen Bedeutungen besitzt und L¹, L² und L³ unabhängig voneinander H oder F bedeuten. Besonders bevorzugt bedeutet R in diesen Verbindungen Alkyl oder Alkoxy mit 1 bis 8 C-Atomen.Component A preferably also contains one or more cyan compounds of the following formulas

wherein R has one of the meanings given for R ¹ in formula I and L ¹ , L ² and L ³ independently of one another are H or F. R in these compounds particularly preferably denotes alkyl or alkoxy having 1 to 8 carbon atoms.

Compounds of the formula IIIb, IIIc and IIIf are particularly preferred, in particular those in which L ¹ and / or L ^{2 are} F. Compounds of the formula IIIh in which L ² H and L ¹ H or F, in particular F, are furthermore preferred.

und/oder eine oder mehrere Verbindungen mit einer polaren Endgruppe ausgewählt aus den folgenden Formeln

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

and / or one or more compounds with a polar end group selected from the following formulas

wherein R has one of the meanings given for R ¹ in formula I and L ³ and L ⁴ independently of one another denote H or F. R in these compounds particularly preferably denotes alkyl or alkoxy having 1 to 8 carbon atoms.

Compounds are particularly preferred of the formulas IVa, IVb, IVc, IVd, IVh and Vi, in particular compounds of the formulas IVa, IVh and Vi.

Preferred liquid crystal mixtures, the used according to the invention can be preferably contain one or more compounds of component A. in a proportion of 15% to 80%, very preferably 20% to 70%. This Compound (s) has (have) a dielectric anisotropy Δε ≥ +3, preferably Δε ≥ +8, in particular Δε ≥ +12.

Preferred liquid crystal mixtures contain one or more compounds of component B, preferably in a proportion of 20 to 85%, very preferably 30 to 80%. The compounds of component B in particular have low values for the rotational viscosity γ ₁ .

und/oder eine oder mehrere Verbindungen ausgewählt aus der Gruppe bestehend aus den Dreiringverbindungen der Formeln IV10 bis IV24

und/oder eine oder mehrere Verbindungen ausgewählt aus der Gruppe bestehend aus den Vierringverbindungen der Formeln IV25 bis IV31

worin R¹ und R² unabhängig voneinander eine der Bedeutungen der Formel I und II besitzen und die 1,4-Phenylen-Gruppen in den Formeln IV10 bis IV19 und den Formeln IV23 bis IV31 auch unabhängig voneinander ein- oder mehrfach durch F substituiert sein können.Component B preferably contains one or more compounds selected from the group consisting of the two-ring compounds of the formulas IV1 to IV9

and / or one or more compounds selected from the group consisting of the three-ring compounds of the formulas IV10 to IV24

and / or one or more compounds selected from the group consisting of the four-ring compounds of the formulas IV25 to IV31

in which R ¹ and R ² independently of one another have the meanings of the formulas I and II and the 1,4-phenylene groups in the formulas IV10 to IV19 and the formulas IV23 to IV31 can also be substituted one or more times independently of one another by F. ,

Compounds of the formulas IV 25 to IV 31 are particularly preferred, in which R ^{1 is} alkyl and R ^{2 is} alkyl or alkoxy each having 1 to 7 carbon atoms. Further preferred are compounds of the formulas IV 25 and IV 31, in which L is F.

Compounds are very preferred of the formulas IV25 and IV31.

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 carbon atoms.

worin
R³ eine Alkenylgruppe mit 2 bis 7 C-Atomen bedeutet,
R⁴ eine der für R¹ in Formel I angegebenen Bedeutungen besitzt oder, wenn m 1 ist, auch Q-Y bedeuten kann,
Q -CF₂-, -OCF₂-, -CFH-, -OCFH- oder eine Einfachbindung bedeutet,
Y F oder Cl bedeutet,
m 0 oder 1 bedeutet, und
L¹ und L² unabhängig voneinander H oder F bedeuten.In a further preferred embodiment, the liquid crystal mixtures contain one or more alkenyl compounds of the formula VI

wherein
R ^{3 represents} an alkenyl group with 2 to 7 C atoms,
R ^{4 has} one of the meanings given for R ¹ in formula I or, if m is 1, can also mean QY,
Q is -CF ₂ -, -OCF ₂ -, -CFH-, -OCFH- or a single bond,
YF or Cl means
m represents 0 or 1, and
L ¹ and L ² independently of one another denote H or F.

Formula VI includes the following sub-formulas

STN LCDs are particularly preferred, which contain at least one compound which is derived from the formulas VI-1 and VI-2 selected is, in particular STN-LCDs, each having at least one connection of the formulas VI-1 and VI-2 contain.

In the formulas VI-1, VI-2 and VI-3, R ³ particularly preferably denotes 1E-alkenyl or 3E-alkenyl with 2 to 7 C atoms.

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

wherein R ^3a and R ^4a each independently represent H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ and "alkyl" means an alkyl group having 1 to 7 carbon atoms.

STN-LCDs according to the invention are particularly preferred, wherein the liquid crystal mixture contains at least one compound selected from the formulas VI-1d and VI-1e. Also preferred are STN-LCDs which contain at least one compound selected from the formulas VI-1a and VI-1c, in which R ^3a and R ^4a each have the same meaning.

Among the compounds of the formula VI-2, those in which L ¹ and L ^{2 are} H are particularly preferred.

Further preferred compounds of the formula VI-2 are those in which R ^{4 is} alkyl with 1 to 8, in particular special 1, 2 or 3 carbon atoms, and R ^{3 is} 1E-alkenyl or 3E-alkenyl having 2 to 7, in particular 2, 3 or 4, carbon atoms.

worin R^3a, R^4a und "alkyl" die vorstehend angegebene Bedeutung haben, insbesondere diejenigen, worin R^3a H bedeutet.Very preferred compounds of formula VI-2 are those selected from the following formulas

wherein R ^3a , R ^4a and "alkyl" have the meaning given above, in particular those in which R ^3a means H.

Among the compounds of the formula VI-3, those are particularly preferred in which one or both of L ¹ and L ^{2 are} F and QY is F or OCF ₃ .

Further preferred compounds of the formula VI-3 are those in which R ^{3 is} 1E-alkenyl or 3E-alkenyl having 2 to 7, in particular 2, 3 or 4, carbon atoms.

The compounds of the formulas VI-1 and VI-2 with a dielectric anisotropy of -1.5 to +1.5 belong to component B as defined above. Polar connections of the Formula VI-2 and in particular formula VI-3 with a dielectric Anisotropy over +1.5 belong to component A as defined above.

The use of connections of the Formula VI leads to mixtures according to the invention with particularly low values for the rotational viscosity and to STN-LCDs with high steepness of the electro-optical characteristic and fast switching times, especially at low temperatures.

worin
R¹ und R² unabhängig voneinander eine der Bedeutungen der Formeln I und II besitzen,
Z -COO-, -CH₂CH₂- oder eine Einfachbindung bedeutet, und
L¹ bis L⁶ unabhängig voneinander H oder F bedeuten.In a further preferred embodiment, the liquid-crystal mixtures contain one or more liquid-crystalline tolan compounds. Due to the high birefringence of the tolan compounds, it is possible to reduce the cell thickness of the STN-LCDs, which leads to significantly shorter switching times. The tolan compounds are preferably selected from the group T, which contains Ta to Th

wherein
R ¹ and R ² independently of one another have one of the meanings of the formulas I and II,
Z is -COO-, -CH ₂ CH ₂ - or a single bond, and
L ¹ to L ⁶ independently of one another denote H or F.

Compounds are particularly preferred of the formula Th.

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

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

The liquid crystal mixtures contain optionally also an optically active component C in such Amount that the ratio between layer thickness (distance of plane-parallel carrier plates) and more natural pitch the chiral nematic liquid crystal mixture larger than 0.2 is suitable for the desired one Twist. Suitable dopants can be found in a wide range known chiral materials and commercially available dopants such as cholesteryl nonanoate, S 811 (Merck KGaA, Darmstadt, Germany) and CB 15 (Merck Ltd., former BDH, Poole, UK) selected become. The choice of it is not critical in itself.

The amount of compounds of the component C. preferably 0 to 10%, in particular 0 to 5%, very preferably 0 to 3%.

The liquid crystal mixtures can also up to 20% of one or more connections with a dielectric Anisotropy of –2 or less (component D) included.

Component D preferably contains one or more compounds with the structural element 2,3-difluoro-1,4-phenylene, such as B. in DE-OS 38 07 801, 38 07 861, 38 07 863, 38 07 864 or 38 07 908. Tolane compounds are particularly preferred with this structural element according to PCT / DE 88100133.

wie in DE-OS 32 31 707 oder DE-OS 34 07 013 .Other known compounds of component D are e.g. B. 2,3-dicyanohydroquinone or cyclohexane derivatives with the structural element

as in DE-OS 32 31 707 or DE-OS 34 07 013 ,

The proportion of compounds of component D containing one or more compounds with one dielectric anisotropy <-1.5 is preferably approximately 0% to 10%, in particular approximately 0% to 5%. The person skilled in the art can easily adjust this proportion in such a way that the desired threshold voltage is generated, it being possible in principle to use all customary liquid crystal compounds with Δε <-1.5.

The contain particularly preferably Ads according to the invention no connections of component D.

The individual connections of the formulas I, II, III, IV, V, VI, T and also other compounds used in the STN-LCDs according to the invention can be used are either known or can be analogous to the known compounds produce.

In particular, the compounds of the formula II have low viscosities, in particular low rotational viscosities, low values for the ratio of the elastic constants (K ₃ / K ₁ ) and therefore bring about short switching times, while the compounds of the formula II have high dielectric anisotropy, especially in the presence of large amounts as in the displays according to the invention cause a reduced threshold voltage.

The expression alkenyl in the meanings of R and R ¹ to R ⁴ comprises straight-chain and branched alkenyl groups, in the case of R having 2 to 7 C atoms, in the case of R, R ² , R ³ and R ⁴ having 2 to 12 C atoms. Straight chain alkenyl groups are preferred. Further preferred alkenyl groups are C ₂ -C ₄ -1E-alkenyl, C ₄ -C ₇ -3E-alkenyl, C ₅ -C ₇ -4-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 and 6-heptenyl. Alkenyl groups with up to 5 carbon atoms are special prefers. Vinyl, 1E-propenyl, 1E-butenyl, 3E-butenyl and 3E-pentenyl, especially vinyl and 3E-butenyl.

• – eine oder mehrere, vorzugsweise zwei bis vier Verbindungen der Formel IIa,
• – 3 bis 35 Gew.-%, vorzugsweise 5 bis 25 Gew.-% von einer oder mehreren, insbesondere einer bis drei Verbindungen der Formel I,
• – 8 bis 45 Gew.-%, vorzugsweise 10 bis 30 Gew.-% von einer oder mehreren, insbesondere zwei bis fünf Verbindungen der Formel II,
• – 10 bis 45 Gew.-%, vorzugsweise 15 bis 35 Gew.-% von einer oder mehreren, insbesondere zwei bis sechs, Cyanverbindungen der Formel III, die besonders bevorzugt aus Formeln IIIb und IIIc ausgewählt sind,
• – 10 bis 60 Gew.-%, vorzugsweise 25 bis 50 Gew.-% von einer oder mehreren, insbesondere zwei bis sechs, Alkenylverbindungen der Formel VI,
• – 5 bis 25 Gew.-%, vorzugsweise 8 bis 20 Gew.-% von einer oder mehreren, insbesondere einer bis drei, Tolanverbindungen der Gruppe T, die besonders bevorzugt aus der Formel Th ausgewählt sind,
• – mehr als 50 Gew.-% Alkenylverbindungen.

In further particularly preferred embodiments, the liquid crystal mixtures according to the invention contain

• One or more, preferably two to four, compounds of the formula IIa,
• 3 to 35% by weight, preferably 5 to 25% by weight, of one or more, in particular one to three, compounds of the formula I,
• 8 to 45% by weight, preferably 10 to 30% by weight, of one or more, in particular two to five, compounds of the formula II,
• 10 to 45% by weight, preferably 15 to 35% by weight, of one or more, in particular two to six, cyano compounds of the formula III, which are particularly preferably selected from formulas IIIb and IIIc,
• 10 to 60% by weight, preferably 25 to 50% by weight, of one or more, in particular two to six, alkenyl compounds of the formula VI,
• 5 to 25% by weight, preferably 8 to 20% by weight, of one or more, in particular one to three, tolan compounds of group T, which are particularly preferably selected from the formula Th,
• - More than 50 wt .-% alkenyl compounds.

• – keine Verbindungen der Komponente B der Formeln IV-1 bis IV-31 und/oder keine Verbindungen der Komponente D enthalten,
• – im Wesentlichen aus Verbindungen der Formeln I, II, III, VI und Gruppe T bestehen.

Further preferred embodiments relate to liquid crystal mixtures which

• Contain no compounds of component B of the formulas IV-1 to IV-31 and / or no compounds of component D,
• - essentially consist of compounds of the formulas I, II, III, VI and group T.

The mixtures according to the invention are particularly notable for use in STN-LCDs with large cell gaps due to their low total switching times (t _tot = t _on + t _off ). Low switching times are a particularly important requirement for STN-LCDs, if they e.g. B. used in laptops to allow better display of cursor movements. Displays with switching times of 300 msec or less, in particular 250 msec or less, are particularly preferred.

The STN-LCDs according to the invention stand out characterized by a low threshold voltage. The threshold voltage is preferably 1.5 V or less.

The liquid crystal mixtures in the STN LCDs according to the invention are dielectric positive with Δε ≥ 1.5. Especially mixtures with Δε ≥ 3 are preferred, very particularly preferably those with Δε ≥ 5.

The liquid crystal _{mixtures according} to the invention have advantageous 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 specified, the value for the cell gap d is determined by the optical anisotropy Δn. In particular with high values for d · Δn, the use of liquid crystal mixtures according to the invention with a higher value for Δn is preferred, since the value for d can then be chosen to be relatively small, which leads to improved values for the switching time. However, liquid-crystal displays according to the invention which contain liquid-crystal mixtures according to the invention with smaller values for Δn are also advantageous due to the switching times features.

The liquid crystal mixtures according to the invention are further characterized by advantageous values for the slope and can especially at temperatures above 20 ° C with high multiplex rates are operated. In addition, the mixtures high stability, high electrical resistance and low frequency dependence the threshold voltage. The liquid crystal displays according to the invention have a wide working temperature range and good viewing angle dependency of contrast.

The structure of the liquid crystal display elements according to the invention from polarizers, electrode base plates and electrodes with a such surface treatment, that the preferred orientation (director) of the adjoining one Liquid crystal molecules from the one to the other electrode usually around amount 160 ° to 720 ° against each other is twisted, corresponds to that for such display elements usual Construction. The term is common Construction here broadly and also includes all modifications and Modifications of the supertwist cells, in particular also matrix display elements. The surface tilt angle on the two support plates can be the same or different. The same tilt angles are preferred.

The tilt angle lies in TN displays according to the invention between the longitudinal axes of the molecules on the surface the base plates and the base plate preferably in the range of 0 ° to 7 °, especially from 0.01 ° to 5 °, very much preferably from 0.1 to 2 °. In STN displays according to the invention the tilt angle is preferably in the range from 1 ° to 30 °, in particular from 1 ° to 12 °, very much preferably from 3 ° to 10 °.

The twist angle of the liquid crystal mixture between the orientation layers on the two base plates the cell is in the range of TN displays according to the invention from 22.5 ° to 170 °, in particular from 45 ° to 130 °, very much preferably from 80 ° to 115 °. at STN displays, the twist angle is in the range of 100 ° to 600 °, in particular from 170 ° to 300 °, very much preferably from 180 ° to 270 °.

The preparation of those which can be used according to the invention liquid crystal mixtures takes place in a more usual way Wise. Usually the one you want Amount of components used in smaller quantities in the Main constituent components dissolved, expedient at elevated temperature. It is also possible, solutions the components in an organic solvent, e.g. B. in acetone, Chloroform or methanol, mix and the solvent after mixing to remove again, for example by distillation.

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

In the present patent application and in the following examples, all chemical structures of the liquid crystal compounds are indicated by acronyms, their transformation into chemical formulas being carried out as indicated below. All radicals C _n H _{2n + 1} and C _m H _{2m + 1} are straight-chain alkyl radicals with n or m carbon atoms. The coding according to Table B goes without saying. In Table A only the acronym for the basic body is given. In individual cases, this acronym is followed by a hyphen and a code for the substituents R ¹ , R ² , L ¹ and L ² as follows:

The given in Tables A and B. Compounds are particularly preferred components of the present Invention.

Table A: (L ¹ , L ² , L ³ ; H or F)

Table B:

The following examples are intended to Explain invention, without limiting it.

The abbreviations have the following meanings:
Δn birefringence at 589 nm and 20 ° C
n _o ordinary refractive index (589 nm, 20 ° C)
Δε dielectric anisotropy (1 kHz, 20 ° C)
ε _⊥ dielectric constant perpendicular to the _longitudinal axis of the molecule (1 kHz, 20 ° C)
T _ave average switching time = 0.5 (T _on + T _off )
T _on time from switching on until reaching 90% of the maximum contrast,
T _off time from switching off until reaching 10% of the maximum contrast,
V ₁₀ threshold voltage (volts)
V ₉₀ saturation voltage
V ₉₀ / V ₁₀ slope
γ _red rotational viscosity (mPas)

Unless otherwise noted, all temperatures above and below are given in degrees Celsius and percentages are% by weight. The values for switching times and viscosities refer to 20 ° C. The switching time is the average t _ave as defined above. The STN-LCD is controlled in multiplex mode with a multiplex rate of 1/64 and a bias of 1/7.

example 1

An STN display contains a liquid crystal mixture with the following properties: clearing point + 95 ° C .DELTA.n .1443 V ₁₀ 1.45 V V ₉₀ / V ₁₀ 1,054 T _ave 149 msec consisting of PCH 3N.FF 18.00% ME2N.F 4.00% ME3N.F 4.00% UZU-3A-N 8.00% CC-5-V 4.00% CC-3-V1 7.00% CVCP-1V-O1 4.00% CVCP V O1 4.50% CVCP-V-1 4.50% CCP-V-1 15.00% CCP-V2-1 15.00% PPTUI-3-2 12.00%

Claims (10)

Supertwist nematic liquid crystal display with - two plane-parallel carrier plates, which form a cell together with a border, - a nematic liquid crystal mixture in the cell with positive dielectric anisotropy, - electrode layers with overlying orientation layers on the inside of the carrier plates, which address each pixel by means of orthogonal series waveforms, - An angle of attack between the longitudinal axis of the molecules on the surface of the carrier plates and the carrier plates from 1 degree to 30 degrees, and - A twist angle of the liquid crystal mixture in the cell from orientation layer to orientation layer according to the amount between 22.5 and 600 °, the nematic Liquid crystal mixture essentially consists of a) 15-80 wt .-% of a liquid crystalline component A, consisting of one or more compounds with a dielectric anisotropy of over +1.5; b) 20-85% by weight of a liquid-crystalline component B, consisting of one or more compounds with a dielectric anisotropy between -1.5 and +1.5; c) 0-20% by weight of a liquid-crystalline component D, consisting of one or more compounds with a dielectric anisotropy of less than -1.5, and d) an optically active component C in an amount such that the ratio between layer thickness (distance the plane-parallel carrier plates) and the natural pitch of the chiral nematic liquid crystal mixture is 0.2 to 1.3, characterized in that the liquid crystal mixture has at least one compound of the formula I

and at least one alkenyl compound of the formula II

contains, wherein R ¹ and R ² independently of one another represent an optionally fluorinated alkyl, alkoxy, alkenyl or alkenyloxy group having 1 to 12 carbon atoms, in which one or two non-adjacent CH ₂ groups are denoted by -O-, -CH = CH-, -CO-, -OCO- or -COO- can be replaced so that O atoms are not directly adjacent to each other, R ^{3 represents} an alkenyl group with 2 to 7 C atoms, and L ¹ and L ² each independently represent H or F. Display according to claim 1, characterized in that it contains one or more compounds of formula IIa

contains, in which k denotes 1, 2, 3, 4 or 5, m and n independently of one another denote 0, 1, 2 or 3, where m + n 5 5, and o denotes 0 or 1. Display according to claim 1 or 2, characterized in that component A is one or more cyan compounds selected from the following formulas

contains in which R has one of the meanings given for R ¹ in formula I and L ¹ , L ² and L ³ independently of one another are H or F. Display according to at least one of Claims 1 to 3, characterized in that it contains one or more alkenyl compounds of the formula VI

contains in which R ^{3 is} an alkenyl group having 2 to 7 carbon atoms, R ^{4 has} one of the meanings given for R ¹ in formula I or, if m is 1, can also be QY, Q is -CF ₂ -, -OCF ₂ -, -CFH-, -OCFH- or a single bond means YF or Cl, m means 0 or 1, and L ¹ and L ² independently of one another denote H or F. Display according to at least one of claims 1 to 4, characterized in that it has at least one compound selected from the formulas VI-1a to VI-1e

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

contains in which R ^3a and R ^4a independently of one another denote H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ and alkyl denotes an alkyl group having 1 to 7 C atoms. Display according to at least one of claims 1 to 5, characterized in that it is one or more tolan compounds selected from the following formulas

contains, wherein R ¹ and R ² independently of one another have one of the meanings given in the formulas I and II. Display according to at least one of claims 1 to 6, characterized in that the liquid crystal mixture 3 to Contains 35% by weight of one or more compounds of the formula I. Display according to at least one of claims 1 to 7, characterized in that the liquid crystal mixture 8 to Contains 45% by weight of one or more compounds of the formula II. Display according to at least one of claims 1 to 8, characterized in that the liquid crystal mixture more than Contains 50 wt .-% of alkenyl compounds. liquid crystal mixture or composition as in at least one of claims 1 to 9 defined.