DE102006047128B4 - Liquid crystal medium and its use - Google Patents

Abstract

A liquid-crystal medium, characterized in that it comprises a) one or more dielectrically positive compounds of the formula I, wherein each R independently represents H, an unsubstituted alkyl or alkenyl radical of up to 12 which is monosubstituted by CN or CF 3 or at least monosubstituted by halogen C atoms, where in these radicals also one or more CH 2 groups are each independently of one another by -O-, -S-, - CH = CH-, -C≡C-, -CO-, -CO-O-, - O-CO- or -O-CO-O- can be replaced so that O atoms are not directly linked, L1 to L7 are each independently H or F, and n is 0 or 1, and b) one or more dielectrically A compound of formula II in which each R0 is independently H, an unsubstituted alkyl or alkenyl radical having up to 12 carbon atoms substituted by CN or CF3 or an alkyl group which is at least monosubstituted by halogen, one or more CH2 Each group independent ig each other by -O-, -S -, - CH = CH, -C≡C-, -CO-, -CO-O-, -O-CO- or -O-CO-O- so may be replaced in that O atoms are not directly linked to each other, ring A1, A2 and A3, independently of one another, YF, Cl or a mono- or polyfluorinated 1-4C alkyl or alkoxy radical, p and q independently of one another, 0 or 1, and ...

Description

The present invention relates to liquid-crystal media and their use in liquid-crystal displays, particularly in liquid-crystal displays which exhibit the TN effect ('twisted nematic', with a nematic structure twisted by about 90 °), the HTN effect ('high performance twisted nematic', twisted by about 100 ° -120 °) or use the STN effect (supertwisted nematic).

Non-active matrix displays that use the TN, HTN, or STN effect are still the most common types of displays. TN displays are well-known. From M. Schadt and W. Helfrich, Appl. Phys. Lett., 18, 127 (1971), STN ads z. From T.J. Scheffer and J. Nehring, Appl. Phys. Lett., 45, 1021 (1984). These and similar electro-optical effects use liquid-crystalline media with positive dielectric anisotropy (Δε).

In such liquid crystal displays, the liquid crystals are used as dielectrics whose optical properties reversibly change upon application of an electric voltage.

Since in displays in general, that is to say also for displays according to these mentioned effects, the operating voltage should be as low as possible, liquid-crystal media are used, which are usually composed predominantly of liquid crystal compounds, which all have the same sign of the dielectric anisotropy and the largest possible dielectric Have anisotropy. At most smaller proportions of dielectrically neutral compounds are used. In liquid crystal media with high positive dielectric anisotropy, predominantly compounds with dielectrically positive anisotropy are used. As a rule, the liquid-crystal media used consist predominantly and mostly even of liquid-crystal compounds having a positive dielectric anisotropy.

Such liquid-crystal media are for example in the DE 10 2004 002 418 A1 and WO 2004/099343 A1 disclosed. In the case of the media described therein and used according to the present application, at most small amounts of dielectrically neutral liquid crystal compounds are used, and in most cases no dielectrically negative compounds, since generally the liquid crystal displays should have the lowest possible drive voltages. For this reason, liquid crystal compounds having the dielectric anisotropy opposite to the dielectric anisotropy of the medium are usually used extremely sparingly or not at all.

The liquid crystal media of the prior art with correspondingly low drive voltages have relatively low clearing points and easily lead to failure of the display at elevated temperatures, eg. B. by the sun.

On the other hand, the driving voltage of the prior art displays is often insufficiently high, especially for displays for portable devices (eg, games, gauges) and watches. The power consumption of these battery-operated devices depends largely on the power consumption of the display and ultimately on their drive voltage. Thus, the characteristic voltages of the liquid crystal media in the liquid crystal cells must be improved without increasing their clearing points.

In addition, the electrical resistance of the media must be sufficiently high and the viscosities of the liquid-crystal media to be improved, so reduced. This is especially true for the rotational viscosity and especially at low temperatures.

Thus, there is a great need for liquid-crystal media which does not have the disadvantages of the prior art media, or at least to a much lesser extent.

Surprisingly, it has been found that liquid crystal displays can be realized which do not have the mentioned disadvantages. In particular, liquid-crystal media according to the invention have high clearing points and particularly low threshold voltages.

• a) eine oder mehrere dielektrisch positive Verbindungen der Formel I
  
  worin R¹ jeweils unabhängig voneinander H, einen unsubstituierten, einen einfach durch CN oder CF₃ oder einen mindestens einfach durch Halogen substituierten Alkyl- oder Alkenylrest mit bis zu 12 C-Atomen, wobei in diesen Resten auch eine oder mehrere CH₂-Gruppen jeweils unabhängig voneinander durch -O-, -S-,
  
  -CH=CH-, -C≡C-, -CO-, -CO-O-, -O-CO- oder -O-CO-O- so ersetzt sein können, dass O-Atome nicht direkt miteinander verknüpft sind, L¹ bis L⁷ jeweils unabhängig voneinander H oder F, und n 0 oder 1 bedeuten,
• b) eine oder mehrere dielektrisch positive Verbindungen der Formel II
  
  worin R⁰ jeweils unabhängig voneinander H, einen unsubstituierten, einen einfach durch CN oder CF₃ oder einen mindestens einfach durch Halogen substituierten Alkyl- oder Alkenylrest mit bis zu 12 C-Atomen, wobei in diesen Resten auch eine oder mehrere CH₂-Gruppen jeweils unabhängig voneinander durch -O-, -S-,
  
  -CH=CH-, -C≡C-, -CO-, -CO-O-, -O-CO- oder -O-CO-O- so ersetzt sein können, dass O-Atome nicht direkt miteinander verknüpft sind, Ring A¹, A² and A³, jeweils unabhängig voneinander,
  
  Y F, Cl oder einen ein- oder mehrfach fluorierten 1-4 C Alkyl- oder Alkoxyrest, p und q unabhängig voneinander, 0 oder 1, und L¹ und L² H oder F bedeuten,
• c) eine oder mehrere dielektrisch positive Verbindungen der Formel IIIA
  
  worin R³ jeweils unabhängig voneinander H, einen unsubstituierten, einen einfach durch CN oder CF₃ oder einen mindestens einfach durch Halogen substituierten Alkyl- oder Alkenylrest mit bis zu 12 C-Atomen, wobei in diesen Resten auch eine oder mehrere CH₂-Gruppen jeweils unabhängig voneinander durch -O-, -S-,
  
  -CH=CH-, -C≡C-, -CO-, -CO-O-, -O-CO- oder -O-CO-O- so ersetzt sein können, dass O-Atome nicht direkt miteinander verknüpft sind, und L¹ H oder F bedeuten, und
• d) eine oder mehrere Verbindungen der Formel IV-1b
  
  worin R⁴ Alkyl mit 1 bis 7 C-Atomen oder Alkenyl mit 2 bis 6 C-Atomen, und X¹ F oder OCHF₂, bedeuten.

In the present invention, the low threshold voltage with simultaneously high clearing point is realized by using liquid crystal media according to the invention. These media included

• a) one or more dielectrically positive compounds of the formula I.
  
  wherein each R ¹ is independently H, an unsubstituted, an alkyl or alkenyl radical having up to 12 C atoms, which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen, and one or more CH ₂ groups in each of these radicals independently of each other by -O-, -S-,
  
  -CH = CH-, -C≡C-, -CO-, -CO-O-, -O-CO- or -O-CO-O- may be replaced so that O atoms are not directly linked to one another, L ¹ to L ^{7 are} each independently H or F, and n is 0 or 1,
• b) one or more dielectrically positive compounds of the formula II
  
  wherein each R ⁰ is independently H, an unsubstituted, an alkyl or alkenyl radical having up to 12 C atoms, which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen, and one or more CH ₂ groups in each of these radicals independently of each other by -O-, -S-,
  
  -CH = CH-, -C≡C-, -CO-, -CO-O-, -O-CO- or -O-CO-O- may be replaced so that O atoms are not directly linked to one another, Ring A ¹ , A ² and A ³ , each independently of one another,
  
  YF, Cl or a mono- or polyfluorinated 1-4C alkyl or alkoxy radical, p and q independently of one another, 0 or 1, and L ¹ and L ² denote H or F,
• c) one or more dielectrically positive compounds of formula IIIA
  
  wherein each R ³ is independently H, an unsubstituted, an alkyl or alkenyl radical having up to 12 C atoms, which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen, and one or more CH ₂ groups in each of these radicals independently of each other by -O-, -S-,
  
  -CH = CH-, -C≡C-, -CO-, -CO-O-, -O-CO- or -O-CO-O- may be replaced so that O atoms are not directly linked to one another, and L ^{1 is} H or F, and
• d) one or more compounds of the formula IV-1b
  
  wherein R ^{4 is} alkyl having 1 to 7 carbon atoms or alkenyl having 2 to 6 carbon atoms, and X ^{1 is} F or OCHF ₂ .

• e) eine oder mehrere dielektrisch positive Verbindungen der Formel IIIB
  
  wobei R³ und L¹ die für IIIA angegebene Bedeutung haben, und
• f) eine oder mehrere Verbindungen ausgewählt aus der Gruppe der Verbindungen der Formeln IV-1 bis IV-5 (allgemein IV)
  
  worin R⁴ Alkyl mit 1 bis 7 C-Atomen, Alkoxy mit 1 bis 7 C-Atomen, oder Alkoxyalkyl, Alkenyl oder Alkenyloxy mit 2 bis 7 C-Atomen, X¹ F, Cl oder einen ein- oder mehrfach fluorierten 1-4 C Alkyl- oder Alkoxyrest, Y¹ H oder F, und Z¹¹ und Z¹², jeweils unabhängig voneinander, -CH₂-CH₂-, -CH=CH-, -CH₂-CF₂-, -CF₂-CH₂-, -CF₂-CF₂-, -OCH₂-, -CH₂O- oder eine Einfachbindung bedeuten, wobei die Verbindungen der Formel IV-1b ausgeschlossen sind.

Preferably, the medium according to the invention for a liquid crystal display additionally contains

• e) one or more dielectrically positive compounds of formula IIIB
  
  wherein R ³ and L ^{1 have} the meaning given for IIIA, and
• f) one or more compounds selected from the group of the compounds of the formulas IV-1 to IV-5 (general IV)
  
  where R ^{4 is} alkyl having 1 to 7 C atoms, alkoxy having 1 to 7 C atoms, or alkoxyalkyl, alkenyl or alkenyloxy having 2 to 7 C atoms, X ¹ F, Cl or a mono- or polyfluorinated 1-4 C is alkyl or alkoxy, Y ^{1 is} H or F, and Z ¹¹ and Z ^{12 are} each independently, -CH ₂ -CH ₂ -, -CH = CH-, -CH ₂ -CF ₂ -, -CF ₂ -CH ₂ -, -CF ₂ -CF ₂ -, -OCH ₂ -, -CH ₂ O- or a single bond, which compounds of formula are excluded IV-1b.

Particularly preferably, the medium additionally contains one or more compounds of the formula IV-1, the compounds of the formula IV-1b being excluded.

The substituents Y and X ^1, under the meanings given above, are preferably Cl, F, -CF ₃ , -OCF ₃ , -OCHF ₂ , -OCHFCF ₃ or -OCF ₂ CHFCF ₃ , in particular F and -OCF ₃ and very particularly preferably F ,

The use according to the invention of the liquid-crystal media is preferably carried out in passively controlled liquid-crystal displays with a twist of the preferred direction of the liquid-crystal layer between the cover layers between 80 and 120 °.

worin R¹, L¹ und L² die jeweilige oben bei Formel I angegebene Bedeutung haben und bevorzugt
L¹ H
bedeutet.In a particularly preferred embodiment, the liquid-crystal medium contains one or more compounds of the formula I selected from the group of the compounds of the formulas I-1 to I-5, very particularly preferably selected from the group of the compounds of the formulas I-1, I-2 and I-3,

wherein R ¹ , L ¹ and L ^{2 have} the respective meaning given above for formula I and preferred
L ¹ H
means.

worin
R⁰ wie oben für Formel I definiert ist und insbesondere
R⁰ einen n-Alkylrest mit 1-7 C-Atomen oder einen Alkenylrest mit 2-7 C-Atomen bedeutet.In a particularly preferred embodiment, the medium contains one or more compounds of the formula II selected from the group of the compounds of the formulas II-1 to II-32, very particularly preferably selected from the group of the compounds of the formulas II-8, II-9, II-19, II-20, II-26 and II-29,

wherein
R ^{0 is} as defined above for formula I and in particular
R ^{0 is} an n-alkyl radical having 1-7 C atoms or an alkenyl radical having 2-7 C atoms.

worin R³ die oben bei Formel IIIA angegebene Bedeutung hat und bevorzugt
R³ einen n-Alkylrest mit 1-7 C-Atomen bedeutet.In a further particularly preferred embodiment, the medium contains one or more compounds of the formula IIIA-1

wherein R ^{3 has} the meaning given above in formula IIIA and preferred
R ^{3 is} an n-alkyl radical having 1-7 C atoms.

worin
R⁴ einen geradkettigen Alkylrest mit 1-7 C-Atomen oder einen geradkettigen Alkenylrest mit 2-6 C-Atomen, und
X F oder OCF₃ bedeutet.In a further particularly preferred embodiment, the medium contains one or more compounds of the formula IV selected from the compounds of the formulas:

wherein
R ^{4 is} a straight-chain alkyl radical having 1-7 C atoms or a straight-chain alkenyl radical having 2-6 C atoms, and
XF or OCF ₃ means.

Among these, very particular preference is given to compounds of the formulas IV-1a. For example, the compounds of formulas IV extend the nematic phase range of the media.

worin
R⁵¹ und R⁵², jeweils unabhängig voneinander, Alkyl mit 1 bis 7 C-Atomen, Alkoxy mit 1 bis 7 C-Atomen, oder Alkoxyalkyl, Alkenyl oder Alkenyloxy mit 2 bis 7 C-Atomen,
Z⁵¹, Z⁵² und Z⁵³, jeweils unabhängig voneinander, -CH₂CH₂-, -CH=CH-, -COO- oder eine Einfachbindung,

jeweils unabhängig voneinander,

p 0 oder 1
bedeutet,
und insbesondere enthält das Medium eine oder mehrere Verbindungen ausgewählt aus den Verbindungen der Formeln V-1 bis V-6:

In a further particularly preferred embodiment, the medium contains one or more compounds of the formula V:

wherein
R ⁵¹ and R ⁵² , each independently of one another, are alkyl having 1 to 7 C atoms, alkoxy having 1 to 7 C atoms, or alkoxyalkyl, alkenyl or alkenyloxy having 2 to 7 C atoms,
Z ⁵¹ , Z ⁵² and Z ⁵³ , each independently of one another, -CH ₂ CH ₂ -, -CH = CH-, -COO- or a single bond,

each independently

p 0 or 1
means
and in particular the medium contains one or more compounds selected from the compounds of the formulas V-1 to V-6:

Alkyl and alkyl * here each independently preferably denote a straight-chain alkyl radical having 1-7 C atoms. The medium preferably contains 5-15% by weight of compounds of the formula V. The compounds of the formulas V, for example, increase the clearing point of the media.

worin R⁶ wie R¹ oben definiert ist, und
Y¹, Y² H oder F bedeuten.In a further preferred embodiment, the medium contains one or more compounds of the formula VI, preferably of the formula VI-1:

wherein R ⁶ is defined as R ¹ above, and
Y ¹ , Y ² signify H or F.

In particularly preferred embodiments, the liquid-crystal media according to the invention contain in total, based on the total mixture in percent by weight:
10% or more of compounds of the formula I, preferably 1 From 0% or more to 40% or less, and more preferably from 15% or more to 30% or less and most preferably from 20% or more to 25% or less of compounds of formula I,
1% or more to 40% or less, preferably 2% or more to 25% or less, more preferably 3% or more to 15% or less and most preferably 4% or more to 10% or less of compounds of formula II .
5% or more to 50% or less, preferably 10% or more to 40% or less, more preferably 15% or more to 25% or less and most preferably 18% or more to 22% or less of compounds of formula III .
5% or more to 60% or less, preferably 15% or more to 50% or less, more preferably 20% or more to 40% or less and most preferably 25% or more to 35% or less of compounds of formula IV .
1% or more to 40% or less, preferably 3% or more to 30% or less, more preferably 5% or more to 25% or less and most preferably 10% or more to 20% or less of compounds of formula V , and
0% or more to 40% or less, preferably 0% or more to 30% or less, more preferably 0% or more to 20% or less and most preferably 5% or more to 15% or less of compounds of formula VI .
wherein the concentration data of the compounds III mean the sum of the concentrations of the compounds IIIA and IIIB and the concentration data of the compounds IV the sum of the concentrations of the compounds IV-1b and IV-1 to IV-5.

As used throughout the present application, the term compounds also written as compound (s) means, unless explicitly stated otherwise, both one and more compounds.

In this case, the individual compounds are used in concentrations of from 1% or more to 30% or less, preferably from 2% or more to 30% or less, and more preferably from 3% or more to 16% or less. Using multiple homologous compounds, higher concentrations of compounds of a general common structure are also solubilized.

In a preferred embodiment, the liquid-crystal media particularly preferably contain a total
10% to 40% of compounds of the formula I,
2% to 25% of compounds of the formulas II,
10% to 40% of compounds of formula III and
15% to 50% of compounds of formula IV.

Most preferably, the liquid-crystal media in this embodiment contain a total of
15% to 30% of compounds of the formula I,
3% to 15% of compounds of the formula II,
15% to 25% of compounds of formula III and
20% to 40% of compounds of formula IV.

The clearing point of the liquid-crystal media of the invention is preferably at least 85 ° C and more preferably at least 90 ° C or above.

The liquid-crystal media according to the invention preferably have a nematic phase of -20 ° C or less to 75 ° C or more, more preferably from -30 ° C or less to 85 ° C or more, and most preferably from -40 ° C or less to 90 ° C or more.

In this case, the term "nematic phase" means, on the one hand, that no smectic phase and no crystallization are observed at low temperatures at the corresponding temperature and, on the other hand, that clarification does not yet occur on heating from the nematic phase. The investigation at low temperatures is carried out in a flow viscometer at the appropriate temperature and checked by storage in test cells with a corresponding layer thickness for electro-optical application for at least 100 hours. When the storage stability at a temperature of -20 ° C. (t _store ) in a corresponding test cell is 1,000 hours or more, the medium is said to be stable at this temperature. At high temperatures, the clearing point is measured in capillaries by conventional methods.

Furthermore, the liquid-crystal media according to the invention are characterized by values of the optical anisotropy (Δn) in the lower central region. The Δn values are preferably in the range of 0.075 to 0.130, more preferably in the range of 0.080 to 0.120, and most preferably in the range of 0.090 to 0.110. The advantage of the liquid-crystal media according to the invention is that lower Δn values can be achieved while maintaining the low threshold voltage and the high clearing point. The Δn values are therefore preferably ≦ 0.11, particularly preferably ≦ 0.105.

In addition, the liquid-crystal media according to the invention have particularly small values for the threshold voltage (V ₁₀ ) of less than or equal to 0.75 V, preferably less than or equal to 0.70 V and particularly preferably less than or equal to 0.65 V.

These preferred values for the individual physical properties are preferably also kept in combination with one another by the media according to the invention.

In the present application, the term halogen generally means fluorine, chlorine, bromine or iodine, in particular fluorine and chlorine.

In the present application, "≤" means less than or equal to, preferably less than and "≥" greater than or equal to, preferably greater.

trans-1,4-Cyclohexylen. 2,5-substituerte Pyran- und 1,3-Dioxanringe sind bevorzugt trans-substituiert.In the present application mean

trans-1,4-cyclohexylene. 2,5-substituted pyran and 1,3-dioxane rings are preferably trans-substituted.

In the present application, the terms "dielectrically positive" compounds mean those compounds with a Δε> 1.5, "dielectrically neutral" compounds those with -1.5 ≦ Δε ≦ 1.5 and "dielectrically negative" compounds those with Δε <- 1.5. Here, the dielectric anisotropy of the compounds is determined by 10% of the compounds are dissolved in a liquid-crystalline host and the capacity of at least one test cell in each case with 20 micron layer thickness is determined with homeotropic and homogeneous surface orientation at 1 kHz. The measuring voltage is typically 0.5 V to 1.0 V, but always less than the capacitive threshold of the respective liquid-crystal mixture.

The host mixture used for dielectrically positive and dielectrically neutral compounds is ZLI-4792 and for dielectrically negative compounds ZLI-2857, both from Merck KGaA, Germany. From the change in the dielectric constant of the host mixture after addition of the test compound and extrapolation to 100% of the compound used, the values for the respective compounds to be investigated are obtained. The compound to be tested is dissolved to 10% in the host mixture. If the solubility of the substance is too low for this purpose, the concentration is halved stepwise until the investigation can be carried out at the desired temperature.

All values given for temperatures in this application are ° C and all temperature differences are differential degrees unless explicitly stated otherwise.

The term threshold voltage in the present application, as is common practice, refers to the optical threshold for 10% relative contrast (V ₁₀ ), unless explicitly stated otherwise.

All concentrations for compounds in blends in this application are given in weight percent (= weight percent, unit [%] or [weight%]) and refer to the corresponding blend or blend component. All physical properties are determined according to the brochure "Merck Liquid Crystals, Physical Properties of Liquid Crystals", (Nov. 1997, Merck KGaA, Germany) and are valid for a temperature of 20 ° C, unless explicitly stated otherwise. Δn is determined at 589 nm and Δε at 1 kHz.

The steepness (S) of the mixtures in a specific test cell is determined from the characteristic slope V ₉₀ / V ₁₀ according to the formula: S = (V ₉₀ / V ₁₀ -1) × 100%.

V₁₀

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

V₉₀

Sättigungsspannung = 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,

t_sum

t_on + t_off (bei 80 Hz Wiederholungsrate),

t_store

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

d

Schichtdicke des Flüssigkristallmediums,

duty

Multiplexrate, und

d/P

Schichtdicke dividiert durch Pitch.

Where:

V ₁₀

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

V ₉₀

Saturation voltage = characteristic voltage 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,

t _sum

t _on + t _off (at 80 Hz repetition rate),

t _store

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

d

Layer thickness of the liquid-crystal medium,

duty

Multiplex rate, and

d / P

Layer thickness divided by pitch.

If necessary, the liquid-crystal media according to the invention can also contain further additives, such as, for example, And chiral dopants (as component D) or nanoparticles. The amount of these additives used is a total of 0% or more to 10% or less based on the amount of the entire mixture, preferably 0.1% or more to 6% or less. The concentration of the individual compounds used is preferably 0.1% or more to 3% or less. The concentration of these and similar additives is not taken into account in the indication of the concentrations and the concentration ranges of the liquid crystal compounds in the liquid-crystal media.

The compositions consist of several compounds, preferably from 3 or more to 30 or less, more preferably from 6 or more to 20 or less and most preferably from 10 or more to 16 or fewer compounds that are mixed in a conventional manner. In general, the desired amount of the minor components is dissolved in the components that make up the main ingredient of the mixture. This is conveniently carried out at elevated temperature. If the selected temperature is above the clearing point of the main constituent, the completion of the dissolution process is particularly easy to observe. However, it is also possible, the liquid crystal mixtures in other conventional ways, for. B. using premixes or from a so-called "multi-bottle system" produce.

A further aspect of the invention is therefore also a process for the preparation of a liquid-crystal medium as indicated above in general or in particular, which comprises mixing the compounds of the stated formulas with further liquid-crystalline cocomponents and optionally adding additives.

Tabelle B:

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 coding according to Table B is self-evident. In Table A, only the acronym for the main body is given. In individual cases, followed by a dash from the acronym for the main body, a code for the substituents R ¹ , R ² , L ¹ , L ² and L ³ : 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 N0M C _n H _{2n + 1} OC _m H _{2m + 1} H H H n0.m OC _n H _{2n + 1} C _m H _{2m + 1} H H H nmFF C _n H _{2n + 1} C _m H _{2m + 1} H F F nm0FF C _n H _{2n + 1} OC _m H _{2m + 1} H F F n C _n H _{2n + 1} CN H H H nN.F C _n H _{2n + 1} CN F H H nN.FF C _n H _{2n + 1} CN F F H nF C _n H _{2n + 1} F H H H nF.F C _n H _{2n + 1} F F H H nF.FF C _n H _{2n + 1} F F F H n0F OC _n H _{2n + 1} F H H H n Cl C _n H _{2n + 1} Cl H H H nCl.F C _n H _{2n + 1} Cl F H H nCl.FF C _n H _{2n + 1} Cl F F H nCF ₃ C _n H _{2n + 1} CF ₃ H H H nCF ₃ .F C _n H _{2n + 1} CF ₃ F H H nCF ₃ .FF C _n H _{2n + 1} CF ₃ F F H n0CF ₃ C _n H _{2n + 1} OCF ₃ H H H n0CF ₃ .F C _n H _{2n + 1} OCF ₃ F H H n0CF ₃ .FF C _n H _{2n + 1} OCF ₃ F F H n0CF ₂ C _n H _{2n + 1} OCHF ₂ H H H n0CF ₂ .F C _n H _{2n + 1} OCHF ₂ F H H n0CF ₂ .FF C _n H _{2n + 1} OCHF ₂ F F H RVSN C _r H _{2r + 1} -CH = CH-C _s H _2s - CN H H H rESn C _r H _{2r + 1} -OC _s H _2s - CN H H H Table A

Table B:

Table C

Stabilizers which can be added, for example, to the mixtures according to the invention are mentioned below.

In a preferred embodiment of the present invention, the media according to the invention comprise one or more compounds selected from the group of compounds of Table C.

Table D

Table D lists chiral dopants which are preferably used in the mixtures according to the invention.

The following examples illustrate the invention without limiting it. However, they illustrate the range of properties that can be preferably realized as well as the preferred compounds to be used. Examples Example 1 Link / shortcut Concentration / mass% Physical Properties PCH 3N.FF 11% T (N, I) = 92 ° C ME-2N.F 2% Δn (20 ° C, 589 nm) = 0.103 ME-3N.F 2.5% TN (90 ° twist, d · Δn = 0.50) PZU-V2-N 7% V ₁₀ (20 ° C) = 0.64 V HP 3N.F 4% Steepness = 70% HP 4N.F 4% HTN (110 ° twist) HP 5N.F 4% d · Δn = 0.60 CDU-2-F 6% d / p = 0.1 CDU-3-F 8th% V ₁₀ (20 ° C) = 0.72 V CDU-5-F 6% Steepness = 51% CCQU-5-F 6% Duty 8, bias 4: CCP 3F.FF 8th% V ₁₀ = 1.72V CCP 5F.FF 6% t _sum (V _op = 2.3 V) = 540 ms CCP 20CF2.FF 6% Duty 16, bias 5: CCP 30CF2.FF 4% V ₁₀ = 2.32V CCP 50CF2.FF 5% t _sum (V _op = 2.85 V) = 649 ms CCPC-33 4% CCPC-34 3.5% t _store (-40 ° C)> 1000 h CCPC-35 3% t _store (-30 ° C)> 1000 h Σ 100% t _store (-20 ° C)> 1000 h

Claims (10)

Liquid-crystal medium, characterized in that it comprises a) one or more dielectrically positive compounds of the formula I,

wherein each R ¹ is independently H, an unsubstituted, an alkyl or alkenyl radical having up to 12 C atoms, which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen, and one or more CH ₂ groups in each of these radicals independently of each other by -O-, -S-,

-CH = CH-, -C≡C-, -CO-, -CO-O-, -O-CO- or -O-CO-O- may be replaced so that O atoms are not directly linked to one another, L ¹ to L ^{7 are} each, independently of one another, H or F, and n is 0 or 1, and b) one or more dielectrically positive compounds of the formula II,

wherein each R ⁰ is independently H, an unsubstituted, an alkyl or alkenyl radical having up to 12 C atoms, which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen, and one or more CH ₂ groups in each of these radicals independently of each other by -O-, -S-,

-CH = CH-, -C≡C-, -CO-, -CO-O-, -O-CO- or -O-CO-O- may be replaced so that O atoms are not directly linked to one another, Ring A ¹ , A ² and A ³ , independently of one another,

YF, Cl or a mono- or polyfluorinated 1-4 C alkyl or alkoxy radical, p and q independently of one another, 0 or 1, and L ¹ , L ^{2 is} H or F, c) one or more dielectrically positive compounds of the formula IIIA,

wherein each R ³ is independently H, an unsubstituted, an alkyl or alkenyl radical having up to 12 C atoms, which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen, and one or more CH ₂ groups in each of these radicals independently of each other by -O-, -S-,

-CH = CH-, -C≡C-, -CO-, -CO-O-, -O-CO- or -O-CO-O- may be replaced so that O atoms are not directly linked to one another, and L ^{1 is} H or F, and d) one or more compounds of formula IV-1b

in which R ^{4 is} alkyl having 1 to 7 C atoms or alkenyl having 2 to 6 C atoms, X ¹ F or OCHF ₂ , contains. Liquid-crystal medium according to claim 1, characterized in that Y in formula II is F. Liquid-crystal medium according to Claim 1 or 2, characterized in that it additionally contains one or more dielectrically positive compounds of the formula IIIB,

wherein each R ³ is independently H, an unsubstituted, an alkyl or alkenyl radical having up to 12 C atoms, which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen, and one or more CH ₂ groups in each of these radicals independently of each other by -O-, -S-,

-CH = CH-, -C≡C-, -CO-, -CO-O-, -O-CO- or -O-CO-O- may be replaced so that O atoms are not directly linked to one another, and L ^{1 is} H or F, contains. Liquid-crystal medium according to one or more of claims 1 to 3, characterized in that it additionally contains one or more compounds selected from the group of compounds of formulas IV-1 to IV-5,

where R ^{4 is} alkyl having 1 to 7 C atoms, alkoxy having 1 to 7 C atoms, or alkoxyalkyl, alkenyl or alkenyloxy having 2 to 7 C atoms, X ¹ F, Cl or a mono- or polyfluorinated 1-4 C is alkyl or alkoxy, Y ^{1 is} H or F, and Z ¹¹ and Z ^{12 are} each independently, -CH ₂ -CH ₂ -, -CH = CH-, -CH ₂ -CF ₂ -, -CF ₂ -CH ₂ -, -CF ₂ -CF ₂ -, -OCH ₂ -, -CH ₂ O- or a single bond, wherein the compounds of formula IV-1b are excluded from claim 1. Liquid-crystal medium according to one or more of claims 1 to 4, characterized in that it contains one or more compounds of formula IV-1 of claim 4, wherein the compounds of formula IV-1b are excluded from claim 1. Liquid-crystal medium according to one or more of claims 1 to 5, characterized in that it contains 10 to 40 wt .-% of one or more compounds of formula I. Liquid-crystal medium according to one or more of claims 1 to 6, characterized in that it contains 1 to 40 wt .-% of one or more compounds selected from the group of compounds of formula II. Liquid-crystal medium according to one or more of claims 1 to 7, characterized in that it has a threshold voltage of at most 0.75 V. Liquid-crystal medium according to one or more of claims 1 to 8, characterized in that it has a clearing point of at least 85 ° C. Use of a liquid-crystal medium according to one or more of claims 1 to 9 in an electro-optical display.