DE4109285A1 - Liq. crystalline medium - contg. fluoro di:fluoro-methoxy benzene cpd. with cyclohexyl-cyclohexyl substit., used in electro=optical display - Google Patents

Abstract

Liquid crystalline (LC) medium based on a mixt. of polar cpds. with positive dielectric anisotropy contains 4-(4-(trans-cyclohexyl) -trans-cyclohexyl)-2-fluoro- or 2,6-difluoro-1-difluoromethoxybenzene cpd(s) of formula (I), where R = 1-7C alk(en)yl, oxaalkyl or fluoroalkyl; L = H or F. (I) and other cpds. used in the medium are either known cpds. or can be prepd. by methods analogous to those used for known cpds. (Int. Patent Application PCT/EO 90 01 471). The medium pref. also contains 4-(trans-cyclohexyl)- or 4-(4-trans-cyclohexyl)-trans -cyclohexyl)-benzene cpd(s). (II), 4-(trans-cyclohexyl-ethyl)- or 4-(4-(trans-cyclohexyl) -trans-cyclohexyl-ethyl)-benzene cpd(s). (III) and/or 4-(4-trans-cyclohexyl-ethyl) -trans-cyclohexyl)-benzene cpd(s). (IV) etc.. In the formulae, X = F, Cl, CF3, OCF3 or OCHF2; Y = H or F; r = 0 or 1. The mixt. contains at least 50 (wt.) of (I)-(IV), pref. 10-50% (I) and 30-70% (II)-(IV). USE/ADVANTAGE - The medium is claimed for use for electrooptical purposes, esp. displays. It is esp. useful in matrix LCDs, TN and STN displays, giving very high specific resistance, low threshold voltage and short switching times. The nematic phase range is unusually wide and the elastic constants very high, whilst the viscosity is also very favourable.

Description

The present invention relates to a liquid crystalline Medium, its use for electro-optical Purposes and advertisements containing this medium.

Liquid crystals are mainly used as dielectrics used in display devices because the optical Properties of such substances by an applied Tension can be influenced. Electro-optical devices are based on liquid crystals well known to the person skilled in the art and can be based on various Effects are based. Such devices are for example cells with dynamic scattering, DAP cells (Deformation of erected phases), guest / host Cells, TN cells with twisted nematic ("twisted nematic ") structure, STN cells (" super-twisted nematic "), SBE cells (" super birefringence effect ") and OMI cells ("optical mode interference"). The Most common display devices are based on the Schadt-Helfrich effect and have a twisted nematic structure.

The liquid crystal materials must have a good chemical and thermal stability and good stability against electric fields and electromagnetic Own radiation. Furthermore, the liquid crystal materials have low viscosity and  short response times in the cells, low threshold voltages and give a high contrast. Furthermore, should it at normal operating temperatures, d. H. in one as wide a range as possible below and above room temperature have a suitable mesophase, for example for the above cells a nematic or cholesterol mesophase. Because liquid crystals in the Usually used as mixtures of several components it is important that the components are together are easy to mix. Other properties like that electrical conductivity, the dielectric anisotropy and the optical anisotropy, depending on the cell type and application area meet different requirements. For example, materials for cells with twisted nematic structure a positive dielectric Anisotropy and low electrical conductivity exhibit.

For example, for matrix liquid crystal displays with integrated non-linear elements for switching individual pixels (MFK displays) media with large positive dielectric anisotropy, broad nematic Phases, relatively low birefringence, very high specific resistance, good UV and temperature stability resistance and low vapor pressure he wishes.

Such matrix liquid crystal displays are known. As non-linear elements for individual switching of the individual pixels can for example be active Elements (i.e. transistors) can be used. Man then speaks of an "active matrix", where two Differentiate types:

• 1. MOS (Metal Oxide Semiconductor) transistors Silicon wafer as a substrate.  
• 2. Thin film transistors (TFT) on a glass plate as a substrate.

The use of single crystal silicon as a substrate material limits the display size, since it is also modular Composition of various partial displays on the Bumps leads to problems.

With the more promising type 2, which is preferred, is usually the TN effect as an electro-optical effect used. There are two technologies: TFT's made of compound semiconductors such. B. CdSe or TFT's based on polycrystalline or amorphous silicon. The latter technology is used worldwide with great intensity worked.

The TFT matrix is on the inside of one glass plate the display applied while the other glass plate carries the transparent counter electrode on the inside. Compared to the size of the pixel electrode is the TFT very small and practically does not disturb the picture. These Technology can also be used for full color images be expanded, with a mosaic of red, green and blue filters is arranged so that each a filter element opposite a switchable picture element lies.

The TFT display usually works as TN cells with crossed polarizers in transmission and are from backlit.

The term MKF displays includes every matrix display with integrated non-linear elements, d. H. next to the active matrix also ads with passive elements like Varistors or diodes (MIM = metal-insulator-metal).  

MLC displays of this type are particularly suitable for TV Application (e.g. pocket TV) or for high information Displays for computer applications (laptop) and in Automobile or aircraft construction. Besides problems regarding the angular dependence of the contrast and the switching times difficulties arise with MLC displays due to insufficiently high specific resistance of liquid crystal mixtures [TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay 84, Sept. 1984: A 210-288 Matrix LCD Controlled by Double Stage Diode Rings, p. 141 ff, Paris; STROMER, M., Proc. Eurodisplay 84, Sept. 1984: Design of Thin Film Transistors for Matrix Addressing of Television Liquid Crystal Displays, p. 145 ff, Paris]. With decreasing resistance the contrast of an MLC display and deteriorates the problem of "after image elimination" can occur. Because the resistivity of the liquid crystal mixture through interaction with the inner surfaces the display generally over the life of an MFK display decreases, a high (initial) resistance is very important in order to obtain acceptable downtimes. In particular With low-voltage mixtures, it was previously not possible to realize very high resistivities. Farther it is important that resistivity is a as little increase as possible with increasing temperature and after exposure to temperature and / or UV. The MFK advertisements from the prior art are not sufficient today's requirements.

There is therefore still a great need for MLC displays with very high specific resistance large working temperature range, short Switching times and lower threshold voltage this Do not show disadvantages or only show them to a lesser extent.  

With TN (Schadt-Helfrich) cells, media are desired enable the following advantages in the cells:

• - extended nematic phase range (in particular too low temperatures)
• - Switchability at extremely low temperatures (out-door use, automotive, avionics)
• - Increased resistance to UV radiation (longer lifetime)

With those available from the state of the art Media is not able to take advantage of these to realize the other parameters at the same time.

With higher twisted cells (STN) media are desirable which is higher multiplexability and / or smaller Threshold voltages and / or broader nematic phase ranges (especially at low temperatures). A further expansion of the is available for this standing parameter space (clearing point, transition smectic-nematic or melting point, viscosity, dielectric Sizes, elastic sizes) urgently desired.

The invention has for its object, media in particular for such MFK, TN or STN displays to provide the above disadvantages not or only to a lesser extent, and preferably at the same time very high resistivities and have low threshold voltages.  

It has now been found that this problem can be solved can, if one according to the invention in advertisements media used.

The invention thus relates to a liquid crystalline Medium based on a mixture of polar Compounds with positive dielectric anisotropy, characterized in that there are one or more connections of the general formula I

contains, wherein R contains alkyl, oxaalkyl, fluoroalkyl or Alkenyl with up to 7 C atoms and L H or F each means.

The invention also relates to electro-optical displays (especially STN or MFK ads with two plane-parallel carrier plates with a border form a cell, integrated non-linear elements for switching individual pixels on the carrier plates and a nematic in the cell Liquid crystal mixture with positive dielectric Anisotropy and high resistivity), such Media included and the use of them Media for electro-optical purposes.

The liquid crystal mixtures according to the invention enable a significant expansion of the available standing parameter space.

The achievable combinations of clearing point, viscosity at low temperature and dielectric anisotropy far surpass previous materials from the State of the art.  

The demand for a high clearing point, nematic phase at -40 ° C and a high Δε has so far been insufficient be fulfilled. Systems such as B. ZLI-3119 have comparable clearing point and comparable favorable viscosities, but have a Δε of only +3.

Other mixing systems have comparable viscosities and values of Δε, however, only have clearing points in the area of 60 ° C.

The liquid crystal mixtures according to the invention enable it at low viscosities at low temperatures (at -30 ° C600, preferably 550 mPa · s; at -40 ° C1800, preferably 1700 mPa · s) simultaneously dielectric anisotropy values Δε5.0, preferably 6.0, clearing points above 75 °, preferably above 80 ° and a high value for the specific resistance to achieve excellent STN and MFK displays can be achieved.

It is understood that by appropriate choice of components the mixtures according to the invention also have higher clearing points (e.g. above 90 °) at higher threshold voltage or lower clearing points at lower threshold voltages while maintaining the other beneficial Properties can be realized. The invention MFK ads preferably work in the first Transmission minimum according to Cooch and Tarry [C. H. Gooch and H.A. Tarry, Electron. Lett. 10, 2-4, 1974; C. H. Gooch and H. A. Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975], wherein here in addition to particularly favorable electro-optical properties such as B. high slope of the characteristic and low Angle dependence of the contrast (DE-PS 30 22 818) same threshold voltage as in an analog display  in the second minimum, a smaller dielectric anisotropy is sufficient. This allows you to use of the mixtures according to the invention in the first minimum realize significantly higher resistivities than with mixtures with cyan compounds. The expert can by appropriate choice of the individual components and whose proportions by weight using simple routine methods required for a given layer thickness of the MLC display Set birefringence.

The media according to the invention also enable short Switching times due to high absolute values of the elastic Sizes.

The viscosity at 20 ° C is preferably ≦ 25 mPa · s. The nematic phase range is preferably at least 70 °, especially at least 80 ° C. Preferably extends this range is at least from -30 ° to + 70 °.

Capacity Holding Ratio (HR) Measurements [p. Matsumoto et al., Liquid Crystals 5, 1320 (1989); K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984); G. Weber et al., Liquid Crystals 5, 1381 (1989)] have shown that mixtures according to the invention Compounds of formula I a significantly smaller decrease of HR with increasing temperature than analog ones Mixtures containing instead of the compounds of Formula I Cyanophenylcyclohexane of the formula

The UV stability of the mixtures according to the invention is much better, d. H. they clearly show one minor decrease in HR under UV exposure.  

The media according to the invention are not only unusual wide nematic phase range also through extraordinarily high elastic constants at very favorable viscosity values, which in particular when used in STN advertisements clearly advantages over State of the art media result.

The media according to the invention are preferably based on several (preferably three or more) compounds of formula I, d. H. the proportion of these connections is 25%, preferably 40%. Already a homologue mix from equal proportions of four connections of formula I, wherein L = H and R ethyl, n-propyl, n-butyl and n-Pentyl means, shows the following parameters:

Melting point: -10 ° C
Clarification point: 135 °
Viscosity at 20 ° C: 32 mPa · s
Δn: 0.090
Δε: +6.7
K1: 17.2 1E-12N (at 21 ° C)
K2: 8.2 1E-12N (at 21 ° C)
K3: 23.2 1E-12N (at 21 ° C)

A homologue mixture consisting of two compounds of the Formula I with L = F (R = n-propyl 34% by weight, R = n-pentyl 66% by weight) shows the following parameters:

Melting point: 27.9 ° C
Clarification point: 129 ° C
Viscosity at 20 ° C: -
Δn: 0.084
Δε: +8.7
K1: 13.4 1E-12N (at 49 ° C)
K2: 6.3 1E-12N (at 49 ° C)
K3: 21.5 1E-12N (at 49 ° C)

The individual compounds of the formulas I to XII and their Sub-formulas used in the media according to the invention are either known or they are can be prepared analogously to the known compounds (International patent application PCT / EP 90 01 471).

Preferred embodiments are given below:

• - Medium additionally contains one or more compounds selected from the group consisting of the general formulas II, III and IV: where the individual radicals have the following meanings:
  R: alkyl, oxaalkyl, fluoroalkyl or alkenyl, each with up to 7 carbon atoms
  X: F, Cl, CF₃, OCF₃ or OCHF₂
  Y: H or F
  r: 0 or 1.
• - Medium additionally contains one or more compounds selected from the group consisting of the general formulas V to VIII: wherein R, X and Y each independently have one of the meanings given in claim 1.
• Medium additionally contains one or more compounds selected from the group consisting of the general formulas IX to XII: wherein R, X and Y each independently have one of the meanings given in claim 1.
• - The proportion of compounds of the formulas I to IV together is at least 50% by weight in the total mixture
• - The proportion of compounds of formula I is in the total mixture 10 to 50% by weight
• - The proportion of compounds of the formulas II to IV in the mixture as a whole is 30 to 70% by weight
• - The medium contains compounds of formula II and III or IV
• - R is straight-chain alkyl or alkenyl with 2 to 7 carbon atoms
• - The medium consists essentially of connections of the formulas I to IV
• - The medium contains further compounds, preferably selected from the following group:
• - The weight ratio I: (II + III + IV) is preferably 1: 4 to 1: 1.
• - Medium essentially consists of connections selected from the group consisting of the general Formulas I to XII.

It has been found that a relatively small proportion of compounds of formula I in a mixture with conventional Liquid crystal materials, but especially with one or more compounds of formula II, III and / or IV to a significant improvement in Response times and low threshold voltages leads, at the same time broad nematic phases with low transition temperatures smectic-nematic to be watched. The compounds of formulas I to IV are colorless, stable and with each other and with others Liquid crystal materials miscible.

The term "alkyl" includes straight chain and branched Alkyl groups with 1-7 carbon atoms, in particular the straight-chain groups methyl, ethyl, propyl, butyl, Pentyl, hexyl and heptyl. Groups with 2-5 carbon atoms are generally preferred.

The term "alkenyl" includes straight-chain and branched Alkenyl groups with 2-7 carbon atoms, in particular the straight chain groups. Especially alkenyl groups are C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl, C₅-C₇-4-alkenyl, C₆-C₇-5-alkenyl and C₇-6-alkenyl, in particular C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-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. Are groups with up to 5 carbon atoms generally preferred.

The term "fluoroalkyl" preferably includes straight chain Groups with terminal fluorine, d. H. Fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorhexyl and 7-fluoroheptyl. Other Positions of the fluorine are not excluded.

The term "oxaalkyl" preferably includes straight-chain radicals of the formula C _n H _{2n + 1} -O- (CH₂) _m , in which n and m each independently represent 1 to 6. Preferably n = 1 and m is 1 to 6.

By a suitable choice of the meanings of R, X and Y can the response times, the threshold voltage, the The steepness of the transmission characteristics etc. in the desired Modified way. For example, lead 1E-alkenyl residues, 3E-alkenyl residues, 2E-alkenyloxy residues and the like usually with shorter response times, improved nematic tendencies and a higher one Ratio of elastic constants k₃₃ (bend) and k₁₁ (splay) compared to alkyl or alkoxy. 4-alkenyl residues, 3-alkenyl residues and the like generally lower threshold voltages and smaller ones Values of k₃₃ / k₁₁ compared to alkyl and alkoxy leftovers. A group -CH₂CH₂- in Z¹ or Z² leads in generally compared to higher values of k₃₃ / k₁₁ to a simple covalent bond. Higher values of k₃₃ / k₁₁ allow z. B. flatter transmission characteristics in TN cells with 90 ° twist (to achieve of gray tones) and steeper transmission characteristics in STN, SBE and OMI cells (higher multiplexability) and vice versa.  

The optimal ratio of the compounds of the Formulas I and II + III + IV largely depend on the desired properties, from the choice of components of formulas I, II, III and / or IV and of choice any other components that may be present. Suitable proportions within the above Area can easily be determined on a case by case basis will.

The total amount of compounds of the formulas I to XII in the mixtures according to the invention are not critical. The Mixtures can therefore contain one or more other components included to optimize various properties. The observed effect on response times and the threshold voltage is usually all the more larger the higher the total concentration of compounds of formulas I to XII.

Contained in a particularly preferred embodiment the media according to the invention compounds of the formula II, III, V and / or VII (preferably II and / or III), wherein preferably X means OCHF₂. A cheap synergistic Effect with the compounds of formula I leads to particularly advantageous properties.

For STN applications, the media preferably contain Compounds selected from the group consisting of Formulas V to VIII, wherein X is preferably OCHF₂.

The media according to the invention can also contain a component A contain one or more compounds with a dielectric anisotropy of -1.5 to +1.5 of the general formula I ′  

wherein
R¹ and R² each independently of one another n-alkyl, n-alkoxy, ω-fluoroalkyl or n-alkenyl with up to 9 C atoms,
the rings A1, A2 and A3 each independently of one another 1,4-phenylene, 2- or 3-fluoro-1,4-phenylene, trans-1,4-cyclohexylene or 1,4-cyclohexenylene,
Z¹ and Z² each independently of one another -CH₂CH₂-, -C≡C-, -CO-O-, -O-CO-, or a single bond,
and
m means 0, 1 or 2.

Component A preferably contains one or more Compounds selected from the group consisting of II1 to II7:

wherein R¹ and R² have the meaning given for formula I ' to have.

Component A preferably additionally contains one or several compounds selected from the group from II8 to II20:

wherein R¹ and R² have the meaning given for formula I ' have and the 1,4-phenylene groups in II8 to II17 each independently of one another also by fluorine one or more times can be substituted.

Component A also preferably contains one or several connections selected from the group consisting of II21 to II25 contains:

wherein R¹ and R² have the meaning given for formula I ' have and the 1,4-phenylene groups in II21 to II25 each independently of one another also by fluorine one or more times can be substituted.

Finally, such mixtures are preferred, the Component A selected one or more compounds from the group consisting of II26 and II27 contains:

wherein C _r H _{2r + 1 is} a straight-chain alkyl group with up to 7 C atoms.

In some cases the addition of compounds proves to be of the formula

wherein
R¹ and R² have the meaning given for formula I '
and
Z⁰ a single bond, -CH₂CH₂-,

means
to suppress smectic phases as advantageous, although this can lower the specific resistance. In order to achieve optimal combinations of parameters for the application, the person skilled in the art can easily determine whether and in what amount these compounds can be added. Usually less than 15%, especially 5-10% is used.

Also preferred are liquid crystal mixtures which one or more connections selected from the Group consisting of III ′ and IV ′ contain:

wherein R₁ and R² have the meaning given in formula I ' to have.  

The type and amount of polar compounds with positive dielectric anisotropy is not critical in itself. The person skilled in the art can be known from a wide range and in many cases also commercially available components and basic mixtures in simple routine tests select suitable materials. Preferably included the media according to the invention one or more compounds of the formula II ′ ′

wherein Z₁, Z₂ and m have the meaning given in formula I ', Q¹ and Q² each independently of the other 1,4-phenylene, trans-1,4-cyclohexylene or 3-fluoro-1,4-phenylene or one of the radicals Q¹ and Q² also means trans-1,3-dioxane-2,5-diyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,4-cyclohexenylene,
R⁰ is n-alkyl, n-alkenyl, n-alkoxy or n-oxaalkyl, each having up to 9 carbon atoms, YH or F and X 'CN, halogen, CF₃, OCF₃ or OCHF₂.

In a preferred embodiment, the inventive ones are based Media for STN or TN applications Compounds of formula I '' wherein X 'is CN. It it goes without saying that smaller or larger proportions of other compounds of the formula I ′ ′ (X ′ ≠ CN) in Question come. For MFK applications contain the invention Media preferably only up to approx. 10% on nitriles of the formula I '' (but preferably none  Nitriles of the formula I ′ ′, but compounds of the formula I ′ with X ′ = halogen, CF₃, OCF₃ or OCHF₂). This media are preferably based on the compounds of the formulas II to XII.

The structure of the STN or MFK display according to the invention from polarizers, electrode base plates and electrodes with surface treatment corresponds to that for such View common design. The term is the usual construction here broadly and includes all Variations and modifications of the MFK display, in particular also matrix display elements based on poly-Si, TFT or MIM.

A major difference between the advertisements according to the invention to the previously common on the basis of the twisted However, the nematic cell consists in the choice of the liquid crystal parameters the liquid crystal layer.

The preparation of the liquid crystal mixtures which can be used according to the invention takes place in a conventional manner. In Usually the amount you want is in less Quantity of components used in the main ingredient constituent components solved, expedient at elevated Temperature. It is also possible to find solutions of the components in an organic solvent, e.g. B. in acetone, chloroform or methanol to mix and the solvent after To remove mixing again, for example by Distillation.

The dielectrics can also be further known to those skilled in the art and contain additives described in the literature. For example, 0-15% pleochroic dyes or chiral dopants can be added.  

C means a crystalline, S a smectic, S _B a smectic B, N a nematic and I the isotropic phase.

V₁₀ denotes the voltage for 10% transmission (viewing direction perpendicular to the plate surface). t _on denotes the switch-on time and t _off the switch-off time at an operating voltage corresponding to 2.5 times the value of V₁₀ · Δn denotes the optical anisotropy and n _o the refractive index. Δε denotes the dielectric anisotropy (Δε = ε _{| |} -ε _┴ , where ε _{| | means} the dielectric constant parallel to the longitudinal axes of the molecule and ε _┴ the dielectric constant perpendicular to it. The electro-optical data were recorded in a TN cell in the 1st minimum (ie at ad · Δn value of 0.5) measured at 20 ° C. unless expressly stated otherwise, the optical data were measured at 20 ° C. unless expressly stated otherwise.

The following examples are intended to illustrate the invention, without limiting it. Before and after are all Temperatures given in ° C. The percentages are Weight percent.

In the present application and in the following examples, the structures of the liquid crystal compounds are indicated by acronyms, the transformation into chemical formulas taking place according to Tables A and B below. All residues C _n H _{2n + 1} are straight-chain alkyl residues 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, a code for the substituents R¹, R², L¹ and L² follows separately from the acronym for the base body:

example 1
PCH-3 18.0
PCH-5F 12.0
PCH-6F 12.0
PCH-7F 10.0
CCP-20CF2.F 3.5
CCP-30CF2.F 3.5
CCP-40CF2.F 3.5
CCP-50CF2.F 3.5
ECCP-33 5.0
CBC-33 5.0
CBC-53 5.0
CBC-55 4.0
CBC-33F 5.0
CBC-53F 5.0
CBC-55F 5.0

Clear point 92 ° C
Viscosity at 20 ° C: 19 mPa · s
Δε: 5.8
Δn: 0.1045

Example 2
CCP-20CF2.F 20.0
CCP-30CF2.F 18.0
CCP-40CF2.F 18.0
CCP-50CF2.F 18.0
EPCH-30CF2 7.0
EPCH-50CF2 7.0
PCH-50CF2 12.0

Clear point 83 ° C
Viscosity at 20 ° C: 20 mPa · s
Δn: 0.0827
Δε: 6.2
V _10/0/20 : 1.80 volts
Viscosity at
-30 ° C: 540 mPas
-40 ° C: 1610 mPas

Example 3
CCP-20CF2.F 15.0
CCP-30CF2.F 15.0
CCP-40CF2.F 15.0
CCP-50CF2.F 15.0
CCP-50CF2 13.0
EPCH-20CF2 9.0
EPCH-30CF2 5.0
EPCH-50CF2 5.0
EPCH-70CF2 2.0
PCH-50CF2 6.0

Clear point 83 ° C
Δn: 0.0818

Example 4
CCP-20CF2.F 17.0
CCP-40CF2.F 17.0
CCP-50CF2.F 17.0
CCP-50CF2 11.0
EPCH-30CF2 6.0
EPCH-50CF2 6.0
PCH-50CF2 6.0
B-30CF2 8.0
BCH-30CF2 12.0

Clear point 87 ° C
Viscosity at 20 ° C: 19 mPa · s
Δn: 0.0985
Δε: 6.3

Claims (10)

1. Liquid-crystalline medium based on a mixture of polar compounds with positive dielectric anisotropy, characterized in that it contains one or more compounds of the general formula I. contains, wherein R is alkyl, oxaalkyl, fluoroalkyl or alkenyl each having up to 7 carbon atoms and LH or F. 2. Medium according to claim 1, characterized in that it additionally contains one or more compounds selected from the group consisting of the general formulas II, III and IV: where the individual radicals have the following meanings: R: alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 7 carbon atoms
X: F, Cl, CF₃, OCF₃ or OCHF₂
Y: H or F
r: 0 or 1. 3. Medium according to claim 1 or 2, characterized in that it additionally contains one or more compounds selected from the group consisting of the general formulas V to VIII: wherein R, r, X and Y each independently have one of the meanings given in claim 2. 4. Medium according to at least one of claims 1 to 3, characterized in that it additionally contains one or more compounds selected from the group consisting of the general formulas IX to XII: wherein R, X and Y each independently have one of the meanings given in claim 2. 5. Medium according to claim 2, characterized in that the proportion of compounds of the formulas I to IV together in the total mixture at least 50% by weight is. 6. Medium according to claim 1 or 2, characterized in that the proportion of compounds of formula I in the total mixture is 10 to 50% by weight.   7. Medium according to at least one of claims 2 to 4, characterized in that the proportion of compounds of the formulas II to IV in the total mixture 30 is up to 70% by weight. 8. Medium according to at least one of claims 1 to 4, characterized in that it consists essentially of Connections selected from the group consists of the general formulas I to XII. 9. Use of the liquid crystalline medium after Claim 1 for electro-optical purposes. 10. Containing electro-optic liquid crystal display a liquid-crystalline medium according to claim 1.