DE4101468A1 - LCD medium contg. dioxanyl, pyrimidinyl or pyridyl benzene cpd. - with substit. contg. fluorine and/or chloride for LCD with low threshold voltage - Google Patents

Abstract

Liquid crystal medium based on a mixt. of middle polar cpds. contains 1-fluoro-, 1-chloro-, 1-trifluoro-methyl-, 1-difluoromethoxy, 1-difluoromethoxy- or 1-trifluoromethoxy-4(5'-alkyl-, 5'-oxaalkyl, 5'-fluoro-alkyl- or 5'-alkenyl-1',3'-dioxan-, pyrimidin- or pyrid-2'-yl)-benzene cpd(s). and/or their 2-fluoro deriv(s). of formula (I): R = alkyl, oxaalkyl, fluoroalkyl or alkenyl with up to 7C; A = a gp. of the formula (a), (b) or (c); X = F, Cl, CF3, OCHF2, OCF2Cl or OCF3; Y = H or F. USE/ADVANTAGE - The medium is used for electrooptical purposes and displays. It is esp. useful for matrix LCDs and combines very high specific resistance with low threshold voltage. It also has much better UV stability than usual, i.e., the redn. in the capacity holding ration when exposed to UV light is much smaller than usual.

Description

The present invention relates to a liquid crystalline Medium, its use for electro-optical purposes and this Media-containing ads.

Liquid crystals are mainly used as dielectrics in display devices used because the optical properties of such Substances are affected by an applied voltage can. Electro-optical devices based on Liquid crystals are well known to those skilled in the art and can based on different effects. Such devices For example, cells with dynamic scattering are DAP cells (Deformation of upright phases), guest / host cells, TN cells with twisted nematic ("twisted nematic") Structure, super-twisted nematic (STN) cells, 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 one twisted nematic structure.

The liquid crystal materials need a good chemical and thermal stability and good stability over electric fields and electromagnetic radiation have. Furthermore, the liquid crystal materials should  have low viscosity and short response times in the cells, low threshold voltages and high contrast result. Furthermore, they should at normal operating temperatures, d. H. in as wide a range as possible below and have a suitable mesophase above room temperature, For example, for the above cells a nematic or cholesteric mesophase. Because liquid crystals usually is used as mixtures of several components, is It is important that the components mix well with each other are. Other properties, such as electrical conductivity, the dielectric anisotropy and the optical anisotropy, have different depending on cell type and application Requirements met. For example, materials should be for Cells with twisted nematic structure have a positive dielectric Anisotropy and low electrical conductivity respectively.

For example, are 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, relative low birefringence, very high resistivity, good UV and temperature stability of the resistor and low Steam pressure desired.

Matrix liquid crystal displays according to the preamble are known. As non-linear elements for individual switching The individual pixels can, for example, active elements (i.e., transistors). One speaks then of an "active matrix", distinguishing two types can:

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

Another categorization is:

• (a) two-terminal devices (diode ring)
• (b) three-terminal devices (TFT)

The use of monocrystalline silicon as a substrate material Restricts the display size, as well as the modular Composition of various sub-displays at the joints too Problems leads.

In the more promising type 2, which is preferred is as electro-optical effect usually used the TN effect. There are two technologies: TFTs made of compound semiconductors such as CdSe or TFTs based on polycrystalline or amorphous silicon. At the latter technology is being worked on worldwide with great intensity.

The TFT matrix is on the inside of a glass plate of the Display applied while the other glass plate on the Inside carries the transparent counter electrode. Compared to the size of the pixel electrode, the TFT is very small and practically does not disturb the picture. This technology can also be used for fully color-suitable image representations are extended, wherein a mosaic of red, green and blue filters arranged in such a way is that ever a filter element a switchable pixel is opposite.

The TFT displays usually work as TN cells crossed polarizers in transmission and are from behind illuminated.  

The term MFK displays here includes every matrix display integrated nonlinear elements, d. H. next to the active one Matrix also displays with passive elements like varistors or Diodes (MIM = metal-insulator-metal).

Such MFK displays are particularly suitable for TV applications (eg pocket TV) or for high-information displays for computer applications (laptop) and in the automotive or Aircraft construction. In addition to problems with the angle dependence the contrast and the switching times result in MFK ads difficulties caused by insufficient high resistivity of the 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. 141ff, Paris; STROMER, M., Proc. Eurodisplay 84, Sept. 1984: Design of Thin Film Transistor for Matrix Addressing of Television Liquid Crystal Display, p. 145ff, Paris]. With decreasing resistance the contrast of a MFK display deteriorates and it can the problem of "after image elimination" occur. Since the specific resistance of the liquid crystal mixture Interaction with the inside surfaces of the display in the general over the lifetime of an MFK ad is decreasing a high (initial) resistance is very important to acceptable To obtain service life. Especially with low-volt mixtures (Threshold voltage V₁₀ 1.5 volts, clearing point 65 ° C) it was previously not possible, very high specific resistances too realize. Furthermore, it is important that the specific Resistance the smallest possible increase with increasing  Temperature and after temperature and / or UV exposure shows. The MFK displays of the prior art do not meet the today's requirements.

There is thus still a great need for MFK ads with very high resistivity and large at the same time Working temperature range, short switching times and lower Threshold voltage, these disadvantages are not or only in show a lesser degree.

The invention is based on the object media in particular for such MFK displays, the above specified disadvantages or only to a lesser extent, at the same time very high specific resistances and low Have threshold voltages.

It has now been found that this problem can be solved if one uses media according to the invention in these MFK displays.

The invention thus relates to a liquid-crystalline Medium based on a mixture of medium polar compounds, characterized in that it is one or more Compounds of the general formula I

in which the individual radicals have the following meanings to have:

R is alkyl, oxaalkyl, fluoroalkyl or alkenyl with each represents up to 7 carbon atoms,

XF, Cl, CF₃, OCHF₂, OCF₂Cl or OCF₃,
YH or F.

The invention also provides electro-optical displays (especially STN or MFK displays with two plane-parallel Support plates that form a cell with a border, integrated non-linear elements for switching individual Pixels on the carrier plates and one located in the cell nematic liquid crystal mixture with positive dielectric anisotropy and high resistivity), containing such media and the use of these Media for electro-optical purposes.

The liquid-crystal mixtures according to the invention make it possible, at low viscosities, simultaneously to achieve threshold voltages preferably 1.65 volts, clearing point above 60 °, preferably above 65 ° and / or a high value for the resistivity, whereby excellent MKF displays can be achieved. It is understood that by suitable choice of the components of the mixtures according to the invention also higher clearing points (eg above 90 °) can be realized at higher threshold voltage (V _th <2.2 volts) to obtain the other advantageous properties. The MFK displays according to the invention preferably operate in the first transmission minimum according to Gooch and Tarry [CH Gooch and HA Tarry, Electron. Lett. 10, 2-4, 1974; CH Gooch and HA Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975], which in addition to particularly favorable electro-optical properties such. B. high steepness of the characteristic and low angle dependence of the contrast (DE-PS 30 22 818) at the same threshold voltage as in an analog display in the second minimum a smaller dielectric anisotropy is sufficient. As a result, significantly higher specific resistances can be achieved using the mixtures according to the invention in the first minimum. By suitable choice of the individual components and their proportions by weight, the person skilled in the art can set the birefringence required for a given layer thickness of the MFK display with simple routine methods.

Measurements of the capacity holding ration (HR) [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 Compounds of the formula I containing mixtures according to the invention a much smaller decrease in HR with rising Have temperature as analogous mixtures containing instead the compounds of formula I cyanophenylcyclohexanes of the formula

The UV stability of the mixtures according to the invention is also considerably better, d. H. they show a much smaller one Decrease in HR under UV exposure.  

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

The individual compounds of the formula I to XII and their Sub-formulas used in the MFK displays according to the invention are either known, or they can be prepared analogously to the known compounds.

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: wherein R, X and Y each independently have one of the meaning given in claim 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 meaning given in claim 1.
• - Medium additionally contains one or more compounds selected from the group consisting of the general formula IX to XII: wherein R, X and Y each independently have one of the meaning given in claim 1.
• - The proportion of compounds of 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 formulas II to IV in Total mixture is 40 to 90 wt .-% (preferably 50-70 wt .-%],
• Y in formula I is H,
• -
• X is OCF₃, CF₃, F or Cl,
• X is OCF₂H,
• - The medium contains compounds of formulas II and III or IV,
• R is straight-chain alkyl or alkenyl with 2 to 7 C atoms,
• - The medium consists essentially of compounds 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 preferred 1: 4 to 1: 1.
• - Medium consists essentially of compounds selected from the group consisting of the general Formulas I to XII.
• - Medium contains one or more compounds of formula I1, I2, I3 and / or I4: wherein R has the meaning given, Q is CH or N, ZF, Cl or H and Y is H or F.

It was found that already a relatively small proportion of Compounds of the formula I in admixture with one or more Compounds of formula II, III and / or IV to a considerable Improvement of response times and low threshold voltages leads, while at the same time broad nematic Phases with low transition temperatures smectic-nematic to be observed. The compounds of formulas I to IV are colorless, stable and with each other and with other liquid crystal materials good mix.

The term "alkyl" includes straight-chain and branched alkyl groups with 1-7 carbon atoms, in particular the straight-chain ones Groups methyl, ethyl, propyl, butyl, pentyl, hexyl and Heptyl. Groups of 2-5 carbon atoms are in general prefers.  

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

The term "fluoroalkyl" preferably includes straight chain Fluorine-terminated groups, d. H. Fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. However, other positions of the fluorine are not locked out.

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

By a suitable choice of the meanings of R, X and Y, the Response times, the threshold voltage, the transconductance of the Transmission characteristics etc. modified in the desired manner become. For example, 1E-alkenyl radicals, 3E-alkenyl radicals, 2E alkenyloxy radicals and the like tend to be shorter Response times, improved nematic tendencies and a  higher ratio of the elastic constant k₃₃ (bend) and k₁₁ (splay) compared to alkyl or alkoxy radicals. 4-alkenyl radicals, 3-alkenyl radicals and the like generally result lower threshold voltages and smaller values of k₃₃ / k₁₁ in Comparison to alkyl and alkoxy radicals. A group -CH₂CH₂- in Z¹ or Z 2 generally leads to higher values of k₃₃ / k₁₁ in Comparison to a simple covalent bond. Higher values of k₃₃ / k₁₁ allow z. B. flatter transmission characteristics in TN cells with 90 ° twist (to achieve shades of gray) and steeper transmission characteristics in STN, SBE and OMI cells (higher multiplexability) and vice versa.

The optimum ratio of the compounds of the formulas I and II + III + IV largely depends on the desired properties, on the choice of the components of the formulas I, II, III and / or IV and the choice of any other existing ones Components off. Suitable proportions within the The range given above can be easy from case to case be determined.

The total amount of compounds of formulas I to XII in the mixtures according to the invention is not critical. The mixtures may therefore contain one or more other components for the purpose of optimizing various properties. He watched Effect on the response times and the threshold voltage is however, usually the larger the higher the total concentration to compounds of formulas I to XII.  

The mixtures according to the invention preferably contain one or more compounds of the formula Ia. The total amount Compounds of the formula Ia in a mixture is preferably at least 10% by weight, more preferably at least 15% by weight.

(X is preferably F or Cl, in particular F).

The mixtures according to the invention preferably contain one or several compounds of formula Ib or Ic. The total amount Compounds of the formula Ib in the mixture is preferably at least 10% by weight, more preferably at least 15% by weight.

The mixtures according to the invention preferably contain one or several compounds of the formula Id or Ie. The total amount Compounds of the formula Ie in a mixture is preferably at least 10% by weight, more preferably at least 15% by weight. Ie is particularly preferred.

The mixtures according to the invention preferably contain one or several compounds of formula If or Ig. The total amount Compounds of the formula Ig in the mixture is preferably at least 10% by weight, more preferably at least 15% by weight. Ig is particularly preferred.

The media according to the invention may further comprise 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 are each independently of one another n-alkyl, ω-fluoroalkyl or n-alkyl having up to 9 C atoms,
the rings A¹, A² and A³ are 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 are each independently -CH₂CH₂- or a single bond, and
m is 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 in formula I '.  

Preferably, component A additionally contains one or more Compounds selected from the group consisting of II8 bis II20:

wherein R¹ and R² have the meaning given in formula I 'and the 1,4-phenylene groups in II8 to II17 each independently also substituted by fluorine mono- or polysubstituted could be.

Furthermore, component A preferably additionally contains one or several compounds selected from the group consisting of II21 to II25 contains:

wherein R¹ and R² have the meaning given in formula I 'and the 1,4-phenylene groups in II21 to II25 are each independently also substituted by fluorine mono- or polysubstituted could be.

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

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

In some cases, the addition of compounds of the formula

wherein

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

means
for the suppression of smectic phases as advantageous, although thereby the resistivity can be lowered. In order to obtain optimum parameter combinations for the application, the person skilled in the art can easily determine whether and, if so, in what quantity these compounds can be added. Normally, less than 15%, especially 5-10% are used.

Further preferred are liquid-crystal mixtures containing one or more several compounds selected from the group consisting of III 'and IV' contain:  

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

The structure of the MFK display of polarizers according to the invention, Electrode base plates and electrodes with surface treatment corresponds to the usual for such displays construction. there the term of the usual construction is here broadly conceived and includes all modifications and modifications of the MFK display, in particular also matrix display elements based poly-Si TFT or MIM.

A significant difference of the displays according to the invention the usual on the basis of twisted nematic Cell, however, is the choice of 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 the Usually, the desired amount is used in lesser quantity Components in the main component making up Components dissolved, expedient at elevated temperature. It is also possible solutions of the components in an organic Solvent, for. In acetone, chloroform or methanol mix and the solvent after mixing again remove, for example by distillation.  

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

C is a crystalline, S is a smectic, S _{B is} a smectic B, N is a nematic and I is the isotropic phase. V₁₀ denotes the voltage for 10% transmission (viewing direction perpendicular to the disk 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 n₀ the refractive index. Δε denotes the dielectric anisotropy (Δε = ε _|| -ε _┴ ), where ε _|| the dielectric constant is parallel to the _longitudinal molecular _axes and ε _{┴ is} the dielectric constant perpendicular thereto. The electro-optical data were measured in a TN cell in the 1st minimum (ie at a d · Δn value of 0.5) 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 to limit them. Above and below are all temperatures in ° C indicated. The percentages are by weight.  

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 the 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 green body is given. In the individual case, a code for the substituents R 1, R 2, L 1 and L 2 follows separately from the acronym for the main body with a dash:

The liquid-crystalline media according to the invention contain preferably in addition to one or more inventive Compounds as further constituents 2 to 40, in particular 4 up to 30 components. Most preferably, these contain Media in addition to one or more compounds of the invention 7 to 25 components. These other ingredients will be preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the classes of biphenyls, terphenyls, phenylcyclohexanes, Cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, Cyclohexylcyclohexenes, cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4'-biscyclohexylbiphenyls, Phenyl or cyclohexylpyrimidines, phenyl or cyclohexylpyridines, Phenyl or cyclohexyl dioxanes, phenyl or cyclohexyl-1,3-dithiane, 1,2-dicyclohexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4-phenyl-cyclohexyl) ethanes, 1-Cyclohexyl-2-biphenylylethane, 1-phenyl-2-cyclohexylphenylethanes and tolans. The 1,4-phenylene groups in these compounds can also be fluorinated.

The most important as further constituents according to the invention Media eligible connections can be through the Formulas 1, 2 and 3 characterize:

R'-L-E-R '' (1)

R'-L-CH₂CH₂-E-R '' (2)

R'-L-C≡C-E-R '' (3)

In formulas 1, 2 and 3, L and E are the same or may be different, each one independently bivalent radical from the group consisting of -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc, -Pyr-, -Dio, -G-Phe- and -G-Cyc- and their  Mirror images formed group, with Phe unsubstituted or fluorine-substituted 1,4-phenylene, Cyc trans-1,4-cyclohexylene or 1,4-cyclohexenylene, Pyr pyrimidine-2,5-diyl or Pyridine-2,5-diyl, dio-1,3-dioxane-2,5-diyl and G 2- (trans-1,4-cyclohexyl) -ethyl, Pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.

Preferably one of the radicals L and E is Cyc, Phe or Pyr. e is preferably Cyc, Phe or Phe-Cyc. Preferably included the media of the invention one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, wherein L and E are selected from the group Cyc, Phe and Pyr and at the same time one or more components selected from the compounds of formulas 1, 2, 3, 4 and 5, wherein one of the Radicals L and E are selected from the group Cyc, Phe and Pyr and the other radical is selected from the group -Phe-Phe-, -Phe-Cyc, -Cyc-Cyc, -G-Phe and -G-Cyc-, and optionally one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, wherein the radicals L and E are selected are from the group -Phe-Cyc, -Cyc-Cyc, -G-Phe- and G-Cyc.

R 'and R "in the compounds of sub-formulas 1a, 2a and 3a are each independently alkyl, alkenyl, alkoxy, Alkenyloxy or alkanoyloxy of up to 8 carbon atoms. at most of these compounds are R 'and R' 'from each other different, one of these radicals usually alkyl or alkenyl is. In the compounds of sub-formulas 1b, 2b and 3b R "OCF₃, -CF₃, OCHF₂, F, Cl or -NCS; R has the case with the Compounds of sub-formulas 1a to 3a indicated meaning and  is preferably alkyl or alkenyl. But other variants the proposed substituents in the compounds of the formulas 1, 2 and 3 are common. Many such substances or also mixtures of these are commercially available. All these Substances are according to literature methods or in Analogously available.

The media according to the invention can be used in addition to components from the Group of compounds 1a, 2a and 3a (group 1) also components from the group of compounds 1b, 2b and 3b (group 2) whose proportions are preferably as follows:

Group 1: 20 to 90%, in particular 30 to 90%,
Group 2: 10 to 80%, in particular 10 to 50%,

wherein the sum of the proportions of the compounds of the invention and the compounds from groups 1 and 2 up to 100% result. Particular preference is given to media which are in addition to the invention Connections contain only components from group 2.

The media according to the invention preferably contain 1 to 40%, in particular preferably 5 to 30% of inventive Links. Further preferred are media containing more as 40%, in particular 45 to 90% of compounds of the invention. The media preferably contains three, four or five compounds of the invention.

The structure of the MFK display of polarizers according to the invention, Electrode base plates and electrodes with surface treatment corresponds to the usual for such displays construction. there  the term of the usual construction is here broadly conceived and includes all modifications and modifications of the MFK display, in particular also matrix display elements based poly-Si TFT or MIM.

A significant difference of the displays according to the invention the usual on the basis of twisted nematic Cell, however, is the choice of liquid crystal parameters the liquid crystal layer.

The preparation of the invention used Liquid-crystal mixtures are carried out in a conventional manner. In Usually, the desired amount will be in lesser quantity used components in the constituting the main component Components dissolved, expedient at elevated temperature. It is also possible solutions of the components in an organic Solvent, for. In acetone, chloroform or methanol mix and the solvent after mixing again remove, for example by distillation.

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

C is a crystalline, S is a smectic, S _{B is} a smectic B, N is a nematic and I is the isotropic phase. T _c is the clearing point NI in ° C. η is the flow viscosity in mPa · s. V₁₀ denotes the voltage for 10% transmission (viewing direction perpendicular to the disk 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 (589 nm, 20 ° C) and n₀ the refractive index. Δε denotes the dielectric anisotropy (Δε = ε _|| -ε _┴ ), where ε _|| the dielectric constant is parallel to the _longitudinal molecular _axes and ε _{┴ is} the dielectric constant perpendicular thereto. The electro-optical data were measured in a TN cell with a plate spacing of 6 microns at 20 ° C, unless expressly stated otherwise. The optical data were measured at 20 ° C unless expressly stated otherwise. V _th is the threshold voltage V _(10,0,20) in volts.

The following examples are intended to illustrate the invention, without to limit them. Above and below are all temperatures in ° C indicated. The percentages are by weight.

example 1 PDX-3F | 15% PDX-5F 13% PYP-5F 13% CCP 2OCF₃ 8th% CCP 3OCF₃ 13% CCP 4OCF₃ 5% CCP 5OCF₃ 12% ECCP-3F · F 13% ECCP 3OCF₃ 8th%

Example 2 PDX-3-CI | 10% PDX-3F · F 11% PCH-5F 14% CCP 2OCF₃ 11% CCP 3OCF₃ 14% CCP 4OCF₃ 7% CCP 5OCF₃ 12% ECCP-3F · F 13% ECCP 3OCF₃ 8th%

Example 3

Example 4

Example 5

Example 6

Example 7

Example 8

Example 9

Example 10 PYP-2F | 15% PYP-3F 13% PYP-56F 13% CCP 2OCF₃ 8th% CCP 3OCF₃ 13% CCP 4OCF₃ 5% CCP 5OCF₃ 12% ECCP-3F · F 13% ECCP 3OCF₃ 8th%

Example 11 PYP-2F | 10% PYP-3F 11% PYP-56F 14% CCP 2OCF₃ 11% CCP 3OCF₃ 14% CCP 4OCF₃ 7% CCP 5OCF₃ 12% ECCP-3F · F 13% ECCP 3OCF₃ 8th%

Example 12 PYP 3OCF₃ | 15% PYP 5OCF₃ 13% PYRP-3OCF₃ 13% CCP 2OCF₃ 8th% CCP 3OCF₃ 13% CCP 4OCF₃ 5% CCP 5OCF₃ 12% ECCP-3F · F 13% ECCP 3OCF₃ 8th%

Example 13 PYRP-3OCF₃ | 10% PYRP-5OCF₃ 11% PCH-5F 14% CCP 2OCF₃ 11% CCP 3OCF₃ 14% CCP 4OCF₃ 7% CCP 5OCF₃ 12% ECCP-3F · F 13% ECCP 3OCF₃ 8th%

Example 14 PYRP-3OCF₃ | 15% PYRP-3F 13% PYRP-5F · F 13% CCP 2OCF₃ 8th% CCP 3OCF₃ 13% CCP 4OCF₃ 5% CCP 5OCF₃ 12% ECCP-3F · F 13% ECCP 3OCF₃ 8th%

Example 15 PYP 5CF₃ | 10% PYRP-5CF₃ 11% PCH-5F 14% CCP 2OCF₃ 11% CCP 3OCF₃ 14% CCP 4OCF₃ 7% CCP 5OCF₃ 12% ECCP-3F · F 13% ECCP 3OCF₃ 8th%

Example 16 PYRP-5CF₃ | 15% PCH-5F 13% PYRP-5F · F 13% CCP 2OCF₃ 8th% CCP 3OCF₃ 13% CCP 4OCF₃ 5% CCP 5OCF₃ 12% ECCP-3F · F 13% ECCP 3OCF₃ 8th%

Example 17

Example 18

Example 19

Example 20

Example 21

Example 22

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Example 26

Example 27

Example 28

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Example 30

Example 31

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Example 37

Example 38

Example 39

Example 40

Example 41

Example 42

Example 43

Example 44

Example 45

Example 46

example 47

A base mixture M₀ consists of

ECCP 3 Cl | 23% ECCP 5Cl 33% ECCP-5Cl · F 24% PCH-6F 20%

The mixtures according to the invention M₁, M₂ and M₃ are each from 90% M₀ and 10% PDX-3Cl (M₁), 10% PYRP-1Cl (M₂) or 10% PYP-3Cl (M₃). Physical parameters of these mixtures are in the following table.

Example 48

Example 49

Claims (8)

1. Liquid-crystalline medium based on a mixture of medium-polar compounds, characterized in that it contains one or more compounds of general formula I. in which the individual radicals have the following meanings:
R is alkyl, oxaalkyl, fluoroalkyl or alkenyl having in each case up to 7 C atoms, XF, Cl, CF₃, OCHF₃, OCF₂Cl or OCF₃,
YH 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, wherein R, X and Y each independently have one of the meaning given in claim 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 and VIII: wherein R, X and Y each independently have one of the meaning given in claim 1. 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 formula IX to XII: wherein R, X and Y each independently have one of the meaning given in claim 1. 5. Medium according to claim 2, characterized in that the Proportion of compounds of the formulas I to IV together in Total mixture is at least 50 wt .-%. 6. Medium according to claim 1 or 2, characterized that the proportion of compounds of formula I in the total mixture 10 to 50 wt .-% is. 7. Medium according to at least one of claims 2 to 4, characterized in that the proportion of compounds of formulas II to IV in the total mixture 40 to 90 wt .-% is. 8. Medium according to at least one of claims 1 to 4, characterized in that it consists essentially of Compounds selected from the group consisting of consists of the general formulas I to XII.