TWI546368B - Liquid crystalline medium and liquid crystal display - Google Patents

Description

Liquid crystal medium and liquid crystal display

This invention relates to liquid crystal media and liquid crystal displays including such media, and more particularly to displays that are addressed by time series multiplexing and, in particular, to super twisted nematic (STN) displays.

Liquid crystal displays (LCDs) are widely used to display information. Use of electro-optical modes such as: twisted nematic (TN)-, super twisted nematic (STN)-, optically compensated bend (OCB)- and electronically controlled birefringence (ECB)-modes, as well as various modifications thereof, and other modes . Except for these modes, all use an electric field that is substantially perpendicular to the substrate, correspondingly perpendicular to the liquid crystal layer, and an electro-optic mode that uses an electric field that is substantially parallel to the substrate and correspondingly parallel to the liquid crystal layer, such as For example, an in-plane switching mode (as disclosed in German Patent No. 40 00 451 and European Patent No. 0 588 568). This electro-optic mode is especially useful for LCDs of modern desktop monitors and is envisioned for use in multimedia application displays.

TN- and STN displays are widely used in, for example, cellular phones and games. In addition to low production costs, some of the greatest advantages of these displays are their relatively low demand for operating voltages and their lower power consumption. The liquid crystal of the present invention is preferably used in such displays.

For such displays, there is a need for novel liquid crystal media with improved performance. In particular, the dielectric anisotropy (Δε) should be high enough to allow a suitably low operating voltage. Preferably, Δε should be above 30 and preferably above 45, but preferably not above 80, and especially not above 70. Otherwise, the resistivity of the mixture is easily low to the extent that it is unacceptable for most STN displays, STN display In this respect, the device has less stringent requirements than displays (AM LCD or AMD) that are addressed by the matrix of electrically actuated components. In addition to this parameter, the medium must exhibit a birefringence (Δn) suitable for a wide range of nematic phases, a suitable range for the electro-optic effect used, a relatively small rotational viscosity, and at least a sufficiently high ratio as mentioned above. resistance.

The display of the present invention is preferably addressed by time-multiplexed multiplex, such as by orthogonal waveforms as proposed by Alt and Pleshko, and by so-called active addressing, particularly for fast switching displays. However, the liquid crystal of the present invention can also be advantageously used in displays that utilize other known addressing methods.

There are various display modes for various composite systems using low molecular weight liquid crystal materials together with polymeric materials, such as polymer dispersed liquid crystal (PDLC)-, nematically curved alignment phase (NCAP)- and polymer network (PN)-systems (eg (for example) as disclosed in WO 91/05 029 or an axisymmetric microdomain (ASM) system and others. In contrast to these, the preferred mode according to the invention uses a liquid crystal medium so oriented on the surface. The surfaces are typically pretreated to achieve a uniform alignment of the liquid crystal material. The display mode of the present invention preferably uses an electric field that is substantially parallel to the composite layer.

LCDs are used for direct view displays and projection displays.

Liquid crystal compositions suitable for use in LCDs, and in particular STN displays, are known from U.S. Patent No. 6,730,372. However, these compositions have significant disadvantages. Most of these, in addition to various defects, also have too low resistivity values and/or require excessive operating voltages. These majority can also result in unfavorably long response times.

Therefore, there is an urgent need to have practical application depending on the display mode used. Liquid crystalline media of the nature, such as a wide nematic phase range, low viscosity, suitable optical anisotropy Δn, and especially high Δε.

Surprisingly, it has now been found that liquid crystal media having suitably high Δε, suitable phase ranges, and Δn can be achieved without exhibiting defects of the prior art materials or exhibiting such defects at least to a significantly lesser extent.

According to the present application, the modified liquid crystal medium comprises at least the following components: a first positive dielectric component, component A, comprising one or more compounds of formula I and one or more selected from the group consisting of formulas II and III. Group of compounds Wherein R ¹ , R ² and R ³ are each independently an alkyl group having 1 to 7 C atoms, an alkoxy group, a fluorinated alkyl group or a fluoroalkoxy group, an alkenyl group having 2 to 7 C atoms, an alkene An oxy, alkoxyalkyl or fluoroalkenyl group, and R ^{1 is} preferably alkenyl, and m is 0 or 1, and a second positive dielectric component, component B, which comprises one or more Compound of formula IV Wherein R ⁴ has the meaning given to R ^{2 in} formula II as Z ⁴ -CO-O- or a single bond, X ⁴ is F or OCF ₃ and Y ⁴ is H or F and, as the case may be, another (third) positive dielectric component, component C, optionally dielectrically neutral component, ie component D, The negative dielectric component, component E, and, as the case may be, the palm component, component F.

Preferably, the first positive dielectric component (ie, component A) comprises one or more strong positive components a dielectric compound (having a dielectric anisotropy of 20 or more, preferably 30 or more), more preferably predominantly, more preferably substantially and particularly preferably consisting entirely of and preferably one or more Compositions of each of Formulas I and III and the preferred Formulas I, II, and III.

Preferably, the liquid crystal mixture of the present invention comprises one or more compounds of formula III wherein m is 0, and/or one or more compounds of formula III wherein m is 1.

In a preferred embodiment of the invention, the liquid crystal mixture according to the invention comprises one or more compounds of the formulae I, II and III.

Preferably, the second positive dielectric component (ie, component B) comprises one or more positive dielectric compounds (the compounds have a relationship between 3 and 19, preferably between 5 and 16 Dielectric anisotropy), more preferably predominantly, more preferably substantially and particularly preferably consists entirely of and preferably consists of one or more compounds of formula IV.

Preferably, the liquid crystal mixture according to the invention comprises one or more compounds of the formula IV, wherein X ⁴ is OCF ₃ and Y ⁴ is H.

Another preferred liquid crystal mixture according to the present invention comprises one or more compounds of formula IV wherein X ⁴ is F and Y ⁴ is F.

In a preferred embodiment of the invention, the liquid crystal mixture according to the invention comprises one or more compounds of the formula IV selected from the group of compounds of the formulae IVa to IVd Wherein R ⁴ has the meaning given above.

In a preferred embodiment of the invention, the liquid crystal mixture according to the invention comprises one or more compounds of the formula IVa.

In a preferred embodiment of the invention, the liquid crystal mixture according to the invention comprises one or more compounds of the formula IVb and/or one or more compounds selected from the group of compounds of the formulae IVc to IVd.

In a preferred embodiment of the invention, the second positive dielectric component (i.e., component B) comprises one or more compounds of formula IV selected from the group of formulae IVa to IVd, more preferably primary, better basic. It is composed entirely of it.

Preferably, the liquid crystal mixture according to the invention comprises another (third) positive dielectric component (i.e. component C). The composition has a dielectric anisotropy of 3 or more, preferably between 3 and 19, and most preferably between 5 and 15. Preferably, it comprises a positively dielectric compound, preferably predominantly, preferably substantially and particularly preferably consisting entirely of it. Preferably, the component comprises one or more positive dielectric compounds of the formula V, more preferably predominantly, more preferably substantially and particularly preferably consisting entirely of Wherein R ⁵ has the meaning given above for R ^{2 in} formula II, Independent of each other and at Appear twice, and the ones are independent of each other In the case of At least one or each of Z ⁵¹ and Z ⁵² are independent of each other and appear twice in Z ⁵¹ , and these are independently -CH ₂ CH ₂ -, -COO-, trans--CH=CH-, trans--CF=CF- In the case of -CH ₂ O-, -CF ₂ O- or a single bond, preferably at least one of the single bonds and preferably (if present) the at least two single bonds, X ⁵ is F, Cl, haloalkyl, haloalkoxy, haloalkenyl or haloalkenyloxy, wherein halo is preferably fluoro and/or chloro, preferably halo and preferably X ⁵ F, OCF ₃ or OCF ₂ H, n is 0, 1 or 2, preferably 1 or 2, and does not include compounds of the formulae IVa to IVd.

Preferably, the liquid crystal mixture according to the invention comprises at least one further component in addition to components A and B. The third component can be any of components C, D and E. Preferably, the third component of the present invention is component C or D, and particularly preferably component C.

It will be apparent that the mixture according to the invention may also comprise the four components, preferably components A, B, C and D, and optionally all four components.

Preferably, the liquid crystal mixture according to the invention comprises a dielectric neutral component, component D. This component has a dielectric anisotropy between -1.5 and +3. Preferably, it comprises one or more dielectric neutral compounds, more preferably it consists primarily, more preferably substantially and particularly preferably consists entirely of it. Preferably, the component comprises one or more dielectric neutral compounds of the formula VI, more preferably predominantly, more preferably substantially and particularly preferably consisting entirely of Wherein R ⁶¹ and R ⁶² are independent of each other and have the meaning given above for R ^{2 in} formula I, Independent of each other and at Appear twice, and the ones are independent of each other In the case of At least one, better two or more Z ⁶¹ and Z ⁶² are independent of each other and appear twice in Z ⁶¹ , and these are independently -CH ₂ CH ₂ -, -COO-, trans--CH=CH-, trans--CF=CF In the case of -, -CH ₂ O-, -OCH ₂ -, -CF ₂ O-, -OCO ₂ - or a single bond, preferably at least one of these is a single bond and is optimal (if present) such At least two are single bonds and I are 0, 1 or 2.

In a preferred embodiment of the invention, the liquid crystal mixture according to the invention comprises one or more compounds of the formula V selected from the group of compounds of the formulae Va to Vf Wherein R ⁵ is an alkyl group having 1 to 7 C atoms, an alkoxy group, a fluoroalkyl group or a fluoroalkoxy group, an alkenyl group having 2 to 7 C atoms, an alkenyloxy group, an alkoxyalkyl group Or a fluoroalkenyl group, X ⁵ independently of each other is F, Cl or a fluoroalkyl or fluoroalkoxy group each having 1 to 4 C atoms or a fluoroalkenyl group each having 2 to 4 C atoms or Fluoroalkenyloxy, preferably F, OCF ₃ or OCF ₂ H, L ⁵¹ to L ⁵⁶ are independently H or F, preferably at least one, preferably L ⁵ , more preferably (preferably) Two or more selected from the group consisting of L ⁵¹ , L ⁵² and L ⁵³ ) are F.

More preferably, one or more selected from the group consisting of Formulas Va-1 to Va-4, Vb-1 to Vb-15, Vc-1 to Vc-4, Vd-1 to Vd-8, Ve-1 to Ve-4 a liquid crystal mixture of a compound of a group of Vf-1 to Vf-4 and Vg-1 to Vg-4 compounds, Wherein R ⁵ is an alkyl group having 1 to 7 C atoms, an alkoxy group, a fluoroalkyl group or a fluoroalkoxy group, an alkenyl group having 2 to 7 C atoms, an alkenyloxy group, an alkoxyalkyl group Or fluoroalkenyl.

In a preferred embodiment of the invention, the liquid crystal mixture according to the invention comprises one or more compounds of the formula Vf-4.

In another preferred embodiment of the invention, which may be the same as the previous embodiment or a different embodiment, the liquid crystal mixture according to the invention comprises component D, and component D comprises selected from the group consisting of formulas VIa to VIh, Preferred from VIa to VId and VIg, a compound of formula VI, preferably selected from the group of VIa and VIg compounds, preferably consists primarily of, and optimally consists of, Wherein R ⁶¹ and R ⁶² are each independently an alkyl group having 1 to 7 C atoms, an alkoxy group, a fluoroalkyl group or a fluoroalkoxy group, an alkenyl group having 2 to 7 C atoms, an alkenyloxy group , alkoxyalkyl or fluorinated alkenyl group and L ⁶ based H or F.

In a preferred embodiment of the invention, the liquid crystal mixture according to the invention comprises one or more compounds of the formula VIg.

Preferably, the liquid crystal mixture comprises one or more compounds of the formula VIa, wherein R ⁶¹ and R ⁶² are alkyl groups, a compound of the formula VIa wherein R ⁶¹ is an alkyl group and R ⁶² is an alkoxy group. A compound of the formula VIa, wherein R ⁶¹ is alkyl and R ⁶² is alkenyl, a compound of the formula VIb, wherein R ⁶¹ and R ⁶² are alkyl, a compound of the formula VIb, wherein R ⁶¹ is alkyl and R ⁶² is alkoxy A compound of the formula VIc, wherein R ⁶¹ and R ⁶² are alkyl, a compound of the formula VIc, wherein R ⁶¹ is alkyl and R ⁶² is alkoxy, a compound of the formula VIc, wherein R ⁶¹ is alkyl and R ⁶² is alkenyl and A compound of formula VId wherein R ⁶¹ and R ⁶² are alkyl.

Preferably, the liquid crystal mixture comprises one or more compounds of the formula VIa in addition to one or more compounds selected from the group of formulae VIb to VId and VIg, more preferably a mixture comprising a compound of the formula VIa wherein R ⁶¹ is an alkyl group and R ⁶² Alkenyl.

Further, the liquid crystal mixture according to the present invention may comprise another optional component, component E, which has a negative dielectric anisotropy and comprises a negative dielectric compound preferably of formula VII, preferably predominantly and preferably. Basically and optimally composed entirely of Wherein R ⁷¹ and R ⁷² independently of one another have the meaning given above for R ^{1 in} formula I, Z ⁷¹ and Z ⁷² are independent of each other -CH ₂ CH ₂ -, -COO-, trans--CH=CH-, trans--CF=CF-, -CH ₂ O-, -CF ₂ O- or single Preferably, at least one of the bonds is a single bond and preferably both are single bonds, and L ⁷¹ and L ⁷² are independently CF or N, preferably at least one of CF and preferably both. Both CF and k are 0 or 1.

It can be used as a palm-like component (i.e., component F) for the palm compound in the palm-to-palm component as well known to the skilled person. These compounds are known to be palmitic dopants such as, for example, cholesteryl citrate (CN) C15 or CB15 (which is commercially available from Merck KGaA). Also useful are, for example, the following palmitic dopants: R-811 and S-811, R-1011 and S-1011 or R-5011 and S-5011, which are pairs of enantiomeric compounds, These are also available from Merck KGaA. The latter allows the desired twist of the cholesterol helix to be selected by using the appropriate enantiomer of the compound.

Preferably, the liquid-crystalline medium according to the invention comprises components A to F and in particular a compound selected from the group of compounds of the formulae I to VII, preferably predominantly and optimally consisting entirely of it.

Included in the present application in the context of a composition means that the indicated entity (eg, medium or component) preferably contains the discussed concentration of 10% or more and optimally 20% or more. Component or the (etc.) compound.

In this context, consisting essentially of: means that the indicated entity contains 55% or more, preferably 60% or more, and most preferably 70% or more of the (etc.) component or the (etc.) Compound.

In this context, consisting essentially of means that the indicated entity contains 80% or more, preferably 90% or more, and most preferably 95% or more of the (etc.) component or the ) compound.

In this context, consisting entirely of is meant that the indicated entity contains 98% or more, preferably 99% or more, and most preferably 100.0% of the (or) component or compound(s) in question.

Particularly preferred are those in which component A comprises a compound selected from the group of compounds of formulae I to III, preferably predominantly and optimally composed entirely of liquid crystal media.

Component E preferably comprises one or more compounds of the formula VII, preferably selected from the group of compounds of the formulae VIIa to VIIc, which are preferably predominantly and optimally composed entirely of Wherein R ⁷¹ and R ⁷² have the corresponding meanings given above for formula VII.

In formulae VIIa to VIIc, R ^{71 is} preferably n-alkyl or 1-E-alkenyl and R ^{72 is} preferably n-alkyl or alkoxy.

Other liquid crystal-derived compounds not specifically mentioned above may also be used in the medium of the invention as appropriate and advantageously. Such compounds are well known to those skilled in the art.

Component A is preferably used in a concentration of 40 to 90%, more preferably 50 to 80%, more preferably 55 to 70%, and most preferably 60 to 65% of all the mixture.

Component B is preferably used in a concentration of from 5 to 50%, more preferably from 7 to 40%, more preferably from 10 to 30%, and most preferably from 15 to 25% of all the mixture.

Component C is preferably used in a concentration of from 0 to 40%, more preferably from 2 to 30%, more preferably from 3 to 20%, and most preferably from 5 to 15% of all the mixture.

Component D is preferably used in a concentration of from 0 to 40%, preferably from 0 to 20% and most preferably from 5 to 15% of all the mixture.

Component E is preferably from 0 to 30%, preferably from 0 to 20%, and most preferably all of the mixture Use at a concentration of 5 to 15%.

Component F is preferably used in a concentration of from 0 to 10%, preferably from 0 to 5%, and most preferably from 0.5 to 2% of all the mixture.

The medium of the present invention may include other liquid crystal compounds as appropriate to adjust physical properties. Such compounds are well known to those skilled in the art. The concentrations in the medium of the invention are preferably from 0% to 30%, more preferably from 0% to 20% and most preferably from 5% to 15%.

Preferably, the liquid crystal medium comprises 50% to 100%, more preferably 70% to 100% and most preferably 80% to 100% and especially 90% to 100% of all components A, B, C, D, E And F (preferred components A, B, C, D and F), which in turn comprise one or more of formulas I, II, III (component A), IV (component B), V (component C), respectively The compounds of VI (component D) and VII (component E) are preferably predominantly and optimally composed entirely of them.

The liquid crystal medium according to the present invention is preferably characterized by a clearing point of 70 ° C or higher, preferably 75 ° C or higher, more preferably 80 ° C or higher and especially 85 ° C or higher.

The Δn of the liquid crystal medium of the present invention is preferably 0.11 or more, more preferably 0.12 or more, still more preferably 0.120 to 0.200, still more preferably 0.120 to 0.180, most preferably 0.120 to 0.126 and especially Between 0.120 and 0.150.

The Δε of the liquid crystal medium according to the present invention at 1 kHz and 20 ° C is preferably 25.0 or more, more preferably 35.0 or more, still more preferably 45 or more, most preferably 55.0 or more, and especially 65.0 or more.

Preferably, the nematic phase of the medium of the invention is extended from at least 0 ° C to 70 ° C, preferably At least from -20 ° C to 70 ° C, optimally at least from -30 ° C to 75 ° C and especially at least from -40 ° C to 80 ° C, wherein "at least" and the lower limit are combined to mean that the phase temperature range extends at least downward to a lower limit and Preferably, the temperature is below the lower limit, and the combination with the upper limit means that the phase temperature range extends at least upward to an upper limit and preferably to a temperature above the upper limit.

The liquid crystal medium according to the present invention preferably has 0.11 or more, more preferably 0.12 or more, more preferably 0.120 to 0.200, more preferably 0.120 to 0.180, and most preferably 0.120 to 0.126 in the STN unit. A threshold voltage (V ₁₀ ) between 0.120 and 0.150, in particular.

In the present application, the term positive dielectric refers to a compound or component of Δε > 3.0, dielectric neutral -1,5 Δε A compound or component having a negative dielectric of Δ ε < -1,5. The Δε system was measured at 1 kHz and 20 °C. The dielectric anisotropy of the compound was determined based on the results of a 10% individual compound solution in the nematic host mixture. The capacitance of the test mixtures is determined in both vertical and uniform alignment units. The cell gap of the two types of cells is about 10 microns. The applied voltage is a rectangular wave having a frequency of 1 kHz and the root mean square value is typically from 0.5 volts to 1.0 volts, however it is always selected to be below the capacitance threshold of the corresponding test mixture.

The mixture ZLI-4792 and the mixture ZLI-3086 (both purchased from Merck KGaA, Germany) were used as the host mixture for the positive dielectric compound and the dielectric neutral and negative dielectric compounds, respectively. The permittivity of the compounds is determined and extrapolated to the 100% concentration of the compound of interest based on the change in the corresponding value of the host mixture after addition of the compound of interest. Such a component having a nematic phase at a measured temperature of 20 ° C, all other components are like a compound Treat the same.

Unless otherwise explicitly stated, the following two terms refer to: the term threshold voltage in this application refers to the optical threshold and is provided for a relative contrast ratio (V ₁₀ ) of 10% and the term saturation voltage refers to the optical system provides a saturation value and a relative ratio of 90% (V _90). The capacitor threshold voltage (V ₀ , also known as Freedericksz - Thrence V _Fr ) is used only when explicitly mentioned.

Unless otherwise expressly stated, the scope of the parameters given in this application includes the limit values.

Unless otherwise expressly stated, all concentrations throughout this application are given in mass percent and refer to the corresponding total mixture, all temperatures are given in degrees centigrade (Celsius) and all temperature differences are given in degrees Celsius. All physical properties have been determined according to "Merck Liquid Crystals, Physical Properties of Liquid Crystals", Status Nov. 1997, Merck KGaA, Germany and are given at a temperature of 20 ° C unless otherwise explicitly stated. The optical anisotropy (Δn) was measured at a wavelength of 589.3 nm. The dielectric anisotropy (Δε) was measured at a frequency of 1 kHz. Threshold voltages and other optoelectronic properties have been determined using test units prepared by Merck KGaA (Germany). The test unit used to determine Δε has a cell gap of 22 microns. The electrode is a circular ITO electrode having a 1.13 cm ² area and a guard ring. The oriented layer was used for the vertically oriented (ε-) lecithin and the polyimine AL-1054 from Japan Synthetic Rubber for uniform orientation (ε _⊥ ). The capacitance was measured using a frequency response analyzer Solatron 1260 using a sine wave of 0.3 V _rms voltage. The light used in electro-optical measurement is white light. The device used was a device sold by Otsuka (Japan). The characteristic voltage has been measured under vertical observation. The threshold (V ₁₀₎ - mid gray (V ₅₀₎ - and saturation (V ₉₀₎ voltages respectively, was determined for 10%, 50% and 90% relative contrast ratio.

The liquid crystal medium according to the present invention may contain other additives and a palmitic dopant in a conventional concentration. The total concentration of the other ingredients is between 0% and 10%, preferably between 0.1% and 6%, based on the total mixture. The concentration of each of the individual compounds used is preferably between 0.1% and 3%. The concentrations of these and similar additives in this application are not included in the concentration and range of the liquid crystal components and compounds of the liquid crystal medium.

The liquid crystal medium according to the invention comprises a plurality of compounds, preferably 3 to 30, more preferably 8 to 20 and most preferably 10 to 16 compounds. These compounds are mixed in a conventional manner. Generally, the amount of the compound to be used in a relatively small amount is dissolved in the compound used in a larger amount. In the case where the temperature is higher than the clearing point of the compound used at a higher concentration, the completion of the dissolution process is particularly easy to observe. However, it is also possible to prepare such media by other conventional methods, for example using so-called premixes which may be, for example, homologous or eutectic mixtures of the compounds, or using so-called multi-bottle systems which are themselves ready-to-use mixtures. .

The liquid crystal medium according to the present invention can be modified in this manner by adding suitable additives so that it can be used in any liquid crystal display of any of the known types such as TN-, TN-AMD, ECB-AMD, VAN-AMD, IPS and OCB LCD), and in particular for composite systems (eg PDLC, NCAP, PN LCD) and especially for ASM-PA LCD.

The melting point T (C, N) of the liquid crystals, the transition T(S, N) from the layer (S) to the nematic (N) phase, and the transparent point T (N, I) are given in degrees Celsius.

In the present application and especially in the following examples, the structures of the liquid crystal compounds are represented by abbreviations (also referred to as acronyms). The abbreviations can be simply converted into corresponding structures according to the following two tables A and B. All of the groups C _n H _2n+1 and C _m H _2m+1 are linear alkyl groups having n and m C atoms, respectively. The explanation in Table B is self-evident. Table A lists only the abbreviations of the structural core. The individual compounds are represented by the core abbreviation followed by the consecutive characters and the designations of the substituents R ¹ , R ² , L ¹ and L ² as follows:

The liquid crystal medium according to the present invention preferably comprises seven or more, preferably eight or more compounds selected from the group of the compounds of Tables A and B, and/or one or more, more Preferably two or more, preferably three or more compounds selected from the group of compounds of Table A are preferably different compounds and/or three or more, more preferably four or more compounds, more preferably five One or more compounds selected from the group of compounds of Table B are preferably different.

In the table below, Table C, there is shown an example of a palmitic compound which is generally used as a palmitic dopant in the liquid crystal medium of the present invention.

In the table below, Table D, there are shown examples of compounds which are generally used as stabilizers in the liquid crystal medium according to the present invention.

Instance

The following examples are given to illustrate the invention and are not intended to limit it in any way.

However, it is a matter for the professional to explain the physical properties that the composition can achieve and in which its scope can be modified. In particular, the combination of the various properties that can be better achieved is thus well defined for the professional.

Example 1

A liquid crystal mixture having the composition and properties given in the table below.

The mixture has a favorable Δn value and a high Δε value and is very suitable for displays operating in the STN mode.

Example 2

A liquid crystal mixture having the composition and properties given in the table below was achieved.

This mixture has advantageous Δn values and high Δε values and is well suited for displays operating in STN mode.

Claims (13)

A liquid-crystalline medium characterized by comprising a first positive dielectric component, component A, comprising one or more compounds of formula I and one or more compounds selected from the group of formulas II and III Wherein R ¹ , R ² and R ³ are each independently an alkyl group having 1 to 7 carbon atoms, an alkoxy group, a fluoroalkyl group or a fluoroalkoxy group, an alkenyl group having 2 to 7 carbon atoms, An alkenyloxy, alkoxyalkyl or fluoroalkenyl group and m system 0 or 1, and a second positive dielectric component, component B, comprising one or more compounds of formula IV Wherein R ⁴ has the meaning given to R ^{2 in} formula II, Z ⁴ is -CO-O- or a single bond, system , or X ⁴ is F or OCF ₃ and Y ⁴ is H or F. The liquid crystal medium of claim 1, wherein the liquid crystal medium comprises a positive dielectric component A comprising one or more compounds of formula I wherein R ¹ is an alkenyl group. The liquid crystal medium of claim 1, wherein R ¹ is selected from the group consisting of CH ₂ =CH-, CH ₂ =CH-(CH ₂ -) _n , or C _n H _2n+1 -CH=CH-, wherein n is 1 to An integer of 5. A liquid crystal medium according to claim 1, wherein R ¹ is C _n H _2n+1 -CH=CH-, and n is an integer of 1 to 5. A liquid crystal medium according to claim 4, wherein R ¹ is 1-buten-1-yl. The liquid crystal medium of any one of claims 1 to 5, wherein the liquid crystal medium comprises a third positive dielectric component, component C, the component comprising one or more compounds of formula V Wherein R ⁵ is an alkyl group having 1 to 7 carbon atoms, an alkoxy group, a fluoroalkyl group or a fluoroalkoxy group, an alkenyl group having 2 to 7 carbon atoms, an alkenyloxy group, an alkoxyalkyl group Or fluoroalkenyl, Independent of each other and at Appear twice, and the ones are independent of each other Under the circumstances, Z ⁵¹ and Z ⁵² independently of one another, and appears twice in the Z ^51, independently of one another and such _{-CH 2 CH 2 -, - COO-} , trans - -CH = CH-, trans - - In the case of CF=CF-, -CH ₂ O-, -CF ₂ O- or a single bond, X ⁵ is a F, Cl, haloalkyl, haloalkoxy, haloalkenyl or haloalkenyloxy group, n-system 0, 1 or 2, and the compounds of the formulae IVa to IVd are not included therein. The liquid crystal medium of any one of claims 1 to 5, wherein the liquid crystal medium comprises a dielectric neutral component, component D, the component comprising one or more compounds of formula VI Wherein R ⁶¹ and R ^{62 are} , independently of each other, an alkyl group having 1 to 7 carbon atoms, an alkoxy group, a fluoroalkyl group or a fluoroalkoxy group, an alkenyl group having 2 to 7 carbon atoms, an olefin oxygen; Base, alkoxyalkyl or fluoroalkenyl, Independent of each other and at Appear twice, and the ones are independent of each other In the case, Z ⁶¹ and Z ⁶² are independent of each other and appear twice in Z ⁶¹ , and these are independently -CH ₂ CH ₂ -, -COO-, trans--CH=CH-, trans- -CF=CF-, -CH ₂ O-, -OCH ₂ -, -CF ₂ O-, -OCO ₂ - or a single bond and l system 0, 1 or 2. The liquid crystal medium of any one of claims 1 to 5, wherein the liquid crystal medium comprises a negative dielectric component, component E, the component comprising one or more compounds of formula VII Wherein R ⁷¹ and R ⁷² are each independently an alkyl group having 1 to 7 carbon atoms, an alkoxy group, a fluoroalkyl group or a fluoroalkoxy group, an alkenyl group having 2 to 7 carbon atoms, an alkenyloxy group , alkoxyalkyl or fluoroalkenyl, system , , or Z ⁷¹ and Z ⁷² are independent of each other -CH ₂ CH ₂ -, -COO-, trans - -CH=CH-, trans--CF=CF-, -CH ₂ O-, -CF ₂ O- or single The keys, L ⁷¹ and L ⁷² are independently CF or N, and k is 0 or 1. The liquid-crystalline medium according to any one of claims 1 to 5, wherein the liquid-crystalline medium comprises one or more compounds of the formula IV selected from the group of compounds of the formulae IVa to IVd, Wherein R ⁴ has the meaning given in claim 1. The liquid crystal medium according to any one of claims 1 to 5, wherein the liquid crystal medium comprises one or more compounds of the formula III as given in claim 1. A liquid crystal display comprising the liquid crystal medium according to any one of claims 1 to 10. A liquid crystal display according to claim 11, characterized in that it is an STN display. A use of a liquid crystal medium according to any one of claims 1 to 10 in a liquid crystal display.