JP5542299B2 - Liquid crystal medium - Google Patents

Description

  The present invention relates to a liquid crystal medium and to a liquid crystal display including it, in particular a twisted nematic (TN) and a super twisted nematic (STN) liquid crystal display, having a very short response time and good steepness and angular dependence.

  TN displays are known, for example, from M. Schadt and W. Helfrich, Appl. Phys. Lett., 18, 127 (1971). STN displays are for example EP 0 131 216 B1; DE 34 23 993 A1; EP 0 098 070 A2; M. Schadt and F. Leenhouts, 17th Freiburg Congress on Liquid Crystals (8.-10.04.87); K. Kawasaki SID 87 Digest 391 (20.6); M. Schadt and F. Leenhouts, SID 87 Digest 372 (20.1); K. Katoh et al., Japanese Journal of Applied Physics, Vol. 26, No. 11, L 1784-L 1786 (1987); F. Leenhouts et al., Appl. Phys. Lett. 50 (21), 1468 (1987); HA van Sprang and HG Koopman, J. Appl. Phys. 62 (5), 1734 (1987); TJ Scheffer And J. Nehring, Appl. Phys. Lett. 45 (10), 1021 (1984), M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (5), 236 (1987) and EP Raynes, Mol. Cryst. Liq. Cryst. Letters Vol. 4 (1), pp. 1-8 (1986).

  The term STN here refers to all relatively highly twisted display elements having a twist angle with a value between 160 ° and 360 °, such as Waters et al. (CM Waters et al., Proc. Soc. Inf. Disp. (New York) (1985) (3rd Intern. Display Conference, Kobe, Japan), display elements, STN-LCD (DE-A 35 03 259), SBE-LCD (TJ Scheffer and J. Nehring, Appl. Phys. Lett. 45 (1984) 1021), OMI-LCD (M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (1987), 236, DST-LCD (EP-A 0 246 842) or BW-STN-LCD (K Kawasaki et al., SID 87 Digest 391 (20.6)).

  STN displays have a significantly better electro-optical characteristic curve and a correspondingly better contrast value compared to standard TN displays, and a significantly lower angular dependence of contrast. It is excellent by the nature.

  Of particular interest are TN and STN displays, which also have very short response times, especially at relatively low temperatures. In order to achieve a short response time, the rotational viscosity of the liquid crystal mixture has been optimized to date with monotrophic and mono-modified additives having a relatively high vapor pressure. However, the response time achieved was not appropriate for all applications.

In order to achieve a steep electro-optic characteristic curve in the display of the present invention, the liquid crystal mixture has a relatively large value for the ratio between the elastic constants K ₃₃ / K ₁₁ and a relatively small value for Δε / ε _⊥. Where Δε is the dielectric anisotropy and ε _で is the dielectric constant perpendicular to the molecular long axis.

In addition to optimizing contrast and response time, other important requirements are made for this type of mixture:
1. Wide d / p window 2. High long-term chemical stability High electrical resistance Low frequency and temperature dependence of threshold voltage.

  The achieved parameter combinations are particularly high multiplex STN displays (having a multiplex ratio on the order of about 1/400), but also moderate and low multiplex STN displays (about 1/64 and respectively) For a TN display (with a multiplex ratio on the order of 1/16), it is still far from appropriate. This is partly due to the fact that the various requirements are influenced by material parameters in the opposite manner.

  Therefore, TN and STN displays, especially moderate, which have a very short response time and simultaneously a large operating temperature range, a high characteristic curve steepness, a good angular dependence of contrast and a low threshold voltage, which meet the above requirements There is a continuing high demand for low and multiplex STN displays.

  Furthermore, modern applications, such as telecommunications, require a liquid crystal mixture having a high positive value of dielectric anisotropy Δε in order to achieve the required low threshold voltage. However, the lowered threshold voltage often results in increased response time. There is therefore a need to provide a liquid crystal mixture having a high positive value of Δε and at the same time a rapid response time.

  The present invention does not have the aforementioned disadvantages or, if at all, only to a relatively low extent, at the same time, especially at low temperatures, high positive Δε, low threshold voltage, short response time, and extremely It has the object of providing novel compounds and liquid crystal media with good steepness, in particular for TN and STN displays.

It has now been found that this object can be achieved when using the liquid crystal medium of the present invention.
The present invention provides compounds of formula I
The present invention relates to a liquid crystal medium containing a compound represented by:

By using the compound of formula I in the mixture for TN and STN displays of the present invention, the following results.
・ Higher steepness of the electro-optical characteristic curve,
-Lower temperature dependence of operating voltage due to improved frequency dependence,
-Faster response time, especially at lower temperatures.

The compounds of the formula I reduce the response time of TN and STN mixtures in particular, while at the same time increasing the dielectric anisotropy and the steepness and reducing the temperature dependence of the threshold voltage.
Furthermore, the mixtures according to the invention are distinguished by the following advantages:
They have a low viscosity,
They have a low threshold voltage and an operating voltage, and they provide a long shelf life in the display at low temperatures.

The present invention further includes
Two outer plates forming cells with the frame,
A nematic liquid crystal mixture with positive dielectric anisotropy arranged in the cell,
An electrode layer having an alignment layer on the inside of the outer plate,
Liquid crystal mixture in the cell for each alignment layer having a tilt angle between the major axis of the molecule on the surface of the outer plate and the outer plate of −0 ° to 30 ° and a value of −22.5 ° to 600 °. Twist angle,

-A) 15 to 75% by weight of liquid crystal component A comprising one or more compounds having a dielectric anisotropy higher than +1.5;
b) 25 to 85% by weight of a liquid crystal component B composed of one or more compounds having a dielectric anisotropy of −1.5 to +1.5;
c) Liquid crystal component D consisting of one or more compounds having a dielectric anisotropy lower than -1.5 0-20% by weight and d) optionally layer thickness (distance of outer plate) and chiral An optically active component C in an amount such that the ratio between the nematic liquid crystal mixture and the natural pitch is about 0.2 to 1.3.
A liquid crystal display having a nematic liquid crystal mixture comprising:
The display is characterized in that a nematic liquid crystal mixture is defined as described herein.

The invention also relates to TN and STN displays, in particular medium and low multiplex STN displays, comprising the liquid crystal mixture of the invention.
The use of the compounds of the formula I in the liquid crystal mixtures according to the invention results in TN and STN displays having a particularly low rotational viscosity value and a high steepness and a quick response time, especially at low temperatures.

In addition to the compounds of the formula I, the liquid-crystal mixtures according to the invention are furthermore preferably of formula II
Where
A is 1,4-phenylene or trans-1,4-cyclohexylene;
a is 0 or 1,
R ³ is an alkenyl group having 2 to 9 carbon atoms;
R ⁴ is an alkyl group having 1 to 12 carbon atoms that is unsubstituted, monosubstituted by CN or CF ₃ , or at least monosubstituted by halogen, wherein these One or more CH ₂ groups in the group are also each independently of the other such that —O—, —S—, —CH═CH—, —C≡ so that the O atoms are not directly bonded to each other. Optionally substituted by C-, -CO-, -CO-O-, -O-CO- or -O-CO-O-,
1 type or 2 types or more of alkenyl compounds represented by these are included.

Particularly preferred compounds of the formula II are those of the following formula:
In which R ^3a and R ^4a are independently of each other H, CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ and alkyl is an alkyl group having 1 to 8 carbon atoms. ,
Is selected from.

Particular preference is given to compounds of the formula IIa, in particular where R ^3a and R ^4a are H or CH ₃ , as well as of the formulas IIe, IIf, IIg, IIh and IIi, in particular where R ^3a is H Or a compound that is CH ₃ .
The compounds of the formulas I and II having a dielectric anisotropy of −1.5 to +1.5 (“dielectrically neutral”) are part of component B as defined above.

In addition to the compounds represented by Formulas I and II, the liquid crystal mixture of the present invention preferably further comprises one or more alkenyl compounds represented by Formula II ^* having a positive dielectric anisotropy. Including.
Where
R ³ is an alkenyl group having 2 to 7 carbon atoms,
Q is CF ₂ , OCF ₂ , CFH, OCFH or a single bond,
Y is F or Cl;
L ¹ and L ² are each independently H or F.

Particularly preferred are compounds of the formula II ^* , wherein L ¹ and / or L ² is F and QY is F or OCF ₃ .
Further preferred are compounds of formula II ^{* in} which R ³ is 1E-alkenyl or 3E-alkenyl having 2 to 7, preferably 2, 3 or 4 carbon atoms.

Highly preferred is the formula II ^* a
In which R ^3a is H, CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ , in particular H or CH ₃ ,
It is a compound represented by these.

The polar compound represented by formula II ^* having a dielectric anisotropy greater than +1.5 is part of component A defined above.
Preferred liquid crystal mixtures comprise one or more compounds of component A , preferably in a proportion of 15% to 75%, more preferably 20% to 65%. These compounds preferably have a dielectric anisotropy of Δε ≧ + 3, more preferably Δε ≧ + 8 and most particularly preferably Δε ≧ + 12.

Component A preferably has the following formula

Where
R is an alkyl, alkoxy or alkenyl group having 1 to 12 carbon atoms, wherein one or more CH ₂ groups in these groups are also each independently of one another O May be substituted by -O-, -CH = CH-, -CO-, -OCO- or -COO- so that the atoms are not directly bonded to each other;
L ¹ , L ² , L ³ and L ⁴ are independently of each other H or F.
1 type, or 2 or more types of cyano compounds selected from these are included.

R in these compounds is preferably alkyl or alkoxy having 1 to 8 carbon atoms or alkenyl having 2 to 7 carbon atoms.
Very particular preference is given to mixtures comprising one or more compounds selected from the formulas IIIb, IIIc, IIId and IIIe, furthermore IIIg, in particular where L ¹ and / or L ² is F.

  Further preferred are alkenyls of formula IIIc and / or IIId, wherein R has 2 to 7 carbon atoms, preferably -alkenyl or 3E-alkenyl, more preferably vinyl, 1E-propenyl, 1E- A mixture comprising one or more compounds which is butenyl, 3E-butenyl or 3E-pentenyl, most preferably 1E-butenyl.

Further preferred is a mixture comprising one or more compounds of the formula IIId, wherein L ³ and L ⁴ are H.
Preferred liquid crystal mixtures preferably comprise from 25 to 85% of one or more compounds of component B. Compounds from group B are particularly superior to these low values for rotational viscosity γ ₁ .

Component B is preferably further represented by the following formula:
One or more compounds selected from the group consisting of the bicyclic compounds represented by: and / or the following formula

One or more compounds selected from the group consisting of tricyclic compounds represented by: and / or the following formula

Including one or more compounds selected from the group consisting of tetracyclic compounds represented by:

here,
R ¹ and R ² are each independently an alkyl group having 1 to 12 carbon atoms that is unsubstituted, monosubstituted by CN or CF ₃ , or at least monosubstituted by halogen Where one or more CH ₂ groups in these groups are also, independently of each other, such that the O atoms are not directly bonded to each other, —O—, —S—, — Optionally substituted by CH═CH—, —C≡C—, —CO—, —CO—O—, —O—CO— or —O—CO—O—,
L is H or F;
Also here, the 1,4-phenylene groups in formulas IV10-IV19 and formulas IV23-IV33 are optionally mono- or polysubstituted by F.

Particularly preferred are compounds of the formulas IV27 to IV33, each having ¹ to 7 carbon atoms, wherein R ¹ is alkyl and R ² is alkyl or alkoxy, especially alkoxy. Preference is further given to compounds of the formulas IV27 and IV33, in which L is F.

Particularly preferred are compounds of formula IV12, IV27 and IV32.
R ¹ and R ² in the compounds of the formulas IV1 to IV33 are particularly preferably straight-chain alkyl or alkoxy having 1 to 12 carbon atoms.

Particular preference is given to formula IV24, preferably wherein R ¹ is alkenyl having 2 to 7 carbon atoms, very particularly preferably formulas IV24a and IV24b.
In which R ^3a is as defined above.
It is a mixture of the present invention comprising one or more compounds selected from

In another preferred embodiment, the liquid crystal mixture has the formula Ta-Ti
Where R ¹ and R ² are as defined in Formula IV above,
Z ⁴ is —CO—O—, —CH ₂ CH ₂ — or a single bond, and L ^{1 to} L ⁶ are each independently H or F.
One or more tolan compounds selected from the group consisting of:

  Particularly preferred are compounds of the formulas Ta, Tb and Tc.

In another preferred embodiment, component A of the liquid crystal mixture of the present invention is further preferably represented by the following formula:

One or more 3,4,5-trifluorophenyl compounds selected from: and / or the following formula

Wherein R is as defined in formula III and L ³ and L ⁴ are independently of each other H or F.
1 type, or 2 or more types of compounds which have the polar terminal group selected from these. Preferably R in these compounds is alkyl or alkoxy having 1 to 8 carbon atoms.

  Particular preference is given to compounds of the formulas Va, Vb, Vc, Vd, Vm, Vn and VIm, in particular compounds of the formulas Va, Vm, Vn and VIm.

In another preferred embodiment, the liquid crystal mixture is of one or more, particularly preferably one, two or three, of formulas VIIa and / or VIIb
Wherein R ⁶ and R ⁷ are defined as R defined in formula III and Y is F or Cl.
The heterocyclic compound represented by these is included.

If desired, the liquid crystal mixture may contain the optically active component C in an amount such that the ratio between the layer thickness (outer plate distance) and the natural pitch of the chiral nematic liquid crystal mixture is greater than 0.2. Including. A number of commercially available chiral dopants are available to those skilled in the art for components such as cholesteryl nonanoate from Merck KGaA, Darmstadt, S-811, S-1011, S-2011, S-3011, S- Useful for 4011 or CB15. The choice of dopant is not critical per se.

The proportion of compound of component C is preferably 0-10%, more preferably 0-5% and especially 0-3%.
The mixtures according to the invention may also optionally contain up to 20% of one or more compounds ( component D ) having a dielectric anisotropy lower than -2.

If the mixture contains compounds of component D , these are preferably one or more compounds containing the structural unit 2,3-difluoro-1,4-phenylene, for example DE-A 38 07 801, 38 07 861, 38 07 863, 38 07 864 and 38 07 908. Particularly preferred are tolans containing this structural unit as described in international patent application WO 88/07514.

Other known compounds of component D are structural units as described, for example, in DE-A 32 31 707 and DE-A 34 07 013
2,3-dicyanohydroquinones derivatives or cyclohexane derivatives.
The liquid crystal display of the present invention preferably does not contain the component D compound.

The term “alkenyl” in the definition of R and R ^{1 to} R ⁷ includes straight-chain and branched alkenyl groups, especially straight-chain groups. Particularly preferred alkenyl _groups, C _{2 ~C} 7 -1E- _alkenyl, C _{4 ~C} 7 -3E- _alkenyl, C _{5 ~C} 7 -4- _alkenyl, C _{6 ~C} 7 -5- alkenyl and _C 7 -6 - alkenyl, in particular _C 2 _{-C 7-1E-alkenyl,} C ₄ -C 7 -3E-alkenyl and _C 5 _-C 7-4-alkenyl.

  Examples of preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3E-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z -Hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5 carbon atoms are generally preferred.

In a particularly preferred embodiment, the liquid crystal mixture comprises:
One or more compounds selected from the formulas IIa to IIi and / or II ^* ,
One or more compounds selected from formulas IIIa to IIIi,
One or more compounds of the formula IV24,
One or more compounds selected from the formulas Ta to Tc,
One or more compounds selected from formulas IV12 and / or IV27 and / or IV32.

In another particularly preferred embodiment, the liquid crystal mixture is
-2 to 30%, preferably 4 to 20% of a compound of formula I,
-0-30%, preferably 3-20% of the compound of formula IV24,
−8 to 70%, preferably 14 to 60% of compounds of the formulas IIa to IIi and / or II ^* ,
-4 to 50%, preferably 5 to 40% of a compound represented by the formula Ta to Tc,
-5 to 40%, preferably 10 to 30% of compounds of formula IIIa to IIIi,
-0 to 20%, preferably 2 to 10% of a compound of formula IV12 and / or IV27 and / or IV32.

The individual compounds of the above formulas and their subordinate formulas as well as other compounds that can be used in the mixtures or TN and STN displays of the present invention are known or prepared analogously to known compounds. Can do.
The mixtures according to the invention are distinguished by a very low total response time (t _sum = ton + toff), especially for use in TN and STN displays with large layer thicknesses.

The liquid crystal mixture used in the TN and STN cells of the present invention is preferably dielectrically positive and Δε ≧ 1. Preference is given to liquid crystal mixtures in which Δε ≧ 5.
The clearing point of the liquid crystal mixture of the present invention is preferably 80 ° C. or higher, more preferably 90 ° C. or higher.

The liquid crystal mixture according to the invention has preferred values for the threshold voltage V _10/0/20 and the rotational viscosity γ ₁ . If the value for the optical path difference d · Δn is specified in advance, the value for the layer thickness d is determined by the optical anisotropy Δn. In particular, it is generally preferred to use a liquid crystal mixture according to the invention having a relatively high value for optical anisotropy at a relatively high value for d · Δn. The reason is that the value for d can then be chosen relatively small, resulting in a more favorable value for response time. However, the liquid crystal display of the present invention comprising the liquid crystal mixture of the present invention having a relatively small value for Δn is also characterized by advantageous values for response time.

  Preferably, the liquid-crystal mixtures of the invention have a birefringence Δn that is> 0.12, very preferably ≧ 0.14. More preferably, the liquid crystal mixture of the present invention has a birefringence Δn of <0.25, very preferably ≦ 0.22.

  The liquid-crystal mixtures according to the invention are further characterized by advantageous values for the steepness of the electro-optical characteristic curve, and can operate with a high multiplex ratio, especially at temperatures above 20 ° C. Furthermore, the liquid-crystal mixtures according to the invention have favorable values for high stability and frequency dependence of electrical resistance and threshold voltage. The liquid crystal display of the present invention has a large operating temperature range and good angular dependence of contrast.

  The preferential orientation (director) of the polarizing plate, the electrode base plate and in each case the liquid crystal molecules adjacent to it is usually twisted from one electrode to the other at a value of 160 ° to 720 ° The structure of the liquid crystal display element of the present invention from the electrode having the surface treatment corresponds to the usual structure for this type of display element. The term “normal structure” is here cited broadly and encompasses all derivatives and modifications of TN and STN cells, in particular also display elements including matrix display elements and additional magnets.

  The surface tilt angles on the two outer plates may be the same or different. The same tilt angle is preferred. Preferred TN displays have a pretilt angle between the major axis of the molecule at the surface of the outer plate and the outer plate of 0 ° to 7 °, preferably 0.01 ° to 5 ° and especially 0.1 to 2 °. . In STN displays, the pretilt angle is 1 ° to 30 °, preferably 1 ° to 12 ° and in particular 3 ° to 10 °.

  The twist angle of the TN mixture in the cell has a value of 22.5 ° to 170 °, preferably 45 ° to 130 ° and in particular 80 ° to 115 °. The twist angle of the STN mixture in the cells between the alignment layers has a value of 100 ° to 600 °, preferably 170 ° to 300 ° and in particular 180 ° to 270 °.

  The liquid crystal mixtures of the present invention are also suitable as liquid crystal media for use in cholesteric liquid crystal displays, in particular SSCT (“surface stabilized cholesteric texture”) and PSCT (“polymer stabilized cholesteric texture”) displays, for example As described in WO 92/19695, US 5,384,067, US 5,453,863, US 6,172,720 and US 5,661,533. Cholesteric liquid crystal displays typically include a cholesteric liquid crystal medium composed of a nematic component and an optically active component, exhibiting a significantly higher helical twist compared to TN and STN displays, and providing circularly polarized light. Shows selective reflection. The reflection wavelength is given by the product of the pitch of the cholesteric helix and the average refractive index of the cholesteric liquid crystal medium.

  For this purpose, one or more chiral dopants are added to the liquid crystal mixture according to the invention, wherein the twisting power and concentration of the dopant is determined so that the resulting liquid crystal medium has a cholesteric phase at room temperature. , Preferably with a reflection wavelength in the visible, UV or IR range of the electromagnetic spectrum, in particular in the range of 400-800 nm.

  Suitable chiral dopants are known to the expert and are commercially available, for example cholesteryl nonanoate (CN), CB-15, R / S-811, R / S-1011, R / S-2011, R / S-3011, R / S-4011 and R / S-5011 (Merck KGaA, Darmstadt). Particularly suitable are high twisting dopants containing chiral sugar groups, in particular sorbitol, mannitol or iditol derivatives, very preferably sorbitol derivatives, as disclosed in WO 98/00428. Further preferred are dopants containing hydrobenzoin groups as described in GB 2,328,207, chiral binaphthyl derivatives as described in WO 02/94805, chiral binaphthol acetal derivatives as described in WO 02/34739, WO 02 The chiral TADDOL derivatives described in / 06265 and chiral dopants having at least one fluorinated linking group and a terminal or central chiral group described in WO 02/06196 and WO 02/06195 is there.

  If two or more dopants are used, they can exhibit the same or opposite sign of the same or opposite twist direction and first-order temperature coefficient of twist.

  A cholesteric liquid crystal medium comprising the liquid crystal mixture of the present invention as a nematic component and one or more chiral dopants as an optically active component is another object of the present invention. Yet another object of the present invention is a cholesteric liquid crystal display, particularly SSCT and PSCT displays, comprising the cholesteric liquid crystal medium described above.

  Liquid crystal mixtures that can be used in the present invention are in a manner which is customary per se, for example a compound of formula I with one or more compounds selected from the above formulas and optionally other compounds or Prepared by mixing with additives. In general, the desired amount of the components used in the smaller amount is dissolved, preferably warmed, in the components making up the main component. It is also possible to mix a solution in which the components are dissolved in an organic solvent such as acetone, chloroform or methanol, mix thoroughly, and then remove the solvent again, for example by distillation. The method of preparing the mixture is another aspect of the present invention.

  The dielectric may also contain other additives known to those skilled in the art and described in the literature. For example, 0-15% of pleochroic dyes, nanoparticles, stabilizers or chiral dopants can be added. Suitable dopants and stabilizers are shown in Tables C and D below.

In this application and in the following examples, the structure of the liquid crystal compound is indicated by an acronym and the conversion to the chemical formula is performed according to Tables A and B. All groups C _n H _{2n + 1} and C _m H _{2m + 1} are linear alkyl groups having n and m carbon atoms, respectively. An alkenyl group has a trans structure. The coding in Table B is self-explanatory. In Table A, only the initials for the basic structure are shown. In individual cases, the initial letters for the basic structure are followed by the codes shown in the table below for the substituents R ¹ , R ² , L ¹ , L ² and L ³ , separated by a dash.

TN and STN displays preferably comprise a liquid crystal mixture composed of one or more compounds from Tables A and B.
Table A: (L ¹ , L ² , L ³ = H or F)

Table C
Table C shows the dopants preferably used in the mixtures according to the invention:

Table D
For example, stabilizers that can be added to the mixtures of the invention are shown below:

  It will be appreciated that variations on the foregoing aspects of the invention can still be made within the scope of the invention. Each feature disclosed in this specification can be replaced by an alternative feature serving the same, equivalent, or similar purpose unless stated otherwise. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

  All of the features disclosed herein may be combined in all combinations, except combinations where at least some of such features and / or steps are mutually exclusive. In particular, the preferred features of the invention are applicable to all aspects of the invention and may be used in all combinations. Similarly, features described in non-essential combinations may be used separately (not in combination).

  It will be appreciated that many of the features described above, particularly preferred embodiments, are independently novel and at the same time are not merely part of the embodiments of the present invention. Independent protection may be sought for these features in addition to or in lieu of all inventions claimed in this application.

Use the following abbreviations:
Clp. Clearing point (nematic-isotropic phase transition temperature),
SN smectic-nematic phase transition temperature,
Δn optical anisotropy (589 nm, 20 ° C.),
Δε dielectric anisotropy (1 kHz, 20 ° C.),
ν _T fluid viscosity (mm ² · s ^{−1 at} T / ° C.),
γ ₁ rotational viscosity (mPa · s at 20 ° C),
k ₁ elastic constant (“spread”, pN at 20 ° C.),
k _” elastic constant (“ twist ”, pN at 20 ° C.),
k ₃ elastic constant ( "bend", pN at 20 ℃),
S Steepness of characteristic curve = (1−V ₉₀ / V ₁₀ ) ^* 100,
d Cell gap (μm),
P cholesteric pitch (μm at 20 ° C.),
Helical twisting force of HTP S-811 (μm ⁻¹ at 20 ° C.),

V ₁₀ threshold voltage = characteristic voltage at a relative contrast of 10%,
V ₅₀ mid-grey voltage = characteristic voltage at 50% relative contrast,
V ₉₀ saturation voltage = characteristic voltage at a relative contrast of 90%,
Response time τ _on + τ _{off at} τ V (τ _on = τ _off )
τ _on Relative contrast increase time from 0% to 90% τ _off Relative contrast decrease time from 100% to 10% M Multiplex ratio and B bias ratio.

  In this specification, all temperatures are given in ° C. Percentages are weight percent. All values relate to 20 ° C unless stated otherwise. The display has a twist of 240 ° and is addressed with a multiplex ratio of 1/64 and a bias of 1/7 unless stated otherwise. Unless otherwise stated, the optical delay is 0.85 μm and the d / P ratio is 0.52.

The invention will now be described in greater detail by reference to the following examples, which are illustrative only and do not limit the scope of the invention.
The liquid crystal mixtures shown in the following examples are themselves prepared and investigated. Next, STN displays, each containing one of these liquid crystal mixtures, are manufactured and investigated. The respective compositions and the corresponding results are shown below.

Example 1

Example 2

Example 3

Example 4

Example 5

Example 6

Example 7

Example 8

Example 9

Example 10

Example 11

Example 12

Example 13

Example 14

Example 15

Example 16

Example 17

Example 18

Example 19

Example 20

Example 21

Example 22

Example 23

Example 24

Example 25

Example 26

Example 27

Example 28

Example 29

Example 30

Example 31

Example 32

Example 33

Example 34

Claims (9)

A liquid crystal medium for a TN or STN liquid crystal display, which is of formula I
And a compound represented by the following formula:
Wherein R ^3a is H, CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ and “alkyl” is an alkyl group having 1 to 8 carbon atoms.
The liquid crystal medium comprising one or more compounds selected from the group consisting of: Furthermore, the formula II
Where
A is 1,4-phenylene or trans-1,4-cyclohexylene;
a is 0 or 1,
R ³ is an alkenyl group having 2 to 9 carbon atoms;
R ⁴ is an alkyl group having 1 to 12 carbon atoms that is unsubstituted, monosubstituted by CN or CF ₃ , or at least monosubstituted by halogen, wherein these One or more CH ₂ groups in the group are also each independently of the other such that —O—, —S—, —CH═CH—, —C≡ so that the O atoms are not directly bonded to each other. Optionally substituted by C-, -CO-, -CO-O-, -O-CO- or -O-CO-O-,
The liquid crystal medium according to claim 1, comprising one or more compounds represented by the formula: Furthermore, the following formula
Where
R is an alkyl, alkoxy or alkenyl group having 1 to 12 carbon atoms, wherein one or more CH ₂ groups in these groups are also each independently of one another O May be substituted by -O-, -CH = CH-, -CO-, -OCO- or -COO- so that the atoms are not directly bonded to each other;
L ¹ , L ² , L ³ and L ⁴ are independently of each other H or F.
The liquid crystal medium according to claim 1, comprising one or more compounds selected from the group consisting of: Furthermore, the following formula
Where
R ¹ and R ² are each independently an alkyl group having 1 to 12 carbon atoms that is unsubstituted, monosubstituted by CN or CF ₃ , or at least monosubstituted by halogen Where one or more CH ₂ groups in these groups are also, independently of each other, such that the O atoms are not directly bonded to each other, —O—, —S—, — Optionally substituted by CH═CH—, —C≡C—, —CO—, —CO—O—, —O—CO— or —O—CO—O—,
The liquid crystal medium according to claim 1, comprising one or more compounds selected from the group consisting of: Furthermore, the following formula
Where
R ¹ and R ² are each independently an alkyl group having 1 to 12 carbon atoms that is unsubstituted, monosubstituted by CN or CF ₃ , or at least monosubstituted by halogen Where one or more CH ₂ groups in these groups are also, independently of each other, such that the O atoms are not directly bonded to each other, —O—, —S—, — Optionally substituted by CH═CH—, —C≡C—, —CO—, —CO—O—, —O—CO— or —O—CO—O—,
L is H or F.
The liquid crystal medium according to claim 1, comprising one or two or more compounds selected from the group consisting of: Furthermore, the formula II ^*
Where
R ³ is an alkenyl group having 2 to 7 carbon atoms,
Q is CF ₂ , OCF ₂ , CFH, OCFH or a single bond,
Y is F or Cl;
L ¹ and L ² are independently of each other H or F.
The liquid-crystal medium in any one of Claims 1-5 containing 1 type, or 2 or more types of compounds represented by these. -2 to 30% of a compound of formula I,
-3 to 30% of a compound of formula IV24a and / or IV24b,
−8 to 70% of compounds of formulas IIa to IIi and / or II ^* ,
-4 to 50% of a compound represented by the formula Ta to Tc,
-5-40% of compounds of formula IIIa-IIIi,
Liquid crystal medium according to any one of claims 4 to 6, characterized in that it contains from 0 to 20% of a compound of the formula IV12 and / or IV27 and / or IV32. Two outer plates forming cells with the frame,
A nematic liquid crystal mixture with positive dielectric anisotropy arranged in the cell,
An electrode layer having an alignment layer on the inside of the outer plate,
Liquid crystal mixture in the cell for each alignment layer having a tilt angle between the major axis of the molecule on the surface of the outer plate and the outer plate of −0 ° to 30 ° and a value of −22.5 ° to 600 °. Twist angle,
-A) consisting of one or more compounds having a dielectric anisotropy higher than +1.5 and having the formula II ^*
Where
R ³ is an alkenyl group having 2 to 7 carbon atoms,
Q is CF ₂ , OCF ₂ , CFH, OCFH or a single bond,
Y is F or Cl;
L ¹ and L ² are independently of each other H or F.
Liquid crystal component A containing 15 or 75% by weight of one or more compounds represented by:
b) consisting of one or more compounds having a dielectric anisotropy of -1.5 to +1.5 and having the formula I
A liquid crystal component B25 to 85% by weight, and c) one or more compounds having a dielectric anisotropy lower than −1.5, and a structural unit 2,3-difluoro- Liquid crystal component D0 to 20% by weight containing one or more compounds containing 1,4-phenylene
A TN or STN liquid crystal display having a nematic liquid crystal mixture comprising
The display according to claim 1, wherein the nematic liquid crystal mixture is the medium according to claim 1.   A method for preparing a liquid crystal medium according to any one of claims 1 to 7, wherein the composition according to claim 1 is converted into one or more compounds according to any one of claims 2 to 7, or Said process by mixing with one or more other compounds and / or additives.