WO1991016396A1

WO1991016396A1 - Liquid crystalline medium

Info

Publication number: WO1991016396A1
Application number: PCT/EP1991/000687
Authority: WO
Inventors: David Coates; Bernhard Rieger; Reinhard Hittich; Eike Poetsch; Volker Reiffenrath; Herbert Plach
Original assignee: MERCK Patent Gesellschaft mit beschränkter Haftung
Priority date: 1990-04-13
Filing date: 1991-04-11
Publication date: 1991-10-31
Also published as: EP0477327A1

Abstract

This invention relates to a liquid crystalline medium based on a mixture of polar compounds with a positive dielectric anisotropy which contains one or more compounds of the general formula (I) in which: L?1, L2 and L3¿ are H or F, X is F, Cl, CF¿3?, OCF3 or OCHF2; one of the radicals Q?1 and Q2 is -C2H¿4- and the other a single bound; and R is alkyl, oxa-alkyl, fluoroalkyl or alkenyl with up to 7 C atoms.

Description

Liquid crystalline medium

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

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

The liquid crystal materials must have good chemical and thermal stability and good stability against electric fields and electromagnetic radiation. Furthermore, the liquid crystal materials should have a low viscosity and result in short response times, low threshold voltages and a high contrast in the cells. Furthermore, they should have a suitable mesophase at the usual operating temperatures, ie in the widest possible range below and above room temperature, for example a nematic or cholesteric mesophase for the above-mentioned cells. Since liquid crystals are generally used as mixtures of several components, it is important that the components are readily miscible with one another. Other properties, such as the electrical

Conductivity, dielectric anisotropy and optical anisotropy have to meet different requirements depending on the cell type and area of application. For example, materials for cells with a twisted nematic structure should have positive dielectric anisotropy and low electrical conductivity.

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

Such matrix liquid crystal displays are known. For example, active elements (ie transistors) can be used as non-linear elements for the individual switching of the individual pixels. One speaks then of an "active matrix", whereby one can distinguish two types: 1. MOS (Metal Oxide Semiconductor) transistors on silicon wafers as substrates.

2. Thin film transistors (TFT) on a glass plate as a substrate.

The use of monocrystalline silicon as the substrate material limits the size of the display, since the modular composition of various partial displays at the joints also leads to problems.

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

The TFT matrix is applied to the inside of one glass plate of the display, while the other glass plate carries the transparent counter electrode on the inside. Compared to the size of the pixel electrode, the TFT is very small and practically does not disturb the image. This technology can also be expanded for fully color-compatible image representations, a mosaic of red, green and blue filters being arranged in such a way that a filter element is located opposite a switchable image element.

The TFT displays work ϊih. ic. usually as TN cells with crossed polarizers in transmission and are illuminated from behind. The term MFK displays here includes every matrix display with integrated non-linear elements, ie in addition to the active matrix also displays with passive elements such as varistors or diodes (MIM = metal-insulator-metal).

Such MFK displays are particularly suitable for TV applications (e.g. pocket TVs) or for high-information

Displays for computer applications (laptop) and in automobile or aircraft construction. In addition to problems with the angle dependence of the contrast and the switching times, there are difficulties with MLC displays due to the insufficiently high specific resistance 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. 141 ff, Paris; STROMER, M., Proc. Eurodisplay 84, Sept. 1984: Design of Thin Film Transistors for Matrix Adressing of Television Liquid Crystal Displays, p. 145 ff, Paris. With decreasing resistance, the contrast of an MLC display deteriorates and the problem of "after image elimination" can occur. Since the resistivity of the liquid crystal mixture generally decreases over the lifetime of an MLC display due to interaction with the inner surfaces of the display, a high (initial) resistance is very important in order to obtain acceptable service lives. In the case of low-voltage mixtures in particular, it has so far not been possible to achieve very high specific resistances. It is also important that the specific resistance shows the smallest possible increase with increasing temperature and after temperature and / or UV exposure. The state-of-the-art MFK displays do not meet today's requirements. There is therefore still a great need for MLC displays with a very high specific resistance with a large working temperature range, short switching times and low threshold voltage, which do not show these disadvantages or only show them to a lesser extent.

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

- extended nematic phase range (especially at low temperatures)

- Switchability at extremely low temperatures (out-door use, automotive, avionics) - Increased resistance to UV radiation (longer service life)

With the media available from the prior art, it is not possible to realize these advantages while maintaining the other parameters.

In the case of higher twisted cells (STN), media are desired which enable greater multiplexability and / or lower threshold voltages and / or wider nematic phase ranges (in particular at low temperatures). For this, a further expansion of the available parameter space (clearing point, smectic-nematic transition or

Melting point, viscosity, dielectric sizes, elastic sizes) urgently desired. The object of the invention is to provide media, in particular for such MFK, TN or STN displays, which do not have the disadvantages indicated above or only to a lesser extent, and preferably at the same time have very high resistivities and low threshold voltages.

It has now been found that this object can be achieved if media according to the invention are used in advertisements.

The invention thus relates to a liquid-crystalline medium based on a mixture of polar compounds with positive dielectric anisotropy, characterized in that it contains one or more compounds of the general formula I.

contains, wherein L ¹ , L ² and L ³ each H or F, XF, Cl, CF ₃ ,

OCF ₃ or OCHF ₂ , one of the radicals Q ¹ and Q ² -C ₂ H ₄ - and the other radical Q ¹ or Q ² a single bond and R alkyl,

Oxaalkyl, fluoroalkyl or alkenyl, each having up to 7 carbon atoms.

The invention also relates to electro-optical displays (in particular STN or MFK displays with two plane-parallel carrier plates which form a cell with a border, integrated non-linear elements for switching individual pixels on the carrier plates and one in the cell located 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 allow a significant expansion of the available parameter space.

The achievable combinations of clearing point, viscosity at low temperature, thermal and UV stability and dielectric anisotropy far exceed previous materials from the prior art.

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

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

At low viscosities and at low temperatures (at -30 ° C. <600, preferably <550 mPa.S; at -40 ° C. <1800, preferably <1700 mPa.s), the liquid crystal mixtures according to the invention simultaneously enable dielectric anisotropy values Δε ≥ 3 , 5, preferably ≥ 4, 0, clear points above

65 °, preferably above 70 ° and to achieve a high value for the specific resistance, as a result of which excellent STN and MKF displays can be achieved. It goes without saying that, by a suitable choice of the components of the mixtures according to the invention, higher clearing points (for example above 90 °) at higher threshold voltages or lower clearing points at lower threshold voltages can be achieved while maintaining 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], where in addition to particularly favorable electro-optical properties such as high slope of the characteristic and low angle dependence of the contrast (DE-PS 30 22 818) with the same threshold voltage as in an analog display in the second At least a smaller dielectric anisotropy is sufficient. This allows the use of the mixtures according to the invention in the first minimum to achieve significantly higher specific resistances than in the case of mixtures with cyan compounds. The person skilled in the art can set the birefringence required for a given layer thickness of the MLC display by means of suitable routine selection of the individual components and their proportions by weight.

The viscosity at 20 ° C is preferably 25 mPa.s. The nematic phase range is preferably at least 70 °, in particular at least 80 °. This range preferably extends at least from -30 ° to + 70 °. Capacity holding ratio (Hr) measurements [S.Matsumoto et al., Liquid Crystals 5th, 1320 (1989); K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984); G. Weber et al., Liquid Crystals 5, 1381 (1989)] have shown that mixtures according to the invention containing compounds of the formula I have a significantly smaller decrease in HR with increasing temperature than analog mixtures containing cyanophenylcyclohexanes of the formula instead of the compounds of the formula I.

The UV stability of the mixtures according to the invention is also considerably better. H. they show a significantly smaller decrease in HR under UV exposure.

In addition to an unusually wide nematic phase range, the media according to the invention are also distinguished by extraordinarily high elastic constants with very favorable viscosity values, which results in distinct advantages over media from the prior art, particularly when used in STN displays.

The media according to the invention are preferably based on several (preferably two or more) compounds of the formula I, i.e. the proportion of these compounds is> 25%, preferably> 40%.

The individual compounds of the formulas I to XII and their sub-formulas which can be used in the media 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

Formula II, III and IV:

II

III IV

where the individual radicals have the following meanings:

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

X: F, Cl, CF ₃ , OCF ₃ or OCHF ₂

Y ¹ and

Y ² : each independently of one another H or F r: 0 or 1. - Medium additionally contains one or more compounds selected from the group consisting of the general formulas V to VIII:

V

VI

VII

VIII

wherein R, X and Y ¹ and Y ² each independently had one of the meanings given in claim 1.

- Medium additionally contains one or more compounds selected from the group consisting of the general formulas IX to XIV:

IX

X

XI

XII

XIII

XIV

wherein R, X and Y ¹ and Y ² each independently have one of the meanings given in claim 1. - The proportion of compounds of the formulas I to IV together is at least 50% by weight in the total mixture - the proportion of compounds of the formula I is in the

Total mixture 10 to 50 wt .-% - the proportion of compounds of the formulas II to IV in

Total mixture is 30 to 70% by weight -

- The medium contains compounds of the formulas II and III or IV - instep straight-chain alkyl or alkenyl with 2 to 7

C atoms - The medium essentially consists 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 preferably 1: 4 to 1: 1. - Medium essentially consists of compounds selected from the group consisting of the general formulas I to XIV.

It has been found that a relatively small proportion of compounds of the formula I in a mixture with conventional liquid crystal materials, but in particular with one or more compounds of the formula II, III and / or IV leads to a considerable improvement in the response times and to low threshold voltages, where At the same time broad nematic phases with low transition temperatures can be observed smectically nematically. The compounds of the formulas I to IV are colorless, stable and readily miscible with one another and with other liquid crystal materials.

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

The term "alkenyl" encompasses straight-chain and branched alkenyl groups having 2-7 carbon atoms, in particular the straight-chain groups. Alkenyl groups in particular are 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, 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 encompasses straight-chain groups with terminal fluorine, ie fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. However, other positions of the fluorine are not excluded.

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

The response times, the threshold voltage, the steepness of the transmission characteristics, etc. can be modified in a desired manner by a suitable choice of the meanings of R, X and Y. For example, 1E-alkenyl residues, 3E-alkenyl residues, 2E-alkenyloxy residues and the like generally lead to shorter response times, improved nematic tendencies and a higher ratio of the elastic constants k ₃₃

(bend) and k ₁₁ (splay) compared to alkyl or alkoxy radicals. 4-alkenyl residues, 3-alkenyl residues and the like generally give lower threshold voltages and smaller values of k ₃₃ / k ₁₁ compared to alkyl and alkoxy residues. A group -CH ₂ CH ₂ - in Z ¹ or Z ² generally leads to higher ones

Values of k ₃₃ / k ₁₁ compared to a simple covalent bond. For example, higher values of k ₃₃ / k ₁₁ enable flatter ones

Transmission characteristics in TN cells with 90 ° twist (for

Achievement of gray tones) and steeper transmission characteristics in STN, SBE and OMI cells (higher multiplexability) and vice versa. The optimal quantitative 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 on the choice of further components which may be present. Suitable proportions within the range given above can easily be determined from case to case.

The total amount of compounds of the formulas I to XII in the mixtures according to the invention is not critical. The mixtures can therefore contain one or more further components in order to optimize various properties. However, the observed effect on the response times and the threshold voltage is generally greater the higher the total concentration of compounds of the formulas I to XIV.

In a particularly preferred embodiment, the media according to the invention contain compounds of the formula II, III, V and / or VII (preferably II and / or III), in which X is CF ₃ , OCF ₃ or OCHF ₂ . A favorable synergistic effect with the compounds of formula I leads to particularly advantageous properties.

For STN applications, the media preferably contain compounds selected from the group consisting of the formulas V to VIII, where X preferably denotes OCHF ₂ .

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

wherein

R ¹ and R ² each independently of one another n-alkyl, fluoroalkyl or n-alkenyl having up to 9 carbon atoms, the rings A ¹ , A ² and A ³

each independently 1,4-phenylene, 2- or 3-fluoro-1,4-phenylene, trans-1,4-cyclohexylene or 1,4-cyclohexenylene,

Z ¹ and Z ^{2 are} each independently of one another -CH ₂ CH ₂ -, C≡C-,

-CO-O-, -O-CO-, or a single bond, and m represents 0, 1 or 2.

Component A preferably contains one or more compounds selected from the group consisting of II1 to II7: II1 II2 II3

II4 II5

II6 II7

wherein R ¹ and R ^{2 have} the meaning given for formula I '.

Component A preferably additionally contains one or more compounds selected from the group consisting of II8 to II20: II8 II9 II10 II11 II12 II13 II14 II15

II16 II17

II18 II19

wherein R ¹ and R ^{2 have} the meaning given for formula I 'and the 1,4-phenylene groups in II8 to II17 each

independently of one another can also be substituted one or more times by fluorine.

Component A also preferably contains one or more compounds selected from the group consisting of II21 to II25 and contains: II21 II22 II23 II24

wherein R ¹ and R ^{2 have} the meaning given in formula I 'and the 1,4-phenylene groups in II21 to II25 each

can be substituted one or more times independently of one another by fluorine. Finally, mixtures of this type are preferred, whose component A contains one or more compounds selected from the group consisting of 1126 and 1127: II26 II27

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

Is C atoms.

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

wherein

R ¹ and R ^{2 have} the meaning given for formula I 'and

Z ° a single bond, -CH ₂ CH ₂ -, or

CH ₂ CH ₂ -

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

Also preferred are liquid crystal mixtures which contain one or more compounds selected from the group consisting of III 'and IV:

III 'IV'

wherein Ri and R ^{2 have} the meaning given for formula I '. The type and amount of polar compounds with positive dielectric anisotropy is not critical. The person skilled in the art can select suitable materials in simple routine tests from a wide range of known and in many cases also commercially available components and base mixtures. The media according to the invention preferably contain one or more compounds of the formula I "

I "

wherein Z ¹ , Z ² and m have the meaning given for formula I ', Q ¹ and Q ² each independently of one another 1,4-phenylene, trans-1, 4-cyclohexylene or 3-fluoro-1,4-phenylene or one of the radicals Q ¹ and Q ² also means trans-1,3-dioxane-2, 5-diyl, pyrimidine-2, 5-diyl, pyridine-2, 5-diyl or 1,4-cyclohexenylene. R ° n-alkyl, n-alkenyl, n-alkoxy or n-oxaalkyl, each having up to 9 carbon atoms, YH or F and X 'CN, halogen, CF ₃ , OCF ₃ or OCHF ₂ . In a preferred embodiment, the media according to the invention for STN or TN applications are based on compounds of the formula I "in which X 'is CN. It is understood that smaller or larger proportions of other compounds of the formula I"(X' = CN) come into question. For MLC applications, the media according to the invention preferably contain only up to about 10% of nitriles of the formula I "(but preferably no nitriles of the formula I", but compounds of the formula I 'with X' = halogen, CF ₃ , OCF ₃ or OCHF ₂ ). These media are preferably based on the compounds of the formulas II to XII.

The structure of the STN or MFK display according to the invention from polarizers, electrode base plates and electrodes with surface treatment corresponds to the design customary for such displays. The term conventional construction is broadly encompassed here and also includes all modifications and modifications of the MLC display, in particular also matrix display elements based on poly-Si TFT or MIM. A significant difference between the displays according to the invention and those previously used on the basis of the twisted nematic cell, however, is the choice of the liquid crystal parameters of the liquid crystal layer. The liquid crystal mixtures which can be used according to the invention are prepared in a manner which is conventional per se. As a rule, the desired amount of the components used in smaller amounts is dissolved in the components which make up the main constituent, advantageously at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent after thorough mixing, for example by distillation.

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

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

V ₁₀ denotes the voltage for 10% transmission (viewing direction perpendicular to the plate surface). t _on denotes the

Switch-on time and t _off the switch-off time for an operating voltage corresponding to 2.5 times the value of V ₁₀ . Δn denotes the optical anisotropy and n ₀ the refractive index. Δε denotes the dielectric anisotropy (Δε = ε ₁ where

the dielectric constant parallel to the longitudinal axes of the molecules and

means the dielectric constant perpendicular to it. The electro-optical data were measured in a TN cell at the 1st minimum (ie at a d n 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 limiting it. All temperatures above and below are given in ° C. The percentages are percentages by weight.

In the present application and in the following examples, the structures of the liquid crystal compounds are indicated by acronyms, the transformation into chemical formulas taking place according to Tables A and B below. All radicals C _n H _{2n + 1} are straight-chain alkyl radicals with n or m carbon atoms. The coding according to Table B goes without saying. In

Table A shows only the acronym for the base body. In individual cases, a code for the substituents R ¹ , R ² , L ¹ , L ² and L ³ follows with a dash, separately from the acronym for the base body:

Table A:

Table B:

example 1

PCH-3 9%.

EBCH-3F 8%

EBCH-3F.F 10%

BECH-3F.F 8% T _c = 73 ° C

CCP-2OCF ₃ 6% Δn = 0.09

CCP-3OCF ₃ 13%

CCP-4OCF ₃ 8%

CCP-5OCF ₃ 13%

CBC-33F 2%

CBC-55F 3%

PCH-5F 10%

PCH-7F 10%

Example 2

PCH-3Cl 12%

PCH-5Cl 10%

PCH-3Cl.F 10%

BECH-3F.F 8%

CCP-2F.F 8%

CCP-3F.F 12%

CCP-5F.F 12%

CCB-3.FF 3%

CCB-5.FF 3%

BCH-3F.F 12%

BCH-5F.F 10% Example 3

PCH-3 9%

EBCH-3F 10%

EBCH-3F.F 12%

BECH-3F.F 9% T _c = 70 ° C

CCP-2OCF ₃ 5% Δn = 0.09

CCP-3OCF ₃ 13%

CCP-4OCF ₃ 5%

CCP-5OCF ₃ 12%

CBC-33F 2%

CBC-5F 3%

PCH-5F 10%

PCH-6F 10%

Example 4

PCH-3Cl 15%

PCH-5Cl 10%

PCH-3Cl.F 10%

BECH-3F.F 10%

CCP-2F.F 10%

CCP-3F.F 12%

CCP-5F.F 12%

CCB-3.FF 3%

CCB-5.FF 3% Example 5

PCH-5F.F 5% T _c = 66 ° C

PCH-6F.F 3% Δn = 0.090

PCH-7F.F 4% V ₁₀ = 1.4 V

CCP-2OCF3.F 9% η = 21 mPa.s

CCP-3OCF3.F 12%

CCP-4OCF3.F 10%

CCP-5OCF3.F 12%

CUP-2F 6%

CUP-3F 9%

CUP-5F 11%

CEUP-3F 10%

CEUP-5F 9%

Example 6

PCH-5F.F 5% T _c = 95 ° C

PCH-7F.F 6% V ₁₀ = 1.85 V

CCP-2OCF3.F 7% Δn = 0.090

CCP-3OCF3.F 10%

CCP-5OCF3.F 9%

CUP-3F 12%

CUP-5F 12%

CEUP-3F 11%

CEUP-5F 12%

CCB-3.FOCF3 6%

CCB-4.FOCF3 5%

CCB-5.FOCF3 5% Example 7

PCH-5CL.F 5% T _c = 97 ° CC

PCH-7CL.F 6% V ₁₀ = 1.8 V

CCP-2OCF3.F 7% Δn = 0.099

CCP-3OCF3.F 10%

CCP-5OCF3.F 9%

CUP-3F 12%

CUP-5F 12%

CEUP-3F 11%

CEUP-5F 12%

CCB-3.FOCF3 6%

CCB-4.FOCF3 5%

CCB-5.FOCF3 5%

The above liquid-crystalline media of Examples 1 to 7 are particularly suitable for MLC displays.

With the aid of the compounds of formula I, however, liquid-crystalline media for STN displays can also be produced.

The liquid-crystalline media for STN displays according to the invention generally have a birefringence between 0.12 and 0.17, preferably 0.12 and 0.15, in particular 0.125 and 0.145.

In addition to the compounds of the formula I, they contain, as polar compounds, one, two or more compounds of the formula I ", preferably those in which X 'is CN or Cl, in particular those selected from the group consisting of I" a to I "u:

l

wherein R ° and X 'has the meaning given for formula I ". The 1,4-phenylene group of the formulas I" a to I "u can be substituted 1 or more times by fluorine. Furthermore, the media according to the invention for STN displays contain 0-40%, preferably 5% to 35%, in particular 10% to 30% of a liquid-crystalline component of the formula I 'with a dielectric anisotropy of -1.5 to +1.5, in particular selected from the group I'a to I'n:

c

i l

in which R ¹ and R ^{2 have} the meaning given for formula I ', but preferably alkyl or alkoxy having 1 to 8, in particular 2 to 5, carbon atoms and the 1,4-phenylene groups, independently of one another, also by fluorine can be substituted several times.

The liquid crystal mixtures used in the STN displays are dielectrically positive with Δε> 1, preferably ≥ 3, in particular ≥ 5.

They have favorable values for the threshold voltage V _th and for the flow viscosity.

The STN mixtures according to the invention are further characterized by advantageous values for the steepness of the electro-optical characteristic curve and can be operated at high multiplex rates.

In addition, they have high stability and favorable values for the electrical resistance and the frequency dependence of the threshold voltage.

The following examples relate to liquid-crystalline media according to the invention for STN cells: Example A

It becomes a liquid crystalline medium for an STN cell

(Twist 240 °), consisting of:

ECCP-3Cl 10.4%

ECCP-5Cl 14.4%

ECCP-5Cl.F 10.4%

PCH-3 9.6%

G9 10.4%

K6 9.6%

CCPC-35 4.8%

D-35 8.0%

ME-2N.F 2.4% 20.0%

This mixture has the following physical properties:

N - I = 99 ° C; Δn = 0, 138 / viscosity (20 ° C) = 24 mm ² / s; V _th = 2.43 volts.

Example B

A liquid-crystalline medium for an STN cell (twist 240 °) is produced, consisting of: ECCP-3Cl 10.4%

ECCP-5Cl 14.4%

ECCP-5Cl.F 10.4%

PCH-3 9.6% G9 10.4%

K6 9.6%

CCPC-35 4.8%

D-35 8.0%

ME-2N.F 2.4% 20.0%

This mixture has the following physical properties:

N - I = 89 ° C; Δn = 0.128; Viscosity (20 ° C) = 23 mm ² / s; V _th = 2.23 volts. Example C

A liquid-crystalline medium for an STN cell (twist 240 °) is produced, consisting of: ECCP-3Cl 8.0%

ECCP-5Cl 8.0%

ECCP-5Cl.F 4.0%

ECCP-3Cl.F 6.4%

K6 9.6%

K9 8.0%

CCPC-35 4.0%

CCPC-33 3.2%

PCH-302 8.8%

CCH-302 20.0% 20.0%

This mixture has the following physical properties:

N - I = 87 ° C; Δn = 0.122 / viscosity (20 ° C) = 17 mm ² / s; V _th = 2.26 volts.

Example D

A liquid-crystalline medium for an STN cell (twist 240 °) is produced, consisting of:

ECCP-3Cl 8.0%

ECCP-5Cl 8.0%

ECCP-5Cl.F 4.0%

ECCP-3Cl.F 6.4%

K6 9.6%

K9 8.0%

CCPC-35 4.0%

CCPC-33 3.2%

PCH-302 8.8%

CCH-302 20.0%

F

20.0%

This mixture has the following physical properties:

N - I = 93 ° C; Δn = 0.131 / viscosity (20 ° C) = 19 mm ² / s;

V _th = 2.35 volts. Example E

ECCP-3Cl 8.0%

ECCP-5Cl 8.0%

ECCP-5Cl.F 4.0%

ECCP-3Cl.F 6.4%

K6 9.6%

K9 8.0%

CCPC-35 4.0%

CCPC-33 3.2%

PCH-302 8.8%

CCH-302 20.0%

20.0%

This mixture has the following physical properties:

N - I = 87 ° C; Δn = 0.123 / viscosity (20 ° C) = 18 mm ² / s; V _th = 2.40 volts. Example F

PCH-3CL 10.0%

PCH-5CL 10.0%

ECCP-3CL 12.0%

ECCP-5CL 12.0%

ECCP-3CL.F 6.0%

CCPC-33 5.0% K6 10.0%

PCH-3 10.0%

G9 5.0%

CBC-33F 3.0%

PYP-3N.F 3.0%

PYP-5N.F 4.0%

10.0%

This mixture has the following properties:

NI 85 ° C; Δn = 0.134 / viscosity (20 ° C): 21 mm ² / s

Δε = +10.6 Example G

PCH-3CL 10.0%

PCH-5CL 10.0%

ECCP-3CL 12.0%

ECCP-5CL 12.0%

ECCP-3CL.F 6.0%

CCPC-33 5.0%

K6 10.0%

PCH-3 10.0%

G9 5.0%

CBC-33F 3.0%

ME3N.F 7.0% 10.0%

This mixture has the following physical properties: NI 85.5 ° C; Δn = 0, 132 / viscosity (20 ° C): 21 mm ² / s;

Δε = 11.0.

Example H

EPCH-3CL 10.0%

PCH-5CL 10.0%

ECCP-3CL 12.0%

ECCP-5CL 12.0%

ECCP-3CL.F 6.0%

CCPC-33 5.0%

K6 10.0%

PCH-3 10.0%

G9 5.0%

CBC-33F 3.0%

ME3N.F 7.0% 10.0%

This mixture has the following physical properties:

NI = 87.5 ° C; Δn = 0.131 / viscosity (20 ° C) = 21 mm ² / s; Δε = 11.0.

Example I

PCH-3CL 10.0%

PCH-5CL 10.0%

ECCP-3CL 12.0%

ECCP-5CL 12.0%

ECCP-3CL.F 6.0% CCPC-33 5.0%

K6 6.0%

PDX-3 10.0%

G9 9.0%

CBC-33F 3.0%

ME3N.F 7.0% 10.0%

This mixture has the following physical properties:

NI = 86 ° C; Δn = 0.129 / viscosity (20 ° C) = 22 mm ² / s; Δε = +12.4.

Example J

ECCP-3CL 15.0%

ECCP-5CL 14.0%

PCH-3 10.0%

BECH-3CL.F 12.0%

EBCH-3CL.F 6.0%

EBCH-5CL 6.0%

PYP-3N.F 6.0%

PDX-3 5.0%

CCPC-33 5.0%

CBC-33F 5.0%

PDX-5 4.0% 12.0%

This mixture has the following physical properties:

NI = 120 ° C; Δn = 0.146 / viscosity (20 ° C) = 29 mm ² / s; Δε = +10.0.

Example K

ECCP-3CL 15.0%

ECCP-5CL 14.0%

PCH-3 10.0%

BECH-3CL.F 12.0%

EBCH-3CL.F 6.0%

EBCH-5CL 6.0%

PYP-3N.F 6.0%

PDX-3 5.0%

CCPC-33 5.0%

PDX-5 4.0%

This mixture has the following physical properties:

NI 118 ° C; Δn = 0.149 / viscosity (20 ° C) = 29.0 mm ² / s; Δε = 10.3.

Example L

ECCP-32 12.0%

ECCP-35 12.0%

PCH-3 12.0%

G9 10.0%

PDX-3CL 8.0%

FET-5CL 10.0% BECH-3CL.F 10.0%

CCPC-33 7.0%

K6 10.0%

PYP-3N.F 4.0%

PYP-5N.F 5.0%

This mixture has the following physical properties:

NI = 82.4 ° C; Δn = 0.142 / viscosity (20 ° C) = 23 mm ² / s; Δε = +10.8.

Example M

CEUP-5CL 12.0%

CEUP-5C1.F 10.0%

ECCP-3CL 10.0%

ECCP-5CL 10.0%

PCH-3 10.0%

G9 10.0%

PCH-3CL 10.0%

PYP-3N.F 5.0%

CCPC-33 4.0%

K6 4.0%

15.0%

This mixture has the following physical properties:

NI 75.5 ° C; Δn = 0.131 / viscosity (20 ° C) = 22 mm ² / s; Δε = +9.9. Example N

A basic mixture (A) consisting of

ECCP-3CL.F 9%

ECCP-5CL.F 5%

ECCP-3CL 10%

ECCP-5CL.F 10%

K6 12%

K9 10%

CCH-303 25%

PCH-302 11%

CCPC-33 4%

CCPC-35 5% has the following properties:

NI 87.5 ° C; Δn = 0.118; Viscosity (20 ° C) 18 mm ² / s;

V _th = 2.31 volts.

STN mixtures according to the invention are produced, consisting of 80% base mixture (A) and 20% of a compound of the formula Ia

la

The physical properties of these mixtures can be found in Table I (threshold stress measured in a 180 ° twisted STN cell):

Example O

A basic mixture (B) consisting of

ECCP-3CL 12.98%

ECCP-5CL 17.98%

ECCP-5CL.F 13.07%

PCH-3 11.99%

G9 12.98%

K6 12%

CCPC-35 5.99%

D-35 10.01%

ME-2N.F 3.0% has the following physical properties:

NI = 94.9 ° C; Viscosity (20 ° C) = 23.05 mm ² / s, Δn = 0.1283;

V _th - 2.34 volts. STN mixtures according to the invention are produced consisting of different amounts of base mixture (B) and a compound of the formula Ia or CEUPnX.L ²

la

CEUP-nX.L ²

The physical properties of these mixtures can be found in Table II (threshold voltages measured in a 240 ° twisted STN cell)

Claims

1. Liquid-crystalline medium based on a mixture of polar compounds with positive dielectric anisotropy, characterized in that it contains one or more compounds of the general formula I.

I

contains, wherein L ¹ , L ² and L ³ each H or F, XF, Cl, CF ₃ , OCF ₃ or OCHF ₂ , one of the radicals Q ¹ and Q ² -C ₂ H ₄ - and the other radical Q ¹ or Q ^{2 is} a single bond and R is alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 7 carbon atoms.

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:

II

III

IV

where the individual radicals have the following meanings:

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

X: F, Cl, CF ₃ , OCF ₃ or OCHF ₂

Y ¹ and

Y ² : each independently of one another H or F r: 0 or 1.

3. Medium according to claim 1 or 2, characterized in that it additionally contains one or more compounds selected from the group consisting of the general formulas V to VIII:

V

VI

VII

VIII

wherein R, r, X, Y ¹ and Y ² each independently have one of the meanings entered in claim 2.

4. Medium according to at least one of claims 1 to 3,

characterized in that it additionally contains one or more compounds selected from the group consisting of the general formula IX to XIV:

IX X

XI

XII

XIII

XIV

wherein R, X, Y ¹ and Y ² each independently have one of the meanings given in claim 2.

5. Medium according to claim 2, characterized in that the proportion of compounds of the formulas I to IV together in the total mixture is at least 50% by weight.

6. Medium according to claim 1 or 2, characterized in that the proportion of compounds of formula I in the total mixture is 10 to 50 wt .-%.

7. Medium according to at least one of claims 2 to 4, characterized in that the proportion of compounds of the formulas II to IV in the mixture as a whole is 30 to 70% by weight.

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 the general formulas I to XIV.

9. Use of the liquid crystalline medium after

Claim 1 for electro-optical purposes.

10. Electro-optical liquid crystal display comprising a liquid crystalline medium according to claim 1.