JP2005232455A - Liquid crystal medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal medium having very short addressing and low threshold voltages for using in a field sequential mode LCD. <P>SOLUTION: The liquid crystal medium contains one or more compounds represented by formula IA and one or more compounds represented by formula IB (wherein R<SP>1</SP>, R<SP>2</SP>and R<SP>3</SP>each represent an alkyl group, ring A represents 1,4-phenylene, 1,4-cyclohexylene, r is 0 or 1, Y<SP>1</SP>to Y<SP>7</SP>each represent H or F, X<SP>0</SP>is F or OCF<SB>3</SB>). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal medium, its use for electro-optic purposes, and a display comprising this medium, in particular to a field sequential mode display.

  Liquid crystals are mainly used as a dielectric in a display device because the optical properties of a substance can be changed by an applied voltage. Electro-optical devices based on liquid crystals are known to those skilled in the art and can be based on various effects. Examples of such devices include cells with dynamic scattering, DAP (deformation of aligned phases) cells, guest / host cells, TN cells with twisted nematic structures, STN (super twisted nematic) cells, SBE. (Super birefringence effect) cell and OMI (Optical mode interference) cell. The most common display device has a twisted nematic structure based on the Schadt Helfrich effect.

  Liquid crystal materials must have good chemical and thermal stability, as well as excellent stability against electric fields and electromagnetic radiation. The liquid crystal material must also have low viscosity and be used in the cell to provide a short address time, low threshold voltage and high contrast.

  They must also have a suitable mesophase, such as a nematic or cholesteric mesophase for the aforementioned cell, at normal operating temperatures (ie, in the widest possible range above or below room temperature). Since liquid crystals are usually used as a mixture of multiple components, it is important that the components are easily miscible with each other. Furthermore, characteristics such as conductivity, dielectric anisotropy and optical anisotropy must satisfy various requirements depending on the cell type and application field. For example, twisted nematic cell materials should have positive dielectric anisotropy and low electrical conductivity.

  For example, for matrix liquid crystal displays (MLC displays) with integrated nonlinear elements for individual pixel switching, large positive dielectric anisotropy, wide nematic phase, relatively low birefringence, very high resistivity A medium with excellent UV and temperature stability and low vapor pressure is desired.

  This type of matrix type liquid crystal display is known. Non-linear elements that can be used for the respective switching of the individual pixels are, for example, active elements (ie transistors). The term “active matrix” is divided into two distinct types.

  1. MOS (metal oxide semiconductor) or other diode on a silicon wafer as substrate.

  2. A thin film transistor (TFT) on a glass plate as a substrate.

  The use of single crystal silicon as the substrate material limits the display size because even module assembly of various component displays creates problems at the connection.

  In the case of the more promising type 2, the TN effect is used as the electro-optic effect. There are two distinct technologies here. That is, for example, a TFT containing a compound semiconductor, such as CdSe, and a TFT based on polycrystalline or amorphous silicon.

  The TFT matrix is formed on the inner surface of one glass plate of the display, and the other glass plate has a transparent counter electrode on the inner surface. Compared to the size of the pixel electrode, the TFT is very small and has virtually no adverse effect on the image. This technology can also be applied to full color displays. There, a mosaic of red, green and blue filters is arranged so that the filter element faces each switchable pixel.

  A TFT display normally operates as a TN cell with a polarizing plate crossed against transmitted light and is illuminated from the back.

  The term MLC here includes any matrix display with integrated nonlinear elements. In other words, in addition to the active matrix, a display including a passive element such as a varistor or a diode (MIM = metal-insulator-metal) is also included.

This type of MLC display is particularly suitable for television applications (eg, pocket televisions), or advanced information display applications for computers (laptops) and used in automobiles or aircraft. In addition to the problem of contrast angle dependence and response time, MLC displays have problems due to insufficiently high resistivity of the liquid crystal mixture (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; and STROMER, M., Proc. Eurodisplay 84, Sept. 1984: Design of
Thin Film Transistors for Matrix Addressing of Television Liquid Crystal
Displays, p.145 ff, Paris). The lower the resistance, the worse the contrast of the MLC display and the afterimage erasure problem. The specific resistance of the liquid crystal mixture generally decreases over the life of the MLC display due to interaction with the internal surface of the display, so a high (initial) resistance is required to obtain an acceptable service life. It is very important to have In particular, in the case of a low-voltage mixture, it has heretofore been impossible to achieve a high resistance value. It is also important that the specific resistance decrease is as small as possible with increasing temperature and after heating and / or UV irradiation. Furthermore, the prior art mixtures are also particularly disadvantageous for low temperature properties, in particular so-called “low temperature stability” (LTS). It is required that no crystallization and / or smectic phase occur even at low temperatures, and that the temperature dependence of viscosity is also as low as possible. The MLC displays known in the prior art do not meet today's requirements.

  Therefore, an MLC display having a very high specific resistance, as well as a wide operating temperature range, a short response time even at low temperatures, and a low threshold voltage, which has or does not have these disadvantages However, there is a continuing need for something less.

  In a TN (Schadt-Helfrich) cell, a medium that facilitates the following advantages in the cell is desired.

-Extended nematic phase range (especially up to low temperatures)
-Switching capability at extremely low temperatures (outdoor applications, automobiles, avionics)
-Increased resistance to UV irradiation (longer lifetime)
With media available from the prior art, these advantages cannot be achieved while retaining other parameters at the same time.

  In the case of a super twist type (STN) cell, a medium that allows larger time-division driving and / or a lower threshold voltage and / or a wider nematic phase range (especially at low temperatures) is desired. For this purpose, it is urgently desired to further expand the range of available parameters (clearing point, smectic-nematic phase transition or melting point, viscosity, dielectric parameter, elastic parameter).

  For applications such as portable watches or calculators, a small monochrome display is typically used, but for applications such as televisions, notebooks, projection systems or camera viewfinders, a full color LCD is desired. The color is typically either by white backlight or ambient light by applying a color filter to the display cell that has a pattern of red (R), green (G) and blue (B) primary pixels in each LCD image. Produced. However, in the normally adopted absorptive RGB color filter, each addressed R, G, B pixel absorbs light of the other two primary colors, so that the brightness decreases. In addition, each LCD image pixel is divided into three RGB subpixels, resulting in a loss of image resolution.

  In order to solve this drawback, a field sequential (FS) LCD device has been proposed. There, instead of using a white backlight and a color filter, a color image is displayed by sequentially and periodically turning on and off light sources having R, G, and B colors. Thus, in the FS LCD, the individual primary color image fields are separated in time rather than in space, and there are only one third of the total display period, so in the case of a single field in a conventional additional color display. In the same way, the three primary color image fields will exist for the same time. FS LCDs therefore require liquid crystal materials with a very fast switching time among others. In addition, the liquid crystal material must have a low threshold voltage and appropriate birefringence so that it can accommodate the desired optical parameters of the display cell.

Accordingly, there is a need for liquid crystal media with very fast response times and low threshold voltages for use in FS LCDs.
Togashi, S. (TOGASHHI, S.), Sekiguchi, Kei. (SEKIGUCHI, K), Tanabe, H. (TANABE, H), Yamamoto, e. (YAMAMOTO, E), Sorimachi, Kei. (SORIMACHI, K), Tajima, e. (TAJIMA, E.), Watanabe, H. (WATANABE, H), Shimizu, H. (SHIMIZU, H), Eurodisplay 84 Proceedings (Proc. Eurodisplay), September 1984, “A 210-288 Matrix LCD Controlled by Double Stage Diode Rings” (A 210-288 Matrix LCD Controlled by Double Stage) (Diode Rings), page 141 et seq., Paris Stromer, M. (STROMER, M), Eurodisplay 84 Proceedings (Proc. Eurodisplay), September 1984, "Design of Thin Film Transistors" (Design of Thin Film Transistors) of Television Liquid Crystal Displays), 145th and later, Paris

  The invention particularly relates to media that do not have the disadvantages mentioned above, or to a lesser extent, if any, especially for MLC, TN or STN displays, preferably at the same time very much The object is to provide a material having a high specific resistance value, a low threshold voltage and a fast switching time. They are particularly suitable for field sequential mode displays.

  This object has been found to be achieved by using the media of the present invention in a display.

  The present invention therefore relates to a liquid crystal medium based on a mixture of polar compounds, which contains one or more compounds of the following formula IA and one or more compounds of the formula IB.

Here, R ¹ , R ² and R ³ are each independently an unsubstituted, mono-substituted by CN or CF ₃ or at least mono-substituted alkyl group having 1 to 12 carbon atoms by halogen, provided that In this group, one or two or more CH ₂ groups may be —O—, —S—, provided that the O atoms are not directly bonded to each other.

, -CH = CH-, -C≡C-, -CO-, -CO-O-, -O-CO- or -O-CO-O-
Y ^{1 to} Y ⁷ are each independently H or F,
X ⁰ is F, Cl, or a halogenated alkyl, halogenated alkenyl, halogenated alkoxy or halogenated alkenyloxy having up to 6 carbon atoms,
A is 1,4-phenylene, 2- or 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene or trans-1,4-cyclohexylene;
r is 0 or 1;

  In the pure state, the compounds of the formulas IA and IB are colorless and form a liquid-crystalline mesophase in the preferred temperature range for electro-optical use. They are chemically and thermally stable and stable to light.

R ¹ , R ² and R ³ in the formulas IA and IB are preferably straight-chain alkyl or alkoxy with up to 12 carbon atoms, very preferably with 2, 3, 4, 5, 6 or 7 carbon atoms.

X ⁰ described above and below is preferably F, Cl, CF ₃ , CHF ₂ , OCF ₃ , OCHF ₂ , OCFHCF ₃ , OCHFHCHF ₂ , OCHFCH ₂ F, OCF ₂ CH ₃ , OCF ₂ CH ₂ F, OCF ₂ CHF _{2, OCF 2 CF 2 CHF 2} , OCF 2 CF 2 CH 2 F, OCFHCF 2 CF 3, OCF 2 CHFCF 3, OCFHCF 2 CHF 2, OCF 2 CF 2 CF 3, OCF 2 CF 2 CClF 2, OCClFCF 2 CF 3 CH = CHF, CF═CF ₂ or CH═CF ₂ , most preferably F or OCF ₃ .

  In particular, preferred compounds of formula IA have the following formula:

Chosen from. Where R ¹ has the meaning defined in formula IA. Highly preferred are compounds of formula IA1.

  Particularly preferred are compounds of formula IB where r is 1. Further preferred are those of formula IB where A is 1,4-phenylene or trans-1,4-cyclohexylene.

  Particularly preferred compounds of formula IB are those selected from the following formulae:

Here, R ² and R ³ have the meanings defined for formula IB, and L ^{1 to} L ⁶ are H or F, independently of each other.

Compounds of formula IB6 are preferred, especially those in which L ^{1 to} L ⁶ are 1, 2 or 3 are F and the others are H, wherein each phenylene ring is 2 or more as L ^1-6 substituents It is preferable not to have F.

  Highly preferred are compounds of formula IB1, IB2 and IB3. Particularly preferred are compounds of formula IB1.

Compounds of formula IA and formula IB are preferably synthesized by methods known per se in the literature (for example the general literature, Houben-Weyl, Methoden der
Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart, etc.). Exactly known and suitable conditions are selected for such synthesis. Further, although not described in detail here, it is possible to use a different method known per se.

  The invention also relates to an electro-optic display comprising this type of liquid crystal medium, in particular a cell, an integrated nonlinear element on the skin for switching each pixel, and a nematic liquid crystal mixture with positive dielectric anisotropy and high resistivity. The STN or MLC display with two parallel skins configured with an outer frame) and the use of these media for electro-optic purposes. In addition to reflective displays, the mixtures of the present invention are also suitable for IPS (in plane switching), OCB (optically compensated bend) applications and VA (vertical alignment) applications. Yes. The mixtures according to the invention are particularly suitable for field sequential (FS) displays.

The liquid crystal mixture according to the invention makes it possible to significantly expand the available parameter range. The achievable combination of high clearing point, low rotational viscosity γ ₁ , fast switching time and low threshold voltage is far superior to prior art conventional materials.

The requirements for a high clearing point, a nematic phase at low temperature and a high positive Δε have heretofore been achieved only to an unsatisfactory extent. Prior art mixtures with high positive Δε, such as MLC-6424 (Merck KGaA, Darmstadt, Germany), exist but only have a low clearing point and a high rotational viscosity γ ₁ . Other mixture systems have good flow viscosity ν ₂₀ and Δε values, but only have a clearing point in the 60 ° C. region.

  The liquid crystal mixture of the present invention has a nematic phase maintained at −20 ° C., preferably up to −30 ° C., particularly preferably up to −40 ° C. Clear point, high resistivity, and fast switching time to achieve excellent STN and MLC displays. In particular, this mixture is characterized by a low voltage drive. The TN threshold is less than 2.0V, preferably less than 1.8V, particularly preferably less than 1.7V. This mixture is particularly useful for TFT displays in field sequential mode.

  Needless to say, by proper selection of the mixture components of the present invention, a higher clearing point (e.g., above 110 ° C.) is achieved or lower at higher threshold voltages while retaining other advantageous properties. It is also possible that a lower clearing point is achieved at the threshold voltage. Achieving a larger Δε and thus a lower threshold voltage is possible as well, with only a slight increase in viscosity. The MLC display of the present invention is preferably operated at Gooch Tally's primary transmission minimum (CH Gooch and HA Tarry, Electron. Lett. 10, 2-4, 1974; CH Gooch and HA Tarry, Appl Phys., Vol. 8, 1575-1584, 1975). Here, in addition to particularly favorable electro-optical properties (eg German patent 3022818) such as the steepness of the characteristic curve and the low viewing angle dependence of contrast, similarities at the second transmission minimum are also possible with smaller dielectric anisotropy. It is enough to get the same threshold voltage as the display. Thereby, by using the mixture of the present invention at the first transmission minimum, an extremely high specific resistance value can be achieved as compared with the case of the mixture containing a cyano compound. Through appropriate selection of the individual components and their amounts, one skilled in the art can determine the birefringence required for the MLC pre-specified layer thickness by a simple routine method.

The flow viscosity ν _{20 at} 20 ° C. is preferably less than 60 mm ² · s ⁻¹ , particularly preferably less than 50 mm ² · s ⁻¹ . The rotational viscosity γ ₁ at 20 ° C. of the mixture according to the invention is preferably less than 120 mPa · s, particularly preferably less than 100 mPa · s. The nematic phase range is preferably at least 90 degrees, more preferably at least 100 degrees. This range preferably extends at least from −20 ° C. to + 80 ° C.

Measurement of capacity retention (HR) [S. Matsumoto et al., Liquid Crystals 5, 1320
(1989); K. Niwa et al., Proc.SID Conference, San Francisco, June 1984, p. 304
(1984); G. Weber et al., Liquid Crystals 5, 1381 (1989)], the mixtures of the present invention containing compounds of formula IA and formula IB have the formula:

Cyanophenylcyclohexanes of the formula:

It has been shown that the reduction in HR is significantly smaller even at higher temperatures compared to mixtures containing these ester compounds instead of compounds of formula IA and IB.

  The UV stability of the mixtures according to the invention is very good. In other words, the reduction in HR is remarkably small even by UV irradiation.

  The mixtures according to the invention preferably contain little (≦ 10 wt%) or particularly preferably no cyano group-containing compounds. The retention values of the mixtures according to the invention are preferably greater than 98% at 20 ° C. and very particularly preferably greater than 99%.

In liquid crystal displays, short switching times are preferred, especially when used for video and TV applications. These applications require a switching time (t _on + t _off ) of less than 25 ms. The upper limit of the switching time is determined by the image repetition rate.

  A preferred embodiment is shown below.

  A liquid crystal medium additionally containing one or more compounds selected from the group consisting of general formulas II to VII.

  In the formula, each group has the following meaning.

R ⁰ represents n-alkyl, alkoxy, oxaalkyl, fluoroalkyl, alkenyl or alkenyloxy each having up to 9 carbon atoms,
X ⁰ represents F, Cl, an alkyl halide having up to 6 carbon atoms, a halogenated alkenyl, a halogenated alkenyloxy or a halogenated alkoxy,
Z ⁰ is —C ₂ H ₄ —, — (CH ₂ ) ₄ —, —CH═CH—, —CF═CF—, —C ₂ F ₄ —, —CH ₂ CF ₂ —, —CF ₂ CH _{2. -, - CH 2 O -,} - OCH 2 -, - COO -, - CHFO -, - OCHF -, - OCF 2 - or _-CF 2 O-,
Y ^{1 to} Y ⁴ each independently represent H or F,
r is 0 or 1;

  The compound of formula IV is preferably of the formula:

Selected from the group consisting of Here, X ⁰ and R ⁰ have the meanings defined in formula II, and X ⁰ is preferably F or OCF ₃ . Particularly preferred are compounds of formula IVa, IVb and IVc.

  The compound of formula VII is preferably selected from the following formula:

Here, X ⁰ and R ⁰ have the meanings defined in formula II, and X ⁰ is preferably F or OCF ₃ . Particularly preferred are compounds of formula VIIb.

  A medium additionally additionally containing one or more of the following compounds:

Where R ¹ and R ² are as defined in formula IB.

  A medium additionally additionally containing one or more alkenyl compounds of the formula

here,
A is 1,4-phenylene or trans-1,4-cyclohexylene;
a is 0 or 1,
L is H or F;
R ³ is an alkenyl group having 2 to 9 carbon atoms,
R ⁴ is synonymous with that defined for R ¹ in Formula IA.

  Particularly preferred compounds of the formula X are those selected from the following formulae:

Here, R ^3a and R ^4a are each independently H, CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ , and alkyl is a linear alkyl group having 1 to 8 carbon atoms.

Particularly preferred are compounds of the formulas Xa and Xf, particularly where R ^3a is preferably H or CH ₃ .

  A medium additionally comprising one or more compounds of the formula XI.

Here, 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, and L ¹ and L ² are H or F, independently of each other.

Particularly preferred are compounds of formula XI wherein L ¹ and / or L ² is F and QY is F or OCF ₃ . Further preferred are compounds of formula XI wherein R ³ is 1E-alkenyl or 3E-alkenyl having 2 to 7 carbon atoms, preferably 2, 3 or 4 carbon atoms.

  Very particular preference is given to compounds of the formula XIa.

Here, R ^3a is H, CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ , particularly preferably H or CH ₃ .

  −

It is.

  A medium containing one or more compounds selected from formulas II, III, IV, V, VI, VII and X;

-R ⁰ is a linear alkyl or alkenyl having 2 to 7 carbon atoms.

  A medium containing 1 to 4 compounds, preferably 1, 2, 3 or 4 compounds of formula IA (most preferably formula IA1).

  A medium containing 1 to 8, preferably 1, 2, 3, 4 or 5 compounds of the formula IB (most preferably formulas IB1 and IB2).

  A medium comprising one or more compounds of the formulas IA, IB, VIIb, VIII and X;

  The proportion of compounds of the formula IA in the medium is 1 to 35%, in particular 1 to 20% by weight.

  The proportion of compounds of the formula IB in the medium is 1 to 55%, in particular 1 to 45, most preferably 1 to 35% by weight.

  A medium consisting essentially of a compound selected from the group consisting of general formulas I to XI;

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

The term “alkenyl” includes straight-chain and branched alkenyl groups having 2 to 7 carbon atoms, 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. Preferable alkenyl is vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl. Examples include 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5 carbon atoms are generally preferred.

  The term “fluoroalkyl” is preferably a straight-chain group having a terminal fluorine, ie fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7- Contains fluoroheptyl. However, other substitution positions of fluorine are not excluded.

The term “oxaalkyl” preferably includes straight-chain groups of the formula C _n H _{2n + 1} —O— (CH ₂ ) _m . However, n and m are 1-6 each independently. Preferably n = 1, preferably m is 1-6.

Even relatively small amounts of mixing of compounds of formula IA and IB with conventional liquid crystal materials (but in particular with one or more compounds of formula II, III, IV, V, VI and / or VII) It is found to be extremely effective in lowering the threshold voltage and achieving a low birefringence, and in a wide nematic phase and at the same time a low smectic-nematic transition temperature is observed, improving storage stability. It was. Particularly preferred media comprise one or more compounds of the formula IV in addition to one or more of the compounds of the formula IA and formula IB, in particular X ⁰ is F, OCHF ₂ or OCF ₃ Preferably it comprises Formula IVa. The compounds of formulas IA, IB and II-VII are colorless, stable and easily miscible with each other and with other liquid crystal materials. Furthermore, the mixtures according to the invention are distinguished by a very high clearing point and a relatively low value of the rotational viscosity γ ₁ .

By appropriate selection of the meanings of R ⁰ and X ⁰ , the address time, threshold voltage, steepness of the transmission characteristic curve, etc. can be modified in a desired manner. For example, the use of 1E-alkenyl groups, 3E-alkenyl groups, 2E-alkenyloxy groups and the like generally results in shorter address times, improved nematic propensity, and elastic constant k ₃₃ (bend) compared to alkyl or alkoxy groups. And a higher ratio of k ₁₁ (spray) can be achieved. 4-Alkenyl groups, 3-alkenyl groups, etc. generally give lower threshold voltages and smaller k ₃₃ / k ₁₁ values compared to alkyl and alkoxy groups.

The CH ₂ CH ₂ group generally gives a higher k ₃₃ / k ₁₁ value compared to the single bond case. Higher k ₃₃ / k ₁₁ makes it easier to achieve a smoother transmission curve (to achieve gray scale), for example in a 90 ° twisted TN cell, and steeper in STN, SBE and OMI cells A simple transmission curve (larger time-division driving) and vice versa.

  Optimal mixing ratios of compounds of formulas IA, IB and II + III + IV + V + VI + VII are present substantially in the desired properties, choice of components of formula IA, IB, II, III, IV, V, VI and / or VII Depends on the choice of other components that may be. Appropriate mixing ratios within the given range can easily be determined from case to case.

  The total amount of compounds of the formulas IA, IB and II to XI in the mixtures according to the invention is not critical. Thus, the mixture can further comprise one or more components for optimization of various properties. However, the observed effect on address time and threshold voltage is generally greater at higher total concentrations of compounds of Formulas IA, IB, and II-XI.

In a particularly preferred embodiment, the medium of the present invention, ^{X 0} _{is, F, OCF 3, OCHF 2} , OCH = CF 2, OCF = CF 2 or formula II~VII is _{OCF 2} -CF 2 H (preferably II , III, IV and / or VII, in particular VIIb). Particularly advantageous properties are obtained due to the favorable synergistic effect with the compounds of the formula I. In particular, mixtures comprising compounds of the formulas IA and IB and in particular mixtures comprising compounds of the formula IVa stand out at low threshold voltages.

  The individual compounds of formulas II to XI and their subformulas used in the medium of the invention are known or can be synthesized by methods analogous to known compounds.

  The configuration of the MLC display of the present invention with a polarizing plate, electrode substrate and surface treated electrode corresponds to the conventional configuration of this type of display. The term “conventional configuration” is used herein in a broad sense and includes all inductions and deformations relating to MLC displays, in particular matrix display elements based on poly-Si TFTs or MIMs.

  In particular, a field sequential mode display is preferred. These displays are based, for example, on TN, OCB (optical compensation bend) or FLC (ferroelectric liquid crystal) mode.

  However, the major difference between the display of the present invention and a display based on a conventional twisted nematic cell is in the selection of the liquid crystal parameters of the liquid crystal layer.

  Liquid crystal mixtures which can be used according to the invention are synthesized in a manner known per se. In general, the components used in smaller amounts are dissolved, preferably warmed, in the components making up the main composition. Furthermore, it is also possible to mix the liquid crystal component solution of an organic solvent such as acetone, chloroform, or methanol and thoroughly mix it, and then remove the solvent again by, for example, distillation.

  The dielectric may further comprise additives known to those skilled in the art and described in the literature. For example, from 0 to 15%, pleochroic dyes, stabilizers or chiral dopants can be added. Suitable dopants and stabilizers are listed in Table C and Table D.

In the present application and the examples shown below, 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 below. The groups C _n H _{2n + 1} and C _m H _{2m + 1} are all linear alkyl groups each having n or m carbon atoms. n and m are preferably 0, 1, 2, 3, 4, 5, 6 or 7. The codes in Table B are self-explanatory. In Table A, only the initial letters relating to the parent structure are shown. In each case, the initial of this parent structure is followed by a code for the substituents R ^{1 *} , R ^{2 *} , L ^{1 *} and L ^{2 *} , separated by a dash.

  Suitable blend components for the blend concept of the present invention are shown in Table A and Table B.

Table A

Table B

Table C
Table C shows the available dopants that are generally added to the mixtures of the present invention. The dopant is preferably added in an amount of 0.1 to 10% by weight, very preferably 0.1 to 6% by weight, based on the mixture.

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

  In addition to one or more of the compounds of the formulas IA and IB, particularly preferred mixtures contain 1, 2, 3, 4, 5 or 6 or more compounds from Table B.

The following examples illustrate the invention without limiting it. Above and below, percentages are percent by weight. All temperatures are given in degrees Celsius. m. p. Represents the melting point, cl. p. Represents a clearing point. Furthermore, C = crystalline state, N = nematic phase, S = smectic phase, and I = isotropic phase. The data between these symbols is the phase transition temperature. Δn represents optical anisotropy, and n ₀ represents a refractive index (589 nm, 20 ° C.). The flow viscosity ν ₂₀ (mm ² / s) and the rotational viscosity γ ₁ (mPa · s) were each measured at 20 ° C. V ₁₀ represents a voltage of 10% transmission (viewing angle perpendicular to the substrate surface). t _on and _{t off represents} the switch-on time and the switch-off time at an operating voltage corresponding to twice the _{V 10.} Δε represents dielectric anisotropy (Δε = ε‖−ε⊥, where ε‖ represents a dielectric constant parallel to the molecular axis, and ε⊥ represents a perpendicular dielectric constant). Electro-optic data were measured at 20 ° C. in a TN cell with a primary transmission minimum (ie, with a d · Δn value of 0.5 μm) unless otherwise stated. Optical data were measured at 20 ° C. unless otherwise stated.

Claims (11)

A liquid crystal medium comprising one or more compounds of the following formula IA and one or more compounds of the formula IB.

(Where
R ¹ , R ² and R ³ are each independently an unsubstituted, mono-substituted by CN or CF ₃ or at least mono-substituted alkyl group having 1 to 12 carbon atoms by halogen, provided that in this group, One or more CH ₂ groups may be —O—, —S—, provided that the O atoms are not directly bonded to each other.

, -CH = CH-, -C≡C-, -CO-, -CO-O-, -O-CO- or -O-CO-O-
Y ^{1 to} Y ⁷ are each independently H or F,
X ⁰ is F, Cl, or a halogenated alkyl, halogenated alkenyl, halogenated alkoxy or halogenated alkenyloxy having up to 6 carbon atoms;
A is 1,4-phenylene, 2- or 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene or trans-1,4-cyclohexylene;
r is 0 or 1; ) 2. A medium according to claim 1, containing one or more of the compounds of formula IA1.

(Wherein R ¹ is as defined in claim 1). 3. A medium according to claim 1 or 2 containing one or more compounds of the formulas IB1 and IB2.

(Wherein R ² and R ³ are as defined in claim 1). The medium according to any one of claims 1 to 3, further comprising one or more compounds selected from the group consisting of general formulas II, III, IV, V, VI and VII.

(Where
R ⁰ represents n-alkyl, alkoxy, oxaalkyl, fluoroalkyl, alkenyl or alkenyloxy each having up to 9 carbon atoms,
X ⁰ represents F, Cl, an alkyl halide having up to 6 carbon atoms, a halogenated alkenyl, a halogenated alkenyloxy or a halogenated alkoxy,
Z ⁰ is —C ₂ H ₄ —, — (CH ₂ ) ₄ —, —CH═CH—, —CF═CF—, —C ₂ F ₄ —, —CH ₂ CF ₂ —, —CF ₂ CH _{2. -, - CH 2 O -,} - OCH 2 -, - COO -, - OCHF -, - CHFO -, - OCF 2 - or _-CF 2 O-,
Y ^{1 to} Y ⁴ each independently represent H or F,
r is 0 or 1; ) The medium according to any one of claims 1 to 4, further comprising one or more compounds represented by the following formula:

(Where
A is 1,4-phenylene or trans-1,4-cyclohexylene;
a is 0 or 1,
L is H or F;
R ³ is an alkenyl group having 2 to 9 carbon atoms,
R ⁴ is synonymous with that defined for R ¹ in Formula IA. ) The medium of any one of Claims 1-5 containing 1 type, or 2 or more types of the compound represented by a following formula.

(Where
R ¹ and R ² are as defined in claim 1,
R ⁰ and X ⁰ are as defined in claim 4;
R ^3a is H, CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ ,
alkyl is a linear alkyl group having 1 to 8 carbon atoms.   7. A medium according to any one of claims 1 to 6, wherein the proportion of the compound of formula IA is 1 to 35% by weight in the total mixture.   8. The medium according to any one of claims 1 to 7, wherein the proportion of the compound of formula IB is 1 to 55% by weight in the total mixture.   Use of the liquid crystal medium according to claim 1 in electro-optical applications.   An electro-optic liquid crystal display comprising the liquid crystal medium according to claim 1.   The electro-optic liquid crystal display according to claim 10, which is a field sequential mode display.