JP2004315819A - Liquid crystal medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal medium having low threshold voltage, low rotational viscosity, rapid response time and at the same time having high specific resistance, high thermal stability, high UV stability and high voltage retention (VHR) in exposing to UV and heating, for displays such as M (matrix) LC, TN, STN (super twist nematic), VA (vertical alignment) or IPS (in-plane switching) display, in particular for TN-TFT (thin film transistor). <P>SOLUTION: The liquid crystal medium comprises one or two or more kind of compounds expressed by general formula I, and one or two or more kind of UV stabilizers. In formula I: Z<SP>1</SP>is -CF<SB>2</SB>O-, -OCF<SB>2</SB>-, etc., Z<SP>2</SP>is -O-, -S-, -CO-, -COO-, -OCO-, -S-CO-, -CO-S-, etc. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal medium comprising a UV stabilizer, its use for electro-optical purposes and a display device comprising this medium.

  Liquid crystals are primarily used as dielectrics in display devices because the optical properties of such materials can be modified by applied voltage. Electro-optical devices based on liquid crystals are very well known to those skilled in the art and can be based on various effects. Examples of such devices are TN cells with twisted nematic structures, STN ("super twisted nematic") cells, ECB ("electrically controlled birefringence") cells, VA ("vertical alignment") cells and IPS ("in-plane switching") cell.

  The most common display devices are based on the Schadt-Helfrich effect and have a twisted nematic structure, for example, in TN and STN cells. These can be operated as a multiplex or as an active matrix display (AMD-TN, AMD = active matrix drive).

  In the case of TN displays, liquid-crystalline media which allow the following advantages in the cell are desirable: extended nematic phase range (especially to low temperatures), switchability at very low temperatures (field use, cars, aircraft). And increased resistance to UV radiation (longer useful life). However, for media available from the prior art, it is not possible to achieve these advantages while maintaining other parameters.

  In the case of a more highly twisted STN display, a liquid crystal medium that allows for greater time-sharing properties and / or lower threshold voltage and / or wider nematic phase range (particularly at lower temperatures) is desirable. To this end, a further expansion of the available parameter range (clearing point, smectic-nematic transition or melting point, viscosity, dielectric parameters, elastic parameters) is urgently desired.

  ECB displays and more recently VA displays include a layer of a liquid crystal medium between two transparent electrodes, where the liquid crystal medium has a negative value for the dielectric (DC) anisotropy Δε. In the switched-off state, the liquid crystal molecules are homeotropic, that is, oriented substantially perpendicular to the electrode surface, or homeotropically tilted. Due to the negative dielectric anisotropy, a reorientation of the liquid crystal molecules parallel to the electrode surface occurs in the switched-on state.

  In VA displays, the uniform parallel alignment of liquid crystal molecules in the switched-on state is usually limited to only a small area within the cell. Between these areas there is a disclination also known as a tilt area. ECB and VA displays have relatively short response times, but need to be further reduced, especially in gray shade response times. From the liquid crystal side, a contribution to this can in principle be made by reducing the rotational viscosity of the liquid crystal (LC) mixture.

  In addition to the known liquid crystal displays (TN, STN, ECB and VA), in which the electric field for reorientation occurs essentially perpendicular to the liquid crystal layer, also the electrical signal is remarkable when the electric field is parallel to the liquid crystal layer. There are displays that result to have different components. This type of display, known as an IPS ("in-plane switching") display, is disclosed, for example, in US Pat.

IPS displays containing known liquid crystal media are characterized by inappropriately long response times and often excessively high operating voltages. Accordingly, there is a need for a liquid crystal medium for IPS displays that does not have these drawbacks or has only a lower degree. For this reason, in addition to a suitable phase range, a low tendency to crystallize at low temperatures, a low birefringence and a suitable electrical resistance, a low threshold voltage (V ₁₀ ) and a low, which are especially crucial for the response time, There are special requirements for liquid crystal materials having a rotational viscosity (γ ₁ ).

Like TN displays, ECB, VA and IPS displays can also operate as matrix displays.
Matrix liquid crystal displays are known. Non-linear elements that can be used to individually switch individual pixels are, for example, active elements (ie, transistors). Next, the term "active matrix" can be used, where a distinction can be made between the two types:
1. MOS (metal oxide semiconductor) or other diode on 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 size of the display. The reason for this is that even with the modular assembly of the various partial representations, problems arise at the joints.
In the preferred and more promising Type 2 case, the electro-optic effect used is usually the TN effect. A distinction is made between the two technologies: TFTs containing compound semiconductors, for example CdSe, or TFTs based on polycrystalline or amorphous silicon. Extensive research efforts are being made worldwide for the latter technology.

  The TFT matrix is applied inside one glass plate of the display, while the other glass plate carries a transparent counter electrode inside. Compared with the size of the pixel electrode, the TFT is extremely small and has almost no adverse effect on the image. This technique can also be extended to a full-color capable display with a mosaic of red, green and blue filters arranged such that a filter element faces each switchable pixel.

TFT displays typically operate as TN cells with crossed polarizers in transmitted light (TN-TFTs) and are back-illuminated.
The term MLC display here includes all matrix displays with integrated non-linear elements, i.e. displays with passive elements, such as varistors or diodes (MIM = metal-insulator-metal) in addition to the active matrix. Including.

  For matrix liquid crystal displays (MLC displays) with integrated non-linear elements for switching individual pixels, for example, large positive dielectric anisotropy, wide nematic phase, relatively low birefringence, very high resistivity, good UV A medium having temperature stability and low vapor pressure is desirable.

  This type of MLC display is particularly suitable for TV applications (for example pocket TVs) and for computer applications (laptops) and advanced information displays for automotive and aircraft construction. In addition to the problems relating to the angle dependence of the contrast and the response time, MLC displays also suffer from difficulties due to inappropriately high specific resistance values of the liquid crystal mixture [NPL 1; NPL 2].

  As the resistance decreases, the contrast of the MLC display decreases, and the problem of afterimage elimination may occur. Since the resistivity of the liquid crystal mixture generally decreases throughout the life of the MLC display due to interaction with the inner surface of the display, high (initial) resistance is critical to obtain an acceptable useful life. is there. Particularly in the case of low-voltage mixtures, it has hitherto been impossible to achieve very high specific resistance values. Furthermore, it is important that the resistivity value has as little a rise as possible with increasing temperature and after thermal and / or UV exposure. The low-temperature properties of the mixtures from the prior art are also particularly disadvantageous. Even at low temperatures, it is required that no crystallization and / or smectic phases occur and that the temperature dependence of the viscosity is as low as possible. Known MLC displays do not meet these requirements.

  Thus, for MLC displays having very high resistivity values and at the same time large operating temperature ranges, short response times and low threshold voltages even at low temperatures, which do not have, or only have a small extent to, the aforementioned disadvantages. A great deal of demand continues.

  In addition to liquid crystal displays that use back-illumination, ie operate transparently and optionally transflectively, reflective liquid crystal displays are also of particular interest. These reflective liquid crystal displays use ambient light for information displays. Therefore, they consume significantly less energy than back-lit liquid crystal displays of corresponding size and resolution. Because the TN effect is characterized by very good contrast, this type of reflective display is easily readable even under bright ambient conditions. This is already known as a simple reflective TN display, as used, for example, in watches and pocket calculators.

  However, the principles can also be applied to high quality, high resolution active matrix address displays, such as TFT displays. Here, already using liquid crystals with low birefringence (Δn), as in the case of commonly used transmissive TFT-TN displays, is necessary to achieve a low optical delay (d · Δn). is necessary. This low optical delay results in a normally acceptable low viewing angle dependence of the contrast (see US Pat. The use of liquid crystals with low birefringence in reflective displays is much more important than in transmissive displays. The reason is that in a reflective display, the effective layer thickness through which light passes is about twice as large as a transmissive display having the same layer thickness.

  In addition to lower power consumption (because back illumination is not required), the advantage of a reflective display over a transmissive display is that it is space saving with very small physical depth and back illumination. The problem due to temperature gradients caused by varying degrees of heating due to the above is reduced.

  In general, the liquid crystal materials for the aforementioned display types must have good chemical and thermal stability and good stability to electric fields and electromagnetic radiation. In addition, liquid crystal materials must have a low viscosity and provide short addressing times, low threshold voltages and high contrast in the cell.

  In addition, they must have a suitable mesophase, for example the nematic or cholesteric mesophase for the aforementioned cells, at normal operating temperatures, ie below and above room temperature, and as broadly as possible. Since liquid crystals are generally used in the form of a mixture of a number of components, it is important that the components are readily miscible with one another. Other properties, such as conductivity, dielectric anisotropy and optical anisotropy, must meet different requirements, depending on the cell type and the area of application. For example, materials for cells having a twisted nematic structure must have positive dielectric anisotropy and low conductivity.

In a TN (Schat-Hellrich) cell, a medium is desirable for the cell that facilitates the following advantages:
An extended nematic phase range (especially in the direction of lower temperatures),
Switching capability at ultra-low temperatures (outdoor use, cars, aircraft),
Increased resistance to UV radiation (longer useful life),
Low threshold (drive) voltage,
-Birefringence high enough to achieve small layer thicknesses and fast response times.

Media available from the prior art achieve these advantages while not allowing other parameters to be maintained.
In particular, the UV stability and voltage holding ratio (VHR) of the liquid crystal medium against heating or UV exposure [NPL 3; NPL 4; NPL 5] and the specific resistance (SR) [NPL 6] , Is often inappropriate. Resistivity is an important quality feature of liquid crystal mixtures. Low SR values can cause an unacceptable decrease in VHR.

International Publication No. 91/10936 pamphlet TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E ., SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H.), Proc. Eurodisplay 84, September 1984: A210-288 Matrix LLC. Matrix LCD Controlled by Double Stage Diode Rings, page 141 et seq., Paris STROMER, M., Proc. Eurodisplay 84, September 1984: Design of Thin Film Transistors for Matrix Addressing of Television Liquid Liquid Crystal Displays (Design of Thin Film Transistors for Matrix Addressing of Television Liquid Crystal Displays), page 145 and later, Paris German Patent 30 22 818 S. Matsumoto et al., Liquid Crystals, 5, 1320 (1989) K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984). Tee, T. Jacob and U. Finkenzeller, `` Merck Liquid Crystals-Physical Properties of Liquid Crystals '', 1997 G. Weber et al., Liquid Crystals, 5, 1381 (1989).

  Thus, the present invention provides a low threshold voltage, a low rotational viscosity, a fast response time and at the same time a high resistivity, preferably without, or only to a reduced extent, the aforementioned disadvantages. MLC, TN, STN, VA or IPS displays of this type, especially TN-TFT displays, with high thermal stability, high UV stability and especially high values of the voltage holding ratio (VHR) during UV exposure and heating The purpose of providing a medium for

  It has now been found that this object can be achieved when the medium according to the invention is used in a display.

で表される化合物および１種または２種以上のＵＶ安定化剤、 The invention relates in particular to a liquid-crystalline medium based on a mixture of polar compounds having a positive dielectric anisotropy, which comprises one or more compounds of the formula I

A compound represented by and one or more UV stabilizers,

−ＣＯ−、−ＣＯ−Ｏ−、−Ｏ−ＣＯ−、−Ｏ−ＣＯ−Ｏ−、−ＣＨ＝ＣＨ−または−Ｃ≡Ｃ−により、Ｏ原子が互いに直接結合しないように置換されていることができ、

は、

であり、 Where:
R has 1 to 15 carbon atoms, and is unsubstituted or is monosubstituted by CN or CF _3, or an alkyl or alkenyl radical which is at least monosubstituted by halogen, where, Further, one or more CH ₂ groups in these groups may each independently be —O—, —S—,

O atoms are substituted by -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CH = CH- or -C≡C- so as not to directly bond to each other. It is possible,

Is

And

Y ^{1 to} Y ⁹ are each independently H or F,
Z ¹ is —CF ₂ O—, —OCF ₂ —, or —COO—;
Z ² represents —O—, —S—, —CO—, —COO—, —OCO—, —S—CO—, —CO—S—, —OCH ₂ —, —CH ₂ O—, —SCH _{2 -, - CH 2 S -,} - CF 2 O -, - OCF 2 -, - CF 2 S -, - SCF 2 -, - CH 2 CH 2 -, - CF 2 CH 2 -, - CH 2 CF 2 - _{, -CF 2 CF 2 -, -} CH = CH -, - CF = CH -, - CH = CF -, - CF = CF -, - C≡C- or a single bond,
X ⁰ is F, Cl, an alkyl, alkenyl or alkoxy halide having 1 to 6 carbon atoms,
r is 0 or 1,
And a liquid crystal medium comprising:

Suitable UV stabilizers are known from the prior art. Many of these compounds are commercially available. Particularly preferred are compounds of formula II

−ＣＯ−、−ＣＯ−Ｏ−、−Ｏ−ＣＯ−、−Ｏ−ＣＯ−Ｏ−、−ＣＨ＝ＣＨ−または−Ｃ≡Ｃ−により、Ｏ原子が互いに直接結合しないように置換されていることができる、直鎖状または分枝状アルキル、あるいは３〜２５個の炭素原子を有し、この各々が、非置換であるか、またはＲもしくはＸ^０により単置換もしくは多置換されている、アリール、ヘテロアリールまたはアルキルアリールであり、
Ｘは、Ｈ、ＦまたはＣｌである、
で表されるＵＶ安定化剤である。 Where:
R ¹ and R ² are each, independently of one another, H or having 1 to 25 carbon atoms and are unsubstituted or monosubstituted by CN or CF ₃ , or At least monosubstituted, wherein one or more CH ₂ groups are each, independently of one another, —O—, —S—,

O atoms are substituted by -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CH = CH- or -C≡C- so as not to directly bond to each other. Linear or branched alkyl, or having 3 to 25 carbon atoms, each of which is unsubstituted or mono- or polysubstituted by R or X ⁰ , Aryl, heteroaryl or alkylaryl,
X is H, F or Cl;
It is a UV stabilizer represented by

The invention further relates to the use of the media of the invention for electro-optical purposes.
The invention further relates to an electro-optical liquid crystal display comprising the liquid crystal medium according to the invention.

The invention further relates to an electro-optical liquid crystal display comprising a liquid crystal medium according to the invention, characterized in that it is a TN, STN, TN-TFT, IPS or VA display.
The invention further relates to an electro-optical liquid crystal display comprising a liquid crystal medium according to the invention, characterized in that it is a reflective or transflective display.

  The compounds of the formula I have a wide range of uses. These compounds can act as base materials from which the liquid crystal medium is mainly composed, or they can be added, in addition to liquid crystal base materials from other groups of compounds, to the dielectric materials of this type of dielectric, for example. The anisotropy and / or optical anisotropy can be modified and / or the threshold voltage and / or the viscosity and / or the low temperature behavior can be optimized.

The compounds of the formula I reduce, in particular, the threshold voltages and the response times of the liquid-crystal mixtures according to the invention.
The addition of UV stabilizers, especially those of the formula II, increases the VHR of the liquid-crystalline media according to the invention when exposed to UV, whereas the VHR of the liquid-crystalline media after heating is impaired with little or no effect. There is nothing. This is a decisive advantage, especially for matrix displays, for example TN-TFT displays.

Thus, the combination of a compound of formula I with a UV stabilizer provides liquid crystal media and displays that have high VHR upon UV exposure and heating and improved threshold voltage and response time at the same time. It becomes possible.
Particularly preferred compounds of the formula I are those in which at least one group Y ¹ , Y ² , Y ⁴ and Y ⁵ is F and Y ³ and Y ⁶ are preferably H.

式中、Ｘ^０、Ｙ^１〜Ｙ^８、Ｚ^１、Ｚ^２およびｒは、式Ｉにおいて定義した通りであり、Ｒ^０は、各々９個までの炭素原子を有するｎ−アルキル、ｎ−アルコキシ、ｎ−オキサアルキル、ｎ−フルオロアルキル、ｎ−フルオロアルコキシまたはｎ−アルケニルである、
から選択される。 The compounds of the formula I are preferably of the following formula:

Wherein X ⁰ , Y ¹ -Y ⁸ , Z ¹ , Z ² and r are as defined in formula I, and R ⁰ is n-alkyl, n-alkoxy, each having up to 9 carbon atoms. , N-oxaalkyl, n-fluoroalkyl, n-fluoroalkoxy or n-alkenyl,
Is selected from

Particularly preferred are compounds of the formula I1.
Particularly preferred are the compounds of the formulas I, I1 and I2, wherein at least one of the radicals Y ¹ , Y ² , Y ⁴ , Y ⁵ , Y ⁷ and Y ⁸ , in particular the radicals Y ¹ , One of Y ² , Y ⁴ and Y ⁵ is F.

Preference is further a compound of formula I, I1 and I2, where, ^{Z 1} is _-CF 2 O-or -OCF ₂ -, particularly preferably _-CF 2 O-a.
Preference is further a compound of formula I, I1 and I2, where, ^{Z 1} is -COO-.
Preference is further a compound of formula I, I1 and I2, where, Z ² is a single bond.

Particularly preferred are the following compounds:

式中、Ｒ^０は、前に定義した通りである、
である。特に好ましいのは、式Ｉ１ａ、Ｉ２ｎおよびＩ２ｗで表される化合物である。

Wherein R ⁰ is as defined above,
It is. Particularly preferred are the compounds of the formulas I1a, I2n and I2w.

Particularly preferred compounds of the formula II are those in which at least one of the radicals R ¹ and R ² is a straight-chain or branched alkyl having 1 to 15 carbon atoms, wherein additionally one or more two or more CH ₂ groups, -COO- or -O-CO-, can be substituted by aryl or alkylaryl having 5-15 carbon atoms, X is preferably H or Cl Compound. Very particularly preferred radicals R ¹ and R ² are methyl, tert-butyl, 2-butyl, 1,1-dimethylpropyl, 1,1,2,2-tetramethylpropyl and 1-methyl-1-phenylethyl. .

Particularly preferred are the following formulas (terminal methyl groups not shown):

またはこれらの化合物の混合物から選択された式ＩＩで表される化合物群である。

Or a group of compounds represented by Formula II selected from a mixture of these compounds.

Particularly preferred are compounds of the formula II1.
Some of the compounds of formulas II and II1-II12 are commercially available as UV stabilizers under the name Tinuvin® (Ciba Spezialitaeten-chemie AG, Basel, Switzerland). it can. Compounds of formula II1 are available, for example, under the name Tinuvin P®.

で表されるものである。 Further suitable UV stabilizers have the formula:

It is represented by

  Compounds 1 and 2 are available from ABCR GmbH, compound 3 is available from Merck KGaA, compound 4 is available from Aldrich, and compound 5 is available from Ciba AG.

  The compounds of the formula I can be prepared as described in the literature (for example in standard academic books, for example Houben-Weyl, Methoden der Organischen Chemie, Georg-Thieme-Verlag, Stuttgart). It is prepared by a method known per se under the reaction conditions that are precisely known and suitable for the above-mentioned reaction. Also here, variants which are known per se, but which are not described in more detail here, can be used.

  In the pure state, the compounds of the formula I are colorless and form liquid-crystalline mesophases in a temperature range which is favorably located for electro-optical use. They are chemically, thermally and light-stable.

If one of the groups R, R ⁰ , R ¹ and R ² in the formulas herein is an alkyl group and / or an alkoxy group, this can be straight-chain or branched. . It is preferably straight-chain and has 2, 3, 4, 5, 6 or 7 carbon atoms and is therefore particularly preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy. , Butoxy, pentoxy, hexyloxy or heptyloxy, further methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy, tridecyloxy or Tetradecyloxy.

  Oxaalkyl is preferably linear 2-oxapropyl (= methoxymethyl), 2-(= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl , 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl .

If one of the radicals R, R ⁰ , R ¹ and R ² is an alkyl radical in which one CH ₂ radical is replaced by —CH ＝ CH—, this can be straight-chain or branched. There can be. It is preferably straight-chain and has 2 to 10 carbon atoms. Thus, this is particularly preferably vinyl, prop-1- or 2-enyl, but-1-, 2- or -3-enyl, pent-1-, -2-, -3- or -4. -Enyl, hex-1-, -2-, -3-, -4- or -5-enyl, hept-1-, -2-, -3-, -4-, -5 or -6-enyl Octo-1-, -2-, -3-, -4-, -5, -6 or -7-enyl, non-1-, -2-, -3-, -4-, -5 -, -6-, -7- or -8-enyl, or dec-1-, -2-, -3-, -4-, -5, -6, -7-, -8- or- 9-enyl.

If one of the groups R, R ⁰ , R ¹ and R ² is an alkyl group in which one CH ₂ group is replaced by —O— and one is replaced by —CO—, these are , Preferably adjacent. Thus, they contain an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. These are preferably straight-chain and have 2 to 6 carbon atoms.

  Thus, they are particularly preferably acetoxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetoxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetoxyethyl, 2-propionyloxy Ethyl, 2-butyryloxyethyl, 3-acetoxypropyl, 3-propionyloxypropyl, 4-acetoxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxy Carbonylmethyl, butoxycarbonylmethyl, 2- (methoxycarbonyl) ethyl, 2- (ethoxycarbonyl) ethyl, 2- (propoxyca Boniru) ethyl, 3- (methoxycarbonyl) propyl, 3- (ethoxycarbonyl) propyl or 4- (methoxycarbonyl) butyl.

When one of the groups R, R ⁰ , R ¹ and R ² is an alkyl group in which two or more CH ₂ groups are replaced by —O— and / or —CO—O—, It can be straight-chain or branched. It is preferably branched and has 3 to 12 carbon atoms. It is therefore particularly preferred that biscarboxymethyl, 2,2-biscarboxyethyl, 3,3-biscarboxypropyl, 4,4-biscarboxybutyl, 5,5-biscarboxypentyl, 6,6-bis Carboxyhexyl, 7,7-biscarboxyheptyl, 8,8-biscarboxyoctyl, 9,9-biscarboxynonyl, 10,10-biscarboxydecyl, bis (methoxycarbonyl) methyl, 2,2-bis (methoxycarbonyl ) Ethyl, 3,3-bis (methoxycarbonyl) propyl, 4,4-bis (methoxycarbonyl) butyl, 5,5-bis (methoxycarbonyl) pentyl, 6,6-bis (methoxycarbonyl) hexyl, 7,7 -Bis (methoxycarbonyl) heptyl, 8,8-bis (methoxycarbonyl) Octyl, bis (ethoxycarbonyl) methyl, 2,2-bis (ethoxycarbonyl) ethyl, 3,3-bis (ethoxycarbonyl) propyl, 4,4-bis (ethoxycarbonyl) butyl or 5,5-bis (ethoxycarbonyl) ) Pencil.

One of the groups R, R ⁰ , R ¹ and R ² is such that one CH ₂ group is unsubstituted or substituted by —CH ＝ CH— and the adjacent CH ₂ group is CO, CO—O or O If it is an alkyl group substituted by -CO, it can be straight-chain or branched. It is preferably straight-chain and has 4 to 13 carbon atoms. Thus, it is particularly preferred that acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8 -Acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl, 2-methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl , 7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl or 9-methacryloyloxynonyl.

If one of the groups R, R ⁰ , R ¹ and R ² is an alkyl or alkenyl group monosubstituted by CN or CF ₃ , this group is preferably straight-chain. Substitution by CN or CF ₃ is possible at any desired position.
If one of the groups R, R ⁰ , R ¹ and R ² is an alkyl or alkenyl group which is at least monosubstituted by halogen, this group is preferably straight-chain and halogen is preferably F Or Cl. In the case of polysubstitution, the halogen is preferably F. The resulting groups also contain perfluorinated groups. In the case of monosubstitution, the fluorine or chlorine substituent can be in any desired position, but is preferably in the ω position.

  Compounds containing branched wing groups R may be important due to their better solubility in conventional liquid crystal substrates, but are especially important as chiral dopants if they are optically active. is there. This type of smectic compound is suitable as a component of a ferroelectric material.

Branching groups of this type preferably contain not more than one chain branch. Preferred branching groups R, R ⁰ , R ¹ and R ² are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, -Ethylhexyloxy, 1-methylhexyloxy and 1-methylheptyloxy.

  The invention also relates to the use of the liquid crystal medium according to the invention for electro-optical purposes, as well as to two plane-parallel skins forming a cell with the frame, an integrated non-linear element for switching individual pixels on the skin. And, it relates to electro-optical displays, in particular STN and MLC displays, having a nematic liquid crystal mixture with a high resistivity, comprising a liquid crystal medium according to the invention, arranged in a cell.

  The liquid-crystal media according to the invention allow a significant expansion of the available parameter range. In particular, the achievable combinations of clearing point, viscosity at low temperature, heat and UV stability and optical anisotropy are far superior to the prior art from the prior art.

  The liquid-crystalline media according to the invention preferably have a nematic phase up to −20 ° C., particularly preferably up to −30 ° C., and especially up to −40 ° C., and more than 70 ° C., particularly preferably more than 75 ° C., especially 80 ° C. Has a clearing point above. These nematic phase ranges preferably extend at least 90 ° C. and particularly preferably at least 100 ° C. This range preferably extends at least from -30C to + 80C.

The dielectric anisotropy Δε of the liquid crystal medium according to the invention is preferably ≧ 5, particularly preferably ≧ 8 and especially ≧ 10.
The liquid-crystalline media of the invention for TN and STN displays preferably have Δn> 0.07, particularly preferably ≧ 0.08 and preferably ≦ 0.2, particularly preferably ≦ 0.16, especially 0.085- It has a birefringence value between 0.15. The liquid-crystalline media of the invention for reflective and transflective displays preferably have birefringence values of ≦ 0.08, particularly preferably ≦ 0.07 and especially ≦ 0.065.

The TN threshold of the liquid crystal medium of the present invention is generally less than 1.7V, preferably less than 1.5V.
The rotational viscosity gamma ₁ of the liquid crystal medium of the present invention at 20 ° C. is preferably <200 mPas and particularly preferably <150 mPas.

  Also, by a suitable choice of the components of the mixture according to the invention, a higher clearing point (for example above 110 ° C.) is achieved at lower dielectric anisotropy values and thus higher, while maintaining other advantageous properties. It is possible to achieve a threshold voltage or a lower clearing point at a higher dielectric anisotropy (e.g.> 12) and thus achieve a lower threshold voltage (e.g. <1.5V) Needless to say. At viscosities that increase only slightly, it is likewise possible to obtain mixtures having a relatively large Δε and thus a relatively low threshold value.

Measurement of voltage holding ratio (VHR), also known as capacitance holding ratio [S. Matsumoto et al., Liquid Crystals 5 , 1320 (1989); K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984); by T. Jacob and U. Finkenzeller, "Merck Liquid Crystals-Physical Properties of Liquid Crystals", 1997], compounds of formula I and UV stabilizers, In particular, the liquid crystal media of the present invention, including those of Formula II, have been shown to have a VHR suitable for MLC displays.

で表されるシアノフェニルシクロヘキサンまたは式

で表されるエステルを含む化合物を、式Ｉで表される化合物に変えて含む類似媒体よりも、温度の上昇に伴うＶＨＲの低下が顕著に小さい。 In particular, the liquid-crystalline media according to the invention comprising the compounds of the formula I contain cyano or 4-cyanophenyl groups, for example of the formula

Cyanophenylcyclohexane represented by the formula or

The decrease in VHR with increasing temperature is significantly smaller than that of a similar medium containing a compound containing an ester represented by the formula (I) instead of the compound represented by the formula (I).

The UV stability of the liquid crystal media according to the invention is also significantly better. That is, they have a significantly reduced VHR when exposed to UV.
After heating at 100 ° C./5 min, the voltage holding ratio VHR of the liquid-crystalline media of the invention is preferably> 90%, particularly preferably> 94%, very particularly preferably> 96% and especially> 98%. .

After UV exposure (2 hours), the voltage holding ratio VHR of the liquid-crystalline media according to the invention is preferably> 75%, particularly preferably> 80%, very particularly preferably> 85% and especially> 90%.
After heating at 100 ° C./5 minutes and UV exposure (2 hours), the voltage holding ratio VHR of the liquid-crystalline media of the invention is preferably> 60%, particularly preferably> 65%, very particularly preferably> 70% and Especially> 77%.

VHR values relate to the measurement method in T. Jacob and U. Finkenzeller, "Merck Liquid Crystals-Physical Properties of Liquid Crystals", 1997, unless stated otherwise.
The liquid-crystalline media according to the invention preferably comprise less than 25% by weight, particularly preferably less than 15% by weight and in particular less than 5% by weight of compounds containing one or more cyano groups, in particular of this type Includes mesogenic or liquid crystalline compounds. Very particular preference is given to liquid-crystalline media which do not contain compounds having one or more cyano groups.

  The transmissive MLC display of the present invention preferably operates at the first minimum Gooch and Tally transmittances [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 the particularly favorable electro-optical properties, for example high steepness of the characteristic curve and low angular dependence of the contrast (DE 30 22 818), lower The dielectric anisotropy is sufficient at the second minimum, at the same threshold voltage as in similar displays. This makes it possible to use the mixture of the invention at the first minimum to achieve a significantly higher resistivity than, for example, a mixture containing a cyano compound.

  The transmissive or transflective MLC display of the present invention is optimized for contrast ratio and optical dispersion, the value of the product d · Δn, the twist angle Φ of the liquid crystal, the fixed axis direction and the polarization of the delay film with respect to the substrate rubbing direction. It operates in a parameter width consisting of the plate transmission direction. The requirements for reflective MLC displays are set forth, for example, in the Digest of Technical Papers, SID Symposium 1998. The person skilled in the art sets the required birefringence for the pre-specified layer thickness of the MLC display by suitably selecting the individual components and their weight ratios using simple and routine methods. be able to.

Preferred embodiments are as follows:
The medium comprises 1 to 4, in particular 1, 2 or 3 compounds of the formula I;
The medium comprises one or more compounds of the formula I1a.
The proportion of the compounds of the formula I in the mixture as a whole is preferably in the range from 2 to 30% by weight, particularly preferably from 3 to 25% by weight and especially from 4 to 20% by weight.

The medium is one, two, three or four, preferably one or two UV stabilizers, preferably of formula II or of formulas 1-4, particularly preferably of formula II And especially UV stabilizers of the formula II1 or II2.
The medium comprises ≧ 0.1% by weight, preferably ≧ 0.3% by weight and particularly preferably ≧ 0.4% by weight of UV stabilizers.
The proportion of UV stabilizers in the mixture as a whole is preferably from 0.01 to 5% by weight, particularly preferably from 0.1 to 2% by weight, very particularly preferably from 0.3 to 1% by weight and in particular 0.4 to 0.8% by weight.

式中、ｒ、Ｘ^０、Ｙ^１〜Ｙ^４およびＲ^０は、式ＩおよびＩ１において定義した通りであり、
Ｚ^０は、−ＣＦ_２Ｏ−、−ＯＣＦ_２−、−Ｃ_２Ｆ_４−、−ＣＦ＝ＣＦ−、−ＣＨ＝ＣＦ−、−ＣＦ＝ＣＨ−、−Ｃ_２Ｈ_４−、−（ＣＨ_２）_４−、−ＯＣＨ_２−または−ＣＨ_２Ｏ−であり、
Ｚ^３は、−Ｃ_２Ｆ_４−、−ＣＦ＝ＣＦ−、−ＣＨ＝ＣＦ−、−ＣＦ＝ＣＨ−、−Ｃ_２Ｈ_４−、−（ＣＨ_２）_４−、−ＯＣＨ_２−または−ＣＨ_２Ｏ−である、
からなる群から選択された１種または２種以上の化合物を含む。 The medium furthermore has the general formulas III to VIII:

Wherein r, X ⁰ , Y ¹ -Y ⁴ and R ⁰ are as defined in formulas I and I1,
Z ⁰ _{is, -CF 2 O -, - OCF} 2 -, - C 2 F 4 -, - CF = CF -, - CH = CF -, - CF = CH -, - C 2 H 4 -, - (CH _{2) 4 -, - OCH 2} - or _-CH 2 is O-,
Z ³ _{is, -C 2 F 4 -, -} CF = CF -, - CH = CF -, - CF = CH -, - C 2 H 4 -, - (CH 2) 4 -, - OCH 2 - or - CH ₂ O—,
Or one or more compounds selected from the group consisting of:

式中、Ｒ^０は、式Ｉ１において定義した通りであり、好ましくは、メチル、エチル、ｎ−プロピル、ｎ−ブチルまたはｎ−ペンチルである、
から選択される。 The compound of formula III is preferably of the formula:

Wherein R ⁰ is as defined in formula I1, and is preferably methyl, ethyl, n-propyl, n-butyl or n-pentyl,
Is selected from

式中、Ｒ^０は、式Ｉ１において定義した通りであり、Ｘ^０は、好ましくはＦまたはＯＣＦ_３である、
から選択される。 The compound of formula IV is preferably of the formula:

Wherein R ⁰ is as defined in formula I1, and X ⁰ is preferably F or OCF ₃ ;
Is selected from

式中、Ｒ^０は、式Ｉ１において定義した通りであり、好ましくはメチル、エチル、ｎ−プロピル、ｎ−ブチルまたはｎ−ペンチルである、
から選択される。 The compound of formula V is preferably of the formula:

Wherein R ⁰ is as defined in formula I1, and is preferably methyl, ethyl, n-propyl, n-butyl or n-pentyl,
Is selected from

The medium furthermore has the general formulas IX to XV:

式中、Ｒ^０、Ｘ^０およびＹ^１〜Ｙ^４は、式ＩおよびＩ１において定義した通りである、
からなる群から選択された１種または２種以上の化合物を含む。Ｘ^０は、好ましくはＦ、Ｃｌ、ＣＦ_３、ＯＣＦ_３またはＯＣＨＦ_２である。Ｒ^０は、好ましくは、各々６個までの炭素原子を有するアルキル、アルコキシ、オキサアルキル、フルオロアルキル、フルオロアルコキシまたはアルケニルである。

Wherein R ⁰ , X ⁰ and Y ¹ -Y ⁴ are as defined in formulas I and I1,
Or one or more compounds selected from the group consisting of: X ⁰ is preferably F, Cl, CF ₃ , OCF ₃ or OCHF ₂ . R ⁰ is preferably alkyl, alkoxy, oxaalkyl, fluoroalkyl, fluoroalkoxy or alkenyl, each having up to 6 carbon atoms.

式中、Ｒ^０およびＸ^０は、式ＩおよびＩ１において定義した通りである、
１，４−フェニレン環は、さらに、ＣＮ、塩素またはフッ素により置換されていることができる。１，４−フェニレン環は、好ましくは、フッ素原子により単置換または多置換されている。 The medium furthermore has the general formulas XVI to XX:
Or one or more compounds selected from the following group consisting of:

Wherein R ⁰ and X ⁰ are as defined in formulas I and I1,
The 1,4-phenylene ring can be further substituted by CN, chlorine or fluorine. The 1,4-phenylene ring is preferably mono- or polysubstituted by a fluorine atom.

式中、Ｒ^５およびＲ^６は、各々、互いに独立して、式Ｉ１におけるＲ^０について定義した通りである、
で表される１種または２種以上の二環式化合物を含む。 The medium is furthermore of the formula XXI

Wherein R ⁵ and R ⁶ are each, independently of one another, as defined for R ⁰ in formula I1;
Or one or more bicyclic compounds represented by the formula:

式中、Ｒ^０は、式Ｉ１において定義した通りであり、Ｒ^１ａおよびＲ^２ａは、各々、互いに独立して、Ｈ、ＣＨ_３、Ｃ_２Ｈ_５またはｎ−Ｃ_３Ｈ_７である、
から選択される。「ａｌｋｙｌ」および「ａｌｋｙｌ^＊」は、以下に定義する通りである。特に好ましいのは、式ＸＸＩａ、ＸＸＩｂ、ＸＸＩｅおよびＸＸＩｆで表される化合物である。 The compound of formula XXI preferably has the formula:

Wherein R ⁰ is as defined in formula I1, and R ^1a and R ^2a are each, independently of one another, H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ ;
Is selected from “Alkyl” and “alkyl ^* ” are as defined below. Particularly preferred are compounds of the formulas XXIa, XXIb, XXIe and XXIf.

式中、Ｒ^１ａは、Ｈ、ＣＨ_３、Ｃ_２Ｈ_５またはｎ−Ｃ_３Ｈ_７である、
から選択された１種または２種以上のアルケニル化合物を含む。 The medium is furthermore represented by formula IIIa, wherein R ⁰ is alkenyl having 2 to 7 carbon atoms, preferably formula IIIa1

Wherein R ^1a is H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ ,
And one or more alkenyl compounds selected from the group consisting of:

式中、「ａｌｋｙｌ」および「ａｌｋｙｌ^＊」は、後に定義する通りである、
から選択された１種または２種以上、好ましくは１種、２種または３種の化合物を含む。 The medium further has the formula:

Wherein “alkyl” and “alkyl ^* ” are as defined below;
And one or more, preferably one, two or three compounds selected from

式中、Ｘ^０、Ｙ^１、Ｙ^２およびＲ^０は、式ＩおよびＩ１において定義した通りである、
で表される１種または２種以上のエステル化合物を含む。 The medium is furthermore of the formula XXIII

Wherein X ⁰ , Y ¹ , Y ² and R ⁰ are as defined in formulas I and I1,
And one or more ester compounds represented by

式中、Ｒ^０は、式Ｉ１において定義した通りである、
から選択される。 The compound of formula XXIII preferably has the formula:

Wherein R ⁰ is as defined in formula I1,
Is selected from

で表される１種または２種以上、特に好ましくは１種または２種のジオキサン化合物を含む。 The medium is preferably of the formula:

And one or more, particularly preferably one or two, dioxane compounds.

式中、Ｒ^６およびＲ^７は、各々、互いに独立して、Ｒ^０またはＸ^０であり、Ｘ^０、Ａ^１、Ｚ^１およびＲ^０は、式ＩおよびＩ１において定義した通りである、
で表される１種または２種以上のデカリン化合物を含む。 The medium is preferably of the formula XXV

Wherein R ⁶ and R ⁷ are each, independently of one another, R ⁰ or X ⁰ , wherein X ⁰ , A ¹ , Z ¹ and R ⁰ are as defined in formulas I and I1,
And one or more decalin compounds.

式中、Ｘ^０およびＲ^０は、式ＩおよびＩ１において定義した通りであり、Ｚは、−ＣＨ_２Ｏ−、−ＯＣＨ_２−、−ＣＯＯ−、−Ｃ≡Ｃ−、−ＣＨ＝ＣＨ−、−ＣＦ_２Ｏ−、−ＯＣＦ_２−、−ＣＦ＝ＣＦ−、−Ｃ_２Ｆ_４−、−ＣＨ＝ＣＨ−（ＣＨ_２）_２−または−（ＣＨ_２）_４−、好ましくは−Ｃ_２Ｆ_４−であり、（Ｆ）は、ＨまたはＦである、
から選択されている。 The compound of formula XXV is preferably of the formula:

Wherein X ⁰ and R ⁰ are as defined in formulas I and I1, and Z is —CH ₂ O—, —OCH ₂ —, —COO—, —C≡C—, —CH ＝ CH— _{, -CF 2 O -, - OCF} 2 -, - CF = CF -, - C 2 F 4 -, - CH = CH- (CH 2) 2 - or - _{(CH 2) 4} -, preferably -C ₂ F ₄ —, (F) is H or F,
Is selected from

R ⁰ in these preferred formulas is preferably straight-chain alkyl having 1 to 8 carbon atoms or straight-chain alkenyl having 2 to 7 carbon atoms.
^{X 0} in these preferred formulas is _{preferably, -CF 3, -C 2 F 5} , -C 3 F 7, -OCF 3, -CH = CHF, - (CH 2) n -CH = CHF, - _{CH = CF 2, - (CH} 2) n -CH = CF 2, -CF = CF 2, - (CH 2) n -CF = CF 2, -OCH = CHF, -OCH = CF 2 or -OCF = CF ₂ .

は、好ましくは、

である。 −

Is preferably

It is.

-R ⁰ is the alkenyl having a linear alkyl or 2-7 carbon atoms having 1 to 8 carbon atoms.
The medium comprises a compound of the formula III, IV, V, VI, VII and / or VIII.
The medium consists essentially of the compounds of the formulas I to VIII and XXI to XXIII.
The total proportion of the compounds of the formulas I to VIII in the mixture as a whole is at least 50% by weight;
The medium consists essentially of a compound selected from the group consisting of the general formulas I to XXV.

The compounds of the formulas I to XXV are colorless, stable and easily miscible with each other and with other liquid crystal materials.
The individual compounds of the formulas I to XXV and their dependent formulas, which can be used in the media according to the invention, are known or can be prepared analogously to known compounds.

The term "alkyl" or "alkyl ^* " refers to linear and branched alkyl groups having 1 to 7 carbon atoms, preferably the linear groups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Is included. However, groups having 2-5 carbon atoms are particularly preferred.

The term "alkenyl" or "alkenyl ^* " embraces straight-chain and branched alkenyl groups having 2-7 carbon atoms, preferably the 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, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z -Hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl and 6-heptenyl. However, in particular, groups having up to 5 carbon atoms are preferred.

The term "fluoroalkyl" preferably refers to linear groups having a terminal fluorine, i.e., fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluorohexyl. -Fluoroheptyl. However, fluorine at other positions is not excluded.
The term “oxaalkyl” is preferably of the formula C _n H _{2n + 1} —O— (CH ₂ ) _m , wherein n and m are each independently 1-6 linear Groups. Preferably, n = 1 and m = 1-6.

  The group “(F)” in one of the structural formulas described herein is F or H.

By suitably selecting the meanings of R ⁰ and X ⁰ , the address time, threshold voltage, steepness of the transmission characteristic curve, and the like can be modified in a desired manner. For example, 1E-alkenyl, 3E-alkenyl and 2E-alkenyloxy groups generally have shorter address times, improved nematic tendency and elastic constants k ₃₃ (bend) compared to alkyl and alkoxy groups. And a high ratio of k ₁₁ (spread). 4-alkenyl and 3-alkenyl radicals are generally compared with alkyl and alkoxy groups, give lower threshold voltages and smaller values of k _{33 /} k _11.

-CH ₂ CH ₂ - group, generally results in higher values of _k 33 _{/ k 11} compared with a single covalent bond. greater values of k ₃₃ / _{k 11,} for example, in a TN cell having a twist of 90 °, (in order to achieve gray shades) easily and flatter transmission characteristic lines, STN, SBE and OMI cells (greater (A large time-sharing characteristic) to facilitate a steeper transmission characteristic curve and vice versa.

  The optimal mixing ratio of the compounds of the formulas I to XXV depends substantially on the desired properties, the choice of the individual compounds of these formulas and of any other components which can be present. Suitable mixing ratios within the aforementioned ranges can easily be determined from case to case.

  The total amount of the compounds of the formulas I to XXV in the mixtures according to the invention is not critical. Thus, the mixture may include one or more other components for the purpose of optimizing various properties. However, the observable effects on addressing time and threshold voltage generally increase as the total concentration of compounds of Formulas I-XXV increases.

  Conventional liquid-crystal materials, but in particular relatively high proportions of the compounds of the formulas I and II, mixed with one or more compounds of the formulas III, IV, V, VI, VII and / or VIII. Even a small ratio resulted in a significant reduction in threshold voltage and low birefringence value, and a broad nematic phase with a low smectic-nematic transition temperature was simultaneously observed and found to have improved shelf life. .

In a particularly preferred embodiment, the medium of the present invention comprises a compound of formula II-XVIII (preferably formula II) wherein X ⁰ is F, OCF ₃ , OCHF ₂ , OCH ＝ CF ₂ , OCF ＝ CF ₂ or OCF ₂ —CF ₂ H. , III and / or IV). The favorable synergistic effect with the compounds of the formula I results in particularly advantageous properties.

  The structure of the STN and MLC displays of the invention from polarizers, electrode substrates and surface-treated electrodes corresponds to the structure customary for displays of this type. Here, the term conventional construction is widely interpreted and also all inductive and modified versions of MLC displays, especially including matrix display elements based on poly-Si TFTs or MIMs, and very particularly transflective and reflective displays. Is included.

However, a significant difference between the display of the present invention and previous conventional displays based on twisted nematic cells lies in the choice of the liquid crystal parameters of the liquid crystal layer.
The liquid crystal mixtures which can be used in the present invention are produced in a manner customary per se. In general, the desired amount of the components used in the smaller amounts is dissolved in the components making up the main component, preferably at elevated temperature. It is also possible to mix the solutions of the components in an organic solvent such as acetone, chloroform or methanol and, after thorough mixing, remove the solvent again, for example by distillation. Furthermore, the mixture can be produced in other conventional ways, for example by using a premix, for example a corresponding mixture, or by using a so-called "multibottle" system.

  The dielectric may also include other additives known to those skilled in the art and described in the literature. For example, 0-15%, preferably 0-10%, of a polychromatic dye and / or a chiral dopant can be added. The individual compounds added are used at a concentration of 0.01 to 6%, preferably 0.1 to 3%. However, the concentration data of the liquid crystal mixture, i.e. the other constituents of the liquid crystalline or mesogenic compounds, are shown without taking into account the concentrations of these additives.

In the present application and in the examples below, the structure of the liquid crystal compounds is indicated by an acronym, the conversion of which into a chemical formula is obtained according to the following tables A and B. All groups C _n H _{2n + 1} and C _m H _{2m + 1} are straight-chain alkyl groups having n and m carbon atoms, respectively. n and m are each independently of the other preferably an integer of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10. The codes in Table B are self-evident. In Table A, only the initials related to the basic structure are shown. In each case, after the acronym for the basic structure, the codes for the substituents R ¹ , R ² , L ¹ and L ² are indicated, separated by a dash:

Preferred mixture components are shown in Tables A and B.
Table A:

Table B:

Table C (dopants):

Table D
Further suitable stabilizers and antioxidants for LC mixtures are described below (n = 0-10, terminal methyl groups not shown):

The following examples are intended to illustrate the invention without limiting it.
As used herein, percentages are weight percentages. All temperatures are given in degrees Celsius. m. p. Indicates a melting point, and cl. p. = Clear point. Further, C = crystalline state, S = smectic phase, N = nematic phase, Ch = cholesteric phase and I = isotropic phase. The data between these symbols indicates the transition temperature. In addition, the following abbreviations are used:

Unless stated dielectric anisotropy ε‖ dielectric constant parallel gamma ₁ other to the long axis of the molecules at the extraordinary refractive index [Delta] [epsilon] 20 ° C. in an optical anisotropy _n e 589 nm and 20 ° C. in [Delta] n 589 nm and 20 ° C. is 20 ° C. Rotational viscosity [mPa · s]
V ₁₀ threshold voltage [V] = 10% Characteristics in relative contrast of the voltage _V 90 90% of the characteristic voltage at a relative contrast [V]
VHR Voltage holding ratio [%]
SR Specific resistance after exposure to UV at room temperature for X hours [Ω · cm]

SR is measured as described in G. Weber et al., Liquid Crystals 5 , 1381 (1989).
VHR is measured as described by T. Jacob and U. Finkenzeller in "Merck Liquid Crystals-Physical Properties of Liquid Crystals", 1997.

Example 1
The nematic liquid crystal mixture H1 consists of:

Mixture M1 is prepared by adding 20% of the compound PUQUA-3-F of the formula I1a to the aforementioned host mixture H1.
Inventive mixture B1 is prepared by adding 20% of PUQUA-3-F and 0.4% of the UV stabilizer Tinuvin P® of the formula II1 to the aforementioned host mixture H1. .

The resistivity values of the mixtures H1, M1 and B1 are measured before and after UV irradiation. The results are shown in Table 1A.
Table 1A

After adding the compound PUQUA-3-F to the mixture H1, the resulting mixture M1 shows a drop in SR, especially on UV exposure. After adding the UV stabilizer to the mixture M1, the mixture B1 obtained according to the invention again shows a significantly higher SR value than the M1, especially after UV exposure.
The VHR of the mixtures H1, M1 and B1 is measured after heating to 100 ° C. and / or after irradiation for 2 hours with UV. The results are shown in Table 1B.
Table 1B

  Mixture B1 of the present invention comprising PUQUA-3-F and a UV stabilizer shows a higher VHR after heating and UV exposure than mixture M1 comprising PUQUA-3-F but without the UV stabilizer. Therefore, adding a UV stabilizer increases not only the UV stability of the mixture, but also the thermal stability.

Example 2
The nematic liquid crystal mixture M2 consists of:

The mixture B2 according to the invention is prepared by adding 0.4% of Tinuvin P® of the formula II1 to the mixture M2. The VHR of M2 and B2 after heating at 100 ° C. and the VHR after 2 hours of UV irradiation are shown in Table 2.
Table 2

  The addition of a UV stabilizer to M2 increases the UV stability and keeps the thermal stability constant.

Example 3
The nematic liquid crystal mixture M3 consists of:

The mixture B3 according to the invention is prepared by adding 0.4% of Tinuvin P® of the formula II1 to the mixture M3. The VHR of M3 and B3 after heating at 100 ° C. and the VHR after 2 hours of UV irradiation are shown in Table 3.
Table 3

  When a UV stabilizer is added to M3, the UV stability is increased and the thermal stability is kept constant.

Claims (14)

A liquid crystal medium, which comprises one or more general formulas I

A compound represented by and one or more UV stabilizers,
Where:
R has 1 to 15 carbon atoms, and is unsubstituted or is monosubstituted by CN or CF _3, or an alkyl or alkenyl radical which is at least monosubstituted by halogen, where, Further, one or more CH ₂ groups in these groups may each independently be —O—, —S—,

O atoms are substituted by -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CH = CH- or -C≡C- so as not to directly bond to each other. It is possible,

Is

And
Y ^{1 to} Y ⁹ are each independently H or F,
Z ¹ is —CF ₂ O—, —OCF ₂ —, or —COO—;
Z ² represents —O—, —S—, —CO—, —COO—, —OCO—, —S—CO—, —CO—S—, —OCH ₂ —, —CH ₂ O—, —SCH _{2 -, - CH 2 S -,} - CF 2 O -, - OCF 2 -, - CF 2 S -, - SCF 2 -, - CH 2 CH 2 -, - CF 2 CH 2 -, - CH 2 CF 2 - _{, -CF 2 CF 2 -, -} CH = CH -, - CF = CH -, - CH = CF -, - CF = CF -, - C≡C- or a single bond,
X ⁰ is F, Cl, an alkyl, alkenyl or alkoxy halide having 1 to 6 carbon atoms,
r is 0 or 1,
A liquid crystal medium, comprising: The following formula:

In the formula, X ⁰ , Y ¹ , Y ² , Y ⁴ , Y ⁵ , Y ⁷ , Y ⁸ , Z ¹ , Z ² and r are as defined in claim 1, and R ⁰ is 9 Having n carbon atoms, n-alkyl, n-alkoxy, n-oxaalkyl, n-fluoroalkyl, n-fluoroalkoxy or n-alkenyl;
2. The medium according to claim 1, comprising one or more compounds selected from the group consisting of: The following formula:

Wherein R ⁰ is as defined in claim 2,
The medium according to claim 1, comprising one or more compounds selected from the group consisting of: Formula II

Where:
R ¹ and R ² are each, independently of one another, H or having 1 to 25 carbon atoms and are unsubstituted or monosubstituted by CN or CF ₃ , or At least monosubstituted, wherein one or more CH ₂ groups are each, independently of one another, —O—, —S—,

O atoms are substituted by -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CH = CH- or -C≡C- so as not to directly bond to each other. Linear or branched alkyl, or having 3 to 25 carbon atoms, each of which is unsubstituted or mono- or polysubstituted by R or X ⁰ , Aryl, heteroaryl or alkylaryl,
X is H, F or Cl;
The medium according to any one of claims 1 to 3, further comprising at least one compound represented by the following formula: The following formula:

The medium according to claim 4, comprising at least one compound selected from the group consisting of: The following formula:

The medium according to any one of claims 1 to 5, comprising at least one compound selected from the group consisting of: Further, general formulas III to VIII:

Wherein r, X ⁰ , Y ¹ -Y ⁴ and R ⁰ are as defined in claims 1 and 2,
Z ⁰ _{is, -CF 2 O -, - OCF} 2 -, - C 2 F 4 -, - CF = CF -, - CH = CF -, - CF = CH -, - C 2 H 4 -, - (CH _{2) 4 -, - OCH 2} - or _-CH 2 is O-,
Z ³ _{is, -C 2 F 4 -, -} CF = CF -, - CH = CF -, - CF = CH -, - C 2 H 4 -, - (CH 2) 4 -, - OCH 2 - or - CH ₂ O—,
The medium according to any one of claims 1 to 6, further comprising one or more compounds selected from the group consisting of compounds represented by the following formulae. Further, the formula XXIII

Wherein X ⁰ , Y ¹ , Y ² and R ⁰ are as defined in claims 1 and 2,
The medium according to any one of claims 1 to 7, comprising one or more compounds represented by the following formulae.   9. The medium according to claim 1, wherein the proportion of the compound of the formula I in the mixture as a whole is in the range from 2 to 30% by weight.   Medium according to any of the preceding claims, characterized in that it comprises at least 0.4% by weight of UV stabilizers.   Media according to any of the preceding claims, having a voltage holding ratio (VHR) of> 90% after heating at 100C / 5 min.   Use of a liquid crystal medium according to any of claims 1 to 11 for electro-optical purposes.   An electro-optical liquid crystal display comprising the liquid crystal medium according to claim 1.   14. The electro-optical liquid crystal display according to claim 13, wherein the display is a TN, STN, TN-TFT, IPS or VA display.