JP5036958B2 - Liquid crystal medium - Google Patents

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 mainly used as dielectrics in display devices because the optical properties of such materials can be modified by the 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 having a twisted nematic structure, 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. They 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 that allow the following advantages in the cell are desirable: expanded nematic phase range (especially to low temperatures), switchability at very low temperatures (outdoor use, automobiles, aircraft) And increased resistance to UV radiation (longer useful life). However, it is not possible for media available from the prior art to achieve these advantages while maintaining other parameters.

  In the case of more highly twisted STN displays, liquid crystal media that allow greater time-sharing characteristics and / or lower threshold voltages and / or wider nematic phase ranges (especially at lower temperatures) are desirable. For this reason, further expansion of the available parameter width (clearing point, smectic-nematic transition or melting point, viscosity, dielectric parameter, elastic parameter) is urgently desired.

  ECB displays and more recent VA displays include a layer of liquid crystal media between two transparent electrodes, where the liquid crystal media has a negative value for dielectric (DC) anisotropy Δε. In the switch-off state, the liquid crystal molecules are homeotropic, i.e. aligned approximately perpendicular to the electrode surface or tilted homeotropically. Due to the negative dielectric anisotropy, realignment of liquid crystal molecules parallel to the electrode surface occurs in the switched-on state.

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

  In addition to the known liquid crystal displays (TN, STN, ECB and VA), where the electric field for reorientation occurs essentially perpendicular to the liquid crystal layer, the electrical signal is also significant when the electric field is parallel to the liquid crystal layer. There are displays that result in having 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 an inappropriate long response time and often an excessively high operating voltage. Accordingly, there is a need for a liquid crystal medium for IPS displays that does not have these drawbacks or only to a lesser extent. For this purpose, in addition to a suitable phase range, low tendency to crystallize at low temperatures, low birefringence and suitable electrical resistance, a low threshold voltage (V ₁₀ ) and low, which is particularly critical for response time There are special requirements for liquid crystal materials having a rotational viscosity (γ ₁ ).

Similar to 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 switch individual pixels individually are, for example, active elements (ie transistors). The term “active matrix” is then used, where a distinction can be made between the two types:
1. MOS (metal oxide semiconductor) or other diode on a silicon wafer as a 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. This is because even if various partial displays are assembled in a modular manner, a problem occurs in the joint portion.
Preferably, in the more promising type 2, the electro-optic effect used is usually the TN effect. A distinction is made between the two technologies: TFTs comprising compound semiconductors such as CdSe, or TFTs based on polycrystalline or amorphous silicon. Research efforts are being made around the world with regard to the latter technique.

  The TFT matrix is applied to the inside of one glass plate of the display, while the other glass plate carries a transparent counter electrode on the 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 so that the filter element faces each switchable pixel.

A TFT display normally operates as a TN cell (TN-TFT) having a crossed polarizing plate in transmitted light, and is illuminated on the back surface.
The term MLC display here includes all matrix displays with integrated non-linear elements, ie 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 nonlinear elements for switching individual pixels, for example, large positive dielectric anisotropy, wide nematic phase, relatively low birefringence, very high specific resistance, good UV And a medium with temperature stability and low vapor pressure is desirable.

  This type of MLC display is particularly suitable for TV applications (eg, pocket TV), and for computer applications (laptops) and advanced information displays for automotive and aircraft construction. In addition to the problems related to the angle dependency of the contrast and the response time, in the MLC display, there is a difficulty due to an inappropriately high specific resistance value of the liquid crystal mixture [Non-Patent Document 1; Non-Patent Document 2].

  As the resistance value decreases, the contrast of the MLC display decreases, which can cause afterimage erasure problems. The specific resistance value of the liquid crystal mixture generally decreases throughout the lifetime of the MLC display due to interaction with the internal surface of the display, so a high (initial) resistance value is very important to obtain an acceptable useful life. is there. In particular, in the case of a low voltage mixture, it has been impossible in the past to achieve a very high specific resistance value. Furthermore, it is important that the resistivity value has the smallest possible increase with increasing temperature and after heat 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 phase 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 that have very high resistivity values and at the same time a large operating temperature range, short response time and low threshold voltage at low temperatures, which do not have or are only to a small extent the aforementioned drawbacks A great demand is continuing.

  In addition to liquid crystal displays that use backside illumination, i.e., operate transmissively and optionally transflectively, reflective liquid crystal displays are also of particular interest. These reflective liquid crystal displays use ambient light for information displays. They therefore consume significantly less energy than back illuminated liquid crystal displays with corresponding sizes and resolutions. Because the TN effect is characterized by a 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, for example as used in watches and pocket calculators.

  However, the principle can also be applied to high quality, high resolution active matrix addressed displays such as TFT displays. Here, already using a liquid crystal having a low birefringence (Δn), as is generally the case in conventional transmissive TFT-TN displays, to achieve a low optical delay (d · Δn) is necessary. This low optical delay results in a normally acceptable low viewing angle dependence of contrast (see Patent Document 2). In reflective displays it is much more important to use liquid crystals with low birefringence than in transmissive displays. This is because, in a reflective display, the effective layer thickness through which light passes is approximately twice as large as that of a transmissive display having the same layer thickness.

  In addition to lower power consumption (because backside illumination is not necessary), the advantages of reflective displays over transmissive displays are that they are space-saving with very low physical depth, and backside illumination. The problem with temperature gradients caused by various degrees of heating due to is reduced.

  In general, the liquid crystal materials for the aforementioned display types must have good chemical and thermal stability and good stability against electric fields and electromagnetic radiation. Furthermore, the liquid crystal material has a low viscosity and must provide a short address time, a low threshold voltage and a high contrast in the cell.

  Furthermore, they must have a suitable mesophase, for example a nematic or cholesteric mesophase for the aforementioned cells, at the normal operating temperature, ie below and above room temperature and in the widest possible range. Since liquid crystals are generally used in the form of a mixture of multiple components, it is important that the components are easily miscible with each other. Other properties, such as conductivity, dielectric anisotropy and optical anisotropy, must meet various requirements depending on the type of cell 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 (Shut-Hellfrich) cell, a medium that facilitates the following advantages is desirable for this cell:
-Expanded 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 thickness and rapid response time.

Media available from the prior art does not make it possible to achieve these advantages and at the same time maintain other parameters.
In particular, UV stability and voltage holding ratio (VHR) [Non-patent document 3; Non-patent document 4; Non-patent document 5] and specific resistance (SR) [non-patent document 6] of a liquid crystal medium with respect to heating or UV exposure are Often inappropriate. Specific resistance is an important quality feature of liquid crystal mixtures. A low SR value can cause an unacceptable drop in VHR.

International Publication No. 91/10936 Pamphlet Togashi S, Sekiguchi K, Tanabe H, Yamamoto E, Sorimachi K, Tajima E, Watanabe H, Shimizu H ., SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H.), Proc. Eurodisplay 84, September 1984: A210-288 Matrix ECD Controlled Matrix LCD Controlled by Double Stage Diode Rings, page 141 onwards, Paris STROMER, M., Proc. Eurodisplay 84, September 1984: Design of Thin Film Transistors for Matrix Addressing of Television Liquid Crystal Displays (Design of Thin Film Transistors for Matrix Addressing of Television Liquid Crystal Displays) German Patent No. 30 22 818 S. Matsumoto et al., Liquid Crystals, 5, 1320 (1989) K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, 304 (1984) T. Jacob and U. Finkenzeller, "Merck Liquid Crystals-Physical Properties of Liquid Crystals" During 1997 G. Weber et al., Liquid Crystals, 5, 1381 (1989)

  Thus, the present invention preferably has a low threshold voltage, a low rotational viscosity, a rapid response time and at the same time a high specific resistance value, to the extent that it does not have the aforementioned disadvantages or is only reduced. Of this type of MLC, TN, STN, VA or IPS displays, especially TN-TFT displays, which have high thermal stability, high UV stability and especially high values of voltage holding ratio (VHR) during UV exposure and heating For the purpose of providing a medium.

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

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 present invention is a liquid-crystalline medium, in particular based on a mixture of polar compounds having positive dielectric anisotropy, which comprises one or more compounds of the formula I

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, Furthermore, one or more of the CH ₂ groups in these groups are each independently of each other —O—, —S—,

O atoms are substituted by —CO—, —CO—O—, —O—CO—, —O—CO—O—, —CH═CH— or —C≡C— so that they are not directly bonded 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, alkyl halide having 1 to 6 carbon atoms, alkenyl or alkoxy,
r is 0 or 1;
In particular, the present invention relates to a liquid crystal medium.

Suitable UV stabilizers are known from the prior art. Many of these compounds are commercially available. Particularly preferred is the 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 1 to 25 carbon atoms, unsubstituted or monosubstituted by CN or CF ₃ , or by halogen At least monosubstituted, wherein one or more CH ₂ groups are each independently of each other —O—, —S—,

O atoms are substituted by —CO—, —CO—O—, —O—CO—, —O—CO—O—, —CH═CH— or —C≡C— so that they are not directly bonded 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 the UV stabilizer represented by these.

The invention further relates to the use of the medium according to the invention for electro-optical purposes.
The invention further relates to an electro-optical liquid crystal display comprising the liquid crystal medium of 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 formula I have a wide range of uses. These compounds can act as the base material from which the liquid crystal medium is mainly composed, or they can be added to liquid crystal base materials from other groups of compounds, for example the dielectric differences of this type of dielectric. The isotropic 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 in particular reduce the threshold voltage and the response time of the liquid-crystal mixtures according to the invention.
The addition of UV stabilizers, particularly those represented by Formula II, increases the VHR of the liquid crystal media of the present invention when exposed to UV, while the VHR of the liquid crystal media after heating is little or not impaired. There is nothing. This is a decisive advantage, especially for matrix displays such as TN-TFT displays.

Thus, the combination of a compound of formula I and a UV stabilizer provides liquid crystal media and displays having simultaneously a high VHR and improved threshold voltage and response time upon UV exposure and heating. 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 compound of formula I is preferably of the following formula:

In which X ⁰ , Y ^{1 to} 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,
Selected from.

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

Preference is furthermore given to compounds of the formulas I, I1 and I2, in which Z ¹ is —CF ₂ O— or —OCF ₂ —, particularly preferably —CF ₂ O—.
Preference is furthermore given to compounds of the formulas I, I1 and I2, in which Z ¹ is —COO—.
Preference is furthermore given to compounds of the formulas I, I1 and I2, in which 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。

Where R ⁰ is as previously defined,
It is. Especially preferred are compounds of formula 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, in which further one or 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 A compound. Very particularly preferred groups 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 is the following formula (terminal methyl group 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 of the formula II selected from mixtures of these compounds.

Particularly preferred are compounds of 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. The compound of formula II1 can be obtained, for example, under the name Tinuvin P®.

で表されるものである。 Further suitable UV stabilizers are of the following 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 are as described in the literature (eg in standard academic books such as Houben-Weyl, Methoden der Organischen Chemie, Georg-Thieme-Verlag, Stuttgart) It is precisely known and is prepared by a method known per se under reaction conditions suitable for the aforementioned reaction. Also here, variants which are known per se but are not mentioned here in more detail can be used.

  In the pure state, the compounds of the formula I are colorless and form a liquid-crystalline mesophase in a temperature range that is preferably located for electro-optical use. They are stable to chemical, thermal and light.

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 linear 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. .

When one of the groups R, R ⁰ , R ¹ and R ² is an alkyl group in which one CH ₂ group is substituted by —CH═CH—, this is straight-chain or branched Can be. This is preferably straight-chain and has 2 to 10 carbon atoms. This is therefore 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 , Oct-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.

When one of the radicals R, R ⁰ , R ¹ and R ² is an alkyl group in which one CH ₂ group is substituted by —O— and one is substituted by —CO— , Preferably adjacent. They therefore 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 substituted by —O— and / or —CO—O— This can be linear or branched. This is preferably branched and has 3 to 12 carbon atoms. This is therefore particularly preferably 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) ) Pentyl.

One of the groups R, R ⁰ , R ¹ and R ² is one in which one CH ₂ group is unsubstituted or substituted by a substituted —CH═CH—, and the adjacent CH ₂ group is CO, CO—O or O In the case of an alkyl group substituted by —CO, this can be linear or branched. This is preferably straight-chain and has 4 to 13 carbon atoms. This is therefore particularly preferably 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.

When 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 linear. Substitution with CN or CF ₃ is possible at any desired position.
If one of the radicals R, R ⁰ , R ¹ and R ² is an alkyl or alkenyl radical that is monosubstituted at least by halogen, this radical is preferably straight-chain and the halogen is preferably F Or it is Cl. In the case of polysubstitution, the halogen is preferably F. The resulting group also contains a perfluorinated group. 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 they are particularly important as chiral dopants when they are optically active. is there. This type of smectic compound is suitable as a component of a ferroelectric material.

This type of branching group preferably comprises no 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, 2 -Ethylhexyloxy, 1-methylhexyloxy and 1-methylheptyloxy.

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

  The liquid crystal medium of the present invention allows a significant expansion of the available parameter width. In particular, the achievable combinations of clearing point, low temperature viscosity, thermal and UV stability and optical anisotropy far exceed the prior art from previous materials.

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

The dielectric anisotropy Δε of the liquid crystal medium according to the invention is preferably ≧ 5, particularly preferably ≧ 8 and in particular ≧ 10.
The liquid-crystalline media according to the invention for TN and STN displays are preferably Δn> 0.07, particularly preferably ≧ 0.08 and preferably ≦ 0.2, particularly preferably ≦ 0.16, in particular 0.085. It has a birefringence value between 0.15. The liquid-crystalline media according to 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 1.7V, preferably lower than 1.5V.
The rotational viscosity γ ₁ of the liquid-crystalline medium according to the invention at 20 ° C. is preferably <200 mPas and particularly preferably <150 mPas.

  Also, by suitable selection of the components of the mixture of the present invention, a higher clearing point (eg, greater than 110 ° C.) is achieved at a lower dielectric anisotropy value while maintaining other advantageous properties, and thus higher. It is possible to achieve a threshold voltage or a lower clearing point at a higher dielectric anisotropy (eg> 12) and thus to achieve a lower threshold voltage (eg <1.5 V) Needless to say. It is likewise possible to obtain a mixture with a relatively large Δε and thus a relatively low threshold, with a correspondingly increasing viscosity.

Measurement of voltage holding ratio (VHR), also known as capacity holding ratio [S. Matsumoto et al., Liquid Crystals 5 , 1320 (1989); K. Niwa et al., Proc. SID Conference, San Francisco, Jun. 1984, p. 304 (1984); T. Jacob and U. Finkenzeller, "Merck Liquid Crystals-Physical Properties of Liquid Crystals", in 1997], compounds of formula I and UV stabilizers, The liquid crystal media of the present invention, particularly including those represented by Formula II, have been shown to have a suitable VHR 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 crystal medium of the present invention comprising a compound of formula I is a cyano group or 4-cyanophenyl group,

Cyanophenylcyclohexane represented by the formula

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

The UV stability of the liquid crystal medium of the present invention is also significantly better. That is, they have a remarkably small decrease in VHR when exposed to UV.
The voltage holding ratio VHR of the liquid-crystalline medium according to the invention after heating at 100 ° C./5 minutes is preferably> 90%, particularly preferably> 94%, very particularly preferably> 96% and in particular> 98%. .

The voltage holding ratio VHR of the liquid-crystalline media according to the invention after UV exposure (2 hours) is preferably> 75%, particularly preferably> 80%, very particularly preferably> 85% and in particular> 90%.
The voltage holding ratio VHR of the liquid-crystalline media according to the invention after heating at 100 ° C./5 min and UV exposure (2 hours) is preferably> 60%, particularly preferably> 65%, very particularly preferably> 70% and In particular> 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 are preferably less than 25% by weight, particularly preferably less than 15% by weight and in particular less than 5% by weight of compounds comprising one or more cyano groups, in particular of this type. Contains mesogenic or liquid crystalline compounds. Very particular preference is given to liquid crystal media which do not contain compounds having one or more cyano groups.

  The transmission type MLC display of the present invention preferably operates at the first transmission minimum of Gooch and Tally [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 steepness of the characteristic curve and low angular dependence of contrast (DE 30 22 818), it is even lower The dielectric anisotropy is sufficient at the second minimum, at the same threshold voltage as in similar displays. This makes it possible to achieve a significantly higher specific resistance value, for example, than in the case of a mixture containing a cyano compound, using the mixture according to the invention at the first minimum value.

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

A preferred embodiment is shown below:
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 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 in particular 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 1-4, particularly preferably of formula II And in particular 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 0.01-5% by weight, particularly preferably 0.1-2% by weight, very particularly preferably 0.3-1% by weight and in particular 0 Within the range of 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 further comprises 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—
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 following formula:

In which R ⁰ is as defined in formula I1 and is preferably methyl, ethyl, n-propyl, n-butyl or n-pentyl.
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 following formula:

In which R ⁰ is as defined in formula I1 and X ⁰ is preferably F or OCF ₃ ;
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 following formula:

In which R ⁰ is as defined in formula I1 and is preferably methyl, ethyl, n-propyl, n-butyl or n-pentyl.
Selected from.

The medium further comprises 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。

In which R ⁰ , X ⁰ and Y ^{1 to} Y ⁴ are as defined in formulas I and I1.
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 is further represented by the general formulas XVI to XX:
One or more compounds selected from the following group consisting of:

In which 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 fluorine atoms.

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 further of the formula XXI

Wherein R ⁵ and R ⁶ are each independently as defined for R ⁰ in formula I1.
1 type, or 2 or more types of bicyclic compounds represented by these are included.

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 is preferably of the following formula:

In which 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 n-C ₃ H ₇ .
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 of the formula IIIa, preferably of formula IIIa1, wherein R ⁰ is alkenyl having 2 to 7 carbon atoms

^Where R ^1a is H, CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ .
1 type or 2 or more types of alkenyl compounds selected from these are included.

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 following formula:

In which “alkyl” and “alkyl ^* ” are as defined later,
1 type or 2 types or more selected from 1, Preferably, 1 type, 2 types, or 3 types of compounds are included.

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 further of the formula XXIII

Wherein X ⁰ , Y ¹ , Y ² and R ⁰ are as defined in formulas I and I1.
1 type or 2 types or more of ester compounds represented by these are included.

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 is preferably of the following formula:

In which R ⁰ is as defined in formula I1.
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 following formula:

1 type or 2 types or more, Especially preferably, 1 type or 2 types of dioxane compounds are included.

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

In which R ⁶ and R ⁷ are each independently R ⁰ or X ⁰ , and X ⁰ , A ¹ , Z ¹ and R ⁰ are as defined in formulas I and I1,
1 type or 2 or more types of decalin compounds represented by these are included.

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 the formula XXV is preferably of the following 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 − and (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 formula III, IV, V, VI, VII and / or VIII.
The medium consists essentially of 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 subordinate formulas that can be used in the medium of the invention are known or can be prepared analogously to known compounds.

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

The term “alkenyl” or “alkenyl ^* ” includes straight-chain and branched alkenyl groups having 2 to 7 carbon atoms, preferably 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, groups having up to 5 carbon atoms are particularly preferred.

The term “fluoroalkyl” is preferably a linear group with a terminal fluorine, ie fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7 -Includes fluoroheptyl. However, fluorine at other positions is not excluded.
The term “oxaalkyl” is preferably represented by the formula C _n H _{2n + 1} —O— (CH ₂ ) _m , wherein n and m are each linear 1 to 6 independently of one another. Includes groups. Preferably, n = 1 and m = 1-6.

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

By suitably selecting the meaning 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 groups, 3E-alkenyl groups and 2E-alkenyloxy groups generally have shorter address times, improved nematic trends and elastic constants k ₃₃ (bending) compared to alkyl and alkoxy groups. And a high ratio of k ₁₁ (spread). 4-Alkenyl and 3-alkenyl groups generally result in lower threshold voltages and lower k ₃₃ / k ₁₁ values compared to alkyl and alkoxy groups.

A —CH ₂ CH ₂ — group generally results in a high k ₃₃ / k ₁₁ value compared to a single covalent bond. A larger value of k ₃₃ / k ₁₁ facilitates a flatter transmission characteristic curve (for example, to achieve a gray shade) in a TN cell having a 90 ° twist, for example, STN, SBE and OMI cells (one layer). It facilitates a steeper transmission curve for large time-sharing characteristics and vice versa.

  The optimum 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 the choice of all other components that can be present. Suitable mixing ratios within the aforementioned range can easily be determined from case to case.

  The total amount of compounds of the formulas I to XXV in the mixtures according to the invention is not critical. Thus, this mixture can contain one or more other ingredients for the purpose of optimizing various properties. However, the observable effect with respect to address time and threshold voltage generally increases with higher total concentration of compounds of Formulas I-XXV.

  A comparative liquid crystal material, but in particular of compounds of the formulas I and II mixed with one or more compounds of the formulas III, IV, V, VI, VII and / or VIII It was found that even a small ratio resulted in a significant decrease in threshold voltage and low birefringence value, and a wide nematic phase with a low smectic-nematic transition temperature was observed simultaneously, improving shelf life. .

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 _OCF 2 -CF ₂ H, wherein II～XVIII (preferably of Formula II , III and / or IV). A 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 present invention from the polarizer, electrode substrate and surface treated electrode corresponds to the structure customary for this type of display. Here, the term conventional structure is broadly interpreted and in particular all inductive and modified versions of MLC displays and in particular transflective and reflective displays comprising matrix display elements based on poly-Si TFTs or MIMs. Is included.

However, a significant difference between the display of the present invention and previous conventional displays based on twisted nematic cells is in the selection of the liquid crystal parameters of the liquid crystal layer.
The liquid crystal mixture which can be used in the present invention is produced by a conventional method. In general, the desired amount of the components used in the lesser amount is dissolved in the components making up the principal constituent, preferably at elevated temperature. It is also possible to mix a solution of the components in an organic solvent, for example acetone, chloroform or methanol, and after mixing well, remove the solvent again, for example by distillation. Furthermore, the mixture can be produced in other customary ways, for example by using a premix, for example an equivalent mixture, or by using a so-called “multibottle” system.

  The dielectric is also known to those skilled in the art and can include other additives described in the literature. For example, 0-15%, preferably 0-10% of pleochroic dyes and / or chiral dopants can be added. The individual compounds added are used at a concentration of 0.01-6%, preferably 0.1-3%. However, the concentration data of the other components of the liquid crystal mixture, i.e. the liquid crystalline or mesogenic compound, are presented without considering the concentration of these additives.

In the present application and in the following examples, the structure of the liquid crystal compound is indicated by an acronym and its conversion to the chemical formula is obtained according to Tables A and B below. All groups C _n H _{2n + 1} and C _m H _{2m + 1} are linear alkyl groups having n and m carbon atoms, respectively. n and m are each independently an integer of preferably 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10. The codes in Table B are self explanatory. In Table A, only the initial letter relating to the basic structure is shown. In each case, the codes for the substituents R ¹ , R ² , L ¹ and L ² are shown, separated by a dash after the initial letters relating to the basic structure:

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 the LC mixture are described below (n = 0-10, terminal methyl groups not shown):

The following examples are intended to illustrate the present invention without limiting it.
In the present specification, the percentage is weight percent. All temperatures are given in degrees Celsius. m. p. Indicates melting point, cl. p. = Clearing point. Furthermore, C = crystalline state, S = smectic phase, N = nematic phase, Ch = cholesteric phase and I = isotropic phase. Data between these symbols indicates the transition temperature. In addition, the following abbreviations are used:

Δn 589 nm and optical anisotropy at 20 ° C. n _e 589 nm and extraordinary refractive index at 20 ° C. Δε Dielectric anisotropy at 20 ° C. Dielectric constant γ ₁ parallel to the long axis of the molecule 20 ° C. unless otherwise stated Rotational viscosity [mPa · s]
V ₁₀ threshold voltage [V] = characteristic voltage at a relative contrast of 10% V ₉₀ characteristic voltage at a relative contrast of 90% [V]
VHR voltage holding ratio [%]
SR Specific resistance [Ω · cm] after exposure to UV for X hours at room temperature

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 is composed of the following.

Mixture M1 is prepared by adding 20% of the compound PUQU-3-F of formula I1a to the aforementioned host mixture H1.
A mixture B1 according to the invention is prepared by adding 20% PUQU-3-F and 0.4% UV stabilizer Tinuvin P® represented by 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 compound PUQU-3-F to mixture H1, the resulting mixture M1 shows a drop in SR, especially upon UV exposure. After adding a UV stabilizer to the mixture M1, the mixture B1 obtained according to the invention again shows a significantly higher SR value than M1, especially after UV exposure.
The VHR of the mixtures H1, M1 and B1 are measured after heating to 100 ° C. and / or after irradiation with UV for 2 hours. The results are shown in Table 1B.
Table 1B

  The mixture B1 of the present invention comprising PUQU-3-F and a UV stabilizer exhibits a higher VHR after heating and UV exposure than the mixture M1 comprising PUQU-3-F but no UV stabilizer. Thus, the addition of UV stabilizers increases not only the UV stability of the mixture, but also the thermal stability.

Example 2
The nematic liquid crystal mixture M2 is composed of the following.

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

  When UV stabilizers are added to M2, UV stability increases and thermal stability remains constant.

Example 3
The nematic liquid crystal mixture M3 is composed of the following.

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

  When UV stabilizers are added to M3, UV stability increases and thermal stability remains constant.

Claims (11)

A liquid crystal medium comprising one or more general formulas I1a

Wherein R ⁰ is n-alkyl having up to 5 carbon atoms,
Characterized the early days containing compound represented by and one or more UV stabilizers, the liquid crystal medium. The medium of claim 1 , wherein R ⁰ has 1 to 3 carbon atoms. The medium of claim 2 , wherein R ⁰ has 2 or 3 carbon atoms. Formula II

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

O atoms are substituted by —CO—, —CO—O—, —O—CO—, —O—CO—O—, —CH═CH— or —C≡C— so that they are not directly bonded 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.
At least, characterized in that it comprises one compound, medium according to any one of claims 1 to 3, in represented. The following formula:

5. A medium according to claim 4 , characterized in that it comprises at least one compound selected from. Furthermore, general formulas III to VIII:

Wherein r, X ⁰ , Y ^{1 to} Y ⁴ and R ⁰ are as defined in claims 1 and 5;
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—
In it characterized in that it comprises a represented by one selected from the group consisting of the compounds or two or more compounds, medium according to any one of claims 1-5. The ratio of the overall compound of the formula I in the mixture, characterized in that it is in the range of 2 to 30 wt%, medium according to any one of claims 1-6. Characterized in that it comprises at least 0.4 wt% of UV stabilizer, medium according to any one of claims 1-7. Use of a liquid crystal medium according to any one of claims 1 to 8 for electro-optical purposes. To any one of claims 1-8 comprising a liquid crystal medium according, electro-optical liquid-crystal display. 11. The electro-optical liquid crystal display according to claim 10 , which is a TN, STN, TN-TFT, IPS or VA display.