JP2004352992A - Liquid crystal medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal medium simultaneously having an extremely large specific resistance value and a low threshold voltage, particularly, a liquid crystal medium for MLC, TN and STN displays. <P>SOLUTION: The liquid crystal medium comprises a mixture of polar compounds having positive dielectric anisotropy as a base material, and the medium comprises one or more compounds represented by formula (1), wherein, R<SP>1</SP>is a (substituted) 1-15C alkyl or the like; X is F, Cl, CN, SF<SB>5</SB>or the like; and L<SP>1</SP>and L<SP>2</SP>are each H or F. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to liquid crystal media, their use in electro-optical applications, and displays containing this media.

  Liquid crystals are in principle used as dielectrics in display devices. The reason for this is that the optical properties of such substances can be changed by the applied voltage. Electro-optical devices based on liquid crystals are widely and sufficiently known to those skilled in the art and can be based on various effects. Examples of such devices include cells with dynamic scattering, DAP (aligned phase deformation) cells, guest / host cells, TN cells with twisted nematic structures, STN (super twist nematic) cells, SBE (super birefringent) Effect) cells and OMI (optical mode interference) cells. Most conventional display devices are based on the Schadt-Helfrich effect and have a twisted nematic structure.

  The liquid crystal material must have good chemical and thermal stability and good stability to electric fields and electromagnetic radiation. Furthermore, the liquid crystal material should have a low viscosity and provide a short addressing time, a low threshold voltage and a high contrast in the cell.

  The liquid crystals must also have a suitable mesophase, for example a nematic or cholesteric mesophase for the cell, at normal operating temperatures, ie in the widest possible temperature range from room temperature to room temperature. Since liquid crystals are generally used as a mixture of a plurality of components, it is important that these components be readily miscible with one another. Still other properties, such as conductivity, dielectric anisotropy and optical anisotropy, must meet various requirements depending on the cell type and field of application. As an example, the material for a cell having a twisted nematic structure must have positive dielectric anisotropy and low electrical conductivity.

As an example, for a matrix liquid crystal display (MLC display) with integrated non-linear elements for switching each pixel, a large positive dielectric anisotropy, a wide nematic phase, a relatively small birefringence, a very large resistivity, A medium with good ultraviolet and temperature stability, and low vapor pressure is desired.
Matrix liquid crystal displays of this type are known. Examples of non-linear elements that can be used to switch each pixel individually include active elements (ie, transistors). This device is also represented by the term "active matrix" and can be divided into two types:
1. MOS (metal oxide semiconductor) or another diode on a silicon wafer as a substrate.
2. Thin film transistors (TFTs) on a glass plate as a substrate.

The use of single crystal silicon as the substrate material limits the size of the display, even with the modular assembly of the various partial displays, as problems occur at the junctions.
For the preferred and more promising Type 2, the electro-optic effect used is usually the TN effect. This effect differs between the two technologies: TFTs containing compound semiconductors, such as CdSe, or TFTs based on polycrystalline or amorphous silicon. Special research is being conducted worldwide on the latter technology.

The TFT matrix is applied to the inside surface of one glass plate of the display, while the inside surface of another glass plate carries a transparent counter electrode. Compared to the size of the pixel electrode, the TFT is very small and has little detrimental effect on the image. The technology will also evolve to a full color compatible display where the red, green and blue filters are arranged in a mosaic fashion such that each filter is opposite to a switchable pixel. Can be.
TFT displays typically operate as TN cells with crossed polarizers in the transmitted light and are illuminated from behind.

As used herein, the term MLC display encompasses all matrix displays with integrated non-linear elements. That is, a display is included that, in addition to the active matrix, also comprises passive elements such as varistors or diodes (MIM = metal-insulator-metal).
This type of MLC display is particularly suitable for TV applications (eg, pocket televisions) or computer applications (laptop type) or for advanced information displays for automobile or aircraft construction. In addition to the problems related to the angle dependence of the contrast and the response time, MLC displays suffer from problems due to insufficiently high resistivity of the liquid crystal mixture (see Non-Patent Documents 1 and 2).

  As the resistance decreases, the contrast of the MLC display decreases, which may cause an afterimage erasure problem. Since the specific resistance of the liquid crystal mixture is generally reduced throughout the life of the MLC display due to interaction with the internal surface of the MLC display, a large (initial) resistance is necessary to obtain an acceptable operating life. The value is very important. Particularly in the case of low-voltage mixtures, it has hitherto been impossible to obtain very large specific resistance values. It is also important that this increase in resistivity be as low as possible after temperature rise and exposure to heating and / or ultraviolet radiation. The low temperature properties of the mixtures from the prior art are also particularly disadvantageous. Even at low temperatures, it is required that crystallization and / or smectic phases do not form and that the temperature dependence on viscosity is as small as possible. However, prior art MLC displays do not meet current requirements.

  In addition to liquid crystal displays that use backside illumination, ie, those that operate by transmission and, if desired, by transflective, special interest is given to reflective liquid crystal displays. These reflective liquid crystal displays use ambient light for displaying information. Therefore, these displays consume significantly less energy compared to a backlit liquid crystal display having a corresponding size and resolution. Since the TN effect is characterized by having very good contrast, a reflective liquid crystal display of this type can be easily read even in bright ambient conditions. This is already known as a simple reflective TN display, as used, for example, in watches and pocket calculators.

  However, this principle can also be applied to high quality and high resolution active matrix displays, such as TFT displays. In this case, it is necessary to use a liquid crystal having a low birefringence (Δn) in order to obtain a small optical retardation (d · Δn) as in the case of a conventional transmission type TFT-TN display. is there. This small optical retardation results in a viewing angle dependency with low contrast that is normally allowed (see Patent Document 1). Since the effective layer thickness through which light passes is almost twice as large as that of a transmissive display having the same layer thickness, a reflective display has a smaller birefringence than a transmissive display. The use of liquid crystals is even more important.

Therefore, it has a wide operating temperature range, a short response time even at low temperatures, and a low threshold voltage, while having a very large specific resistance value and does not have or has these conventional disadvantages. There continues to be a great demand for MLC displays, to a lesser extent.
In the case of a TN (Schat-Helfrich) cell, a medium is desired for the cell that promotes the following advantages:
-Extended nematic phase range (especially even at low temperatures)
-Stable storage even at very low temperatures-Driving ability at very low temperatures (outdoor applications, automobiles, aircraft)
Increased resistance to UV radiation (longer life).

The media available from the prior art are able to achieve these advantages while retaining no other parameters.
For supertwisted (STN) cells, media capable of greater time sharing characteristics and / or lower threshold voltage and / or wider nematic phase range (especially at low temperatures) are desired. Further expansion of the range of parameters available for this purpose (clearing point, smectic-nematic transition or melting point, viscosity, dielectric parameters, elastic parameters) is particularly desired.
German Patent No. 3022818 (DE30222818) Togashi, S. (TOGASHI, S.), Sekiguchi, Kei. (SEKIGUCHI, K), Tanabe, H. et al. (TANABE, H), Yamamoto, E. (YAMAMOTO, E), Sorimachi, Kei. (SORIMACHI, K), Tajima, e. (TAJIMA, E.), Watanabe, H.C. (WATANABE, H), Shimizu, H .; (SHIMIZU, H), Proc. Eurodisplay 84, September 1984, "A210-288 Matrix LCD Controlled by Double Stage Diode Rings", Paris, p. 141, p. (Paris) Stromer, M. (STROMER, M), Proc. Eurodisplay (Proc. Eurodisplay) 84, September 1984, "Design of Thin Film Transistor's DresdixResidryDressionDrystryDrequestResidryDrystryDrequestResidryRefreshingDrystryDrequestResidryRefreshingDrystryDrequestResidryRefreshingDrystryRefreshingDrystryDryTrustResDryTrustResDryTrustResDryTrustingDryStressRefreshingDressTrustingDrysTrustResDryTrustResDryTresidRefreshingDrysTrustResDryTrustingDrysTrustResDrysTrustResDryTrysdRegistryTradingResidryRefreshingDryStoryTradingDresidRescribing. Later, Paris

  It is an object of the present invention to provide a liquid-crystal medium which does not have the above-mentioned disadvantages, or which has at least a small degree of such a disadvantage, and which at the same time has a very high specific resistance and a low threshold voltage at the same time, in particular MLC, It is to provide a liquid crystal medium for a TN or STN display.

It has now been found that this object can be achieved when the medium according to the invention is used in a display. The media according to the invention are distinguished by having a high dielectric anisotropy value and a very low optical anisotropy value. At the same time, the medium has a very low threshold voltage and a very low rotational viscosity gamma _1.
Accordingly, the present invention relates to a liquid crystal medium based on a mixture of polar compounds having a positive dielectric anisotropy, characterized in that this medium contains one or more compounds of the formula I. What you do:

Where:
R ¹ has 1 to 15 carbon atoms and is a halogenated or unsubstituted alkyl or alkoxy group, and one or more CH ₂ groups present in these groups are Each being independent of one another and in which the oxygen atoms are not directly bonded to each other, are replaced by -C≡C-, -C = C-, -O-, -CO-O- or -O-CO-. Well,
X is, F, Cl, CN or SF _5, or a halogenated alkyl group, halogenated alkenyl group, a halogenated alkoxy radical or a halogenated alkenyloxy radical having up to 6 carbon atoms, respectively, and L ¹ And L ² are each independently of one another and are H or F.

The compounds of the formula I are covered by the Chisso protection rights EP 0 882 221 and EP 0 844 229 A1.
The mixtures disclosed under these protective rights have the disadvantage that they have a very high threshold voltage and a relatively low clearing point combined with a large Δn value or a low threshold voltage and at the same time a low clearing point. Having.
The object of the present invention is to provide a liquid crystal mixture having a relatively high clearing point, a low threshold voltage, preferably a threshold voltage of ≦ 1.3 V, in particular <1.25 V and very particularly preferably <1.00 V. provide. The Δn value should preferably be in the range 0.06 to 0.12.

Surprisingly, it has been found that liquid-crystal mixtures containing compounds of the formula I have a high clearing point and a low threshold voltage. The present invention also relates to compounds of formula I. In formula I, compounds wherein L ¹ = L ² = F, and further compounds where L ¹ = L ² = H, are mentioned as particularly preferred compounds. In formula I, compounds where L ¹ ＬL ² ＦF and X ＝ F or OCHF ₂ are mentioned as very particularly preferred compounds. X is _{preferably, CN, F, SF 5,} OCHF 2, OC 2 F 5, OC 3 F 7, OCHFCF 3, OCF 2 CHFCF 3 or OCF _3.

The compounds of the formula I have a wide range of applications. By selecting the substituents, these compounds can be used as the base material mainly constituting the liquid crystal medium; however, the compounds of the formula I can also be added to liquid crystal substrates from other compounds. For example, the dielectric anisotropy and / or the optical anisotropy of such a dielectric can be varied and / or its threshold voltage and / or its viscosity can be optimized.
The compounds of the formula I are colorless in pure form and form liquid-crystalline mesophases in a temperature range which is favorably located for electro-optical applications. These compounds are stable to chemicals, heat and light.

If R ¹ present in formula I is an alkyl group and / or an alkoxy group, this group can be straight-chain or branched. This group is preferably straight-chain and has two, three, four, five, six or seven carbon atoms, and thus is preferably ethyl, propyl, butyl, pentyl, hexyl , Heptyl, ethoxy, propoxy, butoxy, pentoxy, hexyloxy or heptyloxy, and also methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octyloxy, nonyloxy, decyloxy, undecyl It can be oxy, dodecyloxy, tridecyloxy or tetradecyloxy.

  The oxaalkyl group 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-oxa Octyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl is there.

If R ¹ is an alkyl group, wherein one CH ₂ group present in this group is replaced by —CH ＝ CH—, this group can be straight-chain or branched. . This group is preferably straight-chain and has 2 to 10 carbon atoms. Thus, this group is particularly useful for 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 R ¹ is an alkyl group, wherein one CH ₂ group present in the group is replaced by —O— and one CH ₂ group is replaced by —CO—, Are preferably adjacent. Accordingly, these groups contain an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. These groups are preferably straight-chain and have 2 to 6 carbon atoms. Thus, these groups are, in particular, acetoxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetoxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetoxyethyl, 2-propionyloxyethyl , 2-butyryloxyethyl, 3-acetoxypropyl, 3-propionyloxypropyl, 4-acetoxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonyl Methyl, butoxycarbonylmethyl, 2- (methoxycarbonyl) ethyl, 2- (ethoxycarbonyl) ethyl, 2- (propoxycarbonyl Ethyl, 3- (methoxycarbonyl) propyl, 3- (ethoxycarbonyl) propyl or 4- (methoxycarbonyl) heptyl.

R ¹ is an alkyl group, wherein one CH ₂ group present in the group is unsubstituted or replaced by —CH ＝ CH— having a substituent, and the adjacent CH ₂ group is CO or CO—. When replaced by O or O-CO, this group can be straight-chain or branched. This group is preferably straight-chain and has 4 to 12 carbon atoms. Thus, these groups are in particular acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyheptyl, Acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl, 2-methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6 -Methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl or 9-methacryloyloxynonyl.

If R ¹ is an alkyl or alkenyl group and is substituted by one CN or CF ₃ , this group is preferably straight-chain. Substitution by CN or CF ₃ can be at any desired position.
When R ¹ is an alkyl or alkenyl group and is substituted by at least one halogen, this group is preferably straight-chain, and the halogen is preferably F or Cl. When polysubstituted, the halogen is preferably F. The resulting groups also include those that have been perfluorinated. When having one substituent, the fluorine or chlorine substituent can be in any desired position, but is preferably in the ω-position.

Compounds having a branched side-chain group R ¹ are sometimes important because they have good solubility in conventional liquid crystal substrates, but are particularly important when they are optically active, as chiral dopants. is important. This type of smectic compound is suitable as a component of a ferroelectric material.
Such branched groups generally have no more than one chain branch. Preferred branched groups R ¹ are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methylbutyl), 2-methylpentyl, -Methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexyloxy, 1- Methylhexyloxy and 1-methylheptyloxy.

If R ¹ is an alkyl group and two or more CH ₂ groups present in this group are replaced by —O— and / or —CO—O—, this group is a straight-chain It can be in the form of a chain or branched. This group is preferably branched and has 3 to 12 carbon atoms. Thus, this group is in particular biscarboxymethyl, 2,2-biscarboxyethyl, 3,3-biscarboxypropyl, 4,4-biscarboxybutyl, 5,5-biscarboxypentyl, 6,6-biscarboxyhexyl 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, S (ethoxycarbonyl) methyl, 2,2-bis (ethoxycarbonyl) ethyl, 3,3-bis (ethoxycarbonyl) propyl, 4,4-bis (ethoxycarbonyl) butyl or 5,5-bis (ethoxycarbonyl) pentyl It is.

  Compounds of Formula I are described in such publications as standard publications such as those described in Houben-Weyl, Method der organischen Chemie (method of organic chemistry), Georg-Thieme publisher, Stuttgart, and the like. It can be produced under known reaction conditions suitable for the reaction by a method known per se. Although not described in detail herein, variants which are known per se can also be used. As an example, compounds of formula I can be prepared as follows.

Scheme 1

  The invention also provides an electro-optic display (especially two plane-parallel outer substrates forming a cell with the frame, an integrated non-linear element for switching each pixel on the outer substrate, and the cell). STN or MLC displays with nematic liquid crystal mixtures having positive dielectric anisotropy and high specific resistance values) and the use of these media in electro-optical applications.

The liquid-crystal mixtures according to the invention enable a particularly wide range of available parameters.
The achieved combination of clearing point, viscosity at low temperature, thermal and UV stability, and dielectric anisotropy is far superior to conventional mixtures from the prior art.
The requirements for high clearing points, nematic phases at low temperatures and at the same time small Δn have hitherto only been achieved to an unsuitable extent. Mixtures such as, for example, ZLI-3119 have comparable clearing points and comparable preferred viscosities, but their Δε is only +3. Other mixture systems have comparable viscosities and Δε values, but only have clearing points in the region of 60 ° C.

  The liquid-crystal mixtures according to the invention have a nematic phase reduced to −20 ° C., preferably −30 ° C., particularly preferably −40 ° C., while maintaining a temperature above 60 ° C., preferably above 70 ° C., particularly preferably above 80 ° C. At the same time, it is possible to obtain a dielectric anisotropy value Δε of ≧ 8, preferably ≧ 10 and a large specific resistance value, thereby obtaining excellent STN and MLC displays. To be. In particular, the mixture is characterized by having a low operating voltage. The TN threshold voltage is 1.3V or less, preferably 1.25V or less, particularly preferably <1.0V.

  The mixtures according to the invention can obtain higher clearing points (eg above 110 ° C.) at higher threshold voltages, by appropriate selection of their components and also while retaining other advantageous properties. Or a lower clearing point at a lower threshold voltage. Similarly, if the viscosity is correspondingly slightly increased, a mixture having a large Δε value and thus a low threshold voltage can be obtained.

  The MLC display according to the present invention operates favorably with Gooch and Tarry's primary transmission minima (by C. C. Gooch and HA Tarry, Electron. Lett. 10, 2--). CH Gooch and HA Tarry, Appl. Phys. Vol. 8, 1575-1584, 1975). In this case, in addition to the particularly favorable electro-optical properties, such as a large steepness of the characteristic curve and a small angle dependence of the contrast (DE-A 30 22 818), the threshold voltage in similar displays at the secondary transmission minima At the same threshold voltage, a smaller dielectric anisotropy is sufficient. This makes it possible to obtain an exceptionally high specific resistance at the first minimum, by using the mixture according to the invention, as compared to the mixture containing the cyano compound. By appropriate choice of the components and their proportions by weight, the person skilled in the art can use simple and customary methods for setting the birefringence required for a given layer thickness of the MLC display.

The flow viscosity V _{20 at} 20 ° C. is preferably <60 mm ² / sec, particularly preferably <50 mm ² / sec. The rotational viscosity γ ₁ at 20 ° C. of the mixtures according to the invention is preferably <220 mPa · s, particularly preferably <200 mPa · s. The nematic phase range is preferably at least 90 °, especially at least 100 °. This range is preferably extended at least from -20 ° to + 80 °.

Short response times are desired for liquid crystal displays. This is especially true for displays that can play video. This type of display requires a response time of at most 25 ms (total: t _on + t _off ). The upper limit of this response time is determined by the image refresh frequency. In addition to the rotational viscosity gamma _1, the tilt angle also influences the response time. In particular, mixtures containing compounds of the formula I in an amount of> 20% have a tilt of> 2.5 °, preferably> 3.0 °, compared to ZLI-4792, a commercial product from Merck KGaA. Indicates a corner.

で表わされるシアノフェニルシクロヘキサン化合物または式：

で表わされるエステル化合物を含有する類似混合物に比較して、温度の上昇に伴うＨＲの減少を格別に小さくすることが証明された［Ｓ．Ｍａｔｓｕｍｏｔｏ等著、Ｌｉｑｕｉｄ Ｃｒｙｓｔａｌｓ ５、１３２０（１９８９）；Ｋ．Ｎｉｗａ等著、Ｐｒｏｃ．ＳＩＤ Ｃｏｎｆｅｒｅｎｃｅ，Ｓａｎ Ｆｒａｎｃｉｓｃｏ、１９８４年６月、３０４頁（１９８４年）；Ｇ．Ｗｅｂｅｒ等著、Ｌｉｑｕｉｄ Ｃｒｙｓｔａｌｓ ５、１３８１（１９８９）］。 The measured value of the voltage holding ratio (HR) is that the mixture according to the invention containing a compound of the formula I is replaced with a compound of the formula I, for example of the formula:

A cyanophenylcyclohexane compound represented by the formula:

It has been proved that the decrease in HR with increasing temperature is significantly smaller than that of a similar mixture containing an ester compound represented by the formula [S. Matsumoto et al., Liquid Crystals 5, 1320 (1989); Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984); Weber et al., Liquid Crystals 5, 1381 (1989)].

The UV stability of the mixtures according to the invention is also very good. That is, these mixtures show a particularly small decrease in HR upon exposure to ultraviolet light.
Particularly preferred compounds of the formula I are those of the following formulas I-1 to I-10:

In each formula, R ¹ is as defined in formula I.
Among these preferred compounds, the compounds of the formulas I-1, I-2, I-3 and I-4 are mentioned as particularly preferred compounds, in particular of the formulas I-1 and I-2 The compound represented by is particularly preferable.
The present invention still further relates to compounds of formulas I-1 to I-8, wherein R ¹ is as defined above. R ¹ is preferably a straight-chain alkyl or alkenyl group having up to 6 carbon atoms. As particularly preferred compounds, the following are mentioned as particularly preferred compounds:

式中、
alkylは、ＣＨ₃、Ｃ₂Ｈ₅、ｎ−Ｃ₃Ｈ₇、ｎ−Ｃ₄Ｈ₉、ｎ−Ｃ₅H₁₁またはｎ−Ｃ₆Ｈ₁₃である。

Where:
alkyl is _{CH 3, C 2 H 5,} n-C 3 H 7, n-C 4 H 9, n-C 5 H 11 or n-C ₆ H _13.

Preferred embodiments are as follows:
The medium contains one, two or more compounds of the formulas I-1 to I-9;
The medium further comprises one or more compounds selected from the group consisting of the general formulas II to VI:

In each of the above formulas, each group is as defined below:
R ⁰ is an n-alkyl group, alkoxy group, oxaalkyl group, fluoroalkyl group or alkenyl group each having up to 9 carbon atoms,
X ⁰ is F or Cl, or is a halogenated alkyl group, a halogenated alkenyl group, a halogenated oxaalkyl group, a halogenated alkenyloxy group or a halogenated alkoxy group each having up to 6 carbon atoms;
Z ⁰ _{is, -C 2 F 4 -, -} CF = CF -, - C 2 H 4 -, - (CH 2) 4 -, - OCH 2 -, - CH 2 O -, - CF 2 O- or - OCF ₂ —,
Y ^{1 to} Y ⁴ are each independently of one another, and are H or F;
r is 0 or 1.
The compounds of the formula IV are preferably the following compounds:

The medium further comprises one or more compounds selected from the group consisting of the general formulas VII to XII:

In the above formulas, R ⁰ , X ⁰ and Y ^1-4 are each independently of the other and are as defined in claim 3. X ⁰ is preferably F, Cl, CF ₃ , OCF ₃ or OCHF ₂ . R ⁰ is preferably an alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl group, each having up to 6 carbon atoms.
The medium further comprises one or more compounds of the formulas Ea to Ed:

In each of the above formulas, R ⁰ is as defined in claim 3.
The proportion of compounds of the formulas Ea to Ed is preferably from 10 to 30% by weight, in particular from 15 to 25% by weight;
The proportion of the total compounds of the formulas I to VI in the mixture as a whole is at least 50% by weight;
The proportion of compounds of the formula I in the mixture as a whole is from 0.5 to 40% by weight, particularly preferably from 1 to 30% by weight;
The proportion of compounds of the formulas II to VI in the mixture as a whole is from 30 to 80% by weight;

The medium contains a compound of the formula II, III, IV, V and / or VI;
-R ⁰ is a linear alkyl group or alkenyl group having 2 to 7 carbon atoms;
The medium consists essentially of the compounds of the formulas I to VI and XIII;
The medium preferably further comprises a compound selected from the group consisting of the following general formulas XIV to XVIII:

In each of the above formulas, R ⁰ and X ⁰ are as defined above. The 1,4-phenylene ring may be substituted by CN, chlorine or fluorine. The 1,4-phenylene ring is preferably substituted by one or more fluorine atoms.
The medium further comprises one, two, three or four or more, preferably two or three, compounds of the following formulas:

上記各式中、“alkyl”および“alkyl^＊”は、下記定義のとおりである。
本発明の混合物中の式Ｏ１および／またはＯ２で表わされる化合物の割合は、好ましくは５〜１０重量％、特に１から１２重量％、非常に特に好ましくは、３〜１０重量％である。

In each of the above formulas, “alkyl” and “alkyl ^* ” are as defined below.
The proportion of compounds of the formulas O1 and / or O2 in the mixtures according to the invention is preferably from 5 to 10% by weight, in particular from 1 to 12% by weight, very particularly preferably from 3 to 10% by weight.

The medium preferably contains from 5 to 35% by weight of a compound of the formula IVa.
The medium preferably contains one, two or three compounds of the formula IVa, wherein X ⁰ is F or OCF ₃ ;
The medium preferably contains one or more compounds of the formulas IIa to IIg:

上記各式中、Ｒ⁰は上記定義のとおりである。

In each of the above formulas, R ⁰ is as defined above.

In the compounds of the formulas IIa to IIg, R ⁰ is preferably methyl, ethyl, n-propyl, n-butyl or n-pentyl.
The medium preferably contains one or more compounds of the formula:

各式中、Ｒ⁰は上記定義のとおりである。

In each formula, R ⁰ is as defined above.

The medium according to the invention furthermore preferably contains one or more compounds of the formula DD-1 and / or DD-2:

In the formula, R ^ad is each independently of the other and is a linear alkyl or alkoxy group having 1 to 6 carbon atoms.
The proportion of the compounds of the formulas DD-1 and / or DD-2 in the mixtures according to the invention is preferably from 0 to 10% by weight, in particular from 0.1 to 8% by weight, particularly preferably from 0.5 to 4% by weight. % By weight.
The weight ratio of (I) :( II + III + IV + V + VI) is preferably from 1:10 to 10: 1.
The medium consists essentially of a compound selected from the group consisting of the general formulas I to XIII.
In formula IVb and / or IVc in the mixture as a whole, X ⁰ is fluorine and R ⁰ is CH ₃ , C ₂ H ₅ , nC ₃ H ₇ , nC ₄ H ₉ or the proportion of n-C ₅ H ₁₁ compounds that are 2 to 20% by weight, in particular 2 to 15 wt%.

The medium preferably contains compounds of the formulas II to VI, wherein R ⁰ is methyl. The mixtures according to the invention particularly preferably contain compounds of the formula

The medium preferably contains one, two or more, preferably one or two, dioxane compounds of the formula:

In each formula, R ⁰ is as defined above.
The proportion of these dioxane compounds D-1 and / or D-2 in the mixtures according to the invention is preferably from 0 to 30% by weight, in particular from 5 to 25% by weight, very particularly preferably from 8 to 20% by weight. .
The medium preferably contains one, two or more, preferably one or two, pyran compounds of the formulas P-1 to P-4:

各式中、Ｒ⁰は上記定義のとおりである。

In each formula, R ⁰ is as defined above.

各式中、Ｒ^1aおよびＲ^2aはそれぞれ相互に独立し、Ｈ、ＣＨ₃、Ｃ₂Ｈ₅またはｎ−Ｃ₃Ｈ₇であり、Ｒ⁰、alkylおよびalkyl^＊は請求項３に定義されているとおりであるか、または下記定義のとおりである。
上記二環状化合物の中で、化合物Ｚ−１、Ｚ−２、Ｚ−５およびＺ−６は特の好適な化合物として挙げられる。 The medium preferably contains one, two or more bicyclic compounds of the formulas Z1 to Z7:

In each formula, R ^1a and R ^2a are each independently of one another and are H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ , and R ⁰ , alkyl and alkyl ^* are as defined in claim 3 Or as defined below.
Among the above bicyclic compounds, compounds Z-1, Z-2, Z-5 and Z-6 are mentioned as particularly suitable compounds.

The medium further comprises one, two or more compounds having fused rings of the formulas AN1 to AN11:

In each formula, R ⁰ is as defined above.
The media according to the invention are distinguished in particular by a clearing point of> 75 ° C. and a threshold voltage of <1.2 V;
The compounds of the formula I which are mixed with customary liquid-crystal materials and in particular with one or more compounds of the formulas II, III, IV, V and / or VI are relatively few It has been found that even proportions result in a reduced nematic phase with a lower smectic-nematic transition temperature, while at the same time leading to lower threshold voltages and lower birefringence values, thus improving the shelf life.

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

The term "alkenyl" embraces straight-chain and branched alkenyl groups having 2-7 carbon atoms, in particular the straight-chain groups. Suitable 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 there is a C ₂ -C ₇ -1E- alkenyl, C ₄ -C ₇ -3E-alkenyl and C ₅ -C ₇ -4- alkenyl. Examples of particularly suitable alkenyl groups include vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-E Pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5 carbon atoms are generally 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. And fluoroheptyl. However, fluorine at other positions is not excluded.
The term "oxaalkyl" or "alkoxy" preferably of the formula _{C n H 2n + 1 -O- (} CH 2) straight-chain groups (wherein represented by _m, n and m are, independently of one another each , 1-6, and m can also be 0). Preferably, n = 1 and m = 1 to 6, or m = 0 and n = 1 to 3.

By appropriately 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. By way of example, 1E-alkenyl groups, 3E-alkenyl groups, 2E-alkenyloxy groups, and the like generally have shorter addressing times, improved tendency to form nematic phases and elastic constants K ₃₃ (bend) as compared to alkyl and alkoxy groups. ) And K ₁₁ (spray). 4-Alkenyl radicals, 3-alkenyl radicals and the like generally compared with alkyl and alkoxy groups results in a lower threshold voltage and smaller K ₃₃ / K ₁₁ value.
The —CH ₂ CH ₂ — group generally results in a higher K ₃₃ / K ₁₁ value compared to a single covalent bond. A large K ₃₃ / K ₁₁ value facilitates a flatter transmission characteristic curve (giving halftones) in TN cells with a 90 ° twist, for example, and a steeper transmission in STN, SBE and OMI cells. Facilitates the characteristic curve (a larger time division ratio is obtained) and vice versa.

  The optimum weight ratio of the compound of the formula I to the compound of the formula II + III + IV + V + VI depends on the desired properties, the choice of the components of the formula I, II, III, IV, V and / or VI and Substantially depends on the choice of other components that can be present. Suitable mixing ratios within the above range can easily be determined from case to case.

  The total amount of the compounds of the formulas I to XIII in the mixtures according to the invention is not restricted. Thus, these mixtures can contain one or more additional components, which can optimize various properties. However, the effect found on the addressing time and the threshold voltage is generally greater the higher the total concentration of the compounds of the formulas I to XIII.

In a particularly preferred embodiment, the medium according to the invention is a compound of the formulas II to VI (preferably of the formula II, III and / or IV, in particular of the formula IVa) wherein X ⁰ is F, OCF ₃ , OCHF _2, OCHＣＨ. It contains compounds in which CF ₂ , OCF = CF ₂ or OCF ₂ —CF ₂ H. The favorable synergistic effect with the compounds of the formula I results in particularly advantageous properties. In particular, the mixtures containing the compounds of the formula I and the compounds of the formula IVa are distinguished by their low threshold voltage.
The compounds of the formulas I to XVIII and their subformulae which can be used in the medium according to the invention are each known or can be prepared analogously to known compounds.

The structure of the MLC display according to the invention from polarizers, electrode substrates and surface-treated electrodes corresponds to the structure customary for displays of this kind. Here, the term "conventional structure" is to be interpreted broadly and covers all inductive and modified MLC displays, in particular matrix display elements based on poly-Si TFTs or MIMs.
However, an important difference between the display according to the invention and 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 according to the invention can be prepared in a manner which is conventional per se. In general, the desired amounts of the components used in small amounts are dissolved in the components making up the main component, advantageously at elevated temperature. After mixing the solutions of the components in an organic solvent such as acetone, chloroform or methanol and mixing well, the solvent can then be separated again, for example by distillation.
Dielectrics are also known to those skilled in the art and have additional additives disclosed in the publications such as UV stabilizers [eg Tinuvin from Ciba (registered trade name)], antioxidants, free It may contain a radical capture agent and the like. As an example, 0-15% of a multicolor dye or chiral dopant can be added. Suitable stabilizers and dopants are shown in Tables C and D below.

C represents the crystalline phase, S represents the smectic phase, Sc represents the smectic C phase, N represents the nematic phase, and I represents the isotropic phase.
V ₁₀ denotes the voltage for (viewing angle perpendicular to the substrate surface) 10% transmittance. t _on represents the switch-on time at an operating voltage corresponding to 2.0 times the value of V ₁₀ , and t _off represents the switch-off time. Δn represents optical anisotropy. △ epsilon denotes the dielectric anisotropy (△ ε = ε _{‖-epsilon ⊥,} where epsilon _|| denotes the dielectric constant parallel to the molecular longitudinal axis, and epsilon _⊥ denotes the dielectric constant perpendicular thereto) . Electro-optic data were measured at 20 ° C. in the TN cell at the primary minimum (ie, d.Δn value of 0.5 μm) unless otherwise noted. Optical data was measured at 20 ° C. unless otherwise noted.

In this patent application and the examples below, the structure of the liquid crystal compound is indicated by an acronym, and the conversion into the chemical formula is performed according to Tables A and B below. The radicals C _n H _{2n + 1} and C _m H _{2m + 1} are all straight-chain alkyl radicals each having n or m carbon atoms; where n and m are integers, preferably 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12. The codes in Table B are self-explanatory. Table A shows only initials related to the basic structure. In each case, the codes for the substituents R ^{1 *} , R ^{2 *} , L ^{1 *} and L ^{2 *} are indicated, separated by a dash, after the acronym for this basic structure.

The components of the preferred mixture are shown in Tables A and B below.
Table A

Table B

Liquid-crystal mixtures containing at least one, two, three or four compounds from Table B in addition to the compounds of the formula I are mentioned as particularly preferred.
Table C:
Table C shows dopants which can generally be added to the mixtures according to the invention. The mixture preferably contains 0 to 10% by weight, in particular 0.01 to 5% by weight, particularly preferably 0.01 to 3% by weight, of the dopant.

Table D:
By way of example, the following are examples of stabilizers which can be added to the mixtures according to the invention:

The following examples are intended to illustrate the invention, but not to limit it. Throughout the specification, percentages are weight percentages. All temperatures are given in degrees Celsius. m. p. Represents melting point, cl. p. Represents a clearing point. Furthermore, C = crystalline state, N = nematic phase, S = smectic phase, and I = isotropic phase. The data between these symbols is the transition temperature. Δn represents optical anisotropy (589 nm, 20 ° C.), and Δε represents dielectric anisotropy (1 kHz, 20 ° C.). The flow viscosity V ₂₀ (mm ² / sec) and rotational viscosity γ ₁ (mPa · sec) were measured at 20 ° C.

The term "conventional work-up" means that, if desired, water is added to the reaction mixture, the mixture is extracted with dichloromethane, diethyl ether, methyl tert-butyl ether or toluene, the phases are separated, the organic phase is dried, It is then meant to evaporate and then to purify the product by distillation or crystallization at reduced pressure and / or chromatography. The following abbreviations are used in these examples, as well as in the synthesis and reaction schemes.
n-BuLi 1.6 molar solution of n-butyllithium in n-hexane DMAP 4- (dimethylamino) pyridine THF tetrahydrofuran DCC N, N'-dicyclohexylcarbodiimide LDA lithium dimethylamide TsOH toluenesulfonic acid RT room temperature

An example

0.054 mol of propylpropanediol and 0.054 mol of the corresponding cyclohexanealdehyde in 200 ml of toluene containing 0.0055 mol of p-toluenesulfonic acid monohydrate are refluxed on a water separator. Is then cooled reaction mixture was extracted with aqueous NaHCO ₃ solution, to separate the p- toluenesulfonic acid. After drying over Na ₂ SO ₄ and then evaporation, the residue obtained from the organic phase is filtered through silica gel with a 1: 1 (by volume) mixture of toluene / heptane. After evaporation and recrystallization of 19.0 g of the evaporation residue from 60 ml of heptane at -20 ° C., 7.4 g of the pure dioxane derivative are obtained from the filtrate.

Compounds of the formula are prepared analogously:

Example M1

Example M2

Example M3

Example M4

Example M5

Example M6

Example M7

Example M8

Example M9

Example M10

Example M11

Example M12

Example M13

Example M14

Example M15

Claims (12)

A liquid crystal medium based on a mixture of polar compounds having a positive dielectric anisotropy, characterized by containing one or more compounds of the formula I:

Where:
R ¹ has 1 to 15 carbon atoms and is a halogenated or unsubstituted alkyl or alkoxy group, and one or more CH ₂ groups present in these groups are Each being independent of one another and in which the oxygen atoms are not directly bonded to each other, are replaced by -C≡C-, -C = C-, -O-, -CO-O- or -O-CO-. Well,
X is, F, Cl, CN or SF _5, or a halogenated alkyl group, halogenated alkenyl group, a halogenated alkoxy radical or a halogenated alkenyloxy radical having up to 6 carbon atoms, respectively, and L ¹ And L ² are each independently of one another and are H or F. The liquid crystal medium according to claim 1, comprising one, two or three or more compounds represented by formulas I-1 to I-10.

In each of the above formulas, R ¹ is as defined in claim 1. 3. The method according to claim 1, further comprising one or more compounds selected from the group consisting of general formulas II, III, IV, V and VI. Liquid crystal medium:

In each of the above formulas, each group has the following meaning:
R ⁰ is an n-alkyl, oxaalkyl, fluoroalkyl or alkenyl group each having up to 9 carbon atoms,
X ⁰ is F or Cl, or a halogenated alkyl, alkenyl, alkenyloxy, or alkoxy group each having up to 6 carbon atoms;
Z ⁰ _{is, -C 2 F 4, -CF =} CF -, - C 2 H 4 -, - (CH 2) 4 -, - OCH 2 -, - CH 2 O -, - CF 2 O- or -OCF _2-
Y ^{1 to} Y ⁴ are each independently of one another and are H or F;
r is 0 or 1.   4. The liquid-crystalline medium according to claim 3, wherein the proportion of the compounds of the formulas I to VI in the mixture as a whole is at least 50% by weight. The liquid crystal medium according to claim 1, further comprising one or more compounds represented by formulas Ea to Ed.

In each of the above formulas, R ⁰ is as defined in claim 3. 6. A liquid-crystal medium according to claim 1, which comprises one or more compounds of the formulas IIa to IIg.

In each of the above formulas, R ⁰ is as defined in claim 3. The liquid crystal medium according to any one of claims 1 to 6, comprising one or more compounds represented by the formulas O1 and O2.

In each of the above formulas,
Alkyl and alkyl * are each mutually independent and are straight-chain or branched-chain alkyl groups having 1 to 7 carbon atoms. The liquid crystal medium according to any one of claims 1 to 7, comprising one or more dioxane compounds represented by the formulas D1 and / or D2.

In each of the above formulas, R ⁰ is as defined in claim 3.   9. The liquid-crystal medium according to claim 1, wherein the proportion of the compound of the formula I in the mixture as a whole is from 0.5 to 40% by weight.   Use of the liquid crystal medium according to any one of claims 1 to 9 in electro-optical applications.   An electro-optical liquid crystal display containing the liquid crystal medium according to claim 1. Compounds of formulas I-1 to I-8:

Wherein R ¹ is as defined in claim 1.