DE112007000676B4 - Liquid-crystalline medium and its use - Google Patents

Abstract

A liquid-crystalline medium which comprises one or more compounds of the formula I6 in which X denotes F, one or more compounds selected from the group of the compounds: in which n = 1-12,

Description

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

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

The liquid crystal materials must have good chemical and thermal stability and good stability against electric fields and electromagnetic radiation. Further, the liquid crystal materials should have low viscosity and provide short response times, low threshold voltages, and high contrast in the cells.

Furthermore, they should at normal operating temperatures, d. H. have a suitable mesophase in the broadest possible range below and above room temperature, for example, for the above-mentioned cells a nematic or cholesteric mesophase. Since liquid crystals are generally used as mixtures of several components, it is important that the components are readily miscible with each other. Other properties, such as electrical conductivity, dielectric anisotropy and optical anisotropy, must meet different requirements depending on the type of cell and the field of application. For example, materials for cells of twisted nematic structure should have positive dielectric anisotropy and low electrical conductivity.

For example, for matrix liquid crystal displays with integrated non-linear elements for single pixel switching (MFK displays), media with high positive dielectric anisotropy, broad nematic phases, relatively low birefringence, very high resistivity, good UV and temperature stability and low vapor pressure are desired.

• 1. MOS (Metal Oxide Semiconductor) oder andere Dioden auf Silizium-Wafer als Substrat.
• 2. Dünnfilm-Transistoren (TFT) auf einer Glasplatte als Substrat.

Such matrix liquid crystal displays are known. As non-linear elements for individual switching of the individual pixels, for example, active elements (ie transistors) can be used. One speaks then of an "active matrix", whereby one can distinguish two types:

• 1. MOS (Metal Oxide Semiconductor) or other diodes on silicon wafer as a substrate.
• 2. Thin-film transistors (TFT) on a glass plate as a substrate.

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

In the more promising Type 2, which is preferred, the TN effect is usually used as the electro-optic effect. A distinction is made between two technologies: TFTs made of compound semiconductors such as. B. CdSe or TFTs based on polycrystalline or amorphous silicon. The latter technology is being worked on worldwide with great intensity.

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

The TFT displays usually operate as TN cells with crossed polarizers in transmission and are backlit.

The term MFK displays here includes any matrix display with integrated non-linear elements, ie. H. in addition to the active matrix also displays with passive elements such as varistors or diodes (MIM = metal-insulator-metal).

Such MFK displays are particularly suitable for TV applications (eg pocket televisions) or for high-information displays for computer applications (laptops) and in the automotive or aircraft industry. In addition to problems with regard to the angle dependence of the contrast and the switching times, MFK displays have difficulties due to the insufficiently high resistivity of the liquid-crystal mixtures [TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMACHI, K. , TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay 84, Sept. 1984: A 210-288 Matrix LCD Controlled by Double Stage Diode Rings, p. 141 ff, Paris; STROMER, M., Proc. Eurodisplay 84, Sept. 1984: Design of Thin Film Transistors for Matrix Liquid Crystal Displays, p. 145 ff, Paris]. As the resistance decreases, the contrast of a MFK display degrades and the problem of "old image elimination" can arise. Since the resistivity of the liquid crystal mixture decreases by interaction with the internal surfaces of the display, generally over the lifetime of an MFK display, high (initial) resistance is very important in order to obtain acceptable service lives. In particular, in low-volt mixtures, it has not been possible to realize very high resistivities. Furthermore, it is important that the resistivity shows the smallest possible increase with increasing temperature and after temperature and / or UV exposure. Also particularly disadvantageous are the low-temperature properties of the mixtures of the prior art. It is required that no crystallization and / or smectic phases occur even at low temperatures, and that the temperature dependence of the viscosity is as low as possible. The MFK displays from the prior art thus do not meet today's requirements.

In addition to liquid crystal displays which use backlighting, ie are operated transmissively and optionally transflectively, reflective liquid crystal displays are also of particular interest. These reflective liquid crystal displays use the ambient light for information presentation. Thus, they consume significantly less energy than backlit liquid crystal displays of appropriate size and resolution. Since the TN effect is characterized by a very good contrast, such reflective displays are still easy to read even in bright ambient conditions. This is already from simple reflective TN displays, as they are in z. As watches and calculators are used known. However, the principle is also on high quality; higher resolution active matrix driven displays such. B. TFT displays applicable. Here, as with the general conventional transmissive TFT-TN displays, the use of liquid crystals with low birefringence (Δn) is necessary in order to achieve a small optical delay (d · Δn). This small optical delay leads to a mostly acceptable low viewing angle dependence of the contrast (cf. DE 30 22 818 ). For reflective displays, the use of liquid crystals with low birefringence is even more important than for transmissive displays, because with reflective displays the effective layer thickness through which the light passes is approximately twice that of transmissive displays with the same layer thickness.

Thus, there is still a great need for MFK displays with very high resistivity at the same time large working temperature range, short switching times even at low temperatures and low threshold voltage, which do not show these disadvantages or only to a lesser extent.

• – erweiterter nematischer Phasenbereich (insbesondere zu tiefen Temperaturen)
• – Schaltbarkeit bei extrem tiefen Temperaturen (out-door-use, Automobil, Avionik)
• – erhöhte Beständigkeit gegenüber UV-Strahlung (längere Lebensdauer)
• – kleine Schwellenspannung

In TN (Schadt-Helfrich) cells, media are desired which allow the following advantages in the cells:

• - extended nematic phase range (especially at low temperatures)
• - Switchability at extremely low temperatures (out-door-use, automotive, avionics)
• - increased resistance to UV radiation (longer life)
• - small threshold voltage

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

For higher-twisted cells (STN), media are desired which allow for higher multiplexability and / or lower threshold voltages and / or broader nematic phase ranges (especially at low temperatures). For this purpose, a further expansion of the available parameter space (clearing point, transition smectic-nematic or melting point, viscosity, dielectric values, elastic sizes) is urgently desired.

In addition to liquid crystal displays which use backlighting, ie are operated transmissively and optionally transflectively, reflective liquid crystal displays are also of particular interest. These reflective liquid crystal displays use the ambient light for information presentation. Thus, they consume significantly less energy than backlit liquid crystal displays of appropriate size and resolution. Since the TN effect is characterized by a very good contrast, are Such reflective displays even in bright environmental conditions still read well. This is already from simple reflective TN displays, as they are in z. As watches and calculators are used known. However, the principle is also on high-quality, higher-resolution active matrix driven displays such. B. TFT displays applicable. Here, as with the general conventional transmissive TFT-TN displays, it is necessary to use low birefringence liquid crystals (Δn) to achieve a low optical retardation (Δn · d). This small optical delay leads to a mostly acceptable low viewing angle dependence of the contrast (cf. DE 30 22 81 8 ). For reflective displays, the use of liquid crystals with low birefringence is even more important than for transmissive displays, because with reflective displays the effective layer thickness through which the light passes is approximately twice that of transmissive displays with the same layer thickness.

In the publication DE 10 2004 058 002 A1 Liquid-crystalline media are disclosed which may contain there further defined compounds of formula C-2. The document comprises with formula C-2 already generically the compounds of the formula I6 disclosed below

The invention has for its object to provide media especially for such MFK, TN or STN displays that do not have the disadvantages mentioned above, or only to a lesser extent, and preferably at the same time very high resistivities and low threshold voltages. For this task, liquid crystalline compounds are required which have a high clearing point and a low rotational viscosity.

It has now been found that this object can be achieved by using the liquid-crystalline compound of formula I6. The compounds of the formula I6 positively influence the "reliability" and lead to mixtures with particularly low threshold voltages.

worin
X F,
bedeutet,
ein oder mehrere Verbindungen ausgewählt aus der Gruppe der Verbindungen:

worin n = 1–12,
und zusätzlich ein oder mehrere Verbindungen ausgewählt aus den Verbindungen der Formeln H8, H9, DI und/oder DII:

worin
n = 1–12, und
R⁰ n-Alkyl, Oxaalkyl, Alkoxy, Fluoralkyl, Alkenyloxy oder Alkenyl mit jeweils 2 bis 12 C-Atomen bedeutet,
enthält.The invention thus relates to a liquid-crystalline medium based on a mixture of polar compounds having a positive dielectric anisotropy comprising one or more compounds of the formula I6,

wherein
XF,
means
one or more compounds selected from the group of compounds:

where n = 1-12,
and additionally one or more compounds selected from the compounds of the formulas H8, H9, DI and / or DII:

wherein
n = 1-12, and
R ⁰ denotes n-alkyl, oxaalkyl, alkoxy, fluoroalkyl, alkenyloxy or alkenyl having in each case 2 to 12 C atoms,
contains.

The compounds of the formula I6 (also referred to below as compounds of the formula I) are colorless in the pure state and generally form liquid-crystalline mesophases in a temperature range which is favorably located for electrooptical use. In particular, the compounds of the formula I are distinguished by their high dielectric anisotropy and their low values for the rotational viscosity. Chemically, thermally and against light, they are stable.

The compounds of the formula I are prepared by methods known per se, as described in the literature (for example in the standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart) under reaction conditions which are known and suitable for the said reactions. One can also make use of known per se, not mentioned here variants.

Also disclosed are electro-optical displays (in particular STN or MFK displays with two plane-parallel support plates which form a cell with a border, integrated non-linear elements for switching individual pixels on the support plates and a nematic liquid-crystal mixture having positive dielectric anisotropy in the cell and high resistivity) containing such media as well as the use of these media for electro-optical purposes.

The liquid-crystal mixtures according to the invention enable a significant expansion of the available parameter space.

The achievable combinations of clearing point, optical anisotropy, low temperature viscosity, thermal and UV stability and dielectric anisotropy far surpass previous prior art materials.

The requirement for a high clearing point, nematic phase at low temperature and a high Δε has so far been insufficiently fulfilled. Liquid crystal mixtures, such as. Although MLC-6476 and MLC-6625 (Merck KGaA, Darmstadt, Germany) have comparable clearing points and low-temperature stabilities, they have relatively high Δn values as well as higher threshold voltages of approximately ≥1.7 V.

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

The liquid-crystal mixtures according to the invention make it possible to maintain the nematic phase at -20 ° C. and preferably at -30 ° C., particularly preferably at -40 ° C., clearing points above 75 °, preferably above 80 °, simultaneously dielectric anisotropy values Δ∈ ≥ 4, preferably ≥ 6 and to achieve a high resistivity value, resulting in excellent STN and MFK readings. In particular, the mixtures are characterized by low operating voltages. The TN thresholds are below 1.7 V, preferably below 1.5 V, most preferably ≦ 1.3 V.

It is understood that by a suitable choice of the components of the mixtures according to the invention, higher clearing points (eg above 110 °) at higher threshold voltage or lower clearing points at lower threshold voltages can be achieved while retaining the other advantageous properties. Likewise, mixtures can be obtained with a larger Δε and thus lower thresholds at correspondingly little increased viscosities. The MFK displays preferably work in the first transmission minimum according to Gooch and Tarry [CH Gooch and HA Tarry, Electron. Lett. 10, 2-4, 1974; CH Gooch and HA Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975], whereby in addition to particularly favorable electro-optical properties such as low angular dependence of the contrast ( DE-PS 30 22 818 ) at the same threshold voltage as in an analog display in the second minimum a smaller dielectric anisotropy is sufficient. As a result, significantly higher specific resistances can be achieved using the mixtures according to the invention in the first minimum than in the case of mixtures with cyano compounds. By suitable choice of the individual components and their proportions by weight, the person skilled in the art can set the birefringence required for a given layer thickness of the MFK display with simple routine methods.

The flow viscosity ν ₂₀ at 20 ° C is preferably <60 mm ² · s ^-1 , more preferably <50 mm ² · s ^-1 . The nematic phase range is preferably at least 90 °, in particular at least 100 °. Preferably this range extends at least from -30 ° to + 80 °. The rotational viscosity γ ₁ at 20 ° C is preferably <170 mPas · s, more preferably ≤ 165 mPas · s, in particular <150 mPas · s.

oder Ester der Formel

Measurements of the Capacity Holding Ratio (HR) [p. Matsumoto et al., Liquid Crystals 5, 1320 (1989); K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984); G. Weber et al., Liquid Crystals 5, 1381 (1989)] have shown that mixtures according to the invention comprising one or more compounds of the formula I have a significantly smaller decrease in HR with increasing temperature than analogous mixtures comprising instead of the compounds of the formula I. Cyanophenylcyclohexanes of the formula

or esters of the formula

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

The media according to the invention preferably contain one or more (two, three or more) compounds, preferably only one compound of the formula I, d. H. the proportion of these compounds is 1.5-25%, preferably 2-20%, and more preferably in the range of 2-15%.

The individual compounds of the formulas I to X and their sub-formulas which can be used in the media according to the invention are either known or they can be prepared analogously to the known compounds.

• – Das Medium enthält zusätzlich eine oder mehrere Verbindungen ausgewählt aus der Gruppe bestehend aus den allgemeinen Formeln II bis X:
  
  
  
  worin die einzelnen Reste die folgenden Bedeutungen haben: R⁰ n-Alkyl, Oxaalkyl, Alkoxy, Fluoralkyl, Alkenyloxy oder Alkenyl mit 2 bis 12 C-Atomen X⁰ F, Cl, halogeniertes Alkyl, halogeniertes Alkenyl, halogeniertes Alkenyloxy oder halogeniertes Alkoxy mit jeweils bis zu 8 C-Atomen, Z⁰ -CH=CH-, -C₂H₄-, -CH₂O-, -OCH₂-, -(CH₂)₄-, -C₂F₄-, -CF=CF-, -CH=CF-, -CF=CH-, -CF₂O-, -OCF₂- oder -COO-, Y¹, Y², Y³ und Y⁴ jeweils unabhängig voneinander H oder F, und r 0 oder 1.

Preferred embodiments are given below:

• The medium additionally contains one or more compounds selected from the group consisting of the general formulas II to X:
  
  
  
  wherein the individual radicals have the following meanings: R ⁰ n-alkyl, oxaalkyl, alkoxy, fluoroalkyl, alkenyloxy or alkenyl having 2 to 12 C atoms X ⁰ F, Cl, halogenated alkyl, halogenated alkenyl, halogenated alkenyloxy or halogenated alkoxy each with up to 8 carbon atoms, Z ^{0 is} -CH = CH-, -C ₂ H ₄ -, -CH ₂ O-, -OCH ₂ -, - (CH ₂ ) ₄ -, -C ₂ F ₄ -, -CF = CF-, -CH = CF-, -CF = CH-, -CF ₂ O-, -OCF ₂ - or -COO-, Y ¹ , Y ² , Y ³ and Y ⁴ each independently is H or F, and r is 0 or 1.

oder

• – Das Medium enthält insbesondere zusätzlich eine oder mehrere Verbindungen der Formeln
  
  
  
  und/oder
  
  worin R⁰ und Y² die oben angegebene Bedeutung haben.
• – Das Medium enthält vorzugsweise ein, zwei oder drei, ferner vier, Homologe der Verbindungen ausgewählt aus der Gruppe H1 bis H21 (n = 1–12):
  
  
  
  
  Besonders bevorzugt enthalten die erfindungsgemäßen Medien eine oder meherere Verbindungen der Formeln H1, H2, H3, H4, H7, H8, H9, H10, H12, H14, H16, H18, H20, H21 und H22.
• – Das Medium enthält zusätzlich ein oder mehrere Dioxane der Formel DI und/oder DII,
  
  worin R⁰ die in Anspruch 1 angegebenen Bedeutungen hat. Vorzugsweise bedeutet R⁰ in den Verbindungen der Formel DI und/oder DII geradkettiges Alkyl oder Alkenyl mit bis zu 8 C-Atomen.
• – Das Medium enthält zusätzlich eine oder mehrere Verbindungen ausgewählt aus der Gruppe bestehend aus den allgemeinen Formeln XI bis XVI:
  
  worin R⁰, X⁰ Y¹, Y², Y³ und Y⁴ jeweils unabhängig voneinander eine der in Anspruch 2 angegebene Bedeutung haben. Vorzugsweise bedeutet X⁰ F, Cl, CF₃, OCF₃ oder OCHF₂. R⁰ bedeutet vorzugsweise Alkyl, Oxaalkyl, Alkoxy, Fluoralkyl, Alkenyl oder Alkenyloxy.
• – Der Anteil an Verbindungen der Formeln I bis X zusammen beträgt im Gesamtgemisch mindestens 50 Gew.-%.
• – Der Anteil an Verbindungen der Formel I beträgt im Gesamtgemisch 1,5 bis 25 Gew.-%.
• – Der Anteil an Verbindungen der Formeln II bis X im Gesamtgemisch beträgt 25 bis 98,5 Gew.-%.
  
• – Das Medium enthält Verbindungen der Formeln II, III, IV, V, VI, VII, VIII, IX und/oder X.
• – R⁰ ist geradkettiges Alkyl oder Alkenyl mit 2 bis 8 C-Atomen.
• – Das Medium besteht im wesentlichen aus Verbindungen der Formeln I bis XVI.
• – Das Medium enthält weitere Verbindungen, vorzugsweise ausgewählt aus der folgenden Gruppe bestehend aus den allgemeinen Formeln XVII bis XX:
  
  worin R⁰, Y¹ und X⁰ die oben angegebene Bedeutung haben.
• – Das Medium enthält zusätzlich eine oder mehrere Verbindungen der Formel XXI
  
  worin R⁰ und X⁰ die oben angegebene Bedeutung haben. Vorzugsweise bedeutet X⁰ in der Verbindung der Formel XXI F, OCF₃, ferner CF₃. Insbesondere enthalten die erfindungsgemäßen Mischungen Verbindungen der Formel XXIa
  
  Der Anteil der Verbindungen XXI in den erfindungsgemäßen Mischungen beträgt vorzugsweise 2–40%, insbesondere 5–30% und ganz besonders bevorzugt 5–25%.
• – Das Medium enthält weitere Verbindungen, vorzugsweise ausgewählt aus der folgenden Gruppe bestehend aus den Formeln RI bis RXV,
  
  
  worin R⁰ n-Alkyl, Oxaalkyl, Alkoxy, Fluoralkyl, Alkenyloxy oder Alkenyl mit jeweils 2 bis 12 C-Atomen, d 0,1 oder 2, Y¹ H oder F, Alkyl oder Alkyl* jeweils unabhängig voneinander ein geradkettiger oder verzweigter Alkylrest mit 2 bis 8 C-Atomen, Alkenyl oder Alkenyl* jeweils unabhängig voneinander einen geradkettigen oder verzweigten Alkenylrest mit 2 bis 8 C-Atomen bedeuten.
• – Das Medium enthält vorzugsweise eine oder mehrere Verbindungen der Formeln
  
  
  worin n und m jeweils eine ganze Zahl von 1 bis 8 bedeuten.
• – Das Gewichtsverhältnis I: (II + III + IV + V + VI + VII + VIII + IX + X) ist vorzugsweise 1:10 bis 10:1.
• – Das Medium besteht im wesentlichen aus Verbindungen ausgewählt aus der Gruppe bestehend aus den allgemeinen Formeln I bis XXI.
• – Bevorzugte Medien enthalten eine oder mehrere Verbindungen der Formel
  
  worin R⁰ und X⁰ die oben angegebenen Bedeutungen haben. Vorzugsweise bedeutet X⁰ F.

The compound of formula IV is preferred

or

• In particular, the medium additionally contains one or more compounds of the formulas
  
  
  
  and or
  
  wherein R ⁰ and Y ^{2 have} the meaning given above.
• The medium preferably contains one, two or three, further four, homologues of the compounds selected from the group H1 to H21 (n = 1-12):
  
  
  
  
  The inventive media particularly preferably contain one or more compounds of the formulas H1, H2, H3, H4, H7, H8, H9, H10, H12, H14, H16, H18, H20, H21 and H22.
• The medium additionally contains one or more dioxanes of the formula DI and / or DII,
  
  wherein R ⁰ has the meanings indicated in claim. 1 Preferably, R ⁰ in the compounds of the formula DI and / or DII is straight-chain alkyl or alkenyl having up to 8 C atoms.
• The medium additionally contains one or more compounds selected from the group consisting of the general formulas XI to XVI:
  
  wherein R ⁰ , X ⁰ Y ¹ , Y ² , Y ³ and Y ⁴ each independently have one of the meaning given in claim 2. Preferably, X ^{0 is} F, Cl, CF ₃ , OCF ₃ or OCHF ₂ . R ⁰ is preferably alkyl, oxaalkyl, alkoxy, fluoroalkyl, alkenyl or alkenyloxy.
• - The proportion of compounds of formulas I to X together is at least 50 wt .-% in the total mixture.
• - The proportion of compounds of formula I is in the total mixture 1.5 to 25 wt .-%.
• - The proportion of compounds of formulas II to X in the total mixture is 25 to 98.5 wt .-%.
  
• The medium contains compounds of the formulas II, III, IV, V, VI, VII, VIII, IX and / or X.
• R ⁰ is straight-chain alkyl or alkenyl having 2 to 8 C atoms.
• - The medium consists essentially of compounds of formulas I to XVI.
• The medium contains further compounds, preferably selected from the following group consisting of the general formulas XVII to XX:
  
  wherein R ⁰ , Y ¹ and X ^{0 have} the meaning given above.
• - The medium additionally contains one or more compounds of the formula XXI
  
  wherein R ⁰ and X ^{0 have} the meaning given above. Preferably, X ⁰ in the compound of the formula XXI is F, OCF ₃ , furthermore CF ₃ . In particular, the mixtures according to the invention contain compounds of the formula XXIa
  
  The proportion of the compounds XXI in the mixtures according to the invention is preferably 2-40%, in particular 5-30% and very particularly preferably 5-25%.
• The medium contains further compounds, preferably selected from the following group consisting of the formulas RI to RXV,
  
  
  wherein R ⁰ n-alkyl, oxaalkyl, alkoxy, fluoroalkyl, alkenyloxy or alkenyl each having 2 to 12 carbon atoms, d is 0.1 or 2, Y ¹ H or F, alkyl or alkyl * each independently a straight-chain or branched alkyl radical with 2 to 8 C atoms, alkenyl or alkenyl * each independently a straight-chain or branched alkenyl radical having 2 to 8 carbon atoms.
• The medium preferably contains one or more compounds of the formulas
  
  
  wherein n and m each represents an integer of 1 to 8.
• The weight ratio I: (II + III + IV + V + VI + VII + VIII + IX + X) is preferably 1:10 to 10: 1.
• The medium consists essentially of compounds selected from the group consisting of the general formulas I to XXI.
• Preferred media contain one or more compounds of the formula
  
  wherein R ⁰ and X ^{0 have} the meanings given above. Preferably, X is ⁰ F.

It has already been found that a relatively small proportion of compounds of the formula I are admixed with customary liquid-crystal materials, but in particular with one or more compounds of the formula II, III, IV, V, VI, VII, VIII, IX and / or X. results in a considerable lowering of the threshold voltage and too low values for the birefringence, at the same time observing broad nematic phases with low transition temperatures smectic-nematic, thereby improving the storage stability. The compounds of the formulas I to X are colorless, stable and readily miscible with one another and with other liquid crystal materials.

The term "alkyl" or "alkyl *" includes straight-chain and branched alkyl groups having 2 to 8 carbon atoms, in particular the straight-chain groups ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups of 2-5 carbon atoms are generally preferred.

The term "alkenyl" or "alkenyl *" includes straight and branched alkenyl groups of up to 8 carbon atoms, especially the straight chain groups. Particularly preferred alkenyl groups are C ₂ -C ₇ -1E-alkenyl, C ₄ -C ₇ -E-alkenyl, C ₅ -C ₇ -alkenyl, C ₆ -C ₇ -5-alkenyl and C ₇ -6-alkenyl, in particular C C ₂ -C ₇ 1E-Alkenyl, C ₄ -C ₇ 3E-alkenyl and C ₅ -C ₇ -4-alkenyl. Examples of preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups of up to 5 carbon atoms are generally preferred.

The term "fluoroalkyl" preferably includes straight-chain fluoro-end-capped groups, d. H. Fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. Other positions of the fluorine are not excluded.

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

By suitably selecting the meanings of R ⁰ and X ⁰ , the response times, the threshold voltage, the transconductance of the transmission characteristics etc. can be modified in the desired manner. For example, 1E-alkenyl radicals, 3E-alkenyl radicals, 2E-alkenyloxy radicals and the like generally lead to shorter response times, improved nematic tendencies and a higher ratio of the elastic constants k ₃₃ (bend) and k ₁₁ (splay) compared to alkyl or alkoxy. 4-Alkenyl radicals, 3-alkenyl radicals and the like generally give lower threshold voltages and greater values of k ₃₃ / k ₁₁ compared to alkyl and alkoxy radicals.

A group -CH ₂ CH ₂ - in Z ⁰ generally results in higher values of k ₃₃ / k ₁₁ compared to a single covalent bond. Higher values of k ₃₃ / k ₁₁ allow z. B. flatter transmission characteristics in TN cells with 90 ° twist (to achieve shades of gray) and steeper transmission characteristics in STN, SBE and OMI cells (higher multiplexability) and vice versa.

The optimum ratio of the compounds of the formula I with in each case one or more compounds from the group of the formulas II to X depends largely on the desired properties, on the choice of the components of the formulas I, II, III, IV, V, VI, VII, VIII, IX and / or X and from the choice of further optional components. Suitable proportions within the range given above can be easily determined on a case-by-case basis.

The total amount of compounds of the formula I with in each case one or more compounds from the group of the formulas II to XXI in the mixtures according to the invention is not critical. The mixtures may therefore contain one or more other components to optimize various properties. However, the observed effect on the response times and the threshold voltage is generally greater the higher the total concentration of compounds of formulas I to XXI.

In a particularly preferred embodiment, the media according to the invention comprise one or more compounds of the formula II to X (preferably II and / or III) in which X ⁰ OCF ₃ , OCHF ₂ , F, OCH = CF ₂ , OCF = CF ₂ , OCF ₂ CHFCF ₃ , or OCF ₂ -CF ₂ H means. A favorable synergistic effect with the compounds of the formula I leads to particularly advantageous properties.

The inventive mixtures with low optical anisotropy (Δn <0.07) are particularly suitable for reflective displays. Low V _th mixes are particularly suitable for 2.5V drivers, 3.3V drivers and 4V or 5V drivers. For the latter applications, ester-free mixtures are preferred. Furthermore, the mixtures according to the invention are suitable for IPS and FFS applications.

The structure of the MFK display consisting of polarizers, electrode base plates and electrodes with surface treatment corresponds to the construction customary for such displays. Here, the term of the usual construction is broad and includes all modifications and modifications of the MFK display, in particular matrix display elements based on poly-Si TFT or MIM.

However, a significant difference between the disclosed displays and the conventional ones based on the twisted nematic cell is the choice of the liquid crystal parameters of the liquid crystal layer.

The preparation of the liquid crystal mixtures which can be used according to the invention is carried out in a conventional manner. In general, the desired amount of the components used in lesser amount is dissolved in the constituent of the main component, expediently at elevated temperature. It is also possible to use solutions of the components in an organic solvent, e.g. In acetone, chloroform or methanol, and to remove the solvent again after thorough mixing, for example by distillation.

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

C is a crystalline, S is a smectic, S _{C is} a smectic C, N is a nematic and I is the isotropic phase.

V ₁₀ denotes the voltage for 10% transmission (viewing direction perpendicular to the plate surface). t _on denotes the switch-on time and t _off the switch-off time at an operating voltage corresponding to twice the value of V ₁₀ . Δn denotes the optical anisotropy and n _o the refractive index. Δε denotes the dielectric anisotropy (Δε = ε _∥ - ε _⊥ where ε _{∥ means} the dielectric constant parallel to the _longitudinal molecular _axes and ε _⊥ the dielectric constant perpendicular to it). The electro-optical data are measured in a TN cell in the 1st minimum (ie at a d · Δn value of 0.5 microns) at 20 ° C, unless expressly stated otherwise. The optical data are measured at 20 ° C, unless expressly stated otherwise.

All concentrations in this application, unless explicitly stated otherwise, refer to the corresponding mixture or mixture component. All physical properties are determined according to "Merck Liquid Crystals, Physical Properties of Liquid Crystals", status November 1997, Merck KGaA, Germany, and are valid for a temperature of 20 ° C, unless explicitly stated otherwise.

In the present application and in the following examples, the structures of the liquid crystal compounds are indicated by acronyms, wherein the transformation into chemical formulas according to following Tables A and B takes place. All radicals C _n H _{2n + 1} and C _m H _{2m + 1} are straight-chain alkyl radicals with n or m C atoms. n and m are each independently 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15. The coding according to Table B is self-evident Table A is given only the acronym for the main body. In the individual case, a code for the substituents R ¹ , R ² , L ¹ and L ² follows separately from the acronym for the main body with a dash: Code for R ¹ , R ² , L ¹ , L ² R ¹ R ² L ¹ L ² nm C _n H _{2n + 1} C _m H _{2m + 1} H H N0R C _n H _{2n + 1} OC _m H _{2m + 1} H H n0.m OC _n H _{2n + 1} C _m H _{2m + 1} H H n C _n H _{2n + 1} CN H H nN.F C _n H _{2n + 1} CN H F nF C _n H _{2n + 1} F H H n0F OC _n H _{2n + 1} F H H n Cl C _n H _{2n + 1} Cl H H nF.F C _n H _{2n + 1} F H F nF.FF C _n H _{2n + 1} F F F nCF ₃ C _n H _{2n + 1} CF ₃ H H n0CF ₃ C _n H _{2n + 1} OCF ₃ H H n0CF ₃ .F C _n H _{2n + 1} OCF ₃ H F n0CF ₂ C _n H _{2n + 1} OCHF ₂ H H nS C _n H _{2n + 1} NCS H H RVSN C _r H _{2r + 1} -CH = CH-C _s H _2s - CN H H rESn C _r H _{2r + 1} -OC ₂ H CN H H nAm C _n H _{2n + 1} COOC _m H _{2m + 1} H H n0CCF ₂ .FF C _n H _{2n + 1} OCH ₂ CF ₂ H F F

Tabelle B:

Preferred mixture components of the mixtures according to the invention can be found in Tables A and B. TABLE A

Table B:

Table C:

In Table C possible dopants are given, which can be added to the mixtures according to the invention in amounts of 0.1-10 wt .-% in the rule.

Table D:

Stabilizers which can be added, for example, to the mixtures according to the invention are mentioned below.

The following examples are intended to illustrate the invention without limiting it. Above and below, percentages are by weight. All temperatures are in degrees Celsius. Mp means melting point, bp. Clearing point. Furthermore, K = crystalline state, N = nematic phase, S = smectic phase and I = isotropic phase. The data between these symbols represent the transition temperatures. Δn means optical anisotropy (589 nm, 20 ° C.), Δ∈ means dielectric anisotropy (1 kHz, 20 ° C.), the flow viscosity ν ₂₀ (mm ² / sec) becomes 20 ° C determines. The rotational viscosity γ ₁ (mPa · s) is also determined at 20 ° C.

Examples mix

Example M1 CCP 1F.FF 11.00% S → N -40.0 CCP 2F.FF 10.00% Clearing point [° C] +83.5 CCP-20CF ₃ .F 12.00% Δn [589 nm, 20 ° C] +0.0942 CCP-30CF ₃ .F 8.00% γ ₁ [mPa · s] 142 CCP-20CF ₃ 8.00% d · Δn [μm, 20 ° C] 0.50 CCP-30CF ₃ 8.00% Twist [°] 90 CCP-40CF ₃ 6.00% V _10,0,20 [V] 1.26 CCP-50CF ₃ 7.50% CGU-2-F 4.00% PGU-2-F 7.00% CCGU-3-F 4.50% PUQU-0-F 7.00% CCH-35 5.00% CCP-V-1 2.00% Example M2 CCP 1F.FF 11.00% S → N -40.0 CCP 2F.FF 9.00% Clearing point [° C] +83.5 CCP-20CF ₃ .F 12.00% Δn [589 nm, 20 ° C] +0.0944 CCP-30CF ₃ .F 9.50% γ ₁ [mPa · s] 145 CCP-20CF ₃ 8.00% d · Δn [μm, 20 ° C] 0.50 CCP-30CF ₃ 8.00% Twist [°] 90 CCP-40CF ₃ 6.00% V _10,0,20 [V] 1.23 CCP-50CF ₃ 7.00% CGU-2-F 5.50% PGU-2-F 6.00% CCGU-3-F 6.00% PUQU-0-F 7.00% CCH-35 5.00% Example M3 CCP 1F.FF 10.00% -20.0 CCP 2F.FF 10.00% Clearing point [° C] +81.5 CCP 3F.FF 7.00% Δn [589 nm, 20 ° C] +0.0800 CCP-20CF ₃ 8.00% γ ₁ [mPa · s] 146 CCP-30CF ₃ 8.00% d · Δn [μm, 20 ° C] 12:50 CCP-40CF ₃ 6.00% Twist [°] 90 CCP-50CF ₃ 4.00% V _10,0,20 [V] 1.38 CCP-20CF ₃ .F 12.00% CCP-30CF ₃ .F 12.00% CCP-50CF ₃ .F 10.00% CCH-35 1.00% CCH-3CF ₃ 5.00% PUQU-0-F 7.00% Example M4 CCP 1F.FF 8.50% Clearing point [° C] +83.5 CCP 2F.FF 9.00% Δn [589 nm, 20 ° C] +0.0816 CCP-20CF ₃ .F 12.00% γ ₁ [mPa · s] 128 CCP-30CF ₃ .F 6.00% CCP-20CF ₃ 8.00% CCP-30CF ₃ 8.00% CCP-40CF ₃ 6.00% PUQU-0-F 8.00% CGU-2-F 2.50% CCZU-2-F 4.00% CCZU-3-F 14.00% CCZU-5-F 2.00% CC-3-V1 8.00% CCH-35 4.00% Example M5 CCP-20CF ₃ .F 9.00% S → N -30.0 CCP-20CF ₃ 8.00% Clearing point [°] +80.0 CCP-30CF ₃ 8.00% Δn [589 nm, 20 ° C] +0.1029 CCP-40CF ₃ 6.00% γ ₁ [mPa · s] 109 BCH 3F.FF 2.00% d · Δn [μm, 20 ° C] 0.50 PGU-2F 8.00% Twist [°] 90 PGU-3F 5.00% V _10,0,20 [V] 1.22 CGU-2-F 7.00% CCZU-2-F 4.00% CCZU-3-F 14.00% CCZU-5-F 2.00% BCH-32 3.00% CCH-35 4.00% CC-3-V1 13.00% PUQU-0-F 7.00% Example M6 CCP-20CF ₃ 8.00% Clearing point [° C] +83.0 CCP-30CF ₃ 8.00% Δn [589 nm, 20 ° C] +0.1030 CCP-40CF ₃ 6.00% γ ₁ [mPa · s] 114 CCP-20CF ₃ .F 8.00% d · Δn [μm, 20 ° C] 0.50 CCP-30CF ₃ .F 12.00% Twist [°] 90 CCP 2F.FF 10.00% V _10,0,20 [V] 1.25 CGU-2-F 3.00% PGU-2-F 8.00% PGU-3-F 7.00% CCGU-3-F 5.00% CCH-35 5.00% CC-3-V1 13.00% PUQU-0-F 7.00% Example M7 CCP 2F.FF 2.00% Clearing point [° C] +80.0 CCP-20CF ₃ .F 8.00% Δn [589 nm, 20 ° C] +0.1026 CCP-30CF ₃ .F 8.00% γ ₁ [mPa · s] 100 CCP-40CF ₃ .F 6.00% d · Δn [μm, 20 ° C] 0.50 PGU-2-F 8.00% Twist [°] 90 PGU-3-F 5.00% V _10,0,20 [V] 1.29 PGU-5-F 3.00% CGU-2-F 5.00% CCZU-2-F 4.00% CCZU-3-F 14.00% CCZU-5-F 4.00% BCH-32 3.00% CCH-35 5.00% CC-3-V1 13.00% CC-5-V 5.00% PUQU-0-F 7:00% Example M8 BCH 3F.F 10.81% Clearing point [° C] +77.0 BCH 5F.F 9.01% Δn [589 nm, 20 ° C] +0.0963 ECCP-30CF ₃ 4.50% Δε [1 kHz, 20 ° C] 6.8 ECCP-50CF ₃ 4.50% γ ₁ [mPa · s] 116 CBC-33F 1.80% CBC-53F 1.80% CBC-55F 1.80% PCH-6F 7.21% PCH-7F 5.40% CCP-20CF ₃ 7.21% CCP-30CF ₃ 10.81% CCP-40CF ₃ 6.31% CCP-50CF ₃ 9.91% PCH-5F 9.01% PUQU-0-F 9.92% Example M9 CCP 2F.F 7.00% Clearing point [° C] +81.5 CCP 3F.F 17.00% Δn [589 nm, 20 ° C] +0.0797 CPZU-2-F 3.00% γ ₁ [mPa · s] 101 CPZU-3-F 3.00% d · Δn [μm, 20 ° C] 0.50 CCZU-2-F 3.00% Twist [°] 90 CCZU-3-F 9.00% V _10.0.20 [V] 1.69 CCZU-4-F 3.00% CCZU-5-F 3.00% CCP-31 10.00% CCH-34 12.00% PCH 7F.FF 6.00% CCP-3F 5.00% PCH-302 17.00% PUQU-0-F 2.00% Example M10 BCH 3F.FF 18.00% Clearing point [° C] +81 BCH 5F.FF 8.00% Δn [589 nm, 2 ° C] +0.1031 BCH 2F.F 9.00% γ ₁ [mPa · s] 157 BCH 3F.F 9.00% d · Δn [μm, 20 ° C] 0.50 CCP 3F.F 15.00% Twist [°] 90 DCU-3-F 3.00% V _10.0.20 [V] 1.24 DCU-4-F 4.00% DCU-5-F 9.00% CCP-31 10.00% CCP-3F 5.00% CCH-34 7.00% PUQU-0-F 3.00% Example M11 CCH-34 5.00% Clearing point [° C] +80 CCP 2F.F 2.50% Δn [589 nm, 20 ° C] +0.092 CCP 3F.F 13.00% γ ₁ [mPa · s] 165 CCP 4F.F 13.00% d · Δn [μm, 20 ° C] 0.50 CCP 4F.FF 9.00% Twist [°] 90 BCH 2F.F 9.00% V _10.0.20 [V] 1.26 BCH 3F.F 8.50% BCH 3F.FF 8.00% DCU-3-F 3.00% DCU-4-F 5.00% DCU-5-F 8.00% PUQU-0-F 7.00% CCP-31 9.00% Example M12 CCP 3F.F 13.00% Clearing point [° C] +80 CCP 4F.F 13.00% Δn [589 nm, 20 ° C] +0.079 CCP 2F.FF 2.00% γ ₁ [mPa · s] 130 BCH 3F.FF 1.00% d · Δn [μm, 20 ° C] 0.50 CCZU-2-F 3.00% Twist [°] 90 CCZU-3-F 10.00% V _10,0.20 [V] 1.25 CCZU-4-F 3.00% DCU-3-F 3.00% DCU-4-F 5.00% DCU-5-F 8.00% PUQU-0-F 8.00% CCP-3F 3.00% CCP-31 9.00% CCH-34 8.00% PCH-302 11.00% Example M13 CCP 2F.FF 10.00% Clearing point [° C] +81.0 CCZU-2-F 4.00% Δn [589 nm, 20 ° C] +0.0783 CCZU-3-F 12.00% γ ₁ [mPa · s] 80 CCZU-5-F 4.00% d · Δn [μm, 20 ° C] 0.50 CCP-20CF ₃ 8.00% Twist [°] 90 CCP-30CF ₃ 8.00% V _10,0.20 [V] 1.63 CCP-40CF ₃ 6.00% PGU-2-F 4.00% CC-5-V 17.00% CC-3-V1 11.00% PCH-301 4.00% CCP-V-1 2.00% CCH-35 4.00% PUQU-0-F 6.00% Example M14 CCP 1F.FF 10.00% Clearing point [° C] +81.0 CCP 2F.FF 10.00% Δn [589 nm, 20 ° C] +0.0775 CCP 3F.FF 8.00% γ ₁ [mPa · s] 87 CCP-20CF ₃ .F 7.00% d · Δn [μm, 20 ° C] 0.50 CCP-20CF ₃ 8.00% Twist [°] 90 CCP-30CF ₃ 8.00% V _10,0.20 [V] 1.60 CCP-40CF ₃ 6.00% CCP-50CF ₃ 8.00% PGU-2-F 3.00% CC-5-V 12.00% CC-3-V1 12.00% CCH-35 3.00% PUQU-0-F 5.00% Example M15 CDU-2-F 9.00% Clearing point [° C] 77.0 CDU-3-F 4.00% Δn [589 nm, 20 ° C] 0.0950 PGU-2-F 9.00% Δε [kHz, 20 ° C] 12.5 CGZP-2-OT 10.00% γ ₁ [mPa · s] 100 CGZP-3-OT 10.00% CCZU-2-F 3.00% CCZU-3-F 12.00% CC-5-V 13.00% CC-3-V1 11.00% CCP-20CF ₃ 4.00% CCP-30CF ₃ 8.00% PUQU-0-F 7.00%

Claims (8)

Liquid-crystalline medium, characterized in that it contains one or more compounds of the formula I6,

wherein X is F, one or more compounds selected from the group of compounds:

wherein n = 1-12, and additionally one or more compounds selected from the compounds of the formulas H8, H9, DI and / or DII:

wherein n = 1-12, and R ^{0 is} n-alkyl, oxaalkyl, alkoxy, fluoroalkyl, alkenyloxy or alkenyl each having 2 to 12 carbon atoms. Liquid-crystalline medium according to claim 1, characterized in that it additionally contains one or more compounds selected from the group consisting of the general formulas II, III, IV, V, VI, VII, VIII, IX and X,

wherein the individual radicals have the following meanings: R ⁰ n-alkyl, oxaalkyl, alkoxy, fluoroalkyl, alkenyloxy or alkenyl each having 2 to 12 C atoms X ⁰ F, Cl, halogenated alkyl, halogenated alkenyl, halogenated alkenyloxy or halogenated alkoxy with in each case up to 8 C atoms, Z ⁰ -CH = CH-, -CH ₂ O-, -OCH ₂ -, - (CH ₂ ) ₄ -, -C ₂ H ₄ -, -C ₂ F ₄ -, - CF = CF-, -CH = CF-, -CF = CH-, -CF ₂ O-, -OCF ₂ - or -COO-, Y ¹ , Y ² , Y ³ and Y ⁴ each, independently of one another, denote H or F, and r is 0 or 1. Liquid-crystalline medium according to claim 1 or 2, characterized in that it contains one or more compounds of the formulas H8 or H9 according to claim 1. Liquid-crystalline medium according to one or more of claims 1 to 3, characterized in that it contains one or more compounds of formula H9 according to claim 1. Liquid-crystalline medium according to one or more of claims 1 to 4, characterized in that the proportion of compounds of formulas I to X in the total mixture is at least 50 wt .-%. Liquid-crystalline medium according to one or more of Claims 1 to 5, characterized in that it additionally contains one or more compounds of the formulas RI to RXV,

wherein R ⁰ n-alkyl, oxaalkyl, alkoxy, fluoroalkyl, alkenyloxy or alkenyl each having 2 to 12 carbon atoms, d 0, 1 or 2, Y ¹ H or F, alkyl or alkyl * each independently a straight-chain or branched alkyl radical with 2 to 8 C atoms, alkenyl or Alkenyl * each independently of one another denote a straight-chain or branched alkenyl radical having 2 to 8 C atoms. Liquid-crystalline medium according to one or more of claims 2 to 6, characterized in that X ^{0 is} F, OCHF ₂ or OCF ₃ and Y ^{2 is} H or F. Use of the liquid-crystalline medium according to one or more of claims 1 to 7 for electro-optical purposes.