DE102004062962A1 - Liquid crystal medium with helical twisted structure, for electrooptical purposes e.g. cholesteric, surface- or polymer-stabilized cholesteric flexoelectric or active matrix display, contains chiral compound and 2 types of nematic compound - Google Patents

Abstract

Liquid crystal (LC) medium with helical twisted structure contains an optically active component comprising chiral compound(s) of twisting power and concentration giving medium a helix pitch = 1 mu m and a nematic component comprising 2 types of 2- or 3-ring 1-fluoro-, -chloro-, -haloalk(en)yl or -haloalkoxy-4-substituted-benzene compounds, comprising compound(s) (I) with cyclohexyl and/or phenyl rings and (II) with 1,3-dioxan-2-yl or 5-cyclohexyl-1,3-dioxan-2-yl rings. Liquid crystal (LC) medium with helical twisted structure contains an optically active component comprising chiral compound(s) of twisting power and concentration giving medium a helix pitch = 1 mu m and a nematic component comprising 2 types of 2- or 3-ring 1-fluoro-, -chloro-, -haloalk(en)yl or -haloalkoxy-4-substituted-benzene compounds, comprising compound(s) of formula (I) with cyclohexyl and/or phenyl rings and of formula (II) with 1,3-dioxan-2-yl or 5-cyclohexyl-1,3-dioxan-2-yl rings; A 1>, A 2> independently : trans-1,4-cyclohexylene, 1,4-phenylene or 2-fluoro- or 2,6-difluoro-1,4-phenylene; Z 1>, Z 2> : a single bond or bridging group; X 0> : F, Cl or 1-6 C haloalk(en)yl or haloalkoxy; a, b : 0 or 1 The full definitions are given in the DEFINITIONS (Full Definitions) Field. [Image].

Description

The The present invention relates to a liquid-crystalline medium having high twist, its use for electro-optical purposes and this medium containing ads.

liquid crystal displays are known from the prior art. The most common display devices are based on the Schadt-Helfrich effect and contain a liquid crystal medium with twisted nematic structure, such as TN cells ("twisted nematic") with twist angles typically 90 ° and STN cells ("supertwisted nematic ") with twist angles typically 180 to 270 °. Further, ferroelectric liquid crystal displays known to be a liquid crystal medium with twisted smectic structure included. The twisted structure is common in these ads by adding one or more chiral dopants to one nematic or smectic liquid crystal medium achieved.

Furthermore are liquid crystal displays known, the liquid crystal (FK) media with chiral nematic or cholesteric structure. These Media have TN and STN cells compared to the media a much higher one Twist on.

Cholesteric liquid crystals exhibit selective reflection of circularly polarized light, with the direction of rotation of the light vector corresponding to the direction of rotation of the cholesteric helix. The reflection wavelength λ results from the pitch p of the cholesteric helix and the mean birefringence n of the cholesteric liquid crystal according to equation (1): λ = n × p (1)

The Terms "chiral nematic "and" cholesteric "become in the state the technique used side by side. "Chiral nematic" often refers to FK materials consisting of a nematic Host mixture doped with an optically active component which induces a helically twisted superstructure. On the other hand often refers to "cholesteric" chiral FK materials, for Example cholesteryl derivatives that have a "natural" cholesteric phase having helical twist. Both terms will be synonymous used in parallel with the name of the same object. In the present application is for Both of the above types of FK materials use the term "cholesteric" where this term is intended to encompass the broadest meaning of "chiral nematic" and "cholesteric".

Examples for common cholesteric liquid crystal (CFRP) displays are the so-called SSCT ("surface stabilized cholesteric texture ") and PSCT (English "polymer stabilized cholesteric texture "). SSCT and PSCT displays usually contain a CFK medium, which, for example, in the initial state a planar, light one certain wavelength having reflective structure, and by applying an electrical AC pulse switched into a focal conical, light scattering structure can be, or vice versa. When applying a stronger voltage pulse becomes the CFRP medium into a homeotropic, Translated from transparent state where it turns off after quickly turning off the voltage in the planar, or relaxed after slow off in the focal conical state.

The planar orientation of the CFRP medium in the initial state, i. in front Applying a voltage is performed in SSCT displays, for example surface treatment the cell walls reached. Included in PSCT ads the CFK medium additionally a phase-separated polymer or polymer network containing the structure stabilizes the CFK medium in the respectively driven state.

SSCT and PSCT ads generally no backlight. The CFK medium in one Pixel shows selective light reflection in the planar state certain wavelength according to the above Equation (1), so that the Pixel e.g. in front of a black background in the corresponding Reflection color appears.

The Reflection color disappears when switching to the focal conical, scattering or homeotropic, transparent state.

SSCT and PSCT displays are bistable, ie after switching off the electric field, the respective state is retained and is only returned to the initial state by applying a new field. To generate a pixel, therefore, a short voltage pulse is sufficient, in contrast to, for example electro-optical TN or STN displays in which the FK medium in a controlled pixel immediately after switching off the electric field returns to the initial state, so that for the permanent generation of a pixel, a maintenance of the drive voltage is necessary.

Out the reasons above have CFRP displays in comparison to TN or STN displays significantly lower power consumption. In addition, they show in the scattering Condition no or only small angle dependence. They also need no active matrix control as with TN ads, but can be operated in the simpler multiplex or passive matrix method.

WO 92/19695 and US 5,384,067 describe, for example, a PSCT display comprising a CFRP medium having positive dielectric anisotropy and up to 10 wt% of a phase-separated polymer network dispersed in the liquid crystal material. US 5,453,863 describes, for example, an SSCT display comprising a polymer-free CFK medium having positive dielectric anisotropy.

Further Prior art displays using CFRP materials are the so-called flexoelectric displays, in particular those in the "uniformly lying helix mode "(ULH mode). The flexoelectric effect and CFRP materials, which show this effect are e.g. by Chandrasekhar in "Liquid Crystals", 2nd edition, Cambrige University Press (1992), P.G. deGennes et al. in "The Physics of Liquid Crystals ", 2nd edition, Oxford Science Publications (1995), Patel and Meyer, Phys. Rev. Lett. 58 (15), 1538-1540 (1987) and Rudquist et al., Liq. Cryst. 22 (4), 445-449 (1997).

flexoelectric CFRP materials typically have an asymmetric molecular structure and a strong dipole moment. When applying an electric field perpendicular to the cholesteric helical axis become the permanent Oriented dipoles in the direction of the field. At the same time the FK director distorted due to the asymmetric molecular structure, while the Orientation of the cholesteric helical axis remains unchanged. this leads to to a macroscopic polarization of the CFRP material in the field direction, and a shift of the optical axis relative to the helical axis.

Flexoelectric Ads are usually in the so-called "uniformly lying helix "(ULH) mode, such as in P. Rudquist et al., Liq. Cryst. 23 (4), 503 (1997). For this purpose, a layer of a flexoelectric CFRP material with high twist and short helix pitch, typically in the range of 0.2 μm up to 1.0 μm, in particular smaller than 0.5 μm, oriented between two transparent parallel electrodes, that the aligned cholesteric helical axis parallel to the electrodes and the CFRP layer is a macroscopically uniform orientation having. When applying an electric field to the cell vertically to the CFRP layer rotates the FK director and thus the optical axis the sample in the layer plane. If the CFRP layer between two Linear polarizers is brought, this leads to a change the transmission of the linearly polarized light in the CFRP material, which can be exploited in electro-optical displays. The flexoelectric Effect is characterized i.a. through very fast switching times, typically of 6 μs up to 100 μs, as well as good contrast with a high number of gray levels.

flexoelectric Ads can as transmissive or reflective displays, with active matrix control or operated in the multiplex or passive matrix method.

High twist CFRP materials for use in flexoelectric displays are described, for example, in US Pat EP 0 971 016 and GB 2 356 629 described. EP 0 971 016 proposes chirally liquid-crystalline estradiol derivatives for this purpose, GB 2 356 629 the so-called bimesogenic compounds containing two mesogenic groups linked by flexible hydrocarbon chains in combination with chiral dopants.

A CFK medium for the above-mentioned displays can be produced, for example, by doping a nematic FK mixture with a high-twisting chiral dopant. The pitch p of the induced cholesteric helix then results from the concentration c and the twisting power HTP (helical twisting power) of the chiral dopant according to equation (2): p = (HTP × c) -1 (2)

It is possible, too, to use two or more dopants, for example, the temperature dependence To compensate for the HTP of the individual dopants and thus a low temperature dependent the helical pitch and the reflection wavelength of the CFRP medium.

For a use in the above ads should be the chiral dopants the highest possible twisting with low temperature dependence, high stability and good solubility in the liquid crystalline Have host phase. Furthermore they should be the liquid crystalline ones and electro-optical properties of the liquid crystalline host phase preferably do not negatively influence. A high twisting capacity of Dopants are used, inter alia, to obtain small pitches, e.g. desired in cholesteric displays, but also to be able to lower the concentration of the dopant. Thereby on the one hand a possible impairment the properties of the liquid crystal medium reduced by the dopant, and on the other hand the margin in terms of solubility of the dopant increases, so that e.g. also dopants with lower solubility can be used can.

to Use in flexoelectric displays should be CFRP materials Furthermore have a sufficiently strong flexoelectric effect.

As a general rule have to CFRP materials for the use in the above ads a good chemical and thermal stability and a good stability across from have electrical fields and electromagnetic radiation. Furthermore, the liquid crystal materials should a broad cholesteric liquid crystal phase with high clearing point, a sufficiently high birefringence, high positive dielectric Possess anisotropy and low rotational viscosity.

The CFRP materials should also be such that by simple and targeted variation of different reflection wavelengths in particular can be realized in the visible range. They should also have one low temperature dependence the reflection wavelength exhibit.

There liquid Crystals usually used as mixtures of several components, it is important that the Components are readily miscible with each other. Other properties, such as the dielectric anisotropy and the optical anisotropy, have to Depending on the cell type meet different requirements.

With It is the media available from the prior art but not possible favorable Values for to realize all the above parameters.

EP 0 450 025 describes, for example, a cholesteric liquid crystal mixture consisting of a nematic liquid crystal with two or more chiral dopants. However, the mixtures shown therein have only low clearing points. In addition, they contain a high proportion of 26% of chiral dopants. However, high concentrations of dopant generally lead to an impairment of the liquid-crystalline and electro-optical properties of the CFRP medium.

The known from the prior art materials for flexoelectric and CFRP displays often do not have sufficiently wide FK phases, sufficiently low viscosity values and sufficiently high values of dielectric anisotropy. They also need high switching voltages and often do not have the required FK-layer thickness matched Birefringence values.

So is e.g. For many CFRP displays require a CFRP medium with high birefringence Δn for a high reflectivity to achieve while other CFRP displays, e.g. Show their priority high color saturation is (multicolour CFRP ads), low value of Δn need. It However, it has been shown that a reduction birefringence while maintaining the high polarity of the CFRP medium, which for low switching voltages is necessary, with the from the state of Technology known CFK media not sufficiently realized could be.

It There is thus a big one Need for CFRP media with high twist, high operating temperature range, short switching times, low threshold voltage, low temperature dependence the reflection wavelength, and in particular low levels of birefringence, which are the disadvantages the known from the prior art media not or only in lesser degree exhibit.

For an application in CFRP displays, especially in SSCT displays, the CFRP media should Moreover, at the same time good dielectric behavior, a broad Operating temperature range and have a good color saturation.

Of the Invention is based on the object to provide CFRP media, especially for use in flexoelectric displays, CFRP displays such as SSCT and PSCT displays and other bistable CFRP displays which are the above have required properties and the disadvantages of the state of the art The technique known media do not or only to a lesser extent possess.

It it was found that these Task solved can be, if one of such ads media according to the invention used.

und eine oder mehrere Verbindungen der Formel II

enthält, worin
R¹ H, einen unsubstituierten, einen einfach durch CN oder CF₃ oder einen mindestens einfach durch Halogen substituierten Alkyl- oder Alkenylrest mit 1 bis 20 C-Atomen, wobei in diesen Resten auch eine oder mehrere CH₂-Gruppen jeweils unabhängig voneinander durch -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CH=CH- oder -C≡C- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind,

Y¹ bis Y⁴ jeweils unabhängig voneinander H oder F,
Z¹ und Z² jeweils unabhängig voneinander -O-, -S-, -CO-, -COO-, -OCO-, -S-CO-, -CO-S-, -OCH₂-, -CH₂O-, -SCH₂-, -CH₂S-, -CF₂O-, -OCF₂-, -CF₂S-, -SCF₂-, -CH₂CH₂-, -CF₂CH₂-, -CH₂CF₂-, -CF₂CF₂-, -CH=CH-, -CF=CH-, -CH=CF-, -CF=CF-, -C≡C- oder eine Einfachbindung,
X⁰ F, Cl, halogeniertes Alkyl, Alkenyl oder Alkoxy mit 1 bis 6 C-Atomen, und
a und b jeweils unabhängig voneinander 0 oder 1
bedeuten.The invention relates to a liquid-crystalline medium with helically twisted structure containing a nematic component and an optically active component, characterized in that
the optically active component contains one or more chiral compounds whose twisting power and concentration are chosen such that the helix pitch of the medium is ≤1 μm, and
the nematic component one or more compounds of the formula I.

and one or more compounds of the formula II

contains, in which
R ^{1 is} H, an unsubstituted, an alkyl or alkenyl radical having 1 to 20 C atoms, which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen, where one or more CH ₂ groups in these radicals are also each independently O, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CH = CH- or -C≡C- can be replaced so that Atoms are not directly linked,

Y ¹ to Y ^{4 are} each independently H or F,
Z ¹ and Z ^{2 are} each independently of one another -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 F, Cl, halogenated alkyl, alkenyl or alkoxy having 1 to 6 carbon atoms, and
a and b are each independently 0 or 1
mean.

One Another object of the invention is the use of the CFRP media according to the invention for electro-optical Purposes, especially in bistable CFRP displays, CFRP displays such as SSCT and PSCT displays, and in flexoelectric displays.

Another object of the invention is an electro-optical display, in particular a bistable, CFK, SSCT, PSCT or flexoelectric display, with two plane-parallel support plates, which form a cell with a border, and a CFK medium in the cell, wherein the CFK medium a Me dium according to claim 1.

Surprised it was found that it possible is a CFK medium according to the present invention with a reflection wavelength in the visible range and / or a cholesteric phase at room temperature to provide mean to low levels of birefringence and yet has sufficiently high values of the dielectric anisotropy Δε, to realize low switching times. This is the case in the CFRP media according to the invention in particular by using compounds of the formula I and II, together with high-twisting chiral dopants as below described reached.

So leads the Use of the compounds of the formula I and II in the mixtures for CFRP displays according to the invention to a high polarity, i.e. low threshold voltages, short switching times and one wide operating temperature range.

The CFRP media according to the invention show as well by the combination of the compounds of formula I and II when used in CFRP displays excellent properties in terms of color saturation and UV stability. In particular, this CFRP and SSCT displays can be realized, which include the Can represent color red, without due to the high yellow and green shares of the previously known SSCT media orange to act.

there is surprisingly the achievement of high polarity, which for acceptable switching voltages is necessary, not adversely affected.

• – sie besitzen einen breiten cholesterischen Phasenbereich insbesondere bei tiefen Temperaturen und einen hohen Klärpunkt,
• – sie besitzen eine hohe UV-Stabilität.

Furthermore, the mixtures according to the invention are distinguished by the following advantages

• They have a broad cholesteric phase range, especially at low temperatures and a high clearing point,
• - they have a high UV stability.

The Compounds of formulas I and II have a wide range of applications. In dependence of the choice of substituents can these compounds serve as base materials from which liquid crystalline Media for the most part Part are composed; it can but also compounds of the formulas I and II liquid-crystalline base materials be added from other classes of compounds, for example the dielectric and / or optical anisotropy of such a dielectric to influence and / or its threshold voltage and / or its viscosity to optimize. The compounds of formulas I and II are pure Condition colorless and form liquid crystalline Mesophases in a for the electro-optical use favorable located temperature range. Chemical, thermal and against light they are stable.

Especially preferred are CFK media, wherein the nematic component is more than 20%, in particular more than 40%, more preferably more than 50%, more preferably more than 60% of one or more compounds containing a 3,4,5-trifluorophenyl group.

CLC media preferably further comprising at least one compound of formula I wherein X is ^0, Y ¹ and Y ² represent F.

Particular preference is given to compounds of the formula I in which Z ¹ and Z ^{2 are} preferably -O-, -S-, -CO-, -COO-, -OCO-, -S-CO-, -CO-S-, -OCH ₂ -, CH ₂ O-, -CH 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 - or a single bond, especially -COO-, -OCO-, -OCH ₂ -, -CH ₂ O-, -CF ₂ O-, -OCF ₂ -, -CH ₂ CH ₂ -, -CF ₂ CH ₂ -, -CH ₂ CF ₂ -, -CF ₂ CF ₂ - or a single bond.

As a general rule are compounds containing a 3,4,5-trifluorophenyl group, the with another phenyl group a bridge link -CH = CH-, -CF = CH-, -CH = CF-, -CF = CF- or -C≡C-, in particular -CF = CF-, is linked, for use in CFRP media according to the invention, especially for CFRP displays according to the invention, less preferred.

Furthermore, CFRP media comprising a compound of the formula I in which R ^{1 is} alkyl having 1 to 10 C atoms or alkenyl having 2 to 20 C atoms, a is 0 or 1, A ^{1 is} 1,4-phenylene, A ² 1, 4-cyclohexylene, X ⁰ F, Cl or CN, Z ¹ CF = CF and Z ^{2 is} a single bond, especially less preferred for use in CFRP displays.

worin R¹, X⁰, Y¹, Y² und a die in Formel I angegebene Bedeutung besitzen,
R¹ vorzugsweise n-Alkyl, Alkoxy, Fluoralkyl, Alkenyl oder Oxaalkenyl mit jeweils bis zu 9 C-Atomen, und
Z³ COO, C₂H₄, CF₂O oder C₂F₄
bedeuten.The compounds of the formula I are preferably selected from the following formulas

in which R ¹ , X ⁰ , Y ¹ , Y ² and a have the meaning given in formula I,
R ^{1 is} preferably n-alkyl, alkoxy, fluoroalkyl, alkenyl or oxaalkenyl, each having up to 9 C atoms, and
Z ³ COO, C ₂ H ₄ , CF ₂ O or C ₂ F ₄
mean.

worin R¹ und X⁰ die in Formel I angegebene Bedeutung haben, R¹ besonders bevorzugt n-Alkyl mit 1 bis 8 C-Atomen oder Alkenyl mit 2 bis 7 C-Atomen und X⁰ besonders bevorzugt F, Cl, CF₃, OCF₃ oder OCHF₂ bedeuten. Besonders bevorzugt sind Verbindungen der Formel I1a, insbesondere solche worin X⁰ F bedeutet, und Verbindungen der Formel I1c, insbesondere solche worin X⁰ OCF₃ bedeutet.The compounds of formula I1 are preferably selected from the following group

wherein R ¹ and X ^{0 have} the meaning given in formula I, R ¹ particularly preferably n-alkyl having 1 to 8 carbon atoms or alkenyl having 2 to 7 carbon atoms and X ⁰ particularly preferably F, Cl, CF ₃ , OCF ₃ or OCHF ₂ mean. Particular preference is given to compounds of the formula I1a, in particular those in which X ⁰ denotes F, and compounds of the formula I1c, in particular those in which X ⁰ denotes OCF ₃ .

worin R¹ und X⁰ die in Formel I angegebene Bedeutung haben, R¹ besonders bevorzugt n-Alkyl mit 1 bis 8 C-Atomen oder Alkenyl mit 2 bis 7 C-Atomen und X⁰ bevorzugt OCF₃ oder F, besonders bevorzugt F bedeuten. Besonders bevorzugt sind Verbindungen der Formel I2a, I2b und I2c, ferner I2i und I2k, insbesondere solche, worin X⁰ F bedeutet.The compounds of the formula I2 are preferably selected from the following group

wherein R ¹ and X ^{0 have} the meaning given in formula I, R ¹ particularly preferably n-alkyl having 1 to 8 carbon atoms or alkenyl having 2 to 7 carbon atoms and X ⁰ preferably OCF ₃ or F, particularly preferably F , Particular preference is given to compounds of the formulas I 2a, 12b and 12c, furthermore I 2i and I 2k, in particular those wherein X ^{0 is} F.

worin R¹ die in Formel I angegebene Bedeutung hat und besonders bevorzugt n-Alkyl mit 1 bis 8 C-Atomen oder Alkenyl mit 2 bis 7 C-Atomen bedeutet. Besonders bevorzugt sind Verbindungen der Formel IIa und IIe.The compounds of the formula II are preferably selected from the following formulas

wherein R ^{1 has} the meaning given in formula I and particularly preferably n-alkyl having 1 to 8 carbon atoms or alkenyl having 2 to 7 carbon atoms. Particular preference is given to compounds of the formulas IIa and IIe.

worin
A³ 1,4-Phenylen oder trans-1,4-Cyclohexylen,
c 0 oder 1,
R³ eine Alkenylgruppe mit 2 bis 7 C-Atomen,
R⁴ eine Alkyl-, Alkoxy- oder Alkenylgruppe mit 1 bis 12 C-Atomen, wobei auch ein oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -C≡C-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind,
Q CF₂, OCF₂, CFH, OCFH oder eine Einfachbindung,
Y F oder Cl, und
L¹ und L² jeweils unabhängig voneinander H oder F
bedeuten.In addition to the compounds of the formulas I and II, the mixtures according to the invention preferably contain one or more alkenyl compounds selected from the formulas III1 and III2

wherein
A ^{3 is} 1,4-phenylene or trans-1,4-cyclohexylene,
c 0 or 1,
R ^{3 is} an alkenyl group having 2 to 7 C atoms,
R ^{4 is} an alkyl, alkoxy or alkenyl group having 1 to 12 C atoms, whereby also one or two non-adjacent CH ₂ groups are represented by -O-, -CH = CH-, -C≡C-, -CO-, -OCO- or -COO- can be replaced so that O atoms are not directly linked to one another,
Q CF ₂ , OCF ₂ , CFH, OCFH or a single bond,
YF or Cl, and
L ¹ and L ^{2 are} each independently H or F
mean.

worin R^3a und R^4a jeweils unabhängig voneinander H, CH₃, C₂H₅ oder n-C₃H₇ und alkyl eine Alkylgruppe mit 1 bis 8 C-Atomen bedeuten.Particular preference is given to compounds of the formula III1 in which c denotes 1. Further preferred compounds of formula III1 are selected from the following formulas

wherein R ^3a and R ^{4a are} each independently H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ and alkyl is an alkyl group having 1 to 8 carbon atoms.

Particular preference is given to compounds of the formula IIIa, in particular those in which R ^3a and R ^{4a are} CH ₃ , compounds of the formula III1e, in particular those in which R ^{3a is} H, and compounds of the formulas III1f, III1g, III1h and IIIl, in particular those in which R is ^3a H or CH _3.

worin R^3a H, CH₃, C₂H₅ oder n-C₃H₇, insbesondere H oder CH₃ bedeutet.Particularly preferred compounds of formula III2 are those in which L ¹ and / or L ^{2 are} F and QY is F or OCF ₃ . Further preferred compounds of the formula III2 are those in which R ^{3 is} 1E-alkenyl or 3E-alkenyl having 2 to 7, in particular 2, 3 or 4 C atoms. Further preferred compounds of formula III2 are those of formula III2a

wherein R ^{3a is} H, CH ₃ , C ₂ H ₅ or nC ₃ H ₇ , in particular H or CH ₃ .

The Use of compounds of the formula III1 and III2 leads to the Liquid crystal mixtures according to the invention to particularly low values of rotational viscosity and to CFRP displays with fast switching times, especially at low speeds Temperatures.

und/oder eine oder mehrere Verbindungen ausgewählt aus der Gruppe bestehend aus den Dreiringverbindungen der folgenden Formeln

und/oder eine oder mehrere Verbindungen ausgewählt aus der Gruppe bestehend aus den Vierringverbindungen der folgenden Formeln

worin R¹ und R² jeweils unabhängig voneinander eine der für R¹ in Formel I angegebenen Bedeutungen haben, und vorzugsweise jeweils unabhängig voneinander eine Alkyl-, Alkoxy- oder Alkenylgruppe mit 1 bis 12 C-Atomen bedeuten, wobei auch ein oder zwei nicht benachbarte CH₂-Gruppen durch -O-, -CH=CH-, -C≡C-, -CO-, -OCO- oder -COO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind, und L¹ H oder F bedeutet.Preferred liquid-crystal mixtures contain, in addition to the compounds of the formulas I and II, preferably one or more compounds selected from the group consisting of the two-ring compounds of the following formulas

and / or one or more compounds selected from the group consisting of the three-membered compounds of the following formulas

and / or one or more compounds selected from the group consisting of the four-membered compounds of the following formulas

wherein R ¹ and R ² each independently have one of the meanings given for R ¹ in formula I, and preferably each independently represent an alkyl, alkoxy or alkenyl group having 1 to 12 carbon atoms, wherein one or two non-adjacent CH ₂ groups can be replaced by -O-, -CH = CH-, -C≡C-, -CO-, -OCO- or -COO- so that O atoms are not directly linked to each other, and L ¹ H or F means.

The 1,4-phenylene groups in IV10 to IV19 and IV23 to IV26 can each be independently also be substituted by fluorine mono- or polysubstituted.

Particular preference is given to compounds of the formulas IV27 to IV33 in which R ^{1 is} alkyl and R ^{2 is} alkyl or alkoxy, in each case having 1 to 7 C atoms. Further preferred are compounds of formula IV 25 and IV 31, wherein L ^{1 is} F. Very particular preference is given to compounds of the formulas IV6, IV26, IV27 and IV32.

R ¹ and R ² in the compounds of formulas IV1 to IV33 particularly preferably denote straight-chain alkyl or alkoxy having 1 to 12 C atoms.

worin R¹ die oben angegebene Bedeutung hat und vorzugsweise geradkettiges Alkyl mit 1 bis 7 C-Atomen bedeutet.In a further preferred embodiment, the mixtures according to the invention additionally comprise one or more compounds of the formula V

wherein R ^{1 has} the meaning given above and preferably denotes straight-chain alkyl having 1 to 7 carbon atoms.

• – eine oder mehrere Verbindungen der Formel I1a, worin X⁰ F ist,
• – eine oder mehrere Verbindungen der Formel I2a, worin X⁰ F ist,
• – eine oder mehrere Verbindungen der Formel IIa,
• – 1 bis 20, insbesondere 5 bis 15 Verbindungen der Formel I,
• – mehr als 20 %, insbesondere mehr als 30 %, besonders bevorzugt mehr als 35 % einer oder mehrerer Verbindungen der Formel I,
• – 5 bis 50 %, bevorzugt 10 bis 45 % an Verbindungen der Formel I1,
• – 10 bis 65 %, bevorzugt 20 bis 55 % an Verbindungen der Formel I2,
• – 5 bis 60 %, bevorzugt 15 bis 50 % an Verbindungen der Formel II,
• – eine oder mehrere Verbindungen ausgewählt aus den Formeln IV6, IV26 und IV32,
• – eine oder mehrere Verbindungen der Formel V,

In particularly preferred embodiments, the nematic component of the media according to the invention contains

• One or more compounds of the formula I1a in which X ^{0 is} F,
• - one or more compounds of formula I2a in which X is ⁰ F,
• One or more compounds of the formula IIa,
• 1 to 20, in particular 5 to 15 compounds of the formula I,
• More than 20%, in particular more than 30%, more preferably more than 35% of one or more compounds of the formula I,
• From 5 to 50%, preferably from 10 to 45%, of compounds of the formula I1,
• From 10 to 65%, preferably from 20 to 55%, of compounds of the formula I2,
• From 5 to 60%, preferably from 15 to 50%, of compounds of the formula II,
• One or more compounds selected from the formulas IV6, IV26 and IV32,
• One or more compounds of the formula V,

In Another particularly preferred embodiment is the nematic Component consisting essentially of compounds selected from the formulas I1, I2, II, IV6, IV26, IV32 and V.

By suitable choice of the terminal radicals R ⁰ , R ¹ , R ² , R ³ , R ⁴ and X ⁰ in the compounds of formulas I to V, the response times, the threshold voltage and other properties 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 ₃ (bend) and K ₁ (splay) in comparison to alkyl or alkoxy. 4-Alkenyl radicals, 3-alkenyl radicals and the like generally give lower threshold voltages and smaller K ₃ / K ₁ values compared to alkyl and alkoxy radicals.

In the bridge members Z ¹ , Z ² and Z ³ , a -CH ₂ CH ₂ group generally leads to higher values of the ratio of the elastic constant K ₃ / K ₁ compared to a simple covalent bond. Higher values of K ₃ / K ₁ , for example, allow a shorter reflection wavelength without changing the dopant concentration due to the higher HTP.

The optimal ratio the individual compounds of formulas I to V depends largely on the desired Properties of the choice of compounds of formulas I to V and the choice of other optional components from. Suitable proportions within the range given above can be easy from case to case be determined.

In the formulas mentioned above and below, the term "fluorinated alkyl or alkoxy having 1 to 3 C atoms" preferably denotes CF ₃ , OCF ₃ , CFH ₂ , OCFH ₂ , CF ₂ H, OCF ₂ H, C ₂ F ₅ , OC ₂ F ₅ , CFHCF ₃ , CFHCF ₂ H, CFHCFH ₂ , CH ₂ CF ₃ , CH ₂ CF ₂ H, CH ₂ CFH ₂ , CF ₂ CF ₂ H, CF ₂ CFH ₂ , OCFHCF ₃ , OCFHCF ₂ H, OCFHCFH ₂ , OCH ₂ CF ₃ , OCH ₂ CF ₂ H, OCH ₂ CFH ₂ , OCF ₂ CF ₂ H, OCF ₂ CFH ₂ , C ₃ F ₇ or OC ₃ F ₇ , in particular CF ₃ , OCF ₃ , CF ₂ H, OCF ₂ H, C ₂ F ₅ , OC ₂ F ₅ , CFHCF ₃ , CFHCF ₂ H, CFHCFH ₂ , CF ₂ CF ₂ H, CF ₂ CFH ₂ , OCFHCF ₃ , OCFHCF ₂ H, OCFHCFH ₂ , OCF ₂ CF ₂ H , OCF ₂ CFH ₂ , C ₃ F ₇ or OC ₃ F ₇ , more preferably OCF ₃ or OCF ₂ H.

Of the The term "alkyl" includes straight-chain and branched alkyl groups of 1-7 carbon atoms, especially the straight-chain groups methyl, ethyl, propyl, butyl, pentyl, Hexyl and heptyl. Groups of 2-5 carbon atoms are in general prefers.

The term "alkenyl" includes straight-chain and branched alkenyl groups having 2-7 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 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.

Of the The term "fluoroalkyl" preferably includes straight-chain groups with terminal Fluorine, i. Fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluoro-butyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. Other positions However, 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.

halogen is preferably F or Cl, in particular F.

If one of the abovementioned radicals is an alkyl radical and / or an alkoxy radical means it may be straight or branched. Preferably if it is straight-chain, it has 2, 3, 4, 5, 6 or 7 carbon atoms and means Accordingly, ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, Propoxy, butoxy, pentoxy, hexoxy or heptoxy, furthermore methyl, octyl, Nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, Methoxy, octoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or Tetradecoxy.

oxaalkyl preferably denotes straight-chain 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-oxo-octyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

If one of the abovementioned radicals denotes an alkyl radical in which one CH ₂ group has been replaced by --CH =CH--, this may be straight-chain or branched. It is preferably straight-chain and has 2 to 10 C atoms. It therefore means especially vinyl, prop-1, or prop-2-enyl, but-1, 2- or but-3-enyl, pent-1, 2-, 3- or pent-4-enyl, hex 1-, 2-, 3-, 4- or hex-5-enyl, hept-1, 2-, 3-, 4-, 5- or hept-6-enyl, Oct-1, 2-, 3-, 4-, 5-, 6- or oct-7-enyl, non-1-, 2-, 3-, 4-, 5-, 6-, 7- or non-8-enyl, Dec-1 -, 2-, 3-, 4-, 5-, 6-, 7-, 8- or dec-9-enyl.

If one of the abovementioned radicals denotes an alkyl radical in which one CH ₂ group has been replaced by -O- and one by -CO-, these are preferably adjacent. Thus, they include an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. Preferably, these are straight-chain and have 2 to 6 carbon atoms.

she therefore especially acetyloxy, propionyloxy, butyryloxy, Pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, Butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetyloxypropyl, 3-propionyloxypropyl, 4-acetyloxybutyl, Methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, Pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, Butoxycarbonylmethyl, 2- (methoxycarbonyl) ethyl, 2- (ethoxycarbonyl) ethyl, 2- (propoxycarbonyl) ethyl, 3- (methoxycarbonyl) propyl, 3- (ethoxycarbonyl) propyl, 4- (methoxycarbonyl) -butyl.

If one of the abovementioned radicals denotes an alkyl radical in which one CH ₂ group has been replaced by unsubstituted or substituted -CH =CH- and one adjacent CH ₂ group has been replaced by CO or CO-O or O-CO, this may be straight-chain or be branched. Preferably, it is straight-chain and has 4 to 13 carbon atoms. It therefore particularly means 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, 9-methacryloyloxynonyl.

If one of the abovementioned radicals is an alkyl or alkenyl radical which is monosubstituted by CN or CF ₃ , this radical is preferably straight-chain. The substitution by CN or CF ₃ is in any position.

If one of the above radicals one at least simply by halogen substituted alkyl or alkenyl radical, then this radical preferably straight-chain and halogen is preferably F or Cl. In the case of multiple substitution, halogen is preferably F. The resulting radicals shut down also perfluorinated radicals. For single substitution, the fluoro or chlorine substituent in any position, preferably however in the ω position.

links with branched wing groups can occasionally because of a better solubility in the usual liquid crystalline Base materials of importance. But you can especially as chiral dopants are suitable if they are optically active.

branched Groups of this kind usually contain no more than one chain branch. Preferred branched radicals 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-ethylhexoxy, 1-methylhexoxy, 1-methylheptoxy.

If one of the abovementioned radicals represents an alkyl radical in which two or more CH ₂ groups have been replaced by -O- and / or -CO-O-, this may be straight-chain or branched. Preferably, it is branched and has 3 to 12 carbon atoms. It therefore particularly denotes bis-carboxy-methyl, 2,2-bis-carboxy-ethyl, 3,3-bis-carboxy-propyl, 4,4-bis-carboxy-butyl, 5,5-bis-carboxy-pentyl, 6,6-bis-carboxy-hexyl, 7,7-bis-carboxy-heptyl, 8,8-bis-carboxy-octyl, 9,9-bis-carboxy-nonyl, 10,10-bis-carboxy-decyl, 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, 5,5-bis (ethoxycarbonyl) hexyl.

The Optically active component of the CFRP media according to the invention contains a or more chiral dopants whose twisting power and Concentration chosen are that the Helical pitch of the FK medium is less than or equal to 1 micron.

Of the Proportion of the optically active component in the CFRP media according to the invention is preferably ≤ 20 %, in particular ≤ 10 %, more preferably from 0.01 to 7%, most preferably from 0.1 to 5%. The optically active component preferably contains 1 to 6, in particular 1, 2, 3 or 4 chiral dopants.

The Chiral dopants should preferably have a high twistability ("helical twisting power ", HTP) with low temperature dependence exhibit. Furthermore, they should have a good solubility in the nematic Own component and the liquid crystalline Properties of the FK medium do not or only to a small extent impair. You can same or opposite sense of rotation and the same or opposite temperature dependence have the twist.

Particular preference is given to chiral dopants having an HTP of 20 μm ^-1 or more, in particular of 40 μm ^-1 or more, particularly preferably of 70 μm ^-1 or more.

For the optical active component are a variety of commercially available to a person skilled in the art available chiral dopants available, such as. Cholesteryl nonanoate, R / S-811, R / S-1011, R / S-2011, R / S-3011 or CB15 (Merck KGaA, Darmstadt).

Especially suitable dopants are compounds which have one or more chiral residues and one or more mesogenic groups, or one or more aromatic or alicyclic groups, which are combined with the chiral residue form a mesogenic group.

suitable chiral radicals are, for example, chiral branched hydrocarbon radicals, chiral ethanediols, binaphthols or dioxolanes, further on or mehrbindige chiral radicals selected from the group containing sugar derivatives, sugar alcohols, sugar acids, lactic acids, chiral substituted glycols, steroid derivatives, terpene derivatives, amino acids or Sequences of a few, preferably 1-5, amino acids.

Preferred chiral residues are sugar derivatives such as glucose, mannose, galactose, fructose, arabinose, dextrose; Sugar alcohols such as sorbitol, mannitol, iditol, galactitol or their anhydro derivatives, especially dianhydrohexites such as dianhydrosorbide (1,4: 3,6-dianhydro-D-sorbide, isosorbide), dianhydromannitol (isosorbitol) or dianhydroidite (isoidite); Sugar acids such as gluconic acid, gulonic acid, ketogulonic acid; chiral substituted glycol radicals such as mono- or oligoethylene or propylene glycols wherein one or more CH ₂ groups are substituted by alkyl or alkoxy; Amino acids such as alanine, valine, phenylglycine or phenylalanine, or sequences from 1 to 5 of these amino acids; Steroid derivatives such as cholesteryl or cholic acid residues; Terpene derivatives such as, for example, menthyl, neomenthyl, campheyl, pineyl, terpineyl, isolongifolyl, fenchyl, carreyl, myrthenyl, nopyl, geraniyl, linaloyl, neryl, citronellyl or dihydrocitronellyl.

Suitable chiral radicals and mesogenic chiral compounds are, for example, in DE 34 25 503 . DE 35 34 777 . DE 35 34 778 . DE 35 34 779 and DE 35 34 780 DE-A-43 42 280, EP-A-1 038 941 and DE-A-195 41 820.

Especially Preferably, chiral dopants are selected from the group containing Compounds of the following formulas.

vorzugsweise Dianhydrosorbitol, bedeutet,
sowie chirale Ethandiole wie z.B. Diphenylethandiol (Hydrobenzoin), insbesondere mesogene Hydrobenzoinderivate der folgenden Formel

einschließlich der jeweils nicht gezeigten (R, S), (S, R), (R, R) und (S, S) Enantiomere,
worin
B und C jeweils unabhängig voneinander 1,4-Phenylen, welches auch durch L mono-, di- oder trisubstituiert sein kann, oder 1,4-Cyclohexylen,
L H, F, Cl, CN oder optional halogeniertes Alkyl, Alkoxy, Alkylcarbonyl, Alkoxycarbonyl, Alkylcarbonyloxy oder Alkoxycarbonyloxy mit 1-7 C-Atomen,
b 0, 1 oder 2,
c 0 oder 1,
Z⁵ -COO-, -OCO-, -CH₂CH₂- oder eine Einfachbindung, und
R⁵ Alkyl, Alkoxy, Alkylcarbonyl, Alkoxycarbonyl oder Alkylcarbonyloxy mit 1-12 C-Atomen
bedeuten.Further preferred chiral dopants are derivatives of isosorbide, isomannitol or isoidite of the following formula

preferably dianhydrosorbitol, means
and chiral ethanediols such as diphenylethanediol (hydrobenzoin), in particular mesogenic Hydrobenzoinderivate the following formula

including the (R, S), (S, R), (R, R) and (S, S) enantiomers, not shown in each case,
wherein
B and C are each independently of one another 1,4-phenylene, which may also be mono-, di- or trisubstituted by L, or 1,4-cyclohexylene,
L is H, F, Cl, CN or optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1-7 C atoms,
b 0, 1 or 2,
c 0 or 1,
Z ^{5 is} -COO-, -OCO-, -CH ₂ CH ₂ - or a single bond, and
R ^{5 is} alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkylcarbonyloxy having 1-12 C atoms
mean.

The Compounds of the formula XV are described in WO 98/00428. The Compounds of formula XVI are described in GB-A-2 328 207.

All Particularly preferred chiral dopants are chiral binaphthyl derivatives as described in WO 02/94805, chiral binaphthol acetal derivatives such as described in WO 02/34739, chiral TADDOL derivatives as in WO 02/06265 and chiral dopants with at least one fluorinated Bridge group and a terminal or central chiral group as in WO 02/06196 and WO 02/06195 described.

insbesondere solche ausgewählt aus folgenden Formeln

worin B, b, R⁵ und Z⁵ die in Formel XV angegebene Bedeutung haben und Z⁵ insbesondere -OCO- oder eine Einfachbindung bedeutet.Particularly preferred are chiral binaphthyl derivatives of the formula XVII

in particular those selected from the following formulas

wherein B, b, R ⁵ and Z ^{5 have} the meaning given in formula XV and Z ^{5 is} in particular -OCO- or a single bond.

sind besonders bevorzugt.The dopants of the following formula

are particularly preferred.

• – einen oder mehrere Dotierstoffe ausgewählt aus Formel X bis XVI,
• – einen oder mehrere Dotierstoffe der Formel XVII,
• – nicht mehr als einen Dotierstoff, vorzugsweise ausgewählt aus Formel XVII, vorzugsweise in einem Anteil von weniger als 8 %, insbesondere weniger als 5 % der Gesamtmischung (d.h. der Summe des Massenanteile aus nematischer und optisch aktiver Komponente).

In particularly preferred embodiments, the optically active component of the media according to the invention

• One or more dopants selected from formulas X to XVI,
• One or more dopants of the formula XVII,
• No more than one dopant, preferably selected from formula XVII, preferably in an amount of less than 8%, in particular less than 5% of the total mixture (ie the sum of the mass fractions of nematic and optically active component).

In In another particularly preferred embodiment, the media 20 according to the invention contain % or less, in particular 0.01 to 10 of the optically active component.

Especially the chiral dopants of the above formulas XV, XVI and XVII have good solubility in the nematic component, and induce a cholesteric Structure with high twist and low temperature dependence the helical pitch and the reflection wavelength. Thereby can even when using only one of these dopants in small Quantities of CFRP media according to the invention with reflection inks in the visible wavelength range be achieved by high brilliance and low Temperaturabhägigkeit, the especially for suitable for use in SSCT and PSCT displays.

This is a major advantage over the CFRP media from the Prior art, in which usually at least two dopants with the same direction of rotation and opposite temperature dependence the twist needed be (for example, a dopant with positive temperature dependence, i.e. Increase in twist with increasing temperature, and a Dopant with negative temperature dependence) to a temperature compensation the reflection wavelength to achieve. Furthermore are often large amounts of dopants in the known CFRP media needed to achieve reflection in the visible range.

A particularly preferred embodiment The invention therefore relates to a CFRP medium and a CFRP display containing this medium, as described above and below, wherein the chiral component is no more than a chiral compound contains preferably in an amount of less than 15%, in particular less as 10%, more preferably 5% or less. The chiral compound in these media is particularly preferably selected from those described in WO 02/94805, WO 02/34739, WO 02/06265, WO 02/06196 and WO 02/06195 Compounds and from the compounds of formulas X to XVII including their preferred sub-formulas. A CFK medium of this preferred embodiment has a low dependence the reflection wavelength λ of the Temperature T over a wide temperature range.

The Helical pitch of the medium preferably from 130 nm to 1000 nm, in particular from 200 nm to 750 nm, more preferably from 300 nm to 450 nm.

Preferably is the helical pitch chosen so that this Medium light reflected in the visible wavelength range. Of the Term "visible Wavelength range "or" visible spectrum "typically includes the range of wavelengths from 400 to 800 nm. In the preceding and following this term but also the range of wavelengths from 200 to 1200 nm including the UV and infrared (IR) range as well as the far UV and far IR range include.

The Reflection wavelength of the LC medium according to the invention is preferably in the range of 200 to 1500 nm, especially 300 to 1200 nm, more preferably from 350 to 900 nm, most preferably from 400 to 800 nm. Further preferred are FK media with a Reflection wavelength from 400 to 700, especially 400 to 600 nm.

The Wavelength values given above and below refer to the half width of the reflection band, unless otherwise specified.

Especially Preference is given to CFRP media according to the invention with a temperature dependence dλ / dT of 0.6 nm / ° C or less, especially 0.3 nm / ° C or less, especially preferably 0.15 nm / ° C or less, preferably in the range between 0 and 50 ° C, in particular between -20 and 60 ° C, more preferably between -20 and 70 ° C, most preferably in the range of -20 ° C up to a temperature of 10 ° C, in particular 5 ° C, below of the clearing point.

So far Unless otherwise indicated, dλ / dT means the local slope of the Function λ (T), where a nonlinear function λ (T) approximately is described by a 2nd or 3rd degree polynomial.

One Another object of the invention is the use of the CFRP media according to the invention for electro-optical Purposes.

Another object of the invention is also an electro-optical display containing CFRP media according to the invention, in particular an SSCT, PSCT or flexoelectric displays with two plane-parallel support plates, which form a cell with a border, and an in-cell cholesterol liquid crystal mixture.

One Another object of the invention is an electro-optical active matrix display containing CFRP media according to the invention, in particular an AM-CFK display, preferably an AM-SSCT or PSCT display, with two plane-parallel support plates, which form a cell with a border, built-in non-linear Elements for switching individual pixels on the carrier plates, and a cholesteric liquid crystal mixture in the cell, which preferably has a positive dielectric anisotropy and a high resistivity.

The construction of bistable SSCT and PSCT cells is described for example in WO 92/19695, WO 93/23496, US 5,453,863 or US 5,493,430 described. The structure of active matrix CFRP displays is described, for example, in WO 02/086855 and US 2002-0149552.

The relationship d / p between layer thickness of the liquid crystal cell d (distance of the carrier plates) in a CFRP display according to the invention and more natural Helical pitch p of the CFK medium is preferably greater than 1, in particular in the range from 2 to 20, more preferably from 3 to 15, most preferably from 4 to 10.

The CFRP media according to the invention enable a significant extension of the available parameter space. So excel the achievable combinations of reflection wavelength, birefringence, clearing point, Viscosity, thermal and UV stability and dielectric anisotropy by far previous materials from the prior art and make the media of the invention especially suitable for an insert in CFRP displays.

The CFRP media according to the invention preferably have a cholesteric phase down to -20 ° C and preferably to -30 ° C, especially preferably to -40 ° C, and clearing points above 70 ° C, preferably above 90 ° C, more preferably above 110 ° C. The dielectric anisotropy Δε is preferably ≥ 5, in particular ≥ 10, completely more preferably ≥ 15. The birefringence Δn is preferably ≦ 0.15, in particular ≤ 0.10 and preferably ≥ 0.03, in particular ≥ 0.05, preferably between 0.04 and 0.08.

simultaneously own the CFRP media according to the invention low values for the viscosity and high values for the resistivity, resulting in excellent CFRP displays, especially AM-CFK displays. In particular, the Mixtures characterized by small operating voltages.

It understands that through suitable choice of the components of the mixtures according to the invention also higher clearing points (e.g., above 120 ° C) at higher Threshold voltages or lower clearing points at lower threshold voltages realized while preserving the other advantageous properties can be. Likewise at correspondingly little increased viscosities Mixtures with larger Δε and thus lower thresholds are obtained.

The Width of the cholesteric phase region is preferably at least 90 ° C, in particular at least 100 ° C. Preferably this range extends at least from -20 ° to + 60 ° C, more preferably at least from -20 ° to + 70 ° C, very special preferably at least from -20 ° to + 80 ° C.

Also the UV stability the CFRP media according to the invention is considerably better, d. H. they show a much smaller change the reflection wavelength and operating voltage under UV exposure.

A further preferred embodiment of the present invention relates to a CFRP medium according to the invention, which is one or more compounds having at least one polymerizable group contains. Such CFRP media are particularly suitable for use, for example in polymer gel or PSCT displays. The polymerizable compounds can Be part of the nematic and / or chiral component or an additional Form component of the medium.

Suitable polymerizable compounds are known in the art and described in the prior art. The polymerizable compounds may additionally be mesogenic or liquid-crystalline. They may contain one or more, preferably two polymerizable groups. Typical examples of non-mesogenic compounds having two polymerizable groups are alkyl diacrylates or alkyl dimethacrylates having alkyl groups of 1 to 20 carbon atoms. Typical examples of non-mesogenic compounds having more than two polymerizable groups are trimethylolpropane trimethacrylate or pentaerythritol tetra acrylate. Typical examples of mesogenic or liquid-crystalline polymerizable compounds are described, for example, in WO 93/22397, EP 0 261 712 . DE 195 04 224 , WO 95/22586 and WO 97/00600.

Examples of particularly suitable and preferred chiral and achiral polymerizable mono- and di-reactive mesogenic compounds (reactive mesogens) are shown in the following list, which is intended to illustrate the invention without limiting it

In the formulas shown above, P is a polymerisable group, preferably acrylic, methacrylic, vinyl, vinyloxy, propenyl ether, epoxy, oxetane or styryl, x and y are each independently an integer from 1 to 12, D and E are each independently 1, 4-phenylene, which may also be substituted by L ¹ mono-, di-, tri- or tetra-substituted, or 1,4-cyclohexylene, u and v are each independently 0 or 1, Z ⁰ -COO-, -OCO-, - CH ₂ CH ₂ -, -CH = CH-, -C≡C- or a single bond, R ^{0 is} a polar or nonpolar group, Ter is a terpene residue such as menthyl, Chol a cholesteryl group, r 0, 1, 2, 3 or 4 , L, L ¹ and L ^{2 are} each independently H, F, Cl, CN or optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkylcarbonyloxy, alkoxycarbonyl or alkoxycarbonyloxy having 1 to 7 carbon atoms. The phenyl rings in the formulas shown above are optionally substituted by L 1, 2, 3 or 4 times.

The term "polar group" in this context means a group selected from F, Cl, CN, NO ₂ , OH, OCH ₃ , OCN, SCN, optionally fluorinated alkylcarbonyl, alkylcarbonyloxy, alkoxycarbonyl or alkoxycarbonyloxy having up to 4 C atoms or mono -, oligo- or polyfluorinated alkyl or alkoxy having 1 to 4 carbon atoms. The term "non-polar group" in this context means optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkylcarbonyloxy, alkoxycarbonyl or alkoxycarbonyloxy having 1 or more, preferably 1 to 12, carbon atoms, which does not fall under the above definition "polar group".

Next the compounds of the formula I to V and X to XV, the CFRP media one or more other components for optimization different properties included.

The individual compounds of the preceding and following formulas and their Sub-formulas used in the media of the invention can, are either known or they can be analogous to the known ones Connections are made.

The Preparation of the invention usable liquid crystal mixtures takes place in per se usual Wise. In general, the desired Amount of components used in lesser amount in the Main component making up components solved, expedient at elevated temperature. It is also possible, solutions the components in an organic solvent, e.g. in acetone, Chloroform or methanol, to mix and the solvent after mixing to remove again, for example by distillation.

The Liquid crystal mixtures according to the invention can also other additives such as one or more stabilizers or antioxidants contain.

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. The coding according to Table B is self-evident. In Table A, only the acronym for the main body is given. In the individual case, a code for the substituents R ¹ , R ² , L ¹ L ² and L ³ follows separately from the acronym for the main body with a dash:

preferred Mixture components are given in Tables A, B and C.

Table A: (L ¹ , L ² , L ³ = H or F)

Table B:

Table C (dopants):

Table D

Suitable stabilizers and antioxidants for LC mixtures are mentioned below (n = 0-10, terminal methyl groups are not shown):

The The following examples are intended to illustrate the invention without limiting it.

In front- and below, percentages are by weight. All temperatures are given in degrees Celsius. Mp means melting point, bp = Clearing point. Furthermore, K = crystalline state, S = smectic phase, N = nematic phase, Ch = cholesteric phase and I = isotropic Phase. The indications between these symbols represent the transition temperatures represents.

Δn

optische Anisotropie bei 589 nm und 20°C

n_e

außerordentlicher Brechungsindex bei 589 nm und 20°C

Δε

dielektrische Anisotropie bei 20°C

ε∥

Dielektrizitätskonstante parallel zu den Moleküllängsachsen

γ₁

Rotationsviskosität [mPa·sec], soweit nicht anders angegeben bei 20°C

λ

Reflektionswellenlänge [nm], soweit nicht anders angegeben bei 20°C

Δλ

maximale Schwankung der Reflektionswellenlänge [nm] im angegebenen Temperaturbereich, soweit nicht anders angegeben zwischen –20 und +70°C

Furthermore, the following abbreviations are used

.DELTA.n

optical anisotropy at 589 nm and 20 ° C

n _e

extraordinary refractive index at 589 nm and 20 ° C

Δε

dielectric anisotropy at 20 ° C

ε∥

Dielectric constant parallel to the molecular axes

γ ₁

Rotational viscosity [mPa.sec] unless otherwise stated at 20 ° C

λ

Reflection wavelength [nm], unless otherwise stated at 20 ° C

Δλ

maximum fluctuation of the reflection wavelength [nm] in the specified temperature range, unless otherwise specified between -20 and + 70 ° C

The twisting power HTP ("helical twisting power") of a chiral compound which generates a helically twisted superstructure in a liquid crystalline mixture is given by the equation HTP = (p · c) ^-1 [μm ^-1 ]. In this formula, p denotes the helical pitch of the helically twisted phase in μm and c the concentration of the chiral compound (a value of 0.01 for c corresponds to a concentration of 1% by weight, for example). Unless otherwise stated, the preceding and following NTP values refer to a temperature of 20 ° C and the commercially available neutral nematic TN-host mixture MLC-6260 (Merck KGaA, Darmstadt).

to experimental determination of physical parameters was performed according to "Licristal, Physical Properties of Liquid Crystals, Description of the Measurement Methods ", ed. W. Becker, Merck KGaA, Darmstadt, revised Edition, 1998, proceed.

example 1

und 3,02 % des chiralen Dotierstoffs R-5011 der folgenden Formel

und besitzt eine Reflektionswellenlänge λ von 400 nm.A cholesteric mixture C1 contains 96.98% of a nematic component N1 consisting of

and 3.02% of the chiral dopant R-5011 of the following formula

and has a reflection wavelength λ of 400 nm.

Claims (12)

A liquid-crystalline medium having a helically twisted structure containing a nematic component and an optically active component, characterized in that the optically active component contains one or more chiral compounds whose twisting power and concentration are chosen such that the helical pitch of the medium is ≤ 1 μm, and the nematic component one or more compounds of the formula I.

and one or more compounds of the formula II

in which R ^{1 is} H, an unsubstituted, an alkyl or alkenyl radical having 1 to 20 C atoms, which is monosubstituted by CN or CF ₃ or at least monosubstituted by halogen, where in these radicals also one or more CH ₂ groups are each independently may be replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CH = CH- or -C≡C-, that O atoms are not directly linked,

Y ¹ to Y ^{4 are} each independently H or F, Z ¹ and Z ^{2 are} each independently -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 F, Cl, halogenated alkyl, alkenyl or alkoxy having 1 to 6 carbon atoms, and a and b are each independently 0 or 1 Medium according to claim 1, characterized in that it contains one or more compounds selected from the following formulas

in which R ¹ , X ⁰ , Y ¹ , Y ² and a have the meaning given in claim 1, R ¹ preferably n-alkyl, alkoxy, fluoroalkyl, alkenyl or oxaalkenyl having in each case up to 9 C atoms, and Z ³ COO, C ₂ H ₄ , CF ₂ O or C ₂ F ₄ . Medium according to claim 1 or 2, characterized in that it contains one or more compounds selected from the following formulas

wherein R ¹ and X ^{0 have} the meaning given in claim 1. Medium according to at least one of claims 1 to 3, characterized in that it contains one or more compounds selected from the following formulas

wherein R ¹ and R ² each independently have one of the meanings given for R ¹ in claim 1. Medium according to at least one of claims 2 to 4, characterized in that it more than 50% of one or more compounds having a 3,4,5-trifluorophenyl group contains. Medium according to at least one of claims 1 to 5, characterized in that it contains one or more chiral compounds of the following formula

wherein B is 1,4-phenylene, which may also be mono-, di- or trisubstituted by L, or 1,4-cyclohexylene, LH, F, Cl, CN or optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy with 1-7 C atoms, b is 0, 1 or 2, Z ^{5 is} -COO-, -OCO-, -CH ₂ CH ₂ - or a single bond, and R ^{5 is} alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkylcarbonyloxy with 1- 12 C atoms mean. Medium according to at least one of claims 2 to 6, characterized in that the nematic component - 5 up to 50% of compounds of the formula I1, - 10 to 65% of compounds of the formula I2, - 5 to 60% of compounds of formula II contains. Medium according to at least one of claims 1 to 7, characterized in that it a reflection wavelength in the range of 400 to 800 nm. Use of a medium after at least one of claims 1 to 8 for electro-optical purposes. Electro-optical liquid crystal display containing a medium according to at least one of claims 1 to 9. Electro-optical liquid crystal display according to claim 10, characterized in that it a cholesteric, SSCT, PSCT or flexoelectric display is. Electro-optical liquid crystal display according to claim 10 or 11, characterized in that it is an active matrix display is.