The present invention relates to liquid-crystalline (LC) media having positive dielectric anisotropy and to liquid-crystal displays (LCDs) containing these media, especially to displays addressed by an active matrix and in particular to LC displays of the TN, PS-TN, STN, TN-TFT, OCB, IPS, PS-IPS, FFS, HB-FFS PS-HB-FFS, SA-HB-FFS, polymer stabilised SA-HB-FFS, positive VA or positive PS-VA type.
Liquid-crystal displays (LCDs) are used in many areas for the display of information. LCDs are used both for direct-view displays and for projection-type displays. The electro-optical modes used are, for example, the twisted nematic (TN), super twisted nematic (STN), optically compensated bend (OCB) and electrically controlled birefringence (ECB) modes together with their various modifications, as well as others. All these modes utilise an electric field which is generated substantially perpendicular to the substrates and the liquid-crystal layer.
Besides these modes, there are also electro-optical modes that utilise an electric field which is substantially parallel to the substrates or the liquid-crystal layer. For example, WO 91/10936 discloses a liquid-crystal display in which the electric signals are generated in such a way that the electric fields have a significant component parallel to the liquid-crystal layer, and which has since then become known as in-plane switching IPS) display. The principles of operating such a display are descried, for example, by R. A. Soref in Journal of Applied Physics, Vol. 45, No. 12, pp. 5466-5468 (1974).
IPS displays contain an LC layer between two substrates with planar orientation, where the two electrodes are arranged on only one of the two substrates and preferably have interdigitated, comb-shaped structures. On application of a voltage to the electrodes an electric field with a significant component parallel to the LC layer is generated between them. This causes realignment of the LC molecules in the layer plane.
EP 0 588 568, for example, discloses various possibilities for the design of the electrodes and for addressing an IPS display. DE 198 24 137 likewise describes various embodiments of such IPS displays.
Liquid-crystalline materials for IPS displays of this type are described, for example, in DE 195 28 104.
Furthermore, so-called “fringe-field switching” (FFS) displays have been reported (see, inter alia, S.H. Jung et al., Jpn. J. Appl. Phys., Volume 43, No. 3, 2004, 1028), which contain two electrodes on the same substrate, one of which is structured in a comb-shaped manner and the other is unstructured. A strong, so-called “fringe field” is thereby generated, i.e. a strong electric field close to the edge of the electrodes, and, throughout the cell, an electric field which has both a strong vertical component and also a strong horizontal component. FFS displays have a low viewing-angle dependence of the contrast. FFS displays usually contain an LC medium with positive dielectric anisotropy, and an alignment layer, usually of polyimide, which provides planar alignment to the molecules of the LC medium.
Liquid-crystal displays of the IPS and FFS electro-optical mode are in particular suitable for use in modern desktop monitors, TV sets and multimedia applications. The liquid-crystalline media according to the present invention are preferably used in displays of this type. In general, dielectrically positive liquid-crystalline media having rather lower values of the dielectric anisotropy are used in FFS displays, but in some cases liquid-crystalline media having a dielectric anisotropy of only about 3 or even less are also used in IPS displays.
A further improvement has been achieved by the so-called HB-FFS mode. One of the unique features of the HB-FFS mode in contrast to the traditional FFS technology is that it enables higher transmittance which allows operation of the panel with less energy consumption.
Liquid-crystal compositions which are suitable for LCDs and especially for FFS and IPS displays are known in prior art, for example, from JP 07-181 439 (A), EP 0 667 555, EP 0 673 986, DE 195 09 410, DE 195 28 106, DE 195 28 107, WO 96/23 851 and WO 96/28 521. However, these compositions have certain disadvantages. Amongst other deficiencies, most of them result in disadvantageously long addressing times, have inadequate values of the resistivity and/or require excessively high operating voltages. Both an improvement in the operating properties and also in the shelf life are necessary here.
FFS and IPS displays can be operated as active-matrix displays (AMD) or passive-matrix displays (PMD). In the case of active-matrix displays individual pixels are usually addressed by integrated, non-linear active elements such as, for example, thin-film transistors (TFTs), while in the case of passive-matrix displays individual pixels are usually addressed by the multiplex method as known from the prior art.
The displays according to the present invention are preferably addressed by an active matrix, preferably by a matrix of TFT. However, the liquid crystals according to the invention can also advantageously be used in displays having other known addressing means.
Typical applications of in-plane switching (IPS) and fringe field switching (FFS) technologies are monitors, notebooks, televisions, mobile telephones, tablet PCs, etc.
Both the IPS and the FFS technology have certain advantages over other LCD technologies, such as, for example, the vertical alignment (VA) technology, e.g. a broad viewing angle dependency of the contrast.
The provision of further liquid-crystalline media and the use thereof in a display having high transmission, a good black state and a high contrast ratio is a central challenge for modern FFS and IPS applications. In addition, modern applications also require good low-temperature stability and fast addressing times.
The invention has an object of providing liquid-crystalline media, in particular for FFS and IPS displays, but also for TN, positive VA or STN displays, and in particular for active-matrix displays like those addressed by TFTs, which do not exhibit the disadvantages indicated above or only do so to a lesser extent and preferably have high specific resistance, low threshold voltage, high dielectric anisotropy, a good low temperature stability (LTS), fast response times and low rotational viscosities, and enable high brightness.
This and other objects are achieved by providing liquid-crystalline media as described and claimed hereinafter.
It was observed that a high brightness in displays like those of the HB-FFS mode can be achieved by using liquid-crystalline media having positive dielectric anisotropy and also having an increased dielectric constant ε⊥ perpendicular to the longitudinal axes of the liquid-crystalline molecules. This can be achieved by adding a limited amount of liquid-crystalline compounds with negative dielectric anisotropy, which have high ε⊥ properties, to the liquid-crystalline medium whilst maintaining a positive dielectric anisotropy of the entire medium. However, the addition of compounds with high ε⊥ have some drawbacks. For example this can lead to higher values of the rotational viscosity γ1, and consequently to higher values of the ratio γ1/K22 of the rotational viscosity γ1 and the elastic constant K22 for twist deformation, which leads to higher response times. Since K22 is approximately proportional to the elastic constant K11 for splay deformation (the value of K22 is typically about half the value of K11), this can easily be determined by measuring γ1 and K11.
Another disadvantage is that the reliability (VHR) of HB-FFS mixtures can be worse compared to conventional FFS mixtures.
It is an object of the present invention to provide improved liquid-crystal media suitable for the use in HB-FFS displays that do not show the disadvantages described above and which in particular have improved reliability while keeping high transmittance compared to media from the prior art.
To solve the problem, the present invention provides a liquid-crystalline medium according to claim 1.
Advantageous embodiments of the invention are subject of the dependent claims and can also be taken from the description.
The invention includes an LC medium comprising one or more compounds of formula I
in which
—O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another, and in which one or more H atoms may be replaced by halogen, and
one or more compounds selected from the group of compounds of formulae II and III
in which
to
Surprisingly, the media according to the invention show an increased value of ε⊥ and at the same time enable a decrease of the rotational viscosity and the ratios of γ1/K22 and γ1/K11, and enable fast response times in displays using liquid-crystalline media as described and claimed herein. Displays that make use of the media according to the invention are further distinguished by a particularly high contrast and very high reliability.
In particular, the combination of compounds of formula I with compounds of formula II and/or III, and additionally with compounds selected from formulae B and/or Y or their subformulae shown below, leads to liquid-crystalline media which show a moderately positive dielectric anisotropy and at the same time an increased dielectric constant ε⊥ perpendicular to the longitudinal axes of the liquid-crystalline molecules, while maintaining a low rotational viscosity and a low value of the ratio γ1/K11. This enables liquid-crystalline displays, especially of the HB-FFS, FFS and IPS mode, with high brightness and transmission and low response times.
The liquid-crystalline media according to the invention are suitable for mobile applications and TFT applications, such as, for example, mobile telephones and PDAs. Furthermore, the liquid-crystalline media according to the invention are particularly suitably for use in FFS, HB-FFS and IPS displays based on dielectrically positive liquid crystals.
The liquid-crystal media according to the present invention are especially suitable for use in liquid-crystal displays of the FFS, HB-FFS and IPS mode, based on dielectrically positive liquid crystals, and polymer stabilised variants thereof, in particular for large size TV applications.
The invention further relates to the use of a liquid-crystalline medium as described above and below for electro-optical purposes, in particular for the use in liquid-crystal displays, shutter glasses, LC windows, 3D applications, preferably in TN, PS-TN, STN, TN-TFT, OCB, IPS, PS-IPS, FFS, HB-FFS, PS-HB-FFS, SA-HB-FFS, polymer stabilised SA-HB-FFS, positive VA and positive PS-VA displays, very preferably in FFS, HB-FFS, IPS, PS-HB-FFS and PS-IPS displays.
The invention further relates to an electro-optical liquid-crystal display containing a liquid-crystalline medium as described above and below, in particular a TN, PS-TN, STN, TN-TFT, OCB, IPS, PS-IPS, FFS, HB-FFS, PS-HB-FFS, SA-HB-FFS, polymer stabilised SA-HB-FFS, positive VA or positive PS-VA display, preferably a FFS, HB-FFS, IPS, PS-HB-FFS or PS-IPS display.
In the present application, all atoms also include their isotopes. In particular, one or more hydrogen atoms (H) may be replaced by deuterium (D), which is particularly preferred in some embodiments; a high degree of deuteration enables or simplifies analytical determination of compounds, in particular in the case of low concentrations.
Herein, an alkyl radical and/or an alkoxy radical is taken to mean straight-chain or branched alkyl. It is preferably straight-chain, has 2, 3, 4, 5, 6 or 7 C atoms and accordingly preferably denotes ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexyloxy or heptyloxy, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetra-decyl, pentadecyl, methoxy, octyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy, tridecyloxy or tetradecyloxy.
Herein, oxaalkyl preferably denotes straight-chain 2-oxapropyl (=methoxy-methyl), 2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.
Herein, alkenyl, i.e. an alkyl radical in which one CH2 group has been replaced by —CH═CH—, may be straight-chain or branched. It is preferably straight-chain and has 2 to 10 C atoms. Accordingly, it denotes, in particular, vinyl, prop-1- or -2-enyl, but-1-, -2- or -3-enyl, pent-1-, -2-, -3- or -4-enyl, hex-1-, -2-, -3-, -4- or -5-enyl, hept-1-, -2-, -3-, -4-, -5- or -6-enyl, oct-1-, -2-, -3-, -4-, —S—, -6- or -7-enyl, non-1-, -2-, -3-, -4-, —S—, -6-, -7- or -8-enyl, dec-1-, -2-, -3-, -4-, —S—, -6-, -7-, -8- or -9-enyl.
Herein, an alkyl or alkenyl radical which is at least monosubstituted by halogen, is preferably straight-chain, and halogen is preferably F or Cl. In the case of polysubstitution, halogen is preferably F. The resultant radicals also include perfluorinated radicals. In the case of monosubstitution, the fluorine or chlorine substituent may be in any desired position, but is preferably in the ω-position.
Herein, a mono- or polyfluorinated alkyl or alkoxy radical having 1, 2 or 3 C atoms or a mono- or polyfluorinated alkenyl radical having 2 or 3 C atoms is particularly preferably F, Cl, CF3, CHF2, OCF3, OCHF2, OCFHCF3, OCFHCHF2, OCFHCHF2, OCF2CH3, OCF2CHF2, OCF2CHF2, OCF2CF2CHF2, OCF2CF2CHF2, OCFHCF2CF3, OCFHCF2CHF2, OCF2CF2CF3, OCF2CF2CCIF2, OCCIFCF2CF3, OCH═CF2 or CH═CF2, very particularly preferably F or OCF3, furthermore CF3, OCF═CF2, OCHF2 or OCH═CF2.
The compounds of the formula I are preferably synthesised as described in DE 102015004271 A1.
The compounds of formula I are preferably selected from the group of compounds of the formulae I-1 to I-10:
in which R12 denotes alkyl having 1 to 7 C-atoms, preferably ethyl, n-propyl or n-butyl.
Preferably, the medium comprises one or more compounds of formula II, preferably selected from the group of compounds of formulae II-1 to II-3, very preferably from the group of compounds of formulae II-1 and II-2
in which the occurring groups have the respective meanings given under formula II above and in formula II-1 the radicals L23 and L24 denote, independently of each other and of the other parameters, H or F and in formula II-2 preferably
and
denote, independently of each other,
In formulae II-1 to II-3, L21 and L22 or L23 and L24 are preferably both F.
In another preferred embodiment in formulae II-1 and II-2, all of L21, L22, L23 and L24 denote F.
The compounds of formula II-1 are selected from the group of compounds of formulae II-1a to II-1h
in which the occurring groups have the respective meanings given above.
In a preferred embodiment of the present invention the medium comprises one or more compounds selected from the group of compounds of the formulae II-1a to II-1h wherein L21 and L22, and/or L23 and L24 are both F, respectively.
In another preferred embodiment the medium comprises compounds selected from the group of compounds of formulae II-1a to II-1h, wherein L21, L22, L23 and L24 all are F.
Especially preferred compounds of formula II-1 are
in which R2 has the meaning given above.
Preferably the compounds of formula II-2 are selected from the group of compounds of formulae II-2a to II-2c
in which the occurring groups have the respective meanings given above and preferably L21 and L22 are both F.
Preferably the compounds of formula II-3 are selected from the group of compounds of formulae II-3a to II-3e
in which the occurring groups have the respective meanings given above and preferably
L21 and L22 are both F and L23 and L24 are both H or
L21, L22, L23 and L24 are all F.
Especially preferred compounds of formula II-3 are
in which R2 has the meaning given above.
In another preferred embodiment of the present invention compounds of formula III are selected from the group of formulae III-1 and III-2
wherein the occurring groups and parameters have the respective meanings given under formula III above.
Preferably the compounds of formula III-1 are selected from the group of compounds of formulae III-1a and III-1b
wherein the parameters have the respective meanings given above and the parameters L33 and L34, independently of each other and of the other parameters, denote H or F.
Preferably the compounds of formula III-2 are selected from the group of compounds of formulae III-2a to III-2I
in which parameters have the respective meanings given above and L35 and L36, independently of one another, denote H or F.
The compounds of formula III-1a, are preferably selected from the group of compounds of formulae III-1a-1 to III-1a-6
in which R3 has the meaning given above.
In another preferred embodiment the compounds of formula II-2a are selected from the group of compounds of formulae III-2a-1 to III-2a-4
in which R3 has the meaning given above.
The compounds of formula III-2b are preferably selected from the group of compounds of formulae III-2b-1 and III-2b-2, preferably III-2b-2
in which R3 has the meaning given above.
The compounds of formula II-2c, are preferably selected from the group of compounds of formulae III-2c-1 to III-2c-5
in which R3 has the meaning given above.
The compounds of formulae III-2d and III-2e are preferably selected from the group of compounds of formulae III-2d-1 and III-2e-1
in which R3 has the meaning given above.
The compounds of formula III-2f are preferably selected from the group of compounds of formulae III-2f-1 to III-2f-7
The compounds of formula III-2g are preferably selected from the group of compounds of formulae III-2g-1 to III-2g-7
in which R3 has the meaning given above.
The compounds of formula III-2h are preferably selected from the group of compounds of formulae III-2h-1 to III-2h-5
in which R3 has the meaning given above.
The compounds of formula III-2i are preferably selected from the group of compounds of formulae III-2i-1 to III-2i-3
in which R3 has the meaning given above.
The compounds of formula III-2j are preferably selected from the group of compounds of formulae III-2j-1 to III-2j-3
in which R3 has the meaning given above.
The compounds of formula III-2k are preferably selected from the group of compounds of formulae III-2k-1 to III-2k-6
in which R3 has the meaning given above.
The compounds of formula III-21 are preferably selected from the compounds of formula III-21-1
Alternatively or additionally to compounds of formulae III-1 and/or III-2 the media according to the present invention may comprise one or more compounds of formula III-3,
in which the parameters have the respective meanings given under formula III above,
and preferably of formula III-3a
in which the R3 has the meaning given above.
Preferably, the medium according to the invention further comprises one or more compounds of formula IV
in which
R2 under formula II above, preferably R41 is alkyl and R42 is alkyl or alkoxy or R41 is alkenyl and R42 is alkyl,
and
and
is
P is 0, 1 or 2, preferably 0 or 1.
Preferably the liquid crystalline media according to the present invention comprise one or more compounds of formula IV preferably selected from the group of compounds of formulae IV-1 to IV-5
in which R41 and R42 have the respective meanings given under formula IV above and in formulae IV-1, IV-4 and IV-5 R41 preferably is alkyl or alkenyl, preferably alkenyl and R42 preferably is alkyl or alkenyl, preferably alkyl; in formula IV-2 R41 and R42 preferably are alkyl and in formula IV-3 R41 preferably is alkyl or alkenyl, preferably alkyl and R42 preferably is alkyl or alkoxy, preferably alkoxy.
Particularly preferably, the medium according to the invention comprises one or more compounds of formula IV-1 and one or more compounds of formula IV-4.
In a preferred embodiment the medium further comprises one or more compounds of formula IV selected from the group of compounds of formulae IV-6 to IV-13
in which
Alternatively or additionally to compounds of formulae II and/or III the media according to the present invention may comprise one or more compounds of formula V
in which
to
are, independently of each other,
Preferably the media according to the present invention comprises one or more compounds of formula V, preferably selected from the group of compounds of formulae V-1 and V-2
in which the parameters have the respective meanings given above and the parameters L53 and L54 are, independently of each other and of the other parameters, H or F and preferably Z5 is —CH2—CH2—.
Preferably the compounds of formula V-1 are selected from the group of compounds of formulae V-1a and V-1b
in which the R5 has the meaning given above.
Preferably the compounds of formula V-2 are selected from the group of compounds of formulae V-2a to V-2d
in which the R5 has the meaning given above.
Preferably the liquid crystalline media according to the present invention additionally comprise one or more compounds of formula VI
in which
R2 under formula II above, preferably R61 is alkyl and R62 is alkyl or alkenyl, each having up to 7 C atoms,
to
on each occurrence, identically or differently, denote
Preferably the compounds of formula VI are selected from the group of compounds of formulae VI-1 to VI-4
in which R61 and R62 have the respective meanings given under formula VI above and
In a preferred embodiment, the medium according to the invention comprises one or more compounds selected from the group of compounds of the formulae Y and B
in which the individual radicals, on each occurrence identically or differently, have the following meaning:
and
denote
—O—, —CO13 O— or —O—CO— in such a way that O atoms are not linked directly to one another,
In the compounds of formula Y and its subformulae, R1 and R2 preferably denote straight-chain alkyl or alkoxy having 1 to 6 C atoms, furthermore alkenyl having 2 to 6 C atoms, in particular vinyl, 1E-propenyl, 1E-butenyl, 3-butenyl, 1E-pentenyl, 3E-pentenyl or 4-pentenyl.
In the compounds of formula Y and its subformulae, preferably both radicals L1 and L2 denote F. In another preferred embodiment of the present invention, in the compounds of formula Y and its subformulae one of the radicals L1 and L2 denotes F and the other denotes Cl.
In a preferred embodiment of the present invention the medium contains one or more compounds of formula Y that are selected from the following subformulae
in which R1, R2, Zx, Zy, L1 and L2 have one of the meanings given in formula Y or one of the preferred meanings as given above and below,
denotes
Preferably, in the compounds of formula Y1 and Y2 both L1 and L2 denote F or one of L1 and L2 denotes F and the other denotes Cl, or both L3 and L4 denote F or one of L3 and L4 denotes F and the other denotes Cl.
Preferably the medium comprises one or more compounds of the formula Y1 selected from the group consisting of the following subformulae
in which a denotes 1 or 2, alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, and alkenyl denotes a straight-chain alkenyl radical having 2-6 C atoms, and (O) denotes an oxygen atom or a single bond. Alkenyl preferably denotes CH2═CH—, CH2═CHCH2CH2—, CH3—CH═CH—, CH3—CH2—CH═CH—, CH3—(CH2)2—CH═CH—, CH3—(CH2)3—CH═CH— or CH3—CH═CH—(CH2)2—.
Very preferably the medium contains one or more compounds of formula Y1 selected from formulae Y1-2 and Y1-10.
Further preferably the medium comprises one or more compounds of the formula Y2 selected from the group consisting of the following subformulae:
in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, and alkenyl denotes a straight-chain alkenyl radical having 2-6 C atoms, and (O) denotes an oxygen atom or a single bond. Alkenyl preferably denotes CH2═CH—, CH2═CHCH2CH2—, CH3—CH═CH—, CH3—CH2—CH═CH—, CH3—(CH2)2—CH═CH—, CH3—(CH2)3—CH═CH—or CH3—CH═CH—(CH2)2—.
Very preferably the medium contains one or more compounds of formula Y2 selected from formulae Y2-2 and Y2-10.
The proportion of the compounds of formula Y1 or its subformulae in the medium is preferably from 1 to 10% by weight.
The proportion of the compounds of formula Y2 or its subformulae in the medium is preferably from 1 to 10% by weight.
The total proportion of the compounds of formula Y1 and Y2 or their subformulae in the medium is preferably from 1 to 20%, very preferably from 1 to 15%, most preferably from 1 to 10% by weight.
Preferably the medium contains 1, 2 or 3 compounds of formula Y1 and Y2 or their subformulae, very preferably selected from formulae Y1-2, Y1-10, Y2-2 and Y2-10.
Preferably, the medium comprises one or more compounds of formula Y selected from the following subformula
in which
Preferably, both radicals L1 and L2 denote F. Further preferably one of the radicals L1 and L2 denotes F and the other denotes Cl.
The compounds of the formula LY are preferably selected from the group consisting of the following sub-formulae:
in which R1 has the meaning indicated above, (O) denotes an oxygen atom or a single bond, and v denotes an integer from 1 to 6. R1 preferably denotes straight-chain alkyl having 1 to 6 C atoms or straight-chain alkenyl having 2 to 6 C atoms, in particular CH3, C2H5, n-C3H7, n-C4H9, n-C5H11, CH2═CH—, CH2═CHCH2CH2—, CH3—CH═CH—, CH3—CH2—CH═CH—, CH3—(CH2)2—CH═CH—, CH3—(CH2)3—CH═CH— or CH3—CH═CH—(CH2)2—.
Very preferred are compounds of formula LY4.
Preferably the medium contains 1, 2 or 3 compounds of formula LY, very preferably of formula LY4.
The proportion of the compounds of formula LY or its subformulae in the medium is preferably from 1 to 10% by weight.
In a preferred embodiment, the medium according to the invention comprises one or more compounds of formula Y selected from the following subformula
in which R1, R2, L1, L2, Y, y and Zy have the meanings given in formula Y, in which at least one of the rings Y is tetrahydropyran.
The compounds of the formula AY are preferably selected from the group consisting of the following sub-formulae:
in which R1 has the meaning indicated above, (O) denotes an oxygen atom or a single bond, and v denotes an integer from 1 to 6. R1 preferably denotes straight-chain alkyl having 1 to 6 C atoms or straight-chain alkenyl having 2 to 6 C atoms, in particular CH3, C2H5, n-C3H7, n-C4H9, n-05H11, CH2═CH—, CH2═CHCH2CH2—, CH3—CH═CH—, CH3—CH2—CH═CH—, CH3—(CH2)2—CH═CH—, CH3—(CH2)3—CH═CH—or CH3—CH═CH—(CH2)2—.
In another preferred embodiment of the present invention the medium contains one or more compounds of formula Y selected from the following subformula
in which L1, L2, R1 and R2 have one of the meanings given in formula Y or one of the preferred meanings as given above and below.
Preferred compounds of the formula Y3 are selected from the group consisting of the following subformulae
in which, Alkyl and Alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, Alkoxy denotes a straight-chain alkoxy radical having 1-6 C atoms, Alkenyl and Alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-6 C atoms, and O denotes an oxygen atom or a single bond. Alkenyl and Alkenyl* preferably denote CH2═CH—, CH2═CHCH2CH2—, CH3—CH═CH—, CH3—CH2—CH═CH—, CH3—(CH2)2—CH═CH—, CH3—(CH2)3—CH═CH— or CH3—CH═CH—(CH2)2—.
Particularly preferred compounds of the formula Y3 are selected from the group consisting of following subformulae:
in which Alkoxy preferably denotes straight-chain alkoxy with 3, 4, or 5 C atoms.
Preferably in the compounds of formula Y3 and its subformulae both L1 and L2 denote F. Further preferably in the compounds of formula Y3 one of the radicals L1 and L2 denotes F and the other denotes Cl.
The proportion of the compounds of formula Y3 or its subformulae in the medium is preferably from 1 to 10%, very preferably from 1 to 6% by weight.
Preferably the medium contains 1, 2 or 3 compounds of formula Y3 or its subformulae, preferably of formula Y3-6, very preferably of formula Y3-6A.
In another preferred embodiment the present invention the medium contains one or more compounds of formula Y selected from the subformula Y4
in which R5 and R6 each, independently of one another, have one of the meanings indicated above, and
and
each, independently of one another, denote
in which L5 denotes F or Cl, preferably F, and L6 denotes F, Cl, OCF3, CF3, CH3, CH2F or CHF2, preferably F, and preferably at least one of the rings G, I and K is different from unsubstituted benzene.
Preferred compounds of the formula Y4 are selected from the group consisting of the following sub-formulae:
in which R denotes a straight-chain alkyl or alkoxy radical having 1-7 C atoms, R* denotes a straight-chain alkenyl radical having 2-7 C atoms, (O) denotes an oxygen atom or a single bond, and m denotes an integer from 1 to 6. R* preferably denotes CH2═CH—, CH2═CHCH2CH2—, CH3—CH═CH—, CH3—CH2—CH═CH—, CH3—(CH2)2—CH═CH—, CH3—(CH2)3—CH═CH— or CH3—CH═CH—(CH2)2—.
R preferably denotes methyl, ethyl, propyl, butyl, pentyl, hexyl, methoxy, ethoxy, propoxy, butoxy or pentoxy.
The proportion of the compounds of formula Y4 or its subformulae in the medium is preferably from 1 to 10%, very preferably from 1 to 6% by weight.
Preferably the medium contains 1, 2 or 3 compounds of formula Y4 or its subformulae, preferably of formula Y4-1, Y4-2, Y4-3 or Y4-21, in which R preferably denotes alkyl, furthermore alkoxy, each having 1-5 C atoms.
In another preferred embodiment the present invention the medium contains one or more compounds of formula Y selected from the the group consisting of the following subformulae
in which R5 has one of the meanings indicated above for R1, alkyl denotes C1-6-alkyl, Lx denotes H or F, X denotes F, Cl, OCF3, OCHF2 or OCH═CF2, d denotes 0 or 1, and z and m each, independently of one another, denote an integer from 1 to 6.
R5 in these compounds is particularly preferably C1-6-alkyl or -alkoxy or C2-6- alkenyl, d is preferably 1. X in these compounds is particularly preferably F. The LC medium according to the invention preferably comprises one or more compounds of the above-mentioned formulae in amounts of ≥5% by weight.
In the compounds of formula B and its subformulae, R1 and R2 preferably denote straight-chain alkyl or alkoxy having 1 to 6 C atoms, in particular methoxy, ethoxy, propoxy or butoxy, furthermore alkenyl having 2 to 6 C atoms, in particular vinyl, 1 E-propenyl, 1E-butenyl, 3-butenyl, 1E-pentenyl, 3E-pentenyl or 4-pentenyl.
The compounds of formula B are preferably selected of formula B1 and B2
in which alkyl denotes a straight-chain alkyl radical having 1-6 C atoms, and (O) denotes an oxygen atom or a single bond. Very preferred are compounds of formula B1 and B2 in which both groups (O) denote an oxygen atom and alkyl is methyl, ethyl, propyl, butyl, pentyl or hexyl, which are preferably straight-chained. Very preferably one alkyl is ethyl and the other is n-pentyl.
Very preferred are compounds of formula B2.
The proportion of the compounds of formula B, B1 and B2 in the medium is preferably from 1 to 20%, very preferably from 1 to 15%, most preferably from 2 to 10% by weight.
Preferably the medium contains 1, 2 or 3 compounds of formula B, B1 or B2.
Preferably the total proportion of compounds of formula Y and B or their subformulae in the medium is from 2 to 25%, very preferably from 5 to 20%, most preferably from 8 to 20% by weight.
In a preferred embodiment of the present invention the medium comprises one or more compounds of formula IA
in which
—O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by halogen, R12 alternatively denotes F, halogenated alkyl, halogenated alkenyl or halogenated alkoxy.
In the compounds of the formula IA, R11 and R12 preferably each, independently of one another, denote straight-chain alkyl having 1 to 7 C atoms, in particular CH3, n-C2H5 , n-C3H7, n-C4H9, n-C5H11, n-C6H13— or n-C7H15, straight-chain alkoxy having 1 to 6 C atoms, in particular CH3—O, n-C2H5—O, n-C3H7—O, n-C4H9—O, n-C5H11—O or n-C6H13—O, furthermore alkenyl, in particular CH2═CH, CH3CH═CH, CH3CH═CHCH2 or CH3CH2CH═CH, branched alkoxy, in particular (CH3)2CH(CH2)30, and alkenyloxy, in particular CH2═CHO, CH2═CH2CH2O, CH3CH═CHCH2O or CH3CH2CH═CHCH2O.
The parameter “a” in formula IA preferably denotes 1.
Preferred compounds of the formula IA present in the media are the compounds of the formulae IA-1 to IA-3, preferably of formula IA-2,
in which the occurring groups have the meanings given above for formula IA.
In another preferred embodiment, the group R12 in formula IA and its subformulae denotes F, CF3 or OCF3.
In a preferred embodiment the media comprise one or more compounds of the formula IA selected from the group of compounds of formulae IA-O-1 to IA-O-3, preferably of formula IA-O-2
in which the occurring groups have the meanings given above.
In another preferred embodiment the media comprise one or more compounds of the formula IA selected from the group of compounds of formulae IA-S-1 to IA-S-3, preferably of formula IA-S-2,
in which the parameters have the meanings given above.
In a preferred embodiment of the present invention the media comprise one or more compounds selected from the group of compounds of formulae IA-O-1 to IA-O-3 and one or more compounds selected from the group of compounds of formulae IA-S-1 to IA-S-3.
In a preferred embodiment of the present invention the liquid crystalline medium comprises one or more compounds of formula T, preferably in a concentration in the range of from 1% to 60%, more preferably from 5% to 40%, particularly preferably from 8% to 35%,
in which
denotes
one of
on each occurrence, identically or differently, denotes
preferably
more preferably
and, in case n is 2, one of
alternatively denotes
preferably
and
preferably
most preferably
and
Preferably the compounds of formula T are selected from the group of compounds of the formulae T-1 to T-4:
in which
has the meaning given above, and
Especially preferred compounds of formulae T-1, T-2, T-3 and T-4 are selected from the group of compounds of the following formulae T-1-1, T-2-1, T-3-1 to T-3-4 and T-4-1 to T4-4:
in which RS and XS have the meanings given above and preferably RS denotes alkyl having 1 to 7 C atoms and XS denotes CF3.
Above and below, the definitions of the abbreviations (acronyms) of preferred compounds are given in table A to C below.
In further preferred embodiments, the medium according to the invention comprises
The term “alkyl” or “alkyl*” in this application encompasses straight-chain and branched alkyl groups having 1-6 carbon atoms, in particular the straight-chain groups methyl, ethyl, propyl, butyl, pentyl and hexyl. Groups having 2-5 carbon atoms are generally preferred.
The term “alkenyl” or “alkenyl*” encompasses straight-chain and branched alkenyl groups having 2-6 carbon atoms, in particular the straight-chain groups. Preferred alkenyl groups are C2-C7-1 E-alkenyl, C4-C6-3E-alkenyl, in particular C2-C6-1E-alkenyl. Examples of particularly preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl and 5-hexenyl. Groups having up to 5 carbon atoms are generally preferred, in particular CH2═CH, CH3CH═CH.
The term “fluoroalkyl” preferably encompasses straight-chain groups having a terminal fluorine, i.e. fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluoro-butyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. However, other positions of the fluorine are not excluded.
The term “oxaalkyl” or “alkoxy” preferably encompasses straight-chain radicals of the formula CnH2n+1—O—(CH2)m, in which n and m each, independently of one another, denote 1 to 6. m may also denote 0. Preferably, n=1 and m=1-6 or m=0 and n=1-3.
Through a suitable choice of the meanings of R0 and X0, the addressing times, the threshold voltage, the steepness of the transmission characteristic lines, etc., can be modified in the desired manner. For example, 1E-alkenyl radicals, 3E-alkenyl radicals, 2E-alkenyloxy radicals and the like generally result in shorter addressing times, improved nematic tendencies and a higher ratio between the elastic constants k33 (bend) and k11 (splay) compared with alkyl and alkoxy radicals. 4-Alkenyl radicals, 3-alkenyl radicals and the like generally give lower threshold voltages and lower values of k33/k11 compared with alkyl and alkoxy radicals. The mixtures according to the invention are distinguished, in particular, by high Δε values and thus have significantly faster response times than the mixtures from the prior art.
The optimum mixing ratio of the compounds of the above-mentioned formulae depends substantially on the desired properties, on the choice of the components of the above-mentioned formulae and on the choice of any further components that may be present.
Suitable mixing ratios within the range indicated above can easily be determined from case to case.
The total amount of compounds of the above-mentioned formulae in the liquid-crystalline media according to the invention is not crucial. The mixtures can therefore comprise one or more further components for the purposes of optimisation of various properties. However, the observed effect on the desired improvement in the properties of the medium is generally greater, the higher the total concentration of compounds of the above-mentioned formulae.
The individual compounds of the above-mentioned formulae and the sub-formulae thereof which can be used in the liquid-crystalline media according to the invention are either known or can be prepared analogously to the known compounds.
In another preferred embodiment of the present invention the liquid-crystalline medium additionally comprises one or more polymerisable compounds. The polymerisable compounds are preferably selected from formula M
Ra—B1—(Zb—B2)m—RbM
in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning:
Particularly preferred compounds of the formula I are those in which B1 and B2 each, independently of one another, denote 1,4-phenylene, 1,3-phenylene, naphthalene-1,4-diyl, naphthalene-2,6-diyl, phenanthrene-2,7-diyl, 9,10-dihydro-phenanthrene-2,7-diyl, anthracene-2,7-diyl, fluorene-2,7-diyl, coumarin, flavone, where, in addition, one or more CH groups in these groups may be replaced by N, cyclohexane-1,4-diyl, in which, in addition, one or more non-adjacent CH2 groups may be replaced by O and/or S, 1,4-cyclohexenylene, bicycle[1.1.1]pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl, spiro[3.3]heptane-2,6-diyl, piperidine-1,4-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, indane-2,5-diyl or octahydro-4,7-methanoindane-2,5-diyl, where all these groups may be unsubstituted or mono- or polysubstituted by L as defined above.
Particularly preferred compounds of the formula M are those in which B1 and B2 each, independently of one another, denote 1,4-phenylene, 1,3-phenylene, naphthalene-1,4-diyl or naphthalene-2,6-diyl,
Very preferred compounds of formula M are selected from the following formulae:
in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning:
0 L F, Cl, CN or straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms,
Especially preferred are compounds of formulae M2 and M13.
Further preferred are trireaktive compounds M15 to M31, in particular M17, M18, M19, M22, M23, M24, M25, M30 and M31.
In the compounds of formulae M1 to M31 the group
is preferably
in which L on each occurrence, identically or differently, has one of the meanings given above or below, and is preferably F, Cl, CN, NO2, CH3, C2H5, C(CH3)3, CH(CH3)2, CH2CH(CH3)C2H5, OCH3, OC2H5, COCH3, COC2H5, COOCH3, COOC2H5, CF3, OCF3, OCHF2, OC2F5 or P-Sp-, very preferably F, Cl, CN, CH3, C2H5, OCH3, COCH3, OCF3 or P-Sp-, more preferably F, Cl, CH3, OCH3, COCH3 or OCF3 , especially F or CH3.
Preferred compounds of formulae M1 to M31 are those in which P1, P2 and P3 denote an acrylate, methacrylate, oxetane or epoxy group, very preferably an acrylate or methacrylate group.
Further preferred compounds of formulae M1 to M31 are those in which Sp1, Sp2 and Sp3 are a single bond.
Further preferred compounds of formulae M1 to M31 are those in which one of Sp1, Sp2 and Sp3 is a single bond and another one of S1, Sp2 and Sp3 is different from a single bond.
Further preferred compounds of formulae M1 to M31 are those in which those groups Sp1, Sp2 and Sp3 that are different from a single bond denote —(CH2)s1—X″—, in which sl is an integer from 1 to 6, preferably 2, 3, 4 or 5, and X″ is X″ is the linkage to the benzene ring and is —O—, —O—CO—, —CO—O—, —O—CO—O— or a single bond.
Particular preference is given to liquid-crystalline media comprising one, two or three polymerisable compounds of formula M, preferably selected from formulae M1 to M31.
Further preferably the liquid-crystalline media according to the present invention comprise one or more polymerisable compounds selected from Table E below.
Preferably the proportion of polymerisable compounds in the liquid-crystalline medium, preferably selected from formula M and Table E, is from 0.01 to 5%, very preferably from 0.05 to 1%, most preferably from 0.1 to 0.5%.
It was observed that the addition of one or more polymerisable compounds to the liquid-crystalline medium, like those selected from formula M and
Table E, leads to advantageous properties like fast response times. Such a liquid-crystalline medium is especially suitable for use in PSA displays where it shows low image sticking, a quick and complete polymerisation, the quick generation of a low pretilt angle which is stable after UV exposure, a high reliability, high VHR value after UV exposure, and a high birefringence. By appropriate selection of the polymerisable compounds it is possible to increase the absorption of the liquid-crystalline medium at longer UV wavelengths, so that it is possible to use such longer UV wavelengths for polymerisation, which is advantageous for the display manufacturing process.
The polymerisable group P is a group which is suitable for a polymerisation reaction, such as, for example, free-radical or ionic chain polymerisation, polyaddition or polycondensation, or for a polymer-analogous reaction, for example addition or condensation onto a main polymer chain. Particular preference is given to groups for chain polymerisation, in particular those containing a C═C double bond or —C≡C— triple bond, and groups which are suitable for polymerisation with ring opening, such as, for example, oxetane or epoxide groups.
Preferred groups P are selected from the group consisting of CH2═CW1—CO—O—, CH2═CW1—CO—,
CH2═CW2—(O)k3—, CW1═CH—CO—(O)k3—, CW1═CH—CO—NH—, CH2═CW1—CO—NH—, CH3—CH═CH—O—, (CH2═CH)2CH—OCO—, (CH2═CH—CH2)2CH—OCO—, (CH2═CH)2CH—O—, (CH2═CH—CH2)2N—, (CH2═CH—CH2)2N—CO—, HO—CW2W3—, HS—CW2W3—, HW2N—, HO—CW2W3—NH—, CH2═CW1—CO—NH—, CH2═CH—(COO)k1-Phe-(O)k2—, CH2═CH—(CO)k1-Phe-(O)k2—, Phe-CH═CH—, HOOC—, OCN— and W4W5W6Si—, in which W1 denotes H, F, Cl, CN, CF3, phenyl or alkyl having 1 to 5 C atoms, in particular H, F, Cl or CH3, W2 and W3 each, independently of one another, denote H or alkyl having 1 to 5 C atoms, in particular H, methyl, ethyl or n-propyl, W4, W5 and W6 each, independently of one another, denote Cl, oxaalkyl or oxacarbonylalkyl having 1 to 5 C atoms, W7 and W8 each, independently of one another, denote H, Cl or alkyl having 1 to 5 C atoms, Phe denotes 1,4-phenylene, which is optionally substituted by one or more radicals L as defined above which are other than P-Sp-, k1, k2 and k3 each, independently of one another, denote 0 or 1, k3 preferably denotes 1, and k4 denotes an integer from 1 to 10.
Very preferred groups P are selected from the group consisting of CH2═CW1—CO—O—, CH2═CW1—CO—,
CH2═CW2—O—, CH2═CW2—, CW1═CH—CO—(O)k3—, CW1═CH—CO—NH—, CH2═CW1—CO—NH—, (CH2═CH)2CH—OCO—, (CH2═CH—CH2)2CH—OCO—, (CH2═CH)2CH—O—, (CH2═CH—CH2)2N—, (CH2═CH—CH2)2N—CO—, CH2═CW1—CO—NH—, CH2═CH—(COO)k1-Phe-(O)k2—, CH2═CH—(CO)k1—Phe-(O)k2—, Phe-CH═CH— and W4W5W6Si—, in which W1 denotes H, F, Cl, CN, CF3, phenyl or alkyl having 1 to 5 C atoms, in particular H, F, Cl or CH3, W2 and W3 each, independently of one another, denote H or alkyl having 1 to 5 C atoms, in particular H, methyl, ethyl or n-propyl, W4, W5 and W6 each, independently of one another, denote Cl, oxaalkyl or oxa-carbonylalkyl having 1 to 5 C atoms, W7 and W8 each, independently of one another, denote H, CI or alkyl having 1 to 5 C atoms, Phe denotes 1,4-phenylene, k1, k2 and k3 each, independently of one another, denote 0 or 1, k3 preferably denotes 1, and k4 denotes an integer from 1 to 10.
Very particularly preferred groups P are selected from the group consisting of CH2═CW1—CO—O—, in particular CH2═CH—CO—O—, CH2═C(CH3)—CO—O— and CH2═CF—CO—O—, furthermore CH2═CH—O—, (CH2═CH)2CH—O—CO—, (CH2═CH)2CH—O—,
Further preferred polymerisable groups P are selected from the group consisting of vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetane and epoxide, most preferably from acrylate and methacrylate.
If Sp is different from a single bond, it is preferably of the formula Sp″-X″, so that the respective radical P-Sp- conforms to the formula P-Sp″-X″—, in which
Typical spacer groups Sp and -Sp“—X”— are, for example, —(CH2)p1—, —(CH2CH2O)q1—CH2CH2—, —CH2CH2—S—CH2CH2—, —CH2CH2—NH—CH2CH2—or —(SiR0R00—O)p1—, in which p1 is an integer from 1 to 12, q1 is an integer from 1 to 3, and R0 and R00 have the meanings indicated above.
Particularly preferred groups Sp and -Sp″-X″— are —(CH2)0—, —(CH2)0—O—, —(CH2)p1—O—CO—, —(CH2)p1—CO—O—, —(CH2)p1—O—CO—O—, in which p1 and q1 have the meanings indicated above.
Particularly preferred groups Sp″ are, in each case straight-chain, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene, ethylenethioethylene, ethylene-N-methylimino-ethylene, 1-methylalkylene, ethenylene, propenylene and butenylene.
For the production of PSA displays, the polymerisable compounds contained in the liquid-crystalline medium are polymerised or crosslinked (if one compound contains two or more polymerisable groups) by in-situ polymerisation in the liquid-crystalline medium between the substrates of the LC display, optionally while a voltage is applied to the electrodes.
The structure of the PSA displays according to the invention corresponds to the usual geometry for PSA displays, as described in the prior art cited at the outset. Geometries without protrusions are preferred, in particular those in which, in addition, the electrode on the colour filter side is unstructured and only the electrode on the TFT side has slots. Particularly suitable and preferred electrode structures for PS-VA displays are described, for example, in US 2006/0066793 A1.
The combination of compounds of the preferred embodiments mentioned above with the polymerised compounds described above causes low threshold voltages, low rotational viscosities and very good low-temperature stabilities in the liquid-crystalline media according to the invention at the same time as constantly high clearing points and high VHR values.
The use of liquid-crystalline media containing polymerisable compounds allows the rapid establishment of a particularly low pretilt angle in PSA displays. In particular, the liquid-crystalline media exhibit significantly shortened response times, in particular also the grey-shade response times, in PSA displays compared with the media from the prior art.
Preference is generally given to liquid-crystalline media which have a nematic liquid-crystalline phase, and preferably have no chiral liquid crystal phase.
The invention also relates to the use of a liquid-crystalline medium according to the present invention as described above and below for electro-optical purposes, in particular for the use is in shutter glasses, for 3D applications, in TN, PS-TN, STN, TN-TFT, OCB, IPS, PS-IPS, FFS, HB-FFS, PS-FFS, positive VA and positive PS-VA displays, and to electro-optical displays, in particular of the aforementioned types, containing a liquid-crystalline medium according to the present invention as described above and below, in particular a TN, PS-TN, STN, TN-TFT, OCB, IPS, PS-IPS, FFS, HB-FFS, PS-FFS, positive VA (vertically aligned) or positive PS-VA display.
The invention also relates to electro-optical displays, such as, for example, STN or MLC displays, having two plane-parallel outer plates, which, together with a frame, form a cell, integrated non-linear elements for switching individual pixels on the outer plates, and a nematic liquid-crystal mixture having positive dielectric anisotropy and high specific resistance located in the cell, wherein a nematic liquid-crystal mixture is a liquid-crystalline medium according to the present invention as described above and below.
The liquid-crystalline media according to the invention enable a significant broadening of the available parameter latitude. The achievable combinations of clearing point, viscosity at low temperature, thermal and UV stability and high optical anisotropy are far superior to previous materials from the prior art.
The liquid-crystalline media according to the invention, while retaining the nematic phase down to −20° C. and preferably down to −30° C., particularly preferably down to −40° C., and the clearing point ≥75° C., preferably ≥80° C., at the same time allow rotational viscosities γ1 of ≤110 mPa·s, particularly preferably ≤100 mPa·s, to be achieved, enabling excellent MLC displays having fast response times to be achieved. The rotational viscosities are determined at 20° C.
The dielectric anisotropy Δε of the liquid-crystalline media according to the invention at 20° C. and 1 kHz is preferably ≥+1.5, more preferably from +1.5 to +10, more preferably from 2.0 to 7.0, particularly preferably from 2.2 to 4.7.
The birefringence Δn of the liquid-crystalline media according to the invention at 20° C. is preferably from 0.080 to 0.130, very preferably from 0.090 to 0.110.
The rotational viscosity γ1 of the liquid-crystalline media according to the invention is preferably ≤80 mPa s, more preferably ≤70 mPa s, very preferably ≤60 mPa s.
The ratio γ1/K11 (in which yi is the rotational viscosity γ1 and K11 is the elastic constant for splay deformation) of the liquid-crystalline media according to the invention is preferably ≤4.5 mPa·s/pN, very preferably ≤4.2 mPa·s/pN, most preferably ≤4.0 mPa·s/pN.
The nematic phase range of the liquid-crystalline media according to the invention preferably has a width of at least 90° , more preferably of at least 100 ° C., in particular at least 110° . This range preferably extends at least from —25° to +80° C.
It goes without saying that, through a suitable choice of the components of the liquid-crystalline media according to the invention, it is also possible for higher clearing points (for example above 100° C.) to be achieved at higher threshold voltages or lower clearing points to be achieved at lower threshold voltages with retention of the other advantageous properties. At viscosities correspondingly increased only slightly, it is likewise possible to obtain liquid-crystalline media having a higher Δε and thus low thresholds. The MLC displays according to the invention preferably operate at the first Gooch and Tarry transmission minimum [C. H. Gooch and H. A. Tarry, Electron. Lett. 10, 2-4, 1974; C.H. Gooch and H.A. Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975], where, besides particularly favourable electro-optical properties, such as, for example, high steepness of the characteristic line and low angle dependence of the contrast (German patent 30 22 818), lower dielectric anisotropy is sufficient at the same threshold voltage as in an analogous display at the second minimum. This enables significantly higher specific resistance values to be achieved using the mixtures according to the invention at the first minimum than in the case of liquid-crystalline media comprising cyano compounds. Through a suitable choice of the individual components and their proportions by weight, the person skilled in the art is able to set the birefringence necessary for a pre-specified layer thickness of the MLC display using simple routine methods.
Measurements of the voltage holding ratio (HR) [S. 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 liquid-crystalline media according to the invention comprising compounds of the formulae I and II and/or III exhibit a significantly smaller decrease in the HR on UV exposure than analogous mixtures comprising cyanophenylcyclohexanes of the formula
or esters of the formula
The light stability and UV stability of the liquid-crystalline media according to the invention are considerably better, i.e. they exhibit a significantly smaller decrease in the HR on exposure to light, heat or UV.
The construction of the MLC display according to the invention from polarisers, electrode base plates and surface-treated electrodes corresponds to the usual design for displays of this type. The term usual design is broadly drawn here and also encompasses all derivatives and modifications of the MLC display, in particular including matrix display elements based on poly-Si TFTs or MIM.
A significant difference between the displays according to the invention and the hitherto conventional displays based on the twisted nematic cell consists, however, in the choice of the liquid-crystal parameters of the liquid-crystal layer.
The liquid-crystalline media which can be used in accordance with the invention are prepared in a manner conventional per se, for example by mixing one or more compounds of formula I with one or more compounds of the formulae II and/or III and, optionally, with one or more compounds of the formulae Y, B, IA, IV, V and VI or with further liquid-crystalline compounds and/or additives. In general, the desired amount of the components used in lesser amount is dissolved in the components making up the principal constituent, advantageously at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent again, for example by distillation, after thorough mixing.
The liquid-crystalline media may also comprise further additives known to the person skilled in the art and described in the literature, such as, for example, polymerisation initiators, inhibitors, surface-active substances, light stabilisers, antioxidants, e.g. BHT, TEMPOL, microparticles, free-radical scavengers, nanoparticles, etc. For example, 0-15% of pleochroic dyes or chiral dopants can be added. Suitable stabilisers and dopants are mentioned below in Tables C and D.
In a preferred embodiment the liquid-crystalline media contain one or more chiral dopants, preferably in a concentration from 0.01 to 1% by weight, very preferably from 0.05 to 0.5% by weight. The chiral dopants are preferably selected from the group consisting of compounds from Table B below, very preferably from the group consisting of R- or S-1011, R- or S-2011, R- or S-3011, R- or S-4011, and R- or S-5011.
In another preferred embodiment the liquid-crystalline media contain a racemate of one or more chiral dopants, which are preferably selected from the chiral dopants mentioned in the previous paragraph.
In another preferred embodiment of the present invention the liquid-crystalline media contain one or more further stabilisers, preferably selected from Table D, very preferably of the following formula
in which n is an integer from 1 to 6, preferably 3.
Preferably the proportion of stabilisers, like those of formula S, in the liquid-crystalline medium is from 10 to 500 ppm, very preferably from 20 to 100 ppm.
In another preferred embodiment the LC medium according to the present invention contains a self-aligning (SA) additive, preferably in a concentration of 0.1 to 2.5%. An LC medium according to this preferred embodiment is especially suitable for use in polymer stabilised SA-FFS or SA-HB-FFS displays.
In a preferred embodiment the SA-FFS or SA-HB-FFS display according to the present invention does not contain a polyimide alignment layer. In another preferred embodiment the SA-FFS or SA-HB-FFS display according to preferred embodiment contains a polyimide alignment layer.
Preferred SA additives for use in this preferred embodiment are selected from compounds comprising a mesogenic group and a straight-chain or branched alkyl side chain that is terminated with one or more polar anchor groups selected from hydroxy, carboxy, amino or thiol groups.
Further preferred SA additives contain one or more polymerisable groups which are attached, optionally via spacer groups, to the mesogenic group. These polymerisable SA additives can be polymerised in the LC medium under similar conditions as applied for the RMs in the PSA process.
Suitable SA additives to induce homeotropic alignment, especially for use in SA-VA mode displays, are disclosed for example in US 2013/0182202 A1, US 2014/0838581 A1, US 2015/0166890 A1 and US 2015/0252265 A1.
In another preferred embodiment an LC medium or a polymer stabilised SA-FFS or SA-HB-FFS display according to the present invention contains one or more self-aligning additives selected from Table F below.
Furthermore, it is possible to add to the liquid-crystalline media, for example, 0 to 15% by weight of pleochroic dyes, furthermore nanoparticles, conductive salts, preferably ethyldimethyldodecylammonium 4-hexoxybenzoate, tetrabutylammonium tetraphenylborate or complex salts of crown ethers (cf., for example, Haller et al., Mol. Cryst. Liq. Cryst. 24, 249-258 (1973)), for improving the conductivity, or substances for modifying the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases. Substances of this type are described, for example, in DE-A 22 09 127, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26 37 430 and 28 53 728.
In the present invention and especially in the following examples, the structures of the mesogenic compounds are indicated by means of abbreviations also referred to as acronyms. In these acronyms, the chemical formulae are abbreviated as follows using Tables A to C below. All groups CnH2n 1, CmH2m+1 and CIH2n+1 or CnH2n−1, CmH2m-1 and CIH2I−1 denote straight-chain alkyl or alkenyl, preferably 1E-alkenyl, having n, m and I C atoms respectively, where n, m and I, independently of one another, denote an integer from 1 to 9, preferably 1 to 7, or from 2 to 9, preferably 2 to 7, respectively. CoH2o+1 denotes straight-chain alkyl having 1 to 7, preferably 1 to 4, C atoms, or branched alkyl having 1 to 7, preferably 1 to 4, C atoms.
Table A lists the codes used for the ring elements of the core structures of the compounds, while Table C shows the linking groups. Table C gives the meanings of the codes for the left-hand or right-hand end groups. Table D shows illustrative structures of compounds with their respective abbreviations.
in which n and m each denote integers, and the three dots “ . . . ” are place-holders for other abbreviations from this table.
The following table shows illustrative structures together with their respective abbreviations. These are shown in order to illustrate the meaning of the rules for the abbreviations. They furthermore represent compounds which are preferably used.
In a preferred embodiment, the liquid-crystalline media according to the invention comprise one or more polymerisable compounds, preferably selected from the polymerisable compounds of the formulae RM-1 to RM-143. Of these, compounds RM-1, RM-4, RM-8, RM-17, RM-19, RM-35, RM-37, RM-39, RM-40, RM-41, RM-48, RM-52, RM-54, RM-57, RM-64, RM-74, RM-76, RM-88, RM-102, RM-103, RM-109, RM-117, RM-120, RM-121 and RM-122 are particularly preferred.
In a preferred embodiment, the LC media, SA-FFS and SA-HB-FFS displays according to the present invention comprise one or more SA additives selected from formulae SA-1 to SA-34, preferably from formulae SA-14 to SA-34, very preferably from formulae SA-20 to SA-28, most preferably of formula SA-20, in combination with one or more RMs of formula I. Very preferred is a combination of polymerizable compound 1, 2 or 3 of Example 1 below, very preferably of polymerizable compound 3 of Example 1, with an SA additive of formula SA-20 to SA-28, very preferably of formula SA-20.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. The following mixture examples are intended to explain the invention without limiting it.
Above and below, percentage data denote per cent by weight. All temperatures are indicated in degrees Celsius. m.p. denotes melting point, cl.p.=clearing point. Furthermore, C=crystalline state, N=nematic phase, S=smectic phase and I=isotropic phase. The data between these symbols represent the transition temperatures. Furthermore, the following symbols are used
V0 Freedericks threshold voltage, capacitive [V] at 20° C.,
V10 voltage [V] for 10% transmission,
ne extraordinary refractive index measured at 20° C. and 589 nm,
no ordinary refractive index measured at 20° C. and 589 nm,
Δn optical anisotropy measured at 20° C. and 589 nm,
ε_ dielectric susceptibility (or “dielectric constant”) perpendicular to the to the longitudinal axes of the molecules at 20° C. and 1 kHz,
ε∥ dielectric susceptibility (or “dielectric constant”) parallel to the to the longitudinal axes of the molecules at 20° C. and 1 kHz,
Δε dielectric anisotropy at 20° C. and 1 kHz,
cl.p. or
T(N,I) clearing point [° C],
γ1 rotational viscosity measured at 20° C. [mPa·s],
K11 elastic constant, “splay” deformation at 20° C. [pN],
K22 elastic constant, “twist” deformation at 20° C. [pN],
K33 elastic constant, “bend” deformation at 20° C. [pN], and
LTS low-temperature stability of the phase, determined in bulk,
VHR voltage holding ratio.
All physical properties are determined in accordance with “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, status Nov. 1997, Merck KGaA, Germany, and apply for a temperature of 20° C., unless explicitly indicated otherwise.
The nematic mixtures N-1 to N-48 are prepared as follows:
The entire disclosure[s] of all applications, patents and publications, cited herein and of corresponding EP Patent Application No. 18211358.9, filed Dec. 10, 2018, are incorporated by reference herein.
The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.
From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.
Number | Date | Country | Kind |
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18211358.9 | Dec 2018 | EP | regional |