Patent Application
20170335194
The invention relates to a liquid-crystalline medium, in particular based on a mixture of polar compounds, and to the use thereof for an active-matrix display, in particular based on the VA (vertically aligned), PSA (polymer stabilized alignment), PS-VA (polymer stabilized VA), PA-VA (photo alignment-VA), PALC (plasma addressed liquid crystal), FFS (fringe field switching), PS-FFS (polymer stabilized-FFS), IPS (in-plane switching) or PS-IPS (polymer stabilized-IPS) effect.
Media of this type can be used, in particular, for electro-optical displays having active-matrix addressing based on the ECB effect and for IPS (in-plane switching) displays or FFS (fringe field switching) displays.
The principle of electrically controlled birefringence, the ECB effect or also DAP (deformation of aligned phases) effect, was described for the first time in 1971 (M. F. Schieckel and K. Fahrenschon, “Deformation of nematic liquid crystals with vertical orientation in electrical fields”, Appl. Phys. Lett. 19 (1971), 3912). This was followed by papers by J. F. Kahn (Appl. Phys. Lett. 20 (1972), 1193) and G. Labrunie and J. Robert (J. Appl. Phys. 44 (1973), 4869).
The papers by J. Robert and F. Clerc (SID 80 Digest Techn. Papers (1980), 30), J. Duchene (Displays 7 (1986), 3) and H. Schad (SID 82 Digest Techn. Papers (1982), 244) showed that liquid-crystalline phases must have high values for the ratio of the elastic constants K3/K1, high values for the optical anisotropy Δn and values for the dielectric anisotropy of Δ∈≦−0.5 in order to be suitable for use in high-information display elements based on the ECB effect. Electro-optical display elements based on the ECB effect have a homeotropic edge alignment (VA technology=vertically aligned). Dielectrically negative liquid-crystal media can also be used in displays which use the so-called IPS or FFS effect.
Displays which use the ECB effect, as so-called VAN (vertically aligned nematic) displays, for example in the MVA (multi-domain vertical alignment, for example: Yoshide, H. et al., paper 3.1: “MVA LCD for Notebook or Mobile PCs . . . ”, SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book I, pp. 6 to 9, and Liu, C. T. et al., paper 15.1: “A 46-inch TFT-LCD HDTV Technology . . . ”, SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book II, pp. 750 to 753), PVA (patterned vertical alignment, for example: Kim, Sang Soo, paper 15.4: “Super PVA Sets New State-of-the-Art for LCD-TV”, SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book II, pp. 760 to 763), ASV (advanced super view, for example: Shigeta, Mitzuhiro and Fukuoka, Hirofumi, paper 15.2: “Development of High Quality LCDTV”, SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book II, pp. 754 to 757) modes, have established themselves as one of the three more recent types of liquid-crystal display that are currently the most important, in particular for television applications, besides IPS (in-plane switching) displays (for example: Yeo, S. D., paper 15.3: “An LC Display for the TV Application”, SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book II, pp. 758 & 759) and the long-known TN (twisted nematic) displays. The technologies are compared in general form, for example, in Souk, Jun, SID Seminar 2004, seminar M-6: “Recent Advances in LCD Technology”, Seminar Lecture Notes, M-6/1 to M-6/26, and Miller, Ian, SID Seminar 2004, seminar M-7: “LCD-Television”, Seminar Lecture Notes, M-7/1 to M-7/32. Although the response times of modern ECB displays have already been significantly improved by addressing methods with overdrive, for example: Kim, Hyeon Kyeong et al., paper 9.1: “A 57-in. Wide UXGA TFT-LCD for HDTV Application”, SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book I, pp. 106 to 109, the achievement of video-compatible response times, in particular on switching of grey shades, is still a problem which has not yet been satisfactorily solved.
Industrial application of this effect in electro-optical display elements requires LC phases, which have to satisfy a multiplicity of requirements. Particularly important here are chemical resistance to moisture, air and physical influences, such as heat, infrared, visible and ultraviolet radiation and direct and alternating electric fields.
Furthermore, industrially usable LC phases are required to have a liquid-crystalline mesophase in a suitable temperature range and low viscosity.
None of the hitherto-disclosed series of compounds having a liquid-crystalline mesophase includes a single compound which meets all these requirements. Mixtures of two to 25, preferably three to 18, compounds are therefore generally prepared in order to obtain substances which can be used as LC phases. However, it has not been possible to prepare optimum phases easily in this way since no liquid-crystal materials having significantly negative dielectric anisotropy and adequate long-term stability were hitherto available.
Matrix liquid-crystal displays (MLC displays) are known. Non-linear elements which can be used for individual switching of the individual pixels are, for example, active elements (i.e. transistors). The term “active matrix” is then used, where a distinction can be made between two types:
In the case of type 1, the electro-optical effect used is usually dynamic scattering or the guest-host effect. The use of single-crystal silicon as substrate material restricts the display size, since even modular assembly of various part-displays results in problems at the joints.
In the case of the more promising type 2, which is preferred, the electro-optical effect used is usually the TN effect.
A distinction is made between two technologies: TFTs comprising compound semiconductors, such as, for example, CdSe, or TFTs based on polycrystalline or amorphous silicon. The latter technology is being worked on intensively worldwide.
The TFT matrix is applied to the inside of one glass plate of the display, while the other glass plate carries the transparent counterelectrode on its inside. Compared with the size of the pixel electrode, the TFT is very small and has virtually no adverse effect on the image. This technology can also be extended to fully color-capable displays, in which a mosaic of red, green and blue filters is arranged in such a way that a filter element is opposite each switchable pixel.
The term MLC displays here covers any matrix display with integrated non-linear elements, i.e. besides the active matrix, also displays with passive elements, such as varistors or diodes (MIM=metal-insulator-metal).
MLC displays of this type are particularly suitable for TV applications (for example pocket TVs) or for high-information displays in automobile or air-craft construction. Besides problems regarding the angle dependence of the contrast and the response times, difficulties also arise in MLC displays due to insufficiently high specific resistance of the liquid-crystal mixtures [TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay 84, September 1984: A 210-288 Matrix LCD Controlled by Double Stage Diode Rings, pp. 141 ff., Paris; STROMER, M., Proc. Eurodisplay 84, September 1984: Design of Thin Film Transistors for Matrix Addressing of Television Liquid Crystal Displays, pp. 145 ff., Paris]. With decreasing resistance, the contrast of an MLC display deteriorates. Since the specific resistance of the liquid-crystal mixture generally drops over the life of an MLC display owing to interaction with the inside surfaces of the display, a high (initial) resistance is very important for displays that have to have acceptable resistance values over a long operating period.
There thus continues to be a great demand for MLC displays having very high specific resistance at the same time as a large working-temperature range, short response times and a low threshold voltage with the aid of which various grey shades can be produced.
The disadvantage of the frequently-used MLC-TN displays is due to their comparatively low contrast, the relatively high viewing-angle dependence and the difficulty of generating grey shades in these displays.
VA displays have significantly better viewing-angle dependencies and are therefore principally used for televisions and monitors. However, there continues to be a need here to improve the response times, in particular with respect to the use of televisions having frame rates (image change frequency/repetition rates) of greater than 60 Hz. At the same time, however, the properties, such as, for example, the low-temperature stability, must not be impaired.
The invention is based on the object of providing liquid-crystal mixtures, in particular for monitor and TV applications, which are based on the ECB effect or on the IPS or FFS effect, which do not have the above-mentioned disadvantages or only do so to a reduced extent. In particular, it must be ensured for monitors and televisions that they also operate at extremely high and extremely low temperatures and at the same time have short response times and at the same time have improved reliability behavior, in particular have no or significantly reduced image sticking after long operating times.
It was surprisingly that it is possible to improve the rotational viscosities, and the ratio of rotational viscosity and elastic constants, and thus the response times, while maintaining a high reliability and high VHR (voltage holding ratio) values, when using a liquid-crystal mixture as disclosed and claimed hereinafter, which contains an alkenyl compound of formula AN, a quaterphenyl compound of formula Q and a stabilizer of formula S, in particular an LC mixture having negative dielectric anisotropy, preferably in LC displays of the VA or FFS mode.
The use of an LC mixture as disclosed and claimed hereinafter having negative dielectric anisotropy surprisingly results in very low rotational viscosities and in a reduction in the ratio of rotational viscosity and elastic constants, while maintaining a high reliability and high VHR values also after UV exposure. Liquid-crystal mixtures, preferably VA, PS (=polymer stabilized)-VA, PA (=photo alignment)-VA, IPS, PS-IPS, PS-FFS, FFS mixtures, in particular UB-FFS (ultra brightness fringe field switching) mixtures, which have short response times, at the same time good phase properties and good low-temperature behavior can therefore be prepared.
The invention relates to a liquid crystal (LC) medium, preferably with negative dielectric anisotropy, comprising one or more compounds of formula Q, one or more compounds of formula AN, and one or more compounds of formula S
in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning:
or
or
The invention furthermore relates to an LC medium, which comprises one or more compounds of formula Q, one or more compounds of formula AN, one or more compounds of formula S, and further comprises one or more polymerizable compounds.
The invention furthermore relates to an LC medium or LC display as described above and below, wherein the polymerizable compounds are polymerized.
The invention furthermore relates to a process for preparing an LC medium as described above and below, comprising the steps of mixing one or more compounds of formula AN with one or more compounds of formula Q and one or more compounds of formula S, and optionally with further LC compounds and/or additives.
The invention further relates to the use of LC medium in LC displays.
The invention furthermore relates to an LC display comprising one or more compounds of formula I or an LC medium according to the invention, in particular a VA, PS-VA, PA-VA, IPS, PS-IPS, PS-FFS or FFS display, in particular an UB-FFS display, comprising an LC medium as described above and below.
The mixtures according to the invention preferably exhibit very broad nematic phase ranges having clearing points ≧70° C., preferably ≧75° C., in particular ≧80° C., very favorable values for the capacitive threshold, relatively high values for the holding ratio and at the same time very good low-temperature stabilities at −20° C. and −30° C., as well as very low rotational viscosities and short response times.
The mixtures according to the invention are furthermore distinguished by the fact that, in addition to the improvement in the rotational viscosity γ1, high reliability and high VHR values, even after UV exposure, can be achieved.
The mixtures according to the invention are furthermore distinguished by the fact that, in addition to the improvement in the rotational viscosity γ1, relatively high values of the elastic constant K3 for improving the response times can be observed. In particular, the mixtures according to the invention have a particularly low value for the ratio γ1/K3 of rotational viscosity γ1 and elastic constant K3, which is an indicator of a fast response time.
Preferred compounds of formula AN are those wherein RA1 is selected from ethenyl, propenyl, butenyl, pentenyl, hexenyl and heptenyl.
Further preferred compounds of formula AN are those wherein RA1 and/or RA2 is selected from 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—.
Preferred compounds of formula AN are selected from the following formulae:
in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, and alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-7 C atoms. 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—.
Very preferred are compounds of formula AN1, AN3, and AN6.
Further preferred compounds of formula AN are selected from the following subformulae:
in which m denotes 1, 2, 3, 4, 5 or 6, i denotes 0, 1, 2 or 3, and Rb1 denotes H, CH3 or C2H5.
Very preferred compounds of formula AN are selected from the following subformulae:
Most preferred are compounds of formula AN1a2, AN1a5, AN6a1 and AN6a2, in particular the compound of formula AN1a2.
Preferably the proportion of compounds of formula AN in the LC medium is from 2 to 60%, very preferably from 5 to 55%, most preferably from 10 to 50%.
Preferably the LC medium contains 1 to 5, preferably 1, 2 or 3 compounds of formula AN.
In order to achieve a faster response time, a low rotational viscosity γ1 of the LC media and a low cell gap are required. LC media of prior art often use alkenyl and terphenyl compounds to satisfy these requirements.
However, these LC media have control problems due to reduced reliability and a drop of the VHR after UV stress. It was surprisingly found that these problems could be reduced when using a quaterphenyl compound of formula Q in the LC medium.
Thus, in addition to the compounds of formula AN, the LC medium according to the present invention comprises one or more quaterphenyl compounds of formula Q.
Preferred compounds of formula Q are those wherein RQ denotes straight-chain alkyl with 2 to 6 C-atoms, very preferably ethyl, n-propyl or n-butyl.
Preferred compounds of formula Q are those wherein LQ3 and LQ4 are F. Further preferred compounds of formula Q are those wherein LQ3, LQ4 and one or two of LQ1 and LQ2 are F.
Preferred compounds of formula Q are those wherein XQ denotes F or OCF3, very preferably F.
The compounds of formula Q are preferably selected from the following subformulae
wherein RQ has one of the meanings indicated in formula Q or one of its preferred meanings given above and below, and is preferably ethyl, n-propyl or n-butyl.
Especially preferred are compounds of formula Q1, in particular those wherein RQ is n-propyl.
Preferably the proportion of compounds of formula Q in the LC medium is from 0.1 to 5%, very preferably from 0.1 to 2%, most preferably from 0.2 to 1.5%. Higher concentrations of compounds of formula Q can negatively affect the solubility.
Preferably the LC medium contains 1 to 5, preferably 1 or 2 compounds of formula Q.
By using quaterphenyl compound of formula Q and its subformulae it is also possible to at least partially replace terphenyl compounds in the LC host mixture. Thereby it is possible to reduce ODF (one drop fill) mura, whilst maintaining high UV absorption and enabling quick and complete polymerization and strong tilt angle generation.
Thus, in a preferred embodiment of the present invention the LC medium does not contain more than 20% of terphenyl compounds.
In the compounds of formula S, Ra-d each denote preferably methyl or ethyl, very preferably methyl.
In the compounds of formula S, A preferably denotes straight-chain alkylene with 1 to 20 C-atoms, branched alkylene with 2 to 20 C atoms, or cyclic alkylene with 3 to 20 C atoms, all of which are optionally substituted by one or more groups LA.
In the compounds of formula S, A very preferably denotes straight-chain alkylene with 1 to 20 C-atoms or branched alkylene with 2 to 20 C atoms, all of which are optionally substituted by one or more groups LA.
Preferred substituents LA are selected from F, and straight-chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy and alkoxycarbonyloxy, each having up to 12 C atoms and in which one or more H atoms may each optionally be replaced by F or Cl.
Preferred compounds of formula S are selected from the following subformulae
wherein n1 is an integer from 2 to 12 and wherein one or more H-atoms in the radical (CH2)n1 are optionally replaced by a methyl, ethyl, propyl, butyl, pentyl or hexyl group.
Very preferred compounds of formula S are selected from the following subformulae
In a first preferred embodiment of the present invention, the compounds of formula S are selected from those wherein X is H or CH3, preferably H. Preferred compounds of this first preferred embodiment are those of formula S1 and S4, and subformulae S1a, S1b and S4a above.
In a second preferred embodiment of the present invention, the compounds of formula S are selected from those wherein X is O. or OH, preferably O.. Preferred compounds of this second preferred embodiment are those of formula S2 and S3, preferably S2, and subformulae S2a, S2b, S2c and S3a above. Especially preferred are compounds of formula S2a, S2b, S2c, most preferred those of formula S2a.
In a third preferred embodiment of the present invention, the compounds of formula S are selected from those wherein A is branched alkylene with 2 to 20 C atoms which is optionally substituted by one or more groups LA.
Preferred compounds of this second preferred embodiment are those of formula S5 below and those of subformulae S1b and S2c above.
wherein
X is H, CH3, OH or O., preferably H or O.,
RA is methyl, ethyl, propyl, butyl, pentyl or hexyl,
n2 is 0 or an integer from 1 to 12, preferably 0,
n3 is or an integer from 1 to 12.
Preferred compounds of formula S5 are those of subformulae S1b and S2c above.
Preferably the proportion of compounds of formula S or its subformulae in the LC medium is from 10 to 1000 ppm, very preferably from 20 to 500 ppm.
Preferably the LC medium contains 1 to 5, preferably 1, 2 or 3 compounds of formula S or its subformulae.
In another preferred embodiment of the present invention, in addition to the compounds of formula S, the LC medium contains one or more further stabilizers, preferably selected from the following formula
wherein n is an integer from 1 to 6, preferably 3.
Preferably the proportion of additional stabilizers, like those of formula SC, in the LC medium is from 10 to 500 ppm, very preferably from 20 to 100 ppm.
In another preferred embodiment of the present invention the LC medium additionally contains one or more compounds selected from formula AY
in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning:
or
or
Preferred compounds of formula AY selected from the following sub-formulae:
in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-7 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—.
In another preferred embodiment the LC medium comprises one or more compounds of formula AY selected from the following sub-formulae:
in which m and n each, independently of one another, denote 1, 2, 3, 4, 5 or 6, and alkenyl 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—.
The LC medium preferably comprises no compounds containing a terminal vinyloxy group (—O—CH═CH2), in particular no compounds of the formula AN or AY in which RA1 or RA2 denotes or contains a terminal vinyloxy group.
Some further preferred embodiments of the mixtures according to the invention are indicated below.
denotes or
or
Preferably, 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.
The compounds of the formula CY are preferably selected from the group consisting of the following sub-formulae:
The compounds of the formula PY are preferably selected from the group consisting of the following sub-formulae:
denotes
or
denotes
or
The compounds of the formula ZK are preferably selected from the group consisting of the following sub-formulae:
Especially preferred are compounds of formula ZK1.
Particularly preferred compounds of formula ZK are selected from the following sub-formulae:
wherein the propyl, butyl and pentyl groups are straight-chain groups.
Most preferred are compounds of formula ZK1a.
denotes
or
denotes
or
and
The compounds of the formula DK are preferably selected from the group consisting of the following sub-formulae:
denotes
or
Preferably, both radicals L1 and L2 denote F or 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:
The proportion of the biphenyls of the formulae B1 to B3 in the LC mixture is preferably at least 3% by weight, in particular ≧5% by weight.
The compounds of the formula B2 are particularly preferred.
The compounds of the formulae B1 to B3 are preferably selected from the group consisting of the following sub-formulae:
and
each, independently of one another, denote
or
The compounds of the formula T are preferably selected from the group consisting of the following sub-formulae:
Preferred are compounds of formulae T1, T2, T3, T21 and T23, wherein R is preferably alkyl or alkoxy having 1-5 C atoms and R* is preferably CH2═CH—, CH2═CHCH2CH2—, CH3—CH═CH— or CH3—CH2—CH═CH—.
Preferably the LC medium does not contain more than 20% of a terphenyl compound of formula T or any other compound with a terphenyl group.
Preferred media comprise one or more compounds selected from the formulae O1, O3 and O4.
in which
denotes
Particularly preferred compounds of the formula FI are selected from the group consisting of the following sub-formulae:
Particularly preferred compounds of the formulae BC, CR and RC are selected from the group consisting of the following sub-formulae:
Very particular preference is given to mixtures comprising one, two or three compounds of the formula BC-2.
Particularly preferred compounds of the formulae PH and BF are selected from the group consisting of the following sub-formulae:
Preferably, both L1 and L2 denote F or one of L1 and L2 denotes F and the other denotes Cl,
The compounds of the formula Y are preferably selected from the group consisting of the following sub-formulae:
Particularly preferred compounds of the formula Y are selected from the group consisting of the following sub-formulae:
wherein Alkoxy preferably denotes straight-chain alkoxy with 3, 4, or 5 C atoms.
In a preferred embodiment of the present invention the LC medium additionally comprises one or more polymerizable compounds.
The polymerizable compounds are preferably selected from formula M
Ra—B1—(Zb—B2)m—Rb M
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 M 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, coumarine, flavone, where, in addition, one or more CH groups in these groups may each be replaced by N, cyclohexane-1,4-diyl, in which, in addition, one or more non-adjacent CH2 groups may each be replaced by O 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:
Especially preferred are compounds of formulae M2 and M13.
Further preferred are trireactive 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
or
wherein 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 wherein 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 wherein Sp1, Sp2 and Sp3 are a single bond.
Further preferred compounds of formulae M1 to M31 are those wherein one of Sp1, Sp2 and Sp3 is a single bond and another one of Sp1, Sp2 and Sp3 is different from a single bond.
Further preferred compounds of formulae M1 to M31 are those wherein those groups Sp1, Sp2 and Sp3 that are different from a single bond denote —(CH2)s1—X″—, wherein s1 is an integer from 1 to 6, preferably 2, 3, 4 or 5, and X″ is the linkage to the benzene ring and is —O—, —O—CO—, —CO—O—, —O—CO—O— or a single bond.
Further preferred polymerizable compounds of formulae M1 to M31 are those selected from Table D below.
Particular preference is given to LC media comprising one, two or three polymerizable compounds of formula M, preferably selected from formulae M1 to M31.
Preferably the proportion of polymerizable compounds of formula M in the LC medium 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 combination of polymerisable compounds of formula M with the alkenyl compound of formula AN and the quaterphenyl compound of formula Q leads to advantageous behavior of the LC medium, where a quick and complete polymerization, the quick generation of a low pretilt angle which is stable after UV exposure, at the same time a high reliability and high VHR value after UV exposure can be achieved together with a high birefringence. Besides, the LC medium shows high absorption at longer UV wavelengths, so that it is possible to use such longer UV wavelengths for polymerization, which is advantageous for the display manufacturing process.
The polymerizable group P is a group which is suitable for a polymerization reaction, such as, for example, free-radical or ionic chain polymerization, 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 polymerization, in particular those containing a C═C double bond or —C≡C— triple bond, and groups which are suitable for polymerization 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 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, 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—,
and
Further preferred polymerizable 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″—, wherein
X″ is preferably —O—, —S—, —CO—, —COO—, —OCO—, —O—COO—, —CO—NR0—, —NR0—CO—, —NR0—CO—NR00— or a single bond.
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)p1—, —(CH2)p1—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, ethyleneoxyethyl-ene, methyleneoxybutylene, ethylenethioethylene, ethylene-N-methylimino-ethylene, 1-methylalkylene, ethenylene, propenylene and butenylene.
For the production of PSA displays, the polymerizable compounds contained in the LC medium are polymerized or crosslinked (if one compound contains two or more polymerizable groups) by in-situ polymerization in the LC 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 color 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.
Preferably the proportion of the polymerizable compounds in the LC medium is from >0 to <5%, very preferably from >0 to <1%, most preferably from 0.01 to 0.5%.
Preference is given to LC media which have a nematic LC phase, and preferably have no chiral liquid crystal phase.
The combination of compounds of the preferred embodiments mentioned above with the polymerized compounds described above causes low threshold voltages, low rotational viscosities and very good low-temperature stabilities in the LC media according to the invention at the same time as constantly high clearing points and high VHR values.
The use of LC media containing polymerizable compounds allows the rapid establishment of a particularly low pretilt angle in PSA displays. In particular, the LC 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.
The LC media and LC host mixtures of the present invention preferably have a nematic phase range of at least 80 K, particularly preferably at least 100 K, and a rotational viscosity ≦250 mPa·s, preferably ≦200 mPa·s, at 20° C.
In the VA-type displays according to the invention, the molecules in the layer of the LC medium in the switched-off state are aligned perpendicular to the electrode surfaces (homeotropically) or have a tilted homeotropic alignment. On application of an electrical voltage to the electrodes, a realignment of the LC molecules takes place with the longitudinal molecular axes parallel to the electrode surfaces.
The LC media according to the invention are preferably based on compounds with negative dielectric anisotropy, are in particular suitable for use in displays of the PS-VA and PS-UB-FFS (polymer stabilized ultra brightness fringe field switching) type, and preferably have a negative dielectric anisotropy Δ∈, very preferably from −0.5 to −10, most preferably from −2.5 to −7.5, at 20° C. and 1 kHz.
The birefringence Δn in LC media according to the invention, especially for use in displays of the PS-VA and PS-UB-FFS type, is preferably below 0.16, particularly preferably from 0.06 to 0.14, very particularly preferably from 0.07 to 0.12.
The LC media according to the invention may also comprise further additives which are known to the person skilled in the art and are described in the literature, such as, for example, polymerization initiators, inhibitors, stabilizers, surface-active substances or chiral dopants. These may be polymerizable or non-polymerizable.
In a preferred embodiment the LC media contain one or more chiral dopants, preferably in a concentration from 0.01 to 1%, very preferably from 0.05 to 0.5%. 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 LC media contain a racemate of one or more chiral dopants, which are preferably selected from the chiral dopants mentioned in the previous paragraph.
Furthermore, it is possible to add to the LC media, for example, 0 to 15% by weight of pleochroic dyes, furthermore nanoparticles, conductive salts, preferably ethyldimethyldodecylammonium 4-hexoxybenzoate, tetrabutyl-ammonium 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.
The individual components of the preferred embodiments a)-z) of the LC media according to the invention are either known or methods for the preparation thereof can readily be derived from the prior art by the person skilled in the relevant art, since they are based on standard methods described in the literature. Corresponding compounds of the formula CY are described, for example, in EP-A-0 364 538. Corresponding compounds of the formula ZK are described, for example, in DE-A-26 36 684 and DE-A-33 21 373.
The LC 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 of the above-mentioned compounds with one or more polymerizable compounds as defined above, and optionally 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 invention furthermore relates to the process for the preparation of the LC media according to the invention.
It goes without saying to the person skilled in the art that the LC media according to the invention may also comprise compounds in which, for example, H, N, O, Cl, F have been replaced by the corresponding isotopes like deuterium etc.
The following examples explain the present invention without restricting it. However, they show the person skilled in the art preferred mixture concepts with compounds preferably to be employed and the respective concentrations thereof and combinations thereof with one another. In addition, the examples illustrate which properties and property combinations are accessible.
The following abbreviations are used:
(n, m, z: in each case, independently of one another, 1, 2, 3, 4, 5 or 6)
In a preferred embodiment of the present invention, the LC media according to the invention comprise one or more compounds selected from the group consisting of compounds from Table A.
The LC media preferably comprise 0 to 10% by weight, in particular 0.01 to 5% by weight, particularly preferably 0.1 to 3% by weight, of dopants. The LC media preferably comprise one or more dopants selected from the group consisting of compounds from Table B.
The LC media preferably comprise 0 to 10% by weight, in particular 1 ppm to 5% by weight, particularly preferably 1 ppm to 1% by weight, of stabilizers. The LC media preferably comprise one or more stabilizers selected from the group consisting of compounds from Table C.
In a preferred embodiment of the present invention, the mesogenic media comprise one or more compounds selected from the group of the compounds from Table D. Very preferably the LC medium comprises a compound selected from formulae RM-1, RM-2, RM-3, RM-4, RM-5, RM-9, RM-17, RM-42, RM-48, RM-68, RM-87, RM-91, RM-98, RM-99 and RM-101.
In addition, the following abbreviations and symbols are used:
Unless explicitly noted otherwise, all concentrations in the present application are quoted in percent by weight and relate to the corresponding mixture as a whole, comprising all solid or liquid-crystalline components, without solvents.
Unless explicitly noted otherwise, all temperature values indicated in the present application, such as, for example, for the melting point T(C,N), the transition from the smectic (S) to the nematic (N) phase T(S,N) and the clearing point T(N,I), are quoted in degrees Celsius (° C.). 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.
All physical properties are and have been 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., and Δn is determined at 589 nm and Δ∈ at 1 kHz, unless explicitly indicated otherwise in each case.
The term “threshold voltage” for the present invention relates to the capacitive threshold (V0), also known as the Freedericks threshold, unless explicitly indicated otherwise. In the examples, the optical threshold may also, as generally usual, be quoted for 10% relative contrast (V10).
The display used for measurement of the capacitive threshold voltage consists of two plane-parallel glass outer plates at a separation of 25 μm, each of which has on the inside an electrode layer and an unrubbed polyimide alignment layer on top, which effect a homeotropic edge alignment of the liquid-crystal molecules.
The VHR value is measured as follows: The LC mixture is introduced into VA-VHR test cells which comprise an unrubbed VA-polyimide alignment layer. The LC-layer thickness d is approx. 3 μm, unless stated otherwise. The VHR value is determined before and after light exposure at 1 V, 60 Hz, 64 μs pulse (measuring instrument: Autronic-Melchers VHRM-105).
The nematic LC mixture N1 is formulated as follows.
The mixture does not contain a quaterphenyl compound of formula Q.
The nematic LC mixture N2 is formulated as follows.
To 100% of the LC mixture N2 are added 0.005% (50 ppm) of a stabilizer of formula S2a to form mixture M1.
To 99.99% of the LC mixture N2 are added 0.01% (100 ppm) of a stabilizer of formula S2a to form mixture M2.
To 99.975% of the LC mixture N2 are added 0.025% (250 ppm) of a stabilizer of formula S1a to form mixture M3.
The LC mixture compositions are shown in Table 1.
The mixture of example C1 is a comparison mixture which does not contain a quaterphenyl compound of formula Q1, and does not contain a stabilizer.
The mixture of example C2 is a comparison mixture which contains a quaterphenyl compound PPGU-3-F of formula Q1, but does not contain a stabilizer.
The mixtures of examples M1, M2 and M3 according to the invention contain both a quaterphenyl compound PPGU-3-F of formula Q1, and a stabilizer of formula S2a or S1a, respectively.
The mixtures were filled into test VA-VHR cells as described above, and the VHR values were measured before and after UV load, suntest and backlight load test, respectively, as follows:
For the UV load the test cells were exposed to a high pressure Hg lamp (300 nm ˜400 nm) with 50 mW/cm2 for 120 s (6J) and 600 s (30J).
For the suntest the test cells were exposed to a Xenon lamp (300 nm˜800 nm) with 765W/m2 for 1 hr.
For the backlight load test the test cells were exposed to an LED backlight unit as used in an LCD TV panel for 24 hrs, 168 hrs, 336 hrs, 500 hrs and 1000 hrs.
Table 2 shows the results of the UV load test for the mixtures of examples C1 and C2.
From Table 2 it can be seen that mixture of example C2 with a quaterphenyl compound shows a slightly higher VHR value after UV load than the mixture of example C1 without a quaterphenyl compound.
This shows that the addition of the quaterphenyl to the mixture leads to an improved VHR.
Table 3 shows the results of the UV load test for the mixtures of examples C2, M1 and M2.
Table 4 shows the results of the suntest for the mixtures of examples C2, M1 and M2.
Table 5 shows the results of the backlight load test for the mixtures of examples C2, M1 and M2.
From Tables 3-5 it can be seen that the mixtures of examples M1 and M2 with a quaterphenyl compound of formula Q1 and a stabilizer of formula S2a show a significantly higher VHR value after UV load, suntest and backlight load, compared to the mixture of example C2 with a quaterphenyl compound of formula Q1, but without a stabilizer.
This shows that the addition of both a quaterphenyl of formula Q and a stabilizer of formula S to the mixture lead to an significantly improved VHR after UV load, suntest and backlight load.
Table 6 shows the results of the UV load test for the mixtures of examples C2 and M3.
Table 7 shows the results of the suntest for the mixtures of examples C2 and M3.
From Tables 6 and 7 it can be seen that the mixture of example M3 with a quaterphenyl compound of formula Q1 and a stabilizer of formula S1 shows a significantly higher VHR value after UV load and suntest than the mixture of example C2 with a quaterphenyl compound of formula Q1, but without a stabilizer.
This shows that the addition of both a quaterphenyl of formula Q and a stabilizer of formula S to the mixture lead to an significantly improved VHR after UV load and suntest.
The entire disclosures of all applications, patents and publications, cited herein and of corresponding European Application No. EP 16170155.2, filed May 18, 2016 are incorporated by reference herein.
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 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 |
|---|---|---|---|
| 16170155.2 | May 2016 | EP | regional |
