Patent Application
20200339882
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, SA-VA, IPS, PS-IPS, FFS, PS-FFS, UB-FFS or PS-UB-FFS 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 Δε≤−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 aircraft 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.
Another problem which could be observed in TFT displays like those of the UB-FFS mode is the appearance of flicker, which is a time dependent variation in brightness, i.e. the brightness fluctuates during the charging and holding periods in display operation. The main reasons causing flicker include generation of residual DC charge for example due to impurities, an asymmetric voltage between the electrodes or a flexoelectric effect. The flicker induced by the flexoelectric effect can be evaluated by the so-called white flicker method as described in the example section.
Another problem is the occurrence of image sticking (or image burn), wherein the image produced in the LC display by temporary addressing of individual pixels still remains visible even after the electric field in these pixels has been switched off or after other pixels have been addressed. This can be evaluated by measuring the easy axis shift, which indicates the difference between the initial off-state orientation direction of the LC molecules relative to the substrate and their off-state orientation after several addressing cycles.
The invention provides 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 for monitors and televisions the mixtures allow the displays to operate at extremely high and extremely low temperatures and at the same time to have short response times and improved reliability behavior, in particular no or significantly reduced image sticking after long operating times.
The LC medium as described and claimed hereinafter provides these features.
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 stabilised)-VA, SA (=self alignment)-VA, IPS, PS-IPS, PS-FFS, FFS mixtures, in particular UB-FFS (ultra brightness fringe field switching) or PS-UB-FFS mixtures, which have short response times and good reliability, and 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 having negative dielectric anisotropy and comprising one or more compounds of formula LB
in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning:
The invention further relates to the use of an LC medium as described above and below used for electro-optical purposes, in particular for the use in shutter glasses, for 3D applications, or in VA, PS-VA, SA-VA, IPS, PS-IPS, FFS, PS-FFS, UB-FFS or PS-UB-FFS displays.
The invention further relates to an electro-optical LC display containing an LC medium as described above and below, in particular an VA, PS-VA, SA-VA, IPS, PS-IPS, FFS, PS-FFS, UB-FFS or PS-UB-FFS display.
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 LB with one or more further LC compounds and optionally one or more additives.
The LC media 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 LC media 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 LC media 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 LB are selected from the following subformulae:
wherein R1 has one of the meanings given in formula LB and preferably denotes straight-chain alkyl having 1-6 C atoms, very preferably methyl, ethyl, propyl, butyl, pentyl or hexyl, more preferably ethyl or propyl, most preferably propyl.
Very preferred compounds of formula LB are selected from the following subformulae:
wherein R1 has one of the meanings given in formula LB and preferably denotes straight-chain alkyl having 1-6 C atoms, very preferably methyl, ethyl, propyl, butyl, pentyl or hexyl, more preferably ethyl or propyl, most preferably propyl.
Most preferred are compounds of formulae LB-1-1 and LB2-2.
The total proportion of the compounds of formula LB, LB1, LB2 and their subformulae in the LC medium is from >0 to ≤5%, preferably from 0.05 to 4%, very preferably from 0.1 to 3%, more preferably from 0.1 to 2%, most preferably from 0.5 to 1%, by weight.
Preferably the LC medium contains 1, 2 or 3 compounds of formula LB, LB1, LB2 or their subformulae.
In another preferred embodiment of the present invention the LC medium comprises one or more compounds of formula LB1 or its subformulae and one or more compounds of formula LB2 or its subformulae.
In the LC medium according to the present invention one or more of the following advantages could be achieved:
In a preferred embodiment of the present invention the LC medium comprises one or more comprising an alkenyl group, preferably selected from formula AN and AY:
in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning:
Preferred compounds of formula AN and AY are those wherein RA2 is selected from ethenyl, propenyl, butenyl, pentenyl, hexenyl and heptenyl.
Further preferred compounds of formula AN and AY are those wherein L1 and L2 denote F, or one of L1 and L2 denotes F and the other denotes Cl, and L3 and L4 denote F, or one of L3 and L4 denotes F and the other denotes Cl.
The compounds of the formula AN are preferably 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, 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 compounds of the formula AN are selected from the following sub-formulae:
in which m denotes 1, 2, 3, 4, 5 or 6, i denotes 0, 1, 2 or 3, and Rb1 denotes H, CH3 or C2H.
Very particularly preferred compounds of the formula AN are selected from the following sub-formulae:
Most preferred are compounds of formula AN1a2, AN1a5, AN6a1 and AN6a2.
In a preferred embodiment the LC medium contains one or more compounds selected from formula AN1a2, AN1a5 and AN1a6.
Preferably the LC medium or LC host mixture contains 1 to 5, preferably 1, 2 or 3 compounds selected of formula AN or its subformulae.
The proportion of the compounds of formula AN in the LC medium is preferably from 5 to 70%, more preferably from 10 to 60%, most preferably from 20 to 60%.
The compounds of the formula AY are preferably 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, 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 compounds of the formula AY are 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 proportion of compounds of formula AY in the LC medium is preferably from 2 to 50% by weight, very preferably from 5 to 40% by weight, most preferably from 5 to 30% by weight.
Preferably the LC medium or LC host mixture contains 1 to 5, preferably 1, 2 or 3 compounds selected of formula AY or its subformulae.
In a preferred embodiment of the present invention the LC medium comprises one or more compounds of formula AY14, very preferably of AY14a. The proportion of compounds of formula AY14 or AY14a in the LC medium is preferably from 3 to 30% by weight.
The addition of alkenyl compounds of formula AN and/or AY enables a reduction of the viscosity and response time of the LC medium.
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 (—O—CH═CH2).
Further preferred embodiments of the LC medium according to the present invention are those of sections a)-z) below, including any combination thereof:
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 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 polymerisable 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 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 VA, UB-FFS, PS-VA and PS-UB-FFS type, and preferably have a negative dielectric anisotropy Δε, 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 VA, UB-FFS, 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, polymerisation initiators, inhibitors, stabilisers, surface-active substances or chiral dopants. These may be polymerisable or non-polymerisable.
In a preferred embodiment of the present invention the LC medium additionally comprises one or more polymerisable compounds.
The polymerisable 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 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, coumarine, 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:
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, M31 and M32.
In the compounds of formulae M1 to M32 the group
is preferably
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 oder OCF3, especially F or CH3.
Preferred compounds of formulae M1 to M32 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 M32 are those wherein Sp1, Sp2 and Sp3 are a single bond.
Further preferred compounds of formulae M1 to M32 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 M32 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 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 LC media comprising one, two or three polymerisable compounds of formula M, preferably selected from formulae M1 to M32.
Further preferred polymerisable compounds are listed in Table D below.
Preferably the proportion of polymerisable compounds 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%.
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—NHCH2═CW1—CO—NH—, CH3—CH═CH—O—, (CH2═CH)2CH—OCO—, (CH2═CHCH2)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—,
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″—, 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, ethyleneoxyethylene, methyleneoxybutylene, ethylenethioethylene, ethylene-N-methyliminoethylene, 1-methylalkylene, ethenylene, propenylene and butenylene.
For the production of PSA displays, the polymerisable compounds contained in the LC medium are polymerised or crosslinked (if one compound contains two or more polymerisable groups) by in-situ polymerisation 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 polymerisable compounds in the LC medium is from >0 to <5%, very preferably from >0 to <1%, most preferably from 0.01 to 0.5%.
Optionally one or more polymerisation initiators are added to the LC medium. Suitable conditions for the polymerisation and suitable types and amounts of initiators are known to the person skilled in the art and are described in the literature. Suitable for free-radical polymerisation are, for example, the commercially available photoinitiators Irgacure651@, Irgacure184@, Irgacure907, Irgacure369@ or Darocure1173@ (Ciba AG). If a polymerisation initiator is employed, its proportion is preferably 0.001 to 5% by weight, particularly preferably 0.001 to 1% by weight.
In another preferred embodiment the LC medium does not contain a polymerisation initiator.
The LC medium may also comprise one or more stabilisers. Suitable types and amounts of stabilisers are known to the person skilled in the art and are described in the literature. Particularly suitable are, for example, the commercially available stabilisers from the Irganox® series (Ciba AG), such as, for example, Irganox®1076. If stabilisers are employed, their proportion is preferably 10-500,000 ppm, more preferably 50-5,000 ppm, very preferably 50-1,000 ppm.
In another preferred embodiment of the present invention the LC medium contains one or more stabilisers selected from Table C below.
In another preferred embodiment of the present invention the LC medium contains one or more stabilisers selected from the the group consisting of the following formulae
wherein the individual radicals, independently of each other and on each occurrence identically or differently, have the following meanings
Preferred stabilisers of formula S3 are selected from formula S3A
wherein n2 is an integer from 1 to 12, and wherein one or more H atoms in the group (CH2)n2 are optionally replaced by methyl, ethyl, propyl, butyl, pentyl or hexyl.
Very preferred stabilisers are selected from the group consisting of the following formulae
In a preferred embodiment the liquid-crystalline medium comprises one or more stabilisers selected from the group consisting of formulae S1-1, S2-1, S3-1, S3-1 and S3-3.
In a preferred embodiment the liquid-crystalline medium comprises one or more stabilisers selected from Table C below.
Preferably the proportion of stabilisers, like those of formula S1-S3, 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 one or more SA additives selected from formula II or its subformulae. The concentration of the SA additives in the LC medium is preferably from 0.1 to 5%, very preferably from 0.2 to 3%, most preferably from 0.2 to 1.5%.
In a preferred embodiment the LC medium or display according to the present invention contains one or more SA additives selected from Table F below.
In another preferred embodiment the SA-VA or SA-FFS display according to the present invention does not contain a polyimide alignment layer.
Preference is given to LC media which have a nematic LC phase, and preferably have no chiral liquid crystal phase.
In another 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, 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.
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 polymerisable 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 construction of an LC 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 LC display, in particular including matrix display elements based on poly-Si TFTs or MIM.
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.
Above and below, percentage data denote percent by weight; all temperatures are indicated in degrees Celsius.
Throughout the patent application and in the working examples, the structures of the liquid-crystal compounds are indicated by means of acronyms. Unless indicated otherwise, the transformation into chemical formulae takes place in accordance with Tables I-III. All radicals CnH2c+1, CmH2m+1, CnH2n, CmH2m and CkH2k are straight-chain alkyl radicals or alkenyl radicals respectively, in each case having n, m or k C atoms; n and m each, independently of one another, denote 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, preferably 1, 2, 3, 4, 5 or 6, and k is 0, 1, 2, 3, 4, 5 or 6. In Table I the ring elements of the respective compound are coded, in Table the bridging members are listed and in Table III the meanings of the symbols for the left-hand and right-hand side chains of the compounds are indicated.
Preferred mixture components are shown in Table A.
Particular preference is given to liquid-crystalline mixtures which comprise at least one, two, three, four or more compounds from Table A.
Table B indicates possible dopants which are generally added to the mixtures according to the invention. The mixtures preferably comprise 0-10% by weight, in particular 0.001-5% by weight and particularly preferably 0.001-3% by weight, of dopants.
In a preferred embodiment, the mixtures according to the invention comprise one or more polymerizable compounds, preferably selected from the polymerizable compounds of the formulae RM-1 to RM-140. Of these, compounds RM-1, RM-4, RM-8, RM-17, RM-19, RM-35, RM-37, RM-39, RM-40, RM-41, RM-42, RM-50, RM-53, RM-54, RM-56, RM-59, RM-66, RM-76, RM-78, RM-90, RM-93, RM-104, RM-105, RM-111, RM-119, RM-122, RM-123 and RM-124 are particularly preferred.
In a preferred embodiment, the LC media and displays according to the present invention comprise one or more SA additives selected from formulae SA-1 to SA-48, preferably from formulae SA-14 to SA-48, very preferably from formulae SA-20 to SA-34 and SA-48, preferably in combination with one or more RMs of formula M.
The following examples are intended to explain the invention without limiting it.
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 entire disclosures of all applications, patents and publications, cited herein and of corresponding European application No. 19171252.0, filed Apr. 26, 2019, are incorporated by reference herein.
Above and below, unless explicitly noted otherwise, all percentage data denote percent by weight, and relate to the corresponding mixture as a whole, comprising all solid or liquid-crystalline components, without solvents. Furthermore, unless explicitly noted otherwise, all temperatures are indicated in 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.
In addition, the following abbreviations and symbols are used:
All physical properties are and have been determined in accordance with “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Status November 1997, Merck KGaA, Germany, and apply for a temperature of 20° C. 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).
Unless stated otherwise, methods of preparing test cells and measuring their electrooptical and other properties are carried out by the methods as described hereinafter or in analogy thereto.
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 host mixture C1 is formulated as follows.
The LC mixture N1 is formulated by mixing 99.5% of the LC host mixture C1 and 0.5% of the compound LB(S)-3-OT of formula LB2-2.
The LC mixture N2 is formulated by mixing 99.0% of the LC host mixture C1 and 1.0% of the compound LB(S)-3-OT of formula LB2-2.
The LC mixture N3 is formulated by mixing 97.0% of the LC host mixture C1 and 3.0% of the compound LB(S)-3-OT of formula LB2-2.
The LC mixture N4 is formulated by mixing 99.5% of the LC host mixture C1 and 0.5% of the compound LB-3-T of formula LB1-1.
The LC mixture N5 is formulated by mixing 99.0% of the LC host mixture C1 and 1.0% of the compound LB-3-T of formula LB1-1.
The LC mixture N6 is formulated by mixing 97.0% of the LC host mixture C1 and 3.0% of the compound LB-3-T of formula LB1-1.
VHR Values
The VHR values of mixtures C1 and N1 to N3 are measured at 60° C., 3 Hz in UB-FFS VHR test cells before and after light exposure for varying time using a LED lamp.
The results are shown in Table 1.
From Table 1 it can be seen that the mixtures N1 to N3 according to the present invention show VHR values which are comparable to those of reference mixture C1.
White Flicker
The white flicker values of mixtures C1 and N1 to N3 are measured at 25° C., 10 Hz with V100 voltage loading in UB-FFS test cells.
The results are shown in Table 2.
From Table 2 it can be seen that the mixtures N1 to N3 according to the present invention show significantly reduced white flicker compared to reference mixture C1.
Easy Axis Shift by AC Loading
The easy axis shift ΔΦ of mixtures C1 and N1 to N3 are measured at 0 voltage, room temperature for 90 min after stress which 10 Vrms for 2 hrs at 30 Hz in UB-FFS test cell.
The results are shown in Table 3.
From Table 3 it can be seen that the mixtures N1 to N3 according to the present invention show lower easy axis shift ΔΦ compared to reference mixture C1.
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 |
|---|---|---|---|
| 19171252.0 | Apr 2019 | EP | regional |
