Patent Grant
9714381
The invention relates to a liquid-crystalline medium for LC displays, especially for displays without any orientation layer, i.e. polyimide layer which contain at least one self-aligning additive.
Media of this type can be used, in particular, for electro-optical displays having active-matrix or passive-matrix addressing based on the ECB effect.
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).
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 colour-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., SORI-MACHI, 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 reliability of liquid crystal (LC) mixtures is one of the major issues in today's LCD industry. A main aspect is the stability of the liquid crystal molecules towards the light emitted from the backlight unit of the LCD. Light induced reactions of the LC material can cause display defects known as image sticking. This strongly reduces the lifetime of the LCD and is one of the main reliability criterions in LCD industry.
For example, liquid crystal mixtures containing LC materials with alkenyl-moieties often show some kind of degradation during long term backlight irradiation. This degradation can be observed by measuring the Voltage Holding Ratio (VHR) of the LC mixtures which have been objected to backlight irradiation for a defined time period.
Also other kinds of irradiation, like the UV-light, necessary for the curing of reactive mesogens (RMs), especially for the PS-VA technology, may lead to a reduction of the VHR values of a test-cell or of a display. The use of cut-filters in order to reduce this effect is of limited applicability. By increasing the wavelength of the curing-light the VHR is improved, but at the same time the reaction speed of the RMs is reduced and this effect does not fit with the requirements of the LCD industry.
Thus, a solution is needed by which the light induced degradation of a LC mixture is strongly reduced. Especially, in terms of LCD performance, there is an interest to use liquid-crystalline compounds containing an alkenyl side chain in order to achieve faster switching times and hence better moving picture performances. Especially since the trend for LCD TC clearly is to go to higher frame rates, e.g. 200 Hz or higher, also including 3D applications.
The invention thus has an object of providing self-aligning additives and liquid-crystal mixtures, in particular for monitor and TV applications, which are based on the ECB effect especially for VA, PSA and PS-VA applications, 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 have short response times and at the same time have improved reliability behaviour, in particular have no or significantly reduced image sticking after long operating times.
In conventional VA-displays a polyimide (Pl) layer is needed for inducing the required homeotropic orientation of the LC. Beside the significant costs due to its production, unfavourable interaction between Pl and LC often leads to a reduction of the electric resistance of the VA-display. The number of useful LC molecules is thus significantly reduced, at the expenses of the overall switching performances (e.g. higher switching times) of the display. Getting rid of Pl is thus desirable, while providing an alternative for the required homeotropic orientation.
It has now been found that these and other objects can be achieved if LC media according to the invention are used in LC displays, especially in displays without any orientation layer (polyimide layer).
LC mixtures which contain at least one compound of the formula I are already known from WO 2014/090362 A1. Contrary to the mixtures of the prior art the LC mixtures of the present invention combines the use of the aligning additive and of relatively large amounts of materials to enhance to clearing temperature by maintaining a good low temperature stability of at least 1000 h at −20° C. so that the mixtures are preferably suitable for outdoor use.
The present invention MAKES it possible to provide such mixtures with high clearing points of preferably >80° C. and good low temperature stability (LTS).
The invention thus relates to a liquid-crystalline medium which contains
in which
in which
Preferred LC mixtures according to the present invention are characterized by a negative dielectrically anisotropy (Δ∈).
Such kinds of mixtures are highly suitable for the use in displays which do not contain any orientation layer. Liquid crystal display devices, in general have a structure in which a liquid crystal mixture is sealed between a pair of insulating substrates, such as glass substrates, in such a manner that the liquid crystal molecules thereof are orientated in a predetermined direction, and an orientation film is formed on the respective substrates on the side of the liquid crystal mixture. As a material of an orientation film, there is usually used a polyimide (Pl). Homeotropic orientation of the LC molecules is especially necessary for LC modes like PVA, PS-VA, VA, PM (passive matrix)-VA, etc., and can be achieved by the use of self-aligning additives, without the need of an orientation film. The mixtures according to the invention show an improved light and temperature stability compared to LC mixtures without any self-aligning additives.
In a preferred embodiment, the LC mixture according to the invention contains additionally at least one polymerisable compound (also called reactive mesogen (RM)). Such kinds of LC mixtures are highly suitable for Pl-free PS-VA displays. The alignment of the LC molecules is induced by the self-aligning additives and the induced orientation (pre-tilt) may be additionally tuned or stabilized by the polymerization of the RMs, under conditions suitable for a multidomain switching. By the tuning of the UV-curing conditions it is possible in one single step to improve simultaneously switching time and contrast ratio. Reliability of the mixture (VHR) after light stress (both UV-curing and Backlight (BLT)) is improved compared to LC mixtures without any self-aligning additive filled in a “classical” Pl-coated test cell. Furthermore, the UV-curing may be performed by using cut-filters at a wavelength by which the polymerization of the RMs is still reasonably fast and the VHR values are on an acceptable level.
The mixtures according to the invention preferably exhibit very broad nematic phase ranges having clearing points ≧70° C., preferably ≧80° C., in particular ≧90° C., very favourable 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 relatively low rotational viscosities and short response times.
Some preferred embodiments of the mixtures according to the invention are indicated below.
In the compounds of the formulae I R1 preferably denotes straight-chain alkyl, in particular CH3, C2H5, n-C3H7, n-C4H9, n-C5H11, n-C6H13, furthermore alkenyloxy, in particular OCH2CH═CH2, OCH2CH═CHCH3, OCH2CH═CHC2H5, alkoxy, in particular OC2H5, OC3H7, OC4H9, OC5H11 and OC6H13.
In the compounds of the formula I L1, L2 and L3 are each independently preferably H or F or alkyl with 1-5 carbon atoms. In the compounds of the formula I L1, L2 and L3 denotes most preferably H.
m is preferably 0 or 1.
Preferred compounds of the formula I are the compounds of the sub-formulae I-1 to I-36,
in which
R1 has the meanings given in Claim 1, preferably denotes a straight-chain alkyl radical having 1-7 C atoms.
The mixture according to the invention very particularly contains at least one self-aligning additive selected from the following group of compounds of the sub-formulae
in which
alkyl denotes a straight-chain alkyl radical having 1 to 7 carbon atoms, preferably C2H5, n-C3H7, n-C4H9, n-C5H11, n-C6H13 or n-C7H15, most preferably n-C3H7.
Especially preferred mixtures contain a compound of the formula I-2a-1
The compounds of the formula I can be prepared by methods known per se, which are described in standard works for organic chemistry as such, for example, Houben-Weyl, Methoden der organischen Chemie, Thieme-Verlag, Stuttgart.
The compounds of the formula I can be prepared for example as follows:
The media according to the invention preferably contain one, two, three, four or more, preferably one, self-aligning additive, preferably selected from the compounds of the formulae I-1 to I-36.
The self-aligning additives of the formula I are preferably employed in the liquid-crystalline medium in amounts of ≧0.01% by weight, preferably 0.1-10% by weight, based on the mixture as a whole. Particular preference is given to liquid-crystalline media which contain 0.1-5%, preferably 0.1-4%, by weight of one or more self-aligning additives, based on the total mixture, especially additives which are selected from the group of compounds of the formula I-1 to I-36.
The use of preferably 2.5 to 5% by weight of the compounds of the formula I results in a complete homeotropic alignment of the LC layer for conventional LC thickness (3 to 4 μm) and for the substrate materials used in the display industry. Special surface treatment may allow to significantly reduce the amount of the compound(s) of the formula I which means less than 2.5% by weight.
Preferred compounds of the formulae I-A to I-K are the compounds of the formula
in which
alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms,
alkoxy or O-alkyl denotes a straight-chain alkoxy radical having 1-6 C atoms and
L1 and L2 each, independently of one another, denote H, F, Cl, CF3 or CHF2, preferably H or F.
In particular, the following compounds of the formula I-A are preferred
wherein
alkyl, alkyl* and alkoxy have the meanings indicated above.
Preferred sub-formulae of the formula I-A are the compounds of the formula I-A-2a, I-A-4a, I-A-6a and I-A-7a.
Preferred mixtures contain at least one compound of the formula I-A-2a and/or at least one compound of the formula I-A-4a.
Preferred mixtures contain at least one compound of the formula IA-4a and at least one compound of the formula I-A-7a.
Preferred mixtures contain at least one compound of the formula I-A-2a and at least one compound of the formula I-A-4a and at least one compound of the formula I-A-7a.
Especially preferred mixtures contain at least one compound of the formula IA-2a and at least one compound of the formula I-A-4a.
Especially preferred mixtures contain at least one compound of the formula I-A-2a and at least one compound of the formula I-A-4a and at least one compound of the formula I-B-1.
The media according to the invention preferably comprise one, two, three, four or more, preferably one, two or three, compounds of the formula I.
The media according to the invention preferably comprise one, two, three, four or more, preferably one, two or three, compounds of the formulae I-A.
The media according to the invention preferably comprise one, two, three, four or more, preferably one or two compounds of the formula I-B.
The compounds of the formula I-A are preferably employed in the liquid crystalline medium in amounts of 5-60% by weight, preferably 10-60% by weight, based on the mixture as a whole. The compounds of the formula IB are preferably employed in the liquid crystalline medium in amounts of 0-35% by weight, preferably 2-25% by weight, based on the mixture as a whole. The compounds of the formula I-A and I-B are preferably employed in the liquid crystalline medium in amounts of ≧20% by weight, preferably 25-60% by weight, in particular 30-60% by weight, based on the mixture as a whole.
The compounds of the formula I-C to I-I are preferably employed in the liquid crystalline medium in amounts of 0.5-25% by weight, preferably 5-20% by weight, based on the mixture as a whole.
Preferred embodiments of the liquid-crystalline medium according to the invention are indicated below:
Very particularly preferred mixtures comprise compounds O-5b and O-10a:
Preference in particular is given to mixtures according to the invention which comprise the following mixture concepts (the acronyms used are explained in Table A. n and m, each independently of one another denote 1-6):
The mixture according to the invention preferably contains
preferably in amounts of 0.1-10 wt. %, in particular 2.5-5 wt. %,
and/or
The invention furthermore relates to an electro-optical display, preferably a Pl-free display, having active or passive-matrix addressing based on the ECB, VA, PS-VA, PSA, characterised in that it contains, as dielectric, a liquid-crystalline medium according to one or more of Claims 1 to 15.
The liquid-crystalline medium according to the invention preferably has a nematic phase from ≦−20° C. to ≧70° C., particularly preferably from ≦−30° C. to ≧80° C., very particularly preferably from ≦−40° C. to ≧110° C.
The expression “have a nematic phase” here means on the one hand that no smectic phase and no crystallisation are observed at low temperatures at the corresponding temperature and on the other hand that clearing still does not occur on heating from the nematic phase. The investigation at low temperatures is carried out in a flow viscometer at the corresponding temperature and checked by storage in test cells having a layer thickness corresponding to the electro-optical use for at least 100 hours. If the storage stability at a temperature of −20° C. in a corresponding test cell is 1000 h or more, the medium is referred to as stable at this temperature. At temperatures of −30° C. and −40° C., the corresponding times are 500 h and 250 h respectively. At high temperatures, the clearing point is measured by conventional methods in capillaries.
The liquid-crystal mixture preferably has a nematic phase range of at least 60 K and a flow viscosity ν20 of at most 30 mm2·s−1 at 20° C.
The values of the birefringence Δn in the liquid-crystal mixture are generally between 0.07 and 0.26, preferably between 0.09 and 0.20.
The liquid-crystal mixture according to the invention has a Δ∈ of −0.5 to −8.0, in particular −2.5 to −6.0, where Δ∈ denotes the dielectric anisotropy.
The rotational viscosity γ1 at 20° C. is preferably ≦200 mPa·s, in particular ≦150 mPa·s.
The liquid-crystal media according to the invention have relatively low values for the threshold voltage (V0). They are preferably in the range from 1.7 V to 3.0 V, particularly preferably ≦2.5 V and very particularly preferably ≦2.3 V.
For the present invention, the term “threshold voltage” relates to the capacitive threshold (V0), also known as the Freedericks threshold, unless explicitly indicated otherwise.
In addition, the liquid-crystal media according to the invention have high values for the voltage holding ratio in liquid-crystal cells.
For the present invention, the term “dielectrically positive compounds” denotes compounds having a Δ∈>1.5, the term “dielectrically neutral compounds” denotes those having −1.5≦Δ∈<−1.5 and the term “dielectrically negative compounds” denotes those having Δ∈<−1.5. The dielectric anisotropy of the compounds is determined here by dissolving 10% of the compounds in a liquid-crystalline host and determining the capacitance of the resultant mixture in at least one test cell in each case having a layer thickness of 20 μm with homeotropic and with homogeneous surface alignment at 1 kHz. The measurement voltage is typically 0.5 V to 1.0 V, but is always lower than the capacitive threshold of the respective liquid-crystal mixture investigated.
All temperature values indicated for the present invention are in ° C.
The mixtures according to the invention are suitable for all VA-applications, such as, for example, VAN, MVA, (S)-PVA, ASV, PSA (polymer sustained VA) and PS-VA (polymer stabilized VA), preferably for Passive Matrix (PM) Addressing, but are also suitable for Active Matrix Addressing.
The nematic liquid-crystal mixtures in the displays according to the invention generally comprise two components A and B, which themselves consist of one or more individual compounds.
Component A has significantly negative dielectric anisotropy and gives the nematic phase a dielectric anisotropy of ≦−0.5. Preferably component A comprises the compounds of the formulae IIA, IIB and/or IIC, furthermore compounds of the formula III.
The proportion of component A is preferably between 45 and 100%, in particular between 60 and 100%.
For component A, one (or more) individual compound(s) which has (have) a value of Δ∈≦−0.8 is (are) preferably selected. This value must be more negative, the smaller the proportion A in the mixture as a whole.
Component B has pronounced nematogeneity and a flow viscosity of not greater than 30 mm2·s−1, preferably not greater than 25 mm2·s−1, at 20° C.
Particularly preferred individual compounds in component B are extremely low-viscosity nematic liquid crystals having a flow viscosity of not greater than 18 mm2·s−1, preferably not greater than 12 mm2·s−1, at 20° C.
Component B is monotropically or enantiotropically nematic, has no smectic phases and is able to prevent the occurrence of smectic phases down to very low temperatures in liquid-crystal mixtures. For example, if various materials of high nematogeneity are added to a smectic liquid-crystal mixture, the nematogeneity of these materials can be compared through the degree of suppression of smectic phases that is achieved.
The mixture may optionally also comprise a component C, comprising compounds having a dielectric anisotropy of Δ∈≧21.5. These so-called positive compounds are generally present in a mixture of negative dielectric anisotropy in amounts of ≦20% by weight, based on the mixture as a whole.
A multiplicity of suitable materials is known to the person skilled in the art from the literature. Particular preference is given to compounds of the formula III.
In addition, these liquid-crystal phases may also comprise more than 18 components, preferably 18 to 25 components.
The mixtures according to the invention contain one or more compounds of the formula I and one or more compounds of the formula I-A to I-K and preferably contain 4 to 15, in particular 5 to 12, and particularly preferably <10, compounds of the formulae IIA, IIB and/or IIC and optionally III.
Besides compounds of the formula I and at least one compound selected from the group of compounds of the formulae I-A to I-K and the compounds of the formulae IIA, IIB and/or IIC and optionally III, other constituents may also be present, for example in an amount of up to 45% of the mixture as a whole, but preferably up to 35%, in particular up to 10%.
The other constituents are preferably selected from nematic or nematogenic substances, in particular known substances, from the classes of the azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl cyclohexanecarboxylates, phenylcyclohexanes, cyclohexylbiphenyls, cyclohexylcyclohexanes, cyclohexylnaphthalenes, 1,4-biscyclohexylbiphenyls or cyclohexylpyrimidines, phenyl- or cyclohexyldioxanes, optionally halogenated stilbenes, benzyl phenyl ethers, tolans and substituted cinnamic acid esters.
The most important compounds which are suitable as constituents of liquid-crystal phases of this type can be characterised by the formula IV
R20-L-G-E-R21 IV
in which L and E each denote a carbo- or heterocyclic ring system from the group formed by 1,4-disubstituted benzene and cyclohexane rings, 4,4′-disubstituted biphenyl, phenylcyclohexane and cyclohexylcyclohexane systems, 2,5-disubstituted pyrimidine and 1,3-dioxane rings, 2,6-disubstituted naphthalene, di- and tetrahydronaphthalene, quinazoline and tetrahydroquinazoline,
or a C—C single bond, Q denotes halogen, preferably chlorine, or —CN, and R20 and R21 each denote alkyl, alkenyl, alkoxy, alkoxyalkyl or alkoxycarbonyloxy having up to 18, preferably up to 8, carbon atoms, or one of these radicals alternatively denotes CN, NC, NO2, NCS, CF3, SF5, OCF3, F, Cl or Br.
In most of these compounds, R20 and R21 are different from one another, one of these radicals usually being an alkyl or alkoxy group. Other variants of the proposed substituents are also common. Many such substances or also mixtures thereof are commercially available. All these substances can be prepared by methods known from the literature.
It goes without saying for the person skilled in the art that the VA mixture according to the invention may also comprise compounds in which, for example, H, N, O, Cl and F have been replaced by the corresponding isotopes.
Polymerisable compounds, so-called reactive mesogens (RMs), for example as disclosed in U.S. Pat. No. 6,861,107, may furthermore be added to the mixtures according to the invention in concentrations of preferably 0.12-5% by weight, particularly preferably 0.2-2% by weight, based on the mixture. These mixtures may optionally also comprise an initiator, as described, for example, in U.S. Pat. No. 6,781,665. The initiator, for example Irganox-1076 from Ciba, is preferably added to the mixture comprising polymerisable compounds in amounts of 0-1%. Mixtures of this type can be used for so-called polymer-stabilised VA modes (PS-VA) or PSA (polymer sustained VA), in which polymerisation of the reactive mesogens is intended to take place in the liquid-crystalline mixture. The prerequisite for this is that the liquid-crystal mixture does not itself comprise any polymerisable components.
In a preferred embodiment of the invention, the polymerisable compounds are selected from the compounds of the formula M,
RMa-AM1-(ZM1-AM2)m1-RMb M
in which the individual radicals have the following meanings:
Particularly preferred compounds of the formula M are those in which
Very particular preference is given to compounds of the formula M in which one of RMa and RMb or both denote(s) P or P-Sp-.
Suitable and preferred mesogenic comonomers, particularly for use in PS VA displays, are selected, for example, from the following formulae:
in which the individual radicals have the following meanings:
In the compounds of formulae M1 to M41
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 or OCF3, especially F or CH3.
Suitable polymerisable compounds are furthermore listed, for example, in Table D. LC mixtures containing at least one polymerisable compound listed in Table D are especially preferred.
The liquid-crystalline media in accordance with the present application preferably comprise in total 0.1 to 10%, preferably 0.2 to 4.0%, particularly preferably 0.2 to 2.0%, of polymerisable compounds.
Particular preference is given to the polymerisable compounds of the formula M.
The polymerisable compounds are preferably polymerised by photopolymerisation, for example by UV irradiation, often in the presence of at least one suitable initiator. The polymerisation takes place under conditions where the single components of the liquid crystalline mixture as such containing for example single compounds containing an alkenyl side chain like CC-n-V or an alkenyloxy side chain do not polymerize. Suitable conditions for the polymerisation and suitable types and amounts of initiator(s) are known to a person skilled in the art and are described in the literature. Suitable for free-radical polymerisation are, for example, commercially available photoinitiators, for example Irgacure® 651, Irgacure® 184 or Darocure® 1173 (BASF). The polymerisable compound(s) preferably comprise from 0 to 5% by weight, particularly preferably 0.1 to 3% by weight of one or more photoinitiators.
The combination of at least two liquid crystalline compounds, at least one self-aligning additive and preferably with at least one polymerisable compound, in particular one selected from the formula M and/or the formulae M1 to M41, produces low threshold voltages, low rotational viscosities, very good low temperature stabilities (LTS) in the media but at the same time high clearing points and high HR values, and enables the setting or a pretilt angle in VA displays without the need of any alignment layer, e.g., a polyimide layer.
The mixtures according to the invention may furthermore comprise conventional additives, such as, for example, stabilisers, antioxidants, UV absorbers, nanoparticles, microparticles, etc.
The structure of the liquid-crystal displays according to the invention corresponds to the usual geometry, as described, for example, in EP 0 240 379.
Throughout the patent application, 1,4-cyclohexylene rings and 1,4-phenylene rings are depicted as follows:
Throughout the patent application and in the working examples, the structures of the liquid-crystalline compounds are indicated by means of acronyms. Unless indicated otherwise, the transformation into chemical formulae is carried out in accordance with Tables 1-3. All radicals CnH2n+1, CmH2m+1 and Cm′H2m′+1 or CnH2n and CmH2m are straight-chain alkyl radicals or alkylene radicals in each case having n, m, m′ or z C atoms respectively. n, m, m′, z each denote, independently of one another, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, preferably 1, 2, 3, 4, 5 or 6. In Table 1 the ring elements of the respective compound are coded, in Table 2 the bridging members are listed and in Table 3 the meanings of the symbols for the left-hand or right-hand side chains of the compounds are indicated.
A
AI
B
B(S)
C
D
DI
F
FI
G
GI
K
L
LI
M
MI
N
NI
P
S
U
UI
Y
Y(F,Cl)
Y(Cl,F)
Besides the compounds of the formulae IIA and/or IIB and/or IIC, one or more compounds of the formula I and at least one compound of the formulae I-A to I-K the mixtures according to the invention preferably comprise one or more of the compounds from Table A indicated below.
AlK-n-F
AlY-n-Om
AY-n-Om
B-nO-Om
B-n-Om
B(S)-nO-Om
B(S)-n-Om
CB(S)-n-(O)m
CB-n-m
CB-n-Om
PB-n-m
PB-n-Om
BCH-nm
BCH-nmF
BCN-nm
C-1V-V1
CY-n-Om
CY(F,Cl)-n-Om
CY(Cl,F)-n-Om
CCY-n-Om
CCY(F,Cl)-n-Om
CCY(Cl,F)-n-Om
CCY-n-m
CCY-V-m
CCY-Vn-m
CCY-n-OmV
CBC-nmF
CBC-nm
CCP-V-m
CCP-Vn-m
CCP-nV-m
CCP-n-m
CPYP-n-(O)m
CYYC-n-m
CCYY-n-(O)m
CCY-n-O2V
CCH-nOm
CY-n-m
CCH-nm
CC-n-V
CC-n-V1
CC-n-Vm
CC-2V-V2
CVC-n-m
CC-n-mV
CCOC-n-m
CP-nOmFF
CH-nm
CEY-V-n
CEY-n-m
CEY-n-Om
CVY-V-n
CY-V-On
CY-n-O1V
CY-n-OC(CH3)═CH2
CCN-nm
CY-n-OV
CCPC-nm
CCY-n-zOm
CPY-n-(O)m
CPY-V-Om
CQY-n-(O)m
CQIY-n-(O)m
CCQY-n-(O)m
CCQIY-n-(O)m
CPQY-n-(O)m
CPQIY-n-(O)m
CPYG-n-(O)m
CCY-V-Om
CCY-V2-(O)m
CCY-1V2-(O)m
CCY-3V-(O)m
CCVC-n-V
CPYG-n-(O)m
CPGP-n-m
CY-nV-(O)m
CENaph-n-Om
COChrom-n-Om
COChrom-n-m
CCOChrom-n-Om
CCOChrom-n-m
CONaph-n-Om
CCONaph-n-Om
CCNaph-n-Om
CNaph-n-Om
CETNaph-n-Om
CTNaph-n-Om
CK-n-F
CLY-n-Om
CLY-n-m
LYLI-n-m
CYLI-n-m
LY-n-(O)m
COYOICC-n-m
COYOIC-n-V
CCOY-V-O2V
COY-n-Om
COY-n-m
CCOY-V-O3V
CCOY-V-Om
CCOY-1V-Om
CCOY-n-Om
D-nOmFF
PCH-nm
PCH-nOm
PGIGI-n-F
PGP-n-m
PPGU-n-F
PYP-n-mV
PYP-n-m
PYP-n-Om
PPYY-n-m
YPY-n-m
YPY-n-mV
PY-n-(O)m
PP-n-Om
PP-n-m
CB-n-(O)m
B-nO-(O)m
DFDBC-n(O)-(O)m
Y-nO-Om
Y-nO-OmV
Y-nO-OmVm'
CC-n-O
CC-n-1O
PPGU-n-F
Y-nO-OmVm'
YPY-n-mV
PY-n-m
PY-n-Om
PTP-nOmFF
CPTP-nOmFF
PPTUI-n-m
CPTP-nOm
CPTP-nm
PTP-nOm
PTP-nm
C-DFDBC-n-(O)m
DFDBC-n(O)-(O)m
Y-nO-Om
Y-nO-OmV
Y-nO-OmVm'
The liquid-crystal mixtures which can be used in accordance with the invention are prepared in a manner which is conventional per se. 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.
By means of suitable additives, the liquid-crystal phases according to the invention can be modified in such a way that they can be employed in any type of, for example, ECB, VAN, GH or ASM-VA, IPS, FFS, PS-VA, PS-IPS, PS-FFS LCD display that has been disclosed to date.
The dielectrics may also comprise further additives known to the person skilled in the art and described in the literature, such as, for example, UV absorbers, antioxidants, nanoparticles and free-radical scavengers. For example, 0-15% of pleochroic dyes, stabilisers or chiral dopants may be added. Suitable stabilisers for the mixtures according to the invention are, in particular, those listed in Table C.
For example, 0-15% of pleochroic dyes may be added, furthermore conductive salts, preferably ethyldimethyldodecylammonium 4-hexoxybenzoate, tetrabutylammonium tetraphenylboranate or complex salts of crown ethers (cf., for example, Haller et al., Mol. Cryst. Liq. Cryst. Volume 24, pages 249-258 (1973)), may be added in order to improve the conductivity or substances may be added in order to modify 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.
Table B shows possible dopants which can be added to the mixtures according to the invention. If the mixtures comprise a dopant, it is employed in amounts of 0.01-4% by weight, preferably 0.1-1.0% by weight.
Stabilisers which can be added, for example, to the mixtures according to the invention in amounts of up to 10% by weight, based on the total amount of the mixture, preferably 0.01 to 6% by weight, in particular 0.1 to 3% by weight, are shown below in Table C. Preferred stabilisers are, in particular, BHT derivatives, for example 2,6-di-tert-butyl-4-alkylphenols, and Tinuvin 770, as well as Tunivin P and Tempol.
Preferred reactive mesogens (polymerisable compounds) for use in the mixtures according to the invention, preferably in PSA and PS-VA applications are shown in Table D below:
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.
In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.
The entire disclosures of all applications, patents and publications, cited herein and of corresponding application No EP 14002851.5, filed Aug. 15, 2014 are incorporated by reference herein.
The following examples are intended to explain the invention without restricting it. In the examples, m.p. denotes the melting point and C denotes the clearing point of a liquid-crystalline substance in degrees Celsius; boiling points are denoted by b.p. Furthermore:
C denotes crystalline solid state, S denotes smectic phase (the index denotes the phase type), N denotes nematic state, Ch denotes cholesteric phase, I denotes isotropic phase, Tg denotes glass transition temperature.
The number between two symbols indicates the conversion temperature in degrees Celsius.
Conventional work-up means: water is added, the mixture is extracted with methylene chloride, the phases are separated, the organic phase is dried and evaporated, and the product is purified by crystallisation and/or chromatography.
4-Propyl-4′-bromo-2-fluorobiphenyl is prepared according to WO89/03821.
29.3 g (0.100 mol) 4-propyl-4′-bromo-2-fluorobiphenyl are dissolved in THF (800 ml) and cooled to −70° C. After addition of 66 ml (0.105 mol) n-butyl lithium the reaction is stirred for 30 min and then a CO2 stream is passed through the solution until the exothermic reaction ceases. The reaction is warmed to −10° C., poured onto water and acidified with conc. hydrochloric acid. The mixture is extracted with methyl tert. butyl ether (MBT ether) and dried over sodium sulfate. The solvent is evaporated and the residue is recrystallised from n-heptane to give 2′-fluoro-4′-propyl-biphenyl-4-carboxylic acid as colourless crystals.
1.45 g (38 mmol) lithiumaluminium hydride are placed in a flask under toluene (10 ml) and a solution of 12.0 g (46.0 mmol) 2′-fluoro-4′-propylbiphenyl-4-carboxylic acid in THF (250 ml) is added dropwise. The reaction is stirred at room temperature over night and is then hydrolised carefully with 2M hydrochloric acid (100 ml) under ice-cooling. After addition of MTB-ether (50 ml) the aqueous layer was separated and extracted tree times with MTB-ether. The combined organic layers are washed saturated sodium bicarbonate solution and dried over sodium sulfate. The solvent is evaporated and the crude product filtered through silica with heptane/ethyl acetate (8:2). Crystallisation from n-heptane gives (2′-fluoro-4′-propyl-biphenyl-4-yl)-methanol as colourless crystals.
K 50 l
Above and below,
The display used for measurement of the threshold voltage has two plane-parallel outer plates at a separation of 20 μm and electrode layers with overlying alignment layers of JALS-2096 on the insides of the outer plates, which effect a homeotropic alignment of the liquid crystals.
All concentrations in this application relate to the corresponding mixture or mixture component, unless explicitly indicated otherwise. All physical properties are determined as described in “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.
Unless indicated otherwise, parts or percent data denote parts by weight or percent by weight.
For the production of the so-called SA (self-alignment)-VA mixtures according to the present invention the following host mixtures H1 to H120 are used:
H1: Nematic Host-Mixture
H2: Nematic Host-Mixture
H3: Nematic Host-Mixture
H4: Nematic Host-Mixture
H5: Nematic Host-Mixture
H6: Nematic Host-Mixture
H7: Nematic Host-Mixture
stabilised with 0.02% of
H8: Nematic Host-Mixture
H9: Nematic Host-Mixture
H10: Nematic Host-Mixture
H11: Nematic Host-Mixture
H12: Nematic Host-Mixture
H13: Nematic Host-Mixture
H14: Nematic Host-Mixture
H15: Nematic Host-Mixture
H16: Nematic Host-Mixture
H17: Nematic Host-Mixture
H18: Nematic Host-Mixture
H18: Nematic Host-Mixture
H20: Nematic Host-Mixture
H21: Nematic Host-Mixture
H22: Nematic Host-Mixture
H23: Nematic Host-Mixture
H24: Nematic Host-Mixture
H25: Nematic Host-Mixture
H26: Nematic Host-Mixture
H27: Nematic Host-Mixture
H28: Nematic Host-Mixture
H29: Nematic Host-Mixture
H30: Nematic Host-Mixture
H31: Nematic Host-Mixture
H32: Nematic Host-Mixture
H33: Nematic Host-Mixture
H34: Nematic Host-Mixture
H35: Nematic Host-Mixture
H36: Nematic Host-Mixture
H37: Nematic Host-Mixture
H38: Nematic Host-Mixture
H39: Nematic Host-Mixture
H40: Nematic Host-Mixture
H41: Nematic Host-Mixture
H42: Nematic Host-Mixture
H43: Nematic Host-Mixture
H44: Nematic Host-Mixture
H45: Nematic Host-Mixture
H46: Nematic Host-Mixture
H47: Nematic Host-Mixture
H48: Nematic Host-Mixture
H49: Nematic Host-Mixture
H50: Nematic Host-Mixture
H51: Nematic Host-Mixture
H52: Nematic Host-Mixture
H53: Nematic Host-Mixture
H54: Nematic Host-Mixture
H55: Nematic Host-Mixture
H56: Nematic Host-Mixture
H57: Nematic Host-Mixture
H58: Nematic Host-Mixture
H59: Nematic Host-Mixture
H60: Nematic Host-Mixture
H61: Nematic Host-Mixture
H62: Nematic Host-Mixture
H63: Nematic Host-Mixture
H64: Nematic Host-Mixture
H65: Nematic Host-Mixture
H66: Nematic Host-Mixture
H67: Nematic Host-Mixture
H68: Nematic Host-Mixture
H69: Nematic Host-Mixture
H70: Nematic Host-Mixture
H71: Nematic Host-Mixture
H72: Nematic Host-Mixture
H73: Nematic Host-Mixture
H74: Nematic Host-Mixture
H75: Nematic Host-Mixture
H76: Nematic Host-Mixture
H77: Nematic Host-Mixture
H78: Nematic Host-Mixture
H79: Nematic Host-Mixture
H80: Nematic Host-Mixture
H81: Nematic Host-Mixture
H82: Nematic Host-Mixture
H83: Nematic Host-Mixture
H84: Nematic Host-Mixture
H85: Nematic Host-Mixture
H86: Nematic Host-Mixture
H87: Nematic Host-Mixture
H88: Nematic Host-Mixture
H89: Nematic Host-Mixture
H90: Nematic Host-Mixture
H91: Nematic Host-Mixture
H92: Nematic Host-Mixture
stabilized with 0.01% of the compound of the formula
H93: Nematic Host-Mixture
H94: Nematic Host-Mixture
H95: Nematic Host-Mixture
H96: Nematic Host-Mixture
H97: Nematic Host-Mixture
H98: Nematic Host-Mixture
H99: Nematic Host-Mixture
stabilized with 0.03% of
H100: Nematic Host-Mixture
H101: Nematic Host-Mixture
H102: Nematic Host-Mixture
H103: Nematic Host-Mixture
H104: Nematic Host-Mixture
H105: Nematic Host-Mixture
H106: Nematic Host-Mixture
H107: Nematic Host-Mixture
H108: Nematic Host-Mixture
H109: Nematic Host-Mixture
H110: Nematic Host-Mixture
H111: Nematic Host-Mixture
H112: Nematic Host-Mixture
H113: Nematic Host-Mixture
H114: Nematic Host-Mixture
H115: Nematic Host-Mixture
H116: Nematic Host-Mixture
H117: Nematic Host-Mixture
H118: Nematic Host-Mixture
H119: Nematic Host-Mixture
H120: Nematic Host-Mixture
H121: Nematic Host-Mixture
H122: Nematic Host-Mixture
H123: Nematic Host-Mixture
H124: Nematic Host-Mixture
H125: Nematic Host-Mixture
H126: Nematic Host-Mixture
H127: Nematic Host-Mixture
H128: Nematic Host-Mixture
H129: Nematic Host-Mixture
H130: Nematic Host-Mixture
H131: Nematic Host-Mixture
H132: Nematic Host-Mixture
H133: Nematic Host-Mixture
H134: Nematic Host-Mixture
The compound of the formula I-2a-1 (4%) is added to the nematic host mixture H1. The resulting mixture is homogenised and filled into an “alignment-free” test cell (cell thickness d˜4.0 μm, ITO coating on both sides (structured ITO in case of a multi-domain switching), no alignment layer and no passivation layer).
The LC-mixture shows a spontaneous homeotropic (vertical) orientation with respect to the surface of the substrates. The orientation is stable until the clearing point and the resulting VA-cell can be reversibly switched. Crossed polarizers are needed to display the switching.
By using additives like the compound of the formula I-2a-1, no alignment layer (e.g. no Pl coating) is required anymore for PVA, MVA, and other analogue display technologies with vertically aligned liquid crystals.
The compound of the formula I-2a-1 (2%) is added to the nematic host mixture H1. The resulting mixture is homogenised and filled into an “alignment-free” test cell (cell thickness d˜4.0 μm, ITO coating on both sides (structured ITO in case of a multi-domain switching), no alignment layer and no passivation layer).
The LC-mixture shows a spontaneous homeotropic (vertical) orientation with respect to the surface of the substrates. The orientation is stable until the clearing point and the resulting VA-cell can be reversibly switched. Crossed polarizers are needed to display the switching.
By using additives like the compound of the formula I-2a-1, no alignment layer (e.g. no Pl coating) is required anymore for PVA, MVA, and other analogue display technologies with vertically aligned liquid crystals.
The polymerizable derivative RM-1 (0.3%) is added to the nematic LC-mixture of Example M1-a. The resulting mixture is homogenised and filled into an “alignment-free” test cell (cell thickness d˜4.0 m, ITO coating on both sides (structured ITO in case of a multi-domain switching), no alignment layer and no passivation layer).
The LC-mixture shows a spontaneous homeotropic (vertical) orientation, with respect to the surface of the substrates. The resulting VA-cell is treated with UV-light (15 min, 100 mW/cm2) after having applied to the cell a voltage higher than the optical threshold. The polymerizable derivative polymerizes and, as a consequence, the homeotropic self-orientation is stabilized and the tilt of the mixture is tuned. The resulting PSA-VA-cell can be reversibly switched even at high temperatures. The switching times are reduced, compared to the not polymerized system.
Additives like Irganox 1076 (BASF) may be added (e.g. 0.001%) for preventing spontaneous polymerization. UV-cut filter may be used during polymerization for preventing damage of the mixtures (e.g. 340 nm cut-off-filter).
By using additives like the compound of the formula I-2a-1 in combination with RM-1, no alignment layer is required anymore for PSA, PS-VA, and other analogue display technologies with vertically aligned liquid crystals.
The polymerizable derivative RM-41 (0.3%) is added to the nematic LC-mixture of Example M1-a. The resulting mixture is homogenised and filled into an “alignment-free” test cell (cell thickness d˜4.0 μm, ITO coating on both sides (structured ITO in case of a multi-domain switching), no alignment layer and no passivation layer). The resulting cell is treated according to Example 1P a) and similar results are obtained.
By using additives like the compound of the formula I-2a-1 in combination with RM-41, no alignment layer is required anymore for PSA, PS-VA, and other analogue display technologies with vertically aligned liquid crystals.
The compound of the formula I-2a-1 (4%) is added to the nematic host mixtures H2-H134. The resulting mixtures M2 to M134 are homogenised and filled into an “alignment-free” test cell (cell thickness d˜4.0 μm, ITO coating on both sides (structured ITO in case of a multi-domain switching), no alignment layer and no passivation layer).
The LC-mixtures show a spontaneous homeotropic (vertical) orientation with respect to the surface of the substrates. The orientation is stable until the clearing point and the resulting VA-cell can be reversibly switched. Crossed polarizers are needed to display the switching.
The polymerizable derivative RM-1 (0.3%) or RM-41 (0.3%) is added to the nematic LC mixtures of Examples M2-M134. The resulting mixtures are homogenised and filled into an “alignment-free” test cell (cell thickness d˜4.0 μm, ITO coating on both sides (structured ITO in case of a multi-domain switching), no alignment layer and no passivation layer). The resulting cell is treated according to example 1P a). Equivalent results are obtained.
Analogues mixtures like 1P a) to 134 P b) are obtained by mixing the nematic LC mixtures M1 to M134 with RM35 (0.3%), RM43 (0.3%), RM55 (0.3%) or RM83 (0.3%), obtaining mixtures 1P c) to 134 P f). These mixtures are treated according to Example 1P a). In all cases an improvement of the switching times is found.
To the following nematic host mixture
is added
0.4% of the compound of the formula
To the following nematic host mixture
is added
0.4% of the compound of the formula
To the following nematic host mixture
is added
0.4% of the compound of the formula
To the following nematic host mixture
is added
0.4% of the compound of the formula
The multi bottle bottle system is prepared by mixing of
25% of M135
25% of M136
25% of M137
25% of M138
and has the following composition:
The mixtures of Examples M135 to M139 are highly suitable for PM (passive matrix)-VA applications.
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 |
|---|---|---|---|
| 14002851 | Aug 2014 | EP | regional |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20130182202 | Graziano et al. | Jul 2013 | A1 |
| 20140138581 | Archetti et al. | May 2014 | A1 |
| 20150322342 | Archetti et al. | Nov 2015 | A1 |
| Number | Date | Country |
|---|---|---|
| 2014090362 | Jun 2014 | WO |
| Entry |
|---|
| European Search Report dated Dec. 18, 2015 issued in corresponding EP 15002394 application (pp. 1-10). |
| Number | Date | Country | |
|---|---|---|---|
| 20160046863 A1 | Feb 2016 | US |
