WO2004033584A1

WO2004033584A1 - Liquid crystalline media containing polymers

Info

Publication number: WO2004033584A1
Application number: PCT/EP2003/010775
Authority: WO
Inventors: Michael Heckmeier; Melanie Klassen-Memmer; Brigitte Schuler
Original assignee: Merck Patent Gmbh
Priority date: 2002-10-07
Filing date: 2003-09-26
Publication date: 2004-04-22
Also published as: DE10246774A1; JP2006502264A; AU2003275998A1; DE10393439D2; TW200420713A

Abstract

The invention relates to liquid crystalline media containing a) at least one liquid crystalline compound, and b) polymers consisting of at least one polymerisable compound of general formula (I): P1-Sp1-X1-A1-(Z1-A2)n-R

Description

Liquid crystalline media containing polymers

The present invention relates to liquid crystal media, in particular with small birefringence, for use in liquid crystal display systems (displays). These liquid crystal display systems are below. other screens of television sets, computers, e.g. "Notebook" computers or "desktop" computers, control centers and other devices, e.g. Gambling devices, electro-optical displays, such as displays of watches, pocket calculators, electronic (pocket) games, portable data storage devices, such as PDAs (personal digital assistants) or of mobile telephones.

The liquid crystal switching elements typically used in such liquid crystal displays are the known TN (twisted nematic) switching elements, e.g. according to Schadt, M. and Helfrich, W. Appl. Phys. Lett. 18, pp. 127 ff. (1974) and in particular in their special form with small optical delay d-Δn in the range from 150 nm to 600 nm according to DE 30 22 818, STN (super twisted nematic) switching elements such as e.g. according to GB 2 123 163, DE 34 31 871, DE 36 08 911 and EP 0 260 450, IPS (inplane switching) switching elements, such as described in DE 40 00 451 and EP 0 588 568, and VAN (vertically aligned nematic) switching elements as described in Tanaka, Y. et al., K. SID 99 Digest p. 206 ff (1999), Koma et al., International Display Workshop (IDW) "97 pp. 789 ff (1997) and Kim et al., Asia Display 98, pp. 383 ff, (1998).

With these liquid crystal display devices which have been known to date and are largely commercially available, the optical appearance is not sufficient, at least for demanding applications. In particular, the contrast, especially in the case of colored representations, the brightness, the color saturation and the viewing angle dependency of these variables can be improved significantly. Further disadvantages of the liquid crystal display devices are often their lack of spatial resolution and inadequate switching times, in particular in the case of STN switching elements, but also in the case of TN switching elements or IPS (in-plane switching) and VAN (vertically aligned nematic) switching elements, in the case of the the latter in particular if they are to be used for video playback, such as in multimedia applications on computer screens or on televisions. For this purpose in particular, but already for the display of fast cursor movements, short switching times, preferably of less than 32 ms, particularly preferably of less than 16 ms, are desired.

The requirements for the viewing angle dependency of the contrasts strongly depend on the use of the display devices. For example, the horizontal viewing angle range is most important for television screens and computer monitors, whereas centrosymmetrical viewing angle distributions are desired in other applications. In general, it should be noted that the practical acceptance of a display is not primarily based on its contrast or its maximum contrast ratio, but rather that the viewing angle dependence of the contrast is often important. However, these properties have to be weighted differently depending on the application.

TN switching elements with d-Δn in the range from 0.2 μm to 0.6 μm, as described in DE 30 22 818, generally have very good color saturation and color depth, but an insufficient viewing angle range for demanding applications such as e.g. Computer monitors for "desktop" computers.

WO 01/07962 describes liquid crystal switching elements, comprising at least one polarizer and a liquid crystal layer which has an initial orientation in which the liquid crystal molecules are oriented essentially parallel to the substrates and essentially parallel to one another, in which the reorientation of the liquid crystals consists of them output orientation which is essentially parallel to the substrates is caused by a corresponding electric field which is oriented essentially parallel to the substrates in the case of liquid crystal materials with negative dielectric anisotropy and is oriented essentially perpendicular to the substrates in the case of liquid crystal materials with positive dielectric anisotropy, wherein the liquid crystal layer has an extremely low optical delay d-Δn in the range from 0.06 μm to 0.43 μm and the liquid crystal switching element element preferably contains, in addition to the liquid crystal layer, a further birefringent layer, preferably a λ / 4 layer or two λ / 4 layers or a λ / 2 layer, and liquid crystal display systems contain such liquid crystal switching elements.

The liquid crystal switching elements described in WO 01/07962 do not have the disadvantages of the known switching elements, or at least to a significantly reduced extent. They are characterized by a very good contrast with an excellent viewing angle dependence of the contrast. They allow the display of both grayscale and halftone colors over a wide range of viewing angles.

However, the switching times of these liquid crystal switching elements are still in need of improvement.

The object of the invention is to provide suitable liquid-crystalline media which give liquid-crystal switching elements with significantly reduced switching times.

The object is achieved by a medium comprising a) one or more liquid-crystalline compounds and b) polymers composed of one or more polymerizable compounds of the general formula I.

P ¹ -Sp ¹ -X ¹ -A ¹ - (Z ¹ -A ² ) _n -R (I)

in which mean:

RH, F, Cl, CN, SCN, SF ₅ H, N0 ₂ , straight-chain or branched alkyl having 1 to 12 carbon atoms, one or two non-adjacent CH ₂ groups also being -O-, -S-, - CH = CH-, -CO-, -OCO-, -COO-, -O- COO-, -S-CO-, -CO-S-, -CH = CH- or -C≡C- so replaced may be that O and / or S atoms are not directly linked to one another, or -X ² -Sp ² -P ² , P and P are each independently a polymerizable group, preferably

-O (CO) - (CH ₂ ) ₀ -CH = CH ₂ , -O (CO) -CH = CH- (CH ₂ ) _p -H, -CH = CH- (CH ₂ ) _q -H, -0 (CO) -C (CH ₃ ) = CH- (CH ₂ ) _r -H with o, p, q, r = 0 - 8,

Sp ¹ and Sp ² each independently of one another are a spacer group, preferably - (CH ₂ ) _m - with m = 1-8, or a single bond,

X ¹ and X ² each independently of one another -O-, -S-, -OCH ₂ -,

-CH ₂ O-, -CO-, -COO-, -OCO-, -OCO-O, -CO-NR ⁰ -, -NR ° -CO-, -OCH ₂ -, -CH ₂ O-, -SCH ₂ -, -CH ₂ S-, ~ CH = CH-COO-, -OOC-CH = CH- or a single bond,

A ¹ and A ^{2 are} each independently 1, 4-phenylene, in which one or more CH groups can also be replaced by N, 1, 4-cyclohexylene, in which one or more non-adjacent CH ₂ groups can also be replaced by O and / or S can be replaced, 1,4-cyclohexenylene, 1,4-bicyclo- (2,2,2) -octylene, piperidine, 4-diyl, naphthalene-2,6-diyl, decahydronaphthalene- 2,6-diyl, 1, 2,3,4-tetrahydronaphthalene-2,6-diyl or indane-2,5-diyI, where all these groups can be unsubstituted or substituted one or more times by L,

L F, Cl, CN or alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkylcarbonyloxy with 1 to 7 C atoms, in which one or more H atoms can also be replaced by F or Cl,

Z ¹ -O-, -S-, -CO-, -COO-, -OCO-, -O-COO-, -OCH ₂ -,

-CH ₂ 0-, -SCH ₂ -, -CH ₂ S-, -CF ₂ O-, -OCF ₂ -, -CF ₂ -S-, -SCF ₂ -, -CH ₂ CH -, -CF2CH ₂ -, -CH ₂ -CF ₂ -, -CF ₂ -CF ₂ -, -CH = CH-, -CF = CF-, -C≡C-, -CH = CH-COO-, -OCO-CH = CH-, -CR ° R ⁰⁰ - or a single bond, and

R ° and R ⁰⁰ each independently of one another are H or alkyl having 1 to 4 carbon atoms,

n 0, 1 or 2.

It was found that by doping the liquid-crystalline media with the compounds of the formula (I) forming a polymer network and subsequent UV-induced polymerization, liquid-crystalline media with significantly reduced switching times are obtained.

Preferred liquid-crystalline media contain polymerizable compounds selected from the following formulas

P ¹ - (CH ₂ ) _m1 -O- ^ (left)

wherein P ¹ and P ^{2 have} the meaning given above, Z ² and Z ³ each independently of one another have one of the meanings given for Z ¹ , m1 and m2 each independently represent 1 to 8, r1 and r2 each independently represent 0 or 1 , and R ^a and R ^b each independently represent H or CH ₃ , and L ^{1 represents} H or -CH ₃ .

Here, P ¹ and P ^{2 are} preferably selected independently of one another

-O (CO) - (CH ₂ ) ₀ -CH = CH _2j -O (CO) -CH = CH- (CH ₂ ) _p -H, -CH = CH- (CH ₂ ) _q -H with o, p , q = 0-8. Particularly preferred polymerizable compounds are the following compounds (Ij) - (Im).

(In the)

The present application also relates to mixtures for producing the liquid-crystalline media

a) one or more liquid-crystalline compounds, b) one or more polymerizable compounds of the general formula (I), c) optionally one or more polymerization initiators, preferably photoinitiators.

The compounds of the general formula (I) are usually present in amounts of 0.1 to 1% by weight, preferably 0.2 to 0.5% by weight. Suitable photoinitiators are, for example, Irgacure 651 from Ciba. Based on the compounds to be polymerized, these are usually present in amounts of 1 to 10% by weight, preferably 2 to 4% by weight. The invented Liquid-crystalline media according to the invention can be obtained by UV irradiation of these precursor mixtures. It is usually irradiated with light of a wavelength between 300 and 500 nm.

The liquid-crystalline media according to the invention preferably contain 3 to 27, particularly preferably 10 to 21 and very particularly preferably 12 to 18 individual compounds. Containing the individual compounds are preferably used in each case preferably a 1, ^4, - rans-frat.s-Bicyclohexyleneinheit the sub-formula i:

With

Z is a single bond, -CH ₂ CH ₂ - or -CF ₂ -CF ₂ -, and n 1 or 2.

In one of the cyclohexane rings, one or preferably two non-adjacent -CH ₂ groups can also be replaced by oxygen atoms or two adjacent -CH ₂ groups can be replaced by a -CH = CH group.

In the case of compounds with a total of only two six-membered rings, one of the two cyclohexane rings can optionally also be replaced by unsubstituted or optionally double or preferably laterally fluorinated 1,4-phenylene.

The liquid crystal mixtures preferably contain one or more compounds having a structural unit of the formula i in which n = 2.

The liquid crystal mixtures used in the liquid crystal switching elements according to the invention preferably contain

a component A consisting of compounds with 2 six-membered rings, - A component B consisting of compounds with 3 six-membered rings and optionally

- A component C consisting of compounds with 4 six-membered rings.

The liquid crystal mixtures preferably consist essentially of components A, B and optionally C.

Particularly preferred liquid crystal mixtures contain one or more

dielectric neutral compounds of formula II

wherein

R ¹ n-alkyl having 1 to 5 carbon atoms,

R ¹² n-alkyl with 1 to 5 carbon atoms, 1 E-alkenyl, preferably vinyl or n-alkoxy with 1 to 6 carbon atoms

mean,

optionally dielectric positive compounds selected from the group of formulas III and IN '

wherein R ²¹ n-alkyl or 1 E-alkenyl with 3 to 7 or 2 to 8, preferably 5 to 7 or 4 to 6 C atoms,

Z ⁴ a single bond or -CH2CH2-

and

X ³ OCF ₃ , CF ₃ or CH ₂ CH ₂ CF ₃ , preferably CF ₃ or CH ₂ CH ₂ CF ₃

mean,

wherein

R ²¹ n-alkyl or 1 E-alkenyl with 3 to 7 or 2 to 8, preferably with 5 to

7 or 4 to 6 carbon atoms,

Z ^{4 is} a single bond or -CH ₂ CH ₂ -,

χ ⁴ 0CF ₂ H, OCF ₃ or F, preferably F

and

Y ^{2 is} independently H or F.

mean,

and

Compounds of formula IV

wherein

R ³¹ n-alkyl or 1 E-alkenyl with 2 to 7, preferably 2 to 5, carbon atoms,

Z ³¹ and Z ³² each represent a single bond, -CH ₂ CH - or -CF ₂ CF ₂ -, preferably -CH ₂ CH ₂ -, but particularly preferably both are a single bond,

X ^ü OCF ₂ H, OCF ₃ or F,

Y ³ independently of one another H or F,

in the case

X ⁵ = OCF ₂ H preferably both Y ³ = F,

in the case

X ⁵ = F preferably both Y ³ = F,

in the case

X ⁵ = OCF ₃ preferably one Y ³ = F, the other = H,

optionally one or more compounds from the group of compounds of the formulas V and VI

wherein

R ⁴ n-alkyl or 1 E-alkenyl with 2 to 5, preferably with 2 to 5, carbon atoms,

X ⁶ OCF ² H, OCF ³ or F, preferably F or OCF ³ ,

Y ⁴ independently of one another H or F,

in the case of X = F and

preferably both Y ⁴ = F

in the case

X = OCF ³ and particularly preferred in the case

one Y ³ = F, the other = H,

wherein R ⁵ n-alkyl or 1 E-alkenyl with 2 to 5 carbon atoms

Z ^{5 is} a single bond or -CH ₂ CH ₂ -,

X ⁷ F, OCF ₃ or OCF ₂ H,

Y ⁵ independently of one another H or F,

prefers

X ⁷ , Y ⁵ = F

mean,

optionally one or more compounds with a high clearing point selected from the group of compounds of the formulas VII to X

wherein R ⁷¹ and R ⁷² , R ⁸¹ and R ⁸² , R ⁹¹ and R ⁹² , R ¹⁰ and R ¹¹ each

1 * 1 A D independently of one another have the meaning given above for R and R,

L ⁸¹ , L ⁹¹ mean H or F and

X ¹⁰ , Y ¹⁰ and X ¹¹ , Y ¹¹ each independently have the meaning given above for X ⁵ , Y ³ ,

and

optionally one or more compounds of the formula (XIII)

wherein R ¹³ , X ¹³ and Y ¹³ each independently have the meaning given above for R ¹¹ , X ⁵ and Y ³ and

prefers

means.

The liquid crystal mixtures according to the present application preferably contain 4 to 36 compounds, particularly preferably 6 to 25 compounds and very particularly preferably 7 to 20 compounds.

The present invention also relates to an electro-optic liquid crystal scarf element comprising at least one polarizer and a liquid crystal layer which has an initial orientation in which the liquid crystal molecules are oriented essentially parallel to the substrates and essentially parallel to one another, in which the reorientation of the liquid crystals from them output orientation parallel to the substrates is caused by a corresponding electric field which is oriented essentially parallel to the substrates in the case of liquid crystal materials with negative dielectric anisotropy and essentially perpendicular to the substrates in the case of liquid crystal materials with positive dielectric anisotropy, the Liquid crystal layer contains the liquid crystalline medium according to the invention. The liquid crystal layer preferably has an extremely low optical delay d • Δn in the range from 0.06 μm to 0.43 μm and the liquid crystal switching element preferably has a further birefringent layer in addition to the liquid crystal layer, namely preferably a λ / 4 layer or two λ / 4 layers or a λ / 2 layer. The present invention also relates to liquid crystal display systems containing such liquid crystal switching elements. In particular, the liquid crystal display systems (displays) according to the invention are well suited for applications with gray scale display, such as, for example, television sets, computer monitors and multimedia devices.

The liquid crystal switching elements according to the present invention contain a liquid crystal layer with preferably small optical delay, optionally a further birefringent layer, preferably a λ / 4 layer, a λ / 2 layer or two λ / 4 layers and at least one polarizer. The two λ / 4 layers can replace the λ / 2 layer.

The transmissive or transflective liquid crystal switching elements preferably contain a polarizer and an analyzer, which are arranged on opposite sides of the arrangement of liquid crystal layer and birefringent layer. In this application, polarizer and analyzer are collectively referred to as polarizers. The basic structure of the liquid crystal switching elements is described in WO 01/07962, see in particular there Fig. 1a, 1 b and 2.

The liquid crystal layer is usually held between two substrates. At least one of the substrates is translucent, preferably both substrates are translucent. The translucent substrates are e.g. made of glass, quartz glass, quartz or transparent plastics, preferably made of glass and particularly preferably made of borosilicate glass.

With an adhesive frame, the substrates form a cell in which the liquid crystal material of the liquid crystal layer is held. The substrates are preferably planar.

The spacing of the flat substrates is kept essentially constant over the entire surface by means of spacers. The preferred substrate thicknesses are 0.3 mm to 1.1 mm, particularly preferably 0.4 mm to 0.7 mm. For the larger diagonals of the cells, the substrates with the larger thicknesses are preferred.

The liquid crystal switching elements according to the invention are distinguished by very good gray-level capacity, a low dependence of the contrast on the viewing angle even in color displays, a large viewing angle range and low contrast inversion, and in particular by very short switching times. In particular, the inverse contrast, as defined in DE 42 12 744, which e.g. occurs in displays according to DE 30 22 818, in particular significantly reduced at larger viewing angles θ.

In the case of reflective switching elements, the liquid crystal switching elements according to the present application have at least one polarizer and one reflector, at least one polarizer and the reflector being located on opposite sides (i.e. substrates) of the liquid crystal cell. In the case of transmissive or reflective switching elements, these have at least two polarizers, at least one of which is arranged on each of the two opposite sides of the liquid crystal cell (so-called sandwich structure). The obligatory polarizers mentioned are preferably linear polarizers and particularly preferably linear polarizers with a high degree of polarization.

In addition to the obligatory polarizers, the switching elements according to the invention can contain one or more additional polarizers. These can be so-called "clean up" polarizers with a lower degree of polarization but high transmission. But in particular in the case of reflective switching elements, a further polarizer with a high level can also be used

Degree of polarization be present. This is preferably arranged between the liquid crystal cell and the reflector. However, the use of additional polarizers is generally less preferred, since in most cases it leads to a reduction in the transmission. However, it is particularly in connection with so-called brightness-increasing Components that can contain cholesteric polymer films, for example, are common.

In the case of transmissive and transflective displays according to the present invention, the two obligatory polarizers are either crossed or arranged parallel to one another. In this application the directions of arrangement of the polarizers are related to their absorption axes. The crossed arrangement of the polarizers is preferred. The angle of the absorption axes relative to one another (Ψ _pp ) is from 75 ° to 105 °, in particular approximately 90 ° in the case of crossed polarizers and from -15 ° to 15 °, in particular approximately 0 ° in the case of parallel polarizers.

The angle between the absorption axis of the polarizer adjacent to the liquid crystal layer with the direction of the orientation of the director of the liquid crystal material in the unswitched (field-free) state on the adjacent substrate (Ψ _P ι_) is 35 ° to 55 ° and ideally 45 °. This applies to the untwisted orientation of the liquid crystal. In the case of the twisted orientation of the liquid crystal, the reference direction for specifying the angle ΨPL is the projection of the orientation of the liquid crystal director in the middle between the two substrates of the cell onto the substrate adjacent to the polarizer. When using further birefringent layers and / or compensators in addition to the λ / 4 or λ / 2 layers which are mandatory or preferred depending on the embodiment, other angles between the polarizer direction and liquid crystal orientation can also be used. However, these are usually not preferred.

The twist angle (φ) of the liquid crystal layer between the two substrates, in particular in the case of switching elements with a birefringent layer, in particular with a λ / 4 or λ / 2 layer, or with a plurality of birefringent layers, in particular with two λ / 4 layers , is preferably from -20 ° to 20 °, particularly preferably from -10 ° to 10 °, particularly preferably from -5 ° to 5 °, very particularly preferably from -2 ° to 2 ° and most preferably from -1 ° to 1 °. For the preferred embodiment without a birefringent layer, ie without a λ / 4 or λ / 2 layer or layers, the liquid crystal layer is essentially untwisted and particularly preferably untwisted. A twist angle (φ) of -6 ° to 6 ° is preferred. The twist angle is particularly preferably from -1.0 ° to 1.0 °, very particularly preferably -0.5 ° to 0.5 °, particularly preferably 0.0 °.

The liquid crystal materials are oriented on the substrate surfaces by customary methods. For this purpose, the oblique evaporation with inorganic compounds, preferably oxides such as SiO _x , the orientation on antiparallel rubbed surfaces, especially on antiparallel rubbed polymer layers such as polyamide layers, or orientation on photopolymerized anisotropic polymers can be used. With vertical orientation (English: "vertical alignment", VA for short), lecithin or surface-active substances can also be used for homeotropic orientation.

The surface angle of attack on the substrates (φ ₀ , also English: tilt angle or Tilt for short) is in the range from 0 ° to 15 °, preferably in the range from 0 ° to 10 °, particularly preferably in the range from 0.1 ° to 5 ° and particularly preferably in the range from 0.2 ° to 5 ° and most preferably in the range from 0.3 ° to 3 °. The surface angle of attack on the orientation layer on at least one of the substrate surfaces is from 0.5 ° to 3 °. The angle of attack on both substrates is preferably essentially identical.

The electrodes on the substrates are translucent, at least on one of the substrates and preferably on both substrates. Indium tin oxide (ITO) is preferably used as the material for the electrodes, but aluminum, copper, silver and / or gold can also be used.

Since the surface angle of attack in the liquid crystal display elements according to the invention can be small, the use of anisotropically photopolymerizable materials, such as, for example, cinnamic acid derivatives, the so-called “photo orientation” can be used particularly advantageously. This applies in particular to a preferred embodiment of the liquid crystal display elements according to the invention with multidomain switching elements. Here, the individual liquid crystal switching elements or their individual display electrodes (also called picture elements, English pixels) are divided into sub-areas with different orientations of the liquid crystal director, at least in the switched state, but generally also in the unswitched state, so-called domains.

The active electrical switching elements of the active matrix include both bipolar structures and diodes, e.g. MIM diodes or back to back diodes with "reset" if necessary, as well as three-pole structures such as transistors, e.g. Thin film transistors (TFTs from "thin film transistors") or varistors are used. TFTs are preferred for the liquid crystal display devices according to the present application. The active semiconductor medium of these TFTs is amorphous silicon (a-Si), polycrystalline silicon (poly-Si) or cadmium silk (CdSe), preferably a-Si or poly-Si. Here, poly-Si refers equally to high-temperature and low-temperature poly-Si

In the case of liquid crystal switching elements according to a preferred embodiment of the present invention, the liquid crystal layer preferably has an optical delay (d • Δn) from 0.14 μm to 0.42 μm, particularly preferably from 0.22 μm to 0.34 μm, particularly preferably from 0, 25 μm to 0.31 μm, very particularly preferably from 0.27 μm to 0.29 μm and ideally from 0.28 μm.

Liquid crystal materials with a small double refraction Δn are preferably used for this purpose. The birefringence of the liquid crystal materials is preferably 0.02 to 0.09, particularly preferably 0.04 to 0.08, particularly preferably 0.05 to 0.075, very particularly preferably 0.055 to 0.070 and ideally 0.060 to 0.065.

In liquid crystal display devices with liquid crystal cells with a diagonal of up to 6 ", layer thicknesses of the liquid crystal layer from μm to 4 μm and particularly from 2 μm to 3 μm are preferred. In liquid crystal display devices with liquid crystal cells with a diagonal len from 10 "layer thicknesses of the liquid crystal layer from 3 microns to 6 microns and particularly from 4 microns to 5 microns are preferred.

There are two different preferred sub-forms for this preferred embodiment.

In the first of these preferred sub-embodiments of the present invention, the liquid crystal layer has an optical delay (d • Δn) from 0.20 μm to 0.37 μm, preferably from 0.25 μm to 0.32 μm, particularly preferably from 0.26 μm to 0.30 microns, most preferably from 0.27 microns to 0.29 microns, and most preferably from 0.28 microns.

In this preferred sub-embodiment, the display element surprisingly does not require a λ / 4 layer in some applications. Nevertheless, with the appropriate polarizer position, preferably at an angle of essentially 45 ° to the preferred liquid crystal direction, it is characterized by good brightness, excellent contrast and excellent viewing angle dependency and very good grayscale and color level display. Without a λ / 4 layer, a very wide viewing angle area is achieved for the viewing angle Θ, but not for all viewing angles Φ. In contrast to this, the viewing angle area for the switching elements with λ / 4 layer is significantly more centrosymmetric, that is, for all viewing angles Φ it extends to similar, large values of the viewing angle Θ.

In the second of these preferred sub-embodiments of the present invention, the display elements preferably contain a λ / 4 layer and the liquid crystal layer has an optical delay [(d • Δn) ι_c] from 0.10 to 0.45 μm, preferably 0.20 μm to 0.37 μm, particularly preferably from 0.25 μm to 0.32 μm, very particularly preferably from 0.26 μm to 0.30 μm, particularly preferably from 0.27 μm to 0.29 μm, and am most preferably 0.28 µm. The liquid crystal layer thus behaves in the unswitched state approximately like a λ / 2 layer. Also preferred here is an embodiment in which (d • Δn) c differs from 0.28 μm, specifically in the range from 0.10 μm to 0.27 μm or 0.30 μm to 0.45 μm, particularly preferably from 0.14 μm to 0.25 μm or 0.32 μm to 0.42 μm, very particularly preferably from 0.22 μm to 0.25 μm, or from 0.32 μm to 0.34 μm.

In the previous application the wavelength λ refers to the wavelength of the maximum sensitivity of the human eye

554 nm, unless explicitly stated otherwise.

The terms λ / 4 layer and λ / 4 plate, or λ / 2 layer and λ / 2 plate are used interchangeably in the present application as a rule. The term λ in λ / 4-layer and λ / 2-layer means a wavelength in the range of λ ± 30%, preferably λ + 20%, particularly preferably λ ± 10%, particularly preferably λ ± 5% and very particularly preferably λ ± 2%. Unless otherwise stated, the wavelength here is 554 nm. The wavelength of the λ / 4 layer or λ / 2 layer is specified in general and in particular in the case of a noticeable spectral distribution as its central wavelength.

The λ / 4 layer or λ / 2 layer is an inorganic layer or preferably an organic layer, e.g. made of a birefringent polymer, e.g. stretched films (PET) or liquid crystalline polymers.

The use of especially the smaller of the preferred layer thicknesses of the liquid crystal layer is preferred in view of the advantageous, short switching times that can be achieved. In addition, it rather allows the use of conventional liquid crystal materials or at least places less demands on the often difficult realization of the small Δn values.

In contrast, the use of liquid crystal materials with a particularly small Δn is preferred in view of the lower dependence of the layer thickness on the contrast and the background color of the liquid crystal switching elements. In addition, especially in the case of liquid crystal cells with larger diagonals, the production of the display elements in this embodiment is possible with significantly higher yields. For a wide working temperature range, liquid crystal materials with a relatively high clearing point are particularly preferred since the effect of the λ / 4 layer is clearly temperature-dependent due to the temperature dependence of the birefringence of the liquid crystal materials [ΔΠLC (T)] and ΔΠLC (T) for liquid crystal materials with a high Clearing point is relatively low. The temperature dependency of the entire optical arrangement is thus kept relatively small and can, if necessary, also be compensated for more easily.

In a second preferred embodiment of the present invention, the liquid crystal layer has an optical delay of 0.07 μm to 0.21 μm, preferably 0.11 μm to 0.17 μm, particularly preferably 0.12 μm to 0.16 μm, in particular preferably from 0.13 μm to 0.15 μm and very particularly preferably from 0.14 μm. In this preferred embodiment, the display element preferably has at least one birefringent layer, preferably one λ / 2 layer or two λ / 4 layers, in addition to the liquid crystal layer.

For this purpose, liquid crystal materials with a small double refraction Δn are also preferably used. The birefringence of the liquid crystal materials is preferably 0.02 to 0.09, particularly preferably 0.04 to 0.08, particularly preferably 0.05 to 0.07, very particularly preferably 0055 to 0.065 and ideally approximately 0.060.

The layer thickness of the liquid crystal layer is generally 0.5 μm to 7 μm, preferably 1 μm to 5 μm, particularly preferably 1.5 μm to 4 μm and particularly preferably 2 μm to 2.5 μm. Displays with liquid crystal cells with smaller diagonals, in particular in the range from 0.5 "to 6", in particular in the range from 1 "to 4", are particularly preferred.

In this second preferred embodiment, the liquid crystal switching elements preferably contain two λ / 4 layers or particularly preferably one λ / 2 layer. The two λ / 4 layers can be used on different sides of the liquid crystal layer, but they can also be on the same side of the liquid crystal layer. Especially when the optical delay of the liquid crystal layer [(d • ΔΠ) L _C ] is significantly different from 0.14 μm, especially when it is in the range from 0.07 μm to 0.12 μm or from 0.16 μm to 0.21 μm, the use of two λ / 4 layers or one λ / 2 layer is necessary.

The liquid crystal switching elements according to the present application can be operated transmissively, transflectively or reflectively. The transmissive or transflective mode of operation is preferred, the transmissive mode of operation being particularly preferred.

Dielectric or metallic layers can be used as reflectors. Metallic reflector layers are preferred. When using metallic reflectors, a greater variation in the optical delay of the liquid crystal layer can be tolerated. If a dielectric mirror is used, the optical delay of the liquid crystal layer, in particular in the case of the switching elements without a birefringent layer, is essentially λ / 4. When using a second linear polarizer between the liquid crystal layer and the reflector, a dielectric reflector is preferably used, which preferably has a low proportion of depolarized reflection.

Particularly preferred parameter combinations are given in WO 01/07962, Tables 1 and 2.

The invention is illustrated by the example below.

example

Below, the liquid crystalline compounds are represented by acronyms.

"C", "P", "D", "G", "U" and "Z" have the meanings defined below:

Z -C (OK

Furthermore mean:

"n" R = -C _n H _{n +} ι

"V" R = -CH = CH ₂

"VI" R = -CH ⁼ CH-C | H ₂ ι ₊ ι

"kW R = _ ~ Cι _< H] _< -CH ^::::: CH-C | H ₂ ι ₊ -

"On" R = -OC _n H2n + 1

"nO" R = C _n H _{2n +} ιO- iipii X ⁼ -F

"Cl" X -Cl

"OT" X = -OCF ₃

"TO" X __ F ₃ CO-

The substituent on the left side of a structural formula is given first and then - separated by a hyphen - the substituent on the right side.

A liquid crystal switching element with anti-parallel edge orientation and a polyimide orientation layer, a twist angle of 0 ° and a surface tilt angle of 1.4 ° was realized. The switching element contained a λ / 4 layer and crossed polarizers, which took an angle of 45 ° to the rubbing direction of the substrates. The structure of the liquid crystal switching element corresponds to the structure shown in Figure 1 of WO 01/07962. The optical delay of the liquid crystal layer was 0.277 μm. The composition of the liquid crystal mixture used is given in Table 1 below, together with the properties of the mixture as such and the characteristic voltages in the switching element.

Table 1

Composition wt% properties

CC-3-01 5.0 transition T (S, N) <-30.0 ° C

CCZC-3-3 3.0 clearing point T (N, l) = + 68.0 ° C

CCZC-3-5 3.0 Δn (589 nm, 20 ° C) = + 0.0602

CCU-2-F 6.0 Δε (1 kHz, 20 ° C) = + 10.3

CCZU-2-F 6.0 γι (20 ° C) = 161 m Pa s

CCZU-3-F 16.0 d • Δn = 0.277 μm

CCZU-5-F 6.0 Twist = 0 ° C

CDU-2-F 10.0

CDU-3-F 12.0 V ₁₀ (20 ° C) = 1, 22 V

CDU-5-F 8.0 V ₅₀ (20 ° C) = 1.47 V

CC-3-T 9.0 V ₉₀ (20 ° C) = 1.85 V

CC-5-T 12.0

CCPC-3-4 4.0

Σ 100.0

The mixture according to Table 1 was polymerizable with the different concentrations of the compounds Ij given in Table 2 Compound and 2% UV initiator Irgacure 651 doped. After the e / o cells had been filled, polymerization was carried out by irradiation with a UV lamp (peak wavelength 375 nm, irradiance approximately 50 mW / cm ² , 2 minutes).

Then the switching times and electro-optical parameters were measured in the structure described above. To measure the switching times, the switch was made from 0 to 10V. The results are summarized in Table 2 below.

Table 2

The total _{switching time} T _on + T _0ff can be reduced by approximately 20% by adding 1% by weight of polymerizable compound Ij. Furthermore, the higher concentrations (0.75% and 1.0%) show significantly flatter e / o curves. The slope parameter V ₉₀ / V ₁₀ is about 25% larger than without adding the polymer. This is particularly advantageous for controlling gray levels and for reducing the gray level switching time.

Claims

Patent claims

1. Liquid-crystalline medium containing a) one or more liquid-crystalline compounds and b) polymers, composed of one or more polymerizable compounds of the general formula (I)

P ¹ -Sp ¹ -X ¹ -A ¹ -(Z ¹ -A ² ) _n -R (I)

in which mean:

RH, F, Cl, CN, SCN, SF ₅ H, N0 ₂ , straight-chain or branched alkyl with 1 to 12 carbon atoms, whereby one or two non-adjacent CH ₂ groups are also replaced by -O-, -S- ,

-CH=CH-, -CO-, -OCO-, -COO-, -O-COO-, -S-CO-, -CO-S-, -CH=CH- or -C≡C- can be replaced in this way can mean that O and/or S atoms are not directly ^linked to each other, or -X ² -Sp ² -P ² ,

P and P ² each independently contain a polymerizable group, preferably -0(CO)-(CH ₂ )o-CH=CH ₂ , -0(CO)-CH=CH-(CH ₂ ) _p -H, -CH= CH-(CH ₂ ) _q -H, or -0(CO)-C(CH ₃ )=CH-(CH ₂ ) _r -H with o, p, q, r = 0 - 8,

Sp ¹ and Sp ² each independently of one another a spacer group, preferably -(CH ₂ ) _m - with m = 1 - 8, or a single bond,

X ¹ and X ² each independently of one another -O-, -S-,

-OCH ₂ -, -CH ₂ 0-, -CO-, -COO-, -OCO-, -OCO-O, -CO-NR ⁰ -, -NR°-CO-, -OCH ₂ -, -CH ₂ 0-, -SCH ₂ -, -CH ₂ S-, -CH=CH-COO-, -OOC-CH=CH- or a single bond,

A ¹ and A ² are each independently 1,4-phenylene, in which one or more CH-

Groups can be replaced by N, 1,4-cyclohexylene, in which one or more non-adjacent CH ₂ groups can also be replaced by O and/or S, 1,4-cyclohexenylene, 1,4-BicycIo-(2,2 ,2)-octylene,

Piperidine-1,4-diyl, naphthaIyne-2,6-diyl, decahydronaphthalene-2,6-diyl, 1,

2,

3,

4-Tetrahydro-naphthalene-2,6-diyl or lndan-2,

5-diyl, where all of these groups can be unsubstituted or substituted one or more times by L,

L F, Cl, CN or alkyl, alkoxy, alkylcarbonyl,

Alkoxycarbonyl or alkylcarbonyloxy with 1 to 7 carbon atoms, including one or more

H atoms can be replaced by F or Cl,

Z ¹ -O-, -S-, -CO-, -COO-, -OCO-, -O-COO-, -OCH ₂ -, -CH ₂ 0-, -SCH ₂ -, -CH ₂ S-, _-CF20- ,

-OCF ₂ -, -CF ₂ -S-, -SCF ₂ -, -CH ₂ CH ₂ -, -CF CH ₂ -, -CH2-CF2-, -CF2-CF2-, -CH ⁼ CH-, -CF =CF-, -C≡C-, -CH=CH-COO-, -OCO-CH=CH-, CR°R ⁰⁰ or a single bond, and

R ° and R ⁰⁰ each independently H or alkyl with 1 to 4 carbon atoms,

n 0, 1 or 2. Liquid crystalline medium according to claim 1, characterized in that the polymerizable compounds are selected from the following formulas

P -(CH ₂ ) _m1 -0 OO >-0-(CH _{2 2} -P (li)

where P ¹ and P ² have the meaning given above, Z ² and Z ³ each independently have one of the meanings given for Z ¹ , m1 and m2 each independently mean 1 to 8, r1 and r2 each independently mean 0 or 1 , and R ^a and R ^b each independently represent H or CH ₃ , and L ¹ represents H or -CH ₃ .

Liquid-crystalline medium according to claim 1 or 2, characterized in that P ¹ and P ² each independently represent a polymerizable group selected from

-0(CO)-(CH ₂ ) _o -CH=CH ₂ , -0(CO)-CH=CH-(CH ₂ ) _p -H, -CH=CH-(CH ₂ ) _q -H and -0 (CO)-C(CH ₃ )=CH-(CH ₂ ) _r -H with o, p, q, r = 0 - 8.

Liquid-crystalline medium according to one of claims 1 - 3, characterized in that the polymerizable compounds are selected from the following compounds:

_{1 0} 5. Liquid crystalline medium according to one of claims 1 - 4, containing 0.01 - 10% by weight of polymers b).

6. Mixtures for producing liquid-crystalline media according to one of claims 1-5, containing

A ₅ a) one or more liquid-crystalline compounds, b) one or more compounds of the general formula I, c) optionally one or more polymerization initiators.

7. Liquid crystal switching element, comprising a liquid crystal layer 2Q made of the liquid crystalline medium according to one of claims 1

5.

8. An electro-optical liquid crystal display system containing a plurality of liquid crystal switching elements according to claim 7, wherein

_2c these are arranged in matrix form.

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