JP4454057B2 - Liquid crystal medium - Google Patents

Description

及び少なくとも1つの式II；
【化１０】

(式中、
R¹からR³は、それぞれ互いに独立して、炭素原子1個から8個を有するアルキル又はアルコキシであり、
L¹からL³は、それぞれ互いに独立して、H、F又はClであり、
Xは、F又はClであり、
【化１１】

mは、0又は1である)
の化合物を含有する、前記液晶媒体に関する。
【００１８】
好適な態様は：
a) 式Iaから式Id；
【化１２】

(式中、アルキルは、C_1-6-アルキルであり、Lは、H又はFであり、そしてXは、F又はClである)
から選択される化合物を少なくとも1つ含有する液晶媒体であり、特に式Iaの化合物を少なくとも1つ及び／又は式中XがF又はClであり、そしてLが好ましくはHである式Ibの化合物を少なくとも1つ含有する液晶媒体である。
b) 式IIaから式IIe；
【化１３】

(式中、アルキルは、C_1-6-アルキルである)
から選択される化合物を少なくとも3つ含有する液晶媒体であり、特に式IIaの化合物を少なくとも1つ、式IIbの化合物を少なくとも1つ、及び／又は式IIcの化合物を少なくとも1つ含有する液晶媒体である。
c) 式III；
【化１４】

(式中R⁴及びR⁵は、それぞれ独立して、炭素原子1個から8個を有するアルキル、アルコキシ又はアルケニルであり、そして
【化１５】

sは、0又は1である)
の化合物1又は2以上をさらに含有する媒体である。
d) 式I及び式IIから選択される化合物4又は5以上そして式IIIの化合物少なくとも1つを、本質的に含有する媒体である。
e) 式IIの化合物を少なくとも3つ含有する媒体である。
f) 混合物全体の式Iの化合物の割合が、2重量％から15重量％である媒体である。
g) 混合物全体の式IIの化合物の割合が、少なくとも40重量％である媒体である。
h) 混合物全体の式IIIの化合物の割合が、2重量％から15重量％である媒体である。
i) 誘電異方性(Δε)の範囲が-1.5から+1.5である4環化合物を少なくとも1つ含有する液晶媒体である。
j) 式IIIaから式IIId；
【化１６】

(式中、アルキルは、C_1-6-アルキルであり、Rは、C_1-6-アルキル又は-アルコキシ又はC_2-6-アルケニルであり、そしてLは、H又はFである)
から選択される化合物を少なくとも3つ含有する液晶媒体である。
k) 式Iの化合物1又は2以上を2重量％から15重量％、
式IIの化合物1又は2以上を40重量％から85重量％、そして
式IIIの化合物1又は2以上を5重量％から40重量％、
を本質的に含有する液晶媒体である。
【００１９】
本発明は、さらにECB効果を基本とするアクティブマトリクスアドレッシングを有する電気光学プロジェクションディスプレイに関し、上記液晶媒体を、誘電体として含有することを特徴とする前記プロジェクションディスプレイに関する。
【００２０】
液晶混合物は、好ましくは少なくとも80℃のネマティック相幅と、60℃以上、特に70℃以上の透明点、及び20℃で60mPa.s以下の粘度を有する。
【００２１】
本発明による液晶混合物は、約-1.5から約-5、特に約-1.8から約-4のΔεを有する。ここでΔεは、誘電異方性を意味する。
【００２２】
液晶混合物の複屈折率Δnは、一般的に0.07と0.14の間、好ましくは0.08と0.13の間であり、及び／又は誘電率ε||は、3より大きいか又は等しく、好ましくは3.2から4.5である。
【００２３】
誘電体は、さらに当業者にとって公知及び刊行物に記載の添加物を含有することもできる。例えば、多色性染料を0％から15％添加することができ、さらに導電性を改善するための導電性の塩、好ましくはエチルジメチルドデシルアンモニウム4-ヘキソキシベンゾエート、テトラブチルアンモニウムテトラフェニルボレート又はクラウンエーテル類の複合塩(例えば、Haller等による、Mol. Cryst. Liq. Cryst. Volume 24, pages 249-258 (1973)参照)又は誘電異方性、粘度及び／又はネマティック相の整向を改善するための物質を添加できる。そのような物質は、例えばDE-A 22 09 127、同22 40 864、同 23 21 632、同23 38 281、同 24 50 088、同 26 37 430及び同 28 53 728に記載されている。
【００２４】
本発明による液晶相の式Iから式IVの個々の成分は、それぞれ公知であるか、又は刊行物に記載の標準的な方法を基本としているので、それらの調製方法は、当業者による先行技術により容易に誘導することができる。
【００２５】
式Iの化合物に対応するものは、例えばUS 5,328,644又はJP 94-264 059に記載されている。
式IIの化合物に対応するものは、例えばEP 0 364 538に記載されている。
式IIIの化合物に対応するものは、例えばEP 0 132 553、DE 26 36 684及びEP 0 022 183に記載されている。
4環化合物は、例えばEP 0 030 277、EP 0 064 193、JP 19 89 016、JP 002656、EP 0 445 274及びGB 22 40 778に記載されている。
【００２６】
式IIIにおいて“アルケニル”という語は、炭素原子2個から7個を有する直鎖又は分子鎖状アルケニル基を包含する。直鎖アルケニル基が、好適である。さらに好適なアルケニル基は、C₂-C₆-1E-アルケニル、C₄-C₆-3E-アルケニル、C₅-C₆-4-アルケニル、特にC₂-C₆-1E-アルケニル、C₄-C₆-3E-アルケニル及びC₅-C₆-4-アルケニルである。
特に好適なアルケニル基は、ビニル、1E-プロペニル、1E-ブテニル、1E-ペンテニル、1E-ヘキセニル、3-ブテニル、3E-ペンテニル、3E-ヘキセニル、4-ペンテニル、4Z-ヘキセニル、4E-ヘキセニル、5-ヘキセニル及び6-ヘプテニルである。炭素原子6個までを有するアルケニル基が、特に好適である。
【００２７】
本発明によるディスプレイのネマティック液晶混合物は、好ましくは式Iの化合物を2％から15％含有する。
混合物は、好ましくは4から20の式I、式II及び式IIIの化合物、特に5から15の化合物を含有する。
【００２８】
式Iから式IIIの化合物に加えて、他の成分が、例えば混合物全体の45％の量まで、しかし好ましくは35％まで、特に10％まで存在してもよい。
他の成分とは、好ましくはネマティック基体又はネマティック相形成性物質から、特に公知の物質、アゾキシベンゼン類、ベンジリデンアニリン類、ビフェニル類、ターフェニル類、フェニル又はシクロヘキシルベンゾエート類、フェニル又はシクロヘキシルシクロヘキサンカルボキシレート類、フェニルシクロヘキサン類、シクロヘキシルビフェニル類、シクロヘキシルシクロヘキサン類、シクロヘキシルナフタレン類、1,4-ビス-シクロヘキシルビフェニル類又はシクロヘキシルピリミジン類、フェニル-又はシクロヘキシルジオキサン類、任意にハロゲン化されたスチルベン類、ベンジルフェニルエーテル類、トラン類及び置換された桂皮酸類からなる群から、選択される。
【００２９】
この種の液晶相の成分として適切である最も重要な化合物は、式IV；
R^5'-L-G-E-R^6' IV
(式中、L及びEは、1,4-二置換ベンゼン環及びシクロヘキサン環、4,4’-二置換ビフェニル、フェニルシクロヘキサン系及びシクロヘキシルシクロヘキサン系、2,5-二置換ピリミジン環及び1,3-ジオキサン環、2,6-二置換ナフタレン、ジ-及びテトラヒドロナフタレン、キナゾリン及びテトラヒドロキナゾリンを含む群からのそれぞれ炭素環式及び複素環式環系であり、
Gは、
-CH=CH- -N(O)=N-
-CH-CQ- -CH=N(O)-
-C≡C- -CH₂-CH₂-
-CO-O- -CH₂-O-
-CO-S- -CH₂-S-
-CH=N- -COO-Phe-COO-
であるか、又はC-C結合であり、
Qは、ハロゲン、好ましくは塩素であるか、又は-CNであり、そしてR^5'及びR^6'は、それぞれ、炭素原子18個まで、好ましくは8個までを有するアルキル、アルコキシ、アルカノイルオキシ又はアルコキシカルボニルオキシであるか、又はこれらの基の1つが、CN、NCS、NC、NO₂、OCF₃、CF₃、F、Cl又はBrで置換されてもよい)
により特徴づけることができる。
【００３０】
これらの化合物のほとんどでは、R^5'及びR^6'は互いに異なっており、これらの基の1つは、通常、アルキル又はアルコキシ基である。他の提案された置換基の変形も又同様である。そのような物質又はその混合物の多くは、商業的に入手可能である。全てのこれらの物質は刊行物から公知の方法により調製することができる。
【００３１】
本発明による液晶ディスプレイの構造は、例えばEP-A 0 240 379に記載のような通常の構造に相当する。
【００３２】
本発明の例を以下に示すが、これにより限定されるものではない。本明細書中記載の百分率は重量により、全ての温度は℃で示される。
【００３３】
以下の略号を使用する：
【化１７】

【化１８】

上記の化合物は、好適な混合物成分である。
【００３４】
さらに：
Δｎは、20℃及び589nmで測定された光学異方性を示し、
n_eは、20℃及び589nmでの異常光線屈折率を示し、
Δεは、20℃での誘電異方性を示し、
ε‖は、分子軸に対して平行方向の誘電率を示し、
cpは、透明点［℃］を示し、
νは、所定の温度℃での粘度［mm²s^-1］を示す。
【００３５】
しきい値電圧を測定するのに使用したディスプレイは、5μｍの間隔で2枚の平面平行外板があり、及びその外板の内側に液晶のホメオトロピック配向を引き起こす、表面にレシチン配向膜を伴う電極層を有する。
【００３６】
例 1
混合物を、以下のように調製する。
【表１】

【００３７】
例 2
混合物を、以下のように調製する。
【表２】

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal medium based on a mixture of polar compounds having negative dielectric anisotropy, and a display containing the medium, in particular an electro-optic display having an active matrix addressing based on the ECB effect.
[0002]
[Prior art]
The principle of electrically controlled birefringence, the ECB effect, or the DAP effect (alignment phase deformation) was first described in 1971 (MF Schieckel and K. Fahrenschon, “Nematic liquid crystals with vertical alignment in an electric field. ”, Appl. Phys. Lett. 19 (1971), 3912). Subsequently, there are references by JF Kahn (Appl. Phys. Lett. 20 (1972), 1193) and G. Labrunie and J. Robert (J. Appl. Phys. 44 (1973), 4869).
[0003]
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) According to the literature by the liquid crystal phase, the ratio between the elastic constants K ₃ / K ₁ and the optical anisotropy Δn must be large for use in high information display elements based on the ECB effect And the dielectric anisotropy Δε must be between −0.5 and −5. An electro-optic display element based on the ECB effect has a homeotropic edge orientation.
[0004]
Industrial application of this effect in electro-optic display elements requires a liquid crystal phase that must satisfy many requirements. Of particular importance here are chemical resistance to moisture, air and heat, irradiation in the infrared, visible and ultraviolet regions and physical effects such as direct current and alternating electric fields. Furthermore, an industrially usable liquid crystal phase requires a liquid crystal intermediate phase and a low viscosity at an appropriate temperature range.
[0005]
Of the series of compounds having a liquid crystal mesophase disclosed heretofore, no single compound satisfies all these requirements. In general, therefore, a mixture of 2 to 25, preferably 3 to 18, compounds is prepared in order to obtain a material that can be used as a liquid crystal phase. However, since a liquid crystal material having substantially negative dielectric anisotropy and appropriate long-term stability has not been available in the past, an ideal phase cannot be easily produced by this method.
[0006]
Matrix liquid crystal displays (MLC displays) are known. An example of a non-linear element that can be used to switch individual pixels individually is an active element (ie, a transistor). This refers to the “active matrix” and can be distinguished into two types:
1. MOS (metal oxide semiconductor) transistor on a silicon wafer as the substrate,
2. Thin film transistor (TFT) on glass plate as substrate,
It is.
[0007]
For Type 1, the electro-optic effect used is usually dynamic scattering or the guest-host effect. The use of single crystal silicon as a substrate material limits the display size, as even the coordinated assembly of various display components can result in problems with the joint.
[0008]
The more promising type 2 is preferred and the electro-optic effect used is usually the TN effect. Two technologies are distinguished, namely TFTs containing compound semiconductors such as CdSe and TFTs based on polycrystalline or amorphous silicon. Global research efforts are focused on the latter technology.
[0009]
A transparent counter electrode is installed inside one glass plate, and a TFT matrix is provided inside one glass plate of the display. When compared by the size of the pixel electrode, the TFT is very small and therefore has virtually no adverse effect on the image. This technique can also be extended to a full color compatible image display in which a mosaic of red, green and blue filters is arranged so that each filter element is placed opposite a switchable pixel.
[0010]
Conventionally disclosed TFT displays typically operate as TN cells with orthogonal polarizers in transmitted light and illuminate from the rear.
[0011]
The term matrix liquid crystal display here encompasses any matrix display that includes integrated nonlinear elements, ie displays that include passive elements such as varistors or diodes (MIM = metal-insulator-metal) in addition to the active matrix. To do.
[0012]
This type of matrix liquid crystal display is particularly suitable for TV applications (eg pocket TV) or advanced information displays for automobiles or aircraft. In addition to problems with contrast angle dependence and response time, the unfavorable resistivity of the liquid crystal mixture creates difficulties for matrix liquid crystal displays [TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E. , SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay 84, Sept. 1984: A210-288 Matrix LCD controlled by two-stage diode ring, p.141 ff, Paris , STOROMER, M., Proc. Eurodisplay 84, Sept. 1984: Thin-film transistor design for matrix addressing of TV LCDs, p.145 ff, Paris]. As the resistance decreases, the contrast of the matrix liquid crystal display deteriorates. The specific resistance of the liquid crystal mixture is generally reduced by interaction with the internal surface of the display, which generally shortens the lifetime of the matrix liquid crystal display, so large (initial) resistance is acceptable over long-term operation. It is very important for displays that need to have a resistance value.
[0013]
The disadvantages of the matrix liquid crystal-TN displays disclosed in the prior art are due to the relatively low contrast, relatively large viewing angle dependence and difficulty in displaying gray shades of these displays.
[0014]
EP 0 474 062 discloses a matrix liquid crystal display based on the ECB effect. The liquid crystal mixture described therein is based on 2,3-difluorophenyl derivatives containing ester, ether or ethyl bridges and has a small “voltage holding ratio” (HR) value after exposure to ultraviolet light, so it is a projection type. Cannot be used for other displays.
[0015]
Accordingly, there continues to be a great need for matrix liquid crystal displays with very large specific resistances that allow various halftone displays, at the same time, wide operating temperatures, short response times and low threshold voltages.
[0016]
[Problems to be solved by the invention]
The object of the present invention is to provide matrix liquid crystal displays, in particular projection displays, which are based on the ECB effect and at the same time have a very large resistivity, having the above-mentioned disadvantages or very little. And to provide a liquid crystal medium useful for them.
[0017]
[Means for Solving the Problems]
It has now been found that this objective can be achieved when nematic liquid crystal mixtures containing at least one compound of formula I and at least one compound of formula II are used in these display elements.
The present invention therefore provides a liquid crystal medium based on a mixture of polar compounds having negative dielectric anisotropy, comprising at least one formula I;
[Chemical 9]

And at least one formula II;
[Chemical Formula 10]

(Where
R ¹ to R ³ are each independently alkyl or alkoxy having 1 to 8 carbon atoms,
L ¹ to L ³ are each independently H, F or Cl,
X is F or Cl;
Embedded image

m is 0 or 1)
The present invention relates to the above liquid crystal medium.
[0018]
Preferred embodiments are:
a) Formula Ia to Formula Id;
Embedded image

_Where alkyl is C _1-6 -alkyl, L is H or F, and X is F or Cl.
A liquid crystal medium containing at least one compound selected from: in particular at least one compound of formula Ia and / or a compound of formula Ib wherein X is F or Cl and L is preferably H Is a liquid crystal medium containing at least one of the above.
b) Formula IIa to Formula IIe;
Embedded image

( _Wherein alkyl is C _1-6 -alkyl)
A liquid crystal medium comprising at least three compounds selected from: in particular at least one compound of formula IIa, at least one compound of formula IIb, and / or at least one compound of formula IIc It is.
c) Formula III;
Embedded image

Wherein R ⁴ and R ⁵ are each independently alkyl, alkoxy or alkenyl having 1 to 8 carbon atoms and

(s is 0 or 1)
A medium further containing one or more of the compounds.
d) A medium which essentially contains at least one compound 4 or 5 and at least one compound of formula III selected from formula I and formula II.
e) A medium containing at least three compounds of formula II.
f) A medium in which the proportion of the compound of formula I in the total mixture is 2% to 15% by weight.
g) A medium in which the proportion of compounds of the formula II in the total mixture is at least 40% by weight.
h) A medium in which the proportion of the compound of formula III in the total mixture is 2% to 15% by weight.
i) A liquid crystal medium containing at least one tetracyclic compound having a dielectric anisotropy (Δε) in the range of −1.5 to +1.5.
j) Formula IIIa to Formula IIId;
Embedded image

Wherein alkyl is C _1-6 -alkyl, R is C _1-6 -alkyl or -alkoxy or C _2-6 -alkenyl and L is H or F.
A liquid crystal medium containing at least three compounds selected from:
k) 2 to 15% by weight of a compound of formula I 1 or 2 or more,
40% to 85% by weight of compound II or more of formula II and 5% to 40% by weight of compound 1 or 2 of formula III,
Is essentially a liquid crystal medium.
[0019]
The present invention further relates to an electro-optic projection display having an active matrix addressing based on the ECB effect, and to the projection display comprising the liquid crystal medium as a dielectric.
[0020]
The liquid crystal mixture preferably has a nematic phase width of at least 80 ° C., a clearing point of 60 ° C. or more, in particular 70 ° C. or more, and a viscosity of 60 mPa.s or less at 20 ° C.
[0021]
The liquid crystal mixture according to the invention has a Δε of about −1.5 to about −5, in particular about −1.8 to about −4. Here, Δε means dielectric anisotropy.
[0022]
The birefringence Δn of the liquid crystal mixture is generally between 0.07 and 0.14, preferably between 0.08 and 0.13, and / or the dielectric constant ε || is greater than or equal to 3, preferably 3.2 to 4.5. It is.
[0023]
The dielectric may further contain additives known to those skilled in the art and described in the publications. For example, pleochroic dyes can be added from 0% to 15%, and further conductive salts to improve the conductivity, preferably ethyldimethyldodecyl ammonium 4-hexoxybenzoate, tetrabutyl ammonium tetraphenyl borate or Improved crown ether complex salts (see, for example, Haller et al. Mol. Cryst. Liq. Cryst. Volume 24 , pages 249-258 (1973)) or dielectric anisotropy, viscosity and / or nematic phase alignment Substances to do so can be added. Such substances 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.
[0024]
Since the individual components of formula I to formula IV of the liquid crystal phases according to the invention are each known or based on standard methods described in the publication, their preparation methods are prior art by those skilled in the art. Can be guided more easily.
[0025]
Corresponding compounds of the formula I are described, for example, in US 5,328,644 or JP 94-264 059.
Corresponding compounds of the formula II are described, for example, in EP 0 364 538.
Corresponding compounds of the formula III are described, for example, in EP 0 132 553, DE 26 36 684 and EP 0 022 183.
Tetracyclic compounds are described, for example, in EP 0 030 277, EP 0 064 193, JP 19 89 016, JP 002656, EP 0 445 274 and GB 22 40 778.
[0026]
In formula III, the term “alkenyl” includes straight or molecular chain alkenyl groups having from 2 to 7 carbon atoms. Straight chain alkenyl groups are preferred. Further suitable alkenyl groups are C ₂ -C ₆ -1E-alkenyl, C ₄ -C ₆ -3E-alkenyl, C ₅ -C ₆ -4-alkenyl, in particular C ₂ -C ₆ -1E-alkenyl, C ₄ -C ₆ -3E-alkenyl and C ₅ -C ₆ -4- alkenyl.
Particularly preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 5 -Hexenyl and 6-heptenyl. Particularly preferred are alkenyl groups having up to 6 carbon atoms.
[0027]
The nematic liquid crystal mixture of the display according to the invention preferably contains 2% to 15% of a compound of formula I.
The mixture preferably contains 4 to 20 compounds of formula I, formula II and formula III, in particular 5 to 15 compounds.
[0028]
In addition to the compounds of the formulas I to III, other components may be present, for example up to 45% of the total mixture, but preferably up to 35%, in particular up to 10%.
The other components are preferably from nematic substrates or nematic phase-forming substances, in particular known substances, azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexylbenzoates, phenyl or cyclohexylcyclohexanecarboxyl. Rates, phenylcyclohexanes, cyclohexylbiphenyls, cyclohexylcyclohexanes, cyclohexylnaphthalenes, 1,4-bis-cyclohexylbiphenyls or cyclohexylpyrimidines, phenyl- or cyclohexyldioxanes, optionally halogenated stilbenes, benzyl Selected from the group consisting of phenyl ethers, tolans and substituted cinnamic acids.
[0029]
The most important compounds suitable as components of this type of liquid crystal phase are those of formula IV;
R ^{5 '} -LGER ^6' IV
Wherein L and E are 1,4-disubstituted benzene and cyclohexane rings, 4,4′-disubstituted biphenyl, phenylcyclohexane and cyclohexylcyclohexane, 2,5-disubstituted pyrimidine rings and 1,3 Carbocyclic and heterocyclic ring systems from the group comprising -dioxane ring, 2,6-disubstituted naphthalene, di- and tetrahydronaphthalene, quinazoline and tetrahydroquinazoline respectively;
G is
-CH = CH- -N (O) = N-
-CH-CQ- -CH = N (O)-
-C≡C- -CH ₂ -CH _2-
-CO-O- -CH ₂ -O-
-CO-S- -CH ₂ -S-
-CH = N- -COO-Phe-COO-
Or is a CC bond,
Q is halogen, preferably chlorine, or —CN, and R ^{5 ′} and R ^{6 ′} are each alkyl, alkoxy, alkanoyloxy or up to 18 carbon atoms, preferably up to 8 Alkoxycarbonyloxy, or one of these groups may be substituted with CN, NCS, NC, NO ₂ , OCF ₃ , CF ₃ , F, Cl or Br)
Can be characterized.
[0030]
In most of these compounds, R ^{5 ′} and R ^{6 ′} are different from each other, and one of these groups is usually an alkyl or alkoxy group. The other proposed variations of substituents are similar. Many such materials or mixtures thereof are commercially available. All these substances can be prepared from the publications by known methods.
[0031]
The structure of the liquid crystal display according to the present invention corresponds to an ordinary structure as described in EP-A 0 240 379, for example.
[0032]
Examples of the present invention are shown below, but are not limited thereto. All percentages given herein are by weight and all temperatures are in ° C.
[0033]
Use the following abbreviations:
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The above compounds are suitable mixture components.
[0034]
further:
Δn indicates the optical anisotropy measured at 20 ° C. and 589 nm,
n _e indicates the extraordinary refractive index at 20 ° C. and 589 nm,
Δε represents the dielectric anisotropy at 20 ° C,
ε‖ indicates the dielectric constant parallel to the molecular axis,
cp indicates clearing point [° C.]
ν represents the viscosity [mm ² s ⁻¹ ] at a predetermined temperature ° C.
[0035]
The display used to measure the threshold voltage has two planar parallel skins with a spacing of 5 μm, and a lecithin alignment film on the surface that causes liquid crystal homeotropic alignment inside the skin. It has an electrode layer.
[0036]
Example 1
The mixture is prepared as follows.
[Table 1]

[0037]
Example 2
The mixture is prepared as follows.
[Table 2]

Claims (11)

A liquid crystal medium based on a mixture of polar compounds having negative dielectric anisotropy, comprising at least one formula I;

And at least one formula II;

(Wherein R ¹ to R ³ are each independently alkyl or alkoxy having 1 to 8 carbon atoms , X is F or Cl,

m is 0 or 1). Formula Ia;

(Wherein alkyl, C _1-6 - alkyl Le a), characterized in that it contains at least one compound represented by the medium of claim 1. Formula IIa to Formula IIe;

3. A medium according to claim 1 or 2, characterized in that it contains at least three compounds selected from (wherein alkyl is C _1-6 -alkyl). Formula III;

Wherein R ⁴ and R ⁵ are each independently alkyl, alkoxy or alkenyl having 1 to 8 carbon atoms, and

The medium according to any one of claims 1 to 3, further comprising 1 or 2 or more compounds of s is 0 or 1.  The medium according to any one of claims 1 to 4, characterized in that it contains 4 or more compounds selected from formula I and formula II and at least one compound of formula III.  The medium according to any one of claims 1 to 5, further comprising at least one tetracyclic compound having a dielectric anisotropy (Δε) in the range of -1.5 to +1.5.  4. Liquid crystal medium according to claim 3, characterized in that it contains at least one compound of formula IIa and at least one compound of formula IIb and / or formula IIc. Formula IIIa to Formula IIId;

(Wherein alkyl is C _1-6 -alkyl, R is C _1-6 -alkyl or -alkoxy or C _2-6 -alkenyl, and L is H or F) The medium according to claim 1, comprising at least one compound to be produced. 2 to 15% by weight of a compound of formula I or 2 or more,
40% to 85% by weight of compound II or more of formula II and 5% to 40% by weight of compound 1 or 2 of formula III,
The liquid crystal medium according to claim 1, comprising:  10. An electro-optical display having an active matrix addressing based on an ECB effect, wherein the liquid crystal medium according to claim 1 is contained as a dielectric.  11. The display according to claim 10, wherein the display is a projection display.