JP5312723B2 - Nematic liquid crystal mixture and display containing the mixture - Google Patents

Abstract

A liquid crystal mixture contains specific cyano group content compound (1), cyano group compound (1a) (10 wt.% or less) and cyano group compound (1b) (10 wt.% or less). - A liquid crystal mixture contains specific cyano group content compound of formula (1), cyano group compound of formula (1a) (10 wt.% or less) and cyano group compound of formula (1b) (10 wt.% or less). - R1 = 1-12C alkyl, alkoxy or alkenyl, in which 1 or 2 CH2 group which does not adjoining is replaced by -O-, -CH=CH-, -CO-, -OCO, or -COO- and oxygen atom is not further bonded directly;and - R = 1-12C alkyl, alkoxy or alkenyl. - An INDEPENDENT CLAIM is included for liquid crystal display such as twisted nematic, super twisted nematic liquid crystal display, cholesteric liquid crystal display, SSCT display and PSCT display.

Description

  The present invention relates to a novel liquid crystal mixture, its use in liquid crystal displays, in particular twisted nematic (TN) and super twist nematic (STN) liquid crystal displays having a very short response time and good steepness and angular dependence, and the novel mixture The present invention relates to a liquid crystal display containing

  TN displays are known (for example, see Non-Patent Document 1). STN displays are known (for example, Patent Literature 1; Patent Literature 2; Patent Literature 3; Non-Patent Literature 1; Non-Patent Literature 2; Non-Patent Literature 3; Non-Patent Literature 4; Non-Patent Literature 5; Non-Patent Literature 6). Non-patent document 7; Non-patent document 8; Non-patent document 9; and Non-patent document 10). In the present specification, the term STN includes all display elements having a relatively large twist having a twist angle of 160 ° to 360 °, such as a display by Waters (see Non-Patent Document 11), STN-LCDs (see Patent Literature 4), SBE-LCDs (see Non-Patent Literature 12), OMI-LCDs (see Non-Patent Literature 6), DST-LCDs (see Patent Literature 5) and BW-STN-LCDs (Non-Patent Literature) Reference 3).

Compared to a standard TN display, STN displays have a particularly good steepness of the electro-optic characteristic curve, and moderate and relatively high time division ratios with good contrast values, e.g. 32 to 64 or higher. It stands out in that it has a split ratio. In contrast, contrast in TN displays is generally high based on good dark values, and the angular dependence of contrast is lower than STN displays having a low time division ratio, eg, a time division ratio lower than 32.
Of particular importance is that TN and STN displays have very short response times, especially at relatively low temperatures. In order to obtain a short response time, conventionally, almost mono-modified additives having a relatively high vapor pressure have been used to optimize the rotational viscosity of the liquid crystal mixture. However, the response time achieved was not suitable for every application.

In order to obtain a steep electro-optical characteristic curve for the display according to the invention, the liquid crystal mixture must have a relatively large elastic constant K ₃₃ / K ₁₁ ratio value and a relatively small Δε / ε⊥ value ( Where Δε is the dielectric anisotropy and ε⊥ is the dielectric constant perpendicular to the molecular long axis).
In addition to optimizing contrast and response time, this type of mixture has additional important requirements:
1. Wide d / p window;
2. Increased long-term chemical stability;
3. Large electrical resistance;
4). Low temperature and frequency dependence of threshold voltage.

The achieved parameter combinations are still particularly for advanced time division STN displays (with time division ratios in the range of about 1/400), but also medium and low time division STN displays (each about 1/64 to (With a time division ratio in the range of 1/16) and TN displays are far from appropriate. This is due in part to the fact that various requirements are adversely affected by material parameters.
Especially moderate for liquid crystal mixtures with a very short response time and at the same time a wide operating temperature range that meets the above requirements, a large characteristic curve steepness, good contrast angular dependence and a low threshold voltage And there is a continuing need for liquid crystal mixtures for low time division ratio STN displays.

STN displays containing a compound of formula IA having a terminal alkenyl group and a compound of formula IB having a terminal 4-cyano-3-fluorophenyl group or 4-cyano-3,5-difluorophenyl group are disclosed. (For example, see Patent Document 5). However, the threshold voltage and frequency dependence of these mixtures is insufficient for certain applications.
European Patent No. 0131216B1 (EP0131216B1) German Patent No. 3423993 (DE3423993A1) European Patent No. 0098070A2 (EP0098070A2) German Patent No. 3503259 (DE-A 3503259) European Patent No. 0246842 (EP-A 0246842) M. Shut (M. Schadt) and W.W. W. Helfrich, Apple. Fis. Lett. (Appl. Phys. Lett.), 18, 127 (1971). M. M. Schadt and FF. F. Leenhouts, 17th Freiburg Congress on Liquid Crystals (8.1.0.04.87) Kay. K. Kawasaki et al., SID 87 Digest 391 (20.6) M. M. Schadt and FF. F. Leenhouts, S.I. Day 87 Digest 372 (SID87 Digest 372) (20.1) Kay. By K. Katoh et al., Japanese Journal of Applied Physics, Vol. 26, no. 11, L1784-L1786 (1987) F. F. Leenhouts et al., Apple. Fis. Lett. (Appl. Phys. Lett.), 50 (21), 1468 (1987). H. A. H.A. van Sprung and H.H. Gii. By H.G. Koopman, Jay. Apple. Fis. (J. Appl. Phys.), 62 (5), 1734 (1987). Tee. Jay. T.J. Scheffer and Jay. By J. Nehring, Apple. Fis. Lett. (Appl. Phys. Lett.), 45 (10), 1021 (1984). M. M. Schadt and FF. By F. Leenhouts, Apple. Fis. Lett. (Appl. Phys. Lett.), 50 (5), 236 (1987). E. Pee. By Raynes (E.P. Raynes), Mol. Christo. Riki. Christo. Letters (Mol. Cryst. Liq. Cryst. Letters), Vol. 4 (1), 1-8 (1986) Sea. M. W. Waters et al., Proc. Soshi. Inf. Disp. (Proc. Soc. Inf. Disp.) (New York) (1985) (Third Interm. Display Conference, Kobe, Japan) (3rd Interm. Display Conference, Kobe, Japan)) Tee. Jay. T.J. Scheffer and Jay. By J. Nehring, Apple. Fis. Lett. (Appl. Phys. Lett.), 45 (1984).

The compounds of formula I below specifically reduce the response time and threshold voltage of TN and STN mixtures while maintaining or improving (ie reducing) the frequency dependence of the operating voltage and threshold voltage. Even do.
In particular, surprisingly, when using a compound of formula I and further reducing the amount of compound of formula IIIb ^* and / or formula IIIc ^* in the TN and STN mixture, the operating voltage and threshold It has been found that the response time and threshold voltage can be reduced at the same time without significantly damaging or even improving the frequency dependence of the voltage.

Furthermore, the mixtures according to the invention are distinguished in that they have the following advantages:
They have a short response time, especially at low temperatures,
They have a low rotational viscosity,
They have a low threshold voltage and an operating voltage,
-These have a good steepness of the electro-optic characteristic curve,
They have a small frequency dependence of the operating voltage and threshold voltage,
-These enable a long shelf life and operating time of the liquid crystal display at low temperatures.

  The object of the present invention is to the extent that it does not show, or even to a small extent, the said disadvantages, and has a low threshold voltage, especially compared to mixtures from the prior art, and at the same time a short response time, especially at low temperatures and The object is to provide a liquid crystal medium for a liquid crystal display, in particular a liquid crystal medium for TN and STN displays, which has the same or improved frequency dependence of the operating voltage.

（式中、Ｒ¹は、炭素原子１〜１２個を有するアルキル基、アルコキシ基またはアルケニル基であり、これらの基中に存在する１個のＣＨ₂ 基または隣接していない２個のＣＨ₂ 基はさらに、酸素原子が相互に直接に結合しないものとして、−Ｏ−、−ＣＨ＝ＣＨ−、−ＣＯ−、−ＯＣＯ−または−ＣＯＯ−により置き換えられていてもよい） It has been found that the above problem can be solved by using the following nematic liquid crystal mixture. The nematic liquid crystal mixture according to the invention is characterized by a liquid crystal mixture containing at least one compound of the formula I:

(Wherein, R ¹ represents an alkyl group having 1 to 12 carbon atoms, alkoxy group or alkenyl group, these one CH ₂ group or not adjoining present in group two CH ₂ The group may further be replaced by -O-, -CH = CH-, -CO-, -OCO- or -COO-, assuming that the oxygen atoms are not directly bonded to each other)

（各式中、Ｒは、炭素原子１〜１２個を有するアルキル基、アルコキシ基またはアルケニル基である）。 This mixture is characterized in that it contains less than 10% by weight of the compound of formula IIIb ^* and less than 10% by weight of the compound of formula IIIc ^* :

(In each formula, R is an alkyl, alkoxy or alkenyl group having 1 to 12 carbon atoms).

（式中、Ｒ¹は、炭素原子１〜１２個を有するアルキル基、アルコキシ基またはアルケニル基であり、これらの基中に存在する１個のＣＨ₂ 基または隣接していない２個のＣＨ₂ 基はさらに、酸素原子が相互に直接に結合しないものとして、−Ｏ−、−ＣＨ＝ＣＨ−、−ＣＯ−、−ＯＣＯ−または−ＣＯＯ−により置き換えられていてもよい） Accordingly, this application is a liquid crystal mixture containing one or more compounds of formula I:

(Wherein, R ¹ represents an alkyl group having 1 to 12 carbon atoms, an alkoxy group or an alkenyl group, these one CH ₂ group or not adjoining present in group two CH ₂ The group may further be replaced by -O-, -CH = CH-, -CO-, -OCO- or -COO-, assuming that the oxygen atoms are not directly bonded to each other)

（各式中、Ｒは、炭素原子１〜１２個を有するアルキル基、アルコキシ基またはアルケニル基である）。 A liquid crystal mixture characterized in that the mixture contains less than 10% by weight of a compound of formula IIIb ^* and less than 10% by weight of a compound of formula IIIc ^* :

(In each formula, R is an alkyl, alkoxy or alkenyl group having 1 to 12 carbon atoms).

The invention also relates to corresponding liquid crystal mixtures for use in liquid crystal displays, in particular TN and STN displays, in particular in the medium to high time division range.
The present invention is also a liquid crystal display,
Two outer substrates that together with the frame form a cell,
A nematic liquid crystal mixture having positive dielectric anisotropy arranged in the cell,
An electrode layer having an alignment film present inside the outer substrate;
Have
The tilt angle between the major axis of the molecule on the outer substrate surface and the outer substrate is 0 to 30 degrees, and the twist angle from the alignment film to the alignment film of the liquid crystal mixture in the cell is 22.5 ° to 600 ° Has the number of

-Nematic liquid crystal mixture
a) 15 to 80% by weight of liquid crystal component A composed of one or more compounds having a dielectric anisotropy greater than +1.5,
b) 20 to 85% by weight of liquid crystal component B composed of one or more compounds having a dielectric anisotropy of −1.5 to +1.5,
c) a liquid crystal component D consisting of one or more compounds having a dielectric anisotropy smaller than −1.5, 0 to 20% by weight, and d) film thickness (distance of the outer substrate), if desired An amount of the optically active component C such that the ratio of the chiral nematic liquid crystal mixture to the natural pitch is about 0.2 to 1.3;
In a liquid crystal display containing
It relates to a liquid crystal display characterized in that the nematic liquid crystal mixture is a mixture according to the invention as described herein.

Particularly preferred compounds of the formula I are those in which R ¹ present in the molecule is an alkyl group having 1 to 8 carbon atoms or an alkenyl group having 2 to 7 carbon atoms. Very particularly preferably, the radical R ¹ is ethyl, n-propyl and n-pentyl, and vinyl and propen-1-yl.

The mixtures according to the invention preferably contain, in addition to the compound of the formula I, one or more alkenyl compounds of the formula II:

Where
A ⁴ is 1,4-phenylene or trans-1,4-cyclohexylene,
R ³ is an alkenyl group having 2 to 7 carbon atoms,
R ⁴ is an alkyl group, alkoxy group or alkenyl group having 1 to 12 carbon atoms, the two CH ₂ groups not one CH ₂ group or adjacent present in the group addition, As oxygen atoms not directly bonded to each other, they may be replaced by -O-, -CH = CH-, -CO-, -OCO- or -COO-,
a is 0 or 1;
The compounds of the formula II in which a is 1 are mentioned as particularly preferred compounds.

Particularly preferred compounds of formula II are selected from formulas IIa to IIi:

In the above formulas, R ^3a and R ^4a are each independently H, CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ , and alkyl is alkyl having 1 to 8 carbon atoms. It is a group.
Compounds of formula IIa, in particular compounds in which R ^3a and R ^4a present in the molecule are CH ₃ , and compounds of formula IIe, formula IIf, formula IIg, formula IIh and formula IIi, in particular in the molecule A compound in which R ^3a present in is H or CH ₃ is particularly preferred.

The use of the compounds of the formula II gives particularly low rotational viscosity values for the liquid-crystal mixtures according to the invention, and TN and STN displays with a large steepness and a rapid response time, especially at low temperatures.
The mixtures according to the invention preferably contain, in addition to the dielectrically neutral alkenyl compound of the formula II, one or more dielectrically positive alkenyl compounds of the formula II ^* :

式中、
Ｒ³は、炭素原子２〜７個を有するアルケニル基であり、
Ｑは、ＣＦ₂、ＯＣＦ₂、ＣＦＨ、ＯＣＦＨまたは単結合であり、
Ｙは、ＦまたはＣｌであり、および
Ｌ¹およびＬ²は、それぞれ相互に独立し、ＨまたはＦである。

Where
R ³ is an alkenyl group having 2 to 7 carbon atoms,
Q is CF ₂ , OCF ₂ , CFH, OCFH or a single bond,
Y is F or Cl, and L ¹ and L ² are each independent of each other and are H or F.

Particularly preferred are compounds of formula II ^* in which L ¹ and / or L ² is F and QY is F or OCF ₃ .
Furthermore, compounds of formula II ^* in which R ³ is 1E-alkenyl or 3E-alkenyl having 2 to 7, especially 2, 3 or 4 carbon atoms are mentioned as particularly preferred compounds.
The compounds of the formula II ^* a are mentioned as particularly preferred compounds:

式中、Ｒ^3aは、Ｈ、ＣＨ₃、Ｃ₂Ｈ₅またはｎ−Ｃ₄Ｈ₇、特にＨまたはＣＨ₃である。

In which R ^3a is H, CH ₃ , C ₂ H ₅ or n-C ₄ H ₇ , in particular H or CH ₃ .

Compounds of formula I and polar compounds of formula II ^* having a dielectric anisotropy greater than +1.5 should be classified as component A as defined above.
In accordance with the proviso conditions of claim 1, the mixture according to the invention can also include one or more cyano compounds of the following formulas in addition to the compounds of the formula I:

In each of the above formulas,
R is an alkyl group having 1 to 12 carbon atoms, an alkoxy group or an alkenyl group, also one more CH ₂ groups to CH ₂ groups or non-adjacent present in the group, As those in which the oxygen atoms are not directly bonded to each other, they may be replaced by -O-, -CH = CH-, -CO-, -OCO- or -COO-, preferably 1 to 8 carbon atoms An alkyl group or an alkoxy group, or an alkenyl group having 2 to 7 carbon atoms, and L ^1-4 are each independently H or F.

Provided, however, that the proportion of compounds of the formula IIIb and formula IIIc in the mixture according to the invention in which L ¹ and L ² are F and R is an alkyl, alkenyl or alkoxy group is less than 10% each. .
In the mixtures according to the invention, the proportions of the compounds of the formulas IIIb ^* and IIIc ^* are preferably ≦ 8% each, particularly preferably ≦ 5% each.
Suitable compounds of formula IIIa and formula IIIb are listed below:

Mixtures that contain neither the compound of formula IIIb ^* nor the compound of formula IIIc ^* are mentioned as preferred mixtures. Also present in the molecule is a compound of formula IIIb, wherein L ¹ is F, L ² is H or F, and R is an alkyl, alkenyl or alkoxy group, or a compound of formula IIIc Mixtures that do not contain also are mentioned as particularly preferred mixtures. Mixtures containing neither the compound of formula IIIb nor the compound of formula IIIc are mentioned as very particularly preferred mixtures.
In a preferred embodiment, component A is one or more 3,4,5-trifluorophenyl compounds represented by the following formula:

And / or a compound having one or more polar end groups represented by the following formula:

Wherein R is as defined above, and L ³ and L ⁴ are each independently of each other H or F. R present in these compounds is particularly preferably An alkyl group or an alkoxy group having 1 to 8 carbon atoms).
The preferred liquid crystal mixture contains one or more compounds of component A , preferably in a proportion of 15 to 80%, particularly preferably 20 to 70%. These compounds have a dielectric anisotropy of Δε ≧ + 3, in particular a dielectric anisotropy of Δε ≧ + 8, particularly preferably a dielectric anisotropy of Δε ≧ + 12.

The preferred liquid crystal mixture contains one or more compounds of component B in a proportion of preferably 20 to 85%, particularly preferably 30 to 75%. Group B compounds, particularly those containing alkenyl groups, stand out in that they have a low numerical value, especially with regard to rotational viscosity γ ₁ .
In addition to one or more compounds of formula II, component B is preferably a compound selected from the group consisting of one or more bicyclic compounds of the following formula:

And / or a compound selected from the group consisting of one or more tricyclic compounds represented by the following formula:

および／または１種または２種以上の下記式で表わされる四環状化合物からなる群から選択される化合物：

And / or a compound selected from the group consisting of one or more tetracyclic compounds represented by the following formula:

(In the above formulas, R ¹ and R ² are each independently an alkyl group, an alkoxy group or an alkenyl group having 1 to 12 carbon atoms, and one existing in these groups. The CH ₂ group or two or more non-adjacent CH ₂ groups can also be defined as —O—, —CH═CH—, —CO—, —OCO— or —, as oxygen atoms are not directly bonded to each other. May be replaced by COO-, and L is H or F).

  The 1,4-phenylene groups present in IV10 to IV19 and IV23 to IV33 are independent of each other and may be substituted with one or more fluorine atoms.

In formulas IV17 to IV31, compounds in which R ¹ is an alkyl group and R ³ is an alkyl group or an alkoxy group, in particular alkoxy, are mentioned as particularly suitable compounds (the alkyl group and alkoxy group are each a carbon Having 1 to 7 atoms). In formulas IV27 and IV29, compounds in which L is F are also mentioned as preferred compounds.
The compounds of the formulas IV2, IV27 and IV28 are mentioned as very particularly preferred compounds.

R ¹ and R ² present in the compounds of the formulas IV1 to IV33 are particularly preferably linear alkyl groups or alkoxy groups having 1 to 12 carbon atoms.
If desired, the liquid crystal mixture contains the optically active component C in an amount such that the ratio of the layer thickness (outer substrate spacing) to the natural pitch of the chiral nematic liquid crystal mixture is greater than 0.2. For this component, one of ordinary skill in the art can obtain a number of chiral dopants, several of which are commercially available, for example, cholesteryl nonanoate, S-811 from Merck KGaA, Darmstadt, And CB15 (BDH, Poole, UK). There is no limitation on the choice of the dopant.

The proportion of the compound of component C is preferably 0 to 10%, particularly 0 to 5%, particularly preferably 0 to 3%.
The mixture according to the invention also preferably contains one or more liquid crystal tolan compounds. Tran compounds have a large birefringence value Δn, which allows the use of relatively thin layer thicknesses while significantly reducing response time. These tolan compounds are preferably selected from the group consisting of:

In each of the above formulas,
R ¹ and R ² are as defined above,
Z ⁴ is —CO—O—, —CH ₂ CH ₂ — or a single bond, and L ^{1 to} L ⁶ are each independently H or F.
Compounds represented by the formula Ta, formula Tb and formula Th are mentioned as particularly preferred compounds.

Particularly preferred compounds are those in which one, two or three of the groups L ^{1 to} L ⁶ is F and the others are H in the formula Te, provided that L ¹ and L ² or L ³ and L ⁴ , or L ⁵ and L ⁶ are both compounds that are not simultaneously F.

The proportion of compounds from the group consisting of Ta, Tb and Th is preferably 5 to 50%, in particular 10 to 40%.
The proportion of compounds of the formulas Ta to Th is preferably 2 to 55%, in particular 5 to 35%.
The mixtures according to the invention can also optionally contain one or more compounds having a dielectric anisotropy smaller than −2 in an amount of up to 20% ( component D ).

When the mixture contains component D , these are preferably one or more compounds containing the structural unit 2,3-difluoro-1,4-phenylene, for example DE-A 3807801, 3807786, 3807863, 3807864 or 3807908. The tolan compounds containing this structure described in the international patent application PCT / DE88 / 00133 are mentioned as particularly suitable compounds.
Another known compound of component D is a 2,3-dicyanohydroquinone or cyclohexane derivative containing the following structural units as described, for example, in DE-A 3321707 or DE-A 3407003:

The liquid crystal mixture according to the invention preferably contains the compound of component D.
The term “alkenyl” in the definition of R, R ¹ , R ² , R ³ and R ⁴ includes straight-chain and branched alkenyl groups, especially straight-chain groups, where R, R ¹ And R ² contains 1 to 12 carbon atoms, and R ³ and R ⁴ contain 2 to 7 carbon atoms. Particularly preferred alkenyl groups are, C ₂ -C ₇ -1E- alkenyl, C ₄ -C ₇ -3E- alkenyl, C ₅ -C ₇ -4- alkenyl, C ₆ -C ₇ -5- alkenyl and C ₇ - 6 alkenyl, in particular C ₂ -C ₇ -1E- alkenyl, C ₄ -C ₇ -3E-alkenyl and C ₅ -C ₇ -4- alkenyl.

Examples of suitable alkenyl groups include vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5 carbon atoms are generally preferred.
The compounds of formula I, formula II, formula III, formula IV, formula V, formula VI and formula T and their auxiliary formulas that can be used in TN and STN displays according to the present invention are respectively known or Or it can manufacture similarly to a well-known compound.

In a preferred embodiment, the mixture contains the following components:
-One, two or three compounds of the formula I,
1 to 2 or more compounds of the formula I, 3 to 45%, in particular 5 to 35%, particularly preferably 10 to 30%,
≦ 8%, preferably ≦ 5%, particularly preferably not containing this compound of the formula IIIb ^*
Compounds of the formula IIIb in which L ¹ is F, L ² is H or F and R is an alkyl group, alkenyl group or alkoxy group ≦ 8%, preferably ≦ 5%, particularly preferably this compound Does not contain,
In the compound of formula IIIb, R is an alkyl group, alkenyl group or alkoxy group ≦ 8%, preferably ≦ 5%, particularly preferably not containing this compound,

≦ 8%, preferably ≦ 5%, particularly preferably not containing this compound of the formula IIIc ^*
Compounds of formula IIIc, wherein L ¹ is F, L ² is H or F and R is an alkyl, alkenyl or alkoxy group ≦ 8%, preferably ≦ 5%, particularly preferably this compound Does not contain,
In the formula IIIc, R is an alkyl group, an alkenyl group or an alkoxy group ≦ 8%, preferably ≦ 5%, particularly preferably not containing this compound,
−1, 2 or more compounds of the formula Ta, formula Tb and formula Th, 3-40%, in particular 6-35%, particularly preferably 8-25%,

-One or more compounds of formula II, formula II ^* , formula IV9 and formula IV24, 25-75%, in particular 35-65%,
1 selected from compounds of formula IIf, formula IIg, formula IIh, formula IIi and formula II ^* a, in which alkyl is an alkyl group having 1 to 8 carbon atoms and R ^3a is H or CH ₃ A species or two or more alkenyl compounds,
In formula IV9 and / or formula IV24, R ¹ is an alkenyl group having 2 to 7 carbon atoms, and R ² is as defined above, in particular an alkyl group having 1 to 6 carbon atoms, or One or more compounds which are alkoxy groups, in particular one or more compounds of formula IV9a and / or formula IV24a:

In the above formulas, R ^3a is H, CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ , in particular H or CH ₃ , and R ² is as defined above, preferably 1 to Alkyl or alkoxy groups having 6, especially 1, 2 or 3 carbon atoms, very particularly preferably methoxy, ethoxy or n-propoxy.
The proportion of these compounds in the liquid crystal mixture is preferably 2 to 30%, in particular 3 to 20%.
In formula IV2, R ¹ and R ² are preferably alkyl or alkoxy groups having 1 to 6 carbon atoms, in particular R ¹ is an alkyl group, and R ² is 1 to 6 carbon atoms. One or more compounds which are alkoxy groups having

-One or more compounds of formula IV27 and / or formula IV28 (wherein L present in formula IV27 is H or F, particularly preferably F). The proportion of these compounds in the liquid crystal mixture is preferably 10 to 45%, in particular 15 to 40%.
-20% or more of compounds having positive dielectric anisotropy, particularly compounds having Δε ≧ + 12.

In particular, the mixtures according to the invention are distinguished in that they have a very short overall response time (t _tot = t _on -t _off ) when used in TN and STN displays with thick layer thicknesses.
The liquid crystal mixtures according to the invention used in TN and STN cells have a positive dielectric anisotropy of Δε ≧ 1. Liquid crystal mixtures having Δε ≧ 3, in particular Δε ≧ 5, are particularly preferred.

The liquid-crystal mixture according to the invention has favorable values _{relating to} the threshold voltage V _10/0/20 and the rotational viscosity γ ₁ . When the numerical value d · Δn of the optical pitch difference is specified in advance, the layer thickness value d is determined by the optical anisotropy Δn. In particular, in the case of a relatively large d · Δn value, it is generally preferred to use a liquid crystal mixture according to the invention having a relatively large optical anisotropy value, since the d value can be selected relatively small, which further influences the response time A favorable numerical value is obtained. However, the liquid crystal display according to the present invention containing the liquid crystal mixture according to the present invention having a smaller Δn value is also characterized by having an advantageous response time value.

  The liquid-crystal mixtures according to the invention are also characterized by having advantageous numerical values for the steepness of the electro-optic characteristic curve and can be operated with a high time-sharing ratio, especially at temperatures above 20 ° C. Furthermore, the liquid crystal mixture according to the present invention has high stability and favorable numerical values related to the frequency dependence of electric resistance and threshold voltage. The liquid crystal display according to the present invention has a wide operating temperature range and good contrast angle dependence.

  Electrode surface-treated so that the preferential orientation (director) of the polarizing plate, the electrode substrate and the liquid crystal molecules adjacent to each other is usually twisted from one electrode to the other by a numerical value of 160 ° to 720 ° The structure of the liquid crystal display element according to the present invention corresponds to the usual structure relating to this type of display element. The term “normal structure” is to be interpreted broadly and encompasses all of the inductive and modified forms of TN and STN cells, in particular display elements with matrix display elements and additional magnets.

The surface tilt angles of the two outer substrates may be the same or different. The same tilt angle is preferred. A suitable TN display has a tilt angle of 0 ° to 7 °, preferably 0.01 ° to 5 °, especially 0.1 ° to 2 °, between the molecular long axis of the outer substrate surface and the outer substrate. In STN displays, this tilt angle is 1 ° to 30 °, preferably 1 ° to 12 °, in particular 3 ° to 10 °.
The twist angle of the TN mixture in the cell has a value of 22.5 ° to 170 °, preferably 45 ° to 130 °, in particular 80 ° to 115 °. The twist angle of the STN mixture in the cell from the alignment film to the alignment film has a value of 100 ° to 600 °, preferably 170 ° to 300 °, particularly 180 ° to 270 °.

  Liquid crystal mixtures which can be used according to the invention can be prepared in a manner which is customary per se. In general, the desired amounts of the various components used in small amounts are dissolved in the components making up the principal component, preferably at elevated temperature. The components can be mixed in an organic solvent such as acetone, chloroform or methanol, and after mixing, the solvent can be separated again, for example, by distillation.

  The liquid crystal mixtures according to the invention are also cholesteric liquid crystal (CLC) displays, in particular SSCT [“surface stabilized cholesteric texture”] and PSCT [“polymer stabilized cholesteric texture”] displays. Suitable for use as a liquid crystal medium in a display such as described in, for example, WO 92/19695, US 5,384,067, US 5,453,863, US 6,172,720 or US 5,661,533 . CLC displays typically contain CLC media consisting of optically active and nematic components that have a particularly large helical twist compared to TN and STN displays and also exhibit selective reflection of circularly polarized light. This reflection wavelength corresponds to the product of the pitch of the cholesteric spiral and the average refractive index of the CLC medium.

  For this purpose, in the liquid-crystal mixture according to the invention, the liquid-crystal medium has a cholesteric phase at room temperature, and its twisting ability and concentration are preferably in the visible, UV or IR region of the electromagnetic spectrum, in particular in the region of 400 to 800 nm. One or more chiral dopants selected in such a manner as to have a certain reflection wavelength are added.

  Suitable dopants are known to those skilled in the art and include, for example, cholesteryl nonanoate (CN), CB15, R / S-811, R / S-1011, R / S-2011R / S-3011 or R / S-4011. (Merck KGaA Darmstadt). Highly twisted dopants containing chiral sugar groups, in particular dianhydrohexitol derivatives, such as isosorbitol, isomannitol or isoiditol derivatives, preferably the sorbitol derivatives described in WO 98/00428 are mentioned as preferred. Furthermore, chiral ethane diol derivatives, such as 1,2-derivatives of diphenyl-1,2-dihydroxyethane (benzylene glycol, hydrobenzoin), preferably mesogenic hydrobenzoins according to GB-A-2,328,207 Derivatives are mentioned as preferred. Very particularly suitable dopants are the chiral binaphthyl derivatives described in WO 02/94805, the chiral binaphthyl acetal derivatives described in WO 02/34739, the chiral TADDOL derivatives described in WO 02/06265, and described in WO 02/06196 and WO 02/06195. A chiral dopant containing at least one fluorinated crosslinking group and a terminal or central chiral group.

When two or more dopants are added, they can have the same or opposite twist and the same or opposite twist temperature dependence.
The invention furthermore relates to a CLC medium in which the liquid crystal mixture contains as nematic component, the liquid crystal mixture according to the invention and one or more chiral dopants as optically active components. The invention further relates to CLC displays, in particular SSCT and PSCT displays, containing the above CLC media.
This type of dielectric can also contain additional additives known to those skilled in the art and disclosed in publications. As an example, 0-15% of multicolor dyes can be added.

In the present specification and examples below, the structures of the liquid crystal compounds are indicated by abbreviations, and the conversion to chemical formulas is achieved according to Tables A and B below. The groups C _n H _{2n + 1} and C _m H _{2m + 1} are all linear alkyl groups each having n or m carbon atoms. Alkenyl groups have the trans-configuration. The codes in Table B are self-explanatory. In Table A, only abbreviations relating to the basic structure are shown. In each case, the abbreviations relating to this basic structure are followed by the codes shown in the table below for the substituents R ¹ , R ² , L ¹ , L ² and L ³ , separated by a dash.

  The TN and STN displays preferably contain a liquid crystal mixture composed of one or more components from Tables A and B below.

Table A : (L ¹ , L ² , L ³ = H or F)

Table B:

Table C:
Table C shows dopants that can generally be added to the mixtures according to the invention.

Table D:
By way of example, stabilizers that can be added to the mixture according to the invention are shown below:

Examples The following examples are intended to illustrate the present invention without limiting it. Use the following abbreviations:
cl. p. Clearing point (nematic-isotropic phase-transition temperature)
SN smectic-nematic phase-transition temperature)
Δn Optical anisotropy (589 nm, 20 ° C.)
n ₀ ordinary ray refractive index (589 nm, 20 ° C.)
Δε Dielectric anisotropy (1kHz, 20 ° C)
S characteristic curve steepness = V ₉₀ / V ₁₀
V ₁₀ threshold voltage = characteristic voltage at 10% relative contrast
(Unless otherwise stated, 80 Hz frequency)

V ₉₀ Characteristic voltage at 90% relative contrast t _on Time from switch-on to reaching 90% of maximum contrast t _off Time from switch-off to reaching 10% of maximum contrast t _tot Total response time t _on + t _off
Throughout this specification, all temperatures are given in ° C. Percentages are percent by weight unless otherwise noted. Unless otherwise stated, the display is addressed with a time division ratio of 1/128 and a bias of 1/12. Twist is 240 ° unless stated otherwise.

Comparative Example 1
TN and STN mixture according to example 2 from WO 01/64814 consisting of the following components (mixture V1):

Example 1
The TN and STN mixture according to the invention (mixture M1) consists of the following components:

For mixtures V1 and M1, the threshold voltage V ₁₀ was measured as the frequency of the rectangular voltage function (dV ₁₀ / df). The result is shown in FIG.
The mixture M1 according to the present invention retains other preferred physical properties such as clearing point and birefringence value, for example, compared to the mixture V1 in Comparative Example 1, with a particularly low threshold voltage and a particularly low threshold value. The frequency dependence of the voltage is clearly demonstrated from FIG.
Furthermore, the comparative mixture V1 shows the formation of cold domains at relatively high frequencies (> 5 kHz), so that the threshold voltage can no longer be measured at these frequencies. In contrast, the mixture M1 according to the invention does not show a cold domain even at a frequency of 10 kHz.

Comparative Example 2
TN and STN mixture consisting of the following components (mixture V2):

Example 2
The TN and STN mixture (M2) according to the present invention comprises the following components, and has an exceptionally high clearing point, an exceptionally low threshold voltage, a greater steepness and a faster overall response compared to the mixture V2 of Comparative Example 2. Have time:

Comparative Example 3
TN and STN mixture consisting of the following components (mixture V3):

Example 3
The TN and STN mixture (M3) according to the present invention is composed of the following components, and has a particularly high clearing point, a particularly low threshold voltage, a greater steepness and a faster overall response compared to the mixture V3 of Comparative Example 3. Have time:

Comparative Example 4
TN and STN mixture (V4) consisting of the following components:

Example 4
The TN and STN mixture (M4) according to the invention consists of the following components and has a particularly low threshold voltage and a greater steepness compared to the mixture V4 of Comparative Example 4:

Comparative Example 5
TN and STN mixture (V5) consisting of the following components:

Example 5
The TN and STN mixture (M5) according to the present invention consists of the following components and has an exceptionally high clearing point, a low threshold voltage and a greater steepness while having a comparable overall response time compared to the mixture V5 :

  FIG. 2 shows the frequency dependence of the threshold voltage for M5 and V5. The mixture M5 according to the invention has a particularly small frequency dependence compared to V5.

Comparative Example 6
TN and STN mixture (V6) consisting of the following components:

Example 6a
The TN and STN mixture (M6a) according to the invention consists of the following components and has a faster overall response time while having the same threshold voltage compared to the mixture V6 of Comparative Example 6:

Example 6b
The TN and STN mixture (M6b) according to the invention consists of the following components and has a faster overall response time and a higher clearing point compared to the mixture V6, while having a comparable threshold voltage:

  FIG. 3 shows the frequency dependence of the threshold voltage for M6a, M6b and V6. The mixtures M6a and M6b according to the invention have a particularly small frequency dependence compared to V6.

FIG. 1 is a graph showing the frequency dependence of the threshold voltage for the mixtures V6, M6a and M6b. FIG. 2 is a graph showing the frequency dependence of the threshold voltage for the mixtures M5 and V5. FIG. 3 is a graph showing the frequency dependence of the threshold voltage for the mixtures M1 and V1.

Claims (10)

A liquid crystal mixture containing at least one compound of formula I comprising:

(Wherein, R ¹ represents an alkyl group having 1 to 12 carbon atoms, an alkoxy group or an alkenyl group, these one CH ₂ group or not adjoining present in group two CH ₂ The group may further be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO—, in which the oxygen atoms are not directly bonded to each other),
This mixture
a) 10-30% by weight of a compound of the formula I and ≦ 8% by weight of a compound of the formula IIIb ^* ;
b) 5 to 35% by weight of a compound of the formula I and ≦ 8% by weight of a compound of the formula IIIc ^* ;
c) a compound represented by 5 to 35% by weight of a compound of formula I, ≦ 8% by weight of a compound of formula IIIb ^* compounds and ≦ 8% by weight of a compound of formula IIIc ^* compound represented by represented by
A liquid crystal mixture comprising:

(In each formula, R is an alkyl, alkoxy or alkenyl group having 1 to 12 carbon atoms). Formula IV2, IV27 and one represented by any one of the IV28 or more of compounds of the liquid crystal mixture as claimed in claim 1, characterized in that it comprises containing:

(Wherein R ¹ and R ² are each independently an alkyl or alkoxy group having 1 to 6 carbon atoms, and
L is H or F. ) The liquid crystal mixture according to claim 1 or 2, characterized in that it contains a compound represented by 10 to 30% by weight of a compound of formula I. 4. Liquid crystal mixture according to any one of claims 1 to 3 , characterized in that it contains at least one compound of the formula II and / or formula II ^*.

In each formula,
A ⁴ is 1,4-phenylene or trans-1,4-cyclohexylene,
R ³ is an alkenyl group having 2 to 7 carbon atoms,
R ⁴ is an alkyl group, alkoxy group or alkenyl group having 1 to 12 carbon atoms, the two CH ₂ groups not one CH ₂ group or adjacent present in the group addition, As oxygen atoms not directly bonded to each other, they may be replaced by -O-, -CH = CH-, -CO-, -OCO- or -COO-,
a is 0 or 1,
L ¹ and L ² are each independent of each other and are H or F;
Q is CF ₂ , OCF ₂ , CFH, OCFH or a single bond, and Y is F or Cl.

The liquid crystal mixture according to any one of claims 1 to 4 , which contains one or more compounds represented by the following formulas:

In each formula, R ^3a is H, CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ , and R ² is as defined for R ¹ present in formula I. The liquid crystal mixture according to any one of claims 1 to 5 , comprising one or more compounds represented by the following formulas:

In which R ¹ and R ² are each independently of ^{one another} , as defined for R ¹ present in formula I. One or more liquid crystal mixture as claimed in any one of claims 1 to 6, characterized by containing a compound selected from the following formulas:

In each formula, R ^{3 a} is H ₂ , CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ , and alkyl is an alkyl group having 1 to 8 carbon atoms.   The liquid crystal display containing the liquid-crystal mixture as described in any one of Claims 1-7. A TN or STN liquid crystal display,
Two outer substrates that together with the frame form a cell,
A nematic liquid crystal mixture having positive dielectric anisotropy arranged in the cell,
An electrode layer having an alignment film present inside the outer substrate;
With
The tilt angle between the major axis of the molecule on the outer substrate surface and the outer substrate is 0 to 30 degrees, and the twist angle from the alignment film to the alignment film of the liquid crystal mixture in the cell is 22.5 ° to 600 ° Has the number of
-Nematic liquid crystal mixture
a) 15 to 80% by weight of liquid crystal component A consisting of one or more compounds having a dielectric anisotropy greater than +1.5,
b) 20 to 85% by weight of a liquid crystal component B composed of one or more compounds having a dielectric anisotropy of −1.5 to +1.5,
c) a liquid crystal component D0 to 20% by weight comprising one or more compounds having a dielectric anisotropy smaller than −1.5, and d) film thickness (distance of the outer substrate) and chiral as desired. An amount of the optically active component C such that the ratio of the nematic liquid crystal mixture to the natural pitch is about 0.2 to 1.3;
In the above TN or STN liquid crystal display comprising:
The TN or STN liquid crystal display, wherein the nematic liquid crystal mixture is a liquid crystal mixture according to any one of claims 1 to 7.   A cholesteric liquid crystal display, an SSCT display or a PSCT display containing the liquid crystal mixture according to any one of claims 1 to 7 as an optically active component, as one or more chiral dopants and as a nematic component.

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