JP4873853B2 - Liquid crystal media - Google Patents

Description

  The present invention relates to a liquid crystal medium, the use of the medium for electro-optical purposes, and a display comprising this medium.

Liquid crystals are mainly used as dielectrics in display devices because the optical properties of such materials can be modified by the applied voltage. Electro-optical devices based on liquid crystals are very well known to those skilled in the art and can be based on various effects. Examples of such devices include cells with dynamic scattering, DAP (orientation phase deformation) cells, guest / host cells, TN cells with twisted nematic structures, STN (super twisted nematic) cells, SBE (super birefringence). Effect) cell and OMI (optical mode interference) cell. The most common display devices have a twisted nematic structure based on the Schadt-Helfrich effect.
Liquid crystal materials must have good chemical and thermal stability and good stability against electric fields and electromagnetic radiation. The liquid crystal material should also have a low viscosity and produce a short address time, low threshold voltage and high contrast in the cell.
Furthermore, they should have a suitable mesophase, for example a nematic or cholesteric mesophase for the cell, at the normal driving temperature, ie above room temperature and below as wide as possible. Since liquid crystals are generally used as a mixture of many components, it is important that the components are easily miscible with each other. Other properties such as electrical conductivity, dielectric anisotropy and optical anisotropy must satisfy various requirements, depending on the cell type and field of application. For example, a material for a cell having a twisted nematic structure should have positive dielectric anisotropy and low electrical conductivity.

  For example, for matrix liquid crystal displays (MLC displays) with integrated nonlinear elements to switch individual pixels, large positive dielectric anisotropy, wide nematic phase, relatively low birefringence, very high resistivity, good UV And media with temperature stability and low vapor pressure are desirable.

This type of matrix liquid crystal display is known. Non-linear elements that can be used to individually switch individual pixels are, for example, active elements (ie, transistors). The term “active matrix” is then used to distinguish between the two types:
1. MOS (metal oxide semiconductor) or other diode on a silicon wafer as substrate.
2. Thin layer transistor (TFT) on glass plate as substrate.
The use of single crystal silicon as a substrate material limits the size of the display, as even modular assemblies of various partial displays create problems at the junction.
Preferably, in the more powerful type 2 case, the electro-optic effect used is usually the TN effect. A distinction is made between two technologies: TFTs made of compound semiconductors, such as CdSe, or TFTs based on polycrystalline or amorphous silicon.

The TFT matrix is applied inside one glass plate of the display, while the other glass plate has a transparent counter electrode inside it. Compared with the size of the pixel electrode, the TFT is very small and there is virtually no adverse effect on the image. This technique can also be extended to a full color possibilities display where a mosaic of red, green and blue filters is placed so that the filter element faces each switchable pixel.
A TFT display normally operates as a TN cell with a crossed polarizing plate in transmitted light and is illuminated from the back side.

  The term MLC display here refers to any matrix display with integrated nonlinear elements, ie a display with passive elements such as varistors or diodes (MIM = metal-insulator-metal) in addition to the active matrix. Range.

  This type of MLC display is particularly suitable for TV applications (eg pocket TV) or computer applications (notebook personal computers) and mass information displays for automobile or aircraft construction. In addition to problems with contrast angle dependence and reaction time, MLC displays suffer from difficulties due to insufficiently high resistivity of liquid crystal mixtures [Togashi, S., Sekiguchi, K., Tanabe, H., Yamamoto, E ., Sorimachi, K., Tajima, E., Watanabe, H., Shimizu, H., Proc. Euro Display 84, Sept. 1984: A 210-288 Matrix LCD Controlled by Double Stage Diode Rings, p. 141 ff, Paris; STROMER, M., Proc. Euro Display 84, Sept. 1984: Design of Thin Film Transistors for Matrix Addressing of Television Liquid Crystal Displays, p. 145 ff, Paris]. As the resistance value decreases, the contrast of the MLC display decreases and an afterimage erasing problem may occur. A high (initial) resistance value is very important to obtain an acceptable service life since the specific resistance value of the liquid crystal mixture generally decreases through the lifetime of the MLC display by interaction with the internal surface of the display. In particular, in the case of low voltage mixtures, it has never been possible to achieve very high resistivity values. Furthermore, it is important that the resistivity value shows the smallest possible increase with increasing temperature and after heating and / or UV exposure. The low temperature properties of the mixtures from the prior art, in particular the so-called “low temperature stability” (LTS), are also particularly disadvantageous. It is required that crystallization and / or smectic phases do not occur even at low temperatures and that the temperature dependence of the viscosity is as low as possible. MLC displays from the prior art therefore do not meet today's requirements.

  Therefore, an MLC having a large operating temperature range, a short reaction time even at low temperatures and a low threshold voltage, at the same time, with a very high specific resistance value that does not have these drawbacks or only to a small extent There is a continuing demand for displays.

In a TN (Shut-Helfrich) cell, a medium that facilitates the following advantages within the cell is desirable:
-Expanded nematic phase range (especially towards lower temperatures)
-Switching capability at ultra-low temperatures (outdoor use, automobiles, avionics)
-Increased resistance to UV radiation (longer service life).
Media available from the prior art does not achieve these advantages while retaining other parameters.

For super twist (STN) cells, media that allow greater time sharing characteristics and / or lower threshold voltages and / or wider nematic phase ranges (especially at low temperatures) are desirable. For this purpose, further expansion of the acceptable range of parameters available (clearing point, smectic-nematic transition or melting point, viscosity, dielectric parameter, elastic parameter) is urgently desired.
For TV and monitor applications, media with fast reaction times and low threshold voltages are desirable and require better low temperature stability. Also, some switchable LC layers will require a high birefringence.
Togashi, S., Sekiguchi, K., Tanabe, H., Yamamoto, E., Sorimachi, K., Tajima, E., Watanabe, H., Shimizu, H., Proc. Euro Display 84, Sept. 1984: A 210-288 Matrix LCD Controlled by Double Stage Diode Rings, p. 141 ff, Paris; STROMER, M., Proc.Euro Display 84, Sept. 1984: Design of Thin Film Transistors for Matrix Addressing of Television Liquid Crystal Displays, p 145 ff, Paris

  The present invention therefore does not have or is only to a small extent the aforementioned drawbacks, and preferably at the same time has very high resistivity and low threshold voltage, improved LTS and fast switching time. In particular, it has the object of providing a medium for this type of MLC, TN or STN display.

で表される１種または２種以上の化合物および
式ＩＢ

It has now been found that this object can be achieved when the medium according to the invention is used in a display.
The present invention is therefore a liquid crystal medium based on a mixture of polar compounds,
This is the formula IA

One or more compounds of formula IB and formula IB

−ＣＨ＝ＣＨ−、−Ｃ≡Ｃ−、−ＣＯ−、−ＣＯ−Ｏ−、−Ｏ−ＣＯ−または−Ｏ−ＣＯ−Ｏ−により置き換えられ、
Ｙ^１およびＹ^２は、各々、互いに独立して、ＨまたはＦであり、
Ｘは、Ｆ、Ｃｌまたは６個までの炭素原子を有するハロゲン化アルキル基、アルケニル基、アルコキシ基またはアルケニルオキシ基であり、
Ａは、いずれの場合にも互いに独立して、１，４−フェニレン、ｔｒａｎｓ−１，４−シクロヘキシレンまたは２，３−ジフルオロ−１，４−フェニレンであり、
ＢおよびＣのうち一つは、２，３−ジフルオロ−１，４−フェニレンであり、他方は、１，４−フェニレンまたは２，３−ジフルオロ−１，４−フェニレンであり、そして
ｒは、１または２である、
で表される１種または２種以上の化合物を含むことを特徴とする、前記液晶媒体に関する。 In the formula, the individual groups have the following meanings:
R ¹ and R ² are each independently an alkyl group having 1 to 12 carbon atoms, which is unsubstituted, monosubstituted by CN or CF ₃ , or at least one by halogen. Substituted, one or more CH ₂ groups are optionally in each case independent of one another so that the O atoms are not directly bonded to one another, —O—, —S—,

Replaced by —CH═CH—, —C≡C—, —CO—, —CO—O—, —O—CO— or —O—CO—O—,
Y ¹ and Y ² are each independently H or F,
X is F, Cl or a halogenated alkyl group having up to 6 carbon atoms, an alkenyl group, an alkoxy group or an alkenyloxy group;
A is in each case, independently of one another, 1,4-phenylene, trans-1,4-cyclohexylene or 2,3-difluoro-1,4-phenylene;
One of B and C is 2,3-difluoro-1,4-phenylene, the other is 1,4-phenylene or 2,3-difluoro-1,4-phenylene, and r is 1 or 2,
1 or 2 or more types of compounds represented by these are related with the said liquid-crystal medium characterized by the above-mentioned.

In the pure state, the compounds of the formulas IA and IB are colorless and form liquid-crystalline mesophases in a temperature range conveniently located for electro-optical use. They are chemically, thermally and light stable.
In formulas IA and IB, R ¹ and R ² are preferably straight chain alkyl or alkoxy groups having 1 to 12, very preferably 2, 3, 4, 5, 6 or 7 C atoms. It is.

In formula IA X is preferably F, Cl, CF ₃ , CHF ₂ , OCF ₃ , OCHF ₂ , OCHFHCF ₃ , OCHFHCHF ₂ , OCHFHCH ₂ F, OCF ₂ CH ₃ , OCF ₂ CHF ₂ , OCHFCH ₂ F, OCF _{2 CF 2 CHF 2, OCF 2 CF} 2 CH 2 F, a _{OCFHCF 2 CF 3, OCFHCF 2 CHF} 2, OCF 2 CF 2 CF 3, OCF 2 CF 2 CClF 2, OCClFCF 2 CF 3 or CH = CF _2, most F or OCF ₃ is preferable.

Particularly preferred compounds of the formula IA are compounds selected from the following formulas IA1 to IA8:

式中、
Ｒ^１は、式ＩＡにて与えられた意味を有する、
で表される前記化合物である。非常に好ましくは、式ＩＡ１で表される化合物である。

Where
R ¹ has the meaning given in formula IA,
It is the said compound represented by these. Very particular preference is given to compounds of the formula IA1.

  Particularly preferably, in the compound of formula IB, r is 1. More preferably, in the compound represented by formula IB, A is 1,4-phenylene or trans-1,4-cyclohexylene. More preferably, in the compound of formula IB, one of B and C is 1,4-phenylene and the other is 2,3-difluoro-1,4-phenylene.

Particularly preferred compounds of the formula IB are compounds selected from the following formulas IB1 to IB24:

Where
R ¹ and R ² have the meaning given in formula IB,
It is the said compound represented by these. Very particular preference is given to compounds of the formulas IB1 to IB6, in particular of formula IB1.

  The compounds of the formulas IA and IB are described in the literature (eg Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart, etc.) In a manner known per se, it is prepared in a manner known per se under reaction conditions which are known and suitable for the above-mentioned reactions. Alternatives known per se but not mentioned in more detail here are also used in the present invention.

  The present invention also includes electro-optic displays containing this type of media (particularly the frame, as well as the cell, integrated nonlinear elements for switching individual pixels on the skin, and positive dielectric differences placed in the cell). STN or MLC display with two plane parallel skins forming a nematic liquid crystal mixture of isotropic and high resistivity) and the use of these media for electro-optic purposes. Besides for reflective displays, the mixtures according to the invention are also suitable for IPS (in-plane switching) applications, OCB (light controlled birefringence) applications and VA (vertical alignment) applications.

The liquid crystal mixture of the present invention can significantly extend the acceptable range of available parameters.
In particular, it has been found that by using a liquid crystal mixture comprising compounds of the formulas IA and IB, it is possible to obtain a mixture having a low threshold voltage and an improved LTS.
The achievable combinations of clearing point, rotational viscosity γ ₁ , low Δn and dielectric anisotropy are much better than previous materials from the prior art.
The requirements for the nematic phase at high clearing points, low temperatures and high positive Δε have heretofore been achieved only to an insufficient extent. Despite having prior art mixtures such as MLC-6424 with high positive Δε, for example, it has only a low clearing point and a high value for rotational viscosity γ ₁ . Other blend systems have good flow viscosity ν ₂₀ and Δε values, but only clearing points in the region of 60 ° C.

  The liquid-crystal mixture according to the invention has a nematic phase up to −20 ° C., preferably up to −30 ° C., particularly preferably up to −40 ° C., above 80 ° C., preferably above 90 ° C., particularly preferably 100 ° C. A clearing point greater than 1, a dielectric anisotropy value Δε of ≧ 4, preferably ≧ 5, and a high specific resistance can be achieved, and excellent STN and MLC displays can be obtained. In particular, this mixture is characterized by a low operating voltage. The threshold value of TN is below 2.0V, preferably below 1.7V, particularly preferably below 1.5V.

  By suitable selection of the components of the mixture of the present invention, other advantageous properties are retained to achieve a higher clearing point (eg above 110 ° C.) at higher threshold voltages or lower thresholds It goes without saying that it is possible to achieve a lower clearing point in voltage. It is likewise possible to obtain a mixture with a larger Δε and thus a lower threshold at a correspondingly only slightly increased viscosity. The MLC display of the present invention preferably uses a display that operates at the first transmission minimum of Gooch and Tarry [CHGooch and HATarry, Electron. Lett. 10, 2-4, 1974. CHGooch and HATarry, Appl. Phys., Vol. 8, 1575-1584, 1975], especially, for example, high steepness of characteristic curves and low angular dependence of contrast (German Patent 30 22 818) Besides the preferred electro-optical properties, the lower dielectric anisotropy is sufficient at the second minimum value with the same threshold voltage as the analog display. This makes it possible to achieve a significantly higher specific resistance value at the first minimum value by using the mixture of the present invention than in the case of a mixture composed of a cyanide compound. By suitably selecting the individual components and their weight proportions, one skilled in the art can use a simple and routine method to set the required birefringence for the specified layer thickness of the MLC display. Can do.

The flow viscosity ν _{20 at} 20 ° C. is preferably <60 mm ² · s ⁻¹ , particularly preferably <50 mm ² · s ⁻¹ . The rotational viscosity γ ₁ of the inventive mixture at 20 ° C. is preferably <120 mPa · s, particularly preferably <100 mPa · s. The nematic phase range is preferably at least 90 °, particularly preferably at least 100 °. This range preferably extends from −20 ° to + 80 °.

で表されるシアノフェニルシクロヘキサン類または式

のエステル類を含む類縁体混合物よりも、ＨＲの減少が著しく小さいことを示している。 The measured value of voltage holding ratio (HR) is [S. Matsumoto et al., Liquid Crystals 5 , 1320 (1989); K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984). ); G. Weber et al., Liquid Crystals 5 , 1381 (1989)], a mixture of the invention comprising a compound of formula I is represented, for example, by formula I of the invention with increasing temperature. Instead of compounds

Cyanophenylcyclohexanes represented by the formula

This indicates that the reduction in HR is significantly less than that of an analog mixture containing the esters.

The UV stability of the mixtures according to the invention is also significantly better. That is, the mixture shows a very small reduction in HR upon exposure to UV.
The medium according to the invention preferably contains very small amounts (≦ 10% by weight) of compounds containing cyan groups and very preferably does not contain such compounds. The media retention value of the present invention is preferably> 98%, very preferably> 99% at 20 ° C.

In liquid crystal display devices, short switching times are particularly preferred, especially for use in video and TV applications. These applications require a switching time (t _on + t _off ) shorter than 25 ms. The upper limit of the switching time is determined by the repetition rate of the image.

Preferred embodiments in the present invention are as follows:
In addition to general formulas II to VII:

Here, the individual groups have the following meanings:
R ⁰ : n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 carbon atoms,
X ⁰ : F, Cl, halogenated alkyl having 1 to 6 carbon atoms, halogenated alkenyl, halogenated alkenyloxy or halogenated alkoxy,
_{^{Z 0: -C 2 H 4 -}} , - (CH 2) 4 -, - CH = CH -, - CF = CF -, - C 2 F 4 -, - CH 2 CF 2 -, - CF 2 CH 2 - _{, -CH 2 O -, - OCH} 2 -, - COO -, - is or _-CF 2 is O-, - OCF ₂
Y ^{1 to} Y ⁴ : H or F independently of each other;
r: 0 or 1;
A medium containing one or more compounds selected from the group consisting of:

The compound of formula IV is preferably of the following formula

Where
X ⁰ and R ⁰ have the meanings given in formula II, X ⁰ is preferably F or OCF ₃
Is a compound selected from Particularly preferred are compounds of the formulas IVb and IVc.

The compound of formula VII is preferably of the following formula

Where
X ⁰ and R ⁰ are compounds selected from the meanings given in formula II, wherein X ⁰ is preferably F or OCF ₃ . Particularly preferred are compounds of formula VIIb.

-LC medium in addition to the formula

Where
X ⁰ and R ⁰ have the meanings given in formula II and L is H, F or Cl.
1 type or 2 or more types of compounds selected from are included. X ⁰ is preferably F or Cl. In the compounds of the formulas VIII, IX and X, preferably X ⁰ is Cl or F and L is H. Very particular preference is given to compounds of the formulas IX and X.

-In addition to the medium, the following formula

Where
R ⁰ , X ⁰ and Y ^1-4 are each independently as defined in Formulas II-VII.
1 type or 2 or more types of compounds selected from are included. X ⁰ is preferably F, Cl, CF ₃ , OCF ₃ or OCHF ₂ . R ⁰ is preferably alkyl, oxaalkyl, fluoroalkyl or alkenyl and has up to 6 carbon atoms from each other. Particular preference is given to compounds of the formula XVI, in particular where Y ^1-3 is F and Y ⁴ is H.

式中、
Ｒ^１およびＲ^２は、式ＩＢに定義した通りであり、Ｙ^１は、式ＩＩに定義した通りである、
から選択される化合物を１種または２種以上含む。特に好ましくは、式ＸＸＩＩで表される化合物であり、ここでＹ^１は、Ｆである。
−媒体は加えて、以下の式

式中、
Ａは、１，４−フェニレンまたはｔｒａｎｓ−１，４−シクロへキシレンであり、
ａは、０または１であり、
Ｒ^３は、２〜９個の炭素原子を有するアルケニル基であり、および
Ｒ^４は、式ＩＡにてＲ^１について定義した通りである、
から選択されるアルケニル化合物を１種または２種以上含む。 -In addition to the medium, the following formula

Where
R ¹ and R ² are as defined in formula IB and Y ¹ is as defined in formula II.
1 type or 2 or more types of compounds selected from are included. Particularly preferred are compounds of formula XXII, wherein Y ¹ is F.
-In addition to the medium, the following formula

Where
A is 1,4-phenylene or trans-1,4-cyclohexylene;
a is 0 or 1,
R ³ is an alkenyl group having 2 to 9 carbon atoms, and R ⁴ is as defined for R ¹ in formula IA.
1 type (s) or 2 or more types are included.

Particularly preferred compounds of the formula XXIII are compounds selected from the following formulas XXIIIa to XXIIIi

式中、
Ｒ^３ａおよびＲ^４ａは、各々、互いに独立して、Ｈ、ＣＨ_３、Ｃ_２Ｈ_５またはｎ−Ｃ_３Ｈ_７であり、およびａｌｋｙｌは、１〜８個の炭素原子を有するアルキル基である、
で表される前記化合物である。
特に好ましくは、ＸＸＩＩＩａ、ＸＸＩＩＩｆおよびＸＸＩＩＩｇで表される化合物であり、ここで特にＲ^３ａは、ＨまたはＣＨ_３である。
−媒体は加えて、以下の式

式中、
Ｒ^３は、２〜７個の炭素原子を有するアルケニル基であり、
Ｑは、ＣＦ_２、ＯＣＦ_２、ＣＦＨ、ＯＣＦＨまたは単結合であり、
Ｙは、ＦまたはＣｌであり、および
Ｌ^１およびＬ^２は、各々、互いに独立して、ＨまたはＦである、
で表されるアルケニル化合物を１種または２種以上含む。
特に好ましくは、ＸＸＩＶで表される化合物であり、ここでＬ^１および／またはＬ^２は、Ｆであり、Ｑ−Ｙは、ＦまたはＯＣＦ_３である。さらに好ましくは、式ＸＩで表される化合物であり、ここでＲ^３は、２〜７個の炭素原子、特に２、３または４個の炭素原子を有する１Ｅ−アルケニルまたは３Ｅ−アルケニルである。

Where
R ^3a and R ^4a are each independently of each other H, CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ , and alkyl is an alkyl group having 1 to 8 carbon atoms. ,
It is the said compound represented by these.
Particularly preferred are the compounds represented by XXIIIa, XXIIIf and XXIIIg, in particular R ^3a is H or CH ₃ .
-In addition to the medium, the following formula

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 independently of each other H or F.
1 type or 2 types or more are included.
Particularly preferred is a compound represented by XXIV, wherein L ¹ and / or L ² is F and QY is F or OCF ₃ . More preferred are compounds of the formula XI, wherein R ³ is 1E-alkenyl or 3E-alkenyl having 2 to 7 carbon atoms, in particular 2, 3 or 4 carbon atoms.

式中、
Ｒ^３ａは、Ｈ、ＣＨ_３、Ｃ_２Ｈ_５またはｎ−Ｃ_３Ｈ_７、特にＨまたはＣＨ_３である、
で表される化合物である。
−媒体は加えて、以下の式

式中、
Ｒ^１およびＲ^２は、式ＩＢに定義した通りである、
から選択される化合物を１種または２種以上含む。 Very preferably, the formula XXIVa

Where
R ^3a is H, CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ , in particular H or CH ₃ ,
It is a compound represented by these.
-In addition to the medium, the following formula

Where
R ¹ and R ² are as defined in formula IB,
1 type or 2 or more types of compounds selected from are included.

は、好ましくは

である。

Is preferably

It is.

The medium contains one or more compounds of the formula II, III, IV, V, VI or VII;
-R ⁰ is a straight-chain alkyl or alkenyl having 2-7 carbon atoms;
The medium contains a compound of formula IA1-4, preferably 1, 2, 3 or 4, most preferably a compound of formula IA1;
The medium contains a compound of formula IB1-4, preferably 1 or 2, most preferably a compound of formula IB1;
The medium comprises one or more compounds selected from the formulas IA, IB, IVb, IVc, VIIb, IX, X, XXII, XXIII and XXV;
The proportion of compounds of the formula IA in the medium is 1 to 35%, in particular 1 to 25% by weight.
The proportion of compounds of the formula IB in the medium is 1 to 25%, in particular 1 to 15%, most preferably 1 to 8% by weight.
The medium consists essentially of a compound selected from the group consisting of the general formulas IA, IB and II-XXVI.

The term “alkyl” covers straight-chain and branched alkyl groups having 1 to 7 carbon atoms, especially straight-chain groups that are methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups having 2 to 5 carbon atoms are generally preferred.
The term “alkenyl” covers straight-chain and branched alkenyl groups having 2-7 carbon atoms, especially straight-chain groups. Particularly, alkenyl _groups, 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 preferred alkenyl groups are 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 term “fluoroalkyl” preferably extends to a linear group having a terminal fluorine. That is, it covers fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. However, other positions of fluorine are not excluded.
The term “oxaalkyl” preferably extends to a linear group of the formula C _n H _{2n + 1} —O— (CH ₂ ) _m , where n and m are each independently 1-6. n is preferably = 1, and m is preferably 1 to 6.

A relatively small proportion of conventional liquid crystal materials, but in particular compounds of the formulas IA and IB mixed with one or more compounds of the formulas II, III, IV, V, VI and / or VII However, it was found that a wide nematic phase with a low smectic-nematic transition temperature was simultaneously observed and improved lifetime, resulting in a significant drop in threshold voltage and a low birefringence value. Particular preference is given to one or more compounds of the formulas IA and IB, in addition to one or more compounds of the formula VII, in particular compounds of the formula VIIb A mixture, wherein X ⁰ is F, OCHF ₂ or OCF ₃ . The compounds of the formulas IA, IB and II to VII are colorless, stable and easily miscible with each other and with other liquid crystal materials. Furthermore, the mixtures according to the invention are distinguished by a very high clearing point, ie a relatively low value of rotational viscosity γ ₁ .

By suitably selecting the meanings of R ⁰ and X ⁰ , the address time, threshold voltage, the steepness of the transmission characteristic curve, and the like can be changed in a desired manner. For example, 1E-alkenyl groups, 3E-alkenyl groups, 2E-alkenyloxy groups and the like generally have shorter address times, improved nematic trends and higher elastic constants k ₃₃ (bends) compared to alkyl or alkoxy groups. ) And k ₁₁ (spread) ratio. 4-Alkenyl groups, 3-alkenyl groups, etc. generally have lower threshold voltages and lower k ₃₃ / k ₁₁ values compared to alkyl and alkoxy groups.

A —CH ₂ CH ₂ — group generally results in a higher k ₃₃ / k ₁₁ value compared to a single covalent bond. Higher k ₃₃ / k ₁₁ values, for example, facilitate a flatter transmission characteristic curve in TN cells with 90 ° twist (to achieve gray shades) and steeper transmission in STN, SBE and OMI cells The characteristic curve (larger time-sharing characteristic) is facilitated, and vice versa.

The optimal mixing ratio of the compounds of formula IA, IB and II + III + IV + V + VI + VII is substantially the desired property, selection of the components of formula IA, IB, II, III, IV, V, VI and / or VII, and presence Depends on the choice of other ingredients that will do. Suitable mixing ratios within the above ranges can easily be determined from case to case.
The total amount of compounds of the formulas IA, IB and II to XXVI in the mixtures according to the invention is not critical. The mixture can thus further comprise one or more components for the purpose of optimizing various properties. However, the observed effects on address time and threshold voltage are generally greater as the total concentration of compounds of formula IA, IB and II-XXVI increases.

In a particularly preferred embodiment, the medium according to the invention comprises a compound of the formula II to VII (preferably II, III and / or VII, in particular VIIb), wherein X ⁰ is F, OCF ₃ , OCHF ₂ a _{OCH = CF 2, OCF = CF} 2 or _{OCF 2} -CF 2 H. A favorable synergistic effect with the compounds of the formulas IA and IB results in particularly advantageous properties. In particular, mixtures comprising compounds of the formulas IA, IB and VIIb are distinguished by their low threshold voltage.
The liquid crystal media of the invention comprising compounds of the formulas IA and IB and further comprising compounds of the formulas II to XXVI are characterized by low values of rotational viscosity, high birefringence and good LTS, Fast reaction time is shown. They are particularly suitable for TV, video and monitor applications.
The individual compounds of the formulas IA, IB and II to XXVI and their dependent formulas that can be used in the medium of the invention are known or can be prepared in the same way as known compounds .

The structure of the MLC display of the present invention from the polarizer, electrode substrate and surface treated electrode corresponds to the conventional structure of this type of display. The term “conventional structure” is interpreted broadly herein and covers all inductive and modified forms of MLC displays, including in particular matrix display elements based on poly-Si TFTs or MIMs.
A significant difference between the display of the present invention and conventional displays based on twisted nematic cells, however, is the selection of the liquid crystal parameters of the liquid crystal layer.

  Liquid crystal mixtures that can be used according to the invention are produced in a conventional manner essentially. In general, the desired amount of the components used in smaller amounts will advantageously dissolve in the components making up the main component at elevated temperatures. It is also possible to mix the solution of the components in an organic solvent, for example acetone, chloroform or methanol, and after complete mixing, the solvent can be removed again, for example by distillation.

  The dielectric may also contain other additives known to those skilled in the art and described in the literature. For example, 0-15% of pleochroic dyes, stabilizers or chiral dopants can be added. Suitable dopants and stabilizers are shown in Tables C and D below.

In the current application and in the following examples, the structure of the liquid crystal compound is indicated using an acronym and its conversion to the chemical formula is performed according to Tables A and B below. All groups C _n H _{2n + 1} and C _m H _{2m + 1} are straight chain alkyl groups having n and m carbon atoms respectively; n and m are preferably 0, 1, 2, 3, 4, 5, 6 or 7. The coding in Table B is self-explanatory. In Table A, only the initials for the basic structure are shown. In individual cases, the acronym for the basic structure is followed by a code for the substituents R ¹ , R ² , L ¹ and L ² , separated by a dash.

  Preferred mixture components of the mixture concept of the present invention are shown in Tables A and B.

Table A

Table B

Table C
Table C generally shows dopants that may be added to the compounds of the invention, preferably in a proportion of 0.1 to 10% by weight, very preferably 0.1 to 6% by weight.

Table D
For example, the stabilizers that can be added to the mixtures of the present invention are shown below.

  In addition to one or more compounds of the formulas IA and IB, particularly preferred mixtures comprise 1, 2, 3, 4, 5 or 6 or more compounds from Table B.

[Example]
The following examples illustrate the invention without limiting it. In the present specification, percentage represents weight percent. All temperatures are given in degrees Celsius. m. p. Represents the melting point, cl. p. = Clearing point. Furthermore, C = crystalline state, N = nematic phase, S = smectic phase and I = isotropic phase. The data between these symbols represents the transition temperature. Δn represents an optical anisotropy, _{n o} denotes the refractive index (589nm, 20 ℃). The flow viscosity ν ₂₀ (mm ² / sec) and the rotational viscosity γ ₁ [mPa · s] are each determined at 20 ° C. V ₁₀ represents the voltage for 10% transmission (viewing angle perpendicular to the surface of the plate). t _on represents a switch-on time at an operating voltage corresponding to twice the V ₁₀ value, and t _off represents a switch-off time. [Delta] [epsilon] represents a dielectric anisotropy ([Delta] [epsilon] = epsilon _{‖-epsilon ⊥,} where, epsilon _|| represents the dielectric constant parallel to the long axis of the molecule, epsilon _⊥, relative to the long axis of the molecule Represents the vertical dielectric constant). The electro-optical data were measured in a TN cell at 20 ° C. with a first minimum value (ie d · Δn value of 0.5 μm) unless otherwise specified. Optical data were measured at 20 ° C. unless otherwise stated.

Example 1

Example 2

Example 3

Example 4

Claims (9)

Formula IA

One or more compounds of formula IB 1

A liquid crystal medium based on a mixture of polar compounds, comprising one or more compounds represented by the formula:
Wherein the individual groups have the following meanings:
R ¹ and R ² are each independently an alkyl group having 1 to 12 carbon atoms, which is unsubstituted, monosubstituted by CN or CF ₃ , or at least one by halogen. substituted, one or more CH ₂ groups, have also independently of each other in the case of deviation, so as never O atoms are bonded directly to one another, -O -, - S-,

-CH = CH -, - C≡C - , - CO -, - CO-O -, - O-CO- or -O-CO-O- may be replaced by,
Y ¹ and Y ² are each independently H or F,
X is halogenated alkyl, alkenyl, alkoxy or alkenyloxy having carbon atoms of F, until Cl or six. ) Formula IA1

Where
R ¹ is as defined in claim 1;
The medium according to claim 1, comprising one or more compounds represented by the formula: In addition, general formulas II, III, IV, V, VI and VII

In the formula, the individual groups have the following meanings:
R ⁰ : n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl each having up to 9 carbon atoms,
X ⁰ : F, Cl, halogenated alkyl having 1 to 6 carbon atoms, halogenated alkenyl, halogenated alkenyloxy or halogenated alkoxy,
_{^{Z 0: -C 2 H 4 -}} , - (CH 2) 4 -, - CH = CH -, - CF = CF -, - C 2 F 4 -, - CH 2 CF 2 -, - CF 2 CH 2 - _{, -CH 2 O -, - OCH} 2 -, - COO -, - OCF 2 - or _-CF 2 O-,
Y ^{1 to} Y ⁴ : each independently H or F,
r: 0 or 1;
The medium according to claim 1, comprising one or more compounds selected from the group consisting of: In addition, the following formula XXIII

Where
A is 1,4-phenylene or trans-1,4-cyclohexylene;
a is 0 or 1,
R ³ is an alkenyl group having 2 to 9 carbon atoms, and R ⁴ is as defined for R ¹ in formula IA.
In the represented by compound including one or more, characterized in, medium according to any one of claims 1-3. In addition, the following formulas IVb, IVc, VIIb, IX, X, XVI, XXII, XXIIIa, XXIIIf, XXIIIg and XXV

Where
R ¹ and R ² are as defined in claim 1, R ⁰ is n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl each having up to 9 carbon atoms, X ⁰ is F, Cl, halogenated alkyl having 1 to 6 carbon atoms, a halogenated alkenyl, halogenated alkenyloxy or halogenated alkoxy, Y ¹ to Y ⁴ are each H or F independently of one another , R ^3a is H, CH ₃ , C ₂ H ₅ or n-C ₃ H ₇ , alkyl is an alkyl group having 1 to 8 carbon atoms, and L is H or F ,
The medium according to any one of claims 1 to 4 , comprising one or more compounds selected from the compounds represented by formula (1 ) . The ratio of the overall compound of the formula IA in the mixture, characterized in that 1 to 25 wt%, medium according to any one of claims 1-5. The ratio of the overall compound of Formula IB 1 in the mixture, characterized in that 1 to 25 wt%, medium according to any one of claims 1-6. Use of a liquid crystal medium according to any one of claims 1 to 7 for electro-optical purposes. To any one of claims 1 to 7 containing a liquid crystal medium according, electro-optical liquid-crystal display.