JP2007051291A - Liquid crystal medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal medium that simultaneously exhibits a very high specific resistivity and a low threshold voltage. <P>SOLUTION: The liquid crystal medium comprises one or two or more of each of compounds of formula I and compounds of formula II exhibiting positive dielectric anisotropy. In the formulae, the rings A<SP>1</SP>, A<SP>2</SP>and A<SP>3</SP>are each independently, an F-substituted or unsubstituted, phenyl, cyclohexyl, dioxane or tetrahydropyran ring. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  In principle, liquid crystals are used as dielectrics in display devices. This is because the optical properties of such materials can be changed by the applied voltage. Electro-optical devices based on liquid crystals are particularly 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 (aligned phase deformation) cells, guest / host cells, TN cells with twisted nematic structures, STN (super twist nematic) cells, SBE (super birefringence). Effect) cell and OMI (optical mode interference) cell. Most conventional display devices are based on the Schadt-Helfrich effect and have a twisted nematic structure.

The liquid crystal material must have good chemical stability and stability to heat, and have good electric field and stability against electromagnetic radiation. Furthermore, the liquid crystal material should have a relatively low viscosity and must give the cell a short address time, a low threshold voltage and a large contrast.
Furthermore, the liquid crystal material must have a suitable mesophase, eg a nematic or cholesteric mesophase for the cell, at normal operating temperatures, ie in the widest possible range from room temperature to room temperature. Since liquid crystals are generally used as a mixture of a plurality of components, it is important that these components are easily miscible with each other. Still other properties, such as conductivity, dielectric anisotropy and optical anisotropy, must meet different requirements depending on the cell type and field of application. For example, a material for a cell having a twisted nematic structure must have positive dielectric anisotropy and low conductivity.

  For example, in a matrix liquid crystal display having an integrated nonlinear element for switching individual pixels (MCL display), the medium has high dielectric anisotropy, a wide nematic phase range, relatively low birefringence, and extremely high Specific resistance, good UV and temperature stability and low vapor pressure are desired.

This type of matrix liquid crystal media display is known. An example of a non-linear element that can be used to switch each pixel individually is an active pixel (ie, a transistor). The term “active matrix” can then be used to distinguish between two types:
1. MOS (metal oxide semiconductor) or other diode on a silicon wafer as the substrate.
2. A thin film transistor (TFT) on a glass plate as a substrate.
The use of single crystal silicon as a substrate material limits the size of the display. This is because even if various partial displays are modularly assembled, a problem occurs in the joint portion.
In the more promising type 2, where this is preferred, the electro-optic effect used is usually the TN effect. Differences exist between the two technologies: TFTs containing compound semiconductors such as CdSe, or TFTs based on polycrystalline or amorphous silicon. With regard to the latter technique, intense research efforts are made on a global scale.

The TFT matrix is applied to the inner surface of one glass plate of the display, and the inner surface of the other glass plate carries a transparent counter electrode. Compared to the size of the pixel electrode, the TFT is very small and has virtually no detrimental effect on the image. This technique can also be extended to a full color compatible display in which mosaic red, green and blue filters are arranged so that each filter element is located opposite to the switchable pixels.
A TFT display usually operates as a TN cell with a crossed polarizer in the transmitted light and is projected from the back side.

  In this specification, the term MLC display encompasses any matrix display with integrated non-linear elements. That is, in addition to the active matrix, also displays with passive elements such as varistors or diodes (MIM = metal-insulator-metal) are included.

  This type of MLC display is particularly suitable for advanced information displays for TV applications (eg pocket TV) or computers (laptop type), automobiles or aircraft construction. In addition to the problems related to the angle dependency of the contrast and the response time, the MLC display has a problem due to an insufficient specific resistance value of the liquid crystal mixture (Non-Patent Documents 1 and 2).

  As the resistance value decreases, the contrast of the MLC display deteriorates and the afterimage erasure problem may occur. The specific resistance value of the liquid crystal mixture is generally reduced throughout the life of the MLC display due to its interaction with the inner surface of the MLC display, so a large (initial) specific resistance value is required to obtain an acceptable operating life. Is very important. In particular, in the case of a low voltage mixture, it has been impossible in the past to obtain a very large specific resistance value. It is also important to minimize as much as possible the increase in resistivity with heating and / or after heating and / or UV irradiation. The low temperature properties of the prior art mixtures are also particularly disadvantageous. What is required is that no crystallization and / or smectic phase is formed even at low temperatures, and that the temperature dependence on viscosity is as small as possible. However, MLC displays from the prior art do not meet today's requirements.

  Therefore, as an MLC display, it has an extremely high specific resistance and a wide operating temperature range, a short response time and a low threshold voltage at a low temperature at the same time. A great demand continues to exist.

In the case of a TN (Shut-Helfrich) cell, it is desired that the medium has the following advantages in the cell:
-Expanded nematic phase range (especially to low temperatures),
-Switching capability at ultra-low temperatures (outdoor use, cars, aircraft),
-Increased resistance to UV irradiation (during sunlight and UV coupling of the display) and the resulting longer lifetime.

The media in the prior art can achieve these advantages while at the same time not maintaining other parameters.
In the case of a super twist (STN) cell, a medium is desired with greater time sharing characteristics and / or lower threshold voltage and / or wider nematic phase range (especially at low temperatures). Further expansion of the range of parameters available for this purpose (clearing point, smectic-nematic transition or melting point, viscosity, dielectric parameters, elastic modulus) is particularly desirable.
Proc. Eurodisplay 84, September 1984 by TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H .: A210-288 Matrix LCD Controlled by Double Stage Diode Rings, p. 141 et seq., Pairs; Proc. Eurodisplay by STROMER, M. 84, September 1984: Design of Thin Film Transistors for Matrix Addressing of Television Liquid Crystal Displays, page 145 et seq., Pairs

  It is an object of the present invention to provide a liquid crystal medium which does not have the above-mentioned drawbacks, or is to a lesser extent even if it has them, and preferably also has a very high specific resistance and a low threshold voltage at the same time. It is in.

式中、
Ｒ、Ｒ^０は、独立して、無置換であるかまたはハロゲン化されている１〜１５個の炭素原子を有するアルキル基またはアルコキシ基であり、これらの基中の１個または２個以上のＣＨ_２基は、それぞれ相互に独立して−Ｃ≡Ｃ−、−ＣＦ_２Ｏ−、−ＣＨ＝ＣＨ−、−Ｏ−、−（ＣＯ）Ｏ−、−Ｏ（ＣＯ）−もしくは

により、酸素原子が相互に直接結合しないように置換されていることも可能であり、
Ｌ^１、Ｌ^２およびＬ^３は、相互に独立してＨまたはＦであり、
Ｘは、Ｆ、ＣｌまたはＯＣＦ_３であり、
Ｙは、Ｆ、Ｃｌ、フッ素化されている１〜５個の炭素原子を有するアルキル基またはアルコキシ基であり、さらに、これらの基中の１個のＣＨ_２基は、−Ｏ−によって置換されていることも可能であり、
環Ａ^１、Ａ^２およびＡ^３は、相互に独立して、

であり、
ｐ、ｑは、相互に独立して０または１であり、
ただし、環Ａ^１、Ａ^２およびＡ^３は、ＣＦ_２Ｏブリッジに隣接して位置するときは、ジオキサン環ではない。 It has now been found that this object can be achieved by using the medium of the invention in a display.
That is, the present invention is a liquid crystal medium based on a mixture of polar compounds having positive dielectric anisotropy, comprising one or more compounds of the following formula I, and at the same time one compound of the following formula II: Regarding liquid crystal media containing two or more:

Where
R and R ⁰ are independently an alkyl group or an alkoxy group having 1 to 15 carbon atoms which is unsubstituted or halogenated, and one or two or more of these groups are The CH ₂ groups are independently of each other —C≡C—, —CF ₂ O—, —CH═CH—, —O—, — (CO) O—, —O (CO) — or

Can also be substituted so that the oxygen atoms are not directly bonded to each other,
L ¹ , L ² and L ³ are independently of each other H or F;
X is F, Cl or OCF ₃ ;
Y is F, Cl, a fluorinated alkyl group or alkoxy group having 1 to 5 carbon atoms, and one CH ₂ group in these groups is substituted by —O—. It is also possible that
Rings A ¹ , A ² and A ³ are independent of each other

And
p and q are independently 0 or 1,
However, rings A ¹ , A ² and A ³ are not dioxane rings when located adjacent to the CF ₂ O bridge.

  The liquid crystal medium of the present invention does not have the disadvantages of the conventional liquid crystal medium as described above, or is smaller to the extent that it is present, and in a preferred embodiment, has a very high specific resistance and low threshold. It also has a value voltage.

In the context of the present invention, it is particularly preferred that the mixtures of the formula I include those in which X represents F. Also, the compound of formula I preferably comprises one or more compounds of formula Ia:

In formulas I and Ia, R is preferably straight-chain alkyl or alkenyl, preferably an alkyl chain. The chain length is preferably 3, 5, or 7 carbon atoms, particularly preferably 5 or 7 carbon atoms, most preferably 7 carbon atoms. Most preferably, the component of formula I of the mixture represents a heptyl compound of formula Ib.

The compound of formula II preferably contains one or more of the following formulas II-1 to II-31. Accordingly, the medium preferably contains one or more compounds of the following formula:

式中、Ｒ^０は、請求項１において定義されたとおりである。

In which R ⁰ is as defined in claim 1.

  Preference is given to compounds II-8 and II-9. When using compounds of formula II-8 or II-9, the combined proportion of these in the mixture is preferably 12-60%, most preferably 15-45%. Preferred as an alternative to II-8 and II-9 are compounds of formulas II-1 to II-7 and II-10 to II-31, preferably II-1, II-2, II-3, II-4, II-5, II-6, II-19, II-20, II-21, II-22, II-23, II-24, II-25, II-28 and II-30.

R ⁰ in the compounds of the formulas II and II-1 to II-31 is preferably an alkyl, alkoxy, alkenyl or alkenyloxy group having 1 to 9 carbon atoms, in particular having 2 to 7 carbon atoms Represents an alkyl group.

式中、
Ｒ^１は、無置換であるかまたはハロゲン化されている１〜１５個の炭素原子を有するアルキル基またはアルコキシ基であり、これらの基中の１個または２個以上のＣＨ_２基は、それぞれ相互に独立して−Ｃ≡Ｃ−、−ＣＨ＝ＣＨ−、−Ｏ−、−（ＣＯ）Ｏ−、−Ｏ（ＣＯ）−もしくは

により、酸素原子が相互に直接結合しないように置換されていることも可能であり、
Ｌ^１は、ＨまたはＦであり、
Ｘ^１は、Ｃｌ、ＣＮ、ＳＦ_５、ＮＣＳ、ハロゲン化されている８個以下の炭素原子を有するアルキル基であり、これらの基中の１個または２個以上のＣＨ_２基は、−Ｏ−または−ＣＨ＝ＣＨ−によって、酸素原子が相互に直接結合しないように置換されていることも可能である。 Said medium preferably further comprises one or more compounds of formula III.

Where
R ¹ is an unsubstituted or halogenated alkyl group or alkoxy group having 1 to 15 carbon atoms, and one or more CH ₂ groups in these groups are each Independently of each other —C≡C—, —CH═CH—, —O—, — (CO) O—, —O (CO) — or

Can also be substituted so that the oxygen atoms are not directly bonded to each other,
L ¹ is H or F;
X ¹ is Cl, CN, SF ₅ , NCS, a halogenated alkyl group having 8 or fewer carbon atoms, in which one or more CH ₂ groups are —O It is also possible that oxygen atoms are substituted by-or -CH = CH- so that they are not directly bonded to each other.

式中、ｎは１〜１２であり、好ましくは０〜７であり、とくに１〜５である。 Particularly preferred are compounds of formula IIIa.

In the formula, n is 1 to 12, preferably 0 to 7, and particularly 1 to 5.

The compounds of formulas I and II have a wide range of applications. Depending on the choice of substituents, the compounds can contribute as a base material that favors the composition of the liquid crystal medium; however, the compounds of formulas I and II can be added as liquid crystal base materials to those from other compound classes. It is also possible, for example, to adjust the dielectric anisotropy and in particular the optical anisotropy of this type of dielectric and / or optimize its threshold voltage and / or viscosity.
In the pure state, the compounds of the formulas I and II are colorless and show the formation of liquid-crystalline mesophases in the preferred temperature range for electro-optical use. They are chemically, thermally and light stable.
The compounds of the formula I have already been described in DE 29 07 332.
Compounds of the formula II are described, for example, in EP 786445 A1, WO 2004/048501, or can be prepared by methods analogous thereto.

  The compounds of formulas I and II are prepared by methods known per se and such methods are described in standard literature such as Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart. ). To be precise, it is known and under suitable conditions for the reaction. Modifications known per se can also be used for the production, but they are not described further here in this description.

In the medium according to the invention comprising a compound of formula II and / or a compound of formula III, Y is preferably F or OCF ₃ , in particular F.
When R, R ⁰ and / or R ¹ is an alkyl group and / or an alkoxy group, this may be straight-chain or branched. It is preferably straight-chain and has 2, 3, 4, 5, 6 or 7 carbon atoms. Therefore, preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy, and methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy , Octoxy, nonoxy, decoxy, undecoxy, tridecoxy or tetradecoxy.

R, R ⁰ and / or R ¹ are particularly preferably H, methyl, ethyl, n-propyl, n-pentyl or n-heptyl. L ¹ is preferably H. One of L ² and L ³ is preferably F and the other is H, or both are F. R is particularly preferably n-heptyl. R ⁰ is particularly preferably n-propyl. Y is F, OCF ₃ or CF ₃ , in particular F.

The present invention relates to an electro-optic display (especially as an STN or MLC display) two plane parallel substrate plates forming cells with a frame, an integrated nonlinear element for switching individual pixels on the substrate plate, and a positive dielectric anisotropy. It also relates to those containing this type of medium as having a nematic liquid crystal mixture which has a high resistivity and a high resistivity and is located in the cell, and to the use of the medium for electro-optical purposes.
The liquid crystal mixture of the present invention significantly expands the parameter range that can be used.
The combination of achievable clearing point, low temperature viscosity, temperature and UV stability and dielectric anisotropy is far superior to past materials according to the prior art.

The low threshold voltage, the nematic phase at low temperatures and the high Δε achieved so far have been inadequate.
Other mixture systems have comparable clearing points and Δε values, but only have a relatively high threshold voltage.

  The liquid crystal mixture of the present invention has a threshold voltage of less than 2.0V, preferably less than 1.8V, especially while keeping the nematic phase up to -20 ° C, preferably up to -30 ° C, particularly preferably up to -40 ° C. Preferably it is less than 1.7 V, at the same time the value of dielectric anisotropy Δε is ≧ 5, preferably ≧ 7, and the high clearing point that can be achieved is ≧ 90 ° C., preferably ≧ 100 ° C., most preferably ≧ 105 ° C. Enables the realization of excellent STN and MLC displays. In particular, the mixture has a low drive voltage as a feature, and simultaneously has a high clearing point with a very short response time.

  The MLC display of the present invention preferably operates at the first transmission minimum of Gooch and Tarry [CH Gooch and HA Tarry, Electron. Lett. 10, 2-4, 1974; CH Gooch and HA Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975]. In this case, in addition to the particularly preferred electro-optical properties, such as the steepness in the characteristic curve and the low angular dependence of the contrast (German Patent 30 22 818), the low dielectric anisotropy is also a characteristic of similar displays. Similar to that at the second minimum, the same threshold voltage is sufficient. This makes it possible to achieve a significantly higher specific resistance at the first minimum value when using the mixture of the present invention compared to using a mixture containing a cyano compound. By appropriately selecting the individual components and their weight ratios, one skilled in the art will use a simple, routine method to set the birefringence required for a given layer thickness of the MLC display. be able to.

The flow viscosity at 20 ° C. is preferably <280 mPa · s, particularly preferably <240 mPa · s. The nematic phase range is preferably at least 100 ° C., in particular at least 110 ° C. This range is preferably extended to at least −20 ° C. to + 90 ° C.
Measurement of voltage holding ratio (HR) [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)], the decrease in HR with increasing temperature is very small when the mixture of the present invention containing a compound of formula I is irradiated with UV. It is shown.

The light stability and UV stability of the mixtures according to the invention are also significantly improved. That is, the reduction in HR when exposed to light or UV in these mixtures is significantly less.
The medium according to the invention is preferably based on one or two compounds of the formula I, preferably in a proportion of 5 to 15%, and also multiple (preferably 2 to 6) compounds of the formula II based on. That is, the proportion of the compound of formula II is 12 to 85%, preferably 18 to 60%, particularly preferably 30 to 45%.

The sum of the proportions of the compound of formula I and of the compound of formula II with respect to the total mixture is at least 15%, preferably 15 to 85%, particularly preferably 25 to 60, most preferably 35 to 50%. is there.
Very particular preference is given to the proportion of compounds of the formula I being 5-15% and the proportion of the compounds of the formula II being 18-45%.
The individual compounds of formulas 1 to VII and their ancillary formulas that can be used in the medium of the present invention are known or can be prepared by methods analogous to known compounds.

  As used herein, the meaning of the term “halogenated” means that one residue is substituted for hydrogen by one or more halogens, or is fully halogenated. It may be. Preferred halogen species are Cl and F, especially F.

式中、
Ｒ^２は、ｎ−アルキル、オキサアルキル、フルオロアルキルまたはアルケニルであり、それぞれ９個以下の炭素原子を有し、
Ｘ^０は、Ｆ、Ｃｌ、ハロゲン化されているアルキル、ハロゲン化されているアルケニルまたはハロゲン化されているアルコキシであり、６個以下の炭素原子を有し、好ましくは−ＯＣＦ_３、−ＯＣＨＦ_２またはＦであり、
Ｙ^１およびＹ^２は、それぞれ相互に独立して、ＨまたはＦである。 Preferred embodiments of the invention are shown below:
A medium further comprising one or more compounds of the formula IV:

Where
R ² is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having 9 or fewer carbon atoms,
X ⁰ is F, Cl, halogenated alkyl, halogenated alkenyl or halogenated alkoxy, having 6 or fewer carbon atoms, preferably —OCF ₃ , —OCHF ₂ Or F,
Y ¹ and Y ² are each independently H or F.

A medium comprising, in addition to the compounds of the formulas I and II, one or more preferred compounds of the formulas IVa, IVb, IVc, IVd and / or IVe:

  The proportion of compounds of the formulas IVa to IVe is preferably 5 to 30%, in particular 10 to 25%, most preferably 13 to 21%. Particularly preferred among these compounds are compounds of formula IVa and / or IVc.

A medium comprising one or more compounds of the group consisting of compounds of the formula V, consisting of the formulas Va and Vb:

Wherein R ′ is as defined for R ¹ and X ¹ is as defined above for the compound of formula III. R ′ is preferably alkyl, alkoxy or alkenyl. In the compounds of formula V, ^{X 1} is preferably _{F, Cl, OCF 3, OCHF} 2, OCHFCF 3, OC 2 F 5, C 2 F 5, CF 3, OCF 2 CHFCF 3, CH = CF 2, OCH = CF ₂ , CF = CF ₂ or OCF = CF ₂ . The proportion of these tetracyclic compounds in the mixture is preferably 0 to 10%, most preferably 0 to 6%.

式中、
Ｒ^０、Ｘ^０、Ｙ^１およびＹ^２は、上記において式ＩＩまたは式ＩＶについて定義されたとおりであり、
ＬはＨまたはＦであり、
ＡｌｋｙｌおよびＡｌｋｙｌ*は、それぞれ相互に独立して、１個〜８個の炭素原子を有する直鎖アルキル基である。
好ましくは、前記混合物は、１種または２種以上の式ＶＩ−２のエステル化合物をさらに含み、好ましくは１〜１０％の割合で、最も好ましくは２〜８％の割合で含む。 Said medium may further comprise one or more ester compounds of the formulas VI-1 to VI-5:

Where
R ⁰ , X ⁰ , Y ¹ and Y ² are as defined above for Formula II or Formula IV;
L is H or F;
Alkyl and Alkyl * are each independently a linear alkyl group having 1 to 8 carbon atoms.
Preferably, the mixture further comprises one or more ester compounds of formula VI-2, preferably in a proportion of 1-10%, most preferably in a proportion of 2-8%.

式中、Ｒ^２、Ｒ^３は、それぞれ相互に独立して、式ＩＩにおいてＲ^０について定義されたとおりである。Ｒ^２、Ｒ^３は、好ましくは７個までの炭素原子を有するアルキルである；好ましくは、該媒体は、１種、２種または３種の式ＶＩＩの化合物を含有する。式ＶＩＩの化合物の混合物における割合は、好ましくは０〜１０％であり、最も好ましくは２〜８％である。 A medium further comprising one or more compounds selected from the group consisting of the general formula VII:

In the formula, R ² and R ³ are each independently the same as defined for R ⁰ in Formula II. R ² , R ³ are preferably alkyl having up to 7 carbon atoms; preferably the medium contains one, two or three compounds of formula VII. The proportion in the mixture of compounds of the formula VII is preferably 0-10%, most preferably 2-8%.

  The total proportion of compounds of the formulas I to VII in the mixture is at least 50% by weight; preferably the proportion is 70-100%, most preferably 90-100%.

は、好ましくは

である。 The total proportion of compounds of the formulas III to VII in the mixture is 10 to 85% by weight. ;

Is preferably

It is.

The medium comprises one or more compounds of the formulas III, IV, V, VI and / or VII.
-R ⁰ and R ² are preferably straight chain alkyl having 2 to 7 carbon atoms.
The medium consists essentially of compounds of the formulas I to VII.
The weight ratio of-(I + II) :( III + IV + V + VI + VII) is preferably 1: 4 to 4: 1, in particular 1: 4 to 1: 1.

  Even when a relatively small proportion of the compounds of the formulas I and II are mixed into the usual liquid crystal material, the threshold voltage is increased, in particular by mixing with the compounds of the formulas III, IV, V, VI and / or VII. Has been found to result in a low birefringence with a significant reduction in the product lifetime with a low smectic-nematic transition temperature with a wide nematic phase range.

The terms “alkyl” and “alkyl *” preferably include straight-chain or branched alkyl groups having 1 to 7 carbon atoms, in particular straight-chain groups Methyl, ethyl, propyl, butyl, pentyl, hexyl, and heptyl. Groups having 2 to 5 carbon atoms are generally preferred.
The term “alkoxy” preferably includes the preferred alkyl groups bonded to divalent oxygen.
The term “alkenyl” includes straight-chain and branched alkenyl groups having 2 to 7 C atoms, in particular the straight-chain groups. In particular 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. A particularly preferred group of 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. Alkenyl groups having up to 5 C atoms are generally preferred.

The term “fluoroalkyl” is preferably a linear group having a terminal fluorine, ie fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and Includes 7-fluoroheptyl. However, other positions of fluorine are not excluded.
The term “oxaalkyl” preferably includes linear groups of the formula C _n H _{2n + 1} —O— (CH ₂ ) _m . In the formula, n and m are each independently 1 to 6. n is preferably = 1 and m is preferably 1-6.

By appropriately selecting the meanings of R ¹ , R ² , R ³ and R ⁴ , the address time, the threshold voltage, the steepness of the transmission characteristic curve, and the like can be modified to a desired mode. For example, 1E-alkenyl groups, 3E-alkenyl groups, 2E-alkenyloxy groups and the like generally have shorter address times, improved nematic phase formation tendency and elastic constant k ₃₃ (bend) compared to alkyl and alkoxy groups. ) And k ₁₁ (spray). Groups such as 4-alkenyl groups, 3-alkenyl groups generally provide lower threshold voltages and lower k ₃₃ / k ₁₁ values compared to alkyl and alkoxy groups.

The optimal mixing ratio of the compound of formula (I + II) :( III + IV + V + VI + VII) is determined by the desired physical properties, selection of components of formula I, II, III, IV, V, VI and / or VII and any other components that may be present. Substantially depends on the choice. A suitable mixing ratio within the above range can be easily determined depending on the case.
The total amount of compounds of the formulas I to VII in the mixture according to the invention is not a limiting factor. Thus, the mixture can contain one or more additional components, which can optimize various physical properties. However, the effects found on address time and threshold voltage are generally greater at higher total concentrations of compounds of Formulas I-VII.

  In a particularly preferred embodiment, the medium according to the invention comprises a compound of formula III to VII (preferably formula III and formula IV, in particular formula IIIa and / or IVa and / or IVc). The favorable synergistic effect of the compounds of formula I and / or II results in particularly advantageous physical properties. In particular, mixtures containing compounds of the formulas I and / or II and compounds of the formulas III and V stand out in high dielectric anisotropy as well as low threshold voltages.

The construction of the STN or MLC display of the present invention consisting of a polarizing plate, an electrode base plate and a surface-treated electrode corresponds to the usual design of this type of display. The term normal design is used herein in a broad sense and encompasses anything derived from or modified by an MLC display, in particular matrix display elements based on poly-Si TFTs or MIMs.
However, a significant difference between the display of the present invention and a conventional display based on twisted nematic cells is in the selection of the liquid crystal parameters of the liquid crystal layer.

The liquid crystal mixture that can be used in the present invention can be produced by a method known per se. In general, the desired amount of the component used in the smaller amount is dissolved in the component making up the main component. It is advantageous to carry out at an elevated temperature. It is also possible to mix the component solutions in an organic solvent such as acetone, chloroform or methanol and to remove the solvent again after thorough mixing, for example by distillation.
The dielectric may further include, as additives, those known to those skilled in the art and described in the literature. For example, 0-15% of pleochroic dyes or chiral dopants can be added.
Unless stated otherwise, percentages represent weight percentages.

C represents a crystalline phase, S represents a smectic phase, S _C represents a smectic C phase, N represents a nematic phase, and I represents an isotropic phase.
V ₁₀ indicates a voltage at 10% transmittance (viewing angle is perpendicular to the plate surface), and is generally called a threshold voltage. The saturation voltage (V ₉₀ ) represents a voltage at a transmittance of 90%. V ₉₀ / V ₁₀ is the ratio of these two voltages. t _on denotes the switch-on _time, the _{t off} the switch-off _time, as at an operating voltage corresponding to 2.0 times the value of _{V 10.} Δn represents optical anisotropy, and n ₀ is a refractive index. Δε represents dielectric anisotropy (Δε = ε‖−ε⊥. In this equation, ε‖ is a dielectric constant parallel to the long axis of the molecule, and ε⊥ is perpendicular to the long axis of the molecule. Dielectric constant). The measurement of the electro-optic data is performed at 20 ° C. at the first minimum value (that is, where the d · Δn value is 0.5) in the TN cell, unless otherwise specified. Measurement of optical data is performed at 20 ° C., unless otherwise specified.

In this patent application and the examples below, the structure of the liquid crystal compound is indicated by an acronym, and the conversion to the chemical formula is made according to Tables A and B below. All of the groups C _n H _{2n + 1} and C _m H _{2m + 1} are linear alkyl groups having n and m carbon atoms, respectively. The codes in Table B are self explanatory. Table A shows only the acronym for the mother nucleus. In each case, the initials of this mother nucleus are followed by the hyphens to indicate the codes for the substituents R ¹ , R ² , L ¹ and L ² :

Other preferred mixture components are shown in Tables A and B.

Table C
Table C shows dopants that can be added to the overall mixture of the present invention.

The following examples are intended to illustrate the invention and are not intended to limit the invention. Throughout this specification, percentages are percentages by weight. All temperatures are given in degrees Celsius.

Claims (10)

A liquid crystal medium based on a mixture of polar compounds having positive dielectric anisotropy, comprising one or more compounds of the following formula I and one or more compounds of the following formula II.

Where
R and R ⁰ are independently an alkyl group or an alkoxy group having 1 to 15 carbon atoms which is unsubstituted or halogenated, and one or two or more of these groups are The CH ₂ groups are independently of each other —C≡C—, —CF ₂ O—, —CH═CH—, —O—, — (CO) O—, —O (CO) — or

Can also be substituted so that the oxygen atoms are not directly bonded to each other,
L ¹ , L ² and L ³ are independently of each other H or F;
X is F, Cl or OCF ₃ ;
Y is F, Cl, a fluorinated alkyl group or alkoxy group having 1 to 5 carbon atoms, and one CH ₂ group in these groups is substituted by —O—. It is also possible that
Rings A ¹ , A ² and A ³ are independent of each other

And
p and q are independently 0 or 1,
However, rings A ¹ , A ² and A ³ are not dioxane rings when located adjacent to the CF ₂ O bridge. The liquid crystal medium according to claim 1, further comprising one or more compounds of formula III.

Where
R ¹ is an unsubstituted or halogenated alkyl group or alkoxy group having 1 to 15 carbon atoms, and one or more CH ₂ groups in these groups are each Independently of each other —C≡C—, —CH═CH—, —O—, — (CO) O—, —O (CO) — or

Can also be substituted so that the oxygen atoms are not directly bonded to each other,
L ¹ is H or F;
X ¹ is Cl, CN, SF ₅ , NCS, a halogenated alkyl group having 8 or less carbon atoms, in which one or more CH ₂ groups are —O— Alternatively, oxygen atoms may be substituted by —CH═CH— so that oxygen atoms are not directly bonded to each other.   Liquid crystal medium according to claim 1 or 2, wherein the proportion of the compound of formula II relative to the total mixture is at least 18% by weight. 4. The liquid crystal medium according to any one of claims 1 to 3, further comprising one or more compounds of formula IV.

Where
R ² is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having 9 or fewer carbon atoms,
X ⁰ is F, Cl, halogenated alkyl, halogenated alkenyl or halogenated alkoxy, having 6 or fewer carbon atoms,
Y ¹ and Y ² are each independently H or F. The liquid crystal medium according to claim 1, further comprising one or more compounds of the formulas VI-1 to VI-5.

Where
R ⁰ , X ⁰ , Y ¹ and Y ² are as defined in claim 1 or claim 4;
L is H or F;
Alkyl and Alkyl * are each independently a linear alkyl group having 1 to 8 carbon atoms. 6. Liquid crystal medium according to any of claims 1 to 5, wherein compound 1 further comprises one or more heptyl compounds of formula Ib.

The liquid crystal medium according to any of claims 1 to 6, wherein the compound of formula II further comprises one or more compounds of formula II-1 to II-31.

In which R ⁰ is as defined in claim 1.   8. A liquid crystal medium according to any of claims 1 to 7, wherein the sum of the proportions of the compound of formula I and of the compound of formula II relative to the total mixture is at least 35%.   Use of the liquid crystal medium according to claim 1 for electro-optical purposes.   An electro-optic display containing the liquid crystal medium according to claim 1.