JP2000096058A - Liquid crystal medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal medium capable of providing a display having reduced response time and driving voltage and a greatly high specific resistance by making the liquid crystal medium include a specific polar compound, or the like. SOLUTION: This liquid crystal medium comprises a mixture of polar compounds each having negative dielectric anisotropy as a base and contains one or more compounds of formula I (R1 and R2 are each a 1-8C alkyl or alkoxy; (m) is 0 or 1) and one or more compounds of formula II (ring A is cyclohexyl or the like; (n) is 0 or 1). Preferably, the liquid crystal medium contains one or more compounds each having positive dielectric anisotropy such as a compound of formula III (R3 is R1; L1 is H or F), or the like, and further two or more compounds of formula IV or formula V ((q) is 0 or 1; R4 is a 2-7C alkenyl; ring B is p-phenylene or the like). Preferably, the liquid crystal medium comprises 15-70 wt.% of the compound of formula I, 5-40 wt.% of the compound of formula II, 1-10 wt.% of the compound of formula III and 0-25 wt.% of the compound of formula IV.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal medium containing a polar compound having a negative dielectric anisotropy, and an electro-optical display containing the medium based on the ECB, CSH or VAN effect.

[0002]

2. Description of the Related Art Electrically controlled birefringence (ECB effect),
Alternatively, the principle of the DAP effect (deformation of the alignment phase) was described in 1971 (MF Sc
Hieckel and K. Fahrenschon, "Deformation of Nematic Liquid Crystal with Vertical Alignment in Electric Field", Appl. Phys. Let
t. 19 (1971), 3912) for the first time. JF Kahn (A
ppl.Phys. Lett. 20 (1972), 1193) and G. Labrunie and J. Robert (J. Robert (J. Appl. Phys. 44 (1973), 486)
9) followed this.

[0003] J. Robert and F. Clerc (SID 80 Digest Te
chn. Papers (1980), 3), J. Duchene (Displays 7 (1986),
3) and H. Schad (SID 82 Digest Techn. Papers (1982), 2
44), the liquid crystal phase for use in high-information display elements based on the ECB effect is, high ratio of elastic constants K ₃₃ / K _11,
It has been shown that it must have a large value of the optical anisotropy Δn and a value of the dielectric anisotropy Δε of -0.5 to -5. Electro-optic display elements based on the ECB effect are
-off state) has homeotropic (or vertical) edge orientation.

EC with homeotropic or vertical alignment
Specific types of B displays are CSH (color super homeotropic) or VAN (vertically aligned nematic) type displays. These displays are
Are known from the prior art and are described, for example, by S. Yamauchi
SID 89 Digest, 378 (1989), H. Hirai, JapanD
Japan Displays 89 Digest, 188 (1989) and JF Cle by isplays 89 Digest, 184 (1989) and j.F.
rc, SID 91 Digest, 758 (1991). For a display having a vertical alignment, an optical compensator, for example, an optically uniaxial negative compensation film (optically uniaxial negative compensation film) may be further provided to compensate for light leakage in an off state in an oblique viewing direction.
n film). In particular, it has been reported that CSH displays, while having the ability to provide full color, show low dependence of contrast and gray scale on viewing angle.

In addition, the special design of the electrodes allows the tilt direction in these displays to be controlled without additional pre-tilt processing of the electrodes.
For example, SID 91 Digest, 762 (1991) by T. Yamamoto et al.
The CS is characterized by a special electrode structure that has a large viewing angle and high contrast, induces an oblique electric field in the liquid crystal cell, and does not require electrode pretilt treatment.
H display is described. The above display is
It can be of the active or passive matrix type. For example, ECB and VAN displays are driven by either active matrix or multiplex addressing, while CSH displays have split columns and parallel electrodes (row electronodes), typically like passive or direct matrices. It is a dot matrix type and is driven by multiplex addressing.

[0006] The industrial application of the above effects in electro-optical display elements requires a liquid crystal phase which has to fulfill many requirements. Of particular importance here is moisture,
Air and heat, infrared, visible light, ultraviolet radiation and direct radiation,
As well as chemical resistance to physical effects such as changes in electric fields. Further, a liquid crystal phase that can be used industrially requires a liquid crystal mesophase having an appropriate temperature range and low viscosity.
The group of compounds having a liquid crystal mesophase disclosed hitherto does not include a single compound satisfying all of these requirements. Generally, a mixture of 2 to 25, preferably 3 to 18, compounds is therefore prepared in order to obtain a substance which can be used as a liquid crystal phase. However, liquid crystal materials having substantially negative dielectric anisotropy and adequate long-term stability have not previously been available, so the ideal phase is not easily obtained by this method.

[0007] EP 0 474 062 discloses a matrix liquid crystal display based on the ECB effect. The liquid crystal mixtures disclosed herein are based on 2,3-difluorophenyl derivatives containing an ester, ether or ethyl linking group,
And, since the "voltage holding ratio" (HR) after UV exposure shows a low value, it is completely unsuitable for a projection type display, for example. Therefore, a wide range of driving temperatures, as well as a very large resistivity, allowing to achieve various gray shades, high contrast and wide viewing angles
There continues to be a great demand for ECB, VAN and CSH displays with short response times and low threshold voltages.

Particularly for use in CSH displays, see, in particular, SID 91 Digest, 762 (199) by T. Yamamoto et al.
According to 1), it is desirable to obtain a liquid crystal material exhibiting a wide nematic phase width with improved steepness of electro-optical characteristic curve, fast response time, high birefringence, low viscosity and high clearing point .

[0009]

The object of the present invention is to provide a matrix liquid crystal display, in particular a matrix liquid crystal display based on the ECB, CSH and VAN effects, which does not have the above-mentioned disadvantages or has only a few. And, at the same time, to provide a display with a very high resistivity.

[0010]

SUMMARY OF THE INVENTION A nematic liquid crystal mixture based on a mixture of polar compounds having a negative dielectric anisotropy, comprising at least one compound of the formula I and at least one compound of the formula II, In the display of
It has been found that this task can be achieved by use. By using the liquid crystal mixtures according to the invention in matrix displays of the ECB, CSH or VAN type, it is possible to reduce the response time and the value of the drive voltage and at the same time achieve gray scale capability, a wide viewing angle and a high contrast. it can. In particular, the use of the mixtures according to the invention
In H-type displays it has been found to lead to improved steepness of the electro-optical characteristic curve.

Accordingly, the present invention provides a compound of formula I:

[Formula 11] At least one compound of the formula II;

Embedded image Wherein R ¹ and R ² are each independently of the other alkyl or alkoxy having 1 to 8 carbon atoms,

Embedded image m and n are each independently 0 or 1), and are based on a mixture of polar compounds having a negative dielectric anisotropy.
It relates to an electro-optic display based on the B, CSH or VAN effect.

A preferred embodiment of the invention relates to: a) a medium containing at least one compound having a positive dielectric anisotropy Δε, in particular Δε> +4. b) Formula III;

[Formula 14] Wherein R ³ has ^one of the meanings of R ^{1 in} formula I, L ¹ is H or F, and p is 0 or 1. The present invention relates to a medium containing at least one compound having dielectric anisotropy.

C) Formula IV;

Embedded image Wherein q is 0 or 1, R ² has the meaning of formula I,
And R ⁴ is alkenyl having 2 to 7 carbon atoms).

D) Formula V:

Embedded image (Wherein, R ¹ , R ² , m and

Embedded image Has the meaning of formula I, and

Embedded image The present invention relates to a medium further containing one or more of the following compounds:

E) Formula VI:

Embedded image Wherein R ¹ , R ² have the meaning of formula I, and r is 0 or 1, and further comprises one or more tolane compounds. f) Formula VII;

Embedded image Wherein R ¹ has the meaning of formula I and s is 0 or 1.
And a medium further containing one or more compounds selected from the group consisting of: g) A medium consisting essentially of four or more compounds selected from compounds of the formulas I and II, two or more compounds of the formula VI and at least one compound of the formula III.

H) relates to a medium containing at least three compounds of the formula I. i) relates to a medium containing at least one compound of the formula IV. k) for media in which the proportion of the compound of the formula I in the overall mixture is from 15% to 70% by weight, preferably from 30% to 60% by weight. l) For media in which the proportion of the compound of the formula III in the total mixture is from 1% to 10% by weight, preferably from 2% to 7% by weight.

M) The proportion of the compound of the formula IV in the total mixture is from 0% to 25% by weight, preferably from 5% to 20% by weight.
By weight media. n) at least 40% by weight, preferably 55%, of the tolane compound;
By weight media. o) relates to a medium containing at least 45% by weight, preferably at least 55% by weight, of a compound having 2,3-difluoro-1,4-phenylene groups. p) for media containing 1% to 15% by weight, preferably 2% to 10% by weight, of a compound having a positive dielectric anisotropy. q) relates to a medium containing at least one compound of the formula IV wherein R ⁴ is vinyl, 1E-propenyl, 1E-butenyl, 3E-butenyl or 3E-pentenyl, especially vinyl or 1E-propenyl.

R) Formulas Ia and Ib;

Embedded image Wherein alkyl is an alkyl group having from 1 to 6 carbon atoms, especially at least one compound of formula Ia and at least one compound of formula Ib Regarding the medium to be contained.

S) Formulas IIIa to IIId;

Embedded image Wherein alkyl is an alkyl group having 1 to 6 carbon atoms, especially at least one compound of formula IIIa and / or a compound of formula IIIc It relates to a medium containing at least one.

T) Formulas Va to Vd;

Embedded image Wherein alkyl is an alkyl group having 1 to 6 carbon atoms, R is an alkyl or alkoxy group having 1 to 6 carbon atoms, and L is H or F. Media containing at least three such compounds.

U) from 15% by weight to 7% of one or more compounds of the formula I
0% by weight 5% to 40% by weight of one or more compounds of formula II 1% to 10% by weight of one or more compounds of formula III and 0% by weight of one or more compounds of formula IV With a medium essentially containing 25% by weight.

In formula I, the term "alkenyl" is
Includes straight or branched chain alkenyl groups having 2 to 7 carbon atoms. Linear alkenyl groups are preferred. Further 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. Of these, particularly 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 and 6-heptenyl. Alkenyl groups having up to 5 carbon atoms are particularly preferred.

The present invention further relates to an electro-optical display based on the ECB, CSH or VAN effect, characterized by containing the above liquid crystal medium as a dielectric. The liquid crystal medium of the present invention exhibits a wide nematic phase width with a high clearing point, a large value of birefringence, and a negative value of Δε with a large value of ε _|| and a low absolute value | Δε | (ε _|| Is the dielectric constant parallel to the long molecular axis of the liquid crystal molecules).

The liquid crystal mixture preferably has a nematic phase width of at least 80 ° C., preferably at least 100 ° C., a clearing point of 80 ° C. or more, especially 100 ° C. or more, and
It has a maximum viscosity at 0 ° C. of 60 or less, preferably 40 or less, especially 25 mm ² s ⁻¹ or less. The dielectric constant ε _|| of the mixture of the present invention is 3
Greater, preferably greater than 4.5, more preferably equal to or greater than 6. The liquid-crystal mixtures according to the invention exhibit a dielectric anisotropy Δε of from −0.5 to −5.0, in particular from −1.0 to −3.0, particularly preferably from −1.0 to −2.0.

The birefringence Δn of the liquid crystal mixture is usually greater than 0.15, preferably greater than or equal to 0.20, in particular greater than or equal to 0.23. The liquid crystal display of the present invention is characterized by exhibiting a steep electro-optical characteristic curve, a low threshold voltage and a fast response time. The mixture preferably comprises a compound of formula I to formula VII
Contains 4 to 20, especially 5 to 15. In addition to the compounds of the formulas I to VII, other components can also be present, for example in amounts of up to 45% of the total mixture, but are preferably up to 20%, in particular up to 10%.

The other components are preferably nematic or nematogen substances, particularly known substances, azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexylbenzoates, phenyl or cyclohexylcyclohexanecarboxylates. , Phenylcyclohexanes, cyclohexylbiphenyls, cyclohexylcyclohexanes,
From cyclohexylnaphthalenes, 1,4-bis-cyclohexylbiphenyls or cyclohexylpyrimidines, phenyl- or cyclohexyldioxanes, optionally halogenated stilbenes, benzylphenyl ethers, tolanes and substituted cinnamic acids Selected from the group consisting of:

The most important compounds suitable as components of this type of liquid crystal phase are of the formula VIII; R ⁵ -LGER ⁶ VIII (L and E are 1,4-disubstituted benzene and cyclohexane rings, respectively, 4,4 '-Disubstituted biphenyl, phenylcyclohexane and cyclohexylcyclohexane, 2,5-disubstituted pyrimidine and 1,3-dioxane rings, 2,6-disubstituted naphthalene, di- and tetrahydronaphthalene, quinazoline and tetrahydroquinazoline a carbocyclic or heterocyclic ring systems, G is, -CH = CH- -N (O) = N- -CH-CQ- -CH = N (O) - -C≡C- -CH 2 - CH ₂ --CO-O- -CH ₂ -O- -CO-S- -CH ₂ -S- -CH = N- -COO-Phe-COO- or a CC single bond, and Q is A halogen, preferably chlorine, or -CN, and R ⁵ and R
⁶ is each alkyl, alkoxy, alkanoyloxy or alkoxycarbonyloxy having up to 18 carbon atoms, preferably up to 8 carbon atoms, or one of these groups is optionally CN, NC, NO ₂ , CF ₃ , F,
Cl or Br).

In most of these compounds, R ⁵ and R ⁶ are different from one another, one of these radicals usually being an alkyl or alkoxy radical. Other variants of the proposed replacement are similar. Many of such materials and their mixtures are commercially available. All of these substances can be prepared by methods known from publications.

The liquid-crystalline media according to the invention can also contain further additives known to those skilled in the art and described in the literature.
For example, polychromatic dyes can be added from 0% to 15%,
Further, to improve conductivity, a conductive salt, preferably ethyldimethyldodecylammonium 4-hexoxybenzoate, tetrabutylammonium tetraphenylborate or crown ether (e.g., M
ol.Cryst. Liq. Cryst. Volume 24 , pages 249-258 (19
73)), or substances can be added to improve the dielectric anisotropy, viscosity and / or orientation of the nematic phase. Such substances are, for example, DE-A 22 09 1
27, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26
37 430 and 28 53 728.

The individual components of the liquid-crystalline phases according to the invention of the formulas I to VII are known in each case or the process for their preparation is based on the conventional processes described in the publications. It can be easily derived by the trader from the prior art.

Corresponding compounds of the formula I are, for example, EP
0 308 438. Corresponding compounds of the formula II are described, for example, in EP 0 364 538. Formula III
Those which correspond to the compounds of are described, for example, in EP 0 019 665. Corresponding compounds of the formula IV are, for example, EP
0 122 389. Corresponding compounds of the formula V are, for example, EP 0 132 553, DE 26 36 684 and EP 002
2 183. Corresponding compounds of the formula VI are described, for example, in EP 0 308 438 or EP 0 709 444.

Examples of the present invention will be described below, but the present invention is not limited thereto. In this specification, unless stated otherwise, percentages are by weight and all temperatures are in ° C.
And all physical properties are “Merck Liqu
id Crystals, Physical Properties of Liquid Crystal
Determined by s "ed. W. Becker Merck KGaA, Status Nov. 1997.

The following abbreviations are used:

Embedded image

[0034]

Embedded image

Furthermore Δn represents the optical anisotropy measured at 20 ° C. and 589 nm, n ₀ denotes the ordinary refractive index at 20 ° C. and 589 nm, [Delta] [epsilon] is the dielectric anisotropy at 20 ° C. and 1kHz are shown, epsilon _|| denotes the dielectric constant in the parallel direction to the molecular axis at 20 ° C. and 1 kHz, cp denotes the clearing point [° C.], [nu _i is, ℃ [mm ² s ^-1] Where ν ₁ denotes the rotational viscosity at 20 ° C. [mPa * s], and V ₁₀ to V _th denote the 10% relative contrast at 20 ° C. and normal incidence. The threshold voltage is shown.

[0036]

EXAMPLES Example 1 A liquid crystal mixture is prepared to contain:

【table 1】

Example 2 A liquid crystal mixture is prepared to contain:

[Table 2]

Example 3 A liquid crystal mixture is prepared to contain:

[Table 3]

Example 4 A liquid crystal mixture is prepared to contain:

[Table 4]

Example 5 A liquid crystal mixture is prepared to contain:

[Table 5]

 ──────────────────────────────────────────────────続 き Continuation of front page (71) Applicant 591032596 Frankfurter Str. 250, D-64293 Darmstadt, Federal Republic of Germany (72) Inventor Akihiro Kojima Germany Day-64293 Darmstadt Frankfurter Straße 250 (72) Inventor Kazuo Toya Day-64293 Darmstadt Germany Fulter Strasse 250

Claims (12)

[Claims] A liquid crystal medium based on a mixture of polar compounds having a negative dielectric anisotropy, comprising a compound of the formula I: At least one compound of the formula II; Wherein R ¹ and R ² are each independently of the other alkyl or alkoxy having 1 to 8 carbon atoms, m and n are each independently 0 or 1). 2. The medium according to claim 1, comprising at least one compound having a positive dielectric anisotropy. 3. A compound of formula III: Wherein R ³ has ^one of the meanings of R ^{1 in} formula I, L ¹ is H or F, and p is 0 or 1. 3. The medium according to claim 1, comprising one or more compounds having a dielectric anisotropy. 4. A compound of the formula IV; Wherein q is 0 or 1, R ² has the meaning of formula I,
^4. The medium according to claim 1, wherein R ⁴ is an alkenyl having 2 to 7 carbon atoms). 5. A compound of the formula V: (Wherein, R ¹ , R ² , m and Has the meaning of formula I, and The medium according to any one of claims 1 to 4, wherein the medium comprises one or more of the following compounds. 6. A compound of the formula VI; Wherein R ¹ , R ² have the meaning of formula I and r is 0 or 1, characterized in that they contain one or more compounds of claim 1. A medium according to claim 1. 7. A compound of the formula VII Wherein R ¹ has the meaning of formula I and s is 0 or 1.
The medium according to any one of claims 1 to 6, wherein the medium comprises one or more of the following compounds. 8. It consists essentially of four or more compounds selected from formulas I and II, two or more compounds of formula VI, and at least one compound of formula III. A medium according to any one of claims 1 to 7. 9. The method according to claim 1, wherein the compound having a positive dielectric anisotropy is contained in an amount of 1 to 15% by weight, preferably 2 to 10% by weight. The described medium. 10. The method of claim 1 wherein one or more compounds of the formula I are present in an amount of
0% by weight, 5% to 40% by weight of compound 1 or 2 of formula II, 1% to 10% by weight of compound 1 or 2 of formula III,
And essentially containing from 0 to 25% by weight of one or more compounds of the formula IV.
The medium according to any one of the above. An electro-optic display based on the ECB effect, comprising the liquid crystal medium according to any one of claims 1 to 10 as a dielectric. An electro-optical display based on the CSH effect, comprising the liquid crystal medium according to any one of claims 1 to 10 as a dielectric.