JPH06287559A - Liquid crystal medium - Google Patents

Abstract

PURPOSE: To obtain a liq. crystal medium which has a high birefringence and a nematic phase in a wide temp. range from room temp. to 165°C or higher.

CONSTITUTION: This medium substantially comprises polar component A having a dielectric anisotropy Δε of higher than +2 and a nonpolar component B having a dielectric anisotropy of from -2 to +2, provided that the medium has a clearing point of 165°C or higher, a dielectric anisotropy higher than 8, and an optical anisotropy of from 0.2 to 0.3.

COPYRIGHT: (C)1994,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a liquid crystal medium (LC medium) having high birefringence and having a broad nematic phase between room temperature and temperatures higher than 165 ° C.

[0002]

Liquid crystal display devices (LC display devices) are increasingly using nematic or nematic-cholesteric liquid crystal materials. By changing its optical properties such as light absorption, light scattering birefringence, reflection or color under the influence of an electric field, the function of such a display element is, for example, dynamic scattering, orientation phase deformation, guest-host effect. , Schatt-Helfrich in a twisted cell
Effect, refractive index matching of liquid crystalline droplets in polymer matrix or polymer network (ncap
= Alignment phase of nematic curve type, pdlc = polymer dispersed liquid crystal) or cholesteric-nematic phase transition.

Industrial application of these effects in electronic components requires liquid crystal phases which meet many requirements. Of particular importance here are the chemical resistance to humidity, the resistance to heat, irradiation of infrared rays, visible light and ultraviolet rays, and the resistance to direct and alternating electric fields. Industrially available liquid crystal media are required to have a liquid crystal mesophase, a reasonable optical anisotropy and a high or moderate dielectric anisotropy over a reasonable temperature range. Finally, these liquid crystal media must be free of any self-absorption in the visible light region, i.e. colorless.

None of the previously disclosed series of compounds having a liquid crystalline mesophase contains individual compounds which meet all these requirements. For that reason, the principle is to make a mixture of 4 to 25 (or even more) compound mixtures in order to obtain mixtures usable as liquid crystal media. Usually at least one compound having a low melting point and a high clearing point is further admixed. The result is a mixture whose melting point is usually lower than that of the lower melting point component, but whose clearing point is midway between the clearing points of the components. However, the optimum medium is not easily prepared by this method, since components with high melting points and high clearing points often give the mixture a high viscosity. As a result, the switching times of electro-optical display elements produced in this way change in an unfavorable way.

In order to lower the threshold voltage, a strongly polar nematic compound having a cyan group at the terminal has been added to the LC phase disclosed so far. However, the effective dipole efficiency of these compounds is significantly reduced by the more or less strong antiparallel coupling of these molecules,
As a result, it was necessary to add a relatively large amount of polar compound. This in turn leads to various drawbacks such as the unfavorable elastic properties of the LC phase and high viscosity.

All commercially available liquid crystal media are at 60 ° C. and 15 ° C.
It shows a clearing point between 0 ° C. Any of these media can have very high temperatures, such as displays on furnaces, reactors,
It cannot be used in applications with high temperatures inside for projection systems, light valves for spotlights, etc.

Therefore, liquid crystal media having a high clearing point, low melting point, low viscosity (and thus short switching time) and low threshold voltage, as well as reasonable birefringence for use in standard display cells or in pdlc applications. There is still a great demand for liquid crystals with excellent combined viewing angle characteristics.

[0008]

The object of the present invention is to produce a liquid crystal phase which has a nematic phase in the temperature range required for its purpose and which completely or almost completely does not contain the above-mentioned drawbacks. The liquid crystal medium has a substantial dielectric anisotropy.
When it is composed of a polar component A having ε> +2 and a nonpolar component B having a dielectric anisotropy of −2 to +2, provided that the clearing point of the medium is higher than 165 ° C. and the dielectric anisotropy is When the optical anisotropy is greater than 8 and the optical anisotropy is between 0.2 and 0.3, preferred combinations of material properties, especially at steep threshold rise, viscosity, nematic phase width, viewing angle and low threshold voltage. It has been found that liquid crystal phases are obtained which have an appreciable combination of temperature dependence.

[0009]

The present invention is particularly directed to polar component A
Is based on the cyanide compound of formula I

[0010]

[Chemical 11] However, in this formula, R ¹ is alkyl having 1 to 12 carbon atoms, and further 1 or 2 non-adjacent CH ₂ groups in the alkyl group are oxygen atoms, —CO—,
-O-CO-, -CO-O-, and / or -CH =
It may be substituted with a CH- group, m is 0 or 1, A ¹ is trans-cyclohexylene, 1,4-phenylene, 2- or 3-fluorophenylene, and L ¹ to L ⁴ are Independently, each is hydrogen or fluorine, and further relates to a liquid crystalline medium in which the total proportion of the compound of formula I is 45% by weight or more.

The present invention therefore uses the above-mentioned liquid crystal media, which may contain one or more pleochroic dyes (guest-host system), and media in liquid crystal display elements, especially at elevated temperatures. To provide that.

The invention further provides a liquid crystal display element, in particular an electro-optical display element containing such a medium.

The guest-host system according to the invention generally contains 0.1 to 15, preferably 0.5 to 10, in particular 1 to 7% by weight of pleochroic dyes.

The pleochroic dyes of the guest-host system according to the invention are preferably chosen in such a way that they cover a reasonable part of the visible spectrum and that the absorption in this region is more or less constant. a) A preferred embodiment of the present invention is a liquid crystalline medium, in which the polar component A is I1 to I.
Three

[0015]

[Chemical 12] Consisting of two, three or more compounds selected from the group consisting of: b) the polar component A is of formula I4

[0016]

[Chemical 13] C) a neutral component B is of the formula II

[0017]

[Chemical 14] Of one or more compounds of the formula: R ² and R ^{3 in the} formula have the meanings given for R ¹ , L ⁵ is hydrogen or fluorine and n is 0 or 1. D) The neutral component has the formula II1 to II3

[0018]

[Chemical 15] Consisting of a few compounds selected from

[0019]

[Chemical 16] Of at least one compound of formula B in which R ⁴ has the meaning indicated for R ^1.

[0020]

[Chemical 17] And chemical formula C

[0021]

[Chemical 18] Independently the chemical formula A ¹

[0022]

[Chemical 19] Z ¹ and Z ² each independently represent —CH ₂ CH ₂ — or a single bond, and L ¹ and L 2
² is fluorine or hydrogen, and Q is -OCF ₂
-, - OCFH -, - CF 2 -, - CFH -, - CH 2
CF ₂ —, —O—CH ₂ CF ₂ — or a single bond and X is fluorine or chlorine, and f) the liquid crystal medium is of formula III1.

[0023]

[Chemical 20] It consists of at least two compounds. Furthermore, the invention relates to a medium consisting essentially of a), b) and c) below. a) one or more compounds of the formula I, b) one or more compounds of the formula II, c) one or more compounds of the formula III, in particular where component A is 5-35% of the formula One or more compounds of formula I1, 7.5-20% of one or more compounds of formula I2, 7.5-25% of one or more compounds of formula I3, and 4-15 % Of a few compounds of formula I4.

Another preferred embodiment of the present invention is a liquid crystalline medium consisting essentially of the following 4: 45-65% of formula I3
One or more compounds of the formula II2, 5-15%
One or more compounds of the formula II, 10-20% of formula II
One or more compounds of 3, 10-30% of formula I
II1 one or more compounds.

The medium according to the invention preferably contains a mixture of two or more (preferably three or more) compounds of the formula I. Preferably, the proportion of these cyan compounds is at least 45% by weight. These compounds allow the realization of high clearing points and at the same time high birefringence. In particular, if a compound is used that indicates that one of L ¹ to L ⁴ is fluorine,
A low Δε / ε⊥ ratio can be achieved.

The medium of the invention preferably has a nematic phase range, which occurs during use at room and elevated temperatures, such as in furnace displays, including 0 ° C. to 220 ° C. (wide range of mixtures). S / N ≦ 70 ° C., preferably S / N ≦
40 ° C., especially S / N ≦ 20 ° C. and N / S ≧ 165 ° C.,
Particularly preferred is a medium having N / I ≧ 195 ° C.,
/ I ≧ 200 ° C. is particularly preferable.

Here, S / N indicates the transition temperature of the transition from the smectic phase to the nematic phase, and N / I means the transition temperature of the transition from the nematic phase to the isotropic phase, that is, the clearing point.

All the media according to the invention make it possible to achieve short switching times by virtue of their favorable viscous and elastic properties. Gooch-High Δn type mixture
Used for operation in the secondary or higher minimum of the tally curve. These media are characterized by an improved steepness of the electro-optic curve rise and are suitable for low multiplex TN and pdlc.

Formulas I to III of liquid crystal media according to the invention
The individual compounds of are known or can be synthesized from the prior art by methods that are readily derivable to those skilled in the art. The reason is that these methods are based on the standard methods described in the literature.

Corresponding compounds of the formula I are for example described in British patent applications GB 14 33 130 and GB 20 39.
937 and German Patent Application P 2901 591.
It is described in. Compounds of formula II are for example disclosed in German publications P 29 27 277, P 29 48 836.
And P 31 17 152. Formula II
The compounds of I are for example described in International Patent Application WO 89/0288
4, WO 91/03450, WO 90/01056 and German publication G 30 42 391 and P.
33 17 597.

Surprisingly, the combination of compounds of the formulas I and II has, on the one hand, a broad nematic mesophase with a low smectic-nematic transition temperature and is associated with a very fast switching time due to the preferred viscosity values, especially at high operating temperatures. LC with high dielectric anisotropy
It was found that it represents a medium.

The LC medium according to the invention preferably contains at least one component of formula I, in particular three components and at least two components of formula II, in particular at least three components.

The total proportion of compounds of the formula I and of the formula II is preferably 50 to 85%, in particular 60 to 80%.

R ¹ is preferably alkyl, alkenyl,
Alkoxy or alkoxymethyl, especially straight-chain alkyl or straight-chain alkoxymethyl, each having 1 to 7 carbon atoms.

Preferred compounds of formula I are those of the partial formulas I1 to I4.

In the case of compounds of the partial formula shown above, R
¹ is a linear alkyl group, preferably an alkyl group of 1 to 7 carbon atoms, in which the CH ₂ group is further substituted with —O—, —CH═CH— Good. Particularly preferred radicals R are methyl, ethyl, n-propyl, n-butyl, n-pentyl and n-heptyl.

The following compounds are particularly preferred (n = 1-
7, preferably 2-5).

[0038]

[Chemical 21] Formulas II and I shown above with the radicals R ² / R ³ / R ⁴
In the case of compounds of formula II, the radicals R each independently of one another have ^one of the abovementioned meanings for R ¹ .

In formula III, Q--X is preferably fluorine,
Chlorine, OCF ₃ or OCF ₂ H, especially fluorine, L ⁵ and L ⁶ are hydrogen or fluorine, preferably at least one of which is fluorine.

The polar component A has the formula V

[0041]

[Chemical formula 22] A compound of R ¹ and a group A
¹

[0042]

[Chemical formula 23] Has the previously described meaning, and r is 1 or 2.

When r is 1, the group A ¹

[0044]

[Chemical formula 24] Is preferably 1,4-cyclohexylene.

When r is 2, the group A ¹

[0046]

[Chemical 25] Is preferably 1,4-phenylene.

The production of the phases according to the invention can be carried out in the usual way. Generally, the desired amount of the components used in small amounts is dissolved in the main component, preferably at elevated temperature.
If this temperature is chosen above the clearing point of the main constituent, the completeness of the dissolution process can be observed particularly easily.

However, it is also possible to remove the solvent by mixing with a suitable organic solvent, for example a solution of the components in acetone, chloroform, methanol, and, after thorough mixing, distillation under reduced pressure. It is self-evident that in this method it must be ensured that the solvent does not introduce any contamination or undesired doping agents.

With suitable additives, the liquid crystal phase according to the invention can be modified for use in any of the liquid crystal display element types disclosed hitherto. Such additives are known to the person skilled in the art and are thoroughly described in the literature. In order to improve the electrical conductivity of the substance in order to change the dielectric anisotropy, the viscosity and / or the orientation of the nematic phase, for example a conducting salt, preferably ethyldimethyldodecylammonium 4-hexyloxybenzoate, tetrabutylammonium tetraphenylbora Salts of nato or crown ether complexes (eg, molecular crystal liquid crystals (Mol. Cryst. Liq. Cryst.) Such as I. Heller) 24
Vol. 249-258, 1973) can also be added. Such substances are described, for example, in German Published Patent Application No. 22 09 127, 2240 864, 232.
1 632, 23 38 281, 24 50 08
8, 26 37 430, 28 53 728, 29
02 177.

The following examples illustrate the invention but do not limit it. In the examples, the melting points and clearing points of crystalline materials are given in degrees Celsius. Percentages are weight percentages.

In this patent application and in the examples below, LC
Abbreviations for all chemical structures of compounds
The conversion to the structure is performed as described below. All the rest
Group C _n H_{2n + 1}And C_m H_{2m + 1}Are n and m respectively
Is a linear alkyl group having a carbon atom of. Table B
The mode is self-explanatory. In Table A, abbreviations for core structures
Showed only. For specific compounds, after this abbreviation
A dash and a substituent R¹ , R² , L¹ And L² for
Is followed by the code.

[0052]

[Chemical formula 26]

[0053]

[Chemical 27]

[0054]

[Chemical 28]

[0055]

[Table 1]

[0056]

【Example】

[0057]

[Table 2]

[0058]

[Table 3]

[0059]

[Table 4]

[0060]

[Table 5]

[0061]

[Table 6]

[0062]

[Table 7]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Masaomi Tanaka, Federal Republic of Germany Day -64293 Darmstadt Frankfurther Strasse 250 (72) Inventor, Hiroshi Numata, Federal Republic of Germany Day -64293 Darmstadt Frankfurther Strasse 250

Claims (13)

[Claims] 1. A polar component A having a dielectric anisotropy Δε> +2.
And a non-polar component B having a dielectric anisotropy of -2 to +2
A nematic liquid crystal medium essentially consisting of, but characterized by a clearing point of the medium above 165 ° C., a dielectric anisotropy of more than 8 and an optical anisotropy of 0.2 and 0. It is between 3. 2. A liquid crystalline medium according to claim 1, characterized in that the polar component A is based on a cyanide compound of formula I: However, in this formula, R ¹ is alkyl having 1 to 12 carbon atoms, and further 1 or 2 non-adjacent CH ₂ groups in the alkyl group are oxygen atoms, —CO—,
-O-CO-, -CO-O-, and / or -CH =
It may be substituted with a CH- group, m is 0 or 1, A ¹ is trans-cyclohexylene, 1,4-phenylene, 2- or 3-fluorophenylene, and L ¹ to L ⁴ are Independently hydrogen or fluorine, and the total proportion of compounds of formula I is 45% by weight or more. 3. A liquid crystal medium according to claim 1, wherein the polar component A is I1 to I3. It consists of two, three or more compounds selected from the group consisting of: 4. A liquid crystal medium according to one of claims 1 to 3, wherein the polar component A is of the formula I4 Of one or more compounds of 5. A liquid crystal medium according to one of claims 1 to 4, wherein the non-polar component B is of formula II Of one or more compounds of the formula: wherein R ² and R ³ have the meanings given for R ¹ , L ⁵ is hydrogen or fluorine and n is 0 or 1. . 6. A liquid crystal medium according to one of claims 1 to 5, wherein said non-polar component is of formula II1 to II3 It consists of a few, three or more compounds selected from 7. A liquid crystal medium according to one of claims 1 to 6, characterized in that component A is of formula III Of at least one compound of the formula B wherein R ⁴ has the meaning given for R ¹ and has the formula B And the chemical formula C: Independently of each other, the chemical formula A ¹ Z ¹ and Z ² each independently represent —CH ₂ CH ₂ — or a single bond, and L ¹ and L 2
² is fluorine or hydrogen, and Q is -OCF ₂
-, - OCFH -, - CF 2 -, - CFH -, - CH 2
_{CF 2 -, - O-CH} 2 CF 2 - or a single bond, and X is fluorine or chlorine. 8. Formula III1 8. A liquid crystal medium according to claim 7, comprising at least two compounds of 9. A liquid crystal medium according to one of claims 1 to 8, characterized in that the liquid crystal medium is substantially a) one or more compounds of formula I, b) formula II. And one or more compounds of formula III and c) one or more compounds of formula III. 10. A liquid crystal medium according to one of claims 1 to 9, characterized in that component A is 5
-35% of one or more compounds of formula I1, 7.
5-20% of one or more compounds of formula I2,
It consists of 7.5-25% of one or more compounds of the formula I3 and 4-15% of a few compounds of the formula I4. 11. A liquid crystal medium according to one of claims 1 to 9, characterized in that the liquid crystal medium is substantially 45-65% of one or more compounds of formula I3, 5- It consists of 15% of one or more compounds of formula II2, 10-20% of one or more compounds of formula II3 and 10-30% of one or more compounds of formula III1. 12. Electro-optical display element, characterized in that the electro-optical display element contains a medium according to claim 1. 13. An electro-optical light valve for a spotlight, which is characterized in that the electro-optical light valve for a spotlight contains the medium according to claim 1.