JP2001019961A - Liquid crystal medium and liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject medium having a wide nematic phase range and a low viscosity and useful for a liquid crystal display, etc., by providing a liquid crystal component, etc., and a specific clearing point and a specified cross-over frequency. SOLUTION: This medium comprises (A) a dielectrically negative component, (B) a dielectrically positive component containing an ester compound and (C) a selectively dielectrically neutral component and has >=-80 deg.C clearing point and >=-25 kHz crossover frequency. Furthermore, the component A preferably contains one or more compounds represented by formula I (R11 and R12 are each a 1-7C alkyl, a 1-7C alkoxy, a 2-7C alkenyl or the like; formula II is trans-1,4-cyclohexylene or 1,4-phenylene; Z1 is CH2CH2, COO or the like; n is 0 or 1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The invention relates to liquid crystal media and to liquid crystal displays containing these media, in particular to P
It relates to a display of a complex system such as DLC.

[0002]

2. Description of the Related Art Liquid crystal displays (Liquid Cr)
Yastal Displays (LCDs) are widely used to display information. Electro-optic modes are used, such as twisted nematic (TN), super-twisted nematic (STN), electrically controlled birefringence (ECB) modes, and various variations thereof. In addition to the above-described modes in which each uses an electric field that is substantially perpendicular to the substrate and substantially perpendicular to the liquid crystal layer, for example, in-plane-switching (I-plane).
There are also electro-optical modes, such as the (PS) mode, which use an electric field approximately parallel to the liquid crystal layer for each substrate (compare, for example, DE 40 00 451).

[0003] Thus, besides the many different modes which use a liquid crystal medium which is usually pre-treated and which is oriented on the surface to achieve a uniform alignment of the liquid crystal material, for example, WO 91/0
For example, as disclosed in No. 5029, for example, a polymer dispersed liquid crystal (Polymer Dispersed Liquid Crystal)
d Crystal: PDLC)-, nematic,
Orientation phase surrounded by a curve (Nematic Curvil)
inearlyAligned Phase: NCA
P)-and polymer networks (Polymer)
There is an application using a composite system of a low molecular weight liquid crystal material together with a polymer material such as a Network (PN) -system. These latter ones usually use an electric field approximately perpendicular to the composite layer.

[0004] To accelerate the switching of liquid crystal media in LCDs, particularly the switching-off of active liquid crystal switching elements, "two frequency" addressing methods have been proposed. This addressing method makes use of the fact that dielectrically positive liquid crystal media are usually characterized by negative dielectric anisotropy at high frequencies. This familiar effect can be used to actively switch "off" the liquid crystal switching element. LC Δ
The LC material that addresses the switching element by radio waves of low frequency, usually square wave voltage, where ε is positive, is oriented parallel to the electric field. The same L due to high frequency radio waves, that is, radio waves having a frequency where Δ あ る
By addressing the C switching element, L
The C material is oriented perpendicular to the electric field. Thus, L
Active switching "off" of the C switching element is realized.

One form of PDLC that is particularly suitable according to the present application is the so-called memory-PDLC (MPD for short).
LC) display, for example, Ohyama,
J. Matsuda, H .; , And Eguchi,
K. , SID99 Digest, pp. 648-65
1 (1999). These displays are bistable and their polymer matrix usually has an anisotropic morphology.

[0006] LCDs are used for direct view displays and projection displays. In addition to these uses,
LCDs, especially LCDs comprising a composite system such as PDLC,
In particular, the so-called holographic PDPC (HPDLC) system is used for practical applications. These HPDLC displays are described, for example, in Tanaka, K .; , Kato,
K. Tsuru, S .; , And Sakai, S .; , J
own of the SID, "/ 1, pp.
37-40 (1994), which utilizes Bragg reflection to generate three bright colors, preferably the primary colors. This approach gives excellent bright colors because it does not require polarizers or color filters. A single layer of a periodic structure of polymer and liquid crystal controls the reflection of one particular color. Therefore, in order to realize three main colors, one layer is required for each color. Each of the three layers must be addressed independently. This requires three sets of HPDLC films, each with a corresponding electrode. This large number of layers and corresponding electrodes is difficult to achieve in good yield in mass production, but can be beneficially reduced when a “two frequency” drive method is applied.

However, the well-known principles of the two-frequency driving method have several disadvantages. The first drawback is that conventional liquid crystal mixtures have a much higher crossover frequency (crossover frequency (ν)) for practical applications.
_cross ) is the frequency at which Δε changes its sign from dielectrically positive to dielectrically negative as the frequency increases. )
It is to feature. The next problem is in the low frequency region (Δε _low ) or in the high frequency region (Δε _low ).
_high ), or rather the absolute value of the Δε value in both cases, is too low to allow easy addressing of the LC material. Another problem is that
The orientation of the LC medium on the normal orientation layer is insufficient,
And / or their poor compatibility with the precursors of the composite polymers.

[0008] Thus, a significant need arises for liquid crystal media having the following appropriate properties for practical applications:
A suitable optical anisotropy Δn with a wide nematic phase range, low viscosity, a suitably large absolute value of Δε depending on the display mode used and especially in both the low frequency and high frequency regions (especially like PDLCs). A suitably high Δn) for the composite system, a suitably low crossover frequency between these regions, and good orientation in the alignment film and / or good compatibility with the polymer precursor for the composite system become.

[0009]

SUMMARY OF THE INVENTION It has now been found that, surprisingly, it is possible to realize a liquid crystal medium which can be subjected to a two-frequency drive, which does not have the disadvantages of the above-mentioned prior art, or which, if at all, has such a disadvantage. Was.

[0010]

SUMMARY OF THE INVENTION These improved liquid crystal media are realized by using at least two components: compounds having a negative value of the dielectric anisotropy Δε in the low frequency range, especially at 1 kHz. A first liquid crystal component (referred to as component A) containing a certain dielectrically negative compound, and at the same time, containing an ester compound having a sufficiently positive Δε in a low frequency region, especially at a frequency of 1 kHz; A second liquid crystal component (hereinafter referred to as component B) which is a dielectrically positive component comprising the ester compound of

Preferably, said dielectrically negative liquid crystal component A comprises and preferably consists of a compound of formula I:

Embedded image Wherein R ¹¹ and R ¹² are, independently of one another, an alkyl or alkoxy having 1 to 7 C atoms,
Alkenyl, alkenyloxy or alkoxyalkyl having from 7 to 7 C atoms, R ¹¹ is preferably n-alkyl, preferably having 3 to 5 C atoms, and R ¹² is preferably Preferably n-alkoxy having 2 C atoms,

Embedded image Is trans-1,4-cyclohexylene or 1,4
- phenylene, ^{Z 1} _{is, -CH 2 CH 2 -, -} C
OO—, —C≡C—, —CH ＝ CH— or a single bond, preferably —CH ₂ CH ₂ — or a single bond;
Is 0 or 1.

Preferably, the liquid crystal component B contains and preferably consists of one or more dielectrically positive compounds of the formula II:

Embedded image Wherein R ² is alkyl or alkoxy having 1 to 7 C atoms, or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 C atoms,

Embedded imageIs trans-1,4-cyclohexylene or 1,4
-Phenylene, Z²Is -COO-, -CH₂CH
₂-, -CHO- or a single bond, preferably -C
OO- or a single bond;²¹, L²², L
²³Are independent of each other and are H or F;
Is L ²¹, L²², L²³At least one is F
And most preferably L²²Is F, and m is 0 or
1, preferably 1.

[0013] The liquid crystal medium of the present invention is optionally a dielectrically neutral component, and preferably, and more preferably, contains a dielectrically neutral compound of formula III: And preferably contains other components consisting of those compounds:

Embedded image Wherein R ³¹ and R ³² are independent of one another and are alkyl or alkoxy having 1 to 7 C atoms, or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 C atoms,

Embedded image Are independent of each other, trans-1,4-cyclohexylene, 1,4-phenylene, 3-fluoro-1,4-
Phenylene, 2-fluoro-1,4-phenylene, 2,
3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene, preferably trans-1,4-cyclohexylene, 1,4-phenylene or 3-fluoro-1,4-phenylene. Phenylene, and Z ³ represents —COO—, —CH ₂ CH ₂ —, —CH ₂ O—, —C}.
C- or a single bond, preferably -C≡C-, -CO
O- or a single bond, and o and p are each independently 0 or 1;

Component C is used in particular for adjusting the phase range and the optical anisotropy of the liquid-crystalline medium according to the invention. Compounds of the above formula III in which both o and p are 1 are particularly suitable for increasing the clearing point of the medium, whereas compounds of the formula III in which both o and p are 0 reduce the lower limit of the nematic phase range. Particularly suitable. In particular, ^{Z 3} is -C≡C-
The compounds of formula III are useful for adjusting the Δn of the vehicle.

Hereinafter, preferred embodiments of the liquid crystal medium according to the present invention will be described. The medium preferably contains one or more compounds of the formula Ia:

Embedded image And / or one or more compounds of the following formula Ib:

Embedded image Wherein ^{R 11} and ^{R 12} are defined as in the formula I, also preferably ^{R 1 1} is a n- propyl or n- ^{pentyl, R 12} is ethoxy.

The medium preferably contains at least one or two compounds of the formula IIa:

Embedded image Wherein R ² is defined as in Formula II above, and is preferably n-propyl, n-pentyl, or n-heptyl.

The medium contains a compound selected from the group of compounds of formulas IIIa to IIIc:

Embedded image ^{Wherein, R 31} and ^{R 32} are defined as in the formula III, also preferably ^{R 3 1} is n- alkyl or n- alkenyl and ^{R 32} is n- alkenyl or n- alkoxy, Most preferably, R ³² is alkoxy.

In a preferred embodiment, the liquid-crystalline medium contains one or more compounds of the above formula IIIa, wherein R ³¹ is preferably n-alkyl and R ³²
Is preferably n-alkoxy, both independently of one another, preferably having one or two carbon atoms, and most preferably the sum of the carbon atoms in R ³¹ and R ³² is 2 or 3 and especially 3.

In another preferred embodiment, the liquid-crystalline medium contains one or more compounds of the formula IIIc, wherein R ³¹ is preferably n-alkyl, preferably 2 From 5 to 5 carbon atoms, most preferably 3 carbon atoms, and R ³² is preferably n-alkyl or n-alkoxy, and most preferably methoxy or ethoxy .

The liquid crystal medium is preferably each of the formula I
And one or more compounds of the formulas II and II, and preferably comprises components A and B
50% to 100%, more preferably 70% to 100%,
It is most preferably 80% to 100%, and particularly preferably 90% to 100%.
Contains 100%. The concentration of component C of the liquid crystal medium according to the invention is preferably between 0% and 50%, more preferably between 0% and 50%.
30%, most preferably 0% to 20%, and especially 4% to 1%
6%.

[0021] Alternatively, the liquid crystal medium of the present invention may further contain a liquid crystal compound to adjust physical properties. Such compounds are known to those skilled in the art. The concentration of said compound in the liquid crystal medium according to the present invention is preferably 0% to 30%, more preferably 0% to 20%, and most preferably 5% to 15%.

The liquid-crystalline medium according to the invention has a clearing point of 80 ° C. or higher, preferably 100 ° C. or higher, more preferably 110 ° C. or higher, particularly preferably 120 ° C. or higher.
It is characterized by a clearing point of ℃ or above, most preferably 130 ℃ or above, and especially 140 ℃ or above. Δn of the liquid crystal medium according to the present invention is 0.2
0 or more, preferably 0.22 to 0.4
In the range. For HPDLCs, the Δ
n is more preferably in the range of 0.23 to 0.30;
Most preferably it is in the range of 0.24 to 0.28, and especially in the range of 0.25 to 0.275. On the other hand, MPDL
For Cs, the Δn of the liquid crystal medium is more preferably 0.
21-0.30, most preferably 0.22-0.20.
It is in the range of 0.25, and especially in the range of 0.23 to 0.24.

Special care must be taken to select an appropriate value for the ordinary refractive index (n ₀ ) of the liquid crystal medium. This value should be matched with the refractive index ( _nm ) of the polymer matrix. Preferably, the ordinary index of refraction of the liquid crystal medium differs from the index of refraction of the polymer matrix by 2% or less, most preferably by 1% or less, and especially by 0.4% or less. .

The Δε (Δε _{low at} 100 Hz) of the liquid crystal medium in the low frequency range according to the present invention is preferably +2 or more, and (Δε _{high at} 10 kHz) −2 or less in the high frequency range; More preferably, +3 or more and -3 or less, respectively, most preferably +4 or more and -4 or less, respectively, especially +5 or more and-
5 or less, and ideally +10 or -10, respectively. The preferred limits for Δε in the low and high frequency range can also be combined asymmetrically, for example, +3 or more and -2 or less, and +4 or more and -5 or less, There is also a case where the two are reversed.

According to the present invention, the crossover frequency (ν _cross ) between the low frequency region and the high frequency region, that is, the frequency whose sign changes from positive to negative as the Δε frequency of the liquid crystal medium increases, takes a value of 0. The frequency of the medium is 20 kHz or less, preferably 15 kHz.
kHz or less, more preferably 10 kHz
z or less, in a particularly preferred embodiment this frequency is 9 kHz or less, preferably 7 kHz or less, more preferably 5 kHz or less, most preferably 4kHz
z or less, and especially 3 kHz or less.

The liquid crystal medium according to the invention is preferably at 20 ° C.
Has a viscosity (ν) of up to 80, more preferably 6
It has a viscosity of up to 0, in particular up to 50 mm ² / s ⁻¹ . The corresponding limits at a temperature of 0 ° C. are respectively
600, 450 and 300, and 15,000, 10,000 and 6,000 at a temperature of -20 ° C.
mm ² / s ⁻¹ . As used herein, the term dielectrically positive compound means a compound having Δε> 1,5, and a dielectrically neutral compound is −1,5 <Δε <-1,5.
And a dielectrically negative compound is Δε <−
It is a compound having 1,5. The dielectric anisotropy of a compound is determined from the results of a 10% solution of the individual compound in a nematic host mixture. The volumes of these test mixtures are determined in cells that are homeotropic and homogeneously oriented. The cell gap for both types of cells is approximately 10 μm. The applied voltage has a frequency of 1k
At Hz, the root mean square value is typically a square wave of 0.5 V to 1.0 V, but this voltage is always chosen to be below the capacitive threshold of the respective test mixture.

For dielectrically positive compounds, the mixture ZL
I-4792, and also a mixture ZLI-3086 for dielectrically neutral as well as dielectrically negative compounds, both in Me
rck KGaA, a German product, each used as a host mixture. The dielectric constant of the compound is determined from the change in the respective value of the host mixture upon addition of the compound in question and the 100
% Extrapolated to concentration.

The term threshold voltage, as used herein, relates to the optical threshold and, unless explicitly stated otherwise,
Given for 10% relative contrast (V ₁₀ ). Capacitive threshold voltage (V ₀ , Freeederi
Also referred to as cksz threshold V _Fr. ) Is used only when clearly specified. The parameter ranges given in this application are all including limits, unless explicitly stated otherwise.

Throughout this application, unless otherwise specified, all concentrations are given in weight percent and are for each finished mixture, all temperatures are given in Celsius (Celsius), and All temperature differences are also given in degrees Celsius. All physical properties, unless expressly specified, refer to "Merck Liquid Cr"
Ystals, Physical Properties of Liquid Crystals ", Status N
ov. 1997, Merck KGaA, German
determined according to y and given for a temperature of 20 ° C. Optical anisotropy (Δn) is determined at a wavelength of 589.3 nm. The dielectric anisotropy (Δε) is determined at a frequency of 1 kHz, Δε _low and Δε _high are 10
Determined at frequencies of 0 Hz and 10 kHz. The threshold voltage, as well as all other electro-optical properties,
KGaA, determined by test cells adjusted in Germany. The test cell for determining Δε _low and Δε _high had a cell gap of 22 μm. The electrode is a circular ITO electrode having an area of 1.13 cm ² and having a guard ring. The alignment film is lecithin for homeotropic alignment (ε _‖ ), and Japan Syntheti for homogeneous alignment.
c Polyimide AL-1054 from Rubber. The capacitance was measured using a sine wave having a voltage of 0.3 Vrms by using a frequency response analyzer Solatron 1260
Determined by The light used in the electro-optical measurement was white light. The configuration used was a commercially available device from Otsuka, Japan. Characteristics were determined under vertical observation of the voltage. Threshold _{(V 10)} - mid gray _{(V 50)} -
And saturation (V ₉₀ ) voltages are 10% and 50%, respectively.
%, And 90% relative contrast.

The liquid-crystal medium according to the invention can contain other additives and chiral dopants in the usual concentrations. The total concentration of these other components ranges from 0% to 10%, preferably from 0.1% to 6%, based on the total mixture. The concentrations of the individual compounds used are each preferably in the range from 0.1 to 3%. These and similar additive concentrations are not taken into account in the present application with respect to the values and ranges of the concentrations of the compounds and liquid crystal components of the liquid crystal medium.

The liquid-crystalline medium according to the invention comprises several compounds:
Preferably it consists of 3 to 30, more preferably 5 to 20 and most preferably 6 to 10 compounds. These compounds are mixed in a usual manner. Generally, the compound used in the lower required amount is dissolved in the compound used in the higher amount. If the temperature is above the clearing point of the compound used at high concentration, the completion of the dissolution process is easily observed. However, according to other conventional methods, for example, using a premix which can be a so-called premix, for example an analog, a eutectic, or using a so-called multi-bottle system, It is also possible to prepare the media using a system that is ready to use the mixture itself.

The liquid crystal medium according to the present invention can be prepared by adding a suitable additive to TN-, TN-AMD, ECB.
-, Like VAN-AMD, and especially PDLC-, N
In composite systems, such as CAP- and PN-LCDs, a liquid crystal medium can be used to modify it for use in all known types of liquid crystal displays. The transition T (S, N) from the liquid crystal melting point T (C, N) to the nematic (N) phase and the clearing point T (N, I) are given in degrees Celsius.

In the present application and particularly in the following examples, the structure of the liquid crystal compound is represented by an abbreviation also called an acronym. The conversion of the abbreviations into the corresponding structures is done linearly according to the following two tables A and B. All groups C
_n H _{2n + 1} and C _m H _{2m +1} are straight-chain alkyl groups having n and m C atoms, respectively. The meaning of Table B is self-evident. Table A simply lists the abbreviations for the core portion of the structure. Individual compounds are indicated by core abbreviations with hyphens, and the codes defining substituents R ¹ , R ² , L ² are as follows:

[0034]

[Table 1]

[0035]

Embedded image

[0036]

Embedded image

[0037]

Embedded image

[0038]

Embedded image

[0039]

Embedded image

[0040]

Embedded image

[0041]

Embedded image

[0042]

Embedded image

[0043]

Embedded image

The liquid-crystalline medium according to the invention preferably contains the following compounds: 4 or more compounds selected from the group of compounds of Tables A and B, and / or the group of compounds of Table B 5 or 5 selected from
And / or two or two selected from the group of compounds of Table A
More than one compound.

FIG. 1 shows the frequency dependency of Δε. The results for two liquid crystal media are shown: one for Example 1 (dashed curve) and one for Example 2 (continuous curve). These curves clearly show the frequency behavior of the medium, with two relatively wide ranges of constant or almost constant Δε, one of which is about 10H.
in the low frequency range (Δε _low ) from z to several hundred Hz,
The other is in a high frequency range from about 10 kHz to about 1 MHz (Δ
ε _high ). For both examples shown, these almost constant plateaus of dielectric anisotropy are characterized by the opposite sign of Δε (high frequency range with always negative values),
Are reduced by an area ranging from approximately several hundred Hz to about 10 kHz, which decreases with increasing frequency. Δε is 0
Are shown in the graph by the respective insertion arrows.

FIG. 2, like FIG. 1, shows the frequency dependence of Δε, here for the liquid crystal mixture of Example 4 (mixture 4). The curves also clearly show the frequency behavior of the medium, which now has two relatively wide ranges of constant or almost constant Δε, one range also from about 10 Hz to several hundred Hz. In the low frequency range to cover, the other range from about 20 or 30 kHz to 1M
It is in a high frequency range (Δε _high ) ranging from over Hz. Again for this example, these plateaus with almost constant dielectric anisotropy are characterized by the opposite sign of Δε. The crossover region ranges from approximately 800 Hz to approximately 20 kHz in this example. The crossover frequency of this medium is indicated in the figure by the respective insertion arrow.

FIG. 3 shows characteristic lines of the response of the capacitance of different test cells when the voltage is increased at the characteristic frequency. The asterisks show the results at a frequency of 100 Hz for uniformly oriented cells, and the triangles show the results at a frequency of 100 kHz for homeotropically oriented cells (see text). The given voltage value is a root mean square value (rms). The capacitance threshold changes (increases) the capacitance as the voltage increases
Is determined from the starting point.

FIG. 4, like FIG. 1, shows the frequency dependence of Δε, here for the liquid crystal mixtures of Examples 5 to 7 (mixtures 5 to 7). The curves also clearly show the frequency behavior of the medium, where the medium has a relatively wide range of constant or almost constant Δε, one of which is again in the low frequency range (Δε _low ) ranging from about 10 Hz to several hundred Hz. And the other range is here in the high frequency range, which ranges from about 20 or 30 kHz to 1 MHz. Again for these examples, each plateau of almost constant dielectric anisotropy is characterized by the opposite sign of Δε. The range of the crossover area can be clearly recognized from this figure. The crossover frequency of each of these media is indicated in the graph by a respective inset arrow.

[0049]

EXAMPLES The examples given below illustrate the invention without limiting the invention in any way. However, these examples illustrate the further technical purpose of the present invention. In particular, these examples illustrate a suitable mixing system and demonstrate the desired accessible range of physical parameters.

Example 1 A liquid crystal mixture is realized by:

[Table 2]

This mixture has the following properties:

[Table 3]

The Δε value of this mixture depends on the orientation,
It is determined separately in a cell having a function of the frequency of the sinusoidal voltage of 0.3Vrms at 20 ° C. epsilon _‖ and epsilon _⊥
Is determined as the difference. The results are listed in Table 1 and plotted in FIG.

[0053]

[Table 4]

[0054]

[Table 5] Note: The difference in Δε when compared to ε _‖ −ε _にお_ける in this table is due to a shift in the rounding process.

The PDLC system is described in WO 91/05 02
9 as prepared in Example 1.1.1.
In addition, the HPDLC system is characterized by excellent performance and is published by Tanaka et al.
e SID, "/ 1, pp. 37-40 (1994).

Example 2 A liquid crystal medium is realized as in Example 1, but here it has the following composition:

[Table 6]

This medium has the following properties.

[Table 7] The Δε value of this mixture 2 has been determined as described under Example 1 as a function of frequency. The results are listed in Table 2 and plotted in FIG.

[0058]

[Table 8]

[0059]

[Table 9] Note: The difference in Δε compared to ε _‖ −ε _にお_ける in this table is due to a shift in the rounding process. Two PDLC systems have been prepared as in Example 1 and both have relatively beneficial results.

Example 3 A liquid crystal medium was prepared in the same manner as in the above example, consisting of the following compounds:

[Table 10] This mixture leads to results intermediate to those of Examples 1 and 2.

Example 4 A liquid crystal medium is realized from:

[Table 11]

This mixture has the following properties:

[Table 12] The Δε value of this mixture has been determined as disclosed in Example 1. The results are listed in Table 3 and plotted in FIG.

[0063]

[Table 13] Note: The difference in Δε compared to ε _‖ −ε _にお_ける in this table is due to a shift in the rounding process.

The capacitive threshold voltage of this mixture is such that the cell has a homogeneous orientation used for low frequencies (100 Hz) and a homeotropic orientation used for high frequencies (100 kHz). It has been determined in both of the cells. The results are shown in FIG. The capacitive threshold voltage in the low frequency region is 1.95 V, whereas the capacitive threshold voltage in the high frequency region is 3.95 V.
0V.

The PDLC system having excellent properties is WO
Prepared as disclosed in Example 1.1.1 of 91/05 029 with satisfactory results. This display had good results. In addition, the HPDLC system is based on the Journal of the SID of Tanaka et al., "/ 1, p, characterized by excellent performance.
p. 37-40 (1994).

Example 5 A liquid crystal mixture is realized from:

[Table 14]

This mixture has the following properties:

[Table 15] The Δε value of this mixture has been determined as disclosed in Example 1. The results are listed in Table 4 and plotted in FIG.

[0068]

[Table 16] Note: The difference in Δε compared to ε _‖ −ε _にお_ける in this table is due to a shift in the rounding process.

[0069] Two PDLC systems were prepared as disclosed in Example 1 above. These systems have shown excellent performance.

Example 6 A liquid crystal mixture consists of and is realized:

[Table 17]

This mixture has the following properties:

[Table 18]

The Δε value of this mixture has been determined as disclosed in Example 1. The results are listed in Table 5 and plotted in FIG.

[0073]

[Table 19] Note: The difference in Δε compared to ε _‖ −ε _にお_ける in this table is due to a shift in the rounding process.

Two PDLC systems were prepared as shown in Example 1 and both had good performance as in Example 1.

Example 7 A liquid crystal mixture consists of and is realized:

[Table 20]

This mixture has the following properties:

[Table 21]

The Δε value of this mixture has been determined as disclosed in Example 1. The results are listed in Table 6 and plotted in FIG.

[0078]

[Table 22] Note: The difference in Δε compared to ε _‖ −ε _にお_ける in this table is due to a shift in the rounding process.

As in Example 1, a PDLC system with excellent properties was prepared as disclosed in Example 1.1.1 of WO 91/05029. In addition, Ohyama et al., SID 99 Digest, p.
p. 648-651 (1999),
MPDLC displays with oriented substrates have been prepared. This display had good contrast and excellent bistability.

[Brief description of the drawings]

FIG. 1 shows the frequency dependence of Δε.

2 shows the frequency dependence of Δε, here for the liquid crystal mixture of Example 4. FIG.

FIG. 3 shows a characteristic line of the response of the capacitance of different test cells at a characteristic frequency when the voltage is increased.

FIG. 4 shows the frequency dependence of Δε.
For the liquid crystal mixture.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13 500 G02F 1/13 500 1/1334 1/1334 (71) Applicant 591032596 Frankfighter Str. 250, D-64293 Darmstadt, Federal Republic of Germany (72) Inventor Wen Sawada Germany-64293 Darmstadt Frankfurter Strasse 250

Claims (10)

[Claims] 1. a dielectrically negative liquid crystal component A; and a dielectrically positive liquid crystal component B containing an ester compound.
And-optionally characterized by containing a dielectrically neutral component C,-having a clearing point of 80 ° C or higher and a crossover frequency of-25 kHz or lower. Liquid crystal medium. 2. A liquid crystal medium according to claim 1, wherein the dielectrically negative component A comprises one or more compounds of the formula I: ## STR1 ## Wherein R ¹¹ and R ¹² are independent of each other and are alkyl or alkoxy having 1 to 7 C atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 C atoms, Embedded image Is trans-1,4-cyclohexylene or 1,4
- phenylene, ^{Z 1} is _-CH 2 _CH 2 -, - CO
O-, -CC-, -CH = CH- or a single bond;
n is 0 or 1. 3. The liquid crystal medium according to claim 1, wherein the dielectrically positive component B comprises one or more compounds of the formula II: ## STR3 ## ] Wherein R ² is alkyl or alkoxy having 1 to 7 C atoms, or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 C atoms; Is trans-1,4-cyclohexylene or 1,4-
Phenylene, and Z ² is —COO—, —CH ₂ CH ₂
-, -CHO- or a single bond, preferably -COO-
Or a single bond, L ²¹ , L ²² , and L ²³ are independent of each other, are H or F, and m is 0 or 1. 4. The liquid-crystal medium according to claim 1, wherein component A comprises at least two compounds of the formula I. 5. A liquid crystal medium according to claim 1, wherein component B comprises one or more compounds of the formula II. 6. A composition according to claim 1, wherein component A contains one or more compounds of the formula I with n = 0 and one or more compounds of the formula I with n = 1. 6. The liquid crystal medium according to at least one of claims 1 to 5. 7. A liquid crystal display addressed or addressable by dual frequency driving, wherein the liquid crystal display is addressable.
7. A liquid crystal display, comprising the liquid crystal medium according to at least one of the items 1 to 6. 8. A liquid crystal display according to claim 7, comprising a composite system containing the liquid crystal medium according to at least one of claims 1 to 4 and a polymer. 9. The liquid crystal display system according to claim 7, wherein the liquid crystal display system is a holographic display system. 10. Use of a liquid crystal medium according to at least one of claims 1 to 6 in a liquid crystal system.