DE10143910A1 - Electro-optical liquid crystal display used in supertwisted nematic displays comprises a liquid crystal layer with specific rotation and surface angles - Google Patents

Abstract

Electro-optical liquid crystal display comprises a liquid crystal layer with specific rotation and surface angles giving a low switching time. Electro-optical liquid crystal display comprises a liquid crystal layer with an angle of rotation of 110-360 deg and a surface angle of 2-20 deg and containing a compound of formula (I). R<1> = 1-7C alkyl or alkoxy or 2-7C alkoxyalkyl, alkenyl or alkenyloxy. Independent claims are also included for the following: (1) An indicator with a liquid crystal nematic phase that is at -20 to 70 deg C. (2) A device including the indicator. (3) A liquid crystal medium of the composition.

Description

The present invention relates to liquid crystal media and electro-optical Liquid crystal displays, special STN displays and in particular STN displays with low control voltages.

In such liquid crystal displays, the liquid crystals are called Dielectrics used, the optical properties of which are created of an electrical voltage reversibly change. Electro-optical displays the liquid crystals used as media are known to the person skilled in the art. These liquid crystal displays use various electro-optical ones Effects. The most common of these are the TN (twisted nematic) Effect of a homogeneous, almost planar initial orientation of the Liquid crystals on the surfaces of the substrates and one around 90 ° has twisted nematic structure between the substrates and the STN (supertwisted nematic) effect. The latter two being one homogeneous tilted orientation of the liquid crystals on the substrate surfaces and a twist of usually more than 180 ° up to Have 270 °. With these and similar electro-optical effects liquid-crystalline media with positive dielectric anisotropy (Δε) used.

For STN displays, which include all common and known types of higher twist displays in the present application, such as. B. SBE (Supertwisted Birefringent Effect), GH (Guest Host) STN and OMI (optical mode interference) displays as well as compensated STN displays, such as DSTN (D from double layer) and FSTN (F from film compensated) ) Displays, the liquid crystal director is twisted from one side of the liquid crystal layer to another by a given angle of more than 90 °, typically 180 ° or more, up to 600 °, typically up to 270 °. This is achieved on the one hand by corresponding orientation of the preferred directions of the liquid crystal orientation of the two substrates to one another. The preferred direction of orientation on the substrates is achieved by anisotropic pretreatment, typically by rubbing a special, usually polymeric organic layer in one direction, or by vapor-depositing SiO _x at an angle. On the other hand, a chiral liquid crystal medium is used which consists of mesogenic chiral substances or, most widely, consists of a non-chiral medium to which a chiral substance, a so-called dopant, is added. The last alternative is usually preferred because a variation in the concentration of the dopant enables the twisting of the liquid crystal layer to be set to almost any value.

It should be ensured that the ratio of the layer thickness to the Liquid crystal layer (d) to the undisturbed pitch of the liquid crystal (P of English cholesteric pitch) is big enough to get the one you want To produce twist. This is usually a value of the twist of more than 90 ° (or d / P = 900/360 ° = 0.25) below the desired one Twist set. This so-called geometric limit is so z. B. for cells with a twist of 180 °: 0.5-0.25 = 0.25 and for a cell with 240 ° twist: 0.667-0.25 = 0.417. The upper geometri cal limit is 180 ° higher twist, so at a 0.5 d / P value. When creating an electrical However, tension increases the cholesteric pitch and thus decreases the lower limit of the d / P ratio too. Although the same effect even at the upper limit this can practically not be exploited be in the area of higher doping when applying a electrical voltage an undesirable electro-optical effect occurs. This has the shape of a for director orientation in the middle of the liquid vertical layer of refractive index grating. That is why the over known as strip transition. This effect reduces the top one Limit of possible doping is significant and is mostly, in particular at higher twist angles, much more pronounced than the increase the lower limit when applying the voltage.

However, one is possible for the correct operation of STN displays over the entire display area, but at least over one pixel, the same moderate transition of the liquid crystal layer from the initial orientation necessary for final orientation. The director moves during this transition the liquid crystal layer within each layer imagined in parallel regardless of location in the same direction and at the same angle to each other.  

This desired transition is also called the Freedericksz transition. However, this transition does not occur with all possible parameters binations on. Depending on both properties of the liquid crystals, as well as from the construction of the display occurs when creating an undesirable transition of an electrical voltage due to its visual appearance as a stripe transition or English: striped domain transition / distortion. This Transition becomes the desired Freedericksz transition preferred if the liquid crystal parameters, especially the elastic ones Constants and the dielectric anisotropy are also available for one steep electro-optical characteristics are cheap. It is also characterized by a large d / P ratio favors. And depends not least on the ver averted twist angle and surface angle of attack. The following applies: the larger the twist angle, the larger the upper must Surface angle of attack (English: Surface Tilt Angle, short Tilt) is around one to enable stable operation of the display. Typically, at the commonly used twist angles of 180 °, 220 ° and 240 ° angle of attack of at least 2 °, 3 ° or 4 to 5 ° used.

Because with advertisements in general, also with advertisements after these Effects that the operating voltage should be as low as possible become liquid crystal media with high dielectric anisotropy used in the Usually predominantly and mostly even largely from liquid crystal bonds with the corresponding dielectric anisotropy exist. So with dielectric positive media from compounds with positive dielectric anisotropy. It will typically be mentioned at most valuable amounts of dielectric neutral liquid crystal compounds used. Liquid crystal compounds with that of dielectric Anisotropy of the medium opposite sign of the dielectric Anisotropy is usually used extremely sparingly or not at all puts.

An exception here are the STN advertisements, which are also the subject of pending registration. For STN ads such. B. after DE 41 00 287 dielectric positive liquid crystal media used  that contain dielectric negative liquid crystal compounds to increase the steepness of the electro-optical characteristic.

The pixels of the liquid crystal displays can be in different ways can be controlled. Direct control is common time sequential control using time division multiplexing and the active Control using a matrix of active, electrically non-linear Elements.

In the case of STN displays, control in time-division multiplexing is on most common. Here the columns and rows of a matrix shaped arrangement of liquid crystal switching elements with an control scheme using time-dependent, mutually orthogonal Voltage functions, e.g. B. driven to Alt and Pleschko. in this connection the liquid crystal medium of the liquid crystal display elements reacts in first approximation to the mean value of the control voltage (rms, from English: root mean square "). Especially at higher multiplex ratios nissen and applies to very fast switching liquid crystal switching elements however, this is no longer the case. Here the control can be expedient alternatively by "multiple line addressing", by "active addressing" or the so-called "improved Alt-Pleshko addressing".

Commonly one speaks at multiplex ratios of 1:32 and less of "low multiplex drive", with multiplex conditions in the area from approx. 1: 48 to 1: 100 from "mid multiplex drive" and with multiplex ratio nits of about 1: 128 and more (e.g. 1: 240, 1: 400 or 1: 480) of "high multiplex drive ".

The slope of the electro-optical characteristic curve of the liquid crystal cell must be sufficiently large, the numerical value V ₉₀ / V ₁₀ correspondingly small, in order to be able to control the required number of lines. This also applies to liquid crystal displays with low control voltages. With these, however, the possible variations of the liquid crystal medium have relatively narrow limits. On the one hand, a large proportion of highly dielectric positive connections is required to achieve the required low threshold voltages. As a result, a large part of the components of the medium is predetermined by substances that do not lead to the best slope of the characteristic curve and at the same time limits the space for the use of connections with corresponding cheaper elastic constants and the use of dielectric negative connections is almost impossible. In view of the fact that the liquid crystal displays must have a sufficient working temperature range and short switching times, the selection of possible compounds is also restricted for the remaining constituents of the liquid crystal media.

Compounds of formula (I), and those containing these compounds Liquid crystal media are known from DE 43 25 985.

The characteristic tensions decrease with increasing temperature of the liquid crystal mixtures. This is a corresponding Adjustment of the operating voltage to different temperatures necessary. This can be done manually or z. B. by a electronic regulation. A lower temperature dependence of the characteristic tensions help the effort for compensation of the control voltage or can reduce it, in the best case even make it superfluous. For liquid crystal displays with a pronounced The temperature dependence of the control voltage can increase with falling temperature even the decisive factor for the Limitation of the operating temperature range at low temperatures his. This is especially the case when the available Voltage from the power supply (e.g. batteries or Accumulators) or by the electronic components used is limited.

Also, liquid crystals need to work for ads with a lot of work temperature range over a stable nematic phase in one appropriate temperature range and as low as possible Have switching times, especially at low temperatures.

Thus, it can be seen that a need for liquid crystal displays is eliminated sufficient working temperature range, low temperature dependence  the operating voltage, sufficiently high steepness of the electro-optical Characteristic curve and short switching times, especially at low Operating voltages.

Surprisingly, it has now been found that this is due to the Ver Appropriate liquid crystal medium can be achieved can.

Liquid crystal media with high dielectric anisotropy and a relatively wide operating and storage temperature range are particularly suitable for use in displays according to the invention. The storage stability in liquid crystal cells of liquid crystal layer thickness suitable for the necessary optical delay at -30 ° C. is preferably greater than or equal to 500 hours and particularly preferably greater than or equal to 1000 hours. Liquid crystal media are particularly preferred before their storage stability at -40 ° C is 1000 hours or more. Liquid crystal media are preferably used which contain one or more compound (s) of the formula I.

wherein
R ^{1 is} alkyl or alkoxy with 1 to 7 carbon atoms or alkoxyalkyl, alkenyl or alkenyloxy with 2 to 7 carbon atoms, preferably alkyl or alkoxyalkyl and particularly preferably n-alkyl with 1 to 4 carbon atoms
means
contain.

In a preferred embodiment, the liquid crystal media used according to the present invention contain

• a) one or more dielectric positive compound (s) of the formula I as indicated above
  and or
• b) one or more dielectric positive compound (s) of the formula II
  wherein
  R ² alkyl or alkoxy with 1 to 7 C atoms, preferably n-alkyl or n-alkoxy, particularly preferably with 2 to 5 C atoms, or alkoxyalkyl, alkenyl or alkenyloxy with 2 to 7 C atoms, preferably 1 E- Alkenyl, 1-alkenyloxy or straight-chain alkoxyalkyl, preferably having 2 to 5 carbon atoms and particularly preferably alkyl or alkoxyalkyl,
  Z ²¹ and Z ²² each independently of one another, -CH ₂ CH ₂ -, -CH = CH-, -COO- or a single bond,
  each independently
  Y ²¹ and Y ²² independently of one another, H or F and
  n 0 or 1
  mean
  and / or, preferred and
• c) one or more dielectric neutral compound (s) of the formula III
  wherein
  R ³¹ and R ^{32 are} each independently of one another which have the meaning given above for R ² in formula II and
  Z ³¹ , Z ³² and Z ³³ each independently of one another -CH ₂ CH ₂ -, -CH = CH-, -COO- or a single bond
  each independently
  o and p independently of one another 0 or 1
  however preferred
  R ³¹ and R ³² each independently of one another alkyl or alkoxy with 1-5 C atoms or alkenyl with 2-5 C atoms,
  each independently
  and very particularly preferably at least two of these rings
  and or
  very particularly preferred
  very particularly preferably two adjacent rings are directly linked and preferred
  or
  mean.

In a further preferred embodiment, the liquid-crystal medium used additionally contains one or more compound (s) of the formula IV

R ⁴¹ and R ⁴² are each independently alkyl or alkoxy having 1 to 5 carbon atoms, preferably n-alkyl or n-alkoxy, preferably having 1 to 5 carbon atoms or alkoxyalkyl, alkenyl, alkenyloxy or alkynyl having 2 to 7 carbon atoms. Atoms, preferably straight-chain alkoxyalkyl, 1 E-alkenyl or 1 E-alkenyloxy, preferably with 1 to 5 C atoms,

Z ⁴ COO, CH ₂ CH ₂ , -C∼C- or preferably a single bond, where the phenyl rings can be substituted independently of one another optionally once or twice by F.

Optionally, the liquid crystal medium used contains one or more compound (s) of the formula V.

wherein
R ^{5 has} the meaning given above under formula II for R ² ,

each independently

Z ⁵¹ and Z ⁵² each independently of one another, -CH ₂ -CH ₂ -, -CH = CH-, -COO- or a single bond,
X ⁵ F, Cl, OCF ₂ H, OCF ₃ , CF ₃ ,
Y ⁵¹ and Y ⁵² each independently, H or F and
n ⁵ 0, 1 or 2, preferably 0 or 1
mean.

The liquid crystal medium used preferably contains one or more compounds of the formula II-1

wherein R ² , Z ²¹ ,

Z ²¹ , Y ²¹ and Y ^{22 have} the meaning given above for formula II and are preferred
R ² alkyl with 1 to 9 carbon atoms, preferably n-alkyl, preferably with 2 to 7 carbon atoms,

Z ²¹ -CH ₂ CH ₂ -, -COO- or a single bond, preferred
-COO- or a single bond and
Y ²¹ and Y ^{22 are} each independently H or F
mean.

The medium used particularly preferably contains one or more compounds selected from the group of compounds of the formulas II-1a to II-1c

wherein R ² , A ²¹ , Z ²¹ , Y ²¹ and Y ^{22 have} the meaning given above for formula II-1.

The media preferably contain one or more compounds selected from the group of compounds of the formula II-1a in which
R ² alkyl with 2 to 5 C atoms or alkenyl with 2 to 5 C atoms and,
Y ²¹ and Y ²² H or
R ² alkyl with 2 to 5 carbon atoms and
Y ²¹ and Y ²² F
mean,
and / or the formula II-1b

wherein
R ² alkyl with 2 to 7 carbon atoms or alkoxyalkyl with 2 to 5 carbon atoms, preferably n-alkyl or metoxyalkyl,
Y ²¹ F and
Y ²² H
mean.

The liquid crystal media used according to the invention preferably contain one or more compounds of the formula II-1a selected from the group of compounds of the sub-formulas II-1a1 to 11-1a3:

wherein
R ^{2 has} the meaning given above for formula II-1a and / or one or more compound (s) of formula II-1b selected from the group of compounds of sub-formulas 11-1b1 to 11-1b3:

Liquid-crystal media which use one or more compounds of the formula 11-1c selected from the group of compounds of the sub-formulas II-1c1 to 11-1c3 are likewise preferably used

wherein
n 1 to 9, preferably 2 to 7, and
m 1 to 3
mean contain.

The liquid-crystal medium used preferably contains one or more compounds selected from the group of compounds of the formulas III-1 to III-3:

where R ³¹ , R ³² , Z ³¹ , Z ³² ,

each the above have the meaning given in formula III.

The liquid crystal medium used particularly preferably contains one or more compounds selected from the group of the compounds of the formulas III-1a to III-1e, III-2a to III-2d and III-3a to III-3d:

wherein n and m each independently represent 1 to 5 and o and p each independently and independently of one another represent 0 to 3,

wherein R ³¹ and R ³³ each have the meaning given above under formula III-1 and the phenyl rings may optionally be fluorinated, but not in such a way that the compounds are identical to those of formula II and their sub-formulas. R ³¹ is preferably n-alkyl having 1 to 5 carbon atoms, particularly preferably having 1 to 3 carbon atoms, and R ³² n-alkyl or n-alkoxy having 1 to 5 carbon atoms or alkenyl having 2 to 5 carbon atoms , Of these, the compounds of the formulas III-1a to III-1d, III-2a and III-2d are particularly preferred.

The liquid crystal medium used preferably contains one or more compounds selected from the group of the compounds of the formulas IV-1a to IV-1c, IV-2a to IV-2d and IV-3a to IV-3b:

wherein
R ⁴¹ and R ^{42 have} the meaning given above under formula IV.

The liquid crystal medium used preferably contains one or more compounds selected from the group of the compounds of the formulas V-1a to V-1d, V-2a to V-2d and V-3a and V-3b:

wherein
R ^{5 has} the meaning given above under formula V.

Contain the liquid crystal media used according to the invention preferably 20% to 65% of several dielectric positive connections selected from the group of compounds of the formulas I and II. These are preferred, compounds of the formulas I and one or more various sub-formulas of the formula II, preferably from the group of Compounds of formulas II-1a to II-1c.

In a preferred embodiment, the liquid-crystal media used according to the invention contain a total of the total mixture
4% to 55% of compounds of the formula I,
20% to 60% of compounds of the formula II,
10% to 60% of compounds of formula III and
0% to 30% of compounds of forms IV and / or V.

Here, as in the entire previous application, means if not expressly stated otherwise, the term connections, to Clarification also written as connection (s), both one Connection, as well as multiple connections.

The individual compounds are, as a rule, in concentration NEN from 1% to 30%, preferably from 2% to 20% and particularly preferably used from 4% to 16%.

In a particularly preferred embodiment, the compounds of the different formulas are used in the liquid-crystal media used according to the invention, as summarized in the table below.

In a particularly preferred embodiment which can be identical to the preferred embodiments described above for the preferred concentration ranges and is preferably identical, the liquid crystal media contain

• - One or more compounds of formula I with R ¹ ethoxy or propoxy and / or
• - One or more compounds of formula II-1a with R ² n-alkyl and / or E1-alkenyl and / or
• - One or more compounds selected from the group of Compounds of the formulas III-1a to III-1d and / or
• - One or more compounds selected from the group of Compounds of the formulas III-2 to III-3 and / or
• - One or more compounds selected from the group of Compounds of formulas IV-1a, IV-2a and IV-3b.

Liquid crystal media which meet one or more of the following conditions are particularly preferred. The media included

• - One or more compounds of formula I, in particular in each case Compound in concentrations of 3% to 15%,
• - One or more compounds of formula II-1a, in particular in each case per compound in concentrations from 5% to 30%,
• one or more compounds of the formula III-1, in particular in each case in each case in concentrations of 3% to 15%, preferably at least one compound of both R ^{31 is} alkenyl,
• one or more compounds of the formula III-2, in particular in each case per compound in concentrations of 3% to 20%, preferably at least one compound in which R ³¹ denotes alkylenyl,
• One or more compounds of the formulas III-1a and / or III-1c, especially in concentrations of 4% to 15%, per compound,
• One or more compounds of the formula 111-2a,
• One or more compounds of the formula III-2d,
• - One or more compound (s) of the formula IV-2b and / or the Formula IV-3a and / or formula IV-3b.

The abovementioned preferred ones apply particularly preferably Concentration ranges also for this preferred combination of Links.  

The liquid crystal media used according to the invention have preferably nematic phases of at least from -20 ° C to 70 ° C, preferably from -30 ° C to 80 ° C and very particularly preferably from -40 ° C to 90 ° C. Here, the term means a nematic phase indicate on the one hand that at low temperatures at the corresponding Temperature no smectic phase and no crystallization observed and on the other hand that when heating from the nematic phase no clarification occurs yet. The investigation at low temperatures is in a flow viscometer at the appropriate temperature performed as well as by storage in test cells, one of the electro optical application corresponding layer thickness, for at least 100 Hours checked. At high temperatures, the clearing point becomes after usual methods measured in capillaries.

Furthermore, the liquid crystal media used according to the invention characterized by values of the optical anisotropic ones Particularly suitable for STN displays with common layer thicknesses. The Birefringence values are in the range of 0.100 to 0.180, preferably in the range from 0.120 to 0.170 and very particularly preferably in the range of 0.120 to 0.160 and most preferably in the range from 0.130 to 0.150.

In addition, the liquid crystal displays according to the invention have relative small values for the threshold voltage of less than or equal to 2.0 V, preferably less than or equal to 1.8 V, particularly preferably less than or equal to 1.7 V and very particularly preferably less than or equal to 1.5 V.

The slope values of the electro-optical characteristic of the liquid crystal show are preferably less than or equal to 1.080, particularly preferred less than or equal to 1.040, very particularly preferably less than or equal to 1.030 and in particular less than or equal to 1.020. They usually lie at values of 1.010 or more.

The various preferred ranges of the values for the individual physical properties for the orientation layer and for the liquid crystal material are preferably also observed in combination both with one another and with one another. So z. B. the Invention liquid crystal media in particular the following property combinations:

where, as in the entire application, "≦" is less than or equal to "≧" mean greater or equal.

The temperature dependence of the threshold voltage of the liquid-crystal media according to the invention in liquid-crystal displays according to the invention in the range from -20 ° C. to 20 ° C. is preferably less than or equal to 3.10 ^-3 / °, particularly preferably less than or equal to 2.10 ^-3 / °, particularly preferably less than or equal to 1, 5.10 ^-3 / ° and most preferably less than or equal to 1 .10 ^-3 / °. Here, as in the entire application, the relative values relate to the voltage value at the mean temperature of the temperature range. In the temperature range from 0 ° C. to 40 ° C., the temperature dependence of the threshold voltage of the liquid crystal media according to the invention in liquid crystal displays according to the invention is preferably less than or equal to 3.5.10 ^-3 / °, particularly preferably less than or equal to 2.5.10 ^-3 / °, particularly preferably less than or equal to 1.8.10 ^-3 / ° and most preferably less than or equal to 1.3.10 ^-3 / °. In the temperature range from -20 ° C. to 70 ° C., the temperature dependence of the threshold voltage of the liquid crystal media according to the invention in liquid crystal displays according to the invention is preferably less than or equal to 4.3.10 ^-3 / °, particularly preferably less than or equal to 3.10 ^-3 / °, particularly preferably less than or equal 2.10 ^-3 / ° and most preferably less than or equal to 1.5.10 ^-3 / °.

In the temperature range from -20 ° C to 20 ° C, the temperature dependence of the operating voltage at Mux. 1: 240, bias 1:16 of the liquid crystal media according to the invention in liquid crystal displays according to the invention preferably less than or equal to 9.10 ^-3 / °, particularly preferably less than or equal to 7.10 ^-3 / °, particularly preferably less than or equal to 6.10 ^-3 / ° and most preferably less or equal to 5.10 ^-3 / °. In the temperature range from -20 ° C to 70 ° C, the temperature dependence of the operating voltage at Mux. 1: 240, bias 1:16 of the liquid crystal media according to the invention in liquid crystal displays according to the invention preferably less than or equal to 6.5.10 ^-3 / °, particularly preferably less than or equal to 5.10 ^-3 / °, particularly preferably less than or equal to 4.10 ^-3 / ° and most preferably less than or equal to 3.10 ^-3 / °.

The twist angle of the liquid crystal layer of the invention Liquid crystal displays are preferably 180 ° to 290 °, particularly preferably 180 ° to 270 °, very particularly preferably 180 ° to 260 ° and particularly preferably 200 ° to 245 °.

The surface angle of attack is preferably in the range from 2 ° to 25 °, particularly preferably in the range from 3 ° to 15 °, very particularly preferred in the range from 3 ° to 9 ° and in particular in the range from 4 ° to 7 °. The layer thickness of the liquid crystal layer of the invention The display is preferably 3 µm to 8 µm, particularly preferably 4 µm to 6.5 µm.

The undisturbed cholesteric pitch of the liquid crystal material is preferably 2 µm to 40 µm, particularly preferably 4 µm to 32 µm, particularly preferably 5 μm to 20 μm and very particularly preferred 6 µm to 16 µm.

The term "alkyl" preferably includes straight chain and branched Alkyl groups with 1-7 carbon atoms, especially the straight-chain ones Groups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. groups with 2-5 carbon atoms are generally preferred.  

The term "alkenyl" preferably includes straight-chain and branched alkenyl groups having 2-7 carbon atoms, in particular the straight-chain groups. Particularly 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. Examples of further preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl , 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups of up to 5 carbon atoms are generally preferred.

The term "fluoroalkyl" preferably includes straight chain groups terminal fluorine, d. H. Fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorine butyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. Other positions of fluorine are not excluded.

The term "oxaalkyl" or alkoxyalkyl preferably comprises straight-chain radicals of the formula C _n H _{2n + 1} -O- (CH ₂ ) _m , in which n and m each independently represent 1 to 6. Preferably n = 1 and m is 1 to 6.

By a suitable choice of the meanings of the parameters of the compounds, in particular of R ¹¹ , R ¹² , R ²¹ , R ²¹ , R ³¹ . R ³² , L ¹ and L ² , the response times, the threshold voltage, the steepness of the transmission characteristics etc. can be modified in the desired manner. For example, 1E-alkenyl residues, 3E-alkenyl residues, 2E-alkenyloxy residues and the like generally lead to shorter response times, improved nematic tendencies and a higher ratio of the elastic constants k ₃₃ (bend) and k ₁₁ (splay) compared to alkyl - or alkoxy residues. 4-alkenyl residues, 3-alkenyl residues and the like generally give lower threshold voltages and smaller values of k ₃₃ / k ₁₁ compared to alkyl and alkoxy residues.

A -CH ₂ CH ₂ group generally leads to higher values of k ₃₃ / k ₁₁ compared to a simple covalent bond. Higher values of k ₃₃ / k ₁₁ allow e.g. B. flatter transmission characteristics in TN cells with 90 ° twist (to achieve gray tones) and steeper transmission characteristics in STN, SBE and OMI cells (higher multiplexability) and vice versa.

In the present application, the terms dielectric mean very much strongly positive compounds such compounds with a Δε <20, dielectrically strong positive connections such connections with a Δε in the range from below 20 to Δε = 10, dielectric weakly positive Compounds such compounds with a Δε in the range below 10 up to Δε <1.5, dielectric neutral connections with -1.5 ≦ Δε ≦ 1.5 and dielectric negative connections are those with Δε <-1.5. Here will the dielectric anisotropy of the compounds is determined by 10% of the Compounds are dissolved in a liquid crystalline host and by this mixture has the capacity in at least one test cell each 10 µm density with homeotropic and with homogeneous surface orientation tion is determined at 1 kHz. The measuring voltage is typically 0.2 V to 1.0 V, but always less than the capacitive threshold of the respective liquid crystal mixture.

ZLI-4792 is used as the host mixture for dielectric positive connections and for dielectric neutral and dielectric negative connections ZLI-3086, both used by Merck KGaA, Germany. From the Change the dielectric constant of the host mixture after addition of the compound to be examined and extrapolar ion to 100% of the used connection, the values for the respective to below get seeking connections.

All concentrations in this application are, unless explicitly different noted, stated in percent by mass and refer to the corresponding overall mix. All physical properties are and were developed according to "Merck Liquid Crystals, Physical Properties of Liquid Crystals ", Status Nov. 1997, Merck KGaA, Germany determined and gel for a temperature of 20 ° C, unless explicitly stated otherwise. Δn is determined at 589 nm and Δε at 1 kHz.  

The threshold voltages and the other electro-optical properties were determined in test cells manufactured at Merck KGaA, Germany using white light using a commercial measuring device DMS-301 from Autronic-Melchers, Germany. For this purpose, cells were selected depending on the type of liquid crystals with a thickness corresponding to an optical delay d.Δn of the cells of approximately 0.85 μm. The cells had a twist angle of 240 °. The d / P value was set to 0.53 using the chiral dopant S-811 (Merck KGaA, Darmstadt, Germany). The cells and were operated in the so-called yellow mode. For the standard characterization of the electro-optical properties of the liquid crystal mixtures, in particular the characteristic voltages such as the threshold voltage, cells with SE 4110 from Nissan Chemicals, Japan with a layer thickness of the polyimide of approximately 30 nm were used as an orientation layer. The characteristic tensions were all determined with vertical observation. Unless explicitly stated otherwise, the term threshold voltage refers to the value of the voltage for a relative contrast of 10% (V ₁₀ ). The threshold voltage was thus given as V ₁₀ for 10% relative contrast, the mid-gray voltage V ₅₀ for 50% relative contrast and the saturation voltage V ₉₀ for 90% relative contrast.

For some liquid crystal media, the threshold voltage was also determined as the capacitive threshold V ₀ (also called the Freedericksz threshold).

The liquid crystal media according to the invention can also if necessary contain other additives in the usual amounts. The one used The amount of these additives is the same as that of the chiral ones Dopants, a total of 0% to 10% based on the amount of total mixture, preferably 0.1% to 6%. The concentrations of the individual compounds used is preferably 0.1 to 3%. The Concentration of these and similar additives is given when specifying the Concentrations and the concentration ranges of the liquid crystal bindings in the liquid crystal media are not taken into account.  

The liquid crystal media used according to the invention consist of several compounds, preferably from 3 to 30, particularly preferably from 6 to 20 and very particularly preferably from 10 to 16 compounds which are mixed in a conventional manner. As a rule, the desired quantity of the components used in a smaller quantity the components that make up the main component, expediently at elevated temperature. Is the selected temp rature above the clearing point of the main component, so is the completion It is particularly easy to observe the solution process. However, it is also possible, the liquid crystal mixtures in other usual ways, z. B. using premixes or from a so-called Manufacture "Multi Bottle System".

Suitable additives can be used according to the invention Liquid crystal phases are modified so that they have been used in each known type of STN display can be used.

The examples below serve to illustrate the Erfin dung without restricting it. In the examples are the melting point T (C, N), the transition from smectic (S) to nematic (N) Phase T (S, N) and clearing point T (N, I) of a liquid crystal substance in degrees Celsius specified. The percentages are, unless explicitly different marked, before and after mass percentages and the physical properties are the values at 20 ° C if not explicitly stated otherwise.

All temperatures given in this application are ° C and all temperature differences according to the degree of difference (degrees or °), unless explicitly stated otherwise.

In the present application and in the following examples, the structures of the liquid crystal compounds are indicated by acronyms, the transformation into chemical formulas taking place according to the following tables A and B. All residues C _n H _{2n + 1} and C _m H _{2m + 1} are straight-chain alkyl residues with n or m C atoms. The coding according to Table B is self-evident. In Table A only the acronym for the basic body is given. In individual cases, a code for the substituents R ¹ , R ² , L ² and L ² follows separately from the acronym for the base body:

Table A

Table B

Examples

The following examples illustrate the present invention without it in restrict in any way. However, they give typical cheap ones Embodiments again. From the revelation of the examples go for the specialist further tasks of the present application. In particular, preferred values are the physical properties and their combinations for both the ads and the used materials can be seen.  

example 1

A liquid crystal mixture M 1 was produced. The together settlement and the physical properties of this mixture are in the following table (Table 1) summarized.

Table 1

Composition and properties of the mixture M 1

The liquid crystal medium was tested in its STN test cells characteristic stresses at different temperatures below examined.

The results for the threshold voltage and the saturation voltage, as well as for the operating voltage (V _op ) at a multiplex ratio of 1: 240 and a bias ratio of 1:16 are summarized in the following tables (Tables 2 and 3) for different temperatures.

Table 2

Characteristic voltages of STN cells with the liquid crystal mixture M 1

Table 3

Temperature dependence of the characteristic voltages of STN cells with the liquid crystal mixture M 1

Comparative Example 1

A liquid crystal mixture M 2 was produced. The together settlement and the physical properties of this mixture are in the following table (Table 4) summarized.

Table 4

Composition and properties of the mixture M 2

The liquid crystal medium was, as in Example 1, in STN test cells regarding its characteristic tensions at different Temperatures examined.

The results for the threshold voltage and the saturation voltage, as well as for the operating voltage (V _op ) at a multiplex ratio of 1: 240 and a bias ratio of 1:16 are summarized in the following tables (Tables 5 and 6) for different temperatures.

Table 5

Characteristic voltages of STN cells with the liquid crystal mixture M 2

Table 6

Temperature dependence of the characteristic voltages of STN cells with the liquid crystal mixture M 2

The temperature dependence of the characteristic voltages of the Mixture M 2 of this comparative example is significantly larger, in each case almost or even twice as large by temperature range, like that of the mixture M 1 of Example 1, as in the comparison of Tables 3 and 6 can be seen from the example of the operating voltage.  

Comparative Example 2

A liquid crystal mixture M 3 was produced. The together settlement and the physical properties of this mixture are in the following table (Table 7) summarized.

Table 7

Composition and properties of the mixture M 3

The liquid crystal medium was, as in Example 1, in STN test cells regarding its characteristic tensions at different Temperatures examined.

The results for the temperature dependence of the threshold voltage are summarized in the following table (Table 8).

Table 8

Characteristic voltages of STN cells with the liquid crystal mixture M 3

The temperature dependence of the characteristic voltages of the Mixture M 3 of this comparative example is significantly larger, namely by more than half larger than that of the mixture M 1 of Example 1, such as in comparison of Tables 3 and 8 using the example of the threshold voltage is recognizable.

Claims (11)

1. Containing electro-optical liquid crystal display
a liquid crystal layer between two substrates with orientation layers on the inside of the substrate,
with a twist angle of the liquid crystal layer from one substrate to another in the range from 110 ° to 360 °,
with a surface angle of attack in the range of 2 ° to 20 °,
characterized in that the liquid crystal layer is formed by a medium comprising one or more compounds of the formula 1
wherein
R ¹ denotes alkyl or alkoxy with 1 to 7 C atoms or alkoxyalkyl, alkenyl or alkenyloxy with 2 to 7 C atoms,
contains. 2. Display according to claim 1, characterized in that the liquid crystal medium one or more compounds of formula II
wherein
R ^{2 is} alkyl or alkoxy with 1 to 7 carbon atoms or alkoxyalkyl, alkenyl or alkenyloxy with 2 to 7 carbon atoms,
Z ²¹ and Z ²² each independently of one another, -CH ₂ CH ₂ -, -CH = CH-, -COO- or a single bond,
each independently
Y ²¹ and Y ²² independently of one another, H or F and
n 0 or 1
mean contains. 3. Display according to at least one of claims 1 and 2, characterized in that the liquid crystal medium one or more compounds of formula III
wherein
R ³¹ and R ^{32 are} each independently of one another and have the meaning given for R ² in formula ² and
Z ³¹ , Z ³² and Z ³³ each independently of one another -CH ₂ CH ₂ -, -CH = CH-, -COO- or a single bond
each independently
o and p independently of one another 0 or 1
mean contains. 4. Display according to at least one of claims 1 to 3, characterized in that the liquid crystal medium one or more compounds of formula IV
R ⁴¹ and R ⁴² each independently of one another alkyl or alkoxy with 1 to 5 C atoms, or alkoxyalkyl, alkenyl, alkenyloxy or alkynyl with 2 to 7 C atoms,
Z ⁴ -COO-, -CH ₂ CH ₂ -, -C∼C- or preferably a single bond,
mean, where the phenyl rings independently of one another can optionally be mono- or disubstituted by F contains. 5. Display according to at least one of claims 1 to 4, characterized in that the liquid crystal medium one or more compounds of formula V.
wherein
R ^{5 has} the meaning given above under formula II for R ² ,
each independently
Z ⁵¹ and Z ⁵² each independently of one another, -CH ₂ -CH ₂ -, -CH = CH-, -COO- or a single bond,
X ⁵ F, Cl, OCF ₂ H, OCF ₃ , CF ₃ ,
Y ⁵¹ and Y ⁵² each independently, H or F and
n ⁵ 0, 1 or 2, preferably 0 or 1
mean contains. 6. Display according to at least one of claims 1 to 5, characterized characterized in that the liquid crystal medium is a nematic Has phase that is at least over the range of -20 ° C to 70 ° C extends. 7. Display according to at least one of claims 1 to 5, characterized characterized that they are a small the temperature dependence of the Has operating voltage. 8. Use of an advertisement according to at least one of claims 1 to 7, for displaying information. 9. Device containing a display according to at least one of the Claims 1 to 7. 10. Liquid crystal medium characterized in that it is a Composition as in at least one of the claims 1 to 7 and the undisturbed cholesteric pitch of the Liquid crystal material is 1 µm to 45 µm.