JP2007529767A - Electro-optic light modulator, display and medium - Google Patents

Abstract

The present invention relates to electro-optic light modulators and electro-optic displays and display systems, for example television screens and computer monitors, containing this type of element. The light modulator according to the invention is a cybotactic nematic phase during the operation of the light modulator, and in particular a mesogenic modulation medium characterized by a very short response time in addition to good contrast and low viewing angle dependence. Including. Mesogenic modulation media used in electro-optic light modulation elements are likewise the subject of the present invention.

Description

  The present invention relates to an electro-optic light modulation element and a display including the same. The light modulation element uses a modulation medium having a cybotactic nematic phase at the operating temperature of the element.

  The present invention relates to electro-optic light modulation elements and electro-optic displays and display systems comprising such elements, for example television screens and computer monitors. The light modulation element according to the invention is a cybotactic nematic phase during the operation of the light modulation element, in particular a mesogen modulation medium characterized by a very short response time in addition to good contrast and low viewing angle dependence. Including.

  The invention further relates to a liquid crystal medium having a cybotactic nematic phase and its use as a modulation medium of a light modulation element.

Conventional electro-optic liquid crystal displays are generally known. These displays are operated at a temperature of typically and predominantly nematic phase where the modulation medium is an intermediate phase. However, displays using smectic phase, eg chiral smectic C (S _C ) phase liquid crystals, such as SSFLC (surface stabilized ferroelectric liquid crystal) displays, or thermal address displays, for example, Some displays are used in the smectic A (S _A ) phase. In particular, SSFLC and non-ferroelectric displays exhibit very good fast response, but they are somewhat difficult to manufacture. Furthermore, non-ferroelectric displays are generally very sensitive to mechanical shocks.

  The most widespread displays are TN (twisted nematic) and STN (super twisted nematic) displays, whose liquid crystal cells have electrodes on two substrates on both sides of the liquid crystal medium. Therefore, the electric field is essentially perpendicular to the liquid crystal layer, especially the first mentioned display is used in combination with TFT (Thin Film Transistor) and has a high capacity information and a high resolution display, for example Recently used in laptops and notebook computers, in particular IPS (in-plane switching), for example German Patent No. 4000451 And European Patent No. 0588568) or, alternatively, a VAN (vertically aligned nematic) type liquid crystal display for use in desktop computer monitors has increased. A variant of an electrically controlled birefringence display, a modern variant of an ECB display, in an MVA (multi-domain vertically aligned) display, where multiple domains are stabilized for each addressed electrode. In addition, special optical compensation layers are used and these displays are liquid crystal like TN displays already mentioned. In contrast, an IPS display generally uses an electrode on one substrate, that is, only one side of the liquid crystal layer, that is, a large electric field component parallel to the liquid crystal layer. It is characterized by.

In a typical electro-optic switching element that utilizes the electro-optic effect of a mesogen modulation medium, the response time depends on the viscosity coefficient of the associated modulation medium. The switch-off response time (τ _off ) depends on each elastic constant or combination of elastic constants. For example, in a common TN display, the switch-off response time is proportional to the rotational viscosity (γ ₁ ) of the liquid crystal and inversely proportional to the respective elastic constant (K), as shown in the following equation.

τ _off 〜γ ₁ / K
_{Wherein, K = k 1 -k 2/} 2 + k 3/4,
k ₁ : spreading elastic constant k ₂ : twist elastic constant k ₃ : bending elastic constant.

  An object of the present invention is to develop an optical modulation element that performs high-speed switching. These light modulation elements are, for example, as thin as possible in order to achieve the shortest response time of the modulation medium so that they can be used as FPD (Flat Panel Display) elements such as flat panel screens for computers. Should have a thickness. However, if the diffraction effect has to be optimized, the cell spacing must be chosen relatively large. Furthermore, the display is addressable with a simple electrode structure and the operating voltage must be relatively low. Furthermore, they must have good contrast with low viewing angle dependence for use in electro-optic displays.

  A liquid crystal having a nematic phase can exhibit a cybotactic order. In this phase, as defined in Pure and Applied Chemistry, 73, (2001), pp, 845-895 (see in particular 3.1.2, p. 855), molecules are in a narrow range. Has a smectic arrangement. Liquid crystals having a cybotactic nematic phase are described in, for example, Bobadova-Parvanova, P.A. et al. Cryst. Res. Technol. , 35, (2000), pp. 1321-1330, and Luening, J. et al. et al. , Macromolecules, 34, (2001), pp. 1128-1130 investigated their general characteristics. Stodadinovich, S .; et al. , Physical Review E, 66, (2002), pp. From 060701-1 to 060701-4, the dynamic behavior of the nematic phase of bent-core liquid crystal exhibiting a cybotactic order, also referred to as a cybotactic phase in this specification, was examined. In that document, a dynamic light scattering experiment was performed to determine the dynamics of the relaxation process in this phase. However, no electro-optic use was considered.

Thus, there is a need for improved light modulation elements for use in displays with particularly short response times, for example as required for multimedia applications.
German Patent Invention No. 4000451 European Patent No. 0588568 Pure and Applied Chemistry, 73, (2001), pp, 845 to 895 Bobadova-Parvanova, P.A. et al. Cryst. Res. Technol. , 35, (2000), pp. 1321-1330, and Luening, J. et al. et al. , Macromolecules, 34, (2001), pp. 1128-1130 Stodadinovich, S .; et al. , Physical Review E, 66, (2002), pp. 060701-1 to 060701-4

Surprisingly,
Having at least one light polarizing element;
Having an electrode configuration capable of generating an electric field;
Including mesogenic media,
Is a cybotactic nematic phase at at least one of the operating temperatures of the light modulation element;
It has been found that light modulation elements enable the production of excellent displays.

These light modulation elements are
It is preferred to operate at a temperature at which the mesogenic medium is in the cybotactic nematic phase.

  In general, the contrast, the viewing angle of contrast, and the operating voltage of these light modulation elements are excellent. However, what is most shocking is that the response time of these light modulation elements is particularly short.

  The mesogenic medium is used as a modulation medium for the light modulation element. In this application, the term mesogenic medium applies to a medium that has an intermediate phase and is soluble in or induces an intermediate phase. The intermediate phase is a smectic or preferably a nematic phase. Most preferably, the medium according to the invention, each medium used according to the invention, exhibits a cybotactic nematic phase.

  The medium used for investigating the mesogenic properties of the material, i.e. the components of the compound, e.g. premix and medium without mesogens per se, is preferably a ZLI-4792 nematic mixture from Merck KGaA Darmstadt Germany. . The mesogenic material is preferably extrapolated from a 10% solution of this mixture and has a clearing point of 0 ° C. or higher, preferably 20 ° C. or higher, more preferably 40 ° C. or higher.

  The light modulation element according to the invention preferably comprises a mesogenic modulation medium that is a cybotactic nematic phase at the operating temperature or at least one operating temperature of the light modulation element.

  This medium is advantageously arranged on or under one substrate. In general, the mesogenic medium is placed between two substrates. When the mesogenic medium is disposed between two substrates, at least one of these substrates is light transmissive. The light transmissive substrate may be made of, for example, glass, quartz, or plastic. If a non-light transmissive substrate is used, this can include metals or semiconductors, among others. These media can be used in this way or can be arranged, for example, on a ceramic support.

  If the mesogen modulation medium is itself a polymer medium, the use of a second substrate can be omitted if desired. The polymer mesogenic medium can also be produced in a free standing manner. In this case, no substrate is required.

  The light modulation element according to the present invention has an electrode structure that generates an electric field having an important component perpendicular to the principal plane of the mesogenic medium layer, preferably the principal component. This electrode structure can be designed in a conventional manner. It preferably includes active address elements in order to enable display addressing by the active matrix. This type of active matrix display preferably uses a matrix of active address elements, one assigned to each one of the individual light modulation elements. These active address elements have non-linear current-voltage characteristic lines such as TFTs or MIM (metal insulator metal) diodes.

  The electrode may be made of a transparent material such as indium tin oxide (ITO). In this case, it may be advantageous and sometimes necessary to cover the light modulation element part or parts with a black mask. As a result, the region where the electric field does not work and the region where the component of the light modulation element, for example, the active address element is sensitive to light, are shielded, and the contrast and the performance of the light modulation element are improved. However, the electrode can also include an opaque material, usually a metal. In this case, the use of a separate black mask can be omitted if desired.

  In a preferred embodiment, the substructure of the electrode structure is arranged on two opposing faces of the mesogenic medium. In this case, the portions corresponding to the electrodes are preferably perpendicular to each other or at least a substantial portion of the opposite surface of the light modulation medium, preferably most, and most preferably essentially, when viewed perpendicular to the main surface of the light modulation element. It is preferable to arrange them completely overlapping.

  The operating temperature of the light modulation element generally exceeds the transition temperature of the modulation medium from solid or preferably from smectic phase to cybotactic phase, and generally exceeds this transition temperature by 0.1 ° to 40 °, preferably Is in the range of 0.1 ° to 30 °, and particularly preferably in the range of 0.1 ° to 10 ° beyond this transition temperature.

  The light modulation element according to the present invention includes at least one light polarization element. Furthermore, they preferably further comprise other optical elements. Still other optical elements are either a second element for light polarization, a reflector or a reflector, or a combination of one or more of these elements.

  The optical element is arranged to pass through the at least one polarizing element at least once, both when entering the liquid crystal medium and after exiting the liquid crystal medium when light passes through the mesogenic medium of the light modulation element. The

  In a preferred embodiment of the light modulation element according to the invention, the mesogenic medium is arranged between two polarizers, namely a polarizer and an analyzer. It is preferable to use two linear polarizers. In this embodiment, the absorption axes of the polarizers preferably intersect and form an angle of 90 °.

  The light modulation element according to the present invention optionally comprises one or more birefringent layers. It preferably comprises one λ / 4 layer or a plurality of λ / 4 layers, preferably one λ / 4 layer. The optical attenuation of the λ / 4 layer is preferably about 140 nm.

  The layer thickness (d) of the mesogenic modulation medium is preferably 0.5 μm to 20 μm, particularly preferably 0.6 μm to 10 μm, particularly preferably 0.8 μm to 5 μm, very particularly preferably 1 μm to 3 μm.

  The light modulating element according to the invention is one or more that this list does not cover, such as a birefringent layer (for example a compensation layer), a scattering layer and elements for increasing brightness and / or light generation or viewing angle dependence. Further other optical elements can be further included.

  The contrast of the light modulation element according to the present invention can be compared with that of each light modulation element operating in the electro-optic mode in the same cell structure. If it is found to be slightly inferior, it can easily be improved by adding the respective higher operating voltage. However, their prominent property is their improved response time.

  The light modulation element according to the present invention can be manufactured as a conventional light modulation element operating in a TN mode, that is, a typical TN cell, and is preferably manufactured. These devices have an optical attenuation in the range of 0.35 μm to 0.50 μm, positive contrast, and an absorption axis of the polarizer perpendicular to the preferential orientation of the nematic cybotactic nematic liquid crystal on the adjacent substrate. It is preferable to have.

  The mesogen modulation medium for non-display applications is preferably non-chiral. See Spang Light Modulator (SLM), high-speed electro-optic shutter for telecommunications technology, and more. S. Panarin, Yu. P. , And Farrell, G. In those switching devices described in SPIE 2002, the switching time is typically much shorter than that used for display applications.

  However, the response time of the light modulation element according to the present invention is very short. They are generally values of 15 ms or less, preferably 12 ms or less, and particularly preferably 10 ms or less.

  Also, switching between different gray tones of the light modulation element according to the present invention is relatively faster than a conventional light modulation element using the same electro-optic mode.

  The electro-optic display according to the invention comprises one or more light modulation elements according to the invention. In the preferred embodiment, they are addressed by an active matrix.

  In another preferred embodiment, the light modulation element according to the present invention is addressed in a so-called “field sequential mode”. Here, the switching element can be illuminated with light of different colors sequentially in synchronization with the address. For example, a color wheel, strobe lamp, or flash lamp can be used to generate pulsed colored light.

  The electro-optic displays according to the invention include color filters for the display of colored images, especially if they are used in television screens, computer monitors and the like. This color filter advantageously comprises a mosaic of filter elements of different colors. Typically, a color color filter mosaic element is assigned to each electro-optic light modulation element.

  In a preferred embodiment of the invention, the mesogenic medium according to the invention has a nematic phase in addition to the cybotactic nematic phase. However, since the temperature range of the nematic phase is narrow, it is also possible to use a medium that actually causes a transition from a cybotactic nematic phase to an isotropic phase.

  In a preferred embodiment of the invention, the mesogenic medium according to the invention has a cybotactic nematic phase spanning a range having a width of 10 ° or more, preferably 30 ° or more, most preferably 50 ° or more. Preferably, this range of cybotactic nematic phases extends around the operating temperature of the light modulator element, preferably at its center, preferably at room temperature, and most preferably about 20 ° C.

When the operating temperature of the light modulation element is different from the room temperature, the temperature range of the cybotactic phase includes around the operating temperature, and preferably extends to the center. In some cases, the operating temperature of the light modulation element is higher than room temperature. This is the case for a display with a backlight, for example. In particular, in a projection display, the operating temperature can increase by 60 ° C. or more. Here, the clearing point of the medium according to the invention, respectively the transition temperature T (N _C , I), is preferably in the range from 10 ° C. to 70 ° C., and particularly preferably in the range from 20 ° C. to 50 ° C.

  The cybotactic nematic phase of the mesogenic modulation medium according to the invention is preferably in the temperature range of 1 ° or more, preferably 3 ° or more, more preferably 5 ° or more, most preferably 10 ° or more, particularly preferably 20 ° or more. It is stable. The mesogenic modulation medium according to the invention preferably does not crystallize to temperatures below 10 ° C., particularly preferably temperatures below 0 °, very particularly preferably temperatures below −20 ° C.

In many cases, mesogenic mixtures exhibiting a cybotactic nematic phase are, for example, Δn, Δε, γ ₁ , and k _{1 in} the cybotactic nematic phase as if these mixtures were still normal nematic phases. It is possible to measure macroscopic parameters directly.

For mesogenic modulation media, the presence of the cybotactic phase is due to several means such as X-ray scattering, differential scanning calorimetry (DSC), the observation of different divergence behavior between viscosity constants, especially γ ₁ , And by means such as the elastic constant of the medium and by observing the response time of an electro-optic cell, eg a TN cell.

  In DSC, the presence of a typically cybotactic nematic phase is evident from the presence of transitions with low heat flow and an unusually broad peak.

  For mesogenic modulation media, the presence of the cybotactic nematic phase is preferably detected by observing the response time of the TN cell and / or the different divergence behavior and elastic constants between the viscosity constants of the media.

  According to the present invention, it is preferred to detect the presence of the cybotactic nematic phase used, using both the last two independent methods.

The cybotactic nematic phase is characterized by a large elastic constant compared to the nematic phase. As the temperature decreases, the rotational viscosity (γ ₁ ) of the medium increases logarithmically depending on Arrhenius' law. This behavior extends even to temperatures below the transition temperature from the nematic phase to the cybotactic nematic phase. In contrast to this behavior, the elastic constant of the medium increases significantly when a cybotactic nematic phase occurs. This effect is particularly evident at K ₃ . Typically, the elastic constant is 50% or 3 times greater than that of the nematic phase medium, but the viscosity still follows Arrhenius' law.

The cybotactic nematic phase liquid crystal medium preferably has an elastic constant of k ₁ or k ₃ , most preferably k ₃ , which is comparable to that of a nematic phase, comparable to that of a nematic phase at a given temperature. 20% or more, preferably 50% or more, and most preferably 200% or more.

Preferably the cybotactic nematic phase liquid crystal medium has a large elastic constant at the operating temperature, preferably 20 ° C. Preferably, k ₁ is 11 pN or more, more preferably 13 pN or more, more preferably 15 pN or more, more preferably 20 pN or more, most preferably 25 pN or more, and / or k3 is preferably 14 pN or more, more preferably 16 pN or more, further Preferably it is 20 pN or more, More preferably, it is 30 pN or more, Most preferably, it is 40 pN or more.

Preferably, the liquid crystal medium having a cybotactic nematic phase has a small ratio between the rotational viscosity and the elastic constant, preferably the elastic constant k ₃ . γ ₁ / k ₃ is preferably 4.0 mPa · s / pN or less, more preferably 3.5 mPa · s / pN or less, still more preferably 3.0 mPa · s / pN or less, and even more preferably 2. 5 mPa · s / pN or less, most preferably 2.0 mPa · s / pN or less.

  The mesogenic medium according to the invention preferably has a birefringence at 20 ° C. of preferably 0.06 to 0.35, particularly preferably 0.065 to 0.30, very particularly preferably 0.07 to 0.25. It is preferable to have a rate (Δn). In practice, however, it is generally less than 0.530 and usually less than 0.450.

  As the light modulation element according to the present invention, an element having a negative dielectric anisotropy can be used instead of a mesogen modulation medium having a positive dielectric anisotropy (Δε) in an intermediate phase. It is preferable to use a mesogen modulation medium having positive dielectric anisotropy (Δε) in the intermediate phase.

  If the mesogenic modulation medium has a positive dielectric anisotropy, it has a value of 1 or more and 20 ° C., preferably 3.5 or more, particularly preferably 4.0 or more, very particularly preferably 5.0 or more. .

  If the mesogenic modulation medium has a negative dielectric anisotropy, this preferably has a value of -2.5 or less, particularly preferably -3.0 or less, very particularly preferably -4.0 or less.

  The mesogenic medium according to the invention preferably contains several compounds, preferably 2 to 40 compounds, particularly preferably 5 to 30 compounds, very particularly preferably 7 to 25 compounds.

The mesogenic medium according to the invention with positive dielectric anisotropy according to the invention is
Dielectrically neutral component A, preferably comprising one or more dielectrically neutral biphenyl compounds of formula I,

Wherein R ¹¹ is alkyl or alkoxy having 1 to 15 C atoms, or alkoxyalkyl, alkenyl, alkenyloxy having 1 to 15 C atoms, preferably alkyl or alkoxy,
R ¹² is alkenyl having 2 to 15, preferably 2 to 7 C atoms. )
Preferably an optional dielectrically positive component comprising one or more compounds having a terminal halogen n atom or preferably a terminal halogenated group of formula II and having a positive dielectric anisotropy Component B,

Wherein R ² is n-alkyl or n-alkoxy each having 1 to 7 carbon atoms, or alkenyl, alkenyloxy, alkynyl or alkoxyalkyl each having 2 to 7 carbon atoms, preferably n-alkyl or alkenyl, preferably n-alkyl, vinyl or 1-E-alkenyl, preferably R ³¹ is n-alkyl, R ³² is vinyl or 1-E-alkenyl,

When

Are independent of each other,

And preferably

More preferably at least 1, most preferably at least 2

And
X ² is halogen, preferably F or Cl, or fluorinated alkyl or fluorinated alkoxy each having 1 to 4 C atoms, fluorinated alkenyl or fluorinated alkenoxy having 2 to 4 C atoms each, preferably Is F, Cl, OCF ₃ or OCF ₂ H, more preferably F or Cl, most preferably F;
Y ²¹ , Y ²² , and Y ²³ are independently of each other preferably H or F, but if Y ²¹ and / or Y ²² is F, Y ²³ is H, preferably Y ²¹ is F And
Z ²¹ and Z ²² are each independently a single bond, —CH ₂ —CH ₂ —, —CO—O—, trans—CH═CH—, —CH═CF—, —CF═CH—, —CF ═CF—, —CH═CH—CO—O—, —CF═CF—CO—O—, —CF═CH—CO—O—, —CH═CF—CO—O—, —CF ₂ —O—. , —O—CF ₂ —, —CH ₂ —O—, —O—CH ₂ — or —C≡C—, preferably a single bond, —CH ₂ —CH ₂ —, or —CF ₂ —O—, and Preferably Z ²¹ is a single bond, Z ²² is a single bond or —CF ₂ —O—,
n is 0, 1 or 2, preferably 0 or 1, most preferably 1. )
An optional second dielectrically neutral component C comprising one or more compounds of formula III,

Wherein R ³¹ and R ³² are each independently of each other n-alkyl or n-alkoxy having 1 to 7 carbon atoms, or alkenyl, alkenoxy having 2 to 7 carbon atoms, alkynyl or alkoxyalkyl, preferably n- alkyl or alkenyl, preferably n- alkyl, vinyl or 1-E- alkenyl, preferably R ³¹ is n- alkyl, R ³² is vinyl or 1-E- alkenyl And

When

Are independent of each other,

And preferably

More preferably at least 1, most preferably at least 2

And
Z ³¹ and Z ³² are each independently a single bond, —CH ₂ —CH ₂ —, —CO—O—, trans—CH═CH—, —CH═CF—, —CF═CH—, —CF ═CF—, —CH═CH—CO—O—, —CF═CF—CO—O—, —CF═CH—CO—O—, —CH═CF—CO—O—, —CF ₂ —O—. , —O—CF ₂ —, —CH ₂ —O—, —O—CH ₂ — or —C≡C—, preferably a single bond, —CH ₂ —CH ₂ —, or trans—CH═CH—, preferably Is a single bond, or trans-CH═CH—, preferably a single bond,
m is 0, 1 or 2, preferably 0 or 1, preferably 0, from which compounds of formula I are excluded. )
It is preferable to contain.

  Component A of these media preferably comprises one or more compounds of the formula I, particularly preferably predominantly and very particularly preferably indeed consisting entirely of one or more compounds of the formula I.

Preferred compounds of formula I are those wherein R ¹¹ is alkyl having 1 to 8 C atoms. Very preferably R ¹¹ is methyl, ethyl or propyl, in particular methyl.

Further preferred compounds of formula I are those wherein R ² is vinyl, 1E-propenyl, 1E-butenyl, 3E-butenyl or 3E-pentenyl, in particular 3E-butenyl, or 3E-pentenyl.

  Highly preferred compounds of formula I are compounds selected from the group of formulas Ia and Ib.

(Wherein alkyl is an alkyl group having 1 to 8 C atoms, in particular methyl,
Alkenyl is an alkenyl group having 2 to 7 C atoms, preferably vinyl or 1E-alkenyl, in particular vinyl or 1E-propenyl,
R ^12a is H, methyl, ethyl or n-propyl, especially methyl. )
The compounds B of these media preferably comprise one or more compounds of the formula II, particularly preferably predominantly and very particularly preferably indeed consisting entirely of one or more compounds of the formula II.

  Highly preferred compounds of formula II are those selected from the group of formulas II-1 to II-12.

(Wherein the parameters have their respective meanings given in formula II above, preferably
R ² is 1, alkyl or alkenyl each having 2 to 7 C atoms;
X ² is F, Cl, or fluorinated alkyl or fluorinated alkoxy each having 1 to 4 C atoms, most preferably F. )
Highly preferred compounds of formula II are those selected from the group of formulas II-1a to II-12d.

(Wherein the parameters have their respective meanings given in the above formula II and the respective sub-formulas above.)
Component C of these media preferably comprises one or more compounds of the formula III, particularly preferably predominantly and very particularly preferably indeed consisting entirely of one or more compounds of the formula III.

  Highly preferred compounds of formula III are compounds selected from the group of formulas III-1-1 to III-3-4.

(Wherein the parameters have their respective meanings given in the above formula III and the respective sub-formulas above,
Y ^{31 to} Y ³⁸ are each independently H or F, preferably
R ³¹ and R ³² are each independently of each other n-alkyl, n-alkoxy having 1 to 7 carbon atoms, or alkenyl having 2 to 7 carbon atoms each, preferably n-alkyl or Alkenyl, more preferably n-alkyl, n-alkoxy, vinyl or 1-E-alkenyl, most preferably R ³¹ is n-alkyl or alkenyl, R ³² is n-alkyl, n-alkoxy, vinyl or 1- E-alkenyl,
At most half of the substituents Y ^{31 to} Y ³⁸ present are F, more preferably zero, one, two or three, most preferably zero, one or two of these substituents. Is F.

  Highly preferred compounds of formula III are those selected from the group of formulas III-1-1a to III-3-3c.

(Wherein the parameters have the respective meanings given in the above formula III and the respective subformulae above, particularly preferably
In Formula III-1-1a,
R ³¹ is n-alkyl or alkenyl,
R ³² is n-alkyl, alkenyl or n-alkoxy,
In Formula III-2-1a,
R ³¹ is n-alkyl or alkenyl,
R ³² is n-alkyl. )
In a preferred embodiment of the invention, the medium according to the invention preferably comprises one or more compounds selected from the group consisting of compounds of the formulas I-1 to I-3, which are subformulas of the formula I. .

(In the formula, p is an integer of 0 to 10, preferably 1 to 7, preferably 1 or 2,
q is an integer of 0 to 10, preferably 0 to 3, preferably 0 or 1.
k is an integer of 0 to 8, preferably 0 to 4, preferably 0 or 1.
o is an integer of 1 to 10, preferably 1 to 5, preferably 1, 2 or 3. )
It is particularly preferred that the positive dielectric anisotropy mesogenic medium according to the invention consists mainly of components A to C.

  In a preferred embodiment, the positive dielectric anisotropic mesogenic medium according to the invention is a group consisting of components B and C, preferably of formula II-1a, II-1c, II-1d, II-2a, II-2c, II-3d, II-5a, II-5b, II-6b, II-10a, II-10b, and II-12d, and III-1-1a, III-1-2a, III-2-1a, III It includes one or more components selected from the group consisting of compounds of 2-3-3b, III-3-2a, III-3-2c, III-3-3a, and III-3-3b.

In one embodiment of the invention, the medium has negative dielectric anisotropy. These media according to the present invention are:
Component A ′ comprising one or more compounds having a highly negative dielectric anisotropy of −5 or less,
Optionally, component B ′ consisting of one or more compounds having an intermediate negative dielectric anisotropy of −1.5 to less than −5,
Optionally, component C ′ consisting of one or more dielectrically neutral compounds having a dielectric anisotropy of −1.5 to +1.5,
Optionally, it preferably comprises a component D ′ consisting of one or more compounds having a positive dielectric anisotropy greater than +1.5.

  The mesogenic medium according to the present invention can further comprise conventional concentrations of additives and chiral dopants. The total concentration of these further constituents is in the range from 0% to 10%, preferably in the range from 0.1% to 6%, based on the total mixture. The concentration of these individual compounds ranges from 0.1% to 3%. The concentrations of these compounds and similar components of the mixture are not considered when defining the concentration ranges of the other mixture components.

  The modulation medium is obtained from the compound in the usual manner. The compounds used in small quantities are advantageously dissolved in the compounds used in large quantities. If the temperature during the mixing operation rises above the clearing point of the main component, the completion of dissolution can be easily observed. However, the medium according to the invention can also be prepared by other methods, for example using a premix. Premixes that can be used are, inter alia, homologous compounds and / or eutectic mixtures. However, the premix is also a modulation medium that can already be used. This is the case for the so-called two-bottle or multi-bottle system.

  In this specification, the following applies unless otherwise specified.

  Dielectrically positive compounds have a Δε of> 1.5, dielectrically neutral compounds have a Δε of −1.5 ≦ Δε ≦ 1.5, and dielectrically negative compounds are , <-1.5 Δε. The same definition applies to the components and mixtures of the mixture. The same definition applies to ingredients and media.

  The dielectric anisotropy Δε of a compound, as well as the dielectric anisotropy Δε of a component that cannot be investigated, is the value of a 10% solution of each compound in the host mixture at 1 kHz and 20 ° C., respectively. It is determined by extrapolating to the proportion of 100% compound. The volume of the test mixture is determined in both cells having a homeotropic edge orientation and cells having a uniform edge orientation. The layer thickness of the two cells is about 20 μm. Measurements are made using a square wave with a frequency of 1 kHz and typically an effective voltage (rms, mean square root) of 0.2V to 1.0V. In either case, however, the voltage used is lower than the volume threshold of the mixture investigated in each case.

  As the host mixture, for the dielectrically positive compound, the mixture ZLI-4792 is used, for the dielectrically neutral and dielectrically negative compound, the mixture ZLI-3086 is used, both of which are Merck KGaA, Germany. It is made.

The term threshold voltage herein refers to the optical threshold and is indicated for 10% relative contrast (V ₁₀ ). Intermediate gray and saturation voltages are similarly determined optically and are shown for relative contrasts of 50% and 90%, respectively. This is clearly noted if the capacitance threshold voltage (V ₀ ), also known as the Freedericks threshold, is indicated.

  The range of values shown preferably includes limit values.

  Concentrations are given in weight percent and are based on the complete mixture. The temperature is shown in degrees Celsius (° C.) and the temperature difference is shown in different degrees Celsius (°). All physical properties are described in “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Version of Nov. 1997, Merck KGaA, Germany, and is shown for a temperature of 20 ° C. Optical anisotropy (Δn), also known as birefringence, is determined at a wavelength of 589.3 nm. The dielectric anisotropy (Δε) is obtained at a frequency of 1 kHz.

  In the list of alternative possibilities where only the plural is shown, this also means the singular.

Regarding details of the composition of the medium or its components,
“Contains” means that the concentration of each material, ie component or compound, described in a reference unit in the medium or component is preferably 10% or more, particularly preferably 20% or more, very particularly preferably 30% or more. Means that.

  “Mainly consisting of” means that the concentration of the reference unit of the material is preferably 50% or more, particularly preferably 60% or more, very particularly preferably 70% or more.

  “Substantially completely consists of” means that the concentration of the reference unit of the material is preferably 80% or more, particularly preferably 90% or more, very particularly preferably 95% or more.

Dielectric properties, electro-optic properties (eg, threshold voltage) and response time were determined with test cells manufactured by Merck KGaA, Darmstadt, Germany. The test cell for determining Δε had a circular electrode of indium tin oxide (ITO) with a layer thickness of 22 μm and an area of 1.13 cm ² and a protective conductive ring. For homeotropic alignment for obtaining ε‖, a cell having a polyimide alignment layer aligned homeotropically was used. Instead, lecithin (Merck KGaA) can be used as an aligning agent. The cell for determining ε⊥ had an orientation layer of polyimide AL-3046 made by Japan Synthetic Rubber, Japan. Capacitance was measured using a Hewlett Packard, USA HP4274A LCR Meter with a square wave and typically an effective voltage of 0.3 V _rms . The electro-optic investigation was performed with white light. The characteristic voltage was obtained by vertical observation.

In the present specification, particularly in the examples described below, the structures of chemical compounds are indicated by abbreviations. The respective abbreviations are shown in Tables A and B below. All groups C _n H _{2n + 1} and C _m H _{2m + 1} are straight chain alkyl groups having n and m carbon atoms, respectively. Table B is self-explanatory as it shows in each case the abbreviations of the formula of the homologous compound. In Table A, only the abbreviations for the nuclear structures of the compound types are shown. Each individual compound abbreviation includes these respective appropriate abbreviations for the compound nucleus and the abbreviations for the R ¹ , R ² , L ¹ , and L ² groups shown with dashes in the table below.

The mesogenic medium according to the invention is
It is preferred to include two or more, preferably four or more compounds selected from the group consisting of the compounds of Tables A and B.

<Example>
The examples described below illustrate the invention without any limitation. Furthermore, they show to the person skilled in the art the properties that can be achieved by the invention and in particular the combination of properties.

<Example 1>
A liquid crystal mixture of the following composition is prepared and investigated.

  The following table (Table 1) shows the temperature dependence of some characteristic physical properties of this mesogenic mixture.

  A 90 ° twisted TN electro-optic test cell including a light modulation element including a liquid crystal mixture is manufactured. The substrate is made of glass. A substrate having polished AL-3046 is used as the alignment layer. The cell layer thickness, ie the modulation medium, is 4.72 μm. The optical attenuation (d · Δn) is 0.50 μm.

  A first polarizer is used in front of the cell, and a second polarizer (analyzer) is used after the cell. The absorption axes of the two polarizers form an angle of 90 ° with each other. For each adjacent substrate of the cell, the angle between the polarizer's maximum absorption axis and the polishing direction is 0 °. The voltage-transmission characteristic line was determined using a DMS703 electro-optic measuring machine manufactured by Autronic-Melchers, Karlsruhe, Germany. The operating temperature is changed from 20 ° C to 22 ° C.

Electro-optic modulation elements are characterized by extremely short response times. It was operated by switching a rectangular wave with a frequency of 60 Hz and a voltage of 0 V to 5 V _rms .

In the case of Comparative Example 1, it is readily apparent that T _off increases significantly with decreasing temperature, but remains almost constant for the mixture of Sample 1 of Example 1 (even at a minimum at 20 ° C.). .

As can be seen in Table 3, the elastic constants k ₁ and k ₃ of the mixture of Comparative Example 1 increase slightly with temperature drop, but for the mixture of Example 1, both k ₁ and k ₃ A dramatic increase is observed. This will explain the preferred behavior of the response time T _off of Example 1.

<Comparative Example 1>
A liquid crystal mixture of the following composition is prepared and investigated.

This liquid crystal medium exhibits substantially the same physical property values, T (N, I), Δn, Δε, and γ ₁ at 20 ° C. as in Example 1. However, this medium does not exhibit a cybotactic nematic phase. It was found to have a much smaller elastic constant than Example 1. For example, at a temperature of 20 ° C., k ₃ is 2.6 times smaller than the medium of Example 1, and k ₁ is 1.9 times smaller.

The electro-optic modulation element including this medium in the TN mode has a switch off (τ _off ) response time at 20 ° C. of 9.7 ms, which is rather fast. However, this value is much larger than the device of Example 1 with 6.4 ms. Compare Table 2.

<Comparative Example 2>
A liquid crystal mixture of the following composition is prepared and investigated.

This liquid crystal medium has values of physical properties of T (N, I), Δn, Δε, and γ ₁ (the latter three are at 20 ° C.) as in Comparative Example 1. Very similar to the one. Here, Δn is slightly higher than that of the medium of Example 1, and γ ₁ is also slightly higher.

  The response time of each light modulation element is 12.8 ms, and thus is longer than that of the element of Comparative Example 1 (Comparative Table 1).

<Example 2>
A liquid crystal mixture of the following composition is prepared and investigated.

  The following table (Table 4) shows the temperature dependence of some characteristic physical properties of this mesogenic mixture.

  An electro-optic test cell is prepared as described in Example 1. However, the cell gap used here is 3.2 μm. This cell, like that of Example 1, has very favorable properties. It is characterized by a very fast response time, especially at temperatures in the range of 10 ° C to 14 ° C.

Claims (17)

An electrode configuration;
At least one light polarizing element;
A mesogenic modulation medium,
The light modulation element is
An electro-optic light modulation element that operates at a temperature at which a mesogen modulation medium is a cybotactic nematic phase.   The light modulation element according to claim 1, wherein the electrode configuration is capable of generating an electric field having a main component perpendicular to a surface of the mesogen modulation medium.   The light modulation element according to claim 1, wherein the mesogen modulation medium has a nematic phase.   4. The light modulation element according to claim 1, wherein during operation of the light modulation element, the electrode configuration generates an electric field having a main component parallel to a plane of the mesogen modulation medium. 5. .   While passing through the light modulation element, the light passes through at least one light polarization element in each case before passing through the mesogen modulation medium and after passing through the mesogen modulation medium. The light modulation element according to at least one of claims 1 to 4.   6. The at least one of claims 1 to 5, wherein the electrode comprises at least two parts, and at least one part of the configuration is arranged on either of the two sides of the mesogenic modulation medium. Light modulation element.   The light modulation element according to at least one of claims 1 to 6, further comprising an additional birefringent layer.   An electro-optic display comprising one or more light modulation elements according to claim 1.   9. The electro-optic display according to claim 8, wherein the display is addressed by an active matrix.   An electro-optic display system comprising at least one of the electro-optic displays according to at least one of claims 8 or 9.   The electro-optic display system according to claim 10, wherein the electro-optic display system can be used as a television monitor and / or a computer monitor.   Use of a light modulation element according to at least one of claims 1 to 6 for an information display.   Use of an electro-optic display according to at least one of claims 8 or 9 in an electro-optic display system.   Use of an electro-optic display system according to at least one of claims 10 or 11 for the display of video signals.   A mesogenic modulation medium characterized by having a cybotactic nematic phase.   The mesogen modulation medium according to claim 15 for use in the light modulation element according to at least one of claims 1 to 6.   Use of the mesogenic modulation medium according to claim 15 in an electro-optic light modulation element.