DE10137701B4 - Liquid medium with low threshold voltage and its use - Google Patents

Abstract

b) 25–95 Gew.-% einer oder mehrerer Verbindungen der allgemeinen Formeln II–XI

...Containing liquid crystalline medium
a) 5-35% by weight of the compound of the formula Ib,

b) 25-95% by weight of one or more compounds of the general formulas II-XI

...

Description

The The present invention relates to a liquid-crystalline medium, as well the use of this medium in electro-optical displays.

Liquid crystals are mainly used as dielectrics in display devices, because the optical properties of such substances by an applied Voltage affects can be. Electro-optical devices based on liquid crystals are well known to those skilled in the art and are capable of various effects based. Such devices are for example cells with dynamic scattering, DAP cells (Deformation of aligned phases), guest / host cells, TN (twisted nematic) cells with twisted nematic structure, STN (super-twisted nematic) cells, SBE (superbirefringence effect) cells and OMI (optical mode interference) cells. The most common display devices based on the Schadt-Helfrich effect and have a twisted nematic structure.

The liquid crystal materials have to Generally a good chemical and thermal stability and a good stability across from have electrical fields and electromagnetic radiation. Furthermore, the liquid crystal materials should low viscosity have and in the cells short switching times, low threshold voltages and give a high contrast.

Farther they should be at usual Operating temperatures, d. H. in the widest possible area below and above room temperature, have a suitable mesophase, for example the above cells are a nematic mesophase. Because liquid crystals usually used as mixtures of several components, it is important that the Components are readily miscible with each other. Other properties, like the electrical conductivity, the dielectric anisotropy and the optical anisotropy must each be according to cell type and field of application different requirements suffice. For example, materials for cells should be twisted nematic Structure has a positive dielectric anisotropy and a low one electric conductivity exhibit.

For example are for Matrix liquid crystal displays with integrated non-linear elements for switching individual Pixels (MFK displays) liquid crystalline Media with great positive dielectric anisotropy, broad nematic phases, relatively low birefringence, very high resistivity, good UF and temperature stability and low vapor pressure desired.

such Matrix liquid crystal displays are known. As non-linear elements for individual switching the individual pixels can in addition to passive elements such as varistors or diodes active elements how transistors are used. One speaks then of an "active Matrix".

at The promising TFT (thin film transistor) displays are called electro-optical effect usually the TN effect exploited. One differentiates TFT's from compound semiconductors such. As CdSe or TFT's on the base of polycrystalline or amorphous silicon.

The TFT matrix is on the inside of a glass plate of the display upset while the other glass plate on the inside the transparent counter electrode wearing. Compared to the size of the pixel electrode is the TFT very small and disturbs the picture practically not. This technology can also be used for full color Image displays, with a mosaic of red, green and blue filters is arranged such that each one filter element a switchable picture element opposite lies. The TFT displays usually work as TN cells with crossed polarizers in transmission and are from behind illuminated.

Such MFK displays are used as displays in notebook computers, TV sets (pocket televisions) and in the automotive or aircraft industry. The angular dependence of the contrast and the switching times of these MFK displays are not always satisfactory. Difficulties are also due to a not sufficiently high specific resistance of the liquid-crystal mixtures. As the resistance decreases, the contrast of a MFK display degrades and the problem of "image sticking" may occur. Since the specific resistance of the liquid crystal mixture decreases by interaction with the internal surfaces of the display, generally over the lifetime of an MFK display, high (initial) resistance is very important to obtain acceptable lifetimes. In particular, in the case of mixtures with a low threshold voltage, it has hitherto not been possible to realize very high specific resistances since liquid-crystalline materials having a high positive dielectric anisotropy Δ∈ generally also have a higher electrical conductivity. Furthermore, it is important that the resistivity possible As little as possible increases with increasing temperature as well as after temperature and / or UV exposure. In order to realize short switching times of the displays, the mixtures must also have a low rotational viscosity. In order to enable use of the displays even at low temperatures, for example for outdoor, automotive or avionics applications, no crystallization and / or smectic phases may occur even at low temperatures, and the temperature dependence of the viscosity should be as low as possible. The MFK displays from the prior art do not meet these requirements.

Next Liquid crystal displays, that use a backlight, so transmissive and optionally transflectively operated, are also reflective liquid crystal displays Interesting. Use these reflective liquid crystal displays the ambient light for information presentation. Thus, they consume much less energy than backlit liquid crystal displays with appropriate size and resolution. Here is like the usual ones transmissive TFT-TN displays the use of liquid crystals with low birefringence (Δn) necessary, a slight optical delay (d · Δn) to reach.

It There is thus a big one Demand for MFK displays with very high resistivity at the same time great Working temperature range, short switching times even at low temperatures and low threshold voltage, which does not meet the mentioned disadvantages or only to a lesser extent demonstrate.

• – insbesondere zu tiefen Temperaturen erweiterter nematischer Phasenbereich und geringe Temperaturabhängigkeit der Viskosität für Einsatz der Displays auch bei tiefen Temperaturen;
• – hoher spezifischer Widerstand für eine lange Lebensdauer der Displays;
• – hohe positive dielektrische Anisotropie Δε für niedrige Schwellenspannung V_th;
• – niedrige Doppelbrechung für verbesserten Beobachtungswinkelbereich;
• – geringe Rotationsviskosität γ₁ für kurze Schaltzeiten.

For this purpose, liquid-crystalline media with the following properties are desired:

• - Especially extended to low temperatures nematic phase range and low temperature dependence of the viscosity for use of the displays even at low temperatures;
• - high resistivity for a long life of the displays;
• High positive dielectric anisotropy Δε for low threshold voltage V _th ;
• Low birefringence for improved viewing angle range;
• - low rotational viscosity γ ₁ for short switching times.

In the pamphlets JP 10292173 A and JP 07242874 A Already 4 '- (3,4,5-trifluorophenyl) -4-alkenyl-bicyclohexyl compounds are disclosed as a component of liquid-crystalline media. The older patent application DE 19961702 A1 was considered in the examination procedure.

Of the Invention is based on the object, liquid-crystalline media for MFK, To provide TN or STN ads that are very high specific resistors, low threshold voltages, short switching times and low Birefringence while maintaining the other boundary conditions.

• a) 5–35 Gew.-%, bevorzugt 10–25 Gew.-%, der Verbindung der Formel (Ib)
  
  und
• b) 25–95 Gew.-%, bevorzugt 35–90 Gew.-% einer oder mehrerer Verbindungen der allgemeinen Formeln (II)–(XI):
  
  
  worin R¹, R² gleich oder verschieden sein können und H, Alkyl oder Alkoxy mit 1–15 C-Atomen oder Alkenyl mit 2–15 C-Atomen bedeuten, X F, OCF₃, CF₃ oder OCHF₂ bedeutet, L¹, L², L³, L⁴ gleich oder verschieden sein können und H oder F bedeuten, und Z -CO-O-, -OCF₂-, -CF₂O- oder -C₂H₄- bedeutet.

The problem is solved by containing a liquid-crystalline medium

• a) 5-35% by weight, preferably 10-25% by weight, of the compound of the formula (Ib)
  
  and
• b) 25-95% by weight, preferably 35-90% by weight, of one or more compounds of the general formulas (II) - (XI):
  
  
  in which R ¹ , R ^{2 may be} identical or different and denote H, alkyl or alkoxy having 1-15 C atoms or alkenyl having 2-15 C atoms, XF, OCF ₃ , CF ₃ or OCHF ₂ , L ¹ , L ² , L ³ , L ^{4 may be the} same or different and is H or F, and Z is -CO-O-, -OCF ₂ -, -CF ₂ O- or -C ₂ H ₄ -.

worin
R¹ und R² die oben angegebene Bedeutung haben.Optionally, the liquid-crystalline medium contains up to 40% by weight of compounds of the general formula (XII)

wherein
R ¹ and R ^{2 have} the meaning given above.

The liquid-crystalline medium preferably contains 5-35% by weight of one or more compounds of the formulas (Ia) and (Ic)

R ¹ and R ² may be an alkyl radical or an alkoxy radical having 1-15 C atoms, which may be straight-chain or branched. Preferably, it is straight-chain, has 1, 2, 3, 4, 5, 6 or 7 carbon atoms and is therefore preferably methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, Methoxy, ethoxy, n-propoxy, n-butoxy, n-pentoxy, n-hexoxy or n-heptoxy, furthermore octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, octoxy, nonoxy, decoxy, undecoxy, Dodecoxy, tridecoxy, tetradecoxy or pentadecoxy.

R ¹ and R ² may be an alkenyl radical having 2-15 C atoms, which may be straight-chain or branched. It is preferably straight-chain and has 2 to 7 carbon atoms. Accordingly, it is in particular vinyl, prop-1-, or prop-2-enyl, but-1, 2- or but-3-enyl, pent-1-, 2-, 3- or pent-4-enyl, hex 1-, 2-, 3-, 4- or hex-5-enyl, hept-1, 2-, 3-, 4-, 5- or hept-6-enyl.

It was found that through Use of the compounds of the formulas (Ia) - (Ic) in the liquid-crystalline ones according to the invention Mixtures a strong reduction in the threshold voltage and the rotational viscosity without deterioration of the clearing point across from Comparative blends can be achieved. Furthermore, the specific Increased resistance of the mixtures, without at the same time a reduction of the dielectric anisotropy Δε in purchase must be taken.

mit n = 1–5, l = 2–5.In a preferred embodiment, the liquid-crystalline medium contains as compounds of the general formula (II) compounds of the general formulas (IIa) - (IId)

with n = 1-5, l = 2-5.

mit n = 1–5In a further preferred embodiment, the liquid-crystalline medium contains, as compounds of the general formula (III), compounds of the general formula (IIIa)

with n = 1-5

mit n = 1–5In a further preferred embodiment, the liquid-crystalline medium contains, as compounds of the general formula (V), compounds of the general formula (Va)

with n = 1-5

In a further preferred embodiment, the liquid-crystalline medium contains, as compounds of the general formula (XII), compounds of the general formulas (XIIa) - (XIIc)

• a1) 8–10 Gew.-% der Verbindung der Formel (Ia),
• a2) 5–7 Gew.-% der Verbindung der Formel (Ib), und
• a3) 7–8 Gew.-% der Verbindung der Formel (Ic).

In a further preferred embodiment, the liquid-crystalline medium contains

• a1) 8-10% by weight of the compound of the formula (Ia),
• a2) 5-7% by weight of the compound of the formula (Ib), and
• a3) 7-8% by weight of the compound of the formula (Ic).

In a particularly preferred embodiment is the liquid crystalline Medium of one or more of the compounds of the formula (Ib) and one or more of the compounds of the general formulas (II) - (XII), in particular, it consists of one or more of the compounds of formula (Ib) and one or more of the compounds of general Forms (IIa) - (IId), (IIIa), (Va) and (XIIa) - (XIIc).

In the above formulas (IIa) - (XIIc), C _n H _{2n + 1} , C _m H _{2m + 1} and C _l H _{2l-1 are} preferably the corresponding linear radicals and thus are preferably methyl, ethyl, n-propyl, n-butyl, n-pentyl, vinyl, prop-1-enyl, prop-2-enyl, but-1-enyl, but-2-enyl, but-3-enyl, pent-1-enyl, pent-2- enyl, pent-3-enyl and pent-4-enyl.

The Compounds of the formula (I) - (XII) are represented by methods known per se, as described in the Literature (eg in the standard works such as Houben-Weyl, Methoden of Organic Chemistry, Georg Thieme Verlag, Stuttgart), under reaction conditions, for the above reactions are known and suitable. It can also be known by itself, not closer here mentioned Make use of variants.

Also disclosed are electro-optical displays, in particular reflective STN or MFK displays with two plane-parallel support plates, which form a cell with a border, integrated non-linear Elements for switching individual pixels on the support plates and a nematic liquid crystal mixture in the cell with positive dielectric anisotropy and high resistivity, the liquid-crystalline media according to the invention and the use of these media for electro-optical displays.

The Liquid crystal mixtures according to the invention enable a significant extension of the available parameter space.

The requirement for low threshold voltage V _th and low rotational viscosity at the same time high clearing point and nematic phase at low temperature has so far been insufficiently met.

The achievable combinations of clearing point, rotational viscosity and exceed threshold voltage that of the previous materials from the prior art.

The Liquid crystal mixtures according to the invention enable maintaining the nematic phase at -20 ° C and preferably at -30 ° C, clearing points above 70 ° C, preferably above 80 ° C, simultaneously Birefringence of ≤ 0.11, preferably ≤ 0.10, to achieve a low threshold voltage and at the same time a low rotational viscosity, whereby excellent STN and MFK displays can be realized. Especially are the blends due to small operating voltages and short switching times characterized.

The TN threshold voltages are at a rotational viscosity of ≤ 180 mPa · s generally at ≤ 1.6 V, preferably ≤ 1.4 V and at a rotational viscosity of 140 mPa · s generally at ≤ 1.8 V, preferably ≤ 1.6 V.

Of the Structure of the STN or MFK display from polarizers, electrode base plates and electrodes with surface treatment corresponds to the for Such ads usual Construction. The term of the usual construction is here far collected and includes also all the modifications and modifications of the MFK display, in particular also matrix display elements based on poly-Si TFT or MIM displays.

The Preparation of the invention usable liquid crystal mixtures takes place in per se usual Wise. In general, the desired Amount of components used in lesser amount in the Main component making up components solved, expedient at elevated temperature. It is also possible, solutions the components in an organic solvent, e.g. In acetone, Chloroform or methanol, to mix and the solvent after mixing to remove again, for example by distillation. Farther Is it possible, the mixtures on other conventional Species, e.g. B. by using premixes, z. B. homolog mixtures or using so-called "multi-bottle" systems manufacture.

The Dielektra can also further, known in the art and described in the literature additions contain. For example, you can 0-15% by weight, preferably 0-10 Wt .-%, pleochroic dyes and / or chiral dopants be added. The individual added connections become in concentration of 0.01 to 6 wt .-%, preferably from 0.1 to 3 % By weight used. Here, however, the concentration data the rest Constituents of the liquid-crystal mixtures, So the liquid crystalline or mesogenic compounds, without regard to concentration indicated these additives.

The Invention is explained in more detail by the following example.

example

• – Temperatur des smektisch-nematischen Phasenübergangs S → N [°C];
• – der Klärpunkt [°C]
• – die optische Anisotropie Δn bei 589 nm und 20°C;
• – die Rotationsviskosität γ₁ bei 20°C [mPa·s];
• – die Spannungen für 10%, 50% und 90% Transmission V₁₀, V₅₀ bzw. V₉₀ in Blickrichtung senkrecht zur Plattenoberfläche [V];
• – die dielektrische Anisotropie Δε bei 1 kHz und 20°C.

Komponenten A–M:

A liquid crystal mixture of the indicated composition was prepared from the following components A-M. For this mixture was measured:

• - temperature of the smectic-nematic phase transition S → N [° C];
• - the clearing point [° C]
• The optical anisotropy Δn at 589 nm and 20 ° C .;
• The rotational viscosity γ ₁ at 20 ° C [mPa · s];
• - The voltages for 10%, 50% and 90% transmission V ₁₀ , V ₅₀ and V _{90 viewed} in the direction perpendicular to the plate surface [V];
• - The dielectric anisotropy Δε at 1 kHz and 20 ° C.

Components A-M:

Claims (11)

Liquid-crystalline medium comprising a) 5-35% by weight of the compound of the formula Ib,

b) 25-95% by weight of one or more compounds of the general formulas II-XI

in which R ¹ , R ^{2 may be} identical or different and denote H, alkyl or alkoxy having 1-15 C atoms or alkenyl having 2-15 C atoms, XF, OCF ₃ , CF ₃ or OCHF ₂ , L ¹ , L ² , L ³ , L ^{4 may be the} same or different and is H or F, and Z is -CO-O-, -OCF ₂ -, -CF ₂ O- or -C ₂ H ₄ -. Liquid-crystalline medium according to claim 1, containing up to 40% by weight of compounds of general formula XII

wherein R ¹ and R ^{2 have} the meaning given above. Liquid-crystalline medium according to Claim 1 or 2, containing 5-35% by weight of one or more compounds of the formulas Ia and Ic

Liquid-crystalline medium according to one or more of claims 1 to 3, comprising as compounds of the general formula II compounds of the general formulas IIa-IId

with n = 1-5, l = 2-5. Liquid-crystalline medium according to one or more of claims 1 to 4, comprising as compounds of general formula III compounds of general formula IIIa

with n = 1-5. Liquid-crystalline medium according to one of claims 1 to 5, containing as compounds of the general formula V compounds of general formula Va

with n = 1-5. Liquid-crystalline medium according to one of Claims 1 to 6, containing as compounds of the general formula XII compounds of the general formulas XIIa-XIIc

with n, m = 1-5. liquid-crystalline Medium according to one of the claims 1 to 6, containing a1) 8-10 % By weight of the compound of the formula Ia, a2) 5-7% by weight of the compound of Formula Ib, and a3) 7-8 Wt .-% of the compound of formula Ic. liquid-crystalline Medium according to one of the claims 1 to 8, consisting of one or more of the compounds of Formulas Ib and one or more of the compounds of the general Formulas II-XII. liquid-crystalline Medium according to one of the claims 1 to 9, consisting of one or more of the compounds Ib and one or more of the compounds of general formulas IIa-IId, IIIa, Va and XIIa-XIIc. Use of a liquid-crystalline medium after at least one of the claims 1 to 10 in an electro-optical display.