DD279970A1 - METHOD FOR IMPROVING THE VIEWING PANEL AREA IN OPTOELECTRONIC DISPLAY SYSTEMS - Google Patents

Abstract

The invention relates to a method for increasing the viewing angle range in optoelectronic display systems, in which the nematic mixtures with mixtures of representatives of 4-alkylcyclohexyl-isothiocyanatophenyls and 2- (4-cyanophenyl) -5-alkyl / or. Alkylphenyl-1,3-dioxanes and / or cyanobiphenyls are doped.

Description

Field of application of the invention

The invention relates to a method for increasing the viewing angle range of liquid crystal display devices that can be used for the electronically controlled modulation of the transmitted or reflected light as well as the display of numbers, characters or images.

Characterization of the known prior art

Increasing the information content of liquid crystal displays requires the provision of nematic liquid crystal mixtures which have a low temperature and viewing angle dependence of their properties. This applies in particular to such properties as the threshold voltage, the steepness of the electro-optical characteristic curve, the contrast in the optoelectronic arrangement and the like. a.

While the temperature-dependence of the properties is possible on the one hand by external compensation and, on the other hand, by a strong extension of the temperature range of the generally nematic mixtures, the extension of the viewing angle range for liquid-crystal display devices represents a major problem. The problems become more acute when the liquid crystal displays reach larger dimensions.

With the application of new electro-optical effects, such as STN F. Leenhouts, M. Schadt, J. Appl. Phys. 60 (9), 3275 (1986), SBE T.J. Scheffer, J. Nehrin "Appl. Phys. Lett. 45: 1021 (1984), OMI M. Schadt, F. Leenhouts, Appl. Phys. Lett. 50, 236 (1986), in particular for large-area matrix displays, ways were found for widening the viewing angle ranges. However, reserves are still present here that exist in the particular composition of the liquid-crystalline starting materials. For example, DE-OS 3126362 has described the use of liquid-crystal mixtures in which the ratio of dielectric anisotropy (Δε) and perpendicular dielectric constant (el) is less than Z. These requirements are met in particular by liquid-crystal mixtures in which liquid crystals from the class of substituted phenylcyclohexanes are combined with substituted 1,3-dioxanes. In DE-OS 3433248 it is described that the viewing angle range is greater when the liquid-crystal mixtures fulfill the following properties:

a. K ₃ / K, <0.4 Δεε / εΐ <0.3

b. K ₃ / K, <0.8 Δε / εΐ <0.05, where K ₃ / K,

represents a ratio of the bend / splay elastic constants. However, it is unclear whether it is also possible for LC mixtures that do not meet these conditions, to obtain an increase in the viewing angle range.

Object of the invention

The aim of the invention are liquid crystal displays with a wide viewing angle range on the basis of electro-optical effects.

Explanation of the essence of the invention

The object of the invention is to find liquid crystalline additives having such a composition, which cause an enlargement of the viewing angle range in liquid crystal display devices and transmit this property when doping other nematic mixtures on them.

According to the invention, this object is achieved by the dopants for increasing the viewing angle range mixtures of representatives of the class of 2- (4-cyanophenyl) -5-alkyl (or 5-alkylphetiyl) -1.3-dioxanes and the class of 4-alkylcyclohexyl-4 'isothiocyanatophenyls and / or mixtures of representatives of the class of 4-alkylcyclohexyl-4'-isothiocyanatophenyls and the class of cyanobiphenyls.

A measure of the magnification of the viewing angle range in liquid crystal display devices is the dependence of the electro-optical characteristic on the viewing angle β, which is defined by equation (1):

 -100% (1)

y (V ₂ + V ₁ )

V ₂ voltage value at the electro-optic characteristic curve at 10% absorption with the viewing angle 0 ° or Vi - voltage value at the electro-optical characteristic boi 10% absorption with the viewing angle 40 "or the smaller the value βo-40, the larger the viewing angle range for the Although mixtures of homologous representatives of the individual substance classes have characteristic curves with high viewing angle dependency in electrooptical display devices, mixtures of these substance classes show only a very small viewing angle dependent Pc ^ _40. This is evident from Table 1, by a reduction of the optical anisotropy and a Increasing the Δε / εΐ ratio caused.

embodiments

1. A eutectic dioxane mixture A from the components

CJj - \ ^> - (ö) -CM 39.3Gew .-%

r> 5) - ^ l 43,1Gew,%

has the properties described in Tab. 1.

From a second eutectic mixture B of isothiocyanates with the composition CI! - /> - A- (OV-MCS 36.9% by weight

^{3 7} ''"^ ¹ T

Q] I _ / Ly V- / O · ^ΜΓ ' ^ΰ 46.0% by weight

o 1 «1> V- / '^ 1- /

⁰ G ¹¹ I / ' ^H \] _ t / ~ "~ \ Q _/ ) ^NCS 17.1Gew .-%

the properties are also shown in Tab. 1.

When the components used in mixtures A and B are processed into a eutectic mixture O having the following composition,

^C ^ '~ * 7 "" \ / -ViO / - CN 11,64Uew .-%

C '''il - <> - ( G V-CM 10.19% by weight

6 "lZ-iYy ^^ yfe) - ™ 0.39Gew,%

^c 3 »7 - <sy <oy _{NCS 32 (46Gew} ., _{/ o}

^C 6 ^{ hZ ~ {H / ~ - ~ {O) - ~ NCS 33.22% by weight

^NCS 12.10Gew,%

the viewing angle dependence decreases from the characteristic curve ß _M0 to about 10% compared to 30% or 50% for the mixtures A and B.

Table 1 P ₅₀ (O ⁰ ) ß (M0 (%) Δε Δε / ει K33 / K ,, Δη mixture .1428 30.16 18.2 2.2 1.22 0,149 A .1717 50,00 8.1 2.0 1.94 0.158 B .1438 10.94 18.9 3.5 2.84 0.141 C

2. To the eutectic mixture BDH E5, consisting of cyanobiphenyls, 10 and 30% of the mixture B are added. The occurring change in the viewing angle dependence of the electro-optical characteristic curve is shown in Tab. There is also a marked decrease in the viewing angle dependence β-o and β 10-45.

Table 2

Mixture βo-4o (%) βi <M ₅ (%>

E 5 23.59 16.04

E5 + 10% B 18.38 15.73

E5 + 30% B 0.57 -8.63

3. To a nematic liquid crystal mixture D having the composition

OO

^C , l> n

10% or 30% by weight of mixture B are added.

The change in viewing angle dependence is shown in Table 3. It is to be noted that the value βo_io is lower, independent of the concentration.

Table 3 mixture PtMO (%) D 31,40 D + 10% S 26.16 D + 30% B 26,60

4. For the nematic mixture ZL11216 from Messrs. MERCK, 10% of the dopant mixture C or to the nematic mixture BDH E 5, 20% of the dopant mixture C are added

 The diminished viewing angle dependencies are shown in Table 1.

Table 4 mixture PlWO (%) 1216 24.15 1216 + 10% B 20.97 E5 23.59 E5 + 20% 17,98

Claims (2)

1. A method for increasing the viewing angle range in optoelectronic display systems, characterized in that the LC mixtures, mixtures are added consisting of A-alkylcyclohexyl - ^ - isothiocyanatophenylen and 2- (4-cyanophenyl) -5-alkyl (or 5 -alkylphenyl) -1,3-dioxanes and / or cyanobiphenyls. 2. The method according to claim 1, characterized in that the amount of added dopant mixture is between 1 and 40%.