DD266428A1 - METHOD FOR PRODUCING MULTICOLORED LIQUID CRYSTAL DISPLAYS - Google Patents

Abstract

Method for producing multicolor high contrast liquid crystal displays (color difference). You get different colored displays when the incident light is absorbed at different wavelengths of the visible range. This is achieved according to the invention by doping the LC volume with at least one non-dichroic and at least one dichroic dye. The non-dichroic dye uniformly absorbs light regardless of the electric field. The dichroic dye absorbs the light differently depending on its different spatial position in the display; according to the guest host effect.

Description

For this 1 string drawings

Field of application of the invention

The invention relates to liquid crystal systems for LCD in which the oriented LC volume contains dyes. By applying an electric fold, the LC volume is reoriented, resulting in a color change,

Chnrakterlstlk the known prior art

The preparation of colored LC sequences is possible in two generally different ways.

1. Application of colored polarizers or color films

The investigations on the application of polarizing or colored layers are focused on their use in the cell interior. As a result, can be extended by lower environmental influences, the life and it bostoht the ability to produce multifunctional layers.

In the OS patent 301Θ396 transparent colored alignment layers or insulation layers are described

 Colored oriented transparent layers based on polyamide resins are described in the OS patent 3234110. In this case, printing inks or tints are mixed in with the polymor. OS patent 3027571 describes a layer which has orienting and polarizing properties. In any case, the application of additional colored layers makes the technology of LCD production more difficult,

2. Resolution of pleochrotic dyes in LC mixtures

In this case, the use of the guest-host effect (He ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^) F onontschrift 2410557).

A disadvantage of boidor called effects is too low contrast in the display. In particular, dyes with a high degree of order S are used to increase the contrast (H. Seki, T. Uchida, Y. Shibota, Jap. J. of Appl. Phys. Part 2 VoI 24, No 5, 1985, L. 299-301 ) or dyes with a comparatively lower S - but with a greater overlap dor

νΆ curve, as described in DD patent WP Go 2F / 300077, used.

Basically, however, there is the disadvantage that the change in contrast is obtained only by different intensities at the same wavelength.

To improve the contrast in the LCD, a color change is caused, not primarily by a difference in intensity, but by the application of different wavelengths in the visible range. For example, the use of different colored pleochrotic dyes as guest in Guost host displays is described. However, when using such dye systems, there is the general difficulty of their trouble-free anisotropic categorization into the LC matrix

 As a result, guest-host displays with two different colored pleochrotic dyes will inevitably not have any application internationally.

Object of the invention

The aim of the invention is a liquid crystal mixture for multicolor LCD with high contrast on the basis of different wool lengths in the visible range.

Presentation of the veson of the invention

The invention has for its object to dope a liquid crystal mixture for LCD with dyes that have different physico-chemical properties.

According to the invention the object is achieved in that the liquid crystal mixture at least two dyes are added, but only one has optically anisotropic properties, the second does not have this optical anisotropy. Dor optically enisotropic dichroic dye, which has a degree of order S, is oriented spatially, as in the Guost host display, with its molecules parallel to the nomatic director n. The non-anisotropic dye, which does not have a degree of order S, is in LC volume statistically distributed. Surprisingly, in this case dio oriented LC matrix is not disturbed in its homogeneity.

The non-metallic dye molecule absorbs the incident light uniformly both in the off state and in the on state. It therefore occurs regardless of the variable electric field no change in color. The chromophthalic dye behaved depending on the electrical fold according to the guest-host effect, d. H. the light is differently absorbed according to the different spatial position relative to the light. As dichroic dyes, anthraquinone dyes or azo dyes are used. As non-dichroic dyes it is preferred to use thermosubstituted dye molecules without symmetry properties. An example of this is the yellow dye (I)

<. o Vnh-Y o \ -so ₂ -nh- / o \

(I)

The mixture of the two optically different-acting dye molecules leads to color changes under the influence of the electric field. If the dichrotic dye molecule absorbs the light, the mixed color of the dichroic and non-dichroic dye molecules is formed. If the dichroic dye molecule in the LC volume is spatially oriented by the electric field so that it does not absorb the light, only the color of the non-dichroic dye is effective. The dichrotic dye is either optically switched on to the non-dichroic dye by the guest-host effect - and the corresponding mixed color is formed - or it has no influence on the absorbed wavelength and only the non-dichroic dye is effective. The effect (Farbintonsita't, color fastness) can be further increased if both dyes, both the dichrotic and non-dichroic, have a high molar extinction. As a result, a high color fastness of the display is achieved boi low concentration dos dye in the LC volume. Boido dye species, both dichrotic and non-dichroic, are well soluble in the liquid crystal mixture.

Ausführungsbelspiol

The invention will be explained in more detail in exemplary embodiments and the drawings. Show it

Figure 1 a: LCD in the off state Figure 2 b: LCD In the switched state '-

In the figures, a is the non-dichroic, b is the dichroic dye, and η is the director of the nematic liquid crystal. Example 1: In an LCD is an oriented LC matrix (SLF 104, Sharp) containing 0.5% of a yellow non-dichroic Dye (I) and with 0.5% of a blue dichroic dye (II) (S = 0.6 in SLF104) is doped.

fÖ \ -NH-V

In the de-energized state, not only the dichotomy but also the dichroic dye absorbs the light. The LCD will appear green as the resulting mixed color. When switched on, the dichroic dye absorbs the light

not, the LCD appears yellow.

Example 2:

In an LCD there is an oriented LC matrix (E 5, Merck) containing 0.5% of a yellow non-dichroic dye (I) and 0.75% of a mixture (in the ratio 1: 1) of a red ( III, S = 0.65 in E 5) and a blue (IV, S = C, 6 in E 5) dichroic dye is doped.

C ₂ H ₄ CN

O n / oVn ° N- (OVn (C ₀ H ^ -O-COCH, ) _o

Cl NHCOCH ₃

When de-energized, the LCD appears black. In the switched-on state, the yellow dyes do not absorb the light, the LCD turns yellow.

Claims (3)

1. Liquid crystal mixture with more than one dye for multicolor liquid crystal displays,
characterized by a dye mixture consisting of at least one non-dichroic
Dye and at least one dichroic dye. 2. A liquid-crystal mixture according to claim 1, characterized in that the dichrotic
Dyes consists of anthraquinone dyes and / or azo dyes. 3. Liquid-crystal mixture according to claim 1 and 2, characterized in that the not
dichrotic dyes have no symmetry properties.