DD257889A1 - METHOD FOR PRODUCING COLORED LIQUID CRYSTAL DISPLAYS - Google Patents

Abstract

The invention relates to a process for the preparation of colored liquid crystal displays. By coupling additional substituents on the dichroic dye molecule, which can be in conjugation with the chromophoric group (mesomerism and / or induction), a bathochromic or hypsochromic effect is achieved. As a result, the adsorption of the dye can be targeted in the maximum of u / (l) curve, which is characterized by the eye sensitivity for the light sensation, pushed. With the incorporation of the substituents (also lateral) increases the contrast of the LC display, wherein the degree of order of the dye in the LC display may well drop.

Description

For this 1 page drawings

Field of application of the invention

The invention relates to the production of colored liquid crystal displays, hereinafter LC displays, in which the oriented LC volume is doped with a dichroic dye. Applying an electric field reorients the LC volume (host) and the dichroic dye (guest), resulting in a color change of the system (guest-host effect).

Characteristic of the known state of the art

The production of colored LC displays 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, the life can be extended by lower environmental influences, and it is possible to produce multifunctional layers.

DE-Offenlegungsschrift 3016396 describes transparent colored orientation layers or insulation layers. Colored oriented transparent layers based on polyamide resins are described in DE-Offenlegungsschrift 3234110. In this case, printing inks or inks are added to the polymer. German Patent 30 27 571 describes a layer which has orienting and polarizing properties. In any case, the application of additional colored layers makes it difficult to use the technology in the manufacture of LC displays.

2. Dissolution of pleochrotic dyes in LC mixtures

A distinction can be made here between the use of the guest-host effect (Heilmeier, Appl. Phys. Lett 13, 1968, 91) and the colored "nematic-cholesteric phase change." White-Taylor effect, see DE-Offenlegungsschrift 2,410,557. In general, the highest possible degree of order S of the pleochrotic) dye to the LC volume, to achieve a sufficiently high contrast H of the LC display is the goal as by H. Seki, T. Uchida, Y. Shibata in Japanese Journal of Applied Physics, Part 2, Vol 24, No 5,1985 p 299-301, despite the fact that high degrees of order S are achieved in the range 0.7-0.8, the contrast changes H in LC displays have not been sufficient so far. Host ads internationally not yet enforced.

Object of the invention

The aim of the invention is a colored liquid crystal display with guest-host effect, which has a high contrast value (H).

Explanation of the essence of the invention

The invention is based on the object of finding substances in the process for the production of liquid crystal displays whose absorption range is for the most part in the visible range (380 nm-780 nm).

According to the invention the object is achieved in that in the process for the preparation of liquid crystal displays dichromic dyes, such as anthraquinones or azo dyes, are used as a guest, the functionally possess groups which on the chromophore group of the dye an inductive and / or mesomeric effect (-I- , + I, -M, + M effect). Thus, the absorption of the dye is shifted bathochromic (long-wave) or hypsochromic (short-wave), whereby the absorption of the dye is targeted in the O (A) curve. The overlap with the Ö (A) curve increases, which increases the contrast.

The dichroic azo dyes used according to the invention have the following structure: r- (~O- N = N- (o

N = N- fÖ \ -R

where X corresponds to a substituent with -I or +! - effect and / or -M or + M effect. Such substituents for the individual effects are:

-! Effect: halogen, -NR ₉ , -OR, -CR = CR -C = CR, - < O

+! Effect: - 01®, -N-R, C H "-

- · "ST Π / £ Л -Д,

-M effect: = NR, = NR ₂ , = CR ₂ , = "θ, 5CR, ΞΝ1

+ MEffect: halogen, -OR, -NR ₂ -Of, -OR

Wherein

R and R 'are organic radicals - preferably alkyl, alkoxy or aryl radical.

The substituent denoted by X may be in the o, m or p position of the chromophoric group.

By the incorporation of substituents on the rings (lateral substituent as shown in the following formulas of two dyes) of the long, rod-shaped dichroic dye molecule (IV)

R- / O N-N = N · / O V-R '

(IV)

χ )

if the degree of order S is lowered,

/ ^C 2 ^H 5

N- / O V-N = N

' ^C 2 ^H 5 -N ^ -OCOCH.

^NCH

(1)

S = 0.48

(2)

S = 0.34

The lowering of the degree of order S leads, surprisingly and contrary to the opinion advocated in the literature, see H. Seki, T. Uchida, Y. Shibata in Japan's Journal of Applied Physics, Part 1, VoI. 24, No 5,1985 p. 299-301, however, not to lower the contrast H, but on the contrary to increase.

O ₀ N- (F) - N = N- (F) -

/ ^C 2 ^H 5

/ h / o _o N- (o) -N = N- (F) -n '

_{с н} ' ^{2 5}

(1) H = 1.9

(2)

H = 4.5

By incorporation of the substituent X, which can enter into mesomerism (or induction) with the chromophoric group and thus exert a bathochromic or hypsochromic effect, the degree of order S is lowered. However, the contrast H is increased when the displacement effect is toward the maximum of the light sensitivity of the eye. Contrast H, however, is the quality determining parameter for the LC display.

embodiment

The invention will be explained in more detail with reference to the drawings. Show it

Figure 1: Different transmissions between on and off state of guest host displays. Figure 2: differences of Z ₁ and Z ₂ and the overlaps with the O (A) curve.

The different transmissions between the switched-on or switched-off state of the guest-host display are described by the two curves state 1 and state 2 in FIG.

The change in contrast of the display (light-pressure change) is determined not only by the difference of the transmission Z ₁ and z ₂ , but primarily by their overlap with the Ö (A) curve.

Figure 1 shows that the overlap (narrowed area) with the 0 (A) curve is small, despite the large difference between z and z ₂ - ', which inevitably results in a low contrast.

In Figure 2 it is shown that with a comparative difference of Z ₁ and Z _2, the overlap with the Э (Л) -Kiгѵе is much larger, which has an increased contrast (light impression change).

In an LC display, the LC mixture SLF 104, a mixture of biphenyls and benzoic acid ester - doped with 1% of a dichroic dye - filled. The obtained degree of order S and the contrast H of the displays are shown in the table.

Ex. Name of the dye Order degree S Contrast H Dye with X lateral SubstituentX disposed 1 Dispersscharlach 0.42 3.4 No No 2 Disperse scarlet 3 G 0.39 2.3 No No 3 Disperse 0.48 1.9 No No 4 Disperse 0.31 4.4 Yes Yes 5 Dispersrubin 0.33 4.7 Yes Yes 6 Disperse 0.31 4.6 Yes Yes

Dyes 1-3 do not have a substituent X which can conjugate with the chromophoric group. Dyes 4-6 have substituents that can conjugate with chromophore groups. The resulting hypsochromic effect on Dyes 4-6 increases contrast, although S is lower than Dyes 1-3. The desired goal - a high contrast of the LC display is achieved.

Claims (2)

A process for producing colored liquid crystal displays with a dichroic dye and high contrast, characterized in that the dichroic dye doped to the LC volume has substituents that conjugate with the chromophore group of the dye. 2. The method according to claim 1, characterized in that as substituents in the dye, which are in conjugation to the chromophoric group, preferably: - NR ₂ , -NR ₃ , = NR ₂ , -NL-R, = 0, -OJ = Nt, -OR, -0R ₀ , = CR _{Q |} 3CR, -CrCR, "™ ^L. CL. -CR = CR ₂ , - \ ÖVi halogen, alkyl radical, -Cf R = organofunctional radical
be used.