CH674520A5 - - Google Patents

Description

DESCRIPTION The invention relates to a method for producing colored liquid crystal displays, hereinafter LC displays, with a dichroic dye and high contrast. By applying an electric field, the LC volume (host) and the dichroic dye (guest) are reoriented, which results in a color change in the system (guest-host effect).

Color LC displays can be produced in two generally different ways.

1st variant

Use of colored polarizers or color films

The investigations on the application of polarizing or colored layers are mainly focused on their use in the cell interior. As a result, the lifespan can be extended due to lower environmental influences, and it is possible to produce multifunctional layers.

In DE-Offenlegungsschrift 30 16 396, transparent colored orientation layers or insulation layers are described. Color-orientated transparent layers based on polyamide resins are described in German Offenlegungsschrift 32 34 110. Here, printing inks or inks are added to the polymer. DE 30 27 571 describes a layer which has orienting and polarizing properties. In any case, the application of additional colored layers complicates the technology in the production of LC displays.

2nd variant

Dissolution of pleochroic dyes in LC mixtures

A distinction is made between the use of the guest-host effect (Heilmeier, Appi. Phys. Lett 13, 1968, 91) and the colored nematic-cholesteric phase change (White Taylor effect), see DE laid-open specification 24 10 557. General the highest possible degree of order S of the pleochromatic dye to the LC volume, in order to achieve a sufficiently high contrast H of the LC display, the goal as described by H. Saki, T. Uchida, Y. Shiba-ta in Japan Journal of Applied Physics, Part 2 , Vol. 24, No 5, 1985 pp. 299-301. Despite the achievement of high degrees of order S in the range 0.7-0.8, the contrast changes H in LC displays have so far not been sufficient. As a result, guest host advertisements have not yet gained international acceptance.

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

The object of the invention is to find substances in the process for the production of liquid crystal displays, the absorption range of which is largely in the visible range (380 nm-780 nm).

The solution to this problem is specified in claim 1. It is solved by adding dichroic dyes, such as anthraquinones or azo dyes, to the liquid crystal mixtures in the process for the production of liquid crystal displays, which have functional groups which conjugate with the chromophoric group of the dye and an inductive one or / and exert a mesomeric effect (-1, +1, -M, + M effect).

Thus, the absorption of the dye is shifted bathochromic 20 (long-wave) or hypsochromic (short-wave), whereby the absorption of the dye is specifically pushed into the v / (X) curve. The overlap with the v / (X) curve increases, which increases the contrast.

The dichroic azo-25 dyes used according to the invention have the following structure:

30th

35

40

Î- ^ Ô ^ -N = N- ^ Ô ^ - R *

x

Î- ^ Ô ^ N = N- ^ Ô ^ -. R * x

II

III

45

50

where X is a substituent with -I or + I effect and / or -M or + M effect and R and R 'are organic radicals - preferably alkyl, alkoxy or aryl radicals. Such substituents for the individual effects are:

-I effect: halogen, -nr2, -ör, -cr = cr2 -c s cr, - or2, -fr3

+1 effect: -5iö, -N —r, cnh2n _, -

-M effect: = NR, = NR2, = CR2,

55 = ~ Ö, = CR, s NI

+ M effect: halogen, -OR, -NR2 _ e -Ol,

60 where R represents organofunctional radicals,

The substituent labeled X can be in the o, m or p position to the chromophoric groups.

By incorporating lateral substituents X on the rings (of lateral substituents X) of the elongated, 65 rod-shaped dichroic dye molecule (iv)

R- 0 -R '

(IV)

674 520

the degree of order S is reduced, as can be seen from the following formulas of two dyes. The CN group is attached as a lateral substituent.

0

> s> 0? n_ / xnen.

n '> —f \ c2 h4cn ^ w

(1)

S = 0.48

crth,

/ ovf 'z 5

• n

S C2W4-0C0CH3

(2)

S = 0.34

The lowering of the degree of order S leads surprisingly to the Journal of Applied Physics, Part 1, Vol. 24, No. 5, but contrary to the literature 1985 p. 299-301 does not lead to the lowering of the contradicting opinion, see H Seki, T, Uchida, Y. Shibata in January 20th, but on the contrary to increase.

/ C2H5 PN /

<h <(o2n ^ 7) -n = n / 7) -n ^

C2H5

c2h4cn

(I)

h = 1.9

30th

By incorporating the substituent X, which can mesomerize (or induction) with the chromophoric group and thus exert a bathochromic or hypsochromic effect, the degree of order S is reduced. The contrast H is increased, however, if the shift effect towards the maximum sensitivity to light of the eye takes place. However, the contrast H is the quality-determining parameter for the LC display.

Exemplary embodiment The invention will be explained in more detail below 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 \ and z2 and the overlaps with the v / (Ä,) 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. 1.

c2h4-0c0ch3

(2)

H = 4.5

The change in contrast of the display (change in light impression) is not only determined by the difference in the transmission Z \ and z2, but primarily by their overlap with the v / (X) ~ curve.

35

Figure 1 shows that the overlap (tightened area) with the v / (A,) curve - despite the large difference between Z] and z2 - is small, which inevitably has a low contrast.

40 In FIG. 2 it is shown that with a comparative difference between Zj and z2, the overlap with the v / (A.) Curve is significantly greater, which has an increased contrast (change in Hellein pressure).

45

To confirm the teaching according to the invention, the LC mixture SLF 104, a mixture of biphenylene and benzoic acid ester - doped with 1% of a dichroic dye - is filled into an LC display. The degree of order S obtained and the contrast H of the displays are shown in Table 50.

Example: Name of the dye

Order contrast dye X-lateral grade S H with subordinate tuent X

1

Disperse Scarlet G

0.42

3.4

No no

2nd

Disperse scarlet fever 3G

0.39

2.3

No no

3rd

Disperse orange

0.48

1.9

No no

4th

Disperse yellow

0.31

4.4

Yes / Yes

5

Disperse ruby

0.33

4.7

Yes / Yes

6

Disperse blue

0.31 '

4.6

Yes / Yes

Dyes 1-3 do not have a substituent X that can conjugate with the chromophoric group. Dyes 4-6 have substituents that can conjugate with chromophoric groups. The resulting hypsochromic or bathochromic effect for dyes 4-6 increases the contrast, although S is lower than 65 for dyes 1-3. The desired goal - a high contrast of the LC display - is achieved.

C.

1 sheet of drawings

Claims (2)

674 520 2nd PATENT CLAIMS 1. A process for producing colored liquid crystal displays with a dichroic dye and high contrast, characterized in that the dichroic dye which is added to the liquid crystal mixtures has substituents which come into conjugation with the chromophoric group of the dye. 2. The method according to claim 1, characterized in that as substituents in the dye which are conjugated to the chromophoric group. © © © _ © -nr2, -nr3, = nr2, -n-r, = o, -oi 10th = NI, -or, -0R2, = cr2, sCR, -C S cr, -cr = cr2, -0-, halogen, alkyl radical, -c = N R = organofunctional radical.