GB2201158A

GB2201158A - High contrast coloured-liquid crystal guest-host effect displays

Info

Publication number: GB2201158A
Application number: GB08803758A
Authority: GB
Inventors: Horst Ladwig; Hartwin Obernik; Bernd Raunig; Ernst-Adolf Jauer; Burkhard Costisella; Arno Seeboth
Original assignee: Werk fuer Fernsehelektronik im VEB Kombinat Mikroelektronik VEB; Werk fuer Fernsehelektronik GmbH
Current assignee: Werk fuer Fernsehelektronik im VEB Kombinat Mikroelektronik VEB; Werk fuer Fernsehelektronik GmbH
Priority date: 1987-02-20
Filing date: 1988-02-18
Publication date: 1988-08-24
Anticipated expiration: 2008-02-18
Also published as: CH674520A5; JPS63258981A; GB2201158B; DD257889A1; DE3801798A1; GB8803758D0

Description

1k Title.1, Method for the production of coloured liquid crystal displays

2201 1,sc

This invention relates to the production of coloured liquid crystal displays, hereinafter known as LC displays, wherein the orientating LC volume is doped with a dichroltic dye. By application of an electrical field, the LC volume (host) and the dichroitic dye (guest) are reorientated, resulting in a change in colour of the system (guest-host effect).

The production of coloured LO displays is possible by two generally different routes.

1. Use of coloured Dolarizators or coloured films The investigations for the application of polarizing or coloured layers are directed principally towards their use in the cell interior. By these means, the life can be increased by reduced environmintal influences and the possibility exists of producing multifunctional layers.

r, In DE Offenlegungsschrift (published patent) 30 16 396, transparent. coloured orientating layers or insulating layers are described. Coloured orientating transparent layers on the basis of polyamide resins are described in DE Offenlegungsschrift 32 34 110. Here, printer's inks or inks are admixed to the polymer. In DE patent specification 30 27 571, a layer which possesses orientating and polarizing properties is described. The application of additional coloured layers in all cases renders'more difficult the techno- logy in the production of LC displays.

1 Dissolving of pleochroic dyes in LC mixtures A distinction is made here between the use of the guest-host effect (Heilmeier, Appl. Phys. Lett. 13, 1968, 91) and the coloured nematic- cholesterinic phase change (White Taylor effect)., see.DE Offenlegungsschrift 24 10 557.

In general, the highest possible degree of order S of the pleochroic dye to the LC volume is the objective in order to reach a sufficiently high contrast H of the LC display, as explained by H. Saki, T. Uchida, Y. Shibata in Japan Journal of Applied Physics, Part 2, nrol. 24, No. 5, 1985 pp. 299-301. In spite of the achieving of high degrees of order S in the range 0.7-0.8, the contrast changes H in LC'displays have hitherto not been sufficient. For this reason, guest-host displays have not yet become internationally general.

An object of this invention is to provide-a coloured liquid crystal display with guest-host effect,.wbich possesses a high contrast value (H).

The present inventions seeks,. in the method for the production of liquid crystal displays, to find substances which possess an absorption range lying for the greater part in the visible range (380 nm - 780 nm).

According to the present invention,. this task is achieved in that, in the method for the production of liquid crystal displays, dichroic dyes such as anthraquinones or azo dyes, which possess functional groups that exert upon the chromophoric group of the dye an inductive and/or mesomeric effect (-I, +I1 _M9 +M effect) are used as guest.

11 W I- Thus theabsorption of the dye may be displaced bathochrom.ically (longwaved) or hypsochromically (short-waved), with the result-that the absorption of the dye is intentionally shifted in the V/ X zurve. The overlap with the V/ x curve increases, with the result that the contrast is raised.

The dichroitic azo dyes used according to this invention possess the following structure:

I R N=N RI < -a.

x R-&N=N)-R I x N=N--aR x where X indicates a substituent having -1 or +I effect and/or -M or +M effect and R and RI denote organic residues preferably alkyl-, alkoxyor aryl residues.

Such substituents for the individual effects are: -I effect: Halogen, -NR 21 -OR, -CR=CR 2 +I effect: -01 1 -.& G) -C5CR ' 1 -CR 21 -NR 3 _(9 (9) -N-RP C n H 2n-1 - -M effect: =NR, = NR =CR 2 21 OV ZCR9 =Nl +M effect: Halogen. -.2R, NR 2 - (E) -01 where R represent organofunctional residues.

01 The substituent designated X may be situated in the o, m or p position to the chromophoric group.

iP By the incorporation of lateral substituents X on the rings (of lateral substituents X) of the elongated, rod-shaped dichroitic, dye molecule (IV) R-&N=N-&R (TV) the degree of order S is reduced, as is apparent from the following formulae of two dyes. The CN group is added on as lateral substituent.

V P2 H - CN 0 2 -&N=N-&n C H 5 CN) S)02 N--(:EN=N 2 4 (l) , 2 H 5 N C 2 H 4-OCOCH 3 S = 0. 48 (2) S = 0.34 The reduction in the degree of order S leads', however, surprisingly and In contradiction to the opinion expressed in the literature (see H. Sekiy T. Uchida, Y. Shibata in Japanese Journal of Applied Physics, Part 1, vol. 24, No. 5, 1985 pp. 299-301) not to a reduction in the contrast Hs but to an increase in It.

0 N-&N=N N 2 H 5 2 -& \ C H /2 5 2 1Z 0 1i=n-GN <I, <0 C C 2 H 4 U C 2 H 4 -OCOCH 3 (1) H = 1. 9 (2) H = 4.5 By the incorporation of the substituent X, which can appear with the 7 I chromophoric group in mesomeRism (or induction) and thus can exert a bathochromic or hypsochromic effect, the degree of order S is reduced. The contrast H is, however, increased if the displacement effect takes place towards the maximum of the brightness sensitivity of the eye. The contrast H is, however, the quality-determining parameter for the LC display.

Example of embodiment The invention is explained in more detail below by reference to the drawings.

The figures in the drawings show:

Pig. 1: different transmissions between switched-on and switched-off state of guest-host displays.

Fig. 2: differences of z,, and z 2 and. the overlaps with the V/x curve.

The different transmissions between the switched-on and switched-off states of the guest-host display are described by the two curves state 1 and state 2 in Pig. 1. - The change in contrast of the display (change in impression of brightness) is, however, determined not by the difference of the transmissions z 1 and z 21 but primarily by their overlap with the V/ X curve.

Fig. 1 shows that the overlap (hatched area) with the V/ X --urve isy in spite of a large difference between z 1 and z 21 small, which inevitably leads to a lower contrast.

0 1 In Pig. 2 it is shown that, with a comparable difference between z, and z 2 ' the overlap with the V/K curve is considerably greater, which results in an increased contrast, (change in brightness impression).

In order to verify the theory of this invention, the LC mixture SW 104, a mixture of biphenyls and benzoic acid ester, doped each time with 1% of a dichroitic dye, was filled into an LC display. The degree of order S obtained and the contrast H of the displays is set out in the table.

Example Name of dye Degree of Contrast Dye with X-later order S H substially tuent X arranged Di'spersscharlach G 0.42 3.4 No No (disperse scarlet G) 2 Dispersscharlach 3G 0.39 2.3 No No (disperse scarlet 3G) 3 Dispersorange 0.48 1.9 No No (disperse orange) 4 Dispersgelb, 0.31 4.4 Yes Yes (disperse yellow) Dispersrubin 0.33 4.7 Yes Yes (disperse ruby) 6 Dispersblau 0.31 4.6 Yes Yes (disperse blue) Dyes 1 to 3 do not possess any substituents X which can appear in conjugation with the chromophoric group. Dyes 4 to 6 possess substituents which can occur in conjugation with chromophoric groups. The resultant hypsochromic or bathochromic effect respectively in the dyes 4 to 6 increases the contrast. although S is lower than in dyes 1 to 3. The intended objective, a high contrast of the LC display, is achieved.

01 S 4 A -

Claims

Claims

Method for the production of coloured liquid crystal displays having a dichroitic dye and high contrast, characterized in that the dichroitic dye, with which the LC mixtures are doped, possesses substituents which appear in conjugation with the chromophoric group of the dye.
2. Method according to Claim 1, characterized in that:

(D Q - E) - e NR 21 -NR 3' =NR 21 -2-R, =2, -21 EN1, -2R, OR =CR29!!CR. -CzECR9 2' -CR=CR 2' -&. Halogen, alkyl residue, -CEN where R = organofunctional residue, are preferably used as substituents in the dye which occur in conjugat-ion with the chromophoric group.

Method as claimed in Claim 1, substantial.ly as described in any of the examples disclosed herein.

p Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WCIR 4TP. Further copies may be obtained from The Patent Ofnee, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1187.