Claims
- 1. A liquid crystal layer containing a liquid crystal composition with a central wavelength of selective reflection .lambda..sub.o wherein
- said liquid crystal layer has a short pitch (p) equal to about one order of magnitude less than the layer thickness;
- said liquid crystal composition comprises a nematic liquid crystal compound doped with at least two chiral additives of the same twist sense, wherein said composition has the parameters a and b where a is the reciprocal of the refractive index of 22.degree. C. and b is the linear temperature coefficient of the reciprocal of the refractive index and each chiral additive (k) has the parameters A.sub.K and B.sub.K and A.sub.K is the twisting power (1/p) at 22.degree. C. and B.sub.k is the liner temperature coefficient of the twisting power; and
- the parameters a, b, A.sub.K and B.sub.k are such that .lambda..sub.o is temperature compensated to have temperature independence.
- 2. The liquid crystal layer of claim 1, wherein there are only two additives which have the respective concentrations c.sub.1 and c.sub.2 and satisfy the condition a(c.sub.1 B.sub.1 +c.sub.2 B.sub.2)=b(c.sub.1 A.sub.1 +c.sub.2 A.sub.2).
- 3. The liquid crystal layer according to claim 1, wherein the chiral additives are:
- a. diethyl (4S,5S)-2-trans-4-(p-cyanophenyl)cyclohexyl]-1,3-dioxolane-4,5-dicarboxylate,
- b. (R)-1-methylheptyl-p-[(2S,4R,5S)-5-decyl-4-methyl-m-dioxan-2-yl]benzoate,
- c. 2,2'-p-phenylenebis[(2S,4R,5S)-4-methyl-5-octyl-m-dioxane], and
- d. (R)-alpha-methylheptyl-4'-[(2S,4R,5S)-4-methyl-5-octyl-m-dioxan-2-yl]-4-biphenylcarboxylate.
Priority Claims (1)
Number |
Date |
Country |
Kind |
3948/89 |
Nov 1989 |
CHX |
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Parent Case Info
This is a continuation of application Ser. No. 07/690,893 filed as PCT/CH90/00250, Oct. 26, 1990, published as WO91/06613, May 16, 1991, now abandoned.
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4780240 |
Emoto et al. |
Oct 1988 |
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4939287 |
Bahr et al. |
Jul 1990 |
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0351746 |
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Non-Patent Literature Citations (2)
Entry |
Gobl-Wunsch et al., "Temperature dependence . . . using several chiral additives", Zeitschrift fur Naturforschung, A, 34A (5), pp. 594-599, 1979. |
Schadt et al., "New Liquid Crystal Polarized Color Projection Principle", Jap. J. of Appl. Phys., vol. 29, No. 10, Oct. 1990, pp. 1974-1984. |
Continuations (1)
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Number |
Date |
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Parent |
690893 |
Jun 1991 |
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