Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
2003-05-07
2004-08-10
Huff, Mark F. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C428S001400, C252S299670, C349S183000, C349S193000
Reexamination Certificate
active
06773766
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the use of special polymerizable liquid-crystalline compounds for the production of optical elements having color- and polarization-selective reflection, and to optical elements comprising these compounds in monomeric or polymerized form. The present invention furthermore relates to the use of liquid-crystalline compositions comprising at least one of these compounds and, if desired, one or more chiral compounds for the production of optical elements having color- and polarization-selective reflection.
2. Description of the Background
Numerous compounds are not converted directly into the liquid, unordered state on warming from the crystalline state with a defined short-range and long-range order of the molecules, but instead pass through a liquid-crystalline phase, in which, although the molecules are mobile, the axes of the molecules form, however, an ordered structure. Extended molecules frequently form nematic liquid-crystalline phases, which are characterized by a long-range alignment order through parallel arrangement of the longitudinal axes of the molecules. If a nematic phase of this type comprises chiral compounds, a so-called cholesteric phase forms, which is characterized by a helical superstructure of the longitudinal axes of the molecules. The chiral compound here can be the liquid-crystalline compound itself or it can be added to a nematic liquid-crystalline phase as a chiral dopant.
Liquid-crystalline materials have remarkable optical properties based on their anisotropic ordered state. However, the liquid-crystalline ordered state only occurs in a limited temperature range. The temperature range in which liquid-crystalline phases occur is frequently well above the desired service temperature or extends only over a small temperature range.
There are various ways of obtaining and fixing the order structures desired for the material properties, even in the solid state. Besides glass-like solidification during cooling from the liquid-crystalline state, there is the possibility of copolymerization into polymeric networks or, in the case where the liquid-crystalline compounds contain polymerizable groups, of polymerization of the liquid-crystalline compounds themselves.
The cholesteric liquid-crystalline phase has remarkable properties which make the use of cholesteric liquid crystals or mixtures having cholesteric phases appear suitable for use as color filters and polarizers.
Cholesteric liquid crystals can be converted into a twisted structure by suitable alignment methods. The direction of rotation can be either left-handed or right-handed, depending on the chiral component used. This twisted arrangement of the liquid-crystal molecules results in the known selective reflection of the cholesteric liquid crystals (see, for example, H. Kelker, R. Matz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980, Chapter 7, pp. 293 ff.): circular-polarized light whose wavelength and direction of rotation correspond to the pitch of the liquid crystal is completely reflected. Circular-polarized light with the opposite direction of rotation or with a different wavelength can pass through the cholesteric liquid crystal unhindered.
Accordingly, as regards white unpolarized light, which contains all wavelengths and polarization states, only a narrow circular-polarized band is reflected. Cholesteric liquid crystals can therefore be employed as wavelength-selective reflectors or polarizers. In particular, the possibility of achieving reflection wavelengths from near ultra-violet to well into the infra-red wavelength region through a suitable choice of the type and proportion of chiral groups in the cholesteric liquid crystal is an extraordinary advantage of cholesteric liquid crystals.
The use of cholesteric liquid crystals for the production of color filters and polarizers is disclosed, for example, in U.S. Pat. No. 3,679,290 and R. Maurer, D. Andrejewski, F.-H. Kreuzer, A. Miller, Polarizing Color Filters Made from Cholesteric LC-Silicones, SID Digest 1990, pp. 110-113 and M. L. Tsai, S. H. Chen, S. D. Jacobs, Optical Notch Filters using Thermotropic Liquid Crystalline Polymers, Appl. Phys. Lett. 1989, 24(54), pp. 2395-2397, and EP 0 685 749 B1.
Furthermore, the following specifications describe the use of cholesteric liquid crystals for the formation of optical elements: JP 10197722 A, WO 98/43225, EP 0 859 969, U.S. Pat. No. 5,793,456, GB 2,324,382, U.S. Pat. No. 5,825,444, EP 0 720 041, EP 0 634 674, GB 2,321,529, U.S. Pat. No. 5,762,823, U.S. Pat. No. 3,679,290, U.S. Pat. No. 5,751,384, GB 2,315,072.
For the production of optical components, it is necessary to align the cholesteric liquid crystals or mixtures having a cholesteric phase using suitable methods and to fix them after alignment has taken place. Alignment of the liquid crystals is generally carried out at elevated temperatures in the region of the cholesteric phase by mechanical shear of a cholesteric film between two glass plates. These glass plates are frequently additionally provided with alignment layers, which are intended to ensure defect-free alignment. These alignment layers generally consist of rubbed polyimide layers or polyvinyl alcohol, or electric or magnetic fields are additionally applied in order to ensure good alignment. The crucial factor influencing the rate of alignment is the viscosity of the cholesteric substance used. The cholesteric phase can be fixed by freezing a monomer mixture having a cholesteric phase by a fast crosslinking reaction, such as a photopolymerization. Alternatively, however, polymers of cholesteric materials can also be preserved by supercooling into the glass phase. For use of cholesteric liquid crystals in optical elements, it is necessary that suitable materials can be aligned in processes which can be automated and which can be used on large areas, in such a way that defect-free cholesteric films can be obtained. The multidomains usually obtained adversely affect the optical quality of the films and mean that the high requirements made of optical elements, such as high reflectivity for strictly right-handed or left-handed circular-polarized light, can no longer be met. Furthermore, high requirements are made of optical components in respect of heat and light stability. Thus, the temperatures of up to 200° C. to which optical components, such as polarizers, notch filters, colored filters and compensation films, are subjected briefly during display production must not affect the optical quality of the components. In this respect, the optical elements known from the prior art still do not have completely satisfactory properties.
For the production of optical elements, the aim was therefore to find materials which, besides ready alignability at the lowest possible temperatures, produce high stability of the polymerized films during processing, with excellent optical properties. In particular, materials should be provided which permit the production of optical elements having improved temperature stability.
SUMMARY OF THE INVENTION
We have found that these objects are surprisingly achieved by using polymerizable liquid-crystalline compounds of the general formula I
Z
1
-Y
1
-A
1
-Y
3
-M-Y
4
-A
2
-Y
2
-Z
2
I,
in which
Z
1
and Z
2
, independently of one another, are a radical containing reactive, polymerizable groups;
Y
1
-Y
4
, independently of one another are a single chemical bond, —O—, —S—, —O—CO—, —CO—O—, —O—CO—O—, —CO—NR—, —NR—CO—, —O—CO—NR—, —NR—CO—O— or —NR—CO—NR, where at least one of the groups Y
3
and Y
4
is —O—CO—O—, —O—CO—NR—, —NR—CO—O— or —NR—CO—NR—, and R is C
1
-C
4
-alkyl;
A
1
and A
2
, independently of one another, are a spacer having 2 to 30 carbon atoms, in which the carbon chain may be interrupted by ether oxygen, thioether sulfur or by non-adjacent imino or C
1
-C
4
-alkylimino groups; and,
M is a mesogenic group;
for the production of optical elements having color- and/or polarization-selective reflection.
The term polymerization here is take
Meyer Frank
Schneider Norbert
Schuhmacher Peter
BASF - Aktiengesellschaft
Huff Mark F.
Sadula Jennifer R.
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