Coating processes – Coating remains adhesive or is intended to be made adhesive
Patent
1997-08-15
1998-06-16
Acquah, Samuel A.
Coating processes
Coating remains adhesive or is intended to be made adhesive
528190, 528193, 528219, 528272, 528288, 528289, 528292, 528298, 528300, 528308, 5283086, 528310, 4273855, 427487, B05D 510, C08G 6300, C08G 6344
Patent
active
057666792
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to liquid crystalline chiral nematic polyesters comprising as alcohol component chiral diol structural units of the formula ##STR1## where L is C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, halogen, COOR, OCOR, CONHR or NHCOR, and R is C.sub.1 -C.sub.4 -alkyl or hydrogen, and as acid component dicarboxylic acid residues comprising mesogenic groups.
The invention furthermore relates to use of the novel polyesters and pigments comprising the chiral nematic polyesters.
2. Description of the Background
Liquid crystalline phases, called mesophases, may occur on heating substances with shape anisotropy. The individual phases differ by the spatial arrangement of the centers of mass of the molecules on the one hand and by the arrangement of the molecules with respect to the long axes on the other hand (G. W. Gray, P. A. Winsor, Liquid Crystals and Plastic Crystals, Ellis Horwood Limited, Chichester 1974). The nematic liquid crystalline phase is distinguished by parallel orientation of the long axes of the molecules (one-dimensional order state). Provided that the molecules forming the nematic phase are chiral, the result is a chiral nematic (cholesteric) phase in which the long axes of the molecules form a helical superstructure perpendicular to it (H. Baessler, Festkorperprobleme XI, 1971). The chiral moiety may be present in the liquid crystalline molecule itself or else be added as dopant to the nematic phase, including the chiral nematic phase. This phenomenon was first investigated on cholesterol derivatives (eg. H. Baessler, M. M. Labes, J. Chem. Phys. 52 (1970) 631).
The chiral nematic phase has special optical properties: a high optical rotation and a pronounced circular dichroism resulting from selective reflection of circularly polarized light within the chiral nematic layer. The colors appear different depending on the angle of view and depend on the pitch of the helical superstructure, which in turn depends on the twisting ability of the chiral component. It is possible in this case, in particular by altering the concentration of a chiral dopant, to vary the pitch and thus the wavelength range of the selectively reflected light of a chiral nematic layer. Chiral nematic systems of this type have interesting possibilities for practical use. Thus, a stable, colored network can be produced by incorporating chiral moieties into mesogenic acrylates and orienting in the chiral nematic phase, eg. after photocrosslinking, but the concentration of chiral component therein can no longer be changed (G. Galli, M. Laus, A. Angelon, Makromol. Chemie 187 (1986) 2289). Admixing noncrosslinkable chiral compounds to nematic acrylates makes it possible to prepare, by photocrosslinking, a colored polymer which still contains large amounts of soluble components (I. Heyndricks, D. J. Broer, Mol. Cryst. Liq. Cryst. 203 (1991) 113). It is furthermore possible, by random hydrosilylation of mixtures of cholesterol derivatives and acrylate-containing mesogens with defined cyclic siloxanes and subsequent photopolymerization, to obtain a chiral nematic network in which the chiral component may form a proportion of up to 50% of the material employed; however, these polymers still contain marked amounts of soluble materials (F. H. Kreuzer, R. Mauerer, Ch. Muller-Rees, J. Stohrer, Contribution No. 7, 22nd Liquid Crystals Meeting, Freiburg, 1993).
DE-A-35 35 547 describes a process in which a mixture of cholesterol-containing monoacrylates can be processed, by photocrosslinking, to chiral nematic layers. However, the total amount of the chiral component in the mixture is about 94%. Although a material of this type, as pure side chain polymer, has not very high mechanical stability, the stability can be increased by highly crosslinking diluents.
Many chiral nematic polyesters in which the mesogenic structures are incorporated into the main chain are also known, eg. from S. Vilasagar, A. Blumstein, Mol. Cryst. Liq. Cryst. (1980), 56 (8), 263-9; A. Blumstein
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Etzbach Karl-Heinz
Kricheldorf Hans R.
Meyer Frank
Probst Nicolas
Siemensmeyer Karl
Acquah Samuel A.
BASF - Aktiengesellschaft
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