Compositions – Liquid crystal compositions
Reexamination Certificate
1999-04-16
2001-01-30
Wu, Shean C. (Department: 1721)
Compositions
Liquid crystal compositions
C252S299670
Reexamination Certificate
active
06180025
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
The present invention is described in the German priority application No. 198 17 069.6, filed Apr. 17, 1998, which is hereby incorporated by reference as is fully disclosed herein.
BACKGROUND OF THE INVENTION
Cholesteric liquid-crystalline main-chain polymers (cLCPs) whose color effect is dependent on viewing angle are known and can be prepared in analogy to nematic main-chain polymers by using an additional chiral comonomer (U.S. Pat. No. 4,412,059; EP-A-0 196 785; EP-A-0 608 991; EP-A-0 391 368) or by reacting nematic main-chain polymers (LCPs) with chiral comonomers (EP-A-0 283 273). Cholesteric main-chain polymers possess a helical superstructure and are distinguished by pronounced color effects that are based on selective reflection at the helical superstructure. The precise reflection wavelength in this instance depends in particular on the pitch of the helix. The helical pitch which develops depends essentially on the proportion of the chiral comonomer, on the nature of its incorporation into the polymer, on the degree of polymerization, and on the structure of the chiral comonomer. Furthermore, many systems also show a temperature dependence of the pitch in the cholesteric phase.
Heat-reflecting platelet-shaped particles are known. They generally consist of coated mica platelets. In this case the coat thickness is selected so that the reflection is within the IR range and the platelets are colorless and transparent. Owing to the dependency of the reflection on viewing angle, such platelets do not appear colorless at every viewing angle. When viewed obliquely, they generally show an unwanted greenish color shimmer. Platelets which in addition to their IR reflection exhibit a homogeneous, hiding color effect have not been described to date.
SUMMARY OF THE INVENTION
The invention relates to liquid-crystalline colorant compositions which reflect thermal radiation, to a process for their preparation and to their use.
It is the object of the present invention to provide a material which gives level colorations without inhomogeneities of color and reflects thermal radiation. It has been found that this object is surprisingly achieved by IR-reflective cholesteric liquid-crystalline polymers colored with a light-absorbing colorant, and that, in this way, novel materials are provided in a simple manner.
The present invention provides a colorant composition consisting essentially of one or more cholesteric liquid-crystalline polymers having a pitch of the helical superstructure of from 760 nm to 500 pm, in particular from 760 nm to 25 pm, and of at least one colorant which absorbs light in the visible wavelength range.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
By colorants which absorb light in the visible wavelength range are meant those having at least one absorption maximum between 350 and 750 nm. For the purposes of the present invention, the term colorants embraces both dyes and pigments.
In the unoriented state, a cholesteric liquid-crystalline polymer colored with said colorant has the color of the colorant without any marked heat insulation effect. If such a sample is oriented in the cholesteric phase, then it is possible to observe not only the unchanged color properties of the colorant but also properties of reflecting thermal radiation.
The cholesteric polymers on which the invention is based comprise cholesteric liquid-crystalline main-chain polymers, cholesteric liquid-crystalline side-group polymers, and combined liquid-crystalline main chain/side-group polymers. Cholesteric liquid-crystalline side-group polymers are, for example, polysiloxanes, cyclic siloxanes, polyacrylates or polymethacrylates having mesogens in the side groups. The mesogens in the side group are, for example, cholesterol-substituted phenylbenzoates or biphenols.
The main-chain polymers are preferably liquid-crystalline polyesters, polyamides or polyesteramides which comprise aromatic and/or cycloaliphatic hydroxycarboxylic acids, aromatic aminocarboxylic acids; aromatic and/or cycloaliphatic dicarboxylic acids, and aromatic and/or cycloaliphatic diols and/or diamines; and also one or more chiral, bifunctional comonomers.
Cholesteric liquid-crystalline main-chain polymers are generally prepared from a chiral component and from hydroxycarboxylic acids and/or a combination of dicarboxylic acids and diols. In general, the polymers consist essentially of aromatic constituents. It is, however, also possible to employ aliphatic and cycloaliphatic components, such as cyclohexane dicarboxylic acid.
For the purposes of the present invention preference is given to cholesteric liquid-crystalline main-chain polymers consisting of
a) from 0 to 99.8 mol % of one or more compounds from the group consisting of aromatic hydroxycarboxylic acids, cycloaliphatic hydroxycarboxylic acids and aromatic aminocarboxylic acids;
b) from 0 to 50 mol % of one or more compounds from the group consisting of aromatic dicarboxylic acids and cycloaliphatic dicarboxylic acids;
c) from 0 to 50 mol % of one or more compounds from the group consisting of aromatic and cycloaliphatic diols and diamines; and
d) from 0.1 to 40 mol %, preferably from 1 to 25 mol %, of chiral, bifunctional comonomers;
the sum resulting in 100 mol %.
In the context of the stated percentages, it should be ensured that the stoichiometry—known to the skilled worker—of the functional groups for the polycondensation is secured. In addition, the polymers may also include components having only one functional group or having more than two functional groups, such as dihydroxybenzoic acid, trihydroxybenzenes or trimellitic acid, for example. In this way it is possible to influence the molecular weight of the polymers. The components having more than two functional groups act as branching site in the polymer and should be added only in low concentrations—for example, from 0 to 5 mol %—if the intention is to avoid crosslinking of the material during the condensation.
Particular preference is given to cholesteric main-group polymers which are composed of the following units of the individual monomer groups:
a) aromatic hydroxycarboxylic acids, aminocarboxylic acids:
hydroxybenzoic acids, hydroxynaphthalenecarboxylic acids, hydroxybiphenyl-carboxylic acids, aminobenzoic acids, hydroxycinnamic acids;
b) aromatic dicarboxylic acids, aliphatic dicarboxylic acids:
terephthalic acid, isophthalic acid, biphenyldicarboxylic acids, naphthalenedicarboxylic acids, cyclohexanedicarboxylic acids, pyridinedicarboxylic acids, diphenyl ether dicarboxylic acids, carboxycinnamic acids, and also
c) aromatic diols, aminophenols, diamines:
hydroquinones, dihydroxybiphenyls, tetramethyldihydroxybiphenyls, naphthalenediols, dihydroxydiphenyl sulfones, dihydroxydiphenyl ethers, dihydroxyterphenyls, dihydroxydiphenyl ketones, phenylene diamines, diaminoanthraquinones, dihydroxyanthraquinones, and also
d) chiral, bifunctional monomers:
isosorbide, isomannide, isoidide, camphoric acid, (D)- or (L)-methylpiperazine, (D)-or (L)-3-methyladipinic acid, butane-2,3-diol, and also
where R and R′ in each case independently of one another are H, C
1
-C
6
-alkyl or phenyl, preferably H or CH
3
.
The polymer units described may also include further substituents, such as methyl, methoxy, cyano or halogen, for example.
For the purposes of the present invention, very particular preference is given to polymers comprising one or more monomers from the group consisting of p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, hydroquinone, resorcinol and 4,4′-dihydroxybiphenyl; and also camphoric acid, isosorbide and/or isomannide as chiral component.
In order to obtain the heat insulation effect of the invention it is necessary for the oriented cholesteric polymer or the oriented cholesteric polymer blend to have a helical superstructure with a pitch corresponding to a wavelength in the IR range. The cholesteric compound predominantly reflects that component of radiation whose wavelengt
Schoenfeld Axel
Stohr Andreas
Clariant GmbH
Hanf Scott E.
Jackson Susan S.
Wu Shean C.
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