Compositions – Liquid crystal compositions – Containing pleochroic dye
Patent
1994-06-07
1997-11-25
Lovering, Richard D.
Compositions
Liquid crystal compositions
Containing pleochroic dye
25229901, 106493, 106498, 106 22C, 1061721, 424401, 424 63, 424 706, 501 17, 349 90, 349106, C09K 1900, C08K 500, A61K 7021, C09D 1100
Patent
active
056908571
DESCRIPTION:
BRIEF SUMMARY
This application is filed under 35 U.S.C. 371 and based on PCT/EP92/02799, filed Dec. 3, 1992.
The invention relates to a thermochromic effect pigment comprising a thermochromic liquid crystal material encapsulated with a polymer and coated with one or more inorganic metal oxides or nearly insoluble metal salts.
BACKGROUND OF THE INVENTION
There is a continuously increasing demand for liquid crystal pigment as a coating layer onto a substrate or for use in printing, in lacquer formulations, in plastics and cosmetics. At present, for make-up cosmetics, such as foundations, eye shadows, cheek rouges and other cosmetics thermochromic effect pigments are desired because of their color play.
EP-A-0 383 376 discloses a liquid crystal pigment consisting of a lamellar particle which is coated with a liquid crystalline material. The pigment is manufactured by dissolving a liquid crystalline material in a suitable solvent, dispersing a lamellar particle in the solvent and coating the lamellar particle by precipitating a portion of the liquid crystalline material from the solution onto the lamellar particle. This pigment has the disadvantage that it is not resistant against solvents, has low mechanical stability and poor flowability.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide thermochromic effect pigments with improved resistance against solvents and good mechanical stability and flowability so that they can be used like a common pigment. Furthermore, it is an object of the present invention to modify color play and color change in a definite way.
This object is accomplished according to the present invention by a thermochromic effect pigment comprising an encapsulated thermochromic liquid crystal which is coated with one or more inorganic metal oxides, mixtures of inorganic metal oxides, or nearly insoluble metal salts.
Furthermore, this object is accomplished according to the present invention by a process for preparing thermochromic effect pigments by precipitating a metal oxide or metal salt in an aqueous suspension onto the encapsulated liquid crystal in a well-known manner.
The inorganic metal oxides or metal salts can be selected for example from Al.sub.2 O.sub.3, SnO.sub.2, CaO, SiO.sub.2, ZrO.sub.2, TiO.sub.2, ZnO, MgO or BaSO.sub.4 and can be precipitated on to the encapsulated liquid crystal as a single oxide or as a mixed oxide thereof. The mixed oxide preferably contains silicon dioxide. The amount of metal oxides or salts in the thermochromic effect pigment as a rule is from 2 to 50%, preferably from 5 to 15% by weight, relative to total pigment weight.
The encapsulated thermochromic liquid crystal material is a commercially available material. The liquid crystals are encapsulated by complex coacervation in gelatin and gum arabic (U.S. Pat. No. 2,800,457), coacervation in gelatin (U.S. Pat. reissue 24,899), by interfacial polymerization in polyester (U.S. Pat. No. 3,429,827), by interfacial polymerisation in polyamide (U.S. Pat. No. 3,208,951) or other processes well known in the art.
The amount of polymer in the encapsulated thermochromic liquid crystal material is from 0.1 to 25%, preferably 2 to 10% by weight, relative to total weight of the encapsulated liquid crystal material.
A suitable thermochromic liquid crystal material is Licritherm.RTM. TCC-1001 consisting of a thermochromic liquid crystal encapsulated with gelatin manufactured by Merck Ltd.
The liquid crystal is an admixture of at least three chiral components and optionally at least one non-chiral component. At least one chiral component is a compound of the formulae I or II
R.sup.1 is R* or an alkyl radical or an alkenyl radical with up to 18 C atoms optionally substituted by CN or at least one halogen atom, wherein one or two non-adjacent CH.sub.2 groups of this radicals can also be replaced by --O--, --CO--, --O--CO-- and/or --CO--O--,
A.sup.1 and
A.sup.2 are in each case independently of one another groups can also be replaced by --O-- and/or --S-- and/or which can be substituted in
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patent: 5188815 (1993-02-01), Coates et al.
patent: 5194183 (1993-03-01), Munch et al.
patent: 5338566 (1994-08-01), Gregory et al.
patent: 5376699 (1994-12-01), Sage et al.
patent: 5562763 (1996-10-01), Brucker et al.
Herbski Magarete
Osterried Karl
Sage Ian Charles
Lovering Richard D.
Merck Patent Gesellschaft mit beschrankter Haftung
Metzmaier Daniel S.
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