Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2001-09-18
2004-01-13
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C528S176000, C528S190000, C252S299200, C252S299600, C252S299620
Reexamination Certificate
active
06677042
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to polymer beads comprising an anisotropic polymer material with helically twisted structure, to methods of their preparation, to their use in reflective films, spraying or printing inks or as pigments, for optical or electrooptical, decorative or security applications, to a reflective film comprising one or more polymer beads in a transmissive binder, and to a security marking or security device comprising one or more polymer beads or comprising a reflective film.
BACKGROUND AND PRIOR ART
In prior art encapsulated cholesteric liquid crystals (CLCs) are known for use in decorative or security applications, like for example printing inks, colored images, identification cards, bank notes or other documents of value that should be forge-proof. The CLC material is usually a mixture of low molecular weight CLC compounds that is encapsulated or encased in a transparent shell of e.g. gum arabic or gelatine. Often photochromic or thermochromic CLC mixtures are used which change their color or become colorless when being subjected to photoradiation or to a temperature change, respectively.
CLCs are characterized by a helically twisted structure. A layer of a CLC material with planar alignment, i.e. wherein the cholesteric helix axis is oriented perpendicular to the plane of the layer, shows selective reflection of circular polarized light caused by interaction of incident light with the cholesteric helix. The central wavelength of reflection &lgr; depends on the pitch p and the average refractive index n of the CLC material according to the following equation
&lgr;=
n·p
However, encapsulated CLCs have several disadvantages. For example, the capsules containing the CLCs exhibit only limited long term stability, and can break and release the CLCs. Furthermore, they are sensitive to heat and pressure. Therefore, whereas encapsulated CLCs may be useful for short term applications such as clothing labels etc., they are less suitable for long term security items such as bank notes.
The inventors have found that the above mentioned drawbacks can be avoided by using solid polymer beads comprising a polymerized anisotropic material with helically twisted structure, like for example polymer beads of polymerized liquid crystal material, instead of a low molecular weight LC mixture encapsulated in a polymer shell. Solid LC polymer beads according to the present invention have better chemical and heat resistance and are therefore more suitable for both short and long term applications than encapsulated LCs.
JP 02-281045 discloses liquid crystalline high polymer spherical particles of a thermotropic polymer, like e.g. a polyester, which can be used as particulated moulding material, sinter-molding material, filler for thermoplastic and thermosetting plastic material and filler of heat-resistant paint, enamel and additives. However, JP 02-281045 does not disclose LC polymer beads with a helically twisted structure.
DEFINITION OF TERMS
In connection with polymer beads and reflective films as described in the present application, the following definitions of terms as used throughout this application are given.
The term ‘liquid crystal or mesogenic material’ or ‘liquid crystal or mesogenic compound’ should denote materials or compounds comprising one or more rod-shaped, board-shaped or disk-shaped mesogenic groups, i.e. groups with the ability to induce liquid crystal phase behavior. Rod-shaped and lath-shaped mesogenic groups are especially preferred. The compounds or materials comprising mesogenic groups do not necessarily have to exhibit a liquid crystal phase themselves. It is also possible that they show liquid crystal phase behavior only in mixtures with other compounds, or when the mesogenic compounds or materials, or the mixtures thereof, are polymerized.
For the sake of simplicity, the term ‘liquid crystal material’ is used hereinafter for both liquid crystal materials and mesogenic materials, and the term ‘mesogen’ is used for the mesogenic groups of the material.
The term ‘helically twisted structure’ refers to anisotropic materials, like for example liquid crystal materials, that exhibit a chiral mesophase wherein the mesogens are oriented with their main molecular axis twisted around a helix axis, like e.g. a chiral nematic (=cholesteric) or a chiral smectic phase. Materials exhibiting a cholesteric phase or chiral smectic C phase are preferred. Particularly preferred are materials exhibiting a cholesteric phase.
The term ‘film’ includes self-supporting, i.e. free-standing, films that show more or less pronounced mechanical stability and flexibility, as well as coatings or layers on a supporting substrate or between two substrates.
The term ‘beads’ includes, besides others and preferably spherical particles, rotational elliptic particles, egg shaped particles, e.g. particles which are rotationally symmetric to one axis, droplet shaped particles, pellets, but also less symmetrical particles like spheres with protrusions. Particles with cylinder symmetry and more or less spherical particles are especially preferred.
It was found that the molecular helices in the inventive polymer beads do not have to be perfectly ordered, but sufficiently ordered so that the beads show a significant degree of selectivity in reflection of light. In the foregoing and the following, this type of partial, incomplete or adequate orientation of the molecular helices in the inventive polymer beads is referred to as “partial ordering” or “partially ordered”.
SUMMARY OF THE INVENTION
One object of the present invention is polymer beads comprising an anisotropic polymer material with helically twisted structure.
Another object of the invention is a method of preparing polymer beads according to the present invention.
Another object of the invention is the use of polymer beads according to the present invention in reflective films, spraying or printing inks or as pigments, for optical or electrooptical, decorative or security applications.
Another object of the invention is a reflective film comprising one or more polymer beads according to the present invention in a transmissive binder.
Another object of the invention is a security marking or security device comprising one or more polymer beads or comprising a reflective film according to the present invention.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the invention are directed to
polymer beads with an average diameter from 0.5 to 100 &mgr;m, preferably from 1 to 20 &mgr;m, very preferably from 4 to 10 &mgr;m,
polymer beads wherein the anisotropic polymer material is a linear or crosslinked cholesteric side chain polymer,
polymer beads wherein the anisotropic polymer material forms a three-dimensional network,
polymer beads exhibiting selective reflection of circularly polarized light, with the central wavelength of reflection being in the range from 200 nm to 1000 nm,
polymer beads wherein the central wavelength of reflection is in the UV range, preferably from 200 nm to 380 nm,
polymer beads wherein the central wavelength of reflection is in the visible range, preferably from 380 nm to 720 nm,
polymer beads wherein the central wavelength of reflection is in the IR range, preferably from 720 nm to 1000 nm,
polymer beads wherein the reflected wavelength is substantially independent of the viewing angle,
polymer beads reflecting circularly polarized light of a single handedness, i.e. either right-handed or left-handed circularly polarized light,
polymer beads wherein the molecular helices in the liquid crystal polymer material exhibit partial ordering,
polymer beads obtainable by emulsion, suspension or dispersion polymerization of droplets comprising a polymerizable chiral liquid crystal material.
a reflective film comprising at least two different polymer beads,
a reflective film wherein said at least two different polymer beads r
Coates David
Greenfield Simon
Kuntz Matthias
Patrick John
Acquah Samuel A.
Merck Patent GmbH
Millen White Zelano & Branigan P.C.
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