Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Mica flake
Reexamination Certificate
1999-09-21
2001-09-18
Berman, Susan W. (Department: 1711)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Mica flake
C428S001400, C428S001310, C428S029000, C428S324000, C428S325000, C428S327000, C428S195100, C428S407000, C506S022000, C506S022000, C506S022000, C506S022000, C506S022000, C506S022000, C106S031150, C106S031270, C523S205000, C252S299010, C252S299100, C252S582000, C252S586000
Reexamination Certificate
active
06291065
ABSTRACT:
The invention relates to pigment flakes comprising a chiral liquid crystalline polymer material, said chiral liquid crystalline polymer material serving as carrier material or being coated onto a carrier material, characterized in that the pigment flakes comprise at least one dye that is chemically bound to the polymer.
The invention further relates to methods of manufacturing such pigment flakes and to the use of such pigment flakes in paints, printing inks, spray paints, cosmetic products or coloured plastics, optical elements and security applications.
Liquid crystals with chiral mesophases, in particular cholesteric liquid crystals, show extraordinary colour effects, like for example a high colour saturation, a wide colour range and iridescent appearance, due to their property of reflecting selected wavelengths of incident light. They have therefore been proposed for the preparation of pigments and inks.
In order to achieve good colour properties, a uniform and stable alignment of the liquid crystal molecules with the orientation of the helix axis parallel to the viewing direction is required. This can be achieved by preparing pigment flakes or platelets of a prealigned cholesteric polymer material.
Polymer pigment flakes are produced e.g. by coating a thin film of a cholesteric polymer material onto a substrate and aligning the material to achieve uniform orientation of the helical axis normal to the surface of the substrate. The film is then cured and ground to yield small flat flakes. The pigment flakes can be dispersed e.g. in a transparent binder for the use as inks or paints. The pigment flakes and inks can be used at room temperature without the need of further alignment.
Regarding the broad range of applications for chiral liquid crystal pigment flakes it is desirable for the expert to have available further pigments of this type which are easy to synthesize and fulfill the various requirements as described above.
Pigments comprising cholesteric liquid crystal polymers are described in prior art.
The European Patent 0 601 483 discloses cholesteric pigment flakes made of polysiloxanes with side chains comprising chiral cholesterol moieties and methacrylate groups as crosslinking agent
However, the preparation of pigments according to the EP 0 601 483 is complicated as it requires at least three subsequent reaction steps wherein polymerizable material is used. First, a linear or cyclic polysiloxane backbone is prepared, onto which then side chains bearing chiral moieties and polymerizable methacrylate groups are attached. Finally the polymerizable side chains are crosslinked upon preparation of the pigment flakes.
Thus, there is a demand for chiral liquid crystal pigment flakes that can be made in a very simple mamer which also enables.easy and direct control of the optical and mechanical properties of the product.
Another important aspect of the present invention is to provide new materials for the preparation of liquid crystal pigment flakes. Thus, it has been found that, when the specific optical properties of a chiral liquid crystal polymer are combined with those of a fluorescent dye, which can be chemically linked to the liquid crystal polymer, it is possible to achieve new pigments with extraordinary colour appearance.
The WO 95-32247 discloses interference pigments comprising liquid crystalline polymers which are made of mono- and difunctional nematic and chiral (meth)acrylates, epozades or vinyl ethers. However, there is no hint to polymers comprising fluorescent dyes.
Liquid crystal polymers comprising dichroic or fluorescent dyes have been described in prior art for the use as optical storage materials or fluorescent displays, e.g. in the EP 090 282, EP 171 045, EP 260 687, EP 399 279, EP 422 535 or EP 630 954. However, these documents only mention linear polymers. They also give no hint to use the materials for the preparation of pigments.
One of the aims of the present invention is to provide pigment flakes which have the properties and advantages as described above, and which can be prepared in a simple way that also enables to easily and directly control the properties of the product.
Another aim of the invention is to extend the pool of liquid crystalline pigments available to the expert. Other aims of the present invention are immediately evident to the person skilled in the art from the following detailed description.
The term ‘flakes’ as it is used throughout the claims and the description of this invention comprises small size particles with dimensions of 1 &mgr;m to 2 mm. These particles can be granules of a symmetric or unsymmetric shape as well as platelets having average lateral dimensions several times larger than the thickness, or mixtures of both platelets and granules. Platelet shaped pigment flakes are especially preferred.
The term ‘chiral liquid crystalline polymer’ as used throughout the claims and the description of this invention encompasses polymers that exhibit a chiral mesophase, like e.g. a chiral nematic (=cholesteric) or a chiral smectic phase. Polymers exhibiting a chiral nematic phase or a chiral smectic C phase are preferred. Particularly preferred are polymers exhibiting a chiral nematic phase.
The terms polymerizable or reactive mesogen, polymerizable or reactive mesogenic compound, polymerizable or reactive liquid crystal and polymerizable or reactive liquid crystalline compound as used in the foregoing and the following comprise compounds with a rodlike, boardlike or disklike mesogenic group. These mesogenic compounds do not necessarily have to exhibit mesophase behaviour by themselves. In a preferred embodiment of the present invention they show mesophase behaviour in mixtures with other compounds or after polymerization of the pure mesogenic compounds or of the mixtures comprising the mesogenic compounds.
One of the objects of the present invention are pigment flakes comprising a chiral liquid crystalline polymer material, said chiral liquid crystalline polymer material serving as carrier material or being coated onto a carrier material, characterized in that the pigment flakes comprise at least one dye that is chemically bound to the liquid crystalline polymer.
Preferred embodiments of the present invention relate to
Pigment flakes wherein at least one of the chemically bound dyes is a fluorescent dye.
Pigment flakes that additionally comprise one or more dyes or pigments which are not chemically bound to the liquid crystalline polymer material.
Pigment flakes wherein the liquid crystalline polymer material forms a three dimensional network.
Pigment flakes with a thickness from 0.1 to 100 &mgr;m and lateral dimensions from 1 to 1000 &mgr;m.
Pigment flakes wherein mica is used as carrier material.
Another object of the present invention are pigment flakes comprising a chiral liquid crystalline polymer material, said chiral liquid crystalline polymer material being coated onto a carrier material, wherein said pigment flakes are obtainable from a chiral polymerizable mesogenic material by a process comprising the following steps
a) coating a thin layer of the chiral polymerizable mesogenic material onto the carrier material,
b) aligning the chiral polymerizable mesogenic material in the coated layer into a uniform orientation,
c) polymerizing said chiral polymerizable mesogenic material by exposure to heat or actinic radiation.
Another object of the present invention are pigment flakes comprising a chiral liquid crystalline polymer material, said chiral liquid crystalline polymer material serving as carrier material, wherein said pigment flakes are obtainable from a chiral polymerizable mesogenic material by a process comprising the following steps
a) coating a thin layer of the chiral polymerizable mesogenic material onto a substrate or between two substrates,
b) aligning the chiral polymerizable mesogenic material in the coated layer into a uniform orientation,
c) polymerizing said chiral polymerizable mesogenic material by exposure to heat or actinic radiation,
d) optionally removing the substrate, or, if two
Coates David
Derow Stephan
Kuntz Matthias
Pfaff Gerhard
Poetsch Eike
Berman Susan W.
Merck Patent GmbH
Millen White Zelano & Branigan
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