Patent Description:
Color shifting inks, and other coating compositions containing reflective pigments in a carrier, are used for security and decorative purposes.

<CIT>, in the name of Yamamoto, referred to hereafter as '<NUM>, teaches an aqueous composition including glittering pigments, such as metal coated glass particles, coated with a water repellent material for improving glittering properties of the composition. The coating on the particles is produced by mixing uncoated particles with a solution of the water repellent material, shaking the mixture for <NUM> minutes, and subsequently drying the mixture. This process yields particles enveloped in the water-repellent coating.

Disadvantageously, images made using pigments disclosed in '<NUM> are sensitive to mechanical wear, because bonds between hydrophobic surfaces of the pigments and the aqueous carrier are weak, and the pigment particles easily shed from the surface of the carrier. <CIT> and <CIT> are also useful in understanding the present invention. <CIT> discloses a pigment which has a reflective layer surrounded by a sealant, consisting of a hydrophobic or a hydrophilic material. <CIT> discloses an uncoated asymmetrical reflective flake comprising a metal reflector layer, wherein the metal reflector layer has a concave side and a convex side opposite to the concave side, for reflecting light.

An object of the present invention "is to overcome shortcomings of the prior art and provide reflective flakes with improved reflectivity for use in a carrier medium, as well as a cost effective method of manufacturing such flakes.

Accordingly, the present invention relates to an asymmetrical reflective flake as defined in claim <NUM>.

Another aspect of the present invention relates to a method of manufacturing a plurality of flakes as defined in claim <NUM>.

Another aspect of the present invention provides a coating as defined in claim <NUM>. The present invention presents a flake having an asymmetrical feature. The flake has a first side and a second side and includes a metal reflector layer for reflecting light, wherein a first surface of the metal reflector layer is a concave surface, and a second surface of the metal reflector layer, opposite to the first surface, is a convex surface, for reflecting light, and a coating of a carrier-repellent material supported by the reflector layer, wherein the carrier-repellent material is coated on the first side and is absent from the second side, for orienting the flake in a carrier so that the flake rests upon the carrier having the first side at least partially out of the carrier and the second side immersed in the carrier. The flake can have an asymmetrical feature, such as a color shifting coating on a single surface of the reflector layer, comprising a dielectric layer on the reflector layer, and a coating of an absorber material on the dielectric layer, for providing a color shifting effect on the first side of the flake; wherein another surface of the reflector layer is absent at least the absorber material, and wherein the second side of the flake is absent the color shifting effect. Alternatively, the asymmetrical feature is a relief symbol on a single surface of tire reflector layer. Alternatively, the asymmetrical feature is an asymmetrical profile of the metal reflector layer, wherein one surface of the reflector layer is a concave surface having depression of at least <NUM>, and another surface of the reflector layer is a convex surface, for affecting direction of reflected light.

The invention will be described in greater detail with reference to the accompanying drawings which represent preferred embodiments thereof, wherein:.

Dispersed in a carrier thin-film pigment flakes form special-effect coatings. According to the instant invention, a thin-film layered flake includes a metal reflector layer having a reflectivity of at least <NUM>%, for providing high reflectivity of the coating. Also, the flake has a carrier-repellent layer of one side thereof for aligning the flake on a surface of the carrier with a predetermined side up, which is important for asymmetrical flakes.

An asymmetrical flake is a flake having an asymmetrical feature, such as a color shifting effect visible only on one side of the flake, or an image correctly reproduced on one side of the flake, whereas another side has a reverse image or no image at all. Alternatively, the asymmetrical feature is a profile of the layers forming the flake; by way of example: one surface of the reflector layer, as well as other layers, is a concave surface, and another surface of the reflector layer is a convex surface.

Conventional pigment flakes are usually symmetrical, such as the aforementioned Yamamoto's glittering pigments or flakes disclosed in <CIT>, referred to hereafter as '<NUM>. The conventional flakes orient randomly in a liquid carrier, as far as the thickness of the coating permits.

Random orientation of asymmetrical flakes in the carrier would decrease or even eliminate the benefits of making flakes asymmetrical. For example, among one-sided color-shifting flakes in a thin carrier coating, only approximately a half of the flakes would lie with a color-shifting side up. Moreover, among lens-shaped flakes in a thin carrier coating, some of the flakes would have a concave side up, and others - a convex side up, thus undesirably mutually canceling produced optical effects.

The flakes of the instant invention have a layer of a material repellent to the carrier on a single side thereof, the side designed to reflect light impinged on the coating. Coated on an object within a liquid carrier, these flakes spontaneously self-assemble to rest upon the carrier having the carrier-repellent side at least partially out of the carrier and another side immersed in the carrier.

The carrier-repellent material is a hydrophobic material for flakes used in a water-based carrier, or an oleophobic material for flakes in an oil-based carrier or in another organic carrier. Generally, the choice of the carrier-repellent material depends on the type of the carrier, so that a carrier-repellent surface is not-wettable by the carrier, that is a contact angle between the surface and the liquid carrier is greater than <NUM>°.

The flake of the instant invention preferably has a diameter in the range of <NUM> micron to <NUM> microns and a thickness between <NUM> and <NUM> microns. The thickness is substantially constant, so that variations of the thickness are not higher than <NUM>%.

In the instant invention, a microsculptured reflector flake has a concave side and a convex side opposite thereto, wherein only the concave side is coated with a carrier repellent material. With reference to <FIG>, an object <NUM> is printed with a water based ink coating <NUM> having microsculptured flakes dispersed therein, such as a flake <NUM> consisting of a reflector layer <NUM>, a hydrophobic layer <NUM> supported by the reflector layer <NUM>, and an optional protective layer <NUM>, by way of example made of MgF<NUM>. The layer of a hydrophobic material <NUM> deposited on the concave surface of the flake <NUM> forces it to flip in the wet ink vehicle <NUM> in such a fashion, that the concave surface of the flake <NUM> faces away from the object <NUM>. By way of example, the hydrophobic material is scandium fluoride or WRI Patinal® manufactured by Merck.

The microsculptured flake can also be embossed in a such way that it bears an image or a symbol on its surface, such an embossed flake <NUM> in <FIG>.

Examples of a suitable reflective material for the reflector layer <NUM> include aluminum, silver, iron, tantalum, indium, rhenium, copper, silver, gold, platinum, palladium, nickel, cobalt, niobium, chromium, tin, and reflective alloys. Alternatively, the reflector layer <NUM> is a reflective thin-film optical stack.

Optionally, the flake <NUM> includes additional layers, e.g. for modifying the color of light reflected by the reflector layer <NUM>.

With reference to <FIG>, the flake <NUM> preferably has a diameter D in the range of <NUM>-<NUM> microns and a thickness of the flake h in the range of <NUM>-<NUM> microns. For the purpose of this application, a concave surface is understood as having a depression of a depth d in the range of <NUM> - <NUM> microns, or having a ratio d/D between <NUM> - <NUM>, or having a radius of curvature R in the range of <NUM> microns - <NUM>. Accordingly, a convex surface is understood as having an elevation within the same ranges.

The two-dimensional shape of the flake shown in <FIG> is a square with sides in the range from <NUM> x <NUM> microns to <NUM> x <NUM> microns. Alternatively, the microsculptured flakes of the instant invention can have other than a square two-dimensional shapes, such as a hexagon shown in <FIG>, a diamond, etc..

The concave and convex surfaces of the flakes can be shaped so as to be a portion of a spherical surface or a portion of a quasi-spherical surface, a portion of a parabolic or quasi-parabolic surface, or a trough-shaped portion of a cylindrical surface, etc. The partial spherical and quasi-spherical shaped flakes have an average radius of curvature R (see <FIG>) in the range of <NUM> microns to <NUM>. and variations in the radius of curvature not higher than <NUM>%. The choice of radius R depends on the flake size and the thickness of the ink or paint coating. A trough-shaped flake, that is, a flake that conforms to a portion of a cylinder, is shown in <FIG>; its surface is curved only along the axis <NUM>, and not curved along the other axis <NUM>.

The microsculptured flakes of the instant invention can be either completely curved or have a flat area adjacent to a depression or elevation. In one embodiment shown in <FIG>, a concave flake surface is segmented, wherein a depression <NUM> is adjacent to a substantially flat region <NUM> having an average peak-valley distance deviation of no more than <NUM>. Accordingly, the opposite side of the flake is a segmented convex surface having a flat region adjacent to an elevation.

In reference to <FIG>, the concave and convex flake surfaces can have a form of a pyramid. By way of example, <FIG> shows a flake having a square-based pyramid elevation surrounded by a flat adjacent region.

In one embodiment of the instant invention, the reflector flake has the convex side coated with die carrier repellent material. Such flakes self-assemble on the surface of the carrier with the convex side up thus forming a light-scattering surface.

According to another embodiment of the instant invention, taggant flakes having a relief image on the surface thereof are coated with a carrier-repellent material on one side. The taggant flakes, also referred to as taggent flakes, are disclosed in <CIT>, referred to hereafter as '<NUM>. By the way of example, square taggant flakes have the letters "JDSU" in the center thereof, as shown in <FIG>. When an object, for example a paper document, is printed with water-based ink containing such taggant flakes without a hydrophobic coating, the flakes orient randomly, as far as the thickness of the coating permits, sec <FIG>. As a result, the "JDSU" image is visible on one portion of the flakes, and an opposite image - on another portion of the flakes. The hydrophobic coating on one side of the taggant flakes aligns the flakes on the surface of a water-based carrier with the "JDSU" image the top surface of the flakes thus readable to the observer as shown in <FIG>.

According to one embodiment of the present invention, an asymmetrical color shifting flake <NUM> shown in <FIG> includes a Fabry-Perot interference filter consisting of a reflector layer <NUM>, a dielectric layer <NUM> on one side of the reflector layer <NUM>, and an absorber layer <NUM> on the dielectric layer <NUM>, for providing a color shifting effect on one side of the flake <NUM>. Another side of the flake <NUM> does not provide any color shifting effect since there is no absorber layer supported by said other side of the reflector layer <NUM>. Optionally, a protective dielectric layer (not shown) is supported by the second side of the reflector Layer <NUM>. The flake <NUM> includes a carrier-repellent layer <NUM> supported by the absorber layer <NUM>.

Optionally, the second side of the flakes of the instant invention is coated with a hydrophilic or oleophilic material.

In another embodiment, an asymmetrical color shifting flake has two dielectric layers, similar to the dielectric layer <NUM>, on both sides of the reflector layer <NUM>, and two absorber layers, similar to the absorber layer <NUM>, on the dielectric layers, for providing a color shifting effect on both sides of the flake, and a carrier-repellent coating on a single side of the flake.

With reference to <FIG>, an object <NUM> is printed with an ink coating <NUM>, including a water-based carrier and flat flakes dispersed therein, such as a flake <NUM>. The flake <NUM> consists of a reflector layer <NUM> and a hydrophobic layer <NUM> made of a hydrophobic material repellent to the water-based carrier, and supported by the reflector layer <NUM>. The hydrophobic layer <NUM>, deposited on a first surface <NUM> of the flake <NUM>, forces the flake to self-align in the wet ink <NUM> so that the first surface <NUM> of the flake <NUM> faces away from the object <NUM> and a second flake surface <NUM> is immersed in the carrier.

Suitable materials for the spacer layer includes zinc sulfide (ZnS), zinc oxide (ZnO), zirconium oxide (ZrO2), titanium dioxide (TiO2), diamond-like carbon, indium oxide (In203), indium-tin-oxide ("ITO"), tantalum pentoxide (Ta2O5), ceric oxide (CeO2), yttrium oxide (Y2O3), europium oxide (Eu2O3), iron oxides such as (II)diiron(III) oxide (Fe3O4) and ferric oxide (Fc2O3), hafnium nitride. (HfN), hafnium carbide (HfC), hafnium oxide (HfO2), lanthanum oxide (La2O3), magnesium oxide (MgO). neodymium oxide (Nd2O3), praseodymium oxide (Pr6 OH), samarium oxide (Sm2O3), antimony trioxide (Sb2O3), silicon (Si), silicon monoxide (SiO), germanium (Ge), selenium trioxide (Se2O3), tin oxide (SnO2), tungsten trioxide (WO3), silicon dioxide (SiO2), aluminum oxide (A1203), metal fluorides such as magnesium fluoride (MgF2), aluminum fluoride (A1F3), cerium fluoride (CeF3), lanthanum fluoride (LaF3), sodium aluminum fluorides (e.g., Na3AIF6 or Na5A13F14), neodymium fluoride (NdF3), samarium fluoride (SMF3), barium fluoride (BaF2), calcium fluoride (CaF2), lithium fluoride (LiF), and combinations thereof, and organic monomers and polymers including dienes or alkenes such as acrylates (e.g., methacrylate), perfluoroalkenes, melanin and its derivatives, combinations thereof, and the like.

Examples of suitable absorber materials include chromium, nickel, iron, titanium, aluminum, tungsten, molybdenum, niobium, combinations, compounds or alloys thereof, such as INCONEL® (Ni-Cr-Fe), metals mixed in a dielectric matrix, or other substances that are capable of acting as a uniform or selective absorber in the visible spectrum. Alternatively, the absorber can also be a dielectric material such as an iron oxide (e.g., Fe2O3), silicon monoxide (SiO), chromium oxide (Cr2O3), carton, titanium sub-oxide (TiOx), metal carbides, metal carbo-nitrides, combinations thereof, and the like. Metal absorber layers are generally deposited in a layer that is sufficiently thin so as to allow substantial transmission of light through the absorber layer.

In another embodiment shown in <FIG>, a flat reflector flake <NUM> differs from the flake <NUM> shown in <FIG> by having additional layers <NUM> and <NUM> on one or both sides of the reflector layer <NUM>. Each of the additional layers <NUM> and <NUM> may be a protective layer, and/or a colored layer, by way of example made of MgF<NUM> or any of chemically stable oxides, fluorides, and polymers, for modifying color of the light reflected by the reflector layer <NUM>.

The flakes of the instant invention are manufactured by vacuum deposition of a desirable thin-film multi layered stack onto a substrate. Suitable substrates may be formed from polymeric materials, such as PET, or metals. The methods of thin film deposition are known in the art and include methods of vacuum condensation or chemical vapor deposition (CVD), spraying, dip-coating, etc..

Manufacturing of asymmetrically shaped flakes, such as described above with references to <FIG>, requires a non-flat substrate, having the surface thereof embossed with a predetermined three dimensional shape, as taught in '<NUM> and <CIT>, referred to hereafter as '<NUM>. By way of example; the flakes shown in <FIG> are manufactured using a substrate having tranches forming a frame on the surface thereof and a concave or convex region within the frame; and the flakes shown in <FIG> are manufactured using a substrate with a relief symbol within the frame. The thin film stack including a reflector layer and a carrier-repellent layer, is molded, for example, by vacuum deposition a reflecting material and other materials onto the substrate.

In one embodiment of the instant invention, the layer of the carrier-repellent material is the last layer of the thin film stack deposited onto the substrate prior to stripping off the flakes. The method of manufacturing of the flakes includes the following steps: providing a substrate, optionally structured as described above, depositing the metal reflective material to form the metal reflector layer over the substrate, and then coating the carrier-repellent material over the metal reflector layer. Optionally, layers of other materials are deposited on the substrate before deposition of the reflector layer, such as a release layer made of a water-soluble or solvent-soluble material, and/or protective layer made of a chemically stable non-soluble material. Optionally, layers of other materials are deposited on the metal reflector layer before deposition of the carrier-repellent material, such as the dielectric layer <NUM> and the absorber layer <NUM> shown in <FIG>.

Alternatively, the layer of the carrier-repellent material is deposited directly on the substrate, or onto a release layer. The release layer may be an organic solvent soluble or water soluble coating such as sodium chloride, cryolite, acrylic resins, cellulosic propionates, (polyvinyl pyrrolidine) polyvinyl alcohol or acetate, and the like. All other layers forming the flake, including the metal reflector layer, arc deposited over the release layer. Optionally, one or more layers of other materials are deposited on the layer of the carrier-repellent material, before deposition of the metal reflector layer, by way of example, the dielectric layer <NUM> and the absorber layer <NUM> shown in <FIG>. The release material dissolves in the carrier during the stripping procedure.

Organic or inorganic carrier-repellent material can be deposited by vacuum evaporation or by immersion of the coated side of the substrate into a chemical bath prior to stripping flakes off the substrate. The evaporation substance Patinal® by Merck is an example of a vacuum deposited organic material. Scandium fluoride is an example of an inorganic vacuum deposited hydrophobic material. DuPont Zonyl® is one example of many fluorosurfactant materials for a dip coating of the substrate with deposited thin film stack. Other materials such as different perfluoropolymers are also suitable for die surface treatment of the substrate with deposited thin film stack.

In one embodiment, the substrate with the deposited thin film stack is coated by dipping into a carrier-repellent solution as illustrated by <FIG>. In reference to <FIG>, a concave-shaped substrate <NUM> has a post-coated multi-layered composition on its surface. The substrate <NUM> is embossed with concave shapes <NUM> of a radius C surrounded with flat regions <NUM> and separated by deep trenches <NUM>. The substrate <NUM> is coated with a multi-layered stack <NUM> and subsequently immersed into a chemical bath with a carrier-repellent solution <NUM> allowing a hydrophobic material to be deposited on the concave side of the potential flakes. The deep trenches <NUM> allow the deposited film structure to break here as described in '<NUM>.

Fig- <NUM> is an image of the embossed substrate <NUM> prior to separating the potential flakes. The substrate <NUM> has multiple concave areas <NUM>,'flat regions <NUM>, and trenches <NUM> to break the coating into the potential flakes having a hexagonal two-dimensional form.

For deposition a hydrophobic material on the convex side of the potential flakes, a convex embossed substrate <NUM> shown in <FIG> is coated with the thin-film stack <NUM> and immersed in the bath for the carrier-repellent deposition.

By way of example, the substrates <NUM> and <NUM> are made of polyester; the thin film stack <NUM> is a MgF<NUM>/Al/MgF<NUM> structure, and the carrier-repellent material is WRI Patinal® manufactured by Merck KGaA.

Subsequently, the deposit is stripped off the substrate and separated into flakes with a single carrier-repellent side.

It has been found that coating of the flake surface with a carrier-repellent material does not affect the surface smoothness or the surface reflectance of a single flake, and improves the color performance of a coating with multiple flakes in a carrier.

The following example illustrates the color performance of an ink having asymmetrical color-shifting flakes therein.

Two different types of flakes have been prepared. For the first type, an asymmetrical layered structure MgF<NUM>/Al/ MgF<NUM>/Cr was deposited onto a flat polyester substrate, stripped off, and ground to the averaged size of <NUM> microns. The total thickness of the flake was close to one micron. One side of a resulting flake with the layer of chromium had the magenta color changing to gold with the tilt of the sample up to <NUM>°. The opposite side of the flake had a bright silver color.

Flakes of the second type had the same structure MgF<NUM>/Al /MgF<NUM>/Cr/ with a thin layer of WRI Patinal® on the top of the chromium layer. The WRI Patinal® did not change appearance of the magenta/gold color of this particular side of the flake.

Flakes of each type were mixed with transparent Sericol Rotary Screen Ink vehicle in the quantity of <NUM> wt. % and printed on the paper through a <NUM> mesh silk screen, transported to the UV lamp and cured in the UV light until solidifying. The color travel of the prints was analyzed with a Zeiss goniospectrophotometer.

Results of the analysis are shown in a CIELab color plot in <FIG>. The curve <NUM> corresponds to the sample without a hydrophobic coating containing the flakes of the first type. The color travel of this curve is very small because the aluminum side of the flakes greatly reduces chroma of the ink. This is a well known fact. The curve <NUM> corresponds to the sample with the hydrophobic coating where WRI Patinal® was deposited on the top of the magenta/gold side of the flake. Color travel of this flake is very large, because the flakes in the carrier flipped so that the colored side appeared on the surface of the ink.

Two portions of gold-to-green color-shifting flakes were prepared as described above, except with the MgF<NUM> thickness being increased; one portion of (he flakes had a carrier-repellent coating, and another portion of the flakes had no carrier-repellent coating. Difference in the color travel of the color-shifting pigment flakes without and with a layer of the carrier-repellent material is shown in <FIG>, where a gold/green color travel of a conventional pigment is shown by a curve <NUM>, and a color travel of a pigment flake having one side coated with a carrier-repellent material is shown by a curve <NUM>. These two portions of pigment flakes were mixed with ink vehicle and printed on a paper substrate as described in above.

Dynamic Color Area (DCA) described, for example, in <CIT>, is a measure of a dynamic "colorfulness" of a light interference pigment, hence useful in comparing color shifting performances of gonioapparent materials. <FIG> represents DCA values of the two pigments illustrated by <FIG>: a bar <NUM> is the DCA value of the conventional pigment flake, and a bar <NUM> is the DCA value of the pigment flake having one side coated with a carrier-repellent material, which is about <NUM> times higher than the DCA of the conventional pigment, thus illustrating better color shifting performance of the flake coated with the carrier-repellent material in accordance to the instant invention.

Flakes of the instant invention tend to self-assemble on the surface of the carrier, to appear, at least partially, out of the carrier, and parallel to each other, reflecting incident light in the same direction and providing high reflectance of prints with metallic reflective pigments and a high chroma of prints with color-shifting pigments. Some flakes may not reach the surface of the carrier, for example being obstructed by other flakes. It is desirable to chose the concentration of the flakes in the carrier and the thickness of the coating so that at least <NUM>% of the flakes rest upon the carrier having the first side up.

It has been proved experimentally, see <FIG>, that a coating with the flakes having carrier-repelling material on one side, has the reflectivity higher than a coating with conventional symmetrical color shifting flakes such as disclosed in '<NUM>. The difference in reflectivity is due to the fact that in the carrier, the flakes of the instant invention self-align so that they rest at the surface of the carrier parallel to the substrate and to each other having the first color shifting side at least partially out of the carrier and the second, non color shifting, side immersed in the carrier and turned away from the observer. The present invention provides a mechanism for orienting flakes with a predetermined side up, or flipping, thus enabling multiple application requiring asymmetrical flakes, for example parabolic micro reflectors or microtaggants bearing a particular readable relief symbol.

In comparison to the glittering pigments disclosed in '<NUM>, the flakes of the instant invention do not shed from the carrier, since the second side of the flake is not hydrophobic.

Claim 1:
An asymmetrical reflective flake (<NUM>) having a first side and a second side, for use in a carrier, the asymmetrical reflective flake comprising:
a metal reflector layer (<NUM>), wherein a first surface of the metal reflector layer is a concave surface, and a second surface of the metal reflector layer, opposite to the first surface, is a convex surface, for reflecting light; and
a coating of a carrier-repellent material supported by the metal reflector layer, wherein the carrier-repellent material is on a first side of the flake, and wherein a second side of the flake is absent the carrier-repellent material, the carrier-repellent material being on the first side of the flake for self-assembling the flake in the carrier so that the flake rests upon the carrier having the first side at least partially out of the carrier and the second side immersed in the carrier