Mixture of magnetically orientable color shifting flakes and non-magnetically orientable color shifting flakes exhibiting a common color

Pigment flakes are blended together wherein some are magnetically alignable and exhibit a color shift from a first color to a second color with a change in viewing angle; and some are pigment flakes which exhibit a color shift from the first color to a third color or vice versa with a change in viewing angle, wherein the first, second and third colors are three different colors. The flakes are coated upon a substrate and magnetically alignable flakes are magnetically aligned. The non-magnetically alignable flakes are not aligned by the magnetic field and lie flat upon the substrate they are coated on. By judiciously selecting the angle upon which the magnetic flakes are oriented, an effect is created whereby an observer sees a color shift from a first color to a second or a first color to a third, when orienting the substrate by tilting it at different particular angles. The coated substrate can be used in security applications such as on currency or secure instruments.

FIELD OF THE INVENTION

This invention relates to color shifting pigment and coatings, particularly the type used on banknotes, labels, security documents and those requiring an appealing coating or a security color shift coating.

BACKGROUND OF THE INVENTION

Color shifting coatings are well known and can be found on some United States banknotes and on banknotes of many other countries. Although printed or hot stamped diffractive structures are color changing and are sometimes said to be color shifting, this invention relates primarily a color shift that occurs through thin film interference effects; that is, from multilayered thin film coatings having a reflector, a spacer and an absorber or a stack of interference layers. U.S. Pat. Nos. 6,236,510, 5,570,847, and 5,279,657 are some exemplary patents in the name of Roger Phillips where thin film interference flakes are disclosed. U.S. Pat. Nos. 7,258,900, 7,047,883 and 7,517,578 in the name of Raksha et al. disclose magnetically alignable thin film pigment flakes and methods of aligning such flakes. All of the abovementioned patents and applications are incorporated herein by reference, for all purposes.

United States patent application US 20080069979, incorporated herein by reference, entitled “Security image coated with a single coating having visually distinct regions” discloses a security image which is formed from flakes having a first color with flakes having a second different color mixed within a carrier uniformly. The flakes having the second color are magnetically orientable and the flakes having the first color are non-magnetic and do not align or orient in a magnetic field. By exposing at least a single coated region to a magnetic field that is substantially orthogonal to the substrate upon which the coating of flakes is coated, a visible region having the first color is provided as the magnetic flakes are upstanding and the non-magnetic flakes are lying flat upon the substrate. In another region where there is no magnetic field applied, a visible region having a third perceived color that is different from the first color or the second color seen. Although interesting effects are provided using this method, the instant invention affords a flexibility in which way the coating is viewed or from where the incident light is located.

This invention takes advantage of the fact that magnetic and non-magnetically oriented flakes behave differently in the presence of a magnetic field. Furthermore carefully selecting goniochromatic characteristics of the flakes and the angle of the magnetic field, yields a very useful security coating which exhibits a color shift when tilted from East to West or North to South; and wherein the security coating exhibits a different color when tilted from East to West or North to South, and wherein the same color is exhibited when the coating is viewed at normal angle.

It is an object of this invention to produce a coating that has two different color shifting effects when observed from two different directions and the same color when observed at normal angle.

It is an object of this invention to produce a color shift between a first and second color when tilted about a first axis, and that produces a color shift from the first to a third color when tilted about an axis orthogonal to the first axis, wherein the first, second and third colors are three visually distinguishable different colors.

It is a further object of this invention to use a mixture of magnetically oriented magnetic color shifting flakes and non-magnetic non-oriented color shifting flakes wherein a color of the flakes is the same at normal incidence.

It is a further object of this invention to use a mixture of only two different flake types arranged and fixed in a particular orientation upon a substrate, to yield a color shift from a first to a second color, or from the first to a third color depending upon the tilt of the substrate.

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention there is provided a blend of pigment flakes comprising a first plurality of the magnetically alignable pigment flakes which exhibit a color shift from a first color to a second color with a change in viewing angle; and

a second plurality of flakes having a color shift from the first color to a third color or vice versa with a change in viewing angle, wherein the first, second and third colors are three different colors.

In accordance with another aspect of the invention there is provided a coating comprising blend of magnetically aligneble magnetic and non-magnetic flakes, wherein the magnetic flakes have a color shift through thin film interference with a change in viewing angle from a first color to a second color and wherein the non-magnetic flakes have a color shift through thin film interference with a change in viewing angle from a third color to the first color.

In accordance with an aspect of the invention there is provided a blend of pigment flakes comprising a first plurality of non-magnetic pigment flakes (aligned parallel to the substrate) which exhibit a color shift from a first color to a second color with a change in viewing angle; and

a second plurality of magnetic flakes magnetically aligned at the angle to the

substrate having a color shift from the first color to a third color or vice versa with a change in viewing angle, wherein the first, second and third colors are three different colors.

DETAILED DESCRIPTION

This invention provides a mixture of two types of flakes; magnetically orientable flakes and non-magnetically orientable flakes. The flakes have a common characteristic. The two types of flakes are thin film interference color shifting flakes which shift from a same color to a different color when tilted with respect to the observer or when the angle of incident light is changed to affect a color shift. Therefore, when the mixture of flakes are coated upon a substrate and a magnetic field is applied so as to align the magnetic flakes in a preferred alignment, as the substrate is tilted from East to West, there is a color shift from a first color to a second; and as the substrate is tilted from North to south, there is a color shift from the second color to a third color, wherein the first, second and third colors are different colors which can be visually distinguished.

The present invention uses a blend of magnetic and non-magnetic pigment particles as well. The magnetic particles are multi-layer flakes, which have a layer of magnetically alginable material. The blend of magnetic and non-magnetic flakes is dispersed in a binder, preferably an organic binder and can be printed as shown inFIG. 2on a flexible or non-flexible substrate. The ink or paint202is printed on the top of the substrate201. The ink or paint contains magnetic particles203and non-magnetic pigment particles204. The particles can be purposefully shaped or may be random shaped particles. The flakes can be as small as 1 micron across and as large as 100 microns across a surface thereof. In further forming the coating upon a substrate an external magnetic field is applied to the printed article in the direction205; and, all of the magnetic pigment particles orient themselves parallel to the field and to each other in a direction of the field at the angle α206to the substrate and to the surface of non-magnetic particles. The non-magnetic particles204are unaffected by the magnetic field and become oriented parallel or close to parallel to the substrate201. As a result of the different spatial position of the magnetic and non-magnetic particles in the ink or paint, the magnetic and non-magnetic particles reflect incident light in a different direction with respect to an observer as it is illustrated inFIGS. 3 and 4.

For the purposes of illustration only the non-magnetically alignable flakes are octagonal shaped flakes and the aligned flakes203and205are square shaped. Furthermore, only for the purposes of illustration to visibly differentiate between the two types of flakes a checkerboard and dotted pattern on used on the magnetic and non-magnetic flakes respectively. In reality the flakes are not patterned in this way.

For the purposes of illustration only the magnetically alignable flakes are hexagonal shaped flakes and the aligned flakes203and205are square shaped. Furthermore, only for the purposes of illustration to visibly differentiate between the two types of flakes a checkerboard and dotted pattern on used on the magnetic and non-magnetic flakes respectively. In reality the flakes are not patterned in this way.

Turning now toFIG. 3, when light rays from the distant light source301at location having coordinates XYZ with X=0 impinge upon the surface of the non-magnetic platelets at the region0they are reflected back in the direction303to a location having coordinates XYZ where X=0 and Y<0. Projection vectors of incident and reflected rays of light at the XY coordinates are at points A and B respectively.

Referring now toFIG. 4the light from the same light source reflects differently from the magnetically aligned particles than it did from the non-magnetic particles shown inFIG. 3. The light from the source401with the same coordinates XYZ with X=0 comes to the region0of the printed article along the direction402and reflects from counterclockwise tilted magnetic platelets in the direction403with coordinates XYZ where Y=0 and X<0. Projection vectors of incident and reflected rays of light at the XY coordinates now are at points A and C respectively.

To reduce the influence of colors of one pigment, for example the magnetic pigment on the colors of another pigment, for example the non-magnetic pigment, one common color is used in the blend pigments. An example of these pigments is illustrated inFIG. 1. They are magnetic gold to green shifting pigment101and non-magnetic green to blue shifting pigments102, wherein green is the common color shared by both pigments. The magnetic pigment101has a green color when its particles are magnetically oriented at 45° to non-magnetic particles. Non-magnetic green to blue pigment102has green color at 0° because it is parallel to the substrate. Both pigments display the same color at the normal angle of observation of the article or substrate as illustrated inFIG. 5. Most of the incoming light rays are reflected back by non-magnetic color-shifting pigment particles, that is the octagonal platelets with polka dotted pattern exhibiting green color. The magnetically oriented particles are also exhibit a green color because they were aligned at 45° to the substrate. When the article is tilted away from the observer as illustrated inFIG. 6it is rotated along the X-axis inFIG. 3. The color of non-magnetic particles, the hexagon with polka dotted pattern particles changes to blue according to the curve102inFIG. 1. As was mentioned earlier, the polka dotted and checkerboard effects in the figures are merely illustrative ways of differentiating the two types of flakes in the figures. The flakes do not actually have these patterns.

To reduce the influence of colors of one pigment, for example the magnetic pigment on the colors of another pigment, for example the non-magnetic pigment, one common color is used in the blend pigments. An example of these pigments is illustrated inFIG. 1. They are magnetic gold to green shifting pigment101and non-magnetic green to blue shifting pigments102, wherein green is the common color shared by both pigments. The magnetic pigment101has a green color when its particles are magnetically oriented at 45°to non-magnetic particles. Non-magnetic green to blue pigment102has green color at 0° because it is parallel to the substrate. Both pigments display the same color at the normal angle of observation of the article or substrate as illustrated inFIG. 5. Most of the incoming light rays are reflected back by non-magnetic color-shifting pigment particles501, that is the hexagonal platelets with polka dotted pattern exhibiting green color. The magnetically oriented particles are also exhibit a green color because they were aligned at 45° to the substrate. When the article is tilted away from the observer as illustrated inFIG. 6it is rotated along the X-axis inFIG. 3. The color of non-magnetic particles, the hexagon with polka dotted pattern particles changes to blue according to the curve102inFIG. 1. As was mentioned earlier, the polka dotted and checkerboard effects in the figures are merely illustrative ways of differentiating the two types of flakes in the figures. The flakes do not actually have these patterns.

When the article is tilted along the Y-axis to the left as illustrated inFIG. 7magnetic particles oriented with their planes coincident with the observation direction become invisible. However, when the article is tilted to the right as shown inFIG. 8magnetic particles, squares with the checker pattern become highly visible and the article switches to a gold color.

Turning now toFIGS. 9a, through10bmagnetic gold to green and non-magnetic green to blue were used in this exemplary embodiment. Visual appearance of this combination of pigments can be seen while viewingFIGS. 9athrough10b. The green color of the print, containing these pigments, can be seen at normal angle of observation as illustrated inFIG. 9a. When the sample is tilted away from the observer as inFIG. 9bthe color appears as blue. Tilting back to the normal angle restores the green color as inFIG. 10a. Tilting the sample to the right shifts color to gold is shown inFIG. 10b.

The blend of color shifting pigments of this invention can be used on banknotes, labels, security documents and those requiring an appealing coating or a security color shift coating.