Structured surfaces that exhibit color by rotation
View Patent ↗An optically variable device is disclosed having a substrate with an array of pyramidal structures formed upon it or within it. The structures are coated with an optically variable color-shifting coating. Each of the structures form a pyramidal-like having at least three slanted faces and wherein one or more colors seen when viewing the pyramids vary as substrate is rotated at least 30 degrees about an axis orthogonal to the substrate. In order to see a color shift the device is rotated around the surface normal of the substrate, while keeping the angle of incidence to the light source the same, and keeping the viewing angle the same. Various forms of pyramids may be used, however pyramids with planar faces are most suitable.
1. An optically variable device comprising a substrate having an array of structures formed thereon, therein or supported thereby,
wherein said structures are coated with an optically variable color-shifting coating, wherein each of the structures forms a pyramidal structure and wherein each pyramidal structure has at least three slanted faces,
wherein a color shift is seen when viewing the array of the pyramidal shaped structures as the array of the pyramidal shaped structures is rotated at least 30 degrees about an axis orthogonal to the substrate,
wherein the color shift seen when rotating the array of the pyramidal shaped structures results from addition of substantially identical color shifts of individual pyramidal shaped structures.
2. An optically variable device as defined in claim 1 , where the dimensions of the pyramids are below eye resolution.
3. An optically variable device as defined in claim 1 , where the dimensions of the pyramids are less than 100 microns.
4. An optically variable device as defined in claim 1 , wherein spaces or structures that differ from the array of structures are provided between said array of structures so as to form visible indicia, sized discernable without magnification.
5. An optically variable device as defined in claim 1 , having visible indicia formed therein distinguishable from the array of pyramidal structures.
6. An optically variable device as defined in claim 2 , wherein the height to base ratio of at least 50% of the pyramidal structures is in the range of 0.4 to 1.4.
7. An optically variable device as defined in claim 2 , wherein a first plurality of the pyramidal structures are oriented in a first predetermined orientation and wherein a second plurality of the pyramidal structures are oriented in a second different orientation so that the first plurality of structures appear to be a different color than the second plurality of structures.
8. An optically variable device as defined in claim 1 , wherein a first group of contiguous pyramidal structures differs from a second group of contiguous pyramidal structures and wherein of the first and second groups forms visually distinguishable indicia.
9. An optically variable device as defined in claim 1 , wherein the slope of each of the faces of a pyramidal structure forms a different angle with the substrate.
10. An optically variable device as defined in claim 1 , wherein the slope of each the faces of a pyramidal structure forms a same angle with the substrate.
11. An optically variable device as defined in claim 2 , wherein the plurality of structures form an array of pyramidal structures and wherein the thickness of the optically variable coating on each of the faces is a same substantially uniform thickness.
12. An optically variable device as defined in claim 2 , wherein the thickness of the optically variable coating on adjacent faces of the pyramid is a different thickness.
13. An optically variable device as defined in claim 1 , wherein the coating is a single cavity Fabry-Perot structure.
14. An optically variable device as defined in claim 1 , wherein the coating is a multi-cavity Fabry-Perot structure.
15. An optically variable device as defined in claim 1 , wherein a plurality of pyramids are at least one of tetrahedron pyramids, square pyramids, pentagonal pyramid and a frustum pyramids with flat tops.
16. An optically variable device as defined in claim 15 , wherein at least one of the faces on at least a plurality of the pyramids have a diffraction grating formed therein.