Multichannel optically variable device
A security element, a security device including a security element and a method of manufacturing a security device. The element having focusing elements and image elements, the image elements are located in an object plane such that each image element is associated with one of the focusing elements, wherein the object plane includes at least first and second distinct subregions, and an image element within the first subregion is phase-displaced by a phase-displacement distance with respect to an image element within the second subregion, and wherein the first and second subregions produce first and second optically variable images or part-images.
1. A security element comprising:
a plurality of focusing elements; and
an object plane including at least four subregions, each subregion including a corresponding image element,
wherein each image element is associated with one of the focusing elements,
wherein each image element is phase-displaced by a phase-displacement distance with respect to image elements within other subregions,
wherein each of the at least four subregions correspond to pixels of a greyscale image having at least four grey levels, the grey levels determined by the phase displacements between the image elements in the subregions,
wherein each of the at least four subregions produces a positive state image at a first viewing angle and a negative state image at a second viewing angle, and different subregions display a switch between the positive and negative state images at different viewing angles,
wherein the subregions collectively produce a half-tone or continuous-tone image which appears to change contrast substantially continuously as the viewing angle changes.
2. The security element according to claim 1 , wherein the focusing elements are located a distance from the object plane which is less than the focal length of the focusing elements.
3. The security element according to claim 2 , wherein the distance t is such that the focal point width of the focusing elements in the object plane is substantially equal to the size of the image elements, or differs from the size of the image elements by a predetermined amount whilst still producing the first and second images or third and fourth images.
4. The security element according to claim 1 , wherein image elements of the subregions are phase-displaced by different distances relative to the associated focusing elements.
5. The security element according to claim 1 , wherein the focusing elements are on one side of a transparent or translucent substrate.
6. The security element according to claim 5 , wherein the image elements are on the opposite side of the transparent or translucent substrate.
7. The security element according to claim 1 , wherein the images of each subregion change brightness and/or contrast as the viewing angle is changed.
8. The security element according to claim 1 , wherein the image elements are gravure-printed elements.
9. The security element according to claim 1 , wherein the image elements are embossed, offset-printed, screen-printed or flexographically printed elements.
10. The security element according to claim 1 , wherein the image elements are line elements.
11. The security element according to claim 10 , wherein each of the line elements has a width which is substantially equal to or greater than half the width of the focussing elements.
12. The security element according to claim 1 , wherein the phase-displacement distance is less than or equal to half the width of the focusing elements.
13. The security element according to claim 1 , wherein the focusing elements are refractive or diffractive cylindrical lenses, or zone plates.
14. The security element according to claim 1 , wherein the focusing elements are refractive or diffractive part-spherical or polygonal-base microlenses.
15. A method of forming a security device, comprising:
providing a transparent or translucent substrate;
applying a plurality of focusing elements to a first surface of the substrate; and
applying a plurality of image elements to another surface of the substrate comprising an image surface, the image surface including at least four subregions, each subregion having a corresponding image element and each image element being associated with one of the focusing elements; and
phase-displacing each image element with respect to image elements within the other subregions,
wherein each of the at least four subregions correspond to pixels of a greyscale image having at least four grey levels, the grey levels determined by the phase displacements between the image elements in the subregions, wherein the subregions collectively produce a half-tone or continuous-tone image which appears to change contrast substantially continuously as the viewing angle changes, wherein each of the at least four subregions produces a positive state image at a first viewing angle and a negative state image at a second viewing angle, and different subregions display a switch between the positive and negative state images at different viewing angles.
16. The method according to claim 15 , wherein the focusing elements are applied by embossing.
17. The method according to claim 16 , wherein the focusing elements are embossed in a layer of radiation-curable ink applied to the first surface of the substrate.
18. The method according to claim 15 , wherein the image elements are applied by gravure printing.
19. The method according to claim 15 , wherein the image elements are applied by embossing, offset printing, screen printing or flexographic printing.
20. The method according to claim 15 , wherein image elements of the subregions are phase-displaced by different distances relative to the associated focusing elements.