Security elements and method of manufacture thereof

Abstract

A security element including: a first layer having a first surface; an array of image regions across the surface, each including at least first and second sub-regions; a first array of plasmonic nanostructures in or on the surface across the first sub-regions, defining in each a corresponding portion of a first image; a second array across the second sub-regions, defining in each a corresponding portion of a second image; wherein each sub-region has a respective average inclination and the average inclinations of the first sub-regions are such that the first image is displayed at least at a first viewing angle and those of the second sub-regions are such that the second image is displayed at least at a second viewing angle different from the first and the second image is substantially not or only partially displayed at least at the first angle. Also, a method of manufacturing the security element.

1 . A security element comprising:
 a first layer having a first surface;   an array of image regions across the first surface, each image region comprising at least a first sub-region and a second sub-region;   a first array of plasmonic nanostructures provided in or on the first surface across the first sub-regions, the first array of plasmonic nanostructures defining in each first sub-region a corresponding portion of a first image; and   a second array of plasmonic nanostructures provided in or on the first surface across the second sub-regions, the second array of plasmonic nanostructures defining in each second sub-region a corresponding portion of a second image;   wherein the first surface is arranged such that each sub-region has a respective average inclination and wherein the average inclinations of the first sub-regions are such that the first image is displayed at least at a first viewing angle and wherein the average inclinations of the second sub-regions are such that the second image is displayed at least at a second viewing angle different from the first viewing angle and such that the second image is substantially not displayed or only partially displayed at least at the first viewing angle.   
     
     
         2 . A security element according to  claim 1 , wherein the average inclinations of the first and second sub-regions are such that the first image is substantially not displayed or only partially displayed at least at the second viewing angle. 
     
     
         3 . A security element according to  claim 1 , wherein each first sub-region has substantially the same first average inclination. 
     
     
         4 . A security element according to  claim 1 , wherein each second sub-region has substantially the same second average inclination. 
     
     
         5 . A security element according to  claim 3 , wherein the first and second average inclinations differ by at least 45°. 
     
     
         6 . (canceled) 
     
     
         7 . (canceled) 
     
     
         8 . (canceled) 
     
     
         9 . A security element according to  claim 1 , wherein the average inclinations of the first sub-regions are such that the first image is displayed over a first viewing angle range and wherein the average inclinations of the second sub-regions are such that the second image is displayed over a second viewing angle range, wherein the first and second viewing angle ranges do not overlap or only partially overlap one another. 
     
     
         10 . (canceled) 
     
     
         11 . A security element according to  claim 1 , wherein the array of image regions comprises a regular array of image regions. 
     
     
         12 . (canceled) 
     
     
         13 . (canceled) 
     
     
         14 . A security element according to  claim 1 , wherein the array of image regions comprises a two-dimensional array of image regions. 
     
     
         15 . A security element according to  claim 1 , wherein the array of image regions comprises an array of elongate image regions, each elongate image region extending in a first direction along the first surface, the array of elongate image regions being arranged along a second direction along the first surface substantially perpendicular to the first direction along the first surface. 
     
     
         16 . A security element according to  claim 15 , wherein each elongate image region is divided lengthwise into at least the first and second sub-regions. 
     
     
         17 . (canceled) 
     
     
         18 . (canceled) 
     
     
         19 . (canceled) 
     
     
         20 . (canceled) 
     
     
         21 . (canceled) 
     
     
         22 . (canceled) 
     
     
         23 . (canceled) 
     
     
         24 . (canceled) 
     
     
         25 . (canceled) 
     
     
         26 . (canceled) 
     
     
         27 . (canceled) 
     
     
         28 . (canceled) 
     
     
         29 . A security element according to  claim 1 , wherein the plasmonic nanostructures of the first and/or second arrays of plasmonic nanostructures are discontinuously provided across the corresponding first and/or second sub-regions to provide image information of the corresponding first and/or second image. 
     
     
         30 . A security element according to  claim 1 , wherein the plasmonic nanostructures of the first and/or second arrays of plasmonic nanostructures vary in at least one of their shape, size and spacing across the corresponding first and/or second sub-regions to provide image information of the corresponding first and/or second image. 
     
     
         31 . A security element according to  claim 1 , wherein each first and/or second sub-region has a width on the first surface of 5 to 50 μm. 
     
     
         32 . A security element according to  claim 1 , wherein the first and/or second array of plasmonic nanostructures comprises a two-dimensional array of nanopillars, each nanopillar comprising a dielectric body topped by a continuous metal cover layer. 
     
     
         33 . A security element according to  claim 1 , wherein the first and/or second array of plasmonic nanostructures comprises a continuous metal base layer, a continuous dielectric layer on the continuous metal base layer and a two-dimensional array of metallic nanodiscs on the continuous dielectric layer overlapping the continuous metal base layer. 
     
     
         34 . A security element according to  claim 1 , wherein the first and/or second array of plasmonic nanostructures comprises a two-dimensional array of nanoholes, each nanohole comprising an aperture through a metal layer, the metal layer being arranged on a substrate. 
     
     
         35 . A security element according to  claim 1 , wherein the first and/or second array of plasmonic nanostructures comprises a one-dimensional or two-dimensional sub-wavelength grating structure formed in a dielectric layer, the one-dimensional or two-dimensional sub-wavelength grating structure being coated in a metal layer. 
     
     
         36 . (canceled) 
     
     
         37 . (canceled) 
     
     
         38 . A security element according to  claim 1 , wherein the first surface is arranged such that each first and/or second sub-region is substantially convex. 
     
     
         39 . (canceled) 
     
     
         40 . A security element according to  claim 1 , wherein the array of image regions comprises a two-dimensional array of image regions, wherein each image region is substantially convex along two orthogonal directions, and wherein each image region defines a two-dimensional array of convex sub-regions having different average inclinations, each set of sub-regions comprising a respective array of plasmonic nanostructures defining corresponding portions of a respective image, such that the different images are exhibited at different viewing angles in two orthogonal directions of tilt of the security element by the corresponding sub-regions in combination. 
     
     
         41 . (canceled) 
     
     
         42 . (canceled) 
     
     
         43 . A method of manufacturing a security element comprising:
 providing a first layer having a first surface   forming the first surface of the first layer so as to define an array of image regions across the first surface, each image region comprising at least a first sub-region and a second sub-region, wherein, each sub-region has a respective average inclination;   providing in or on the first surface across the first sub-regions a first array of plasmonic nanostructures defining in each first sub-region a corresponding portion of a first image; and   providing in or on the first surface across the second sub-regions a second array of plasmonic nanostructures defining in each second sub-region a corresponding portion of a second image;   wherein the average inclinations of the first sub-regions are such that the first image is displayed at least at a first viewing angle and wherein the average inclinations of the second sub-regions are such that the second image is displayed at least at a second viewing angle different from the first viewing angle and such that the second image is substantially not displayed at least at the first viewing angle.   
     
     
         44 . (canceled) 
     
     
         45 . (canceled) 
     
     
         46 . (canceled)