Security document with embossed multi-level doe

Abstract

A security document comprising a substrate including at least one region of transparent or translucent plastics material forming a window or half-window area, and a security device integrated into the window or half-window area, wherein the security device is formed from an embossed radiation curable ink, the security device including a diffractive structure comprising a multi-level diffractive optical element (DOE).

1 . A security document comprising a substrate including at least one region of transparent or translucent plastics material forming a window or half-window area, and a security device integrated into the window or half-window area, wherein the security device is formed from an embossed radiation curable ink, the security device including a diffractive structure comprising a multi-level diffractive optical element (DOE). 
     
     
         2 . A security document according to  claim 1  wherein the multi-level DOE is a binary DOE having two phase levels. 
     
     
         3 . A security document according to  claim 1  wherein the multi-level diffractive optical element includes a numerical-type diffractive optical element (DOE). 
     
     
         4 . A security document according to  claim 1  wherein the multi-level DOE has more than two phase levels. 
     
     
         5 . A security document according to  claim 4  wherein the multi-level DOE has up to 16 phase levels. 
     
     
         6 . A security document according to  claim 1  wherein at least some of the phase levels store encrypted data. 
     
     
         7 . A security document according to  claim 1  wherein the multi-level DOE is an asymmetric diffractive optical element. 
     
     
         8 . A security document according to  claim 1  wherein the diffractive optical element is a transmission DOE. 
     
     
         9 . A security document according to  claim 1  wherein the embossed security device includes at least two different embossed relief structures embossed into the same side of the radiation cured ink, each forming a different security element integrated within the same area to form a composite security device, wherein at least one of the embossed relief structures is a multi-level DOE. 
     
     
         10 . A security document according to  claim 9  wherein the composite security device includes another diffractive relief structures. 
     
     
         11 . A security document according to  claim 9  wherein the composite security device includes a non-diffractive relief structure forming a security element. 
     
     
         12 . A security document according to  claim 1 , wherein the security device includes a light transmissive security element. 
     
     
         13 . A security document according to  claim 1 , wherein the document is a banknote. 
     
     
         14 . A method of manufacturing a security document comprising the steps of:
 providing a substrate including at least one region of transparent plastics material forming a window or half-window area;   applying a radiation curable ink to at least one side of the substrate in at least the window or half-window area; and   embossing the ink and curing with radiation to form a security element within the window or half-window area, wherein the embossed ink forms a security device including a diffractive structure comprising a multi-level diffractive optical element.   
     
     
         15 . A method according to  claim 14  wherein the at least one region of transparent plastics material forms a window, and wherein an opacifying layer is applied to each side of a transparent polymeric substrate with each opacifying layer omitted in the region forming the window. 
     
     
         16 . A method according to  claim 14  wherein the one region of transparent plastics material forms a half-window, and wherein at least one opacifying layer is applied to one side of the substrate to completely cover said one side and at least one opacifying layer is applied to the opposite side of the substrate except in the region forming the half-window. 
     
     
         17 . A method according to  claim 14  wherein the radiation curable ink is a transparent ink or lacquer formed from a clear resin material. 
     
     
         18 . A method according to  claim 14  wherein the radiation curable ink is a metallic ink composition. 
     
     
         19 . A method according to  claim 18  wherein a metallic ink composition is applied to the embossed transparent ink. 
     
     
         20 . A method according to  claim 18  wherein the metallic ink composition is applied in a layer which is sufficiently thin to allow the transmission of light. 
     
     
         21 . A method according to  claim 14  wherein the radiation curable ink is applied in a Gravure printing process. 
     
     
         22 . A method according to  claim 14  wherein the radiation curable ink is simultaneously embossed and cured with UV radiation.