Fluorescent micro-particles embedded in a pigmented fluorescent coating for optical document security

Abstract

A security feature ( 1 ) that is used with a substrate ( 2 ). The security feature includes a plurality of fluorescent micro-particles ( 1 A) that form a background component of the security feature and a plurality of fluorescent discrete particles ( 1 B) that form a foreground component of the security feature. The discrete particles are larger in size than the micro-particles and are optically distinguishable from the micro-particles under at least one illumination condition. In the preferred embodiment the security feature is applied as a coating to the substrate, and the security feature further includes a coating binder ( 1 C) in which the micro-particles and the discrete particles are contained. The coating binder can be made of, for example, at least one of an ink base, an adhesive, an epoxy, a varnish, a polymer solution, or a dry material having binding properties. The coating binder may be substantially transparent or substantially opaque. The discrete particles are optically distinguishable from the micro-particles under long wavelength ultraviolet light and/or under short wavelength ultraviolet light. Under no or low magnification conditions the security feature exhibits a generally uniform color to the naked eye, while in one embodiment under higher magnification conditions the discrete particles exhibit a first color while the micro-particles of the background component exhibit a second color, while in another embodiment the discrete particles exhibit a first color while the micro-particles of the background component exhibit a lack of color, while in a further embodiment the micro-particles of the background component exhibit a first color while the discrete particles exhibit a lack of color. The security feature exhibits a fluorescent signature having attributes given by at least one of particle count per unit area, specific particle size range which may or may not differ by fluorescent color, relative intensities of measured spectral emission peaks due to foreground component particle fluorescence versus background component micro-particle fluorescence and specific emission wavelength values of measured spectral emission peaks due to foreground component particle fluorescence versus background component micro-particle fluorescence.

What is claimed is:  
     
         1 . A security feature that is used with a substrate, comprising: 
 a plurality of fluorescent micro-particles that form a background component of said security feature; and    a plurality of fluorescent discrete particles that form a foreground component of said security feature, said discrete particles being larger in size than said micro-particles and being optically distinguishable from said micro-particles under at least one illumination condition.    
     
     
         2 . A security feature as in  claim 1 , wherein said security feature is applied as a coating to said substrate, and further comprising a coating binder in which said micro-particles and said discrete particles are contained.  
     
     
         3 . A security feature as in  claim 2 , wherein said coating binder is comprised of at least one of an ink base, an adhesive, an epoxy, a varnish, a polymer solution, or a dry material having binding properties.  
     
     
         4 . A security feature as in  claim 1 , wherein said discrete particles are optically distinguishable from said micro-particles under long wavelength ultraviolet light.  
     
     
         5 . A security feature as in  claim 1 , wherein said discrete particles are optically distinguishable from said micro-particles under short wavelength ultraviolet light.  
     
     
         6 . A security feature as in  claim 1 , wherein under no or low magnification conditions the security feature exhibits a generally uniform color to the naked eye, while under higher magnification conditions the discrete particles exhibit a first color while the micro-particles of the background component exhibit a second color.  
     
     
         7 . A security feature as in  claim 1 , wherein under no or low magnification conditions the security feature exhibits a generally uniform color to the naked eye, while under higher magnification conditions the discrete particles exhibit a first color while the micro-particles of the background component exhibit a lack of color.  
     
     
         8 . A security feature as in  claim 1 , wherein under no or low magnification conditions the security feature exhibits a generally uniform color to the naked eye, while under higher magnification conditions the micro-particles of the background component exhibit a first color while the discrete particles exhibit a lack of color.  
     
     
         9 . A security feature as in  claim 1 , wherein said security feature exhibits a fluorescent signature having attributes given by at least one of particle count per unit area, specific particle size range which may or may not differ by fluorescent color, relative intensities of measured spectral emission peaks due to foreground component particle fluorescence versus background component micro-particle fluorescence and specific emission wavelength values of measured spectral emission peaks due to foreground component particle fluorescence versus background component micro-particle fluorescence.  
     
     
         10 . A security feature as in  claim 1 , wherein said discrete particles have a size in the range of about 10 microns to about 20 microns in diameter.  
     
     
         11 . A security feature as in  claim 1 , wherein said micro-particles have a size in the range of about 0.2 microns to about 2 microns in diameter.  
     
     
         12 . A security feature as in  claim 1 , wherein an average size of said discrete particles is greater by a factor of at least five than an average size of said micro-particles.  
     
     
         13 . A security feature as in  claim 1 , wherein an average size of said discrete particles is greater by a factor of at least one order of magnitude than an average size of said micro-particles.  
     
     
         14 . A security feature as in  claim 2 , wherein said coating binder is substantially transparent.  
     
     
         15 . A security feature as in  claim 2 , wherein said coating binder is substantially opaque.  
     
     
         16 . A security feature as in  claim 1 , wherein said discrete particles are optically distinguishable in a first way from said micro-particles when viewed under short wavelength ultraviolet light, and are optically distinguishable in a second way from said micro-particles when viewed under long wavelength ultraviolet light.  
     
     
         17 . A reader system comprising a plurality of light sources and a magnification optics coupled to an imaging system, said reader system comprising a controller for illuminating a security feature using said plurality of light sources, said security feature comprising a plurality of fluorescent micro-particles that form a background component of said security feature and a plurality of fluorescent discrete particles that form a foreground component of said security feature, said discrete particles being larger in size than said micro-particles and being optically distinguishable from said micro-particles when illuminated by at least one of said plurality of light sources, said controller cooperating with said imaging system for resolving a fluorescent signature of said security feature, said fluorescent signature having attributes given by at least one of particle count per unit area, specific particle size range which may or may not differ by fluorescent color, relative intensities of measured spectral emission peaks due to foreground component particle fluorescence versus background component micro-particle fluorescence and specific emission wavelength values of measured spectral emission peaks due to foreground component particle fluorescence versus background component micro-particle fluorescence.  
     
     
         18 . A reader system as in  claim 17 , wherein said security feature is applied as a coating to a substrate using a coating binder in which said micro-particles and said discrete particles are contained.  
     
     
         19 . A method for reading a security feature, comprising steps of: 
 operating a reader system having a plurality of light sources and magnification optics coupled to an imaging system for illuminating the security feature using said plurality of light sources, said security feature comprising a plurality of fluorescent micro-particles that form a background component of said security feature and a plurality of fluorescent discrete particles that form a foreground component of said security feature, said discrete particles being larger in size than said micro-particles and being optically distinguishable from said micro-particles when illuminated by at least one of said plurality of light sources; and    responsive to the illuminating, resolving a fluorescent signature of said security feature, said fluorescent signature having attributes given by at least one of particle count per unit area, specific particle size range which may or may not differ by fluorescent color, relative intensities of measured spectral emission peaks due to foreground component particle fluorescence versus background component micro-particle fluorescence and specific emission wavelength values of measured spectral emission peaks due to foreground component particle fluorescence versus background component micro-particle fluorescence.    
     
     
         20 . A method as in  claim 19 , and comprising a preliminary step of applying said security feature as a coating to a substrate using a coating binder in which said micro-particles and said discrete particles are contained.