Security Article Having a Switching Feature

Abstract

A security laminate for authenticating an article and a method for authenticating articles is disclosed. The security laminate includes a transparent binder layer and retroreflective microspheres such that the security laminate exhibits a covert switching effect when exposed to particular conditions.

What is claimed is: 
     
         1 . A method of authenticating an article, comprising the steps of:
 providing a security laminate comprising:
 a substrate having indicia thereon; 
 a transparent binder layer; 
 a first plurality of dry retroreflective microspheres in a first area positioned over a first portion of the indicia; and 
 a second plurality of wet retroreflective microspheres in a second area positioned over a second portion of the indicia; 
 wherein the first plurality of dry retroreflective microspheres and the second plurality of wet retroreflective microspheres protrude from the binder layer; 
   exposing the security laminate to a first condition and observing the security laminate under the first condition to determine the viewability of the first portion of the indicia and the second portion of the indicia;   exposing the security laminate to a second condition and observing the security laminate under the second condition to determine the viewability of the first portion of the indicia and the second portion of the indicia;   exposing the security laminate to a third condition and observing the security laminate under the third condition to determine the viewability of the first portion of the indicia and the second portion of the indicia; and   authenticating the article, if,
 under the first condition, the first portion of the indicia and the second portion of the indicia are viewable, 
 under the second condition, the first plurality of retroreflective microspheres at least partially hide the first portion of the indicia and the second portion of the indicia is viewable, and 
 under the third condition, the first portion of the indicia is viewable and the second plurality of retroreflective microspheres at least partially hide the second portion of the indicia. 
   
     
     
         2 . The method of  claim 1 , wherein the first condition comprises ambient light and a first medium exhibiting a specified refractive index in contact with the first and second pluralities of retroreflective microspheres, the second condition comprises retroreflective light and a second medium exhibiting a specified refractive index in contact with the first plurality of retroreflective microspheres and the third condition comprises retroreflective light and a second medium exhibiting a specified refractive index in contact with the second plurality of retroreflective microspheres. 
     
     
         3 . The method of  claim 2 , wherein the first medium exhibits a refractive index between 1.00 and 1.20, the second medium exhibits a refractive index between 1.00 and 1.20, and the third medium exhibits a refractive index between 1.25 and 1.35. 
     
     
         4 . A method of authenticating an article, comprising the steps of:
 providing a security laminate comprising:
 a transparent binder layer; and 
 an area having a plurality of retroreflective microspheres comprising dry retroreflective microspheres and wet retroreflective microspheres; 
 wherein the plurality of retroreflective microspheres protrude from the binder layer, and 
 wherein at least a portion of the plurality of retroreflective microspheres comprise one or more concentric optical interference layers; 
   exposing the security laminate to a first condition and observing the area having a plurality of retroreflective microspheres for a color under the first condition;   exposing the security laminate to a second condition and observing the area having a plurality of retroreflective microspheres for a color under the second condition; and   authenticating the article, if,
 under a first condition, the area of the security laminate exhibits a color, and 
 under a second condition, the area of the security laminate exhibits a different color. 
   
     
     
         5 . The method of  claim 4 , wherein the first condition comprises retroreflective light and a first medium exhibiting a specified refractive index in contact with the first plurality of retroreflective microspheres and the second condition comprises retroreflective light and a second medium exhibiting a specified refractive index in contact with the second plurality of retroreflective microspheres. 
     
     
         6 . The method of  claim 5 , wherein the first medium exhibits a refractive index between 1.00 and 1.20, and the second medium exhibits a refractive index between 1.25 and 1.35. 
     
     
         7 . A method of authenticating an article, comprising the steps of:
 providing a security laminate comprising:
 a transparent binder layer; and 
 a first plurality of dry retroreflective microspheres in a first area; and 
 a second plurality of wet retroreflective microspheres in a second area; 
 wherein the plurality of retroreflective microspheres protrude from the binder layer; 
   exposing the security laminate to a first condition and observing the brightness of the first area and second area under the first condition;   exposing the security laminate to a second condition and observing the brightness of the first area and second area under the second condition; and   authenticating the article, if,
 under a first condition, the brightness of the first plurality of retroreflective microspheres is greater than the brightness of the second plurality of microsphere, and 
 under a second condition, the brightness of the second plurality of retroreflective microspheres is greater than the brightness of the first plurality of retroreflective microspheres. 
   
     
     
         8 . The method of  claim 7 , wherein the first condition comprises retroreflective light and a first medium exhibiting a specified refractive index in contact with the first plurality of retroreflective microspheres and the second condition comprises retroreflective light and a second medium exhibiting a specified refractive index in contact with the second plurality of retroreflective microspheres. 
     
     
         9 . The method of  claim 8 , wherein the first medium exhibits a refractive index between 1.00 and 1.20, and the second medium exhibits a refractive index between 1.25 and 1.35.