Thermochromic ink composition

Abstract

A thermochromic ink composition is provided for use on security documents such as checks which provides a reversible color change in response to heat. The ink composition includes a thermochromic aqueous slurry and an ink vehicle comprising either a phenolic modified rosin and a compatible oil, a styrene maleic anhydride resin and a glycol, or an acrylic resin varnish. The ink composition is printed on at least a portion of a substrate using letterpress printing methods and provides enhanced adhesion to toner when applied to areas of a substrate which are subsequently printed with a non-impact printing device such as a laser printer.

What is claimed is:  
     
         1 . A security document comprising a substrate having first and second surfaces; said substrate having a thermochromic ink composition applied to at least a portion of said first or second surface, said thermochromic ink composition comprising a thermochromic aqueous slurry and an ink vehicle; wherein said thermochromic ink composition provides enhanced adhesion for toner particles printed thereon.  
     
     
         2 . A security document as claimed in  claim 1  wherein said ink vehicle is selected from the group consisting of: 1) a phenolic modified rosin and an oil compatible with said rosin, or 2) at least one styrene maleic anhydride resin and a glycol, or 3) an acrylic resin varnish.  
     
     
         3 . A method of applying a thermochromic ink composition comprising an encapsulated thermochromic pigment and an ink vehicle, said method comprising the steps of: 
 a) providing a substrate having first and second surfaces,    b) applying said thermochromic ink composition onto at least a portion of said first or second surface of said substrate; and    c) printing tone over at least a portion of the area of said first or second surface containing said thermochromic ink composition.    
     
     
         4 . The method of  claim 3  wherein said thermochromic ink composition is applied to said substrate by a letterpress printing process.  
     
     
         5 . The method of  claim 3  wherein said thermochromic ink composition provides enhanced adhesion of said toner to said substrate.