Use of photo catalytic material for self-cleaning banknotes

Abstract

Self-cleaning banknotes are provided using coatings, inks and additives which are photo-active and catalytic to reactions which are effective in breaking up organic contaminants or dirt to allow for the self-cleaning of banknotes by ambient light exposure as well as the cleaning of processed banknotes using equipment with more intense optical excitation, thus increasing their usable life. The invention is usable with all substrates and particularly polymeric substrates such as biaxially-oriented polypropylene (BOPP). The invention further discloses a system which allows a certain class of fitness parameters to cause these banknotes to be redirected to a cleaning module, be reevaluated, and then either returned to circulation or rejected and/or destroyed. In addition, inks which are photo-catalytic can be used for extending the life of the banknotes in printed regions.

What is claimed: 
     
         1 . A substrate material comprising:
 a base sheet material; and   a photo-catalytic material on or about said base sheet material;   wherein said photo-catalytic material, when energized, generates the transfer of electrons and holes that generate hydroxyl and other radicals that in turn cause chemical oxidation and reduction reactions on or about said sheet material.   
     
     
         2 . The substrate material of  claim 1 , wherein said substrate is a banknote. 
     
     
         3 . The substrate material of  claim 1 , wherein said photo-catalytic material is selected from the group consisting of: an additive within said base sheet material, a coating on the surface of said base sheet material and an additive within ink used to print on the surface of said base sheet material. 
     
     
         4 . The substrate material of  claim 1 , wherein said photo-catalytic material is a nanoparticle metal oxide material.
 The substrate material of  claim 1 , wherein said photo-catalytic material is modified TiO 2 .   
     
     
         5 . The substrate material of  claim 1 , wherein said photo-catalytic material is a nanoparticle semiconductor material. 
     
     
         6 . The substrate material of  claim 1 , wherein said photo-catalytic material is anatase TiO2. 
     
     
         7 . The substrate material of  claim 6 , wherein said anatase TiO2 is in nanoparticle form. 
     
     
         8 . The substrate material of  claim 1 , wherein said photo-catalysis is initiated using ultraviolet energy having a wavelength in the 200 nm-400 nm region. 
     
     
         9 . The substrate material of  claim 1 , wherein said photo-catalysis is initiated using ultraviolet energy having a wavelength in the 360 nm-400 nm region. 
     
     
         10 . The substrate material of  claim 1 , wherein said oxidation and reduction reactions effect a cleaning of the surface of the substrate material. 
     
     
         11 . The substrate material of  claim 10 , further comprising:
 a system that employs a sensor to determine fitness data relating to said substrate;   said system making a decision based on said fitness data to clean the substrate   said system applies energy to initiate photo-catalysis;   removes dirt from said substrate using a wash, gas jet, or mechanical means; and   reevaluates the fitness of said substrate using a sensor to determine whether to return the substrate to circulation or to destroy or reject the substrate.   
     
     
         12 . A system for cleaning a substrate material comprising:
 a sensor to determine fitness data relating to said substrate having a photocatalytic material on or about said substrate;   making a decision based on said fitness data to clean the substrate;   applying energy to excite said photo-catalytic material and initiate photo-catalysis;   removing dirt from said substrate using a wash, gas jet, or mechanical means; and   reevaluating the fitness of said substrate using a sensor to determine whether to return the substrate to circulation or to reject or destroy the substrate.   
     
     
         13 . The system of  claim 12 , wherein said substrate is a banknote. 
     
     
         14 . The system of  claim 12 , wherein said photo-catalytic material is selected from the group consisting of: an additive within said base sheet material, a coating on the surface of said base sheet material and an additive within ink used to print on the surface of said base sheet material. 
     
     
         15 . The system of  claim 12 , wherein said photo-catalytic material is a nanoparticle metal oxide material. 
     
     
         16 . The system of  claim 12 , wherein said photo-catalytic material is a nanoparticle semiconductor material. 
     
     
         17 . The system of  claim 12 , wherein said photo-catalytic material is anatase TiO2. 
     
     
         18 . The system of  claim 17 , wherein said anatase TiO2 is in nanoparticle form. 
     
     
         19 . The system of  claim 12 , wherein said photo-catalysis is initiated using ultraviolet energy having a wavelength in the 200 nm-400 nm region. 
     
     
         20 . The system of  claim 12 , wherein said photo-catalysis is initiated using ultraviolet energy having a wavelength in the 200 nm-400 nm region.