Printing

Abstract

An image article comprises a substrate having a security image coated on at least a portion thereof, which security image effects less than 50% reflectance of radiation of a wavelength between 800 and 900 nm, wherein the security image comprises a defined infrared-absorbing compound, for example Pigment Green 8, wherein said infrared-absorbing compound does not create a strongly coloured security image.

1 . An image article comprising a substrate having a security image coated on at least a portion thereof, which security image effects less than 50% reflectance of radiation of a wavelength between 800 and 900 nm, wherein the security image comprises an infrared-absorbing compound selected from: 
     
       
         
         
             
             
         
       
     
     or a salt or polymer thereof, wherein
 M is a metal selected from a group 3-10 (Group IIIB-VIII) element or a lanthanide; 
 R 1  is selected from hydrogen, phosphonate, sulphonate, nitro, halo, cyano, thiocyano, thioalkyl, thioaryl, alkyl, alkoxy, aryl, aryloxy, amines, substituted amines and substituted aryl; 
 one of R 2  and R 3  is oxygen and the other of R 2  and R 3  is NO; 
 n is a number corresponding to half the co-ordination number of the metal M; 
 each L and L′ is independently a ligand complexed to the metal M; and 
 y is a number corresponding to the co-ordination number of the metal M; 
 
     wherein said infrared-absorbing compound does not create a strongly coloured security image. 
   
   
       2 . An image article according to  claim 1  wherein M is selected from iron, cobalt and lanthanum. 
   
   
       3 . An image article according to  claim 1  wherein the infrared absorbing compound is a salt of formula: 
     
       
         
         
             
             
         
       
     
     wherein M, n and R 1 , R 2  and R 3  are as defined in  claim 1 , X is a metal cation selected from a group 1 or 2 metal and aluminium, and the product of m and t corresponds to the total number of negative charges on the compound. 
   
   
       4 . An image article according to  claim 3  wherein the salt is selected from: 
     
       
         
         
             
             
         
       
     
   
   
       5 . An image article according to  claim 1  wherein the infrared absorbing compound is of the formula: 
     
       
         
         
             
             
         
       
     
     wherein M, R 2  and R 3  are as defined in  claim 1 , L1-L6 and L1′-L6′ are ligands independently selected from chlorine, bromine, hydroxyl, water, or any number of pairs of L3-L6 and/or L3′-L6′ may be combined as a single ligand forming a ring structure with metal M, and may be formed from 1,3-dinitroso-2,4-dihydroxybenzene, or 1,5-dinitroso-2,6-dihydroxynaphthalene, connected to the metal M via the nitroso and hydroxyl groups. 
   
   
       6 . An image article according to  claim 1  wherein the infrared-absorbing compound is a dendritic polymer in which each M is complexed to three dinitroso-2,4-dihydroxybenzene or three dinitroso-2,6-dihydroxynaphthalene groups (preferably 1,3-dinitroso-2,4-dihydroxybenzene, 1,5-dinitroso-2,6-dihydroxynaphthalene or 1,5-dihydroxy-4,8-dinitrosonaphthalene). 
   
   
       7 . An image article according to  claim 6  in which the infra-red absorbing compound is selected from: 
     
       
         
         
             
             
         
       
     
   
   
       8 . An image article according to  claim 1  wherein the article is a banknote. 
   
   
       9 . An image article according to  claim 1  further comprises one or more additional security elements. 
   
   
       10 . An image article according to  claim 9  which includes covert and overt security elements. 
   
   
       11 . (A method of manufacturing an image article comprising the steps of:
 (a) providing a substrate; and   (b) image-wise coating an infra-red absorbing compound selected from:   
     
       
         
         
             
             
         
       
     
     or a salt or polymer thereof, onto at least a portion of the substrate to form a security image which is not strongly coloured and which effects less than 50% reflectance of radiation of a wavelength between 800 and 900 nm, wherein:
 M is a metal selected from a group 3-10 (Group IIIB-VIII) element or a lanthanide; 
 R 1  is selected from hydrogen, phosphonate, sulphonate, nitro, halo, cyano, thiocyano, thioalkyl, thioaryl, alkyl, alkoxy, aryl, aryloxy, amines, substituted amines and substituted aryl; 
 one of R 2  and R 3  is oxygen and the other of R 2  and R 3  is NO; 
 n is a number corresponding to half the co-ordination number of the metal M; 
 each L and L′ is independently a ligand complexed to the metal M; and 
 y is a number corresponding to the co-ordination number of the metal M. 
 
   
   
       12 . A method according to  claim 10  wherein in step (b) the compound is image-wise coated onto the substrate in a composition containing the infrared absorbing compound and one or more further pigments and/or one or more dyes. 
   
   
       13 . The use of a compound of formula: 
     
       
         
         
             
             
         
       
     
     or a salt or polymer thereof, coated on at least a portion of the substrate, as an infrared radiation-absorbing additive in a security image coated on a substrate of an image article, wherein:
 M is a metal selected from a group 3-10 (Group IIIB-VIII) element or a lanthanide; 
 R 1  is selected from hydrogen, phosphonate, sulphonate, nitro, halo, cyano, thiocyano, thioalkyl, thioaryl, alkyl, alkoxy, aryl, aryloxy, amines, substituted amines and substituted aryl; 
 one of R 2  and R 3  is oxygen and the other of R 2  and R 3  is NO; 
 n is a number corresponding to half the co-ordination number of the metal M; 
 each L and L′ is independently a ligand complexed to the metal M; and 
 
     y is a number corresponding to the co-ordination number of the metal M; 
     wherein said security image is not strongly coloured. 
   
   
       14 . A method of verifying the authenticity of an image article as defined in  claim 1 , the method comprising exposing said image article to radiation having a wavelength of between 800 and 900 nm, and measuring the reflectance of said radiation.