Method for marking items for identification

Abstract

A method for marking or tagging individual microparticles using a near infrared fluorophore for identification is provided. The near infrared fluorophore is included with one or more layers comprising the microparticle. Desirably, the coating layers contain colorants such as dyes and/or pigments which increases the total possible combinations that may be used to identify the marked material. There is further provided a method for marking a material using these microparticles containing a near infrared fluorophore.

We claim:  
     
         1 . A method for identifying or locating solid particulate materials comprising incorporating near infrared fluorophores in or on said materials.  
     
     
         2 . A method of tagging individual units of production of a substance with microparticles, comprising incorporating into said substance microparticles having a plurality of distinguishable layers wherein at least one layer includes at least one near infrared fluorophore.  
     
     
         3 . The method of  claim 2  where at least one of said distinguishable layers comprises a near infrared fluorophore and at least one visual dye or colorant, wherein said near infrared fluorophore is selected from the classes of phthalocyanines, naphthalocyanines and squaraines corresponding to Formulae I, II and III herein.  
     
     
         4 . The method of  claim 2  wherein each of said microparticles is about 1 to about 1000 microns at its broadest dimension in the color sequence.  
     
     
         5 . The method of  claim 3  wherein said near infrared fluorophore is present in a concentration less than about 1000 ppm.  
     
     
         6 . A method according to  claim 3  wherein at least one distinguishable layer is formed from a polymeric material having suitable dyes and/or near infrared fluorophores admixed therein.  
     
     
         7 . The method according to  claim 6  in which the polymer is a polyester.  
     
     
         8 . The method according to  claim 6  in which the polymer is a polyurethane.  
     
     
         9 . The method according to  claim 6  in which the polymer is a polyamide.  
     
     
         10 . The method according to  claim 6  in which the polymer is an epoxy.  
     
     
         11 . The method of  claim 3  wherein each microparticle comprises a solid nucleus concentrically coated with distinguishable layers of different colors and at least two near infrared fluorophores, and said layers having a thickness of from about 5 microns to about 15 microns.  
     
     
         12 . The method of  claim 11  wherein said layers are formed from pigmented polymeric material.  
     
     
         13 . The method of  claim 11  wherein said nuclei are essentially spherical particles between about 1 and about 1000 microns in diameter.  
     
     
         14 . The method of  claim 3  wherein each of said microparticles has two surfaces that are generally flat and parallel to each other across its broadest dimension and are substantially the same thickness.  
     
     
         15 . The method of  claim 14  wherein said distinguishable layers of said microparticles are formed by a series of substantially uniform layers having a thickness less than about 100 microns.  
     
     
         16 . The method of  claim 14  wherein said distinguishable layers of said microparticles are formed by a series of substantially uniform layers having a thickness less than about 50 microns.  
     
     
         17 . The method of  claim 14  wherein said distinguishable layers of said microparticles are formed by a series of substantially uniform layers having a thickness of from about 5 microns to about 25 microns.  
     
     
         18 . The method of  claim 14  wherein said microparticles have a thickness less than about 500 microns.  
     
     
         19 . Method of  claim 14  wherein said microparticles are formed from colored polyethylene films.  
     
     
         20 . A uniquely encoded microparticle comprising a plurality of distinguishable layers wherein said layers are encoded via a sequence of visually color distinguishable dyed and/or pigmented layers, wherein at least one layer includes at least one near infrared fluorophore of  claim 3 .  
     
     
         21 . The microparticles of  claim 20  comprising at least three colored layers and wherein each microparticle is between about 1 and about 1000 microns in its broadest dimension across the color sequence.  
     
     
         22 . The microparticle of  claim 20  wherein each of said microparticles has two surfaces that are generally flat and parallel to each other across its broadest dimension and are substantially the same thickness.  
     
     
         23 . The microparticle of  claim 22  wherein said distinguishable layers of said microparticles are formed by a series of substantially uniform layers having a thickness less than about 100 microns.  
     
     
         24 . The microparticle of  claim 23  wherein said microparticles have a thickness less than about 500 microns.  
     
     
         25 . The microparticles according to  claim 20  wherein said microparticles are essentially spherical.