Method of tagging a substrate

Abstract

The present invention relates to a method of tagging a substrate with a covert, spectroscopically detectable security feature, wherein a liquid treatment composition comprising at least one acid is deposited onto a substrate, which comprises at least one external surface comprising a salifiable alkaline or alkaline earth compound.

1 . A method of tagging a substrate with a covert, spectroscopically detectable security feature, the method comprising the following steps:
 a) providing a substrate, wherein the substrate comprises at least one external surface comprising a salifiable alkaline or alkaline earth compound,   b) providing a liquid treatment composition comprising at least one acid,   c) applying the liquid treatment composition onto at least one region of the at least one external surface to form at least one surface-modified region on or within the at least one external surface, and   d) applying an opaque top layer over the at least one surface-modified region obtained in step c).   
     
     
         2 . The method of  claim 1 , wherein the at least one external surface of step a) is in form of a laminate or a coating layer comprising the salifiable alkaline or alkaline earth compound. 
     
     
         3 . The method of  claim 1 , wherein the substrate is selected from the group consisting of paper, cardboard, containerboard, plastic, non-wovens, cellophane, textile, wood, metal, glass, mica plate, marble, calcite, nitrocellulose, natural stone, composite stone, brick, concrete, and laminates or composites thereof, preferably paper, cardboard, containerboard or plastic. 
     
     
         4 . The method of  claim 1 , wherein the at least one external surface and the substrate of step a) are made from the same material, preferably the substrate comprises the salifiable alkaline or alkaline earth compound in form of a filler material. 
     
     
         5 . The method of  claim 1 , wherein the salifiable alkaline or alkaline earth compound is an alkaline or alkaline earth oxide, an alkaline or alkaline earth hydroxide, an alkaline or alkaline earth alkoxide, an alkaline or alkaline earth methylcarbonate, an alkaline or alkaline earth hydroxycarbonate, an alkaline or alkaline earth bicarbonate, an alkaline or alkaline earth carbonate, or a mixtures thereof, preferably the salifiable alkaline or alkaline earth compound is an alkaline or alkaline earth carbonate being preferably selected from lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium magnesium carbonate, calcium carbonate, or mixtures thereof, more preferably the salifiable alkaline or alkaline earth compound is calcium carbonate, and most preferably the salifiable alkaline or alkaline earth compound is a ground calcium carbonate, a precipitated calcium carbonate and/or a surface-treated calcium carbonate. 
     
     
         6 . The method of  claim 1 , wherein the at least one acid is selected from the group consisting of hydrochloric acid, sulphuric acid, sulphurous acid, phosphoric acid, citric acid, oxalic acid, acetic acid, formic acid, sulphamic acid, tartaric acid, phytic acid, boric acid, succinic acid, suberic acid, benzoic acid, adipic acid, pimelic acid, azelaic acid, sebaic acid, isocitric acid, aconitic acid, propane-1,2,3-tricarboxylic acid, trimesic acid, glycolic acid, lactic acid, mandelic acid, acidic organosulphur compounds, acidic organophosphorus compounds, HSO 4   − , H 2 PO 4   −  or HPO 4   2− , being at least partially neutralized by a corresponding cation selected from Li + , Na + , K + , Mg 2+  or Ca 2+ , and mixtures thereof, preferably the at least one acid is selected from the group consisting of hydrochloric acid, sulphuric acid, sulphurous acid, phosphoric acid, oxalic acid, boric acid, suberic acid, succinic acid, sulphamic acid, tartaric acid, and mixtures thereof, more preferably the at least one acid is selected from the group consisting of sulphuric acid, phosphoric acid, boric acid, suberic acid, sulphamic acid, tartaric acid, and mixtures thereof, and most preferably the at least one acid is phosphoric acid and/or sulphuric acid. 
     
     
         7 . The method of  claim 1 , wherein the liquid treatment composition further comprises a fluorescent dye, a phosphorescent dye, an ultraviolet absorbing dye, a near infrared absorbing dye, a thermochromic dye, a halochromic dye, metal ions, transition metal ions, magnetic particles, quantum dots, or a mixture thereof. 
     
     
         8 . The method of  claim 1 , wherein the liquid treatment composition comprises the acid in an amount from 0.1 to 100 wt.-%, based on the total weight of the liquid treatment composition, preferably in an amount from 1 to 80 wt.-%, more preferably in an amount from 3 to 60 wt.-%, and most preferably in an amount from 10 to 50 wt.-%. 
     
     
         9 . The method of  claim 1 , wherein the liquid treatment composition is applied in form of a continuous layer or a pattern of repetitive elements or repetitive combination(s) of elements, preferably selected from the group consisting of circles, dots, triangles, rectangles, squares, or lines. 
     
     
         10 . The method of  claim 1 , wherein the opaque top layer is a top coat, a pigment layer, an overprint, a metal coating, a metal foil, a fibre layer, a laminate, a polymer foil, or a paper. 
     
     
         11 . The method of  claim 1 , wherein the covert security feature is detectably by a spectroscopic method selected from the group consisting of infrared spectroscopy, X-ray spectroscopy, and combinations thereof, preferably the covert security feature is detectably by a spectroscopic method selected from the group consisting of FTIR spectroscopy, X-ray diffractometry (XRD), energy-dispersive X-ray spectroscopy (EDS), and combinations thereof. 
     
     
         12 . A tagged substrate comprising a covert, spectroscopically detectable security feature, obtainable by a method according to  claim 1 . 
     
     
         13 . A product comprising a tagged substrate according to  claim 12 , wherein the product is a branded product, a security document, a non-secure document, or a decorative product, preferably the product is a perfume, a drug, a tobacco product, an alcoholic drug, a bottle, a garment, a packaging, a container, a sporting good, a toy, a game, a mobile phone, a compact disc (CD), a digital video disc (DVD), a blue ray disc, a machine, a tool, a car part, a sticker, a label, a tag, a poster, a passport, a driving licence, a bank card, a credit card, a bond, a ticket, a postage or tax stamp, a banknote, a certificate, a brand authentication tag, a business card, a greeting card, or a wall paper. 
     
     
         14 . Use of a tagged substrate according to  claim 12  in security applications, in overt security elements, in covert security elements, in brand protection, in microlettering, in micro imaging, in decorative applications, in artistic applications, in visual applications, or in packaging applications. 
     
     
         15 . A method of verifying the authenticity of a product, comprising the following steps:
 I) providing a product with a tagged substrate comprising a covert, spectroscopically detectable security feature according to  claim 12 ,   II) recording a spectrum of the substrate by a spectroscopic method, and   III) detecting the presence of the security feature by comparing the recorded spectrum with a library of spectra of tagged substrates according to  claim 12 .