IMPROVED WATERFASTNESS OF CONCEALED INK JET IMAGES
Original Publication Date: 1992-Apr-30
Included in the Prior Art Database: 2004-Apr-05
Xerox Disclosure Journal
A liquid ink composition suitable for ink jet printing comprising a liquid vehicle and a colorless waterfast fluorescent material is disclosed. The composition may be utilized to prepare concealed ink jet images, that is images invisible to the naked eye under visible light, which are detectable under illumination with an ultraviolet light source. Printing concealed ink jet images is useful for document handling and identification, document authentication and recognition, such as barcodes and glyphs, and various security document applications, for example, bank notes, currencies, bonds, stock certificates, and confidential reports. Concealed images may be prepared on a paper or an equivalent substrate using an ink jet printer, for example, continuous and drop-on-demand types, and a liquid ink containing colorless fluorescent dye compounds and optional additives. Desired waterfastness of the ink composition is achieved by reaction or interactions between functional groups of the fluorescent dye and the paper substrate. Chemical reaction or interaction of, for example, sulfonic acid salts, triazines, amines, amides or triazole functional groups of a fluorescent dye with cellulose and various additives (multivalent salts, acidic ingredients, and the like) result in reduced water solubility of the fluorescent dye on the imaged area. The fluorescent dye on the imaged area may undergo a chemical change or form hydrogen bonds on paper substrates producing a waterfast concealed but UV detectable image. Further, the water solubility of the dye compound, formulation stability and waterfastness of ink images may be controlled by the hydrophobicity of the dye compound selected.