| abstract |
Ink compositions described are suitable for ink jet printing (ink jet inks) and are highly effective for simultaneously imparting visible and fluorescent images. In the preferred forms, both a dark, visible image and a complementary fluorescent image will be visually discernable as well as machine readable to enable efficient hand and automated processing or handling of the objects printed. These results are achieved by ink formulations that moderate the typically occurring phenomenon of quenching while possessing the physical properties necessary for an ink jet ink. In one form, the inks comprise a first colorant comprising at least one fluorescent dye, the fluorescent dye emitting light within a characteristic emission band when excited by fluorescent-exciting radiation; a second colorant having a light absorption band at longer wavelengths than the characteristic emission band of the first colorant, the second colorant comprising a water-soluble polymeric dye of effective molecular configuration to inhibit quenching of fluorescence of said first colorant due to collisional and resonance energy transfer with said second colorant; and an aqueous liquid vehicle comprising water and a water-soluble vehicle in sufficient amounts to achieve an ink viscosity and surface tension effective for application of the ink to a substrate in a predetermined pattern by ink jet printing. The colorants are present in combination in the aqueous ink in amounts effective to cause the ink, when dry, to exhibit a dark color due to the net absorption spectra of the colorants in the visual range and machine-readable or visually-discernable fluorescence when subjected to fluorescent-exciting radiation. |