Pigment particles for invisible marking applications

摘要

A pigment composition includes a crystalline thermoplastic polyester resin having residues of at least one dicarboxylic acid and a near-infrared fluorescing compound having a fluorescence between about 650 nm to about 2500 nm associated with the crystalline thermoplastic polyester, wherein the polyester has an intrinsic viscosity (IV) of less than about 0.37. A preferred polyester is polybutylene terephthalate. Another aspect is a method for providing a detectable or identifiable marking that is invisible to the unaided eye on a surface of a substrate is also provided. The method includes the steps of applying to the surface a marking composition comprising a suitably compatible marking fluid containing the fluorescent pigment composition. The near infrared fluorescing pigment composition is useful in letterpress, flexographic and gravure printing applications.