US Patent 7175901 Retroreflective inks

The combination of ingredients, especially for use in the formulation of a one or two-pack retroreflective ink, comprising retroreflective elements, microbeads additional to said retroreflective elements and/or constituting said retroreflective elements at least in part, binder chemicals for attaching the retroreflective elements and microbeads to a substrate to which the ink is to be applied, and a coupling agent for coupling the microbeads and cross-linking the binder chemicals, the coupling agent being unreactive until the printing process is carried out.