Security thread comprising an optically variable structure

摘要

A security thread for embedding in or on a sheet such as a document, currency or packaging is disclosed, wherein the thread has a thin film interference structure (21, 35) deposited thereon. The structure (21, 35) may be a Fabry-Perot structure in the form of a single filter, or may be plural filters, spaced side-by-side. The thread appears to have separated interference filters deposited thereon. Preferably the thread is first roll coated with oil using an oil-ablation technique to remove deposited material in situ in the coating process. A magnetic layer (52, 66) may be deposited within, behind or in front of the thin film interference structure (21, 35).