Security document with nano-pattern

Abstract

A counterfeit-resistant document comprises a substrate and a nano-pattern of nano-structures disposed on the substrate, wherein the nano-pattern is configured for forming a latent message (e.g., a warning or alert message) that appears on a copy of the document. The nano-pattern forms one of a foreground and a background of the latent message; and another pattern, e.g., a conventional pattern or another nano-pattern, forms the other of the foreground and background of the latent message. The nano-pattern and the other pattern are configured, such that the foreground and background exhibit substantially similar visual densities on an original of the document, and exhibit substantially different visual densities on the copied document. This can be accomplished by forming the nano-pattern with nano-structures (e.g., polygons, circles, ovals, crosses, x's, or alpha-numerical characters), which are composed of plurality of adjacent rectilinear and/or curvilinear elements that are configured to trap printing matter, such as ink or toner, when electronically copied, thereby darkening the nano-pattern on the copied document. Trapping of the printing matter is facilitated by the design and miniature size of the adjacent elements that form the nano-structures (preferably, one and one-half point print size or less).