Covert security coating

Abstract

A multilayer thin film filter is disclosed an organic dielectric layer serving as a spacer layer in a Fabry-Perot structure. The dielectric has embossed regions of varying thicknesses wherein the thickness within a region is substantially uniform. Each different region of a different thickness produces a different color (shift). The size of one of the embossed adjacent regions is such that the color of said one region is uniform and cannot be seen by a human eye as different in color from the uniform color of an adjacent region thereto, and wherein the color within a region can be seen with magnification of at least 10:1. This serves as a covert color coding system useful as a security device.

Description

[0001] Cross References to Related Applications [0002] [01] This application claims priority to US Patent Application No. 60 / 691,499, filed June 17, 2005, which is incorporated herein by reference. technical field [0003] [02] The present invention generally relates to thin-film optical coatings for the manufacture of security articles, and also to the manufacture of diffractive surfaces which can be used as security articles in various applications, for example with color shifting or optically variable Hologram or grating for the background. In particular, the invention relates to the field of coating and / or embossing dielectric substrates to provide gratings or holograms, preferably in a vacuum roll coating chamber, while producing Chromagrams in vacuum TM type device or build a basic device on it to make a Chromagram TM type device. The invention also relates to the fabrication of invisible optical devices having dielectric layers of variable thickness. For example, ...

AI Technical Summary

Problems solved by technology

[0019] [17] Contrary to Holmes et al., the prior art U.S. Patent No. 6,987,590 provides a different novel Chromagram TM , where no separation layer is required, but where there are separate color shifting and holographic effects

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