Uptically variable security devices

Abstract

A security article (10) includes a light transmissive substrate (12) having a first surface and an opposing second surface, with the first surface having an optical interference pattern (14) such as a holographic image pattern or an optical diffraction pattern thereon. A color shifting optical coating (16) is formed on the substrate such as on the interference pattern or on the opposing second surface of the substrate, with the optical coating providing an observable color shift as the angle of incident light or viewing angle changes. Various processes can be utilized to form the security article (10), such as vacuum coating processes, lamination, laser scribing, and laser imaging. The security article (10) can be affixed to a variety of objects through various attachment mechanisms, such as pressure sensitive adhesives or hot stamping processes, to provide for enhanced security measures such as anticounterfeiting.

Description

technical field

[0001] The present invention relates generally to thin film optical coatings for use in the manufacture of security articles. In particular, the invention relates to the fabrication of diffractive surfaces such as holograms or gratings with color shifting or optically variable backgrounds that can be used as security articles in various applications. Background technique

[0002] Color shifting pigments and colorants are already used in many applications ranging from automotive paints to security inks for security documents and currency. Such pigments and colorants have the property of changing color when the angle of incident light changes or the viewing angle of the observer shifts. The main method used to obtain such color shifting colorants is to disperse the flakes in a medium, such as paint or ink, and then apply the medium to the surface of the object, wherein the flakes generally consist of multilayer films with specific optical properties . [000...

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