Optically variable security devices
An optical device is formed by hot stamping a demetallized hologram to an optically variable foil or to a coating of optically variable ink. In another embodiment a hologram is hot stamped to a banknote or document printed with a color-shifting ink.
1 . A method of manufacturing a device for providing an image having an optically variable feature, comprising:
a) providing a diffractive structure for forming at least a portion of the image;
b) providing an optically variable structure distinct from the diffractive structure, for providing the optically variable feature to the image, wherein the optically variable structure changes color with a change in angle of incident light, and wherein the optically variable structure comprises a first reflector layer, an absorber layer, and a dielectric layer between the reflector and absorber layers;
c) covering the diffractive structure or the optically variable structure with an adhesive;
d) after steps (a)-(c), activating, with energy, the adhesive and coupling the diffractive structure and the optically variable structure together in a predetermined mutual arrangement, wherein the energy activated adhesive forms a layer;
wherein the diffractive structure comprises a relief pattern and a high refraction index layer made of a material having an index of refraction no less than 1.65; and
wherein the diffractive structure comprises a patterned opaque coating so that the diffractive structure has opaque regions and light transmissive regions.
2 . The method as defined in claim 1 , wherein the opaque regions are configured for preventing light incident on the diffractive structure from propagating through to the optically variable structure via the layer of the energy activated adhesive, and the light transmissive regions are configured for allowing light incident on the diffractive structure to propagate through to the optically variable structure via the layer of the energy activated adhesive.
3 . The method as defined in claim 1 , wherein in step (a) comprises providing a second reflector layer to the diffractive structure.
4 . The method as defined in claim 3 , wherein the second reflector layer is partially demetallized.
5 . The method as defined in claim 4 , wherein the second reflector layer is segmented so that the reflector layer has one or more light transmissive windows, so that the optically variable structure is visible through said windows.
6 . The method as defined in claim 3 wherein the optically variable structure comprises a coating with a plurality of multilayer optical interference flakes therein or thereon.
7 . The method as defined in claim 1 , wherein step (a) comprises providing a substrate having a first side supporting the diffractive structure, wherein the first side of the substrate has a first region wherein the diffractive structure is therein or thereon, and the first side of the substrate has a second region wherein the diffractive structure is absent, and in step (c) the layer of the energy activated adhesive is adjoined to the first side of the substrate so that the optically variable structure is adhesively bound solely to the substrate and coupled to the diffractive structure by the surrounding adhesive.
8 . A device manufactured by the method defined in claim 1 .
9 . The method as defined in claim 1 , wherein the diffractive structure includes a grating to form a light transmissive region for allowing light incident on the diffractive structure to propagate through to the optically variable structure via the layer of the energy activated adhesive.
10 . The method as defined in claim 1 , wherein the diffractive structure includes indicia.
11 . The method as defined in claim 1 , wherein the diffractive structure includes a substrate having the grating impressed on a surface of the substrate.
12 . The method as defined in claim 1 , wherein the diffractive structure includes a protective coating.
13 . The method as defined in claim 1 , wherein the adhesive includes covert flakes.
14 . The method as defined in claim 13 , wherein the covert flakes include charms, taggants, shaped pigments, magnetic flakes, or fluorescent pigments.
15 . The method as defined in claim 1 , wherein in step (c) the adhesive covers the diffractive structure or the optically variable structure in a pattern.
16 . The method as defined in claim 15 , wherein the diffractive structure has regions not bonded to the optically variable structure based upon the pattern.
17 . The method as defined in claim 15 , wherein the pattern of adhesive forms a frame around the diffractive structure.