Security device with metameric features using diffractive pigment flakes
View Patent ↗A metameric optical structure is disclosed having first optical structures comprising diffractive flakes having diffractive structures thereon, and a second optical structures having non-diffractive flakes which may have other special effect properties, such as color shifting. At one angle of incidence or one viewing angle, near normal. The hues match and at other angles they do not match. The diffractive flakes are preferably magnetically aligned so that the grating structures are parallel. Disclosed is also an image formed of at least a first region of diffractive flakes and a second region of non-diffractive flakes wherein the regions are adjacent one another and wherein one of the regions forms a logo, symbol or indicia that appears or disappears in dependence upon the angle of viewing.
1. An optically variable article comprising:
a substrate having a first surface and a second surface;
first and second optical devices having different optical properties formed on first and second regions, respectively, carried by the first surface or the second surface of the substrate, one of the first and second optical devices being optically variable and forming a pair with the other of the first and second optical devices, wherein said first and second optical devices are carried by the substrate in spaced-apart positions to permit viewing at the same time by the human eye, wherein said first and second optical devices appear to the human eye to have the same matching color at one angle of incidence between 0 degrees and 90 degrees for a color match angle and being without color match at other angles of incidence, wherein the first optical device comprises a diffractive optical structure having a diffractive pattern defined therein or thereon ,wherein the second optical device is diffractive or color shifting or is comprised of reflective flakes in a tinted carrier, wherein the diffractive optical structure includes magnetically aligned diffractive flakes.
2. An optically variable article as defined in claim 1 wherein the magnetically aligned diffractive flakes are color shifting flakes.
3. An optically variable article as defined in claim 2 wherein one of the first and second regions forms a logo, indicia, or image and wherein the other of the first and second regions forms a visible background to the logo, indicia or image at angles where the two regions are unmatched in color.
4. An optically variable article as defined in claim 3 wherein the color match angle is angle of incidence of 30 degrees or greater.
5. An optically variable article as defined in claim 4 wherein there is essentially no visible diffraction when a color match is seen, and wherein the second optical device includes a plurality of optical effect flakes.
6. An optically variable article as defined in claim 4 wherein one of said first and second optical devices is non-optically variable.
7. An optically variable article as defined in claim 6 , wherein wherein one of the first and second device have flakes that are disposed in a colored carrier.
8. An optically variable article as defined in claim 7 wherein at least one of the first and second optical devices includes a metal-dielectric interference stack.
9. An optically variable article as defined in claim 2 wherein a plurality of the optically variable diffractive flakes are oriented to be out-of-plane and at least partially upstanding with respect to the substrate.