US-12623480-B2 - Optical security element

US12623480B2US 12623480 B2US12623480 B2US 12623480B2US-12623480-B2

Abstract

An optical security element may be printed on a substrate. The optical security element may include a plurality of bifunctional pigment flakes provided in a binder. A bifunctional pigment flake in the plurality of bifunctional pigment flakes may comprise a first surface having a diffraction grating relief with a first modulation, and a second surface having a second modulation that is smaller than the first modulation. The plurality of bifunctional pigment flakes are arranged such that, in a presence of incident light, diffraction colors are exhibited by a first subset of the plurality of bifunctional pigment flakes that are in a first region of the optical security element, and an interference color is exhibited by a second subset of the plurality of bifunctional pigment flakes that are in a second region of the optical security element.

Inventors

Vladimir P. Raksha
Kees-Jan DELST
Paul T. Kohlmann

Assignees

VIAVI SOLUTIONS INC.

Dates

Publication Date: 20260512
Application Date: 20240314

Claims (20)

1 . An optical security element printed on a substrate, the optical security element comprising: a plurality of bifunctional pigment flakes provided in a binder, wherein a bifunctional pigment flake in the plurality of bifunctional pigment flakes comprises a first surface having a diffraction grating relief with a first modulation, and a second surface having a second modulation that is smaller than the first modulation, wherein the plurality of bifunctional pigment flakes are arranged such that, in a presence of incident light: a set of colors are exhibited by a first subset of the plurality of bifunctional pigment flakes that are in a first region of the optical security element, and an additional color is exhibited by a second subset of the plurality of bifunctional pigment flakes that are in a second region of the optical security element.
2 . The optical security element of claim 1 , wherein the first region is distinct from the second region such that the set of colors and the additional color are non-blended.
3 . The optical security element of claim 1 , wherein tilt angles of bifunctional pigment flakes in the first subset of the plurality of bifunctional pigment flakes with respect to the substrate are greater than 45 degrees.
4 . The optical security element of claim 1 , wherein tilt angles of bifunctional pigment flakes in the second subset of the plurality of bifunctional pigment flakes with respect to the substrate are less than 45 degrees.
5 . The optical security element of claim 1 , wherein the second modulation is at least 50% smaller than the first modulation.
6 . The optical security element of claim 1 , wherein the plurality of bifunctional pigment flakes are arranged to form a plurality of concentric rings within the binder, wherein the first region corresponds to a first subset of the plurality of concentric rings and the second region corresponds to a second subset of the plurality of concentric rings.
7 . The optical security element of claim 1 , wherein the plurality of bifunctional pigment flakes are arranged to form a structure within the binder, wherein the first region corresponds to a first section of the structure and the second region corresponds to a second section of the structure.
8 . The optical security element of claim 1 , wherein the plurality of bifunctional pigment flakes comprises a plurality of opaque bifunctional pigment flakes.
9 . The optical security element of claim 1 , wherein the plurality of bifunctional pigment flakes comprises a plurality of transparent bifunctional pigment flakes.
10 . A method for printing an optical security element on a substrate, comprising: providing, on the substrate, a binder that includes a plurality of magnetizable bifunctional pigment flakes, wherein a magnetizable bifunctional pigment flake in the plurality of magnetizable bifunctional pigment flakes comprises a first surface having a diffraction grating relief with a first modulation and a second surface with a second modulation that is smaller than the first modulation; applying a magnetic field to the binder using one or more magnets, wherein the magnetic field orients the plurality of magnetizable bifunctional pigment flakes according to the magnetic field, wherein the plurality of magnetizable bifunctional pigment flakes are oriented such that, in a presence of incident light: a set of colors are exhibited in a first region of the optical security element by a first subset of the plurality of magnetizable bifunctional pigment flakes, and a different color is exhibited in a second region of the optical security element by a second subset of the plurality of magnetizable bifunctional pigment flakes; and setting or hardening the binder.
11 . The method of claim 10 , wherein the first region is distinct from the second region such that the set of colors and the different color are non-blended.
12 . The method of claim 10 , wherein the magnetic field orients the plurality of magnetizable bifunctional pigment flakes such that tilt angles of the first subset of the plurality of magnetizable bifunctional pigment flakes in the first region with respect to the substrate are greater than 45 degrees.
13 . The method of claim 10 , wherein the magnetic field orients the plurality of magnetizable bifunctional pigment flakes such that tilt angles of the second subset of the plurality of magnetizable bifunctional pigment flakes in the second region with respect to the substrate are less than 45 degrees.
14 . The method of claim 10 , wherein the second modulation is at least 50% smaller than the first modulation.
15 . The method of claim 10 , wherein the magnetic field orients the plurality of magnetizable bifunctional pigment flakes to form a plurality of concentric rings of magnetizable bifunctional pigment flakes within the binder.
16 . The method of claim 10 , wherein the magnetic field orients the plurality of magnetizable bifunctional pigment flakes to form a structure within the binder.
17 . A printed optical security element, comprising: a first region comprising a first subset of a plurality of bifunctional pigment flakes disposed in a binder, wherein the first subset of the plurality of bifunctional pigment flakes are arranged such that, in a presence of incident light, a set of colors are exhibited in the first region of the printed optical security element, and a second region comprising a second subset of the plurality of bifunctional pigment flakes disposed in the binder, wherein the second subset of the plurality of bifunctional pigment flakes are arranged such that, in the presence of the incident light, another color is exhibited in the second region of the printed optical security element, wherein the first region is distinct from the second region such that the set of colors and the other color are non-blended.
18 . The printed optical security element of claim 17 , wherein a bifunctional pigment flake in the plurality of bifunctional pigment flakes comprises a first surface having a diffraction grating relief with a first modulation and a second surface having a second modulation that is smaller than the first modulation.
19 . The printed optical security element of claim 17 , wherein tilt angles of bifunctional pigment flakes in the first subset of the plurality of bifunctional pigment flakes with respect to a substrate of the printed optical security element are greater than 45 degrees.
20 . The printed optical security element of claim 17 , wherein tilt angles of bifunctional pigment flakes in the second subset of the plurality of bifunctional pigment flakes with respect to a substrate of the printed optical security element are less than 45 degrees.

Description

BACKGROUND An article, such as a banknote, may include a printed optical security element (e.g., an anti-counterfeiting feature) that uses a color-shifting interference pigment comprising a plurality of magnetizable pigment flakes. The magnetizable pigment flakes are dispersed in a thin layer of ink printed on the article and color-shifting is provided based on reflection of incident light from the pigment flakes. Generally, the magnetizable pigment flakes are aligned in a particular manner by applying a magnetic field to the ink prior to drying. As one example, a curved magnetic field can be used to align the magnetizable pigment flakes such that the pigment flakes are tilted at different angles relative to a substrate of the article, so as to cause the pigment flakes to reflect incident light in different directions (depending on the angle of orientation of a given pigment flake). Here, the direction of reflection for a given pigment flake is governed by the tilt angle and the law of reflection. The law of reflection states that when a light ray is incident on a smooth surface, an angle of reflection of the light ray is equal to an angle of incidence of the light ray. SUMMARY In some implementations, an optical security element printed on a substrate includes a plurality of bifunctional pigment flakes provided in a binder, wherein a bifunctional pigment flake in the plurality of bifunctional pigment flakes comprises a first surface having a diffraction grating relief with a first modulation, and a second surface having a second modulation that is smaller than the first modulation, wherein the plurality of bifunctional pigment flakes are arranged such that, in a presence of incident light: diffraction colors are exhibited by a first subset of the plurality of bifunctional pigment flakes that are in a first region of the optical security element, and an interference color is exhibited by a second subset of the plurality of bifunctional pigment flakes that are in a second region of the optical security element. In some implementations, a method for printing an optical security element on a substrate includes providing, on the substrate, a binder that includes a plurality of magnetizable bifunctional pigment flakes, wherein a magnetizable bifunctional pigment flake in the plurality of magnetizable bifunctional pigment flakes comprises a first surface having a diffraction grating relief with a first modulation and a second surface with a second modulation that is smaller than the first modulation; applying a magnetic field to the binder using one or more magnets, wherein the magnetic field orients the plurality of magnetizable bifunctional pigment flakes according to the magnetic field, wherein the plurality of magnetizable bifunctional pigment flakes are oriented such that, in a presence of incident light: diffraction colors are exhibited in a first region of the optical security element by a first subset of the plurality of magnetizable bifunctional pigment flakes, and an interference color is exhibited in a second region of the optical security element by a second subset of the plurality of magnetizable bifunctional pigment flakes; and setting or hardening the binder. In some implementations, a printed optical security element includes a first region comprising a first subset of a plurality of bifunctional pigment flakes disposed in a binder, wherein the first subset of the plurality of bifunctional pigment flakes are arranged such that, in a presence of incident light, diffraction colors are exhibited in the first region of the optical security element, and a second region comprising a second subset of the plurality of bifunctional pigment flakes disposed in the binder, wherein the second subset of the plurality of bifunctional pigment flakes are arranged such that, in the presence of the incident light, an interference color is exhibited in the second region of the optical security element, wherein the first region is distinct from the second region such that the diffraction colors and the interference color are non-blended. BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A-1B are examples associated with a conventional optical security element comprising a plurality of magnetizable pigment flakes that are aligned to different angles. FIG. 2 is an example of magnetizable pigment flakes oriented in a cylindrical structure. FIG. 3 is a diagram illustrating a color distribution along a width of a conventional optical security element. FIG. 4 is a diagram illustrating an optically active element formed by reflection elements that are molded into an embossing lacquer and coated with a reflection-enhancing coating. FIG. 5 is a diagram illustrating an example of a bifunctional pigment flake as described herein. FIG. 6 is a diagram illustrating a particular example of modulation reduction of a surface of a multilayer optical structure of a bifunctional pigment flake. FIGS. 7A-7B are diagrams associated with an example i