Anisotropic magnetic flakes
First Claim
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1. An anisotropic magnetic flake, for forming a reflective coating, comprising a two-dimensional layered structure having a thickness in a range of 50 nm to 10 microns and a longest planar dimension in a range of 1 micron to 500 microns, the two-dimensional layered structure comprising:
- a continuous magnetic layer, absent of a grating, for aligning the anisotropic magnetic flake substantially parallel to a surface of the reflective coating when the anisotropic magnetic flake is disposed in a liquid carrier and under influence of an external magnetic field,the continuous magnetic layer having a first surface and an opposing second surface; and
a first reflector layer disposed on the first surface and a second reflector layer disposed on the second surface, such that the continuous magnetic layer is contained therebetween,wherein the continuous magnetic layer comprises a magnetic material having a coercivity of less than about 2000 Oe and has a structure that provides in-plane magnetic anisotropy oriented in a direction that is at an angle of at least 20 degrees relative to the longest planar dimension,wherein the direction of the in-plane magnetic anisotropy is substantially orthogonal to two substantially parallel sides, of the two-dimensional layered structure, for alignment of the anisotropic magnetic flake side-by-side with one or more other anisotropic magnetic flakes of a same structure, andwherein a gap between the anisotropic magnetic flake and an anisotropic magnetic flake, of the one or more other anisotropic magnetic flakes, is no greater than 500 nm.
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Abstract
The invention relates to anisotropic, reflective, magnetic flakes. In a liquid carrier and under influence of an external magnetic field, the flakes attract to one another side-by-side and form ribbons which provide higher reflectivity to a coating and may be used as a security feature for authentication of an object.
91 Citations
24 Claims
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1. An anisotropic magnetic flake, for forming a reflective coating, comprising a two-dimensional layered structure having a thickness in a range of 50 nm to 10 microns and a longest planar dimension in a range of 1 micron to 500 microns, the two-dimensional layered structure comprising:
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a continuous magnetic layer, absent of a grating, for aligning the anisotropic magnetic flake substantially parallel to a surface of the reflective coating when the anisotropic magnetic flake is disposed in a liquid carrier and under influence of an external magnetic field, the continuous magnetic layer having a first surface and an opposing second surface; and a first reflector layer disposed on the first surface and a second reflector layer disposed on the second surface, such that the continuous magnetic layer is contained therebetween, wherein the continuous magnetic layer comprises a magnetic material having a coercivity of less than about 2000 Oe and has a structure that provides in-plane magnetic anisotropy oriented in a direction that is at an angle of at least 20 degrees relative to the longest planar dimension, wherein the direction of the in-plane magnetic anisotropy is substantially orthogonal to two substantially parallel sides, of the two-dimensional layered structure, for alignment of the anisotropic magnetic flake side-by-side with one or more other anisotropic magnetic flakes of a same structure, and wherein a gap between the anisotropic magnetic flake and an anisotropic magnetic flake, of the one or more other anisotropic magnetic flakes, is no greater than 500 nm. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification