Anisotropic Magnetic Flakes

• US 20090072185A1
• Filed: 09/19/2008
• Published: 03/19/2009
• Est. Priority Date: 07/31/2001
• Status: Active Grant

• Current Assignee: Viavi Solutions, Inc. (Lumentum Holdings Inc.)
• Original Assignee: JDS Uniphase Corporation (Lumentum Holdings Inc.)
• Inventors: Kohlmann, Paul T., Teitelbaum, Neil, Raksha, Vladimir P., Phillips, Roger W., Coombs, Paul G., Markantes, Charles T., Argoitia, Alberto
• Granted Patent: US 9,662,925 B2
• Time in Patent Office: Days
• US Class Current: 252/62.51R
• CPC Class Codes: B42D 2033/16 Magnetic or magnetisable material
• CPC Class Codes: B42D 2033/18 Reflecting material
• CPC Class Codes: B42D 2035/14 Dot or raster patterns
• CPC Class Codes: B42D 25/29 Securities; Bank notes
• CPC Class Codes: B42D 25/328 Diffraction gratings; Holograms
• CPC Class Codes: B42D 25/369 Magnetised or magnetisable materials
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01P 2004/02 obtained by optical microscopy
• CPC Class Codes: C01P 2004/03 obtained by SEM
• CPC Class Codes: C01P 2004/61 Micrometer sized, i.e. from 1-100 micrometer
• CPC Class Codes: C01P 2004/62 Submicrometer sized, i.e. from 0.1-1 micrometer
• CPC Class Codes: C01P 2004/64 Nanometer sized, i.e. from 1-100 nanometer
• CPC Class Codes: C01P 2006/42 Magnetic properties
• CPC Class Codes: C01P 2006/60 Optical properties, e.g. expressed in CIELAB-values
• CPC Class Codes: C09C 1/0015 Pigments exhibiting interference colours, e.g. transparent platelets of appropriate thinness or flaky substrates, e.g. mica, bearing appropriate thin transparent coatings
• CPC Class Codes: C09C 1/0021 comprising a core coated with only one layer having a high or low refractive index
• CPC Class Codes: C09C 1/0078 Pigments consisting of flaky, non-metallic substrates, characterised by a surface-region containing free metal
• CPC Class Codes: C09C 2200/1054 the core consisting of a metal
• CPC Class Codes: C09C 2200/304 Thickness of intermediate layers adjacent to the core, e.g. metallic layers, protective layers, rutilisation enhancing layers or reflective layers
• CPC Class Codes: C09C 2200/306 Thickness of an absorbing layer
• CPC Class Codes: C09C 2200/308 : Total thickness of the pigment particle
• CPC Class Codes: C09C 2200/401 : Inorganic protective coating
• CPC Class Codes: C09C 2210/40 : Embossed layers
• CPC Class Codes: C09C 2220/20 : PVD, CVD methods or coating in a gas-phase using a fluidized bed
• CPC Class Codes: C09D 11/037 : characterised by the pigment
• CPC Class Codes: C09D 11/50 : Sympathetic, colour changing or similar inks
• CPC Class Codes: C09D 201/00 : Coating compositions based on unspecified macromolecular compounds
• CPC Class Codes: C09D 5/004 : Reflecting paints; Signal paints
• CPC Class Codes: C09D 7/61 : inorganic
• CPC Class Codes: C09D 7/70 : characterised by shape, e.g. fibres, flakes or microspheres
• CPC Class Codes: H01F 1/0027 : Thick magnetic films forming thick magnetic films H01F41/16
• CPC Class Codes: H01F 10/08 : characterised by magnetic layers H01F10/32 takes precedence ; applying thin magnetic films to substrates H01F41/14
• CPC Class Codes: H01F 41/16 : the magnetic material being applied in the form of particles, e.g. by serigraphy , to form thick magnetic films or precursors therefor H01F41/18 -H01F41/24 take precedence
• CPC Class Codes: Y10T 428/24372 : Particulate matter
• CPC Class Codes: Y10T 428/2982 : Particulate matter [e.g., sphere, flake, etc.]

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.

Claims

1. An anisotropic magnetic flake for forming a reflective coating,

comprising a layered structure

having a thickness in the range of 50 nm-10 microns,

having a two-dimensional shape with a longest planar dimension in the range of 1-500 microns, and

comprising:

a magnetic layer for aligning the flake substantially parallel to the surface of the reflective coating, when said flake is disposed in a liquid carrier under influence of an external magnetic field;

wherein the magnetic layer has a structure which provides in-plane magnetic anisotropy forming an angle of at least 20 degrees with the longest planar dimension.

2. A flake defined in claim 1,

wherein the magnetic layer is a continuous magnetic layer absent of a grating, the two-dimensional shape has two sides substantially parallel to each other,

and wherein the in-plane magnetic anisotropy of the magnetic layer is substantially orthogonal to said two sides for alignment of the flake side-by-side with one or more flakes of a same structure when said flakes are disposed in a liquid carrier under influence of an external magnetic field while forming the reflective coating.

3. A flake defined in claim 2, wherein the two-dimensional shape is a rectangular shape with equal or unequal sides and the in-plane magnetic anisotropy of the magnetic layer is substantially parallel to a side of the rectangular shape.

4. A flake defined in claim 1, further comprising first and second reflector layers supported by the magnetic layer, first and second dielectric layers supported by the first and second reflector layers, respectively, and first and second absorber layers supported by the first and second dielectric layers, respectively, for providing a color-shifting optical effect.

5. A method of manufacturing a flake defined in claim 2, comprising the steps of:

a) providing a substrate for supporting a releasable coating, which includes the magnetic layer formed of a magnetic material;

b) embossing or etching the substrate with a plurality of frames having the two-dimensional shape with the two sides substantially orthogonal to a first direction, before or after the releasable coating is applied to the substrate;

c) coating the substrate with the releasable coating so as to provide the magnetic layer having a magnetic anisotropy in the first direction, wherein the releasable coating upon removal from the substrate breaks apart into the flakes; and

,

d) removing the releasable coating from the substrate and breaking it into the flakes.

6. A method defined in claim 5, wherein in step (c) the substrate is moving in the first direction.

7. A method defined in claim 5, wherein the substrate is curved.

8. A method defined in claim 5, wherein step (c) includes using at least two sources of the magnetic material which provide the magnetic material to a same portion of the substrate at different angles.

9. A method defined in claim 8, wherein the at least two sources of the magnetic material provide the magnetic material to the same portion of the substrate simultaneously.

10. A method defined in claim 8, wherein the at least two sources of the magnetic material provide the magnetic material to the same portion of the substrate at different times.

11. A method defined in claim 5, wherein step (c) includes moving the substrate in the first direction and using two sources of magnetic material disposed so that a line connecting the two sources is substantially orthogonal to the first direction.

12. A method defined in claim 5, wherein step (c) includes moving the substrate in the first direction and using two sources of magnetic material disposed so that a line connecting the two sources is substantially parallel to the first direction.

13. A method defined in claim 5, wherein step (c) includes annealing of the magnetic material in a magnetic field.

14. A method defined in claim 5, wherein step (c) includes Xe-ion-irradiation of the magnetic material.

15. A coating comprising a solidified carrier and a plurality of flakes having the structure defined in claim 1 dispersed therein,

wherein all flakes of the plurality of flakes have a same two-dimensional shape, such that two sides thereof are substantially parallel to each other, and have the magnetic layer such that the in-plane magnetic anisotropy is substantially orthogonal to said two sides;

and wherein a portion of the flakes forms a ribbon of at least three flakes adjacent to one another so as to be side-by-side with gaps between the flakes of no greater than 500 nm, when said flakes are disposed in a liquid carrier under influence of an external magnetic field while forming the coating.

16. A coating defined in claim 15, wherein the portion of the flakes form two or more ribbons adjacent to one another so as to be side-by-side with gaps between the ribbons of no greater than 4 micron, whereby forming a tile array of flakes.

17. A method of authentication of an object having thereon a coating defined in claim 15, comprising the step of identifying a ribbon.

18. A flake defined in claim 1, further comprising a second reflector layer having reflectivity of greater than 40%.

19. A flake defined in claim 2, further comprising an indicia.

20. A flake defined in claim 19, wherein the indicia is symmetrical with respect to a direction of the in-plane magnetic anisotropy.

21. A method defined in claim 5, wherein step (b) includes embossing or etching the substrate with an indicia.

22. A flake defined in claim 1, wherein the magnetic layer has a non-periodic linear grating structure comprising a plurality of ridges and grooves substantially parallel to each other and forming the angle of at least 20 degrees with the longest planar dimension.

23. A flake defined in claim 1, wherein the magnetic layer has a diffractive grating structure comprising a plurality of ridges and grooves substantially parallel to each other and forming the angle of at least 20 degrees with the longest planar dimension.

24. A flake defined in claim 1, wherein the magnetic layer comprises a plurality of magnetic stripes substantially parallel to each other and forming the angle of at least 20 degrees with the longest planar dimension.

25. A coating defined in claim 15, wherein each of the plurality of flakes has a symmetric indicia and the plurality of flakes form at least 70% of all flakes having an indicia thereon in the coating.