Multiple Band Reflector with Metal and Dielectric Layers

• US 20070279748A1
• Filed: 06/06/2006
• Published: 12/06/2007
• Est. Priority Date: 06/06/2006
• Status: Active Grant

• Current Assignee: CPFilms Inc. (Eastman Chemical Company)
• Original Assignee: CPFilms Inc. (Eastman Chemical Company)
• Inventors: Li, Jaime Antonio, Barth, Steven Allen
• Granted Patent: US 7,564,628 B2
• Time in Patent Office: Days
• US Class Current: 359/584
• CPC Class Codes: G02B 5/0875 the reflecting layers comprising two or more metallic layers
• CPC Class Codes: G02B 5/286 having four or fewer layers, e.g. for achieving a colour effect

Abstract

Now, according to the present invention, multiple band optical reflectors are provided that utilize a stack of metal and dielectric layers to create a reflection curve in the visible spectrum that has multiple peak intensities. Reflectors of the present invention comprise at least two dielectric layers that have differing thicknesses, with metal layers disposed therebetween. The use of metal layers in the present invention, as opposed to using alternating layers of dielectric materials, results in a reflector that is substantially thinner than a conventional two dielectric reflector.

Claims

1. A multiple band visible light reflector, comprising:

a substrate;

a stack disposed on said substrate or on one or more intervening layers that are disposed on said substrate, wherein said stack comprises;

a first metal layer disposed in contact with said substrate;

a first dielectric layer disposed in contact with said first metal layer;

a second metal layer disposed in contact with said first dielectric layer; and

,

a second dielectric layer disposed in contact with said second metal layer;

wherein said first dielectric layer and said second dielectric layer have a difference in thickness of at least 6 percent optical thickness; and

,

wherein said reflector reflects light over the visible spectrum in at least two reflection peaks, wherein the intensity of each reflection peak is at least 45% of incident light at the same wavelength as said each reflection peak and the intensity of valleys between said reflection peaks are no more than 50% of the average intensities of said reflection peaks.

2. The reflector of claim 1, wherein said substrate is transparent and flexible.

3. The reflector of claim 1, wherein said substrate is poly(ethylene terephthalate).

4. The reflector of claim 1, wherein said substrate has a metallized surface disposed in contact with said first metal layer.

5. The reflector of claim 1, wherein said metallized surface comprises chromium or aluminum having a thickness of at least 40 nanometers.

6. The reflector of claim 1, wherein said reflector absorbs any visible light that is not reflected.

7. The reflector of claim 1, wherein a portion of any visible light that is not reflected is transmitted.

8. The reflector of claim 1, wherein said first metal layer and said second metal layer each comprise silver.

9. The reflector of claim 1, wherein said first metal layer has a thickness of 15 to 60 nanometers.

10. The reflector of claim 1, wherein said second metal layer has a thickness of 15 to 60 nanometers.

11. The reflector of claim 1, wherein said first dielectric layer and said second dielectric layer have an optical thickness difference of at least 8%.

12. The reflector of claim 1, wherein said first dielectric layer and said second dielectric layer have an optical thickness difference of at least 10%.

13. The reflector of claim 1, wherein said first dielectric layer and said second dielectric layer comprise the same material.

14. The reflector of claim 1, wherein said first dielectric layer and said second dielectric layer comprise different materials.

15. The reflector of claim 1, wherein said first dielectric layer comprises TiO₂, Nb₂O₅, MgF₂, Ta₂O₅, SiO₂, In₂O₃, SnO₂, or Indium Tin Oxide, and said second dielectric layer comprises TiO₂, Nb₂O₅, MgF₂, Ta₂O₅, SiO₂, In₂O₃, SnO₂, or Indium Tin Oxide.

16. The reflector of claim 1, wherein said first dielectric layer comprises TiO₂, Nb₂O₅, or SiO₂ and said second dielectric layer comprises TiO₂, Nb₂O₅, or SiO₂.

17. The reflector of claim 1, wherein said reflector further comprises a third metal layer disposed in contact with said second dielectric layer;

and, a third dielectric layer disposed in contact with said third metal layer.

18. The reflector of claim 1, wherein said reflector further comprises a fourth metal layer disposed in contact with said third dielectric layer;

and, a fourth dielectric layer disposed in contact with said fourth metal layer.

19. The reflector of claim 1, wherein said stack has a thickness of less than 0.5 microns.

20. An item comprising a multiple band visible light reflector as an anti-counterfeiting measure, wherein said reflector comprises:

a substrate;

a stack disposed on said substrate or on one or more intervening layers that are disposed on said substrate, wherein said stack comprises;

a first metal layer disposed in contact with said substrate;

a first dielectric layer disposed in contact with said first metal layer;

a second metal layer disposed in contact with said first dielectric layer; and

,

a second dielectric layer disposed in contact with said second metal layer;

wherein said first dielectric layer and said second dielectric layer have a difference in thickness of at least 6 percent optical thickness; and

,

wherein said reflector reflects light over the visible spectrum in at least two reflection peaks, wherein the intensity of each reflection peak is at least 45% of incident light at the same wavelength as said each reflection peak and the intensity of valleys between said reflection peaks are no more than 50% of the average intensities of said reflection peaks.

21. A method of confirming the authenticity of an item, comprising the steps:

A) directing a light of known wavelengths at said item;

B) reflecting said light off of a multiple band visible light reflector that said item comprises, wherein said reflector comprises;

a stack disposed on said substrate or on one or more intervening layers that are disposed on said substrate, wherein said stack comprises;

a first metal layer disposed in contact with said substrate;

a first dielectric layer disposed in contact with said first metal layer;

a second metal layer disposed in contact with said first dielectric layer; and

,

a second dielectric layer disposed in contact with said second metal layer;

wherein said first dielectric layer and said second dielectric layer have a difference in thickness of at least 6 percent optical thickness; and

,

wherein said reflector reflects light over the visible spectrum in at least two reflection peaks, wherein the intensity of each reflection peak is at least 45% of incident light at the same wavelength as said each reflection peak and the intensity of valleys between said reflection peaks are no more than 50% of the average intensities of said reflection peaks.

C) confirming that reflected light matches a knows pattern of reflection from said reflector.