Retroreflective dichroic reflector

• US 6,157,486 A
• Filed: 01/13/1998
• Issued: 12/05/2000
• Est. Priority Date: 01/13/1998
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Wong, Mel Y., Garland, Wilson C., Wheatley, John A., Weber, Michael F., Ouderkirk, Andrew J., Benson, Olester Jr., Fellows, Benjamin T.
• Primary Examiner(s): SCHUBERG, DARREN E
• Application Number:
  US09/006,579
• Time in Patent Office: 1,057 Days
• Field of Search: 359/497, 359/498, 359/530, 359/584, 359/589, 359/590
• US Class Current: 359/487.05
• CPC Class Codes: G02B 5/124 plural reflecting elements forming part of a unitary plate or sheet
• CPC Class Codes: G02B 5/128 transparent spheres being embedded in matrix
• CPC Class Codes: G02B 5/287 comprising at least one layer of organic material

Abstract

Various combinations of retroreflective sheeting and multilayer polymeric reflective films are disclosed. The reflective film includes alternating layers of at least a first and second polymer, the alternating layers being configured to exhibit a high reflectance for light within a first spectral range and a low reflectance for light within a second spectral range. At least two of the alternating layers can have out-of-plane indices of refraction which differ by no more than 50% of the maximum in-plane refractive index difference. The polymeric layers can define optical repeating units arranged in a sequence to have a specific thickness profile designed to give sharpened spectral transitions. The retroreflective layer preferably exhibits retroreflectance in all planes of incidence, but alternately it can be retroreflective in at least one plane of incidence but not in at least one other plane of incidence.

Claims

1. A reflective article having a front side and a rear side in relation to an observer, comprising a dichroic reflector proximate the front side and a retroreflective layer proximate the rear side, the retroreflective layer being oriented to reflect light transmitted by the dichroic reflector back through the dichroic reflector, the dichroic reflector comprising alternating layers of at least a first and second polymer, the alternating layers being configured to exhibit a relatively high reflectance for normally incident light within a first spectral range and a relatively low reflectance for normally incident light within a second spectral range.

2. The article of claim 1, wherein at least the first polymer layers are birefringent.

3. The article of claim 2, wherein, over a wavelength range of interest, at least two adjacent layers in the dichroic reflector have indices of refraction along an axis perpendicular to a plane of the dichroic reflector which differ by no more than 50% of the maximum in-plane refractive index difference between the two adjacent layers.

4. The article of claim 3, wherein a plurality of pairs of adjacent layers in the dichroic reflector have indices of refraction along the axis perpendicular to the plane of the dichroic reflector which differ by no more than about 20% of the maximum in-plane refractive index difference between the respective pairs of adjacent layers over the wavelength range of interest.

5. The article of claim 4, wherein substantially every pair of adjacent layers in the dichroic reflector has indices of refraction along the axis perpendicular to the plane of the dichroic reflector which are substantially the same.

6. The article of claim 2, wherein the first polymer is selected from the group consisting of:

polyethylene naphthalate, and copolymers and blends thereof based upon naphthalene dicarboxylic acid;

polyethylene terephthalate, and copolymers and blends thereof based upon terephthalic acid;

polybutylene naphthalate, and copolymers and blends thereof based upon naphthalene dicarboxylic acid; and

polybutylene terephthalate, and copolymers and blends thereof based upon terephthalic acid.

7. The article of claim 1, wherein the dichroic reflector comprises a plurality of optical repeating units (ORUs) with associated optical thicknesses, the ORUs arranged in a sequence of decreasing optical thickness along a given direction adjacent a sequence of non-decreasing optical thickness.

8. The article of claim 7, wherein the sequence of ORUs arranged in a non-decreasing optical thickness has an optical thickness profile selected from the group consisting of a flat, graded linear, and curved profile.

9. The article of claim 8, wherein the ORUs are arranged in a first and second set of ORUs each having a monotonically decreasing optical thickness profile and at least one set of ORUs having a non-decreasing optical thickness profile.

10. The article of claim 9, wherein the at least one set of ORUs has a curved optical thickness profile.

11. The article of claim 7, wherein at least one of the sequences of ORUs has an optical thickness profile with a nonzero second derivative.

12. The article of claim 11, wherein at least a portion of the first spectral range is at wavelengths greater than 700 nm.

13. The article of claim 12, wherein the first spectral range comprises a reflection band having a full width at half maximum of at least about 50 nm.

14. The article of claim 1, wherein the second spectral range includes most of the range from 400 to 700 nanometers.

15. The article of claim 14, wherein the dichroic reflector has less than 50% reflectance over the second spectral range.

16. The article of claim 15, wherein the dichroic reflector has less than about 20% reflectance from 400 to 700 nm.

17. The article of claim 1, wherein the dichroic reflector has an absorption of no greater than about 1% over the first and second spectral ranges.

18. The article of claim 1, wherein the first and second spectral range are discontinuous and intermeshed to define a series of reflection and transmission bands.

19. The article of claim 18, wherein at least some of the reflection and transmission bands have approximately equal bandwidths.

20. The article of claim 1, wherein the dichroic reflector is selected from the group consisting of a polarizer and a mirror.

21. The article of claim 1, wherein the retroreflective layer exhibits retroreflectance in at least one plane of incidence but not in at least one other plane of incidence.

22. The article of claim 1, wherein the retroreflective layer comprises a structured surface.

23. The article of claim 22, wherein the structured surface includes shapes selected from the group consisting of cube corner elements, linear prisms, and pyramids.

24. The article of claim 22, wherein the retroreflective layer further comprises a seal film covering the structured surface.

25. The article of claim 22, wherein the retroreflective layer further comprises a metallic coating on the structured surface.

26. The article of claim 1, wherein the retroreflective layer comprises beaded sheeting.

27. The article of claim 1, further comprising a protective film covering the dichroic reflector.

28. The article of claim 27, wherein the protective film comprises acrylic.

29. The article of claim 27, further comprising an adhesive layer carried by the retroreflective layer at the rear side of the article.

30. The article of claim 1, wherein the article is substantially nontransmissive.

31. The article of claim 30, wherein the retroreflective layer includes a metallic specularly reflective layer.

32. The article of claim 1, wherein the dichroic reflector is laminated to the retroreflective layer.

33. The article of claim 1, wherein at least a portion of the retroreflective layer is cast and cured on the dichroic reflector.

34. The article of claim 1, wherein the retroreflective layer comprises a glittering cube corner retroreflective sheeting.

35. The article of claim 1, wherein the dichroic reflector comprises a plurality of optical repeating units (ORUs), the ORUs having in one or more first regions of the dichroic reflector a first thickness variation profile that substantially defines a transmission band, the ORUs having in one or more second regions of the dichroic reflector a second thickness variation profile different from the first thickness variation profile that substantially defines a bandedge slope of the transmission band.