Retroreflective articles

1. A retroreflective article comprising:

a layer of optical elements, the optical elements consisting essentially of:

transparent microspheres, a transparent polymeric polyurethane layer disposed on the transparent microspheres, and at least one reflective layer, wherein the reflective layer is disposed on the transparent polymeric polyurethane layer; and

a bead bond layer, wherein the transparent polymeric polyurethane layer comprises a dried layer prepared from an aqueous polyurethane dispersion.

2. The retroreflective article of claim 1 , wherein the aqueous polyurethane dispersion comprises a functionalized polyurethane.

3. The retroreflective article of claim 2 , wherein the functionalized polyurethane comprises a silane terminated polyurethane.

4. The retroreflective article of claim 1 , wherein the aqueous polyurethane dispersion further comprises dispersed pigment particles and the transparent polymeric polyurethane layer comprises a colored transparent polymeric polyurethane layer.

5. The retroreflective article of claim 4 wherein the pigment particles comprise nanopigment particles.

6. The retroreflective article of claim 1 , wherein the aqueous polyurethane dispersion further comprises one or more additives, the additives comprising silane-functional compounds, pigments, dyes, UV stabilizers, antioxidants, UV absorbers, property modifiers, performance enhancers, or combinations thereof.

7. The retroreflective article of claim 6 , wherein the additive comprises a silane-functional compound comprising a bi-functional silane.

8. The retroreflective article of claim 1 , wherein the transparent polymeric polyurethane layer has a thickness of from 0.1 to 100 micrometers.

9. The retroreflective article of claim 1 , wherein the reflective layer comprises a reflective metal layer comprising a layer of layer of aluminum, silver, or a combination thereof, or a multi-layer dielectric reflective layer comprising a layer of SiO 2 , cryolite, TiO 2 , CaF 2 , MgF 2 , ZnS, Nb 2 O 5 , Ta 2 O 5 , ZrO 2 , or a combination thereof.

10. The retroreflective article of claim 9 , wherein the reflective layer comprises a multi-layer dielectric reflective layer and wherein the retroreflectivity of retroreflective article is greater than the retroreflectivity of an article with same multi-layer dielectric reflective layer and no transparent polymeric polyurethane layer.

11. The retroreflective article of claim 9 , wherein the reflective layer comprises a multi-layer dielectric reflective layer and wherein the multi-layer dielectric reflective layer has a reduced dichroic effect than an article with same multi-layer dielectric reflective layer and no transparent polymeric polyurethane layer.

12. The retroreflective article of claim 9 , wherein the transparent polymeric polyurethane layer functions as a low refractive index layer of the multi-layer dielectric reflective layer.

13. The retroreflective article of claim 1 , wherein the article is wash durable.

14. The retroreflective article of claim 4 , wherein the colored transparent polymeric polyurethane layer is a colorfast layer.

15. An article of clothing comprising:

a fabric with a first major surface and a second major surface; and

a retroreflective appliqué attached to the first major surface of the fabric, the retroreflective appliqué comprising:

a layer of optical elements, the optical elements consisting essentially of:

transparent microspheres, a transparent polymeric polyurethane layer disposed on the transparent microspheres, and at least one reflective layer, wherein the reflective layer

is disposed on the transparent polymeric polyurethane layer; and

a bead bond layer, wherein the transparent polymeric polyurethane layer comprises a dried layer prepared from an aqueous polyurethane dispersion.

16. A method of preparing a retroreflective article comprising:

providing a polymeric carrier layer with a first major surface and a second major surface;

providing transparent microspheres;

partially embedding the transparent microspheres into the first major surface of the polymeric carrier layer such that the beads at least partially protrude from the first major surface of the polymeric carrier layer to form a layer of microspheres;

depositing a coating composition comprising a an aqueous polyurethane dispersion on the layer of microspheres;

drying the coating composition to form a transparent polyurethane polymeric layer on the layer of transparent microspheres;

depositing one or more reflective layers on at least a portion of the first major surface of the polymeric carrier layer and the layer of microspheres;

applying a bead bond layer to the layer of microspheres; and

removing the polymeric carrier layer.

17. The method of claim 16 , wherein the aqueous polyurethane dispersion comprises a functionalized polyurethane.

18. The method of claim 17 , wherein the functionalized polyurethane comprises a silane terminated polyurethane.

19. The method of claim 16 , wherein the aqueous polyurethane dispersion further comprises one or more additives, the additives comprising silane-functional compounds, pigments, dyes, UV stabilizers, antioxidants, UV absorbers, property modifiers, performance enhancers, or combinations thereof.

20. The method of claim 19 , wherein the additive comprises a silane-functional compound comprising a bi-functional silane.

21. The method of claim 16 , wherein the transparent polymeric polyurethane layer has a thickness of from 0.1 to 100 micrometers.

22. The method of claim 16 , wherein the reflective layer comprises a reflective metal layer comprising a layer of layer of aluminum, silver, or a combination thereof, or a dielectric reflective layer comprising a layer of SiO 2 , cryolite, TiO 2 , CaF 2 , MgF 2 , ZnS, Nb 2 O 5 , Ta 2 O 5 , ZrO 2 , or a combination thereof.

23. An article comprising:

a polymeric carrier layer with a first major surface and a second major surface;

a layer of optical elements, partially embedded in the first major surface of the polymeric carrier layer, the optical elements consisting essentially of:

transparent microspheres, a transparent polymeric polyurethane layer disposed on the transparent microspheres, and at least one reflective layer, wherein the reflective layer is disposed on the transparent polymeric polyurethane layer; and

a bead bond layer disposed on the reflective layer, wherein the transparent polymeric polyurethane layer comprises a dried layer prepared from an aqueous polyurethane dispersion.