Thermoformable three dimensional retroreflective article and method of manufacture
A three dimensional retroreflective article having an outer surface with a reflectivity of at least about 200 lux, and method for making such an article from a thermoformable laminate is provided. The laminate includes a base layer of thermoformable plastic sheet material; and a layer of microbeads configured in a high-density arrangement and silvered on their bottom sides to enhance retroreflectivity. The microbeads are adhered to an outer surface of the base layer by a thermoformable cushion coat which may include a phosphorescent pigment to further enhance reflectivity. A protective sheet of transparent thermoformable sheet material overlies and may be in contact with the layer of microbeads. The laminate is heated and thermoformed into a self supporting three dimensional article having a pre-selected shape and an encapsulated bead retroreflective surface having a reflectivity of at least about 200 lux. The thermoforming step imparts sufficient non-planarity in the resulting retroreflective surface so that retroreflective dead spots created by contact between the microbeads and the protective sheet of transparent sheet material are effectively optically cancelled by overlapping zones of retroreflectivity generated by the microbeads.
1. A method for making a three dimensional article having a high intensity retroreflective outer surface, comprising the steps of:
adhering a plurality of retroreflective microbeads having a variation in diameter in a high-density arrangement onto a base layer of thermoformable plastic sheet material;
overlying a protective sheet of transparent, thermoformable sheet material in contact with the retroreflective microbeads adhered to the base layer to form a combination layer, wherein said protective sheet engages a top surface of some of the microbeads to form airspaces and create infrequent tangential point contact between at least a portion of said protective sheet and some of the microbeads;
applying sufficient heat to the combination layer to render it thermoformable; and
thermoforming the heated combination layer into a three dimensional article having a pre-selected shape and an encapsulated bead retroreflective surface having a reflectivity of at least about 200 lux;
wherein the protective sheet comprises glycol-modified polyethylene terephthalate (PETG); and
wherein the protective sheet has a thickness of 20 mils to 30 mils.
2. The method of claim 1 , wherein the retroreflective microbeads have an average diameter of between about 2 and 4 mils and are adhered to said layer of thermoformable plastic sheet material by a cushion coat.
3. The method of claim 2 , wherein said cushion coat includes a phosphorescent pigment to enhance the reflectivity of said surface.
4. The method of claim 1 , including a further step of cooling the combination layer to allow formation of an air space after the step of thermoforming.
5. The method of claim 1 , including a further step of applying a metalized layer after the step of adhering the microbeads to the base layer.
6. The method of claim 1 , including a further step of peeling the base layer off after the step of applying sufficient heat.
7. The method of claim 1 , wherein said three dimensional article has a curved or faceted surface.
8. The method of claim 1 , wherein the base layer is formed from PETG.
9. The method of claim 1 , wherein the microbeads are semi-silvered, having a silvered side that is adheringly engaged to said base layer.
10. The method of claim 1 , wherein the protective sheet of transparent material is colored.
11. The method of claim 1 , wherein the thickness of the base layer is between about 4 to 12 times an average diameter of the microbeads.
12. The method of claim 1 , wherein the thickness of the protective sheet is between about 2 to 10 times an average diameter of the microbeads.
13. The method of claim 1 , wherein the thickness of the protective sheet is between about 4 to 8 times an average diameter of the microbeads.
14. The method of claim 1 , wherein the microbeads have an average diameter of between about 40 and 90 microns.
15. The method of claim 2 , wherein the cushion coat comprises a polyvinyl copolymer, a thermoplastic polyurethane, and an aminoplast resin.
16. The method of claim 1 , wherein the variation is ±15%.
17. The method of claim 2 , wherein the cushion coat has a thickness of approximately ⅔ the average diameter of the microbeads.
18. The method of claim 1 , wherein the microbeads are metallized.