Foam security substrate

1. A security substrate comprising at least one oriented, high melt-strength polypropylene foam layer comprising homo- and copolymers containing 50 weight percent or more propylene monomer units, and having a melt strength in the range of 25 to 60 cN at 190° C. and at least one security element which provides visual, tactile or electronic authentification of the security substrate or a security document derived therefrom, said foam layer having two substantially smooth major surfaces wherein the foam layer has an R A value of <10 according to ANSI B46.

2. The security substrate of claim 1 wherein said foam layer having a cellular morphology through the thickness of the layer.

3. The security substrate of claim 1 wherein said security element is a visual security element that changes appearance in a reversible, predictable and reproducible manner by the application of heat or pressure, by variation in the angle of viewing, or by the adjustment of lighting conditions.

4. The security substrate of claim 3 wherein said visual security element is selected from the group of printed indicia, reverse printing, color shifting, metameric, polarizing, fluorescent, luminescent, phosphorescent, pearlescent, holographic, reflective, metallic, magnetic films, threads, particles or fibers; watermarks, transparent or translucent regions, liquid crystals; optical lenses, microlenses, Fresnel lenses, optical filters, polarizing filters, photochromic elements, thermochromic elements, Moiré patterns, refractive, lenticular and transparent grids, embossed elements or other three-dimensional elements, and combinations of the above.

5. The security substrate of claim 1 wherein said security element is an embossment.

6. The security element of claim 5 wherein said embossment provides a substantially transparent region.

7. A multilayer article comprising the foam layer of claim 1 and at least one thermoplastic film layer.

8. The multilayer article of claim 7 wherein said security element is integral to said thermoplastic film layer.

9. The multilayer article of claim 7 wherein said security element is integral to said foam layer.

10. The multilayer article of claim 7 wherein said security element layer in the thermoplastic film layer is revealed through a substantially transparent region in said foam layer.

11. The multilayer article of claim 7 comprising at least two security elements, which in registration, provide a visual security element.

12. The multilayer article of claim 7 , wherein said security element comprises at least one core embedded in the thermoplastic film layer.

13. The multilayer article of claim 12 wherein said security element is coextruded with said foam layer by an inclusion coextrusion process.

14. The multilayer article of claim 7 having two high melt-strength, oriented polymer foam layers and a thermoplastic film layer disposed therebetween.

15. The multilayer article of claim 7 wherein said thermoplastic film layer is coextruded with said foam layer.

16. The multilayer article of claim 7 wherein said thermoplastic film layer is laminated to said foam layer.

17. The multilayer article of claim 7 comprising said thermoplastic film layer and said high melt strength foam layer, the multilayer article having a bending stiffness of at least 40 Newtons.

18. The security substrate of claim 1 comprising a security element on a surface of said foam layer.

19. The security substrate of claim 1 comprising a security element dispersed in said foam layer.

20. The security substrate of claim 1 wherein said security element is laminated to said foam layer.

21. A security document comprising the substrate of claim 1 .

22. The security substrate of claim 1 wherein the foam has an average cell size of less than 100 micrometers, prior to orientation.