Foams based on thermoplastic polyurethanes
Expandable thermoplastic polyurethane comprising blowing agent, wherein the Shore hardness of the thermoplastic polyurethane is from A 44 to A 84.
1. A method of making a sole for an article of footwear, the method comprising:
expanding thermoplastic polyurethane beads; and
exposing the expanded thermoplastic polyurethane beads to a temperature between 100° C. and 140° C. in a closed mold,
wherein the expanded thermoplastic polyurethane beads are fused to one another in the closed mold to form the sole.
2. The method of claim 1 , wherein exposing the expanded thermoplastic polyurethane beads to a temperature between 100° C. and 140° C. comprises exposing the expanded thermoplastic polyurethane beads to steam at a temperature between 100° C. and 140° C.
3. The method of claim 1 , wherein the expanded thermoplastic polyurethane beads have a density between 5 g/l and 600 g/l.
4. The method of claim 1 , wherein the expanded thermoplastic polyurethane beads have a diameter between 0.2 mm and 20 mm.
5. The method of claim 4 , wherein the diameter is between 0.5 mm and 15 mm.
6. The method of claim 4 , wherein the diameter is between 1 mm and 12 mm.
7. The method of claim 1 , wherein the sole comprises a midsole.
8. The method of claim 1 , wherein the expanded thermoplastic polyurethane beads are spherical.
9. The method of claim 1 , wherein the expanded thermoplastic polyurethane beads are based on a polyether alcohol or a polyester alcohol.
10. A method of making a sole for an article of footwear, the method comprising:
mixing thermoplastic polyurethane with a blowing agent to form expandable thermoplastic polyurethane beads;
expanding the thermoplastic polyurethane beads; and
fusing the expanded thermoplastic polyurethane beads to one another to form the sole,
wherein a melting range of the thermoplastic polyurethane starts below 130° C. when measured by differential scanning calorimetry (DSC) with a heating rate of 20 K/min.
11. The method of claim 10 , wherein the sole comprises a midsole.
12. The method of claim 10 , wherein the sole comprises an insole.
13. The method of claim 10 , wherein the expanded thermoplastic polyurethane beads form the entire sole.
14. The method of claim 10 , wherein the sole comprises a density between 8 g/l and 600 g/l.
15. The method of claim 10 , wherein the expanded thermoplastic polyurethane beads have a diameter between 0.2 mm and 20 mm.
16. The method of claim 15 , wherein the diameter is between 0.5 mm and 15 mm.
17. The method of claim 15 , wherein the diameter is between 1 mm and 12 mm.
18. The method of claim 10 , wherein fusing the expanded thermoplastic polyurethane beads to one another to form the sole comprises placing the expanded thermoplastic polyurethane beads in a closed mold and exposing the expanded thermoplastic polyurethane beads to a temperature between 100° C. and 140° C.
19. The method of claim 10 , wherein the blowing agent comprises between 0.1% and 40% of the total weight of the thermoplastic polyurethane.