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:
impregnating thermoplastic polyurethane pellets with a blowing agent in aqueous suspension under pressure to form thermoplastic polyurethane beads;
depressurizing the thermoplastic polyurethane beads to allow the thermoplastic polyurethane beads to expand; and
fusing the expanded thermoplastic polyurethane beads to one another to form the sole.
2. The method of claim 1 , wherein the impregnating occurs at a temperature of at least 100° C.
3. The method of claim 2 , wherein the temperature is between 100° C. and 150° C.
4. The method of claim 2 , wherein the temperature is between 110° C. and 145° C.
5. The method of claim 2 , wherein the depressurizing occurs without cooling the thermoplastic polyurethane beads.
6. The method of claim 1 , wherein the impregnating occurs at a pressure between 2 bar and 100 bar.
7. The method of claim 1 , wherein a time for the impregnating is between 0.5 hours and 10 hours.
8. The method of claim 1 , further comprising cooling the thermoplastic polyurethane beads before the depressurizing.
9. The method of claim 8 , wherein the cooling results in a temperature between 20° C. and 95° C.
10. The method of claim 1 , wherein the blowing agent comprises organic liquids.
11. The method of claim 1 , wherein the blowing agent comprises inorganic gases.
12. The method of claim 1 , wherein the blowing agent comprises between 0.1% and 40% of the total weight of the thermoplastic polyurethane pellets.
13. The method of claim 1 , wherein the sole comprises a midsole.
14. The method of claim 1 , wherein the sole comprises an insole.
15. The method of claim 1 , wherein the expanded thermoplastic polyurethane beads have a diameter between 0.2 mm and 20 mm.
16. The method of claim 1 , wherein the expanded thermoplastic polyurethane beads are spherical.
17. The method of claim 1 , 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.
18. The method of claim 1 , wherein the expanded thermoplastic polyurethane beads have a density between 5 g/l and 600 g/l.