Foams based on thermoplastic polyurethanes

Abstract

Expandable thermoplastic polyurethane comprising blowing agent, wherein the Shore hardness of the thermoplastic polyurethane is from A 44 to A 84.

Claims

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.

Description

EXAMPLE 1

(1) Foam Bead Production

(2) 100 parts of the TPUs stated in Table 1 in the form of pellets each weighing about 2 mg, 250 parts by weight of water, 6.7 parts of tricalcium phosphate, and 20 parts of n-butane were introduced, with stirring, into an autoclave and heated to the temperature stated in Table 2. The contents of the pressure vessel were then discharged through a basal valve and depressurized, while the pressure in the tank was kept constant by introducing, under pressure, nitrogen or the blowing agent used. The foam beads were freed from adherent residues of auxiliaries via washing with nitric acid and water and were air-dried at 50° C.

(3) The impregnation conditions and the resultant bulk densities of the expanded beads are found in Table 2.

(4) TABLE-US-00002 TABLE 2 n- Butane [parts Temperature Bulk density TPU of Table 1 by weight] [° C.] [g/L] A 20 112 300 A 20 114 170 B 20 119 240 B 20 120 190 B 20 122 140 B 20 125 120

EXAMPLE 2

(5) Production of Moldings

(6) The foam beads produced in Example 1 were charged into a preheated mold, with pressure and compaction. The mold was heated by steam at from 1.0 to 4.0 bar, i.e. at temperatures of from 100° C. to 140° C., on alternate sides.

(7) The mold was then depressurized and cooled with water and, respectively, air, and opened, and the mechanically stable molding was removed.