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: melting thermoplastic polyurethane and a blowing agent in an extruder; discharging the melted thermoplastic polyurethane and blowing agent from the extruder to form thermoplastic polyurethane beads; expanding the thermoplastic polyurethane beads; and fusing the expanded thermoplastic polyurethane beads to one another to form the sole.

2. The method of claim 1, wherein the thermoplastic polyurethane and the blowing agent are introduced into the extruder together.

3. The method of claim 1, wherein the thermoplastic polyurethane and the blowing agent are introduced into the extruder separately.

4. The method of claim 1, wherein the thermoplastic polyurethane and the blowing agent are introduced into the extruder at different locations.

5. The method of claim 1, wherein the thermoplastic polyurethane and the blowing agent are introduced into the extruder at one location.

6. The method of claim 1, wherein the extruder comprises a single-screw extruder.

7. The method of claim 1, wherein the extruder comprises a double-screw extruder.

8. The method of claim 1, wherein the extruder is operated at a temperature between 150° C. and 250° C.

9. The method of claim 1, wherein the extruder is operated at a temperature between 180° C. and 210° C.

10. The method of claim 1, wherein the blowing agent comprises a hydrocarbon.

11. The method of claim 1, wherein the blowing agent comprises between 0.1% and 40% of the total weight of the thermoplastic polyurethane.

12. The method of claim 1, wherein the sole comprises a midsole.

13. The method of claim 1, wherein the expanded thermoplastic polyurethane beads have a diameter between 0.2 mm and 20 mm.

14. The method of claim 1, wherein the expanded thermoplastic polyurethane beads are spherical.

15. 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.

16. The method of claim 1, wherein the expanded thermoplastic polyurethane beads have a density between 5 g/l and 600 g/l.

17. The method of claim 1, wherein the discharging occurs under temperature and pressure conditions such that the expanding does not occur during the discharging and the thermoplastic polyurethane beads formed by the discharging are expandable thermoplastic polyurethane beads.

18. The method of claim 17, wherein the discharging occurs under water at a pressure between 2 bar and 20 bar and a temperature between 5° C. and 95° C.

19. The method of claim 1, wherein the expanding occurs during the discharging.

20. The method of claim 1, wherein the discharging occurs into conditions that do not inhibit the thermoplastic polyurethane beads from expanding.

21. The method of claim 1, wherein the discharging occurs directly into atmospheric pressure.

Description

(1) The examples below are intended for further illustration of the invention:

(2) TABLE-US-00001 TABLE 1 Soft phase Thermoplastic polyurethane Composition [mol] Composition [mol] 1,4- Molar 1,4- Shore Adipic Butane- Poly- mass Soft Butane- 4,4′- hard- TPU acid diol THF [g/mol] phase diol MDI ness A 1 1 — 800 1.00 0.44 1.44 A78 B — — 1 1333 1.00 0.97 1.97 A72

(3) The Shore hardness of the PU elastomers was determined to DIN 53 505.

EXAMPLE 1

Foam Bead Production

(4) 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.

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

(6) TABLE-US-00002 TABLE 2 TPU of n-Butane [parts by Temperature Bulk density Table 1 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

Production of Moldings

(7) 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.

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