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 process for production of expanded thermoplastic polyurethane foam beads, comprising: (i) melting a thermoplastic polyurethane whose Shore hardness is from A 44 to A78, together with from 0.1 to 40% by weight, based on the total weight of pellets, of a blowing agent, if appropriate with additives, in an extruder, and (ii) pelletizing the melt without devices which inhibit foaming to produce expanded thermoplastic polyurethane foam beads; wherein the blowing agent is a volatile organic compound having a boiling point from −25 to 150° C. at 1013 mbar selected from the group consisting of hexane, heptane, octane, an alcohol, a ketone, an ester, an ether and a carbonate, the thermoplastic polyurethane comprises a polytetralhydrofuran of a molar mass of from 600 g/mol to 2500 g/mol, and the thermoplastic polyurethane exhibits a melting range, measured by DSC using a heating rate of 20 K/min, that starts below 130° C., and the thermoplastic polyurethane has at most a melt flow rate of 250 g/10 min at 100° C. with an applied weight of 21.6 kg to DIN EN ISO 1133.

2. The process according to claim 1, wherein the Shore hardness of the thermoplastic polyurethane is from A 62 to A78.

3. The process according to claim 1, wherein the thermoplastic polyurethane comprising blowing agent comprises from 5 to 80% by weight of organic and/or inorganic fillers, based on the total weight of the thermoplastic polyurethane comprising blowing agent.

4. A process for production of foam moldings, which comprises producing expanded thermoplastic polyurethane foam beads according to the process of claim 1 and fusing them in a closed mold by steam at a temperature of from 100° C. to 140° C.

5. The process according to claim 1, wherein the thermoplastic polyurethane is impregnated in (i) with 1 to 30 parts by weight, based on 100 parts by weight of the thermoplastic polyurethane, of a C.sub.4-10 alkane as blowing agent.

6. The process according to claim 1 wherein a density of the expanded thermoplastic polyurethane foam beads is from 10 to 300 g/l.

7. The process according to claim 1 wherein a diameter of the expanded thermoplastic polyurethane foam beads is from 1 to 12 mm.

8. The process according to claim 1, wherein said expanded thermoplastic polyurethane foam beads have a spherical or elongated shape.

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 TPU of n- Butane Temperature Bulk density Table 1 [parts 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.