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 producing expanded thermoplastic polyurethane foam beads, comprising: (i) extruding a thermoplastic polyurethane exhibiting a Shore hardness that ranges from A62 to A84 and, if appropriate together with additives, to give pellets with an average diameter that ranges from 0.2 to 10 mm, (ii) impregnating the pellets with from 0.1 to 40% by weight, based on the total weight of the pellets, of a blowing agent in aqueous suspension, under pressure of 2 to 100 bar (absolute) at temperatures in the range from 110 to 145 C., and then (iii) depressurizing said impregnated pellets to produce expanded thermoplastic polyurethane foam beads, 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.

2. The process according to claim 1, wherein the thermoplastic polyurethane has at most a melt flow rate of 250 g/10 min at 190 C. with an applied weight of 21.6 kg to DIN EN ISO 1133.

3. The process according to claim 1, wherein the thermoplastic polyurethane is based on a polytetrahydrofuran of a molar mass that ranges from 600 g/mol to 2500 g/mol.

4. The process according to claim 1, wherein the thermoplastic polyurethane is based on a polyester alcohol of a molar mass that ranges from 600 g/mol to 900 g/mol.

5. The process according to claim 1, wherein said thermoplastic polyurethane comprises from 5 to 80% by weight of an organic filler, an inorganic filler, or a combination thereof, based on the total weight of the thermoplastic polyurethane.

6. The process according to claim 1, wherein said impregnating of said pellets in step (ii) is conducted in suspension in a closed reactor and said depressurizing in step (iii) is carried out without cooling.

7. The process according to claim 1, wherein said Shore hardness of said thermoplastic polyurethane is from A 62 to A 80.

8. The process according to claim 1, wherein said pellets are impregnated in step (ii) 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.

9. The process according to claim 1, wherein said impregnation of the pellets in step (ii) is carried out in aqueous suspension in the presence of 0.05 to 10% by weight of a suspending agent.

10. The process according to claim 1, wherein said expanded thermoplastic foam beads have a density from 10 to 300 g/l.

11. The process according to claim 1, wherein said expanded thermoplastic foam beads have a diameter from 1 to 12 mm.

12. The process according to claim 1, wherein said Shore hardness of said thermoplastic polyurethane is from A 62 to A 82.

13. The process according to claim 1, wherein said Shore hardness of said thermoplastic polyurethane is from A 72 to A 78.

14. The process according to claim 1, wherein in operation iii) the impregnated pellets are depressurized to a pressure of 1 to 3 bar (absolute) in an intermediate container.

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

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 [parts by Table 1 weight] Temperature [ C.] Bulk density [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.