Bead foam compression molding method for low density product
Disclosed is a method for molding a foamed article, such as a midsole or outsole for footwear, in which a desired amount of thermoplastic polyurethane foam beads are placed in a compression mold in the shape of the article and the mold is brought to a peak temperature of from about 130° C. to about 180° C. over a period of from about 300 to about 1500 seconds, then cooled to from about 5° C. to about 80° C. over a period of from about 300 to about 1500 seconds within about 30 seconds after the peak temperature is reached. The foamed article made by the method has a density of from about 0.1 to about 0.45 g/cm 3 .
1. A method for molding a foamed article, comprising:
placing a desired amount of thermoplastic polyurethane foam beads in a compression mold in the shape of an article, wherein the thermoplastic polyurethane foam beads have a density of from about 0.01 to about 0.3 g/cm 3 ;
closing the mold;
bringing the mold to a peak temperature of from about 130° C. to about 180° C. over a period of from about 300 to about 1500 seconds;
cooling the mold to a temperature of from about 5° C. to about 80° C. over a period of from about 300 to about 1500 seconds within about 30 seconds after the peak temperature is reached; and
removing the article.
2. A method according to claim 1 , wherein the peak mold temperature is from about 140° C. to about 170° C.
3. A method according to claim 1 , wherein the thermoplastic polyurethane foam beads have a density of from about 0.01 to about 0.1 g/cm 3 .
4. A method according to claim 1 , wherein the thermoplastic polyurethane foam beads comprise a thermoplastic polyurethane with a melt flow index of at least about 160 grams/10 min. (at 190° C., 21.6 kg) as measured according to ASTM D1238.
5. A method according to claim 1 , wherein the thermoplastic polyurethane foam beads comprise an elastomeric thermoplastic polyurethane with a melt flow index of from about 180 to about 250 grams/10 min. (at 190° C., 21.6 kg) as measured according to ASTM D1238.
6. A method according to claim 1 , wherein the thermoplastic polyurethane foam beads comprise an elastomeric thermoplastic polyurethane selected from the group consisting of thermoplastic polyester-polyurethanes, polyether-polyurethanes, and polycarbonate-polyurethanes.
7. A method according to claim 1 , wherein the thermoplastic polyurethane foam beads comprise elastomeric thermoplastic polyester-polyurethane.
8. A method according to claim 1 , wherein the thermoplastic polyurethane foam beads comprise an elastomeric thermoplastic polyether-polyurethane.
9. A method according to claim 8 , wherein the elastomeric thermoplastic polyether-polyurethane is a reaction product of diphenylmethane diisocyanate.
10. A method according to claim 1 , wherein the thermoplastic polyurethane foam beads have a diameter of from about 0.5 mm to about 1.5 cm.
11. A method according to claim 1 , wherein the thermoplastic polyurethane foam beads have a compact outer skin.
12. A method according to claim 1 , wherein the thermoplastic polyurethane foam beads and the mold are each at a temperature below about 80° C.
13. A method according to claim 1 , wherein the amount of the thermoplastic polyurethane foam beads placed in the mold is selected to provide a foamed article having a density of from about 0.1 to about 0.45 g/cm 3 .
14. A method according to claim 1 , wherein the mold is brought to the peak temperature over a period of from about 300 to about 1200 seconds.
15. A method according to claim 1 , wherein the peak temperature is selected to produce a skin thickness of from about 9 to about 200 micrometers.
16. A method according to claim 1 , wherein the mold is cooled over a period of from about 300 to about 1200 seconds.
17. A method according to claim 1 , wherein the mold cooling step is begun immediately after the peak temperature is reached.
18. A method according to claim 1 , wherein the mold is cooled at a rate of from about 0.09 to about 0.55° C./second.