Method and thermoplastic foamed article
A method for making a low density foamed article includes placing a desired amount of thermoplastic polyurethane foam beads in a cavity of an injection mold and closing the mold; combining in an extruder connected to the mold a molten polymer selected from the group consisting of thermoplastic polyurethane elastomers and thermoplastic ethylene-vinyl acetate copolymers with both a physical or chemical blowing agent other than a supercritical fluid present in an amount up to about 15 wt % based on molten polymer weight and a supercritical fluid that is at least one of about 0.1 to about 5 weight percent of supercritical CO 2 based on molten polymer weight or about 0.1 to about 4 weight percent of supercritical N 2 based on molten polymer weight, to form a mixture and injecting the mixture into the mold and foaming the mixture to form the low density foamed article.
1. A method for making a low density foamed article, comprising:
placing an amount of thermoplastic polyurethane foam beads in a cavity of a mold and closing the mold, wherein the thermoplastic polyurethane foam beads have a density of from about 0.01 g/cm 3 to about 0.1 gm/cm 3 ;
combining in an extruder connected to the mold a molten elastomeric ethylene-vinyl acetate copolymer with
(a) chemical blowing agent and
(b) a supercritical fluid,
to form a mixture, wherein the blowing agent (a) is present in an amount up to about 15 weight percent based on total polymer weight in the mixture and the supercritical fluid (b) comprises at least one of about 0.1 to about 5 weight percent of supercritical CO 2 based on total polymer weight and about 0.1 to about 4 weight percent of supercritical N 2 based on total polymer weight, and injecting the mixture into the mold and foaming the mixture to form a foamed article,
injecting the mixture into the mold at an injection pressure of from 110 MPa to about 207 MPa; and
wherein the foamed article has a density of about 0.2 to less than 0.3 g/cm 3 .
2. The 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. as measured according to ASTM D1238 using a 21.6 kg weight and a temperature of 190° C.
3. The 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. as measured according to ASTM D1238 using a 21.6 kg weight and a temperature of 190° C.
4. The 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.
5. The method according to claim 1 , wherein the thermoplastic polyurethane foam beads comprise elastomeric thermoplastic polyester-polyurethane.
6. The method according to claim 1 , wherein the thermoplastic polyurethane foam beads comprise an elastomeric thermoplastic polyether-polyurethane.
7. The method according to claim 6 , wherein the elastomeric thermoplastic polyether-polyurethane is a reaction product of diphenylmethane diisocyanate.
8. The 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.
9. The method according to claim 1 , wherein the chemical blowing agent is present in an amount in an amount from about 3 to about 12 wt % based on the molten elastomeric ethylene-vinyl acetate copolymer weight.
10. The method according to claim 1 , wherein the supercritical fluid is one of from about 0.5 to about 3 weight percent of supercritical CO 2 based on total polymer weight in the mixture and from about 0.4 to about 2.5 weight percent of supercritical N 2 based on total polymer weight in the mixture.
11. The method according to claim 1 , wherein the mixture further comprises a crosslinker.
12. The method according to claim 1 , wherein the mold comprises a porous tool.
13. The method according to claim 12 , wherein the porous tool has a pore size of from about 3 micrometers to about 20 micrometers.
14. The method according to claim 12 , wherein the porous tool is a porous metal or metal alloy.
15. The method according to claim 12 , wherein the porous tool is an insert that is about the dimensions of the mold cavity.
16. The method according to claim 12 , wherein the porous tool comprises a plurality of inserts spaced within the mold cavity.
17. The method according to claim 1 , wherein the molten elastomeric ethylene-vinyl acetate copolymer comprises from about 25 weight percent to about 50 weight percent vinyl acetate content.
18. A foamed article made by the method of claim 1 .
19. The foamed article according to claim 18 , wherein the article has a density of from about 0.2 to about 3 g/cm 3 .
20. The foamed article according to claim 18 , wherein the article is a cushion or cushioning element for an article of footwear, protective equipment, or clothing.