Method for producing expanded thermoplastic elastomer particles

A process for production of expanded thermoplastic elastomer beads having an uninterrupted skin, said process consisting essentially of;

• a) impregnating a blowing agent into thermoplastic elastomer beads to give impregnated thermoplastic elastomer beads, the thermoplastic elastomer beads being surrounded by a gaseous medium that has an impregnating temperature Ta, wherein the absolute pressure of the gaseous medium is greater than ambient pressure, and wherein the thermoplastic elastomer beads are selected from thermoplastic polyester elastomers, thermoplastic copolyamides or thermoplastic polyurethanes, or mixtures thereof,
• b) expanding the impregnated thermoplastic elastomer beads by exposing the thermoplastic elastomer beads to a pressure reduction at a first expanding temperature Tb to give expanded thermoplastic elastomer beads and
• c) optionally a fusing step, wherein the expanded thermoplastic elastomer beads are fused together at a fusing temperature Tc to form at least one shaped part,
• wherein the thermoplastic elastomer beads are made from amorphous thermoplastic elastomer, partly crystalline thermoplastic elastomer, or mixtures thereof, and the impregnating temperature Ta, the first expanding temperature Tb and the fusing temperature Tc each depend on the thermoplastic elastomer wherein,
• i. if the thermoplastic elastomer is amorphous, the impregnating temperature Ta, the first expanding temperature Tb and the fusing temperature Tc are higher than a first limiting temperature TG-40, wherein the first limiting temperature TG-40 is 40° C. below the glass transition temperature TG according to DIN EN ISO 11357-2:2013-09 of the thermoplastic elastomer beads not being impregnated, or
• ii. if the thermoplastic elastomer is partly crystalline, the impregnating temperature Ta, the first expanding temperature Tb and the fusing temperature Tc are higher than the glass transition temperature TG according to DIN EN ISO 11357-2:2013-09 of the nonimpregnated thermoplastic elastomer beads and lower than a second limiting temperature TS-5 which is 5° C. below the melting temperature TS according to DIN EN ISO 11357-3:2013-04 of the thermoplastic elastomer beads not being impregnated.