Kojiro Inamori and Masahiro Okadome
Thermoin tube SN-UGA is a copper tube covered with polymer foam that has been developed as a part of air conditioning systems for large datacenters. As a main cover material, polypropylene (PP) was used because it shows superior heat resistance and high thermal insulation. In the past, foaming of the PP covering of SN-UGA has been carried out by a chemical method using azodicarbonamide (ADCA) as a foaming agent. But this method has a disadvantage in that the ammonia generated as a by-product of ADCA decomposition causes tarnishing of the copper tube. In this paper, we have investigated PP foaming with CO2. CO2 has the effect of decreasing the melt viscosity and promoting coalescence of cells, but this was successfully overcome by using a tandem extrusion system and adding rubber component with the PP. As a result, 5-fold expansion of PP foam was obtained.