What polymer characteristics are needed to make injection moulded tubes?
Injection moulding of tubes requires polymers that have two essentially conflicting properties. These are: • Very high melt flow indices (MFIs) to enable them to flow easily down long, thin walls so as to fill the mould, and • Outstanding ESCR (environmental stress crack resistance) to enable them to resist cracking caused by aggressive stress-crack agents found in most products. It is well known that as polymer MFI increases, so its ESCR deteriorates. Until the development of Zestron’s technology, all attempts to make larger-sized injection moulded tubes failed because the only polymers then available that had sufficiently high MFIs to enable them to fill a tube mould had such poor ESCR that tubes made from them failed the pack trials and were thus unsuitable for commercial use.
