TPE-based syringe stoppers are smooth operators

New medical-grade thermoplastic elastomers (TPEs) from Teknor Apex (Pawtucket, RI) for injection molded plunger stoppers provide improved syringe performance and are less costly and easier to mold than natural and isoprene rubber, said the company. The TPE-based stoppers also have processing advantages compared with thermoplastic vulcanizate (TPV) elastomers. Teknor Apex Co. will introduce the compounds in booth S22045 at NPE2018.

A low coefficient of friction enables the stoppers molded from the new Medalist TPEs to achieve a consistent piston release and travel force in both glass and plastic syringe barrels, said Teknor Apex. The compounds can be over-molded onto plungers, eliminating an assembly step. In addition to grades for over-molding onto polypropylene, specialty grades are available that, unlike TPVs, can be over-molded onto engineering resins like polycarbonate, ABS, PC/ABS, acrylic, acetal, PBT and COPE. Unlike most TPVs, the Medalist TPEs do not require pre-drying.

The Medalist TPEs exhibit improved compression set in comparison with competing TPEs, making possible a more secure seal, said Teknor Apex. The compounds can be molded in high-cavitation tooling. All grades are sterilizable and are available in natural or black colors.

Rubber has been the predominant material for use in syringe stoppers, but TPEs are a better alternative, according to Teknor Apex. For one thing, the curing step required in rubber processing is eliminated, minimizing concerns about extractables and leachables. Also, TPE scrap can be recycled and the molding cycles are shorter. More intricate designs and tighter dimensional tolerances can be achieved, as well.

“Stoppers must move smoothly against the wall of the syringe barrel, provide an exceptional seal to preserve the integrity of the drug and be chemically inert to prevent interaction with the syringe contents,” said Ross van Royen, Senior Market Manager, Regulated Products. “Teknor Apex has developed a portfolio of Medalist TPEs that meet these performance requirements while providing substantial economic advantages because of their ease of processing.”

Medalist compounds are produced in ISO 13485–certified facilities in the United States and Singapore.