After rigorous experimentation with many polymer chemistries and blends, Teknor Apex produced a standard blow molding compound, Medalist MD 12445, for replacing latex, NBR or PVC. Work on equipment modification, tooling and mold design took place at the Denville, NJ facility of FGH Systems, a blow molding specialist that represents well-known equipment OEMs and operates a mold shop, product development laboratory and trial processing lines.
Breather bags posed a design and processing challenge because they must be pleated to lie flat when not in use yet form a round “balloon” with uniform wall thickness when inflated, noted Eric Hohmann, owner of FGH Systems.
“While TPEs—TPVs in particular—have found use in the injection blow molding process for parts like automotive rack and pinion boots and ducts, extrusion blow molding has normally been used with stiff or non-elastomeric resins like HDPE, PP and PVC,” said Hohmann. “For the breather bag, the challenge was to produce a complex part in a continuous extrusion process with an eight-cavity mold.”
Besides developing designs to meet these challenges, FGH Systems supplied the Milacron Uniloy shuttle blow molding equipment used for commercial production.
“To perfect techniques for molding TPEs, we carried on many trials on our own pilot lines and at customer plants, experimenting with molding machines, screw designs, extrusion heads and molds, along with several Medalist formulations from Teknor Apex,” said Hohmann. “As a result of our success, extrusion blow molding of TPEs can now be applied to other complex designs for hollow parts, bottles or bags in the medical device industry and beyond.”
While injection molding produces solid parts, blow molding creates hollow parts in core-less molds in which pressurized air is used to force a molten plastic parison against the wall of the mold to form a finished part.
The Medalist MD 12445 compound is a 45 Shore A grade, but Teknor Apex can develop softer or harder compounds to suit specific applications. The new compound is sterilizable by means of gamma irradiation or ethylene oxide. It exhibits a high level of tear resistance.
While injection molding produces solid parts, blow molding creates hollow parts in
core-less molds in which pressurized air is used to force a molten plastic
parison against the wall of the mold to form a finished part.
Economic benefits of switching from dip molding to extrusion blow molding
Breather bags are used during surgery to control the flow of air to a patient under anesthesia. They are single-use, disposable items, capable of being inflated by compressed air. Sizes vary to accommodate patient sizes or ages.
Historically these bags were made of natural-rubber (NR) latex in a process called dip molding. Though protein allergies forced a move from NR latex to NBR latex, the substitute was more expensive than NR latex and the dipping process more inefficient.
TPE bags provide significant cost savings because extrusion blow molding replaces labor-intensive dip molding with high-volume processing, because thermoplastics have no need for the curing step required for thermoset rubber, and because of lower raw material costs. In addition, TPEs avoid concerns about the extractable or leachable remnants of curing agents.
All Medalist medical elastomers are made with FDA-compliant ingredients, compliant with ISO 10993-5 and REACH SVHC, free of phthalates and animal-derived raw materials and produced in an ISO13485 facility.
