Two plastics suppliers to the medical device industry have demonstrated a strong, chemical-resistant bond between thermoplastic elastomers (TPEs) and a clear copolyester substrate known for its toughness and chemical resistance.
Peel strength was measured in 90-degree pull test on a Zwick tensionometer with 100 mm/min. pulling rate in accordance with DIN EN 1464.
In 90-degree peel tests of test specimens produced in a two-shot molding process, three Medalist medical-grade TPEs from Teknor Apex Company provided durable bonds to four of Eastman’s Tritan copolyesters. Specifically formulated to adhere to copolyester and other engineering thermoplastics, the Medalist compounds exhibited high levels of peel strength. The peel tests that showed high peel strengths with adhesive failures demonstrate excellent Tritan TPE over-molding performance. The combination of high peel strength and adhesive failure is considered desirable for over-molded applications.
The bond strength between Medalist TPEs and Tritan exhibited very little loss even after soaking test samples for 48 hours in disinfecting chemicals, including a 70% isopropyl alcohol, Clorox bleach, and a 20% intralipids solution, which is a fat emulsion used as an intravenously administered nutrient.
Medalist compounds tested included three grades: MD-34940, MD-34950, and MD-34959, with Shore A durometers of 42, 50, and 59, respectively. Tritan grades MX711, MX811, MXF321, and MXF421, provided a good range of physical properties. All three Medalist compounds in combination with all four Tritan resins showed very little loss of bond strength after chemical exposure.
Graph shows peel strength test results for one Medalist TPE over-molded onto four Tritan substrates. Blue shows average peel strength, whereas peak peel strength is indicated by gray in background.
Over-molding TPEs onto copolyester offers medical device designers a combination of hard and soft materials that are advantageous in medical components. Soft TPEs are desirable for grips, gaskets, seals, and soft-touch elements on rigid medical housings and other components.
“By combining Medalist TPEs and Tritan copolyesters, manufacturers can improve the ergonomics, aesthetics, or functionality of medical devices,” said Dr Yubiao Liu, global medical technical platform lead, Eastman. “The combination of soft TPEs with rigid copolyester substrates can enhance grip, add texture or comfort, yield a tight seal, or provide damping characteristics.”
Medalist TPEs combine the performance of thermoset rubber with the processing ease of thermoplastics, making them superior alternatives to silicones, PVC, and TPUs, noted Ross van Royen, senior market manager for Teknor Apex. “We have developed Medalist TPEs to meet the most stringent requirements of the health care industry and produce them in multiple ISO-13485-certified facilities with only FDA-listed food-grade ingredients. All grades are biocompatible in accordance with ISO-10993-5, are RoHS and REACH SVHC compliant, and contain no phthalates, latex proteins, or BPA.”