In the wearables sector, which is growing by leaps and bounds, user comfort is key. It’s doubly important in the medical wearables space, where these devices increasingly perform vital monitoring and therapeutic functions. If the device is uncomfortable to wear, patient compliance dips. And that is a compelling reason why designers of medical wearable devices should consider heat sealing as the go-to bonding method, according to Lance Crawford of Thermal Press International, a manufacturer of assembly equipment based in Livermore, CA.
Medical device manufacturers traditionally have relied on either ultrasonic welding or adhesives to join products, said Crawford. Both methods have drawbacks, however.
Ultrasonic welding is a well-established technology that produces consistent results at low cost, but the resulting products may have sharp edges.
Adhesives are a more comfortable option, but they present challenges during the manufacturing process, according to Crawford, notably curing time, which affects productivity.
Medical equipment manufacturers are often surprised to discover that heat sealing is an easily applicable technology for quickly and consistently producing high volumes of wearable devices without the shortfalls of other welding techniques, said Crawford.
In heat sealing, a thermoplastic elastomer is melted over the desired component forming a tight, powerful weld. Because the bond relies on liquefied plastic, it has no sharp edges. Heat sealing bonds are soft to the touch and almost invisible in the finished product. Patients report these devices to be more comfortable and easier to regularly use than products manufactured using ultrasonic welding techniques, said Crawford.
Heat sealing is more efficient than the use of adhesives from a manufacturing perspective because it takes just a few seconds. A properly calibrated thermal press can join together 10 to 30 pieces per minute compared with gluing, which may take minutes per component, according to Crawford.
“Heat staking works well with thermoplastics,” Crawford told PlasticsToday. “The plastics can have fillers, but depending on the percentage of fillers—more than 33%—and type—glass, for example—the results and parameters can be affected.”
As for cost considerations, Crawford told PlasticsToday that machinery, tooling and maintenance expenses should all be evaluated for a total cost comparison.