Ultrasonic welding

Ultrasonic welding joins layers of plastic film by applying high-frequency mechanical vibration. Friction at the interface melts the plastic locally, and when the vibration stops the layers cool under pressure into a single bond. No adhesive or external heating element is required.

How it is used in packaging

A familiar example is the header of an OPP bag: the double-layer hang area is ultrasonically welded so that the sombrero or euro hole cut into it is stiffer and less likely to tear. The technique is also used for sealing some capsules and lids and on certain form-fill-seal machines.

Advantages

• No added adhesive, so the joint is clean and odour-free.
• Heat is generated only at the joint, limiting the effect on surrounding film and print.
• Short cycle times suitable for high-volume production.
• Vibration can partly clear product residue from the seal area, an advantage over conventional heat sealing in some applications.

Limitations

Bond strength depends on film type, thickness, pressure and weld time, and not every material combination welds equally well. Test with samples before committing to a production setup.