heatsealing

Heat sealing is a method of joining thermoplastic materials by applying heat and pressure to a hot interface, causing a thin layer to melt and fuse when cooled. It is widely used to seal flexible packaging films, laminates, and pouches.

In operation, a film or tray with a heat-seal layer is placed between two heated jaws or a sealing bar. The jaws are heated to a set temperature, pressure is applied for a defined dwell time, and the assembly is cooled to form a solid bond. Material compatibility between the seal surface and the mating film determines seal strength and integrity.

Equipment ranges from impulse sealers, which deliver a short, high-energy pulse to form a seal, to constant-heat bar sealers and rotary sealers for longer runs. Common seal materials include polyolefins such as polyethylene and polypropylene, PET, and multilayer laminates that have a heat-sealable layer. Films are selected for their sealant layer, thickness, clarity, and barrier properties.

Key process parameters are sealing temperature, dwell time, and sealing pressure; too high a temperature or long dwell can cause burn-through or material degradation, while too low a temperature can yield weak seals. Pre-cleaning and, in laminated films, proper surface preparation influence seal quality.

Applications include food packaging, medical and pharmaceutical bags, consumer goods packaging, and industrial laminates. Advantages of heat sealing include speed, low waste, and absence of solvents. Limitations include material compatibility constraints, potential damage to temperature-sensitive contents, and the need for maintenance of heat-seal equipment.

Safety considerations cover hot surfaces and fumes, and environmental considerations include compatibility with recycling streams and the use of recyclable or compostable seal layers.