Meaning
The minimum temperature at which a polymer film can be thermally bonded to itself under a specified pressure and dwell time defines the start of its heat-sealing range. A lower seal initiation temperature allows packaging lines to run at faster speeds because the film requires less heat to form a secure bond. This property is determined primarily by the melting point and crystallinity of the sealant resin used in the film’s skin layer.
Film converters measure this value to evaluate the suitability of a film for high-speed form-fill-seal packaging machinery.
Packaging Velocity
High-speed lines require resins that bond quickly. A low seal initiation temperature reduces the energy required during short dwell times. This prevents the sealing jaws from overheating the adjacent film layers.
Optimized properties allow manufacturers to maximize throughput without sacrificing seal strength.
Resin Selection
Metallocene-catalyzed polyethylenes and plastomers are often selected for film formulations because they offer a lower seal initiation temperature than traditional low density polyethylenes. These specialized resins feature a narrow molecular weight distribution and uniform branch distribution, which results in a sharp melting transition. This molecular design allows the film to seal at lower temperatures while maintaining high hot-tack strength.
Using these materials helps packaging plants reduce their energy consumption.
Mechanical Evaluation
Determining the precise seal initiation temperature involves producing a series of seals at increasing temperatures and measuring their peel strength. The seal initiation temperature is defined as the temperature at which the seal strength reaches a specified threshold, often set at standard forces like one or two Newtons per fifteen millimeters of width. These tests are conducted using a peel tester at a constant peel angle and speed.
The resulting data allow engineers to set the safe operating limits for the packaging line.
