heatsealability

Heatsealability is the ability of materials, typically polymer films or coatings, to form a stable bond when subjected to heat and pressure and to retain that bond during handling and use. In practical terms it describes how readily two surface layers can fuse to create a seal that remains intact under normal conditions. Heat-sealable bonds are common in packaging and labeling, where a controlled melt and interdiffusion at the interface produce the seal.

The factors that govern heatsealability include the chemistry of the sealable layer (often a thermoplastic polymer with a defined melting range), layer structure and thickness, crystallinity and orientation, and the presence of additives or coatings. Interfacial compatibility between the sealable layer and adjacent materials, surface energy, and moisture content can all influence seal formation. In polyolefin-based systems, for example, a suitable heat-seal layer such as LDPE or an EVA-containing layer is designed to melt and fuse with its counterpart without degrading the surrounding material.

Measurement and performance characteristics commonly used to assess heatsealability include seal strength (often reported in newtons per unit width), seal initiation temperature, the sealing window (the temperature range that yields acceptable seals), and hot-tack viability. Testing can involve peel or shear tests on sealed joints, as well as accelerated aging to evaluate seal durability.

Applications span packaging films and pouches, labeling adhesives, and protective coatings, frequently in multilayer structures where a dedicated heat-seal layer is combined with a strong barrier or mechanical layer. Achieving reliable heatsealability requires balancing seal performance with other material properties such as toughness, transparency, and barrier performance.