Barrier Protection
Extruded polymer coatings provide the necessary resistance to water, moisture vapor, and grease on paperboard substrates. A polyolefin barrier layer is commonly applied to board intended for liquid packaging, paper cups, and frozen food boxes. The most frequent choice is low-density polyethylene, which is applied via extrusion coating directly onto the moving paper web.
This continuous film prevents liquid from penetrating the fibrous network, which would otherwise soften the board and cause the package to collapse. The thickness of the polymer is tailored to the shelf-life requirements of the product. By providing a chemically inert surface, the polymer prevents any direct contact between the beverage and the raw paper fibres.
Heat Sealing
Thermal bonding properties enable rapid carton forming on high-speed filling lines. When the board is converted into cartons, the polyolefin barrier layer serves as a hot-melt adhesive that seals the flaps when heat and pressure are applied. This eliminates the need for external glues, which speeds up the packaging process.
The melt flow index of the polymer is controlled to ensure that the seal forms instantly.
Recyclability Challenge
Sustainable packaging initiatives demand a reduction in non-biodegradable components. Although a polyolefin barrier layer provides excellent protection, it complicates the recycling of the used paperboard. Specialized repulping mills must use mechanical agitation to separate the plastic film from the cellulose fibres.
New developments focus on water-dispersible alternative coatings that can be processed in standard recycling systems.
