Polymer Bonding
Heat-sealing or extrusion-bonding of low-density polyethylene, polypropylene, or other olefinic films to paperboard surfaces creates water-resistant and grease-resistant composite packaging materials. Polyolefin lamination can be accomplished using solvent-borne, water-borne, or solvent-less adhesive chemistries, or by extruding a molten polymer web directly onto the paper fibers. This process is the industrial standard for liquid packaging boards, paper cups, and frozen-food boxes.
The plastic layer provides a liquid-tight barrier and a heat-sealable surface, while the underlying paperboard offers structural support.
Surface Treatment
Low surface energy of polyolefin films requires specific treatment before extrusion or adhesive bonding to ensure adequate adhesion to the polar paperboard. Corona discharge or flame treatment is used to oxidize the polyolefin surface, generating polar functional groups that can bond with the adhesive. Without this modification, the weak chemical interaction at the boundary leads to rapid delamination during processing or filling.
Monitoring the surface energy after treatment is critical to ensuring the longevity of the laminated bond.
Processing Parameters
Controlling melt temperature, line speed, and nip pressure on the laminator is essential to avoid thermal degradation of the polymer. Incorrect heat settings can cause odor issues or reduce the heat-seal efficiency of the finished material.
