Polyurethane Soft Touch Film Selection for Folding Cartons
Polyurethane soft-touch films provide superior scratch resistance and score fold integrity compared to BOPP but require higher temperature control and lower web yields.
Dry Bond Strength
Lamination Cohesion
Dry bond strength measures the specific force required to peel apart a multi-layer flexible packaging laminate or a laminated paperboard substrate after the adhesive carrier has completely evaporated or cured. Modern converting plants monitor this mechanical property to verify that extrusion coatings, water-based adhesives, or solventless polyurethane systems maintain structural integrity under mechanical stress. The evaluation protocol requires conditioning sample strips at strict temperature and humidity levels before a tensile testing machine strips the plies apart at a constant angle and speed.
Converting facilities on high-speed extrusion lines set minimum peel resistance thresholds to prevent delamination during subsequent pouch making, bag forming, or thermal sealing operations. Board convertors reject rolls falling beneath specified pound-force per inch thresholds because loose plies fail barrier requirements and trap moisture inside pharmaceutical or food barrier pouches.
Adhesion Mechanics
Interfacial bonding relies on mechanical anchoring into microscopic substrate pores and chemical wetting across dissimilar surfaces. Polyethylene extrusions bond poorly to untreated paperboard substrates due to low surface energy, which necessitates high-intensity corona discharge treatment on the press line prior to lamination. Primer application modifies surface tension characteristics and promotes covalent bonding between cellulosic fibres and extruded thermoplastic resins.
Adhesive coat weights measured in grams per square meter dictate final peel values, and insufficient dry film thickness leaves microscopic voids that act as stress concentration points under load. Temperature spikes during subsequent hot foil stamping or thermal lamination cycles soften specific adhesive polymers and induce premature ply separation in finished carton panels.
Environmental Stress
Moisture migration through permeable paperboard substrates degrades interior adhesive layers and reduces laminate resistance over extended storage periods. Elevated ambient temperatures accelerate plasticizer migration from printing inks into the adhesive interface, which systematically degrades internal cohesion and lowers measured peel values over time. Flexographic lamination lines therefore require careful monitoring of nip roll pressure profiles during initial web combination to ensure uniform adhesive transfer across uneven paper surfaces.
Laminated packaging materials destined for chilled distribution networks undergo rigorous thermal cycling tests to confirm that sub-freezing temperatures do not embrittle the adhesive matrix and trigger catastrophic delamination failures. Peel resistance values establish the maximum mechanical load a multi-layer flexible package withstands before structural failure occurs at the weakest interfacial boundary.