Barrier Layer
Extruded barrier layers protect paperboard fibers from moisture, grease, oxygen, and liquid penetration in food packaging applications. Applying a polyethylene coating onto virgin paperboard substrates produces water-impermeable barriers essential for paper cups, frozen food cartons, ovenable trays, and liquid packaging board. High-pressure extrusion lines chill molten low-density polymer directly onto the moving paperboard web, creating an integral moisture seal and heat-sealable layer.
Extrusion Adhesion
Adhesion between the polymer film and paperboard fibers relies on mechanical keying, melt temperature, web tension, and surface oxidation during extrusion. Low polyethylene coating weight reduces material cost and aids recycling, but thin coatings risk micro-pinholes that allow moisture penetration into the paperboard core. Corona oxidation treatment of the board surface raises surface energy, improving resin adhesion at high line speeds.
In liquid packaging board construction, multiple layers of low-density and linear low-density polymer are co-extruded with aluminum foil or ethylene vinyl alcohol to block oxygen and light transmission. Excessively high melt temperatures oxidize the polymer film excessively, causing off-odors that contaminate sensitive food products like milk or water.
Thermal Sealing
Continuous polymer layers enable rapid heat sealing during high-speed carton converting operations. Heat-seal strength prevents liquid leakage along side seams and bottom closures. Consistent polyethylene coating guarantees uniform barrier performance across all converted packaging units.
