Coating Structure
Functional polymer films applied to paperboard substrates prevent moisture vapor transmission and liquid penetration in barrier packaging applications. In liquid packaging board and chilled food containers, a polyethylene barrier layer forms a continuous hydrophobic film bonded directly to the fibrous paper structure. Applied through hot melt extrusion, this thermoplastic layer protects paper fibres from water weakening and oil migration during storage.
The thickness of the polymer coat is tailored to balance barrier performance against repulpability requirements in waste recovery systems.
Deposition Process
Extrusion machinery melts polymer pellets and forces liquid resin through a flat die onto a moving paperboard web. As molten film contacts paper fibres in the nip between a chill roll and pressure roll, the polyethylene barrier layer anchors mechanically into porous surface structures before solidifying instantly. Maintaining precise melt temperatures ensures proper polymer viscosity, promoting interface adhesion without burning or pinhole formation.
Online thickness gauges scan the web continuously to control die gap adjustments, maintaining uniform coat weight across wide web widths. Proper film continuity prevents liquid migration through micro-cracks when paperboard cartons undergo creasing and heat sealing on high-speed filling lines.
Recycling Limit
Poor interfacial adhesion leads to film delamination during box scoring and converting operations. High polymer coating weights hinder repulping efficiency in standard paper recycling mills, requiring specialized mechanical hydrapulpers to separate plastic films from cellulose fibres. Thermal limits restrict direct oven heating of polyethylene-coated board.
