Film Sealing
A converting procedure bonds a transparent plastic polymer sheet onto a printed paperboard substrate using applied heat and nip roll pressure. Thermal film lamination creates a protective barrier against moisture and grease while enhancing the visual depth of offset graphics on folding cartons. This protective process applies a layer of oriented polypropylene or polyethylene terephthalate over the paper base.
The operational boundary stops where extrusion coating begins, since extruded polymers melt directly onto substrates without a preformed carrier film. Converters set the nip roller temperature between one hundred degrees Celsius and one hundred twenty degrees Celsius depending on the polymer grade.
Heat Bond
Heated metal rollers melt the low temperature extrusion resin coated on the underside of the plastic web before the nip point presses both webs together. Polymer adhesion relies on controlled dwell time and roller pressure to prevent delamination during subsequent die cutting and scoring operations. Substrate moisture content exceeding five percent causes steam bubbles beneath the transparent layer and ruins the bond strength.
Operators monitor speed settings to maintain tension across the web and avoid curl defects in the finished sheets. High speed runs demand precise cooling stages immediately after the nip to set the polymer before stacking occurs.
Barrier Layer
Surface energy levels on the plastic web must exceed thirty six dynes per centimetre to accept the adhesive layer without chemical priming. Static charges accumulate rapidly during high speed unwinding and require ionization bars before the lamination nip to prevent dust attraction. Post lamination processes place high mechanical stress on the glued interface during flat bed creasing and carton folding.
The finished composite material retains stiffness properties from the base paperboard while gaining chemical resistance from the polymer overlay. Surface finishing treatments determine the final gloss level or matte texture of the packaging component.
