How Paper Is Coated Calendered and Finished
Inline blade coating and soft-nip calendering establish surface uniformity, while targeted finishing passes balance visual embellishment against repulpability.
Corona Discharge
Surface Treatment
Converting operations that apply aqueous coatings or extrusion polymers to synthetic films and papers require high surface energy to ensure proper adhesion. A corona discharge is a localized electrical breakdown of air caused by a high-voltage electrode held close to a grounded roll. This process generates reactive species and ozone that oxidize the substrate surface, which creates polar molecular groups that attract inks and adhesives.
It modifies the topmost molecular layer of the material without affecting its bulk mechanical properties. This treatment allows water-based inks to wet out evenly across otherwise hydrophobic plastics.
Process Variable
The effectiveness of the electrical treatment depends on the generator power, line speed and electrode gap. Higher line speeds reduce the dwell time, which requires a corresponding increase in electrical power to maintain the target treatment level. Over-treatment can cause pinholes or reverse-side treatment, where the film sticks to itself on the wound roll.
Because the oxidized groups on the treated surface are temporary, converters must print or coat the material within a specified timeframe before the treatment decays.
Adhesion Benefit
Polar groups created on the polymer surface prevent ink flaking and improve the bond strength of laminate layers. This ensures that the finished packaging does not delaminate during distribution.