Thermal Activation
The temperature of the compression rollers in a lamination unit determines the initial flow and wet-out of the applied adhesive. The solventless lamination nip temperature is a critical machine setting that ensures the liquid polyurethane spreads evenly across the secondary web. This thermal energy lowers the adhesive viscosity during the fraction of a second that the two films are pressed together.
Flow Behavior
High viscosity in solventless adhesives can lead to an uneven, dimpled surface finish known as orange peel. By optimizing the solventless lamination nip temperature, operators reduce the adhesive viscosity, allowing it to flow and completely wet both paper and film surfaces. If the temperature is set too low, the adhesive cannot coat the substrate uniformly, which results in trapped air bubbles and poor optical clarity.
Conversely, excessive heat can cause thin film webs to stretch or deform under the mechanical tension of the laminating line.
Bond Optimization
Packaging converters adjust the heat of the lamination nip to balance initial tack with dimensional stability. High-speed running demands that the adhesive develops enough green strength to hold the webs together before the full chemical cure occurs. Achieving the correct solventless lamination nip temperature helps initiate the polymerization reaction, speeding up the curing time while avoiding curl or tunneling issues in the finished reel.
Regular monitoring of the nip roll temperature using infrared sensors helps maintain consistency across long production runs.
