Inline Breaker Bar Geometry Optimization and Reverse-Side Fluid Dampening Dynamics
Breaker bar geometry and reverse fluid dampening control film lamination curl by balancing plastic yield strain and z-direction substrate moisture gradients.
Film Lamination Curl
Structural Distortion
Differential expansion and contraction between a plastic film and a paperboard base result in a curved deformation of the finished laminate. Common in book covers and food packaging, film lamination curl arises when the bond between layers occurs under uneven tension. The film usually has a higher thermal expansion coefficient than the board.
As the composite cools or the humidity changes, the two materials pull against each other with different strengths.
Moisture Sensitivity
Paperboard is a hygroscopic material that swells as it absorbs water vapor while plastic films remain largely unaffected by humidity. This discrepancy causes film lamination curl to worsen when the environmental conditions shift. If the board expands while the film stays stable, the sheet curls toward the film side.
Proper conditioning of the board before lamination helps mitigate this effect. This relationship between the two layers is the primary cause of post-production warping.
Production Control
Adjusting the brake tension on the film unwind stand provides a way to pre-stress the material before it meets the adhesive. Too much tension in the film will lead to a convex curl once the web is cut into sheets. Modern laminators use heated rollers to relax the film before application.
This thermal treatment reduces the internal energy stored in the plastic.