In many scenarios, more is better, but not always in the world of laminating. Too much of a good thing — in regard to tension on laminating rolls — is counterproductive.
Most standard two-sided laminators operate on the principle of equality – it is important that roll tension is equal on both film rolls. If the tension (often controlled by applying more or less pressure onto a spring on one or both ends of the lamination roll feed mandrel) is too high on either the top or bottom roll, the laminated piece will typically curl in that direction. So – if there is too much tension on the top roll, the web of laminated plastic and ultimately the finished piece, will have an upcurl on the ends; the more uneven the tension, the more the curl in that direction.
To set roll tension properly, begin by completely unloosening the mandrel pressure settings, then turning them until the springs just grab as a starting point. Once engaged, make a one-half radius turn on both the top and bottom mandrels. From there, watch the ’wet-out‘ point on the heat shoe or heated roller. The ’wet-out‘ point is the place where the film adhesive, typically EVA, melts, turning from a milky white to a clear shiny surface, which looks ’wet‘. In most cases, wet-out should happen at about midway onto the roller or heat shoe, or in the middle from where the film first contacts the heat source to the nip point or pressure point where the films and substrate are bonded.
To adjust, make one-quarter radius turns on the mandrels, being careful to apply the same to the top mandrel as to the bottom mandrel. Once applied, test flatness of laminated products by trimming pieces and laying them on a flat surface to check for any curling issues.