The lamination of two materials that have different thicknesses can pose special problems. Many types of laminating equipment employ nip rollers to bring the different substrates together at the moment of lamination. When one or both of the materials wrap around a nip roller, and the material has comparative thickness, the feed length of that
substrate is altered. This is most common when laminating foams to fabrics. If the foam wraps the nip roller by, say, 180 degrees, the feed length of the foam will be greater than 180 degrees of the roller face – the thicker the foam, the greater the disparity.
When laminating a thick foam to a fabric, we often make sure that the fabric selected is extensible and forgiving. This forgiveness allows the fabric to bond to the foam without inordinate stress at the adhesive interface. This is often simply a matter of selecting a knit, versus a woven (or non-woven) fabric. Knit fabrics will usually stretch or compress enough to compensate for disparity of feed length. This, in turn, will allow the finished composite to lay flat (normally a desirable characteristic of the laminate).
The other most common laminating technique to deal with this problem (other than using a forgiving fabric) is to bring the two substrates together in a flat condition, such that they approach the nip rollers at a tangent to the rollers. This is the principal behind most “flat-bed” laminators. Not a perfect solution, however, this techniques can pose problems with getting the bonding agent to the interface, especially when the thicker substrate is too thick (say, 1” or greater).
Ultimately it falls on the laminator to devise an approach that is calculated to succeed with the substrates involved, and that approach may have to depart from general rules.