In this article, I would like to address a relatively common issue — called ‘silvering’ — that can occur during the lamination process. Frequently my customers will claim, especially those with older equipment, that they are getting bubbles beneath the surface of their lamination. They might explain that it is all over the surface, or perhaps they’ll describe a particular pattern. Initially, they think it’s a lamination issue; however, more often than not it is a result of what we call silvering.
’Silvering‘: Caused by a Lack of Heat, Pressure, or Both
Silvering is caused by a lack of heat, a lack of pressure, or a combination of both, which keeps the glue on the laminate from being fully compressed down into the valleys on the surface of the paper. This sometimes happens when using very thin films over very rough paper because there is simply not enough force. However, in most cases it’s because an older machine is being used, having insufficient pressure on the sides of the rollers – often pancake cylinders are being used (like an old D&K) — instead of the newer machines that utilize cantilevered pressure cylinders.
Silvering can be subtle and can impact the richness of the finished product. As an example, I recently witnessed a solid black sheet being printed on an Indigo. The machine it was run on was not using very much pressure. When we over-laminated it with a soft touch film, even though the soft touch was 1.5 mil — which contains a lot of adhesive — it was not getting down into the nooks and crannies of the paper surface. The pressure simply wasn’t there. We then adjusted the pressure, and using the same 1.5 mil Karess™ film and the same machine, we produced a much richer black simply because we were squeezing the Karess™ product down very tightly, thus easing out all of the air. The result was zero silvering and a much richer black!
“Because we were squeezing the Karess™ product down very tightly, thus easing out all of the air, the result was zero silvering and a much richer black!”
To conclude, if you are experiencing problems with bubbles on the laminate surface it is most likely not a lamination problem. Begin experimenting by increasing the heat. But with the heat up, be careful to reduce the amount of tension or pull on the unwind roll so you don’t trigger any unnecessary shrinkage in the finished product.