Silvering is not a clear indication that there is poor overlaminate adhesion. As of right now, we have no solution to silvering. We know that first laminating cold, then warm laminating the whole construction may assist in accelerating the "wetting out" process of silvering, but does not promote overlaminate adhesion initially.
Silvering is the visual effect seen when laminating an overlaminate film on to a UV printed graphic. This effect usually appears as a silver or hazy effect across the print, most noticeable over darker colors of the print.
Cause of Silvering
Silvering is caused by the uneven surface texture of UV prints. UV ink does not cure onto films as smoothly as solvent or latex printed graphics. The uneven surface creates a rough texture which is hard for an adhesive to fully adhere to.
Solution to Silvering
Currently, we have no solution to silvering. First laminating the overlaminate onto the print cold, then running the whole print (lam + film) through the pinch rollers with heat assist on appears to accelerate the process of silvering fading away, but does not completely eliminate silvering nor does it necessarily promote initial adhesion of the overlaminate to the graphic. Heat assist lamination during the first pass (applying the overlaminate to the print) is not recommended because the heat could potentially stretch the overlaminate putting stress on the film.
Generally, it is preferred to clear coat UV prints due to the lack of silvering.
Adhesion Problems Due to Silvering
Silvering is a problem visually for end users as this is an unintended effect that lessens the quality of the print. This effect has also led to the hypothesis that silvering may affect the adhesion of the overlaminate to the print. A Technical Service Case was performed to confirm this hypothesis and it was found that overlaminates tend to have a higher adhesion bond to UV inks than solvent or latex (see graph below). There is no direct correlation between peel adhesion and silvering.
The chart below shows the average peel adhesion of Series 3210 on 3M Superflex UV ink, HP 360 Latex ink, and Roland XR-640 at room temperature and 0 C after 3 hrs of dwelling. The UV ink has a higher average peel adhesion of both Latex and Solvent inks.