What are fisheyes? / What causes fisheyes?
Fisheyes is a term used by label printers to describe randomly distributed ring-shaped marks that appear in most self-wounds. Fisheyes are a characteristic feature of self-wound films caused by air entrapment between the film and adhesive during the winding processes. As the roll builds up, the pressure on these ‘air pockets’ causes regional adhesive flow, creating the fisheye appearance.
Why do they wet-out?
Fisheyes are not defects and generally become undetectable once the film is applied to label stock. During lamination, the air is eliminated from between the layers of self-wound and the adhesive flows on the substrate. During the first 24-72 hours this adhesive flow eliminates the appearance of the fisheyes. The pressure inside rolls of finished labels also helps the fisheyes to wet out.
Why might fisheyes fail to wet-out?
Although rare, fisheyes occasionally do not wet out. If they are still visible after 72 hours the following process parameters should be checked:
Ink adhesion: If the ink is not well dried or poorly adhered to the substrate, the adhesive on the overlaminate may not flow out properly to eliminate the fisheyes.
Lamination: Pressure sensitive adhesives require sufficient application of pressure for optimal results. Too little pressure (<20 psi) may not cause sufficient flow. This is of particular concern when changing overlaminate thicknesses. 25-35 psi is typically sufficient lamination pressure.
Substrate type: Dark, heavy ink coverage or metalized substrates are particularly challenging for fisheye wetout. This is larlgely due to the high contrast achieved on these surfaces. Overlaminate choice including adhesive type or use of an ‘easy release’ overlaminate can generally mitigate the occurance of fisheyes on these types of substrates. acpo offers many product options to help you get the best appearance from your press work.