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FLEXO Magazine : July 2014
were purchased at various stores and the packages were analyzed. Even with acceptable opacity, often achieved by running a double “bump” of ink, the mottled, pinholed surface reflects less light. As a result, the printed white color looks dull and dirty, and does not have the visual characteristics of solid white polyethylene substrates, which is the “holy grail” of print on transparent substrates. In order to correlate numerical data with visual impact of the ink laydown, flexo plate analyzers were used. Captured images were compared with the mottle factor measurement. The higher the mottle number, the more visible were the defects in the ink laydown. Lower mottle numbers correlated with a smoother, more consistent layer of white ink. Test results indicated that an industry average mottle factor achieved by various plate, tape and anilox combinations ranged between 16 and 21. According to Recchia, any mottle factor greater than 30 indicates poor ink transfer and did, in fact, correspond with highly pinholed print samples. Mottle numbers of 10 and below were achieved when the ink laydown was good, with little visible pinholing. Test prints with a mottle number less than five were significantly better in appearance. Anything below a mottle of one would be considered featureless white coverage. The smoothest and pinhole free results that the R&D team achieved came in at 0.7 . The team considered this to be a significant improve- ment and not a far reach from their ultimate goal of matching white polyethylene, which has a mottle factor of 0.17. “ This is especially impressive considering the simultaneous increase of ink opacity by more than two points in the same samples,” Recchia adds. “By choosing the optimum combination of plate durometer, plate surface treatment, anilox volume and mounting tape density, printers will gain better transfer of white ink, increase opacity and improve overall appearance of their product—in one pass and without loss of speed. This is a potential game changer for entire flexo industry." ” 54 FLEXO | JULY 2014