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FLEXO Magazine : June 2011
Technologies & Techniques Troubleshooting for UV Flexo Inks solutions for Adhesion, spitting, Pinholing and Cracking By Dean Radford Nearly all UV flexo inks are promoted as user-friendly and low-maintenance, but as with any ink or print system, troubles may still arise. Problems with adhe- sion, curing, spitting, pinholing and cracking of the print ink film are the most common issues. The catch is that the solutions traditionally used in troubleshooting for solvent- or water-based inks will not necessarily work with UV products. Problems should be addressed case by case, first by deter- mining the cause, then by tapping into options ranging from minor adjustments to full-scale maintenance. Poor AdhesIon Poor adhesion with UV inks often stems from insufficient ink curing. This is especially true with strong, dark colors. Inadequate curing can manifest itself by the presence of an unusually strong odor, tracking through the press and poor chemical/solvent resistance off press. Remedies include re- ducing press speed, reducing color strength and incorporat- ing some additional photo-initiator (consult your ink supplier). Other causes are mechanical in nature. An aging lamp or dirty reflectors can cause insufficient curing. The problem can also be a substrate with a low dyne level. Possible solutions include using corona treatment, applying a primer and changing the substrate itself. Photo credits: Courtesy of siegwerk usA Co. 74 FLeXO June 2011 www.flexography.org Finding the Cause • Poor adhesion with UV inks often stems from insuf- ficient ink curing. • Spitting is caused by poor rheology or flow and is often associated with the pigment load of the ink, the resultant viscosity or the press speed. • Pinholing is nearly always the result of poor wetting or ink leveling. • Cracking usually occurs when the substrate is stressed by temperature changes. • Curing contributes to most of the issues that arise with UV inks. When in doubt, check the cure!
Sustainable Spring 2011