When There's No Cure

The ability to measure the UV energy output from your lamps can provide valuable information when dealing with curing problems.

by Tom Polischuk, Editor-in-Chief

UV FLEXOGRAPHIC PRINTING is well established in the package printing industry and its impact has been significant. The use of UV inks is at the top of many lists when discussing the reasons for the significant quality improvements of flexo printing over the past several years.

Many converters are multi-year veterans in the application of UV technologies, but many others have recently made the jump into this new technology arena. Routine processing problems come with the territory, but they are so much more prevalent and frustrating when applying new technologies and working through a learning curve.

What this means is that more often, converters are facing the problem of what to do when the UV ink is just not curing properly. For starters, it's critically important for converters to have close working relationships with their ink, substrate, and UV curing system suppliers to deal with both routine problems and the more difficult challenges that crop up at the most inopportune times.

One of the first approaches that converters can take is to check out and verify that the UV curing system is working as it should. There is an array of tools available, and it's a necessary and much simpler proposition, than jumping into analytical chemical analysis of what are fairly complex UV inking systems.

First, some of the chemistry

In my initial discussion with Mark Hahn, VP of sales and marketing for AAA Press International (Arlington Heights, Ill.), he gave an overview of the ink chemistry, and therefore, what the UV curing equipment is targeted to accomplish. According to Hahn, inks and coatings contain three key elements for proper curing—monomers, oligomers, and photoinitiators. Monomers and oligomers are the reactive components, while photoinitiators are the components activated by the UV energy to set off the curing process for the inks/coatings. "Typically, ink manufacturers will put specific photoinitiators into the inks for surface cure, depth of cure, bonding, and other ink features," explains Hahn. "A standard medium-pressure, mercury vapor lamp will produce a specific intensity curve with peak irradiance being at 365 nanometers (nm). Ink manufacturers try to match their ink chemistry to this curve for optimum curing performance."