Sign & Digital Graphics

April '18

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S I G N & D I G I T A L G R A P H I C S • April 2018 • 33 DIGITAL PRINTING AND FINISHING DIGITAL GRAPHICS UV-Cure Inks: The Good the Bad and the Ugly Where UV-curable inkjet inks have excelled and where they have fallen short Ray Work, Ph.D., heads Work Associates, a consultant firm specializing in inkjet printing technologies, applications and markets. He worked for more than 28 years in research, research management, busi- ness development and business manage- ment with DuPont. Dr. Work holds a Ph.D. in physical inorganic chemistry from the University of New Orleans. He can be reached via email at workassociates@ comcast.net, or visit his website www.workassoc.com. B Y R A Y W O R K , P H . D . Think Ink What's in UV-Curable Ink? Today there are at least four different types of UV-curable inkjet ink technologies. The early versions were designed for arc lamp curing and had several drawbacks due to the high heat the lamps produced and their generation of ozone, and the toxic outgassing from vinyl media. Today UV inks for LED curing systems are quite common and avoid these problems. Like all UV-curable inks, they con- tain acrylic polymers called monomers and oligomers. They are the organic chemicals that make up most of the ink. When crosslinked they form the polymeric structure encapsulating the colorants and bonding the ink to the substrate. The process of curing requires the formation of "free radi- cals" that act to crosslink or chemically bond the acrylic poly- mers to one another and the substrate. To generate the required free radicals, a photoinitiator chemical is incorporated with sen- sitizers in the ink formulation. They absorb the UV light and use that energy to create the "free radicals." The sensitizer is a dye selected to efficiently absorb the UV light emitted by the A s advances in inkjet technology have progressed for wide- format and grand-format display graphic applications, developers have strived to provide high quality, increased productivity, better image durability and lower cost. Safety and environmental responsibility have also been consider- ations. Here we will discuss UV-curable inks and how they have attempted to meet these needs better than alternative technologies; where they have excelled and also where they have fallen short. (Image courtesy of Agfa Graphics)

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