Sign Builder Illustrated - October 2008 - (Page 36)

combine with monomers to form polymers. One difference between the two is that monomers are very small particles with a low molecular weight, whereas oligomers are larger molecules with a high molecular weight. Their function in the ink formulation is different too. Oligomers are “reactive resins” that form the backbone of the molecular chain to which the monomers bond in the polymerization process. Of course, monomer and oligomers aren’t the only components that comprise a UV-curable ink. Other components include photoinitiators, pigments, and additives. When the ink is exposed to UV light, photoinitiators absorb the UV energy and break down into reactive components that initiate the polymerization process. As the smaller molecules polymerize, they entrap the pigments (which give the ink its color) and the additives in the cured solid inks. Not all photoinitiators are alike. In formulating UV-curable inks, two types of photoinitiators are used. The most common or traditional type is called free radical. When the free radical photoini- tiator absorbs certain wavelengths of UV light, radicals are released. If you were around in the turbulent era of the 1960s, you know that radicals were agitators. The radicals in the ink are agitators too. They start the chemical reaction known as “cross-linking,” which bonds one polymer chain to another. Cross-linking occurs almost instantaneously. (Note: You’ll notice that I qualified my statement with the adverb “almost.” With some UV-curable inks, there’s a postcure period in which the inks continue to cure after the initial curing process.) The other type of photoinitiator is called cationic. These formulations have been around for years in the screen print and flexographic printing markets. Cationic UV inks cure differently than free radical inks. Once the curing process is initiated, it keeps going and going and going (just like the Energizer® Bunny), until the ink is cured. In the past, cationic UV inks haven’t been the most popular ink for inkjet applications, because of fears that the curing process was uncontrollable and posed a potential risk of ink curing in the printer and the printheads (which are very expensive to replace). “Some people have the notion that once the cationic curing process starts, it sets off a chain reaction that’s never-ending,” says Curt Brey, director of digital solutions for Gerber Scientific Products (www.gspinc.com). “No one has discovered a source of perpetual energy. Every reaction has a beginning and an end—and this is certainly true of the cationic curing process.” Whereas some UV inks use free radicals to get the cross-linking process going, cationic UV inks use special acids that act as the catalyst for the chemical reaction. “The big benefit of that chemical process is that cationic UV inks have much longer cross-links than the shorter cross-links of free radical inks,” Brey says. “It’s those longer cross-links that give cationic inks good adhesion, good flexibility, and good durability.” The longer a molecular chain, then the better it is. Brey explains that because longer molecular chains become intertwined or entangled, they bond together better (which gives the inks better elongation). Not all cationic UV inks are created equal. Most cationic require intensity to completely cure. Not all of them, though, work that way. Gerber’s new GerberCAT™ cationic UV-inks (which were formulated for their Solara ion printer) utilize low-energy lamps that generate very little heat. (Note: UV curing units can generate heat that can warp or damage some plastic films.) For all practical purposes, their inks cure at room temperature. When printing on some heat-sensitive materials (such as some plastics), the advantage of lowtemperature curing is that the print media doesn’t warp. Another printer utilizing curing lamps that emit very low curing heat is the Mimaki UJV-160 ( www.mimakiusa.com), a new UV-curable inkjet printer using an LED light source. Not only does this type of low-energy system cut power consumption considerably, but the low curing temperatures allow printing on heat-sensitive plastics. Similar to cooking food in a microwave oven, the UV-LED light source cures the ink from the inside out. What Is Post Cure? Exposure to UV light initiates the chemical reaction that causes the ingre- See Us At SGIA Booth 3003 – Atlanta, GA – Oct 15-18, 2008! 36 Sign Builder Illustrated October 2008

Table of Contents Feed for the Digital Edition of Sign Builder Illustrated - October 2008

Sign Builder Illustrated - October 2008 Contents SBI Agenda Quotes & Comments Contributors Revving Up for WrapQuest Dispatches Sign Show Sandblasted and Dimensional Sign Rescue, Part Three UV Ink and Printer Update, Part One Black is Black! Makin' Money With Molded Letters Making a Monster A Custom Built Sign Shop The Evolution of Architectural and ADA�Signage Finishing That Makes the Cut Maximizing In-store Signage and P-O-P Displays Wide Format Opportunities Panel Saws: A Precise Cut SBI Marketplace Q&A

Sign Builder Illustrated - October 2008

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