The Science of Solvent, UV, and LED Inkjet

He was a bit odd but Fred Hein also was a good teacher. As we walked the halls between classes in high school, students would hear Fred—“Don’t call me Mr. Hein,” the one-time hippie instructed us—slowly drawl the word “physics” outside his lab room door. The tall, slender scientist’s frizzy-long hair framed his smiling-yet-eerie face as the single word oozed enthusiastically from his thin lips: “Physics,” he repeated again and again. This tactic was Fred’s own, strange way of recruiting prospective students for his popular course – and it worked. That, plus getting to go on a year-end field trip to a Six Flags amusement park because physics, like printing, is everywhere; it’s all around us.

“You do not have to be very observant to see the growth occurring in wide format graphics,” said Bruce Carson, CEO of diversified print firm The Dot Printer and Bindery (Irvine, CA), which tripled its large-format digital capacity last August by adding an EFI VUTEk GS2000 flatbed inkjet printer. The eight-color machine prints up to 80-inch graphics imaged direct to rigid substrates with resolutions up to 1,000 dots per inch (dpi). “From special event flags, to vehicle graphics, to signage at baseball parks, to floor graphics, to shopping malls, it is everywhere and expanding rapidly,” Carson observed.

Inkjet printing science is a blend of chemistry and physics; chemical physics, if you will. The challenge for inkjet inks is the conflicting requirements for a coloring agent that will stay on the surface versus rapid disbursement of the carrier fluid. There are academic papers on the topic of strong ultraviolet (UV) radiation exposures used to instantly cure ink, which I’m sure would make my old physics teacher smile, God rest his free-loving soul. But the difference between UV-cured and solvent-based technologies goes further than the ink chemistries. Which type of formulation is used depends on many factors – and these aren’t always obvious at first glance. It all comes down to what you want to produce now and in the future, and what you are producing it on: the media.

“Printing is the simple part,” half jested Larry Salomon, VP of Wide Format for Agfa Graphics in North America. “The complex part is [all] the media and finishing choices,” stressed the 25-year wide-format print veteran, who has had stints with Charette and Pitman. “Agfa has over 25,000 media SKUs [stock-keeping units], from 24 inches to five meters wide.”

With so many variables, when consulting with customers and prospects on which inkjet route to take, Salomon said there is “no Swiss-Army-Knife approach.” Agfa typically conducts an informal survey that includes two key questions:

1. What is your current production system in place?
2. What are your most common print applications? (What percentage of work is going outdoors, for example, or is printed on rigid vs. flexible media?)

Most people ballpark the second answer, but some are able to provide detailed, 12-month analyses of the type of work produced in their shops. It’s not always a case of either/or—solvent or UV; flatbed or roll-to-roll. More often than not, Salomon added, if a wide-format print firm has more than five employees and/or at least $500,000 in annual sales, it most likely has multiple pieces of production equipment on the floor. Some print firms do a little of everything (posters, banners, backlit, vehicle graphics), he explained, while some specialize in a niche such as exhibits.

Image duration is no longer an issue, as both solvent and UV inkjet printed pieces can survive up to five years “if done on the ‘right’ media and laminated,” Salomon noted. And where image quality is concerned, “it’s impossible to tell the difference from three feet or further away,” he added.