This is a tale of two different perspectives on digital UV-curing flatbed imaging. Two shops, each with different business models, answer some candid questions about handling UV-curing equipment. Neither firm is in the “printing business” per se, but rather in the business of delivering value to their customers.

Not only are they in synch with each other regarding their customer base, but they are in complete agreement on key issues including the importance of cleanliness and equipment maintenance as elements toward gaining the greatest return on investment. When it comes to digital equipment, they both have roll-to-roll printers and UV-curing digital flatbeds.

Both companies contend that not all color matches are created equal, that source files are the key to accuracy, and that shops should be wary of a print buyer who’s most technical phrase about color is “more pop”. But as different as their business models are, they share very similar philosophies and goals.

Source One Digital is an all-digital shop based in Muskegon, Mich. Source One pushes the digital imaging envelope by constantly investing in state-of-the-art output devices, which currently includes a Gandinnovations Jeti 3150 UV-curing flatbed printer in addition to two Gandinnovations grand-format printers. We spoke with Randy Crow, the firm’s CEO.

Pittsburgh-based Custom Printed Graphics (CPG) is a digi-screen shop — an operation that runs both screen and digital printing equipment. The 35-year-old “job shop” specializes in imaging onto everything — from T-shirts, to close-tolerance functional panels, decals and display graphics. Among the shop’s digital printing equipment is a VUTEk PressVu UV 320/400 UV-curing flatbed. We spoke with Larry Ennis, who owns and operates CPG with his brother Ken.

TALE OF TWO PERSPECTIVES

Q: Is digital imaging a core competency or is it used to complement, supplement or replace screen-printing?
Randy — Source One has been digitally printing for about a decade. We went with a digital flatbed to complement and supplement the scope of our digital product line. Rigid stocks, improved outdoor durability and backlit signage can now be offered easily as roll-to-roll flexible images.
Larry — For CPG, the decision to go digital was predicated on several different criteria. Digital complements, supplements and/or replaces certain segments of screen printing operations. Once we standardized our color, the complementary aspect was seen as re-orders. Supplemental processing includes prototypes and sales samples. Digital can effectively replace screen for short press runs, and what we define as “short” is getting bigger!

Q: What is the most common cause of surface flaws, and what do you do about them?
Randy — “Cleanliness is next to productivity;” that’s a paradigm that keeps banding down to a minimum in our shop. The most common cause is nozzle drop-out, which is often times due to dirt, in the factory, on the stock or both. The dreaded “solution” to nozzle drop-out is to wipe the head, which ruins the head — pronto. As a result of proactive maintenance, Source One has virtually eliminated surface anomalies and flaws, and our piezo printheads seem to last “forever” because they don’t create issues that force us to wipe the heads.
Larry — Periodically we run into surface flaws due to head-strikes or stock variance. We tackle a huge variety of substrate types, edges, sizes and shapes. On thermally-sensitive stocks we are careful to operate at a speed that prevents shrinkage from the radiant energy output from the UV lamp. As a standard operating procedure, we try to keep the image in the “sweet-spot” of the substrate and will wipe “greasy” surfaces with IPA to ensure better ink adhesion.

Q: Which stocks challenge the ink’s adhesion? Is there anything you can do to improve adhesion?
Randy — We’ve had issues with aluminum, both raw and the more commonplace roller-coated polyester base type. We abrade the surface of aluminum panels as a standard operating procedure. Adhesion requires proper wetting; so we delay the cure settings some to allow the ink to grip to the stock before polymerization during production.
Larry — Free-radical curing UV inks for digital are termed low molecular weight — they contain no resin, which promotes film integrity, durability and permanence. Therefore, UV-curable digital ink systems will not always adhere to Coroplast and styrene. We will frequently run a test print to gauge various levels of cure and we regularly wipe the slippery surfaces with IPA. We post-check the cure overnight, and under extreme circumstances, may resort to a conveyorized UV reactor to post-treat the ink.

Author’s note: UV digital inks must be thin enough (low viscosity) to be jetted through the small openings in the piezo printhead nozzles. For this reason they cannot contain high concentrations of oligomers (high-viscosity resins). In turn, UV digital inks tend to have a low molecular weight; inherently they are not as durable as their resin-rich, screen-printed counterparts.

Q: Printing at high speed is more profitable, but does it create surface flaws?
Randy — When we run at top production speed — particularly on slick stocks — the printheads no longer make simple geometric shaped dots. They tend to create tadpole-shaped dots that will often leave a seam — lines in the print stroke direction. Standard operating procedure is simply to slow down (per stock) for better detail, resolution and contrast.
Larry — At times we may see artifacts at top printing speeds — like those tadpole-shaped dots. They result from higher speeds and the gap between the printhead and the stock. In our digital operation, we work on behalf of our long-term customers to balance efficiency with effectiveness. “Don’t gold plate it” is the goal for some of our customers, which means the signage may be more price-sensitive when hanging 30 feet in the air.

Author’s note: Artifacts are a result of a bad combination of imaging speed, stock surface energy, distance from ink to stock and the nature of the ink. Slowing down is one option, but less of this is required when the ink is a good fit, and the flatbed’s software is made to minimize surface variability.

Q: What about backlit image densities?
Randy —For us, backlit signage is the exception and not the rule. When required, once we achieve single-pass color balance, we run a double-pass that effectively eliminates the “washed-out” look of single-pass colorants.
Larry — We sometimes alter the mid-tones when running backlit images in order to enhance the colorfulness of the image. The mid-tones create color, particularly on backlit parts. We have worked to duplicate backlit digital with screen so repeat orders, samples and prototypes represent production runs with digital and screen.

Author’s note: Backlit images must be run at higher ink density because transmitted light passes through the image to the observer. With frontlit graphics, light strikes the image, goes through the ink color to the stock, is partly absorbed by the stock, and then is reflected back through the color a second time. Two passes is a good average compensation for backlit images.

Backlit images need to be run at higher ink densities. At CPG, operators sometimes alter the mid-tones when running backlits such as this one, in order to enhance the colorfulness of the image.

Q: How often should you have to replace Piezo inkjet heads?
Randy — We’ve only needed to replace one or two printheads in more than a year of operation at one-and-a-half shifts a day. I think our high level of operator skill, consistent equipment maintenance and cleanliness have helped us here a lot.
Larry — Replacement of the piezo printheads is a part of the cost of doing business. But frankly, our UV-curing printer is less than a year old, so head replacement has not yet become an issue. However, we proactively maintain our equipment and insist on well-trained staff and high-caliber equipment.