Laser engraved anilox rolls

As demands for higher anilox cell counts increase, manufacturers are developing new strategies for creating

the best anilox roll cell configurations.

While the printing industry as a whole waits for its flat line to break and begin an upward climb, one segment remains relatively healthy and competitive. Flexo, the once red-headed stepchild, continues to eke out market share as more consumer goods manufacturers elect to protect and decorate their products with the pouches, bags, sleeves, and shrink wraps that are especially well-suited to the flexo process.

Flexo's place at the packaging table has been hard won. Though the process has enticing economic advantages for many applications, it has battled quality issues for decades. Today, however, we no longer have to say flexo quality approaches that of offset and gravure printing. Flexo quality very often is that of offset and gravure—thanks to new presses, new ink formulations, digital imaging and plating technologies, and advances in the manufacturing and use of anilox rolls.

The anilox roll is often referred to as the heart of the flexo printing process. This cylinder, honeycombed with millions of miniscule cells, is used in combination with a fine wiping blade to ink the printing plate. Up until the early 1980s, few would say this delivery system was lovely, though. The cells were mechanically engraved on a chrome surface that wore and plugged easily, compromising ink transfer to the plate and subsequently making it difficult to achieve and control color densities.

Then came the advent of laser roll engraving. Manufacturers now used multi-gas CO2 lasers to vaporize inking cells into rolls fabricated with a new chromium oxide ceramic surface. The lasers were more accurate devices and could create sharper, more consistent cell structures. In addition, the ceramic was harder than chrome. Thinner steel doctor blades could be used to wipe excess ink from the cylinder face with less wear and cell volume loss.

Lasers literally revolutionized the anilox industry, and the exponential improvements in ink control at press in turn, vitalized the flexo industry. For the past 20 years, anilox manufacturers have been tweaking and honing the process in pursuit of the perfect sweetheart anilox roll. The best conventional wisdom defines that roll as having a dynamically balanced base to eliminate press vibration. It would also have a surface that is dense and durable, and can be exactingly engraved with cells that have high, predictable volumes and superb release characteristics.

A pair of approaches

Each manufacturer employs its own highly proprietary combination of roll coating formulation and laser technology—but they're all after pretty much the same result. Says Scott McLaughlin of Praxair Surface Technologies, "Our R&D today is basically focused on satisfying our customers' desires for higher line counts and being able to maintain ink densities for process printing."

Higher screen counts require higher anilox cell counts—more engraving lines per inch. More cells mean smaller cells. Smaller cells present an order of magnitude more problems both to manufacture and in use. Praxair's solution for that requirement is to use a YAG laser, which the company says can produce engravings of much higher volumes at much higher line counts (see illustrations) over a CO2 laser.

Regardless of the engraving technology (and vendors certainly don't agree on which is best), there are some very practical challenges of running higher line rolls—keeping the rolls clean, for one thing. Another issue according to McLaughlin is score lines—circumferential flaws caused by particles of ink, tiny splinters of doctor blade material, or other foreign objects lodged between the surfaces of the blade and the roll.

In addition to formulating a harder coating/ engraving combination more resistant to scoring and corrosion, Praxair has teamed with BTG, which holds a worldwide patent on ceramic-tipped doctor blades. The agreement makes Praxair the exclusive U.S. distribution channel for these Swiss-made blades, which it claims wear without splintering and are safer than steel blades.

North Carolina-based ARC International uses other charms to quicken flexo's heartbeat. Explains General Manager Steven Wilkinson, "The early '90s brought us thermal YAG with multiple hits, higher speeds, and higher volume cells relative to higher line counts. But, we've still been engraving into chromium oxide." Five months ago, ARC released a dramatically different ceramic coating.

Wilkinson claims the new material eliminates the porosity inherent in the current formulation and has a much smaller particle size. That small particle size, combined with a special anti-plugging agent, creates an extremely dense coating that engraves more uniformly using its thermal YAG or modified CO2 technologies. Wilkinson says the anti-plugging agent can improve ink release from the cells to 85-90 percent versus 75-80 percent from a conventional chromium oxide roll, with the added benefit of being resistant to plugging. And that, he says, "leads to printers being able to run longer, faster, and cleaner, with better volume-evolved densities, much reduced blade wear, and ultimately enhanced quality and consistency of the print."

There are other benefits—environmental ones for instance. The elimination of certain elements is arguably cleaner and safer. Plus, the process isn't prone to "recast" a condition in which liquefied ceramic particles re-solidify on the cell walls.

Wilkinson is so hyped on the potential of this formulation, developed under the direction of Owner Michael Foran, "time-served engraving engineer," that it's hard not to catch his enthusiasm when he claims "it's going to do for our industry, in terms of ceramic anilox rolls and glue and metering rolls for the corrugated industry, what DuPont's Teflon® did for non-stick cookware."

Something up the sleeve

Another strategy for today's anilox roll manufacturers is to apply their coating and engraving techniques to make anilox sleeves for cantilevered press designs. Sleeves offer a number of advantages, not the least of which is ergonomic. They are lighter weight, and can often be mounted and removed safely by a single operator.

The biggest advantage of running a sleeve configuration over an integral roll press is probably economic. As more printers take on shorter runs, set-up times become critical to financial success. Though the engraved sleeves are more expensive than conventional rolls, they save time on press, and they're easier to handle and inventory.

There are disadvantages, too. They present engraving challenges over whole rolls, and their portability may make them more prone to handling damage. The manufacturers that do offer sleeves report the demand is still small for the installed population of presses, but growing.

With the present level of ongoing research and development into this most critical process component, anilox roll manufacturers are helping to keep the pace for flexo's growth in the industry.

by: Terri McConnell