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FLEXO Magazine : December 2011
“Granted, some of the ink savings was a result of deploying fewer ink stations to achieve customer requirements,” said Apex’s technical sales guru Nick Harvey. “But, for example, reducing 15 percent in yellow ink consumption on one com- mon station, is remarkable in scale.” As if that wasn’t enough good news, after the trial the printer ran an additional 400,000 meters/1,312,000 feet (at full- speed of 400 meters/1,300 feet per minute) using CMYK plus white and never had to stop the press for cleaning, adjust- ment for dot gain or ink density. On the “green” side, volatile organic compound (VOC) emissions using GTT rollers were reduced by 25 percent compared with conventional anilox. S CURVE The 60° hexcell laser-engraved ceramic surface was a game-changing improvement over mechanically-engraved chrome rolls. But, continuous improvement strategies have long dictated that product development teams search for other surface engraving geometries that might do a bet- ter job moving ink from the doctor blade chamber to the printing plate. Better ink replenishment and delivery can enhance performance. Open-channel trihelical and elongated-hexcell laser en- gravings have long been available from anilox manufacturers as an alternative to conventional hexagonal-cell anilox surfac- es. It wasn’t until 2008 that an “S-curve” or slalom shape was applied to an engraved channel and uncovered the possibilities for more predictable and complete ink-to-plate transfer. “T he standard hexcell anilox engravings simply weren’t keeping up with the new plate technology,” observed Apex Group of Companies Technical Di- rector Martien Hendricks. “Hexcell anilox also couldn’t deliver superfine dots without high pres- sure, frequent cleaning, and slower press speeds. So, we got to work to build a better engraving.” THINK LIKE INK According to Hendricks, the physical behavior of fluid determines how well ink is transferred from the doctor blade ink chamber onto an anilox surface and then onto the plate. “ With a hexcell—which is basically a hole or a cup—the ink from the chamber is forced into these little cups at great pres- sure, which results in aeration. We call it ‘ink stress. ’ This bub- bly, turbulent ink is then transferred to the plate. But because of speed, pressure and turbulence, the ink typically adheres to the plate unevenly and squeezes up or ‘spits’ between the plate dots. ” The results, said Hendricks, are dot gain, mottling, dirty plates, plugged anilox cells, and unpredictable densities. That’s only part of the story. After transfer of ink to plate, a typical hexcell still retains residual ink. “ With finer plate dot screens, a hexcell needs to be smaller, yet also deeper, to hold the necessary ink volume. To deliver a desired density, the ink requires more pigment, which means more plate pressure is required to lift up the thicker ink from the cell,” Hendricks de- scribed. “ The problem is that finer and deeper hexcells, thicker ink, and more pressure combine to leave ink behind in the cells—ink that should’ve transferred to the plate. Now your little hexcell cup, with leftover ink, travels back into the blade cham- ber with an air bubble that must be displaced. Replenishing the cell in this situation requires yet more chamber pressure. ” With conventional hexcell technology, whether 30°, 60° or even elongated cells, “One can never be sure about the volume of the cell, especially if there is dried ink or surface wear,” warned Hendricks. “And the extreme pressures required to inject ink into the cells practically causes the ink to explode out of the chamber onto the plate which makes predictability difficult, to say nothing about blade, plate, and anilox erosion caused by high-pressure friction.” GO WITH THE FLOW “It became clear that the problem with hexcells was the end wall of the cell,” recalled Hendricks. “ That’s where all the pressure builds up and where the air is trapped. It’s like a pothole on the highway.” After years of research into new laser engraving geometries for anilox surfaces, including partial-walls and angled barriers, Hendricks arrived at a pat- tern which allows ink to “flow ” ever so slightly, thus reducing stress, aeration, and the need for high pressures. “ With our open slalom channel, air escapes without mixing with the ink at doctoring. And at the ink-to-plate transfer, the ink has an escape route down the channel, instead of oozing or spitting up between the plate dots.” Ink vessel geometry comparison April 18-19, 2012 I-X Center Cleveland, Ohio USA All Converting. All The Time. Bringing solutions to converters – wherever you are! First stop: CLEVELAND. Boasting one of the highest concentrations of U.S. converting operations from flexible packaging and tag & label, to folding carton and corrugated containers, CPP EXPO-Cleveland offers you a venue that most effectively ensures your goals and ROI will be achieved. Being right in the back yard of some of the key CPGs and major converters makes participation and attendance time-efficient, with little impact on travel budgets for your potential customers. Registration is now open! Use source code FM1 – you’ll automatically be entered to win an iPAD2 which will be delivered at CPP in April! Try NEW, NOW! Contact us today and let’s start discussing 2012 and beyond. Contact firstname.lastname@example.org or call (201) 881-1632. Visit CPPEXPO.com New Strategies New Locations New Prospects Official Publication of CPP EXPO: Sponsored by: CPP EXPO is produced and managed by HA BRUNO LLC. 34 FLEXO december 2011 www.flexography.org Deep conventional anilox cells trap ink while cell wall surface mass reduces ink area, thus inhibiting reliable ink replenishment. GTT channels are 40-60% shallower and land mass is reduced by 66% for greater ink transfer surface area and replenishment. GTT slalom channels reduce ink stress at the doctoring phase for a more controlled ink-to-plate transfer. iNk Vessel GeOmeTry COmPArisON