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FLEXO Magazine : October 2009
46 FLEXO OCTOBER 2009 www.flexography.org Cellular foam is a necessary part of the flexo reproduc- tion process. Since its introduction many decades ago, the industry has seen many variations and iterations of this technology, most of which have advanced print perfor- mance while showing, in some cases, an increase in produc- tivity. But at the end of the day, have we really seen more than a tweaking of the same core fundamentals? The purpose of this technical article is the introduction of a radically new option for providing the cushioning/damp- ening required for a stepped advance in flexography. Early adopters believe displacement cushioning will advance flexography to the next level, to better compete with offset and gravure printing. CONTROLLED CUSHIONING The technology used to mount and provide dampening for flexo plates has changed very little in the past 10 years. Yes, there have been improvements, but there have been no new game-changing technological breakthroughs until now. Since its introduction, compressible mounting tapes all utilize a cellular structure as a means to provide the dampening layer in an attempt to reduce press bounce and improve latitude on impression settings. A cellular structure (open or closed) is the integration of two components, elastomer and air. Both components collectively and/or independently can act as a compression layer, but are they actually compressing or just displacing the energy caused by external pressure? Air can compress to various levels. Elastomers, on the other hand, can only displace external pressure through move- ment. This forces the balancing of performance character- istics between solid ink coverage and high ink density, while attempting to maintain sharp crisp type, tones, and reverses. The end result is a compromise that affects productivity and quality. Another problem with cellular structures is that over time the cell structure fails, the foam begins to collapse, and the print results deteriorate over the length of the pressrun. Who wants to worry about the finished job looking different from the beginning of the run to the end? On long runs, cel- lular foam tape often needs replacement to bring the job back within specification to finish the run. FLEXO NEWSPAPER: EARLY ADOPTERS Displacement cushioning technology was first adapted for use on flexo newspaper presses. Since its introduction, it has been in continuous use on flexo newspaper presses throughout the U.S. for more than two years. In commercial use, the prod- uct has proven to be nearly crush-proof. On web breaks and web wraps, plates may be destroyed, but the displacement cushions remain damage free. In a print application where cushions stay on press for typically three to six months, records show an average life in excess of 26 months. Frank Anthony of the Chattanooga Times Free Press, stated, I originally thought that displacement technology would have a press life of one and one-half to two years. With our recent web cut down and plate thickness change, we redressed the press and removed cushions well over two years old. The cushions we removed had significant life remaining. Just think about the labor savings when cushions last four to five times longer than cellular foam. In the two-plus years of having displacement cushions on our press we never replaced even one because of a web break or wrap. This displacement technology provides high solid ink density for uniform solids, without mottling, while eliminating smutting. This is accomplished through the unique physical characteristics of the product that allows a firm impression on the solids while relieving the stress on the highlight, quarter tone, and mid tone dots. Although flexo newspapers can expect to spend upwards of three times the price of conventional cellular cushions, based on actual use, the effective price over time is approxi- mately 25 percent lower (not including the performance ben- efits over and above the direct savings). With such a strong ROI, displacement technology adds real value to the press- room, the finance department, and even more importantly improves print consistency for your advertising customers. THE GREEN COMPONENT The terms carbon footprint" and sustainability" increas- ingly play a roll in how a company is judged, determining whether or not we are good corporate citizens. The significant reduction of cushion replacement reduces the newspapers' environmental impact. This is accomplished by significantly reducing cushion waste sent to the landfill, reduced paper waste due to the elimination of smutting, and the reduction in VOCs used to clean the cylinders before cushion installation. Displacement Cushioning A Real Alternative to Cellular Foam By John Rastetter FIGURE 1. Typical cellular compressible mounting tape, structure is not uni- form with weak areas for cell failure. FIGURE 2. Displacement cushioning technology. As impression is applied, the elastomer lines displace into the surrounding area, providing improved damp- ening without a cell structure that can breakdown. TECHNOLOGIES & TECHNIQUES
Sustainable Fall 2009