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FLEXO Magazine : June 2012
cardboard is not enough protection. Other than perhaps stopping dirt from being transferred from the lifting strap. A thicker, more substantial cover that can withstand marking from sharp objects, such as the side frame of the press, or the chamber holder, is much more suitable. While you might think that you have only grazed a roll if you knock it against a solid surface, there is a good chance that the ceramic coating will be fractured. When run in the press, ink, water and solvent can migrate through to the metal core, which can result in galvanic corrosion and ultimately failure of the coating itself. If the edge of the anilox is hit, it will often result in coating chipping, as this is the weakest area of the coating. This will cause damage to the doctor blade and the seal and will gradually migrate around the full circumference of the roll, if not filled in with an epoxy resin immediately when it has occurred. Although this is not a permanent fix, it will reduce the final failure and further chipping for several weeks or months. Unless a completely square edge is required, one should ask the supplier to apply a small bevel to the edge of the roll during the manufacturing process; this will dramatically reduce the chipping of any roll if accidently hit on its edge. Minimizing damage to the edge of the anilox can also help reduce scoring of the anilox, which is caused by ceramic particles that break up. These particles then get into the ink or coating and become trapped between the doctor blade and the surface of the anilox. Ceramic particles are inert, so they cannot be pulled out with rare earth magnets and are generally too small to be fil- tered out. Filters and rare earth magnets should be used as standard on all presses to help reduce the presence of other particles, such as metal, large clumps of pigment, resins and any other foreign object that may have got into the ink system. All of these elements can and will cause scoring to the anilox surface if caught between the blade and the engraved surface. Now, as originally stated, plugging or filling of the engraved cell, regardless of its configuration is the primary reason for failure of most anilox to perform consistently. This is what causes the biggest concern for the majority of printers. The first question however, is at what point should an anilox be cleaned? And how do you make the decision to do this? For many printers the decision is all too often based on a judg- ment call. The operator or manager decides, based on the ink density, coat weight or laydown, as visually seen by the naked eye. Clearly, this is not based on any empirical data and is often an incorrect decision, as it may be an issue of the ink chemistry, viscosity or pH of an ink or coating. That said, it is relatively easy to see obvious plugged cells with a 100X microscope or greater magnification. And, with practice, most experienced printers can make a reasonable decision. Today, sophisticated interferometry devices allow for more accurate measurements to be taken and a log to be kept of each roll throughout its run life. While these devices are expensive, they are beginning to prove useful for most print shops that are serious about maintaining a consistent result from their anilox inventory. THREE CLEANING OPTIONS So, how do you clean your anilox? Should you scrub them by hand as is often the case or should you use some form of mechanical device to do the job for you? There is no doubt that manual cleaning has been, and still is, the most common form of roll cleaning carried out by most operators. Yet, when questioned, most managers understand it is the least efficient and most costly method of cleaning. No matter how much time or effort an operator is given, it is impossible to clean an anilox uniformly across and around its entire face, particularly with larger rolls. Even if the pigments and resins of the various chemistries that are in use were readily resoluble, manual scrubbing has, and continues to prove to be an ineffective method of cleaning any anilox. This leaves some form of mechanical cleaning. Historically, there have been three major cleaning systems: blasting, high velocity liquid and ultrasonic. Blast systems consist of three options, sodium bicarbonate, plastic pellets and dry ice. All are effective but each is prone to operator manipulation, which can potentially lead to damage to a Anilox Covers – Protect Your Investment! • For use with anilox rolls, engraved cylinders or other costly rolls • Cost effective protection with quantity discounts • Available in clear or yellow for enhanced pressroom awareness • Custom print available • Solvent resistant & easily cleaned • Diameters from 2.5” to 20.0”. Lengths up to 240.0” Xymid, LLC • 5141 Craig Rath Blvd. • Midlothian, VA 23112 • Phone 804-744-5229 • FAX 804-744-5331 Web Site – www.flexoprintsleeves.com or xymid.com and click on “PRINTSLEEVES” Xymid ProTekTM Slit Cover • Cover is slit down the length for easy mounting or demounting both in or out of press • Cover overlaps to ensure complete roll protection • Excellent memory, will not “stretch” after multiple uses Xymid ProTek-ERTM Non-slit Cover • Non-slit cover with rubber end ring on one end for secure stop against roll • Primarily for rolls without journals or shafts • Approximately 5/32” larger than covered roll Plastic pellet blasting system Modern ultrasonic system 94 FLEXO june 2012 www.flexography.org