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FLEXO Magazine : July 2008
TECHNOLOGIES & TECHNIQUES timely, and there is limited handling of the roll which prevents damage to the engraving. Auto-wash is the other method of on-press cleaning. It is cur- rently available for most wide-web presses today. These units work by circulating chemicals through the chamber system as the anilox continues to rotate for a set amount of time after the ink has flushed from its chamber. The units are very efficient with rinsing and should require little if any follow up. Typically, all needed print stations can be cleaned in a short period of time, which allows rapid changeovers from job to job. A storage tank holds the clean chemical while the used portion is sent to a separate storage tank for solvent reclamation or waste water processing, depending on its makeup. Do not allow the anilox to run dry after the auto-wash process is complete as scor- ing or engraving damage may occur from friction. Off press cleaning_ Offline or off-press cleaning systems are secondary methods for cleaning anilox rolls which cannot be ef- fectively cleaned in press. This technique involves the removal of anilox rolls from the press and requires more time, which adds a risk of handling damage. Potential damage and lost time can be mitigated if the removal, transportation and location of the anilox are efficiently managed while out of the press. Map out your press area beforehand so the roll gets to its des- tination in a safe and timely manner. All off-press systems need to have designated employees assigned with the task of using and maintaining the equipment. This greatly decreases the risk of damage to the aniloxs while increasing the odds for the achieve- ment of clean anilox cells. There are two types of mechanical cleaning available today. Both soda blast and poly bead units use fine and specific blast media propelled from a nozzle by compressed air. The spray head traverses across the face of the roll and blasts media at the cells while the anilox rotates in the enclosed unit. There are several key points to remember concerning blast systems. Consistent control of the air pressure, while always using the recommended pres- sure setting from the manufacturer, will keep the compressed air free of condensed moisture and oil. Why is this important? Excess air pressure can accelerate particles to a speed that can cause im- pact damage to the surface of the roll. This usually happens when the system is manipulated to compensate for dirty engravings due to an improperly working unit. Maintenance and occasional cleaning of the units may be nec- essary tasks for the rotating mechanism, spray head and media delivery system. For example, the spray head track may become clogged with used media and prevented from moving, which keeps the blast concentrated on one area of the roll, possibly causing damage. Make sure the distance from the spray head and angle of the spray head to the roll is at manufacturer settings for the entire length of the roll, to ensure consistent and roll-safe cleaning. Be sure to use the right media for each situation. If you are not sure, it's best to contact the cleaning unit manufacturer and anilox supplier. Ultrasonic units are another effective offline cleaning method that involves the following combined factors of time, tempera- ture, chemistry and sound waves. The roll rotates on the surface of the heated tank solution by a set of rollers and belt attached to a drive motor engaging the journal of the anilox. The solu- - tion does most of the cleaning by emulsifying the ink residue and the ultrasonic cavitation is used to finish the process. Be sure to use the appropriate cleaning solution at the correct dilu- tion. Maintaining the integrity of the cleaning solution prevents the temptation to use excessive time in the ultrasonic cycle to compensate for worn or contaminated solution. Overuse of the ultrasonic cycle can cause damage to the engraving. Poor solu- tion quality means poor and lengthy cleaning cycles and frus- tration for the user. Be sure to rinse the roll with water and dry thoroughly. Power wash units are becoming more popular in the industry today. These units work in conjunction with temperature-con- trolled chemicals sprayed for a predetermined amount of time. Once the chemistry cycle is complete, water from high pressure jets removes the ink from the cells of the anilox and the roll is air-spray dried. As with all cleaning methods previously discussed in this article, wipe the roll down thoroughly (with alcohol or ace- tate if necessary) to remove any remaining water from its surface after the cleaning process is complete. Residual water on the roll will leave hard-water spots as it dries on the roll surface which shows in the print if not removed. Whether using on-press or off-press techniques, be sure to fol- low set guidelines and procedures for cleaning. For rolls going into storage, be sure to use roll covers or other protection, so the units are still clean and undamaged when needed. DOCUMENTATION A reliable tool for evaluating the performance of your aniloxes is documentation. Always keep a cleaning log available at each off-press cleaning station and have an inventory roster of anilox rolls available for the operators to reference. A roll that continu- ously appears on the cleaning log may indicate a worn engrav- ing. Rolls that are worn are mistaken for plugged anilox and get passed from press to press. Identify these rolls and have them evaluated for wear by the anilox supplier. If there is an issue, cor- rect it away from the press to prevent it from being mistakenly "proofed" repeatedly on press. The costs associated with worn anilox are great when factoring in the amount of time and wasted material at press ink matching. It is essential to document the following information on a clean- ing log: roll number or identification, engraved cells per inch (CPI), original or current volume of the anilox, any noticeable damage and most importantly why the unit is being cleaned. If a reason for cleaning the roll includes such problems as plugging and striping, those issues can be rectified with cleaning. If docu- mentation indicates "color pulling up weak," and it appears for the same roll multiple times, there may be a wear issue with it or the wrong roll could be getting selected for the job. Regardless, documentation helps to finetune what is happen- ing at press. Inventory documentation comes in many differ- ent forms. Engravings in the deadband area, tags, magnets and stamped journals are some of the more popular methods used. A full roster of available rolls should be kept at each press so infor- mation from cleaning logs and inventory documentation can be shared with all press operators. This further reduces the odds that anilox performance and press setup is left to guesswork. J U L Y 2008 www.f I exog ra p hy.o rg FLEXO
Flexo Sustainable Fall 2008