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FLEXO Magazine : June2010
Technologies & Techniques 52 FLeXO june 2010 www.flexography.org Troubleshooting Guide: Feathering By Patrick Mollman and Roger Hall One common problem that press operators face is feathering. Feathering is defined as uneven edges around the print dot. The photo offers a common visual reference of this problem. Like many troubleshooting problems, there are multiple causes of feather- ing. The causes can range from very simple adjustments to more involved ink formulation issues. Causes of feather- ing could include the following: • Ink is drying on plate. • Incorrect pressure between anilox roller and plate cylinder. • Ink viscosity is too high. • Incorrect anilox roller. • Lint on plate from wiping cloth. • Resins in the ink precipitating out under certain circumstances and drying onto stereo. • Improper setting of the ink roller nip. • Improper plate relief. • Low spot on the plate causing over impression. In order for an operator to determine the true origin of one of the above mentioned causes, an operator should first visibly check the plate surface, being sure that there is not dried ink, lint or other foreign particles present. Also, the press operator or assistant should check the ink viscosity or reset the deck in order to further define the root cause of the feathering problem. Once the causal analysis has been completed and the root cause has been determined, the following corrective actions could be implemented dependent upon the root cause: • If the ink is drying on the plate, the operator should clean the plate and have the ink blender adjust the solvent blend by adding retarder to the ink. This will ensure that there is no draft from the hot air blower on to the plate, thus drying the ink onto the plate. • If there is incorrect pressure between the anilox roller and plate cylinder, the press operator should reset the deck, thus adjusting the pressure. • If the ink viscosity is too high, the viscosity should be lowered by adding the appropriate solvent. The operator should also check if ink trays are covered and remove any obstacle. • If the incorrect anilox roller was used, the operator should replace it with the correct roller for the particular print job. • If lint appears on plate from the wiping cloth, the opera- tor should clean the plate thoroughly. In this cleaning, as well as future cleanings, a lint-free wiping cloth should be used. Cleaning materials with the appropriate means helps to extend the life of the equipment being used. • If the resins in the ink are precipitat- ing out under certain circumstances and drying onto stereo, the operator / ink blender should avoid using a tacky ink. A solvent blend that would keep resin in solution should be used instead. • If there is improper setting of the ink roller nip, the operator should control / adjust the pressure setting of the ink roller nip. • If plate relief is in question, the opera- tor should question platemaking pro- cess and ensure relief is not an issue. • If the operator is experiencing a low spot of plate material or other cylin- der issues, prepress personnel must provide the correct tools so that the operator can reproduce with minimum plate impression. If you are still experiencing feather- ing issues, the operator should contact the ink vendor for further causal analy- sis to be performed. As with any process printing, opera- tors must be given the tools to provide a repeatable, quality finished product to the customer. With troubleshooting issues like feathering, prepress plays a large roll in predicting success. Prepress ensures plate cylinders or sleeves have a run out or total indi- cated runout (TIR) of less than .0005in. In addition, the printer must make sure to use the correct cushion back and plate material for optimum transfer and minimum dot reproduc- tion. Prepress also assumes responsibility for ensuring that all bearings and/or bushings are in proper working condition so that bounce or slop is not a factor. Producing a repeat- able press characterization and implementing processes will allow operators to follow what was learned and measure all components, such as density and dot gain. n ABOUT THE AUTHORS: Patrick Mollman is a technical lab manager in the Product Stewardship Division of the lab at Siegwerk. He attended Creighton University majoring in Chemistry. In 1995, he joined Color Converting Industries (now Siegwerk) as a lab assistant. As a lab technician, he spent most time improving ink manufacturing and disper- sion. He also spent several years in Print Services developing process printing inks and testing on press. Roger Hall is a national account service representative at Siegwerk. He began in the printing ink industry in 1980 at Inmont. In 1987, he joined Color Converting Industries (now Siegwerk) in the R&D lab. Hall has held many positions in- cluding customer in-house technicians, technical positions in R&D and his recent position. He has spent a great deal of his time with Siegwerk working to develop and improve Sieg- werk’s flexographic and gravure technologies. Art by siegwerk north America. FLX_June2010_mech.indd 52 6/10/10 9:39 AM