by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
FLEXO Magazine : June2010
Technologies & Techniques 60 FLeXO june 2010 www.flexography.org In flexography, the print defect referred to as “chatter” or “chatter marks” appear as distinct narrow parallel bands, as opposed to lines, running across the width of the printed substrate. They are perpendicular to the direction of the substrate’s movement. These bands usually appear darker or heavier than the intended density but may be lighter than the surrounding print. While this defect may appear on any substrate or occur on any press, it is more widely reported in narrow web and label presses. There are multiple types of chatter; each manifesting a bit differently and each having different causes. The primary types of chatter are: Doctor Blade Chatter. This appears as consistent distinct narrower parallel bands running the full width of the web. Doctor blade chatter is more common on single blade meter- ing systems. • Doctor blade chatter is caused by intermittent doctor blade contact resulting from: • Too high (greater than 35°) a blade-to-anilox contact angle making the blade flutter. • Too rough an anilox surface finish, and • A doctor blade that is too thin, too flexing or • A doctor blade that is made from coarsely structured steel (high coefficient of friction). To correct or prevent doctor blade chatter: • Adjust the blade’s contact angle by bringing the blade closer to the anilox or by lowering the contact point. • Use a thicker less flexing doctor blade material. • Use a high-density micro-structured doctor blade. Gear Mark Chatter. Consistent continuously repeating parallel bands running the full width of the web that are wider than those resulting from doctor blade chatter is usually the result of gear mark chatter. This is caused by slippage be- tween the plate cylinder and substrate resulting from: • Worn, dirty or ungreased gears. • Worn or dirty bearings. Correcting gear mark chatter is simply a matter of proper maintenance. • Check bearings by feeling bearing blocks to detect excess vibration. • Keep bearings clean / prevent ink from migrating into blocks. • Do not grease bearings. Impression Cylinder Chatter. This can be defined as paral- lel bands running the full width of the web that may be intermit- tent; that is, the bands may start and stop across the web. This is the most common type of chatter and is caused by: • Excess pressure between plate and substrate. • Uneven pressure between plate and substrate caused by • Plate and impression cylinders not set parallel, or • Plate and impression cylinders bearings / TIR / taper issues. • Inconsistent plate material thickness, hardness. • Cut marks on plate cylinder. • Web flutter at transfer point. Correcting and preventing impression chatter is a mater of: • Backing the plate away from the substrate one or two clicks. • Changing to a softer or harder mounting tape (softer – if the problem appears on screens and harder if appear- ing on solids). • Changing to a different plate material—one better able to hold a smaller dot. • Making sure bounce bars/bearer bars are used to keep the web positioned against the impression cylinder. • Verifying accuracy of bearings and cylinder TIR/taper. The causes of chatter are primarily mechanical. Chatter prevention begins with making sure the mechanical toler- ances are adequate, known, specified to suppliers, verified and maintained. Avoid buying cheap, low-quality press components. Regularly check for wear. The success of a job is determined well before it arrives at press. The first step in the troubleshooting process is to prevent problems by assuring components are correct. The next step is to operate with the least amount of setting pressure. Your qualified materials supplier of ink, cylinder and doctor blades can assist you to establish a customized training and trouble shooting protocol for your pressroom. n ABOUT THE AUTHOR: Paul Sharkey is president of FLXON Inc. His passion is for the elimination of waste in the flexo- graphic printing process. Troubleshooting Guide: Chatter By Paul sharkey Chatter in a printed image. Photo courtesy Xymid llC. Nobody Gets More Traffic Nobody Gets More Traffic With 85,000+ unique views every month, no other online publication in the printing/converting industry even comes close. FFTA/FTA/FLEXO Magazine | 900 Marconi Ave., Ronkonkoma, NY 11779-7212 | 631-737-6020 FLEXO@flexography.org FLX_June2010_mech.indd 60 6/10/10 9:40 AM