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FLEXO Magazine : November 2010
Technologies & Techniques To achieve these goals, you must have the press and its consumables working together. This is done by moni- toring and controlling of all the vari- ables. We have all seen this many times: the issue seems to be resolved and then it resurfaces again. The key is to resolve the root cause, not the superficial ones. It’s the components and how well they are maintained and kept working at their peak condition. It’s monitoring and controlling the films, inks, and adhesives for any issues. Testing the end product before an issue becomes a problem is the key, and the only way to do this is to establish proper testing procedures for control and monitoring of all the variables. Below is a list of variables and con- sumables, with questions pertaining to them, and input to each one: Film and Lamination. Is it treated on both sides or just on one? What is the surface tension of it? How consistent is the treatment from roll to roll, batch to batch? From past experience, testing the dyne level and verifying the treat- ment and the proper treated side of the film before putting it on the press elimi- nates a very important variable, and can be done with minimal downtime or even before it is brought to the press without any downtime. Fo r bottle wrap film and lamination, there are multiple types of adhesive that can be used—water-based, UV, solvent, and solventless—but, we will keep this to what I see as the most used one, which is UV adhesive. Film for bottle wrap is typically guar- anteed to keep its dyne for six months to a year, and typically has a dyne level of 38 to 42. Material vendors will say that you should not need to corona treat, but corona treatment will help prevent issues and re-energize the substrate, giving you higher obtainable speeds and better print quality. Lamination for bottle wrap film is treated on one or both sides and typi- cally has a dyne level of 38 to 40. This will maintain for a year and should not need corona treatment. Other issues with some laminations are related with slitting or running on certain bottle applicators. Typically issues running films are: 1. Elongation of substrate, too much tension or press issues. The repeat will be shorter than the specified print length per the print cylinders teeth or repeat size. 2. Roller not turning in press or idlers not turning or scraping something. This can cause a loss in coeffi- cient of friction (COF) and corona treatment. If this is occurring, you will see deposits of white powder on idlers, or anywhere contact is being made. With film and its low tension needs, the idlers must have low inertia bearings for idlers contacting the web. 3. Product curl. Improper balanced web tension, web and press temperatures, high and uneven nip pressure and high humid- ity can cause curl. Zero curl is virtually unattainable on a routine basis. There are multiple curl issues that can occur not just in the web direction, but across the web. Defining them, finding the cause, and setting up preventive measures and documentation to www.flexography.org november 2010 FLeXO 91 FLX_Nov10_mech.indd 91 11/1/10 2:26 PM
Sustainable Fall 2010