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FLEXO Magazine : November 2010
Technologies & Techniques Right Tape/Right Plate: How Do I Tell? Determining Factors=Foam Compressibility, Resiliency & Durability The correct plate mounting tape plays an integral role in optimizing the performance of the plate. In order to know which tapes you should choose to optimize the plates’ performance, it is good to know several characteristics of mounting tapes: 1. Foam compressibility: This is critical to the amount of support the plate needs to transfer the correct amount of ink to the substrate. A more compressible foam will allow for more control of dot gain, while a less compressible foam will give added support to transfer more ink that is needed for solids and large text. Various film reinforce- ment of the foam can also affect the accuracy of the dis- placement of pressure on the foam cells: a more flexible reinforcement will allow the foam to compress differently than a firmer reinforcement (See Figures 1 and 2). 2. Foam resiliency: This is the ability of the foam to recover quickly and accurately, allowing the plate to transfer the ink consistently, even at high press speeds. 3. Foam durability: This is the ability of the foam to com- press and recover consistently during long press runs, even when a higher impression setting is required. 4. Tape thickness tolerance: A low thickness tolerance al- lows for a more accurate impression setting across the width of the web, avoiding the need to over impress to compensate for too much variation in thickness. Other things to consider are: 1. Substrate: The type of substrate will affect how the ink transfers, which will require the correct foam compress- ibility. 2. Plate type: The durometer of polymer, type of plate (digital or analog) processing type (solvent or thermal) will factor into how the ink transfers. Typically, the plate should be harder than the foam, or else the plate will compress in the impression set, distorting the image. In most cases, digital plates require firmer foam plate mounting tapes than analog plates. 3. Print image: a. Print image on the plates can contribute to various print defects, like banding. You can address this defect by staggering the images on the plate, or positioning the screens at the lead edge of the plate, when possible. Foams that deflect pressure more accurately will aid in reducing the occurrence of this print defect. b. In general, plates containing combination print should be mounted with a medium-firm foam, rather than a soft foam. Choosing a softer foam can lead to over impression, which can defeat the purpose of the softer foam due to increasing the hardness of the foam. c. Firmer foam will allow for a lighter impression setting. This will provide adequate ink delivery for solid ink density needs, while controlling excessive dot gain. These hints should be helpful as you decide which tapes should be used with your plates. If you have any questions, you should contact your tape supplier. n Editor’s Note: This article was authored and submitted by experts at Lohmann Technologies Corp., Hebron, KY. FIguRe 1: Double-sided flexible Pe reinforcement. All art courtesy lohmann Technologies Corp. FIguRe 2: Rigid PeT film reinforcement on one side. • Tape plays an integral role in optimizing the perfor- mance of the plate. • Film reinforcement of foam can affect accuracy of displacement of pressure on cells. • In general, plates containing combination print should be mounted with a medium-firm foam, rather than a soft foam. 52 FLeXO novembeR 2010 www.flexography.org FLX_Nov10_mech.indd 52 11/1/10 2:25 PM
Sustainable Fall 2010