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FLEXO Magazine : January 2010
www.flexography.org JANUARY 2010 FLEXO 35 • Dry weight is what you would expect to have for your target after the substance dries on the web. Wet weight comes before the drying process of water or solvent systems. • Press speeds, metering pressure and hardness of the rubber meter roll can change the coat weight in two- roll, un-bladed systems. • The basis of the construction---film/film, film/paper, BOPP, etc.---is helpful in looking for cases of incom- patibility or dive-in on the substrate. Good Information Makes for Successful Coating Applications By Sean Teufler Have you been involved with a situation where a prod- uct failed because you applied too much or too little of a coating? Perhaps you selected a recommended anilox but just didn't get the expected results. Whichever the case, the end result is that you are not getting the functional- ity of the product your customer needs. So what should you do to get positive results? The key to making a coating ap- plication successful is getting good information to calculate the required volume. Volume determination requires you to take a few steps. Typically, your primary objective is to understand where to ob- tain the information, and the second step is to document what information is important. Once you get all the required data, work with the anilox supplier to calculate what anilox you will need. Detailed below in sequence is the method used for get- ting information and discerning what facts are important to a calculation for required volume. CONTACT/GENERAL INFORMATION This is required from all parties, especially the customer and the coating supplier. Contacts are critical for confirming data and collecting missing information. General information would include the specific coating information, such as the product number, physical data contained in an MSDS, and any information related to the composition of the final wet or dry product going to press for printing. Specification/techni- cal sheets are also available for coatings, which generally describe proper application requirements. Technical information is always useful in single-component coatings (like UV and water-based, where the product re- ceives very little alteration from supplier to press) and critical in the case of solvent coatings, which become complicated by the addition of solvents/dilutions, as well as cross-linkers or any other materials. Don't overlook dilution and mixture schedules. They become important guides in the calculation of coat weight. Once you have gath- ered all available information about the compo- nents of your product and the contact information for the persons who are the experts you can rely on for good advice, it is time to disseminate the information. APPLICATION TARGET RANGE In other words, determine how much coating you want to apply over how much area. Applica- tion targets are commonly defined by coating sup- pliers in the following: imperial unit of pounds per ream or metric in grams per square meter (gsm). Make sure you have the correct unit of measure. Ream size is the area covered by the application target weight. Other possible choices for describing the ap- plication target are micron or mil value for film thickness. If you are given a range (example 1.0 to 1.5 lbs/ream), be sure to include it and be pre- pared to refine the value. Typically, if the weight in that range is non-specific, the median weight of 1.25lbs/ream from the example would be the de- fault target. Contact the coating supplier to clarify the range to a specific target weight. COATING WEIGHT MEASURED There are two possibilities for the measured coat weight; wet or dry. Dry weight is what you would expect to have for your target after the substance dries on the web. Wet weight comes before the drying process of water or solvent systems. The weight of UV does not change because there is no evapo- ration, just cross-linking and solidification of the coating, so it can be considered wet or dry. The solids content considered in the application of water or solvent-based coatings is af- fected by wet or dry designation, so always clarify. Viscosity and application requirements determine anilox cell geometry. TECHNOLOGIES & TECHNIQUES
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