PFFC - November 2008 - (Page 33)

The views and opinions expressed in Technical Reports are those of the author(s), not those of the editors of PFFC. Please address comments to the author(s). WEB COATING Process Characterization The ability to measure and control the variables in the entire web coating process is essential to the manufacture of a uniform, high quality, low-cost product. By Edward D. Cohen, Edward D. Cohen Consulting Inc. he web coating process has u Process measurements result from about 15 major components, process control properties, e.g., the and each of these components, dry bulb and solvent concentration in turn, has many hardware of the returning dryer air. This can subsystems. All these hardware subsysbe used to calculate the actual drying tems contain process variables that must performance in each zone. The actual be measured and controlled to ensure coating weight on the substrate is they are stable and within control limits. another variable. The result is several hundred process u Fundamental coater properties include variables that need to be characterized to drying air slot velocity and roll conditions guarantee a reproducible, cost-effective as well as coating applicator conditions. process. All process components are critical, and none should be ignored. These measurements should be stored in a historical database. Then they can Process Variables be used to troubleshoot defects, maintain There are three basic data classes to be quality, and identify process components characterized. that need to be improved. u Process T control variables include line speed, web tension, drying air, drybulb temperature, coating solution temperature, and flow rate to the applicator, pump speed, and many others. These vary depending on the product type and must be measured and maintained with established control limits. on a paper log sheet. This data could be entered manually into a computer system. However, the process was time consuming, expensive, and could have significant errors because of incorrect data entry into the computer or missing data. As the technology developed and hardware costs decreased, the utilization of computer data acquisition increased. In addition, the low hardware costs also resulted in additional data points being collected and more accurate process characterization. There was an improved understanding of the fundamentals of the process. Recent technological advances in process measurement, data collection and information systems, computer performance, and data storage have resulted in the availability Technology Has Advanced of new, low-cost, precise measurement and Previously, the ability to obtain and anadigital data acquisition systems for the web lyze all the needed characterization data coating process. These systems give the was limited because of several factors. The converter the ability to do a thorough promeasurement, control, and data acquisicess characterization at a very low cost. tion technology was expensive and limited Also, since the data is available in digital in the variables that could be measured. format, it can be analyzed easily to deterThe needed data initially was obtained mine defect causes, areas of poor reproon a strip chart or manually recorded ducibility, and performance of individual NOVEMBER 2008 | 33 WWW.PFFC-ONLINE.COM TECHNICAL REPORT http://WWW.PFFC-ONLINE.COM

Table of Contents Feed for the Digital Edition of PFFC - November 2008

PFFC - November 2008 Contents First Glance Calendar of Events From the Editor Web Lines Process Management News Clips Narrow Web & Label Reporter Narrow Web & Label: What’s New Products TLMI Awards Card Making Web Coating Ink Dispensing Lab/Pilot/Technical Facilities Directory Testing & Measuring Products What’s New Products Services Directory Classified Marketplace Advertisers Index Experience Speaks

PFFC - November 2008

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