PFFC - November 2008 - (Page 35)

WEB COATING u Filter pressures versus time; u Temperature and viscosity values u In-line injection addition rate; u Cleanliness of kettles and transfer lines. during coating; nation from drying air, and non-uniform air delivery to coating surface. To get good quality and high productivity, the following variables must be controlled: u Web temperature all zones; u Dry bulb, both supply and return, u Substrate roll physical conditions; u Coated roll length; u Performance and conditions of u Vibration levels; u Roll speeds. transport rolls; Coating Applicator in all zones; u Solvent concentration, both supply and return, in all zones and wet bulb or dew point if aqueous; u Air flow volume in supply and u Gap between applicator and coating return ducts; rolls, measured with substrate in place; u Slot velocity in selected nozzles both u Gap TD uniformity; average and profile; u Roll speeds, gaps, and direction for u Filter pressure on dryer air in all zones each roll in multiroll coaters; and motor amperage; u Roll surface quality; u Dryer air balance; u Flow rates to roll coating pan; u Actual solvent removal in each zone, u Solution and applicator temperatures. which can be calculated from drying air volume and solvent leveling return air; For a slot die coater, these are the spe- u The dry point of a coating, which is cific variables to be characterized: the location in the dryer where the coating is essentially free of liquid. It u Gap between slide lip and coating roll; can be detected by measuring solvent u Vacuum box vacuum level and clearance; level, film web temperatures, or by u Flow rate to slot die; visual observation. The exact location u Solution and applicator temperatures; in the dryer and the uniformity in the u Shims in distribution channel; TD should be measured and recorded. u Die lip configuration; Under no circumstances should the u Die plate and support identifying moving web ever be touched. numbers; u Die lip sharpness. On-Line Measurements There are two new technology systems— There are some general variables on-line coating measurement and surface that should be characterized for all defect inspection—that are essential coating methods: characterization techniques. Each of these has its own data storage and analyu Vibration levels of the coating station sis system, which also can be included in and coating rolls; an overall plant information system. u Cleanliness of all coating applicator hardware and transfer lines; u On-line coating weight gauge to u Temperature and relative humidity measure coating weight, MD and TD (RH) of coating applicator ambient air; profiles, and roll-to-roll averages; u Coater room temperature and RH; u Surface inspection systems to identify u Level of airborne particulates, defects, frequency, type, and location. contaminants, and pollutants in coater room ambient air. Web Handling The web handling system must transport The Drying Process the web through the coater at a uniform The function of the dryer is to remove line speed without distorting the subsolvent from wet coating without introstrate or creating defects. Uniform line ducing any physical or chemical defects speed is essential to uniform coating in the dried coating. The drying rate is weight. These are the key variables to be determined by the air velocity level and measured in the transport system: uniformity, line speed, solvent concentration in drying air, and the difference in u Line speed, average, and variability; temperature between coating and dry u Tension levels in each zone—average bulb of air. and variability; Quality can be affected by high air u Drive motors’ performance; velocity disturbing the coating, contami- u Edge alignment; There are several variables that influence the coating quality and coverage level. The specific variables to be characterized for a roll coating process include the following: WWW.PFFC-ONLINE.COM Storage The coating process raw materials, coating solutions, and coated rolls are stored at various times. The ambient temperature and RH of the storage facilities should be controlled and measured. Process Control & Information Systems Process control and information systems are computer systems that automate and regulate the operations in a continuous coating line. They control, monitor, record, and store all the independent process variables. They can use several types of control logic based on the needs of the process. In addition, they perform several other functions, such as measure and record the dependent variables in the process. Also, they record all of the roll bookkeeping functions, uncoated and coated roll information, and raw material lots. The system also can interact with surface inspection systems so defect levels can be correlated with process variables. The obtained data can be analyzed by several statistical routines, such as JMP and Minitab statistical software. Edward D. Cohen, Ph.D., is a technical consultant for the Assn. of Industrial Metallizers, Coaters & Laminators (AIMCAL). He has 40+ years of experience in research and manufacturing technology. Contact him at 480-836-9452; cohened146@aol.com. This article, along with future articles by other authors, is provided as a cooperative effort between PFFC and AIMCAL. Authors contribute to AIMCAL’s technical and education offerings, which include the association’s Fall Technical Conference, Converting School, and Ask AIMCAL. Want To Learn More? For more information on optimization of the coating process, see PFFC’s Special Report on coating and laminating in February 2008, or visit our website at www.pffc-online.com and click on the “One Stop” category: Coat/Laminate. NOVEMBER 2008 | 35 http://www.pffc-online.com 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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