Comparative Design and Performance of Primer Dryers for High-Speed Extrusion Coaters, 2005 European PLACE Conference

The drying of a low-solids primer for extrusion coaters is accomplished with hot air dryers using “slot-over-roll” and “air bar flotation” designs. At typical line speeds of 200 to 300 m/min, the simplistic configuration of slots-over rolls is effective and nearly as efficient as the flotation approach. As line speeds begin to approach 600 m/min and more, the increased drying loads and air flow dynamics of a fast moving web must be accommodated in both dryer styles. The flotation dryer with air bars on both sides of the web, is able to affect a significantly greater heat transfer coefficient at these higher speeds. Consequently, the flotation dryer can use a lower temperature for drying air and will consume less heating energy. At the higher line speeds, the entrainment of air between the web and the support rollers can create web stability problems for the slots-over-rolls dryer design. The non-contacting nature of flotation dryers negates the adverse interaction with the moving web to provide web stability that is independent of line speed.