Multiple roll systems: Steady‐state operation

Roll coaters for applying liquid coating to continuous strip or web are, with some two‐roll exceptions, systems of three or more rolls in which liquid passes through two or more gaps or nips between rolls. Yet most of the literature on roll coating is devoted to some of the 11 distinct flows in individual gaps or nips. This article analyzes how the final coated layer thickness in several types of forward roll transfer and reverse roll coating systems depends, at steady state, on the number of rolls, their speeds, the gaps between roll pairs, and the doctoring of recycle films from the rolls. The inputs to the analysis are elementary mass balances at the gaps, and simple gap performance equations that approximate well the available experimental and theoretical findings about flow rates and film‐splits at individual gaps. The results are fundamentals‐based means of understanding, comparing, predicting, and ultimately designing performance of multiple roll systems.