Wet Coagulation Bath Design and Control
topic
Wet coagulation baths immerse PU-coated fabric in water or water-DMF mixtures at defined DMF concentration of 0 to 15 percent and temperature of 20 to 40 degrees Celsius for 2 to 8 minutes, with bath composition and temperature controlling the rate of solvent-water exchange that determines the microporous cell structure of the coagulated PU layer from closed-cell structure at fast coagulation to open interconnected cells at slower controlled coagulation achieved by DMF addition to the coagulation bath.
Role
Controls the microporous structure formation of the PU coating that determines breathability and waterproofness through bath composition and temperature management during the solvent exchange coagulation process, with bath DMF concentration being the critical control parameter that governs whether the coagulated PU forms a dense microporous structure for moderate breathability or an open cell structure for maximum breathability by controlling the thermodynamic driving force for phase separation.