Bath Concentration and Add-on Control in Wet-on-Wet Padding

One concern associated with wet-on-wet processing is the changing chemical concentration in the pad bath. After processing for several hundred yards or so, chemical add-on considerably decreases, resulting in poor performance properties of finished goods or decreased shade depth. To obtain a constant bath concentration and add-on, an appropriate initial concentration and a reconstitution stream with higher concentration than the initial concentration should be used. The validity of a mathematical model relating parameters in wet-on-wet padding is proven by experimental data from both laboratory and production scales. Using that model, changes in pad bath concentration can be quantitatively described. For given processing conditions and add-on requirements, an initial pad concentration and a different reconstitution concentration can be obtained from the model to assure a constant add-on from the beginning to the end of the wet-on-wet process.