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 o r so, chemical add-on considerably decreases, resulting in poor performance properties of finished goods or decreased shade depth. To obtain a constan t bath concentration and add-on, an appropriate initial concentration and a reconstitution stream with higher concentration than the initial concentra tion should be used. The validity of a mathematical model relating paramete rs in wet-on-wet padding is proven by experimental data from both laborator y and production scales. Using that model, changes in pad bath concentratio n can be quantitatively described. For given processing conditions and add- on requirements. an initial pad concentration and a different reconstitutio n 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.