Quality Defect
Gradual variations in color depth or hue from the beginning to the end of a fabric production run represent a major defect in continuous dyeing. The head to tail shade drift is caused by a progressive change in the concentration of the dye bath during the run. This defect leads to unsellable fabric or requires sorting of finished rolls into different batches.
It is a critical parameter monitored during final fabric inspection.
Process Cause
Unequal rates of dye and water consumption by the moving fabric strip cause the bath concentration to shift. When the head to tail shade drift shows a lighter color at the end, it indicates that the dye is being absorbed faster than the liquid. If the tail is darker, the fabric is absorbing the water faster, leaving a more concentrated dye bath.
This imbalance is driven by the affinity of the dye for the fiber.
Control Method
Automated dosing systems combat this problem by continuously feeding a concentrated stock solution to replenish the bath. To prevent head to tail shade drift, the replenishment formula is calculated based on the dye substantivity and the specific liquor pickup of the fabric. Regular spectrophotometric measurements of the fabric during the run verify the consistency of the color.
This feedback allows fine tuning of the dosing ratio.
Fabric Impact
Highly textured fabrics or blended yarns increase the risk of this color variation. The different absorption rates of the fibers make the system more sensitive to concentration changes.
