Process Malfunction
Shade variations in continuous fabric dyeing where the color depth increases from the beginning to the end of a production run represent a specific defect. The reverse tailing phenomenon occurs when the solvent is absorbed by the fabric at a faster rate than the dyestuff, leading to a more concentrated bath. This results in the final rolls of fabric having a deeper shade than the initial rolls.
It is the opposite of normal tailing.
Mechanism and Cause
Low dyestuff substantivity combined with high fabric moisture absorbency drives this concentration change in the pad trough. During reverse tailing, the fabric acts as a sponge that extracts the water while leaving the dye molecules behind in the reservoir. As more fabric passes through the bath, the concentration of the remaining liquid rises, and the fabric takes up more dye.
This creates a distinct color gradient over the length of the batch.
Prevention Strategy
Formulators prevent this issue by adjusting the initial concentration of the bath and the feed rate of the replenishment solution. To stop reverse tailing, the feeding stock solution is formulated with a lower concentration of dye than the starting bath. This dilutes the concentrating liquor in the trough and maintains a stable equilibrium.
Continuous monitoring of the bath density and fabric color ensures the effectiveness of these adjustments.
Fiber Sensitivity
Synthetics or pre-treated cotton fabrics with high hydrophilic properties are particularly prone to this problem. The rapid capillary action of these materials accelerates the selective solvent absorption.
