1. Levelness in exhaust dyeing

Two processes are important to attain leveling in batch dyeing

(1) Dye builds up gradually and distributes evenly on the surface of the fiber.
(2) Absorbed dye diffuses evenly into the fiber.

The dye should be distributed uniformly in the fiber in a short time by controlling these two processes effectively in order to attain level dyeing in a short time.

A uniform distribution of the dye on the fiber surface plays an important role for effective level dyeing, and to this end the dye should be supplied throughout the fiber at the rate corresponding to the rate of dyeing.

The final exhaustion will be attained quicker and the dyeing time will be shorter, when the rate of dyeing is high, however, when the rate of dyeing exceeds the rate of supply of the dye, a uniform distribution cannot be attained thus leading to unlevel dyeing. The rate of dyeing can be set at a quicker rate, if the dye can be supplied at a higher rate.

The supply of dye means that the transfer and the smooth supply of dye from the area where the fiber cannot absorb to the area where the fiber can absorb in the dyebath, in other words, the decrease of dye in the dyebath near the fiber due to the absorption by the fiber is immediately covered by the dye in the gross dyebath.

The rate of dyeing can be controlled by the dyeing conditions such as the dyebath temperature, pH, inorganic salt and other auxiliaries etc., and the supply of dye can be controlled by the physical conditions of the dyebath such as the circulation of the dye liquor, the flux and the rate of circulation of the material, etc..