Saminathan Ratnapandian

Pad – batch
This simple process involves padding the fabric with a dye solution containing a suitable dye and auxiliaries and then winding up the padded fabric onto a suitable roller. For dye fixation, the fabric wound on the roller is left undisturbed without steaming for 6–24 hours at ambient temperature. This process is therefore often called ‘cold’ pad-batch dyeing. During fixing, the fabric roll should preferably be rotated at low speed to avoid drainage of the internal liquid. In order to minimise evaporation from the exposed surfaces and edges of the roll, the fabric roll is wrapped with a plastic film. Finally, the fabric is thoroughly washed to remove unfixed dye and residual
chemicals [11, 55]. The pad-batch dyeing process is the most economical of all pad dyeing processes for the reactive dyeing of cotton. It is claimed that this process is more economical than exhaust dyeing, mainly due to minimal energy requirements [56].


Pad – dry – cure
Curing in dry heat for 60–120 seconds may be used to fix the dyes after padding. A curing temperature of 160^○C helps the formation of crosslinks in the finishing of cotton. Urea as humectant and dilute alginate solution as anti-migrant are special components of the padding liquor for cotton. Urea retains sufficient water to serve as a fluid medium for dye diffusion while alginate helps to avoid shade variation between the face and back of the fabric or the two-sided effect [11, 56, 57].


Pad (dye) – dry – pad (chemical) – steam
This two-step process sequence is widely employed for continuous dyeing of cotton fabrics using vat dyes. The fabric is first padded in a neutral dye solution that contains additional humectants and anti-migrants and dried in a hot flue drier. After drying, the fabric is padded with a solution of auxiliaries and other chemicals followed by steaming. The steam provides the necessary energy and additional moisture required to complete the dye-fibre reaction [11, 52]. Intermediate drying has been eliminated by employing super-heated steam and short steaming duration (flash-ageing), to make the process more efficient.