Dyeing can be performed using continuous or batch processes. In batch
dyeing, a certain amount of textile substrate, usually 100 to 1,000 kilograms,
is loaded into a dyeing machine and brought to equilibrium, or near
equilibrium, with a solution containing the dye. Because the dyes have an
affinity for the fibers, the dye molecules leave the dye solution and enter the
fibers over a period of minutes to hours, depending on the type of dye and
fabric used. Auxiliary chemicals and controlled dyebath conditions (mainly
temperature) accelerate and optimize the action. The dye is fixed in the fiber
using heat and/or chemicals, and the tinted textile substrate is washed to
remove unfixed dyes and chemicals. Common methods of batch, or exhaust,
dyeing include beam, beck, jet, and jig processing. Pad dyeing can be
performed by either batch or continuous processes.
In continuous dyeing processes, textiles are fed continuously into a dye range
at speeds usually between 50 and 250 meters per minute. Continuous dyeing
accounts for about 60 percent of total yardage of product dyed in the industry
(Snowden-Swan, 1995). To be economical, this may require the dyer to
process 10,000 meters of textiles or more per color, although specialty ranges
are now being designed to run as little as 2,000 meters economically.
Continuous dyeing processes typically consist of dye application, dye fixation
with chemicals or heat, and washing. Dye fixation is a measure of the amount
of the percentage of dye in a bath that will fix to the fibers of the textile
material. Dye fixation on the fiber occurs much more rapidly in continuous
dying than in batch dyeing.
Each dyeing process requires different amounts of dye per unit of fabric to be
dyed. This is significant since color and salts in wastewater from spent dyes
are often a pollution concern for textile facilities. In addition, less dye used
results in energy conservation and chemical savings. The amounts of dye used
depends on the dye is exhausted from the dyebaths which determines the
required dyebath ratio. The dyebath ratio is the ratio of the units of dye
required per unit of fabric and typically ranges from 5 to 50 depending on the
type of dye, dyeing system, and affinity of the dyes for the fibers.
Dyeing processes may take place at any of several stages of the manufacturing
process (fibers, yarn, piece-dyeing). Stock dyeing is used to dye fibers. Top
dyeing is used to dye combed wool sliver. Yarn dyeing and piece dyeing,
done after the yarn has been constructed into fabric.