The working of a continuous dyeing process is described here. The textile
substrates are feeded continuously into a dye range. The speeds can vary
between 50 to 250 meters per minute. According to Industry estimates
Continuous dyeing is a popular dyeing method and accounts for around 60% of
total yardage of the products that are dyed.
A Continuous dyeing process typically consists the following. Dye
application, dye fixation with heat or chemicals and finally washing.
Continuous dyeing has been found to be most suitable for woven fabrics.
Mostly continuous dye ranges are designed for dyeing blends of polyester and
cotton. The step of padding plays a key role in the operation of continuous
dyeing. Sometimes Nylon carpets are also dyed in continuous processes, but
the design ranges for them is unlike that for flat fabrics. Warps are also
dyed in continuous process. Very good examples of such warp dyeing are long
chain warp dyeing and slasher dyeing using indigo.
A continuous dye range has been found useful and economically sustainable
for dyeing long runs of a given shade. One important factor that separates
continuous dyeing from batch dyeing is the tolerance factor for color
variation. That is more for continuous dyeing as compared to batch dyeing.
This is so because of two reasons a) the speed of the process. b) presence
of a large number of process variables which affects dye application. The
process that is illustrated below is designed for dyeing of blended fabric
of polyester and cotton.
Some of the popular methods in continuous dyeing process are Pad-steam,
Wet-steam, thermosol dyeing, TAK dyeing, space dyeing, and pad-steam dyeing
long chain warp dyeing etc.
Continuous and to some extent semi-continuous dyeing
processes both are less prone to water consumption than batch dyeing, but
results in high concentration of residues. If some strict control measures
are taken up it is possible to reduce this losses of concentrated liquor.
The following steps may prove useful.
- Applying low add-on liquor application systems along with minimising
of volume capacity of the dip through when pad dyeing techniques are in
operation.
- Adoption of latest dispensing systems, where the chemicals get
dispensed on-line as separate streams. They gets mixed only at the
moment just before the delivery to the applicator.
- Using any of the following systems for dosing of the padding liquor.
Important to know that it should be strictly according to the
measurement of the pick up:
- A proper measurement of the dyeing liquor quantity consumption in
comparison to the processed fabric. The resulting values thus
obtained are processed automatically and applied in preparing the
next comparable batch.
- Application of the technique of rapid batch dyeing. Here the
dyestuff solution is prepared just in time, with steps that are
based on on-line measurement of the pick up. This proves better than
those dyestuff that is kept prepared already for the whole batch
before the commencement of the dyeing batch.
- To increase washing efficiency based on the proven principles like
reduction of carry-over and counter-current washing.
Optimizing
the Continuous dyeing Process
