Dyeing is the process of imparting
colors to a textile material through a dye (colour). Dyes are obtained from
flowers, nuts, berries and other forms of vegetables and plants as well as from
animal and mineral sources. These are known as natural dyes.
The other class of
dyes is known as synthetic dyes. These are based on a particular type of
chemical composition. Some of these dyes are- Acid ( Anionic) dyes, Basic (
Cationic) dyes, Neutral- Premetalized dyes, sulfur dyes, vat dyes, reactive
dyes, pigment dyes etc.
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Color is applied to fabric by different methods of
dyeing for different types of fiber and at different stages of the textile
production process. These methods include Direct dyeing; Stock dyeing; Top
dyeing; Yarn dyeing; Piece dyeing; Solution pigmenting or dope dyeing; Garment
dyeing etc. Of these Direct dyeing and Yarn Dyeing methods are the most popular
ones.
Space Dyeing:-
In this method, the yarn is dyed at intervals along its
length. For these two procedures- knit- deknit method and OPI Space-Dye
Applicator- are adopted. In the first method, the yarn is knitted on either a
circular or flat-bed knitting machine and the knitted cloth is then dyed and
subsequently it is deknitted. Since the dye does not readily penetrate the
areas of the yarn where it crosses itself, alternated dyed and undyed spaces
appear. The OPI Space-Dye Applicator technique produces multi coloured space-
dyed yarns. The yarns are dyed intermittently as they run at high speeds of
upto 1000 yards (900 m) per minute through spaced dyebaths with continuous
subjection to shock waves produced by compressed air assuming supersonic
velocities. |
The yarns are wound on spools, cones or similar units and these
packages of yarn are stacked on perforated rods in a rack and then immersed in
a tank. In the tank, the dye is forced outward from the rods under pressure
through the spools and then back to the packages towards the center to
penetrate the entire yarn as thoroughly as possible.
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Direct Dyeing
When
a dye is applied directly to the fabric without the aid of an affixing agent,
it is called direct dyeing. In this method the dyestuff is either fermented
(for natural dye) or chemically reduced ( for synthetic vat and sulfur dyes)
before being applied. The direct dyes, which are largely used for dyeing
cotton, are water soluble and can be applied directly to the fiber from an
aqueous solution. Most other classes of synthetic dye, other than vat and
sulfur dyes, are also applied in this way.
Yarn Dyeing
When
dyeing is done after the fiber has been spun into yarn, it is called Yarn
dyeing. There are many forms of yarn dyeing- Skein (Hank) Dyeing, Package
Dyeing, Warp-beam Dyeing,and Space Dyeing.
Skein (Hank)
Dyeing
The
yarns are loosely arranged in skeins or hanks. These are then hung over a rung
and immersed in a dyebath in a
Warp-beam Dyeing
It
is similar to package dyeing but more economical. Here, yarn is wound on to a
perforated warp beam, immersed in a tank and dyed under pressure.
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