"The process of applying color to fiber stock, yarn or fabric is called dyeing
." There may or may not be thorough penetration of the colorant into the fibers
Dyes can be used on vegetable, animal or man made fibers only if they have the
affinity to them. Textile dyes include acid dyes, used mainly for dyeing wool,
silk and nylon and direct or substantive dyes, which have a strong affinity for
cellulose fibers. Mordant dyes require the addition of chemical substances,
such as salts to give them an affinity for the material being dyed. They are
applied to cellulose fibers, wool or silk after such materials have been
treated with metal salts. Sulfur dyes, used to dye cellulose, are inexpensive,
but produce colors lacking brilliance. Azoic dyes are insoluble pigments formed
within the fiber by padding, first with a soluble coupling compound and then
with a diazotized base. Vat dyes, insoluble in water, are converted into
soluble colorless compounds by means of alkaline sodium hydrosulfite. These
colorless compounds are absorbed by the cellulose, which are subsequently
oxidized to an insoluble pigment. Such dyes are colorfast. Disperse dyes are
suspensions of finely divided insoluble, organic pigments used to dye such
hydrophobic fibers as polyesters, nylon and cellulose acetates.
Reactive dyes combine directly with the fiber, resulting in excellent
colorfastness. The first ranges of reactive dyes for cellulose fibers were
introduced in the mid-1950. Today, a wide variety is available.
Methods of Dyeing
1) Bale Dyeing:
This is a low cost method to dye cotton cloth. The material is sent without
scouring or singeing, through a cold water bath where the sized warp has
affinity for the dye. Imitation chambray and comparable fabrics are often dyed
2) Batik Dyeing:
This is one of the oldest forms known to man. It originated in Java. Portions
of the fabric are coated with wax so that only un-waxed areas will take on the
dye matter. The operation may be repeated several times and several colors
may used for the bizarre effects. Motifs show a mélange, mottled or
streaked effect, imitated in machine printing.
3) Beam Dyeing:
In this method the warp is dyed prior to weaving. It is wound onto a perforated
beam and the dye is forced through the perforations thereby saturating the yarn
4) Burl or speck Dyeing:
This is done mostly on woolens or worsteds, colored specks and blemishes are
covered by the use of special colored links which come in many colors and
shades. It is a hand operation.
5) Chain Dyeing:
This is used when yarns and cloth are low in tensile strength. Several cuts or
pieces of cloth are tacked end-to-end and run through in a continuous chain in
the dye color. This method affords high production.
6) Cross Dyeing :
This is a very popular method in which varied color effects are obtained in the
one dye bath for a cloth which contains fibers with varying affinities for the
dye used. For example, a blue dyestuff might give nylon 6 a dark blue shade,
nylon 6,6 a light blue shade, and have no affinity for polyester area unscathed
7) Jig Dyeing:
This is done in a jig, kier, vat, beck or vessel in an open formation of the
goods. The fabric goes from one roller to another through a deep dye bath until
the desired shade is achieved.
8) Piece Dyeing:
The dyeing of fabrics in the cut, bolt or piece form is called piece dyeing. It
follows the weaving of the goods and provides a single color for the material,
such as blue serge, a green organdy.
9) Random Dyeing : Coloring
Coloring only certain designated portions of the yarn. There are three ways of
doing this type of coloring:
Skeins may be tightly dyed in two or more places and dyed at one
side of the dye with one color and at the other side with another one. Color
may be printed onto the skeins which are spread out on the blanket fabric of
the printing machine.
Cones or packages of yarn on hollow spindles may be arranged to form channels
through which the yarn, by means of air-operated punch, and the dyestuff are
drawn through these holes by suction. The yarn in the immediate area of the
punch absorbs the dye and the random effects are thereby attained
10) Raw Stock Dyeing:
Dyeing of fiber stock precedes spinning of the yarn. Dyeing follows the
degreasing of wool fibers and drying of the stock.
11) Solution Dyeing:
This is also called dope dyeing or spun dyeing, the pigment color is bonded-in
in the solution and is picked up as the filaments are being formed in the
liquor. Cellulosic and non-Cellulosic fibers are dyed to perfection by this
method. The colors are bright, clear, clean and fast.
12) Yarn dyed:
Yarn which has been dyed prior to the weaving of the goods; follows spinning of
the yarn. It may be done in either partial immersion or total immersion of the
Process of Dyeing
The dyeing of a textile fiber is carried out in a solution, generally aqueous,
known as the dye liquor or dye bath. For true dyeing to have taken place,
coloration of fabric and absorption are important determinants.
The coloration must be relatively permanent: that is not readily removed by
rinsing in water or by normal washing procedures. Moreover, the
dyeing must not fade rapidly on exposure to light.
The process of attachment of the dye molecule to the fiber is one of
absorption: that is the dye molecules concentrate on the fiber surface.
There are four kinds of forces by which dye molecules are bound to the fiber:
1) Ionic forces
2) Hydrogen bonding
3) Vander Wals' forces and
4) Covalent chemical linkages
Dyeing of Wool:
In the dyeing of wool which is a complex protein containing about 20 different
amino acids, the sulfuric acid added to the dye bath forms ionic linkages with
the amino groups of the protein. In the process of dyeing, the sulfate anion
(negative ion) is replaced by a dye anion.
In the dyeing of wool, silk and synthetic fibers, hydrogen bonds are probably
set up between the azo, amino, alkyl amino and other groups and the amino
Co-NH-groups. Covalent chemical links are brought about in the dye-bath by
chemical reaction between a fiber-reactive dye molecule, one containing a
chemically reactive center and a hydro-oxy group of a cotton fiber, in the
presence of alkali.
The Chemistry of the Dyeing Process : Exhaustion
In any dyeing process, whatever the chemical class of dye being used, heat must
be supplied to the dye bath; energy is used in transferring dye molecules from
the solution to the fiber as well as in swelling the fiber to render it more
receptive. The technical term for this process is exhaustion.
Levelness: An Important Quality
Evenness of dyeing, known as levelness is an important quality in the dyeing of
all forms of natural and synthetic fibers. It may be attained by the control of
dyeing conditions viz.,
1. By agitation to ensure proper contact between dye liquor and substance
being dyed and by use of restraining agents to control rate of dyeing or
Serious consideration has recently been given to the methods of dyeing in which
water as the medium is replaced by solvents such as the chlorinated
hydrocarbons used in dry cleaning. The technological advantages in solvent
1. Rapid wetting of textiles
2. Less swelling
3. Increased speed of dyeing per given amount of material
4. Savings in energy, as less heat is required to heat or evaporate
Thus it eliminates the effluent (pollution) problems associated with the
conventional methods of dyeing and finishing.
Machinery and Equipment
Modern dyeing machines are made from stainless steels. Steels containing up to
4% molybdenum are favored to withstand the acid conditions that are
A dyeing machine consists essentially of a vessel to contain the dye liquor,
provided with equipment for heating, cooling and circulating the liquor into
and around the goods to be dyed or moving the goods through the dye liquor. The
kind of machine employed depends on the nature of the goods to be dyed. Labor
and energy costs are high in relation to total dyeing costs: the dyers aim
is to shorten dyeing times to save steam and electrical power and to avoid
spoilage of goods.
The conical-pan loose-stock machine is a widely used machine. Fibers are held
in an inner truncated conical vessel while the hot dye liquor is mechanically
pumped through. The fiber mass tends to become compressed in the upper
narrow half of the cone, assisting efficient circulation. Leveling
problems are less important as uniformity may be achieved by blending the dyed
fibers prior to spinning.
The Hussong machine is the traditional apparatus. It has a long, square-ended
tank as a dye bath into which a framework of poles carrying hanks can be
lowered. The dye liquor is circulated by an impeller and moves through a
perforated false bottom that also houses the open steam pipe for heating.
In modern machines, circulation is improved at the points of contact between
hank and pole. This leads to better leveling and elimination of irregularities
caused by uneven cooling.
In package-dyeing machines dye color may be pumped in rather two directions:
1)Through the perforated central spindle and outward through the package
2) By the reverse path into the outer layers of the package and out of the
spindle. In either cases levelness is important.
Some package-dyeing machines are capable of working under pressure at
temperatures up to 130C.
The winch is the oldest piece of dyeing machine and takes its name from
the slated roller that moves an endless rope of cloth or endless belt of cloth
at full width through the dye liquor. Pressurized-winch machines have been
developed in the U.S.
In an entirely new concept, the Gaston County jet machine circulates fabric in
rope form through a pipe by means of a high-pressure jet of dye color. The
jet machine is increasingly important in high-temperature dyeing of synthetic
fibers, especially polyester fabrics. Another machine is the jig. It has a
V-shaped trough holding the dye color and guide rollers to carry the cloth at
full width between two external, powered rollers, the cloth is wound onto each
roller alternately, that is, the cloth is first moved forward, then backward
through the dye color until dyeing is complete. Modern machines, automatically
controlled and programmed, can be built to work under pressure.