INDEX

SNO TOPIC

1 INTRODUCTION

2 DYIENG OF FABRICS

3 METHODS OF DYIENG

4 PROCESS OF DYEING

CHEMISTRY OF DYEING
5
PROCESS

6 REMOVAL OF DYES

7 CONCLUSION
 INTRODUCTION

The process of applying colour to Fibre stock, yarn or fabric is called

dying" There may or may not be thorough penetration of the colourant
into the fibres or yarns, Dyes can be used on vegetable, animal or
man-made fibres only if they have 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
fibres. 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 fibres, 001 or silk after such materials have been
treated with metal salts. Sulphur Dyes, used to dye cellulose, are
inexpensive, but produce colours lacking brilliance. Azonic dyes are
insoluble pigments formed within the fibre by adding, first with a
soluble coupling compound and then with a diazotized base.

DYEING OF FABRICS
 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 this way.

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 will take on the dye matter. The operation may be repeated
several times and several colours may used for the bizarre effects.
Motifs show a melange, mottled or streaked effect, imitated in
machine printing.

3. Beam Dyeing:
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 with colour.

4. Burl or speck Dyeing:

This is done mostly on woollens or worsteds, coloured
specks and blemishes are covered by the use of special coloured
 links which come in many colours 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 colour. This
method affords high production.

6. Cross Dyeing:
This is a very popular method in which varied colour
effects are obtained in the one dye bath for a cloth which
contains fibres 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 or white.

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 colour for the material, such as blue serge, a
green organdy.
9. Random Dyeing:
Colouring only certain designated portions of the yarn.
There are three ways of doing type of colouring: Skeins may be
tightly dyed in two or more places and dyed at one side of the
dye with one colour and at the other side with another one.
Colour 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 there by attained.

10.Raw stock Dyeing:

 Dyeing of fibre stock precedes spinning of the yarn.
Dyeing follows the degreasing of wool fibres and drying of the
stock.

11.Solution Dyeing:
This is also called dope dyeing or spun dyeing; the
pigment colour is bonded in in the solution and is picked up as
the filaments are being formed in the liquor. Cellulosic and non-
cellulosic fibres are dyed to perfection by this method. These
colours 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 yarn.
 PROCESS OF DYEING

The dyeing of a textile fibre is carried out in a solution, generally

aqueous, known as the dye liquor or dye bath. For true dyeing to have
taken place, colouration of fabric and absorption are important
determinants.
Colouration:
The colouration 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.
Absorption:
The process attachment of the dye molecule to the fibre is one of
absorption: that is the dye molecules concentrate on the fibre surface.
There are four kinds of forces by which dye molecules are bound to
the fibre:

1. Ionic forces
2. Hydrogen bonding
3. Vander Wals' forces
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 sulphate anion (negative ion) is replaced by a dye anion.
In the dyeing of wool, silk and synthetic fibres, hydrogen bonds are
probably set up between the azo, amino, alkyl amino another groups
and the amino Co-NH-groups. Covalent chemical links are brought
about in the dye-bath by chemical reaction between a fibre-reactive
dye molecule, one containing a chemically reactive centre and a
hydro-oxy group of a cotton fibre, in the presence of alkali.
 CHEMISTRY OF 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 fibre as well as in
swelling the fibre 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 fibres. 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 strike, Solvent Dyeing 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 dyeing are: 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
per- chloro-ethylene. 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 favoured to withstand the acid
conditions that are common. 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. Fibres are held in an inner
truncated conical vessel while the hot dye liquor is mechanically
pumped through. The fibre mass tends to become compressed in the
upper narrow half of the cone, assisting efficient circulation.
Levelling problems are less important as uniformity may be achieved
by blending the dyed fibres 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 levelling and
elimination of irregularities caused by uneven cooling. In package-
dyeing machines dye colour may be pumped in rather two directions:
1. Through the perforated central spindle and outward through the
package or
2. By the reverse path into the outer layers of the package and out
of the spindle. In either case 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

REMOVAL OF DIES
If things go wrong in the dyeing process, the dyer may be forced to
remove the dye already applied by a process called "stripping" or
discharging. This normally means destroying the dye with powerful
reducing agents such as sodium hydrosulfite or oxidizing agents such
as hydrogen peroxide or sodium hypochlorite. The process often risks
damaging the substrate (fibre). Where possible, it is often less risky to
dye the material a darker shade, will black often being the easiest or
last option.
 CONCLUSION

• The dyeing process is one of the key factors in the successful trading
of textile products.
• Dyeing methods have not changed much with time. • Basically
water is used to clean, dye and apply chemicals to the fabrics, and
also to rinse the treated fibres or fabrics.
• The changing technology, from hand power, to water power to steam
and then to electricity, fundamentally changed the textile industry, its
product marketability and its profitability.
• Now its time for another change! Plasma technology is poised to
change the concept of textile wet processing, as we all know
Innovation never ends.