Methods of dyeing

The process of applying color to fiber stock, yarn or fabric is called dyeing. Dyeing is the
process of imparting color to the fiber/yarn or fabric by the application of dyes or
pigments. Color is produced between the dye molecule and the fiber or fabric. The bond
between dye molecule and fiber may be strong or weak depending on the dye used.
Dyeing enhances the aesthetic look of the fabric. It is one of the surface ornamentation
methods.
The method chosen for dyeing depends on fiber content, fabric weight, type of dye, and
degree of penetration required in the finished product.in the mass production, time is
money, so processes in which the goods travel quickly through a machine are used
whenever possible. Dying and after washing require a great deal of water, and waste
water contributes to stream pollution. Minimize the environmental impact of dyeing
and finishing continuous to be major industrial goal.
Many methods and processes are used in dyeing. The methods tend to involve one of
three ways combining the dye bath with textile: the textile circulate in a dye bath, dye
bath is circulated around the bath, and both textile and dye bath are circulated
together.
Methods of dyeing are following:
1. Batch dyeing 2. Beck, reel or winch dyeing
3. Jig dying 4. Pad dyeing
5. Package dyeing 6. Combination dyeing
7. Jet dyeing 8. Paddle machines, Rotatory drums, or Tumblers
9. Continuous machine
1. Batch dyeing
Batch dyeing is also known as exhaust dyeing. In this process, textile is circulated
through the dye bath. Batch dyeing can be used for textiles in any stage of production
from fiber to product but tends to be used for smaller lots or shorter yardages. The
process has good flexibility in terms of color selection, and the cost is low. Temperature
can be controlled for the dye-fiber combination. Equipment used includes the beck, pad,
and jig.
2. Beck, reel or winch dyeing
The oldest type of piece dyeing is beck, reel, or winch dyeing. This method is done to
dye the fabrics of longer length. The fabric is circulated through the dye bath in
tensionless rope form. The ends of the fabric are tied together to form a loop. The fabric
moves over a rail onto a winch reel which immerses it into the dye bath and lifted in and
out of the dye bath by a reel. The process is repeated till the fabric is dyed uniformly and
to the desired color shade. This method is used on lightweight fabric that cannot
withstand the tension of the other methods, and on heavy goods especial woolens. In
beck dyeing, a pressurized liquor ratio of 5:1 or 4:1 is used. Liquor ratio refers to the
weight of solution as compared with the weight of textile to be dyed. Thus the liquor
ratios of 5:1 have five time as much liquid as compared to the textile by weight. Beck
dyeing is generally used for fabric length ranging from 50 to 1000 meter in rope or full
width forms.
It is a simple, low cost or versatile method. Fabrics are subjected to low wrap tension,
and bulking of yarns occur. Beck dyeing use large amount of water, chemicals and
energy. It is also cause abrasion, creasing and distortion of some fabrics when dyed in
rope form.
3. Jig dying
Jig dyeing uses a stationary dye bath with two rolls above the bath. The fabric is held on
rollers at full width and passed through the dye bath. The fabric is let off from one roller
into the dye bath and wound on to the other roller. After one cycle, the process is
reversed and the fabric is let off from the second roller to the first. The process is
repeated till the desired color strength is achieved. Acetate, rayon, and nylon are usually
jig dyed. In jig dying, much larger runs of fabric at open width are used, several
thousand meter is common. The way the fabric is moved in the process create great
wrap tension. Fabrics that may crease in rope forms dyed in this manner, such as,
carpet, some twills, and some satin.
4. Pad dyeing
In pad dyeing, the fabric is run through the dye bath in open width and then squeeze
between two nip rollers that force the dye into the fabric with pressure. Because the
pad box hold the very small amount of dye bath or dye liquor, this is economical way to
piece dye. The cloth run through the machine at a rapid rate, 30 to 300 yards a minute.
Pad-steam processes are common methods of dyeing fabric.
5. Package dyeing
In package dyeing, the dye bath is forced through the textile. Normally the textile in the
yarn stage, and the yarn is wound on a perforated core of stainless steel, plastic, or
paper and placed on a perforated spindle in a pressurized machine. This technique is
also use for some fiber and fabric dyeing. In beam dyeing, the yarn or fabric is wound on
perforated beams. This method is practical for fabrics whose wrap is one color and
filling another. In skein dyeing, the yarn skeins are hung in the machine and the dye
circulates around the hanging skeins. Package dyeing is used primarily for bulky yarns
such as acrylic and wool for knit and carpet. Liquor ratio are high to ensure uniformity of
the dyeing, usually ranging from 10:1 to 4:1 (depending on the process, dye-fiber
combination, and quality desired).
6. Combination dyeing
In combination dyeing, both the textile and the dye bath are circulated. Techniques
include jet dyeing, paddle machines, rotatory drums, tumblers, and continuous dyeing.
7. Jet dyeing
In Jet Dyeing process, the fabric being dyed is circulated in a rope form through a closed
system dyeing machine on a jet flow of the dye bath. The fabric is moved by the fast
moving dye bath. Since no pressure and little tension occurs with the material, even
delicate fabrics can be dyed using this process. Most jet dyeing machines can be
pressurized and are capable of achieving dyeing temperatures exceeding the boiling
point of water. Because of its rapid speed fabric wrinkling is minimal. Low wrap tension
helps develop bulk and fullness. High temperature result in rapid dyeing, increase
efficiency of dyes and chemicals, good fastness characteristics. However, equipment and
maintains costs are high, foaming can be a problem and some fabrics may be abraded in
the process.
8. Paddle machines, Rotatory drums, or Tumblers
Paddle machines and rotatory drums are used primarily for product dyeing. Both the
dye bath and the product circulated by a paddle or rotation of the drum.
Tumblers are similar to rotatory drums except they tilt forward for easier loading and
unloading. Tumblers are used in product dyeing and in abrasive or chemical washes.
9. Continuous machine
Continuous machines, called ranges, are used for large fabric lots. Ranges include
compartments for wetting-out, dyeing, after treatment, washing and rinsing. Both fabric
and yarns are dyed. About 25 percent of all carpet, and cotton/polyester blends is
colored in this way. Continuous dyeing is efficient for long runs, but color tolerance may
be relaxed for this method because of the variable involved. This technique is most
commonly used in union dyeing of blends, but it is also used in cross dyeing. In one-bath
dyeing, both dyes are present in one bath. One bath process used for disperse/direct
dye combination in many medium dark shades. The two bath process used for heavier
weight goods, darker shades, or dyes that cannot be combined in one bath. In this
process, the dye is added from two separate dye baths, one for each dye type.
The thermosl process was develop for polyester. It is a continuous method in which the
dye is padded onto the fabric and dry heat is used to move the dye into the fiber and fix
it there.
The long chain method is continuous dyeing of yarn. It is usually involves indigo or sulfur
dyes. Yarn is immersed in the dye, squeezed to remove excess dye, and skyed to oxidize
and develop the color and fix the dye inside the fiber. Consecutive dip as and skying
progressively darken the shade until desired color is reached.