Denim

DENIM
Manufacturing Process
Submitted By : Abdul Ahad
Khan
Roll No. : 17-TE-01
Submitted To : Sir Asad
Firm : BZU College of Textile
Engineering

Introduction
The story of jeans begins in the mid19th century simultaneously in
two European cities:
Nîmes in France, where the fabric itself was created, the so-called
“Serge de Nîmes” which led to the name “denim”.
Genoa in Italy, where the color comes from, called in French “Bleu
de Gênes” which led to the expression “blue jeans”. The fabric and
color come together to become the jeans, denim.
Denim Fabric
Denim is a strong, durable fabric constructed in a twill weave with
indigo and white yarns. The blue/indigo yarns are the lengthwise or
“warp” threads (parallel to the selvage). The white yarns run across
the fabric width (the weft threads). Denim is traditionally woven
with 100%-cotton yarn; however, today it’s blended with polyester,
to control shrinkage and wrinkles, and Lycra to add stretch. Today,
denim has many faces. It can be printed, striped, brushed, napped
and stonewashed.
“ Denim is an indigo-dyed cotton
twill fabric in which the weft passes
under two or more warp fibers. ”

Denim Fabric Construction
Denim is made from rugged tightly woven twill in which the weft passes
under two or more warp threads. Lengthwise, the yard is dyed with indigo or
blue dye; horizontal yarns remain white. The yarns have a very strong twist
to make them more durable, but this also affects the denim’s colour.
The yarns are twisted so tightly that indigo dye usually colours only the
surface, leaving the center of the yarn white. The blue strands become the
threads that show on the outside of your denim and the white are the ones
that make the inside of your denim look white. This produces the familiar
diagonal ribbing identifiable on the reverse of the fabric. Through wear, the
indigo yarn surface gives way, exposing the white yarn underneath which
causes denim to fade. Jeans are basic 5 pocket pants or trousers made from
denim.
Famous Denim Terms
 Stonewashing: A process that physically removes colour and adds
contrast. Jeans and stones are rotated together for a set period of time.
The washing time dictates the final colour of the fabric – the longer the
denim and stones are rotated the lighter the colour becomes and more
contrast is achieved. The denim is then rinsed, softened and tumble
dried.
 River Washing: A washing process using a combination of pumice
stones and cellulose enzymes to give denim a vintage, worn hand. The
washer is loaded only with stones and fabric for the first cycle.
Enzymes are introduced for the second stage in combination with the
stones and they are tumbled until a naturally aged look is produced.
 Indigo: The dye used for denim, initially taken from the Indigofera
tinctoria plant. The majority of indigo used today is synthetically made.
Natural indigo has a slight red cast. Indigo dye (vat dye) is not soluble
in water in normal condition. To make water Soluble, reduction is done
by using reducing agent named sodium hydroSulphite (Na2 S2O4)
(trade name - Hydrose)

Process Flow for Denim Manufacturing
The warp yarn (length-wise) used in denim fabrics is uniquely prepared for
denim manufacturing compared to conventional woven fabrics. The yarn
goes through numerous processing steps before it is placed on the weaving
machine. Unlike the warp yarn, most filling yarn (width-wise) is put onto
yarn packages and delivered directly to the weaving machine where it is
inserted into the fabric without any further preparation in the same manner
as conventional woven fabrics. The following flow chart reveals the
necessary steps in the manufacture of denim fabrics, beginning with the
production of the warp yarns used.

Yarn Spinning
The initial stage of spinning is Opening and Blending. Opening begins with
baled cotton fiber being separated into small tufts. A blend of cotton fibers is
made on each opening line. Cotton is delivered by air suction from the
Opening and Blending lines, through additional cleaning and blending
machines, to the Cards. The major functions of Carding are to remove
foreign matter and short fibers, form the cotton into a web and convert the
web into a rope-like form known as a sliver. The drawing process produces
a single, uniform sliver from six card slivers. The additional blending,
paralleling of fibers and cleaning in this process produces a sliver for
Spinning. Individual fibers are twisted into yarn. After the cotton fibers are
spun into yarn, the yarn is wound into a large package (cones).
“ The process of making fibrous
materials into yarn threads ”

Warping
Normally, yarns are collected in a sheet form where the yarns lie parallel to
each other and in the same plane onto a beam, which is a cylindrical barrel
with side flanges. This is known as beam warping. For ball warp denim, the
yarns are brought together and condensed into a rope before being wound
onto a relatively short cylindrical barrel (sometimes called the shell or log)
that has no end flanges. In both cases, the supply yarn packages are placed
on spindles, which are located in a framework called a creel.
Beam Warping Ball Warping
Ball Warping
In ball warping (Figure 5), 250 to 400 yarn ends are pulled from the creel.
The yarns then pass through a comb-like device (sometimes called a hack
or reed), which keeps each warp yarn separate and parallel to its
neighboring ends. At intervals of every 1000 or 2000 yards (or meters), a
lease string is placed across the sheet of warp yarns to aid yarn separation
for the re- beaming operation, which will occur later. The yarns then go
“The parallel winding of warp ends from
many winding packages (cone, cheese) on
to a common package (warp beam) is
called warping.”

through a funnel-shaped device called a trumpet or condenser, which
collapses and condenses the sheet of yarn into rope form. This device is
located at the base of the warper head and traverses back and forth,
guiding the newly formed rope of yarn onto a log. The rope must be wound
at a constant tension to keep the yarns from tangling.
Beam Warping
Beam warping maintains the yarns in an open sheet form and winds the
yarns parallel to each other onto a slightly wider flanged beam. These yarns
will not go through the rope indigo dye range, but are left “natural” and will
end up either slasher dyed or in an undyed fabric, which can later be piece
dyed, garment dyed, or left natural. Another option would be to beam dye
the yarns using a dye other than indigo.

Dyeing of Denim
Rope Dyeing
In rope dyeing, ball warps are continuously fed into the rope or chain-dyeing
range for application of the indigo dyeing. Typically, 12-36 individual ropes
of yarn are fed side-by-side simultaneously into the range. The ropes are
kept separate from each other throughout the various parts of the dye range.
For example, if the total number of ends on the loom beam is 3,456, and
each ball would have 288 ends, then the dye set would have a total of 12 ball
warps. If there can only be a multiple of 10 balls on the dye range, then
there would be 345 ends on 9 balls and 351 ends on the tenth ball.
Machine usually has a length of 1700-1800 m of rope at one time during
operation. We also use leading ropes and attach the rope with it which is to
be dyed. So, during the process, the rope passes through machine and
leading ropes remains in the machine. We don’t have to adjust the input
rope repeatedly, instead we can alter change the recipe in tank as per our
requirement and then attach our input rope with leading process.
“The process of applying specific color to
fiber, yarn or fabric is called dyeing of
denim. The specific color is indigo.”

Process Sequence in Rope Dyeing
Pre-wetting: In the rope dyeing range the ropes are first passed through
multipurpose box. It can consist of wetting agents, detergents and Caustic to
remove the wax content and naturally occurring impurities in yarn such as
dirt, minerals, ash, pectin and removal of trapped air from yarns through
wetting the yarn. Sequestering agent is used to make the water soft. It can
also consist of recipe of bleaching to improve luster of ropes. Sky rollers are
installed for oxidation.
Hot wash: The ropes are hot washed at 80 – 90º C to remove the sodium
hydroxide left in the yarn after pre-wetting, otherwise it will change the pH
values of dye – bath.
Cold wash: After hot wash, the yarn ropes are fed through a cold wash
bath to bring back to its room temperature.
Dyeing: The ropes of yarn are then fed into the Indigo dye baths. The pH of
the indigo dye bath should be maintained between 10.5 to 11.5. At this level,
the dye affinity is very high. pH is maintained by the addition of caustic
soda. Squeeze rollers are installed to squeeze extra dye.
Shades in Denim
There are four kinds of shades in denim. These are:
 Self-shade
 Bottoming shade
 Topping shade
 Sandwich shade
Self-shade: In this shade, we acquire desired shade (light or dark) of
denim in fabric. We simply add wetting agents, sequestering agents in the
pre-wetting box and the rope pass through pre-wetting box, washers and
then through dye box which consists of indigo dye, sodium hydrosulfite,
caustic and water. Sky rollers are installed for oxidation. We produce recipe
in mixing tanks 3 hours before machine working. Acquirement of shade
intensity (dark or light) depends on usage of dye boxes and time of
interaction between rope and dye.
No of dye boxes α shade intensity
Time of interaction α shade intensity.

There is a chamber along with dye box which provides fresh dye with the
help of pump and thus maintains uniformity of dye shades
Bottoming shade: This shade involves sulfur black bottom and indigo
top of the substrate. In attainment of bottoming shade, we add sulfur black
with reducing agent (Sodium hydrosulfite) and Caustic (NaOH) in
multipurpose box. When ropes pass through box, they develop black color
but sulfur requires higher oxidation so sky roller are installed or we modify
oxidation process by adding acetic acid (CH3COOH) or little amount of
hydrogen peroxide (H2O2) in washers for oxidation keeping strength of
ropes in mind.
Topping shade: In case of attainment of topping shade, recipe of
scouring (caustic + wetting agent + sequestering agent) is added in
prewetting box. After the rope pass through pre-treatment box, washers it
passes through dye box which consists of indigo dye. After indigo dyeing the
rope passes through 7th dye box which has sulfur black dye and eventually
sulfur black attaches on the rope. 8th and last dye box consists of acetic acid
which oxidizes the dye. After dyeing, the rope pass through washer then
drying takes place and is collected in coiler cans.
Sandwich shade: In sandwich shade, we add recipe of scouring and
sulfur black in pre-wetting box. When the rope passed the pre-wetting box it
develops black color and oxidation takes place. After washing the rope
enters the dye boxes and is dyed with indigo till 6th dye box and when the
rope enters 7th box it is dyed with sulfur black or sulfur yellow. After dyeing,
oxidation takes place in 8th box as it contains acetic acid. The rope then
passes through washers, drying section and then collected in coiler cans.
Tests in denim rope dyeing
There are several tests conducted during denim rope dyeing after every
30mins. These are:
 Titration: To check concentration of Na2S2O4.
 Spectrophotometer: To check g/l of indigo dye.
 pH meter: To check the pH of dye solution.

Washing: After the dyeing process, the ropes of yarn are rinsed in several
water baths to remove any unfixed dye. Rubbing fastness of indigo, which is
a very important parameter can be improved through washing.
Drying and Coiling: After the washing, the ropes are dried by hot cylinder
and coiled in can.
Slasher Dyeing
Slasher dyeing is a more convenient and reasonable method than rope
method because rope dyeing using indigo is not desirable for manufacturers.
The step of slasher dyeing is same as rope dyeing before the addition of
dyes. For slasher dyeing, indigo is applied in a series of multiple dip and sky
application to build up a fairly deep shade. If the arrangement of the slasher
dyeing does not allow multiple dips and sky applications, then only light and
medium shades can be obtained from indigo.
Slasher dyeing has a number of advantages and unique characteristics.
Slasher dyeing employs a sheet of yarn, which is wounded directly onto a
warp beam rather than ropes of yarn, so additional handling can be skipped.
It can work well with lightweight denims. Moreover, this method requires
less machines floor space, suitable for smaller production runs, so it has a
quicker turn over time, and is more flexible in its response to changes in the
market. This method required lower machinery cost and lower dye costs for
specific fabric types. Additionally, the slasher dyeing technique can be used
for other cotton dyes and thus can produce a wide variety of colors other
than indigo blue.

Beam Dyeing
Bean dyeing is the most commonly used denim dyeing method. Most of the
dyes are applicable for this method. They are sulfur dyes, reactive dyes,
direct dyes, vat dyes as well as indigo. Therefore, it can provide large range
of color for denim fabric other than just indigo blue. Other than this
advantage, bean dyeing can also be applied on both fabric and yarn in open
width rolled onto a perforated beam.
One of the dyeing techniques that have been used for dyeing warp yarn for
denim is beam dyeing. This technique uses not only indigo, but also reactive
dyes, direct dyes as well as sulfur dyes and vat dyes so that it can provide a
large range of colors to denim fabric. Therefore, this technique gains high
acceptance among clothing industry.
For the bean dyeing technique, hundreds of individual yarns are wounded
parallel to each other around a perforated core beam with flanges on each
end. The beam is then loaded into a cylindrical dye vessel that is sealed, so
dye liquor can be pumped through the perforations in the beam and then
through the yarn. After dyeing, the yarn is washed, extracted, dried, and
added to other beams for slashing and weaving.

Re-Beaming
Once the warp yarns are rope dyed, it is then necessary to change the yarn
alignment from a rope form to a sheet form before entering the next process,
which is slashing or sizing. Beaming or re-beaming (Figure 10) involves
pulling the ropes of yarn out of storage tubs and moving them upward to a
guiding device (sometimes called a satellite). This upward travel allows the
ropes to untangle before nearing the beamer head. Once the ropes come
down from the guiding device, they go through tensioning rollers to help
further the separation of the ropes before going through a comb at the
warper, which separates individual yarn ends and keeps them parallel to one
another. From the comb, the warp yarns are guided onto a flanged section
beam. Multiple warp section beams are made forming a set of beams, which
will be the yarn supply for the slashing operation. Each set normally
contains 8 to 14 section beams. At this point, there should be no crossed,
lost, or tangled ends on the beams. The total number of yarns on all the
beams in the set should meet specifications for the given fabric to be woven.
The beams need to be in good condition with smooth inside flanges, to be
non-eccentric barrels, and to contain no high or low selvages. The selvage is
the edge of the yarn sheet where it touches the beam flange at each end of
the beam. It is critical that all the yarns wound onto a given section beam be
under equal tension. This is maintained by using guides, tension devices,
and stop motion controls.

Slashing (Sizing)
The main purpose for sizing warp yarns is to encapsulate the yarn with a
protective coating. This protective coating reduces yarn abrasion that takes
place during the weaving operation and reduces yarn hairiness preventing
adjacent yarns from entangling with one another at the weaving machine.
Also, this protective coating keeps the indigo dye from rubbing off during
the weaving process.
Size Box
Weaving
Denim fabrics are woven by interlacement of indigo dyed warp and grey
weft. The sequence or order of interlacement of warp and weft may be varied
in order to produce different denim weave designs. Although the traditional
denim is a 3/1 RHT warp faced fabrics, a variety of denim fabric are made
with different weave designs, such as 2/1 twill weave etc. Denim usually
involves coarser yarns.

Finishing
Various finishes are used for denim to improve or attain various
properties. A proper finishing process is essential for the
performance and the appearance of denim fabric.
These processes are:
 Singeing:
Singeing is a process that uses a gas flame to burn off the fluff or
tiny hairs on the surface of denim fabric. This process burns away
surface material that makes the fabric look fuzzy. It is carried out to
obtain a cleaner and smoother appearance of denim fabrics. This
process enhances the color, and the fabric wettability is also
increased.
 De-sizing:
It is the process which is done to remove size material and to
improve fabric comfort.
 Washing:
Different kinds of washings are given to denim to attain versatility
and to get various effects on denim. The chemicals used in washing
usually are caustic, wetting agent, sequestering agent etc. The
concentration of chemicals depends on GSM of denim fabric.
 Mercerizing:
Mercerization is an industrial process involving sodium hydroxide,
wetting agents and sequestering agents for denim fabrics to
increase the lustre and dye ability. In addition to increasing the
fabric lustre, it also improves its strength. It is an optional process
as it significantly increases the cost of denim.
 Over-dyeing:
Traditional indigo dyed denim fabric can be over dyed as part of a
finishing process. The preparation requirements for overdyeing are
the same as for any other dyeing process. Usually both sides of
denim fabric are dyed to attain special look and appearance.
 Packing: At the end, packaging of denim is done. This can be
done in various ways.

Garments Washing
Attainment of versatility and diversified effects on garment
is known as garments washing.
Types of garments washing
1) Garments wet process 2) Garments dry process
Garments wet process
Attainment of versatility and diversified effects on garment by
application of water and chemicals. This process involves:
 Enzyme wash:
It is done to provide softness in fabric. Cellulose enzyme is used
which break cellulose chain and remove fabric stiffness and
toughness.
 Stone wash:
Pumice stones are used in this washing. These are circular shaped
stones to give garment various effects. If added with enzyme it
greatly increases softness.
 Bleaching:
The bleaching is performed to discolor the denim color in specific
locations. The degree of bleaching action dependson the strength of
the bleach, temperature and duration of the treatment. Chemicals
like NaCl, NaClO2, are used in this process.
 KMnO4 Spray:
KMnO4 is an oxidizing agent which when used oxidizes the dye for
lowering the shade as per desired.
 Coating:
Coating is a simple process for covering the surface or back of
denim fabric with chemicals or dyestuffs in order to gain or improve
various surface properties such as waxy, oily, glossy, paper, leather,
silicone, etc.

Garments dry process:
This involves processes like:
 Scrapping:
Attainment of special effect on denim garments by scrapping (using
sandpaper).
 Sand blasting:
Attainment of special effect on denim garments by high speed blast
of sand particles. In this process, high pressure/speed sand
particles are bombarded on garment in a close container.
 Laser beaming:
Attainment of special effect on denim garments by using laser light.
In this process, laser light is targeted on garment to rupture the
fabric at various sides on garment to get a stylish look.

Denim

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