Sir Owais Presntation 2A

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Contents

INTRODUCTION ............................................................................................................................................. 2

ABOUT DENIM FABRIC .................................................................................................................................. 3

INDIGO DYES: ................................................................................................................................................ 4

DENIM DYEING TECHNOLOGIES ................................................................................................................... 8

ROPE DYEING TECHNOLOGY ......................................................................................................................... 9

SLASHER DYEING TECHNOLOGY ................................................................................................................. 13

DIFFERENCES ............................................................................................................................................... 15

Process sequence for Indigo dye topping and bottoming with Sulphur Dye: ............................................ 16

Process sequence for Sulphur Dye topping and bottoming with Indigo dye ............................................. 17

CONCLUSION ............................................................................................................................................... 18

BIBLOGRAPHY ............................................................................................................................................. 19

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INTRODUCTION

DENIM:

Denim is a rugged cotton twill textile, in which the weft passes under

two or more warp threads. This produces the familiar diagonal ribbing

identifiable on the reverse of the fabric, which distinguishes denim from

cotton duck.

The term "Denim" has developed from the city of Nimes in France;

denim was produced for the first time by "serge de Nimes". In the

nineteenth century heavy cotton fabrics were produced in the Rhone Valley region ofFrance. These fabrics were known as tissue de Nimes and Blue de Genes. The term

denim and jeans derive fro m these designations.

Italian sailors from Genoa wear cotton trousers and the French call Genoa and the

people who live there, "Genes." The name "jeans" was applied to the pants as well.

The word dungarees (usually plural) is one of the few mainstream English words to

have come from Hindi, one of the major languages of India. In English, dungaree is

usually used to refer specifically to blue denim fabric, and in plural to refer to clothes,

especially trousers, made of such material.

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ABOUT DENIM FABRICThe classical denim is a heavy fabric made from 100%

cotton and woven from coarse indigo dyed warp and greyundyed weft yarn. The traditional denim is hard-wearing,

high density fabrics with a high mass per unit area and a

3/1 or 2/1- twill weave construction.

Denim is available in attractive indigo blue shades and is

made for a variety of applications and in a wide range of qualities and shades. Classical

denim is made from 100% cotton dyed with Indigo blue shades. Besides classic indigo

blue, denim is also dyed in other fashion shades and colors, the most popular being

black denim. Denim is comfortable, fashionable, affordable and durable and popular in

all the age group. Denim is available in different weight ranges from 6 16 oz/sq yd

which is categories as light denim 10-12 oz/sq yd., heavy denim 14-16 oz/sq. yd.

In a twill weave (used in denim), the fabric is constructed by interlacing warp and filling

yarns in a progressive alternation which creates a diagonal effect on the face, or right

side, of the fabric and has a surface of diagonal parallel ridges. In some twill weave

fabrics, the diagonal effect may also be seen clearly on the back side of the fabric

surface. Due to the denim's right-hand twill construction, one color predominates on the

fabric. Also, because of this way of weaving the threads to make the fabric, the fabric is

very strong and durable.

Denim fabric is unique in its connection with one color - blue. The warp yarn is

traditionally dyed with the blue pigment obtained from indigo dye. Indigo was the most

significant natural dye known to mankind until the introduction of synthetic dyes, at the

end of the 19th century. The durability of indigo as a color and it's darkness of tone

made it a good choice, when frequent washing was not possible. In 1894, indigo was no

longer needed - a synthetic dye process was perfected.

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INDIGO DYES:

BACKGROUND:

Indigo dyestuff is basically extracted from varieties of indigo plant. Indigo was

known throughout the ancient world for its ability to color fabrics a deep blue.

Egyptian artifacts suggest that indigo was employed as early as 1600 B.C. and it

has been found in Africa, India, Indonesia, and China.

The dye imparts a brilliant blue hue to fabric. Indigo is unique in its ability to

impart surface color while only partially penetrating fibers. When yarn dyed with

indigo is untwisted, it can be seen that the inner layers remain uncolored.

The dye also fades to give a characteristic worn look and for this reason it is

commonly used to color denim.

Originally extracted from plants, today indigo is synthetically produced on an

industrial scale. It is most commonly sold as either a 100% powder or as a 20%

solution .

Demand for indigo dramatically increased during the industrial revolution, in part

due to the popularity of Levi Strausss blue denim jeans. The natural extraction

process was expensive and could not produce the mass quantities required forthe burgeoning garment industry.

Chemists began searching for synthetic methods of producing the dye. In 1883

Adolf von Baeyer researched indigos chemical st ructure.

Later, based on this observation, K. Heumann identified a synthesis pathway to

produce indigo. Within 14 years their work resulted in the first commercial

production of the synthetic dye.

In 1990s, the German based company BASF AG was the worlds leadingproducer. In recent years, the synthetic process used to produce indigo has

come under scrutiny because of the harsh chemicals involved. New, more

environmentally responsible methods are being sought.

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also initially changes the color of the dye from its blue color to a very pale greenish

yellow color. The leuco form of indigo forms a coating on the outer layer of the cotton

yarn. The yarn is then exposed to the air, where the indigo become insoluble by

oxidation. The oxygen in air converts the soluble indigo dye to its original insoluble form

and back to its original blue color. The chemical reaction is shown:

Simplified description of the reduction/oxidation of Indigo

When the indigo dye oxidized, it becomes trapped into the outer layers of the cotton

yarn. In a single passage of indigo dye, a small amount of dye being deposited on the

yarn surface which causes light blue shade. In order to obtain deep indigo blue shades,

the cotton yarn should be subjected to repeatedly dye with indigo dye. The indigo dye is

layered by dyeing in a multiple passes of the rope into the soluble indigo dye and then

subsequently exposing it to the oxygen in the air for oxidation. This multiple passing of

yarn into dye bath is known as dipping. Normally, the cotton yarns are dyed with indigo

dye in at least 4 to 8 passages of the dye bath. After every passage of dye bath the

yarns are exposed to air and followed by further dipping in soluble indigo dye bath. After

every passage of the dye bath all the oxidized indigo dyestuff fixed on the surface of the

cotton fiber/ yarn, only a small portion of indigo is replaced by fresh indigo. This results

in the increase in the depth of shades.

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CHEMICAL PROPERTIES:

Indigo is a dark blue crystalline powder that melts at 390 392C. It is insoluble in

water, alcohol, or ether but soluble in chloroform, nitrobenzene, or concentrated sulfuric

acid. The chemical structure of indigo corresponds to the formula C 16H10N2O2.

The naturally occurring substance is indican, which is colorless and soluble in water.

Indican can easily be hydrolyzed to glucose and indoxyl. Mild oxidation, such as by

exposure to air, converts indoxyl to indigo.

The manufacturing process developed in the late 1800s is still in use throughout the

world. In this process, indoxyl is synthesized by the fusion of sodium phenylglycinate in

a mixture of sodium hydroxide and sodamide.

Several simpler compounds can be produced by decomposing indigo; these

compounds include aniline and picric acid. The only chemical reaction of practical

importance is its reduction by urea to indigo white. The indigo white is reoxidized to

indigo after it has been applied to the fabric.

Indigo treated with sulfuric acid produces a blue-green color. It became available in the

mid-1700s. Sulfonated indigo is also referred to as Saxon blue or indigo carmine .

Tyrian purple was a valuable purple dye in antiquity. It was made from excretions of a

common Mediterranean Sea snail. In 1909 its structure was shown to be 6,6 -

dibromoindigo. It has never been produced synthetically on a commercial basis .

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DENIM DYEING TECHNOLOGIES

INDIGO dyeing is accomplished by repeatedly immersing the yarn in the dye for a

specified time and then passing it through an oxidation section where dye the dye is

developed. Each time the yarn is immersed and oxidized the shade becomes darker.

The yarn is actually coated with indigo leaving the centre white. This white centre is

needed in order to give the wash done effect that is desired for todays fashion. Uneven

dyeing may cause streaking in the finished fabric. The goal of every denim producer is

to dye yarn in a fashion that eliminates the danger of uneven shades and streaks.

The two methods of dyeing yarn for denim are:

1. Rope dyeing method.

2. Slasher dyeing method .

The primary difference between these two different approaches to produce indigo-dyed

warp yarn is the sequence of steps between yarn manufacturing and weaving. Slasher

dyeing involves two steps namely: beam warping and slasher dyeing. Rope dyeing

involves four steps: ball warping, rope dyeing, rebeaming and slashing.

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ROPE DYEING

TECHNOLOGY

Rope Dyeing is considered a

superior dyeing technology where

the dyeing uniformity achieved is

better than other Indigo Dyeing technologies like Slasher Dyeing.

However, Rope Dyeing is a also a more difficult dyeing technology. One needs tomaster its nitty gritties to get the best out of the system.

With rope range, one to four slasher sets may dyed at the same time, With 24 rope

range being the most logical option which produces two slasher sets simultaneously.

The re-beaming required with rope dyeing in order to put the yarn onto section beams

for loading into the slasher creel, creates a unique extra processing steps. It also offers

the opportunity to repair ends broken at warping or dyeing, which minimizes breakoutand laps at sizing. This break in rope dyeing and slashing also makes it possible to mix

yarns of different colors in order to produce denim stripes, while with the slashing-dyer,

production of stripes is impractical.

With respect to shade control of original and wash down indigo styles, the rope range

has a distinct advantage because of its ability to run sequential yarn sets without

stopping. The unique nature of indigo dyeing makes it very difficult to start dyeing with

the yarn matching the target shade. Wuth rope range once tha machine is started andthe target shade is achieved the rope range can be operated continuously for days by

simply tying the reserve yarn onto the end of the running set of yarn.

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Techn ica l Cons ide ra t ions in Rope Dye ing

fo r Ind igo dyed Den im

The passage of yarn in rope dyeing is as follows:

Pre-scouring >hot wash >cold wash > Dye baths > hot wash >cold

wash > application of softener

Pre-scouring

The objectives of pre-scouring are the removal of wax content from cotton, removal of

trapped air from cotton yarn and Making yarn wet This is done at 90 C. We use the

following ingredients at pre-scouring stage:

Caustic Soda : Its quantity depends upon the quality of cotton fibers used in the mixing.

Generally we take 2-4% of caustic soda. It removes the wax by the action of

soapanification.

Wetting agent: It is anionic in nature

Sequestering Agent: Even with the use of water softening, it is very difficult to find the

desired softness in water. So we use the agent to make the water soft.

Why Trapped Air should be removed. The reason for this can be understood as follows:

In 1 kg of yarn, there is approximately 2 liters of air. 1 liter of air decomposes 1.8 liters

of Sodium Hydrosulphide. It will cause uneven dyeing and more consumption of Sodium

Hydrosulphide (hydro). Absorbency of yarn may be checked after scouring.

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Hot wash :

As some caustic is carried by the yarn after pre-scouring, so hot water is given at 70-

800C. If this is not done, this yarn will go into the dye-bath which will change the pH of

the dye-bath.

Cold Wash :

After hot wash, yarn temperature is more. To bring it back to its room temperature, cold

wash is given to it.

INDIGO DYEING :

Indigo is not a perfect vat color. It may be called a trash vat color. The constant ofsubstantivity for other colors is 30, for indigo it is only 2.7. So there is a need of 5 to 6

dye baths and make the use of multi-dip and multi-nip facility to increase the

penetration.

The dyeing is done at room temperature as indigo belongs to Ik class of vat dyes, where

dyeing is done at room temperature and oxidation is done by air only and not by

chemicals. If oxidizing agents are used, they will cause stripping of colors.

Indigo is not soluble in water. So it is reduced with Sodium Hydrosulphide. Then caustic

soda is added to make sodium salt of vat colors to make it soluble. To reduce 1 kg of

Indigo, 700 gms of sodium hydrosulphide is required. However some extra SHS needs

to be taken to avoid some decomposition of SHS.

Practically it is prepared in the following sequence

-Take indigo

-Add caustic

-Then reducing agent

When caustic is added to indigo, it is an exothermic reaction. It is allowed to cool down,

then before sending it to feeder; sodium hydro-sulphide is added. Reducing agent is not

added first as it will be decomposed first, so consumption of it will increase. It is also not

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SLASHER DYEING TECHNOLOGY

The basic unit of denim production is the slasher set. At ball or beam weaving the yarn

wound up from warper to produces one slasher set. One slasher set produces a fixed

number of loom beams for weaving with a slasher dyer only one set for the slasher may

be dyed at one time.

With a combined slasher dyer it is necessary to start and stop the dyeing process with

each yarn set. This means that it will be difficult to achieve the target shade until

hundreds of yarn has been run. Also when slasher dyer slows down at the end of each

yarn set, the wash down shade will be altered in the last several hundred meters of yarn

set. Slasher dyeing because of yarn being formed into flat sheets does have an

advantage in dyeing yarn for the lighter weight fabrics made with yarn counts higher

than the 16s because the larger number of yarns in the rope being dyed makes it more

difficult for the opening process in beaming. Also the capital investment is considerablylower the the rope process only because only one machine is required.

In slasher dyeing the warp threads are processed lying parallel to each other. Sizing

directly follows dyeing. The reason of this is probably that sizers also experimented on

their machine with combined sizing and dyeing. Hence trials were carried out both with

pigment dyestuffs and with indigo. If indigo is applied as a pigment in the size, a dull

blue grey results. It was, therefore, obvious that the machine builders were called on to

design a separate dyeing machine to be installed in front of the sizing machine.

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As with the rope dyeing machine, the slasher machines also have advantages and

disadvantage

Advantages are:

The open warp dyeing machine is smaller than a rope dyeing machine, which

means that the prime costs are lower.

Rope opening is avoided. Owing to the paralleled warp threads, the wetting process is shorter and a

wetting trough may be adequate.

The immersion and oxidation times are much shorter.

Setting up or stabilization of the dye baths is affected faster.

The holding capacity of the vat is seldom more than 800 liters.

Disadvantages are:

Unlike rope dyeing, when dyeing the open warp, there is no friction between the

threads in the vicinity of the guide rollers. Hence the rub and wash fastness

standards of rope dyeing are often not achieved.

The hydrosulphite consumption is much higher owing to the greater surface of

the textile goods.

If the individual processing stages of a slasher are considered, 1-2 wetting vats, 4-8 dye

becks and 3 rinsing troughs are required. The immersion and oxidation times lie

between 10-20s or 45-60s.

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DIFFERENCES

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Process sequence for Indigo dye toppingand bottoming with Sulphur Dye:

The yarn can be dyed with Indigo topping and Sulphur bottoming in order to achieve

vast shade range. The process layout is given :

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Process sequence for Sulphur Dyetopping and bottoming with Indigo dye

The yarn can be dyed with sulphur dye topping and Indigo dye bottoming as per

requirement of shades. In topping with sulphur dye, the yarn is dyed with indigo dye first

and then with sulphur dye. The process layout is given :

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CONCLUSIONModern day denim is no longer the basic blue denim that we have been accustomed to

in years past. Todays market demands are for a wide variety of fabric styles and color

and weights.

Denim equipment has successfully applied vat reactive direct disperses sulfur and

naphthol dyes, for a wide range of possible color effects. Sulfur dyes are the most

secondary dyes used in this business today.

There is also a strong trend towards mercerizing the yarn during the dyeing process.This process gives the yarn a better dye affinity fabric lustre and strength as well as

popular fashion effects such as brighter more appealing garments.

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BIBLOGRAPHY

Pakistan textile journal may 1999.

www.fibre2fashion.com

www.textilepedia.blogspot.com/.../ dyeing -process- for-den im -rope- dyeing .html

www.denimsandjeans.com

www.wikipedia.org