indigo dyeing final

Adwait Mahesh Deshpande

Indigo Dyeing

A

Seminar

SUBMITTED TO THE

INSTITUTE OF CHEMICAL TECHNOLOGY

IN PARTIAL FULFILMENT OF THE

REQUIREMENTS FOR THE DEGREE OF

BACHELOR OF TECHNOLOGY

IN

DEPARTMENT OF FIBRES AND TEXTILE PROCESSING TECHNOLOGY

UNDER THE GUIDANCE

OF

Prof. Shukla

BY


FINAL YEAR B. TECH- SEMESTER VII

INSTITUTE OF CHEMICAL TECHNOLOGY,

Deemed to be University

MATUNGA, MUMBAI- 400 019

SUBMITTED on 15th October 2010

1 Indigo Dyeing


Sr. No. Topic Page

No.

1 A Brief History Of Indigo Dyeing

2 Physical and Chemical properties

3 Synthesis Of the Indigo Dye

4 Dyeing Procedures for Polyester and Cotton

5

6

7

2 Indigo Dyeing


1. A Brief History of Indigo Dyeing

Indigo plants originate from different parts of the world and produce a colorfast, deep

blue dye. The plant was first domesticated in India during the Indus Valley period

between the fourth and the second millennium b.c. Many varieties of the indigo plant

exist throughout the world. One species originates from east and southern Africa, another

from tropical America. Indigofera tinctoria, believed to be native to Asia and now widely

distributed and naturalized all over the tropics. I.tinctoria is the species that was first

domesticated in India and predominantly cultivated over the centuries for commerce. The

name “indigo” is derived from the Greek for “of India” and refers to the Indian

subcontinent.

Indigo was mentioned in manuscripts dating as far back as the fourth century b.c. The

historical record of indigo is patchy, but references were made by Marco Polo who saw

indigo during a visit to the southern tip of India in 1298. Around this time, Arab traders

had introduced indigo to the Mediterranean region, where it became available in small

quantities. The cultivation of indigo on a large scale started in the sixteenth century in

India, particularly in the north.

During the Middle Ages indigo moved like other valuable articles of trade through

established caravan routes, primarily overland from India through Baghdad into Europe.

By the sixteenth century the Portuguese, and later the Dutch, had established trade routes

by sea to India, making indigo much more accessible to the average European. By 1516,

the Portuguese were importing large quantities of indigo (along with spices and other

valuable goods from eastern ports) by ship into Europe.

Indigo Arrives in Europe by Sea Trade

Soon after its appearance in European ports, the trade of indigo was inhibited by powerful

guilds in many European countries. Until indigo, the primary European source for dye was

3 Indigo Dyeing


the indigenous woad plant. Woad had been cultivated extensively in France, Germany and

England since the Roman Empire. European woad-growers and merchants saw indigo as

serious competition, since it was a better dye producing deeper, more colorfast blues.

Nevertheless, bans did not stop the flow indigo into Europe. Soon after the establishment of

Portuguese trade routes, Spain began cultivating indigo in its new world colonies, first setting

up plantations in the mid-1500s along the Pacific coast of Central America. By the close of

the seventeenth century, indigo was moving into Europe from east (Portuguese, Dutch, and

English) and west (Spanish). At this time, the French joined the fray with the establishment

of indigo plantations on the eastern part of modern day Haiti in 1697. When the German

woad industry eventually collapsed, a large population, whose livelihood depended on woad,

was plunged into abject poverty.

Indigo Plantations in the West Indies and South Carolina

By the late 1600s indigo was marketed legally in most European countries. Until this time,

India was the main supply of indigo for the British, who resented the monopoly on the dye

held by Indian traders and merchants. The British faced difficulties ensuring a regular supply

of indigo and controlling quality. The price of indigo also fluctuated drastically. The British

soon joined the Spanish and French, who were already cultivating indigo on plantations in

the new world. The British first established indigo plantations in its West Indian territories

(Jamaica), and then in its colonies in North America, most notably in South Carolina, as a

new source for the dye. Producing indigo was labor intensive and, in the West Indies and

American colonies, only possible through a system of slavery. Contemporary accounts

indicate that when prices were high, indigo dyestuff could be exchanged for slaves; it is said

that a planter in South Carolina could fill his bags with indigo and ride to Charleston to buy a

slave with the contents, “exchanging indigo pound for pound of negro weighed naked.”

Back to India

Soon after the loss of the American colonies and the drying up of French supplies of indigo,

Britain pressed for a return to India as a source. However, this time, they sought to control

production. In the nineteenth century, Bengal in northeastern India became the world’s main

4 Indigo Dyeing


source of indigo, by now in great demand to supply the textile industries of the Industrial

Revolution and to dye many European service uniforms. Throughout the century natural

indigo was far more valuable than any other dyestuff and Bengal’s indigo production far

outweighed that of the rest of the world. For the earlier part of the nineteenth century it may

be fair to say that the industry created gainful employment for Indians. But, after the first

quarter of the nineteenth century, Indians were generally forced to cultivate indigo on their

best land and faced exploitation and cruel maltreatment by British planters.

Denim and the Invention of Synthetic Indigo

The earliest known pre-cursor for jeans is the Indian export of a thick cotton cloth dyed in

indigo, in the 16th century, known as dungaree. Sailors of the time frequently used the fabric

5 Indigo Dyeing


to make clothing. For the past century, almost all indigo used in denim manufacturing has

been man-made. Synthetic indigo was first produced for commercial use in 1897, when the

German chemical company BASF (Badische Anilin und Soda Fabrik) introduced the dye

based on the findings of the Berlin chemist Adolf von Baeyer. BASF called its new product

“indigo pure.” Soon other European companies, including dyeworks in France and

Switzerland, began producing their own synthetic indigo, and natural indigo entered its final

irreversible decline on the international market. The situation of the peasants of India got

even worse with the chemical replication of indigo from the late 19th century onwards. The

pressures on the “planters” (British estate owners) to make a profit and survive in these

circumstances increased the pressure on those involved in indigo cultivation, extraction, and

processing.

6 Indigo Dyeing


2. Physical and Chemical properties

The first laboratory synthesis of indigo was achieved by Adolf von Baeyer in 1878, and

in 1883 he revealed the structural formula to Heinrich Caro, at that time head of the

research laboratories at BASF.

2.1 Physical Properties

The systematic name of indigo, also known as indigotin, is 2-(1,3-dihydro-3- oxo-2H-

indol-2-ylidene)-1,2-dihydro-3H-indol-3-one or 2,2 ´-biindolinylidene- 3,3´-dione. It

exists as blue-violet needles or prisms with a pronounced coppery luster. It sublimes

above 170°C as a red-violet vapor that condenses on cooling to form dark violet needles.

The melting point is 390.392°C.

Indigo is practically insoluble in water, dilute acids, and dilute alkalis, but slightly soluble

in polar, high-boiling solvents such as aniline, nitrobenzene, phenol, phthalic anhydride,

and dimethyl sulfoxide. Some polar solvents destroy indigo when it is dissolved in them

at the boil.

The dye is positively solvatochromic, the absorption maximum in a polar solvent such as

dimethyl sulfoxide being 620 nm, that is, 12 nm higher than in a nonpolar solvent such as

carbon tetrachloride. Characteristic of indigo is the unusually deep shade compared with

other conjugated systems of similar size. This is explicable in terms of the special

arrangement of the atoms in the basic chromophore and the high polarizability of the

charge distribution, which is strongly influenced by the ability of the molecule to form

hydrogen bonds.

Intra- and intermolecular hydrogen bonding are the explanation for indigo’s extremely

low solubility and high melting point. X-ray analysis and IR studies demonstrate the

existence of intermolecular hydrogen bonds in the solid state. The very long-wave IR

absorption of the carbonyl band at 1626 cm can be regarded as characteristic of the

7 Indigo Dyeing


indigo structure. By comparison, the carbonyl band of dehydroindigo is situated at 1724

cm. Bond orders and charge densities in the indigo molecule have been calculated

and compared with the results of X-ray analysis. These studies confirm the structural

formula and answer questions about the basic chromophore of the dye.

2.2 Chemical Properties

Indigo is very stable to light and heat. The molecule does not readily undergo

electrophilic or nucleophilic substitution. However, it can be successfully sulfonated

in concentrated sulfuric acid to give the tetrasulfonic acid, and halogenated in

nitrobenzene to introduce up to six halogen atoms.

Indigo is readily reduced by various reducing agents such as zinc dust, sodium dithionite,

hydroxyacetone, and hydrogen, or by electrochemical means. In an alkaline medium, a

salt (for example the sodium salt) of leuco indigo is produced, which can be converted by

acids to so-called indigo white.

Indigo (1)

8 Indigo Dyeing


The yellow-brown soluble vat form of indigo has affinity for animal and vegetable fibers,

making it possible for indigo to be used in dyeing. Upon oxidation with air, it forms blue

indigo again, fixed on the fiber. The dye tends to adhere mainly to the surface of cotton

fibers, whereas on the polypeptide fibers of wool or silk the bonding is more salt like.

This explains the fact that the fastness to light, rubbing, and washing are poorer on cotton

than on wool. The difference in shade between dyeing on the two fiber types is also due

to the different bonding mechanisms.

Oxidation of the indigo dye molecule results in formation of dehydroindigo. Oxidation

with permanganate or chromate splits the molecule, forming isatin. Oxidation and

reduction of the indigo system are accompanied by corresponding changes in the

spectroscopic properties.

3. Synthesis For thousands of years, indigo was produced from plant material containing low

concentrations of indican, a precursor of the dye. Indican is split by enzymes and

converted to indigo by oxidation. Indigo can be synthesized from D-glucose by

genetically modified strains of coli bacteria, presumably by a process that resembles

biosynthesis in plants.

3.1 Chemical Synthesis

9 Indigo Dyeing


Synthetic indigo was made by A. von Baeyer in 1870 by treating isatin with phosphorus

trichloride and phosphorus in acetyl chloride. He obtained isatin by oxidizing indigo. The

first complete synthesis of indigo was achieved in 1878, when von Baeyer succeeded in

deriving isatin from phenylacetic acid.

First total synthesis of Indigo

Another synthetic route proposed by von Baeyer began with o-nitrocinnamic acid and led

to o-nitrophenylpropiolic acid, which could be converted to indigo directly on the textile

fiber with mild reducing agents under alkaline conditions.

For a few years o-nitrophenylpropiolic acid was sold commercially as “little indigo”.

Von Baeyer also synthesized indigo by a fascinatingly simple reaction between o-

nitrobenzaldehyde and acetone in alkaline solution. The product, o-nitrophenyllactic acid

ketone, splits off acetic acid and water and dimerizes to form indigo.

10 Indigo Dyeing


Hoechst and BASF tried to develop the von Baeyer processes industrially. However, a

breakthrough to a cost-effective industrial synthesis was not possible. The nitration step

was in each case insufficiently selective and therefore expensive.

Heumann I Process

In 1890 Karl Heumann published a synthetic method based on aniline. It involved reating

aniline with chloroacetic acid to form N-phenylglycine salt, fusing this in potassium

hydroxide to convert it to indoxylate (di-salt), and finally hydrolyzing and oxidizing the

indoxylate to indigo. Since the high reaction temperature (300° C) needed caused partial

decomposition, the yield (10% of theoretical) was too low for large-scale production.

Only the stoichiometric addition of sodium amide discovered by J. Pfleger of Degussa in

1901, as a highly effective condensing agent for the indoxylate melt, produced yields of

up to 90% at reaction temperatures of around 220°C. Hoechst and BASF launched this

process on an industrial scale.

After the ring-closure reaction, the yellow indoxylate present as the di-Na/K salt in the

alkaline melt is hydrolyzed with water. Oxidation of the monosalt of indoxylate takes

place in air at 80.90° C. A suspension of blue indigo results in an aqueous alkaline

medium. Small amounts of byproducts, such as aniline, Nmethylaniline, and anthranilic

acid, are also produced.

Indigo is isolated from the indigo suspension by cake filtration, washed with water, and

further processed into the various commercial forms of indigo or vat indigo. The mother

11 Indigo Dyeing


liquor from the filtration step can be regenerated and reused in the manufacturing process

as an anhydrous alkaline melt. N-Phenylglycine in the form of an alkali metal salt is the

starting material for the Heumann I synthesis.

Heumann PG salt synthesis

Heumann II Process

In the Heumann II process, starting from anthranilic acid, N-phenylglycine-o-carboxylic

acid, prepared from anthranilic acid and chloroacetic acid, is added in the form of the

alkali metal salt to a KOH/NaOH melt at 200°C to produce indoxylcarboxylic acid salt.

After hydrolysis and decarboxylation, the product is oxidized in air to yield indigo.

12 Indigo Dyeing


On account of the carboxyl group in the ortho position, ring closure occurs more readily

than in the case of N-phenylglycine salt. This makes it possible to attain yields of

between 70 and 90 %, even without the use of sodium amide. Isolation of indigo from the

suspension is carried out as in the Heumann I synthesis

by filtration, washing, and drying. This method was employed by BASF from 1897

onwards to produce and market the first synthetic indigo on an industrial scale. Indigo is

insoluble in aqueous alkaline media and to be useful in dyeing it must be converted into

soluble leuco indigo. In dyehouses this is done mostly by reducing it with sodium

dithionite in the presence of alkali.

The idea of liberating the dyer from the burden of vatting the dye and of integrating

this reduction step into the synthesis process is not new. For example, indigo can be

vatted with reducing agents that were commonly used in the past, such as zinc dust and

iron(II) sulfate. However, reduction with hydrogen in the presence of a catalyst such as

nickel or palladium is preferable, also from an ecological viewpoint.

Various forms of leuco indigo are available today. BASF Indigo Vat 60% Grains is

produced by evaporating to dryness an aqueous leuco indigo solution in the presence of

molasses. The molasses stabilizes the leuco indigo against oxidation. The resulting dye,

13 Indigo Dyeing


with an indigo content of 60 %, is a specialty product that, because it is so easy to use,

mainly finds application in the production of indigo dyeings for commercial art purposes.

Liquid commercial forms of leuco indigo are becoming increasingly significant. Thus, a

20% and, as new market standard, a 40% solution of an alkali metal salt of leuco indigo

are available. In addition to simple metering, the liquid dye allows dyehouses to dispense

with much of the sodium dithionite and alkali needed for dyeing with indigo granules.

Furthermore, the resin like residues produced by the reduction with hydrosulfite do not

occur.

Environmental AspectsOn account of its low solubility, indigo is degraded to only a very small extent in

biological wastewater clarification plants. However, over 90% is adsorbed onto activated

sludge and is thus eliminated from the wastewater. Indigo’s classification in Germany’s

official list of water-polluting substances is WGK 1, corresponding to the lowest

polluting potential. A strain of bacteria capable of degrading indigo was discovered by

the Hong Kong Institute of Biotechnology.

3.2 Biotechnological Synthesis

In General

Suitable plants for producing indigo are the indigo plant (Indigofera tinctoria ), woad (

Isatis tinctoria ), and Chinese indigo (Polygonium tinctorium). The latter is still grown on

the island of Shikoku in Japan and is used for blue dyeing. These plants all contain up to

0.8% of the glucoside indican. Enzymatic splitting of indican into indoxyl and glucose is

carried out in a fermentation vat containing a carbohydrate-based material, such as bran

or starch, and alkaline additives (potash, lime, or ammonia).

14 Indigo Dyeing


The enzyme responsible for cleaving indican is indoxyl- -D-glucosidase, which is formed

on the plant by microorganisms. The resulting indoxyl, which under alkaline conditions is

soluble in water, is discharged from the fermentation vat and oxidized to indigo by

operation. The insoluble dye is isolated by precipitation and air drying. The fermentation

mix can also be used directly for dyeing. The textile is impregnated with the fermenting

mash and then .blued. by oxidation in the air. This type of dyeing was carried out with

woad (Isatis tinctoria ). Pure indigo dye was not extracted from woad because of its low

content of indican.

Microbiological Synthesis

In the 1980s, indigo was successfully produced by microbiological techniques in the

USA. The development of a fermentation process involving genetically modified strains

of coli bacteria capable of forming usable amounts of indigo from D-glucose represented

a new, biosynthetic route to indigo.

Biotransformation of Indoles

It was reported in the technical literature as early as 1956 that bacteria are able to convert

indole to indigo. The bacteria use the enzyme naphthalene dioxygenase to oxidize indole

to indoxyl. Apparently the substrate specificity of this enzyme is not very pronounced, so

that besides naphthalene, which is oxidized to 1,2-dihydroxynaphthalene, it also accepts

indole as a substrate. Two process variants for carrying out this biotransformation are

described. In the first, the biotransformation is carried out in a homogeneous aqueous

system. The critical quantity is the indole concentration, since too high an indole

concentration causes the biomass to die off . In the second, the biotransformation is

carried out in a two-phase system. The biomass, containing the catalyst, is in the aqueous

15 Indigo Dyeing


phase, while the substrate is supplied in an organic solvent. In both process variants, the

indoxyl formed is spontaneously oxidized to indigo by atmospheric oxygen.

Bacterial De-Novo Synthesis

The basic idea behind this variant is to use the synthetic potential of bacteria to produce

the indole precursor. Although indole does not occur as an intermediate in bacterial

metabolism, it appears as an enzyme-linked intermediate in the biocatalytic

transformation of D-glucose to L-tryptophan. The crucial biosynthetic step is the

conversion of indole-3-glycerine phosphate to L-tryptophan by the enzyme tryptophan

synthase.

The essential stages of the multistep route used by nature to synthesize aromatic

amino acids were elucidated in the 1950s by studies on mutant bacteria (e.g. Aerobacter

and Escherichia coli): the cyclization of D-glucose to 5-dehydroquinic acid and the

formation of shikimic acid. The first aromatic compound in the reaction chain is

anthranilic acid:

Bioindigo -Shikimic acid path (simplified). Preparation of indigo by bacterial de novo synthesis.

16 Indigo Dyeing


Biotechnological techniques allow the genetic coding for the enzyme tryptophan synthase

in E. coli to be modified in such a way as to liberate the originally enzyme-linked

intermediate indole. If E. coli is simultaneously implanted with the coding for

naphthalene dioxygenase from the bacterium Pseudomonas putida, the modified

microorganism can convert the liberated indole directly to cis-indole-2,3-dihydrodiol,

which splits off water and is oxidized to indigo.

Indigoid Dyes

A problem in the biotechnological synthesis of indigo is the disposal of the large amounts

of biomass produced. Application as a fertilizer is not yet a ready option, because of the

possible liberation of genetically modified microorganisms. Alternative disposal

methods, such as an efficient clarification plant or incineration, are associated with

additional costs.

Commercial grades:

The following commercial forms of indigo are available worldwide:

In non reduced form as

1. indigo granules

2. indigo powder

3. indigo paste (alkaline)

In reduced form as

1. vat indigo 60%

2. vat indigo 40% (20 %) solution

17 Indigo Dyeing


4. Dyeing Procedures for Polyester and Cotton

Laboratory Scale dyeing

The typical dyeing procedure for polyester is 8g/L sodium hydrosulfite,

1g/L sodium hydroxide, and 1 % owf indigo at 120°C for 30 minutes.

After dyeing, the reduced indigo in the polyester fabrics is air-oxidized

at 100°C for over 10 minutes. The indigo dye is reduced in aqueous

solutions of 4 g/L sodium hydrosulfite (Na2S2O4), 2.88 g/L sodium

hydroxide (NaOH), and 30 g/L sodium sulfate (Na2SO4) at 50°C.

Cotton fabrics are put into the reduced indigo solution where the bath

ratio is 50:1 and the dye concentration is 0.05– 0.2 % owf. The cotton

fabrics were dyed at 50°C for 30 minutes. After dyeing, the reduced

indigo in the cotton is air oxidized at room temperature for over 10

minutes, then washed with an aqueous solution of 5 g/L anionic

soaping agent at 80°C for 10 minutes.

Dyeing polyester fabrics with indigo dyes is successful under certain conditions, which

coordinate the rate of sodium hydrosulfite and sodium hydroxide. When the sodium

hydrosulfite concentration is 8 g/L, the optimum dyeing concentration of sodium

hydroxide is 0.5–1.0 g/L in the dye bath solution at 120°C. It seems that the role of non-

ionic reduced indigo formation is important in this dyeing method. The dyeing

temperature is effective, and well-dyed polyester fabrics are obtained at 120°C. The

maximum wavelength of polyester fabrics dyed with indigo is clearly different from that

of cotton fabrics. Polyester has a richer blue color than cotton when they are both dyed

with the indigo. The rub fastness of polyester dyed with indigo is superior to that of

cotton.

18 Indigo Dyeing


Industrial Scale Dyeing

Now processing and dyeing methods for indigo warps were introduced from 1978- 1987

to obtain a higher productivity and savings in dyeing or to achieve the required darker

shades (hard rock washing, super blue, soft denim), or softness of the yarn for final

finishing. The following table gives you a comparison of the possible processing stages

such as:

1. Indigo rope dyeing process

2. Indigo one sheet dye slashing

3. Indigo double sheet dyeing

4. Dye 1 for 6 (continuous dye slashing)

5. Dye 1for 6 with dyemer (continuous mercerization dyeing and sizing).

For the five major Indigo dyeing methods for the basic denim, super blue denim, soft

denim, stone wash denim, we also must take into consideration that a certain appearance

of the garments is only achieved after a certain washing method. (Chemical washing,

stone washing, hard rock washing), use of certain sizing agents (soft denim) or irregular

appearance in warp or weft direction by using a yarn with slubs and neps (antic denim).

The final finishing methods have influence on fabric construction and dyeing methods.

CONVENTIONAL CLASSICAL CONTINUOUS INDIGO ROPE DYEING

The classical rope dyeing system is very labour intensive and consists of:-

· Ball warping

· Indigo dyeing

· Rebeaming on long- chain-beamer

· Sizing

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Yarn from the ring spinning machine is wound on automatic winding machines on to

a suitable package either cylindrical or 5057 cone. The winders are directly linked to

the ring spinning frames and the cops joint by splicing. OE yarns are directly creeled

up on the Ball warper.

The requires No. of ends (usually 380 – 420 ends) are assembled into a rope. These ends

are wound onto a core. The rope is guided similar as a cross wound package and wound

into a ball, length of ball approx. 12 – 15.000 meters. A lease is inserted at the start and

end of the rope. The facilitate Rebeaming every 1000 meters an additional lease is

inserted. Usually 18 – 24 ropes are simultaneously process on the rope dyeing machine.

Prior to dyeing, the ropes are boiled out and treated with caustic-soda and wetting agent

to remove from the cotton oil, impurities which could influence the fastness for the dye.

To dye with indigo, the ropes are immersed into the dye-bath. To dye in rope 30 – 60

seconds immersion (20 meters yarn) and 60 - 180 seconds are required for the oxidation

of the Indigo dyestuff to ensure that also ends in the centre of the rope are equally dyed.

Please note that squeezing pressure is important 5 tons as fastness of colour and shade

depends on even squeezing pressure. The comparatively long immersion and oxidation

time requires a comparatively expensive equipment of machinery.

In order to obtain the required deep shade of blue colour the ropes are 5 – 6 times

immersed in a sequence of dye boxes with an oxidation range then so called skying after

each dye box. (Indigo belongs to the group of the vat dyes which is watersoluble in

eeduced solution and becomes an insoluble pigment when oxidized.

Having passed the dyeing and oxidation rage the ropes are guided through 2 or 3 washing

boxes to wash off excessive loss pigments in the last box softener are added to ease the

opening of the ropes. They are dried in series of cans. The dried ropes which contain 380

– 420 ends are then deposited into large coilers Rebeaming with 300 – 380 ends per rope

is easer. These coilers are placed behind the long chain beamer where the Rebeaming and

20 Indigo Dyeing


opening of the ropes takes place. In order to guarantee even yarn tension through

rebeaming on to a back beam ready for sizing

the ropes are guided over a tension device which is placed approx. in 10 -11 meters

distance from the long chain beamer. Broken ends which very really happen process

of the rope are repaired at this process stage. Initially these machines were supplied

without yarn stop motion but are available now a days on special request. This is of

major importance as lost ends, fluff, 3 – tail ends and yarn remnants can cause inferior

performance in weaving.

The so prepared beck beams are now sized in a sizing machine preferably with 2 size

boxes. The size pick up varies between 8 – 10%. In Europe mainly modified starches

with binders are used, whilst in USA certain low % of PVA is applied sin combination

with starches by some companies. Depending on the final finishing process (washed

denim) with no filler also CMC gives excellent performance in weaving.

CONTINUOUS SLASHER DYEING

Contrary to the Indigo rope dyeing system, for the continuous slasher dyeing and sizing

back beams are used. That means that the total No of ends required for a weavers beam

are dyed, dried, sized and dried simultaneously. The back beam contains similar to rope

380 – 420 ends but distributed evenly over the width of 140 or 160 cm between the

flanges so the end lay parallel to each other, warp length 12 – 15.000 meters, similar to

the rope dyeing system the full No of ends are pretreated (washed) dyed in 4 dye boxes

and oxidized, no softener are used in the last wash box.

We must however consider that the squeezing effect is lower and therefore the danger

streakiness and shade variation from centre to out side is also higher. Consequently it

would be better to deduce the warping width rather to 140 cm instead of using warper

beams with 160 – 180 cm warping width. The immersion time in the dye boxes is approx.

10 – 15 seconds and time for oxidation 30 – 60 second. The final result is a weaver’s

beam. This system allows the installation of less expensive dye rage and less additional

preparatory machinery. One of the disadvantages in previous year when warp preparation

21 Indigo Dyeing


(knots, weak, thick places) was not kept at a very high level was that ends sown in the

dyeing range could cause major colour variation through machine stops.

DOUBLE SHEET CONTINUOUS DYEING

Patents applied for double shade dyeing by E. Godau date back as 1976. With the system

dyeing sizing is done in 2 operations. The main reason for dyeing of 2 sheets

simultaneously is achieved a more even dyed sheet, that means 8000 – 8200 end are

dyed, oxidized, dried and the full length of the warper’s beam 12.000 – 15.000 meters

flange diameter. These beams are transported with the aid of air cushions to the sizing

machine, and the yarn sheet sized in double size boxes. Immersion time and oxidation

time is the same as with continuous slasher dyeing.

With double sheet dyeing the linear warp thread density is doubled. Therefore:

Squeezing effect is increased; an even squeezing over the whole width is achieved,

Condensation and concentration of ends at one spot show compared to single sheet

dyeing no colour strips formation, streakiness or shading in the finished fabric. The

production out put of the dyeing is increased by 75%. Dyeing of 3 layers of yarn

simultaneously is possible but very difficult to control the beaming on 3 big warp

batches. Unfortunately the double sheet dyeing machine as well as the rope dyeing range

cannot be linked with a sizing machine which must be regarded as an advantage as the

processes of dyeing and sizing must be carried out separately.

Loop dye system 1 for 6

Similar to the sheet dyeing systems 10 – 16 warper’s beams with the total number of ends

required for the weaver beams are used. The warper’s beams are placed in a moveable

warp creel which can be loaded whilst one set is in rotation. The yarn sheet is guided to

the soaking bath through a feed-in system with tension compensation rollers. The soaking

bath has the task to prepare the yarn for the following dyeing operation.

The yarn sheet after having been immersed into a single indigo dye bath runs into a long

loop where oxidation takes place. As you can see from the slide the back beams are

22 Indigo Dyeing


inside the yarn sheet passes through the dye box as often as necessary to obtain the

required deepness of shade.

One of the advantages is:

Ideal utilization of Hydrosulphite is through squeezing 4 – 6 layers simultaneously and

oxidation of yarn in a comparatively long oxidation loop. After the oxidation the yarn

sheet is guided through 2 washing boxes into a yarn accumulator and finally on to a

series of drying cans, dried up to 25 – 30% final moisture content prior being immersed

into size boxes, dried and wound onto a weavers beam.

The molecules are controlled DC drive to maintain warp tensions. Temperatures are

automatically controlled as well as the PH value in the dye box. The automatic control

unit of the PH value supplies automatically hydrosulfite and caustic soda to stabilize the

present value from the start to end of a dye set.

All rollers are contact with the dyed sheet are fluted, they keep the sheet in position and

reduce deposit of dye and build-up of other deposit (fluff). In addition to width is

controlled by guides to ensure even distribution of the yarn layer over the whole width of

the dyed sheet.

All accumulators placed between washing boxes and drying cans guarantees a continuous

production of the dye range when a weaver beam has to be exchanged at the head stock.

The creels can be loaded with back beam with 1200 mm diameter which allows to warp

approx. 36.800 meters of yarn, count No 7, 5 (tex 78) or 50.000 m count No 10 (tex 60).

This means that depending on the count normally one cyl-spool is used in warping to fill

a warper’s beam.

WARPING SPEED

PRODUCTION

Speed varies between 1000 m/min, 35 m/min. No 5, 5 (tex 107) and 42 m/min. No

10 (tex 60)

23 Indigo Dyeing


MACHINE STOPS DURING SIZING

For 36800 m, 4 recorded on expansion comb.

WASTE OF MATERIAL

Approximately - 15-20 kg per set.

TIME REQUIRED FOR CHANGE OF SET

2 hours

Linear warp densities in the squeeze.

The linear density in the nip is calculated in the same manner as for sizing.

Q= linear thread density

F= ends in cm -1

D= diameter of yarn

D= 0,921 mm = 0,921 = 0, 29125

Nm 10 = 3.1622

Q= F x D

As already mentioned previously the warp density has an influence on colour fastness. A

higher squeezing effect is achieved due to the over laying of the watp ends this also gives

more side to side squeezing, therefore reduce strips formation. The high squeezing effect

results also in better, quicker and proper oxidation and better colour fastness.

It must be mentioned that recommended dip and oxidation times on warp dyeing ranges

are of little use if not the squeezing effect is taken into consideration. Under a given

squeeze pressure, for instance 500 kg the squeezing effect of the mentioned 4- dyeing

systems can be compared. We can see that similar squeezing effect can be achieved with

the loop dyeing system 1 for 6 (75%) as with rope dyeing 70 – 110%. Double dyeing

24 Indigo Dyeing


with 2 layers width with 150 cm gives approx. 80% squeezing effect, whilst single sheet

slasher dyeing varies depending on count between 100 – 130%.

As only one short indigo dye bath is deeded only one feeding tanks, no separate feeding

of chemicals is necessary.

Dye liquor is use in 1500 1 instead of 6-4500 1, therefore less chemicals in use at same

time.

· Lower power consumption.

· Fine counts can be dyed as well

· For dark shades, black shades or other shades needed by fashion, other indanthrene dye

stuff can be directly added into the indigo dye bath (indanthrene yellow or orange).

LOOP DYE 1 FOR 6 COMBINED WITH DYEMER

The demand for dark shades specially dark marine blue for super blue denims also led to

new ideas in indigo dyeing ranges have been increased between 8-15 dye boxes with

corresponding oxidation ranges. In some cases, Hydroxyacetone has been specially

treated with high frequency. Besides achieving a darker shaded with the desire greenish

touch it is very suitable for biological treatment.

In order to achieving ring dyeing, mercerized yarn has also been used. A mercerizing

prevents penetration of dye stuff into the inner code it is suitable for this purpose to

obtain an optical blue effect and superior colour fastness and behavior in washing.

Mercerizing is very costly, therefore new ways is continuous mercerizing and indigo

dyeing was found.

DYEMER

The dyemer range is integrated. For impregnation padder for hot caustic solution is

placed after the heating system. The yarn is guided over could cylinders and with an

adjustable roller the tension of the yarn sheet can be adjusted according to the required

tension prior to the scouring in 2 more boxes.

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After having passed this, the yarn sheet is immersed into the dye box and the same

process as with the loop dye method is repeated.

INDIGO ROPE DYEING

SLASHER (INDIGOFLOW) DYEING

Indigoflow

We can explain the indigo flow dyeing tech as, every phase included the impregnation of

the yarn with the Leuco solution, in ALKALINE bath and at temperature relatively low

to oxidation it follows, after squeezing a pressure a passage in air to allow the Leuco to

oxidation and to become blue and therefore insoluble.

Oxidation

The oxidation is very important in the dyeing process; the purpose of the oxidation is

to get the permanent dye on the yarn and to eliminate the insolubility of the dye stuff in

the water.

According to the practical experience the average time for a perfect oxidation is about 60

seconds, this means that after the first dyeing/squeezing the yarn has to remain exposed

in the air for about 60 seconds before being dipped again in the second dyeing vat and so

on for all the following dyeing.

The dyeing mean time can be calculated in about 30/35 meters of yarn per minutes

therefore keeping as base the machine with eight dye vats. The total yarn in the oxidized

can be calculated as m 35 x 8 = 280 meters.

But Indigoflow with their special device “Rapidsky” only eight meters per dye vat of

yarn remain in the Rapidsky device. That means the total saving of yarn with Rapidsky is

24 x 8 = 216 meters.

FLEXIBILITY IN USE

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The high degree of evolution that can be reached by completing the basic machine with

the mercerizing and an intermediate drying can group, a steamer and a special double

circuit system for bath circulation system, enabling separation of vats and that allows the

maximum flexibility in use. In addition to the classical indigo blue it thus possible to dye

the modern mercerized to dye the modern mercerized indigo blue and black, the new

indigo supper blue the per-dyed indigo, as well as the large range of colour denim with

sulphurs, indanthrene, naphtholes, direct, relatives and pigments dyes.

THE CIRCULATION SYSTEM

This system has a ingenious and perfect dye bath circulation system. Through a variable

flow pump, the dye bath is sent from the circulation vat to the first dyeing vat, and from

this by means of an overflow system with special conveyors/mixers, to the next vat and

so on until it falls back into the circulation vat, where it is filtered its temperature is

adjusted and colour Hydrosulphite and soda are automatically added. This system is very

simple and dose not required maintenance. Dye bath circulation vat, stainless steel made,

complete with interchangeable bucket filters, automatic level adjustment, temperature

control and dosing of colours, Hydrosulphite and soda.

ACCUMULATORS

This system have to Gravity accumulators for automatic storage of the dye yarn when the

slasher machines stops for beam change complete with finned stainless steel rollers for

synchronization and safety devices.

MERCERIZATION

Mercerization causes morphological and mechanical changes in the yarn thus increasing

its resistance and dye affinity (dye stuff) saving, mercerized warp makes it possible to

obtain a better texture handle and look as well as particular chromatic effect on the ready

made cloth.

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MERCERIZED PROCESS

Mercerizing group consisting of soda process vat with circulation pump and filter, timing

cans neutralize and washing vats with 10 tons squeezing foulards, automatic feeding and

electronic yarn tension regulation devices.

TECHNICAL CHARACTERISTICS

1. Reduced capacity dye vat with semicircular bottoms and with only 2-3 large diameter

immersed rollers, to avoid the yarn breaking and tangling and to reduce the bath quantity.

2. Squeezing foulards with special rollers enabling a uniform squeeze effect over the

entire width under all pressure conditions.

3. In order to eliminate the cleaning operations and to help the colour oxidation this

system has special fining on the surface on the rollers of the oxidizers and accumulators.

4. Compactness, thus being accessible and easy to handle.

Ropes are stronger and less subjective to broken ends that, if they do occur, will tend to

pass through the machine. Ropes are braided from let-off creels to provide continuous

operation. Therefore there is no yarn waste from beam set splicing stops or shade tailing

from dye class changes. Standards pretreatment consists of counter flow scour/boxes.

Optional mercerizing section adds a caustic box plus skying rolls to provide proper

reaction time before washing. This adds important properties such as improved dye

affinity, fabric luster and strength as well as popular faction effects.

Rope dyeing is economical and well suited for processing chambers, dark shades, over

dye and fashion colours. These would include sulfur, reactive and vat dyes. Multiple dips

of indigo and proper oxidation time and in the skying section achieve depth of shade.

Basic range consists of eight box/sky sections. High production and/or deep fashion blue

ay require more sections.

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Dyestuff preparation circulation and custom designed chemical and system allow full

flexibility for variation dyestuff application. Morrison’s color kitchen for caustic,

Hydrosulphite and indigo are supplied with filters and stand by pumps to allow

uninterrupted operation. Large diameter feed and return lines assure content level in the

each dye box.

After dyeing the ropes enter multiple wash boxes for rinsing and chemical application.

Ropes are than carefully dried to 6% moisture or steam heated drying cylinders. Coilers

lay the individual ropes into drums in a pattern to facilitate the subsequent rebeaming

operation.

The 350 plus ends per rope are blended during the rebeaming (post dye) stage, and then

further randomized when the twelve beams set are sized prior to weaving virtually

guaranteeing side/side colour uniformity.

SLASHER DYEING VS ROPE DYEING

Slasher Dyeing Rope Dyeing

Requires lesser floor Space Floor space required more than indigo flowIs a continuous process or beam process It is not a continuous process, including

ball warping. Rebeaming critical.

The mercerizing process is easy and simple Mercerizing difficult due to rebeaming

Less man power required More man power required for ball warping and

rebeaming

The capacity of one dye Dye bath is 100 litres to save the expensive indigo dye

stuff. The dye bath has three rollers. (one is bigger than the other two)

The dye baths are in customized shapes.

The capacityof dye stuff is 2.5 lits. The dye

bath have five rollers of the same size.

Yarn count allowed – 1-30 counts Yarn count allowed – 1-16 counts

Flexibility offered for different shades of

dyeing.

Only blue and black colours can be dyed onto

the fabric.

Any type of denim can be produced. Only classic denim can be produced.

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Cheaper than the rope dyeing technology We get it for a price of $ 2.85 per metre in the

international market.

30 Indigo Dyeing

indigo dyeing final

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