Dye Industry - Copy

7/24/2019 Dye Industry - Copy

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Table of Contents

Definition of Dye ..................................................................................................................................... 2

History of Dye ......................................................................................................................................... 2

Textile Fibers ........................................................................................................................................... 3

Classification of Dyes by Use or Application ........................................................................................... 5

Nomenclature of Dyes ............................................................................................................................ 8

Dyeing Technology.................................................................................................................................. 9

Printing ................................................................................................................................................. 12

Nontextile Use of Dye ........................................................................................................................... 13

Dye Intermediates ................................................................................................................................ 15

Dye Manufacturing Process .................................................................................................................. 16


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1. Definition of Dye

Dyes are substance used to impart colour to textiles, paper, leather and other materials

such that the colouring is not readily altered by washing, heat, light or other factors to which the

material is likely to be exposed. Dyes differ from pigments, which are finely ground solids which

are dispersed in a liquid, such as paint or ink, or blended within other materials. Most dyes areorganic compounds whereas pigments may be inorganic.

2. History of Dyes

2.1. Natural Dyes

Until the 1850s virtually all dyes were obtained from natural sources, most commonly

from vegetables, such as plants, trees, lichens and from insects. Solid evidence that dyeing

methods are more than 4000 years old has been provided by dyed fabrics found in Egyptian

tombs. Ancient hieroglyphs describe extraction and application of natural dyes. Countless

attempts have been made to extract dyes from brightly coloured plants and flowers, yet only a

dozen or so natural dyes found widespread. Undoubtedly most attempts failed because most

natural dyes are not highly stable and occur as compensate of mixtures, the successful of

separation of which would be unlikely by the crude methods employed in ancient times.

Nevertheless, studies of these dyes in the 1800s provided a base for development of synthetic

dyes, which dominated the market by 1900.

2.2. Synthetic Dyes

In 1856, the first commercially successful synthetic dye, mauve, was serendipitously

discovered by the British chemist William H. Perkin, who recognized and quickly exploited its

commercial significance. The introduction of mauve in 1857 triggered the decline in dominance

of natural dyes in world markets. Mauve had a short commercial lifetime, but its success

catalyzed activities that quickly led to the discovery of better dyes.

The synthetic dye industry arose directly from studies of coal tar. By 1850, coal tar was

an industrial nuisance because only a fraction was utilized. It attracted the attention of chemists

as a source of new organic compounds, isolable by distillation. German chemist, August

Wilhelm von Hoffman directed the Royal College of Chemistry. He trained most of the students

in English dye industry, one of whom is Perkin. By trial and error, reactions of coal tar

compounds were found to yield useful dyes. By 1914 the synthetic dye industry was firmly

established in Germany, where 90 percent of the worlds dyes were produced.

A few new dye types were introduced in the 20th

century, and major challenges were

posed by the introduction of synthetic fibers, which held a major share of the world market, and

by technological advances.


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3. Textile Fibers

Textile fiber is the raw materials to produce various types of textile finished products. A

fiber that can be spun into yarn or processed into textile as such as a woven kit, knit, fabric, lace,

non-woven and others alike by means of an appropriate interlacing method.

3.1. Natural Fibers

3.1.1. Cotton

Cotton fibers are comprised mainly of cellulose, a long-chain polymer of

anhydroglucose units connected to ether linkages. Polymers can be classified into two,

the primary and secondary alcohol groups uniformly distributed throughout the length of

polymer chain. These hydroxyl groups impart high water absorption characteristics to the

fiber and can act as reactive sites. The morphology of cotton fiber is complex series of

reversing spiral fibrils. The fiber in total is convoluted collapsed tube with a high degree

of twist occurring along the length of the fiber.

3.1.2. Flax

Flax is also a cellulosic fiber but has a greater degree of crystallinity than cotton.

The morphology of flax is quite different from that of cotton. Flax fibers have a long

cylindrical shape with a hallow core. In recent years, its commercial importance as textile

fiber has decreased significantly.

3.1.3. Wool

Wool fibers are comprised mainly of proteins: the polypeptide polymers in wool

are produced from some 20 alpha-amino acids. The major chemical features of

polypeptide polymer chain and the cystine crosslinks, which occur in random spacing

between the polymer chains. The polymer contains many amine, carboxylic acid and

amide groups, which contribute in part to the water-absorbent nature of fiber.

The morphology of the wool is complex. There is an outer covering over the fiber,

the cortical. There are also overlapping scales having a ratchet configuration that causes

shrinkage and felting. The coefficient of friction in wool fibers is vastly different between

the tip and the root. Wool can be made washable by chemically abrading the scales or

coating the fibers with another polymer.

3.1.4. Silk

Silk, like wool, is a protein fiber but of much simpler chemical and morphological

make-up. It is comprised of six alpha-amino acids and is the only continuous-filament

natural fiber. Silk fiber is spun by the silkworm as a smooth double strand, each part


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having a trilobal cross-section. This configuration helps give silk its lustrous appearance.

The fiber is unwound from the cocoon the silkworm spins as it prepares its chrysalis.

Because of the labor-intensiveness of sericulture and subsequent preparation of the fiber,

silk remains a luxury fiber.

3.2 Regenerated Fibers

3.2.1. Rayon

Viscose rayon, like cotton, is comprised of cellulose. In the manufacturing

process, wood pulp is treated with alkali and carbon disulfide to form cellulose xanthate.

The reaction mass is forced through a spinneret and precipitated in an acid coagulation

bath as it is formed into a continuous filament. The fiber has a round striated cross-

section. Rayon staple is made by breaking the continuous strands into staple-length of

fibers. Viscose rayon is conventionally produced in diameters varying from 9 to 43

microns.

3.2.2 Acetate

Triacetate and diacetate fibers are manufactured by the chemical treatment of

cellulose obtained from refined wood pulp or purified cotton lint. Most of the hydroxyl

groups are acetylated by treating the cellulose with acetic acid. Acetate is made by the

saponification of one of the acetylated groups. The conversion of hydroxyl groups causes

these fibers to be hydrophobic and changes the dyeing characteristic drastically from

those of the normal cellulosic fiber. Triacetate fibers are spun by mixing the isolated

reaction product with methylene chloride and alcohol. The spinning solution (dope) is

forced through the spinneret and dry-spun into continuous filaments. An alternate way of

wet spinning is also possible.

3.3 Synthetic Fibers

3.3.1. Nylon

Nylon is a polyamide fiber. There are two major types of polymer fiber that are

used in textiles. Type 6,6 is made by using hexamethylene glycol and adipic acid. Type 6

is made by polymerizing -caprolactam. Nylon fibers are made by melt-spinning the

molten polymer. The result is a continuous filament fiber of indeterminate fiber. The

cross-section is usually round, trilobal, or square with hallow channels when used as

carpet fiber.


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3.3.2 Polyester

Polyester is made by the polymerization reaction of a diol and a diester. The main

commercial polymer is formed by a condensation reaction using ethylene glycol and

terepthalic acid. Fibers are made by melt-spinning. The fiber is usually spun with a round

cross-section. Polyester is the most-used synthetic fiber around the world.

3.3.3. Acrylics

Acrylics are made from the polymerization of acrylonitrile and other co-

monomers to allow dyeability. The fibers are produced by either solvent-spinning or wet

spinning. Acrylics have found a niche market as a substitute for wool or in wool blends,

in awnings or boat covers. Acrylic fibers are quick drying and wrinkle resistant.

3.3.4. Polyolefin

Polyolefin fibers are produced from the polymerization of ethylene or propylenegas. The fibers made from these polymers are melt-spun. The cross-sections are round

and the fibers are smooth. They have extremely low dye affinity and moisture

absorbance.

3.3.4. Elastane

Elastane fibers are formed by dry-spinning or solvent-spinning. The cellulosic and

natural fibers are the most hydrophobic.

3.3.5. Microdenier Fibers

This fiber is less than one denier per filament. Yarns made from microdenier

filaments are able to give silk-like hand to fabrics.

4. Classification of Dyes by Use or Application

4.1. Reactive Dyes

These dyes form a covalent bond with the fiber, usually cotton, although they are used to

a small extent on wool and nylon. This class of dyes was first introduced commercially in 1956,

made it possible to achieve extremely high washfastness properties by relatively simple dyeing

methods. A marked advantage of reactive dyes over direct dyes is that their chemical structures

are much simpler; their absorption spectra show narrower absorption bands and the dyeing are

brighter. High-purity reactive dyes are used in the ink-jet printing of textiles, especially cotton.


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4.2. Disperse Dyes

These are substantially water-insoluble nonionic dyes for application to hydrophobic

fibers from aqueous dispersion. They are used predominantly on polyester and to a lesser extent

on nylon, cellulose, cellulose acetate and acrylic fibers. Thermal transfer printing and dye

diffusion thermal transfer (D2T2) processes for electronic photography represent niche marketfor selected members of this class.

4.3. Direct Dyes

These water-soluble anionic dyes, when dyed from aqueous solution in the presence of

electrolytes, are substantive to and have high affinity for cellulosic fibers. Their principal use is

the dyeing of cotton and regenerated cellulose, paper, leather and nylon. Most of the dyes in this

class are polyazo compounds. After treatments are frequently applied to the dyed material to

improve washfastness properties, include chelation with salts of metals, and treatment with

formaldehyde or a cationic dye-complexing resin.

4.4. Vat Dyes

These water-insoluble dyes are applied mainly to cellulosic fibers as soluble leuco salts

after reduction in an alkaline bath, usually with sodium hydrogensulfite. Following exhaustion

onto the fiber, the leuco forms are reoxidized to the insoluble keto forms and aftertreated to

redevelop the crystal structure. The principal chemical classes of vat dyes are anthraquinone and

indigoid.

4.5. Sulfur Dyes

These dyes are applied to cotton from an alkaline reducing bath with sodium sulfide as

the reducing agent. Numerically this is relatively small group of dyes. The low cost and

washfastness properties of the dyeing make this class important from an economic standpoint.

However, they are under pressure from an environmental viewpoint.

4.6. Cationic (Basic) Dyes

These water-soluble cationic dyes are applied to paper, polyacrylonitrile, modified nylons

and modified polyesters. Their original use was for silk, wool and tannin-mordanted cotton when

brightness of shade was more important than fastness to light and washing. Basic dyes are water-

soluble and yield colored cations in solution. For this reason they are frequently referred to ascationic dyes. The principal chemical processes are diazahemicyanine, triarylmethane, cyanine,

hemicyanine, thiazine, oxazine and acridine. Some basic dyes show biological activity and are

used in medicine as antiseptics.

4.7. Acid Dyes

These water-soluble anionic dyes are applied to nylon, wool, silk and modified acrylics.


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They are also used to some extent for paper, leather, ink-jet printing, food and cosmetics.

4.8. Solvent Dyes

These water-insoluble but solvent-soluble dyes are devoid of polar solubilizing groups

such as sulfonic acid, carboxylic acid or quaternary ammonium. They are used for coloringplastics, gasoline, oils and waxes. The dyes are predominantly azo and anthraquinone, but

phthalocyanine and triarylmethane dyes are also used.

Table 4.1 Usage Classification of Dyes

Class Principal substrates Method ofApplication

Chemical Types

Acid Nylon, wool, silk, paper,inks and leather

Usually from neutralto acidic dyebaths

Azo(includingprematellized),

anthraquinone,triphenylmethane,

azine, xanthene, nitroand nitroso,

Azoic components

and composition

Cotton, rayon, cellulose

acetate and polyester

Fiber impregnated

with couplingcomponent and

treated with a solutionof stabilized

diazonium salt

azo

Basic Paper, polyacrylonitrile,

modified nylon,polyester and inks

Applied from acidic

dyebaths

Cyanine,

hemicyanine,diazahemicyanine,

diphenylmethane,triarylmethane, azo,

azine, xanthene,acridine, oxazine and

anthraquinone

Direct Cotton, rayon, paper,

leather and nylon

Applied from neutral

or slightly alkalinebaths containing

additional electrolyte

Azo, phthalocyanine,

stilbene and oxazine

Disperse Polyester, polyamide,

acetate, acrylic and

plastics

Fine aqueous

dispersions often

applied by hightemperature/pressureor lower temperature

carrier methods; dyemay be padded on

cloth and baked on orthermofixed

Azo, anthraquinone,

styryl, nitro and

benzodifuranone


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Fluorescent

Brightners

Soaps and detergents, all

fibers, oils, paints andplastics

From solution,

dispersion orsuspension in a mass

Stilbene, pyrazoles,

coumarin, andnaphthalinides

Food, drug andcosmetic

Foods, drugs andcosmetics

Azo, anthraquinone,carotenoid, and

triarylmethaneMordant Wool, leather and

anodized aluminum

Applied in

conjunction with Crsalts

Azo and

anthraquinone

Oxidation Bases Hair, fur and cotton Aromatic amines, andphenols oxidized on

the substrate

Aniline black andindeterminate

structures

Reactive Cotton, wool, silk and

nylon

Reactive site on dye

reacts with functionalgroup on fiber to bind

dye covalently under

influence of heat andpH

Azo, anthraquinone,

phthalocyanine,formazan, oxazine

and basic

Solvent Plastic, gasoline,

varnishes, lacquers,stains, inks, fats, oils

and waxes

Dissolution in the

substrate

Azo,

triphenylmethane,anthraquinone and

phthalocyanine

Sulfur Cotton and rayon Aromatic substrate

vatted with sodiumsulfide and reoxidized

to insoluble sulfur-containing products

on fiber

Indeterminate

structure

Vat Cotton, rayon and wool Water-insoluble dyessolubilized by

reducing with sodiumhydrogensulfite, then

exhausted on fiberand reoxidized

Anthraquinone(including polycyclic

quinones) andindigoids

5. Nomenclature of Dyes

Dyes are named by either by their commercial trade name or by their Colour Index (C.I)name. The commercial names of dyes are usually made up of three parts. The first is a trademark

used by the particular manufacturer to designate both the manufacturer and the class of dye, the

second is the color and the third is a series of letters and numbers used as a code by the

manufacturer to define more precisely the hue and also to indicate important properties of the

dye.


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The CI name for a dye is derived from the application class to which the dye belongs, the

color or the hue of the dye and a sequential number. A five digit CI number is assigned to a dye

when its chemical structure has been disclosed by the manufacturer. The following example

illustrates these points:

Chemical Structure:

Molecular Formula: C33H20O4

Chemical Abstract Name: 16,17-dimethoxydinaphthol[1,2,3-cd:3`,2`,1`-lm]perylene-5,10-dione

Trivial Name: Jade Green

CI Name: C.I. Vat Green 1

C.I. Number: C.I. 59825

Application Class: vat

6. Dyeing Technology

The goal of every dyeing is a colored textile in the desired shade, homogeneous in hue

and depth of shade, produced by an economic process and which exhibits satisfactory fastnessproperties in the finished state.

Although modern automation techniques have been introduced for color measurement,

metering of dyes and auxiliaries, and automatic control of the dyeing process much human

intervention is still required. Fibers can only be standardized to a limited extent, due to biologicaland environmental factors, in growing cotton or raising sheep. To remain flexible with regard tofashion and fastness properties, dyeing is carried out at the end of the production process

whenever possible.

The textile material needs a pretreatment before dyeing. Wool must be washed to removewax and dirt and is sometimes bleached; cotton must be boiled and bleached to remove pectins

and cotton seeds then it will undergo mercerization. Sizes and spinning oil must be eliminated.


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6.1. Principle of Dyeing

Basically there are three methods of dyeing textile: Mass dyeing, dyeing of synthetic

polymer before fiber formation; Pigment dyeing, affixing an insoluble colorant on the fibersurface with a binder; Exhaustion dyeing from an aqueous bath with dyes that have an affinity

for the fiber. Exhaustion dyeing will be discussed more in detail since it is the most used processin the industry.

In exhaustion dyeing, the dye is transported to the fiber surface by motion of the dye

liquor or the textile. It is then adsorbed on the fiber surface and diffuses into the fiber. Finally, itis fixed chemically or physically. The dye can be applied to the textile discontinuously or

continuously by immersing the textile in a concentrated bath and squeezing off excess liquor,followed by separate steps for diffusion and fixation in the fiber.

The speed of exhaustion of individual dyes can vary widely, depending on their chemical

and physical properties, the kind of textile used could also affect this. The dyeing factor dependstemperature, liquor ratio, dye concentration, and the chemicals and auxiliary products in the dye

bath. High dyeing rates bear the danger of unlevel dyeings. Dyes have to be carefully selectedwhen used together in one recipe.

The end of the dyeing process is characterized by the equilibrium phase. Under standardconditions, the distribution coefficient of the dye between liquor and fiber is constant; in other

words, the rate of desorption and adsorption are equal. When the dyeing is carried outcontinuously, it is important that the dye application must be homogeneous and avoid migration

during subsequent steps. Leveling out a dyeing after fixation of the dye is tedious and time-consuming.

6.2. Bath Dyeing Technology

6.2.1. Circulating Machines


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The goods are packed loose and the liquor is pumped through the goods. Thepump characteristics and the density of the material determine the circulating speed of the

liquor and the necessary dyeing time.

6.2.2. Circulating-Goods Machine

Traditional dyeing equipment belongs to this group. Fabric is moved as a rope or

in open width by mechanical means or liquor jet produced by a circulating pump.

6.2.3. Process Control in Bath Dyeing

Bath dyeing runs discontinuously, automatic process control must work in cycles.

A completely automated dyeing process is almost impossible to achieve, because thereare a lot of variables determine the result of dyeing and a wide range of operating factorsinteract with each other during dyeing. A precondition for automatically controlling the

dyeing process is detailed knowledge of the characteristics of the fiber to be dyed, thedyes and auxiliary to be used and the equipment available. To assure level dyeing from

the beginning of the exhaustion curves for the dyes combined in one recipe must becontrolled. This requires constant color measurement of dye concentration.

6.3. Continuous and Semi-Continuous Dyeing

Continuous dyeing means treating fabric in a process unit in which application of the dye

to the fabric and fixations are carried out continuously. Continuously working units areassembled into lines of consecutive processing steps, sometimes including pretreatment of thefabric. Fabric will be treated in an open-width, any unevenness in the equipment across the width

of the goods to unlevel dyeing. The width of the goods and longitudinal tension influence eachother. The running speed determines the dwelling time in the treatment unit. Any interruption in

the process will lead to the spoilage of the fabric.


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7. Printing

A wide variety of techniques exist for applying dyes by printing. Four kinds of printing

have long been recognized: direct, dyed, discharge and resist.

Direct printing is the application of a painting paste containing dye, thickeners andauxiliaries directly to the fabric by rollerprinting. The dominant technique is screen printing.

Discharge printing is the application of dischargeable dye and then printed with adischarge paste in the desired pattern. The discharge dye may contain a discharge-resistant dye.

Printing is most often done with rotary screens etched in the design to be printed. Printing

paste is fed constantly to the center of the rotating screens from a nearby supply and a squeegee

pushes the colored paste through the holes in the screen, leaving the dye paste only in theintended areas, a separate screen is required for each color in the pattern.

The current machines are very successful at furnishing one of a kind and for use in rapid

prototyping.


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7.1. Pigment Dyeing and Printing

Pigment dyeing and printing are processes that compete with the more conventional

means of dyeing and printing. These processes use water-insoluble dyes or pigments that arebound to the surfaces of pigments that are bound to the surfaces of fabrics with resins. A paste or

an emulsion, containing pigment and resin or a resin-former, is applied to the fabric. The goodsthen are dried and cured by heat to produce the finished dyeing or print. During the heating or

curing, fabric, resin and pigment become firmly bonded together. This method of colorapplication is economical and produces good results. It should be noted that the pigment is

confined to the surface of the fabric and can be selected without regard for fiber affinity.

8. Nontextile Uses of Dye

Colorants for nontextile use have been developed mainly for use in hair dyeing,photography, biomedical applications and electronics and reprographics. In several nontextile

applications, dyes are not used for their ability to deliver color. Instead, they are used because oftheir potential electrical properties, ability to absorb IR radiation.

8.1. Liquid Crystal Dyes

Dyes for liquid crystalline media typically have nonionic structure, high purity, solubility

and compatibility with the medium, a transition dipole that is parallel with the alignment axis ofthe molecular structure, and good alignment with the liquid crystal molecule. Example includes

the disazo and anthraquinone dyes, which are shown below.

8.2. Ink-jet Dyes

Inkjet dyes are higky concentrated colorants specifically designed for todays inkjetmarkets. These ultra pure dyes are low in chlorides and prepared to meet all the standard criteria

for the inkjet industry. Inkjet printing is meticulously produced using comprehensive purificationand filtration processes. The quality of an inkjet printing is very much influenced by the physic-

chemical properties of printing ink.

Dye inks are prepared by dissolving of the liquid colored dyes into a fluid carrier. Thismakes the dyes easy to apply. When it is applied to a paper, the dyes are absorbed very


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uniformly so they reflect light very evenly. As the printing is a high precision job the inkjet dyesneed to have superior quality in terms of colors, physical properties and stability. Generally

direct, reactive and acid dyes are used as dyes for inkjet ink.

8.3. Thermal and Pressure-Sensitive Printing

In pressure-sensitive printing technology the color former is dissolved in a solvent andencapsulated. The use of pressure ruptures microcapsules containing the color former, whichgenerates color upon contacting a developer. Black prints are usually obtained from fluorans or

from color-former mixtures.

8.4. Organic Photoconductors and Toners

Photoconductors and toners are used in photocopiers and laser printers to produce

images. Organic photoconductors are consists of a charge-generating layer and a charge-transporting layer. The former is comprised of pigments and the latter is comprised of electron-

rich organic compounds that are usually colorless. Suitable organic pigments for chargegeneration include azo pigments, tetracarboxydiimides, polycyclic quinones, phthalocyanine,

perylenes and squarylium compounds.

Colorants are used in toners to provide color and control the electrostatic charge on tonerparticles. Diarylides and monoarylides have been used as the yellow pigments in colored tones.

The magenta pigments are often quinacridones and the cyan pigments are copperphthalocyanines.

8.5. Infrared Absorbing Dyes

Infrared dyes include indolenincyanines and azulenium compounds, both of which areused in optical reading materials.

8.6. Laser Dyes

Lasers are which dyes comprise the active medium have become of the most widely used

types. The key virtue of these systems is their ability to cover virtually the entire fluorescencespectral region. Accordingly, the most commonly used dyes are highly fuorescent.

8.7. Biomedical Dyes

Dyes can be used clinically in bioanalysis and medical diagnostics and in the treatment ofcertain diseases.

8.8. Hair Dyes

About 80% of the dyes used in hair coloring are known as oxidation hair dyes. Theremaining 20% of the available hair dyes are mainly synthetic dyes that have affinity for protein

substrates. Oxidation dyes are produced directly on hair by oxiding diamines with suitableoxiding agent. In this regard, the diamines have been referred as primary intermediates and the

oxidizing agent as the developer.


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8.9. Photographic Dyes

Color photography is still one of the most important and interesting nontextile uses for

synthetic dyes. The chemistry employed is the same to that of oxidation of hair dyes, in that anoxidizable substrate is combined with a coupler to produce the target colorant. In this case the

diamine is referred to as the developer and it is oxidized by silver halide in the photographicfilm. The oxidized developer then reacts with the coupler to form the dye.

9. Dye Intermediates

The dye intermediates are generally found as petroleum downstream products. For

application they are further processed. On processing they are transformed to finished dyes andpigments. The dye intermediates are vital inputs for a number of major industries. Some of the

major industries they serve are textiles, plastics, paints, printing inks and paper. Further, dyeintermediates also serve as an important raw material for the acid, reactive and direct dyes. A

major application of dye intermediates are found in hair dyes.

Most dye intermediates are prepared by reaction involving electrophilic or nucleophilicsubstitution processes. The electrophilic processes include nitration, sulfonation, and

halogentation reactions, and the nucleophilic processes include hydroxylation and aminationreactions.

Other key dye intermediates are prepared by oxidation and reduction processes. The most

common dye intermediates are shown below.


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10. Dye Manufacturing Process

Each chemical and physical step in the process can generate process wastewater, solid

waste and air emissions. The anthraquinone-based vat dyes require more synthetic steps than the

acid, basic, direct, disperse and reactive dye classes. The multiple chemical reactions increase

the consumption of raw materials, resulting in vat dyes having the highest ratio of raw materials

to finished dye as compared to the other dye classes. Wastewater from the manufacture of vat

dyes is on the order of 8,000 liters per kg of product compared to a maximum of 700 liters per kgfor the other dye classes.

The most significant material losses in dye production come from incomplete chemical

reactions. The yield of the various reactions discussed in section III B ranges from 39 to 98

percent, with an average of only 79 percent of theory. Some of the vat dyes require five or more

synthetic steps. If each step averages a 79 percent yield, the overall yield of a five step process is

only 31 percent of theory. If seven steps are required, which is the case for Vat Brown 1, the

overall yield is only 19 percent of theory.

Most of the raw materials used in the manufacture of vat dyes are hazardous since they

are ignitable, corrosive, or toxic. The low yields result in hazardous chemicals in the wastewater

and in solid wastes such as solvent still bottoms and filtration clarification sludges.The wastewater from vat dye synthesis will contain unreacted raw materials and

byproducts which are soluble, in addition to inorganic salts formed by neutralization. The heavy

metal catalysts and reagents used in key intermediate steps, such as mercury, arsenic, copper and

chromium, are primarily found in the wastewater as soluble salts, and can contaminate soil and

groundwater if improperly treated or disposed of.


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The acid, basic, direct, disperse, and reactive dye classes are generally manufactured in

aqueous media. Vat dyes, however, require high boiling solvents in many of the intermediate

steps, since temperatures over 200 deg. C are necessary to drive the reactions. The most

common solvents are nitrobenzene, naphthalene and the chlorinated solvents chlorobenzene, 1,

2-dichlorobenzene (o-dichlorobenzene), and 1, 2, 4-trichlorobenzene (trichlorobenzene). All of

these solvents are hazardous chemicals with the potential of severe environmental contamination.

In the vat dye industry, the solvents can be recovered by collecting the mother liquor

from the filtration step in a distillation vessel equipped with a condenser and receiver. However,

it is more common to use a venuleth (paddle) dryer. This is a horizontal rotary vacuum dryer

used to obtain dry powder from wet cake or solutions and to recover the solvent at the same

time. Steam is supplied to an exterior jacket and to a hollow shaft and paddles within the unit.

Solvent recovery generates still bottoms that must be removed from the equipment

between batches in order to facilitate heat transfer. The tarry residue is scraped from the interior

of the equipment and usually packed in drums for disposal. The spent solvent still bottoms from

vat dye manufacture are listed as hazardous wastes. The still bottoms may also contain unreactedraw materials and reaction byproducts.

Filtration operations also result in solid waste when off-specification intermediates or

dyes are purified by recrystallization in solvents. Diatomaceous earth and activated carbon are

typically added to the solution to adsorb the unreacted raw material or other impurities and to

prevent blinding of the filter media. The filtration clarification sludge from vat dye operations

will likely contain RCRA-listed hazardous wastes including organic chemicals and heavy metals.

Empty raw material containers represent another source of potentially hazardous solid

waste disposed of by dye manufacturers. The chemicals can stick to the walls of the container or

to the paper or plastic liners.

It was common practice in the dye industry to pack the spent still bottoms and filtrationsludge wastes in steel drums. Many of these disposal locations became Superfund sites or state

hazardous waste sites due to the serious contamination of soil and groundwater from the

drummed wastes.

11. Azo Dyes

Azoic Dyes are classified either according to the fibers for which these can be used

economically or the methods by which these dyes are applied. These dyes cannot be applied

directly on the fibers as dyes. Actually, these dyes are produced within the fibers itself. For this

production, first the fiber is impregnated with one component of these dyes and then the fiber istreated in another component of these dyes. In this way the AZO dyes are formed. This specialty

makes these dyes very fast to washing within the fabric market.

When these dyes are used upon the cellulose fabric then initially this fabric starts to suffer from

poor rub fastness. This is due to the deposition of the free pigments on the surface of the fabric.

This problem can be rectified by boiling the fabric in soap.


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AZO Dyeing Process is such a process in which the insoluble azoic dye is produced on

the or within the fiber. By treating a fiber with diazoic and coupling components, this process

can be achieved. After adjusting the dye bath conditions appropriately, the two above mentioned

components react. From this reaction the required insoluble AZO dye is produced. This is a

unique technique. The required color can be changed by altering of the diazoic and coupling

components.

12. Triphenylmethane Dyes

It is any member of a group of extremely brilliant and intensely coloured synthetic

organic dyes having molecular structures based upon that of the hydrocarbon triphenylmethane.

They have poor resistance to light and to chemical bleaches and are used chiefly in copying

papers, in hectograph and printing inks, and in textile applications for which lightfastness is not

an important requirement.

The triphenylmethane derivatives are among the oldest man-made dyes, a practical

process for the manufacture of fuchsine having been developed in 1859. Several other membersof the class were discovered before their chemical constitutions were fully understood. Crystal

violet, the most important of the group, was introduced in 1883.

The range of colours is not complete but includes reds, violets, blues, and greens. They

are applied by various techniques, but most belong to the basic class, which are adsorbed from

solution by silk or wool, but have little affinity for cotton unless it has been treated with

a mordant such as tannin.

13. Xanthene Dyes

Xanthene is a yellow organic heterocyclic compound. It is soluble in diethyl ether.Xanthene is used as a fungicide and it is also a useful intermediate inorganic synthesis.

Derivatives of xanthene are commonly referred to collectively as xanthenes, and among

other uses are the basis of a class of dyes which includes fluoroscein, eosins, and rhodamines.

Xanthene dyes tend to be fluoroscent, yellow to pink to bluish red, brilliant dyes. Many xanthene

dyes can be prepared by condensation of derivates of phthalic anhydrous with derivates of or 3-

ominophenol.


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References

Kent, James A., Kent and Riegels Handbook of Industrial Chemistry and Biotechnology,

11thedition, Springer Science+Business Media LLC, 2007

Hunger, Klaus, Industrial Dyes, WILEY-VCH Verlag GmbH and Co KgaA, 2003

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Vat Dyes: Chemistry, Manufacture and Waste Streams. http://www.tasanet.com.

Retrieved from February 4, 2015 from

http://www.tasanet.com/knowledgeCenterDetails.aspx?docTypeID=1&docCatID=6&docID=257

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http://www.chm.bris.ac.uk/webprojects2002/price/classify.htm

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structure
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