Textile Dyeing Process Dyeing is a method which imparts beauty to the textile by applying various colors and their shades on to a fabric. Dyeing D yeing can be done at any stage of the manufacturing of textile- fiber, yarn, fabric or a finished textile product including garments and apparels. The property of color fastness depends upon two factors- selection of proper d ye according to the textile material to be dyed and selection of the method for dyeing the fiber, yarn or fabric.
The following figures illustrate with process flow diagrams the whole operation of finishing processes and how the dyeing process is a part and parcel of the process of textile making.
Materials used in the Textile Dyeing Process Materials that are used in textile dyeing process include water, fibre, yarn or cloth. Fu rther, these include a host of process chemicals like •
!cids, e.g. acetic, formic.
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!lkalis- "a#$, potassium hydroxide, sodium carbonate.
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%leaches- $ydrogen peroxide, sodium hypo h ypo chlorite, sodium chlorite etc.
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Dyes, for example direct, disperse, pigment, vat.
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&alts, e.g. "a'l.
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&i(e, e.g. )*!, starch.
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&tabilisers from sodium silicate, sodium nitrate also organic stabilisers.
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&urfactants
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!uxiliary finishes, like fire retardant, softener
The Dyes are classified based on the products to which they can be applied and the chemical nature of each dye. Dyes are complex unsaturated aromatic having characteristics like solubility, intense color, substansiveness and fastness. ! dye-formulation is supposed to have approximately +- pure dyestuff. /t is mostly observed that dyestuffs delivered in powder form have a higher value. 0hile a lower value is obtained for the li1uid formulations. Dyes may be classified in several ways 2e.g., according to chemical constitution, application class, end-use3.
Chemical classification of the Dyes Dyes can be divided according to the nature of their Chromophore: Group
Uses
Category !cridine dyes, derivatives of acridine 4'5"-and4'5' :
Textiles, leather
Category !nthra1uinone dyes, derivatives of anthra1uinone 4'5# : and4'5'
Textiles
!rylmethane dyes Category :
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Diarylmethane dyes, based on diphenyl methane
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Triarylmethane dyes, based on triphenyl methane
Category !(o dyes, based on a -"5"- a(o structure : Category 'yanine dyes, derivatives of phthalocyanine : Category Dia(onium dyes, based on dia(onium salts : Category "itro dyes, based on the -"#6 nitro functional group : Category "itroso dyes, are based on a -"5# nitroso functional :
Category )hthalocyanine dyes, derivatives of phthalocyanine 4'5" :
)aper
Category 7uinone-imine dyes, derivatives of 1uinone :
0ool and paper
!(in dyes Category :
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8urhodin dyes
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&afranin dyes, derivatives of safranin -'-"5'- -'-"-'
9eather and textile
Category :anthene dyes, derived from xanthene -#-';$<- :
'otton, &ilk and 0ool
Category /ndophenol dyes, derivatives of indophenol 4'5"-and4'5# :
'olor photography
Category #xa(in dyes, derivatives of oxa(in -'-"5' 5'-#-'5 :
'alico printing
Category #xa(one dyes, derivatives of oxa(one : Category Thia(in dyes, derivatives of thia(in : Category Thia(ole dyes, derivatives of thia(ole 4'5"-and-&-5 : Category Fluorene dyes, derivatives of fluorene : Category =hodamine dyes, derivatives of rhodamine : Category )yronin dyes :
Dyes according to the nuclear structure !ccording to the "uclear &tructure, dyes are categori(ed into two groups •
'ationic Dyes
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!nionic Dyes
/ntermediate
Industrial Classification of the Dyes Textile /ndustries use dyestuff in large amount, so at this level a classification can be done according to their performances in the dyeing processes. The most consumable dye is !(o dye, around ; of the total dyestuffs of the world are based on this dyes. Ma>or classes of dyes in textile finishing is given here •
!cid
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!(oic
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%asic
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Direct
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Disperse
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=eactive
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&olvent
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&ulphur
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*at
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Mordant
Classification based on the source of materials 'lassification of dyestuff is mainly depend upon the nature of the source from which it is made. !ccordingly the classification could be •
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"atural Dyes &ynthetic Dyes
ther important dyes %ased on various applications, a number of other classes of dyes have also been established, that includes the following •
#ptical %righteners - ?sed primarily for textile fibres and paper.
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Fluorescent Dyes - ! very innovative dye. ?sed for application in sports good etc.
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9euco Dyes - $as a wide variety of applications including electronic industries and papers.
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#xidation Dyes - ?sed mainly for hair.
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9eather Dyes - ?sed for leather.
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Fuel Dyes - !s the name suggests it is used in fuels.
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&olvent Dyes - For application in wood staining and production of colored lac1uers, solvent inks, waxes and coloring oils etc.
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/nk>et Dyes - 0riting industry including the ink>et printers.
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&moke Dyes - ?sed in military activities.
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&ublimation Dyes - For application in textile printing.
Classification of Dyes Dyes can be classified in several ways, each class has a very uni1ue chemistry, structure and particular way of bonding. &ome dyes can react chemically with the substrates forming strong bonds in the process, and others can be held by physical forces. &ome of the prominent ways of classification are given below •
"atural @ &ynthetic
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#rganic @ /norganic
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%y area and method of application
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'hemical classification - %ased on the nature of their respective chromophores.
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%y nature of the 8lectronic 8xcitation 2i.e., energy transfer colorants, absorption colorants and fluorescent colorants3.
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!ccording to the dyeing methods o
!nionic 2for )rotein fibre3
o
Direct 2'ellulose3
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Disperse 2)olyamide fibres3
?& /nternational Trade 'ommission has advocated the most popular classification of d yes. This system classifies dyes into +6 types, which are given below Group
!pplication
Direct
'otton, cellulosic and blended fibres
*at dyes
'otton, cellulosic and blended fibres
&ulphur
'otton, cellulosic fibre
#rganic pigments
'otton, cellulosic, blended fabric, paper
=eactive
'ellulosic fibre and fabric
Disperse dyes
&ynthetic fibres
!cid Dyes
0ool, silk, paper, synthetic fibres, leather
!(oic
)rinting /nks and )igments
%asic
&ilk, wool, cotton
Methods of Textile Dyeing
'olor is applied to fabric by different methods of dyeing for d ifferent types of fiber and at different stages of the textile production process. These methods include Direct dyeing, &tock dyeing, Top dyeing, Aarn dyeing, )iece dyeing, &olution pigmenting or dope dyeing, Barment dyeing etc. Textile materials are generally dyed using two processes. They are the following •
%atch Dyeing )rocess
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'ontinuous or &emi- 'ontinuous )rocess
The follo"ing chart gives a comparison bet"een batch dyeing and continuous dyeing
! natural or synthetic substance used to add a color or to change the color of something. Dyes are the coloring material that color commodities of our day to day use. Dyes are applied everywhere, from )lastic toys for children to that fabrics you wear, from food to woodC hardly there is any industry where dyes are not used commercially. ! dye is a colored substance that has an affinity to the substrate to which it is being applied. /t is an ionising and aromatic organic compounds. The d ye is generally applied in an a1ueous solution, and may re1uire a mordant to improve the fastness of the dye on the fiber. 0ith the help of dyes we can easily manipulate things according to our liking. !t the very basic level the use of color in identifying individual components of tissue sections can be accomplished primarily with dyes. Dyes are applied to nu merous substrates for example to textiles, leather, plastic, paper, food etc. The rule that we apply to other chemicals is similarly applicable to dyes also. They also get completely or atleast partially soluble in which it is being put to. For example certain kind of dyes can be toxic, carcinogenic or mutagenic and can be ha(ardous to health.
#volution of Dyes /t was in 6; %' when earliest written records of the use of dyestuffs were found in 'hina. The preparation and application of dyestuffs is one of the oldest forms of human activities. 8vidences of which were found by 8xcavation at archeological sites where ancient fabrics were unearthed. There is also mention of it in the %ible and other works of classical anti1uity. The real breakthroughs in the history of dyes came in +; when a teenager who was experimenting at his makeshift laboratory in home made a certain discovery that acted as a sort of launching pad for the modern chemicals industry. 0illiam )erkin an +-year-old student was working on chemical synthesis of natural products. /n a classic case of serendipity, the young 0illiam )erkin chanced upon his now famous E!niline MauveE dye while he was attempting to synthesi(e 1uinine, the only cure for malaria. )erkin named his color Mauveine, after the French name of non-fast color which was made of natural dyes. &o Mauve 2a basic dye3 was the first synthetic dye stuff. Mauve was a derivative of coal tar. /t was the first mass-produced dye, that was commercially available and the idea was born that a color could be made in the factory. /t was indeed a revolution.
$hat ma%es the Dyes colored & Dyes are basically ionising and aromatic compounds, they have 'hromophores present in them. Their structures have !ryl rings that has delocalised electron systems. These structures are said to be responsible for the absorption of electromagnetic radiation that has varying wavelengths,
based upon the energy of the electron clouds. 'homophores make the dyes proficient in their ability to absorb radiation. 'hromophores act by making energy changes in the delocalised electron cloud of the dye. This alteration invariably results in the compound absorbing radiation within the visible range of colors and not outside it. $uman eyes detects this absorption, and responds to the colors. 8lectrons may result in loss of color, their removal may cause the rest of the elec trons to revert to the local orbits. ! very good example is the &chiffEs reagent. !s &ulphurous acid reacts with )ararosanilin, what happens is that a &ulphonic group attaches itself to the compoundEs central carbon atom. This hampers the con>ugated double bond system of the 7uinoid ring, and causes the electrons to become localised. !s a conse1uence the ring ceases to be a 'hromophore. !s a result, the dye becomes colorless. To conclude chromophores are the atomic configurations which has delocalised electrons. Benerally they are represented as carbon, nitrogen, oxygen and sulphur. They can have alternate single and double bonds.
'o" can the color of the Dyes be altered & The color of the dyes are altered by the Modifiers. The 'olor modifiers of methyl or ethyl groups are responsible for any alteration in the dyesC they alter the energy in the delocalised electrons. There is a progressive alteration of color by adding a particular modifier. For example Methyl *iolet &eries. The follo"ing diagram explains "hat happens to the color of the dyes "hen modifiers are added( )tep ! : 0hen no methylgroup is added the original dye Pararosanil as it is called is red in colour.
)tep * : !s Four Methyl groups are added the reddish purple dye Methyl *iolet is obtained.
)tep C : 0ith the addition of more groups a purple blue dye 'rystal *iolet is obtained. /t has in it six such groups.
)tep D : Further addition of a seventh methyl group the dye that is obtained is called Methyl green.
$hat gives the Dyes )olubility and Cohesiveness & !uxochrome, the only substance responsible for providing solubility and cohesiveness to dyes. !n auxochrome is a group of atoms attached to a chromophore which modifies the ability of that chromophore to absorb light. 8xamples include the hydroxyl group 2-#$3, the amino group 2 "$63, and an aldehyde group 2-'$#3. The presence of an auxochrome in the chromogen molecule is essential to make a dye. $owever, if an auxochrome is present in the meta position to the chromophore, it does not affect the color. !uxochrome has the ability to intensify colors. /t is a group of atoms which attaches to nonionising compounds yet has the ability to ionise. !uxochromes are of two types, positively charged or negatively charged.
