Textile coloration, dyeing and printing of textile materials

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Wolkite University
College of Engineering and Technology
Textile Engineering Department
Textile coloration
By:
Gezu K.
2012

INTRODUCTION TO TEXTILE COLORATION

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Textilecolorationreferstotheprocessof
impartingcolortotextilematerials.
COLORATION DEFINED
DYEING
PRINTING
Onlycertainareaofthesubstrate
getscoloredbasedondesign
requirement.
Thewholesubstrategetsthe
colorbyimmersing intoa
solutionofthecolor.
Thetextilematerialmaybeinoneofseveralformssuchasfiber,
yarn,fabric,garment,etc.

DYES/PIGMENTS
Coloringmattersarerequiredtoprovidethedesiredcolorto
textilesubstrates
Thesesubstancesareknownasdyestuffsandpigments
Ingeneraldyes/pigmentsareorganicmolecules
Adyeissolubleintheapplicationmediaandis
substantivetothetextilesubstrate.
Apigmentisinsoluble&isnotsubstantivetothe
textilesubstratebinding[byadhesiveagent].
No interaction with fiber

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HistoricalDevelopment of Dyes
Dyedevelopment stages Driving forces
Natural dyes Poor substantivity & poor fastness
Use of mordant with natural dyes Long and difficult process
Indigo[Water insoluble pigment]Goodfastness but sill long process
First synthetic dye [Mauveine]Affinity for few fibers only &poor light fastness
Acid typeazo dyes Acid dyeing of wool andsilk
Direct substantive dyes Poor wet/wash fastness
Synthetic indigo vat dye Processdifficulty
Fiber reactive dyes Limited substantivity [Hydrophobic fibers]
Disperse dyes For hydrophobic fibers [method of application]
Dyes

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SUBSTANTIVITY AFFINITY
Coloredcompoundswhichareabsorbedbythefiberfromasolution
orsuspensionwheretheyaresubsequentlyfixed.

Colour and Constitution of dyes
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chromogen:chromogen:
achemicalcompoundthatiseithercolouredorcanbemadecolouredbythe
attachmentofsuitablesubstituents–thechromophoreandthe
auxochrome(s)arepartofthechromogen;
Chromophore (chromophoric group):Chromophore (chromophoric group):
Anorganiccompoundappearscolorduetothepresenceof
unsaturatedgroupsinit,suchgroupsarechromophores
responsiblefortheappearanceofcolor
alldyescontainedarylringsbearingunsaturatedgroupswhich
termed‘chromophores

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Some typical chromophores are,
Thecolourintensityincreaseswiththenumberof
chromophoresordegreeofconjugated.

Auxochrome:
a substituent group in a chromogen that influences its colour.
such as –OH or –NH–groups,
Thepresenceofauxochromsinthechromogenmoleculeis
essentialtomakeitadye
auxochromesare acidicsuch as carboxylic and sulphonicgroups
and in basicauxochromes includes amino and hydroxyl groups.

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Diazo groupDiazo group
Amino group
chromogen
chromophore
auxochroms
azobenzene
yellow 4,4′-diaminoazobenzene

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HISTORICALDEVELOPMENT OF DYES
Dyedevelopment stages Driving forces
Natural dyes Poor substantivity & poor fastness
Use of mordant with natural dyes Long and difficult process
Indigo[Water insoluble pigment]Goodfastness but sill long process
First synthetic dye [Mauveine]Affinity for few fibers only &poor light fastness
Acid typeazo dyes Acid dyeing of wool andsilk
Direct substantive dyes Poor wet/wash fastness
Synthetic indigo vat dye Processdifficulty
Fiber reactive dyes Limited substantivity [Hydrophobic fibers]
Disperse dyes For hydrophobic fibers [method of application]

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Scientific classificationbased on chemical structure
Example: Anthraquinone dyes, Azo dyes etc.
Technical classification based on dyeing properties
Example: Direct dyes, Acid dyes, Disperse dyes etc.
Commercialclassificationbasedonmanufacturers’aspects
[Brand names based on fastness, method of dyeing and so on]
Example:Indanthrene,Remazol,Procion,etc
CLASSICATION OF DYES

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BASICDYES
DISPERSEDYES
MORDANTDYES
METALCOMPLEXDYES
OTHERDYES*
[Sulphur,chromeetc]
CLASSIFICATION BASED ON DYEING PROPERTIES
DIRECTDYES
REACTIVEDYES
VATDYES
AZOICDYES
ACIDDYES

DYESELECTION
Type of fiber present
Form of textile material & degree of levelness
Fastness properties required
Dyeing method used
Availability of machinery
Customer color requirement
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Cost & Environment

Interaction ofmatter with light
Lightisaformofenergypropagatedathighspeedinthe
formofelectromagneticwaves.
Limitedrangeoftheelectromagneticwavedetectedbyhumaneye
Responseoflight:matterinteraction
ABSORBANCE REFLECTION
VISIBLE RANGE [400 –700nm]
COLOR & DYES

Colorisproducedduetoselectiveabsorptionofthe
visiblelight.Thereflectedportionofthevisiblelight
correspondstothecoloroftheobject.
ALL REFLECTED
ALL ABSORBED
WHITE
BLACK

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Wavelength (nm) Absorbed Light Reflected Light
400 -440 Violet Greenish-yellow
440 -480 Blue Yellow
480 -510 Blue-green Orange
510 -540 Green Red
540 -570 Yellowish-green Magenta
570 -580 Yellow Blue
580 -610 Orange Greenish-blue
610 -700 Red Blue-green
Colorsoftypicalspectralbandsandperceivedcolors
afterabsorptionbyamaterialviewedinwhitelight

Preparationofdyesolution[Dyeandauxiliarychemicals]
Applicationofthedye
Fixationofthedye
Aftertreatment
Batch
Continuous
DYEING METHODS
SALIENT FEATURES OF DYEING PROCESS
The stages/steps in dyeing process are:
EXHAUSTION
IMPREGNATION
Semi continuous

Padding and squeezing
Fixation [Batching , Steam or hot air ]
Rinsing
Drying
CONTINOUS DYEING
PADDER

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Semi Continuous
Thefabricisfirstpassedthoughwiththedye-liquor,thatiscalleda
paddingmachineorpaddingmangle.Thenitissubjectedtobatch
wisetreatmentinajigger
stored with a slow rotation for many hours
dyeing consists of
Pad-batch,at room temp.
Pad-roll at increased temp. by employing a heating chamber
This helps in fixation of the dyes on to the fiber
The dye is applied continuously by a padding.
The fixationand washingremains discontinuous

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BATCH DYEING
Discontinuoussystemofdyeing
Thedyebathisallowedtoexhaustbyprovidingthenecessarycondition
Dyefixationtakesplaceinthedyebath
CIRCULATINGLIQUOR IN A STATIONARY MATERIAL
MATERIAL MOVEMENT IN A STATIONARY LIQUOR
CIRCULATION OF BOTH LIQUOR AND MATERIAL
Three general types of BD machine

AFTERTREATMENT
Washing in detergent at or near the boil [Soaping]
Treatment with chemicals to improve fastness
Application of simple finishing chemicals
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DYEABILITY FACTORS
LIQUOR RATIO
DYE CHARCTERISTICS
DYEBATH ADDITIONS
DYEING CONDIIONS
FIBER CHRACTERISTICS CRYSTALLINITY & HYDROPHILICITY
STRUCTURE & DIFFUSEABILITY
TIME & TEMPERATURE
SALTS & OTHER AUXILARIES
TYPE OF MACHINE

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Exhaustion referstotheamountofdyetransferredfromdye-bathtothe
substrateinthedyeingprocess.

Co: initial concentration of dye in dye bath
Cs= concentration during the process
Dyefixationmeansthereactionbetweenthedyeandfibermolecules.
EXHAUSION AND FIXATION
E % =(Co –Cs)/Co * 100
PROCESS TERMINOLOGIES

COLOUR YIELD
DEPTH OF SHADE
Paleness or dullness of a given shade
Shade depth per a given amount of dye

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DYE MIGRATION
LEVELLING
Tendency of dye transfer from heavily dyed region
Uniformity of shade throughout the substrate

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FASTNESS
LIQUOR RATIO
Resistance to color change or color removal
Ratio of weight of material to volume of liquor
COMPATIBILITY
Dyes having same or similar rates of dyeing

THEORY OF
DYEING

Fundamental steps in dyeing
From molecular point of view dyeing process involves
•Transport of dye from dye bath to fiber
surface
•Adsorption on the surface of fiber
•Diffusion in the fiber interior
•Fixation of dye
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STUDIES ON THEORY OF DYEING
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THERMODYNAMIC APPROACH
KINETIC APPROACVH
Dyeing equilibrium
Rate of Dyeing

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Exhaustionofthedyeinsolutiontakesplaceindyeingprocess
Aftertheinitialincreaseinthedegreeofexhaustion,iteventuallybecomesconstant.
Nonettransferofdyefromsolutiontothefiber.Atthispointdyeingequilibriumisestablished.
DYEING EQUILIBRIUM
Subsidiaryequilibriaisestablishedbetweendyedissolvedinthe
bath&dyeadsorbedonfibersurface;betweendyedadsorbed&
dyediffusedinthefiber.
Nernst Isotherm
Langmuir Isotherm
Freundlich Isotherm
Inthecaseofdyeingequilibria,
themostcommonlyencountered
adsorptionisothermsarethe
partitionisotherm:

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Nernst Isotherm
Dye is equally divided betweensolution and fiber
whichistypicallydisplayedfor
theadsorptionofdisperse
dyesonhydrophobicfibers
suchasPES.

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Rapid sorption limited by accessibility of fiber surface sites
Freundlich Isotherm
theadsorptionofdirect
dyesoncottonandother
cellulosicfibers.

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Sorption limited by fixed number of adsorption sites
Langmuir Isotherm
theadsorptionofanionicdyes(e.g.
non-metallizedaciddyes)onwool,
silkandPAfibers,aswellasbasic
dyesonPANfibers.

AFFINITY
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TheattractionofthedyestofibersisgenerallyexpressedasAFFINITY.
Duringdyeingmasschangesoccurthatchangethermodynamicfunctions
Thechemicalpotentialisdefinedasthechangeinfreeenergyofa
systemthatoccurswhenthecompositionchangesbyaunitmolar
amountofsubstance,allothervariablessuchasthetemperature,
pressureandtheamountsofothercomponentsremainingconstant.
CHEMICAL POTENTIAL
µ = µ0+ RT ln (a)

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Inthecaseofdyeing,ifthechemicalpotentialofthedyeinsolutionishigher
thaninthefiber,thedyewilltransfertothefiber.
Thechemicalpotentialinsolutionfalls;thatinthefiberincreases.
Atequilibrium,thechemicalpotentialofthedyeinthefiberisequaltothe
chemicalpotentialofthedyeinthesolution.
Thestandardaffinityofadyeforafiberisdefinedasthedifferenceofthe
standardchemicalpotentialsofthedyeinthetwophases.

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Thestandardaffinityisthechangeinchemicalpotentialofdyewhenone
moleistransferredfromstandardstateinsolutiontostandardstateinthefiber.
Thestandardmolarfreeenergychangefordyeing
Enthalpy of dyeing [-ΔHo]
Entropy of dyeing [ΔSo]
Immobilization of dye in the fiber
MEASUREOFSTRENGTHOFDYE-FIBERBONDS

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EXOTHERMIC NATURE OF DYEING
Establishmentofequilibriuminvolvesdecreaseinthetotalfree
energy
Henceheatisgivenoutduringdyeing
Exothermicreactionsarefavoredatlowtemperatures

Fick'sLawofdiffusion:Therateoftransportofdye(dQ/dt)
acrossagivenareaisproportionaltoconcentrationgradient
RATE OF DYEING

•Therateofdyeingincreaseswithincreasingtemperature.
•Theequilibriumuptakeofdyedecreasesowingtothe
exothermicnatureofdyeadsorption.
Effect of Temperature on Dye Diffusion

MODELS OF DYE DIFFUSION
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FREE VOLUME

Cotton, flaxand CLY
Hydrophobic substrates such
as PES

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Rapid Dyeings @ shorter half dyeing time
HALF DYEING TIME
The time required for the exhaustion to reach half [50%] of is equilibrium value.

FACTORS ON RATE OF DYEING
Type/constructionofmaterial
Dyebathtemperature&pH
Typeofdye-bathadditions
Liquorratio
Degreeofagitation

DYE-FIBER INTERACTIONS
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Ionic links
Hydrogen bonds
Covalent bonds
Physical forces

Cellulosic dyeing
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Direct dye
Reactive dye
Vat/indigo dye
Sulphur dye

Dyeing of Cellulosic Textiles
Dyes for cellulosic fibers:
•CottonandothercellulosicfiberscanbedyedwithReactive,
Direct,Vat,Sulphur,Azoic,Phtalogen,PigmentandMordantdyes.
•Applicationmethods,dyeingcharacteristics,cost,fastness
propertiesandcolorrangearedifferforeachdye.
•Theyhavetheirownparticularadvantagesanddisadvantages.
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DIRECT DYEING

Dyeingprocesseswhichinvolveuseofdirectdyes
Directdyesaresocalleddirectbecausetheyareappliedtocellulosic
fibertextilesdirectlywithouttheneedforamordant.
TypicalcharacteristicsofDirectDyes
•Inherentsubstantivitytocottonandothercellulosics
•Donotrequiremordant,dyeingprocedureisquitesimple.
•Directdyesareanionicinnature
•Theiraqueoussolutionsdyecottonusuallyinthepresenceofan
electrolytesuchasNaClorNa2SO4.
•Generallythesedyesarewatersoluble
•Relativelyinexpensive,availableinafullrangeofhuesbutnotnoted
(known)fortheircolorbrilliance.
Introduction

•Directdyesusuallyhavelinearlongcoplanarmolecular
structure
•Sulphonatedazodyesconstitutethepredominantgroupof
directdyes
•Theirmajordrawbackistheirpoortomoderatefastnessto
washing.
•Varioustreatmentstoimprovefastness
•DyeSolubilitydependson
Numberofsolublizinggroups,
Molecularweightand
temperatureofdyeing
After treatment
Solubilizinggroup

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Bybringingdyebathtoboilgraduallyandholdingatboil
whilstthedyediffusesintothefiber.
Inabsenceofelectrolytesomedirectdyeswillnotdye
celluloseatall.
Usuallyappliedwiththeadditionofelectrolyteatornearthe
boil.
Dyeingwithdirectdyesiscarriedoutinneutralsolution
Simpledyeingprocedure
Requirementofsoftwaterforsomedirectdyesduring
application
Applicationofdirectdyestocellulose

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CLASSIFICATION OF DIRECT DYES
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CHEMICAL STRUCTURE OF CHROMOPHORE
DIRECT AZOIC DYES
DIRECT THIAZOLIC DYES
Classificationbasedonchemicalstructureisnotsignificantforthe
dyerbecausedyeswithsimilarconstitutioncanhavequitedifferent
applicationandfastnessproperties.

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DYEING PROPERTIES [EQUALIZING]
Class A: Self leveling
Class B: Average leveling
Class C: Poor leveling
ThemostcommonclassificationofdirectdyesisthatoftheSocietyof
DyersandColorists(SDC),basedontheirlevellingabilityandtheir
responsetoincreaseinthedyeingtemperatureandtoaddedsaltduring
exhaustdyeing.

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Class A: Self leveling
Lowmolecularweight=>mono-andbis-azodyeswithseveral
anionicsulphonategroupspermolecule.
Goodmigration,eveninthepresenceofsalt.
Severalsulphonatedgroupspermolecule
Goodsolubilityandnoaggregation
Lowsubstanivity
Largeamountofsaltforexhaustion

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Dyeingisstartedat50°Cinthepresenceofaddedsalt,
thebathheatedtotheboilover30–40min,anddyeing
continuedattheboilforuptoanhour.
Severalfurthersaltadditions,ofincreasingsize,are
requiredtopromoteexhaustion,thetotalamountofsalt
(5–20%owfNaCl)dependinguponthedepthofshade
andtheliquorratio.

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Class B: Salt Controllable
MolecularweighthigherthanClassA
LowersulphonatedgroupsthanClassAdyes
Mediumsolubilityanddegreeofaggregation
Lowtomoderatesubstanivity[Absenceofsalt]
Saltsensitive&exhaustwellwithsaltaddition

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Class C: Temperature controllable
Highmolecularweight
Fewsulphonatedgroupspermolecule
Lesssolubilityandhighdegreeofaggregation
Highsubstantivity
Verysensitivetosaltaddition
Levelingbycontroloftemperature&levelingagents

TYPE MIGRATION LEVELING FASTNESS
Class A Good Self leveling Low
Class B Medium Medium levelingModerate
Class C Poor Poor leveling High
AdditionalClassificationParameters:
Further treatment, continuous dyeing, high temperature dyeing
COMPARISON OF DIRECT DYES

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DIRECT DYE SUBSTANTIVITY FOR CELLULOSE
Long,coplanardyemoleculescansitontopofacellulose
polymerchainwiththearomaticringsparalleltotheglucose
rings.
Possibilityofhydrogenbondformation
Vanderwallsandothersecondaryforcesofinteraction

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Theirlongflat(coplanar)structureenablesthemtoliealonga
cellulosechaininregisterwithhydroxylgroupsandresultsin
effectivevanderwaalsforces.

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Dyeing methods
Theselectionofspecificdirectdyesfordyeingcellulosic
fibresdependson
Theirdyeingproperties,
Theparticularfastnessrequirements,
Anyaftertreatmentsusedtoimprovethe
washingfastness,and
Theparticularfinishingprocessesinvolved.

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AtypicaldyeingprocessforaClassBdirectdyeoncotton
EXHAUST DYEING

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Immerse the
wetted fabric
NaCl NaCl
40
o
C
100
o
C
35 min
25min 35min

Salient Features of Batch Dyeing
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Solutionpreparationstartswithsmalldyepastetowhichisadded
sufficienthotwaterfordissolution
Wettingagentassistpenetrationandleveldyeing
Depthenhancementbycontrollingsaltaddition&temperature
Examples
Hankandpackagedyeingforcottonyarns
Jiggerforwovenfabrics
Winchforknittedfabrics

PAD DYEING
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Majorpaddyeingoperation s:
Paddyeingmethodsareonlyusedonfabrics
Padwithdyesolution,padwithsaltbathandroll
Padwithdyesolution,dry,padwithsaltsolutionandsteam
Padwithsalt,padwet-on-wetwithdyesolutionandsteam
Dyes with less strike rates are preferable.
Migration of Class A during steaming/drying & very rapid strike
by Class C dyes
Class B dyes are better choice for continuous dyeing
Less Suitable for continuous dyeing

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FACTORS AFFECTING DIRECT DYEING
EFFECT OF SALT
Celluloseimmersedinwaterdevelopsanegativesurface
potential
Repulsionbetweennegativechargeofcellulosesurface&anionic
dyemolecule
Theaddedsaltprovidessodiumionstocounteractthenegative
surfacepotentialofthewetcotton
Henceincreaseinexhaustionofdirectdyes
Commercialdirectdyesalreadycontainmuchelectrolyte.

Thenatureoftheanionoftheaddedelectrolytehaslittle
influenceontheamountofadsorbeddye.
Therefore,NaClandNa2SO4,atthesametotalsodiumion
concentration,haveaboutthesameinfluence.
Ahigherpositivechargeonthecationpromotesincreased
adsorptionbecausemetalionscounteractthenegativesurface
potentialmoreeffectively,thusdecreasingtherepulsionof
approachingdyeanions.
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B is more salt sensitive than A

EFFECT OF TEMPERAURE
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•Temperatureincreasesdyemigrationandrateofdyeing.
•Equilibriumexhaustiondecreaseasdyeingtemperature
increases
DYE DEAGGREGATION
RATE OF DYEING
EXHUASTION

Thesediversevariationsofdirectdyeexhaustiondependontwo
opposinginfluencesoftheincreasingdyeingtemperature.
1.Thesearetheusualeffectofincreasingtemperaturedecreasingthe
dyebathexhaustionbecausedyeingisexothermic,andits
enhancementofthedyeingrateparticularlyatlowertemperatures.
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2.Increasingtemperaturealsopromotesdyede-aggregationinthe
dyeingsolutionliberatingmoreindividualdyemoleculestoenterthe
fibre.
ThedyesCIDirectYellow12,DirectRed81andDirectYellow28have
maximumexhaustionat30°C(a),60°C(b)and100°C(c),
Respectively.
Forexample,openjigdyeingmachinescannotachievedyeing
temperaturesmuchabove85°C.
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GreaternegativepotentialunderalkalinepHandretardation
Increasing dissociation of a number of cellulose hydroxyl groups
Oxycellulose(overbleaching)presencereductioninexhaustion
anddepth Higherproportionofcarboxylgroups
Alkalinereductionofazoicdyesreducingcoloryield
Acidbathsspeciallystrongacidnotsuitable
[Cellulose Damage]
DyeingofcottonwithdirectdyesatneuralpH
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EFFECT OF DYEING PH
Reduce exhaustion
Carboxylate ions repel the dye anions of like charge.

EFFECT OF LIQUOR RATIO
Lowerliquorratioenhancesexhaustionforsubstantivedyes
Dyeingatlowliquorratio
Decreasestheamountofwastedyeinthe
effluent.
Consumeslesswaterandsteam,and
Allowsagivensaltconcentrationwithless
addedsalt.

Inhibittheformationoflargeraggregatesandincreasethe
proportionofdyeinthemonomolecularform.Hencesolubilisation
isincreased.
EFFECT OF SURFACTANT
TIME OF DYEING
Theproductionoflevelandwell-penetrateddyeingsisusually
favoredbyanincreasedtimeofdyeing,althoughprolongeddyeing
atboilsometimesresultsinthedecompositionofdirectdyes.

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DIRECT DYEING OF DIFFERENT CELLULOSIC FIBERS
COTTON< MERCERIZED COTTON < LINEN < VISCOSE RAYON
Dyeingofblendsofthesecellulosefibreswithdirectdyes,theydonot
absorbdyesatthesamerateortothesameextentbecauseofthe
differencesintheirmorphology.
Withdyesoflowsubstantivity,nepsusuallyabsorblessdyeand
appearaspalerspotsonthefabric.Sinceimmaturefibresgivemuch
greaterratesofdyedesorption,thepalerdyednepsmaynotappearuntil
afterwashing.
Improvedbymercerizationbeforedyeingswellsthe
immaturefibres
Therateofdyeingincreasesasthediameterofafibredecreases

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Directdyeshavehighersubstantivityforregularviscosethanforcotton
becauseviscoseislesscrystallineandorientedsoithasamuchgreater
internalsurface.
Itismoreaccessiblethanregularcotton
Mercerizedcottonwillabsorbmoredyeandbedarkerincolorthan
normalcottondyedinthesamebath.

HIGH TEMPERATURE DYEING
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Conventionaldirectdyeingprocess@boil
Hightemperaturedyeingupto130C
Reductivecleavageathighertemperature
Decompositionofdirectdyes
REDUCTION OF DYES USED IN STRIPPING & DISCHARGE PRINTING
POOR WET/WASH FASTNESS

AFTERTREATMENT OF DYEINGS WITH DIRECT DYES
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Aftertreatmentiscarriedouttoimprovewashingfastness
Basicprincipleinvolvedisincreasingthedye’smolecularweight
Adsorbeddyebecomesinsolublized&haslowdiffusioncoefficient
Impactonhueandlightfastness
Aftertreatmentsaredifficultandcostlytocarryout
Replacementsofdirectdyestodayreduceuseofaftertreatment
Reactive dye

AFTERTREATMENTS IN DIRECT DYEING
•Metal complex formation
•Aftertreatment with formaldehyde
•Use of cationic fixatives
•Based on resin crosslinkks
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METAL COMPLEX FORMATION
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Treatmentwithacidiccoppersluphatesolutionfortheformation
ofacomplexbetweencopperandadsorbeddye

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FORMALDEHYDE TREATMENT
Basedonformationofmethylenebridgebetweenadsorbed
directdyemolecules

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TREATMENT WITH CATIONIC FIXATIVES
Cationicagentsofrelativelyhighmolecularweightformwater-
insolublesaltlikemoleculewithanionicdirectdye.
Precipitationofanionicdyesinthecottonwithacationicsurfactant
orpolymerinwarmwater
Basedonadditionofcrosslinkingagentsusedforeasycare
finishing
Directdyedcelluloseiscrosslinkedusingcrosslinkingagents
Surfacedyeshavelesstendencyofmovement
Washfastnessisimprovedduetostronganchoringeffect
RESIN TREATMENT
Reduce the fastness
lightThe change in hue is only slight
Decreasethelightfastnessandgiveahuechange.
Amino resins

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Ionicbondsinvolvetheattractionbetweenoppositelycharged
chemicalgroupsonthedyeandfibre.
Example

REACTIVE DYEING

INTRODUCTION
•Poorwashingfastnessbecauseonlyweakpolaranddispersion
forcesbindthedyemoleculestothecellulosepolymerchains.
•Weakerforcesofinteraction(Hydrogenandphysicalbond)
[Dye–fiber]
Immobilizingdyemoleculebycovalentbondformationwith
reactivegroupsinfiber
Easily diffuse out of the cotton
during washing.
Adyewhichiscapableofreactingchemicallywithasubstrateto
formacovalentdyesubstratelinkage
Direct dye
Reactive dye

Cont. …
A
L
K
A
L
I
N
E
Mild
Theroleofthealkaliistocauseacidicdissociationofsomeofthe
hydroxylgroupsinthecellulose,anditisthecellulosateion(Cell–O–)
thatreactswiththedye.
Reactive chlorine atom on the triazine ring
Anionicandwatersolublelikedirectdye

Simplemolecularstructure&lowsubstantivity
Highdegreeofwashfastness
Brightshade
Completecolorgamut/widecolorrange
Relativelysimpledyeingprocedure[noredoxsystem]
Versatileinapplication[bothbath&continuous]
Characteristics of Reactive Dyes

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STRUCTUREOF REACTIVE DYES
Solubilizinggroup(S)
Chromophore(C)
Bridgegroup(B)
Reactivegroup(RG)withaleavinggroup(X)attachedtoit
≥1 sulphonic acid substituents
Reacts with Cell-OH
Color + Substantivity
Links R with C

Thereactivegroupmustexhibitadequatereactivitytowardscotton,
butbeoflowerreactivitytowardswaterthatcandeactivateitby
hydrolysis.
Thedye–fibrebond,onceformed,shouldhaveadequatestabilityto
withstandrepeatedwashing.

THE REACTIVE SYSTEM
TRIAZINYL RING VINYL SULPHONE
Reactivedyeslooklikedirect,butwithaddedreactivegroup
Anionicandwatersolublelikedirectdyes
NH

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MECHANISM OF DYEING WITH REACTIVE DYES
Reactivegroupsareoftwomaintypes
1.Thosereactingwithcellulosebynucleophilicsubstitutionoflabile
leavinggroupssuchaschlorine,fluorine,methylsulphoneor
nicotinylleavinggroupactivatedbyanadjacentnitrogenatomina
heterocyclicring

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Innucleophilicsubstitution,amobilehalogenatomofthedyeis
substitutedbytheionizednucleophilicoxygengroupofthecellulose
(Cell-O).

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2.Reactionwithcellulosebynucleophilicadditiontoacarbon–
carbondoublebond,activatedbyanadjacentelectron-attracting
sulphonegroup.
Thevinylsulphonegroupisusuallygeneratedbyeliminationof
sulphateionfromsulphatoethylsulphonewithalkali.
CELLULOSE ETHER FORMATION

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Covalent bond formation
Innucleophilicaddition,aprotonandtheionizedoxygengroup
ofthecelluloseareaddedtotheactivegroupofthedye.
Thebest-knowndyesofthisgroup–thevinylsulphones–carrya
protectivegroup,whichiseliminatedevenatafairlylowpHand
setsthereactivegroupfreeduringdyeing.

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Dyed sample
Hydrolysis

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BasisofClassification
Basedonchemicalstructure
Basedondyeingproperty
Commercial–Manufactureraspectofbrandname
CLASSIFICATIONOF REACTIVE DYES

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[AZO & ANTHRAQUINONE]
MONOFUNCTIONAL BIFUNCTIONAL
HOMOBIFUNCTIONAL
HETROBIFUNCTIONAL
REACTIVE GROUP
CHROMOPHORE GROUP
Basedonchemicalstructure
POLY-FUNCTIONAL

Monofunctional Reactive Dyes
Presenceofreactivegroup(oneortwo)atasinglelocationondye
molecule
Reactivedyesdevelopedatearlystagesweremono-functionaltypical
examplesare
Mono-chlorotriazine
Di-chlorotriazine(tworeactivegroupslocatedonthesame
triazinering)
Vinylsulphone

DICHLOROTRIAZINYL [DCT]
Monofunctional Reactive Dyes
MONOCHLOROTRIAZINYL [MCT]
VINYLSULPHONE [VS]
No separation of reactive groups
from each other
Reactive group attached to a single
Chromophore

107
DCT
MCT
VS
Low reactivity
Medium reactivity
Highreactivity

108
Other Monofunctional Reactive Dyes

BIFUNCTIONAL REACTIVE DYES
•Presenceoftworeactivegroupsofsametype(monoordichloro
triazine)ordifferenttypes(monochlorotriazineandvinylsulphone).
•Attwodifferentlocationsinthedyemolecule.
•Showhighexhaustion,highfixation
•Bettercoloryield
•Reducedpollution:lessdyeineffluent
•Verypopularforexhaustdyeing.
•Highexhaustionisduetohighmolecularweightsimilartodirect
dyes,highaffinitytocotton
•Reactwithcellulosewithcrosslinkformation.

BIFUNCTIONAL REACTIVE DYES
BIS(AMINOCHLOROTRIAZINYL )
AMINOCHLOROTRIAZINE -SULPHATOETHYLSULPHONE

111
BIS(SULPHATOETHYLSULPHONE )
Homobifunctional Reactive Dyes
Consist of two similar reactive groups

112
Reactive Dye Reactivity
Differentreactivegroupsofreactivedyesshowawiderangeofreactivity
Themorereactivethedyesthelessweakerthealkalirequiredand
Thelowerthereactivityofreactivegroupofthedyetowardsthealkaline
cellulose,thehigherthefinaldyeingtemperaturerequired.

113
DYE REACTIVITY DYEING TEMP. pH
DCT
HIGH
20 -40
Weak alkali (NaHCO3
or Na2CO3)
MCT
LOW
80 -85
Strongalkali
(Na2CO3 or NaOH)
MFT
MODERATE
40 -60
Moderatelyalkaline
VS
MODERATE 40 -60 Moderatelyalkaline
NT*
MODERATE TO HIGH
100 -130
Neutral
ALKALISUSED: Sodium bicarbonate, sodium carbonate & sodium hydroxide/Sodium silicate

CLASSIFICATION BASED ON DYEING PROPERTY
114
Alkalicontrollablereactivedyes
Saltcontrollablereactivedyes
Temperaturecontrollablereactivedyes
On the basis of dyeing temperature
COLD BRAND, WARM BRAND & HOT BRAND

ALKALI-CONTROLLABLE REACTIVE DYES
Havehighreactivityandonlymoderatesubstantivity
Appliedatrelativelylowtemperatures
Leveldyeingrequirescarefulcontroloftheadditionofalkali
Examples:DCT,DFCPandVS

Thesearedyesofrelativelylowreactivity
Theyhaveappreciablesubstantivity
Dyeingtemperatureashighas85°C
Requirescarefuladditionofsalt
Examples:MCTandMFT
SALT-CONTROLLABLE REACTIVE DYES

117
•Attemperaturesabovetheboilintheabsenceofalkali
•Noauxiliaryproductadditionindyebath
•Controloverrateoftemperaturerise
Examples:NTreactivedyes
TEMPERAURE-CONTROLLABLE REACTIVE DYES

Cold BRAND dyes -fixation temperature of 30-40°C
 Warm BRAND dyes -fixation temperature of 50-80°C
Hot BRAND dyes-fixation temperature of > 80°C
•Lowersubstantivitydyesdiffuseeasilyintofibersandareeasyto
washoutunfixeddyesbutlessexhaustion.
•Highersubstantivedyesgivehigherbathexhaustion,better
reactionwithfiber,butgreaterdifficultyofremovingunfixeddye

120
Reactivedyesinamixtureshouldallexhaustandreactwiththe
fiberataboutthesamerate.
Dyeswithdifferentreactivegroupsanddifferentsubstantivityare
available
Mixdyeswithsametypeofreactivegrouphavingthesame
substantivity.
Compatibledyeingbehaviourisafunctionofalltheprocess
variablesandrequirescarefulcontrolofthedyeingparameters.
Dyeing compatibility of reactive dyes
Ideally
Different dyeing characteristics and reactivities.
Requirescarefulcontrolofthedyeingtemperature,saltandalkali
concentrations,thedyeingtimeandtheliquorratio.

PROBLEMS IN DYEING WIH REACTIVE
DYES
Hydrolysis[particularlyforhighreactivityseries,e.g.DCT]
Lowleveloffixationwhendyeingusingahighliquorratio
Appreciabledyeconcentrationsinthedyehouseeffluent
Highsaltconcentrationsarealsopresent
Less than 70% of the original dye reacts with the fibre.
For exhaustion

122
Precipitationorinsolublizationbymetalionsinwatersupply
Freechlorinehydrolyzeanddye-fiberbondbreakage
Unreactedchlorineatomsinthedye’sreactivegroupmayhydrolyze
underwarmhumidstorageconditions,liberatingHCl.
Catalyzesthehydrolysisofthedye–fibrebond.
Calcium,magnesiumorheavymetalions

INITIAL EXHAUSTION [NEUTRAL PHASE]
123
Dyeingisstartedinneutralaqueous-littlelikelihoodofdye-fiber
reaction-capableofmigrationtopromoteleveldyeing
Salt/neutralelectrolyteisaddedgraduallytopromoteexhaustion
(higherconc.Comparedtodirectdyeing).
Temperatureisgraduallyincreasedtoaidpenetrationofdyeassist
migration;
Dyeabsorptiondependinguponsubstantivity
STAGES INREACTIVE DYEING PROCESS

124
FIXATION (REACTION) [ALKALINE PHASE]
FixationatalkalinepH
Alkalifacilitatesdissociationofcellulosehydroxylgroups;
Nucleophiliccellulosateionsbegintoreactwiththedye.
Fixationofdyesresultsinadditionaldyeabsorption,re-establishes
dyeingequilibrium.
Dyeabsorptionfromsolutionandreactionwiththefiberthen
progressuntilnofurtherdyeistakenup.

AFTERTREATMENT [POST –DYEING WASHING]
125
Unfixedandhydrolyzeddyeoncotton
Residualalkaliandsalt
Asmuchaspossibleunfixeddyemustbewashedoutofthe
dyeing
Ifnot,desorptionofthisdyeduringwashingbytheconsumercan
causestainingofothermaterialsinwash.
I.Successiverinsinginwarmwater
II.Thoroughwashingusingaboilingdetergentsolution(soaping)
III.FinalrinsinginwarmwaterthencoldwashDRYING

REACTIVE DYEING METHODS
126
Both exhaustion and padding methods canbe used
JIGGER
WINCH
PAD-BATCH
PAD-DRY
PAD-STEAM
SOFT WATER

Levelwell-penetrateddyeing'srequirecarefulpreparationofthe
material.
Materialavailablefordyeinginneutral,uniform&readily
absorbent
Residualsizemustalwaysberemovedfromwovengoodsbecause
oftheriskofdyewastagebyreactionwithhydroxylgroupsinsize
PREPARATION

128
ALKALI/SALT/SEQUESTERANT/WETTING AGENTS
Alltracesofresidualchlorineorperoxycompoundsmust
beremovedpriortodyeing,otherwiselossofreactivityand
destructionofdye
Variationincoveringabilityofnepsofimmaturecotton
needforeffectivemercerizationorcausticization

129
BATCHDYEING
Alkaline

130

131
a=dyeindyebath
b=hydrolyseddyeonthefiber
c=fixeddye
d=dyetobewashedout

ProblemsEncounteredincontinuousdyeing
(1)Dyesoflowsubstantivityaredesirabletoavoidpreferentialdye
absorptionduringpaddingandtheinitialcolortailingthatit
causes.
(2)Highdyeconcentrationfordeepshadesthatmayexceed
limitingsolubilityofdye[useofureafordisaggregation]
CONTINUOUS DYEING
Veryrapidfixation(<60s)athightemperaturesthatispossiblein
fullycontinuousdyeinggiveshighproductivityforlongrunsofa
givencolor.
Tailing is shade variation along the length of the fabric
Urea helps to break up dye aggregates

3]whenusingpre-preparedalkalinesolutionsofreactivedyes
Stability of dye/alkaline mixture
[hydrolysis dye’s reactive group in pad bath will result in a loss of
fixed color.]
[Pad –dry –Pad]
4)Migrationcontrolandheatinguniformity
[Anti-migrant]
(5)Finalrinsingandsoapingofgoodsdyed@highspeedwithless
timeofcontact
salt as an anti-migrant and also a thickening agent
such as sodium alginate
Counter current washing

134
Thelowerlimitofliquorratioinbatchwisedyeingisabout5:1.
Paddingmethodsextendthisfurthertotherange1:1to0.5:1.
Enhanced exhaustion and fixation
ADVANTAGE
DYE SELECTION
Excellent solubility
moderate substantivity, and
versatile reactivity

135
Single-padsequence:dyeandalkaliareappliedtogether
Double-padsequence:dyeandalkaliarepaddedseparately,
withorwithoutanintermediatedryingstep.
Padding
PAD –DRY –WASH
PAD –BATCH -WASH
PAD –DRY –BAKE -WASH
PAD –DRY –STEAM -WASH
PAD –DRY –PAD -BATCH –WASH
PAD –DRY –PAD -STEAM -WASH
PAD –DRY –PAD -WASH
SINGLE PAD DOUBLE PAD

1.Impregnationofthewell-prepareddryfabricinasolution
ofdyeandalkaliatambienttemperature
A4:1dye-to-alkalisolutionvolumeratioisverycommon.
Thedyeandalkalisolutionsareusuallymixedjustbefore
paddingusingmeteringpumpstomaintainthecorrect
ratio.
2.Uniformsqueezingofsurplusliquorfromthefabricasit
passesthroughthemanglenip.
PAD –BATCH DYEING
1000 –10000m
CPB[Cold PadBatch]

137
3.Wrappingofthebatchedrollofwetfabricinpolythenefilm
4.Washing-off
5.Drying
SLOW ROTATION
Cost Reduction Scheme
To avoid drainage of the internal liquid within the batch.
Storageatambienttemperatureforaspecifieddwelltime(2–
24h),dependingondyereactivityandpH)
The more reactive dyes give effective fixation within 2–6 h.

138
PAD–HEAT/DRY DYEING
Suitableforreactivedyeswithfairlyhighreactivity.
Thefabricisfirstpaddedwithadyesolutioncontainingsodium
bicarbonate.
Duringdrying,bicarbonateisconvertedintocarbonate,whichgives
ahigherpHandmoreeffectivefixation
Thedyesolutionalsocontainsahighconcentrationofurea(100
g/l).
Retain water during drying
Increases dye solubility
Pollution problem
Nutrients for algal growth

139
PAD –STEAM DYEING
Inthisprocess,goodsarepaddedwithasolutioncontainingreactive
dyes,saltandappropriatealkali.
Hothumidconditionsduringsteamingtendtocauseexcessive
hydrolysisofreactivegroupandlowercoloryield.
Two-stagewet-on-wetpaddingisusedtoavoidanintermediate
dryingstep.
Sufficientpickupandminimumcolorbleedingmustbeensured
During dyeing of terry towel and other pile fabrics
Selecteddyesaresuitableandthe
manufacturer’srecommendationsshould
befollowed.

140
Thedyesolutionisquitestable,becausethereisnoalkali
Anti-migrantshelptominimizemigrationduringinitialdrying
Intermediatedryingensuresuniform&highpick-upofchemical
solution&minimizesbleedingofdye
Sodiumhydroxideisthepreferredalkali
Pad–dry–pad–steam
Thefabricispaddedwithaneutralsolutionofthereactivedyes,
driedandthenpaddedwiththealkalisolutioncontainingsalt
beforesteaming

141
TEMPERATURE/TIME
FACTORS AFFECTING REACTIVE DYEING
PH [ALKALI]
SALT & OTHER AUXILARY
MLR

142
Dyeingtemperatureischosenbasedonreactivity
Timedependingonexhaustionandleveling
Selectionofalkalibasedonreactivity&easeofhydrolysis
Effectofsaltissimilartodirectdyeingprocess
Largeramountofsaltduetolowmolecularweightandlarge
numberofsulphonicgroupsperreactivedyemolecule
SelectionofMLRconsideringtendencyofhydrolysisand
solubility

143
Itisnotusualtoexceedadye-bathpHof11:Hydrolysis.
Forpolysulphonateddyes,oneeffectofdyeingatpHabove11isthe
decreaseinsubstantivityofthedyefortheincreasinglyanionic
dissociatedcellulose.
Somedyesactuallydesorbfromthefiberintothedye-bathwhenthe
alkaliisaddedatthestartofthefixationstagegivingasudden
decreaseinthedegreeofexhaustion.
LARGE AMOUNT OF SALT
Longer LR m/c ---dyes of higher substantivity are preferred

144
Viscosefibersgivehigherfixationandexhaustionof
reactivedyesthancotton.
Foridenticalconditions,exhaustionandfixation
increaseintheorder:
COTTON, MERCERISED COTTON, VISCOSE.
Becauseoftheeaseofswellingofviscose,thedyeingpHand
temperatureforagivendyeisdifferentthanforcotton

145
Dyeingsareresistanttocolorstrippingwithhotaqueous
pyridine,asolventthatremovesdirectdyesfromcotton.
Dyeingsofcottonobtainedwithbifunctionaldyesexhibit
reducedswellinganddecreasedsolubilityincuprammonium
EVIDENCE FOR COVALENT BOND FORMATION
Thegoodfastnesstowashingofdyeing'swithreactivedyeson
cellulosicfibresisaconsequenceofthestablecovalentbond
formedbetweenthedye’sreactivegroupandthecellulose
polymer.

146
VAT DYE
Gezu K.
2019

Introduction
Vatdyesareoneoftheoldesttypesandwaterinsolubledyes.
Vatdyes‐aseriesofdyesofdifferentchemicalconstitution…containtwoor
moreketo(C=O)groups
Theyarecalleddyesbecause:
i.Chemicalreductionintoawater-solubleleucoform
ii.Substantivityinleucoformforcotton

Insolubleinwater
Havebestoverallfastnessproperties...oftenusedforfabricsthatwillbe
subjectedtoseverewashingandbleachingconditions(toweling,industrialand
militaryuniforms)
Notbrightcolors
Nosubstantivityforcellulose
Havealimitationwithregardstouseofstronglyalkalinesolutions
Mostlycomplexdyestructureswithnoionicgroups
CHARACTERISTICS OF VAT DYES

Cont. …
Vatdyesareusedpredominantlyfordyeingcellulosicfibers.
Althoughleucodyeshavesubstantivityforwoolandnylon,technicalreasons
(damageinwoolandpoorfastnessonnylon)vatdyeapplicationisrestrictedto
celluloseonly.
Thevatpigmentandtheleucocompoundoftenhavequitedifferentcolors
Theprimitivecolorisdevelopedbysubsequentoxidation

Characterizedbycontainingattwoormoreketogroup[C=O]
Mostly complex dye structures with no ionic groups
ChemicalCharacteristics

MECHANISM OF DYEING WITH VAT DYES
Convertingawater-insolubleketo-substitutedcolorantby
reductiontoawater-solubleleucocompound.
Thispenetratesintothefiber,whereitisreoxidisedbacktothe
originalinsolubleform.
Fixationbasedonsecondaryforcesandinsolublization

Theprocessofreductionofvatdyeinaqueousalkalinesolutionisknownas
VATTING.
Sodiumdithionite[sodiumhydrosulphiteorhydros]isusedasreducingagentand
causticsodaasalkali.
Hydrosisaverystrongreducingagent,moreeffectiveathighpHandathigher
concentration.
Controloverconcentration&temperatureforoptimumreduction
Rateofreductiondependsonpigmentdispersion
DISPERSIONSTABILITYFORPROPERREDUCTION
Theprocessofreductionofvatdyeinaqueousalkalinesolutionisknownas
VATTING.
Sodiumdithionite[sodiumhydrosulphiteorhydros]isusedasreducingagentand
causticsodaasalkali.
Hydrosisaverystrongreducingagent,moreeffectiveathighpHandathigher
concentration.
Controloverconcentration&temperatureforoptimumreduction
Rateofreductiondependsonpigmentdispersion
DISPERSIONSTABILITYFORPROPERREDUCTION
Na
2
S
2
O
4
& NaOH

CLASSIFICATIONOFVATDYES
Basedonchemicalstructure
Methodofapplication

Indigo
Anthraquinonoidvatdyes:Basedon
anthraquinonewhichgiveleucocompoundsof
relativelyhighaffinity
Based on chemical structure
a)Dyesderivedfromindigo–bothnaturalandsynthetic
Anthraquinon
e
Indigoidvatdyes:Derivativesofindigowhichgiveleuco
compoundsofrelativelylowaffinity
b) Dyes derived from anthraquinone –most
of vat dyes
Indigodyesgivemorebrilliantcolorsthan
anthraquinoneButtheirlightandwashfastnessare
notasgood

Classification Based on Application/dyeing properties
IN[INDANTHRENE NORMAL]
IW[INDANTHRENE WARM]
IK[INDANTHRENE COLD{KALT}]

UseofconcentratedNaOH
Havehighmolecularweight
Highvattingtemperatures(60°C)
Highdyeingtemperatures(60°C)
Highsubstantivity
Nosaltadditiontothedyebath
THE IN (INDANTHRENE NORMAL)

IW [INDANTHRENE WARM] DYES
ModerateconcentrationofNaOH
LowervattingtemperaturethanINdyes(50°C)
LowerdyeingtemperaturesthanINdyes(50°C)
Moderatesubstantivity
Someamountofsaltadditiontoaidexhaustion

IK[INDANTHRENE COLD {KALT}] DYES
LowconcentrationofNaOH
Lowervattingtemperature(40°C)
Dyeingatroomtemperature(20°C).
Poorsubstantivity
Considerableamountofsaltadditionforgoodexhaustion

Thevattingtemperatureisoftenhigherthanthesubsequentdyeingtemperature.
Toavoiddecompositionofhydrosanddecreasestheriskofover-reduction

1)Reductionofthepigmenttothesolubleleucocompound
2)Absorptionoftheleucocompoundbythecottonduringdyeing
3)Oxidationoftheabsorbedleucocompoundinthecotton,reformingthe
insolublepigmentinsidethefibers.
4)Soapingtoremovepigmentlooselyadheringtothefibersurfacesandtodevelop
thetrueshadeandfastnessproperties
Key Steps in Vat Dyeing Of Cotton
Air Oxidation Or Chemical Oxidants
Recrystallization/Aggregation
Preparationofthevatcontainingtheleucoformsofthedyes
Water-solubleleucocompound

Application of Vat Dyes on Cellulose
i.Reduction of pigment to soluble leuco compound, a process called vatting;
Converting a water-insoluble keto-substituted colorant by reduction to a water-
soluble enolate leuco compound.
ii.Absorption of leuco compound by cotton; water-soluble enolate leuco
penetrates into the fiber, where it is reoxidised back to the original insoluble
form.
iii.Fixation based on secondary forces and insolublization. Oxidation of absorbed
leuco compound in cotton, reforming insoluble pigment inside the fibers.

Themostimportantreducingagentin
vatdyeingissodiumdithionite
(Na2S2O4),referredtoas
hydrosulphiteorhydros.
ReductionofVatdyes
Vatdyesareavailableasfinepowdersorgrains,
andasliquiddispersionsorpastes.
Theinsolublepigmentisextensivelymilledwith
dispersantssuchassodiumligno-sulphonatesto
produceverysmallparticles
InthepresenceofNaOH-alkali

Controloverconcentrations&temperatureforoptimumreduction
Rateofreductiondependsonpigmentdispersion
Dispersionstabilityforproperreduction

SomeQuinonevatdyescanbeover-reducedreductionofmorethanonepair
ofketogroups(C=O)
Over-reducedvatdyesgivehavepoorsubstantivityforcotton;moredifficultto
oxidize;producesdullershades;giveslowercoloryield.

Others...sodiumsulphoxylateformaldehydeandsodiumsulphoxylate
acetaldehyde,particularlyinprintingandincontinuousdyeingprocesses.
Cont’d
Othersauxiliaries....neutralsalts(toincreasesubstantivity),wetting,sequestering
anddispersingagents,levelingagent.
Helptoovercomedyeingproblemscausedbyinadequatepretreatment.

ALKALI PREVENT VAT ACID FORMATION
Causticsoda‐isusedfor:
1.Theformationoftheleuco:pH=12‐13needed.
2.Thetransformationofcelluloseintoalkali‐cellulose,
3.Neutralizationofacidproductsofdecompositionofhydros
Cont’d

Absorption and levelling
Alkalineleucovatdyeexhaustsveryfastontocelluloseuntilequilibriumis
attained.
Thehigherthesubstantivitythehigheristheexhaustion
HighconcentrationofNa
+
fromsodiumhydrosulfiteandsodiumhydroxide
facilitateexhaustion

Becauseofthis,manydyeshavearapidstrike;dyebathmaybe80–90%
exhaustedwithin10minutes.
Themorerapidlydyeexhausts,thegreateristheriskofobtaininganunleveled
dyeing.
High electrolyte content
Use of retardants

Adsorption Isotherm For Vat Dyes On Cotton

Substantivity of Leuco Vat Dyes for Cotton
H-bondsb/nhydroxylgroupsandphenolateiongroups,oraminooramide
substituentsareimportant
Moleculesofleucovatdyesarelargeandalsocoplanarityofstructureis
essential.

Oxidation and subsequent process/soaping
Oncethedyehasbeenabsorbedbythefiberintheformofaleucoderivative,its
oxidationtakesplace.
Theleucoderivativemustbeoxidized
Anyexcesshydrosulphitemustbeeliminated
Theexcessofalkalinityinthefibermustbe
neutralized
Leucodyeisthenreconvertedintoitsoriginalformbyoxidation.
Carriedoutwithoxidizingagentslikehydrogenperoxide,sodiumperborate,Sodium
dichromateorpercarbonate.
ThehigherthetemperatureandthelowerthepH,thehighertherateofoxidation
reactions

Dyesthatareeasytoreducearemoredifficulttooxidize,andviceversa.
Chemicaloxidantspreferredbecausetheygivemorerapidanduniformoxidation
throughoutthematerial.

Soaping
Removespigmentdepositedonfibersurfacethatwouldwashorruboffinuse.
Involvesthoroughlywashinggoodsinadetergentsolutionatornearboiling
point.
Itimprovesthelight,washingandrubbingfastnessofthedyeing.
Soapingprobablyinvolvesre-crystallizationofoxidizedanddispersedvatdye
particles
Crystallizationresultsinslightchangeinhueandimprovementsinfastness
properties.Neutralizingwithaceticacidsolutionandfinalrinsing.

Twomethods:
1.Dyeingwithreducedvat‐thedyeintheformofsolubleleucoisputinto
contactwiththecellulosicfiber,isabsorbedbyitandthenoxidizedinthe
fiberitself.
2.Dyeingbypigmentation‐theinsolubledyeintheformofafinedispersionis
depositedonthesurfaceofthefiber;reducedinanalkalinesolutionwhich
causesrapidabsorption,finally,theprocessiscontinuedasinthereducedvat
system.
Dyeing Processes

DYEING METHODS
Bothbatchandcontinuousmethodsareused
Batch–(hotmethod,warmmethodandcoldmethod)‐leveling
problemduetohighdyeingrate
Continuousmethod–mostlyusedmethod(mostcommonispad‐steam
process)

Exhaust Dyeing: Typical Vat Dyeing Cycle
Leuco Process
Intheleucoprocessthematerialtobe
dyedisenteredintoaprepareddye
liquorthatcontainsthefullyvatted
dye,alkali(causticsoda)and
reducingagent(hydrosulphite),
togetherwithvariousamountsof
Salt,
Dispersingagent,
Sequesteringagentand
Levellingagent,asrequired.

High Degree Of Fastness
Pre-oxidation
Ancillary Chemicals
[Chelating Agents, Wetting Agents, Sequesterants , Dispersants]
Over-reduction
Over-oxidation
Effective Pretreatment
General features Of Vat Dye
Washingfastness
Lightfastness

VATDYEINGFAULTS
Unlevellness [inadequate oxidation, salt, temperature]
Poor penetration (rapid heating result surface deposition)
Dull shade due to over-reduction
Staining [inadequate vatting, rinsing & circulation]
Poor rub fastness [inadequate vatting, poor soaping]
Incorrect shade [Soaping too short or low energy]
Fiber damage

DENIM AND INDIGO VAT
DENIMisawarpfacedtwillfabricmadefrom
cottonyarns
Thewarppredominatesonthesurface
Dyedyarnsinthewarpandundyedyarnsinthe
weft
Smallwhiteflecksdistributedinadarkerbasic
color
JEANSmadefrombluedenimismostpopular
Inexpensive,durable,versatile

Indigoisappliedinaseriesof‘dips’,withintermediatesqueezingandatmospheric
oxidation.
Reductionofindigotosolubleleuco-indigo
Multipledip-squeeze-oxidizeoftheyarn
Rinsing,soaping&drying
Blue-dyed warps wash down to an attractive blue
No staining on the white yarns
STONEWASHINGFORFADEDLOOK

The goods are threaded through each box and skyed
Thefirstboxisusedtowetoutthematerial.
Insubsequentboxes,thegoodsareimmersedintheleucoIndigosolutionfor
10–30s,squeezedandskyedfor2mintooxidisetheleucodyetoIndigo.
Thisprocessofseveraldipsandoxidationsisthenrepeatedinasecondseriesof
boxes,andsoon.
Deepshadesbuiltupbyrepeateddippinginthedyebathaftereachoxidation.
Severalrinsingandwashingboxescompletetheprocess.

SULPHUR DYES
SULPHURdyesconstitutethelargestclassofdyesintermsofquantity
Likevatdyesappliedtocellulosicsbyredoxmechanism
Theinsolublepigmentisconvertedintothesubstantiveleucocompoundby
reductionandtheleucoformissubsequentlyoxidizedinsidethefiber.
Chromophorebasedonsulphurcontainingcompounds
ThedyescontainTHIAZINESANDTHIOZOLES
Limitedcolorgamut[Knownforblack]
SULPHURBLACK

THIAZOLES
THIAZINES
Sulphur containing aromatic heterocyclic linked by sulphide bonds

Ontreatmentofanaqueousdispersionoftheinsolublepigmentwithsodium
sulphide,thesulphidelinksarereducedformingindividualheteroaromaticunits
withthiolgroups.
DYEING PROCESS WITH SULPHUR DYES
Thesearesolubleinthealkalinesolutionintheformofthiolateionsthathave
substantivityforcellulose.
Afterdyeing,thethiolateionsinthefiberscanbere-oxidizedbacktothe
polymericpigment.
Lowtomoderatesubstantivityforcellulose
Saltadditiontopromoteexhaustion
RINSED, OXIDIZED SOAPED

Reduce
d
Sulphurdyesareimportantforblack,navy,brown,olive
andgreencolorsinmediumtoheavydepths,being
relativelyinexpensive.

SODIUMSULPHIDE[Na
2S]ISUSEDASTHEREDUCINGAGENT

Sulphurdyeshavethedullestrangeofcolorsofalldyeclassesbutarerelatively
inexpensive.
Whenblackcoloranddullshadesareneeded,withgoodfastnessatreasonablecost,
sulphurdyesareirreplaceable.
Cottondyedwithsomesulphurblacksbecomestenderedonstoringunderwarm
humidconditions.Formationofsulphuricaciddueoxidationofdye.
Jigandpadsteamforwovenfabrics
Largeamountsofsodiumsulphideusedintheapplicationofsulphurdyes,posea
significantenvironmentalproblem.
OVER-REDUCTION

CATIONIC [BASIC] DYEING
Dyescontainingbasicfunctionalgroupsthatareprotonated
Organiccations
Dyefiberswithanionicsitesbyaprocessofionexchange
Mostlyappliedforacrylic,woolandsilk
Lowsubstantivityforcotton

Dyeadsorptionbyacrylicfibersinvolvesinteractionbetweenanionic
sulphonate/sulphatepolymerendgroupsandcationicdyemolecules
TRIPHENYL METHANE ANTHRAQUINONE

ACID DYEING

Aciddyesareappliedinacidicmedia
•Aciddyesareusuallysodiumsaltsofsulphonicacidsorless
frequentlyofcarboxylicacids
•Anionicinaqueoussolution
•Affinityforfiberswithcationicsites
•Usuallysubstitutedammoniumiongroupsinfibers
•Cationiccharacterbyacidabsorption
•Affinityforwool,silkandnylon
INTRODUCTION

MECHANISM OF DYEING WITH ACID DYES
Ionicinteractionbetweendyeanionsandamino
groupsoffibers
Vanderwaalsforcesexertedbetweenhydrophobicdyeanion&
hydrophobicpartsoffiberadjacenttoaminogroups

Inwool,thenumbersofaminoandcarboxylicacidgroupsarealmost
equal(820and770mmolkg–1,respectively)
ISOELECTRIC POINT OF WOOL: Equal numbers of cationic and anionic groups [pH ~5]

Basedonchemicalstructureofchromophore
CLASSIFICATION OF ACID DYES
AZO DYES ANTHRAQUINONE

Basedondyeingcharacteristics
GROUP I: LEVELLING ACID DYES
GROUP II: MILLING ACID DYES
GROUP III: SUPERMILLING ACID DYES
Millingis the process by which wool is treated, in weakly alkaline solution, with
considerable mechanical action to promote felting.

201
MOLECULAR WEIGHTOFDYE
SOLUBILITYORDEGREEOFSULPHONATION
DYEINGPH
DEGREEOFAGGREGATION
DEGREEOFMIGRATION/LEVELLNESS
DEGREEOFWETFASTNESS
COMPARISON FEATURES

203
LEVELLING ACID DYES
1.AddGlauber’ssaltplussulphuricacid
2.Adddye
3.Rinse

204
Strongacidareneededtoachievegoodexhaustion
Glauber’ssaltactsasaretarding/levelingagent
Leveldyeingcontrolledbyusinglesssulphuricacid
initially
DecreasingexhaustiononincreasingdyebathpH
above4,andwithincreasingtemperature
Smallmolecularsizeforgoodpenetrationintopores

205
MILLING ACID DYES
1.Ammoniumsulphate/acetate+Aceticacid
2.Adddye
3.Rinse

206
Highermolecularweightsandgreatersubstantivityforwool
thanlevellingaciddyes
Weakacidsortheirsaltsarerequired(sodiumacetateor
ammoniumsulphate)
Haveonesulphonategroupperdyemoleculeandlowerwater
solubility
Dyeingstartsinthepresenceofammoniumsulphate
Additionofaceticacidtopromoteexhaustion
Bothionexchangeandhydrophobicinteractions
Glauber’ssaltisneveradded
Highconcentrationofsodiumionssuppressesfibernegative
chargeandresultshighexhaustionwithminimumleveling

207
SUPERMILLING ACID DYES
1.Ammoniumsulphate/acetate
2.Adddye
3.Rinse

208
AmmoniumacetateorsulphateisusedatnearlyneutralpH
Morehydrophobicthanmillingaciddyes
Characterizedbypresenceoflongalkylchains
LowerpHresultsrapidexhaustionandunlevellness
Ratecontrolbytemperatureincrease
Highdegreeofaggregationevenatboil

209
Auxiliariesareusedinwooldyeingtopromoteleveling.
Twomaintypesoflevellingagents:ANIONICANDCATIONIC/NON-IONIC.
Wooladsorbsanioniclevelingagentsandtheyretarddye
absorptionbyinitiallyblockingthecationicammoniumionsites.
Moresubstantivedyeanionseventuallydisplaceanionicproduct.
Anionicsurfactantswithlongalkylchainshavehigherfibre
substantivity.
LEVELLING AGENTS
Cationic polyethoxylated amine

210
Cationicagentsformacomplexwiththeanionicdyeinthe
dye-bathandpreventitsuptakebythewool.
Thenon-ionicportionofthistypeofproductkeepsthe
auxiliary–dyecomplexdispersedinsolution.
Avoiditsprecipitationinthebathoronthematerialsurface.
Freedyemoleculesareliberatedasthedyeingtemperature
increasessincethecomplexislessstableathighertemperatures

211
PROBLEMS IN ACID DYEING OF WOOL
TemperatureandpHcontrol
Skitterydyeingortippydyeiing
Ringdyeing
Shadevariation

DISPERSE DYEING

DISCOVERY
•Cellulosetriacetatefibersandpoordyeability
•Hydrophobiccharacter;couldnotbepenetrated
bywater,&notbedyedbywatersolubledyes.
•Therewaslittlepointintreatingfiberswithamixtureofpuredye
andwaterbecauseparticleswouldnotbedistributeduniformly.
•Incorporatingsurface-activeagentwithdyeensuresuniform
distributionofdyeinthedye-bath,allowinguniformdyeings
DISPERSE DYES

INTRODUCTION
Dispersedyesarenon-ionicandslightlysolubleinwater
Applied in the form of fine aqueous dispersions
Dyeparticlesareabletopenetratefiberduringdyeingina
molecularlydispersedstateandareheldinfiber
Dispersedyeshaveaffinityforsyntheticfibers
Polyester,nylon,celluloseacetateandacrylic
fibers
COMPACTNESS
[CRYSTALLINITY/ORIENTATION ]
HYDROPHOBICITY

Dyeing of polyester with disperse dye
Polyesterishydrophobicandcharacterizedby
compactphysicalstructure
PETisnonionicandthermoplasticfibers
Becauseofnonionicitneedsnonionicdye
Dyeableonlywithdispersedye

Chemical constitution
Simplelowmolecularnonionicmonoazoand
anthraquinonewithpolargroupsforslightsolubility
requiredindyeing.
DISPERSION STABILITY
DYE SOLUBILITY
PARTICLE SIZE
Hydrophobic dye ‘dissolving’ in hydrophobic fiber

Stablesuspensionofthedyesisachievedbyusing
dispersingagentinthepreparationofthedyes.
Thesolubility(slight)dependsonthepresenceof
polargroupssuchasOH,NO
2,-CH
2–CH
2–OHand
theparticlesize.
Ingeneraltheparticlesizeofdyemustbeverysmall.
Thisisinfluencedbythedegreeofgrindingand
affectsdisaggregationofdyehencedegreeof
absorption.

REASONABLE RATE OF DYEING
HIGHTEMPERATURE INREFERENCE TOTg
DYEINGACCELERATORS [CARRIERS]
FREE VOLUME THEORY

POLYESTER DYEING METHODS
DYEINGWITHCARRIERATBOIL
Benzoicandphenoliccompounds
unpleasantodoursandaretoxic
HIGHTEMPERATURE PRESSUREDYEING
DYEINGBYTHERMOSOL PROCESS
Exhaust and continuous

Carrier dyeing method
Acarrierisanorganiccompounddissolvedinthedyebathandwhich
increasetherateofdyeing
Mechanism:
Thepolyesterfibersabsorbthecarrierandswell.
Swellingcanimpedeliquorflowinpackagescausingunlevelness.
Theoveralleffectseemstobeloweringofthepolymer(Tg),thus
promotingpolymerchainmovementsandcreatingfreevolume.
Thisspeedsupthediffusionofthedyeintothefibers.

221
Dyeing Temperature 100
o
C
Alternatively,thecarriermayformaliquidfilmaroundthesurface
ofthefiberinwhichthedyeisverysoluble,thusincreasingtherateof
transferintothefiber

HTHP dyeing method
Thedyeingofpolyesterwithdispersedyesattheboilis
slowbecauseofthelowrateofdiffusionofthedyesinto
thefiber.
Theactivationenergyfordiffusionisquitehighand
raisingthedyeingtemperaturefrom100to130°C
considerablyincreasestherateofdyediffusion.

223
HTHP DYEING
Dyeing Temperature ~ 130
o
C

224
Paddingfabricwithadispersionofdispersedyes
(use of a migration inhibitor in the pad bath)
Dryingusinghotflueairdryerorbyinfraredradiation
Heatinginair,orbycontactwithhotmetalsurface,toa
temperatureintherangeof190–220°Cfor1–2min.
Thefabricapproachesthemaximumtemperature,thedispersedyes
begintosublimeandthepolyesterfibersabsorbthevapours.
THERMOSOL DYEING

225
Dyeing Temperature ~ 220 C
Dryingisusedtominimizethemigrationduringheating
DuringheatingdyeswillbeconvertedintogaseousstateandPETfibershas
veryhighaffinitytotheegaseousdispersedyes

Incaseofdyeingwithdispersedye,temperatureplaysan
importantrole.
Fortheswellingoffiber,temperatureabove130°Cisrequiredif
hightemperaturedyeingmethodisapplied.Againincaseof
carrierdyeingmethod,thisswellingoccursat90-100°C.
Ifitiskeptformoretime,thendyesublimationandlossof
fabricstrengthmayoccur.
Effect of Temperature

227
FordispersedyeingthedyebathshouldbeacidicandpH
shouldbeinbetween4.5-5.5.
FormaintainingthispH,generallyaceticacidisusedatthispH
dyeexhaustionissatisfactory.
Duringcolordevelopment,correctpHshouldbemaintained
otherwisefastnesswillbeinferiorandcolorwillbeunstable.
EffectofpH

Textile Auxiliaries
1.DispersingAgent-makethedyesolutionstable
anddisperseinthedyebath.
2.Acid-adjustpHtothesuitableconditionforthe
dyebath.
3.Carrier-swellthefiberanddissolvethedyeto
makethedyegettingintofiber.
4.Levelingagent-makemorelevelingdyeing(some
willhaveadverseeffectonslowerdyeing)
5.Water-dyeingmedia

229
MODIFICATION OF POLYESTER
IMPROVED DYEABILITY
Cationic Dyeable Polyester [CDP]
Copolymerization for lower Tg

230
DYEING BLEND FIBERS (UNION DYEING)

Why blending ???
Achievingeconomicadvantagesviablendingofexpensive
fiberswithcheaperones
Enhancingperformanceandqualitypropertiesvia
combinationofdesirablepropertiesofbothfibercomponents
Prolongingthedurabilityoftextileproductviaincorporation
ofamoredurablefibercomponent,etc

Fiber classes according to affinity to dyes
GroupA:Acidandpre-metallizedaciddyesfordyeingwool,
silk,nylonandpolyurethane(electrostaticbond)
GroupB:Basicdyesforacrylicsandmodacrylics,cationic
dyeablepolyesters(electrostaticbond)
GroupC:Cellulosicdyes,e.g.reactive,direct,vat,sulphur,
etc.viaformationofphysicaland/orcovalentbonds
GroupD:Dispersedyesforpolyester,celluloseacetate,nylon
andpolyurethanesviahydrophobicbonding

Color effects obtained by dyeing blends
Solideffect:Allfibercomponentsareidenticallycolored
Reserveeffect:Onetypeoffiberiskeptwhite
Shadoweffect:(toneintone)dyeingAllcomponents
coloredtothesamehuebutofvaryingdepthofshades.
Contrasteffect:fibercomponentsaredyedincontrast
hues.,
orange-blackblue-yellow

Methods of dyeing blends
1-bath1-stepmethod:reducescostofdyeingdrasticallydue
tonearly50%reductioninuseofwater,heat,chemicals,time
andmanpower
1-bath2-stepmethod:materialhandlingisremarkablyless,as
theblendonceloadedremaintheretillcompletionofdyeing
forbothcomponents;thesamebathisusedfordyeingboth
thesefiberssavingwaterandenergy
2-bath2-stepmethod:todyeblendsmadefibersofdifferent
nature-morehandlingofmaterial,hugewaterconsumption,
doubledloading/unloadingtime,moremanpower

IMPORTANT FACTORSIN DYEING BLENDS
DYEBATHCONDITIONS
dyeauxiliaries
dyebathtemperature
stressonfabric
CROSS-STAININGOFDIFFERENTFIBERS
Thecoloureffectsandfastnessproperties
required;
Theprocesscosts.

Inmostcases,methodofblenddyeingissimilarto
thatofdyeingindividualcomponentfiberswith
particulartypesofdyesselected
Thisissobecausemostbinaryblendsaremixtures
ofasyntheticandanaturalfiber.
Insuchcases,thereisminimalcross-staining.

Dyeing cotton/polyester blends
Dyeingpropertiesofpolyesterandcottonarequitedifferent-mostly
thetwofibersdyedseparately
Polyestercomponentisinvariablydyedfirstwithofdispersedyes
Forcotton,thereisachoiceofdyes,actualselectiondependingon
desiredcolor,typeoffinishingrequired,demandedfastness
properties,costsetc
Cottonisusuallydyedwithreactive,direct,sulphur,vat,orazoicdyes
Reactive/dispersedyecombinationisthemostpopular

Ifcottonisdyedfirstdyeingofpolyesterat120–130°Ccanchange
shadeofdyedcotton-cottondyesarelessstableathigh
temperatures.
Dyeingpolyesterbeforecottonallowsreductionclearingofany
dispersedyeonthepolyestersurfaceorstainingcotton-cross
stainingofcottonbydispersedyescanbeaproblem.
Oncepolyesterisdyedanydetrimentaleffectsofcottondyeing
assistantssuchasalkaliandsaltondispersedyesareavoided.

major areas of concern in dyeing of cotton/polyester
Degreeofcross-staining
Dispersedyesstaincottonbutanioniccottondyesusuallycompletelyreserve
polyester.
Dispersedyesselectedshouldbethosethatgiveminimalcottonstaining
Interactionsbetweendyesandauxiliaries
Whenpresentinsamebathmanydispersedyesarenotstableunderalkaline
reducingconditionsusedinleucovatdyeing.
Saltandalkalifordyeingcottonwithreactivedyesoftenhaveaharmfuleffecton
dispersingagentfordispersedyesandcauseparticleaggregation;

Conditions for fixation or aftertreatment
Cottondyesmustbestabletohightemperaturesin
Thermosolprocess-iftobeappliedsimultaneouslyor
beforedispersedyes.
Notpossibletocleardispersedyesstainingcottonwith
analkalinehydrossolutionifcottonisalreadydyed.
Alltypesofdyesusedtocolorcottonwillbereduced
undertheseconditionsandcolordestroyed.

Disperseandreactivedyesareadded,temperatureraisedto
130°Catacidicconditionstofixdispersedye.
Dyebathisthencooledto80°Candsodiumcarbonateis
addedtofixthereactivedye,beforewashing.
Reactivedyefixationandclearingofsurfacedispersedyesis
combinedhere,makingPCsinglebathdyeingpossible
Developments in PC Blend Dyeings

TEXTILE PRINTING
Gezu k
WolkiteUniversity
2012

Textileprintingisrelatedtodyeingbut,whereasin
dyeingprocesswholefabricisuniformlycoveredwith
onecolor,inprintingoneormorecolorsareappliedtoit
incertainpartsonly,andinsharplydefinedpatterns.
ATYPEOFCOLOURATIONFORIMPARTINGCOLORINSPECIFICAREA
ONASUBSTRATEBASEDONPATTERNORDESIGNREQUIREMENT.
Textile Printing Defined

DIFFERENCES BETWEEN
DYEING AND PRINTING

PRINTING
Printinginvolveslocalizedcoloration
Thisisachievedbyapplyingthickenedpastescontainingdyes
orpigmentsontofabricsurfaceaccordingtoagivencolordesign
Thepastemustcolorallthevisiblefibersontheprintedsurface
Soitmustpenetratesomewhatintotheyarnstructure
Ifthepasteistoothinitwillspread,givingpoorprintdefinition
andpenetratetoofarintotheyarnsdecreasingthecoloryield

PRINTING PROCESS
PREPARATION OF PRINT PASTE
APPLICATION OR PRINTING
DRYING
FIXATION

DYE OR PIGMENT
THICKENER
BINDER
AUXILIARIES
PRINT PASTE INGREDIENTS

Imparttherequiredcolorofdesignasperrequirement
Dyesarechosenwithrespecttotheiraffinity
Example:Reactivedyesforcotton,aciddyesforwool,disperse
dyesforpolyesterandsoon
Pigmentsareappliedforallkindsoffibertextiles
DYE OR PIGMENT

Tolocalizetheprintingpasteonthedesiredareaofthe
fabric.
Enables the print paste to stay in place once it is deposited onto the fabric
Clear cut design and proper outline definition of print
Naturaland syntheticthickeners are available
Based mainly on polysaccharidesand polyacrylic acids
THICKENER
Optimum Viscosity

Desirablepropertiesofthickenersusedinpigmentprinting:
lowsolidcontent
clearandcolorless
don’tdecreasethefastnessandhandoftextileprints
goodlevelingpowerwithoutspreadingsideways.

Pigmentsarefixedbybindershencebindersprovidedurabilityofthepigment
onthefabric.
Apigmentbinderistheresinthatformsathree-dimensionalfilmonthe
surfaceofthefiber.
Thisfilmcontainsthedispersionoftextilepigmentandwill
acttoadherethepigmenttothesurfaceofthesubstrate.
Thepermanenceofthisfilmisdependentonthepolymertypeandthe
applicationconditions.
BINDER

Crosslinking agents to improve fastness
Softeners to improve handle of pigment printed
fabric
Defoamers to prevent foam generation
Humectants to increase water content of the paste
catalyst and so on
AUXILIARIES

DifferenttechniquescanbeusedtotransferthepasteTO
textilesubstrate .
Thetransfercanbebymeansofblocks,screens,rollers:
reproductionofimage.
Thereispossibilityofdigitizingdesignandtransferimage
withoutreproduction.
APPLICATION OF PRINT PASTE

DRYING AND CURING (STEAMING)
The main purpose of drying is to control migration
Curing/steaming for fixation of pigment/dye
Cylinder dryers and stenterscan be used
Curing temperatures depend on the fiber
180
o
C for pigment, 205
o
C for dispersed dye

Inthecaseofdyeprints,theprintedfabricis
thoroughlywashedthendriedafterfixation.
Necessarytoremovethickener,alkali,other
ingredientsofprintpasteleftonfabricafter
fixation.
Couldinterferewithsubsequentfinishing
processes.
Pigmentsareoftenprintedonfinished
AFTERWASHING

Reactivedyesforcottonfibershasgiventhepossibilityof
usingonlyonetypeofdyeandsimpleapplicationconditions,
inplaceofthecomplexpermutationsnecessary
Reactivedyesproducebrilliantshadesofverygood
fastnessandlevelingpropertiesoncellulosicfibers.
Nexttopigmentprintingthemostimportantprinting
methodisprintingwithreactivedyes.
REACTIVE DYE PRINTING

Selectionofthickeners isveryimportantforreactivedye
printings;andtheselectionofproperreactivedyesalsoplays
amajorrole.
Normallylowreactivedyesarepreferredforprintingoncotton.
Becausethestabilityofthelowreactivedyesishighin
printingpaste.
Furthermoreforobtaininggoodeffect properpretreatmentof
fabricbeforeprintingisveryimportant.

Requirements of an ideal thickener for reactive printing
•Good compatibility and no affinity or reactivity
with dye
•Good flow property
•Good swelling and moisture absorption capacity
during steaming for dye fixation
•Quickdryingtopreventbleeding&goodwater
solubilityforeasyremoval

Conventional reactive printing thickener
Theusualpolysaccharidethickenerssuchasstarchand
gumsusedinprintingarenotsuitableforprintingwith
reactivedyes
Asallthesecontainprimaryhydroxylgroupsintheir
molecularstructureandreactwithreactivedyes.
Sodiumalginateiswidelyusedforreactivedyeprinting.Itis
ananionicpolymer,hasonlytwofreeOHgroups.

Polysaccharide illustration
Thereactionbetweenalginateanddyeislimitedbyanionrepulsion
ofalginate'scarboxylgroupsanddye'ssulfonicacidgroups.

Moderate to low reactivity dyes such as MCT and VS
Reactive dyes in printing
Dyeshavinglesssubstantivitytowardscellulosearepreferredfor
printing.
Becauseofgreatereaseof“washingoff”andavoidanceof
stainingofadjacentwhiteareas.
Printingpastesmadefromlessreactivedyeshave betterstorage
stability andthisisofconsiderableimportance.
Thereactiveprintpastenormallycontainsreactivedye,
sodiumbicarbonate/carbonate,urea,sodiumalginateand
water.
DCTisnotrecommended

PIGMENT PRINTING
DIFFERENCE BETWEEN DYE AND PIGMENT
PIGMENT
NO AFFINITY TO FIBRE
INSOLUBLE IN WATER
NEED BINDER FOR FIXATION ONTO FIBRE
DYE
AFFININTY TO FIBRE
WATER SOLUBLE OR CAN BE MADE WATER SOLUBLE
HELD ON FIBRE DYE-FIBRE INTERACTIVE FORCES
MOST WIDELY USED

MECHANISM OF BINDING
SEQUENCE:
PRINT > DRY > CURE (DRY HEAT)
DURINGCURINGBINDERPOLYMERIZESANDFORMSASTRONG
FILM.
BINDERFILMEMBEDESPIGMENTCOLOURANDALSOSTRONGLY
ADHERESTOTHEFIBRE.
BINDERISAPRE-POLYMERAVAILABLEINTHEFORMOF
AQUESOUSEMULSION
CROSSLINKING

CHOICE OF THICKENER
DYEPRINTINGTHICKENERSARENOTSUITABLE.
INTERACTWITHBINDER,REDUCEINTERATIONWITHFIBRE.
AFFECTINGTHEFASTNESSPROPERTIES
SUITABLE THICKENERS
EMULSION THICKENER
SYNTHETIC THICKENER
DEVELOPMENT OF VISCOSITY
HMW COPOLYMERS OF ACRYLIC ACID
OIL + WATER EMULSIONS

ADVANTAGES OF PIGMENT PRINTING
PRACTICALLYALLTYPESOFFIBRESANDBLENDSCANBEPRINTED
PIGMENTCOLOURSCANBEREADILYMIXEDWITHEACHOTHER
TOGETQUICKSHADEMATCHING
NOAFTERTREATMENTSUCHASWASHING&SOAPINGREQUIRED
DISADVANTAGES
HARSH FABRIC FEEL DUE TO BINDER FILM
LOW RUBBING FASTNESS

FIBERCHARACTERISTICS
YARNTYPES
FABRICCONSTRUCTION
CONSIDERATIONS ON PRINTING PROCESS

STYLES OF PRINTING
There are two basic styles of printing
Direct printing andIndirect printing
DIRECT PRINTING
Thedyeorthepigmentisprintedonthefabricinthepasteform
andanydesiredpatternmaybeproduced
Designsprinteddirectlyusingpigmentsordyesonwhiteor
coloredbackground
Isthemostimportantprintingstyleandthemostpopularas
comparedtoindirectstyle

INDIRECT PRINTING
IP is classified into two categories
Discharge printing
thedye.
Indischargestyle,thefabricisdyedtotherequiredgroundcolor.
Next,thefabricisprintedwithachemicalthatselectivelydestroys
thedye.
Thisallowsprintingofwhitedesignsonagroundcolorofanydepth
withapatterndefinitionthatismuchhigherthanwouldbepossibleby
directcolorprinting.
Ifthepastecontainsdyesresistanttothedischargingagent,these
dyes,calledilluminatingcolors,willcolortheprintedareas.

Resististhetermthatdescribespreventionofdyeingprocessbyapplication
ofaphysicalorchemicalsubstancetofabrictopreventadye’saccessto
fabric.
Resistagentscanbewaxes,thickeners,surfactants,organicacids,oxidizing
agents,orreducingagents.
Indischargestyle,thefabricisdyedtotherequiredgroundcolor.Next,the
fabricisprintedwithachemicalthatselectivelydestroysthedye.
Resist printing

BATIK
TIE-DIE

Inbatikeffectthefabriciscoatedwithwax
andthendyedwithsuitabledyes
dependingonthefiber.
Intie-dieeffectfirstthefabricistiedin
certainportionstolowerthepenetrationof
dyeintothefiberandthendyeingis
carriedoutconventionally.

Methods of Printing
Non contact printing
Contact printing

STENCIL PRINTING
BLOCK OR SURFACE PRINTING
ENGRAVED ROLLER PRINTING
SCREEN PRINTING
TRANSFER AND DIGITAL PRINTING
TECHNIQUES OR METHODOF PRINTING
Refers to the technical means by which pastes are put onto design areas

Stencil printing
Stencilprintingistheprocessofcutouttherequired
designsontheplasticpapers
Thesurfaceofthepapersshouldbesmooth
Colorantsaresmallermolecularweight(noneedof
washing)
Pastesareforcedoutthroughcuttingoutshapesfrom
papersontofabricunderneath
Theideaofscreenprintingisoriginatedfromstencil
printing

BLOCK PRINTING
Itistheoldestandsimplestwayofprinting
Inthismethodawoodenblockwitharaisedpatternonthe
surfacewasdippedintotheprintingcolorantandthenpressed
facedownontofabric.
Thedesiredpatternwasobtainedbyrepeatingtheprocess
usingdifferentcolors.
Generallythewoodenblockiscarvedoutofhand
Printingisdonemanually

Screenismadeofwovenfabricsfirmlyattachedtoa
suitableframe
Mostlyofnylon/silk/polyester
Thescreenistheimagecarriermadefromaporousmesh
stretchedtightlyoverametalorwoodenframe.
Reproducepatternsasperdesignrequirement.
SCREEN PRINTING
SCREEN, INK, SQUEEGEE

281
( Majorstepinscreenprinting)
(1)theselectionofthefabricandtheprinteddesign
(2)thechoiceofthesizeandarrangementofdesign’s
repeatrectangle
(3)thenecessarycolorseparationofthedesign
Colorseparationinvolvesreproduction
ofthepatternforeachcoloronseparate
clearfilmswithopaquetracer.
Screen production

Single color Multi color

285
Thescreeniscoatedwithaphoto-sensitiveemulsion.
Atypicalpolymerispolyvinylalcohol,its
crosslinkingsensitizedbyammoniumdichromate.
Thecoatedscreenisdried
Exposedbeneathdiapositiveforthegivencolor
All operations take place in a dark-room!!
Screen Preparation Steps Screen Preparation Steps
Lacquer

Theresthardens(becomeinsoluble)
Theinkedzones,correspondingtoparticular
colorpattern,donottransmitultravioletlightused
forexposure.
Thelayerofpolymeronthescreenbeneaththe
patternisthusnotexposedanddoesnotcrosslink.
Theresthardens(becomeinsoluble)
Thenon-exposedpolymerremainssolubleandcanbewashed
out,leavingthescreenopeninthoseareas.
Anysmallholesinhardenedareasonscreenarepaintedover.

MIXINGPHOTO-EMULSION
COATING
DRYING
PREPARINGPOSITIVE
EXPOSING
WASHINGANDDRYING

288288
Flatscreenprintingcanbecarriedoutbyhandandautomaticallyby
usingdifferentmachines.
Rotaryscreenprintingiscarriedoutbyfullycontinuousmachines.
TYPES OF SCREEN PRINTING
FLAT SCREEN PRINTING
Inflatscreenprinting,ascreen
onwhichprintpastehasbeen
appliedisloweredontoasection
offabric.Asqueegeethen
movesacrossthescreen,forcing
theprintpastethroughthe
screenandintothefabric.
ROTARY SCREEN PRINTING
Thetubularscreensrotateatthe
samevelocityasthefabric,the
printpasteisdistributedinsidea
tubularscreen,whichisforced
intothefabricasitispressed
betweenthescreenandaprinting
blanket(acontinuousrubber
belt).

•Printingiscarriedoutonaflat,solidtablecoveredwith
alayerofresilientfeltandawashableblanket.
•Heatfordryingtheprintedfabricmaybeprovidedeitherunder
theblanketorbyhotairfansabovethetable.
•Fabricmovementorshrinkagemustbeavoidedinorder
tomaintainregistrationofthepattern.
HAND SCREEN PRINTING

Theprocessconsistsofforcingprintpastethroughthe
openareasofthescreenwithasyntheticrubber
squeegee(rubberbladecontainedinwooden/metalsupport)
Therubberbladeisdrawnsteadilyacrossthescreenataconstant
anglespeedandpressure.
Thescreeniswashedimmediatelyafteruse.Ifthisisnotdone,
pastedriesonscreenandclogsupdesign.

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MANUAL

SEMI-AUTOMATIC FLAT SCREEN PRINTING
296
Themanualprocesshasbeensemi-automatedby
mountingthescreeninacarriage.
Insemi-automatedscreenprinting,amechanicallydriven
squeegeetransfersthecolor.
Longtables,typically20–60mlong,areused,andsome
provisionisusuallymadefordryingtheprintedfabric.
Verypopularwherethescaleofproductionisnot
large,orwherecapitalinvestmentislimited.

FULLY AUTOMATIC FLAT-SCREEN PRINTING
•Toincreasethespeedofflat-screenprinting,itwas
necessarytodeviseamethodofprintingallthe
colorssimultaneously.
•Allthescreensforthedesign(onescreenforeachcolor)are
positionedaccuratelyalongtopofalongendlessbelt(blanket)on
topofwhichisthefabrictobeprinted.
•Thefabricisgummedtotheblanketattheentryendand
movesalongwiththeblanketinanintermittentfashion,
onerepeatdistanceatatime.

•Allcolorsindesignareprintedsimultaneouslywhile
thefabricisstationary ;thenthescreensarelifted
andthefabricandblanketmoveon.
•Whenthefabricapproachestheturningpointoftheblanket,
itispulledoffandpassesintoadryer.
•Thesoiledblanketiswashedanddriedduringitsreturn
passageontheunderside.

PRODUCTIVITY

Correctfabricplacementisvitalforaccurate
registrationofthedifferentcoloredpatterns.
Aslightpatternoverlappreventsawhitegap
betweentwoprintedcolors.

301
Themainfaultinscreenprintingispoorpatternregistration
Inaccurate screen placement
Inaccurate fabric movement
Fabric slippage on the blanket (poor adhesion)
Distortion of screen mesh by drag of squeegee
PROBLEMS IN FLAT SCREEN PRINTING
SLOW PRINTING PROCESS [5 -10m/min]

302
Number of squeegee passes
LOW PRODUCTION RATE
Morethanonepassisusedtoachieveuniformityandadequatepenetration,
especiallyinblotchareas,forthickfabricsorirregularsurface
Squeegeetakeslongertomovealongthescreen
wheretherepeatdistancesarelarge
Efficiency of the dryer
Ifthedryerisshort,oriftemperatureindryeristoolow,printingspeedwill
havetobereducedinordertoensuretheprintedfabricisadequatelydried.

ROTARY SCREEN PRINTING
Theprocessinvolvesinitiallyfeedingfabricontothe
rubberblanket.Asthefabrictravelsundertherotary
screens,thescreensturnwiththefabric.
Printpasteiscontinuouslyfedtotheinteriorofthescreen
throughacolorpipe.

•Asthescreenrotates,squeegeedevicepushesprintpaste
throughthedesignareasofthescreenontothefabric.
•Asinflat-bedscreenprinting,onlyonecolorcanbeprintedbyeach
screen.Afterpasteapplication,theprocessisthesameasflat
screenprinting.

305
Byconvertingthescreen-printingprocessfromsemi-
continuoustocontinuous,higherproductionspeedsare
obtained.
Typicalspeedsarefrom45-100mpmforrotaryscreenprinting
dependingupondesigncomplexityandfabricconstruction.
Continuouspatternssuchaslinearstripesarepossible.
Rotaryscreenmachinesaremorecompactthanflatscreen
machinesforthesamenumberofcolorsinthepattern(less
floorspace).

306
Gluestreaks–fromtherubberblanket
Colorout–fromalackofprintpaste
Creasedfabric
Pinholesinanyscreen
Damagetothescreenleadingtomisprints
Lintonthefabriccausespick-off
Withprintdesigns,colorapplicationmustbecorrectthefirsttime,
becauseprintingdefectscannotberepaired.
General screen printing defects

307
Longprocesssetuptimeforcolorandpattern
change
Screenproductionisslowandexpensive
Screensrequireconsiderablestoragespace
Limitations Specific to Rotary Screen Printing

ROLLER PRINTING
Engravedrollerprintingisamoderncontinuousprinting.
Thedesignisengravedonthesurfaceofametalroller,to
whichdyeisapplied,andtheexcessisscrapedoffthe
roller'ssurface,leavingdyeintheengravedsections.
Whenitrollsacrossthefabric,thedyeontheroller
transferstothefabric.

TRANSFER PRINTING
Heattransferprintingisatechniquewherepaperisprinted,followedby
thetransferofthedesignfromthepaperontothetextilefabric.
Commercialprocessinvolvesprintingreleasepaperwithpigments.
Thedesignonpaperisplacedontothefabric,heatedso
thatthepigmentbindersoftens,releasesfromthepaper,
andadherestothefabric.
Heattransferprintingiscleanandenvironment
friendly
Theonlyby-productisthepapercarrier.
Transferringanimagetofabricfromapapercarrier.Whenheat
andpressureareappliedtothispapertheinksaretransferred.

DIGITAL PRINTING
It is the more advanced type of printing.
This includes :-
 Jet spray printing
 Electrostatic printing
 Photo printing
 Differential printing

Rotary Screen Printing60%
Automatic Flat Bed 18%
Other methods 22%
WORLD PRODUCTION SHARE

Textile coloration, dyeing and printing of textile materials

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Textile coloration, dyeing and printing of textile materials

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